U.S. patent application number 12/120664 was filed with the patent office on 2008-10-02 for optical articles and sol-gel process for their manufacture.
Invention is credited to Fulvio Costa, Lorenzo Costa, Lucia Gini.
Application Number | 20080237904 12/120664 |
Document ID | / |
Family ID | 33017983 |
Filed Date | 2008-10-02 |
United States Patent
Application |
20080237904 |
Kind Code |
A1 |
Costa; Fulvio ; et
al. |
October 2, 2008 |
OPTICAL ARTICLES AND SOL-GEL PROCESS FOR THEIR MANUFACTURE
Abstract
An optical article, having an almost complete isotropy and
dimensions equal to or lower than 500 .mu.m, is prepared in which
the sol-gel procedure comprises a preliminar step wherein the mould
is cool filled with a sol containing the interesting oxide
precursors, the sol gelation, the gel drying, the removal of gel
from the mould and the final miniaturization of the dried gel. The
optical article can be used for optic telecommunications.
Inventors: |
Costa; Fulvio; (Sommo (PV),
IT) ; Costa; Lorenzo; (Sommo (PV), IT) ; Gini;
Lucia; (Novara, IT) |
Correspondence
Address: |
SMITH, GAMBRELL & RUSSELL
SUITE 3100, PROMENADE II, 1230 PEACHTREE STREET, N.E.
ATLANTA
GA
30309-3592
US
|
Family ID: |
33017983 |
Appl. No.: |
12/120664 |
Filed: |
May 15, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10550161 |
Sep 20, 2005 |
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PCT/EP04/02327 |
Mar 8, 2004 |
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12120664 |
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Current U.S.
Class: |
264/2.5 |
Current CPC
Class: |
C03B 19/12 20130101;
Y10T 428/24802 20150115 |
Class at
Publication: |
264/2.5 |
International
Class: |
B29D 11/00 20060101
B29D011/00 |
Claims
1-7. (canceled)
8. Process for the preparation of a mould for the manufacture of an
optical article of final miniaturized dimensions formed of pure
silicon dioxide, optionally modified by the addition of one or more
oxides of elements other than silicon, having essentially complete
isotropy and wherein dimensions of said article are equal to or
lower than 500 .mu.m, the process comprising the following steps:
a) preparation of an original high precision mould; b) reproducing,
in a silicon rubber one or more imprints, having the same size and
a reversed symmetry with respect to said mould; c) preparation, by
the employment of a mould obtained in step a) or imprint obtained
in step b), of a first optical article having reduced dimensions
and reversed symmetry with respect to the starting mould or imprint
according to a sol-gel procedure in which the sol-gel procedure
comprises a preliminary step of filling the mould which is cool
with a sol containing a pure silica precursor, gelling the sol to
form a gelled sol, drying the gelled sol to form a dried gel,
removing the dried gel from the mould, whereby a miniaturized first
optical article is obtained; d) repeating the preparation of
optical articles by the sol-gel procedure according to step c)
and/or by an imprint according to step b), until the desired
dimension is achieved.
9. Process for the preparation of a mould according to claim 1 in
which the mould of item a) is produced from a nickel/phosphorus
alloy on an aluminum carrier or an aluminum alloy.
10. Process for the preparation of the optical article of final
miniaturized dimensions formed of pure silicon dioxide, optionally
modified by the addition of one or more oxides of elements other
than silicon, having essentially complete isotropy and wherein
dimensions of said article are equal to or lower than 500 .mu.m
said process comprising one or more of the following operations
that, all together, can be continuously carried out as a cascade
and/or stopped at the desired or suitable step: a) preparing at
least one original high precision mould having an average roughness
lower than 20 nm; b) reproducing, in a silicone rubber, one or more
imprints, having the same size and a reversed symmetry with respect
to said mould; c) preparing, by the employment of the original
mould obtained in step a) or an imprint obtained in step b), of a
first optical article having reduced dimensions and reversed
symmetry with respect to the original high precision mould or
imprint according to a sol-gel procedure; d) preparing, inside the
so obtained optical article, of a further optical article again
having reduced sizes and reversed symmetry, or of an imprint
according to the preceding step b); e) repeating the preparation of
further optical articles by the sol-gel procedure and/or imprints
according to b), until desired miniaturized dimensions or, the
lowest dimensions on the ground of the physical limitation of the
process is achieved; f) separation, in relation with any step, of
the imprint and/or the optical article obtained, in which the
sol-gel procedure comprises a preliminary step wherein the mould is
cooled and filled with a sol containing a pure silicon oxide
precursor, the sol is gelled, the gel is dried, the gel is removed
from the mould and the dried gel is miniaturized.
