Optical weight regulation unit, method and optical neural network system

Abstract

The application provides an optical weight regulation unit, method and optical neural network system, relates to the technical field of optical computing and optical neural network. The application breaks the structure limitation of a traditional single-heating-segment heater by dividing the heater into multiple independently controlled heating segments, and provides a physical basis for multiple independent control; the independent addressing and accurate control of each heating segment are realized by controlling each heating segment by an independent driving circuit, the performance bottleneck of a single high-precision DAC in a traditional scheme is avoided, and the complexity and cost of the driving circuit are significantly reduced; the effective refractive index of the waveguide is changed by the joint action of the heating segments on the same ring waveguide, the synergistic effect of multiple control signals is realized, and conditions for improving the regulation precision are created.

Description

Technical Field

[0001] This invention relates to the fields of optical computing and optical neural network technology, and in particular to an optical weight control unit, method and optical neural network system. Background Technology

[0002] Optical Neural Networks (ONNs) are considered a crucial technological path to overcome the bottlenecks of traditional electronic computing in the post-Moore's Law era due to their high bandwidth, low latency, and high parallelism. Among them, silicon-based optoelectronic integrated microring resonator (MRR) arrays are the core devices for achieving optical weight modulation. By adjusting the resonant wavelength of the microrings through thermo-optic or electro-optic effects, their transmittance can be changed, thereby achieving linear modulation of the optical signal weights.

[0003] Currently, the mainstream technical solution for achieving micro-ring weighting is to integrate a single-segment metal heater above the micro-ring waveguide, using a digital-to-analog converter (DAC) to provide analog voltage. Joule heating alters the waveguide temperature, thereby changing the effective refractive index and shifting the resonant peak. The control accuracy of this solution directly depends on the DAC's resolution. To achieve high-precision weighting (e.g., 8 bits or more), a high-bit-count DAC is required.

[0004] However, existing technologies suffer from the following drawbacks: Weighting units based on traditional micro-ring structures generally employ fixed bit precision designs, with the number of weight states strongly tied to the precision of the external digital-to-analog converter (DAC). First, there is a fundamental contradiction between DAC speed and precision. High-precision DACs typically have limited operating speeds (on the order of hundreds of MHz) and significantly increased power consumption; a typical 8-bit 10GS / s DAC can consume 100-200mW. In optical computing chips requiring large-scale parallel weight arrays (such as those containing hundreds of micro-rings), DAC power consumption will account for the vast majority of the total system power consumption; for example, in some architectures, DAC power consumption can even account for more than 60% of the total system energy consumption. Furthermore, high-precision DACs also face a trade-off between speed, power consumption, and cost, leading to limited system modulation rates and increased hardware costs. In addition, in lightweight network scenarios requiring only binary weights, traditional solutions still require the use of DACs, resulting in significant waste of hardware cost and power consumption, and a lack of flexibility and scalability. These problems severely limit the deployment and application of optical computing hardware in low-power edge computing scenarios. Summary of the Invention

[0005] In view of this, the core technical problem to be solved by the present invention is: how to break through the strong binding relationship between DAC accuracy and weight accuracy in the traditional micro-ring weight control scheme, and achieve high equivalent accuracy optical weight control while reducing system power consumption and hardware complexity.

[0006] In a first aspect, the present invention provides an optical weighting control unit, including a microring resonator and a heater. The heater is divided into k independently controlled heating segments, each of which is controlled by an independent driving circuit. The driving circuit is used to output an electrical signal to the corresponding heating segment. The heating segments work together on the ring waveguide of the microring resonator. The effective refractive index of the waveguide is changed by the thermal field or electric field generated by the heating segments, thereby controlling the transmittance of the microring resonator.

[0007] Optionally, when the physical structure of each heating segment is the same, the driving circuit is an N-bit DAC, where N≥1; the driving circuit utilizes the square nonlinearity of the thermo-optic effect to make the number of weighted states reach the combination number C(2^3). N +k-1, k).

[0008] Optionally, when the number of bits in the driving circuit is 1, the driving circuit is a digital logic output; when the number of bits in the driving circuit is 1, the driving circuit is a digital logic output; if the physical structure of each heating segment is the same, the number of weighted states is k+1; if the physical parameters of each heating segment are different and the phase shift level corresponding to the unit voltage has a gradient distribution, the number of weighted states is 2. k .

[0009] Optionally, the physical parameters of each heating segment are different, and the phase shift magnitude corresponding to the unit voltage of each heating segment exhibits a gradient distribution, so that the weighted state number reaches 2. Nk .

