Compact snapshot real-time imaging spectrometer

The described spectral imaging system, referred to as a Snapshot Hyperspectral Imaging Fourier Transform (SHIFT) spectrometer, is capable of acquiring spectral image data of a scene in a single integration of a camera, is ultra-compact, inexpensive (commercial off-the-shelf), has no moving parts, and can produce datacubes (x, y, λ) in real time. Based on the multiple-image FTS originally developed by A. Hirai [1], the presented device offers significant advantages over his original implementation. Namely, its birefringent nature results in a common-path interferometer which makes the spectrometer insensitive to vibration. Furthermore, it enables the potential of making the instrument ultra-compact, thereby improving the portability of the sensor. By combining a birefringent interferometer with a lenslet array, the entire spectrometer consumes approximately 15×15×20 mm3, excluding the imaging camera. The theory of the birefringent FTS is provided, followed by details of its specific embodiment and a laboratory proof of concept of the sensor. Post-processing is currently accomplished in Matlab, but progress is underway in developing real-time reconstruction capabilities with software programmed on a graphics processing unit (GPU). It is anticipated that processing of >30 datacubes per second can be achieved with modest GPU hardware, with spatial/spectral data of or exceeding 256×256 spatial resolution elements and 60 spectral bands over the visible (400-800 nm) spectrum. Data were collected outdoors, demonstrating the sensor's ability to resolve spectral signatures in standard outdoor lighting and environmental conditions as well as retinal imaging.