CN110967831A

CN110967831A - Optical imaging system and head-mounted display equipment

Info

Publication number: CN110967831A
Application number: CN201811152376.9A
Authority: CN
Inventors: 林涛; 孙洁; 李燕; 陈全明
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2018-09-29
Filing date: 2018-09-29
Publication date: 2020-04-07
Anticipated expiration: 2038-09-29
Also published as: CN110967831B; CN113156693A

Abstract

The embodiment of the application discloses an optical imaging system and a head-mounted display device, relates to the field of optics, and solves the problem that the watching experience of a user is low. The optical imaging system includes a polarizer, a polarization converter, an 1/4 wave plate, a first reflective liquid crystal, and a second reflective liquid crystal. A polarizing plate for transmitting the first polarized light; a polarization converter for transmitting the first polarized light or for converting the first polarized light into the second polarized light; 1/4 wave plate is used for converting the polarized light output by the polarization converter into circularly polarized light, the polarized light output by the polarization converter is the first polarized light or the second polarized light, and the circularly polarized light is the first circularly polarized light or the second circularly polarized light; the first reflective liquid crystal is for reflecting circularly polarized light, or for transmitting circularly polarized light and the second reflective liquid crystal is for reflecting circularly polarized light. The embodiment of the application is used for the augmented reality process.

Description

Optical imaging system and head-mounted display equipment

Technical Field

The embodiment of the application relates to the field of optics, in particular to an optical imaging system and a head-mounted display device.

Background

Augmented Reality (AR) refers to a technology that enables a virtual world on a display screen to be combined and interacted with a real world scene through position and angle calculation of a video of a camera and an image analysis technology. Conventional AR display is based on binocular parallax, and depth information is obtained by parallax fusion of left and right eyes to produce a scene with a stereoscopic effect. But causes great discomfort to the user when rendering a near object due to a vergence-accommodation conflict problem. To solve the above problems, the prior art proposes to implement AR light field display by displaying a digital image with depth information. AR light field display may also be referred to as volumetric display. Fig. 1 is a simplified illustration of an optical imaging system provided in the prior art. The AR light field display system includes a microdisplay (microdisplay), a liquid lens, a half-mirror and a spherical mirror. The micro display emits unpolarized light, the unpolarized light reaches the spherical reflector through the liquid lens and the half-transmitting and half-reflecting mirror, the spherical reflector reflects the unpolarized light, and the light is reflected through the half-transmitting and half-reflecting mirror. The liquid lens is applied with different voltages to change the focal length, images with different distance information are generated, and therefore the distance of the virtual images is adjusted, and AR light field display is achieved. However, the liquid lens response speed is less than the human visual frequency limit (e.g., 60HZ/S), resulting in slower switching speed between different focal planes, which affects the viewing experience of the user.

Disclosure of Invention

The embodiment of the application provides an optical imaging system and a head-mounted display device, and solves the problem that the watching experience of a user is low.

In order to achieve the above purpose, the embodiment of the present application adopts the following technical solutions:

in a first aspect, an embodiment of the present application provides an optical imaging system, including: the optical imaging system includes: the liquid crystal display panel comprises a polarizing plate, a polarization converter, an 1/4 wave plate, a first reflection type liquid crystal and a second reflection type liquid crystal, wherein the polarizing plate, the polarization converter, the 1/4 wave plate, the first reflection type liquid crystal and the second reflection type liquid crystal are sequentially arranged. Wherein: a polarizing plate for transmitting the first polarized light; a polarization converter for transmitting the first polarized light or for converting the first polarized light into the second polarized light; when the polarization converter is used for transmitting the first polarized light, the 1/4 wave plate is used for converting the first polarized light into a first circularly polarized light; the first reflective liquid crystal is used for reflecting the first circularly polarized light, or the first reflective liquid crystal is used for transmitting the first circularly polarized light and the second reflective liquid crystal is used for reflecting the first circularly polarized light; when the polarization converter is used for converting the first polarized light into the second polarized light, the 1/4 wave plate is also used for converting the second polarized light into the second circularly polarized light; the first reflective liquid crystal is also for transmitting the second circularly polarized light and the second reflective liquid crystal is for reflecting the second circularly polarized light, or the first reflective liquid crystal is for reflecting the second circularly polarized light.

The optical imaging system provided by the embodiment of the application modulates the polarization of polarized light through the polarization converter, and can reflect the polarized light in different polarization states on the reflective liquid crystal at different distances from the display by utilizing the polarization selectivity of the reflective liquid crystal, so that the AR light field display of a plurality of depth layers is realized. Compared with the existing liquid lens, the reflective liquid crystal has long service life, is more stable, has higher response speed, and effectively improves the user experience.

