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Browse Prior Art Database

Dual-Fiber Drive System

IP.com Disclosure Number: IPCOM000102325D
Original Publication Date: 1990-Nov-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 2 page(s) / 53K

Publishing Venue

IBM

Related People

Stilwell Jr, GR: AUTHOR

Abstract

The disclosed system provides a means for sending data on either single-mode (SM) fiber, or multi-mode (MM) fiber, with common transducers on both ends of the link. The optical signal is coherent when SM fiber is used and incoherent when MM fiber is used. Thus, the proper optical signal to provide the maximum transmission distance and the maximum data rate is used.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 65% of the total text.

Dual-Fiber Drive System

       The disclosed system provides a means for sending data on
either single-mode (SM) fiber, or multi-mode (MM) fiber, with common
transducers on both ends of the link.  The optical signal is coherent
when SM fiber is used and incoherent when MM fiber is used.  Thus,
the proper optical signal to provide the maximum transmission
distance and the maximum data rate is used.

      Data for transmission, properly encoded as required by the
protocol being used, is sent to the laser driver via a modulator, as
shown in the figure.  The modulator modulates a carrier (oscillator
output) with the data and presents this modulated signal to the laser
via the laser driver. The carrier is selected, using the oscillator
gate input, based on the fiber being used in the link.

      If the link is SM fiber, the gate signal is off and the carrier
is DC.  The modulated signal to the laser is a replica of the data.
The laser transmits coherent light as is required for best
performance on SM fiber.

      If the fiber is MM fiber, the gate signal is turned on. The
carrier is a very high frequency, typically several GHz. Since the
carrier is much faster than the data rate, it imparts minimal jitter
to the signal.

      It is well known that fast signals cause the laser wavelength
to shift slightly (chirp).  Chirp is caused by the change in the
optical index as injection current changes in the laser cavity. Chirp
occurs during each of the carr...