CN114114738A

CN114114738A - Liquid crystal grating with adjustable period, optical waveguide component and display device

Info

Publication number: CN114114738A
Application number: CN202010882963.4A
Authority: CN
Inventors: 马珂奇; 向恩来; 赵瑜
Original assignee: Ningbo Sunny Opotech Co Ltd
Current assignee: Ningbo Sunny Opotech Co Ltd
Priority date: 2020-08-28
Filing date: 2020-08-28
Publication date: 2022-03-01
Anticipated expiration: 2040-08-28
Also published as: CN114114738B; WO2022042444A1; CN116324602A

Abstract

The application provides a period adjustable liquid crystal grating, includes: a liquid crystal layer including a plurality of liquid crystals; the liquid crystal display panel comprises two alignment film layers, a liquid crystal display panel and a liquid crystal display panel, wherein the alignment film layers are used for giving initial director of liquid crystal; a common electrode layer; the driving electrode layer comprises a first electrode and a second electrode, the first electrode and the second electrode are respectively provided with a plurality of control deflection parts which are equal in width and equal in distance and are connected in series, the grating period of the liquid crystal grating is switched by controlling the voltage applied to the first electrode and/or the second electrode, so that light rays with different wavelengths are diffracted to ensure that the diffraction angle is constant, and the problems of color cast and dispersion caused by the fact that light rays with different wavelengths are diffracted are solved; the liquid crystal grating provided by the application can switch the period, so that full-color display can be realized, and the liquid crystal grating is light, thin, small and exquisite, high in diffraction efficiency, large in incident light angle range and large in viewing angle.

Description

Liquid crystal grating with adjustable period, optical waveguide component and display device

Technical Field

The application relates to the technical field of optical transmission, in particular to a liquid crystal grating with adjustable period, an optical waveguide component and a display device.

Background

The display equipment is mainly used for displaying pictures or videos to human eyes, and can be widely applied to the fields of virtual reality, augmented reality, mixed reality, military and the like.

The display device mainly comprises a projection light machine and an optical waveguide component, wherein the projection light machine outputs image light to the optical waveguide component, and the optical waveguide component is used for receiving the image light and diffracting and transmitting the image light to the left and right human eyes, so that a 3D effect is formed.

However, the image light has a plurality of colors, and the wavelengths of the different colors of light are different, so that the diffraction angles of the different colors of light are different, and the diffraction efficiencies of the different colors of light in the same grating structure are also different, thereby causing chromatic dispersion or chromatic aberration (chromatic aberration is the chromatic aberration caused when the different colors of light are not mixed according to the expected ratio).

Disclosure of Invention

The present application provides a liquid crystal grating with adjustable period to solve the problem of color shift or dispersion.

An embodiment of the present application provides a liquid crystal grating with an adjustable period, including:

a substrate;

the protective layer is arranged opposite to the substrate at intervals;

a liquid crystal layer including a plurality of liquid crystals;

the two alignment film layers are respectively positioned on two sides of the liquid crystal layer and between the substrate and the protective layer, and the alignment film layers are used for giving an initial director of the liquid crystal;

a common electrode layer; and

a driving electrode layer, disposed opposite to the common electrode layer and respectively located at the outer sides of the two alignment film layers and located between the substrate and the protective layer, wherein the driving electrode layer includes a first electrode and a second electrode, the first electrode and the second electrode respectively have a plurality of control deflection parts with equal width and equal interval and connected in series, the sum of the width of the control deflection parts and the interval between the control deflection parts defines a structural period,

after the first electrode and/or the second electrode and the common electrode are applied with voltage, the liquid crystal deflection director in the area covered by the control deflection part of the first electrode and/or the second electrode applied with voltage forms a grating structure to diffract the light incident to the liquid crystal grating,

and switching the grating period of the liquid crystal grating by controlling the voltage applied to the first electrode and/or the second electrode so as to diffract light rays with different wavelengths and ensure a certain diffraction angle.

In one embodiment, the driving electrode layer is a single-layer structure, the first electrode and the second electrode are located in the same layer, and the structural periods of the first electrode and the second electrode are different;

the first electrode is configured to be in a voltage applied state when diffracting a first light, and the second electrode is configured to be in a voltage applied state when diffracting a second light.

In one embodiment, the first light is blue light and a portion of green light, and the second light is red light and another portion of green light.

In one embodiment, the structural period of the first electrode is 300nm to 400nm, and the structural period of the second electrode is 600nm to 800 nm.

In one embodiment, the driving electrode layer is of a single-layer structure, the first electrode and the second electrode are located in the same layer, and the structural period of the first electrode and the structural period of the second electrode are the same;

the first electrode or the second electrode is configured to be in an applied voltage state when diffracting a first light ray, and the first electrode and the second electrode are configured to be in a common applied voltage state when diffracting a second light ray.

In one embodiment, the first light is red light and a portion of green light, and the second light is blue light and another portion of green light.

In one embodiment, the side of the first electrode having the control deflection portion is disposed opposite the side of the second electrode having the control deflection portion, and the control deflection portion of the first electrode or the control deflection portion of the second electrode can be inserted into the two control deflection portions of the second electrode or a gap between the two control deflection portions of the first electrode.

In one embodiment, the driving electrode layer is of a multi-layer (e.g., dual-layer) structure including at least two layers, the first electrode and the second electrode are respectively located in the two layers, and the first electrode and the second electrode have different structural periods;

the first electrode is configured to be in a voltage applied state when diffracting the first light, and the second electrode is configured to be in a voltage applied state when diffracting the second light.

In one embodiment, the structural period of the first electrode is 300nm to 600nm, and the structural period of the second electrode is 500nm to 800 nm.

In one embodiment, the driving electrode layer further comprises a third electrode, the third electrode has a plurality of control deflection parts which are equal in width and equal in spacing and are connected in series, and the structural periods of the first electrode, the second electrode and the third electrode are different;

the first electrode is configured to be in a voltage applied state when diffracting a first light, the second electrode is configured to be in a voltage applied state when diffracting a second light, and the third electrode is configured to be in a voltage applied state when diffracting a third light.

In one embodiment, the first light is blue light, the second light is green light, and the third light is red light.

In one embodiment, the driving electrode layer is of a multi-layer (e.g. dual-layer) configuration, comprising at least two sub-layers, and the first electrode, the second electrode and the third electrode are respectively located in the two sub-layers in a mode that the two electrodes are arranged in a common layer and the other electrode is arranged separately.

