ZAOPO, Antonio (Pirelli Labs S.p.A, Viale Sarca 222, Milano, I-20126, IT)
GERBELLA, Giorgio (Pirelli Labs S.p.A, Viale Sarca 222, Milano, I-20126, IT)
COLOMBO, Marco (Pirelli Labs S.p.A, Viale Sarca 222, Milano, I-20126, IT)
ZAOPO, Antonio (Pirelli Labs S.p.A, Viale Sarca 222, Milano, I-20126, IT)
GERBELLA, Giorgio (Pirelli Labs S.p.A, Viale Sarca 222, Milano, I-20126, IT)
| CLAIMS
1. Optical device comprising:
(a) a substrate;
(b) at least one core layer including a polymer material with nonlinear optical properties comprising at least one copolymer obtained by copolymerizing at least one monomer or oligomer having at least two polymerizable groups, said at least one monomer or oligomer being at least partially fluorinated, with at least one optically active cromophore having at least two polymerizable groups able to react with the polymerizable groups of said at least one monomer or oligomer.
2. Optical device according to claim 1, wherein said optical device is: an optical waveguide, an optical modulator, an electrooptical modulator, an optical switch, a frequency converter, an optical parametric oscillator, an optical parametric amplifier, or a data processor.
3. Optical device according to claim 2, wherein said optical device is an optical waveguide.
4. Optical device according to claim 2, wherein said optical device is an optical modulator.
5. Optical device according to claim 4, wherein said optical device is an electrooptical modulator.
6. Optical device according to any one of the preceding claims, wherein said polymer material with nonlinear optical properties has optical losses not higher than 1 dB/cm, measured at a wavelength of 1550 nm.
7. Optical device according to claim 6, wherein said polymer material with nonlinear optical properties has optical losses of from 0.2 dB/cm to 0.5 dB/cm, measured at a wavelength of 1550 nm.
8. Optical device according to any one of the preceding claims, wherein said at least one monomer or oligomer having at least two polymerizable groups is perfluorinated.
9. Optical device according to any one of the preceding claims, wherein said at least one optically active cromophore having at least two polymerizable groups is non- fluorinated or at least partially fluorinated.
10. Optical device according to claim 9, wherein said at least one optically active cromophore having at least two polymerizable groups is non-fluorinated.
11. Optical device according to any one of the preceding claims, wherein said at least one optically active cromophore having at least two polymerizable groups comprises at least two aromatic rings, said aromatic rings being linked by a divalent bridging groups.
12. Optical device according to claim 11, wherein said at least two polymerizable groups of said at least one optically active cromophore are positioned on different aromatic rings.
13. Optical device according to any one of the preceding claims, wherein said substrate (a) is selected from: glass, quartz, aluminum, phosphorous doped oxide on silicon wafers, thermal oxide coated silicon wafers, conductive indium-tin oxide-coated glass, or mixture thereof.
14. Optical device according to any one of the preceding claims, wherein said at least one monomer or oligomer having at least two polymerizable groups is selected from compounds having the following general formula (I):
A-R-R f -R'-A' (I)
wherein:
- R and R', which may be equal or different from each other, are divalent bridging groups which are selected from: alkenyl, arenyl, ester, ether, amide, or urethane groups;
A and A', which may be equal or different from each other, are polymerizable groups, which are selected from:
CH 2 =C(X)COO-;
CH 2 =C(X)COO-(CH 2 ) q -OOC-;
CH 2 =CHO-;
YLC-CH •
^ \ / O H 7 C-CH-CH 7 O λ / O
O=C=N-;
HO-;
wherein X is a hydrogen atom, a fluorine or a chlorine atom, or a methyl group and q is an integer of from 1 to 4, extremes included;
R f is a divalent perfluorinated group which is selected from:
-(CF 2 ) X -; -CF 2 O-[(CF 2 CF 2 O) m (CF 2 O) n ]-CF 2 -;
-CF(CF 3 )O(CF 2 ) 4 O[CF(CF3)CF 2 O] P CF(CF 3 )-;
wherein:
x is an integer of from 1 to 20, extremes included;
m, n, and p, which may be equal or different from each other, are 0 or integers of from 1 to 20, extremes included.
15. Optical device according to claim 14, wherein said compounds having general formula (I) are selected from perfluorinated diacrylates having the following formulae:
wherein:
X is a hydrogen atom, or a methyl group;
x and m, which may be equal or different from each other, are integers of from 2 to 8, extremes included;
y is O, 1, or 2;
or mixtures thereof.
16. Optical device according to any one of the preceding claims, wherein said at least one optically active chromophore having at least two polymerizable groups is selected from compounds having the following general formula (II):
M-[CR]-M' (II)
wherein:
M and M', which may be equal or different from each other, are polymerizable groups, which are selected from:
CH 2 =C(X)COO-;
CH 2 =C(X)COO-(CH 2 ) q -OOC-;
CH 2 =CHO-;
H 9 C-CH-
\ / O
HX-CH — CH 9 O
2 \ / O
O=C=N-;
HO-; wherein X is a hydrogen atom, a fluorine or a chlorine atom, or a methyl group and q is an integer of from 1 to 4, extremes included;
CR is a chromophore divalent group deriving from a chromophore of the following formulae (III) or (IV):
wherein:
D is an electron-donating group which is selected from: -NH 2 ; -N(CHa) 2 ; -N(CH 2 CH 3 ) 2 ; or -N(CH 2 CH 3 )(Y) wherein Y is selected from alkyl alcohols such as -(CH 2 ) q OH wherein q' is an integer of from 1 to 4, extremes included, optionally fluorinated alkyl esters, or alkyl silane derivatives;
Q is a divalent bridging group which is selected from: -N=N-; -CH=CH-; -CH=N-; -N=CH-;
A is an electron-accepting group which is selected from: -NO 2 ; -C(CN)C(CN) 2 ; -N=C(R 1 )(R 2 ), wherein R 1 and R 2 , which may be equal or different from each other, are a hydrogen atom, a methyl group, or a C n F 2n+ ] group wherein n is an integer of from 1 to 20;
Xi, X 2 , X 3 , X 4 , which may be equal or different from each other, are a hydrogen atom, or a fluorine atom;
Ai and A 2 which may be equal or different from each other, are electron-accepting groups which are selected from: -NO 2 ; -C(CN)C(CN) 2 ; -CN; -CF 3 ; or -N=C(Ri)(R 2 ), wherein R 1 and R 2 , which may be equal or different from each other, are a hydrogen atom, a methyl group, or a C n F 2n+I group wherein n is an integer of from 1 to 20.
