The United Technologies Research Center of East Hartford, Connecticut, USA, an unincorporated business unit of United Technologies Corporation (UTC), and the Communications Research Centre Canada (CRC), a laboratory of the Canadian government, have combined their patents relating to optical Fiber Bragg Gratings in a cross-license agreement.

Under a combined portfolio covering about 13 patents worldwide, third parties can be granted non-exclusive, worldwide, royalty-bearing licenses to develop and manufacture products using the combined patents. Under the cross-license agreement, UTC has the exclusive worldwide right to license the patent portfolio, except in Canada, where CRC handles the licensing.

Introduction to Fiber Bragg Gratings

Since their market introduction in 1995, the use of optical Fiber Bragg Gratings in commercial products has grown exponentially, largely in the fields of telecommunications and stress sensors. The demand for more bandwidth in telecommunication networks has rapidly expanded the development of new optical components and devices (especially Wavelength Division Multiplexers). Bragg Gratings have been vital in the phenomenal growth of some of these products, and are recognized as one of the most significant enabling technologies for fiber optic communications in the last decade.

The Concept

A "Bragg Grating" is a periodic or aperiodic perturbation of the effective absorption coefficient and/or the effective refractive index of an optical waveguide. More simply put, a Bragg Grating can reflect a predetermined narrow or broad range of wavelengths of light incident on the grating, while passing all other wavelengths of the light.

The capability to photo-imprint gratings in optical fibers requires that the glass be photosensitive, an effect discovered in 1978 by CRC's Dr. Kenneth Hill. This phenomenon, called photosensitivity, involves the irradiation of an optical waveguide with a laser beam of ultraviolet light to change the refractive index of the core of the waveguide. By irradiating the fiber with an intensive pattern that has a periodic (or aperiodic) distribution, a corresponding index perturbation is permanently induced in the core of the waveguide. The result is an index grating that is photo-imprinted in the optical waveguide.

As a result, the Bragg Grating becomes a very selective spatial reflector in the core of the fiber. Any change to the spatial period of the grating, or index of refraction, will cause a proportional shift in the reflected and transmitted spectrum, as shown in the diagram to the left.

Concurrent research and development by CRC and UTC on methods of fabricating various designs of Bragg Gratings led to independent filings of a number of patents worldwide, which have been combined in one portfolio.

Features

• Bragg Gratings have low insertion losses and are compatible with existing optical fibers used in telecommunication networks.
• Bragg Gratings allow low-cost manufacturing of very high quality wavelength-selective optical devices.
• Phase masks used to photo-imprint the Gratings allow manufacturing that is relatively simple, flexible, low-cost and large-volume.

Applications

Bragg Gratings have proven attractive in a wide variety of optical fiber applications, such as:

• Narrowband and broadband tunable filters
• Optical fiber mode converters
• Wavelength selective filters, multiplexers, and add/drop Mach-Zehnders
• Dispersion compensation in long-distance telecommunication networks
• Gain equalization and improved pump efficiency in erbium-doped fiber amplifiers
• Spectrum analyzers
• Specialized narrowband lasers
• Optical strain gauges in bridges, building structures, elevators, reactors, composites, mines and smart structures

Clients

More than 30 clients worldwide have licensed the UTC/CRC patent portfolio since January 1995. Clients range from large systems and components suppliers to small start-up companies servicing specialty markets. Their goal is to use the Fiber Bragg Gratings to increase the efficiency of their optical communication products.

The explosive growth of optical communications means there is more room in the market for makers of Fiber Bragg Grating products. United Technologies Corporation handles licensing for companies that want to establish manufacturing operations worldwide, except for Canada. Canadian companies wishing to obtain a license should deal directly with the Communications Research Centre Canada.

UTC License

United Technologies Corporation (UTC) offers a Component Supplier License that is non-exclusive, non-transferable, worldwide, and royalty-bearing. This license allows clients to make, have made, use, offer for sale, and sell Fiber Bragg Gratings made with technology in the UTC/CRC patent portfolio.

As of January 2001, requirements under this portfolio include:

• A one-time, non-refundable license fee of $600,000 U.S.
• A royalty payment of 2.5% of either the Net Invoice Price or the Aggregate Component List Price for each licensed product sold by the licensee
• Quarterly reports indicating the total royalty due for the preceding quarter
• An itemized listing of the licensed products sold within 60 days of the due date indicated in the license agreement

Patent Portfolio

Included in the UTC and CRC Fiber Bragg Gratings licenses are the following U.S.-issued patents:

UTC Patents

5,042,897

Optical waveguide embedded light re-directing Bragg Grating arrangement

5,061,032

Optical waveguide embedded light re-directing and focusing Bragg Grating arrangement

5,048,913

Optical waveguide embedded transverse spatial mode discrimination filter

5,388,173

Method and apparatus for forming aperiodic gratings in optical fiber

CRC Patents

5,104,209

Method of creating an index grating in an optical fiber and a mode converter using the index grating

5,216,739

Method of creating an index grating in an optical fiber and a mode converter using the index grating

5,367,588

Method of fabricating Bragg Gratings using a silica glass phase grating mask and mask used by same

5,495,548

Photosensitization of optical fiber and silica waveguides

PROTECTION

All associated CRC patents:

Case #10005: Method of creating an index grating in an optical fiber and a mode converter using the index grating
U.S. Patent #5,104,209
Canadian Patent #2,057,232

Case #10005: Method of creating an index grating in an optical fiber and a mode converter using the index grating
U.S. Patent #5,216,739
Canadian Patent #2,072,831

Case #10064: Method of fabricating Bragg Gratings using a silica glass phase grating mask and mask used by same
U.S. Patent #5,367,588
Canadian Patent #2,087,511
British Patent #2,272,075
French Patent #2,697,642
German Patent #43 37 103
Japanese Patent #2,929,569

Case #10071: Photosensitization of optical fiber and silica waveguides
U.S. Patent #5,495,548
Canadian Patent #2,115,906
British Patent #2,275,350
French Patent #2,704,323
German Patent #44 04 874
Italian Patent #01282113
Japanese Patent #3,011,308
Spanish Patent #2,107,365

CONTACTS

For manufacturing worldwide:

Sean O'Brien
Intellectual Property Counsel
United Technologies Research Center
411 Silver Lane
East Hartford, CT, USA 06108
Tel: (860) 610-7467
Fax: (860) 610-7248
OBrienSW@utrc.utc.com
www.utrc.utc.com

For manufacturing in Canada:

Jeet Hothi
Director, Technology Transfer Office
Communications Research Centre Canada
3701 Carling Ave., Box 11490, Station H
Ottawa, Ontario, Canada K2H 8S2
Tel: (613) 990-2089
Fax: (613) 990-7671
Internet: jeet.hothi@crc.gc.ca
www.crc.gc.ca