Transmission Characteristics Of Fibers Research Articles

Influence of cladding tube structure on transmission characteristics of negative curvature terahertz fiber

A novel type of polarization negative curvature terahertz fiber has been designed, which has a cladding region composed of two long semi-circular cladding tubes in the horizontal direction and four long semi-elliptical cladding tubes in the oblique direction. The optimal fiber dimensions are determined to investigate the internal relationship between polarization characteristics and fiber cladding structure. The transmission performances of the negative curvature fiber are investigated by varying the thickness of fiber cladding tubes and adjusting the structural characteristics of cladding tubes in different directions. Relatively good transmission performances can be obtained with a cladding tube thickness of 80 μm. The birefringence can be stably maintained at the order of 10−4, and the confinement loss of the x-polarized mode at 2.55 THz is 0.036 dB cm−1. Moreover, the dispersion coefficient of the two polarized modes is stable between ±0.6 ps (THz·cm)−1 in the 2.3–2.6 THz band. The bent performance of the designed fiber at 2.52 THz is also discussed. The results show that the fiber has low bending sensitivity, and can still maintain excellent birefringence and low confinement loss in the bending state. For the y polarization, the birefringence can be basically stabilized at the order of 10−4 within a bending radius of 10–60 cm.

A metasurface structure-assisted terahertz negative curvature fiber

Negative curvature fibers have the benefits of high bandwidth, low loss, and provide higher transmission performances. Birefringence of the fiber is particularly important, with potential application value in communication, imaging and other fields. In this paper, a metasurface structure-assisted terahertz negative curvature fiber is designed to improve the birefringence characteristic. This work breaks through the conditional design ideas, and theoretically analyzes the effect of adding gold microstructures in the cladding structures on the transmission characteristics of negative curvature fibers. The investigation results show that the birefringence of the designed fiber exhibits a significant increase in most frequency range between 1.75–2.4 THz compared to the results before adding gold microstructures. The maximum birefringence reaches as high as 0.00216 when the frequency is 2.175 THz and θ is 90°. Compared to the original frequency, the birefringence has increased by nearly an order of magnitude. The highest birefringence has been increased to 3.5 times. In addition, the influences of the gold microstructures on the confinement loss, waveguide dispersion, and effective mode field area are also investigated. This fiber provides a reference for the design of high birefringence terahertz fibers in the future.

Anti-resonant hollow-core terahertz fiber based on Bragg structure elements

An anti-resonant hollow-core terahertz fiber applying Bragg structure as the basic unit is presented, the basic unit is composed of two or three concentric tubes which is cut and connected by an outer ring. Simulations results show that the proposed fiber has the transmission characteristics of both conventional anti-resonant structure and Bragg fiber, and its confinement loss could be 2–3 orders of magnitude lower than that of an anti-resonant hollow-core terahertz fiber composed of only a single semi-tube as the anti-resonant unit, and the total transmission loss is one order of magnitude lower, which can achieve a low transmission loss of 0.5 dB/m or less with the bandwidth of 0.15 THz. In addition, the appropriated choice of the outer ring diameter can effectively suppress the mode coupling between the core and cladding, thereby reducing its confinement loss and bending loss. The proposed fibers show great potential for applications in terahertz wave communication and the fabrication of terahertz sensors.

Variable Aperture Technique for Measuring Mode Field Diameters Corresponding to Laguerre Gaussian Spot Size of Higher-Order Modes of Few-Mode Fibers

The mode field diameter (MFD) is an essential parameter for understanding the transmission characteristics of optical fibers. A variable aperture (VA) technique is a standard test method for measuring the MFD of single-mode fibers. Unfortunately, the conventional one cannot measure the MFDs of some higher-order modes correctly because its measurement procedure is standardized for measuring the MFD of the fundamental mode. The conventional VA technique aligns the position of the optical fiber through a peak intensity search on the premise that the fundamental mode, whose intensity is maximum at the beam center, is measured. How to align the position of the optical fiber when measuring the MFD of higher-order modes has not yet been investigated. In this paper, we describe the principle and formulas based on the VA technique for measuring the MFD of a given higher-order mode in few-mode fibers (FMFs). Then, we propose a novel procedure for measuring the MFDs of FMFs. The test apparatus of our technique is almost the same as that of the conventional VA technique except for the use of a mode selective coupler. One can measure the MFDs of arbitrary modes in FMFs correctly by adjusting the position of the fiber under test using the fundamental mode before starting the measurement. Proof-of-principle experiments were performed for three kinds of FMFs, and the experimental results showed that our procedure is useful for characterizing the MFD of each mode.

