System and method for improving optical communication sensitivity

Abstract

The invention discloses a system for improving optical communication sensitivity, which comprises an optical transmitting module, an optical receiving module and a digital signal processing module, and is characterized in that the optical transmitting module is used for realizing direct-current equalization and dynamically adjusting Bias Tee direct-current bias according to an input signal, so that the peak-to-peak value of an output radio-frequency signal is V pi and is symmetrical about a zero level; the optical receiving module is used for converting an optical signal into an electric signal by the APD and converting an analog signal into a digital signal by the ADC; the digital signal processing module is used for recovering and demodulating the digital signal to obtain original information; and meanwhile, the theoretical receiving sensitivity of different duty ratios OOK-RZ can be speculated according to the condition of an optical communication system. According to the system and the method for improving the optical communication sensitivity provided by the invention, the extinction ratio of the optical signal output by the MZM modulator is improved; the sensitivity of an optical communication system can be effectively improved; and according to the condition of the optical communication system, the theoretical receiving sensitivity of different duty ratios OOK-RZ is speculated.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to a system and method for improving the sensitivity of optical communication. Background Art

[0002] With the rapid development of artificial intelligence and other technologies, human beings' demands for communication speed, security and reliability are constantly increasing. Traditional communication technologies are gradually showing their limitations, and satellite laser communication has become an effective solution. Satellite laser communication uses laser as a carrier and has the advantages of high speed, large capacity, high security, strong anti-interference ability, small size, light weight and low power consumption. It is widely used in inter-satellite and satellite-to-ground information transmission.

[0003] In optical communication systems, the extinction ratio of the transmitter signal has a key impact on the system sensitivity. The extinction ratio determines the signal-to-noise ratio of the receiver signal and plays an important role in the quality of signal transmission. A high extinction ratio can effectively improve the quality of the received signal and reduce the system bit error rate, thereby improving the reliability of the system and extending the communication distance of the satellite. In addition, the return-to-zero (RZ) modulation format has higher peak power, stronger anti-interference ability and lower inter-symbol interference than the non-return-to-zero (NRZ) modulation format, further improving system performance.

[0004] At present, the research on improving the extinction ratio is mostly based on the bias voltage control of the modulator. For example, Luo Ying et al. proposed in "Laser Communication Methods, Devices and Equipment" that a discrete cascade bias controls multiple cascades in the modulation group to achieve high extinction ratio pulse modulation, but it is necessary to accurately control the phase and bias voltage matching between multiple modulators. The cascade structure is complex and increases power consumption and volume. The above methods are mostly designed for DC balanced signals. For DC unbalanced signals (such as PPM, RZ), Yang Lei et al. adopted a cascaded Mach-Zehnder modulator (MZM) structure in "Cascaded MZM High Extinction Ratio Optical Signal Generation System, Control Method, Chip and Terminal". On the basis of comprehensive tracking of the bias voltage of each MZM, the peak-to-peak value of the input signal is considered to optimize the extinction ratio, but the influence of the DC bias of the DC unbalanced signal on the working point offset of the MZM modulator is ignored, resulting in a decrease in the extinction ratio of the output optical signal, thereby affecting the sensitivity of the system. Therefore, for DC unbalanced signals, controlling the DC bias of the drive signal to increase the extinction ratio of the transmitted optical signal is crucial to improving the sensitivity of the system. Summary of the invention

[0005] In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is the problem of high complexity of the communication link, low extinction ratio and low system sensitivity in the existing satellite laser communication. Therefore, the present invention provides a system and method for improving the sensitivity of optical communication, using OOK-RZ modulation signal, RZ performance is better than NRZ under the same average optical power; improving the extinction ratio of the optical signal output by the MZM modulator; while keeping the peak optical power of the modulated transmitted optical signal unchanged, reducing the duty cycle of the OOK-RZ modulation signal can effectively improve the sensitivity of the optical communication system; and according to the conditions of the optical communication system, such as the duty cycle of the optical signal at the transmitting end, the extinction ratio of the optical signal, the influence of system noise, APD responsivity, APD shot noise and other parameters, the theoretical receiving sensitivity of OOK-RZ with different duty cycles is inferred.

