TuB 4 80 to 10 Gbitls Demultiplexing using Fiber Cross - Phase Modulation and Optical Filtering

Future ultra high bit-rate optical time division multiplexed (OTDM) systems may require all-optical demultiplexing to down convert high bit-rate data to e.g. 10 Gbit/s or 40 Gbit/s where electronic circuits can be used. Many suggestions of such demultiplexers have been proposed over the years. The most common device is the nonlinear optical loop mirror (NOLM) that allows switching due to cross phase modulation (XPM) in either a fiber [ l ] or a semiconductor optical amplifier (SOA) [2]. Another approach is to use four wave mixing (FWM) in either a SOA or a fiber [3]. In all these schemes the switch window for the demultiplexed OTDM channel can usually not be shorter than the pulse width of the control pulse that initiates the XPM or FWM, and thus a very short, high quality, optical pulse is required [4]. Here we demonstrate a new demultiplexer based on XPM in a fiber that utilizes the derivative feature of XPM induced spectral broadening. The basic idea is that the leading edge of the control pulse generates a red shift of the spectrum of the XPM modulated input signal, and the trailing edge generates a blue shift. We have previously reported wavelength conversion using this technique where the incoming data phase modulate continuous wave (CW) light with subsequent conversion to amplitude modulation [5]. Here, only one of the OTDM data channels in the high bit-rate data is spectrally broadened and that channel can then be extracted with a narrow band optical band-pass filter at either side of the original spectrum. Thus, only one edge of the control pulse governs the width of the demultiplexing switch window, if dispersive walk-off is neglected. Therefore a control pulse broader than the actual bit slot can be used for demultiplexing. Another important feature of this demultiplexer compared to the NOLM is that it is not an interferometer, which makes the device completely insensitive to environmental disturbances even though a long length of fiber is used.