HK1023411A - Optical guide - Google Patents

Description

Optical waveguide device

Technical Field

The present invention relates to a device for directing and dispersing, converging and dispersing light, made from different monomers arranged in a random copolymer. The invention is also applicable to other mechanical and optical devices requiring high shape and dimensional stability at high temperatures.

State of the art

There are many materials and techniques for making polymer optical waveguides and polymer fibers, for example, see: hornak, ed., "Polymers for light and linked plastics", Marcel Dekker, New York, 1992.

The most common method of manufacturing polymer waveguides is to ultraviolet irradiate and chemically modify the portion of the film that will become the optical waveguide part through a photographic mask, and then etch the remaining portion with a solvent. The photographic mask is typically a piece of quartz glass containing a layer of chrome, wherein holes in the chrome layer constitute a waveguide pattern (waveguiddepattern) so that the waveguide material can be exposed to ultraviolet light (or other types of radiation).

Optical waveguides are mainly used for long-distance optical telecommunications and are typically glass fibers.

For short distances (< 100cm) inside electronic hardware, polymer optical waveguide technology has some potential compared to corresponding glass and plastic fiber alternatives due to its low cost. This is particularly the case when several joints are required and the waveguide pattern is relatively complex, including for example y-type joints. If polymer waveguide technology is used, the price of optical components such as couplers (e.g. 1: 8 splitters or combiners), wavelength selective components (WDM-components) etc. may be reduced.

In EPA 10446672, a method of manufacturing an optical waveguide from a polymeric material is disclosed. The polymeric material mentioned in this invention is an "ethylenically unsaturated polymer modified with an acrylic alicyclic epoxy compound ester group" or a "fully epoxidized bisphenol a-formaldehyde novolac". A photoinitiator and a solvent are added to these materials.

The waveguide pattern of the invention is determined by exposing the core and cladding of the waveguide to radiation at different levels so that the level of cross-linking between the core and cladding varies and hence the refractive index varies.

The disadvantage of the above copolymers is that the material attenuation is rather high, about 0.3dB/cm at 1300 nm.

Disclosure of Invention

One problem with polymer material optical waveguides is that they are more susceptible to attenuation of optical signals than are corresponding glass optical waveguides, especially in those wavelength bands (1300nm,1550nm) that are of interest for telecommunications.

Another problem is that commercially available standard fibers generally cannot be used at temperatures above 80 ℃ for longer periods of time because they are typically made from acrylic plastics with glass transition (softening) points close to 100 ℃.

The attenuation requirements vary from waveguide application to waveguide application, but a typical maximum attenuation of 0.1dB/cm at a wavelength of 1300nm is required for the following purposes:

1/enabling optical communication within or between electronic products on one printed circuit board, e.g. within a device box (megazine), through one back side to another printed circuit board and a back side on another printed circuit board, or

2/capable of manufacturing elements with negligible attenuation of the optical material, such as optical couplers, (splitter components, WDM-components, etc.).

In addition, the refractive index gradient between the core of the optical waveguide to be printed and the surrounding material must be tunable. In so-called multimode waveguides (multi mode waveguides), the refractive index of the core should be 0.020 greater than that of the surrounding cladding, which are optically matched to multimode glass fibers. For single mode waveguides (single mode waveguides), the corresponding value is about 0.005.

It would be a further advantage if the refractive index of the waveguide core could be as similar as possible to that of the corresponding standard glass fiber core (multimode or single mode) to reduce the intensity of reflections occurring between material interfaces having different refractive indices.

In many applications, large areas need to be printed at reasonable cost, and the requirements for optical waveguide patterns are very stringent, i.e., it is in fact required that the photographic mask with the optical waveguide pattern can be placed in direct contact with the non-adhesive polymer "dry film" used for printing (i.e., "contact printing"). For materials that are "wet films" prior to curing, it is desirable that the mask be separated from the polymer film at the time of printing, i.e., "near printing.

It is highly desirable that the temperatures required for the manufacturing process be as low as possible, particularly to enable the use of certain low cost, low temperature resistant substrates. The waveguide substrate may be a hard printed circuit board substrate such as a relatively soft thin polymer film (flexible foil) of silicon, FR-4 (glass fiber reinforced epoxy), or polyester, polyimide, or the like.

The present invention is directed to solving the above problems by materials and processing techniques that fully satisfy the following requirements:

1/low attenuation (wavelength 1300nm < 0.1dB/cm), measured with dispersive light.

