Terahertz frequencies experiments has motivated the development of new sources, detectors and optical components. Here we will present a review of THz bandpass filters ranging from 0.4 to 10？THz. We also demonstrate our fabrication process, simulations and experimental results. 1. Introduction and Review 1.1. Basic Concepts The terahertz, or far infrared range within electromagnetic spectrum placed between microwaves and midinfrared wavelengths, correspond to wavelengths from 3 millimeters up to 3 micrometers. Moreover, the transition between these two spectral bands represents the transition of two different technologies: electronics and photonics (Figure 1). These issues bring us technological challenges to develop new sources, detectors, filters, and other important components [1, 2]. Figure 1: Electromagnetic spectrum showing the terahertz range between microwaves and infrared ranges. Recently, terahertz range has attracted the interest around the world because its innovative applications including different areas as nondestructive tests, military and civilian security, chemistry, medicine, biology, and others [3–6]. Especially after terrorist attacks on September 11th, terahertz research has increased abruptly because all possible defense applications. THz radiation can be transmitted through different materials, which became possible to “see” through clothes, shoes, bags, plastics, and paper envelops, allowing the identification of chemical and biological agents like illicit drugs and explosives [3, 5]. 1.1.1. Terahertz Metal Mesh Filters A metal mesh filter, which is a type of frequency selective surfaces (FSS), can be defined by a thin metal film (few to tenths of microns of thickness) which is perforated, using different geometries, in a two-dimensional array. These filters are compact and present an easy and available fabrication process. They also could act as high pass, low pass, band-pass, or reject band filters and this is the most important characteristics of them in other words, their optical behavior can be changed selecting the proper geometry and their parameters dimensions [7]. There are some examples of FSS geometries in the literature presenting different spectral response. In Figure 2, it shows few examples of band pass, high pass, and reject band filters. Figure 2: Examples of filters presented in literature: (a) reject band peak at 6.9 and 20.3？THz; (b) reject band peak at 3.8 and 7.0？THz; (c) reject band peak at 2.7 and 5.9？THz [ 20]; (d) band pass filter at 1.7？THz; (e) high-pass filter at 1.1？THz [ 21]; (f) blocking of
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