WO2006003582A1

WO2006003582A1 - Polarisation-independent liquid crystal beam deflector

Info

Publication number: WO2006003582A1
Application number: PCT/IB2005/052099
Authority: WO
Inventors: Stein Kuiper; Bernardus H. W. Hendriks; Emile J. K. Verstegen
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2004-06-29
Filing date: 2005-06-24
Publication date: 2006-01-12

Abstract

The present invention relates to a liquid crystal beam deflector (200, 230), which comprises a first isotropic material (206), an adjacently positioned first liquid crystal material (210), one or more electrodes (204, 226), and a second isotropic material (216), an adjacently positioned second liquid crystal material (218). The one or more electrodes (204, 226) are adapted to excite the first and second liquid crystal materials (210, 218) and thereby control incident light polarized in any direction.

Description

Polarisation- independent liquid crystal beam deflector

FIELD OF INVENTION

This invention relates to a system for deflecting a laser beam with the use of a liquid crystal element. In particular, the invention relates to a beam deflector, which is independent of the polarisation of the laser beam.

BACKGROUND OF INVENTION

A system for steering a light beam, such as described in international patent application no. WO 01/73504, which hereby is incorporated in the present specification by reference, uses electrical operation for controlling the light beam and provides a grating (PMMA) and a liquid crystal material in a cavity. When the liquid crystal is not being addressed there is a mismatch between the liquid crystal and the grating causing the grating to diffract the light in a specified direction. On the other hand, when the liquid crystal is addressed to match its refraction index to the grating, the light is not diffracted by the grating. Hence the light travels in different directions when the liquid crystal is not addressed and addressed. The incident light needs to have a polarization direction that is the same as the liquid crystal extraordinary light direction. Hence the system is not independent on polarization and thus cannot redirect or actively control an un-polarized light beam, that is a white light.

SUMMARY OF THE INVENTION

An object of the present invention is therefore to provide a polarization- independent liquid crystal beam deflector insensitive to polarisation of incident light, which redirects and actively controls an un-polarized light beam by means of controlling a prism- like optical structure. It is a further object of the present invention to provide a system and method using said liquid crystal beam deflector for deflecting a laser beam.

A particular advantage of the present invention is the provision of a beam deflector which is flat and thereby easy to apply to various optical stacks of layers. The above objects and advantage together with numerous other objects, advantages and features, which will become evident from below detailed description, are obtained according to a first aspect of the present invention by a liquid crystal beam deflector for deflecting incident light beam independently of polarization of said incident light comprising a first isotropic material adapted to receive said incident light beam, an adjacently positioned first liquid crystal material adapted to receive light exiting said first isotropic material and to control light polarized in a first direction of said light exiting said first isotropic material, and one or more electrodes adapted to excite said first liquid crystal material. The liquid crystal beam deflector may be characterized in further comprising a second isotropic material adapted to receive light exiting said first liquid crystal material, an adjacently positioned second liquid crystal material adapted to receive light exiting said second isotropic material and to control light polarized in a second direction of said light exiting said second isotropic material, and said one or more electrodes further being adapted to excite said second liquid crystal material. The liquid crystal beam deflector according to the first aspect of the present invention may further comprise a first substrate layer adapted to protect a first outward facing surface of said liquid crystal deflector and a second substrate layer adapted to protect a second outward facing surface of said liquid crystal deflector. The substrate layers provide protection of liquid crystal so that the deflector may be used for a wide variety of purposes. The liquid crystal beam deflector according to first aspect of the present invention may further comprise a first alignment layer adapted to interface said first liquid crystal material and said second isotropic material. The liquid crystal beam deflector may further comprise a second alignment layer adapted to interface said second liquid crystal material and said second substrate layer. The alignment layers provide alignment between the layers. The first and second alignment layers may be adapted to provide a uni-axial alignment, a homeotropic alignment, or a combination thereof.

A first transparent conductor of said one or more electrodes may be positioned adjacent to said first substrate layer, or the first transparent conductor of said one or more electrodes may be positioned adjacent to said first alignment layer. A second transparent conductor of said one or more electrodes may be positioned adjacent to said second substrate layer.

The first and second liquid crystal materials have an orientation characterized by a first and second director, respectively, which first and second director are orthogonal relative to one another. The above objects, advantages, and features together with numerous other objects, advantages and features, which will become evident from below detailed description, are obtained according to a second aspect of the present invention by use of a liquid crystal beam deflector according to the deflector according to the first aspect of the present invention for deflecting a laser beam communicating optical data through a liquid and/or a gas such as water or oil and/or air.

The above objects, advantages, and features together with numerous other objects, advantages and features, which will become evident from below detailed description, are obtained according to a third aspect of the present invention by a sender for use in an optical transmission system comprising a deflector according to the first aspect of the present invention.

