Abstract
We propose and theoretically
demonstrate the extinction ratio (ER) enhanced all-optical tunable wavelength
conversion based on cascaded second-harmonic generation and difference-frequency
generation (cSHG/DFG) in a periodically poled lithium niobate (PPLN) waveguide
by setting the signal at the quasi-phase matching (QPM) wavelength. The conversion
performance including extinction ratio enhancement, conversion efficiency,
and tunable bandwidth are analyzed systematically. Both analytical solutions
with clear physical insights and detailed simulation results are presented.
The proposed cSHG/DFG is compared with the conventional one on the extinction
ratio enhancement effect. The analytical expression predicts that the suggested
cSHG/DFG can effectively enhance the extinction ratio by two times in dB with
a short waveguide. The simulation results show that the extinction ratio enhancement
drops off with the increase of the waveguide length due to propagation loss
and power depletion. It is easy to perform tunable operation, i.e. the converted
idler can be tuned in a wide wavelength range simply by changing the pump
wavelength. There is a tradeoff between tunable bandwidth, extinction ratio
enhancement, and conversion efficiency. In addition, wavelength multicasting
with extinction ratio enhancement is also demonstrated. Moreover, the potential
of performance improvement in terms of optical signal-to-noise ratio (OSNR)
and Q-factor is also investigated.
© 2008 IEEE
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