A wavelength locking system for a silicon oxide microring resonator

Abstract

This invention discloses a wavelength locking system for a silicon oxide microring resonator, comprising a photoelectric conversion module, a feedback control module, a radio frequency drive module, an interdigital transducer, a zinc oxide film, a lock-in amplifier module, two analog-to-digital conversion modules, and a digital-to-analog conversion module. The radio frequency drive module generates an alternating electrical signal and applies it to the interdigital transducer, causing the zinc oxide film to vibrate mechanically and generate surface acoustic waves that propagate to the vicinity of the silicon oxide microring resonator, inducing mechanical stress and strain, changing the refractive index distribution of the silicon oxide microring resonator, and modulating the frequency, phase, and intensity of the internal optical signal. The feedback control module adjusts the thermal power of the microring heater based on the voltage signals output by the lock-in amplifier module and the photoelectric conversion module, thereby adjusting the resonant wavelength of the silicon oxide microring resonator and locking the wavelength of the optical signal output by the silicon oxide microring resonator to the target wavelength. The advantage is that it can accurately lock the wavelength of the silicon oxide microring resonator, resulting in a high wavelength locking effect.

Description

Technical Field

[0001] This invention relates to wavelength locking systems, and more particularly to a wavelength locking system for a silicon oxide microring resonator. Background Technology

[0002] With the advent of the information age, information technologies such as cloud computing, big data, the Internet of Things, and artificial intelligence are developing rapidly. The accelerated digital transformation of traditional industries and people's lifestyles undoubtedly poses greater challenges to the data transmission rate and stability of communication networks. Optical communication is a communication method that uses light as the transmission medium, typically transmitting signals through optical fibers. Compared to traditional electrical communication using copper cables, optical communication has significant advantages in transmission rate, data capacity, network bandwidth, signal crosstalk, transmission distance, signal attenuation, and resistance to electromagnetic interference, and is developing towards the goals of longer distances, higher speeds, and greater capacity.

[0003] Microring resonators (MRRs), as an important type of photonic device, have a relatively simple structure, typically composed of straight and curved waveguides. Common waveguide materials include silicon (Si) and silicon oxide (SiO2). Silicon-based MRRs have radii of only a few micrometers, offering small size and high performance, making them suitable for high-level integration with very large-scale integrated circuits (VLSI). Silicon oxide-based MRRs have simple manufacturing processes and low waveguide losses, and are commonly used to fabricate large-radius sensors and optical gyroscopes. Regardless of the material, MRRs offer advantages such as wavelength selectivity, compact structure, and compatibility with CMOS technology, leading to their widespread application in optical filters, optical delay lines, biosensors, and optical neural networks.

[0004] In practical applications, microring resonators are typically integrated with microring heaters to form an optical chip. When a silicon-based microring resonator is integrated with a microring heater, silicon is used as the substrate and silicon oxide as the cladding. The microring resonator is attached to the substrate, and the microring heater is attached to the cladding. When a silicon oxide microring resonator is integrated with a microring heater, silicon oxide is used as both the substrate and the cladding. The silicon oxide microring resonator is attached to the substrate, and the microring heater is attached to the cladding.

[0005] The performance of microring resonators is highly susceptible to manufacturing processes and temperature fluctuations. Even slight changes in waveguide geometry during manufacturing can cause a ±1nm drift in the resonant wavelength. Furthermore, the resonant wavelength also drifts with temperature variations. Misalignment between the input laser wavelength and the resonant wavelength degrades the microring resonator's performance. This is particularly critical in high-precision applications such as data center interconnects, optical biosensing, and quantum communication, where the accuracy of the resonant wavelength is paramount. Therefore, to eliminate interference from temperature drift and manufacturing errors and ensure proper operation, it is essential to address the self-calibration and locking issues of the microring resonator's resonant wavelength.

[0006] Bergman et al. from Columbia University designed a thermal stability feedback control system for a microring resonator, also known as a wavelength locking system for microring resonators. This wavelength locking system includes a dithering signal module, a photoelectric conversion module, an AD633 module, a low-pass filter module, and a feedback control module. The dithering signal module outputs a dithering electrical signal to the microring heater and the AD633 module. Under the control of the dithering electrical signal output from the dithering signal module, the microring heater generates a corresponding thermal wave action for the microring resonator. The optical signal in the microring resonator is thermally modulated, and the modulated optical signal is then output to the photoelectric conversion module. The photoelectric conversion module converts the optical signal output from the microring resonator into a voltage signal and outputs it to the AD633 module. The AD633 module mixes the voltage signal from the photoelectric conversion module with the jitter signal from the jitter module to obtain a mixed signal, which is then output to the low-pass filter module. The low-pass filter module performs low-pass filtering on the mixed signal from the AD633 module to obtain a filtered signal, i.e., an error signal, which is output to the feedback control module. The feedback control module outputs a feedback voltage to the microring heater based on the error signal from the AD633 module. This feedback voltage is superimposed with the jitter signal output from the jitter module to adjust the thermal power of the microring heater, thereby changing the thermal power output of the microring heater and thus changing the resonant wavelength of the microring resonator.

[0007] The aforementioned microring resonator thermal stability feedback control system employs thermo-optical modulation for wavelength locking. Due to the high thermal conductivity of silicon, it can accurately lock the resonant wavelength of the silicon-based microring resonator. However, silicon oxide has low thermal conductivity, preventing the aforementioned microring resonator thermal stability feedback control system from quickly and effectively modulating the optical signal in the silicon oxide microring resonator. This results in delays in subsequent responses, weakening the system's ability to promptly compensate for wavelength drift in the silicon oxide microring resonator. Consequently, the aforementioned microring resonator thermal stability feedback control system cannot accurately lock the wavelength of the silicon oxide microring resonator, resulting in an unsatisfactory wavelength locking effect. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a wavelength locking system for silicon oxide microring resonators that can accurately lock the wavelength and has a good wavelength locking effect.

