CA1127886A - Method of producing inline hologram lens - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A method of producing an inline hologram lens is disclosed which includes the steps of, recording on a first photo-sensitive layer a holographic interference pattern which results from the simultaneous irradiation of the layer by a reference wave beam and a subject wave beam, the two beams being in off-axis with each other and the latter beam being perpendicular to the layer, forming an off-axis hologram lens by developing the first photo-sensitive layer, facing a second photo-sensitive layer to the off-axis hologram lens, irradiating the off-axis hologram lens by a reference wave beam for reproducing, irradiating simultaneously the second photo-sensitive layer perpendicularly by a reproduced subject wave beam as a subject from the off-axis hologram lens and a reference wave beam through the off-axis hologram lens, and developing the second photo-sensitive layer.
An optical reproducing head is also described through which a laser beam from a laser source is irradiated to an optically recorded medium and through which a reflected beam from the record medium is led to a photo-detector. In this case, the optical reproducing head has a beam splitter, a quarter wave plate an inline hologram lens produced by the method described above, and a device for sticking the been splitter, the quarter wave plate and the inline hologram lens together by transparent adhesive.

Description

~L~27~3~6 BACKGROUND OF T~E I~NTION
~ .
Field of ~he Invent~on , . . ,, ..~
Th~ pre~ent invention relate~ gene-rally to a ~ethod of producing a hologr~m len~ and i~ directed ~orR parti~ularly to a me~hod o produc-lng an inline hologram len~.
~he invention relates al50 to an inline hologr~m len~ produced by the novel method.
The in~ention further relates to a novel optical reproduclng head using th~ abov~ inline hologr~m len~.
De~cri~tion of the P.r~or Art In the art, ther~ has been pxopo~ed no method wh~ch can eas~ly produce an inline holo-gram leaa wlth a large N~Ao ~numerical aperture3.
A prior art op~ic~l reproducing head can not be free of many defect~ ~uch ~8 it i3 hea~y, expen~ive ~nd 80 on.
O~JECTS AND ~UMMAR~ OF THE INV~N~ION
_ _ _ Accord~ngly, an ob~ec~ o~ the pre~nt ~nvention i~ to provide a novel method o~ produ~l~g a hologram lens fr~e of the de~ect enc~untered in the prlor art.
Another objsct of the invent~on i~
to pro~ide a novel method of produc~ng an inl~ne hol~gram l~n~.
A ~urther ob~ect of the ~nv~nt~on to proviae an inline holo~ram lens.
A yet f-lrther ob~ect of the invention is to provide an optical reproau~-ng head~

.~

~ccording to an aspect of the present invention, a method of producing an inline hologram lens is prov~ ded wh~ ch comprises the steps of, re-cording on a first photo-sen5iti~e 1ayer the holo-graphic interference pattern which results from the simultaneous irrad~ation of sa~d la~er by a reference wave beam and a subject wave ~eam, said two beam~
be~ng off-ax~s with each other and the latter beam being perpendicular to said layer, forming an off -axis hologram lens by developing sa~d ~rst photo -sensi~ive layer, facing a second photo-~en~itive layer to said off-aY.is hologram lens, irradiat~ng sa~d hologram lens by a reference wave beam for reprc~ucing, irradiatin~ simulltaneously sai~ second photo-sensitive layer perpendicularly by a reproduced sub~ect wave ~eam as a sub~ect from said off-axis hologram lens and a r~ rence wave ~eam through sa~d off-axis hologram lens, ana develop~ng -~aid second photo-sensitive layer.
Ano~her aYpect of the invention, ~here ~s provided an inline holo~ram lens produced by the above methodO
A further asp~ct of the lnvent~on, an optical reproduc~ng ~ead through i~ provided w~ich a laser ~eam from a laser source i~ irradiated to an opt~cally recorded med~um and through which a re~lected beam from sald record med~tlm is led to a photo-~etector, sa~d optical reproducing he ad compris ing, (a~ a beam splitter, (b) a quarter wave plate, ., 3L3L2~7 886 (c) ~n ~nl~ne hologra~ lens produced by a method comprising the step~ of recoraing on a fir~t photo-sensitive layer the holographic ~nter-feren oe pattern wh~ch results from the sim~lt~neou~
S lrradiation of ~aid layer by a reference wave beam and a sub~ect wave ~eam, said two beams being off -axis w~th each other and the latter beam being perpendicular to said layer, forming an off-axl~
hologram lens by aeveloping said fir~t photo-sen~i~iYe layer, fac~ng a second pho~o-sen~itive layer to sa~d off-axis hologram lens, ~rradiating said off -axis hologr~m lens by a referen~e wave beam for reproducing, irradiating simultaneously sa~d ~econd photo-sen~itive layer perpendicularly by a reproducea ; . 15 subject wave beam a~ a subject from said off-ax~
hologram lens and a reference wave beam throuah said off-axi~ hologram lens, and developing sa~d second ; photo-sensitive layer; and (d~ mean~ for stick~ng said beam spl~ter the ~uarter p~ate and the inline hologram lens together by a transparent adhesive.
The other objec~s, features and : advanta~es o~ the present invention will ~ecome apparent from the foll~wing descr~ption taken in conjunctlon wi~h the accompanying arawings through which the like references desi~nate the same element~
and parts.
BRIE:F DESCRIPTION OF l~IE DRAWI~JGS
-Figs. 1 to 4 are respecti~ely schema-tic dlagrams used to explaln the record and re-proauction ~ethods of paior art hologra~ lense~;

