C. De Bernardi

Erbium-activated silica–titania planar waveguides on silica-on-silicon substrates prepared by rf sputtering

Abstract Erbium-activated silica–titania planar waveguides were prepared by radio-frequency (rf) sputtering technique. Silica-on-silicon substrates obtained by plasma-enhanced chemical vapor deposition (PECVD) and rf sputtering (RFS) were employed. The refractive indices, the thickness and the propagation losses of the waveguides were measured. The refractive index and the roughness of the silica substrates produced by RFS appear to be dependent on the thickness. Thermal annealing, which is a necessary condition to obtain light propagation, induces a decrease of the refractive index in the silica substrates. The waveguide deposited on PECVD substrate exhibits several propagating modes with an attenuation coefficient 1.7 dB/cm compared with 12.2 dB/cm measured for the waveguide deposited on silica substrate produced by RFS technique. Emission of the 4 I 13/2 → 4 I 15/2 transition with a 53 nm bandwidth was observed.

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.

Deterministic and Statistic Circuit Assignment Architectures for Optical Switching Systems

The dimension of a non-blocking optical switching array network is limited by a series of factors: the physical size, the loss and crosstalk of the switching element, the relatively small physical size of the substrate, the loss introduced by the fiber-substrate coupling as well as the large radii imposed on the waveguide to minimize bend loss.

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.

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>>

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.

Time and temperature influence on surface index change in K+‐Na+ ion exchanged optical waveguides

An accurate analysis of optical waveguides made by Na‐K ion exchange in glass is presented. A strict correlation between surface index change, guide birefringence, surface stress, and relaxation as a function of time and temperature is demonstrated.

High Accuracy Determination Of Semiconductor Substrate And Waveguide Refractive Index By Prism Coupling

Measurements of the refractive index of semiconductor materials, both in wafer and in waveguide form, are presented. The technique used to this purpose is based on radiation coupling into the material by a prism; this method is used for the first time on semiconductors, by means of a silicon prism. Accuracy to the fourth decimal place is demonstrated, in favorable comparison to the best available data.