Optical modulator with sink waveguide

Abstract

An optical modulator includes a modulation region, an input port, an output port, and a sink port, and a modulation actuator. The modulation region includes a non-uniform arrangement of two or more different materials having different refractive indices. The input port is optically coupled to the modulation region to inject an optical carrier into the modulation region. The output port is optically coupled to the modulation region to receive and transmit a modulated signal having a high state and a low state. The sink port is optically coupled to the modulation region. A modulation actuator is disposed adjacent to the modulation region and adapted to apply modulation biases to the modulation region that affect 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 modulation signal is modulated to a low state.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of U.S. patent application Ser. No. 17 / 884,970, filed on Aug. 10, 2022, the contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates generally to photonic devices and, in particular, to optical modulators. Background Art

[0004] Optical modulators are active components that allow the user to modulate the power level of an optical signal via an applied bias. The bias is typically achieved by varying a voltage that tunes the refractive index of the material in some area of ​​the integrated device in an optoelectronic, thermo-optical, or mechano-optical manner. When the bias is modulated at high speeds (GHz rates), information and data can be encoded and sent to a remote receiver via an optical carrier.

[0005] Typical modulators are designed by humans using well-understood components (e.g., a combination 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" with which their performance can be improved and tuned. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following drawings, wherein like reference numerals indicate like parts throughout the various views unless otherwise indicated. Not all instances of an element must be labeled so as not to clutter the drawings where appropriate. The drawings are not necessarily drawn to scale, with emphasis instead placed on illustrating the principles being described.

[0007] Figure 1 An optical modulator with a sink waveguide for power recycling is shown according to an embodiment of the present disclosure.

[0008] Figure 2A A loss function for inverse design of an optical modulator according to an embodiment of the present disclosure is shown.

[0009] Figure 2B It is shown how the sink loss function may be altered in accordance with an embodiment of the present disclosure so as not to penalize transmission into the sink port during the ON state of the optical modulator, while still obtaining acceptable operating efficiency of the optical modulator.

[0010] Figure 3 Included are graphs showing iterative inverse design of modulation regions using a loss function according to an embodiment of the present disclosure.

[0011] Figure 4 is a flow chart illustrating the operation of an optical modulator with a sink waveguide for power recycling according to an embodiment of the present disclosure.

[0012] Figure 5A An optical modulator having input ports, output ports, and sink ports oriented parallel to each other is shown according to an embodiment of the present disclosure.

[0013] Figure 5B An optical modulator with an input port oriented perpendicular to the sink and output ports is shown in accordance with an embodiment of the present disclosure.

[0014] Figure 5C An optical modulator with two sink ports is shown according to an embodiment of the present disclosure.

[0015] Fig. 6A A demonstrative simulation environment for simulating the operation of a physical device according to an embodiment of the present disclosure is shown.

[0016] Figure 6B An operational simulation of a physical device according to an embodiment of the present disclosure is shown.

[0017] Figure 6C An adjoint simulation (back-propagation) of performance loss errors through a simulated environment is shown in accordance with an embodiment of the present disclosure.

[0018] Fig. 7A is a flow chart illustrating example time steps of operation and accompanying simulations for inverse designing an optical modulator according to an embodiment of the present disclosure.

[0019] Figure 7B is a flowchart showing the relationship between operation simulation and adjoint simulation (back propagation) according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0020] Embodiments of systems, devices, and methods of operation for an inversely designed 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 relevant 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.

[0021] References throughout this specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the phrases "in one embodiment" or "in an embodiment" appearing 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.

[0022] During the operation of conventional optical modulators, a large portion of the optical carrier is wasted. For example, conventional on-off keying modulation schemes may 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 creates heat accumulation within the optical modulator that needs to be dissipated. Thus, conventional optical modulators may be designed with a larger bulk substrate, where the larger bulk substrate is thermally coupled to a heat sink to adequately reject and manage the wasted power.

[0023] The embodiments described herein use inverse design techniques to design the modulation region of an optical modulator to reject or recycle wasted optical power by transferring the wasted optical power to a sink port or sink waveguide, where the sink port or sink waveguide can then take the optical power away from the modulator to prevent harmful heat accumulation. This technology keeps the power in the optical domain so that the power can be directed away from the optical modulator instead of being dissipated as heat within the optical modulator. Keeping the rejected power in the optical domain 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 optical power of the carrier rejected during the logic low or logic off coding state of the optical modulator is effectively directed out of the modulation region via the sink port and the sink waveguide. In various embodiments, the optical power is then collected using an integrated optical receiver (e.g., a photovoltaic or optoelectronic device, etc.). For example, a photodiode or photovoltaic cell can convert the 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 not only promote more compact optical modulators that are less dependent on heat sinks, but also promote more energy-efficient optical modulators.

