Measurement Of Effective Refractive Index Research Articles

In-situ measurement of effective refractive index of glass waveguides (invited)

In-situ measurement of effective refractive index of glass waveguides (invited)

Wedge-cell technique as a simple and effective method for chromatic dispersion determination of liquid crystals

In this letter we present a wedge-cell method and then compare it with other techniques that can be used to determinate refractive indices of liquid crystalline materials. This simple goniometric technique is of particular significance when used for liquid crystalline materials characterized by high refractive indices, for which refractometric methods are approaching their upper limits. Importantly, a measurement technique proposed here requires relatively small amount of a liquid crystalline material and gives appropriate results for different light sources from the wide spectral range, allowing thus for chromatic dispersion curves (in different temperatures) to be obtained. Full Text: PDF References M.O. Ko, S. Kim, J. Kim, B.W. Lee, M.Y. Jeon, "Measurement of Effective Refractive Index of Nematic Liquid Crystal in Fabry-Perot Etalon", J. Opt. Soc. Korea 19, 346 (2015). CrossRef K. Thingujama, S. Sarkara, B. Choudhurya, A. Bhattacharjeea, "Effect of Temperature on the Refractive Indices of Liquid Crystals and Validation of a Modified Four-Parameter Model", Acta Phys. Polonica A 122(4), 754 (2012). CrossRef T.A. El-Dessouki, M. Roushdy, N.I. Hendawy, M.M. Naoum, A.A. Zaki, "Optical Measurements of Thermotropic Liquid Crystals", J. Modern Physics 4, 39 (2013). CrossRef J. Li, S. Wu, S. Brugioni, R. Meucci, S. Faetti, "An Experimental Method for Determination of the Refractive Index of Liquid Samples Using Michelson Interferometer" J. Appl. Phys. 97, 073501 (2005). CrossRef B. Abbas, M.A. Khalil, "An Experimental Method for Determination of the Refractive Index of Liquid Samples Using Michelson Interferometer", Acta Phys. Polonica A 129, 59 (2016). CrossRef S.R. Kachiraju, D. A. Gregory, "Determining the refractive index of liquids using a modified Michelson interferometer", Opt. Laser Techn. 44, 2361 (2012). CrossRef J. Yan, M. Jiao, L. Rao, S. Wu, "Direct measurement of electric-field-induced birefringence in a polymer-stabilized blue-phase liquid crystal composite", Opt. Expr. 18, 11450 (2010). CrossRef K.A. Rutkowska, U.A. Laudyn, R.T. Rutkowski, M.A. Karpierz, T.R. Wolinski, J. Wójcik, "Nonlinear light propagation in photonic crystal fibers filled with nematic liquid crystals", Proc. SPIE 6582, 658215 (2007). CrossRef J. Li, C. Wen, S. Gauza, R. Lu, S. Wu, "Refractive indices of liquid crystals for display applications", J. Display Techn. 1, 51 (2005). CrossRef K. Rutkowska, A. Kozak, K. Orzechowski, "Chromatic dispersion measurements of selected liquid crystalline materials for integrated optics applications," Proc. SPIE (in press) (2016). E. Nowinowski-Kruszelnicki, J. Kędzierski, Z. Raszewski, L. Jaroszewicz, R. Dąbrowski, M. Kojdecki, W. Piecek, P. Perkowski, K. Garbat, M. Olifierczuk, "High birefringence liquid crystal mixtures for electro-optical devices", Optica Applicata 42, 167 (2012). DirectLink

First Results in Near and Mid IR Lithium Niobate-Based Integrated Optics Interferometer Based on SWIFTS-Lippmann Concept

High-resolution spectrometers are nowadays achievable in compact devices using integrated optics. The approach developed here consists in obtaining a static interferogram by means of a Fresnel reflection at the waveguide output (Lippmann interference between forward and backward beams) and then sample the fringes by periodically etching the waveguide with transverse nanogrooves, that will collect a negligible part of the flux. We present the first SWIFTS-Lippmann interferometer in the near and mid-infrared, thanks to high form factor grooves obtained by focused ion beam in lithium niobate, which opens the way to electrooptic modulation of the interferogram and thus, sampling on-chip, without any moving part. Possible applications are high-resolution spectroscopy and accurate measurement of effective refractive index of a waveguide. A measurement of the effective group refractive index of the guided mode is presented.

