Bias voltage automatic control circuit and method and silicon-based light modulator

Abstract

The invention relates to the technical field of optical communication, in particular to a bias voltage automatic control circuit and method and a silicon-based optical modulator. Through cooperative adaptation of the control circuit, the drive circuit, the signal generation circuit and the signal detection circuit, differential sine disturbance signals are accurately coupled to the radio frequency modulation phase shifter of the silicon-based light modulator, and synchronous detection of average light current and the disturbance signals is achieved by means of a built-in light detector. And the control circuit is linked with the driving circuit to accurately adjust the driving current of the thermo-optic phase shifter and efficiently lock a bias working point. The problems that a traditional scheme is low in precision and complex in circuit are solved, the locking speed and stability are improved, meanwhile, hardware design is simplified, the number of components is reduced, the requirement for miniaturization of a high-speed silicon-based optical module is met, working point drifting caused by environment changes is effectively restrained, and the optical signal quality and the long-term working performance of a communication system are guaranteed.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, and in particular to an automatic bias voltage control circuit, method, and silicon-based optical modulator. Background Technology

[0002] Silicon-based optical modulators offer advantages such as small size, high integration, high modulation efficiency, and lower cost. In-phase quadrature silicon-based optical modulators (IQ modulators) based on dual parallel Mach-Zehnder modulator structures have received widespread attention in recent years as core optical devices in coherent optical communication systems. Typically, during long-term operation, the characteristics of an IQ modulator change with variations in environmental temperature and mechanical vibration, causing its static operating point to drift. This significantly impacts the quality of the modulated optical signal and degrades the performance of the communication system. To stabilize the operating point of the IQ optical modulator, automatic bias voltage control technology is needed to lock the modulator's bias point, ensuring long-term stable operation.

[0003] Currently, there are two ways to implement automatic bias control technology for MZ silicon-based optical modulators. The first method is to use average optical power detection to achieve closed-loop control. The average photocurrent of the split output optical signal is detected by a photodetector to achieve closed-loop locking. This method is only applicable to intensity modulation formats and is easily affected by changes in the input optical signal. Therefore, the accuracy of the average optical power locking method is relatively low.

[0004] Another method is to use the disturbance detection method to achieve closed-loop control. This involves introducing a small-signal, low-frequency sine wave or square wave onto the DC BIAS voltage of the modulator, amplifying and detecting a portion of the optical signal at the output of the modulator through an AC amplifier circuit, and then using a back-end sampling circuit and control circuit to detect the same-frequency or multiplied-frequency signal. By controlling the DC bias point, the same-frequency or multiplied-frequency signal is adjusted to a minimum to achieve closed-loop control of the DC bias point. However, this method is complex to implement and requires numerous circuit components, making it difficult to implement in miniaturized high-speed optical modules.

[0005] Therefore, overcoming the shortcomings of the existing technology is an urgent problem to be solved in this technical field. Summary of the Invention

[0006] The technical problem to be solved by this invention is how to solve the problem of bias operating point drift of silicon-based optical modulators caused by environmental changes, and the problem that traditional bias voltage control schemes have low accuracy, complex circuits, and are difficult to adapt to the miniaturization of high-speed modules, which in turn affect the quality of optical signals and the long-term working performance of communication systems.

[0007] The present invention adopts the following technical solution: In a first aspect, an automatic bias voltage control circuit is provided, comprising a control circuit, a drive circuit, a signal generation circuit, and a signal detection circuit; the control circuit is connected to the drive circuit, the signal generation circuit, and the signal detection circuit respectively. The output of the driving circuit is connected to the thermo-optical phase shifter of the silicon-based optical modulator, the output of the signal generation circuit is connected to the radio frequency modulation phase shifter of the silicon-based optical modulator, and the input of the signal detection circuit is connected to the built-in photodetector of the silicon-based optical modulator. The control circuit is used to output a sinusoidal perturbation signal, and the signal generation circuit is used to generate a differential sinusoidal perturbation signal based on the sinusoidal perturbation signal, and couple the differential sinusoidal perturbation signal to the radio frequency modulation phase shifter; The signal detection circuit is used to detect the average photocurrent and disturbance signal of the silicon-based optical modulator and feed the detection results back to the control circuit. The control circuit is used to control the driving circuit to output the corresponding driving current to the thermo-optical phase shifter based on the detection results, so as to lock the bias operating point of the silicon-based optical modulator.

[0008] Preferably, the control circuit includes a controller, a digital-to-analog converter (DAC), and an analog-to-digital converter (ADC); the DAC and the ADC are respectively connected to the controller; the controller is connected to the drive circuit. The controller is used to output the sinusoidal disturbance signal to the signal generation circuit via the digital-to-analog converter; The analog-to-digital converter is used to acquire the detection results output by the signal detection circuit; The controller is used to control the drive circuit to output a corresponding drive current to the thermo-optical phase shifter based on the detection result, so as to adjust the DC bias operating point of the silicon-based optical modulator and lock the bias operating point of the silicon-based optical modulator.

[0009] Preferably, the signal generation circuit includes a signal conversion unit and a coupling unit; The signal conversion unit is connected to the digital-to-analog converter, and the first coupling terminal of the signal conversion unit is connected to the coupling unit. The second coupling terminal of the coupling unit is used to receive the reverse bias voltage signal of the PN junction of the silicon-based optical modulator. The output terminal of the coupling unit is connected to the radio frequency modulation phase shifter. The signal conversion unit is used to convert the sinusoidal perturbation signal into the differential sinusoidal perturbation signal. The coupling unit is used to couple the differential sinusoidal perturbation signal and the reverse bias voltage signal of the PN junction of the silicon-based optical modulator to the radio frequency modulation phase shifter.

[0010] Preferably, the signal conversion unit includes at least two sets of signal conversion sub-units; the input terminals of the two sets of signal conversion sub-units are respectively connected to the output terminal of the digital-to-analog converter; the output terminals of the two sets of signal conversion sub-units are respectively connected to the input terminal of the coupling unit. The signal conversion subunit includes an adjustment subunit and a differential conversion subunit; the analog-to-digital converter, the adjustment subunit, and the differential conversion subunit are connected in sequence; the output terminal of the differential conversion subunit is connected to the coupling unit. The adjustment subunits are used to adjust the amplitude and resolution of the sinusoidal disturbance signal to obtain an intermediate signal. The differential conversion subunit is used to convert the intermediate signal into the differential sinusoidal perturbation signal.

[0011] Preferably, the regulating subunit includes a capacitor C1, a resistor R1, and a resistor R3; One end of capacitor C1 is connected to one output terminal of the digital-to-analog converter, and the other end of capacitor C1 is connected to one end of resistor R1. The other end of resistor R1 is connected to one end of resistor R3 and the input terminal of the differential conversion subunit. The other end of resistor R3 is used to receive a reference voltage.

[0012] Preferably, the differential conversion subunit includes a first operational amplifier U1A, resistors R2, R4, and R5, a second operational amplifier U1B, and a capacitor C3; The positive input terminal of the first operational amplifier U1A is connected to one end of the resistor R1 and one end of the resistor R3, respectively; the output terminal of the first operational amplifier U1A is connected to the negative input terminal of the first operational amplifier U1A, one end of the resistor R4, and the input terminal of the coupling unit, respectively. The other end of resistor R4 is connected to the negative input terminal of the second operational amplifier U1B, one end of resistor R2 is used to receive the reference voltage, and the other end of resistor R2 is connected to the positive input terminal of the second operational amplifier U1B. The output terminal of the second operational amplifier U1B is connected to one end of the resistor R5, one end of the capacitor C3, and the input terminal of the coupling unit, respectively; the other end of the resistor R5 and the other end of the capacitor C3 are connected to the negative input terminal of the second operational amplifier U1B, respectively.

