Bias voltage calibration method

Abstract

The application provides a bias voltage calibration method, and relates to the field of communication. The method comprises the following steps: setting the bias voltage of an I-path sub-MZI as a first initial voltage value and the bias voltage of a Q-path sub-MZI as a second initial voltage value, performing bias voltage calibration on a parent MZI to determine a third candidate calibration voltage value of the parent MZI; based on the third candidate calibration voltage value of the parent MZI, respectively calibrating the bias voltage of the I-path sub-MZI and the bias voltage of the Q-path sub-MZI to obtain a first candidate calibration voltage value of the I-path sub-MZI and a second candidate calibration voltage value of the Q-path sub-MZI; and in the case that the first candidate calibration voltage value is equal to the first initial voltage value and the second candidate calibration voltage value is equal to the second initial voltage value, determining that the first candidate calibration voltage value, the second candidate calibration voltage value and the third candidate calibration voltage value are the bias voltage calibration results of an IQ-type electro-optical modulator.

Description

Technical Field

[0001] This invention relates to the field of communications, and more particularly to a calibration method for an optical communication device, and more specifically, to a bias voltage calibration method. Background Technology

[0002] In optical communication systems, IQ-type electro-optic modulators offer significant advantages: they support higher-order modulation formats, meeting the demands of high-speed coherent optical communication; simultaneously, their excellent spectral efficiency allows for the transmission of more data per wavelength, significantly increasing system capacity. Furthermore, in QKD (Quantum Key Distribution) systems, the introduction of IQ-type electro-optic modulators effectively mitigates mode effect problems. The principle of IQ-type electro-optic modulators is to independently modulate the amplitude and phase of an optical carrier using in-phase (I) and quadrature (Q) signals, thereby achieving higher-order modulation formats. IQ-type modulators are generally based on a dual-parallel Mach-Zehnder modulator structure, including a mother MZI composed of an I-channel sub-MZI (Mach-Zehnder Interferometer) and a Q-channel sub-MZI connected in parallel. The phase difference between the two optical waves is controlled by electrical signals, achieving arbitrary symbol mapping on the complex plane.

[0003] During initial commissioning or periodic maintenance, IQ-type electro-optic modulators require bias voltage calibration to reach their optimal operating point voltage. In the mainstream modulation format QPSK (Quadrature Phase Shift Keying), the I-path sub-MZI and Q-path sub-MZI need to be biased at the zero point, while the main MZI needs to be biased at the Q point. For QPSK modulation, existing bias voltage calibration techniques mainly utilize pilot signal methods and power monitoring methods. The pilot signal method superimposes an AC signal onto the I / Q path bias, monitors the AC component in the output optical signal, adjusts the DC bias, and performs calibration by detecting specific frequency components. This method is complex and unsuitable for silicon-based electro-optic modulators biased by thermo-optic effects. The conventional power monitoring method scans N voltage points across the full-wave voltage range for each bias path to calibrate the bias voltage, resulting in a time complexity of O(n log n). In other words, the time consumed in the calibration process is proportional to the cube of N, resulting in slow debugging speed. Although some studies have proposed new bias voltage calibration methods, reducing the time complexity of bias voltage calibration to... That is, the time consumed in the calibration process is proportional to the square of N. However, the calibration of IQ type electro-optic modulators still suffers from high computational complexity and excessively long calibration time. Summary of the Invention

[0004] In view of this, the present invention provides a bias voltage calibration method for IQ type electro-optic modulators.

[0005] In one aspect of the present invention, a bias voltage calibration method is provided, applied to an IQ-type electro-optic modulator. The IQ-type electro-optic modulator includes a main MZI composed of I-channel sub-MZIs and Q-channel sub-MZIs connected in parallel. The bias voltage calibration method includes: calibrating the bias voltage of the main MZI by setting the bias voltage of the I-channel sub-MZI to a first initial voltage value and the bias voltage of the Q-channel sub-MZI to a second initial voltage value, thereby determining a third candidate calibration voltage value for the main MZI; based on the third candidate calibration voltage value of the main MZI... Select calibration voltage values ​​and calibrate the bias voltages of the I-channel sub-MZI and the Q-channel sub-MZI respectively to obtain the first candidate calibration voltage value of the I-channel sub-MZI and the second candidate calibration voltage value of the Q-channel sub-MZI; and when the first candidate calibration voltage value is equal to the first initial voltage value and the second candidate calibration voltage value is equal to the second initial voltage value, determine the first candidate calibration voltage value, the second candidate calibration voltage value and the third candidate calibration voltage value as the bias voltage calibration result of the IQ type electro-optic modulator.

[0006] According to an embodiment of the present invention, when the bias voltage of the I-path sub-MZI is set to a first initial voltage value and the bias voltage of the Q-path sub-MZI is set to a second initial voltage value, the bias voltage calibration of the mother MZI is performed to obtain a local optimum value of the mother MZI bias voltage calibration. The local optimum value of the mother MZI bias voltage calibration is then substituted into the subsequent calibration process to obtain local optimum values ​​of the bias voltage calibration of the I-path sub-MZI and the Q-path sub-MZI, respectively. The final bias voltage calibration result is obtained by using a judgment condition. Compared with the prior art, which requires arranging and combining N bias voltage values ​​of the I-path sub-MZI, N bias voltage values ​​of the Q-path sub-MZI, and N bias voltage values ​​of the mother MZI to determine the optimal operating point, the bias voltage calibration method of the present invention can significantly reduce the time complexity of bias voltage calibration of the IQ type electro-optic modulator, thereby reducing the bias voltage calibration time of the IQ type electro-optic modulator.

[0007] The bias voltage calibration method according to embodiments of the present invention is suitable for quick manual debugging in the laboratory, and also for rapid debugging during the production or maintenance of ultra-large batch modulators. Attached Figure Description

[0008] The above and other objects, features and advantages of the present invention will become more apparent from the following description of embodiments of the invention with reference to the accompanying drawings, in which:

[0009] Figure 1 A schematic diagram of the structure of an IQ type electro-optic modulator to which the bias voltage calibration method of the present invention can be applied is shown;

[0010] Figure 2A flowchart of a bias voltage calibration method according to an embodiment of the present invention is shown;

[0011] Figure 3 A schematic diagram of the equipment connection of a calibration device for calibrating the bias voltage of an IQ type electro-optic modulator using the bias voltage calibration method of the present invention is shown.

[0012] Figure 4 A flowchart of a bias voltage calibration method according to another embodiment of the present invention is shown;

[0013] Figure 5 A simulation diagram of the phase difference obtained by the bias voltage calibration method according to an embodiment of the present invention is shown;

[0014] Figure 6 A schematic diagram of the iteration step frequency of the bias voltage calibration method according to an embodiment of the present invention is shown. Detailed Implementation

[0015] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the invention. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the invention for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0016] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0017] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0018] Figure 1 A schematic diagram of an IQ-type electro-optic modulator to which the bias voltage calibration method of the present invention can be applied is shown.

