Optical waveguides – With disengagable mechanical connector – Optical fiber to a nonfiber optical device connector
Reexamination Certificate
2000-04-25
2001-06-26
Healy, Brian (Department: 2874)
Optical waveguides
With disengagable mechanical connector
Optical fiber to a nonfiber optical device connector
C385S014000, C385S049000, C385S130000, C385S131000
Reexamination Certificate
active
06250819
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the field of integrated optic circuits or IOCs and more specifically to miniature optical components formed by the mounting of a chip comprising optic waveguides on an optic fiber connection support.
Recent developments in integrated optic circuits enable the incorporation of numerous active or passive optic elements (gratings, mirrors, etc.) and the association of various photonic functions (emitter, detector, diode, laser and other function) or electro-optical functions (modulator, coupler and other functions) in a miniature chip which in this case is practically an optical mini-bench.
In general, an integrated optic circuit is formed by a chip comprising a set of functional optical elements connected by optic waveguides conducting the processed light signals. The optical elements and the waveguides are implanted on the substrate of the chip.
2. Description of the Prior Art
Various types of substrate and different implant technologies have been implemented, in the prior art, to develop integrated optic circuits. In particular, there are known integrated optic circuit structures that associate the following substrates and layout technologies:
silicon (Si) with nitride or silica deposition,
germanium (Ge),
gallium arsenide (GaAs), with epitaxy,
indium phosphide (InP), with epitaxy,
lithium niobate (LiNbO
3
), with metal diffusion,
glass, with ion exchange technology, and
polymers, with insulation or molding of guides; and this list is not exhaustive.
The substrate of an integrated optic circuit may be a semiconductor substance, especially silicon, or a non-conductive substance. The electrical properties are not of vital importance.
The use of integrated optic circuits is of considerable importance in fiber-optic telecommunications networks. In particular, it is being planned to incorporate signal-processing functions, by means of integrated optic circuits, in the communication lines themselves. The integrated optic circuits are thus destined to carry out on-line processing functions such as routing, multiplexing, demultiplexing, modulation, switching, and optic signal amplification.
The main obstacle to the development of the use of integrated optic circuits is the problem of the connection between optic fibers and optic circuit waveguides, because the fibers and guides have microscopic cores and need to be perfectly aligned for the effective transmission of the optical signals.
The problem, firstly, is to obtain very precise positioning of the cores of the optic fibers in the alignment of the axes of the waveguides implanted in a substrate chip.
Secondly, the problem is to obtain a stable, reliable and permanent attachment of the fibers to the waveguides.
In the manual method, each microscopic fiber is made to coincide with the respective microscopic waveguide and then the fiber and the guide are glued together by laboratory methods of mechanical or piezoelectric micropositioning. These methods are costly and cannot be envisaged for industrial-scale production.
There are hybridization methods which start with the positioning of a layer of optic fibers in a series of parallel groves hollowed out in a support so as to pre-arrange the fibers in a plane with a specified spacing between each fiber and the other fibers. Then, an integrated optic circuit is implanted in the substrate of a chip with optic waveguides traced out on the surface of the substrate block. The waveguides extend axially to the edge of the chip so as to be in a plane with the same spacing between them as between the fibers.
The problem then lies in adjusting the chip with respect to the fiber support so as to position the series of waveguides very precisely in the alignment of the layer of optic fibers.
The usual method in which the chip is positioned after the support, the waveguides are aligned in the axis of the fibers by manual action on an optical detection bench and then the chip is glued or soldered to the support has drawbacks of cost, lack of reliability and lack of industrial reproducibility.
An article by E.J. MURPHY, “Fiber Attachment for Guided Wave Devices” in the Journal of Lightwave Technology, June 1998, Vol. 6, No. 6 describes a developed technique that proposes the forming of two microscopic ribs to align a fiber support on the surface of the chip. This support comprises two plates that sandwich the fibers in the grooves. One of the plates is extended so that the plate and the chip overlap partially. The two micrometer-sized ribs of the chip fit into two grooves, free of fibers, hollowed out in supporting plates. The ribs are formed at the same time as the waveguides of the silicon chip, by the etching of the silicon passivation layer on the surface of the substrate.
One drawback of this technique is that the chip and the support are not fixed together but simply laid and aligned on top of each other. There is no mechanical holding whatsoever between the chip and the fiber support. Furthermore, the two micrometer-sized ribs do not prevent a tilting of the support around the axis of the ribs and a loss of alignment.
These methods and this technique are but partial and unsatisfactory mechanical approaches, so much so that they have been supplanted by what are called “flip-chip” techniques.
In the known flip-chip techniques, the chip comprising the waveguides is superimposed on a motherboard hollowed out with axial grooves in which fibers are positioned. The motherboard is therefore used as a support for the fibers and the chip.
The motherboard is generally formed by silicon, a crystalline material in which grooves can be made with excellent directivity. This enables the perfect alignment of the optic fibers and their precise positioning in a transversal plane.
The fibers are held fixed in the grooves by a plate or counter-plate hollowed out with grooves that are complementary to the grooves of the motherboard. This plate or counter-plate covers the layer of fibers positioned in the grooves of the motherboard so that each fiber is sandwiched in the hollow formed by two grooves and is held in position.
The problem then is to transfer the integrated optic circuit chip with precision on to the motherboard, in making the waveguides coincide with the optic fibers.
An article by W. HUNZIKER et al., entitled “Self-aligned Flip-chip Packaging of Tilted Semiconductor Optical Amplifier Arrays on Si Motherboard” in “Electronics Letters”, March 1995, Vol. 31, No. 6, describes a technique for transferring a chip comprising waveguides to a motherboard hollowed out with grooves, with automatic positioning, the guides being embedded in the grooves. The fixing of the chip to the motherboard is obtained by the melting of intercalary solder stripes.
One drawback of this technique is that the guides undergo mechanical constraints that are harmful to the transmissions of optical signals.
Another drawback of this technique is that it is appropriate only when the waveguides have dimensions in the range of those of the grooves and the fibers, which is generally not the case since the dimensions of the waveguides varying according to the type of substrate.
An article by Q. LAI and the same authors, entitled “Silica on Si waveguides for self-aligned fibre array coupling using flip-chip Si V-groove Technique”, in September 1996, in “Electronics Letters”, Vol. 32, No. 20, describes an improvement of this technique in which each guide is bordered by two raised lateral ribs. Each pair of ribs bordering a guide rests on the two flanks of a respective groove, thus positioning the guide in the axis of the groove and of the fiber.
One drawback of these techniques is that there is no provision for attaching the chip and the motherboard which are simply laid one on the other. One of the directional parameters of alignment therefore is not set with precision.
The attachment requires subsequent steps of glueing or soldering which have the drawback either of being irreversible or of taking the substrate to high temperature.
Another drawback of th
Armbruster Vincent
de Labachelerie Michel
Devoldere Nicole
Jeannot Jean-Claude
Kaou Neila
Blakely & Sokoloff, Taylor & Zafman
Healy Brian
Highwave Optical Technologies
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