Micro-ring modulator feedback control system for realizing optical modulation amplitude and linearity optimization

Abstract

The invention belongs to the technical field of micro-ring modulator optimization, and particularly relates to a micro-ring modulator feedback control system for realizing optical modulation amplitude and linearity optimization. A low-speed PAM-4 test signal easy to process is generated through a test code generation module and is pre-distorted through a feedback control module to drive a micro-ring modulator, a signal acquisition module acquires a response signal of the modulator in real time, and an eye pattern calculation module extracts current light modulation amplitude and linearity of quantitative performance from the response signal and calculates the light modulation amplitude and linearity of the micro-ring modulator. And the feedback control module synchronously adjusts the working points of the micro-ring modulator based on the indexes to optimize the light modulation amplitude, and adjusts the pre-distortion coefficient to optimize the linearity, thereby solving the problems of performance compromise and power consumption increase caused by the separation of the light modulation amplitude and the linearity optimization in the prior art. Compared with the prior art, collaborative optimization is achieved, and energy efficiency is improved while performance compromise is avoided.

Description

Technical Field

[0001] This application belongs to the field of micro-ring modulator optimization technology, specifically relating to a micro-ring modulator feedback control system that optimizes optical modulation amplitude and linearity. Background Technology

[0002] In an era of rapid evolution in optoelectronic convergence and fully integrated technologies, micro-ring modulators (MRMs) have become key devices due to their high integration and low power consumption. However, they face two core problems when modulating four-level pulse amplitude modulation (PAM-4) signals. First, MRMs are extremely sensitive to temperature drift, which can easily cause the operating point to deviate from the optimal position, resulting in a significant reduction in optical modulation amplitude (OMA) and directly degrading modulation performance. Second, the inherent Lorentz-type nonlinear transfer function of MRMs can distort the ideal equally spaced PAM-4 levels into unequally spaced optical power outputs, causing signal distortion and inter-symbol interference. These two problems together lead to a sharp increase in the system bit error rate, requiring complex thermal tuning and digital equalization for compensation, thus limiting the full realization of their performance and power consumption advantages.

[0003] Current mainstream approaches treat OMA optimization and Relative Level Metric (RLM) optimization as two separate tasks. For OMA optimization, a common approach is to use an MRM (Mechanical Management Controller) operating point control circuit to bias and stabilize the MRM's operating point at a position with a large OMA. For RLM optimization, mainstream designs tend to pre-distort the PAM-4 signal from the transmitter drive perspective to compensate for the nonlinear effects caused by the MRM. While both approaches have some effect, they often compromise on one aspect, making it difficult to achieve a balanced optimization. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this application is to provide a micro-ring modulator feedback control system that optimizes optical modulation amplitude and linearity. This system aims to solve the problem that current micro-ring modulator optimization generally treats the optimization of optical modulation amplitude and linearity separately, lacking integrated processing methods, thus resulting in performance trade-offs and increased power consumption.

[0005] The first aspect of this application relates to a micro-ring modulator feedback control system for optimizing optical modulation amplitude and linearity, comprising a micro-ring modulator and a driving module for driving the micro-ring modulator, and further comprising: a test code generation module, a signal acquisition module, an eye diagram calculation module, and a feedback control module; the output terminal of the test code generation module is connected to the first input terminal of the feedback control module; the first output terminal of the feedback control module is connected to the input terminal of the driving module; the input terminal of the signal acquisition module is connected to the output terminal of the micro-ring modulator; the output terminal of the signal acquisition module is connected to the input terminal of the eye diagram calculation module; the output terminal of the eye diagram calculation module is connected to the second input terminal of the feedback control module; the second output terminal of the feedback control module is connected to the micro-ring modulator. The input terminal of the ring modulator; the test code generation module is configured to generate a PAM-4 test signal below the operating speed and output it to the feedback control module for predistortion based on the predistortion coefficient; the feedback control module is used to output the predistorted test signal to the drive module to excite the drive signal; the signal acquisition module is configured to acquire the response signal generated by the micro-ring modulator in response to the drive signal; the eye diagram calculation module is configured to obtain the current optical modulation amplitude and current linearity of the micro-ring modulator based on the response signal; the feedback control module is also configured to adjust the operating point of the micro-ring modulator based on the current optical modulation amplitude and adjust the predistortion coefficient based on the current linearity to achieve optical modulation amplitude and linearity optimization.

[0006] In one embodiment, the test code generation module is configured to generate a periodic PAM-4 test signal.

[0007] In one embodiment, the signal acquisition module includes a photodetector, an amplification unit, and a high-pass filter connected in sequence; the photodetector, amplification unit, and high-pass filter are configured to acquire a response optical signal, convert the response optical signal into a response electrical signal, amplify the gain, filter out DC output, and send it to the eye diagram calculation module.

[0008] In one embodiment, the eye diagram calculation module includes: a multi-phase sampling analog-to-digital converter unit and a calculation unit; the input terminal of the multi-phase sampling analog-to-digital converter unit is connected to the output terminal of the signal acquisition module; the output terminal of the multi-phase sampling analog-to-digital converter unit is connected to the input terminal of the calculation unit; the output terminal of the calculation unit is connected to the input terminal of the feedback control module; the multi-phase sampling analog-to-digital converter is configured to synchronously sample and convert multiple levels of the response signal to obtain the sampled value of each level; the calculation unit is configured to simultaneously obtain the current optical modulation amplitude and the current linearity based on the initial value and sampled value of each level.

[0009] In one embodiment, the multi-phase sampling analog-to-digital converter unit includes: four analog-to-digital converters controlled by different phase clocks; Each of the analog-to-digital converters is configured to sample and convert the four levels of the response signal at different phases within the same period, and synchronously acquire the sampled values ​​of the four levels and output them to the computing unit.