[0010] Optionally, a pre-calibration lookup table is also included, which is used to compensate for inter-segment thermal crosstalk, thereby improving the accuracy of weight control.

[0011] Secondly, the present invention provides a weighted control method based on a multi-segment modulated microring resonator, comprising the following steps: S1, providing a microring resonator and a heater, wherein the heater is divided into k independently controlled heating segments; S2, applying an independent electrical signal to each heating segment, wherein the electrical signal is provided by the output of a driving circuit; S3, by combining the electrical signals of each heating segment, the effective refractive index of the waveguide is nonlinearly changed using the thermo-optic effect, thereby controlling the transmittance of the microring resonator.

[0012] Optionally, the driving circuit is an N-bit DAC or a digital logic output; when the physical structure of each heating section is the same, the driving circuit is an N-bit DAC. The driving circuit uses the square nonlinearity of the thermo-optic effect to make the number of weighted states reach the combination number C(2). N+k-1, k); When N=1, the driving circuit is a digital logic output, and the number of weighted states is k+1 or 2. k .

[0013] Optionally, the physical parameters of the heating sections are different, and the phase shift magnitude corresponding to the unit voltage of each section is distributed in a gradient, so that the weighted state number reaches 2. Nk .

[0014] Optionally, it also includes a step of compensating for inter-segment thermal crosstalk by using a pre-calibrated lookup table.

[0015] Thirdly, the present invention provides an optical neural network system, comprising: an optical weighting control unit as described above; an optical input device for inputting an optical signal into the input straight waveguide of the optical weighting control unit; and an optical output device for receiving the weighted optical signal from the output straight waveguide of the optical weighting control unit.

[0016] The implementation of this invention offers the following advantages: By dividing a traditional single-segment heater into k independently controlled heating segments, each controlled by an independent drive circuit, this invention achieves high-precision optical weighting with low hardware complexity. Specifically, dividing the heater into multiple independently controlled heating segments breaks the structural limitations of traditional single-segment heaters, providing a physical basis for multi-segment independent control. By controlling each heating segment with an independent drive circuit, independent addressing and precise control of each segment are achieved, avoiding the performance bottleneck of a single high-precision DAC in traditional schemes and significantly reducing the complexity and cost of the drive circuit. Furthermore, by having all heating segments act together on the same ring waveguide, changing the effective refractive index of the waveguide, the synergistic effect of multiple control signals is realized, creating conditions for improving control precision. In summary, this invention provides a physical carrier for multi-segment independent control through a segmented heater structure. Independent drive control ensures the precise controllability of each segment, thereby effectively combining these independent control signals to achieve high-precision optical weighting, ultimately achieving high-precision with low-complexity hardware and breaking through the strong binding relationship between DAC precision and weighting precision in traditional schemes. Attached Figure Description

[0017] Figure 1 As one embodiment, this invention presents a schematic diagram of a micro-ring structure of a heater having k heating segments with identical physical structures. Figure 2 In one embodiment, the thermo-optic modulation transmission curve corresponding to the micro-ring resonator of a heater having k heating segments with identical physical structures; Figure 3 As one embodiment, this invention presents a schematic diagram of a micro-ring structure of a heater having k heating segments with different physical structures.

[0018] In the picture: 1. Ring waveguide; 2. Straight waveguide; 3. Heater. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The step numbers in the following embodiments are only for ease of explanation and do not limit the order of the steps. The execution order of each step in the embodiments can be adapted according to the understanding of those skilled in the art.

[0020] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0021] In the following description, when referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims. In the description of this application, it should be understood that the terms "first," "second," "third," etc., are used only to distinguish similar objects and are not necessarily used to describe a specific order or sequence, nor should they be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0022] Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0023] Example 1 In this embodiment, as Figure 1An optical weighting control unit is shown, including a micro-ring resonator (MRR) 1 and a heater 3. The heater 3 is divided into k independently controlled heating segments, each controlled by an independent driving circuit. The driving circuit is used to output an electrical signal to the corresponding heating segment. All heating segments act together on the ring waveguide 1 of the micro-ring resonator. The effective refractive index of the waveguide is changed by the thermal field or electric field generated by the heating segment, thereby controlling the transmittance of the micro-ring resonator.

[0024] Specifically, in this embodiment, the effective refractive index of the waveguide is changed by the thermo-optical effect generated by the heating section.