[0024] Figure 1 An optical modulator 100 with a sink port / waveguide for power recycling according to an embodiment of the present disclosure is shown. The 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 conditioning circuit 135, a modulation controller 140, and other circuits 145. The illustrated embodiment of the modulation region includes a non-uniform arrangement of two different materials 107 and 108 having different refractive indices.

[0025] The modulation region 105 may also be referred to as a “designed region” or “active region” where the pattern of discrete regions of material 107 and 108 operates to selectively direct an inbound optical carrier 150 received via input port 110 to either output port 115 or sink port 120 via refraction / scattering under the influence of modulation actuator 125. This selective directing implements an on-off keying modulation scheme where optical power is primarily diverted to output port 115 during an on or high logic state of the modulation wave 155 or primarily diverted to sink port 120 during an off or low logic state of the modulation wave 155. In this manner, data signal 160 is modulated onto optical carrier 150 to generate modulated wave 155.

[0026] Materials 107 and 108 are discrete regions of materials having different refractive indices, whose refractive indices change in response to a bias (e.g., 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 segments 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 other embodiments, materials 107 and 108 may be implemented as discrete regions of intrinsic silicon and doped silicon, discrete regions of differently doped silicon, or may be a combination of other types of semiconductor materials (e.g., III-V semiconductor materials, etc.). In one embodiment, modulation region 105 is approximately 1.5um×1.2um, and ports 110, 115, and 120 are waveguide segments having a width of 200nm and a length of 600nm. Discrete regions of material 107 and 108 may be realized as aggregates of each material type 107 or 108 in incremental pixel / voxel sizes of 5 nm x 5 nm. Of course, other pixel / voxel resolutions may be realized.

[0027] Modulation is achieved via a modulation bias, which is applied to the modulation area 105 via a modulation actuator 125, which in turn is driven by a modulation controller 140 in response to a data signal 160. Thus, the modulation controller 140 may include a modulation / demodulation circuit and a driver circuit for driving the modulation actuator 125. The modulation actuator 125 may be implemented using several technologies. In one embodiment, the modulation actuator 125 includes electrodes surrounding the sides of the modulation area 105, and the modulation bias is an applied voltage and / or an injected current. In another embodiment, the modulation actuator 125 includes one or more heating elements surrounding the modulation area 105, and the modulation bias is an adjustable temperature. In yet another embodiment, the modulation actuator 125 includes an electromechanical actuator (e.g., a piezoelectric crystal, a micro-electromechanical system, etc.) surrounding the modulation area 105, and the modulation bias is an adjustable pressure. Each of these modulation biases is used to change the refractive index of materials 107 and 108 , thereby affecting the scattering / refraction of optical carrier 150 to be selectively directed between output port 115 and sink port 120 .

[0028] In the illustrated embodiment, the input port 110, the output port 115, and the sink port 120 are all adjacent to the modulation region 105 and operate as optical inputs or outputs for propagating waves. Although the input port 110, the output port 115, and the sink port 120 are referred to as "ports", these ports may include a longitudinal length in the direction of light propagation. In this way, the input port 110, the output port 115, and the sink port 120 can be implemented as a waveguide segment having a core and a cladding that is physically adjacent to or otherwise optically coupled to the modulation region 105 at one end, and the input port 110, the output port 115, the sink port 120, and the modulation region 105 are all planar waveguide segments. These planar waveguide segments can be embedded in semiconductor materials such as silicon on insulator (SOI) systems, photonic integrated circuits (PICs), etc.

[0029] The non-uniform arrangement of materials 107 and 108 forms a loss function 205 (see Figure 2A), where the loss function 205 is defined as the sum of the transmission loss function 210 at the output port 115, the reflection loss function 215 at the input port 110, and the sink loss function 220 at the sink port 120. The inverse design technique may consider a layout of an optical modulator (such as the optical modulator 100) constructed with the input port 110, the modulation (design) region 105, the output port 115, and the 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 the materials 107 or 108. Thus, these parallel simulations calculate the light transmission from the input port 110 to the output port 115 as a function of the refractive index perturbation T(dn).

