JOURNAL OF LIGHTWAVE TECHNOLOGY, VOL. 18, NO. 10,OCTOBER 2000 1453 A Performance Analysis of All-Optical Clock Extraction Circuit Based on Stimulated Brillouin Scattering Xiang Zhou, Member, IEEE, Hossam H. M. Shalaby, Senior Member, IEEE, Lu Chao, Member, IEEE, T. H. Cheng, Member, IEEE, and Peida Ye, Fellow, IEEE Abstract—In this paper, we develop an analytical method to deal with the timing performance in an optical clock extraction circuit based on stimulated Brillouin scattering (SBS). Three kinds of SBS active filters are considered and their frequency-transfer functions are obtained under the assumption that pump depletion caused by SBS is negligible. When pump depletion is taken into account, an SBS active filter acts as a nonlinear filter. To investigate the timing performance at this situation, we introduce the concept of “dy- namic frequency-transfer function” to describe its frequency-re- sponse property for a fixed-signal light and pump light. Using the obtained “frequency-transfer function,” we give analytical expres- sions for both root-mean-square (rms) phase jitter and rms ampli- tude jitter of the extracted optical clock, in which we have taken the impacts of SBS gain, pump light linewidth, optical pulse chirp, and pump detuning into account. Finally, a detailed numerical in- vestigation on the timing performance for the three active filters is presented. Index Terms—All-optical signal processing, optical active filter, optical clock extraction, optical tank circuit, rms amplitude jitter, root-mean-square (rms) phase jitter, stimulated Brillouin scattering (SBS). I. INTRODUCTION T HERE is a growing demand for very-high-speed data transmission and processing systems, that exceed the speed limit of conventional electronic circuits. All-optical signal processing is the most promising scheme to achieve such system because of its potential of ultrahigh-speed response. System synchronization is one of the serious problems in con- structing all-optical signal processing systems, such as all-op- tical regenerative repeaters, all-optical time-division switching systems, and all-optical demultiplexers. In order to realize the system synchronization, an all-optical clock extraction circuit, which recovers a timing information from an incoming optical data stream and produces an optical clock without an interme- diate electric stage is required. Up to the present, several optical timing extraction techniques suitable for high-speed operations have been demonstrated, some examples include inject-locking of a mode-locked laser [1], [2], optical phase-lock loop (PLL) [3], [4], optical passive tank circuit based on Fabry–Perot resonator [5], [6], and optical active tank Manuscript received March 28, 2000. X. Zhou, H. H. M. Shalaby, L. Chao, and T. H. Cheng are with the School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798. P. Ye is with the Beijing University of Posts and Telecommunications, The Office of President, Beijing, 100876, China. Publisher Item Identifier S 0733-8724(00)09096-4. circuit based on stimulated Brillouin scattering (SBS) [7]–[9]. Each of these methods has advantages and drawbacks. For the mode-locked laser, high-quality clock can be recovered, however, when setting up the laser the cavity length must be tuned carefully. For optical PLL, extremely stable operation is obtainable but such a technique is very complex and more suitable for clock extrac- tion at the frame rate. Compared with the previous two methods, optical passive tank circuit based on Fabry–Perot resonator has the advantages of ultrahigh-speed operation and simple config- uration due to its passive structure. For this circuit, however, it is impossible to independently control the center frequency of each passband and the free-spectral range (FSR). Consequently, there exists a tradeoff between the carrier frequency control and the FSR variation of the resonator, also carrier frequency varia- tion will introduce a phase wander in the extracted optical clock [10]. To overcome some of these drawbacks, an active optical tank circuit based on the comb-shaped gain spectrum generated by a Brillouin amplifier was proposed and demonstrated [7]–[9]. In [7], Kawakami et al. use several continuous-wave (CW) lights with different center frequencies as pumps to amplify multiple clock-related line spectral components of the optical data signal. In their systems, the center frequency of each pump light can be tuned separately; as a result, absolute-gain band frequency and FSR can be independently controlled. In [8], Butler et al.directly use the comb spectral components of the signal light as the pump lights.Inthisscheme,theclockcanberecoveredinopticaldomain without the knowledge of the incoming data bit rate, moreover, it can also be used for multiwavelength all-optical clock recovery, as was shown in [9]. In this paper, we present an analytical study on the timing performance of the active optical tank circuit based on SBS. To our knowledge, this is the first time this issue is being dealt with. Through the classical parameter-coupling model of stim- ulated scattering, we find that an SBS active filter acts as a linear filter when pump depletion cased by SBS is negligible. Based on this, we obtain its frequency-transfer function. When pump depletion cased by SBS cannot be neglected, an SBS ac- tive filter becomes a nonlinear filter. To investigate the timing performance at this instance, we introduce the concept of “dy- namic frequency-transfer function” to describe its frequency-re- sponse property for a fixed signal light and pump light. Then, by using the obtained “frequency-transfer function,” we give ana- lytical expressions for both root mean square (rms) phase jitter and rms amplitude jitter of the extracted optical clock. Using these formulas, we present a detailed numerical investigation 0733–8724/00$10.00 © 2000 IEEE