Reverse-engineered optical modulator

Abstract

The optical modulator includes a modulation region, an input port, an output port, and a modulation actuator. The modulation region includes a heterogeneous arrangement of two or more different materials having different refractive indices to structure the modulation region to manipulate one or more optical properties of an optical carrier wave in response to a modulation bias. The input port is optically coupled to the modulation region to inject the optical carrier wave into the modulation region. The modulation actuator is positioned proximate to the modulation region and adapted to apply a modulation bias to the modulation region to generate a modulated wave. The modulation bias adjusts at least one of the different refractive indices of the heterogeneous arrangement to provide variable control of one or more optical properties of the optical carrier wave. The output port is optically coupled to the modulation region to receive the modulated wave.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Patent Application No. 17 / 970,141, filed October 20, 2022, the contents of which are incorporated herein by reference.

[0002] The present disclosure relates generally to photonic devices, and more particularly to optical modulators. [Background technology]

[0003] Optical modulators are active devices that allow users to modulate optical signals through an applied bias. This bias is typically achieved by varying a voltage that electro-optically, thermo-optically, or mechano-optically adjusts the refractive index of a material in a region of the integrated device. When the bias is modulated at high speeds (e.g., gigahertz speeds), information and data can be encoded and transmitted to a remote receiver.

[0004] Typical modulators are designed by humans using well-understood components (e.g., a combination of a waveguide-based phase shifter and a directional coupler or modulated ring resonator). However, these traditional components have limitations, such as a large footprint and a limited number of "knobs" that can be used to improve and fine-tune performance. [Brief explanation of the drawings]

[0005] Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, in which like reference numerals refer to like parts throughout the various views unless otherwise specified. Not every instance of an element is necessarily labeled, so as to avoid cluttering the figures where appropriate. The figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles described. [Figure 1A] 1 illustrates a reverse-designed optical modulator according to one embodiment of the present disclosure. [Figure 1B]1B illustrates a top view of a portion of the inverse-designed optical modulator of FIG. 1A according to one embodiment of the present disclosure. [Figure 1C] 1B illustrates a cross-sectional view of a portion of the inverse-designed optical modulator of FIG. 1A according to one embodiment of the present disclosure. [Figure 1D] 1B illustrates a cross-sectional view of a portion of the inverse-designed optical modulator of FIG. 1A according to one embodiment of the present disclosure. [Figure 1E] 1B illustrates a cross-sectional view of a portion of the inverse-designed optical modulator of FIG. 1A according to one embodiment of the present disclosure. [Figure 1F] 1B shows a more detailed view of an exemplary modulation region of the reverse-designed optical modulator of FIG. 1A, according to one embodiment of the present disclosure. [Figure 2A] 1 illustrates a loss function for an inverse design of an optical modulator, according to one embodiment of the present disclosure. [Figure 2B] 1 illustrates an exemplary optical modulator response curve of a reverse-designed optical modulator, according to one embodiment of the present disclosure. [Figure 3] FIG. 1 illustrates an iterative process in which modulation domains are optimized to reduce a loss metric, according to one embodiment of the present disclosure. [Figure 4] 1 shows a flowchart detailing an exemplary operation of a reverse-designed optical modulator, according to one embodiment of the present disclosure. [Figure 5] 1 shows a flowchart detailing an iterative process for designing a reverse-engineered optical modulator, according to one embodiment of the present disclosure. [Figure 6A] FIG. 1 illustrates a demonstrative simulated environment for simulating the operation of a physical device, according to one embodiment of the present disclosure. [Figure 6B] FIG. 1 illustrates a physical device operation simulation according to one embodiment of the present disclosure. [Figure 6C] FIG. 1 illustrates an adjoint simulation (backpropagation) of performance loss error through a simulated environment, according to one embodiment of the present disclosure. [Figure 7A] 1 is a flowchart illustrating exemplary time steps of operational and adjoint simulations used to reverse-design an optical modulator, according to one embodiment of the present disclosure. [Figure 7B] 1 is a flowchart illustrating the relationship between behavioral simulation and adjoint simulation (backpropagation) according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0006] Embodiments of systems, devices, methods of operation, and design methods for reverse-designed optical modulators are described herein. In the following description, numerous specific details are set forth to provide a thorough understanding of the embodiments. However, those skilled in the art will recognize that the techniques described herein can be practiced without one or more of the specific details, or with other methods, components, materials, etc. In other cases, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring certain aspects.

[0007] References throughout this specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrase "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0008] Described herein are embodiments of inverse-designed optical modulators, which are photonic devices capable of manipulating one or more optical properties (e.g., frequency, phase, polarization, power, or a combination thereof) of an optical carrier wave (e.g., a waveform that can be modulated to convey information) by applying a modulation bias (e.g., voltage, pressure, or temperature) to the optical modulator. It is understood that the optical modulator embodiments described herein can be designed to overcome one or more bottlenecks of conventional optical modulators. For example, one significant performance bottleneck of conventional optical modulators is due to a nonlinear relationship between the manipulated optical property and the applied modulation bias. For example, a nonlinear relationship may exist when adjusting a bias (e.g., voltage) to modulate the power (e.g., intensity or amplitude) of an optical carrier wave in a conventional optical modulator. Such a nonlinear relationship may result from the material properties and / or components of the conventional optical modulator (e.g., a ring resonator, optical power splitter, or other optical components included in a photonic integrated circuit). Nonlinearities can cause distortion in the transmitted signal and may limit the overall performance (e.g., data rate) of conventional optical modulators. Furthermore, it is understood that conventional optical modulators have limited parameters that can adjust their performance. For example, conventional optical modulators can accommodate optical waveguides formed from lithium niobate, which limits the parameters that can be adjusted or designed for the waveguide. As a result, in order to design high-performance, compact devices that can compensate for the bottlenecks of conventional optical modulators, a method for designing optical modulators with more adjustable parameters is needed.

[0009] Embodiments described herein utilize inverse design methods to create optical modulators (e.g., for photonic integrated circuits) that can compensate for or otherwise design around bottlenecks (e.g., response nonlinearity, size, or other) of conventional optical modulators. Specifically, a photonic device is designed having a "modulation region" that has a non-uniform arrangement of two or more different materials with different refractive indices to structure the modulation region to manipulate one or more optical properties of an optical carrier in response to a modulation bias. The modulation region is coupled to two or more ports (e.g., input and output ports) and modulation actuators (e.g., to apply and / or adjust an applied voltage, current, temperature, and / or pressure to the modulation region) to form an optical modulator. To generate a modulation region design, an iterative inverse design approach is utilized, with multiple bias points applied to the optical modulator (e.g., different magnitudes of bias applied by a modulation actuator and / or different changes in one or more of the refractive indexes of a non-uniform arrangement of the modulation region caused by the bias) simulated or otherwise considered in parallel to determine a modulation region design that forms an optical modulator that meets target performance parameters. More specifically, an optimization objective (e.g., a loss function in which output power is minimized) is constructed that considers the multiple bias points. In some embodiments, the optimization objective may implement a target response curve (e.g., monotonic, linear, or nonlinear) for the optical modulator, which may compensate for bottlenecks present in conventionally designed optical modulators.

