Bias point detection method, control method, detection circuit, control circuit and radar

Abstract

The embodiments of the present invention provide a bias point detection method, a control method, a detection circuit, a control circuit and a radar, wherein the bias point detection method is suitable for detecting whether the MZ modulator works at a preset bias point, including: loading a square wave perturbation signal on the bias voltage of the MZ modulator; detecting the output light intensity at different levels of the square wave perturbation signal to determine whether the bias point of the MZ modulator is offset relative to the preset bias point. The implementation difficulty of the MZ modulator bias point detection circuit can be reduced by using the embodiments of this specification, thereby reducing the implementation cost and circuit power consumption.

Description

Technical Field

[0001] The embodiments of this specification relate to the technical field of electro-optical intensity modulation, and in particular to a bias point detection method, a control method, a detection circuit, a control circuit, and a radar. Background Art

[0002] Electro-optic modulation works by utilizing the electro-optic effect of certain crystal materials where the refractive index changes under the action of an external electric field.

[0003] The electro-optic modulator with Mach-Zehnder (MZ) interferometer structure has the advantages of high modulation rate, low propagation loss, low driving voltage and small wavelength dependence. It is widely used in dense wavelength division multiplexing, digital optical communication or electro-optical conversion modulation of analog carrier signals.

[0004] Reference Figure 1 The basic structural diagram of the MZ modulator shown in the figure, the MZ modulator 10 includes two waveguide arms 12, 13 and an input waveguide 11 and an output waveguide 14. The electro-optical effect principle of crystal materials is applied to adjust the electric field on the waveguide arms to produce an optical path difference between the two arms. The light transmitted by the two waveguide arms interferes when coupled to the output waveguide 14, and the phase modulation is converted into intensity modulation. Specifically, a bias voltage V can be applied to the DC bias end bias of the two waveguide arms 12. bias , the injected light Ein transmitted by the input waveguide 11 is divided into two parts with equal power, which are respectively coupled into the two waveguide arms 12 and 13, and then coupled to the output waveguide 14 to synthesize a beam of output light Eout. When the light propagates in the two waveguide arms, an electric field can be applied through a pair of electrodes at the DC bias end Bias to change the waveguide refractive index and perform phase modulation on the light. Since the light is subjected to different phase modulations when transmitted in the two waveguide arms, the intensity modulation of the injected light Ein is formed after interference, wherein the power of the output light Eout is determined by the bias voltage V of the DC bias end bias. bias In addition, a high-frequency modulation signal is loaded on the radio frequency signal end RF on the waveguide arm 13 to perform frequency modulation on the light.

[0005] The modulation voltage of a general MZ modulator can be expressed as: X(t) = Vdc + Vac(t), where Vdc is the DC bias voltage and Vac(t) is the high-frequency AC modulation signal applied by the RF terminal. When no AC modulation signal is applied (i.e., Vac(t) = 0), the output light intensity curve of the MZ modulator is as follows: Figure 2 As shown in the figure, this curve is called the output characteristic curve of the MZ modulator. The corresponding bias voltage is called Vπ. (n is an integer) when the output optical power is minimum, such as Figure 2The Null point is called the Minimum Transmission Point (MITP). The peak point of the output characteristic curve is called the maximum transmission point (MATP), where the output optical power is the maximum. correspond Figure 2 The Quad point of the output characteristic curve (which includes the Quad- point and the Quad+ point).

[0006] A certain bias voltage is applied to the MZ modulator to make it modulate the light intensity. This working state corresponds to a point on the output characteristic curve, which is called the working point or bias point. When the output characteristic curve remains unchanged, the bias point of the MZ modulator can be changed by changing the bias voltage.

[0007] However, the individual differences of MZ modulators are relatively large. Under the same conditions, the output characteristic curve position is different, and the bias voltage corresponding to the corresponding bias point (such as MITP) is also different. In addition, the MZ modulator is easily affected by external environmental factors such as temperature and mechanical stress during operation, causing the output characteristic to drift. Figure 2 Taking the MZ modulator working in MITP as an example, the initial output characteristic curve When the corresponding voltage is Vπ, a bias voltage Vπ is applied to the MZ modulator to make it work at MITP (the Null point of the output characteristic curve); when the output characteristic drifts, it can be regarded as the output characteristic curve shifting left / right relative to the horizontal axis, so that Vπ no longer corresponds to MITP, and the bias point of the MZ modulator shifts relative to MITP. Output characteristic drift will cause the modulator to work unstably and the output signal to degrade, thereby affecting the performance of the entire optical system, and even causing the entire optical system to fail to work properly. Therefore, it is necessary to detect and automatically control whether the bias point of the modulator is offset relative to the predetermined bias point.

[0008] Reference Figure 3 The bias point detection principle diagram of the MZ modulator is shown in FIG. Figure 3 It can be seen that the bias point of the MZ modulator can be detected by loading a 1 kHz low-frequency sinusoidal disturbance signal on the MZ modulator.

[0009] Reference Figure 4 The bias point control circuit of the MZ modulator shown in FIG. Figure 4 Sub-figure (a) in FIG. 4 shows a schematic diagram of the relationship between the bias point control circuit 40 and the MZ modulator. Figure 4Sub-figure (b) in FIG. 4 shows a specific structure of the bias point control circuit 40, which includes: a transimpedance amplifier (TIA), an analog-to-digital converter (ADC), a field programmable gate array chip (FPGA), a digital-to-analog converter (DAC) and an amplifier (AMP). Figure 3 and Figure 4 The sub-figures (a) and (b) in the figure illustrate the control principle: a DC bias voltage is loaded on the DC bias end of the MZ modulator to make it work at MITP, and a low-frequency sinusoidal disturbance signal ds with a frequency of 1KHz is introduced at the DC bias end to make the bias voltage of the MZ modulator fluctuate slightly with ds; the output light Eout is divided into two parts, one part is used as the signal light Eout1, and the other part is used as the detection light Eout2, which is input to the photodiode PD. The signal of the photodiode PD is sampled by TIA and ADC and sent to FPGA, which calculates the harmonic components of the detection light. When the bias point is between MITP and MATP, the first harmonic corresponding to the disturbance signal ds is suppressed, and the second harmonic amplitude is the maximum value; when the bias point is at the Quad point, the first harmonic amplitude is the maximum value and the second harmonic is suppressed. The offset of the bias point relative to MITP is judged by calculating the first harmonic component. After calculating the offset, the DC bias voltage is adjusted by adjusting the DAC and AMP until the bias point of the MZ modulator returns to MITP.

[0010] However, the bias point detection and control scheme of the above-mentioned MZ modulator requires expensive ADC and DAC devices. The ADC and DAC have many pins and complex packaging, and need to be implemented by FPGA chips through algorithms. Therefore, the above-mentioned method is costly and power-hungry. Summary of the invention

[0011] In view of this, one aspect of the embodiments of this specification provides a bias point detection method, a detection circuit and a radar, which can reduce the difficulty of implementing the bias point detection circuit of the MZ modulator, thereby reducing the implementation cost and circuit power consumption.

[0012] Another aspect of the embodiments of this specification provides a bias point control method, a control circuit and a radar, which can reduce the difficulty of implementing the bias point control circuit of the MZ modulator, thereby reducing the implementation cost and circuit power consumption.

[0013] First, an embodiment of this specification provides a bias point detection method, which is suitable for detecting whether an MZ modulator operates at a preset bias point. The method includes:

[0014] Loading a square wave perturbation signal on the bias voltage of the MZ modulator;

[0015] The output light intensity at different levels of the square wave perturbation signal is detected to determine whether the bias point of the MZ modulator is offset relative to the preset bias point.

[0016] Optionally, the square wave perturbation signal includes a first level and a second level;

[0017] The detecting the output light intensity of the square wave perturbation signal at different levels to determine whether the bias point of the MZ modulator is offset relative to a preset bias point includes:

[0018] When a first light intensity corresponding to the first level is not equal to a second light intensity corresponding to the second level, it is determined that the bias point of the MZ modulator is offset relative to the preset bias point.

[0019] The embodiment of this specification also provides a bias point control method, the method comprising:

[0020] Using the bias point detection method described in any of the above embodiments to perform detection;

[0021] When the bias point of the MZ modulator shifts, a compensation signal is provided to adjust the bias voltage of the MZ modulator.

[0022] Optionally, the preset bias point is a minimum transmission point;

[0023] The above-mentioned bias point detection method is used for detection, wherein the first level is higher than the second level;

[0024] When the bias point of the MZ modulator is offset, providing a compensation signal to adjust the bias voltage of the MZ modulator includes:

[0025] When the first light intensity is greater than the second light intensity, reducing the bias voltage of the MZ modulator;

[0026] When the first light intensity is less than the second light intensity, the bias voltage of the MZ modulator is increased.

[0027] Optionally, the preset bias point is a maximum transmission point;

[0028] The bias point detection method of the above embodiment is used for detection, wherein the first level is higher than the second level;

[0029] When the bias point of the MZ modulator is offset, providing a compensation signal to adjust the bias voltage of the MZ modulator includes:

[0030] When the first light intensity is greater than the second light intensity, increasing the bias voltage of the MZ modulator;

[0031] When the first light intensity is less than the second light intensity, the bias voltage of the MZ modulator is reduced.

[0032] The embodiment of the present specification further provides a bias point detection circuit, coupled to the MZ modulator, the MZ modulator being adapted to operate at a preset bias point, the detection circuit comprising:

[0033] A square wave perturbation module, coupled to the bias end of the MZ modulator, adapted to output a square wave perturbation signal to the bias end of the MZ modulator, so that the bias voltage of the MZ modulator fluctuates with the square wave perturbation signal;

[0034] The sampling module is coupled to the output end of the MZ modulator and is suitable for detecting the output light intensity of the square wave perturbation signal at different levels to determine whether the bias point of the MZ modulator is offset relative to the preset bias point.

[0035] Optionally, the sampling module includes:

[0036] A detection unit, adapted to detect the optical signal output by the MZ modulator and convert the optical signal into an electrical signal;

[0037] The sampling unit is coupled to the detection unit, and acquires the electrical signals corresponding to different levels of the square wave perturbation signal respectively, and outputs sampling signals.

[0038] Optionally, the detection unit includes:

[0039] A photodiode, adapted to convert the optical signal output by the MZ modulator into an electrical signal;

[0040] The transimpedance amplifier is suitable for amplifying the electrical signal.

[0041] Optionally, the sampling unit includes:

[0042] A first sampling capacitor, coupled between the detection unit and ground, adapted to sample the square wave perturbation signal at a first level to obtain a first sampling signal;

[0043] The second sampling capacitor is coupled between the detection unit and the ground, and is suitable for sampling the second level of the square wave perturbation signal to obtain a second sampling signal.

[0044] Optionally, the sampling unit further includes:

[0045] A first voltage follower, adapted to buffer the first sampling signal;

[0046] The second voltage follower is adapted to buffer the second sampling signal.

[0047] Optionally, the sampling module also includes: a switching unit, coupled to the detection unit, suitable for controlling the sampling module to sample the electrical signal output by the detection unit at the same frequency as the square wave perturbation module, and respectively obtaining a first sampling signal when the square wave perturbation signal is at a first level and a second sampling signal when the square wave perturbation signal is at a second level, and outputting the first sampling signal through the first output terminal and outputting the second sampling signal through the second output terminal.

[0048] Optionally, the detection circuit also includes: a control module, coupled to the square wave perturbation module and the switch unit respectively, suitable for outputting a square wave signal, a first part of the square wave signal is used to generate the square wave perturbation signal, and a second part of the square wave signal is used to generate a sampling control signal.