[0030] The optimization objective of the inverse design method is constructed as a function of this transmission, L(T(dn)), and is designed to optimize for a desired T(dn). The objective is constructed in such a way that the resulting structure / pattern is able to direct light through the sink port 120 when the transmission in the desired output port 115 is low or off. This enables control of power that would otherwise be lost. This power can be further recycled by other components accompanying the optical modulator 100 (e.g., the modulation controller 140 or other circuits 145) without adversely affecting the optical modulator 100.

[0031] Inverse design is operated using a design simulator (also known as a design model) configured with an initial design or pattern for the 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. The specific performance parameters of the 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 the loss function 205 to calculate a performance loss value, which can be a scalar value (e.g., the mean square error between the simulated performance value and the target performance value). The distinguishable nature of the design model enables back propagation via an adjoint simulation of a performance loss error, which is the difference between a simulated output value and an expected / target performance value. The performance loss error (e.g., a loss gradient) is back propagated through the design model during the adjoint simulation to generate a structural design error at the input port 110. Back propagation of the performance loss errors facilitates the calculation of additional performance gradients, such as structural gradients representing 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, which can then be used by a structural optimizer to perform an iterative gradient descent (e.g., stochastic gradient descent) that optimizes or refines the initial structural design to generate a revised structural design for the modulation region 105. The forward and reverse simulations can then be iterated until the performance loss values ​​fall within acceptable design criteria (referred to as saturation). The above description is merely an example inverse design technique that can be used to refine or optimize the features and topology of the optical modulator 100. It will be appreciated that other inverse design techniques may also be implemented alone or in combination with other conventional design techniques.

[0032] The inverse design techniques described above may be applied to determine the specific material combinations, feature sizes, and feature arrangements (ie, patterns) to achieve the desired power at each port for a given logic state of the optical modulator 100 using the loss function 205. Figure 2A , the loss function 205 is a function of x, where x is a vector representing the structural pattern of the materials 107 and 108 having different refractive indices. The transmission loss function 210 is defined by the transmitted power T at the output port 115 for the on and off logic states. Similarly, the reflection loss function 215 is defined by the reflected 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. Figure 2B An alternative sink penalty function 225 is shown that omits the term that penalizes the power S at the sink port 120 during the ON logic state of the optical modulator 100 .

[0033] Figure 3 Included are graphs showing iterative inverse design of modulation region 105 using loss function 205 according to embodiments of the present disclosure. Graph 305 shows how loss function 205 saturates to a minimum after approximately 140 forward and adjoint simulations. Graph 310 shows how the transmitted power T at output port 115 saturates around 0.7 for logic on at three different wavelengths (e.g., 1545nm, 1550nm, and 1555nm) and saturates around 0.1 for logic off at those same wavelengths. Graph 315 shows how the reflected power R at input port 110 saturates to below 0.035 for both logic on and logic off at three wavelengths (e.g., 1545nm, 1550nm, and 1555nm). The reflected power R at input port 110 is wasted power and is therefore undesirable. Graph 320 shows how the sink power S at the sink port 120 saturates around 0.7 for logic off at three different wavelengths (eg, 1545 nm, 1550 nm, and 1555 nm), and saturates at close to 0.1 for logic on across those same wavelengths.

[0034] Return to Figure 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. This rejected optical power can be converted into electrical power via the optical receiver 130, rather than being wasted and converted into heat. The optical receiver 130 can be implemented using an optoelectronic device or photovoltaic device (such as a photodiode, a photocell, or other device). The pulsed current is then rectified or otherwise regulated using 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. The regulated power can then be coupled to the power modulation controller 140 itself and / or other circuits 145 that may also be embedded on the chip with the optical modulator 100.

[0035] Figure 4 4 is a flow chart illustrating a process 400 of the operation of the optical modulator 100 according to an embodiment of the present disclosure. The order in which some or all of the process blocks appear in the process 400 should not be considered limiting. Rather, one of ordinary skill in the art having the benefit of the present disclosure will appreciate that some of the process blocks may be performed in various orders not shown, or even in parallel.

[0036] In process block 405, an optical carrier 150 is received at the modulation region 105 via 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 directed 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 the PIC with the optical modulator 100, or a different off-chip device whose output is directed to the input port 110.