[0010] FIG. 1 shows an inverse-designed optical modulator 100 according to one embodiment of the present disclosure. The illustrated embodiment of the optical modulator 100 includes a modulation region 105, an input port 110, an output port 115, optional ports 120, a modulation actuator 125, a modulation controller 140, and other circuitry 145. The illustrated embodiment of the modulation region 105 includes a non-uniform arrangement of two or more different materials (e.g., a first material 107 and a second material 108) having different refractive indices to structure the modulation region 105 to manipulate one or more optical properties (e.g., frequency, phase, polarization, power, or a combination thereof) of an optical carrier wave 150 in response to a modulation bias (e.g., an adjustable voltage, current, pressure, or temperature) applied to the modulation region 105. The input port 110 is optically coupled to the modulation region 105 to inject the optical carrier wave 150 into the modulation region 105. The modulation actuator 125 is disposed proximate to the modulation region 105 and is adapted to apply a modulation bias to the modulation region 105 to generate a modulated wave 155 (e.g., to carry information, correct distortion, etc.). The output port 115 is optically coupled to the modulation region 105 to receive the modulated wave 155. In some embodiments, the inverse-designed optical modulator 100 includes an optional port 120. While only one of the optional ports 120 is shown, it will be understood that in some embodiments, there may be two or more optional ports 120. However, in other embodiments, the inverse-designed optical modulator 100 may not include the optional port 120 (e.g., except for the input port 110 and the output port 115, no other ports are directly coupled to the modulation region 105).

[0011] The modulation region 105, sometimes referred to as the “design region” or “active region” of the optical modulator 100, is a region in which a modulation bias (e.g., an applied voltage, current, temperature, pressure) can variably adjust at least one of the different refractive indices contained in a heterogeneous arrangement of two or more different materials. For example, the two or more different materials can include a first material 107 and a second material 108, each having a respective refractive index that can change in response to a modulation bias applied to the modulation region 105. The degree to which the at least one of the different refractive indices changes is based at least in part on the magnitude of the modulation bias and the material properties of at least one of the two or more different materials (e.g., the electro-optic coefficient of the first material 107 or the second material 108). In the illustrated embodiment, the modulation region 105 is structured as an optical cavity (e.g., a resonant cavity), and the heterogeneous arrangement of the first material 107 and the second material 108 results in a material interface pattern that, in response to a modulation bias, provides the intended function for the optical modulator 100. It is understood that the response to the modulated bias may also include when the magnitude of the modulated bias is zero or a reference value (e.g., when the modulated bias corresponds to an applied voltage, a zero magnitude of the modulated bias may correspond to 0V or ground; when the modulated bias corresponds to an applied pressure or temperature, a zero or reference magnitude of the modulated bias may correspond to ambient pressure or temperature, etc.).

[0012] In some embodiments, the pattern of discrete regions of first material 107 and second material 108, under the influence of modulation actuator 125, operates to selectively steer (e.g., via refraction, scattering, reflection, dispersion, or otherwise) an inbound optical carrier wave 150 received via input port 110 to either output port 115 or optional port 120 (e.g., to implement an ON-OFF keying modulation scheme in which optical power is directed primarily to output port 115 during an ON or HIGH logic state of modulated wave 155, or primarily to optional port 120 during an OFF or LOW logic state). In other words, the modulated 155 wave includes multiple states, each based on the magnitude of a modulation bias, the multiple states including a HIGH state and a LOW state. In some embodiments, the non-uniform arrangement of first material 107 and second material 108 is structured to steer, scatter, or reflect a portion (e.g., in terms of optical power) of optical carrier wave 150 away from output port 115 when modulated wave 155 is modulated to a low state or an intermediate state between a high state and a low state. In some embodiments, the portion of optical carrier wave 150 steered away from output part 115 is directed to optional port 120. In other embodiments, an ON-OFF keying modulation scheme may be implemented by modulating other aspects of one or more optical properties of optical carrier wave 150 (e.g., other than power or amplitude, such as frequency, phase, polarization, or a combination thereof). In the same or other embodiments, optical modulator 100 may be used to correct distortions or otherwise provide active and / or variable manipulation of one or more optical properties of optical carrier wave 150 to generate modulated wave 155. For example, distortions in optical carrier 150 may be corrected or compensated for by adjusting the frequency, phase, polarization, or power of optical carrier 150. In such embodiments, since the distortions are not necessarily fixed, it becomes particularly important that the response curve of the optical modulator is known to provide variable control over one or more optical properties of optical carrier 150.By adjusting the response curve in a particular manner (e.g., linear, non-linear, monotonic, or other), it becomes possible to adjust one or more optical properties of the optical carrier 150 in a targeted and reliable manner. It will be appreciated that ON-OFF keying modulation, distortion correction, or other schemes may be implemented by adapting the modulation actuator 125 to impart a data signal 160 onto the optical carrier 150 to generate a modulated wave 155 via a modulation bias.

[0013] In some embodiments, other circuitry 145 may include an optical receiver (e.g., an optoelectric or photovoltaic device such as a photodiode, photocell, or other) and / or power regulator circuitry (e.g., a rectifier such as a diode, a storage capacitor, and / or other conventional regulation circuitry) to receive a portion of optical carrier wave 150 (e.g., when modulated wave 155 is modulated to a state other than a HIGH or ON logic state), which may be utilized to recover rejected optical power and convert the recovered optical power into electrical power (e.g., to power modulation controller 140).

[0014] Referring back to modulation region 105, first material 107 and second material 108 are discrete regions of material having different refractive indices that change in response to a bias (e.g., an applied voltage, a current, a temperature, a pressure). In one embodiment, first material 107 and second material 108 may be a waveguide core material and a waveguide cladding material, respectively. The core and cladding materials may be the same as the core and cladding materials used to form the waveguide sections of input port 110, output port 115, and / or optional port 120. For example, first material 107 may be a semiconductor material (e.g., silicon, a III-V semiconductor material, a II-VI semiconductor material, lithium niobate, or other semiconductor material), while second material 108 may be an oxide material (e.g., silicon dioxide). In yet other embodiments, the first material 107 and the second material 108 may be implemented as discrete regions of intrinsic and doped silicon, discrete regions of differently doped silicon, or combinations of other types of semiconductor materials (e.g., III-V semiconductor materials, II-VI semiconductor materials, lithium niobate, combinations thereof, etc.). In one embodiment, the modulation region 105 is approximately 1.5 um x 1.2 um, while the ports 110, 115, and 120 are waveguide sections 200 nm wide and 600 nm long. The discrete regions of the first material 107 and the second material 108 may be implemented as agglomerations of each material type in incremental pixel or voxel sizes of 5 nm x 5 nm. In other words, a non-uniform arrangement of the first material 107 and the second material 108 may be reproducible by a schematic defined by multiple pixels or voxels having an area of ​​5 nm x 5 nm. Of course, other pixel or voxel resolutions may be implemented (e.g., areas greater than 5 nm x 5 nm or less than 5 nm x 5 nm, pixels or voxels of different sizes, uniform pixel or voxel size, non-uniform pixel or voxel size, or other configurations).