In one possible design in combination with the first aspect, the polarization converter comprises twisted nematic liquid crystals. The frequency of applying power to the twisted nematic liquid crystal can be larger than the visual frequency limit of human eyes (for example, 60HZ/S), so that the switching speed between different focal planes is increased, and the user experience is effectively improved. In particular, the polarization converter, in particular for transmitting the first polarized light in case of power-up of the polarization converter; the polarization converter is specifically used for converting the first polarized light into the second polarized light under the condition that the polarization converter is not powered.

In combination with the first aspect, in another possible design, the polarization converter may include a liquid crystal variable phase retarder and a zero-order 1/4 waveplate, wherein: the liquid crystal variable phase retarder is used for converting the first polarized light into elliptical polarized light; and a zero-order 1/4 wave plate for converting elliptically polarized light into first polarized light or second polarized light. The frequency of electrifying the liquid crystal variable phase delayer can be larger than the visual frequency limit of human eyes (for example, 60HZ/S), so that the switching speed between different focal planes is improved, and the user experience is effectively improved.

In combination with the first aspect or the possible designs described above, in another possible design, the first reflective liquid crystal and the second reflective liquid crystal are both cholesteric liquid crystals. The first reflective liquid crystal may be disposed in a parallel-aligned liquid crystal cell, and the second reflective liquid crystal may be disposed in a parallel-aligned liquid crystal cell. Therefore, the reflective liquid crystal does not need to be switched in time sequence, and the polarized light in different polarization states can be reflected on the reflective liquid crystal at different distances from the display, so that AR light field display is realized.

In another possible design, in combination with the first aspect or the possible design described above, the optical imaging system further includes a display, which is located before the polarizer in the sequential arrangement of the polarizer, the polarization converter, the 1/4 wave plate, the first reflective liquid crystal, and the polarizer in the second reflective liquid crystal, and the display is configured to emit video light toward the polarizer, the video light being configured to transmit the first polarized light to the polarizer.

With reference to the first aspect or the possible designs described above, in another possible design, the optical imaging system further includes a lens group. The lens set may include different optical elements to transmit or reflect polarized light with different polarization states, and in one possible design, the lens set includes a transflective prism and an imaging lens, and the components are sequentially arranged according to the sequence of the display, the polarizer, the polarization converter, the 1/4 wave plate, the transflective prism, the imaging lens, the first reflective liquid crystal and the second reflective liquid crystal, wherein: the half-transmitting and half-reflecting prism is used for transmitting the circularly polarized light transmitted by the 1/4 wave plate; the imaging lens is used for transmitting the circularly polarized light transmitted by the semi-transparent semi-reflective prism; and the semi-transmitting and semi-reflecting prism is used for reflecting the circularly polarized light reflected by the first reflection type liquid crystal or the second reflection type liquid crystal. In another possible design, the lens group includes a half mirror, and all surfaces of the half mirror are curved surfaces. The components are sequentially arranged according to the sequence of the display, the polaroid, the polarization converter, the 1/4 wave plate, the half-transmitting and half-reflecting mirror, the first reflection type liquid crystal and the second reflection type liquid crystal; wherein: and the half-transmitting and half-reflecting mirror is used for transmitting 1/4 wave plate transmitted circular polarized light and reflecting the circular polarized light reflected by the first reflection type liquid crystal or the second reflection type liquid crystal.

In a second aspect, an embodiment of the present application provides an optical imaging system, including: the liquid crystal display panel comprises a polaroid, an 1/4 wave plate and at least two reflecting units, wherein the components are sequentially arranged according to the sequence of the polaroid, a 1/4 wave plate and the at least two reflecting units, and the reflecting units comprise a 1/2 wave plate and a reflecting liquid crystal. Wherein: a polarizing plate for transmitting the first polarized light; 1/4 wave plate for converting the first polarized light into first circularly polarized light; the target reflecting unit in the at least two reflecting units is used for reflecting circularly polarized light, when no other reflecting unit exists between the target reflecting unit and the 1/4 wave plate, the 1/2 wave plate in the target reflecting unit is used for transmitting the first circularly polarized light or converting the first circularly polarized light into the second circularly polarized light, the reflective liquid crystal in the target reflecting unit is used for reflecting the first circularly polarized light transmitted from the 1/2 wave plate in the target reflecting unit or reflecting the second circularly polarized light converted by the 1/2 wave plate in the target reflecting unit, and the circularly polarized light is the first circularly polarized light or the second circularly polarized light; 1/2 wave plates in the target reflection unit are used for transmitting circularly polarized light or converting the polarization state of the circularly polarized light when other reflection units exist between the target reflection unit and the 1/4 wave plates; any one of the reflection units located between the 1/4 wave plate and the target reflection unit is used for transmitting circularly polarized light, and any one of the reflection units satisfies: if the reflection-type liquid crystal in the reflection unit can transmit the circularly polarized light received by the reflection unit, the 1/2 wave plate in the reflection unit is used for transmitting the circularly polarized light; if the reflective liquid crystal in the reflection unit cannot transmit the circularly polarized light received by the reflection unit, the 1/2 wave plate in the reflection unit is used for converting the polarization state of the circularly polarized light, so that the reflective liquid crystal transmits the converted circularly polarized light.

