Automatic bias voltage control device and method for Mach-Zehnder modulator based on swing method

Abstract

The invention relates to an automatic bias control device and method for a Mach-Zehnder modulator based on a swing method. The automatic bias control device comprises a laser, a radio frequency source, the Mach-Zehnder modulator, a photoelectric detector, an adder, an operational amplifier, an analog-to-digital converter, a single chip microcomputer and a digital-to-analog converter. The output end of the laser is connected with the input end of the Mach-Zehnder modulator; the output end of the radio frequency source is connected with the radio frequency input end of the Mach-Zehnder modulator; the output end of the Mach-Zehnder modulator is connected with the input end of the photoelectric detector; the output end of the photoelectric detector is connected with the input end of the summator; the output end of the summator is connected with the input end of the operational amplifier; the output end of the operational amplifier is connected with the input end of the analog-to-digital converter; the output end of the analog-to-digital converter is connected with the single chip microcomputer; the output end of the single-chip microcomputer is connected with the input end of the digital-to-analog converter. And the output end of the digital-to-analog converter is connected with the bias control end of the Mach-Zehnder modulator.

Description

Technical Field

[0001] The invention relates to the fields of optical communication and microwave photonics, and in particular to an automatic bias control device and method for a Mach-Zehnder modulator based on a swing method. Background Art

[0002] With the continuous development of optical communication technology, microwave photonic technology has become a research hotspot in related fields due to its advantages such as large bandwidth, low loss and low latency. The electro-optic modulator is one of the key components in analog optical communication systems, which is used to load information signals onto the optical carrier output by the laser to achieve electro-optical modulation. Among them, the Mach-Zehnder modulator made of passive optical waveguide lithium niobate material has become one of the most frequently used optical modulation devices due to its fast modulation speed, wide modulation bandwidth, low optical loss, wavelength-independent modulation characteristics and extremely fast electro-optical response characteristics.

[0003] After the input light enters the MZM, it is divided into two signals with the same frequency and phase and enters the two optical branches of the MZM respectively. By applying a DC bias voltage on the optical branch to change the refractive index of the optical waveguide, the phase of the light wave is changed to achieve phase modulation. At the output end, the light interference of the two branches is coupled into an interference signal with varying intensity to achieve light intensity modulation. In short, the MZM converts the change of the electrical signal into the change of the optical signal by controlling the externally applied bias voltage, thereby achieving electro-optical modulation. However, due to the influence of the material and structure of the MZM, its transmission curve will slowly drift with factors such as the external environment temperature and humidity, mechanical vibration, input device optical power, and the aging of the device itself, and change the position of its bias voltage operating point accordingly. This will cause the working state of the MZM to be unstable, resulting in problems such as transmission signal distortion, increased bit error rate, and deterioration of the extinction ratio, resulting in reduced system performance or even unusable, thereby affecting the transmission performance of the entire optical communication system.

[0004] Therefore, the bias control technology for stabilizing the MZM working point plays a vital role. However, the existing commonly used bias control technologies based on average optical power and pilot signals are susceptible to the unstable power of the light source itself, have low control accuracy, complex peripheral circuit design, and are not easy to integrate, and further exploration and research are needed. Therefore, it is urgent to propose an automatic bias control device and method for a Mach-Zehnder modulator based on the swing method. Summary of the invention

[0005] The purpose of the present invention is to provide a Mach-Zehnder modulator automatic bias control device and method based on a swing method to solve the problems existing in the above-mentioned prior art.

[0006] To achieve the above object, the present invention provides the following solutions:

[0007] An automatic bias control device for a Mach-Zehnder modulator based on a swing method, comprising: a laser, a radio frequency source, a Mach-Zehnder modulator, a photodetector, an adder, an operational amplifier, an analog-to-digital converter, a single-chip microcomputer, and a digital-to-analog converter;

[0008] The output end of the laser is connected to the input end of the Mach-Zehnder modulator;

[0009] The output end of the radio frequency source is connected to the radio frequency input end of the Mach-Zehnder modulator;

[0010] The output end of the Mach-Zehnder modulator is connected to the input end of the photodetector;

[0011] The output end of the photodetector is connected to the input end of the adder;

[0012] The output end of the adder is connected to the input end of the operational amplifier;

[0013] The output end of the operational amplifier is connected to the input end of the analog-to-digital converter;

[0014] The output end of the analog-to-digital converter is connected to the single-chip microcomputer;

[0015] The output end of the single chip microcomputer is connected to the input end of the digital-to-analog converter;

[0016] The output end of the digital-to-analog converter is connected to the bias control end of the Mach-Zehnder modulator.