[0019] like Figure 1As shown, the IQ type electro-optic modulator includes an input waveguide 101, a mother MZI 102, an I-channel sub-MZI 103, a Q-channel sub-MZI 104, an I-channel RF electrode 105, a Q-channel RF electrode 106, an I-channel bias electrode 107, a Q-channel bias electrode 108, a mother bias electrode 109, and an output waveguide 110. The I-channel sub-MZI 103, the Q-channel sub-MZI 104, and the mother bias electrode 109 are optically connected through a specific optical waveguide to form the mother MZI 102; the I-channel sub-MZI 103 has an I-channel RF electrode 105 (which can be any traveling-wave electrode structure) and an I-channel bias electrode 107 fabricated on its optical path; the Q-channel sub-MZI 104 has a Q-channel RF electrode 106 (which can be any traveling-wave electrode structure) and a Q-channel bias electrode 108 fabricated on its optical path. The light source enters the IQ type electro-optic modulator structure from the light input terminal through the input waveguide 101. By applying different bias voltages to the I-path bias electrode 107, the Q-path bias electrode 108 and the mother bias electrode 109, different optical powers can be output from the light output terminal through the output waveguide 110.

[0020] Figure 2 A flowchart of a bias voltage calibration method according to an embodiment of the present invention is shown.

[0021] like Figure 2 As shown, the bias voltage calibration method includes operations S210 to S230.

[0022] In operation S210, when the bias voltage of the I-path sub-MZI is set to the first initial voltage value and the bias voltage of the Q-path sub-MZI is set to the second initial voltage value, the bias voltage calibration of the mother MZI is performed to determine the third candidate calibration voltage value of the mother MZI.

[0023] The bias voltage is a DC voltage applied to the I-channel sub-MZI, Q-channel sub-MZI, or main MZI. Its core purpose is to control the operating point of the modulator, ensuring it operates within the desired specific region. The calibration of the bias voltage involves applying appropriate bias voltage values ​​to the I-channel sub-MZI, Q-channel sub-MZI, and main MZI to compensate for manufacturing errors and environmental drift in the IQ-type electro-optic modulator, thus maintaining it at its optimal operating point.

[0024] The bias voltage can be applied through a DC bias electrode or through a thermal tuner.

[0025] For example, the optical waveguide of an IQ type electro-optic modulator usually has multiple DC bias electrode pins corresponding to MZI. The DC voltage source has a corresponding DC voltage output port that can apply a specific DC voltage value. By connecting the DC voltage source to the corresponding port of the IQ electro-optic modulator with a cable, the specific bias voltage values ​​of the I-channel sub-MZI, Q-channel sub-MZI, and mother MZI can be set.

[0026] The first initial voltage value and the second initial voltage value are the specific voltage values ​​output by a DC voltage source or other electronic device that can provide a stable DC voltage at the corresponding ports of the IQ type electro-optic modulator.

[0027] The first and second initial voltage values ​​can be any voltage values ​​between zero and twice the half-wave voltage. The half-wave voltage is the change in driving voltage required to change the output light intensity of the MZI from its maximum value (on-state) to its minimum value (off-state), or from its minimum value to its maximum value. The half-wave voltage is related to the specific characteristics of the IQ-type electro-optic modulator. For a specific modulator product, the half-wave voltage can be obtained from the product's datasheet.

[0028] For example, when the half-wave voltage is 3V, the first and second initial voltage values ​​can be any values ​​between 0 and 6V. The first initial voltage value can be set to 1V, and the second initial voltage value to 4V. The bias voltage calibration of the mother MZI can be obtained through the following steps:

[0029] During the bias voltage calibration process of the mother MZI, it is necessary to ensure that the first and second initial voltage values ​​remain constant. Then, multiple different specific voltage values ​​are applied to the DC bias electrode pins corresponding to the mother MZI through a DC voltage source. The output of the IQ type electro-optic modulator is connected to a photodetector or optical power meter. While adjusting the bias voltage value output by the DC voltage source to the mother MZI, the output optical power of the IQ type electro-optic modulator is recorded through a photodetector or optical power meter to obtain a graph showing the relationship between the bias voltage value and the output optical power value. Finally, the third candidate calibration voltage value can be determined based on the graph showing the relationship between the bias voltage value and the output optical power value.

[0030] In operation S220, based on the third candidate calibration voltage value of the mother MZI, the bias voltage of the I-path sub-MZI and the bias voltage of the Q-path sub-MZI are calibrated respectively to obtain the first candidate calibration voltage value of the I-path sub-MZI and the second candidate calibration voltage value of the Q-path sub-MZI.

[0031] To calibrate the bias voltage of the I-path sub-MZI and the Q-path sub-MZI, the bias voltage of the mother MZI needs to be fixed at the previously obtained third candidate calibration voltage value.

[0032] During the calibration of the bias voltage of the I-channel MZI, the bias voltage of the Q-channel MZI also needs to be fixed at a specific voltage value. Then, multiple different specific voltage values ​​can be applied to the DC bias electrode pins corresponding to the I-channel MZI through a DC voltage source. The output of the IQ-type electro-optic modulator is connected to a photodetector or optical power meter. While adjusting the bias voltage value output by the DC voltage source to the I-channel MZI, the output optical power of the IQ-type electro-optic modulator is recorded through the photodetector or optical power meter to obtain a graph showing the relationship between the bias voltage value and the output optical power value. Finally, the first candidate calibration voltage value can be determined based on the graph showing the relationship between the bias voltage value and the output optical power value.

[0033] During the calibration of the bias voltage of the Q-path MZI, the bias voltage of the I-path MZI needs to be fixed at a specific voltage value. Then, multiple different specific voltage values ​​can be applied to the DC bias electrode pins corresponding to the Q-path MZI using a DC voltage source. The output of the IQ-type electro-optic modulator is connected to a photodetector or optical power meter. While adjusting the bias voltage value output by the DC voltage source to the Q-path MZI, the output optical power of the IQ-type electro-optic modulator is recorded using a photodetector or optical power meter to obtain a graph showing the relationship between the bias voltage value and the output optical power value. Finally, the second candidate calibration voltage value can be determined based on the graph showing the relationship between the bias voltage value and the output optical power value.

[0034] In operation S230, if the first candidate calibration voltage value is equal to the first initial voltage value and the second candidate calibration voltage value is equal to the second initial voltage value, the first candidate calibration voltage value, the second candidate calibration voltage value, and the third candidate calibration voltage value are determined as the bias voltage calibration results of the IQ type electro-optic modulator.

