Large dynamic microwave photon coherent link based on polarization multiplexing

Abstract

The invention relates to the technical field of microwave photons, and provides a large dynamic microwave photon coherent link based on polarization multiplexing, which comprises a light emitting end part, a light amplification link part and a light receiving end part which are sequentially connected through polarization maintaining optical fibers, the light transmitting end part is provided with a radio frequency input port, and the light receiving end part is provided with a radio frequency output port; the optical transmitting end part is used for performing microwave processing and modulation on an input radio frequency signal and transmitting an obtained optical signal to the optical amplification link part; the optical amplification link part is used for performing polarization-maintaining amplification on the optical carrier radio frequency signal and transmitting the optical carrier radio frequency signal to the optical receiving end part; and the optical receiving end part is used for demodulating the optical signal after polarization-maintaining amplification, restoring a radio-frequency signal and outputting the radio-frequency signal. According to the invention, a coherent light scheme is introduced to improve the link dynamic range, and the problem that a stable signal transmission system is difficult to realize by a current coherent microwave photon link can be solved.

Description

Technical Field

[0001] This invention relates to the field of microwave photonics technology, and more specifically, to a large dynamic microwave photonic coherent link based on polarization multiplexing. Background Technology

[0002] Microwave photonic links are a method of transmitting radio frequency (RF) signals over long distances by loading RF signals onto optical signals. They are the core of optical domain processing and transmission of RF signals and have wide applications in radar, communications, and electronic warfare. The core performance indicators of microwave photonic links include link gain, noise factor (NF), and spurious-free dynamic range (SFDR). Among these, SFDR is particularly critical, directly determining the system's ability to detect weak signals under strong interference.

[0003] Existing technologies for implementing microwave photonic links are mainly divided into two categories: incoherent and coherent links. Incoherent microwave photonic links primarily utilize intensity modulation and direct detection, offering advantages such as simple principles, small size, and low cost. However, their core performance is affected by factors such as modulator nonlinearity, laser relative intensity noise, and detector shot noise, making further optimization of the dynamic range difficult. Coherent microwave photonic link schemes, on the other hand, can utilize external modulation techniques and balanced detection methods to suppress common-mode noise and improve linearity, effectively enhancing the dynamic range of the microwave photonic link. However, coherent microwave photonic links require the simultaneous transmission of signal light and local oscillator light while maintaining their phase correlation characteristics. Due to the diverse types and complex composition of components, achieving a stable signal transmission system is challenging. Therefore, adopting an integrated approach to realize coherent microwave photonic links has become a consensus in the development of microwave photonics technology. Summary of the Invention

[0004] Link dynamic range is a core performance indicator of microwave photonic links. Current incoherent solutions are limited by system noise and power consumption, making it difficult to improve the link dynamic range. This invention provides a large dynamic range coherent microwave photonic link based on polarization multiplexing, introducing a coherent optical scheme to improve the link dynamic range and solve the problem that current coherent microwave photonic links struggle to achieve stable signal transmission systems.

[0005] The present invention provides a large dynamic range microwave photonic coherent link based on polarization multiplexing, comprising an optical transmitter section, an optical amplification link section, and an optical receiver section connected sequentially by polarization-maintaining optical fibers; the optical transmitter section has an RF input port, and the optical receiver section has an RF output port; The optical transmitter section is used to process and modulate the input radio frequency signal through microwave, and transmit the resulting optical signal to the optical amplification link section; The optical amplification link section is used to amplify the optical radio frequency signal while maintaining polarity and transmit it to the optical receiving end section. The optical receiver section is used to demodulate the polarization-maintaining amplified optical signal, restore the radio frequency signal, and output it.

[0006] In a preferred embodiment, the optical emitting end portion includes a microwave preprocessing portion, a laser, an emitting end modulation chip, and an emitting end control circuit; The transmitter modulation chip has ports including an optical input port, an optical output port, an RF input port, a low-frequency input port, and a low-frequency output port. The input port of the microwave preprocessing section is connected to the RF input port of the transmitter modulation chip, the output port of the microwave preprocessing section is connected to the RF input port of the transmitter modulation chip, and the output port of the transmitter control circuit is connected to the low-frequency input port of the transmitter modulation chip. The output port of the laser is connected to the optical input port of the transmitter modulation chip via a lens group, and the low-frequency output port of the transmitter modulation chip is connected to the input port of the transmitter control circuit. The optical output interface of the transmitter modulation chip is connected to the input port of the optical amplification link section.

