The Photonic Research Of Microwave Signal Generation And Modulation

In recent years,with the rapid development of optical communication and wireless communication,microwave photonics has become a hot subject.Compared with the traditional electric field,the optical domain has many advantages,including large operating bandwidth,high frequency,small size,low power consumption,and anti-electromagnetic interference and so on.Therefore,this paper will focus on the two aspects,which includes the use of optical methods to generate microwave signals and the use of optical methods to deal of microwave signals.By using optical methods to generate microwave signals,firstly,the advantages and disadvantages of various optical interferometers are compared and analyzed in this paper.Because the optical fiber Sagnac interferometer has the advantages of good stability,low cost,and is not easy to be affected of temperature,the optical fiber Sagnac interferometer is chosen to generate the comb spectrum.Secondly,in order to obtain the comb spectrum of tunable wavelength spacing,the Sagnac interferometer is inserting two different length of polarization maintaining fiber(PMF).through the contrast analysis,the 11 m and 35 m PMF length were found to generate the best effect of comb spectrum.the wavelength spacing in the range of 0.132nm-0.212 nm by using the polarization controller(PC)for flexible adjustment.Finally,using a fiber Bragg grating(FBG)as a narrow-band filter,the dual wavelength is generated from the comb spectrum,and generated microwave signal by using the photoelectric detector(PD)to beat.the microwave signal is adjustable frequency range of 16.4 GHz-26.2 GHz,and the signal-to-noise ratio(SNR)more than 30 dB.It can be seen that the microwave signal generated based on the two section PMFs Sagnac interferometer in this paper has the characteristics of low cost,good frequency tunability and flexible operation,which will have a widely application value.By using optical method to deal with microwave signals,firstly,the advantages and disadvantages of various electro-optic modulators are compared and analyzed in this paper.Because the phase modulator(PM)has the characteristics of low cost,simple system,and is not easy to be affected by the zero drift,the PM is chosen to study.By using A single mode fiber(SMF)and PM to constitute a dual parallel structure,the phase modulation signal is converted into intensity modulated signal(PM-IM).Secondly,the same parameters PM is inserted the SMF.By injecting 10 G,20G radio frequency(RF)signal to the PM1 port and injecting the rate of 2 Gbit/s,2.5 Gbit/s binary sequence to the PM2 port,the phase shift of the phase coding microwave signal is obtained.Finally,the phase shift of phase encoding microwave signal data is lead to Matlab,which is transformation of autocorrelation function and comparative analysis.when the RF signal is 20 G and the rate of binary sequences is 2.5 Gbit/s and the cycle of 6.4ns,the autocorrelation function of the full width at half maximum(FWHM)is 0.388 ns.This phase coding microwave signal of best pulse compression ratio is 16.5.It is shown that the dual phase modulator based on the dual phase modulator can obtain high compression ratio of the phase coded microwave signal,and it is easy to be integrated,which has great commercial value.