18-04-2012, 03:49 PM
MANUFACTURING OF THE FIBER BRAGG GRATINGS
[attachment=20310]
INTRODUCTION
The fiber Bragg gratings has become very important components in optical applications. Because they have several unique properties, they can be used, e.g. for stabilization of lasers, filtering in telecommunications and for sensor applications. Bragg grating is basically the band-pass filter which represents the phase grating. This filter reflects the wavelength accordant with Bragg condition and transfers the others. Fiber Bragg gratings are represented by the fiber with the refractive index changes in the core. Gratings with highest quality were made by the UV laser beam over the last years. During the exposure by the laser beam is formed the change of the refractive index with spatial period Λ. Refractive index of fiber grating in the fiber core is like distributive mirror. The wavelength of the light beam, which is reflected with the maximum effect, is called tuned Bragg wavelength λBragg. Equation describes the spatial period and Bragg wave-length depends on effective refractive index of distribution medium neff:
FABRICATION TECHNIQUES
Most of methods intended to fabrication of fiber gratings are used to exposure of the fiber the UV laser light. Several methods of the writing processes are used for FBGs creating. Methods, which are used to the creating of required FBGs, are called Off-line methods. These methods are used after the optical fiber fabrication. The Off-line methods contain three main techniques: The interferometric technique, the point by point technique and the phase mask technique. Each of technique has own advantages and disadvantages.
THE POINT BY POINT TECHNIQUE
In this technique the pulse excimer laser is used to writing the changes of refractive index to the core of the optical fiber.
The change of refraction index is induced along the core of the fiber a step at a time. A single pulse of the UV light from an excimer laser passes through a mask to the core of the fiber containing a slit and thus the refractive index of the corresponding core section increases locally. The fiber is then translated through a distance corresponding to the grating pitch in parallel direction to the fiber axis and the process is repeated to form the grating structure in the fibers core [1].
CONCLUSION
From the above described fabrication techniques should be used the point by point method and the phase mask method for the fabrication of FBGs. The masks needed to fabrication can be realized by the electron litograph. This litograph is disposable in Institute of Scientific Instruments Brno as well as lasers needed for FBG fabrication. The fabricated FBGs will be used for the wavelength stabilization of Lasers diodes.
[attachment=20310]
INTRODUCTION
The fiber Bragg gratings has become very important components in optical applications. Because they have several unique properties, they can be used, e.g. for stabilization of lasers, filtering in telecommunications and for sensor applications. Bragg grating is basically the band-pass filter which represents the phase grating. This filter reflects the wavelength accordant with Bragg condition and transfers the others. Fiber Bragg gratings are represented by the fiber with the refractive index changes in the core. Gratings with highest quality were made by the UV laser beam over the last years. During the exposure by the laser beam is formed the change of the refractive index with spatial period Λ. Refractive index of fiber grating in the fiber core is like distributive mirror. The wavelength of the light beam, which is reflected with the maximum effect, is called tuned Bragg wavelength λBragg. Equation describes the spatial period and Bragg wave-length depends on effective refractive index of distribution medium neff:
FABRICATION TECHNIQUES
Most of methods intended to fabrication of fiber gratings are used to exposure of the fiber the UV laser light. Several methods of the writing processes are used for FBGs creating. Methods, which are used to the creating of required FBGs, are called Off-line methods. These methods are used after the optical fiber fabrication. The Off-line methods contain three main techniques: The interferometric technique, the point by point technique and the phase mask technique. Each of technique has own advantages and disadvantages.
THE POINT BY POINT TECHNIQUE
In this technique the pulse excimer laser is used to writing the changes of refractive index to the core of the optical fiber.
The change of refraction index is induced along the core of the fiber a step at a time. A single pulse of the UV light from an excimer laser passes through a mask to the core of the fiber containing a slit and thus the refractive index of the corresponding core section increases locally. The fiber is then translated through a distance corresponding to the grating pitch in parallel direction to the fiber axis and the process is repeated to form the grating structure in the fibers core [1].
CONCLUSION
From the above described fabrication techniques should be used the point by point method and the phase mask method for the fabrication of FBGs. The masks needed to fabrication can be realized by the electron litograph. This litograph is disposable in Institute of Scientific Instruments Brno as well as lasers needed for FBG fabrication. The fabricated FBGs will be used for the wavelength stabilization of Lasers diodes.