Fibers with high birefringence and low loss offer notable benefits in the areas of sensing, communication, and polarization filtering. An asymmetry subwavelength suspended-core terahertz (THz) fiber composed of rectangular and arc-shaped dielectric layers is studied. Simulation results show that the fiber has both ultra-high birefringence and low loss characteristics. The birefringence value is higher than 0.038 from 0.8 to 1.0 THz, and the transmission losses of two polarization modes are lower than 0.5247 dB/cm when the thicknesses of all dielectric layers are the same. We note that the birefringence value can be further increased by adjusting the thickness of the rectangular dielectric layer. The birefringence value reaches the order of 10−1 in the frequency range of 0.82 to 1.98 THz. At 0.82 THz, the losses for x- and y-polarization modes are 0.3705 and 0.0754 dB/cm, respectively. Therefore, this type of fiber will be of great significance in eliminating the adverse influences of polarization effects in THz systems.
A terahertz (THz) hollow-core Bragg waveguide constructed by cascading waveguide units with supporting bridges (SPBs) on different air rings is proposed. The influence of the SPBs on the transmission loss of the waveguide is demonstrated numerically. Results show that the SPBs in the first air ring play the most important role in the transmission loss. By reasonably selecting the length ratio of the waveguide units, the waveguide absorption loss can be reduced to less than 0.4 dB / m in a wide bandwidth range of 0.53 to 0.73 THz, which is at least 2 orders lower than the material absorption loss.
A THz hollow-core Bragg waveguide constructed by cascading waveguide units with supporting bridges on different air rings is proposed. The influence of the supporting bridges on the transmission loss of the waveguide is demonstrated numerically. Results show that the supporting bridges in the first air ring play the most important role on the transmission loss. By reasonably selecting the length ratio of the waveguide units, the waveguide transmission loss can be reduced to less than 0.5 dB/m in range from 0.572 to 0.62THz, and the loss of the proposed Bragg waveguide are close to those of the IHC Bragg waveguide.
A relatively simple design of a terahertz (THz) polarization splitter based on an asymmetric dual-suspended-core fiber is proposed. One core is formed by two intersecting rectangular dielectric strips with dissimilar thickness, whereas the other is a round solid core suspended by crossed dielectric strips with the same thickness. The distance between the cores can be adjusted to ensure a short splitting length and low transmission loss. A THz polarization splitter with a length of 1.27 cm is realized with a low transmission loss of 0.53 and 0.67 dB for the x- and y-polarization modes, respectively. An extinction ratio of about −20 dB and a broad bandwidth of 0.046 THz are demonstrated.
Single-mode operation with low-bending loss based on few-mode optical fiber is investigated. The fiber is designed with a group of ring modes in the cladding. The higher-order modes in the fiber can be eliminated by splicing with the single-mode optical fiber and bending the fiber to induce a strong coupling between the ring modes and the higher-order modes. Experimental results show that the bending losses of the LP01 mode can be lower than 0.001 dB/turn for a low-bending radius of 7.5 mm. The low-bending loss and the low splicing loss characteristics are also demonstrated. The proposed fiber can be bent multiple turns with a small bending radius which is preferable for fiber-to-the-home-related applications.
The technique of eliminating the higher-order modes in a few-mode optical fiber is proposed. The fiber is designed with a group of defect modes in the cladding. The higher-order modes in the fiber can be eliminated by bending the fiber to induce strong coupling between the defect modes and the higher-order modes. Numerical simulation shows the bending losses of the LP01 mode are lower than 1.5×10-4 dB/turn for the wavelength shorter than 1.625 μm. The proposed fiber can be bent multiple turns at small bending radius which are preferable for FTTH related applications.
A few-mode microstructured optical fiber is designed for low bending loss applications. Low-index rods and air-holes are applied to lower the splicing loss with the standard single-mode optical fiber (SMF) and to achieve ultra-low bending loss. Numerical results show that the proposed fiber can realize low bending loss of 0.004 dB/turn at the bending radius of 5 mm and low splicing of 0.04 dB with the standard SMF.
Based on the coupled-mode theory, Cherenkov second harmonic generation (CSHG) from a channel waveguide has been analyzed and discussed in detail. The conversion efficiency with only conversion depletion and the conversion efficiency with conversion depletion and propagation loss are obtained respectively, the results show that for the case of low conversion efficiency the conversion depletion can be neglected, but for the case of high conversion efficiency we must take conversion depletion into account, and the propagation loss must be taken into accounted for the both. Furthermore, the nonlinear phase shift (NPS) of the fundamental beam can be maximized by choosing appropriate grating period and appropriate waveguide thickness, which makes the configuration have a promising potential to realize all-optical switches.
In an earlier approach, the 2-D acoustical field profiles on the substrate region are often calculated with BPM. In this
paper, we present a new approach based on the finite element - artificial transmitting boundary method and calculate the
2-D acoustical field on the substrate region.
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