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CN-115728712-B - Coherent detection system

CN115728712BCN 115728712 BCN115728712 BCN 115728712BCN-115728712-B

Abstract

The invention provides a coherent detection system which is characterized by comprising a frequency mixing module and a balance detection module, wherein the frequency mixing module is used for coupling signal light with local oscillation light, the balance detection module is used for eliminating signal direct current components and improving signal to noise ratio of signals, and through the design, the signal to noise ratio of echo signals can be improved.

Inventors

  • LEI SHUYU

Assignees

  • 宁波飞芯电子科技有限公司

Dates

Publication Date
20260505
Application Date
20210831

Claims (6)

  1. 1. The coherent detection system is characterized by comprising a frequency mixing module and a balance detection module, wherein the frequency mixing module is used for coupling signal light with local oscillation light, the balance detection module is used for eliminating signal direct current components and improving signal to noise ratio, and the balance detection module comprises a first input electric signal, a second input electric signal and a first output voltage signal; the circuit of the balance detection module comprises a first photodiode, a second photodiode, a first operational amplifier, a first resistor, a second operational amplifier, a second resistor and a first transimpedance amplifier, wherein the cathode of the first photodiode is connected with one end of the first resistor, the two ends of the first resistor are respectively connected with two input ends of the first operational amplifier, the anode of the second photodiode is connected with one end of the second resistor, the two ends of the second resistor are respectively connected with two input ends of the second operational amplifier, and the anode of the first photodiode and the cathode of the second photodiode are respectively connected with the input ends of the first transimpedance amplifier; I 0 and I 180 are two paths of optical signals with a phase difference of 180 degrees, I 0 irradiates on the first photodiode, passes through the first resistor and then passes through the first operational amplifier to obtain the first input electric signal; i 180 irradiates on the second photodiode, passes through the second resistor and then passes through the second operational amplifier to obtain the second input electric signal; And I 0 irradiates the output current on the first photodiode and I 180 irradiates the output current on the second photodiode, a first output voltage signal is obtained through the first transimpedance amplifier, a third output signal is obtained through operation of the first input electric signal and the second input electric signal, and a fifth output electric signal is obtained through operation of the first output voltage signal and the third output signal.
  2. 2. The coherent detection system of claim 1, further comprising a delay accumulation module for delaying an original signal for a time before adding to the original signal.
  3. 3. The coherent detection system of claim 2, wherein the delay time is less than 1/4 period of the original signal.
  4. 4. The coherent detection system of claim 1, wherein an ac amount of the first input electrical signal is 180 ° out of phase with an ac amount of the second input electrical signal.
  5. 5. The coherent detection system of claim 1, wherein said balanced detection module comprises a third input electrical signal, a fourth input electrical signal, and a second output voltage signal; The circuit of the balance detection module comprises a third photodiode, a fourth photodiode, a third operational amplifier, a third resistor, a fourth operational amplifier, a fourth resistor and a second transimpedance amplifier, wherein the cathode of the third photodiode is connected with one end of the third resistor, the two ends of the third resistor are respectively connected with two input ends of the third operational amplifier, the anode of the fourth photodiode is connected with one end of the fourth resistor, the two ends of the fourth resistor are respectively connected with two input ends of the fourth operational amplifier, and the anode of the third photodiode and the cathode of the fourth photodiode are respectively connected with the input ends of the second transimpedance amplifier; I 90 and I 270 are two paths of optical signals with a phase difference of 180 degrees, I 90 irradiates on the third photodiode, passes through the third resistor and then passes through the third operational amplifier to obtain the third input electric signal; I 270 irradiates on the fourth photodiode, passes through the fourth resistor and then passes through the fourth operational amplifier to obtain the fourth input electric signal; And I 90 irradiates the output current on the third photodiode and I 270 irradiates the output current on the fourth photodiode, a second output voltage signal is obtained through the second transimpedance amplifier, the third input electric signal and the fourth input electric signal are operated to obtain a fourth output electric signal, and the second output voltage signal and the fourth output electric signal are operated to obtain a sixth output electric signal.
  6. 6. The coherent detection system of claim 1, wherein the output of the mixing module is a four-way output with a 90 ° phase difference.