~L;Z7~

Fig., ~ i~ a s~hematlc di~gram used to axplain the racord method c>f a prie)r art inl~ ne hologram len~;
Yig. 6 i~i a sehematic dia~r~m 3how~ ng an ex ample of the m~thod of maXing an inline holo~ran lens accc~rdin~ to the ~resent invention;
Fig . 7 i~ a schematic di ~r~m ~howing anothe:r e2s;~mple of U~e method of pxoduc~ng an inline holo~ram lens according to the ins7ention;
F~. 8 i~ a ~chematic diagram u~ed to e~plaln an example o the method of mak~ ng an of f -axi~ hologrDm len~ llsed in ~:he example~ shown in Fig~. 6 and 7;
Fig. 9 i~i a cros~-sect~onal riew showing the hologrz~n lens m~de by the record method ~hown in Fig. 6, 7 or 8;
Fig~ 0 10 and 11 are respect~ vely ~chematic di agram~ sh~w-Lng examples of the repro-duction methods for malc:L~3g ar~ inlir~e hologram len3;
F~g~ 12 i s a schem~tic ~.ia~ram showing a prior art optical signal reproduct~on head system, F~ g . 13 i~ a cross-seetional vi ew ~howing an ex 3~mple of the ~ nlin~ hologr~n l~n~
m~de ~ the inventlon ana u~ed ~n an optical ~ignal reprOauctiOn he~a ~ystem; and Fig .. 14 i s a c:rs: ss-sectional v~ew showing ~nother example o~ the holo~ram len~ mad~
by the invention and u~ed in the opt~cal signaï
reproductis:~n heafl.

~2'7~6 DES~IPTION OF ~rHE: pREFERREn EMBODIME~rS
~3efore deæcribing the present invention, a hologrz~n lens will b~ described~
A3 the hologram lens, there are proposed an inli ne hologram lens and an of~-~axis hologram len~O
The record~ ng and reproducing theory o~ ~e t:wo hologx~n len~a~ will be now briefly aescribed~
Firstly, tho~e of th~ o:Ef-~s holo-gram lens will b~s discr~bed. As ~hown in Fi~. 1, on the recor~ surface (photo-sen~it~ve) sur~ce r of a hologram record medium E~5B, irradiatea are a record ~ub~ect wave beam ~spherical wav~ be~n) A
~nd a record re~erence wave beam (plane or ~pherical W~ eam) B each at the incident angle of about 45 with re~pect $o the mormal to the ~urface r, na~m~ly at the off-axiæ, ~lo tha~ an off-axi~ holo~ram lenæ portion HL' of, ~or example, a ai~c-shape, whi~ onslstæ of an ~ nte~rference ima~e or pattern, iY recorded . The de~c:ription of the develop~ ng treatment of the recoraea surface r will be omittedO
In th~ case, the record sub~Qct ~a~s beam A is prov~ded by us~ng an optical len~ and i5 such ~ beam which c:onv~r~e~ r focu~es at a ps~int P and diver~es a~t~r the point P. Further, both ~e beams n 2s ~a B are provided from the la~er beam em~ tted rom the same 1 a~er 11 ght source . Thuæ; an of ~-axis hologram len~ OX-L i~ mad~.
When the off~ holo~r~nn lens OX-II i~ reproduc~d, aæ ~hown in Fig. 2, a reprod~tckion re~Feren~e wave be~m B' ~imilar to ~e heam B ~hown DLZ7~

in FigO 1 1~ irradiated on ~he off~ hologr~m~
l~n~ portion }1~' from the side oppo~ite to the record surface r alon~ lthe ex~ending llne of recora refere~e wave beam B shown in Fig. 1. Then, a reproduction 3ubjec:t wa~e heE~n A' i~ n3prQduced frar ~e side of record surface r which beam i~' is csnverged or fot:ussed to a point P'. On the contrE~ry, when the reproduction reference wa~e beam i~ irradialted on the record surf ace r of rec:tsrd med~ HR same a~ the record re~erence wave beam B ir~ Fig . 1 but di~ferent to that of Fi g . 2, a reproductlon ~ub~ect wave beam is reproduced from the surface of record medium H~ oppo:3ite to the record surface r which is diverged along the extena-ing l~ne of recoxa sub~ect wave beam A ln Flg. 1.
Now, the inline hologr~an len~ will be de~cribed. 1~8 ~hown in ~ig. 3, th~ record 6ubj~ct wave beam (~pherlcal walre be~an) A and the record refes~ence wave be~m ~plani~ or æpheri~al b~
B are irr~diated on the recor~ surfa~e r of holo-gra3n re~ord m~ , ~hlch be2ms ~ and B are ~:oinc~ent ~rl optica~ s ln the nonnal d~ rection i,e. inl~ne w~th Qach other, to form an inl~ne holo ~rzlm lens portion RL cons~ sting o~ an intererenca ~magef3 or pa~tern. The other o~ th~ inline hologr2~sn len~ $s sub~tan~ially ~ame as that shown in Fig . 1. ~hu~, an inl ~ ne holo~ram l~n~ I~L
i~ pro~uced~
When the inline hologram lens I~
3 O is rep~-oduced, ~ f y as ~hown in Fig . 4 ~ a reproauct~ on - B ~

