Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This invention relates to improvements to a
device for permanently joining together in pairs at
least one pair of optical fibers by means of a reflec-
ting surface of spherical shape. The ends of ,he fibers
are placed in one and the same plane which also contains
the center of curvature of said reflecting surface. Thus
the entire energy which leaves one fiber passes after
reflection into the fiber which is placed symmetrically
with respect to the center of curvature. This device is
described in French Patent Specification 2 441 860.
According to the present invention, the device
is improved by making use of a surface which is only
partially reflecting. It is thus possible not only to
join two fibers together in pairs but also to collect part
of the energy propagated in the fibers. This energy is
collected by transmission through said partially transpa~
rent surface and can be either detected by a photoelectric
receiver or focused on another fiber.
The splice contemplated in the present specifi-
cation for joining together at least two fibers comprisesa refracting body provided with at least one housing and
one reflecting surface having a conc~avity which is directed
towards the housing as described in the above-mentionned
patent. The splice is distinguished by the fact that said
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reflecting surface is partially transparent and permits
exchange of radiation through said surface between at least
one of the fibers located within the housing and means
located outside the refracting body.
Further advantages will become apparent upon
consideration of the following description and accompany-
ing drawings, wherein :
- Fig. 1 illustrates a splice according to the
invention as described in French Patent 2 441 860;
- Fig. 2 illustrates a splice in which part of
the energy is collected in accordance with the invention
by means of a large-area photodiode ;
- Fig. 3 illustrates a splice in which part of
the energy is collected in accordance with the invention by
means of a small-area photodiode ;
- Fig. 4 illustrates a splice in which part of
the energy coupled with another fiber is collected in
accordance with the invention ;
- Figs. 5 and 6 illustrate a splice for demulti-
plexing signals at different wavelengths ;
- Fig. 7 illustrates a splice for multiplexing
in accordance with the invention ;
- Fig. 8 illustrates an electrolytic cell for
controlling the reflection ;
- Fig. 9 illustrates an electrolytic-cell
switching assembly.
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Fig. 1 shows the principle of the splice of the
fibers Fl and F2 in accordance with French Patent 2 441 860. The
ends of the fibers Fl and F2 are applied against a plane P.
The references El, Cl and E2, C2 designate respectively
S the protective jackets and cores of the fibers Fl and F2.
The spherical reflecting surface H has a center of curvature
at 0. The two fibers Fl and F2 are placed symmetrically
with respect to said point 0 in order to ensure that the
beam 10 emerging from the exit face 11 and having an
angular aperture ~ produces after reflection from the sur-
face H a beam 20 which has the same angular aperture and
enters the fiber F2 via the entrance face 12.
According to the presentinvention, the surface H
is only partially reflecting and the fraction of incident
energy thus transmitted can be employed either for detecting
or for recoupling in a third fiber. The surface H can also
receive radiation which will be transmitted to at least one
of the ends of fibers Fl and F2.
An assembly according to the invention for
partial detection of the optical power S propagated within
the fiber Fl is shown in Fig. 2. If is the coefficient
of transmission of the surface H and if no loss is taken
into account for the sake of simplicity, a power as falls
on the detector Rl and a power (l-a) S is recoupled in the
fiber F2. If I is the current delivered by the photo-
detector Rl in respect of the power S, then a current I
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corresponds to the partial detection.
This assembly accordingly makes it possible to
collect part of the power propagated by a fiber in order
t:o detect part of the power during transmission.
In Fig. 2, there is shown one example of con-
struction of the assembly by means of a terminal E of trans-
parent material provided with the partially reflecting
spherical surface H at one end and with a cylindrical bore
for centering the fibers Fl and F2 at the other end. The
fiber ends are placed in the plane which contains the
center of curvature of the surface H.