[0013] Preferably, the coupling unit includes a first coupling capacitor, a first coupling resistor, a second coupling capacitor, and a second coupling resistor. One end of the first coupling capacitor is connected to the output terminal of the first operational amplifier U1A, and one end of the first coupling resistor is used to receive the reverse bias voltage signal of the PN junction of the silicon-based optical modulator. The other end of the first coupling capacitor and the other end of the first coupling resistor are respectively connected to the radio frequency modulation phase shifter; One end of the second coupling capacitor is connected to the output terminal of the second operational amplifier U1B, and one end of the second coupling resistor is used to receive the reverse bias voltage signal of the PN junction of the silicon-based optical modulator. The other end of the second coupling capacitor and the other end of the second coupling resistor are respectively connected to the radio frequency modulation phase shifter.

[0014] Preferably, the signal detection circuit includes a multiplexing unit, a DC photocurrent detection unit, and an AC photocurrent detection unit; The control terminal of the multiplexing unit is connected to the controller; the input terminal of the multiplexing unit is connected to the built-in photodetector of the silicon-based optical modulator; the output terminal of the multiplexing unit is connected to the DC photocurrent detection unit and the AC photocurrent detection unit; the output terminals of the DC photocurrent detection unit and the AC photocurrent detection unit are connected to the analog-to-digital converter. The multiplexing unit is used to switch between different channels of built-in photodetectors for optical power monitoring. The DC photocurrent detection unit is used to monitor the average photocurrent output by the silicon-based optical modulator. The AC photocurrent detection unit is used to monitor the disturbance signal output by the silicon-based optical modulator.

[0015] In a second aspect, an automatic bias voltage control method is provided, applied to the automatic bias voltage control circuit as described in the first aspect, the method comprising: The control circuit outputs a sinusoidal perturbation signal, and the signal generation circuit generates a differential sinusoidal perturbation signal based on the sinusoidal perturbation signal, and couples the differential sinusoidal perturbation signal to the radio frequency modulation phase shifter; The signal detection circuit detects the average photocurrent and disturbance signal of the silicon-based optical modulator and feeds back the detection results to the control circuit. The control circuit controls the driving circuit to output a corresponding driving current to the thermo-optical phase shifter based on the detection result, so as to lock the bias operating point of the silicon-based optical modulator.

[0016] Thirdly, a silicon-based optical modulator is provided, wherein the bias voltage automatic control circuit described in the first aspect is used to control the bias operating point of the silicon-based optical modulator, wherein: The two polarization states each include an I-channel MZI unit, a Q-channel MZI unit, and a Phase-channel MZI unit; the Q-channel MZI unit and the Phase-channel MZI unit are connected in series and then connected in parallel with the I-channel MZI unit. The modulation arms of both the I-channel MZI unit and the Q-channel MZI unit are equipped with thermo-optical phase shifters and radio frequency modulation phase shifters. The Phase-channel MZI unit is equipped with a thermo-optical phase shifter to achieve a 90° phase difference between the I-channel and Q-channel optical signals and quadrature modulation output. Both polarization outputs of the silicon-based optical modulator are equipped with built-in photodetectors for bias operating point locking and monitoring.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention precisely couples a differential sinusoidal disturbance signal to the RF modulation phase shifter of a silicon-based optical modulator through the coordinated adaptation of control circuits, drive circuits, signal generation circuits, and signal detection circuits. A built-in photodetector enables synchronous detection of the average photocurrent and the disturbance signal. The control circuit, in conjunction with the drive circuit, precisely adjusts the drive current of the thermo-optical phase shifter, efficiently locking the bias operating point. This solution addresses the problems of low accuracy and circuit complexity in traditional solutions, while improving locking speed and stability. It also simplifies hardware design, reduces component usage, meets the miniaturization requirements of high-speed silicon-based optical modules, effectively suppresses operating point drift caused by environmental changes, and ensures optical signal quality and long-term performance of the communication system. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of a silicon-based optical modulator provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of an automatic bias voltage control circuit provided in an embodiment of the present invention; Figure 3 This is another structural schematic diagram of a silicon-based optical modulator provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of a control circuit provided in an embodiment of the present invention; Figure 5 This is another structural schematic diagram of an automatic bias voltage control circuit provided in an embodiment of the present invention; Figure 6 This is a schematic diagram of a signal generation circuit provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of the structure of a signal conversion subunit provided in an embodiment of the present invention; Figure 8This is a schematic diagram of the structure of a coupling unit provided in an embodiment of the present invention; Figure 9 This is another structural schematic diagram of a coupling unit provided in an embodiment of the present invention; Figure 10 This is a schematic diagram of a signal detection circuit provided in an embodiment of the present invention; Figure 11 This is another structural schematic diagram of a signal detection circuit provided in an embodiment of the present invention; Figure 12 This is a schematic flowchart of an automatic bias voltage control method provided in an embodiment of the present invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] Unless the context otherwise requires, throughout the specification and claims, the term "comprising" is interpreted as openly inclusive, meaning "including, but not limited to." In the description of the specification, terms such as "one embodiment," "some embodiments," "exemplary embodiment," "example," "specific example," or "some examples" are intended to indicate that a particular feature, structure, material, or characteristic associated with that embodiment or example is included in at least one embodiment or example of this disclosure. The illustrative representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics mentioned may be included in any suitable manner in any one or more embodiments or examples; that is, although they may be incorporated into embodiments or examples using the above terms for reasons such as order and position, it does not limit them to be incorporated in combination by a single embodiment or example.

[0022] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, "a plurality of" means two or more. Furthermore, for example, the description may use the prefix "A" or "B" to describe the same type of nouns as two independent entities. In this case, the corresponding features defined with "A" and "B" are used only to distinguish between similar entities and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0023] In describing some embodiments, the terms "coupled," "coupled," and "connected," and their derivative expressions, may be used. For example, the term "connected" may be used in describing some embodiments to indicate that two or more components have direct physical or electrical contact with each other. Similarly, the term "coupled" may be used in describing some embodiments to indicate that two or more components have direct physical or electrical contact. However, the terms "connected" or "coupled" may also refer to two or more components that do not have direct contact with each other but still cooperate or interact with each other, such as "optical coupling," "wireless connection," etc. The embodiments disclosed herein are not necessarily limited to the scope of this invention.

[0024] Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0025] Example 1: Before describing the aforementioned bias voltage automatic control circuit, this embodiment first proposes a silicon-based optical modulator. In one embodiment, such as... Figure 1 As shown, the silicon-based optical modulator includes two polarization states, each comprising an I-channel MZI unit, a Q-channel MZI unit, and a Phase-channel MZI unit. The Q-channel MZI unit and the Phase-channel MZI unit are connected in series and then in parallel with the I-channel MZI unit. The modulation arms of both the I-channel and Q-channel MZI units are equipped with a thermo-optical phase shifter (i.e., Heater1) and an RF modulation phase shifter (i.e., RFXI1 and RFXI2, RFXQ1 and RFXQ2). The Phase-channel MZI unit is equipped with a thermo-optical phase shifter (i.e., Heater2) to achieve a 90° phase difference between the I-channel and Q-channel optical signals and quadrature modulation output. Both polarization outputs of the silicon-based optical modulator are equipped with built-in photodetectors (i.e., MPD_X and MPD_Y) for bias operating point locking monitoring.

