Patent Description:
<CIT> and <CIT> disclose near eye displays including lasers and a waveguide receiving light emitted by the lasers.

A system includes a waveguide and an edge-emitting laser. The edge-emitting laser is configured to lase coherent light into the waveguide. The edge-emitting laser includes an optical cavity having an active gain section and a passive section.

In a waveguide-based laser scanning display, there are myriad (e.g., millions) light paths resulting from multiple interactions of image light beams propagating through a waveguide and grating structures (e.g., surface relief grating SRG). As such, there are myriad possible interactions between light beams with different optical path lengths (OPLs). A laser is a coherent light source where certain OPLs that are proportional to an optical cavity length of the laser form temporal coherence peaks. If an OPL of the waveguide matches any of the coherence OPLs of the laser, an interference fringe may be formed. An interference fringe may create an artifact in an image presented by the waveguide-based laser scanning display. Such an artifact may degrade the perceived image quality of the waveguide-based laser scanning display.

Accordingly, the present disclosure is directed to a waveguide-based laser scanning display including an edge-emitting laser configured to lase coherent light into a waveguide. The edge-emitting laser includes an optical cavity having a total length that reduces or avoids fringe interference of the coherent light propagating through the waveguide. In particular, the optical cavity length may be tuned to ensure that the OPLs supported by the waveguide do not match the coherence OPLs of the coherent light output from the laser. For example, increasing the optical cavity length to larger than a maximum OPL supported by the waveguide guarantees avoiding all fringe interference.

Increasing the optical cavity in a manner that increases the length of the active gain section causes an increase in the laser threshold current, and hence the power consumption of the laser. To both reduce/avoid fringe interference and keep the laser power consumption low, the optical cavity may be configured to have both an active gain section and a passive section. The active gain section is configured to amplify an optical power of light reflecting within the optical cavity. The passive section increases a functional length of the optical cavity without further amplifying the optical power of the light reflecting within the optical cavity. In this way, the overall length of the optical cavity satisfies the fringe mitigation requirements while the laser's output power and power consumption is determined mainly by the length of the active gain section. Such a laser may consume less power than a laser having the same optical cavity, but where the active gain section occupies the entire length of the optical cavity instead of achieving the greater optical cavity length with a passive section.

<FIG> shows aspects of an example implementation environment for a near-eye display system <NUM>. As illustrated herein, near-eye display system <NUM> is a component of a head-mounted electronic device <NUM>, which is worn and operated by a user <NUM>. The near-eye display system <NUM> is configured to present virtual imagery in the user's field of view. In some implementations, user-input componentry of the wearable electronic device <NUM> may enable the user to interact with the virtual imagery. The wearable electronic device <NUM> takes the form of eyeglasses in the example of <FIG>. In other examples, the wearable electronic device <NUM> may take the form of goggles, a helmet, or a visor. In still other examples, the near-eye display system <NUM> may be a component of a non-wearable electronic device, such as a heads-up display.

The near-eye display system <NUM> may be configured to cover one or both eyes of the user <NUM> and may be adapted for monocular or binocular image display. In examples in which the near-eye display system <NUM> covers only one eye, but binocular image display is desired, a complementary near-eye display system may be arranged over the other eye. In examples in which the near-eye display system covers both eyes and binocular image display is desired, the virtual imagery presented by near-eye display system <NUM> may be divided into right and left portions directed to the right and left eyes, respectively. In scenarios in which stereoscopic image display is desired, the virtual imagery from the right and left portions, or complementary near-eye display systems, may be configured with appropriate stereo disparity so as to present a three-dimensional subject or scene.

<FIG> shows an example near-eye display system <NUM> that uses a laser assembly <NUM> as an illumination source. The laser assembly <NUM> includes lasers 202A (e.g., a red laser), 202B (e.g., a green laser), and 202C (e.g., a blue laser). Although only three lasers are shown, it will be appreciated that the laser assembly <NUM> may include any suitable number of lasers. For example, the laser assembly <NUM> may include <NUM>, <NUM>, <NUM>, <NUM>, or more than <NUM> red lasers; <NUM>, <NUM>, <NUM>, <NUM>, or more than <NUM> green lasers; <NUM>, <NUM>, <NUM>, <NUM>, or more than <NUM> blue lasers; and <NUM>, <NUM>, <NUM>, <NUM>, or more than <NUM> lasers of other colors. Any combination or modification in the number of lasers may also be available (e.g., <NUM> red, <NUM> green, <NUM> blue, or <NUM> red, <NUM> green, <NUM> blue, etc.). Accordingly, any number of lasers may be used to irradiate/illuminate pixels for generating image content.

