Waveguide systems or structures or parts thereof, containing...

Details Waveguide systems or structures or parts thereof, containing... Waveguide systems or structures or parts thereof, containing...

2002-05-06

2004-04-06

Gorr, Rachel (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Nitrogen-containing reactant

C385S123000

Reexamination Certificate

active

06716958

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to optical elements in the field of waveguide systems or waveguide structures, e.g. arrayed wave guide components, prepared by copolymerization of specific polyfunctional cyanates and fluorinated monocyanates, as well as to the use of said copolymers for the preparation of said structures.
Organic polymers are increasingly interesting materials in the optical or microoptical field, in integrated optics or in microsystem techniques. In these fields, they may be used in optical instruments and apparatuses or parts thereof as well as in special optics as lenses, prisms, for fixation of optical systems, as support material for optical layers and as translucent coating materials for mirrors or lenses. Organic polymers may be used in optical fibres and for the preparation of waveguide structures. Their technical handling is relatively easy, and their density is lower in comparison to glass.
Specifically, if such plastics or organic polymers are to be used as a waveguide, a variety of requirements are to be met. The refractive index of the material should be variable in a range as broad as possible and should be adaptable to that of specific substrates. If used in the optical communication engineering, low absorptions of the materials are required at 1.3 and 1.55 &mgr;m. The loss due to attenuation caused by volume defects (non-homogenities, microbubbles, microfissures) should be minimized. Besides specific technological requirements, e.g. preparation of layers and structurability, specific provisions for the use of organic polymers as waveguide structures in integrated optics are the thermal and thermo-mechanical stability, adapted extension coefficients and long term stability of optical properties.
2. Description of the Related Art
Until now, polymethacrylates and polycarbonates have been mainly used for optical purposes. Both classes of polymers have an excellent light transmittance, but their thermal and thermo-mechanical stability is not sufficient due to their chemical structure. Thus, polymethacrylates and polycarbonates cannot practically be used at temperatures exceeding 130° C. which is due to their relatively low glass transition temperatures. In addition, both types of polymers are linear, un-crosslinked polymers. This has the adverse effect that they are partly solubilized in case multilayer-systems are prepared via the application of dissolved components, e.g. by spin-coating each layer. Consequently, the layer structures as obtained are not sufficiently delimitated and neat which, however, is an essential for the preparation of waveguide structures.
There are other high performance polymers which have glass transition temperatures of more than 180° C. Examples are polyarylethersulfones, polyarylsulfones, polyaryletherketones, polyimides and polyetherimides, the processing of which, however, is more difficult than that of polymethacrylates and polycarbonates. Another disadvantage of these systems is the relatively high optical loss at wave lengths of 1.3 and 1.55 &mgr;m, relevant in communication engineering.
Polyperfluorocyclobutanes (PFCB) are a relatively new class of high performance polymers. Upon thermal curing they yield unsoluble cross-linked polymers which are characterized by high thermal stability. Waveguide layers prepared from PFCB show very low optical losses of 0.2 dB/cm at 1550 nm.
Also, polycyanurates have been used for the preparation of optical components. U.S. Pat. Nos. 5,208,892 and 5,165,959 describe the preparation of polycyanate resins made of a single monomer (either fluorinated or non-fluorinated). German Offenlegungsschrift DE 44 35 992 A1 describes optical elements prepared from polycyanurate resins. The resins are made by polymerization of dicyanate or polycyanate compounds, optionally in mixture with di- or polyphenols or di- or polyglycidyl compounds. Like polyperfluorocyclobutanes, polycyanurates yield unsoluble cross-linked polymers upon thermal curing, and these polymers are as well characterized by high thermal stability. They are specifically useful due to their excellent adhesional force on a variety of substrates, for example silicon, silica or a variety of organic polymers. Refractive index and glass transition temperature of the cured cross-linked polymers may be varied in broad ranges, due to the easy availability of a great number of di- and mono-functional cyanate monomers which may be copolymerized with each other. Polycyanurates of the kind mentioned above are partly commercially available. Completely cured polycyanurates known in the art which consequently are stable for long terms may have optical losses of about 0.2 dB/cm at 1.3 &mgr;m. However, the optical losses are not less than 0.5dB/cm at 1.55 &mgr;m which is important in communication engineering technologies.
SUMMARY OF THE INVENTION
The present invention provides copolymers, obtainable by copolymerization of at least one monocyanate, derived from a partly or fully fluorinated alcohol (“fluorinated monocyanate”), and at least one specific difunctional organic cyanate. It has been found that such copolymers are specifically valuable in the preparation of optical waveguide systems or structures thereof having low optical losses at 1.3 and at 1.55 &mgr;m.
Throughout the invention, “partly fluorinated” means that at least one fluorine atom is present in the molecule. “Fully fluorinated” means that hydrogen atoms are completely substituted by fluorine atoms. The whole molecules, or single organic radicals or groups (e.g. methyl, methylene, alkyl, aryl groups), respectively, may be fully fluorinated.
DETAILED DESCRIPTION OF THE INVENTION
As fluorinated monocyanate, one, two, three or even more monocyanates of formula I may be used
N≡C—O—R  (I)
wherein R is C(R′)
2
—CFR″
2
, wherein each R′ is, independently from the other, hydrogen or fluorine or an optionally substituted, preferably fluorinated alkyl or alkenyl group having preferably 1 to 13, more preferably 3 to 11 carbon atoms. Each of R″ may independently be defined as R′. Further, R″ may have an arylic structure. Preferably, R is a straight, branched, or cyclic non-aromatic hydrocarbon radical or an non-aromatic hydrocarbon radical comprising a cyclic structure. Preferably, the non-aromatic hydrocarbon radical has 1 to 15, more preferably 3 to 12 carbon atoms. It is to note that each of the carbon atoms of R may carry 1, 2 or, if it is a terminal carbon atom, 3 fluorine atoms. Fully fluorinated carbon atoms (—CF
3
, —CF
2
—) are preferred. Further, it is preferred that one or both of R′ are hydrogen and/or one of R″ is fluorine or a partly or fully fluorinated alkyl and the other is a partly or, more preferable, fully fluorinated alkyl which may be straight, branched or cyclic. Specific examples for the cyanates of formula (I) are —CH
2
—CF
2
—CF
3
, —CH
2
—CF
2
—CF
2
—CF
3
, —CH
2
—C(CF
3
)
2
F, —CH
2
—CF
2
—CF
2
—CF
3
.
For the preparation of the said copolymer, one, two, three or even more difunctional organic cyanates may be used. The expression “difunctional” means that two NCO groups are present in the molecule. The NCO groups are bound to organic radicals via the oxygen atom. The difunctional cyanate may be, but is not necessarily, partly or fully fluorinated. The organic structure of the difunctional cyanate or cyanates is selected under difunctional cyanates of formula II:
wherein R
1
to R
4
and R
5
to R
8
are independently from each other hydrogen, optionally substituted C
1
-C
10
alkyl, C
3
-C
8
-cycloalkyl, C
1
-C
10
-alkoxy, halogen, phenyl or phenoxy, the alkyl or aryl groups being unfluorinated, partly fluorinated or fully fluorinated, Z is a chemical bond, SO
2
, CF
2
CH
2
, CHF, CH(CH
3
), isopropylene, hexafluoroisopropylene, n- or iso-C
1
-C
10
alkylene which may be partly or fully fluorinated, O, NR
9
with R
9
being hydrogen or C
1
-C
10
alkyl, N═N, CH═CH, C(O)O, CH═N, CH═N—N═CH, alkyloxyalkylene having 1 to 8

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