Optical: systems and elements – Lens
Reexamination Certificate
2000-06-15
2001-12-25
Acquah, Samuel A. (Department: 1711)
Optical: systems and elements
Lens
C528S190000, C528S191000, C528S193000, C528S194000, C358S901100, C359S678000, C359S831000, C524S081000
Reexamination Certificate
active
06333821
ABSTRACT:
SUMMARY
The invention relates to optical elements from an optically isotropic, fully aromatic polyester with a glass transition temperature T
g
≧180° C.
DESCRIPTION
The invention relates to optical elements made of optically isotropic plastic and especially those made of a fully aromatic polyester with a glass transition temperature T
g
≧180° C.
Organic polymers are of increasing interest as materials for use in optics, micro optics, integrated optics, optical telecommunications technology and microsystems technology. In this context, they have found many uses in components of optical equipment, as well as in special optics such as lenses, lens arrays, prisms, mirrors, and as a transparent coating material for optical components. There is an especially large demand for optical components in optical telecommunications technology, optical interconnection technology, and optical sensory technology. Some examples of the components that are in demand are branching devices, couplers, beam re-routing units, optical switches and attenuation structures. These optical elements can be manufactured from typical semiconductor materials, and especially from organic polymers.
Polymers can generally be processed technologically advantageously through injection molding, stamping technology or from a solution.
The desired characteristics of such a polymer for optical use are the least possible optical attenuation at the relevant wavelengths (in optical telecommunications technology, preferably 1.3 and 1.5 &mgr;m), high resistance to moisture, the greatest possible stability against temperatures, especially in terms of the optical characteristics, a variable refraction index for adjusting to the specific requirements of the components, and good processability.
Especially when it is used as a waveguide, many demands are placed on the polymer. The refraction index of the material should be as variable as possible and adjustable to the particular substrate. When used in optical telecommunications technology, low material absorption at 1.3 and 1.5 &mgr;m is required, i.e. an optical loss of less than 1.0 dB/cm. Attenuation loss through volume defects (inhomogeneity, micro-bubbles) must also be kept to a minimum. In addition to certain technological requirements such as the production of layers and structurability, in particular thermal and thermo-mechanical stability, matched expansion coefficients and less shrinking are prerequisites for the use of polymers as waveguide structures in integrated optics.
For many of the above-mentioned uses of optical polymers, long-term thermal stability of the mechanical and optical qualities in the temperature range from ≧80° C. is especially desirable. Known simple thermoplastic polymers with good optical qualities, such as polymethylmethacrylate or polycarbonate, are suitable for such long-term application temperatures. The glass transition temperature only lies in the range approximately 105 to 130° C. so that long-term stability is no longer guaranteed.
Polymers with a glass transition temperature ≧180° C. are advantageous for such applications. Some examples of such high-performance plastics are polyimides, polyetherimides, polyarylsulfones, polyaryletherketones or polyarylethersulfones. However, these plastics are generally difficult or expensive to process, due to their relatively restricted solubility or complicated temperature management. The application of these high T
g
polymers for optical systems is described in various patents, such as JP-A-61-144738, JP-A-61-005986, DE-A-3915734, U.S. Pat. No. 4,477,555, EP-A-0254275, DE-A-3429074, DE-A-3927498, DE-A-4228853, and DE-A-3636399. Another disadvantage of these systems is the relatively high optical absorption in the wavelengths of 1.3 and 1.5 &mgr;m used in telecommunications technology. In addition, these materials are often characterized by high double refraction. Very low optical absorption is found in polycyanurates (DE-C-4435992); however, these high temperature network polymers do not always have satisfactory removability from the mold when they are processed by stamping or casting techniques. As a result, technologically advantageous processing is very difficult using these techniques.
It is also known that polyesters are characterized by good optical qualities, see EP-A-0 242 959, EP-A-0 184 716, and EP-A-0 076 133. However, only fully aromatic polyesters or polyarylates have a glass transition temperature ≧180° C. Polyarylates tend to go through partially crystalline, liquid crystalline or crystalline phases, which would clearly limit its use as an optical material, due to the resulting high scattering loss. The above-mentioned patents also describe only optically anisotropic polyesters. Isotropic, amorphous polyesters are required for use as optically transparent materials, e.g. in optical communications technology.
Isotropic polyesters that contain 9,9-Bis[4-(2-hydroxyethoxy)phenyl]fluorene as diolcomponents are also described, see EP-A-0 653 451, EP-A-0 396 418, and EP-A-0 380 027. However, these have relatively high optical losses in the wavelengths used in communications technology, and some have significantly low glass transition temperatures.
The task of the present invention was therefore to select polyesters that are created from as simple as possible monomer components, which on the one hand have a glass transition temperature ≧180° C., have low optical absorption at 1.3 and 1.5 &mgr;m, and are easy to process. On the other hand, they should not have crystalline, partial, or liquid crystal phases and should be capable of being processed into optical elements.
Surprisingly, this task was solved by the use of fully aromatic polyesters, in particular copolyarylates, predominantly of known basic components. The methods for the synthesis of such polyesters, e.g. using water extracion agents, converting dicarbonic acids into bisphenoles or bisphenolates into dicarbonic acid dichlorides, are known.
The fully aromatic polyester used in accordance with the present invention, with a glass transition temperature T
g
≧180° C., are preferably fully aromatic copolyarylates. Of course, homopolyarylates can also be used. In particular, the aromatic dicarbonic acids and aromatic dihydroxy compounds listed below can be used as components for the fully aromatic polyesters.
The discovered copolyarylates are preferably obtained from mixtures of aromatic dicarbonic acids and aromatic dihydroxy compounds. These polyarylates are characterized by optically virtually amorphous qualities, good solubility in lacquer solvents, low optical absorption at 1.3 and 1.5 &mgr;m, and good film formation. The glass transition temperature for these copolyarylates is above 180° C.
Especially well suited for the optical elements in accordance with the present invention are dicarbonic acids based on the following structures
in which R stands for hydrogen or fluoride
The aromatic dihydroxy compounds are preferably of the following structures:
in which R can stand for H or F.
Generally suited for the production of the polyesters for use in accordance with the present invention are polyester derivatives of benzene, napthaline, biphenyl, diphenyl-ethers, diphenyl-sulfone and diphenyl-methane, each with 2 hydroxy or carboxy functions. These can have one or several hydrogen atoms and/or fluorine atoms and/or methyl groups and/or trifluorenethyl groups as substituents.
The polyester used in accordance with the present invention should have a molecular weight in the range of 8,000 to 250,000, preferably from 12,000 to 120,000.
The copolyesters produced in a polycondensation reaction have a glass transition temperature T
g
≧180° C. They are well soluble in common lacquer solvents, such as cyclohexanon, ethoxyethylacetate and methoxypropylacetate, and can be processed into transparent films or layers through spin coating or dip coating. Their refractive index at 633 nm is 1.4 to 1.6, preferably in the range from 1.45 to 1.57. In accordance with the present invention, under certain copolyester compo
Brauer Andreas
Dannberg Peter
Kruger Hartmut
Neumann Waltraud
Acquah Samuel A.
Alcatel
Sughrue & Mion, PLLC
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