Patent Publication Number: US-11397327-B2

Title: Method of manufacturing a grating waveguide combiner for an optical engine

Description:
BACKGROUND 
     Technical Field 
     The present disclosure is generally directed to systems, devices, and methods relating to optical engines, for example, optical engines for laser projectors used in wearable heads-up displays or other applications. 
     Description of the Related Art 
     A projector is an optical device that projects or shines a pattern of light onto another object (e.g., onto a surface of another object, such as onto a projection screen) in order to display an image or video on that other object. A projector necessarily includes a light source, and a laser projector is a projector for which the light source comprises at least one laser. The at least one laser is temporally modulated to provide a pattern of laser light and usually at least one controllable mirror is used to spatially distribute the modulated pattern of laser light over a two-dimensional area of another object. The spatial distribution of the modulated pattern of laser light produces an image at or on the other object. In conventional scanning laser projectors, at least one controllable mirror may be used to control the spatial distribution, and may include: a single digital micromirror (e.g., a microelectromechanical system (“MEMS”) based digital micromirror) that is controllably rotatable or deformable in two dimensions, or two digital micromirrors that are each controllably rotatable or deformable about a respective dimension, or a digital light processing (“DLP”) chip comprising an array of digital micromirrors. 
     In a conventional laser projector comprising an RGB (red/green/blue) laser module with a red laser diode, a green laser diode, and a blue laser diode, each respective laser diode may have a corresponding respective focusing lens. Each of the laser diodes of a laser module are typically housed in a separate package (e.g., a TO-38 package or “can”). The relative positions of the laser diodes, the focusing lenses, and the at least one controllable mirror are all tuned and aligned so that each laser beam impinges on the at least one controllable mirror with substantially the same spot size and with substantially the same rate of convergence (so that all laser beams will continue to have substantially the same spot size as they propagate away from the laser projector towards, e.g., a projection screen). In a conventional laser projector, it is usually possible to come up with such a configuration for all these elements because the overall form factor of the device is not a primary design consideration. However, in applications for which the form factor of the laser projector is an important design element, it can be very challenging to find a configuration for the laser diodes, the focusing lenses, and the at least one controllable mirror that sufficiently aligns the laser beams (at least in terms of spot size, spot position, and rate of convergence) while satisfying the form factor constraints. 
     A head-mounted display is an electronic device that is worn on a user&#39;s head and, when so worn, secures at least one electronic display within a viewable field of at least one of the user&#39;s eyes, regardless of the position or orientation of the user&#39;s head. A wearable heads-up display is a head-mounted display that enables the user to see displayed content but also does not prevent the user from being able to see their external environment. The “display” component of a wearable heads-up display is either transparent or at a periphery of the user&#39;s field of view so that it does not completely block the user from being able to see their external environment. A “combiner” component of a wearable heads-up display is the physical structure where display light and environmental light merge as one within the user&#39;s field of view. The combiner of a wearable heads-up display is typically transparent to environmental light but includes some optical routing mechanism to direct display light into the user&#39;s field of view. 
     Examples of wearable heads-up displays include: the Google Glass®, the Optinvent Ora®, the Epson Moverio®, and the Sony Glasstron®, just to name a few. 
     The optical performance of a wearable heads-up display is an important factor in its design. When it comes to face-worn devices, users also care a lot about aesthetics and comfort. This is clearly highlighted by the immensity of the eyeglass (including sunglass) frame industry. Independent of their performance limitations, many of the aforementioned examples of wearable heads-up displays have struggled to find traction in consumer markets because, at least in part, they lack fashion appeal or comfort. Most wearable heads-up displays presented to date employ relatively large components and, as a result, are considerably bulkier, less comfortable and less stylish than conventional eyeglass frames. 
     Direct Laser Writing 
     Femtosecond laser micro-machining is a direct-laser-write and rapid prototyping technique that provides great potential for optical device fabrication. Strong focusing of femtosecond laser light into transparent glass can induce positive refractive index modifications up to 0.01 refractive index units (MU) within the material and without surface damage. Since then, ultrafast (femto/pico-second) lasers have been shown to enable flexible 3D structuring of various glasses, and has led to the demonstration of many types of optical devices (waveguides, couplers, Bragg gratings, waveplates, etc.) that serve as building blocks for 3D optical circuits. 
     Direct-laser-writing uses ultrashort laser pulses to confine strong nonlinear optical interactions that may induce, for example, positive or negative refractive index changes in bulk transparent materials for creating optical waveguides (WGs). The mechanisms by which direct-laser-write modifications occur include, but are not limited to, multiphoton ionization, avalanche ionization, electron-atom collisions, plasma interactions, thermal effects (e.g. diffusion, heat accumulation), energy dissipation, and material cooling leading to inhomogeneous solidification. For direct-laser-writing waveguides, waveguide performance can be tuned and optimized by, but not limited to, the writing laser&#39;s properties (pulse duration, pulse temporal shape, bandwidth and shape, pulse repetition rate, wavelength, polarization, and beam spatial shape) and the focusing conditions (lens numerical aperture, air/liquid immersion, translation direction and speeds). 
     BRIEF SUMMARY 
     According to one or more implementations of the present disclosure, an optical engine may be summarized as including: a base substrate; a plurality of laser diodes, each of the plurality of laser diodes bonded directly or indirectly to the base substrate; at least one laser diode driver circuit operatively coupled to the plurality of laser diodes to selectively drive current to the plurality of laser diodes; a plurality of collimation lenses, each of the plurality of collimation lenses positioned proximate a respective one of the plurality of laser diodes collimates light emitted therefrom; a cap comprising at least one wall and at least one optical window that, together with the base substrate, define an interior volume sized and dimensioned to receive at least the plurality of laser diodes and the plurality of collimation lenses, the cap being bonded to the base substrate to provide a hermetic or partially hermetic seal between the interior volume of the cap and a volume exterior to the cap, and the optical window positioned and oriented to allow beams of light emitted from the plurality of laser diodes through the collimation lenses to exit the interior volume; and a grating waveguide combiner positioned proximate the optical window of the cap, the grating waveguide combiner comprising a plurality of input grating couplers and at least one output grating coupler, in operation, the grating waveguide combiner receives a plurality of beams of light at the respective plurality of input grating couplers and combines the plurality of beams of light to provide a collimated aggregated beam of light at the output grating coupler. 
     The grating waveguide combiner may include a first grating waveguide and a second grating waveguide. Each of the first and second grating waveguides may include at least two input grating couplers. The grating waveguide combiner may include at least four waveguides. The plurality of collimation lenses may be formed as a micro-optic lens array. The plurality of collimation lenses may be bonded to the base substrate. The grating waveguide combiner may be bonded to the base substrate proximate the optical window of the cap. 
     The optical engine may further include a common collimation lens positioned and oriented to receive and collimate the aggregate beam of light from the output grating coupler of the grating waveguide combiner. The common collimation lens may include an achromatic lens or an apochromatic lens. 
     The optical engine may further include at least one diffractive optical element positioned and oriented to receive the aggregate beam of light, in operation, the at least one diffractive optical element may provide wavelength dependent focus correction for the aggregate beam of light. 
     The optical engine may further include a plurality of chip submounts bonded to the base substrate, wherein each of the laser diodes are bonded to a corresponding one of the plurality of chip submounts. The plurality of laser diodes may include a red laser diode to provide a red laser light, a green laser diode to provide a green laser light, a blue laser diode to provide a blue laser light, and an infrared laser diode to provide infrared laser light. The base substrate may be formed from at least one of low temperature co-fired ceramic (LTCC), aluminum nitride (AlN), or alumina. 
     The at least one laser diode driver circuit may be bonded to a first surface of the base substrate, and the plurality of laser diodes and the cap may be bonded to a second surface of the base substrate, the second surface of the base substrate opposite the first surface of the base substrate. The at least one laser diode driver circuit, the plurality of laser diodes, and the cap may be bonded to a first surface of the base substrate. The plurality of laser diodes and the cap may be bonded to the base substrate, and the at least one laser diode driver circuit may be bonded to another substrate separate from the base substrate. 
     Each of the laser diodes may include one of an edge emitter laser or a vertical-cavity surface-emitting laser (VCSEL). 
     According to one or more implementations of the present disclosure, a laser projector may be summarized as including: an optical engine, comprising: a base substrate; a plurality of laser diodes, each of the plurality of laser diodes bonded directly or indirectly to the base substrate; at least one laser diode driver circuit operatively coupled to the plurality of laser diodes to selectively drive current to the plurality of laser diodes; a plurality of collimation lenses, each of the plurality of collimation lenses positioned proximate a respective one of the plurality of laser diodes collimates light emitted therefrom; a cap comprising at least one wall and at least one optical window that, together with the base substrate, define an interior volume sized and dimensioned to receive at least the plurality of laser diodes and the plurality of collimation lenses, the cap being bonded to the base substrate to provide a hermetic or partially hermetic seal between the interior volume of the cap and a volume exterior to the cap, and the optical window positioned and oriented to allow beams of light emitted from the plurality of laser diodes through the collimation lenses to exit the interior volume; and a grating waveguide combiner positioned proximate the optical window of the cap, the grating waveguide combiner comprising a plurality of input grating couplers and at least one output grating coupler, in operation, the grating waveguide combiner receives a plurality of beams of light at the respective plurality of input grating couplers and combines the plurality of beams of light to provide a collimated aggregated beam of light at the output grating coupler; and at least one scan mirror positioned to receive the aggregate beam of light output at the output grating coupler of the grating waveguide combiner, the at least one scan mirror controllably orientable to redirect the aggregate beam of light over a range of angles. 
     The grating waveguide combiner may include a first grating waveguide and a second grating waveguide. Each of the first and second grating waveguides may include at least two input grating couplers. The grating waveguide combiner may include at least four waveguides. 
     The plurality of collimation lenses may be formed as a micro-optic lens array. The plurality of collimation lenses may be bonded to the base substrate. The grating waveguide combiner may be bonded to the base substrate proximate the optical window of the cap. 
     The optical engine of the laser projector may further include a common collimation lens positioned and oriented to receive and collimate the aggregate beam of light from the output grating coupler of the grating waveguide combiner. The common collimation lens may include an achromatic lens. The common collimation lens may include an apochromatic lens. 
     The optical engine of the laser projector may further comprise at least one diffractive optical element positioned and oriented to receive the aggregate beam of light, in operation, the at least one diffractive optical element may provide wavelength dependent focus correction for the aggregate beam of light. 
     The optical engine of the laser projector may further include a plurality of chip submounts bonded to the base substrate, wherein each of the laser diodes are bonded to a corresponding one of the plurality of chip submounts. The plurality of laser diodes may include a red laser diode to provide a red laser light, a green laser diode to provide a green laser light, a blue laser diode to provide a blue laser light, and an infrared laser diode to provide infrared laser light. The base substrate may be formed from at least one of low temperature co-fired ceramic (LTCC), aluminum nitride (AlN), or alumina. 
     The at least one laser diode driver circuit may be bonded to a first surface of the base substrate, and the plurality of laser diodes and the cap may be bonded to a second surface of the base substrate, the second surface of the base substrate opposite the first surface of the base substrate. The at least one laser diode driver circuit, the plurality of laser diodes, and the cap may be bonded to a first surface of the base substrate. The plurality of laser diodes and the cap may be bonded to the base substrate, and the at least one laser diode driver circuit may be bonded to another substrate separate from the base substrate. Each of the laser diodes may be one of an edge emitter laser or a vertical-cavity surface-emitting laser (VCSEL). 
     According to one or more implementations of the present disclosure, a wearable heads-up display (WHUD) may be summarized as including: a support structure that in use is worn on the head of a user; a laser projector carried by the support structure, the laser projector comprising: an optical engine, comprising: a base substrate; a plurality of laser diodes, each of the plurality of laser diodes bonded directly or indirectly to the base substrate; at least one laser diode driver circuit operatively coupled to the plurality of laser diodes to selectively drive current to the plurality of laser diodes; a plurality of collimation lenses, each of the plurality of collimation lenses positioned proximate a respective one of the plurality of laser diodes collimates light emitted therefrom; a cap comprising at least one wall and at least one optical window that, together with the base substrate, define an interior volume sized and dimensioned to receive at least the plurality of laser diodes and the plurality of collimation lenses, the cap being bonded to the base substrate to provide a hermetic or partially hermetic seal between the interior volume of the cap and a volume exterior to the cap, and the optical window positioned and oriented to allow beams of light emitted from the plurality of laser diodes through the collimation lenses to exit the interior volume; and a grating waveguide combiner positioned proximate the optical window of the cap, the grating waveguide combiner comprising a plurality of input grating couplers and at least one output grating coupler, in operation, the grating waveguide combiner receives a plurality of beams of light at the respective plurality of input grating couplers and combines the plurality of beams of light to provide a collimated aggregated beam of light at the output grating coupler; and at least one scan mirror positioned to receive the aggregate beam of light output at the output grating coupler of the grating waveguide combiner, the at least one scan mirror controllably orientable to redirect the aggregate beam of light over a range of angles. 
     The grating waveguide combiner may include a first grating waveguide and a second grating waveguide. Each of the first and second grating waveguides may include at least two input grating couplers. The grating waveguide combiner may include at least four waveguides. 
     The plurality of collimation lenses may be formed as a micro-optic lens array. The plurality of collimation lenses may be bonded to the base substrate. The grating waveguide combiner may be bonded to the base substrate proximate the optical window of the cap. 
     The optical engine of the laser projector may further include a common collimation lens positioned and oriented to receive and collimate the aggregate beam of light from the output grating coupler of the grating waveguide combiner. The common collimation lens may include an achromatic lens or an apochromatic lens. 
     The optical engine of the laser projector may further comprise at least one diffractive optical element positioned and oriented to receive the aggregate beam of light, in operation, the at least one diffractive optical element may provide wavelength dependent focus correction for the aggregate beam of light. 
     The optical engine of the laser projector may further include a plurality of chip submounts bonded to the base substrate, wherein each of the laser diodes are bonded to a corresponding one of the plurality of chip submounts. The plurality of laser diodes may include a red laser diode to provide a red laser light, a green laser diode to provide a green laser light, a blue laser diode to provide a blue laser light, and an infrared laser diode to provide infrared laser light. The base substrate may be formed from at least one of low temperature co-fired ceramic (LTCC), aluminum nitride (AlN), or alumina. 
     The at least one laser diode driver circuit may be bonded to a first surface of the base substrate, and the plurality of laser diodes and the cap may be bonded to a second surface of the base substrate, the second surface of the base substrate opposite the first surface of the base substrate. The at least one laser diode driver circuit, the plurality of laser diodes, and the cap may be bonded to a first surface of the base substrate. The plurality of laser diodes and the cap may be bonded to the base substrate, and the at least one laser diode driver circuit may be bonded to another substrate separate from the base substrate. The plurality of laser diodes and the cap may be bonded to the base substrate, and the at least one laser diode driver circuit may be mounted to the support structure of the WHUD. 
     Each of the laser diodes may be one of an edge emitter laser or a vertical-cavity surface-emitting laser (VCSEL). The WHUD may further include a processor communicatively coupled to the laser projector to modulate the generation of light signals. The WHUD may further include a transparent combiner carried by the support structure and positioned within a field of view of the user, in operation the transparent combiner directs laser light from an output of the laser projector into the field of view of the user. 
     According to one or more implementations of the present disclosure, a method of manufacturing an optical engine may be summarized as including: bonding a plurality of laser diodes directly or indirectly to a base substrate; coupling at least one laser diode driver circuit to the laser diodes, in operation the at least one laser diode driver circuit selectively drives current to the laser diodes; bonding a plurality of collimation lenses to the base substrate proximate the plurality of laser diodes; bonding a cap comprising at least one wall and at least one optical window to the base substrate, the at least one wall, the at least one optical window, and at least a portion of the base substrate together delimit an interior volume sized and dimensioned to receive at least the plurality of laser diodes and the plurality of collimation lenses, the bonding of the cap to the base substrate providing a hermetic or partially hermetic seal between the interior volume of the cap and a volume exterior to the cap, and the optical window positioned and oriented to allow light emitted from the laser diodes through the collimation lenses to exit the interior volume; and bonding a grating waveguide combiner proximate the optical window of the cap, the grating waveguide combiner comprising a plurality of input grating couplers and at least one output grating coupler, in operation, the grating waveguide combiner receives a plurality of beams of light at the respective plurality of input grating couplers and combines the plurality of beams of light to provide a collimated aggregated beam of light at the output grating coupler. 
     Bonding a plurality of collimation lenses to the base substrate may include bonding a micro-optic lens array to the base substrate. The method may further include actively or passively aligning the collimation lenses. 
     Bonding a grating waveguide combiner proximate the optical window of the cap may include writing the plurality of input grating couplers and at least one output grating coupler into a waveguide medium, and subsequently bonding the waveguide medium proximate the optical window of the cap. Bonding a grating waveguide combiner proximate the optical window of the cap may include bonding a writeable waveguide medium proximate the optical window of the cap, and subsequently writing the plurality of input grating couplers and at least one output grating coupler into the waveguide medium. 
     The method may further include: bonding each of the laser diodes indirectly to the base substrate by bonding each laser diode to a respective chip submount; and bonding each chip submount to the base substrate. Bonding each laser diode to a respective chip submount may include bonding each laser diode to a respective chip submount using a eutectic gold tin (AuSn) solder process. Bonding each chip submount to the base substrate may include step-soldering each chip submount to the base substrate. Bonding each chip submount to the base substrate may include bonding each chip submount to the base substrate using at least one of a reflow oven process, thermosonic bonding, thermocompression bonding, transient liquid phase (TLP) bonding, or laser soldering. Bonding each chip submount to the base substrate may include bonding a chip submount that has a red laser diode bonded thereto, bonding a chip submount that has a green laser diode bonded thereto, bonding a chip submount that has a blue laser diode bonded thereto, and bonding a chip submount that has an infrared laser diode bonded thereto. 
