Optical fibre systems

1978 ◽  
Vol 289 (1356) ◽  
pp. 135-150 ◽  
Keyword(s):  
Semiconductor Lasers ◽  
Optical Fibre ◽  
Light Emitting Diode ◽  
Beam Quality ◽  
Single Mode ◽  
Laser Source ◽  
Fibre Strength ◽  
Optical Source ◽  
Light Emitting ◽  
Wide Range

The present state of research and development into optical fibre systems for applications in telecommunications is reviewed and some of the principal problems remaining are discussed. Attenuations close to the intrinsic limits of the materials available have been reached in laboratory fibres and losses in optical cables installed under normal working conditions are below 5 dB/km. Bandwidths available range from 20 MHz km, in step-index multimode fibres with light emitting diode sources, to 10 GHz km with single-mode fibres and semiconductor lasers. If a truly monochromatic laser source operating in the region of minimum material dispersion becomes available then individual fibre capacities up to, or beyond, 100 GHz km are feasible. The major problems in cabling have already been largely overcome but further improvements in fibre strength, homogeneity and reproducibility are awaited. The difficulties are technological rather than fundamental and will succumb to good innovative engineering within the next few years. The same may be said of the requirements for such mundane, but vitally important, components as splices, connectors, couplers and even the lowly jack plug. Excellent and encouraging progress is being made with all of these items. Of the major hurdles remaining, that of a suitable optical source is by far the most difficult. The lifetime and reliability of existing semiconductor lasers are improving only slowly and need to be increased by at least an order of magnitude. It would also be an advantage if their line width, coherence and beam quality could be made to approximate more closely those of an ideal laser. Fortunately light emitting diodes can also be used if adequate lasers do not become available, but at the expense of system bandwidth and repeater spacing. Technological forecasting is fraught with hazards for the unwary but it is reasonable to expect systems to be operating in the telephone network in the 1980s at capacities from 140 Mbit/s to 500 Mbit/s at repeater spacings of at least 5 km and perhaps as high as 20 km. Serious study of the application of optical fibres to underwater cables will also have begun. If simple fibre cables can be made cheaply enough for use in installations to individual subscribers a wide range of new developments become possible, but these problems are more relevant to the 1990s.

scholarly journals LED Rail Signals: Full Hardware Realization of Apparatus with Independent Intensity by Temperature Changes

Electronics ◽  
2021 ◽  
Vol 10 (11) ◽  
pp. 1291
Author(s):  
Giuseppe Schirripa Schirripa Spagnolo ◽  
Fabio Leccese
Keyword(s):  
Temperature Sensor ◽  
Energy Efficient ◽  
Light Emitting Diode ◽  
Junction Temperature ◽  
Light Emitting ◽  
Temperature Changes ◽  
Wide Range ◽  
International Regulations ◽  
Long Lifetime ◽  
Set Up

Nowadays, signal lights are made using light-emitting diode arrays (LEDs). These devices are extremely energy efficient and have a very long lifetime. Unfortunately, especially for yellow/amber LEDs, the intensity of the light is closely related to the junction temperature. This makes it difficult to design signal lights to be used in naval, road, railway, and aeronautical sectors, capable of fully respecting national and international regulations. Furthermore, the limitations prescribed by the standards must be respected in a wide range of temperature variations. In other words, in the signaling apparatuses, a system that varies the light intensity emitted according to the operating temperature is useful/necessary. In this paper, we propose a simple and effective solution. In order to adjust the intensity of the light emitted by the LEDs, we use an LED identical to those used to emit light as a temperature sensor. The proposed system was created and tested in the laboratory. As the same device as the ones to be controlled is used as the temperature sensor, the system is very stable and easy to set up.

scholarly journals Optical whispering-gallery mode barcodes for high-precision and wide-range temperature measurements

2021 ◽  
Vol 10 (1) ◽  
Author(s):  
Jie Liao ◽  
Lan Yang
Keyword(s):  
High Precision ◽  
Dynamic Range ◽  
Single Mode ◽  
Whispering Gallery Mode ◽  
Temperature Measurements ◽  
Laser Source ◽  
Multiple Modes ◽  
Whispering Gallery ◽  
Wide Range ◽  
Thermal Sensing

