City Research Online

Abstract

This work both investigates the critical state of the Vernier effect scheme in which the interferometric spectra of the sensing interferometer and the reference interferometer attain equal free spectral ranges (FSRs) at a specific wavelength, and then explores how the zero point of the FSR-difference curve can be used to determine the unique wavelength (UWL) of the Vernier envelope. The analysis carried out has revealed a new mechanism for realizing dual-parameter measurement. Furthermore, building on this, a compact sensing scheme has then been proposed as a proof of the concept, where this mechanism has been verified using only a single sensing interferometer. By selecting the central wavelength of the measurement range as the turning point and generating an inverted spectrum of the sensing spectrum as the reference, the resulting output Vernier envelope features a UWL. This positive approach introduces a uniquely identifiable wavelength in the conventional Vernier envelope and enables dual-parameter sensing by simultaneously tracking the UWL intensity variation and the wavelength shift of the peak or dip adjacent to the UWL. The effectiveness of the proposed scheme has then been experimentally validated through temperature and humidity measurements, as exemplars. The investigation of the critical FSR-equality condition thus provides new insights for increasing the number of measurable parameters, thereby offering a promising pathway towards novel Vernier schemes with distinctive spectral characteristics and enhanced capabilities for multi-parameter measurement.

Publication Type:	Article
Additional Information:	© 2026 IEEE. This accepted manuscript is made available under the terms of the Creative Commons Attribution License (CC-BY), which permits unrestricted use, distribution and reproduction in any medium, provided the original work is properly cited.
Publisher Keywords:	Interferometers, Humidity, Image sensors, Optical fiber sensors, Parameter estimation, Wavelength measurement, Spectral analysis
Subjects:	Q Science > QC Physics T Technology > TA Engineering (General). Civil engineering (General)
Departments:	School of Science & Technology School of Science & Technology > Department of Engineering
SWORD Depositor:	Symplectic Administrator

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