RESUMEN
We demonstrated the optical frequency transfer over a 96 km urban business network in Shanghai. The key factors affecting the optical frequency transmission system, such as fiber link quality, feedback compensation strength, and out-of-loop fiber temperature variation, are studied for the urban fiber link characteristics. The effective suppression technique of complex urban fiber link noise with different feedback compensation parameters is studied. With active phase noise suppression, the optical frequency stability can reach 1.9×10-16 at 1 s and 2.2×10-18 at 10,000 s over a 96 km urban fiber link. This work potentially plays an important role in optical clock frequency comparison, and it makes a good foundation for future research on long-distance optical frequency transfer over an urban business network.
RESUMEN
We propose a novel scheme that uses only a single passive phase compensation device to achieve stable optical and radio frequency joint transfer. The phase noises of optical and radio frequency can be simultaneously compensated by passively embedding their phase information on the two optical carrier sidebands generated by an electro-optical modulator without using the phase discrimination and active servo controller. As a result, this scheme has many advantages, such as high spectral purity, short settling time and infinite compensation accuracy. We experimentally demonstrate the joint transfer of optical and 1 GHz RF over 120 km fiber spools. The optical frequency stability achieves 6.9 × 10-17 at 1 s and 7.03 × 10-19 at 10000 s, while the 1 GHz RF is 6.47 × 10-13 at 1 s and 3.96 × 10-16 at 10000 s.
RESUMEN
We demonstrate a new optical pulse amplitude modulation (PAM) scheme where joint ultrastable time-frequency and gigabit ethernet data transfer with the same laser wavelength is realized. Time transmission is compatible with the White Rabbit (WR) based on gigabit ethernet networks, and frequency transmission is achieved by using 100MHz radio frequency (RF) modulation and the round-trip compensation methods. The laser is on-off keying (OOK) modulated by the WR signal, the RF and WR signal are modulated by optical PAM in a Mach-Zehnder interferometer modulator (MZM), and the local and remote site are connected by 96km urban fiber in Shanghai. The experimental results demonstrate that the frequency instabilities are 5.7E-14/1 s and 5.9E-17/104s, and the time interval transfer of 1 pulse per second (PPS) signal with less than 300fs stability after 104 s are obtained. This novel scheme can transmit frequency signals at hydrogen-maser-level stability in the gigabit ethernet network.
RESUMEN
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.
RESUMEN
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.
RESUMEN
A novel optical injection locking amplifier with acousto-optic modulator based phase modulation and a coherent detection scheme for optical frequency transfer applications is experimentally demonstrated in this study. A commercial distributed feedback diode laser is injection-locked to the resonant frequency of the optical signal with an optical fiber path length of hundreds of kilometers. This provides approximately 59 dB gain and ensures that the input carrier frequency fractional stability can be as good as 10-20 at 1000 s. The amplifier was tested for the transfer of a commercial narrow-linewidth laser in a 180 km fiber link to a remote site with only a single amplification step. The transferred frequency at the remote end reached 10-20 at 20000 s, which is suitable for optical frequency distribution and remote comparison between optical atomic clocks.
RESUMEN
Quantum key distribution provides unconditional security for communication. Unfortunately, current experimental schemes are not suitable for long-distance fiber transmission because of phase drift or Rayleigh backscattering. In this Letter we present a unidirectional intrinsically stable scheme that is based on Michelson-Faraday interferometers, in which ordinary mirrors are replaced with 90 degree Faraday mirrors. With the scheme, a demonstration setup was built and excellent stability of interference fringe visibility was achieved over a fiber length of 175 km. Through a 125 km long commercial communication fiber cable between Beijing and Tianjin, the key exchange was performed with a quantum bit-error rate of less than 6%, which is to our knowledge the longest reported quantum key distribution experiment under field conditions.