[0035] During the bias voltage calibration process, the first initial voltage value, second initial voltage value, first candidate calibration voltage value, second candidate calibration voltage value, and third candidate calibration voltage value obtained in each calibration process need to be recorded and saved for bias voltage calibration result determination or for subsequent further bias voltage calibration work. For example, the first candidate calibration voltage value, first initial voltage value, second candidate calibration voltage value, second initial voltage value, and third candidate calibration voltage value can be stored in specialized computer software, and the voltage values ​​can be compared and the results determined by a computer program. If the first candidate calibration voltage value is not equal to the first initial voltage value, or the second candidate calibration voltage value is not equal to the second initial voltage value, an iterative operation can be performed, using the first candidate calibration voltage value as the updated first initial voltage value and the second candidate calibration voltage value as the updated second initial voltage value, to continue a new round of bias voltage calibration for the IQ type electro-optic modulator.

[0036] In embodiments of the present invention, it is necessary to calibrate the specific bias voltage values ​​required for each of the I-channel sub-MZI, Q-channel sub-MZI, and mother MZI in the IQ-type electro-optic modulator. The local optimum value of the mother MZI is the specific bias voltage value required to be set for the mother MZI to achieve the optimal operating point of the IQ-type electro-optic modulator, given that the bias voltages of the I-channel sub-MZI and Q-channel sub-MZI already have preset voltage values. Based on the same principle, both the I-channel sub-MZI and Q-channel MZI have local optima.

[0037] Through the embodiments of the present invention, the local optimum value of the bias voltage calibration of the mother MZI can be obtained. The local optimum value of the bias voltage calibration of the mother MZI can be substituted into the subsequent calibration process to obtain the local optimum value of the bias voltage calibration of the I-path sub-MZI and the local optimum value of the bias voltage calibration of the Q-path sub-MZI respectively. The final bias voltage calibration result is obtained by using the judgment condition, which can significantly reduce the bias voltage calibration time of the IQ type electro-optic modulator.

[0038] According to an embodiment of the present invention, when the bias voltage of the I-channel sub-MZI is set to a first initial voltage value and the bias voltage of the Q-channel sub-MZI is set to a second initial voltage value, the bias voltage calibration of the mother MZI is performed to determine a third candidate calibration voltage value for the mother MZI, including:

[0039] The bias voltage of the I-path sub-MZI is set as the first initial voltage value, and the bias voltage of the Q-path sub-MZI is set as the second initial voltage value. Multiple preset bias voltage values ​​are applied to the mother MZI to determine multiple third optical power output values ​​of the IQ type electro-optic modulator when the bias voltage of the mother MZI is each of the multiple preset bias voltage values.

[0040] Based on multiple third optical power output values, the third calibration optical power output value of the mother MZI is determined, and the third calibration voltage value corresponding to the third calibration optical power output value is determined.

[0041] Obtain the candidate calibration voltage value of the mother MZI determined in the previous mother MZI bias voltage calibration process to obtain the first historical calibration voltage value.

[0042] If the third calibration optical power output value is less than or equal to the optical power output value corresponding to the first historical calibration voltage value, the third calibration voltage value is determined as the third candidate calibration voltage value.

[0043] The preset bias voltage value is a number of different specific voltage values ​​applied to the DC bias electrode pin corresponding to the mother MZI by a DC voltage source.

[0044] According to embodiments of the present invention, the number of preset bias voltage values ​​can be any positive integer, for example, 1, 2, 5, 10, 20, or 100 preset bias voltage values ​​can be applied to the mother MZI. The specific values ​​of the multiple preset bias voltage values ​​can be any voltage value between zero and twice the half-wave voltage. For example, when the half-wave voltage is 5V and the number of preset bias voltage values ​​is 10, the preset bias voltage values ​​can be 1V, 2V, 3V, 4V, 5V, 6V, 7V, 8V, 9V, or 10V.

[0045] The method described above can be used to apply a first initial voltage value and a second initial voltage value to the I-path MZI and the Q-path MZI, while adjusting the bias voltage value output by the DC voltage source to the mother MZI, and recording the output optical power of the IQ-type electro-optic modulator through a photodetector or optical power meter, thereby obtaining multiple preset bias voltage values ​​and their corresponding multiple third optical power output values.

[0046] The third calibration optical power output value is selected from multiple third optical power output values ​​using a specific algorithm. For example, if there are 2n+1 third optical power output values, these 2n+1 third optical power output values ​​can be sorted by size, and the (n+1)th largest third optical power output value can be selected as the third calibration optical power output value, where n is any natural number.

[0047] The third calibration voltage value, corresponding to the third calibration optical power output value, refers to the bias voltage value applied to the mother MZI when the bias voltages of the I-channel and Q-channel MZIs are the first and second initial voltage values, and the output optical power of the IQ-type electro-optic modulator is the third calibration optical power output value. During the previous bias voltage calibration process, the third candidate calibration voltage value determined in the previous bias voltage calibration is obtained and used as the first historical calibration voltage value required for this bias voltage calibration. The relationship between the previous bias voltage calibration and this voltage calibration is that the first and second initial voltage values ​​of this bias voltage calibration are the first and second candidate calibration voltages determined after the previous bias voltage calibration.

[0048] Through the embodiments of the present invention, the local optimal value of the current mother MZI bias voltage calibration is compared with the local optimal value of the previous mother MZI bias voltage calibration. When the local optimal value of the current mother MZI bias voltage calibration is less than or equal to the local optimal value of the previous mother MZI bias voltage calibration, a more accurate local optimal value of the mother MZI bias voltage calibration can be obtained.

[0049] According to an embodiment of the present invention, the third calibration optical power output value of the mother MZI is determined based on multiple third optical power output values, including:

[0050] The average third optical power output value is obtained by averaging the maximum and minimum third optical power output values ​​among multiple third optical power output values.

[0051] The third optical power output value that is closest to the average third optical power output value is determined from multiple third optical power output values ​​to obtain the third calibration optical power output value.

[0052] For example, when multiple third optical power output values ​​are 1 mW, 3 mW, 5 mW, 7 mW, 13 mW, 15 mW, and 17 mW respectively, the maximum third optical power output value is 17 mW, the minimum third optical power output value is 1 mW, and the calculated average third optical power output value is 9 mW. Among the multiple third optical power output values, the third optical power output value closest to 9 mW is 7 mW. Therefore, 7 mW is selected as the third calibration optical power output value.

[0053] Through the embodiments of the present invention, the local optimal value of the current MZI bias voltage calibration process can be obtained.

[0054] According to an embodiment of the present invention, when the bias voltage of the I-channel sub-MZI is set to a first initial voltage value and the bias voltage of the Q-channel sub-MZI is set to a second initial voltage value, the bias voltage calibration of the mother MZI is performed to determine a third candidate calibration voltage value for the mother MZI, including:

[0055] The bias voltage of the I-path sub-MZI is set as the first initial voltage value, and the bias voltage of the Q-path sub-MZI is set as the second initial voltage value. Multiple preset bias voltage values ​​are applied to the mother MZI to determine multiple third optical power output values ​​of the IQ type electro-optic modulator when the bias voltage of the mother MZI is each of the multiple preset bias voltage values.

