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From the August 3, 1992 "EE Times", front page article.   "FYI".

		Two Field Write-Once Videodiscs
		===============================

TOKYO -- Two new technologies hit the videodisc market last week, when
Hitachi Ltd and Pioneer Electronic Corp. separately announced new
write-once optical recording systems.

Hitachi researchers experimented with disc materials to devise an
original format, called reflection-phase-shift recording, for a system
aimed at the industrial market.  Engineers at Pioneer, in collaboration
with researchers at Toyo Ink Manufacturing Co Ltd, developed a new
organic-dye medium for optical video recording.  It is used in a system
whose low production cost and full laserdisc compatibility are tailored
for the consumer market.

Both systems produce discs compatible with the existing laserdisc
format.  Although Hitachi's discs cannot be used on today's laserdisc
players, the recorder/player that plays its discs will also play
conventional laserdiscs.  Pioneer's discs can play on existing
laserdisc players.

Both the Hitachi and Pioneer units allow users to write once to disc
using a laser beam with a 780nm wavelength -- the same wavelength used
in conventional laserdisc and compact disc players.  Each of the
systems is based on analog FM video-signal recording, as are
conventional LDs.

Systems for recording video on optical discs already exist, such as
rewritable magneto-optical discs and write-once optical media that use
an organic dye that responds to an argon gas laser.  But they require
expensive equipement and are used mostly for commercial applications.
They are not compatible with laserdiscs.

Pioneer executives believe cost considerations will attract home
users.  "Even though this is a write-once videodisc, we'd expect
customers would be willing to embrace it, as more and more people are
beginning to find discs are much more reliable, durable, and easier to
handle compared with tapes", said a company spokesman.

The technology, unveiled last week at the Institute of Television
Engineers of Japan, could appear as a commercial product within a
couple of years, the spokesman said.

Hitachi
-------
But Yoshihiko Noro, chief researcher at Hitachi's Image and Media
Systems Lab, doubts consumers will rush to accept a write-once
technology for home use.  "More immediate and practical applications
lie in high-quality videodisc productions in small quantities and with
a shortened production period", he said.  "Discs that need to be
produced for presentations or demonstrations in public would be ideal
for our system".

Theoretically, Hitachi's optical-disc technology could be adapted to
permit video recording in Japan's high-definition TV format,
MUSE-HiVision, Noro said.  The adaptations would involve such design
changes as refining the disc pitches and making the disc's recording
layers thinner.  Hitachi has turned out demonstration models of its
system and plans to launch it next spring.
...
Because the reflectivity of Hitachi's write-once videodisc is about 25%
-- far lower than the 75% to 85% reflectivity of laserdiscs -- and
because its tracking phase is reversed, the write-once disck cannot be
played back on existing laserdisc players.  But by changing the gain of
the preamplifiers of the optical head and the phase of the tracking
servo in a conventional laserdisc player, Hitachi engineers developed a
player/recorder that accepts both commercial laserdiscs and the new
write-once discs.

Pioneer
-------
Aiming at the consumer market, Pioneer and Toyo Ink Manufacturing
developed a high-sensitivity optical recording organic dye that
undergoes no physical transformation during recording and that employs
low-cost, spin-coating thin-film production.  "Our first intuition was
to look for organic-dye thin films similar to those already used in
recordable CDs", the spokesman said.  But the conventional dye medium
transforms itself and creates sub-micron dents, melts, and other
changes in the recording layer during the laser-beam recording
process.  The irregularities produced by the metamorphosis can increase
the "jitter" of played-back signals.

Moreover, the conventional dye medium requires a comparitively high
laser power output to effect a favorable physical transformation in the
recording layer, particularly for analog FM video recording, since the
linear velocity is 10 to 20 times faster than that of CDs or digital
audio recording.

To overcome those problems, Pioneer engineers developed a pre-grooved
optical disc comprising polycarbonate with a recording layer ot the
newly developed, spin-coated organic dye; a reflect layer; and a
protection layer.

During recording/playback tests using an optical pickup common to CD
recorder/players, Pioneer's system provided jitter of less than 5ns and
yielded picture quality comparable to that of conventional laserdiscs,
said the company.