     Coupling at least one laser diode driver circuit to the laser diodes may include: bonding a plurality of electrical connections to the base substrate, each electrical connection coupled to a respective laser diode in the plurality of laser diodes; providing a coupling between each of the plurality of electrical connections and the at least one laser diode driver circuit; and bonding an electrically insulating cover to the base substrate over the plurality of electrical connections, and bonding the cap to the base substrate may include bonding the cap to the base substrate and the electrically insulating cover. Providing a coupling between each of the plurality of electrical connections and the at least one laser diode driver circuit may include: bonding a plurality of electrical contacts to the base substrate, each electrical contact coupled to a respective one of the plurality of electrical connections; and providing a coupling between each of the electrical contacts and the at least one laser diode driver circuit. 
     Bonding the plurality of laser diodes directly or indirectly to a base substrate may include bonding the laser diodes directly or indirectly to a first surface of the base substrate, and bonding a cap to the base substrate may include bonding a cap to the first surface of the base substrate, and the method may further include bonding the at least one laser diode driver circuit to a second surface of the base substrate, the second surface of the base substrate opposite the first surface of the base substrate. Bonding the plurality of laser diodes directly or indirectly to a base substrate may include bonding the laser diodes directly or indirectly to a first surface of the base substrate, and bonding a cap to the base substrate may include bonding a cap to the first surface of the base substrate, and the method may further include bonding the at least one laser diode driver circuit to the first surface of the base substrate. Bonding a cap to the base substrate may include bonding a cap to the base substrate using at least one of a seam welding process, a laser assisted soldering process, or a diffusion bonding process. 
     The method may further include positioning and orienting a collimation lens to receive and collimate the aggregate beam of light from the output facet of the photonic integrated circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the drawings, identical reference numbers identify similar elements or acts. The sizes and relative positions of elements in the drawings are not necessarily drawn to scale. For example, the shapes of various elements and angles are not necessarily drawn to scale, and some of these elements may be arbitrarily enlarged and positioned to improve drawing legibility. Further, the particular shapes of the elements as drawn, are not necessarily intended to convey any information regarding the actual shape of the particular elements, and may have been solely selected for ease of recognition in the drawings. 
         FIG. 1A  is a left side, sectional elevational view of an optical engine, in accordance with the present systems, devices, and methods. 
         FIG. 1B  is a front side, sectional elevational view of the optical engine also shown in  FIG. 1A , in accordance with the present systems, devices, and methods. 
         FIG. 2  is a flow diagram of a method of operating an optical engine, in accordance with the present systems, devices, and methods. 
         FIG. 3  is a schematic diagram of a wearable heads-up display with a laser projector that includes an optical engine, and a transparent combiner in a field of view of an eye of a user, in accordance with the present systems, devices, and methods. 
         FIG. 4  is an isometric view of a wearable heads-up display with a laser projector that includes an optical engine, in accordance with the present systems, devices, and methods. 
         FIG. 5  is a flow diagram of a method of manufacturing an optical engine, in accordance with the present systems, devices, and methods. 
         FIG. 6  is a top plan view of a photonic integrated circuit for wavelength multiplexing that includes a plurality of grating couplers on a surface thereof, the photonic integrated circuit followed by a common collimation lens and an optional diffractive optical element, in accordance with the present systems, devices, and methods. 
         FIG. 7  is a left side sectional elevational view of an optical engine that includes a plurality of laser diodes inside a hermetically or partially hermetically sealed package coupled to the photonic integrated circuit of  FIG. 6  for wavelength multiplexing, and a common collimation lens and an optional diffractive optical element, in accordance with the present systems, devices, and methods. 
         FIG. 8  is a top plan view of a photonic integrated circuit for wavelength multiplexing followed by a common collimation lens and an optional diffractive optical element, in accordance with the present systems, devices, and methods. 
         FIG. 9  is a left side sectional elevational view of an optical engine that includes a plurality of laser diodes inside a hermetically or partially hermetically sealed package coupled to a photonic integrated circuit of  FIG. 8  for wavelength multiplexing, and a common collimation lens and an optional diffractive optical element, in accordance with the present systems, devices, and methods. 
         FIG. 10  is a schematic diagram of a laser writing system which can be used to write photonic integrated circuits in accordance with the present systems, devices, and methods. 
         FIG. 11  is a flow diagram of a method of manufacturing an optical engine including writing a photonic integrated circuit, in accordance with the present systems, devices, and methods. 
         FIGS. 12A, 12B, and 13  are schematic diagrams of laser writing systems which can be used to write photonic integrated circuits in writeable glass already bonded to a substrate or circuit, according to at least two illustrated implementations. 
         FIG. 14  is a left side sectional elevational view of an optical engine that includes a plurality of laser diodes inside a hermetically or partially hermetically sealed package coupled to a photonic integrated circuit for wavelength multiplexing via a directly written waveguide, in accordance with the present systems, devices, and methods. 
         FIG. 15  is a left side sectional elevational view of an optical engine that includes a plurality of laser diodes coupled to a photonic integrated circuit for wavelength multiplexing via a directly written waveguide, wherein the waveguide is formed in a waveguide medium that also provides a hermetic or partially hermetic seal for the plurality of laser diodes, in accordance with the present systems, devices, and methods. 
         FIGS. 16A and 16B  are isometric views of optical engines including an insulating cover which prevents undesired electrical signal transmission from electrical connections, and showing implementations of optical engines having differing positions for a laser diode driver circuit in accordance with the present systems, devices, and methods. 
         FIG. 17A  is a left side sectional elevational view of an optical engine that includes a plurality of laser diodes inside a hermetically sealed package, and further includes a grating waveguide combiner that inputs light emitted from the plurality of laser diodes and outputs a superimposed collimated beam, in accordance with the present systems, devices, and methods. 
         FIG. 17B  is a front side elevational view of the optical engine of  FIG. 17A , in accordance with the present systems, devices, and methods. 
         FIG. 18  is an isometric view of a laser diode, showing a fast axis and a slow axis of a light beam generated by the laser diode, in accordance with the present systems, devices, and methods. 
         FIG. 19A  is a left side sectional view of a set of collimation lenses for collimating a beam of light separately along different axes. 
         FIG. 19B  is a top side sectional elevational view of the set of collimation lenses of  FIG. 19A . 
         FIGS. 19C and 19D  are isometric views of exemplary lens shapes which could be used as lenses in the implementation of  FIGS. 19A and 19B . 
         FIG. 20A  is a left side sectional view of a set of collimation lenses for circularizing and collimating a beam of light. 
         FIG. 20B  is a top side sectional elevational view of the set of collimation lenses of  FIG. 20A . 
         FIGS. 20C and 20D  are isometric views of exemplary lens shapes which could be used as a collimation lens in the implementation of  FIGS. 20A and 20B . 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed implementations. However, one skilled in the relevant art will recognize that implementations may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well-known structures associated with computer systems, server computers, and/or communications networks have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the implementations. 
     Unless the context requires otherwise, throughout the specification and claims that follow, the word “comprising” is synonymous with “including,” and is inclusive or open-ended (i.e., does not exclude additional, unrecited elements or method acts). 
     Reference throughout this specification to “one implementation” or “an implementation” means that a particular feature, structure or characteristic described in connection with the implementation is included in at least one implementation. Thus, the appearances of the phrases “in one implementation” or “in an implementation” in various places throughout this specification are not necessarily all referring to the same implementation. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more implementations. 
     As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the context clearly dictates otherwise. 
     The headings and Abstract of the Disclosure provided herein are for convenience only and do not interpret the scope or meaning of the implementations. 
     One or more implementations of the present disclosure provide laser-based optical engines, for example, laser-based optical engines for laser projectors used in wearable heads-up displays or other applications. Generally, the optical engines discussed herein integrate a plurality of laser dies or diodes (e.g., 3 laser diodes, 4 laser diodes) within a single, hermetically or partially hermetically sealed, encapsulated package. As discussed further below with reference to  FIGS. 6-9 , in at least some implementations, photonic integrated circuits having input facets (e.g., edge couplers, grating couplers) may be used to wavelength multiplex beams of light emitted by the plurality of laser diodes into a coaxially superimposed aggregate beam. Alternatively, each wavelength of light may be channeled individually through the photonic integrated circuit. As discussed below with reference to  FIGS. 14-15 , in at least some implementations, the laser diodes are coupled to the photonic integrated circuit via directly written waveguides. In at least some implementations, the waveguide medium in which the waveguides are written may also provide a seal for the laser diodes, thereby eliminating the need for a separate cap to hermetically or partially hermetically seal the laser diodes on a base substrate, for example. 
     As discussed below with reference to  FIGS. 17A-17B , in at least some implementations, an optical engine may include a grating waveguide combiner that inputs light emitted from the plurality of laser diodes and outputs a superimposed collimated beam, as discussed further below with reference to  FIGS. 17A and 17B . Such optical engines may have various advantages over existing designs including, for example, smaller volume, lower weight, better manufacturability, lower cost, faster modulation speed, etc. The material used for the optical engines discussed herein may be any suitable materials, e.g., ceramics with advantageous thermal properties, etc. As noted above, such features are particularly advantages in various applications including WHUDs. 
       FIG. 1A  is a left side, elevational sectional view of an optical engine  100 , which may also be referred to as a “multi-laser diode module” or an “RGB laser module,” in accordance with the present systems, devices, and methods.  FIG. 1B  is a front side, elevational sectional view of the optical engine  100 . The optical engine  100  includes a base substrate  102  having a top surface  104  and a bottom surface  106  opposite the top surface. The base substrate  102  may be formed from a material that is radio frequency (RF) compatible and is suitable for hermetic sealing. For example, the base substrate  102  may be formed from low temperature co-fired ceramic (LTCC), aluminum nitride (AlN), alumina, aluminum nitride (AlN), Kovar®, other ceramics with suitable thermal properties, etc. The term Kovar® generally refers to iron-nickel-cobalt alloys having similar thermal expansion coefficients to glass and ceramics, thus making Kovar® materials particularly suitable for forming hermetic seals which remain functional in a wide range of temperatures. 
     The optical engine  100  also includes a plurality of chip submounts  108   a - 108   d  (collectively  108 ) bonded (e.g., attached) to the top surface  104  of the base substrate  102 . The plurality of chip submounts  108  are aligned in a row across a width of the optical engine  100  between the left and right sides thereof. Each of the plurality of chip submounts  108  includes a laser diode  110 , also referred to as a laser chip or laser die, bonded thereto. In particular, an infrared chip submount  108   a  carries an infrared laser diode  110   a , a red chip submount  108   b  carries a red laser diode  110   b , a green chip submount  108   c  carries a green laser diode  110   c , and a blue chip submount  108   d  carries a blue laser diode  110   d . In operation, the infrared laser diode  110   a  provides infrared laser light, the red laser diode  110   b  provides red laser light, the green laser diode  110   c  provides green laser light, and the blue laser diode  110   d  provides blue laser light. Each of the laser diodes  110  may comprise one of an edge emitter laser or a vertical-cavity surface-emitting laser (VCSEL), for example. Each of the four laser diode/chip submount pairs may be referred to collectively as a “laser chip on submount,” or a laser CoS  112 . Thus, the optical engine  100  includes an infrared laser CoS  112   a , a red laser CoS  112   b , a green laser CoS  112   c , and a blue laser CoS  112   d . In at least some implementations, one or more of the laser diodes  110  may be bonded directly to the base substrate  102  without use of a submount  108 . It should be appreciated that although some implementations discussed herein describe laser diodes as chips or dies on submounts, other dies or types of devices, e.g., p-side down devices, may be used as well. 
     The optical engine  100  also includes a laser diode driver circuit  114  bonded to the bottom surface  106  of the base substrate  102 . The laser diode driver circuit  114  is operatively coupled to the plurality of laser diodes  110  via suitable electrical connections  116  to selectively drive current to the plurality of laser diodes. In at least some implementations, the laser diode driver circuit  114  may be positioned relative to the CoSs  112  to minimize the distance between the laser diode driver circuit  114  and the CoSs  112 . Although not shown in  FIGS. 1A and 1B , the laser diode driver circuit  114  may be operatively coupleable to a controller (e.g., microcontroller, microprocessor, ASIC) which controls the operation of the laser diode driver circuit  114  to selectively modulate laser light emitted by the laser diodes  110 . In at least some implementations, the laser diode driver circuit  114  may be bonded to another portion of the base substrate  102 , such as the top surface  104  of the base substrate. In at least some implementations, the laser diode driver circuitry  114  may be remotely located and operatively coupled to the laser diodes  110 . In order to not require the use of impedance matched transmission lines, the size scale may be small compared to a wavelength (e.g., lumped element regime), where the electrical characteristics are described by (lumped) elements like resistance, inductance, and capacitance. 
     Proximate the laser diodes  110  there is positioned an optical director element  118 . Like the chip submounts  108 , the optical director element  118  is bonded to the top surface  104  of the base substrate  102 . In the illustrated example, the optical director element  118  has a triangular prism shape that includes a plurality of planar faces. In particular the optical director element  118  includes an angled front face  118   a  that extends along the width of the optical engine  100 , a rear face  118   b , a bottom face  118   c  that is bonded to the top surface  104  of the base substrate  102 , a left face  118   d , and a right face  118   e  opposite the left face. The optical director element  118  may comprise a mirror or a prism, for example. 
     The optical engine  100  also includes a cap  120  that includes a vertical sidewall  122  having a lower first end  124  and an upper second end  126  opposite the first end. A flange  128  may be disposed around a perimeter of the sidewall  122  adjacent the lower first end  124 . Proximate the upper second end  126  of the sidewall  122  there is a horizontal optical window  130  that forms the “top” of the cap  120 . The sidewall  122  and the optical window  130  together define an interior volume  132  sized and dimensioned to receive the plurality of chip submounts  108 , the plurality of laser diodes  110 , and the optical director element  118 . The lower first end  124  and the flange  128  of the cap  120  are bonded to the base substrate  102  to provide a hermetic or partially hermetic seal between the interior volume  132  of the cap and a volume  134  exterior to the cap. 
     As shown best in  FIG. 1A , the optical director element  118  is positioned and oriented to direct (e.g., reflect) laser light received from each of the plurality of laser diodes  110  upward (as shown) toward the optical window  130  of the cap  120 , wherein the laser light exits the interior volume  132 . 
     The cap  120  may have a round shape, rectangular shape, or other shape. Thus, the vertical sidewall  122  may comprise a continuously curved sidewall, a plurality (e.g., four) of adjacent planar portions, etc. The optical window  130  may comprise an entire top of the cap  120 , or may comprise only a portion thereof. In at least some implementations, the optical window  130  may be located on the sidewall  122  rather than positioned as a top of the cap  120 , and the laser diodes  110  and/or the optical director element  118  may be positioned and oriented to direct the laser light from the laser diodes toward the optical window on the sidewall  122 . At least some implementations may not include optical director element  118  such that laser light from the laser diodes may be output towards the optical window on the sidewall  122  without the need for intervening optical elements. In at least some implementations, the cap  120  may include a plurality of optical windows instead of a single optical window. 
     The optical engine  100  also includes four collimation/pointing lenses  136   a - 136   d  (collectively  136 ), one for each of the four laser diodes  110   a - 110   d , respectively, that are bonded to a top surface  138  of the optical window  130 . Each of the plurality of collimation lenses  136  is positioned and oriented to receive light from a corresponding one of the laser diodes  110  through the optical window  130 . In particular, the collimation lens  136   a  receives light from the infrared laser diode  110   a  via the optical director element  118  and the optical window  130 , the collimation lens  136   b  receives light from the red laser diode  110   b  via the optical director element and the optical window, the collimation lens  136   c  receives light from the green laser diode  110   c  via the optical director element and the optical window, and the collimation lens  136   d  receives light from the blue laser diode  110   d  via the optical director element and the optical window. 
     Each of the collimation lenses  136  is operative to receive laser light from a respective one of the laser diodes  110 , and to generate a single color beam. In particular, the collimation lens  136   a  receives infrared laser light from the infrared laser diode  110   a  and produces an infrared laser beam  138   a , the collimation lens  136   b  receives red laser light from the red laser diode  110   b  and produces a red laser beam  138   b , the collimation lens  136   c  receives green laser light from the green laser diode  110   c  and produces a green laser beam  138   c , and the collimation lens  136   d  receives blue laser light from the blue laser diode  110   d  and produces a blue laser beam  138   d.    
     The optical engine  100  may also include, or may be positioned proximate to, a beam combiner  140  that is positioned and oriented to combine the light beams  138   a - 138   d  received from each of the collimation lenses  136  into a single aggregate beam  142 . As an example, the beam combiner  140  may include one or more diffractive optical elements (DOE) and/or refractive/reflective optical elements that combine the different color beams  138   a - 138   d  in order to achieve coaxial superposition. An example beam combiner is shown in  FIG. 3  and discussed below. 
     In at least some implementations, the laser CoSs  112 , the optical director element  118 , and/or the collimation lenses  136  may be positioned differently. As noted above, laser diode driver circuit  114  may be mounted on the top surface  104  or the bottom surface  106  of the base substrate  102 , depending on the RF design and other constraints (e.g., package size). In at least some implementations, the optical engine  100  may not include the optical director element  118 , and the laser light may be directed from the laser diodes  110  toward the collimation lenses  136  without requiring an intermediate optical director element. Additionally, in at least some implementations, one or more of the laser diodes may be mounted directly on the base substrate  102  without use of a submount. 
     For the sake of a controlled atmosphere inside the interior volume  132 , it may be desirable to have no organic compounds inside the interior volume  132 . In at least some implementations, the components of the optical engine  100  may be bonded together using no adhesives. In other implementations, a low amount of adhesives may be used to bond at least one of the components, which may reduce cost while providing a relatively low risk of organic contamination for a determined lifetime (e.g., 2 or more years) of the optical engine  100 . The use of adhesives may result in a partial hermetic seal, but this partial hermetic seal may be acceptable in certain applications, as detailed below. 