2/solid state direct pattern printability, i.e. the photographic mask can be brought into direct contact with the polymer film used for printing (negative photoresist),

3/Low operating temperature (< 130 ℃ C.), so that substrates with limited temperature stability can be used, an

4/Adjustable refractive index, i.e.the copolymers produced can be used in single-mode and multimode waveguides.

The present invention constitutes a new group of random copolymers of different monomers, wherein said monomers and their ratios make it possible to have tailor-made use-dependent properties, such as optical attenuation (transparency), refractive index, thermal stability and mechanical properties and to meet the above-mentioned set of requirements items 1-4.

Copolymers useful in optical waveguides have a molecular weight of about Mn15,000 to Mn70,000(Mn index average molecular weight) before crosslinking, which allows these solid materials to be coated as thin films on a substrate using, for example, a spin or slit coater, when dissolved in a suitable solvent. The film thickness after drying is typically 1 to 50 μm depending on, for example, the solution viscosity, the dryness and the manner of coating.

Copolymers useful in other plastic compositions having permanent shapes and relatively high temperature resistance have molecular weights of about Mn15,000 to Mn5,000,000 prior to crosslinking. These components can be produced, for example, by injection molding, extrusion, embossing and other thermoplastic machining processes and then crosslinked into parts having a permanent shape (permanently shaped CD discs, such as fresnel lenses, homogeneous or gradient index optical lenses, optical mirrors and mechanical control elements on substrates). Material

The group a monomers may provide substantially low optical attenuation and may be used in waveguide cores and waveguide claddings with at least one type B monomer capable of causing chemical crosslinking. The type a monomers may be, for example:

2,3,4,5, 6-pentafluorostyrene,

2,3,4,5, 6-pentachlorostyrene,

2,3,4,5, 6-pentabromostyrene,

2,3,4,5, 6-pentafluorophenyl methacrylate,

2,3,4,5, 6-pentafluorophenyl acrylate,

2,3,4,5, 6-pentachlorophenyl acrylate,

2,3,4,5, 6-pentachlorophenyl methacrylate,

2,3,4,5, 6-pentabromophenyl acrylate,

2,3,4,5, 6-pentabromophenyl methacrylate,

the acrylic acid is a tetrafluoroethylene-ethyl ester,

the acrylic acid is tetrachloroethyl ester,

tetrabromoethyl acrylate (TBPO) is used,

1, 1-dihydroperfluorocyclohexylmethyl methacrylate,

(ii) a tert-butyl methacrylate,

(ii) an isobutyl methacrylate, a tert-butyl methacrylate,

acrylic acid 1H, 1H-heptafluorobutyl ester,

1H, 1H-heptafluorobutyl methacrylate,

methacrylic acid 1H,1H, 7H-dodecafluoroheptyl ester,

acrylic acid 1H,1H,2H, 2H-heptadecafluorododecyl ester,

acrylic acid 1H,1H, 4H-hexafluorobutyl ester,

methacrylic acid 1H,1H, 4H-hexafluorobutyl ester,

the hexafluoroisopropyl acrylate is used as a polymerization initiator,

the hexafluoroisopropyl methacrylate (HFP) is used,

acrylic acid 1H, 1H-pentadecafluorooctyl ester,

methacrylic acid 1H, 1H-pentadecafluorooctyl ester,

the perfluorocyclohexylmethyl methacrylate is reacted with a perfluorocyclohexylmethyl ester,

2-perfluorooctyl ethyl methacrylate,

the reaction product of (1) a trifluoro-isopropyl methacrylate,

the acrylic acid (methacrylic acid) is triethoxy hydroxyl silane ester,

2,2, 2-trifluoroethyl acrylate,

2,2, 2-trifluoroethyl methacrylate, and the corresponding monomers in which the H atom is substituted by a D atom (deuterium) or by other heavier atoms such as F, Cl, Br, etc., such as perfluorostyrene, or generally the ethylenic monomer CH₂= CXY, wherein hydrogen atom may be substituted by F, X-group may be H, F, Cl, CH₃Or CF₃And F may, for example, be of the phenyl type containing H-atoms, of the acrylate type, of a linear, branched, cyclic group on an ester group, for example, of the ether type, or in which D (deuterium), F, Cl, Br, OD or other substituents replace all or part of H-atoms. It should be preferred to use as few chemical structures (monomers) as possible of the H atoms. However, complete replacement of the hydrogen atoms with fluorine or deuterium is often impractical and/or economically unfeasible, so that the trade-off between different properties and costs defines the "stoichiometry" and choice of monomers.

