Research On Dual Comb System Based On Locking To Narrow Linewidth Lasers And Their Ranging Application

Femtosecond optical frequency combs are widely used in precision measurement applications because of their excellent time-frequency domain characteristics,such as narrow pulse width,wide spectral range,high longitudinal mode resolution and high repetition rate stability.Particularly,the dual comb technology is applied to the absolute distance measurement,which perfectly combines the three elements of distance measurement---range,accuracy and update rate.However,the simple combination of two common combs can't meet the experimental requirements of high-precision dual comb ranging system,needing special locking method to suppress the comb linewidth and reduce the frequency domain noise.In this paper,dual comb system with low noise and high coherence is realized by phase locking to narrow linewidth lasers,and dual comb absolute distance measurement system is built to carry out high precision ranging experiments.The main work of this dissertation can be summarized as follows:1.The basic principle of Pound-Drever-Hall laser frequency stabilization method is described.Two continuous wavelength lasers with different wavelengths(1542 nm and 1560 nm)are locked to an ultra-stable Fabry-Perot cavity by using this method.And narrow-linewidth lasers with Hz linewidth are obtained respectively.2.A dual comb system based on phase locking to narrow linewidth lasers is studied and implemented in this paper.Two Erbium-doped optical frequency combs with repetition rates of about 200 MHz and repetition rate difference of about 17 k Hz are constructed.A dual comb system with low noise and high coherence is realized by phase locking to narrow linewidth lasers.After phase locking,single comb can achieve the Hz comb linewidth and dual comb can obtain the sub-Hz relative comb linewidth.The dual comb system can be used as sources in the dual comb applications,which can meet the requirements of precision experiments such as dual comb spectral analysis and dual comb interference ranging.3.The dual comb ranging numerical model is established and the dual comb absolute distance measurement system is built.At the same time,a method to improve ranging accuracy by time-domain superposition of interference patterns is proposed,and the numerical simulation is in agreement with the experimental results.In this paper,the phase information is obtained by Fourier transform to calculate absolute distance.The ranging accuracy is about 4.88 ?m when only using the time-of-flight method.After the time-domain superposition of interference patterns,the ranging accuracy can be increased to 295 nm.