Micro-controller based air pressure monitoring instrumentation system using optical fibers as sensor

This paper describes a micro-controller based instrumentation system to monitor air pressure using optical fiber sensors. The principle of macrobending is used to develop the sensor system. The instrumentation system consists of a laser source, a beam splitter, two multi mode optical fibers, two Light Dependent Resistance (LDR) based timer circuits and a AT89S8252 micro-controller. The beam splitter is used to divide the laser beam into two parts and then these two beams are launched into two multi mode fibers. One of the multi mode fibers is used as the sensor fiber and the other one is used as the reference fiber. The use of the reference fiber is to eliminate the environmental effects while measuring the air pressure magnitude. The laser beams from the sensor and reference fibers are applied to two identical LDR based timer circuits. The LDR based timer circuits are interfaced to a micro-controller through its counter pins. The micro-controller samples the frequencies of the timer circuits using its counter-0 and counter-1 and the counter values are then processed to provide the measure of air pressure magnitude.     

Proposal for a 94-GHz phase-reversal optical modulator using a loaded transmission line

One of the most important problems associated with the design of external travelling wave optical modulators operating at very high frequency is the reduction of microwave loss associated with the electrode structure. With this in view, a new design for a Ti:LiNbO/sub 3/ narrow-band optical modulator is proposed for operation at 94 GHz. It uses a low-loss loaded transmission line with dielectric overlay and uses phase-reversals to achieve phase matching. Numerical simulations predict a required 21-dBm drive power for full on-off switching at 94 GHz.     

Junction CCD optical line sensor

An optical line sensor based on a junction CCD is presented. The expected good quantum efficiency of a junction CCD appears to be better than 0.8. In addition, this type of CCD has excellent blooming suppression. The resolution is 49.5 ?m and the sensor is driven by a 3-phase clock.     

采用频域光延迟线的光学相干层析成像

频域光延迟线是一种光学扫描结构,其基本组成是一个衍射光栅、一个透镜和一个扫描镜.把频域光延迟线应用到光学相干层析成像系统中,可以使参考臂扫描速率至少达到数m/s以上,从而实现视频速率的图像获取.从几何光学的角度分析了频域光延迟线的工作原理,分析结果表明在扫描角很小的情况下,入射光的光程或相位变化频率与扫描角频率有较好的线性关系.基于这一结构的光学相干层析成像的结果证明可以避免活体生物组织位移引入的图像模糊.另外,还提出了一种基于微执行器的新扫描装置.     

Bandwidth characteristics of optical transmission line constructed with short-length optical fibers

This paper clarifies the bandwidth characteristics of a VAD-fabricated optical line constructed with short-length optical fibers. The refractive index profiles of these optical fibers are slightly distorted from the ideal profile. Their bandwidth characteristics are calculated and measured under the overfill mode distribution (OMD) and the equilibrium mode distribution (EMD) excitations. As a result, some of the optical fibers are shown to have extremely narrow bandwidths at the short fiber length under OMD excitation as compared with those under EMD excitation. The concatenation factor of the optical line consequently becomes a smaller value than that of an optical line constructed with long-length optical fibers. In addition, the measurement results of the optical subscriber transmission line field trial are shown to be in good agreement with those obtained in this paper.     

An 800 Mbit/s optical transmission experiment using a single-mode fiber

It has been confirmed by a preliminary transmission experiment that a repeater spacing at 800 Mbits/s can be lengthened up to 7.3 km, by using a combination of a low-loss single-mode fiber and a well designed AlGaAs laser. The laser is modulated by a signal current superimposed on a dc bias current above the threshold. This modulation scheme avoids the spectrum broadening of the laser at the cost of extinction ratio degradation. A discrepancy of about 13 dB exists between the measured and the calculated error-rate performance curves. The major part of the discrepancy, 10 dB, is due to the extinction ratio degradation.     

An analytical model for alloyed ohmic contacts using a trilayer transmission line model

This paper describes a Transmission Line Model approach to the modeling and analysis of alloyed planar ohmic contacts. It briefly reviews the standard Transmission Line Model (TLM) commonly used to characterize a planar ohmic contact. It is shown that in the case of a typical Au-Ge-Ni alloyed ohmic contact, a more realistic model based on the TLM should take into account the presence of the alloyed layer at the metal-semiconductor interface. In this paper, such a model is described. It is based on three layers and the two interfaces between them, thus forming a Tri-Layer Transmission Line Model (TLTLM). Analytical expressions are derived for the contact resistance Re and the contact end resistance Rc of this structure, together with a current division factor, S. Values for the contact parameters of this TLTLM model are inferred from experimentally reported values of Re and Re for two types of contact. Using the analytical outcomes of the TLTLM, it is shown that the experimental results obtained using a standard TLM can have considerable discrepancies.<>     

长途光传输线路技术的发展

光纤线路性能制约着高速率、大容量，远距离光传输系统的发展与应用，文章简要分析了光纤线路技术的最新发展，展望了主要技术的应用前景。     

Low-cost 2 Mbit/s optical local line transmission system using single-mode fibre

A laboratory demonstration is reported in which low-cost optoelectronic devices are used for transmission over 9/125 ?m single-mode fibre at 2 Mbit/s. This novel system has been designed for application in local network and office systems where optical device cost constraints present severe restrictions on the technology options.     