[0010] In one embodiment, the feedback control module includes: a control unit, a predistortion adjustment unit, and an operating point adjustment unit; the input terminal of the control unit is connected to the output terminal of the eye diagram calculation module; the first output terminal of the control unit is connected to the input terminal of the operating point adjustment unit; the output terminal of the operating point adjustment unit is connected to the input terminal of the micro-ring modulator; the first input terminal of the predistortion adjustment unit is connected to the output terminal of the test code generation module; the second input terminal of the predistortion adjustment unit is connected to the second output terminal of the control unit; the output terminal of the predistortion adjustment unit is connected to the input terminal of the drive module; the control unit is configured to generate a first digital control signal and a second digital control signal based on the current optical modulation amplitude and the current linearity; the predistortion adjustment unit is configured to adjust the predistortion coefficient based on the first digital control signal, perform predistortion processing on the test signal, and output the processed signal to the drive module; the operating point adjustment unit is configured to generate an analog adjustment amount according to the second digital control signal and output it to the micro-ring modulator to control the operating point.

[0011] In one embodiment, the predistortion adjustment unit includes: three current sources and three independent current digital-to-analog converters; the output of each current digital-to-analog converter is connected to the control terminal of a current source; the output of each current source is connected to a different signal branch in the drive module; each current digital-to-analog converter is configured to control the corresponding current source to output different predistortion control currents based on a first control signal and inject them into the corresponding branch of the drive module to independently adjust the amplitude of each eye in the PAM-4 signal.

[0012] In one embodiment, the operating point adjustment unit includes: a power digital-to-analog converter; the power digital-to-analog converter is configured to receive a second control signal from the control unit and output thermally tuned power corresponding to the second control signal to the micro-ring modulator to adjust its resonant wavelength, thereby controlling the operating point.

[0013] The second aspect of this application relates to a feedback control method for a microring modulator to optimize optical modulation amplitude and linearity, comprising: predistorting a PAM-4 test signal below its operating speed based on a predistortion coefficient and generating a drive signal; acquiring a response signal generated by the microring modulator in response to the drive signal; obtaining the current optical modulation amplitude and current linearity of the microring modulator based on the response signal; adjusting the operating point of the microring modulator based on the current optical modulation amplitude and adjusting the predistortion coefficient based on the current linearity to optimize the optical modulation amplitude and linearity.

[0014] In one embodiment, adjusting the operating point of the micro-ring modulator based on the current optical modulation amplitude and adjusting the predistortion coefficient based on the current linearity to optimize the optical modulation amplitude and linearity includes: adjusting the operating point of the micro-ring modulator based on the current optical modulation amplitude to maximize the optical modulation amplitude; and, under the condition of maximizing the optical modulation amplitude, adjusting the predistortion coefficient based on the current linearity until the amplitudes of the three eyes of the response signal are equal to optimize the optical modulation amplitude and linearity.

[0015] Overall, the technical solutions conceived in this application have the following beneficial effects compared with the prior art: By employing a closed-loop feedback control system comprising a test code generation module, a signal acquisition module, an eye diagram calculation module, and a feedback control module, the test code generation module generates an easily processed low-speed PAM-4 test signal, which is then pre-distorted by the feedback control module to drive a micro-ring modulator. The signal acquisition module acquires the modulator's response signal in real time, and the eye diagram calculation module extracts the current optical modulation amplitude and linearity of the quantization performance from it. Based on these indicators, the feedback control module synchronously adjusts the operating point of the micro-ring modulator to optimize the optical modulation amplitude and adjusts the pre-distortion coefficient to optimize the linearity. This solves the performance trade-off and increased power consumption problems caused by separating the optimization of optical modulation amplitude and linearity in existing technologies.

[0016] Compared with existing technologies, it achieves synergistic optimization of optical modulation amplitude and linearity, improving energy efficiency while avoiding performance compromise. Attached Figure Description

[0017] Figure 1 This is one of the structural block diagrams of the micro-ring modulator feedback control system for optimizing optical modulation amplitude and linearity provided in the embodiments of this application; Figure 2 This is the second structural block diagram of the micro-ring modulator feedback control system for optimizing optical modulation amplitude and linearity provided in the embodiments of this application; Figure 3 This is a partial selection diagram of a micro-ring modulator feedback control system for optimizing optical modulation amplitude and linearity provided in an embodiment of this application; Figure 4 This is a schematic diagram of the eye diagram calculation signal provided in an embodiment of this application; Figure 5 This is a schematic diagram of the OMA and RLM optimization process provided in the embodiments of this application; Figure 6 This is a preferred PAM-4 signal eye diagram pre-distortion calibration circuit provided in the embodiments of this application; Figure 7 This is a diagram showing the OMA optimization results provided in the embodiments of this application; Figure 8This is a diagram showing the RLM optimization results provided in the embodiments of this application; Figure 9 This is a flowchart illustrating the micro-ring modulator feedback control method for optimizing optical modulation amplitude and linearity provided in an embodiment of this application.

[0018] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 10 is the test code generation module; 20 is the signal acquisition module; 30 is the eye diagram calculation module; 40 is the feedback control module; 31 is the multi-phase sampling analog-to-digital conversion unit; 32 is the calculation unit; 41 is the control unit; 42 is the predistortion adjustment unit; 43 is the operating point adjustment unit. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0020] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent three cases: A exists alone, A and B exist simultaneously, and B exists alone. In this application, the symbol "" indicates that the related objects are in an "or" relationship, for example, A / B means A or B.

[0021] In this application, the terms "first" and "second," etc., are used to distinguish different objects, not to describe a specific order of objects. For example, "first response message" and "second response message," etc., are used to distinguish different response messages, not to describe a specific order of response messages. The term "connection" in this application can refer to a direct circuit connection or signal transmission via a communication protocol.

[0022] In the embodiments of this application, the terms "exemplary" or "for example" are used to indicate that something is an example, illustration, or description. Any embodiment or design that is described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or design. Specifically, the use of the terms "exemplary" or "for example" is intended to present the relevant concepts in a specific manner.

[0023] In the description of the embodiments of this application, unless otherwise stated, "multiple" means two or more, for example, multiple processing units means two or more processing units, multiple elements means two or more elements, etc.

[0024] Current optimization of micro-ring modulators generally treats the optimization of optical modulation amplitude and linearity separately, lacking integrated processing methods, thus resulting in performance trade-offs and increased power consumption.

[0025] Based on this, this application proposes an embodiment of a micro-ring modulator feedback control system for optimizing optical modulation amplitude and linearity. Please refer to... Figure 1 , Figure 1 This is one of the structural block diagrams of the micro-ring modulator feedback control system for optimizing optical modulation amplitude and linearity provided in the embodiments of this application.

