Zhengyong Li

Microbuckling Solution of Elastic Memory Laminates under Bending

Elastic memory composite (EMC) can endure a much higher nominal bending strain than the ultimate strain of reinforced fibers. Experimental studies have confirmed that microbuckling and post-microbuckling response for compressively loaded fibers in the soft matrix are the primary deformation mechanism for EMC to realize a large bending deformation. However, classical buckling solutions developed for hard-matrix composites cannot effectively predict the microbuckling onset and post-microbuckling response of soft-matrix composites under bending. In this study, a simplified 1D solution is proposed by combining matrix shear energy with Timoshenko’s elastic foundation energy. Based on the experiment results of carbon-fiber/resin EMC laminates under bending, the new solution exhibits to be effective in predicting the microbuckling wavelength and the onset of critical compressive stress and strain. In addition, the location of neutral-strain surface and failure modes are also discussed.

Quaternion Approach to the Measurement of the Local Birefringence Distribution in Optical Fibers

A method to structure the Jones quaternion utilizing Pauli matrices is proposed, improving the quaternion theory of polarization optics. It is proved that the Stokes quaternion is the double product of the Jones quaternion and its Hermitian transpose and that the rotation axis of the output three-adjacent-point Stokes quaternions is a mapping from the rotation axis of the three-adjacent-reflection-point Stokes quaternions in the optical fiber and that the rotation angle among the output three adjacent points is the doubleness of the rotation angle among the three adjacent reflection points in the optical fiber. The three-point quaternion method to measure birefringence distribution is proposed and implemented, the experimental result shows that the average birefringence is 0.263/m in the fiber under test, and the corresponding average beat length is 26 m. We also demonstrated the paraxial approximate quaternion Baker-Campbell-Hausdorff formula of exponential quaternions multiplying for cascaded optical components; then, a quaternion interpolation method to estimate the error of birefringence measurement is proposed, and the relative error calculated was less than 5%. The previously cited works indicate that the quaternion algorithm is very effective in the research of the polarization in optical fibers.

Method to measure the second-order birefringence vector distribution along optical fibers based on high-speed polarization optical time domain reflectometry

Based on a high-speed polarization optical domain reflectometry, an innovative method to measure the second-order birefringence vector distribution along optical fibers was proposed and implemented in this paper. Some interesting data were obtained along a 1 km long single mode fiber by only one detection. The second-order birefringence magnitude distribution curve can reflect both magnitude and direction change information of the first-order birefringence, and it was more stable (except the catastrophe points) than that of the first-order. The larger variable range of the second-order birefringence magnitude may provide a higher sensitivity than the first-order for birefringence-based distributed sensors.

Laser coherence measurement based on optical pulses interference

By using a feedback-stabilized fiber Mach-Zehnder interferometer (MZI) with a PZT-based phase shifter, a novel method for measurement of laser coherence length is demonstrated based on pulses interference. Experimental results show that the coherence length is closed to that measured by the commercial optical spectrometer, and the partial coherence phenomenon is observed. Our scheme can measure not only the high-coherence laser but also low-coherence pulses, which is widely used in coherent laser measurement and application. OCIS codes: 030.0030, 260.3160, 320.5550. doi: 10.3788/COL201210.S20301.

Polarization temporal signal processor for ultrahigh-speed optical communication applications

An all-optical polarization temporal signal processor is demonstrated, which performs well in 40-Gbits/s optical signal differentiation with error of ∼0.1 and efficiency of ∼12%, 80-GHz 3.3-ps optical pulse generation, and reshaping for 250-fs optical pulse.

The three point method for measurement of P-OTDR sensor

A new method for measurement of local birefringence is proposed for P-OTDR sensor, based on the sequentially obtained three points of state of polarization (SOP) and a high speed polarization analyzer. In this method only one input SOP is needed and the measurement results are insensitive to the input SOP. The distribution of local birefringence vector along a 1km single mode fiber was precisely measured with 2 cm accuracy, only once detection is enough for the measurement.

All-Optical Clock Frequency Multiplication Based on SOA-assisted Mach-Zehnder Interfering

We present a novel scheme of all-optical clock frequency doubling and quadrupling based on Mach-Zehnder interfering with a polarization-sensitive semiconductor optical amplifier (SOA). Then we experimentally demonstrate the frequency doubling of 5 G-bit/s optical clock signal, and quadruple 2.5 G-bit/s signal to stable short pulse train with pulse FWHH ~55 ps. Our relatively concise scheme is convenient to be upgraded to 40 G-bit/s and applicable to high-speed optical communications.

Temperature-effect measurement of Fresnel reflection by polarization optical time domain reflectometry (POTDR)

We propose a POTDR setup and investigate the Rayleigh scatter and Fresnel refection. A piezoelectric polarization controller (PPC) is applied in this setup. Based on the transfer matrix theory of the PPC, the state of polarization (SOP) of the Fresnel reflection is analyzed under different temperature. In the experiment, we find that when any part of the fiber is affected by the temperature, the SOP of Fresnel reflection will be changed.

Experiment and analysis based on polarization optical time domain reflectometry (POTDR)

New polarization properties have been observed from the Fresnel reflection on the waveforms of OTDR with the commercial OTDR produced by Anritsu company. Then a better POTDR system was established in order to discover the accurate properties, and more remarkable result was obtained by the Serial Data Analyser(SDA5000A).