We demonstrate an extended cavity Faraday laser system using an antireflection-coated laser diode as the gain medium and the isotope ${}^{87}\mathrm{Rb}$ Faraday anomalous dispersion optical filter (FADOF) as the frequency selective device. Using this method, the laser wavelength works stably at the highest transmission peak of the isotope ${}^{87}\mathrm{Rb}$ FADOF over the laser diode current from 55 to 140 mA and the temperature from 15°C to 35°C. Neither the current nor the temperature of the laser diode has significant influence on the output frequency. Compared with previous extended cavity laser systems operating at frequencies irrelevant to spectacular atomic transition lines, the laser system realized here provides a stable laser source with the frequency operating on atomic transitions for many practical applications.

High sensitive underwater wireless optical communication (UWOC) in shallow water or FSO-UWOC convergent applications suffers severely from solar noise and other background noise interference. This paper presents experimental demonstrations of broadband background noise resistant air-water and underwater wireless optical communication by using a pair of spectrum matched 852 nm Cs atomic Faraday line laser and filter, with a narrow passband of only 1 GHz. Experimental results show that by using the Faraday atomic line laser and filter, the Q factor can be improved by 3.37 dB compared to using the interference filter, and 14.67 dB compared to system without using noise resistant filter. A numerical model for UWOC system performance affected by broadband background noise with various filtering conditions is presented, where both the numerical and experimental results match each other quite well. Based on the experimental results substantiated model, performance of UWOC under solar noise interference is numerically studied. The numerical results show that under strong solar noise interference, the maximum depth of the receiver is extended from 0.77 m to 3.79 m for FSO-UWOC system and from 0.87 m to 3.54 m for UWOC system. It proves that FADOF can provide considerable performance improvement for both UWOC and FSO-UWOC system with broadband background noise interferences.

We demonstrate a Faraday laser at Cs-D2 resonance line 852 nm using a Cs Faraday optical filter as frequency-selecting element. In contrast to typical diode laser with high stability of the emission frequency by additional control systems, our Faraday laser offers stable output frequency exactly set by the peak transmission frequency of the Cs 852 nm Faraday optical filter. The system works stably over a range of laser diode (LD) current from 60 to 130 mA and the LD temperature from 14 to 35 $$^{\circ }$$∘ C, as well as the 48-h wavelength fluctuation range of no more than ± 2 p.m. A most probable linewidth of 17 kHz with Lorentz fitting is obtained by beating between two identical laser systems. The wavelength of our system is stabilized within transmission frequency region of 852 nm Faraday optical filter, and the peak of the transmission is corresponding to Cs atomic Doppler broadened line at the cell temperature of 41 $$^{\circ }$$∘ C and the magnetic field of 330 G, making it suitable for laser-pumped Cs gas-cell and atomic beam frequency standard, etc. Moreover, this scheme is firstly used on Cs atom, opening new doors in research of Faraday laser and its applications.

Previous studies of the Faraday anomalous dispersion optical filter (FADOF) mainly focus on the weak signal light filtering, without regard for the influences of the signal light intensity on the filter itself. However, in some applications the signal light is strong enough to change the filter’s performance. In this work, the influences of the signal light intensity on the transmittance spectrum is experimentally investigated in a 780 nm ${}^{85}\mathrm{Rb}$ FADOF in both the line-center and wings operation modes. The results show that the transmittance spectrum varies significantly with the signal light intensity. As the signal light increases, some existing transmittance peaks decline, some new transmittance peaks appear, and the maximum transmittance peak frequency may change. The spectrum in strong signal lights can be quite different from those calculated by programs in the condition of weak signal lights. These results are important for applications of the FADOF in the condition of strong signal lights.

Ghost imaging reconstructs the image based on the second-order correlation of the repeatedly measured light fields. When the observed object is moving, the consecutive sampling procedure leads to a motion blur in the reconstructed images. To overcome this defect, we propose a novel method of ghost imaging to obtain the motion information of moving object with a small number of measurements, in which the object could be regarded as relatively static. Our method exploits the idea of compressive sensing for a superior image reconstruction, combining with the low-order moments of the images to directly extract the motion information, which has the advantage of saving time and computation. With the gradual motion estimation and compensation during the imaging process, the experimental results show the proposed method could effectively overcome the motion blur, also possessing the advantage of reducing the necessary measurement number for each motion estimation and improving the reconstructed image quality.

The large-scale clock network is the key ingredient to obtain high precision in many scenarios, from fundamental research to cutting-edge applications. The advantage of the time synchronization among microwave clocks is their cost, size, and accessibility. Here, we demonstrate a femtosecond-level time synchronization of microwave clocks through a commercial link of 205.86 km via dual-comb-enhanced optical two-way time transfer, which achieves a 6.23-fs residual time deviation between synchronized timescales at 1 s and an instability below 6×10⁻¹⁸ at 10,000 s. Further, the high-precision time synchronization of microwave clocks significantly enhances the probe ability of subtle reciprocity changes of fiber to the sub-picosecond level. This work provides a path toward secure fiber time-frequency networks to support future microwave-clock-based precise timing and sensing systems.