[0007] In a preferred embodiment, the transmitter modulation chip is implemented as a single chip and includes a polarization-maintaining beam splitter, an MZM modulation region, an optical coupler, a photodetector, an adjustable attenuator, and a polarization beam combiner. The optical input port of the transmitter modulation chip is connected to the input port of the polarization-maintaining beam splitter. The polarization-maintaining beam splitter includes two output ports. One output port is connected to the optical input port of the MZM modulation region, and the output port of the MZM modulation region is connected to the input port of the optical coupler. One output port of the optical coupler is connected to the input port of the photodetector. The other output port of the optical coupler is connected to the input port of the polarization combiner. The other optical output port of the polarization-maintaining beam splitter is connected to the input port of the adjustable attenuator, and the output port of the adjustable attenuator is connected to the other input port of the polarization combiner. The output port of the photodetector is connected to the input port of the transmitter control circuit.

[0008] In a preferred embodiment, the transmitter control circuit is used to control the phase difference between the two arms of the MZM modulation region to be 180°.

[0009] In a preferred embodiment, the transmitter control circuit includes a first analog-to-digital converter, a first processor, and a first digital-to-analog converter; the input port of the first analog-to-digital converter is connected to the low-frequency output port of the transmitter modulation chip, and the output port of the first digital-to-analog converter is connected to the low-frequency input port of the transmitter modulation chip.

[0010] In a preferred embodiment, the function of the polarization combiner is to combine two optical signals, namely the local oscillator optical signal and the optical radio frequency signal, with one optical signal in TE mode and the other optical signal in TM mode.

[0011] In a preferred embodiment, the optical amplification link employs a dual polarization-maintaining amplifier to achieve synchronous amplification of optical signals in two polarization states, TE mode and TM mode, with consistent amplification factors.

[0012] In a preferred embodiment, the optical receiver portion includes a phase-shift optical mixer chip, a balanced detector, a microwave coupler, an output microwave channel, and a receiver control circuit. The phase-shift optical mixer chip includes one optical input port, two optical output ports, and one electrical input port; the balanced detector includes two optical input ports and one electrical output port; the microwave coupler includes one input port and two output ports; the input port of the optical receiver is directly connected to the optical input port of the phase-shift optical mixer chip; the two optical output ports of the phase-shift optical mixer chip are connected to the two optical input ports of the balanced detector; the electrical output port of the balanced detector is connected to the input port of the microwave coupler; one output port of the microwave coupler is connected to the input port of the receiver control circuit, and the other output port is connected to the input port of the output microwave channel; the output port of the receiver control circuit is connected to the electrical input port of the phase-shift optical mixer chip.

[0013] In a preferred embodiment, the phase-shifting optical mixer chip includes a polarization beam splitter, a phase modulator, and a 180° optical mixer; The polarization beamsplitter includes one optical input port and two optical output ports; the phase modulator includes one optical input port, one optical output port, and one electrical input port; the 180° optical mixer includes two optical input ports and two optical output ports; the optical input port of the phase-shift optical mixer chip is directly connected to the optical input port of the polarization beamsplitter; one optical output port of the polarization beamsplitter is connected to the optical input port of the phase modulator, and the other optical output port is connected to one optical input port of the 180° optical mixer; the other optical input port of the 180° optical mixer is connected to the optical output port of the phase modulator; the electrical input port of the phase-shift optical mixer chip is directly connected to the electrical input port of the phase modulator, and the two optical output ports of the phase-shift optical mixer chip are directly connected to the two optical output ports of the 180° optical mixer.

[0014] In a preferred embodiment, the receiver control circuit includes a second analog-to-digital converter, a second processor, and a second digital-to-analog converter. The input port of the second analog-to-digital converter is connected to the lower power output port of the microwave coupler, and the output port of the second digital-to-analog converter is connected to the electrical input port of the phase-shift optical mixer chip.

