A 3X3 plastic optical fiber (POF) twisted coupler has been fabricated as a compact sensor of multiple variables. The POFs are twisted into a combined body and the clad was removed by chemical method. Three LEDs of red, green, and blue colors can be used to shape a broad spectrum. Each led was connected at a different input port of the coupler. Since the twisted coupler makes the coupling of light from the input ports, we have a wide spectrum at each one output port. We develop a different sensor at each one output coupler: mass concentration (At the output-1), and curvature (At the output-2). The multi-sensing proposed in this work can increase the number of sensors as increase the number of output ports, and the bandwidth increase as increase the colors of light sources. On the other hand, we can use a wide spectrum lamp in a single input port and in the same way make multiple sensors in the output ports. The variation is evident in all wavelengths of the spectrum for measurements of sugar concentrations and fiber curvature. However, we can directly associate the sugar concentration variations with the spectrum in a range from 570 to 600 nm; and across the full spectrum for curvature measurements.
We propose to use the fast Fourier transformation (FFT) to analyze the spectral data of passively mode-locked fiber lasers, with the purpose of characterizing and classifying the different pulsed regimes arising in these lasers. The results show temporal information at the sub-ps scale. Specially, in the Fourier domain, the spectra of bound solitons depict several solitons with relative phases of π/2 and close to 0, distributed into a window that extends beyond the limited span of the autocorrelator. Besides, the FFT amplitude traces can help to classify the multi-pulse regimes generated by the laser; in particular, the exponential decay of intensity in such amplitude traces can be a fingerprint of noise-like pulses. Furthermore, the amplitude traces show some modulation that we attribute to Kelly’s sidebands. The proposed technique allows examining spectra from a mode-locked fiber laser independently of the active medium or laser cavity configuration without the need to use ultrafast photo- detectors.
Solar concentrators generate energy according to the amount of radiant flux that is converted into electrical energy using a solar cell. The optimal alignment of the solar cell and the aperture stop of the concentrator photovoltaic (CPV) solar system is a critical parameter for fabricating and manufacturing steps. We designed, developed, fabricated, and verified an optoelectronic system to test alignment of CPV solar system modules that is portable and robust to implement as a step in the assembly line. In addition to the components employed in systems previously, we implement an alignment module. It consists of a thin prism in four orientations in a plane normal to the optical axis of the unit under test and its control system. Its advantage is robustness against its positioning and orientation errors. Simulations and experimental results are presented.
The ballistic photons have been proposed for biological-tissue characterization. These photons keep its propagation direction when they are propagated through a material. They are rapidly attenuated in accordance with the density and thickness of the medium. The penetration depth for these photons is about 9 millimeters in human tissue. This attenuation may provide information to detect an inhomogeneity in the material (a possible tumor in human tissue). In order to enhance the detection of ballistic photons, interferometric setups have been proposed. Unfortunately, these setups only allow transmission measurement at a single point. We propose a novel technique using Risley prisms for area-scan with ballistic photons.
Mueller matrix polarimetric imaging (MMPI) provides precise microstructural information of biological samples and has been applied to the detections of various abnormal tissues. Once the Mueller matrix is determined for a particular anisotropic material, polar decomposition is applied to determine the singular values of optical anisotropies, such as depolarization, diattenuation, retardance and optical rotation. In this work, ex-vivo cancerous and noncancerous tissues were imaged by the MMPI technique using 3 different radiation wavelengths (460, 532 and 633 nm). The samples under study were cancerous and noncancerous tissues from colon. The results show that the optical anisotropies from biological samples are different. As we know, cancer changes the structure and concentration of biomedical substances from healthy tissue. One of the structures that is affected by cancer is collagen. This structure contributes to the diatenuation and retardance values. Therefore the values of diatenuation and retardance are different from the malignant and healthy tissues. We demonstrate that MMPI and polar decomposition are useful tools to discriminate healthy tissue and cancerous tissue from different parts of the body.
In the last thirty years, thousands of extra-solar planets have been detected. The overwhelming majority of these detections were performed by indirect techniques. Only a few tens have been detected by direct methods, because the current technology limitations. The rotational shearing interferometer (RSI) has been proposed as a promising technique for the direct detection of extra-solar planets. The RSI is insensitive to rotationally symmetrical wavefronts. This feature allows it to distinguish between a symmetrical wavefront generated by an star alone and an asymmetrical wavefront generated by a star-planet system. However the aperture and resolution of this method is limited by the size of the Dove prisms. We propose the use of an image-inverting interferometer (III) as alternative to the RSI. The III is equivalent to a RSI with a rotation of pi. It conserves the detection features of the RSI. Additionally the III uses mirrors instead Dove prisms avoiding its size limitations.