     Generally, “hermetic” refers to a seal which is airtight, that is, a seal which excludes the passage of air, oxygen, and other gases. “Hermetic” within the present specification carries this meaning. Further, “partially hermetic” as used herein refers to a seal which limits, but does not necessarily completely prevent, the passage of gases such as air. “Partially hermetic” as used herein may alternatively be stated as “reduced hermiticity”. In the example above, adhesives may be used to bond components. Such adhesives may result in a seal being not completely hermetic, in that some amount of gasses may slowly leak through the adhesive. However, such a seal can still be considered “partially hermetic” or as having “reduced hermiticity”, because the seal reduces the flow of gasses therethrough. 
     In one example application, even in an environment with only partial hermiticity, the life of laser diodes  110  and transparency of optical window  130  may be maintained longer than the life of a battery of a device, such that partial hermiticity may be acceptable for the devices. In some cases, even protecting interior volume  132  from particulate with a dust cover may be sufficient to maintain laser diodes  110  and transparency of optical window  130  for the intended lifespan of the device. In some cases, laser diodes  110  and transparency of optical window  130  may last for the intended lifespan of the device even without a protective cover. Various bonding processes (e.g., attaching processes) for the optical engine  100  are discussed below with reference to  FIG. 5 . 
       FIG. 2  is a flow diagram of a method  200  of operating an optical engine, in accordance with the present systems, devices, and methods. The method  200  may be implemented using the optical engine  100  of  FIGS. 1A-1B , for example. It should be appreciated that methods of operating optical engines according to the present disclosure may include fewer or additional acts than set forth in the method  200 . Further, the acts discussed below may be performed in an order different than the order presented herein. 
     At  202 , at least one controller may cause a plurality of laser diodes of an optical engine to generate laser light. As discussed above, the plurality of laser diodes may be hermetically or partially hermetically sealed in an encapsulated package. The laser diodes may produce light sequentially and/or simultaneously with each other. At  204 , at least one optical director element may optionally receive the laser light from the laser diodes. The optical director element may comprise a mirror or a prism, for example. As discussed above, in at least some implementations the optical engine may be designed such that laser light exits the optical engine without use of an optical director element. 
     At  206 , the at least one optical director element, if included, may direct the received laser light toward an optical window of the encapsulated package. For example, the optical director element may reflect the received laser light toward the optical window of the encapsulated package. In implementations without at least one optical director element, the laser light generated by the plurality of laser diodes may be output directly toward the optical window of the encapsulated package. 
     At  208 , a plurality of collimation lenses may collimate the laser light from the laser diodes that exits the encapsulated package via the optical window to generate a plurality of differently colored laser light beams. The collimation lenses may be positioned inside or outside of the encapsulated package. As an example, the collimation lenses may be physically coupled to the optical window of the encapsulated package. 
     At  210 , a beam combiner may combine the plurality of laser light beams received from each of the collimation lenses into a single aggregate beam. The beam combiner may include one or more diffractive optical elements (DOE) that combine different color beams in order to achieve coaxial superposition, for example. The beam combiner may include one or more DOEs and/or one or more refractive/reflective optical elements. An example beam combiner is shown in  FIG. 3  and discussed below. 
       FIG. 3  is a schematic diagram of a wearable heads-up display (WHUD)  300  with an exemplary laser projector  302 , and a transparent combiner  304  in a field of view of an eye  306  of a user of the WHUD, in accordance with the present systems, devices, and methods. The WHUD  300  includes a support structure (not shown), with the general shape and appearance of an eyeglasses frame, carrying an eyeglass lens  308  with the transparent combiner  304 , and the laser projector  302 . 
     The laser projector  302  comprises a controller or processor  310 , an optical engine  312  comprising four laser diodes  314   a ,  314   b ,  314   c ,  314   d  (collectively  314 ) communicatively coupled to the processor  310 , a beam combiner  316 , and a scan mirror  318 . The optical engine  312  may be similar or identical to the optical engine  100  discussed above with reference to  FIGS. 1A and 1B . Generally, the term “processor” refers to hardware circuitry, and may include any of microprocessors, microcontrollers, application specific integrated circuits (ASICs), digital signal processors (DSPs), programmable gate arrays (PGAs), and/or programmable logic controllers (PLCs), or any other integrated or non-integrated circuit. 
     During operation of the WHUD  300 , the processor  310  modulates light output from the laser diodes  314 , which includes a first red laser diode  314   a  (R), a second green laser diode  314   b  (G), a third blue laser diode  314   c  (B), and a fourth infrared laser diode  314   d  (IR). The first laser diode  314   a  emits a first (e.g., red) light signal  320 , the second laser diode  314   b  emits a second (e.g., green) light signal  322 , the third laser diode  314   c  emits a third (e.g., blue) light signal  324 , and the fourth laser diode  314   d  emits a fourth (e.g., infrared) light signal  326 . All four of light signals  320 ,  322 ,  324 , and  326  enter or impinge on the beam combiner  316 . Beam combiner  316  could for example be based on any of the beam combiners described in U.S. Provisional Patent Application Ser. No. 62/438,725, U.S. Non-Provisional patent application Ser. No. 15/848,265 (U.S. Publication Number 2018/0180885), U.S. Non-Provisional patent application Ser. No. 15/848,388 (U.S. Publication Number 2018/0180886), U.S. Provisional Patent Application Ser. No. 62/450,218, U.S. Non-Provisional patent application Ser. No. 15/852,188 (U.S. Publication Number 2018/0210215), U.S. Non-Provisional patent application Ser. No. 15/852,282, (U.S. Publication Number 2018/0210213), and/or U.S. Non-Provisional patent application Ser. No. 15/852,205 (U.S. Publication Number 2018/0210216). 
     In the illustrated example, the beam combiner  316  includes optical elements  328 ,  330 ,  332 , and  334 . The first light signal  320  is emitted towards the first optical element  328  and reflected by the first optical element  328  of the beam combiner  316  towards the second optical element  330  of the beam combiner  316 . The second light signal  322  is also directed towards the second optical element  330 . The second optical element  330  is formed of a dichroic material that is transmissive of the red wavelength of the first light signal  320  and reflective of the green wavelength of the second light signal  322 . Therefore, the second optical element  330  transmits the first light signal  320  and reflects the second light signal  322 . The second optical element  330  combines the first light signal  320  and the second light signal  322  into a single aggregate beam (shown as separate beams for illustrative purposes) and routes the aggregate beam towards the third optical element  332  of the beam combiner  316 . 
     The third light signal  324  is also routed towards the third optical element  332 . The third optical element  332  is formed of a dichroic material that is transmissive of the wavelengths of light (e.g., red and green) in the aggregate beam comprising the first light signal  320  and the second light signal  322  and reflective of the blue wavelength of the third light signal  324 . Accordingly, the third optical element  332  transmits the aggregate beam comprising the first light signal  320  and the second light signal  322  and reflects the third light signal  324 . In this way, the third optical element  332  adds the third light signal  324  to the aggregate beam such that the aggregate beam comprises the light signals  320 ,  322 , and  324  (shown as separate beams for illustrative purposes) and routes the aggregate beam towards the fourth optical element  334  in the beam combiner  316 . 
     The fourth light signal  326  is also routed towards the fourth optical element  334 . The fourth optical element  334  is formed of a dichroic material that is transmissive of the visible wavelengths of light (e.g., red, green, and blue) in the aggregate beam comprising the first light signal  320 , the second light signal  322 , and the third light signal  324  and reflective of the infrared wavelength of the fourth light signal  326 . Accordingly, the fourth optical element  334  transmits the aggregate beam comprising the first light signal  320 , the second light signal  322 , and the third light signal  324  and reflects the fourth light signal  326 . In this way, the fourth optical element  334  adds the fourth light signal  326  to the aggregate beam such that the aggregate beam  336  comprises portions of the light signals  320 ,  322 ,  324 , and  326 . The fourth optical element  334  routes the aggregate beam  336  towards the controllable scan mirror  318 . 
     The scan mirror  318  is controllably orientable and scans (e.g. raster scans) the beam  336  to the eye  306  of the user of the WHUD  300 . In particular, the controllable scan mirror  318  scans the laser light onto the transparent combiner  304  carried by the eyeglass lens  308 . The scan mirror  318  may be a single bi-axial scan mirror or two single-axis scan mirrors may be used to scan the laser light onto the transparent combiner  304 , for example. In at least some implementations, the transparent combiner  304  may be a holographic combiner with at least one holographic optical element. The transparent combiner  304  redirects the laser light towards a field of view of the eye  306  of the user. The laser light redirected towards the eye  306  of the user may be collimated by the transparent combiner  304 , wherein the spot at the transparent combiner  304  is approximately the same size and shape as the spot at the eye  306  of the user. The laser light may be converged by the eye  306  to a focal point at the retina of eye  306  and creates an image that is focused. The visible light may create display content in the field of view of the user, and the infrared light may illuminate the eye  306  of the user for the purpose of eye tracking. 
       FIG. 4  is a schematic diagram of a wearable heads-up display (WHUD)  400  with a laser projector  402  in accordance with the present systems, devices, and methods. WHUD  400  includes a support structure  404  with the shape and appearance of a pair of eyeglasses that in use is worn on the head of the user. The support structure  404  carries multiple components, including eyeglass lens  406 , a transparent combiner  408 , the laser projector  402 , and a controller or processor  410 . The laser projector  402  may be similar or identical to the laser projector  302  of  FIG. 3 . For example, the laser projector  402  may include an optical engine, such as the optical engine  100  or the optical engine  312 . The laser projector  402  may be communicatively coupled to the controller  410  (e.g., microprocessor) which controls the operation of the projector  402 , as discussed above. The controller  410  may include or may be communicatively coupled to a non-transitory processor-readable storage medium (e.g., memory circuits such as ROM, RAM, FLASH, EEPROM, memory registers, magnetic disks, optical disks, other storage), and the controller may execute data and/or instruction from the non-transitory processor readable storage medium to control the operation of the laser projector  402 . 
     In operation of the WHUD  400 , the controller  410  controls the laser projector  402  to emit laser light. As discussed above with reference to  FIG. 3 , the laser projector  402  generates and directs an aggregate beam (e.g., aggregate beam  336  of  FIG. 3 ) toward the transparent combiner  408  via at least one controllable mirror (not shown in  FIG. 4 ). The aggregate beam is directed towards a field of view of an eye of a user by the transparent combiner  408 . The transparent combiner  408  may collimate the aggregate beam such that the spot of the laser light incident on the eye of the user is at least approximately the same size and shape as the spot at transparent combiner  408 . The transparent combiner  408  may be a holographic combiner that includes at least one holographic optical element. 
       FIG. 5  is a flow diagram of a method  500  of manufacturing an optical engine, in accordance with the present systems, devices, and methods. The method  500  may be implemented to manufacture the optical engine  100  of  FIGS. 1A-1B  or the optical engine  312  of  FIG. 3 , for example. It should be appreciated that methods of manufacturing optical engines according to the present disclosure may include fewer or additional acts than set forth in the method  500 . Further, the acts discussed below may be performed in an order different than the order presented herein. 
     At  502 , a plurality of laser diodes may be bonded to a respective plurality of submounts. In at least some implementations, this method may be performed by an entity different than that manufacturing the optical engine. For example, in at least some implementations, one or more of the plurality of laser diodes (e.g., green laser diode, blue laser diode) may be purchased as already assembled laser CoSs. For ease of handling and simplification of the overall process, in at least some implementations it may be advantageous to also bond laser diodes that cannot be procured on submounts to a submount as well. As a non-limiting example, in at least some implementations, one or more of the laser diodes may be bonded to a corresponding submount using an eutectic gold tin (AuSn) solder process, which is flux-free and requires heating up top 280° C. 
     At  504 , the plurality of CoSs may be bonded to a base substrate. Alternatively, act  502  could be skipped for at least one or all of the laser diodes, and act  504  could comprise bonding the at least one or all of the laser diodes directly to the base substrate. The base substrate may be formed from a material that is RF compatible and is suitable for hermetic sealing. For example, the base substrate may be formed from low temperature co-fired ceramic (LTCC), aluminum nitride (AlN), alumina, aluminum nitride (AlN), Kovar®, etc. Since several CoSs are bonded next to each other on the same base substrate, it may be advantageous to either “step-solder” them sequentially or to use a bonding technique that does not rely on re-melting of solder materials. For step-soldering, each subsequent soldering step utilizes a process temperature that is less than the process temperatures of previous solder steps to prevent re-melting of solder materials. It may also be important that the laser diode-to-submount bonding does not re-melt during bonding of the CoSs to the base substrate. Bonding technologies other than step-soldering that may be used include parallel soldering of all CoS in reflow oven process, thermosonic or thermocompression bonding, transient liquid phase (TLP) bonding, laser soldering, etc. Some of these example bonding technologies are discussed below. 
     For parallel soldering of all CoSs in a reflow oven process, appropriate tooling is required to assure proper bonding and alignment during the process. An advantage of this process is the parallel and hence time efficient bonding of all CoSs at once and even many assemblies in parallel. A possible disadvantage of this process is the potential loss of the alignment of components during the reflow process. Generally, a soldering cycle ideally needs a few minutes of dwell time. Preheating may be used to reduce the soldering time, which requires a few minutes for such a process depending on the thermal mass of the components being bonded. Thus, a batch process may be used with regular soldering to reduce the assembly costs with high throughput at the expense of alignment tolerance. 
     For thermosonic or thermocompression bonding, thick gold metallization may be used but no extra solder layer is required. The temperatures for thermocompression bonding might be as high as 300 to 350° C. to have a good bond with a good thermal conductivity. Thermosonic bonding may be used to reduce the pressure and temperature needed for bonding, which may be required for at least some components that might not tolerate the temperatures required for thermocompression bonding. 
     Transient liquid phase (TLP) bonding may also be used. There are many different reaction couples that may be used, including gold-tin, copper-tin, etc. With this method, a liquid phase is formed during the bonding which will solidify at the same temperature. The re-melting temperatures of the bond are much higher than the soldering temperatures. 
     In at least some implementations, laser soldering may be used to bond some or all of the components of the optical engine. Generally, the thermal characteristic of the parts to be bonded may be important when implementing a laser soldering process. 
     Subsequent reflows of solder are not recommended due to liquid phase reaction or dissolution mechanisms which may reduce the reliability of the joint. This could result in voiding at the interface or a reduction in strength of the joint itself. In order to mitigate potential reflow dissolution problems, other options can be taken into consideration, which do not rely on extreme heating of the device and can be favorable in terms of production cost. For example, bonding of the base substrate with adhesives (electrically conductive for common mass, or non-conductive for floating) may be acceptable with respect to heat transfer and out-gassing as discussed regarding partial hermetic sealing above. 
     Further, in at least some implementations, a reactive multi-layer foil material (e.g., NanoFoil®) or a similar material may be used as a solder pre-form, which enables localized heat transfer. A reactive multi-layer foil material is a metallic material based on a plurality (e.g., hundreds, thousands) of reactive foils (aluminum and nickel) that enables die-attach soldering (e.g., silicon chip onto stainless steel part). In such implementations, dedicated heat transfer support metallizations may be deposited onto the two components being joined together. This method may be more advantageous for CoS-to-base substrate mounting compared to chip-to-submount bonding. Generally, bonding using reactive multi-layer foil materials enables furnace-free, low-temperature soldering of transparent or non-transparent components, without reaching the bonding temperatures for solder reflow processes. Reactive multi-layer foil materials can be patterned with a ps-laser into exact preform shapes. 
     At  506 , the optical director element, if included, may be bonded to the base substrate proximate the laser CoSs. The optical director element may be bonded to the base substrate using any suitable bonding process, including the bonding processes discussed above with reference to act  504 . 
     At  508 , the laser diode driver circuit may optionally be bonded to the base substrate. As noted above, the laser diode driver circuit may be bonded to the base substrate such that the distance between the laser diode driver circuit and the laser CoSs is minimized. This may also comprise positioning a plurality of electrical connections which operatively couple the laser diode driver circuit to the plurality of laser diodes as shown in  FIGS. 16A and 16B . In alternative implementations, the laser diode driver circuit may be bonded to a separate base substrate from the other components mentioned above as shown in  FIG. 16B . The process used to bond the laser diode driver circuit to the base substrate may be any suitable bonding process, such as bonding processes commonly used to bond surface mount devices (SMD) to circuit boards. In other alternative implementations, the laser diode driver circuit may be mounted directly to a frame of a WHUD. For implementations where the laser diode drive circuit is not bonded to the same base substrate as the other components mentioned above, a plurality of electrical contacts and electrical connections could be bonded to the base substrate, each electrical connection operatively connecting a respective electrical contact to a respective laser diode. Subsequently, the at least one laser driver circuit could be operatively coupled to the electrical contacts, which will then electrically couple the laser diode drive circuit to the electrical connections and consequently to the laser diodes. Exemplary arrangements of electrical connections and electrical contacts is discussed later with reference to  FIG. 16B . 
     At  510 , the cap may optionally be bonded to the base substrate to form a hermetic or partially hermetic seal as discussed above between the interior volume of the encapsulated package and an exterior environment. As noted above, it may be desirable to maintain a specific atmosphere for the laser diode chips for reliability reasons. In at least some implementations, adhesive sealing may be undesirable because of the high permeability of gases. This is especially the case for blue laser diodes, which emit blue laser light that may bake contamination on facets and windows, thereby reducing transparency of the optical window. However, as detailed above regarding  FIGS. 1A and 1B , partial hermiticity, a particulate dust cover, or even no protective cover may be acceptable for certain applications. In implementations where the cap would be bonded over electrical connections which connect the at least one laser diode driver circuit to the plurality of laser diodes, such as when the at least one laser diode driver circuit is bonded to the same side of a base substrate as the laser diodes, or when the at least one laser diode driver circuit is coupled to electrical contacts bonded to the same side of the base substrate as the laser diodes, an electrically insulating cover can first be bonded to the base substrate over the electrical connections. Subsequently, the cap can be bonded at least partially to the electrically insulating cover, and potentially to a portion of the base substrate if the insulating cover does not fully encircle the intended interior volume. In this way, at least a portion of the cap will be bonded to the base substrate indirectly by being bonded to the electrically insulating cover. In some implementations, the entire cap could be bonded to the base substrate indirectly by being bonded to an electrically insulating cover which encircles the intended interior volume. Exemplary electrically insulating covers are discussed later with reference to  FIGS. 16A and 16B . 
