A miniaturized modulator bias control device and control method
By designing a miniaturized modulator bias control device and using a closed-loop control method to stabilize the modulator bias point, the problem of signal instability of the modulator at different temperatures is solved, enabling high-requirement applications without spurious signals, and suitable for communication and optical sensing technologies.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NO 55 INST CHINA ELECTRONIC SCI & TECHNOLOGYGROUP CO LTD
- Filing Date
- 2026-04-22
- Publication Date
- 2026-06-12
AI Technical Summary
In the existing technology, the output signal of the Mach-Zehnder interferometer intensity modulator is unstable under different ambient temperatures, and the pilot control scheme introduces spurious signals, making it unsuitable for applications requiring high spurious-free dynamic range.
A miniaturized modulator bias control device is designed, including a photoelectric conversion unit, an amplification and filtering unit, a signal processing and control unit, and a driving unit. Through a closed-loop control method, the bias point of the modulator is adjusted in real time to avoid introducing additional spurious signals.
It achieves stable control of the modulator bias point, is suitable for scenarios with high requirements for spurious-free dynamic range, and is miniaturized and highly compatible, applicable to communication technology, microwave photonics and optical sensing technology.
Smart Images
Figure CN122194507A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of optical fiber communication technology, and in particular to a miniaturized modulator bias control device and control method. Background Technology
[0002] The intensity modulator employs a Mach-Zehnder interferometer (MZI) structure. Its output power varies cosinely with the applied voltage, and it is mainly used in long-distance optical fiber communication, offering advantages such as miniaturization, high bandwidth, low loss, and high integration. However, due to the pyroelectric effect of the modulator and the temperature sensitivity of the crystal material itself, the modulation response curve of the modulator will drift under different ambient temperatures. If a fixed bias voltage is applied to the modulator, its operating state will change significantly under different ambient temperatures, leading to instability in the output signal. Therefore, real-time control of the modulator's bias voltage is necessary.
[0003] Currently, there is a bias control scheme that uses pilot signals to control the modulator's operating point: a pilot signal is applied to the modulator, and the operating point is controlled to operate stably by judging the harmonic components in the modulator's output light. However, this scheme introduces additional spurious signals and is not suitable for application scenarios that require improved spurious-free dynamic range of the link. Summary of the Invention
[0004] Purpose of the invention: The purpose of this invention is to provide a miniaturized modulator bias control device and control method to achieve stable control of the bias point of a Mach-Zehnder modulator without causing deterioration of spurious signals in the radio frequency link.
[0005] Technical solution: To achieve the above objectives, the present invention provides a miniaturized modulator bias control device, comprising a photoelectric conversion unit, an amplification and filtering unit, a signal processing and control unit, and a driving unit connected in sequence. The output terminal of the driving unit is connected to the bias control signal terminal of the Mach-Zehnder modulator; the input terminal of the photoelectric conversion unit receives the modulated optical signal output by the Mach-Zehnder modulator.
[0006] Preferably, the device includes a housing, inside which an upper layer is placed a digital integrated circuit board including a signal processing and control unit. The digital integrated circuit board has a double-sided layout, with labeled components placed on the front and bare dies placed on the back, sintered onto a step inside the housing. The lower layer is placed an analog integrated circuit board including a photoelectric conversion unit, an amplification and filtering unit, and a driving unit. The analog integrated circuit board has a single-sided layout, with labeled components and bare dies placed on the front and low-temperature sintered to the bottom of the housing on the back. The digital integrated circuit board and the analog integrated circuit board are electrically connected through a ball-mounting process.
[0007] Preferably, the photoelectric conversion unit includes a photodiode, a gating switch, and a transimpedance amplifier. The common terminal of the gating switch is connected to the cathode of the photodiode, and the other terminal is connected to different resistors of the transimpedance amplifier. The output of the transimpedance amplifier is connected to an amplification and filtering unit.
[0008] Preferably, the amplification and filtering unit includes two operational amplifiers. One operational amplifier is connected to a resistor and a capacitor to form a bandpass filter, which is used to bandpass filter the signal output by the photoelectric conversion unit, retain the pilot fundamental signal and the second harmonic signal, and amplify the signal before outputting it. The other operational amplifier is connected to a resistor and a capacitor to form a low-pass filter, which is used to retain the DC component output by the photoelectric conversion unit.