[0015] In summary, this invention introduces a coherent optical scheme to improve the dynamic range of the link and can solve the problem that current coherent microwave photonic links are difficult to achieve a stable signal transmission system. The specific beneficial effects are as follows: 1. This invention utilizes a balanced detector to eliminate common-mode noise and improve the dynamic range of the link.

[0016] 2. The MZM modulation region of the transmitter modulation chip of the present invention can operate at the minimum operating point, reducing the signal optical power. Combined with the splitting ratio adjustment of the polarization maintaining beam splitter, the link optical power and the power consumption of the optical amplifier can be significantly reduced.

[0017] 3. This invention utilizes polarization beam combiners and polarization beam splitters to achieve non-interference transmission and amplification of optical signals of the same wavelength in the same optical fiber, preventing optical phase changes introduced by optical link transmission.

[0018] 4. This invention utilizes a feedback control circuit to introduce a 1kHz low-frequency signal, thereby enabling real-time monitoring and feedback control of the phase difference between the input modulator operating point and the output optical path without interfering with the radio frequency signal transmission. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a large dynamic microwave photonic coherent link based on polarization multiplexing, provided as an embodiment of the present invention.

[0020] Figure 2 This is a schematic diagram of the structure of the light emitting end portion in an embodiment of the present invention.

[0021] Figure 3 This is a simulation diagram of the second harmonic and the first harmonic in an embodiment of the present invention.

[0022] Figure 4 This is a schematic diagram of the optical receiver portion in an embodiment of the present invention.

[0023] Figure 5 This is a simulation diagram of the phase difference between the two arms of the MZM modulation region in an embodiment of the present invention.

[0024] Figure 6 This is a control flowchart of the transmitter control circuit in an embodiment of the present invention.

[0025] Figure 7 This is a graph showing the trend of microwave signal-to-noise ratio at the output of the dual polarization-maintaining amplifier in an embodiment of the present invention.

[0026] Figure 8 This is a simulation diagram of the phase difference between the local oscillator optical signal and the optical radio frequency signal in an embodiment of the present invention. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0028] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0029] Example like Figure 1 As shown, this embodiment of the invention provides a large dynamic range microwave photonic coherent link based on polarization multiplexing, including an optical transmitter section, an optical amplification link section, and an optical receiver section connected sequentially by polarization-maintaining optical fibers; the optical transmitter section has an RF input port, and the optical receiver section has an RF output port.

[0030] The optical transmitter section is used to process and modulate the input radio frequency signal through microwave, and transmit the resulting optical signal to the optical amplification link section; The optical amplification link section is used to amplify the optical radio frequency signal while maintaining polarity and transmit it to the optical receiving end section. The optical receiver section is used to demodulate the polarization-maintaining amplified optical signal, restore the radio frequency signal, and output it.

[0031] like Figure 2 As shown, the optical transmitter section includes a microwave preprocessing section, a laser, a transmitter modulation chip, and a transmitter control circuit.

[0032] The transmitter modulation chip includes the following ports: an optical input port, an optical output port, an RF input port, a low-frequency input port, and a low-frequency output port. The input port of the microwave preprocessing section is connected to the RF input port of the transmitter modulation chip (or directly serves as the RF input port of the transmitter modulation chip). The output port of the microwave preprocessing section is connected to the RF input port of the transmitter modulation chip. The output port of the transmitter control circuit is connected to the low-frequency input port of the transmitter modulation chip. The output port of the laser is connected to the optical input port of the transmitter modulation chip via a lens assembly (LENS). The low-frequency output port of the transmitter modulation chip is connected to the input port of the transmitter control circuit. The optical output interface of the transmitter modulation chip is connected to the input port of the optical amplification link section.

[0033] The light signal emitted by the laser is shaped by the lens group and then enters the optical input port of the transmitter modulation chip. After being modulated by the transmitter modulation chip, it is output to the optical amplification link from the optical output port of the transmitter modulation chip.

[0034] The input radio frequency (RF) signal is preprocessed by the microwave preprocessing section before entering the transmitter modulation chip, which then uses the preprocessed RF signal to modulate an optical signal. The microwave preprocessing section performs functions including microwave amplification, passband filtering, gain control, and phase control.