17. Optical device according to claim 16, wherein said at least one optically active chromophore having at least two polymerizable groups is selected from compounds having having general formula (II) wherein:
M is CH 2 =C(X)COO- wherein X is a hydrogen atom or a methyl group;
M' is CH 2 =C(X)COO-(CH 2 ) q -OOC- wherein X is a hydrogen atom or a methyl group and q is 2;
CR is a chromophore divalent group deriving from a chromophore of the following formulae (III):
wherein:
D is -N(CH 2 CH 3 )(CH 2 ) q -OH wherein q' is 2;
Q is -N=N-;
A is -NO 2 ;
Xi, X 2 , X 3 , X 4 , are hydrogen atoms.
18. Optical device according to any one of claim 16 or 17, wherein
said polymerizable group M is linked to the aromatic ring of the chromophore divalent group containing the electron-donating group D, preferably through said electron-donating group D;
said M' polymerizable group is linked to the aromatic ring of the chromophore divalent group containing the electron-acceptor group A, in a meta or ortho position with respect to said electron-acceptor group A.
19. Optical device according to claim 18, wherein said polymerizable group M is linked to the aromatic ring of the chromophore divalent group containing the electron-donating group D through said electron-donating group D.
20. Process for manufacturing an optical device comprising the following steps:
(i) making a polymerizable composition blending at least one monomer or oligomer having at least two polymerizable groups, said at least one monomer or oligomer being at least partially fluorinated, with at least one optically active chromophore having at least two polymerizable groups able to react with the polymerizable groups of said at least one monomer or oligomer;
(ii) coating a substrate with the polymerizable composition obtained in step (i);
(iii) subjecting the coated substrate of step (ii) to poling by applying an electric field;
(iv) copolymerizing the polymerizable composition applied to said substrate while maintaining the electric field.
21. Process for manufacturing an optical device according to claim 20, wherein said at least one monomer or oligomer having at least two polymerizable groups is present in the polymerizable composition in an amount of from 50% by weight to 99% by weight with respect to the total weight of the polymerizable composition.
22. Process for manufacturing an optical device according to claim 21, wherein said at least one monomer or oligomer having at least two polymerizable groups is present in the polymerizable composition in an amount of from 70% by weight to 98% by weight with respect to the total weight of the polymerizable composition.
23. Process for manufacturing an optical device according to any one of claims 20 to 22, wherein said at least one optically active chromophore having at least two polymerizable groups is present in the polymerizable composition in an amount of from 0.5% by weight to 25% by weight with respect to the total weight of the polymerizable composition.
24. Process for manufacturing an optical device according to claim 23, wherein said at least one optically active chromophore having at least two polymerizable groups is present in the polymerizable composition in an amount of from 1% by weight to 15% by weight, with respect to the total weight of the polymerizable composition.
25. Process for manufacturing an optical device according to any one of claims 20 to 24, wherein said polymerizable composition comprises at least one phothoinitiator.
26. Process for manufacturing an optical device according to claim 25, wherein said at least one phothoinitiator is selected from: acylphosphinoxides, benzophenones, benzilketales, dialkoxyacetophenones, hydroxyalkylacetophenones, aminoalkylphenones, thioxanthones, or mixtures thereof.
27. Process for manufacturing an optical device according to claim 25 or 26, wherein said at least one photoinitaitor is present in the polymerizable composition in an amount of from 0.2% by weight to 5% by weight with respect to the total weight of the polymerizable composition.
28. Process for manufacturing an optical device according to claim 27, wherein said at least one photoinitaitor is present in the polymerizable composition in an amount of from 0.5% by weight to 2% by weight with respect to the total weight of the polymerizable composition.
29. Process for manufacturing an optical device according to any one of claims 20 to 28, wherein said polymerizable composition comprises at least one multifunctional monomer or oligomer having at least three polymerizable groups.
30. Process for manufacturing an optical device according to claim 29, wherein said at least three polymerizable groups are selected from:
CH 2 =C(X)COO-;
CH 2 =C(X)COO-(CH 2 ) q -OOC-;
CH 2 =CHO-;
H 7 C-CH •
λ / o
ELC-CH — CH,0 O
O=C=N-; HO-;
wherein X represents an hydrogen atom, a fluorine or a chlorine atom; a methyl group.
31. Process for manufacturing an optical device according to claim 29 or 30, wherein said at least one multifunctional monomer or oligomer having at least three polymerizable groups is selected from compounds having the following formulae:
O CH 1 O — C-CH=CH,
H 2 C=CH — C — O— CH 2 - C — CH 2 OH
CH 2 O — C CH=CH 2 ;
O
or mixtures thereof.
32. Process for manufacturing an optical device according to any one of claims 29 to 31 , wherein said at least one multifunctional monomer or oligomer having at least three polymerizable groups is present in the polymerizable composition in an amount of from 0% by weight to 30% by weight with respect to the total weight of the polymerizable composition.
33. Process for manufacturing an optical device according to claim 32, wherein said at least one multifunctional monomer or oligomer having at least three polymerizable groups is present in the polymerizable composition in an amount of from 2% by weight to 20% by weight with respect to the total weight of the polymerizable composition.
34. Process for manufacturing an optical device according to any one of claims 20 to 33, wherein said coating step (ii) is carried out by spin-coating.
35. Process for manufacturing an optical device according to any one of claims 20 to 34, wherein said poling step (iii) is carried out via electrodes or by a corona field.
