Optical modulator having a sink waveguide

Abstract

An optical modulator comprises a modulation region, input, output, and sink ports, and a modulation actuator. The modulation region comprises a non-uniform arrangement of two or more different materials having different refractive indices. An input port is optically coupled to the modulation region to inject an optical carrier into the modulation region. An output port is optically coupled to the modulation region to receive and emit a modulated signal having high and low states. A sink port is optically coupled to the modulation region. The modulation actuator is positioned in proximity to the modulation region and is adapted to apply a modulation bias to the modulation region that affects the different refractive indices of the non-uniform arrangement to selectively steer a portion of the optical power of the optical carrier to the sink port when the modulated signal is modulated to a low state.

Description

Technology Field

[0001] Cross-reference regarding related applications

[0002] This application claims the benefit of U.S. Patent Application No. 17 / 884,970 filed on August 10, 2022, the contents of which are incorporated herein by reference.

[0003] Technology field

[0004] The present disclosure generally relates to photonic devices, and specifically to optical modulators. Background Technology

[0005] An optical modulator is an active component that allows a user to modulate the power level of an optical signal through an applied bias. This bias is typically achieved by changing a voltage that electro-optically, thermally-optically, or mechanically-optically adjusts the refractive index of a material in a specific region of the integrated device. When the bias is modulated at high speeds (GHz rates), information and data can be encoded and transmitted via an optical carrier to a distant receiver.

[0006] Typical modulators are designed by humans using well-understood components (e.g., combinations of waveguide-based phase shifters and directional couplers or modulated ring resonators). However, these conventional components have limitations: they have a large footprint and a limited number of "knobs" that can be used to improve and modify their performance. Brief explanation of the drawing

[0007] Non-limiting and non-comprehensive embodiments of the present invention are described with reference to the following drawings, in which similar reference numbers refer to similar parts across various views unless otherwise specified. Where appropriate, not all instances of elements are labeled to avoid cluttering the drawings. The drawings are not necessarily drawn to scale, but emphasis is given to exemplify the principles being described. FIG. 1 illustrates an optical modulator having a sink waveguide for power recycling according to one embodiment of the present disclosure. FIG. 2a illustrates a loss function for inverse engineering of an optical modulator according to one embodiment of the present disclosure. FIG. 2b illustrates how a sink loss function can be modified to obtain an acceptable operating efficiency of an optical modulator without adversely affecting transmission to the sink port during the ON state of the optical modulator, according to one embodiment of the present disclosure. FIG. 3 includes charts illustrating iterative inverse engineering of a modulation region using a loss function according to one embodiment of the present disclosure. FIG. 4 is a flowchart illustrating the operation of an optical modulator having a sink waveguide for power recycling according to one embodiment of the present disclosure. FIG. 5a illustrates an optical modulator according to one embodiment of the present disclosure, in which an input port, an output port, and a sink port are oriented parallel to each other. FIG. 5b illustrates an optical modulator according to one embodiment of the present disclosure, in which the input port is oriented perpendicularly to the sink port and the output port. FIG. 5c illustrates an optical modulator having two sink ports according to one embodiment of the present disclosure. FIG. 6a illustrates an illustrative simulated environment for simulating the operation of a physical device according to one embodiment of the present disclosure. FIG. 6b illustrates a simulation of the operation of a physical device according to one embodiment of the present disclosure. FIG. 6c illustrates an adjoint simulation (backpropagation) of performance loss error through a simulated environment according to one embodiment of the present disclosure. FIG. 7a is a flowchart illustrating exemplary time steps for operations and accompanying simulations used to reverse engineer an optical modulator according to one embodiment of the present disclosure. FIG. 7b is a flowchart illustrating the relationship between operation simulation and accompanying simulation (backpropagation) according to one embodiment of the present disclosure. Specific details for implementing the invention

[0008] Embodiments of a system, apparatus, and method of operation for a reverse-engineered optical modulator having a sink waveguide capable of providing power recycling are described herein. In the following description, numerous specific details are provided to provide a thorough understanding of the embodiments. However, a person skilled in the art will recognize that the technologies described herein may be implemented without one or more specific details or with other methods, components, materials, etc. In other cases, known structures, materials, or operations are not illustrated or described in detail to avoid obscuring specific aspects.