[0056] The average third optical power output value is obtained by averaging the maximum and minimum third optical power output values ​​among multiple third optical power output values.

[0057] The third optical power output value closest to the average third optical power output value is determined from multiple third optical power output values ​​to obtain the third calibration optical power output value, and the third calibration voltage value corresponding to the third calibration optical power output value is determined.

[0058] Obtain the candidate calibration voltage value of the mother MZI determined in the previous mother MZI bias voltage calibration process to obtain the first historical calibration voltage value.

[0059] If the third calibration optical power output value is greater than the optical power output value corresponding to the first historical calibration voltage value, the fourth calibration voltage value of the mother MZI is determined based on the multiple fourth optical power output values ​​of the IQ type electro-optic modulator determined in the previous mother MZI bias voltage calibration process.

[0060] The fourth calibration voltage value was determined to be the third candidate calibration voltage value.

[0061] The methods for determining the third calibration optical power output value and the first historical calibration voltage value are as described above and will not be repeated here.

[0062] In the previous calibration process of the mother MZI bias voltage, multiple preset bias voltage values ​​were applied to the mother MZI while the bias voltage values ​​of the I-path sub-MZI and Q-path sub-MZI were fixed, thereby obtaining multiple corresponding optical power output values ​​of the IQ type electro-optic modulator, which were then used as multiple fourth optical power output values.

[0063] A specific fourth optical power output value can be selected from multiple fourth optical power output values ​​using a specific algorithm, and then the fourth calibration voltage value corresponding to that fourth optical power output value can be determined.

[0064] A specific fourth optical power output value can be the largest fourth optical power output value among multiple fourth optical power output values, the smallest fourth optical power output value among multiple fourth optical power output values, or the second largest fourth optical power output value, etc.

[0065] The fourth calibration voltage value refers to the bias voltage value applied to the mother MZI when the bias voltages of the I-path sub-MZI and Q-path sub-MZI during the previous bias voltage calibration process are the first initial voltage value and the second initial voltage value, and the output optical power of the IQ type electro-optic modulator is the specific fourth optical power output value.

[0066] The relationship between the previous bias voltage calibration and the current voltage calibration is as follows: the first initial voltage value and the second initial voltage value of the current bias voltage calibration are the first candidate calibration voltage and the second candidate calibration voltage determined after the previous bias voltage calibration.

[0067] Through the embodiments of the present invention, the process optimal value of the current mother MZI bias voltage calibration is compared with the local optimal value of the previous mother MZI bias voltage calibration. When the process optimal value of the current mother MZI bias voltage calibration is greater than the local optimal value of the previous mother MZI bias voltage calibration, a more accurate local optimal value of the mother MZI bias voltage calibration can be obtained.

[0068] According to an embodiment of the present invention, the fourth calibration voltage value of the mother MZI is determined based on multiple fourth optical power output values ​​of the IQ-type electro-optic modulator determined in the previous mother MZI bias voltage calibration process, including:

[0069] The average fourth optical power output value is obtained by averaging the maximum and minimum fourth optical power output values ​​among multiple fourth optical power output values.

[0070] The fourth calibrated optical power output value is obtained by determining the fourth optical power output value that is second closest to the average fourth optical power output value from multiple fourth optical power output values.

[0071] Determine the fourth calibration voltage value corresponding to the fourth calibration optical power output value.

[0072] For example, when multiple fourth optical power output values ​​are 1 mW, 3 mW, 7 mW, 9 mW, 11 mW, and 13 mW respectively, the maximum fourth optical power output value is 13 mW, the minimum fourth optical power output value is 1 mW, and the calculated average fourth optical power output value is 7 mW. Among the multiple fourth optical power output values, the second closest to 7 mW is 9 mW. Therefore, 9 mW is selected as the fourth calibration optical power output value.

[0073] The fourth calibration voltage value, which corresponds to the fourth calibration optical power output value, refers to the bias voltage value applied to the mother MZI when the bias voltages of the I-channel sub-MZI and the Q-channel sub-MZI are the first initial voltage value and the second initial voltage value, and the output optical power of the IQ type electro-optic modulator is the fourth calibration optical power output value during the previous bias voltage calibration process.

[0074] Through the embodiments of the present invention, when the optimal value of the current mother MZI bias voltage calibration process is greater than the local optimal value of the previous mother MZI bias voltage calibration, the local optimal value of the optical power output value in the current mother MZI bias voltage calibration process can be obtained.

[0075] According to an embodiment of the present invention, based on the third candidate calibration voltage value of the mother MZI, the bias voltages of the I-path sub-MZI and the Q-path sub-MZI are calibrated respectively to obtain the first candidate calibration voltage value of the I-path sub-MZI and the second candidate calibration voltage value of the Q-path sub-MZI, including:

[0076] With the bias voltage of the main MZI set to the third candidate calibration voltage value and the bias voltage of the Q-path sub-MZI set to the second initial voltage value, the bias voltage calibration of the I-path sub-MZI is performed to determine the first candidate calibration voltage value of the I-path sub-MZI.

[0077] With the bias voltage of the main MZI set to the third candidate calibration voltage value and the bias voltage of the I-path sub-MZI set to the first candidate calibration voltage value, the bias voltage calibration of the Q-path sub-MZI is performed to determine the second candidate calibration voltage value of the Q-path sub-MZI.

[0078] A third candidate calibration voltage value and a second initial voltage value can be applied to the mother MZI and the Q-path sub-MZI respectively using a DC voltage source, and the voltage values ​​need to be kept constant during the calibration process. Then, multiple different specific voltage values ​​are applied to the DC bias electrode pins corresponding to the I-path sub-MZI using a DC voltage source, and the output of the IQ-type electro-optic modulator is connected to a photodetector or optical power meter. While adjusting the bias voltage value output by the DC voltage source to the I-path sub-MZI, the output optical power of the IQ-type electro-optic modulator is recorded using a photodetector or optical power meter, thereby obtaining a graph showing the relationship between the bias voltage value and the output optical power value. Finally, the first candidate calibration voltage value can be determined based on the graph showing the relationship between the bias voltage value and the output optical power value.

[0079] Subsequently, a third candidate calibration voltage value and a first candidate calibration voltage value are applied to the mother MZI and the I-path sub-MZI respectively using a DC voltage source, and the voltage values ​​need to be kept constant during the calibration process. Next, multiple different specific voltage values ​​are applied to the DC bias electrode pins corresponding to the Q-path sub-MZI using a DC voltage source, and the output of the IQ-type electro-optic modulator is connected to a photodetector or optical power meter. While adjusting the bias voltage value output by the DC voltage source to the Q-path sub-MZI, the output optical power of the IQ-type electro-optic modulator is recorded using a photodetector or optical power meter, thereby obtaining a graph showing the relationship between the bias voltage value and the output optical power value. Finally, the second candidate calibration voltage value can be determined based on the graph showing the relationship between the bias voltage value and the output optical power value.