36. Process for manufacturing an optical device according to claim 35, wherein said poling step (iii) is carried out a corona field.
37. Process for manufacturing an optical device according to any one of claims 20 to
36, wherein said poling step (iii) is carried out at room temperature (23 °C).
38. Process for manufacturing an optical device according to any one of claims 20 to
37, wherein said copolymerization step (iv) is carried out by means of actinic radiation, such as UV radiation, infrared radiation, electron beam, ion or neutron beam, X-ray radiation.
39. Process for manufacturing an optical device according to claim 38, wherein said copolymerization step (iv) is carried out by means of UV radiation.
40. Polymer material with nonlinear optical properties comprising at least one copolymer obtained by copolymerizing at least one monomer or oligomer having at least two polymerizable groups, said at least one monomer or oligomer being at least partially fluorinated, with at least one optically active cromophore having at least two polymerizable groups able to react with the polymerizable groups of said at least one monomer or oligomer.
41. Polymer material with nonlinear optical properties according to claim 40, wherein said polymer material has optical losses not higher than 1 dB/cm, measured at a wavelength of 1550 nm.
42. Polymer material with nonlinear optical properties according to claim 41, wherein said polymer material has optical losses of from 0.2 dB/cm to 0.5 dB/cm, measured at a wavelength of 1550 nm.
43. Polymer material with nonlinear optical properties according to any one of claims 40 to 42, wherein said at least one monomer or oligomer having at least two polymerizable groups is perfluorinated.
44. Polymer material with nonlinear optical properties according to any one of claims 40 to 43, wherein said at least one optically active cromophore having at least two polymerizable groups is non-fluorinated or at least partially fluorinated.
45. Polymer material with nonlinear optical properties according to claim 44, wherein said at least one optically active cromophore having at least two polymerizable groups is non-fluorinated.
46. Polymer material with nonlinear optical properties according to any one of claims 40 to 45, wherein said at least one optically active cromophore having at least two polymerizable groups comprises at least two aromatic rings, said aromatic rings being linked by a divalent bridging groups.
47. Polymer material with nonlinear optical properties according to claim 46, wherein said at least two polymerizable groups of said at least one optically active cromophore are positioned on different aromatic rings.
48. Polymerizable composition comprising:
at least one monomer or oligomer having at least two polymerizable groups, said at least one monomer or oligomer being at least partially fluorinated;
at least one optically active cromophore having at least two polymerizable groups able to react with the polymerizable groups of said at least one monomer or oligomer.
49. Polymerizable composition according to claim 48, wherein said at least one monomer or oligomer having at least two polymerizable groups is perfluorinated.
50. Polymerizable composition according to claim 48 or 49, wherein said at least one optically active cromophore having at least two polymerizable groups is non- fluorinated or at least partially fluorinated.
51. Polymerizable composition according to claim 50, wherein said at least one optically active cromophore having at least two polymerizable groups is non- fluorinated.
52. Polymerizable composition according any one of claims 48 to 51, wherein said at least one optically active cromophore having at least two polymerizable groups comprises at least two aromatic rings, said aromatic rings being linked by a divalent bridging groups.
53. Polymerizable composition according to claim 52, wherein said at least two polymerizable groups of said at least one optically active cromophore are positioned on different aromatic rings.
54. Polymerizable composition according to any one of claims 48 to 53, wherein said at least one monomer or oligomer having at least two polymerizable groups is present in the polymerizable composition in an amount of from 50% by weight to 99% by weight with respect to the total weight of the polymerizable composition.
55. Polymerizable composition according to claim 54, wherein said at least one monomer or oligomer having at least two polymerizable groups is present in the polymerizable composition in an amount of from 70% by weight to 98% by weight with respect to the total weight of the polymerizable composition.
56. Polymerizable composition according to any one of claims 48 to 55, wherein said at least one optically active chromophore having at least two polymerizable groups is present in the polymerizable composition in an amount of from 0.5% by weight to 25% by weight with respect to the total weight of the polymerizable composition.
57. Polymerizable composition according to claim 56, wherein said at least one optically active chromophore having at least two polymerizable groups is present in the polymerizable composition in an amount of from 1% by weight to 15% by weight with respect to the total weight of the polymerizable composition.
58. Polymerizable composition according to any one of claims 48 to 57, wherein said said polymerizable composition comprises at least one phothoinitiator as defined according to any one of claims 26 to 28.
59. Polymerizable composition according to any one of claims 48 to 58, wherein said polymerizable composition comprises at least one multifunctional monomer or oligomer having at least three polymerizable groups as defined according to any one of claims 29 to 33. |
Title: Optical device and polymer material with nonlinear optical properties
Applicant: PIRELLI & C. S.p.A.
DESCRIPTION
Background of the invention
The present invention relates to an optical device and to a polymer material with nonlinear optical properties.
More in particular, the present invention relates to an optical device including a polymer material with nonlinear optical properties comprising at least one copolymer obtained by copolymerizing at least one monomer or oligomer having at least two polymerizable groups, said at least one monomer or oligomer being at least partially fluorinated, with at least one optically active cromophore having at least two polymerizable groups able to react with the polymerizable groups of said at least one monomer or oligomer.
Furthermore, the present invention also relates to a polymer material with nonlinear optical properties comprising at least one copolymer obtained by copolymerizing at least one monomer or oligomer having at least two polymerizable groups, said at least one mononomer or oligomer being at least partially fluorinated, with at least one optically active cromophore having at least two polymerizable groups able to react with the polymerizable groups of said at least one monomer or oligomer.
Related art
A waveguide is any structure which allows the propagation of a wave through its length despite diffractive effects, and possible curvature of the guide structure. An optical waveguide device is an optical structure capable of guiding a beam of laser light along light channels in the waveguide, and is defined by an extended region of increased index of refraction relative to the surrounding medium. The optical waveguide device typically includes both the light channels in which light waves propagate in the waveguide, and surrounding cladding which confine the waves in the channel. The strength of the guiding, or the confinement, of the wave depends on the wavelength, the index difference, and the guide width.
