All-optical Switching of 80 Gb/s Data Packets using a Wavelength Converter Controlled by a Monolithically Integrated Optical Flip-flop

We demonstrate all-optical switching of 80 Gb/s data-packets using an optical wavelength converter that consists of an SOA and an optical filter. The wavelength converter is controlled by a monolithically integrated optical flip-flop memory. Introduction High-speed all-optical switches offer advantages in power consumption, foot-print and switching architectures compared to their electronic counterparts [1]. An essential building block of an alloptical packet switch is an optical flip-flop memory that is used to store the switch decision information. It has been demonstrated in [2] that an optical flip-flop based on two symmetrically coupled lasers can control an optical packet switch. In that particular configuration, the optical flip-flop state was set by an optical header recognizer, and the flip-flop controls a wavelength routing switch. The flip-flop presented in [2] had a switching time of about 2 μs, since it was implemented using fiber pig-tailed components, which made that the cavity length of each laser was in the order of 10 meters. Recently, we realized a monolithically integrated version of the flip-flop used in [3]. This flip-flop exhibits single-mode operation, has 35 dB contrast ratio between the states and switches state in about 2 ns. In this paper, we show that a wavelength converter controlled by this flip-flop allows error-free wavelength conversion at 80 Gb/s. A clear open eye indicates that the system can also operate error-free at 160 Gb/s. Moreover, we demonstrate that this system is capable of switching data packets with duration of 35 ns and a guard time of 15 ns. System Our experimental setup is shown in Fig. 1a. The system under investigation consists of two parts: an integrated optical flip-flop (FF) and an all-optical wavelength converter (AOWC). At the transmitter side, a 10-Gb/s 2−1 return-to-zero (RZ) pseudo random binary sequence (PRBS) data packet consisting of 1.9-ps optical pulses is multiplexed to 80-Gb/s by using a passive fiber-based pulse interleaver. The 80 Gb/s data packets have duration of 35 ns, separated by 15 ns of guard time. The data packets are combined with the continuous wave (CW) output from the FF, and are fed into the AOWC via a 3-dB coupler. The optical flip-flop is an integrated InP/InGaAsP two state coupled laser device, fabricated on a InP/InGaAsP material wafer, which contains active areas with 1550 nm emission wavelength InGaAsP for semiconductor optical amplifiers (SOAs). A deep/shallow double etch process was employed to construct the waveguides. Deep etching permitted small radius waveguide bends and thus small device dimensions (2.4×0.8mm). The wave-guide mask is shown in Fig. 1c. The use of an arrayed waveguide grating (AWG) and ring laser configuration permits monolithic integration without the need for cleaved facets. Details of the FF can be found in [2]. The FF is packaged by using a Peltier cooled micro-mechanical sub-assembly. The coupling efficiency is -5 dB, given the lens radii of 15 μm of the 4-fibre array and the geometrical dimensions of the waveguides (0.6×2 μm). The operation of the FF is described in [4]. In brief, the FF has two stable states. In State 1, Laser 1 is lasing, suppressing Laser 2. In this state the FF