[0035] The transmitter modulation chip is implemented as a single chip, and its chip materials include thin-film lithium niobate, lithium tantalate, etc. The internal functional units of the transmitter modulation chip include a polarization-maintaining beam splitter, an MZM modulation region (Mach-Zehnder Modulator), an optical coupler, a photodiode detector (PD), an adjustable attenuator, and a polarization combiner.

[0036] The interconnection relationships of the functional units within the transmitter modulation chip are as follows: the optical input port of the transmitter modulation chip is connected to the input port of the polarization-maintaining beam splitter. The polarization-maintaining beam splitter includes two output ports, one of which is connected to the optical input port of the MZM modulation region, and the output port of the MZM modulation region is connected to the input port of the optical coupler. One output port of the optical coupler (usually a low-coupling-efficiency port) is connected to the input port of the photodetector. The other output port of the optical coupler is connected to the input port of the polarization combiner. The other optical output port of the polarization-maintaining beam splitter is connected to the input port of the adjustable attenuator, and the output port of the adjustable attenuator is connected to the other input port of the polarization combiner. The output port of the photodetector is connected to the input port of the transmitter control circuit.

[0037] The signal flow relationship among the components of the transmitter modulation chip is as follows: the optical signal received by the transmitter modulation chip is split into two paths by the polarization-maintaining beam splitter. One optical signal (local oscillator signal) enters the polarization combiner through the adjustable attenuator, where the gain of the electro-optic conversion is controlled by the adjustable attenuator. The other optical signal is converted into an optical radio frequency signal by the MZM modulation region. The optical radio frequency signal is split into two paths again by the optical coupler. One optical radio frequency signal enters the polarization combiner and is polarized and combined with the local oscillator signal. The combined beam is output to the input port of the optical amplification link section. The other optical radio frequency signal is converted into an electrical signal by the photodetector and then input to the transmitter control circuit for detecting the working status of the MZM modulation region.

[0038] The function of the polarization combiner is to combine two optical signals, namely the local oscillator optical signal and the optical radio frequency signal, with one optical signal in TE mode and the other in TM mode.

[0039] The MZM modulation region includes an RF modulation electrode and a DC modulation electrode. The RF modulation electrode is connected to the RF input port of the transmitter modulation chip, and the DC modulation electrode is connected to the low-frequency input port of the transmitter modulation chip. The pre-processed RF signal is loaded onto the optical signal through the RF modulation electrode; the DC signal and pilot signal from the transmitter control circuit are used to control the modulation operating point and modulate the pilot signal through the DC modulation electrode.

[0040] The transmitter control circuit includes a first analog-to-digital converter (ADC), a first processor (MCU), and a first digital-to-analog converter (DAC). The input port of the first ADC is connected to the low-frequency output port of the transmitter modulation chip, and the output port of the first DAC is connected to the low-frequency input port of the transmitter modulation chip. The electrical signal from the photodetector of the transmitter modulation chip is converted into a digital signal by the first ADC, then processed and analyzed by the first processor to generate an output signal. The output signal is converted into an analog signal by the first DAC and connected to the DC modulation electrode of the MZM modulation region of the transmitter modulation chip. The output signal includes a DC signal and a pilot signal, thereby controlling the operating state of the DC modulation electrode of the MZM modulation region.

[0041] The above solution requires stabilizing the operating point of the MZM modulation region at its minimum operating point, i.e., a 180° phase difference between the two arms. The function of the transmitter control circuit is to monitor the operating point of the transmitter modulation chip in real time and adjust the MZM bias voltage via a DC signal to stabilize the operating point position.

[0042] The specific implementation method of its software logic is as follows: (1) The transmitter control circuit continuously superimposes a small signal (AC signal) of x kHz on the DC modulation electrode of the MZM modulation region. This small signal will also be modulated on the optical carrier. Therefore, the optical carrier radio frequency signal output by the MZM will contain a pilot signal of x kHz and a harmonic component of 2x kHz. (2) The optical radio frequency signal output from the MZM modulation region is split and detected, and then converted into a digital signal by the first analog-to-digital converter. The digital signal enters the first processor for fast Fourier transform processing to extract the amplitude of the x kHz and 2x kHz signal components. (3) Calculate the amplitude ratio of the second harmonic to the first harmonic component, and use this to determine the current operating point; Figure 3 It can be seen that the amplitude ratio will increase rapidly near the minimum operating point; (4) After confirming the current working point, adjust the DC signal output by the first digital-to-analog converter accordingly to ensure that the working point of the MZM modulation area is near the minimum working point.