[0049] Optionally, the square wave perturbation module includes: a square wave signal amplifying unit, which amplifies the first part of the square wave signal to obtain the square wave perturbation signal.

[0050] Optionally, the square wave perturbation module further includes: a buffer unit, coupled between the output end of the control module and the square wave signal amplifying unit, suitable for buffering the first part of the square wave signal output by the control module.

[0051] The embodiment of this specification also provides a bias point control circuit, the control circuit comprising:

[0052] The bias point detection circuit described in any of the above embodiments comprises the square wave perturbation module and the sampling module;

[0053] The compensation module is coupled between the bias point detection circuit and the bias terminal of the MZ modulator, and is adapted to provide a compensation signal to adjust the bias voltage of the MZ modulator when the bias point of the MZ modulator is offset.

[0054] Optionally, the compensation module is adapted to output a compensation signal in a corresponding direction based on a magnitude relationship between sampling signals corresponding to different levels of the square wave perturbation signal, so as to adjust the bias voltage of the MZ modulator.

[0055] Optionally, the square wave perturbation signal includes a first level and a second level, wherein the first level is higher than the second level, and the preset bias point is a minimum transmission point;

[0056] The compensation module is adapted to reduce the bias voltage of the MZ modulator when a first light intensity corresponding to the first level is greater than a second light intensity corresponding to the second level; and to increase the bias voltage of the MZ modulator when the first light intensity is less than the second light intensity.

[0057] Optionally, the square wave perturbation signal includes a first level and a second level, wherein the first level is higher than the second level, and the preset bias point is a maximum transmission point;

[0058] The compensation module is adapted to increase the bias voltage of the MZ modulator when a first light intensity corresponding to the first level is greater than a second light intensity corresponding to the second level; and to reduce the bias voltage of the MZ modulator when the first light intensity is less than the second light intensity.

[0059] Optionally, the compensation module includes: an integration circuit unit, whose first input end is suitable for receiving the first sampling signal, whose second input end is suitable for receiving the second sampling signal, and whose output end outputs the integral of the difference between the first sampling signal and the second sampling signal over time to determine the compensation direction and compensation amount of the compensation signal.

[0060] Optionally, the sampling unit includes a first output terminal suitable for outputting a first sampling signal and a second output terminal suitable for outputting a second sampling signal; and the integration circuit unit includes:

[0061] An operational amplifier comprising the first input terminal, the second input terminal and an output terminal;

[0062] an energy storage component, coupled between the first input terminal and the output terminal of the operational amplifier;

[0063] A first resistor, coupled between a first output terminal of the sampling unit and a first input terminal of the operational amplifier;

[0064] The second resistor is coupled between the second output terminal of the sampling unit and the second input terminal of the operational amplifier.

[0065] Optionally, the integration circuit unit further includes:

[0066] A third resistor is coupled between the output terminal of the operational amplifier and ground;

[0067] An enable switch is coupled between the control module and the enable terminal of the operational amplifier, and is suitable for enabling the operational amplifier to work in response to an enable signal output by the control module, wherein the enable signal is generated when the control module determines that only the operational amplifier in the bias point control circuit is not in a working state.

[0068] Optionally, the preset bias point is a minimum transmission point, the first input terminal of the operational amplifier is a negative input terminal, and the second input terminal of the operational amplifier is a positive input terminal.

[0069] Optionally, the preset bias point is a maximum transmission point, the first input terminal of the operational amplifier is a positive input terminal, and the second input terminal of the operational amplifier is a negative input terminal.

[0070] The embodiment of this specification also provides a radar, the radar comprising:

[0071] A laser, suitable for generating continuous laser light with stable intensity and frequency as the injection light;

[0072] An MZ modulator operates at a preset bias point to modulate the intensity of the injected light, and is adapted to perform frequency modulation on the injected light based on a modulation signal to generate output light;

[0073] An optical splitter, coupled to the MZ modulator, for dividing the output light into a signal light and a detection light;

[0074] The bias point detection circuit described in any of the aforementioned embodiments is coupled to the MZ modulator and the optical splitter, and is adapted to detect whether the MZ modulator operates at a preset bias point based on the detection light.

[0075] The embodiment of this specification also provides another radar, the radar comprising:

[0076] A laser, suitable for generating continuous laser light with stable intensity and frequency as the injection light;

[0077] An MZ modulator operates at a preset bias point to modulate the intensity of the injected light, and is adapted to perform frequency modulation on the injected light based on a modulation signal to generate output light;

[0078] An optical splitter, coupled to the MZ modulator, for dividing the output light into a signal light and a detection light;

[0079] The bias point control circuit described in any of the foregoing embodiments is coupled to the spectrometer and the MZ modulator, and is suitable for detecting whether the bias point of the MZ modulator is offset based on the detection light, and providing a compensation signal to adjust the bias voltage of the MZ modulator when the bias point of the MZ modulator is offset.

[0080] By adopting the bias point detection method in the embodiment of this specification, by loading a square wave perturbation signal on the bias voltage of the MZ modulator and detecting the output light intensity at different levels of the square wave perturbation signal, it is possible to determine whether the bias point of the MZ modulator is offset relative to the preset bias point. Since the disturbance loaded on the bias voltage of the MZ modulator is a square wave perturbation signal, the signal waveform is simple relative to a sine wave signal or a signal of other waveforms. During the entire bias point detection process, it is only necessary to detect the output light intensity at different levels of the square wave perturbation signal, without the need for algorithm coordination, to determine whether the bias point of the MZ bias device is offset relative to the preset bias point, thereby reducing the difficulty of implementing the MZ modulator bias point detection method, and thus reducing the implementation cost.

[0081] By adopting the bias point control method in the embodiment of this specification, on the one hand, in the bias point detection process, since the square wave perturbation signal is loaded on the bias voltage of the MZ modulator, the signal waveform is simple compared to the sine wave signal or other waveform signals. In the entire bias point detection process, it is only necessary to detect the output light intensity at different levels of the square wave perturbation signal, without the need for algorithm coordination, to determine whether the bias point of the MZ bias device is offset relative to the preset bias point, thereby reducing the difficulty of implementing the MZ modulator bias point detection process; on the other hand, when the bias point of the MZ modulator is detected to be offset, a corresponding compensation signal is directly provided to adjust the bias voltage of the MZ modulator. Therefore, by adopting the above control method, the MZ modulator can be operated at the preset bias point, and the entire process does not require any algorithm coordination, thereby reducing the difficulty of implementing the MZ modulator bias point control method, and further reducing the implementation cost.

[0082] By adopting the bias point detection circuit in the embodiment of this specification, the square wave perturbation module outputs a square wave perturbation signal to the bias end of the MZ modulator, and the sampling module samples the output light intensity of the square wave perturbation signal at different levels. By detecting the output light intensity, it is possible to determine whether the bias point of the MZ modulator is offset relative to the preset bias end, and the entire detection circuit does not need to adopt expensive devices such as ADC and DAC. Therefore, the difficulty of implementing the bias point detection circuit of the MZ modulator can be reduced, thereby reducing the circuit power consumption and implementation cost.

[0083] Furthermore, a first voltage follower and a second voltage follower are provided in the sampling unit. The first voltage follower can buffer the first sampling signal, and the second voltage follower can buffer the second sampling signal, thereby improving the stability of the sampling signal.

[0084] Furthermore, the sampling module also includes a switching unit, which can be coupled to the detection unit to control the sampling module to sample the electrical signal output by the detection unit at the same frequency as the square wave perturbation module, and respectively obtain a first sampling signal when the square wave perturbation signal is at a first level and a second sampling signal when the square wave perturbation signal is at a second level, thereby synchronously obtaining the output light intensity change when interfered by the square wave perturbation signal at a minimum sampling frequency, thereby further reducing the power consumption of the entire detection circuit.

[0085] Furthermore, the bias point detection circuit also includes a control module, which can output a square wave signal, and the detection module is coupled to the square wave perturbation module and the switch unit respectively. On the one hand, the first part of the square wave signal in the square wave signal is used to generate the square wave perturbation signal; on the other hand, the second part of the square wave signal in the square wave signal is used to generate a sampling control signal. Since the square wave perturbation signal has the same frequency as the sampling control signal, the sampling module can use the same frequency as the square wave perturbation module to sample the electrical signal output by the detection unit, and synchronously obtain the accurate influence of the square wave perturbation signal on the bias voltage, thereby ensuring the sampling accuracy with the minimum sampling frequency.

[0086] Using the bias point control circuit in the embodiment of this specification, on the one hand, the bias point detection circuit can detect whether the bias point of the MZ modulator is offset according to the output light intensity at different levels of the square wave perturbation signal collected by the sampling module, that is, by detecting the magnitude of the output light intensity, it can be determined whether the bias point of the MZ modulator is offset relative to the preset bias point; on the other hand, when it is determined that the bias point of the MZ modulator is offset, the compensation module provides a corresponding compensation signal to adjust the bias voltage of the MZ modulator so that the MZ modulator works at the preset bias point. It can be seen from the above that the entire bias point control circuit does not need to use expensive devices such as ADC and DAC, so it can reduce the difficulty of implementing the MZ modulator bias point control circuit, and thus reduce the circuit power consumption and implementation cost.

[0087] Furthermore, the compensation module includes an integration circuit unit, whose first input end is suitable for receiving the first sampling signal, whose second input end is suitable for receiving the second sampling signal, and whose output end outputs the integral of the difference between the first sampling signal and the second sampling signal over time to determine the compensation direction of the compensation signal. The circuit is simple to implement and can ensure control accuracy.

[0088] Further, the integration circuit unit includes an operational amplifier, a third resistor and an enable switch. On the one hand, since the third resistor is coupled between the output terminal of the operational amplifier and the ground, when the operational amplifier is in a non-working state, the third resistor can pull down the output terminal voltage of the operational amplifier to a potential of 0V; on the other hand, since the enable switch is coupled between the control module and the enable terminal of the operational amplifier, and the enable signal is generated when the control module determines that only the operational amplifier in the bias point control circuit is not in a working state, the controller can generate the enable signal after all devices other than the operational amplifier in the bias point control circuit are running, trigger the enable switch to enable the operational amplifier to start working, and enable the MZ modulator to work at a bias point where the bias voltage is closest to 0V, thereby avoiding the bias voltage corresponding to the bias point exceeding the working voltage range of the operational amplifier as the temperature drifts, causing the bias point control circuit to fail, thereby improving the reliability of the bias point control circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0089] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0090] Figure 1 A basic structural diagram of an MZ modulator is shown;

[0091] Figure 2 A schematic diagram of an output light intensity curve of an MZ modulator is shown;

[0092] Figure 3 A schematic diagram of the working point detection principle of an MZ modulator is shown;

[0093] Figure 4 A connection relationship between an MZ modulator control circuit and an MZ modulator and a schematic diagram of their specific structure are shown;

[0094] Figure 5 A flow chart of a bias point detection method in an embodiment of this specification is shown;

[0095] Figure 6 A flow chart of a bias point control method in an embodiment of this specification is shown;

[0096] FIG. 7A to FIG. 7C A schematic diagram showing the principle of a method for detecting a bias point of an MZ modulator in an embodiment of this specification is shown;

[0097] FIG. 8A to FIG. 8C A schematic diagram showing another MZ modulator bias point detection method and control method in an embodiment of this specification is shown;

[0098] Fig. 9 A schematic diagram of the structure of a bias point detection circuit in an embodiment of this specification is shown;

[0099] Fig.10 A specific structural schematic diagram of a bias point detection circuit in a specific application in an embodiment of this specification is shown;

[0100] Fig.11A and Fig. 11B A sampling signal timing diagram of a sampling module in an embodiment of this specification is shown;

[0101] Fig.12 A schematic diagram of the structure of a bias point control circuit in an embodiment of this specification is shown;

[0102] Fig.13 A schematic diagram of an output characteristic curve of an MZ modulator in an embodiment of this specification is shown;

[0103] Fig.14 A schematic diagram of the structure of a radar in an embodiment of this specification is shown;

[0104] Fig.15 A schematic diagram of the structure of another radar in an embodiment of this specification is shown. DETAILED DESCRIPTION

[0105] As described in the background technology, the current detection and control scheme of the bias point of the MZ modulator requires expensive devices such as ADC and DAC. The ADC and DAC have many pins, complex packaging, and need to be implemented by FPGA through algorithm. Therefore, this method is costly and power-hungry.