The above objects, advantages, and features together with numerous other objects, advantages and features, which will become evident from below detailed description, are obtained according to a fourth aspect of the present invention by a receiver for use in an optical transmission system comprising a deflector according to the first aspect of the present invention.

The above objects, advantages, and features together with numerous other objects, advantages and features, which will become evident from below detailed description, are obtained according to a fifth aspect of the present invention by a transmitter for use in an optical transmission system comprising a deflector according to the first aspect of the present invention.

The above objects, advantages, and features together with numerous other objects, advantages and features, which will become evident from below detailed description, are obtained according to a sixth aspect of the present invention by a lamppost for use in an optical transmission system wherein said lamppost comprises a deflector according to the first aspect of the present invention.

The second through sixth aspect of the present invention may obviously incorporate any of the features of the deflector according to the first aspect of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non- limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawing, wherein:

Fig. 1, shows liquid crystal beam deflector according to the prior art techniques generally used; and Figs. 2a and 2b, show a liquid crystal beam deflector according to a first and second embodiment of the present invention, respectively.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the following description of the various embodiments, reference is made to the accompanying figures, in which by way of illustration various embodiments are shown. It is to be understood that other embodiments may be utilized, and structural and functional modifications may be made without departing from the scope of the present invention. Figure 1, shows a liquid crystal beam deflector according to the prior art techniques, which beam deflector is designated in entirety by reference numeral 100. The beam deflector 100 comprises an isotropic material 102, such as polymethyl methacrylate (PMMA), and a liquid crystal 104 material, such as a nematic type material.

Incident polarized light 108 is received on a first optically transparent layer 106 incorporating a first electrode (not shown in figure 1) and communicated to the isotropic material 102 and the liquid crystal material 104 before exiting through a second optically transparent layer 110 incorporating a second electrode (not shown in figure 1). The first and second electrodes address the liquid crystal material 104 so as to control the deflection of the incident polarized light 108 thereby generating an output light beam 112.

As described the beam deflector 100 redirects the incident polarized light 108 by altering the refractive index of the liquid crystal 104. The angle, under which the light beam 108 is deflected, depends on the tree-dimensional position of the refracting surface separating the liquid crystal material 104 from the isotropic material 102 and on the difference between the extraordinary refractive index and the ordinary refractive index.

Figure 2a, shows a liquid crystal beam deflector according to a first embodiment of the present invention and designated in entirety by reference numeral 200. The beam deflector 200 comprises a first substrate layer 202 incorporating a transparent first conductor 204 and receiving incident light, which may be un-polarized light. The first substrate layer 202 is positioned adjacent to a first isotropic material 206 e.g. PMMA, which together with a first liquid crystal material 210 defines a first deflector section 208. The beam deflector 200 further comprises a second deflector section 212 separated from the first polarization beam deflector 208 by a first alignment layer 214. The second deflector section 212 comprises a second isotropic material 216, e.g. PMMA, and a second liquid crystal material 218. Directors 220 and 222 of the first and second liquid crystal materials 210 and 218, respectively, are at right angles. Care should be taken with the allowable deflection deviations of both polarization. One of the polarizations may become influenced, if the second deflector section 212 is passed under a certain angle.

The beam deflector 200 further comprises a second substrate layer 224 incorporating a transparent second conductor 226 and separated from the second deflector section 212 by a second alignment layer 228.

The first and second transparent conductors 204 and 226 are positioned on the first and second substrate layers 202 and 224. By exiting the first and second transparent conductors 204 and 226 the refractive indices of the liquid crystal materials 210 and 218 are changed thereby deflecting the incident light polarized in both a first and second direction. Figure 2b shows a liquid crystal beam deflector according to a second embodiment of the present invention and designated in entirety by reference numeral 230. The beam deflector 230 comprises the same elements as the beam deflector 200 according to the first embodiment, which elements are numbered likewise.

The beam deflector 230 differs from the beam deflector 200 by having the first transparent conductor 204 positioned adjacent to the alignment layer 214.

In general, the final stack of layers constituting the beam deflector according to the first and second embodiments of the present invention, shown in figures 2a and 2b, appears similar. Although alignment layers 214 and 228 are only shown on the lower surfaces of the liquid crystal materials 210 and 218, in principle, all surfaces of covering the liquid crystal materials 210 and 218 may be supplied with an alignment layer.

Combinations of uni-axial alignment on one interface and homeo tropic alignment on the other interface are possible embodiments of the alignment layers 214 and 228. The alignment is achieved by using dedicated alignment materials such as polyimides. Further, the directors 220 and 222 have orientations that may provide twisted nematic, cholesteric and splay conformation modes. The correct director 220 and 222 orientation is achieved by rubbing the alignment layers 214 and 228 against a cloth.