[0009] Throughout this specification, references to "one embodiment" or "one embodiment" mean that a specific feature, structure, or characteristic described in relation to that embodiment is included in at least one embodiment of the present invention. Accordingly, appearances of phrases such as "in one embodiment" or "in one embodiment" at various locations throughout this specification do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0010] During the operation of conventional optical modulators, a significant portion of the optical carrier is wasted. For example, conventional on-off keying modulation schemes can cause the optical power of the optical carrier to be rejected or wasted during the off-logic state. This wasted energy not only reduces the efficiency of these conventional optical modulators but also generates heat accumulation within the modulator that must be dissipated. Therefore, conventional optical modulators may be designed with larger bulk substrates thermally coupled to a heat sink to properly reject and manage the wasted power.

[0011] The embodiments described herein use reverse engineering techniques to design the modulation region of an optical modulator, thereby rejecting or recycling wasted optical power by diverting it to a sink port or sink waveguide, and subsequently, the sink port or sink waveguide can carry the optical power away from the modulator to prevent harmful heat accumulation. This technique can retain power in the optical region, so that the power is diverted away from the optical modulator rather than being dissipated as thermal energy within the optical modulator. Retaining rejected power in the optical region not only enables the creation of smaller and more compact optical modulators but also provides opportunities to create more efficient optical modulators. In particular, the optical power of the carrier that is rejected during the logic low or logic off encoding state of the optical modulator is efficiently diverted out of the modulation region through the sink port and sink waveguide. In various embodiments, this optical power is subsequently harvested using an integrated optical receiver (e.g., a photovoltaic cell or photoelectric device, etc.). For example, a photodiode or photocell can convert this rejected optical power to power other circuits or even power the modulation controller (e.g., modulation driver) of the optical modulator itself. The embodiments described herein facilitate more energy-efficient optical modulators as well as simpler optical modulators that rely less on heat sinks.

[0012] FIG. 1 illustrates an optical modulator (100) having a sink port / waveguide for power recycling according to one embodiment of the present disclosure. An illustrated embodiment of the optical modulator (100) includes a modulation region (105), an input port (110), an output port (115), a sink port (120), a modulation actuator (125), an optical receiver (130), a power control circuit (135), a modulation controller (140), and other circuits (145). An illustrated embodiment of the modulation region includes a non-uniform arrangement of two different materials (107 and 108) having different refractive indices.

[0013] The modulation region (105) may also be referred to as a “design region” or “active region” in which the pattern of discrete regions of the materials (107 and 108) operates to selectively steer the inbound optical carrier (150) received through the input port (110) to the output port (115) or sink port (120) under the influence of the modulation actuator (125) through refraction / scattering. This selective steering implements an on-off keying modulation scheme in which the optical power is primarily directed to the output port (115) during the on or high logic state, or primarily directed to the sink port (120) during the off or low logic state of the modulated wave (155). In this way, the data signal (160) is modulated onto the optical carrier (150) to generate the modulated wave (155).

[0014] The materials (107 and 108) are discrete regions of a material having different refractive indices, and the refractive indices change in response to a bias (e.g., applied voltage, current, temperature, pressure). In one embodiment, the materials (107 and 108) may be a waveguide core material and a waveguide cladding material, respectively. These core and cladding materials may be the same core and cladding materials used to form waveguide sections of an input port (110), an output port (115), and a sink port (120). For example, the material (107) may be silicon, and the material (108) may be silicon dioxide. In other embodiments, the materials (107 and 108) may be implemented as discrete regions of intrinsic silicon and doped silicon, discrete regions of differently doped silicon, or combinations of other types of semiconductor materials (e.g., III-V semiconductor materials, etc.). In one embodiment, the modulation region (105) is approximately 1.5 µm x 1.2 µm, and the ports (110, 115, 120) are waveguide sections having a width of 200 nm and a length of 600 nm. Discrete regions of the materials (107 and 108) can be implemented as composites of each material type (107 or 108) with incremental pixel / voxel sizes of 5 nm x 5 nm. Of course, other pixel / voxel resolutions can be implemented.

[0015] Modulation is achieved through a modulation bias applied to a modulation region (105) via a modulation actuator (125), and the modulation actuator (125) is driven by a modulation controller (140) in response to a data signal (160). Accordingly, the modulation controller (140) may include a modulation / demodulation circuit along with a driver circuit for driving the modulation actuator (125). The modulation actuator (125) may be implemented using a number of techniques. In one embodiment, the modulation actuator (125) includes electrodes surrounding the sides of the modulation region (105), and the modulation bias is an applied voltage and / or injected current. In another embodiment, the modulation actuator (125) includes one or more heating elements surrounding the modulation region (105), and the modulation bias is an adjustable temperature. In 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 serves to change the refractive index of the materials (107, 108), which ultimately affects the scattering / refraction of the optical carrier (150) to selectively steer between the output port (115) and the sink port (120).