[0026] In this embodiment, the micro-ring modulator feedback control system includes, in addition to the original micro-ring modulator and the driving module that drives the micro-ring modulator, a test code generation module 10, a signal acquisition module 20, an eye diagram calculation module 30, and a feedback control module 40.

[0027] It should be noted that the output of the test code generation module 10 is connected to the first input of the feedback control module 40; the first output of the feedback control module 40 is connected to the input of the drive module; the input of the signal acquisition module 20 is connected to the output of the micro-ring modulator; the output of the signal acquisition module 20 is connected to the input of the eye diagram calculation module 30; the output of the eye diagram calculation module 30 is connected to the second input of the feedback control module 40; and the second output of the feedback control module 40 is connected to the input of the micro-ring modulator.

[0028] It should be noted that the test code generation module 10 is configured to generate a PAM-4 test signal at a speed lower than the operating speed, and output it to the feedback control module 40 for predistortion based on the predistortion coefficient. The feedback control module 40 is used to output the predistorted test signal to the drive module to excite the drive signal.

[0029] Understandably, generating a PAM-4 test signal at a lower communication rate than the system's normal operating speed aims to reduce the difficulty and cost of real-time signal processing and acquisition, while still accurately reflecting the modulator's static and dynamic characteristics. This module can be implemented using a pseudo-random sequence generator in a field-programmable gate array (FPGA), microcontroller (MCU), or application-specific integrated circuit (ASIC). The feedback control module 40 receives this test signal and calls upon internally stored predistortion coefficients—a set of digital correction parameters used to compensate for the modulator's nonlinear transfer function—to perform digital predistortion processing on the signal. The processed digital signal is then output to the drive module via a digital-to-analog converter, thereby exciting a predistorted and shaped analog drive signal.

[0030] It should be noted that the signal acquisition module 20 is configured to acquire the response signal generated by the micro-ring modulator in response to the driving signal. The eye diagram calculation module 30 is configured to obtain the current optical modulation amplitude and current linearity of the micro-ring modulator based on the response signal.

[0031] Understandably, the signal acquisition module 20 is responsible for acquiring the response signal generated by the micro-ring modulator to the driving signal, i.e., the final output optical signal. In fact, the backend can now include a photodetector to convert the optical signal into current, and then convert it into a digital signal via a transimpedance amplifier and an analog-to-digital converter. Alternatively, for higher precision measurements, an integrated coherent receiver solution can be used. The eye diagram calculation module 30 processes the acquired digitized response signal, forming an eye diagram by synchronously superimposing signal waveforms within multiple unit intervals, and calculating key performance indicators based on this eye diagram: the current optical modulation amplitude, typically extracted from the difference in average optical power corresponding to the logical "maximum" and "minimum" in the eye diagram, and the current linearity, which can be measured by calculating the signal error vector amplitude or analyzing the spacing uniformity between different levels of the PAM-4 signal.

[0032] It should be noted that the feedback control module 40 is also configured to adjust the operating point of the micro-ring modulator based on the current optical modulation amplitude and adjust the predistortion coefficient based on the current linearity to achieve optical modulation amplitude and linearity optimization.

[0033] Understandably, the core feedback control module 40, which can be based on an FPGA, DSP, or CPU, generates control signals based on the current optical modulation amplitude index provided by the eye diagram calculation module 30. For example, it adjusts the DAC via the control signals to change the voltage applied to the micro-ring thermal modulator, thereby adjusting the operating point of the micro-ring modulator, i.e., the offset of its resonant wavelength relative to the laser wavelength, to track the optimal modulation efficiency point. Simultaneously, based on the current linearity index, it updates its internal pre-distortion coefficients using specific algorithms, such as the Least Mean Square Error (LMS) algorithm or lookup table methods, to counteract nonlinear distortion.

[0034] It is important to note that these two adjustment processes are performed collaboratively under the same control logic, rather than sequentially or independently. For example, the control algorithm can search for a joint optimization objective that achieves the target optical modulation amplitude and minimizes linearity error. Through this integrated feedback control, the system can dynamically enable the micro-ring modulator to operate simultaneously at a higher optical modulation amplitude and better linearity, thereby achieving synergistic optimization of optical modulation amplitude and linearity and avoiding the performance trade-offs that may occur during independent optimization.

[0035] In this embodiment, a closed-loop feedback control system is employed, comprising a test code generation module, a signal acquisition module, an eye diagram calculation module, and a feedback control module. The test code generation module generates an easily processed low-speed PAM-4 test signal, which, after pre-distortion by the feedback control module, drives a micro-ring modulator. The signal acquisition module acquires the modulator's response signal in real time. The eye diagram calculation module extracts the current optical modulation amplitude and linearity, quantizing the performance, from this signal. Based on these indicators, the feedback control module synchronously adjusts the operating point of the micro-ring modulator to optimize the optical modulation amplitude and adjusts the pre-distortion coefficient to optimize linearity. This solves the performance trade-offs and increased power consumption problems caused by separating optical modulation amplitude and linearity optimization in existing technologies. Compared to existing technologies, this approach achieves synergistic optimization of optical modulation amplitude and linearity, improving energy efficiency while avoiding performance compromises.

[0036] Furthermore, this application proposes an improved embodiment. Please refer to... Figure 2 , Figure 2 This is the second structural block diagram of the micro-ring modulator feedback control system for optimizing optical modulation amplitude and linearity provided in the embodiments of this application.

[0037] In this embodiment, the eye diagram calculation module 30 includes a multi-phase sampling analog-to-digital conversion unit 31 and a calculation unit 32.

[0038] It should be noted that the input terminal of the multi-phase sampling analog-to-digital converter unit 31 is connected to the output terminal of the signal acquisition module 20; the output terminal of the multi-phase sampling analog-to-digital converter unit 31 is connected to the input terminal of the calculation unit 32; and the output terminal of the calculation unit 32 is connected to the input terminal of the feedback control module 40.

[0039] Understandably, in terms of connectivity, the input of the multi-phase sampling analog-to-digital converter unit 31 is connected to the output of the signal acquisition module 20. This means it receives the response signal, which has been converted into an electrical signal, from the signal acquisition module 20; this signal is typically an analog signal. The output of the multi-phase sampling analog-to-digital converter unit 31 is connected to the input of the calculation unit 32, meaning this unit transmits the converted digital sampled value data to the calculation unit 32 for processing. The output of the calculation unit 32 is connected to the input of the feedback control module 40, indicating that the calculated performance parameters are sent to the feedback control module 40 for decision-making.

