Bandpass filters based on π-phase-shifted long-period fiber grating have been theoretically analyzed and experimentally fabricated by the electric-arc technique. Calculations and numerical simulations, based on coupled mode theory associated with the F-matrix method, have shown that the isolation of lateral rejected bands is maximum when the total length of the grating is optimised and the π-phase-shift inserted when the transmission at the desired resonance wavelength is -6.9dB. Two π-phase-shifts are introduced at optimised positions to obtain a large bandwidth of the badpass filter. We have fabricated the first bandpass filters that have lateral rejected bands isolation higher than 20 dB and bandpass filters with very large flat-top bandwidths (FWHM =19.5 nm) around 1538 nm peak, the fabricated filters are characterized by a very low insertion loss (<0.5 dB).
We have fabricated Long Period Grating filters in two Dual Concentric Core Fibers by an electric arc discharge technique. The gratings have induced coupling between the fundamental modes of the two cores. We have obtained filter with rejected band around 1220 nm and 1559 nm respectively, characterized by insertion loss lower than 0.5 dB. We also have investigated the inteest of using this fiber to implement a highly selective Mach-Zehnder interferometer with a 2.4 nm inter-fringe. Despite the high Ge-doping of the used fiber, thermal characterizations show a temperature sensitivity of the transmitted spectrum similar to that of the same grating written in a standard Single Mode Fiber.
We have used a CO2 laser as a heating source to fabricate a single-mode fiber couplers. The process consists of fusing and stretching two standard single model fibers initially maintained in lateral contact. We have fabricated 3 dB couplers at 1500 nm with insertion loss < 0.5dB. We also have fabricated multiplexers such as a 100% coupler at 1310 nm and at 1550 nm. The channel isolation of these components are > 30dB with a bandwidth of 30 nm at -30dB. Finally, a coupler with a long constant waist have been fabricated.
A simple method of fabricating long-period fiber gratings, by performing an electric discharge to optical fiber, is presented. Standard single mode fiber is used without hydrogen loading. Grating filters present competitive characteristics, very low insertion loss and high dynamic rejections. We have performed high temperature characterizations of realized gratings in the range 30 - 1200 degree(s)C. Resonance wavelength shifts behavior and grating stability at several annealing cycles have been investigated. The temperature sensitivity are in good agreement with recent published works. Irreversible evolution of the peak shifts is to be emphasized.
We present the fabrication of long period fiber grating, in non-hydrogenated standard telecommunication fiber, using an electric discharge. We have obtained a gratin with low insertion loss, dynamic rejection of 37.5dB at 1530 nm and bandwidth of 16.3nm at -3 dB. The performances are competitive compared to literature. We have demonstrated the flexibility of the process by fabricating band pass and compact concatenated filters.
We have fabricated Long Period Fiber Gratings (LPFG), using non-hydrogenated standard single-mode fiber (SMF28TM), with an electric arc discharge, issued from a commercial splicer. We have obtained gratings with low insertion loss and isolation of 37.5 dB at 1530 nm. The bandwidth at -3 dB (FWHM) is evaluated to be 16 nm. Evolution of the spectral responses (peaks isolation, bandwidth) are explored. We have performed temperature characterization of the realized gratings between 0 degrees C and 750 degrees C. The gratings exhibit a robust and stable behavior to temperature annealing. We showed a spectral shift of the resonance peaks with temperature, these evolutions are worthy of note. We have studied and experimented phase-shift filters. The filters performances are competitive compared to literature. These characterizations provide a set of phenomena to help explanation of the inscription mechanism of the gratings. The fabrication is simple, it does not require to hydrogenate the fiber. The control of the filter parameters makes it possible to produce any filter profile. We have demonstrated the simplicity and flexibility of the process.
Hemispherical microlenses have been fabricated at the end of a single-mode optical fiber by a new two-steps method which uses only a continuous CO2 laser. In the first step, the fiber is heated by the laser and stretched until its split resulting in two symmetrical tapers. In the second step, we form the microlenses by laser melting the taper ends. Parameters of heating and stretching are automated and optimized to ensure the reproducibility. The microlens characterization, including the focal length and beam waist measurements, has been performed. It shows the interest of the microlens-fiber to several applications.
An optic fiber sensor based on the intermodal interference principle was integrated in a composite material structure to detect impacts and vibrations. Six fibers were integrated at the top of a carbon/epoxy composite panel and arranged to form a regular network on the structure. A series of impacts at various positions on the plate were performed using an instrumented hammer. The spectral responses of the optic sensors were compared to a reference piezoelectric accelerometer. Moreover a determination of the impacts position was performed with the arrival times measure of the generated acoustic wave front to the optic sensors. These tests proved the great sensitivity of this type of sensor, its integration easiness and the possibility to localize an impact on composite structures with a very simple device.
This sensor is based on the optical coupling between two optical fibers, submitted simultaneously to the same constraint. Due to the geometrical deformations, photoelasticity, and evanescent field this coupling was studied theoretically and experimentally, and used to build a time multiplexed sensor network by coupling short pulses. This arrangement has high sensitivity and resolution, without some drawbacks of the classical OTDR.
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