Research On Improving The Signal-to-noise-ratio Of Laser Detection Based On Vector Light

In this work,we list the domestic and foreign research progress on vector beam generations,applications and characteristic of tight focus.We summarize the outstanding advantages and disadvantages of them.Then we analyse the status quo,in the field of laser detection,that the noise with same frequency of the signal can not filter out when they are received at the same time.We put forward a system that radial-polarization Bessel-Gauss light serve as signal,the coherent light or the incoherent background noise received at the same time with signal.The scheme has the first block before the lens front surface,and the second block at the center of lens surface,a high numerical aperture lens is used to focus,and a small hole is used to filter the noise in the image plane.The signal light in the image plane is concentrated at the center of the plane,while the imge of the blockd noise in image plane is an bright ring,which satisfies the lens imaging theorem.Choosig the right parameters can make the signal and noise separate in the image plane,the pinhole serve as the noise filtering.We can calculate the signal-to-noise ratio after filtering out the noise by the pinhole.Based on this system,an binary diffraction element is used to optimize the SNR of the detection.The phase-type modulation element is used to replace the second block,which can reduce the loss in energy and reduce the size of the signal light field in the image surface.The aperture angle parameters of the binary diffraction element with the smallest signal distribution on the image plane are obtained by simulation,the distribution of coherent noise and incoherent noise on the image plane is given,and the signal-to-noise ratio at the image plane under the two kinds of noise is calculated.The above parameters are not the optimal SNR of the whole system when integrated signal and noise together,that is,when the radial-polarization light is focused optimally,the SNR of the system is lower than the optimal SNR.Based on the purpose of this article and the demand,the coherent noise or the incoherent background noise with signal light is received at the same time,the signal-to-noise ratio at the image plane within fixed range reach to the best one as the constraint condition,to optimize the above conditions.Let aperture angles iterate over in different value ranges,the value ranges and step size are reduced at the same time to obtained the best numerical aperture angle and the optimal signal-to-noise ratio.