Current medical imaging technologies allow visualization of tissue anatomy in the human body at resolutions ranging from 100 micrometers to 1 millimeter. These technologies are generally not sensitive enough to detect early-stage tissue abnormalities associated with diseases such as cancer and atherosclerosis, which require micrometer-scale resolution. Here, optical coherence tomography was adapted to allow high-speed visualization of tissue in a living animal with a catheter-endoscope 1 millimeter in diameter. This method, referred to as "optical biopsy," was used to obtain cross-sectional images of the rabbit gastrointestinal and respiratory tracts at 10-micrometer resolution.

In Vivo Endoscopic Optical Biopsy with Optical Coherence Tomography

The diffraction tomography theorem is adapted to one-dimensional length measurement. The resulting spectral interferometry technique is described and the first length measurements using this technique on a model eye and on a human eye in vivo are presented.

Measurement of intraocular distances by backscattering spectral interferometry

Photoplethysmography and its application in clinical physiological measurement

Femtosecond two-photon direct laser writing is used to create 100-µm-scale high-performance multi-lens objectives.

Two-photon direct laser writing of ultracompact multi-lens objectives

McDonaldʼs Blood Flow in Arteries

We have developed a self-contained, liquid tunable microlens based on polyacrylate membranes integrated with compact on-chip thermo-pneumatic actuation fabricated using full-wafer processing. Silicone oil is used as the optical liquid, which is pushed or pulled into the lens cavity via an extended microfluidic channel structure without any pumps, valves or other mechanical means. The heat load generated by the thermal actuator is physically isolated from the lens chamber. The back focal length may be tuned from infinity to 4 mm with a maximum power consumption of 300 mW. The principal application is fine tuning of the back focal length, for which tuning time constants as small as 100 ms are suitable. Scientists in Germany have designed a fluid-based microlens with a widely tunable focal length. Developed by Wei Zhang and co-workers at the University of Freiburg, the lens consists of a circular fluidic chamber filled with silicone oil and sandwiched between a glass substrate and a flexible polyacrylate membrane. The fluid chamber is connected to an air chamber via a microfluidic channel and the entire structure is housed in a protective silicon micromachined frame. The lens’ focal length is tuned between values of infinity and 4 mm by applying a voltage to a heating element in the air chamber. Expansion of the heated air forces more oil into the fluid chamber, causing the membrane to deform and thus the shape of the lens to change.

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Wafer-scale fabricated thermo-pneumatically tunable microlenses

In this paper, the metrology and fabrication concepts at Carl Zeiss will be reviewed. The present status in the fabrication of specific EUVL mirrors will be reported as well.

Mirror substrates for EUV lithography: progress in metrology and optical fabrication technology

An integrated tunable microlens, whose focal length may be varied over a range of 3 to 15 mm with total power consumption below 250 mW, is presented. Using thermo-pneumatic actuation, this adaptive optical microsystem is completely integrated and requires no external pressure controllers for operation. The lens system consists of a liquid-filled cavity bounded by a distensible polydimethyl-siloxane membrane and a separate thermal cavity with actuation and sensing elements, all fabricated using silicon, glass and polymers. Due to the physical separation of thermal actuators and lens body, temperature gradients in the lens optical aperture were below 4°C in the vertical and 0.2°C in the lateral directions. Optical characterization showed that the cutoff frequency of the optical transfer function, using a reference contrast of 0.2, varied from 30 lines/mm to 65 lines/mm over the tuning range, and a change in the numerical aperture from 0.067 to 0.333. Stable control of the focal length over a long time period using a simple electronic stabilization circuit was demonstrated.

Completely integrated, thermo-pneumatically tunable microlens

Employing Bessel beams in imaging takes advantage of their self-reconstructing properties to achieve small focal points while maintaining a large depth of focus. Bessel beams are efficiently generated using axicons, and their utility in scanning imaging systems, such as optical coherence tomography (OCT), has been demonstrated. As these systems are miniaturized to allow, for example, endoscopic implementations, micro-axicons are required to assure the maintenance of a large depth of focus. We demonstrate here the design, fabrication, and application of molded micro-axicons for use in silicon-based micro-optical benches. It is shown that arrangements of multiple convex and concave axicons may be implemented to optimize the depth of focus in a miniaturized OCT system, using a telescopic optical arrangement of considerably shorter optical system length than that achievable with classical micro-optics.

Highly compact imaging using Bessel beams generated by ultraminiaturized multi-micro-axicon systems.

In a facet mirror with a number of mirror facets, wherein the mirror facets are provided with reflecting surfaces, the mirror facets are mounted jointly in a basic body via bearing devices. The mirror facets comprise mirror bodies contacting at the periphery with the bearing devices via a surface, line or point contact. The preferred field of use of the facet mirrors is a projection objective of a projection exposure machine in microlithography for fabricating semiconductor elements.

Andreas Seifert

Papers

Wafer-scale fabricated thermo-pneumatically tunable microlenses

Mirror substrates for EUV lithography: progress in metrology and optical fabrication technology

Completely integrated, thermo-pneumatically tunable microlens

Highly compact imaging using Bessel beams generated by ultraminiaturized multi-micro-axicon systems.

Facet mirror having a number of mirror facets