[0026] The silicon-based optical modulator employs a dual parallel Mach-Zehnder in-phase orthogonal (DPMZ IQ) architecture, with two independent polarization states at its core. Here, polarization state refers to the vibration direction attribute of the optical signal. The symmetrical design of the two polarization states enables parallel signal transmission, which is crucial for improving the capacity of coherent optical communication. Each polarization state is equipped with one MZI unit, a Q MZI unit, and a Phase MZI unit. The MZI unit, as the basic module of optical modulation, achieves phase and amplitude adjustment of the optical signal through the interference effect of light, and is the core unit constituting the IQ modulation structure.

[0027] From a topological perspective, in each polarization state, the Q-path MZI unit is first connected in series with the Phase-path MZI unit to form a composite functional module, and then connected in parallel with the I-path MZI unit to ultimately constitute a complete IQ modulation core. The purpose of this arrangement is that the I-path and Q-path MZI units are the core channels for quadrature modulation, carrying in-phase (I-path) and quadrature (Q-path) optical signals respectively. The series connection of the Phase-path and Q-path MZI units is to precisely introduce a 90° phase difference into the Q-path signal, ensuring that both the I and Q optical signals meet the output requirements of quadrature modulation. This series-parallel topology combination is crucial for realizing the DPMZ IQ structure and ensuring the phase consistency of the modulation signal, and also provides a stable signal foundation for the bias locking of subsequent control circuits.

[0028] In terms of phase shifter configuration, both the I-channel and Q-channel MZI units employ a dual-phase shifter design in their modulation arms, integrating both a thermo-optical phase shifter and an RF modulation phase shifter. The thermo-optical phase shifter, based on the thermo-optical effect of silicon, adjusts the driving current to change the temperature of the silicon material, thereby altering the refractive index to achieve phase adjustment. Its advantages include high adjustment accuracy and strong stability. The RF modulation phase shifter, based on the plasma dispersion effect of silicon, changes the carrier concentration by applying an RF electrical signal to achieve high-speed phase adjustment, adapting to high-speed signal modulation requirements. The Phase-channel MZI unit, however, only uses a thermo-optical phase shifter. This is because the core function of the Phase channel is to provide a fixed 90° phase difference, without participating in high-speed signal modulation. The stable characteristics of the thermo-optical phase shifter are sufficient to meet the phase adjustment requirements, simplifying the structure, reducing device costs, and avoiding redundant design that could affect module integration.

[0029] In one embodiment, refer to Figure 1 R L The modulator termination matching resistor is called MMI, which stands for Multimode Interference (MMI).

[0030] To precisely meet the locking requirements of the automatic bias voltage control circuit, both polarization outputs of the silicon-based optical modulator are equipped with built-in photodetectors, i.e., miniature photodetectors. Their core function is to convert optical signals into electrical signals in real time and provide feedback on changes in optical power. The main purpose of setting up built-in photodetectors is to provide dedicated signal targets for signal detection by the control circuit. The built-in photodetectors can directly capture the average optical power (corresponding to the average photocurrent) output by the silicon-based optical modulator and the disturbance signals injected by the control circuit, convert them into electrical signals, and feed them back to the control circuit so that the control circuit can determine in real time whether the bias operating point has drifted. If an external detector is used, it will increase the complexity of the circuit connection and introduce signal loss. The built-in design can improve detection accuracy and module integration, perfectly meet the miniaturization requirements of high-speed optical modules, and at the same time provide a direct and reliable feedback signal for bias locking.

[0031] Example 2: Based on the silicon-based optical modulator proposed in Embodiment 1, and in order to solve the problems in the prior art, this embodiment proposes an automatic bias voltage control circuit. In one embodiment, such as... Figure 2 As shown, it includes a control circuit, a drive circuit, a signal generation circuit, and a signal detection circuit; the control circuit is connected to the drive circuit, the signal generation circuit, and the signal detection circuit respectively; the output terminal of the drive circuit is connected to the thermo-optical phase shifter of the silicon-based optical modulator (e.g., Figure 1 Heater1 and Heater2 in the circuit are connected, and the output of the signal generation circuit is connected to the radio frequency modulation phase shifter (e.g., in the silicon-based optical modulator). Figure 1 The signal detection circuit is connected to the built-in photodetector of the silicon-based optical modulator (e.g., RFXI1 and RFXI2, RFXQ1 and RFXQ2, etc.), and the input terminal of the signal detection circuit is connected to the built-in photodetector of the silicon-based optical modulator (e.g., RFXI1 and RFXI2, RFXQ1 and RFXQ2, etc.). Figure 1 The MPD_X and MPD_Y in the circuit are connected; the control circuit is used to output a sinusoidal perturbation signal, the signal generation circuit is used to generate a differential sinusoidal perturbation signal based on the sinusoidal perturbation signal, and couple the differential sinusoidal perturbation signal to the radio frequency modulation phase shifter; the signal detection circuit is used to detect the average photocurrent and perturbation signal of the silicon-based optical modulator, and feed the detection result back to the control circuit, the control circuit is used to control the driving circuit to output a corresponding driving current to the thermo-optical phase shifter based on the detection result, so as to lock the bias operating point of the silicon-based optical modulator.

[0032] The equivalent circuit model of the PN junction of the silicon-based optical modulator is as follows: Figure 3 As shown, RF- (such as RFXI1 and RFXQ1) are the input pins for radio frequency signals. XIBIAS1 and XIBIAS2 are the cathodes of the PN junctions on the two arms of the XI-channel MZI unit, respectively. The anode of the PN junction is grounded. R LMatch the modulator termination resistor.

[0033] In one embodiment, the core objective is to simplify hardware circuit design while meeting the requirements for bias point locking speed and accuracy, thereby achieving a high-speed, miniaturized module design capable of automatically locking and maintaining the optimal bias operating point of a silicon-based optical modulator (e.g., a Mach-Zehnder modulator). Due to material properties, temperature variations, and aging, the "operating point" (e.g., quadrature point, peak point) of the transmission curve (light intensity output vs. thermo-optical phase shifter bias) of a silicon-based optical modulator can drift. Without control, the performance of the silicon-based optical modulator (e.g., extinction ratio, linearity) will severely degrade. This embodiment uses a closed-loop feedback system to detect the operating point state in real time and automatically adjust it to stabilize it at the set value.

[0034] The control circuit first generates a low-frequency, small-amplitude sinusoidal perturbation signal. This sinusoidal perturbation signal is not used to modulate the optical signal, but rather serves as a probe to detect the shift in the operating point. Simultaneously, the control circuit receives feedback information from the signal detection circuit and calculates a correction amount using an internal algorithm, such as PID (Proportional-Integral-Derivative) or its variants. Finally, it outputs a control command to the drive circuit to adjust the bias of the thermo-optical phase shifter.

[0035] Furthermore, the sinusoidal perturbation signal output by the control circuit is fed into a signal generation circuit. The main function of this circuit is to process the single-ended perturbation signal (i.e., the sinusoidal perturbation signal) into a pair of differential sinusoidal perturbation signals with equal amplitude and opposite phase. These differential sinusoidal perturbation signals are then coupled to the two differential electrodes of the radio frequency modulation phase shifter of the silicon-based optical modulator. The purpose of this is to add a weak low-frequency perturbation to the optical carrier without significantly affecting high-speed data modulation; the effect is equivalent to applying a small periodic jitter to the bias point of the silicon-based optical modulator.

[0036] In one embodiment, a built-in photodetector integrated within the silicon-based optical modulator monitors the output optical power of the modulator and converts it into an average photocurrent. Due to the injected perturbation signal, the average photocurrent contains a small AC component with the same frequency as the perturbation. The core task of the signal detection circuit is to simultaneously detect two pieces of information: first, the magnitude of the average photocurrent, which directly reflects the output optical power; and second, to accurately extract the amplitude and phase of the AC perturbation component caused by the perturbation signal from the average photocurrent.