[0017] A method for automatic bias control of a Mach-Zehnder modulator based on a swing method, the method comprising:

[0018] A laser and a radio frequency source are provided to output a laser signal of a preset wavelength and a microwave signal of a preset frequency respectively;

[0019] Using Mach-Zehnder modulator, the optical signal is electro-optically modulated;

[0020] Using a photodetector, the modulated optical signal is converted into an electrical signal;

[0021] The electrical signal is processed by an adder, an operational amplifier, and an analog-to-digital converter in sequence to convert the electrical signal into a digital signal;

[0022] Input the digital signal into the single chip microcomputer, and obtain the swing difference ΔP at the bias voltage U of the Mach-Zehnder modulator according to a preset swing function;

[0023] According to the preset swing function, the swing method is used to find the bias voltage U at the minimum or maximum operating point of the Mach-Zehnder modulator. min or U max ;

[0024] Based on the bias voltage at the minimum or maximum operating point of the Mach-Zehnder modulator, a swing difference is obtained using a preset swing function;

[0025] Based on the swing difference at the minimum or maximum operating point of the Mach-Zehnder modulator, the output bias voltage of the digital-to-analog converter is controlled to achieve bias voltage control at the minimum or maximum operating point of the Mach-Zehnder modulator.

[0026] Optionally, the preset swing function includes:

[0027] Setting the center bias voltage U and the offset bias voltage ΔU, as well as the transmission characteristic curve of the Mach-Zehnder modulator;

[0028] The single-chip microcomputer is used to control the digital-to-analog converter, and the output bias voltage U-ΔU controls the Mach-Zehnder modulator. The output light intensity P of the Mach-Zehnder modulator is collected by the analog-to-digital converter. - ;

[0029] The single chip microcomputer is used to control the digital-to-analog converter, and the output bias voltage U+ΔU acts on the Mach-Zehnder modulator. The output light intensity P of the Mach-Zehnder modulator is collected by the analog-to-digital converter. + ;

[0030] The output light intensity P corresponding to the bias voltage U+ΔU + Subtract the output light intensity P corresponding to the bias voltage U-ΔU - , obtain the swing difference ΔP.

[0031] Optionally, implementing bias control of the Mach-Zehnder modulator at a minimum or maximum operating point includes:

[0032] Set the initial point bias and bias interval;

[0033] According to the initial point bias voltage U1, the swing difference ΔP1 is obtained by using the preset swing function;

[0034] A while loop is used to determine whether the minimum or maximum operating point of the Mach-Zehnder modulator has not been found. If the loop judgment is true, the following loop body is executed:

[0035] Determine the bias voltage U2 of the second point according to the bias voltage interval set during initialization, and calculate the swing difference ΔP2;

[0036] Determine whether there is a minimum or maximum working point U between these two points U1 and U2 min or U max; If there is no minimum or maximum operating point between the two points, update the second point to the initial point and calculate the swing difference and repeat the while loop; if there is a minimum or maximum operating point between the two points, execute the following steps:

[0037] Calculate the swing difference multiple times according to the bias voltages U1 and U2 at the two points, and get the average value and According to the swing difference ΔP=P + -P - ,in V f (t) is the microwave signal output by the RF source, and P + and P - Substituting ΔP, we obtain When the offset bias voltage ΔU and the RF modulation voltage V f When (t) is fixed, the swing difference ΔP and the center bias voltage U satisfy the sinusoidal function relationship, and the bias voltage corresponding to the zero point of the swing difference curve is the bias voltage at the minimum or maximum operating point of the MZM 3 transmission curve;

[0038] Set the minimum or maximum working point and the two points on its left and right sides to have the same slope; the average of U1, U2 and their corresponding swing difference and the minimum or maximum working point U0 and its corresponding swing difference 0, we get Then seek When ΔP changes from negative to positive, the obtained U0 is the bias voltage U at the minimum operating point. min On the contrary, when ΔP changes from positive to negative, the obtained U0 is the bias voltage U at the maximum operating point. max .