[0037] In process block 410, the optical carrier 150 is modulated within the modulation region 105 in response to a modulation bias applied by the modulation actuator 125. The modulation actuator 125 drives the modulation bias based on the data signal 160 received at the modulation controller 140. In the illustrated embodiment, the modulation region 105 includes a non-uniform arrangement of materials 107 and 108, each having a different refractive index, which disperses (e.g., scatters, refracts) the optical carrier 150 in a controlled manner such that a majority of the optical power of the optical carrier 150 is directed / directed to the output port 115 in an on or high logic state (process block 415), or a majority of the optical power is directed / directed to the 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 the modulation region 105 in response to the data signal 160.

[0038] The modulation bias affects the power guidance and thus affects the logic state encoded on the optical carrier 150 at the output port 115 by causing a small change in the refractive index of the materials 107 and 108. Each discrete region of the materials 107 or 108 that together form a pattern or non-uniform arrangement represents a binary continuous block (uniform region) of the material 107 or 108 having a uniform refractive index. Applying the modulation bias across the entire non-uniform arrangement causes a small change in the refractive index of each continuous block of the material 107 / 108, which guides the optical power to the output port 115 or the sink port 120 depending on the modulation bias. As previously mentioned, the materials 107 and 108 can be implemented as discrete regions of two different materials (such as silicon and silicon oxide), but other material combinations can also be used. The overall pattern or non-uniform arrangement of the materials 107 and 108 within the modulation region 105 can be determined via inverse design using forward and adjoint simulations, where the forward and adjoint simulations seek to minimize the loss function 205 presented above. Of course, other design techniques and loss functions may be implemented to achieve a patterned or non-uniform arrangement of materials 107 and 108 as desired for a particular application of the optical modulator 100 .

[0039] Finally, in process block 425, the optical power rejected or directed to sink port 120 during the logic low or off state is diverted into optical receiver 130 where it is recycled or collected for beneficial use (as opposed to being discarded as heat and conducted away via a heat sink). Beneficial use may include powering modulation controller 140 itself or other circuitry 145.

[0040] FIG. 5A to FIG. 5C Three example floor plans of a deviating optical modulator 100 are shown according to embodiments of the present disclosure. Figure 1 An optical modulator 100 is shown in which the waveguide segments of the input port 110 and the output port 115 are parallel to each other and disposed on opposite sides of the modulation region 105 from each other, but the waveguide segment of the sink port 120 is oriented perpendicular to the waveguide segments of the input port 110 and the output port 115. In contrast, Figure 5A An optical modulator 500 is shown wherein the waveguide segments of the input port 110 , the output port 115A, and the sink port 120A are all aligned parallel to one another, wherein the output port 115A and the sink port 120A are disposed on a common side of the modulation region 105A opposite the input port 110 . Figure 5B An optical modulator 501 is shown in which the waveguide sections of the sink port 120 and the output port 115B are both perpendicular to the waveguide section of the input port 110. Finally, Figure 5C Another example optical modulator 502 is shown with two sink ports 120B and 120C, where both sink ports 120B and 120C are perpendicular to the input port 110 and the output port 115C. It should be appreciated that FIG. 5A to FIG. 5C The floor plan modifications shown in are not exhaustive. Other floor plan modifications may include ports with tilted orientations, ports of different cross-sectional sizes, etc. The modulation regions 105A, 105B, and 105C may all be designed using the same inverse design method described herein.

[0041] FIG. 6A to FIG. 6C The initial setup, operation simulation, and adjoint simulation of a simulation environment 601 for optimizing structural parameters of a physical device (e.g., optical modulator 100, 500, 501, or 502) using a design model according to an inverse design embodiment are respectively shown. The simulation environment 601 and the corresponding initial setup, operation simulation, adjoint simulation, and structural parameter optimization can be implemented via a physical simulator using Maxwell's equations. FIG. 6A to FIG. 6C As shown, the simulation environment is represented in two dimensions, however, it should be appreciated that higher dimensions (e.g., three-dimensional space) may also be used to describe the simulation environment 601 and the physical devices. FIG. 6A to FIG. 6COptimization of structural parameters of the physical device shown in can be achieved, among other things, via simulations (eg, time forward and backward propagation) that model field responses (eg, electric and magnetic) using finite-difference time-domain (FDTD) methods.

