Photonics package with tunable liquid crystal lens

A photonics package that incorporates a liquid crystal lens situated between a light source and a waveguide or output element of the package. The liquid crystal lens may focus or collimate light passing through it. This may be useful, for example, to focus light from a light source on or at an entry of a waveguide. Certain embodiments may include or incorporate routing or optical elements between the light source and the liquid crystal lens, and/or on a side of the lens opposite a side on which the light source is located.

FIELD

The described embodiments relate generally to photonics packages incorporating a liquid crystal lens, and more particularly to a photonics package having a liquid crystal lens that can be tuned to focus, collimate, or steer light from a light source.

BACKGROUND

Photonics packages may be extraordinarily small and are used in many applications from telecommunications to next-generation computing device architectures. Photonics packages also have relatively small power requirements, making them suitable for incorporation into many devices.

However, photonics packaging processing may be difficult, costly, and time-consuming. Even small misalignments or other mismatches between components of a photonics package may lead to the package having unacceptable operation or even being inoperable. These mismatches may be introduced when components are made, during manufacture of the photonics package (for example, when the components are placed on a substrate), or as the photonics package ages or operates.

SUMMARY

One embodiment described herein takes the form of a photonics package, comprising: a light source operable to emit a light output; a tunable liquid crystal lens operable to switch between a base state and a light steering state, and configured to receive the light source; a waveguide configured to receive the light output; and optics configured to steer the light output; wherein the optics are positioned between the tunable liquid crystal lens and one of the light source or waveguide; the tunable liquid crystal lens switches from the base state to the light steering state in response to an applied voltage; and, when in the light steering state, the tunable liquid crystal lens steers the light output toward the waveguide or other optical components.

Another embodiment described herein takes the form of a method for operating a photonics package, comprising: emitting a light output from a light source; determining whether an operating parameter is acceptable; in response to determining that the operating parameter is unacceptable, tuning a liquid crystal lens through which the light output passes; in response to tuning the liquid crystal lens, determining that the operating parameter is acceptable; and in response to determining that the operating parameter is acceptable, maintaining the tuning of the liquid crystal lens.

These and other embodiments will be apparent upon reviewing the specification and figures in their entirety, and the foregoing are examples rather than limitations.

The use of shading or cross-hatching is meant in indicate surfaces that have been cross-sectioned rather than any particular type of material or color. Structures, components, elements and the like shown in the accompanying figures are illustrative only and are not intended to convey or require any particular scale or spatial relationship.

DETAILED DESCRIPTION

Generally, embodiments described herein are directed to a photonics package, which may be or include one or more photonics integrated circuits (“PIC”), that incorporates a liquid crystal lens situated between a light source and a waveguide or output element of the package. The liquid crystal lens may focus or collimate light passing through it. This may be useful, for example, to focus light from a light source on an entry of a waveguide. Certain embodiments may include or incorporate routing or optical elements between the light source and the liquid crystal lens, as well as on a side of the lens opposite a side on which the light source is located. The term “optical element” generally refers to a structure through which light may pass and that alters a parameter of the light in some fashion, such as a lens, phase shifter, or collimator. A “routing element” is typically a structure that channels light or through which light propagates, such as a waveguide, mirror or other reflector, outcoupler, grating coupler, or the like.

The focusing/collimating properties of the liquid crystal lens may be changed by applying a voltage to the lens. The voltage may tune the liquid crystal lens' properties, adjusting the focal point of light passing through the lens as one example. As the voltage changes, the light's focal point may likewise change. In this manner, the liquid crystal lens may be dynamically tuned to account for variances in positioning of the lens, waveguide, light source, and/or other optics relative to one another. Such variances may arise during assembly of a photonics integrated circuit or other photonics package. In particular, pick and place operations used to set the various components of the photonics circuit may introduce small misalignments between components, insofar as the pick and place operations may have a minimum error in their ability to locate and/or position elements on a substrate.

