SNR analysis and Hadamard mask modification of DMD Hadamard Transform Near-Infrared spectrometer

The noise of Hadamard Transform (HT) Near Infrared (NIR) spectrometer includes not only the detector circuit noise but also the illumination noise. Hadamard Transform reduces the detector noise while increases the illumination noise. If the relative power intensity is large, the noise of Hadamard method will be greater than that of scanning method. This will lose the significance of Hadamard Transform. In this paper the SNRs of the Hadamard method and scanning method are analyzed. The condition of boosting SNR of spectrometer by Hadamard transform is given. When the condition is not matched, a Hadamard mask of variable height stripes is proposed which the SNR of Hadamard method can be improved. In this paper a HT NIR spectrometer based on 0.45-inch DMD is designed with the spectrum range from 1350 nm to 2500 nm. Several experiments are done with the designed spectrometer. It is shown that with the Hadamard mask of variable height stripes the average SNR is improved by a factor of 2.2 at the short wavelength band and by a factor of 2.8 on the long wavelength band, and the minimum SNR on the whole wavelength band is improved by a factor of 2.3.