Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1999-06-28
2002-09-17
Spyrou, Cassandra (Department: 2872)
Optical waveguides
With optical coupler
Input/output coupler
C385S031000, C385S034000, C385S043000, C385S095000, C385S096000, C385S097000, C385S098000, C385S099000, C385S115000, C385S046000, C065S382000, C065S387000, C606S117000, C606S118000, C606S119000, C606S120000
Reexamination Certificate
active
06453090
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the assembly or splicing between two optical components, particularly an optical fibre and another optical component, whereby the latter can e.g. be another optical fibre (particularly a multicore fibre) or a lens or microlens (particularly a graded-index or GRIN lens). The optical fibre can also be a multicore fibre. Another example of an optical element which can be assembled or spliced with the aid of the invention is a lens-prism assembly. The invention also relates to the assembly of an optical component and a substrate, e.g. a semiconductor or metal substrate. The component can e.g. be an optical fibre or a lens.
2. Discussion of the Background
The article by K. Kinoshita entitled “End preparation and fusion splicing of an optical fiber array with CO
2
laser” published in Applied Optics, vol. 18, No. 19, pp 3256-3260, 1979 describes the fusion of optical fibres with the aid of a CO
2
laser. The article by K. Egashira entitled “Analysis of thermal conditions in CO
2
laser splicing of optical fibers” published in Applied Optics, vol. 16, No. 10, pp 2743-2746, 1977 also relates to fibre-fibre splicing using a CO
2
laser.
The article by K. Nakatate et al entitled “Silica based rod lens for the medical fiberscope” published in Proceedings SPIE, 1994 relates to a fibre-lens bonding. It uses a technology identical to that of fibre-fibre fusion using an electric arc. It involves a meeting of the surfaces to be contacted.
This procedure is only applicable to small diameter optical elements (less than 200 &mgr;m). Microlenses are produced using the same procedures as those used for producing the optical fibres. Thus, the glasses obtained for the lenses melt at temperatures comparable with the fibre fusion temperatures, which obviously makes fusion or welding easier. Consequently, this procedure cannot generally be applied to the production of an assembly of two random optical components.
In general terms, all these procedures lead to a deformation of the contacting surfaces by heating. In the case of fibre-fibre splicing, fusion leads to a deformation of the end of the fused together fibres. Moreover, in general, the optical fibres are prepared beforehand by cleaving, but the perpendicularity of the interface with respect to the fibre axis is not guaranteed in this procedure. Thus, fusion requires a plastic deformation obtained by exerting an axial pressure.
A known method for assembling two random optical components, e.g. a lens and a prism, involves bonding. However, bonding is chemically sensitive to certain solvents and leads to a poor mechanical strength for small surfaces. It also requires the introduction of a material (the adhesive), which reduces the optical quality of the path which can be followed by a beam. Bonding is more particularly used for the assembly of a lens and a multicore fibre with a view to the preparation of microendoscopes.
Endoscopy and in particular microendoscopy enables a medical practitioner to acquire information or images of internal parts of the human body, such as the stomach, lungs, heart, blood vessels or eye.
An apparatus for performing such a procedure is diagrammatically shown in
FIG. 1
, where reference
2
designates a light source focussed by a lens
4
at the entrance end of a light guide
6
. The latter is usually connected to a plurality of optical fibres
8
,
10
located on the periphery of a multicore fibre
12
. Thus, an illuminating beam
14
can be directed onto an area
16
of an organ to be observed, which reflects radiation
18
onto a lens
20
connected to the entrance end of a multicore fibre
12
. As the latter has a coherent bundle of individual cores, the latter consequently transmit the light in an ordered manner between them and the image obtained at the exit end
22
of the multicore fibre corresponds to the image formed at its entrance end. Means for storing, analyzing and/or representing the image can also be provided in combination with this apparatus.
This imaging procedure is e.g. described in the articles by A. Katzir: “Optical fibers in medicine”, Scientific American, vol. 260 (5), pp 120-125, 1989 and “Optical fiber techniques (medicine)”, Encyclopedia of Physical Science and Technology, vol. 9, pp 630-646, 1987.
FIG. 2
illustrates the presentday production of the lens-multicore fibre assembly. A metal tube
24
maintains the lens
20
in front of the multicore fibre
12
and an adhesive
26
ensures the optical continuity and prevents the lens from passing out of the tube
24
. This procedure gives good results, but has the disadvantage of requiring difficult manipulation, of reducing the optical quality by introducing a supplementary medium
26
between the lens and the multicore fibre and of making the endoscope very vulnerable to the necessary heating-based sterilization stages. Moreover, bonding takes place blind in the tube
24
and without any accurate control. In view of the tolerances of the tube, the bonding action is random and very variable.
In general terms, the assembly or splicing of two optical components or an optical component and a substrate by bonding also suffers from a certain fragility and is not compatible with high or very high temperature uses, particularly when a sterilization is necessary.
U.S. Pat. No. 5,208,885 describes a process for producing a connection between a waveguide on a substrate and an optical fibre. A glass paste, whose melting point is lower than the temperature to which the waveguide can be heated is applied to the optical fibre and/or to the waveguide. The glass paste is heated in order to bring about the connection between the fibre and the waveguide.
More specifically, the glass can consist of a borosilicate-aluminium-lead mixture and heating can be brought about using a laser, e.g. a CO
2
laser or an excimer laser.
The procedure described in this document does not solve the optical problems, i.e. the optical deterioration and disturbance to the beam when the latter has to traverse the glass connection. The implementation of this procedure with a view to producing an imaging device, e.g. an endoscope is consequently impossible. Moreover, the application given relates to a weld between materials (made from glass) having similar compositions (SiO
2
/Si substrate with a weakly doped SiO
2
fibre) melting at high temperatures, which provides the choice for the weld of multiple glass compositions melting at lower temperatures, as well as different production procedures.
The material adopted in said document for the weld (glass paste) is difficult to dose due to the evaporation of the binder, which considerably modifies the volume thereof.
The paste can also undergo chemical deteriorations making it inappropriate for use in optics. Moreover, the homogenization necessary for reducing diffusion involves a temperature rise up to 1000° C., which is unacceptable when certain optical components have to be contacted or welded to one another.
Finally, the use of glasses melting at low temperatures is not necessarily an advantage if their optical properties (refractive index) and thermal properties (expansion) are too different from those of the optical elements. For example, the respective expansion coefficients of a multicore fibre and a lens are respectively 5.10
−7
and 100.10
−7
.
Finally, for the implementation described in said document (plunging the end of a fibre in a glass bath) does not make it possible to carry out a precise check on the deposited glass quantity, or on the alignment of the elements to be welded prior to the melting of the layer. This procedure also involves a good wettability.
EP-678 486 (Gould Electronics) describes a process for producing a bond or a lateral coating or covering between glass-based components.
The assembly is obtained with the aid of a glass-based composition, which is heated, e.g. with the aid of a CO
2
laser or an electric arc. The wettability properties of the surfaces are essential to the assembly.
Here again, the document does
Conde Ramiro
Depeursinge Christian
Andromis S.A.
Curtis Craig
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Spyrou Cassandra
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