Jan Draheim

Optical characterization of adaptive fluidic silicone-membrane lenses

We present an extended optical characterization of an adaptive microfluidic silicone-membrane lens at a wavelength of 633 nm, respectively 660 nm. Two different membrane variations; one with a homogeneous membrane thickness, and one with a shaped cross section, have been realized. This paper includes the theoretical predictions of the optical performance via FEM simulation and ray tracing, and a subsequent orientation dependent experimental analysis of the lens quality which is measured with an MTF setup and a Mach-Zehnder interferometer. The influence of the fabrication process on the optical performance is also characterized by the membrane deformation in the non-deflected state. The lens with the homogeneous membrane of 5 mm in diameter and an aperture of 2.5 mm indicates an almost orientation independent image quality of 117 linepairs/mm at a contrast of 50%. The shaped membrane lenses show a minimum wave front error of WFE(RMS) = 24 nm, and the lenses with a planar membrane of WFE(RMS) = 31 nm at an aperture of 2.125 mm.

Variable aperture stop based on the design of a single chamber silicone membrane lens with integrated actuation

In this Letter we report on the fabrication and testing of an extremely thin variable aperture stop based on the design of a single chamber adaptive membrane lens with integrated actuation. The aperture consists of a ring-shaped piezoelectric bending actuator with an elastic silicone membrane in the center. The formed cavity is filled with a nontransparent fluid and sealed with a glass platelet. In a voltage range up to 80 V, an opening of the aperture of 4.55 mm in diameter is obtained. The transmission in comparison to a standard mechanical aperture stop is maximum 6% lower.

Fabrication of a fluidic membrane lens system

We present the fabrication process of a fluidic membrane lens system with an integrated piezoelectric pumping actuator. The optical unit and the pumping unit are fabricated through casting using a hot embossing machine. Two different systems, one with a homogeneous membrane thickness, and one with an inhomogeneous membrane thickness distribution, are manufactured. The influence of the volume shrinkage of the silicone during curing on the membrane shape and on the focal length is analyzed. The assembled system achieves a focal length between +52.4 mm and −70.9 mm at a piezovoltage of ±40 V. The full-scale response time of the system is below 24 ms.

Single chamber adaptive membrane lens with integrated actuation

In this work we introduce an extremely thin single chamber adaptive fluidic membrane lens with an integrated piezoelectric bending actuator. The height of the system is 1.76 mm and the membrane diameter 10 mm. The lens consists of a ring shaped piezo bending actuator with an optical clear silicone membrane in the center. A refractive power range of 11.3 dpt is achieved at a piezo voltage between ±40 V. The system shows a maximum resolution of 189 lp/mm measured at 50 % contrast and a focal length of 200 mm.

Fluidic zoom lens system using two single chamber adaptive lenses with integrated actuation

We report on a thin zoom lens system using a compact design and an effective fabrication process for flat adaptive fluidic single chamber membrane lenses made of PDMS. The lenses consist of a ring shaped piezo bending actuator with a transparent silicone membrane in the center. A zoom ratio of Z = 1.42 is obtained using two lenses with a membrane diameter of 4 mm. The overall system thickness is only 4.4 mm.

Closed-loop pressure control of an adaptive single chamber membrane lens with integrated actuation

We introduce a closed-loop pressure control of a single chamber adaptive fluidic membrane lens with an integrated piezoelectric bending actuator. For this purpose a pressure sensor is integrated into the lens and allows for a measurement of the chamber pressure as a function of the refractive power. The linear relation between pressure and refractive power allows to eliminate the typical hysteresis effects of piezo actuators.

Particle swarm optimization on a new parametric model of a deformable membrane lens

The particle swarm optimization (PSO) method is applied to a new parametric lens model based on Zernike polynomials as basis functions. A fluid membrane lens is optimized to yield a particular focal length. Measurements on a manufactured prototype verify the computed results.

An adaptive objective for optical motion correction in MRI

We present an adaptive membrane lens that is compatible with a magnetic resonance (MR) imaging system, as a part of an objective for in-bore optical motion tracking and correction. Compatibility tests with the high magnetic fields of a 3 T scanner and the shielding of the adaptive lens are discussed. For tracking of a marker an adaptive wide-angle objective has been designed and characterised. The measured mean distortions of the objective are between −2.05 and −2.6 %. The tracking system was verified in a MR scanner model.