Li Zheng-Yong

A New Distributed Measurement of Birefringence Vectors by P-OTDR Assisted by a High Speed Polarization Analyzer

A new polarimetric optical time domain reflectometry (P-OTDR) measurement device assisted by a high speed polarization analyzer is designed and a new algorithm, which can be used to accurately measure the birefringence vector, is proposed. In this method, only one measurement is required and the result is insensitive to the input state of polarization. An 1-km single mode fiber (SMF) is measured and the distribution of the local birefringence vector along the SMF is obtained with a resolution of 2 cm.

Matrix-Based Polarization Analysis and Application of Semiconductor Optical Amplifiers

Employing the Mueller matrix method with polar decomposition, we analyse the polarization rotation (PR) effects in semiconductor optical amplifiers (SOAs) and demonstrate that the PR angle is linear to the birefringence dependent gain while the average PR coefficient is about 0.625 for the employed SOA. It is further evident that the current and optical intensity dependent PRs rotate reversely around the same axis. Thus we propose an optical-electric synchronous control scheme to obtain orthogonal polarization states with power-equalization, and implement it by a polarization-sensitive SOA. The polarization duration time is about 10 ns which is applicable to high-speed polarization state generation.

Distributed Measurement of Birefringence by P-OTDR Assisted with Piezoelectric Polarization Controller

We propose a new polarization sensitive optical time domain reflectometry (P-OTDR) setup assisted with a piezoelectric polarization controller (PPC). The input state of polarization can be changed by varying the voltage of PPC without any rotatable instrument, and only one optical receiver is used to detect the backward beam. We measure a single mode fibre and get the distribution of birefringence along the SMF.

Generalized Principal-State-of-Polarization Analysis and Matrix Model for Piezoelectric Polarization Controllers

We introduce a generalized concept of principal state of polarization (PSP) to analyse the piezoelectric polarization controller (PPC) and find each PPC unit can be described by a rotation matrix determined by the PSP. Our PPC has three components, each made of a jaw and a piezoelectric actuator with the squeezing direction tilted 0°, 45° and 0°, which are driven by a tunable power supply. We demonstrate that all the polarization rotation angles are linear to driving voltages and the PSP of unit 2 is nearly orthogonal to others which are almost equal. Taking some approximate treatments we obtain the matrix model of our PPC with respect to three driving voltages. The average error of our theoretical model is 1.51°, and the polarization response time is < 50 μs, which is promising to realize an open-loop control of polarization.

Phase-locked all-optical differential polarization demodulation

A novel scheme of differential polarization demodulation is presented and demonstrated based on a polarized asymmetrical Mach?Zehnder interferometer configuration with polarization control. To enhance the stability of the demodulator, a phase-lock device is designed, and it is composed of a symmetric 3 ? 3 coupler and a feedback circuit. For further establishing a differential polarization-shift keying (DPolSK) transmission system, we successfully carry out the demodulation experiments on 10-Gb/s DPolSK optical signals for the first time. Due to the all-optical structure with phase-lock, our scheme is available to realize the DPolSK optical communication in practical optical fiber systems.

Principal State Analysis for a Compact in-Line Fiber Polarization Controller

A compact in-line fiber-based polarization controller (FPC) made of a rotatable fiber squeezer is investigated in detail with the Mueller matrix model established based on the generalized principal state of polarization (PSP). The PSP caused by the fiber squeezing is in the equator plane, which turns around S3 axis on the Poincare sphere when rotating the squeezer. Subsequently, a programmable polarization control method is proposed to realize the polarization conversion between arbitrary polarization states, in which only two parameters of phase shift and rotation angle need to be controlled. This type of FPC, which has a highly compact structure, lower insertion loss, and can be directly embedded into any fiber devices without any extra delay, will be an ideal PC for high-speed optical communication and all-optical signal processing.

All-Optical Time Slot Interchange Using a Cascaded Optical Buffer

A novel scheme of all-optical time slot interchanger employing two cascaded re-circulating optical buffers based on nonlinear polarization rotation in semiconductor optical amplifiers is proposed. The experimental system exhibits full interchangeable capability on three 512-bit packets at 10 Gbits/s. Theoretically, each packet length is up to 123ns with the maximum buffer depth 30%.

Mueller-Matrix-Based Differential Rotation Method for Precise Measurement of Fiber Birefringence Vector

The method of complete polar decomposition for arbitrary Mueller matrixes is introduced to analyze the birefringence vector induced in a fiber, and then based on the Mueller matrix (MM) method, three kinds of computation methods including the absolute, the relative, and the differential rotation methods are proposed and investigated in detail. A computer-controlled measure system is employed to measure the Mueller matrix and birefringence vector for a 2.5-km fiber system with length 5 mm under lateral press in complicated environment with much perturbation. Experimental results show that the differential rotation (DR) method is the optimal approach to achieve fiber birefringence vectors in a large dynamic range of lateral press on fibers in perturbed situations, which reaches the highest linearity of 0.9998 and average deviation below 2.5%. Further analyses demonstrate that the DR method is also available for accurate orientation of lateral press direction and the average deviation is about 1.1°.