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# Forward and backward THz-wave difference frequency generations from a rectangular nonlinear waveguide

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Institute of Photonics Technologies, Department of Electrical Engineering, National Tsinghua University, Hsinchu 30013, Taiwan.
(Impact Factor: 3.49). 11/2011; 19(24):24577-82. DOI: 10.1364/OE.19.024577
Source: PubMed

ABSTRACT

We report forward and backward THz-wave difference frequency generations at 197 and 469 μm from a PPLN rectangular crystal rod with an aperture of 0.5 (height in z) × 0.6 (width in y) mm(2) and a length of 25 mm in x. The crystal rod appears as a waveguide for the THz waves but as a bulk material for the optical mixing waves near 1.54 μm. We measured enhancement factors of 1.6 and 1.8 for the forward and backward THz-wave output powers, respectively, from the rectangular waveguide in comparison with those from a PPLN slab waveguide of the same length, thickness, and domain period under the same pump and signal intensity of 100 MW/cm(2).

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ABSTRACT: We design an AlGaAs-based terahertz photonic crystal waveguide (PCW) to achieve terahertz-wave difference frequency generation (DFG) from near-infrared light sources. The PCW structure provides a tight confinement of terahertz-wave field, resulting in a good mode field overlap of three waves. The unique phase matching condition between two pump waves and terahertz Bloch wave can be satisfied through choosing appropriate waveguide parameters and pump wavelengths. With the coupled-mode equations derived from modal theory for describing the light propagation, we simulate the continuous terahertz DFG process, and a high power-normalized conversion efficiency of $0.7632 \times 10^{-4}$ W $^{-1}$ for 3 THz generation is obtained.
Journal of Lightwave Technology 07/2012; 30(13):2156-2162. DOI:10.1109/JLT.2012.2192908 · 2.97 Impact Factor
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##### Article: Elliptically polarized THz-wave generation from GaP-THz planar waveguide via collinear phase-matched difference frequency mixing
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ABSTRACT: We carried out terahertz (THz)-wave generation from the GaP planar waveguides under collinear phase-matched difference-frequency mixing of two near-infrared sources. TE- and TM-mode of THz-waves were generated simultaneously by adjusting the polarization direction of two incident infrared sources. The phase shift between TE- and TM-mode of THz-wave in the waveguide was dependent on the waveguide length and contributed to the generation of the elliptical polarized THz-wave. The ellipticity of generated THz-wave increased as waveguide length increased. We indicated the possibility of control of rotational direction of elliptical polarization of emitted THz wave.
Optics Express 11/2012; 20(23):26082-8. DOI:10.1364/OE.20.026082 · 3.49 Impact Factor
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##### Article: Long-range parametric amplification of THz wave with absorption loss exceeding parametric gain
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ABSTRACT: Optical parametric mixing is a popular scheme to generate an idler wave at THz frequencies, although the THz wave is often absorbing in the nonlinear optical material. It is widely suggested that the useful material length for co-directional parametric mixing with strong THz-wave absorption is comparable to the THz-wave absorption length in the material. Here we show that, even in the limit of the absorption loss exceeding parametric gain, the THz idler wave can grows monotonically from optical parametric amplification over a much longer distance in a nonlinear optical material until pump depletion. The coherent production of the non-absorbing signal wave can assist the growth of the highly absorbing idler wave. We also show that, for the case of an equal input pump and signal in difference frequency generation, the quick saturation of the THz idler wave predicted from a much simplified and yet popular plane-wave model fails when fast diffraction of the THz wave from the co-propagating optical mixing waves is considered.
Optics Express 01/2013; 21(2):2452-62. DOI:10.1364/OE.21.002452 · 3.49 Impact Factor
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