In some instances (though not all), the laser assembly <NUM> also includes a collimating lens assembly <NUM> (or other diffractive optical element) that is structured to direct light to another location or otherwise operate on the light in some manner. In this example, each of the lasers 202A, 202B, and 202C has a corresponding collimating lens 204A, 204B, 204C. In some implementations, however, a single collimating lens may be used for more than one laser.

The near-eye display <NUM> includes combination optics <NUM> configured to spatially combine the light beams lased from the plurality of lasers 202A, 202B, and 202C into a single light beam.

The near-eye display <NUM> includes a micro-electro-mechanical mirror system (MEMs) <NUM>, though the principles disclosed herein are applicable to any type of laser-based display unit and not only to architectures with the MEMs <NUM>. The MEMs <NUM> is configured to collect laser light from the combination optics <NUM>, which combines light lased from three different sources (i.e., the lasers 202A, 202B, and 202C) into a single light beam. Additionally, the MEMs <NUM> is configured to direct laser light 208A (which, in this example includes red laser light, green laser light, and blue laser light) to a waveguide <NUM>. Furthermore, the MEMs <NUM> is configured to redirect its mirrors/mirror array so that the laser light 208A is aimed at different locations at the waveguide <NUM>. As shown, laser lights 208B and 208C are aimed at different locations on the waveguide <NUM>. In this manner, the MEMs <NUM> is able to route light to different locations by adjusting the aim of its corresponding mirror array. It will be appreciated that the laser lights 208A-C may be modulated to include varying degrees or intensities (or even an absence of any one or more) of red, green, blue, or other color, laser light.

The waveguide <NUM> is configured to redirect or propagate the laser light 208A-C to a desired location which is viewable by a user's eye <NUM>. It will be appreciated that waveguide <NUM> may be any type of waveguide display (e.g., a surface relief grating waveguide).

The laser light 208A-C enters the waveguide <NUM> via an entry grating <NUM>. The laser light 208A-C then propagates (e.g., via total internal reflection) through the waveguide <NUM> until it reaches an exit grating <NUM>. It will be appreciated that the angles with which the laser light 208A-C enters the waveguide <NUM> are preserved as the laser light 208A-C propagates through the waveguide <NUM>. This condition is shown by the different angles that each of the respective laser lights 208A-C propagate through the waveguide <NUM>. By configuring the entry grating <NUM> and the exit grating <NUM> to meet certain design parameters, the MEMs <NUM> is able to use waveguide <NUM> to propagate light towards the user's eye <NUM>.

The laser assembly <NUM> and the MEMs <NUM> may be controlled by a controller <NUM>. The controller <NUM> may be configured to control the MEMs <NUM>, in conjunction with the laser assembly <NUM> to progressively scan a set of pixels <NUM> to a target display area for a user's eye <NUM> to view (e.g., by adjusting the mirror array so that the combined RGB laser beam or light is aimed at different locations) individual pixels of that image in such a rapid manner that the entirety of the image appears before the user's eye <NUM> without the user realizing that the image was progressively scanned pixel by pixel and line by line. In this way, the near-eye display system <NUM> may project or render image content for a user to view.

The MEMs <NUM> may be able to scan an image (i.e., pixels of that image) at any image resolution or range of image resolutions (e.g., in cases where foveated rendering is used). For example, in some implementations, the MEMs <NUM> is configured to scan RGB light from the laser assembly <NUM> with a resolution of <NUM>,<NUM> pixels by <NUM>,<NUM> pixels, or any other resolution.

There are various instances in which, due to the wave properties of laser light, fringe interference can occur. Laser light output from the waveguide is a composite of multiple separate waveforms with different optical path lengths (OPLs). Such a composite waveform may have multiple peaks (i.e., coherence peaks where OPLs of different light beams have temporal coherence) and valleys as a result of combining each of the multiple waveforms. <FIG> shows a graph <NUM> of an example composite waveform of laser light output from a laser. The composite waveform has a plurality of coherence peaks spaced apart by valleys. The distance between the coherence peaks is proportional to the effective length of the optical cavity of the laser. The shape of the coherence peaks is defined by the laser gain spectrum of the laser. In this example, the active gain section occupies the entire optical cavity and has a length of <NUM>.