[0006] To achieve the above object, the present invention provides a system for improving the sensitivity of optical communication, including an optical transmitting module, an optical receiving module and a digital signal processing module. The optical transmitting module is used to realize DC balance, dynamically adjust the Bias Tee DC bias according to the input RF signal, so that the peak-to-peak value of the output RF signal is V π And it is symmetrical about the zero level, so that the Mach-Zehnder modulator MZM emits an optical signal with a high extinction ratio; the optical receiving module includes a photodetector APD and an analog-to-digital converter ADC, the APD converts the optical signal emitted by the optical transmitting module into an electrical signal, and converts the analog signal into a digital signal through the ADC; the digital signal processing module is used to recover and demodulate the digital signal to obtain the original information; at the same time, according to the conditions of the optical communication system, the theoretical receiving sensitivity of different duty cycle return-to-zero codes (OOK-RZ) can be inferred.

[0007] Furthermore, the optical transmission module includes a signal source, a front Bias Tee, a driving amplifier, a rear BiasTee, a laser and an MZM modulator; wherein the signal source is used to transmit OOK-RZ modulated signals with different duty cycles, and the DC components of the input and output signals of the driving amplifier are adjusted by the front Bias Tee and the rear Bias Tee respectively, so that the peak-to-peak value of the OOK-RZ electrical signals with different duty cycles after passing through the driving amplifier is V π It is symmetrical about the zero level, and modulates the radio frequency signal onto the optical signal through the MZM modulator to obtain a high extinction ratio optical signal; at the same time, the bias control point of the MZM modulator is adjusted to be located at the orthogonal working point to perform linear modulation to keep the peak power of the transmitted optical signal unchanged.

[0008] Furthermore, the driving amplifier is configured as a linear driving amplifier.

[0009] Further, the laser is configured to use a laser with high optical power and narrow line width.

[0010] Furthermore, the MZM modulator is configured as an external modulation mode.

[0011] The present invention provides a method for improving the sensitivity of an optical communication system, comprising the following steps:

[0012] Step 1: The signal source randomly generates an original sequence, adds frame header information and OOK-RZ modulation to the original transmission data, generates a modulated signal with adjustable duty cycle, and sends the modulated signal;

[0013] Step 2: Use the host computer to control the bias voltage of the MZM modulator so that the modulator works at the orthogonal working point for linear modulation;

[0014] Step 3: For the OOK-RZ modulation signals with different duty cycles, the Bias Tee input bias voltage is adjusted according to the duty cycle through the front Bias Tee, the driving amplifier, and the rear Bias Tee, so that the amplitude of the OOK-RZ signals with different duty cycles after amplification is V π And it is symmetrical about the zero level;

[0015] Step 4: The laser is connected to the optical input of the MZM modulator as a light source, and the amplified RF signal is connected to the electrical input of the MZM modulator to complete the modulation of the optical signal and output an optical signal with a high extinction ratio;

[0016] Step 5: The optical receiving module converts the transmitted optical signal into an electrical signal through APD reception, and converts the analog signal into a digital signal through ADC sampling;

[0017] Step 6: The digital signal processing module performs pre-processing such as resampling and filtering on the digital signal, and then performs data judgment, bit synchronization, frame synchronization, and decoding to restore the original information.

[0018] Furthermore, the signal source randomly generates an original sequence, adds frame header information and OOK-RZ modulation to the original transmission data, generates a modulation signal with an adjustable duty cycle and sends the modulated signal. Specifically, the signal source randomly generates an original sequence, adds frame header information and OOK-RZ modulation to the original transmission data, generates a modulation signal with an adjustable duty cycle of 50% and 25%, and sends the modulated signal at a rate of 10Mbps.

[0019] Furthermore, the OOK-RZ signal is expressed as:

[0020] s(t)=Ab k p(t-kT b )

[0021] Where A represents the peak amplitude of the signal, b k represents the Kth bit, T b Represents the symbol period, kTb represents the start time of the kth bit, and p(t) represents the bit-normalized pulse form.

[0022] Further, in step three, for the OOK-RZ modulation signals with different duty cycles, the Bias Tee input bias voltage is adjusted according to the duty cycle through the front Bias Tee, the driving amplifier, and the rear Bias Tee, so that the amplitude of the OOK-RZ signals with different duty cycles after amplification is V π And about zero level symmetry, specifically including, for the OOK-RZ modulation signals with different duty cycles, the front Bias Tee adjusts the DC component added to the input RF signal of the driver amplifier according to the duty cycle of the transmitted OOK-RZ signal, so that the peak-to-peak value of the output RF signal of the driver amplifier is V π The post-Bias Tee adjusts the DC component added to the output RF signal of the driver amplifier to ensure that the amplitude of the driving signal input to the MZM modulator is symmetrical about the zero level.