[0039] Optionally, the constraint condition for setting the bias voltage interval is to ensure that the minimum or maximum operating point of the MZM 3 is not missed during the search and the number of searches is minimized.

[0040] Optionally, determine whether there is a minimum or maximum operating point U between the two points U1 and U2 min or U max include:

[0041] If the swing difference at these two points satisfies ΔP1<0 and ΔP2>0, it is considered that there is a minimum operating point U between U1 and U2. min If the swing difference at these two points satisfies ΔP1>0 and ΔP2<0, it is considered that there is a maximum operating point U between U1 and U2. max .

[0042] Optionally, implementing bias control of the Mach-Zehnder modulator at a minimum or maximum operating point further includes:

[0043] The single chip microcomputer controls the digital-to-analog converter to output a bias voltage at a minimum or maximum operating point to a bias control pin of the Mach-Zehnder modulator;

[0044] The analog-to-digital converter collects the output light intensity at the minimum or maximum operating point of the Mach-Zehnder modulator;

[0045] When the Mach-Zehnder modulator is at its minimum or maximum operating point, the bias voltage control of MZM 3 at its minimum or maximum operating point is achieved by cyclically detecting the current ΔP value and ensuring that ΔP=0 or is less than the set threshold. When it is detected that ΔP exceeds the threshold limit, the bias voltage is adjusted to meet the threshold requirement again, and the adjusted bias voltage is updated to the bias voltage of the minimum or maximum operating point.

[0046] The beneficial effects of the present invention are:

[0047] The bias control technology is mainly realized through software algorithm, which has simple structure, low cost and easy system integration;

[0048] The swing method is used to find the working point of the MZM by detecting the size of the swing difference ΔP, that is, the difference in the output light intensity of points near the center bias voltage U, which improves the influence of noise in the traditional structure;

[0049] The present invention can realize the regulation and control of the minimum or maximum working point of the MZM through the swing method, which can effectively improve the working stability of the MZM;

[0050] When searching for the minimum or maximum working point, the swing method scans at a certain bias interval, and the scanning speed can be flexibly controlled, which is highly practical.

[0051] By judging the positive and negative changes of the swing difference ΔP, the drift direction of the working point can be distinguished, which helps to stabilize the working point and improve the control efficiency of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0053] Figure 1 It is a schematic diagram of an automatic bias control device for a Mach-Zehnder modulator based on a swing method according to an embodiment of the present invention;

[0054] Figure 21 is the relationship between the bias voltage U and the swing difference ΔP when the bias voltage U is located at different positions of the minimum operating point according to the embodiment of the present invention; wherein (a) is the left side of the minimum operating point, (b) is the minimum operating point, and (c) is the right side of the minimum operating point;

[0055] Figure 3 1 is the relationship between the bias voltage U and the swing difference ΔP when the bias voltage U is located at different positions of the maximum operating point according to the embodiment of the present invention; wherein (a) is the left side of the maximum operating point, (b) is the maximum operating point, and (c) is the right side of the maximum operating point;

[0056] Figure 4 The swing difference curve and the partial enlarged diagram of the embodiment of the present invention;

[0057] Figure 5 This is a flow chart of an algorithm for finding the minimum or maximum operating point of an MZM based on a swing method according to an embodiment of the present invention;

[0058] Among them, 1: laser; 2: RF source; 3: MZM; 4: photodetector; 5: adder; 6: operational amplifier; 7: analog-to-digital converter; 8: microcontroller; 9: digital-to-analog converter. DETAILED DESCRIPTION

[0059] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0061] like Figure 1 As shown, this embodiment proposes an automatic bias control device for a Mach-Zehnder modulator based on a swing method, comprising: a laser, a radio frequency source, a Mach-Zehnder modulator, a photodetector, an adder, an operational amplifier, an analog-to-digital converter, a single-chip microcomputer, and a digital-to-analog converter;

[0062] The output end of the laser is connected to the input end of the Mach-Zehnder modulator;

[0063] The output end of the radio frequency source is connected to the radio frequency input end of the Mach-Zehnder modulator;

[0064] The output of the Mach-Zehnder modulator is connected to the input of the photodetector;

[0065] The output end of the photodetector is connected to the input end of the adder;

[0066] The output terminal of the adder is connected to the input terminal of the operational amplifier;

[0067] The output terminal of the operational amplifier is connected to the input terminal of the analog-to-digital converter;

[0068] The output end of the analog-to-digital converter is connected to the microcontroller;

[0069] The output terminal of the single chip microcomputer is connected to the input terminal of the digital-to-analog converter;

[0070] The output end of the digital-to-analog converter is connected to the bias control end of the Mach-Zehnder modulator.

