Dual wavelength filtering properties and applications of the π-phase-shifted sampled fiber Bragg gratings

Multi-π-phase-shifted fiber Bragg gratings and π-phase-shifted sampled fiber Bragg gratings(SFBGs) with dual wavelength filtering properties are compared.Results show that both of these gratings have the dual wavelength reflective spectra.However,the side lobe of the reflective spectrum of π-phase-shifted SFBGs is lower than that of multi-π-phaseshifted gratings.By adjusting the duty cycle in the range of 0.66-0.80,the filtering properties of π-phase-shifted SFBGs are optimized,and the side lobe suppression ratio(SLSR) is the lowest when the duty cycle is 0.75.The application of the π-phase-shifted SFBGs in the dual-wavelength laser is also demonstrated.     

Method of correlation function for analyzing cross-sensitivity of strain and temperature in fiber grating sensors

A novel method of correlation function for analyzing cross-sensitivity between strain and temperature is reported for the first time in this paper. Using the new method,the correlative characteristics between strain and temperature of fiber Bragg grating sensors are studied both theoretically and experimentally The experimental results accord with the theoretical calculations.     

Frequency Variations of π-equivalent Circuit Parameters of a Junction Transistor †

One of the most useful small-signal equivalent circuit representations is based on a m-equivalent circuit representation of the transistor in a common-emitter connection. This m-equivalent circuit representation is more readily and commonly employed in circuit analysis or design in comparison with a ^'-equivalent circuit representation. The variation of equivalent circuit parameters at high frequencies in the π-equivalent circuit representation was determined by Giacoletto experimentally. Unfortunately, however, we have no example but the above, in spite of this problem being very common and important. The exact expression for π-equivalent circuit parameters is too complicated to be calculated. The result may be somewhat simplified by expanding the hyperbolic function into a Taylor series and retaining only the first few terms. Numerical values of these approximate expressions are calculated and then compared with values calculated from the corresponding exact expression. Furthermore, w-equivalent circuit parameters relative to low-frequency values are given as a function of frequency relative to f_T and f_α. The π-equivalent circuit parameters of a p-n-p germanium alloy-junction transistor of the diffusion (homogeneous base) type are obtained by measuring small-signal h parameters under the low-level injection conditions with an impedance bridge. Then, it is made clear that they are in reasonably good agreement with theoretical values. The approximate expression for α is proposed, where α is analysed in terms of magnitude and phase shift. It is shown that it is more exact and more useful than the expressions such as the Thomas-Moll expression, etc., as a result of discussing the errors in the approximations of the equations.     

Temperature and refractive index sensing characteristics of an MZI-based multimode fiber–dispersion compensation fiber–multimode fiber structure

We proposed an optical fiber sensor with simple multimode fiber (MMF)–dispersion compensation fiber (DCF)–multimode fiber structure based on Mach–Zehnder Interferometer (MZI) and researched its temperature and refractive index (RI) sensing characteristics. The sensing principle is based on the interference between core and cladding modes of DCF due to the large core diameter mismatch. Spectral analyses demonstrate that the transmission spectrum is mainly formed by the interference between the dominant excited cladding mode and core modes. The experimental results show that the proposed sensor has high temperature sensitivity of 0.118 nm/°C in the range of 20–250 °C and RI sensitivity of 66.32 nm/RIU within the linear sensing range of 1.33–1.39 RIU. Therefore, the characteristics of compact size, low cost, easy fabrication, high sensitivities, and good anti-interference ability make this sensor have extensive application prospects.     

Energy efficiency optimization of cognitive relay network based on cooperative spectrum sensing

This paper focuses on the energy efficiency of cognitive relay(CR) networks with cooperative sensing, joint optimization of the sensing time and the signal-to-noise ratio(SNR) is studied to maximize the energy efficiency of CR network. Theoretical analysis shows that there exists an optimal sensing time and optimal SNR to make the energy efficiency maximized under a constraint of detection probability. Simulation results illustrate that the optimal fusion rule performs better than the OR rule and the AND rule in terms of the energy efficiency. By properly designing the fusion rule threshold as well as the number of cooperative sensing users, the energy efficiency of CR networks can be further improved.     