[0009] Preferably, the signal processing and control unit includes an analog-to-digital converter, a digital-to-analog converter, and a digital processor connected in sequence; the analog-to-digital converter includes two input terminals, which are respectively connected to the two output terminals of the amplification and filtering unit, for converting the two analog signals output by the amplification and filtering unit into digital signals; the digital processor is used to measure the amplitude of the pilot fundamental component, the amplitude of the pilot second harmonic component, and the amplitude of the DC component; the output terminal of the digital-to-analog converter is connected to the input terminal of the driving unit.
[0010] Preferably, the driving unit includes an operational amplifier and several resistors and capacitors connected together to form an active adder amplifier circuit, which is used to superimpose and amplify the two signals output by the signal processing and control unit.
[0011] The control method for a miniaturized modulator bias control device according to the present invention includes:
[0012] The Mach-Zehnder modulator outputs a modulated optical signal under the bias control signal and in the working state. Based on the acquired optical signal, it judges whether the current optical power is within the effective range of the current transimpedance amplifier. If not, it changes the working state of the gating switch until the optical power is within the effective range of the current transimpedance amplifier.
[0013] When the optical power is within the effective range of the transimpedance amplifier, the Mach-Zehnder modulator is subjected to unsteady-state and steady-state control, including:
[0014] When the Mach-Zehnder modulator is in an unsteady-state operation, the driving unit outputs a bias control signal superimposed with the pilot signal to the Mach-Zehnder modulator, acquires the current optical signal, and decomposes it into the pilot fundamental signal and the second harmonic signal. First, the bias value of the Mach-Zehnder modulator is adjusted so that the amplitude ratio of the current second harmonic component to the fundamental component is minimized. Then, by dynamically adjusting the bias control signal, the amplitude ratio of the current second harmonic component to the fundamental component is controlled to remain equal to the ratio of the target operating point of the Mach-Zehnder modulator. At this time, the Mach-Zehnder modulator enters a steady-state operation.
[0015] When the Mach-Zehnder modulator is in steady-state operation, the amplitude of the current DC component is first used as the reference value for closed-loop control. Then, the drive unit outputs a bias control signal without the pilot signal superimposed to the Mach-Zehnder modulator to acquire the optical signal in real time and calculate the amplitude of the DC component. The difference is obtained by comparing it with the reference value. If the difference is greater than the set threshold, the current steady-state control is exited and the Mach-Zehnder modulator enters unsteady-state control.
[0016] Preferably, the determination of whether the current optical power is within the effective range of the current transimpedance amplifier includes: if the digital quantity corresponding to the DC component output by the photoelectric conversion unit reaches the maximum or minimum value of the analog-to-digital converter range, then the current resistance value needs to be adjusted.
[0017] Preferably, the pilot frequency of the pilot signal is <3kHz and the pilot power consumption is <5%Pπ.
[0018] Preferably, the optical signal acquired based on the output modulated optical signal of the Mach-Zehnder modulator is subjected to bandpass filtering and low-pass filtering respectively to obtain the pilot fundamental wave signal, the second harmonic signal, and the DC component. The pilot fundamental wave signal, the second harmonic signal, and the DC component are then subjected to FFT processing to obtain the amplitude of the pilot fundamental wave component, the amplitude of the pilot second harmonic component, and the amplitude of the DC component, respectively.
[0019] Beneficial effects: The present invention has the following advantages: 1. The present invention constructs a closed-loop control device based on a photoelectric conversion unit, an amplification and filtering unit, a signal processing and control unit and a driving unit. At the same time, it combines a bias control method to achieve stable control of the modulator's bias point. It is not affected by the input optical power and does not affect the RF link. It can be applied to scenarios that require high requirements such as improving the spurious-free dynamic range of the link.
[0020] 2. This invention can also control the modulator bias at any point, and modify the control point, loop parameters, etc. through serial communication, which has the advantages of flexible control, high reliability and strong compatibility.
