Recent progress in WDM systems requires the use of large number of channels at narrow spacing. Thus, it becomes important to control the optical frequency of each laser precisely. For example, when the channel spacing is 50 GHz, the frequency of each laser (operating at 10 Gb/s) should be stabilized to better than ±2.5 GHz [1]. However, because of aging, the frequencies of DFB lasers may drift up to a few tens of GHz even when their operating conditions (such as bias current and temperature) remain constant [2]. Recently, there have been some efforts to improve the frequency stability of WDM lasers by using etalon filters, fiber gratings, or AWG's as frequency reference [3]-[5]. However, most of these techniques require as many phase-sensitive detectors as the number of WDM channels. Thus, it becomes complicate and expensive as the WDM channels are increased. In this paper, we propose and demonstrate a simple technique for the simultaneous stabilization of multiple WDM lasers. This technique utilizes a solid etalon filter and a digital signal processing (DSP) board.
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