[0071] Specifically, in this embodiment, a Mach-Zehnder modulator automatic bias control device based on the swing method includes a laser 1, a radio frequency source 2, an MZM 3, a photodetector 4, an adder 5, an operational amplifier 6, an analog-to-digital converter (ADC) 7, a single-chip microcomputer 8, and a digital-to-analog converter (DAC) 9;

[0072] The output end of the laser 1 is connected to the input end of the MZM 3;

[0073] The output terminal of the RF source 2 is connected to the RF input terminal of the MZM 3;

[0074] The output end of the MZM 3, i.e., the Mach-Zehnder modulator, is connected to the input end of the photodetector 4 to convert the optical signal into an electrical signal;

[0075] The output end of the photodetector 4 is connected to the input end of the adder 5;

[0076] The output terminal of the adder 5 is connected to the input terminal of the operational amplifier 6;

[0077] The output terminal of the operational amplifier 6 is connected to the input terminal of the ADC 7;

[0078] The output end of the ADC 7 is connected to a general-purpose input / output (GPIO) port of the single-chip computer 8;

[0079] The output terminal of the single chip microcomputer 8 is connected to the input terminal of the DAC 9;

[0080] The output terminal of the DAC 9 is connected to the bias control terminal of the MZM 3 .

[0081] This embodiment also proposes a Mach-Zehnder modulator automatic bias control method based on the swing method, the method comprising:

[0082] A laser and a radio frequency source are provided to output a laser signal of a preset wavelength and a microwave signal of a preset frequency respectively;

[0083] Using Mach-Zehnder modulator, the optical signal is electro-optically modulated;

[0084] Using a photodetector, the modulated optical signal is converted into an electrical signal;

[0085] The electrical signal is processed by an adder, an operational amplifier, and an analog-to-digital converter in sequence and converted into a digital signal;

[0086] Input the digital signal into the single chip microcomputer, and obtain the swing difference ΔP at the bias voltage U of the Mach-Zehnder modulator according to a preset swing function;

[0087] According to the preset swing function, the swing method is used to find the bias voltage U at the minimum or maximum operating point of the Mach-Zehnder modulator. min or U max ;

[0088] Based on the bias voltage at the minimum or maximum operating point of the Mach-Zehnder modulator, a swing difference is obtained using a preset swing function;

[0089] Based on the swing difference at the minimum or maximum operating point of the Mach-Zehnder modulator, the output bias voltage of the digital-to-analog converter is controlled to achieve bias voltage control at the minimum or maximum operating point of the Mach-Zehnder modulator.

[0090] Furthermore, the preset swing function includes:

[0091] Setting the center bias voltage U and the offset bias voltage ΔU, as well as the transmission characteristic curve of the Mach-Zehnder modulator;

[0092] The single-chip microcomputer is used to control the digital-to-analog converter, and the output bias voltage U-ΔU controls the Mach-Zehnder modulator. The output light intensity P of the Mach-Zehnder modulator is collected by the analog-to-digital converter. - ;

[0093] The single chip microcomputer is used to control the digital-to-analog converter, and the output bias voltage U+ΔU acts on the Mach-Zehnder modulator. The output light intensity P of the Mach-Zehnder modulator is collected by the analog-to-digital converter. + ;

[0094] The output light intensity P corresponding to the bias voltage U+ΔU + Subtract the output light intensity P corresponding to the bias voltage U-ΔU - , obtain the swing difference ΔP.