The optical imaging system provided by the embodiment of the application modulates the polarization of polarized light through the 1/2 wave plate, and can reflect the polarized light in different polarization states on the reflective liquid crystal at different distances from a display by utilizing the polarization selectivity of the reflective liquid crystal, so that the AR light field display of a plurality of depth layers is realized. Compared with the existing liquid lens, the reflective liquid crystal has long service life, is more stable, has higher response speed, and effectively improves the user experience.

In one possible design, in combination with the second aspect, the 1/2 wave plate includes twisted nematic liquid crystals. Therefore, the switching speed between different focal planes is improved, and the user experience is effectively improved. Specifically, in the case of power-up of the 1/2 wave plate, the 1/2 wave plate is specifically configured to transmit either the first circularly polarized light or the second circularly polarized light; in the case where the 1/2 wave plate is not powered, the 1/2 wave plate is specifically used to convert first circularly polarized light into second circularly polarized light or to convert second circularly polarized light into first circularly polarized light.

In a further possible design in combination with the second aspect or the possible designs described above, each of the at least two reflective liquid crystals is a cholesteric liquid crystal. Each of the at least two reflective liquid crystals is disposed in a parallel-aligned liquid crystal cell. Therefore, at least two 1/2 wave plates can be respectively electrified according to the frequency greater than the visual frequency limit of human eyes, the polarization of polarized light is modulated by the 1/2 wave plate, and the polarized light in different polarization states can be reflected on the reflective liquid crystal at different distances from the display by utilizing the polarization selectivity of at least two reflective liquid crystals, so that the AR light field display of a plurality of depth layers is realized.

Alternatively, at least two reflective liquid crystals may reflect polarized light of the same polarization state, or at least two reflective liquid crystals may reflect polarized light of different polarization states, for example, reflective liquid crystals with odd ordinal numbers may reflect polarized light of a first polarization state, and reflective liquid crystals with even ordinal numbers may reflect polarized light of a second polarization state.

In another possible design, in combination with the second aspect or the possible design described above, the optical imaging system further includes a display, which is located before the polarizer in the sequential arrangement of the polarizer, the 1/4 wave plate, and the polarizer in the at least two reflection units, and which is configured to emit video light toward the polarizer, the video light being configured to transmit light of the first polarization through the polarizer.

With reference to the second aspect or the possible design described above, in another possible design, the optical imaging system further includes a lens group. The lens group may comprise different optical elements to achieve transmission or reflection of polarized light of different polarization states. In one possible design, the lens group comprises a half-mirror prism and an imaging lens, which are arranged in order of the display, the polarizer, the 1/4 wave plate, the half-mirror prism, the imaging lens and the at least two reflecting units, wherein: the half-transmitting and half-reflecting prism is used for transmitting the circularly polarized light transmitted by the 1/4 wave plate; the imaging lens is used for transmitting the circularly polarized light transmitted by the semi-transparent semi-reflective prism; and the semi-transmitting and semi-reflecting prism is used for reflecting the circularly polarized light reflected by the target reflecting unit. In another possible design, the lens assembly includes a half mirror, all surfaces of the half mirror are curved, and the components are arranged in sequence according to the display, the polarizer, the 1/4 wave plate, the half mirror and the at least two reflection units. Wherein: and a half mirror for transmitting 1/4 the circularly polarized light transmitted by the wave plate and reflecting the circularly polarized light reflected by the target reflecting unit.

In a third aspect, an embodiment of the present application provides a head-mounted display device, including: the optical imaging system of any preceding claim, and a processor and a display, the processor being configured to control the display to display an image.

In addition, the technical effects brought by the design manners of any aspect can be referred to the technical effects brought by the different design manners in the first aspect and the second aspect, and are not described herein again.

In the embodiments of the present application, the names of the optical imaging system and the head-mounted display device do not limit the devices themselves, and in practical implementations, the devices may be presented by other names. Provided that the function of each device is similar to the embodiments of the present application, and fall within the scope of the claims of the present application and their equivalents.