Likewise, photonics circuits, structures, and the like (collectively, “photonics structures”) may suffer from drift during operation and/or as they age. Thermal expansion may cause drift during operation, while components may shift as the photonics structure ages. Similarly, individual components of a photonics package may have relatively minor differences in dimension from one component to another. For example, two waveguides may have the same dimensions within a tens of nanometers tolerance (or the like), generally resulting from pick-and-place accuracy and/or dicing accuracy. Even minor differences in dimensions between otherwise identical components may lead to a mismatch in a photonics package; such mismatches may, in turn, yield reduced power or output from the photonics package, otherwise introduce signal loss, or may even result in inoperability. The dynamically tunable liquid crystal lens may offset these issues by steering light form a light source to another routing element of the photonics package, such as a waveguide, outcoupler, or the like.

“Steering,” as that term is used here, refers to adjusting a focal length, focal point, angle, or width of light (e.g., spot size) (collectively, “parameters”) passing through the liquid crystal lens. The light is “adjusted” insofar as it changes a parameter of the light when compared to the light propagating through the photonics package in the absence of the liquid crystal lens.

Additionally, the liquid crystal lens may be retuned periodically to ensure all or most light from a light source (whether LED, laser, laser diode, or otherwise) efficiently reaches a subsequent routing element in the photonics package. Thus, if the photonics package suffers an impact that misaligns the light source from the routing element, the liquid crystal lens may be retuned to offset the misalignment. Likewise, the liquid crystal lens may be retuned one or more times during the photonics package's operation to account for thermal drift, thermal expansion, and so on. Some embodiments may monitor an ambient temperature or the temperature of one or more elements of the photonics package and tune the liquid crystal lens accordingly. For example, as the temperature of a light source increases, the liquid crystal lens may be retuned to account for thermal effects due to this rising temperature.

Although embodiments are generally discussed herein as employing a tunable liquid crystal lens between a light source and a waveguide (with or without intervening optics), it should be appreciated that a tunable liquid crystal lens can be placed and used between PICs, between a PIC and a fiber output, between a PIC and a detector, or generally between a PIC and any other optical structure or element. Collectively, these, along with a waveguide, are termed “optical output structures.” Accordingly, in any embodiment described herein, the waveguide and/or light source may be replaced with any of the foregoing optical output structures or elements.

FIG.1generally depicts a sample photonics package100that may incorporate a tunable liquid crystal lens. The photonics package100may include a photonics integrated circuit110as well as various optical elements that are not part of the PIC. The PIC110and other optical elements may be mounted to a common substrate to form the photonics package100. Accordingly, it should be understood that the photonics package100includes not only the PIC110, but can (in some embodiments) include separate elements that are mounted to the common substrate, free space optical elements, and the like.

As one example and as shown inFIG.1, the photonics package100may include a light source120, initial optics130, a liquid crystal lens140, and secondary optics150in addition to the photonics integrated circuit110. Similarly, the photonics integrated circuit110may incorporate a waveguide160(or any other optical output structure), an outcoupler170, and any other suitable element that adjusts or directs light. Such suitable elements may include, by way of example and not limitation, multiplexers, demultiplexers, Echelle gratings, couplers, collimators, and the like.

The light source120emits a light output that is ultimately received by the PIC110. The light is typically divergent light, although this is not necessary in all embodiments. The light source120may be a laser diode, a III-V laser, or the like. In some embodiments, the light source120may be part of the PIC110while in other cases (and as shown inFIG.1) it may be located off-chip.

The light output emitted from the light source120may pass through initial optics130. Initial optics130may be any optical element(s) that shape or adjust the emitted light output. Examples of initial optics130include a lens (including ball lenses, spherical lenses, aspheric lenses, cylindrical lenses, and so on), prisms (including micro-prisms), mirrors, and other reflective, refractive, or light-steering elements. Initial optics130may be omitted in certain embodiments.

