Study Of Terahertz Wave Modulator

Terahertz wave is located between microwave and infrared light and has a lot of electromagnetic properties,however,it is called “THz gap” owing to limited knowledge about terahertz radiation.Currently,with the development of terahertz technology,the problems of generating and detecting terahertz waves have been solved.But,compared with the well explored contiguous microwaves and infrared light,how to manipulate terahertz wave conveniently and effectively is an existing and urgent problem,which is caused by lacking of proper terahertz functional devices.The advent of metamaterial provides a solution to this problem,since its unique electromagnetic interaction at THz regime absented in natural materials.In a terahertz system,terahertz modulators are significant,especially for short-range wireless THz communication or ultrafast interconnections,sophisticated imaging.With the help of such modulators,amplitude and phase modulation,resonance frequency shift,polarization state switch,change in spatial propagation direction could be achieved.Nevertheless,for current modulators,there still exist many problems,such as the small modulation depth,the slow modulation speed,the narrow operation bandwidth.Therefore,it is important and meaningful to study terahertz modulator,which can facilitate practical terahertz applications.In this paper,we designed and demonstrated some types of terahertz modulator based on metamaterial,analyzed and measured their features and performances by using CST Microwave Studio and terahertz time domain spectroscopy system.Ours original works are listed as follow:Firstly,an optically controlled terahertz modulator based on the electromagnetic induced transparency-like effect(EIT-like)of the metamaterial structure is proposed and demonstrated.A modulation depth of 63% was measured at 0.33 THz in our study.The modulation action arises from the destructive interference between the resonators composed of high-resistivity silicon and gold resonators,which is coupling between bright mode and dark mode.Utilizing terahertz time domain spectrometer(THz-TDS),we show that the transmission properties of the structures can be tuned by an externally applied pump beam.By comparing the modulation depth with and without the structures producing EIT-like behavior,and the bare silicon's modulation depth,it is found that the modulation performance can be significantly improved with employment of EIT effect.Our study provides an alternative route to facilitate potential applications in terahertz range.Second,we demonstrated a polarization independent and optical-controlled terahertz modulator based on hybrid metamaterials.Here,we attempted to broaden the bandwidth by packing four resonators with different geometries into a single unit cell for multiband responses.Experimental validations confirm an intensity modulation depth more than 90% by changing the pump power between 0 and 2.5 W,spanning 0.45-0.85 THz.Moreover,the device also has a perfect polarization independent characteristic.Here,a modulator to achieve high modulation,structural simplicity,polarization independence and broadband modulation all together is established.Further optimization may generate improvement of device performance and practical applications.Third,a hybrid metamaterial made electrically tunable terahertz modulator with two independent channels is established and demonstrated.The implemented Schottky structures consist of metallic squares with tips and crosses,which respectively form two types Schottky structures on an n-doped gallium arsenide(Ga As).Based on the anticipated frequencies,we can choose one of Schottky structure or both Schottky structures to separately or simultaneously modulate the transmission under bias voltage.Moreover,the maximum modulation depth can reach ~46% at 0.95 THz when the depletion zones near the gaps of the cross are mainly controlled.In addition,we also estimated the modulation speed of the device can reach ~0.27 MHz.In conclusion,we focused on study of terahertz modulators,and proposed some types of novel structure,optimized and improved modulation performance,which boost development of terahertz functional devices and terahertz technology.