11. Process for the preparation of an optical article according to
claim 3 in which the mould is previously submitted to surface
treatments by means of appropriate antiadhesive agents.
12. Process for the preparation of a mould for manufacture of a
miniaturized pure silica optical article, of final miniaturized
dimensions formed of pure silicon dioxide, optionally modified by
the addition of one or more oxides of elements other than silicon,
having essentially complete isotropy and wherein dimensions of said
article are equal to or lower than 500 .mu.m, comprising the
following steps: a) preparing an original high precision mould
having an average roughness lower than 20 nm; b) reproducing, in a
silicone rubber, one or more initial imprints, having the same size
and reversed symmetry with respect to said original mould; c)
preparing, by the employment of the original mould obtained in step
a) or an imprint obtained in step b), a pure silica optical article
having reduced dimensions and reversed symmetry with respect to the
original mould or initial imprint according to a sol-gel procedure
in which the sol-gel procedure comprises a preliminary step of
filling said mould in a cool state with a sol containing pure
silicon oxide precursors, gelling the sol, drying the sol to form a
dried gel, removing the dried gel from the mould and miniaturizing
the dried gel to obtain a pure silica optical article, d) preparing
a further pure silica optical article again having reduced sizes
and reversed symmetry with respect to the pure silica optical
article produced in step c), or of an imprint according to the
preceding step b); e) repeating the preparation of pure silica
optical articles by sol-gel procedure and/or imprints according to
step b) to obtain pure silica optical article of successively
reduced dimensions, until the desired miniaturized dimensions is
achieved; and f) separating the imprint of a mould with the desired
miniaturized dimensions.
13. Process for the preparation of a mould according to claim 5 in
which the mould of item a) is produced from a nickel/phosphorus
alloy on an aluminum carrier or aluminum alloy.
14. Process for the preparation of a pure silica optical article of
miniaturized dimensions comprising: a) preparing at least one
original high precision mould; b) reproducing, in a silicone
rubber, one or more imprints, having the same size and a reversed
symmetry with respect to said original mould; c) preparing, by the
employment of one or more of the original mould or imprints from
step b), of a pure silica optical article having reduced dimensions
and reversed symmetry with respect to the original mould or one or
more of said imprints; according to a sol-gel procedure in which
the sol-gel procedure comprises a preliminary step of filling an
original mould which is cool with a sol containing pure silica and
hydrolyzied TEOS at a pH of 4, gelling the sol to form a gelled sol
within 60 minutes, drying the gelled sol with aerogel in an
autoclave to form a dried gel, removing the dried gel from the
mould to obtain an optical article, d) preparing, using the so
obtained optical article, a further optical article again having
reduced size and reversed symmetry with respect to the article
produced in step c), or of imprints according to the preceding step
b); e) repeating the preparation of pure silica optical articles by
the sol-gel procedure and/or imprints according to b), of reduced
dimensions with respect to the article produced in step d), until
the desired miniaturized dimensions or, the lowest dimensions on
the ground of the physical limitation of the process is achieved;
f) separating of the imprint and/or the optical article obtained in
step e).
15. Process for the preparation of an optical article according to
claim 7 in which the original mould is previously submitted to
surface treatments by means of appropriate antiadhesive agents.