[0016] In the illustrated embodiment, the input port (110), output port (115), and sink port (120) are each adjacent to the modulation region (105) and operate as optical inputs or outputs for propagating waves. Although the input port (110), output port (115), and sink port (120) are referred to as "ports," these ports may include a longitudinal length in the direction of optical propagation. Accordingly, the input port (110), output port (115), and sink port (120) may be implemented as waveguide sections having a core and cladding having one end that is physically adjacent to or otherwise optically coupled to the modulation region (105). In various embodiments, the input port (110), output port (115), sink port (120), and modulation region (105) are all planar waveguide sections. These planar waveguide sections can be embedded within semiconductor materials such as SOI (silicon-on-insulator) systems, PIC (photonic integrated circuit), or others.

[0017] The non-uniform arrangement of materials (107 and 108) forms a pattern determined based on the iterative minimization of a loss function (205) (see FIG. 2a), which is defined as the sum of a transmission loss function (210) at an output port (115), a reflection loss function (215) at an input port (110), and a sink loss function (220) at a sink port (120). Inverse engineering techniques can consider the layout of an optical modulator, such as an optical modulator (100) composed of an input port (110), a modulation (design) region (105), an output port (115), and a sink port (120). Multiple bias points of the optical modulator are simulated in parallel by constructing device geometries or patterns of materials (107 and 108) that use the same overall topology but have different perturbations dn = [dn1, dn2, dn3,...] for the refractive index in one of the materials (107 or 108). Thus, these parallel simulations calculate the optical transmission from the input port (110) to the output port (115) as a function of the refractive index perturbation T(dn).

[0018] The optimization objective of the reverse engineering method is configured as a function L(T(dn)) of this transmission and is designed to be optimized for a desired T(dn). The objective is to configure the resulting structure / pattern in such a way that light can be directed through the sink port (120) when it is desirable for the transmission at the output port (115) to be low or off. This enables control over otherwise lost power. This power can be further recycled by other components accompanying the optical modulator (100) (e.g., a modulation controller (140) or other circuit (145)) without adverse effects on the optical modulator (100).

[0019] Inverse engineering is performed using a design simulator (also known as a design model) composed of an initial design or pattern for a modulation region (105) to perform a forward operation simulation of the initial design (e.g., using Maxwell's equations for electromagnetics). The output of the forward operation simulation is a simulated field response at the output port (115) and the sink port (120). Specific performance parameters of this output field response can be selected as parameters of interest (e.g., power loss, wavelength, etc.) and are referred to as simulated performance parameters. The simulated performance parameters are used by a loss function (205) to calculate a performance loss value, which can be a scalar value (e.g., the mean squared difference between the simulated performance values ​​and the target performance values). The differentiable nature of the design model enables backpropagation through the concomitant simulation of a performance loss error, which is the difference between the simulated output values ​​and the desired / target performance values. Performance loss errors (e.g., loss gradients) are backpropagated through the design model during concomitant simulation to generate structural design errors at the input port (110). Backpropagation of performance loss errors facilitates the calculation of additional performance gradients, such as structural gradients, which represent the sensitivity of performance loss values ​​to changes in structural material properties of the modulation region (105) (e.g., topology or pattern of the materials (107 and 108)). These gradients are output as structural design errors, which can then be used by a structural optimizer to perform iterative gradient descent (e.g., stochastic gradient descent) to optimize or refine the initial structural design to generate a modified structural design of the modulation region (105). Subsequently, forward and reverse simulations can be repeated until the performance loss value falls within acceptable design criteria (referred to as saturation).The above description is merely an exemplary reverse engineering technique that can be used to refine or optimize the features and topology of the optical modulator (100). It is recognized that other reverse engineering techniques may be implemented alone or in combination with other conventional design techniques.

[0020] The aforementioned reverse engineering techniques can be applied to determine specific material combinations, feature sizes, and feature arrangements (i.e., patterns) to achieve desired power at each port for a given logic state of the optical modulator (100) using a loss function (205). Referring to FIG. 2a, the loss function (205) is a function of x, where x is a vector representing the structural pattern of materials (107, 108) having different refractive indices. The transmission loss function (210) is defined by the transmission power (T) at the output port (115) for the on and off logic states. Similarly, the reflection loss function (215) is defined by the reflection power (R) at the input port (110) for the on and off logic states, and the sink loss function (220) is defined by the power (S) at the sink port (120) for the on and off logic states. FIG. 2b illustrates an alternative sink loss function (225) that omits a term that disadvantages the power (S) at the sink port (120) during the on logic state of the optical modulator (100).

