The scientific community has been exploring new concepts as a result of the usage of optical fibers as absolute measurement sensors. While cross-sensitivity is a common issue with optical fiber sensors, this issue has been mitigated by simultaneous measurement techniques. But when it comes to absolute measurements, these methods have some limitations. The white light interferometer, which offers a superb solution for a range of applications, especially for absolute temperature measurement, is one of the most often used methods for absolute measurements.

This paper proposes a proof of concept for a reflective fiber optic sensor based on multimode interference, designed to measure glucose concentrations in aqueous solutions that mimic the range of glucose concentrations found in human saliva. The sensor is fabricated by splicing a short section of coreless silica fiber into a standard single-mode fiber. By studying the principles of multimode interference and Self-imaging it was developed a sensing head that has a total length of 29.1 mm, approximately equal to the second self-image cycle. This sensing head allowed us to detect low concentrations of glucose (ranging from 0 to 268 mg/dl).

A new approach to detect and analyze transverse acoustic mode resonances (TAMRs), responsible for forward Brillouin scattering in optical fibers, is reported using optical whispering gallery modes (WGMs). TAMRs generate perturbations in the geometry and the dielectric permittivity of the fiber that couples the acoustic and optical resonances. This interaction is exploited to probe opto-excited TAMRs exhibiting an optimal efficiency for detecting low-order TAMRs.

Upconverting particles (UCPs) are building blocks of modern photonics. They cannot be used only as imaging agents but also as contactless sensing units. UCPs have already been used for sensing forces, temperature, mechanical properties, and chemical composition. The sensitivity of the luminescence of UCPs to different external stimulus opens the possibility of using them as multiparametric sensors capable of one-shot description of medium possibilities. However, the use of UCPs for multiparametric sensing is limited because of bias: different external stimuli have an identical impact on the luminescence of UCPs. Bias makes impossible the reliable interpretation of the luminescence generated by UCPs and produces erroneous readouts. Avoiding bias requires the development of new strategies in the analysis of UCPs luminescence when used as sensors. In this work, we demonstrate how a single β-NaYF4: Yb3+, Er3+ UCP within an optical trap can provide unbiased measurements of temperature and viscosity. Decoupling thermal and mechanical measurements is achieved by using the luminescence of coupled states for thermal sensing and the polarization of luminescence for the determination of viscosity. The simultaneous and unbiased temperature/viscosity sensing from a single UCP is demonstrated in a series of proof-of-concept experiments

Applying the inverse-source technique, we have developed an analytical model describing the angular radiation and source-plane spatial-spectral coherence property of white light emitting diodes (LEDs) and demonstrated it experimentally. A corresponding elementary-field representation, which benefits by simplifying the treatment of partially coherent beam shaping and imaging problems, is formulated. Moreover, we identify spectral parts of white LED’s spectrum that follow Wolf’s scaling law of spectral invariance.