Note: Descriptions are shown in the official language in which they were submitted.
C A N A D A
APPLICANT: CANON KABUSHIKI KAISHA
TITLE: RECORDING AND REPRODUCTION SYSTEM
RECORDING AND REPRODUCTION SYSTEM
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an optical
memory or optical recording and reproduction system.
More particularly, the present invention relates to a
writable and rewritable optical memory medium having a
memory layer comprising a polymer liquid crystal, and
an optical recording and reproduction system using the
optical recording medium.
At present, the optical memory system has been
commercialized because of its large capacity and random
accessibility. A variety of types of the system have
been commercialized including the type of reproduction
only such as the digital audio disk (compact disk CD)
and the laser video disk (LD). Further, commercial
examples of the type allowing optical recording include
the writable optical disk (WO) and the optical card
(oC), which utilize phase transition of a metal film or
pit formation in an organic dye film.
At present, research on the rewritable-type
optical disk has been developed, including one using an
opto magnetic effect and one using a phase transition,
of which the commercialization has been aimed at.
Further, a polymer liquid crystal has been also
proposed as a data recording medium (Japanese Laid-Open
Pat. Applns. JP-A 59-10930, 59-35989 and 62-154340).
- 2 _ 2~ ~ &~
Among the above, the compact disk(CD) has been
the most developed one commercially.
The compact disk (CD, which is an optical
memory medium for reproduction only, requires only a
simple optical system which has been made compact.
However, CD requires complicated production steps and
is not adapted to production in a small quantity. In
order to overcome such a difficulty, a writable-type CD
using phase transition of a metal film or pit formation
in an organic dye film as used in the writable-type
optical dlsk ~WO) has been proposed as being suitable
~or production in a small quantity. However, the
writable-type CD involves several difficultie,s, such as
lower reflectivity and contrast than the conventional
CD and also requires a complicated structure thereof
and a complicated optical system than the conventional
CD. Furthermore, the writable-type CD cannot be read
by the current CD reproduction or readout system.
SUMMA~Y OF THE INVENTION
In view of the above-mentioned problems
accompanying the conventional memory media~ an object
of the present invention is to provide a writable and
rewritable optical memory or recording medium requiring
only a simple optical system for recording and/or
reproduction.
Further objects of the present invention are to
2 ~ 8
-- 3
provide a recording method suitable for the memory
medium and an optical recording and/or reproduction
system suitable for the memory medium.
According to a principal aspect: of the present
invention, there is provided a memory medium including
a memory layer comprising a polymer liquid crystal and
a reflection layer disposed on a substrate so that a
reproduction beam is transmitted through the memory
layer, reflected at the reflection layer and re-
transmitted through the memory layer, wherein thememory layer comprises a non-record part and a record
part having a re~ractive index changed from tha-t o~ the
non-record part so that the non-record part and the
record part have a difference in optical thickness of
the memory layer suitable for causing interferential
diffraction of a reproduction beam of coherent light
incident to the record part and the non-record part to
allow readout of the recorded data.
These and other objects, features and
advantages of the present invention will become more
apparent upon a consideration of the following
description of the preferred embodiments of the present
invention taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates a recording and/or
2 ~
reproduction system including a memory medium according
to the present invention.
Figures 2 and 3 are respectively a partial
schematic sectional view of an embGdiment of the memory
medium according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The memory layer of the memory medium according to
the present invention may suitably comprise a
thermotropic polymer liquid crystal. Examples thereof
may include a side chain~type polymer liquid crystal
which comprise a main chain of a methacrylic acid
polymer, a siloxane polymer, etc., and a meaogen or
low molecular weight liquid crystal unit in side chains
thereof like pendants; and also a main chain-type
polymer liquid crystal comprising a mesogen unit in its
main chain, such as those of the polyester-type or
polyamide-type, as used in the field of high-strength
and high-modulus, heat-resistant fiber or resin.
These polymer liqu:id crystals may assume
smectic phase, nematic phase, cholesteric phase or
another phase or can also be a discotic liquid crystal.
Specific examples of the polymer liquid
crystal used in the present invention are enumerated
hereinbelow while other polymer liquid crystals can
also be used in the present invention.