[0080] Through the embodiments of the present invention, the local optimal value of the I-path sub-MZI bias voltage can be determined based on the local optimal value of the mother MZI bias voltage, and the local optimal value of the Q-path sub-MZI bias voltage can be determined based on the local optimal value of the mother MZI bias voltage and the local optimal value of the I-path sub-MZI bias voltage.

[0081] According to an embodiment of the present invention, based on the third candidate calibration voltage value of the mother MZI, the bias voltages of the I-path sub-MZI and the Q-path sub-MZI are calibrated respectively to obtain the first candidate calibration voltage value of the I-path sub-MZI and the second candidate calibration voltage value of the Q-path sub-MZI, including:

[0082] With the bias voltage of the main MZI set to the third candidate calibration voltage value and the bias voltage of the I-path sub-MZI set to the first initial voltage value, the bias voltage calibration of the Q-path sub-MZI is performed to determine the second candidate calibration voltage value of the Q-path sub-MZI.

[0083] With the bias voltage of the main MZI set to the third candidate calibration voltage value and the bias voltage of the Q-path sub-MZI set to the second candidate calibration voltage value, the bias voltage calibration of the I-path sub-MZI is performed to determine the first candidate calibration voltage value of the I-path sub-MZI.

[0084] A third candidate calibration voltage value and a first initial voltage value can be applied to the mother MZI and the I-path sub-MZI respectively using a DC voltage source, and the voltage values ​​need to be kept constant during the calibration process. Then, multiple different specific voltage values ​​are applied to the DC bias electrode pins corresponding to the Q-path sub-MZI using a DC voltage source, and the output of the IQ-type electro-optic modulator is connected to a photodetector or optical power meter. While adjusting the bias voltage value output by the DC voltage source to the Q-path sub-MZI, the output optical power of the IQ-type electro-optic modulator is recorded using a photodetector or optical power meter, thereby obtaining a graph showing the relationship between the bias voltage value and the output optical power value. Finally, a second candidate calibration voltage value can be determined based on the graph showing the relationship between the bias voltage value and the output optical power value.

[0085] Subsequently, a third candidate calibration voltage value and a second candidate calibration voltage value are applied to the mother MZI and the Q-path sub-MZI respectively using a DC voltage source, and the voltage values ​​need to be kept constant during the calibration process. Next, multiple different specific voltage values ​​are applied to the DC bias electrode pins corresponding to the I-path sub-MZI using a DC voltage source, and the output of the IQ-type electro-optic modulator is connected to a photodetector or optical power meter. While adjusting the bias voltage value output by the DC voltage source to the I-path sub-MZI, the output optical power of the IQ-type electro-optic modulator is recorded using a photodetector or optical power meter, thereby obtaining a graph showing the relationship between the bias voltage value and the output optical power value. Finally, the first candidate calibration voltage value can be determined based on the graph showing the relationship between the bias voltage value and the output optical power value.

[0086] Through the embodiments of the present invention, the local optimal value of the Q-path sub-MZI bias voltage can be determined based on the local optimal value of the mother MZI bias voltage, and the local optimal value of the I-path sub-MZI bias voltage can be determined based on the local optimal value of the mother MZI bias voltage and the local optimal value of the Q-path sub-MZI bias voltage.

[0087] According to an embodiment of the present invention, when the bias voltage of the mother MZI is set to the third candidate calibration voltage value and the bias voltage of the Q-path sub-MZI is set to the second initial voltage value, the bias voltage calibration of the I-path sub-MZI is performed to determine the first candidate calibration voltage value of the I-path sub-MZI, including:

[0088] The bias voltage of the mother MZI is set to the third candidate calibration voltage value, the bias voltage of the Q-path MZI is set to the second initial voltage value, and multiple preset bias voltage values ​​are applied to the I-path MZI to determine multiple first optical power output values ​​of the IQ type electro-optic modulator when the bias voltage of the I-path MZI is a multiple preset bias voltage value.

[0089] The minimum first optical power output value is determined from multiple first optical power output values ​​to obtain the first calibrated optical power output value.

[0090] Determine the first calibration voltage value corresponding to the first calibration optical power output value to obtain the first candidate calibration voltage value.

[0091] The method for determining multiple preset bias voltage values ​​of the I-path MZI and the method for applying the bias voltage are similar to the method for determining multiple preset bias voltage values ​​of the mother MZI mentioned above, and will not be described in detail here.

[0092] For example, when the multiple first optical power output values ​​are 1 mW, 3 mW, 7 mW, 9 mW, 11 mW, and 13 mW respectively, the smallest first optical power output value is 1 mW, so the first calibration optical power output value is determined to be 1 mW.

[0093] The first calibration voltage value corresponding to the first calibration optical power output value refers to the bias voltage value applied to the I-path MZI when the bias voltage of the mother MZI is the third candidate calibration voltage value, the bias voltage of the Q-path MZI is the second initial voltage value, and the output optical power of the IQ type electro-optic modulator is the first calibration optical power output value during the bias voltage calibration process.

[0094] The first candidate calibration voltage value is the first calibration voltage value corresponding to the first calibration optical power output value.

[0095] Through the embodiments of the present invention, the local optimum value of the sub-MZI bias voltage can be determined based on the local optimum value of the mother MZI bias voltage.

[0096] According to an embodiment of the present invention, when the bias voltage of the mother MZI is set to the third candidate calibration voltage value and the bias voltage of the I-path sub-MZI is set to the first candidate calibration voltage value, the bias voltage calibration of the Q-path sub-MZI is performed to determine the second candidate calibration voltage value of the Q-path sub-MZI, including:

[0097] The bias voltage of the mother MZI is set to the third candidate calibration voltage value, the bias voltage of the I-path sub-MZI is set to the first candidate calibration voltage value, and multiple preset bias voltage values ​​are applied to the Q-path sub-MZI to determine multiple second optical power output values ​​of the IQ type electro-optic modulator when the bias voltage of the Q-path sub-MZI is a multiple preset bias voltage value.

[0098] The minimum second optical power output value is determined from multiple second optical power output values ​​to obtain the second calibration optical power output value.

[0099] Determine the second calibration voltage value corresponding to the second calibration optical power output value to obtain the second candidate calibration voltage value.

[0100] The method for determining multiple preset bias voltage values ​​of the Q-path MZI and the method for applying the bias voltage are similar to the method for determining multiple preset bias voltage values ​​of the mother MZI mentioned above, and will not be described in detail here.

