Optical waveguides – Planar optical waveguide – Thin film optical waveguide
Reexamination Certificate
1999-11-16
2002-01-22
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
Planar optical waveguide
Thin film optical waveguide
C385S131000, C385S132000
Reexamination Certificate
active
06341190
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to organic optical components and preparation thereof. Optical components may be used to transmit and/or manipulate light signals in various fields of technology such as telecommunications, data communications, avionic communications, sensor networks, automotive control systems, display and backlighting.
More specifically components are intended for passive light transmission and/or manipulation including polarisation control, transmission, distribution, splitting, combining, multiplexing, phase filtration.
Active optical components requiring electrical connections to power and/or control circuitry are also envisaged.
Specific optical components of the invention include waveguides, strip waveguides, bends, Y-junctions, blazed grating couplers, power splitters, star couplers, holographic gratings, holograms, phase filters, circuitry interconnections, bridging devices, lens arrays and the like.
2. Description of Related Art
A diverse number of organic components are known. U.S. Pat. Nos. 4,593,974 and 4,547,040 (Yamamoto) disclose components comprising embedded organic optical fibres, obtained using extrusion techniques. U.S. Pat. No. 5,455,883 (Shigeta) discloses optical input connections for displays. Organic optical components comprising two or more polymers having different refractive indices are a means of providing more complex light guiding components with excellent optical properties. Increasingly these are favoured over the inorganic counterparts, the preparation of which is increasingly difficult in line with the need for need complex and miniaturised components.
Unfortunately organic optical components suffer high optical losses both by polymer absorption itself and by leakage from imprecise structures and misaligned components. Cross talk between components in high density systems is also a problem.
Organic optical components usually comprise two or more polymers having different refractive indices. The polymer having the higher refractive index when surrounded by the other polymer can function as a waveguide which allows for the transmission and manipulation of a light signal. The higher refractive index polymer is usually introduced into the other resin which is then cured.
Specifically polymer moulding processes have been used involving the filling of mould cavities to produce rigid mouldings with flat faces which can be further processed to provide polymer analogues of optical devices produced using inorganic materials, for example as disclosed in U.S. Pat. No. 5,136,678 (Yoshimura) and U.S. Pat. No. 5,113,471 (Inaishi). Two flat surfaces one provided with channels for filling with resin when the two surfaces are squeezed together is an unreliable method of producing well defined channel waveguides due to the difficulty of avoiding a thick layer of material being formed between waveguides than can allow optical cross-talk between channels. Bonding the two surfaces together before introducing the channel filling resin can be achieved by capillary filling but is time consuming and can be unreliable for complex and large area. Yoshimura and Inaishi disclose a method for preparing optical waveguides by first injection moulding a flat substrate with a number of grooves, next an UV curable resin is filled in the grooves to form a core material. The resin is then irradiated with UV light to cure the core material. Finally a coating is applied to the substrate and core material by a spin, spray, casting, etc method. This procedure an uneven residual layer since a portion of the resin inevitably spills outside the grooves. As the guides described by Yoshimura and Inaishi are very simple, ie no bends or junctions which are overlay critical, it is likely that the importance of an overlay was not appreciated by Yoshimura.
More recent investigators have found that trying to fill injection moulded waveguides by squeezing out the excess (as in Yoshimura) is not a reliable method and have resorted to filling waveguides that have enclosed channels performed using a top cladding by capillary filling or using vacuum assistance, ie using liquid crystal cell filling methods.
Prior art batch processes have been used to define channel waveguides in inorganic or polymer coatings on rigid wafers using lithographic, multistep, materials addition and subtraction processes.
Other production techniques have been developed specifically to avoid spillage of resin or as an alternative dispersing with the need to inject resin, in an attempt to attain acceptable optical losses, uniform output and consistent performance, increasing the incentive to use optical components. However with these there is a practical limit to the size of waveguides which can be manufactured. Since the resin must be poured in grooves in a flat substrate, the groove must be sufficiently large to receive the resin, and the device for pouring the resin must be sufficiently sophisticated to ensure the resin does not overflow the grooves. Therefore prior to the invention, polymeric optical waveguides smaller than 100 micron were not manufactured which did not have a relatively thick layer of polymer of variable thickness which produced unacceptably high losses.
Lithographic techniques, for example, as disclosed in Inamura et al, “Electronics Letters”, 27 (15), 1342-1343 (Jul. 18, 1991) and Matsura et al “Electronics Letters”, 29 (3), 267-271 (Feb. 4, 1993) conventionally entail fabricating a waveguide comprising of core and buff layers on substrate by waveguide patterns fabricated using photolithography, core ridges then formed by reactive ion etching until the buffer layer surface is exposed and finally the core ridges covered with a spin coated cladding layer, relies on immersing the waveguide pattern entirely subsequent removal of residual material. U.S. Pat. No. 5,265,185 discloses a similar process using a combination of spin coating and then etching. Although the resulting product has no residual overlayer as a result of the reactive ion etching, the technique is time consuming and laborious and not suited to further miniaturisation. Imamura discloses mono and multi mode waveguides comprising film thicknesses of 8 and 15 micron using specific low optical loss polymers and reporting low optical losses.
Capillary techniques, for example as disclosed in U.S. Pat. No. 5,265,184 (Lebby et al) are also known as a means to avoid residual overlay from ation. In these techniques a waveguide mould is obtained and an encasing lid glued on top. Waveguide shaped cavities are then filled by capillary action with resin subsequently curing. Lebby injects resin into the channels. It is important to avoid cavitation, bubble formation, striations and the like. These considerations become more important the more complex the optical component, the finer the channel and the greater the total mould surface area. Accordingly complex or extensive products obtained using this technique are commercially unviable.
A further technique which avoids overlay formation is known as selective photopolymerisation, for example as disclose in EP 0 420 592 (Nippon Telegraph and Telephone Corporation), U.S. Pat. No. 5,265,185 (United States of America, Secretary of the Army) and Booth et al J Heatwave Technol, 7(10), 1452. Monomers contained in a polymer are selectively polymerised to change the refractive index to make a pattern like optical waveguide. Specifically a mask having a predetermined patter is mounted on a polymer sheet or substrate composed of a transparent polymer which contains a low refractive index monomer and the sheets or substrate are irradiated with UV rays through the mask to selectively polymerise the low refractive index monomer, replicating the patterns. The photopolymerised portion of the polymer has a lower refractive index than the polymer matrix. The polymer sheet is heated in vacuum toremove unreacted monomers which remain in areas unexposed by UV rays. As a result unexposed portions of the polymer consists of the high refractive index polymer al
Carter Neil
Grierson Thomas Harvey
Ryan Timothy George
Summersgill Philip
Epigem Limited
Palmer Phan T. H.
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