[0021] FIG. 3 includes charts illustrating iterative inverse engineering of a modulation region (105) using a loss function (205) according to one embodiment of the present disclosure. Chart (305) illustrates how the loss function (205) saturates to a minimum value after approximately 140 forward and consequential simulations. Chart (310) illustrates how the transmitted power (T) at the output port (115) saturates to about 0.7 for logic on at three different wavelengths (e.g., 1545 nm, 1550 nm, and 1555 nm) and to about 0.1 for logic off at those same wavelengths. Chart (315) illustrates how the reflected power (R) at the input port (110) saturates to less than 0.035 for both logic on and logic off at three wavelengths (e.g., 1545 nm, 1550 nm, and 1555 nm). The reflected power (R) at the input port (110) is wasted power and is therefore undesirable. The chart (320) illustrates how the sink power (S) at the sink port (120) saturates to about 0.7 for logic off at three different wavelengths (e.g., 1545 nm, 1550 nm, and 1555 nm) and saturates to close to 0.1 for logic on across those same wavelengths.

[0022] Referring again to FIG. 1, the sink port (120) is optically coupled to the optical receiver (130) to receive the optical power rejected during the logic off / low state of the optical modulator (100). Instead of being wasted and converted into heat, this rejected optical power can be converted into electrical power through the optical receiver (130). The optical receiver (130) may be implemented as a photoelectric or photovoltaic device such as a photodiode, a photocell, or something else. Subsequently, the pulsing current is rectified or otherwise regulated by a power regulation circuit (135). The power regulation circuit (135) may include a rectifier (e.g., a diode), a storage capacitor, and / or other conventional regulation circuits. Subsequently, the regulated power may be coupled to power the modulation controller (140) itself and / or another circuit (145) that may be embedded on-chip together with the optical modulator (100).

[0023] FIG. 4 is a flowchart illustrating a process (400) of operation of an optical modulator (100) according to one 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, a person skilled in the art having the benefit of the present disclosure will understand that some of the process blocks may be executed in various unexecuted orders, or even in parallel.

[0024] In the process block (405), an optical carrier (150) is received in the modulation region (105) through the input port (110). The optical carrier (150) may be a continuous wave generated by a laser source (e.g., a laser diode, etc.) that is guided into the input port (110) along a single-mode waveguide (e.g., a planar waveguide, an optical fiber, etc.). The laser source may be an on-chip device integrated into a PIC having an optical modulator (100), or a separate off-chip device whose output is guided into the input port (110).

[0025] In process block (410), the optical carrier (150) is modulated within the modulation region (105) in response to a modulation bias applied by a modulation actuator (125). The modulation actuator (125) drives the modulation bias based on a data signal (160) received from a modulation controller (140). In the illustrated embodiment, the modulation region (105) comprises a non-uniform arrangement of materials (107 and 108) having different refractive indices, respectively, which disperse (e.g., scatter, refract) the optical carrier (150) in a controlled manner such that most of the optical output of the optical carrier (150) is directed / steered to the output port (115) in an on or high logic state (process block (415)) or most of the optical power is directed / steered to the sink port (120) in an off or low logic state (process block (420)). Of course, the logic state is determined by a modulation bias applied across the modulation region (105) in response to the data signal (160).

[0026] The modulation bias affects power steering and thus affects the logic state encoded on the optical carrier (150) at the output port (115) by inducing small changes in the refractive index of the materials (107 and 108). Each discrete region of the materials (107 or 108) collectively forming a pattern or non-uniform arrangement represents a binary, adjacent block (uniform region) of the material (107 or 108) having a uniform refractive index. The application of a modulation bias across the entire non-uniform arrangement causes small changes in the refractive index of each adjacent block of the material (107 / 108), which steers the optical power to the output port (115) or sink port (120) according to the modulation bias. As previously mentioned, the materials (107 and 108) may be implemented as discrete regions of two different materials, such as silicon and silicon oxide, but other combinations of materials may also be used. The overall pattern or non-uniform arrangement of the materials (107 and 108) within the modulation region (105) can be determined through inverse engineering using forward and consequential simulations that attempt to minimize the loss function (205) presented above. Of course, other design techniques and loss functions may be implemented to achieve a pattern or non-uniform arrangement of the materials (107, 108) according to the requirements of the specific application of the optical modulator (100).