- 5 _ 2~ 8
(In the following formulas (1~ - (13), p = 5 - 1000,
1 ~ n1 < 15)
( 1 )
O O
~o~CH=N~oC~CH2t~ C~
(2)
C~I3 O
~O~l=N-N=C~OC~c~l2~1
CH3 O
(3)
Il <~ ~ (~-~Co~CH2CH2ot~
O O
(4)
~OC~FO~c 2 ) n 1 ]
O O
~o~,~octCH2t~1 C ]
(6)
O O
-~O~CH=CH~oCtCH2~1 C
- 6 - 2~
(7)
O O
~O~CH2~2o~o~cH2~2oc~cH2~1
S (8~
O O
~1~N=N~1O~CH2CH2O) nl
(9)
O
~ ~1~CH2CH2
(10)
O O
~ O~CO~OC~O~CH
( 1 1 )
O O
~O~1O~O1~~CH2)n1 3
(12)
o o
~O~OC~O~CH ) O~CO~O~CH2)n1 ]
(13)
7~ 2)nl -~-
O O O
5 (In the following formulas (14) - 117), p = 5 - 1000
p1+p2 = 5 - 1000, q = 1 - 16, q1 = 1 - 16 and
q2 = 1 - 16.)
(14)
ICH3
~CH2-C ~
O=C CH3
~CH2~-qCO ~ OC ~ COCH2C~C2H5
O O O
(15)
CH3
2 lC~
O=C O
O~CH2~qO~CO~OCH3
(16)
fH3
~CH2 lCt~
O=C
1~CH2~-qO ~ OCH3
- 8 - 2~
(~7)
fH3 fH3
--~CH2-1C3pl (C 2
o=c o=c
0 1~CH2 ~2 ~ COO ~ oc~3
CH
~q 1
O ~ COO ~ CN
(In the following formulas (18) - (62), * denotes the
location of an asymmetric carbon atom, and n2 = 5 -
1 000 . )
(~8)
~CH2-fH~ CH~ CH--CH2cH2cH2cEI
COO~COO~--' 3
~CH2-C(CN3)~;2 ~f~C32~3
CO-NH~CH2~1 COO
(m1 = 2 - 10)
9 2 ~
(20)
tCH2 -C ( CH3 )~ ~H2~3CH~CH
coo~cH2t~ coo 3
~m1 = 2 - 10)
~21 )
lc~3
10tCH2 IC~
O=C O CH3
O~CH2~m2CO ~ COO ~ COO~C~2~2CHC2H5
(m2 = 2 - 15)
(22)
3 3 f
20 ~ 32~3
(23)
' ~CH2 1CH~n2
O=C CH3
25 O~CH ) O~co2~ocH2cHcH2cH3
(m2 = 2 - 15)
3 ~'
- 10 -
( 2 4 )
H
~C 2 I t~
~CH2 ) m-2O~CO2~OCH2-CH-CH2CH3
CH3
(m2 = 2 - 15)
~25)
fH3
~2
o O~CF~2~m2O~CO2~OCH2- IH-~::H2CH3
C 3
(m2 = 2 - 15)
(26 )
Cl
~CH2--C1 ~2
O ~CH2~2~c2 ~
CH3
(m2 = 2 - 15)
11 - 2 0 ~ 8
(27)
CH3 ~O3,~
(CH2)m
(m2 = 2 - 15)
( 2 8 ) iCH3 l H3
CH~T CH~CE~2~3 I H
ICH 2 1l ~ 3
CH- C~O~CH2~q3C~O
~kx
CH2 0
CH--C-O~CH2) p30~-CN
~Y
¦ n2
(x~y = 1, q3 = 1 - 10, p3 = 1 - 10)
(29)~
CH 0 O
1 2 11 ll
CH3--C C-O~CH2 ) q3O~C~O~OC83
x CH ~CH3 1~3 1 3
CH~3CH
~5 CH 2 If 1 ~C~ ~ C~13
CH -C--C_O~cH2~C-O
,Y
n2
(x+y = 1, q3 = 1 - 1 0 , p4 = 1 - 15 )
- 12- 2~
(30)
tCH -CHt~
O=C O
O~CH2+2~c-o~OcH3
(31 )
CH3
~CH2-fE*~
O=C
10ltCH2~ O~CN
(32)
7H3
~si-o~
15O=C O
( CH2~~C--O~ocH3
(33)
O O
20~o~o-ctcH2 ) m2
~o~o-c-cH2cH~cH2t--2 3
(m2 = 2 - 15, x+y = 1 )
- 13- 2~
(34 )
O O O O
~C~OC~CO~CO-R1 0~-
O O O O
~C~OB~CO~C-OR2O~
fH3
R1 = -CH2CH2CH~CH2~ R2 = ~CH
(x+y= 1, m, = 2 - 15)
(35)
O O O O
