1.5μm Tunable Wavelength Filter with Wide Tuning Range and High Constant Gain Using Phase Controllable DFB LD

Abstract

A tunable wavelength filter with constant transmissivity (gain) and bandwidth is a key device for wavelength division multiplexing networks. Such a filter has recently been demonstrated with a multi-electrode DFB LD[1]. This filter is biased at just below the threshold current in operation. It has two current injection sections, and the transmission wavelength and gain are controlled by changing the two currents. Since each current causes simultaneous change of the wavelength and the gain, it is difficult to obtain a large transmission wavelength tuning range maintainig a large gain. Thus, tuning range has been restricted to 20.6GHz. We demonstrate here a wide range tunable wavelength filter which uses a phase controllable distributed feedback laser diode(PC DFB LD). We call this filter a PC DFB LD filter. In this filter, the gain and the wavelength are controlled almost separately. Therefore, tuning range as wide as 43GHz has been achieved. This wavelength tuning range is the widest of any semiconductor tunable wavelength filter, to our knowledge. In the wavelength tuning operation, 27dB gain and 5GHz bandwidth have been maintained.