In the manufacture of optical waveguides, 2,2,4,5, 6-pentafluorostyrene, "p-FSt" and perfluorostyrene are preferred because they are less prone to cracking when coated with a cladding layer than acrylate polymers.

In the manufacture of optical fibers, the choice of monomers is a major performance and cost issue, since polymers containing such monomers differ only slightly in their manufacturing difficulty.

The choice of monomer is a balance between price and performance (characteristics) when manufacturing the plastic component.

Group B monomers provide pattern printability primarily through pendant groups capable of chemical crosslinking and are used with at least one a-type monomer. The B-type monomer may be, for example:

glycidyl methacrylate, 2,3, epoxypropyl methacrylate,

glycidyl acrylate, 2,3, epoxypropyl acrylate, or other epoxy-containing monomers and the corresponding monomers having the H-atom replaced with a D-atom (deuterium) or other heavier atom such as F, Cl or the like to reduce optical attenuation.

In manufacturing an embedded waveguide including a core and a cladding, at least one monomer of the A-group of monomers is used for the core together with at least one monomer of the B-group of monomers. The same is true for the cladding, but where the monomer is selected to provide a suitable refractive index gradient with respect to the core. For a typical multimode waveguide, the refractive index gradient is about 0.020, the refractive index in the core being higher. Typical gradients are about 0.005 for single mode waveguides and about 0.080 for glass fibers.

As an alternative to the above-described complete freedom of choice of monomers, copolymers containing similar monomers A and B can be used in both the core and the cladding. The necessary difference in refractive index between the core and the cladding can be obtained by varying the molar ratio of the monomers therein. One copolymer for the core and another copolymer for the cladding may be prepared, for example, using only two monomers (one monomer selected from group a and another monomer selected from group B) by varying the molar ratio of the monomers of group a to the monomers of group B.

The choice of A-and B-type monomers will also be governed by other desirable characteristics, such as mechanical properties, thermal properties, environmental properties, processability, cost, etc. Photoinitiator

A commercial proton generating photoinitiator, Union Carbide UVI6974, comprising triphenylsulfonium hexafluoroantimonate (antimone) and 4,4 (phenyl) phenyldiphenylsulfonium hexafluoroantimonate may be used. Other proton generating photoinitiators may also be used.

Special photoinitiators may be required for highly fluorinated polymer systems. Preferably, photoinitiators having a similar structure and fluorine content to the polymer are used. The photoinitiators may also be arranged as pendant groups on the copolymer backbone. Crosslinking initiator for epoxy group

The hydrogen-abstraction-bearing compound can be used to dissociate the epoxy groups and thereby enable crosslinking after fiber formation. For example, gaseous ammonia, NH may be used₃Or ammonia in solution, or amine compounds.

One advantage of the present invention is the relatively high temperature stability, which can withstand short term exposure up to 300 ℃ and relatively long term exposure at temperatures above 120 ℃.

Another advantage is that different compounds can be used to dissociate the copolymer. It is possible to use, for example, gaseous ammonia, NH₃Or in solution, amine compounds, acids or lewis acids like BF3 and complexes thereof. The initiating group may be an anionic, anionic radical, cationic or cationic radical.

Yet another advantage of the present invention is the possibility of tailor-made use-dependent properties such as optical attenuation (transparency), refractive index, thermal stability and mechanical properties.

A further advantage of the present invention is that the above requirements of items 1 to 4 can be met simultaneously, which is simpler and better than the prior art.

Preferred embodiment materials for lower and upper cladding layers of printable patterns in optical waveguides

The lower cladding material can be, for example, a copolymer of tert-butyl methacrylate ("tButMA") and glycidyl methacrylate ("GMA") in a molar ratio of 95: 5 to 50: 50, preferably 90: 10 to 70: 30. The molecular weight (number average) may be 5,000 to 500,000, preferably 15,000 to 50,000. The photoinitiator content may be 0.3 to 15%, preferably 0.5 to 1.5%. Material for crosslinkable cladding in optical fiber

The coating polymer can be a copolymer of a group A monomer and glycidyl methacrylate GMA, and the molar ratio of the group A monomer to the glycidyl methacrylate GMA is 99: 1-20: 80, preferably 95: 5-60: 40. The molecular weight (number average) may be 15,000 to 5,000,000, preferably 100,000 to 1,000,000. Pattern-printable material for optical waveguide core

The core polymer may be, for example, a copolymer of perfluorostyrene ("p-f-St") and glycidyl methacrylate ("GMA") in a molar ratio of 95: 5 to 20: 80, preferably 90: 10 to 50: 50. The molecular weight (number average) may be 5,000 to 500,000, preferably 15,000 to 50,000. The photoinitiator content may be 0.2 to 15%, preferably 0.5 to 1.5%. Pattern-printable material for optical fiber core

The core polymer can be, for example, a copolymer of methyl methacrylate ("MMA") and glycidyl methacrylate ("GMA") in a molar ratio of 99: 1 to 20: 80, preferably 95: 5 to 75: 25. The molecular weight (number average) may be 15,000 to 5,000,000, preferably 100,000 to 1,000,000.