7~

reference wave be~m B ' s~milar to l:he recora re:~erence wa~e be2un B 3hown in F~g. 3 i5 irradiated on the inline holo~ram lens portion HL from the surface r of record ~ide oppo~ite to the re~ii~H~a along the ~xtending ]Lln2 of beam B, a reproduced subject w~?e beam A' 4 ~ reproduced fro~ the record surface r which convarge3 or i~OCU5~ S at a point A'.
In thi~ ca~, it i~ also pos~ible that th~ repro-ductloll re~erenca wa~e ~eam i~ ~rradiated on the record surface r of hols:~gram recc>rd medium HR to reproduce the di~3rgin~ ~ub~ect wa~re b¢a~.
The other of Flg. 4 is sllbstantially ~ame as th~t o 3~ig. 2.
The hologram len~ thus made is liLght in w2ilght and ~nall in s~ze. Further, by de~irably sel~ctln~ a mother lens, whlch i8 to proviae a sub~ect wa~e b~m, a len~ with a de~ired N.l~ umeri~al apertur~ ) and an opera~ing d~tanco ~an be made, ana ~t ~ e ma~ produced by dllpl~-ca~ion s~ne in ~harac~teri~
By the way, an ob~e~t~ ve lan~, whi~h i~ u~ed as, for examp~e, an optical ~ignal reproduction he~a ~n an DptiCal. ~igrlal r~production appara~us, ha~ a rather large M~Ao r and ~n ~h~
a3~t an opt~ cal len~, con~ s~lng of a number of 1~3n~
~et~ 8iIl~ilar to the ob~ective lens of a microscope~
u~ed w~dely. Rowever~ such an ob~ctllv~
ler~ Gan not be m~de ~mall ~n ~i~e a2ld light in we~ght:r 80 that upon ~ocu~;51ng ~ervo 9~nee the ob~ective~ len~ i~ moved up and downl a rather lar~e mechanical energy ~s r~quired hence the ~ervo devica bec~me~ l~rge in ~ize.
Thereforep lt is ae~ired to use the above holo~r~n lens a~ the objective lens of an S optlca7 slgnal reproduct~on head. ~Io~ver, an o~-axis hologram len~ i~ not a~sirea a~ the ob~es~ti~ve lens of th~ optical ~lgnal~ repr~duc~tion head by the followin~ re~asosl~.
One of the r~ason~ i8 a~ follows.
Since the objective 18n8 i9 moved up an~ ao~?n b3!
~e 0cu~3sing se~o a~ de~crlb~l abo~re, ît i8 nec~
e~sary that the reproduction r~erence~ w~ve beam imultaneou~ly moved Mp and down :Ln parallel to be irradiated positively on the len~ portion of the of~ hol~ram lens. In the oase of an inline holo~ram lens, ~ince the moving dir~etion of ~he len~ i~ coincident wlth the diraction of t~e reproductlon re:~erence wa~re beam, l~ un nece~;sary to mosre the reproauction r~ferenc2 wave beam simultaneoll~lyO
~he ot~er 0~ the rea5~n~ iS as ~ollows, It i~ ne~e~ary that the o~-axis hologr~m lens i 8 rotatea and ad3u~ted fc~r the r~productiLon reerenc~ wave bsz~n about three axe~

2~ perper~di~lar ~rith one another to hr~ng the fo~
~ing or ct~n~rerging po~nt of ~he reproductlon ~ub-~ect wave beam to a pre~et2rmined po~ltioll~
Thi~ ad~u~ tment i~ Yery compli~ated and a~no~t impos~ble when the N,A. o~ the le2~ lar~e.
q~he inl~ ne hologram l~n~ is almost ~ree o~ ~he ~vve di~r~icult ad~ustmerltO

7'81~i From the abo~re, it wlll be understood that the ~ nlin~ hologram len~ i~ de~ired a~ an ob~ective len~ of an optical signa:L reproaucinq head.
Although the recor~ manner of the i~line hologram le3~s i~ de~cri~ rie~ly with r~ference to Fig. 3r ~t w~ e deE;c~ribed in detail with reference to Fig . 5 . The record ~ub; ect wave beam A and record reference wave beam B, whlc~
are s:oinc~dent in optical ax~ ~ on th~ nonnal to the record sur~ace r o:E hologr~m res~ord med~
~re irradia!tea on ~ circular area of record ~urface (photo-sensitiv~ sur~acs) r of holoqram record medium HR to ~orm the inl~ne hologram len~ por~on ~L which con~i~t3 of int~r~erence patterns. In th~s cu32, ï5 both ~ asld B ar~ proYid~d ~y the las~r be~m from a la~er b~am or light ~our~e ~5., The record ~ub~ect waYe beam ~ i~
prep~red by the following manner. A part o the ~aser be~n ~plan~ ~ave be~3 frc~m ~he laser light ~ource 1.5 i~ ~ rrad~ ated through two be~m ~plitt~3r3 B~l ana BS2 on a mother lens topt~call convex lens~
Ll ~o be focus3sed at a point P ~whi~h corre~pond~
to th~ r~ar ~os~al po~nt of lens Ll) a~d to be diverg~
ed there~rom to thereby produce a spherlcal wave b~ whi~h iæ~ the record sub~act wave b2~m A3.
~ile ~ th~ recora re~f~rence wa~e ~ieam B is prepared by the follow~ns manner. A part oi~ the la~er be~m fr~m tha laser light source LS is reflacte!d on the ~eam ~pli~er BSl, ~urther re~lected on two mlrrors Ml and ~2 and then lnc1dQnt on an a~x~llary 7~ 6 1QnS ~optlcal convex lens3 1.2. The beam ~mitted from ~e len~ L~ is oous~ed at a cenl:er point Q
on ~he be~n splitter BS2 (which s:orr~ponds to the rear focal point o~ len~ L2), then reflected on the beam spli~t~r BS2 and passed ~ro7~gh the mother lens I.l to be ~he record ref~rence wave bea~m B ~which is a parallel plane wave beam~.
~en this ca~e, the N. A. of inline hologrzm lens IN-I. thus made d~pends upon tha N.A.
of mother lens I.l~ so that when th~ inl~ne hologr~un len~ IN-L i~ usea a~ the obj~ct~ve lens of an optical ~ignal ~ ~ reproduc~ ng head, it is neces~ary to select the ~t.A. o~ inline hologrE~n lens IN-~ rather large. There~ore, in this ca~e, len~es with large N.A. mu~t be of course u~ed a~ ~he lenses Ll and I-2.
When an ordinary optical lens is usad a~ oach of ~h~ lense s Ll and L~, a lens con~ -~i~ting a m~mber of lan~ set~ must be used as in ~h~ ob~ective lens o a microsco~e. As the N.A.
become~ large, the focal point~ o~ lens~s ~ .2 Rre pos~t~oned wi1:hin the mirror cylinder with the re~ul~ that the r~corcl method of the ~ nlille hologr2 m lens ~hown in F~. 5 be~come~ ~mposs~ble.
In order to avoid thl~ problem, the ~ollow~n~ re~rd methc~ of an lnline hologram len~ with lar~e N.A. has been proposed., That is, a beam ~3p~ittex 1s provided ~n OppO5~19' relatlon to a hologrE~I rec:Qrd medium, an optieal len~ ~n~i~t~
i ng of a number o~ lens set~; is loc~ated at th~
oppos~ te sidç! o:f the beam sp~itter as an ob~ective 2'7~