Ring cavity fiber laser based on Fabry-Pérot interferometer for high-sensitive micro-displacement sensing

A ring cavity fiber laser based on Fabry-Pérot interferometer (FPI) is proposed and demonstrated experimentally for micro-displacement sensing. Simulation results show that the dips of the FPI transmission spectrum are sensitive to the cavity length of the FPI. With this characteristic, the relationship between wavelength shift and cavity length change can be established by means of the FPI with two aligned fiber end tips. The maximum sensitivity of 39.6 nm/μm is achieved experimentally, which is approximately 25 times higher than those in previous reports. The corresponding ring cavity fiber laser with the sensitivity for displacement measurement of about 6 nm/μm is implemented by applying the FPI as the filter. The proposed fiber laser has the advantages of simple structure, low cost and high sensitivity.     

Strong fiber Bragg grating based asymmetric Fabry–Perot sensor system with multiple reflections for high sensitivity enhancement

A fiber Bragg grating based (FBG-based) Fabry–Perot (FP) sensor system utilizing multiple reflections between two strong FBGs with different reflectiveties to enhance the sensitivity is proposed. The different interference signals are obtained by using different multiple-path-matched Michelson interferometers (MIs). The system is lighted by the ultra-narrow line width erbium-doped fiber ring laser and the signal is demodulated by phase-generated carrier (PGC) scheme. The method to choose the optimal parameters of the FBG-based asymmetric FP sensor and the different matching MIs is analyzed. The experimental results show that each matching MI can steadily enhance the sensitivity of the demodulated signal in the bandwidth of 80–8000 Hz. The sensitivity of the system can be enhanced about 19.1 dB when the light reflects nine times between the two FBGs. Further more, this system can be used to extend the dynamic range and the effective working bandwidth and so on.     

Design and experimental analysis of fiber grating vibration demodulation system based on the 3 × 3 coupler

A novel fiber grating vibration demodulation system, based on 2×2 and 3×3 couplers, is designed. Based on the phase unwrapping algorithm, the three-way asymmetrical output of the 3×3 coupler and demodulation state characteristics of the system when the vibration signal includes high harmonic waves are analyzed in simulations. The result shows that when the three-way output is asymmetrical, the maximum deviation of demodulation signal is 1.625%, and when the vibration signal includes high harmonic waves, the maximum deviation of demodulation signal is 0.9%. The corresponding experiment is conducted. The experimental result shows that the dynamic resolution of the system is 25.22 nɛ / $ \sqrt {Hz} $ \sqrt {Hz} when the vibration pitch is 5.5 Hz.     

Laser stripping of fiber Bragg grating polymer coating using pulsed 10.6 μm TEA CO2 laser

Stripping the polymer coating is the first step for the fabrication of fiber Bragg grating (FBG). The conventional stripping approaches are labor intensive and time consuming. Because of high precision and throughput, as well as non-contacting, laser stripping obtained more and more attention in recent years. This paper reports the primary experiments on laser stripping of polymer coating from FBG using pulsed transverse electric atmospheric (TEA) CO2 laser with wavelength of 10.6μm and pulse width of 2μs. Using cylindrical lenses, the coating can be removed thoroughly at one time. The theoretical analysis and experimental investigations were carried out. The influence of laser fluence and pulse number on stripping quality has been investigated. Scanning electron microscopy (SEM), optical microscope, and electrical balance were employed to detect the quality removal. The result shows that excellent quality removal is possible by using pulsed 10.6μm TEA CO2 laser.     

Applications of antimony–silicate glasses for fiber optic amplifiers

The performance of rare-earth-doped fiber amplifiers based on antimony–silicate glasses is reviewed. Erbium-doped antimony silicate has intrinsically flat gain in the conventional (C-band) erbium gain window enabling a 48 nm C-band amplifier. A modified composition induces a substantial red-shift in the signal excited state absorption, which in turn enables bandwidth extension of the long wavelength (L-band) to 1620 nm. Thulium-doped antimony silicates provide up to 60 nm of bandwidth in the S-band ranging from 1460 to 1520 nm. Local coupling of the thulium ions to low phonon sites prevents the lifetime quenching typical of thulium-doped silicates. Thulium-doped antimony silicates provide an efficient wider-band alternative to fluoride materials.     