[0042] Fig. 6A An example rendering of a simulation environment 601-A describing an electromagnetic device is shown. The simulation environment 601-A represents the simulation environment 601 at an initial time step (e.g., initial setup) for optimizing structural parameters of a physical device. The physical device described by the simulation environment 601 can correspond to an optical modulator 100 having a designable region 605 (e.g., modulation region 105) in which structural parameters of the simulation environment can be designed, modified, or otherwise changed. The simulation environment 601 includes an excitation source 615 (e.g., Gaussian pulse, wave, waveguide mode response, etc.) at the location of the input port 110. The electric and magnetic fields (e.g., field response) within the simulation environment 601 (and the physical device) can change in response to the excitation source 615. A specific setup of initial structural parameters, excitation sources, performance parameters, and other metrics (i.e., initial description) for a first principles simulation of the physical device is input before the operational simulation begins.

[0043] As shown, the simulation environment 601 (and the subsequent physical device) is described by a plurality of voxels 610, which represent individual elements of the two-dimensional (or three-dimensional) space of the simulation environment. Each voxel is shown as a two-dimensional square, but it should be appreciated that the voxel can be represented as a cube or other shape in a three-dimensional space. It should be appreciated that the specific shape and dimension of the plurality of voxels 610 can be adjusted depending on the simulation environment 601. It should also be noted that only a portion of the plurality of voxels 610 is shown to avoid blurring other aspects of the simulation environment 601. Each of the plurality of voxels 610 is associated with one or more structural parameters, field values ​​for describing the field response, and source values ​​for describing the excitation source at a specific location within the simulation environment 601. For example, the field response may correspond 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, which 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.

[0044] Figure 6BAn example operational simulation of the simulation environment 601-B is shown at a particular time step where the excitation source 615 is active (e.g., generating a wave originating from the excitation source 615 that propagates through the simulation environment 601). As mentioned, the physical device is an optical modulator operating at a frequency of interest and having a particular waveguide mode (e.g., a transverse electromagnetic mode, a transverse electric mode, etc.), and the excitation source is at the input port 110. The operational simulation occurs at multiple time steps (see Figure 3 ), including the time steps shown. When performing the operational simulation, changes to the field response (e.g., field values) are updated for each of the plurality of voxels 610 in response to the excitation source 615 and based at least in part on the structural parameters of the physical device at each of the plurality of time steps. Similarly, in some embodiments, the source values ​​are updated for each of the plurality of voxels (e.g., in response to electromagnetic waves from the excitation source 615 propagating through the simulation environment). It should be recognized that the operational simulation is incremental, and as time moves forward through each of the plurality of time steps, the field values ​​(and source values) are incrementally updated at each time step. It should also be noted that in some embodiments, the updating is an iterative process, and the update of each field and source value is based at least in part on the previous update of each field and source value.

[0045] When performing an operational simulation, a performance loss function (e.g., TLoss, RLoss, and SLoss) can be calculated at each port 615, 620, and 625 based at least in part on a comparison (e.g., mean square error) between the field response at a specified time step (e.g., the final time step of the operational simulation) and the expected field response. The performance loss value can be described in terms of a specific performance value (e.g., power). The structural parameters can be optimized for the specific performance value.

[0046] Figure 5C An example back propagation of a performance loss error backward within a simulation environment 601-C describing a physical device is shown. In one embodiment, the adjoint performance simulation injects the performance loss error at the output port 620 and the sink port 625 as a reverse excitation source for stimulating a reverse field response through the voxel 610 of the simulation environment 601-C. The adjoint performance simulation of the performance loss error determines the effect of changes in the structural parameters of the voxel 610 on the performance loss value (e.g., the loss function 205).

[0047] Fig. 7A7 is a flow chart 700 showing example time steps for a time forward simulation 710 and back propagation 750 within a simulation environment according to an embodiment of the present disclosure. Flow chart 700 is one possible implementation that a design model may use to perform a forward operation simulation 710 and back propagation 750 of a simulation environment. In the illustrated embodiment, the forward operation simulation utilizes an FDTD method to model the field response (both electric and magnetic fields) at multiple time steps in response to an excitation source. More specifically, the time-dependent Maxwell equations (in partial differential form) are discretized to solve for the field vector components (e.g., FIG. 6A to FIG. 6C The field response of each of the multiple voxels 610 of the simulated environment 601 in FIG.

