Optical waveguides – Integrated optical circuit
Reexamination Certificate
1997-04-18
2001-04-03
Bovernick, Rodney (Department: 2874)
Optical waveguides
Integrated optical circuit
C385S129000, C385S130000, C385S132000
Reexamination Certificate
active
06212307
ABSTRACT:
TECHNICAL FIELD AND PRIOR ART
The invention relates to an integrated optical stray light filtering device.
The invention applies to any integrated optical device, particularly in the field of optical microsystems, e.g. for telecommunications, or in the field of integrated optical microsensors.
Such a device incorporates an optical microguide, which is defined by a core known as the microguide core between two media, whose respective refractive indices are lower than the refractive index of the microguide core.
Thus, by definition, such a guide structure results from the superimposing of three media, the intermediate medium (the core) having a refractive index higher than that of the two other media. A microguide is a particular guide structure, whereof at least one of the three media constituting the guide structure is laterally limited (e.g. by etching) in order to ensure a lateral light confinement.
An integrated optical device incorporating a microguide is diagrammatically shown in plan view in FIG.
1
. The device is designated overall by the reference
2
and has a microguide
4
extended by two microguides
6
and
8
. The illustrated device also has an input connection
10
and output connections
12
,
14
.
The input connection can be connected to one or more light sources optionally incorporating focussing means or, as shown in
FIG. 1
, an optical fibre
16
permitting the formation of a flexible link between a light source and the device
2
. At the output, the light can be coupled to optical fibres
18
,
20
or to detectors, i.e. in general terms to light collection means. The connection between the sources or fibres, or the collection means takes place by positioning these various elements in front of input or output microguides. Different methods have been produced for obtaining such connections, one being described in FR-A-2 659 148.
However, the alignment always takes place with a certain tolerance, which is consequently not perfect. Thus, particularly at the input of the integrated optical device, there is always a slight light loss. This is represented in
FIG. 1
, where the rays or beams
22
,
24
represent the stray light escaping from the input fibre
16
in the integrated structure
2
. This stray light is in most cases confined in the guide structure and propagates therein. It generally undergoes reflections and will interfere with the useful signals sampled by the collection means (fibres
18
and
20
in
FIG. 1
) at the output of the microguides
6
,
8
. This effect is far from being negligible and is greater in integrated optics than in conventional optics, because the light there is wholly or partly confined in the plane of the guide structure of the device. At present no method exists making it possible to obtain freedom from said stray light, so that there is a deterioration to the operating quality of the device, particularly in terms of signal-to-noise ratio in the case of integrated optical sensors.
DESCRIPTION OF THE INVENTION
The invention relates to an integrated optical device having an optical microguide of index n
0
between two layers of respective refractive indices n
1
and n′
1
such that n
1
<n
0
and n′
1
<n
0
, and filtering means constituted by at least one reflector element placed on at least one side of the microguide, the reflector elements having at least one element etched in the layers of index n
1
and/or n′
1
and/or n
0
.
These filtering means are able to filter by reflection the stray light propagating in the device in the vicinity of the microguide.
More specifically, the layers of indices n
1
and n′
1
in each case define a plane on either side of the microguide. The filtering means etched in the layers of indices n
1
and/or n′
1
and/or n
0
permit the filtration of the stray light propagating “horizontally”, i.e. in the plane of the microguide and/or layers of indices n
1
and n′
1
.
The reflector elements are produced in the media of refractive index n
1
and/or n′
1
and/or n
0
and can consequently be produced during the production of the integrated optical structure. In addition, such reflector elements can advantageously be placed in the vicinity of output connections of the integrated optical device, so as to reflect light liable to interfere with possible light recovery or collection means. However, such elements can also be placed at the input of the device or at any other location requiring stray light filtering.
Reflector elements can be placed on either side of the microguide, thus ensuring a filtering of the light of the two sides of the microguide.
One face of the reflector element or elements can be covered with a reflecting layer, made from a material incorporating gold, chromium, aluminium, platinum, silver, copper or a dielectric material.
In order to improve the filtering efficiency, the device can incorporate at least two reflector elements arranged in succession, e.g. in a direction parallel to the optical microguide of index n
0
.
The reflector element or elements can be oriented perpendicular Cc) the microguide direction and can also be inclined with respect to the microguide axis.
In particular, when the device also has an element for collecting the light carried by the microguide, said collection element having an acceptance angle &agr;
C
, the reflector element can advantageously be inclined with respect to the microguide axis by an angle
β
<
π
2
-
α
c
-
arcsin
(
n
3
n
2
)
,
where n
3
is the index of the medium forming the reflector and n
2
the effective index of the structure surrounding the microguide, where the reflector is produced.
According to an embodiment, the reflector element contains air of index 1.
If the collection element is an optical fibre with a core of index n
4
and a cladding of index n
5
, we obtain:
α
c
=
arcsin
(
n
4
2
-
n
5
2
)
.
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patent: 4773063 (1988-09-01), Hunsperger et al.
patent: 4781424 (1988-11-01), Kawachi et al.
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patent: 5182787 (1993-01-01), Blonder et al.
patent: 5263111 (1993-11-01), Nurse et al.
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patent: 5473721 (1995-12-01), Myers et al.
patent: 5664032 (1997-09-01), Bischel et al.
patent: 5710854 (1998-01-01), Myers et al.
patent: 5742045 (1998-04-01), Parker et al.
patent: 5940548 (1999-08-01), Yamada et al.
patent: 0 397 337 (1990-11-01), None
patent: 2 659 148 (1991-09-01), None
patent: 2 223 860 (1990-04-01), None
patent: 0144608 (1986-07-01), None
patent: 0269129 (1988-11-01), None
patent: WO 95/34010 (1995-12-01), None
Patent Abstracts of Japan, vol. 14, No. 274 (P-1061), Jun. 13, 1990, JP-02-081005, Mar. 22, 1990.
Labeye Pierre
Pouteau Patrick
Bovernick Rodney
Commissariat A l'Energie Atomique
Kim Ellen E.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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