In one embodiment, the drive electrode layer is of a three-layer construction comprising three layers, the first, second and third electrodes being located within the three layers respectively.

In one embodiment, the structural period of the first electrode is 400nm to 500nm, the structural period of the second electrode is 500nm to 600nm, and the structural period of the third electrode is 600nm to 700 nm.

In one embodiment, the common electrode layer and the driving electrode layer are ITO conductive layers.

In one embodiment, the thickness of the liquid crystal layer is 1um to 2 um.

An embodiment of the present application further provides an optical waveguide assembly, including:

the waveguide sheet is used for the total reflection transmission of light rays in the waveguide sheet;

the coupling-in unit is arranged on one surface of the waveguide sheet and is used for coupling light into the waveguide sheet, and the coupling-in unit is the liquid crystal grating in any embodiment; and

the coupling-out unit and the coupling-in unit are arranged on the same surface of the waveguide sheet, the coupling-out unit is used for coupling light out of the waveguide sheet to a visible area, the coupling-out unit is the liquid crystal grating in any embodiment, and the grating period of the coupling-out unit and the grating period of the coupling-in unit are synchronously switched so as to couple in and then couple out the light with the same wavelength.

In one embodiment, the waveguide sheet has a thickness of 0.3mm to 2.5mm and a refractive index of 1.4 to 2.2.

An embodiment of the present application provides a display device, including:

the projection optical machine is used for sequentially projecting light rays with various wavelengths; and

an optical waveguide component according to any of the embodiments above, wherein a coupling-in unit and a coupling-out unit of the optical waveguide component synchronously and sequentially switch out a grating period corresponding to a wavelength of light projected by the projector, so that the coupling-in unit couples the light projected by the projector into a waveguide of the optical waveguide component, the waveguide transmits the light to the coupling-out unit, and the coupling-out unit couples the light out to a visible region,

by switching the grating periods of the coupling-in unit and the coupling-out unit, light rays with different wavelengths are diffracted to ensure a certain diffraction angle.

In one embodiment, the light projector sequentially projects light beams with different wavelengths at a certain frequency, and the frequency of the grating period switched by the coupling-in unit and the coupling-out unit is consistent with the frequency of the projected light beams.

In one embodiment, the light projector projects light rays with two wavelengths, and the projection frequency is not less than 120 Hz.

In one embodiment, the projector projects light rays with two wavelengths and respectively comprises a first light ray and a second light ray, wherein the first light ray is blue light and a part of green light with the wavelength close to the blue light, and the second light ray is red light and the other part of green light with the wavelength close to the red light.

In one embodiment, the projection light machine projects light rays with three wavelengths and respectively includes a first light ray, a second light ray and a third light ray, the first light ray is a blue light ray, the second light ray is a green light ray, and the third light ray is a red light ray.

In one embodiment, the light projector projects at least partially linearly polarized light.

In one embodiment, the projector light machine includes an lcos display.

Has the advantages that:

the liquid crystal grating with the adjustable period is provided with a first electrode and a second electrode in a driving electrode layer, the first electrode and the second electrode are respectively provided with a plurality of control deflection parts which are equal in width and equal in interval and are connected in series, and the grating period of the liquid crystal grating is switched by applying voltage to the first electrode and/or the second electrode, so that the problems of color cast and chromatic dispersion caused by diffraction of light rays with different wavelengths are solved. The liquid crystal grating that this application provided is owing to can switch the cycle, and then can diffract the light of different wavelength and do not have the problem of colour cast dispersion, can diffract the light of different colours promptly, thereby make the display device who has the liquid crystal grating that this application provided need not the stack multiunit on the waveguide piece and couple in, the full-color demonstration can be realized to the coupling grating, make display device comparatively frivolous, small and exquisite, and because the grating cycle is equivalent with the wavelength of light, thereby diffraction efficiency is high, incident light angle range is big, and can use the display device's of the liquid crystal grating that this application provided angle of field is big.

Drawings

The advantages of the above and/or additional aspects of the present invention will become apparent and readily appreciated from the following description of the embodiments taken in conjunction with the accompanying drawings of which:

fig. 1 is a schematic structural diagram of a display device in the prior art;

FIG. 2 is a schematic structural diagram of a liquid crystal grating with adjustable period according to an embodiment of the present disclosure;

fig. 3 is a schematic structural diagram of a driving electrode layer according to an embodiment of the present disclosure;

fig. 4 is a schematic diagram illustrating a working state of a liquid crystal grating according to an embodiment of the present application;

FIG. 5 is a schematic structural diagram of a driving electrode layer according to another embodiment of the present disclosure;

fig. 6 is a schematic structural diagram of a liquid crystal grating according to an embodiment of the present application;

FIG. 7 is a schematic structural diagram of a driving electrode layer of the liquid crystal grating shown in FIG. 6;

FIG. 8 is a schematic structural diagram of an optical waveguide assembly according to an embodiment of the present application;

fig. 9 is a schematic structural diagram of a display device according to an embodiment of the present application.

Wherein, the correspondence between the reference numbers and the part names in fig. 1 to 9 is:

1. a projection light machine; 2. an optical waveguide assembly; 21. a waveguide sheet; 22. coupling in a grating; 23. coupling out the grating; 3. a substrate; 4. a protective layer; 5. a liquid crystal layer; 51. a liquid crystal; 6. aligning the film layer; 7. a common electrode layer; 8. a driving electrode layer; 81. a first electrode; 82. a second electrode; 83. a control deflection unit; 9. a blocking member; 10. an optical waveguide assembly; 101. a waveguide sheet; 102. a coupling-in unit; 103. a coupling-out unit; 11. a projection light machine.

Detailed Description

In order that the above objects, features and advantages of the present invention can be more clearly understood, a more particular description of the invention will be rendered by reference to the appended drawings. It should be noted that the embodiments and features of the embodiments of the present application may be combined with each other without conflict.

Fig. 1 is a schematic structural diagram of a display device in the prior art.