Description
[0001] The present invention refers to optical components
consisting of silicon oxide, as such or suitably combined, in final
or nearly final dimensions, having an almost totally isotropy and
sizes equal to or lower than 500 .mu.m; furthermore the invention
relates to the means used to carry out the preparation of such
optical articles, as well as to the process for the preparation of
both of them.
[0002] It is known that the optical materials, particularly the
transparent optical materials, are typical materials of known
machining difficulty and, sometimes, troublesome preparation
because their fragility and hardness which, for example, are
conditioning the hot molding by causing optical components and
devices not being generally acceptable for reasons of product
quality.
[0003] Usually, the methods for the production of uncommon
morphology optical elements comprise reducing suitable preforms
through extremely accuracy lens milling operations: These are
methods requiring a very precise handling even through the
employment of suitable equipment, this sometimes being the reason
of difficult repeatibility and poor process flexibility.
[0004] One solution has been achieved by producing aspheric lenses
through high temperature and pressure preparations, directly from
suitable preforms of the desired optical material: however, the
method has applicability limits, needs sophisticated equipment and
can be carried out only through considerable investment.
[0005] One method for reducing costs consists in the use of organic
optical material, i.e. plastic material, which can be melted and
molded using very economical processes. However, the employment of
plastic material is sometimes the cause of dimensional defects of
final optical product, because of the insufficiently controllable
material shrinkage during the molding treatment.
[0006] The Applicant is able to overcome all drawbacks being in the
processes for the preparation of optical materials according to the
known art, by means of the object defined in the European patents
no.586.013 and no.705.797 it may freely use: according to such
patents, it is possible to prepare perfectly and completely
isotropic optical components in their final or nearly final
dimensions by applying thermochemical densification treatment to an
amorphous monolithic aerogel of silica, and/or other oxides, by the
use of high precision tools and the former preparation of such
aerogel via a so called sol-gel process during which the
intermediate products, till the gel formation, undergo an ultrawave
treatment.
[0007] The final optical product, obtainable through tolerable
investments and absolutely repeatable methods, is characterized by
very high precision and dimensional steadfastness: however, it is
such and the relevant preparation method is advantageous when the
optical article dimensions are beyond a threshold, under which
machining difficulties may arise in the mould formation formation,
particularly in the preparation of moulds representing
microstructures which cannot be processed by means of the common
machining tools such as, for example, the microlens matrix or other
periodic microstructures needing a dimensional resolution of each
element under the entrusting threshold of the existing machinery.
Such difficulties increase in the case of preparation of optical
articles in the peculiar microoptical field, wherein positioning
and lining up problems have to solve of the magnitude order of
micron and lower, and that, furthermore, has applications other
than the ones pertaining to the traditional optic such as
telecommunications, pick-up laser, semiconductor laser, optical
memory.
[0008] The Applicant has now found it is possible to overcome all
above drawbacks and to consequently prepare optical articles, till
to the lowest possible dimensions, according to an economically
advantageous and repeatable method, which substantially consists in
a preliminar arrangement of the desired dimension moulds and the
subsequent use thereof in the preparation of the very optical
article.
[0009] Therefore the present invention relates to a process for the
preparation of moulds suitable to manufacture optical articles, as
well as for the preparation of such optical articles, these
consisting silicon oxide, as such or whit suitable additives, and
characterized by an almost total isotropy and dimensions equal to
or lower than 500 .mu.m, which process comprises one or more of the
following operations that, all together, can be continuously
carried out in a fall and/or stopped at the desired or suitable
step:
[0010] a. preparation of an original high precision mould;
[0011] b. possible reproduction, in a siliconic rubber or other
suitable compound, of one or more imprints, having the same sizes
and a reversed symmetry with respect to the moulds obtainable
through the preceding steps;
[0012] c. preparation, by the employment of one or more of the
products obtained in the preceding steps, of the optical article
having reduced dimensions and reversed symmetry with respect to the
starting mould/imprint; according to a sol-gel procedure;
[0013] d. possible preparation, inside the so obtained optical
article, of a further article again having reduced sizes and
reversed symmetry, or of imprints according to the preceding item
b);
[0014] e. and so on, possibly, through the preparation of optical
articles by sol-gel procedures and/or imprints according to b),
till the desired dimensions or, anyhow, till the lowest dimensions
on the ground of the physical limit of the process;
[0015] f. possible separation, in relation with any step, of the
imprint and/or the article obtained in the very step.
