GB2206977A - Integrated optical switch using movable liquid - Google Patents

Abstract

An integrated optical switch comprises two solid optical wave guide channels 10, 11 which cross and have a common solid-fluid interface 14 such that light from one channel 11b may undergo total internal reflection at the interface 14 into the other channel 10b. A reservoir 17, 13, 18 containing a dielectric liquid 15 of the same refractive index as that of the channels 10, 11 crosses the channels, part of its boundary constituting the said interface 14. Electro-capillary action on the liquid 15 is used to move a bead of the liquid selectively over and away from the interface 14, to cause the light selectively to be transmitted or reflected at the interface. <IMAGE>

Description

Integrated Optical Switch This invention relates to an integrated optical switch for selectively diverting light from one solid optical wave guide channel to another. Large numbers of such devices may be formed in a common substrate; the channels may for example be of ion-exchanged glass in a glass substrate.

It is known to use a liquid crystal in such a switch.

Externally-applied electromagnetic fields vary the polarising effect of the liquid crystal medium, and this may be used selectively to switch polarised light. The object of the invention is to provide an integrated optical switch, i.e. an optical switch which may be implemented as an integrated optical device, which is polarisation independent.

Accordingly, the invention provides an integrated optical switch comprising two solid optical wave guide channels which meet and have a common solid-fluid interface in the region at which they meet such that light from one may undergo total internal reflection at the interface into the other, means for containing a dielectric liquid in a region bounded partly by the interface, and means for moving the liquid selectively between a reflection position, at which the liquid is held remote from the interface and is replaced by a different medium so as to cause the said total internal reflection, and a transmission position, at which the liquid is held at the interface to allow light to be transmitted through the liquid.

Thus the switch operates by moving the liquid between the reflection and transmission positions.

Preferably, the waveguide channels are relatively inclined and cross at straight intermediate regions thereof, the interface being a planar surface bisecting the angle at which the waveguide channels cross. In this case, when the liquid is at the transmission position light is transmitted straight across the interface down the same waveguide channel, without reflection into the other channel (or with a smaller proportion reflected into the other channel).

Preferably, the integrated optical switch is part of a multiple beam switching device in which several wave guide channels from one edge thereof are made to cross several wave guide channels from another edge thereof, and one such optical switch is provided at each of the crossing points. The advantage of the invention in such a beam switching device is that the channels from one edge may be inclined at any selected angle, for example 900, to those channels from the other edge, allowing the device to be made very compact.

The said different medium is preferably air. The term "solid-fluid interface" is however intended to include interfaces between the solid waveguides and any different medium which is not solid.

The means for moving the liquid preferably comprises means for selectively applying an electro-magnetic field across a portion of the containing means so as selectively to attract the dielectric liquid towards that portion. The portion is preferably remote from the interface, such that attraction of the dielectric liquid into that portion removes the liquid from the interface.

The means for moving the dielectric liquid preferably further comprises restoring means for opposing the attraction of the dielectric liquid towards the said portion. The restoring means is preferably constituted by the configuration of the boundary provided by the containing means, such that capillary action at an interface between the dielectric liquid and the boundary continuously biases the liquid away from the said portion.

Such a capillary effect is disclosed in our copending British Patent Application No. 8711211 in the context of a wedge-shaped region between two prisms, the tapering of the wedge biasing the dielectric liquid between the prisms towards the narrower end.

In order that the invention may be better understood, a preferred embodiment will now be described, by way of example only, with reference to the accompanying diagramatic drawings, in which: Figure 1 is a plan view of an integrated optical switch which embodies the invention; Figure 2 is an enlarged view of the central portion of Figure 1; Figure 3 is a section, to an enlarged scale, taken on the line III-III of Figure 1; and Figure 4 is a plan view of an integrated beam switching device including several integrated optical switches of the type shown in Figure 1.

With reference to Figures 1 to 3, an integrated optical device including a switch comprises a conducting substrate 30 such as silicon underlying an intermediate glass layer 12. Two perpendicular channels 10, 11 are formed in the surface of the intermediate glass layer 12 by ion exchange, or by other conventional techniques such as deposition and etching. For example, metal ions such as sodium ions diffused into the glass are exchanged for other metal ions such as silver, as is known. These channels constitute optical wave guides, since their refractive index differs from that of. the intermediate glass layer 12.

A dumbell shaped reservoir 13, 17, 18 is cut from the intermediate glass layer 12, its base being defined by the upper surface of the conducting layer 30, using e.g. a process such as reactive ion etching as is known. The neck region 13 of the reservoir is a straight channel which cuts across the meeting point of the two wave guide channels 10, 11, at an angle which bisects the 900 angle of inclination of the two wave guide channels. This provides a solid-air planar interface 14 at the region at which the left hand portion llb of channel 11 meets the lower portion 10b of channel 10, and provides corresponding interfaces 19 with the other portions 10a, lla of the channels 10, 11.The interface 14 is such that light from the left hand portion llb of channel 11 undergoes total internal reflection into the lower portion 10b of channel 10, and vice versa, when the medium on the other side of the interface is air, as shown in Figure 1.

