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Electromagnetic Simulation Using The Fdtd Method

Distributed fiber-optic vibration sensors receive extensive investigation and play a significant role in the sensor panorama. Optical parameters such as light intensity, phase, polarization state, or light frequency will change when external vibration is applied on the sensing fiber. In this paper, various technologies of distributed fiber-optic vibration sensing are reviewed, from interferometric sensing technology, such as Sagnac, Mach-Zehnder, and Michelson, to backscattering-based sensing technology, such as phase-sensitive optical time domain reflectometer, polarization-optical time domain reflectometer, optical frequency domain reflectometer, as well as some combinations of interferometric and backscattering-based techniques. Their operation principles are presented and recent research efforts are also included. Finally, the applications of distributed fiber-optic vibration sensors are summarized, which mainly include structural health monitoring and perimeter security, etc. Overall, distributed fiber-optic vibration sensors possess the advantages of large-scale monitoring, good concealment, excellent flexibility, and immunity to electromagnetic interference, and thus show considerable potential for a variety of practical applications.

https://www.mdpi.com/1424-8220/16/8/1164/pdf

Distributed Fiber-Optic Sensors for Vibration Detection

Endophytes as in vitro production platforms of high value plant secondary metabolites.

Segmenting silicon waveguides at the subwavelength scale produce an equivalent homogenous material. The geometry of the waveguide segments provides precise control over modal confinement, effective index, dispersion and birefringence, thereby opening up new approaches to design devices with unprecedented performance. Indeed, with ever-improving lithographic technologies offering sub-100-nm patterning resolution in the silicon photonics platform, many practical devices based on subwavelength structures have been demonstrated in recent years. Subwavelength engineering has thus become an integral design tool in silicon photonics, and both fundamental understanding and novel applications are advancing rapidly. Here, we provide a comprehensive review of the state of the art in this field. We first cover the basics of subwavelength structures, and discuss substrate leakage, fabrication jitter, reduced backscatter, and engineering of material anisotropy. We then review recent applications including broadband waveguide couplers, high-sensitivity evanescent field sensors, low-loss devices for mid-infrared photonics, polarization management structures, spectral filters, and highly efficient fiber-to-chip couplers. We finally discuss the future prospects for subwavelength silicon structures and their impact on advanced device design.

/pdf/subwavelength-grating-metamaterial-structures-for-silicon-253awniogk.pdf

Subwavelength-Grating Metamaterial Structures for Silicon Photonic Devices

This paper presents the first available report in the literature of a system aimed at the detection and classification of threats in the vicinity of a long gas pipeline. The system is based on phase-sensitive optical time-domain reflectometry technology for signal acquisition and pattern recognition strategies for threat identification. The system operates in two different modes: 1) machine+activity identification, which outputs the activity being carried out by a certain machine; and 2) threat detection, aimed at detecting threats no matter what the real activity being conducted is. Different strategies dealing with position selection and normalization methods are presented and evaluated using a rigorous experimental procedure on realistic field data. Experiments are conducted with $\text{eight}$ machine+activity pairs, which are further labeled as threat or nonthreat for the second mode of the system. The results obtained are promising given the complexity of the task and open the path to future improvements toward fully functional pipeline threat detection systems operating in real conditions.

/pdf/toward-prevention-of-pipeline-integrity-threats-using-a-nfcvk47n5p.pdf

Toward Prevention of Pipeline Integrity Threats Using a Smart Fiber-Optic Surveillance System

Based on a multimode interference (MMI) coupler in slot waveguide structures, an ultracompact wavelength demultiplexer operating at 1.30 and 1.55mum wavelengths is proposed and designed by using a full-vector mapped Galerkin mode solver and a modified three-dimensional full-vector beam propagation method. The tapered waveguide structures are applied to connect the input/output channels and the MMI section for reducing excess loss. The modal characteristics of the slot waveguides are analyzed and the evolution of the injected field in whole device are demonstrated. The results show that a MMI section of 119.8mum in length, which is only 27.5% length of that of the MMI coupler by using conventional rib waveguides, is achieved with the contrasts of 26.03 and 28.14dB at wavelengths 1.30 and 1.55mum, respectively, and the insertion losses are below 0.2dB at both wavelengths.

Design of an ultracompact MMI wavelength demultiplexer in slot waveguide structures

A compact polarization beam splitter (PBS) for silicon-based slot waveguides is proposed, where an asymmetrical multimode waveguide (AMW), cut by a right angle at one corner, is employed to efficiently separate the TE and TM modes. With the unique modal properties of the slot waveguides, the input TE mode almost passes through the AMW and enters into the bar port, while the input TM mode forms a mirror image at the cross port due to the self-imaging effect. Tapered waveguide structures and S-bend are incorporated into the PBS for enhancing the performance. Results show that a PBS with an AMW of 2.3 μm in length is achieved, where the extinction ratios are 16.6 and 20.9 dB, respectively, for TE and TM modes, and the insertion losses are 1.37 and 0.81 dB, respectively, at the wavelength of 1.55 μm, and the bandwidths can cover the entire C-band for both polarizations. In addition, fabrication tolerances to the structural parameters are investigated and field evolution along the propagation distance through the designed PBS is also demonstrated.

Compact Polarization Beam Splitter for Silicon-Based Slot Waveguides Using an Asymmetrical Multimode Waveguide

A Modified full-vectorial finite-difference beam propagation method based on H-fields for optical waveguides with step-index profiles

A theoretical analysis of amplification characteristics of bi-directional erbium-doped fiber amplifiers with single erbium-doped fiber

In this paper we propose and demonstrate the scheme of vibration pattern recognition and classification in the OTDR based distributed optical-fiber vibration sensing system. We set up the engineering system with signal processing PC for perimeter security in some high-tech park in Nanjing. Three types of disturbing actions, including climbing up and kicking at the wall by a person, and watering on the sensing optical fiber cable same as the rain falling on, are implemented. By using level crossing rate (LCR), we can obtain their individual pattern features, so that the eigenvalue database for three disturbing actions can be built in the system. By comparing three types of vibrations, the differences among these can be given out. The results show three vibration patterns can be recognized and classified effectively.

Xiaohan Sun

Papers

Design of an ultracompact MMI wavelength demultiplexer in slot waveguide structures

Compact Polarization Beam Splitter for Silicon-Based Slot Waveguides Using an Asymmetrical Multimode Waveguide

A Modified full-vectorial finite-difference beam propagation method based on H-fields for optical waveguides with step-index profiles

A theoretical analysis of amplification characteristics of bi-directional erbium-doped fiber amplifiers with single erbium-doped fiber

Vibration pattern recognition and classification in OTDR based distributed optical-fiber vibration sensing system