Study On Fiber-optic Frequency Transfer Based On Passive Phase Noise Compensation

Recently,with the development of technology,the stability of atomic clock has been greatly improved.Atomic clocks available on the market have been able to achieve the stability of 10^-16 at an averaging time of one day.However,the stability of conventional frequency transfer based on satellite is limited to¹0^-15 at an averaging time of 10⁵ s for multipath effects and delay fluctuations caused by troposphere and ionosphere.Taking advantages of wide bandwidth,low attenuation and better reliability,fiber-optic frequency transfer has been considered as a promising way to reach higher stability and has been well studied.The internal and external fluctuations of fiber links will degrade stability of the signal while delivered through optical fibers.Phase noise compensation is indispensable.Active phase noise compensation schemes have been well studied and commonly been applied,which dynamically measure the round-trip phase fluctuations and accordingly control tunable phase compensators in the optical domain and/or the electrical domain to cancel the phase fluctuations.The feedback loop control based active schemes,however,require high-precise phase error measurement,fast and large range compensators,and corresponding feedback control algorithms.These make the system become complex.Recently,a passive phase-conjugation compensation scheme based on frequency-mixing has been proposed,which simplify the complexity of the system and provide an endless compensation range.However,existing passive phase noise compensation schemes suffer noise resulting from backscattering or fiber link asymmetry.So in this paper,we have proposed an improved passive phase noise compensation for optic-fiber frequency transfer.Based on frequency dividing and filtering while employing identical carrier wavelength,the backscattering noise can be eliminated and the symmetry can be improved.The stability of the frequency transfer system can be improved.The main work of the paper includes:?1?The existing optical frequency transfer schemes are introduced. The advantages and disadvantages of existing passive phase noise compensation schemes are also introduced.The noises induced by fiber link and its effect are also introduced.?2?The improved passive phase noise compensation scheme for optical frequency transfer is proposed and theoretical analyzed.The frequency conversion modules are selected and tested based on theoretical analysis.?3?The principle of phase noise testing is introduced and the corresponding divider circuits are produced.The proposed scheme and its contrastive scheme which suffers from backscattering are tested for 40 km transfer.The proposed scheme can provide a system stability of 3.9?10^-14/s and 1.2?10^-16/10⁴s.At the same time,the contrastive scheme provide a system stability of 1.5?10^-13/s,which proves that the proposed scheme can suppress backscattering noise effectively.