~O~OC~CO~OC-R3C ~
O O O O
~O~OC~CO~OC--R4C~)~
fH3
R3 = -CH2CH~CH2~ R4 = ~CH2 )~
(x+y = 1, m2 = 2 - 1 5 )
- 14 - 20~ ~6~
(36)
~0~N-,N~-o- I~CH~2CH_CH2_C ~
0 CH3
CH 3 CH 0 0
N~o-CtCH2~m2 3
(x+y = 1, m2 = 2 - 15)
t37)
~C~0-C~C-0~C~O-cH2- I EI~30
0 0 0 0 CH3
(m3 = 1 - 5 )
(38)
~C-CH2-CI:~CHz+2c~O~C-cH~o~n2
(39)
~A-O-CH2-CH-O) X (B-O-CH2-fH-O~
CH3 CH3 n2
A = C~O--I~C-O~O
0 0~0 0
~x+y = 1 )
- 15 - 2~
(40 ~
r * *
~A-O-CH2 -cH-ot~;c-o-cH2 -CH~-O~ _
CH3 CH3 n2
5O~O- ICl ~C-O~ ICl -
C - lCI~O lCI~ICI-O~ICI -
( 4 1 )
HO~ ICl~O-C~C-O~C-O- ~ CH2)m~IH o3 ~2
O O O O R
(m4 = 1 - 3, 1 = 1 - 20)
(42)
15E~fO- (CH2)m~N-N~ (CH2tm5O-~-cH2-cH2 IH CH2 ICI~
(O) CH O n2
H H 3
(m5 = 0 - 5)
20 (43)
H~O- (CH2)ms~cH=cH
H H
- ( CH2 ) m5o-c-cH2cH2cH-cH2-c 3~ OH
O CH3 O
(m5 = 0 - 5)
1 ~ - 2 ~
(44 )
H~O- (CH2 ) m5~N=N~
2 ) m5 ICl -CH2-CH2- I H--CH2-C~ OH
O CH3 O
(m5 = 0 - 5)
(45)
H~O- (CH2)m5~C
H H
t5 (CH2 ) m5 ll CH2~CH2~ I H-CH2-C~ OH
(m5 = 0 - 5)
(46 )
Br
~C~O--C~-C--O~C-O~cH2 ) 10~;~
O O O O
- 17 - 2 ~
The above polymer liquid crystals can be used
singly or in a mixture of two or more species. It is
also preferable to mix a low-molecular weight liquid
crystal with such a polymer liquid crystal to control
the refractive index.
A polymer liquid crystal having a
ferroelectric liquid crystal phase is preferred because
it allows a high-speed writing under an electric field
to provide a higher productivity.
Examples of ferroelectric polymer liquid
crystals may include those represented by the following
formulas:
(CH2- IH)n fH3
COO(CH2)12O ~ 2* 2 5
.
- 18 - 2 ~
~CH -CH~ CH3
COO~CH2 ~ 1 2 ~COO~ 2 * 2 5
~CH2--CH~ IH3
COO~CH2 ) 12 ~COO~COOCHC2H5
~CH -CH~ Cl 3
COO~CH2~1 20~COO~COoCHC3H7
~CH2 -CH~ CH3
cootCH2 ) 1 2O~COO~COOCHC6H~ 3
/
- 19 -
The above polymer liquid crystal or its
composition may preferably be one having a glass
transition point so as to stably retain memorized data.
It is particularly preferred to store written data
below the glass transition temperature in view of
stable storability of the data.
The memory layer may have a thickness of 0.05
- 10 pm, preferably 0.1 - 5 lum, and may be easily
formed on a substrate by dipping, bar coating, spin
coating, etc.
