Two multi-path interferometers were developed using cleaved silica microspheres. A microsphere on top of a singlemode fiber tip was cleaved with a focused ion beam. The asymmetry introduced in the structure generates a new set of optical paths due to random reflections inside the microsphere. The obtained reflection spectrum presents a random-like interferometric behavior with strong spectral modulation of around 3 dB amplitude. Two distinct regions can be observed when a fast Fourier transform is applied. The first involves two cavities at a lower frequency and the second region involves a band of frequencies that is originated by the random interferometric reflections. These two spectral characteristics can be separated using low-pass and high-pass filters, respectively. A correlation method was used to obtain a temperature response from the two-cavity component. A similar structure was also created in a microsphere of multimode fiber. The microsphere was cleaved by polishing the structure with a certain angle. The interference between the different optical paths can be seen as the superposition of several two-wave interferometers, which can be discriminated through signal processing. Temperature sensing was also explored with this structure. The sensitivity to temperature is more than 3-fold for smaller cavities. Moreover, a sensitivity enhancement is also verified if a correlation method is used.
KEYWORDS: Brain, Fiber Bragg gratings, In vivo imaging, Temperature metrology, Sensors, Fiber optics sensors, Fiber optics tests, Fiber optics, Body temperature, Surgery
This work reports on the development of an optical fiber sensor based fiber Bragg Grating (FBG) probe for in vivo measurements of brain temperature. The major goal of this work is to demonstrate that the changes in brain temperature induced by drugs is an important reality, which could provide new valuable information on the mechanisms of drug action and open new therapeutic approaches. This probe can be interrogated using a portable optical measurement setup, allowing for measurements to be performed outside of standard optical laboratories.
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