Optial Pumping Terahertz Modulators Based On Black Silicon And Its Imaging Application

With the development of the terahertz radiation source and detection technology,terahertz filtering,absorption,modulation and other functional devices have been developed rapidly.Terahertz has an important application value in the fields of wireless communication,medical testing,human security inspection,military radar and other fields because of its unique nature.Among them,terahertz imaging has gradually become a great research upsurge in the terahertz field.At present,there are many factors restricting the development of terahertz imaging technology,one of them is how to obtain high performance terahertz control devices.Terahertz imaging requires that the modulator have a large enough modulation depth to improve the imaging resolution,the requirements for the modulation rate are relatively low.Optical control modulation is one of the most important ways to realize array imaging because it is easy to realize array control.At present,the mode of modulation by laser irradiation of semiconductor silicon requires a large amount of laser power to achieve sufficient modulation depth,however,the reflected light will seriously affect the stability and security of the entire application system.Based on this background,we propose a low reflectivity black silicon optical controlled terahertz modulator.Firstly,etching of the microscale Pyramid structure and micro nanostructures on high resistance silicon by chemical etching.These two structures have a very low reflectivity of light in the range of 250nm-1100 nm,which can greatly improve the utilization of laser and improve the modulation depth.Secondly,the time domain spectrum,frequency domain spectrum and transmission spectrum of the Pyramid structure and micronano structure are tested by the terahertz time-domain spectroscopy test platform.We experimentally proved that the Pyramid structure can greatly improve the modulation depth,and gain a larger modulation depth at a smaller laser power.Which is not affected by the laser wavelength,there is a very high modulation depth even in a short wavelength laser.Under the action of 638 nm laser,the modulation depth of Pyramid structure can reach more than 90% at 0.8W,while only 30% of the silicon wafer under the same condition.Thirdly,the modulation rate is tested by terahertz dynamic test platform.It is concluded that the Pyramid structure and micronano mixing structure are equivalent to ordinary silicon wafer at modulation rate,but have greater modulation depth.We carry out the simulation calculation by the finite element method,verify the experimental results and analyze the influence of the structure size of Pyramid on the terahertz transmittance.The conclusion is that the Pyramid height mainly affects the terahertz transmittance while the bottom edge of Pyramid main influence the frequency.Finally,a terahertz space imaging system is constructed by combining a spatial light modulator and a Pyramid terahertz modulator.And successfully completed 3×3 array imaging and 6×6 array imaging.Which provides a new technical approach for the terahertz rapid imaging.