Research On Terahertz Wave Switch Based On Prism Coupling Structure

In recent years, terahertz wave is undoubtedly a new disquisitive field, which is located in the transition zone of macro electronics and micro photonics. The breakthrough of the terahertz radiation source and the terahertz electromagnetic wave detection technology promote sadly arisen of the terahertz wave functional devices. Tetahertz wave switch is one of the most important functional devices. In the process of reflecting electromagnetic wave, compared with the geometric optical reflection point, the actual reflection may undergo a lateral shift, which is called Goos-H?nchen shift. This paper designs terahertz wave swtiches based on the Goos-H?nchen shift of the prism coupling structure and has carried on theoretical calculation as good as simulation verfication.1. Temperature control terahertz wave switch which is based on the prism coupling structure is designed. The structure of the designed switch consisits of two layers of materials: a high-index prism and a temperature-sensitive material. The terahertz wave is incident from the left side of the prism, a terahertz wave detector is fixed at the prism external position of the reflected terahertz wave beam.The meterial of the film is temperature sensitive meterial indium antimonide(In Sb). When the ambient temperature changes, the dielectric constant of the In Sb will change, which affects the reflection coefficient of the prism-film struture. As a result, the Goos-H?nchen shift of the structure will be affected. We consider a TE-polarized terahertz wave beam with incidence angle 45.78°, incidence frequency 0.857 THz. When the ambient temperature is 210 K, the Goos-H?nchen shift of reflective terahertz wave is almost zero, this moment, the terahertz wave detector which is fixed at the right of prism can detect the reflected terahertz wave, we define that the proposed switch is at the terahertz wave "on" state. When the ambient temperature is 200 K, there has a large Goos-H?nchen shift of reflected terahertz wave beam about for 2.785 mm, the terahertz detector could not detect the reflected terahertz wave beam. Thus, we can define that the proposed switch is at terahertz wave "off" state. The calculation of extinction ratio is 24.3d B of the designed switch.The designed device realizes the function of the switch well.2. This part designs a magnetically controlled terahertz wave switch based on prism coupling structure. The structure of the designed magnetically controlled switch consists of high-index prism and magnetic meterial lutetium bismuth garnet(Lu Bi IG). The terahertz wave is incident from the left side of the prism, a terahertz wave detector is fixed at the prism external position of the reflected terahertz wave beam. The electromagnetism characteristic of Lu Bi IG changes with the transformation of externally applied magnetic field. The permittivity of magnetic thin film can change by changing the magnitude of the external applied magnetic field, which can change the reflection coefficient of reflected terahertz wave. As a result, the Goos-H?nchen shift of the reflected terahertz wave changes by changing the magnitude of the external applied magnetic field. When a TE-polarized terahertz wave beam incident with incidence angle 42.68°, incidence frequency 0.8571 THz which is the operating frequency of terahertz wave, the thickness of magnetic meterial material film 150μm. When there is no applied magnetic field, that is to say the applied magnetic field is B=0T, the Goos-H?nchen shift of reflective terahertz wave is almost zero, at this moment, the terahertz wave detector which is fixed at the right of prism can detect the reflected terahertz wave, at this time, we define the proposed switch at the terahertz wave "on" state. When the applied magnetic field is B=30.8T, there has a large Goos-H?nchen shift of reflected terahertz wave beam about for 1.826 mm, the terahertz detector could not detect the reflected terahertz wave beam. Thus, we can define that the proposed switch is at terahertz wave "off" state. The designed device well achieves the function of the switch. The calculation of extinction ratio is 17.12 d B of the designed magnetic switch.3. Based on the prism coupling structure, two kinds of electronically controlled terahertz wave switch are proposed.(1) The electronically controlled terahertz wave switch based on liquid crystals: this structure of the designed switch is prism-top electrode rectangular ring-liquid crystal-bottom electrode. The terahertz wave is incident from the left side of the prism, a terahertz wave detector is fixed at the prism external position of the reflected terahertz wave beam. The refractive index of liquid crystal can change by electric field excitation on electrodes, thus the reflection coefficient of the struture will change. As a result, the Goos-H?nchen shift of the structure can be affected. The incident terahertz wave is TM-polarized terahertz wave, and the incident angle is 30°, the incidence frequency is 0.8571 THz. When there is no applied electric field, the refractive index of liquid crystal is 1.53. Then, the Goos-H?nchen shift of reflective terahertz wave is almost zero, at this moment, the terahertz wave detector which is fixed at the right of prism can detect the reflected terahertz wave, at this time, we define the proposed switch at the terahertz wave "on" state. When there has an applied electric field, the refractive index of liquid crystal is 1.75, there has a large Goos-H?nchen shift of reflected terahertz wave beam about for 2.36 mm, the terahertz detector could not detect the reflected terahertz wave beam. Thus, we can define that the proposed switch is at terahertz wave "off" state.(2) The electronically controlled terahertz wave switch based on graphene: this structure is prism-graphene-Si O2-Si. The upper surface of graphene is used as the top electrode. The lower surface of the Si layer is used as the bottom electrode. When the is a applied bias between top electrode and bottom electrode, the permittivity of graphene changes, thus the reflection coefficient of the struture will change. As a result, the Goos-H?nchen shift of the structure can be affected. At last the designed structure realizes function of switch. This structure can gain a very large about for 250 times of the incident wavelength. And this switch response very fast as high as several picoseconds.