An hollow-core terahertz fiber applying anti-resonant Bragg structure as the basic unit is proposed. Simulations results shown that the proposed THz fiber shows both the transmission characteristics of a conventional anti-resonant structure and a Bragg fiber. The confinement loss of which could be two-three orders of magnitude lower than that of an anti-resonant structure fiber consists of a single anti-resonant ring, and the total loss is one order of magnitude lower, the transmission loss of the proposed THz fiber could be 0.5 dB/m or less with a relative wide bandwidth of 0.15 THz.
In this paper, a polymer optical fiber (POF) bending sensor based on a tapered structure is proposed. At the outset, tapered POFs with different tapered sizes are prepared by flame-heated drawing technique, the bending characteristics of tapered POF sensor under different cone waist diameters are investigated. The experimental results show that the sensor sensitivity is largest when the cone waist diameter is 1/3 of the diameter of POF, where the size of the latter is 500μm. On this basis, a dual U-shaped structure POF angle sensor based on tapered is designed. The experimental measurement shows that its angular sensitivity is improved to 0.0871 dB/°, its linearity is 0.994, and its sensing sensitivity is 6 times that of the conventional tapered structure. This structure has the advantages of high sensitivity to bending, small size and low cost, and has potential application prospects in the field of measuring the bending angle of human joints.
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.
In this article, a mode converter based on irregularly distributed long period fiber gratings(LPGs) is proposed. The mode conversion characteristics of LP01 mode to LP02 mode are analyzed by beam propagation method. The effects of the cross-section shape and diameter of the gratings on the mode conversion efficiency and bandwidth are analyzed. Mode conversion bandwidth between the LP01 mode and the LP02 mode is found strongly dependent on the interaction between the mode fields and the LPG section.
A kind of bending-insensitive multicore fiber (MCF) is proposed. The core adopts a low-mode gradient index structure to form a seven-core few-mode fiber. The finite element method is used to simulate and analyze the bending loss of the central core and the outer core, the crosstalk between the core modes, and the influence of core parameters on the crosstalk performance. Data simulation results show that even for a small bending radius of 5 mm, the bending loss of this MCF is much lower than the attenuation loss of the fiber, and the crosstalk between the adjacent cores is less than −20 dB. Therefore, independent information transmission between cores can still be realized under a small bending radius.
The exotic properties of topological photonic crystals (PCs) have a series of application prospects in the field of optical communication. We present a Y-shaped beam splitter based on topologically protected waveguide, which consists of the topologically trivial PCs with line defect. The investigation results indicate it has the merits of unidirectional propagation, robustness, and excellent transmission performance. Compared with magnetic-optical PC beam splitter, the proposed configuration composed of rods with silicon material that can realize topological beam-splitting effect in the absence of external magnetic field and has a smaller size. It is suitable for miniaturization to implement in all-optical network as an optical communication device.
In this paper, a polarization filter based on photonic crystal fiber (PCF) with nanoscale gold film is proposed and analyzed theoretically. The cross-section of the structure is composed of four-layer air holes with a hexagonal lattice and two symmetrical air holes in the sub-internal layer are coated with gold film. We research that the PCF structure parameters affect the performances of the polarization filter through employing the finite element method. It is indicated by the numerical results that the resonance strength in y-polarization direction can reach a most value of 272.8 dB/cm at the communication wavelength of 1.55 μm. The extinction ratio can be better than 20 dB within a wavelength range from 1.45 μm to 1.75 μm when the length of the PCF is longer than 500μm. Therefore, such a length can make the communication filtering effect be realized using a shorter fiber. The calculated results can provide some references to the design of polarization micro-filter devices.
A kind of bending-insensitive multi-core fiber is proposed. The core adopts a low-mode gradient index structure to form a seven-core few-mode fiber. The finite element method is used to simulate and analyze the bending loss of the center core and the outer core, the crosstalk characteristics between modes, and the influence of core parameters on the crosstalk performance. Data simulation results show that when the bending radius of this multi-core fiber is 5mm, the bending loss is much lower than the fiber attenuation loss, and the crosstalk between adjacent cores is less than -20dB. Therefore, independent information transmission between cores can still be realized under a small bending radius.
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 novel mode converter which is based on long period fiber grating (LPFG) is proposed. A graded-index optical fiber is introduced to induce strong mode coupling at wide bandwidth. By optimize the fiber configuration and parameters, and the appropriate choice of grating parameter, high mode conversion efficiency with cross-talk lower than -20 dB and wide operation bandwidth over 180 nm can be achieved.
A two-core optical fiber composed of a single-mode core and a few-mode core is proposed. Index-matched coupling between two fundamental modes in two cores can be achieved by applying a long-period fiber grating in the few-mode core. Mode-field conversion between the small mode-field area and the large mode-field area with low loss can be achieved by this configuration. Numerical simulation shows that the operation bandwidth of the mode-field converter can be as large as 36 nm if the insertion loss of the converter should be lower than 0.5 dB. Results show that this structure has higher conversion efficiency and lower cross talk as compared to the scheme of direct connection between the single-mode fiber and the few-mode fiber.
The mode characteristics of few-mode step-index optical fibers composed of a center core and a few assistant cores are investigated. Each fourfold mode in the optical fiber can be split into two twofold modes, avoiding strong mode coupling during the transmission process. In addition, two-mode operation in the fiber with a wide wavelength range of 1.42 to 1.9 μm is demonstrated numerically. We also investigated the coupling characteristics of the two-core configuration that can effectively separate the LP01 and LP11 modes.
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.
Design strategies for high-sensitivity refractive index sensors based on the principle of wavelength-selective resonant coupling in dual-core photonic crystal fibers are presented. Phase matching at a single wavelength can be achieved between an analyte-filled microstructured core and a small core with a down-doped rod or one small air hole in the center, thus enabling selectively directional resonant-coupling between the two cores. The transmission spectra of the output light presents a notch at the index-matched wavelength, yielding a resonant wavelength depending on the refractive index of the analyte. Numerical simulations demonstrate that both of the two proposed sensors can be used for highly sensitive detection of low-index analyte. In particular, the configuration realized by introducing the fiber with a small air hole in one core can be used to the detection of the analyte index around 1.33 and the sensitivity reach to 1.2×104 nm per refractive index unit (RIU). In addition, the detection limit is as low as 2.5×10−7 RIU at na = 1.33.
Based on the analysis of birefringence and leakage properties in rectangular lattice photonic crystal fibers(PCFs), we presented a technique of improving the properties of the fibers by the introduction of a doped-core. The influence of pure silica core, silica core with small air-hole, and a doped silica core on the mode profiles of the fiber are investigated and discussed. The influence of doping level on that of birefringence and leakage losses of the fibers is also explored, which is realized by applying the mutipole method. Our numerical simulation proves that, for PCFs with anisotropic claddings, it's possible to obtain an increased birefringence by doping, while maintaining or even reducing the leakage loss by increasing the hole pitch of the fiber. The technique eliminates the disadvantage of deforming mode field by the introduction of small air-hole core and the mode field of the fiber is also increased.
We report a plastic holey fiber that has a strongly anisotropic structure. The polarization property of this microstructured plastic fiber was investigated. The result shows it has a high birefringence.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.