Multifunctional axilenses for multi-color IR imaging devices and spectroscopy

Conventional diffractive lenses are based on devices such as Fresnel Zone Plates (FZPs) that provide focusing of a specific radiation wavelength over a fixed focusing plane. Recently, diffractive axilens components have been demonstrated that additionally provide the capability to focus light over a large depth of field taking advantage of radially-dependent focusing. However, these devices do not provide spectral selectivity and control of the spatial location of the focal spots. Spectral selectivity is a highly desirable feature for imaging and spectroscopy applications that is currently obtained by developing expensive multi-band absorbing materials or by using specialized external optics that limit the size and integration of multi-color devices. The invention solves these fundamental problem by enabling a compact, high-efficiency, integrated solution that combines diffractive axilenses and wavelength-selective grating capabilities in a single optical device. This is achieved by spatially modulating the optical phase according to periodic or aperiodic (chirp) functions that enable focused beam steering in direct proportion to the wavelength of the incoming radiation. This can be achieved using a number of phase modulation profiles that provide unprecedented control in the spatial-spectral characteristics of focused light spots on agiven plane. The inventors have quantitatively analyzed pixel cross talks, wavelength spectra and point spread functions (PSFs) demonstrating large bandwidths in the IR region (7-10microns wavelength) with diffraction-limited focal spots. Proof-of-concept devices were designed using both scalar diffraction theory and full-vector 3D Finite Element simulations and fabricated using a specialized 3-mask lithographic process. The proposed approach works with any transparent materials and enables the focusing of radiation with different wavelengths on different spatial locations on the same detection plane without defocusing effects (see presentation slides). Direct fabrication of the devices on the back substrate layer of a pixel detector array can focus radiation of different colors through the substrate and on different pixels on the photodector plane thus enabling multi-spectral capabilities. Misty Farrell 617-358-3795

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