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Polarization-Sensitive Optical Coherence Tomography for Brain Tumor Characterization
摘要： Complete removal of brain tumor is of the most interest to a surgeon because the resection area directly relates to recurrence rate. Although there are many biomedical imaging modalities applied to locate the positions of tumors, they lack the spatial resolution to precisely delineate the boundary between brain tumor and normal brain tissues and are also inconvenient to be used intraoperatively. This study aims to examine the feasibility of label-free, polarization-sensitive optical coherence tomography (PS-OCT) for distinguishing brain tumors from normal brain tissues. Ex vivo samples were obtained from two patients with grade II and II-III glioma; healthy porcine brain tissues were utilized as the control group. In the results obtained from normal porcine brain, white matter contains significantly higher birefringent property over grey matter indicated by phase retardation. Based on the knowledge obtained from porcine brain experiment, a similar high-birefringent tissue is observed partially on the edge of the sliced glioma, and such tissue is considered as white matter because glioma originates through the mutation of the healthy white matter's glia cells. Additionally, differences between grey matter and brain tumor are not apparent based on phase retardation images and further histogram analysis. The capability of PS-OCT for distinguishing glioma from white matter is demonstrated. It could be a potential system to facilitate safe and maximum resection area, and finally, lead to ameliorated outcomes.
关键词： optical polarization,white matter,Brain tumor,optical coherence tomography
更新于2025-09-23 15:22:29
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Study of Polarization Strategy for High Power Millimeter Wave with Two Identical Reflective Gratings
摘要： For high-power millimeter systems, re?ective gratings (RGs) are usually used to control the wave polarization. This paper presents the polarization strategy with two identical RGs. We use the coordinate transformation method for the RG design. A code based on this method is checked by numerical examples and also low-power experiments. Experiments are carried out at frequencies of 60, 70, and 105 GHz. Four gratings are manufactured for test. We present and compare calculated results of the coordinate transformation method with the numerical results of the integral method and low-power test results. The comparison results indicate that the calculation results of the code are accurate and reliable. Finally, the polarization strategy with two identical RGs is studied with the code. Parameters and polarization characteristics including the bandwidth of designed gratings are given.
关键词： optical polarization,Gratings,millimeter-wave (mmW) technology
更新于2025-09-23 15:21:21
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Split-off states in tunnel-coupled semiconductor heterostructures for ultrafast modulation of spin and optical polarization
摘要： We present a theoretical analysis of the split-off states emerging due to a tunnel coupling between a remote bound state and a semiconductor quantum well (QW). The on-site Coulomb repulsion and the spin splitting of the bound state have been considered. The split-off states emerge in the band gap of the QW and reveal themselves as two solitary peaks in the photoluminescence (PL) from the QW. The peaks have opposite circular polarization and their spectral position strongly depends on the tunnel coupling strength. We suggest a mechanism of ultrafast PL polarization switching by means of electrical modulation of the tunnel coupling by an external gate. The obtained results open a new possibility for the spin and optical polarization control in nanoscale systems.
关键词： split-off states,photoluminescence,optical polarization,semiconductor heterostructures,tunnel coupling,spin polarization
更新于2025-09-23 15:21:01
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Integration of chiral cellulose nanocrystal films in silica optical fibers
摘要： Cellulose nanocrystals have attracted great attention as new “wonder” materials for photonic applications owing to their unique property of spontaneous self-assembly to form chiral nematic films. Here, the incorporation of chiral cellulose nanocrystal films on a photonic waveguide is demonstrated for the first time – in the form of integrated silica optical fibers with a helicoid nanocrystal film on their input facet. In order to achieve repeatable cholesteric ordering across the fiber core modal area, a fabrication method was developed where several optical fiber facets form part of a larger flat surface, which acts as the substrate for the planar anchoring of the cellulose nanocrystals. The resultant optical fibers exhibit significant circular dichroism (almost 40%) in transmission and act as all-fiber spectral filters. The proposed fabrication technique provides a simple, low-cost method for developing chiral silica optical fibers that remain compatible with standard telecommunication fiber technology. It is envisioned that the incorporation of cellulose nanocrystals in other optical fiber types will enable the development of a new class of fiber devices.
关键词： optical films,optical device fabrication,optical materials,optical polarization,fiber optics,optical fibers,optical fiber devices
更新于2025-09-23 15:19:57
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Polarization-Insensitive Laser Scanning and Profiling using Amplitude-Modulated CW Scheme
摘要： Laser scanners have emerged as powerful instrument for high-precision 3D geometry measurement. However, such attractive laser scanners have failed to address to drop of receiving power due to laser’s interaction with the surface of the object under measurement. This is a serious weakness of laser scanning systems since it can result in data deterioration and data loss in the acquired 3D point clouds. Numerous studies have been carried out on laser illumination on rough surfaces and have shown that interference between backscattered lights within the laser beam spot forms speckles which affect the level of the receiving power. In this article, we propose a laser scanner having a rapid and continuous polarization scrambling function and cope with the drop in the receiving power. This is the first report of speckle reduction with depolarization approach for laser scanning used for industrial measurement.