In some embodiments, the initial optics130may take the form of, or may incorporate, an optical isolator. The isolator may reduce feedback to the light source, thereby increasing stability of the light source's light output.

The initial optics130may steer the light output from the light source120. For example, the initial optics130may include a lens that focuses or collimates light, such as a ball lens. The light may be steered by the initial optics prior to the light being focused (or otherwise steered) by the liquid crystal lens140. The light received by the initial optics130may be collimated light from a laser, divergent light from a laser diode, convergent light from another optical element, and so on.

The liquid crystal lens140may be located between the initial optics130and secondary optics150, as shown inFIG.1. In some embodiments, one or both of the initial optics130and secondary optics150may be omitted, so that the liquid crystal lens140receives the light output directly from the light source110and/or passes the light output directly to the waveguide160(or other element of the PIC110). The liquid crystal lens140may be electrically tunable, such that applying a voltage to the liquid crystal lens140changes a focal length, propagation path, propagation angle, spot size, or other parameter of the light output. The liquid crystal lens140may steer the light output not only by changing the focal point of the light, but also by adjusting an output angle of the light output as it passes through the liquid crystal lens140(e.g., adjusting the propagation angle and/or propagation path). Put another way, the liquid crystal lens140may “bend” the light to account or compensate for out-of-tolerance placement or positioning of the waveguide160relative to the light source120(e.g., mismatch between the light source and waveguide or other optical output structure). Changing a focal point, output angle, output path, spot size, or other parameter of the light output are all examples of steering the light output by the liquid crystal lens140.

In some embodiments, the liquid crystal lens140may be variably tunable and/or dynamically tunable. A “variably tunable” liquid crystal lens140may adjust steering of the light output across a range of values or options, rather than in merely a binary on/off manner. For example, as voltage increases, the light's focal length may continue to change or its output angle may continue to change. For variably tunable liquid crystal lenses140, the amount of steering done by the lens may vary with a voltage applied to the lens. By contrast, a “dynamically tunable” liquid crystal lens140may have voltage applied at different times during operation of the photonics package100. The dynamically tunable liquid crystal lens140may vary voltage during operation to account for changes in an operating parameter of the photonics package such as thermal expansion or drift, for example. While some examples of a liquid crystal lens140may be both variably tunable and dynamically tunable, other examples may be only one of variably tunable or dynamically tunable.

AlthoughFIG.1illustrates a photonics package having a single liquid crystal lens140, certain embodiments may employ multiple liquid crystal lenses140. Similarly, multiple liquid crystal lenses140may be packaged together and, optionally, share a common substrate or layer, as discussed below with respect toFIGS.2and3. Further, some embodiments may employ a liquid crystal lens140between the light source120and initial optics130or between the secondary optics150and waveguide160.

The light output may be steered by the liquid crystal lens140to the secondary optics150, generally to account or compensate for some mismatch in the photonics package between the light source120and the waveguide160. As with the initial optics130, the secondary optics150may be any element, or combination of elements, that steers the light output received from the liquid crystal lens. The secondary optics may be one or more of a ball lens, cylindrical lens, aspheric lens, spherical lens, mirror or other reflector, micro-prism or other refractor, collimator, or the like. The secondary optics150generally steer the light output from the liquid crystal lens140to the waveguide160of the PIC110(or other input element of the PIC, or other optical output structure). In some embodiments, the secondary optics150may be omitted. In many embodiments, the initial optics130and the secondary optics150may be the same optical elements, although in other embodiments they may be different. In certain embodiments, the liquid crystal lens140may steer the light output to one of a number of different elements, such as different optics or different waveguide inputs, rather than to a single element or input. Thus, in these embodiments the liquid crystal lens may be used to select or alter a light path in addition to, or instead of, fixedly steering light to a single component.

