Source wavelength dependence of modulation frequency responses of 1.55-um DFB LDs measured with active layer photomixing technique

With the active layer photomixing technique, parasitic-free intrinsic modulation frequency responses of semiconductor laser diodes (LD's) can be measured. But the mechanism of the carrier density modulation, and consequently, the region where the carrier density is modulated, depends on the wavelengths of the injected beams. In this paper, the modulation frequency response of a 1.55 µ m distributed feedback LD has been measured with the active layer photomixing technique under two distinct conditions; one is the case when the carrier density is modulated by the band-band absorption, and the other by the stimulated emission. The measured modulation frequency responses are quite different from each other. Especially, the response at the relaxation oscillation frequency in the band-band absorption case is suppressed about 1 OdB compared with that in the stimulated emission one.