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Principles Of Optics Electromagnetic Theory Of Propagation Interference And Diffraction Of Light

A highly sensitive temperature sensor is demonstrated experimentally, which is fabricated based on a Fabry–Perot interferometer (FPI) filled with polydimethylsiloxane (PDMS). The sensor’s sensitivity is −0.653 nm/°C by utilizing the thermal expansion effect of PDMS, which has been greatly improved compared to that of the traditional FPI temperature sensor. Moreover, in order to further improve the sensitivity, a scheme where two parallel FPI structures are used to form the Vernier effect is proposed, which are a sensing FPI and reference FPI, respectively. Such a temperature sensor based on the FPI filled with PDMS and the Vernier effect exhibits a high temperature sensitivity of 17.758 nm/°C. Meanwhile, the proposed sensors show the advantages of high sensitivity, simplicity, and low cost.

Highly sensitive PDMS-filled Fabry-Perot interferometer temperature sensor based on the Vernier effect.

Spectrally resolved photoacoustic imaging is promising for label-free imaging in optically scattering materials However, this technique often requires acquisition of a separate image at each wavelength of interest This reduces imaging speeds and causes errors if the sample changes in time between images acquired at different wavelengths We demonstrate a solution to this problem by using dual-comb spectroscopy for photoacoustic measurements This approach enables a photoacoustic measurement at thousands of wavelengths simultaneously In this technique, two optical-frequency combs are interfered on a sample and the resulting pressure wave is measured with an ultrasound transducer This acoustic signal is processed in the frequency-domain to obtain an optical absorption spectrum For a proof-of-concept demonstration, we measure photoacoustic signals from polymer films The absorption spectra obtained from these measurements agree with those measured using a spectrophotometer Improving the signal-to-noise ratio of the dual-comb photoacoustic spectrometer could enable high-speed spectrally resolved photoacoustic imaging

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Dual-comb photoacoustic spectroscopy.

Simultaneous measurement of pressure and temperature in seawater is realized based on polydimethylsiloxane (PDMS) sealed microfiber Mach–Zehnder interferometer (MZI). Benefitting from the high thermal-optic coefficient and large elasticity of PDMS, high sensitivity and robust structure can be obtained. In theoretical modeling, significant enhanced pressure response in fiber is observed clearly, and pressure or temperature sensitivities are calculated theoretically. In experiment, PDMS sealed MZI is fabricated by a two-step sealing method. Using this MZI, sensitivity of 13.31 nm/MPa for pressure sensing and −7.41 nm/°C for temperature sensing are demonstrated, respectively, which are about one order higher than bare fiber MZIs (without PDMS sealing). To verify the accuracy of sensor, several tests under arbitrarily pressure and temperature are performed with average errors of 4.38% and 1.44%, respectively. In addition, effects of encapsulation on avoiding cross-sensitivity with salinity, PDMS thickness on pressure sensitivity, response time, repeatability, time stability, and polarization of the sensor are also evaluated by experiment. Sensors demonstrated here show advantages of low cost, simple fabrication, robust and compact structure, high-pressure resistance, high sensitivity, good repeatability, and long-term stability.

Simultaneous Measurement of Pressure and Temperature in Seawater with PDMS Sealed Microfiber Mach-Zehnder Interferometer

Understanding transport phenomena and governing mechanisms of different physical and chemical processes in porous media has been a critical research area for decades. Correlating fluid flow behaviour at the micro-scale with macro-scale parameters, such as relative permeability and capillary pressure, is key to understanding the processes governing subsurface systems, and this in turn allows us to improve the accuracy of modelling and simulations of transport phenomena at a large scale. Over the last two decades, there have been significant developments in our understanding of pore-scale processes and modelling of complex underground systems. Microfluidic devices (micromodels) and imaging techniques, as facilitators to link experimental observations to simulation, have greatly contributed to these achievements. Although several reviews exist covering separately advances in one of these two areas, we present here a detailed review integrating recent advances and applications in both micromodels and imaging techniques. This includes a comprehensive analysis of critical aspects of fabrication techniques of micromodels, and the most recent advances such as embedding fibre optic sensors in micromodels for research applications. To complete the analysis of visualization techniques, we have thoroughly reviewed the most applicable imaging techniques in the area of geoscience and geo-energy. Moreover, the integration of microfluidic devices and imaging techniques was highlighted as appropriate. In this review, we focus particularly on four prominent yet very wide application areas, namely “fluid flow in porous media”, “flow in heterogeneous rocks and fractures”, “reactive transport, solute and colloid transport”, and finally “porous media characterization”. In summary, this review provides an in-depth analysis of micromodels and imaging techniques that can help to guide future research in the in-situ visualization of fluid flow in porous media.

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Review of Microfluidic Devices and Imaging Techniques for Fluid Flow Study in Porous Geomaterials.

Effect of mechanical stress on optical properties of polydimethylsiloxane

Periodic structures prepared by two-beam interference method

The investigation of the light-induced changes of refractive index in a LiNbO3: Fe sample in case of strip-like illumination is presented in the contribution. The changes of the refractive index are visualized by interferograms of the sample obtained for various orientation of the illuminated strip and various polarization of the light used during interferogram creation. The investigation shows that character of the dependences of the refractive index on the coordinate perpendicular to the illuminated strip is different for different strip orientation. It indicates the possibility that for different orientation of gradient of the illumination the different mechanisms are responsible for changes of the refractive index.

Investigation of symmetry of photorefractive effect in LiNbO 3

Effect of mechanical stress on optical properties of polydimethylsiloxane II - Birefringence

In this contribution we present some results of a study of a refractive index inhomogeneity near the boundary of polydimethylsiloxane (PDMS) samples. We have observed inhomogeneities of the refractive index at PDMS–glass, PDMS–brass, PDMS–Teflon, PDMS–polystyrene and PDMS–PDMS boundaries. The greatest changes of the refractive index were observed at the PDMS–PDMS boundary where an increase of the refractive index in a narrow region close to the boundary was observed. It gives the possibility for guiding light. The existence of such a waveguide was proved by the fact that the boundary also guided light when samples containing PDMS–PDMS boundaries had been bent.

Norbert Tarjányi

Papers

Effect of mechanical stress on optical properties of polydimethylsiloxane

Periodic structures prepared by two-beam interference method

Investigation of symmetry of photorefractive effect in LiNbO 3

Effect of mechanical stress on optical properties of polydimethylsiloxane II - Birefringence

Effect of boundary on refractive index of PDMS