     During the sealing process, the atmosphere may be defined by flooding the package accordingly. For example, the interior volume of the encapsulated package may be flooded with an oxygen enriched atmosphere that burns off contaminants which tend to form on interfaces where the laser beam is present. The sealing itself may also be performed so as to prevent the exchange between the package atmosphere and the environment. Due to limitations concerning the allowed sealing temperature, e.g., the components inside the package should not be influenced, in at least some implementations seam welding or laser assisted soldering/diffusion bonding may be used. In at least some implementations, localized sealing using a combination of seam welding and laser soldering may be used. 
     At  512 , the collimation lenses may be actively aligned. For example, once the laser diode driver circuit has been bonded and the cap has been sealed, the laser diodes can be turned on and the collimations lenses for each laser diode can be actively aligned. In at least some implementations, each of the collimation lenses may be positioned to optimize spot as well as pointing for each of the respective laser diodes. 
     At  514 , the beam combiner may be positioned to receive and combine individual laser beams into an aggregate beam. As discussed above, the beam combiner may include one or more diffractive optical elements and/or one or more refractive/reflective optical elements that function to combine the different color beams into an aggregate beam. The aggregate beam may be provided to other components or modules, such as a scan mirror of a laser projector, etc. 
       FIG. 6  is a top plan view of a photonic integrated circuit  600  for wavelength multiplexing followed by a common collimation lens  602  and an optional diffractive optical element  604 . The photonic integrated circuit  600  may be a component in an optical engine, such as an optical engine  700  of  FIG. 7 , an optical engine as shown in  FIG. 12A , or an optical engine as shown in  FIG. 12B  discussed further below. The photonic integrated circuit  600  includes a plurality of input facets  612   a - 612   d  and at least one output facet  608  (e.g., output optical coupler or grating output coupler). In  FIG. 6 , input facets  612   a - 612   d  are shown as grating couplers (also referred to as “diffractive grating couplers” or “grating input couplers”) on a top surface  606  thereof, but other input facets are possible such as illustrated in  FIG. 12B  discussed below. In operation, the photonic integrated circuit  600  receives a plurality of beams of light  610   a - 610   d  that are coupled to the photonic integrated circuit via the input facets  612   a - 612   d , respectively, and wavelength multiplexes the plurality of beams to provide a coaxially superimposed aggregate beam of light  614  that exits the photonic integrated circuit at the output facet  608 , such as an output optical coupler or grating output coupler. Compared to edge coupling, in at least some applications using grating input couplers for input facets  612   a - 612   d  may allow for relaxed tolerances for beam alignment. Generally, the photonic integrated circuit  600  may include one or more diffractive optical elements (DOE) and/or refractive/reflective optical elements that combine the different color beams  610   a - 610   d  in order to achieve coaxial superposition. 
     Following out-coupling of the aggregate beam  614  from the output facet  608  of the photonic integrated circuit  600 , the aggregated beam is collimated via the common collimation lens  602 . In at least some implementations, the collimation lens  602  may be either an achromatic lens or an apochromatic lens (or lens assemblies), depending on the particular optical design and tolerances of the system. In at least some implementations, one or more diffractive optical elements  604  may be used to provide wavelength dependent focus correction. 
       FIG. 7  is a left side sectional elevational view of the optical engine  700 . The optical engine  700  includes several components that may be similar or identical to the components of the optical engine  100  of  FIGS. 1A and 1B . Thus, some or all of the discussion above may be applicable to the optical engine  700 . 
     The optical engine  700  includes a base substrate  702  having a top surface  704  and a bottom surface  706  opposite the top surface. The base substrate  702  may be formed from a material that is radio frequency (RF) compatible and is suitable for hermetic sealing. For example, the base substrate  702  may be formed from low temperature co-fired ceramic (LTCC), aluminum nitride (AlN), alumina, aluminum nitride (AlN), Kovar®, etc. 
     The optical engine  700  also includes a plurality of chip submounts  708  (only one chip submount visible in the sectional view of  FIG. 7 ) that are bonded (e.g., attached) to the top surface  704  of the base substrate  702 . The plurality of chip submounts  708  are aligned in a row across a width of the optical engine  700  between the left and right sides thereof. Each of the plurality of chip submounts  708  includes a laser diode  710 , also referred to as a laser chip or laser die, bonded thereto. In particular, an infrared chip submount carries an infrared laser diode, a red chip submount carries a red laser diode, a green chip submount carries a green laser diode, and a blue chip submount carries a blue laser diode. In operation, the infrared laser diode provides infrared laser light, the red laser diode provides red laser light, the green laser diode provides green laser light, and the blue laser diode provides blue laser light. Each of the laser diodes  710  may comprise one of an edge emitter laser or a vertical-cavity surface-emitting laser (VCSEL), for example. Each of the four laser diode/chip submount pairs may be referred to collectively as a “laser chip on submount,” or a laser CoS  712 . Thus, the optical engine  700  includes an infrared laser CoS, a red laser CoS, a green laser CoS, and a blue laser CoS. In at least some implementations, one or more of the laser diodes  710  may be bonded directly to the base substrate  702  without use of a submount  708 . 
     The optical engine  700  also includes a laser diode driver circuit  714  bonded to the bottom surface  706  of the base substrate  702 . The laser diode driver circuit  714  is operatively coupled to the plurality of laser diodes  710  via suitable electrical connections  716  to selectively drive current to the plurality of laser diodes. Generally, the laser diode driver circuit  714  may be positioned relative to the CoSs  712  to minimize the distance between the laser diode driver circuit  714  and the CoSs  712 . Although not shown in  FIG. 7 , the laser diode driver circuit  714  may be operatively coupleable to a controller (e.g., microcontroller, microprocessor, ASIC) that controls the operation of the laser diode driver circuit  714  to selectively modulate laser light emitted by the laser diodes  710 . In at least some implementations, the laser diode driver circuit  714  may be bonded to another portion of the base substrate  702 , such as the top surface  704  of the base substrate, similar to the implementations shown in  FIG. 16A . In at least some implementations, the laser diode driver circuitry  714  may be remotely located and operatively coupled to the laser diodes  710 . In order to not require the use of impedance matched transmission lines, the size scale may be small compared to a wavelength (e.g., lumped element regime), where the electrical characteristics are described by (lumped) elements like resistance, inductance, and capacitance. 
     Proximate the laser diodes  710  there is positioned an optical director element  718 . Like the chip submounts  708 , the optical director element  718  is bonded to the top surface  704  of the base substrate  702 . In the illustrated example, the optical director element  718  has a triangular prism shape that includes a plurality of planar faces. In particular the optical director element  718  includes an angled front face  718   a  that extends along the width of the optical engine  700 , a rear face  718   b , a bottom face  718   c  that is bonded to the top surface  704  of the base substrate  702 , a left face  718   d , and a right face  718   e  opposite the left face. The optical director element  718  may comprise a mirror or a prism, for example. In at least some implementations, the angled front face  718   a  may be curved to provide fast axis collimation of the laser light from the laser diodes  710 . 
     The optical engine  700  also includes a cap  720  that includes a vertical sidewall  722  having a lower first end  724  and an upper second end  726  opposite the first end. A flange  728  may be disposed around a perimeter of the sidewall  722  adjacent the lower first end  724 . Proximate the upper second end  726  there of the sidewall  722  there is a horizontal (as shown) optical window  730  that forms the “top” of the cap  120 . The sidewall  722  and the optical window  730 , along with a portion of the top surface  704  of the base substrate  702 , together define an interior volume  732  sized and dimensioned to receive the plurality of chip submounts  708 , the plurality of laser diodes  710 , and the optical director element  717 . The lower first end  724  and the flange  728  of the cap  720  are bonded to the base substrate  702  to provide a hermetic or partially hermetic seal between the interior volume  732  of the cap and a volume  734  exterior to the cap. 
     The optical director element  718  is positioned and oriented to direct (e.g., reflect) laser light received from each of the plurality of laser diodes  710  upward (as shown) toward the optical window  730  of the cap  720 , wherein the laser light exits the interior volume  732 . 
     The cap  720  may have a round shape, rectangular shape, or other shape. Thus, the vertical sidewall  722  may comprise a continuously curved sidewall, a plurality (e.g., four) of adjacent planar portions, etc. The optical window  730  may comprise an entire top of the cap  720 , or may comprise only a portion thereof. In at least some implementations, the optical window  730  may be located on the sidewall  722  rather than positioned as a top of the cap  720 , and the laser diodes  710  and/or the optical director element  718  (if present) may be positioned and oriented to direct the laser light from the laser diodes toward the optical window on the sidewall  722 . In at least some implementations, the cap  720  may include a plurality of optical windows instead of a single optical window  730 . 
     In at least some implementations, the optical engine  700  optionally includes four collimation lenses  736  (only one visible in the sectional view of  FIG. 7 ), one for each of the four laser diodes  710 . In other implementations, the collimation lenses  736  are omitted. In the illustrated implementation, the collimation lenses  736  are bonded to a bottom surface of the optical window  730  in a row, although the collimation lenses may be positioned differently in other implementations. For example, in at least some implementations, the collimation lenses  736  may be positioned outside of the package (e.g., outside of the interior volume  732 ) rather than inside the package as shown in  FIG. 7 . Each of the plurality of collimation lenses  736  may be positioned and oriented to receive light from a corresponding one of the laser diodes  710 , and to direct collimated light upward (as shown) through the optical window  730  toward the photonic integrated circuit  600 , which is shown “inverted” in  FIG. 7  (relative to  FIG. 6 ) so that the input facets  612   a - 612   d  (collectively,  612 ) on the surface  606  of the photonic integrated circuit face a top surface  738  of the optical window  730  of the cap  720 . 
     The optical director element  718  and the collimation lenses  736  (when present) direct the beams of light  610   a - 610   d  (see  FIG. 6 ) into the photonic integrated circuit  600  via the input facets  612   a - 612   d . The photonic integrated circuit  600  may be bonded to the top surface of the optical window  730 , as shown in  FIG. 7 . In at least some implementations, the photonic integrated circuit  600  may be bonded to the top surface  704  of the base substrate  702  instead. As discussed above, in operation, the photonic integrated circuit  600  receives a plurality of beams of light  610   a - 610   d  via the input facets  612   a - 612   d  (e.g. grating couplers), respectively, and wavelength multiplexes the plurality of beams to provide a coaxially superimposed aggregate beam of light  614  that exits the photonic integrated circuit at the output optical coupler  608 . 
     In at least some implementations, the laser diodes  710  may be directly coupled to the photonic integrated circuit  600 . In such implementations, the laser diodes  710  may be positioned immediately adjacent to a waveguide structure (e.g., photonic integrated circuit or other waveguide structure) such that sufficient coupling (e.g., acceptable insertion loss) is achieved. For example, in at least some implementations, the photonic integrated circuit  600  may function as the optical window of the package itself. 
     Following out-coupling of the aggregate beam  614  from the output facet  608  of the photonic integrated circuit  600 , the aggregated beam may be collimated via the common collimation lens  602 . In at least some implementations, the common collimation lens  602  may be bonded to the top surface  704  proximate the photonic integrated circuit  600 . In at least some implementations, the collimation lens  602  may be either an achromatic lens or an apochromatic lens, depending on the particular optical design and tolerances of the system. In at least some implementations, the optical engine  700  may include one or more diffractive optical elements  604  to provide wavelength dependent focus correction. 
     In at least some implementations, at least some of the components may be positioned differently. As noted above, the laser diode driver circuit  714  may be mounted on the top surface  704  or the bottom surface  706  of the base substrate  702 , or may be positioned remotely therefrom, depending on the RF design and other constraints (e.g., package size), similarly to as discussed with reference to  FIGS. 16A and 16B  below. In at least some implementations, the optical engine  700  may not include an optical director element (e.g., optical director element  718  of  FIG. 7 ), and the laser light may be directed from the laser diodes  710  toward the optical window  730  directly, with our without collimation lenses  736 . Additionally, in at least some implementations, one or more of the laser diodes  710  may be mounted directly on the base substrate  702  without use of a submount. Further, in at least some implementations, in the case of an inorganic or acceptably organic waveguide (e.g., photonic integrated circuit), coupling may be accomplished inside the encapsulated package. Such feature eliminates the requirement for a separate window, as the waveguide services as the window (e.g., optical window  730 ). In such implementations, the plurality of grating couplers of the photonic integrated circuit may be positioned inside the interior volume of the encapsulated package and the at least one optical output coupler of the photonic integrated circuit may be positioned outside of the interior volume, for example. 
     For the sake of a controlled atmosphere inside the interior volume  732 , it may be desirable to have no organic compounds inside the interior volume  732 . In at least some implementations, the components of the optical engine  700  may be bonded together using no adhesives. In other implementations, a low amount of adhesives may be used to bond at least one of the components, which may reduce cost while providing a relatively low risk of organic contamination for a determined lifetime (e.g., 2 or more years) of the optical engine  700 . Similarly to as detailed above regarding  FIGS. 1A and 1B , partial hermiticity, a particulate dust cover, or even no protective cover may be acceptable for certain applications. Various bonding processes (e.g., attaching processes) for the optical engine  700  are discussed above with reference to  FIG. 5 . 
     In at least some implementations, the collimation lenses  736  (when present) and the collimation lens  602  may be actively aligned. In at least some implementations, the CoSs  712 , the cap  720  (including optical window  730 ), and/or the photonic integrated circuit  600  may be passively aligned. Further, depending on the particular design, it may be advantageous to utilize a smaller base substrate  702  and use an additional carrier substrate instead. 
       FIG. 8  is a top plan view of a photonic integrated circuit  800  for wavelength multiplexing followed by a common collimation lens  802  and an optional diffractive optical element  804 . The photonic integrated circuit  800  may be a component in an optical engine, such as an optical engine  900  of  FIG. 9  or an optical engine of  FIG. 13  discussed further below. The photonic integrated circuit  800  includes at least one input optical edge  806  having at least one input facet and at least one output optical edge  808  having at least one output facet. In the example of  FIG. 8 , input edge  806  includes four input facets  806   a ,  806   b ,  806   c , and  806   d , whereas output edge  808  includes one output facet  808   a . However, it is within the scope of the present systems, devices, and methods to include any appropriate number of input facets and output facets. Similar to the photonic integrated circuit  600  of  FIG. 6 , in operation the photonic integrated circuit  800  receives a plurality of beams of light  810   a - 810   d  that are edge coupled to the photonic integrated circuit at the input optical edge  806 , and wavelength multiplexes the plurality of beams to provide a coaxially superimposed aggregate beam of light  812  that exits the photonic integrated circuit at the output optical edge  808  through output facet  808   a . Generally, the photonic integrated circuit  800  may include one or more diffractive optical elements (DOE) and/or refractive/reflective optical elements that combine the different color beams  810   a - 810   d  in order to achieve coaxial superposition. 
     Following out-coupling of the aggregate beam  812  from the output optical edge  808  of the photonic integrated circuit  800 , the aggregated beam is collimated via the common collimation lens  802 . In at least some implementations, the collimation lens  802  may be either an achromatic lens or an apochromatic lens (or lens assemblies), depending on the particular optical design and tolerances of the system. In at least some implementations, one or more diffractive optical elements  804  may be used to provide wavelength dependent focus correction. 
       FIG. 9  is a left side sectional elevational view of the optical engine  900 . The optical engine  900  includes several components that may be similar or identical to the components of the optical engine  100  of  FIGS. 1A and 1B . Thus, some or all of the discussion above may be applicable to the optical engine  900 . 
     The optical engine  900  includes a base substrate  902  having a top surface  904  and a bottom surface  906  opposite the top surface. The base substrate  902  may be formed from a material that is radio frequency (RF) compatible and is suitable for hermetic sealing. For example, the base substrate  902  may be formed from low temperature co-fired ceramic (LTCC), alumina, aluminum nitride (AlN), Kovar®, etc. 
     The optical engine  900  also includes a plurality of chip submounts  908  (only one chip submount visible in the sectional view of  FIG. 9 ) that are bonded (e.g., attached) to the top surface  904  of the base substrate  902 . The plurality of chip submounts  908  are aligned in a row across a width of the optical engine  900  between the left and right sides thereof. Each of the plurality of chip submounts  908  includes a laser diode  910 , also referred to as a laser chip or laser die, bonded thereto. In particular, an infrared chip submount carries an infrared laser diode, a red chip submount carries a red laser diode, a green chip submount carries a green laser diode, and a blue chip submount carries a blue laser diode. In operation, the infrared laser diode provides infrared laser light, the red laser diode provides red laser light, the green laser diode provides green laser light, and the blue laser diode provides blue laser light. Each of the laser diodes  910  may comprise one of an edge emitter laser or a vertical-cavity surface-emitting laser (VCSEL), for example. Each of the four laser diode/chip submount pairs may be referred to collectively as a “laser chip on submount,” or a laser CoS  912 . Thus, the optical engine  900  includes an infrared laser CoS, a red laser CoS, a green laser CoS, and a blue laser CoS. In at least some implementations, one or more of the laser diodes  910  may be bonded directly to the base substrate  902  without use of a submount  908 . 
     The optical engine  900  also includes a laser diode driver circuit  914  bonded to the bottom surface  906  of the base substrate  902 . The laser diode driver circuit  914  is operatively coupled to the plurality of laser diodes  910  via suitable electrical connections  916  to selectively drive current to the plurality of laser diodes. Generally, the laser diode driver circuit  914  may be positioned relative to the CoSs  912  to minimize the distance between the laser diode driver circuit  914  and the CoSs  912 . Although not shown in  FIG. 9 , the laser diode driver circuit  914  may be operatively coupleable to a controller (e.g., microcontroller, microprocessor, ASIC) that controls the operation of the laser diode driver circuit  914  to selectively modulate laser light emitted by the laser diodes  910 . In at least some implementations, the laser diode driver circuit  914  may be bonded to another portion of the base substrate  902 , such as the top surface  904  of the base substrate, similar to the implementation shown in  FIG. 16A . In at least some implementations, the laser diode driver circuitry  914  may be remotely located and operatively coupled to the laser diodes  910 , similar to the implementations shown in  FIG. 16B . In order to not require the use of impedance matched transmission lines, the size scale may be small compared to a wavelength (e.g., lumped element regime), where the electrical characteristics are described by (lumped) elements like resistance, inductance, and capacitance. 