[0106] In the specific implementation, continue to refer to Figure 1 , assuming that the angular frequency of the MZ modulator injected light Ein is ω0, and the angular frequency of the high-frequency AC modulation signal loaded on the RF end is ω m After modulation, the output light Eout contains not only the angular frequency ω0 component of the incident light Ein, but also ω0±ω m ,ω0±2ω m ,ω0±3ω m ...and other optical frequency components, generating multi-order optical sidebands. Among them, the expressions of the odd-order and even-order optical sideband intensities are:

[0107] 2n+1 order:

[0108] 2n order:

[0109] In the above two equations, E0 is the injected light intensity, J is the Bessel function, V m cos(ω m t) is the modulation signal, Indicates the modulation system.

[0110] From the above two equations, we can know that the intensity of each order of optical sideband is determined by two factors: modulation signal and DC bias. Without changing the modulation signal, the intensity of each order of sideband can be changed by adjusting the bias voltage. Figure 2 It is known that in When P 2n Get the maximum value, corresponding to Figure 2 The peak point in the MZ modulator is the peak point in the MATP. At this time, the odd-order sidebands are suppressed and the even-order sidebands are at their maximum intensity. When P 2n+1 Get the minimum value, corresponding to Figure 2 The Null point in , that is, the MZ modulator works in MITP, at this time, the odd-order sideband intensity is the largest, and the even-order sideband is suppressed.

[0111] In the application of frequency modulated continuous wave (FMCW) radar, the DC bias point of the MZ modulator is at MITP, the carrier is suppressed, and the output light has only odd harmonics, which is the bias point required by the radar.

[0112] In other applications, depending on the requirements for the intensity of each order of optical sidebands, it may be necessary to operate the MZ modulator at different bias points, such as MATP or Quad-, Quad+.

[0113] As described in the background technology section, the MZ modulator is easily affected by the external environment during operation, causing the output characteristic curve to shift. The position (phase) of the bias point corresponding to the initially applied bias voltage on the output characteristic curve changes, and the offset of the bias point will cause the entire modulator to work unstable and the output signal to degrade, which will in turn affect the performance of the entire optical system and even cause the entire optical system to fail to work properly.

[0114] To this end, based on the above-mentioned relationship characteristics between the output light intensity and the bias voltage, the embodiments of this specification provide corresponding bias point detection schemes and control schemes. The bias point detection scheme in the embodiments of this specification and the control scheme based on the bias point detection scheme are described in detail below.

[0115] First, the embodiments of this specification provide a bias point detection method suitable for detecting whether an MZ modulator operates at a preset bias point. Specifically, a square wave perturbation signal can be loaded on the bias voltage of the MZ modulator, and the output light intensity at different levels of the square wave perturbation signal can be detected to determine whether the bias point of the MZ modulator is offset relative to the preset bias point.

[0116] Since the disturbance loaded on the bias voltage of the MZ modulator is a square wave perturbation signal, the waveform of the square wave perturbation signal is simple compared to a sine wave signal or a signal of other waveforms. During the entire bias point detection process, it is only necessary to detect the output light intensity at different levels of the square wave perturbation signal, and no algorithm is required to determine whether the bias point of the MZ bias device is offset relative to the preset bias point. Therefore, the difficulty of implementing the MZ modulator bias point detection method can be reduced, thereby reducing the implementation cost.

[0117] In order to enable those skilled in the art to better understand the principles and advantages of the bias point detection method of the embodiments of this specification, a detailed description is given below through specific embodiments with reference to the accompanying drawings.

[0118] Reference Figure 5 The flowchart of a bias point detection method in the embodiment of this specification is shown. In some embodiments of this specification, the following steps can be used to determine whether the MZ modulator is working at a preset bias point:

[0119] S10, applying a square wave perturbation signal to the bias voltage of the MZ modulator.

[0120] S11, detecting the output light intensity of the square wave perturbation signal at different levels to determine whether the bias point of the MZ modulator is offset relative to a preset bias point.

[0121] A DC bias voltage is loaded on the MZ modulator, and a square wave perturbation signal is loaded on the DC bias voltage. Since the square wave perturbation signal has different levels, the bias voltage of the MZ intensity modulator will fluctuate as the level of the square wave perturbation signal changes. Different levels of the square wave perturbation signal correspond to different bias voltages. By detecting the output light intensities corresponding to different levels and judging whether the detection results corresponding to the corresponding levels are equal, it can be determined whether the bias point of the MZ modulator is offset relative to the preset bias point. The bias point here refers to the bias point corresponding to the DC bias voltage.

[0122] From the above, it can be seen that since the disturbance loaded on the bias voltage of the MZ modulator is a square wave perturbation signal, the signal waveform is simple compared to a sine wave signal or a signal of other waveforms. During the entire bias point detection process, it is only necessary to detect the output light intensity at different levels of the square wave perturbation signal. Without the need for complex algorithms, it is possible to detect whether the bias point of the MZ bias modulator is offset relative to the preset point.

[0123] In a specific implementation, the square wave perturbation signal may include a first level and a second level. When the square wave perturbation signal is loaded onto the bias voltage of the MZ modulator, by detecting the magnitude of the first light intensity E1 corresponding to the first level and the second light intensity E2 corresponding to the second level, it can be determined whether the bias point of the MZ modulator is offset relative to the preset bias point.

[0124] Specifically, when the first light intensity E1 corresponding to the first level is not equal to the second light intensity E2 corresponding to the second level, it is determined that the bias point of the MZ modulator is offset relative to the preset bias point; and when the first light intensity E1 corresponding to the first level is equal to the second light intensity E2 corresponding to the second level, it is determined that the bias point of the MZ modulator is not offset relative to the preset bias point.

[0125] When it is detected that the bias point of the MZ modulator is offset relative to the preset bias point, in order to stabilize the working state of the MZ modulator, corresponding operations need to be performed to adjust the bias voltage of the MZ modulator so that the MZ modulator works at the preset bias point. Therefore, the embodiments of this specification also provide a corresponding bias point control method.

[0126] Reference Figure 6 In some embodiments of the present specification, a bias point control method is shown. Specifically, the bias voltage of the MZ modulator can be adjusted according to the following steps:

[0127] S20, applying a square wave perturbation signal to the bias voltage of the MZ modulator.

[0128] S21, detecting the output light intensity of the square wave perturbation signal at different levels to determine whether the bias point of the MZ modulator is offset relative to a preset bias point.

[0129] For the description of steps S20 and S21 , reference may be made to the detailed description of the bias point detection method in the aforementioned embodiment, which will not be repeated here.

[0130] S22, when the bias point of the MZ modulator shifts, providing a compensation signal to adjust the bias voltage of the MZ modulator.

[0131] As mentioned above, if the square wave perturbation signal may include a first level and a second level. Through step S21, when it is detected that the first light intensity corresponding to the first level in the square wave perturbation signal and the second light intensity corresponding to the second level are different, it can be determined that the bias point of the MZ modulator is offset. Further, according to the magnitude of the first level and the second level and the magnitude of the light intensity corresponding to the level, a corresponding compensation signal can be directly provided to increase or decrease the magnitude of the bias voltage of the MZ modulator, so that the MZ modulator operates at the preset bias point.

[0132] In some specific embodiments, the preset bias point may be MITP. For the convenience of description, assuming that the first level may be higher than the second level, a corresponding control method may be adopted according to the detection results of the first light intensity E1 corresponding to the first level and the second light intensity E2 corresponding to the second level to adjust the bias voltage of the MZ modulator. Specifically, when the first light intensity E1 is greater than the second light intensity E2, the bias voltage of the MZ modulator may be reduced; when the first light intensity E1 is less than the second light intensity E2, the bias voltage of the MZ modulator may be increased.

[0133] In some other specific embodiments, the preset bias point may be MATP. For the convenience of description, it is still assumed that the first level may be higher than the second level. At this time, a corresponding control method may be adopted according to the detection results of the first light intensity E1 corresponding to the first level and the second light intensity E2 corresponding to the second level to adjust the bias voltage of the MZ modulator. Specifically, the opposite adjustment process is adopted when the preset bias point is MITP, that is, when the first light intensity E1 is greater than the second light intensity E2, the bias voltage of the MZ modulator may be increased; when the first light intensity E1 is less than the second light intensity E2, the bias voltage of the MZ modulator may be reduced.

[0134] It can be seen from the above control process that, on the one hand, in the bias point detection process, since the square wave perturbation signal is loaded on the bias voltage of the MZ modulator, the signal waveform is simple compared to the sine wave signal or other waveform signals. In the entire bias point detection process, it is only necessary to detect the output light intensity corresponding to the different levels of the square wave perturbation signal, without the need for algorithm coordination, to determine whether the bias point of the MZ bias device is offset relative to the preset bias point, thereby reducing the difficulty of implementing the MZ modulator bias point detection method; on the other hand, when the bias point of the MZ modulator is detected to be offset, a corresponding compensation signal is directly provided to adjust the bias voltage of the MZ modulator. Therefore, by adopting the above bias point control method, the MZ modulator can be realized to work at the preset bias point, and the entire bias voltage adjustment process does not require the coordination of the algorithm, thereby reducing the difficulty of implementing the MZ modulator bias point control method, and thus reducing the implementation cost.

[0135] The following are respectively FIG. 7A to FIG. 7C as well as FIG. 8A to FIG. 8C , describes in detail how the embodiments of this specification detect the bias point of the MZ modulator and describes the corresponding control method.

[0136] In the embodiments of the present specification, a preset bias point of the MZ modulator is selected according to actual needs, a corresponding bias voltage is loaded at the bias end of the MZ modulator, and a square wave perturbation signal ds is loaded on the MZ modulator bias voltage, wherein the square wave perturbation signal ds includes a first level and a second level. Assuming that the first level is higher than the second level, by detecting a first light intensity E1 corresponding to the first level and a second light intensity E2 corresponding to the second level of the square wave perturbation signal ds, the actual offset direction of the MZ modulator bias point relative to the preset bias point can be determined, thereby determining different control strategies.

[0137] In a specific implementation, the frequency of the square wave perturbation signal may differ from the frequency of the modulation signal by several orders of magnitude, for example, when a high frequency modulation signal is loaded at the RF end, a low frequency square wave is loaded on the bias voltage. In some optional examples, the frequency of the square wave perturbation signal may be 100 Hz to 100 KHz.

[0138] First, a specific example of an MZ modulator operating in a MITP scenario is used for illustration. Specifically, a DC bias voltage V0 is applied to the DC bias end of the MZ modulator, and a low-frequency square wave (for example, a frequency of 1 KHz is used as an example) is applied to the DC bias voltage V0 as the square wave perturbation signal ds, and the amplitude of the square wave perturbation signal is represented by Vs, then the bias voltage of the MZ modulator fluctuates between V0+Vs and V0-Vs.

