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Acousto-optic tunable filter (AOTF) is a novel device for spectrometer. The electronic tunability qualifies it with the
most compelling advantages of higher wavelength scan rate over the conventional spectrometers that are mechanically
tuned, and the feature of large angular aperture makes the AOTF particularly suitable in imaging applications. In this
research, an AOTF-based near-infrared imaging spectrometer was developed. The spectrometer consists of a TeO2
AOTF module, a near-infrared imaging lens assembly, an AOTF controller, an InGaAs array detector, an image
acquisition card, and a PC. A precisely designed optical wedge is placed at the emergent surface of the AOTF to deal
with the inherent dispersion of the TeO2 that may degrade the spatial resolution. The direct digital synthesizer (DDS)
techniques and the phase locked loop (PLL) techniques are combined for radio frequency (RF) signal synthesis. The
PLL is driven by the DDS to take advantage of both their merits of high frequency resolution, high frequency scan rate
and strong spurious signals resistance capability. All the functions relating to wavelength scan, image acquisition,
processing, storge and display are controlled by the PC. Calibration results indicate that the spectral range is 898~1670
nm, the spectral resolution is 6.8 nm(@1064 nm), the wavelength separation between frames in the spectral image
assembly is 1.0 nm, and the processing time of a single image is less than 1 ms if a TV camera with 640×512 detector is
incorporated. A prototype device was assembled to test the capability of differentiating samples with similar
appearances, and satisfactory results were achieved. By this device, the chemical compositions and the distribution
information can be obtained simultaneously. This system has the most advantages of no moving parts, fast wavelength
scan and strong vibration resistance. The proposed imaging spectrometer has a significant application prospect in the
area of identification of camouflaged target from complex backgrounds. In addition, only the objective lens and its
accessories are required to be replaced for its use in microscopic spectral imaging system, which may be popularized to
a large number of other possible applications.
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