Additionally, some embodiments may place an index-matching material, such as an epoxy, between the tunable liquid crystal lens140and either or both of the initial optics130and secondary optics150. This index-matching material may reduce reflection loss without significantly impacting performance of the photonics package100. In some embodiments, the index-matching material has a refractive index of about 1.5 to 1.6, and in certain embodiments the refractive index is 1.55.

The PIC110generally includes a waveguide or other input element that receives the steered light output from the secondary optics150. The light output propagates from the waveguide through the PIC, and ultimately to an outcoupler170that emits the light output from the PIC110. It should be appreciated that the waveguide160may not be coupled directly to the outcoupler170in many embodiments. Rather, intermediary photonics circuitry may separate the two, such that the light output travels through this intermediary photonics circuitry. Examples of such circuitry include multiplexers, demultiplexers, collimators, gratings, couplers, decouplers, additional waveguides, modulators, filters, other optical output structures, and so on. Such circuitry is omitted fromFIG.1for the sake of simplicity. In some embodiments, the waveguide160may be replaced by a prism, mirror, or other reflector. Likewise, in some embodiments, the outcoupler170may take the form of a grating coupler, cavity dumper, and so on.

Generally, then, the function of the liquid crystal lens140is to steer a light output from the light source120to the waveguide160, regardless of whether the light source120is a laser diode, LED, laser, or other light source. In ideal photonics packages100the liquid crystal lens140may not actively steer the light output in any way. Practically speaking, however, ideal photonics packages100are difficult or even impossible to achieve. Pick and place operations are often used to align the light source120, initial optics130, secondary optics150, and/or PIC110on a common substrate or otherwise with respect to one another. Fiducials used for pick and place operations may be slightly misaligned in some instances; in others, pick and place machinery may have an inherent placement tolerance. During operation, components such as the light source120may undergo thermal expansion. The light source may experience thermal drift, as well. Any two instances of the same component (such as the light source120, optics130,150, and so on) may have slightly different dimensions resulting from manufacturing limitations. Components and/or the substrate on which the components rest may experience volumetric change as the photonics package is cured during assembly.

Any and all of the foregoing may result in misalignment of the light source120with respect to the waveguide160(or other optical output structure), which reduces coupling efficiency between the two and ultimately results in output loss from the PIC110. The tunable liquid crystal lens140may steer the light to account for such misalignment, thereby increasing coupling efficiency and delivering a greater percentage of the light output from the light source120to the waveguide160. Not only may this result in greater efficiency, it may increase part yield during manufacture of photonics packages. Embodiments employing a tunable liquid crystal lens140may mitigate as much as 2-8 dB of optical power that might otherwise be lost.

It should be appreciated that multiple liquid crystal lenses may be used in a single embodiment, although embodiments described herein illustrate the use of a single liquid crystal lens. Further, in embodiments employing multiple tunable liquid crystal lenses, such lenses may be optically coupled to one another, optically separated from one another by intervening optics, or both (e.g., some liquid crystal lenses may be optically coupled to one another while others are optically coupled to other structures, such as optics).

FIG.2is a cross-sectional view of a sample tunable liquid crystal lens140with no voltage applied to the lens, whileFIG.3shows the tunable liquid crystal lens140with an applied voltage. The liquid crystal lens140structure shown inFIGS.2and3is but one example structure, and other liquid crystal lenses may be used in various embodiments.

Generally, the liquid crystal lens140has first and second liquid crystal layers220a,220bseparated by a common substrate210. First and second exterior substrates200a,200bbound the outer sides of the liquid crystal lens. Generally, the common substrate210and exterior substrates200a,200bare optically transparent such that the light output from the light source120(as shown inFIG.1) may pass through an entirety of the liquid crystal lens140under certain circumstances.