If the receiver has a small sensitive surface
area s, the assembly according to the invention is shown in
Fig. 3. The transmitted beam is focused by a lens Ll on
the surface s of the receiver R2. As in the previous case,
the fraction aS of the incident power is detected and the
fraction (l-a) S is recoupled in the fiber F2.
According to the invention, the power aS trans-
mitted by the surface H can be utilized for recoupling in
a third optical fiber F3. This is the case of Fig. 4. A
lens L2 focuses the transmitted beam on the fiber F3 which
propagates the power aS. The assembly of Fig. 4 thus
makes it possible to distribute the optical power from one
fiber to a plurality of fibers.
In an alternative embodiment of the invention,
the power of the optical signal within the fiber F1 is
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frequency-multiplexed and contains for example the power
Sl(~l) at the wavelength ~1 and the power S2(~2) at the
wavelength ~2. The surface H has a coating which is
reflecting at the wavelength ~1 and which transmits at the
wavelength ~2' It is then possible to place a detector in
the same manner as in the assembly of Fig. 3. As shown in
Fig. 5, the detector delivers the current I2(~2) correspond-
ing to the power S2(~2). The reflected power Sl(~l) is
coupled in the fiber F2.
Fig. 6 shows a demultiplexing assembly in which
the incident powers Sl(~l) and S2(~2) are separated by the
dichroic mirror and recoupled towards the fibers F2 and F3
respectively.
The assembly of Fig. 7 also permits frequency-
multiplexing by inverse return of the light. Thus a powerS2(~2) which propagates within the fiber F3 is coupled in
the fiber Fl by means of the lens L5 and through the
dichroic mirror. The power Sl(~l) which propagates within
the fiber F2 is also coupled in the fiber Fl by reflection
from the dichroic mirror H. An additional fiber which is
separate from F3 could be combined with the fiber F2.
In an alternative embodiment of the invention,
the spherical surface H is made either reflecting or trans-
parent by electric control means.
One example of construction is shown in Fig. 8
which utilizes the known principle of electrolytic cells in
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order to carry out a display function.
The spherical surface H of the terminal E is
covered by a transparent electrode e2, a projecting
flange of which is applied against the cylindrical face of
said terminal.
An organic electrolyte 22 is enclosed by a thin
glass plate 23 and a cylindrical member 24. A ring-shaped
silver electrode el is fixed on the plate 23. A voltage V
can be applied between the electrodes el and e2 by means of
an electric control generator 100.
If the potential of the electrode e2 is negative,
the silver of the electrolyte is deposited thereon, with
the result that the spherical surface is thus made
reflecting. On the other hand, if the potential of the
electrode is positive, the silver is dissolved, is
deposited on the electrode el and the cell becomes trans-
parent.
To summarize, it may be stated that a negative
pulse of V makes the device reflecting and a positive pulse
re-establishes transparency.
One example of application in accordance with the
invention is shown in Fig. 9. A terminal El contains the
optical fibers F4 or F5 and a terminal E2 contains the
optical fibers F6 and F7. The two terminals El and E2 are
provided with electrolytic cells Cl and C2 and a lens Lg
focuses a beam emerging from the fiber F4 on the fiber F7
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and a beam emerging from the fiber F6 on the fiber F5.
If the pulse V applied to both cells is negative,
the optical power propagated within the fiber F4 is
coupled in the fiber F5 and the power propagated within the
fiber F6 is coupled in the fiber F . On the other hand,
in the case of a pOSitiye pulse, the cells Cl and C2
become transparent and coupling is obtained between the
fibers F4, F7 and F6, F5. This device therefore performs
the function of a double switch.
It is apparent that the use of an electrolytic
cell for the assemblies of Figs. 2, 3 and 4 permits
switching of a fiber to a receiver or to another fiber and
possible switching to two fibers.
In the case of the assemblies illustrated in the
drawings, it is possible as already shown in the main
patent to place within the bore of the terminal 2n fibers
which are symmetrical in pairs with respect to the center
of curvature.
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