Application of thin diamond films in low-coherence fiber-optic Fabry Pérot displacement sensor

AbstractThe novel fiber-optic low coherence sensor with thin diamond films is demonstrated. The undoped and boron-doped diamond films were elaborated by the use of the microwave plasma enhanced chemical vapor deposition (μPE CVD) system. The optical signal from the Fabry–Pérot cavity made with the application of those thin films is sensitive to displacement. The sensor characterization was made in the range of 0–600μm. The measurements were performed using two superluminescent diodes (SLD) with central wavelengths of 1290mm and 1550mm and the output signal was analyzed by the measurement of the modulation change of spectral pattern. Furthermore, very good coefficient of the determination R2>0.9565 and the visibility of optical measured signal equal to 95.6% were achieved

Blood equivalent phantom vs whole human blood, a comparative study

Preclinical research of biomedical optoelectronic devices is often performed with the use of blood phantoms — a simplified physical model of blood. The aim of this study is the comparison and distinction between blood phantoms as well as whole human blood measurements. We show how the use of such phantoms may influence the incorrect interpretation of measured signal. On the other hand, we highlight how the use of blood phantoms enables to investigate the phenomena that otherwise are almost impossible to be noticed

Optimization of a Fabry-Perot Sensing Interferometer Design for an Optical Fiber Sensor of Hematocrit Level

Continuous measurement of the hematocrit level in blood can potentially be performed using optical fibre sensors. The Fabry-Perot interferometric sensors are a promising candidate in this application. The most important step in the design of the sensor is design of the sensing interferometer. Adequate cavity length and high interference contrast are two most important requirements in this application. The design method of the sensing interferometer presented in this paper uses a Gaussian beam approximation. In order to verify the design, an optical fibre Fabry-Perot interferometer with adjustable cavity length was built. Its performance was tested, confirming validity of the design approach

Shaping of coherence function of sources used in low-coherent measurement techniques

In low-coherent measurement techniques, such as: low-coherent interferometry, low-coherent reflectometry and low-coherent optical tomography, the coherence length of the source is one of the critical parameters of the designed system. The coherence length of the source effects the resolution of the measurement system. Commercially available low-coherent sources, as the most popular one - SLDs, have the coherence length at the range of 20-40 $\mu$m. In many applications it is too little to get the required resolution of the measurement. Hence, it is necessary to use some techniques to change the coherence length of the source. It is possible to do so by shaping the spectral characteristic of the source. One of the most effective methods is to use a combination of a few properly chosen sources called synthesizing multiwavelength combination of sources.
In this article, authors analyses the dependence between the spectral characteristic of the synthesized source and the coherence length. The result of theoretical investigation and simulations will show that the use of synthesized source can greatly reduce the coherence length. Additionally, it will be presented that it is possible to reduce the source coherence length by changing its spectral shape

Theoretical and experimental investigation of low-noise optoelectronic system configurations for low-coherent optical signal detection

In low-coherent measurement techniques two kinds of optical signal processing can be used -spectral and temporal. When the temporal signal processing is used, the most critical problem is to identify the position of the central fringe in the interference fringe pattern. It is so important because this position corresponds to the zero of optical path difference and gives information about a measurand. Therefore, it is necessary to use the low-noise optical signal detection set-up in the low-coherent measurement systems. One of the most effective methods of noise-reduction in low-coherent system is using detection system in balanced configuration. In this article, authors present the designed low-coherent optical signal detection system. This system enables us to perform balanced and un-balanced detection, which allows to compare parameters of both configurations. The authors describe theoretical and experimental investigation of balanced and un-balanced low-coherent optical signal detection system

Theoretical and experimental investigation of Optical Coherent Tomography topologies

Optical Coherent Tomography is a measurement technique, which enables us to visualize the internal structure of the investigated object with very high resolution. In OCT systems on order to detect the measured signal the measurement techniques such as: optical frequency domain reflectometry (OFDR) and optical low-coherent reflectometry (OLCR), are employed. In both methods it is necessary to use at least one interferometer. Up today a few topologies for Optical Coherent Tomography have been employed. Still, the most popular is configuration with Michelson interferometer, but also Fizuea is performed as well. Furthermore, it is known that using balanced configuration interferometer topologies is possible to effectively reduce noise-to-signal ratio. Hence, the use of the second interferometer is necessary. In this situation a few of interferometer topologies can be used. In this article the theoretical and experimental investigation of interferometer topologies for Optical Coherent Tomography will be analyzed. The optimal configuration of the designed system has been presented. By the use of a special configuration, our OCT system is sensitive to change of polarization of measured signals

Multi-layered tissue head phantoms for noninvasive optical diagnostics

Extensive research in the area of optical sensing for medical diagnostics requires development of tissue phantoms with optical properties similar to those of living human tissues. Development and improvement of in vivo optical measurement systems requires the use of stable tissue phantoms with known characteristics, which are mainly used for calibration of such systems and testing their performance over time. Optical and mechanical properties of phantoms depend on their purpose. Nevertheless, they must accurately simulate specific tissues they are supposed to mimic. Many tissues and organs including head possess a multi-layered structure, with specific optical properties of each layer. However, such a structure is not always addressed in the present-day phantoms. In this paper, we focus on the development of a plain-parallel multi-layered phantom with optical properties (reduced scattering coefficient $\mu_{s}^{\prime}$ and absorption coefficient μa) corresponding to the human head layers, such as skin, skull, and gray and white matter of the brain tissue. The phantom is intended for use in noninvasive diffuse near-infrared spectroscopy (NIRS) of human brain. Optical parameters of the fabricated phantoms are reconstructed using spectrophotometry and inverse adding-doubling calculation method. The results show that polyvinyl chloride-plastisol (PVCP) and zinc oxide (ZnO) nanoparticles are suitable materials for fabrication of tissue mimicking phantoms with controlled scattering properties. Good matching was found between optical properties of phantoms and the corresponding values found in the literature