Research On Narrow Band Spectral Protection Micro-Nano Optical Filtering Technology For Imaging System

Since the laser invented,the research of laser weapons has been paid much attention by many countries in the world.At present,blinding laser weapons which are the maturest laser weapons,can saturate the pixel of photodetector and lead to interference spot on the image surface by its high light intensity,and even make the detector instantly "blind".With the continuous development of laser weapons,the way to protect the imaging interference of laser weapons has always been a very focused field.In this paper,the research status and the prospect of laser protection for imaging system and narrowband spectral protection filter based on micro/nano optics are analyzed.Taking the wavelength of 532 nm interference laser as an example,a series of micro-nano narrow band filters applied for visible light imaging system are designed.Based on the principle of perfect absorption and guided mode resonance(GMR),the design and performance analysis of the four types of filters(groups)are completed,providing the idea and guidance for narrow-band spectral protection scheme based on micro-nano optics principle.Firstly,the principles of GMR and finite difference time-domain(FDTD)algorithm are introduced and brief derivated.Based on the guidance of GMR theory,1-D transmission-type narrowband spectral protection filter was designed,and its working performance was analyzed from aspects of structur al parameters,polarization sensitivity,angle tolerance and abilities of spectral protection.After confirming the characteristics of E7 liquid crystal(E7-LC),a tunable filter was designed with the E7-LC based on the original structure of 1-D filter,which can cope with the drift of interference wavelength and compensate the shift of protective wavelength caused by processing errors.Secondly,in order to optimize the polarization insensitive characteristics of polarization filter,based on the theory of 2-D GMR,a 2-D transmission-type narrowband filter taking the 1-D filter as the prototype was designed.The 2-D filter is able to protect the target wavelength in arbitrary polarized direction within a very narrow field of view(FOV)by reflection,while maintaining high visible light transmittance.The working performance of the 2-D filter was analyzed in detail from aspects of structural parameters,angle tolerance and spectral protection abilities.The tunability optimization of 2-D filter was realized by using E7-LC and the analysis of corresponding working performance was carried out.Then,in order to broaden the FOV of the protective filter,a wide-field transmission-type narrow-band filter was designed based on the 2-D triangular array GMRF.After analyzing the angle tolerance and polarization sensitivity of the filter,the advantages whose resonance wavelength changes little with the change of incident light's angle of inclination provide a lot of possibility of optimization.The methods of using double-sided etching filter and combining multiple filters improve the performance of the filter(group),making it insensitive to both polarization and incident angle,which break through the limitation of extremely narrow FOV in former two types of filter.However,increasing the number of filters is a double-edged sword.Based on the analysis of the advantages and disadvantages of the multi-chip method,this paper provides the guidance and advice for application.Finally,the mechanism of the perfect absorption was analyzed,with emphasis on the impedance matching theory,LC equivalent circuit model and reflection coherence model explaining the perfect absorption phenomenon.Based on the metal-dielectric-metal(MDM)structure,a reflection-type narrowband filter with wide FOV was designed.Starting with the grating-type 1-D MDM structure which has fewer structural parameters,a polarized narrow-band absorption filter was designed,and then the 1-D unit structure was extended in 2-D,realizing the narrow-band absorption without polarization by rotational symmetry.The designed 2-D filter has a wider FOV than the transmission-type filters,and can achieve narrow-band absorption aiming at the target wavelength,while maintaining a very high reflectivity to the visible light.The angle tolerance and thermal stability of the filter were analyzed emphatically,and the corresponding guidance is given according to the protection requirements.