[0025] In this embodiment, when the physical structure of each heating segment is identical, the driving circuit is an N-bit DAC, where N≥1. The driving circuit utilizes the square nonlinearity of the thermo-optic effect to potentially achieve a large number of non-equidistant phase-shift states. Ideally, if the phase shift values ​​generated by each heating segment are distinct and linearly independent, the total number of phase-shift states could theoretically reach M=2. N The number of combinations in which k values ​​can be repeatedly selected is C(2). N +k-1, k). In practical applications, degeneracy needs to be minimized by optimizing the layout of the heating section or the range of the driving voltage in order to approximate this theoretical value.

[0026] In this embodiment, the heating section can be straight, meandering, or arranged in segments along the ring waveguide; the segments can be evenly distributed or non-uniformly distributed to optimize thermal efficiency.

[0027] In this embodiment, as Figure 1 As shown, the optical weighting control unit includes: a microring resonator and multiple heaters 3. The microring resonator includes two straight waveguides 2 and a ring waveguide 1. The heaters 3 are mounted on or to the side of the ring waveguide 1. The heaters 3 are divided into k electrically independent but physically identical heating segments (S1, S2, ..., S...). k Each heating segment is controlled by an independent driving circuit, which can be an N-bit DAC (N≥1). When N=1, the driving circuit is a simple digital logic output, i.e., high and low levels. The k heating segments work together on the same ring waveguide, and the total phase change they produce is the sum of the contributions of each segment, which ultimately determines the transmittance y at the output of the micro-ring resonator.

[0028] Specifically, the principle of adjusting the weighted state number of the microring resonator is to generate Joule heating by applying current to the resistor of the heater 3 located above the ring waveguide 1. The heat is conducted to the ring waveguide 1 through the dielectric. Due to the thermo-optic effect, the effective refractive index of the ring waveguide 1 changes, causing a phase shift in the light and resulting in a redshift of the transmission spectral line of the microring resonator, thereby altering the transmittance of the microring resonator at the initial resonant wavelength. For a conventional microring resonator structure with a single-segment heater 3, assuming the DAC driving the heater 3 has a resolution of N-bit, corresponding to 2... N In each voltage state, the optical power at the output terminal is also a total of 2. N This is due to its transmittance. The relationship between the phase change and the resonance peak near the resonance peak is monotonic (e.g., one side of the Lorentz line), such as... Figure 2 As shown. The transmittance y at the lower end of the microring resonator can be expressed as: Formula (1); Where t and These represent the self-coupling coefficient and mutual coupling coefficient between the straight waveguide and the ring waveguide, respectively. A represents the amplitude attenuation coefficient. j is in imaginary units, indicating that the optical field coupling between adjacent waveguides will add a π / 2 phase change. θ represents the phase change experienced by the optical field as it travels back and forth in the ring waveguide. Phase change Changes in the effective refractive index of ring waveguide 1 Cause, that is: Formula (2); in Let be the radius of the ring waveguide 1. The effective refractive index change originates from the thermo-optical effect of silicon, namely: Formula (3); in is the integral factor of the overlap between the optical field and the waveguide material, and Formula (4); Thermo-optic coefficient of silicon Temperature change Caused by Joule heating generated by the heater, assuming the resistance of heater 3 is... Apply voltage The heat power generated at that time is: Formula (5); Under steady-state conditions, the temperature rise of ring waveguide 1 is proportional to the power, that is: Formula (6); in The thermal resistance is determined by the structure and thermal conductivity of the material of the ring waveguide 1. Therefore, the relationship between voltage and phase change is: Formula (7); That is, square nonlinearity.

[0029] In this embodiment, as Figure 1 As shown, when the heaters 3 in segment k have the same physical size and resistance value, each heater 3 is driven by the same N-bit DAC, therefore each segment has There are 1 possible thermal power states, N≥1. Since the phase shift caused by the thermo-optical effect is proportional to the square of the voltage, the phase shift set for each heating segment is {0, a, 4a, 9a, ..., (M-1)}. 2 a} (where a is a constant). For k segments, the total phase shift Φ is the sum of k values. Since the segments are identical, Φ is determined only by the multiset of voltage values ​​(i.e., the number of times each voltage is selected), and is independent of the order. Therefore, the number of realizable states for Φ is equal to the number of combinations C(M+k-1, k) where k values ​​can be repeatedly selected from M values. That is, the maximum number of realizable states for y is Formula (8); For example, when N=4 (M=16) and k=4, C(19,4)=3876, which is equivalent to approximately 12 bits of precision. The scheme in this embodiment utilizes square nonlinearity to break the degeneracy caused by linear equal-interval phase shifts, allowing the actual number of states to approach the upper limit of the combination number.

