Variable gain acquisition circuit applied to high-speed silicon optical module and optical module

Abstract

The utility model relates to the technical field of optical communication, in particular to a variable gain acquisition circuit applied to a high-speed silicon optical module and an optical module, the high-speed silicon optical module comprises an MZM modulator, a main path monitoring diode and an auxiliary path monitoring diode of a tap output in an output optical path of the MZM modulator are connected with respective corresponding variable gain transimpedance amplification circuits, and the main path monitoring diode and the auxiliary path monitoring diode are connected with the corresponding variable gain transimpedance amplification circuits. The signal output end of the variable gain transimpedance amplification circuit is connected to the signal input end of the MCU through the analog-to-digital converter, and the signal output end of the MCU is connected to the signal input end of the MZM modulator through the digital-to-analog converter. According to the utility model, the variable gain transimpedance amplification circuit is utilized to monitor the main path monitoring diode MPDmain and the auxiliary path monitoring diode MPDsub of the tap output in the output light path of the MZM modulator in real time, stable and more accurate sampling can be realized under the condition of different current magnitudes, and the gain can be adjusted in real time according to the change condition of the sampling value.

Description

Technical Field

[0001] The utility model relates to the technical field of optical communications, and in particular to a variable gain acquisition circuit and an optical module applied to a high-speed silicon optical module. Background Art

[0002] The basic principles of the current high-speed optical modules based on silicon photonic modulation are as follows: Figure 3 As shown in the figure, in order to achieve real-time tracking and adjustment of the optimal operating point, it is necessary to monitor the main monitoring diode MPD_main and the auxiliary monitoring diode MPD_sub, which tap approximately 2% of the optical power in the output optical path, in real time and adjust and lock them according to the changes. Therefore, how to stably and accurately collect these two MPDs is the key to achieving good control modulation.

[0003] The commonly used method at present is to use resistors for termination, such as Figure 4 As shown, the voltage is then collected by the analog-to-digital converter ADC in the circuit or the microcontroller unit MCU with ADC. Due to the particularity of silicon photonic modulation, MPD sampling involves real-time tracking during normal use and the minimum power requirement when the light is turned off. The accuracy of the sampling directly affects the overall performance of the module. Although it is very simple to use resistors to collect voltage, due to the process consistency issues of silicon photonic modulators and the fact that the tap current varies with temperature and exhibits certain nonlinear characteristics, this solution cannot take into account all situations using a fixed resistance value. For example, when the MPD current is 200μA, a 2K resistor is selected, and the sampling voltage is 400mV. If the current changes to 1mA, the sampling voltage becomes 2V. At this time, if VCC is lower than 2V, it will cause saturation, making the sampling value inaccurate. At the same time, the conventional way to adjust the phase bias point of the MZM modulator, that is, the Mach-Zehnder electro-optical modulator, is to monitor the optical power entering and emitted by the MZM modulator and make judgments based on thresholds or other relationships, such as Figure 5 As shown in the figure, PD1 is the photodiode that monitors the optical power entering the MZM modulator, while PD2 and PD3 are the photodiodes that monitor the optical power emitted by the MZM modulator. However, using PD1, PD2, and PD3 to monitor power and determine the phase bias point based on thresholds can introduce significant errors. Furthermore, the slope efficiency of the laser varies at high and low temperatures, leading to significant variations in PD1. This error cannot be eliminated, easily leading to over- or under-compensation, and complicating the adjustment algorithm.

[0004] Based on this, how to improve the sampling accuracy and optimize the phase bias point modulation accuracy is a technical problem that needs to be solved urgently. Utility Model Content

[0005] The purpose of the utility model is to provide a variable gain acquisition circuit and optical module for high-speed silicon photonic modules, which are designed using a variable gain transimpedance amplifier to improve sampling accuracy and phase bias point modulation accuracy.

[0006] The utility model is implemented through the following technical solution: a variable gain acquisition circuit applied to a high-speed silicon photonic module, wherein the high-speed silicon photonic module includes an MZM modulator, wherein a main monitoring diode and an auxiliary monitoring diode tapped out of an output optical path of the MZM modulator are connected to respective corresponding variable gain transimpedance amplifier circuits, wherein a signal output end of the variable gain transimpedance amplifier circuit is connected to a signal input end of an MCU via an analog-to-digital converter, and the signal output end of the MCU is connected to a signal input end of the MZM modulator via a digital-to-analog converter.

[0007] According to a preferred embodiment, the variable gain transimpedance amplifier circuit includes an amplifier and a transimpedance branch connected across the reverse input and output ends of the amplifier, the reverse input end of the amplifier is connected to the virtual ground through the corresponding main / auxiliary monitoring diode, and the transimpedance branch is connected to a feedback resistor and a feedback capacitor, and the feedback resistor and feedback capacitor are arranged in parallel.

[0008] According to a preferred embodiment, the amplifier is an operational amplifier with a small offset voltage and a small input leakage current.

