INTRODUCTION

Terahertz radiation, or simply terahertz (THz), has become a popular research topic among both fields of Photonics and Microelectronics. Terahertz radiation includes electromagnetic waves from 0.1 THz to 10 THz, which is located in an embarrassing range between microwaves and optical waves, or so-called terahertz gap.

Although first studied in 1896, due to the lack of efficient source and sensitive detection equipment, this topic regain attention among scientists until 1980s. Presently, terahertz radiation is considered as a promising light source, whose application includes biology, medicine, chemistry, security… and so on.

A common method to generate terahertz radiation is through nonlinear crystal. Since the refractive index of these crystals, or materials, are much larger than air, terahertz radiation would thus suffer from huge Fresnel loss, anti-reflection (AR) coating is required.

However, wavelength of terahertz can be as long as 100um, which makes traditional means such as quarter-wave AR coating impractical. Therefore, we developed certain pattern cut of high resistive float zone (HRFZ) silicon wafer, which is highly penetrable for terahertz. We proposed a structure shaped like a square wave, or a binary structure, whose spatial period is 125um.

By using a dicing saw, we would be able to cut such pattern on a silicon wafer. As shown in the following graph, we had actually fabricated it and took some pictures of it under a microscope, with the averaged dimensions labeled on the image. We not only cut the pattern in 1D but also 2D, since the property of 2D structure is thought to be polarization independent but 1D would be easier to fabricate.

Furthermore, we put the fabricated structure into a terahertz time-domain spectrometer (THz-TDS), and measure the transmission, reflection properties.

This TDS system is able to compare a THz pulse waveform penetrated through a sample with a reference pulse in time domain. Taking Fourier transform of these data gives us the spectral response of our grating structure. Amplitude and power transmittance, as well as transmittance phase information can be found in the following plot.

Aside from the experimental results, we also computed the expected properties of such structure, both 1D and 2D, with ANSYS developed HFSS. In addition to the actual structure we fabricated, we also simulated several possibilities, including single/double sided, as well as half-period shifted ones. Here we show the property of simulated single-sided 2D structure in the abstract, others would be presented in the main contents.

Both simulation and experimental results point out there is a transmission window around 0.2THz. However, the THz radiation generated from lithium niobate locates at roughly 2.0 THz, which is 10 times higher than our original design. Thus, in the future work, we might shrink the structure for 10 times and thus meet the goal.


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心得感想

At first, I would like to thank my instructor, Prof. Yen-Chieh Huang, for providing a chance to visit laboratories in foreign countries, and of course, all the efforts and resources spent on me.

Second, I would like to thank several senior members from HOPE lab, NTHU. They are Kuan-Yan Huang, Wei-Che Tsai, Shi-Chi Su, and especially Yu-Chung Chiu. Without their generosity of sharing experience and providing with suggestions and technical supports, I can never finish this report.

Third I would like to thank several companies from Taiwan. They are DISCO, Atecom Wafer, Shi-Chi Instruments, TCFSH, Global Wafer and Yuan Fa Instruments, especially the latter twos. Without the sample HRFZ silicon wafer from Global Wafer and dicing services from Yuan Fa, as well as comments and instructions from the other listed companies, I can never fabricate the samples and take them to Russia.

Fourth I would like all the members in Laboratory of Informational Optics, IAS, SB RAS, especially Alexander Mamrashev, Nazar Nicolaev, Surgey Kuznetsov and Prof. Oleg Potaturkin. Special thanks to their technical instructions and hospitality.

Lastly I would love to thank my parents. Without their support, either substantial or mental, it is impossible for me to finish this report.