Search Results (6)

In this paper, we report the use of crossed polarizer technique to measure the differential group delay (DGD) of few-mode optical fiber (FMF). The windowed Fourier transform (WFT) is applied in the analysis of beat length measurement in the spectral domain to obtain the dependence of DGD as a function of wavelength. The birefringence of polarization-maintaining fiber (PMF) and the DGD of FMF are measured by applying our method. We discuss the noise background, the width of DGD peaks, and the possible errors introduced in the optical path in the modified crossed polarizer technique. Full article

We have demonstrated the use of a flat multi-wavelength Brillouin erbium-doped fiber laser (MWBEFL) based on a Sagnac loop with an unpumped erbium-doped fiber (Un-EDF) as a high-sensitivity sensor. A Sagnac loop with a Un-EDF was used as power equalizer to achieve multi-wavelength power flatness by adjusting the birefringence beat length properly. In the experiments, the best result obtained in terms of Brillouin Stokes lines and output power flatness was ±0.315 dB and the optical signal-to-noise ratio (OSNR) was 18.97 dB within a 33 nm bandwidth range from 1532.0 nm to 1565.0 nm. The flatness of the 33 nm bandwidth range varied from ±0.315 dB to ±1.38 dB and the average OSNR was about 17.51 dB. The peak power values of Brillouin Stokes lines observed under different wavelengths were extremely close and their range of fluctuation was about ±0.37 dB. These experimental results were close to our previous experimental values obtained using a passive Sagnac loop with a Un-EDF. The flat range covering almost the entire C-band has broad application prospects in high-sensitivity distributed optical fiber sensing and wavelength-division multiplexing. Full article

A 1.55 μm AlGaInAs multi-quantum-well (MQW) ridge waveguide polarization mode controller (PMC) is proposed. The design is based on an asymmetric half-ridge waveguide structure in which the ridge is shallow etched on one side and has a deeply etched mesa structure on the other side. The Finite-Element Method (FEM) was used to simulate the PMC and optimize its structural parameters comprehensively. Furthermore, the fabrication tolerances were also investigated in detail. The optimized PMC has a polarization conversion efficiency (PCE) of around 92.5% with a half-beat length of 1250 μm. When the PMC length was fixed at 1250 μm, to achieve a PCE derivation less than 8%, the tolerances for the ridge waveguide width and shallow etch height were 1.60 μm to 1.65 μm and 2.13 μm to 2.18 μm, respectively. In order to reduce interband gap absorption loss, the quantum well intermixing (QWI) technique was used in the model to realize a blueshift (200 nm) in the PMC. QWI is a simple, flexible, and low-cost technique for fabricating a PMC integrated with a laser diode and reduces parasitic reflections, which would otherwise degrade the overall performance. QWI also eliminates MQW material anisotropy and alleviates the birefringence effect without the need for regrowth, achieving nearly uniform properties as a bulk material. Full article

The correlation and power distribution of intercore crosstalk (ICXT) field components of weakly coupled multicore fibers (WC-MCFs) are important properties that determine the statistics of the ICXT and ultimately impact the performance of WC-MCF optical communication systems. Using intensive numerical simulation of the coupled mode equations describing ICXT of a single-mode WC-MCF with intracore birefringence and linear propagation, we assess the mean, correlation, and power distribution of the four ICXT field components of unmodulated polarization-coupled homogeneous and quasi-homogeneous WC-MCFs with a single interfering core in a wide range of birefringence conditions and power distribution among the field components at the interfering core input. It is shown that, for homogeneous and quasi-homogeneous WC-MCFs, zero mean uncorrelated ICXT field components with similar power levels are observed for birefringence correlation length and birefringence beat length in the ranges of $\left[0.5\mathrm{m},10\mathrm{m}\right]$ and $\left[0.1\mathrm{m},10\mathrm{m}\right]$, respectively, regardless of the distribution of power between the four field components at the interfering core input. Full article

Rayleigh, Brillouin and Raman scatterings in fibers result from the interaction of photons with local material characteristic features like density, temperature and strain. For example an acoustic/mechanical wave generates a dynamic density variation; such a variation may be affected by local temperature, strain, vibration and birefringence. By detecting changes in the amplitude, frequency and phase of light scattered along a fiber, one can realize a distributed fiber sensor for measuring localized temperature, strain, vibration and birefringence over lengths ranging from meters to one hundred kilometers. Such a measurement can be made in the time domain or frequency domain to resolve location information. With coherent detection of the scattered light one can observe changes in birefringence and beat length for fibers and devices. The progress on state of the art technology for sensing performance, in terms of spatial resolution and limitations on sensing length is reviewed. These distributed sensors can be used for disaster prevention in the civil structural monitoring of pipelines, bridges, dams and railroads. A sensor with centimeter spatial resolution and high precision measurement of temperature, strain, vibration and birefringence can find applications in aerospace smart structures, material processing, and the characterization of optical materials and devices. Full article

Brillouin scattering in optical fiber describes the interaction of an electro-magnetic field (photon) with a characteristic density variation of the fiber. When the electric field amplitude of an optical beam (so-called pump wave), and another wave is introduced at the downshifted Brillouin frequency (namely Stokes wave), the beating between the pump and Stokes waves creates a modified density change via the electrostriction effect, resulting in so-called the stimulated Brillouin scattering. The density variation is associated with a mechanical acoustic wave; and it may be affected by local temperature, strain, and vibration which induce changes in the fiber effective refractive index and sound velocity. Through the measurement of the static or dynamic changes in Brillouin frequency along the fiber one can realize a distributed fiber sensor for local temperature, strain and vibration over tens or hundreds of kilometers. This paper reviews the progress on improving sensing performance parameters like spatial resolution, sensing length limitation and simultaneous temperature and strain measurement. These kinds of sensors can be used in civil structural monitoring of pipelines, bridges, dams, and railroads for disaster prevention. Analogous to the static Bragg grating, one can write a moving Brillouin grating in fibers, with the lifetime of the acoustic wave. The length of the Brillouin grating can be controlled by the writing pulses at any position in fibers. Such gratings can be used to measure changes in birefringence, which is an important parameter in fiber communications. Applications for this kind of sensor can be found in aerospace, material processing and fine structures. Full article