Flexible And Extensible Semiconductor Terahertz Modulator

Terahertz(THz)wave is electromagnetic wave at the wavelength from 0.03 mm to 3 mm;and the frequency from 0.1 THz to 10 THz,Which is located between microwave and infrared light in the electromagnetic wave spectrum.In this frequency range,it is not suitable for the use of optical theory,nor is it suitable for the theory of microwave.Terahertz modulation can control the intensity or phase of terahertz waves under the action of external excitation sources.Different modulators have important applications in different systems according to their performance,and They have been developing rapidly in recent years.Meanwhile,with the development of science and technology,flexible wearable devices are becoming more and more important in the devices research.Silicon is usually an important material for terahertz optical modulation with moderate modulation rate.The intensity of terahertz wave is modulated by the generation and recombination of photo-generated carriers.Because of the long diffusion length(tens of microns)of photo-generated carriers in silicon.large silicon as a terahertz spatial modulator has poor spatial resolution.In this thesis we successfully fabricated a flexible semiconductor terahertz optical modulator by attaching an array of small pieces of silicon(less than 3 mm)on a flexible PDMS substrate,aiming at reducing the silicon diffusion of photo generated carriers between pixels to improve the spatial resolution of terahertz wave spatial modulator.The pulsed terahertz source not only has good time resolution,but also has rich spectrum information.As a result,it is very necessary to study the spatial control technology of the pulsed terahertz source.For the small silicon,the size of the silicon coupon is close to the wavelength of the terahertz wave.A portion of the terahertz wave pulse passes through the silicon,while the rest part passes through the air,resulting in two separate terahertz pulse in the time domain spectroscopy and thus an absorption peak in the transmittance spectrum.In this thesis,the interaction between silicon of different thicknesses and sizes and terahertz waves is studied systematically,and their optical modulation were studied.The modulation depth is 13% at the absorption peak and 30% at the higher frequency.Gold nanoparticle monolayer can significantly enhance the optical modulation depth.In addition,Matlab software was used to establish a mathematical model to simulate the interaction and modulation of terahertz waves with small size silicon.By scanning a single small size silicon,it is found that the imaging at the absorption peak has the best contrast.For arrayed semiconductor terahertz modulators,the distance between the silicon can affect the intensity of the absorption peaks.At the same time,the contrast for spatial modulation has also been significantly improved with the arrayed sample.At the end,micro-sized silicon arrays have been fabricated by microelectronic manufacturing technology,which has been tested for optical modulation.This paper studies terahertz spatial light modulators with moderate modulation rate and improved spatial resolution,providing a new modulator solution for terahertz spatial compressive sensing imaging.