[0009] The technical solution adopted by this invention to solve the above-mentioned technical problems is as follows: a wavelength locking system for a silicon oxide microring resonator, comprising a photoelectric conversion module and a feedback control module. The photoelectric conversion module is used to receive the optical signal output by the silicon oxide microring resonator and convert the optical signal into a voltage signal for output. It also includes a radio frequency drive module, an interdigital transducer, a zinc oxide film for generating a piezoelectric effect, a phase-locked amplification module, two analog-to-digital conversion modules, and a digital-to-analog conversion module. The two analog-to-digital conversion modules are referred to as the first analog-to-digital conversion module and the second analog-to-digital conversion module, respectively. The radio frequency drive module is used to generate an alternating electrical signal output. The zinc oxide film covers the cladding of the optical chip formed by integrating the silicon oxide microring resonator and the microring heater. The cladding layer is separated from the microring heater, and the microring heater is attached to it. The interdigital transducer is attached to the zinc oxide film. The interdigital transducer is used to receive the alternating electrical signal output from the radio frequency drive module. Under the excitation of the alternating electrical signal, it generates periodic surface acoustic waves that are transmitted to the silicon oxide microring resonator. These waves periodically interact with the optical signal inside the silicon oxide microring resonator, modulating the optical signal. The modulated optical signal is then output to the photoelectric conversion module. The photoelectric conversion module converts the optical signal output from the silicon oxide microring resonator into a voltage signal and outputs this voltage signal to the lock-in amplifier module. The second analog-to-digital converter (ADC) is used to receive the voltage signal output from the photoelectric conversion module and the alternating current signal output from the radio frequency drive module. The ADC performs coherent demodulation on the received voltage signal and the alternating current signal to obtain a voltage signal characterizing the spectral information and spectral slope information of the internal optical signal of the silicon oxide microring resonator. This voltage signal is then output to the first ADC module. The first ADC module periodically samples the voltage signal output from the lock-in amplifier module, obtaining a sample signal for each sampling period, which is then output to the feedback control module. The second ADC module receives the voltage signal output from the photoelectric conversion module and periodically samples the received voltage signal, obtaining a sample signal for each sampling period. The signal is output to the feedback control module. The second analog-to-digital converter (ADC) and the first ADC have the same sampling frequency. The feedback control module is used to obtain a feedback control signal for each cycle based on the sampling signals output to it by the first ADC and the second ADC in each cycle, and outputs it to the ADC. The ADC is used to perform digital-to-analog conversion on the feedback control signal output to it by the feedback control module in each cycle, and outputs a feedback control voltage to the micro-ring heater to adjust the thermal power of the micro-ring heater in real time, thereby adjusting the resonant wavelength of the silicon oxide micro-ring resonator, so that the optical signal output by the silicon oxide micro-ring resonator is locked at the target wavelength.

[0010] Compared with the prior art, the advantages of this invention lie in the following: by setting up an RF drive module, an interdigital transducer, a zinc oxide film, a lock-in amplifier module, two analog-to-digital converter modules, and a digital-to-analog converter module, when the alternating electrical signal generated by the RF drive module is applied to the interdigital transducer, the zinc oxide film, being attached to the interdigital transducer, will undergo mechanical vibration due to electrostriction, forming a surface acoustic wave on its surface. When this surface acoustic wave propagates to the vicinity of the silicon oxide microring resonator, it induces mechanical stress and strain, thereby changing the refractive index distribution of the silicon oxide microring resonator and modulating the frequency, phase, and intensity of the optical signal inside it. In addition, the lock-in amplifier module receives the voltage signal output from the photoelectric conversion module and the alternating electrical signal output from the RF drive module, and performs coherent demodulation on the received voltage signal and the alternating electrical signal to obtain a voltage signal characterizing the spectral information and spectral slope information of the optical signal inside the silicon oxide microring resonator. The first analog-to-digital converter module and the second analog-to-digital converter respectively process the voltage signal output from the lock-in amplifier module and the photoelectric conversion module. The voltage signal output by the conversion module is periodically sampled in real time to obtain periodic sampling data. The feedback control module obtains an error signal based on the periodic sampling data obtained by the first analog-to-digital converter and the second analog-to-digital converter. Based on the error signal, the thermal power of the micro-ring heater is adjusted to regulate the resonant wavelength of the silicon oxide micro-ring resonator, so that the wavelength of the optical signal output by the silicon oxide micro-ring resonator is locked at the target wavelength. Thus, it can be seen that the present invention uses an acousto-optic modulation mechanism based on an interdigital transducer and a feedback mechanism implemented by the feedback control module to simultaneously tune the resonant wavelength of the silicon oxide micro-ring resonator. It does not depend on the thermal conductivity of the material, and is therefore not limited by the low thermal conductivity of silicon oxide material. It can extract the error signal characterizing the current state of the silicon oxide micro-ring resonator more quickly to tune the silicon oxide micro-ring resonator. The response speed is fast, significantly improving the modulation rate of the silicon oxide micro-ring resonator. It has strong real-time feedback capability and adjustment capability, and can accurately lock the wavelength of the silicon oxide micro-ring resonator, with excellent wavelength locking effect.

