THEORY OF MODULATION OF AN INJECTION-LOCKED SEMICONDUCTOR DIODE-LASERWITH APPLICATIONS TO LASER CHARACTERIZATION AND COMMUNICATIONS

The current-modulation properties of an injection-locked semiconductor diode laser are investigated, with focus on the two values of detunin g at which the intensity or the phase-modulation sensitivity of the sl ave laser is a minimum. The master laser's frequency for minimum AM mo dulation is located near the lower edge of the locking band, and the c ondition for minimum FM response is just that of synchronization befor e injection, a stable operating point at 2% injection level that coinc ides with the point of maximum modulation bandwidth. The relaxation-os cillation resonance in the modulation spectrum can be largely removed by passage through a dispersive medium such as an optical fiber so tha t instead of deteriorating by fiber dispersion, the combined bandwidth of a properly designed system, in which the fiber length is limited o nly by loss, can exceed that of the injection-locked laser alone. In a nother application an accurate determination of the line-broadening fa ctor, cu, from the solitary-laser output power and the power at the tw o mentioned operating points is shown possible. The harmonic distortio n is also evaluated, as relevant to cu measurement and high-bandwidth modulation. (C) 1997 Optical Society of America.