GB2176023A - An optical switch or sensor - Google Patents

Abstract

An optical switch or sensor may be formed from a single bimorph member bimetallic strip or bimagneto strictive which is formed with a slot 9 which divides it into two parts. A mounting member is moulded on to the free ends of each bimorph part and may be divided into two by the same slot as divides the two parts of the bimorph. Optical fibres 16 may be located in grooves on the mounting member. In operation signals are applied to the bimorph parts so as to make them bend simultaneously in opposite directions. The amount of movement may be limited by the widths of saw-cuts 14 so as to ensure that in each switching position the optical fibres line up with each other. <IMAGE>

Description

SPECIFICATION An optical switch or sensor This invention relates to an optical switch or sensor.

It has previously been proposed to construct an optical switch by arrangement an optical fibre so that it can be moved between positions where its end is in alignment with the end of one of two further optical fibres. One technique for doing this is described in Applied Optics 15th November, 1978 Volume 17 Number 22. A similar technique is described in Electronic Letters 23rd October, 1980 Volume 16 Number 22. In this known, technique the movement of the optical fibre is effected by securing it to a piezoelectric "bender" which is a piezoelectric member with electrodes attached and arranged so that expansion and contraction of one side or surface is restrained thereby causing the member to bend when a suitable voltage is applied across the electrodes. This bending movement is transferred to the movable optical fibre to produce the switching effect.The preferred form of bender is a so called "bimorph" in which the means for restraining expansion and contraction includes another piezoelectric member or layer. In a bimorph the two piezoelectric members or layers are arranged so that when one expands in a given direction the other contracts in the same direction thus accentuating the bending action.

A disadvantage of the type of optical switch described above is that it requires a considerable voltage to drive it. Another problem is that the bimorph expands and acontracts with temperature variations and this can cause misalignment of the fibres. In this connection it is explained that the alignment needs to be maintained to within about 2 microns in some cases.

According to this invention there is provided an optical switch or sensor comprising first and second optical conductors mounted on respective piezoelectric benders and means for applying voltages to different benders so that they bend simultaneously in opposite directions, thereby bringing or tending to bring the optical conductors into and out of alignment with each other.

It can readily be appreciated that the use of two bimorph members arranged to bend in opposite directions can double the sensitivity of the device enabling a smaller voltage to be used. It can also ensure that both optical conductors are affected equally by temperature variations of the bimorph.

The two bimorph members can conveniently be made by forming a slot in a single bimorph member and then removing part of each outer electrode so that opposite voltages can be applied to the two halves.

Preferably the optical conductors are secured to the bimorph members by apply a single mounting member, e.g., by moulding it in position, and then splitting the mounting member into two parts, each attached respectively to one of the bimorph members. In this arrangement the mounting member is adapted to hold the optical conductors in a specified position and may be formed with grooves for this purpose. In this way it can be ensured that the optical conductors are correctly aligned in the finished product.

The idea of aligning the optical conductors in this way is considered particularly advantageous since the problem of alignment is a very serious one in the arrangements as described in the papers previously referred to. Thus, according to another aspect of this invention there is provided a method of making an optical switch comprising first and second optical conductors mounted on respective first and second members at least one of which is of the type which includes two layers which canbe made to undergo relative expansion and contraction thereby causing the member to bend and thereby bringing or tending to bring the optical conductors into or out of alignment; in which method the conductors are mounted on material forming or to form the first and second members by applying to it a single mounting member carrying or adapted to carry the optical conductors, and then splitting it into two parts each attached respectively to a part of the material which forms or is to form the first and second member.

Two ways in which the invention may be performed will now be described by way of example with reference to the accompanying drawings in which; Figure 1 illustrates an optical switch constructed in accordance with the invention for switching a light from one optical fibre between two further optical fibres; and Figure 2 illustrates a cross-over switch also constructed in accordance with the invention.

Referring to Figure 1, the illustrated switch comprises a bimorph 1. The principle of operation of a bimorph is described in a paper entitled "Bender Bimorph Scanner Analysis" by J.J. Shaffer and D.L. Fried, Applied Optics April 1970 Volume 9 Number 4. It comprises two layers 2 and 3 of piezoelectric material on which outer conductive layers 4 and 5 are deposited. They are separated by a third conductive layer 6. The piezoelectric layers 2 and 3 are poled in opposite directions so that when a voltage is applied between the electrodes 4 and 5 one of the layers expands in its length dimension 1 whilst the other one contracts thereby causing the bimorph to bend. The central electrode 6 is used during the poling process and is not used in operation of the device.However in an alternative arrangement electrodes 4 and 5 alone could be used in the poling process to pole both layers in the same direction. The central electrode 6 would then be required to be used during operation of bimorph, e.g., by earthing it, so that electric fields could be applied in opposite directions to the two piezoelectric layers.

The illustrated structure is manufactured by taking a single bimorph 1 and removing a part of each outer conductive layer 4 and 5 as shown at 7 to form four outer electrodes 4A, 4B, 5A, 5B. A plastics moulding 8 is now moulded onto the top of the bimorph. A slot 9 is now sawn through the moulding 8 and through the bimorph 1 thus forming two joined bimorph members each having its own optical fibre mounting element at its free end.

Two metal inserts 10 and 11 are now secured in position. Each insert is secured by adhesive in a groove formed in a lug 12 on one part of the optical fibre mounting element and is secured, also be adhesive, to abutment means 13 on the other part of the mounting- member.

