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Precise Control Of Optical Phase And Coherent Synthesis In Femtosecond Laser Based Optical Frequency Combs

Posted on:2021-10-20Degree:DoctorType:Dissertation
Country:ChinaCandidate:H C TianFull Text:PDF
GTID:1480306548474484Subject:Optical Engineering
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Optical frequency combs are laser sources which are capable of generating discrete,equal-spaced and highly coherent comb modes.Optical frequency comb technique provides a significant bridge to transfer the stability between optical frequency and radio frequency.The advances of this technology greatly promote the development of precision spectroscopy,optical time/frequency transfer,optical frequency division,long-distance transfer of time/frequency references and high-precision distance measurement.Benefiting from the wide spectral outputs,femtosecond lasers have become the best choice for the fulfilment of optical frequency combs.Within the precise control of the repetition frequency and carrier-envelope offset frequency of the pulse train from femtosecond lasers,a stable optical frequency comb both in the time domain and frequency domain can be obtained.Based on the precise control of repetition rate,carrier-envelope offset frequency and conherent pulse synthesis in optical frequency combs,the major contents in this synthesis are summarized as follows:1.The theoretical models of timing jitter,carrier-envelope phase noise and comb line noise are systematically studied.The origins of noise are analyzed.The methods of frequency stability evaluation of femtosecond laser have been studied.Power spectrum analysis and the variance analysis could reveal the stability of optical frequency combs in frequency domain and time domain,respectively.The impacts of the thermal noise and shot noise generated by the photodetector during the photo-electric detection on the signal-to-noise ratio of signal have been studied.2.The precise optical synchronization between two independent yetterbium-doped fiber optical frequency combs for 5 consecutive days has been achieved for the first time.After synchronization,the rms value of residual time error signal from in-loop optical cross-correlation system is 103 as.The rms value of residual time error signal from out-of-loop optical cross-correlation system is 733 as.Overlapping allen variance stability of in-loop error signal is 8.11×10-22 in 1.31×105 s.Overlapping allen variance stability of out-of-loop error signal is 1.36×10-20 in1.31×105 s.The integration of the in-loop noise power spectrum in the frequency range from 10 MHz to 10 k Hz is 430 as.The excess timing jitter induced from optical fiber has been studied.Integrated timing jitter of 5-meter long fiber is 64.7 as.The optical heterodyne method based on three-mixer design and cross-correlation algorithm has been studied.3.The optical heterodyne detection method is applied to achieve ultra-broad range and ultra-high-precision power spectrum measurement of carrier-envelope phase noise for the first time.The carrier-envelope phase noise power spectrum measurement with a dynamic range exceeding 270 d B in the Fourier frequency range from 5 m Hz to 8 MHz is achieved.The phase noise measurement resolution is below1?rad/?Hz.Using power spectrum analysis,Hadamard variance analysis and Kendall cross-correlation analysis,the origin of noise has been revealed.The relative phase noise between two optical solitons has been characterized for the first time.The integrated relative phase noise of the two optical solitons is only 3.5 mrad and the relative line width is only at?Hz level.4.The power spectra have been characterized using an asymmetric fiber delay line with high precision for the first time.The frequency noise power spectra of frep,fceo and?n in the optical frequency comb are measured.The origins of timing jitter and comb-line noise have been studied.The anti-correlation characteristics between n×frepnoise and fceo noise are discovered.The system verified the crosstalk between frep,fceoand?n stabilization phase-locked loops.5.The long-term stable coherent pulse synthesis of two independent yetterbium-doped fiber has been realized for the first time.A balanced optical cross-correlation system and an extra-cavity acousto-optic frequency shifter are applied to lock the repetition frequencies between two lasers and the relative carrier-envelope offset frequency respectively,to achieve coherent pulse synthesis.After synthesis,the integration value of the residual time jitter of the two pulses is 380as and the integration value of the residual relative relative-envelope noise is 375mrad.The Mach-Zehnder interferometer was used to evaluate the coherence of the two pulses after coherent synthesis.The contrast of the spectral interferemetric fringes after synthesis is 58%.Within 60 minutes,the rms value of relative carrier-envelope phase drift between the two pulses is 165 mrad.And the spots of the two lasers have obvious fringes.
Keywords/Search Tags:Timing jitter, carrier-envelope phase, optical frequency comb, coherent pulse synthesis
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