[0040] It should be noted that the multi-phase sampling analog-to-digital converter is configured to synchronously sample and convert multiple levels of the response signal to obtain the sampled value of each level; the calculation unit 32 is configured to simultaneously obtain the current optical modulation amplitude and the current linearity based on the initial value and sampled value of each level.

[0041] Understandably, the multi-phase sampling analog-to-digital converter unit 31 is configured to simultaneously sample and convert multiple levels of the response signal—typically four discrete levels for PAM-4 signals—into digital values. Multi-phase sampling here does not refer to serial sampling in time, but rather to a technique capable of capturing voltage values ​​near different level decision moments of the signal in parallel or at high speed within a unit interval or across multiple symbol cycles. One feasible implementation is to use a time-interleaved analog-to-digital converter, where multiple low-speed ADC sub-channels operate in parallel with alternating clock phases to achieve a high sampling rate, thereby covering the complete range of signal changes from the lowest to the highest level in one or a few samples, efficiently acquiring sampled voltage values ​​representing each level. Alternative device choices could include a single ADC with an ultra-high sampling rate, or a Flash ADC architecture combining sample-and-hold circuitry with a parallel comparator array.

[0042] Understandably, the calculation unit 32 is configured to obtain the current optical modulation amplitude and the current linearity simultaneously through a specific algorithm based on the sampled values ​​of each level obtained by the multi-phase sampling analog-to-digital conversion unit 31 and with reference to the known initial values ​​of each level, i.e. the theoretical values ​​of the undistorted ideal PAM-4 signal level emitted by the test code generation module 10.

[0043] Specifically, the calculation unit 32 can first statistically average the sampled values ​​of each level to obtain the actual average voltage or optical power characterization value for each level. The current optical modulation amplitude can be directly obtained by calculating the difference between the average sampled values ​​of the highest and lowest levels. For the current linearity, the calculation unit 32 can calculate the distance between adjacent actual levels and compare it with the ideal equal spacing, i.e., the ideal linearity. The linearity is quantified by evaluating the uniformity of these spacings, such as by calculating the differential nonlinearity error. This process is simultaneous, meaning that the same set of sampled data is processed, and two performance parameters are calculated in parallel, rather than performing two independent calculations sequentially. Through this integrated hardware calculation path, the system can quickly and efficiently extract the accurate performance metrics required for feedback control, providing a real-time data foundation for subsequent joint optimization.

[0044] In this embodiment, the feedback control module 40 includes: a control unit 41, a predistortion adjustment unit 42, and an operating point adjustment unit 43.

[0045] It should be noted that the input terminal of the control unit 41 is connected to the output terminal of the eye diagram calculation module 30; the first output terminal of the control unit 41 is connected to the input terminal of the operating point adjustment unit 43; the output terminal of the operating point adjustment unit 43 is connected to the input terminal of the micro-ring modulator; the first input terminal of the predistortion adjustment unit 42 is connected to the output terminal of the test code generation module 10; the second input terminal of the predistortion adjustment unit 42 is connected to the second output terminal of the control unit 41; and the output terminal of the predistortion adjustment unit 42 is connected to the input terminal of the drive module.

[0046] Understandably, the input of control unit 41 is connected to the output of eye diagram calculation module 30, meaning that control unit 41 receives the two digitized performance parameters—current optical modulation amplitude and current linearity—calculated by eye diagram calculation module 30. The first output of control unit 41 is connected to the input of operating point adjustment unit 43, and the second output of control unit 41 is connected to the second input of predistortion adjustment unit 42. These two paths are used to transmit different control commands generated by control unit 41. The output of operating point adjustment unit 43 is connected to the input of micro-ring modulator, applying a physical adjustment signal to the micro-ring modulator. The first input of predistortion adjustment unit 42 is connected to the output of test code generation module 10 to receive the original digital test signal; the output of predistortion adjustment unit 42 is connected to the input of drive module to output the predistorted test signal.

[0047] It should be noted that the control unit 41 is configured to generate a first digital control signal and a second digital control signal based on the current optical modulation amplitude and the current linearity; the predistortion adjustment unit 42 is configured to adjust the predistortion coefficient based on the first digital control signal, perform predistortion processing on the test signal, and output the processed signal to the drive module; the operating point adjustment unit 43 is configured to generate an analog adjustment amount according to the second digital control signal and output it to the micro-ring modulator to control the operating point.

[0048] Understandably, the control unit 41 is the core decision-making part of the feedback control module 40. It is configured to run a specific control algorithm, such as gradient descent, lookup table iterative search, or proportional-integral-derivative (PID) control algorithm, based on the received current optical modulation amplitude and current linearity, thereby generating two digital control signals. The first digital control signal aims to optimize linearity, and the second digital control signal aims to optimize the optical modulation amplitude. These two signals are essentially digital data representing control quantities.

[0049] Understandably, the predistortion adjustment unit 42 is a digital signal processing path configured to perform two key operations: First, it dynamically adjusts the predistortion coefficients used internally based on a first digital control signal from the control unit 41. These coefficients can be stored in an updatable lookup table or used as parameters of a polynomial predistorter. Second, it uses the updated predistortion coefficients to perform real-time predistortion processing on the raw test signal directly input from the test code generation module 10, i.e., performing a nonlinear transformation on the digital signal to pre-compensate for the modulator's nonlinearity. The processed digital signal is then output to the drive module. Alternatively, the predistortion adjustment unit 42 can also be integrated into the digital front-end within the drive module.

[0050] Understandably, the operating point adjustment unit 43 is an analog control path configured to generate an analog adjustment quantity based on the second digital control signal from the control unit 41. The core function of this unit is to perform digital-to-analog conversion and signal conditioning. For example, it could be a high-precision digital-to-analog converter (DAC) that converts the digital control word into an analog voltage or current; to drive capacitive loads, such as the thermoelectrodes of a thermo-optic modulator, or to provide sufficient power, a buffer amplifier or current source may also be connected afterward. Ultimately, this analog adjustment quantity, such as a DC bias voltage or heating current, is output to the corresponding control terminal of the microring modulator, such as a thermal phase shifter or bias electrode, controlling the resonant state of the microring, i.e., its operating point, by changing the refractive index of the silicon waveguide. Through this division of labor, the feedback control module 40 achieves coordinated control of linearity correction in the digital domain and operating point adjustment in the analog domain.

