Optical control of period doubling in a gain-switched Fabry-Perot laser diode and its application in all-optical clock division

Optical injection is shown to be an effective means to suppress or to enhance period doubling of a gain-switched laser diode. The role that the injection plays depends on whether the laser resonance frequency is larger or smaller than half the modulation frequency. Reversible control of period doubling has been demonstrated experimentally using a modulated injection source. An injection power as low as 0.03 mW has been used to control the output pulse repetition frequency of the slave laser. The response time is measured to be shorter than 100 ps. The phenomenon has been applied successfully for use in all-optical clock frequency division. Replacing the electrical modulation with an input clock signal at 19.6 GHz, a frequency-halved output clock with a remarkable low-level phase noise (-87.7 dBc/Hz at 10 kHz offset frequency) has been obtained. The change in the phase noise level is observed to be smaller than 1 dB over a frequency detuning range of 400 MHz.