[0043] The optical amplification link employs a dual polarization-maintaining amplifier to achieve synchronous amplification of optical signals in two polarization states, TE mode and TM mode, with consistent amplification factors, thereby enabling gain control of coherent microwave photons.

[0044] like Figure 4 As shown, the optical receiver section includes a phase-shift optical mixer chip, a balanced detector, a microwave coupler, an output microwave channel, and a receiver control circuit.

[0045] The phase-shift optical mixer chip includes one optical input port, two optical output ports, and one electrical input port; the balanced detector includes two optical input ports and one electrical output port; the microwave coupler includes one input port and two output ports. The input port of the optical receiver is directly connected to the optical input port of the phase-shift optical mixer chip; the two optical output ports of the phase-shift optical mixer chip are connected to the two optical input ports of the balanced detector; the electrical output port of the balanced detector is connected to the input port of the microwave coupler; one output port of the microwave coupler is connected to the input port of the receiver control circuit, and the other output port is connected to the input port of the output microwave channel; the output port of the receiver control circuit is connected to the electrical input port of the phase-shift optical mixer chip.

[0046] The optical signal received by the optical receiver is processed by the phase-shift optical mixer chip and then converted into an electrical signal by a balanced detector. The electrical signal generated by the balanced detector is split into two paths by a microwave coupler: one path, with lower power (e.g., 1 / 100), enters the receiver control circuit to monitor the output RF power of the microwave photonic link. Simultaneously, the receiver control circuit identifies and processes this signal to generate a corresponding modulation signal, which is then input into the phase-shift optical mixer chip for optical phase modulation. The other path, with higher power, enters the output microwave channel for signal output.

[0047] The functions of the output microwave channel include microwave amplification, passband filtering, gain control, and phase control.

[0048] The phase-shifting optical mixer chip is implemented as a single chip, and its chip materials include thin-film lithium niobate, lithium tantalate, etc. Its internal components include a polarization beam splitter, a phase modulator, and a 180° optical mixer.

[0049] The interconnections between the components within the phase-shift optical mixer chip are as follows: the polarization beamsplitter includes one optical input port and two optical output ports; the phase modulator includes one optical input port, one optical output port, and one electrical input port; and the 180° optical mixer includes two optical input ports and two optical output ports. The optical input port of the phase-shift optical mixer chip is directly connected to the optical input port of the polarization beamsplitter. One optical output port of the polarization beamsplitter is connected to the optical input port of the phase modulator, and the other optical output port is connected to one optical input port of the 180° optical mixer. The other optical input port of the 180° optical mixer is connected to the optical output port of the phase modulator. The electrical input port of the phase-shift optical mixer chip is directly connected to the electrical input port of the phase modulator, and the two optical output ports of the phase-shift optical mixer chip are directly connected to the two optical output ports of the 180° optical mixer.

[0050] The signal flow relationship inside the phase-shift optical mixer chip is as follows: the optical signal received by the phase-shift optical mixer chip is split into two paths by the polarization beam splitter: one optical signal directly enters the 180° mixer; the other optical signal, after phase correction by the phase modulator, also enters the 180° optical mixer; the two optical signals are mixed in the 180° optical mixer to form two mixed optical outputs to the balanced detector; wherein the phase modulator is controlled by the receiver control circuit to achieve optical phase control.

[0051] The receiver control circuit includes a second analog-to-digital converter (ADC), a second processor (MCU), and a second digital-to-analog converter (DAC). The input port of the second ADC is connected to the lower power output port of the microwave coupler, and the output port of the second ADC is connected to the electrical input port of the phase-shift optical mixer chip. A small portion of the electrical signal output from the balanced detector is split off by the microwave coupler and enters the receiver control circuit for processing, thereby generating a modulation signal, which is then output to the phase modulator of the phase-shift optical mixer chip. The function of the receiver control circuit is to stabilize the phase difference between the local oscillator signal and the optical radio frequency signal at 90°. Under a 90° phase difference, both the DC and AC signals output by the balanced detector can reach their maximum values.

