GB2179464A - Electro-optical light gate manufacture - Google Patents

Abstract

An electro-optical light gate is produced by taking a PLZT strip 1 mounted on a glass substrate and forming, on a face of the strip, 256 equispaced grooves of 35 mu m width and 200 mu m depth in a single sawing action. Cement, applied to the grooved face by stamping, is used to fix the strip 1 to glass substrate 4, thereby forming channels 3; once each channel is provided with a contact pad 5, conductive material is vacuum-injected into all the channels with a multi-nozzled piston. <IMAGE>

Description

SPECIFICATION Electro-optical light gate manufacture The present invention relates to a method of manufacturing an electro-optical light gate and to an electro-optical light gate made in accordance with such a method.

It is well-known that ferroelectric ceramics, for example lead lanthanum zirconium titanate (hereinafter referred to as PLZT), have a number of characteristics which render them particularly suitable for use in electro-optical light gates. U.S. Patent 3873187 describes a method of making a light gate incorporating PLZT, the method involving mounting a strip of this material on a substrate and then making parallel cuts across the PLZT strip and into the substrate so as to form individual elements. Thereafter the grooves are filled with conducting material using a scraper and the resultant surface, formed partly of PLZT and of conducting material, is covered by a second subtrate material.In the resultant device, when an appropriate electric field is applied to the elements, then the plane of polarization of polarized light passing through the element is rotated; by using an analyzer, the light can be modulated or gated according to appropriate variation of applied field.

An object of the present invention is to provide a method of manufacturing light gates, which method is particularly suited to commercial use and to mass-production.

Another object of the present invention is to provide a light gate which is of better quality than, and provides improved performance over, that made by conventional manufacturing methods.

The present invention provides a method of manufacturing an electro-optical light gate, the method comprising: taking a strip of appropriate ferroelectric material; forming at least one groove in a surface of the strip; applying a substrate to the grooved surface of the strip and over the groove(s) thereby to form one or more channels; and then inserting electrically conductive material into the channel(s).

In this way, the interfacing between the grooved surface of the strip and the substrate is achieved prior to application of the conductive material, thereby effectively eliminating the possibility of the conductive material being sandwiched between the PLZT and the substrate in unwanted areas.

Preferably, the conductive material is inserted into the channel(s) by injection; for example, the channel(s) may be evacuated, whereinafter an air-operated piston holding a predetermined amount of conductive material is brought into connection with the channel(s).

Preferably, the substrate is applied to the grooved surface of the strip by glueing. In one form, glue or cement is deposited on the uncut portions of the grooved face of the strip, and then the substrate is pressed against that face thereby to contact, and be fixed against, only those uncut portions. One particularly advantageous method of depositing glue or cement on the uncut portions is to stamp the grooved face against a surface having a thin layer of glue, thereby transferring a substantially even coating. By appropriate control of the glue layer depth, an adequate coating can be assured while minimising or eliminating the risk of glue sticking to the groove walls.

Preferably in the method a plurality of grooves, all parallel to one another, are formed in the strip of electro-optical material; moreover, advantageously all grooves are formed in a single surface of that strip.

Preferably, the method also includes the step of mounting at least one control circuit on the substrate for operation of the light gate. Furthermore, the substrate may be metallised to provide the necessary connections so that light modulation of the gate array can be operated by the control circuits by the provision of appropriate voltages to the conducting material in each channel.

The present invention also provides an electro-optical light gate which is made by the method defined hereinabove.

In order that the invention may more readily be understood, a desription is now given, by way of example only, reference being made to the accompanying drawings, in which: Figure 1 is a perspective view of a portion of a light gate during its manufacturing according to the present invention; Figure 2 is a plan view of the light gate at the injection stage of the manufacture process; and Figure 3 and 4 are schematic representations of the two principal steps in the injection stage.

A plate of PLZT material of dimensions 50mm by 50mm by 250 Am, is mounted on a glass block. Then it is cut into forty strips, each of 25mm length and 1 mm width, and 256 equi-spaced grooves (of 35 ,um width and 200,um depth) are cut in each slice in order to provide elements which are of 65 m width and 200 Hm depth; all cutting is achieved in a single sawing action.

