阅读说明：本技术 基于Sagnac环和I/Q探测的全光微波频移相移装置及测量方法 (All-optical microwave frequency shift phase shift device based on Sagnac loop and I/Q detection and measuring method ) 是由 高永胜 康博超 徐源皓 谭庆贵 贺丰收 樊养余 刘准钆 于 2020-11-29 设计创作，主要内容包括：本发明提供了一种基于Sagnac环和I/Q探测的全光微波频移相移装置,从激光源输出的光信号通过光耦合器注入到DE-MZM中,DE-MZM的偏置点通过直流偏压进行控制；光耦合器的输出的光信号通过EDFA将光信号放大后,再通过DWDM分离出上边带和下边带,上边带和下边带各自构成一路光信号,两路光信号各自进入一个PD的输入端,光电探测后得到光电流,光电流携带的多普勒频移信息或相位信息通过后端ADC处理。本发明实现信号的频率和相位测量,结构简单,具有很强的可操作性；采用对称度高的调制器、精准的偏压控制来提高测量系统的稳定性和精确性,实现高精度且稳定的宽带微波光子测量系统。(The invention provides an all-optical microwave frequency shift phase shift device based on a Sagnac ring and I/Q detection, wherein an optical signal output from a laser source is injected into a DE-MZM through an optical coupler, and the bias point of the DE-MZM is controlled through direct current bias voltage; an optical signal output by the optical coupler is amplified by the EDFA, an upper sideband and a lower sideband are separated by DWDM, the upper sideband and the lower sideband respectively form one path of optical signal, the two paths of optical signals respectively enter an input end of a PD, a photocurrent is obtained after photoelectric detection, and Doppler frequency shift information or phase information carried by the photocurrent is processed by the rear-end ADC. The invention realizes the frequency and phase measurement of signals, has simple structure and strong operability; the high-symmetry modulator and the accurate bias control are adopted to improve the stability and the accuracy of the measuring system, and the high-accuracy and stable broadband microwave photon measuring system is realized.)

1. An all-optical microwave frequency shift phase shift device based on Sagnac ring and I/Q detection comprises a laser source, a DE-MZM, an optical coupler, a lug-doped fiber amplifier, a two-channel dense wavelength division multiplexer, two photodetectors and an analog-to-digital converter, and is characterized in that:

according to the all-optical microwave frequency shift phase shift device based on the Sagnac ring and I/Q detection, an optical output end of a laser source is connected with a port 1 of an optical coupler, a port 3 of the optical coupler is connected with an optical input port of a DE-MZM, a port 4 of the optical coupler is connected with an optical output port of the DE-MZM, a port 2 of the optical coupler is connected with an EDFA input port, an output optical signal of a port 3 of the coupler is injected into the port 4 of the coupler through the DE-MZM, an output optical signal of the port 4 of the coupler is injected into the port 3 of the coupler through the DE-MZM, a Sagnac loop is formed, an output port of the EDFA is connected with a common input port of a dual-channel DWDM, two output; the local oscillator signal is connected to one radio frequency port of the DE-MZM, and the radio frequency signal to be tested is connected to the other radio frequency port of the DE-MZM;

injecting an optical signal output from a laser source into the DE-MZM through an optical coupler, wherein the bias point of the DE-MZM is controlled through direct current bias; an optical signal output by a port 2 of the optical coupler is amplified by an EDFA, an upper sideband and a lower sideband are separated by DWDM, the upper sideband and the lower sideband respectively form one path of optical signal, the two paths of optical signals respectively enter an input end of a PD, a photocurrent is obtained after photoelectric detection, and Doppler frequency shift information or phase information carried by the photocurrent is processed by a rear-end ADC.

2. A measurement method using the Sagnac loop and I/Q detection based all-optical microwave frequency-shift phase-shift device of claim 1, characterized by comprising the following steps:

defining the optical signal, the local oscillator signal and the signal to be measured output by the laser source as follows:

E(t)＝E₀exp(j2πf_ct) (1)

E_Lo(t)＝V_Losin(2πf_Lot) (2)

wherein E₀Electric field amplitude, f, of the light signal output for a laser source_cIs the frequency, V, of the optical signal_LoIs the amplitude of the local oscillator signal, f_LoIs the frequency, V, of the local oscillator signal_RFIs the amplitude of the signal to be measured, f_RFIs the frequency of the signal to be measured,the phase of the signal to be measured; the optical signal after being output and modulated by the DE-MZM is as follows:

wherein alpha is_MFor the insertion loss, V, of DE-MZM_πIs the half-wave voltage of the modulator, theta is the phase difference introduced by the dc bias of the DE-MZM, on the other hand, another optical carrier outputted from the optical coupler port 4 is injected into the output port of the DE-MZM, and the optical signal passes through the Sagnac loop, and is combined with the optical signal outputted from the DE-MZM in the optical coupler, and is outputted from the optical coupler port 2, and the expression is:

