Novel integrated optic intensity modulator based on mode coupling

The analysis, design, realization, and measurements of a novel intensity modulator are reported. The operating principle is based on mode coupling between a passive low-loss SiON waveguide and an electro-optic high-loss polymer waveguiding structure. Matching the waveguides is critical and results in severe demands for the technology. Extended simulations by the Coupled Mode Theory, the Leaky Wave Model, and Finite Difference Beam Propagation Method resulted in the design of several modulator structures. After realization, modulation could be demonstrated at 632 nm and at 1523 nm using lossy waveguiding modes and surface plasmon modes.     

Temperature dependence of the hyperfine field in amorphous Fe2O3

Mössbauer spectroscopy was used to follow the hyperfine field at ⁵⁷Fe nuclei in amorphous Fe₂O₃. The value of H_hf at T = 0, 470 kG, indicates $\text{J}\text{=}\text{5}\text{2}$ for the Fe ions, while the reduced hyperfine field versus reduced temperature closely follows a $\text{J}\text{=}\text{1}\text{2}$ Brillouin function. This result is at variance with theoretical predictions for a spin glass and is also different from amorphous metals with a high content of magnetic ions as reported in the literature. Paramagnetic Mössbauer spectra of amorphous mixed oxides of Fe₂O₃ with ZnO and CoO show that the ⁵⁷Fe nuclei in all amorphous ferric oxides studied so far are coordinated in a manner similar to the d site in β F₂O₃, and distinctly different from the coordination in their crystalline form.     

A numerical study of solitary waves in a non-linear Bragg reflector

A two-dimensional time domain finite difference beam propagation method, based on the slowly varying envelope approximation is presented. Expressions to correct this approximation and to include third-order non-linear effects are given. The method is applied on solitary waves in a non-linear Bragg reflector, assuming realistic materials parameters.     

Design of 1480-nm diode-pumped Er3+-doped integrated optical amplifiers

Abstact Erbium-doped Y₂O₃ integrated optical amplifiers are designed for low-threshold operation and 3 dB amplification. The most important design parameter for minimal threshold, the erbium concentration, is found to have an optimum value of 0.35 at% for a given waveguide structure with 1.0 dB cm^-1 background loss. The corresponding threshold power is 7 mW. The pump power to obtain 3 dB gain is found to be 22 mW for an amplifier with an optimum erbium concentration of 0.6 at% and 2.8 cm length. At 30 mW pump power the maximum gain is shown to be 5 dB.Designing is done using a comprehensive numerical model of an erbium-doped integrated optical amplifier. In the model two-dimensional intensity-dependent overlap integrals are used, which allow arbitrary erbium dopant profiles and waveguide crosssections. Concentration-dependent effects such as quenching and upconversion are also included in the model.Input parameters for the model are determined from measurements on an unoptimized Er: Y₂O₃ optical waveguide amplifier. Amplification simulations and gain measurements of the unoptimized waveguides are found to be in close agreement, providing a sound basis for the design calculations.     

The polar magneto-optic Kerr rotation of ferromagnetic perovskites (La,Bi, Sr)MnO3

The polar magneto-optic Kerr rotation of the perovskites Bi_xLa_1?x?y Sr_yMnO₃ is reported for wavelengths between 0.25 and 0.7 μm at 78 and 300 K. The presence of bismuth enhances strongly the Kerr rotation around 0.27 μm at 78 K (for x = 0.25 and y = 0.3 the rotation is 2.3 deg at 0.29 μm).     

Asymmetric co-evaporated Co-Cr films: magnetic parameters and reversal mechanism

The magnetic parameters of co-evaporated Co–Cr films, where Cr was deposited obliquely, are investigated. Process-induced compositional separation enhanced the energy product. When the substrate was rotated during evaporation, the perpendicular characteristics were lost.     

Morphology and texture of co-evaporated Co-Cr films

The microstructure of co-evaporated Co-Cr films is investigated. The columnar morphology is tilted towards the main source. Due to the geometry effect of opposing vapour directions, compositional separation occurs. With AES direct proof of this was established. Consequently it is unnecessary to increase the substrate temperature to obtain enhanced energy products.     

Novel integrated optic intensity modulator based on mode coupling

Abstract

The analysis, design, realization, and measurements of a novel intensity modulator are reported. The operating principle is based on mode coupling between a passive low-loss SiON waveguide and an electro-optic high-loss polymer waveguiding structure. Matching the waveguides is critical and results in severe demands for the technology. Extended simulations by the Coupled Mode Theory, the Leaky Wave Model, and Finite Difference Beam Propagation Method resulted in the design of several modulator structures. After realization, modulation could be demonstrated at 632 nm and at 1523 nm using lossy waveguiding modes and surface plasmon modes.     

Magnetic properties of the garnets Bi0·8Ca2χT2·2-2.χFe5-χVχ]O12

The behaviour of the magnetization, Curie temperature, Mössbauer spectra, and lattice parameter is studied in the garnet series Bi_0·8Ca_2.χT_2·2-2.χFe_5-χV_χ]O₁₂. The shape of magnetization vs temperature curves shows only a minor dependence on x. The hyperfine field at the octahedral ⁵⁷Fe nuclei at 5°K decreases linearly with x (12·5kOe per substituted V neighbour), while that at the tetrahedral ⁵⁷Fe nuclei is not affected. The dependence of the Curie temperatures and hyperfine fields on x is discussed in relation to the Fe-O-V-O-Fe exchange. The influence of Bi substitution is consistent with the idea of a geometric effect.