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1H NMR study of molecular order and dynamics in CBC9CB Liquid Crystal
摘要： Molecular order and dynamics of the CB-C9-CB liquid crystalline dimer exhibiting the nematic (N) and the twist bend nematic (Ntb) phases were investigated by proton NMR spectroscopy, using fields of 0.78 T and 7.04 T, and relaxometry. The first relaxometry experiments for a very wide Larmor frequency domain (8 kHz - 300 MHz) on this system, using a combination of standard and fast field cycling NMR techniques, were performed. The spectroscopy results in the Ntb phase allowed us to probe the local molecular orientation relative to the Ntb helix axis. The relaxation data were analyzed considering order director fluctuations (ODF), molecular self-diffusion (SD) and local molecular rotations/reorientations (R) relaxation mechanisms. Global fits of theoretical relaxation models, as a function of temperature and Larmor frequency, for the phases under investigation, allowed for the determination of rotational correlation times, diffusion coefficients, viscoelastic parameters, correlation lengths and activation energies (in the case of thermally activated mechanisms). A clear difference between the structures of the N and Ntb phases was detected from the results of proton spin-lattice relaxation through distinct temperature and frequency dependencies' signatures of the collective modes. Significant pre-transitional effects were observed at the N-Ntb phase transition both from relaxometry and spectroscopy data. The experimental results correlate to data and models for comparable liquid crystalline systems.
关键词： molecular dynamics,liquid crystal,nematic phase,twist bend nematic phase,NMR spectroscopy,relaxometry
更新于2025-09-19 17:15:36
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - The Loss Characteristics of Curved Fiber at Small Radius
摘要： Curved optical fiber sticking onto a round structure has many applications, such as mandrel acoustic sensors and fiber-length scratchable phase modulators. However, the components’ performances are limited by the transmission loss of the wound fibers. In this paper, the bending loss characteristic of curved fiber at small radius is experimentally demonstrated. A modified five-layer slab waveguide theory is used, which indicates that the bend loss has distinct oscillations at small radius. When the bending radius is smaller, the oscillation period changes more observably. In the experiment, single-mode fiber is bended on the outer surface of cylinders with various radius. The experimental result is consistent with theoretical analysis one.
关键词： bend loss,Fiber bending,mode coupling,whispering gallery modes (WGMs)
更新于2025-09-16 10:30:52
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Bend performance of single trench large mode area fiber with step-index core
摘要： Bend performance of a single trench large mode area fiber with a step-index core is investigated. The introduced step-index core distribution of the fundamental mode. Numerical results demonstrate the designed fiber can achieve a high loss ratio (as high as 886) at the wavelength of 2 μm when the bend radius is only 10 cm.
关键词： step-index core,large mode area fiber,single trench,bend
更新于2025-09-16 10:30:52
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Novel S-Bend Resonator Based on a Multi-Mode Waveguide with Mode Discrimination for a Refractive Index Sensor
摘要： In this paper, a multi-mode waveguide-based optical resonator is proposed for an integrated optical refractive index sensor. Conventional optical resonators have been studied for single-mode waveguide-based resonators to enhance the performance, but mass production is limited owing to the high fabrication costs of nano-scale structures. To overcome this problem, we designed an S-bend resonator based on a micro-scale multi-mode waveguide. In general, multi-mode waveguides cannot be utilized as optical resonators, because of a performance degradation resulting from modal dispersion and an output transmission with multi-peaks. Therefore, we exploited the mode discrimination phenomenon using the bending loss, and the resulting S-bend resonator yielded an output transmission without multi-peaks. This phenomenon is utilized to remove higher-order modes e?ciently using the di?erence in the e?ective refractive index between the higher-order and fundamental modes. As a result, the resonator achieved a Q-factor and sensitivity of 2.3 × 103 and 52 nm/RIU, respectively, using the variational ?nite-di?erence time-domain method. These results show that the multi-mode waveguide-based S-bend resonator with a wide line width can be utilized as a refractive index sensor.
关键词： multi-mode waveguide,integrated optical sensor,mode discrimination,refractive index sensor,S-bend resonator
更新于2025-09-16 10:30:52
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Optimum design of an optical waveguide: Determination of the branching angle of s-bend waveguides
摘要： In this paper, the authors introduce a new expression to describe the branching angle of an s-bend waveguide. This expression is useful for designing s-bend waveguides because of the di?culty of determining the branching angle of such a waveguide. The optimum value of the branching angle leads to the optimization of output power, which contributes to high performance levels of optical devices. The waveguide was designed with a device designing tool that uses the beam propagation method (BPM) in modeling the design. Mathematical expressions are used to characterize the branching angle based on the available waveguide design parameters. The waveguide design is also integrated into the optical network to ensure the design’s compatibility with the network and to validate the overall performance of the optical device in the network. Based on the s-bend waveguide design, it has been found that its branching angle strongly depends on two parameters: the lateral o?set of curve, h, and the length of the s-bend waveguide, L. The simulation results were analyzed to determine the optimum branching angle. The optimum value of the branching angle of the s-bend waveguide is 3.03°, with a produced output power of 96.9%. With the support of the two parameters, h and L, the branching angle from the equation obtained in this study is helpful in designing waveguides to produce high-performance optical devices.