[0052] The operating logic of the receiving end control circuit is as follows: it receives the optical signal output by the microwave coupler through the second analog-to-digital converter, and after the second processor performs control and judgment, it controls the phase modulator in the phase-shifting optical mixer chip through the output of the second digital-to-analog converter to realize the optical phase change, so that the signal power received by the second analog-to-digital converter reaches and stabilizes at the maximum value.

[0053] Application Examples The microwave photonic link includes an optical transmitter section, an optical amplification link section, and an optical receiver section.

[0054] The optical transmitter section includes a microwave preprocessing unit, a laser, a transmitter modulation chip, and a transmitter control circuit. The light emitted by the laser is rectified by a lens group and then enters the transmitter modulation chip, where it is modulated before entering the optical amplification link. The input radio frequency (RF) signal is processed by the microwave preprocessing unit and then enters the transmitter modulation chip, where the RF signal is loaded onto the optical carrier and enters the optical transmission link.

[0055] The transmitter modulation chip is implemented using monolithic integration. Its internal functional units include: polarization-maintaining beam splitter, MZM modulation region, optical coupler, photodetector, adjustable attenuator and polarization beam combiner, which can realize electro-optic modulation and optical signal processing functions.

[0056] In the optical transmitter section, the TE mode optical signal emitted by the laser is shaped by the lens group and enters the polarization-maintaining beam splitter built into the transmitter modulation chip. It is split into two TE mode optical signals: one of them is used as the local oscillator optical signal and enters the polarization combiner after passing through the adjustable attenuator; the other enters the MZM modulation region, and after electro-optic modulation, it becomes an optical radio frequency signal, which also enters the polarization combiner.

[0057] The function of a polarization combiner is to convert one of two input TE-mode optical signals into TM-mode signals through polarization rotation, and then combine the two optical signals into a single beam (containing both TE and TM modes). In this example, after receiving a local oscillator optical signal and an optical carrier RF signal, both in TE mode, the polarization combiner converts the local oscillator optical signal into TM-mode signals and combines the two optical signals into a single output beam. This allows the two optical signals of the same wavelength to propagate in the same waveguide without interference, while also ensuring the phase consistency of the local oscillator optical signal and the optical carrier RF signal in the transmission link.

[0058] The electro-optic modulation function of the optical transmitter is jointly implemented by the transmitter modulation chip and the transmitter control circuit. The MZM modulation region has a Mach-Zehnder structure and includes RF modulation electrodes and DC modulation electrodes. The RF modulation electrodes contain amplified and processed radio frequency signals, carrying the information to be transmitted. The DC modulation electrodes contain DC signals (bias voltage) and AC signals (low-frequency modulation), both of which originate from the transmitter control circuit. The DC signal is used to adjust the operating point of the MZM modulation region, and the AC signal is used for real-time monitoring of the operating point.

[0059] The selection of the operating point of the MZM modulation region has a significant impact on link performance. Simulations were performed on the phase difference between the two arms of the MZM modulation region with a fixed polarization beam splitter splitting ratio of 1:1. Figure 5As shown, when the phase difference between the two arms of the MZM modulation region is ±180°, the output optical power of the modulation region is at its minimum, and the microwave photonic link can achieve its maximum gain.

[0060] like Figure 6 As shown, the function of the transmitter control circuit is to transmit a pilot signal (e.g., 1kHz) through the first digital-to-analog converter, then detect the pilot signal output by the photodetector through the first analog-to-digital converter, extract the amplitudes of the 1kHz and 2kHz frequency components based on the processor, and modulate them in the MZM modulation area through the DC modulation electrode, and calculate the ratio of the two to obtain the current operating point position. The optical signal output from the optical transmitter enters the optical amplification link section for transmission and amplification. This section employs a dual polarization-maintaining amplifier, enabling synchronous amplification of TE and TM mode optical signals. The optical signal output from the optical amplification link section then enters the optical receiver section.

[0061] The function of the optical receiver is to perform photoelectric conversion on the input optical radio frequency signal to extract the radio frequency signal. The optical receiver includes a phase-shift optical mixer chip, a balanced detector, a microwave coupler, a receiver control circuit, and an output microwave channel. Among them, the phase-shift optical mixer chip includes a polarization beam splitter, a phase modulator, and a 180° optical mixer.