Preparation and transmission characteristics of seven-core few-mode fiber with low loss and low inter-core crosstalk.

Seven-core five-mode fiber and single-core five-mode fiber with the same core structure by high and low refractive index double rings are prepared based on plasma chemical vapor deposition. The transmission characteristics of the single-core few-mode fiber and the seven-core few-mode fiber are measured and characterized by building an experimental platform. The prepared single-core few-mode fiber can stably transmit five LP modes at 1550 nm, which not only has low loss characteristics, but also has excellent bending resistance. Furthermore, the transmission loss of the prepared seven-core fiber is lower than 0.4 dB/km, and the inter-core crosstalk is lower than -50 dB/km, which realizes the high-density and low-crosstalk transmission of the multi-core fiber. The prepared seven-core few-mode fiber can solve the capacity limitation of single-mode fiber, which will contribute the development of future communication systems.

Measurement of differential mode group delay in few-mode fiber with correlation optical time-domain reflectometer.

A measurement system of differential mode group delay (DMGD) in few-mode fiber with correlation optical time-domain reflection was proposed. A photonic lantern used in the system can be utilized for mode separation and selection and can generate six LP modes: LP01,LP11a,LP11b,LP21a,LP21b, and LP02. The signal reflected by the end of the fiber is correlated with the data sequence sent, which realizes the single-ended measurement of 5 km few-mode fiber DMGD. This method is not destructive for detecting fiber transmission systems and is simple and easy to implement. It can be used for detecting fiber transmission characteristics in the mode-division multiplexing communication system.

Postirradiation Transmission Characteristics of CYTOP Fiber Exposed by Gamma Radiation

We investigated offline the evolution of radiation-induced attenuation (RIA) in polymer perfluorinated cyclic transparent optical polymer (CYTOP) optical fiber irradiated with different gamma radiation doses of 1–50 kGy. We considered the wavelength range varying from 800 up to 1750 nm. The RIA spectra measured at different times after irradiation have qualitatively similar shapes. However, quantitatively the RIA evolution significantly depends on the spectral range: in the short-wavelength part, the transmission partly recovers, while in the infrared, at wavelengths above 1300 nm the RIA grows and then saturates becoming permanent. The effects of temperature and photobleaching on RIA dynamics are examined. The ability of the fiber transmission recovery is investigated in the 600–1750-nm range with the use of climatic chamber.

Mode Transmission Characteristics of Heterogeneous Helical Cladding Large Mode Area Fiber

Mode Transmission Characteristics of Heterogeneous Helical Cladding Large Mode Area Fiber

Efficient Virtual Network Embedding of Cloud-Based Data Center Networks into Optical Networks

The demand for data center bandwidth has exploded due to the continuous development of cloud computing, causing the use of network resources close to saturation. Optical network has become an encouraging technology for many burgeoning networks and parallel/distributed computing applications because of its huge bandwidth. This article focuses on efficient embedding of data centers into optical networks, which aims to reduce complexity of the network topology by using the parallel transmission characteristics of optical fiber. We first present a novel virtual network embedding (VNE) mathematical model used for optical data center networks. Then we derive a priority of location VNE algorithm according to node proximity sensing and path comprehensive evaluation. Furthermore, we propose routing and wavelength assignment for DCNs into optical networks, and identify the lower bound of the required number of wavelengths. Extensive evaluations show that the proposed embedding algorithm can reduce the average waiting time of virtual network requests by 20 percent, increase the request acceptance rate and revenue-overhead ratio by 13 percent, as compared to the latest VNE algorithm.