[0030] The beneficial effect of this embodiment is that it utilizes the square nonlinearity of the thermo-optical effect and the statistical diversity of multi-segment state combinations to achieve high-precision optical weight control with low hardware complexity. A specific example is as follows: Using k identical heater segments 3, an N-bit DAC was used to achieve an equivalent bit count of approximately log2(C(2)). N The control precision of +k-1, k)) is much greater than that of N. For example, when N=4 and k=4, the equivalent precision reaches 12 bits; when N=2 and k=8, the equivalent precision reaches 8.5 bits, which directly breaks through the limitation of the DAC's own precision on the weight precision.

[0031] To achieve the same modulation accuracy, this embodiment requires fewer bits. Low-bit DACs can operate at high frequencies (several GS / s), while high-precision DACs are limited by settling time and typically have lower speeds. This scheme, through multi-segment parallel low-bit control, can support higher modulation rates while maintaining high equivalent accuracy, making it suitable for high-speed optical computing.

[0032] It should be noted that, in addition to the thermo-optic effect, the segmented modulation concept of this invention is also applicable to the electro-optic effect (such as carrier injection and PN junction modulation). Simply replace the heater with segmented electrodes and use the plasma dispersion effect to achieve phase shift.

[0033] Example 2 Based on Embodiment 1, this embodiment provides another optional solution for the optical weight control unit.

[0034] In this embodiment, as Figure 3 As shown, the physical parameters of each heating section of heater 3 are different, and the phase shift magnitude corresponding to the unit voltage of each heating section exhibits a gradient distribution, resulting in a weighted state number of 2. Nk The remaining undescribed parts of this embodiment are consistent with those of Embodiment 1.

[0035] In this embodiment, as Figure 3 As shown, when the physical parameters (such as length or resistance) of the k heating segments are designed to be different, the phase shift magnitudes of each segment exhibit a gradient distribution. For example, the phase shift corresponding to a unit voltage in the i-th segment is set to... And satisfy: (Similar to binary weights) Formula (9).

[0036] At this point, each heating segment is controlled by an N-bit DAC, and its phase shift set is { Since the weighting condition is satisfied, each voltage combination corresponds to a unique total phase shift. Therefore, the maximum number of states with achievable transmittance y is: Formula (10); That is equivalent to Bit precision. This embodiment achieves completely independent control without degeneracy, but the impact of thermal crosstalk on precision must be considered. During actual driving, the optical power transmittance (i.e., weighted states) at the output of the straight waveguide 2 of the micro-ring resonator under different voltage combinations in each heating segment can be pre-tested. A one-to-one mapping lookup table between voltage and weight values ​​can be established. Based on this lookup table (LUT) calibration algorithm, the target weight is mapped to the driving signal combination of each segment, thereby compensating for crosstalk effects and making the actual number of weighted states approach the theoretical number of states. The DAC output can first undergo voltage-to-current conversion, using a current-driven mode to improve thermal response linearity.

[0037] Example 3 This embodiment provides another optional solution for the optical weight control unit, based on Embodiment 1.

[0038] In this embodiment, when the number of bits in the driving circuit is 1 (i.e., N=1), the driving circuit is a digital logic output, and the number of weighted states is k+1 or 2.k .

[0039] Specifically, when N=1, each heater segment 3 requires only two voltage states (high / low). In this case, the drive circuit can be simplified to a digital logic output, eliminating the need for a DAC. If the physical parameters of the k heater segments 3 are identical, the total phase shift depends only on the number of activated heating segments, resulting in a total of k+1 states. If the physical parameters of the k heater segments 3 are different, such as a geometric increase in length, then... It has multiple states, equivalent to k-bit precision, and is completely controlled by digital signals, resulting in extremely low power consumption.

[0040] The beneficial effects of this embodiment are as follows: when N=1, the use of a DAC is completely eliminated, and the DAC is usually one of the most power-consuming components in an optical computing system. For networks that only require binary or a small number of weights, this solution can directly use digital control, avoiding the redundant overhead of the DAC; for networks that require high-precision weights, the precision can be improved by increasing the number of segments k, and the power consumption is linearly related to k rather than exponentially, thus exhibiting good scalability.

[0041] Example 4 This embodiment provides an optical weighting control method based on the above embodiments.

[0042] In this embodiment, the optical weighting control method includes the following steps: S1. Provide a micro-ring resonator and heater 3, wherein heater 3 is divided into k independently controlled heating sections; S2. Apply an independent electrical signal to each heating section. The electrical signal is provided by the output of the drive circuit. S3. By combining the electrical signals of each heating section, the effective refractive index of the waveguide is changed nonlinearly using the thermo-optic effect, thereby controlling the transmittance of the micro-ring resonator.