[0101] For example, when the multiple second optical power output values ​​are 2 mW, 4 mW, 6 mW, 9 mW, 11 mW, and 13 mW respectively, the smallest second optical power output value is 2 mW. Therefore, the second calibration optical power output value is determined to be 2 mW.

[0102] The second calibration voltage value corresponding to the second calibration optical power output value refers to the bias voltage value applied to the Q-path MZI when the bias voltage of the mother MZI is the third candidate calibration voltage value, the bias voltage of the I-path sub-MZI is the first initial voltage value, and the output optical power of the IQ type electro-optic modulator is the second calibration optical power output value during the bias voltage calibration process.

[0103] The second candidate calibration voltage value is the second calibration voltage value corresponding to the second calibration optical power output value.

[0104] Through the embodiments of the present invention, the local optimum value of the Q-path sub-MZI bias voltage can be determined based on the local optimum value of the mother MZI bias voltage.

[0105] According to an embodiment of the present invention, based on the third candidate calibration voltage value of the mother MZI, the bias voltages of the I-path sub-MZI and the Q-path sub-MZI are calibrated respectively to obtain the first candidate calibration voltage value of the I-path sub-MZI and the second candidate calibration voltage value of the Q-path sub-MZI, including:

[0106] The bias voltage of the mother MZI is set to the third candidate calibration voltage value, the bias voltage of the Q-path MZI is set to the second initial voltage value, and multiple preset bias voltage values ​​are applied to the I-path MZI to determine multiple first optical power output values ​​of the IQ type electro-optic modulator when the bias voltage of the I-path MZI is a multiple preset bias voltage value.

[0107] The minimum first optical power output value is determined from multiple first optical power output values ​​to obtain the first calibrated optical power output value.

[0108] Determine the first calibration voltage value corresponding to the first calibration optical power output value to obtain the first candidate calibration voltage value.

[0109] The bias voltage of the mother MZI is set to the third candidate calibration voltage value, the bias voltage of the I-path sub-MZI is set to the first candidate calibration voltage value, and multiple preset bias voltage values ​​are applied to the Q-path sub-MZI to determine multiple second optical power output values ​​of the IQ type electro-optic modulator when the bias voltage of the Q-path sub-MZI is a multiple preset bias voltage value.

[0110] The minimum second optical power output value is determined from multiple second optical power output values ​​to obtain the second calibration optical power output value.

[0111] Determine the second calibration voltage value corresponding to the second calibration optical power output value to obtain the second candidate calibration voltage value.

[0112] According to an embodiment of the present invention, based on the third candidate calibration voltage value of the mother MZI, the bias voltages of the I-path sub-MZI and the Q-path sub-MZI are calibrated respectively to obtain the first candidate calibration voltage value of the I-path sub-MZI and the second candidate calibration voltage value of the Q-path sub-MZI, including:

[0113] The bias voltage of the mother MZI is set to the third candidate calibration voltage value, the bias voltage of the I-path sub-MZI is set to the first initial voltage value, and multiple preset bias voltage values ​​are applied to the Q-path sub-MZI to determine multiple second optical power output values ​​of the IQ type electro-optic modulator when the bias voltage of the Q-path sub-MZI is each of the multiple preset bias voltage values.

[0114] The minimum second optical power output value is determined from multiple second optical power output values ​​to obtain the second calibration optical power output value.

[0115] Determine the second calibration voltage value corresponding to the second calibration optical power output value to obtain the second candidate calibration voltage value.

[0116] The bias voltage of the mother MZI is set to the third candidate calibration voltage value, the bias voltage of the Q-path MZI is set to the second candidate calibration voltage value, and multiple preset bias voltage values ​​are applied to the I-path MZI to determine multiple first optical power output values ​​of the IQ type electro-optic modulator when the bias voltage of the I-path MZI is a multiple preset bias voltage value.

[0117] The minimum first optical power output value is determined from multiple first optical power output values ​​to obtain the first calibrated optical power output value.

[0118] Determine the first calibration voltage value corresponding to the first calibration optical power output value to obtain the first candidate calibration voltage value.

[0119] Figure 3 A schematic diagram of the equipment connection is shown for a calibration device that can be used to calibrate the bias voltage of an IQ type electro-optic modulator using the bias voltage calibration method of the present invention.

[0120] like Figure 3 As shown, the light output from the polarization-maintaining output laser 301 enters the IQ type electro-optic modulator 302, and the multi-channel DC power supply 303 applies a bias voltage to the IQ type electro-optic modulator 302. The output light of the IQ type electro-optic modulator 302 enters the optical power meter 304.

[0121] Figure 4 A flowchart of a bias voltage calibration method according to another embodiment of the present invention is shown.

[0122] like Figure 4 As shown, the bias voltage calibration method according to another embodiment of the present invention includes operations S410 to S460.

[0123] In operation S410, the bias voltage of the I-channel MZI is set to the first initial voltage value, and the bias voltage of the Q-channel MZI is set to the second initial voltage value.

[0124] During operation of S420, the bias voltage of the mother MZI is calibrated to obtain the third candidate calibration voltage value.

[0125] In operation S430, based on the third candidate calibration voltage value of the mother MZI, the bias voltage of the I-path sub-MZI and the bias voltage of the Q-path sub-MZI are calibrated respectively to obtain the first candidate calibration voltage value of the I-path sub-MZI and the second candidate calibration voltage value of the Q-path sub-MZI.

[0126] In operation S440, it is determined whether the judgment condition that the first candidate calibration voltage value is equal to the first initial voltage value and the second candidate calibration voltage value is equal to the second initial voltage value is met.

[0127] If the judgment conditions are met, operation S450 is executed, and the first candidate calibration voltage value, the second candidate calibration voltage value, and the third candidate calibration voltage value are the bias voltage calibration results of the IQ type electro-optic modulator.

[0128] If the judgment condition is not met, operation S460 is executed, the first candidate calibration voltage value is used as the updated first initial voltage value, the second candidate calibration voltage value is used as the updated second initial voltage value, and the bias voltage calibration of the IQ type electro-optic modulator continues.

[0129] The detailed process of bias voltage calibration for the I-path sub-MZI, Q-path sub-MZI, and mother MZI is as described above and will not be repeated here. Through the embodiments of the present invention, the global optimal value of bias voltage calibration can be determined by iteratively calculating the local optimal values ​​of the bias voltage calibration for the I-path sub-MZI, Q-path sub-MZI, and mother MZI.

[0130] Figure 5 A simulation diagram of the phase difference obtained by the bias voltage calibration method according to an embodiment of the present invention is shown.

[0131] like Figure 5 As shown, the horizontal axis represents the number of iterations of the bias voltage calibration method, the vertical axis on the left represents the phase difference value corresponding to the solid line, and the vertical axis on the right represents the phase difference value corresponding to the dashed line.