[0016] Some of the above operative steps may be furtherly
detailed:
[0017] a) a mould is prepared, hereinafter defined as original
mould, made by aluminum alloy or in other material with a suitable
chemical stability and able to undergo a precision machining
processing;
[0018] b) one or more imprint are prepared in siliconic rubber or
other suitable compound; having the same sizes and a reversed
symmetry (mirror image) with respect to the original mould;
[0019] c) by the use of the so obtained imprint as a new mould
(resulting symmetrically reversed with respect to the original
mould) a molded manufactured article is prepared trough a sol-gel
process in silica glass which has lower dimensions according to the
linear shrinkage coefficient and the same symmetry as the original
mould. The so obtained silica glass can be find application either
as optical component or as a mould for a following molding
operation;
[0020] d) the so obtained manufactured article can be used as a
reversed imprint in view of a further operation to sol-gel produce
an optical article having further reduced dimensions and reversed
symmetry (mirror image) with respect to the original mould.
[0021] The use of the reversed imprint made by a siliconic rubber
(or other material) is a possible one and may be repeated during
the process route, if necessary or opportune according to the man
skilled in the art.
[0022] The preparation of the original mould according to item a)
can be the first operation of the fall process according to the
present invention, or it may be carried out independently, and the
obtained mould may be suitably stored, to be subsequently
employed.
[0023] Such a preparation occurs according to techniques well known
to the people skilled in the art, and the choice thereof
substantially depends on the sizes of the mould itself. The
technique grounds, starting from the conventional ones, are:
[0024] use of numerically controlled machines;
[0025] use of special machine tools provided with a "turning
diamond";
[0026] use of cutting machine to treat conventional optical
networks;
[0027] microscopic geometry based technologies providing
photolitographic techniques combined with microerosion
techniques;
[0028] ablation through high power laser radiations.
[0029] The materials employed to prepare the original moulds
commonly are metal alloys, preferably nickel/phosphorous based
alloys on aluminum carriers, or aluminum alloys commercially known
as "anticorodal" such as, for instance, the ones defined as follows
by UNI rules: 9006/1, 9006/2, 9006/4, 9006/5, 9006/6. Of course it
is possible the use of any other carrier with the necessary
workability and steadiness properties. Also the replication of
these moulds into siliconic rubber (or other material) imprints,
without any risk occurring onto the original mould, is carried out
according to procedures well known to the people skilled in the
art. The main purpose of this preparation step is the production of
an opportune, even if not necessary, mould number in view of any
subsequent operation, as well as the maintenance of the original
mould.
[0030] Inside the moulds obtained thereby, in the original one as
well as in the subsequent imprints, other manufactured articles
employable as moulds or optical articles are then produced, having
reduced dimensions and, time by time, reversed symmetry, through
sol-gel procedures: the sol-gel processes are carried out according
to the well known technologies, on the ground of just common
principles and methods, about which reference can be made to the
field literature, patents too such as U.S. Pat. No. 4.317.668, No.
4.426.216, No. 4.432.956 e No. 4.806.328.
[0031] When the production, at any step of the above fall process,
aims to obtain an optical article; the dried gel is removed from
the mould to be submitted to a suitable isotropic
miniaturization.
[0032] The composition of the moulds and/or optical articles
prepared after the step b) of the inventive process, comprises a
silicon oxide, as such or added by oxides of elements modifying the
properties thereof, in particular way le optical properties.
