PERFORMANCE IMPLICATIONS OF THE THERMAL-INDUCED FREQUENCY DRIFT IN FAST WAVELENGTH SWITCHED SYSTEMS WITH HETERODYNE-DETECTION

The frequency modulation response and timing dynamics of a two-section DFB laser are determined by carrier and thermal modulation of the act ive layer refractive index. In response to a step change in the inject ion current for switching between channels in a wavelength division mu ltiplexed system, the optical frequency changes rapidly due to the car rier effect, and then slowly drifts toward a steady state value due to the thermal effect. For wavelength switched applications with heterod yne detection, the drifting of the optical frequency broadens the spec trum of the IF signal and may impose a limit on the time that the sign al remains within the IF passband (residency time), The TF spectral br oadening and residency time are investigated theoretically and experim entally. Based upon a minimum mean square error fit between experiment al and theoretical FM responses, the dependence of the spectral broade ning and residency time on the bias condition of the laser and the opt ical frequency snitching interval is characterized.