[0023] Furthermore, the bias control of the MZM modulator is performed through the host computer so that the modulator works at the orthogonal working point for linear modulation. The working point of the MZM modulator is determined by the modulator bias voltage. Specifically, the bias control is performed based on the pilot method, and a small-amplitude pilot signal is introduced into the DC bias so that it is input into the modulator together with the RF signal and the DC voltage for modulation. A part of the output signal is input into the control feedback terminal to digitally detect the harmonics of the pilot signal and perform feedback compensation.

[0024] Technical Effects

[0025] The present invention provides a method and system for improving the sensitivity of optical communication, adopting OOK-RZ modulation signal, and the RZ performance is better than NRZ under the same average optical power; DC balance is achieved through the front Bias Tee-driving amplifier-rear Bias Tee structure, and the Bias Tee DC bias is dynamically adjusted according to the input signal, so that the peak-to-peak value of the output RF signal is V π And it is symmetrical about the zero level, thereby improving the extinction ratio of the optical signal output by the MZM modulator; the MZM modulator works at the orthogonal transmission point, and while keeping the peak optical power of the modulated transmitted optical signal unchanged, reducing the duty cycle of the OOK-RZ modulated signal can effectively improve the sensitivity of the optical communication system; in addition, the system can also infer the theoretical receiving sensitivity of OOK-RZ with different duty cycles based on the conditions of the optical communication system, such as the duty cycle of the optical signal at the transmitting end, the extinction ratio of the optical signal, the influence of system noise, APD responsivity, APD shot noise and other parameters.

[0026] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic diagram of a system for improving optical communication sensitivity according to a preferred embodiment of the present invention;

[0028] Figure 2 It is a schematic diagram of the Bias Tee structure of a system for improving the sensitivity of optical communication according to a preferred embodiment of the present invention;

[0029] Figure 3 It is a schematic diagram of waveforms of OOK-RZ modulation signals with different duty ratios in a system for improving the sensitivity of optical communication according to a preferred embodiment of the present invention;

[0030] Figure 4 It is a theoretical simulation diagram of OOK-RZ signal sensitivity with different duty cycles at the same extinction ratio (13dBm) of a system for improving optical communication sensitivity in a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0032] In the following description, specific details such as specific internal procedures and techniques are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present invention. However, it should be clear to those skilled in the art that the present invention may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present invention.

[0033] like Figure 1 As shown, an embodiment of the present invention provides a system for improving the sensitivity of optical communication, including an optical transmitting module, an optical receiving module and a digital signal processing module, wherein the optical transmitting module includes a signal source, a front Bias Tee, a driving amplifier, a rear Bias Tee, a laser and an MZM modulator, and the optical transmitting module adopts an OOK-RZ modulation signal, realizes DC balance through a front BiasTee-driving amplifier-rear Bias Tee structure, and dynamically adjusts the Bias Tee DC bias according to the input signal, so that the output RF signal peak-to-peak value is V π And it is symmetrical about the zero level, so as to improve the extinction ratio of the optical signal output by the MZM modulator;

[0034] The optical receiving module converts the received optical signal into an electrical signal through the APD, and the ADC converts the analog signal into a digital signal;

[0035] The digital signal processing module recovers and demodulates the digital signal to obtain the original information; at the same time, the theoretical receiving sensitivity of OOK-RZ with different duty cycles can be inferred according to the conditions of the optical communication system.

[0036] Among them, the signal source in the optical transmitter module transmits OOK-RZ modulated signals with different duty cycles. The front Bias Tee adjusts the DC component added to the input RF signal of the driver amplifier according to the duty cycle of the transmitted OOK-RZ signal, so that the peak-to-peak value of the output RF signal of the driver amplifier is V π , the post-Bias Tee adjustment adds the DC component of the RF signal output by the driver amplifier to ensure that the amplitude of the driving signal input to the MZM modulator is symmetrical about the zero level, thereby improving the extinction ratio of the transmitted optical signal; the MZM modulator modulates the amplified OOK-RZ RF signal onto the optical signal, and at the same time adjusts the bias control point of the MZM modulation to the orthogonal working point for linear modulation, keeping the peak power of the transmitted optical signal unchanged, reducing the duty cycle of the OOK-RZ signal, and improving the sensitivity of the optical communication system.

