Methods and apparatus for spectral imaging

#Spectral imaging combines both imaging and spectroscopy. In general, imaging technology can provide intensity information at points in an image plane I(x, y), where (x, y) designates the location on the image plane. A typical spectrometer, as used in spectroscopy, can provide a single spectrum I(λ), i.e., intensity information at each wavelength λ (spectral component). In comparison, spectral imaging can provide a spectral image I(x, y, λ) that includes spectral intensity at each point in the image plane. Therefore, a spectral image can be viewed as a cube of information (also referred to as a datacube) represented by a three-dimensional (3D) data set, where two dimensions represent spatial coordinates (e.g., x and y) and the third dimension represents a spectral coordinate (e.g., λ). Conventionally, a spectral image I(x, y, λ) can be decomposed into either a collection of many images, each of which is measured at a distinct wavelength, or into a collection of pixels, each of which includes a detailed spectral curve.

#Unlike conventional color imaging (e.g., with a color camera), which uses only three primary colors, spectral imaging can utilize many more color channels, thereby improving the color differentiation capabilities. In addition, spectral imaging can reach spectral regimes that might not be accessible to conventional color imaging, such as the infrared or Terahertz (THz) regime. Therefore, spectral imaging can be useful when precise spectral or color information is desirable (e.g., to distinguish between similarly colored objects or measure overlapping fluorescent signals) or when an image of the scene is desired (e.g., if the object of interest is not uniformly one color, the area of interest contains multiple objects, or scenes in which a single-point spectrometer would not accurately sample or cover the area of interest).

#Spectral images can be acquired via several methods. One method of spectral imaging uses a set of narrow band filters, each of which can transmit light around a particular wavelength (e.g., within a bandwidth of 10 nm). This method captures a full spectral image by measuring one image at a time but each time at a different wavelength.

#The skilled artisan will understand that the drawings primarily are for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily to scale; in some instances, various aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features. In the drawings, like reference characters generally refer to like features (e.g., functionally similar and/or structurally similar elements).

#FIG. 1 shows a schematic of a spectral imaging system including a filter and a refractive index modulator.

#FIGS. 2A-2C illustrate a spectral imaging system including a bundle of multimode fibers.

#Overview

#To address, at least partially, the issues in conventional spectral imaging techniques, systems and methods described herein transmit light reflected or scattered from an object or scene to be imaged into a filter having a variable refractive index. A modulator is employed to modulate the variable refractive index of the filter. At each distinct refractive index, an optical pattern of the light after the filter is recorded. A linear transform is then carried out over these optical patterns to convert these optical patterns to a spectral image of the object or scene.

#Systems and methods described herein do not use narrow-band filters to acquire different spectral channels in the spectral image. Instead, spectral channels are reconstructed from the linear transform of the optical patterns, which substantially preserve the intensity distribution and spectral bandwidth of the incident light. The preservation of spectral bandwidth in each optical pattern can result in improved signal-to-noise ratio (SNR) through the Fellgett advantage (also referred to as multiplex advantage). High spatial resolution can be achieved by the preservation of intensity distribution. In addition, systems and methods here do not use complicated moving or steering components, compact and robust apparatus can be constructed.