Drawings

FIG. 1 is a simplified illustration of an optical imaging system provided in the prior art;

FIG. 2 is a diagram illustrating a first exemplary structure of an optical imaging system according to an embodiment of the present disclosure;

FIG. 3 is a diagram illustrating a second exemplary structure of an optical imaging system according to an embodiment of the present disclosure;

fig. 4 is a third structural example of an optical imaging system according to an embodiment of the present disclosure;

fig. 5 is a diagram illustrating a structure of an optical imaging system according to an embodiment of the present disclosure;

fig. 6 is a diagram illustrating a structure of an optical imaging system according to an embodiment of the present disclosure;

fig. 7 is a sixth structural example of an optical imaging system according to an embodiment of the present disclosure;

fig. 8 is a seventh structural example of an optical imaging system according to an embodiment of the present disclosure;

fig. 9 is a diagram eight illustrating a structure of an optical imaging system according to an embodiment of the present application;

fig. 10 is a first view illustrating a structure of a head-mounted display device according to an embodiment of the present disclosure;

fig. 11 is a second structural example of a head-mounted display device according to an embodiment of the present application.

Detailed Description

In the embodiments of the present application, words such as "exemplary" or "for example" are used to mean serving as an example, instance, or illustration. Any embodiment or design described herein as "exemplary" or "e.g.," is not necessarily to be construed as preferred or advantageous over other embodiments or designs. Rather, use of the word "exemplary" or "such as" is intended to present concepts related in a concrete fashion.

Before describing embodiments of the present application, some of the words referred to in this document are defined to assist in understanding the present document.

Light field refers to the amount of light that passes through each point in each direction. Depth information perception is a prerequisite for human beings to produce stereoscopic vision.

To solve the problem of low viewing experience for users, the present application provides an optical imaging system, as shown in fig. 2, which includes a polarizer (polarizer)201, a polarization converter 202, a 1/4 wave plate 203, a first reflective liquid crystal 204, and a second reflective liquid crystal 205. The components are arranged in sequence according to the sequence of the polaroid, the polarization converter, the 1/4 wave plate, the first reflection type liquid crystal and the second reflection type liquid crystal. In the optical imaging system, the polarization of polarized light is modulated by the polarization converter, the polarization selectivity of the reflective liquid crystal is utilized, the reflective liquid crystal is not required to be switched in a time sequence, and the polarized light in different polarization states can be reflected on the reflective liquid crystal at different distances from the display, so that AR light field display is realized. Compared with the existing liquid lens, the reflective liquid crystal has long service life, is more stable, has higher response speed, and effectively improves the user experience. The so-called AR light field is displayed as a digital image with depth information.

The polarizing plate is an optical element that can polarize natural light. The polarizer may be classified into a natural polarizer and an artificial polarizer. Natural polarizers are made of crystals. The artificial polaroid is a composite material formed by laminating a polarizing film, an inner protective film, a pressure-sensitive adhesive layer and an outer protective film. The polarizing plate can be classified into a black-and-white polarizing plate and a color polarizing plate according to the ground color of the polarizing plate. The polarizing plate may be classified into three types of transmission, transflective, and transflective, depending on the application of the polarizing plate. For example, an absorbing polarizer (absorbing polarizer). Has the functions of shielding and transmitting incident light. For example, longitudinal light can be transmitted and transverse light can be shielded; alternatively, the light is transmitted in the lateral direction and shielded in the longitudinal direction. In the present embodiment, the polarizer may be a linear polarizer. For example, a metal wire grid type, a multilayer birefringent polymer film type, or a MacNeille type, or the like. The polarized light transmitted by the linearly polarizing plate is linearly polarized light. The linearly polarized light may be P light or S light. Understandably, unpolarized light encompasses both p-light and s-light. P light refers to light rays with a polarization direction parallel to a reference plane related to the structure of the polarizer, and S light refers to light rays with a polarization direction perpendicular to the reference plane. In general, linear polarizers transmit P light and shield S light.

A polarization converter is a device that converts the polarization state of polarized light. In the embodiment of the present application, the polarization converter may be a Twisted Nematic (TN) liquid crystal. Twisted nematic liquid crystals consist of two conductive substrates sandwiching a liquid crystal layer. When the twisted nematic liquid crystal is not energized, the polarization direction of incident polarized light passing through the twisted nematic liquid crystal is rotated by 90 degrees; when the twisted nematic liquid crystal is energized and the twisted nematic liquid crystal is erected, the polarization direction of incident polarized light passing through the twisted nematic liquid crystal remains unchanged, and polarized light of the same polarization state as the incident polarized light is still emitted. It should be noted that the frequency of applying power to the twisted nematic liquid crystal can be greater than the frequency limit of human visual sense (e.g. 60HZ/S), so that the switching speed between different focal planes is increased, and the user experience is effectively improved.