[0139] Reference FIG. 7A to FIG. 7CThe schematic diagram of the principle of a method for detecting and controlling a bias point of an MZ modulator in an embodiment of the present specification is shown in FIG. bias represents the bias voltage, the vertical axis E represents the output light intensity, the first level corresponding to the low-frequency perturbation signal ds is represented by 1, and the bias voltage is V0+Vs at this time; the second level is represented by 0, and the bias voltage is V0-Vs at this time. It can be understood that the 1 and 0 here do not represent the actual potential at the first level and the second level, but only represent a relative potential difference.

[0140] like Fig. 7A As shown, the bias point P0 of the MZ modulator when the bias voltage is V0 is MITP, and when the bias voltage fluctuates with V0 as the center and Vs as the amplitude, the bias points corresponding to the first level 1 and the second level 0 are symmetrical with respect to MITP on the output characteristic curve, and the output light intensities corresponding to the two bias points are the same. Therefore, when the first light intensity E1 corresponding to the first level 1 detected is the same as the second light intensity E2 corresponding to the second level 0, it can be determined that the MZ modulator is working at MITP at this time, corresponding to the output light intensity curve L1a, and the bias voltage of the MZ modulator does not need to be adjusted.

[0141] like Figure 7B As shown in FIG. 1 , when the output characteristic curve of the MZ modulator shifts to the left, as shown in curve L1b, the initial bias point P0 of the modulator at the bias voltage V0 deviates from MITP, and V0 is greater than the bias voltage corresponding to MITP. When the bias voltage fluctuates with V0 as the center and Vs as the amplitude, the output light intensity of the bias point corresponding to the first level 1 is higher than the output light intensity of the bias point corresponding to the second level 0. Therefore, when the first light intensity E1 corresponding to the first level 1 detected is greater than the second light intensity E2 corresponding to the second level 0, the reference Figure 7B It can be seen that the current bias point of the MZ modulator is shifted to the right relative to MITP on the output characteristic curve. At this time, the bias voltage of the MZ modulator can be reduced, as shown by arrow Lf1.

[0142] Reference Figure 7C It can be seen that when the output characteristic curve of the MZ modulator shifts to the right, as shown in the curve L1c, the initial bias point P0 of the modulator at the bias voltage V0 deviates from MITP, and at this time V0 is less than the bias voltage corresponding to MITP. When the bias voltage fluctuates with V0 as the center and Vs as the amplitude, the output light intensity of the bias point corresponding to the first level 1 is lower than the output light intensity of the bias point corresponding to the second level 0. Therefore, when the first light intensity E1 corresponding to the first level 1 detected is lower than the second light intensity E2 corresponding to the second level 0, refer to Figure 7CIt can be seen that the current bias point of the MZ modulator is shifted to the left relative to MITP on the output characteristic curve. At this time, the bias voltage of the MZ modulator should be increased, as shown by arrow Rg1.

[0143] Next, a specific example of the MZ modulator working in the MATP scenario is used for explanation. Specifically, a DC bias voltage V0 is applied to the DC bias point of the MZ modulator, and a low-frequency square wave (for example, the frequency can be 1KHz) is applied to the DC bias voltage V0 as the square wave perturbation signal ds, and the amplitude of the square wave perturbation signal is represented by Vs, then the bias voltage of the MZ modulator fluctuates between V0+Vs and V0-Vs.

[0144] Reference FIG. 8A to FIG. 8C FIG. 1 is a schematic diagram showing another MZ modulator bias point detection method and control method in an embodiment of the present specification, wherein the horizontal axis V bias represents the bias voltage, the vertical axis E represents the output light intensity, the first level corresponding to the low-frequency perturbation signal ds is represented by 1, and the bias voltage is V0+Vs at this time; the second level is represented by 0, and the bias voltage is V0-Vs at this time. It can be understood that the 1 and 0 here do not represent the actual potential at the first level and the second level, but only represent a relative potential difference.

[0145] like Fig. 8A As shown, the bias point P1 of the MZ modulator when the bias voltage is V0 is MATP, and when the bias voltage fluctuates with V0 as the center and Vs as the amplitude, the bias points corresponding to the first level 1 and the second level 0 are symmetrical relative to MATP on the output characteristic curve, and the output light intensities corresponding to the two bias points are the same. Therefore, when the first light intensity E1 corresponding to the first level 1 detected is the same as the second light intensity E2 corresponding to the second level 0, it can be determined that the MZ modulator is working at MATP at this time, corresponding to the output light intensity curve L2a, and there is no need to adjust the bias voltage of the MZ modulator.

[0146] like Figure 8B As shown in FIG. 1 , when the output characteristic curve of the MZ modulator shifts to the left, as shown in curve L2b, the initial bias point P1 of the modulator at the bias voltage V0 deviates from MATP, and at this time V0 is greater than the bias voltage corresponding to MATP. When the bias voltage fluctuates with V0 as the center and Vs as the amplitude, the output light intensity of the bias point corresponding to the first level 1 is higher than the output light intensity of the bias point corresponding to the second level 0. Therefore, when it is detected that the first light intensity E1 corresponding to the first level 1 is greater than the second light intensity E2 corresponding to the second level 0, refer to Figure 8B It can be seen that the current bias point of the MZ modulator is shifted to the right relative to MATP on the output characteristic curve. At this time, the bias voltage of the MZ modulator can be increased, as shown by arrow Rg2.

[0147] Reference Figure 8C It can be seen that when the output characteristic curve of the MZ modulator shifts to the right, as shown in the curve L2c, the initial bias point P1 of the modulator at the bias voltage V0 deviates from MATP, and at this time V0 is less than the bias voltage corresponding to MATP. When the bias voltage fluctuates with V0 as the center and Vs as the amplitude, the output light intensity of the bias point corresponding to the first level 1 is lower than the output light intensity of the bias point corresponding to the second level 0. Therefore, when the first light intensity E1 corresponding to the first level 1 detected is lower than the second light intensity E2 corresponding to the second level 0, refer to Figure 8C It can be seen that the current bias point of the MZ modulator is shifted to the left relative to MATP on the output characteristic curve. At this time, the bias voltage of the MZ modulator should be reduced, as shown by arrow Lf2.

[0148] The embodiments of this specification also provide a bias point detection circuit corresponding to the above bias point detection method, and a bias point control circuit corresponding to the above bias point control method. The following is a detailed description through specific circuits with reference to the accompanying drawings.

[0149] First, the bias point detection circuit of the embodiment of this specification is described in detail below through specific embodiments with reference to the accompanying drawings.

[0150] Fig. 9 1 shows a schematic diagram of the structure of a bias point detection circuit. In some embodiments of this specification, Fig. 9 As shown, the bias point detection circuit 90 is coupled to the MZ modulator 9A, wherein the MZ modulator 9A is suitable for operating at a preset bias point, and the bias point detection circuit 90 may specifically include: a square wave perturbation module U1 and a sampling module U2, wherein:

[0151] The square wave perturbation module U1 is coupled to the bias end of the MZ modulator 9A, and is suitable for outputting a square wave perturbation signal to the bias end of the MZ modulator 9A, so that the bias voltage of the MZ modulator 9A fluctuates with the square wave perturbation signal;

[0152] The sampling module U2 is coupled to the output end of the MZ modulator 9A, and is suitable for detecting the output light intensity of the square wave perturbation signal at different levels to determine whether the bias point of the MZ modulator 9A is offset relative to the preset bias point.

[0153] To facilitate understanding and implementation by those skilled in the art, the following reference is made to Fig. 9 , the detection principle of the bias point detection circuit 90 is introduced:

[0154] When the MZ modulator 9A is working, the square wave perturbation module U1 outputs a square wave perturbation signal to the bias end of the MZ modulator 9A. Under the action of the square wave perturbation signal, the bias voltage at the bias end of the MZ modulator 9A shows an up and down fluctuation trend. Correspondingly, the output light intensity of the MZ modulator 9A is affected by the bias voltage, and the output light intensity of the output end of the MZ modulator 9A will also fluctuate accordingly.

[0155] Therefore, the sampling module U2 can sample the output light intensity of the square wave perturbation signal at different levels. For example, the square wave perturbation signal has a first level and a second level, then the sampling module U2 can detect the first light intensity E1 corresponding to the first level, and the second light intensity E2 corresponding to the second level. Combined with the correlation between the above-mentioned bias point and the size relationship between the first light intensity E1 and the second light intensity E2, according to the size relationship between the first light intensity E1 and the second light intensity E2, it can be determined whether the bias point of the MZ modulator 9A is offset relative to the preset bias point.

[0156] It can be seen from the above that by adopting the above-mentioned bias point detection circuit, during the entire detection process, it is only necessary to detect the output light intensity at different levels of the square wave perturbation signal to determine whether the bias point of the MZ modulator 9A is offset relative to the preset bias point. The entire circuit does not need to use expensive devices such as ADC and DAC. Therefore, it can reduce the difficulty of implementing the bias point detection circuit of the MZ modulator 9A, thereby reducing the circuit power consumption and implementation cost.

[0157] In order to enable those skilled in the art to better understand and implement, some implementable examples of each module in the bias point detection circuit of this specification are shown below.

[0158] Continue to refer to Fig. 9 In some embodiments of this specification, Fig. 9 As shown, the sampling module U2 may specifically include a detection unit U21 and a sampling unit U22, wherein:

[0159] The detection unit U21 is adapted to detect the optical signal output by the MZ modulator 9A and convert the optical signal into an electrical signal;

[0160] The sampling unit U22 can be coupled to the detection unit U21 to respectively obtain the electrical signals corresponding to different levels of the square wave perturbation signal and output a sampling signal S.

[0161] Using the sampling module U2 in the above embodiment, the detection unit U21 detects the optical signal output by the MZ modulator 9A and converts the detected optical signal into an electrical signal. For example, the optical signal can be converted into a current signal or a voltage signal and output to the sampling unit U22 coupled thereto.

[0162] The sampling unit U22 can collect electrical signals corresponding to different levels of the square wave perturbation signal, generate corresponding sampling signals S and output them.

[0163] The sampling signal S can be used to indicate whether the bias point of the MZ modulator 9A is offset relative to the preset bias point.

[0164] As mentioned above, the square wave perturbation signal loaded to the bias end of the MZ modulator 9A has different levels. The following is an exemplary description using the square wave perturbation signal ds including a first level and a second level as an example, and it is assumed that the first level is greater than the second level. In order to obtain the output light intensity at different levels of the square wave perturbation signal ds, the sampling module U2 may also include a switch unit U23, which may be coupled to the detection unit U21, and is suitable for controlling the sampling module U2 to sample the electrical signal output by the detection unit U21 at the same frequency as the square wave perturbation module U1, and respectively obtain the first sampling signal S when the square wave perturbation signal is at the first level 1. C1 and the second sampling signal S when the square wave perturbation signal is at the second level 0 C2 , and the first sampling signal S C1 And the second sampling signal S C2 Output through the output terminal.

[0165] In a specific implementation, in order to realize that the sampling module U2 uses the same frequency as the square wave perturbation module U1 to sample the electrical signal output by the detection unit U21, and synchronously obtain the accurate influence of the square wave perturbation signal on the bias voltage, continue to refer to Fig. 9 The bias point detection circuit 90 may further include a control module U3, which may be coupled to the square wave perturbation module U1 and the switch unit U23 respectively, and is suitable for outputting a square wave signal, wherein the first part of the square wave signal is used to generate the square wave perturbation signal, and the second part of the square wave signal is used to generate a sampling control signal.

[0166] In some embodiments of the present specification, the control module U3 can be implemented by a processing chip such as a central processing unit (CPU), FPGA, MCU, etc., or by an application specific integrated circuit (ASIC) or one or more integrated circuits configured to implement the embodiments of the present invention.