lens, the l ~er bec~n rom a 1 3E~er li~ht so~lrce is incident on the objectlve lens, the cliverging beam emitted therefrom ~s irradi ated on the ho~ o-gran re~ord medium throu~h ~he beam spl ltt~r as ~ reco~d sub~ect wa~e beam r the lase~ heam is al50 incid~nt s~n an auxillary len~ to be a record re-ference wave beam, this r~3cord refe~2nce wave ~eam i~ reflected on ~he ahove be~n ~plitter, c~fl then the reflected beam i5 lrradiate~l on the hologram record meaium.
~.7ith the above record method, since the record subiect wave bean? ~spherical bean~ from the ob~ective lens passes throu~h the beam splitter, it i~ sub~ected to aberration.
To avoid this defect, it is necessary that a spe-ci a:L ob~e ~tive lens is ul~ed to thereby correct the aberration o~ the recorfl sub~ect wave he~nn Qr a similar beam splitter is provided upon re-production. T~is is, however, not ~o pre.Eerred in view of practia~l use.
Now, the method :For manufacturincr an inline hologram lens wlth a large ~.A~ accord-in~ to the present in~entlon, ~hic~ ~ ~ free of the prlor defects and oan e~ly manuacture an inllne hologram lens, wlll be aescribe~.
Pn example of the in~Tention will be descri~e~l wi th re~erence to Fig . ~S r In thi~
exa:mple, an o~f- axi~ holo~ram lens OX-L, whi~
made by using a record sub~es~t wave beam ana a ~o record reference be~ in off-axis with ea~h sther 8~36 and ha~ a diffraction e~i~iency les~ ~han 100%
is u~ed a~ a mother len~ (o~ect~e l~n~).
T~ method of making ~he off-axis holo~ram lens OX-L, ~pecially it3 record method wi~l b~ des-cribed l~er with refe~ence to Fig. 8. The o~f -axi~ holQgram len~ OX-L i8 formed vf a hologram reoord medlum HR2, whtch ¢onsists o a ~lass sub-~trate GS and a photo-$en~itive layer ~re~ord layer) K coated on the gla~s substrate GS.
On the center portion of photo-~en~itive lay0r ~, recor~ed is a ai~-shaped off-a~i~ hologram lens portion HLl whi~h i~ then devel~ped a~ described later. In this ¢ase, the off-axis hologram lens OX-L ~g 80 formed t~at when a reproduction reference wave beam ~pl~ne or sph~rical wave beam, in ~his ex~mple, the pl~me wave beam iY used) B' ~s irradiated on the lens portion HL' in the photo ; -~en~tive layer K through ~he glass ~ub~trat~ GS
at the angle of about 45 w~th respect to ~he 2D normal on the len~ portion HL', a reproduction ~ub~ect wave ~m A' i8 reproduced from the photo-~ens~tive layer K which has the opti~l axi~ alon~ ~ha normal and i~ focu~e~ at a point p.
-In Fig~ 6, ~Rl de~i~nates a hologr~m reoora medi~ on which an inline hologram l~n~ IN-L ls to be ~orm~d and whi~h is ormed of a gl~8 ~ub~trate GS and a photo sensit~ve layer The of~ holo~ram len~ OX-L, 7~

servin~ as the mother len~, is ~aced to the holoqram record meclium ~IRl. In this case, the of~a~ls hologra~ len~ OX~ so located or the holo~r~n re~r~ medium HRl that the photo-sensiti~e layer S R of the former is parallel to the photo-~ensit ~ve layer R of the latter w~th a precle~erm~ned distancs.
The la~r be~m ~paral lel pl~ne wave be~n) from a laser liqht source ~S i~ parti~l-ly reflected on a beam splitter ~fi, ~urther r~3flected on a mirror M, and the re~lected beam ~parallel pla~e wave ~eam~ thereon i~ irradiated on the photo--sensitlve layer R throu~h the ~l~s~ sub~trate GS of of~-axis holo~ram lens OX~I, as the! reproduction reference wa~re beam ~'. Then, from the off~
holo~rEan lens OX-L ~ reproduce~ 1~ the reproductio ~ub~ect wave heam A' whlch is :eocus~ea at a point ~? and then diverc~eA therefrom. Thi~ beam ~' i9 incident on the photo-~e!n~t~ve lay~r R of hologram record medium ~Rl as a record ~ub~ect wave bean i~.
~he la~er ~eam ~rom the laser ligllt so~lr~e LS ~art~ally passe~ ~hrough the beam 8pl~ t~r B~, when through ~he off-~?xls holo~xam lenE; OX-I.
ana i~ ~ nc~ den~ on the photo-s~nsitive layer g of hologram record medium ~IRl as a reGord re~erenc2 wave be~m B wh~ch is in ~nl~ne rel~t~on tc> the re~ord sub~3ect wa~re ~eam A ~nEmely, the beams A
an~l B are3 co~ nc~ent ~n op~ . Thu~, a fli~ haped ~line hologram lens portlon ~I. i9 formed on the cent~r portic,n o ~oto-~ensitive la~er ~ o~ r~cord medium ~Rl. Thi~ record medium ~Rl is the~ suh~ected to developinc~ proces~, whlch will be describe(l later, to be an inline hologram lens IN-IJ.
Another axam~?le of the invention will be descrihed w;th reerence to Flg. 7. In ~his example, the ofe-ax19 holoc~ram len~ OX-L serving a~
the mother lens is so located for the hologram record medium ~Rl that the g~s sub~tr~te GS of the former i5 in contact w~th the photo-sensitive layer R of the latter which are di~po~ed ~imilar to that shown in Fiq, 6. Then, the recording a~ the inline holo~ram lens IN-I. i9 ca~ried out.
In this ca~e, the reprodu~tion and recnr~ sub~ect beams P~' anfl ~ become each such a ~pherical wave b~z~n which diver~es from an ima~inal polnt P
Now, a description will be ~iven or the mannex to manufacturle tha of~f-E~xi8 holo~ram lens OX-L u~ed a~ the mother lens with reerence to Fig. 8. ~ record sub~ect wave tsPherical ~0 ~rave) be~ irradiatea on the photo-sensitive laver X o~ hologr2dn record medi~m IIR2, wh~ch further ~ncludes the qla~s ~ub~trate GS, ~ such a manner Ikha~t the optical axi~ of the beam A ~ s coincident with th! normal to the pho'co-sen~:i~Je layer R, and a record reIerence wave tParallel plane wave) he~m B is also lrrad~ atea on the photo-~ensitive layer in ~tlch a manne~ that its opti~al axis :i ntersects ~he normal at about 45. Thu~, a di~c-shaped of-ax~ holc~ram lells portion ElL' is recorded on the cerlter portic1n of the photo-~en~iti~Te layer K.

