Novel 1.55-μm multielectrode DFB source for coherent transmission systems

Abstract

A multielectrode 1.55-μm distributed-feedback (DFB) laser with an interdigitated p-contact is discussed. Superior single-longitudinal-mode (SLM) operation has been observed with this device, which has a continuous tuning range of over 20 angstrom and a flat FM response. Current spreading between the fingers of the interdigitated contact reduces the net round-trip phase change. Thus, within operating conditions, differential pumping leads to continuous wavelength tuning without mode hops. Up to 15-angstrom continuous tuning can be obtained with approximately 5% power variation. A high FM efficiency of 800 MHz/mA was observed for a 3-dB FM response from 100 kHz to 2 GHz. The FM response and output power at a fixed modulation frequency of 500 MHz were measured as a function of DC bias current. At high bias currents, spatial hole-burning effects decrease the carrier density directly under the ridge and consequently allow the carrier density in the channels to increase. This reduces the overall gain clamping and allows a more efficient response to the modulation frequency. As the clamping is more stringent in a buried-heterostructure DFB laser, this is an added advantage of the ridge waveguide DFB structure. Thus, a relatively large FM efficiency can be achieved without compromising the output power. Show more