High-Speed All-Optical Switches Based on Cascaded SOAs

Abstract

Lots of research efforts have been focused to realize all-optical high-speed switches through nonlinear optical elements, for instance, high nonlinear fibers (HNLF), nonlinear waveguides as well as semiconductor optical amplifiers (SOAs). All-optical switches incorporating SOAs is one of the particularly attractive candidates due to their small size, high nonlinearities (low switching energy required) and ease of integration. All-optical switches also keep the network transparent, enhance the flexibility and capacity in network, and offer the function of signal regeneration, therefore SOAs provide various attractive alloptical functions in high-speed signal processing in fiber communication systems (Stubkjaer, 2000; Poustie, 2007), including all-optical AND/XOR logic gates, wavelength conversion (WC), optical-time division multiplexing (OTDM) de-multiplexing, optical signal regeneration and so on, which will be essential to the implementation of future wavelength division multiplexing (WDM) or optical packet switching (OPS) networks. However, the operation speed of SOA based switches is inherently limited by its relative slow carrier lifetime (in an order of 100 ps) (Manning et al., 2007). Various schemes have been proposed to enhance the operation speed of SOA-based all-optical devices, for instance, 160 Gb/s and 320 Gb/s wavelength conversion was reported by using a detuned narrow band-pass filter to spectrally select one of the side-bands (blue-shifted or redshifted) of the output signal (Liu et al., 2006, 2007). In this case, the SOA operation speed can be increased via the chirp effect on the SOA output associated with the SOA ultrafast gain dynamics. It has been shown that, the CW modulation response time has been reduced from 100 ps to 6 ps via filter detuning (Liu et al., 2006, 2007). Although using a detuned filter after the SOA can improve the optical signal-to-noise ratio (OSNR) of the output when comparing with the case of using a non-detuned filter (Leuthold, 2002), however the OSNR of the output signal will degrade to a large extent since the optical carrier was suppressed. Recently, all-optical high-speed switches based on the cascaded SOAs were proposed and demonstrated. In Fig. 1, an all-optical switch incorporating two cascaded SOAs was proposed as an alternative high-speed technique, which was dubbed as “turbo-switch” (Manning et al., 2006; Yang et al., 2006, 2010), while preserving the OSNR of the output signal. An error-free wavelength conversion was demonstrated at 170 Gb/s (Manning et al., 2006). In addition, the operating speed of an all-optical XOR gate was also demonstrated at