Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1998-01-29
2001-10-30
Scott, Jr., Leon (Department: 2881)
Optical waveguides
With optical coupler
Input/output coupler
Reexamination Certificate
active
06310996
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the writing of Bragg reflection gratings in optical waveguides by exercise of the photorefractive effect in materials, such as germania doped silica. An early method of writing such gratings is described in U.S. Pat. No. 4,474,427, this method involving directing intense ultra-violet light into one end of a length of optical waveguide having a reflector at the far end so that a standing wave is set up within the waveguide. Subsequently, a lateral method of writing such a grating was disclosed in U.S. Pat. No. 4,725,110 in which a beam-splitter is used to divide a beam of ultra-violet light into two beams which are reflected in two mirrors to form and interference fringe pattern in the waveguide. This writing method is sometimes known as the holographic method. A further alternative method, sometimes known as the grating method, involves creating an equivalent fringe pattern close behind a diffraction grating illuminated with normally incident ultra-violet light, this method being described for instance in U.S. Pat. No. 5,351,321. Typically a phase grating is employed for this purpose, and the depth of the grating elements chosen for suppression of the zero order diffraction. The waveguide is located close behind the diffraction grating because it is here that the required fringe pattern, which is generated by interference between the +1 and −1 diffraction orders, is least disrupted by power diffracted into higher order modes.
An exception to this close proximity arrangement of diffraction grating and waveguide is described in the paper by J R Armitage entitled, ‘Fibre Bragg Reflectors written at 262 nm Using a Frequency Quadrupled Diode-Pumped Nd
3+
:YLF Laser’, Electronics Letters, 24th Jun. 1993 Vol. 29, No. 13, pages 1181-3. In this instance the +1 and −1 diffraction orders are arranged to be incident upon a fused silica block. After reflection in the side walls of this block, the two beams emerge from the far end of the block and form an interference fringe pattern in the core of an optical fibre waveguide located behind the block. One advantage of this greater separation between the diffraction grating and the waveguide is that it enables a zero order beam stop to be located on the fused silica block to prevent any zero order light from reaching the fringe pattern generated by the interference between the +1 and −1 diffraction orders and thereby reducing the visibility of that fringe pattern.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of writing a Bragg reflection grating in an optical waveguide using a diffraction grating located at a sufficient distance from the waveguide as to make it readily possible to include aperture defining means to control the illumination of the waveguide so as to provide a high visibility fringe pattern, and at the same time to use separated portions of the diffraction grating for the generation of that fringe pattern.
Particularly in the case of the writing of long Bragg reflection gratings, such use of two separated zones of illumination of the diffraction grating has the advantage of reducing the deleterious effects in the optical performance of the resulting Bragg reflection grating caused by the presence of random stitch errors in the diffraction grating used to write that Bragg reflection grating.
According to a first aspect of the present invention there is provided a method of writing a Bragg grating in a photosensitive optical waveguide by irradiating the waveguide with an interference fringe pattern generated by the passage of electromagnetic radiation in two spatially separated zones via a diffraction grating oriented to have diffracting elements of the diffraction grating extending at an angle to the waveguide axis.
According to a second aspect of the present invention there is provided a method of writing a Bragg grating in a photosensitive optical waveguide by irradiating the waveguide with an interference fringe pattern generated by the passage of electromagnetic radiation via a diffraction grating oriented to have diffracting elements of the diffraction grating extending at an angle to the waveguide axis, wherein a beam of light is divided into two spatially separated components arranged to be incident upon the diffraction grating in two spatially separated zones, and the fringe pattern is generated by interference between one diffracted order of one of the two components and one diffracted order of the other component.
Other advantages and features of the invention will be readily apparent from the following description of the preferred embodiments, the drawings and the claims.
REFERENCES:
patent: 4474427 (1984-10-01), Hill et al.
patent: 4725110 (1988-02-01), Glenn et al.
patent: 5351321 (1994-09-01), Snitzer et al.
patent: 5636304 (1997-06-01), Mizrahi et al.
patent: 5668901 (1997-09-01), Keck et al.
patent: 5745615 (1998-04-01), Atkins et al.
patent: 5748814 (1998-05-01), Painchaud et al.
patent: 5837169 (1998-11-01), Rourke
patent: 5867618 (1999-02-01), Ito et al.
patent: 5881186 (1999-03-01), Starodubov
patent: 5945261 (1999-08-01), Rourke
patent: 6072926 (2000-06-01), Cole et al.
Armitage, J. R., “Fibre Bragg Reflectors Written At 262nm Using a Frequency Quadrupled Diode-Pumped Nd3+:YLF Laser,” Electronic Letters, vol. 29, No. 13, Jun. 24, 1993, pp. 1181-1183.
Jr. Leon Scott
Lee Mann Smith McWilliams Sweeney & Ohlson
Nortel Networks Limited
LandOfFree
Writing Bragg gratings in optical waveguides does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Writing Bragg gratings in optical waveguides, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Writing Bragg gratings in optical waveguides will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2604530