[0011] Further, the voltage signal output by the photoelectric conversion module is denoted as V0, the voltage signal output by the lock-in amplifier module is denoted as V1, the sampling frequencies of the first analog-to-digital converter and the second analog-to-digital converter are the same, the sequence index of the sampling time of the first analog-to-digital converter and the second analog-to-digital converter is denoted as n, n = 1, 2, 3, ...; the sampling signal obtained by the second analog-to-digital converter at the nth sampling time is denoted as V0[n], the sampling signal obtained by the first analog-to-digital converter at the nth sampling time is denoted as V1[n], and the feedback control signal obtained by the feedback control module at the nth sampling time based on the sampling signal output by the first analog-to-digital converter and the second analog-to-digital converter at the nth sampling time is denoted as Vheater[n]; the specific process by which the feedback control module obtains the feedback control signal Vheater[n] at the nth sampling time based on the sampling signal output by the first analog-to-digital converter and the second analog-to-digital converter at the nth sampling time is as follows:

[0012] Step 1: Set the feedback error signal at the nth sampling time as Feedback[n] and the slope as k[n]. Calculate Feedback[n] and k[n] using formulas (1) and (2) respectively:

[0013] Feedback[n] = V1[n] / V0[n] (1)

[0014] k[n]={V1[n]-V1[n-1]} / {V0[n]-V0[n-1]} (2)

[0015] In formula (1), when n = 1, V1[n-1] = 0, V0[n-1] = 0. When n ≠ 1, V1[n-1] represents the sampling signal obtained by the first analog-to-digital converter at the (n-1)th sampling time, and V0[n-1] represents the sampling signal obtained by the second analog-to-digital converter at the (n-1)th sampling time.

[0016] Step 2: Determine Vheater[n] based on Feedback[n] and k[n], specifically:

[0017] If Feedback[n] is less than 0 and k[n] is less than or equal to 0, then let Vheater[n] = Vheater[n-1] + 0.1;

[0018] If Feedback[n] is less than 0 and k[n] is greater than 0, then let Vheater[n] = Vheater[n-1] + 0.01;

[0019] If Feedback[n] is greater than 0 and k[n] is greater than 0, then let Vheater[n] = Vheater[n-1] - 0.01;

[0020] If Feedback[n] is greater than 0 and k[n] is less than or equal to 0, then let Vheater[n] = Vheater[n-1] - 0.1;

[0021] If Feedback[n] equals 0, then directly set Vheater[n] = Vheater[n-1];

[0022] Wherein, when n=1, Vheater[n-1]=0, and when n≠1, Vheater[n-1] represents the feedback control signal at the (n-1)th sampling time obtained by the feedback control module based on the sampling signal output to it by the first analog-to-digital converter module and the second analog-to-digital converter module at the (n-1)th sampling time.

[0023] Furthermore, the photoelectric conversion module includes a photodiode, a first operational amplifier, a first resistor, and a first capacitor. The first operational amplifier has a non-inverting input, an inverting input, an output terminal, a positive power supply terminal, and a negative power supply terminal. The positive terminal of the photodiode and the non-inverting input of the first operational amplifier are both grounded. The negative terminal of the photodiode, the inverting input of the first operational amplifier, one end of the first resistor, and one end of the first capacitor are connected. The positive power supply terminal of the first operational amplifier is connected to a positive voltage VCC, and the negative power supply terminal of the first operational amplifier is connected to a negative voltage VEE. The output terminal of the first operational amplifier, the other end of the first resistor, and the other end of the first capacitor are connected, and this connection terminal is the output terminal of the photoelectric conversion module. The photodiode is used to receive the optical signal generated by the silicon oxide microring resonator under external optical signal excitation, and the output terminal of the photoelectric conversion module is used to output a voltage signal.

[0024] Furthermore, the phase-locked amplifier module includes a multiplier and a low-pass filter. The multiplier includes a first chip (model AD633), a second capacitor, and a second resistor. The X1 pin of the first chip is connected to one end of the second capacitor and one end of the second resistor. The other end of the second resistor, the X2 pin, Y2 pin, and Z pin of the first chip are all grounded. The other end of the second capacitor is the first input terminal of the multiplier, used to input the voltage signal output by the photoelectric conversion module. The Y1 pin of the first chip is the second input terminal of the multiplier, used to input the alternating current signal output by the RF drive module. The W pin of the first chip is the output terminal of the multiplier. The VS+ pin of the first chip is connected to a positive power supply, and the VS- pin of the first chip is connected to a negative power supply. The low-pass filter has an input terminal and an output terminal. The input terminal of the low-pass filter is connected to the output terminal of the multiplier. The output terminal of the low-pass filter is used to output a voltage signal characterizing the spectral information and spectral slope information of the silicon oxide microring resonator.

[0025] Furthermore, the low-pass filter includes a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a third capacitor, a fourth capacitor, a fifth capacitor, a sixth capacitor, a seventh capacitor, an eighth capacitor, and a ninth capacitor, a second operational amplifier, a third operational amplifier, a fourth operational amplifier, and a fifth operational amplifier. Each of the second, third, fourth, and fifth operational amplifiers has a non-inverting input, an inverting input, an output terminal, a positive power supply terminal, and a negative power supply terminal. The positive power supply terminals of the second, third, fourth, and fifth operational amplifiers are all connected to a positive voltage VCC, and the negative power supply terminals of the second, third, fourth, and fifth operational amplifiers are all connected to a negative voltage VEE. One end of the third resistor is the input terminal of the low-pass filter, and the other end of the third resistor is connected to one end of the fourth resistor and one end of the fourth capacitor. The other end of the fourth resistor is connected to one end of the third capacitor and the non-inverting input of the second operational amplifier. The inverting input and output terminal of the third operational amplifier are connected, as are the other ends of the fourth capacitor and one end of the fifth resistor. The other end of the fifth resistor is connected to one end of the sixth resistor and one end of the sixth capacitor. The other end of the sixth resistor is connected to one end of the fifth capacitor and the non-inverting input of the third operational amplifier. The inverting input and output terminal of the third operational amplifier, the other end of the sixth capacitor and one end of the eighth resistor are connected. The other end of the eighth resistor is connected to one end of the seventh resistor and one end of the eighth capacitor. The other end of the seventh resistor is connected to one end of the seventh capacitor and the non-inverting input of the fourth operational amplifier. The inverting input and output terminal of the fourth operational amplifier, the other end of the eighth capacitor and one end of the ninth resistor are connected. The other end of the ninth resistor is connected to one end of the ninth capacitor and the non-inverting input of the fifth operational amplifier. The inverting input and output terminal of the fifth operational amplifier are connected, and their connection point is the output terminal of the low-pass filter. The other ends of the third capacitor, the fifth capacitor, the seventh capacitor and the ninth capacitor are all grounded.

