Abstract

Semiconductor lasers with cavity length about few millimeters and beyond and incorporating some passive sections and optical fibers like DBR become now to be popular for mode-locking with repetition rate in gigahertz region. Such lasers, if operating in single-mode cw regime, are very attractive also for use in coherent optical communications, since increasing of laser length to, say, 1 cm may help to make them much more tolerant to back reflections¹ and reduce the laser linewidth down to kHz- region.² This however requires high side mode suppression ratio (MSR), that seems to be questionable when the optical filter bandwidth is much larger than mode spacing.

© 1994 Optical Society of America