GB1599507A

GB1599507A - Optical apparatus including a liquid crystal matrix

Info

Publication number: GB1599507A
Application number: GB1331578A
Authority: GB
Original assignee: Eltro GmbH and Co
Current assignee: Eltro GmbH and Co
Priority date: 1977-05-14
Filing date: 1978-04-05
Publication date: 1981-10-07
Also published as: FR2390751B3; FR2390751A1; DE2722018A1; DE2722018C2

Description

(54) OPTICAL APPARATUS INCLUDING A LIQUID CRYSTAL MATRIX (71) We, ELTRO GmbH GESELLSCHAFT FtJR STRAHLUNGSTECHNIK, a German limited liability company, of 6900 Heidelberg 1, Kurpfalzring 106, Federal Republic of Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to optical apparatus including a liquid crystal matrix.

A known liquid crystal matrix comprises a pair of parallel spaced electrode plates each having a plurality of light permeable electrode strips, the strips of one plate being arranged in an x-direction and the strips of the other plate being arranged in a y-direction, and a liquid crystal layer which fills the space between the plates, which matrix can be so selectively energised yia the individual electrode strips that each matrix element can be varied in its light permeability or brightness, according to the voltages applied to the strips.

Such a matrix is described in for example German Patent Specification Nos. 2,227,055 and 2,237,996. In these the matrix is used as an electro-optical display device. A similar display device is also described in German Specification No. 2,508,619, in which the operation of the device is dependent upon a sound level.

A diaphragm-shutter combination operating with controllable liquid crystals is known in the field of photography from German Specification No. 2,428,012 and also Specification No.

2,526,496.

It is an object of the invention to exploit the properties of the per se known liquid crystal matrix in the field of optronics.

According to this invention, there is provided electro-optical apparatus for controlled detection of electromagnetic radiation present in a field of view of the apparatus, comprising: a liquid crystal matrix in which the spacing between adjacent elements of the matrix is less than the distance between opposite sides of an element; an optical device for passing radiation from the field of view to the matrix; an electronic control device connected to the matrix; and a detector to receive radiation which has been passed through the matrix and to produce an electrical signal in response to the radiation; wherein the matrix and the control device are constructed and arranged such that in operation of the apparatus the matrix elements are selectively energised to provide a controllable mask in the form of an area of reduced or zero radiation permeability, which area is variable in position and disposed in the matrix so as to restrict passage of radiation from a selected part or parts of the field of view and thereby to permit passage of radiation without such restriction from another selected part or parts in the field of view to the detector.

Also according to this invention there is provided a method of selecting discrete portions of an optical image produced in electro-optical apparatus, wherein a liquid crystal matrix in which the spacing between adjacent elements of the matrix is less than the distance between opposite sides of an element, is placed in the path of radiation passing through the apparatus to a detector arranged to produce an electrical signal in response to incident radiation, and wherein an electronic control device connected to the matrix is operated to cause selected elements of the matrix to become relatively impermeable to the radiation so as to produce a mask which attenuates or cuts off radiation from a source or sources in that part of the field of view corresponding to the selected elements.

The objects situated in the field of view may by actual solid objects or may be in the form of interference rays. An advantage which can be derived from the invention is the elimination of the need for a mechanical diaphragm and associated drive mechanism in the vicinity of the image field. This saves space and avoids the electro-magnetic interference caused by vibration originating in such a mechanism.

An advantageous further development of the invention resides in that the variable mask may comprise either at least one radiation impervious matrix element surrounded by radiation pervious matrix elements or a plurality of impervious matrix elements surrounding a "window" of at least one pervious matrix element. The size, form and location of such a "window" in the matrix is electronically adjustable as required.

It is also possible to scan the field of view which is of interest by means of a movable "window", controlled via an electronic driver, which travels through the matrix elements of the horizontal or vertical electrode strips one after another. Such a "window" preferably moves in the manner of reading, that is to say from the left-hand upper edge towards the right-hand lower edge of the matrix.

With regard to the location of such a matrix in an optical system, assuming that at any given time during scanning only one matrix element is pervious, and that, of the total radiation from the field of view passing through an optical system onto the matrix only one image point reaches a radiation detector downstream of the matrix, then the liquid crystal matrix can be located in front of the image plane of the optical system to save space.

Apparatus in accordance with the invention has applications in the field of missile guidance, in which, for example, infra-red radiation emitted by a target is used to home the missile onto the target. The variable mask may be controlled so as to select a particular portion of the infra-red image produced in the guidance system, or alternatively to block intefering radiation which could otherwise cause the missile to miss the target.

The invention will now be described by way of example with reference to the drawing, in which:- Figure 1 is a diagram of a liquid crystal matrix energised to form a positive diaphragm; and Figure 2 is a diagram of an electro-optical apparatus including a liquid crystal matrix scanning device.