[0021] 3. The bias control device has high integration and small size, and can be used as an independent control module in conjunction with the modulator. It is conducive to miniaturization and modular design, and is applicable to fields such as communication technology and its automatic control, microwave photonics, and optical sensing technology. Attached Figure Description
[0022] Figure 1 A schematic diagram of a miniaturized modulator bias control device;
[0023] Figure 2 Schematic diagram of hardware implementation for a miniaturized modulator bias control device;
[0024] Figure 3 This is a block diagram of the bias control logic based on a miniaturized modulator bias control device;
[0025] Figure 4 This is a flowchart of the unsteady-state control based on a miniaturized modulator bias control device;
[0026] Figure 5 This is a flowchart of the steady-state control based on a miniaturized modulator bias control device;
[0027] Figure 6 This is a schematic diagram illustrating the long-term optical power stability of a miniaturized modulator bias control device. Detailed Implementation
[0028] The technical solution of the present invention will be described in detail below with reference to the embodiments and accompanying drawings.
[0029] Figure 1 This is a schematic diagram of the miniaturized modulator bias control device of the present invention. The device employs a multi-layer stacked design to achieve a SIP modular design: the upper layer houses the digital integrated circuit board for signal processing and control units, with a double-sided layout; labeled components are placed on the front, and bare dies are placed on the back, sintered onto a step inside the housing; the lower layer houses the analog integrated circuit board containing photoelectric conversion units, amplification and filtering units, and drive units, with a single-sided layout; labeled components and bare dies are placed on the front, and the back is low-temperature sintered to the bottom of the housing (for placing the circuit board). Electrical connection between the digital and analog integrated circuit boards is achieved through a ball-mounting process. This design improves signal integrity, solves the heat dissipation problem, and the entire module is only 13 mm * 13 mm in size. Conventional modulator bias control devices are planar board-level structures, which are large in size and lack versatility.
[0030] like Figure 2 As shown in the hardware implementation schematic, this device includes a photoelectric conversion unit, an amplification and filtering unit, a signal processing and control unit, and a drive unit.
[0031] The photoelectric conversion unit includes a photodiode, a gating switch, and a transimpedance amplifier. The common terminal of the gating switch is connected to the cathode of the photodiode, and the other terminal is connected to different resistors in the transimpedance amplifier. The output of the transimpedance amplifier is connected to an amplification and filtering unit. By controlling the state of the gating switch according to the input optical power, the resistance value of the transimpedance amplifier can be switched, which can significantly improve the effective input optical power range of the modulator bias control.
[0032] The amplification and filtering unit includes an operational amplifier and several resistors and capacitors to achieve active filtering. One path is a bandpass filter, which bandpass-filters the signal output from the photoelectric conversion unit, retaining the pilot fundamental signal and the second harmonic signal, and then amplifies the signal before output. The other path is a low-pass filter, which retains only the DC component output from the photoelectric conversion unit. This unit facilitates subsequent signal detection and processing.
[0033] The signal processing and control unit includes an analog-to-digital converter (ADC), a digital-to-analog converter (DAC), and a digital microcontroller (MCU). The ADC converts the analog signal output from the amplification and filtering unit into a digital signal. The MCU then performs FFT analysis on the two digital signals to obtain the amplitudes of the pilot fundamental component, the second harmonic component, and the DC component. A closed-loop control algorithm is used to obtain the bias control voltage, and the MCU then converts the digital signal back into an analog signal for output.
[0034] The driving unit includes an operational amplifier and several resistors and capacitors to form an active adder amplifier circuit, which superimposes and amplifies the two signals output by the signal processing and control unit, while improving the bias control load capacity and is compatible with modulators with both thermal and electronic tuning modes.
[0035] like Figure 3 As shown, the drive unit generates a bias control signal to control the working state of the Mach-Zehnder modulator (MZM) and emit corresponding light. After the photoelectric conversion unit collects the signal, it is processed by the amplification and filtering unit and the signal processing and control unit to obtain the bias value corresponding to the set bias angle. Finally, the drive unit generates a bias control signal.
[0036] In this example, the specific implementation steps of the modulator arbitrary automatic bias point control method are as follows:
[0037] Step 1: The light source generates continuous light, which enters the modulator MZM for modulation. Then, the output light of the modulator passes through a beam splitter, allowing 1% of the optical signal to be connected to the modulator control device.