[0027] Finally, in the process block (425), optical power that is rejected or directed to the sink port (120) during logic low or off states is directed into the optical receiver (130), where the power is recycled or harvested for beneficial use (rather than being wasted in the form of thermal heat and conducted elsewhere through the heat sink). Beneficial use may include supplying power to the modulation controller (140) itself or to another circuit (145).

[0028] FIGS. 5a-c illustrate three exemplary planar deviations from an optical modulator (100) according to embodiments of the present disclosure. FIG. 1 illustrates an optical modulator (100) in which waveguide sections of an input port (110) and an output port (115) are parallel to each other and positioned on opposite sides of a modulation region (105), but a waveguide section of a sink port (120) is oriented perpendicularly to the waveguide sections of the input port (110) and the output port (115). In contrast, FIG. 5a illustrates an optical modulator (500) in which waveguide sections of an input port (110), an output port (115A), and a sink port (115A) are all aligned parallel to each other and an output port (115A) and a sink port (120A) are positioned on a common side of a modulation region (105A) facing the input port (110). FIG. 5b illustrates an optical modulator (501) in which waveguide sections of both the sink port (120) and the output port (115B) are perpendicular to the waveguide section of the input port (110). Finally, FIG. 5c illustrates another exemplary optical modulator (502) having two sink ports (120B and 120C) that are perpendicular to both the input port (110) and the output port (115C). It should be recognized that the planar modifications illustrated in FIG. 5a-c are not comprehensive. Other planar modifications may include obliquely oriented ports, ports of various cross-sectional sizes, etc. The modulation regions (105A, B, and C) can all be designed using the same reverse engineering method described herein.

[0029] FIGS. 6a-6c illustrate, respectively, an initial setup, operation simulation, and concomitant simulation of a simulated environment (601) for optimizing structural parameters of a physical device (e.g., optical modulators (100, 500, 501, or 502)) as a design model according to a reverse engineering embodiment. The simulated environment (601) and the corresponding initial setup, operation simulation, concomitant simulation, and structural parameter optimization can be achieved through a physical simulator using Maxwell's equations. As illustrated in FIGS. 6a-6c, the simulated environment is represented in two dimensions, but it is recognized that a higher number of dimensions (e.g., three-dimensional space) can also be used to describe the simulated environment (601) and the physical device. In some embodiments, the optimization of the structural parameters of the physical device illustrated in FIGS. 6a-6c can be achieved through simulations (e.g., time-forward and backpropagation) utilizing a finite-difference time-domain (FDTD) method to model field responses (e.g., both electric and magnetic).

[0030] FIG. 6a illustrates an exemplary rendering of a simulated environment (601-A) describing an electromagnetic device. The simulated environment (601-A) represents a simulated environment (601) at an initial time stage (e.g., initial setup) for optimizing the structural parameters of a 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., a modulation region (105)) in which the structural parameters of the simulated environment can be designed, modified, or otherwise changed. The simulated environment (601) includes an excitation source (615) (e.g., a Gaussian pulse, a waveguide mode response, etc.) at the location of the input port (110). The electric and magnetic fields (e.g., field response) within the simulated environment (601) (and the physical device) may change in response to the excitation source (615). Specific settings for initial structural parameters, excitation sources, performance parameters, and other metrics (i.e., initial descriptions) for the first-principles simulation of a physical device are entered before the operation simulation begins.

[0031] As illustrated, the simulated environment (601) (and subsequently the physical device) is described by a plurality of voxels (610) representing individual elements of the two-dimensional (or three-dimensional) space of the simulated environment. Each of the voxels is illustrated as two-dimensional squares, but it is recognized that the voxels may be represented as cubes or other shapes in three-dimensional space. It is recognized that the specific shape and number of dimensions of the plurality of voxels (610) may be adjusted according to the simulated environment (601). It is further noted that only some of the plurality of voxels (610) are illustrated so as not to obscure other aspects of the simulated environment (601). Each of the plurality of voxels (610) is associated with one or more structural parameters, a field value for describing the field response, and a source value for describing an excitation source at a specific location within the simulated environment (601). The field response may correspond, for example, to a vector describing the electric field and / or magnetic field at a specific 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 partially on structural parameters and an excitation source (615).