[0026] Furthermore, the thickness of the zinc oxide film is 2.2 micrometers. Attached Figure Description

[0027] Figure 1 This is a structural block diagram of the wavelength locking system of the silicon oxide microring resonator of the present invention;

[0028] Figure 2A top view of the optical chip when the interdigital transducer and zinc oxide film of the wavelength locking system of the silicon oxide microring resonator of the present invention are integrated onto the optical chip;

[0029] Figure 3 A cross-sectional view of the optical chip when the interdigital transducer and zinc oxide film of the wavelength locking system of the silicon oxide microring resonator of the present invention are integrated onto the optical chip;

[0030] Figure 4 The circuit diagram shows the photoelectric conversion module of the wavelength locking system of the silicon oxide microring resonator of the present invention.

[0031] Figure 5 The circuit diagram shows the phase-locked amplifier module of the wavelength locking system for the silicon oxide microring resonator of this invention. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0033] Example 1: As Figures 1 to 3As shown, a wavelength locking system for a silicon oxide microring resonator includes a photoelectric conversion module and a feedback control module. The photoelectric conversion module receives the optical signal output from the silicon oxide microring resonator and converts it into a voltage signal output. It also includes a radio frequency (RF) drive module, an interdigital transducer, a zinc oxide film for generating a piezoelectric effect, a phase-locked amplification module, two analog-to-digital (ADC) conversion modules, and a digital-to-analog (DAC) conversion module. The two ADC modules are referred to as the first ADC module and the second ADC module. The RF drive module generates an alternating electrical signal output. The zinc oxide film covers the cladding of the optical chip formed by integrating the silicon oxide microring resonator and the microring heater. The cladding separates the microring heater from the microring heater, allowing the microring heater to be attached to it. Interdigital transducers are attached to the zinc oxide film. The interdigital transducers receive the alternating electrical signal output from the RF drive module and, under the excitation of this alternating electrical signal, generate periodic surface acoustic waves that propagate to the silicon oxide microring resonator. These waves periodically interact with the optical signal inside the silicon oxide microring resonator, modulating the optical signal. The modulated optical signal is then output to the photoelectric conversion module. This module converts the optical signal output from the silicon oxide microring resonator into a voltage signal and outputs this voltage signal to the lock-in amplifier module. The second analog-to-digital converter (ADC) receives the voltage signal output from the photoelectric conversion module and the alternating current signal output from the RF drive module. It then coherently demodulates the received voltage signal and the alternating current signal to obtain a voltage signal characterizing the spectral information and spectral slope of the optical signal inside the silicon oxide microring resonator. This voltage signal is output to the first ADC module. The first ADC module periodically samples the voltage signal output from the lock-in amplifier module, obtaining a sampled signal for each period, which is then output to the feedback control module. The second ADC module receives the voltage signal output from the photoelectric conversion module and periodically samples it, obtaining a sampled signal for each period. The sample signal is output to the feedback control module. The second analog-to-digital converter module and the first analog-to-digital converter module have the same sampling frequency. The feedback control module is used to obtain the feedback control signal for each cycle based on the sample signal output to it by the first and second analog-to-digital converter modules for each cycle. The feedback control module is used to perform digital-to-analog conversion on the feedback control signal output to it by the feedback control module for each cycle, and obtain the feedback control voltage output to the micro-ring heater. The heat power of the micro-ring heater is adjusted in real time, thereby adjusting the resonant wavelength of the silicon oxide micro-ring resonator, so that the optical signal output by the silicon oxide micro-ring resonator is locked at the target wavelength.

[0034] In this embodiment, the thickness of the zinc oxide film is 2.2 micrometers.

[0035] In this embodiment, when the alternating electrical signal generated by the RF drive module is applied to the interdigital transducer, the zinc oxide film, being attached to the transducer, undergoes mechanical vibration due to electrostriction, forming surface acoustic waves (SAWs) on its surface. When these SAWs propagate to the vicinity of the silicon oxide microring resonator, they induce mechanical stress and strain, thereby altering the refractive index distribution of the silicon oxide microring resonator and modulating the frequency, phase, and intensity of the optical signal within it. Furthermore, the lock-in amplifier module receives the voltage signal output from the photoelectric conversion module and the alternating electrical signal output from the RF drive module, and performs phase-multiplication on the input voltage signal and the alternating electrical signal. Dry demodulation yields voltage signals characterizing the spectral information and spectral slope information of the optical signal inside the silicon oxide microring resonator. The first analog-to-digital converter (ADC) and the second ADC periodically sample the voltage signals output by the lock-in amplifier module and the photoelectric conversion module, respectively, to obtain periodic sampling data. The feedback control module obtains an error signal based on the periodic sampling data obtained by the first ADC and the second ADC. Based on the error signal, the feedback control module adjusts the thermal power of the microring heater to regulate the resonant wavelength of the silicon oxide microring resonator, thereby locking the wavelength of the optical signal output by the silicon oxide microring resonator to the target wavelength.