[0051] It is important to clarify that one of the core innovations of this solution lies in utilizing PAM-4 test signals at speeds below normal operating conditions. This provides a foundation for the real-time, synchronous extraction of two key performance indicators—optical modulation amplitude and linearity—on the same hardware computing path. Traditional high-speed online monitoring is often limited by signal processing bandwidth and computational complexity, making it difficult to accurately and efficiently acquire these two inherently restrictive parameters simultaneously during system operation. However, using low-speed test signals significantly reduces the requirements for signal acquisition, such as the speed of analog-to-digital converters (ADCs), and real-time processing, such as the computing power of digital signal processors (DSPs). This allows the system to stably capture and calculate accurate voltage values ​​representing each level within one or several symbol cycles through multi-phase sampling and other methods, with lower hardware costs and power consumption. This enables the synchronous derivation of optical modulation amplitude and linearity. This synchronous measurement mechanism based on low-speed signals is a prerequisite for subsequent closed-loop collaborative optimization. Furthermore, the profound innovation of this solution lies in its pioneering shift at the feedback control level, transforming the optimization of optical modulation amplitude and linearity from the traditional discrete, sequential, or alternating processing mode into a truly dynamic and collaborative control. Current solutions often treat operating point adjustment and predistortion coefficient adjustment as two independent or weakly correlated loops, leading to competition or trade-offs in the optimization process. This solution, through an integrated feedback control module, uses synchronously measured current OMA and linearity data. Within the same control cycle, the control unit executes a unified optimization algorithm to generate control commands to adjust the operating point and predistortion coefficient separately. This allows the system to proactively seek the maximum OMA while satisfying the target linearity constraint, or the optimal linearity while ensuring the target OMA, achieving a Pareto optimal trade-off between the two dimensions. This collaborative control mechanism fundamentally changes the optimization paradigm of micro-loop modulators, solving the performance loss or additional power consumption problems caused by fragmented processing, and represents a substantial advancement in achieving high-performance, high-efficiency silicon optical links.

[0052] Based on the above, this embodiment provides a feasible specific implementation method. Please refer to... Figure 3 , Figure 3 This is a partial selection diagram of a micro-ring modulator feedback control system for optimizing optical modulation amplitude and linearity provided in an embodiment of this application.

[0053] In this embodiment, the test code generation module 10 is configured to generate a periodic PAM-4 test signal. Periodicity means that the PAM-4 signal pattern repeats at fixed intervals in time. A typical implementation is to generate a short sequence of four levels in a specific order and output the sequence cyclically.

[0054] Specifically, this implementation generates a PAM-4 test code sequence of "1, 2, 3, and 4" through internal digital circuitry. Here, "1, 2, 3, and 4" do not refer to specific voltage values, but rather a simplified representation of the sequential numbering of the four PAM-4 symbol levels from lowest to highest. In actual digital circuit implementations, this typically corresponds to a set of periodically occurring, sequentially appearing 2-bit binary codes, which, after subsequent digital-to-analog conversion, are mapped to four equally spaced or specifically regulated analog voltage levels. A typical and efficient way to generate this sequence is to design a simple cyclic state machine or use a small circularly addressed read-only memory (ROM) in a Field-Programmable Gate Array (FPGA) or Application-Specific Integrated Circuit (ASIC) to store and continuously output this fixed digital code sequence.

[0055] Understandably, compared to complex pseudo-random sequences, this extremely simple deterministic sequence containing all four levels in an ordered manner offers significant advantages. It enables rapid signal synchronization and precise sampling point positioning at the receiving end with extremely low complexity and delay. Since the sequence is completely known and repeats periodically, the system can easily predict the precise timing of each level's occurrence, thereby driving the multi-phase sampling analog-to-digital converter 31 to synchronously sample each level at the optimal time. This ensures that the initial values ​​of each level provided for subsequent calculations are absolutely accurate and stable, and that the sampling values ​​of each level are acquired with the highest efficiency and best determinism. This efficient and reliable sampling mechanism is the key foundation for realizing the innovative function of synchronously calculating the current optical modulation amplitude and current linearity.

[0056] In this embodiment, the signal acquisition module 20 includes a photodetector, an amplification unit, and a high-pass filter connected in sequence. The photodetector, amplification unit, and high-pass filter are configured to acquire the response optical signal, convert the response optical signal into a response electrical signal, amplify the gain, filter out the DC output, and send it to the eye diagram calculation module 30.

[0057] Specifically, a conventional monitor photodiode (MPD) is used as the photodetector. Its function is to convert the response light signal carrying modulation information output from the micro-ring modulator into a corresponding weak photocurrent signal. This is a mature and reliable photoelectric conversion scheme. The transimpedance amplifier (TIA) is directly connected after the MPD, forming a classic MPD+TIA combination. The core function of the TIA is to linearly convert the current signal output from the MPD into a voltage signal and perform preliminary amplification.

[0058] A key design feature of this implementation is that the gain of the TIA is set to be adjustable. This can be achieved by selecting a TIA chip with programmable gain control or through external circuitry, such as an adjustable feedback resistor network. The adjustable gain mechanism allows the system to adapt to different input optical power levels. For example, when the input optical power is high, the gain can be reduced to prevent saturation, and when the input optical power is low, the gain can be increased to ensure a sufficient signal level, thus ensuring compatibility with application scenarios with different input optical power and guaranteeing the signal dynamic range.

[0059] Following the TIA, a high-pass filter circuit is added. This circuit filters out the DC component from the PAM-4 test signal. This is because the voltage signal after TIA conversion contains both a DC component reflecting the average optical power and an AC component reflecting modulation information. The high-pass filter, implemented as a first-order RC passive circuit or an active filter, has its cutoff frequency set much lower than the signal symbol rate, allowing the AC component to pass while blocking the DC component. After this processing, the signal output to the subsequent eye diagram calculation module 30 retains only the AC component containing OMA and RLM information. Filtering out DC contributes to more stable and accurate subsequent calculations because it eliminates the influence of operating point drift or laser power fluctuations on the DC component, allowing the algorithm to extract the optical modulation amplitude and the relative level distribution information characterizing linearity more purely from the AC waveform.

