Direct transverse load profile determination using the polarization-dependent loss spectral response of a chirped fiber Bragg grating.

The determination of stress profiles created by transverse loads was proved to be important in different domains, such as structural health monitoring and biomechanics, and, more specifically, in the prostheses domain. In this paper, we report an original method to estimate the transverse load profile from the polarization-dependent loss (PDL) spectrum of a chirped fiber Bragg grating (CFBG). This method makes use of the relationship between the integration of the PDL of a CFBG, and the force profile has the advantage of not requiring any iterative method to estimate the transverse load profile. The relationship linking the integration of the PDL and the force profile is demonstrated using an analytical approximation of the transmission spectrum of CFBGs. The validity of this method for the determination of non-uniform load profiles is then shown using a numerical analysis. An experimental demonstration is finally reported using a 48 mm-long CFBG subject to different step transverse load profiles.

Distribution profiling of a transverse load using the DGD spectrum of chirped FBGs.

In this paper, we propose a new method to determine the longitudinal distribution of a non-uniform transverse force applied to an optical fiber. For that purpose, we use a chirped fiber Bragg grating (CFBG) for which we monitor the polarization parameters in reflection. In particular, we demonstrate that the differential group delay (DGD) spectrum of the CFBG is an imprint of the load profile so that it can be used for the shape determination of an applied load. Thereafter, we discuss the influence of the CFBG parameters on the achievable accuracy and resolution of our technique. An experimental validation is finally reported with two 48 mm long CFBGs subject to step transverse load profiles.

All-fiber tunable optical delay line.

We present a tunable optical delay line based on the use of a single chirped fiber Bragg grating written into a standard single mode optical fiber. In the proposed scheme, the delay is induced through the Bragg grating differential group delay curve. This is achieved by launching orthogonally polarized optical pulses in both directions into the Bragg grating and by controlling its local birefringence. This bidirectional propagation allows to compensate the second-order dispersion. The setup is suitable to delay pulses with a spectral width just less than the grating reflection bandwidth, which is particularly useful in the context of forthcoming wavelength division multiplexing ultra-high bit rate lightwave systems. In this work, the performances of the setup are investigated using a pulsed laser delivering 6.3 ps Fourier transform limited pulses at 1548 nm. A maximum delay of 120 ps (about 20 times the pulse width) is reported experimentally.

Reduction of polarization related effects in superimposed fiber Bragg gratings.

Fiber Bragg gratings, and more specifically, superimposed fiber Bragg gratings (SIFBGs), are attractive commercial solutions for several multiband telecommunication applications. However, as a part of a telecommunication system, the polarization dependent properties present in SIFBGs due to the fabrication process dramatically limit their possible implementation in high bit rate optical communications. The development of techniques for the reduction of differential group delay (DGD) and the polarization dependent loss (PDL) in system components is then crucial. We present a simple method to reduce the DGD and the PDL induced during the fabrication of SIFBGs. The proposed fabrication method consists of irradiating the fiber core from different well controlled directions depending on the total number of expositions. We theoretically predict and experimentally demonstrate a reduction of the DGD and the PDL after each illumination.