GB2030319A - Optical fibre switching arrangements - Google Patents

Abstract

Optical coupling between two optical fibres 12 and 13 is made or broken by moving the end of fibre 13 which is supported on an elongate component 7 which can be moved by means of a magnetic field. Component 7 may be mounted at one end in the manner of an armature tongue. Preferably, the fibres are attached to the tongues of an electromagnetic relay. By providing a further stationary fibre, a change-over switch can be made (Fig. 2 not shown). <IMAGE>

Description

SPECIFICATION Optical switching arrangements The present invention relates to optical switching arrangements.

The term "optical fibre" is used herein to mean a fibre for transmitting radiation which obeys the laws of optics whether in the visible frequency range or not.

Optical communications transmission employing optical fibres (optical waveguides) requires switches which interrupt the transmission of light from one fibre to another. Light can pass substantially without loss between the ends of two optical fibres if the fibres have plane-parallel terminal surfaces and are positioned at a short distance from one another so that one fibre end is in alignment with the other fibre end, i.e. one fibre virtually represents an extension of the other.

Optical contact can be broken by movement of one fibre end out of alignment with the other fibre end. This can be effected by mechanical sliding movement of components to which the fibre ends are secured. However, a switch of this kind requires both that the supports and sliding surfaces be accurately adjusted and that large masses are moved. This results in an expensive construction and reduced operating reliability as malfunctions can occur due to wear.

The magazine "Electronic letters" 12/15 (1 975), page 388 describes a changeover switch by means of which optical contact between one fibre end and another can be broken and switched over to another fibre end. This switch consists of a glass tube into one end of which are cemented two parallel optical fibre ends of equal length. An optical fibre which is to be switched over between the two first optical fibres is cemented into the other end of the glass tube, and this fibre end extends through a nickel sleeve. A magnet arrangement for producing a variable magnetic field is arranged on the glass tube so that it is possible by changing the external magnetic field to move the fibre end which is supported by the nickel sleeve out of alignment with one fibre end and into alignment with the other of the two firstmentioned fibre ends.

In this switch, the support for the mobile glass fibres is not moved mechanically along sliding surfaces. This reduces wear, but means that the fibre is not well supported over a long section so that the arrangement is extremely sensitive to both its orientation and to vibration.

For many purposes, e.g. in monitoring devices for optical fibres, switches are however required which are characterised by a high degree of operating reliability and simple construction. In contrast, the requirements regarding switching times, crosstalk attenuation and transfer losses between the fibre ends when the contact is closed are of subordinate significance.

According to the invention, there is provided an optical switching arrangement comprising a first and a second optical fibre, the first fibre being mounted at its end on a movable elongate support member which is mounted atone end only and is at least partially of magnetic material, the support member being movable with the first fibre by a magnetic field between one position in which said first and second fibres are in axial alignment at least at their ends so that they are optically coupled together and another position in which the fibres are not optically coupled together.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example to -the accompanying drawings in which: Figure 1 schematically illustrates a laboratory model of an on/off switch; and Figure 2 schematically illustrates a change-over switch.

Figure 1 shows a switch containing a magnetic coil 4 which is driven via a control line 3 and is arranged in a housing 1 which preferably consists of plastics material and is provided with an easily attached, dust-tight and water-tight cover 2. A nickel-iron-core 5 of coil 4 carries a substantially rigid contact tongue 6 acting as a stop means. In the region of the magnetic flux of the magnetic coil 4 and its core 5 there is arranged a mobile ferromagnetic contact tongue or armature tongue 7 which may be produced from the nickel-iron alloy Vakuvit. One end of this contact tongue 7 is secured to the housing 1, whereas the other end 8 carries a longitudinal slot.This movable slotted end 8 extends towards the rigid contact tongue e and, although tongue 7 overlaps tongue 6 at its end region, when the magnetic coil is de-excited, it adopts a position above the plane of tongue 6 at a distance h which corresponds to the travel of the moving contact tongue 7. When the magnetic coil 4 is excited, tongue 7 moves towards the rigid tongue 6 and strikes against the latter. These components are already contained in a commercially available Reed contact, e.g. the "SG-Gm-contact C 39209-A 26-A 3" contact produced by Siemens Aktiengesellschaft. The only difference to this commercially available Reed contact is that the glass casing and shield gas filling have been dispensed with.Furthermore in the illustrated laboratory model, in order to achieve a greater travel, the mobile end of the contact tongue 7 has been lengthened by cementing the contact tongues onto glass plates 9 and 1 9 which form a bridge. It is, however, possible to omit the glass plates 9 and 10.