[0062] The optical signal received at the optical receiver is a combined optical signal of the same wavelength, including a TE-mode optical carrier radio frequency signal and a TM-mode local oscillator signal. This combined optical signal is split into two paths by a polarization beamsplitter. One path is phase-modulated by a phase modulator, and the two paths then enter a 180° optical mixer together. The two outputs of the 180° optical mixer are directly connected to the two inputs of a balanced detector. The function of the balanced detector is to achieve photoelectric conversion, while simultaneously eliminating common-mode noise in the link and improving the dynamic range of the link.

[0063] The polarization-maintaining beam splitter of the phase-shifting optical mixer chip does not have an equal splitting ratio; it can be 10:1, 100:1, 1000:1, etc. In the simulation, the output optical power of the dual polarization-maintaining amplifier was fixed at 15dBm, and the splitting ratio of the polarization-maintaining beam splitter was adjusted to obtain the trend of the output microwave signal-to-noise ratio as shown below. Figure 7 As shown, optimizing the polarization-maintaining beam splitter ratio is key to effectively improving link performance.

[0064] Figure 7 In the graph, the horizontal axis represents the logarithm of the refraction ratio, with values ​​ranging from 0 to 3, corresponding to a refraction ratio increase from 1:1 to 1000:1. Figure 7 As can be seen, with the increase of the splitting ratio, that is, the increase of the energy proportion of the modulation branch, the link signal-to-noise ratio increases significantly under the same dual polarization-maintaining amplifier power. The adjusted link signal-to-noise ratio can be improved by more than 20dB.

[0065] The phase difference between the two optical signals in the 180° optical mixer of the input phase-shift optical mixer chip will affect the link performance. Simulations will be performed to analyze this. Figure 8 As shown, when the phase difference between the local oscillator optical signal and the optical carrier radio frequency signal is ±90°, the link gain reaches its maximum, and at this time, the signal amplitude output by the balanced detector can reach its maximum.

[0066] Therefore, the function of the receiver control circuit is to monitor and control the phase difference between the local oscillator signal and the optical radio frequency signal, so that the signal amplitude output by the balanced detector can reach its maximum. Specifically, an internal second analog-to-digital converter receives a small portion of the signal from the microwave coupler, and this second digital-to-analog converter adjusts the optical phase of the phase modulator in the phase-shifting optical mixer chip, thereby maximizing the output radio frequency signal and improving the dynamics of the microwave photonic link.

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A large dynamic range microwave photonic coherent link based on polarization multiplexing, characterized in that, It includes an optical transmitter section, an optical amplification link section, and an optical receiver section connected in sequence via polarization-maintaining optical fibers; the optical transmitter section has an RF input port, and the optical receiver section has an RF output port; The optical transmitter section is used to process and modulate the input radio frequency signal through microwave, and transmit the resulting optical signal to the optical amplification link section; The optical amplification link section is used to amplify the optical radio frequency signal while maintaining polarity and transmit it to the optical receiving end section. The optical receiver section is used to demodulate the polarization-maintaining amplified optical signal, restore the radio frequency signal, and output it.

2. The large dynamic range microwave photonic coherent link based on polarization multiplexing according to claim 1, characterized in that, The optical transmitter section includes a microwave preprocessing section, a laser, a transmitter modulation chip, and a transmitter control circuit. The transmitter modulation chip has ports including an optical input port, an optical output port, an RF input port, a low-frequency input port, and a low-frequency output port. The input port of the microwave preprocessing section is connected to the RF input port of the optical transmitter section, the output port of the microwave preprocessing section is connected to the RF input port of the transmitter modulation chip, and the output port of the transmitter control circuit is connected to the low-frequency input port of the transmitter modulation chip. The output port of the laser is connected to the optical input port of the transmitter modulation chip via a lens group, and the low-frequency output port of the transmitter modulation chip is connected to the input port of the transmitter control circuit. The optical output interface of the transmitter modulation chip is connected to the input port of the optical amplification link section.