[0167] In a specific implementation, in order to ensure the stability of the output of the MZ modulator 9A and improve the accuracy of the entire system, the amplitudes of the first level and the second level of the square wave perturbation signal are much smaller than the amplitude of the bias voltage at the bias end of the MZ modulator 9A. As a specific example, the level amplitude of the square wave perturbation signal can be 1% of the bias voltage of the MZ modulator 9A.

[0168] In addition, regarding the selection of the frequency of the square wave perturbation signal, when the frequency of the sampling signal S is the same as the frequency of the square wave perturbation signal, on the one hand, if the sampling frequency is high, the feedback of the sampling signal and the corresponding adjustment of the bias voltage to the preset bias point are relatively fast; on the other hand, if the sampling frequency is too high, the bandwidth of the circuit needs to be increased so that the response frequency of the circuit is higher than the sampling frequency, which will increase the difficulty of circuit design. Therefore, in the specific application process, the above two factors can be taken into consideration to select a suitable frequency value.

[0169] Continue to refer to Fig. 9 In some embodiments of the present specification, the square wave perturbation module U1 may include a square wave signal amplifying unit U11. If the square wave signal amplifying unit U11 is coupled to the control module, the first part of the square wave signal may be amplified to obtain the square wave perturbation signal ds.

[0170] In a specific implementation, the square wave perturbation module U1 may further include a buffer unit U12, which may be coupled between the output end of the control module U3 and the square wave signal amplification unit U11, and is suitable for buffering the first part of the square wave signal output by the control module U3. By providing the buffer unit U12 in the square wave perturbation module U1, impedance matching may be achieved to avoid energy loss during the transmission of the first part of the square wave signal.

[0171] In order to enable those skilled in the art to better understand and implement, a detailed example is given below through a structural schematic diagram of a bias point detection circuit in a specific scenario.

[0172] Reference Fig.10 As shown in the structural diagram of the bias point detection circuit, the bias point detection circuit 100 can be coupled to the MZ modulator 10A.

[0173] Similar to the above-mentioned embodiment, the bias point detection circuit 100 may also include a square wave perturbation module U1 , a sampling module U2 , and optionally a control module U3 .

[0174] The following reference Fig.10 The optional application examples of each module are described separately.

[0175] First, in a specific implementation, the sampling module U2 may include a detection unit U21, a sampling unit U22 and a switch unit U23.

[0176] like Fig.10 As shown, as a specific example, the detection unit U21 may include a photodiode PD and a transimpedance amplifier TIA, wherein:

[0177] The photodiode PD is adapted to convert the optical signal output by the MZ modulator 10A into an electrical signal;

[0178] The transimpedance amplifier TIA is suitable for amplifying the electrical signal.

[0179] In a specific implementation, the optical signal output by the MZ modulator 10A is transmitted through an optical splitter ( Fig.10 The optical signal (not shown) is split into two parts, one part of which can be used as the detection light Eout1, and the photodiode PD converts the optical signal serving as the detection light Eout1 into an electrical signal. For example, the optical signal can be converted into a current signal and output to a transimpedance amplifier TIA coupled thereto, and the transimpedance amplifier TIA converts the current signal into a voltage signal and performs low-noise amplification processing with a preset intensity to obtain a corresponding amplified signal.

[0180] When the photodiode PD works in the linear region, the amplitude of its output electrical signal is proportional to the intensity of the light signal. Therefore, the amplitude of the electrical signal converted by the PD from the light signal can be sampled, and the light intensity can be represented by the amplitude of the electrical signal.

[0181] In some embodiments of the present specification, the sampling unit U22 may include: a first sampling unit C1 and a second sampling capacitor C2, wherein:

[0182] The first sampling capacitor C1 is coupled between the detection unit U21 and the ground, and is suitable for sampling at the first level of the square wave perturbation signal to obtain a first sampling signal S C1 ;

[0183] The second sampling capacitor C2 is coupled between the detection unit U21 and the ground, and is suitable for sampling at the second level of the square wave perturbation signal to obtain a second sampling signal S C2 .

[0184] In a specific implementation, in order to ensure the stability of the sampling signal, in practical applications, the sampling unit U22 may further include a first voltage follower VF1 and a second voltage follower VF2, wherein the first voltage follower VF1 may be coupled to the first sampling capacitor C1, and the second voltage follower VF2 may be coupled to the second sampling capacitor C2, wherein: the first voltage follower VF1 is suitable for converting the first sampling signal S C1The second voltage follower VF2 is adapted to buffer the second sampling signal S C2 Buffering.

[0185] In some embodiments of this specification, the switch unit U23 can be implemented by a single-pole double-throw switch, such as Fig.10 As shown in the figure, the single-pole double-throw switch in the switch unit U23 includes an input end (i.e., a moving end), a first output end S1 and a second output end S2. The switch unit U23 can select different conduction paths based on the sampling control signal SEL generated by the control module U3, so that the sampling module U2 collects sampling signals S at different levels.

[0186] Reference Fig.11A and Fig. 11B The sampling signal timing diagram of the sampling module in the embodiment of the present specification is shown, wherein the first part of the square wave signal in the square wave signal output by the control module U3 generates a square wave perturbation signal ds, the frequency of the sampling control signal SEL generated by the second part of the square wave signal is the same as the frequency of the square wave perturbation signal ds, and the low level of the sampling control signal SEL corresponds to the high level of the square wave perturbation signal ds.

[0187] In the specific implementation, refer to Fig.11A and Fig. 11B Combined with Fig.10 When the sampling control signal SEL is at a high level, the input end of the switch in the switch unit U23 is closed to the second output end S2 based on the sampling control signal SEL, that is, the second output branch is turned on, and accordingly, the square wave perturbation signal ds is at a second level (corresponding to a low level), and the transimpedance amplifier TIA in the detection unit U21 outputs an electrical signal corresponding to the corresponding output light intensity signal. The second sampling capacitor C2 in the sampling module U2 can sample the electrical signal dts output by the transimpedance amplifier TIA, and sample to obtain a second sampling signal S where the square wave perturbation signal ds is at a second level. C2 Next, the sampling control signal SEL is changed to a low level, and the second sampling signal S C2 The input end of the switch in the switch unit U23 remains unchanged, and the input end of the switch in the switch unit U23 is closed with the first output end S1 based on the sampling control signal SEL, that is, the first output branch is turned on, and accordingly, the square wave perturbation signal ds is at the first level (corresponding to the high level), and the first sampling capacitor C1 in the sampling module U2 can sample the electrical signal output by the transimpedance amplifier TIA, and sample to obtain the first sampling signal S when the square wave perturbation signal ds is at the first level. C1 . Continue to refer to Fig.10The switch unit U23 switches on the first output branch and the second output branch alternately based on the selection signal SEL, and samples the electrical signal output by the TIA at the corresponding level of the square wave perturbation signal ds by the corresponding sampling capacitor, so as to obtain the first sampling signal S C1 and the second sampling signal S C2 The first sampling signal S C1 and the second sampling signal S C2 Together, they form a sampling signal S where the square wave perturbation signal ds is located at different levels.

[0188] When the bias point of the MZ modulator is not shifted (ie, it works at the MITP point or the MATP point), Fig.11A As shown, a square wave perturbation signal ds is applied to the bias end of the MZ modulator. If the discharge of the capacitor is not considered, no matter whether the square wave perturbation signal ds is in the first level state or the second level state, the output light intensity of the MZ modulator remains unchanged, that is, E1=E2. Therefore, at this time, the electrical signal dts output by the detection unit U21 is a straight line. Correspondingly, the first sampling signal S C1 and the second sampling signal S C2 , the two have the same amplitude and remain unchanged, and they are also a straight line.

[0189] If the bias point of the MZ modulator is offset relative to MITP or MATP, then E1≠E2. Accordingly, the amplitudes of the electric signal dts at different levels of the square wave perturbation signal ds are not equal. The first sampling signal S C1 and the second sampling signal S C2 The magnitudes are not equal either.

[0190] Reference Fig. 11B In the sampling period from t0 to t1, the amplitude of the first level and the second level of the electric signal dts output by the detection unit U21 corresponding to the square wave perturbation signal ds are not equal. Specifically, Fig. 11B As shown in the figure, the amplitude of the electric signal dts at the first level of the square wave perturbation signal ds is lower than the amplitude of the electric signal dts at the second level of the square wave perturbation signal ds. C1 Corresponding to the amplitude of the electric signal dts when the square wave perturbation signal ds is at the first level, the second sampling signal S C2 The amplitude of the electric signal dts corresponding to the square wave perturbation signal ds being the second level is given by Fig. 11B It can be seen that at this time S C1 <S C2 , indicating that E1<E2. Figure 7CThe description of the MZ modulator should be increased at this time to make its bias voltage close to MITP. The increase in bias voltage can reduce the difference between E1 and E2, which is reflected in the electrical signal. Fig. 11B As shown, the signal amplitude of the electric signal dts output by the detection unit U21 and the corresponding second sampling signal S are detected during the period t1 to t2. C2 The amplitude decreases; starting from time t2, the detection unit U21 outputs the amplitude of the dts signal corresponding to the first level of the square wave perturbation signal ds and the corresponding first sampling signal S C1 The amplitude of the first sampling signal S C1 With the second sampling signal S C2 The signal amplitude difference is reduced. However, due to the first sampling signal S C1 and the second sampling signal S C2 The amplitudes of are still not equal, and the bias voltage of the MZ modulator should be further increased to make its bias voltage continue to approach MITP. Fig. 11B As shown, the bias voltage of the MZ modulator is continuously increased, and the first sampling signal S detected in each signal cycle is C1 With the second sampling signal S C2 The signal amplitude difference gradually decreases until the first sampling signal S C1 and the second sampling signal S C2 The amplitude difference is equal, that is, S C1 =S C2 When , the bias point of the MZ modulator returns to MITP and the bias voltage is no longer adjusted.

[0191] If E1>E2, the electrical signal dts should be Fig. 11B The curve shown is inverted, and accordingly, the first sampling signal S C1 and the second sampling signal S C2 The upper and lower positions are exchanged accordingly, which will not be explained here.

[0192] Using the sampling module of the above embodiment, during the whole sampling process, the switch unit U23 switches to another output end of the switch (for example, switches from the second output end S2 of the switch unit U23 to the first output end S1) as the sampling control signal SEL changes, and another output path (for example, the transimpedance amplifier TIA to the first output end out1) is turned on. The signal sampling value (for example, the second sampling signal S C2) remains unchanged, after the switch unit switches on the current output path (transimpedance amplifier TIA to the second output terminal out2) again, the signal sampling value obtained by sampling the current sampling branch changes accordingly with the signal amplitude of the electrical signal dts output by the detection unit U21, and if the signal amplitude of the electrical signal dts output by the detection unit U21 does not change, the signal sampling value obtained by sampling continues to remain unchanged.

[0193] It should be noted that the embodiments of this specification do not limit the switch conduction order, as long as the sampling signals at different levels can be obtained. In other embodiments, the input end of the switch and the first output end S1 may be closed first, and the input end of the switch and the second output end S2 may be closed later.

[0194] Continue to refer to Fig.10 In some embodiments of the present specification, the square wave perturbation module U1 may include a square wave signal amplifying unit U11, and optionally, the square wave perturbation module U1 may also include a buffering unit U12.