Optionally, the polarization converter may also include a liquid crystal variable phase retarder and a zero-order 1/4 waveplate. Among them, the polarization direction of the incident polarized light needs to be 45 ° from the fast axis and the slow axis of the liquid crystal variable phase retarder. The difference in retardation between the fast and slow axes of the liquid crystal variable phase retarder converts linearly incident polarized light into elliptically polarized light, and the major and minor axes of the elliptically polarized light are 45 ° with respect to the fast and slow axes of the liquid crystal variable phase retarder. Understandably, the major axis of the elliptically polarized light is 45 ° relative to the fast axis of the liquid crystal variable phase retarder, and the minor axis of the elliptically polarized light is 45 ° relative to the slow axis of the liquid crystal variable phase retarder. Wherein, the retardation is a phase difference value generated by the refractive index of the liquid crystal variable phase retarder. The magnitude of the ellipticity varies with the phase difference between the fast and slow axes. The fast axis and the slow axis of the zero-order 1/4 wave plate are at an angle of 45 degrees relative to the fast axis and the slow axis of the liquid crystal variable phase retarder; thus, the elliptically polarized light exiting from the liquid crystal variable phase retarder passes through the zero-order 1/4 plate and is converted back into linearly polarized light, and the polarization angle of the exiting linearly polarized light will depend on the ellipticity generated by the liquid crystal variable phase retarder. For example, a liquid crystal variable phase retarder for converting a first polarized light into an elliptically polarized light; and a zero-order 1/4 wave plate for converting elliptically polarized light into first polarized light or second polarized light.

The 1/4 wave plate may also be referred to as a 45 degree phase retarder. 1/4 the waveplate is made of a birefringent material. When the light vector of the linearly polarized light forms +/-45 degrees with the fast axis or the slow axis of the 1/4 wave plate, the light passing through the 1/4 wave plate is the circularly polarized light; on the contrary, when the circularly polarized light passes through 1/4 wave plate, the circularly polarized light becomes linearly polarized light.

The first and second reflective liquid crystals are Cholesteric Liquid Crystals (CLC). Cholesteric liquid crystals are composed of a substrate and liquid crystal. Cholesteric liquid crystal molecules are flat and arranged into layers, molecules in the layers are parallel to each other, long molecular axes are parallel to the plane of the layers, and the long molecular axes of different layers slightly change and are arranged into a spiral structure along the normal direction of the layers. In the embodiment of the present application, the first reflective liquid crystal and the second reflective liquid crystal are not required to have the openability and the closability, that is, the first reflective liquid crystal and the second reflective liquid crystal are not required to be powered up. Under the condition that the first reflective liquid crystal and the second reflective liquid crystal are not electrified, the polarization selectivity can be realized through the structures of the first reflective liquid crystal and the second reflective liquid crystal. The phenomenon in which the spatial distribution of the light wave electric vector vibration loses symmetry with respect to the propagation direction of light is called polarization of light. It is the most obvious sign that shear waves are distinguished from other longitudinal waves. Only transverse waves can produce polarization phenomena, so the polarization of light is another example of the wave nature of light. In a plane perpendicular to the propagation direction, transverse vibrations are contained in all possible directions and have the same amplitude in any direction on average, and light having such transverse vibrations symmetrical to the propagation direction is called natural light (unpolarized light). Light whose vibration loses this symmetry is generally referred to as polarized light. The polarized light may be classified into linearly polarized light, partially polarized light, circularly polarized light, and elliptically polarized light. When looking at the light direction, all the electric vectors rotating clockwise are called right-handed elliptical polarized light, and all the electric vectors rotating counterclockwise are called left-handed elliptical polarized light.

As shown in fig. 3, the optical imaging system may further include: a lens group 301 and a display 302. The lens group 301 is located between the 1/4 wave plate 203 and the first reflective liquid crystal 204. The components are arranged in sequence according to the display, the polaroid, the polarization converter, the 1/4 wave plate, the lens group, the first reflective liquid crystal and the second reflective liquid crystal.

Specifically, the display 302 is configured to emit video light to the polarizer 201, and the video light is configured to transmit light of a first polarization through the polarizer. A polarizer 201 for transmitting light of a first polarization from video light emitted from the display. It should be noted that the display is an image source (image source) for displaying an image. In embodiments of the present application, the display may be a microdisplay. For example, a Liquid Crystal Display (LCD), a liquid crystal on silicon (LCoS), an organic light-emitting display (OLED), a Micro-light-emitting diode (Micro-LED), or the like may be used. The video light emitted by the display may be polarized or unpolarized. For example, LCDs emit polarized light. The OLED emits unpolarized light.