[0036] Therefore, unlike traditional wavelength locking systems that rely on the thermal conductivity of materials and employ conventional thermo-optic modulation, the wavelength locking system of this invention uses an acousto-optic modulation mechanism based on interdigital transducers and a feedback mechanism implemented by a feedback control module to simultaneously tune the resonant wavelength of the silicon oxide microring resonator. This avoids dependence on the thermal conductivity of materials and overcomes the limitations of traditional wavelength locking systems that rely on the thermal conductivity of materials in silicon oxide microring resonators. It can extract error signals characterizing the current state of the silicon oxide microring resonator more quickly, has a fast response speed, strong real-time feedback capability, and can efficiently and accurately lock the wavelength of the silicon oxide microring resonator to the target wavelength, resulting in a good wavelength locking effect on the silicon oxide microring resonator.

[0037] Example 2: This example is basically the same as Example 1, except that: In this example, the voltage signal output by the photoelectric conversion module is denoted as V0, the voltage signal output by the lock-in amplifier module is denoted as V1, the sampling frequencies of the first analog-to-digital converter module and the second analog-to-digital converter module are the same, the sequence index of the sampling time of the first analog-to-digital converter module and the second analog-to-digital converter module is denoted as n, n = 1, 2, 3, ...; the sampling signal obtained by the second analog-to-digital converter module at the nth sampling time is denoted as V0[n], the sampling signal obtained by the first analog-to-digital converter module at the nth sampling time is denoted as V1[n], and the feedback control signal obtained by the feedback control module at the nth sampling time based on the sampling signal output by the first analog-to-digital converter module and the second analog-to-digital converter module at the nth sampling time is denoted as Vheater[n]; the specific process of the feedback control module obtaining the feedback control signal Vheater[n] at the nth sampling time based on the sampling signal output by the first analog-to-digital converter module and the second analog-to-digital converter module at the nth sampling time is as follows:

[0038] Step 1: Set the feedback error signal at the nth sampling time as Feedback[n] and the slope as k[n]. Calculate Feedback[n] and k[n] using formulas (1) and (2) respectively:

[0039] Feedback[n] = V1[n] / V0[n] (1)

[0040] k[n]={V1[n]-V1[n-1]} / {V0[n]-V0[n-1]} (2)

[0041] In formula (1), when n = 1, V1[n-1] = 0 and V0[n-1] = 0. When n ≠ 1, V1[n-1] represents the sampled signal obtained by the first analog-to-digital converter at the (n-1)th sampling time, and V0[n-1] represents the sampled signal obtained by the second analog-to-digital converter at the (n-1)th sampling time.

[0042] Step 2: Determine Vheater[n] based on Feedback[n] and k[n], specifically:

[0043] If Feedback[n] is less than 0 and k[n] is less than or equal to 0, then let Vheater[n] = Vheater[n-1] + 0.1;

[0044] If Feedback[n] is less than 0 and k[n] is greater than 0, then let Vheater[n] = Vheater[n-1] + 0.01;

[0045] If Feedback[n] is greater than 0 and k[n] is greater than 0, then let Vheater[n] = Vheater[n-1] - 0.01;

[0046] If Feedback[n] is greater than 0 and k[n] is less than or equal to 0, then let Vheater[n] = Vheater[n-1] - 0.1;

[0047] If Feedback[n] equals 0, then directly set Vheater[n] = Vheater[n-1];

[0048] Wherein, when n=1, Vheater[n-1]=0, and when n≠1, Vheater[n-1] represents the feedback control signal at the (n-1)th sampling time obtained by the feedback control module based on the sampling signal output to it by the first analog-to-digital converter module and the second analog-to-digital converter module at the (n-1)th sampling time.

[0049] In this embodiment, during the operation of the wavelength locking system of the silicon oxide microring resonator, the optical signal generated by the external laser is always present and output to the silicon oxide microring resonator. Therefore, the photoelectric conversion module can sense the optical signal, and its output voltage signal V0 is not 0. The sampling signal V0[n] obtained by the second analog-to-digital conversion module sampling the voltage signal V0 at the nth sampling time will also not be 0. That is, the situation where V0[n] equals 0 and cannot be calculated in formula (1) will not occur. Secondly, before reaching the locked state (that is, when Feedback[n] equals 0), the feedback control signal input to the microring heater is constantly changing. The feedback control signal at the current sampling time is different from that at the previous sampling time. The optical signal output by the silicon oxide microring resonator after being adjusted by the thermal power of the microring heater will also be different. That is, the output voltage signals V0[n] and V0[n-1] after the photoelectric conversion module are also different. Therefore, the situation where V0[n]-V0[n-1] equals 0 and cannot be calculated in formula (2) will not occur. In actual use, if V0[n] = 0 or V0[n] - V0[n-1] = 0, it indicates that the wavelength locking system has malfunctioned. At this time, the feedback control module will report an error and terminate the feedback control operation.

[0050] In this embodiment, Feedback[n], calculated by dividing V1[n] by V0[n], is essentially a normalization of V1[n]. This eliminates the influence of changes in the optical signal power input from the laser (external light source) to the silicon oxide microring resonator on the wavefield locking system. The feedback control of the wavelength locking system relies solely on the signal ratio change obtained after normalizing V1[n], unaffected by fluctuations in the optical signal power input from the laser (external light source) to the silicon oxide microring resonator, ensuring stable control performance. Furthermore, by introducing the slope k[n], the wavelength locking system can accurately distinguish between the rising and falling segments of the feedback curve, avoiding the ambiguity caused by non-monotonic feedback curves. This avoids the multiple solutions problem caused by relying solely on the Feedback[n] threshold, ensuring that the adjustment direction of the feedback control signal Vheater[n] is unique. Based on different combinations of Feedback[n] and k[n], the wavelength locking system adopts a segmented adjustment strategy. This design enables the wavelength locking system to respond specifically to different state changes, avoiding over- or under-adjustment and improving the stability and accuracy of the wavefield locking system.

