2156 IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 16, NO. 9, SEPTEMBER 2004 Optical Label Swapping in a Packet-Switched Optical Network Using Optical Carrier Suppression, Separation, and Wavelength Conversion Jianjun Yu, Member, IEEE, Gee-Kung Chang, Senior Member, IEEE, and Qimin Yang Abstract—We have experimentally demonstrated for the first time how to realize label swapping in an optical network where the label and payload are generated using optical carrier suppression and separation. The bit-error-rate performance for both the payload and label are evaluated at different nodes in this optical network. Index Terms—Optical carrier suppression and separation (OCSS), optical label switching, optical network, wavelength conversion. I. INTRODUCTION M ANY RESEARCHERS are exploring optical packet-switching technology without expensive elec- tronic termination and regeneration of the payload traffic at each node of the optical networks [1]–[6]. One of the most promising approaches is optical label switching which enables routing and forwarding of ultrahigh bit rate packets directly in the optical layer. Recently, we have demonstrated a novel method, namely, the optical carrier suppression and separation (OCSS) technique to generate optical label and payload with fixed frequency spacing [5]. The principle of this method has been reported in [5] and an eight-channel wavelength-divi- sion-multiplexing signal, each channel with individual payload and label, has been transmitted over 200 km [6]. In this letter, we will demonstrate how to further exploit the technique in a multiple node network, and the experiment focuses on label swapping within the core node. II. OPTICAL CORE ROUTER DESIGNS Fig. 1 shows proposed label swapping configuration within an optical core router using the OCSS technique and wavelength conversion technique. Assume the incoming packet has its label and payload at wavelength and , respectively. Using the same OCSS technique, the wavelengths are given by , , where is the carrier wavelength of the source before the OCSS, is the speed of light, and is the modulation frequency of sinusoid clock for optical carrier suppression. Therefore, the frequency spacing and wavelength Manuscript received January 9, 2004; revised May 17, 2004. This work was supported in part by a grant from Georgia Research Alliance and Bellsouth. J. Yu and G.-K. Chang are with the School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0250 USA (e-mail: jianjun@ece.gatech.edu). Q. Yang is with the Engineering Department, Harvey Mudd College, Clare- mont, CA 91711 USA. Digital Object Identifier 10.1109/LPT.2004.833045 Fig. 1. Optical core router configuration. spacing between the label and payload are and , respectively. The payload and label are separated by using op- tical filtering technique. The detected label at is processed electronically to make packet forward decision or to generate a new label as required. In multiple node networks, however, if each node uses a different distributed feedback (DFB) laser to generate the new label, it becomes very challenging to maintain a fixed frequency spacing between the label and payload be- cause of the wavelength drifting from gradual temperature vari- ation and aging. To keep the same frequency spacing of the new label and new payload, we employ the same OCSS technique within the core router to first generate two lightwaves at wave- length of and , respectively. Here, , . The lightwave at is used to carry the new label through a lithium-niobate modulator (LN-MOD). And the payload at its original wavelength is converted to the other lightwave at by wavelength conversion. As a result, the new payload and new label has a wavelength spacing of or a frequency spacing of . Although wavelength spacing is changed, this change is relatively small for the given fixed . For example, when is 10 GHz, the wavelength spacing be- tween the payload and label is 0.078 nm at nm, and it is changed to be 0.081 nm if nm. Wavelength conversion schemes can be realized using semiconductor optical amplifier based on cross-phase modulation (XPM) or cross-gain 1041-1135/04$20.00 © 2004 IEEE