A slot 14 of very narrow width (80 microns in this particular example) is sawn through the abutment means 13 so as to form two co-operating and opposed abutment faces. The saw cut is made in a direction lateral with respect to the direction of relative movement of the free ends of the bimorph members. In this way relative bending of the two parts of the bimorph member is limited to 80 microns in each direction from the centre position illustrated.

The mounting member 8 is formed, during the moulding process, with three grooves 15A,15B and 15C grooves 15B and 15C are spaced 160 microns apart. The groove 15A is positioned so as to be-aligned with a position mid way between grooves 15B and 15C. The grooves are used to locate three respective optical fibres 16A, 16B and 16C which are secured in position using adhesive.

In operation a signal is applied on line 17 whether light from fibre 16A is required to be switched to fibre 16B or fibre 16C. In response to this signal a switching signal generator 18 produces a voltage of +40 volts on line 19 and zero on line 20 or vice versa depending on the switching condition required. Depending on the switching condition selected the two parts of the bimorph member are made to bend in opposite directions such that the optical fibre 6A is aligned with a selected one of the optical fibres 16B or 16C. Accurate alignment is made possible in the lateral direction by the saw cuts 14 whilst alignment in the vertical direction is ensured by the fact that the two parts 8A and 8B of the mounting member were moulded in one piece with the grooves 15 being formed before the slot 9 was cut.

In an alternative construction the mounting member could be preformed and then secured on the bimorph by adhesive. Another alternative construction technique would be to use two separate bimorph elements connected together at one pair of adjacent ends and to apply the mounting member onto the other ends. However this technique is not preferred since it cannot be guaranteed that the two elements would be affected equally by changes in ambient conditions such as temperature. Also difficulty might be experienced in spacing the two bimorph elements accurately apart.

The illustrated construction is designed for use in switching optical signals from one path to another as an end result in itself. However the techniques described can be used to produce an optical sensor for producing a measurement or other indication of a physical property. For example the illustrated system could be used to sense voltage; the ratio of the optical outputs from 16B and 16C being indicative of the voltage applied across lines 19 and 20. This assumes that some light from fibre 16A enters both lines 16B and 16C at ail conditions of the bimorph. There will of course have to be an optical sensor at the output of lines 16B and 16C. In an alternative arrangement the lines 16B and 16C could be replaced by a single line, the output of which is indicative of voltage.

In another alternative arrangement, the bimorph is replaced bny a bimetallic strip. Such an arrange-ment may be used as a heat sensor. If, instead ofa bimetallic strip, a biamagneto strictive is used, the resulting device may be used to sense magnetic fields.

An alternative switch is shown in Figure 2. In this switch the bimorph is divided into three parts. The centre part is designed to bend in one direction and the two outer parts are designed to bend in the other direction. Optical fibres are mounted in grooves on the three parts in the manner illustrated so as to produce a cross-over switching action. In the embodiment of the invention shown in Figure 2 the optical fibres are shown as being applied directly on the bimorph but it is to be understood that in practice it would be preferable to use a mounting member constructed along similar principles to that illustrated in Figure 1.

Claims (15)

1. An optical switch or sensor comprising first and second optical conductors mounted on respective piezoelectric benders and means for applying voltages to the different benders so that they bend simultaneously in opposite directions, thereby bringing to tending to bring the optical conductors into and out of alignment with each other.

2. A switch or sensor according to Claim 1 in which each bender member comprises first and second piezoelectric layers between respective first and second electrodes and separated by a third electrode, the first piezoelectric layers being formed in one piece and the second piezoelectric layers also being formed in one piece and the benders being separated by a slot extending through the said pieces.

3. A switch or sensor according to Claim 2 in which the third electrode of each bender member is formed by a common conductive layer.

4. A switch or sensor according to any preceding claims including abutment means for limiting relative bending movement of the benders to a limit position where the optical conductors are in alignment or a fixed amount out of alignment.

5. A switch or sensor according to any preceding claim in which the or each bender is a bimorph member.

6. A switch or sensor according to Claim 1 and substantially as described with reference to Figure 1 of the accompanying drawings and substantially as illustrated therein.

7. A switch or sensor according to Claim 1 and substantially as described with reference to Figure 2 of the accompanying drawings and substantially as illustrated therein.

8. A method of making an optical switch or sensor comprising first and second optical conductors mounted on respective first and second members at least one of which is of the type which includes two layers which can be made to undergo relative expansion and contraction thereby causing the member to bend and thereby bringing or tending to bring the optical conductors into or out of alignment; in which method the conductors are mounted on material forming or to form the first and second members by applying to it a single mounting member carrying or adapted to carry the optical conductors, and then splitting it into two parts each attached respectively to a part of the material which forms or is to form the first and second member.

9. A method according to Claim 8 including the step of forming two parts of the mounting member, before or after it is split into its two parts, with grooves; and then securing the optical conductors in the grooves.

10. A method according to Claims 8 or 9 in which the first and second members are formed by cutting a slot in a signle member.

11. A method according to Claim 10 in which the operation of cutting the slot also serves to split the mounting member into the said two parts.

12. A method according to any one of Claims 8 to 11 comprising the step of producing abutment means which limits the amount of relative bending movement of the member by producing a saw-cut of specified width in a direction lateral with respect to the direction of relative bending movement.

13. A method according to Claim 12 comprising the step of joining together the two separated parts of the mounting member and then forming the said saw-cut.

14. A method accoridng to claim 8 and substantially as described with reference to Figure 1 of the accompanying drawings.

15. A method according to Claim 8 and substantially as described with reference to Figure 2 of the accompanying drawings.