For the purpose of lnitial alignment of the
polymer li~uid crystal constituting the memory medium
according to the present invention, it is possible to
use an alignment film, which may be a film having a
homogeneous alignment characteristic of, e.g., a
polymer film, such as polyvinyl alcohol, polyimide,
polyamide or polyamide-imide, or an oblique vapor-
deposition film of an inorganic material, such as SiO2.
It is possible to subject such an alignment film to a
uniaxial aligning treatment, such as rubbing. Uniaxial
aligning treatment may also be effected by shearing.
It is also possible to apply a homeotropic aligning
treatment, such as a silane coupling agent, lecithin,
poly(vinylidene fluoride-tetrafluoroethylene3
copolymer, poly(vinylidene fluoride-trifluoroethylene)
copolymer, etc.
The reflection layer for reflecting a beam
- 20 -
having passed through the memory layer and having the
reflected beam re-enter the memory layer may comprise a
metal film of Al, Au, Ag, etc., or a dielectric mirror,
in a thickness of ~.01 - 100 ~m, preferably 0.05 - 10 ~m.
The substrate may be a plate or a sheet of
glass, plastic, etc.
The memory medium according to the present
invention may be initially subjected to writing so as
to provide a memory medium which may be exchangeable
with a conventional digital audio disk. The writing
may be effected by heat-mode by using a laser beam, an
electric field alone or a combination of heat-mode
writing and an electric field. Further, it is also
possible to utilize an optical alignment due to a
third-order non-linear susceptibility by means of
strong laser light.
In order to effect the reproduction by
interferential diffraction, it is necessary to make the
width of a record part having a varied refractive index
narrower than the spot diameter of the reproduction
beam incident on the memory layer. For this purpose,
it is preferred to use a writing beam of, e.g., short-
wavelength laser light, having a smaller spot or pit
diameter than that of the reproduction beam.
Alternatively, it is also effective to use a writing
beam having a radial Gaussian intensity distribution to
provide a thermal distribution pattern in the memory
- 21 - 2 ~
layer, thus forming in the memory layer a record part
having a varied refractive index in a wldth smaller
than the spot diameter of the writing beam. A polymer
liquid crystal has a clear threshold temperature for a
phase transition and also a low heat conductivity, so
that it is easy to effect a spot or pit recording in a
width ~or diameter) smaller than the spot diameter of a
laser beam having a radial intensity distribution. In
case of such a smaller spot recording, the resultant
spot or pit is liable to yield a degraded reproduction
signal, but a good reproduction signal can be obtained
even in such a case by utilizing interferentlal
dif~raction. In order to use interferential
diffraction for reproduction, a phase difference of ~y4
~ wavelength of reproduction light) is used.
Such a phase difference can be obtained by a relatively
small memory layer thickness by using a polymer liquid
crystal which shows a large refractive index change
accompanying a phase transition, and thus a record part
having a width smaller than the spot diameter of the
writing beam can be effected further easily.
The above writing beam and reproduction beam
can he issued from the same light source. In such a
case, the intensities and/or effective pulse durations
~depending on unit pulse duration and number of pulses
which may be arbitrarily selected) of the respective
beams may be made different from each other.
- 22 ~ ~
Preferred examples of the light source used
for the above purpose may include gas lasers, such as
He-Ne gas laser and Ar2~ gas laser; solid lasers, such
as ruby laser, glass laser and YAG laser, and also
semiconductor lasers. Further, the second harmonic or
third harmonic of such laser light can be used for
providing coherent light of a shorter waveform.
In order to use such a laser beam for writing
in a memory layer according to the heat mode, it is
desired to incorporate a dye showing a selective
absorptivity for a laser beam used in the memory layer.
Examples of dyes used or the purpose may include those
represented by the ollowing formulas.
- 2 3
NH2 NH2
~N=N~N=N~
3Na S03Na
Dire~t Red 28
OH OH
,~N=N~N=N~q
H2N ~o3Na NaO3S~H2
Direct Violet 12
~1 OH 0~13 OCH3 OH ~12
~ 2 ~ ~ N=N ~ 3Na
S03 a S03Na
Direct Blue 1
~H2 OH OCH3 OCH3 OH ~H2
~ N~N ~ N=N ~
~ Y~50 Na
NaO3S S03Na NaO3S 3
Direct Blue 15
-2~
NaO3S - Cu - O O - CU-O
- N=N ~ ~ N=N
~ 3 a NaO3S NH
Direct Blue 98
OH OCH3 3
~ - N=N ~ N= ~
NaO3 N~12
SO3Na
Direct Blue 151
OH
NaO3S ~ N=N ~ N=N
~ NHOO
NaO3S
Direct Red 81
NaO3S OCH3 C 3 /COONa
HO ~ N=N ~ NHCONH ~ N=N ~ OH
Direct Yellow 44
. .
