An imaging spectrometer employing tunable hyperchromatic microlenses

We present the design, fabrication and characterization of hydraulically-tunable hyperchromatic lenses for two-dimensional (2D) spectrally-resolved spectral imaging. These hyperchromatic lenses, consisting of a positive diffractive lens and a tunable concave lens, are designed to have a large longitudinal chromatic dispersion and thus axially separate the images of different wavelengths from each other. 2D objects of different wavelengths can consequently be imaged using the tunability of the lens system. Two hyperchromatic lens concepts are demonstrated and their spectral characteristics as well as their functionality in spectral imaging applications are shown. Lenses with an extremely large chromatic dispersion are used in a hyperspectral imager that does not use mechanical scanning. Hans Zappe and co-workers from the University of Freiburg and Technische Universität Ilmenau in Germany designed and fabricated hybrid ‘hyperchromatic’ lenses consisting of a diffractive Fresnel lens and a tunable microfluidic lens. This combination provides a large tunable longitudinal chromatic dispersion that can be used to image a single wavelength onto an imaging plane. By tuning the dispersion, a series of images for several different wavelengths can be captured across the 450−900 nanometre spectral range and compiled into a hyperspectral image without moving any optical parts. The tuning is accomplished by varying the fluidic pressure inside the microfluidic lens and hence the surface curvature of the lens.