As shown in fig. 1, the display device includes a projector optical machine 1 and an optical waveguide assembly 2, and the optical waveguide assembly 2 includes a waveguide sheet 21 and an incoupling grating 22 and an outcoupling grating 23 provided on the waveguide sheet 21. The projection light engine 1 projects light to the coupling grating 22, and the coupling grating 22 diffracts the light to couple the light into the waveguide 21. The light is transmitted to the coupling-out grating 23 by total reflection in the waveguide sheet 21, and the coupling-out grating 23 diffracts the light to couple the light out of the waveguide sheet 21 to the visible region and be observed by human eyes. The light projected by the projection light engine 1 is visible light, and the visible light has various colors, and the light wavelengths of the different colors are different. The exit angle of light diffraction is related to the wavelength and the grating period, and then the exit angles of light with different wavelengths after being diffracted by the same grating are different, so that chromatic dispersion or color cast can occur.

Based on the technical problem, the liquid crystal grating with the adjustable grating period is provided, so that when light with different wavelengths needs to be diffracted, the corresponding period is switched, the emergent angle of the diffracted light is the same, and the problem of chromatic dispersion or color cast is solved.

The light of three colors, red, green and blue, is the basic color light, and the projector 1 only needs to project the three colors of light, and can display the light of other colors by the superposition combination of two or three colors. And then the grating only need diffract the light of these three kinds of wavelength, and then the adjustable liquid crystal grating of cycle that this application provided only need can switch out two kinds of cycles or three kinds of cycles can.

The longest wavelength of the red light is 622-760 nm, the middle wavelength of the green light is 492-577 nm, and the shortest wavelength of the blue light is 435-450 nm. The wavelength of a portion of the green light is similar to the red light and the wavelength of another portion of the green light is similar to the blue light, and the grating can be arranged to be capable of switching out two periods. When the grating is in the first period, it is used to diffract red light and a portion of green light. And when the grating has a second period, the grating is used for diffracting blue light and another part of green light.

The grating may also be arranged to be switchable out of three periods: when the grating is in the first period, the grating is used for diffracting red light; when the grating is in the second period, the grating is used for diffracting green light; when the grating is in the third period, it is used to diffract blue light.

Next, the liquid crystal grating with adjustable period provided in the present application will be described in detail based on the above basic design concept.

Example 1

Fig. 2 is a schematic structural diagram of a liquid crystal grating with an adjustable period according to an embodiment of the present application, and fig. 3 is a schematic structural diagram of a driving electrode layer according to an embodiment of the present application.

As shown in fig. 2 and fig. 3, the liquid crystal grating with adjustable period provided in this embodiment includes:

a substrate 3;

a protective layer 4 arranged opposite to the substrate 3 at a distance;

a liquid crystal layer 5 including a plurality of liquid crystals 51;

two alignment film layers 6, the two alignment film layers 6 are respectively positioned at two sides of the liquid crystal layer 5 and between the substrate 3 and the protective layer 4, and the alignment film layers 6 are used for giving initial directors of the liquid crystal 51;

a common electrode layer 7; and

and the driving electrode layer 8 is arranged opposite to the common electrode layer 7, is respectively positioned on the outer sides of the two alignment film layers 6 and is positioned between the substrate 3 and the protective layer 4, the driving electrode layer 8 comprises a first electrode 81 and a second electrode 82, the first electrode 81 and the second electrode 82 respectively have a plurality of control deflection parts 83 which are equal in width and equal in interval and are connected in series, and the sum of the width of each control deflection part 83 and the interval between the control deflection parts 83 is defined as a structural period.

After the first electrode 81 and/or the second electrode 82 and the common electrode layer 7 are applied with voltage, the liquid crystal 51 in the area covered by the control deflection part 83 of the first electrode 81 and/or the second electrode 82 applied with voltage deflects the director to diffract the light incident to the liquid crystal grating, and the liquid crystal 51 deflecting the director in the liquid crystal layer 5 is configured to have the grating period of the liquid crystal grating (that is, the structural period of the first electrode 81 and/or the second electrode 82 is the grating period of the liquid crystal grating).

The grating period of the liquid crystal grating is switched by controlling the voltage applied to the first electrode 81 and/or the second electrode 82, so as to diffract light rays with different wavelengths and ensure a certain diffraction angle.

The detailed working principle is as follows:

when a voltage is applied to the first electrode 81 and/or the second electrode 82 and a voltage is applied to the common electrode layer 7, an electric field is formed between the control deflection unit 83 of the first electrode 81 and/or the second electrode 82 and the common electrode layer 7, and the liquid crystal 51 located in the electric field changes the director. However, no electric field is formed at the position where the control deflection unit 83 is not disposed on the first electrode 81 and/or the second electrode 82, and the director of the liquid crystal 51 at the corresponding position is not changed.

Fig. 4 is a schematic diagram of a working state of a liquid crystal grating according to an embodiment of the present application.

As shown in fig. 4, a light ray passing through the liquid crystal 51 with its director changed will generate a birefringence effect into two light rays, ordinary and extraordinary rays, respectively. The ordinary rays and the extraordinary rays have different refractive indexes, resulting in a phase difference when the ordinary rays and the extraordinary rays are transmitted in the liquid crystal 51 molecules, thereby realizing phase modulation of the light, i.e., forming a phase grating.

The structural period of the first electrode 81 or the second electrode 82, or the structural period after the first electrode 81 and the second electrode 82 are combined is the grating period of the liquid crystal grating. That is, the grating period of the liquid crystal grating can be set by setting the structural period of the first electrode 81 and the second electrode 82.

According to the liquid crystal grating provided by the application, the first electrode 81 and the second electrode 82 are arranged in the driving electrode layer 8, the first electrode 81 and the second electrode 82 are respectively provided with a plurality of control deflection parts 83 which are equal in width and equal in spacing and are connected in series, and the grating period of the liquid crystal grating is switched by applying voltage to the first electrode 81 and/or the second electrode 82, so that the problems of color cast and dispersion caused by diffraction of light rays with different wavelengths are solved. Further, the optical waveguide component 2 or the display device using the liquid crystal grating provided by the present application does not need to arrange a plurality of sets of coupled-in and coupled-out gratings 23 on the waveguide sheet 21 to diffract light rays with different wavelengths, and further, the optical waveguide component 2 or the display device using the liquid crystal grating provided by the present application has a simple structure, is light, thin and small, and is simple in manufacturing process.