AbstractTemperature is one of the most fundamental physical properties to characterize various physical, chemical, and biological processes. Even a slight change in temperature could have an impact on the status or dynamics of a system. Thus, there is a great need for high-precision and large-dynamic-range temperature measurements. Conventional temperature sensors encounter difficulties in high-precision thermal sensing on the submicron scale. Recently, optical whispering-gallery mode (WGM) sensors have shown promise for many sensing applications, such as thermal sensing, magnetic detection, and biosensing. However, despite their superior sensitivity, the conventional sensing method for WGM resonators relies on tracking the changes in a single mode, which limits the dynamic range constrained by the laser source that has to be fine-tuned in a timely manner to follow the selected mode during the measurement. Moreover, we cannot derive the actual temperature from the spectrum directly but rather derive a relative temperature change. Here, we demonstrate an optical WGM barcode technique involving simultaneous monitoring of the patterns of multiple modes that can provide a direct temperature readout from the spectrum. The measurement relies on the patterns of multiple modes in the WGM spectrum instead of the changes of a particular mode. It can provide us with more information than the single-mode spectrum, such as the precise measurement of actual temperatures. Leveraging the high sensitivity of WGMs and eliminating the need to monitor particular modes, this work lays the foundation for developing a high-performance temperature sensor with not only superior sensitivity but also a broad dynamic range.

scholarly journals Spectroscopy Transmittance by LED Calibration

Sensors ◽  
2019 ◽  
Vol 19 (13) ◽  
pp. 2951 ◽  
Author(s):  
Daniel Carreres-Prieto ◽  
Juan T. García ◽  
Fernando Cerdán-Cartagena ◽  
Juan Suardiaz-Muro
Keyword(s):  
Real Time ◽  
Light Emitting Diode ◽  
Research Work ◽  
Cost Effective ◽  
Spectral Width ◽  
Calibration Procedure ◽  
Pollution Monitoring ◽  
Light Emitting ◽  
Wide Range ◽  
Incandescent Lamps

Local administrations demand real-time and continuous pollution monitoring in sewer networks. Spectroscopy is a non-destructive technique that can be used to continuously monitor quality in sewers. Covering a wide range of wavelengths can be useful for improving pollution characterization in wastewater. Cost-effective and in-sewer spectrophotometers would contribute to accomplishing discharge requirements. Nevertheless, most available spectrometers are based on incandescent lamps, which makes it unfeasible to place them in a sewerage network for real-time monitoring. This research work shows an innovative calibration procedure that allows (Light-Emitting Diode) LED technology to be used as a replacement for traditional incandescent lamps in the development of spectrophotometry equipment. This involves firstly obtaining transmittance values similar to those provided by incandescent lamps, without using any optical components. Secondly, this calibration process enables an increase in the range of wavelengths available (working range) through a better use of the LED’s spectral width, resulting in a significant reduction in the number of LEDs required. Thirdly, this method allows important reductions in costs, dimensions and consumptions to be achieved, making its implementation in a wide variety of environments possible.

A High Efficiency Step-Up WLED Driver with Wide Range PWM Dimming

2012 ◽  
Vol 588-589 ◽  
pp. 884-887
Author(s):  
Fei Xu ◽  
Le Nian He
Keyword(s):  
Pulse Width Modulation ◽  
High Efficiency ◽  
Light Emitting Diode ◽  
System Efficiency ◽  
Current Sensing ◽  
Light Emitting ◽  
Wide Range ◽  
Simulation Results ◽  
Peak Value ◽  
Pwm Dimming

A high efficiency step-up White Light Emitting-diode (WLED) driver with PWM dimming is presented in this paper. An integrated current sensing technique is used to improve system efficiency. Meanwhile, a novel PWM(pulse width modulation) dimming scheme is proposed to achieve wide range dimming frequency, which can be adaptive to dimming frequency from 200Hz to 200 KHz. The proposed driver is designed with CSMC 0.5um 40V bipolar-CMOS-DMOS process. Simulation results verify the functionality of the design and high efficiency is realized, with a peak value of 94.12% at 5.5V-input and 200mA-load.