[0015] Modulation is achieved by a modulation bias applied to modulation region 105 via modulation actuator 125, which is driven by modulation controller 140 (e.g., a microcontroller, an application specific integrated circuit, a field programmable gate array, or other configurable controller coupled to or including memory) in response to data signal 160. Thus, modulation controller 140 may include modulation / demodulation circuitry along with driver circuitry that drives modulation actuator 125. Modulation actuator 125 may be implemented using several techniques for applying an adjustable electric field, temperature, or pressure to modulation region 105. In one embodiment, modulation actuator 125 includes electrodes surrounding the sides of modulation region 105, and the modulation bias is an applied voltage and / or an injected current. In another embodiment, modulation actuator 125 includes one or more heating elements surrounding modulation region 105, and the modulation bias is an adjustable temperature. In yet another embodiment, the modulation actuator 125 includes an electromechanical actuator (e.g., a piezoelectric crystal, a microelectromechanical system, etc.) surrounding the modulation region 105, and the modulation bias is an adjustable pressure. Each of these modulation biases functions to adjust at least one of the different refractive indices of the inhomogeneous arrangement (e.g., the first material 107 and / or the second material 108) to provide variable control of one or more optical properties of the optical carrier wave 150. Specifically, the change in the refractive index of the inhomogeneous arrangement changes how the optical carrier wave in at least one of the first material 107 or the second material 108 subsequently affects scattering, refraction, reflection, and / or dispersion of the optical carrier wave 150 within the modulation region 101 to form the modulated wave 155. It will be further understood that the modulation actuator 125 can surround the modulation region 105 in various ways. For example, if FIG. 1A is a top view of the modulation region 105, the electrodes of the modulation actuator 125 may lie along a common plane with the modulation region 105. In the same or other embodiments, the modulation region 105 may be sandwiched between two or more electrodes (see, eg, Figures 1C-1E).

[0016] FIG. 1B shows a top view of a portion of the inverse-designed optical modulator of FIG. 1A according to one embodiment of the present disclosure. In the illustrated embodiment, input port 110, output port 115, and optional port 120 are adjacent to modulation region 105 and operate as optical inputs or outputs for propagating waves, respectively. Although input port 110, output port 115, and optional port 120 are referred to as "ports," these ports may include longitudinal lengths in the direction of optical propagation. Thus, input port 110, output port 115, and optional port 120 may be implemented as waveguide sections having a core and cladding with one end physically abutting or otherwise optically coupled to modulation region 105. In various embodiments, input port 110, output port 115, optional port 120, and modulation region 105 are all planar waveguide sections. These planar waveguide sections may be embedded in semiconductor materials such as silicon-on-insulator (SOI) systems, photonic integrated circuits (PICs), or others. In some embodiments, the core and cladding materials may correspond to the silicon and silicon dioxide of input port 110, output port 115, and optional port 120. In the same or other embodiments, the core and cladding materials may correspond to first material 107 and second material 108 of modulation region 105. In still other embodiments, the core and cladding materials of input port 110, output port 115, and optional port 120 may be different from first material 107 and / or second material 108.

[0017] It should be understood that the design of optical modulator 100 is not limiting. Rather, in some embodiments, the number (or presence) of optional ports 120 may be configured based on the intended function of optical modulator 100. Specifically, the configuration of optical modulator 100 may vary depending on which of one or more optical properties of optical carrier 150 is modulated by modulation region 105 in response to a modulation bias. For example, if optical modulator 100 is a polarization or phase modulator of optical carrier 150, it may not be necessary to divert a portion of optical carrier 150 from output port 115, and therefore it may not be necessary to include optional ports 120. However, in other scenarios, it may be advantageous to configure optical modulator 100 to include one or more of optional ports 120. For example, if the optical modulator is a power or amplitude modulator of the optical carrier wave 150, the optional port 120 may correspond to or otherwise include a sink port for receiving a portion of the optical power of the optical carrier wave 150 (e.g., when the modulated wave 155 is in a state other than a HIGH or ON state, such as an OFF or LOW state, or an intermediate state between HIGH and LOW). Of course, it will be understood that even if the optical modulator 100 is adapted to modulate the power or amplitude of the optical carrier wave 150, the optical modulator 100 may still not include the optional port 120 in certain embodiments (e.g., the modulation region 105 may direct a portion of the optical carrier wave 150 away from the output port 115 so that it is reflected back to the input port 110, scattered outside the modulation region 105, or otherwise not included in the modulated wave 155 when the modulated wave 155 is in a state other than a HIGH or ON state).

[0018] In the illustrated embodiment, modulation region 105 is a substantially planar structure, with input port 110, output port 115, and optional port 120 each being coplanar with modulation region 115 but abutting different sides thereof. In other embodiments, input port 110, output port 115, and optional port 120 may each abut a common side of modulation region 105. In yet other embodiments, only two selected from the group including input port 110, output port 115, and optional port 120 may abut the common side of modulation region 105, while the unselected ports in the group may abut the side of modulation region 105 adjacent to or opposite the common side. As previously mentioned, it will be understood that optional port 120 is not limited to an individual port, and in some embodiments, optional port 120 may include multiple ports that may be variously positioned around modulation region 120. Further, in the illustrated embodiment, modulation region 120 is laterally surrounded by peripheral region 109, which may have a homogeneous composition (e.g., corresponding to two of the different materials forming modulation region 105, such as first material 107, second material 108, or any other material) that forms a material interface boundary 151 that extends continuously and contiguous laterally around modulation region 105, except where input port 110, output port 115, and optional port 120 interface or otherwise abut modulation region 105. In some embodiments, the homogeneous composition of peripheral region 109 corresponds to silicon dioxide. It is understood that material interface boundary 151 corresponds to a location where the refractive index changes due to different materials interfacing, and may collectively form a boundary of the optical cavity (e.g., to help mitigate against optical carrier 150 exiting modulation region 105 through regions other than ports 110, 115, and / or 120). It is understood that the material interface boundaries (e.g., material interface boundary 151 and / or the material interface boundaries formed by the discrete regions formed by first material 107 and second material 108) at least partially define the functionality of optical modulator 100.

[0019] 1C-1E illustrate cross-sectional views of a portion of the inverse-designed optical modulator of FIG. 1A according to one embodiment of the present disclosure. More specifically, FIGS. 1C-1E illustrate vertical schematic views or stacks of various layers that may be included in the optical modulator 100 shown in FIG. 1A. However, it is understood that the illustrated embodiments are not exhaustive, and certain features or elements may be omitted to avoid obscuring certain aspects of the present invention. As shown in FIG. 1C, the optical modulator 100 includes a substrate 102, a cladding layer 104, an active layer 106, a cladding layer 108, and a modulation actuator 125. In some embodiments, the optical modulator 100 may be a photonic integrated circuit or a silicon photonic device that is partially or otherwise compatible with conventional fabrication techniques (e.g., lithography techniques such as photolithography, electron beam lithography, sputtering, thermal evaporation, physical and chemical vapor deposition, etc.).

