Abstract
GaP terahertz (THz) two-dimensional (2D) photonic crystal (PC) waveguides with line defects were fabricated using inductively-coupled plasma reactive-ion etching (ICP-RIE) in Ar/Cl2 gas chemistries. THz-wave generation from the fabricated PC waveguides was demonstrated under collinear phase-matched difference-frequency generation (DFG), using Cr:Forsterite (Cr:F) lasers as the incident source. We compared the THz-wave output characteristics of the PC waveguides with that of GaP planar waveguides. The collinear phase-matching conditions in the DFG process were satisfied for 300- and 500-μm-wide PC waveguide structures at 0.7 and 0.6 THz, respectively. The additional output peaks that appeared near the edge of the photonic band gap, around 0.5 THz, were attributed to the guiding modes in the PC waveguide; no such peaks appeared in the non-patterned ridge waveguides. These experimental results suggest that the phonon-polariton confinement in THz-PC waveguides based on the GaP crystal could be used to enhance the nonlinear optical effect for THz-wave generation.
Highlights
Terahertz-wave (THz-wave) sources have attracted a great deal of attention because the THz frequency region has a number of important potential applications in the medical and imaging fields [1,2]
The collinear phase-matching conditions in the difference-frequency generation (DFG) process were satisfied for 300- and 500-μm-wide photonic crystal (PC) waveguide structures at 0.7 and 0.6 THz, respectively
We have reported THz-wave generation from GaP-THz rod and rib-waveguide structures and confirmed the enhancement of the conversion efficiency in the DFG process, using the wave-guiding effect for THz waves [23,24]
Summary
Terahertz-wave (THz-wave) sources have attracted a great deal of attention because the THz frequency region has a number of important potential applications in the medical and imaging fields [1,2]. DFG can be used to produce tunable, narrow linewidth, high-power THz-waves, with ns-pulsed and continuous wave (CW) operation at room temperature [18,19]. This DFG process is suitable for wave sources used in THz telecommunications and in-situ security screening. A GaP crystal is an attractive nonlinear optical material for coherent THz-wave generation via the DFG process, due to its transparent properties in the infrared and THz regions and relatively high conversion efficiency due to THz phonon-polariton excitation [7-10,12-14]. We have reported THz-wave generation from GaP-THz rod and rib-waveguide structures and confirmed the enhancement of the conversion efficiency in the DFG process, using the wave-guiding effect for THz waves [23,24].
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