Yutaka Fukuchi
Tokyo University of Science, Japan
Title: Technique of selective and tunable wavelength conversion employing quasi-phase matched lithium niobate devices with dual pump configuration
Biography
Biography: Yutaka Fukuchi
Abstract
All-optical and tunable wavelength converters (WCs) can off er many attractive functions such as optical channel routing, optical add-drop multiplexing, optical label processing and dynamic light-path establishment for constructing transparent and scalable wavelength-division multiplexed (WDM) networks or future optical packet switched systems. Th e potential of such WCs has already been revealed in a number of system experiments. To date, a selective and tunable WC (STWC) has been realized by employing the cascaded second-order nonlinear eff ect of sum frequency mixing (SFM) and diff erence frequency mixing (DFM) in a quasi-phase-matched (QPM) lithium niobate (LN) device. In this technique, a signal light and two pump lights 1 and 2, which have angular frequencies ωs, ωp1 and ωp2, respectively are launched on the device with a QPM frequency of ωQPM; to satisfy the QPM condition, ωp1 is set to 2ωQPM–ωs; SFM between the signal light and the pump light 1 then produces a sum-frequency component at 2ωQPM; a wavelength-converted output fi nally appears at 2ωQPM–ωp2 through DFM between the 2ωQPM component and the pump light 2. Generally, the wavelength conversion effi ciency of the QPM-LN devices or the output power of the wavelength-converted signal light increases dramatically as the length of the LN crystal becomes longer. In such a dual-pumped wavelength conversion scheme, however, the available signal bandwidth is strictly limited by the QPM bandwidth of the device. In other words, the crystal length of the QPM-LN device has to be optimally determined so that the QPM bandwidth corresponds to or is slightly broader than the bandwidth of the original signals to be wavelength-converted. In this paper, we review a technique of the QPM-LN-based STWC from an arbitrary wavelength to another arbitrary one. Through wavelength conversion experiments using short optical pulses for the QPM-LN devices having diff erent crystal length, we investigate the bandwidth limitation in the dual pump confi guration. We show that the minimum pulse width to be wavelength-converted without waveform distortion is proportional to the length of the LN crystal, and also reveal that that ratio is 1.6ps/cm. By utilizing this critical value as a performance metric, we demonstrate highly effi cient selective and tunable wavelength conversion of 40-Gbit/s data signals using a QPM-LN waveguide device with an optimum crystal length of 5cm.This device is quite attractive for channel-by-channel wavelength conversion in 40-Gbit/s dense WDM (DWDM) systems thanks to many excellent features such as wide range of wavelength tunability, high conversion effi ciency, modulation format free, adequate signal bandwidth and selectivity of 100-GHz-spaced DWDM channels.