~L~2788~

ThereaftQr, the photo-ses~siti~e layer ~ i8 aeVelOped prov~de ~he o~f-ax~ hologra~n lens 0~ ~.
Il this ca3e, the rec~rd ~ub~e~t w~ve be~n A i~
prc~duced by the follow~ng ma~er. ~hat i~, the la~er beam ~lparallel plane wa~Te) fr~m ~ la3er llgh~ ~ource ~S ~ part~ ally pa~ed through a beam 3plitter B5, th~n ~nc:ident on an ~uxill~ry len~
~optical len~) ~2, ar;~ then fo~us~ed at a polnt Q (xear focal point len~ I-2~. The ~pher~ al ~rave beam diverging from the po~nt Q i~ inc~ nt on a mother len~ Ll ~ob~ectlve len~ ana made of a er of lens ~et~ to focu~ the 1be3m a~ a po~nt P. The ~pher~ cal w~ve beam dlverging ~ro7n ths point P i8 u~3~1 a~ the recs~rd ~ub~e~t wa~re ~2ain A.
~h~ re~ord referenae wave b~am 1~ pro~lrided by the :following manner. ~hat i8, the laser beam from the laser light sollrce LS
i~ partially ~ ect~d on l~e be~m ~plltt~r ~5, and ~0 then ~urth2r reflected on a m~rror Mo qh~ }~eam reflectea on the mirror M i~ u~3d a~ ~he r~cord reer~nce wa~re baam B
An ob~ct~v~ l~ns of a miCroscQpe wi th th~ ~ r A . of, for exampl~, O . 4 or 0, 5 i ~ Qm-ployed a~ th~ moth~r len~ I.l. The aper~ure of off-æis ~ologra3n 12n8 pc:~rtion E~L' ~ elected, for e3t~mple, 2~mn in diameter and the op~ration dl~tan~3 ~ereof i~, for example, 2.3mm. Accord~ngly, the ~nline hologram l~ns portion ~IL of inline ho~ ~xam len~ IN-L s~own in F~ g . ~ ha~ aperture -- ~7 --~L~Z71~8i~

of 2n~n and operating di~tance of 2. 3n~.
A~3 the 1 a~er 1~ ~t ~ource ~S u3ed in the examples of Fig~. 6, 7 and 8/ such laser lighlt ~c)urces may be used whic~ produce the ~oïlow~
ing la3er beam, respectively.
~rgon laser beam ~ A = ~880 A) ~rypton lassx beam ~ ~ - 6471 A3 Coloring laser beam ( ~ ~ 6330 A,3 He-~e laser ~eam ( ~ - ~32B A) lû The kind of photo-serl~itive la~yer3 R o~ hologram record medlum~ HRl and EIR2 ~ho~n in Figs . 6, 7 and 8 is s~le~ted in accordance w~ th lthe la~er beam.
~ext, an example of makin~ the hologram record mediums HP<l, HR2 an~l hologram len~è~ IN-I~, OX-L w~ a now de~cribed.
That i9, a suitable amc)unt oY layer hardening a~en~ ~uch a~ a~ueous sol~tion of ~elatin added with foxmaldehyde glyoxa~ is ~ept at ~bout 40C"
wh~le a glaæs substrate with the thicknes3 of l~n and a sp~ nner are kept at a}~out 40C.
~hen, the 2lqUeOU5 solution of gelatln i8 coated 0~ the gl as~: 8ub8tra~ b~ t~e spinner . ~n this case, the coating thickness of ~lati n aqu~ous ~olution on thQ gla~ ~ub~trate ~s ~elected such that the thi~cness o~ dried coating ~ ~ SmDn in the hologrmn rec:or~ m~dium for the off-ax~s hologram len~ and 15mm for the ~ nline hologram lens . Th~ gel atin water ~olution coated on the gl~ ub~trate is dried to ~e a gelatin ~ 18 -~L~ILZ7i~