scholarly journals Light-Emitting Diode Based Photoacoustic Imaging System

2020 ◽  
Author(s):  
Ebrahim Najafzadeh ◽  
Parastoo Farnia ◽  
Alireza Ahmadian ◽  
Hossein Ghadiri
Keyword(s):  
Imaging System ◽  
Photoacoustic Imaging ◽  
Light Emitting Diode ◽  
Imaging Modality ◽  
Optical Excitation ◽  
Poly Vinyl Alcohol ◽  
Ultrasound Images ◽  
Light Emitting ◽  
Non Invasive ◽  
Wide Range

Purpose: A Photoacoustic Imaging (PAI) as a non-invasive hybrid imaging modality has the potential to be used in a wide range of pre-clinical and clinical applications. There are different optical excitation sources that affect the performance of PAI systems. Our goal is proving the capability of the Light-Emitting Diode (LED) based PAI system for imaging of objects in different depths. Materials and Methods: In this study the Full Width of Half Maximum (FWHM) and Contrast to Noise Ratio (CNR) of LED-based PAI system is evaluated using agar, and Poly-Vinyl Alcohol Cryogel (PVA-C) phantoms. Results: The results show that axial and lateral FWHM of the photoacoustic image in agar phantom 1%, are 0.59 and 1.16 mm, respectively. It is capable of distinguishing objects about 250 µm. Furthermore, one of the main improvements of photoacoustic images is achieved by proposed LED-based system that is a 26% higher CNR versus the ultrasound images. Conclusion: Therefore, the provided technical characteristics in this study have made designed LED-based PAI system as a suitable tool for preclinical and clinical imaging.

Resonant cavity light emitting diode for a polymer optical fibre system

2002 ◽  
Vol 17 (6) ◽  
pp. R1-R9 ◽  
Author(s):  
M Pessa ◽  
M Guina ◽  
M Dumitrescu ◽  
I Hirvonen ◽  
M Saarinen ◽  
...  
Keyword(s):  
Optical Fibre ◽  
Light Emitting Diode ◽  
Resonant Cavity ◽  
Light Emitting

The Single-Mode Light-Emitting-Diode

1993 ◽  
pp. 369-378 ◽  
Author(s):  
I. Schnitzer ◽  
E. Yablonovitch ◽  
A. Scherer ◽  
T. J. Gmitter
Keyword(s):  
Light Emitting Diode ◽  
Single Mode ◽  
Light Emitting

Investigation and Optimization of Laser Welding of Ti-6Al-4 V Titanium Alloy Plates

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Fabrizia Caiazzo ◽  
Vittorio Alfieri ◽  
Gaetano Corrado ◽  
Francesco Cardaropoli ◽  
Vincenzo Sergi
Keyword(s):  
Laser Welding ◽  
Titanium Alloys ◽  
Beam Quality ◽  
Tensile Tests ◽  
Laser Source ◽  
Face Centered Cubic ◽  
Butt Welding ◽  
Specific Strength ◽  
Wide Range ◽  
Predicted Values

Titanium alloys are employed in a wide range of applications, from aerospace to medicine. In particular, Ti-6Al-4 V is the most common, thanks to an excellent combination of low density, high specific strength, and corrosion resistance. Laser welding has been increasingly considered as an alternative to traditional techniques to join titanium alloys. An increase in penetration depth and a reduction of possible welding defects are indeed achieved; moreover, a smaller grain size in the fused zone (FZ) is benefited in comparison to either tungsten inert gas (TIG) or plasma arc welding, thus improving the tensile strength of the welded structures. This study was carried out on 3 mm thick Ti-6Al-4 V plates in square butt welding configuration. The novelty element of the investigation is the use of a disk-laser source, which allows a number of benefits thanks to better beam quality; furthermore, a proper device was developed for bead protection, as titanium is prone to oxidation when in fused state. A three-level factorial plan was arranged in face-centered cubic scheme. The regression models were found for a number of crucial responses and the corresponding surfaces were discussed; then a numerical optimization was carried out. The suggested condition was evaluated to compare the actual responses to the predicted values; X-ray inspections, Vickers micro hardness tests, and tensile tests were performed for the optimum.

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