[0037] After receiving feedback from the signal detection circuit, the control circuit analyzes whether the average photocurrent is near the target value. More importantly, it demodulates the AC disturbance component into a DC error signal through demodulation (e.g., multiplication and low-pass filtering). The sign and magnitude of this error signal directly indicate the direction and extent of the current operating point's offset from the target point (such as the peak point or quadrature point). For example, near the peak point, the error signal is zero; deviating from the peak point will produce a non-zero error signal.

[0038] Finally, based on the calculated error signal, the control circuit sends a command to the drive circuit. The drive circuit, acting as a power output stage, converts the digital control command into an analog drive current capable of driving the thermo-optical phase shifter. The thermo-optical phase shifter is essentially a micro-heater; by changing its temperature through current, it utilizes the thermo-optical effect of silicon to alter the optical phase of the waveguide. By adjusting this drive current, the system can actively and inversely compensate for phase drift caused by various factors, pulling the operating point back and locking it at the target position, thereby locking the bias operating point of the silicon-based optical modulator.

[0039] In one embodiment, such as Figure 4 As shown, the control circuit includes a controller, a digital-to-analog converter (DAC), and an analog-to-digital converter (ADC); the DAC and the ADC are respectively connected to the controller; the controller is connected to the drive circuit; the controller is used to output the sinusoidal perturbation signal to the signal generation circuit through the DAC; the ADC is used to acquire the detection result output by the signal detection circuit; the controller is used to control the drive circuit to output a corresponding drive current to the thermo-optical phase shifter based on the detection result, so as to adjust the DC bias operating point of the silicon-based optical modulator, thereby locking the bias operating point of the silicon-based optical modulator.

[0040] In one embodiment, the controller is mainly used to generate a digital sequence through an algorithm (such as direct digital frequency synthesis), which represents the discrete sampling points of the low-frequency sinusoidal disturbance signal; receive digital signals representing the detection results from the analog-to-digital converter and run control algorithms (such as proportional-integral-derivative algorithms); calculate the correction amount to be applied to the thermo-optical phase shifter based on the detection results; and output corresponding digital control commands.

[0041] In one embodiment, the sinusoidal perturbation signal generated by the controller is a digital code and cannot be directly used to drive analog circuits. The function of the digital-to-analog converter is to convert the digital sequence output by the controller into a real, smooth analog voltage signal in real time, i.e., the final sinusoidal perturbation signal. The sinusoidal perturbation signal is output to the downstream signal generation circuit for further processing and injection into the radio frequency modulation phase shifter.

[0042] In one embodiment, the detection result output by the signal detection circuit (including the DC average photocurrent and AC disturbance component) is a continuous analog electrical signal. The role of the analog-to-digital converter is to acquire the analog signal and quantize it into a series of digital codes at a fixed sampling rate, which are then fed back to the controller. This allows the controller to obtain the real-time operating status of the silicon-based optical modulator.

[0043] In one embodiment, to improve accuracy, the analog-to-digital converter can be a 16-bit high-precision ADC (Analog to Digital Converter), and the digital-to-analog converter can be a 12-bit high-precision DAC (Digital-to-Analog Converter). Both the analog-to-digital converter and the digital-to-analog converter have multiple input terminals and output terminals.

[0044] In one embodiment, such as Figure 5 As shown, for example, the controller and digital-to-analog converter convert a sinusoidal disturbance signal DDS_OUT of a certain frequency. <0> and sinusoidal perturbation signal DDS_OUT <1> It is transmitted to the signal generation circuit.

[0045] In one embodiment, such as Figure 5 and Figure 6 As shown, the signal generation circuit includes a signal conversion unit and a coupling unit; the signal conversion unit is connected to the digital-to-analog converter, and the first coupling terminal of the signal conversion unit is connected to the first coupling terminal of the coupling unit; the second coupling terminal of the coupling unit is used to receive the reverse bias voltage signal of the PN junction of the silicon-based optical modulator; the output terminal of the coupling unit is connected to the radio frequency modulation phase shifter; the signal conversion unit is used to convert the sinusoidal perturbation signal into the differential sinusoidal perturbation signal; the coupling unit is used to couple the differential sinusoidal perturbation signal and the reverse bias voltage signal of the PN junction of the silicon-based optical modulator to the radio frequency modulation phase shifter.

[0046] The signal generation circuit is used to load the single-ended sinusoidal disturbance signal emitted by the control circuit for detection onto the working electrode of the high-speed modulator in an interference-free manner. This requires solving two key problems: first, converting the single-ended signal into a better differential form; and second, ensuring that the disturbance signal can coexist harmoniously with the modulator's original DC bias and high-frequency data signal.

[0047] The output of a digital-to-analog converter (DAC) is typically a single-ended sinusoidal perturbation signal relative to ground. The signal conversion unit converts the input single-ended signal into a pair of analog voltage signals with equal amplitude and exactly opposite phase (180 degrees out of phase), i.e., differential sinusoidal perturbation signals. Because differential signals have a natural suppression effect on external common-mode noise (such as power supply noise and crosstalk), they ensure that weak probe signals remain pure during transmission. Silicon-based optical modulators typically employ a push-pull structure for their RF modulation phase shifters, consisting of a pair of PN junctions (or similar elements), and their ideal driving method is a differential signal. Differential perturbations can act symmetrically on the two electrodes, achieving more efficient and linear optical phase modulation.

[0048] In one embodiment, the first coupling terminal of the coupling unit receives a differential sinusoidal perturbation signal from the signal conversion unit. The second coupling terminal receives a reverse bias voltage signal from the PN junction of the silicon-based optical modulator (this is a DC voltage used to set the operating point of the RF modulator, ensuring that it operates in the appropriate depletion region to achieve efficient electro-optic modulation).

[0049] For disturbance signals, the coupling unit presents a low-impedance path for low-frequency disturbance signals, allowing them to be transmitted from the first coupling terminal to the output terminal with almost no loss. Simultaneously, it blocks the DC component, preventing the disturbance circuit from affecting the DC bias source of the PN junction. For DC bias, the coupling unit presents a high impedance or a DC path (depending on the specific design), ensuring that the DC reverse bias voltage can be stably and without attenuation applied to the RF electrode at the output terminal from the second coupling terminal. At the same time, it prevents DC voltage from flowing into the sensitive differential signal drive circuit, thus providing protection.

[0050] Finally, at the output of the coupling unit, the low-frequency differential perturbation signal and the DC reverse bias voltage are linearly superimposed. This synthesized signal is then directly fed into the differential electrode of the RF modulation phase shifter of the silicon-based optical modulator.

[0051] In one embodiment, such as Figure 7 As shown, the signal conversion unit includes at least two sets of signal conversion subunits; the input terminals of the two sets of signal conversion subunits are respectively connected to the output terminal of the digital-to-analog converter; the output terminals of the two sets of signal conversion subunits are respectively connected to the input terminal of the coupling unit; the signal conversion subunit includes an adjustment subunit and a differential conversion subunit; the analog-to-digital converter, the adjustment subunit, and the differential conversion subunit are connected in sequence; the output terminal of the differential conversion subunit is connected to the coupling unit; the adjustment subunit is used to adjust the amplitude and resolution of the sinusoidal disturbance signal to obtain an intermediate signal; the differential conversion subunit is used to convert the intermediate signal into the differential sinusoidal disturbance signal.

[0052] Reference Figure 5 and Figure 7 In this embodiment, the signal conversion unit presents a dual-branch symmetrical layout (to meet the requirements of the silicon-based optical modulator I and Q RF modulation phase shifters in Embodiment 1). It includes at least two sets of signal conversion sub-units. The input ends of the two sets of sub-units are connected in parallel to the output end of the digital-to-analog converter of the control circuit, and the output ends are respectively connected to the two input ports of the coupling unit to form two independent signal conversion paths.