layer which ~8 a mother material s~f the photo--~en~:~ ti~r~ layer.
Nex~ proces~ to give the phc>to-~enslt~vity to the gelatin layer w$11 be described.
The photo-sens~ tivlty to the blue or green ~beam is given to the gelat~n layer by the foll~wing manner. That i~, the gel~tin la~er i~ in~er~ed in 2 to 10 weight percent~ o aqueous solution of ~mnonium bichromat~ in about 10 minutes, th~n taken out gr&dually therefro~n, held vertically and then dried in a darkro~.
The phot o-sen~ itivi~ to the red beam i8 given to the gelatin layer by ~uch a mamler that a aqueous ~olut~on of 2 we~ght ~ of ~nonium bic~romate and 1 x 10 3 mol~fe o~ methylene blue coloring agent iE~ add~d! with a~nnonium to hav~3 about 10 pH, then the ~elatin layer i~ i~ersed in ~hi~ a~ueous ~olu~ion in al~out 18 minutes and 2Q then ~rled in the ~low~ng atmo3phere including alranonia and drled nitrogen.
~y the above manner, the hologram r~cord m~d~um con~ ing of lthe gla~ ~ubstr~te and ~ photo-~en~iti~e la~er R ~hereon i~ m~nu-factured.
The expl o~ure to the photo-sens~ t~ve l~yer ~ of the hologram record me~ium ~ carried out as aescribed in col~nectlon w~ th Figs~ 6, 7 and 8. In ~ ca~e, the irra~liation energy o~ the la~er beam i~ 6el~c:ted ahout 100 to l~OOmJ/cm2.

. . ...

~788~i q~he hologra;n record med~um, whose photo-sensitlYI!3 layer is axposetl, is ~nner~ed ~ n wa~ex. ~n en the photo-sens~tive layer has thQ
photo-sensi~ivi~ to ~e blue or ~reen heE~n, it i~
llmner~ed in the flowixlg wat:er at about 20 C in a~c~ut one hour, and when the photo-sensiti~e layer has t:he photo~sensitivlty to ~he recl beam, ~ t ~s lm-mer~ea in water at about 40C in about 30 mlnutes.
Thereafter, the hologram record medi~ ~s i~ner~ed iLn a~ueou~ solution o~ 50 ~ opropan~31 in about 10 minutes. th~3n drippe~ in a~eou~ ~olut~on of 90 % isopropanol in ~everal seconds, then i~nerse~
~ n 100 ~ isopropanol in about 10 minutes, and then rapialy dried by hot wina. Thas, the de~relopin~
tre~nent ls ~inished.
The photo-~en~ittve la~er, whose mothe!lr mate~ri~l ~8 a ge'Latin layer, has molsture ab~orption property, ~o that i~ it i~ left a~ ~t is, there may occNr such a ~ear that the hologram lens d~ s~ppear3 0 To avoi~ thls fear ~ as ~hown in F~g. g, a ~over gla~s CG with ~he thickne~s of about 150 ~ M 1~ bondea to the photo-Yensitive layer K by means of xes~n which ~ hardened by ult:ra~ olet rays. Thu~, the holog~n lerlse~
OX-~ and I~N~JJ ~! made.. In khe arawing~ ot-her than F1g. 9, the ~o~r~3r gla~ CG is omltted.
Now, t~e manner to manufac~ture a ~la~ line hologx~n len~ I~-L' hy u~in~ ~he inline hologr~m ïen~ ~N-L khu~ producefl a~ the mother len~ w:i ll be described .

~ 2~ --~'27B86 A8 shown in Fig~ 10, hologr3~n record me~liums ~Pcl and HRl ' are xo a~ sposed that the photo-3en~itive l~yer R of tha la~ter, ~hich i~ to be a ~la~e inline hologram lens :rN-L ' ~s ~aced to the photo-~en~iti~e l~yer K of ~he former, whlch 18 50 ~ in ~iffraction effic~ency, wlth a predeterm~ned di~3tanc~. ~hen, the la~er be~n from a laser light ~ource I.S ~ irradiated on the gla~s ~ubstrate GS D:E hi:>logram record med~n l~Rl. Tn this casa, a part of ~e beam ~50~
used a~ a reproduction r~ference wave be~m B' and the remainin~ bean (5096) 1~ used a~ a r~coxd re-ference wave beam B for the hoïo~ram record medium ~Rl ' . Thus, ~rom th.e mother inllne holograan lens ~N-L, reproduced i.s a rcproduct~ on ~ub~ect wa~re beam ~' which is ~'oc:u~ed at a point P and which i8 ln turn irxadi,at:ed on the hologram racor~l m~d~um HRl' a~ a re~ordl s~ec~t wa~ beam A to ~orla a hol~sgram len~ portion ~L on ~e photo -sensitive llsyer ~ th~:recs~
A ~l~ve inline hologram len~ IN~L ' can be ~lso made b~ the m&nner ~hown in Fig. llo ~n ~ oasa, ~he photo-~ensitive layer ~ o hologr~n recQrd medium l~ in dlrect contact wi"ch ~e gl a~ ub~trate GS o~ mother ~line hologra~m lens XN-I, wlth bo~h hologr~a re~ord medi~n~ EIRl and HRl ~ being locatea in the ~ama order as in Flg . 1û . I n thl ~3 case, reproduet~ on an~ record sub~ect wave bea3n~ A' and ~ ara both sph~rica1 q~ave b~ d~rerged ~r~m an imagina1 point P.

7~6 Accordin~ to the method of the present inYention descr~ea above, the inllne hologram lens wlth a large N.A~ can be easily manu-factured.
Now, a descriptlon will be given on an optical s~gnal reproauction head in which an ~nclined hologram lens made ~y the methoa of the present invention i~ used.
A prior art optical signal reproduction bead will be now de~cribed w~th reference to Fig. 12.
In the figure, 1 desig~ates a laser l~ght source such a~ ~e-~e laser light source which emits, for example, a P-polarl~ed l~ght tlinez~ polarized l~ght) laser bez~ Th~8 la~er be~m from the laser l~ght ~ource 1 is reflected on a mirror 2 to be changed by 90 in direction zmd then incident ~hrough a ~eam spl$tter 3 on a quater or plate 4. In ~hi~ 4A plate 4, the P~p~larizea laser beam i~ converted from th~ linear polarizea l~ght.into a c~rcular polar~zed light wh~h i~ focus- -~ed through an ob~ect~ve len~ 5 on thP rec~rd surface of ~ disc-~haped opt~cal rec~rd med~u~ 6 on which ~- information s~gnal~ such as an audlo s~gn~ deo , signal and ~o on, wh~ch are pulse-c~de-modulated, ~re recorded a8 a ~pir3~ track con~istin~ of pit rows thereof. qhe reflecte~ light on ~he recor~
medlum 6 i~ agaln inc~dent on ~he 4 ~l~te ,4~thr~ou~
~he ob~ective leng 5. In the ~ plate 4, the c~rcular polari~ed l~ght is convertea in to an S-polarized l~ght ~ ear polar~zed light) la~er ." ~., '~