[0009] According to a preferred embodiment, two transresistance branches are provided, and the two transresistance branches are connected to corresponding feedback resistors and feedback capacitors, respectively.

[0010] According to a preferred embodiment, the capacitance values of the two feedback capacitors satisfy the following formula:

[0011]

[0012] In the above formula, C F is the capacitance value of the feedback capacitor, R F is the resistance value of the feedback resistor corresponding to the feedback capacitor, GBP is the gain bandwidth product of the operational amplifier, C S It is the parasitic capacitance of the main monitoring diode or the auxiliary monitoring diode.

[0013] According to a preferred embodiment, each of the transimpedance branches is connected to two corresponding analog switches.

[0014] According to a preferred embodiment, one of the analog switches is arranged in a feedback loop of the transimpedance branch.

[0015] The utility model also provides a high-speed silicon photonic module, comprising the variable gain acquisition circuit as described above.

[0016] The technical solution of a variable gain acquisition circuit and an optical module for a high-speed silicon photonic module provided by the present invention has at least the following advantages and beneficial effects: (1) The present invention uses a variable gain transimpedance amplifier circuit to monitor the main monitoring diode MPD_main and the auxiliary monitoring diode MPD_sub tapped out of the output optical path of the MZM modulator in real time, which can achieve stable and more accurate sampling under different current conditions, and can adjust the gain in real time according to the change of the sampling value, which can reduce the requirements for indicators such as the resolution of the ADC and DAC, and save external ADC and DAC resources; (2) Based on the variable gain acquisition circuit, phase locking can be achieved only by relying on the main monitoring diode MPD_main and the auxiliary monitoring diode MPD_sub, and good consistency can be maintained at high and low temperatures. It has good stability and is easy to implement, and can avoid monitoring the optical power entering the MZM modulator, which can improve the adjustment accuracy of the phase bias point. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is an overall block diagram of the variable gain acquisition circuit provided in Example 1 of the present utility model;

[0018] Figure 2 A schematic diagram showing the principle of a variable gain transimpedance amplifier circuit according to embodiment 1 of the present invention;

[0019] Figure 3 This is a simplified schematic diagram of the current high-speed optical module based on silicon photonic modulation;

[0020] Figure 4 This is a simple schematic diagram of the current collection using termination resistors;

[0021] Figure 5 A schematic diagram of the PD layout for adjusting the phase bias point of the MZM modulator. DETAILED DESCRIPTION

[0022] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0023] Example 1

[0024] Figure 1 This is an overall block diagram of a variable gain acquisition circuit for a high-speed silicon photonic module provided by Example 1 of the present utility model. Figure 1As shown, the high-speed silicon photonic module includes an MZM modulator. After the MZM modulator undergoes dual-arm modulation, the output optical path is divided into a main path (main) and an auxiliary path (sub).

[0025] Specifically in this embodiment, the variable gain acquisition circuit is designed as follows:

[0026] The main monitoring diode MPD_main and the auxiliary monitoring diode MPD_sub tapped out in the output optical path of the MZM modulator are connected to their respective corresponding variable gain transimpedance amplifier circuits, and the variable gain transimpedance amplifier circuits are used to collect the MPD_main and MPD_sub currents.

[0027] It should be noted that the use of a variable gain transimpedance amplifier circuit to monitor the main monitoring diode MPD_main and the auxiliary monitoring diode MPD_sub tapped out of the MZM modulator output optical path in real time can achieve stable and more accurate sampling under different current conditions.

[0028] Furthermore, the signal output of the variable-gain transimpedance amplifier circuit is connected to the signal input of an MCU via an analog-to-digital converter (ADC). The MCU is configured to analyze the collected data, for example, by determining the phase bias point using a threshold or voltage difference. This is not further detailed here. The signal output of the MCU is connected to the signal input of the MZM modulator via a digital-to-analog converter (DAC). Based on the analysis results, the MCU uses the DAC to adjust the voltages of the two arms of the MZM modulator in real time to achieve the optimal operating point of the MZM modulator.

[0029] In one implementation of this embodiment, see Figure 2 As shown, the variable gain transimpedance amplifier circuit includes an amplifier and a transimpedance branch connected across the inverting input and output of the amplifier. The inverting input of the amplifier is connected to virtual ground via a corresponding main / auxiliary monitoring diode MPD, while the non-inverting input is grounded. The transimpedance branch is connected to a feedback resistor and a feedback capacitor, which are arranged in parallel.

[0030] It should be noted that all the current Id in the monitor diode flows through the feedback resistor, one end of which is at virtual ground. Therefore, the output voltage is equal to the product of the feedback resistor value and the current Id. To ensure this approximate calculation, the amplifier uses an operational amplifier (OPA) with low offset voltage and low input leakage current. A low input offset voltage can reduce the dark current of the monitor diode. In this embodiment, the maximum offset voltage of the amplifier is 100μV, and the maximum leakage current is 500pA.

