Browse Prior Art Database

Automatic System Gain Control for Analog Fiber-Optic Links

IP.com Disclosure Number: IPCOM000099544D
Original Publication Date: 1990-Feb-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 2 page(s) / 69K

Publishing Venue

IBM

Related People

Naylor, AR: AUTHOR [+2]

Abstract

A simple method of continuously calibrating analog fiber-optic link systems during use, in order to compensate for the degradation and variabilities of link interface components and of the transmission media. The analog output signal level is accurately maintained if link length is changed, or if link components degrade with time and temperature. The transfer function of light-emitting diodes (LEDs) is known to degrade with age and to be variable from one sample to another. These factors make the use of LEDs for analog datalinks problematical. This disclosure describes a low-cost system for controlling the overall gain of a fiber-optic data link without the need for feedback across the optical interface.

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Automatic System Gain Control for Analog Fiber-Optic Links

       A simple method of continuously calibrating analog
fiber-optic link systems during use, in order to compensate for the
degradation and variabilities of link interface components and of the
transmission media.  The analog output signal level is accurately
maintained if link length is changed, or if link components degrade
with time and temperature.  The transfer function of light-emitting
diodes (LEDs) is known to degrade with age and to be variable from
one sample to another.  These factors make the use of LEDs for analog
datalinks problematical.  This disclosure describes a low-cost system
for controlling the overall gain of a fiber-optic data link without
the need for feedback across the optical interface.  The work
originates from investigations into monitor interfaces but is
applicable, with modification, to any analog optical data
transmissions system.

      The application of this method to a CRT monitor analog video
link is described with reference to Fig. 1.  During each line
blanking period the input to the video digital-to-analog converter
(DAC) is switched to all ones for the duration of the horizontal
pulse.  This causes a "peak white" signal to be transmitted over a
fiber-optic link to the monitor.

      Referring to Fig. 2, the Link Receiving Amplifier (LRA)
contains an Automatic Gain Control (AGC) Circuit, the gain of which
is controlled by the output of a differential amp...