The structure composed of a single mode silica-titania slab waveguide on a BK7 glass substrates and a grating coupler embossed at the interface of slab waveguide to ambient is studied. Reported studies are focused on optimization of thickness of the slab waveguide, length of grating period and coupling angle, aiming at maximization of coupling angle homogeneous sensitivity, which is a product of effective index coupling angle sensitivity and slab waveguide homogeneous sensitivity. If effective index coupling angle sensitivity is varying with grating period then it has a local minimum. At this minimum coupling angle homogeneous sensitivity depends only on slab waveguide homogeneous sensitivity and a refractive index of medium where coupling angle is measured. Effective index coupling angle sensitivity is monotonous if is varying with waveguide film thickness. Monotonicity sign depends on grating period. Coupling angle homogeneous sensitivity considered a function of waveguide film thickness may have local maximum. However, depending on grating period, it can also be strictly increasing or decreasing function of waveguide film thickness, depending on a diffraction order, in which case it becomes very high. However in this case, coupling angle is quickly increasing and reaches π/2.
This paper raises two questions concerning guiding properties of silica-titania rib waveguides. The first one is a relationship between silica-titania rib waveguides morphological parameters and their single mode operation regime. A set of these parameters includes rib height t, width w and a thickness h of a parent slab waveguide. It was shown that if a parent slab waveguide thickness is equal or higher to the value which maximizes homogeneous sensitivity of a fundamental TM mode then, depending on a value of rib width, there can be single or double range of rib height values for which the rib waveguide is single modal for quasi-TM modes. The second issue concerns an analysis of a magnitude of bend losses. It was shown that a magnitude of bend losses in silica-titania rib waveguides can be small enough allowing their application in designing of planar integrated optical circuits. The magnitude of bend losses is significantly decreased when slab waveguides adjacent the rib are cut-off.
This work is devoted to studying the dielectric/metal multilayer planar waveguide structure that is composed of a highrefractive index, single mode, silica-titania film deposited on a BK7 glass substrate. The waveguide film is loaded with a thin gold film, through a thin silica film. It is assumed that a semi-infinitive cover have the same refractive index as the water. There are presented and analyzed spectral characteristics of effective indexes of TM-polarized: dielectric and surface plasmon polariton (SPP) modes. Analysis of these characteristics is aimed at finding conditions for exciting the dielectric TM0 mode and two SPP modes: antisymmetric and symmetric. Assuming that excitation is done with a field distribution of the unloaded TM0 mode carried in this structure if the gold film is not present. The analysis is carried for the gold film having thicknesses dm=50 nm. It is shown, that conditions for matching effective indexes of the unloaded TM0 mode and SPP modes are met in a broad range of silica film thickness. The presence of the silica film is indispensable for reduction of a refractive index difference between loaded and unloaded TM0 modes. It is shown that a sensitivity of this structure toward a small change of the cover refractive index is inconsiderably dependent on silica film thickness for the antisymmetric SPP mode. On the contrary, a sensitivity of the symmetric SPP mode, whose refractive index undergoes a discontinuous change with respect to wavelength changes its sign in function of the buffer film thickness.
The sol-gel technology allows preparation of thin silica films ranging in porosity from dense to highly porous. These films can function as a matrix binding molecules of the pH-sensitive dyes and can be utilized as the sensitive films for intensity based planar evanescent wave chemical sensors. Sensitive properties of these dyes decreases in time due to aging processes. We report characterization of weakening of sensing properties of highly porous silica films doped with the bromocresole purple (BCP). In the presence of the gaseous ammonia, the absorption band (AB) of protonated BCP centered at λ=430 nm, is shifted toward λ=591 nm due to deprotonation, resulting in the increase of sensitive films absorption in the range of wavelengths of shifted AB. Two sets of films were investigated. Films from the first one were cyclically exposed to the ammonia and stored isolated from the daylight. Films from the second set weren't exposed to the ammonia and were stored in a staining jar exposed to the daylight. A depth of the AB at λ=430 nm was measured using a spectrophotometer. A sensitivity of the films toward ammonia was measured using LED emitting at center wavelength λ=610 nm. As was shown, the sensitivity of these films exposed to the ammonia diluted in dry air, and isolated from the daylight, decreases in time exponentially. The magnitude of that decrease monotonically depends on the ammonia concentration. It was also shown that the daylight causes quick aging of films not exposed to the ammonia. A depth of the AB centered at λ=430 nm relatively quickly decreased when compared with films isolated from the daylight and exposed to the ammonia.