~L~278~i be~m and ~e~ ciderlt url the beam splitter 3 which refle!ct~ the inci~eTlt laser beam ln the later~ direction in FigO 12 and introdllce~ the reflected laser beam to a photo-diode 7 ~ervin~
S ~ a light receiving elemf!~nt. Th~ s llght rsc:eivlng el~menlt 7 then produce~ a reproauced output si~nal.
In the above prior art optical 5ig-nal reprodu~tion head, an optical len3, which consi~t~ of a num~er of ~et lenses ~imilar to those used in a micro~cope, iq employed as the ob~ectlve len~ 5, and thl~ ob~ective len~ 5 i~ mo~red up and d~wn along it~ optical axi~ direction by electro-m~netio means or linear motor ~though not ~hown in Fig. 12) to carry out the iFocus ~ervo.
Furth2r, a~ the mlrror 2, ~ galvano-mirror i~
used, which i~ rotated in re~pon~ to th~ tracXlng di~pl~cement to achieve the ~ra~king servo generally.
As de~rlbed abov~, in ~e prior art, the optical lens con~ist~ng of a number of set len~e~ ~ 8 u~ea a~ t~e ob~e~ e len~ 5, ~o that the obj~cti~re len~s 5 i~ rath2r hea~yO
T~s, ln order to mov~ the opt~al len~ 5 up and down along its optical axls direct~on for ~h2 focus ~erv~, a rathsr la3rge m~chani~al energy ~ ~ r~quir~d and al~o the ler~ 5 i~ v~ry expen~ive.
Further, thera may oc~r ~uch a fear th~t the relat.~re po~t~onal relat~on i3MQ~ he optical elesQ~nts ~ilï chan~e ~n l~p~e of t~ n~:e ~h~
optical sys~ean 1~ loeated in ~pa~. Thu~, ~ ~3 ~L~2~78~

it can not be a~Toided in the art ~at all the opticaï
system occupi es a rathex 1 arge space f actor O
If aTI inline holo~ram lens mada by the method of the present inventi on i~ u~ed in place of the ob~ecti~e l~n~ 5 of the optical ~ignal re-productiorl head r the ~ve defect of the pr~ or art can b~ removed.
~n example of the optical ~ignal reproduction head ~ i n which a hologram len~ (inline hologram len6) made by the present invention ls u~ed, will be described wlth reference to Fig. :3 .
In the example of Fig. 13, a hologram lens is ~ed as the ob~ect:ive len~ 5 in the above prior art optical signal r epxoduction head, ana the beæ~n ~plitter 3, -~ plalte 4 and hologram lens 5 are bonded together ~y light~pas~-permi~sible ~transparent) ~dhe~ive ag~nt~
In the example of Flg. 13, the beam splitt2r ~pol~rized light beam ~plitter 1 3 is mad~
by, ~r ex~P~ple, the ~ollc)win~ mannern On each of the inclined ~urfa~s of 45-pri~s 3a and 3b, ~ormed ~ a multl-layer film 3s:~ which ~;erves tv bor~d both the prism~ 3 a sr~l 3b ~ogeth~r as the }: eam splitter 3 ~hich is a c~bis: body with one sectlon of about 5nnn and 30~m~F in weight., The ~ plat2 4 i~ made o a~ exten~îon ~ilm of polymer (for exampl~, polypropyl~ne) ~ sele!cted a~ 15 ,um in thick-ne~s, which ~3 ~elected ~ n respon~e to ~he wavelength o 63~8 A o~ Ne laser beam, and neg:le~ible ~m~ll enough in weight a~ compared ~ith ~hat o be~ t-ter 3.
-- ~4 ~. 9L;~7~

The hologram ~ob~ective) lens 5 i8 made of an inline hologr~ lens made by the method of the in~ention which i~ maae as follows, For example, on the surface of a square gla58 plate or substrate 5b with one section of 5 mm and the thickness of 1 mm, formed is a photo-sensi~i~e layer 5a, and a disc-shaped lens portion 5a' ~8 formed on the center portion of photo-sensiti~e layer 5a. ~n thi~ case, the lens portio~ 5a' i~ selected about 0.4 in N.A., about 2.3 mm in operation distance, and about 2 mm in aperture.
qhe 4 plate 4 ~ bo~ded to the lower surface of pri~m 3b of beam splitter 3 through a light-pass-permi~sible adhesive layer 8, the glass ~5 plate 5b-of inline hologram lens 5 is bonded to the lower surface of ~ plate 4 through another light -pass-permi~si.ble adhesive layer 8, ana a co~er gla~s plate 9 i5 bonded to the lower surface of photo-sens~- :
tive layer Sa of hologr~m lens 5 through a further light-pass-permi~sible adhes~ve layer 8 A~ the 1 ight~pass-permi~sible adhe~ive layer 8, an ultraviblet-r~y hardening adhesive (for example, PHOTO-BOND : Trade Mark) iQ used whose refractive ~ndex i~ substantially ~æme as that of ; 2~ gla~s.
ThP cover glas~ plate 9 ~ 5 a glass square plate w~th one ~ec~ion of S mm and the thi~knesY
of O.lS mm. The total we~ght of hol~gram lens S and co~e~ glass pl~te 9 ~s about 70 mg, and th2 total welght of beam splitter 3, ~ plate 4y - 2~ -~ ,:

~2~

hologx~n lens 5 and cover glas~ pla~e 9, whi~ih are bonded ts~ether as shown in Fig . 13, i s ~elected smaller than about 40û mg.
Further, as the light receiving S element 7, a pho~e-dioae ls us~d, by way o:E example, ~d a~tached to the side surfa~e of pri~m 3b o~
beam ~plitter 3 . In th~ 3 ~ase I light-pas~
-permissi~le adhesive can 1: e al80 u~ed to bond the llgh~ receivin~ eleme~t 7 to the prism 3b o beam splitter 30 In the optical ~ignal reprodu~tion head described in s:~olmection with Fig. 13, since the hologr~n len~ has the! gla~s ~ubstrate and al30 the cover ~las~, when it~ photo-sensit~ve lEIyer i.8 made of mainly gelatin, ~lo as to avoid the d~appear of the hologram lens due to the mo~sture ab~orbing property of gç!latin, the head become~ complicated in con~truction and require~ man~r nun~er of ~orking proce3se~ therefor.
~nother example of the ~p~ al ~ignal reprodu~tion head, wh~ch i~ light in ~eight, ~imple in ~onstruc~on and easy in mas~ufacturing, will be now aa5~ib~d. In thi~ example, a hologram len~
sed a~3 the ob~ectiva len~ S in the opti~:al sign~l reproduction haaa ~hown ~n Fig. 12 and the 4 plate 4 i~ u~ed ~ th~ ~u~s~rate or protac~i~re pla~3 of the holc)gr~m le~s.
One ~xa~nple of the above will be des~ribed now with refç~rence to Fig., 14 in whlc:h the part~ or element~ correspo~ding to tho~e of '78~16 Fig. 13 are marlcea wi~t the same reference~ and their description will be omltted.
In the example of Fig. 14, a~ the objective le~s 5, a hologram len~ 1~ used and a~
the ~ubstra~e (tran~parent suSstrate ) of hologr~n lens 5 t the 4A pl~te 4 is employe~. The photo-~en8itive l~yer Sa, on whic:h the hologram lert~ portion 5 a~ i~ formea, of holograrlt 1en8 5 i8 bonded to the lower ~urface o f pr~ sm 3b o~ be~nt ~plitter 3 through li~t~pass-permi~s~ble ~gent l ayer 8 to be an int2gral body . Further, ~imilar to the exampl~ o~ F~g. 13, the light re-ceiv~ ng element ~ bonded to the ~ide surf ace o~
prism 3b of be am 8pl '~ tter 3 through light-pa~
-pernt~ 8S ble agent.
When the holograTn lens 5 i3 taken a~ a ~ingle unit, the ~ plate may be used a~
the cover gla~s 9 of the example shown in Fig. 13.
.` It will ~e apparent that mally .~ 20 modifiaat:~ons ~d variation~ could bs ~f fected by cne 3killed ~n t}~ art without depart~n~ frc)m ~e ~pirits or ~c:ope of ~he novel ¢onc~p~s o~ t3hs~
pr~ent invent1 on, 9t:) that the scope o~ the ~ n~entlon ~hould be dat~rmined by the append~d cl aim~ only .

Claims (8)

WE CLAIM AS OUR INVENTION

1. A method of producing an inline hologram lens, comprising the steps of:
a) recording on a first photo-sensitive layer a holographic interference pattern which results from the simultaneous irradiation of said layer by a reference wave beam and a subject wave beam, said two beams being off-axis with each other and the latter beam being perpendi-cular to said layer;
b) forming an off-axis hologram lens by developing said first photo-sensitive layer to c) facing a second photo-sensitive layer to said off-axis hologram lens;
d) irradiating said off-axis hologram lens by a reference wave beam for reproducing;
e) irradiating simultaneously said second photo sensitive layer perpendicularly by a reproduced subject wave beam as a subject from said off-axis hologram lens and a re-ference wave beam through said off-axis hologram lens; and f) developing said second photo-sensitive layer.

2. A method of producing an inline hologram lens according to claim 1, wherein said all reference and subject wave beams are coherent beams.

3. A method of producing an inline hologram lens according to claim 2, wherein said subject wave beam is formed by passing the coherent beam through an objective lens with a large numerical aperture.

4. An inline hologram lens produced by the method of claim 1.

5. An optical reproducing head through which a laser beam from a laser source is irradiated to an optically recorded medium and through which a reflected beam from said recorded medium is led to a photo-detector, said optical reproducing head, comprising:
a) a beam splitter:
b) a quarter wave plate c) an inline hologram lens produced by a method comprising the steps of recording on a first photo-sensitive layer the holographic interference pattern which results from the simultaneous irradiation of said layer by a reference wave beam and a subject wave beam, said two beams being off-axis with each other and the latter beam being perpendicular to said layer, forming an off axis hologram lens by developing said first photo-sensitive layer, facing a second photo-sensitive layer to said off-axis hologram lens, irradiating said off-axis hologram lens by a reference wave beam for reproducing, ir-radiating simultaneously said second photo sensitive layer perpendicularly by a reproduced subject wave beam as a subject from said off -axis hologram lens and a reference wave beam through said off-axis hologram lens, and develop-ing said second photo-sensitive layer, and d) means for sticking said beam splitter the quarter plate and the inline hologram lens together by a transparent adhesive.

6. An optical reproducing head according to claim 5, wherein said inline hologram lens further having a base plate and a protective plate.

7. An optical reproducing head according to claim 6, wherein said quarter wave plate is used both as a quarter wave plate and a base plate of said hologram lens.

8. An optical reproducing head according to claim 6, wherein said quarter wave plate is used both as a quarter wave plate and a protective plate of said hologram lens.