[0095] Specifically, in this embodiment, a proposed automatic bias control method for a Mach-Zehnder modulator based on a swing method specifically includes the following steps:

[0096] Step 1: Connect the output of laser 1 to the input of MZM 3, and the output of RF source 2 to the RF input of MZM 3. Turn on laser 1 and RF source 2, set laser 1 to output a laser with a wavelength of λ, and RF source 2 to output a microwave signal V f (t), the frequency is f, where V represents the voltage value of the microwave signal and t is the time variable;

[0097] Step 2: The output end of the MZM 3 is connected to the input end of the photodetector 4, and the photodetector 4 converts the received optical signal into an electrical signal;

[0098] Step 3: The output of the photodetector 4 is connected to the input of the adder 5, and the output of the adder 5 is sent to the operational amplifier 6 for amplification to improve the sensitivity of the data acquisition of the ADC 7;

[0099] Step 4: The output end of the operational amplifier 6 is connected to the input of the ADC 7 to convert the analog electrical signal into a digital signal and send it to the single chip microcomputer 8;

[0100] Step 5: The single chip microcomputer 8 obtains the swing difference ΔP at the bias voltage U through programming. The swing function is specifically implemented as follows. Selecting the center bias voltage U and the offset bias voltage ΔU, the transfer characteristic curve of the MZM 3 in an ideal situation can be expressed as Where P out and P in are the output and input light intensity of MZM 3, V π is the half-wave voltage, V f (t) is the RF modulation voltage, V bias is the bias voltage. Due to its symmetry, the position of the center bias voltage U can be determined according to the relationship between the output light intensity P of MZM 3 when the bias voltages are U-ΔU and U+ΔU respectively. The microcontroller 8 controls the DAC 9 to output the bias voltage U-ΔU to control MZM 3, and then the output light intensity P of MZM 3 is collected by the ADC 7. - Next, the single chip microcomputer 8 controls the DAC 9 to output the bias voltage U+ΔU to act on the MZM 3, and controls the ADC 7 to collect the output light intensity P of the MZM 3 at this time. + The swing difference ΔP is defined as the output light intensity P corresponding to the bias voltage U+ΔU + Subtract the output light intensity P corresponding to the bias voltage U-ΔU - When the center bias voltage U is located at different positions of the transmission curve, the value and change of the swing difference ΔP are different, such as Figure 2 , Figure 3 As shown; among them, Figure 2 (a) is the left side of the minimum working point, Figure 2 (b) is the minimum working point, Figure 2 (c) is the right side of the minimum working point; where, Figure 3 (a) is the left side of the maximum working point, Figure 3 (b) is the maximum working point, Figure 3 (c) is the right side of the maximum working point;

[0101] Step 6: The present invention uses the single chip microcomputer 8 to implement the swing method to find the minimum or maximum working point of the MZM 3. The algorithm implementation process is as follows: Figure 5 First, the system initialization configuration is performed, which mainly includes the declaration of the swing function, the definition of the initial point and bias interval, the initialization of the ADC and DAC modules, etc.

[0102] Step 7: Obtain the swing difference ΔP1 using the swing function according to the initial point bias voltage U1;

[0103] Step 8: Use a while loop to determine whether the minimum or maximum operating point of MZM 3 is not found. If the loop judgment is true, execute the following loop body;

[0104] Step 9: Determine the bias voltage U2 of the second point according to the bias voltage interval set during initialization, and calculate the swing difference ΔP2. The setting of the bias voltage interval should ensure that the minimum or maximum operating point of MZM 3 is not missed during the search, and the number of searches should be reduced as much as possible;

[0105] Step 10: Use software algorithm to determine whether there is a minimum or maximum working point U between the two points U1 and U2 min or U max If the swing difference at these two points satisfies ΔP1<0 and ΔP2>0, it is considered that there is a minimum operating point U between U1 and U2. min If the swing difference at these two points satisfies ΔP1>0 and ΔP2<0, it is considered that there is a maximum operating point U between U1 and U2. max If the above judgment conditions are not met, that is, there is no minimum or maximum working point between the two points, the second point is updated to the initial point and the swing difference is calculated to repeat the while loop. If the above judgment conditions are met, the following steps are executed;

[0106] Step 11: Calculate the swing difference multiple times based on the bias voltages U1 and U2 at the two points and take the average value and According to the above analysis, the swing difference ΔP=P + -P - ,in Substitute into the above formula and simplify it to get It can be seen that when the offset bias voltage ΔU and the RF modulation voltage V f When (t) is fixed, the swing difference ΔP and the center bias voltage U satisfy the sinusoidal function relationship. The bias voltage corresponding to the zero point of the swing difference curve is the bias voltage at the minimum or maximum operating point of the MZM 3 transmission curve, as shown in Figure 4 As shown;