wherein, J_±n(. is) isA first class of bezier functions of order + -n,andfor modulating index, the optical signal output by the coupler port 4 is subjected to power amplification through an EDFA, and the amplified optical signal is injected into a dual-channel DWDM; adjusting the central wavelength of the optical carrier to enable the optical carrier to be positioned between two channels of DWDM, thereby separating the upper and lower sidebands of the optical signal into two optical channels; the optical signals output by the two optical channels are respectively expressed as:

wherein beta is_EAnd alpha_DRespectively representing the gain of the EDFA and the insertion loss of the DWDM;

after photoelectric detection, the output photocurrent of the Photodiode (PD) in each channel is respectively expressed as:

setting theta to 45 degrees by adjusting the DC bias of the DE-MZM; the photocurrent after photodetection is expressed as:

when applied to Doppler shift measurement, the Doppler shift of the echo signal to be measured is denoted as f_d＝f_LO-f_RFAfter photoelectric detection, an expected frequency shift term is obtained:

i_up(t)∝cos(2πf_dt-45°) (12)

i_down(t)∝cos(2πf_dt+45°) (13)

performing ADC sampling quantization by ADC and digital signal processing by using the low-frequency DFS signals obtained by the formulas (12) and (13), performing digital signal processing calculation to obtain DFS frequency shift information, and identifying DFS with different symbols by using the phase difference of signals of two channels; thereby realizing Doppler frequency shift measurement with direction discernable.

3. The measurement method of the all-optical microwave frequency-shift phase-shift device based on Sagnac loop and I/Q detection according to claim 2, characterized in that:

when the phase shift of the radio frequency signal is detected, the phase difference between the radio frequency signal to be detected and the local oscillator signal is expressed asThe frequency of the LO signal is equal to the frequency of the RF signal to be measured f_Lo＝f_RF(ii) a The phase term to be measured is obtained through equations (10) and (11) after photoelectric detection:

the output results of the I path and the Q path are input to a DSP signal processing module after being subjected to analog-to-digital conversion, and are obtained through the calculation of a formula (14) and a formula (15)Thereby realizing the phase shift measurement.

Technical Field

The invention relates to the field of microwave photon measurement, in particular to microwave photon Doppler frequency shift measurement and phase measurement.

Background

Microwave measurement systems are an indispensable module in modern electronic devices. In satellite communications, electronic countermeasure and radar systems, there is a need to process high-speed broadband microwave signals with operating frequencies up to tens of GHz, which presents a significant challenge to the speed and bandwidth of microwave measurement systems.

In recent years, microwave photon measurement technology has attracted great interest as an emerging research field. The method can utilize the inherent advantages of photonics, such as large instantaneous bandwidth, electromagnetic interference resistance and the like, to measure the Doppler frequency shift and the phase of the large-bandwidth microwave signal in a wider frequency range. Meanwhile, the electromagnetic isolation advantage of the microwave photon technology can obviously improve the anti-interference performance of the microwave photon measurement system.

In a microwave photon measurement system, a local oscillation signal and a signal to be measured must be modulated by an optical carrier at a receiving end, after photon signal processing is performed in an optical domain, photoelectric detection is performed to obtain a photocurrent including required frequency and phase information, digital signals are obtained through analog-to-digital conversion, and finally the required frequency and phase information are obtained through digital signal processing. However, the presently disclosed microwave photon measurement system usually uses a cascade of a plurality of modulators to achieve the measurement of the signal, which is complicated and has poor stability.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides an all-optical microwave frequency shift phase shift device and a measuring method based on a Sagnac loop and I/Q detection. In the microwave photon measurement system, the local oscillation Signal and the Signal to be measured realize electro-optic modulation in a Sagnac loop through a Dual-electrode Mach-Zehnder Modulator (DE-MZM), and frequency discrimination information and phase discrimination information are obtained by combining I/Q detection and Digital Signal Processing (DSP), so that Doppler frequency shift and phase measurement of a broadband radio frequency Signal are realized. The DE-MZM used by the system has a simple structure, avoids the influence of optical signal polarization, and greatly improves the stability of the system.

