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Method of Reducing Crosstalk between Data Sites in Time Domain Hole-Burning

IP.com Disclosure Number: IPCOM000117013D
Original Publication Date: 1995-Dec-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 93K

Publishing Venue

IBM

Related People

Jefferson, M: AUTHOR [+2]

Abstract

The idea that information could be stored in the inhomogeneous absorption band of a solid at low temperatures was first patented by (1) and has been subsequently discussed by many authors (2). (3) proposed an alternative approach which utilizes so-called "photon echoes" to store multiple data bits in a single spot. This method stores the information by means of modulation of the ground state population of the absorbing species by interference between a "reference pulse" and a temporally complex "data pulse" which contains the desired data in a serial format (4). Application of a reference pulse at a later time causes a free induction decay of the absorbing ions which is modulated temporally in such a way as to reproduce the original "data pulse".

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This is the abbreviated version, containing approximately 51% of the total text.

Method of Reducing Crosstalk between Data Sites in Time Domain Hole-Burning

      The idea that information could be stored in the inhomogeneous
absorption band of a solid at low temperatures was first patented by
(1) and has been subsequently discussed by many authors (2).  (3)
proposed an alternative approach which utilizes so-called "photon
echoes" to store multiple data bits in a single spot.  This method
stores the information by means of modulation  of the ground state
population of the absorbing species by interference between a
"reference pulse" and a temporally complex "data pulse" which
contains the desired data in a serial format (4).  Application of a
reference pulse at a later time causes a free induction decay of the
absorbing ions which is modulated temporally in such a way as to
reproduce the original "data pulse".  This technique has been used to
store 1600 data bits in a single spot in a rare earth ion system (5).

      An obvious difficulty in using this approach to realize a high
density storage system is the potential for serious crosstalk created
when the powerful reference pulse partly illuminates data stored in a
location adjacent to the desired spot.  This situation will cause an
additional photon echo coincident with the desired echo which will
distort it and lead to error in the detected bits.  Because the
nature of this storage concept more-or-less demands that the media be
of non-negligible thickness, effects due to beam diffraction, angular
misalignments, scattered light, and so forth will be difficult to
remove entirely.  This crosstalk could be such a serious issue as to
force drastic reduction in the storage density so as to reduce the
crosstalk to tolerable levels.

      A technique is disclosed by which the effect of crosstalk as
described above may be entirely eliminated or drastically reduced.
Work by (3) has shown that the phase coherency of the reference beam
is very important for the recovery of the stored data.  This is
obvious when it is realized that the nature of the stored data is
that of a hologram in frequency space between the spectrum of the
reference pulse and that the data pulse.

      Other preliminary experiments have been done which show that
psuedo-random phase modulation of the reference pulse during writing
can be used to eliminate photon echoes recalled using a different
psuedorandom code, and a proposal has been made to use this effect
for data encryption, in order to make a secure storage device (6).

      Proposed is a totally different use of this effect, namely
as a means of eliminating crosstalk echoes from adjacent data storage
sites.  If phase modulated reference pulses are used, and if each
data site has been assigned a different psuedo random reference
pulse, then...