[0132] This represents the phase difference between the two arms of the I-path MZI after the nth iteration. This represents the phase difference between the two arms of the Q-path MZI after the nth iteration. This represents the phase difference between the two arms of the mother MZI after the nth iteration. Figure 5 It includes nine simulation sub-graphs of the iterative process, each corresponding to a different random initial phase. For example, for Figure 5 Figure a in and The initial phase difference of the I-channel MZI is 2.35, and the initial phase difference of the Q-channel MZI is 5.97.

[0133] The solid lines marked with squares represent the correspondence between the number of iterations and the phase difference between the two arms of the I-path MZI, the solid lines marked with circles represent the correspondence between the number of iterations and the phase difference between the two arms of the Q-path MZI, and the solid lines marked with triangles represent the correspondence between the number of iterations and the phase difference between the two arms of the mother MZI.

[0134] After several iterations, the phase difference between the two arms of the I-path sub-MZI, the phase difference between the two arms of the Q-path sub-MZI, and the phase difference between the two arms of the mother MZI quickly converge to a fixed value. For example, in Figure 5 In Figure a, the phase difference between the two arms of the I-path MZI and the two arms of the Q-path MZI converge rapidly to around π in the third and subsequent iterations. The π / 2 coordinate precision on the left ordinate is insufficient for judging the convergence speed. To further determine the convergence speed, π is subtracted from the phase difference between the two arms of the I-path MZI, and the result is used as the ordinate of the dashed line marked with a square, corresponding to the right ordinate. For the same reason, the dashed line marked with a circle represents the relationship between the calculated phase difference between the two arms of the Q-path MZI minus π and the number of iterations; the dashed line marked with a triangle represents the relationship between the calculated phase difference between the two arms of the mother MZI minus π / 2 or 3π / 2 and the number of iterations; and the black dashed line represents the reference line for exponential decay.

[0135] by Figure 5 Taking Figure a as an example, the initial phase difference of the I-path sub-MZI is 2.35, and the initial phase difference of the Q-path sub-MZI is 5.97. After two iterations, the phase differences of both the I-path and Q-path sub-MZI converge to near π, at which point the phase difference of the mother MZI converges to near 0. In the third iteration, the phase differences of the I-path and Q-path sub-MZI are even closer to π, and the phase difference of the mother MZI converges to near π / 2, which is consistent with the phase difference values ​​of the three MZIs required for the optimal operating state of the modulator. Figure 5 Similar to diagram a in the text, Figure 5 Figure b in the middle Figure 5 Figure c in the middle Figure 5 d in the diagram Figure 5 The e-graph in the middle Figure 5 f-graph in Figure 5 g-graph in Figure 5 h-graph in Figure 5 The i-figures in the figure correspond to the relationship between the number of iterations and the phase difference value of each MZI after each bias voltage calibration, under different initial phase differences of the I-path MZI and the Q-path MZI.

[0136] Based on the trend of the dashed line corresponding to the right vertical axis, it can be shown that the phase difference between the I-path sub-MZI, the Q-path sub-MZI, and the mother MZI has a super-exponential decay convergence speed and can converge within an average of 3 iterations. That is, based on this method, the modulator can reach the optimal working state by calibrating the bias voltage three times on average.

[0137] Figure 6 A schematic diagram of the iteration step frequency of the bias voltage calibration method according to an embodiment of the present invention is shown.

[0138] During the bias voltage calibration process, multiple preset bias voltage values ​​need to be applied to a certain MZI to determine the multiple optical power output values ​​of the IQ type electro-optic modulator when the bias voltage is one of the multiple preset bias voltage values. This process is called voltage scanning, and the number of preset bias voltage values ​​is the number of voltage scanning points during the bias voltage calibration process. Figure 6 It includes 6 sub-plots. The difference between the different sub-plots lies in the number of voltage scan points during the bias voltage calibration process. Figure 6 In graph a, the number of voltage scan points is 10. Figure 6 In graph b, the number of voltage scan points is 50. Figure 6 In diagram c, the number of voltage scan points is 100. Figure 6 The voltage scan points in the d-graph are 200. Figure 6 In diagram e, the number of voltage scan points is 300. Figure 6 In the f-graph, the number of voltage scan points is 500. Each sub-graph is a statistical graph showing the frequency of the number of iterations required for each initial random bias point to reach convergence after simulation with 5000 initial random bias points. The horizontal axis represents the number of bias voltage calibration iterations required for each initial random bias point to reach convergence, and the vertical axis represents the number of sets with that number of iterations in the 5000 sets of data. In an embodiment of the present invention, if the difference between the phase difference of the MZI corresponding to the current calibration result and the phase difference of the MZI corresponding to the optimal operating point is less than or equal to 2π / N, the current calibration result can be taken as the final convergence result, where N is the number of voltage scan points. For example, in Figure 6In Figure a, for 5000 initial random bias points, more than 2000 initial random bias points converge after one iteration, more than 1500 initial random bias points converge after two iterations, and more than 500 initial random bias points converge after three iterations. It can be observed that for a certain number of scan points N, the frequency of iteration steps follows a Poisson distribution.

[0139] Table 1 shows the average number of iterations required to reach convergence at the preset initial random bias point under different voltage scan points.

[0140] Table 1: Average number of iterations corresponding to the number of voltage scan points

[0141]

[0142] As shown in Table 1, it can be found that the average number of iterations corresponding to the number of voltage scan points N is related to... Approximately proportional.

[0143] Figure 5 , Figure 6 Both Table 1 and Table 2 are for Figure 1 The simulation was performed using the single-arm bias structure shown. The same method applies when the bias in the sub-modulator or the master modulator is a push-pull structure.

[0144] The bias voltage calibration method according to an embodiment of the present invention calibrates the modulator bias point using only optical power monitoring, without requiring complex feedback circuits and radio frequency electrical signals, making the debugging equipment simple and the adjustment process quick and efficient.

[0145] The bias voltage calibration method according to embodiments of the present invention is applicable to quick manual debugging in the laboratory of IQ type modulators with all materials, all RF electrode structures, and all bias electrode structures, and is also applicable to rapid debugging during the production or maintenance of ultra-large batch modulators.

[0146] Those skilled in the art will understand that the features described in the various embodiments of the present invention can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in the present invention. In particular, the features described in the various embodiments of the present invention can be combined and / or combined in various ways without departing from the spirit and teachings of the present invention. All such combinations and / or combinations fall within the scope of the present invention.

[0147] The embodiments of the present invention have been described above. However, these embodiments are merely illustrative and not intended to limit the scope of the invention. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of the invention, and all such substitutions and modifications should fall within the scope of the invention.