     The optical engine  900  also includes a cap  920  that includes a vertical sidewall  922  and a horizontal wall or top portion  925 . The vertical sidewall  922  includes a lower first end  924  and an upper second end  926  opposite the first end. A flange  928  may be disposed around a perimeter of the sidewall  922  adjacent the lower first end  924 . Within a portion of the vertical sidewall  922  there is an optical window  930  positioned proximate the laser diodes  910  to pass light therefrom out of the cap  920 . In some implementations, optical window  930  can extend from base substrate  902  to top portion  925 , such that one side of cap  920  is formed entirely by optical window  930 . The sidewall  922  and the optical window  930  together define an interior volume  932  sized and dimensioned to receive the plurality of chip submounts  908  and the plurality of laser diodes  910 . The lower first end  924  and the flange  928  of the cap  920  are bonded to the base substrate  902  to provide a hermetic or partially hermetic seal between the interior volume  932  of the cap and a volume  934  exterior to the cap. 
     The cap  920  may have a round shape, rectangular shape, or other shape. Thus, the vertical sidewall  922  may comprise a continuously curved sidewall, a plurality (e.g., four) of adjacent planar portions, etc. The optical window  930  may comprise an entire side of the cap  920 , or may comprise only a portion thereof. In at least some implementations, the cap  920  may include a plurality of optical windows instead of a single optical window  930 . 
     The optical engine  900  also includes four coupling lenses  936  (only one visible in the sectional view of  FIG. 9 ), one for each of the four laser diodes  910  that are bonded to the top surface  904  of the base substrate  902  in a row. Each of the plurality of coupling lenses  936  is positioned and oriented to receive light from a corresponding one of the laser diodes  910  through the optical window  930 . 
     The coupling lenses  936  couple the beams of light  810   a - 810   d  (see  FIG. 8 ) into the photonic integrated circuit  800  via the input optical edge  806 . The photonic integrated circuit  800  may be bonded to the top surface  904  of the base substrate  902  proximate the row of coupling lenses  936 . As discussed above, in operation, the photonic integrated circuit  800  receives a plurality of beams of light  810   a - 810   d  at the input optical edge  806 , and wavelength multiplexes the plurality of beams to provide a coaxially superimposed aggregate beam of light  812  that exits the photonic integrated circuit at the output optical edge  808 . 
     In at least some implementations, the laser diodes  910  may be “butt” coupled to the photonic integrated circuit  800 . In such implementations, the laser diodes  910  may be positioned immediately adjacent to a waveguide structure (e.g., photonic integrated circuit or other waveguide structure) such that sufficient coupling (e.g., acceptable insertion loss) is achieved without the use of a coupling lens. 
     Following out-coupling of the aggregate beam  812  from the output optical edge  808  of the photonic integrated circuit  800 , the aggregated beam may be collimated via the common collimation lens  802 , which may be bonded to the top surface  904  proximate the photonic integrated circuit  800 . In at least some implementations, the collimation lens  802  may be either an achromatic lens or an apochromatic lens, depending on the particular optical design and tolerances of the system. In at least some implementations, the optical engine  900  may include one or more diffractive optical elements  804  bonded to the top surface  904  of the base substrate  902  to provide wavelength dependent focus correction. 
     In at least some implementations, at least some of the components may be positioned differently. As noted above, the laser diode driver circuit  914  may be mounted on the top surface  904  or the bottom surface  906  of the base substrate  902 , or may be positioned remotely therefrom, depending on the RF design and other constraints (e.g., package size). In at least some implementations, the optical engine  900  may include optical director element (e.g., optical director element  118  of  FIG. 1 ), and the laser light may be directed from the laser diodes  910  toward the coupling lenses  936  via an intermediate optical director element. Additionally, in at least some implementations, one or more of the laser diodes  910  may be mounted directly on the base substrate  902  without use of a submount. Further, in at least some implementations, in the case of an inorganic or acceptably organic waveguide (e.g., photonic integrated circuit), coupling may be accomplished inside the encapsulated package. Such feature eliminates the requirement for a separate window, as the waveguide services as the window (e.g., optical window  930 ). In such implementations, the at least one optical input edge of the photonic integrated circuit may be positioned inside the interior volume of the encapsulated package and the at least one optical output edge of the photonic integrated circuit may be positioned outside of the interior volume, for example. 
     For the sake of a controlled atmosphere inside the interior volume  932 , it may be desirable to have no organic compounds inside the interior volume  932 . In at least some implementations, the components of the optical engine  900  may be bonded together using no adhesives. In other implementations, a low amount of adhesives may be used to bond at least one of the components, which may reduce cost while providing a relatively low risk of organic contamination for a determined lifetime (e.g., 2 or more years) of the optical engine  900 . Similarly to as detailed above regarding  FIGS. 1A and 1B , partial hermiticity, a particulate dust cover, or even no protective cover may be acceptable for certain applications. Various bonding processes (e.g., attaching processes) for the optical engine  900  are discussed above with reference to  FIG. 5 . 
     Due to the divergent beam from each of the laser diodes  910  and the lateral distances between the laser diodes, the coupling lenses  936 , and the photonic integrated circuit  800 , it may be advantageous to minimize a distance between the respective output facets of the laser diodes  910  and the optical window  930 . For the same reason, it may be advantageous to minimize the thickness of the optical window  930  and the size of the flange  928  of the cap  920  so that the coupling lenses  936  can be positioned relatively close to the output facets of the laser diodes  910 . In at least some implementations, output window  930  and coupling lenses  936  could be formed as a single element. 
     In at least some implementations, the coupling lenses  936  and the collimation lens  802  may be actively aligned. In at least some implementations, the CoSs  912 , the cap  920  (including optical window  930 ), and/or the photonic integrated circuit  800  may be passively aligned. Further, depending on the particular design, it may be advantageous to utilize a smaller base substrate  902  and use an additional carrier substrate instead. 
       FIG. 10  is a schematic diagram of a laser writing system  1000  in accordance with the present systems, designs and methods. Laser writing system  1000  comprises at least writing laser  1010 , focusing optic  1012 , writeable glass  1020  and translatable mount  1030 . Although the term “glass” is used herein for convenience, any appropriate laser-writable material could be used in place of writeable glass  1020 , such as organically modified ceramics (ORMOCER), for example. Writing laser  1010  emits laser light  1011 . Laser light  1011  comprises short (femptosecond and/or picosecond length) pulses of laser light; consequently, laser light  1011  has extremely high peak instantaneous power. Focusing optic  1012  focuses laser light  1011  to focal point  1013 . Writeable glass  1020  may comprise a contiguous piece of glass or similar transparent material, which is typically transparent to the laser light  1011  emitted by the writing laser  1010 ; in other words the light emitted by the writing laser generally will not be absorbed by the glass via typical (linear) optical processes. At the focal point  1013 , the intensity of laser light  1011  is very high due to the combination of spatial focusing (focusing the beam of writing laser light  1011  to a small point  1013 ) and temporal focusing (emitting the laser light  1011  as extremely short femptosecond or picosecond pulses). The high intensity of light at the focal point  1013  allows nonlinear optical processes such as multiphoton absorption, avalanche ionization, Coulomb collisions (causing lattice ionization and breakdown), and heat conduction to occur in the writeable glass  1020 , absorbing the light and changing the refractive index of the glass. The change in refractive index may be a positive increase in refractive index. 
     Writeable glass  1020  can be physically coupled to translatable mount  1030 , such as by using clamps  1021 , adhesive, or any other appropriate coupling mechanism. Such coupling mechanism is preferably removable, such that writeable glass  1020  can be detached from translatable mount  1030  after laser writing is complete. Translation of translatable mount  1030  in the X, Y, and/or Z direction will result in corresponding translation of writeable glass  1020 , moving the location of focal point  1013  within writeable glass  1020 . Translating the writeable glass  1020  relative to focal point  1013  can create a region of changed refractive index in the writeable glass  1020 . An increased refractive index in this region causes any light channeled therethrough to experience total internal reflection, thus forming waveguide  1022 . In other words, waveguide  1022  can be formed as a continuous path of increased refractive index within writeable glass  1020  created by laser light  1011  at focal point  1013 . 
     The technique of  FIG. 10  can be used to laser write at least one waveguide into writeable glass  1020 . For example, a photonic integrated circuit could be written, such as photonic integrated circuit  600  described with regards to  FIG. 6  or photonic integrated circuit  800  described with regards to  FIG. 8 . Inputs facets  612   a ,  612   b ,  612   c , and  612   d  (such as grating couplers), or input facets  806   a ,  806   b ,  806   c , and  806   d  could also be written using this technique. 
     Writing at least one waveguide may include writing an individual waveguide for each wavelength of light impinging on the writeable glass  1020 , where each waveguide comprises a respective input facet (such as an input grating coupler) and a respective output facet. Each output facet may be positioned to provide light to other components or modules, such as a scan mirror of a laser projector, etc. In one implementation, four waveguides could be written into writeable glass  1020 , one waveguide for each beam of light  610   a ,  610   b ,  610   c , and  610   d . Four grating couplers could also be written, one for each waveguide. In another implementation, four waveguides could be written into writeable glass  1020 , one waveguide for each beam of light  810   a ,  810   b ,  810   c , and  810   d.    
     Writing at least one waveguide may include writing a waveguide combiner, wherein the waveguide combiner combines individual laser beams into a coaxially superimposed aggregate beam. Writing a waveguide combiner may include writing at least one: directional coupler (DC), Y-branch, whispering gallery mode coupler, or multi-mode interference coupler. The aggregate beam may be provided to other components or modules, such as a scan mirror of a laser projector, etc. 
     In other implementations, the photonic integrated circuit  600  or the photonic integrated circuit  800  may include one or more diffractive optical elements (DOE) and/or refractive/reflective optical elements that combine the different color beams  610   a - d  or  810   a - d  in order to achieve coaxial superposition. 
     Alternatively, instead of writing a waveguide combiner, individual waveguides could be written which do not strictly coaxially superimpose the beams of light, but instead bring each beam of light close together. That is, the input facet (e.g. grating coupler) for each waveguide in the photonic integrated circuit can be positioned relatively far from the other input facets, to receive laser light from a respective laser diode, but the output facets for each of the waveguides can be positioned relatively close together. In other words, a spacing between the output facets of each waveguide can be smaller than a spacing of the input facets of each waveguide. In such an implementation, each waveguide can be optimized for performance with light of a corresponding wavelength, for example to ensure that each wavelength of light exits the photonic integrated circuit with the same divergence angle as each other wavelength. The output of each individual waveguide can be placed close enough together (on the order of 10s of microns) such that that the light output by each individual waveguide may still follow the same optical path through the rest of a projector, display, or WHUD assembly where the photonic integrated circuit is implemented. 
       FIG. 11  is a flow diagram of a method  1100  of manufacturing an optical engine, in accordance with the present systems, devices, and methods. The method  1100  may be implemented to manufacture the optical engine  700  of  FIG. 7  or the optical engine  900  of  FIG. 9 , for example. It should be appreciated that methods of manufacturing optical engines according to the present disclosure may include fewer or additional acts than set forth in the method  1100 . Further, the acts discussed below may be performed in an order different than the order presented herein. 
     Method  1100  can include at least acts  1102 ,  1104 ,  1106 ,  1108 ,  1110 ,  1112 ,  1114 , and  1116 . Acts  1102 ,  1104 ,  1106 ,  1108 , and  1110  substantially correspond to acts  502 ,  504 ,  506 ,  508 , and  510 , respectively, of method  500  in  FIG. 5 , such that the disclosure of these acts with reference to  FIG. 5  is also applicable to  FIG. 11 . As such, the details of these acts in  FIG. 11  will not be repeated in the interests of brevity. 
     At  1112 , a photonic integrated circuit is laser written in writeable glass, using for example the techniques described with regards to  FIG. 10 . The photonic integrated circuit may be similar to photonic integrated circuit  600  described with reference to  FIG. 6  or photonic integrated circuit  800  described with reference to  FIG. 8 . Specifically, the photonic integrated circuit can include at least one input facet and at least one output facet. In operation, the photonic integrated circuit can receive a plurality of beams of light that are coupled to the photonic integrated circuit at a plurality of input facets (e.g. grating couplers), and wavelength multiplex the plurality of beams of light to provide a coaxially superimposed aggregate beam of light that exits the photonic integrated circuit at the output facet. Alternatively, in operation, the photonic integrated circuit can receive a plurality of beams of light that are coupled to the photonic integrated circuit at a plurality of input facets (e.g. grating couplers), redirect the plurality of beams of light to exit the photonic integrated circuit at a plurality of spatially close output facets. 
     At  1114 , the writeable glass including the photonic integrated circuit is bonded to the cap or the base substrate. Any appropriate bonding technique may be used, including those described with reference to acts  502 ,  504 ,  506 ,  508 , and  510  in  FIG. 5 . In some implementations, the photonic integrated circuit may be positioned against an optical window of the cap, such that laser light from the laser diodes may pass through the optical window directly into the input facets of the photonic integrated circuit. Alternatively, the photonic integrated circuit may be positioned directly against the cap, such that the photonic integrated circuit acts as the optical window, and laser light from the laser diodes may directly enter the input facets of the photonic integrated circuit. In other implementations, the photonic integrated circuit may be spatially separated from the cap. 
     In order for light to travel through a photonic integrated circuit, the light emitted by each laser diode should preferably be aligned with a respective input facet of the photonic integrated circuit with high precision; mis-alignment of greater than 10 micrometers may significantly reduce the efficiency of the photonic integrated circuit. An output facet of each laser diode may have dimensions smaller than four square micrometers; aligning such small components to such high precision presents a non-trivial technical challenge. 
     In one implementation, each input facet of the photonic integrate circuit could be written as a grating coupler as shown in  FIG. 6 , which increases the tolerances for misalignment. 
     In act  1116 , a collimation lens may be provided such that a coaxially superimposed beam of light from the output edge of the photonic integrated circuit will be collimated by the collimation lens. The collimation lens may optionally optimize the spot (e.g., circularize) the coaxially superimposed beam. In some implementations, more than one collimation lens may be provided if the light output from the photonic integrated circuit is not a fully coaxially superimposed beam. The collimation lens or lenses may be actively aligned after the other components are assembled, or may be passively aligned such that appropriate alignment is achieved during assembly. 
     As mentioned above, aligning a photonic integrated circuit such that each input facet of the photonic integrated circuit lines up with a beam of light emitted by each laser diode with high-precision presents a non-trivial challenge. The present systems, devices, and methods provide a solution to this challenge, by producing photonic integrated circuits where the fabrication process includes an alignment process, obviating the need for a later mechanical alignment process, as discussed below with reference to  FIGS. 12, 12B, and 13 . Direct laser writing (DLW) as disclosed herein is a process by which photonic integrated circuits may be fabricated with high precision that allows for intrinsic alignment. 
       FIG. 12A  is a left side sectional view of photonic integrated circuit writing system  1200   a . Photonic integrated circuit writing system  1200   a  includes components that may be substantively similar to components of optical engine  700  and components of laser writing system  1000 . Unless context below dictates otherwise, the disclosure of components in  FIG. 7  and  FIG. 10  is applicable to similarly numbered components in  FIG. 12A  and will not be repeated in the interests of brevity. Photonic integrated circuit writing system  1200   a  includes laser writing system  1000 , which, during operation, writes a photonic integrated circuit in a block of writeable glass  1020  in a manner similar to the operation of laser writing system  1000  described above with reference to  FIG. 10 . Photonic integrated circuit writing system  1200   a  can be utilized to manufacture an optical engine using a process that is similar in at least some respects to method  1100  of  FIG. 11 , but with photonic integrated circuit writing system  1200   a , act  1114  can be performed before act  1112 , as detailed below. 
     Writeable glass  1020  is bonded to cap  720  prior to writing a photonic integrated circuit therein, using any of the bonding techniques discussed above. The writeable glass  1020  may comprise a contiguous piece of glass or similar transparent material that undergoes a change in refractive index when exposed to high-intensity laser light. Bonding the writeable glass to the cap includes positioning and orienting the writeable glass  1020  relative to each laser diode  710  to place the writeable glass  1020  in the path of the beam of light emitted by each laser diode  710 , such that the beam of light emitted by each laser diode  710  impinges on the writeable glass. 
     Writeable glass  1020  can be positioned against optical window  730 , such that beams of light from laser diodes  710  pass through optical window  730  directly into writeable glass  1020 . Alternatively, the writeable glass  1020  may optionally form optical window  730 . 
     The entire base substrate  702  and all components bonded thereto can be physically coupled to translatable mount  1030 , such as with clamps  1021 , adhesives, and/or any other appropriate coupling mechanism. Such coupling mechanism is preferably removable, such that base substrate  702  and all components bonded thereto can be detached from translatable mount  1030  after laser writing of writeable glass  1020  is complete. 
     With writeable glass  1020  bonded indirectly to base substrate  702  via cap  720 , and base substrate  702  physically coupled to translatable mount  1030 , at least one waveguide  1022  can be laser written into writeable glass  1020  by translating base substrate  702  and all components thereon using translatable mount  1030 . At least one input facet  612  (for example at least one grating input coupler) can also be written into writeable glass  1020  by translating base substrate  702  and all components thereon using translatable mount  1030 . Consequently, writeable glass  1020  becomes a photonic integrated circuit. 
     To determine where the at least one waveguide  1022  should be written, laser diodes  710  could be activated, thus causing beams of light therefrom to impinge on writeable glass  1020 . Writing laser  1010  can be aligned to directly write waveguides and input facets (e.g. grating couplers as shown in  FIG. 12A ) at the exact location where the beams of light from laser diodes  710  impinge on the writeable glass  1020 . In this way, the input facets of the resulting photonic integrated circuit will be accurately aligned with the laser diodes, ensuring efficient incoupling of the beams of light into the photonic integrated circuit. 
