All-optical frequency conversion using nonlinear dynamics of semiconductor lasers subject to external optical injection

There has been much effort devoted to frequency conversion technology due to strong demand for optical communication systems. A frequency converter converts an incoming optical carrier of one frequency to an outgoing optical carrier of another frequency while preserving the quality of carried data. The all-optical approach is promising for such a purpose because not only the complexity and power consumption of a converter are much reduced but also the flexibility and reconfigurability are greatly improved. However, most proposed methods, such as applying cross gain modulation in semiconductor optical amplifiers, suffer from the need of a probe or a pump beam besides the incoming optical carrier, making systems complicated and costly. In this study, we propose to use semiconductor lasers as frequency converters instead, where no probe or pump beam is necessary. When a semiconductor laser is subject to an incoming optical carrier, equivalently an external optical injection, it can enter into period-one dynamics through Hopf bifurcation. By taking advantage of the dynamics, tens of gigahertz of frequency conversion can be achieved, which can be continuously and dynamically tuned by controlling the injection level and frequency. The conversion efficiency and transmission efficiency can also be varied through the change of both injection parameters. Their behaviors as functions of the parameters, however, are opposite to each other. High conversion efficiency is observed to achieve under low levels of injection, where strong filtering of frequency may not be necessary and significant signal amplification can be achieved. Low bit-error-rate and a 3-dB penalty are also observed, suggesting the quality of carried data is preserved.