Claims

1. A bias voltage calibration method, characterized in that, The method, applied to an IQ-type electro-optic modulator, wherein the IQ-type electro-optic modulator includes a mother MZI composed of I-channel sub-MZIs and Q-channel sub-MZIs connected in parallel, comprises: When the bias voltage of the I-channel sub-MZI is set to a first initial voltage value and the bias voltage of the Q-channel sub-MZI is set to a second initial voltage value, multiple preset bias voltage values ​​are applied to the mother MZI to determine multiple third optical power output values ​​of the IQ type electro-optic modulator when the bias voltage of the mother MZI is each of the multiple preset bias voltage values. Based on the plurality of third optical power output values, the third calibration optical power output value of the mother MZI is determined, and the third calibration voltage value corresponding to the third calibration optical power output value is determined; Obtain the candidate calibration voltage value of the mother MZI determined in the previous mother MZI bias voltage calibration process to obtain the first historical calibration voltage value; If the third calibration optical power output value is less than or equal to the optical power output value corresponding to the first historical calibration voltage value, the third calibration voltage value is determined to be the third candidate calibration voltage value. Based on the third candidate calibration voltage value of the mother MZI, the bias voltages of the I-path sub-MZI and the Q-path sub-MZI are calibrated respectively to obtain the first candidate calibration voltage value of the I-path sub-MZI and the second candidate calibration voltage value of the Q-path MZI; and When the first candidate calibration voltage value is equal to the first initial voltage value and the second candidate calibration voltage value is equal to the second initial voltage value, the first candidate calibration voltage value, the second candidate calibration voltage value, and the third candidate calibration voltage value are determined as the bias voltage calibration result of the IQ type electro-optic modulator.

2. The method according to claim 1, characterized in that, The method further includes: If the third calibration optical power output value is greater than the optical power output value corresponding to the first historical calibration voltage value, the fourth calibration voltage value of the mother MZI is determined based on the multiple fourth optical power output values ​​of the IQ type electro-optic modulator determined in the previous mother MZI bias voltage calibration process. The fourth calibration voltage value is determined to be the third candidate calibration voltage value.

3. The method according to claim 1, characterized in that, The process of determining the third calibration optical power output value of the mother MZI based on the plurality of third optical power output values ​​includes: The average third optical power output value is obtained by averaging the maximum and minimum third optical power output values ​​among the plurality of third optical power output values. The third calibrated optical power output value is obtained by determining the third optical power output value that is closest to the average third optical power output value from the plurality of third optical power output values.

4. The method according to claim 2, characterized in that, The determination of the fourth calibration voltage value of the mother MZI based on multiple fourth optical power output values ​​of the IQ-type electro-optic modulator determined in the previous mother MZI bias voltage calibration process includes: The average fourth optical power output value is obtained by averaging the maximum and minimum fourth optical power output values ​​among the plurality of fourth optical power output values. From the plurality of fourth optical power output values, a fourth optical power output value that is second closest to the average fourth optical power output value is determined to obtain a fourth calibrated optical power output value; Determine the fourth calibration voltage value corresponding to the fourth calibration optical power output value.

5. The method according to claim 1, characterized in that, The third candidate calibration voltage value based on the mother MZI is used to calibrate the bias voltage of the I-path sub-MZI and the bias voltage of the Q-path sub-MZI, respectively, to obtain the first candidate calibration voltage value of the I-path sub-MZI and the second candidate calibration voltage value of the Q-path MZI, including: With the bias voltage of the mother MZI set to the third candidate calibration voltage value and the bias voltage of the Q-path sub-MZI set to the second initial voltage value, the bias voltage calibration of the I-path sub-MZI is performed to determine the first candidate calibration voltage value of the I-path sub-MZI. With the bias voltage of the mother MZI set to the third candidate calibration voltage value and the bias voltage of the I-path sub-MZI set to the first candidate calibration voltage value, the bias voltage calibration of the Q-path sub-MZI is performed to determine the second candidate calibration voltage value of the Q-path sub-MZI.

6. The method according to claim 5, characterized in that, The step of setting the bias voltage of the mother MZI to the third candidate calibration voltage value and the bias voltage of the Q-path sub-MZI to the second initial voltage value, and then performing bias voltage calibration of the I-path sub-MZI to determine the first candidate calibration voltage value of the I-path sub-MZI, includes: The bias voltage of the mother MZI is set to the third candidate calibration voltage value, the bias voltage of the Q-path sub-MZI is set to the second initial voltage value, and multiple preset bias voltage values ​​are applied to the I-path sub-MZI to determine multiple first optical power output values ​​of the IQ type electro-optic modulator when the bias voltage of the I-path sub-MZI is one of the multiple preset bias voltage values. The smallest first optical power output value is determined from the plurality of first optical power output values ​​to obtain the first calibrated optical power output value; A first calibration voltage value corresponding to the first calibration optical power output value is determined to obtain the first candidate calibration voltage value.

7. The method according to claim 5, characterized in that, When the bias voltage of the mother MZI is set to the third candidate calibration voltage value and the bias voltage of the I-path sub-MZI is set to the first candidate calibration voltage value, the bias voltage calibration of the Q-path sub-MZI is performed to determine the second candidate calibration voltage value of the Q-path sub-MZI, including: The bias voltage of the mother MZI is set to the third candidate calibration voltage value, the bias voltage of the I-channel sub-MZI is set to the first candidate calibration voltage value, and multiple preset bias voltage values ​​are applied to the Q-channel sub-MZI to determine multiple second optical power output values ​​of the IQ type electro-optic modulator when the bias voltages of the Q-channel sub-MZI are the multiple preset bias voltage values ​​respectively. The minimum second optical power output value is determined from the plurality of second optical power output values ​​to obtain the second calibration optical power output value; Determine the second calibration voltage value corresponding to the second calibration optical power output value to obtain the second candidate calibration voltage value.

8. The method according to claim 1, characterized in that, The third candidate calibration voltage value based on the mother MZI is used to calibrate the bias voltage of the I-path sub-MZI and the bias voltage of the Q-path sub-MZI, respectively, to obtain the first candidate calibration voltage value of the I-path sub-MZI and the second candidate calibration voltage value of the Q-path MZI, including: With the bias voltage of the mother MZI set to the third candidate calibration voltage value and the bias voltage of the I-path sub-MZI set to the first initial voltage value, the bias voltage calibration of the Q-path sub-MZI is performed to determine the second candidate calibration voltage value of the Q-path sub-MZI. With the bias voltage of the mother MZI set to the third candidate calibration voltage value and the bias voltage of the Q-path sub-MZI set to the second candidate calibration voltage value, the bias voltage calibration of the I-path sub-MZI is performed to determine the first candidate calibration voltage value of the I-path sub-MZI.

9. The method according to claim 1, characterized in that, The method further includes: If the first candidate calibration voltage value is not equal to the first initial voltage value, or if the second candidate calibration voltage value is not equal to the second initial voltage value, the first candidate calibration voltage value is used as the updated first initial voltage value, and the second candidate calibration voltage value is used as the updated second initial voltage value, in order to calibrate the bias voltage of the IQ type electro-optic modulator.

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