InGaAs/InGaAsP multiple quantum well distributed feedback lasers

A description is given of 1.5-μm lasers grown entirely by atmospheric pressure metalorganic vapor-phase deposition. InGaAs/InGaAsP Fabry-Perot separate confinement heterostructure QW lasers with cleaved mirrors have been shown to operate well when the number of quantum wells was four or higher. In the present case, due to the large feedback provided by the DFB gratings, the number of quantum wells has been reduced to three. The lasers have threshold currents of 20-30 mA with a cavity length of 300-700 μm. Some devices operated in a single longitudinal mode at up to 10 mW CW output power. Measured linewidths of these devices, using both Fabry-Perot and delayed self heterodyne techniques, are shown. A tunable phase-shifted DFB laser was fabricated adding an intracavity passive QW phase modulator section. When the voltage of the phase modulator section was adjusted every device could be operated with a single longitudinal mode and switching between single or double DFB mode operation was possible. Under single mode operation, small signal voltage modulation of the modulator section results in fast modulation of the effective refractive index due to the quantum confined electrooptic effect. The FM modulation response of the laser diode as a function of frequency is shown.