Thereafter the forty grooved strips are dismantled, each being remounted in a jig for application of a thin layer of ultraviolet-hardening cement to the grooved surface. In order to achieve this, the grooved surface is stamped against a substrate onto which a thin spun layer of ultraviolet-hardening cement has been placed, so that an even coating of the cement is transferred to those portions of the strip which make contact i.e. the portions of that surface not being the grooves. The thickness of the cement layer on the substrate before transfer is chosen such as to ensure that an adequate coating is applied to the PLZT strip while preventing any significent amounts of the cement sticking to the walls of the groove.

Then the PLZT strip is placed, with its cement-coated surface in contact, against a metallised glass substrate, the resultant assembly is clamped together and exposed to ultraviolet radiation in order to set the cement.

The resultant unit is illustrated in Fig. 1 which shows the PLZT strip 1 with a number of grooves 2 such as to form channels 3 once the strip is fixed to glass substrate 4. Each channel 3 has a respective metallised contact pad 5.

The next stage of the manufacturing process involves filling the channels 3 with an appropriate electrically conductive material. In order to achieve this, the conductive material is injected into the channels using a unit which is illustrated in Fig. 2 and consists of an injector block 10 having an air-operable piston 11 able to move in a dispensing chamber 12, in order to urge conductive material through outlets 13 which are aligned with channels 3 of the PLZT strip 1. Fig. 2 shows the substrate 4 for the PLZT strip 1 as having four control circuits 14 eventually used in the operation of the light gate.

The injection stage is described in greater detail by reference to the principal steps shown in Figs. 3 and 4. A rubber pressure clamp 15 (which was not shown in Fig. 2 for the purpose of simplicity) is placed over the assembled PLZT strip 1 and substrate 4, and then the injection unit incorporating block 10 and piston 11 is suitable positioned with the outlets 13 aligned with channels 3. A valve 16 is closed, and then a vacuum pump 17 is operated in order to evacuate the channels 3; at this stage a metered amount of conducting material 18 is supplied to the dispensing chamber 12 (see Fig. 3). Once the conduit to pump 17 has been closed off with the vacuum in channels 3 maintained, valve 1 is opened so that the air-operated piston 11 urges the conductive material 18 into channels 3 (see Fig. 4).

Subsequently, control circuits 14 are located on substrate and are electrically connected to the light gates formed in the PLZT strip 1 by conductive tracks 19.

The manufacturing method described above ensures that the conductive material is substantially wholly contained within the grooved portions of the PLZT strip, it being most unlikely that the conductive material could intrude into the regions in which the uncut portions of the grooved surface interface with the substrate 4. Any such intrusions, which tend to occur frequently in conventional manufacturing methods, tend to provide a substantial detrimental effect to the operation of the device as a light gate, because the applied electrical field (and therefore the rotation effect on polorized light) is not uniform throughout the PLZT strip. Another advantage of the above described manufacturing method is that it enables the application of the cement (for the fixing together of the strip 1 and substrate 4) to be excluded from the groove walls, thereby further ensuring the uniformity of electric fields in the device.

Moreover the above described method is particularly suited to commercial use, especially mass-production manufacture, in that it requires only a single sawing action to form a slice of PLZT material into a number of separate strips, each suitably grooved.

A light gate array made by the above described method can be used in any appropriate application; such an array is particularly suited for use in a low-cost medium speed, non-impact electrophotographic printer.

Claims (8)

1. A method of manufacturing an electrooptical light gate, the method comprising: taking a strip of appropriate ferroelectric material; forming at least one groove in a surface of the strip; applying a substrate to the grooved surface of the strip and over the groove(s) thereby to form one or more channels; and then inserting electrically conductive material into the channel(s).

2. A method according to Claim 1, wherein-the channel(s) is or are evacuated, wherein after an air-operated piston holding a predetermined amount of conductive material is brought into connection with the channel(s).

3. A method according to Claim 1 or Claim 2, wherein glue or cement is deposited on the uncut portions of the grooved face of the strip, and then the substrate is pressed against the face thereby to contact, and be fixed against, only those uncut portions.

4. A method according to Claim 3, wherein the step of depositing glue or cement on the uncut portions comprises stamping the grooved face against a surface having a thin layer of glue, thereby transferring a substantially even coating.

5. A method according to anyone of the preceding Claims, wherein a plurality of grooves, all parallel to one another, are formed in a single surface of the strip of electro-optical material.

6. A method according to any one of the preceding Claims, comprising the step of mounting at least one control circuit on the substrate for operation of the light gate.

7. A method of manufacturing an electrooptical light gate, the method being substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

8. An electro-optical light gate produced by the method of any one of Claims 1 to 7.