FR2525777A1 - Fibre=optic transmission line lateral or transverse coupler - has polished plane surface cut into fibre and inclined w.r.t. axis to form notch with 45 degree angle - Google Patents

Abstract

The plane surface is one of the faces of a notch (3) cut in the fibre and making an angle of 45 degrees with its axis. The notch is covered by a cap (4) in a varnished shield leaving a bubble of air in the volume of the notch. An axial light beam (5) is totally reflected by the polished surface and leaves the fibre, transversally (6). For application of the coupler to a fibre-optic transmission line, a series of couples spaced one from the other are arranged along the fibre, each coupler having associated with it a signal emitter or receiver. For the direct coupling of two fibres each having a coupler, the fibres are placed parallel to one another with the l- couplers opposite each other on opposing regions of the fibres. In a liq. level indicator using the coupler, the polished surface forms a bevelled end of the fibre which is placed vertically w.r.t. the liq. surface, and a light source is placed at the level of the bevel and opposite it.

Description

LATERAL OR TRANSVERSE COUPLER FOR OPTICAL FIBERS
The present invention relates to a lateral, or transverse, coupler for optical fibers.

 The object of the invention is to provide a simple means of bringing light into or out of an optical fiber intended for the transmission of information.

 Naturally, the same means can be used for the simple transmission of a luminous flux for lighting purposes.

 Currently, if we only use the ends of an optical fiber as interfaces, we limit ourselves to direct transmission between a transmitter and a receiver.

If you want to make a driver or "bus" serving several stations, you must with current technology:
break the continuity of the fiber
introduce complex and expensive devices into the cutout, such as separators, T, X, star couplers.

 Thus, in the case of a single transmitter having to serve two receivers, a single fiber starting from this transmitter will be connected by a connector to a branch of a T-coupler whose two other branches will be respectively connected by two connectors to two others fibers each leading to one of the receptors.

 In this type of assembly1 one encounters difficulties linked to the thinness of the optical fibers and to the mechanical precision required by the optics.

 To get rid of the use of these complex components and. tricky implementation, a usual solution is to use only point to point links, multiplexing being rejected in the electrical field.

 Thus, for the solution of the previous problem, the outgoing transmitter is connected by optical fiber to a relay receiver, the latter electrically exciting two secondary transmitters each linked by an optical fiber to one of the two terminal receivers.

 The present invention proposes to provide another simpler solution in which in particular a single optical fiber can be used directly and without break in continuity for the connection of a transmitter with any number of receivers, this fiber being provided for this purpose with several lateral couplers according to the invention.

 These couplers according to the invention also make it possible, as will be seen below, to simply carry out a large number of applications such as, in the field of data transmission: coupling of fibers or mixing and separation of beams for example , or, in the field of lighting: flat side lighting devices, or presence indicators, or between liquid level detectors.

 A lateral coupler, according to the invention, for optical fiber is characterized in that it consists of a polished flat surface, inclined relative to the axis of the fiber, and extending over at least part of the cross-section of this fiber.

 Preferably the flat surface is one of the faces of a notch made in the fiber and makes an angle substantially equal to 450 with the axis of the fiber.

 According to another embodiment, the notch is covered with a plug in a protective varnish leaving an air bubble in the volume of said notch.

 In the application of the coupler according to the invention to a signal transmission line constituted by an optical fiber, a series of couplers spaced from each other being provided on said fiber, each of the couplers is associated with a transmitter or a receiver of signal.

For the direct coupling of two fibers using couplers according to the invention, the two fibers are arranged parallel to each other and each comprise a coupler, these two couplers being arranged (e.g.

 head-to-tail) opposite one another on the opposite regions of the fibers.

 In a level indicator using a coupler according to the invention and in which the polished surface constitutes a terminal bevel at the end of the fiber, the fiber can be arranged vertically with respect to the surface of the liquid and a light source is placed at the level of the bevel , opposite this one.

 As a variant, a second optical fiber also comprising a bevel is arranged transversely to the first so that the bevels are parallel to each other and slightly spaced.

The characteristics and advantages of the invention will become more apparent from the following description, given solely by way of example, with reference to the accompanying drawings in which
- Figure 1 schematically illustrates, in perspective, an embodiment of the non-axial coupler according to the invention
- Figure 2 is a side view, partly in section, of the coupler of Figure 1
- figilJcs 3 tt 4 schematically show two uses of the coupler according to the invention, for reception and for transmission respectively
- Figure 5 is a diagram of a "serial" transmission between a transmitter and several receivers
- Figures C a 8 show various arrangements of the coupler according to the invention used in bidirectional coupling ("full-duplex");
- tcs Figures 9 and 10 show applications of the coupler according to the invention to the constitution of a mixer or a separator, respectively;
- tcs Figures 71 and 12 illustrate an application of the coupler according to the invention for direct coupling between optical fibers, parallel or perpendicular respectively
- Figures 13 14 and 15 show the use of the coupler according to the invention in the field of lighting, for flat lighting in an endoscope, or to constitute a presence indicator
- ic figu 16 ct Zz illustrate the application of the coupler according to the invention to the production of a liquid level detector
- Your Figure 18 is a detail view, in section, of the embodiment
practice of this detector.

