Abstract

The real-world applications of terahertz (THz) technology necessitate versatile adaptive optical components, for example, modulators. In this chapter, we begin with a brief review on different techniques for THz modulation. After that, we introduce the extraordinary features of graphene along with its advantages and disadvantages as channel materials for field effect transistor (FET). We then discuss two types of graphene FET-based THz modulators, one is rigid and another is flexible. The feasibility of the high-quality THz modulators with different graphene FET structures has been successfully demonstrated. It is observed that by tuning the carrier concentration of graphene by electrical gating, the THz modulation can be obtained with relatively large modulation depth, broad width band, and moderate speed. This chapter helps the reader in obtaining guidelines for the proper choice of a specific structure for THz modulator with graphene FET.

Highlights

  • The terahertz region of the electromagnetic spectrum roughly extends from 0.1 to 10 THz, corresponding to wavelengths from 3 mm to 30 μm

  • Qi-Ye Wen and his co-workers demonstrated an interesting Si nanostructure for optically driven THz modulators [26]. They showed that nanotip (SiNT) arrays made from silicon wafer can be utilized as antireflection layers for both THz wave and visible light to achieve a low-loss and spectrally broadband THz modulator with a remarkably enhanced modulation depth (MD)

  • A typical type of flexible modulator is a fieldgrating device, with which the intensity or phase of THz wave can be modulated by electrical gating or laser, but its properties remain unchanged under device deformation

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Summary

Introduction

The terahertz region of the electromagnetic spectrum roughly extends from 0.1 to 10 THz, corresponding to wavelengths from 3 mm to 30 μm. Qi-Ye Wen and his co-workers demonstrated an interesting Si nanostructure for optically driven THz modulators [26] They showed that nanotip (SiNT) arrays made from silicon wafer can be utilized as antireflection layers for both THz wave and visible light to achieve a low-loss and spectrally broadband THz modulator with a remarkably enhanced MD. Further research is ongoing to overcome this problem [27] Another method of THz modulation is to thermally tune the electrical conductivity and the optical response of semiconductors or metal oxides, especial those materials with insulatormetallic phase transition [15, 28–31]. A semiconductor-based field-effect transistor (FET) is a very useful architecture to fabricate effective THz modulators

Graphene and graphene field-effect transistors
Enhanced GFET THz modulator with high-k dielectric layer
Fabrication and characteristics of the enhanced THz modulator
Modulation properties of the enhanced THz modulator
Flexible THz modulator based on graphene FET
Modulation properties of the flexible THz modulator
Conclusion
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