Coherent light generators – Optical fiber laser
Reexamination Certificate
1997-10-29
2001-01-23
Scott, Jr., Leon (Department: 2881)
Coherent light generators
Optical fiber laser
C385S080000, C385S139000
Reexamination Certificate
active
06178187
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical fiber laser device provided with a laser active substance inside an optical fiber for receiving an activating light from outside and performing a laser oscillation.
2. Description of the Related Art
In a field of optical communication or optical processing technique, development of an inexpensive laser device with a higher output is requested. It is heretofore known that an optical fiber laser device has a high possibility for satisfying such request.
In the optical fiber laser device, by appropriately selecting a core diameter, a difference in refractive index between a core and a clad and the like, an oscillating mode can be relatively easily made single. Also, by confining light at a high density, interaction of a laser active substance and light can be enhanced. Further, by lengthening the device, a long interacting length can be obtained. Therefore, a spatially high quality of laser beams can be generated at a high efficiency. Consequently, a high quality of laser beams can be obtained relatively inexpensively.
Here, to realize a higher output or higher efficiency of laser beams, an activating light needs to be efficiently introduced to a laser active ion doping region (usually, a core portion) in an optical fiber. However, when the core diameter is set in accordance with wave guide conditions of a single mode, the core diameter is restricted to about dozen of microns or less of the laser active ion doping region (usually, the core portion). It is usually difficult to efficiently introduce the activating light to such a small diameter. To overcome this problem, for example, a so-called double clad type of a fiber laser is proposed.
FIG. 5
is an explanatory view of the double clad type of the fiber laser. As shown in the figure, in the double clad type of the fiber laser, on an outer periphery of a clad portion
16
provided is a second clad portion
17
which is constituted of a transparent substance having a refractive index much lower than that of the clad portion
16
. By total reflection resulting from a difference in refractive index between the second clad portion
17
and the clad portion
16
, an activating light
13
introduced from an end face is enclosed in the clad portion
16
and a core portion
15
. When the enclosed activating light repeatedly passes the doping region of a laser active ion (usually, a core portion
14
), the activating light is gradually absorbed by the laser active ion. Thereby, a laser beam with a high output can be obtained (reference document; E. Snitzer, H. Po. Fhakimi, R. Tumminelli, and B. C. McCllum, in Optical Fiber Sensors Vol. 2 of 1988 OSA Technical Digest Series (Optical Society of America, Washington, D.C., 1988), paper PD5.).
In the double clad type of the fiber laser, an inlet port of the activating light can be enlarged as much as dozens to thousands of microns. Therefore, the activating light can be easily introduced to the fiber. Also, a region where laser oscillation takes place can be restricted to dozens of to several microns. Therefore, a light with a laser oscillating wavelength can be advantageously propagated in a single mode, and a highly dense light can be enclosed.
However, the optical fiber laser usually has an disadvantage that a laser oscillating condition is largely varied by an influence of disturbances, for example, oscillation, pressure, sound and the like. This is because in the optical fiber, a laser amplifying medium itself is inseparably formed integrally with a laser resonator itself. Further, a medium has a very large asbestos ratio. The optical fiber is given flexibility, but lacks mechanical strength. Therefore, the influence of disturbances is much enlarged. The positive use of the influence is advantageous in a fiber sensor and the like. Conversely, this is largely disadvantageous for a usual solid laser device. For example, in the optical fiber laser, a transverse mode can be considerably strictly controlled because of clear boundary conditions given by fiber transmission. However, a frequency control or the like relating to a vertical mode of a resonator is difficult. In this respect, it should be said that the optical fiber laser is close to a laser using liquid as a medium, rather than to a solid laser.
SUMMARY OF THE INVENTION
An object of the invention is to provide an optical fiber laser device which can also precisely perform a frequency control or the like in relation to a vertical mode of a resonator.
To attain this and other objects, the invention provides an optical fiber laser device provided with a laser active substance inside an optical fiber for receiving an activating light from outside and performing a laser oscillation. The optical fiber is partially or entirely covered and fixed by a hardening substance.
In the optical fiber laser device, the optical fiber is remarkably longer as compared with each distance on three-dimensional coordinate axes representing a magnitude of a region in which the optical fiber is contained. In the region, the optical fiber is repeatedly folded and wound to be disposed therein. The region is filled without clearance with the hardening substance.
Also in the optical fiber laser device, the hardening substance is a hardening organic resin, a glass, a hardening inorganic medium, or a metal.
Further in the optical fiber laser device, the hardening substance is a transparent substance which has a refractive index value equal to or less than a refractive index value of a substance constituting a clad portion of the optical fiber.
The invention also provides an optical fiber laser device provided with a laser active substance inside an optical fiber for receiving an activating light from outside and performing a laser oscillation. The optical fiber is remarkably longer as compared with each distance on three-dimensional coordinate axes representing a magnitude of a region in which the optical fiber is contained. In the region, the optical fiber is repeatedly folded and wound to be disposed therein.
The optical fiber is integrally formed and fixed in such a manner that adjacent portions of the repeatedly folded and wound optical fiber partially or entirely adhere close to one another to a degree to which an interface between a core and a clad is not disturbed.
In the optical fiber laser device, the optical fiber has a clad with a rectangular cross section.
Also in the optical fiber laser device, the optical fiber is a double clad type of an optical fiber in which further on an outer periphery of the clad, a second clad is formed.
REFERENCES:
patent: 4733938 (1988-03-01), Lefevre et al.
patent: 5136680 (1992-08-01), Seike et al.
patent: 5259051 (1993-11-01), Burack et al.
patent: 05297228 (1993-12-01), None
Patent Abstracts of Japan, vol. 095, No. 010, Nov. 30, 1995 & JP 07 184597A (Shin Etsu Chem Co. Ltd.) Jul. 21, 1995, abstract.
Patent Abstracts of Japan, vol. 018, No. 092 (P-1693) Feb. 15, 1994 & JP 05 297228 A (Fujitsu Ltd), Nov. 12, 1993, abstract and Figs. 1-6.
Lie A et al., “Rectangular Double-Clad Fibre Lase With Two End Bundle Pump”, Electronic Letters, Aug. 29, 1996, IEE, UK, vol 32, No. 18, pp. 1673-1674, XP000637825, ISSN 0013-5194, abstract; Fig. 1.
Patent Abstracts of Japan, vol. 097, No. 006. Jun. 30, 1997 & JP 09 055556 A (Oki Electric Ind. Co. Ltd.) Feb. 25, 1997, abstract.
Patent Abstracts of Japan, vol. 097, No. 005, May 30, 1997 & JP 09 026379A (Fujitsu Ltd; Nippon Telegr & Teleph Corp) Jan. 28, 1997, abstract.
Ueda et al., “Future of High Power Fiber Lasers”, Second International Conf. on Modern Laser Physics (MPLP), Novosibirsk, Russia, Jul. 28-Aug.2, 1997, vol. 8, No. 3, pp. 774-781, Laser Physics, May-Jun. 1998, MAIK Nauka/Interperiodica.
Publishing, Russia, pp. 779-780, figs. 12-14 Ueda, “Optical Cavity and Future Style of High Power Fiber Lasers”, SPIE vol. 3267—Laser Resonators, San Jose, CA USA Jan. 26-27, 1998, vol. 3267, pp. 14-22, XP 002092368, ISSN 0277-786X, Proceedings of the SPIE- International Society for Optical Engi
Jr. Leon Scott
Perman & Green LLP
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