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Optics Letters

Widely tunable 34 μm band difference frequency generation using apodized χ^(2) grating

Takeshi Umeki, Masaki Asobe, Y. Nishida, Osamu Tadanaga, K. Magari, T. Yanagawa, Hiroyuki Suzuki

Published Apr 3, 2007• 32 citations
Publisher

Abstract

We achieved apodization in a quasi-phase-matched wavelength converter. The new design yields a large bandwidth and a flat phase-matching response with a high conversion efficiency. Using the method, we demonstrate widely tunable 3.4 microm band difference frequency generation in a LiNbO3 ridge waveguide.
DOI
10.1364/ol.32.001129

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Bandwidth enhancement and response flattening of wavelength conversion based on single-pass and double-pass cascaded second harmonic generation and difference frequency generation were investigated in segmented quasi-phase matched (QPM) gratings. It is shown that the signal and pump bandwidths are both efficiently widened by increasing the segment number of the QPM grating and optimising the poling period of each segment. The ripple on the matching response is also very small. The conversion bandwidth in a 3-cm-long three-segment waveguide reaches 150–160 nm, which is over the whole conventional band and long-wavelength band. Larger signal bandwidth can be obtained with a little response flatness penalty and conversion efficiency penalty, which can be compensated by increasing the input pump power. Compared with a sinusoidally chirped optical superlattice device, a wavelength converter based on the segmented gratings has higher conversion efficiency, broader bandwidth and better pump-wavelength tolerance, and is easier to fabricate in practice.
Bandwidth enhancement and response flattening of wavelength conversion based on single-pass and double-pass cascaded second harmonic generation and difference frequency generation in step-segmented quasi-phase matched (QPM) gratings are investigated. For the same waveguide length, high conversion efficiency, flat response and broad signal bandwidth can be obtained simultaneously by optimizing the poling period of the step-segmented QPM structure. The conversion bandwidths in a 3-cm-long five-step-segmented waveguide are 134 nm for single-pass scheme and 132 nm for the double-pass one, respectively, which are both over the whole conventional band and long-wavelength band. The ripple on the matching response can keeps less than 0.2 dB as well.