The common substrate210, first exterior substrate200a, and second exterior substrate200bmay be formed from glass, polymer, crystal, or the like. The substrates210,200a,200bare generally transparent to the wavelengths of the light output, although they may reflect or refract other wavelengths of light. In some embodiments, one or more of the substrates210,200a,200bmay include a polarizer, insulator, or the like, although this is not necessary. Typically, an electrode is formed on each of the exterior substrates200a,200b; generally, the electrode is formed or deposited on an interior surface of each exterior substrate (e.g., the surfaces contacting the liquid crystal layers220a,220b). The electrodes are generally formed from indium-tin-oxide, silver nanowires (or other metal nanomaterials), carbon nanotubes, conductive polymers, or other materials that are substantially transparent with respect to the wavelengths of the light output. In this manner, the electrodes do not block the light output as it passes through the liquid crystal lens140.

A voltage source230is connected to the second exterior substrate200band, through a switch240, to the first exterior substrate200a. (In some embodiments, the switch may be positioned between the voltage source230and the second exterior substrate200binstead). In particular, the voltage source230is connected to the electrodes of the exterior substrates200a,200b. When the switch240is open, no voltage is applied to the substrate electrodes; closing the switch240applies a voltage across the electrodes.

As shown inFIG.2, when no voltage is applied to the liquid crystal lens140, the liquid crystals in the layers220a,220bare unaligned. Accordingly, the liquid crystal lens140is in a base state, in which the lens may steer the light output by a base amount. This base steering by the liquid crystal lens140may adjust a parameter of the light output by a fixed amount or percentage, or may have no effect at all on any parameter, depending on the embodiment. Thus, in some embodiments, when no voltage is applied to the liquid crystal lens140the light output behaves exactly as it would if the liquid crystal lens140were absent; in other embodiments, this may not be the case.

When the switch240is closed as shown inFIG.3, the voltage source230applies a voltage across the electrodes of the first and second exterior substrates200a,200band the liquid crystal lens140enters a light steering state. The voltage causes the liquid crystals in the liquid crystal layers220a,220bto align, as shown in the figure. When the liquid crystal layers220a,220bare in this light steering state, the light output from the light source120is steered by the liquid crystal lens140. Generally, the configuration shown inFIG.3, where the liquid crystals are fully or near-fully aligned, may correspond to the tunable liquid crystal lens140maximally steering the light output. Further, althoughFIG.3shows the crystals as fully aligned along axes running from a top to a bottom of the liquid crystal lens140, it should be understood that this is shown for illustrative purposes only. The liquid crystals may be “fully aligned” when their major axes are parallel to one another, or in any other position where the crystals are generally axially aligned with one another.

Some embodiments may be binary, where the liquid crystal layers220a,220bswitch back and forth between the configurations shown inFIGS.2and3(e.g., the base state and light steering state) and have no other stable states. Other embodiments may vary alignment of the liquid crystals in the liquid crystal layers220a,220bwith the amount of voltage applied by the voltage source230to the electrodes of the exterior substrates200a,200b. Thus, at zero voltage, the liquid crystal lens140may be in the state shown inFIG.2, corresponding to a minimal or zero steering state. When a voltage equal to or above a threshold is applied by the voltage source230, the liquid crystal lens140may be in the state shown inFIG.3, corresponding to a maximal light steering state. Voltages between zero and the threshold voltage, as applied to the liquid crystal lens140, may cause the lens to steer the light input progressively more (e.g., enter or occupy a series of increasing light steering states). That is, as the voltage increases, the amount of steering performed by the liquid crystal lens140likewise increases. Liquid crystal lenses140where light steering corresponds to applied voltage, such that there are multiple increasing light steering states, are examples of variably tunable liquid crystal lenses.

Variably tunable liquid crystal lenses140may operate according to a step function, where voltage is applied in discrete steps and so the light source is steered in discrete steps. Other variably tunable liquid crystal lenses may operate in a non-stepped, smoother manner where applied voltage may be more finely controlled and so light steering may be correspondingly finely controlled. In some embodiments, maximal steering may correspond to a complete blockage of light by the liquid crystal lens140, while in others maximal steering results in maximum adjustment of a parameter (such as spot size, propagation angle, focal length, and the like) by the liquid crystal lens.

