System and method for permanently writing a diffraction grating in a low phonon energy glass medium
AssigneeUniversite Laval
InventorsReal Vallee, Martin Bernier, Dominic Faucher
Life of this patent
Estimating the term…
Abstract
A system and method for permanently writing diffraction gratings in low phonon energy glass waveguides are shown. Ultrashort light pulses are generated and made to form two beams synchronously superimposed in the waveguide, therefore forming an interference pattern corresponding to the desired grating. The light pulses are focussed so that the light intensity in the waveguide exceeds a filamentation threshold. The exposure of the waveguide to these light pulses is controlled temporally and spatially in order to limit detrimental thermal effects induced by the high-intensity pulses in the glass medium of the waveguide.
Claims22
A system for permanently writing a diffraction grating, comprising:
- a waveguide made of a low phonon energy glass medium;
- light generating means for generating ultrashort light pulses;
- an optical assembly for superposing two beams of said light pulses synchronously in said waveguide and forming therein an interference pattern corresponding to said diffraction grating, said optical assembly focussing said light pulses so that a light intensity in said waveguide exceeds a filamentation threshold;
- and
- controlling means for spatially and temporally controlling an exposure of the waveguide to said light pulses in order to limit grating erasing thermal effects induced in the glass medium by said light pulses.
A system for permanently writing a diffraction grating in a waveguide made of a low phonon energy glass medium, said system comprising:
- light source for generating a primary beam of ultrashort light pulses;
- an optical assembly comprising:
- a phase mask positioned in a path of said primary light beam proximate the waveguide for superposing two beams of said light pulses synchronously in said waveguide and forming therein an interference pattern corresponding to said diffraction grating;
- and
- a focussing element disposed between the light source and the phase mask, said focussing element focussing the light pulses on said waveguide so that a light intensity in said waveguide exceeds a value such that a critical plasma density for permanent modification of said glass medium is reached;
- and
- controlling means for spatially and temporally controlling an exposure of the waveguide to said light pulses in order to limit grating erasing thermal effects induced in the glass medium by said light pulses;
- said controlling means comprising:
- a scanning assembly for scanning one of the focussing element and waveguide with respect to the other and transversally to the path of the light pulses;
- a modulating element disposed in a path of said light pulses, said modulating element temporally modulating said light pulses to form at least one burst of said light pulses;
- an interrupting mechanism for interrupting said exposure of the waveguide to the light pulses;
- and
- a monitoring assembly for monitoring optical properties of the waveguide, said monitoring assembly being in communication with said interrupting mechanism to activate the same according to said optical properties.
A method for permanently writing a diffraction grating in a waveguide made of a low phonon energy glass medium, said method comprising the steps of:
- a) generating ultrashort light pulses;
- b) superposing two beams of said light pulses synchronously in said waveguide and forming therein an interference pattern corresponding to said diffraction grating;
- c) focussing said light pulses so that a light intensity in said waveguide exceeds a filamentation threshold;
- and
- d) spatially and temporally controlling an exposure of the waveguide to said light pulses in order to limit grating erasing thermal effects induced in the glass medium by said light pulses.
Dependencies are inferred from the claim text.