Description

Coherent detection system Technical Field The invention relates to the technical field of detection, in particular to a coherent detection system. Background The coherent detection is to mix the signal light and the local oscillation light to output the difference frequency component of the signal light and the local oscillation light, and the difference frequency component is absorbed by the receiving surface of the detector to generate photocurrent, and the difference frequency component keeps the amplitude, frequency and phase information of the signal light, so that the holographic detection of the signal light is realized. Compared with direct detection, the method has the advantages of strong detection capability, high conversion gain, high signal-to-noise ratio, strong anti-interference capability and the like, and is widely applied to the fields of coherent optical communication, remote sensing, laser radar speed measurement, ranging and the like. In the coherent detection device, one path of linearly polarized light generated by a laser is often used as emission light to generate signal light after passing through a detection target, the other path of linearly polarized light is used as local oscillation light to be coherent with the signal light, and the relevant light is converted into an electric signal through a receiving surface of a detector for analysis and measurement of parameters such as speed, distance and the like. The key function of the optical mixer in the coherent detection system is to coherently mix two beams of signal light with similar frequency, constant phase difference and same polarization direction with the wavefront of the local oscillation light, and then process intermediate frequency signals by using a subsequent photoelectric balance detector and a signal recovery processing circuit, so that the optical mixer is also a modem essentially. The photo balance detector is typically composed of two identical photodiodes (typically semiconductor photodiodes PIN) and a subtractor. The PIN converts the received optical signal into an electrical signal and performs subtraction to output a current signal of a difference value between the two signals, and in theory, the photoelectric conversion efficiency, response bandwidth, response time, noise and other working characteristics of the two photodiodes are consistent. Since the photodiodes have different conversion efficiencies to light waves with different wavelengths, the sensitivity of the coherent detection system is limited, and the noise of the photodiodes directly affects the sensitivity of the optical receiver, so that the performance of the photoelectric balance detector has a great influence on the coherent detection system. In severe environments such as laser remote ranging, imaging, speed measurement, underwater, foggy days and the like, the amplitude of an echo signal is greatly reduced due to medium attenuation, and a pulse waveform is distorted and widened due to medium refraction and scattering. However, the amplitudes and frequency band characteristics of noise signals such as shot noise, dark noise, thermal noise and the like are basically unchanged, so that the target echo is submerged in the noise, and the received signal-to-noise ratio is small. There is a need for a coherent detection system that improves the signal-to-noise ratio of the echo signal. Disclosure of Invention The present invention aims to solve the above-mentioned drawbacks of the prior art, and provides a coherent detection system, so as to solve the problem of low signal-to-noise ratio of echo signals in the related art. In order to achieve the above purpose, the technical scheme adopted by the embodiment of the invention is as follows: an embodiment of the present invention provides a coherent detection system, which is characterized by comprising: the mixing module and the balance detection module; The frequency mixing module is used for coupling the signal light with the local oscillation light; the balance detection module is used for eliminating the direct current component of the signal and improving the signal-to-noise ratio of the signal. Optionally, the coherent detection system further includes a delay accumulation module, where the delay accumulation module is configured to delay an original signal for a certain time and then add the delayed original signal to the original signal. Optionally, the delay time is less than 1/4 period of the original signal. Optionally, the balance detection module includes a first input and a second input and a first output. Optionally, the ac amount of the first input is 180 ° out of phase with the ac amount of the second input. Optionally, the first input and the second input are operated to obtain a third output, and the first output and the third output are operated to obtain a fifth output. Optionally, the balance detection module includes third and fourth inputs and a second output. Optionally,