Ultra-low noise optical injection locking amplifier with AOM-based coherent detection scheme

All-fiber low-frequency shifter based on acousto-optic interaction and its heterodyne vibration response

We demonstrate two all-fiber low-frequency shift schemes based on the acousto-optic interaction in a few-mode fiber (FMF). Two acoustically induced fiber gratings (AIFGs) are cascaded in reverse to achieve an efficient cycle conversion between LP₁₁ and LP₀₁ core modes in the FMF while obtaining a frequency shift of 1.8 MHz. In addition, a long-period fiber grating (LPFG) is employed to replace the AIFG, which achieves a lower frequency shift of 0.9 MHz, and its tunable wavelength range exceeds 100 nm. Both schemes show the characteristics of an upward frequency shift. Moreover, we also present a heterodyne detection system based on the above frequency shift schemes, which is verified in response to micro-vibration signals ranging from tens to hundreds of kilohertz, as well as speech signals in a lower frequency range. The experimental results show that these all-fiber frequency shift schemes have potential applications, such as in fiber optic hydrophones, laser speech detection, and fiber optic sensors.

Absolute phase marking technology and fiber-optic remote coherent phase transmission

Fiber-optic time and frequency synchronization technology demonstrates ultra-high synchronization performance and has been gradually applied in various fields. Based on frequency synchronization, this study addressed the problems of period ambiguity and initial phase uncertainty of the phase signal to realize the coherent transmission of the phase. An absolute phase marking technology was developed based on high-speed digital logic with zero-crossing detection and an optimized control strategy. It can realize picosecond-level absolute phase marking and provide a picosecond-level ultra-low peak-to-peak jitter pulse marking signal to eliminate phase period ambiguity and determine initial phase and transmission delay. Thus, by combining the high-precision phase measurement capability of the synchronized frequency signal and long-distance ambiguity elimination capability of the pulse-per-second signal, a high-precision remote coherent phase transmission over an optical fiber is realized. After frequency synchronization, the peak-to-peak jitter between the local and remote phase-marking signals can be only 3.3 ps within 10,000 s measurement time. The uncertainty of the coherent phase transmission is 2.577 ps. This technology can significantly improve the phase coherence of fiber-optic time and frequency transmission and provide a new approach to achieve peak-to-peak picosecond-level reference phase marking and high-precision fiber-optic remote coherent phase transmission. This demonstrates broad application prospects in coherence fields such as radar networking.

High-stability and multithreading phase-coherent receiver for simultaneous transfer of stabilized optical and radio frequencies

We demonstrate a high-stability and multithreading coherent receiver for simultaneous distribution of stabilized optical and radio frequencies (RFs). The technique is based on a monolithic electroabsorption modulator integrated with a distributed feedback laser, which can purify and amplify the optical carrier while recovering the RF signal as a high-speed photodetector. The large-dynamic-range and high-bandwidth phase-locking system preserves the stability of the receiver for optical and RF signals to 3.5×10^-20 and 6.4×10^-18 at 1000 s, respectively. Furthermore, a dual-stabilization system using this novel receiver is proposed for simultaneous transfer of ultrastable optical carriers and RF signals over a 263 km fiber link. The transferred frequency stabilities of the optical carrier and the 9.1 GHz signal are 6.5×10^-20 and 1.6×10^-17, respectively, for an averaging time of 10,000 s.