[0048] like Fig. 7A As shown, flowchart 700 includes update operations for operating a simulation 710 and a portion of an accompanying simulation 750. The operating 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 (e.g., from initial field values ​​711) in electric and magnetic fields of a plurality of voxels describing a simulated environment and / or physical device that collectively correspond to field responses. More specifically, update operations (e.g., 712, 714, and 716) are iterative and based on field responses, structural parameters 704, and one or more physical stimulus sources 708. Each update operation is followed by another update operation that represents a successive step forward in time within a plurality of time steps. For example, update operation 714 updates field values ​​713 based on field responses determined from a previous update operation 712, source 708, and structural parameters 704 (see, e.g., Figure 6B Similarly, update operation 716 updates field value 715 based on the field response determined from update operation 714 (see, e.g., Figure 7B ). In other words, at each time step of the operational simulation, the field values ​​(and therefore the field responses) are updated based on the previous field responses and structural parameters of the physical device. Once the last time step of the operational simulation 710 is performed, the loss value 718 (e.g., based on the predetermined loss function 720 or the loss function 205) can be determined. The loss gradient determined from block 752 can be treated as an adjoint or virtual source (e.g., a physical stimulus or excitation source originating from the output region) that is back-propagated inversely (incrementally through multiple time steps from the final time step until the initial time step is reached) to determine the structural gradient 768.

[0049] In the illustrated embodiment, the FDTD solution (e.g., time forward simulation 710) and back propagation 750 problems are graphically described at a high level using only "update" and "loss" operations and their corresponding gradient operations. A simulation is initially set up where structural parameters of the simulation environment (and electromagnetic device), excitation sources, and initial field states are provided. As previously discussed, the field states are updated based on the structural parameters in response to the excitation sources. More specifically, the update operation is given by φ, where for here, corresponds to the total number of time steps (e.g., a number of time steps) of the time forward simulation, corresponds to the time step the field response of the simulated environment at (the field values ​​associated with the electric and magnetic fields for each of the plurality of voxels), corresponds to the time step an excitation source(s) of the simulated environment at (source values ​​associated with the electric and magnetic fields for each of the plurality of voxels), and Corresponds to structural parameters that describe the topology and / or material properties of an electromagnetic device.

[0050] Note that using the FDTD method, the update operation can be specifically expressed as:

[0051]

[0052] That is, the FDTD update is linear with respect to the field and source terms. Specifically, and It depends on the structural parameters and act on the field Heyuan Here, we assume that where N is the number of FDTD field components in the time forward simulation. In addition, the loss operation is given by Given, it takes as input a computed field and produces a single real-valued scalar (e.g., a loss value) that can be reduced and / or minimized.

[0053] In modifying or otherwise optimizing the structural parameters of an electromagnetic device, the relevant quantity to be produced is It is used to describe the change of loss value with respect to the change of structural parameters of electromagnetic equipment and is expressed as Fig. 7A The “structural gradient” shown in .

[0054] Figure 7B 780 is a diagram illustrating the relationship between an update operation for an operation simulation and an adjoint simulation (eg, back propagation) according to an embodiment of the present disclosure. More specifically, Figure 7B Summarizes the calculation of structural gradient The operations and accompanying simulation relationships involved include The update operation 714 of the operation simulation updates the field values ​​713 of the plurality of voxels at the i-th time step Update to the next time step (i.e., time step), which corresponds to the field value 715 Gradient 755 is utilized to determine the gradient for back-propagation (e.g., updating operation 756 backward in time). It is used at least in part in combination with gradient 769 to calculate the structural gradient is the contribution of each field to the loss value L. Note that this is a partial derivative and therefore does not take into account Therefore, using the Relational Loss Gradient It can also be used to calculate structural gradients and corresponds to the total derivative of the field with respect to the loss value L. At a particular time step The loss gradient at equal Finally, using the value corresponding to the field gradient It is from each time / update step pair contribution. Given by:

[0055]

[0056] For completeness, the full form of the first time in the sum It is expressed as:

[0057]

[0058] Based on the definition of φ as described in equation (1), note that which can be substituted into equation (3) to obtain the accompanying update for back-propagation (e.g., an update operation such as update operation 756), which can be expressed as:

[0059]

[0060] The adjoint update is the backpropagation of the loss gradients from later time steps to earlier time steps and can be referred to as The reverse solution of Structural Gradient The second term in the sum is expressed as:

[0061]

[0062] For the specific form of φ described by equation (1).

[0063] Some of the processes explained 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, which, when executed by a machine, will cause the machine to perform the described operations. Additionally, the processes may be embodied in hardware, such as an application specific integrated circuit ("ASIC") or otherwise.