[0060] In this embodiment, please refer to Figure 4 , Figure 4 This is a schematic diagram of the eye diagram calculation signal provided in an embodiment of this application. The multi-phase sampling analog-to-digital converter unit 31 includes: 4 analog-to-digital converters controlled by clocks of different phases, which are respectively configured to sample and convert the 4 levels of the response signal in the same period but with different phases, synchronously acquire the sampled values ​​of the 4 levels and output them to the calculation unit 32.

[0061] Specifically, each ADC is matched with its own sampling clock, forming four parallel sampling and quantization channels. Each analog-to-digital converter is configured to sample, quantize, and generate a corresponding digital signal for one level in the PAM4 signal. These quantized digital outputs, i.e., the values ​​converted from analog to digital, are synchronously output to the computing unit 32.

[0062] like Figure 4 As shown in the waveform diagram on the right, the PAM-4 test signal at the top is sampled by the four equally spaced phase difference sampling signals below at strictly synchronized times, indicated by the red dashed lines. The block diagram on the left corresponds to this hardware implementation: the modules labeled ADC1 to ADC4 in the diagram perform synchronized operations on the same input signal according to the above sampling clock triggering order, and the results are sent to the calculation unit 32.

[0063] Specifically, the sampling and A / D conversion process is as follows: Assuming the symbol of the current test signal sequence is "1" and the sampling clock of the ADC is phase "1", then ADC1 is started at the current moment, samples symbol "1", completes quantization and digital conversion, and stores the information of symbol "1". This process continues until the sampling and conversion of symbols "1, 2, 3, 4" are completed. After receiving the signal output from the 4-phase sampling ADC, the digital codes representing symbol "1" and symbol "4" are subtracted, and the absolute value is obtained to get the OMA. By calculating the difference between adjacent symbols, the three eye sizes of the PAM-4 signal can be obtained, thus yielding the RLM.

[0064] It should be noted that the calculation methods for OMA and RLM can be referenced in the following example algorithms.

[0065] Suppose that the four level symbols "1, 2, 3, 4" of the PAM-4 signal are converted into digital codes after A / D conversion as follows: , , , .

[0066] Then, the OMA of the MRM at the current working point can be represented as: .

[0067] It is understandable that the size of the third eye of the MRM at the current working point can be represented as: ; ; .

[0068] Understandably, based on the definition of RLM, it is only necessary to adjust the predistortion coefficient of the drive circuit through feedback to achieve... This will allow you to obtain the optimal RLM.

[0069] Therefore, please refer to Figure 5 , Figure 5 This is a schematic diagram of the OMA and RLM optimization process provided in the embodiments of this application.

[0070] It should be noted that the process begins with stimulating the MRM using a test signal. The entire optimization is divided into two main stages, performed sequentially. The first stage is optical modulation amplitude optimization, which aims to find the maximum optical modulation amplitude. The control unit first controls the operating point adjustment unit to scan its operating points. At each operating point, the system monitors and calculates the four level values ​​of the PAM-4 signal through the signal acquisition and eye diagram calculation module, thereby obtaining the current optical modulation amplitude value. The control unit continuously determines whether the current operating point results in the optical modulation amplitude reaching its maximum value. If not, the control unit continues to instruct the operating point adjustment unit to perform step adjustments and repeats the monitoring and calculation process, forming a closed-loop search. Once it is determined that the optical modulation amplitude has reached its maximum value, the operating point selection is completed, and this optimal operating point is locked to proceed to the next stage.

[0071] It should be noted that the second stage is linearity optimization. This stage is performed at the operating point determined in the first stage, which generates the maximum optical modulation amplitude, with the goal of optimizing the signal linearity (expressed as relative level margin, RLM). At this fixed operating point, the system monitors and calculates the four level values ​​of the PAM-4 signal again, and obtains the three eye diagram openings formed by these four levels, i.e., the sizes of the three eyes. The control unit then determines whether the sizes of these three eyes are equal. If they are not equal, the ratio of the three tail currents used in the drive module to generate the PAM-4 multi-level signal is adjusted to change the relative positions between the levels. Then, the system re-monitors and calculates under the new tail current ratio and makes another judgment. This cycle continues until the sizes of the three eyes are equal. At this point, the system further determines whether the linearity has reached the optimal level, i.e., the optimal RLM. If the optimal level is reached, the entire optimization process ends, and the system enters a steady-state operating mode. This process, through a sequential and coordinated approach of first maximizing the optical modulation amplitude and then optimizing the linearity at this operating point, ultimately achieves comprehensive optimization of the two key performance indicators.

[0072] Specifically, please refer to Figure 6 , Figure 6 This application provides a preferred PAM-4 signal eye diagram predistortion calibration circuit. The predistortion adjustment unit 42 includes: three current sources and three independent current digital-to-analog converters; the output terminal of each current digital-to-analog converter is connected to the control terminal of a current source; the output terminal of each current source is connected to a different signal branch in the drive module; the multiple current digital-to-analog converters are configured to control the corresponding current sources to output different predistortion control currents based on a first control signal and inject them into the corresponding branches of the drive module, so as to independently adjust the amplitude of each eye in the PAM-4 signal.

[0073] Understandably, to achieve independent adjustment of the three eyes in the PAM-4 signal, three current DACs are used to independently adjust the tail current source of each branch, with each tail current source corresponding to the amplitude control of one eye. Assuming the power supply for this stage of the circuit is VDD, the PAM-4 signal levels 1 to 4 are respectively: ; ; ; .

[0074] The size of the three eyes in the PAM-4 signal is: ; ; .

[0075] Therefore, feedback regulation is achieved through a current DAC. , The size of the signal is such that the independent conditions for PAM-4 signals from all three eyes can be achieved.

[0076] Specifically, the operating point adjustment unit 43 includes a power digital-to-analog converter; the power digital-to-analog converter is configured to receive a second control signal from the control unit 41 and output the thermally tuned power corresponding to the second control signal to the micro-ring modulator to adjust its resonant wavelength, thereby controlling the operating point.