Furthermore, the contact tongues 6 and 7 may be arranged inside the coil body. In this case, the coil body and possibly the rigid tongue 6 can serve as a protection means and as a housing.

Two optical fibres 12 and 13 which are to be switched lead into the housing 1 and corresponding plugs 1 The end of fibre 12 is directly cemented onto the rigid tongue 6. Fibre 13 extends along mobile tongue 7, is guided by the longitudinal slot in end 8 of tongue 7, and is positioned by crossbars 1 4 and 1 5. The positioning is such that when the contact is in the open state this fibre end is out of alignment with the line 16 of the fibre 12 by an amount corresponding to the length of travel, whereas when the contact is closed, (i.e. when the mobile slotted contact tongue end 8 strikes against the contact tongue 6), it is in a position of alignment.

The terminal surfaces of the fibre ends are such that in this closed, aligned position they are plane parallel to one another and are spaced from one another only by a short distance d. The tongue 6 can also advantageously contain a longitudinally directed guide groove to receive the fibre end 12.

In mass production, these guide grooves can be produced photolithographically by thick-film technology.

The illustrated laboratory model had a spacing dof about ten microns and a travel distance h of about 1 50 microns. Gradient index fibres having an outer diameter of 1 30 microns and a numerical aperture of about 0.15 were. used as light conducting fibres 12 and 13, but stepped index fibres are also suitabie for this purpose. A cyanolite adhesive was used to attach the fibres to respective contact tongues. The crosstalk attenuation (switching attenuation) of the switch amounted to 39.2 dB over 10,000 switching cycles. As the adhesive used results in a certain degree of light scattering at the fibre ends, but was worn away at the fibre ends during the course of the continuous experiment, the crosstalk attenuation improved over the course of the experiment.In the first experimental switch of this type the transfer loss at the gap d amounted to 8.7 dB, but was improved to 0.5 dB by careful adjustment of the fibres.

For this switch the duration of the switch-on process was about 20 ms. After this switch-on time, the fibre ends which, during switch-on chatter, are initially still moved towards one another, are at rest and no further fluctuations in light transmission occur. Where any fluctuations were noticed, these could be traced to mechanical vibrations of the portions of fibre located outside the switch and to fluctuations in intensity of the irradiated light.

Although crosstalk attenuation and switch-on time can be further improved by further optimising the switch, these experimental results are themselves adequate for many applications e.g. in monitoring devices.

As described, the armature tongue 7 abuts against a stop means 6 when the contact is closed in Figure 1. It is also possible to provide a second stop means against which the armature tongue abuts when the contact is open.

The armature tongue 7 forms a supportforthe movable optical fibre and reduces vibrations thereof. By means of the stop means, it is possible to provide determinate opening and closing positions.

In Figure 1 , the stationary optical fibre end is supported by the stop means 6. This may be achieved by cementing or otherwise securing the two fibre ends to the armature tongue and the stop means respectively so that when the contact is closed their plane-parallel terminal surfaces lie opposite one another in alignment in the desired manner. The fibre ends can be cemented along the entire length of the suppOrts, but at least a sufficient number of attachment points are provided to ensure that the fibres do not vibrate to any noticeable extent on the supports.

The magnetic coil 4, armature tongue 7 and stop means 6 may be constructed as in an electromagnetic relay.

Commercially available electromagnetic relays can be used to construct the switching arrangement without the need to provide a separate electrical circuit -- i.e. the armature and stop means do not require to carry a flow of electrical current. Electrical current flow of this kind is only provided where an electric contact is to be opened and closed together with the optical coupling. Generally speaking, the armature tongue and the stop means merely serve to support the fibre ends which are to be optically coupled. It is advantageous to use electromagnetic relays operating in accordance with the so-called Reed contact principle, in which case however, it is possible to dispense with a shield gas provided electrical make and break contacts are absent.

In the case of Reed relays the armature tongue and the stop means are composed of a magnetic material. Frequently, one contact tongue, (the stop means) is rigid whereas the other contact tongue, the armature tongue, constitutes a spring clamped at one end and movable by a magnetic field against its resetting force. The two contact tongues are connected to the core of the magnetic coil in such a way that when the coil is energised the tongues are magnetised and abut against one another so that the contact is closed.When the magnetic coil is de-energised, the mobile tongue end lifts up from the rigid tongue end, the amount of movement of the mobile tongue determines the switching attenuation (crosstalk attenuation) since the passage of light from one fibre end into another is more effectively suppressed the greater the distance between the lines of alignment of the two fibre ends when separated.