[0020] In one embodiment, a silicon-on-insulator (SOI) wafer may first be provided, including a support substrate (e.g., a silicon substrate) corresponding to substrate 102, a silicon dioxide dielectric layer corresponding to cladding layer 104, a silicon layer (e.g., intrinsic, doped, or other), and an oxide layer (e.g., intrinsic, grown, or other). In one embodiment, the silicon in active layer 106 may be selectively etched by lithography to create a pattern on the SOI wafer that is transferred to the SOI wafer via a dry etching process (e.g., via a photoresist mask or other hard mask) to remove portions of the silicon. The silicon may be etched all the way down to cladding layer 104 to form voids, which may then be backfilled with silicon dioxide, which is then encapsulated with silicon dioxide to form cladding layer 108. In one embodiment, there may be several etch depths, including a full etch depth of silicon, to obtain the target structure. In one embodiment, the silicon may be 220 nm thick, and therefore the full etch depth may be 220 nm. In some embodiments, this may be a two-step encapsulation process in which two silicon dioxide depositions are performed with an intermediate chemical mechanical planarization used to provide a flat surface.

[0021] FIG. 1D illustrates a more detailed view of a portion of the active layer 106 (relative to FIG. 1C ) along with a portion of the peripheral region 109 that includes the input port 110, the output port 115, or the optional port 120. More specifically, the portion of the active layer 106 shown in FIG. 1D may correspond to a waveguide section of one of the input port 110, the output port 115, or the optional port 120. In the illustrated embodiment, the active layer 106 includes a first material 107 having a refractive index of n1 and a second material 108 having a refractive index of n2, different from n1. The homogeneous and contiguous regions of the first material 107 and the second material 108 may form a waveguide or a portion of a waveguide that corresponds to the input port 110, the output port 115, or the optional port 120 illustrated in FIGS. 1A-1B . In some embodiments, the cladding layers 104 and 108 may have a homogeneous composition corresponding to the second material 108 (e.g., silicon dioxide). Note that the illustrated embodiment of Figure 1D does not show the modulation actuator 125, as the illustrated cross section extends through one of the input port 110, the output port 115, or the optional port 120, and it may not be necessary to apply a modulation bias to the input port 110, the output port 115, or the optional port 120.

[0022] 1E illustrates a more detailed view of the active layer 106 (relative to FIG. 1C ) along with the modulation region 105 illustrated in FIGS. 1A and 1B . As previously described, the modulation region 105 includes a first material 107 (e.g., silicon) and a second material 108 (e.g., silicon dioxide), which are discrete regions of homogeneous composition unevenly interspersed to form a plurality of interfaces 111 that collectively form a material interface pattern. Each of the plurality of interfaces 111 forming the interface pattern corresponds to a change in refractive index that collectively structures the modulation region 105 (i.e., based on the shape and arrangement of the first material 107 and the second material 108) in combination with a modulation bias to at least partially provide the function of the optical modulator 100 (i.e., manipulation of one or more optical properties of an optical carrier wave to generate a modulated wave).

[0023] As shown, active layer 106 is disposed between cladding layer 104 and cladding layer 108, which are disposed between substrate 102 and modulation actuator 125. In some embodiments, modulation actuator 125 may correspond to an electrode, and substrate 102 may correspond to a counter electrode. In some embodiments, an adjustable bias (e.g., voltage) may be applied between modulation actuator 125 and substrate 102 to generate a bias across modulation region 105. It is understood that in other embodiments, temperature or pressure may be applied to modulation region 105 via modulation actuator 125. Furthermore, it is understood that in some embodiments, cladding layer 104 and / or cladding layer 108 may be omitted.

[0024] As shown in FIGS. 1C-1E, in the illustrated embodiment of optical modulator 100, the refractive index change is shown as being consistent in the vertical direction (i.e., it is understood that first material 107 and second material 108 form an interface that is substantially perpendicular or orthogonal to the lateral plane or cross-section of optical modulator 100). However, in the same or other embodiments, multiple interfaces (e.g., interface 111 illustrated in FIG. 1E) may not be substantially orthogonal to the lateral plane or cross-section of optical modulator 100.

[0025] FIG. 1F shows a more detailed view of the modulation region 105 of the inverse-designed optical modulator of FIG. 1A , according to one embodiment of the present disclosure. As shown, the modulation region 105 includes a non-uniform arrangement of two or more different materials (e.g., a first material 107 and a second material 108) having different refractive indices to structure the modulation region 105 to manipulate one or more optical properties of an optical carrier in response to a modulation bias. In some embodiments, the first material 107 and the second material 108 correspond to silicon and silicon dioxide, respectively. However, as described in embodiments of the present disclosure, the first material 107 and the second material 108 may be materials other than silicon or silicon dioxide (e.g., the first material 107 or the second material 108 may correspond to lithium niobate, a III-V semiconductor material, a II-VI semiconductor material, differently doped regions of silicon, or a combination thereof). In the illustrated embodiment, the discrete regions of the first material 107 and the second material 108 may form one or more islands of a given material included in the modulation region 105. For example, the non-uniform arrangement of the first material 107 and the second material 108 may include a first island 113 of the first material 107 laterally surrounded by the second material 108, and a second island 114 of the second material 108 laterally surrounded by the first material 107. It is understood that the non-uniform arrangement of the first material 107 and the second material 108 forms a pattern that is determined based on iterative minimization of a loss function (see, for example, loss function 205 shown in FIG. 2A ).

[0026] 2A illustrates a loss function 205 for an inverse design of an optical modulator, according to one embodiment of the present disclosure. Loss function 205 is an example of a loss function that may be utilized as an objective function for generating the design or schematic of modulation region 105 illustrated in FIGS. 1A and 1B. However, it will be appreciated that in other embodiments, a different or more robust loss function may be utilized in place of loss function 205.

[0027] As previously described, the non-uniform arrangement includes a discrete pattern of two or more different materials (e.g., first material 107 and second material 108), with the pattern selected based on iterative minimization of a loss function (or, more specifically, minimization of the output of the loss function) incorporating multiple different states of optical modulator 100, each associated with a different refractive index change. By incorporating multiple states (e.g., based on the magnitude of the modulation bias applied to modulation region 105), each representing a different refractive index change, the response curve of optical modulator 100 can be tailored to perform in a predetermined manner (e.g., monotonic, and linear or nonlinear). Advantageously, fine-tuning how the optical modulator operates can compensate for shortcomings in conventional optical modulators or otherwise enable an optical modulator with improved control over one or more optical properties. Inverse design techniques can consider the layout of an optical modulator, such as optical modulator 100 constructed with input port 110, modulation (design) region 105, output port 115, and optional port 120. Multiple bias points of the optical modulator are simulated in parallel by constructing device geometries or patterns of the first material 107 and the second material 108 using the same overall topology but with different perturbations to the refractive index in at least one of the first material 107 or the second material 108. These parallel simulations thus calculate the optical transmission from the input port 110 to the output port 115 in the illustrated embodiment as a function of the magnitude of the refractive index perturbation or change (Δn) or the modulation bias itself. It should be understood that while transmission (T) is utilized in the embodiment of the loss function 205 shown in FIG. 2A , other properties of the optical carrier may also be determined in addition to or instead of transmission (e.g., polarization phase, frequency, etc.).