[0032] FIG. 6b illustrates an exemplary operation simulation of a simulated environment (601-B) at a specific time step in which the excitation source (615) is activated (e.g., generating waves originating from the excitation source (615) propagating through the simulated environment (601)). As mentioned, the physical device is an optical modulator operating at a frequency of interest and having a specific waveguide mode (e.g., transverse electromagnetic mode, transverse electric mode, etc.), and the excitation source is located at an input port (110). The operation simulation occurs over a plurality of time steps (see FIG. 3) including the illustrated time step. When performing the operation simulation, changes to the field response (e.g., field value) for each of the plurality of voxels (610) are updated in response to the excitation source (615) and at least partially based on the structural parameters of the physical device at each of the plurality of time steps. Similarly, in some embodiments, the source value is updated for each of the plurality of voxels (e.g., in response to electromagnetic waves from the excitation source (615) propagating through the simulated environment). It is recognized that the operation simulation is incremental, and that the chapter values ​​(and source values) are updated incrementally at each time step as time advances for each of the multiple time steps. It is further noted that in some embodiments, the update is an iterative process, and that the update of each chapter and source value is based at least partially on the previous update of each chapter and source value.

[0033] When performing a motion simulation, performance loss functions (e.g., TLoss, RLoss, and SLoss) can be calculated at each port (615, 620, and 625) based at least partially 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 motion simulation) and the desired field response. Performance loss values ​​can be described in terms of specific performance values ​​(e.g., power). Structural parameters can be optimized for these specific performance values.

[0034] FIG. 5c illustrates an exemplary backpropagation of a performance loss error in the reverse direction within a simulated environment (601-C) describing a physical device. In one embodiment, the accompanying performance simulation injects the performance loss error at the output port (620) and sink port (625) as a type of reverse excitation source to stimulate a reverse field response through the voxels (610) of the simulated environment (601-C). The accompanying performance simulation of the performance loss error determines the effect of changes in the structural parameters of the voxels (610) on the performance loss value (e.g., loss function (205)).

[0035] FIG. 7a is a flowchart (700) illustrating exemplary time steps for time-forward simulation (710) and backpropagation (750) in a simulated environment according to one embodiment of the present disclosure. The flowchart (700) is one possible implementation that a design model can use to perform forward operation simulation (710) and backpropagation (750) of the simulated environment. In the illustrated embodiment, the forward operation simulation models the field response (both electric and magnetic) in response to an excitation source in multiple time steps using the FDTD method. More specifically, time-dependent Maxwell equations (in partial derivative form) are discretized to solve the field vector components (e.g., the field response of each of the multiple voxels (610) of the simulated environment (601) in FIG. 6a-6c).

[0036] As illustrated in FIG. 7a, the flowchart (700) includes update actions for parts of the motion simulation (710) and the accompanying simulation (750). The motion simulation (710) occurs over a plurality of 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 in the electric and magnetic fields (e.g., from initial field values ​​(711)) of a plurality of voxels describing a simulated environment and / or physical device that collectively corresponds to a field response. More specifically, the update actions (e.g., 712, 714, and 716) are iterative and are based on the field response, structural parameters (704), and one or more physical stimulus sources (708). Each update action is followed by another update action, which represents successive steps that advance in time within a plurality of time steps. For example, the update operation (714) updates the field values ​​(713) (e.g., see FIG. 6b) based on the field response determined from the previous update operation (712), sources (708), and structural parameters (704). Similarly, the update operation (716) updates the field values ​​(715) (e.g., see FIG. 7b) based on the field response determined from the update operation (714). In other words, at each time step of the operation simulation, the field values ​​(and thus the field response) are updated based on the previous field response and the structural parameters of the physical device. When the final time step of the operation simulation (710) is performed, the loss value (718) can be determined (e.g., based on a predetermined loss function (720) or loss function (205).The loss gradients determined from block (752) can be treated as accompanying or virtual sources (e.g., physical stimuli or excitation sources originating from the output region) that are backpropagated in reverse (from the final time step through multiple time steps until the initial time step is reached incrementally) to determine the structural gradient (768).

[0037] In the illustrated embodiment, the FDTD solution (e.g., time-forward simulation (710)) and backpropagation (750) problems are illustrated at a high level using "update" and "loss" behaviors, as well as corresponding gradient behaviors. The simulation is initially set up, where the structural parameters, excitation source, and initial field states of the simulated environment (and electromagnetic device) are provided. As previously discussed, the field states are updated in response to the excitation source based on the structural parameters. More specifically, the update behavior is given by φ, where About is. Here, corresponds to the total number of time steps (e.g., multiple time steps) for time-forward simulation, and is a time step Corresponding to the field response of the simulated environment in (field values ​​associated with the electric and magnetic fields of each of the multiple voxels), and is a time step Corresponding to the excitation source(s) of the simulated environment (source values ​​associated with the electric and magnetic fields for each of the multiple voxels), corresponds to structural parameters that describe the topology and / or material properties of an electromagnetic device.

