Mr. Matthias Rungenhagen Profile

Matthias Rungenhagen

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Proceedings Article | 26 September 2009 Paper

Monostatic Ladar demonstrator with micro-optical bidirectional beam control

Matthias Rungenhagen, Manuel Kunz, Eugen Romasew, Hans Dieter Tholl

Proceedings Volume 7483, 74830Q (2009) https://doi.org/10.1117/12.829132

KEYWORDS: Diffraction, LIDAR, Beam controllers, Diffraction gratings, Sensors, Wavefronts, Beam steering, Receivers, Signal detection, Telescopes

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In recent times the importance of Ladar systems for military applications increases rapidly. Prevalent application in this area is 3D imaging. Conventional 3D scanning systems usually employ mirror-based mechanisms. Often these suffer from bulky architecture and a fixed scanning pattern. In this paper we describe an experimental monostatic Ladar setup with micro-optical bidirectional beam control. This system offers certain advantages like random beam pointing and a compact design due to transmissive optical elements with combined emitter and receiver channel. Our publication depicts the setup of a Ladar demonstrator with micro-optical beam steering at lab-level. The range finding system is based on time-of-flight principle at near infrared wavelength. Due to monostatic configuration a single detector is used for start and stop pulse generation. The beam steering is accomplished with decentred micro-lens arrays, which are driven by a precision alignment system. The micro-optical elements act as entrance and exit aperture simultaneously. The results of laboratory characterization measurements and data evaluations complete our overview of the accomplished work.

Proceedings Article | 2 October 2008 Paper

Continuous laser beam steering with micro-optical arrays: experimental results

J. Bourderionnet, M. Rungenhagen, D. Dolfi, H. Tholl

Proceedings Volume 7113, 71130Z (2008) https://doi.org/10.1117/12.800120

KEYWORDS: Microlens array, Beam steering, Phased arrays, Phased array optics, Diffraction, Phase shifts, Ceramics, Modulators, Electro optics, Scanners

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High resolution inertialess beam steering systems are required for numerous applications, including laser radar, multitarget designation or active imaging. We present a 1.55μm operating continuous laser beam steering system based on the cascading of an electro-optic PMN-PT ceramic optical phased array (OPA) and of two piezoactuated microlenses arrays (MLA). The function of the single devices and the principle and the operation of the combination of both are explained. Then we describe the experimental setup which was realized and outline the test results. The MLA large angle scanner consists of two MLAs, one of which can be moved with respect to the other by piezodrivers. This setup acts as a blazed grating and thus results in a discrete beam steering. Each steering position corresponds to a multiple of 2pi phase shift between adjacent beamlets. In order to get a continuous steering, we combined the MLA scanner with an electro-optic ceramic OPA. The OPA generates the piston distribution that compensates the phase difference between adjacent beamlets of the MLAs and reconstructs a continuous wavefront. The PMN-PT OPA consists in 64 phase modulators with 210µm period and a 0.5 fill factor. The maximum required voltage corresponding to the 2π phase shift is 150 Volts at 1.55µm. The OPA is imaged on the 105μm period MLAs with a 0.5-magnification telescope. The two MLAs are in a Keplerian telescope with field lenses arrangement. The steering performances of the MLAs alone are +/-12° scan angle with 28 discrete positions. Using the combined architecture, we were able to resolve 64 angular directions between each of these 28 positions. We thus experimentally obtained a continuous steering at 1.55μm over +/-12° with an angular resolution of 0.24mrad, i.e. 1800 resolved directions, with only 64+1 control voltages.

Proceedings Article | 10 October 2007 Paper

Adaptive laser beam steering with micro-optical arrays

Matthias Rungenhagen, Hans Dieter Tholl

Proceedings Volume 6738, 67380G (2007) https://doi.org/10.1117/12.737290

KEYWORDS: Wavefronts, Beam steering, Phase shifting, Diffraction, Microlens array, Diffraction gratings, Spatial light modulators, Liquid crystals, Phase shifts, Near infrared

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Micro-lens arrays of large formats are well suited for agile laser beam steering. State-of-the-art beam steering devices comprise three microlens arrays which are distributed among two cascaded substrates. The substrates are decentered laterally by piezoelectric transducers. This arrangement acts like a blazed grating structure with variable blaze angle. Beam steering with blazed grating micro-lens arrays suffers from non-uniformity of the optical parameters across the aperture which leads to a reduction of the spatial coherence between the interfering beamlets and an increase in the beam divergence. This disadvantage can be resolved by combining the blazed grating beam steerer with an array of phase shifting elements. If the number of phase shifting elements (pixels) is sufficiently large, several pixels cover one subaperture of the blazed grating and phase piston as well as higher wavefront errors (tip/tilt, defocus) may be corrected. In the VIS and NIR spectral range large format liquid crystal spatial light modulators (SLM) are available for adaptive correction of the wavefront of each subaperture of the blazed grating beam steerer. Spatial light modulators based on micro-mirrors or electro-optical ceramics which cover a broader spectral range up to the MWIR are under development. This paper outlines the concept of adaptive compensation of the wavefront error of each subaperture in a blazed grating beam steerer. The combination of micro-lens arrays with large format spatial light modulators for the NIR and the MWIR spectral ranges will be described. Investigations and measurements at component level (micro-lens arrays and a commercially available liquid-crystal-on-silicon spatial light modulator) at 1.5 μm will be presented in order to support the theory.

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