Chuanxin Wu

WDM-based radio frequency dissemination in a tree-topology fiber optic network.

In this paper, we propose and demonstrate a scheme to achieve point-to-multipoint dissemination of radio frequency (RF) signals in a local area fiber optic network with tree topology based on wavelength-division multiplexing (WDM) technique. The phase changes caused by the fluctuations of the transfer links are passively canceled at remote end instead of at local end, which makes it feasible to flexibly build a tree-topology local area dissemination network with great cost-effectiveness. For the first time, we study the limit of long-term performance which is caused by temperature-induced variation of group velocity dispersion (TIVGVD) in dissemination networks using WDM techniques. In the proof-of-concept experiments, 38.5 km and 50 km fiber links are established to disseminate a 1 GHz frequency signal with fractional instability of 10(-17) order after 10(4) s averaging time. Then 17.4 nm wavelength spacing is introduced between local carrier and user carrier to verify the theoretical analysis. Under a controlled fiber temperature variation of about 21 °C, the obtained overlapping Allan deviation (ADEV) agrees well with the simulation results after 10(4) s time scales, which proves the validity of our theory. The theory has practical values in predicting and optimizing the capacity and performance of a WDM-based local area RF dissemination network.

Stable radio frequency dissemination by simple hybrid frequency modulation scheme

In this Letter, we propose a fiber-based stable radio frequency transfer system by a hybrid frequency modulation scheme. Creatively, two radio frequency signals are combined and simultaneously transferred by only one laser diode. One frequency component is used to detect the phase fluctuation, and the other one is the derivative compensated signal providing a stable frequency for the remote end. A proper ratio of the frequencies of the components is well maintained by parameter m to avoid interference between them. Experimentally, a stable 200 MHz signal is transferred over 100 km optical fiber with the help of a 1 GHz detecting signal, and fractional instability of 2×10(-17) at 10(5) s is achieved.

Large-dynamic-range time pre-compensation scheme for fiber optic time transfer

In this paper we experimentally demonstrate a transmission delay compensation scheme for precise fiber-optic time transfer. The scheme is based on a clock counter and an electronic variable delay line, which theoretically can provide unlimited compensation range. We perform successive tests in three optical fiber links of different lengths in which both continuous drifts and abrupt hop of the transmission delay are effectively compensated. The total transmission delay variation induced in the experiments is much larger than most of the reported cases. This large-dynamic compensation scheme is quite suitable for time transfer links whose transmission delay varies a lot.

Use of the Stokes Parameters of FBG for Transverse Strain Sensing and the Optimization of the Grating Structure

Abstract In this paper, the birefringence effects on fiber Bragg grating (FBG) written into standard single mode fiber under transverse load are analyzed. The evolutions of states of polarization (SOPs) of transmitted light in linear birefringence gratings are studied. We demonstrate that the first normalized Stokes parameter (s1) of the transmitted light in FBG has monotonous relationship with linear birefringence induced by transverse load and can be advantageously used for real-time transverse strain sensor, which is different from the basic sensing theory of the FBG sensors based on direct spectral analysis. The evolution of s1 of FBG in transmission with respect to the transverse load is studied experimentally, and a sensitivity of about 0.089/N is obtained. We also design a special gratings structure to reduce the effect of cross-sensitivity which is typically a limitation of most FBG sensors. The simulations show a great dependence of measurement performances with respect to the shape of transmission spectrum.

Online evolution reconstruction from a single measurement record with random time intervals for quantum communication

Online reconstruction of a time-variant quantum state from the encoding/decoding results of quantum communication is addressed by developing a method of evolution reconstruction from a single measurement record with random time intervals. A time-variant two-dimensional state is reconstructed on the basis of recovering its expectation value functions of three nonorthogonal projectors from a random single measurement record, which is composed from the discarded qubits of the six-state protocol. The simulated results prove that our method is robust to typical metro quantum channels. Our work extends the Fourier-based method of evolution reconstruction from the version for a regular single measurement record with equal time intervals to a unified one, which can be applied to arbitrary single measurement records. The proposed protocol of evolution reconstruction runs concurrently with the one of quantum communication, which can facilitate the online quantum tomography.

A Quick Method of Measuring the Transmission Time of Optical Fiber

It is difficult to determine the peak of optical signal transmission time in the time transfer system based on single photon detector. In order to solve the problem, a novel scanning measurement method is proposed to quickly measure the optical signal transmission time, taking the advantages of the remainder theorem and the peak scanning means. The experimental results demonstrate that the new method can not only achieve high accuracy of less than 10 ns between the computed result and the real peak, but also save time in the peak determination.

Quantum key distribution with silent active polarization compensation without a reference optical beam

The birefringence of fiber quantum channel is compensated for without a reference optical beam always in an interrupt way. We propose and demonstrate a scheme of continuous active polarization compensation based on the feedback of the quantum bit error rate. Two experiments with and without compensation are performed in lab and the records of sifted key rate and quantum bit error rate prove that the scheme is effective.

Fiber-based multipoint dissemination of radio frequency in tree topology

In this paper, a scheme is proposed to achieve multipoint dissemination of radio frequency in fiber optic network with tree topology. The phase changes of the frequency signal are canceled at the remote end by a passive phase conjugation scheme, which makes it feasible to build a tree-topology dissemination network with high cost effectiveness and flexibility. In the proof-of-concept experiment, a 50 km point-to-point 1 GHz frequency delivery link is first established with fractional instability of 5.96×10-17 for 20000 s averaging time. Then another branch is connected to the local end by fiber spool of 38.5 km to test multipoint dissemination performance. Respective fractional instability of 7.41×10-17 and 4×10-17 at 20000 s averaging time shows that this simple and effective scheme is free of mutual interference on multipoint-accessed condition and able to construct a flexible radio frequency dissemination network.

A novel dispersion flattened and single-mode terahertz photonic crystal fiber with material-filled structure

A novel kind of terahertz (THz) photonic crystal fibers (PCFs) based on the material-filled structure is proposed in this paper. Different materials can be selectively filled into parts of air-holes in the designed THz PCFs, and then perfect features such as single-mode transmission and ultra-flattened dispersion are obtained easily in large frequency ranges near 1THz. Employing full-vectorial finite element method (FEM) and plane wave expansion method (PWE), confinement losses and modal dispersion with different structural parameters and diverse refractive indices of the filled materials are investigated respectively. Numerical results show that the proposed PCFs have acceptable confinement losses, low and flattened dispersions whose absolute values are lower than 1ps/nm*km. Moreover, its structure is simple and its feature is insensitive to variations of parameters. It is helpful for PCFs design and real fabrication in the potential THz applications.

Comparative Study of Two Methods of Extend Optical Fiber Time Transfer Distance

Bi-direction Erbium-doped Optical Fiber Amplifier (BEDFA) and clock discipline module cascade mode both can extend optical fiber time transfer distance. This paper based on the system of Round-trip optical fiber time transfer, using research and produce by themselves BEDFA and clock discipline module cascade mode to extend time transfer distance, realized the relative experiment system, and carry experiment research out. Experiment discovery the former method, insert every one BEDFA time, transfer jitter increases 72.4 ps (1 σ) . While the latter method, insert every one clock discipline module leading to 244.2 ps (1 σ) time jitter. The result shows: long-term stability of BEDFA methods is better than clock discipline module, but short-term stability is worse.