[0053] In any branch, each signal conversion subunit includes a conditioning subunit and a differential conversion subunit connected in series. The input of the conditioning subunit is directly connected to the single-ended sinusoidal perturbation signal output from the digital-to-analog converter (e.g., DDS_OUT). <0> The voltage amplitude of the sinusoidal disturbance signal is controlled within a reasonable range that does not interfere with the normal RF modulation signal but can be captured by the subsequent detection circuit (avoiding excessively strong disturbances that affect the optical signal quality, or excessively weak disturbances that cause detection failure). By matching the reference voltage and the resistor, the voltage accuracy of the signal is improved, and distortion of small-amplitude disturbance signals during transmission is avoided. The accurate intermediate signal obtained after this processing is transmitted to the subsequent differential conversion subunit.

[0054] In one embodiment, refer to Figure 7 As shown, the adjustment subunit includes a capacitor C1, a resistor R1, and a resistor R3; one end of the capacitor C1 is connected to one output terminal of the digital-to-analog converter, the other end of the capacitor C1 is connected to one end of the resistor R1, and the other end of the resistor R1 is connected to one end of the resistor R3 and the input terminal of the differential conversion subunit; the other end of the resistor R3 is used to receive a reference voltage.

[0055] Among them, capacitor C1 is a DC blocking coupling capacitor, which blocks the DC component in the output signal of the digital-to-analog converter, allowing only the AC sinusoidal disturbance signal to pass through, thus avoiding DC interference with the accuracy of subsequent differential conversion, and also playing a role in signal coupling and transmission. Resistors R1 and R3 form a voltage divider adjustment network. By matching their resistance values, the amplitude of the sinusoidal disturbance signal can be precisely controlled, that is, the original signal amplitude is adjusted to the optimal range that "does not affect the normal operation of the RF modulation phase shifter, and can be stably captured by the subsequent signal detection circuit" (for example, avoiding excessive disturbance amplitude that leads to optical signal distortion, or too small a disturbance amplitude that leads to detection failure). The reference voltage (VREF) provides a stable reference for amplitude adjustment, and together with the voltage divider network, it improves the voltage resolution of the signal, ensuring that even small amplitude disturbance signal changes can be accurately preserved, avoiding signal distortion in the preprocessing stage.

[0056] The signal processing flow of the entire adjustment subunit is as follows: the single-ended sinusoidal disturbance signal output by the digital-to-analog converter is coupled by capacitor C1 through DC blocking, and then enters the voltage divider adjustment network composed of resistors R1 and R3. Under the reference support of the reference voltage (VREF), the amplitude calibration and resolution improvement are completed, and finally a precise and stable intermediate signal is formed, which is transmitted to the differential conversion subunit for subsequent single-ended to differential conversion.

[0057] The core function of the differential converter subunit is to convert a single-ended intermediate signal into a differential sinusoidal perturbation signal. In one embodiment, referencing... Figure 7 As shown, the differential conversion subunit includes a first operational amplifier U1A, resistors R2, R4, and R5, a second operational amplifier U1B, and a capacitor C3. The positive input terminal of the first operational amplifier U1A is connected to one end of resistor R1 and one end of resistor R3, respectively. The output terminal of the first operational amplifier U1A is connected to the negative input terminal of the first operational amplifier U1A, one end of resistor R4, and the input terminal of the coupling unit, respectively. The other end of resistor R4 is connected to the negative input terminal of the second operational amplifier U1B. One end of resistor R2 is used to receive a reference voltage, and the other end of resistor R2 is connected to the positive input terminal of the second operational amplifier U1B. The output terminal of the second operational amplifier U1B is connected to one end of resistor R5, one end of capacitor C3, and the input terminal of the coupling unit, respectively. The other ends of resistor R5 and capacitor C3 are connected to the negative input terminal of the second operational amplifier U1B, respectively.

[0058] The differential conversion subunit adopts a dual operational amplifier symmetrical topology, and its core function is to convert the intermediate signal output by the adjustment subunit into a differential sinusoidal disturbance signal with strong anti-interference capability.

[0059] Reference Figure 7 The first operational amplifier U1A, with its output terminal fed back to the negative input terminal, forms a voltage follower (a special form of the non-inverting proportional amplifier circuit, with a gain of 1). It is primarily used to match the output impedance of the adjustment subunit with the impedance of subsequent circuits, preventing distortion of the intermediate signal during transmission. Simultaneously, it does not change the voltage amplitude of the intermediate signal, only enhancing its load-carrying capacity, ensuring that the subsequent resistor R4 branch can stably acquire the signal. Furthermore, utilizing the operational amplifier's high input impedance and low output impedance characteristics, it filters out minor noise in the intermediate signal, resulting in a cleaner signal.

[0060] The second operational amplifier U1B forms an inverting proportional amplifier circuit through resistors R2 (reference input), R4 (signal input), and R5 (feedback resistor), and forms a compensation network with capacitor C3. Resistor R2 is used to introduce the reference voltage (VREF) into the positive input terminal of the second operational amplifier U1B, providing a stable reference for inverting amplification and ensuring that the output signal of the second operational amplifier U1B and the output signal of the first operational amplifier U1A form a symmetrical differential (i.e., equal amplitude and opposite phase), avoiding DC offset of the differential signal.

[0061] The resistor R4 serves as the input resistor for the second operational amplifier U1B, coupling the intermediate signal output from the first operational amplifier U1A to the negative input terminal of the second operational amplifier U1B. It also controls the amplitude of the input signal to prevent excessive signal strength from causing operational amplifier saturation. The resistor R5 acts as a negative feedback resistor, working in conjunction with resistor R4 to set the amplification factor of the second operational amplifier U1B (amplification factor = -R5 / R4). This ensures that the amplitude of the negative signal output from the second operational amplifier U1B is completely consistent with the amplitude of the positive signal output from the first operational amplifier U1A, satisfying the symmetry requirements of the differential signal. The capacitor C3 is used for phase compensation and filtering. On one hand, it suppresses high-frequency oscillations of the operational amplifier, ensuring stable circuit operation (suitable for high-frequency signal scenarios in high-speed optical modules). On the other hand, it filters out high-frequency noise after amplification, making the waveform of the differential signal more regular.

[0062] In one embodiment, the reference voltage (VREF) provides a fixed reference potential to the second operational amplifier U1B through resistor R2. Its core purpose is to calibrate the common-mode voltage of the differential signal, so that the positive terminal signal output by the first operational amplifier U1A and the negative terminal signal output by the second operational amplifier U1B change symmetrically around VREF, thereby avoiding common-mode interference in the differential signal (most of the electromagnetic noise in high-speed optical modules is common-mode interference, and symmetrical differential signals can effectively cancel this interference).

[0063] Finally, refer to Figure 7 The positive terminal signal output by the first operational amplifier U1A (i.e., DDS_OUTP) <0> The signal at the negative terminal of the second operational amplifier U1B (i.e., DDS_OUTN) <0> This forms a complete differential sinusoidal perturbation signal, which is then superimposed on the reverse bias voltage of the PN junction through a coupling unit and transmitted to the RF modulation phase shifter of the silicon-based optical modulator. The other branch works similarly and will not be discussed further here.

[0064] In one embodiment, the operational amplifiers proposed in this embodiment are all powered by a positive power supply, wherein the positive power supply VCC power supply chip is an ultra-low noise low dropout linear regulator.

[0065] In one embodiment, the structure and principle of the other branch are the same as described above, and will not be explained in detail here.

