Method for apodizing a planar waveguide grating
View Patent ↗A method for making an apodized Bragg grating in a photosensitive, planar, linear waveguide. A photosensitive, planar, linear waveguide is provided on a surface of a substrate. A patterned phase mask is placed between the waveguide and a laser beam. The waveguide is exposed through the phase mask to the laser beam wherein either the laser beam is moving at a substantially constant velocity with respect to the substrate and phase mask, or the substrate and phase mask are moving at a substantially constant velocity with respect to the laser beam. The beam has a smoothly varying intensity profile, and the exposure is conducted at an angle of more than 0° and less than 90° to the longitudinal axis of the waveguide under conditions sufficient to induce a modulation in the index of refraction of the waveguide and impart an apodized Bragg grating in the waveguide corresponding to the phase mask pattern.
1. A process for forming an apodized Bragg grating in a photosensitive, planar, linear waveguide which consists essentially of:
providing a photosensitive, planar, linear waveguide on a surface of a substrate, which waveguide defines a longitudinal axis;
positioning a patterned phase mask between the waveguide and a laser beam having a guassian intensity profile;
exposing the waveguide through the phase mask to the laser beam wherein either the laser beam is moving at a substantially constant velocity with respect to the substrate and phase mask, or the substrate and phase mask are moving at a substantially constant velocity with respect to the laser beam, which beam has a smoothly varying intensity profile, and which exposure is conducted at an angle of more than 0° and less than 90° to the longitudinal axis under conditions sufficient to induce a change in the index of refraction to the waveguide and impart an apodized Bragg grating in the waveguide corresponding to the phase mask pattern.
2. The process of claim 1 wherein the angle ranges from about 1° to about 45°.
3. The process of claim 1 wherein the angle ranges from about 3° to about 15°.
4. The process of claim 1 wherein the waveguide comprises a doped glass composition.
5. The process of claim 1 wherein the waveguide comprises a germanium doped glass composition.
6. The process of claim 1 wherein the waveguide comprises a photopolymerizable composition.
7. The process of claim 1 wherein the laser beam is held stationary arid the substrate and phase mask move with respect to the laser beam.
8. The process of claim 1 wherein the substrate and phase mask are held stationary and the laser beam moves with respect to the substrate and phase mask.
9. The process of claim 1 wherein the surface of the substrate comprises an undercladding composition which has an index of refraction less than that of the waveguide.
10. The process of claim 1 wherein the waveguide comprises an overcladding composition on a core, the process further comprising the step of applying the overcladding composition onto the core either before or after exposure, which overcladding composition has an index of refraction less than that of the core.