Additionally, <FIG> shows a graph <NUM> of interference fringes of the waveguide. In instances where the interference fringes do not overlap with the coherence peaks of the laser light, the interference fringes do not create artifacts in an image output from the waveguide. In the depicted example, interference fringes <NUM>, <NUM>, and <NUM> do not overlap with coherence peaks of the laser light and thus do not create artifacts in the image. However, interference fringe <NUM> overlaps with coherence peak <NUM> and interference fringe <NUM> overlaps with coherence peak <NUM>. These overlapping interference fringes create artifacts in the image output from the waveguide. For example, these interference fringes may result from back scattering and/or back reflections combining with the outgoing laser light exiting the waveguide. As a result of these interference fringes, various different bright and dark rings/spots are created. <FIG> shows an example image <NUM> including artifacts <NUM> and <NUM> caused by such interference fringes. The artifacts <NUM>, <NUM> include irregularities in terms of brightness. The presence of such artifacts in an image can lower the perceived quality of the image and thereby negatively affect the user experience. In the depicted example, the artifact <NUM> distorts the appearance of a dragon in image <NUM>. Further, the artifact <NUM> distorts the appearance of a fireball shot by a wizard at the dragon.

In order to reduce fringe interference that creates artifacts in an image output from the waveguide, a laser assembly may be designed to reduce or avoid fringe interference of coherent light propagating through the waveguide. Such a laser assembly may include an optical cavity having a total length that is tuned to ensure that the OPLs supported by the waveguide do not match the coherence OPLs of the coherent light output from the laser. For example, increasing the optical cavity length to larger than a maximum OPL supported by the waveguide guarantees avoiding all fringe interference.

Increasing the optical cavity in a manner that increases the length of the active gain section causes an increase in the laser threshold current, and hence the power consumption of the laser. To both reduce/avoid fringe interference and keep the laser power consumption low, the optical cavity may be configured to have two sections - an active gain section and a passive section. <FIG> schematically shows an example laser assembly <NUM> having a two-section optical cavity that is tuned to reduce fringe interference from a corresponding waveguide. The laser assembly <NUM> may be representative of any of the lasers 202A, 202B, 202C of the laser assembly <NUM> included in the near-eye display system <NUM> shown in <FIG>. Continuing with this example, the laser assembly <NUM> may be particularly configured to reduce fringe interference caused by a waveguide, such as the waveguide <NUM> shown in <FIG>.

The laser assembly <NUM> includes an optical cavity <NUM> positioned on a substrate <NUM>. The optical cavity <NUM> includes an active gain section <NUM> and a passive section <NUM>. The active gain section <NUM> may be optically coupled to the passive section <NUM> via a transmissive interface <NUM>. In the depicted example, the active gain section <NUM> is edge coupled to the passive section <NUM> via the transmissive interface <NUM>. The transmissive interface <NUM> may be any suitable interface between the two sections of the optical cavity <NUM> that supports low coupling loss. It will be appreciated that the active gain section <NUM> may be optically coupled to the passive section <NUM> in any suitable manner.

The active gain section <NUM> is the source of optical gain within the laser assembly <NUM>. The active gain section <NUM> is configured to amplify an optical power of light reflecting within the optical cavity. The gain/amplification results from the stimulated emission of electronic or molecular transitions of an active gain medium of the active gain section <NUM> to a lower energy state from a higher energy state previously populated by a pump source. Laser pumping of the active gain section <NUM> may be performed using different pump sources, such as electrical currents or light generated by discharge lamps or by other lasers, for example. In one particular example, the active gain section <NUM> is configured as a reflective semiconductor optical amplifier (RSOA).

The passive section <NUM> increases a functional length of the optical cavity <NUM> without further amplifying the optical power of the light reflecting within the optical cavity <NUM>. In some implementations, the passive section <NUM> is substantially transparent to the light reflecting within the optical cavity <NUM>.

The passive section <NUM> includes a reflective end <NUM> and the active gain section <NUM> includes a selectively reflective end <NUM>. The two reflective ends <NUM> and <NUM> may allow coherent light to reflect back and forth within the optical cavity. Each time a light beam passes through the active gain section, the optical power of the light beam may be amplified. The selectively reflective end <NUM> may be partially transparent to allow coherent light <NUM> to be output from the laser assembly <NUM>. In other implementations, the reflective end <NUM> may be selectively reflective and/or partially transparent to allow coherent light to be output from the laser assembly <NUM> via the passive section <NUM>.