Influence of width of launch beam distribution and mode coupling on transmission characteristics of W-type plastic optical fibers

We show strong effects of width of the launch beam’s angular distribution on bandwidth and mode coupling in W-type plastic optical fibers (POFs). In general, the broader this width, the stronger the coupling and the lower the bandwidth—but the bandwidth drop due to this effect tapers off with distance from the input end and ceases at lengths over 25 m as the steady state distribution is reached. With increasing the strength of mode coupling, the equilibrium mode distribution is reached at shorter fiber lengths, which results in slower bandwidth decrease and finally in higher bandwidth at longer fiber lengths for fibers with larger coupling coefficients D. These results are aimed at aiding designers and application integrators of W-type POFs, particularly in employing laser, LED or vertical cavity surface emitting laser (VCSEL) light source.

Study on Physical Effects of Optical Fiber Transmission Characteristics Under Nonlinear Optical Effects

Photonic crystal fiber has a special light guiding mechanism and structural tunability, which can produce singular dispersion characteristics and high nonlinearity, which provides new conditions for the research in the field of nonlinear fiber optics. Due to the combined action of a variety of nonlinear optical effects, photonic crystal fibres with different structural parameters and transmission characteristics can produce rich nonlinear spectra under different pump light pulse parameters. We use the photonic crystal fiber cladding section to conduct nonlinear optical experimental research, and obtain the broadband spectral output of soliton wave and dispersive wave. The theoretical analysis and experimentally measured spectra include blue-shifted dispersion waves in the visible light band near 0.5 μm, residual pump light in the 0.82 μm band, soliton waves in the 1.1 μm band, and red-shifted broadband dispersive waves near 2 μm. Corresponding to this, the formation and redshift of solitons can be clearly seen in the time domain, and there is no more oscillation secondary peak in the femtosecond transmission pulse.

Double-trench assisted thirteen-core five-mode fibers with low crosstalk and low non-linearity

Information technology has an increasingly strong demand for high-speed and large-capacity optical fiber networks. Space division multiplex(SDM) is a new generation of optical fiber communication technology which can be several times in communication capacity higher than the wavelength division multiplexing systems. In this paper, we present a kind of 13-core 5-mode fiber with double trench structure to meet the demand for high-speed and large-capacity information transmission in the future. In order to solve the crosstalk problem in SDM, a double-trench structure is adopted to better limit the light energy in the fiber core, thus reducing the crosstalk between cores and modes. The crosstalk and transmission characteristics of multi-core fiber are calculated and analyzed by the full vector finite element method and coupled power theory. After the optimization of structural parameters, the fiber can stably transmit LP<sub>01</sub>, LP<sub>11</sub>, LP<sub>21</sub>, LP<sub>02</sub> and LP<sub>31</sub> in the band of 1.3–1.7 μm; when the signal is transmitted at the 1.55 μm for 60 km, the inter-core crosstalks corresponding to the adjacent fiber cores in the above five modes are –122.37 dB, –114.76 dB, –106.28 dB, –100.68 dB and –92.813 dB, respectively; the effective refractive index difference between adjacent modes is greater than 1.026 × 10<sup>–3</sup>; inter-core and inter-mode crosstalk can be effectively suppressed. The corresponding non-linear coefficients of the 5-modes are 0.74 W<sup>–1</sup>·km<sup>–1</sup>, 0.82 W<sup>–1</sup>·km<sup>–1</sup>, 0.88 W<sup>–1</sup>·km<sup>–1</sup>, 1.26 W<sup>–1</sup>·km<sup>–1</sup>, 0.93 W<sup>–1</sup>·km<sup>–1</sup>, which can maintain low non-linear transmission. The structure of fiber is simple and compact, and the preform can be fabricated by vapor deposition method and stack method, then the 13-core five-mode fiber with low crosstalk and low nonlinear can be further drawn, which can be used in a long distance high-speed and large-capacity fiber transmission system.

Long-term Transmission Characteristics of CYTOP Fiber Exposed to Gamma Radiation

We investigated post-irradiation variations of the radiation induced attenuation (RIA) of polymer perfluorinated (CYTOP) optical fiber exposed to gamma radiation. The RIA measured five months after the irradiation was qualitatively similar to that measured several hours after irradiation. However, quantitatively the RIA post-irradiation evolution significantly depends on the spectral range: in the visible range, the transmission partly recovers, while in the infrared, at wavelengths above 1300 nm the RIA grows and then saturates becoming permanent. The latter feature is prospective for gamma radiation dosimetry as a permanent long-term indicator of received radiation dose.