The photoinitiator content, if any, may be 0.2 to 1.5%. Polymer solution

Suitable solvents for the polymer and photoinitiator may be selected according to known principles described in A.F. Barton, "Handbook of solubility parameters and other coherence parameters," CRC Press Boca Raton Ann Arbor, Boston, London 1991.

In the manufacture of the optical waveguide, each material is dissolved in an appropriate solvent together with a photoinitiator. The solvent should not adversely affect the polymer, photoinitiator or the substrate. The solvent must be capable of evaporating from the polymer film at a sufficiently rapid rate at moderate elevated temperatures. One suitable solvent may be, for example, cyclohexanone. The amount of polymer may be in the range of 10-70% by weight, so that a layer thickness of 1-5 μm or more can be provided with a spin coater at a speed of 500-5,000rpm or with other coaters.

In the manufacture of optical fibers and optical waveguides, photoinitiators may or may not be added, depending on the method of processing. The photoinitiator content, if any, may be 0.2 to 15%, preferably 0.5 to 1.5%. Examples of methods for preparing an Embedded optical waveguide

Step 1, bottom cladding on substrate:

a solution of a clad polymer is dispersed as a uniform layer on a substrate, such as silicon, glass fiber reinforced epoxy laminate, polyimide film, metal, etc., using a spin coater or other coater, and thereafter the polymer film is exposed to a baking process at a high temperature, typically about 100c, for evaporating the solvent for one minute to several minutes, thus producing a polymer dry film having a typical thickness of 1-50 μm. Thereafter, the entire film is exposed to ultraviolet light to generate an acid of a photoinitiator, which will then assist in crosslinking the epoxy groups. The UV lamp can be, for example, of the Hg-type or the Hg-Xe-type. Typical UV dose is 100-1,000mJ/cm². The uv irradiation is followed by a baking process at about 130 c for about 30 minutes to promote the crosslinking reaction.

Thermal curing and radiation crosslinking (at wavelengths other than ultraviolet light), sometimes without an initiator, may also be used, for example in electron beam curing.

Step 2, waveguide fiber core on the bottom cladding layer:

after coating a core polymer (having a higher refractive index than the cladding polymer) and exposing the polymer film to a baking process for several minutes at an elevated temperature, typically about 100c, for evaporating the solvent, a dry film of polymer is produced with a typical thickness of 1-50 μm. Thereafter, the film is exposed to ultraviolet light through a conventional mask as described above to form the desired waveguide pattern, wherein the irradiated portions of the thin film are crosslinked in the same manner as described above. After the UV irradiation, a baking process was performed as described above. After cooling, the pattern is developed in a suitable solvent, such as cyclohexanone, and the substrate may be sprayed with the solvent or the substrate with the polymer film attached thereto may be immersed in the solvent. And then cleaned or purified with a solvent having a low swelling or dissolving capacity for the core and the cladding.

Step 3, an upper cladding on the waveguide fiber core and the bottom cladding:

the substrate containing the lower cladding and patterned core is then coated with a layer of cladding polymer to produce an embedded waveguide that is completely surrounded by cladding. The same procedure as in step 1 was used. Examples of methods for producing optical fibers

In a method according to one embodiment, the fibers (copolymer or copolymer containing photoinitiator) are irradiated with Ultraviolet (UV) light either together with or after forming so that the added photoinitiator can be activated, after which the fibers are crosslinked. The crosslinking process is preferably carried out at elevated temperatures, near or above the glass transition temperature of the material. Suitable time and temperature values for this process can be obtained, for example, by using differential scanning calorimetry ("DSC") and UV-DSC (UV-attached DSC) tests. Depending on the temperature, the crosslinking time (curing) can generally be adjusted from the order of seconds (on-line) to the order of 24 hours (off-line batch).