[0077] Understandably, when the thermal tuning power is applied to the thermoelectrode, Joule heating is generated, causing a local temperature change in the silicon waveguide, which in turn alters its refractive index, ultimately achieving precise and continuous adjustment of the micro-ring resonant wavelength. By actively and incrementally changing the second digital control signal in Step 1 (OMA optimization), the thermal tuning power output by the operating point adjustment unit 43 also changes accordingly, thus systematically scanning the operating point of the micro-ring modulator. At each scanned operating point, the system evaluates the current OMA value until the optimal operating point that generates the maximum OMA is found and locked, thereby achieving closed-loop control of the operating point and laying the foundation for subsequent linearity optimization.

[0078] Based on the above, tests were conducted. First, without using the feedback control system of this application, a high-speed operating signal was input to obtain a set of test results. Then, the low-speed test signal of the optimized feedback control system of this application was removed, and a high-speed operating signal was re-inputted to obtain a set of test results. The final comparison of the two sets of test results is as follows: Figure 7 and Figure 8 As shown. Figure 7 This is a diagram showing the OMA optimization results provided in the embodiments of this application; Figure 8 This is a graph showing the RLM optimization results provided in an embodiment of this application. It can be seen that after bias point optimization, OMA increased from 250uW to 290uW. The eye diagram RLM improved from 0.67 to 0.95 after optimization.

[0079] In addition, this application proposes an embodiment of a micro-ring modulator feedback control method for optimizing optical modulation amplitude and linearity. Please refer to... Figure 9 , Figure 9 This is a flowchart illustrating the micro-ring modulator feedback control method for optimizing optical modulation amplitude and linearity provided in an embodiment of this application.

[0080] In this embodiment, the micro-ring modulator feedback control method includes steps S10 to S40.

[0081] Step S10: The PAM-4 test signal, which is below the operating speed, is pre-distorted based on the pre-distortion coefficient, and a drive signal is generated.

[0082] Specifically, predistorting the PAM-4 test signal, which operates at speeds below the operating speed, involves the digital signal processing unit using stored predistortion coefficients to perform a nonlinear transformation of the low-speed PAM-4 digital test code in the digital domain. Generating the drive signal involves converting the predistorted digital signal into an analog voltage via a digital-to-analog converter, and then outputting it through a drive amplifier to drive the micro-ring modulator. Alternatively, the predistortion processing can also be partially implemented in the analog domain using nonlinear circuitry.

[0083] Step S20: Acquire the response signal generated by the micro-ring modulator in response to the driving signal.

[0084] Understandably, the physical implementation involves photoelectric conversion and signal conditioning links. For example, the output light signal is converted into current by a photodetector, then converted into a voltage signal by a transimpedance amplifier, and may be sampled into a digital signal by an analog-to-digital converter after gain adjustment and filtering for subsequent processing.

[0085] Step S30: Obtain the current optical modulation amplitude and current linearity of the micro-ring modulator based on the response signal.

[0086] In practical implementation, a multi-phase sampling analog-to-digital converter can be used to simultaneously capture the voltage values ​​of four levels of the PAM-4 signal. The calculation unit then uses these sampled values ​​to perform calculations: the current optical modulation amplitude can be directly obtained from the difference between the average of the highest and lowest levels; the current linearity can be evaluated by calculating the uniformity of the intervals between adjacent levels, i.e., obtaining the three eye size values ​​and comparing the vertical opening of the three eye diagrams. This process is similar to... Figure 5 The steps "monitoring and calculating the four levels of PAM-4" and "obtaining OMA" and "obtaining the size values ​​of the three eyes" correspond to the sub-steps.

[0087] Step S40: Adjust the operating point of the micro-ring modulator based on the current optical modulation amplitude and adjust the predistortion coefficient based on the current linearity to optimize the optical modulation amplitude and linearity.

[0088] Specifically, step S40 includes: adjusting the operating point of the micro-ring modulator based on the current optical modulation amplitude to maximize the optical modulation amplitude; and, under the condition of maximizing the optical modulation amplitude, adjusting the predistortion coefficient based on the current linearity until the amplitudes of the three eyes of the response signal are equal, so as to achieve optimization of optical modulation amplitude and linearity.

[0089] It is understandable that the specific implementation involves two sequential and related phases, such as Figure 5 The process is shown below. In the first stage, the operating point of the micro-ring modulator is adjusted based on the current optical modulation amplitude to maximize the optical modulation amplitude. Figure 5In Step 1, the OMA optimization loop is as follows: By adjusting the power applied to the thermo-optical phase shifter of the micro-ring modulator, its resonant wavelength is systematically scanned, and the OMA is evaluated at each point until the operating point that maximizes the OMA is found and locked, thus completing the selection of the operating point.

[0090] Understandably, in the second stage, under the condition of maximum optical modulation amplitude, the predistortion coefficient is adjusted based on the current linearity until the amplitudes of the response signals for the three eyes are equal. Figure 5 Step 2 RLM optimization loop: At the optimized fixed operating point, adjusting the predistortion coefficient has a physical effect equivalent to adjusting... Figure 5 The linearity is optimized by adjusting the ratio of the three tail currents in the generated PAM-4 multilevel signal and changing the relative amplitude of each driving level. This cycle continues until the vertical opening of the three eyes is equal, at which point the linearity reaches its optimum, and the optimization process ends. This method achieves a systematic joint improvement of two key performance indicators through sequential synergistic optimization: first maximizing OMA, and then optimizing linearity under this constraint.

[0091] Compared with the prior art, the beneficial effects of the micro-ring modulator feedback control method embodiment for optimizing optical modulation amplitude and linearity provided in this application are the same as the beneficial effects of the micro-ring modulator feedback control system embodiment for optimizing optical modulation amplitude and linearity described above, and will not be repeated here.

