Optical modulator with sink waveguide

Abstract

The goal is to improve energy efficiency. [Solution] The optical modulator includes a modulation region, an input port, an output port, a sink port, and a modulation actuator. The modulation region includes a heterogeneous arrangement of two or more different materials having different refractive indices. The input port is optically coupled to the modulation region for injecting an optical carrier wave into the modulation region. The output port is optically coupled to the modulation region for receiving and emitting a modulated signal having a high state and a low state. The sink port is optically coupled to the modulation region. The modulation actuator is disposed proximate to the modulation region and is adapted to apply a modulation bias to the modulation region that affects the different refractive indices of the heterogeneous arrangement to selectively direct a portion of the optical power of the optical carrier wave to the sink port when the modulated signal is modulated to a low state.

Description

[Technical Field]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This application claims priority to U.S. Patent Application No. 17 / 884,970, filed August 10, 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] 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 varying a voltage that adjusts the refractive index of a material in a region of the integrated device electro-optically, thermo-optically, or mechanically. When the bias is modulated at high speeds (GHz rates), information and data can be encoded and transmitted via an optical carrier wave 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 1] FIG. 1 illustrates an optical modulator with a sink waveguide for power recycling, according to one embodiment of the present disclosure. [Figure 2A] FIG. 1 illustrates a loss function for the inverse design of an optical modulator, according to one embodiment of the present disclosure. [Figure 2B] FIG. 10 illustrates how the sink loss function can be modified to not penalize transmission to the sink port during the ON state of the optical modulator while still obtaining acceptable operating efficiency of the optical modulator, according to one embodiment of the present disclosure. [Figure 3] 10 includes a chart illustrating iterative inverse design of a modulation region using a loss function, according to one embodiment of the present disclosure. [Figure 4] 1 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. [Figure 5A] FIG. 1 illustrates an optical modulator with input, output, and sink ports oriented parallel to one another, according to one embodiment of the present disclosure. [Figure 5B] FIG. 1 illustrates an optical modulator having an input port oriented perpendicular to the sink port and output port, according to one embodiment of the present disclosure. [Figure 5C] FIG. 1 illustrates an optical modulator having two sink ports, 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 for operational and adjoint simulations used in the inverse design of 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, and methods of operation for an inverse-design optical modulator with a waveguide sink capable of providing power recycling 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] Throughout this specification, the references 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] During operation of conventional optical modulators, a significant portion of the optical carrier wave is wasted. For example, in conventional ON-OFF keying modulation schemes, the optical power of the optical carrier may be rejected or wasted during the OFF logic state. This wasted energy not only reduces the efficiency of these conventional optical modulators, but also causes heat buildup within the optical modulator that must be dissipated. Therefore, conventional optical modulators may be designed with a larger bulk substrate thermally coupled to a heat sink to properly reject and manage the wasted power.

[0009] The embodiments described herein use inverse design techniques to design the modulation region of an optical modulator to eliminate or recycle wasted optical power by diverting it to a sink port or sink waveguide, which then directs the optical power away from the modulator and prevents harmful heat buildup. This technique keeps the power within the optical region, allowing it to be guided away from the optical modulator rather than dissipating it as thermal energy within the optical modulator. Keeping rejected power within the optical region not only enables the creation of smaller, more compact optical modulators, but also provides the opportunity to create more efficient optical modulators. In particular, the carrier optical power that is rejected during the optical modulator's logic LOW or logic OFF coding state is efficiently guided away from the modulation region via the sink port and sink waveguide. In various embodiments, this optical power is then collected using an integrated optical receiver (e.g., a photovoltaic or photoelectric device). For example, a photodiode or photovoltaic cell can convert this rejected optical power to power other circuitry or to power a modulation controller (e.g., modulation driver) in the optical modulator itself. The embodiments described herein not only facilitate smaller optical modulators that are less reliant on heat sinks, but also more energy efficient optical modulators.

[0010] 1 shows an optical modulator 100 with a sink port / waveguide for power recycling according to one embodiment of the present disclosure. The illustrated embodiment of 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, power conditioning circuitry 135, a modulation controller 140, and other circuitry 145. The illustrated embodiment of the modulation region includes a non-uniform arrangement of two different materials 107 and 108 having different refractive indices.