     Alternatively, the writeable glass  1020  could be illuminated, such as by being backlit if base substrate  702  is at least partially transparent. Writing laser  1010  can then be aligned to directly write waveguides based on locations of shadows caused by laser diodes  710 , CoS&#39;s  712  and optical redirector element  718 . In this way, the input facets of the resulting photonic integrated circuit will be accurately aligned with the laser diodes, ensuring efficient incoupling of the beams of light into the photonic integrated circuit. 
     Aligning the input facets of the photonic integrated circuit to the beams of light during the writing stage will be more accurate than trying to mechanically align a pre-fabricated photonic integrated circuit, due to deviations that can arise in the bonding processes of not only the pre-fabricated photonic integrate circuit, but also the laser diodes. As one example, if each of four laser diodes is randomly misaligned, it would be difficult to align a prefabricated photonic integrated circuit to match the beam of light from each diode, since not only could the photonic integrated circuit be misaligned during the bonding processes, but also the spacing between each laser diode may not match the spacing between each waveguide in the photonic integrated circuit due to the random misalignment of each of the laser diodes. Direct laser writing the photonic integrated circuit after all of the components have been mechanically bonded obviates these issues, by allowing the position and spacing of each laser diode relative to the writeable glass to be accounted for after bonding is complete. 
       FIG. 12B  is a left side sectional view of photonic integrated circuit writing system  1200   b . Photonic integrated circuit writing system  1200   b  includes components that may be substantively similar to components of photonic integrated circuit writing system  1200   a  as discussed with regards to  FIG. 12A . Unless context below dictates otherwise, the disclosure related to components in  FIG. 12A  is applicable to similarly numbered components in  FIG. 12B  and will not be repeated in the interests of brevity. 
     In  FIG. 12B , instead of writing the input facets  612  of the photonic integrated circuit  600  as grating input couplers, a reflective surface is instead written to redirect input beams of light  610  into at least one waveguide  1022  of photonic integrated circuit  600 . For example, the at least one reflective surface could be a planar region with lower index of refraction than the material from which writeable glass  1020  is formed. Consequently, laser light  610  can be redirected by the planar region with lower index of refraction due to total internal reflection. 
     Additionally,  FIG. 12B  illustrates an implementation in which at least one laser diode  710  is a vertical-cavity surface-emitting laser (VCSEL), such that laser light emitted by the laser diode is directed towards optical window  730  without the need for an optical redirecting element. Such a laser diode setup could be implemented in any of the implementations discussed herein. The implementation of  FIG. 12B  does not require the use of a VCSEL, but could instead use a side emitting laser with an optical redirecting element such as shown in  FIGS. 1A and 1B . 
       FIG. 13  is a left side sectional view of photonic integrated circuit writing system  1300 . Photonic integrated circuit writing system  1300  includes components that may be substantively similar to components of optical engine  900  and components of laser writing system  1000 . Unless context below dictates otherwise, the disclosure of components in  FIG. 9  and  FIG. 10  is applicable to similarly numbered components in  FIG. 13  and will not be repeated in the interests of brevity. Photonic integrated circuit writing system  1300  includes laser writing system  1000 , which, during operation, writes a photonic integrated circuit in a block of writeable glass  1020  in a manner similar to the operation of laser writing system  1000  described above with reference to  FIG. 10 . Photonic integrated circuit writing system  1300  can be utilized to manufacture an optical engine using a process that is similar in at least some respects to method  1100  of  FIG. 11 , but with photonic integrated circuit writing system  1300 , act  1114  can be performed before act  1112 , as detailed below. 
     Writeable glass  1020  is bonded to base substrate  902  prior to writing a photonic integrated circuit therein, using any of the bonding techniques discussed above. The writeable glass  1020  may comprise a contiguous piece of glass or similar transparent material that undergoes a change in refractive index when exposed to high-intensity laser light. Bonding the writeable glass to the base substrate includes positioning and orienting the writeable glass  1020  relative to each laser diode  910  to place the writeable glass  1020  in the path of the beam of light emitted by each laser diode  910 , such that the beam of light emitted by each laser diode  910  impinges on an input edge of the writeable glass. 
     Writeable glass  1020  can be butted up against optical window  930 , such that beams of light from laser diodes  910  passes through optical window  930  directly into writeable glass  1020 . Alternatively, the writeable glass  1020  may optionally form optical window  930 . Further, writeable glass  1020  may be bonded directly to at least one of the laser diodes  910  and/or at least one laser CoS  912 . 
     The entire base substrate  902  and all components bonded thereto can be physically coupled to translatable mount  1030 , such as with clamps  1021 , adhesives, and/or any other appropriate coupling mechanism. Such coupling mechanism is preferably removable, such that base substrate  902  and all components bonded thereto can be detached from translatable mount  1030  after laser writing of writeable glass  1020  is complete. 
     With writeable glass  1020  bonded to base substrate  902  and base substrate  902  physically coupled to translatable mount  1030 , at least one waveguide  1022  can be laser written into writeable glass  1020  by translating base substrate  902  and all components thereon using translatable mount  1030 . Consequently, writeable glass  1020  becomes a photonic integrated circuit. 
     To determine where the at least one waveguide  1022  should be written, laser diodes  910  could be activated, thus causing beams of light therefrom to impinge on an input edge of writeable block  1020 . Writing laser  1010  can be aligned to directly write waveguides at the exact location where the beams of light from laser diodes  910  impinge on the writeable block  1020 . In this way, the input of the resulting photonic integrated circuit will be accurately aligned with the laser diodes, ensuring efficient incoupling of the beams of light into the photonic integrated circuit. 
     Alternatively, the writeable glass  1020  could be illuminated, such as by being backlit if base substrate  902  is at least partially transparent. Writing laser  1010  can then be aligned to directly write waveguides at locations where shadows of laser diodes  910  and/or CoS&#39;s  912  appear. In this way, the input of the resulting photonic integrated circuit will be accurately aligned with the laser diodes, ensuring efficient incoupling of the beams of light into the photonic integrated circuit. 
     Aligning the input facets of the photonic integrated circuit to the beams of light during the writing stage will be more accurate than trying to mechanically align a pre-fabricated photonic integrated circuit, due to deviations that can arise in the bonding processes of not only the pre-fabricated photonic integrate circuit, but also the laser diodes. As one example, if each of four laser diodes is randomly misaligned, it would be difficult to align a prefabricated photonic integrated circuit to match the beam of light from each diode, since not only could the photonic integrated circuit be misaligned during the bonding processes, but also the spacing between each laser diode may not match the spacing between each waveguide in the photonic integrated circuit due to the random misalignment of each of the laser diodes. Direct laser writing the photonic integrated circuit after all of the components have been mechanically bonded obviates these issues, by allowing the position and spacing of each laser diode relative to the writeable glass to be accounted for after bonding is complete. 
     In some implementations, a photonic integrated circuit could be manufactured using a combination of the techniques described with reference to  FIGS. 10, 11, 12A, 12B, and 13  as discussed below. 
     In one example, a large portion of a photonic integrated circuit could be first written, except for a small portion of the photonic integrated circuit at the input of writeable glass. Subsequently, the photonic integrated circuit could be bonded to the cap or the base substrate such as in  FIG. 12A, 12B , or  13 , and the remaining small portion of the photonic integrated circuit at the input of the writeable glass could be written to couple the output of each laser diode to the portion of the photonic integrated circuit which is already written. 
     In another example, a first photonic integrated circuit could be written as in  FIG. 10 . Subsequently, the first photonic integrated circuit could be bonded to the cap similar to as in  FIG. 7, 12A , or  12 B, or to the base substrate as in  FIG. 9 or 13 , with the first photonic integrated circuit being spatially separated from the output of each laser diode such that there is a gap between the output from each laser diode and the first photonic integrated circuit. In the area in the output path of each laser diode, a block of writeable glass could be bonded to the cap or to the base substrate in the gap between the output from each laser diode and the first photonic integrated circuit. Subsequently, a second photonic integrated circuit could be written in the writeable glass similar to in  FIGS. 12A, 12B, and 13  to couple the output of each laser diode to an input edge of the previously written first photonic integrated circuit. In such an example, the writeable glass could be formed as the optical window, and/or could be formed to cover a portion of the first photonic integrated circuit.  FIGS. 14 and 15  illustrate exemplary implementations of this setup. 
       FIG. 14  is a left side sectional elevational view of a portion of an optical engine  1400 . The optical engine  1400  includes several components that may be similar or identical to the components of the optical engines  100 ,  700  or  900 . Thus, some or all of the discussion above may be applicable to the optical engine  1400 , and is not repeated herein for the sake of brevity. For example, portions of the optical engine  1400  not shown in  FIG. 14  may be similar or identical to corresponding portions of the optical engine  900  of  FIG. 9 . 
     The optical engine  1400  includes a base substrate  1402  having a top surface  1404  and a bottom surface (not shown) opposite the top surface. The base substrate  1402  may be formed from a material that is radio frequency (RF) compatible and is suitable for hermetic sealing. For example, the base substrate  1402  may be formed from low temperature co-fired ceramic (LTCC), aluminum nitride (AlN), alumina, Kovar®, etc. 
     The optical engine  1400  also includes a plurality of chip submounts  1408  (only one chip submount visible in the sectional view of  FIG. 14 ) that are bonded (e.g., attached) to the top surface  1404  of the base substrate  1402 . The plurality of chip submounts  1408  are aligned in a row across a width of the optical engine  1400  between the left and right sides thereof. Each of the plurality of chip submounts  1408  includes a laser diode  1410 , also referred to as a laser chip or laser die, bonded thereto. In particular, an infrared chip submount carries an infrared laser diode, a red chip submount carries a red laser diode, a green chip submount carries a green laser diode, and a blue chip submount carries a blue laser diode. In operation, the infrared laser diode provides infrared laser light, the red laser diode provides red laser light, the green laser diode provides green laser light, and the blue laser diode provides blue laser light. Each of the laser diodes  1410  may comprise one of an edge emitter laser or a vertical-cavity surface-emitting laser (VCSEL), for example. Each of the four laser diode/chip submount pairs may be referred to collectively as a “laser chip on submount,” or a laser CoS  1412 . Thus, the optical engine  1400  includes an infrared laser CoS, a red laser CoS, a green laser CoS, and a blue laser CoS. In at least some implementations, one or more of the laser diodes  1410  may be bonded directly to the base substrate  1402  without use of a submount  1408 . 
     Although not shown in  FIG. 14 , the optical engine  1400  also includes a laser diode driver circuit (e.g., similar or identical to the laser diode driver circuit  914 ) bonded to a surface of the base substrate  1402  or located remotely therefrom. The laser diode driver circuit  1414  is operatively coupled to the plurality of laser diodes  1410  via suitable electrical connections  1416  to selectively drive current to the plurality of laser diodes. Generally, the laser diode driver circuit  1414  may be positioned relative to the CoSs  1412  to minimize the distance between the laser diode driver circuit  1414  and the CoSs  1412 . Although not shown in  FIG. 14 , the laser diode driver circuit  1414  may be operatively coupleable to a controller (e.g., microcontroller, microprocessor, ASIC) that controls the operation of the laser diode driver circuit  1414  to selectively modulate laser light emitted by the laser diodes  1410 . In at least some implementations, the laser diode driver circuit  1414  may be bonded to another portion of the base substrate  1402 , such as the top surface  1404  of the base substrate. In at least some implementations, the laser diode driver circuitry  1414  may be remotely located and operatively coupled to the laser diodes  1410 . In order to not require the use of impedance matched transmission lines, the size scale may be small compared to a wavelength (e.g., lumped element regime), where the electrical characteristics are described by (lumped) elements like resistance, inductance, and capacitance. Exemplary placements for laser diode driver circuitry are described below with reference to  FIGS. 16A and 16B . 
     In at least some implementations, the optical engine  1400  also includes a cap  1420  that includes a vertical sidewall  1422  and a horizontal wall or top portion  1425 . The vertical sidewall  1422  includes a lower first end  1424  and an upper second end  1426  opposite the first end. A flange  1428  may be disposed around a perimeter of the sidewall  1422  adjacent the lower first end  1424 . Within a portion of the vertical sidewall  1422  there is an optical window  1430  positioned proximate the laser diodes  1410  to pass light therefrom out of the cap  1420 . The sidewall  1422  and the optical window  1430  together define an interior volume  1432  sized and dimensioned to receive the plurality of chip submounts  1408  and the plurality of laser diodes  1410 . The lower first end  1424  and the flange  1428  of the cap  1420  are bonded to the base substrate  1402  to provide a hermetic or partially hermetic seal between the interior volume  1432  of the cap and a volume  1434  exterior to the cap. 
     The cap  1420  may have a round shape, rectangular shape, or other shape. Thus, the vertical sidewall  1422  may comprise a continuously curved sidewall, a plurality (e.g., four) of adjacent planar portions, etc. The optical window  1430  may comprise an entire side of the cap  1420 , or may comprise only a portion thereof. In at least some implementations, the cap  1420  may include a plurality of optical windows instead of a single optical window  1430 . 
     The optical engine  1400  also includes a waveguide medium or material  1460  disposed on the top surface  1404  of the base substrate  1404  between the optical window  1430  of the cap  1420  and a photonic integrated circuit  1450 . The waveguide medium  1460  includes waveguides  1462  (e.g., four waveguides, only one visible in the sectional view of  FIG. 14 ) that are operative to couple the plurality of beams of light emitted by the plurality of laser diodes  1410  from the optical window  1430  of the cap  1420  to input couplers (e.g., edge couplers, grating couplers) on an edge  1452  or top surface  1454  of the photonic integrated circuit  1450 . Each of the plurality of waveguides  1462  is positioned and dimensioned to receive light from a corresponding one of the laser diodes  1410  through the optical window  1430 . The waveguides  1462  may be directly written using the direct laser writing process described above with reference to  FIG. 10, 11, 12A, 12B , or  13 , or any other suitable process. 
     The waveguides  1462  couple the beams of light into the photonic integrated circuit  1450  via input optical edge couplers or grating couplers. The photonic integrated circuit  1450  may be bonded to the top surface  1404  of the base substrate  1402  proximate the waveguide medium  1460 . As discussed above, in operation, the photonic integrated circuit  1450  receives a plurality of beams of light at the input couplers, and wavelength multiplexes the plurality of beams to provide a coaxially superimposed aggregate beam of light that exits the photonic integrated circuit at an output optical edge. 
     In at least some implementations, at least some of the components may be positioned differently. As noted above, a laser diode driver circuit operatively coupled to the laser diodes  1410  may be mounted on the top surface  1404  or the bottom surface of the base substrate  1402 , or may be positioned remotely therefrom, depending on the RF design and other constraints (e.g., package size). In at least some implementations, the optical engine  1400  may include optical director element (e.g., optical director element  118  of  FIG. 1 ), and the laser light may be directed from the laser diodes  1410  toward the waveguide medium  1460  via an intermediate optical director element. In at least some implementations, photonic integrated circuit  1450  and waveguide medium  1460  may be positioned on top of cap  1420 , and the optical window  1430  may be in top portion  1425  of cap  1420 , with light beams from laser diodes  1410  passing through the optical window  1430  on the top portion of cap  1420  into waveguide medium  1460  and subsequently photonic integrated circuit  1450 . Additionally, in at least some implementations, one or more of the laser diodes  1410  may be mounted directly on the base substrate  1402  without use of a submount. Further, in at least some implementations, in the case of an inorganic or acceptably organic waveguide, coupling may be accomplished inside the encapsulated package. Such feature eliminates the requirement for a separate window, as the waveguide medium  1460  services as the window (e.g., optical window  1430 ). In such implementations, the at least one optical input coupler of the photonic integrated circuit may be positioned inside the interior volume of the encapsulated package and the at least one optical output edge of the photonic integrated circuit may be positioned outside of the interior volume, for example. 
     In at least some implementations, the waveguides  1462  may be directly written into the waveguide medium  1460  using any suitable direct writing process, such as that described above with reference to  FIGS. 10, 12A, 12B, and 13 . The waveguide medium  1460  may comprise any suitable photosenstive material. In at least some implementations, the waveguide medium comprises organically modified ceramic (ORMOCER) material, for example. As noted above, coupling to the photonic integrated circuit  1450  may be done either via edge coupling or grating coupling. 
     In the illustrated implementation, the written waveguide  1462  and medium  1460  is spaced apart from the optical window  1430 , and a lens shaped surface  1464  is formed in the medium  1460 . The lens shaped surface  1464  may be sized, dimensioned and oriented to couple beams of light from the laser diodes  1410  into the waveguides  1462  of the waveguide medium  1460 . In other implementations, the waveguide  1462  and or waveguide medium  1460  may be positioned adjacent (e.g., in contact with) at least one of the optical window  1430  of the cap  1430  or the photonic integrated circuit  1450 . 
       FIG. 15  shows a left side sectional elevational view of a portion of an optical engine  1500 . The optical engine  1500  includes several components that may be similar or identical to the components of the optical engines  100 ,  700 ,  900 , or  1400 . Thus, some or all of the discussion above may be applicable to the optical engine  1500 , and is not repeated herein for the sake of brevity. For example, portions of the optical engine  1500  not shown in  FIG. 15  may be similar or identical to corresponding portions of the optical engine  900  of  FIG. 9 . 
     The optical engine  1500  includes a base substrate  1502  having a top surface  1504  and a bottom surface (not shown) opposite the top surface. The base substrate  1502  may be formed from a material that is radio frequency (RF) compatible and is suitable for hermetic sealing. For example, the base substrate  1502  may be formed from low temperature co-fired ceramic (LTCC), aluminum nitride (AlN), alumina, Kovar®, etc. 