[0028] The optimization objective of the inverse design methodology is formulated as one or more optical properties of the optical carrier (e.g., power, polarization, phase, frequency, or a combination thereof). In the illustrated embodiment, the loss function 205 is constructed for the optical power of the transmission or an optical carrier function of this transmission. The loss metric (e.g., Loss(T)) is calculated for the point of interest x iwhere each interest point corresponds to one of multiple states of the optical modulator (e.g., different values ​​for the change in refractive index up to the maximum change in refractive index resulting from different magnitudes of the modulation bias). Thus, each of the interest points may be included in a parallel calculation or simulation of the optical modulator 100 based on a common topology or non-uniform arrangement of the first material 107 and the second material 108. For each interest point in the sum, the loss function is expressed as a sum of two squares (e.g., T ON (x i )-f(x i ) and T OFF (x i )-1+f(x i )), although in other embodiments, a different sum may be used. The function f may be utilized to adjust or otherwise achieve a desired response curve of the optical modulator 100 when optimizing a design. Additionally, it will be appreciated that in some embodiments, a penalty may be utilized to enforce certain criteria (e.g., prioritizing performance relative to maximum and minimum values ​​for refractive index or modulation bias change, such that the ON and OFF logic states of the optical modulator are prioritized over any intermediate logic states located between the ON or OFF logic states).

[0029] The inverse design operates using a design simulator (e.g., a design model) configured with an initial design or pattern of the modulation region 105 to perform a forward operational simulation of the initial design (e.g., using Maxwell's equations of electromagnetics). The output of the forward operational simulation is a simulated electromagnetic field response at the output port 115 and (optionally) at the optional port 120. A particular performance parameter of this output field response may be selected as the parameter of interest (e.g., power loss, wavelength, etc.) and is referred to as the simulated performance parameter. The simulated performance parameter is used by the loss function 205 to calculate a performance loss value or metric, which may be a scalar value (e.g., the mean squared difference between the simulated performance value and the target performance value). The differentiable nature of the design model enables backpropagation through adjoint simulation of the performance loss error, which is the difference between the simulated output value and the desired / target performance value. The performance loss error (e.g., loss gradient) is backpropagated through the design model during adjoint simulation to generate a structural design error at the input port 110. Backpropagation of the performance loss error facilitates the calculation of additional performance gradients, such as structural gradients that represent the sensitivity of the performance loss values ​​to changes in the structural material properties (e.g., the topology or pattern of the first material 107 and the second material 108) of the modulation region 105. These gradients are output as structural design errors and can then be used by a structural optimizer to perform an iterative gradient descent method (e.g., stochastic gradient descent) that optimizes or refines the initial structural design to generate a modified structural design for the modulation region 105. Forward and inverse simulations can then be repeated until the performance loss values ​​fall within acceptable design criteria (referred to as saturation). The above description is merely an example of an inverse design technique that can be used to refine or optimize the features and topology of the optical modulator 100. It should be understood that other inverse design techniques can be implemented alone or in combination with other conventional design techniques.Therefore, the inverse design techniques described above can be applied to determine the specific material combinations, feature sizes, and feature placements (i.e., patterns) to achieve the desired performance at each port for a given logic state of the optical modulator 100 using the loss function 205.

[0030] FIG. 2B shows an exemplary chart 250 of optical modulator response curves 210, 215, and 220, for example, of an inverse-designed optical modulator, according to one embodiment of the present disclosure. It is understood that response curves 210, 215, or 220 may represent optical modulator 100 shown in FIGS. 1A-1F. In the illustrated embodiment, the y-axis corresponds to the transmission at output port 115 versus the change in refractive index (e.g., Δn) or the magnitude of modulation bias (e.g., a change in voltage, current, pressure, or temperature applied to modulation region 105). It is understood that function f of loss function 205 may incorporate the change in refractive index and / or modulation bias as a metric for determining or otherwise simulating the performance of optical modulator 100 at each point of interest (e.g., the transmission at output port 115 as shown in FIG. 2A, or any other one or combination of one or more optical properties of optical carrier 150 as described in embodiments of the present disclosure). Each point marked with a "+" in chart 250 corresponds to the x value of the loss function 205 shown in FIG. 2A. i It will be understood that this corresponds to one of the points of interest included in. However, it will be understood that more or fewer points of interest may be utilized depending on the target granularity desired when designing light modulator 100.

[0031] In the illustrated embodiment, chart 250 shows three exemplary response curves 210, 215, and 220 representing the embodiment of optical modulator 100 shown in FIGS. 1A-1E. In some embodiments, the non-uniform arrangement of first material 107 and second material 108 is structured such that the response curve of optical modulator 100 of the change in one or more optical properties of the optical carrier to a change in the magnitude of the modulation bias or a change in the different refractive index due to the modulation bias is linear, as shown by response curve 210. In other embodiments, the non-uniform arrangement of first material 107 and second material 108 is structured such that the response curve of optical modulator 100 of the change in one or more optical properties of the optical carrier to a change in the different refractive index due to the modulation bias is non-linear, as shown by response curves 215 and 220. It is understood that response curves 210 and 220 are monotonic (e.g., non-increasing or non-decreasing response curves). Specifically, when considering the x-axis of chart 250 from zero change value to maximum change value, response curves 210 and 220 are non-increasing response curves.

[0032] 3 includes a chart illustrating the iterative inverse design of modulation region 105 using loss function 205, according to one embodiment of the present disclosure. Chart 305 shows how loss function 205 saturates to a minimum value after a certain number of time steps of iterative forward and adjoint simulations. Chart 310 shows how the transmitted power T at output port 115 varies for the ON state (e.g., logic HIGH) and OFF state (e.g., logic LOW) of optical modulator 100 as the iterative design of modulation region 105 progresses.

[0033] 4 is a flow diagram illustrating a process 400 of operation of the optical modulator 100, according to an embodiment of the present disclosure. The order in which some or all of the process blocks appear in the process 400 should not be considered limiting. Rather, one of ordinary skill in the art having the benefit of this disclosure will understand that some of the process blocks may be performed in various orders not illustrated, or even in parallel.