The influence of colour and surface topography on the measurement of effective refractive index of offset printed coated papers

This paper explores the influence of colour and surface topography on refractive index measurement by reflection, with particular reference to offset lithography printed coated paper. Previous work has studied the influence of coated paper porosity on the distribution of ink components throughout a printed offset ink film, using the technique of gloss goniophotometry and refractive index measurement. Porous papers were shown to have a fast removal of ink oils, which lead to a surface concentration of organic pigment and consequent depletion of resin binder. The resulting surface was optically rough and gave a less glossy ink film. The theory for gloss goniophotometer refractive index measurement is based upon polarised light reflectance at the interface between two smooth, non-absorbing isotropic media. A printed coated paper is not ideally suited to optical studies, as it is coloured, rough, non-homogeneous and contains particles which are capable of scattering light. This work was therefore carried out to determine the influence of colour and roughness on the measurement of effective refractive index. It is established that the effect of colour on measurement of refractive index is negligible when measured at an angle of 75°. The issue of roughness has not been resolved theoretically, with conflicting references on its effect on the measured RI. However, experimental work in the literature suggests that the effect of roughness on the measured RI is only marginally dependent upon the scale of the roughness.

Dye-doped polymeric waveguides for integrated optics

We present a study of fabrication and characterization of methyl red doped polystyrene waveguides. Optical absorption and mode effective refractive index measurements were performed on a large number of waveguides fabricated on glass substrates prepared by a dip coating technique. It is observed that doping of azo dye increases the index of refraction of the waveguides. The losses, however, decrease initially for dye concentration up to 0.1% and thereafter increase rapidly.

Complex permittivity measurements at Ka-Band using rectangular dielectric waveguide

The rectangular dielectric waveguide (RDWG) technique has been developed for the determination of the dielectric constant of materials from effective refractive index measurements in the Q and W bands. This paper describes the use of an optimization method in conjunction with the RDWG technique for the determination of both the dielectric constant and loss tangent of materials at Ka-Band. The effect of the uncertainty in the measured sample thickness is presented.

Determination of the dielectric constant of materials from effective refractive index measurements

This paper presents an extension to the rectangular dielectric waveguide technique to obtain the permittivity of samples iteratively from the effective refractive index measurements by using the solution of the wave equation. The effective refractive index is presented for several samples in the 33 GHz to 50 GHz frequency range. The method is very fast and simple and provides an accuracy of better than 1% for the determination of permittivity of materials.

Sculptured thin films and glancing angle deposition: Growth mechanics and applications

Sculptured thin films with three dimensional microstructure controlled on the 10 nm scale were fabricated with an evaporation technique. Glancing angle deposition (GLAD) and substrate motion were employed to “sculpt” columnar thin film microstructure into desired forms ranging from zigzag shaped to helical to four-sided “square” helical. Computer control of substrate motion was used to accurately position the substrate and to achieve the desired film structures. The growth mechanics of this novel thin film deposition technique are investigated with density measurements, scanning electron microscopy analysis, and measurements of effective refractive index. Adatom diffusion and atomic shadowing are the dominant growth mechanisms with glancing angle deposition conditions creating extreme shadowing. With controlled rotation of the substrate about two axes during deposition, a dense capping layer can be produced on top of the porous sculptured films. The success of the capping process was found to be strongly dependent on the technique used, with an exponential decrease (θ∝[1−A⋅eB⋅t]) with time of incident flux angle found to be the best to reduce filling of the porous film and fracturing of the capping film. The GLAD technique was found to have potentially promising application in optical, biological, and chemical devices and materials.

