Optical: systems and elements – Diffraction – Using fourier transform spatial filtering
Reexamination Certificate
1998-05-19
2001-01-23
Henry, Jon (Department: 2872)
Optical: systems and elements
Diffraction
Using fourier transform spatial filtering
C359S034000, C359S035000, C359S894000, C385S037000
Reexamination Certificate
active
06178045
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to spatial filters. More particularly the present invention relates to spatial filters for laser beams. While the invention is subject to a wide range of applications, it is especially suited for use in an optical system for writing index gratings in optical waveguides.
BACKGROUND OF THE INVENTION
Soon after the development of practical laser sources, laser beams have been used in industrial applications. Laser beams are currently used to induce refractive index changes in optical waveguide glass and particularly glass used in optical fibers. Index gratings are written into germano-silicate glass optical fibers with interference patterns formed by interfering ultraviolet laser beams. Periodic refractive index changes are induced by the interference pattern resulting in index gratings being formed or written in the fiber. Fiber Bragg gratings and long period fiber gratings are two examples of index gratings that are produced in optical fiber and are utilized in the transmission of optical telecommunication signals. Fiber Bragg gratings can be utilized as selective wavelength reflecting filters in the transmission of light through optical fibers. The spacing of the index gratings in the optical fiber is to provide for the reflection of a particular range of wavelengths while allowing other wavelengths to pass through the index grating without being reflected. The quality of previously produced Fiber Bragg gratings has been hindered by a high level of unwanted reflectivity sidelobes. Reflectivity sidelobes occur when wavelengths of light outside the intended high reflectivity wavelength band are reflected by the grating instead of being properly transmitted through the grating.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a method and apparatuses that substantially obviates one or more of the problems due to the limitations and disadvantages of the related art.
Features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the apparatuses, systems, and methods particularly pointed out in the written description and claims hereof as well as the drawings.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described, the invention includes a spatial filter for high power density laser beams. The high power density laser beam spatial filter is comprised of light diverting members. In another aspect, the invention includes a method of spatially filtering a laser beam including the step of providing a Fourier transformed (focused) laser beam having low spatial frequencies which are a target of the invention and unwanted high spatial frequencies. The method further includes the step of nonabsorptively diverting the high spatial frequency portion of the Fourier transformed laser beam, said high spatial frequency portion comprised of the unwanted high spatial frequencies, away from the low spatial frequency portion of the Fourier transformed laser beam, said low spatial frequency portion comprised of the targeted low spatial frequencies, to produce a low spatial frequency laser beam. In another aspect, the invention includes a spatial filter for a high power density laser beam, said laser beam having high spatial frequencies and low spatial frequencies, the spatial filter comprises a means for nonabsorptively diverting said high spatial frequencies away from said low spatial frequencies. The invention includes a spatial filter comprised of a means for nonabsorptively diverting an outer portion of a laser beam to leave an inner portion of the laser beam with a smooth beam profile. In another aspect, the invention includes a method of making a grating which includes the steps of producing a laser beam and focusing the laser beam in one dimension with a Fourier transforming optical member, such as a lens, to form a line focused laser beam having a central axis. The method further includes the steps of nonabsorptively diverting an outer portion (high spatial frequencies) of the line focused laser beam away from the focus line and the low spatial frequencies of the laser beam, with a nonabsorptive reflecting surface, preferably with total internal reflection, in order to form a one dimension spatially filtered laser beam and then forming an interference pattern with this spatially filtered laser beam to make a grating particularly in an optical waveguide, and more particularly an optical waveguide fiber.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. The accompanying drawings are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention.
REFERENCES:
patent: 3073210 (1963-01-01), Packard
patent: 4093339 (1978-06-01), Cross
patent: 4381137 (1983-04-01), Berg et al.
patent: 4530600 (1985-07-01), Lopez
patent: 4778263 (1988-10-01), Foltyn
patent: 4947413 (1990-08-01), Jewell et al.
patent: 5048938 (1991-09-01), Hizny
patent: 5059013 (1991-10-01), Jain
patent: 5090795 (1992-02-01), O'Meara et al.
patent: 5090798 (1992-02-01), Kphayakawa
patent: 5104209 (1992-04-01), Hill et al.
patent: 5204773 (1993-04-01), Guida
patent: 5272501 (1993-12-01), Nishi et al.
patent: 5309260 (1994-05-01), Mizrahi et al.
patent: 5311606 (1994-05-01), Asakura et al.
patent: 5323267 (1994-06-01), Galarneau et al.
patent: 5331466 (1994-07-01), Van Saarloos
patent: 5357365 (1994-10-01), Ipposhi et al.
patent: 5408553 (1995-04-01), English, Jr. et al.
patent: 5601733 (1997-02-01), Partlo
patent: 5616159 (1997-04-01), Araujo et al.
patent: 0 250 147 (1987-12-01), None
patent: 0 636 586 (1995-02-01), None
patent: 2 146 786 (1985-04-01), None
patent: WO 96/37767 (1996-11-01), None
patent: WO 97/14987 (1997-04-01), None
Ibsen http://wwwibsen.dk/home/pm13technology.htm, Feb. 14, 1997, Phase masks—Technology, Phase masks—Introduction, Phase masks—Applications, Welcome to the home of Diffractive Optics—Ibsen Structures A/S.
Fused Silica Brochure, Corning Incorporated, Jun. 1993, Excimer Grade Fused Silica.
Cook Thomas A.
Modavis Robert A.
Corning Incorporated
Henry Jon
Murphy Edward F.
Short Svetlana Z.
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