[0034] In process block 405, an optical carrier wave 150 is received by the modulation region 105 via an input port 110 optically coupled to the modulation region 105. The modulation region 105 includes a heterogeneous arrangement of two or more different materials (e.g., a first material 107 and a second material 108) having different refractive indices to structure the modulation region 105 to manipulate one or more optical properties (e.g., phase, polarization, power, frequency, or a combination thereof) of the optical carrier wave 150 in response to a modulation bias. The optical carrier wave 150 may be a continuous wave generated by a laser source (e.g., a laser diode, etc.) directed along a single-mode waveguide (e.g., a planar waveguide, an optical fiber, etc.) to the input port 110. The laser source may be an on-chip device integrated into the PIC with the optical modulator 100, or a separate off-chip device whose output is directed to the input port 110. In other embodiments, the optical carrier wave 150 may already have a data signal embedded thereon (e.g., when correcting for distortion, the optical carrier wave 150 may already be carrying information).

[0035] At process block 410, the optical carrier wave 150 is modulated within the modulation region 105 in response to a modulation bias applied by a modulation actuator 125. Specifically, the modulation bias is modulated to generate a modulated wave 155 that is directed to an output port 115 optically coupled to the modulation region 105. The modulation bias adjusts at least one of the different refractive indices of the non-uniform arrangement to provide variable control of one or more optical properties of the optical carrier wave 150. The modulation actuator 125 drives the modulation bias based on a data signal 160 received by a modulation controller 140. In the illustrated embodiment, the modulation region 105 includes a non-uniform arrangement of a first material 107 and a second material 108, each having a different refractive index, that disperses (e.g., scatters, refracts, diffracts, or otherwise changes) the optical carrier wave 150 in a controlled manner to manipulate one or more optical properties (e.g., power, phase, polarization, frequency, or a combination thereof) of the optical carrier wave 150 to generate the modulated wave 155. In some embodiments, the modulation bias in combination with the non-uniform placement of the modulation region 105 can direct / steer a portion of the optical power of the optical carrier 150 toward the output port 115 in an ON or HIGH logic state (process block 415), or a portion of the optical power is directed / steered away from the output port 155 (e.g., toward optional port 120, reflected back to the input port 110, or otherwise scattered or dispersed away from the output port 115) when in a second state (e.g., LOW, OFF, or other intermediate state that is not ON or HIGH) (process block 420). Of course, the logic state is determined by the modulation bias applied across the modulation region 105 in response to the data signal 160. Additionally, it will be appreciated that the magnitude of the optical power directed away from the output port 115 may depend on the magnitude of the modulation bias.For example, when in a logic HIGH or ON state, most of the optical power may be directed toward output port 115, while when in a logic OFF LOW (LOW of OFF) state, most of the optical power may be directed away from output port 155 (e.g., toward optional port 120).

[0036] The modulation bias affects the power steering, and therefore the logic state, encoded on the optical carrier wave 150 at the output port 115 by inducing small changes in the refractive index of the first material 107 and / or the second material 108. Each discrete region of the first material 107 and the second material 108, which collectively form the pattern or non-uniform arrangement, represents a continuous block (homogeneous region) of either the first material 107 or the second material 108, two components, with a uniform refractive index. Application of the modulation bias across the non-uniform arrangement induces small changes in the refractive index of each continuous block of the first material 107 and / or the second material 108, which steers optical power toward or away from the output port 115, depending on the modulation bias. As previously mentioned, the first material 107 and the second material 108 can be implemented as discrete regions of two different materials, such as silicon and silicon oxide, although other material combinations can also be used. The overall pattern or non-uniform arrangement of the first material 107 and the second material 108 within the modulation region 105 can be determined by inverse design using forward and adjoint simulations that seek to minimize the loss function 205 presented above. Of course, other design techniques and loss functions may be implemented to arrive at the pattern or non-uniform arrangement of the first material 107 and the second material 108 depending on the needs of a particular application of the optical modulator 100. Furthermore, while the process 400 focuses on modulating the optical power of the optical carrier 150, it will be understood that other optical properties of the optical carrier 150 may also be adjusted by the modulation bias depending on the loss function utilized to determine the configuration of the optical modulator 100 and the design of the modulation region 105.

[0037] 5 shows a flowchart 500 detailing an iterative process for designing a reverse-engineered optical modulator 100, according to one embodiment of the present disclosure. The order in which some or all of the process blocks appear in process 500 should not be considered limiting. Rather, one of ordinary skill in the art having the benefit of this disclosure will understand that some of the process blocks may be performed in various orders not illustrated, or even in parallel.

[0038] Block 505 indicates configuring a simulation environment to represent a photonic integrated circuit (e.g., optical modulator 100 including modulation region 105, input port 110, output port 115, and optionally optional port 120). The simulation environment may be configured as pixels or voxels (see, e.g., FIG. 6A ), in which structural parameters (e.g., refractive index), optical carrier characteristics (e.g., power, frequency, phase, polarization, etc.), and target performance parameters are set or otherwise configured.

[0039] Block 515 indicates performing an operational simulation of the photonic integrated circuit to determine a loss metric (e.g., based on a loss function such as loss function 205 shown in FIG. 2A). The loss metric can provide information about how the simulated optical modulator performs relative to a target performance metric (see, e.g., FIG. 6B).

[0040] Block 520 depicts backpropagating the loss metric through the simulated environment (e.g., as an adjoint simulation) to determine a structural gradient. It is understood that the structural gradient may identify how changing the structural parameters of each of the voxels or pixels included in the simulated environment may affect the loss metric or value. In this manner, it may be determined which changes in structural parameters for which voxels or pixels can be used to reduce (i.e., optimize) the loss metric or value. For example, it may not make sense to modify the structural parameters of voxels that have limited impact on reducing the loss metric.

[0041] Block 525 indicates modifying the photonic integrated circuit design by updating the structural parameters to reduce the loss metric or value. This may be accomplished, for example, by flipping the structural parameters of voxels with the largest structural gradient to the opposite material (e.g., flipping the material of a given voxel from the first material 107 to the second material 108, or vice versa). Alternatively, small changes to the structural parameters may be utilized instead of flipping. For example, a given voxel may have a material value of 0.5, which may correspond between the first material 107 and the second material 108. As the iterations progress, the material value for a given value may gradually shift toward 0 or 1, indicating that the material should be either the first material 107 or the second material 108.

[0042] Block 530 depicts a check to see if the loss metric converges or otherwise saturates based on after the design of the photonic integrated circuit is modified. If the loss metric does not converge, block 530 proceeds to block 515 and the iterative process continues. However, if the loss metric converges or some other parametric indicates an end of the simulation (e.g., a time or computational cost budget has been reached), block 530 proceeds to block 535 and an output of the optimized design of the photonic integrated circuit is provided (e.g., as a schematic).

[0043] 6A-6C illustrate the initialization, operational simulation, and adjoint simulation of a simulated environment 601, respectively, for optimizing structural parameters of a physical device (e.g., optical modulator 100) having a design model, according to an embodiment of inverse design. The simulated environment 601 and corresponding initialization, operational simulation, adjoint simulation, and structural parameter optimization can be achieved via a physical simulator using Maxwell's equations. As shown in FIGS. 6A-6C, the simulated environment is represented in two dimensions, but it is understood that higher dimensions (e.g., three-dimensional space) can also be used to describe the simulated environment 601 and the physical device. In some embodiments, optimization of the structural parameters of the physical device shown in FIGS. 6A-6C may be achieved via simulation (e.g., time-forward and back-propagation) utilizing finite-difference time-domain (FDTD) methods to model field responses (e.g., both electric and magnetic), among other things.

