Simultaneous Label Erasure and Rewriting using a Single Reflective Semiconductor Optical Amplifier for DPSK/ASK Optical Label Switching

Abstract

In future all-optical packet networks, optical label switching technology is expected to be a promising candidate for fast and accurate data packet transmission [1,2]. To implement such networks, a simple yet low cost optical label swapping technique should be realized at the intermediate nodes. Many research efforts have been developed, based on the promising technique of orthogonal label modulation [3] due to its simple design in optical label swapping [4]. In recent years, the nonlinear phenomenon in semiconductor optical amplifiers has been widely utilized for applications in optical label erasure [5]. Recent advances in the fabrication of reflective semiconductor optical amplifiers (RSOAs) have enabled high small-signal gain, medium saturation power, and direct data modulation to be achieved [6]. In this work, we present the first demonstration of optical label swapping using an RSOA. Specifically, we exploit the high pass filter (HPF) behavior [7] originating from self-gain modulation (SGM) of the saturated RSOA to achieve simultaneous erasure and rewriting of an amplitude-shift-keying (ASK) label. We demonstrate the feasibility of a 1.25 Gb/s amplitude-shift-keying (ASK) label erasure with new label rewrite through direct modulation of the RSOA. Fig. 1 illustrates the concept of optical label switching at an intermediate network node. Initially, a fraction of the optical packets entering the network node are tapped with the tapped signals used to perform a number of time critical functions such as packet label (in the case of label switching)/header (in the case of packet switching) recognition, generation of new label for forwarding, and generation of gating pump signal to perform timing or wavelength conversion or switching functions. The other portions of the incoming optical packet with a ASK label and a differential-phase-shiftkeying (DPSK) payload is directed to an optical buffer for time adjustment. The new label rewriting process is performed at the label erasure and rewriting module, where the old ASK label is simultaneously being erased whilst a new label is inserted on top of the payload. Shown in Fig. 2 is our proof-of-concept experiment. An optical label switched signal with a 1.25 Gb/s 2 31 -1 PRBS ASK label and a 10 Gb/s 2 31 -1 PRBS DPSK payload is generated by externally modulating a continuous light from a DFB laser diode. The extinction ratio of the label is initially set at 2 dB. In order to evaluate the performance of label swapping under different power levels, the optical label switched signal is amplified by an EDFA and is ASE filtered. The signal power is controlled by an attenuator, before launching into the RSOA via the circulator. The input signal saturates the RSOA and experiences a HPF effect under the presence of SGM. Consequently, the low frequency ASK label is suppressed, whilst the highspeed DPSK payload remains unaffected. Meanwhile, the new 1.25 Gb/s ASK label can be rewritten on top of the payload by directly-modulating the carrier density of the RSOA. As a result, simu...

Demonstration of a data remodulation scheme with downstream ASK-DPSK signals and upstream OOK signal using RSOA for WDM-PONs

“…It allows that every bit has light power all the time, without any powerless slots, thus it can release the rate limitation in the upstream direction. RSOA will erase the downstream ASK signal and rewrite upstream OOK signal, its feasibility has been demonstrated in [6]. After injecting DPSK signal into RSOA, the upstream OOK signal remodulated over downstream DPSK signal will not suffer obvious phase-to-intensity signal fluctuation [7].…”