[0195] As a specific example, the square wave signal amplifying unit U11 may include an operational amplifier OA1, and resistors R10 and R20 coupled to the operational amplifier OA1, wherein:

[0196] A first end of the resistor R10 is coupled to the inverting input terminal of the operational amplifier OA1, and a second end of the resistor R10 is coupled to the output terminal of the operational amplifier OA1;

[0197] The non-inverting input terminal of the operational amplifier OA1 is coupled to the ground, the inverting input terminal thereof is coupled to the control module U3 through the resistor R20 , and the output terminal thereof is coupled to the MZ modulator 10A.

[0198] The buffer unit U12 may be coupled between the output end of the control module U3 and the square wave signal amplifying unit U11 , and is suitable for buffering the first part of the square wave signal output by the control module U3 .

[0199] The following combination Fig.10 and Fig.11A , Fig. 11B , the detection process and detection principle of the bias point detection circuit in the embodiment of this specification are described in detail:

[0200] When the MZ modulator 10A is working, in order to detect whether the bias voltage of the MZ modulator 9A is offset relative to the preset bias point, first, the control module U3 can output a square wave signal, wherein the first part of the square wave signal in the square wave signal is used for the square wave perturbation module U1 to generate a square wave perturbation signal, and the second part of the square wave signal in the square wave signal is used to generate a sampling control signal SEL, wherein the square wave perturbation signal can have a first level and a second level, and the first level is higher than the second level. Since the frequency of the square wave perturbation signal is the same as the frequency of the sampling control signal SEL, the sampling control signal SEL can control the on-off between the input terminal and the first output terminal S1 and the second output terminal S2 in the switch unit U23, so that the sampling module U2 uses the same frequency as the square wave perturbation module U1 to sample the electrical signal output by the detection unit U21 to obtain sampling signals at different levels of the square wave perturbation signal.

[0201] After the first part of the square wave signal in the square wave signal is buffered by the buffer unit U12, the perturbation signal is amplified by the square wave signal amplifying unit U11 and output to the bias end of the MZ modulator 10A as a square wave perturbation signal, wherein the amplification factor of the square wave signal amplifying unit U11 is: -R10 / R20, so the amplification factor of the square wave signal can be determined according to the actual application scenario, and resistors R10 and R20 with different resistance values ​​can be selected to output square wave perturbation signals with different voltage amplitudes.

[0202] Under the influence of the square wave perturbation signal, the injected light Ein is modulated by the MZ modulator 10A, and the output optical signal is split by the spectrometer, wherein a part of the optical signal Eout1 is detected by the photodiode PD, and the detected optical signal is converted into an electrical signal. The photodiode PD can convert the detected light intensity into a corresponding current signal, and then the transimpedance amplifier TIA converts the current signal into a voltage signal and amplifies it.

[0203] Under the control of the sampling control signal SEL, the switch unit U23 selects the input end of the conductive switch and the first output end S1 or the input end of the conductive switch and the second output end S2, thereby turning on the corresponding sampling branch, so that the first sampling capacitor C1 and the second sampling capacitor C2 respectively sample the electrical signal output by the transimpedance amplifier TIA at the same frequency as the square wave perturbation signal, and obtains and outputs a corresponding sampling signal.

[0204] For example, under the control of the sampling control signal SEL, the input end of the switch and the first output end S1 are closed first, then the first sampling branch is turned on, and the first sampling capacitor C1 can collect the first sampling signal S at the first level.C1 , and after being buffered by the first voltage follower VF1, it is output through the first output terminal out1; then, the input terminal of the switch and the second output terminal S2 are closed, the second sampling branch is turned on, and the second sampling capacitor C2 can collect the second sampling signal S at the second level. C2 , and after being buffered by the second voltage follower VF2, it is output through the second output terminal out2.

[0205] Since the capacitance cannot change suddenly, and the sampling frequency is relatively high, without considering the capacitance discharge, the capacitance can maintain the original sampling signal amplitude when the switch is disconnected, and when the switch is switched and the corresponding sampling branch is turned on again, the capacitance changes with the amplitude of the electrical signal output by the transimpedance amplifier when the path is turned on next time. For example, when the first sampling branch is turned on, the first sampling signal S collected by the first sampling capacitor C1 is C1 The amplitude of the second sampling signal S is equal to the amplitude of the electrical signal output by the transimpedance amplifier TIA. When the second sampling branch is turned on, the second sampling signal S collected by the second sampling capacitor C2 is C2 The first sampling signal S1 is obtained by collecting the first sampling capacitor C1 and changes accordingly with the amplitude of the electrical signal output by the transimpedance amplifier TIA in the corresponding period of time. When the switch is switched back to the first sampling path, the first sampling signal S2 is obtained by collecting the first sampling capacitor C1 and the first sampling signal S3 is obtained by collecting the first sampling capacitor C1 and the first sampling signal S4 is obtained by collecting the first sampling capacitor C1 and the first sampling signal S5 is obtained by collecting the first sampling capacitor C1 and the first sampling signal S6 is obtained by collecting the first sampling capacitor C1 and the first sampling signal S7 is obtained by collecting the first sampling capacitor C1 and the first sampling signal S8 is obtained by collecting the first sampling capacitor C1 and the first sampling signal S9 ... C1 The amplitude of changes accordingly with the amplitude of the electrical signal output by the transimpedance amplifier TIA.

[0206] More specifically, the square wave perturbation signal ds can be regarded as a square wave signal with 0 as the reference, Vs as the amplitude, and the level fluctuating between +Vs and -Vs. Correspondingly, the bias voltage of the MZ modulator fluctuates between V0+Vs and V0-Vs, and the first sampling signal S C1 It can represent the output light intensity E1 when the bias voltage is V0+Vs, and the second sampling signal S C2 It can represent the output light intensity E2 when the bias voltage is V0-Vs. The output light intensity corresponding to MITP is 0, E1=E2, and the first sampling signal S C1 and the second sampling signal S C2 When V0 is larger or smaller than the bias voltage corresponding to MITP, the output light intensity corresponding to the bias voltage V0 is not 0, then the first sampling signal S C1 and the second sampling signal S C2 The signs are opposite, but the amplitudes are different. By detecting the first sampled signal S C1 and the second sampling signal S C2 By measuring the size of , it can be determined whether the bias voltage of the MZ modulator 10A is offset relative to the preset bias point.

[0207] In a specific implementation, when the first sampling signal SC1 and the second sampling signal S C2 When the sizes of are consistent, it means that the bias point of the MZ modulator 10A has not shifted relative to the preset bias point, that is, the MZ modulator 10A operates at the preset bias point, and the bias voltage of the MZ modulator 10A does not need to be adjusted.

[0208] When the first sampling signal S C1 and the second sampling signal S C2 When the sizes are inconsistent, it means that the bias point of the MZ modulator 10A is offset relative to the preset bias point, that is, the MZ modulator 10A does not work at the preset bias point, and the bias voltage needs to be adjusted to make the MZ modulator 9A work at the preset bias point.

[0209] Based on this, the embodiments of this specification also provide a bias point control circuit corresponding to the above bias point control method, which can perform corresponding compensation when the bias point of the MZ modulator is offset to adjust the bias voltage of the MZ modulator. The following is a detailed introduction through specific embodiments with reference to the accompanying drawings.

[0210] Reference Fig.12 The structure diagram of a bias point control circuit in the embodiment of the present specification is shown. In some embodiments of the present specification, the bias point control circuit 120 can be coupled to the MZ modulator 12A, and the bias point control circuit 120 can include:

[0211] The bias point detection circuit M1 includes the square wave perturbation module M11 and the sampling module M12;

[0212] The compensation module M2 is coupled between the bias point detection circuit M1 and the bias terminal of the MZ modulator 12A, and is adapted to provide a compensation signal to adjust the bias voltage of the MZ modulator 12A when the bias voltage of the MZ modulator 12A is offset.

[0213] From the detection process and principle of the bias point detection circuit described above, it can be known that the bias point detection circuit M1 can detect whether the bias point of the MZ modulator 12A is offset relative to the preset bias point, and output the corresponding detection result to the compensation module M2 coupled to the bias point detection circuit M1. The compensation module M2 receives the detection result of the bias point detection circuit M1 and outputs a corresponding compensation signal to adjust the bias voltage of the MZ modulator 12A so that the MZ modulator 12A works at a preset bias point.

[0214] By using the bias point control circuit 120 in the embodiment of the present specification, when the bias point of the MZ modulator 12A is offset, the corresponding compensation signal can be directly provided without the need for algorithm coordination, so that the MZ modulator 12A can operate at a preset bias point, and the entire control circuit including the bias point detection circuit does not need to sample expensive devices such as ADC and DAC. Therefore, the difficulty of implementing the MZ modulator bias point control circuit 120 can be reduced, thereby reducing the circuit power consumption and implementation cost.

[0215] In order to enable those skilled in the art to better understand and implement, some implementable examples of each module in the bias point control circuit of this specification are shown below.

[0216] Continue to refer to Fig.12 In some embodiments of this specification, Fig.12 As shown, the bias point detection circuit M1 may include a square wave perturbation module M11 and a sampling module M12, and optionally may also include a control module M13, wherein the sampling module M12 may include a sampling unit M122, and the sampling unit M122 may include a circuit suitable for outputting a first sampling signal S C1 The first output terminal out1 is suitable for outputting the second sampling signal S C2 The second output terminal out2.

[0217] The specific structure, circuit connection relationship and working principle of the bias point detection circuit M1 can be referred to Fig.12 , and combined Fig. 9 , Fig.10 , Fig.11A and Fig. 11B And the corresponding description will not be repeated here.

[0218] In order to enable those skilled in the art to better understand and implement, some optional circuit structures of the compensation module M2 are described below through some specific examples.

[0219] In a specific implementation, the compensation module M2 can output a compensation signal in a corresponding direction based on the magnitude relationship of the sampling signals corresponding to different levels of the square wave perturbation signal to adjust the bias voltage of the MZ modulator 12A. More specifically, the compensation module can adopt a matching compensation strategy based on different preset bias points (i.e., whether the preset bias point is the minimum transmission point or the maximum transmission point).

[0220] In the embodiments of this specification, as mentioned above, the magnitude of the sampling signal S can represent the output light intensity of the square wave perturbation signal at different levels.

[0221] As a specific example, the square wave perturbation signal may include a first level and a second level, wherein the first level is higher than the second level. When the preset bias point is the minimum transmission point, the compensation module M2 is suitable for reducing the bias voltage of the MZ modulator 12A when the first light intensity E1 corresponding to the first level is greater than the second light intensity E2 corresponding to the second level; and increasing the bias voltage of the MZ modulator 12A when the first light intensity E1 is less than the second light intensity E2.

[0222] As another specific example, the square wave perturbation signal may include a first level and a second level, wherein the first level is higher than the second level, and when the preset bias point is the maximum transmission point, the compensation module M2 is suitable for increasing the bias voltage of the MZ modulator 12A when the first light intensity E1 corresponding to the first level is greater than the second light intensity E2 corresponding to the second level E2; and reducing the bias voltage of the MZ modulator 12A when the first light intensity E1 is less than the second light intensity E2.

[0223] In some embodiments of the present specification, the compensation module M2 may include: an integration circuit unit M21, a first input terminal of which is suitable for receiving a first sampling signal S C1 , whose second input terminal is suitable for receiving the second sampling signal S C2 , whose output terminal outputs the first sampling signal S C1 and the second sampling signal S C2 The difference is integrated over time to determine the compensation direction and compensation amount of the compensation signal.

[0224] The compensation direction is determined by the change direction of the integral. C1 and the second sampling signal S C2 When the integral of the difference increases over time, the compensation direction is to increase the bias voltage of the MZ modulator; when the first sampling signal S C1 and the second sampling signal S C2 When the integral of the difference over time decreases, the compensation direction is to reduce the bias voltage of the MZ modulator.

