Dual-frequency Light Source With Widely Tunable Frequency Difference Based On Single-side-band Modulator

With the development of precision measurement technology,laser interferometry has become an important part of precision measurement technology.The dual-frequency light source offers strong anti-interference ability,high measurement accuracy and non-contact detection.It has been widely applied in precision measurement applications such as Doppler velocimetry,heterodyne interferometer,and precision atomic clock.The frequency difference of the dual-frequency light source is an important parameter,which directly affects the key parameters such as the system measurement resolution.In this paper,the requirements of frequency difference in different measurement systems and the development status of dual-frequency light source are investigated.Then dual-frequency source with widely tunable frequency difference based on single-side-band modulator is proposed.The dual-frequency source with widely tunable frequency difference based on single-side-band modulator is divided into two parts:the first part is the seed light part for providing single-frequency seed laser;the second part is the frequency shifting part,where the single-frequency light is frequency shifted to produce the dual-frequency light output.The dual-frequency source has several unique advantages.Firstly,the dual-frequency laser is generated from the same single-frequency seed laser.The dual-frequency light source in this paper can avoid the influence of the frequency jitter and phase noise of the single-frequency laser on the dual-frequency laser output.Meanwhile the single-frequency seed laser is separated from the experimental device of generating dual-frequency laser.Consequently,we can choose the single-frequency laser with different properties to meet the different requirements,which is beneficial to the optimization of the dual-frequency light source.Secondly,the amount of frequency shifting is precisely controlled the frequency of the RF drive signal,which can be tuned precisely and continuously.The main work is as follows:1.The principle of and advantages of dual-frequency source with widely tunable frequency difference based on single-side-band modulator is theoretically analyzed.Then we theoretically study the principle of single-side-band modulator and the factors affecting the amount of shifting frequency.Based on the above two points,the frequency difference tuning range of the dual frequency light source is theoretically studied.At last,the properties of dual-frequency sourc such as output power,spectral side mode suppression ratio of dual-frequency laser,signal-to-noise ratio and phase noise of beat signal are theoretical simulation analyzed.2.The process of single-side-band output obtained by single-side-band modulator is experimentally demonstrated.The effects of the single-frequency laser'frequency and RF source'frequency and power on the frequency shifting are experimentally analyzed.The?1-order single-side-band outputs with side mode suppression ratio which are more than 30d B are acquired in experiment.The experiments shows that frequency difference tuning range of the dual-frequency source in this paper is from40k Hz to 30GHz.The stability of the frequency difference is statistically analyzed.For the dual-frequency light with the frequency difference of MHz and GHz,the standard deviation of the frequency difference is in the magnitude of10^-9and10^-11respectively.The effects of single-frequency laser power and RF power on the spectral side mode suppression ratio of dual-frequency source are also experimentally studied.