Intermodal tuning characteristics of an InGaAsP laser with optical feedback from an external-grating reflector

A report is presented on the spectral characteristics of one-side antireflection coated 1.3-μm InGaAsP lasers exposed to strong feedback from an external grating, when the center wavelength of reflection of the grating is tuned continuously from one solitary laser longitudinal mode to the adjacent lower frequency mode. The effect of different residual reflectivities of the coated facet on the tuning characteristics of the laser was investigated experimentally. Bistability in the tuning characteristic is explained using a graphical representation of operating conditions. The stability of single-mode oscillation is found to depend on the offset between the resonance frequency of the solitary laser and the frequency of maximum reflection from the grating. An offset between the oscillation frequency of the laser and the frequency of maximum reflection from the grating is shown to occur