Theory of modulation of an injection-locked semiconductor diode laser with applications to laser characterization and communications

摘要

The current-modulation properties of an injection-locked semiconductor diode laser are investigated, with focus on the two values of detuning at which the intensity or the phase-modulation sensitivity of the slave laser is a minimum. The master laser's frequency for minimum AM modulation is located near the lower edge of the locking band, and the condition for minimum FM response is just that of synchronization before injection, a stable operating point at 2% injection level that coincides with the point of maximum modulation bandwidth. The relaxation-oscillation resonance in the modulation spectrum can be largely removed by passage through a dispersive medium such as an optical fiber so that instead of deteriorating by fiber dispersion, the combined bandwidth of a properly designed system, in which the fiber length is limited only by loss, can exceed that of the injection-locked laser alone. In another application an accurate determination of the line-broadening factor, cu, from the solitary-laser output power and the power at the two mentioned operating points is shown possible. The harmonic distortion is also evaluated, as relevant to cu measurement and high-bandwidth modulation. (C) 1997 Optical Society of America.