[0037] like Figure 2 As shown in the figure, the Bias Tee has three ports, RF port (RF), DC bias port (DC) and RF & DC port (RF&DC). The DC bias port can add DC bias to the RF signal without affecting the RF signal passing through the main transmission path. The driver amplifier is a linear driver amplifier with the characteristics of large bandwidth, low noise and flat gain, so that the peak-to-peak value of the OOK-RZ modulated signal with different duty cycles after amplification is V π .

[0038] The MZM modulator is an external modulation modulator, the bias voltage is controlled at a linear operating point, and the modulated optical signal has a high extinction ratio.

[0039] The optical receiving module includes APD and ADC. It uses highly sensitive InGaAs-APD to convert the optical power signal into photocurrent and then into electrical signal, and converts the analog signal into digital signal through ADC.

[0040] Among them, APD adopts InGaAs-APD, which integrates a low-noise broadband transimpedance amplifier, boost and temperature compensation circuit, and has the characteristics of high gain and high sensitivity.

[0041] The digital signal processing module performs pre-processing such as resampling and digital filtering on the received digital signal, and then performs data judgment, bit synchronization, and frame synchronization to restore the original information and complete the signal demodulation. At the same time, according to the conditions of the optical communication system, such as the duty cycle of the optical signal at the transmitting end, the extinction ratio of the optical signal, the influence of system noise, APD responsivity, APD shot noise and other parameters, the theoretical receiving sensitivity of OOK-RZ with different duty cycles is inferred.

[0042] In this embodiment, the specific steps of a method for improving optical communication sensitivity are as follows:

[0043] Step 1: The signal source randomly generates the original sequence, adds frame header information to the original transmission data, performs OOK-RZ modulation, generates a modulation signal with a duty cycle of 50% and 25% adjustable, and sends the modulated signal at a rate of 10Mbps. The OOK-RZ signal can be expressed as:

[0044] s(t)=Ab k p(t-kT b )

[0045] Where A represents the peak amplitude of the signal, b k represents the Kth bit, T b Represents the symbol period, kT b represents the start time of the kth bit. Since the MZM modulator has a differential input, the normalized pulse form p(t) of a single bit with a pulse duration of τ is expressed as:

[0046]

[0047] Step 2: The bias voltage of the MZM modulator is controlled by the host computer so that the modulator works at the orthogonal working point for linear modulation; the modulator bias voltage determines the working point of the MZM modulator. This embodiment performs bias control based on the pilot method, introduces a small amplitude pilot signal in the DC bias, and inputs it into the modulator together with the RF signal and DC voltage for modulation, and inputs a part of the output signal to the control feedback end to digitally detect the harmonics of the pilot signal and perform feedback compensation. The transfer function of the MZM modulator can be expressed as:

[0048]

[0049] In the formula, I in Indicates the modulator input optical signal power, I out Indicates the modulator output optical signal power, V π It represents the voltage required for the two arms of the MZM modulator to produce a π phase change, that is, the half-wave voltage, V DC is the modulator bias voltage, V RF(t) represents the modulator input RF signal. The MZM modulator bias voltage V is controlled by the host computer. DC The modulator operates at the quadrature bias point. DC The value satisfies the following formula (in this embodiment, K=0):

[0050]

[0051] Step 3: Amplify and control the DC bias of the modulated signal through the pre-Bias Tee, driver amplifier, and pre-Bias Tee to obtain a more ideal modulator input RF signal V RF (t).

[0052] For the OOK-RZ modulation signals with different duty cycles, the pre-Bias Tee adjusts the DC component added to the input RF signal of the driver amplifier according to the duty cycle of the transmitted OOK-RZ signal, so that the peak-to-peak value of the output RF signal of the driver amplifier is V π , but it will cause the DC component c, the amplified signal s 1 (t) can be expressed as:

[0053]

[0054] The amplified signal s 1 (t) Peak-to-peak value is V π It can increase the modulation depth of the MZM modulator, but the DC component caused will cause the modulator operating point to shift. Therefore, by adjusting the DC component added to the output RF signal of the driver amplifier through the post-Bias Tee, the amplitude of the driving signal input to the MZM modulator is symmetrical about the zero level, thereby eliminating the influence of the DC component on the modulator operating point, making the MZM modulator work stably, thereby improving the extinction ratio of the transmitted optical signal. At this time, the output signal s 2 (t) is the modulator input RF signal V rF (t) can be expressed as:

[0055]

[0056] Step 4: Laser provides a stable light source I in Connected to the optical input of the MZM modulator, the amplified RF signal V RF (t) is connected to the electrical input of the MZM modulator. The MZM modulator works at the orthogonal bias point to complete the modulation of the optical signal and output an optical signal I with a high extinction ratio. out :

[0057]

[0058] Step 5: The optical receiving module uses a high-response APD to receive the transmitted optical signal, converts the optical power signal into a photocurrent and then into an electrical signal, amplifies the received signal through an integrated amplifier circuit, and then samples the analog signal through an ADC according to a set sampling frequency to convert it into a digital signal, which is convenient for subsequent digital signal processing (DSP).

