Hyperspectral Imaging Camera using Wavefront

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  • Hyperspectral Imaging Camera using Wavefront Division Interference (WDI) ERAN BAHALUL,1 ASAF BRONFELD,1 SHLOMI EPSHTEIN,2 YORAM SABAN,2 AVI KARSENTY,1 YOEL ARIELI 1,* 1Jerusalem College of Technology, Havaad Haleumi 21, Jerusalem 9116001, Israel 2Ben-Gurion University of the Negev, Beer Sheva 8410501, Israel *Corresponding author: arieli.yoel@gmail.com

    Received XX Month XXXX; revised XX Month, XXXX; accepted XX Month XXXX; posted XX Month XXXX (Doc. ID XXXXX); published XX Month XXXX

    A new approach for performing hyperspectral imaging is introduced. The hyperspectral imaging is based on Fourier transform spectroscopy, where the interference is performed by wavefront division interference rather than amplitude division interference. A variable phase delay between two parts of the wavefront emanating from each point of an object is created by a spatial light modulator (SLM) to obtain variable interference patterns. The SLM is placed in the exit pupil of an imaging system, thus enabling conversion of a general imaging optical system into an imaging hyperspectral optical system. The physical basis of the new approach is introduced, and an optical apparatus is built.

    OCIS codes: (140.3490) Lasers, distributed-feedback; (060.2420) Fibers, polarization-maintaining; (060.3735) Fiber Bragg gratings; (060.2370) Fiber optics sensors.

    http://dx.doi.org/10.1364/OL.99.099999

    A multispectral or hyperspectral imaging system images an object and provides the emanating light spectrum from each pixel of the object. The different wavelengths emitted or reflected from the object characterize the substance of the examined object, and hence, the different parts that compose the object can be identified. Multispectral or hyperspectral imaging provides a 3D data cube of information regarding the object by combining the two-dimensional image of the object with its spectral data. Hyperspectral imaging is used in several domains of applications, such as medical science [1] agriculture [2], defense [3], astronomy and space surveillance [4], detection [5], geology [6], and earth observation [7]. Moreover, due to the continuously growing importance of hyperspectral imaging, complete reference books have already been published [8], as well as comparative international reports [9]. Because hyperspectral imaging provides a 3D data cube of information, despite the imaging sensor being inherently two-dimensional, a scanning operation is usually adopted to construct the 3D spectral image data cube. Many methods have been developed to fulfill this requirement. The early methods include spectral scanning ( scan) using an optical filter wheel [10], push broom scanning along one spatial axis (y axis) of a line spectral image (x image), and

    interferometer spectral imaging (such as mechanical scanning Fourier transform (FT) spectrometry [11] and static FT). There are some other methods using dynamic tunable filters, such as liquid crystal tunable filter [12] and acousto-optic tunable filter (AOTF) [13], which do not involve mechanical scanning motion. Those scanning-based approaches have a relatively long 3D image acquisition time, making them only suitable for imaging relatively stable stationary objects. For applications on time-varying objects or moving scenes, approaches for acquiring spectral image data in a single image snapshot have been reported, such as computed-tomography imaging spectrometer (CTIS) [14] and holographic spectral imaging system (HSIS) [15]. In this article, we present a new approach for performing hyperspectral imaging [16]. The hyperspectral imaging is based on Fourier transform spectroscopy, where the interference is performed by wavefront division interference (WDI) rather than amplitude division interference (ADI). This approach enables the conversion of a general imaging optical system into an imaging hyperspectral optical system by introducing a thin SLM in any plane in the imaging system. This addition of the SLM only slightly diminishes the optical performance of the imaging system and thus does not require a special optical design. The basic hyperspectral imaging optical system is shown in Fig. 1. The light from each point of the object is imaged to the image plane to form the image. On its path, the light's wavefront originated from each point is divided by the SLM into two parts, with one part of the wavefront being delayed relative to the other part. The relative phase delay between the two parts is given by:

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    where is the wavelength and is the optical path difference (OPD) between the two parts of the wavefront. When the two parts of the wavefront intersect to obtain the imaged objects point, they interfere according to the relative phase delay between them. As the OPD between the two wavefront's parts is increased progressively, each wavelength in the objects light oscillates between destructive and constructive interference states. The integral intensity of all wavelengths detected by the detector as a function of the OPD performs the interferogram at a certain object's point.

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