[0066] After obtaining the differential sinusoidal perturbation signals corresponding to the two branches, in one embodiment, such as Figure 8 As shown, the coupling unit includes a first coupling capacitor (i.e., Cs1), a first coupling resistor (i.e., Rs1), a second coupling capacitor (i.e., Cs2), and a second coupling resistor (i.e., Rs2). One end of the first coupling capacitor is connected to the output terminal of the first operational amplifier U1A, and one end of the first coupling resistor is used to receive the reverse bias voltage signal of the PN junction of the silicon-based optical modulator. The other ends of the first coupling capacitor and the other ends of the first coupling resistor are respectively connected to the radio frequency modulation phase shifter. One end of the second coupling capacitor is connected to the output terminal of the second operational amplifier U1B, and one end of the second coupling resistor is used to receive the reverse bias voltage signal of the PN junction of the silicon-based optical modulator. The other ends of the second coupling capacitor and the other ends of the second coupling resistor are respectively connected to the radio frequency modulation phase shifter.

[0067] Among them, reference Figure 8 As shown in the figure, DDS_OUTN<0 or 1> (corresponding to the differential negative signal output by the second op-amp U1B) and DDS_OUTP<0 or 1> (corresponding to the differential positive signal output by the first op-amp U1A) are connected to the VBIAS_DDS_OUT series ports (such as VBIAS_DDS_OUTN0 and VBIAS_DDS_OUTP0) through capacitors (i.e., the first coupling capacitor and the second coupling capacitor of the coupling unit).

[0068] Figure 8 The MZ_VBIAS (i.e., the reverse bias voltage signal of the PN junction of the silicon-based optical modulator) is connected to the VBIAS_DDS_OUT series ports through resistors (i.e., the first coupling resistor and the second coupling resistor of the coupling unit).

[0069] The output of each VBIAS_DDS_OUT port (such as VBIAS_DDS_OUTN0) is directly connected to the bias interface of the RF modulation phase shifter (such as TX0_XBIAS1, TX0_QBIAS1, etc. in the figure), while the RFX11, RFX01, and other modules next to the interface are the RF modulation phase shifters of the silicon-based optical modulator.

[0070] The coupling unit structure of the other branch is as follows Figure 9 As shown, no further explanation will be given here. Figure 8 Taking the TX0_XBIAS1 pathway as an example: First coupling capacitor (DDS_OUTP in the diagram) <0> (The capacitor between VBIAS_DDS_OUTP0 and the first op-amp U1A) is connected to the differential positive disturbance signal output by one end and to VBIAS_DDS_OUTP0 by the other end. The first coupling resistor (the resistor between MZ_VBIAS and VBIAS_DDS_OUTP0 in the diagram): one end is connected to MZ_VBIAS (PN junction reverse bias voltage), and the other end is connected to VBIAS_DDS_OUTP0. Finally, the output of VBIAS_DDS_OUTP0 is directly connected to the bias interface TX0_XBIAS1 of the RF modulation phase shifter.

[0071] The connection logic of other branches in the diagram (such as TX0_QBIAS1 and TX1_XBIAS1) is completely the same as above, only corresponding to the RF modulation phase shifters of different channels.

[0072] Among them, the first coupling capacitor and the second coupling capacitor are DC blocking capacitors, which only allow the differential sinusoidal disturbance signal of AC nature to pass through (blocking the DC component). This avoids the DC signal from interfering with the waveform of the disturbance signal, and ensures that the disturbance signal can be accurately superimposed on the optical signal, providing a basis for the subsequent signal detection circuit to capture the disturbance.

[0073] The MZ_VBIAS connected to the first and second coupling resistors is the reverse bias voltage (DC) of the PN junction of the silicon-based optical modulator's radio frequency phase shifter. The radio frequency phase shifter operates based on the plasma dispersion effect of the PN junction and must rely on the reverse bias voltage to maintain the carrier distribution state, which is a prerequisite for its high-speed modulation.

[0074] By combining capacitors and resistors, the AC differential perturbation signal and the DC reverse bias voltage are coupled into a single signal. This provides the necessary DC bias for each RF modulation phase shifter and allows the perturbation signal to act on the optical signal. At the same time, the layout of multiple VBIAS_DDS_OUT ports in the figure is adapted to the needs of the modulator's multi-channel (I-channel, Q-channel, different polarization states) RF phase shifters, ensuring that each phase shifter can obtain an independent coupling signal to support the precise locking of the subsequent bias operating point.

[0075] In one embodiment, refer to Figure 8 Among them, the differential sinusoidal perturbation signal DDS_OUTP <0> DDS_OUTN <0> and DDS_OUTP <1> DDS_OUTN <1> The signals are coupled to the PN junction reverse bias voltage signal MZ_VBIAS through the corresponding coupling capacitors and coupling resistors, respectively, to generate the coupled signals: VBIAS_DDS_OUTN0, VBIAS_DDS_OUTP0, VBIAS_DDS_OUTN1 and VBIAS_DDS_OUTP1.

[0076] Specifically, the coupled signals VBIAS_DDS_OUTN0 and VBIAS_DDS_OUTP0 are input to the XI and YI paths of silicon-based optical modulators TX0 and TX1; the coupled signals VBIAS_DDS_OUTN1 and VBIAS_DDS_OUTP1 are input to the XQ and YQ paths of modulators TX0 and TX1. The differential sinusoidal perturbation signal DDS_OUTP... <0> DDS_OUTN <0> and DDS_OUTP <1> DDS_OUTN <1> The reverse bias voltage signal MZ_VBIAS of the PN junction is coupled to another set of coupling capacitors and another set of coupling resistors to generate the coupled signals VBIAS_DDS_OUTN2, VBIAS_DDS_OUTP2, VBIAS_DDS_OUTN3, and VBIAS_DDS_OUTP3, respectively.

[0077] Specifically, the coupled signals VBIAS_DDS_OUTN2 and VBIAS_DDS_OUTP2 are input to the XI and YI paths of silicon-based optical modulators TX2 and TX3; the coupled signals VBIAS_DDS_OUTN3 and VBIAS_DDS_OUTP3 are input to the XQ and YQ paths of silicon-based optical modulators TX2 and TX3.

[0078] In one embodiment, such as Figure 10 As shown, the signal detection circuit includes a multiplexing unit, a DC photocurrent detection unit, and an AC photocurrent detection unit. The control terminal of the multiplexing unit is connected to the controller. The input terminal of the multiplexing unit is connected to the built-in photodetectors of the silicon-based optical modulator, and the output terminal of the multiplexing unit is connected to the DC photocurrent detection unit and the AC photocurrent detection unit, respectively. The output terminals of the DC photocurrent detection unit and the AC photocurrent detection unit are respectively connected to the analog-to-digital converter. The multiplexing unit is used to switch the built-in photodetectors of different channels for optical power monitoring. The DC photocurrent detection unit is used to monitor the average photocurrent output by the silicon-based optical modulator. The AC photocurrent detection unit is used to monitor the disturbance signal output by the silicon-based optical modulator.

[0079] The multiplexing unit can be an 8:1 precision multiplexer with extremely low leakage current, capable of monitoring the photocurrent of 8 MPDs from 4 DPMZ IQ modulators. In one embodiment, the multiplexing unit is model TMUX1108.

[0080] The core function of the multiplexing unit is to switch the monitoring channel in a time-division manner. Since the silicon-based optical modulator contains multiple polarization state and I / Q MZI units, corresponding to multiple built-in photodetectors, configuring a separate detection circuit for each detector would significantly increase the hardware cost and module size. The multiplexing unit allows the controller to switch to the MPD of the target channel as needed and transmit the photocurrent signal of that channel to the subsequent detection unit. This achieves full coverage monitoring of multi-channel optical power, simplifies the circuit structure, and adapts to the miniaturization requirements of high-speed optical modules.