The liquid crystal grating provided by the application can diffract light with different wavelengths without the problem of color cast dispersion due to the fact that the period can be switched, and light with different colors can be diffracted, so that full-color display can be achieved without overlapping multiple groups of coupling-in and coupling-out gratings 23 on the waveguide sheet 21, and the display device is light, thin and small.

The structural period of the first electrode 81, the structural period of the second electrode 82, or the length of the structural period after the first electrode 81 and the second electrode 82 are combined corresponds to the wavelength of the light to be diffracted, that is, the length of the structural period of the first electrode 81, the length of the structural period of the second electrode 82, or the length of the structural period after the first electrode 81 and the second electrode 82 are combined is equivalent to or slightly different from the wavelength of the light to be diffracted, so that the liquid crystal grating provided by the present application has high diffraction efficiency and a wide incident light angle range, and the display device to which the liquid crystal grating provided by the present application can be applied has a large field angle.

The liquid crystal grating provided by the application can control the phase modulation degree of light by controlling the voltage value applied to the first electrode 81 and/or the second electrode 82, and the function is flexible and convenient.

The first electrode 81 and the plurality of control deflection units 83 of the second electrode 82 provided in this embodiment may be electrically connected to each other by wires or may be electrically connected to each other by electrode pads. The electrodes are electrically connected in an electrode plate mode, and the manufacturing process of the electrodes is simple and convenient.

In this embodiment, the voltage applied to the first electrode 81 or the second electrode 82 is an alternating current.

Since the liquid crystal grating provided in this embodiment has two electrodes (the first electrode 81 and the second electrode 82) disposed on the driving electrode layer 8, that is, the liquid crystal grating provided in this embodiment has two grating periods. The manner of providing two grating periods for the liquid crystal grating by disposing two electrodes includes, but is not limited to, the following three.

The first mode is as follows:

as shown in fig. 3, the driving electrode layer 8 has a single-layer structure, the first electrode 81 and the second electrode 82 are located in the same layer, and the first electrode 81 and the second electrode 82 have different structural periods. The first electrode 81 is configured to be in a voltage applying state when diffracting the first light, the second electrode 82 is configured to be in a voltage applying state when diffracting the second light, the length of the structural period of the first electrode 81 corresponds to the wavelength of the first light (the length of the structural period of the first electrode 81 is equal to or not different from the wavelength of the first light), the length of the structural period of the second electrode 82 corresponds to the wavelength of the second light (the length of the structural period of the second electrode 82 is equal to or not different from the wavelength of the second light), and the diffraction efficiency is high.

The working principle of the liquid crystal grating is as follows:

when a voltage is applied to the first electrode 81 and no voltage is applied to the second electrode 82, the liquid crystal grating is in a state of a first period (a1+ b1), and the structural period of the first electrode 81 is the grating period of the liquid crystal grating.

When a voltage is applied between the first electrode 81 and the common electrode, an electric field is formed between the control deflection unit 83 of the first electrode 81 and the common electrode, and the liquid crystal 51 in the electric field is deflected (changes the director), while the liquid crystal 51 at the corresponding position where the control deflection unit 83 is not provided is not deflected. The light passing through the directionally deflected liquid crystal 51 has a birefringence effect and becomes two rays, ordinary and extraordinary rays, respectively. The ordinary rays and the extraordinary rays have different refractive indexes, causing a phase difference when the ordinary rays and the extraordinary rays are transmitted in the molecules of the liquid crystal 51, thereby achieving phase modulation of the light, i.e., forming a phase grating, thereby diffracting the light.

When a voltage is applied to the second electrode 82 and no voltage is applied to the first electrode 81, the liquid crystal grating is in a state of a second period (a2+ b2), and the structural period of the second electrode 82 is the grating period of the liquid crystal grating.

When a voltage is applied to the second electrode 82 and the common electrode layer 7, an electric field is formed between the control deflection unit 83 of the second electrode 82 and the common electrode layer 7, and the liquid crystal 51 in the electric field is deflected (changes the director), and the liquid crystal 51 at the corresponding position where the control deflection unit 83 is not provided is not deflected. The light passing through the directionally deflected liquid crystal 51 has a birefringence effect and becomes two rays, ordinary and extraordinary rays, respectively. The ordinary rays and the extraordinary rays have different refractive indexes, causing a phase difference when the ordinary rays and the extraordinary rays are transmitted in the molecules of the liquid crystal 51, thereby achieving phase modulation of the light, i.e., forming a phase grating, thereby diffracting the light.

Further, the first light is blue light and a part of green light, and the second light is red light and another part of green light.

Further, the structural period of the first electrode 81 is 300nm to 400nm, and the structural period of the second electrode 82 is 600nm to 800 nm.

Furthermore, the side of the first electrode 81 having the control deflection part 83 is opposite to the side of the second electrode 82 having the control deflection part 83, and the control deflection part 83 of the first electrode 81 or the control deflection part 83 of the second electrode 82 can be inserted into the gap between the two control deflection parts 83 of the second electrode 82 or the two control deflection parts 83 of the first electrode 81, so that the space is saved, and the whole liquid crystal grating is thinner and smaller.

The second mode is as follows:

fig. 5 is a schematic structural diagram of a driving electrode layer according to another embodiment of the present disclosure. As shown in fig. 5, the driving electrode layer 8 is a single-layer structure, the first electrode 81 and the second electrode 82 are located in the same layer, and the first electrode 81 and the second electrode 82 have the same structural period. The first electrode 81 or the second electrode 82 is arranged to be in a voltage applied state when diffracting the first light, the first electrode 81 and the second electrode 82 are arranged to be in a voltage applied state when diffracting the second light, the length of the structural period of the first electrode 81 or the second electrode 82 corresponds to the wavelength of the first light (the length of the structural period of the first electrode 81 or the second electrode 82 is equal to or not different from the wavelength of the first light), the length of the structural period after the first electrode 81 and the second electrode 82 are combined corresponds to the wavelength of the second light (the length of the sum of the width of the control deflecting portion 83 and the distance between the control deflecting portion 83 of the first electrode 81 and the control deflecting portion 83 of the second electrode 82 is equal to or not different from the wavelength of the second light), and the diffraction efficiency is high.

Further, the first light is red light and a portion of green light, and the second light is blue light and another portion of green light.

