Juan Wei

Stable radio transfer via an optic cable with multiple fibers based on passive phase error correction

A novel passive phase error correction technique for stable radio transfer via an optic cable with three fibers is proposed. The single-tone radio (at f0) to be transmitted is first frequency-divided by 2. The half-frequency signal is transmitted to the receiver through one fiber of the cable and then frequency-tripled. The obtained signal is mixed with another half-frequency signal that passes the optic cable three times through different fibers. The filtered frequency component at f0 has the same phase with that of the original radio. Both the phase delay and its variation during fiber transmission are removed, which enables an endless phase error correction. The proposed technique can avoid the use of extra radio frequency sources and bidirectional transmission in the same fiber. An experiment is carried out for the delivery of a 6 GHz radio signal through a 1.5 km ribbon type fiber optic cable. The time delay variation of ~350 ps induced by the 6°C temperature change can be confined to ±1.3 ps using the proposed technique.

Passive phase correction for stable radio frequency transfer via optical fiber

The transfer of radio frequency (RF) signal via optical fiber is widely adopted in distributed antenna systems and clock standard disseminating networks. To suppress the phase variation caused by fiber length fluctuation, passive phase correction technique based on frequency mixing has been proved as a promising approach due to its significant advantages over the traditional active compensation technique in terms of complexity, compensation speed, and compensation range. The phase correction can be done either in the transmitter or in the receiver, but it usually requires many stages of electronic mixing and auxiliary microwave signals, which not only increases the cost of the link but also degrades the quality of the transmitted signal. In addition, the effect of chromatic dispersion, polarization mode dispersion, and coherent Rayleigh noise in the optical fiber will further deteriorate the phase noise of the signal after transmission. In this paper, an analytical model for the stable RF transfer system based on passive phase correction is established, and the techniques developed in the last few years in solving the problems of the method are described. Future prospects and perspectives are also discussed.

A compact optical-microwave phase detector based on a polarization modulator

A compact optical-microwave phase detector is proposed and its performance is evaluated by synchronizing an 8-GHz oscillator to a 250-MHz mode-locked laser. The residual out-of-loop phase noise at 1 Hz and 100 kHz offset are −115 dBc/Hz and −146 dBc/Hz respectively. And the RMS timing jitter is 600 as when integrated from 100 kHz to 1 Hz. The proposed phase detector has a compact structure and is easy to implement using all commercial devices to achieve subfemtosecond synchronization between optical pulses and microwave oscillators.

Phase stable radio distribution over optic cable by phase conjugation using an optical frequency comb

A phase stable radio frequency (RF) distribution technique is proposed and experimentally demonstrated. The system transmits optical frequency comb lines through an optic cable with multiple fibers. At the receiver, RF phase variation is removed by frequency mixing based on phase conjugation. In the proposed system, round-trip transmission is implemented through different fibers, thus the signal degradation due to bidirectional fiber transmission is eliminated. Besides, electrical frequency manipulations are not required because different frequency components can be generated by beating the comb lines at a photodetector, which leads to a simplified structure and alleviated signal distortion. Another advantage of the proposed scheme is that a series of phase stabilized frequencies at In times (n is a positive integer) of the comb spacing can be obtained simply by tuning the electrical filters. In the experiment, phase stable distribution of a 5 GHz signal and a 10 GHz signal over a 1.5 km optic cable is successfully demonstrated in a temperature varying environment. The residual delay variation of the 5 GHz signal is confined within ±1.1 ps, and the phase noise of the signal is well preserved after fiber distribution.

Post phase correction for stable fiber delivery of radio-frequency signal

A simple, compact, cost-effective post-phase correction method for stable fiber transfer of RF signal is proposed and demonstrated. By employing only one LO source and two frequency mixers, a RF signal is transmitted to the local station with very small phase jitter. An experiment is performed. When a 6-GHz RF signal is delivered through a 20-km SMF, effective cancellation of the phase jitter induced by the environment perturbations is achieved. The residual jitter is less than 0.07 rad.

Stable radio frequency transfer via optical fiber based on passive phase correction

The transfer of radio frequency (RF) signal via optical fiber is widely used in distributed antenna systems. To compensate the phase variation caused by fiber length fluctuation, passive phase correction technique is proposed with obvious advantages over the traditional active phase correction method. This paper reviews the recent developments of the stable RF transfer based on passive phase correction. The operation principles of several reported schemes are presented and the performance is evaluated and compared. Although good results have been achieved in such schemes, they can only be used for single frequency transfer. Thus, passive phase correction technique for stable transfer of wideband RF signals should be investigated in the future.