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Browse Prior Art Database

Emitter-Dotted Modulator for Clock Recovery in Optical Communication

IP.com Disclosure Number: IPCOM000121021D
Original Publication Date: 1991-Jul-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 60K

Publishing Venue

IBM

Related People

Moulic, JR: AUTHOR [+2]

Abstract

This article describes a practical fiber-optic modulator configuration for synchronization and clock recovery in an optical data link using the pilot-tone technique [*]. The pilot tone is a sine wave, synchronous to and superimposed on a non-return-to-zero (NRZ) digital data stream, as shown in Fig. 1. The frequency of the pilot is equal to the data bit rate, or an integer multiple thereof. Its amplitude is less than that of the digital signal.

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Emitter-Dotted Modulator for Clock Recovery in Optical Communication

      This article describes a practical fiber-optic modulator
configuration for synchronization and clock recovery in an optical
data link using the pilot-tone technique [*].  The pilot tone is a
sine wave, synchronous to and superimposed on a non-return-to-zero
(NRZ) digital data stream, as shown in Fig. 1.  The frequency of the
pilot is equal to the data bit rate, or an integer multiple thereof.
Its amplitude is less than that of the digital signal.

      The modulation configuration, as shown in Fig. 2, uses emitter-
dotted outputs from two separate emitter-coupled logic (ECL) 10116
circuits (within the same physical package).  One differential input
pair is driven by a 100 mV sine signal, nominally centered around
ground, and a ground reference.  Another 10116 circuit receives the
digital signal, at standard ECL levels, and a reference voltage Vbb
(available on-chip from the 10116).  The outputs of the two circuits
are then tied together (dotted) and connected to a pull-down voltage
through a laser or LED and a resistor. The pull-down voltage can be
varied, as can the sine wave amplitude and offset, to improve the
symmetry and purity of the sine wave signal both high and low
(logical "1" and logical "0") digital data.

      Each ECL output circuit can source at least 50 mA. When the
modulated signal is adjusted for best wave shape, current through the
laser diode may be excessive. ...