The overall length (L) of the optical cavity <NUM> satisfies the fringe mitigation requirements while the power consumption is determined mainly by a length (LA) of the active gain section <NUM>. The length (LA) of the active gain section <NUM> may be determined based on the laser requirement (e.g., power consumption and power output) for the particular application. A length (LP) of the passive section can be selected, given a particular active gain section length (LA), to provide an overall length (L) that avoids the fringe OPLs that are imposed by the waveguide. The length (LA) of the active gain section may be longer, shorter, or the same length as the length (LP) of the passive section. As one non-limiting example, the length (LA) of the active gain section is <NUM> and a total length of the optical cavity is <NUM>. The length (LA) of the active gain section, the length (LP) of the passive section, and/or the length (L) of the optical cavity may be any suitable length. Such a laser assembly <NUM> may consume less power than a laser having the same optical cavity length, but where the active gain section occupies the entire length of the optical cavity instead of achieving the greater optical cavity length with a passive section.

<FIG> shows a graph <NUM> of an example composite waveform of laser light output from the laser assembly <NUM> shown in <FIG>. The composite waveform has a plurality of coherence peaks spaced apart by valleys. Additionally, <FIG> shows a graph <NUM> of interference fringes of the waveguide <NUM> shown in <FIG>. The length (L) of the optical cavity <NUM> of the laser assembly <NUM> is designed to avoid the overlap of the fringes with the laser coherence peaks. In particular, none of the interference fringes <NUM>, <NUM>, <NUM><NUM>, <NUM>, and <NUM> overlap with the coherence peaks <NUM>, <NUM>, <NUM>, and <NUM>. In this example, overlap can be reduced to a minimum by increasing the cavity length to <NUM>. Note that the coherence OPLs of a laser can be extracted from the laser's coherence function which shows the degree of laser temporal coherence for different OPLs and is proportional to the Fourier Transform of its spectrum.

The laser assembly <NUM> may be fabricated in any suitable manner using any suitable fabrication techniques. <FIG> show different techniques for fabricating the laser assembly <NUM>. The depicted examples include active and passive sections on a monolithic integration of an optical cavity of the laser assembly. In some examples, the laser assembly <NUM> may be fabricated using a single step epitaxial process. <FIG> show different examples of laser assemblies fabricated using different single step epitaxial processes.

<FIG> schematically shows an example laser assembly <NUM> including an active gain layer <NUM> and a passive layer <NUM>. Both the active gain layer <NUM> and passive layer <NUM> may be grown in one single epitaxial step. Further, the transparent waveguide sections <NUM> (e.g., 706A, 706B, 706C) may be created afterwards by locally removing the active gain layer <NUM>. In this approach special structures such as vertical tapers <NUM> (e.g., 708A, 708B) may be used to efficiently couple the light from the active gain layer <NUM> to the passive layer <NUM> and vice versa.

<FIG> schematically shows an example laser assembly <NUM> where a composite waveguide includes the active layer. In this example, no vertical coupling is used between the active and passive sections <NUM>, <NUM> on the substrate layer <NUM>. The challenge in this design is the discontinuity between the active and passive sections which causes coupling loss and reflection. However, the discontinuity can be reduced by covering the structure with a cladding layer <NUM> using an additional growth step. As an example, the cladding layer <NUM> may include gallium nitride (GaN) or gallium arsenide (GaAs).

<FIG> schematically shows an example laser assembly <NUM> including an active gain section <NUM> and a passive section <NUM> formed using quantum wells. The active gain section (or layer) <NUM> includes a plurality of quantum wells. The passive section <NUM> may be initially formed as an active layer and then may be made passive by capping it with a material which generates vacancies in the semiconductor crystal of the quantum wells. These vacancies may be generated by implanting ions into the capping layer and diffusing the ions throughout the layer when the wafer is annealed at low temperature. These vacancies cause the quantum well atomic species to intermix with the atomic species of the adjacent barrier layers that leads to an increase of the effective bandgap of the quantum wells, such that the section becomes fully passive and transparent. In some examples, such intermixing can increase the band gap wavelength of the active material by more than <NUM>, so that it becomes fully transparent. During this process, the active gain section may be protected by a mask.

In some examples, the laser assembly may be fabricated using a multi-step epitaxial process. <FIG> shows an example laser assembly <NUM> where an active gain section <NUM> and a passive section <NUM> are created in different growth steps. In a first growth step, the active gain section <NUM> is grown on a substrate <NUM>. Next the active gain section <NUM> is masked and the exposed area is etched away. In a second selective area regrowth step, the etched-away area is replaced with a transparent waveguide stack <NUM>. In a third growth step, a substrate layer <NUM> is grown on the passive section <NUM>. Such a multi-step growth process may provide a large flexibility in the epitaxial layer structure and in the doping levels of the laser assembly <NUM>.

