Wavelength Shift Measurement With Resonance Characteristic Prediction Algorithm Using Intensities at Discrete Wavelengths

Abstract

In this article, we proposed a resonance characteristic prediction algorithm (RCPA) for calculating resonance characteristics using intensities at discrete points of wavelength. Given fundamental information of the resonator, such as free spectral range (FSR) and full-width half maximum (FWHM), the RCPA can be easily applied to reduce the cost and size of the measurement system for an optical resonator sensor. For example, with intensities at two wavelength points, the whole wavelength characteristics of the resonator can be generated from the derived fitting equation. To verify the RCPA, we designed and fabricated a Fabry-Perot interferometer (FPI) using 300 μm of SU-8 2100 as a cavity medium and 100 nm of Cr thin film on a glass substrate. The fabricated FPI had an FSR of 2.35 nm and an FWHM of 1.59 nm. We observed that the wavelength characteristics of the FPI (1535-1537.5 nm) shifted by 0.33 nm/°C when the temperature changed from 25.3 °C to 27.1 °C in steps of 0.2 °C. With an optimized wavelength spacing of 0.31 nm adopted for this article, we confirmed that the resonance characteristic generated from the RCPA followed the same tendency with an average error of 6 pm and a maximum error of 14 pm, as compared with the full spectrum result from the optical spectrum analyzer. We also analyzed the errors due to the changing point number and point spacing. Based on the experimental results, we verified that the resonance characteristic can be measured successfully using at least two intensities at different wavelengths.