Design and Calibration of Liquid Crystal Tunable Filter Based Spectral Imaging System

As evidence of hyperspectral and multispectral imaging for the quality inspections of food and agricultural products accumulates, the design and calibration of a spectral imaging device is gaining increasing interest. Liquid crystal tunable filter (LCTF) based spectral imaging, an important branch of modern spectral imaging, has many advantages in food quality and safety inspections. This paper presents the design, integration, and calibration of an LCTF based shortwave infrared spectral imaging system. The system consists of an LCTF, an InGaAs camera, a near-infrared lens, an illumination unit, and the data acquisition software. It was designed to capture hyperspectral or multispectral images in the spectral range of 900 - 1700 nm. The principles and key points of designing the LCTF-based spectral imaging system are summarized and discussed. A series of tests were conducted to calibrate the linearity of the system output, measure the field of view, enhance the system spectral sensitivity, measure the spatial and spectral resolution of the system, evaluate the stability of the system, the image distortion, and reduce the spectral noise of the system output. Results of calibration tests indicated that this system satisfied the design criteria for both spatial and spectral domains. The presented design and calibration methodologies are applicable to the electronic filter-based spectral imaging systems in other applications.