Abstract

The narrow-spectral-linewidth laser diode is a key device to construct the coherent optical communication systems. The long cavity distributed feedback (DPB) laser is expected to show the narrow linewidth. Very recently, we have reported that a narrow spectral linewidth of 1.7 MHz was obtained for a 1.2 mm cavity length DFB laser¹⁾. The long cavity is essential for narrowing the linewidth. However, the long cavity DPB laser often gives multiple- longitudinal -mode operation because of the small threshold gain difference between DFB modes and also because of the reduction in the gain difference at high injection level due to the effect of the spatial hole burning^. The cavity length was limited by these problem and the linewidth narrowing was not realized.

© 1988 Optical Society of America