Pekka Ayras

High-efficiency switchable flat diffractive ophthalmic lens with three-layer electrode pattern and two-layer via structures

A general design for switchable, flat, liquid crystal diffractive lens with three-layer electrode pattern and two-layer via structures is reported for near-, intermediate-, and distance-vision corrections of presbyopic eyes. The microfabricated transparent concentric ring electrodes are distributed in two layers and different voltages are applied to each electrode through bus lines in another layer. Connection between the electrodes and the bus lines is achieved by vias (conducting holes for vertical interconnections) in the third dimension. For demonstration, a lens is first tuned with a focal length of 1m (1 diopter add power), eight-level phase modulation, and diffraction efficiency above 92% and then reconfigured to operate as a 2 diopter four-level lens with a diffraction efficiency of 78%. The lens operates with low voltages and a rise time of 150ms. This design methodology allows the aperture needed for practical use and a power-failure-safe configuration.

Diffraction gratings in sol-gel films by direct contact printing using a UV-mercury lamp

Abstract We report on the fabrication of diffraction gratings in photosensitive sol–gel thin films by direct contact printing using a UV-mercury lamp. Titanium amplitude masks were used to replicate diffraction gratings into photosensitive sol–gel films by contact printing with an incoherent UV-light source. Gratings with 1-μm period were fabricated in sol–gel films. The diffraction efficiencies of each diffracted order were measured and compared to theoretical values. The demonstrated process of contact printing using a regular UV-light source in the optically compatible sol–gel material has potential for large-scale fabrication of submicrometer gratings at very low cost.

Binary-phase zone-plate arrays based on hybrid solgel glass

An organically modified silane zirconate-based solgel material is used for the fabrication of binary-phase zone-plate arrays. The synthesized hybrid solgel material has a negative tone under UV exposure and can be patterned by a UV-lithography process. The transmittance of the material is nearly 100%, and the refractive index is 1.52. Two different diffractive lens arrays with focal lengths of 5 and 42 cm have been fabricated. The average roughness of the zone surface is less than 20 nm. The diffraction efficiencies of the lens arrays are measured as a function of modulation depth and exposure dose. A diffraction efficiency of 30% is achieved.

BIREFRINGENCE CONTROL FOR ION-EXCHANGED CHANNEL GLASS WAVEGUIDES

We show that at 1.55-mum wavelength the waveguide birefringence of ion-exchanged channel waveguides in glass can be broadly tuned by a potassium and silver double-ion exchange. Two different potassium and silver double-ion-exchange processes are used to make surface waveguides with negligible waveguide birefringence. This process is crucially important in the manufacture of devices for dense wavelength-division multiplexing systems. The dependence of the waveguide birefringence on the channel width is also reported.

Multilevel structures in sol-gel thin films with a single UV-exposure using a gray-scale mask

Multilevel structures in sol-gel thin films with a single step process are demonstrated. A negative-tone hybrid sol-gel material is UV-exposed through a gray-scale calibration mask. Test strips of different depths and a continuous test profile are demonstrated. A maximum depth difference exceeding 1.5 μm is obtained, which permits the fabrication of multilevel diffractive elements for use in visible light. This method of using sol-gel material with a gray-scale mask has the potential for low-cost fabrication of complex multilevel micro-optical structures.

Thin-film chemical sensors with waveguide Zeeman interferometry

We describe a highly sensitive chemical sensor scheme using a channel waveguide with a selective surface coating based on polarimetric Zeeman interferometry. The sensing is based on measurement of the phase difference between TE and TM modes propagating in the anisotropic waveguide structure under exposure to toluene vapour. A real-time and reversible response at low ppm level is observed. Modelling results of the sensor structure to further increase its sensitivity are presented.

High-efficiency switchable diffractive lens

We demonstrate that, by using circular array of electrode pattern and applying multi-level phase modulation in each zone, a high-efficiency switchable electro-optic diffractive lens using liquid crystal as the active medium can be produced as a switchable eyewear. The lens is flat and the thickness of the liquid crystal is 5 μm. Two different designs are presented. In one design, all the patterned electrodes are distributed in one layer with a 1-μm gap between the electrodes. In the other design, the odd- and even-numbered electrodes are separately patterned in two layers without any lateral gaps between the electrodes. In both cases, vias are made for interconnection between the electrodes and the conductive wires. With the one-layer electrode design, both 1-diopter and 2-diopter 8-level lenses are demonstrated with an aperture of 10 mm. With the two-layer electrode design, a 2-diopter, 15-mm, 4-level lens is demonstrated. The diffraction efficiency of the 8-level lens can be higher than 90%. The ON- and OFF-state of the electrically controlled lens allow near- and distance-vision respectively for presbyopic eyes. The focusing power of the lens can be adjusted to be either positive or negative. The focusing power of the 8-level lens can be adjusted for near-, intermediate-, and distance vision. The lens is compact and easy to operate with fast response time, low voltages and low power dissipation. This is the first demonstration of the switchable lenses that almost meet the requirements for spectacle lens.

Fabrication of hybrid sol-gel glass diffractive elements

Organically modified photosensitive hybrid glasses are synthesized and used for the fabrication of diffractive optical elements. The material synthesis is based on a sol-gel process. The materials are spin-deposited onto glass substrate that also have a significant role in the component assembly. The synthesized material has a negative tone property under UV-radiation and they can be patterned by a conventional UV- lithography process. Binary diffractive lenses are photoimprinted through an amplitude contact mask. Optical properties and surface roughness of the materials and elements are evaluated. Diffraction efficiencies of the elements are also measured. The process and material optimization for the reliable fabrication of integrated optics devices is carried out.

Strip-loaded structure for ion-exchanged Er3+-doped glass waveguide amplifiers

A new strip-loaded structure for ion-exchanged waveguide amplifiers in Er3+-doped glass is suggested. The fabrication of these waveguides lacks steps such as mask deposition and burial process that can be critical for some glasses. A simple numerical modeling shows that similar, or even higher, gain values as in ion-exchanged buried waveguides can be achieved. Preliminary experimental data for the fabrication of the strip-loaded structure are also reported.

Birefringence control for ion-exchanged channel waveguides at 1.55 μm wavelength

We show at 1.55 micrometer wavelength that the waveguide birefringence of ion-exchanged channel waveguides in glass can be broadly tuned by a potassium and silver double-ion- exchange. Two different potassium and silver double-ion- exchange processes are used to make surface waveguides with negligible waveguide birefringence. This is of crucial importance in making devices for dense wavelength division multiplexing (DWDM) systems. The dependence of the waveguide birefringence on the channel width is also reported.