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Filter Method to use Self-Pulsating Lasers at Gigabit Data Rates

IP.com Disclosure Number: IPCOM000113788D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 57K

Publishing Venue

IBM

Related People

Hogan, WK: AUTHOR [+3]

Abstract

IBM and other manufacturers of fiber optic link products, operating at data rates less than 300 Mb/s, use self-pulsating type short-coherence length lasers to control or eliminate modal noise on multi-mode optical fibers. By sorting for HIGH Self Pulsation Frequency (SPF) devices, these lasers can be extended for use at data rates from 300 Mb/s to 600 Mb/s. Present techniques do not allow for the use of existing self-pulsating type lasers for higher data rate link applications because the SPF lies within the receiver bandwidth.

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Filter Method to use Self-Pulsating Lasers at Gigabit Data Rates

      IBM and other manufacturers of fiber optic link products,
operating at data rates less than 300 Mb/s, use self-pulsating type
short-coherence length lasers to control or eliminate modal noise on
multi-mode optical fibers.  By sorting for HIGH Self Pulsation
Frequency (SPF) devices, these lasers can be extended for use at data
rates from 300 Mb/s to 600 Mb/s.  Present techniques do not allow for
the use of existing self-pulsating type lasers for higher data rate
link applications because the SPF lies within the receiver bandwidth.

      In a typical fiber optic receiver, the transimpedance stage of
the preamplifier and the post amplifier both provide low pass
filtering.  However, the roll-off characteristics of these circuits
are typically each 2nd order (approximately 20 dB / decade), and they
would not alone sufficiently attenuate the self-pulsating signal.
Inclusion of a higher-order low-pass filter (4th order or 6th order)
between the preamplifier and the postamplifier adds attenuation to
the SPF signal without attenuating the data signal.  The low pass
filter design needs to exhibit tight control of the corner frequency
and provide low deviations from linear phase response.

      Implementation of a low pass filter, having properties as
described in the preceding paragraph, requires radio frequency or
microwave design principles in which each resistor, capacitor, and
inductor is rep...