In this paper, we demonstrate a micro-optical wall pressure sensor concept based on the optical modes of dielectric resonators. The sensing element is a spherical micro-resonator with a diameter of a few hundred micrometers. A latex membrane that is flush mounted on the wall transmits the normal pressure to the sensing element. Changes in the wall pressure perturb the sphere's morphology, leading to a shift in the optical modes. The wall pressure is measured by monitoring the shifts in the optical modes. Prototype sensors with polydimethylsiloxane micro-spheres are tested in a steady two-dimensional channel flow and in a plane wave acoustic tube. Results indicate sensor resolutions of ∼20 mPa and bandwidth of up to 2 kHz.

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In this paper, we carried out experiments to investigate dome-shaped microlaser based on the whispering gallery modes for remote wall temperature sensing. The dome-shaped resonator was made of Norland blocking adhesive (NBA 107) doped with a solution of rhodamine 6G and ethanol. Two different configurations are considered: (i) resonator placed on top of a thin layer of 10:1 polydimethylsiloxane (10:1 PDMS), and (ii) resonator encapsulated in a thin layer of 10:1 PDMS. The microlaser was remotely pumped using a Q switch Nd:YAG laser with pulse repetition rate of 10 Hz, pulse linewidth of 10 ns, and pulse energy of 100  μJ/cm². The excited optical modes showed an average optical quality factor of 10⁴ for both configurations. In addition, the measurements showed sensitivity to temperature of ~0.06  nm/°C and a resolution of 1°C for both configurations. This sensitivity was limited by the resolution of the experimental setup used in these studies.

In this Letter, we study a novel untethered photonic wall pressure sensor that uses as sensing element a dome-shaped micro-scale laser. Since the sensor does not require any optical or electrical cabling, it allows measurements where cabling tends to be problematic. The micro-laser is made by a mixture of Trimethylolpropane Tri(3-mercaptopropionate), commercial name THIOCURE and Polyethylene (glycol) Diacrylate (PEGDA) mixed with a solution of rhodamine 6G. Two different volume ratios between the THIOCURE and the PEGDA are studied, since different ratios lead to different mechanical properties. In addition, two different sensor configurations are presented: (i) sensor coupled to a membrane, that allows differential wall pressure measurement and (ii) sensor without membrane that allows absolute wall pressure measurement. The sensitivity plots are presented in the paper for both sensor configurations and polymer ratios.

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Whispering gallery mode (WGM) resonators exhibit a high quality factor Q and a small mode volume; they usually exhibit high resolution when used as sensors. The light trapped inside a polymeric microcavity travels through total internal reflection generating the WGMs. A laser or a lamp is used to power the microlaser by using a laser dye embedded within the resonator. The excited fluorescence of the dye couples with the optical modes. The optical modes (laser modes) are seen as sharp peaks in the emission spectrum with the aid of an optical interferometer. The position of these optical modes is sensitive to any change in the morphology of the resonator. However, the laser threshold of these microlasers is of few hundreds of microjoules per square centimeter (fluence) usually. In addition, the excitation wavelength's light powering the device must be smaller than the microlasers size. When metallic nanoparticles are added to the microlaser, the excited surface plasmon couples with the emission spectrum of the laser dye. Therefore, the fluorescence of the dye can be enhanced by this coupling; this in turn, lowers the power threshold of the microlaser. Also, due to a plasmonic effect, it is possible to use smaller microlasers. In addition, a new sensing modality is enabled based on the variation of the optical modes' amplitude with the change in the morphology's microlaser. This opens a new avenue of low power consumption microlasers and photonics multiplexed biosensors.

In this paper, we propose to use spherical microlasers which can be attached to the surface of bones for in vivo strain monitoring applications. The sensing element is made with a mixture of polymers namely PEGDA-700 and Thiocure TMPMP mixed at 4:1 ratio in volume doped with rhodamine 6G laser dye. Solid state microlasers are fabricated by curing droplets from the liquid mixture with UV light. The sensing principle relies on the morphology dependent resonances (MDRs); any changes in the strain of the bone causes a shift of the optical resonances, which can be monitored. The bone is made of a simulated cortical bone fabricated with photopolymer resin via additive manufacturing process. The path light within the resonator is found perpendicular to the bone axis and slightly tilted. Therefore, the sensor measures, thorough Poisson effect, the strain due to bending. Two experiments are conducted: i) negative bone deflection (loading) and positive bone deflection (unloading) for a strain range from 0 to 2.35 x 10-3 m/m. Sensitivity values are ~19.489 nm/? and 19.660 nm/? for loading and unloading experiments respectively (less than 1% percentage error). In addition, the resolution of the sensor is 1x10-3 e (m/m) and the maximum range is 11.58x10-3 e (m/m). The quality factor of the microlaser is maintaining about constant (order of magnitude 104) during the experiments. This sensor can be used when bone location accessibility is problematic.