[0011] The modulation region 105 is sometimes referred to as the "design region" or "active region," in which a pattern of discrete regions of materials 107 and 108, under the influence of modulation actuator 125, operates to selectively direct an inbound optical carrier wave 150 received through input port 110, via refraction / scattering, to either output port 115 or sink port 120. This selective directing implements 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 to sink port 120 during an OFF or LOW logic state. In this manner, a data signal 160 is modulated onto the optical carrier wave 150, generating the modulated wave 155.

[0012] Materials 107 and 108 are discrete regions of material having different refractive indices that change in response to a bias (e.g., an applied voltage, current, temperature, pressure). In one embodiment, materials 107 and 108 may be a waveguide core material and a waveguide cladding material, respectively. The core and cladding materials may be the same core and cladding materials used to form the waveguide sections of input port 110, output port 115, and sink port 120. For example, material 107 may be silicon and material 108 may be silicon dioxide. In yet other embodiments, materials 107 and 108 may be implemented as discrete regions of intrinsic and doped silicon, discrete regions of differentially 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 um by 1.2 um, and the ports 110, 115, and 120 are waveguide sections 200 nm wide and 600 nm long. The discrete regions of materials 107 and 108 may be implemented as a collection of each material type 107 or 108 in incremental pixel / voxel sizes of 5 nm by 5 nm. Of course, other pixel / voxel resolutions may be achieved.

[0013] Modulation is achieved via a modulation bias applied to modulation region 105 via modulation actuator 125, which is driven by modulation controller 140 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. 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 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, modulation actuator 125 includes an electromechanical actuator (e.g., piezoelectric crystal, microelectromechanical system, etc.) surrounding modulation region 105, and the modulation bias is an adjustable pressure. Each of these modulation biases acts to change the refractive index of materials 107 and 108, which in turn affects the scattering / refraction of optical carrier 150 for selectively directing it between output port 115 and sink port 120.

[0014] In the illustrated embodiment, input port 110, output port 115, and sink port 120 are adjacent to modulation region 105 and each operate as an optical input or output for propagating a wave. Although input port 110, output port 115, and sink port 120 are referred to as "ports," these ports may include longitudinal lengths in the direction of light propagation. Thus, input port 110, output port 115, and sink 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, sink port 120, and modulation region 105 are all planar waveguide sections. These planar waveguide sections may be embedded within semiconductor materials, such as silicon-on-insulator (SOI) systems, photonic integrated circuits (PICs), and the like.

[0015] 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 output port 115, a reflection loss function 215 at input port 110, and a sink loss function 220 at sink port 120. The inverse design technique can consider the layout of an optical modulator, such as optical modulator 100, which is comprised of input port 110, modulation (design) region 105, output port 115, and 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 using the same overall topology but with different perturbations to the refractive index dn = [dn1, dn2, dn3, ...] in one of materials 107 or 108. These parallel simulations then calculate the transmission of light from input port 110 to output port 115 as a function of the refractive index perturbation T(dn).

[0016] The optimization objective of the inverse design methodology is constructed as a function of this transmission L(T(dn)) and is designed to optimize for the desired T(dn). The objective is constructed so that the resulting structure / pattern can direct light through the sink port 120 when low or off transmission at the output port 115 is desired. This allows control over power that would otherwise be lost. This power can be further reused by other components associated with the optical modulator 100 (e.g., modulation controller 140 or other circuitry 145) without detrimentally affecting the optical modulator 100.

[0017] Inverse design operates using a design simulator (also known as 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 for electromagnetics). The output of the forward operational simulation is a simulated field response at the output port 115 and the sink port 120. Specific performance parameters of this output field response may 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 the loss function 205 to calculate a performance loss value, 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 allows for 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 of the modulation region 105 (e.g., the topology or pattern of materials 107 and 108). 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 (called saturation). The above descriptions are merely exemplary inverse design techniques 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.