[0059] Step six: The digital signal processing module resamples the digital signal according to the target sampling multiple and matches the digital filter to eliminate the interference of noise on the signal; then selects the appropriate decision threshold according to the signal, compares the received signal sampling value with the set threshold, and obtains a '0', '1' bit sequence; then adopts the digital phase-locked loop method to use the phase detector to determine whether it is ahead or behind, and adjusts the phase by adding and subtracting pulses to achieve bit synchronization, ensuring sampling at the best sampling point; then performs correlation operations based on the frame header information inserted into the transmitted signal to find the position with the largest correlation to achieve frame synchronization, and finally recovers the original information through OOK-RZ decoding based on the duty cycle to complete the demodulation of the information.

[0060] By improving the extinction ratio of the optical signal transmitted by the MZM modulator through the above method, and adopting the OOK-RZ modulation format with a low duty cycle, the sensitivity of the communication system can be effectively improved, the communication distance can be extended, and the reliability of communication can be improved. According to the transmission rate of the specific embodiment, the extinction ratio and duty cycle of the transmitted optical signal, the APD responsivity and shot noise, the system noise analysis, etc., the theoretical receiving sensitivity of the OOK-RZ signal with different duty cycles can be inferred and compared with the experimental results. It is inferred that the theoretical receiving sensitivity of the OOK-RZ signal with different duty cycles can be expressed as:

[0061]

[0062] in,

[0063]

[0064] i 1 (t) and σ 1 (t) are the high-level signal amplitude and noise standard deviation, i 0 (t) and σ 0 (t) are the low-level signal amplitude and noise standard deviation, respectively; D is the duty cycle; ε is the extinction ratio; K is the receiver responsivity; C is the receiver shot noise; T b represents the symbol period of the transmitted signal; N(f) represents the system noise, including signal-related noise and signal-independent noise.

[0065] like Figure 3 As shown in the figure, compared with the NRZ signal, the RZ signal has a bThe high level is only maintained for a period of time τ, and returns to zero level for the rest of the time, reducing the duty cycle of the signal pulse.

[0066] like Figure 4 As shown, the present invention provides a method and system for improving the sensitivity of optical communication. According to the conditions of the communication system, the theoretical receiving sensitivity of OOK-RZ modulation signals with different duty cycles is estimated. When the extinction ratio (13dBm) of the transmitted optical signal is the same, the OOK-RZ modulation signal is used to improve the sensitivity of the system by reducing the duty cycle; at the same time, there is an optimal duty cycle to make the system most sensitive.

[0067] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A system for improving the sensitivity of optical communication, characterized in that: It includes an optical transmitting module, an optical receiving module and a digital signal processing module. The optical transmitting module is used to realize DC balance, dynamically adjust the Bias Tee DC bias according to the input RF signal, so that the peak-to-peak value of the output RF signal is V π And it is symmetrical about the zero level, so that the Mach-Zehnder modulator MZM emits an optical signal with a high extinction ratio; the optical receiving module includes a photodetector APD and an analog-to-digital converter ADC, the APD converts the optical signal emitted by the optical transmitting module into an electrical signal, and converts the analog signal into a digital signal through the ADC; the digital signal processing module is used to recover and demodulate the digital signal to obtain the original information; at the same time, according to the conditions of the optical communication system, the theoretical receiving sensitivity of different duty cycle return-to-zero codes (OOK-RZ) can be inferred.

