Martin Amberg

Integrated free-space optical interconnect fabricated in planar optics using chirped microlens arrays.

We present a compact design for an integrated interconnect based on a hybrid imaging setup combining microchannel and conventional imaging. Within this setup the conventional imaging is performed by an aluminum-coated spherical lens. The aberrations introduced by this spherical mirror to the channels of the interconnect can be compensated by channel-wise adapted microlenses located at the in- and output interfaces. These microlenses are used for collimating or refocusing the beams, respectively. Within this paper we present the design of the microlens array with individually shaped lenses referred to as chirped mircolens array (cMLA) based on numerical optimization and the use of fitting functions. Further on we focus on the fabrication of the chirped microlens arrays by laser lithography and first experimental results of coupling efficiencies of singlemode as well as multimode fibers for the realized prototypes.

Tuneable planar integrated optical systems

Planar integrated free-space optical systems are well suited for a variety of applications, such as optical interconnects and security devices. Here, we demonstrate dynamic functionality of such microoptical systems by the integration of adaptive liquid-crystal-devices.

Fabrication technologies for chirped refractive microlens arrays

Conventional microlens arrays consist of a repetitive arrangement of a unit cell on a fixed pitch. In a chirped array, the inflexibility of a regular structure has been overcome. Here, the array consists of individually shaped lenses which are defined by a parametric description of the cells optical function. We propose different fabrication methods for chirped microlens arrays and present experimentally obtained data. Reflow of photoresist is an established technology for the fabrication of microlenses with superior optical performance. For the generation of a chirped microlens array the photolithographic mask for patterning the resist to be melted has to be chirped. We present an algorithm for mask generation with an example of an ultra-thin camera objective. Inherent to the reflow process stringent limitations to viable surfaces apply. For achieving more arbitrary surfaces, laser lithography and also 2-photon polymerization are employed. In both methods the structures are decomposed into pixels. In laser lithography the local height is converted into an intensity value for the exposure. This variable dose writing locally changes the solubility of the resist in the development process leading to the required surface profile. We propose a writing scheme enabling structure heights of several ten microns with sufficient height discretization. 2-photon polymerization is a rapid prototyping method. Here, a small volume of a UV-curing organic-inorganic co-polymer is hardened in the tight focus of the writing beam. The volume pixel to be exposed is addressed by piezoelectric translation stages. Experimentally obtained structures and performed tests of the optical quality are presented.

Ultraprecision micromilling of freeform optical elements for planar microoptical systems integration

Planar microoptical systems integration is a powerful approach for the fabrication of optical systems and has been demonstrated for a large variety of applications. The folded optical axis in combination with planar fabrication technologies enables highly integrated and rugged optical systems. In this geometry, however, specific care is necessary to avoid aberrations resulting from the oblique optical axis. A purely diffractive implementation of these systems generally leads to an efficiency of only a few percent. Combining classical refractive optics with diffractive correction elements increases the overall efficiency. However, the purely refractive implementation suffered from the lack of fabrication technologies for freeform microoptical elements. We present the results of the first fabrication of freeform refractive correction elements combined with standard off-the-shelf refractive microlenses to form a completely refractive planar integrated optical system using ultraprecision micromilling. Experiments confirm the increased optical performance of the systems by integrating two micromachined reflective correction elements. Both elements have a size of 2.4 x 2.4 mm2 with a peak-to-valley surface profile depth of 2.6 μm. They are fabricated with an average roughness height < 40 nm and a surface tolerance < 400 nm.

Single-step replication of a highly integrated PDMS optofluidic analysis system

Micromilling is a promising technology for the fabrication of surface profiles with optical quality. We present a highly integrated optofluidic system made of polydimethylsiloxane (PDMS). The system is replicated in a single-step process from a micromilled polymethyl methacrylate master mold. It already includes the reservoirs, the channel system, as well as the optical interconnect surfaces for high numerical aperture objectives. We demonstrate the potential of this approach by laser-based three-dimensional optical manipulation within the replicated system. To our knowledge, this is the first time that a PDMS membrane is used as a well-defined channel wall for an optical trapping setup.

Integrated freespace optical fluorescence detector for micro fluidic applications

Fluorescence detectors are applied for various applications in biomedical research, e.g. for pH-sensoring or single-cell detection. Free space optical systems offer the advantage of compact and efficiently integrated systems with benefits in the terms of systems alignment and optical functionality. On the other hand, due to the lab-on-a-chip character many fluidic systems, such as segmented flow systems, are very compact and thus compatible with integrated optical systems. We discuss the potential of the integration of the segmented flow approach in complex free space optical microsystems. The design and realization of a highly integrated fluorescence detector is demonstrated. The system is fabricated by ultra precision micromilling which allows one to monolithically integrate freeform optical elements for optimized optical performance.

Integrated Micro-Opto-Fluidic Systems for Optical Manipulation of Cell Cultures

Microfluidic systems have a large variety of applications in biomedicine and life sciences. The goal of the reseach is to develop integrated optofluidic microsystems which combine the microfluidic channels and parts of the optical functionality.

Tuneable Planar Integrated Optical Systems

Planar integrated free-space optical systems are well suited for a variety of applications, such as optical interconnects and security devices. Here, we demonstrate for the first time dynamic functionality of such microoptical systems by the integration of adaptive liquid-crystal-devices.

Design considerations for integrated microoptical systems combining refractive and diffractive optical components

Planar integrated microoptical systems have been demonstrated for a variety of applications such as optical interconnects, sensing and security applications. Diffractive optical elements provide the necessary design freedom to optimize the optical performance of such systems along the folded optical axis. For enhanced optical efficiency it is necessary to combine diffractive and refractive elements within such systems. Hereby the refractive components provide most of the optical power while the diffractive elements are used as correction elements for optimized system performance. The integration of refractive components has significant consequences on the geometry of planar integrated optical systems as well as on the optical systems design. Based on this approach we present various designs for efficient planar-optical (phase-contrast) imaging systems. We compare various possibilities for the simulation of diffractive and holographic optical components and their integration in the design of planar microoptical systems. To this end we apply commercial design software (e.g. ZemaxTM, ASAPTM) as well as self programmed tools.