Abstract

Broadband amplification is useful for WDM fiber communication. The retracing behaviors of phase-matching curves in χ⁽²⁾ nonlinearity have great potential for broaband optical parametric processes and difference-frequency generation and hence for WDM applications’. Such retracing behaviors with birefringence phase matching in several nonlinear crystals have been studie². In this paper, we report the implementation of broaband optical parametric generation in periodically poled LiNbO₃ (PPLN) based on a novel phase-matching retracing behavior. The retracing behavior was implemented with non-collinear pumping of a PPLN optical parametric process (OPG). The length of the PPLN was 1.9 cm. Fig. 1 shows four experimental signal spectra of different pump angles with 29.5-μm period PPLN and temperature fixed at 190 °C. The pump wavelength was 1064 nm (a Q-switched Nd:YAG laser). When the PPLN crystal was rotated, we could see that the central wavelength (λ_sc) and full-width-at-half-maximum spectral width (Δλ_s) of signal spectra varied from λ_sc = 1.563 μm with Δλ_s = 8.5 nm (collinear case) to the broadest spectrum of λ_s = 1.81 μm with Δλ_s = 300 nm (from 1.66 μm to 1.96 μm). With further rotation, the signal spectral width was reduced to 140 nm (centered at 1.84 μm). At the broa est spectral width, the corresponding bandwidth of idler is 635 nm. Those results are summarized in Fig. 2. The symbols indicate the signal spectral peak position, and the vertical bars show the corresponding spectral FWHW ranges of phase matching. The solid curve stands for the theoretic prediction under the same conditions of our experiment. The experimental results are quite consistent with the theoretical predictions. Besides the results above, in this paper we will also iscuss the OPG results pumped with a Ti:sapphire laser and broadband signal amplification based on difference-frequency generation.

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