[0092] It should be understood that expressions such as “comprising” and “may include” used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as “comprising” and / or “having” are to be interpreted as indicating a particular characteristic, number, operation, constituent element, component, or combination thereof, but not to exclude the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0093] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A micro-ring modulator feedback control system for optimizing optical modulation amplitude and linearity, comprising a micro-ring modulator and a driving module for driving the micro-ring modulator, characterized in that, Also includes: The module includes a test code generation module, a signal acquisition module, an eye diagram calculation module, and a feedback control module. The output of the test code generation module is connected to the first input of the feedback control module; the first output of the feedback control module is connected to the input of the drive module; the input of the signal acquisition module is connected to the output of the micro-ring modulator; the output of the signal acquisition module is connected to the input of the eye diagram calculation module; the output of the eye diagram calculation module is connected to the second input of the feedback control module; and the second output of the feedback control module is connected to the input of the micro-ring modulator. The test code generation module is configured to generate a PAM-4 test signal at a speed lower than the operating speed and output it to the feedback control module for predistortion based on the predistortion coefficient. The feedback control module is used to output the pre-distorted test signal to the drive module to excite the drive signal; The signal acquisition module is configured to acquire the response signal generated by the micro-ring modulator in response to the driving signal; The eye diagram calculation module is configured to obtain the current optical modulation amplitude and current linearity of the micro-ring modulator based on the response signal; the feedback control module is further configured to adjust the operating point of the micro-ring modulator based on the current optical modulation amplitude and adjust the predistortion coefficient based on the current linearity to achieve optical modulation amplitude and linearity optimization.

2. The micro-ring modulator feedback control system for optimizing optical modulation amplitude and linearity as described in claim 1, characterized in that, The test code generation module is configured to generate a periodic PAM-4 test signal.

3. The micro-ring modulator feedback control system for optimizing optical modulation amplitude and linearity as described in claim 1, characterized in that, The signal acquisition module includes a photodetector, an amplification unit, and a high-pass filter connected in sequence. The photodetector, amplification unit, and high-pass filter are configured to acquire the response optical signal, convert the response optical signal into a response electrical signal, amplify the gain, filter out the DC output, and send it to the eye diagram calculation module.

4. The micro-ring modulator feedback control system for optimizing optical modulation amplitude and linearity as described in claim 1, characterized in that, The eye diagram calculation module includes: a multi-phase sampling analog-to-digital conversion unit and a calculation unit; The input terminal of the multi-phase sampling analog-to-digital converter is connected to the output terminal of the signal acquisition module; the output terminal of the multi-phase sampling analog-to-digital converter is connected to the input terminal of the calculation unit; the output terminal of the calculation unit is connected to the input terminal of the feedback control module. The multi-phase sampling analog-to-digital converter is configured to synchronously sample and convert multiple levels of the response signal to obtain the sampled value of each level; The computing unit is configured to simultaneously acquire the current optical modulation amplitude and the current linearity based on the initial values ​​of each level and the sampled values.

5. The micro-ring modulator feedback control system for optimizing optical modulation amplitude and linearity as described in claim 4, characterized in that, The multi-phase sampling analog-to-digital conversion unit includes: four analog-to-digital converters controlled by different phase clocks; Each of the analog-to-digital converters is configured to sample and convert the four levels of the response signal at different phases within the same period, and synchronously acquire the sampled values ​​of the four levels and output them to the computing unit.

6. The micro-ring modulator feedback control system for optimizing optical modulation amplitude and linearity as described in claim 1, characterized in that, The feedback control module includes: a control unit, a predistortion adjustment unit, and an operating point adjustment unit; The input terminal of the control unit is connected to the output terminal of the eye diagram calculation module; the first output terminal of the control unit is connected to the input terminal of the operating point adjustment unit; the output terminal of the operating point adjustment unit is connected to the input terminal of the micro-ring modulator. The first input terminal of the predistortion adjustment unit is connected to the output terminal of the test code generation module; the second input terminal of the predistortion adjustment unit is connected to the second output terminal of the control unit; the output terminal of the predistortion adjustment unit is connected to the input terminal of the drive module. The control unit is configured to generate a first digital control signal and a second digital control signal based on the current optical modulation amplitude and the current linearity; the predistortion adjustment unit is configured to adjust the predistortion coefficient based on the first digital control signal, perform predistortion processing on the test signal, and output the processed signal to the drive module. The operating point adjustment unit is configured to generate an analog adjustment amount based on the second digital control signal and output it to the micro-ring modulator to control the operating point.

7. The micro-ring modulator feedback control system for optimizing optical modulation amplitude and linearity as described in claim 6, characterized in that, The predistortion adjustment unit includes: three current sources and three independent current-to-analog converters; The output of each current digital-to-analog converter is connected to the control terminal of one of the current sources; the output of each current source is then connected to a different signal branch in the drive module. Each of the current digital-to-analog converters is configured to control the corresponding current source to output different predistortion control currents based on a first control signal and inject them into the corresponding branch of the drive module to independently adjust the amplitude of each eye in the PAM-4 signal.

8. The micro-ring modulator feedback control system for optimizing optical modulation amplitude and linearity as described in claim 6, characterized in that, The operating point adjustment unit includes: a power digital-to-analog converter; The power digital-to-analog converter is configured to receive a second control signal from the control unit and output the thermally tuned power corresponding to the second control signal to the micro-ring modulator to adjust its resonant wavelength, thereby controlling the operating point.

9. A feedback control method for a micro-ring modulator to optimize optical modulation amplitude and linearity, characterized in that, include: The PAM-4 test signal, which is below the operating speed, is predistorted based on the predistortion coefficient, and a drive signal is generated. The response signal generated by the micro-ring modulator in response to the driving signal is acquired; The current optical modulation amplitude and current linearity of the micro-ring modulator are obtained based on the response signal; The operating point of the micro-ring modulator is adjusted based on the current optical modulation amplitude, and the predistortion coefficient is adjusted based on the current linearity to optimize the optical modulation amplitude and linearity.

10. The micro-ring modulator feedback control method for optimizing optical modulation amplitude and linearity as described in claim 9, characterized in that, The operating point of the micro-ring modulator is adjusted based on the current optical modulation amplitude, and the predistortion coefficient is adjusted based on the current linearity to optimize the optical modulation amplitude and linearity, including: Adjust the operating point of the micro-ring modulator based on the current optical modulation amplitude to maximize the optical modulation amplitude; Under the condition of maximum optical modulation amplitude, the predistortion coefficient is adjusted based on the current linearity until the amplitudes of the three eyes of the response signal are equal, so as to optimize the optical modulation amplitude and linearity.

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