[0225] The compensation amount is determined by the change in the integral. Specifically, the compensation amount is related to the first sampling signal S C1 and the second sampling signal S C2 The integral of the difference over time is positively correlated.

[0226] The compensation module M2 in the above embodiment is used, and the integration circuit unit M21 is used according to the first sampling signal S C1 and the second sampling signal S C2The integration of the difference over time can generate a corresponding compensation signal, including a compensation direction and a compensation amount, so that the bias voltage of the MZ modulator 12A can be adjusted so that the MZ modulator 12A works at a preset bias point.

[0227] Continue to refer to Fig.12 , and combined with the specific embodiment of the bias point detection circuit mentioned above, it can be known that the sampling unit M122 can specifically include a first sampling signal S C1 The first output terminal out1 is suitable for outputting the second sampling signal S C2 The second output terminal out2.

[0228] The integration circuit unit M21 may include an operational amplifier AMP, an energy storage component M211, a first resistor R1 and a second resistor R2, wherein:

[0229] The operational amplifier AMP comprises the first input terminal, the second input terminal and an output terminal;

[0230] The energy storage component M211 is coupled between the first input terminal and the output terminal of the operational amplifier AMP;

[0231] The first resistor R1 is coupled between the first output terminal out1 of the sampling unit M122 and the first input terminal of the operational amplifier AMP;

[0232] The second resistor R2 is coupled between the second output terminal out2 of the sampling unit M122 and the second input terminal of the operational amplifier AMP.

[0233] As a specific example, the energy storage component M211 may be a third capacitor C3.

[0234] The voltage output from the output terminal of the operational amplifier AMP reflects the first sampling signal S C1 and the second sampling signal S C2 The difference is integrated over time. When the integral increases, the voltage at the output of the operational amplifier AMP increases, and the compensation direction is to increase the bias voltage of the MZ modulator. Conversely, when the integral decreases, the voltage at the output of the AMP decreases, and the compensation direction is to decrease the bias voltage of the MZ modulator.

[0235] The specific compensation amount is positively correlated with the voltage change amount outputted from the output terminal of the operational amplifier AMP.

[0236] The above describes the basic control principle of the bias point control circuit in the embodiments of this specification and some examples of basic circuit implementation. In specific implementations, the bias point control circuit can be further expanded or optimized according to specific requirements or problems actually encountered in specific application scenarios. Some optimization examples are shown below.

[0237] The output characteristic curve of the modulator is periodic and can be expressed as a sine wave that repeats infinitely in the horizontal direction, so there are many MITPs, such as Fig.13 As shown in FIG. 1 , MITP1 , MITP2 , MITP3 , etc., each MITP corresponds to a bias voltage of a different magnitude.

[0238] In a specific implementation, since the open-loop impedance of the operational amplifier AMP is very large, when the entire circuit is working, if there is a certain deviation between the non-inverting input terminal and the inverting input terminal of the operational amplifier AMP, the output of the operational amplifier AMP is the maximum voltage value Vmax or the minimum voltage value Vmin. Fig.13 Combined with Fig.12 , the integration circuit unit will feed back the maximum output voltage Vmax to the bias terminal, directly increasing the bias voltage to Vmax. For example, the bias voltage Vmax is Fig.13 Between PI1 and PI2, based on the compensation principle of the bias point control scheme of the aforementioned embodiment, it can be known that the output characteristic curve, that is, the waveform of the sine wave is adjusted in the downward direction (if the bias voltage Vmax is higher than the most recent MITP, the bias voltage Vmax is reduced; if the bias voltage Vmax is lower than the most recent MITP, the bias voltage Vmax is increased). In other words, it is adjusted towards the trough direction of the sine wave rather than the rising direction of the waveform.

[0239] Depend on Fig.13 The relationship between the bias voltage Vmax and the minimum transmission points MITP1, MITP2 and MITP3 shows that at this time, we can only move closer to the minimum transmission point MITP3 located at PI2. At this time, the bias voltage corresponding to PI2 is relatively high. Combined with the above adjustment principle and referring to Figure 7C Since the output characteristic curve corresponding to the bias voltage Vmax is located in the descending section of the sine wave, and the corresponding working point is located on the left side of the minimum transmission point MITP3, that is, the current bias point of the MZ modulator 12A is shifted to the left relative to the minimum transmission point MITP3 on the output characteristic curve, the bias voltage of the MZ modulator 12A should be increased at this time so that the MZ modulator 12A works at the minimum transmission point MITP3.

[0240] However, if the bias voltage PI2 corresponding to the minimum transmission point MITP3 is too high, it may exceed the voltage range of the circuit operation, thereby causing the corresponding circuit to fail. Therefore, it is necessary to set the position of the bias point when the MZ modulator 12A is started, so that the MZ modulator 12A can work at the minimum transmission point closest to 0V (such as MITP2) every time it is started.

[0241] For this purpose, refer to Fig.12 , the integration circuit unit M21 may also include the following circuit components:

[0242] A third resistor R3 is coupled between the output terminal of the operational amplifier AMP and ground;

[0243] The enable switch S3 is coupled between the control module M13 and the enable terminal of the operational amplifier AMP, and is suitable for enabling the operational amplifier AMP to work in response to the enable signal ENB output by the control module M13, wherein the enable signal ENB is generated when the control module M13 determines that only the operational amplifier AMP in the bias point control circuit 120 is not in a working state.

[0244] On the one hand, by coupling the third resistor R3 to the output end of the operational amplifier AMP, since the third resistor R3 is coupled to the ground, the potential of the output end of the operational amplifier AMP can be pulled down to the potential 0V when the operational amplifier AMP is in a non-operating state; on the other hand, since the enable switch S3 is coupled between the control module M13 and the enable end of the operational amplifier AMP, and the enable signal ENB is generated in the bias point control circuit 120 after the control module M13 determines that the control module M13 is to be determined, therefore, the controller can wait for all devices in the bias point control circuit except the operational amplifier to be operated, and only when the operational amplifier AMP is not in a working state, generate the enable signal ENB, trigger the enable switch S3 to close, and then enable the operational amplifier to start working, so that the MZ modulator 12A can work at the bias point closest to 0V, thereby avoiding the voltage corresponding to the bias point exceeding the operating voltage range of the operational amplifier AMP with temperature drift, resulting in failure of the bias point control circuit 12A, thereby improving the reliability of the bias point control circuit.

[0245] As can be seen from the above, by using the above-mentioned integration circuit, the output signal of the operational amplifier AMP can be pulled down to the ground through the third resistor R3, and the control unit M13 can determine that only the operational amplifier in the control circuit is in a non-working state, and then generate an enable signal ENB, so that the output of the operational amplifier AMP is fed back from 0, and the bias voltage of the MZ modulator is adjusted from 0V, so that it can be stabilized at MITP which is closest to 0V. Fig.13 This is MITP1 shown in PI-1.

[0246] Another advantage of using the above-mentioned integration circuit is that the operating voltage is closest to 0 and the voltage amplitude is low, so the adjustable range of the bias voltage is large and it is not easy to exceed the operating voltage range of the circuit.

[0247] In a specific implementation, for the MZ modulator 12A working at different preset bias points, the compensation module M2 adjusts the bias voltage of the MZ modulator 12A in different ways, and accordingly, the connection method between the operational amplifier AMP and the sampling unit M122 is also different.

[0248] As a specific example, when the preset bias point is the minimum transmission point MITP, the first input terminal of the operational amplifier AMP is a negative input terminal, and the second input terminal of the operational amplifier AMP is a positive input terminal. That is, the first input terminal of the operational amplifier AMP is coupled to the first voltage follower VF1, and the second input terminal thereof is coupled to the second voltage follower VF2.

[0249] As another specific example, when the preset bias point is the maximum transmission point MATP, the first input terminal of the operational amplifier AMP is a positive input terminal, and the second input terminal of the operational amplifier AMP is a negative input terminal. That is, the first input terminal of the operational amplifier AMP is coupled to the second voltage follower VF2, and the second input terminal thereof is coupled to the first voltage follower VF1.

[0250] The following reference Fig.12 , the working principle of the bias point control circuit 120 is described in detail.

[0251] The working principle of the bias point detection circuit M1 in the bias point control circuit 120 may refer to the contents of the bias point detection circuit described in any embodiment, which will not be described in detail here.

[0252] The working principle of the compensation module M2 is: when other modules in the bias point control circuit 120 are in working state, and the compensation module M2 is not in working state, the control module M13 generates an enable signal ENB, and when the enable switch S3 is closed in response to the enable signal ENB, the operational amplifier AMP starts to work.

[0253] After the operational amplifier AMP starts to work, the bias point detection circuit M1 outputs a first sampling signal S through the first output terminal out1. C1 to the first input terminal of the operational amplifier AMP; and outputting the second sampling signal S through the second output terminal out2 C2 To the second input terminal of the operational amplifier AMP.

[0254] The output end of the operational amplifier AMP can obtain the first sampling signal S C1 and the second sampling signal S C2 The first sampling signal S is an integral value of the difference over time, and the voltage at the output end of the operational amplifier AMP changes with the integral value. C1 and the second sampling signal S C2 When the magnitudes are the same, the signal amplitudes at the positive input and negative input of the AMP are the same, the voltage at the output of the AMP is stable, and the bias voltage of the MZ modulator remains unchanged; when the signal amplitude at the positive input of the AMP is higher than the signal amplitude at the negative input, the output voltage of the AMP increases, and the bias voltage of the MZ modulator increases; when the signal amplitude at the negative input of the AMP is higher than the signal amplitude at the positive input, the output voltage of the AMP decreases, and the bias voltage of the MZ modulator decreases. Thus, the bias voltage of the MZ modulator 12A is adjusted so that the MZ modulator 12A operates at a preset bias point.

[0255] In a specific example, when the preset bias point of the MZ modulator 12A is the minimum transmission point MITP, the bias voltage of the MZ modulator 12A may be adjusted according to the following strategy:

[0256] When the signal value of the first input terminal of the operational amplifier AMP is greater than the signal value of the second input terminal, that is, the first sampling signal S C1 The sampling value is greater than the second sampling signal S C2 The sampling value of , at this time, the output voltage of the operational amplifier AMP decreases, and accordingly, the bias voltage of the MZ modulator 12A decreases.

[0257] When the signal value of the second input terminal of the operational amplifier AMP is greater than the signal value of the first input terminal, that is, the second sampling signal S C2 The sampling value is greater than the first sampling signal S C1 At this time, the output voltage of the operational amplifier AMP increases, and accordingly, the bias voltage of the MZ modulator 12A increases.

[0258] When the signal value of the first input terminal of the operational amplifier AMP is equal to the signal value of the second input terminal, that is, the first sampling signal S C1 The sampling value is equal to the second sampling signal S C2 At this time, the MZ modulator 12A operates at the minimum bias point MITP, and there is no need to adjust the bias voltage of the MZ modulator 12A.

[0259] Reference Fig.12 Combined with Fig. 11B, it can be known from the above embodiment that if the first sampling signal S C1 The second sampling signal S C2 The sampling values ​​of are inconsistent, such as Fig. 11B The first sampling signal S corresponding to the period t1 to t3 C1 and the second sampling signal S C2 , based on the first sampling signal S during the period t1 to t2 C1 and the second sampling signal S C2 By integrating the difference, the amplitude corresponding to the compensation signal output by the operational amplifier can be obtained ( Fig. 11B (not shown). In the following time period, considering the circuit bandwidth, the bias voltage may not be adjusted to the preset bias point at one time. Therefore, for example, starting from the next signal cycle, the amplitude difference of the electric signal dts output by the detection unit M121 corresponding to the square wave perturbation signal ds at different levels will be reduced, and accordingly, the first sampling signal S C1 and the second sampling signal S C2 The amplitude difference of the first sampling signal S is reduced, and the amplitude difference continues to decrease in the next signal cycle, and the detection and compensation adjustment are performed continuously until the first sampling signal S C1 and the second sampling signal S C2 The amplitudes of are equal, then the MZ modulator 12A operates again at the preset bias point, such as Fig. 11B In the embodiment, after time t7, the MZ modulator 12A operates at the preset minimum transmission point again.