关键词： S-bend waveguide,Optical device,Branching angle
更新于2025-09-12 10:27:22
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Analysis and design of TEM-TE11 coaxial waveguide bend mode converters
摘要： Two coaxial waveguide bend mode converters that transform coaxial transverse electromagnetic mode to TE11 coaxial waveguide mode are presented in this paper. Both converters are designed and optimized on the basis of the strictly derived mode coupling coefficients. Conversion efficiencies of both converters are over 99% and the power-handling capacities reach a gigawatt level. The combined dual-bend mode converter is fabricated and tested. The experimental results coincide well with the theoretical calculations and simulations, which demonstrates the feasibility of the designed converter.
关键词： Mode converter,high-power microwave,waveguide bend,mode coupling
更新于2025-09-11 14:15:04
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Ultra-Sharp Multimode Waveguide Bends with Subwavelength Gratings
摘要： Mode-division multiplexing (MDM) is attractive to enhance the link capacity of optical interconnects by using multiple mode-channels in multimode bus waveguides. As sharp waveguide bends are very important for realizing dense photonic integrated circuits, here ultra-sharp multimode waveguide bends for MDM systems are proposed and demonstrated by using subwavelength grating waveguide structures on silicon. An ultra-sharp S-bend with a radius of 10 μm is realized for the ?rst time to enable a low-loss and low-crosstalk MDM optical interconnect with three mode-channels. For this proposed ultra-sharp subwavelength grating multimode waveguide bend (SMWB) with a 90° bending angle, the theoretical excess losses for the TE0, TE1, and TE2 modes are 0.1–0.3 dB, 0.18–0.22 dB, and 0.3–0.5 dB, respectively, in a wavelength band of 1500–1600 nm. Meanwhile, inter-mode crosstalks are very low (less than ?30 dB) for all mode-channels. For the fabricated 90°-SMWB, the excess losses for the TE0, TE1, and TE2 modes are 0.1–0.3 dB, 0.2–0.4 dB, and 0.3–0.7 dB while the inter-mode crosstalk is approximately ?22 dB in a wavelength band of 1520–1600 nm. The proposed SMWB is also extended for more than three mode-channels.
关键词： bend,multimode,waveguide,silicon
更新于2025-09-11 14:15:04
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Estimation of Crack Mouth Opening Displacement in Concrete Using Optical Fiber Sensors
摘要： Concrete is a multi-phase composite material and used widely in construction industry because of high compressive strength and low cost. Its limited tensile strength makes it prone to cracking. Important parameters like characteristic length, fracture energy Gf critical crack width WC are used to understand cracks in concrete. The crack width is estimated either as crack mouth opening displacement (CMOD/COD) or as crack tip opening displacement (CTOD). Several optical and non-optical methods can provide information about crack presence but do not provide information on crack opening and crack width which are important from considerations of durability. To this end we present our research results in three point bend tests on pre-notched concrete samples (M-20 composition) using (a) Intensity based plastic optic fiber (POF) using phase difference measurement method (b) Fiber Bragg grating (FBG) method. The CMOD estimation and relative sensitivity of these methods will be presented.
关键词： Phase difference method,UTM,Crack mouth opening displacement,FBGs,Three point bend specimens,Prenotched concrete,Plastic optical fiber
更新于2025-09-11 14:15:04
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Higher-order coupling mode for orientation-dependent bend measurement using an off-axis FBG inscription over few-mode fiber
摘要： An off-axis fiber Bragg grating (FBG) was proposed and demonstrated for orientation-dependent bend measurement. The FBG was formed in a few-mode fiber (FMF) over core and cladding via high peak power femtosecond laser and phase mask technique. Three clear resonances were observed in the reflection spectrum, which were corresponding to fundamental mode (LP01), first-order mode (LP11) and the coupling mode (LP01-11). LP01-11 mode presents highly intensity response to the fiber bend without any wavelength change due to its unique mode field. And the FBG eccentric inscription further enhances the polarization of LP01-11 so that the sensor was directionally sensitive to the fiber bend by the intensity interrogation. Moreover, the wavelength-referenced temperature information could be demonstrated together with the fiber bend. The sensor was a good candidate for bend and temperature measurement simultaneously.
关键词： orientation-dependent bend sensor,Femtosecond laser,FM-FBG
更新于2025-09-10 09:29:36
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Synthesis of Curved CuIn1-xGax(S1-ySey)2 Nanocrystals and Complete Characterization of their Diffraction Contrast Effects
摘要： Herein, we report the synthesis and complete structural characterization of curved CuIn1-xGax(S1-ySey)2 (x = y = 0.5) nanocrystals, which adopt a 2D nanoplate morphology and crystallize in the hexagonal wurtzite phase. A detailed transmission electron microscopy (TEM) analysis reveals that the 2D nanoplates are predominately [001]-oriented and exhibit a unique bend contour pattern, due to curvature on the (001) basal plane. The contrast behavior of bend contours in this system is further supported through specimen tilting experiments inside the TEM, in combination with dark-field (DF) imaging in both TEM and scanning TEM (STEM) modes. This bending is believed to originate from the proximity effect of the top and bottom (001) surfaces.
关键词： bend contours,CuIn1-xGax(S1-ySey)2,hexagonal wurtzite phase,TEM,nanocrystals
更新于2025-09-09 09:28:46