The working principle of the liquid crystal grating is as follows:

when a voltage is applied to any one of the first electrode 81 and the second electrode 82, the liquid crystal grating is in a state of a first period (c1+ d1), and the structural period of the first electrode 81 or the second electrode 82 is the grating period of the liquid crystal grating. At this time, the working principle of the liquid crystal grating is similar as above, and is not described herein again.

The first electrode 81 and the second electrode 82 are applied with voltage at the same time, the liquid crystal grating is in a state of a second period (c2+ d2), and the sum of the width of the control deflection part 83 and the distance between the control deflection part 83 of the first electrode 81 and the control deflection part 83 of the second electrode 82 is the grating period of the liquid crystal grating.

When a voltage is applied to any one of the first electrode 81 and the second electrode 82, the grating period of the liquid crystal grating is larger than that when a voltage is applied to both the first electrode 81 and the second electrode 82, and further, when a voltage is applied to any one of the first electrode 81 and the second electrode 82, the liquid crystal grating is suitable for diffracting all red light and a part of green light close to the wavelength of red light, and when a voltage is applied to both the first electrode 81 and the second electrode 82, the liquid crystal grating is suitable for diffracting all blue light and the other part of green light close to the wavelength of blue light.

The third mode is as follows:

fig. 6 is a schematic structural diagram of a liquid crystal grating according to an embodiment of the present application, and fig. 7 is a schematic structural diagram of a driving electrode layer of the liquid crystal grating shown in fig. 6.

As shown in fig. 6 and 7, the driving electrode layer 8 has a two-layer structure, the first electrode 81 and the second electrode 82 are respectively located in two sub-layers, the first electrode 81 and the second electrode 82 have different structural periods, and the first electrode 81 is configured to be in a voltage-applied state when diffracting the first light and the second electrode 82 is configured to be in a voltage-applied state when diffracting the second light. The length of the structural period of the first electrode 81 corresponds to the wavelength of the first light (the length of the structural period of the first electrode 81 is equal to or slightly different from the wavelength of the first light), the length of the structural period of the second electrode 82 corresponds to the wavelength of the second light (the length of the structural period of the second electrode 82 is equal to or slightly different from the wavelength of the second light), and the diffraction efficiency is high.

The working principle of the liquid crystal grating is as follows:

the first electrode 81 is applied with voltage, the second electrode 82 is not applied with voltage, the liquid crystal grating is in a state of a first period, the structural period of the first electrode 81 is the grating period of the liquid crystal grating, and the working principle of the liquid crystal grating is the same as the above, which is not described herein again.

The second electrode 82 is applied with voltage, the first electrode 81 is not applied with voltage, the liquid crystal grating is in a state of a second period, the structural period of the second electrode 82 is the grating period of the liquid crystal grating, and the working principle of the liquid crystal grating is the same as the above, which is not described herein again.

Further, the structural period of the first electrode 81 is 300nm to 600nm, and the structural period of the second electrode 82 is 500nm to 800 nm.

Further, the control deflection portion 83 of the first electrode 81 is disposed opposite to the control deflection portion 83 of the second electrode 82, or the controllable deflection portion 83 of the first electrode 81 is disposed in the same direction as the control deflection portion 83 of the second electrode 82, which is not particularly limited herein.

In the present embodiment, the thickness of the substrate 3 is 0.5mm to 1 mm.

In the present embodiment, the protective layer 4 is made of a glass material, and the thickness of the protective layer 4 is smaller than that of the substrate 3. Further, the thickness of the protective layer 4 is 0.1mm to 0.3 mm.

In the present embodiment, the thickness of the liquid crystal layer 5 is 1um to 2 um.

In the present embodiment, the common electrode layer 7 and the driving electrode layer 8 are ITO (indium tin oxide) conductive layers.

In the present embodiment, the control deflection portion has a strip shape.

Example 2

In the present embodiment, the driving electrode layer 8 further includes a third electrode 84, the third electrode 84 has a plurality of control deflection units 83 with equal width and equal spacing and connected in series, and the first electrode 81, the second electrode 82 and the third electrode 84 have different structural periods. The first electrode 81 is configured to be in a voltage applying state when diffracting the first light, the second electrode 82 is configured to be in a voltage applying state when diffracting the second light, and the third electrode 84 is configured to be in a voltage applying state when diffracting the third light, the length of the structural period of the first electrode 81 corresponds to the wavelength of the first light (the length of the structural period of the first electrode 81 is equivalent to or not much different from the wavelength of the blue light), the length of the structural period of the second electrode 82 corresponds to the wavelength of the second light (the length of the structural period of the second electrode 82 is equivalent to or not much different from the wavelength of the green light), the length of the structural period of the third electrode 84 corresponds to the wavelength of the third light (the length of the structural period of the third electrode 84 is equivalent to or not much different from the wavelength of the red light), and the diffraction efficiency is high.

The working principle of the liquid crystal grating is as follows:

voltage is applied to the first electrode 81, no voltage is applied to the second electrode 82 and the third electrode 84, the liquid crystal grating is in a state of a first period, and the structural period of the first electrode 81 is the grating period of the liquid crystal grating.

A voltage is applied to the second electrode 82, no voltage is applied to the first electrode 81 and the third electrode 84, the liquid crystal grating is in a state of a second period, and the structural period of the second electrode 82 is the grating period of the liquid crystal grating.

A voltage is applied to the third electrode 84, no voltage is applied to the first electrode 81 and the second electrode 82, the liquid crystal grating is in a state of a third period, and the structural period of the third electrode 84 is the grating period of the liquid crystal grating.

The liquid crystal grating that this embodiment provided has set up three electrode in drive electrode layer 8 for three kinds of grating periods can be switched out to the liquid crystal grating, thereby make the light of every wavelength can both have the grating period that corresponds with it, every grating period only need correspond the light of a wavelength promptly, and then the grating period can set up more accurate, and the diffraction angle of better control emergent light solves colour cast and dispersive effect better.

Further, the first light is blue light, the second light is green light, and the third light is red light.

Further, the structural period of the first electrode 81 is 400nm to 500nm, the structural period of the second electrode 82 is 500nm to 600nm, and the structural period of the third electrode 84 is 600nm to 700 nm.

In one embodiment, the driving electrode layer 8 is a dual-layer structure, the first electrode 81, the second electrode 82 and the third electrode 84 are respectively located in two sub-layers in a mode that two electrodes are arranged in a common layer and the other electrode is arranged separately, the number of electrode layers is small, and thus the liquid crystal grating is thinner.

