Twin fiber grating tunable dispersion compensator

A new tunable dispersion compensator that does not suffer from higher order dispersion is reported. The device consists of two quadratically chirped fiber Bragg gratings, each with linear strain actuators. The module has a tuning range of 500 ps/nm and a bandwidth of 0.5 nm. In a 40-Gb/s return-to-zero system, the dispersion penalty tolerance is extended from 100 to 600 ps/mm     

Efficient inverse scattering algorithm for the design of grating-assisted codirectional mode couplers

An efficient method for the design of optical devices based on codirectional grating-assisted mode coupling is presented. A low-complexity algorithm is developed to calculate the coupling function of a grating that accurately matches an arbitrarily given target spectral response. The method relies on the synthesis of the grating impulse response by means of an exact differential layer-peeling algorithm.     

Effects of random phase and amplitude errors in optical fiber Bragggratings

This paper studies the influence of random phase and amplitude fabrication errors on the performance of optical filters based on fiber Bragg gratings (FBG's). In particular, we analyze two effects of particular importance for optical communications: the excess crosstalk induced in apodized gratings commonly used in wavelength-division-multiplexing (WDM) systems, and the time-delay fluctuations that appear in chirped gratings employed to compensate the fiber dispersion. A statistical model is presented to explain these effects in terms of the coherence length of the grating fabrication procedure     

An efficient inverse scattering algorithm for the design ofnonuniform fiber Bragg gratings

Presents an efficient method for the design of complex fiber Bragg gratings. The method relies on the synthesis of the impulse response of the grating by means of a differential layer-peeling algorithm. The algorithm developed takes into account all the multiple reflections inside the grating, giving an exact solution to the inverse scattering problem. Its low algorithmic complexity enables the synthesis of long fiber gratings. The method is illustrated by designing several filters with interest for optical fiber communication systems: dispersionless bandpass filters and second- and third order dispersion compensators     

Reconstruction of gratings from noisy reflection data

The worst-case error amplification factor in reconstructing a grating from its complex reflection spectrum is shown to be of the order 1/T(min), where T(min) is the minimum transmissivity through the grating. For a uniform grating with coupling coefficient-length product kappaL, the error amplification is exp(2kappaL). The exponential dependence on the grating strength shows that spatial characterization of gratings from a measured reflection spectrum is impossible if the grating is sufficiently strong. For moderately strong gratings, a simple regularization technique is proposed to stabilize the solution of the inverse-scattering problem of computing the grating structure from the reflection spectrum.     

Acoustooptic attenuation filters based on tapered optical fibers

This paper studies the acoustooptic interaction induced by an acoustic flexural wave among the optical propagation modes supported by tapered optical fibers. We have investigated the evolution of the acoustooptic resonance condition as the fiber is progressively tapered, showing that the taper radius can be regarded as a new degree of freedom in the design of acoustooptic filters. Finally, we demonstrate a novel acoustooptic filter based on nonuniform tapers for dynamic gain flattening of optical fiber amplifiers     

Simultaneous distributed measurement of strain and temperature fromnoise-initiated Brillouin scattering in optical fibers

The simultaneous determination of strain and temperature distributions from the measurement of noise-initiated Brillouin scattering (NIBS) power and frequency shift in optical fibers is discussed. Equations governing the growth of the NIBS signal are derived and from these, we calculate the dependence of the Brillouin power on temperature and strain. We study the potential problem given by the need to normalize the nonlinear Brillouin signal and present a new technique that solves this problem by mathematically combining the values of the Stokes and anti-Stokes powers to produce a linear effective power. Experimental results are presented that support this theory and allow the verification of the coefficients governing the dependence of the Brillouin power and frequency shift on temperature and strain. The signal-to-noise ratio of the sensor is discussed, and it is found that the noise associated with the field statistics plays a limiting role in the sensor performance and that an optimum value for the Brillouin gain factor can be determined. A simultaneous distributed temperature and strain sensor is demonstrated; preliminary results show a strain resolution of 100-μm strain, a temperature resolution of 4°C, and a spatial resolution of 40 m, over a sensing length of 1200 m     

Measurement of axial stress at high spatial resolution in ultraviolet-exposed fibers

High-spatial-resolution measurements of axial-stress profiles of UV-irradiated fibers are reported, providing diagnostic information and a technique for the direct observation of UV-written grating structures. Measurements have been made with a spatial resolution of ~0.3 mum, which is capable of resolving detail within the pitch of the gratings.