Miniaturized fiber-coupled  optical spectrometers with temperature compensation based on injection moulding

Frank Gindele; Christian Novotny

doi:10.1117/12.471983

15 April 2003 Miniaturized fiber-coupled optical spectrometers with temperature compensation based on injection moulding

Frank Gindele, Christian Novotny

Author Affiliations +

Proceedings Volume 4943, Fiber-based Component Fabrication, Testing, and Connectorization; (2003) https://doi.org/10.1117/12.471983
Event: Photonics Fabrication Europe, 2002, Bruges, Belgium

Abstract

A miniaturized optical spectrometer module has been developed and realized in polymer by injection moulding. The spectrometer is designed for the visible (VIS, 380 nm-750 nm) and near infrared spectral (NIR, 680 nm-1100 nm) range. The assembled module has a size of a match box with a spectral resolution (Rayleigh criterion) of <7 nm /10 nm for the visible and <7 nm/8 nm for the near infrared spectrum depending on the pixel width of the used detectors. The stray light has been reduced well below 0.5 % for the VIS-module (VIS: filter OG550, measured at 500 nm) and NIR-module (NIR: filter RG850, measured at 790 nm). To avoid a wavelength shift caused by a thermal expansion of the system, a passive temperature compensation unit is designed. As a result of this the temperature shift between -40 °C and +70 °C can be reduced to <0.03 nm/K. To guarantee a flexible application of the spectrometer the measurement signal is coupled into the spectrometer by a fibre to free-space coupling unit with a 90° beam deflection. In order to use injection moulded components for optical sensors, mould inserts with a high optical quality are required. A toroidal optical mirror with an average surface roughness of Ra<20 nm and a radial shape accuracy as high as 0.2 % (0.1 mm) and optical gratings for the visible and near infrared spectral range with a planarity of 4 μm/cm and an absolute diffraction efficiency as high as 80 % can be fabricated. LIGA-technology, ultra-precision machining and electro-forming processes are applied. All optical elements have been replicated in polycarbonate (PC) with comparable characteristics. The spectrometer set up is based on a modular concept. This enables a high position accuracy of the elements to each other (few tens of μm) and a variation of specification (wavelength and resolution).

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Frank Gindele and Christian Novotny "Miniaturized fiber-coupled optical spectrometers with temperature compensation based on injection moulding", Proc. SPIE 4943, Fiber-based Component Fabrication, Testing, and Connectorization, (15 April 2003); https://doi.org/10.1117/12.471983

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