Numerical Analysis of Micro-Lens Array to the Mid-IR Range

New interferometric IR techniques have recently been developed to allow Sun-Jupiter-like detections in deep space. These techniques demand a high angular resolution, a high sensitivity towards signal detection buried in noise, and a well-defined bandwidth of spectral resolution. Micro-lens arrangements have helped increase the use of these parameters for IR detectors. In this paper we present a finite element method (FEM)-based simulation of a typical micro-lens array, to be used in mid-IR cameras, where the aperture geometry and radius of curvature are varied for design optimization. Moreover, we show the spot and optical aberrations produced by two types of geometrical arrangements. This procedure could be helpful in improving the IR detector signal in the exoplanets exploration, in systems placed outside of the earth’s atmosphere.

Study of the Transcription Effects of Pressing Dies with Ultrasonic Polishing on Glass Molding

The micro lens array (MLA) has played an important role in optical systems for the past few years, and the precision of pressing dies has dominated the quality of MLAs in glass molding. Few studies have covered the transcription effects on surface roughness of pressing dies for this technology. Therefore, this research utilized pressing dies to produce a sine-wave lens array on glass molding, to transform the Gauss-distributed spotlight into a uniform straight one and then characterize the transcription effects of these lenses. Pressing dies with a sine-wave shape were firstly cut by wire electrical discharge machining (WEDM), and then ultrasonic polishing using diamond abrasives was applied to finish the sine-wave surface with an original roughness of 0.2 μm Ra. Next, the sine-wave lens arrays were pressed by glass molding at the appropriate pressure and temperature, before evaluating the transcription effects of transforming the Gauss-distributed spotlight into a uniform straight one. The result showed that the sine-wave lens array stuck easily to the pressing die and then ruptured during glass molding due to the poor surface roughness of pressing tool. However, the diamond abrasive with appropriate sizes could establish good surface roughness on pressing dies via ultrasonic polishing, and the pressing die with a low surface roughness of 0.08 μm Ra was able to successfully perform MLA in the glass molding. However, only pressing dies with a surface roughness smaller than 0.023 μm Ra could produce precision glass lenses to transform the Gauss-distributed spotlight into a uniform straight one.

Development of computer-controlled atmospheric pressure plasma structuring for 2D/3D pattern on fused silica

Fused silica with structured and continuous patterns is increasingly demanded in advanced imaging and illumination fields because of its excellent properties and functional performance. Atmospheric pressure plasma, based on pure chemical etching under atmospheric pressure, is developed as a promising fabrication technique for fused silica due to its deterministic high material removal rate, controllable removal imprint and no mechanical load. The stable and controllable Gaussian-shape removal function makes computer-controlled plasma tool potential to generate complex structures with high accuracy, efficiency and flexibility. In the paper, computer-controlled atmospheric pressure plasma structuring (APPS) is proposed to fabricate 2D/3D patterns on fused silica optics. The capacitively coupled APPS system with a double-layer plasma torch and its discharge characteristics are firstly developed. By means of multi-physics simulation and process investigation, the stable and controllable Gaussian-shape removal function can be achieved. Two different structuring modes, including discrete and continuous APPS, are explored for 2D/3D patterns. A series of structuring experiments show that different kinds of 2D patterns (including square lens array, hexagon lens array and groove array) as well as complex 3D phase plate patterns have been successfully fabricated, which validates the effectiveness of the proposed APPS of 2D/3D patterns on fused silica optics.

Direct laser writing method for micro-lens fabrication on the fiber facet

We present a way for micro-lens and micro-lens array fabrication on the fiber facet by direct laser writing (DLW) method. The proposed setup for DLW printing on the fiber facet can protect objective lens and makes it possible to safely using a wide range of resists. Microlens fabricated on the single-mode optical fiber facet is demonstrated. Based on lens-on-fiber system we proposed concept of the micro-lenses on baseplate array printed on the multi-core fiber, where each lens is rigidly aligned with the core. One of the possible micro-lenses on the baseplate array is presented and its optical properties such as focal spot size and resolution are investigated. The possible application of the proposed micro-lens array is complex optical elements, such as micro-objectives with optimized optical design. Moreover, suggested freeform lens array can find application in high-accuracy wavefront sensing.