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CN-122017798-A - Laser detection background noise suppression system and method based on vortex light characteristics

CN122017798ACN 122017798 ACN122017798 ACN 122017798ACN-122017798-A

Abstract

The application relates to a laser detection background noise suppression system and method based on vortex light characteristics, which belong to the technical field of laser detection and optical filtering, and utilize response difference of laser (coherent light) and sunlight (incoherent light) under vortex phase modulation, wherein signal light is subjected to phase modulation to form a hollow annular light ring with zero central intensity and main energy expansion on a focal plane, and background light is not modulated due to phase incoherence and forms a solid circular spot with highly concentrated central energy after focusing. The incoherent light spot at the central axis is blocked in physical space through the circular shielding sheet, so that vortex signal light at the annular area can pass through the circular shielding sheet without damage, and the signal to noise ratio is greatly improved.

Inventors

  • ZHANG MENGYING
  • LIU YIDONG

Assignees

  • 电子科技大学

Dates

Publication Date
20260512
Application Date
20260228

Claims (8)

  1. 1. The laser detection background noise suppression system based on vortex light characteristics is characterized by comprising a modulation end, a transmission end and a filtering end, wherein a cascade architecture formed by a double-vortex phase modulation element and a telescope system is adopted, and the traditional solid Gaussian distribution is converted into hollow annular distribution with a large-diameter dark nucleus through step phase superposition of laser.
  2. 2. The system of claim 1, wherein the receiver entrance is positioned with a first vortex wave plate to spiral phase modulate the laser light and at this point the laser light is expanded and balanced to the entrance face with lenses l 0 and l 1 .
  3. 3. The system of claim 1, wherein the first shutter blade radius is 24um and the circular center second shutter blade radius is 3mm.
  4. 4. The system of claim 1, wherein the diaphragm diameter D is 20 mm-40 mm, gaussian beam waist The order of the first vortex wave plate is [10,20], the order of the second vortex wave plate is [20,40], the focal length of the lens l 1 is 100mm-300mm, the focal length of the lens l 2 is 40mm-60mm, and the focal length of the lens l 3 is 40mm-60mm.
  5. 5. The method for suppressing the background noise of the laser detection based on the vortex light characteristics is characterized by comprising the following steps of: S1, vortex light generation, namely, laser emitted by a laser radar is incident into a vortex wave plate and converted into light field distribution to meet the requirement Where r is the radial coordinate, i.e. the distance from a certain point to the center of the beam cross-section, For azimuthal coordinates, i.e. the angular position of a point in the beam cross-section, For the radial light field distribution, I is an imaginary number unit, l is a topological charge number, Representing phase as a function of azimuth Is linearly changed; s2, filtering the sun light center, namely placing a first shielding sheet with a circular center and a radius r behind the glass plate, wherein the laser has vortex rotation and has a central dark spot, the radius of the dark spot is larger than r, and filtering the sun light center; S3, increasing the topological charge number of the laser, namely adopting a double-vortex wave plate structure, increasing the dark nucleus radius on a focal plane through cascading of a first vortex wave plate and a second vortex wave plate, and reserving a tolerance space for placing a physical shielding plate; S4, filtering out sunlight, namely circularly distributing focal plane laser after the lens l 2 at the moment, wherein the sunlight is dark spots, placing a second shielding sheet on the incident surface of the lens l 3 , and filtering out the sunlight to obtain high signal-to-noise ratio laser; S5, laser radar integration, namely integrating a first vortex wave plate and a lens l 0 at the front end of the transmitting module, and integrating a second vortex wave plate, a first shielding plate with a round center, a second shielding plate with a round center and a lens l 1 l 2 l 3 at the receiving module.
  6. 6. The method of claim 5, wherein the circular center radius r = 24um of the first occlusion sheet.
  7. 7. The method of claim 5, wherein the cascading of the first vortex plate l=16 and the second vortex plate l=32 brings the total topological charge number to 48.
  8. 8. The method of claim 5, wherein the circular center radius r = 3mm of the second occlusion sheet.

Description

Laser detection background noise suppression system and method based on vortex light characteristics Technical Field The invention belongs to the technical field of laser detection and optical filtering, relates to a laser detection background noise suppression system and method based on vortex light characteristics, and particularly relates to a device and method for realizing separation of a signal and background noise by utilizing characteristic difference of laser (signal) and sunlight (background noise). Background Among the laser detection technologies, the laser radar plays an important role in the fields of atmospheric weather, environment and the like because of the capability of three-dimensional imaging and high-precision ranging. Currently, there is urgent need for atmospheric observation data with high space-time resolution in researches such as weather forecast, weather service, weather change, atmospheric environment and the like, so that research on laser radar technology and method in all days is imperative. Both background radiation and multiple scattered light reduce the signal-to-noise ratio of the signals detected by the lidar (light detection and ranging) and the optical communication system, and solar background light is the dominant interference noise during daytime lidar detection. In the prior art, the denoising technology of strong sun background light in the daytime is a key technology for realizing the full-time and high-precision detection of the laser radar, and is also a serious problem of the detection of the laser radar in the full-time at present. At present, denoising of solar background light can be classified into hardware denoising and software denoising. Existing hardware denoising methods, for example, can suppress solar background light to a certain extent by using a narrow-band or ultra-narrow-band interference filter, but are limited by the limited bandwidth, and can only be used for laser radar detection at night and in the morning and evening. The F-P interference filter has a relatively stable structure and is not limited by wavelength, but the processing technology is complex and the cost is high. The telescope receiving system with a small view field can reduce solar background noise and improve the detection capability of the laser radar. However, due to the overlapping of the spectrum of the atmospheric echo signal and the solar background light and the characteristics of nonlinearity and non-stationarity of the echo signal, the solar background light cannot be effectively filtered by adopting a hardware filtering method. In recent years, many scholars have also performed research on software denoising, for example, a moving average method can improve the signal-to-noise ratio of a laser radar echo signal, but lose effective data points and reduce accuracy. The wavelet denoising method has good time-frequency localization characteristics and can be used for signal processing with low signal-to-noise ratio. The empirical mode decomposition method has the characteristics that priori information is not needed, the decomposition is completely dependent on the signal, and the empirical mode decomposition method is suitable for the condition of higher signal-to-noise ratio, but has the problems of mode aliasing and the like. The aggregate empirical mode decomposition method has also proven suitable for noise reduction of atmospheric lidar signals. It is therefore of great importance to find new optical filters that take into account the effects of atmospheric turbulence, which are available throughout the day and which effectively increase the signal-to-noise ratio. The combination of a vortex beam with a lidar has attracted attention by researchers in order to find a new way to improve the signal-to-noise ratio (SNR) of the signal captured by the lidar. Partial progress has been made in the related fields of vortex light and laser radar denoising, for example, laguerre-Gaussian laser beam carrying orbital angular momentum is used as an emission light source, a photon sieve is used as a diffraction filter of a receiving end to physically separate a laser radar return signal from solar background noise, a Spatial Light Modulator (SLM) is used to modulate the laser beam into a vortex light beam, different response behaviors of the coherence difference of a light field in spatial mode evolution are utilized to realize physical separation, but the method does not discuss wave front distortion caused by turbulence in real atmosphere, simulation of sunlight by a point light source has certain limitation, and multiple scattering possibly occurs in practical situations to destroy a spiral wave front is not considered. Based on the above analysis, it is important how to design a spiral filter, and on the basis of fully considering solar angular spread (opening angle) and atmospheric transmission effect, it is significant to significantly improve the signal-to-noise ratio.