Tag: 2003

source: © 2003 IEEE Photonics Technology Letters

We demonstrate a new technique that enables us to measure the structure of highly reflecting fiber Bragg gratings. The impulse response function is measured from both sides of the grating using a low-coherence spectral interferometry technique. An inverse scattering algorithm is used to extract the refractive-index profiles from the measured impulse responses. The reconstruction of the grating is performed by combining the refractive-index profiles, measured from both sides of the grating. The transfer function of the optical spectrum analyzer is measured and used to correct the measured results. The interrogation of an apodized grating with a reflectivity of 99.91% is demonstrated. [Read more…]

Fig. 1. Schematic description of the experimental setup used to measure the structure of highly reflecting fiber Bragg gratings. The interference spectrum of a wave reflected from the grating and a wave reflected from a reference mirror is measured from both sides of the grating by changing the state of the optical switches. PC is a polarization controller.

S. Keren, A. Rosenthal, M. Horowitz, “Measuring the structure of highly reflecting fiber Bragg gratings,” IEEE Photonics Technology Letters ( Volume: 15 , Issue: 4 , April 2003 )

source: © 2003 Optical Society of America

We demonstrate a new method for measuring changes in temperature distribution caused by coupling a high-power laser beam into an optical fiber and by splicing two fibers. The measurement technique is based on interrogating a fiber Bragg grating by using low-coherence spectral interferometry. A large temperature change is found owing to coupling of a high-power laser into a multimode fiber and to splicing of two multimode fibers. Measurement of the temperature profile rather than the average temperature along the grating allows study of the cause of fiber heating. The new measurement technique enables us to monitor in real time the temperature profile in a fiber without the affecting system operation, and it might be important for developing and improving the reliability of high-power fiber components. [Read more…]

Fig. 1 Schematic description of the experimental setup used to measure the temperature profile caused (a) by coupling a high-power argon-ion laser beam into a fiber and (b) by splicing two optical fibers.

Vladimir Goloborodko, Shay Keren, Amir Rosenthal, Boris Levit, and Moshe Horowitz, “Measuring temperature profiles in high-power optical fiber components,” Appl. Opt. 42, 2284-2288 (2003)

source: © 2003 IEEE Journal of Quantum Electronics

We demonstrate a new inverse scattering algorithm for reconstructing the structure of highly reflecting fiber Bragg gratings. The method, called integral layer-peeling (ILP), is based on solving the Gel’fand-Levitan-Marchenko (GLM) integral equation in a layer-peeling procedure. Unlike in previously published layer-peeling algorithms, the structure of each layer in the ILP algorithm can have a nonuniform profile. Moreover, errors due to the limited bandwidth used to sample the reflection coefficient do not rapidly accumulate along the grating. Therefore, the error in the new algorithm is smaller than in previous layer peeling algorithms. The ILP algorithm is compared to two discrete layer-peeling algorithms and to an iterative solution to the GLM equation. The comparison shows that the ILP algorithm enables one to solve numerically difficult inverse scattering problems, where previous algorithms failed to give an accurate result. The complexity of the ILP algorithm is of the same order as in previous layer peeling algorithms. When a small error is acceptable, the complexity of the ILP algorithm can be significantly reduced below the complexity of previously published layer-peeling algorithms.. [Read more…]

Fig. 1. Reconstructed modulation index n1(z) of a uniform grating with a refractive index modulation amplitude n1=6.5×10−4, a length of 4 mm, and a maximum reflectivity of 99.99%, calculated using the ILP algorithm (solid line), the FDLP algorithm (dashed line), and iterative solution to the GLM equation with 70 iterations (dotted line). The reflection spectrum was sampled over a bandwidth of 40 nm with a resolution of 0.01 nm. The figure shows that an excellent reconstruction of the grating was obtained using the ILP algorithm, while the FDLP algorithm and the iterative solution to the GLM equation gave a large error. The inset of the figure shows a zoom on the profile close to the input end of the grating.

Amir Rosenthal and Moshe Horowitz, “Inverse scattering algorithm for reconstructing strongly reflecting fiber Bragg gratings,” IEEE Journal of Quantum Electronics ( Volume: 39 , Issue: 8 , Aug. 2003 )