Polymer materials with nonlinear optical properties (also known as NLO polymer materials), in particular second order NLO properties (such as, e.g. the Pockels effect), are usually formed by a"guest-host system", i.e., by a polymer matrix in which are
dispersed organic molecules (such as, optically active chromophores). Said organic molecules have the typical D-π-A structure, where D and A are electron-donating and electron-accepting groups, respectively, connected by a π-conjugated system.
Said NLO polymer materials are particularly useful in order to obtain optical devices such as, for example, electrooptical modulators. Modulators are one of the main elements of a telecomunication optical networks.
In order to give rise to high second order NLO properties, in particular to a high electrooptical coefficient, the NLO polymer material must be noncentrosymetric.
In order to obtain noncentrosymetric materials, a strong electric field is usually applied to the polymer material including, as already reported above, a polymer matrix and at least one optically active chromophore, working at a temperature close to the glass transition temperature (Tg) of the polymer matrix. This process, known as "poling" allows to orient the optically active chromophore along a preferred direction. Once the orientation has been completed, the polymer material is cooled, still in the presence of said electric field, in order to "freeze" the orientation of the optically active chromophore into the polymer matrix (i.e,. to allow a stable orientation of the optically active chromophore).
However, said process does not allow to achieve a high concentration of the optically active chromophore onto the polymer matrix and, above all, it does not provide a stable orientation of the optically active chromophore into the polymer matrix. Consequently, the nonlinear optical properties of the so obtained NLO polymer materials tend to decay over time so negatively affecting the optical performances of the optical devices including the same.
Efforts to enhance the orientation stability of the optically active chromophore onto the polymer matrix, have been already made.
For example, Bosc et al. in: "Journal of Applied Science" (1999), Vol. 74, pg. 974-982, discloses a process which comprises the steps of grafting at least one optically active chromophore onto a polymer backbone so obtaining a side-chain NLO polymer materials; subjecting to poling the obtaining side-chain NLO polymer materials, while heating it at the glass transition temperature (Tg) of the polymer, and subsequently cooling to freeze the optically active chromophore orientation, still in the presence of the electric field. The obtained NLO polymer materials are said to be able of maintaining good non-linear optical properties over time.
Although said process allows to obtain NLO polymer materials showing a good orientation stability of the optically active chromophore at room temperature, when the NLO polymer materials are subjected to high temperatures, said orientation immediately decreases. Since during the assembly of optical devices short excursion to high temperatures occurs often, the optical performances of the optical devices including said NLO polymer materials may be negatively affected.
Moreover, high temperatures may also damage the polymer matrix used. For this reason, the selection of the polymer matrix to be used for the NLO polymer materials is limited to those tolerating such high temperatures.
United States Patent US 6,610,219 discloses a functional optical material for use in an optical system comprising a polymer preferably selected from the group consisting of a thermoplastic polymer, a thermosetting polymer, and a combination of thermoplastic and thermosetting polymers, said themoplastic and/or thermosetting polymer containing carbon-hydrogen and/or carbon-fluoride functionality; one or more optically active chromophores blended and/or copolymerized with said polymer system; a compatibilizer copolymerized with said polymer system and an adhesion promoter copolymerized with said polymer system. Said compatibilizer is avoided in the case at least one of the optical active choromophores is fluorinated. The abovementioned functional optical material is said to have an improved thermal stability, an excellent water resistance and an excellent adhesion to silica surfaces, indium tin oxide coatings and gold electrodes. Moreover, it is said that the fluorine containing chromophore could be put into the polymer up to 30% or greater loading while still maintaining low refractive index for the total system.
According to the Applicant, the above disclosed NLO materials may show some disadvantages.
Applicant has noticed that, said NLO polymer materials, being side-chain NLO polymer materials (i.e, the optically active chromophore is grafted onto the polymer backbone through one functionalized end, the other end remaining free), are not able to maintain their nonlinear optical properties over time.
Moreover, the Applicant has noticed that, when the optically active chromophore is blended and/or copolymerized with an already formed polymer, a self-polymerization of the optically active chromophore may occur so causing a decrease on the amount of the grafted chromophore onto the polymer backbone: consequently, a decreasing in the nonlinear optical properties of the obtained NLO polymer material may occur. Furthermore, the Applicant has noticed that, the presence of a compatibilizer in said
- A -
NLO polymer material may interfere with the working wavelengths of the optical devices including the same.
Summary of the invention
The Applicant has faced the problem of providing an optical device having good nonlinear optical properties, in particular in term of electrooptical coefficient and low optical losses, and being able to maintain said good nonlinear optical properties over time.
The Applicant has now found that it is possible to obtain such an optical device by providing a polymer material with nonlinear optical properties (i.e., NLO polymer material) comprising at least one copolymer obtained by copolymerizing at least one monomer or oligomer having at least two polymerizable groups, said at least one monomer or oligomer being at least partially fluorinated, with at least one optically active cromophore having at least two polymerizable groups able to react with the polymerizable groups of said at least one monomer or oligomer. Said NLO polymer material shows good nonlinear optical properties. Moreover, as the optically active chromophore is part of the copolymer main chain (i.e., each end of the optically active chromophore is linked onto the copolymer main chain), said chromophore is able to maintain its orientation onto the copolymer over time: consequently, said NLO polymer material maintain its nonlinear optical properties over time. Furthermore, said NLO polymer material has a good electrooptical coefficient. Moreover, said NLO polymer material has low optical losses.
According to a first aspect, the present invention relates to an optical device comprising:
(a) a substrate;
(b) at least one core layer including a polymer material with nonlinear optical properties comprising at least one copolymer obtained by copolymerizing at least one monomer or oligomer having at least two polymerizable groups, said at least one monomer or oligomer being at least partially fluorinated, with at least one optically active cromophore having at least two polymerizable groups able to react with the polymerizable groups of said at least one monomer or oligomer.
Said optical device may be an optical waveguide, an optical modulator, an electrooptical modulator, an optical switch, a frequency converter, an optical parametric oscillator, an optical parametric amplifier, or a data processor.