Fabrication and characterization of dye doped polyester–polyurethane optical waveguides

A systematic study of the fabrication and characterization of planar optical waveguides based on polyester-polyurethane coatings was done. Mode effective refractive index measurements were performed on a large number of these waveguides fabricated on glass substrates prepared in different conditions. The results indicate that the effect of the dye is to increase the refractive index of the waveguides. The losses in the guides, however, initially decreased from 0.9 to approximately 0.5 dB/cm when the dye concentration was approximately 0.1% but increased drastically (>30 dB/cm) for guides with greater dye concentrations.

Fabrication and characterization of polyester and acrylic polyurethane optical waveguides

Asystematic study of the fabrication and characterization of planar optical waveguides based on polyester and acrylic polyurethane coatings has been made. Mode effective refractive-index measurements have been made on a large number of these waveguides fabricated on glass prepared in different conditions. The results show that the mixture of polyester and acrylic polyol in the initial solution can be used to control the refractive index from 1.563 to 1.595. The propagation losses are estimated to be 10-20 and 6-12 dB/cm for polyester and acrylic-based waveguides, respectively.

Fabrication and characterization of titanium-indiffused proton-exchanged optical waveguides in Y-LiNbO_3

We report a systematic study of the fabrication and characterization of planar optical waveguides in Y-LiNbO3 by a process that combines titanium indiffusion and proton exchange (TIPE) techniques. Mode effective refractive-index measurements have been made on a large number of TIPE guides fabricated at various temperatures exchanged for different durations. The data have been analyzed to calculate the values of the diffusion coefficient and the activation energy for the proton exchange process in these guides. m-line scans indicate that there is a considerable amount of scattering in TIPE guides; the quality, however, improves with the increase of exchange time.

Characterisation of proton-exchange slab optical waveguides in x-cut LiNbO3

The paper reports on a systematic study of planar optical waveguides in X-cut LiNbO3 fabricated by the proton-exchange technique. The extent of the exchange process was monitored by measuring the infrared absorption peak at 3510 cm−1. It was established that the waveguide profile could be accurately modelled by a step index change with Δn = 0.127 at λ0 = 632.8 nm and Δn = 0.096 at λ0 = 1150 nm. From the mode effective refractive index measurements, the effective diffusion coefficients for the exchange process were calculated. A value for the activation energy for the proton-exchange process was established. The effect of off-Y-axis propagation on the mode effective indices of the waveguide was studied. A waveguide mode cutoff at 29° from the C-axis was established. The lowest optical losses measured in single-mode planar waveguides were 1.4 dB/cm at λ0 = 632.8 nm and 1.3 dB/cm at λ0 = 1150 nm for light propagating normal to the C-axis.

Measurement of Effective Refractive Index of GaInAsP Grown on (100)GaAs by LPE

Mesure de l'indice de refraction, et des parametres de diodes laser qui fonctionnent dans le visible. Les compositions sont calculees en utilisant les longueurs d'onde des pics de photoluminescence et les constantes cristallines mesurees par diffraction des rayons X. Les resultats montrent que l'indice de refraction depend de la composition

Characterization of proton-exchange slab optical waveguides in z-cut LiNbO3

We report the results of a systematic study on planar optical waveguides fabricated in z-cut LiNbO3 by proton exchange in benzoic acid. It was found that the refractive index varied with depth and could be accurately modeled by a step index profile with Δn=0.126. Diffusion coefficients have been calculated from mode effective refractive index measurements, assuming a step index profile, and hence a value for the activation energy for the proton exchange process has been deduced. The lowest measured optical propagation loss in single-mode waveguide at a 633-nm wavelength was 2.4 dB/cm.

Temperature-independent thin-film optical waveguide

The concept of having the effective refractive index of an optical waveguide mode be independent of temperature is introduced. It is shown that this concept should be realizable with a Corning 7059 glass thin-film waveguide supported on a SiO(2)-Si substrate for a waveguide thickness of 0.37 microm. Measurements of effective refractive index as a function of temperature confirm this prediction of temperature independence in that they show a very small variation with temperature for a 0.35-microm thick waveguide in comparison with that for a 0.98-microm thick waveguide.