C2H5 ~ N=N ~ CH=CH ~ N=N ~ C2H5
S03Na S03Na
Direct Yellow 12
- 25- 2~ 8
NaO3S~N=N~N=N~CH=CH~N02
O S03Na S03Na
Direct Orange 39
5 OCH3 OEl
02N ~ CH=CH ~ N=N ~ N=N ~ ~
SO3Na SO3Na CH3 NaO3 3
OCH
: 1002N~CH=CH~N=N~N-N~
SO3Na SO3Wa H3 NaO3S N'l--
OCH3 OH
02N~CH=CH~N=N~N=N~
SO3Na SO3Na OCH3 Na3 NH~
OCH3 C~
02N~CH=CH~N=N~N=N~ NH2
S03Na So3Na OCH3NaO3S
O2N~CH=CH~N=N~N-N~ NH~
SO3Na SO3Na CH3 NaO3S
- 26 ~ $ ~ ~
o--Cu--O
02N~CH=CH~N= N~N=N~
S03Na S03Na S03Na
NaO3S
OC2H5
2N ~ CH=CH ~ N=N ~ $ N=N, ~ _NH2
S03Na S03Na 9 ~ NaO3S
S03Na
OCH 3
H2N ~ CH=CH ~ N=N ~ N=N
S03Na SO3Na OCH3 NaO3S NH~
NH2
CO~ N_~C H
O NH2
H1 7C80H6C3NH 0 NH2
~>- R
O NH2
~ U
NH2 N1~2 0 NH2 S
- 2 7 ~ ~ ~3 `~ ~
HgC4 ~ O NH2
~$ C
O NEI2 S
o
~¢~ COO~Rl -
NH~R
R~NH O
o NH ~R
NH2 OH
HgC4 o~ OC4Hg
OH O NH2
NH O OH
' $~OR
OH O ~aEI2
o NH2
COO {~ R
O ~
-- 28
OH O OH
R~O ~ O~R
NH2 NH2
9 4 ~NH O NH
R~O~ ~R
OH NH2
NH2 CH3
CHCH2~CH2CH<
CH4 OH
O NH
~ CO ~ ~ ~R2
o OH
NH O OH
j~o R~o~ (~R
OH NH2
o NH;~
~CONH~R
~5 o NH2
$
- 29 -
HgC4~N=N~N=N~N=N~ N
OH O OH
R~o~O ~ R
OH O NH2
O NH
(~) {~ R1
O OH
9 4 ~N N~N=N~N=N~N / 2 5
,_~ ~C H
HgC4~N=N~N=N~N~ 2 5
HgC4~00C~N=N~N=N~N/ 2
~N=N~N=N~N /
HgC4~N=N~N=N~OC3H7
2 ~
-- 30 --
HgC4OCOCH=CH~N=N~N=N~N=N~OC2H4OC4H1 3
CH3 CH 3
H1 2C6OC2H4OCOCH C ~N=N~N=N~OC2H4Oc6Hl 2
HO O NH2
~J~ OC2H5
H N O CH
~0 2
Disperse Blue 214
HO O NH2
~ C8H1 7
15H2N O OH
(CH3) 2N~IH
~0 O NH ~(OEI3) 2
O ~
~0~
O OEI
~5 Disperse Red 60
- 31 ~
O ~
~0~ C4Hg
o OH
o NH2
9 19
O OH
10(~N=N ~N=N~
HO CH
Disperse Yellow 56
~COOC4Hg
NBa2 N~a2
Ba2N~ j~
NBa2
~}N (~ . Cl04
Ba2N~ ~ NBa2
NBa2 N~2
- 32 -
Ba N NBa
N~N~ e
s ~ ~
Ba2N NBa2
Ba2N ~NBa2
N~ N C104
Ba2N NBa2
/
- 33 ~
The memory layer comprising a polymer liquid
crystal (composition) according to the present
invention may be provided with a record part and a non-
record part having different optical thicknesses through
a refractive index change at the record part, whereby
coherent light causes interferential diffraction at the
boundary between the record part and the non-record
part. The record part and non-record part may
preferably be formed as a combination of two phases
selected from, e.g., the ~ollowing phases of a polymer
liquid crystal.