[0260] In some other specific examples, when the preset bias point of the MZ modulator 12A is the maximum transmission point MATP, the bias voltage of the MZ modulator 12A may be modulated according to the following strategy:

[0261] When the signal value of the first input terminal of the operational amplifier AMP is greater than the signal value of the second input terminal, that is, the first sampling signal S C1 The sampling value is greater than the second sampling signal S C2 At this time, the output voltage of the operational amplifier AMP increases, and accordingly, the bias voltage of the MZ modulator 12A increases.

[0262] When the signal value of the second input terminal of the operational amplifier AMP is greater than the signal value of the first input terminal, that is, the second sampling signal S C2 The sampling value is greater than the first sampling signal S C1 The sampling value of , at this time, the output voltage of the operational amplifier AMP decreases, and accordingly, the bias voltage of the MZ modulator 12A decreases.

[0263] When the signal value of the first input terminal of the operational amplifier AMP is equal to the signal value of the second input terminal, that is, the second sampling signal S C2 The sampling value is equal to the first sampling signal S C1 At this time, the MZ modulator 12A operates at the maximum bias point MATP, and there is no need to adjust the bias voltage of the MZ modulator 12A.

[0264] It can be seen from the above adjustment process that the bias voltage of the MZ modulator can be automatically adjusted through the voltage change at the output end of the operational amplifier AMP, so that the MZ modulator 12A works at a preset bias point.

[0265] The bias point control circuit 120 in the above embodiment is adopted, and the bias point detection circuit M1 therein continuously detects, and when the bias voltage of the MZ modulator 12A shifts, a compensation signal is provided through the compensation module M2 to automatically adjust the bias voltage of the MZ modulator 12A, so that the MZ modulator 12A always operates at a preset bias point.

[0266] In a specific implementation, the bias point detection circuit can be applied to various laser application occasions and corresponding equipment. An application example in a radar is given below.

[0267] In the embodiment of this specification, the radar may be a frequency modulated continuous wave radar. Fig.14 The schematic diagram of the structure of the radar shown in FIG. 1 , in a specific implementation, the radar 140 may include: a laser 141, an MZ modulator 142, a spectrometer 143 and a bias point detection circuit 144, wherein:

[0268] The laser 141 is suitable for generating a continuous laser with stable intensity and frequency as the injected light Ein;

[0269] The MZ modulator 142 operates at a preset bias point to perform intensity modulation on the injected light Ein, and is adapted to perform frequency modulation on the injected light based on a modulation signal RF to generate an output light Eout;

[0270] The optical splitter 143 is coupled to the MZ modulator 142 to split the output light Eout into signal light and detection light;

[0271] The bias point detection circuit 144 is coupled to the MZ modulator 142 and the optical splitter 143 , and is adapted to detect whether the MZ modulator 142 operates at a preset bias point based on the detection light.

[0272] The specific implementation of the bias point detection circuit 144 can refer to the specific introduction of the above-mentioned embodiment, which will not be described in detail here.

[0273] Similarly, the bias point control circuit in the aforementioned embodiment can be applied to various laser application occasions and corresponding equipment. An application example in a laser radar is given below.

[0274] In the embodiments of this specification, taking the application in frequency modulated continuous wave radar as an example, refer to Fig.15 The schematic diagram of another radar structure shown in FIG. 1 , the radar 150 may include: a laser 151, an MZ modulator 152, a beam splitter 153 and a bias point control circuit 154, wherein:

[0275] The laser 151 is suitable for generating continuous laser light with stable intensity and frequency as the injected light Ein;

[0276] The MZ modulator 152 operates at a preset bias point to modulate the intensity of the injected light Ein, and is adapted to perform frequency modulation on the injected light based on a modulation signal RF to generate an output light Eout;

[0277] The optical splitter 153 is coupled to the MZ modulator 152 to split the output light into signal light and detection light;

[0278] The bias point control circuit 154 is coupled to the spectrometer 153 and the MZ modulator 152, and is suitable for detecting whether the bias voltage of the MZ modulator 152 is offset based on the detection light, and providing a compensation signal to adjust the bias voltage of the MZ modulator 152 when the bias voltage of the MZ modulator 152 is offset.

[0279] The specific implementation of the bias point control circuit 154 can refer to the specific introduction of the aforementioned embodiment, which will not be described in detail here.

[0280] Although the embodiments of the present invention are disclosed above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A bias point control circuit, characterized in that: include: A bias point detection circuit is coupled to an MZ modulator, the MZ modulator is suitable for operating at a preset bias point, and the bias point detection circuit includes a square wave perturbation module and a sampling module, wherein: the square wave perturbation module is coupled to the bias end of the MZ modulator, and is suitable for outputting a square wave perturbation signal to the bias end of the MZ modulator, so that the bias voltage of the MZ modulator fluctuates with the square wave perturbation signal; the sampling module is suitable for acquiring electrical signals corresponding to different levels of the square wave perturbation signal, and outputting a first sampling signal and a second sampling signal; A compensation module is coupled between the bias point detection circuit and the bias end of the MZ modulator, and is adapted to directly output a compensation signal of a corresponding direction to the bias end when the bias point of the MZ modulator is offset, based on the magnitude relationship between the first sampling signal and the second sampling signal corresponding to different levels of the square wave perturbation signal, so as to adjust the bias voltage of the MZ modulator; wherein the compensation module comprises: an integration circuit unit, whose first input end is adapted to receive the first sampling signal, whose second input end is adapted to receive the second sampling signal, and whose output end outputs the integral of the difference between the first sampling signal and the second sampling signal over time, so as to determine the compensation direction and compensation amount of the compensation signal; The integration circuit unit comprises: An operational amplifier comprising the first input terminal, the second input terminal and an output terminal; an energy storage component, coupled between the first input terminal and the output terminal of the operational amplifier; A first resistor, coupled between a first output terminal of the sampling module outputting the first sampling signal and a first input terminal of the operational amplifier; A second resistor, coupled between a second output terminal of the sampling module outputting the second sampling signal and a second input terminal of the operational amplifier; A third resistor is coupled between the output terminal of the operational amplifier and ground; The enable switch is coupled to the enable terminal of the operational amplifier and is adapted to enable the operational amplifier to operate in response to an enable signal, wherein the enable signal is generated in the bias point control circuit only when the operational amplifier is not in an operating state.

2. The bias point control circuit according to claim 1, characterized in that: The sampling module is coupled to the output end of the MZ modulator and is further adapted to detect the output light intensity of the square wave perturbation signal at different levels to determine whether the bias point of the MZ modulator is offset relative to the preset bias point.

3. The bias point control circuit according to claim 2, characterized in that: The sampling module comprises: A detection unit, adapted to detect the optical signal output by the MZ modulator and convert the optical signal into an electrical signal; The sampling unit is coupled to the detection unit, and obtains the electrical signals corresponding to different levels of the square wave perturbation signal respectively, and outputs sampling signals. The sampling unit includes a first output end suitable for outputting the first sampling signal and a second output end suitable for outputting the second sampling signal.

4. The bias point control circuit according to claim 3, characterized in that: The detection unit comprises: A photodiode, adapted to convert the optical signal output by the MZ modulator into an electrical signal; The transimpedance amplifier is suitable for amplifying the electrical signal.

5. The bias point control circuit according to claim 3, characterized in that: The sampling unit comprises: A first sampling capacitor, coupled between the detection unit and ground, adapted to sample the square wave perturbation signal at a first level to obtain the first sampling signal; The second sampling capacitor is coupled between the detection unit and the ground, and is suitable for sampling the second level of the square wave perturbation signal to obtain the second sampling signal.

6. The bias point control circuit according to claim 5, characterized in that: The sampling unit also includes: A first voltage follower, adapted to buffer the first sampling signal; The second voltage follower is adapted to buffer the second sampling signal.

7. The bias point control circuit according to any one of claims 3 to 6, characterized in that: The sampling module also includes: a switching unit, coupled to the detection unit, suitable for controlling the sampling module to sample the electrical signal output by the detection unit at the same frequency as that of the square wave perturbation module, respectively obtaining a first sampling signal when the square wave perturbation signal is at a first level and a second sampling signal when the square wave perturbation signal is at a second level, and outputting the first sampling signal through a first output terminal and outputting the second sampling signal through a second output terminal.

8. The bias point control circuit according to claim 7, characterized in that: Also includes: The control module is coupled to the square wave perturbation module and the switch unit respectively, and is suitable for outputting a square wave signal, wherein a first part of the square wave signal is used to generate the square wave perturbation signal, and a second part of the square wave signal is used to generate a sampling control signal.

9. The bias point control circuit according to claim 8, characterized in that: The square wave perturbation module comprises: The square wave signal amplifying unit amplifies the first part of the square wave signal to obtain the square wave perturbation signal.

10. The bias point control circuit according to claim 9, characterized in that: The square wave perturbation module also includes: The buffer unit is coupled between the output end of the control module and the square wave signal amplifying unit, and is suitable for buffering the first part of the square wave signal output by the control module.

11. The bias point control circuit according to claim 1, characterized in that: The square wave perturbation signal includes a first level and a second level, wherein the first level is higher than the second level, and the preset bias point is a minimum transmission point; The compensation module is adapted to reduce the bias voltage of the MZ modulator when a first light intensity corresponding to the first level is greater than a second light intensity corresponding to the second level; and to increase the bias voltage of the MZ modulator when the first light intensity is less than the second light intensity.

12. The bias point control circuit according to claim 1, characterized in that: The square wave perturbation signal includes a first level and a second level, wherein the first level is higher than the second level, and the preset bias point is a maximum transmission point; The compensation module is adapted to increase the bias voltage of the MZ modulator when a first light intensity corresponding to the first level is greater than a second light intensity corresponding to the second level; and to reduce the bias voltage of the MZ modulator when the first light intensity is less than the second light intensity.

13. The bias point control circuit according to claim 8, characterized in that: The control module is coupled to the enable switch and is adapted to generate the enable signal when it is determined that only the operational amplifier in the bias point control circuit is not in a working state.

14. The bias point control circuit according to claim 1, characterized in that: The preset bias point is a minimum transmission point, the first input terminal of the operational amplifier is a negative input terminal, and the second input terminal of the operational amplifier is a positive input terminal.

15. The bias point control circuit according to claim 1, characterized in that: The preset bias point is a maximum transmission point, the first input terminal of the operational amplifier is a positive input terminal, and the second input terminal of the operational amplifier is a negative input terminal.

16. A radar, characterized in that: include: A laser, suitable for generating continuous laser light with stable intensity and frequency as the injection light; An MZ modulator operates at a preset bias point to modulate the intensity of the injected light, and is adapted to perform frequency modulation on the injected light based on a modulation signal to generate output light; An optical splitter, coupled to the MZ modulator, for dividing the output light into a signal light and a detection light; The bias point control circuit described in any one of claims 1 to 15 is coupled to the spectrometer and the MZ modulator, and is suitable for detecting whether the bias point of the MZ modulator is offset based on the detection light, and providing a compensation signal to adjust the bias voltage of the MZ modulator when the bias point of the MZ modulator is offset.

Images