In one embodiment, the drive electrode layer 8 is a three-layer construction, with the first, second and

third electrodes

81, 82, 84 being located within three separate layers, respectively.

Those skilled in the art will readily recognize that in other embodiments, more than four electrodes may be disposed in the driving electrode layer 8 of the liquid crystal grating to provide more grating periods for the liquid crystal grating, and shall also fall within the scope of the present application. And the electrode layer is not limited to be provided with two or three electrode layers, and a technical solution of providing more than four electrode layers should also be within the scope of the present application.

Example 3

As shown in fig. 2, the liquid crystal grating provided in this embodiment further includes a blocking member 9, and the blocking member 9 is disposed between the two alignment film layers 6 and disposed around the liquid crystal 51 to prevent the liquid crystal 51 from overflowing.

Example 4

The liquid crystal grating provided in this embodiment further includes a plurality of spacers (not shown), and the plurality of spacers are arranged between the two alignment film layers 6 in a certain pattern to support the two alignment film layers 6 and maintain and determine a distance therebetween.

Specifically, the spacers are small balls having a diameter corresponding to the thickness of the liquid crystal layer 5 or columns having a height corresponding to the thickness of the liquid crystal layer 5.

Example 5

The present embodiment further provides a method for manufacturing a liquid crystal grating, which is used for manufacturing the liquid crystal grating described in any of the above embodiments, and the manufacturing method includes the following steps:

providing a substrate 3, and cleaning the substrate 3,

providing a protective layer 4 and cleaning the protective layer 4;

forming a common electrode layer 7 by sputtering a conductive layer on the substrate 3, forming a drive electrode layer 8 by sputtering a conductive layer on the protective layer 4, and disposing a first electrode 81 and a second electrode 82 each having a plurality of equally-wide and equally-spaced control deflection units 83 connected in series, or forming a common electrode layer 7 by sputtering a conductive layer on the substrate 3, forming a drive electrode layer 8 by sputtering a conductive layer, and disposing a first electrode 81 and a second electrode 82 each having a plurality of equally-wide and equally-spaced control deflection units 83 connected in series, and forming a common electrode layer 7 by sputtering a conductive layer on the protective layer 4;

spin-coating alignment film layers 6 on the common electrode layer 7 and the driving electrode layer 8 respectively, and aligning, wherein the directions of the alignment film layers 6 on the common electrode layer 7 and the alignment film layers 6 on the driving electrode layer 8 are opposite;

gluing the substrate 3 and the protective layer 4 into a liquid crystal 51 box;

and pouring liquid crystal 51 between the alignment film layer 6 on the common electrode layer 7 and the alignment film layer 6 on the driving electrode layer 8, and sealing to complete the manufacture of the liquid crystal grating.

The liquid crystal grating manufactured by the method for manufacturing a liquid crystal grating provided in this embodiment arranges the first electrode 81 and the second electrode 82, which respectively have a plurality of equally wide and equally spaced control deflection units 83 connected in series, in the driving electrode layer 8, so that the manufactured liquid crystal grating can switch the grating period of the liquid crystal grating by applying a voltage to the first electrode 81 and/or the second electrode 82, thereby solving the problems of color shift and chromatic dispersion caused by diffracting light rays with different wavelengths. Moreover, the optical waveguide component 2 or the display device using the liquid crystal grating manufactured by the method does not need to arrange a plurality of groups of coupled-in and coupled-out gratings 23 on the waveguide sheet 21 to diffract light rays with different wavelengths, and the optical waveguide component 2 or the display device using the liquid crystal grating manufactured by the method has a simple, light, thin and small structure.

The liquid crystal grating manufactured by the method can switch the period, and further can diffract light with different wavelengths without the problem of color cast dispersion, namely, can diffract light with different colors, so that the display equipment of the liquid crystal grating manufactured by the method can realize full-color display without overlapping a plurality of groups of coupling-in and coupling-out gratings 23 on the waveguide sheet 21, and the display equipment is light, thin and small.

The structural period of the first electrode 81 or the structural period of the second electrode 82 or the combined structural period length of the first electrode 81 and the second electrode 82 of the liquid crystal grating manufactured by the manufacturing method corresponds to the wavelength of light to be diffracted, namely the structural period of the first electrode 81 or the structural period of the second electrode 82 or the combined structural period length of the first electrode 81 and the second electrode 82 is equal to or slightly different from the wavelength of the light to be diffracted, so that the liquid crystal grating manufactured by the method has high diffraction efficiency and a large incident light angle range, and the viewing angle of a display device of the liquid crystal grating manufactured by the method can be large.

The liquid crystal grating manufactured by the method can control the phase modulation degree of light by controlling the voltage value applied to the first electrode 81 and/or the second electrode 82, and has flexible and convenient functions.

Further, after aligning the alignment films, before the substrate 3 and the protective layer 4 are bonded to the liquid crystal 51 cell, the method further includes: spacers are spin coated on the substrate 3.

In the present embodiment, the cleaning substrate 3 includes: the substrate 3 was ultrasonically cleaned with acetone, methanol and isopropanol for 10 minutes, respectively.

In this embodiment, the alignment film is aligned by a rubbing alignment method or an optical alignment method.

Example 6

Fig. 8 is a schematic structural diagram of an optical waveguide assembly according to an embodiment of the present application.

As shown in fig. 8, the present embodiment also provides an optical waveguide assembly 10 including:

a waveguide sheet 101 for total reflection transmission of light therein;

the incoupling unit 102 is arranged on one surface of the waveguide sheet 21 and used for incoupling light into the waveguide sheet 21, and the incoupling unit 102 is a liquid crystal grating described in any one of the above embodiments; and

the coupling-out unit 103 and the coupling-in unit 102 are disposed on the same surface of the waveguide sheet 21, the coupling-out unit 103 is used for coupling light out of the waveguide sheet 21 to the visible region, the coupling-out unit 103 is a liquid crystal grating according to any of the above embodiments, and the grating period of the coupling-out unit 103 and the grating period of the coupling-in unit 102 are synchronously switched to couple in and out light with the same wavelength.