Optimization of Plasma Etching Parameters and Mask for Silica Optical Waveguides

Optical waveguides in silica-on-silicon are one of the key elements in optical communications.The processes of deep etching silica waveguides using resist and metal masks in RIE plasma are investigated.The etching responses,including etching rate and selectivity as functions of variation of parameters,are modeled with a 3D neural network.A novel resist/metal combined mask that can overcome the single-layer masks’ limitations is developed for enhancing the waveguides deep etching and low-loss optical waveguides are fabricated at last.     

Simultaneous measurement of temperature and liquid refractive index based on fiber open Fabry-Pérot cavity and Bragg grating

A temperature and refractive index sensor based on fiber Bragg grating (FBG) end surface cascade open Fabry-Pérot (FP) cavity has been designed and demonstrated experimentally. The open FP cavity has been fabricated on the end face of an FBG by dislocation fusion in this work, the open FP cavity could be used for refractive index sensing, and the temperature is measured by the FBG. The working principle of the sensor and the method of improving the sensitivity are analyzed by theoretical simulation. The refractive index sensitivity of the sensor is 1 108.4 nm/RIU, while the maximum fluctuation of the sensor stability experiment detection is 0.005 nm. The results show that it has satisfactory characteristics. The sensor is a compact all-fiber structure, so it has potential applications in the field of temperature refractive index sensing, such as biomedical and capacitor electrolyte detection.     

Service characterization for cost/benefit optimization of?enhanced?UMTS

In this paper an all-IP Enhanced-Universal Mobile Telecommunications System (E-UMTS) is considered, where enhancements include link level behavior, high-speed downlink packet access (HSDPA) channel, resource management, Diffserv architecture, and Radio Resource Management schemes. An overview of E-UMTS deployment scenarios and service needs is presented based on the views of relevant players. Deployment and mobility scenarios are considered, including expected population density and usage of service mix for three environments, namely offices, urban/vehicular, and business city center. In addition, based on population and service penetration values, E-UMTS traffic generation and activity models are described and characterized. Based on these scenarios and characterizations, system level simulations are carried out and the enhanced service quality performance is demonstrated, including blocking probability, handover failure probability and end-to-end delay in each deployment scenario. By using system level simulations, services and environmental conditions can be mapped into deployment strategies (and supported system capacity) whose evaluation is essential prior to field trials and real implementation. On the one hand, costs depend on the prices of the spectrum, equipment, operation and maintenance, as well as on the number of cells which, in turn, depends on the cell radius. On the other, revenues depend on the price per MB and on the supported throughput. As the goal of operators and service providers is to maximize the profit, the profit in percentage was obtained for the three considered scenarios. Its optimum values are found for cell radii around 31, 257, and 310 m for offices, vehicular and business city center scenarios, respectively.     

Review Article Tactile sensing for mechatronics—a state of the art survey

In this paper we examine the state of the art in tactile sensing for mechatronics. We define a tactile sensor as a device or system that can measure a given property of an object or contact event through physical contact between the sensor and the object. We consider any property that can be measured through contact, including the shape of an object, texture, temperature, hardness, moisture content, etc.A comprehensive search of the literature revealed that there was a significant increase in publications on tactile sensing from 1991 onwards. Considerable effort in the 1980s was spent investigating transduction techniques and developing new sensors, whilst emphasis in more recent research has focused on experiments using tactile sensors to perform a variety of tasks.This paper reports on progress in tactile sensing in the following areas: cutaneous sensors, sensing fingers, soft materials, industrial robot grippers, multifingered hands, probes and whiskers, analysis of sensing devices, haptic perception, processing sensory data and new application areas.We conclude that the predominant choice of transduction method is piezoelectric, with arrays using resistive or capacitive sensing. We found that increased emphasis on understanding tactile sensing and perception issues has opened up potential for new application areas. The predicted growth in applications in industrial automation has not eventuated. New applications for tactile sensing including surgery, rehabilitation and service robotics, and food processing automation show considerable potential and are now receiving significant levels of research attention.     

