Jochen Bähr

Index-distributed planar microlenses for three-dimensional micro-optics fabricated by silver-sodium ion exchange in BGG35 substrates

Fabrication of planar microlens arrays by silver-sodium ion exchange is possible by using a new glass type, optimized for this technology. Because of its nonlinear diffusion response it is well suited to the fabrication of microlens arrays. We show that the diffusion coefficient can be described theoretically by an exponential concentration dependence. The parameters of the planar microlenses are measured interferometrically and by imaging experiments. Because of the specific index distribution, new evaluation techniques for the determination of lens parameters from interferometric measurements have been applied. We also present a simple model that relates the achievable lens parameters to the diffusion conditions.

Realization and optimization of planar refracting microlenses by Ag–Na ion-exchange techniques

We report the fabrication of planar microlenses with numerical apertures (N.A.s) of 0.2 by field-assisted Ag-Na ion exchange in glass. To measure the N.A. of microlenses, different definitions can be used. We discuss the issue of measuring the N.A. and suggest an additional definition based on diffraction-limited performance. According to a simple model, the N.A. of a spherical lens is limited by the maximum index difference. Owing to this model, the N.A. for Ag-Na ion exchange is limited to a value of ~0.1. From measurements of microlenses, fabricated by field-assisted ion exchange, we obtained N.A.s as high as 0.2, providing for diffraction-limited performance within the whole aperture.

Homogenous concept for the coupling of active and passive single-mode devices by utilizing planar gradient-index lenses and silicon-V grooves.

A new concept for a common interface between passive and active single-mode devices is proposed. The submicrometer alignment accuracy necessary for efficient coupling of single-mode devices is extended to the range of some 10 mum by beam expansion with planar gradient-index microlenses; the increased angular sensitivity is satisfied by the use of planar surfaces. The imaging system is used off axis, resulting in a suppression of backreflections in the range >60 dB. Of many possible variations of components (fibers, waveguides, optoelectronic integrated circuits, edge-emitting lasers, vertical-cavity surface-emitting lasers, photodiodes), the coupling of fibers and waveguides is examined in detail. Expected coupling efficiency and sensitivity to lateral misalignment are calculated by use of a modified beam-propagation method. In this way, the overall performance of the connector can be compared with existing connector concepts, and the feasibility of the concept is proven. Experimental results for the fiber-fiber connector are given.

Hemispherical-rod microlens as a variant fractional Fourier transformer

It is shown that a hemispherical-rod microlens can act as a fractional Fourier transform device with a continuously varying degree of fractionality. It is believed to be the first proposed device to perform such a task; its most immediate applications include optical tomography.

H-ROD: A new and versatile microoptical component

We present the semi cylindrical H-ROD elements as a new and versatile microoptical component. With field assisted ion exchange semi cylindical index distributions can be integrated in a planar glass substrate. By combination of two identical elements an integrated GRIN ROD lens can be realized. Furthermore a smi cylindrical element can also be utilized for imaging by using internal reflection (H-ROD). Aside of this the H-ROD provides direct access to the filter plane, which offers a wide range of applications.

Design and fabrication of arbitrary, non-separable continuous phase elements

We proposed a method for designing arbitrary two -dimensional continuous phase elements. With this method, phase anomalies due to amplitude zeros can be avoided completely. Fabricated examples using direct write in resist and also ion exchange are presented.

Phase-space measurements of micro-optical objects

The phase-space measurement of micro-optical objects with submillimeter dimensions is reported for the first time to our knowledge. The experimental data were compared with simulated results from interferometric measurements and were found to be in good agreement.