Polarisation optical time domain reflectometry for statistical evaluation of polarisation mode dispersion

The authors shows that a commercial optical time domain reflectometer can be modified to measure the statistical nature of polarisation mode dispersion along the length of a communications grade fibre with short-length PMDs<4 ps/km.<>     

Modal dependence of the photoelastic coefficient in multimode,step-index optical fiber time domain systems

A simple ray-optic approach for the analysis of strained step-index multimode fibers is shown to lead to the determination of the photoelastic coefficient in an optical-fiber time-domain system. The theoretical model includes the dependence of the photoelastic coefficient a on the modal content of the fiber and explains some of the experimental discrepancies observed in high-resolution reentrant-loop-based sensing systems. For high-step-index 200-240 μm fibers with higher numerical resolution, the value of a is shown to vary from -0.2 to -0.3, which matches closely with experimental results     

Regenerative periodic pulse trains in linear, single-mode opticalfibers: effect of finite source linewidths

A periodic pulse train launched within a linear dispersive optical fiber regenerates itself at distances that depend on the period of the pulse train. The effect of using a single longitudinal-mode laser source with a Gaussian power spectrum to modulate a periodic pulse train is considered, and the resulting expressions for regenerative periodic pulse trains are analyzed as functions of the source linewidth. It is shown that these pulse trains decay exponentially. Effects of operating such systems in the first- and second-order dispersion regimes are considered     

Band-rejection fibre filter using periodic core deformation

Grating-based all-fibre bandstop filters were fabricated by introducing periodic deformations in the core of the fibre with a CO₂ laser by first ablating the surface of the fibre and then annealing it. These devices, which can be tailored to any wavelength, have a broad bandwidth (10 nm), high peak wavelength rejection (>20 dB), low insertion loss (<0.3 dB), a very flat response outside the rejection band, and a short physical length (6 mm)     

Fiber-optic dual-technique sensor for simultaneous measurement ofstrain and temperature

Polarimetric and two-mode differential interferometric schemes incorporated in an elliptical-core fiber are able to resolve strain and temperature simultaneously with resolutions of 10 μm/m and 5°C, respectively. A technique, based on the evaluation of the condition number of a matrix, is shown to be useful in evaluating comparative merits of multiparameter sensing schemes. The determinant of the beat length matrix is expressed in terms of mode propagation constants, and a method for designing specialized fibers suitable for simultaneous measurement of strain and temperature is proposed. Experimental results for four fibers are presented and cross-sensitivity issues are discussed     

Optical fiber-based dispersion compensation using higher ordermodes near cutoff

Higher order spatial modes in optical fibers exhibit large, negative chromatic dispersion when operated near their cutoff wavelength. By using a spatial mode-converter to selectively excite a higher order mode in specially designed multimode fiber, this dispersion can be used to compensate the positive dispersion in conventional single-mode fiber spans. In this paper, issues related to compensating fiber and mode-converter design are explored. Experimental measurements in specially designed two-mode fibers operated in LP₁₁ mode show negative dispersion as large as -70 ps/nm·km at 1555 nm. Pulse propagation and system experiments employing spatial mode-converters to excite LP₁₁ mode in a two-mode fiber demonstrate the feasibility of this technique for dispersion compensation in lightwave systems     

Spectrographic analysis of boron nitride for trace impurities

A d.c. arc emission spectrographic method has been developed for the determination of nine trace impurities in boron nitride. The charge for exciting the sample contains equal quantities of boron nitride and graphite (containing 2% NaF as carrier and 1% La(2)O(3) as an internal standard). The method is useful in the determination of impurities in the range 2-1000 ppm, with a mean relative standard deviation of 13%.     

800 Gbit/s (80×10.66 Gbit/s) transmission over 3200 km ofnon-zero dispersion shifted fibre with 100 km amplified spans employingdistributed Raman amplification

80×10.66 Gbit/s wavelength division multiplexing transmission over 3200 km fibre with 100 km amplifier spacing and 50 GHz channel spacing is demonstrated. Error-free transmission of all 80 channels is achieved by employing distributed Raman amplification, forward error correction and low dispersion slope TrueWave^R fibre     

Long-period fiber gratings as band-rejection filters

We present a new class of long-period fiber gratings that can be used as in-fiber, low-loss, band-rejection filters. Photoinduced periodic structures written in the core of standard communication-grade fibers couple light from the fundamental guided mode to forward propagating cladding modes and act as spectrally selective loss elements with insertion losses act as backreflections <-80 dB, polarization-mode-dispersions <0.01 ps and polarization-dependent-losses <0.02 dB     

Variable-ratio, polarisation-insensitive, 3*3 fused biconical tapered couplers

The authors present a polarisation-insensitive, 3*3 fused biconical tapered coupler with a variable screw gauge that can change the coupling ratios from a splitting percentage of 11%-44%-45% to a uniformity of 33%-33%-34%, with excess loss maintained below 1.1 dB. The fabrication and packaging methods are described and wavelength tunability of the coupler is demonstrated.<>