Giant refractometric sensitivity by combining extreme optical Vernier effect and modal interference

Abstract

The optical Vernier effect consists of overlapping responses of a sensing and a reference interferometer with slightly shifted interferometric frequencies. The beating modulation thus generated presents high magnified sensitivity and resolution compared to the sensing interferometer, if the two interferometers are slightly out of tune with each other. However, the outcome of such a condition is a large beating modulation, immeasurable by conventional detection systems due to practical limitations of the usable spectral range. We propose a method to surpass this limitation by using a few-mode sensing interferometer instead of a single-mode one. The overlap response of the different modes produces a measurable envelope, whilst preserving an extremely high magnification factor, an order of magnification higher than current state-of-the-art performances. Furthermore, we demonstrate the application of that method in the development of a giant sensitivity fibre refractometer with a sensitivity of around 500 µm/RIU (refractive index unit) and with a magnification factor over 850.

Optical Vernier Effect: Recent Advances and Developments

“…An example is the recent work of Gomes et al., where the authors showed that it is possible to combine the optical Vernier effect with mode interference, reaching M ‐factors an order of magnitude higher than what could be reached until now. [ 76 ] Moreover, the method preserves a measurable Vernier envelope, whilst achieving extremely high M ‐factors. The authors reported a record M ‐factor of over 850 and a giant refractive index sensitivity of about 500 000 nm RIU −1 .…”

Study of the Vernier Effect Based on the Fabry–Perot Interferometer: Methodology and Application

“…For example, an effective way to improve the detection range of the Vernier effect is to use signal processing technology to expand the envelope periodically [33]. The development of higher sensitivity also can be combined with new modes, such as the use of a low-mode interferometer to modulate the large envelope of the Vernier effect, which allows the excellent wavelength offset performance of the large envelope to be retained [32].…”

“…In another report by the author, the use of a modal interference combined with extreme optical Vernier effects to produce a measurable envelope while maintaining extremely high magnification is proposed. This method demonstrated the ultra-sensitive fiber refraction with a sensitivity of 500 µm/RIU, and the calculated magnification was higher than 850 times that of normal magnification [32]. Recently, people have also begun to consider signal processing methods to solve the envelope problem.…”

One-Dimensional High-Q Silicon Nanoparticle Chain Resonators for Refractive Index Sensing

“…These sensors are bulky and require a large amount of analyte. Another way to boost S is to utilize the optical Vernier effect in two coupled interferometers. , This method also increases the device footprint as well as the complexity of the sensor design. On the other hand, the FoM is defined as S normalized by the full width at half-maximum (FWHM) of the resonance mode, i.e., FoM = S /fwhm.…”