Optical: systems and elements – Diffraction – From grating
Reexamination Certificate
1998-12-08
2001-03-20
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Diffraction
From grating
C359S566000, C359S577000, C359S900000, C385S037000
Reexamination Certificate
active
06204969
ABSTRACT:
CLAIM OF PRIORITY
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. § 119 from an application for AMPLITUDE MASK, AND APPARATUS AND METHOD FOR MANUFACTURING LONG PERIOD GRATING FILTER USING THE SAME earlier filed in the Korean Industrial Property Office on Dec. 8, 1997 and there duly assigned Serial No. 66751/1997.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical passive element, and more particularly, to an amplitude mask and an apparatus and method for manufacturing a long period grating filter using the same.
2. Description of the Related Art
With the recent developments in optical communications, a long period grating filter used as an optical passive element is attracting much attention. The long period grating filter couples a core mode in which light travels through the core of an optical fiber to a cladding mode, and is manufactured by periodically changing the refractive index of the core of an optical fiber sensitive to ultraviolet rays. That is, the refractive index of a portion exposed to light increases, and that of a non-exposed portion does not change, thus a periodic change in refractive index is generated. In order to couple the core mode to the cladding mode, the following Equation 1 must be satisfied:
β
co
-
β
cl
n
=
2
π
Λ
(
1
)
wherein &bgr;
co
is the propagation constant of the core mode, &bgr;hd cl
n
is the propagation constant of an n-th order cladding mode, and &Lgr; is a grating period.
When 2&pgr;m/&lgr; (here, n is a refractive index) is substituted for &bgr; in Equation 1, Equation 1 becomes n
co
−n
cl
=&lgr;/&Lgr;. Accordingly, the period &Lgr; and the refractive index difference (n
co
−n
cl
) must be determined to couple a certain wavelength to the cladding mode. The refractive index difference can be obtained by appropriately irradiating ultraviolet laser light to an optical fiber that is sensitive to ultraviolet rays.
An earlier long period grating filter manufacturing apparatus comprises a high-output excimer laser optical source, a mirror, a lens, a silica mask, and an optical fiber. The optical source emits ultraviolet laser light. The mirror changes the path of laser light emitted by the optical source. The lens adjusts the focus of laser light whose path has been changed by the mirror. The silica mask selectively passes the laser light passed through the lens. The optical fiber has a core in which a long period grating is formed by being irradiated by the laser light passed through the silica mask to the optical fiber.
When the laser light passes through the lens and is irradiated upon the optical fiber contacting the silica mask, the refractive index of the optical fiber changes at regular periods, and the long period grating is formed on the optical fiber. Light is passed through the optical fiber using an optical source and is detected by a detector, and thus the optical characteristics of the long period grating filter are obtained.
In the long period grating filter manufacturing apparatus described above, the silica mask is comprised of chrome patterns obtained by coating and patterning chromium Cr on a silica substrate. The laser light is selectively passed by these chrome patterns. However, the chrome pattern has a damage threshold of 100 mJ/cm
2
, which makes it impossible to effectively use a high-output excimer laser light. Also, the silica mask is manufactured by forming the chrome patterns on the silica substrate, and thus has only one period which is determined by an initially designed pattern. Therefore, amplitude masks having different periods are required in order to obtain long period grating filters having different periods, thereby increasing manufacturing costs.
SUMMARY OF THE INVENTION
To solve the above problems, it is an object of the present invention to provide an amplitude mask which is comprised of two coupled masks each having a regular period and whose period is consecutively changed by rotating the two masks in opposite directions a predetermined amount, and an apparatus and method for manufacturing a long period grating filter using the same.
Accordingly, to achieve the above object, there is provided an amplitude mask for periodically passing laser light to an optical fiber when a long period grating is manufactured by selectively passing the laser light to the optical fiber, comprising: two masks having periodically alternating pass areas for passing the laser light and nonpass areas for preventing passing of the laser light, wherein the two masks are continuously rotated in opposite directions, and the period of the pass area thus continuously changes.
To achieve the above object, there is provided a long period grating filter manufacturing apparatus comprising: a laser optical source for emitting laser light; an amplitude mask portion whose period is controlled by overlapping two masks each having a predetermined period and rotating the two overlapped masks a predetermined angle, and which selectively passes the laser light to an optical fiber in which a long period grating is to be formed, according to the controlled period; and a rotation means for rotating the two masks a predetermined angle in opposite directions.
To achieve the above object, there is provided a long period grating filter manufacturing apparatus comprising: a laser optical source; a mirror for changing the path of laser light emitted by the laser optical source; a lens for adjusting the focus of laser light whose path has been changed; an amplitude mask portion whose period is controlled by overlapping two masks each having a predetermined period and rotating the two overlapped masks a predetermined angle, and which selectively passes the laser light passed through the lens to an optical fiber in which a long period grating is to be formed, according to the controlled period; a detector for detecting a coupling peak of a long period grating filter formed on the optical fiber; and a controller for controlling the period of the amplitude mask to obtain a desired coupling peak wavelength by receiving a wavelength at the coupling peak from the detector.
To achieve the above object, there is provided a method of manufacturing a long period grating filter, comprising the steps of: overlapping two masks in each of which pass regions passed by laser light alternate with non-pass regions, and rotating the two masks in opposite directions; irradiating the laser light to an optical fiber via the pass regions formed at predetermined periods in the two rotated masks and forming a long period grating on the optical fiber; and measuring a coupling peak due to the long period grating by passing light through the optical fiber on which the long period grating has been formed, and controlling the angle of rotation at which the two masks are rotated so that the measured coupling peak is achieved at a desired wavelength.
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patent: 5604829 (1997-02-01), Bruesselbach
patent: 5619603 (1997-04-01), Epworth et al.
patent: 5620495 (1997-04-01), Aspell et al.
patent: 5830622 (1998-11-01), Canning et al.
patent: 5953471 (1999-09-01), Espindola et al.
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patent: 0978738 (2000-09-01), None
S. J. Mihailov, et al. “Recording of Efficient High-Order Bragg Reflectors in Optical Fibres by Mask Image Projection and Single Pulse Exposure with an Excimer Laser”. Electronics Lett. vol. 30, No. 9, pp. 707-709, Apr. 1994.*
L. Zhang, et al., “Design adn Realization of Long-Period Grating Devices in Conventional and High Birefringence Fibers and Their Novel Applications as Fiber-Optic Load Sensors”., IEEE J. Selected Topics in Quantum Electronics, vol. 5, No. 5, pp 1373-1378, Apr. 1994.
Bushnell , Esq. Robert E.
Jr. John Juba
Samsung Electronics Co,. Ltd.
Spyrou Cassandra
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