The technical scheme adopted by the invention for solving the technical problem comprises the following steps:

an all-optical microwave frequency shift phase shift device based on Sagnac ring and I/Q detection comprises a laser source, a DE-MZM, an optical coupler, a lug-Doped Fiber Amplifier (EDFA), a two-channel Dense Wavelength Division Multiplexer (DWDM), two Photodetectors (PD) and an Analog-Digital Converter (ADC), wherein the optical output end of the laser source is connected with a port 1 of the optical coupler, a port 3 of the optical coupler is connected with an optical input port of the DE-MZM, a port 4 of the optical coupler is connected with an optical output port of the DE-MZM, a port 2 of the optical coupler is connected with an EDFA input port, as shown in figure 1, an output optical signal of a port 3 of the coupler is injected into a port 4 of the coupler through the DE-MZM, an output optical signal of the port 4 of the coupler is injected into a port 3 of the coupler through the DE-MZM, an output port of the EDFA is connected with a common input port of the dual-channel DWDM, two output ports of the dual-channel DWDM are respectively connected with one PD, and the two PDs are respectively connected to the ADC; the local oscillator signal is connected to one radio frequency port of the DE-MZM, and the radio frequency signal to be tested is connected to the other radio frequency port of the DE-MZM;

injecting an optical signal output from a laser source into the DE-MZM through an optical coupler, wherein the bias point of the DE-MZM is controlled through direct current bias; an optical signal output by a port 2 of the optical coupler is amplified by an EDFA, an upper sideband and a lower sideband are separated by DWDM, the upper sideband and the lower sideband respectively form one path of optical signal, the two paths of optical signals respectively enter an input end of a PD, a photocurrent is obtained after photoelectric detection, and Doppler frequency shift information or phase information carried by the photocurrent is processed by a rear-end ADC.

A method for adjusting and measuring an all-optical microwave frequency shift phase shift device based on Sagnac loop and I/Q detection comprises the following detailed steps:

defining the optical signal, the local oscillator signal and the signal to be measured output by the laser source as follows:

E(t)＝E₀exp(j2πf_ct) (1)

E_Lo(t)＝V_Losin(2πf_Lot) (2)

wherein E₀Electric field amplitude, f, of the light signal output for a laser source_cIs the frequency, V, of the optical signal_LoIs the amplitude of the local oscillator signal, f_LoIs the frequency, V, of the local oscillator signal_RFIs the amplitude of the signal to be measured, f_RFIs the frequency of the signal to be measured,the phase of the signal to be measured; the optical signal after being output and modulated by the DE-MZM is as follows:

wherein alpha is_MFor the insertion loss, V, of DE-MZM_πIs the half-wave voltage of the modulator, theta is the phase difference introduced by the dc bias of the DE-MZM, on the other hand, another optical carrier outputted from the optical coupler port 4 is injected into the output port of the DE-MZM, and the optical signal passes through the Sagnac loop, and is combined with the optical signal outputted from the DE-MZM in the optical coupler, and is outputted from the optical coupler port 2, and the expression is:

wherein, J_±n(. cndot.) is a first class Bessel function of order + -n,andfor modulating index, the optical signal output by the coupler port 4 is subjected to power amplification through an EDFA, and the amplified optical signal is injected into a dual-channel DWDM; adjusting the central wavelength of the optical carrier to enable the optical carrier to be positioned between two channels of DWDM, thereby separating the upper and lower sidebands of the optical signal into two optical channels; the optical signals output by the two optical channels are respectively expressed as:

wherein beta is_EAnd alpha_DRespectively representing the gain of the EDFA and the insertion loss of the DWDM;

after photoelectric detection, the output photocurrent of the Photodiode (PD) in each channel is respectively expressed as:

setting theta to 45 degrees by adjusting the DC bias of the DE-MZM; the photocurrent after photodetection is expressed as:

when applied to Doppler shift measurement, the Doppler shift of the echo signal to be measured is denoted as f_d＝f_LO-f_RFAfter photoelectric detectionTo get the desired frequency shift term:

i_up(t)∝cos(2πf_dt-45°) (12)

i_down(t)∝cos(2πf_dt+45°) (13)

performing ADC sampling quantization by ADC and digital signal processing by using the low-frequency DFS signals obtained by the formulas (12) and (13), performing digital signal processing calculation to obtain DFS frequency shift information, and identifying DFS with different symbols by using the phase difference of signals of two channels; thereby realizing Doppler frequency shift measurement with direction discernable.

When the phase shift of the radio frequency signal is detected, the phase difference between the radio frequency signal to be detected and the local oscillator signal is expressed asThe frequency of the LO signal is equal to the frequency of the RF signal to be measured f_Lo＝f_RF(ii) a The phase term to be measured is obtained through equations (10) and (11) after photoelectric detection:

the output results of the I path and the Q path are input to a DSP signal processing module after being subjected to analog-to-digital conversion, and are obtained through the calculation of a formula (14) and a formula (15)Thereby realizing the phase shift measurement.

The all-optical broadband microwave measuring system has the advantages that the all-optical broadband microwave measuring system with a simple structure is adopted, local oscillation signals and signals to be measured are respectively modulated through two electrodes of the DE-MZM, DWDM separates upper and lower sidebands, and the working point of a tuning modulator constructs I/Q down-conversion, so that the frequency and phase of the signals are measured. The invention has simple structure and strong operability; the invention can adopt a modulator with high symmetry degree and accurate bias control to improve the stability and the accuracy of the measurement system and realize a high-accuracy and stable broadband microwave photon measurement system.