 In the embodiment chosen and shown in Figures 1 and 2, the coupler according to the invention, housed directly on a cylindrical optical fiber 1, consists of a polished flat surface 2, inclined relative to the axis of the fiber, this surface 2 being, in this example, one of the faces of a notch 3 formed in said fiber. In the example shown, the depth of this notch is less than half the diameter of the fiber. To protect the polished face 2 of the notch from air, it is protected by a plug 4 of a protective varnish, covering the notch and leaving an air bubble in the volume of said notch .

 The coupler according to the invention ensures total reflection of a light beam 5 channeled axially in the optical fiber 1 and meeting the surface 2, this beam leaving transversely of the fiber at 6.

 Naturally, if we want to ensure an exit of the beam at right angles to the axis of the fiber, the surface 2 must be inclined at 45 relative to the axis, but in this case, so that the total reflection takes place, the refractive index of the material of the fiber must be sufficiently high.

 Plastic optical fibers lend themselves particularly well to the implementation of the invention because, compared to glass fibers, they ot a relatively large diameter, allowing their manipulation; moreover the polish of the reflecting face can be obtained by surface fusion by means of a heating tool, for example. Yet another advantage, in particular in the latter case and in particular if the notch has only a limited depth, lies in the fact that this notch does not cause the initiation of rupture.

 FIG. 3 shows the coupler according to the invention used to allow the exit of a part intercepted by the face 2 of the beam 5, substantially perpendicular to the axis of the beam, at 6, towards a receiver 7, the rest of the beam n not being deflected.

 The optical fiber 1 is surrounded by a mechanical sheath 8 and is stripped locally from this sheath to allow the realization of the coupling notch.

 In FIG. 4, the coupler according to the invention is used to allow the introduction of a beam 9, coming from a transmitter 10, into the fiber 1, perpendicular to the axis of the latter and opposite of the coupler, this beam reflected by the face 2 after radial crossing of the fiber, being channeled at 11 therein.

 Thus, the coupling notch according to the invention makes it possible either to deflect a part of the light rays passing through the fiber towards the outside, or to inject light into the latter, light from an external source. It will be noted that the fiber behaves like a cylindrical lens for the transverse rays and ensures good directivity to the external light beam (fig. 3).

 It is possible to arrange a succession of couplers 2 on a fiber 1 (FIG. 5) and to associate with each of these couplers a receiver 7, a single transmitter 12 supplying the fiber with light signals.

 Each transmitter (or source) and receiver can be deposited directly on the surface of the fiber and beech held there by a sleeve, which can also ensure the rigidity of the fiber and avoid breaking by stress at the level of the notch.

 A coupler according to the invention can also be used as a bidirectional coupler (full duplex) as shown in fig. 6.

 A transmitter 14, for example a light emitting diode (LED) transversely injects a signal reflected along the axis of the fiber, while the adjacent end of the fiber is associated with a receiving photodiode 15, the whole being housed in a box 16.

 A simpler version is shown in FIG. 7, and in a variant of FIG. 8, the end of the fiber cut at a bevel at 17 reflects the beam towards the photodiode 15.

 One can also use two neighboring couplers 2 each directed towards one end of the fiber 1 to inject in the two directions of this fiber the light coming from a single emitter 18 (Fig. 9), or on the contrary, to collect on a single receiver 19 light from both ends of the fiber (Fig. 10).

 In the same field of application, by judiciously arranging (e.g.

head to tail), facing each other, two couplers according to the invention each arranged on a fiber, the two associated fibers being arranged parallel to each other, it is possible to pass a light signal d 'one fiber in the other (Fig. 11), the couplers being arranged on the opposite faces of the fibers.

 The same type of coupling can take place between two fibers arranged perpendicular to each other (Fig. 12), the beam leaving one of the fibers axially, attacking the other fiber transversely and being reflected on a coupler according to the invention along the axis of this other fiber.

 In a field more specifically relating to lighting, a bevel 20 directly formed at the end of a fiber 1 makes it possible to bring to this end the light from a source 21 disposed at the other end of the fiber (FIG. 13 ); the bevel 20 being adjacent to the end of an endoscope 22, a very flat lighting device is thus produced.

