Narrow Linewidth Photonic Microwave Generation Based On An Optically Injected Semiconductor Laser Under Subharmonic Modulation

Microwave photonics is a new technology that combines wireless communication technology and optical technology.The main research is to generate,convert,process,distribute and transmit microwave wireless signals by optical methods.Photonic microwave has the advantages of high frequency,can be transmitted in optical fiber,easy to carry out wavelength division multiplexing,free from electromagnetic interference and so on.It is widely used in satellite communication,radar system,Radio-over-Fiber(RoF)communication system,and other fields,especially in the field of RoF communication.The RoF communication system can be regarded as a microwave photonic link used to transmit,distribute,and return wireless signals,and is an important application of microwave photonics in the field of broadband wireless communication.The common photonic microwave technologies mainly includes direct modulation,external modulation,optical heterodyne and so on.These technologies have their own advantages,but they also have room for improvement in some key performance parameters.In recent years,the methods of generating photonic microwave by photoelectronic oscillator(OEO)and period-one(P1)oscillation of an optically injected semiconductor laser has been widely concerned.The former can generate microwave signals with high stability and low phase noise,and the microwave signals generated by the latter have the advantages of high frequency,single sideband spectral structure characteristics,and large frequency tunable range.In this work,the generation of narrow linewidth photonic microwave using the period-one dynamics of an optically injected distributed feedback semiconductor laser(DFB-LD)subject to 1/2 subharmonic modulation by an OEO is proposed.The photonic microwave frequency locking effect and line width compression effect in this scheme were investigated experimentally.In this scheme,OEO is used as the signal source to provide subharmonic modulation signal due to the low phase noise and high stability of microwave signal generated by OEO.The results show that the optically injected DFB-LD at P1 oscillation can output photonic microwave with single-sideband(SSB)spectral structure,but the linewidth of the microwave signal is wide(on the order of MHz).After the P1 oscillation of optically injected DFB-LD subject to 1/2 harmonic modulation using the microwave signal with frequency of 7.62 GHz produced by OEO,the resulting photonic microwave is locked at 15.24 GHz.The linewidth is effectively compressed to 1 kHz,and the SSB phase noise is-94 dBc/Hz,which is comparable to the level of microwave signal noise produced by OEO.