Study On The Theory Of Weak Near-Infrared Images In Nematic Liquid Crystals Via Stochastic Resonance

With the rapid development of laser technology,the importance of optical signal processing,especially weak light signal enhancement and detection technology has become increasingly prominent.However,when the optical signal is annihilated by strong noise,it is often difficult to achieve effective extraction with traditional techniques.At this time,noise is often considered to be harmful,strong noise has a very serious interference to the signal.With the development of nonlinear science and technology,it has been found that the signal-to-noise ratio of the system does not necessarily decrease when increasing the noise.In some nonlinear systems,the signal-to-noise ratio is improved at a specific noise intensity,and the noise at this time is beneficial to the system,which is stochastic resonance.In this thesis,the near-infrared image reconstruction technology in nematic liquid crystals via stochastic resonance is theoretically studied,which includes:1.The research background of traditional weak light signal detection technology and the problems to be solved in weak light signal detection technology are analyzed.Therefore,the concept of optical stochastic resonance is introduced,the development process and current situation of stochastic resonance are briefly introduced.2.The generation mechanism of spatial incoherent optical modulation instability is discussed.Incoherent optical modulation instability gain coefficient is derived by Wigner-Moyal transform method,and the principle of modulation instability in the reconstruction enhancement process of strongly scattered images is also analyzed.3.A near-infrared(NIR)image reconstruction method based on molecular reorientation of nematic liquid crystals(NLCs)doped with the azo-dye methyl red(MR)is theoretically proposed.Using the molecular reorientation effect of MR doped NLCs,the light intensity required for near infrared image reconstruction is reduced by3-4 orders of magnitude compared with that of undoped NLCs.In a multiplicative noise system with a wavelength of 1064 nm,the effects of magnetic field direction,magnetic field intensity,and coherence length.the incident light intensity and the dye doping concentration on the reconstruction effect are numerically simulated.The best NIR light image reconstruction can be achieved at an incident light intensity of0.9W/cm~2by reasonably controlling the relevant parameters.The correlation coefficient of reconstructed images increased from 0.26 to 0.54.4.A NIR weak-light image reconstruction method based on double modulation of electric and magnetic fields leading to the reorientation of dye-doped NLCs molecules.The numerical results show that the optimal reorientation of liquid crystal molecules can be achieved and the best results of NIR weak light image reconstruction can be obtained at a voltage of 2.4 V,a magnetic field of 0.16 T and an incident light intensity of 30mW/cm~2 when the incident wavelength is 1550 nm and the voltage is applied to the light incident surface and the light exit surface of the NLCs on the basis of magnetic field modulation.The correlation coefficient of reconstructed images increased from 0.2 to 0.61.