Early LEDs were packaged in metal cases similar to those of transistors, with a glass window or lens to let the light out. Modern indicator LEDs are packed in transparent molded plastic cases, tubular or rectangular in shape, and often tinted to match the device color. Infrared devices may be dyed, to block visible light. More complex packages have been adapted for efficient heat dissipation in high-power LEDs. Surface-mounted LEDs further reduce the package size. LEDs intended for use with fiber optics cables may be provided with an optical connector.
LEDs are made in different packages for different applications. A single or a few LED junctions may be packed in one miniature device for use as an indicator or pilot lamp. An LED array may include controlling circuits within the same package, which may range from a simple resistor, blinking or color changing control, or an addressable controller for RGB devices. Higher-powered white-emitting devices will be mounted on heat sinks and will be used for illumination. Alphanumeric displays in dot matrix or bar formats are widely available. Special packages permit connection of LEDs to optical fibers for high-speed data communication links.
The light from LEDs can be modulated very quickly so they are used extensively in optical fiber and free space optics communications. This includes remote controls, such as for television sets, where infrared LEDs are often used. Opto-isolators use an LED combined with a photodiode or phototransistor to provide a signal path with electrical isolation between two circuits. This is especially useful in medical equipment where the signals from a low-voltage sensor circuit (usually battery-powered) in contact with a living organism must be electrically isolated from any possible electrical failure in a recording or monitoring device operating at potentially dangerous voltages. An optoisolator also lets information be transferred between circuits that do not share a common ground potential.
The demands of optical fiber-based biomedical applications can, in many cases, outstrip the capabilities of lens-based commercially available fiber optic rotary joints. In some circumstances, it is necessary to use very broad spectral bandwidths (near UV to short-wave IR) and specialized optical fibers, such as double-clad fiber, and have the capacity to accommodate high rotational velocities. The broad spectrum, stretching down into the UV, presents two problems: (1) adequate chromatic correction in the lenses across the entire bandwidth and (2) strong UV absorption by the fluids used to lubricate the rotary joint. To accommodate these types of applications, we have developed an ultra-wideband lensless fiber optic rotary joint based on the principle that when two optical fibers are coaligned and placed in contact (or very close), the optical losses at the junction are very low. The advances demonstrated here enable excellent performance (
DJAFAR K. MYNBAEV, PHD, is a professor at the New York City College of Technology (CUNY) Electrical and Telecommunications Engineering Technology Department. He has spent a significant part of his career working at telecommunications in general and optical communications in particular fields and has published more than 100 papers on these subjects. He currently holds over two dozen patents and is a well-known speaker at conferences worldwide. In 2001, he, with Lowell L. Scheiner, published a book entitled Fiber-Optic Communications Technology. LOWELL L. SCHEINER was an acclaimed writer and editor in the engineering and technology industries. He worked for numerous publications concerning technology and design in his main capacity and at major corporations as a public relations consultant. Lately, he was a professor at NYU Tandon School of Engineering. Permissions Request permission to reuse content from this site
CSC 409 Optical Fiber Communication 3 credits Wave propagation in single mode and multimode optical fibers. Step-index and graded index fibers. Gaussian approximation of fields in single mode fiber, spot size, equivalent step index of single mode fiber. Material, waveguide and internodes dispersions. Polarization and birefringent fibers. Ray theory, optimal profile, mode coupling in multimode fiber. Optical fiber measurement and characterization. Launching efficiencies in multimode and single mode fibers. (Prerequisite: CSC 430, Senior Standing)
CSC 485 Telecommunication Engineering 3 credits To present a general introduction to telecommunications aspects such as signal acquisition, transmission and processing in communication systems. This subject provides general telecommunication knowledge. Including: Characteristics of typical communication channels; Typical signals (speech, audio, video, data) and their characteristics; Basic analogue and digital techniques; Key techniques in handling transmission system issues (modulation, coding, multiplexing, etc); System performance and evaluation (channel noise, inters symbol interference, bit error rate, etc.); Major communication systems including telephony, radio, TV, satellite, mobile phone, optical fiber, radar and networks. (Prerequisite: CSC 430) 2b1af7f3a8