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Modelling and Optimization of Complex Fiber Diffractive Structures
Helán, Radek ; Lazar,, Josef (referee) ; Tománek, Pavel (referee) ; Urban, František (advisor)
The thesis discusses the fiber Bragg gratings simulations, analysis and design. In the present time, there are several methods to simulate fiber gratings response based on the stated parameters that define their dimensions and material features. However, this work deals with a different issue, that is the synthesis of the input parameters for demanded spectral responses. The main aim of the work is to achieve a synthesis method that would help to discover parameters describing advanced grating structure, based on the required spectral reflectivity. The basic demand for the parameter synthesis is an achievement of the real values in terms of the consequent production of the suggested structure. The described synthesis method considers advanced fiber grating structure as a structure of several uniform grating sections. The input parameters are estimated in steps, using the well-known direct methods in order to obtain grating responses and feedback to establish the parameters changes. The principle methods involve establishment of initial input parameter values and necessary subsequent algorithm leading to optimize the required spectral response. The initial values are calculated by a simplified model based on the coupled theory equations that are handled for the periodic disturbances in cylindrical waveguide. The following optimization uses the multiple thin film stack and transfer matrix methods. The properties of grating structure spectral reflectivity are step by step calculated while using these direct methods. Input parameters are established in the next several steps. Establishment of input parameters is done subsequently, based on the demanded and calculated output spectral reflectivity properties. Optimizing process is limited by possibilities of the grating manufacture technology. It is possible to assemble arbitrary fiber grating structure taking in term the demanded spectral response. Nevertheless, the calculated input parameters are real for the following manufacture. This method could be used to design optical band stop filter, high-pass and low-pass filters or filters for special applications.
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Study of the influence of geometrical parameters of phase binary gratings on their optical response for the preparation of optical fiber sensors
Krátký, Stanislav ; Kolařík, Vladimír ; Mikel, Břetislav ; Helán, R. ; Urban, F.
For exposure to optical fibers through a phase grating, it is necessary to tune the geometrical parameters of the grating very well. In this paper, we study the effect of the grating period, grating diameter, grating depth, and polarisation of the incident laser beam on the efficiency of diffraction orders. A suitably tuned grating generates diffraction orders with the desired efficiency, thereby guaranteeing the formation of the desired motif in the exposed optical fiber.
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Optical fiber sensors for measurement strain and vibration
Mikel, Břetislav ; Helán, R. ; Buchta, Zdeněk ; Holík, M. ; Jelínek, Michal ; Číp, Ondřej
We present optical fiber sensors to measurement strain and vibration. The sensors are based on fiber Bragg gratings (FBG). We prepared construction of strain sensors with respect to its implementation on the outer surface of concrete structures and with compensation of potential temperature drifts. These sensors are projected with look forward to maximal elongation and strength which can be applied to the sensor. Each sensor contains two optical fibers with FBGs. One FBG is glued into the sensor in points of fixation which are in the line with mounting holes. This FBG is prestressed to half of measurement range, than the stretching and pressing can be measured simultaneously by one FBG. The second FBG is placed inside the sensor without fixation to measure temperature drifts. The sensor can be used to structure health monitoring.
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Modelling and Optimization of Complex Fiber Diffractive Structures
Helán, Radek ; Lazar,, Josef (referee) ; Tománek, Pavel (referee) ; Urban, František (advisor)
The thesis discusses the fiber Bragg gratings simulations, analysis and design. In the present time, there are several methods to simulate fiber gratings response based on the stated parameters that define their dimensions and material features. However, this work deals with a different issue, that is the synthesis of the input parameters for demanded spectral responses. The main aim of the work is to achieve a synthesis method that would help to discover parameters describing advanced grating structure, based on the required spectral reflectivity. The basic demand for the parameter synthesis is an achievement of the real values in terms of the consequent production of the suggested structure. The described synthesis method considers advanced fiber grating structure as a structure of several uniform grating sections. The input parameters are estimated in steps, using the well-known direct methods in order to obtain grating responses and feedback to establish the parameters changes. The principle methods involve establishment of initial input parameter values and necessary subsequent algorithm leading to optimize the required spectral response. The initial values are calculated by a simplified model based on the coupled theory equations that are handled for the periodic disturbances in cylindrical waveguide. The following optimization uses the multiple thin film stack and transfer matrix methods. The properties of grating structure spectral reflectivity are step by step calculated while using these direct methods. Input parameters are established in the next several steps. Establishment of input parameters is done subsequently, based on the demanded and calculated output spectral reflectivity properties. Optimizing process is limited by possibilities of the grating manufacture technology. It is possible to assemble arbitrary fiber grating structure taking in term the demanded spectral response. Nevertheless, the calculated input parameters are real for the following manufacture. This method could be used to design optical band stop filter, high-pass and low-pass filters or filters for special applications.
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Simulation of Fiber Bragg Gratings for Semiconductor Laser Stabilization
Helán, R. ; Mikel, Břetislav
Fiber Bragg gratings (FBGs) are one of the most enveloping optical devices in telecommunications and sensor systems. Work is aimed to design of FBGs with utilization especially in sensor systems and laser interferometry for semiconductor laser stabilization at wavelength about 760nm. FBG is sampled and described as sandwich structure of dielectric media layers. Then the T-matrix method is applied to calculation of spectral properties of the grating. This method provides design of arbitrary gratings widely used in many optical systems, such as band filters, in-fiber sensors or fiber grating lasers and amplifiers for their unique properties.
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Návrh apodizovaných-chirpovaných vláknových mřížek založený na metodách vrstveného dielektrika a přenosových matic
Helán, R. ; Urban, F. ; Mikel, Břetislav
This paper discusses methods for calculation properties of apodized-chirped fiber Bragg gratings (FBGs). These are one of the most enveloping optical devices in telecommunications and sensor systems. Work is aimed to design of FBGs with utilization especially in sensor systems and laser interferometry for semiconductor laser stabilization at wavelength about 760nm. FBG is described by periodic spatial function of effective mode index, including apodization and chirp profiles. Sampling makes function discrete and each sample represents one layer of dielectric media. The transfer matrix is made for each step. The overall transfer matrix is created by multiplying of these step-matrices. The spectral characteristic and group delay are calculated from overall transfer matrix at the end. This method provides design of arbitrary gratings, which are widely used in many optical systems, such as band filters, in-fiber sensors or fiber grating lasers and amplifiers for their unique properties.
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