For the demands of wide operating temperature for fiber-optic time and frequency synchronization applied to the actual system of distributed coherent detection, we propose an absolutely consistent phase synchronization method. Assisted by time delay, in the way of phase locking, we accomplish absolute consistent bias reference point control at different operating temperatures. Respectively at different environment temperature of -40°C and 50°C, the experimental results reveal 100 MHz frequency stabilities of 3.1694 E-13 at 1 s and 3.1513 E-13 at 1 s and the relative difference was less than 0.6%. The average value of 1pps delay was 275102808.1 ps and 275102864.9 ps respectively, and the relative difference was less than 0.1%. The 1pps synchronization accuracy is 21.1744 ps and 26.2030 ps separately.
We demonstrate high-precision free-space time and frequency transfer (FSTFT) based on laser in the presence of motion with digital phase-locked loop. Radio frequency with 1 GHz and time signal with one pulse per second (1 PPS) are transmitted over 108 m indoor atmospheric link. The experimental results reveal remarkable frequency stability with instabilities of 1.5E-14 at 1 s and 8.0E-16 at 100 s, even in the presence of a time-varying link characterized by speeds of ± 1.5 m/s. And time interval transfer of 1 PPS signal with 32 ps standard deviation of time delay jitter is obtained.
We propose and demonstrate a feedback tunable self-injection locked (SIL) narrow linewidth laser, the feedback light intensity is dynamically adjusted to find the best locking state. The self-injection locked laser is composed of distributed feedback (DFB) semiconductor laser and high quality (Q) factor silicon nitride (SiN) external cavity, tunable sagnac loop reflector is used to achieve arbitrary ratio of feedback light and output light on the basis of add-drop type high Q microring resonator (MRR). The results show that the SIL state is closely related to the ratio of feedback light. When the optical feedback ratio is higher than -14 dB, a robust SIL state can be achieved, and the locking state is independent of the phase of the feedback light, the intrinsic linewidth is narrowed from 130 kHz to 1 kHz. By optimizing the ratio of feedback light to -9.3 dB, a narrow linewidth output of 345 Hz can be achieved. This work has important application value in the field of coherent laser communication and coherent detection.
In coherent test system like sensing, imaging and communication, the coherence of the light source is very important. Our recent advances focusing on the measurement of noise characterization of highly coherent laser and its applications in the coherent test system are reviewed. Using the noise spectrum and statistic characterization to represent the coherence is proposed. And the parallel 3-step phase-shift measurement method from 500nm to 2000nm based on the 120-degree phase difference fiber interferometer is also proposed to measure the noise characterization. Some kinds of typical highly coherent laser applied in the coherent sensing and imaging system are measured. And the impact of their performance on the application system are also discussed.
Low noise laser sources with narrow linewidth and low intensity noise are key tools in a broad range of applications such as optical sense, microwave photonics, coherent optical communications and so on. The report gives an introduction about our research progress of the narrow-linewidth single frequency DFB fiber lasers. An internally developed DFB fiber laser is developed. The noise characteristic of laser output is studied in detail. The frequency noise in low Fourier frequency is reduced via using the low noise pump and intracavity optical negative feedback. Furthermore, an injecting lock scheme is used to reduce the intensity noise. A fiber laser output with low frequency noise and low intensity noise has been demonstrated.
A compact short-cavity fiber laser configured with
Er3+/Yb3+ highly co-doped phosphate glass fiber which has linear
polarization and single frequency output is fabricated experimentally. The threshold power of the laser is about 30mW,
and larger than 100mW output power is achieved with slope efficiency of 20% at 1549nm. At the meantime, sine
modulation, positive pulse and chaos state in the output power at different experimental condition are observed. And a
new theoretical model is proposed to describe the mechanism of the observed intensity instability behavior in the fiber
laser and the numerical results proved its feasibility. It is confirmed that the self-pulsing behavior is mainly caused by
different small external feedback. So there is an efficient way to overcome self-pulsing behavior in the compact single
polarized fiber laser by minimizing the external feedback.
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