[0018] 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 power at each port for a given logic state of the optical modulator 100 using loss function 205. Referring to FIG. 2A, loss function 205 is a function of x, where x is a vector representing the structural pattern of materials 107 and 108 having different refractive indices. Transmission loss function 210 is defined by the transmitted power T at output port 115 for the ON and OFF logic states. Similarly, reflection loss function 215 is defined by the reflected power R at input port 110 for the ON and OFF logic states, and sink loss function 220 is defined by the power S at sink port 120 for the ON and OFF logic states. FIG. 2B shows an alternative sink loss function 225 that omits a term that penalizes the power S at sink port 120 during the ON logic state of the optical modulator 100.

[0019] FIG. 3 includes a chart illustrating the iterative inverse design of the modulation region 105 using the loss function 205, according to one embodiment of the present disclosure. Chart 305 shows how the loss function 205 saturates to a minimum after approximately 140 forward and adjoint simulations. Chart 310 shows how the transmitted power T at the output port 115 saturates near 0.7 for logic ON at three different wavelengths (e.g., 1545 nm, 1550 nm, and 1555 nm) and near 0.1 for logic OFF at these same wavelengths. Chart 315 shows how the reflected power R at the input port 110 saturates below 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 therefore undesirable. Chart 320 shows how the sink power S at sink port 120 saturates near 0.7 for logic OFF at three different wavelengths (e.g., 1545 nm, 1550 nm, and 1555 nm), and saturates near 0.1 for logic ON over those same wavelengths.

[0020] Returning to FIG. 1 , the sink port 120 is optically coupled to the optical receiver 130 to receive the optical power rejected during the logical OFF / LOW state of the optical modulator 100. Instead of being wasted and converted to heat, this rejected optical power can be converted into electrical power via the optical receiver 130. The optical receiver 130 may be implemented using optoelectric or photovoltaic devices such as photodiodes, photocells, etc. The pulsed current is then rectified or regulated in a power conditioning circuit 135. The power conditioning circuit 135 may include a rectifier (e.g., a diode), a storage capacitor, and / or other conventional conditioning circuitry. The regulated power may then be coupled to the power modulation controller 140 itself and / or other circuitry 145, which may be embedded on-chip with the optical modulator 100.

[0021] 4 is a flowchart illustrating a process 400 of operation of the 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, 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.

[0022] In process block 405, an optical carrier wave 150 is received at modulation region 105 via input port 110. 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 input port 110. The laser source may be an on-chip device integrated into the PIC with optical modulator 100, or a separate off-chip device whose output is directed to input port 110.

[0023] At process block 410, optical carrier wave 150 is modulated within modulation region 105 in response to a modulation bias applied by modulation actuator 125. Modulation actuator 125 drives the modulation bias based on a data signal 160 received at modulation controller 140. In the illustrated embodiment, modulation region 105 includes a non-uniform arrangement of materials 107 and 108, each having a different refractive index, that disperse (e.g., scatter, refract) optical carrier wave 150 in a controlled manner so that either a majority of the optical power of optical carrier wave 150 is directed / directed to output port 115 in an ON or HIGH logic state (process block 415), or a majority of the optical power is directed / directed to sink port 120 in an OFF or LOW logic state (process block 420). Of course, the logic state is determined by the modulation bias applied across modulation region 105 in response to data signal 160.

[0024] The modulation bias affects the power induction, and therefore 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. Collectively, the discrete regions of materials 107 or 108 form a pattern or non-uniform arrangement, representing binary contiguous blocks (uniform regions) of either material 107 or 108 with a uniform refractive index. Application of the modulation bias across the non-uniform arrangement induces small changes in the refractive index of each contiguous block of material 107 / 108, inducing optical power at the output port 115 or the sink port 120, depending on the modulation bias. As previously mentioned, materials 107 and 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 materials 107 and 108 within the modulation region 105 can be determined through inverse design using forward and adjoint simulations that attempt to minimize the loss function 205 presented above. Of course, other design techniques and loss functions may be implemented to arrive at a pattern or non-uniform arrangement of materials 107 and 108 depending on the needs of a particular application of light modulator 100 .

