Miniaturized UV/VIS spectrometer made by MOEMS technology

Abstract

In recent years, many compact spectrometers for purposes such as environmental monitoring and process quality control in industrial production have been realized. However, most of them still employ spectrometer mounts with focal lengths in the range of several cm. Therefore, their size is about that of a palm which is too large for OEM-use in handily sized optical sensor equipment. Accordingly, we have developed a thumb-sized, truly miniaturized spectrometer for the spectral range 340nm to 750nm, which is particularly suited for use inside hand-held or portable color management sensor equipment. The spectrometer is using a self-imaging, aberration-corrected concave grating with very short focal length and a blazed grating profile for high diffraction efficiency. The grating is replicated onto the top of a convex glass lens using nano-imprint technology. Opposite to the concave grating, a dedicated C-MOS image sensor with an in-built on-chip slit is placed. The slit with a width of 75μm is formed into the silicon chip using MEMS technology. Due to this advanced technology, the distance between the sensor area and the slit is as small as 1mm. Based on this high level of integration, the number of optical components could be kept to a minimum and the distance between the concave grating and C-MOS image sensor is about 8.5mm only. In summary, we have realized a well-performing miniaturized spectrometer with an extremely small package size of 28mm - 17mm - 13mm and a weight of only about 9g, which is highly suited for integration into optical sensing equipment.