Impulse Response Measurement of Spooled and Twisted Few-Mode Multi-Core Fiber for Short-Range Optical Links

The impact of bending and twisting on the impulse response matrix is investigated using optical vector network analysis. The heterogeneous 36-core 3-mode fiber under test is spooled at bending radii of 8 cm to 50 cm and additionally up to 4 twists per meter along the longitudinal direction are applied. The by-design large differential mode group delay of the fiber enables comprehensive measurement of the inter-mode-group cross-talk of the fiber impulse response matrix, which is directly measured with an optical vector network analyzer. A maximal inter-mode-group cross-talk of −28.1 dB is observed over all 36 cores. Furthermore, no significant changes related to the bending radii or additional strain by twisting the fiber were detected. These results demonstrate that the transmission characteristics of few-mode fibers with large differential mode group delay are fairly unaffected by bend- and twist-related perturbations which may prove beneficial for short-range mode-group multiplexed transmission systems using partial multiple-input multiple-output equalization in conjunction with mode-selective multiplexers.

Improvement of transmission characteristics of step-index multimode fibers using variable mode controller

The mode dispersion induced in step-index multimode fibers significantly deteriorates the transmission characteristics and bandwidth. To overcome this existing problem, we suppressed the delay of the transmission signal through mode redistribution realized by applying a torsional stress to a fiber using a variable mode controller (VMC). By suppressing the transmission delay, the transmission characteristics and bandwidth of the fiber set in the VMC have been improved. The mode of the fiber set in the VMC achieves an equilibrium mode distribution by mode redistribution. Therefore, the near- and far-field patterns of the VMC were largely stable.

Design and coupling characteristics of terahertz dual-core anti-resonant fiber

The THz wave has good photonic and electronic properties, and has high penetration for non-polar materials, but its own photon energy is low. In addition, the THz wave also has characteristics such as wide bandwidth and large communication capacity, thereby making the THz wave possess important academic value and wide application prospects in the fields of non-destructive testing, biomedical imaging and communication. The development of THz technology requires not only high-performance THz waveguide technology for efficient transmission of THz waves, but also important optical devices such as optical switches, modulators, and couplers that are suitable for THz bands. With the in-depth study of THz waveguide technology, researchers have proposed many high-performance THz waveguide structures, such as metal hollow core tube waveguide, parallel metal plate waveguide, photonic crystal fiber and microstructure hollow core fibers, among which hollow-core photonic crystal fibers and hollow-core anti-resonant fibers (HC-ARF) have developed rapidly in recent years. So far, THz single-mode single-polarization fiber and high-birefringence fiber have been widely studied, but the researches on the fiber structure and devices that realize THz wave directional coupling are relatively rare. In this paper, we study the influences of the arrangement and distribution of the inner and outer claddings of HC-ARF on transmission characteristics, and thus design a new type of THz dual-core anti-resonant fiber. Compared with ordinary quartz fiber couplers and dual-core photonic crystal fibers, it can utilize a relatively simple structure and achieve directional coupling above 2 THz. Using the finite element analysis method to theoretically analyze the loss characteristics and coupling characteristics of the fiber, it is found that HC-ARF changes the periodic arrangement and distribution of the inner cladding tube within a certain range, which can achieve mode leakage without affecting the fiber transmission characteristics. So the THz dual-core anti-resonant fiber can be designed by using the mode leakage coupling mechanism. By changing the core distance and core gap size, the directional coupling with a coupling length of 0.72 m is realized at a transmission frequency of 2.5 THz. This terahertz dual-core anti-resonance fiber will have an important application value in terahertz optical devices such as terahertz optical switches, modulators and couplers.