2. A system for improving optical communication sensitivity as claimed in claim 1, characterized in that: The optical transmission module includes a signal source, a front Bias Tee, a driving amplifier, a rear Bias Tee, a laser and an MZM modulator; wherein the signal source is used to transmit OOK-RZ modulated signals with different duty cycles, and the DC components of the input and output signals of the driving amplifier are adjusted by the front Bias Tee and the rear Bias Tee respectively, so that the peak-to-peak value of the OOK-RZ electrical signals with different duty cycles after passing through the driving amplifier is V π It is symmetrical about the zero level, and modulates the radio frequency signal onto the optical signal through the MZM modulator to obtain a high extinction ratio optical signal; at the same time, the bias control point of the MZM modulator is adjusted to be located at the orthogonal working point to perform linear modulation to keep the peak power of the transmitted optical signal unchanged.

3. A system for improving optical communication sensitivity as claimed in claim 2, characterized in that: The driving amplifier is configured as a linear driving amplifier.

4. A system for improving optical communication sensitivity as claimed in claim 2, characterized in that: The laser arrangement uses a laser having high optical power and narrow line width.

5. A system for improving optical communication sensitivity as claimed in claim 2, characterized in that: The MZM modulator is set to an external modulation mode.

6. A method for using a system for improving optical communication sensitivity as claimed in any one of claims 1 to 5, characterized in that: The following steps are involved: Step 1: The signal source randomly generates an original sequence, adds frame header information and OOK-RZ modulation to the original transmission data, generates a modulated signal with adjustable duty cycle, and sends the modulated signal; Step 2: Use the host computer to control the bias voltage of the MZM modulator so that the modulator works at the orthogonal working point for linear modulation; Step 3: For the OOK-RZ modulation signals with different duty cycles, the Bias Tee input bias voltage is adjusted according to the duty cycle through the front Bias Tee, the driving amplifier, and the rear Bias Tee, so that the amplitude of the OOK-RZ signals with different duty cycles after amplification is V π And it is symmetrical about the zero level; Step 4: The laser is connected to the optical input of the MZM modulator as a light source, and the amplified RF signal is connected to the electrical input of the MZM modulator to complete the modulation of the optical signal and output an optical signal with a high extinction ratio; Step 5: The optical receiving module converts the transmitted optical signal into an electrical signal through APD reception, and converts the analog signal into a digital signal through ADC sampling; Step 6: The digital signal processing module performs pre-processing such as resampling and filtering on the digital signal, and then performs data judgment, bit synchronization, frame synchronization, and decoding to restore the original information.

7. A method for improving the sensitivity of optical communication system as claimed in claim 6, characterized in that: The signal source randomly generates an original sequence, adds frame header information and OOK-RZ modulation to the original transmission data, generates a modulation signal with an adjustable duty cycle and sends the modulated signal. Specifically, the signal source randomly generates an original sequence, adds frame header information and OOK-RZ modulation to the original transmission data, generates a modulation signal with an adjustable duty cycle of 50% and 25%, and sends the modulated signal at a rate of 10Mbps.

8. A method for improving the sensitivity of optical communication system as claimed in claim 7, characterized in that: The OOK-RZ signal is expressed as: s(t)=Ab k p(t-kT b ) Where A represents the peak amplitude of the signal, b k represents the Kth bit, T b Represents the symbol period, kT b represents the start time of the kth bit, and p(t) represents the bit-normalized pulse form.

9. A method for improving the sensitivity of optical communication system as claimed in claim 6, characterized in that: Step 3: For the OOK-RZ modulation signals with different duty cycles, the Bias Tee input bias voltage is adjusted according to the duty cycle through the front Bias Tee, the driving amplifier, and the rear Bias Tee, so that the amplitude of the OOK-RZ signals with different duty cycles after amplification is V π And about zero level symmetry, specifically including, for the OOK-RZ modulation signals with different duty cycles, the front Bias Tee adjusts the DC component added to the input RF signal of the driver amplifier according to the duty cycle of the transmitted OOK-RZ signal, so that the peak-to-peak value of the output RF signal of the driver amplifier is V π The post-Bias Tee adjusts the DC component added to the output RF signal of the driver amplifier to ensure that the amplitude of the driving signal input to the MZM modulator is symmetrical about the zero level.

10. A method for improving the sensitivity of optical communication system according to claim 6, characterized in that: The bias control of the MZM modulator is performed through the host computer so that the modulator works at the orthogonal working point for linear modulation. The working point of the MZM modulator is determined by the modulator bias voltage. Specifically, the bias control is performed based on the pilot method, and a small-amplitude pilot signal is introduced into the DC bias, so that it is input into the modulator together with the RF signal and the DC voltage for modulation, and a part of the output signal is input into the control feedback end to digitally detect the harmonics of the pilot signal and perform feedback compensation.

Images