Conversion of 40 Gb/s OTDM to 4×10 Gb/s WDM Channels with Extinction Ratio Enhancement by Pump-Modulated Four-Wave Mixing Using Time- and Wavelength-Interleaved Laser Pulses Gordon K. P. Lei and Chester Shu Department of Electronic Engineering and Center for Advanced Research in Photonics, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong Email: kplei@ee.cuhk.edu.hk Abstract We demonstrate simultaneous demultiplexing from 40 Gb/s OTDM to 4x10 Gb/s WDM channels by pump- modulated four-wave mixing with a time- and wavelength-interleaved pulsed source. An extinction ratio enhancement of ~2.6 dB is achieved. Introduction While optical time-division multiplexing (OTDM) is a promising technology in long-haul fiber-optic communication, wavelength-division multiplexing (WDM) remains important in metro networks. Different approaches have been demonstrated to perform OTDM to WDM conversion with multi-channel acquisition, including cross-phase modulation (XPM) in a semiconductor optical amplifier (SOA) [1], four-wave mixing (FWM) in a highly nonlinear fiber [2], and cross- absorption modulation (XAM) in an electro-absorption modulator (EAM) [3]. In recent years, pump-modulated FWM has been rigorously pursued for all-optical signal processing. The regenerative property of the approach has been demonstrated [4-5]. In this paper, we report the conversion of 40 Gb/s OTDM to 4×10 Gb/s WDM channels by pump-modulated four-wave mixing. Our approach exploits a time- and wavelength-interleaved pulsed source that has previously been generated by different approaches and used in applications including analog-to-digital conversion, wavelength multicasting and all-optical sampling [6-8]. With the regenerative property of pump-modulated FWM, the extinction ratios of the demultiplexed channels are enhanced compared to that of the 40 Gb/s OTDM input data. Principle and Experimental Setup The experimental setup is shown in Fig.1. Four CW laser outputs are obtained from a WDM source. The four branches are combined with couplers and directed to the input of a phase modulator. The phase modulator is driven by a 10 GHz RF signal, introducing a 10 GHz chirp on the CW lights. The CW lights are then transmitted in an 8.4 km single-mode fiber (SMF) that introduces a dispersion of -142 ps/nm. Owing to frequency chirp introduced in the phase modulator, different portions of the CW lights lase at different instantaneous frequencies. As a result, the CW lights are turned into short pulses after group velocity dispersion in the SMF. At the same time, since the four CW lights are of different wavelengths, inter-channel time delay occurs between adjacent channels. By optimizing the phase modulation depth, the wavelength spacing and the dispersion [9-10], a 4 × 10 GHz time- and wavelength- interleaved pulsed source is generated. Fig.1. Experimental setup. EDFA: erbium-doped fiber amplifier; EOM: electro-optic modulator; MLFL: mode-locked fiber laser; MUX: multiplexer; OBPF: optical band-pass filter; OTDL: optical tunable delay line; PCF: photonic crystal fiber; PM: phase modulator; PRBS: pseudorandom binary sequence; SMF: single mode fiber. To produce a 40 Gb/s OTDM signal, a 10-GHz pulsed source is obtained from the output of a mode-locked fiber laser (MLFL). The laser pulses are modulated by an electro-optic modulator with a 2 7 -1 pseudorandom binary sequence (PRBS) and optically multiplexed to 40 Gb/s. The 40 Gb/s OTDM data are then combined with the time- and wavelength-interleaved pulses. A tunable optical delay line is added after the multiplexer to ensure synchronization between the two light branches. The combined signal is directed to an erbium-doped fiber amplifier through a polarization controller and is then amplified to 27 dBm. FWM occurs inside the photonic crystal fiber (PCF) and four new wavelengths are generated. As different wavelength components reside at different time slots in the time- and wavelength- interleaved pulsed source, each converted wavelength component contains information in a particular channel of the OTDM data. By filtering out the four generated components, four WDM channels are obtained. As a result, OTDM to WDM conversion is achieved. FK4 978-1-4244-4103-7/09/$25.0 © 2009 IEEE