Conversion between optical ASK and optical FSK using nonlinear dynamics of semiconductor lasers

When a semiconductor laser is subject to an incoming optical carrier, equivalently an external optical injection, it can enter nonlinear period-one dynamics through Hopf bifurcation due to the radical modification in field-carrier coupling of the injected laser which results from the dynamical competition between injection-imposed laser oscillation and injection-shifted cavity resonance. Equally-separated spectral components appear, of which intensity and frequency depend strongly on the injection level and frequency. This suggests that a dynamical amplitude or frequency variation of the incoming optical signal, such as amplitude-shift keying (ASK) or frequency-shift keying (FSK), respectively, would lead to corresponding dynamical variation in amplitude and frequency of each spectral component. Therefore, by properly selecting the optical frequency of the output optical carrier and by minimizing the residual ASK and FSK modulation, both ASK-to-FSK and FSK-to-ASK conversions can be achieved, where bit-error ratio down to 10 ^-12 is achieved with a slight power penalty. Only a typical semiconductor laser is necessary as the key conversion unit. In addition, frequency shifts of the optical carrier can also be achieved, which allows a simultaneous frequency conversion of the optical carrier if required.