Researches On The Character Of Electro-optic Modulator And The Generation Of Optical Frequency Comb By Using Electro-optic Modulator

Nowadays,the infrastructure of 100 gigabit optical transmission networks have been commercial.The next-generation single channel optical network will be 400 gigabit or 1 terabit system.In order to satisfy the dramatically increasing need of system capability,especially further improving the spectrum efficiency,a lot of technologies have been introduced,including kinds of multiplexing,advanced high-order modulation,coherent reception,digital signal processing and so on.Among those technologies,the superchannel is recognized as the key technology to achieve beyond-100 G transmission system.The multi-carriers(or called OFC)generator works as the optical source of superchannel and provides optical carriers with the same performance.The recirculating frequency shifter based on single-side band modulation(SSB-RFS)is one of the schemes to generate OFC at present.While,to generate high quality carriers which meet the requirements of systems,this scheme should be optimized.There are two issues should be solved.On the one hand,the power variation of output carriers should be low,that is,the spectrum of carriers should be flat.On the other hand,the crosstalk and noise should be suppressed,and including the high order harmonic wave caused by the nonlinearity of modulator,and the ASE noise introduced by EDFA.That is,the OSNR should meet the requirements.This thesis conducts the research work based on this two problems.The first issue is solved by suppressing the third order crosstalk.The high order harmonic waves derived from nonlinearity of modulator,in which the third order is the main factor that influences the flatness of output carriers.Thus,improving the linearity of modulator could cripple the third order crosstalk.The second issue is solved by choosing suitable driving voltage.By this way,the power shifted efficiency(PSE)of modulator could be improved,and the EDFA gain is reduced,hence the ASE noise is decreased.Therefore the specific solution is replacing the conventional IQ modulator(CIQM)of the RFS by Linear IQ modulator(LIQM),by which the third order crosstalk will be suppressed effectively.At the same time RFS could works at high RF driving voltage for the larger linearity range of LIQM.In this thesis,we studied electro-optic modulator and the OFC generator based on SSB-LIQM-RFS.And the main innovations are as follows:(1)We proposed a renewed SSB-LIQM-RFS scheme,in which the convention IQ modulator is replaced by linear IQ modulator,and achieved the generation of high quality multi-carriers.(2)The physical mechanism of LIQM suppressing the third order crosstalk and reducing of noise is analyzed.And the simulation proved the theoretical analysis.Compared with the SSB-CIQM-RFS,the SSB-LIQM-RFS could generate larger number of OFC and the flatness and OSNR of output carriers are improved drastically.(3)We developed an optical transmitter with high Extinction Ratio,above 15 dB,which is based on cascade MZ modulators scheme with the bias voltage is stabilized.This transmitter is used to calibrate the ER measurement of digital oscilloscope.Furthermore,we analyzed the main factors that influence the accuracy of the ER measurement and find a calibration scheme.And this setup could measure the Calibrating Factor directly.