[0051] Example 3: This example is basically the same as Example 1, except that: in this example, as Figure 4 As shown, the photoelectric conversion module includes a photodiode D1, a first operational amplifier U1, a first resistor R1, and a first capacitor C1. The first operational amplifier U1 has a non-inverting input, an inverting input, an output terminal, a positive power supply terminal, and a negative power supply terminal. The positive terminal of the photodiode D1 and the non-inverting input of the first operational amplifier U1 are both grounded. The negative terminal of the photodiode D1, the inverting input of the first operational amplifier U1, one end of the first resistor R1, and one end of the first capacitor C1 are connected. The positive power supply terminal of the first operational amplifier U1 is connected to a positive voltage VCC, and the negative power supply terminal of the first operational amplifier U1 is connected to a negative voltage VEE. The output terminal of the first operational amplifier U1, the other end of the first resistor R1, and the other end of the first capacitor C1 are connected, and this connection terminal is the output terminal of the photoelectric conversion module. The photodiode D1 is used to receive the optical signal generated by the silicon oxide microring resonator under the excitation of an external optical signal, and the output terminal of the photoelectric conversion module is used to output a voltage signal.

[0052] In this embodiment, in the photoelectric conversion module, photodiode D1 receives the optical signal generated by the silicon oxide microring resonator under external optical signal excitation, and generates a corresponding current output to the inverting input of the first operational amplifier U1 based on the optical signal. The first operational amplifier U1, the first resistor R1, and the first capacitor C1 constitute a transimpedance amplifier. The first resistor R1 serves as a feedback resistor, and the first capacitor C1 serves as a feedback capacitor. The first resistor R1 and the first capacitor C1 are connected in parallel to increase the stability and operating bandwidth of the photoelectric conversion module. The voltage signal output by the output terminal of the first operational amplifier U1 is the product of the current generated by photodiode D1 and the resistance value of the first resistor R1. Without affecting other performance, the first resistor R1 should be as large as possible to overcome the noise of the subsequent stage.

[0053] Example 4: This example is basically the same as Example 1, except that: in this example, as Figure 5 As shown, the lock-in amplifier module includes a multiplier and a low-pass filter. The multiplier includes a first chip U2 (model AD633), a second capacitor C2, and a second resistor R2. The X1 pin of the first chip U2 is connected to one end of the second capacitor C2 and one end of the second resistor R2. The other end of the second resistor R2, the X2 pin, Y2 pin, and Z pin of the first chip U2 are all grounded. The other end of the second capacitor C2 is the first input terminal of the multiplier, used to input the voltage signal output by the photoelectric conversion module. The Y1 pin of the first chip U2 is the second input terminal of the multiplier, used to input the alternating current signal output by the RF drive module. The W pin of the first chip U2 is the output terminal of the multiplier. The VS+ pin of the first chip U2 is connected to the positive power supply, and the VS- pin of the first chip U2 is connected to the negative power supply. The low-pass filter has an input terminal and an output terminal. The input terminal of the low-pass filter is connected to the output terminal of the multiplier. The output terminal of the low-pass filter is used to output a voltage signal characterizing the spectral information and spectral slope information of the silicon oxide microring resonator.

[0054] In this embodiment, the low-pass filter includes a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a third capacitor C3, a fourth capacitor C4, a fifth capacitor C5, a sixth capacitor C6, a seventh capacitor C7, an eighth capacitor C8, and a ninth capacitor C9, a second operational amplifier U3, a third operational amplifier U4, a fourth operational amplifier U5, and a fifth operational amplifier U6. Each of the second operational amplifier U3, third operational amplifier U4, fourth operational amplifier U5, and fifth operational amplifier U6 has a non-inverting input, an inverting input, and an output input. The positive and negative power supply terminals of the second operational amplifier U3, third operational amplifier U4, fourth operational amplifier U5, and fifth operational amplifier U6 are all connected to a positive voltage VCC, and the negative power supply terminals are all connected to a negative voltage VEE. One end of the third resistor R3 is the input terminal of the low-pass filter, and the other end of the third resistor R3 is connected to one end of the fourth resistor R4 and one end of the fourth capacitor C4. The other end of the fourth resistor R4 is connected to one end of the third capacitor C3 and the second operational amplifier U6. The non-inverting input of amplifier U3 is connected to the inverting input and output of the second operational amplifier U3, the other end of the fourth capacitor C4 is connected to one end of the fifth resistor R5, the other end of the fifth resistor R5 is connected to one end of the sixth resistor R6 and one end of the sixth capacitor C6, the other end of the sixth resistor R6 is connected to one end of the fifth capacitor C5 and the non-inverting input of the third operational amplifier U4, the inverting input and output of the third operational amplifier U4, the other end of the sixth capacitor C6 is connected to one end of the eighth resistor R8, and the other end of the eighth resistor R8 is connected to one end of the seventh resistor R7 and one end of the eighth capacitor C8. The other end of the seventh resistor R7 is connected to one end of the seventh capacitor C7 and the non-inverting input of the fourth operational amplifier U5. The inverting input and output of the fourth operational amplifier U5, the other end of the eighth capacitor C8 and one end of the ninth resistor R9 are connected to one end of the ninth capacitor C9 and the non-inverting input of the fifth operational amplifier U6. The inverting input and output of the fifth operational amplifier U6 are connected, and its connection point is the output of the low-pass filter. The other ends of the third capacitor C3, the fifth capacitor C5, the seventh capacitor C7 and the ninth capacitor C9 are all grounded.

