Generation Of Microwave Frequency Combs Based On A Semiconductor Laser Subject To Incoherent Optical Feedback

Microwave frequency combs (MFCs) can provide multiple frequency microwave signals, so they have a great application prospect in radar detection, broadband wireless communication and so on. Traditional microwave frequency combs generating scheme based on electrical way can acquire microwave frequency comb signal whose bandwidth can reach several GHz, even more than a dozen GHz, but its applications are very limited because of this microwave frequency comb can not be tuned flexibly. In addition, limited by electronic frequency neck, this kind of electronic circuit scheme is difficult to expand. In recent years, based on an optical method to generate microwave frequency comb has received a wide attention. For the incoherent optical feedback semiconductor laser (SL) system, the optical feedback affects not the light field but the laser’s carriers. On one hand, it avoids the optical phase sensitivity which always influenced by the case of the coherent optical feedback. On the other hand, incoherent optical feedback semiconductor laser system belong to the full optical system, it does not suffer from electronic bandwidth limitations, it can satisfy the requirements to generate ultra broadband microwave frequency combs.Based on a semiconductor laser with incoherent optical feedback, an novel all-optical scheme for generating tunable and broadband microwave frequency combs is proposed and investigated numerically. The results show that, under suitable operation parameters, the SL with incoherent optical feedback can be driven to operate at a regular pulsing (RP) state, and the generated MFCs have bandwidths broader than 40 GHz within a 10 dB amplitude variation. For a fixed bias current, the line spacing (or repetition frequency) of the MFCs can be easily tuned by varying the feedback delay time and the feedback strength, and the tuning range of the line spacing is increased with the increase of the bias current. The linewidth of the MFCs is sensitive to the variation of the feedback delay time and the feedback strength, and a linewidth of tens of KHz can be achieved through finely adjusting the feedback delay time and the feedback strength. Additionally, mappings of amplitude variation, repetition frequency and linewidth of MFCs in the parameter space of the feedback delay time and the feedback strength are presented.