Some liquid crystal lenses140are dynamically tunable. That is, the voltage source230may apply voltage to the exterior substrates200a,200bwhen operating parameters of the photonics package require the light output to be steered. A feedforward or feedback loop may be used to determine when to apply such voltage, as examples. Parameters such as coupling efficiency, optical power output, temperature, size, and the like of the photonics package (or individual components thereof) may be measured by a sensor. The sensor's output may be used in the aforementioned feedback or feedforward loop to determine when to apply the voltage to the liquid crystal lens140in order to steer the light output, and for how long. Such sensors and loop control schemes may likewise be employed with variably tunable lenses. Many embodiments employ liquid crystal lenses140that are both variably and dynamically tunable.

The foregoing discussion ofFIGS.2and3presume that the liquid crystals of the liquid crystal lens140are aligned when a voltage is applied by the voltage source230and unaligned when there is no applied voltage. It should be appreciated that some embodiments apply a constant minimum voltage to the liquid crystal lens140, and so references to a zero voltage may, in some embodiments, encompass a minimum positive voltage. Likewise, although the liquid crystal lens is discussed as having its electrodes on the exterior substrates200a,200b, it should be appreciated that this is but one example position of the electrodes. One or more of the electrodes may be on a side of the common substrate210, for example, particularly if at least one of the exterior substrates is grounded.

FIG.4illustrates one sample operation of the liquid crystal lens140. Here, the light output from the light source120is spread by the initial optics130and impacts the liquid crystal lens140. The liquid crystal lens140, in turn, focuses the light output (e.g., adjusts its focal length) on or in the secondary optics150. The secondary optics, in turn, may further focus or collimate the light such that it propagates to the waveguide160or other optical output structure. Thus, the liquid crystal lens140acts as a positive lens.

FIG.5illustrates an embodiment similar toFIG.4, except that the liquid crystal lens140spreads the light output from the light source120rather than focuses it. Here, the liquid crystal lens140acts as a negative lens. Whether the liquid crystal lens140acts as a positive or negative lens may depend on a degree and/or nature of the mismatch between the light source120and the waveguide160of the photonics package100. It should be appreciated that, in many embodiments, a liquid crystal lens140may operate in either fashion. Other embodiments may employ multiple liquid crystal lenses140, with some functioning as positive lenses and some as negative lenses.

FIG.6is a flowchart illustrating a sample method600for using a liquid crystal lens to adjust an optical output of a photonics package. Initially, the various components of the photonic package are placed in operation610. This may be through a pick and place operation, growing or depositing certain components on a substrate, or the like.

In operation620, the photonics package is activated and an operating parameter of the photonics package is measured. This measurement may be performed by a sensor that is part of the photonics package or by one that is separate therefrom. A separate sensor may be used during bench testing, reliability testing, or manufacture, for example. An integrated sensor may be used in these scenarios as well and/or may be used during normal operation of the photonics package. “Operating parameters” may include a temperature, size, volume, angular alignment, efficiency, output and so on of the photonics package as a whole or any individual component of the photonics package.

In operation630, it is determined whether the operating parameter is acceptable. In some cases this equates to determining if the operating parameter is above a threshold (as where the operating parameter is coupling efficiency, output power, or the like), below a threshold (as where the operating parameter is temperature, drift, angular alignment, volume, and so on), or equal to a number (as where the operating parameter is a binary value).

The method600may be performed when the photonics package is initially assembled to ensure it operates within acceptable parameters. Additionally, operations620-650may be performed at various times (or substantially continuously) while the photonics package operates or is in service. Some embodiments may execute operations620-650in response to a specific event, such as a drop, shock, or impact, or after a specified time period (e.g., to account for aging). Some embodiments may perform these operations every time the photonics package is activated or deactivated.