According to one preferred embodiment, said optical device is an optical waveguide.
According to a further preferred embodiment, said optical device is an optical modulator, preferably, an electrooptical modulator.
According to a further aspect, the present invention also relates to a polymer material with nonlinear optical properties comprising at least one copolymer obtained by copolymerizing at least one monomer or oligomer having at least two polymerizable groups, said at least one monomer or oligomer being at least partially fluorinated, with at least one optically active cromophore having at least two polymerizable groups able to react with the polymerizable groups of said at least one monomer or oligomer.
According to one preferred embodiment, said polymer material with nonlinear optical properties has optical losses not higher than 1 dB/cm, preferably of from 0.2 dB/cm to 0.5 dB/cm, measured at a wavelength of 1550 run.
According to a further aspect, the present invention also relates to a polymerizable composition comprising:
at least one monomer or oligomer having at least two polymerizable groups, said at least one monomer or oligomer being at least partially fluorinated;
at least one optically active cromophore having at least two polymerizable groups able to react with the polymerizable groups of said at least one monomer or oligomer.
According to one preferred embodiment, said at least one monomer or oligomer having at least two polymerizable groups is perfluorinated.
According to one preferred embodiment, said at least one optically active cromophore having at least two polymerizable groups is non-fluorinated or at least partially fluorinated, more preferably non-fluorinated.
According to a further preferred embodiment, said at least one optically active cromophore having at least two polymerizable groups comprises at least two aromatic rings, said aromatic rings being linked by a divalent bridging groups.
According to a further preferred embodiment, said at least two polymerizable groups of said at least one optically active cromophore are positioned on different aromatic rings.
According to one preferred embodiment, said polymerizable composition may further comprise at least one photoinitaitor.
According to one preferred embodiment, said polymerizable composition may further
comprise at least one multifunctional monomer or oligomer having at least three polymerizable groups.
According to a further aspect, the present invention also relates to a process for manufacturing an optical device.
Detailed description of the preferred embodiments
According to one preferred embodiment, said substrate (a) may be selected for example, from: glass, quartz, aluminum, phosphorous doped oxide on silicon wafers, thermal oxide coated silicon wafers, conductive indium-tin oxide-coated glass, or mixture thereof.
According to one preferred embodiment, said at least one monomer or oligomer having at least two polymerizable groups may be selected, for example, from compounds having the following general formula (I):
A-R-R f -R'-A' (I)
wherein:
- R and R, which may be equal or different from each other, are divalent bridging groups which may be selected, for example, from: alkenyl, arenyl, ester, ether, amide, or urethane groups;
A and A', which may be equal or different from each other, are polymerizable groups, which may be selected, for example, from:
CH 2 =C(X)COO-;
CH 2 =C(X)COO-(CH 2 ) q -OOC-;
CH 2 =CHO-;
H 9 C-CH •
\ / O
HX- CH- CHX)
2 \ /
O
O=C=N-;
HO-;
wherein X is a hydrogen atom, a fluorine or a chlorine atom, or a methyl group and q is an integer of from 1 to 4, extremes included;
Rf is a divalent perfluorinated group which may be selected, for example, from:
-(CF 2 ) X -; -CF 2 O-[(CF 2 CF 2 O) m (CF 2 O) n ]-CF 2 -;
-CF(CF 3 )O(CF 2 ) 4 O[CF(CF3)CF 2 O]pCF(CF3)-;
wherein:
x is an integer of from 1 to 20, preferably of from 2 to 10, extremes included;
m, n, and p, which may be equal or different from each other, are 0 or integers of from 1 to 20, preferably of from 2 to 10, extremes included.
According to a further preferred embodiment, said compounds having general formula (I) may be selected, for example, from perfluorinated diacrylates having the following formulae:
wherein:
X is a hydrogen atom, or a methyl group;
x and m, which may be equal or different from each other, are integers of from 2 to 8, extremes included;
y is 0, 1, or 2;
or mixtures thereof.
Examples of monomer or oligomer having at least two polymerizable groups which may be used according to the present invention and are commercially available are the products Eguide™ ZPU, or Exguide™ WIR30, from ChemOptics.
According to one preferred embodiment, said at least one optically active chromophore having at least two polymerizable groups may be selected, for example, from compounds having the following general formula (II):
M-[CR]-M' (II)
wherein:
M and M', which may be equal or different from each other, are polymerizable groups, which may be selected, for example, from:
CH 2 =C(X)COO-;
CH 2 =C(X)COO-(CH 2 ) q -OOC-;
CH 2 =CHO-;
HX-CH •
2 \ / O
HX-CH — CH 7 O -
2 \ / ^ °
O=C=N-;
HO-;
wherein X is a hydrogen atom, a fluorine or a chlorine atom, or a methyl group and q is an integer of from 1 to 4, extremes included;
CR is a chromophore divalent group deriving from a chromophore of the following formulae (III) or (FV):
wherein:
D is an electron-donating group which may be selected, for example, from: -NH 2 ; -N(CH 3 ) 2 ; -N(CH 2 CH 3 ) 2 ; -N(Y) 2 or -N(CH 2 CH 3 )(Y) wherein Y may be selected, for example, from alkyl alcohols such as, for example, -(CH 2 ) q OH wherein q' is an integer of from 1 to 4, extremes included, optionally fluorinated alkyl esters, or alkyl silane derivatives;
Q is a divalent bridging group which may be selected, for example, from: -N=N-; -CH=CH-; -CH=N-; or -N=CH-;
A is an electron-accepting group which may be selected, for example, from: -NO 2 ; -C(CN)C(CN) 2 ; or -N=C(Ri)(R 2 ), wherein R 1 and R 2 , which may be equal or different from each other, are a hydrogen atom, a methyl group, or a C n F 2n+! group wherein n is an integer of from 1 to 20, extremes included;
X 1 , X 2 , X 3 , X 4 , which may be equal or different from each other, are a hydrogen atom, or a fluorine atom;
Ai and A 2 which may be equal or different from each other, are electron-accepting groups which may be selected, for example, from: -NO 2 ; -C(CN)C(CN) 2 ; -CN; -CF 3 ; or -N=C(Rj)(R 2 ), wherein Ri and R 2 , which may be equal or different from each other, are a hydrogen atom, a methyl group, or a C n F 2n+I group wherein n is
an integer of from 1 to 20, extremes included.
