Browse Prior Art Database

Multichannel Optical Network Using Optical Subcarrier Multiplexing

IP.com Disclosure Number: IPCOM000119630D
Original Publication Date: 1991-Feb-01
Included in the Prior Art Database: 2005-Apr-02
Document File: 4 page(s) / 184K

Publishing Venue

IBM

Related People

Bates, RJS: AUTHOR [+2]

Abstract

This article describes a method for constructing multiple-access networks based on optical subcarrier multiplexing. The method divides the aggregate bandwidth of the communication medium among multiple transmission subchannels.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 35% of the total text.

Multichannel Optical Network Using Optical Subcarrier Multiplexing

      This article describes a method for constructing
multiple-access networks based on optical subcarrier multiplexing.
The method divides the aggregate bandwidth of the communication
medium among multiple transmission subchannels.

      Advances in laser and receiver technologies enable a large
number of stations to be interconnected in a star topology by means
of a passive optical coupler.  Such networks offer a reliable and
inexpensive means for implementation of local-area and room-area
networks, multiprocessor interconnection networks, I/O buses, and
workstation clusters.  Although the optical medium used in an optical
passive-star network allows bandwidths of several gigabits/second,
there are many practical limitations to exploiting this bandwidth.
One of them is the overhead introduced by the medium-access protocol.
Two of the most widely used protocols for control of access to the
medium are CSMA/CD (Carrier-Sense Multiple-Access with
Collision-Detection), and the token bus.  Both the above protocols
limit the utilization of the medium when the number of stations is
large. In the case of CSMA/CD, frequent collisions between stations
degrade the performance.  In the case of token-bus, the performance
is limited by the token-rotation time, which increases with the
number of stations.  These inefficiencies become especially
significant at very high speeds, resulting in poor media-utilization.

      Optical subcarrier multiplexing (OSCM) provides a means to
divide the aggregate bandwidth of the optical medium in an optical
passive-star network into multiple channels, each offering a fraction
of the aggregate bandwidth.  The basic concepts of OSCM in a
multi-access network are described in (*).  On the transmitter side,
the data in each channel modulates a subcarrier signal in the
electronic domain.  A variety of modulation techniques can be
employed here.  The modulated subcarrier, in turn, modulates a laser
transmitter by intensity- modulation.  The star coupler superimposes
the individual subcarrier signals and broadcasts them to the
receivers.  The detector in each station receives all the subcarrier
channels.  One of the channels can be separated from this composite
signal by mixing with a local oscillator which is tuned to the
frequency of the subcarrier used to modulate the original signal.
The demodulated signal is then amplified and detected to yield the
original data.

      The method is illustrated in the figure.  A network typically
consists of N stations connected to a central optical passive
star-coupler by means of duplex fiber-links.  The aggregate bandwidth
B of the medium is divided into K subchannels.  For simplicity, the
bandwidth of each subchannel is taken as equal to B/K.  The stations
are partitioned into mutually exclusive groups such that stations in
a particular group share the same receiving subchannel.  Fo...