Proceedings of 29th European Conference on Optical Communication (ECOC2003), vol. 3, pp. 794-795,Rimini, Italy, September 21-25, 2003 Semiconductor Based True All-Optical Synchronous Modulator for 3R Regeneration T. Tekin, C. Bornholdt, J. Slovak, M. Schlak, B. Sartorius, J. Kreissl, S. Bauer, C. Bobbert, W. Brinker, B. Maul, Ch. Schmidt, H. Ehlers Fraunhofer-Institut für Nachrichtentechnik, Heinrich-Hertz-Institut Einsteinufer 37, 10587 Berlin, Germany. www.hhi.fraunhofer.de Tel.: +49 30 31002 703, Fax: +49 30 31102 241, Email: tekin@hhi.fhg.de, Email: bornholdt@hhi.fhg.de Abstract True all-optical synchronous modulation at 40 Gbit/s is demonstrated for the first time. Self-pulsating PhaseCOMB-lasers and MZIs with integrated 2mm long SOAs are developed and applied. Excellent re-timing and partial re-shaping of degraded signals is demonstrated. Introduction Optical 3R signal regeneration (re-amplification, re- timing, re-shaping) is a key function, needed in all- optical networks to overcome the transmission limita- tions. Synchronous modulation is one important tech- nique for realizing re-timing and partially also re- shaping /1/. The synchronous modulation block is de- picted in Fig. 1 on the right side. It consists of an in- tensity and phase modulator and a clock recovery providing the retiming quality of the regeneration. The first block acts as an amplification and decision stage in front of the synchronous modulator. It is always needed for a full 3R regeneration. Leclerc et al. /1, 2/ assembled a wavelength preserving synchronous modulation type 3R regenerator, that applies pulse compression in a nonlinear fiber and subsequent spectral filtering in the first block. Excellent perform- ance at 40 Gbit/s has been verified in loop tests on four WDM channels over 10.000 km. synchronous modulation degraded data λ IN regenerated data λ OUT = λ IN all-optical clock recovery all-optical modulator amplification & decision stage block 1 Fig. 1: Principle of true all-optical 3R regeneration Raybon et al. /3/ used two-stage wavelength conver- sion in a nonlinear fiber as first regenerator block. Loop experiments at 40 Gbit/s showed transmission over distances exceeding the way to the moon and back. The efficiency of synchronous modulation thus has been demonstrated. However, in both regenerators the clock recovery has been done in the electrical domain. O-E conversion is required which is expensive and limits the speed. In this paper we present the first true all-optical syn- chronous modulator. Compact semiconductor devices are developed and their combined function for syn- chronous modulation is evaluated at 40 Gbit/s. Components for Synchronous Modulation The device applied for clock recovery is an InP based self-pulsating PhaseCOMB-laser comprising two de- tuned DFB lasers and an integrated phase section /4/. This PhaseCOMB is a very compact, DC-current con- trolled device with a total length below 1 mm. The emission wavelength is set to 1545 nm for driving the modulator effectively. A 40 Gbit/s RZ data signal is launched via a circulator into the PhaseCOMB-laser (Fig. 2). The self-pulsation is synchronized to the data rate by carrier density modulation and by fast intra- band effects. The synchronization is polarization in- sensitive due to the optimized strained bulk het- erostructure of the device. As shown in Fig. 2, the PhaseCOMB-laser extracts a low jitter clock signal out of the PRBS data stream and emits a sinusoidal pulse stream at 40 GHz. λ in    λ out DFB1 phase DFB2 PhaseCOMB 1 mm    Fig. 2: Synchronization of the PhaseCOMB-laser to a 40 Gbit/s PRBS data signal and the packaged device The second key component for the all-optical syn- chronous modulator is based on a monolithically inte- grated MZI with SOAs /5/. We used 2 mm long SOAs for optimizing the efficiency of the optically controlled modulation. The polarization independent bulk SOAs butt-coupled to the passive waveguide sections are fabricated in an etched mesa buried heterostructure geometry within pn-blocking layers. The polarization sensitivity of the monolithically integrated MZI is less than 1 dB. To reduce the residual reflections of the antireflection coated facet, the waveguides of the MZI are angled by 7° to the cleaved facets. Fig. 3 shows the packaged monolithically integrated MZI with multi- fiber connections. Fig. 3: Monolithically integrated MZI module with multi fiber arrays for chip coupling Performance of Synchronous Modulator In order to investigate the characteristics of synchro- nous modulator, a 40 Gbit/s PRBS 2 7 -1 RZ data stream (1552 nm) is coupled into the all-optical clock recovery (PhaseCOMB) (Fig. 3). The extracted 40 GHz clock signal (1545 nm) is split into two parts