[0033] An example of the modification of the optical-properties of
the silica glasses consists in the refraction index increase, that
is obtained by a suitable chemical formulation of the sol, which
precursors of the appropriate oxide are added to, particularly
titanium and/or germanium oxides. By following the same trick,
other optical properties are modified such as the optical
dispersion, through the addition of precursors of oxides of
elements belonging to the lanthanium group. The addition of
appropriate active oxide precursors to sol can promote also the
modification of properties other than the optical ones: for
instance, the silica glass thermomechanical properties, mainly the
specific thermic dilatation may be reduced beyond one magnitude
order if the glass formulation comprises a titanium oxide fraction.
Moreover it is possible to give the silica glass novel functional
properties such as, for instance, the photoluminescence with
peculiar emittance and excitation spectrum selectivities that can
be obtained by the presence of traces of oxides particularly active
in the field such as the appropriate excited rare earth oxides.
[0034] In the case of use of the manufactured article obtained via
the inventive process as a mould, the same submitted to surface
treatments by means of appropriate antiadhesive agents that permit
the removal of the product subsequently obtained therein, either
optical component or mould again to prosecute the miniaturization
fall process.
[0035] An example for the preparation of a silica glass mould is
given by the surface silanization to passivate all surface active
sites (hydroxyl groups or hydroxyl groups precursors) in order to
avoid the adhesion of the silicic gel that is aimed to be
molded.
EXAMPLES
Example No. 1
Diamond Cutting Structure
A. Manufacture of the Original Mould
[0036] An original mould was prepared as specified hereinafter.
Drawings according to the FIGS. 1 and 2 were supplied by a shop
qualified for very high precision works through the commercially
known "turning diamond" machine tool, by which it is possible to
finish off a metal surface having an average roughness lower than
20 nm.
[0037] The material to build the original mould was an aluminum
alloy, commercially known as "CERTAL".
[0038] The structure of the original mould was a 48 mm diameter
ring fully covered by square pyramids having a 2 mm side and about
1.75 mm height. The structured ring was in the center of a metal
disk made by aluminum alloy "CERTAL" and having a 56 mm
diameter.
[0039] A view of the structure is in the FIG. 1 showing, at sizes
doubled with respect to the true ones, the structure layout. The
single square pyramid is illustrated, with strongly enlarged sizes,
(10:1) by the lateral view of the FIG. 2.
[0040] The structure to be build, integrally formed by rectilinear
segments of dimensions not lower than about 2 mm, was, as far as
that kind of drawing was concerned, in a size range well compatible
with the type of machine used. The prototype of the original mould
satisfying required specifications, was easily obtained by the
encharged shop.
B. Reversed Symmetry Replication Through Siliconic Rubber
Imprint
[0041] An imprint of the original mould was obtained by using the
suitable compound ELASTOSIL M4601 produced by WACKER CHEMIE GmbH
according the usual procedure suggested by the very producer.
C. Miniaturized Replication N.1, in Silica Glass
[0042] The siliconic rubber imprint obtained in B was used as a
mould for a conventional high precision moulding silicic sol,
according to U.S. Pat. No. 5,948,535.
[0043] Accordingly, the following operation was carried out: 100 gr
of TEOS (tetraethylorthosilicate) were put into a 1000 ml
borosilicate glass flask, under a suitable stirring of a magnetic
anchor. 306 g of 0.01 NHCl in bidistilled water were added to TEOS
in the flask. The TEOS complete hydrolysis was achieved by an
ultrasound probe treatment over 10 minutes. Hydrolysis ethanol was
partially extracted under reduced pressure by a 150 ml volume
liquid. 60 g of AEROSIL SiO2, OX-50 DEGUSSA A.G., were added to the
residue recovered from the rotating evaporator and properly
homogenized and centrifuged. The silicic sol, before being poured
into the siliconic rubber mould, was brought to pH 4 through a
gradual addition of a 0.5N watery ammonium hydroxide.
[0044] The sol gelation occurred in about 60 minutes. The obtained
gel was conventionally treated, according to U.S. Pat. No.