[0038] Note that using the FDTD method, update behavior can be specifically described as follows:

[0039]

[0040] In other words, FDTD updates are linear with respect to chapter and source terms. Specifically, and are structural parameters ( It depends on ) and each chapter( ) and sources( These are linear operators acting on ). Here, Assuming that, where N is the number of FDTD field components in the time-forward simulation, the loss behavior is It is given as, which takes the calculated fields as input and generates a single real-valued scalar (e.g., loss value) that can be reduced and / or minimized.

[0041] In relation to modifying or otherwise optimizing the structural parameters of an electronic device, the relevant quantity to be generated is This is used to explain the change in loss values ​​with respect to changes in the structural parameters of the electromagnetic device and is indicated by the "structural slope" exemplified in Fig. 7a.

[0042] FIG. 7b is a chart (780) illustrating the relationship between an update operation for operation simulation and an accompanying simulation (e.g., backpropagation) according to one embodiment of the present disclosure. More specifically, FIG. 7b shows a structural gradient As a summary of the operations and accompanying simulation relationships involved in calculating, these and Includes. The update operation (714) of the operation simulation is Multiple voxel field values ​​at the nth time step (713, ) chapter values(715, The next time step corresponding to ) (i.e., Updates in the time step. The gradients (755) are for backpropagation (e.g., update operation in reverse in time (756)). It is used to determine, which is combined with slopes (769), at least partially, structural slope It is used to calculate. is the contribution of each chapter to the loss value L. Since this is a partial derivative, Note that it does not consider the causal relationship of. Therefore, including relationships is used. Loss gradient is structural gradient It can also be used to calculate, and corresponds to the total derivative of the field with respect to the loss value L. Specific time step Loss gradient at Is It is equal to the sum of. Finally, corresponding to the field slope is used, which is from each time / update step It is the contribution to. is given as follows:

[0043]

[0044] For completeness, total The full form of the first hour in is expressed as follows:

[0045]

[0046] Based on the definition of φ as described by mathematical formula 1, Note that, this can be substituted in Equation 3 to arrive at an accompanying update for backpropagation (e.g., update operations such as update operation (756)), which can be expressed as follows:

[0047]

[0048] or

[0049]

[0050] The accompanying update is the backpropagation of loss gradients from the subsequent time step to the previous time step, and It can be referred to as the inverse solution for. Structural gradient The second term within the sum is expressed as follows for a specific form of φ described by Equation 1:

[0051]

[0052] Some of the processes described above are explained in relation to computer software and hardware. The described techniques may constitute machine-executable instructions implemented within a tangible or non-transient machine (e.g., computer)-readable storage medium, and when executed by a machine, the instructions will cause the machine to perform the described operations. Additionally, the processes may be implemented within hardware such as application-specific integrated circuits ("ASICs") or others.

[0053] A tangible machine-readable storage medium comprises any mechanism that provides (i.e., stores) information in a non-transient form accessible by a machine (e.g., a computer, a network device, a personal digital assistant, a manufacturing tool, any device having a set of one or more processors, etc.). For example, a machine-readable storage medium includes writable / non-writable media (e.g., read-only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, etc.).

[0054] The foregoing description of the exemplified embodiments of the invention, including those described in the abstract, is not intended to be comprehensive or to limit the invention to the exact forms disclosed. While specific embodiments and examples of the invention are described herein for illustrative purposes, as recognized by those skilled in the art, various modifications are possible within the scope of the invention.

[0055] Such modifications may be made to the present invention in consideration of the foregoing description. The terms used in the following claims should not be interpreted as limiting the present invention to the specific embodiments disclosed in the specification. Rather, the scope of the present invention should be determined entirely by the following claims, which should be interpreted in accordance with established principles for interpreting claims.