[0081] In one embodiment, the function of the DC photocurrent detection unit is to capture the average photocurrent of the optical signal. The average photocurrent corresponds to the base power of the output optical signal of the silicon-based optical modulator and is the core basis for determining the initial state of the bias operating point. When the modulator bias operating point drifts due to environmental changes (such as temperature fluctuations), the average power of the output optical signal will change synchronously. The DC detection unit converts this photocurrent into a corresponding DC voltage signal, which is transmitted to the controller via an analog-to-digital converter, providing the controller with a basic reference for whether the operating point has deviated. In one embodiment, such as Figure 11 As shown, the signal detection circuit further includes a preamplifier transimpedance amplifier, and the DC photocurrent detection unit includes a low-pass filter. The output terminal of the preamplifier transimpedance amplifier is connected to one end of the low-pass filter and the input terminal of the AC photocurrent detection unit, respectively. The other end of the low-pass filter is connected to the analog-to-digital converter, thereby realizing the detection of the average optical power output by the modulator.

[0082] In one embodiment, the signal generation circuit couples the differential sinusoidal perturbation signal to the RF modulation phase shifter of the silicon-based optical modulator, and the differential sinusoidal perturbation signal is output synchronously with the optical signal. The AC photocurrent detection unit is used to filter out the DC component of the optical signal, amplify and extract only the AC perturbation signal, and convert it into a corresponding electrical signal for transmission to the controller. The amplitude and phase changes of the perturbation signal are key to the controller's determination of the direction and degree of bias operating point offset. For example, when the bias operating point is in the optimal state, the feedback amplitude of the perturbation signal will reach a minimum value (or exhibit specific phase characteristics). The controller can accurately adjust the drive circuit based on this feedback to achieve operating point locking. In one embodiment, referencing Figure 11 As shown, the AC photocurrent detection unit includes an AC coupling output circuit, a non-inverting AC amplifier circuit, and a filter circuit. The input terminal of the AC coupling output circuit is connected to one output terminal of the preamplifier transimpedance amplifier, and the output terminal of the AC coupling output circuit is connected to the input terminal of the non-inverting AC amplifier circuit to achieve secondary amplification of the Dither disturbance signal. The output terminal of the non-inverting AC amplifier circuit is connected to the input terminal of the filter circuit, and the output terminal of the filter circuit is connected to the analog-to-digital converter. The Dither signal is sampled through the analog-to-digital converter to lock the bias operating point of the silicon-based optical modulator.

[0083] Based on the above structure, under the scheduling of the controller, the multiplexing unit first switches to the built-in photodetector of the target channel and synchronously transmits the photocurrent signal of the channel to the DC photocurrent detection unit and the AC photocurrent detection unit. The DC photocurrent detection unit collects the average photocurrent to feed back the basic state, and the AC photocurrent detection unit collects the disturbance signal to feed back the details of the operating point offset. After the two types of signals are converted into digital signals by the analog-to-digital converter, they are transmitted to the controller together to provide it with complete feedback basis, and finally support the closed-loop locking of the bias operating point.

[0084] In summary, this embodiment, through the coordinated adaptation of the control circuit, drive circuit, signal generation circuit, and signal detection circuit, precisely couples the differential sinusoidal disturbance signal to the RF modulation phase shifter of the silicon-based optical modulator. The built-in photodetector enables synchronous detection of the average photocurrent and the disturbance signal. The control circuit, in conjunction with the drive circuit, precisely adjusts the drive current of the thermo-optical phase shifter, efficiently locking the bias operating point. This solution not only solves the problems of low accuracy and circuit complexity in traditional solutions but also improves locking speed and stability. Furthermore, it simplifies hardware design, reduces the number of components, adapts to the miniaturization requirements of high-speed silicon-based optical modules, effectively suppresses operating point drift caused by environmental changes, and ensures optical signal quality and long-term performance of the communication system.

[0085] Example 3: This embodiment proposes an automatic bias voltage control method. In one embodiment, such as... Figure 12 As shown, the method includes: Step 101: The control circuit outputs a sinusoidal disturbance signal, the signal generation circuit generates a differential sinusoidal disturbance signal based on the sinusoidal disturbance signal, and couples the differential sinusoidal disturbance signal to the radio frequency modulation phase shifter.

[0086] The control circuit first outputs a single-ended sinusoidal perturbation signal. This signal enters the signal generation circuit, where the signal conversion unit converts it from single-ended to differential, generating a differential sinusoidal perturbation signal with stronger anti-interference capabilities. Subsequently, the coupling unit couples this differential perturbation signal together with the reverse bias voltage of the PN junction required by the RF modulation phase shifter of the silicon-based optical modulator, and finally injects it into each RF modulation phase shifter.

[0087] Step 102: The signal detection circuit detects the average photocurrent and disturbance signal of the silicon-based optical modulator and feeds back the detection results to the control circuit.

[0088] The silicon-based optical modulator's built-in photodetector (MPD) captures the output optical signal, including perturbation characteristics, in real time and converts it into photocurrent. The signal detection circuit, through a multiplexing unit, synchronously transmits the photocurrent of the target channel to both the DC and AC photocurrent detection units: the DC unit extracts the average photocurrent reflecting the fundamental power of the optical signal, while the AC unit filters out the DC component and specifically extracts the sinusoidal perturbation signal superimposed on the optical signal. These two detection results are converted into electrical signals and fed back to the control circuit via an analog-to-digital converter, providing complete feedback data for subsequent bias point determination.

[0089] Step 103: The control circuit controls the driving circuit to output a corresponding driving current to the thermo-optical phase shifter based on the detection result, so as to lock the bias operating point of the silicon-based optical modulator.

[0090] In this process, after receiving the detection feedback, the control circuit combines the amplitude and phase characteristics of the average photocurrent and the disturbance signal to determine whether the current bias operating point deviates from the optimal state. In one embodiment, the deviation can be calculated using a PID algorithm to generate a corresponding adjustment command. The drive circuit then outputs a precise drive current based on this command, which acts on the thermo-optical phase shifter of the silicon-based optical modulator. The thermo-optical phase shifter adjusts the phase of the optical signal by changing its own temperature and refractive index, ultimately pulling the bias operating point back and stabilizing it at the target position, completing the entire closed-loop locking process.

[0091] This embodiment achieves precise coupling of the differential sinusoidal disturbance signal to the RF modulation phase shifter of the silicon-based optical modulator through the coordinated adaptation of the control circuit, drive circuit, signal generation circuit, and signal detection circuit. The built-in photodetector enables synchronous detection of the average photocurrent and the disturbance signal. The control circuit, in conjunction with the drive circuit, precisely adjusts the drive current of the thermo-optical phase shifter, efficiently locking the bias operating point. This solution addresses the problems of low accuracy and circuit complexity in traditional solutions, while improving locking speed and stability. It also simplifies hardware design, reduces component usage, meets the miniaturization requirements of high-speed silicon-based optical modules, effectively suppresses operating point drift caused by environmental changes, and ensures optical signal quality and long-term performance of the communication system.

[0092] For the specific structure of the automatic bias voltage control circuit, please refer to Embodiment 1, which will not be repeated in this embodiment.