5,948,535, converted to aerogel and densified to silica glass.
[0045] The obtained product, as very pure silica glass, was a
miniaturized replication of the original mould. It is possible to
note, through an eye inspection, that the structure of the original
mould was faithfully reproduced in the glass replication with an
isotropic linear reduction of all sizes by a factor of about 2.
D. Reversed Symmetry Imprint No. 2
[0046] By using the silica glass product obtained in the preceding
operation, a novel imprint was prepared according to the procedure
previously disclosed in B with reference to the original mould.
E. Silica Glass Miniaturized Replication No. 2
[0047] The siliconic rubber imprint obtained in D was employed as a
mould according to a procedure similar to the one previously
specified in the operation C. The obtained silica glass product was
a very good quality replication of the original mould structure
once miniaturized in C, and, the second time, in E. It is possible
to note, through an eye inspection, that the structure of the
original mould was apparently faithfully reproduced with an
isotropic linear shrinkage of a factor equal to 4.
[0048] The same procedure was applied to reach, through subsequent
operations of siliconic imprint as well as of miniaturization in
silica glass, a third and a fourth reduction level of reduction of
the original mould structure.
[0049] The results of the dimensional analyses of all silica glass
structures obtained thereby are summarized in the table 1.
TABLE-US-00001 TABLE 1 reduction reduction reduction reduction
original 1 2 3 4 disk 56.0 28.0 14.0 7.0 3.5 external diameter (mm)
square 2.0 1.0 0.5 0.25 0.125 pyramid side (mm)
[0050] The table 1 data outline the inventive level and the
industrial utility of the disclosed invention: a microstructure was
obtained through a novel "cascade" process allowing to use the
conventional mechanical processing high precision to build the
original mould as well as to transfer the same precision to a
micrometric scale through the new cascade miniaturized process.
Example No. 2
Microlens Matrix
A. Original Mould Manufacture
[0051] An original mould was prepared according to the disclosure
of example n. 1, paragraph A, but one difference: the square
pyramids having a 2 mm side and a 1.75 mm height of the example 1
were now substituted by truncated square pyramids, fully equal to
the above described pyramids, but being truncated at a 1.6 mm
height.
B. Reversed Symmetry Replication Through Siliconic Rubber.
[0052] One original mould imprint was obtained by means of the
procedure already disclosed in the paragraph B of the example
1.
C. Silica Glass Miniaturized Replication N. 1
[0053] An original mould replication was prepared through the
procedure already described in the paragraph C of the example 1.
The silica glass original replication, having good optical
properties, was similar to the original one, also having a
morphology ideally corresponding to the morphology of the original
mould, according to one to one correspondence. Only the dimensions
were smaller being linearly reduced by a factor of 2. Particularly
the base side of the truncated pyramid was reduced to 1 mm and the
height to 0.82 mm.
[0054] The obtained manufactured article was used in the optical
field as microlens matrix. Accordingly, an object was put under the
ground containing the truncated pyramid square bases, 15 mm for
therefrom. The imagine was collected and focused by a lens having
the optical axis perpendicular to the base ground on the structure
side, sited to see the structure even if in the opposite side with
respect to the object: therefore, vertically above the truncated
pyramids.
[0055] The results are photographically illustrated in the FIG. 3,
showing the object, constituted by a triangular mark with the
number 02, faithfully reproduced through multiple imagines, each
one produced from a different lens of the circular matrix, i.e.
from a truncated pyramid of the molded structure.
[0056] As a control, the FIG. 4 shows, under the same optical
conditions, the same pyramidal structure, the object having been
removed: clearly, there is no multiple imagine of the object.
[0057] The manufactured article, prepared according to this example
was used, in the same example, as optical device so called "fly
eye", i.e. as the multichannel lens of an optical system able to
show an object at 360 degree latitude above a determined horizon.
The comparison between the FIGS. 3 and 4 outlines that the result
was obtained.
* * * * *