Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1999-12-23
2001-11-27
Healy, Brian (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S050000, C385S051000, C385S052000, C385S014000
Reexamination Certificate
active
06324323
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to the packaging of integrated optical waveguide circuits, and more particularly to the alignment of optical fibers to input and output ports of the waveguide circuit and for maximizing the optical energy transferred between the optical fibers and input/output ports of the waveguide circuits.
BACKGROUND
Integrated optical waveguide circuits (IOWCs) are photonics counterparts of electronic integrated circuits (ICs). They are used to perform different operations for processing optical signals in optical or opto-electronics domain. They have a broad range of applications such as in optical telecommunication networks, sensors, and biomedical apparatuses.
An IOWC has a number of input and output waveguides that have to be attached to optical fibers before it can be used by the consumers. However, the attachment of fibers to waveguides with the objective of maximizing optical power coupling between the fiber and waveguide imposes several technological challenges. That is because firstly the core diameter of fibers and waveguides are typically small, e.g. 2 to 20 microns, and secondly they are not often equal. The former makes the fiber to waveguide alignment extremely critical and the latter causes the loss of some optical power due to mismatch between the mode sizes of the fiber and waveguide. Any small misalignment between the fiber and waveguide core axis can increase the coupling loss of optical power significantly, whereas the mismatch between the core size of the fiber and waveguide will result in loss of optical power even at the perfect alignment position. However waveguides with small core diameter and higher numerical aperture than single mode fibers are more desirable in order to decrease the total length of an IOWCs. Therefore one should often compromise between the inherent joint loss of waveguides of different core sizes and the total length of the IOWCs.
There are two conventional methods of attaching fiber to waveguides, one is by manual or active alignment, and the other by automatic alignment. A combination of automatic and manual alignment is also possible. In the manual method, each individual optical fiber is abutted to the input or output waveguides by careful adjustment of the fiber position in front of the waveguide while monitoring the efficiency of the light coupling and affixing the fiber using adhesive and the like at the optimum position. Although manual alignment results in a better coupling loss, it is very time consuming thus making the packing of IOWCs very expensive. Also because of the use of adhesives used in affixing the fiber to the waveguide, the manual method does not provide very reliable results.
As for the automatic alignment method, it is known to use a substrate having alignment grooves to align the fiber core and waveguide and also to support the fiber. Alignment grooves for this purpose are also known in integrated optical circuits. While grooves provide lateral and angular alignment they cannot provide precise vertical alignment since, within a micron, precision control of the depth of the grooves is very difficult. Automatic alignment methods have been disclosed, for instance, in U.S. Pat. Nos. 4,796,975, 5,393,371, 5,175,781, 5,297,228, 5,361,382, and 5,600,745.
In U.S. Pat. No. 5,175,781 issued on Dec. 29, 1992 to Hockaday et al, there is disclosed a method of attaching fiber to integrated optic chips (IOC) by forming alignment grooves, using laser ablation on the IOC followed by cutting the surface ends of the waveguides by dicing saw, disposing optical fibers within the grooves, and securing the fibers with adhesives to attach the fiber to the IOC permanently. This method again cannot insure vertical alignment and doesn't solve the core size mismatch problem.
In U.S. Pat. No. 5,361,382 to Nakamatira et al, another method of connecting optical waveguide and optical fiber has been disclosed. In that disclosure waveguides are made on one substrate. An optical connector is formed on a second substrate. The substrates have means for aligning them together and the second substrate has alignment grooves with fibers embedded therein. Adhesive and the like are used to fix the optical connector substrate and waveguide substrate after aligning the substrates. In a subsequent U.S. Pat. No. 5,297,228 from the same applicants, fiber aligning jigs are aligned with the optical waveguides using markers and are abutted to each other by laying a common guide pin along the corresponding prefabricated pin grooves on the fiber aligning jig and waveguide substrate. This method also suffers from the low reliability of using adhesive and also the loss associated with the fiber and waveguide core mismatch.
In U.S. Pat. No. 5,600,745, issued on February 1997 to Hsinchu et al, there is disclosed a preferred method of chemically etching of V-grooves and V-grooves with a predetermined lateral angle to precisely adjust the fibers to the waveguide in the vertical direction. This method however uses adhesives to abut the fibers to the waveguide and it doesn't address the core size mismatching problem.
SUMMARY OF THE INVENTION
The present invention seeks to provide a method of providing a package of an optical waveguide and optical fibers which seeks to overcome the above problems.
Accordingly, the present invention provides a method of forming such a package upon a first rigid substrate and in which optical fibers are disposed within alignment grooves in a surface of the substrate with a compressible layer disposed between each fiber and its corresponding alignment groove surface. In this method, a second compressible layer is disposed over the optical fibers and the layers and the fibers are sandwiched between the substrate and a further substrate. The substrates are pressed towards each other thereby compressing the layers and forcing each of the optical fibers further into its alignment groove and into optical alignment with the optical waveguide. With this method and using the compressible layers, alignment of the fibers can be successfully achieved without the use of adhesive while the assembly is held together with its parts being relatively immoveable.
Ideally, the first and second rigid substrates are disposed between rigid plates, the rigid plates being forced towards each other into desired relative positions for he purpose of pressing the substrates towards each other for the above purpose.
In a preferred method, the rigid plates are forced towards each other at a plurality of localized positions of the plates so as to adjust the force applied between and the distance between the rigid plates at each of the localized positions.
The invention also includes a package of an optical waveguide and optical fibers with first and second substrates sandwiching between them an arrangement of a plurality of the fibers disposed between compressive material layers. Each of the fibers is contained within a groove formed within one of the rigid substrates and one of the compressible layers is disposed between each fiber and its corresponding groove.
In the above method and package of the invention, the alignment grooves may be made using lithography and an associated etching method, such as dry etching, chemical etching, whichever is suitable for the waveguide and substrate materials, or by laser ablation; forming other grooves may be done utilizing a dicing saw or any other suitable cutting means to cut the grooves. The depth of these grooves exceeds the depths of the alignment grooves and has a width of few hundred microns. The method also includes forming a lens at the tip of the fiber by dipping into a transparent flowable material, i.e. adhesive such as sol-gel liquid glass; and hardening it to form a plano-convex lens at the end of the fiber.
REFERENCES:
patent: 4046454 (1977-09-01), Pugh, III
patent: 4796975 (1989-01-01), Lukas et al.
patent: 5015059 (1991-05-01), Booth et al.
patent: 5134676 (1992-07-01), Boillot et al.
patent: 5175781 (1992-12-01), Hockaday et al.
patent: 5297228 (19
Benham Victor
Hatami-Hanza Hamid
Healy Brian
Kueffner Friedrich
Nu-Wave Photonics Inc.
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