The paper presents the concept of forming ammonia sensor based on a planar waveguide structure. It is an amplitude sensor produced on the basis of the multimode waveguide. The technological base for this kind of structure is the ion exchange method and the sol-gel method. The planar multimode waveguide of channel type is produced in glass substrate (soda-lime glass of Menzel-Glaser company) by the selective Ag+↔Na+ ion exchange. On the surface of the glass substrate a porous (~40%) silica layer is produced by the sol-gel method. This layer is sensitized to the presence of ammonia in the surrounding atmosphere by impregnation with Bromocresol Purple (BCP) dye. Therefore it constitutes a sensor layer. Spectrophotometric tests carried out showed about 50% reduction of cross-transmission changes of such sensor layer for a wave λ=593 nm caused by the presence of 25% ammonia water vapor in its ambience. The radiation source used in this type of sensor structure is a light emitting diode LED. The gradient channel waveguide is designed for frontal connection (optical glue) with a standard multimode telecommunications waveguide 62.5/125μm.
This work presents results of the theoretical analysis as well as the results of experimental study on sensing structures with grating couplers. Grating couplers with a groove density of 1250g/mm were produced by us using the method of master grating embossing in a sol film. The waveguide films SiO2:TiO2 of high refractive index have been produced using the sol-gel method
The paper is devoted to the sensitive films for application in chemical sensors. These films, made of the sol-gel derived porous silica, were fabricated via a sol-gel dip-coating method. We have obtained silica layers of the minimum refractive index of ~ 1.22 and porosity ~47%. These layers were sensitized with a pH indocator - bromocresole purple. The indicator was introduced into porous silica layers by means of impregnation. Methods and results of characterization of porous silica films, before and after sensitization are presented in this paper. It was shown that films are very sensitive toward ammonia.
This paper presents an analysis of the possibilities of producing waveguide structures of the inverted-rib type. Such structures can be produced on the basis of planar gradient strip waveguides (channel waveguides) produced in a glass substrate by the ion exchange method. The glass surface is then covered with a thin uniform optical layer with a high refractive index. The thickness of this layer is less than the cut off thickness for the used wavelength. The wave propagation is therefore possible in the gradient area only. The homogeneous sensitivity of such waveguides is much greater than in case of single-mode waveguides without a uniform layer. The paper presents the calculations of homogeneous sensitivity for single-mode waveguides of the rib type, the inverted rib waveguides and the gradient waveguides. The use of single-mode inverted rib waveguides in the design of the planar interferometer in the Young configuration was proposed.
This paper presents the design and theoretical characterization of a composite uniform-gradient planar waveguide polarimetric interferometer. Presented structure is composed of an Ag+↔Na+ ion-exchange based waveguide formed in Borosilicate 33 glass substrate and a uniform, sol-gel based, silica-titania film. Characteristics of homogeneous sensitivity difference for TE0-TM0, TE0-TE1 and TM0-TM1 modes in function of the uniform film refractive index and the gradient waveguide refractive index profile are given. Because thermal annealing is an inseparable part of the sol-gel process, the gradient index waveguide is subjected to a rediffusion process. The original refractive index profile is flattened. It was shown that a presence of the gradient waveguide increases sensitivity differences over values which can be obtained for single layer uniform silica-titania waveguides. Moreover, it was shown that a range of uniform film thickness values, for which sensitivity difference of the composite structure is maximized, is downshifted to a range which can be much easier obtained with a sol-gel process.
The paper presents complex waveguide structures which have been fabricated on a basis of the gradient waveguide on the top of which a uniform waveguide film of high refractive index is deposited. The gradient waveguides were fabricated using the ion exchange method, whereas the uniform film with the application of the sol-gel method. The application of such a waveguide structure in the system of difference interferometer makes it possible to obtain high sensitivities of the effective refractive index against the changes of sensor layer parameters, in particular when the interference of the basic mode TM0 with the first order mode TM1 is applied. The paper presents the theoretical analysis of complex waveguide structures, their fabrication technology and the results of experimental studies.
This paper presents an analysis of the magnetic field influence on a planar differential interferometer that uses a magneto-sensitive ferronematic layer. Due to a magnetic field interaction a nematic matrix changes its orientation in a TM mode polarization plane. In consequence, a propagation constant changes only for a TM mode, and a phase difference between TE and TM modes is changed under magnetic field influence. An influence of the optical and geometric parameters of the presented structure on the phase difference of propagating modes is presented.
This work presents a system for magnetic field intensity measurements. The idea of measurements is based on an influence of external magnetic field on the polarization state of singlemode light propagating along optical fibers. In the paper some experimental results of testing investigations of the system for measurements magnetic field of high intensity are presented. The final aim of the investigation outlined below is to work out magnetic field intensity sensors which, together with optical fiber temperature sensors and electric field intensity sensors, will make possible, in the future, to monitor fully operation of electromagnetic power units such as, for example, high voltage power transformers.
This work presents the new method that allows determining the polarization state of light which propagate in optical fibers. One shown also the experimental results of application the elaborated method for mesaure of magnetic field of high inteisty. The final aim of this investigation will be the elaboration of magnetic intensity sensors, which together fiber optic temperature sensors and intensive of electric field sensors make possible, in the future, to monitor the state of work of electromagnetic power arrangements, first of all - high voltage power transformers.