Browse Prior Art Database

Fault-Tolerant Laser Transmitter Design

IP.com Disclosure Number: IPCOM000104916D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 4 page(s) / 116K

Publishing Venue

IBM

Related People

Georgiou, CJ: AUTHOR [+3]

Abstract

Disclosed is a fault-tolerant and fully-balanced laser transmitter design. This laser transmitter has very small switching noise in a dense optical interconnect environment due to its balanced configuration. Furthermore, the redundancy provided by this transmitter architecture increases the reliability of an optical interconnect and eliminates the possibility of link failure which usually results from laser failures.

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Fault-Tolerant Laser Transmitter Design

      Disclosed is a fault-tolerant and fully-balanced laser
transmitter design.  This laser transmitter has very small switching
noise in a dense optical interconnect environment due to its balanced
configuration.  Furthermore, the redundancy provided by this
transmitter architecture increases the reliability of an optical
interconnect and eliminates the possibility of link failure which
usually results from laser failures.

      Conventional laser transmitter designs using a differential
current switch (GaAs) or an emitter-coupled pair (silicon bipolar) to
drive laser diodes are vulnerable to switching noise frequently
arising in a dense interconnect environment [1].  This is due to the
imbalance load of a laser diode which usually consists of a large
capacitance and inductance presented to the driver.  A large current
transient thus occurs at high frequency operation when several of
these transmitters have to share a common power supply.  Furthermore,
the reliability of this type of laser transmitter array is limited by
the lifetime of the laser diodes.  A failure of any of the laser
diodes will disable the whole transmitter array.

      In this disclosure, a new architecture of laser transmitter is
proposed to overcome the switching noise and reliability problems
which frequently arise in a laser transmitter array design.  This
design, as shown in the figure, consists of the basic driver
circuitry, two laser diodes, two monitor photodiodes, monitor logic,
and a photonic switch.

      Under normal operating conditions, the input differential
signals are passed uninverted to the driver.  Light from the laser on
the right arm of the differential emitter-coupled pair is coupled to
the output fiber or waveguide through the photonic switch since it is
in the cross state (without bias).  The other laser diode under such
a circumstance merely serves as a dummy load; therefore, the
switching noise is greatly reduced [2].

      When the laser diode on the right arm fails, the monitor
circuit will detect this situation and invert the input as well as
switch the photonic switch into the bar state (with bias).
Furthermore, a current bypassing transistor is turned on at this
moment just in case the failure mode of the laser turns the laser
into an open circuit.  The output light signal is not affected and
retains the same logical correspondence with the logical input.  A
perfect load balance under such a situation can no longer be
maintained, but it is still much more balanced than the situation
when no dummy load is provided.

      If the other laser diode fails, the monitor circuit will also
detect this situation and turn on the bypass transistor for that
laser diode.  The state of the photonic switch, however, is
uncha...