~1) isotropic phase,
~2) homeotropically aligned nematic phase,
~3) homogeneously aligned nematic phase,
~4) homeotropically aligned smectic phase,
~5) homogeneously aligned smectic phase,
~6) homogeneously aligned cholesteric phase,
(7) focal-conically aligned cholesteric phase,
~8) homogeneously aligned chiral smectic phase,
~9) homeotropically aligned chiral smectic phase.
These phases may be formed by adjustment of
writing conditions either by direct heating or
preferably heating by laser beam irradiation under or
in the absence of an electric field, etc., and may be
fixed preferably by cooling below the glass transition
temperature. The thickness (d) of the memory layer may
be controlled in advance to provide an optical
- 34 - 2~
thickness difference (~n-d = ~/4 - ~8) suitable for
readout between the record portion showing a refractive
index n1, and the non-record portion showing a
refractive index n2 depending on the resultant
refractive index difference ~n (- ¦n1 - n2¦). The
refractive index difference may preferably be 0.01 or
above, particularly 0.05 or above, so as not to
require an excessively large thickness of the recording
layer for providing an optimum optical thickness
difference. The upper limit of the re~ractive index
difference may be governed by a particular polym~r
liquid crystal used and generally 0.4 or below. The
resultant optical thickness difference between the
record part and the non-record part is reproduced by
interferential diffraction of linearly polarized light,
circularly polarized light and non-polarized light
having a coherency.
The present invention will be explained more
specifically with reference to Examples.
Example 1
Figure 1 shows an embodiment of a recording
and reproduction apparatus using a memory medium
according to the present invention.
A memory medium 5 comprising a transparent
substrate 6 and a memory layer 7 comprising a polymer
liquid crystal and a reflection layer 8 disposed on the
substrate is irradiatedl e.g., by a laser beam of 830
- 35 -
mn and 20 mW from a laser 1 to form record pits 7b each
having a width of 0.4 um and surrounded by a non-record
part 7b in the memory layer 7. The thickness (d) of
the memory layer 7 is controlled provide an optical
thickness difference (~n~d~ of 1/4~ - 1/8A with respect
to the wavelength (~) of a reproduction beam described
below between the record pits 7b and the surrounding
non-record part 7a having a refractive index difference
~ n).
A continuous reproduction beam of 830 nm and 1
mW from the laser 1 is caused to pass through a
polarization beam splitter 2, a quarter wave plate 3
and an objective lens 4 to be focused onto the meMory
layer 7 having the record pits of the memory medium 5
through the substrate 5.
The spot laser beam incident to the memory
medium 5 is transmitted through the memory layer 7,
reflected at the reflection layer 8 and re-transmitted
through the memory layer 7 to enter the objective lens
4. When the spot beam having a spot diameter of, e.g.,
1.2 ~m which is larger than the width (e.g. 0.4 ~m) of
a record pit 7b strides over the record pit, a portion
of the spot beam passing through the record pit 7b is
caused have an optical path difference of a half the
25 wavelength of the reproduction beam (e.g., a phase
difference of ~) with a portion of khe beam having
passed through the non-record part 7a during the
$
- 3~ -
reciprocation through the memory layer 7 on the surface
of the substrate 6. These portions of the spot beam
both reflected from the reflection layer 8 causes
interferential diffraction with each other to
remarkably decrease the quantity of reflected light
incident to the objective lens 4. The reflected light
quantity is detected by a detection optical system
similar to a conventional CD pickup optical system
including a detector 9.
The above-mentioned record pit width of, e.g.,
0.~ ~m and reproduction beam spot diameter of, e.g.,
1.2 ~m have been determined so as to provide a maximum
intererential dlffraction effect.
The above mentioned optical thickness between the
record refractive index pit and the non-record past
provides a maximum signal 8/N ratio when it is approx.
