S. Morasca

Optical components in polymers

Samples of PMMA [Poly-(Methyl-Meth-Acrylate)] were modified by ionizing radiation (especially UV-radiation) in order to generate regions of increased refractive index. These waveguiding structures were used to build optical power splitters and optical polarizers simply by varying the exposure time. The refractive index profile and the variation in thickness of the waveguides for different exposure times were observed. Also the cut-off- wavelength and the spectral absorption behavior for different exposure times were measured. The compaction at the surface was used to build up diffraction gratings with grating constants of 4 micrometer to 20 micrometer. By annealing the samples the diffraction efficiency was increased.

Two‐photon absorption in In1−x−yGaxAlyAs/InP waveguides at communications wavelengths

We have observed and measured two‐photon absorption in In1−x−yGaxAlyAs/InP waveguides grown by molecular beam epitaxy over the wavelength range of 1.5–1.65 μm. The values of β2, the two‐photon absorption coefficient, were 63 and 20 cm/GW for waveguides of compositions x=0.32, y=0.17 and x=0.15, y=0.31, respectively. These values are comparable with those predicted by scaling laws. We estimate the associated nonlinear refractive index coefficient n2 and discuss the implications for all‐optical switching.

Compositional and stress-optical effects in glass waveguides: Comparison between KNa and AgNa ion exchange☆

Abstract An experimental analysis of the effects of composition, stress and stress relaxation on the refractive index changes in optical waveguides fabricated in soda-lime glass by ion exchange is presented. Stress was determined by waveguide birefringence via analysis of effective modal indices, while compositional profiles are obtained by EDX and RBS measurements. Results are compared for the K+Na+ and for the Ag+Na+ process; it is shown that in soda-lime glass the stress-induced index change is comparable to the compositional term for the K+Na+ process, while for the Ag+Na+ exchange the stress term is much less important and the refractive index change is due only to the compositional term.

Effects of water vapor on refractive index profiles in Ti:LiNbO 3 planar waveguides

A systematic investigation on the effects of water vapor during Ti:LiNbO 3 waveguide fabrication is reported, including optical and spectroscopic analysis. Extraordinary index profiles are changed by the presence of H 2 O in the diffusion atmosphere, while outdiffused waveguides are not suppressed. The resulting profiles cannot be explained by a simple change of the Ti diffusion coefficient, and more complex models should be developed to describe the phenomena.

Measurement of group effective index in integrated semiconductor optical waveguides

The effective group index of InGaAsP/InP moderately diluted multiple quantum well (MQW) waveguides grown by metalorganic chemical vapor deposition (MOCVD/sur) on InP has been measured in the 1.55- mu m spectral region. The technique used is based on the Fourier analysis of the spectral transmission function of a resonant cavity formed by the waveguide itself. Accuracy to the third decimal place is demonstrated, and differences between TE and TM indexes are also evidenced.<<ETX>>

A highly dispersive wavelength division demultiplexer in InGaAlAs-InP for 1.5 mu m operation

A novel integrated optical wavelength division demultiplexer in InGaAlAs-InP is described. It uses interference between the fundamental (zeroth) and second-order modes in a symmetric waveguide structure. Experimental results show that this device is twice as dispersive as two-mode interference (TMI) devices based on interference between the fundamental and antisymmetric modes. Channel spacings between 15 mu m and 40 nm were obtained with channel isolation in excess of +or-10 dB.<<ETX>>

REFRACTIVE INDICES OF INGAALAS GROWN BY MOLECULAR BEAM EPITAXY

The accurate determination of the refractive indices of InGaAlAs, grown by molecular beam epitaxy, is reported for the first time. The method used, modal, cutoff spectroscopy, is applied to InGaAlAs/InP single heterostructure waveguides, with compositions corresponding to band‐gap wavelengths in the range of 1.02–1.12 μm. The refractive indices are determined at different wavelengths between 1.1 and 1.6 μm, with an accuracy better than 10−3.

Effects of potassium concentration and induced stress on the refractive index profile of K+-Na+ ion-exchanged glass waveguides

Abstract An extensive investigation into the optical properties of K+-Na+ ion-exchanged waveguides in soda-lime glass over a wide range of time and temperature is described. From accurate measurements of effective indices, refractive-index profiles and birefringence are obtained, and by use of microalytical techniques (RBS, EDX) ion concentration profiles are measured. Comparison of these profiles allows a quantitative separation of the compositional and the stress optical contributions to the overall change in refractive index; the time behaviour of stress thermal relaxation processes explains the evolution of the profile shape.

Refractive indices of semiconductor films measured by waveguide cutoff spectroscopy

It is shown that by measuring the cutoff wavelengths of supported modes in waveguides it is possible to determine accurately the refractive index of the guiding layer. This method has been applied to InGaAsP/InP waveguides, and their refractive indices are obtained with accuracy to the third decimal place.

Spectroscopic properties of Er3+-doped glasses for the realization of active waveguides by ion-exchange technique

The fabrication of different types of Er3+-doped glasses and the study of their absorption and emission spectra, cross sections, lifetimes, and bandwidths are described. The purpose is to get guidelines for the synthesis of the appropriate glasses to manufacture active planar waveguides. The feasibility of active integrated optical waveguides by ion-exchange on these glasses is also demonstrated, using an Er3--doped soda-lime glass.