[0055] In this embodiment, the multiplier uses an AD633 chip as its main component. A second capacitor C2 is connected in series with pin X1 of the AD633 chip as a DC blocking capacitor to isolate the DC component of the voltage signal output by the photoelectric conversion module. Simultaneously, a second resistor R2 is connected in parallel with the DC blocking capacitor to form an RC high-pass filter, preventing waveform distortion that might occur when the AD633 chip is connected in series with the DC blocking capacitor. The low-pass filter is implemented using a Butterworth-type low-pass filter circuit. It processes the signal through a multi-stage operational amplifier to improve the signal-to-noise ratio. Based on usage requirements, appropriate parameters are selected for the third resistor R3, fourth resistor R4, fifth resistor R5, sixth resistor R6, seventh resistor R7, eighth resistor R8, ninth resistor R9, third capacitor C3, fourth capacitor C4, fifth capacitor C5, sixth capacitor C6, seventh capacitor C7, eighth capacitor C8, and ninth capacitor C9 to determine the cutoff frequency and gain of the low-pass filter.

[0056] In summary, the wavelength locking system for silicon oxide microring resonators of this invention employs an acousto-optic modulation mechanism based on interdigital transducers and a feedback mechanism implemented by a feedback control module to simultaneously tune the resonant wavelength of the silicon oxide microring resonator. When locking the wavelength of the silicon oxide microring resonator, it does not rely on the thermal conductivity characteristics of the material and is not limited by the low thermal conductivity of silicon oxide. It can extract the error signal characterizing the current state of the silicon oxide microring resonator more quickly, exhibiting a fast response speed, significantly improving the modulation rate and real-time feedback capability, and efficiently and accurately locking the wavelength to the target wavelength. The wavelength locking system for silicon oxide microring resonators of this invention can be effectively used for wavelength locking of silicon oxide microring resonators and has broad application prospects in the field of silicon oxide microring resonators.

Claims

1. A wavelength locking system for a silicon oxide microring resonator, comprising a photoelectric conversion module and a feedback control module, wherein the photoelectric conversion module receives an optical signal output from the silicon oxide microring resonator and converts the optical signal into a voltage signal for output, characterized in that... It also includes an RF drive module, interdigital transducers, a zinc oxide film for generating piezoelectric effect, a phase-locked loop amplifier module, two analog-to-digital converters (ADCs), and a digital-to-analog converter (DAC). The two ADCs are referred to as the first ADC and the second ADC. The RF drive module generates an alternating electrical signal output. The zinc oxide film covers the cladding of the optical chip integrated with the silicon oxide microring resonator and the microring heater, separating the cladding from the microring heater, which is then attached to it. The interdigital transducers are attached to the zinc oxide film and are used to receive the alternating electrical signal output from the RF drive module. Under the excitation of the alternating electrical signal, periodic surface acoustic waves are generated and transmitted to the silicon oxide microring resonator. These waves periodically interact with the optical signal inside the silicon oxide microring resonator, modulating the optical signal. The modulated optical signal is then output to the photoelectric conversion module. This module converts the optical signal output from the silicon oxide microring resonator into a voltage signal and outputs this voltage signal to the lock-in amplifier module. The lock-in amplifier module receives the voltage signal output from the photoelectric conversion module and the alternating electrical signal output from the radio frequency drive module, and then... The alternating electrical signal is coherently demodulated to obtain a voltage signal characterizing the spectral information and spectral slope information of the optical signal inside the silicon oxide microring resonator. This voltage signal is output to the first analog-to-digital converter (ADC). The first ADC periodically samples the voltage signal output from the lock-in amplifier module, obtaining a sampled signal for each period and outputting it to the feedback control module. The second ADC receives the voltage signal output from the photoelectric conversion module and periodically samples it, obtaining a sampled signal for each period and outputting it to the feedback control module. With the same sampling frequency as the first analog-to-digital conversion module, the feedback control module is used to obtain a feedback control signal for each cycle based on the sampling signals output to it by the first and second analog-to-digital conversion modules in each cycle, and output it to the digital-to-analog conversion module. The digital-to-analog conversion module is used to perform digital-to-analog conversion on the feedback control signal output to it by the feedback control module in each cycle, and output the feedback control voltage to the micro-ring heater to adjust the thermal power of the micro-ring heater in real time, thereby adjusting the resonant wavelength of the silicon oxide micro-ring resonator, so that the optical signal output by the silicon oxide micro-ring resonator is locked at the target wavelength.