3. The large dynamic range microwave photonic coherent link based on polarization multiplexing according to claim 2, characterized in that, The transmitter modulation chip is implemented in a single-chip manner, including a polarization-maintaining beam splitter, an MZM modulation region, an optical coupler, a photodetector, an adjustable attenuator, and a polarization beam combiner. The optical input port of the transmitter modulation chip is connected to the input port of the polarization-maintaining beam splitter. The polarization-maintaining beam splitter includes two output ports. One output port is connected to the optical input port of the MZM modulation region, and the output port of the MZM modulation region is connected to the input port of the optical coupler. One output port of the optical coupler is connected to the input port of the photodetector. The other output port of the optical coupler is connected to the input port of the polarization combiner. The other optical output port of the polarization-maintaining beam splitter is connected to the input port of the adjustable attenuator, and the output port of the adjustable attenuator is connected to the other input port of the polarization combiner. The output port of the photodetector is connected to the input port of the transmitter control circuit.

4. The large dynamic range microwave photonic coherent link based on polarization multiplexing according to claim 3, characterized in that, The transmitter control circuit is used to control the phase difference between the two arms of the MZM modulation region to be 180°.

5. The large dynamic range microwave photonic coherent link based on polarization multiplexing according to claim 2, characterized in that, The transmitter control circuit includes a first analog-to-digital converter, a first processor, and a first digital-to-analog converter; the input port of the first analog-to-digital converter is connected to the low-frequency output port of the transmitter modulation chip, and the output port of the first digital-to-analog converter is connected to the low-frequency input port of the transmitter modulation chip.

6. The large dynamic range microwave photonic coherent link based on polarization multiplexing according to claim 2, characterized in that, The function of the polarization combiner is to combine two optical signals, namely the local oscillator optical signal and the optical radio frequency signal, with one optical signal in TE mode and the other in TM mode.

7. The large dynamic range microwave photonic coherent link based on polarization multiplexing according to claim 5, characterized in that, The optical amplification link uses a dual polarization-maintaining amplifier to synchronously amplify optical signals in both TE and TM polarization states, with the same amplification factor.

8. The large dynamic range microwave photonic coherent link based on polarization multiplexing according to claim 1, characterized in that, The optical receiver section includes a phase-shift optical mixer chip, a balanced detector, a microwave coupler, an output microwave channel, and a receiver control circuit. The phase-shift optical mixer chip includes one optical input port, two optical output ports, and one electrical input port; the balanced detector includes two optical input ports and one electrical output port; the microwave coupler includes one input port and two output ports; the input port of the optical receiver is directly connected to the optical input port of the phase-shift optical mixer chip; the two optical output ports of the phase-shift optical mixer chip are connected to the two optical input ports of the balanced detector; the electrical output port of the balanced detector is connected to the input port of the microwave coupler; one output port of the microwave coupler is connected to the input port of the receiver control circuit, and the other output port is connected to the input port of the output microwave channel; the output port of the receiver control circuit is connected to the electrical input port of the phase-shift optical mixer chip.

9. The large dynamic range microwave photonic coherent link based on polarization multiplexing according to claim 8, characterized in that, The phase-shifting optical mixer chip includes a polarization beam splitter, a phase modulator, and a 180° optical mixer. The polarization beamsplitter includes one optical input port and two optical output ports; the phase modulator includes one optical input port, one optical output port, and one electrical input port; the 180° optical mixer includes two optical input ports and two optical output ports; the optical input port of the phase-shift optical mixer chip is directly connected to the optical input port of the polarization beamsplitter; one optical output port of the polarization beamsplitter is connected to the optical input port of the phase modulator, and the other optical output port is connected to one optical input port of the 180° optical mixer; the other optical input port of the 180° optical mixer is connected to the optical output port of the phase modulator; the electrical input port of the phase-shift optical mixer chip is directly connected to the electrical input port of the phase modulator, and the two optical output ports of the phase-shift optical mixer chip are directly connected to the two optical output ports of the 180° optical mixer.

10. The large dynamic range microwave photonic coherent link based on polarization multiplexing according to claim 8, characterized in that, The receiver control circuit includes a second analog-to-digital converter, a second processor, and a second digital-to-analog converter. The input port of the second analog-to-digital converter is connected to the lower power output port of the microwave coupler, and the output port of the second digital-to-analog converter is connected to the electrical input port of the phase-shift optical mixer chip.

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