The working principle of the optical waveguide component 2 provided in the present embodiment is as follows:

the incoupling unit 102 and the outcoupling unit 103 are switched to a period corresponding to the wavelength of the light to be diffracted. Incident light enters the incoupling unit 102, the incoupling unit 102 incouples light into the waveguide sheet 21, the light is totally reflected in the waveguide sheet 21 and transmitted to the outcoupling unit 103, and the outcoupling unit 103 couples the light out to a visible region so as to be observed by human eyes.

The coupling-in unit 102 and the coupling-out unit 103 of the optical waveguide component 2 provided in this embodiment are liquid crystal gratings with adjustable grating periods, so that when the optical waveguide component 2 transmits light with different wavelengths, the grating periods can be switched to correspond to the wavelengths of the light to be transmitted, thereby avoiding color shift and dispersion. And because the grating period is equivalent to the wavelength of the light, the diffraction efficiency of the light is high, and the angle allowable range of the incident light is large.

The optical waveguide assembly 2 provided in this embodiment further has a switchable grating period, so that it is not necessary to fabricate multiple sets of in-out gratings 23 on the waveguide sheet 21 to diffract light with different wavelengths to achieve full-color display, and the optical waveguide assembly is simple in structure, thinner, and smaller. And the full-color display is realized, the attenuation of the angle of view is avoided, and the optical performance is high.

In the present embodiment, the waveguide sheet 21 has a thickness of 0.3mm to 2.5mm and a refractive index of 1.4 to 2.2.

Example 7

As shown in fig. 9, the present embodiment also provides a display device including:

a projection light machine 11 for sequentially projecting light rays with various wavelengths; and

an optical waveguide component 10, where the optical waveguide component 10 is the optical waveguide component 10 according to any of the above embodiments, a coupling-in unit 102 and a coupling-out unit 103 of the optical waveguide component 10 synchronously and sequentially switch out a grating period corresponding to a wavelength of light projected by a projector 11, so that the coupling-in unit 102 couples the light projected by the projector 11 into a waveguide sheet 101 of the optical waveguide component 10, the waveguide sheet 101 transmits the light to the coupling-out unit 103, and the coupling-out unit 103 couples out the light to a visible region,

by switching the grating periods of the coupling-in unit 102 and the coupling-out unit 103, light with different wavelengths is diffracted to ensure a certain diffraction angle.

The grating periods of the coupling-in unit 102 and the coupling-out unit 103 of the optical waveguide component 10 provided by the present embodiment are switchable, so that different light beams have diffraction of the coupling-in unit 102 and the coupling-out unit 103 with corresponding grating periods, thereby avoiding color shift and chromatic dispersion.

And because the grating periods of the coupling-in unit 102 and the coupling-out unit 103 are switchable, full color display can be realized without overlapping multiple groups of gratings on the waveguide sheet 21, and the structure is simple, light, thin and small. And the full-color display is realized, the attenuation of the angle of view is avoided, and the optical performance is high. And because the grating period is equivalent to the wavelength of the light, the diffraction efficiency of the light is high, and the angle allowable range of the incident light is large.

Specifically, the projection light engine 11 sequentially projects a plurality of light beams with different wavelengths at a certain frequency, and the frequency of the grating period switched by the coupling-in unit 102 and the coupling-out unit 103 of the optical waveguide assembly 101 is the same as the frequency of the projected light beams.

In the present embodiment, the projector engine 1 projects light with two wavelengths, and the projecting frequency is not less than 120 Hz.

In one embodiment, the projector engine 11 projects light of two wavelengths and respectively a first light and a second light, the first light being a blue light and a portion of green light having a wavelength close to the blue light, the second light being a red light and another portion of green light having a wavelength close to the red light.

In another embodiment, the light projector 11 projects light of three wavelengths, which are a first light, a second light and a third light, respectively, where the first light is blue light, the second light is green light, and the third light is red light.

In one embodiment, the projector engine 11 projects at least partially linearly polarized light.

In one embodiment, the projector engine 11 comprises an lcos display.

In the description of the present invention, it should be noted that the terms "upper", "lower", and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, which are only for convenience in describing the present invention and simplifying the description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and operate, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; the communication may be direct, indirect via an intermediate medium, or internal to both elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art. In addition, in the description of the present invention, "a plurality" means two or more unless otherwise specified.

The present invention is not limited to the above preferred embodiments, and any modifications, equivalent replacements, improvements, etc. within the spirit and principle of the present invention should be included in the protection scope of the present application.

Claims

1. A liquid crystal grating with adjustable period, comprising:

a substrate (3);

the protective layer (4) is arranged opposite to the substrate (3) at intervals;

a liquid crystal layer (5) including a plurality of liquid crystals (51);

two alignment film layers (6), wherein the two alignment film layers (6) are respectively positioned on two sides of the liquid crystal layer (5) and positioned between the substrate (3) and the protective layer (4), and the alignment film layers (6) are used for giving initial directors of liquid crystals (51);

a common electrode layer (7); and

a driving electrode layer (8) which is arranged opposite to the common electrode layer (7) and is respectively positioned at the outer sides of the two alignment film layers (6) and is positioned between the substrate (3) and the protective layer (4), wherein the driving electrode layer (8) comprises a first electrode (81) and a second electrode (82), the first electrode (81) and the second electrode (82) are respectively provided with a plurality of control deflection parts (83) which are equal in width and equal in interval and are connected together in series, the sum of the width of each control deflection part (83) and the interval between the control deflection parts (83) is defined as a structural period,

after the first electrode (81) and/or the second electrode (82) and the common electrode are/is applied with voltage, the liquid crystal (51) in the coverage area of the control deflection part (83) of the first electrode (81) and/or the second electrode (82) applied with voltage deflects a director to form a grating structure, and diffracts light incident to the liquid crystal grating,

the grating period of the liquid crystal grating is switched by controlling the voltage applied to the first electrode (81) and/or the second electrode (82) so as to diffract light rays with different wavelengths and ensure a certain diffraction angle.

2. The liquid crystal grating according to claim 1, wherein the driving electrode layer (8) is of a single-layer structure, the first electrode (81) and the second electrode (82) are located in the same layer, and the structural periods of the first electrode (81) and the second electrode (82) are different;

the first electrode (81) is configured to be in a voltage applied state when diffracting a first light ray, and the second electrode (82) is configured to be in a voltage applied state when diffracting a second light ray.

3. The liquid crystal grating of claim 2, wherein the first light is blue light and a portion of green light, and the second light is red light and another portion of green light.

