OpenVNT: An Open Platform for VIS-NIR Technology

Abstract

Spectrometers measure diffuse reflectance and create a “molecular fingerprint” of the material under investigation. Ruggedized, small scale devices for “in-field” use cases exist. Such devices might for example be used by companies in the food supply chain for inward inspection of goods. However, their application for the industrial Internet of Things workflows or scientific research is limited due to their proprietary nature. We propose an open platform for visible and near-infrared technology (OpenVNT), an open platform for capturing, transmitting, and analysing spectral measurements. It is built for use in the field, as it is battery-powered and transmits data wireless. To achieve high accuracy, the OpenVNT instrument contains two spectrometers covering a wavelength range of 400–1700 nm. We conducted a study on white grapes to compare the performance of the OpenVNT instrument against the Felix Instruments F750, an established commercial instrument. Using a refractometer as ground truth, we built and validated models to estimate the Brix value. As a quality measure, we used coefficient of determination of the cross-validation (R2CV) between the instrument estimation and ground truth. With 0.94 for the OpenVNT and 0.97 for the F750, a comparable R2CV was achieved for both instruments. OpenVNT matches the performance of commercially available instruments at one tenth of the price. We provide an open bill of materials, building instructions, firmware, and analysis software to enable research and industrial IOT solutions without the limitations of walled garden platforms.

Design of a Prism-Grating Wide Spectral Range Transmittance Imaging Spectrometer

“…Table 2 provides a means to determine the optimal combination of N-PK52A and HZF6 materials, which minimizes the secondary spectrum of the system while also satisfying the tolerable focus color shift. By utilizing Equations ( 5)- (7), the optical power of lenses made from these materials can be determined, with values of Φ 1 = 0.01 and Φ 2 = −0.0038 assigned to each, respectively. Utilizing only two lenses in the system will not correct for all aberrations.…”

“…The widening of the working spectral range of the imaging spectrometer has led to serious axial chromatic aberration and secondary spectrum in the system, which affects the imaging quality of the system [7]. As shown in Figure 1, tilting the image plane can improve the imaging quality, but this structure is not conducive to later installation and adjustment, and there is axial chromatic aberration that causes spectral crosstalk during detection.…”

“…Based on Equations ( 5)- (7), and (10), it is evident that the Abbe numbers of the chosen glass materials should differ considerably, while the relative dispersion coefficients should have only minor differences to minimize the secondary spectral coefficient and eliminate the secondary spectrum within the system. Therefore, it is possible to correct the axial chromatic aberration and secondary spectrum of the transmissive optical system by selecting appropriate materials with low chromatic aberration and distributing the optical focal power of the combined lenses reasonably.…”

A 380-1100nm spectrum matching light source with high spectral resolution, throughput, speed, and stability

“…It offers a full wavelength range (380nm to 1100nm) of spectral matching with high spectral power. The source can be a valuable tool for ambient sensor or image sensor calibration [8,15,23,24], display calibration, hyperspectral imaging, spectroscopy [3,4,16,24], healthcare [12,14], radiometry [2,18,19,21], diagnostics and biomedical-related applications [7,9,12,20,22], which also need to consider the ambient light or NIR light effects and simulate the detailed spectral profiles of arbitrary light sources with more extended wavelength range and high fidelity.…”

“…Energetiq's broadband spectrum matching light source (Chromatic Spectral Engine (CSE)) with the visible range of 380nm to 800nm has been successful in unlimited spectral profile matching in the visible range [1]. With new requirements from applications and customers [2,3,4,5,6,7,8,9,10], the wavelength range is extended from the range of 380nm ~ 800nm to 1100nm. This wavelength range extension makes it possible for spectral matching in silicon detectors sensitive range of both Visible and NIR with reasonable flux and spectral resolution.…”