[0043] In this embodiment, the driving circuit is an N-bit DAC or a digital logic output; When each heating section has the same physical structure, the driving circuit is an N-bit DAC. The driving circuit utilizes the square nonlinearity of the thermo-optic effect to make the number of weighted states reach the combination number C(2). N +k-1, k); When N=1, the driving circuit is a digital logic output, and the number of weighted states is k+1 or 2. k .

[0044] In this embodiment, when the physical parameters of each heating segment are different, and the phase shift magnitude corresponding to the unit voltage of each segment exhibits a gradient distribution, the weighted state number reaches 2. Nk .

[0045] In this embodiment, the method further includes a step of compensating for inter-segment thermal crosstalk by using a pre-calibrated lookup table.

[0046] Example 5 This embodiment provides an optical neural network system based on the above embodiments.

[0047] In this embodiment, the optical neural network system includes: Such as the optical weighting control unit mentioned above; An optical input device for inputting optical signals into the input straight waveguide of the optical weighting control unit; An optical output device is used to receive the weighted optical signal from the output straight waveguide of the optical weighting control unit.

[0048] In one possible embodiment, the heaters 3 of multiple micro-ring resonators in the optical weight control unit can be uniformly controlled to form a shared drive circuit, thereby further reducing the chip area and power consumption required by the optical neural network system.

[0049] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the embodiments described. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. An optical weighting control unit, comprising a microring resonator and a heater, characterized in that: The heater is divided into k independently controlled heating sections, each controlled by an independent drive circuit. The drive circuit outputs an electrical signal to the corresponding heating section. All heating sections act together on the ring waveguide of the microring resonator, changing the effective refractive index of the waveguide through the thermal or electric field generated by the heating sections, thereby controlling the transmittance of the microring resonator.

2. The optical weighting control unit according to claim 1, characterized in that: When the physical structure of each heating segment is the same, the driving circuit is an N-bit DAC, where N≥1; the driving circuit utilizes the square nonlinearity of the thermo-optic effect to make the number of weighted states reach the combination number C(2^3). N +k-1, k).

3. The optical weighting control unit according to claim 1, characterized in that: When the number of bits in the driving circuit is 1, the driving circuit is a digital logic output. If the physical structure of each heating segment is the same, the number of weighted states is k+1; if the physical parameters of each heating segment are different and the phase shift magnitude corresponding to the unit voltage has a gradient distribution, the number of weighted states is 2. k .

4. The optical weighting control unit according to claim 1, characterized in that: Each heating segment has different physical parameters, and the phase shift magnitude corresponding to a unit voltage in each heating segment exhibits a gradient distribution, resulting in a weighted state number of 2. Nk .

5. The optical weighting control unit according to claim 1, characterized in that: It also includes a pre-calibration lookup table, which is used to compensate for inter-segment thermal crosstalk, thereby improving the accuracy of weight control.

6. An optical weighting control method, characterized in that, Includes the following steps: S1. Provide a microring resonator and a heater, wherein the heater is divided into k independently controlled heating sections; S2. Apply an independent electrical signal to each of the heating sections, the electrical signal being provided by the output of the drive circuit; S3. By combining the electrical signals of each heating section, the effective refractive index of the waveguide is changed, thereby controlling the transmittance of the micro-ring resonator.

7. The optical weighting control method according to claim 6, characterized in that: The driving circuit is an N-bit DAC or a digital logic output; When each of the heating sections has the same physical structure, the driving circuit is an N-bit DAC. The driving circuit utilizes the square nonlinearity of the thermo-optic effect to make the number of weighted states reach the combination number C(2). N +k-1, k); When N=1, the driving circuit is a digital logic output, and the number of weighted states is k+1 or 2. k .

8. The optical weighting control method according to claim 6, characterized in that: The heating sections have different physical parameters, and the phase shift magnitude corresponding to the unit voltage of each heating section exhibits a gradient distribution, resulting in a weighted state number of 2. Nk .

9. The optical weighting control method according to claim 6, characterized in that: It also includes the step of compensating for inter-segment thermal crosstalk by using a pre-calibrated lookup table.

10. An optical neural network system, characterized in that, include: The optical weighting control unit as described in any one of claims 1 to 5; An optical input device is used to input optical signals to the input straight waveguide of the optical weighting control unit; An optical output device is used to receive a weighted optical signal from the output straight waveguide of the optical weighting control unit.

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