2. The wavelength locking system for a silicon oxide microring resonator according to claim 1, characterized in that... The voltage signal output by the photoelectric conversion module is denoted as V0, and the voltage signal output by the lock-in amplifier module is denoted as V1. The sampling frequencies of the first analog-to-digital converter (ADC) and the second ADC are the same. The sequence index of the sampling time of the first ADC and the second ADC is denoted as n, n = 1, 2, 3, ... The sampling signal obtained by the second ADC at the nth sampling time is denoted as V0[n], and the sampling signal obtained by the first ADC at the nth sampling time is denoted as V1[n]. The feedback control signal obtained by the feedback control module at the nth sampling time based on the sampling signal output by the first ADC and the second ADC at the nth sampling time is denoted as Vheater[n]. The specific process by which the feedback control module obtains the feedback control signal Vheater[n] at the nth sampling time based on the sampling signal output by the first ADC and the second ADC at the nth sampling time is as follows: Step 1: Set the feedback error signal at the nth sampling time as Feedback[n] and the slope as k[n]. Calculate Feedback[n] and k[n] using formulas (1) and (2) respectively: Feedback[n] = V1[n] / V0[n] (1) k[n]={V1[n]-V1[n-1]} / {V0[n]-V0[n-1]} (2) In formula (1), when n = 1, V1[n-1] = 0, V0[n-1] = 0. When n ≠ 1, V1[n-1] represents the sampling signal obtained by the first analog-to-digital converter at the (n-1)th sampling time, and V0[n-1] represents the sampling signal obtained by the second analog-to-digital converter at the (n-1)th sampling time. Step 2: Determine Vheater[n] based on Feedback[n] and k[n], specifically: If Feedback[n] is less than 0 and k[n] is less than or equal to 0, then let Vheater[n] = Vheater[n-1] + 0.1; If Feedback[n] is less than 0 and k[n] is greater than 0, then let Vheater[n] = Vheater[n-1] + 0.01; If Feedback[n] is greater than 0 and k[n] is greater than 0, then let Vheater[n] = Vheater[n-1] - 0.01; If Feedback[n] is greater than 0 and k[n] is less than or equal to 0, then let Vheater[n] = Vheater[n-1] - 0.1; If Feedback[n] equals 0, then directly set Vheater[n] = Vheater[n-1]; Wherein, when n=1, Vheater[n-1]=0, and when n≠1, Vheater[n-1] represents the feedback control signal at the (n-1)th sampling time obtained by the feedback control module based on the sampling signal output to it by the first analog-to-digital converter module and the second analog-to-digital converter module at the (n-1)th sampling time.

3. The wavelength locking system for a silicon oxide microring resonator according to claim 1, characterized in that... The photoelectric conversion module includes a photodiode, a first operational amplifier, a first resistor, and a first capacitor. The first operational amplifier has a non-inverting input, an inverting input, an output terminal, a positive power supply terminal, and a negative power supply terminal. The positive terminal of the photodiode and the non-inverting input of the first operational amplifier are both grounded. The negative terminal of the photodiode, the inverting input of the first operational amplifier, one end of the first resistor, and one end of the first capacitor are connected. The positive power supply terminal of the first operational amplifier is connected to a positive voltage VCC, and the negative power supply terminal of the first operational amplifier is connected to a negative voltage VEE. The output terminal of the first operational amplifier, the other end of the first resistor, and the other end of the first capacitor are connected, and this connection terminal is the output terminal of the photoelectric conversion module. The photodiode is used to receive the optical signal generated by the silicon oxide microring resonator under external optical signal excitation, and the output terminal of the photoelectric conversion module is used to output a voltage signal.

4. The wavelength locking system for a silicon oxide microring resonator according to claim 1, characterized in that... The phase-locked amplifier module includes a multiplier and a low-pass filter. The multiplier includes a first chip (AD633), a second capacitor, and a second resistor. The X1 pin of the first chip is connected to one end of the second capacitor and one end of the second resistor. The other end of the second resistor, the X2 pin, Y2 pin, and Z pin of the first chip are all grounded. The other end of the second capacitor is the first input terminal of the multiplier, used to input the voltage signal output by the photoelectric conversion module. The Y1 pin of the first chip is the second input terminal of the multiplier, used to input the alternating current signal output by the RF drive module. The W pin of the first chip is the output terminal of the multiplier. The VS+ pin of the first chip is connected to a positive power supply, and the VS- pin of the first chip is connected to a negative power supply. The low-pass filter has an input terminal and an output terminal. The input terminal of the low-pass filter is connected to the output terminal of the multiplier. The output terminal of the low-pass filter is used to output a voltage signal characterizing the spectral information and spectral slope information of the silicon oxide microring resonator.

5. The wavelength locking system for a silicon oxide microring resonator according to claim 4, characterized in that... The low-pass filter includes a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a third capacitor, a fourth capacitor, a fifth capacitor, a sixth capacitor, a seventh capacitor, an eighth capacitor, and a ninth capacitor; a second operational amplifier, a third operational amplifier, a fourth operational amplifier, and a fifth operational amplifier. Each of the second, third, fourth, and fifth operational amplifiers has a non-inverting input, an inverting input, an output terminal, a positive power supply terminal, and a negative power supply terminal. The positive power supply terminals of the second, third, fourth, and fifth operational amplifiers are all connected to a positive voltage VCC, and the negative power supply terminals of the second, third, fourth, and fifth operational amplifiers are all connected to a negative voltage VEE. One end of the third resistor is the input terminal of the low-pass filter. The other end of the third resistor is connected to one end of the fourth resistor and one end of the fourth capacitor. The other end of the fourth resistor is connected to one end of the third capacitor and the non-inverting input of the second operational amplifier. The phase input and output terminal, the other end of the fourth capacitor and one end of the fifth resistor are connected. The other end of the fifth resistor is connected to one end of the sixth resistor and one end of the sixth capacitor. The other end of the sixth resistor is connected to one end of the fifth capacitor and the non-inverting input of the third operational amplifier. The inverting input and output terminal of the third operational amplifier, the other end of the sixth capacitor and one end of the eighth resistor are connected. The other end of the eighth resistor is connected to one end of the seventh resistor and one end of the eighth capacitor. The other end of the seventh resistor is connected to one end of the seventh capacitor and the non-inverting input of the fourth operational amplifier. The inverting input and output terminal of the fourth operational amplifier, the other end of the eighth capacitor and one end of the ninth resistor are connected. The other end of the ninth resistor is connected to one end of the ninth capacitor and the non-inverting input of the fifth operational amplifier. The inverting input and output terminal of the fifth operational amplifier are connected, and their connection point is the output terminal of the low-pass filter. The other ends of the third capacitor, the fifth capacitor, the seventh capacitor and the ninth capacitor are all grounded.

6. The wavelength locking system for a silicon oxide microring resonator according to claim 1, characterized in that... The zinc oxide film has a thickness of 2.2 micrometers.

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