     The optical engine  1500  also includes a plurality of chip submounts  1508  (only one chip submount visible in the sectional view of  FIG. 15 ) that are bonded (e.g., attached) to the top surface  1504  of the base substrate  1502 . The plurality of chip submounts  1508  are aligned in a row across a width of the optical engine  1500  between the left and right sides thereof. Each of the plurality of chip submounts  1508  includes a laser diode  1510 , also referred to as a laser chip or laser die, bonded thereto. In particular, an infrared chip submount carries an infrared laser diode, a red chip submount carries a red laser diode, a green chip submount carries a green laser diode, and a blue chip submount carries a blue laser diode. In operation, the infrared laser diode provides infrared laser light, the red laser diode provides red laser light, the green laser diode provides green laser light, and the blue laser diode provides blue laser light. Each of the laser diodes  1510  may comprise one of an edge emitter laser or a vertical-cavity surface-emitting laser (VCSEL), for example. Each of the four laser diode/chip submount pairs may be referred to collectively as a “laser chip on submount,” or a laser CoS  1512 . Thus, the optical engine  1500  includes an infrared laser CoS, a red laser CoS, a green laser CoS, and a blue laser CoS. In at least some implementations, one or more of the laser diodes  1510  may be bonded directly to the base substrate  1502  without use of a submount  1508 . 
     Although not shown in  FIG. 15 , the optical engine  1500  also includes a laser diode driver circuit (e.g., similar or identical to the laser diode driver circuit  914 ) bonded to a surface of the base substrate  1502  or located remotely therefrom, similarly to as described with regards to  FIGS. 16A and 16B  below. The laser diode driver circuit  1514  is operatively coupled to the plurality of laser diodes  1510  via suitable electrical connections  1516  to selectively drive current to the plurality of laser diodes. 
     The optical engine  1500  also includes a photonic integrated circuit  1550  bonded to the top surface  1504  of the base substrate  1502  proximate facets  1511  of the laser diodes  1510 . In operation, the photonic integrated circuit  1550  receives a plurality of beams of light at input couplers (e.g., edge couplers, grating couplers), and wavelength multiplexes the plurality of beams to provide a coaxially superimposed aggregate beam of light that exits the photonic integrated circuit at an output optical edge (not shown in  FIG. 15 ). 
     In the illustrated implementation, the laser CoSs  1512  and electrical connections  1516  (e.g., wirebonds) are covered with a waveguide and sealing medium  1560 , which may also cover at least a portion of an edge  1552  and a top surface  1554  of the photonic integrated circuit  1550 . Advantageously, the waveguide and sealing medium acts as a sealing material for the laser CoSs  1512 , eliminating the need for a separate cap (e.g., cap  1420  of  FIG. 14 ) to provide a hermetically or partially hermetically sealed package. 
     The waveguide medium  1560  includes directly written waveguides  1562  (e.g., four waveguides, only one visible in the sectional view of  FIG. 15 ) that are operative to couple the plurality of beams of light emitted at the facets  1511  of the plurality of laser diodes  1510  to input couplers (e.g., edge couplers, grating couplers) on the edge  1552  or top surface  1554  of the photonic integrated circuit  1550 . Each of the plurality of waveguides  1562  is positioned and dimensioned to receive light from a corresponding one of the laser diodes  1510 . The waveguides  1562  may be directly written using any suitable process, such as direct laser writing as described with reference to  FIGS. 10, 12A, 12B, and 13  above. 
     The waveguides  1562  couple the beams of light into the photonic integrated circuit  1550  via an input optical edge couplers or grating couplers. The photonic integrated circuit  1550  may be bonded to the top surface  1504  of the base substrate  1502  proximate the waveguide medium  1560 . As discussed above, in operation, the photonic integrated circuit  1550  receives a plurality of beams of light at the input couplers, and wavelength multiplexes the plurality of beams to provide a coaxially superimposed aggregate beam of light that exits the photonic integrated circuit at an output optical edge. 
     In at least some implementations, photonic integrated circuit  1550  may be positioned above laser diodes  1510 , and waveguide and sealing medium  1560  may be formed to cover laser diodes  1510  and photonic integrated circuit  1550 . At least one waveguide  1562  can be directly written in waveguide medium  1560  to couple beams of light emitted by laser diodes  1510  to input couplers on photonic integrated circuit  1550 , using for example the techniques discussed above regarding  FIGS. 10, 12A, 12B, and 13 . 
     Although several different materials may be used for direct waveguide writing, in at least some implementations, an ORMOCER material may be used which is tailored to the particular needs concerning writing as well as transmission wavelengths. 
       FIGS. 16A and 16B  are isometric views showing implementations of optical engines having differing positions for a laser diode driver circuit. The implementations shown in  FIGS. 16A and 16B  are similar in at least some respects to the implementations of  FIGS. 1A, 1B, 7, 9, 12A, 12B, 13, 14, and 15 , and one skilled in the art will appreciate that the description regarding  FIGS. 1A, 1B, 7, 9, 12A, 12B, 13, 14, and 15  are applicable to the implementations of  FIGS. 16A and 16B  unless context clearly dictates otherwise. 
       FIG. 16A  shows an optical engine  1600   a  which includes a base substrate  1602 . The base substrate  1602  may be formed from a material that is radio frequency (RF) compatible and is suitable for hermetic sealing. For example, the base substrate  1602  may be formed from low temperature co-fired ceramic (LTCC), aluminum nitride (AlN), alumina, Kovar®, etc. 
     The optical engine  1600   a  also includes a plurality of laser diodes aligned in a row across a width of the optical engine  1600   a , including an infrared laser diode  1610   a , a red laser diode  1610   b , a green laser diode  1610   c , and a blue laser diode  1610   d . In operation, the infrared laser diode  1610   a  provides infrared laser light, the red laser diode  1610   b  provides red laser light, the green laser diode  1610   c  provides green laser light, and the blue laser diode  1610   d  provides blue laser light. Each of the laser diodes may comprise one of an edge emitter laser or a vertical-cavity surface-emitting laser (VCSEL), for example. In  FIG. 16A , laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d  are shown as being bonded (e.g., attached) directly to base substrate  1602 , as described above with regards to act  504  in  FIG. 5 , but one skilled in the art will appreciate that laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d  could each be mounted on a respective submount, similar to as in  FIGS. 1A and 1B . 
     The optical engine  1600   a  also includes a laser diode driver circuit  1614  which can be bonded to the same surface of base substrate  1602  as the laser diodes  1610   a ,  1610   b ,  1610   c ,  1610   d . In alternative implementations, laser diode driver circuit  1614  can be bonded to a separate base substrate, such as in  FIG. 16B  discussed later. The laser diode driver circuit  1614  is operatively coupled to the plurality of laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d  via respective electrical connections  1616   a ,  1616   b ,  1616   c ,  1616   d  to selectively drive current to the plurality of laser diodes. In at least some implementations, the laser diode driver circuit  1614  may be positioned relative to the laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d  to minimize the distance between the laser diode driver circuit  1614  and the laser diodes. Although not shown in  FIG. 16A , the laser diode driver circuit  1614  may be operatively coupleable to a controller (e.g., microcontroller, microprocessor, ASIC) which controls the operation of the laser diode driver circuit  1614  to selectively modulate laser light emitted by the laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d . In at least some implementations, the laser diode driver circuit  1614  may be bonded to another portion of the base substrate  1602 , such as the bottom surface of the base substrate  1602 . In at least some implementations, the laser diode driver circuitry  1614  may be remotely located and operatively coupled to the laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d . In order to not require the use of impedance matched transmission lines, the size scale may be small compared to a wavelength (e.g., lumped element regime), where the electrical characteristics are described by (lumped) elements like resistance, inductance, and capacitance. 
     Proximate the laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d  there is optionally positioned an optical director element  1618 . Like the laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d , the optical director element  1618  is bonded to the top surface of the base substrate  1602 . The optical director element  1618  may be bonded proximate to or adjacent each of the laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d . In the illustrated example, the optical director element  1618  has a triangular prism shape that includes a plurality of planar faces, similar to optical director element  168  in  FIGS. 1A and 1B . The optical director element  1618  may comprise a mirror or a prism, for example. 
     The optical engine  1600   a  also includes a cap  1620  similar to cap  120  in  FIGS. 1A and 1B  or cap  920  in  FIG. 9 . For clarity, cap  1620  is shown as being transparent in  FIG. 16A , though this is not necessarily the case, and cap  1620  can be at least partially formed of an opaque material. In the illustrated implementation, cap  1620  can include a horizontal optical window  1630  that forms the “top” of the cap  1620 . Although optical window  1630  in  FIG. 16A  is shown as comprising the entire top of cap  1620 , in alternative implementations optical window could comprise only a portion of the top of cap  1620 . Cap  1620  including optical window  1630  defines an interior volume sized and dimensioned to receive the plurality of laser diodes  1610   a ,  1610   b ,  1610   c ,  1610   d , and the optical director element  1618 . Cap  1620  is bonded to the base substrate  1602  to provide a hermetic or partially hermetic seal between the interior volume of the cap  1620  and a volume exterior to the cap  1620 . The optical director element  1618  is positioned and oriented to direct (e.g., reflect) laser light received from each of the plurality of laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d  upward toward the optical window  1630  of the cap  1620 , wherein the laser light exits the interior volume, similar to  FIGS. 1A and 1B . 
     The cap  1620  may have a round shape, rectangular shape, or other shape, similarly to as described regarding  FIGS. 1A and 1B  above. The optical window  1630  may comprise an entire top of the cap  1620 , or may comprise only a portion thereof. In alternative implementations, optical window  1630  could be positioned on a side of cap  1620  to allow beams of light from laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d  to exit the cap through a side portion thereof. In such an implementation, each of laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d  can be a side-emitting laser, and optical engine  1600   a  may not include optical redirector element  1618 . 
     In at least some implementations, the cap  1620  may include a plurality of optical windows instead of a single optical window. 
     The optical engine  1600   a  can also include four collimation/pointing lenses similarly to as discussed regarding  FIGS. 1A and 1B  above. Each of the collimation lenses can be operative to receive laser light from a respective one of the laser diodes  1610   a ,  1610   b ,  1610   c , or  1610   d , and to generate a single color beam. 
     The optical engine  1600   a  may also include, or may be positioned proximate to, a beam combiner that is positioned and oriented to combine the light beams received from each of the collimation lenses or laser diodes  1610   a ,  1610   b ,  1610   c , or  1610   d  into a single aggregate beam. As an example, the beam combiner may include one or more diffractive optical elements (DOE) and/or one or more refractive/reflective optical elements that combine the different color beams in order to achieve coaxial superposition. Exemplary beam combiners are shown and discussed with reference to  FIG. 3, 7, 9, 12A, 12B , or  13 . 
     In at least some implementations, the laser diodes  1610   a ,  1610   b ,  1610   c ,  1610   d , the optical director element  1618 , and/or the collimation lenses may be positioned differently. As noted above, laser diode driver circuit  1614  may be mounted on a top surface or a bottom surface of the base substrate  1602 , depending on the RF design and other constraints (e.g., package size). In at least some implementations, the optical engine  1600   a  may not include the optical director element  1618 , and the laser light may be directed from the laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d  toward collimation lenses without requiring an intermediate optical director element. Additionally, in at least some implementations, one or more of the laser diodes may be mounted indirectly on the base substrate  1602  with a submount. 
     Optical engine  1600   a  in  FIG. 16A  also includes an electrically insulating cover  1640 . In  FIG. 16A , laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d  are each connected to laser diode driver circuitry  1614  by a respective electrical connection  1616   a ,  1616   b ,  1616   c , or  1616   d  positioned as described above with regards to act  508  in  FIG. 5 . Electrical connections  1616   a ,  1616   b ,  1616   c , and  1616   d  run across a surface of the base substrate  1602 . As described above with regards to act  510  in  FIG. 5 , electrically insulating cover  1640  is placed, adhered, formed, or otherwise positioned over electrical connections  1616   a ,  1616   b ,  1616   c , and  1616   d , such that each of the electrical connections  1616   a ,  1616   b ,  1616   c , and  1616   d  run through electrically insulating cover  1640 . Also as described above with regards to act  510  in  FIG. 5 , cap  1620  is placed, adhered, formed, or otherwise positioned over electrically insulating cover  1640 , such that cap  1620  does not contact any of the electrical connections  1616   a ,  1616   b ,  1616   c , or  1616   d . For clarity, cap  1620  is shown as being transparent in  FIG. 16A , though this is not necessarily the case, and cap  1620  can be at least partially formed of an opaque material. Electrically insulating cover  1640  can be formed of a material with low electrical permittivity such as a ceramic, such that electrical signals which run through electrical connections  1616   a ,  1616   b ,  1616   c , and  1616   d  do not run into or through electrically insulating cover  1640 . In this way, electrical signals which run through electrical connections  1616   a ,  1616   b ,  1616   c , and  1616   d  can be prevented from running into or through cap  1620 , which can be formed of an electrically conductive material. Although  FIG. 16A  shows electrically insulating cover  1640  as extending along only part of a side of cap  1620 , one skilled in the art will appreciate that electrically insulating cover  1640  can extend along an entire side length of cap  1620 . 
     One skilled in the art will appreciate that the positions of laser diode driver circuitry  1614 , electrical connections  1616   a ,  1616   b ,  1616   c ,  1616   d , and electrically insulating cover  1640  as shown in  FIG. 16A  could also be applied in other implementations of the subject systems, devices and methods. For example, in the implementations of  FIGS. 1A and 1B , laser diode driver circuitry  114  could be positioned on top surface  104  of base substrate  102 , and electrical connections  116  could run across top surface  104  under an electrically insulating cover, such that electrical connections  116  do not contact any conductive portion of cap  120 . 
       FIG. 16B  is an isometric view an optical engine  1600   b  similar in at least some respects to optical engine  1600   a  of  FIG. 16A . One skilled in the art will appreciate that the description of optical engine  1600   a  in  FIG. 16A  is applicable to optical engine  1600   b  in  FIG. 16B , unless context clearly dictates otherwise. The optical engine  1600   b  includes a base substrate  1603   a . Similar to base substrate  1602  in  FIG. 16A , base substrate  1603   a  may be formed from a material that is radio frequency (RF) compatible and is suitable for hermetic sealing. For example, the base substrate  1603   a  may be formed from low temperature co-fired ceramic (LTCC), alumina, Kovar®, etc. 
     One difference between optical engine  1600   b  in  FIG. 16B  and optical engine  1600   a  in  FIG. 16A  relates to what components are bonded (e.g. attached) to base substrate  1603   a . In optical engine  1600   b , each of: laser diodes  1610   a ,  1610   b ,  1610   c ,  1610   d ; cap  1620 ; electrical connections  1616   a ,  1616   b ,  1616   c ,  1616   d ; and electrically insulating cover  1640  are bonded (e.g., attached) to base substrate  1603   a . However, laser diode driver circuit  1614  is not necessarily bonded directly to base substrate  1603   a . Instead, laser diode driver circuit  1614  could be bonded to a separate base substrate  1603   b . Similar to base substrate  1602  in  FIG. 16A  and base substrate  1603   a  in  FIG. 16B , base substrate  1603   b  may be formed from a material that is radio frequency (RF) compatible and is suitable for hermetic sealing. For example, the base substrate  1603   b  may be formed from low temperature co-fired ceramic (LTCC), alumina, Kovar®, etc. In an alternative implementation, laser diode drive circuit  1614  may not need to be bonded to a substrate at all, and could simply be mounted directly to a frame of a WHUD. 
     For implementations where laser diode drive circuit  1614  is not bonded to base substrate  1603   a , electrical contacts  1617   a ,  1617   b ,  1617   c , and  1617   d  could be bonded to base substrate  1603   a , each at an end of a respective electrical connection  1616   a ,  1616   b ,  1616   c , or  1616   d  as described above with regards to act  508  in  FIG. 5 . In this way, electrical contacts  1617   a ,  1617   b ,  1617   c , and  1617   d  could be used to electrically couple laser diode drive circuit  1614  to electrical connections  1616   a ,  1616   b ,  1616   c , and  1616   d  and consequently laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d.    
     Although the implementations of  FIGS. 16A and 16B  illustrate examples which include cap  1620 , cap  1620  could be replaced by a waveguide and sealing medium similar to as described with reference to  FIG. 15 . 
     For example, a waveguide and sealing medium could be disposed on base substrate  1602  in  FIG. 16A  to cover the plurality of laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d ; optical director element  1618  (if included); and at least a portion or all of electrical connections  1616   a ,  1616   b ,  1616   c , and  1616   d . Laser diode driver circuitry  1614  could optionally be covered as well, or left uncovered. In this way, electrical connections  1616   a ,  1616   b ,  1616   c , and  1616   d  will connect laser diode circuitry  1614  to laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d  through the waveguide and sealing medium. 
     As another example, a waveguide and sealing medium could be disposed on base substrate  1603   a  in  FIG. 16B  to cover the plurality of laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d ; optical director element  1618  (if included); and a portion of electrical connections  1616   a ,  1616   b ,  1616   c , and  1616   d . Electrical contacts  1617   a ,  1617   b ,  1617   c , and  1617   d  could be left uncovered, such that laser diode circuitry  1614  can be coupled thereto. In this way, electrical connections  1616   a ,  1616   b ,  1616   c , and  1616   d  will connect laser diode circuitry  1614  to laser diodes  1610   a ,  1610   b ,  1610   c , and  1610   d  via electrical contacts  1617   a ,  1617   b ,  1617   c , and  1617   d , through the waveguide and sealing medium. 
       FIG. 17A  is a left side sectional elevational view of an optical engine  1700 .  FIG. 17B  is a front side elevational view of the optical engine  1700 . The optical engine  1700  includes several components that may be similar or identical to the components of the optical engines discussed above. Thus, some or all of the discussion above may be applicable to the optical engine  1700 . 
     The optical engine  1700  includes a base substrate  1702  having a top surface  1704  and a bottom surface  1706  opposite the top surface. The base substrate  1702  may be formed from a material that is radio frequency (RF) compatible and is suitable for hermetic sealing. For example, the base substrate  1702  may be formed from low temperature co-fired ceramic (LTCC), aluminum nitride (AlN), alumina, etc. 
