Search results for "Fiber optic"
showing 10 items of 193 documents
Ultra-sensitive fluorescence spectroscopy of isolated surface-adsorbed molecules using an optical nanofiber.
2009
The strong radial confinement and the pronounced evanescent field of the guided light in optical nanofibers yield favorable conditions for ultra-sensitive surface spectroscopy of molecules deposited on the fiber. Using the guided mode of the nanofiber for both excitation and fluorescence collection, we present spectroscopic measurements on 3,4,9,10-perylenetetracarboxylic dianhydride molecules (PTCDA) at ambient conditions. Surface coverages as small as 1 per thousand of a compact monolayer still give rise to fluorescence spectra with a good signal to noise ratio. Moreover, we analyze and quantify the self-absorption effects due to reabsorption of the emitted fluorescence light by circumjac…
Glowing optical fiber designs and parameters
1997
Side-emitting optical fiber designs and main parameters have been studied. A simplified model to describe emission of the 'glowing' fiber is developed. Basic expressions for the emission parameters as functions of the input radiation intensity, distance along the fiber axis and scattering efficiency longitudinal distribution are given for several design modifications. The model assumptions have been checked experimentally by testing silica core side-glowing optical fiber samples.
Long period gratings formed in depressed cladding fibres
1997
There has been a significant interest in long period gratings, primarily due to their applications in gain-flattened erbium doped fibre amplifiers [1]. Up till now, cladding modes supported by the glass-air interface of an optical fibre have been used in a forward mode coupling scheme involving also the guided fundamental mode of the optical fibre. Here we propose an alternative technique. In a single mode depressed cladding fibre of an appropriate design (an example is given in fig. 1), the higher order LP11 mode can be made to be a leaky mode in such a structure, i.e. it can propagate for a short length before being stripped off the high index region beyond the depressed cladding. This en…
Q-switching of an all-fiber laser by acousto-optic modulation of a fiber Bragg grating.
2009
We report active Q-switching of an all-fiber laser using a Bragg grating based acousto-optic modulator. Q-switching is performed by modulating a fiber Bragg grating with an extensional acoustic wave. The acoustic wave modulates periodically the effective index profile of the FBG and changes its reflection features. This allows controlling the Q-factor of the cavity. Using 1 m of 300 ppm erbium-doped fiber and a maximum pump power of 180 mW, Q-switch pulses of 10 W of peak power and 82 ns wide were generated. The pulse repetition rate of the laser can be continuously varied from few Hz up to 62.5 kHz.
Fiber laser with combined feedback of core and cladding modes assisted by an intracavity long-period grating
2011
We present a fiber laser made in a single piece of conventional doped-core fiber that operates by combined feedback of the fundamental core mode LP((0,1)) and the high-order cladding mode LP((0,10)). The laser is an all-fiber structure that uses two fiber Bragg gratings and a long-period grating to select the modes circulating in the cavity; the laser emits at the coupling wavelength between the core mode LP((0,1)) and the counterpropagating cladding mode LP((0,10)) in the Bragg gratings. This work demonstrates the feasibility of high-order mode fiber lasers assisted by long-period gratings.
Radiation hardening of FBG in harsh environments
2014
International audience; The difficulties encountered in the implementation of a temperature or strain sensor based on Fiber Bragg Grating in a harsh radiative environment are introduced. We present the choices made to select both a radiation-resistant fiber in terms of transmission and also the grating inscription conditions necessary to write radiation tolerant FBGs in such fibers with a femto-second laser. The response of different classes of gratings was also studied under radiation at high doses (>1MGy). The comparison between F- and Ge-doped fibers was highlighted.
Fiber Bragg gratings with various chirp profiles made in etched tapers
1996
We have studied, both theoretically and experimentally, fibre Bragg gratings with a number of different chirp profiles. These chirp profiles can be easily achieved with a recently demonstrated technique involving a taper of desired profile being etched into the cladding of a fibre. Performances of gratings with linear, quadratic, periodically modulated and step chirp profiles are numerically analysed. The versatility of the technique is demonstrated when linearly and quadratically chirped gratings were made as examples of continuous chirp and gratings with step chirps were made as examples of discontinuously chirped structure.
Simple high-resolution wavelength monitor based on a fiber Bragg grating
2004
A compact and low-cost device for monitoring the peak wavelength of single-peak spectral distributions is presented. The system is based on the transmission properties of a fiber Bragg grating when its period is modulated. Different types of optical signal, such as the emission of distributed-feedback lasers and the reflection of a broadband optical source produced by fiber gratings used in sensor systems, can be measured with this device. We demonstrate that a high wavelength resolution of micro 1 pm can be achieved and that our proposal can be used for real-time monitoring.
Simultaneous temperature and ac-current measurements for high voltage lines using fiber Bragg gratings
2006
We present an optical ac-current sensor, based on a fiber Bragg grating stretched by a magnetostrictive material, which enables a simultaneous measurement of high ac-currents and temperature. The proposed system is appropriated to monitor high voltages lines and can be installed without interrupting the current line, being characterized by an inherent electrical isolation.
Ultra-flat SPM-broadened spectra in a highly nonlinear fiber using a fiber Bragg grating based parabolic pulse shaper
2006
We demonstrate the generation of ultra-flat broadened spectra by seeding a nonlinear fiber with parabolic pulses shaped using a fiber grating. Applications in pulse compression and spectral slicing are shown.