Symmetry-broken silicon disk array as an efficient terahertz switch working with ultra-low optical pump power

The advancement of terahertz technology in recent years and its applications in various fields lead to an urgent need for functional terahertz components,among which a terahertz switch is one example of the most importance because it provides an effective interface between terahertz signals and information in another physical quantity.To date many types of terahertz switches have been investigated mainly in the form of metamaterials made from metallic structures and optically-active medium.However,these reported terahertz switches usually suffer from an inferior performance,e.g.,requiring a high pump laser power density due to a low quality factor of the metallic metamaterial resonances.In this paper,we report and numerically investigate a symmetry-broken silicon disk based terahertz resonator array which exhibits one resonance with ultrahigh quality factor for normal incidence of the terahertz radiations.This resonance,which can never be excited for regular circular Si disks,can help to realize a superior terahertz switch with which only an ultra-low optical pump power density is required to modify the free carrier concentration in Si and its refractive index in the terahertz band.Our findings demonstrate that to realize a high terahertz transmittance change from 0 to above 50%,the required optical pump power density is more than 3 orders of magnitude smaller than that required for a split-ring resonator(SRR)based terahertz switch reported in the literature.

Ultra-compact terahertz switch with graphene ring resonators

We propose and numerically demonstrate a compact terahertz wave switch which is composed of two graphene waveguides and three graphene ring resonators. Changing the bias voltage of the Fermi level in the center graphene ring, the resonant mode can be tuned when the plasmon waves in the waveguides and rings are coupled. We theoretically explain their mechanisms as being due to bias voltage change induced carrier density of graphene modification and the coupling coefficients of graphene plasmon effect after carrier density change, respectively. The mechanism of such a terahertz wave switch is further theoretically analyzed and numerically investigated with the aid of the finite element method. With an appropriate design, the proposed device offers the opportunity to ‘tune’ the terahertz wave ON–OFF with an ultra-fast, high extinction ratio and compact size. This structure has the potential applications in terahertz wave integrated circuits.

Study of photoexcited-carrier dynamics in GaAs photoconductive switches using dynamic terahertz emission microscopy

We propose dynamic terahertz(THz) emission microscopy(DTEM) to visualize temporal–spatial dynamics of photoexcited carriers in electronic materials. DTEM utilizes THz pulses emitted from a sample by probe pulses irradiated after pump pulse irradiation to perform time-resolved two-dimensional mapping of the THz pulse emission, reflecting various carrier dynamics. Using this microscopy, we investigated carrier dynamics in the gap region of low-temperature-grown Ga As and semi-insulating Ga As photoconductive switches of the identical-dipole type. The observed DTEM images are well explained by the change in the electric potential distribution between the electrodes caused by the screening effect of the photoexcited electron-hole pairs.

Actively controllable terahertz switches with graphene-based nongroove gratings

We systematically investigated the tunable dynamic characteristics of a broadband surface plasmon polariton(SPP) wave on a silicon-graded grating structure in the range of 10–40 THz with the aid of single-layer graphene.The theoretical and numerical simulated results demonstrate that the SPPs at different frequencies within a broadband range can be trapped at different positions on the graphene surface, which can be used as a broadband spectrometer and optical switch. Meanwhile, the group velocity of the SPPs can be modulated to be several hundred times smaller than light velocity in vacuum. Based on the theoretical analyses, we have predicted the trapping positions and corresponding group velocities of the SPP waves with different frequencies. By appropriately tuning the gate voltages, the trapped SPP waves can be released to propagate along the surface of graphene or out of the graded grating zone. Thus, we have also investigated the switching characteristics of the slow light system, where the optical switching can be controlled as an "off" or "on" mode by actively adjusting the gate voltage. The slow light system offers advantages, including broadband operation, ultracompact footprint, and tunable ability simultaneously, which holds great promise for applications in optical switches.

A novel terahertz device with multi-function of polarization and switch based on phase transition of VO_2

A terahertz(THz) polarizer and switch structure is proposed based on the phase transition of vanadium dioxide(VO_2). When VO_2 is in the insulation phase, the resonance frequencies of the proposed structure are 1.49 THz and 1.22 THz for the x- and y-polarization, respectively. It can perform as a THz polarizer with extinction ratios of 52.5 dB and 17 dB for the y- and x-polarization, respectively; When VO_2 transforms into metallic phase, the resonance frequency for x-polarization wave shifts from 1.49 THz to 1.22 THz, while that remains still for the y-polarization component. It means that the structure can work as a polarization-dependent THz switch with a high extinction ratio of 32 dB.

Electromagnetically induced transparency in terahertz metamaterial based on two-bright-mode resonator

An electromagnetically induced transparency(EIT) in metamaterial resonator with two bright modes and one dark mode at the terahertz(THz) band is numerically and experimentally demonstrated. Different from two kinds of the traditional passive modulations, our design can realize the passive modulation of EIT phenomenon by adding another bright mode resonator. Simulated and experimental results show that the transmission peak varies for incident THz waves with different polarization directions due to its asymmetric structure, which provides a novel way to realize high efficiency switch and modulation.

Topology and analysis of an N-stage cascaded polymer eight-port microring optical router with 7N channel wavelengths

Eight-port optical routers are widely used in cluster-mesh photonic networks-on-chip(No C). By using 24 groups of cross-coupling two-ring resonators, a 1-stage 8-port polymer optical router is proposed, which can optically route 7 channel wavelength data streams along definite path in two-dimensional(2D) plane. Under the selected 7 channel wavelengths, the insertion losses along all routing paths are within 0.02-0.58 d B, the maximum crosstalk of all routing operations is less than-39 d B, and the device footprint size is about 0.79 mm2. Then, a universal novel structure and routing scheme of N-stage cascaded 8-port optical router are presented, which contains 7N channel wavelengths. Because of the good scalability in wavelength, this device shows potential application of wideband signal routing in optical No C.