On measuring the permittivity of “living” wood for microwave remote sensing

A procedure for measuring the permittivity of “living” wood is proposed. The permittivity of the trunk of a growing tree ε ₁ ^* has been measured by this procedure. Simultaneously, samples of wood of the same tree have been taken and their permittivities ε ₀ ^* determined under laboratory conditions. The obtained values has been compared, and considerable disagreement between measured ε ₁ ^* and ε ₀ ^* has been revealed. The study has been performed to model the reflection of microwaves from the forest.     

Synthesized Parameters of MIG for 200 kW, 42 GHz Gyrotron

In this paper, a synthesized design of the magnetron injection gun (MIG) for a 200 kW, 42 GHz gyrotron is presented. The synthesis steps involve the selection of the type of the MIG, the development of the design criteria, the selection of initial design parameters and the development of a program for the estimation of the synthesized parameters for the MIG design. The presented approach estimates the cathode, the beam and the anode parameters, enabling one to build a synthesis model of a complete MIG system.     

Selection of Parameters of the Primary Feed of the Luneberg Lens for the Sum–Difference Operating Mode

Excitation of the Luneberg lens by an arc antenna array of open-ended rectangular waveguides forming the H₁₀ wave is studied. Technical limitations imposed on the array of primary feeds in order to form the sum and difference operating modes of the antenna system are discussed.     

Design and Optimization of a novel structure for efficient side-coupling of high power double-cladding fiber lasers

A novel structure for efficient side-coupling of high power double-cladding fiber lasers is presented. The maximum cou- pling efficiency of this structure is more than 90% for TM-polarization in the 1 and -1 order but is only 40% for TE- polarization. Thus, a multi-layer stair-structure is introduced and optimized by combining transmission algorithm and genetic algorithm to obtain higher coupling efficiencyηfor TE-polarization and the maximum coupling efficiency almost reaches to 70%.     

Rate–distortion optimization of multi-exposure image coding for high dynamic range image coding

High dynamic range (HDR) images have many practical applications because they offer an extended dynamic range and a more realistic visual experience. A HDR image is usually stored in floating-point format, so pre-processing is required to make the HDR image compatible with coding standards. A transfer function is also used to achieve better coding efficiency. Typically, HDR images are generated using several low dynamic range (LDR) images with different exposures. Instead of compressing the HDR image when it is generated from images with multiple exposures, this study proposes a technique to compress the multi-exposure images. The HDR image generation, as well as the multi-exposure images fusion, can be realized in the decoder. The proposed framework encodes the multi-exposure images using MV-HEVC where the inter-view redundancy is well exploited when an accurate intensity-mapping function between the multi-exposure images has been established. Multi-exposure image coding is used to produce a high-quality HDR image so the rate–distortion optimization (RDO) is modified by considering both the reconstruction quality of the current block and its effect on the multi-exposure fused image. A Lagrange multiplier is modified to maintain a balance between the rate and the modified distortion during the RDO process. Compared to encoding the generated HDR image using HEVC range extension, the experimental results show that the proposed technique achieves significant bitrate savings for equivalent quality in terms of HDR-VDP-2.     

Performance evaluation of path optimization schemes for inter‐switch handoff in wireless ATM networks

One of the major design issues in wireless ATM is the support of inter‐switch handoff. An inter‐switch handoff occurs when a mobile terminal moves to a new base station connecting to a different switch. Recently, a two‐phase handoff protocol has been proposed to support inter‐switch handoff in wireless ATM networks. With the aim of shortening handoff delay while using the network resources efficiently, the two‐phase handoff protocol employs path extension for each inter‐switch handoff, followed by path optimization if necessary. To implement the two‐phase handoff protocol efficiently, we need to determine when to trigger path optimization. In this paper, we propose and analyze three path optimization schemes, namely: periodic, exponential, and Bernoulli, for the two‐phase handoff protocol. The design objective is to determine the time to invoke path optimization such that the average cost per connection is minimized. We develop a discrete time analytical model and a discrete‐event simulation model for comparing the performance of the three path optimization schemes. Results indicate that the Bernoulli path optimization scheme outperforms the other two schemes by providing a lower average cost per connection. The proposed models can also be adapted to analyze other path optimization schemes in general. This revised version was published online in July 2006 with corrections to the Cover Date.