The polarization converter 202, upon power up of the polarization converter, is configured to transmit light of a first polarization. Generally, the polarization converter is used to transmit P light, and in the embodiment of the present application, the first polarized light may be P light. Of course, the polarization converter may also be used to transmit S light.

1/4 wave plate 203 for converting the first polarized light into first circularly polarized light.

And a lens group 301 for transmitting the first circularly polarized light transmitted from the 1/4 wave plate.

The first reflective liquid crystal 204 is configured to reflect the first circularly polarized light and transmit polarized light in other polarization states. For example, second circularly polarized light.

The lens group 301 is further configured to reflect the first circularly polarized light reflected from the first reflective liquid crystal.

The polarization converter 202 is used for converting the first polarized light into the second polarized light when the polarization converter is not powered. If the first polarized light is P light, the second polarized light may be S light.

1/4, waveplate 203, also serves to convert the second polarized light into second circularly polarized light.

And a lens group 301 for transmitting the second circularly polarized light transmitted from the 1/4 wave plate.

And a first reflective liquid crystal 204 for transmitting the second circularly polarized light.

And the second reflective liquid crystal 205 is used for reflecting the second circularly polarized light and transmitting polarized light in other polarization states.

And the lens group 301 is also used for reflecting the second circularly polarized light reflected by the second reflective liquid crystal.

Thus, the first circularly polarized light and the second circularly polarized light reflected by the combined lens group form a virtual image of the image displayed by the display in the real scene, i.e. the virtual image of the image displayed by the display is combined with the real scene.

Alternatively, the first reflective liquid crystal is used to reflect the first circularly polarized light, and the second reflective liquid crystal is used to reflect the second circularly polarized light, which is only an illustrative example and is not limited in this application. In practical application, the liquid crystal can also be a first reflective liquid crystal which is used for reflecting the second circularly polarized light and transmitting polarized light in other polarization states. And the second reflective liquid crystal is used for reflecting the first circularly polarized light and transmitting polarized light in other polarization states.

It should be noted that the first reflective liquid crystal may be disposed in the liquid crystal cell with parallel alignment, and the second reflective liquid crystal may also be disposed in the liquid crystal cell with parallel alignment. The first reflective liquid crystal can be used as a left-handed cholesteric liquid crystal, and the second reflective liquid crystal can be used as a right-handed cholesteric liquid crystal. The levorotatory cholesteric liquid crystal and the dextrorotatory cholesteric liquid crystal both include nematic liquid crystal and chiral dopant, and the proportion of the chiral dopant in the levorotatory cholesteric liquid crystal and the dextrorotatory cholesteric liquid crystal can range from 1 to 10%. When the polarization state of the incident light is chirally matched with the chiral dopant in the reflective liquid crystal, the nematic liquid crystal has a reflection characteristic to the incident light; when the polarization state of the incident light is not matched with the chirality of the chiral dopant in the reflective liquid crystal, the nematic liquid crystal has a transmission characteristic to the incident light. Of course, the first reflective liquid crystal can also be used as a right-handed cholesteric liquid crystal, and the second reflective liquid crystal can also be used as a left-handed cholesteric liquid crystal. The embodiments of the present application do not limit this. The polarized light reflected by the left-handed cholesteric liquid crystal can be referred to as left-handed circularly polarized light. The polarized light reflected by the right-handed cholesteric liquid crystal may be referred to as right-handed circularly polarized light. The first circularly polarized light may be left circularly polarized light, and the second circularly polarized light may be right circularly polarized light; alternatively, the first circularly polarized light may be right-circularly polarized light, and the second circularly polarized light may be left-circularly polarized light.

Further, different optical elements may be included for the lens groups to achieve transmission or reflection of polarized light of different polarization states. For example, in one implementation, as shown in fig. 4, the lens group 301 may include a half-mirror 3011 and an imaging lens 3012. The components are sequentially arranged according to the sequence of the display, the polaroid, the polarization converter, the 1/4 wave plate, the half-transmitting and half-reflecting prism, the imaging lens, the first reflection type liquid crystal and the second reflection type liquid crystal.

The half mirror 3011 is an imaging lens that allows incident light to be partially transmitted and partially reflected. For example, a film with 50% transmission and reflectance. Wherein, transmission is an emergence phenomenon that incident light passes through an object through refraction. The object to be transmitted is a transparent or translucent body, such as glass or a color filter. If the transparent body is colorless, most of the light is transmitted through the object except for a few light that is reflected. In order to express the degree of light transmitted by an object, the transmittance (transmittance) is generally expressed by the ratio of the intensity of light after transmission to the intensity of light of incident light after the incident light transmits through the film. The ratio of the intensity of the light reflected back to the intensity of the incident light is indicative of the reflectivity (reflectivity). In the embodiment of the present application, the half mirror may be a half prism.