4. The liquid crystal grating according to claim 3, wherein the first electrode (81) has a structural period of 300nm to 400nm, and the second electrode (82) has a structural period of 600nm to 800 nm.

5. The liquid crystal grating according to claim 1, wherein the driving electrode layer (8) is of a single-layer structure, the first electrode (81) and the second electrode (82) are located in the same layer, and the structural periods of the first electrode (81) and the second electrode (82) are the same;

the first electrode (81) or the second electrode (82) is configured to be in a voltage applied state when diffracting a first light ray, and the first electrode (81) and the second electrode (82) are configured to be in a common voltage applied state when diffracting a second light ray.

6. The liquid crystal grating of claim 5, wherein the first light is red light and a portion of green light, and the second light is blue light and another portion of green light.

7. Liquid crystal grating according to any one of claims 2 to 6, characterized in that the side of the first electrode (81) having a control deflection (83) is arranged opposite the side of the second electrode (82) having a control deflection (83), and the control deflection (83) of the first electrode (81) or the control deflection (83) of the second electrode (82) is insertable into a gap between two control deflections (83) of the second electrode (82) or two control deflections (83) of the first electrode (81).

8. Liquid crystal grating according to claim 1, characterized in that the driving electrode layer (8) is of a multilayer construction comprising at least two sub-layers, the first electrode (81) and the second electrode (82) being located within the two sub-layers, respectively, the first electrode (81) and the second electrode (82) having different structural periods;

the first electrode (81) is configured to be in a voltage-applied state when diffracting a first light ray, and the second electrode (82) is configured to be in a voltage-applied state when diffracting a second light ray.

9. The liquid crystal grating of claim 8, wherein the first light is blue light and a portion of green light, and the second light is red light and another portion of green light.

10. The liquid crystal grating according to claim 8, wherein the first electrode (81) has a structural period of 300nm to 600nm, and the second electrode (82) has a structural period of 500nm to 800 nm.

11. The liquid crystal grating according to claim 1, wherein the driving electrode layer (8) further comprises a third electrode having a plurality of control deflection parts (83) of equal width and equal spacing connected in series, and the first electrode (81), the second electrode (82) and the third electrode have different structural periods;

the first electrode (81) is configured to be in a voltage applied state when diffracting a first light ray, the second electrode (82) is configured to be in a voltage applied state when diffracting a second light ray, and the third electrode is configured to be in a voltage applied state when diffracting a third light ray.

12. The liquid crystal grating of claim 11, wherein the first light is blue light, the second light is green light, and the third light is red light.

13. Liquid crystal grating according to claim 11, characterized in that the driving electrode layer (8) is of a multilayer construction comprising at least two sub-layers, the first (81), second (82) and third electrodes being located in the two sub-layers respectively in a pattern of a common arrangement of the two electrodes and a separate arrangement of the other electrode.

14. Liquid crystal grating according to claim 11, characterized in that the drive electrode layer (8) is of a three-layer construction comprising three layers, the first electrode (81), the second electrode (82) and the third electrode being located within the three layers, respectively.

15. The liquid crystal grating of claim 12, wherein the first electrode (81) has a structural period of 400nm to 500nm, the second electrode (82) has a structural period of 500nm to 600nm, and the third electrode has a structural period of 600nm to 700 nm.

16. Liquid crystal grating according to claim 1, characterized in that the common electrode layer (7) and the drive electrode layer (8) are ITO conductive layers.

17. A liquid crystal grating according to claim 1, characterized in that the thickness of the liquid crystal layer (5) is 1um to 2 um.

18. An optical waveguide assembly, comprising:

the waveguide sheet (101) is used for transmitting light rays in a total reflection mode;

a coupling-in unit (102) disposed on one surface of the waveguide sheet (101) for coupling light into the waveguide sheet (101), wherein the coupling-in unit (102) is the liquid crystal grating according to any one of claims 1 to 17; and

a coupling-out unit (103) disposed on the same surface of the waveguide sheet (101) as the coupling-in unit (102), wherein the coupling-out unit (103) is used for coupling light out of the waveguide sheet (101) to a visible region, the coupling-out unit (103) is the liquid crystal grating according to any one of claims 1 to 17, and a grating period of the coupling-out unit (103) and a grating period of the coupling-in unit (102) are synchronously switched to couple in and out light with the same wavelength.

19. The optical waveguide assembly (10) of claim 18, wherein the waveguide sheet (101) has a thickness of 0.3mm to 2.5mm and a refractive index of 1.4 to 2.2.

20. A display device, comprising:

the projection light machine (11) is used for sequentially projecting light rays with various wavelengths; and

an optical waveguide component (10), the optical waveguide component (10) being the optical waveguide component (10) according to claim 18 or 19, wherein the coupling-in unit (102) and the coupling-out unit (103) of the optical waveguide component (10) synchronously switch the grating period corresponding to the wavelength of the light projected by the projector (11) in turn, so that the coupling-in unit (102) couples the light projected by the projector (11) into the waveguide sheet (101) of the optical waveguide component (10), the waveguide sheet (101) transmits the light to the coupling-out unit (103), and the coupling-out unit (103) couples the light out to the visible region,

by switching the grating periods of the coupling-in unit (102) and the coupling-out unit (103), light rays with different wavelengths are diffracted to ensure a certain diffraction angle.

21. The display device according to claim 20, wherein the light projector (11) projects light of a plurality of different wavelengths sequentially at a certain frequency, and the frequency at which the coupling-in unit (102) and the coupling-out unit (103) switch out the corresponding grating periods is consistent with the frequency of the projected light.

22. The display device according to claim 20, wherein the projector (11) projects light of two wavelengths at a frequency of not less than 120 Hz.

23. A display device as claimed in claim 20, characterized in that the projector (11) projects light of two wavelengths, a first light being blue light and a part of the green light having a wavelength close to blue light, and a second light being red light and another part of the green light having a wavelength close to red light.

24. The display device according to claim 20, wherein the projector (11) projects light of three wavelengths, which are a first light, a second light and a third light, respectively, wherein the first light is blue light, the second light is green light, and the third light is red light.

25. A display device as claimed in any one of claims 20 to 24, characterized in that the projection light machine (11) projects at least partially linearly polarized light.

26. A display device according to any one of claims 20 to 24, wherein the projector (11) comprises an lcos display.