Fabry-Perot interferometers are optical resonators used for developing high-resolution sensing devices. With the ability to detect and resolve the fine features of a transmission spectrum with high precision, these devices are commonly used to determine the resonant modes of a laser cavity, which often feature closely-spaced spectral peaks with narrow line widths. The most common configuration of a Fabry-Perot interferometer is a resonator consisting of two highly reflective, but partially transmitting, spherical mirrors that are facing one another. In this work, we present an experiment of how the academic knowledge acquired can be applied to the development of technologies that improve the quality of life. We believe that the teaching of experiment-oriented topics, combined with a dynamic and dialogue-based classroom delivery, can encourage greater class participation. This experiment is designed around commonly used optoelectronic devices, such as LEDs, to engage students' interest. Additionally, students will learn to investigate non-trivial features of such devices, for example, that it is possible to relate the emission spectrum of a resonant cavity to physical parameters that affect the cavity, such as temperature or refractive index.
The COVID-19 pandemic caused by the SARS-CoV-2 virus has brought global healthcare systems to their knees. The spike protein on the surface of the virus is a critical component for viral entry into human cells and therefore is a prime target for diagnosis and therapeutics. In recent years, the integration of photonic technology with biosensors has emerged as a promising approach due to its high sensitivity, specificity, and real-time detection capabilities. Optical fibres are one of the most versatile platforms for photonic technology-based biosensors, owing to their small size, low cost, and compatibility with various transduction methods. In this work, we present photonic technology based on optical fibres for the detection of the spike protein present in the SARS-CoV-2 virus. The proposed method involves the use of ad hoc synthesized peptides that specifically bind to the spike protein. The synthesized peptides are immobilized on the surface of the external face of an asymmetric Fabry-Perot cavity fabricated at the end face of a standard optical fibre, which acts as a biosensor. The presence of the spike protein in the sample causes a change in the refractive index, which is detected as variations in the visibility of the spectrum generated in Fabry-Perot cavity. The experimental results carried out have detected spike protein on buffered solutions with an LOD of 0.3 ng/ml. The proposed method offers several advantages over existing biosensors, including high sensitivity, real-time detection, and ease of integration into existing diagnostic platforms. We believe that the proposed photonic technology-based approach can significantly contribute to the development of biosensors for the early diagnosis of COVID-19 and other diseases.
In this work, we report a new approach for fabricating a high sensitivity lysozyme biosensing. The aforementioned device consists of an optimized Fabry-Perot micro-cavity (FPC) fabricated onto cleaved end of a standard single mode fibre (SMF). The sensitive part of our device is the external face of the FPC, which was ad-hoc functionalized in order to provide high selectivity and high sensitivity. From the experimental test carried out, we have found that our sensor has a sensitivity higher than others reported so far, to the best of our knowledge. In addition, the platform introduced here can operate over a broad wavelength which makes it adaptable to different sensing targets. In addition, our sensor offers several advantages such as repeatability of fabrication, wide operating range and small size and weight, which benefit its sensing applications.
In this work, we present a concept and method to fabricate miniature, high-quality optical fiber interferometers for sensing applications. The sensitive part of our devices consists of an off-center polymer micro-cap bonded on the end of a single mode fiber (SMF). The SMF end can be cleaved with a small angle or polished flat. In our devices, the reflection from the interface between the polymer and the external medium can be adjusted with an axial misalignment between the core of the SMF and the polymer micro-cap. This allows us to control the fringe contrast of the interference pattern. We fabricated several samples and they were tested as temperature, refractive index, and humidity sensors. In each case, our sensors were compared with commercial ones. Our results suggest that our devices are as accurate and sensitive as wellcalibrated electronic sensors. The sensitivities were found to be 270 pm/°C for temperature sensing and 0.04 RH% for humidity sensing. As refractometers, our interferometers have a resolution of 10-4 over a broad measuring range that goes from 1 to 1.54. Some applications of the devices here proposed can be monitoring of temperature or humidity in small spaces and refractive index of liquids inside of micro-fluidic channels. An advantage of our sensors is their broad operating wavelength range (from 800 to 1600 nm, approximately). In addition, the thermo-optic or thermal-expansion coefficients of polymers can be tailored. This may allow, for example, to tailor the performance of our sensor depending on the parameter to be sensed.
Based on the attractive elasto-optic properties of single-mode microstructured polymer optical fibres (SM mPOFs) reported elsewhere,10 mode polarisation may be used as sensing probe for several parameters of interest like mechanical pressure. We report on a simplified detection scheme that does not require measuring the actual polarisation state of the light emerging from the mPOF. A polariser and a photodetector in a proper configuration are only required. The detected light intensity shows a high linearity with applied force to the mPOF.
The polarisation state of light may be exploited in single-mode polymer mPOFs for sensing purposes.
The bend-induced birefringence varies linearly with the inverse square of the bend radius, whereas the
twist-induced polarisation rotation varies linearly with the bre twist angle. Both e ects are highly reproducible and show higher sensitivity than their glass counterparts.
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