[0025] Finally, in process block 425, optical power rejected or directed to sink port 120 during the logic low or off state is directed to optical receiver 130, where it is recycled or collected for beneficial use (as opposed to being wasted in the form of heat and conducted through a heat sink). Beneficial use may include powering modulation controller 140 itself or other circuitry 145.

[0026] 5A-5C show three exemplary floorplan deviations from optical modulator 100, according to embodiments of the present disclosure. FIG. 1 shows optical modulator 100 in which the waveguide sections of input port 110 and output port 115 are parallel to each other and located on opposite sides of modulation region 105 from each other, while the waveguide section of sink port 120 is oriented perpendicular to the waveguide sections of input port 110 and output port 115. In contrast, FIG. 5A shows optical modulator 500 in which the waveguide sections of input port 110, output port 115A, and sink port 115A are all aligned parallel to each other, and output port 115A and sink port 120A are located on a common side of modulation region 105A, opposite input port 110. FIG. 5B shows optical modulator 501 in which the waveguide sections of sink port 120 and output port 115B are both perpendicular to the waveguide section of input port 110. Finally, FIG. 5C illustrates another exemplary optical modulator 502 having two sink ports 120B and 120C, both of which are perpendicular to the input port 110 and the output port 115C. It should be understood that the floorplan modifications illustrated in FIGS. 5A-5C are not exhaustive. Other floorplan modifications may include diagonally oriented ports, ports of different cross-sectional sizes, etc. Modulation regions 105A, B, and C may all be designed using the same inverse design methodology described herein.

[0027] 6A-6C illustrate the initialization, operational simulation, and adjoint simulation of a simulated environment 601 for optimizing structural parameters of a physical device (e.g., optical modulators 100, 500, 501, or 502) having a design model, according to one 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. While the simulated environment is depicted in two dimensions as shown in FIGS. 6A-6C, 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 depicted in FIGS. 6A-6C can be achieved via simulation (e.g., time forward and backward propagation) utilizing finite-difference time-domain (FDTD) methods to model field responses (e.g., both electric and magnetic), among other things.

[0028] FIG. 6A shows an example rendering of a simulated environment 601-A illustrating 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 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., 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 (e.g., field response) within the simulated environment 601 (and the physical device) may change in response to the excitation source 615. Before an operational simulation begins, a specific configuration (i.e., an 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.

[0029] 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 .

[0030] 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 operating at a frequency of interest and having a particular waveguide mode (e.g., transverse electromagnetic mode (TEM) mode, transverse electric mode (TE) mode), and the excitation source is at input port 110. The operational simulation occurs over multiple time steps, including the illustrated time step (see FIG. 3 ). 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.

[0031] When performing an operational simulation, a performance loss function (e.g., T Loss , R Loss , and S Loss ) may be calculated at each port 615, 620, and 625 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.

[0032] 5C 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 sink 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).

[0033] 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 the forward motion simulation 710 and backpropagation 750 of the 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, the time-dependent Maxwell's equations (partial differential 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 of FIGS. 6A-6C ) over multiple time steps.

[0034] 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 simulation environment and / or physical devices that collectively correspond to field responses. More specifically, update operations (e.g., 712, 714, and 716) are iterative and based on the field responses, 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 field values ​​713 (e.g., see FIG. 6B ) based on the field responses determined from the previous update operation 712, sources 708, and structural parameters 704. Similarly, update operation 716 updates field values ​​715 (see, e.g., FIG. 7B ) 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 motion simulation 710 has been executed, loss values ​​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 structural gradient 768.

[0035] 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 for i=1,...,n

[0036]

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[0037] Using the FDTD method, the update operation is specifically described as follows:

[0038]

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[0039] That is, the FDTD update is linear in the field and source terms. Specifically,

[0040]

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[0041]

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[0042] In terms of modifying or otherwise optimizing the structural parameters of an electromagnetic device, the relevant quantities to be generated are:

[0043]

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[0044] 7B is a chart 780 illustrating the relationship between update operations for a motion simulation and adjoint simulation (e.g., backpropagation), according to one embodiment of the present disclosure. More specifically, FIG. 7B summarizes the relationship between motion simulation and adjoint simulation with the calculation of structural gradients, and the structural gradients

[0045]

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[0050]

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[0055]

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[0058] For completeness, the first complete form of the sum

[0059]

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[0061] Based on the definition of φ as explained by Eq. (1),

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[0064] The adjoint update is the backpropagation of the loss gradient from later time steps to earlier time steps,

[0065]

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[0067] 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 the 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

[0068] 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.).