[0044] FIG. 6A shows an exemplary rendering of a simulated environment 601-A describing an electromagnetic device. The simulated environment 601-A represents the simulated environment 601 at an initial time step (e.g., initial setup) for optimizing the structural parameters of the physical device. The physical device described by the simulated environment 601 may correspond to an optical modulator 100 having a designable region 605 (e.g., modulation region 105) where the structural parameters of the simulated environment may be designed, modified, or otherwise changed. The simulated environment 601 includes an excitation source 615 (e.g., a Gaussian pulse, a wave, a waveguide mode response, etc.) at the input port 110. The electric and magnetic fields within the simulated environment 601 (and the physical device) may change in response to the excitation source 615 (e.g., field response). Before operational simulation begins, a specific configuration (i.e., initial description) of the initial structural parameters, excitation source, performance parameters, and other metrics of a first-principles simulation of the physical device is input.

[0045] As shown, the simulated environment 601 (and subsequent physical devices) is described by a plurality of voxels 610, each representing an individual element of the simulated environment's two-dimensional (or three-dimensional) space. While each voxel is shown as a two-dimensional square, it is understood that the voxels may be represented as a cube or other shape in three-dimensional space. It is understood that the specific shape and dimensions of the plurality of voxels 610 may be adjusted depending on the simulated environment 601. Furthermore, it should be noted that only a portion of the plurality of voxels 610 is shown to avoid obscuring other aspects of the simulated environment 601. Each of the plurality of voxels 610 is associated with one or more structural parameters, field values ​​for describing a field response, and source values ​​for describing an excitation source at a particular location within the simulated environment 601. The field response may correspond to, for example, a vector describing the electric and / or magnetic field at a particular time step for each of the plurality of voxels 610. More specifically, the vector may correspond to a Yee lattice that discretizes Maxwell's equations to determine the field response. In some embodiments, the field response is based at least in part on the structural parameters and the excitation source 615 .

[0046] FIG. 6B illustrates an exemplary operational simulation of simulated environment 601-B at a particular time step in which excitation source 615 is active (e.g., generating waves originating from excitation source 615 propagating through simulated environment 601). As described above, the physical device is an optical modulator that may be operating at a frequency of interest and may have a particular waveguide mode (e.g., a transverse electromagnetic mode, a transverse electric mode, etc.), and the excitation source is at input port 110. The operational simulation is performed over multiple time steps (see FIG. 3 ), including the illustrated time step. When performing the operational simulation, changes to the field response (e.g., field values) for each of the plurality of voxels 610 are updated in response to excitation source 615 and are based, at least in part, on structural parameters of the physical device at each of the plurality of time steps. Similarly, in some embodiments, source values ​​are updated for each of the plurality of voxels (e.g., in response to electromagnetic waves from excitation source 615 propagating through the simulated environment). It is understood that the motion simulation is incremental, with the field values ​​(and source values) being incrementally updated at each time step as time progresses for each of a plurality of time steps. It is further noted that in some embodiments the updating is an iterative process, with each field and source value update being based at least in part on previous updates of each field and source value.

[0047] When performing an operational simulation, a performance loss function (e.g., loss (T) as shown by loss function 205 shown in FIG. 2A ) may be calculated at port 620 (e.g., corresponding to output port 115) and / or other ports (e.g., ports 615 and / or 625, depending on one or more metrics being optimized) based at least in part on a comparison (e.g., mean square difference) between the field response at a specified time step (e.g., the final time step of the operational simulation) and the desired field response. The performance loss value may be described in terms of a particular performance value (e.g., power). Structural parameters may be optimized for this particular performance value.

[0048] 6C illustrates an exemplary backpropagation of a performance loss error in the reverse direction within a simulated environment 601-C that describes a physical device. In one embodiment, the adjoint performance simulation injects the performance loss error into output port 620 and optionally optional port 625 as a type of backexcitation source to stimulate a backfield response through voxel 610 of simulated environment 601-C. The adjoint performance simulation of the performance loss error determines the effect of changes in the structural parameters of voxel 610 on the performance loss value (e.g., loss function 205).

[0049] 7A is a flowchart 700 illustrating exemplary time steps of a time-forward simulation 710 and backpropagation 750 within a simulated environment, according to one embodiment of the present disclosure. Flowchart 700 is one possible implementation in which a design model can be used to perform a forward motion simulation 710 and backpropagation 750 of a simulated environment. In the illustrated embodiment, the forward motion simulation utilizes the FDTD method to model the field response (both electric and magnetic) at multiple time steps in response to an excitation source. More specifically, time-dependent Maxwell's equations (partial differential form) are discretized to solve field vector components (e.g., the field response of each of multiple voxels 610 of the simulated environment 601 of FIGS. 6A-6C ) over multiple time steps.

[0050] As shown in FIG. 7A , flowchart 700 includes update operations for a motion simulation 710 and a portion of an adjoint simulation 750. Motion simulation 710 occurs over multiple time steps (e.g., from an initial time step to a final time step over a predetermined or conditional number of time steps having a specified time step size) and models changes (e.g., from initial field values ​​711) in the electric and magnetic fields of multiple voxels that describe the simulated environment and / or physical devices that collectively correspond to field responses. More specifically, the update operations (e.g., 712, 714, and 716) are iterative and based on the field responses, the structural parameters 704, and one or more physical stimulus sources 708. Each update operation is followed by another update operation and represents successive steps forward in time within the multiple time steps. For example, update operation 714 updates the field values ​​based on the field responses determined from the previous update operation 712, the sources 708, and the structural parameters 704. Similarly, an update operation 716 updates the field values ​​based on the field response determined from update operation 714. In other words, at each time step of the motion simulation, the field values ​​(and therefore the field response) are updated based on the previous field response and structural parameters of the physical device. Once the final time step of the motion simulation 710 is performed, a loss value 718 may be determined (e.g., based on a predetermined loss function 720 or loss function 205). The loss gradient determined from block 752 may be treated as an adjoint or virtual source (e.g., a physical stimulus or excitation source occurring in the output domain) that is back-propagated backward (from the final time step incrementally through multiple time steps until an initial time step is reached) to determine a structural gradient 768.

[0051] In the illustrated embodiment, the FDTD solution (e.g., time-forward simulation 710) and backpropagation 750 problem are described graphically from a high level using only "update" and "loss" operations and their corresponding gradient operations. A simulation is first set up where the structural parameters of the simulated environment (and electromagnetic devices), excitation sources, and initial field states are provided. As previously mentioned, the field states are updated in response to the excitation sources based on the structural parameters. More specifically, the update operation is given by φ, where x = 1,...,n for i = 1,...,n. i+1 =φ(x i ,b i , z), where n corresponds to the total number of time steps (e.g., multiple time steps) for the time-forward simulation, and x i corresponds to the field response of the simulated environment at time step i (the field values ​​associated with the electric and magnetic fields at each of the voxels), and b i where σ corresponds to the excitation sources of the simulated environment at time step i (source values ​​associated with the electric and magnetic fields for each of the multiple voxels), and z corresponds to structural parameters describing the topology and / or material properties of the electromagnetic device.

