Apparatus and method of fabricating long-period fiber grating

Optical waveguides – With optical coupler – Input/output coupler

Reexamination Certificate

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Details

C359S566000

Reexamination Certificate

active

06229941

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus and method of fabricating a long-period fiber grating and more particularly, to an apparatus for fabricating a long-period fiber grating using a string which vibrates with a predetermined period.
2. Description of the Related Art
Typical long-period fiber gratings are elements for coupling a core mode, in which light travels through the core of an optical fiber, to a cladding mode, and thus are well suited to gain-flattening of an erbium doped fiber amplifier (EDFA) since they do not act as a reflective type device.
Long-period fiber gratings can be fabricated by a methods of using an amplitude mask on which a light transmission
on-transmission portion has a predetermined period; by vibrating an optical fiber at a predetermined period; or by a method of applying stress to the optical fiber at a predetermined period.
In the method of using an amplitude mask, the refractive index of the core of an optical fiber, which is sensitive to ultraviolet rays, is periodically varied using an amplitude mask having a predetermined period. That is, to obtain an arbitrary coupling peak wavelength &lgr;, the refractive index difference between the core and cladding of an optical fiber is formed by directly projecting an ultraviolet laser onto an amplitude-modulated mask having a grating cycle &Lgr;, thereby fabricating a long-period fiber grating. Here, the coupling peak wavelength value &lgr; is determined by the following Equation 1:
&lgr;=(n
core
−n
cladding
)&Lgr;  (1)
wherein n
core
is the refractive index of the core, n
cladding
is the refractive index of the cladding, and &Lgr; is the period of an amplitude mask.
A conventional apparatus for fabricating a long-period fiber grating using an amplitude mask includes an amplitude mask mounted on a fiber, and a laser source for irradiating laser light onto the amplitude mask. However, in the method of using an amplitude mask, the period of the amplitude mask is determined according to the intended coupling peak wavelength to be obtained. Therefore, the ultraviolet laser may be collimated with various methods or a dual mask may be applied when the period of the amplitude mask is changed.
The long-period fiber grating can also be fabricated by vibrating an optical fiber or by applying stress using comb-shaped probes. However, these alternative methods have problems in that stability and reproducibility are difficult, and the devices required to fabricate the long-period fiber grating are large.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an improved method of fabricating a long-period fiber grating.
It is also an object of the present invention to provide an improved apparatus for fabricating a long-period fiber grating.
It is a further object of the invention to provide a method of fabricating a long-period fiber grating with excellent stability and reproducibility.
It is a yet further object of the present invention to provide a method of fabricating a long-period fiber grating in which no collimation of the laser is required when changing the period of the fiber.
It is a still further object of the present invention not to require a dual mask.
To achieve the above objectives of the present invention, the present invention provides an apparatus and method of fabricating a long-period fiber grating by locating a string which vibrates at a predetermined cycle over a fiber and illuminating an ultraviolet laser on the string and the fiber.
Accordingly, to achieve the above objective, the present invention provides a long-period fiber grating fabrication apparatus including: a fiber; a string, one end of which is fixed, that is located over the fiber and vibrates at a predetermined vibration frequency; a vibrating portion, which vibrates the string at the vibration frequency, to which the other end of the string is connected; and a laser source for illuminating laser light on the string and the fiber, wherein the laser light is periodically transmitted by the fiber due to the vibration of the string, and thus the refractive index of the fiber is changed.
To achieve the above objectives, the present invention also provides a long-period fiber grating fabrication apparatus including: a fiber; a string, one end of which is fixed, that is located over the fiber and vibrates at a predetermined vibration frequency; a vibrating portion, which vibrates the string at the vibration frequency, to which the other end of the string is connected; a period controller connected to the vibrating portion for controlling the period of the string by moving the vibrating portion upward and downward; and a laser source for illuminating laser light onto the string, wherein the laser light is periodically transmitted by the fiber due to the period-controlled vibration of the string, and thus the refractive index of the fiber is changed.
To achieve the above objectives, the present invention provides a long-period fiber grating fabrication method including the steps of: aligning a string over a fiber in the longitudinal direction of the fiber; forming a standing wave by vibrating the string at a predetermined vibration frequency; and illuminating laser light to the vibrating string and the fiber, wherein the laser light is periodically transmitted by the fiber due to the vibration of the string, and thus the refractive index of the fiber is periodically changed.


REFERENCES:
patent: 5951881 (1999-09-01), Rogers et al.
patent: 6038358 (1999-09-01), Nishiki

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