According to a further preferred embodiment, said at least one optically active chromophore having at least two polymerizable groups may be selected, for example, from compounds having having general formula (II) wherein:
M is CH 2 =C(X)COO- wherein X is a hydrogen atom or a methyl group;
M' is CH 2 =C(X)COO-(CH 2 ) q -OOC- wherein X is a hydrogen atom or a methyl group and q is 2;
CR is a chromophore divalent group deriving from a chromophore of the following formulae (III):
wherein:
D is -N(CH 2 CH 3 )(CH 2 VOH wherein q' is 2;
Q is -N=N-;
A is -NO 2 ;
X 1 , X 2 , X 3 , X 4 , are hydrogen atoms.
According to a further preferred embodiment:
said polymerizable group M is linked to the aromatic ring of the chromophore divalent group containing the electron-donating group D, preferably through said electron-donating group D;
said M' polymerizable group is linked to the aromatic ring of the chromophore divalent group containing the electron-acceptor group A, in a meta or ortho position with respect to said electron-acceptor group A.
Said optically active chromophore having at least two polymerizable groups may be obtained by functionalizing an optically active cromophore having general formulae
(III) or (FV) with at least two polymerizable groups (i.e. M and M'), according to processes known in the art such as disclosed, for example, by Bosc et al. in: "Journal of Applied Science" (1999), Vol. 74, pg. 974-982. Further details about the synthesis of said compounds having general formula (II) may be found in the examples which follow.
According to a further aspect, the present invention also relates to a process for manufacturing an optical device comprising the following steps:
(i) making a polymerizable composition blending at least one monomer or oligomer having at least two polymerizable groups, said at least one monomer or oligomer being at least partially fluorinated, with at least one optically active chromophore having at least two polymerizable groups able to react with the polymerizable groups of said at least one monomer or oligomer;
(ii) coating a substrate with the polymerizable composition obtained in step (i);
(iii) subjecting the coated substrate of step (ii) to poling by applying an electric field;
(iv) copolymerizing the polymerizable composition applied to said substrate while maintaining the electric field.
According to one preferred embodiment, said at least one monomer or oligomer having at least two polymerizable groups is present in the polymerizable composition in an amount of from 50% by weight to 99% by weight, preferably from 70% by weight to 98% by weight, with respect to the total weight of the polymerizable composition.
According to one preferred embodiment, said at least one optically active chromophore having at least two polymerizable groups is present in the polymerizable composition in an amount of from 0.5% by weight to 25% by weight, preferably from 1% by weight to 15% by weight, with respect to the total weight of the polymerizable composition.
As disclosed above, said polymerizable composition may further comprise at least one phothoinitiator.
According to one preferred embodiment, said at least one phothoinitiator may be selected, for example, from: acylphosphinoxides, benzophenones, benzilketales, dialkoxyacetophenones, hydroxyalkylacetophenones, aminoalkylphenones, thioxanthones, or mixtures thereof.
Specific examples of phothoinitiators which may be advantageously used according to
the present invention are: diphenyl(2,4,6-trimethylbenzoyl)phosphinoxide, diphenylacylphenylphosphinoxide, 2,4,6-trimethylbenzoylethoxyphenyl-phosphinoxide, benzophenone, methylbenzophenone, 4-phenylbenzophenone,
4,4'bis(dimethylamino)benzophenone, 4,4'-bis(diethylamino)benzophenone, 2,2- dimethoxy-2-phenylacetophenone, dimethoxyacetophenone, diethoxyacetophenone, 2- hydroxy-2-methyl- 1 -phenylpropan- 1 -one, 2-benzyl-2-dimethylamino- 1 -(4- morpholinophenyl)-butan-l-one, 2-methyl-l-[4(methoxythio)-phenyl]-2- morpholinopropan-2-one, 2-isopropylthioxantone, 4-isopropylthioxanthone, 2,4- dimethylthioxanthone; or mixtures thereof. Diphenyl(2,4,6- trimethylbenzoyl)phosphinoxide is particularly preferred.
Examples of photoinitiators which may be used according to the present invention and are commercially available are the products Irgacure ® 819, Darocur ® TPO from Ciba Speciality Chemicals.
According to one preferred embodiment, said at least one photoinitaitor is present in the polymerizable composition in an amount of from 0.2% by weight to 5% by weight, preferably from 0.5% by weight to 2% by weight, with respect to the total weight of the polymerizable composition.
As disclosed above, said polymerizable composition may further comprise at least one multifunctional monomer or oligomer having at least three polymerizable groups. Preferably, said polymerizable groups may be selected, for example, from:
CH 2 =C(X)COO-;
CH 2 =C(X)COO-(CH 2 ) q -OOC-;
CH 2 =CHO-;
HX-CH •
\ / O
HX-CH — CH 7 O •
2 \ / 2 °
O=C=N-;
HO-;
wherein X represents an hydrogen atom, a fluorine or a chlorine atom; a methyl group
and q is an integer of from 1 to 4, extremes included.
According to one preferred embodiment, said at least one multifunctional monomer or oligomer having at least three polymerizable groups, may be selected, for example, from compounds having the following formulae:
O O CH 2 O -C-CH=CH 2
H 2 C=CH — C — 0-CH 2 C — CH 2 CH 3
CH 2 O — C CH=CH 2
O
O
O CH 2 O -C-CH=CH 2
H 2 C-CH — C — C-CH 2 - C — CH 2 OH
CH 2 O — C CH=CH 2
O
or mixtures thereof.