[0093] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An automatic bias voltage control circuit, characterized in that, It includes a control circuit, a drive circuit, a signal generation circuit, and a signal detection circuit; the control circuit is connected to the drive circuit, the signal generation circuit, and the signal detection circuit respectively. The output of the driving circuit is connected to the thermo-optical phase shifter of the silicon-based optical modulator, the output of the signal generation circuit is connected to the radio frequency modulation phase shifter of the silicon-based optical modulator, and the input of the signal detection circuit is connected to the built-in photodetector of the silicon-based optical modulator. The control circuit is used to output a sinusoidal perturbation signal, and the signal generation circuit is used to generate a differential sinusoidal perturbation signal based on the sinusoidal perturbation signal, and couple the differential sinusoidal perturbation signal to the radio frequency modulation phase shifter; The signal detection circuit is used to detect the average photocurrent and disturbance signal of the silicon-based optical modulator and feed the detection results back to the control circuit. The control circuit is used to control the driving circuit to output the corresponding driving current to the thermo-optical phase shifter based on the detection results, so as to lock the bias operating point of the silicon-based optical modulator.

2. The bias voltage automatic control circuit according to claim 1, characterized in that, The control circuit includes a controller, a digital-to-analog converter (DAC), and an analog-to-digital converter (ADC); the DAC and the ADC are respectively connected to the controller; the controller is connected to the drive circuit. The controller is used to output the sinusoidal disturbance signal to the signal generation circuit via the digital-to-analog converter; The analog-to-digital converter is used to acquire the detection results output by the signal detection circuit; The controller is used to control the drive circuit to output a corresponding drive current to the thermo-optical phase shifter based on the detection result, so as to adjust the DC bias operating point of the silicon-based optical modulator and lock the bias operating point of the silicon-based optical modulator.

3. The bias voltage automatic control circuit according to claim 2, characterized in that, The signal generation circuit includes a signal conversion unit and a coupling unit; The signal conversion unit is connected to the digital-to-analog converter, and the first coupling terminal of the signal conversion unit is connected to the coupling unit. The second coupling terminal of the coupling unit is used to receive the reverse bias voltage signal of the PN junction of the silicon-based optical modulator. The output terminal of the coupling unit is connected to the radio frequency modulation phase shifter. The signal conversion unit is used to convert the sinusoidal perturbation signal into the differential sinusoidal perturbation signal. The coupling unit is used to couple the differential sinusoidal perturbation signal and the reverse bias voltage signal of the PN junction of the silicon-based optical modulator to the radio frequency modulation phase shifter.

4. The bias voltage automatic control circuit according to claim 3, characterized in that, The signal conversion unit includes at least two sets of signal conversion sub-units; the input terminals of the two sets of signal conversion sub-units are respectively connected to the output terminal of the digital-to-analog converter; the output terminals of the two sets of signal conversion sub-units are respectively connected to the input terminal of the coupling unit. The signal conversion subunit includes an adjustment subunit and a differential conversion subunit; the analog-to-digital converter, the adjustment subunit, and the differential conversion subunit are connected in sequence; the output terminal of the differential conversion subunit is connected to the coupling unit. The adjustment subunits are used to adjust the amplitude and resolution of the sinusoidal disturbance signal to obtain an intermediate signal. The differential conversion subunit is used to convert the intermediate signal into the differential sinusoidal perturbation signal.

5. The bias voltage automatic control circuit according to claim 4, characterized in that, The adjustment subunit includes a capacitor C1, a resistor R1, and a resistor R3; One end of capacitor C1 is connected to one output terminal of the digital-to-analog converter, and the other end of capacitor C1 is connected to one end of resistor R1. The other end of resistor R1 is connected to one end of resistor R3 and the input terminal of the differential conversion subunit. The other end of resistor R3 is used to receive a reference voltage.

6. The bias voltage automatic control circuit according to claim 5, characterized in that, The differential conversion subunit includes a first operational amplifier U1A, resistors R2, R4, and R5, a second operational amplifier U1B, and a capacitor C3; The positive input terminal of the first operational amplifier U1A is connected to one end of the resistor R1 and one end of the resistor R3, respectively; the output terminal of the first operational amplifier U1A is connected to the negative input terminal of the first operational amplifier U1A, one end of the resistor R4, and the input terminal of the coupling unit, respectively. The other end of resistor R4 is connected to the negative input terminal of the second operational amplifier U1B, one end of resistor R2 is used to receive the reference voltage, and the other end of resistor R2 is connected to the positive input terminal of the second operational amplifier U1B. The output terminal of the second operational amplifier U1B is connected to one end of the resistor R5, one end of the capacitor C3, and the input terminal of the coupling unit, respectively; the other end of the resistor R5 and the other end of the capacitor C3 are connected to the negative input terminal of the second operational amplifier U1B, respectively.

7. The bias voltage automatic control circuit according to claim 6, characterized in that, The coupling unit includes a first coupling capacitor, a first coupling resistor, a second coupling capacitor, and a second coupling resistor. One end of the first coupling capacitor is connected to the output terminal of the first operational amplifier U1A, and one end of the first coupling resistor is used to receive the reverse bias voltage signal of the PN junction of the silicon-based optical modulator. The other end of the first coupling capacitor and the other end of the first coupling resistor are respectively connected to the radio frequency modulation phase shifter; One end of the second coupling capacitor is connected to the output terminal of the second operational amplifier U1B, and one end of the second coupling resistor is used to receive the reverse bias voltage signal of the PN junction of the silicon-based optical modulator. The other end of the second coupling capacitor and the other end of the second coupling resistor are respectively connected to the radio frequency modulation phase shifter.

8. The bias voltage automatic control circuit according to claim 2, characterized in that, The signal detection circuit includes a multiplexing unit, a DC photocurrent detection unit, and an AC photocurrent detection unit; The control terminal of the multiplexing unit is connected to the controller; the input terminal of the multiplexing unit is connected to the built-in photodetector of the silicon-based optical modulator; the output terminal of the multiplexing unit is connected to the DC photocurrent detection unit and the AC photocurrent detection unit; the output terminals of the DC photocurrent detection unit and the AC photocurrent detection unit are connected to the analog-to-digital converter. The multiplexing unit is used to switch between different channels of built-in photodetectors for optical power monitoring. The DC photocurrent detection unit is used to monitor the average photocurrent output by the silicon-based optical modulator. The AC photocurrent detection unit is used to monitor the disturbance signal output by the silicon-based optical modulator.

9. An automatic bias voltage control method, characterized in that, The method, applied to the bias voltage automatic control circuit as described in any one of claims 1-8, comprises: The control circuit outputs a sinusoidal perturbation signal, and the signal generation circuit generates a differential sinusoidal perturbation signal based on the sinusoidal perturbation signal, and couples the differential sinusoidal perturbation signal to the radio frequency modulation phase shifter; The signal detection circuit detects the average photocurrent and disturbance signal of the silicon-based optical modulator and feeds back the detection results to the control circuit. The control circuit controls the driving circuit to output a corresponding driving current to the thermo-optical phase shifter based on the detection result, so as to lock the bias operating point of the silicon-based optical modulator.

10. A silicon-based optical modulator, characterized in that, The bias voltage automatic control circuit as described in any one of claims 1-8 is used to control the bias operating point of the silicon-based optical modulator, wherein: The two polarization states each include an I-channel MZI unit, a Q-channel MZI unit, and a Phase-channel MZI unit; the Q-channel MZI unit and the Phase-channel MZI unit are connected in series and then connected in parallel with the I-channel MZI unit. The modulation arms of both the I-channel MZI unit and the Q-channel MZI unit are equipped with thermo-optical phase shifters and radio frequency modulation phase shifters. The Phase-channel MZI unit is equipped with a thermo-optical phase shifter to achieve a 90° phase difference between the I-channel and Q-channel optical signals and quadrature modulation output. Both polarization outputs of the silicon-based optical modulator are equipped with built-in photodetectors for bias operating point locking and monitoring.

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