关键词： Interference,Optical polarization,Shape measurement,Laser radar,Surface roughness
更新于2025-09-19 17:13:59
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Polarization Modulation Instability in All-Normal Dispersion Microstructured Optical Fibers With Quasi-Continuous Pump
摘要： We report the experimental observation of the polarization modulation instability (PMI) effect in all-normal dispersion (ANDi) microstructured optical ?bers (MOFs) with quasi-continuous pumping. The small unintentional birefringence (～10?5), that any realistic non-polarization maintaining MOF exhibits, contributes to this nonlinear effect. PMI can produce two sidebands whose polarization state is orthogonal to the polarization of the pump. In this work, only one type of PMI process is observed, i.e., when the pump is polarized along the slow axis of the ?ber and sidebands are generated in the fast axis mode. This PMI process was studied experimentally in two ANDi ?bers with different dispersion features and pumped with long (700 ps) pump pulses at 1064 nm. Experimental results are compared with theoretical calculations, with reasonably good agreement.
关键词： Four-wave mixing,Optical polarization.,Microstructured optical ?bers,Chromatic dispersion,Fiber nonlinear optics
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Temperature Dependence of Magnetic Permeability and Optical Polarization Rotation of Gallium-Terbium Garnet Crystals
摘要： Faraday isolators (IF) are widely used in high-power fiber lasers in order to eliminate the detrimental influence of back reflections during the laser operation. One of the most widespread materials used for IF is a gallium-terbium garnet (TGG) crystal due to its appropriate magneto-optical properties. However, heating of magneto-optical crystals due to absorption of laser radiation deteriorates IF properties. Non-uniform heating leads to mechanical stresses and, therefore, to non-uniform polarization distortions. Values of optical absorption coefficients of TGG greatly depend on a crystal growth technology. Determination of the temperature dependence of optical absorption of TGG crystal was also one of the goals of this research. Optical absorption coefficient of cylindrical TGG sample (diameter d = 0.4 cm, length l = 2 cm) at 1060 nm wavelength was measured using laser calorimetry, i.e. by measuring the temperature of the crystal heated by transmitting laser radiation. Dependence of the crystal heating on transmitted optical power was 1.1±0.1 K/W. Absorption coefficient was calculated by solving the heat balance equation. Its value has increased from 1.6*10-3 cm-1 to 1.9*10-3 cm-1 as a result of heating from 22 oC to 43 oC. Also the contribution of the temperature dependent magnetic permeability μ(T) of TGG on the polarization rotation angle β was experimentally estimated. Temperature dependence of the magnetic permeability of TGG crystal was experimentally measured using resonant impedance spectroscopy. The value of TGG magnetic permeability was about 1.008 at room temperature (20 oC) and has decreased by Δμ = ? 1.2*10-4 when the crystal was heated to 80 oC. The temperature dependences of the polarization axis rotation angle change Δβ were measured in the cases of the uniform heating of TGG sample in a furnace and its nonuniform heating by transmitting linearly polarized laser radiation up to 30 W of optical power (1064 nm wavelength, 2 mm beam diameter). Applied magnetic field strength was 0,4 T, full angle of polarization axis rotation – 17,5 deg. Taking into account the measurement errors Δβ(T) ? (5 ± 0.25)*10-2 deg/ oC for both cases. It should be noticed that narrower laser beams can lead to greater differences due to the presence of larger temperature gradients. Consideration of the measurement results of μ(T) and β(T) revealed that the contribution of magnetic permeability variation with temperature to an overall polarization rotation angle change is almost 90 times lower than the thermally induced change of Verdet constant. Nevertheless, μ(T) influence should be considered if a precise control of polarization axis angle is required.
关键词： gallium-terbium garnet,Faraday isolators,TGG,magnetic permeability,temperature dependence,optical polarization rotation
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE Avionics and Vehicle Fiber-Optics and Photonics Conference (AVFOP) - Arlington, VA, USA (2019.11.5-2019.11.6)] 2019 IEEE Avionics and Vehicle Fiber-Optics and Photonics Conference (AVFOP) - Barium Titanate Electro-Optic Modulators
摘要： Barium titanate is a highly desired material for the development of advanced linear phase modulators due to its exceptional electro-optic coefficient, r51, that is over 20 times larger than the largest used in lithium niobate, r33. While the large r51 value in barium titanate has been reported, its utilization in modulators has been limited due to the difficulty in aligning the optical polarization with the crystal axes to maximize the electro-optic effect. Here we discuss the use of off-diagonal electro-optic tensor elements in thin film barium titanate modulators, present recent results, and go into further detail about the challenges and opportunities of using r51 in modulators.
关键词： barium,optical polarization,birefringence,Electrooptic modulators,nonlinear optics,slot waveguide,titanate
更新于2025-09-11 14:15:04
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Transverse relaxation determination based on light polarization modulation for spin-exchange relaxation free atomic magnetometer
摘要： A transverse relaxation determination of spin-exchange relaxation free (SERF) magnetometer based on polarization modulation technique is proposed. Compared with the radio-frequency (RF) excitation and light intensity excitation methods used in SERF magnetometer, the light polarization modulation method has a high stability in low-frequency range, which indicates a more accurate transverse relaxation measurement.
关键词： linewidth,spin-exchange relaxation free (SERF) magnetometer,optical polarization modulation
更新于2025-09-09 09:28:46