Claims

Claim 1 An optical modulator comprising: a modulation region comprising a non-uniform arrangement of two or more different materials having different refractive indices; an input port optically coupled to the modulation region for injecting an optical carrier into the modulation region; an output port optically coupled to the modulation region for receiving and emitting a modulated signal having a high state and a low state; a sink port optically coupled to the modulation region; a modulation actuator disposed in proximity to the modulation region and adapted to apply a modulation bias to the modulation region that affects the different refractive indices of the non-uniform arrangement to selectively steer a portion of the optical power of the optical carrier to the sink port when the modulated signal is modulated to the low state; an optical receiver optically coupled to the sink port to harvest a portion of the optical power rejected from the modulation region during the low state of the modulated signal; and a modulation controller coupled to the modulation actuator—the modulation controller being at least partially powered by the portion of the optical power rejected from the modulation region. Claim 2 An optical modulator according to claim 1, wherein the non-uniform arrangement comprises a pattern of discrete regions of a core material and a cladding material for forming the input, output, and sink ports. Claim 3 An optical modulator according to claim 1, wherein the two or more different materials include a semiconductor material and an oxide material. Claim 4 An optical modulator according to claim 1, wherein the non-uniform arrangement comprises a pattern of discrete regions of the different materials, and the pattern is selected based on the iterative minimization of a loss function defined as the sum of the transmission loss of the output port, the reflection loss of the input port, and the sink loss of the sink port. Claim 5 An optical modulator according to claim 1, wherein the modulation actuator comprises one of: 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 an electromechanical actuator adapted to apply the modulation bias as an adjustable pressure across the modulation region. Claim 6 delete Claim 7 delete Claim 8 An optical modulator according to claim 1, wherein the input port, the output port, and the sink port all include waveguide sections physically adjacent to the modulation region. Claim 9 An optical modulator according to claim 8, wherein the waveguide sections of the input port and the output port are aligned parallel to each other, and the waveguide section of the sink port is aligned perpendicularly to the waveguide sections of the input and output ports. Claim 10 An optical modulator according to claim 8, wherein the waveguide sections of the input, output and sink ports are all aligned parallel to each other, and the output and sink ports are positioned on opposite sides of the modulation region as the input ports. Claim 11 An optical modulator according to claim 8, wherein the waveguide sections of the sink port and the output port are all perpendicular to the waveguide section of the input port. Claim 12 In claim 8, the above-mentioned sink port includes a first sink port, and the above-mentioned optical modulator further includes a second sink port optically coupled to the modulation region. Claim 13 A method of operation of an optical modulator, comprising: receiving an optical carrier from an input port optically coupled to the modulation region in a modulation region, wherein the modulation region comprises a non-uniform arrangement of two or more different materials having different refractive indices; modulating a modulation bias applied to the modulation region based on a data signal to generate a modulated signal at an output port optically coupled to the modulation region, wherein the modulation bias affects the different refractive indices of the non-uniform arrangement to selectively steer the optical power of the optical carrier between the output port and a sink port optically coupled to the modulation region; directing a first majority of the optical power of the optical carrier to the output port when the modulated signal is modulated to an ON state based on a first logic state of the data signal; directing a second majority of the optical power of the optical carrier to the sink port when the modulated signal is modulated to an OFF state based on a second logic state of the data signal; and using an optical receiver optically coupled to the sink port, the optical power directed to the sink port A method comprising: a step of harvesting at least a second majority of the optical power of an optical carrier; and a step of supplying power to an electronic circuit with the second majority of the optical power harvested from the optical carrier during the off state. Claim 14 delete Claim 15 In claim 13, the step of supplying power to the electronic circuit comprises the step of supplying power at least partially to a modulation controller that controls the modulation bias applied to the modulation region. Claim 16 In claim 13, the method comprises, wherein the above-mentioned non-uniform arrangement comprises a pattern of discrete regions of a core material and a cladding material for forming the input, output, and sink ports. Claim 17 A method according to claim 13, wherein the non-uniform arrangement comprises a pattern of discrete regions of the different materials, and the pattern is selected based on iterative minimizations of a loss function defined as the sum of the transmission loss of the output port, the reflection loss of the input port, and the sink loss of the sink port. Claim 18 In claim 17, the pattern of the discrete regions is determined during the inverse design of the optical modulator using the loss function to seed the accompanying simulations of the optical modulator for each of the iterative minimizations. Claim 19 In claim 13, the step of modulating the modulation bias applied to the modulation region comprises one of the steps of: applying an adjustable voltage across the modulation region; heating the modulation region; or applying an adjustable pressure to the modulation region. Claim 20 A method according to claim 13, wherein the input port, the output port and the sink port all comprise waveguide sections physically adjacent to the modulation region. Claim 21 In claim 13, the step of diverting a second majority of the optical power of the optical carrier to the sink port when the modulated signal is modulated to the off state comprises the step of directing a second majority of the optical power of the optical carrier to a plurality of sink ports including the sink port.

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