The beam deflector 200 and 230, according to the first and second embodiment of the present invention, may advantageously be applied in optical data transport between fibre optical cables and homes through laser communication on for example lampposts.

Alternatively or additionally the first and second embodiment of the present invention may advantageously be utilized for submarine laser communication in the sea or for above land and submarine laser communication in oil lines.

A well-established and widely used way to transport data is by making use of optical fibres. These optical fibres are particularly suited for cost-effective transportation of data over large distances. Since an optical fibre distribution net in residential areas is very expensive, it has recently been proposed to transport data using well collimated light beams which transport the data from lamppost to lamppost. However, experience has shown, that lampposts are not sufficiently rigid in their construction and consequently movements in the top of the lampposts may occur, which movements may interrupt the laser beam providing the data transmission between the lampposts. In order to prevent the laser beam from being interrupted an active guiding of the laser is required to keep the laser beam on a transmitting lamppost directed to the detector on a receiving lamppost. Furthermore, upon arrival at the receiving lamppost the laser beam must often be redirected to provide the right data at the right location. If mirrors according to prior art technologies are used mechanical means are necessary to change the direction of the laser beam. This is undesirable because of the mechanical means are generally very sensitivity to vibrations. On the other hand, the beam deflectors 200 and 230 according to the first and second embodiment of the present invention may be utilized for this purpose, since these beam deflectors 200 and 230 are not prone to vibration sensitivity and are not very susceptible to wear.

Claims

CLAIMS:

1. A liquid crystal beam deflector (200, 230) for deflecting incident light beam independently of polarization of said incident light comprising a first isotropic material (206) adapted to receive said incident light beam, an adjacently positioned first liquid crystal material (210) adapted to receive light exiting said first isotropic material (206) and to control light polarized in a first direction of said light exiting said first isotropic material (206), and one or more electrodes (204, 226) adapted to excite said first liquid crystal material (210), and characterized in further comprising a second isotropic material (216) adapted to receive light exiting said first liquid crystal material (210), an adjacently positioned second liquid crystal material (218) adapted to receive light exiting said second isotropic material (218) and to control light polarized in a second direction of said light exiting said second isotropic material (218), and said one or more electrodes (204, 226) further being adapted to excite said second liquid crystal material (218).

2. A liquid crystal beam deflector (200, 230) according to claim 1 further comprising a first substrate layer (202) adapted to protect a first outward facing surface of said liquid crystal deflector (200, 230) and a second substrate layer (224) adapted to protect a second outward facing surface of said liquid crystal deflector (200, 230).

3. A liquid crystal beam deflector (300, 230) according to any of claims 1 to 2 further comprising a first alignment layer (214) adapted to interface said first liquid crystal material (210) and said second isotropic material (216).

4. A liquid crystal beam deflector (200, 230) according to any of claims 1 to 3, wherein a first transparent conductor (204) of said one or more electrodes (204, 226) is positioned adjacent to said first substrate layer (202).

5. A liquid crystal beam deflector (300, 230) according to any of claims 1 to 3, wherein said first transparent conductor (204) of said one or more electrodes (204, 226) is positioned adjacent to said first alignment layer (214).

6. A liquid crystal beam deflector (300, 230) according to any of claims 2 to 5 further comprising a second alignment layer (228) adapted to interface said second liquid crystal material (218) and said second substrate layer (224).

7. A liquid crystal beam deflector (300, 230) according to claims 1 to 6, wherein a second transparent conductor (226) of said one or more electrodes (204, 226 is positioned adjacent to said second substrate layer (224).

8. A liquid crystal beam deflector (300, 230) according to claims 1 to 7, wherein first and second liquid crystal materials (210, 218) have an orientation characterized by a first and second director (220, 222), respectively, which first and second director (220, 222) are orthogonal relative to one another.

9. A liquid crystal beam deflector (300, 230) according to claim 1 to 8, wherein said first and second alignment layers (214, 228) are adapted to provide a uni-axial alignment, a homeotropic alignment, or a combination thereof.

10. Use of a liquid crystal beam deflector (300, 230) according to claims 1 to 9 for deflecting a laser beam communicating optical data through a liquid and/or a gas such as water or oil and/or air.

11. A sender for use in an optical transmission system comprising a deflector (300, 230) according to any of claims 1 to 9.

12. A receiver for use in an optical transmission system comprising a deflector (300, 230) according to any of claims 1 to 9.

13. A transmitter for use in an optical transmission system comprising a deflector (300, 230) according to any of claims 1 to 9.

14. A lamppost for use in an optical transmission system, wherein said lamppost comprises a deflector (300, 230) according to any of claims 1 to 9.