M. Suleyman Demokan

Performance analysis of a time-division-multiplexed fiber Bragg grating sensor array by use of a tunable laser source

The results of an investigation of the performance of a time-division-multiplexed (TDM) fiber Bragg grating (FBG) sensor array using a tunable laser source are reported. The system performance is found limited by the extinction ratio of the optical pulse modulator used for pulse amplitude modulation. Formulas that relate the crosstalk to the extinction ratio of the optical pulse modulator, the modulation parameters of the tunable laser, and the optical path differences among sensing channels are derived. Computer simulation shows that an array of 20 FBG sensors with 3 /spl mu//spl epsi/ resolution can be realized with a commercially available single Mach-Zehnder type optical pulse modulator of -35-dB extinction ratio.

Development of a fibre-optic sensor for partial discharges in oil-filled power transformers

Abstract Determination of partial discharge locations in large oil-filled power transformers is unreliable and difficult using external acoustic sensors, and internal sensors would need to be non-metallic. Thus the use of a fibre-optic coil as an acoustic sensor would allow the detection and location of partial discharges with potentially a much greater sensitivity. This paper describes the design of such a sensor and its signal processing requirements, its construction and its initial testing. The sensor was found to be able to detect 1-Pa acoustic pressure waves under optimum conditions; and to detect partial discharges in small artificial voids in an oil-bath.

FMCW multiplexing of fiber Bragg grating sensors

We report on the use of frequency-modulated continuous wave (FMCW) techniques for multiplexing fiber Bragg grating (FBG) sensors. This technique is based on the modulation of light intensity from a broadband source by a linear swept-frequency RF carrier. Signals from the FBG sensors located at different positions in an array are separated in frequency domain and demodulated using a tunable optical filter. The potential and limitation of the technique are discussed. A three-sensor FMCW multiplexed FBG array of parallel topology and a six-sensor hybrid FMCW/WDM system were experimentally demonstrated with -30 dB crosstalk between sensors and 2 /spl mu//spl epsi/ resolution in terms of root mean square (RMS) strain value.

Parallel image processing with one-dimensional DSP arrays

Abstract This paper describes a study of parallel image processing algorithms implemented on a one-dimensional DSP array. DSPs are developed for computationally intensive signal processing operations. Recently introduced parallel DSPs can be used for all levels of image processing operations and they provide easy development of a parallel system. In addition, due to the computing power delivered by these processors, we can employ coarse grain parallelism instead of the traditional fine-grain parallelism. Modularity, expandability and easy programming are other advantages of parallel DSPs. In this paper, parallel implementation of some selected image processing algorithms is described and performance results are presented.

Optimal sensing of current based on an extrinsic Sagnac interferometer configuration

The theory and experimental verification of an optical current sensor based on an extrinsic Sagnac interferometer configuration is presented. Superior performance with regard to current sensitivity and input/output linearity, and simple installability of the sensor makes it very suitable for remote current sensing in power distribution applications.

Communication in a multi-layer MIMD system for computer vision

Algorithms in computer vision are computationally intensive and have distinct characteristics. Message-passing MIMD computers are popular architectures for computer vision due to their flexibility and asynchronous structure. However, performance of parallel programs executed on these systems is dependent on the efficiency of inter-processor communication. This paper describes a software system developed to handle complex communication mechanisms for a system designed for computer vision applications. The system is constructed with TI320C40 DSPs and employs the distributed memory MIMD paradigm. A set of experiments has been conducted to determine the hardware parameters of the communication links of the processors. Furthermore, the performances of the communication algorithms developed, which are frequently required in parallel vision algorithms, are presented. These results will be useful in optimizing performance of parallel programs developed for the system.

All-optical packet switching with all-optical header processing using Fabry-Perot laser diodes

We will describe recent results in all-optical packet switching with all-optical header processing using Fabry-Perot laser diodes (FP-LD). First, we will report an all-optical header processor and control signal generator using a single FP-LD with a special two-intensity-level control signal and a novel self-routing address format for the data packets. We then show that the special control signal can be generated by direct modulation of a DFB laser with square electrical pulses thus simplifying implementation. We will demonstrate that a single Fabry-Perot laser diode can also serve as an all-optical on/off switch with all-optical header processing. The header rate is 5 Gb/s and the payload rate is 10 Gb/s. The all-optical on/off switch can also be realized by using a FP-LD as the header processor only and executing the packet switching at a separate stage. The two-stage implementation of all-optical on/off switch eliminates the residue header bits problems if only a single FP-LD is used. Finally, we propose an all-optical packet-switched ring network which can be constructed from the all-optical on/off switches demonstrated.

TDM of FBG sensors by use of a tunable laser source

The results of an investigation of the performance of a TDM FBG sensor array using a tunable laser source are reported. The system performance is found to be limited by the extinction ratio of the optical pulse modulator used for pulse amplitude modulation. Formulas that relate the crosstalk to the extinction ratio of the optical pulse modulator, the modulation parameters of the tunable laser, and the optical path differences among sensing channels are derived. Computer simulation shows that an array of 20 FBG sensors with 3 (mu) (epsilon) resolution can be realized with a commercially available single Mach-Zehnder type optical pulse modulator of -35 dB extinction ratio. Experiments with a 4-FBG sensor array demonstrated a strain resolution of about 3.98 (mu) (epsilon) with an optical pulse modulator of about -24 dB extinction ratio.

Highly sensitive long-period fiber grating temperature sensor

A novel technique to increase the temperature sensitivity of LPGs by exploiting the relatively large thermal coefficient of index-matching fluid to induce a large spectral shift of the LPG is reported in this paper. It is shown that the wavelength shift with temperature for such a LPG sensor can be as much as 1,500 times larger than that of sensors made of fiber Bragg gratings. A LPG-based temperature sensor with a resolution of about 0.03 degree(s)C is reported.

Highly sensitive temperature sensor using long-period fiber grating

In this paper, we report a novel technique to increase the temperature sensitivity of a LPG by nearly two hundred times by exploiting the extremely large dependence of the spectral shift of an LPG on its ambient refractive index. The temperature coefficient of the packaged LPG sensor was measured to be 8.8 nm/ degree(s)C from 16 degree(s)C to 20 degree(s)C which is about 180 times higher than an unpackaged LPG. Correspondingly, it is about 800 times more sensitive than a fiber Bragg grating sensor which has a typical temperature coefficient of 0.011 nm/ degree(s)C.