Browse Prior Art Database

Optical Amplification of Reflected Light to Increase Signal To Noise Ratio in Optical Read Back Systems

IP.com Disclosure Number: IPCOM000122025D
Original Publication Date: 1991-Oct-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 74K

Publishing Venue

IBM

Related People

Rubin, KA: AUTHOR [+3]

Abstract

It is well known that increased signal to noise ratio (SNR) in optical read-back can be directly translated into increased linear bit density. This is primarily due to the fact that increased SNR leads to a corresponding decrease in pulse jitter, thereby allowing the designer a larger margin in the channel for the increased bit shifts that come with decreased bit to bit spacing. This article describes a technique for increasing the SNR of an optical read-back system which is dominated by either electronic or shot noise wherein an optical amplifier placed in the read-back path is used to increase the intensity of light incident on the photodetectors.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Optical Amplification of Reflected Light to Increase Signal To Noise
Ratio in Optical Read Back Systems

      It is well known that increased signal to noise ratio
(SNR) in optical read-back can be directly translated into increased
linear bit density.  This is primarily due to the fact that increased
SNR leads to a corresponding decrease in pulse jitter, thereby
allowing the designer a larger margin in the channel for the
increased bit shifts that come with decreased bit to bit spacing.
This article describes a technique for increasing the SNR of an
optical read-back system which is dominated by either electronic or
shot noise wherein an optical amplifier placed in the read-back path
is used to increase the intensity of light incident on the
photodetectors.

      Noise in an optical read-back system is comprised of several
components: media, write, laser, shot and electronic noises.  Of
these the first three scale linearly with laser read power, shot
noise scales as the square root of laser read power, while electronic
noise is independent of laser read power.  Since the signal scales
linearly with laser read power, the SNR can be improved by increasing
laser read power in the cases where the system is dominated by shot
or electronic noises.  High data rate optical channels which require
high electronic bandwidth are an example of an optical system where
electronic noise, which increases with bandwidth, could be the
dominant noise source.  Low light level systems, such as
magneto-optic recording systems at short wavelengt...