A dielectric liquid 15, preferably an organic solvent with a low viscosity and a high dielectric constant such as xylene or bromonaphthalene, is contained within the reservoir, normally within one 17 of the bell-shaped end regions 17, 18 and extending into the neck region 13. The remainder of the reservoir is filled with air 16, although alternative media, gaseous or liquid, immiscible with the dielectric liquid 15, could be used instead of air. As shown in Figure 2, the neck region 13 tapers to provide a capillary effect on the dielectric liquid 15 which biases the liquid 15 towards the interface 14, i.e. away from the portion of the reservoir which normally contains the liquid.As shown in Figure 1, a planar electrode 21, parallel to the intermediate glass layer 12, overlies the bell-shaped region 17 of the reservoir; a corresponding electrode (not shown) is provided beneath the reservoir by the conducting substrate 30. Thus a major proportion of the dielectric liquid 15 is sandwiched between the two electrodes. A voltage is selectively applied across the electrodes, in use, to attract the dielectric liquid 15 further into the bell-shaped portion 17 of the reservoir, in opposition to the restoring force provided by capillary action in the tapering neck region 13. The arrangement is such that the liquid-air boundary 20 is moveable from one end of the interface 14 to the other end, depending on whether a voltage is applied or is not applied across the electrodes. At each such position, the dielectric liquid 15 is in equilibrium between the electro-capillary force between the electrodes and the restoring capillary force provided by the tapering neck region 13. At one position, the interface 14 is a solid-air interface as described above; at the other position, the interface 14 changes into a solid-liquid interface.

An alternative restoring force that may be used is the differential pressure between the two bell-shaped portions 17 of the reservoir.

By choosing the refractive index of the dielectric liquid 15 to be the same as, or nearly the same as, that of the wave guide channels, 10, 11, a large proportion of the light is transmitted across the interface and through the dielectric liquid into the same waveguide channel.

Movement of the dielectric liquid thus switches between reflection and transmission, or between reflection and at least partial transmission.

In the example shown in Figure 4, an integrated optical device 40 consists of a multiple beam switching device. Several waveguide channels 43 terminate at one edge 41 of an optical chip 40, and several other wave guide channels 44 terminate at an adjacent edge 42. The two sets of channels 43, 44 intersect at multiple crossing points 45, at an angle e which may be 900 so as to achieve the greatest compactness of the device. At each crossing point 45, an integrated optical switch, as shown in Figure 1, is formed. As is usual in such a device, many of the components of the switch are common; for example, the conductive layer 30 and intermediate glass layer 12 extend throughout the chip 40.One electrode (not shown) extends over substantially the whole area of the crossing points 45; individual electrodes 21 for each integrated optical switch are electrically isolated from each other. Drive voltage is conveyed to each of the electrodes 21 from terminals at one of the edges of the chip 40, by conventional means.

As shown in Figure 3, a dielectric layer 31 is formed over the intermediate glass layer 12 to protect the waveguide channels 10, 11, and a protective glass layer 32 is bonded over the whole integrated optic switch. The layer 32 may be fabricated with either the common electrode or patterned electrodes on it. The bonding material is chosen for compatibility with glasses and impermeability to the liquid used.

The structure of the wave guide channels need not necessarily be as described above. Alternatively, chemical vapour deposition techniques could be used, or selective etching techniques, as are known in the art.

Further, while the reservoir has been described as being of dumbell shape in plan view, it will be clear that many alternative configurations are possible. Further, the continuous restoring force, acting in opposition to the electro-capillary effect, may be provided by alternative means, for example, by a corresponding electro-capillary effect pulling the liquid in the opposite direction, using another pair of electrodes.

With optical wave guide channels of about 10 micrometres in width, the response time of the optical switch of the type described with reference to the drawings has bèen found to be about 10 milliseconds. This of course is substantially slower than the pico-second speeds of polarisation-dependent switches such as those using lithium niobate crystal, but, in comparison with such faster devices, the invention allows the channels to intersect at any angle including 900, and is polarisation independent.

Claims (12)

1. An integrated optical switch comprising two solid optical wave guide channels which meet and have a common solid-fluid interface at their meeting region such that light from one may undergo total internal reflection at the interface into the other, means for containing a dielectric liquid in a region bounded partly by the interface, and means for moving the liquid selectively between a reflection position, at which the liquid is held remote from the interface and is replaced by a different medium so as to cause the said total internal reflection, and a transmission position, at which the liquid is held at the interface to allow light to be transmitted through the liquid.

2. A switch according to claim 1, wherein the wave guide channels are relatively inclined and cross at straight intermediate regions thereof, the interface being a planar surface bisecting the angle at which the waveguides cross.

3. A switch according to claim 1 or 2, wherein the said different medium is air.

4. A switch according to claim 1, 2 or 3, wherein the means for moving the liquid comprises means for selectively applying an electro-magnetic field across a portion of the containing means so as to selectively attract the dielectric liquid towards that portion.

5. A switch according to claim 4, wherein the portion is remote from the interface, such that attraction of the liquid into that portion removes the liquid from the interface.

6. A switch according to claim 4 or 5 wherein the means for moving the liquid further comprises restoring means opposing the attraction of the dielectric liquid towards the said portion.

7. A switch according to claim 6, wherein the restoring means is constituted by the configuration of the boundary provided by the containing means, such that capillary action at an interface between the dielectric liquid and the boundary continuously biases the liquid away from the said portion.

8. A switch according to claim 7, wherein at least a section of the boundary tapers so that it is wider at the said portion than it is remote from the portion.

9. A switch according to any preceding claim, wherein the dielectric liquid has the same, or substantially the same, refractive index as that of the wave guide channels.

10. A multiple beam switching device in which several wave guide channels from one edge thereof are made to cross several wave guide channels from another edge thereof, and an optical switch in accordance with any preceding claim is provided at each of the crossing points.

11. An integrated optical switch substantially as described herein with reference to Figures 1 to 3 of the accompanying drawings.

12. An integrated optical device substantially as described herein with reference to the accompanying drawings.