Abstract
Smartphone-based optical spectrometers allow the development of a new generation of portable and cost-effective optical sensing solutions that can be easily integrated into sensor networks. However, most commonly the spectral calibration relies on the external reference light sources which have known narrow spectral lines. Such calibration must be repeated each time the fiber and diffraction grating holders are removed from the smartphone and reattached. Moreover, the spectrometer wavelength scale can drift during the measurement because of the smartphone temperature fluctuations. The present work reports on a novel spectral self-calibration approach, based on the correspondence between the light wavelength and the hue features of the spectrum measured using a color RGB camera. These features are caused by the nonuniformity of camera RGB filters’ responses and their finite overlap, which is a typical situation for RGB cameras. Thus, the wavelength scale should be externally calibrated only once for each smartphone spectrometer and can further be continuously verified and corrected using the proposed self-calibration approach. An ability of the plug-and play operation and the temperature drift elimination of the smartphone spectrometer was experimentally demonstrated. Conducted experiments involved interrogation of optical fiber Fabry-Perot interferometric sensor and demonstrated a nanometer-level optical path difference resolution.
Highlights
Optical fiber sensors (OFS) are an emerging research topic, gaining a lot of attention from both academia and industry
The performance of the developed smartphone-based OFS interrogation system and the proposed spectral self-calibration approach was verified experimentally, for which we have carried out two experiments
The wavelength-to-pixel number calibration of a smartphone-based spectrometer with conventional pre-calibration is lost after the fiber and diffraction grating holders are shifted or removed and reattached
Summary
Optical fiber sensors (OFS) are an emerging research topic, gaining a lot of attention from both academia and industry. OFS are an ideal choice for various sensing tasks, including biomedical, oil and gas, avionics, structure health monitoring and others Their advantages are small size, biocompatibility, chemical neutrality, ability to perform remote measurements and multiplex several sensors, electromagnetic neutrality and absence of electric currents or radiofrequency fields in the sensing element. After the smartphones became widespread and deeply integrated into our everyday routines, it was proposed to use them as the core elements of portable optical spectrometers [14,15], which can be applied to interrogation of optical sensors [16,17,18] and OFS in particular [19] This relatively narrow research field is rapidly emerging, with examples of intensity-based [20], SPR-based [19,21,22], EFPI [23] and chirped FBG-based [24] sensors interrogation reported so far. We have identified two reference points in the hue distribution of the measured spectrum, whose positions in the optical spectrum can be measured and used further to deduce the wavelength scale of the measured spectrum
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