High‐Performance Photo‐Induced Spatial Terahertz Modulator Based on Micropyramid Silicon Array

Abstract

Reconfigurable conductive pattern created by photoexcitation of high‐resistivity semiconductor provides a powerful approach to realize broadband spatial terahertz modulators (STM), which are highly demanded for constructing cost‐effective and compact terahertz (THz) system. Here a high performance all‐optical STM is proposed and realized based on silicon micropyramid arrays (Si‐MPA), which not only enhances the light harvesting across a broad wavelength range, but also greatly increases the active area for THz modulation. Upon illuminating the Si‐MPA by light with various wavelengths, modulation depth (MD) of four times larger than that of bare silicon is achieved. A maximum MD of 93.8% is obtained under 638 nm laser with a low power density of 1 W cm−2. Reconfigurable THz imaging system based on the Si‐MPA modulator and a single‐element detector is constructed, with which precise THz beam mapping and fast real‐time imaging with 225 pixels are demonstrated. This Si‐MPA‐based STM with large MD at low illumination power density is promising for many THz applications including imaging, beam shaping, holographic projection, etc.

Photo-Excited Silicon-Based Spatial Terahertz Modulators

“…This different wavelength dependence renders the Si-MPA a superior candidate to constructing a fast THz imager with digital light processing projector (DLP). As a proof of concept, precise THz beam mapping and fast real-time imaging with 225 pixels were demonstrated [56]. Very recently, we further realized an enhanced photomodulation efficiency under low illumination density by microtexturing and passivating the Si surface, where as high as 91% MD was obtained at only 0.53 W/cm 2 photodoping [57].…”

“…Such high reflectivity not only cripples the modulation efficiency, but also introduces disturbance or noise into the quasi-optical THz system, which greatly limits the achievable tenability and versatility of Si-based STMs. To overcome such deficiencies, our group proposed two different all-optical spatial STMs based on nano-or micro-structuring the Si surface [55,56].…”

“…With such a nano-textured surface, significantly increased transmittance as high as 90% of THz wave was observed and this improvement is strongly dependent with length of nanowires, as shown in However this performance-enhanced SiNT-based STM requires a rigorous and subtle balance between the tip shape, wire length and filling ratio but it can only realize a limited improved modulation depth (MD) of 75%. To find a more practicable scheme, an easier anisotropic wet chemical etching technique was adopted [56]. By utilizing the anisotropic response of Si to KOH, pyramid-resembled microstructures were produced on the Si surface, as the SEM image shows in Figure 8 (a).…”

Terahertz Metamaterial Absorbers

“…[ 69 ] This design concept is useful for fabricating the high‐speed thermal emitters and spatial light modulators in terahertz frequency band since such simple structure greatly reduces the processing difficulty. [ 82 ] The resonance mode can be referred to the waveguide mode, which is a hybrid of magnetic and electric modes. The incident wave is coupled into the all‐dielectric structure to avoid reflection.…”

Ultra-Thin Terahertz Deflection Device Based on Laser Direct Writing Graphene Oxide Paper

“…The terahertz band (0.1~10 THz) has already developed rapidly in the last two decades [ 1 ] and has been used in security imaging [ 2 ], biological detection [ 3 ], 6G communication [ 4 ] and other fields. In addition to a large number of terahertz functional devices, such as terahertz modulators [ 5 , 6 ] and terahertz absorbers [ 7 , 8 , 9 ], there is an increasing demand for THz beam control devices with beam steering and forming capabilities, especially terahertz wavefront modulation devices [ 10 , 11 ]. The phased array antennas were often used to achieve beam steering and forming.…”