[0052] Using the FDTD method, the update operation can be specifically described as follows: φ(x i ,b i ,z)=A(z)x i +B(z)b i (1) That is, the FDTD update is linear in the field and source terms. Specifically,

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[0055] In terms of modifying or otherwise optimizing the structural parameters of an electromagnetic device, the relevant quantities to be generated are:

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[0057] 7B is a chart 780 illustrating the relationship between update operations and adjoint simulation (e.g., backpropagation) for a behavioral simulation, according to an embodiment of the present disclosure. More specifically, FIG. 7B illustrates the relationship between the structural gradient

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[0078] Some processes described above are described in terms of computer software and hardware. The described techniques may constitute machine-executable instructions embodied in a tangible or non-transitory machine (e.g., computer) readable storage medium that, when executed by a machine, causes the machine to perform the described operations. Furthermore, the processes may be embodied in application specific integrated circuits ("ASICs") or other hardware, such as

[0079] A tangible, machine-readable storage medium includes any mechanism that provides (i.e., stores) information in a non-transitory form accessible by a machine (e.g., a computer, a network device, a personal digital assistant, a manufacturing tool, any device with a set of one or more processors, etc.). For example, machine-readable storage media include recordable / non-recordable media (e.g., read only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, etc.).

[0080] The above description of illustrated embodiments of the present invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise form disclosed. While specific embodiments of and examples for the present invention have been described herein for illustrative purposes, those skilled in the art will recognize that various modifications are possible within the scope of the present invention.

[0081] These modifications can be made to the invention in light of the above detailed description. In general, the terms used in the following claims should not be construed to limit the invention to the specific embodiments disclosed herein. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.

Claims

1. An optical modulator, a modulation region comprising a non-uniform arrangement of two or more different materials having different refractive indices to structure the modulation region to manipulate one or more optical properties of an optical carrier in response to a modulation bias; an input port optically coupled to the modulation region for injecting the optical carrier into the modulation region; a modulation actuator disposed proximate the modulation region and adapted to apply the modulation bias to the modulation region to generate a modulated wave, the modulation bias adjusting at least one of the different refractive indices of the non-uniform arrangement to provide variable control of the one or more optical properties of the optical carrier wave; an output port optically coupled to the modulation region for receiving the modulated wave; An optical modulator comprising:

2. The optical modulator of claim 1 , wherein the one or more optical properties include at least one of a frequency, a phase, a polarization, or a power of the optical carrier.

3. The optical modulator of claim 2 , wherein the modulation actuator is adapted to impart a data signal to the optical carrier wave to generate the modulated wave via the modulation bias.

4. The optical modulator of claim 2, wherein the non-uniform arrangement is further structured such that a response curve of the optical modulator of a change in the one or more optical properties of the optical carrier to a change in the magnitude of a modulation bias or a change in the different refractive indices due to the modulation bias is linear.

5. The optical modulator of claim 2 , wherein the non-uniform arrangement is further structured such that a response curve of the optical modulator of a change in the one or more optical properties of the optical carrier to a change in the different refractive indices due to the modulation bias is non-linear.

6. The optical modulator of claim 5 , wherein the response curve is further monotonic.

7. 2. The optical modulator of claim 1, wherein the modulated wave comprises a plurality of states based on the magnitude of the modulation bias, the plurality of states comprising a HIGH state and a LOW state, and the non-uniform arrangement is structured to steer, scatter, or reflect a portion of the optical carrier wave away from the output port when the modulated wave is modulated to the LOW state.

8. The optical modulator of claim 1 , wherein the two or more different materials include a semiconductor material and an oxide material.

9. The modulation actuator is an electrode adapted to apply the modulation bias as an adjustable voltage across the modulation region; a heating element adapted to apply the modulation bias as an adjustable temperature across the modulation region; or 10. The optical modulator of claim 1, comprising one of: an electromechanical actuator adapted to apply the modulation bias as an adjustable pressure across the modulation region.

10. 2. The optical modulator of claim 1, wherein the non-uniform arrangement comprises a pattern of discrete regions of the two or more different materials, the pattern being selected based on iterative minimization of a loss function incorporating multiple different states of the optical modulator, each associated with a different refractive index change.

11. 2. The optical modulator of claim 1, wherein the input port and the output port comprise corresponding waveguide sections that physically abut the modulation region.

12. 12. The optical modulator of claim 11, further comprising a peripheral region that laterally surrounds the modulation region, the peripheral region extending continuously laterally around the modulation region except where two or more ports abut the modulation region, the two or more ports including the input port and the output port.

13. The optical modulator of claim 12 further comprising a sink port abutting the modulation region, wherein the two or more ports include the sink port.

14. 13. The optical modulator of claim 12, wherein the peripheral region has a homogeneous composition, the peripheral region including a first material included in the two or more different materials.

15. 2. The optical modulator of claim 1, wherein the two or more different materials include a first material and a second material, and the non-uniform arrangement includes first islands of the first material laterally surrounded by the second material, and second islands of the second material laterally surrounded by the first material.

16. 1. A method of operating an optical modulator, comprising: receiving an optical carrier wave at a modulation region from an input port optically coupled to the modulation region, the modulation region including a non-uniform arrangement of two or more different materials having different refractive indices to structure the modulation region to manipulate one or more optical properties of the optical carrier wave in response to a modulation bias; modulating the modulation bias applied to the modulation region to generate a modulated wave, the modulation bias adjusting at least one of the different refractive indices of the non-uniform arrangement to provide variable control of the one or more optical properties of the optical carrier wave, the modulated wave being directed to an output port optically coupled to the modulation region; and A method comprising:

17. modulating the modulation bias to impart a data signal to the optical carrier wave to generate the modulated wave; directing a majority of the optical power of the optical carrier wave to the output port when the modulated wave is modulated to a HIGH state based on a first logic state of the data signal; diverting a second majority of the optical power of the optical carrier from the output port when the modulated signal is modulated to a LOW state based on a second logic state of the data signal; 17. The method of claim 16, further comprising:

18. The method of claim 16 , wherein the one or more optical properties include at least one of a frequency, a phase, a polarization, or a power of the optical carrier.

19. modulating the modulation bias applied to the modulation region; applying an adjustable voltage across said modulation region; heating the modulation region; or applying an adjustable pressure to the modulation region.

20. 17. The method of claim 16, wherein the non-uniform arrangement is further structured such that a response curve of the optical modulator of a change in the one or more optical properties of the optical carrier to a change in the magnitude of a modulation bias or a change in the different refractive indices due to the modulation bias is linear.

21. 17. The method of claim 16, wherein the non-uniform arrangement is further structured such that a response curve of the optical modulator of a change in the one or more optical properties of the optical carrier to a change in the different refractive indices due to the modulation bias is monotonic.

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