[0069] 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.

[0070] 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 should 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; 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 proximate 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 direct 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 modulator comprising:

2. The optical modulator of claim 1 , wherein the non-uniform arrangement comprises a pattern of discrete regions of core and cladding material to form the input port, the output port, and the sink port.

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

4. 2. The optical modulator of claim 1, wherein the non-uniform arrangement comprises a pattern of discrete regions of the different materials, the pattern being selected based on 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.

5. The modulation actuator is an electrode adapted to apply the modulation bias across the modulation region as an adjustable voltage; a heating element adapted to apply the modulation bias across the modulation region as an adjustable temperature; or an electromechanical actuator adapted to apply the modulation bias as an adjustable pressure across the modulation region; including one of the following:

2. The optical modulator according to claim 1.

6. 2. The optical modulator of claim 1, further comprising an optical receiver optically coupled to the sink port to collect the portion of the optical power rejected from the modulation region during the LOW state of the modulated signal.

7. 7. The optical modulator of claim 6, further comprising: 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.

8. The optical modulator of claim 1 , wherein the input port, the output port, and the sink port all comprise waveguide sections physically adjacent to the modulation region.

9. 9. The optical modulator of claim 8, wherein the waveguide sections of the input port and the output port are aligned parallel to one another and the waveguide section of the sink port is aligned perpendicular to the waveguide sections of the input port and the output port.

10. 9. The optical modulator of claim 8, wherein the waveguide sections of the input port, the output port, and the sink port are all aligned parallel to one another, and the output port and the sink port are positioned on opposite sides of the modulation region as the input port.

11. 9. The optical modulator of claim 8, wherein the waveguide sections of the sink port and the output port are both perpendicular to the waveguide section of the input port.

12. The sink port includes a first sink port, and the optical modulator includes: The optical modulator of claim 8 further comprising a second sink port optically coupled to the modulation region.

13. 1. A method of operating an optical modulator, comprising: receiving an optical carrier wave in a modulation region from an input port optically coupled to the modulation region, the modulation region comprising 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, the modulation bias affecting the different refractive indices of the non-uniform arrangement to selectively steer 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; diverting 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; A method comprising:

14. collecting, with an optical receiver optically coupled to the sink port, at least a portion of the second majority of the optical power of the optical carrier diverted to the sink port; powering electronic circuitry using the portion of the second majority of the optical power harvested from the optical carrier during the OFF state; and The method of claim 13 further comprising:

15. 15. The method of claim 14, wherein powering the electronic circuitry comprises at least partially powering a modulation controller that controls the modulation bias applied to the modulation region.

16. The method of claim 13 , wherein the non-uniform arrangement comprises a pattern of discrete regions of core material and cladding material to form the input port, the output port, and the sink port.

17. 14. The method of claim 13, wherein the non-uniform arrangement comprises a pattern of discrete regions of the different materials, the pattern being selected based on iterative minimization of a loss function defined as the sum of a transmission loss at the output port, a reflection loss at the input port, and a sink loss at the sink port.

18. 18. The method of claim 17, wherein the pattern of discrete regions is determined during inverse design of the optical modulator using the loss function to seed an adjoint simulation of the optical modulator for each of the iterative minimizations.

19. modulating the modulation bias applied to the modulation region; applying an adjustable voltage across the modulation region; heating the modulation region; or applying an adjustable pressure to the modulation region; 14. The method of claim 13, comprising one of:

20. The method of claim 13 , wherein the input port, the output port, and the sink port all comprise waveguide sections physically adjacent to the modulation region.

21. 14. The method of claim 13, wherein diverting the 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 directing the second majority of the optical power of the optical carrier to a plurality of sink ports including the sink port.

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