[0031] Furthermore, there are two transresistance branches, each of which is connected to a corresponding feedback resistor and feedback capacitor. All current Id of the monitoring diode flows through the feedback resistor R1 and / or R2, so the output voltage is equal to the product of the resistance value of the feedback resistor R1 and / or R2 and the current Id.

[0032] In a preferred embodiment, in order to ensure stable operation of the operational amplifier and to achieve a second-order Butterworth frequency response, the capacitance values of the two feedback capacitors C1 and C2 satisfy the following formula:

[0033]

[0034] In the above formula, C F is the capacitance value of feedback capacitor C1 and / or C2, R F is the resistance of the feedback resistor R1 and / or R2 corresponding to the feedback capacitor C1 and / or C2, GBP is the gain bandwidth product of the operational amplifier, C S It is the parasitic capacitance of the main monitoring diode or the auxiliary monitoring diode.

[0035] Furthermore, an analog switch is connected to the transimpedance branch. It should be noted that the introduction of an analog switch may introduce errors due to its on-resistance and leakage current, and the on-resistance causes voltage and temperature-related gain errors, while the leakage current causes offset errors, especially at high temperatures. Therefore, in this embodiment, each of the transimpedance branches is connected to two corresponding analog switches S1 and S2, thereby avoiding the above problems. In addition, one of the analog switches is set in the feedback loop of the transimpedance branch, such as S1, so that the output voltage depends on the current through the selected feedback resistors R1 and / or R2, while the output of the other analog switch S2 is connected to a high-impedance load, so the error generated is negligible.

[0036] In addition, the following briefly explains the principle of phase locking using only the main monitoring diode MPD_main and the auxiliary monitoring diode MPD_sub:

[0037] At the current temperature, the DAC output value is adjusted according to the eye diagram quality, that is, the voltage applied to the two arms of the MZM modulator is adjusted. The transmitter specifications of the IEEE 802.3 protocol are used to comprehensively determine whether the current voltage setting value is at the optimal phase bias point. Then, by collecting the values of the main monitoring diode MPD_main and the auxiliary monitoring diode MPD_sub, the proportional factor coefficient σ is obtained by substituting them into the following formula: MPD main The main monitoring diode MPD_main acquisition value, MPD sub Collects the value of the auxiliary monitoring diode MPD_sub.

[0038] Furthermore, when the temperature changes, a real-time closed-loop adjustment is performed based on the threshold range σ+ρ, where ρ is an adjustment factor, and its value can be 0.05 to 0.15. It can be adjusted according to actual conditions without specific restrictions.

[0039] Example 2

[0040] This embodiment provides a high-speed silicon photonic module based on the technical solution provided in Example 1. The high-speed silicon photonic module includes the variable gain acquisition circuit as described in Example 1.

[0041] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A variable gain acquisition circuit for a high-speed silicon photonic module, wherein the high-speed silicon photonic module includes an MZM modulator, characterized in that: The main monitoring diode and the auxiliary monitoring diode tapped out in the output optical path of the MZM modulator are connected to their respective corresponding variable gain transimpedance amplifier circuits. The signal output end of the variable gain transimpedance amplifier circuit is connected to the signal input end of the MCU via an analog-to-digital converter, and the signal output end of the MCU is connected to the signal input end of the MZM modulator via a digital-to-analog converter.

2. The variable gain acquisition circuit for high-speed silicon photonic modules according to claim 1, wherein: The variable gain transimpedance amplifier circuit includes an amplifier and a transimpedance branch connected across the reverse input and output ends of the amplifier, the reverse input end of the amplifier is connected to the virtual ground through the corresponding main / auxiliary monitoring diode, the transimpedance branch is connected to a feedback resistor and a feedback capacitor, and the feedback resistor and feedback capacitor are arranged in parallel.

3. The variable gain acquisition circuit for high-speed silicon photonic modules according to claim 2, wherein: The amplifier is an operational amplifier with small offset voltage and small input leakage current.

4. The variable gain acquisition circuit for a high-speed silicon photonic module according to any one of claims 2 to 3, wherein: There are two transresistance branches, and the two transresistance branches are connected to respective corresponding feedback resistors and feedback capacitors.

5. The variable gain acquisition circuit for high-speed silicon photonic modules according to claim 4, wherein: The capacitance values of the two feedback capacitors satisfy the following formula: In the above formula, C F is the capacitance value of the feedback capacitor, R F is the resistance value of the feedback resistor corresponding to the feedback capacitor, GBP is the gain bandwidth product of the operational amplifier, C S It is the parasitic capacitance of the main monitoring diode or the auxiliary monitoring diode.

6. The variable gain acquisition circuit for high-speed silicon photonic modules according to claim 4, wherein: Each of the transimpedance branches is connected to two corresponding analog switches.

7. The variable gain acquisition circuit for high-speed silicon photonic modules according to claim 6, characterized in that: One of the analog switches is arranged in a feedback loop of the transimpedance branch.

8. A high-speed silicon photonic module, characterized in that: The method comprises the variable gain acquisition circuit according to any one of claims 1 to 7.

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