 The bevel 20 is advantageously cut with a cutting angle a greater than 45 "(Fig. 14): this gives better reflectivity and provides lighting in front of the end of the endoscope.

 Many other applications are possible: for example, the light of a lamp 23 placed opposite the bevel 20 of a fiber 1 (FIG.

15) is transmitted to the eye of an observer 24, or not, depending on whether an object 25 releases or masks this lamp: this constitutes a witness of the presence of an object. Similarly, a liquid level indicator can be produced in the manner indicated in FIGS. 16 to 18,
An optical fiber i, the end of which is cut to form a reflecting face 2, is arranged vertically above the surface 26 of a liquid and a lamp 27 is arranged opposite the bevel opposite the face 2. When the bevel is out of the liquid in the air, the light from the lamp is channeled into the fiber (Fig. 16).

 When the level of the liquid rises and the bevel is immersed, the difference between the refractive indices of the fiber material and of the liquid is small enough so that there is no longer any reflection on side 2 and the light passes pr2tiqurmer.te whole through this face (Fig. 17). There is no longer any transmission of light through the fiber 1, and so depending on whether the upper end of the latter is lit or not, it is known that the level of the liquid is located below or above the bevel.

 The device can be completed by means of a second optical fiber 30, also comprising a bevel placed parallel opposite the first and slightly spaced therefrom (fiber shown in broken lines in FIGS. 16 and 17).

 Depending on the level of the liquid, the light from the lamp is either channeled into fiber 1 (Fig. 16), or transmitted to fiber 30 and channeled therein (Fig. 17).

 FIG. 18 schematically illustrates an embodiment of a level indicator device.

 In the plastic casing 31 of a light-emitting diode, the light source 27, constituted by a light-emitting diode, illuminates the bevelled end of the fiber 1. An axial opening 32 allows the possible positioning of the second fiber 30 or the evacuation of the liquid.

 The coupler according to the invention does not claim to have very good performance in terms of yield and insertion losses.

 On the other hand, it is distinguished by its reciprocity and also its direction.

 It allows the removal of optical connectors, which, added to its low manufacturing cost, results in a great economy of use.

 We can provide a final assembly of the fiber with its couplers and we then have a ready-to-use component, but we can also provide an assembly "on the ground" from the raw fiber.

 Of course, the present invention is not limited to the embodiments described and shown and it is capable of numerous variants accessible to those skilled in the art, without departing from the spirit of the invention. 'invention.

Thus, to effect the transfer of a light signal from a first fiber to a second parallel fiber 1, as shown in FIG. 11, it is possible to arrange the face 2 of the coupler of the second fiber in two different positions relative to the side 2 of the first fiber. In the position shown in Figure 11, the faces 2 are parallel and located on opposite sides of the fibers and the light signal passes from one fiber to another without changing direction. By placing the faces 2 in a specular position relative to the contact line of the two fibers 1, the light signal is passed from one fiber to the other by reversing its direction in the second fiber.

Claims (8)

 1.- Lateral coupler for optical fiber, characterized in that it consists of a polished flat surface (2), inclined relative to the axis of the fiber (1), and extending over at least part of the section of this fiber.  2.- Coupler according to claim 1, characterized in that the planar surface (2) is .'one of the faces of a notch (3) formed in the fiber (1).  3. Coupler according to claim 2, characterized in that the notch (3) is covered with a plug (4) in a protective varnish leaving an air bubble in the volume of said notch.  4. Coupler according to any one of claims 1 to 3, characterized in that the planar surface (2) makes an angle less than or equal to 45 "with the axis of the fiber.  5.- Application of the coupler according to one of claims 1 to 4 to a signal transmission line constituted by an optical fiber, this line being characterized in that a series of couplers (2) spaces from each other being provided on said fiber, a signal transmitter or receiver is associated with each of the couplers.  6.- Device for the direct coupling of two fibers using couplers according to one of claims 1 to 4, characterized in that the two fibers are arranged parallel to each other and each comprise a coupler (2), these two couplers being arranged head to tail, facing one another, on the opposite regions of the fibers (1).  7.- liquid level indicator using a coupler according to claim 1, the polished surface then constituting an end bevel at the end of the fiber, characterized in that said fiber (1) is disposed vertically with respect to the surface (26) of the liquid and in that a light source (27) is placed at the level of the bevel (2), opposite the latter.  8. An indicator according to claim 7, characterized in that a second optical fiber (30) also comprising a bevel is disposed transversely to the first so that the bevels (2) are parallel to each other and slightly spaced.