The imaging lens 3012 is an optical element made of a transparent substance. The material of the imaging lens may be glass or optical resin. The optical resin is an organic compound which is easy to be injection molded or compression molded, is not easy to break and has good light transmittance, and the density is less than 1.6g/cm 3. Glass imaging lenses may also be referred to as phase-independent imaging lenses. The optical resin imaging lens may also be referred to as a phase-dependent imaging lens. A phase-independent imaging lens means that light of different polarization directions does not introduce a phase difference when passing through the device, or that no birefringence effect is present in the device. The phase-dependent imaging lens means that when passing through the device, polarization characteristics are changed, stray light or ghost images are caused, and the device has a birefringence effect, so that the imaging definition is reduced. For example, the light (p light or s light) that should be transmitted linearly polarized becomes transmission elliptically polarized light, and the light that should be transmitted circularly polarized becomes transmission elliptically polarized light. Generally, an imaging lens used in an optical imaging system is a glass imaging lens. In the embodiment of the present application, the imaging lens may be a glass lens.

And the transflective prism 3011 is used for transmitting 1/4 the first circularly polarized light transmitted by the wave plate, and the second circularly polarized light.

And an imaging lens 3012 for transmitting the first circularly polarized light transmitted by the half-mirror prism and the second circularly polarized light.

The transflective prism 3011 is further configured to reflect the first circularly polarized light reflected by the first reflective liquid crystal or the second reflective liquid crystal, and reflect the second circularly polarized light.

It should be noted that the half-mirror prism is used to transmit half of the incident light and reflect the other half. The effective optical path of the present application is only illustrated in the figure, and in practical application, the transflective prism is used for transmitting the first circularly polarized light transmitted by the 1/4 wave plate and the second circularly polarized light, and it is understood that the first circularly polarized light transmitted by the 1/4 wave plate and the second circularly polarized light are reflected by the transflective prism. The transflective prism is also used for reflecting part of the first circularly polarized light reflected by the first reflective liquid crystal or the second reflective liquid crystal and the second circularly polarized light, and part of the first circularly polarized light reflected by the first reflective liquid crystal or the second reflective liquid crystal can be understood and transmitted by the transflective prism.

In another implementation, as shown in fig. 5, the lens group may include a half mirror 3013, all surfaces of the half mirror being curved. The curved surface half-transmitting half-reflecting mirror can transmit partial polarized light and has the function of focusing. The components are arranged in sequence according to the display, the polaroid, the polarization converter, the 1/4 wave plate, the half-mirror, the first reflection type liquid crystal and the second reflection type liquid crystal. And the half-mirror 3013 is used for transmitting 1/4 the first circularly polarized light transmitted by the wave plate, and the second circularly polarized light. The half mirror 3013 is further configured to reflect the first circularly polarized light reflected by the first reflective liquid crystal or the second reflective liquid crystal, and the second circularly polarized light.

It should be noted that, in order to satisfy the Gooch-Tarry condition to achieve non-dispersive polarization rotation, the liquid crystal birefringence Δ n and the liquid crystal cell thickness d should satisfy

Where λ represents the wavelength of light. The value of λ may be the center wavelength of the optical wavelength; the value range of the liquid crystal box thickness d can be 0.5 micrometer (mum) -20μm; the value range of the liquid crystal birefringence delta n can be 0.05-0.3; the liquid crystal dielectric anisotropy Δ ∈ may range from 0.1 to 40. Illustratively, if λ is 532 nanometers (nm), the cell thickness d can be 3 μm, the birefringence Δ n of the liquid crystal can be 0.156, and the dielectric anisotropy Δ ε of the liquid crystal can be 2.4. Under the condition that the applied frequency of the polarization converter is 1KHz and the voltage is 12Vrms, the measured rise time is 3.52 milliseconds (ms) and the measured fall time is 520 microseconds (mus), so that compared with the existing liquid lens, the switching response speed of the focal plane is higher, and the user experience degree is effectively improved.

Fig. 6 is a diagram illustrating a structure of an optical imaging system according to an embodiment of the present disclosure. The optical imaging system includes: polarizers 601, 1/4 wave plate 602 and at least two reflecting units 603. The components are arranged in order of a polarizing plate, 1/4 wave plates, and at least two reflecting units including a 1/2 wave plate 6031 and a reflective liquid crystal 6032.

The polarizer 601 is used for transmitting the first polarized light from the video light emitted from the display.