Monitoring power transmission lines using a wireless sensor network

Power transmission is the bulk transfer of electrical energy from power plants to sub‐stations. A wireless sensor network is a promising technology for transmission line monitoring due to its low cost, easy installation, large‐scale coverage, and fault tolerance characteristics. A wireless sensor network is application‐specific; therefore, we investigate the new features and requirements of the wireless sensor network used in transmission line monitoring. Then, we propose an efficient wireless sensor network framework, which includes a clustering algorithm to simplify network management and to balance the network's energy consumption and a hybrid media access control (MAC) (H‐MAC) protocol to handle traffic variability. The framework takes advantage of the features of network topology and traffic pattern to optimize the protocols' performance on real time and energy efficiency. The results indicate that the H‐MAC shows a significant improvement in the network's reliability, real‐time performance, and energy efficiency, and the cluster hierarchy can balance the network's energy consumption. Furthermore, the cluster hierarchy also prolongs the network's lifetime. Copyright © 2014 John Wiley & Sons, Ltd.     

Fast transmission line coupling calculation using a convolutiontechnique

A fast method for the calculation of the mutual coupling between transmission lines is presented. The method is based on using the convolution of the incident field and the current induced by a Dirac impulse type field. Only first-order coupling between the lines is taken into account. This means that only the current induced by the source line is taken into account and all currents resulting from induction by this induced current are discarded. The technique is orders of magnitude faster than traditional moment method techniques because no large matrix equations need to be solved     

Optical soliton communication in a positively and negativelydispersion-allocated optical fibre transmission line

A bright optical soliton described by a nonlinear Schrodinger equation can survive even in a positive dispersion region as long as the average dispersion has a negative value. This allows us to combine fibres with large positive and large negative dispersion, which in turn will enable us to introduce solitons in a commercial system     

Polarimetric optical fiber sensor using a frequency stabilizedsemiconductor laser

Improved performance of a polarimetric optical fiber sensor for remote temperature measurement by the use of a frequency-stabilized semiconductor laser is discussed. The temperature change is measured from the phase delay between two orthogonally polarized modes in a polarization-maintaining fiber. The sensor output signal is demodulated utilizing direct modulation of the laser frequency. The center frequency of the modulated laser is locked to a Fabry-Perot interferometer by controlling the injection current. The minimum detectable temperature is evaluated experimentally to be less than 0.005°C, which is several times smaller than that obtained with the free-running laser     

基于无线传感技术的光传输设备的设计

提出了基于无线传感技术的光传输设备的应用,解决了传统的低速业务在有线光传输领域中的缺陷,重点阐述了光传输设备的硬件系统、无线传感器模块、通信协议和软件系统等模块的设计与实现。     

An embedded transmission scheme using PPM signaling with symmetric error-correcting codes for optical CDMA

An embedded transmission (ET) scheme is proposed to easily apply error-correcting codes into optical code-division multiple-access (CDMA) systems for immunity from multiple-access interference (MAI). The ET scheme offers high transmission capability over the traditional scheme using pulse position modulation (PPM) signaling, because a 2/sup J/-ary symbol of each user is embedded in the signature sequence with 2/sup J/ weighted positions. Furthermore, the ET scheme with 2/sup J/-ary PPM signaling makes the optical CDMA system J parallel transmission systems, because J bits consisting of 2/sup J/-ary symbol are separately decided. Since such a separate decision is a comparison decision, the effect of MAI added in the optical channel is converted to symmetric errors in the individual parallel transmission systems. Using the symmetric error-correcting (SEC) code immunizes the individual parallel transmission systems against MAI more easily than the embedded-modulation scheme described in because the ET scheme avoids using the asymmetric error correcting code, which is difficult to implement. We analyze the bit error rate under Poisson photon counting channel and show that the ET scheme has an advantage of good energy efficiency over the traditional scheme in applying SEC codes.     

An improved approach of optical loss measurement using photocurrent and optical transmission in an electroabsorption modulator

We report an improved method to extract the optical absorption coefficient of a semiconductor electroabsorption modulator. Only the transmission and photocurrent data are needed with this method. The method makes it possible to obtain the optical coupling efficiency between laser and modulator, photocurrent conversion efficiency, and optical absorption coefficients from experimental data.     

Configuration of the optical transmission line using stimulated Raman scattering for signal light amplification

Expansion of a repeater spacing of optical transmission line is investigated using forward stimulated Raman scattering generated by a 1.34-μm Nd:YAG laser to amplify the signal light. Achievable repeater spacing at the 1.42-μm wavelength transmission is numerically estimated on the basis of coupled power equations and experimentally obtained Raman gain for various core-cladding index difference. A transmission distance of more than 200 km is predicted for an input signal light power of 100 μw and a pump power of 200 mW using a fiber with a relative index difference of 1 percent.     

High-speed data transmission on an optical fiber using a byte-wideWDM system

The advantages and problems of using wavelength division multiplexing (WDM) to transmit byte-wide data in parallel through a single-mode optical fiber are studied. The principle problem which is particular to byte-wide transmission is shown to be bit skew caused by group delays of the different transmission wavelengths. The aggregate bit rate of the byte-wide link is shown to be equal to the aggregate bit rate of the serial link for all byte sizes     

Specific contact resistance using a circular transmission line model

The measurement of the specific contact resistance of ohmic contacts to semiconductors can be made in a number of ways. One of the methods uses a transmission line model of an ohmic contact on a semiconductor and this paper describes the application of the transmission line model to a contact test pattern of circular symmetry. By using a circular test pattern, the mesa etch step necessary for the standard rectangular test pattern may be omitted, thus simplifying test pattern fabrication.     

Impedance transformation using a hyperbolic cosine-squared tapered transmission line

A closed-form equation for the impedance transformation of an arbitrarily complex load, using a hyperbolic cosine-squared tapered transmission line, is presented. Design charts are also given. A numerical example is considered and results indicate a tremendous reduction in size, in comparison to other forms of lines, when hyperbolic cosine-squared lines are employed to match a large complex impedance to a real 50 Ω impedance.