<FIG> shows an example laser assembly <NUM> where each of an active gain section <NUM> and a passive section <NUM> is grown on separate wafers. Each wafer may be grown with an optimum epitaxial recipe for the particular section. Further, each of the active and passive sections <NUM> and <NUM> may be lifted off their separate substrates and placed onto a common carrier substrate <NUM>. The active gain section <NUM> may be edge coupled with the passive section <NUM> on the carrier substrate. It will be appreciated that a laser assembly may be made using any suitable fabrication technique.

<FIG> schematically shows a simplified representation of a computing system <NUM> configured to provide any to all of the compute functionality described herein. Computing system <NUM> may take the form of one or more head-mounted, near-eye display devices, personal computers, network-accessible server computers, tablet computers, home-entertainment computers, gaming devices, mobile computing devices, mobile communication devices (e.g., smart phone), virtual/augmented/mixed reality computing devices, wearable computing devices, Internet of Things (IoT) devices, embedded computing devices, and/or other computing devices. For example, computing system <NUM> may be representative of the head-mounted electronic device <NUM> in <FIG>.

Computing system <NUM> includes a logic subsystem <NUM> and a storage subsystem <NUM>. Computing system <NUM> may optionally include a display subsystem <NUM>, input subsystem <NUM>, communication subsystem <NUM>, and/or other subsystems not shown in <FIG>.

Logic subsystem <NUM> includes one or more physical devices configured to execute instructions. For example, the logic subsystem <NUM> may be configured to execute instructions that are part of one or more applications, services, or other logical constructs. The logic subsystem <NUM> may include one or more hardware processors configured to execute software instructions. Additionally or alternatively, the logic subsystem <NUM> may include one or more hardware or firmware devices configured to execute hardware or firmware instructions. Processors of the logic subsystem <NUM> may be single-core or multicore, and the instructions executed thereon may be configured for sequential, parallel, and/or distributed processing. Individual components of the logic subsystem <NUM> optionally may be distributed among two or more separate devices, which may be remotely located and/or configured for coordinated processing. Aspects of the logic subsystem <NUM> may be virtualized and executed by remotely-accessible, networked computing devices configured in a cloud-computing configuration.

Storage subsystem <NUM> includes one or more physical devices configured to temporarily and/or permanently hold computer information such as data and instructions executable by the logic subsystem <NUM>. When the storage subsystem <NUM> includes two or more devices, the devices may be collocated and/or remotely located. Storage subsystem <NUM> may include volatile, nonvolatile, dynamic, static, read/write, read-only, random-access, sequential-access, location-addressable, file-addressable, and/or content-addressable devices. Storage subsystem <NUM> may include removable and/or built-in devices. When the logic subsystem <NUM> executes instructions, the state of storage subsystem <NUM> may be transformed - e.g., to hold different data.

The logic subsystem <NUM> and the storage subsystem <NUM> may cooperate to instantiate one or more logic machines. As used herein, the term "machine" is used to collectively refer to the combination of hardware, firmware, software, instructions, and/or any other components cooperating to provide computer functionality. In other words, "machines" are never abstract ideas and always have a tangible form. A machine may be instantiated by a single computing device, or a machine may include two or more subcomponents instantiated by two or more different computing devices. In some implementations a machine includes a local component (e.g., software application executed by a computer processor) cooperating with a remote component (e.g., cloud computing service provided by a network of server computers). The software and/or other instructions that give a particular machine its functionality may optionally be saved as one or more unexecuted modules on one or more suitable storage devices. As examples, the logic subsystem <NUM> and the storage subsystem <NUM> may be implemented as a controller, such as controller <NUM> shown in <FIG>.

When included, display subsystem <NUM> may be used to present a visual representation of data held by storage subsystem <NUM>. In some implementations, display subsystem may include one or more virtual-, augmented-, or mixed reality displays. As an example, display subsystem <NUM> may be implemented as the near-eye display system <NUM> shown in <FIG>.

When included, input subsystem <NUM> may comprise or interface with one or more input devices. An input device may include a sensor device or a user input device. Examples of user input devices include a keyboard, mouse, touch screen, or game controller. Example NUI componentry may include a microphone for speech and/or voice recognition; an infrared, color, stereoscopic, and/or depth camera for machine vision and/or gesture recognition; a head tracker, eye tracker, accelerometer, and/or gyroscope for motion detection and/or intent recognition.

