Search results for "Diffraction grating"
showing 10 items of 75 documents
Tunable microwave photonic filter based on chirped fiber gratings working with a single optical carrier at constant wavelength
2007
This paper presents a tunable transversal filter working with a single optical carrier at constant wavelength. The filter consists of a set of chirped gratings whose time delay is tuned with respect to the emission wavelength of a fiber laser by a piezoelectric actuator; extra lengths of fiber are inserted in the filter arms in order to avoid interferences between signals reflected in different gratings. Two and three taps filters are experimentally demonstrated, the filters transfer function is electronically tuned within the free spectral range.
Analysis of multiple internal reflections in a parallel aligned liquid crystal on silicon SLM
2014
Multiple internal reflection effects on the optical modulation of a commercial reflective parallel-aligned liquid-crystal on silicon (PAL-LCoS) spatial light modulator (SLM) are analyzed. The display is illuminated with different wavelengths and different angles of incidence. Non-negligible Fabry-Perot (FP) effect is observed due to the sandwiched LC layer structure. A simplified physical model that quantitatively accounts for the observed phenomena is proposed. It is shown how the expected pure phase modulation response is substantially modified in the following aspects: 1) a coupled amplitude modulation, 2) a non-linear behavior of the phase modulation, 3) some amount of unmodulated light…
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…
Spatial information transmission using axial temporal coherence coding
2007
We present an approach that can be used for transmission of information through space-limited systems or for superresolution. The spatial information is coded with different axial temporal coherence by interfering every spatial region in the input with the same region, but with a certain known delay in the longitudinal axis. Every spatial region has different delay. After mixing all of the spatial information, it is transmitted through the space-limited system. At the detection the information is passed through a similar interference setup containing certain axial delay. By temporally scanning along the longitudinal axis, each time a different spatial region that was coded with the correspo…
Effective length of short Fabry-Perot cavity formed by uniform fiber Bragg gratings
2009
In this paper, we describe the properties of Fabry-Perot fiber cavity formed by two fiber Bragg gratings in terms of the grating effective length. We show that the grating effective length is determined by the group delay of the grating, which depends on its diffraction efficiency and physical length. We present a simple analytical formula for calculation of the effective length of the uniform fiber Bragg grating and the frequency separation between consecutive resonances of a Fabry-Perot cavity. Experimental results on the cavity transmission spectra for different values of the gratings' reflectivity support the presented theory.
<title>Bragg and asymmetric-relief reflection gratings in As-S-Se thin films</title>
2005
Bragg and asymmetric-relief gratings and their formation in the amorphous As-S-Se films are discussed. Due to the high refractive index and its photoinduced change, the films are useful in holography. The thickness of the As0.4S0.15Se0.45 and As0.4S0.3Se0.3 films used in the Bragg gratings is optimized. The dependence of the dimaction efficiency of the asymmetric-relief gratings on the conditions of recording, chemical treating, and reading out (polarization and angle) is studied.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Exact analytic expressions for electromagnetic propagation in a finite one-dimensional periodic multilayer
2004
Translation Matrix Formalism has been used to find an exact analytic solution for light propagation in a finite one-dimensional (1-D) periodic stratified structure. This modal approach allows to derive a closed formula for the electric field in every point of the structure, by simply imposing a convenient form for the boundary conditions. As an example it is also shown how to extend this result to gratings featuring defects.
Ultrafast beam shaping with high-numerical-aperture microscope objectives
2009
Ultrafast diffraction results in spatiotemporal un-coupling of the wave field, inducing spectral anomalies and pulse stretching. Localized compensation may be achieved via angular dispersion driven by diffractive optical elements (DOEs). We report on an DOEs-based beam shaper of ultrashort optical pulses with high spatiotemporal resolution. Inspection of the validity of our approach is performed in the single-cycle regime.
Debye representation of dispersive focused waves
2006
We report on a matrix-based diffraction integral that evaluates the focal field of any diffraction-limited axisymmetric complex system. This diffraction formula is a generalization of the Debye integral applied to apertured focused beams, which may be accommodated to broadband problems. Longitudinal chromatic aberration may limit the convenience of the Debye formulation and, additionally, spatial boundaries of validity around the focal point are provided. Fresnel number is reformulated in order to guarantee that the focal region is entirely into the region of validity of the Debye approximation when the Fresnel number of the focusing geometry largely exceeds unity. We have applied the matri…
High-visibility interference fringes with femtosecond laser radiation.
2009
We propose and experimentally demonstrate an interferometer for femtosecond pulses with spectral bandwidth about 100 nm. The scheme is based on a Michelson interferometer with a dispersion compensating module. A diffractive lens serves the purpose of equalizing the optical-path-length difference for a wide range of frequencies. In this way, it is possible to register high-contrast interference fringes with micrometric resolution over the whole area of a commercial CCD sensor for broadband femtosecond pulses.