     The optical engine  1700  also includes a plurality of chip submounts  1708  (four chip submounts  1708   a - 1708   d  shown in  FIG. 17B ) that are bonded (e.g., attached) to the top surface  1704  of the base substrate  1702 . The plurality of chip submounts  1708  are aligned in a row across a width of the optical engine  1700  between the left and right sides thereof. Each of the plurality of chip submounts  1708  includes a laser diode  1710 , also referred to as a laser chip or laser die, bonded thereto. In particular, an infrared chip submount  1708   a  carries an infrared laser diode, a red chip submount  1708   b  carries a red laser diode, a green chip submount  1708   c  carries a green laser diode, and a blue chip submount  1708   d  carries a blue laser diode. In operation, the infrared laser diode provides infrared laser light, the red laser diode provides red laser light, the green laser diode provides green laser light, and the blue laser diode provides blue laser light. Each of the laser diodes  1710  may comprise one of an edge emitter laser or a vertical-cavity surface-emitting laser (VCSEL), for example. Each of the four laser diode/chip submount pairs may be referred to collectively as a “laser chip on submount,” or a laser CoS  1712 . Thus, the optical engine  1700  includes an infrared laser CoS, a red laser CoS, a green laser CoS, and a blue laser CoS. In at least some implementations, one or more of the laser diodes  1710  may be bonded directly to the base substrate  1702  without use of a submount  1708 . 
     The optical engine  1700  also includes a laser diode driver circuit  1714  bonded to the bottom surface  1706  of the base substrate  1702 . The laser diode driver circuit  1714  is operatively coupled to the plurality of laser diodes  1710  via suitable electrical connections  1716  to selectively drive current to the plurality of laser diodes. Generally, the laser diode driver circuit  1714  may be positioned relative to the CoSs  1712  to minimize the distance between the laser diode driver circuit  1714  and the CoSs  1712 . Although not shown in  FIG. 17 , the laser diode driver circuit  1714  may be operatively coupleable to a controller (e.g., microcontroller, microprocessor, ASIC) that controls the operation of the laser diode driver circuit  1714  to selectively modulate laser light emitted by the laser diodes  1710 . In at least some implementations, the laser diode driver circuit  1714  may be bonded to another portion of the base substrate  1702 , such as the top surface  1704  of the base substrate, similar to the implementation shown in  FIG. 16A . In at least some implementations, the laser diode driver circuitry  1714  may be remotely located and operatively coupled to the laser diodes  1710 , similar to the implementation shown in  FIG. 16B . For example, the laser diode driver circuitry  1714  may be bonded to another substrate separate from base substrate  1702 , or may be mounted directly to a frame or support structure of a WHUD in which the optical engine  1700  is implemented. The electrical connections  1616   a - 1616   d , electrical contacts  1617   a - 1617   d , and electrically insulating cover  1640  of  FIGS. 16A and 16B  could also be implemented in optical engine  1700  shown in  FIGS. 17A and 17B . In order to not require the use of impedance matched transmission lines, the size scale may be small compared to a wavelength (e.g., lumped element regime), where the electrical characteristics are described by (lumped) elements like resistance, inductance, and capacitance. 
     The optical engine  1700  also includes a cap  1720  that includes a vertical sidewall  1722  and a horizontal wall or top portion  1725 . The vertical sidewall  1722  includes a lower first end  1724  and an upper second end  1726  opposite the first end. A flange  1728  may be disposed around a perimeter of the sidewall  1722  adjacent the lower first end  1724 . Within a portion of the vertical sidewall  1722  there is an optical window  1730  positioned proximate the laser diodes  1710  to pass light therefrom out of the cap  1720 . The sidewall  1722  and the optical window  1730  together define an interior volume  1732  sized and dimensioned to receive the plurality of chip submounts  1708  and the plurality of laser diodes  1710 . The lower first end  1724  and the flange  1728  of the cap  1720  are bonded to the base substrate  1702  to provide a hermetic seal between the interior volume  1732  of the cap and a volume  1734  exterior to the cap. 
     The cap  1720  may have a round shape, rectangular shape, or other shape. Thus, the vertical sidewall  1722  may comprise a continuously curved sidewall, a plurality (e.g., four) of adjacent planar portions, etc. The optical window  1730  may comprise an entire side of the cap  1720 , or may comprise only a portion thereof. In at least some implementations, the cap  1720  may include a plurality of optical windows (e.g., four optical windows, one for each of the laser diodes  1710 ) instead of a single optical window  1730 . 
     The optical engine  1700  also includes four collimation/pointing lenses  1736 , one for each of the four laser diodes  1710  that are bonded to the top surface  1704  of the base substrate  1702  in a row. Each of the plurality of collimations lenses  1736  may be positioned and oriented to receive light from a corresponding one of the laser diodes  1710  and to direct collimated light through the optical window  1730 . In at least some implementations, the collimation lenses  1736  may comprise one micro-optic lens array that is passively aligned and bonded inside the hermetic housing provided by the cap  1720 . In at least some implementations, the collimation lenses  1736  may be positioned outside of the cap  1720  and may receive light from the laser diodes  1710  via the optical window  1730 . 
     The collimations lenses  1736  couple the collimated beams of light toward a diffractive grating waveguide combiner  1750  which combines the light to provide a superimposed collimated beam  1756  ( FIG. 17A ). In the illustrated implementation, the grating waveguide combiner  1750  includes two waveguides  1750   a  and  1750   b  stacked proximate each other (e.g., with or without space therebetween), but in other implementations a different number (e.g., four) of waveguides may be used, depending on the particular design. The waveguides  1750   a  and  1750   b  may be bonded to the top surface  1704  of the base substrate  1702  or otherwise positioned proximate the optical window  1730  to receive the collimated beams of light from the collimation lenses  1736 . 
     In the illustrated implementation, the grating waveguide combiner  1750  includes four input grating couplers  1752   a - 1752   d  which receive a collimated light beam from the collimation lenses  1736   a - 1736   d , respectively, and an output grating coupler  1754  that outputs the superimposed collimated beam  1756  ( FIG. 17A ). As an example, the waveguide  1750   a  may include input grating couplers  1752   a  and  1752   b  for receiving infrared light and red light, respectively, and the waveguide  1750   b  may include input grating couplers  1752   c  and  1752   d  for receiving green light and blue light, respectively. In this example, the waveguide  1750   a  may pass or otherwise direct the red light and green light to the waveguide  1750   b.    
     The output grating coupler  1754  may be disposed on a surface of the waveguide  1750   b  facing away from the optical window  1730  to output the superimposed collimated light  1756  to another component (e.g., one or more diffractive optical elements) of the optical engine  1700  or to a laser projector of which the optical engine is a part. For example, following out-coupling of the aggregate beam  1756  from the output grating  1754  of the waveguide  1750   b , the aggregated beam may be collimated via a common collimation lens (e.g., lens  802  of  FIGS. 8 and 9 ). In at least some implementations, the collimation lens may be either an achromatic lens or an apochromatic lens (or lens assemblies), depending on the particular optical design and tolerances of the system. In at least some implementations, one or more diffractive optical elements (e.g., diffractive optical elements  804  of  FIGS. 8 and 9 ) may be used to provide wavelength dependent focus correction or other functionality. 
     Waveguide combiner  1750 , input grating couplers  1752   a - 1752   d , and output grating coupler  1754  can be formed and positioned using any appropriate method. As one example, waveguide combiner  1750 , input grating couplers  1752   a - 1752   d , and output grating coupler  1754  can be formed using the technique described with reference to  FIGS. 10 and 11 . In particular, waveguide combiner  1750 , input grating couplers  1752   a - 1752   d , and output grating coupler  1754  could be written in writeable glass and/or waveguide medium user a laser writing assembly, and subsequently positioned on base substrate  1702 . As another example, writeable glass and/or waveguide medium could be positioned on base substrate, and waveguide combiner  1750 , input grating couplers  1752   a - 1752   d , and output grating coupler  1754  can subsequently be directly laser written therein, such as by using similar techniques to those described with reference to  FIGS. 12A, 12B, 13, 14 and 15 . 
     Throughout this application, collimation lenses have been represented in the Figures by a simple curved lens shape. However, the subject systems, devices, and methods can utilize more advanced collimation schemes, as appropriate for a given application. 
       FIG. 18  shows an exemplary situation where using an advanced collimation scheme would be helpful.  FIG. 18  is an isometric view of a laser diode  1800 . The laser diode  1800  may be similar or identical to the various laser diodes discussed herein. The laser diode  1800  outputs a laser light beam  1802  via an output facet  1804  of the laser diode.  FIG. 18  shows the divergence of the light  1802  emitting from the laser diode  1800 . As shown, the light beam  1802  may diverge by a substantial amount along a fast axis  1806  (or perpendicular axis) and by a lesser amount in the slow axis  1808  (parallel axis). As a non-limiting example, in at least some implementations, the light beam  1802  may diverge with full width half maximum (FWHM) angles of up to 40 degrees in the fast axis direction  1806  and up to 10 degrees in the slow axis direction  1808 . This divergence results in a rapidly expanding elliptical cone. 
       FIGS. 19A and 19B  show an exemplary collimation scheme that can be used to circularize and collimate an elliptical beam such as that shown in  FIG. 18 .  FIG. 19A  illustrates an orthogonal view of the fast axis  1806  of light beam  1802  emitted from laser diode  1800 .  FIG. 19B  illustrates an orthogonal view of the slow axis  1808  of light beam  1802  emitted from laser diode  1800 . As shown in  FIG. 19A , a first lens  1900  collimates light beam  1802  along fast axis  1806 . As shown in  FIG. 19B , first lens  1900  is shaped so as to not substantially influence light beam  1802  along slow axis  1808 . Subsequently, as shown in  FIG. 19B , light beam  1802  is collimated along slow axis  1808  by a second lens  1902 . As shown in  FIG. 19A , second lens  1902  is shaped so as to not substantially influence light beam  1802  along fast axis  1806 . In essence, light beam  1802  is collimated along fast axis  1806  separately from slow axis  1808 . By collimating light beam  1802  along fast axis  1806  separately from slow axis  1808 , the collimation power applied to each axis can be independently controlled by controlling the power of lens  1900  and lens  1902  separately. Further, spacing between each of laser diode  1800 , lens  1900 , and lens  1902  can be controlled to collimate light beam  1802  to a certain width in each axis separately. If light beam  1802  is collimated along fast axis  1806  to the same width as slow axis  1808 , light beam  1802  can be circularized. Because light beam  1802  will typically diverge faster in the fast axis  1806 , it is generally preferable to collimate light beam  1802  along fast axis  1806  first, then collimate light beam  1802  along slow axis  1808  after. However, it is possible in certain applications to collimate light beam  1802  along slow axis  1808  first, and subsequently collimate light beam  1802  along fast axis  1806  after. This can be achieved by reversing the order of first lens  1900  with second lens  1902 , with respect to the path of travel of light beam  1802 . 
       FIGS. 19C and 19D  are isometric views which illustrate exemplary shapes for lenses  1900  and  1902 . Each of lens  1900  and  1902  can be for example a half-cylinder as in  FIG. 19C , a full cylinder as in  FIG. 19D , a quarter cylinder, a three-quarter cylinder, any other partial cylinder, or any other appropriate shape. Lenses  1900  and  1902  can be similarly shaped, or can have different shapes. 
       FIGS. 20A and 20B  illustrate an alternative collimation scheme.  FIG. 20A  illustrates an orthogonal view of the fast axis  1806  of light beam  1802  emitted from laser diode  1800 .  FIG. 20B  illustrates an orthogonal view of the slow axis  1808  of light beam  1802  emitted from laser diode  1800 . As shown in  FIG. 20A , a first lens  2000  redirects light beam  1802  along fast axis  1806 , to reduce divergence of light beam  1802  along fast axis  1806 . As shown in  FIG. 20B , first lens  2000  is shaped so as to not substantially influence light beam  1802  along slow axis  1808 . Preferably, first lens  2000  will reduce divergence of light beam  1802  along fast axis  1806  to match divergence of light beam  1802  along slow axis  1808 . That is, first lens  2000  preferably circularizes light beam  1802 . Subsequently, as shown in  FIGS. 20A and 20B , light beam  1802  is collimated along both fast axis  1806  and slow axis  1808  by a second lens  2002 . As shown in  FIGS. 20A and 20B , second lens  2002  is shaped similarly with respect to both the fast axis  1806  and the slow axis  1808 , to evenly collimate light beam  1802 . In essence, first lens  2000  circularizes light beam  1802 , and subsequently second lens  2002  collimates light beam  1802  along both axes. First lens  2000  can for example be shaped similarly to lens  1900  or lens  1902  discussed above, and shown in  FIGS. 19C and 19D . Second lens  2002  can for example be shaped as a double convex lens as illustrated in  FIG. 20C , or a single convex lens (convex on either side) as illustrated in  FIG. 20D , or any other appropriate shape of collimating lens. 
     The collimation schemes illustrated in  FIGS. 19A-19D and 20A-20D , and discussed above could be used in place of any of the collimation lenses described herein, including at least collimation lenses  136   a ,  136   b ,  136   c ,  136   d.    
     A person of skill in the art will appreciate that the teachings of the present systems, methods, and devices may be modified and/or applied in additional applications beyond the specific WHUD implementations described herein. In some implementations, one or more optical fiber(s) may be used to guide light signals along some of the paths illustrated herein. 
     The WHUDs described herein may include one or more sensor(s) (e.g., microphone, camera, thermometer, compass, altimeter, and/or others) for collecting data from the user&#39;s environment. For example, one or more camera(s) may be used to provide feedback to the processor of the WHUD and influence where on the display(s) any given image should be displayed. 
     The WHUDs described herein may include one or more on-board power sources (e.g., one or more battery(ies)), a wireless transceiver for sending/receiving wireless communications, and/or a tethered connector port for coupling to a computer and/or charging the one or more on-board power source(s). 
     The above description of illustrated embodiments, including what is described in the Abstract, is not intended to be exhaustive or to limit the embodiments to the precise forms disclosed. Although specific embodiments of and examples are described herein for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the disclosure, as will be recognized by those skilled in the relevant art. The teachings provided herein of the various embodiments can be applied to other portable and/or wearable electronic devices, not necessarily the exemplary wearable electronic devices generally described above. 
     For instance, the foregoing detailed description has set forth various embodiments of the devices and/or processes via the use of block diagrams, schematics, and examples. Insofar as such block diagrams, schematics, and examples contain one or more functions and/or operations, it will be understood by those skilled in the art that each function and/or operation within such block diagrams, flowcharts, or examples can be implemented, individually and/or collectively, by a wide range of hardware, software, firmware, or virtually any combination thereof. In one embodiment, the present subject matter may be implemented via Application Specific Integrated Circuits (ASICs). However, those skilled in the art will recognize that the embodiments disclosed herein, in whole or in part, can be equivalently implemented in standard integrated circuits, as one or more computer programs executed by one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs executed by on one or more controllers (e.g., microcontrollers) as one or more programs executed by one or more processors (e.g., microprocessors, central processing units, graphical processing units), as firmware, or as virtually any combination thereof, and that designing the circuitry and/or writing the code for the software and or firmware would be well within the skill of one of ordinary skill in the art in light of the teachings of this disclosure. 
     When logic is implemented as software and stored in memory, logic or information can be stored on any processor-readable medium for use by or in connection with any processor-related system or method. In the context of this disclosure, a memory is a processor-readable medium that is an electronic, magnetic, optical, or other physical device or means that contains or stores a computer and/or processor program. Logic and/or the information can be embodied in any processor-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions associated with logic and/or information. 
     In the context of this specification, a “non-transitory processor-readable medium” can be any element that can store the program associated with logic and/or information for use by or in connection with the instruction execution system, apparatus, and/or device. The processor-readable medium can be, for example, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus or device. More specific examples (a non-exhaustive list) of the computer readable medium would include the following: a portable computer diskette (magnetic, compact flash card, secure digital, or the like), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM, EEPROM, or Flash memory), a portable compact disc read-only memory (CDROM), digital tape, and other non-transitory media. 
     The various embodiments described above can be combined to provide further embodiments. To the extent that they are not inconsistent with the specific teachings and definitions herein, at least the following are incorporated herein by reference in their entirety: U.S. Provisional Patent Application Ser. No. 62/438,725, U.S. Non-Provisional patent application Ser. No. 15/848,265 (U.S. Publication Number 2018/0180885), U.S. Non-Provisional patent application Ser. No. 15/848,388 (U.S. Publication Number 2018/0180886), U.S. Provisional Patent Application Ser. No. 62/450,218, U.S. Non-Provisional patent application Ser. No. 15/852,188 (U.S. Publication Number 2018/0210215), U.S. Non-Provisional patent application Ser. No. 15/852,282, (U.S. Publication Number 2018/0210213), U.S. Non-Provisional patent application Ser. No. 15/852,205 (U.S. Publication Number 2018/0210216), U.S. Provisional Patent Application Ser. No. 62/575,677, U.S. Provisional Patent Application Ser. No. 62/591,550, U.S. Provisional Patent Application Ser. No. 62/597,294, U.S. Provisional Patent Application Ser. No. 62/608,749, U.S. Provisional Patent Application Ser. No. 62/609,870, U.S. Provisional Patent Application Ser. No. 62/591,030, U.S. Provisional Patent Application Ser. No. 62/620,600, U.S. Provisional Patent Application Ser. No. 62/576,962, U.S. Provisional Patent Application Ser. No. 62/760,835, U.S. Non-Provisional patent application Ser. No. 16/201,664, U.S. Non-Provisional patent application Ser. No. 16/168,690, U.S. Non-Provisional patent application Ser. No. 16/171,206, U.S. Non-Provisional patent application Ser. No. 16/203,221, U.S. Non-Provisional patent application Ser. No. 16/216,899, U.S. Non-Provisional patent application Ser. No. 16/231,019, and/or PCT Patent Application PCT/CA2018051344. Aspects of the embodiments can be modified, if necessary, to employ systems, circuits and concepts of the various patents, applications and publications to provide yet further embodiments. 
     These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.