Thus, when Reed relays of this kind are used, the entire mobile contact tongue is formed as a metal component which is moved by the magnetic field and which is mounted at one end by clamping. If special spring characteristics are desired which cannot be attained by magnetisable materials, it may be advantageous to manufacture the mobile armature tongue partially from a different material and to construct only the end of the mobile contact tongues of magnetic material movable by a magnetic field. Under certain circumstances, it may be advantageous not to clamp the armature tongue, but, for example, to hinge it.

A switch of this kind may be used as a changeover switch in order selectively to form optical contact between a mobile fibre end and one of two other fibre ends. For this purpose, the armature tongue and the fibre end which it supports can be moved between two stop means.

The two other fibre ends are supported, e.g. by respective stop means, in such manner that when the armature tongue strikes against either of the two stop means the mobile fibre end is aligned at a short distance opposite a respective fibre end.

Figure 2 schematically illustrates the contact tongue ends and the fibre ends attached thereto in a change-over switch. One contact portion 20 of the switch is provided on its upper side with a stop means 21 composed of a non-magnetic metal, e.g. brass, and on its lower side with a corresponding stop means 22 composed of a ferro-magnetic metal, e.g. iron-nickel. Two fibre ends 25 and 26, which are separated from one another by a spacer 24, pass through a longitudinal groove 23 in this contact portion 20 so that their ends project into the interspace between the two stop means in parallel and to an equal length.

Projecting into this interspace from the opposite side is the end of a mobile, ferromagnetic contact portion 27 on which a light-conducting fibre end 28 is secured and which carries a lateral arm 29. The contact portion 27 and the stop means 22 are subjected to the magnetic field of a magnetic coil (not shown) as a result of which the portion 27 can be moved. When the magnetic coil is de-energised, arm 29 strikes against the fixed stop means 21 so that the fibre end 28 comes into alignment with the fibre 25. When the magnetic coil is energised, however, the contact portion 27 abuts against the lower stop means 22 and the fibre end 28 comes into alignment with the other fibre end 26. In this way it is possible selectively to form optical contact between the fibre 28 and either fibre 25 orfibre 26.

Claims (13)

1. An optical switching arrangement comprising a first and a second optical fibre, the first fibre being mounted at its end on a movable elongate support member which is mounted at one end only and is at least partially of magnetic material, the support member being movable with the first fibre by a magnetic field between one position in which said first and second fibres are in axial alignment at least at their ends so that they are optically coupled together and another position in which the fibres are not optically coupled together.

2. An arrangement according to claim 1 wherein said support member is entirely of metal.

3. An arrangement according to claim 1 or 2 wherein said support member comprises an armature tongue and a metal component.

4. An arrangement as claimed in any one of claims 1 to 3 wherein a magnetic coil is provided for producing said magnetic field.

5. An arrangement as claimed in any one of claims 1 to 4 wherein said support member abuts against a stop means when in said one position.

6. An arrangement according to claims 4 and 5 wherein the magnetic coil, armature tongue and stop means are designed as in an electromagnetic relay.

7. An arrangement according to claim 5 or 6 wherein said second fibre is supported by the stop means.

8. An arrangement according to claims 6 and 7 wherein the armature tongue and the stop means are respective contact tongues.

9. An arrangement as claimed in any one of claims 1 to 8 wherein there is provided a further fibre at a position for optical coupling with said first fibre when the support member is in said another position thus providing a change-over switch.

10. An arrangement according to claim 9 when dependent on claim 5 wherein said support member abuts a further stop means in said another position.

11. An arrangement according to claim 10 wherein said further fibre is mounted on said further stop means.

12. An arrangement as claimed in any one of claims 1 to 11, wherein the fibre ends are secured in guide grooves in their respective supports.

13. An arrangement as claimed in claim 9, wherein the guide grooves are produced photolithographica Ily by the planar thick film technique.

1 4. An optical switching arrangement substantially as hereinbefore described with reference to Figure 1 orto Figure 2 of the accompanying drawing.

1 5. Switch for opening and closing an optical contact between two light conducting fibres which are arranged opposite one another in alignment, wherein at least one fibre end is supported by a metal component which can be moved by a magnetic field in contact-free fashion, and, in order to open the contact, is moved out of alignment with the other fibre end by a change in the magnetic field, characterised in that the metalcomponent is secured to an armature tongue which is mounted on one side, and the light conducting fibre which is held at its end on the metal component is supported by the armature tongue.