Device for producing apodized gratings

Details Device for producing apodized gratings Device for producing apodized gratings

1999-05-14

2001-11-06

Berman, Jack (Department: 2881)

Radiant energy

Irradiation of objects or material

C385S037000

Reexamination Certificate

active

06313473

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to a device for producing apodized gratings.
2. Description of the Related Art
Apodized gratings are particularly important for telecommunications applications, such as dense wavelength division multiplexing and dispersion compensation, because well-designed apodization profiles can considerably suppress the sidelobes in the grating reflection spectra. J. Martin et al. disclosed a method of producing apodized gratings (ELECTRONICS LETTERS, May 12, 1994, Vol.30, No.10, pp.811-812). Referring to
FIG. 1
, an optical fiber
11
and a phase mask
12
are movably mounted on a translation stage
13
, wherein the optical fiber
11
is placed behind the phase mask
12
. Then, a UV beam
14
is projected through the phase mask
12
to write gratings on the optical fiber
11
. In this method, however, any offset of the beam position relative to the optical fiber center during the translation results in a corresponding variation of the average refractive index of the optical fiber. The variation of the average refractive index imparts an often undesired chirp to the gratings. To resolve such a problem, W. H. Loh et al. disclosed a moving fiber-scanning beam technique (OPTICS LETTERS, Oct. 15, 1995, Vol.20, No.20, pp.2051-2053). Referring to
FIG. 2
, an optical fiber
21
is mounted on a computer-controlled stage
23
which slowly moves with respect to a phase mask
22
. A UV beam
24
is reflected by a moving mirror
25
to pass through the phase mask
22
so as to write gratings on the optical fiber
21
. By the movement of the UV beam, variation of the average refractive index of the optical fiber is totally avoided because the average UV fluence along the length of the grating is the same. However, simultaneously control of the movement of the stage
23
and the mirror
25
is required in this system. Such a system is very complex.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a device that solves the above-mentioned problems.
In accordance with the object of the present invention, a device for producing apodized gratings on a stationary optical fiber is provided. The device includes a slit-generating means, a stationary phase mask and a stationary writing-beam-generating means. A slit is generated by the slit-generating means. A writing beam is generated by the stationary writing-beam-generating means to pass through the slit and the stationary phase mask and then focus on the stationary optical fiber for a plurality of exposure time periods. The slit is adjustable in width so that the slit has a plurality of widths during the plurality of exposure time periods, respectively.
In the present invention, neither the UV-generating means nor the optical fiber is moved. Therefore, controlling the device of the present invention is much simpler than controlling the device of the prior art. In addition, the problem of chirps does not arise because the UV-generating means does not move with respect to the optical fiber.


REFERENCES:
patent: 5104209 (1992-04-01), Hill et al.
patent: 5953471 (1999-09-01), Espindola et al.
patent: 6043497 (2000-03-01), Quetel et al.
patent: 6160261 (2000-12-01), Hoshino
Article entitled “Novel Writing Technique of Long and Highly Reflective In-Fibre Gratings” by J. Martin et al., (Electronics Letters, 12th May 1994, vol. 30, No. 10, pp. 811-812).
Article entitled “Complex Grating Structures With Uniform Phase Masks Based On The Moving Fiber-Scanning Beam Technique” by W.H. Loh et al. (Optics Letters, Oct. 15, 1995, vol. 20 No. 20, pp. 2051-2053).

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