RMSTCAF: The rapid measurement system for transmission characteristics of astronomical fibers

The fiber link between a telescope and a spectrograph is an attractive solution to improve the performance of astronomical instruments. The throughput of the observing system is mainly current concerned by the astronomer. The throughput of fiber link system is limited by the transmission efficiency (TE) and focal ratio degradation (FRD) of the fibers.The rapid measurement system for transmission characteristics of astronomical fibers (RMSTCAF) is an instrument to measure the output focal ratio (OFR), TE, the throughput of the fiber in a certain focal ratio and fiber endface quality. The number of optical fibers used in multi-object spectroscopy (MOS) and integral field spectroscopy (IFS) are increasing. It will be a time-consuming and huge burden to measure the FRD and TE of these fibers, especially the dynamic characteristics of high density optical cables. We designed this instrument to solve this problem.The system uses the encircled energy (EE) of the output energy of the fiber to determine the focal ratio of the optical fiber. With two measurement arms, the RMSTCAF provides feedback compensation to reducing the influence of incident light source fluctuation and realizes the closed-looped real-time measurement of the optical fiber transmission characteristics. The powermeters with double probes was used to suppress the environmental stray light to improve the measurement precision of the system with different wavelength. Used this system, we measured the critical focal ratio of the optical fiber with Numerical Aperture (NA) 0.128, the OFR average value within EE95 is F/3.83, compared with theoretical Fcritical/3.87, the error is 1.1%. We repeatedly connected the fiber with NA0.124 to the system and measured TE and OFR within EE90 and EE95. The standard deviation of them is 0.002, 0.03 and 0.02.As a universal measuring platform, RMSTCAF can meet the measurement requirements of minimum core diameter of 30 μm, minimum incident focal ratio F/2.6 and wavelength range of 400–850 nm. It has good repeatability and environmental adaptability. It would provide effective data for the design and evaluation of astronomical instruments with fiber link.

Enhancement of the bandwidth of W-type glass optical fibers in the infrared wavelength region

Abstract Transmission characteristics (bandwidth and steady state loss) of multimode W-type glass optical fibers are investigated by solving the time-dependent power flow equation. Results show how the bandwidth in W-type glass optical fibers can be enhanced by shifting from the red to infrared wavelength region for different depths and widths of the intermediate layer as well as for different launch excitations. Such characterization of these fibers is consistent with their manifested effectiveness in reducing modal dispersion and bending loss.

Theoretical analysis of high-sensitive seawater temperature and salinity measurement based on C-type micro-structured fiber

A new sensing method for simultaneous measurement of seawater temperature and salinity by C-type micro-structured fiber was proposed. The C-type fiber structure formed by removing the outer wall of one pore from a six holes micro-structured fiber, which would bring in birefringence and broke original pattern of degeneracy. By optimizing the parameters of this fiber structure, X polarization and Y polarization of fundamental mode were separate. Therefore, it could be used for double parameter measurement. Besides, gold film coated on the surface of structure to enhance sensing sensitivity by Surface Plasmon Resonance (SPR) principle. In this study, finite element analysis method was used to analyze the spectral transmission characteristics of C-type micro-structured optical fiber. The surface of wedge-shaped defect was contacted with seawater directly to feel salinity; meanwhile, thermo-optic material filled into pores to detect the temperature of seawater. Through model analysis, it was proved that the proposed filling structure could produce two SPR loss valleys, which had different responses to temperature and salinity. Under optimized structure, maximum salinity sensitivity of 1.402 nm/‰ was obtained for X-polarization and maximum temperature sensitivity of −7.609 nm/ °C was obtained for Y polarization, which demonstrated that the designed scheme could not only solve the cross sensitivity problem of two parameters but also achieve high sensitivity. In addition, C-type micro-structured fiber is non-cascade integrated, strong stability, and flexibility in design, which has great potential for sensing applications.

Design of a novel photonic crystal fiber filter based on gold-coated and elliptical air holes

In recent years, photonic crystal fibers have played an important role in the field of optical communications, and the addition of metal materials to photonic crystal fibers have offered new ways to improve the transmission characteristics of optical fibers. We design a new type of gold-coated photonic crystal filter, which utilizes the surface plasmon resonance effect, and study it by using the finite element method. In this paper, we optimise the structure parameters and analyze the numerical results. The numerical results show that the thickness of metal layer and the air holes near the fiber core strongly affect the performance of the polarization filter. For the operating wavelength of 1550 nm, the loss in the y-polarization direction can be as high as 906.9 dB/cm, which is much larger than the x-polarization direction. When the fiber length is longer than 100 μm, the crosstalk in the wavelength range from 1.4 μm to 1.9 μm is greater than 20 dB. The proposed optical fiber can find application as an optical fiber polarization filter.