Referring firstly to Figure 1, a typical liquid crystal matrix 1 has a series of electrode strips X1 to Xn and Y1 to Yn arranged adjacent one another in the vertical and horizontal directions respectively. The strips are of transparent material and are electrically insulated in respect of one another. Both the electrode strips X1 to Xn and also the electrode stips Y1 to Yn in each case are formed by a plate. The two plates are arranged face to face and are spaced apart for example by 10 mm, the intermediate space being filled with a layer of liquid crystal material. At each location where one strip crosses another, a matrix element is formed. As shown in Fig. 1, it can be seen that the strips are arranged such that the width of each element is relatively large compared with the spacing between adjacent elements.

The individual matrix elements are energisable by the application of a voltage between the relevant electrode strips running in the X and the Y directions. The matrix and its electronic control circuit can be so designed that for e:rurrnple the element X4 Y1 appears as an impervious dark area (shaded in Figure 1) when both of the electrode strips corresponding to it are activated. The element X3 Y2 on the other hand appears as part of a pervious "window", since no voltage is being applied to an associated electrode. Between these two extremes, varying degrees of transparency in an element can be obtained by adjusting the voltage level applied to the two corresponding electrodes, or by applying voltage to only one of the two electrodes.

In Figure 1, in addition to the above-described known properties of a liquid crystal matrix, use of the matrix as a variable diaphragm is shown.

This can be in positive or negative form, i.e.

either a pervious "window" 2 (as in Figure 1) or a central impervious area can be produced.

The window 2 of Figure 1 is formed by four adjacent matrix elements. In the application of the invention to a guided weapon system, it is possible for example to observe and take aim at a target through the window 2, and any interference radiation surrounding the target will be masked by the live and therefore impervious matrix elements surrounding the window. It is possible to observe and take aim through only a single matrix element or through any other number of adjacent elements, the position of the "window" in the matrix being variable according to the arrangement of the applied voltages.

In practice, such a variable diaphragm used in a missile guidance system can enable the gunner automatically to aim a missile at a target through an electronic sight. If this target is for example a tank, then the missile may miss its target if the tank puts out a corresponding heat source or fires in due time. In the case of a missile operating on the HOT or MILAN principle (in which the entire spectrum of rays incident upon such a weapon is broken down into two spectral ranges behind a common objective lens, the infra-red range then being fed to a goniometer and the visible range to the gunner's eyepiece) such interference can be avoided by locating a diaphgragm in accordance with the invention in front of the goniometer modulator, and by controlling the position of the window in response to the goniometer output signal representing the deviation of the missile from the target.

In the case of the application of a liquid crystal matrix as a negative diaphragm (not shown) an object such as a particular source of interference may be masked or faded out directly by means of at least one impervious matrix element. A dark matrix element, which corresponds most closely to the conventional image of a diaphragm, can be produced anywhere on the liquid crystal matrix.

Figure 2 shows, in the direction of radiation passage, a field of view 3 (which may be notional, or physically embodied in the form of a screen bearing an image) from which radiation passes through an optical system 4 to a liquid crystal matrix 1. The matrix elements are so actuated via an electronic line and gap driver 9 that at any given time only one image point 5 reaches a detector 6, which feeds an electrical signal (corresponding to the brightness of the image point) via an amplifier 7 to a load 8. The bright ness data is thereby available at the point 10.

With this arrangement, the individual matrix elements are so actuated that at any time only one element is radiation pervious, the window thus formed travelling line-wise in the matrix.

In this way, the field of view 3 is serially scanned and its content is represented by a serial video signal.

WHAT WE CLAIM IS: 1. Electro-optical apparatus for controlled detection of electromagnetic radiation present ion a field of view of the apparatus, comprising: a liquid crystal matrix in which the spacing between adjacent elements of the matrix is less than the distance between opposite sides of an element; an optical device for passing radiation from the field of view to the matrix; an electronic control device connected to the matrix; and a detector to receive radiation which has been passed through the matrix and to produce an electrical signal in response to the radiation; wherein the matrix and the control device are constructed and arranged such that in operation of the apparatus the matrix elements are selectively energised to provide a controllable mask in the form of an area of reduced or zero radiation permeability, which area is variable in position and disposed in the matrix so as to restrict passage of radiation from a selected part or parts of the field of view and thereby to permit passage of radiation without such restriction from another selected part or parts in the field of view to the detector.

2. Apparatus according to claim 1 arranged to produce an image of a source or sources of radiation in the field of view at a predetermined image plane substantially coincident with the matrix.