1/4 of the wavelength of the reproduction beam as is
known with the conventional CD technology. However, an
optical thickness of approx. 1/~ of the wavelength is
preferred so as to effect a tracking control detection
according to the push-pull method. As a result, it is
desired that the optical thickness difference is
generally within the range of 1/4 - 1/8 of the
wavelength of the reproduction beam.
The memory medium may be formed in the shape
of the disk in the same size as a conventional CD disk,
and the formation o-E the refractive index pit at the
`$
- 37 -
time of recording may be effected according to a
similar format as the pit fo~mation of the CD disk,
whereby a disk-shaped memory medium applicable to a
conventional CD drive unit can be obtained.
Example 2
An embodiment of the memory medium having a
laminar structure as shown in Figure 2 was prepared in
the following manner.
A substrate 16 was coated with a methanol
solution of a silane coupling agent (Toray Silicone SZ
6032~ by spin coating, followed by curing to form a
homeotropic alignment film 19.
Then, the following polymer liquid crystal
15--1CH2-ICH ~
COO ~CH2~0~COO~oCH3
was dissolved in dichloroethane at a concentration of 5
wt.%, and into the solution, the following near
infrared-absorbing dye
(C2H5)2N~ ,~N(C2H5)2
//~
C=CH-CH=CH-C C10
~ / ~
(C2H5)2N N(C2H5)2
2 ~ 8
~ 38 -
was dissolved in a proportion of 1 wt.% of the polymer
liquid crystal. The resultant solution was applied
onto the alignment film 19 by spin coating and dried to
form a memory layer 17, followed by vapor deposition of
Al to form an approx. 2 ~um-thick r~flection layer~
Then, the memory layer 17 was heated into isotropic
phase and then cooled to form a homeotropically aligned
memory layer 17. Then, the memory layer 17 was
irradiated for writing with a laser beam of 830 nm and
20 mW from a semiconductor laser 1 in Figure 1 to form
a record pit 17b having a width of 0.8 jum surrounded by
a non-record part 17a.
The memory medium was incorporated in a
readout sy9t.em as ~hown in Figure 1 and the memory
layer 17 was illuminated with a reproduction beam of
830 nm and 1 mW having a spot diameter of 2.4 um,
whereby the reflected light quantities were measured to
be 5 % and 40 % with respect to the illumination light
for the record part 17b and the non-record part 17a,
respectively.
Example 3
Another embodiment of the memory medium
according to the present invention was prepared as
shown in Figure 3.
A substrate 116 coated with a vapor-deposited
ITO transparent electrode 20 formed by sputtering was
further coated with a polyamic acid solution ("PIQ",
- 39 -
mfd. by Hitachi Kasei Kogyo K.K., non-volatile matter
content: 3u0 wt.%~, followed by heating for 30 min. at
120C, 60 min. at 200C and 30 min. at 350C, to form a
polyimide alignment film 119~ which was then provided
with a uniaxial alignment characteristic by rubbing.
Then, the following polymer liquid crystal
~ CH2-CH~
COO ~ CH2 ~ O ~ COO ~ CN
1 0
was di5solved in dichloroethane at 5 wt.~, and the
ollowing dichroic colorant
NH2 OH /CH3
_ ~ o-C3H6O C6H13
bH O NH2
was added thereto in a proportion of 1 wt.% of the
polymer liquid crystal, and the resultant solution was
20 applied by spin coating, followed bs~ drying to form a
memory layer 117, which was then covered by a 2 ~m-
thick vapor deposition layer of Al to form a reflection
layer 118. The memory layer 117 in the memory medium
was heated into isotropic phase and then gradually
25 cooled to form a homogeneously aligned memory layer.
Then, the memory layer 117 was irradiated for writing
with an He-Ne laser beam of 633 nm and 10 mW under
- 40 - ~ 8
application of an AC electric ield from an AC supply
between the transparent electrode 20 and the reflection
layer 118.
The thus written memory medium was
incorporated in a reproduction system using a
reproduction laser beam of 830 nm and 1 mW shown in
Figure 1, whereby the reflected light quantities from
the recorded part and the non-record part were measured
to be 10 % and 35 %, respectively.
As described above, according to the present
invention, there is provided a memory medium which can
be used in a simple optical system as used ln a
conventional digital audio disk apparatus. The memory
medium can be prepared by a very simple process such as
spin coating and can be easily written and erased, so
that it constitutes a good memory medium suitable for
production in a small scaleO