[0038] Step Two: The miniaturized modulator bias control device is powered on. After the photoelectric conversion unit detects the output optical power of the modulator, it is amplified and filtered by the amplification and filtering unit. The analog-to-digital converter (ADC) in the signal processing and control unit converts the two processed analog signals into digital signals. The MCU then determines whether the optical power is within the effective range of the current transimpedance amplifier: If the digital value corresponding to the DC component output by the photoelectric conversion unit reaches the maximum or minimum value of the ADC range, the current resistance value is considered unsuitable and needs adjustment. Reaching the minimum value indicates that the resistance of the transimpedance amplifier is too small and needs to be increased; reaching the maximum value indicates that the resistance of the transimpedance amplifier is too large and needs to be decreased. At this time, the MCU issues a command to change the state of the switching gating switch until the optical power is within the effective range of the transimpedance amplifier. If the optical power is within the range, the state of the gating switch remains unchanged.
[0039] Step 3: When the optical power is within the effective range of the transimpedance amplifier, the bias point of the modulator is controlled. First, the driving unit loads a low-frequency, small-amplitude pilot signal onto the modulator, such as a pilot frequency <3kHz, pilot power consumption <5%Pπ, and amplitude of 0.2mV. The amplification and filtering unit performs low-pass filtering on the optical signal through multiple stages of filters, and then the signal processing and control unit analyzes the detected signal.
[0040] 1. When the modulator has not yet reached the target operating point, it is in a non-steady-state condition. At this time, the signal processing and control unit performs FFT analysis on the sampled signal to obtain the fundamental component and the second harmonic component. The ratio of the second harmonic component to the fundamental component is calculated, and the modulator's bias voltage is adjusted to minimize this ratio. The non-steady-state control process is as follows: Figure 4 As shown.
[0041] 2. Real-time detection of the ratio of the second harmonic component to the fundamental component, closed-loop control to maintain this value equal to the ratio of the target operating point, at which point the modulator operates to a steady-state state.
[0042] 3. During steady-state operation, the amplitude of the current DC component is determined and used as the reference for closed-loop control. At this time, power-based control is switched to the input method, and the pilot component on the modulator is removed to avoid increasing RF signal spurious signals. The real-time DC component amplitude is determined by the optical power detected by the input detector and compared with the reference value. If the difference is large, it is considered a significant change, and the system re-enters unsteady-state control; if the difference is small, power-based control continues. The steady-state control flow is as follows: Figure 5 As shown.
[0043] This embodiment further provides long-term optical power stability of the miniaturized modulator bias control device, such as... Figure 6 As shown.
[0044] In summary, this invention addresses the shortcomings of existing solutions by proposing a novel miniaturized modulator bias control device and method. It is applicable to fields such as communication technology and its automatic control, microwave photonics, and optical sensing technology, offering advantages such as flexible control, high reliability, miniaturization, and strong compatibility. Based on this invention, the modulator can be biased at any operating point without introducing additional spurious signals, making it suitable for a wide range of scenarios.
Claims
1. A miniaturized modulator bias control device, characterized in that, It includes a photoelectric conversion unit, an amplification and filtering unit, a signal processing and control unit, and a driving unit connected in sequence. The output terminal of the driving unit is connected to the bias control signal terminal of the Mach-Zehnder modulator. The input terminal of the photoelectric conversion unit receives the modulated optical signal output by the Mach-Zehnder modulator.
2. The miniaturized modulator bias control device according to claim 1, characterized in that, The device includes a housing. A digital integrated circuit board, comprising a signal processing and control unit, is placed on the upper layer of the housing. The digital integrated circuit board has a double-sided layout, with labeled components on the front and bare chips on the back, sintered onto a step inside the housing. An analog integrated circuit board, comprising a photoelectric conversion unit, an amplification and filtering unit, and a driving unit, is placed on the lower layer. The analog integrated circuit board has a single-sided layout, with labeled components and bare chips on the front and low-temperature sintered to the bottom of the housing on the back. Electrical connection between the digital and analog integrated circuit boards is achieved through a ball-mounting process.