[0107] Step 12: The zero point of the swing difference curve can be approximately regarded as a straight line, so it can be considered that the slopes of the two straight lines formed by the minimum or maximum working point and the two points on its left and right sides are equal. And the minimum or maximum working point U0 and its corresponding swing difference 0, we can get Then seek When ΔP changes from negative to positive, the obtained U0 is the bias voltage U at the minimum operating point. min On the contrary, when ΔP changes from positive to negative, the obtained U0 is the bias voltage U at the maximum operating point. max ;

[0108] Step 13: The single chip microcomputer 8 controls the DAC 9 to output the bias voltage at the minimum or maximum operating point to the bias control pin of the MZM 3;

[0109] Step 14: ADC 7 collects the output light intensity at the minimum or maximum working point of MZM 3;

[0110] Step 15: At the minimum or maximum operating point of MZM 3, the value of ΔP should be 0. After finding the minimum or maximum operating point of MZM 3, the bias voltage control of MZM 3 at the minimum or maximum operating point is realized by cyclically detecting the current ΔP value and ensuring that ΔP = 0 or less than the set threshold. When it is detected that ΔP exceeds the threshold limit, the bias voltage is adjusted in a certain step to meet the threshold requirement again, and the adjusted bias voltage is updated to the bias voltage of the minimum or maximum operating point.

[0111] This embodiment mainly implements bias control technology through software algorithm, which has simple structure, low cost and easy system integration;

[0112] The swing method is used to find the working point of the MZM by detecting the size of the swing difference ΔP, that is, the difference in the output light intensity of points near the center bias voltage U, which improves the influence of noise in the traditional structure;

[0113] The present invention can realize the regulation and control of the minimum or maximum working point of the MZM through the swing method, which can effectively improve the working stability of the MZM;

[0114] When searching for the minimum or maximum working point, the swing method scans at a certain bias interval, and the scanning speed can be flexibly controlled, which is highly practical.

[0115] By judging the positive and negative changes of the swing difference ΔP, the drift direction of the working point can be distinguished, which helps to stabilize the working point and improve the control efficiency of the system.

[0116] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. An automatic bias control device for a Mach-Zehnder modulator based on a swing method, characterized in that: include: Lasers, RF sources, Mach-Zehnder modulators, photodetectors, adders, operational amplifiers, analog-to-digital converters, microcontrollers, digital-to-analog converters; The output end of the laser is connected to the input end of the Mach-Zehnder modulator; The output end of the radio frequency source is connected to the radio frequency input end of the Mach-Zehnder modulator; The output end of the Mach-Zehnder modulator is connected to the input end of the photodetector; The output end of the photodetector is connected to the input end of the adder; The output end of the adder is connected to the input end of the operational amplifier; The output end of the operational amplifier is connected to the input end of the analog-to-digital converter; The output end of the analog-to-digital converter is connected to the single-chip microcomputer; The output end of the single chip microcomputer is connected to the input end of the digital-to-analog converter; The output end of the digital-to-analog converter is connected to the bias control end of the Mach-Zehnder modulator.

2. A method for automatic bias control of a Mach-Zehnder modulator based on a swing method, characterized in that: The automatic bias control device for a Mach-Zehnder modulator based on a swing method as claimed in claim 1 is applied, and the method comprises: A laser and a radio frequency source are provided to output a laser signal of a preset wavelength and a microwave signal of a preset frequency respectively; Using Mach-Zehnder modulator, the optical signal is electro-optically modulated; Using a photodetector, the modulated optical signal is converted into an electrical signal; The electrical signal is processed by an adder, an operational amplifier, and an analog-to-digital converter in sequence to convert the electrical signal into a digital signal; Input the digital signal into the single chip microcomputer, and obtain the swing difference ΔP at the bias voltage U of the Mach-Zehnder modulator according to a preset swing function; According to the preset swing function, the swing method is used to find the bias voltage U at the minimum or maximum operating point of the Mach-Zehnder modulator. min or U max ; Based on the bias voltage at the minimum or maximum operating point of the Mach-Zehnder modulator, a swing difference is obtained using a preset swing function; Based on the swing difference at the minimum or maximum operating point of the Mach-Zehnder modulator, the output bias voltage of the digital-to-analog converter is controlled to achieve bias voltage control at the minimum or maximum operating point of the Mach-Zehnder modulator.