In a method according to another embodiment, the fiber (copolymer or photoinitiator-containing copolymer) is exposed to an external crosslinking initiator (a curing machine) either together with or after forming, which initiator diffuses into the optical fiber. The epoxy groups are opened in the curing machine to allow the "ring-opened" epoxide to react further and cause crosslinking. The diffusion process and subsequent crosslinking process are preferably carried out at elevated temperatures, near or above the glass transition temperature of the material to reduce the time consumption of the process. Suitable time temperature values for this process can be obtained, for example, by using DSC tests. The crosslinking process can likewise be carried out rapidly on-line or slowly off-line in batches, depending on who is more technically and economically appropriate.

In both alternative embodiments, the core and cladding may use the disclosed materials and processing techniques. Furthermore, the core may be independently prepared according to the disclosed materials and processing techniques, while the cladding is added using conventional techniques well known to those skilled in the art. This process can be easily incorporated into the fabrication of the fiber core.

In another embodiment, a thermoplastic gradient index preform ingot is prepared, which can then be filled into fibers that can be crosslinked. As mentioned above, the starting material is a copolymer or a copolymer with or without a photoinitiator. The process for preparing a preform ingot having a gradient refractive index is described in detail below:

yasuhiro Koike, Graded index materials and Components, A, Hornak, ed, "Polymers for light wave and Integrated optics", Chapter III, Marcel Dekker, New York 1992.

The invention is of course not limited to the above-described embodiments but may be varied within the scope of the appended claims.

Claims (21)

1. An optical waveguide device made from a polymeric material comprising a photoinitiator and different monomers arranged in a random copolymer, characterised in that the first monomer is glycidyl acrylate (2, 3-epoxypropyl acrylate) and the second monomer is 2,3,4,5, 6-pentafluorostyrene ("p-F-St"), the photoinitiator comprising 4,4 (phenyl) phenyl diphenyl sulphonium hexafluoroantimonate and triphenyl sulphonium hexafluoroantimonate.

2. Device according to claim 1, characterized in that the first monomer is glycidyl methacrylate (2, 3-epoxypropyl methacrylate).

3. A device according to claims 1-2, characterized in that the second monomer is perfluorostyrene.

4. A device according to claims 1-2, characterized in that at least one hydrogen atom ("H") in at least one of the monomers is replaced by a deuterium atom [ (D ").

5. Device according to claims 1-2, characterized in that at least one hydrogen atom ("H") in at least one monomer is substituted by a halogen atom, such as fluorine, chlorine, bromine, etc.

6. Device according to claims 1-2, characterised in that at least one hydrogen atom ("H") in at least one monomer is replaced by CH₃-molecular substitution.

7. The apparatus of claim 6, wherein at least one CH₃At least one hydrogen atom ("H") in the molecule is substituted by a halogen atom, such as fluorine, chlorine, bromine, etc.

8. Device according to claims 1-7, characterized in that at least one hydrogen atom ("H") in at least one monomer is substituted by a phenyl group.

9. Device according to claims 1-7, characterized in that at least one hydrogen atom ("H") in at least one monomer is replaced by an acrylate group.

10. Device according to claims 1-7, characterized in that at least one hydrogen atom ("H") in at least one monomer is replaced by an ether group.

11. Device according to claims 8-10, characterized in that at least one hydrogen atom ("H") in at least one of the phenyl, acrylate or ether groups is substituted by a halogen atom, such as fluorine, chlorine or bromine.

12. The device according to claims 1-11, characterized in that the core in the device comprises a random copolymer having a first molar ratio between the monomers and the cladding comprises the same random copolymer but with a molar ratio between the monomers different from the molar ratio of the core, so that the refractive index of the core is higher than that of the cladding.

13. The device according to claims 1-12, characterized in that the core and the cladding comprise different random copolymers, provided that the core has a higher refractive index than the cladding.

14. Device according to claims 1-13, characterized in that the device is designed as a waveguide.

15. Device according to claims 1-14, characterized in that the device is designed as an optical fiber.

16. The apparatus of claim 15, wherein said optical fiber comprises a refractive index gradient wherein the refractive index is greatest in the center.

17. Device according to claim 16, characterized in that the crosslinking initiator of the epoxy group is ammonia (NH)₃)。

18. The apparatus of claim 17, wherein the ammonia is provided in the form of gaseous ammonia or in solution.

19. Device according to claim 18, characterized in that the crosslinking initiator of the epoxy groups is an amine compound.

20. Device according to claim 19, characterized in that the crosslinking initiator of the epoxy group is an acid, such as a lewis acid.

21. A device according to claims 1-14, characterized in that said device comprises an optical lens.