The communication subsystem <NUM> may be configured for communication via personal-, local- and/or wide-area networks.

In an example, a system, comprises a waveguide, and an edge-emitting laser configured to lase coherent light into the waveguide, the edge-emitting laser including an optical cavity having an active gain section and a passive section, wherein the active gain section is configured to amplify an optical power of light reflecting within the optical cavity, wherein the passive section increases a functional length of the optical cavity without further amplifying the optical power of the light reflecting within the optical cavity, and wherein a total length of the optical cavity reduces fringe interference of the coherent light propagating through the waveguide. In this example and/or other examples, the total length of the optical cavity may be configured such that coherence peaks of optical path lengths (OPLs) of the coherent light output from the optical cavity do not match interfering OPLs in the waveguide. In this example and/or other examples, the length of the active gain section may be different than a length of the passive section. In this example and/or other examples, the length of the passive section may be greater than the length of the active gain section. In this example and/or other examples, the passive section may be substantially transparent to the light reflecting within the optical cavity. In this example and/or other examples, the active gain section may be edge coupled to the passive section. In this example and/or other examples, the active gain section and the passive section may be optically coupled via vertical optical tapers. In this example and/or other examples, the optical cavity may include a plurality of layers including a gallium nitride or gallium arsenide cladding layer. In this example and/or other examples, the active gain section may include a plurality of active quantum wells, and the passive section may include a plurality of passive quantum wells made transparent via ion implantation. In this example and/or other examples, the active gain section and the passive section may be formed as separate epitaxial layers on different substrates, and the active gain section and the passive section may be optically coupled to a common carrier substrate. In this example and/or other examples, an energy requirement of the edge-emitting laser may be less than an equivalent edge-emitting laser having an active gain section with a same length as the total length of the optical cavity.

In an example, a system comprises a waveguide, and an edge-emitting laser configured to lase coherent light into the waveguide, the edge-emitting laser including an optical cavity having an active gain section and a passive section, wherein the active gain section is configured to amplify an optical power of light reflecting within the optical cavity, wherein the passive section increases a functional length of the optical cavity, thereby reducing fringe interference of the coherent light propagating through the waveguide. In this example and/or other examples, the passive section may increase a functional length of the optical cavity without further amplifying the optical power of the light reflecting within the optical cavity. In this example and/or other examples, the functional length of the optical cavity may be configured such that coherence peaks of optical path lengths (OPLs) of the coherent light output from the optical cavity do not match interfering OPLs in the waveguide. In this example and/or other examples, the length of the active gain section may be different than a length of the passive section. In this example and/or other examples, the length of the passive section may be greater than the length of the active gain section. In this example and/or other examples, the passive section may be substantially transparent to the light reflecting within the optical cavity. In this example and/or other examples, the active gain section may be edge coupled to the passive section. In this example and/or other examples, the active gain section and the passive section may be optically coupled via vertical optical tapers.

In an example, a near-eye display comprises a waveguide configured to propagate coherent light towards a user's eye, and an edge-emitting laser configured to lase the coherent light into the waveguide, the edge-emitting laser including an optical cavity having an active gain section optically coupled to a passive section.

Claim 1:
A near-eye display system (<NUM>), comprising:
a waveguide (<NUM>) configured to propagate coherent light towards a user's eye (<NUM>); and
a laser assembly (<NUM>) comprising one or more edge-emitting lasers (202A, 202B, 202C) and a collimating lens assembly (<NUM>), the collimating lens assembly (<NUM>) including one or more collimating lenses (204A, 204B, 204C), the laser assembly (<NUM>) configured to lase coherent light into the waveguide (<NUM>), each edge-emitting laser (202A, 202B, 202C) including an optical cavity (<NUM>) having an active gain section (<NUM>) and a passive section (<NUM>);
wherein the active gain section (<NUM>) is configured to amplify an optical power of light reflecting within the optical cavity (<NUM>),
wherein the passive section (<NUM>) increases a functional length (LA) of the optical cavity (<NUM>) without further amplifying the optical power of the light reflecting within the optical cavity (<NUM>), and
wherein a total length (L) of the optical cavity (<NUM>) is configured such that fringe interference (<NUM>, <NUM>, <NUM>, <NUM>) of the coherent light (<NUM>; <NUM>) propagating through the waveguide (<NUM>) is avoided, wherein fringe interference creates artifacts (<NUM>, <NUM>) in an image output (<NUM>) from the waveguide (<NUM>).