Abstract
Here, we propose an efficient scheme for terahertz (THz) wave generation on the basis of difference frequency mixing (DFM) using a GaP ridge waveguide embedded in a silicon slot waveguide. Phase matching in the DFM process, between the nonlinear polarisation wave induced by two near-infrared pumps and the generated THz wave in the low-refractive-index slot waveguide, was achieved by utilizing the modal birefringence of the fundamental transverse electric- and transverse magnetic-like modes at telecom wavelengths in the GaP ridge waveguide. The effective cross-sectional area of the THz wave in the waveguide was small, 220 μm2 at 2.26 THz, resulting in a photon conversion efficiency of 5.7 × 10-2%. The THz output power approached the multi-μW level using the proposed waveguide structure.
Highlights
Terahertz (THz) sources, which operate in the wavelength range of 0.1–10 THz, have attracted a great deal of attention with regard to material science, biochemistry, security, and non-destructive testing applications; the availability of THz sources has advanced development in numerous areas by tuning to the specific eigenmodes of materials derived from optical phonons, inter- or intra-molecular vibration, and hydrogen bonding [1]–[6].Nonlinear optics (NLO) facilitate efficient generation of THz waves, by converting near-infrared frequencies to the THz regime
We describe a GaP ridge waveguide-based THzwave generator embedded in a silicon-slot THz-waveguide structure
We demonstrated efficient THz wave generation from a GaPbased ridge waveguide embedded in a Si slot waveguide
Summary
Terahertz (THz) sources, which operate in the wavelength range of 0.1–10 THz, have attracted a great deal of attention with regard to material science, biochemistry, security, and non-destructive testing applications; the availability of THz sources has advanced development in numerous areas by tuning to the specific eigenmodes of materials derived from optical phonons, inter- or intra-molecular vibration, and hydrogen bonding [1]–[6]. A semi-insulating GaP single crystal is one of the promising NLO materials compared with other ones such as GaAs, GaSe, and LiNbO3 due to the following features: relatively high nonlinear optical susceptibility (50 pm/V at 1.55 μm [12]) wide transparency ranges for both infrared and THz regions, and low multiphoton absorption coefficient at telecom wavelength. Compared with bulk NLO crystals, THz waveguides made from NLO crystals, such as GaAs, GaP, and LiNbO3, with a cross-sectional size on the order of the THz wavelength considered, effectively confine the generated THz waves [13]–[21]. Strong confinement of the THz wave in the air-gap region of slot waveguide resulted in a high conversion efficiency, compared with that obtained using conventional dielectric waveguides
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