Plastic and nonmetallic article shaping or treating: processes – Outside of mold sintering or vitrifying of shaped inorganic... – Including plural heating steps
Patent
1987-12-28
1989-06-13
Lee, John D.
Plastic and nonmetallic article shaping or treating: processes
Outside of mold sintering or vitrifying of shaped inorganic...
Including plural heating steps
264 11, 350 9629, 350 9634, 427164, 427322, G02B 610
Patent
active
048386340
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to optical waveguides and includes a method of fabricating waveguide structures.
BACKGROUND OF THE INVENTION
In principle, optical waveguides comprise a thin film or layer of material supported on a substrate of lower refractive index. A ray of light may be propagated within the thin film of higher refractive index material. The ray is confined by total internal reflection at the thin film/substrate interface and at the film/air space boundary. Waveguides are also used for roles additional to merely guiding light. For example, by combining the waveguide with a non-linear element, structures can be produced which are useful in optical logic and signal processing application.
Traditionally, waveguides have been constructed from inorganic materials such as glasses which may be doped with inorganic materials, such as metal or semi-conductor compounds. In order to produce a device which combines waveguiding and non-linear optical properties, it has generally been the practice to grow a single crystal layer onto a suitable base substrate. Such techniques are laborious and complex.
In contrast, the use of organic materials for waveguide construction has been considered to suffer from disadvantages such as lack of stability, insufficient purity, poor optical properties and the difficulty of controlling the incorporation of dopant materials.
SUMMARY OF THE INVENTION
According to the present invention there is provided a method of producing an organic waveguide which comprises treating a transparent plastics substrate with a solution in an inert solvent of an organic dopant which is absorbed into the surface of the substrate, under conditions such that a surface layer is formed having a refractive index which is greater than that of the substrate.
The process of the present invention enables a polymer substrate having the necessary optical properties, (including transparency, clarity and good surface properties), to be doped with a sufficient amount of a suitable organic compound to produce a local change in the refractive index of a surface region of the polymer. Provided that the resultant refractive index of the surface layer is greater than that of the bulk polymer, the resulting structures can be used as a waveguide. Moreover, by selecting organic dopant compunds which possess non-linear optical properties, a non-linear waveguide can be produced in a single production step.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a refractive index/depth (wavelengths) relationship and shows a typical profile for C1NA
FIG. 2 shows an output/input relationship. The response of a DAN waveguide is shown.
FIG. 3 shows an output/input result obtained with an o-NA waveguide.
FIG. 4(a) shows a planer waveguide, 4(b) shows a curved stripe waveguide and 4(c) shows a Y-junction broadening stripe waveguide.
In essence, the process of the present invention, which we have termed "solvent-assisted indiffusion" or (SAID), involves the contacting of the polymer substrate in a two-phase system comprising the organic dopant and a saturated solution of the dopant. The solvent acts as a transfer medium which allows dopant molecules to come into contact with the surface of the substrate at a constant rate while at the same time giving an even distribution over the substrate. Presence of solid dopant suspended in the solution ensures a constantly saturated solution and steady state conditions. Dopant molecules reaching the surface of the substrate face a choice between continued solvation and entry into the substrate to form a solid solution. Molecules which do enter the surface may then diffuse further into the matrix. Ideally, a large dopant concentration should be achieved near the surface but not penetrate far into the bulk polymer. This would give an effective waveguide with good non-linear properties (depending on the nature of the organic dopant), but would avoid the creation of a thick waveguide supporting many modes.
In effect, a surface layer is formed in the polymer matrix form
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patent: 4749245 (1988-06-01), Kawatsuki et al.
Nomura et al, "Fiber Optic Sheets of Ridged Polymer Films," Applied Optics, vol. 14, No. 3, Mar. 1975, pp. 586-588.
Kato et al, "Polymer Thin Film Optical Waveguide," Electronics & Commun. in Japan, vol. 65, No. 11, Nov. 1982, pp. 101-107.
Tomaru et al, "Organic Crystals Growth for Optical Channel Waveguides," Optics Commun., vol. 50, No. 3, Jun. 1984, pp. 154-156.
Bennion Ian
Brettle Jack
Glenn Robert
Goodwin Martin J.
Trundle Clive
Lee John D.
The Plessey Company PLC
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