Evaluation of the frequency instability limited by Dick effect in the microwave 199Hg＋ trapped-ion clock

In the microwave 199Hg＋ trapped-ion clock, the frequency instability degradation caused by the Dick effect is un- avoidable because of the periodical interrogating field. In this paper, the general expression of the sensitivity function g（t） to the frequency fluctuation of the interrogating field with Nπ-pulse （N is odd） is derived. According to the measured phase noise of the 40.5-GHz microwave synthesizer, the Dick-effect limited Allan deviation of our 199Hg＋ trapped-ion clock is worked out. The results indicate that the limited Allan deviations are about 1.75 ×10-13/√τ and 3.03 ×10-13/√τ respectively in the linear ion trap and in the two-segment extended linear ion trap under our present experimental parameters.

Modeling of cascaded high isolation bidirectional amplification in long-distance fiber-optic time and frequency synchronization system

We propose a physical model of estimating noise and asymmetry brought by high isolation Bi-directional erbiumdoped fiber amplifiers(Bi-EDFAs),no spontaneous lasing even with high gain,in longdistance fiber-optic time and frequency(T/F)synchronization system.It is found that the Rayleigh scattering noise can be suppressed due to the high isolation design,but the amplified spontaneous emission(ASE)noise generated by the high isolation Bi-EDFA and the bidirectional asymmetry of the transmission link caused by the high isolation Bi-EDFA will deteriorate the stability of the system.The calculated results show that under the influence of ASE noise,the frequency instability of a 1200 km system composed of 15 high isolation Bi-EDFAs is 1.773×10^(-13)/1 s.And the instability caused by asymmetry is 2.6064×10^(-16)/30000–35000 s if the total asymmetric length of the bidirectional link length is 30 m.The intensity noises originating from the laser and detector,the transfer delay fluctuations caused by the variation in ambient temperature and the jitter in laser output wavelength are also studied.The experiment composed of three high isolation Bi-EDFAs is done to confirm the theoretical analysis.In summary,the paper shows that the short-term instability of the T/F synchronization system composed of high isolation Bi-EDFAs is limited by the accumulation of ASE noise of amplifiers and the laser frequency drift,while the long-term instability is limited by the periodic variation in ambient temperature and the asymmetry of the amplifiers.The research results are useful for pointing out the direction to improve the stability of the fiber-optic T/F synchronization system.

Revisiting the laser frequency locking method using acousto-optic frequency modulation transfer spectroscopy

We present a laser frequency locking system based on acousto-optic modulation transfer spectroscopy（AOMTS）. Theoretical and experimental investigations are carried out to optimize the locking performance mainly from the view of the modulation frequency and index for the specific scheme of AOMTS. An FWHM linewidth of 63 kHz is achieved and the frequency stability in terms of Allan standard deviation reaches1.4 × 10^（-12） at 30 s. The frequency shifting capacity is validated throughout the acousto-optic modulator bandwidth while the laser is kept locked. This work offers a different but efficient choice for applications calling for both stabilized and tunable laser frequencies.