[0064] Tangible machine-readable storage media include 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 having 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.).

[0065] The above description of the illustrated embodiments of the present invention (including what is described in the Abstract) is not intended to be exhaustive or to limit the present invention to the precise forms disclosed. Although specific embodiments and examples of the present invention are described herein for illustrative purposes, various modifications may be made within the scope of the present invention as will be appreciated by those skilled in the relevant art.

[0066] These modifications can be made to the present invention in light of the above detailed 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. On the contrary, the scope of the present invention will be determined entirely by the appended claims, which will be interpreted in accordance with established principles of claim interpretation.

Claims

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 to inject an optical carrier into the modulation region; an output port optically coupled to the modulation region to receive and transmit a modulated signal having a high state and a low state; Sink port, optically coupled to the modulation area; as well as A modulation actuator is disposed adjacent to the modulation region and is adapted to apply a modulation bias affecting the non-uniformly arranged different refractive indices to the modulation region to selectively direct a portion of the optical power of the optical carrier to the sink port when the modulation signal is modulated to a low state.

2. The optical modulator according to claim 1, wherein The non-uniform arrangement includes a pattern of discrete areas of core material and cladding material used to form the input ports, output ports, and sink ports.

3. The optical modulator according to claim 1, wherein: The two or more different materials include semiconductor materials and oxide materials.

4. The optical modulator according to claim 1, wherein: The non-uniform arrangement includes a pattern of discrete regions of different materials, wherein the pattern is selected based on an iterative minimization of a loss function defined as the sum of a transmission loss at an output port, a reflection loss at an input port, and a sink loss at a sink port.

5. The optical modulator according to claim 1, wherein: The modulating actuator comprises one of the following: an electrode adapted to apply a modulation bias as an adjustable voltage across a modulation region; a heating element adapted to apply a modulation bias as an adjustable temperature across the modulation region; or An electromechanical actuator is adapted to apply a modulation bias as an adjustable pressure across a modulation region.

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

7. The optical modulator according to claim 6, further comprising: A modulation controller is coupled to the modulation actuator, wherein the modulation controller is powered at least in part by the portion of the optical power rejected from the modulation region.

8. The optical modulator according to claim 1, wherein: The input ports, output ports, and sink ports all include waveguide segments that physically adjoin the modulation region.

9. The 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 perpendicular to the waveguide sections of the input port and the output port.

10. The optical modulator according to claim 8, wherein: The waveguide sections of the input port, output port, and sink port are all aligned parallel to each other, with the output port and sink port being disposed on opposite sides of the modulation region from the input port.

11. The optical modulator according to 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 optical modulator according to claim 8, wherein: The sink port includes a first sink port, and the optical modulator further includes: The second sink port is optically coupled to the modulation area.

13. A method for operating an optical modulator, the method comprising: receiving an optical carrier at a modulation region from an input port optically coupled to the 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 the data signal to generate a modulated signal at an output port optically coupled to the modulation region, wherein the modulation bias affects the non-uniformly arranged different refractive indices to selectively direct optical power of an 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 modulation signal is modulated to an on state based on the first logic state of the data signal; and When the modulation signal is modulated to an off state based on the second logic state of the data signal, a second majority of the optical power of the optical carrier is directed to the sink port.

14. The method according to claim 13, further comprising: collecting, with an optical receiver optically coupled to the sink port, at least a portion of a second majority of the optical power of the optical carrier transferred to the sink port; as well as During the off state, the electronic circuit is powered using the portion of the second majority of optical power collected from the optical carrier.

15. The method according to claim 14, wherein: Powering the electronic circuitry includes at least partially powering a modulation controller that controls a modulation bias applied to the modulation zone.

16. The method according to claim 13, wherein: The non-uniform arrangement includes a pattern of discrete areas of core material and cladding material used to form the input ports, output ports, and sink ports.

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

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

19. The method according to claim 13, wherein: Modulation The modulation bias applied to the modulation region includes one of the following: applying an adjustable voltage across the modulation region; Heating the modulation area; or Apply adjustable pressure to the adjustment area.

20. The method according to claim 13, wherein: The input ports, output ports, and sink ports all include waveguide segments that physically adjoin the modulation region.

21. The method according to claim 13, wherein: Diverting a second majority of the optical power of the optical carrier to the sink port when the modulation signal is modulated to the off state includes diverting 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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