According to one preferred embodiment, said at least one multifunctional monomer or oligomer having at least three polymerizable groups is present in the polymerizable composition in an amount of from 0% by weight to 30% by weight, preferably from 2% by weight to 20% by weight, with respect to the total weight of the polymerizable
composition.
According to one preferred embodiment, said coating step (ii) is carried out by spin- coating.
According to one preferred embodiment, said poling step (iii) is carried out via electrodes, or by a corona field. Corona field is particularly preferred.
According to one preferred embodiment, said poling step (iii) is carried out at room temperature (23°C).
According to one preferred embodiment, said copolymerization step (iv) is carried out by means of actinic radiation, such as, for example, UV radiation, infrared radiation, electron beam, ion or neutron beam, X-ray radiation. UV radiation is particularly preferred.
More in particular, for example, the optical device according to the present invention, may be prepared as follows.
Once the optically active chromophore having at least two polymerizable groups was synthesized, a polymerizable composition comprising at least one of said chromophore, at least one monomer or oligomer having at least two polymerizable groups, at least one photoinitiator and, optionally, at least one multifunctional monomer or oligomer having at least three functional groups, was prepared, by blending all said components, at room temperature (23 °C). The resulting polymerizable composition was stirred overnight, at room temperature (23 °C), and subsequently laid down by spin-coating (2000 rpm - 3000 rpm) onto indium-tin oxide (ITO) coated glass substrate to obtain a 4 μm - 5 μm thick film. Prior to use, the substrate was cleaned, preferably in a dust free atmosphere, with a solvent solution such as, for example, an isopropylic alcohol solution, and subsequently rinsed twice with distilled water. The cleaned substrate may be optionally treated with an adhesion promoter (such as, for example, ZAP 1020 from ChemOptics, said adhesion promoter being laid down by spin-coating (2000 rpm — 3000 rpm) onto indium-tin oxide (ITO) coated glass substrate which was subsequently baked on a hotplate, at 110°C, for 3 min - 4 min.
The orientation of the optically active chromophore was induced by poling applying a corona field and copolymerization was simultaneously accomplished by UV irradiation. Poling apparatus was contained in a sealed transparent vessel in which nitrogen was fluxed until humidity was below 20%. Typical voltages of from +5 kV to + 7 kV were applied to a 20 μm diameter gold wire electrode for 10 min - 30 min, placed
horizontally, at a distance of 1 cm above the film. UV curing was accomplished irradiating the sample through a lateral quartz window with a mercury (Xenon) lamp (LOT-Oriel model 66142, power: 500W) for 5 min - 10 min. UV light was focused on the film by means of a 45° oriented mirror.
The present invention will now be illustrated in further detail by means of the attached Fig. 1 which shows a guided wave electrooptical modulator employing a polymer material having nonlinear optiacl properties according to the present invention.
In particular, in Fig. 1, a film 50 of the polymer material according to the present invention is formed on a conductive substrate 51 having an insulative coating 52. The film 50 has a Mach-Zehnder two-arm interferometric waveguide structure. A top electrode 53 is placed on one arm 54 of the interferometer. The substrate is kept at ground potential. As voltage is applied to and removed from across the arm 54 by means of top electrode 53 and conducting substrate 51, an electric field is produced in the arm 54 of the interferometer. This field changes the index of refraction of the material due to the linear electrooptical effect possessed by the film 50. This results in an effective change in optical path length in arm 54 of the interferometer relative to the other arm which, in turn, produces either constructive or destructive interference of the light at the recombination point 55. As the voltage is modulated so as to alternate between constructive and destructive conditions, the output intensity exhibits a maximum and minimum value, respectively.
Further characteristics and advantages of the invention will be more apparent from the following examples which are given for purely indicative purposes and without any limitation of the present invention.
In the scope of the present description and in the following claims, all the numerical measurements indicating quantity, parameters, percentages, etc, are to be considered as preceded by the term "about" unless specified otherwise. Moreover, all the intervals of numerical measurement include all possible combinations of maximum and minimum numerical value, as well as all the possible intermediate intervals, other than those specifically indicated in the text.
Example 1
Synthesis of the dimethacrylate optically active chromophore
The synthesis of the dimethacrylate chromophore was carried out as follows.
(a) Synthesis of 2-fN-ethyl, N-phenyl)aminoethylmethacrylate having the following
formula:
2.509 g (24 mmol) of methacryloyl chloride (Aldrich), dissolved in 5 ml of dry methylene chloride, were added dropwise to a 30 ml solution of dry methylene chloride containing 3.305 g (20 mmol) of 2-(N-ethylanilino)ethanol (Aldrich) and 2.024 g (24 mmol) of triethylamine. 5 mg of hydroquinone were subsequently added as radical protective agent of methacrylic groups. The solution was maintained, at reflux temperature, for 12 hours, subsequently cooled and washed with water until a solution having pH = 7 was obtained. The obtained organic phase was recovered, subsequently dried over sodium sulfate, and the solvent was removed by rotary evaporation to obtain a pale violet oil (yield: 78%).
(b) Synthesis of 4'-[N-(2-methacryloxyethyl)-N-ethyl]amino-4-nitro-2-carboxy- azobenzene having the following formula:
0.227 g (5.68 mmol) of sodium hydroxide, dissolved in 15 ml of deionized water, was added to 1.034 g (5.68 mmol) of 2-amino-5-nitrobenzoic acid and the mixture was heated at 60°C to dissolve the acid. 2.238 g (22.72 mmol) of hydrochloric acid at 37%, dissolved in 30 ml of water, was then added dropwise and the solution was cooled to 0°C. Subsequently, 0.392 g (5.68 mmol) of sodium nitrite, dissolved in 20 ml of water, was slowly added and the mixture was maintained, at O 0 C, for 2 hours. Then, 1.325 g (5.68 mmol) of 2-(N-ethyl-N-phenyl)aminoethylmethacrylate was added, the mixture was heated at room temperature (23 °C), and was stirred overnight. The resulting precipitate was collected by filtration and washed with water at 40°C, then it is purified via chromatography on silica gel (eluent: methylene chloride/diethyl ether 7/3 v/v). A solid product was obtained (yield: 20%).