3. Apparatus according to claim 1 or claim 2, wherein the liquid crystal matrix comprises a pair of parallel spaced electrode plates each having a plurality of radiation permeable electrode strips, the strips of one plate being arranged in an x-direction and the strips of the other plate being arranged in a y-direction substantially at right angles to the x-direction, and a liquid crystal layer filling the space between the plates, each individual element ofthe matrix being selectively energisable via the individual electrode strips to vary its radiation permeability according to the level of the applied voltage.

4. Apparatus according to any preceding claim, wherein the matrix and the control device are arranged in use to form a variable diaphragm, at least one element of the matrix being impervious to radiation, and the elements surrounding the impervious element or elements being pervious to radiation, thereby blanking or fading out a selected part of an image.

5. Apparatus according to any of claims 1 to 3, wherein the matrix and the control device are arranged in use to form a variable diaphragm, at least one element of the matrix being pervious to radiation, and the elements surrounding the pervious element or elements being impervious to radiation, thereby blanking or fading out all but a particular selected part of an image.

6. Apparatus according to any of claims 1 to 3 or to claim 5, wherein the electronic control device includes means for successively energising and de-energising the matrix elements to scan the field of view by means of a movable scanning window comprising one or more radiation pervious elements.

7. Apparatus according to claim 6 wherein the matrix is operable such that at any given time during a scanning operation only one matrix element is pervious to radiation, and, of the radiation from the field of view passing through the optical device onto the matrix, only those of one image spot corresponding to the one matrix element arrive on the detector, the detector producing an electrical signal corresponding to the brightness of the image point.

8. A missile guidance system having an electronic sight for use by an operator when aiming a missile at a target, the system including apparatus according to any preceding claim to select or fade out a portion of an image of the target area.

9. A guidance system according to claim 8 including an infra-red goniometer, the liquid crystal matrix being disposed upstream of the goniometer to fade out infra-red radiation emanating from an interfering source in the vicinity of the target.

10. A guidance system according to claim 9 wherein the matrix forms a variable diaphragm which is automatically controllable in response to a deviation signal from the goniometer.

11. A method of selecting discrete portions of an optical image produced in electro-optical apparatus, wherein a liquid crystal matrix, in which the spacing between adjacent elements of the matrix is less than the distance between opposite sides of an element, is placed in the path of radiation passing through the apparatus to a detector arranged to produce an electrical signal in response to incident radiation, and wherein an electronic control device connected to the matrix is operated to cause selected elements of the matrix to become relatively impermeable to the radiation so as to produce a mask which alternates or cuts off radiation from a source or sources in that part of the field of view corresponding to the selected elements.

12. A method according to claim 11 wherein the control device is operated to cause an element or a plurality of mutually adjacent elements of the matrix to become relatively impermeable so as to create a masking area surrounded by an area of relatively high permeability, which masking area is variable in

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. via an electronic line and gap driver 9 that at any given time only one image point 5 reaches a detector 6, which feeds an electrical signal (corresponding to the brightness of the image point) via an amplifier 7 to a load 8. The bright ness data is thereby available at the point 10. With this arrangement, the individual matrix elements are so actuated that at any time only one element is radiation pervious, the window thus formed travelling line-wise in the matrix. In this way, the field of view 3 is serially scanned and its content is represented by a serial video signal. WHAT WE CLAIM IS:

1. Electro-optical apparatus for controlled detection of electromagnetic radiation present ion a field of view of the apparatus, comprising: a liquid crystal matrix in which the spacing between adjacent elements of the matrix is less than the distance between opposite sides of an element; an optical device for passing radiation from the field of view to the matrix; an electronic control device connected to the matrix; and a detector to receive radiation which has been passed through the matrix and to produce an electrical signal in response to the radiation; wherein the matrix and the control device are constructed and arranged such that in operation of the apparatus the matrix elements are selectively energised to provide a controllable mask in the form of an area of reduced or zero radiation permeability, which area is variable in position and disposed in the matrix so as to restrict passage of radiation from a selected part or parts of the field of view and thereby to permit passage of radiation without such restriction from another selected part or parts in the field of view to the detector.

position to cut off or reduce radiation from one or more unwanted sources of radiation.

13. A method according to claim 11, wherein the control device is operated to cause substantially the whole effective area of the matrix to become relatively impermeable with the exception of a relatively permeable window comprising one element or a plurality of mutually adjacent elements, thereby to select for transmission through the apparatus the radiation from a particular source in the field of view, and to reject interfering radiation from surrounding parts of the field of view.

14. A method according to claim 11 wherein successive elements of the matrix are energised and de-energised one after the other to cause a window of relatively high permeability to move across the matrix so as to scan the field of view.

15. A method according to any of claims 11 to 14, wherein the matrix is placed at or near the image plane of the optical device.

16. Electro-optical apparatus constructed and arranged substantially as herein described and shown in the accompanying drawing.

17. A method of selecting discrete portions of an image substantially as herein described with reference to the drawing.