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Data Conversion Enhances Transmission Over Optical Link

IP.com Disclosure Number: IPCOM000035117D
Original Publication Date: 1989-Jun-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Gibson, BD: AUTHOR [+2]

Abstract

This article describes a fiber optics transmission system with a self-adjusting bias. Advanced laser printheads require non-return- to-zero (NRZ) data signals and a data clock signal to be sent at high frequencies over long distances. Optical fibers have low transmission loss and low electromagnetic emission characteristics. The output reference voltage of the selected optical receiver varies a great extent due to temperature fluctuations and device-to-device differences. These variations are in the range of the peak-to-peak output signal. Because of this characteristic, the transitions of NRZ data cannot be reliably detected at the receiver's output without periodically adjusting a compare threshold for each receiver.

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Data Conversion Enhances Transmission Over Optical Link

This article describes a fiber optics transmission system with a self-adjusting bias. Advanced laser printheads require non-return- to-zero (NRZ) data signals and a data clock signal to be sent at high frequencies over long distances. Optical fibers have low transmission loss and low electromagnetic emission characteristics. The output reference voltage of the selected optical receiver varies a great extent due to temperature fluctuations and device-to-device differences. These variations are in the range of the peak-to-peak output signal. Because of this characteristic, the transitions of NRZ data cannot be reliably detected at the receiver's output without periodically adjusting a compare threshold for each receiver.

Gating the data signals with the data clock converts the output signals to return-to-zero signals. Because this type data has a maximum DC component of half the data amplitude, the receiver's output voltage transitions can be simply detected. From the figure, it can be seen that the DC component of the output signal is subtracted, leaving a minimum peak amplitude of half that of the peak- to-peak value. A threshold of less than half the amplitude voltage is set and the signal is detected. The signal is then clocked with the data clock to regenerate the NRZ data.

The advantages to this arrangement are that it eliminates the need for individual threshold adjusting, a major advantage because of t...