Drawings

FIG. 1 is a schematic diagram of the all-optical microwave measurement system based on Sagnac loop and I/Q detection.

Fig. 2 shows waveforms of the signals in the same direction and orthogonal directions obtained in the experiment of example 1.

Fig. 3 shows the simulated signal power of the I/Q two channels in example 2.

Fig. 4 shows phases of signals to be measured obtained by simulation calculation in embodiment 2.

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

As shown in fig. 1, the microwave photon measurement system comprises a laser source, an optical coupler, a DE-MZM, an EDFA, a DWDM and a PD, wherein an optical signal of the laser source is input to a port 1 of the optical coupler, a port 3 of the optical coupler is connected with an optical input port of the DE-MZM, a port 4 of the optical coupler is connected with an optical output port of the DE-MZM, a port 2 of the optical coupler is connected with an input end of the EDFA, an output end of the EDFA is connected with an input port of the dual-channel DWDM, and two output ports of the dual-channel DWDM are respectively connected with; the local oscillator signal and the signal to be measured are respectively connected with two radio frequency ports of the DE-MZM.

Example 1:

the device in the embodiment comprises: the device comprises a laser source, an optical coupler, a DE-MZM, a direct current voltage source, two microwave signal sources, an EDFA, a DWDM, a PD, a spectrometer and an oscilloscope. Two microwave signal sources respectively generate two paths of radio frequency signals of local oscillation transmitting signals and echo signals to be detected, the two signals are respectively connected with two radio frequency ports of a DE-MZM, direct current bias of a modulator is controlled through a direct current voltage source, DWDM separates upper and lower side bands of modulated optical signals and divides the modulated optical signals into two paths of optical signals, two output ends of DWDM are respectively connected to the input end of a PD, the output end of the PD is connected with an oscilloscope, time domain waveforms are sampled through the oscilloscope, and the size and the direction of Doppler frequency shift can be obtained through calculation of a computer.

Selecting an optical carrier wave generated by a laser source to be 1549.9nm, wherein the optical power is 12 dBm; the two microwave signal sources respectively generate local oscillator emission sine signals with the frequency of 20GHz and the power of 10dBm and echo radio-frequency signals to be detected with the frequency of 20.001GHz and the power of 0 dBm. The half-wave voltage of the DE-MZM is 3.5V, and the extinction ratio is 32 dB; the central wavelength of two channels of DWDM is 1549.9nm, the channel bandwidth is 50GHz, and the adjacent channel crosstalk is 32 dB; the responsivity of PD is 0.8A/W;

adjusting the output voltage of the direct-current voltage source to enable the bias angle of the DE-MZM to be 45 degrees, enabling the phase difference between the local oscillation optical sideband of the optical signal and the optical sideband of the signal to be detected to be 45 degrees, enabling the phase difference between the signal output by the PD of the I path and the signal output by the PD of the Q path to be 90 degrees, enabling the two paths of output signals to be homodromous difference frequency signals of the local oscillation transmitting signal and the radio-frequency signal of the echo to be detected, enabling the frequency to be the Doppler frequency shift signal of the echo to be detected, enabling the frequency to be 1MHz, and enabling. The phase of the Q output signal is 90 degrees ahead of that of the I output signal, which indicates that the Doppler shift is positive.

Example 2:

next, phase measurements are made in the examples.

The local oscillator radio frequency signal source generates a radio frequency signal with the frequency of 20GHz and the power of 10 dBm; the radio frequency signal source to be tested generates a radio frequency signal with the frequency of 20GHz and the power of 0dBm, the phase of the signal to be tested is adjusted through a phase shifter at the rear end of the radio frequency source to be tested, and the responsiveness of PD is 0.8A/W;

the I and Q path devices and the setting are unchanged, two paths of PD output signals are input into the oscilloscope, the phase of the signal to be detected is changed through the phase shifter, and the power of the two paths of output signals is shown in figure 3 along with the change of the phase shift;

the power of the two paths of signal output signals is input into a computer, and the phase is calculated through MATLAB, so that the measured phase is shown in figure 4.

In conclusion, the all-optical microwave measuring device and method based on the Sagnac loop and the I/Q detection are simple and easy to implement, large in working bandwidth and high in measuring accuracy.

In conclusion, the above-described embodiments are merely examples of the present invention and are not intended to limit the scope of the present invention, it should be noted that, in the light of the disclosure of the present invention, those skilled in the art may make many equivalent variations and substitutions, and the modulator structure, rf frequency, optical carrier wavelength, optical carrier power, fiber length, etc. may be changed. Such equivalent modifications and substitutions, as well as adjustments to the frequency range, should also be considered to be within the scope of the present invention.