Research Of Tunable Microwave Frequency Comb Generation Technology Based On Modulator

Microwave frequency comb(MFC)is a signal composed of discrete microwave frequency components distributed at equal intervals.It not only has the permeability of wave signal,selective heating,small thermal inertia,photo-likeness,informationality and non-ionization,but also has advantages of wider bandwidth and more microwave components than a single microwave signal,so it has important applications in many areas,such as high-speed optical communication,medical,measurement,industrial processing and remote sensing.Therefore,the way to produce high-performance MFC with wide bandwidth,good flatness and tunable line spacing has been the pursuit of domestic and foreign scholars.At present,the MFC production schemes are mainly divided into two major categories: electrical and optical.the MFC technology generated by electricity is mainly frequency synthesis technology,and the optical generation technology of MFC can be mainly divided into MFC generation based on the nonlinear effect of tunnel junction in scanning tunneling microscope(STM),MFC generation based on nonlinear dynamics of semiconductor laser.MFC generation based on mode-locked lasers and external modulator-based modulation to generate MFC.The MFC generated by these schemes has their own advantages in terms of bandwidth,average power,carrier-to-noise ratio and flatness,but each has its own shortcomings.The MFC generation technology is studied to improve the performance of various aspects of MFC and the specific work is as follows.A scheme based on cascaded multiple quantum well electro-absorption modulator(MQW-EAM)and frequency modulator(FM)to generate tunable MFC is proposed.After the introduction of the working principle and the establishment of the model,the optical communication system design software Optisystem is used to simulate the scheme.The MFC with a spectrum bandwidth of 300 GHz has an average power of-36.82 dBm,a carrier-to-noise ratio of 42 dB and a flatness of 8.72 dB.The linewidth of the light source,the input optical power,the frequency of the RF drive signal,and the frequency offset of the FM are studied.The effect of the small signal gain of the erbium-doped fiber amplifier(EDFA)and the responsiveness of the photodetector(PD)on the resulting MFC signal.The results show that changing the frequency of the RF signal can realize the tuning of the frequency interval of the MFC signal between 5 and 20 GHz,which improves the application flexibility of the scheme.The frequency offset of the FM affects the spectrum bandwidth of the MFC signal a lot.The output multi-band microwave signal is insensitive to the linewidth of the input source;appropriately increasing the input power of the source,the small signal gain of the EDFA or the responsiveness of the PD is advantageous for generating an MFC signal with a higher average power.A scheme based on MQW-EAM in critical state to generate ultra-flat tunable MFC is proposed.After the introduction of the working principle and the establishment of the model,the optical communication system design software Optisystem is used to simulate the scheme.The MFC with a spectral bandwidth of 300 GHz has an average power of-29.86 dBm,a carrier-to-noise ratio of 49 dB and a flatness of 0.02 dB.The effects of the linewidth of the light source,the input optical power,the frequency and voltage of the RF signal,and the bias voltage of the MQW-EAM,the small signal gain of EDFA and the responsiveness of PD on the generated MFC are studied.Results indicates that the frequency interval of the generated MFC can be tuned between 5 and 20 GHz by adjusting the frequency of the RF signal,which improves the flexibility of the scheme's application;this scheme is insensitive to the linewidth of the input source;the performance of the MFC can be improved by properly adjusting the input optical power,the voltage of the RF signal,the small signal gain of the EDFA,and the responsiveness of the PD.