(c) Synthesis of dimethacrylate optically active chromophore having the following formula:
1.17 g (2.75 mmol) of 4'-[N-(2-methacryloxyethyl)-N-ethyl]amino-4-nitro-2- carboxyazobenzene and 0.43 g (3.3 mmol) of hydroxyethylmethacrylate (Aldrich) were dissolved in 100 ml of dry acetone. Subsequently, 0.681 g (3.3 mmol) of dicyclohexylcarbodiimide (Aldrich), dissolved in 10 ml of dry acetone, were added and the solution was maintained 24 hours, under stirring, at room temperature (23 °C). The urea formed as by-product during the reaction, was collected by filtration, the solvent was removed by rotary evaporation, and the resulting product was purified via chromatography on silica gel (eluent: diethyl ether/hexane 7/3 v/v). A dark red solid product was obtained (yield: 90%).
The obtained solid product has the following melting point (determined by a capillary melting point apparatus): 89°C - 91 °C.
The obtained solid product was also subjected to proton nuclear magnetic resonance ( 1 HNMR) analysis which was carried out on Bruker 500 MHz instruments. The resulting chemical shifts are the following:
1 H NMR - 500 MHz (δ in CDCl 3 ): 1.27 (t 3H, a); 1.90 (s 3H, e'); 1.94 (s 3H, e); 3.55 (q 2H, b); 3.74 (t 2H, c); 4.38 (t 2H, d); 4.43 (t 2H, c'); 4.62 (t 2H, d'); 5.54 and 5.60 (s IH IH, f f ); 6.09 and 6.11 (s IH IH, f f ); 6.80 (d 2H, h); 7.75 (d IH, j); 7.86 (d 2H, i); 8.37 (d IH, k); 8.64 (s IH, 1).
Example 2 (comparative)
A 5 μm thick film was prepared by spin-coating (3000 rpm) onto a indium-tin oxide (ITO) coated glass substrate a polymerizable composition comprising:
- 2% by weight of Disperse Red 1 (Aldrich);
97.5% of 1 ,6-hexanedioldiacrylate (Aldrich);
0.5% of photoinitiator (Irgacure ® 819 - (Ciba Specialty Chemicals).
Prior to use, the abovementioned substrate was cleaned, in a dust free atmosphere, with an isopropyl alcohol solution and subsequently rinsed twice with distilled water. The cleaned substrate, was subsequently treated with an adhesion promoter (ZAP 1020 from ChemOptics), said adhesion promoter being laid down onto the cleaned substrate by spin-coating (3000 rpm) and baked on a hotplate, at 110°C, for 3 min.
The film was then subjected to poling and UV radiation operating as follows.
A poling apparatus was contained in a sealed transparent vessel in which nitrogen was fluxed until humidity was below 20%. A voltage of +5 kV was applied to a 20 μm diameter gold wire electrode for 10 min which placed horizontally 1 cm above the film. UV radiation was carried out by irradiating the film through a lateral quartz window with a mercury (Xenon) lamp (LOT-Oriel model 66142, power: 500W) for 5 min. UV light was focused on the film by means of a 45° oriented mirror.
The obtained film was subjected to the following characterizations to determine its nonlinear optical properties and its optical losses.
The nonlinear optical properties were measured by means of second harmonic generation (SHG coefficient) which was carried out using a Quantel Brilliant Q- switched Nd: YAG laser (frequency up to 10 Hz, 5 ns pulse duration, 400 mJ per pulse), which provides the fundamental beam output at 1064 nm. The SHG coefficient was determined by the Maker fringe technique. Intensity of the SHG signal was recorded as a function of the incident angle of the fundamental beam. SHG signal was monitored by Hamamatsu 1P28 photomultiplier tube. Absolute values of d 33 were calculated calibrating the system with a quartz crystal as a reference material.
The optical losses measurement was performed on the obtained film by using a Metricon 2010 Prism Coupler (Metricon Corporation, US).
The obtained results are the following:
SHG signal decrease and was lower than 10% with respect to the initial value of 0.7 pm/V, after 24 hours, at room temperature (23 °C);
the optical losses were higher than 2.5 dB/cm, at a wavelength of 1550 nm.
Example 3 (comparative)
Operating as disclosed in Example 2, a 5 μm thick film was prepared by spin-coating
onto a indium-tin oxide (ITO) coated glass substrate a polymerizable composition comprising:
97.5% of a blend of perfluorinated diacrylates and triacrylates monomers and oligomers (Exguide™ ZPU 450 - ChemOptic);
- 2% of Disperse Red 1 (Aldrich);
0.5% of Irgacure ® 819 (Ciba Specialty Chemicals).
The obtained film was subjected to the following characterizations to determine its nonlinear optical properties and its optical losses operating as disclosed in Example 2.
The obtained results are the following:
- SHG signal decrease and was lower than 15% with respect to the initial value of 0.8 pm/V, after 24 hours, at room temperature (23°C);
the optical losses was lower than 0.2 dB/cm, at a wavelength of 1550 nm.
Example 4 (invention)
Operating as disclosed in Example 2, a 5 μm thick film was prepared by spin-coating onto a indium-tin oxide (ITO) coated glass substrate a polymerizable composition comprising:
94.5% of a blend of perfluorinated diacrylates and triacrylates monomers and oligomers (Exguide™ ZPU 450 - ChemOptic);
5% of dimethacrylate optically active chromophore obtained in Example 1;
- 0.5% of Irgacure ® 819 (Ciba Specialty Chemicals).
The obtained film was subjected to the following characterizations to determine its nonlinear optical properties and its optical losses operating as disclosed in Example 2.
The obtained results are the following:
SHG signal was equal to 2 pm/V, said SHG signal did not decrease and was maintained both after 24 hours at room temperature and after aging test (i.e., the film was stored, in air, at 80 0 C, for 1500 hours);
the optical losses was lower than 0.3 dB/cm, at a wavelength of 1550 nm.
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