In this work, we proposed the usage of a rotating polarizer-analyzer polarimeter to retrieve retardance parameters of a sample by treating it as an elliptical retarder that can be characterized by three parameters: total retardance, fast axis orientation and an ellipticity related parameter. By employing the Mueller matrix approach, we developed the demodulation algorithm to retrieve each parameter with the association of the Fourier series analysis. We present experimental results considering dextrose concentrations diluted in distilled water scaling in a range from 30mg/dl to 45mg/dl. For comparison purposes, we employed the method of rotating an analyzer and compare the optical activity variation for both methods.
The imaging and digital processing of anisotropic optical properties of in vivo skin may be helpful in the assessment of its heterogeneous anatomy and physiological functioning. The interaction between polarized light and this organ provides information about the structural order beneath the epidermal layer. However, penetration depth is limited by optical absorption and scattering that are related to local skin characteristics such as pigment density, connective tissue organization, and cutaneous layer thickness. In this work, in vivo healthy skin of a murine model was analyzed using Mueller imaging polarimetry. A gray-level co-occurrence matrix analysis of diattenuation, birefringence, and depolarization measures in four different skin locations showed texture properties that can be used to distinguish local physiology.
We present a novel interferometer that we call the differential shearing interferometer (DSI). It incorporates a set of Risley prisms in a Sagnac interferometric configuration. The Risley prisms deviates the beam in both propagation directions. This interferometer interferes two beams displaced in the same direction, but with different magnitudes. The resultant interferogram is the directional derivative of the wavefront. The interferometer sensitivity depends on the difference between the beam deviations. This deviation is controlled by the position of the Risley prisms inside the beam path and their angular orientations. The advantages of quasi-common-path configuration include its low sensitivity to vibrations.
Most of skin pathologies, including melanoma and basal/squamous cell carcinoma, are related to alterations in external
and internal order. Usually, physicians rely on their empirical expertise to diagnose these ills normally assisted with
dermatoscopes. When there exists skin cancer suspicion, a cytology or biopsy is made, but both laboratory tests imply an
invasive procedure. In this regard, a number of non-invasive optical techniques have been proposed recently to improve
the diagnostic certainty and assist in the early detection of cutaneous cancer. Herein, skin optical properties are derived
with a multispectral polarimetric dermatoscope using three different illumination wavelength intervals centered at 470,
530 and 635nm. The optical device consist of two polarizing elements, a quarter-wave plate and a linear polarizer,
rotating at a different angular velocity and a CCD array as the photoreceiver. The modulated signal provided by a single
pixel in the acquired image sequence is analyzed with the aim of computing the Stokes parameters. Changes in
polarization state of selected wavelengths provide information about the presence of skin pigments such as melanin and
hemoglobin species as well as collagen structure, among other components. These skin attributes determine the local
physiology or pathology. From the results, it is concluded that optical polarimetry will provide additional elements to
dermatologists in their diagnostic task.
Mueller matrix polarimetric imaging (MMPI) provides a complete characterization of an anisotropic optical medium. Subsequent single value decomposition allows image interpretation in terms of basic optical anisotropies, such as depolarization, diattenuation, and retardance. In this work, healthy in-vivo skin at different anatomical locations of a biological model (Rattus norvegicus) was imaged by the MMPI technique using 532nm coherent illumination. The body parts under study were back, abdomen, tail, and calvaria. Because skin components are randomly distributed and skin thickness depends on its location, polarization measures arise from the average over a single detection element (pixel) and on the number of free optical paths, respectively. Optical anisotropies over the imaged skin indicates, mainly, the presence of components related to the physiology of the explored region. In addition, a MMPI-based comparison between a tumor on the back of one test subject and proximal healthy skin was made. The results show that the single values of optical anisotropies can be helpful in distinguishing different areas of in-vivo skin and also lesions.
A number of optical techniques have been reported in the scientific literature as accomplishable methodologies to diagnose diseases in biological tissue, for instance, diffuse reflectance spectroscopy (DRS) and optical polarization imaging (OPI). The skin is the largest organ in the body and consists of three primary layers, namely, the epidermis (the outermost layer exposed to the world), the dermis, and the hypodermis. The epidermis changes from to site to site, mainly because of difference in hydration. A lower water content increase light scattering and reduce the penetration depth of radiation. In this work, two hairless mice have been selected to evaluate their skin features by using DRS and OPI. Four areas of the specimen body were chosen to realize the comparison: back, abdomen, tail, and head. From DRS, it was possible to distinguish the skin nature because of different blood irrigation at dermis. In the other hand, OPI shows pseudo-depolarizing regions in the measured Mueller images related to a spatially varying propagation of the scattered light. This provides information about the cell size in the irradiated skin.
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