Jesper Arentoft

Second-harmonic imaging of poled silica waveguides

Electric-field poled silica-based waveguides are characterized by measurements of second-harmonic generation (SHG) and of the linear electro-optic effect (LEO). A SHG scanning technique allowing for high-resolution imaging of poled devices is demonstrated. Scans along the direction of the poling field show that the second-order optical nonlinearity is located near the interface between differently doped glass layers. Both SHG and LEO measurements indicate that the ratio between the main elements of the second-order nonlinear optical susceptibility tensor, χ33(2) and χ31(2), is significantly smaller than three.

Theoretical analysis of finite-height semiconductor-on-insulator-based planar photonic crystal waveguides

A planar photonic crystal waveguide based on the semiconductor-on-insulator (SOI) materials system is analyzed theoretically. Two-dimensional (2-D) calculations and comparison with dispersion relations for the media above and below the finite-height waveguide are used to obtain design guidelines. Three-dimensional (3-D) calculations are given for the dispersion relations and field profiles. The field profiles obtained using 2-D and 3-D calculations are qualitatively similar. However, we find that compared with 2-D calculations, the frequencies of the guided modes are shifted and the number of guided modes changes. The theoretically predicted frequency intervals, where the waveguide supports leakage-free guidance of light, are compared with an experimental measurement for propagation losses. Two out of three frequency intervals coincide with low-measured propagation losses. The poor guidance of light for the third frequency interval is explained theoretically by investigating the vertical localization of the guided modes.

Thermally poled channel waveguides with polarization-independent electrooptic effect

We present a systematic investigation of the poling-induced electrooptic (EO) effect in germanium and nitrogen codoped channel waveguides. The channel waveguides show attractive properties: (1) almost polarization independent EO effect; (2) a flat frequency response with the modulation frequency up to 100 kHz; and (3) low linear loss and low polarization dependent loss, which demonstrate great technological potential.

Evidence of space-charge effects in thermal poling

The in situ thermal poling processes in germanosilicate fibers for positive and negative poling voltages are significantly different. Thermal poling of silica fibers consists of two processes: the faster linear process of charge migration and the subsequent single exponential process of charge ionization. Both the shielding electrical field due to charge migration and the ionization electrical field due to charge ionization are able to be frozen-in at room temperature and lead to the residual linear electrooptic effects. The observations support that the mechanism of the induced electrooptic effects is based on space charge electrical fields instead of dipole/bond orientation.

Direct mapping of light propagation in photonic crystal waveguides

Abstract Using near-field optical microscopy, we directly map the propagation of light in the wavelength range of 1510–1560 nm along bent photonic crystal waveguides formed by removing a single row of holes in the triangular 400-nm-period lattice and connected to access ridge waveguides, the structure being fabricated on silicon-on-insulator wafers. Based on the near-field optical images measured, we determine the bend loss to be below 2 dB in the range of 1510–1530 nm, identify the associated loss channels, and obtain an upper limit of 930 nm for the guided mode width intensity distribution at 1510 nm.

Second-harmonic scanning optical microscopy of poled silica waveguides

Second-harmonic scanning optical microscopy (SHSOM) is performed on electric-field poled silica-based waveguides. Two operation modes of SHSOM are considered. Oblique transmission reflection and normal reflection modes are used to image the spatial distribution of nonlinear susceptibilities in the sample surface plane and in depth. It is shown that the spatial resolution in normal reflection mode can be better than 1 μm for second-harmonic images. A simple qualitative description of this operation mode is suggested and found to be in good agreement with the results obtained. Advantages and limitations of the two operation modes when used for SHSOM studies of poled silica-based waveguides are discussed. The influence of surface defects on the resulting second-harmonic images is also considered.

Designing finite height photonic crystal waveguides; confinement of light and dispersion relations

Guidelines are obtained for characteristic design parameters of finite-height photonic crystal waveguides using diagrams of photonic bandgaps for infinite-height photonic crystals. This is achieved by requiring photonic crystal designs with bandgaps well below a fundamental upper frequency limit for leakage-free guidance of light related to the properties of the media above/below the finite-height photonic crystal waveguide. The approach has the advantage that it can be applied to a large number of diagrams for infinite-height crystals that are already available in the literature, and furthermore the approach is not computer intensive compared to more rigorous numerical approaches to three-dimensional structures. We consider optical waveguide designs based on introducing a line defect in photonic crystals with air holes arranged on a triangular lattice in a silicon slab. For the media above/below the slab we consider the choices of silica and air. Dispersion relations are calculated for various waveguide designs. The analysis reveals a complex distribution of bands related to guided modes and provides information on how the guidance properties are modified as the waveguide width is changed. Furthermore, the analysis reveals the existence of bandgaps that are almost omni-directional. For a specific choice of photonic crystal waveguide placed on a silica substrate these bandgaps that have previously been overlooked gives the only possibility of leakage-free bandgap guidance of TM-polarized light.

Realization of robust photonic crystal waveguides designed to reduce out-of-plane scattering

We have realized environmentally stable silicon-on-insulator based photonic crystal waveguides. The waveguide structure is designed to minimize scattering at semiconductor/hole interfaces. Transmission measurements and IR pictures indicate efficient guiding through straight and bent waveguides.

Positive and negative thermal poling of germanosilicate fibres

In situ measurements of thermal poling of germanosilicate fibers under positive and negative poling voltages show different dynamics of a linear electro-optic effect induced into fibers. The mechanism for the induced electro-optic effect is addressed.

Bragg gratings as probes to determine nonlinearities induced by thermal poling

By negative thermal poling of a Bragg grating we have found the poling induced second- and third-order nonlinearities along with the induced dc electric field for both polarizations in a silica waveguide.