Linear Modulation Electro-optic Frequency Shift And Application

There are a very wide range of commercial and scientific applications of frequency shift of lasers.And there are mainly two methods to realize it.One method based on acousto-optic frequency shift realizes nonlinear frequency shift,which usually can only realize the magnitude of MHz frequency shift with a very narrow tuning range.Another method based on electro-optic frequency shift with sawtooth or sinusoidal signal realizes linear frequency shift,which can realize arbitrary frequency shift and has better tunability than the method based on acousto-optic frequency shift.In this thesis,the applications of electro-optic frequency shift method with sawtooth and sinusoidal signals in low-frequency half-wave voltage measurement of MachZehnder Modulator(MZM)are researched.The main contents of this thesis are as follows:1?The principle of realizing electro-optic frequency shift with an electric sawtooth signal is derived in detail.The effect of frequency shift can be characterized by a parameter named spurious suppression ratio,which is affected by three factors of the sawtooth signal including the peak-to-peak voltage,the ratio of sweep time in a period and the linearity of the signal.Then the application of electro-optic frequency shift method with a sawtooth signal in low-frequency half-wave voltage measurement of MZM is researched,which is realized by moving the sinusoidal signal with lower frequency to the sawtooth signal with higher frequency.By comparing the amplitude of the two beating spectrum lines,the modulation coefficient can be obtained.Then the half-wave voltage of the MZM corresponding to the frequency of the sinusoidal signal can be got with the help of the modulation coefficient.In the experiment,a 50 kHz sawtooth signal is used to measure the half-wave voltage of the MZM at the modulation port when the frequency of the sinusoidal signal is from 10 Hz to 5 kHz.2?The application of electro-optic frequency shift method with a sinusoidal signal in low-frequency half-wave voltage measurement of MZM is researched,which is not affected by the extinction ratio of MZM.It is realized by adjusting the direct-current(dc)component of the sinusoidal signal loaded at the bias port of the MZM to get two beating results after a photodetector.The modulation coefficient is obtained by comparing the amplitude of the beating spectrum lines of the two results,and the half-wave voltage of the MZM corresponding to the frequency of the sinusoidal signal can be obtained with the help of the modulation coefficient.In the experiment,the half-wave voltage of the MZM at the modulation port when the frequency of the sinusoidal signal is from 10 Hz to 200 kHz and the half-wave voltage of the MZM at the bias port when the frequency of the sinusoidal signal is from 10 Hz to 1 MHz are respectively measured.3?The application of electro-optic frequency shift method with two sinusoidal signals in low-frequency half-wave voltage measurement of MZM is researched.Without adjusting the dc component of the sinusoidal signal loaded at the bias port of the MZM,the lowfrequency half-wave voltage of MZM can be measured with arbitrary splitting ratio.It is verified by simulating that the scheme is not affected by the extinction ratio as well as the dc component of the sinusoidal signal at the bias port of the MZM.