Wavelength-division-multiplexing (WDM) technology is now recognized as one of the key technologies in optical communications systems. This is because it has great potential to enhance system design and flexibility. This paper reviews state-of-the-art optical multi/demultiplexers (MUX/DEMUX) and WDM system design. Various system applications are also summarized.

Review and status of wavelength-division-multiplexing technology and its application

A communications network has a plurality of nodes interconnected by an optical transmission medium. The transmission medium is capable of a carrying a plurality of wavelengths organized into bands. A filter at each node for drops a band associated therewith and passively forwards other bands through the transmission medium. A device is provided at each node for adding a band to the transmission medium. Communication can be established directly between a pair of nodes in the network sharing a common band without the active intervention of any intervening node. This allows the network to be protocol independent. Also, the low losses incurred by the passive filters permit relatively long path lengths without optical amplification.

WDM optical network with passive pass-through at each node

The invention relates to certain compounds or pharmaceutically acceptable salts, solvates, clathrates, or prodrugs thereof, that are useful as immunosuppressive agents and for treating and preventing inflammatory conditions, allergic disorders, and immune disorders.

Compounds for inflammation and immune-related uses

The technical feasibility of applying a fiber-optic multilevel QAM (quadrature amplitude modulation) subcarrier multiplexing scheme to a multichannel conventional TV signal transport is explored. This transport scheme has some advantageous features. Because a digital subcarrier modulation scheme is used, a high-quality transmission performance is expected to be achieved, if the bit error is sufficiently small over a transmission line and the required carrier-to-noise ratio (CNR) is relatively small among the many candidates of subcarrier modulation schemes. The use of multilevel modulation allows the bandwidth to be efficiently utilized; consequently, up to 40-channel uncompressed digital TV signals are estimated to be accommodated in the frequency region of the VHF and UHF bands, where well-developed and inexpensive electronics can be easily applied. >

Fiber-optic subcarrier multiplexing video transport employing multilevel QAM

The pulse width modulation (PWM) technique has been revisited and analyzed to evaluate its merits for application to analog signal transmission in fiber-optic links. Fourier analysis of the PWM signal reveals that it can be used as a vehicle to launch an analog signal onto optical fiber when a symmetrical natural sampling process is used. The SNR of the modulated signal depends on the timing jitter of the carrier pulses and a wide-band (45 MHz) SNR of 45 dB has been obtained with a commercially available multimode laser transmitter. A linear dynamic range of over 50 dB has been experimentally demonstrated. The full fiber bandwidth can be utilized by using a very high pulse carrier frequency, while a more popular pulse frequency modulation technique provides about a 10-MHz analog signal bandwidth when 1 km of multimode fiber is used in conjunction with a short wavelength (0.87 μm) LED transmitter. Analog transmission capability was experimentally demonstrated by constructing a simple video link using common laboratory equipment. The performance of the video link supports the PWM modulation theory developed here and elsewhere. The experimental results indicated that PWM is potentially very attractive for low-cost broad-band local area network (LAN) application, including future highly interactive offices, hospitals, and automated factory floors.

Pulse width modulation for analog fiber-optic communications

Future subscriber loops will provide various services including broad-band video. Fiber optic technology is the key for introducing these services. The Electrical Communication Laboratories (ECL) of Nippon Telegraph and Telephone Public Corporation (NTT) have been promoting research and development on basic technology of fiber optic subscriber loops, and studying the ways to use fiber optic subscriber loops for new services. As one of the programs, a field trial of fiber optic subscriber loops was planned and conducted in the Yokosuka area from April 1980 until May 1981. This paper first describes fiber optic transmission technologies for subscriber loops. Then, the system configuration and experimental results of the Yokosuka field trial are presented.

K. Nosu

Papers

A Field Trial of Fiber Optic Subscriber Loop Systems Utilizing Wavelength-Division Multiplexers