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Wavelength-division multiplexed (WDM) transmission is now indispensable for increasing transmission capacity and for realizing all optical networks. But, it requires the wavelength stabilization of each laser diode (LD) to avoid adjacent channel cross talk and signal reduction at receivers. Most wavelength stabilization schemes have used a Fabry-Perot (FP) etalon with absolute wavelength reference,' or synchronized etalon filter providing identical sets of absolute references2 Above schemes, however, need complicated control circuits and algorithms, and provide only equally spaced wavelengths. Furthermore, for optical add/drop nodes, which require only a few optical sources and sometimes need frequency offset for added channels, a simple and decentralized wavelength control is preferred.In this paper, we present a simple and yet effective way of wavelength stabilization using a fiber grating, which is known to provide high stability so as to keep the wavelength variation < 0.05 nm over 100 "C with a thermal pa~kaging.~ Because our scheme is based on a level detection technique using both transmission and reflection profiles of a fiber grating, it doesn't require dithering signals or complex electronics. Furthermore, for the convenience of an operator it provides wavelength warning lamps, which indicates the current wavelength position compared with the reference. Figure 1 shows our wavelength stabilization scheme and Fig. 2 its principle. As can be seen in Fig. 2, the reference wavelength A,, where Fiber Grating Transmitted I Lamp1 WM45grating. Fig. 1. Schematic diagram of the wavelength stabilization using a fiber 2. T r a n s m i t t e d ( + ) Reflected(-) s t / / ;Lo ho+Ah ho+2Ah A wavelength WM45 Fig. 2. Principle of the proposed scheme.we want the LD wavelength to stay, is Ah away from the reflection peak of the fiber grating. If the input wavelength is shorter than the reference, then the wavelength control circuit increase the TEC current of the LD until its wavelength moves to the reference, and vice versa. Figure 3 shows the measurement result of wavelength deviation while distributed feedback [(DFB) LD bias current was incremented by 2 mA for each step over 10 mA. This test was done to simulate LD aging process, that usually requires more bias current to have constant output power. As illustrated in the figure, wavelength was fixed at the initial value when the proposed wavelength control was applied, while about +0.011 nm/mA of wavelength drift was found under constant temperature. And the standard deviation of wavelength variation during a short time period was also found to de-0.12 -0.1 2 0.08 1 L + 0.06 r_ 0) 0.04 7 i 0.02 a, 2 0 -n n7 I TEC Control ".--125mA ' 27mA 29mA 31mA 33mA 35mA I -0.04 Bias current of laser diode WM45Wavelength deviation vs. the bias current of a DFB LD; standard deviation of wavelength variation (a) with TEC control: 9.85 pm; (b) with wavelength control: 5.98 pm. Fig. 3.