Abstract

A frequency- or phase-modulated laser diode, whose output frequency is sufficiently narrow, is an essential device in coherent optical transmission systems⁽¹⁾. Although DFB lasers have been shown effective as FM oscillators^(2,3), the linewidths are several tens of MHz, which may be broad for a transmitter in an FSK heterodyne system. Recently, we proposed a coupled phase-shift DFB structure, which consists of a plural of quarter-wave phase shifted DFB lasers coupled through another quarter-wave phase shifts^(4). It was pointed out that this structure provides a narrow-linewidth, monolithically constructed laser diode. This result was obtained, because the cavity length can be expanded without increasing the spatial hole burning along the axial direction^(4).

© 1988 Optical Society of America