3. The automatic bias control method of Mach-Zehnder modulator based on the swing method according to claim 2, characterized in that: The preset swing function includes: Setting the center bias voltage U and the offset bias voltage ΔU, as well as the transmission characteristic curve of the Mach-Zehnder modulator; The single-chip microcomputer is used to control the digital-to-analog converter, and the output bias voltage U-ΔU controls the Mach-Zehnder modulator. The output light intensity P of the Mach-Zehnder modulator is collected by the analog-to-digital converter. - ; The single chip microcomputer is used to control the digital-to-analog converter, and the output bias voltage U+ΔU acts on the Mach-Zehnder modulator. The output light intensity P of the Mach-Zehnder modulator is collected by the analog-to-digital converter. + ; The output light intensity P corresponding to the bias voltage U+ΔU + Subtract the output light intensity P corresponding to the bias voltage U-ΔU - , obtain the swing difference ΔP.

4. The automatic bias control method of Mach-Zehnder modulator based on the swing method according to claim 2, characterized in that: Bias control to achieve minimum or maximum operating point of the Mach-Zehnder modulator includes: Set the initial point bias and bias interval; According to the initial point bias voltage U1, the swing difference ΔP1 is obtained by using the preset swing function; A while loop is used to determine whether the minimum or maximum operating point of the Mach-Zehnder modulator has not been found. If the loop judgment is true, the following loop body is executed: Determine the bias voltage U2 of the second point according to the bias voltage interval set during initialization, and calculate the swing difference ΔP2; Determine whether there is a minimum or maximum working point U between these two points U1 and U2 min or U max ; If there is no minimum or maximum operating point between the two points, update the second point to the initial point and calculate the swing difference and repeat the while loop; if there is a minimum or maximum operating point between the two points, execute the following steps: Calculate the swing difference multiple times according to the bias voltages U1 and U2 at the two points, and get the average value and According to the swing difference ΔP=P + -P - ,in V f (t) is the microwave signal output by the RF source, and P + and P - Substituting ΔP, we obtain When the offset bias voltage ΔU and the RF modulation voltage V f When (t) is fixed, the swing difference ΔP and the center bias voltage U satisfy the sinusoidal function relationship, and the bias voltage corresponding to the zero point of the swing difference curve is the bias voltage at the minimum or maximum operating point of the MZM 3 transmission curve; Set the minimum or maximum working point and the two points on its left and right sides to have the same slope; the average of U1, U2 and their corresponding swing difference and the minimum or maximum working point U0 and its corresponding swing difference 0, we get Then obtain When ΔP changes from negative to positive, the obtained U0 is the bias voltage U at the minimum operating point. min On the contrary, when ΔP changes from positive to negative, the obtained U0 is the bias voltage U at the maximum operating point. max .

5. The automatic bias control method of Mach-Zehnder modulator based on the swing method according to claim 4, characterized in that: The constraint condition for setting the bias voltage interval is to ensure that the minimum or maximum operating point of the MZM 3 is not missed during the search and to ensure that the number of searches is minimized.

6. The automatic bias control method of Mach-Zehnder modulator based on the swing method according to claim 4, characterized in that: Determine whether there is a minimum or maximum working point U between these two points U1 and U2 min or U max include: If the swing difference at these two points satisfies ΔP1<0 and ΔP2>0, it is considered that there is a minimum operating point U between U1 and U2. min If the swing difference at these two points satisfies ΔP1>0 and ΔP2<0, it is considered that there is a maximum operating point U between U1 and U2. max .

7. The automatic bias control method of Mach-Zehnder modulator based on the swing method according to claim 2, characterized in that: Implementing bias control of the Mach-Zehnder modulator at the minimum or maximum operating point also includes: The single chip microcomputer controls the digital-to-analog converter to output a bias voltage at a minimum or maximum operating point to a bias control pin of the Mach-Zehnder modulator; The analog-to-digital converter collects the output light intensity at the minimum or maximum operating point of the Mach-Zehnder modulator; When the Mach-Zehnder modulator is at its minimum or maximum operating point, the bias voltage control of MZM 3 at its minimum or maximum operating point is achieved by cyclically detecting the current ΔP value and ensuring that ΔP=0 or is less than the set threshold. When it is detected that ΔP exceeds the threshold limit, the bias voltage is adjusted to meet the threshold requirement again, and the adjusted bias voltage is updated to the bias voltage of the minimum or maximum operating point.

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