3. The miniaturized modulator bias control device according to claim 1, characterized in that, The photoelectric conversion unit includes a photodiode, a gating switch, and a transimpedance amplifier. The common terminal of the gating switch is connected to the cathode of the photodiode, and the other terminal is connected to different resistors of the transimpedance amplifier. The output of the transimpedance amplifier is connected to an amplification and filtering unit.
4. The miniaturized modulator bias control device according to claim 3, characterized in that, The amplification and filtering unit includes two operational amplifiers. One operational amplifier is connected to a resistor and a capacitor to form a bandpass filter, which is used to bandpass filter the signal output by the photoelectric conversion unit, retain the pilot fundamental signal and the second harmonic signal, and amplify the signal before outputting it. The other operational amplifier is connected to a resistor and a capacitor to form a low-pass filter, which is used to retain the DC component output by the photoelectric conversion unit.
5. The miniaturized modulator bias control device according to claim 4, characterized in that, The signal processing and control unit includes an analog-to-digital converter, a digital-to-analog converter, and a digital processor connected in sequence. The analog-to-digital converter has two input terminals, which are respectively connected to the two output terminals of the amplification and filtering unit, and is used to convert the two analog signals output by the amplification and filtering unit into digital signals. The digital processor is used to measure the amplitude of the pilot fundamental component, the amplitude of the pilot second harmonic component, and the amplitude of the DC component. The output terminal of the digital-to-analog converter is connected to the input terminal of the driving unit.
6. The miniaturized modulator bias control device according to claim 5, characterized in that, The driving unit includes an operational amplifier and several resistors and capacitors connected together to form an active adder amplifier circuit, which is used to superimpose and amplify the two signals output by the signal processing and control unit.
7. A control method applied to the miniaturized modulator bias control device according to any one of claims 3 to 6, characterized in that, include: When the Mach-Zehnder modulator is in an unsteady-state operation, the driving unit outputs a bias control signal superimposed with the pilot signal to the Mach-Zehnder modulator, acquires the current optical signal, and decomposes it into the pilot fundamental signal and the second harmonic signal. First, the bias value of the Mach-Zehnder modulator is adjusted so that the amplitude ratio of the current second harmonic component to the fundamental component is minimized. Then, by dynamically adjusting the bias control signal, the amplitude ratio of the current second harmonic component to the fundamental component is controlled to remain equal to the ratio of the target operating point of the Mach-Zehnder modulator. At this time, the Mach-Zehnder modulator enters a steady-state operation. When the Mach-Zehnder modulator is in steady-state operation, the amplitude of the current DC component is first used as the reference value for closed-loop control. Then, the drive unit outputs a bias control signal without the pilot signal superimposed to the Mach-Zehnder modulator to acquire the optical signal in real time and calculate the amplitude of the DC component. The difference is obtained by comparing it with the reference value. If the difference is greater than the set threshold, the current steady-state control is exited and the Mach-Zehnder modulator enters unsteady-state control.
8. The miniaturized modulator bias control method according to claim 7, characterized in that, The Mach-Zehnder modulator outputs a modulated optical signal under the bias control signal and in the working state. Based on the acquired optical signal, it judges whether the current optical power is within the effective range of the current transimpedance amplifier. If not, it changes the working state of the gating switch until the optical power is within the effective range of the current transimpedance amplifier. When the optical power is within the effective range of the transimpedance amplifier, it performs non-steady-state and steady-state control on the Mach-Zehnder modulator.
9. The miniaturized modulator bias control method according to claim 7, characterized in that, The frequency of the pilot signal is <3kHz, and the pilot power consumption is <5%Pπ.
10. The miniaturized modulator bias control method according to claim 7, characterized in that, The optical signal acquired based on the output modulated optical signal of the Mach-Zehnder modulator is subjected to bandpass filtering and low-pass filtering respectively to obtain the pilot fundamental wave signal, the second harmonic signal, and the DC component. The pilot fundamental wave signal, the second harmonic signal, and the DC component are then processed by FFT to obtain the amplitude of the pilot fundamental wave component, the amplitude of the pilot second harmonic component, and the amplitude of the DC component, respectively.