1/4 wave plate 602, for converting the first polarized light into the first circularly polarized light.

The target reflecting unit of the at least two reflecting units is for reflecting circularly polarized light,

when no other reflection unit exists between the target reflection unit and the 1/4 wave plate, the 1/2 wave plate in the target reflection unit is used for transmitting the first circularly polarized light or converting the first circularly polarized light into the second circularly polarized light, the reflective liquid crystal in the target reflection unit is used for reflecting the first circularly polarized light transmitted by the 1/2 wave plate in the target reflection unit or reflecting the second circularly polarized light converted by the 1/2 wave plate in the target reflection unit, and the circularly polarized light is the first circularly polarized light or the second circularly polarized light.

The 1/2 wave plate in the target reflecting unit serves to transmit circularly polarized light or convert the polarization state of circularly polarized light when other reflecting units exist between the target reflecting unit and the 1/4 wave plate.

Any one of the reflection units located between the 1/4 wave plate and the target reflection unit is used for transmitting circularly polarized light, and any one of the reflection units satisfies: if the reflection-type liquid crystal in the reflection unit can transmit the circularly polarized light received by the reflection unit, the 1/2 wave plate in the reflection unit is used for transmitting the circularly polarized light; if the reflective liquid crystal in the reflection unit cannot transmit the circularly polarized light received by the reflection unit, the 1/2 wave plate in the reflection unit is used for converting the polarization state of the circularly polarized light, so that the reflective liquid crystal transmits the converted circularly polarized light.

Wherein an 1/2 waveplate and a reflective liquid crystal are used to achieve a focal plane of a depth layer. For example, a first 1/2 waveplate and a first reflective liquid crystal are used to achieve the focal plane of the first depth layer, a second 1/2 waveplate and a second reflective liquid crystal are used to achieve the focal plane of the second depth layer, and so on, and an nth 1/2 waveplate and an nth reflective liquid crystal are used to achieve the focal plane of the nth depth layer. Note that the 1/2 wave plate functions as the polarization converter in each of the above embodiments, and the 1/2 wave plate may be a twisted nematic liquid crystal or a niobic acid LiNbO 3.

It should be noted that at least two reflective liquid crystals may be used to reflect polarized light of the same polarization state, and may also be used to reflect polarized light of different polarization states, for example, an odd-numbered reflective liquid crystal may reflect polarized light of a first polarization state, and an even-numbered reflective liquid crystal may reflect polarized light of a second polarization state. In the embodiment of the present application, the polarization state of the polarized light passing through the 1/2 wave plate can be determined by whether the 1/2 wave plate is powered or not, so that the polarized light is reflected on the reflective liquid crystal at different distances by changing the polarization state of the polarized light.

Illustratively, with the i-th 1/2 wave plate energized, the i-th 1/2 wave plate is used to transmit the first circularly polarized light. The ith reflective liquid crystal can reflect the first circularly polarized light, i.e. a focal plane is formed at the depth layer where the ith reflective liquid crystal is located. A jth 1/2 wave plate for transmitting the first circularly polarized light in the case where the ith reflective liquid crystal transmits the first circularly polarized light and the jth 1/2 wave plate is energized; the jth reflective liquid crystal can be used to reflect the first circularly polarized light and transmit polarized light of other polarization states. The jth 1/2 wave plate is any one of the at least two 1/2 wave plates 1/2, and the jth reflective liquid crystal is any one of the at least two reflective liquid crystals, wherein i is not equal to j. M reflective liquid crystals in the ith reflective liquid crystal and the jth reflective liquid crystal are used for transmitting the first circularly polarized light, and m 1/2 wave plates are electrified.

In addition, the jth 1/2 waveplate is also used to convert the first circularly polarized light to the second circularly polarized light in the case where the jth 1/2 waveplate is not energized. The jth reflective liquid crystal can be used to reflect the second circularly polarized light and transmit polarized light of other polarization states. Alternatively, the jth reflective liquid crystal may be used to transmit the second circularly polarized light. After the jth reflective liquid crystal transmits the second circularly polarized light, the reflective liquid crystal after the jth reflective liquid crystal may reflect the second circularly polarized light according to the method described above.

In the case where the ith 1/2 wave plate is not powered, the ith 1/2 wave plate is used to convert the first circularly polarized light into the second circularly polarized light. The ith reflective liquid crystal can reflect the second circularly polarized light, i.e. a focal plane is formed at the depth layer where the ith reflective liquid crystal is located. A jth 1/2 wave plate for transmitting the second circularly polarized light in a case where the ith reflective liquid crystal transmits the second circularly polarized light and the jth 1/2 wave plate is energized; and the j-th reflective liquid crystal is used for reflecting the second circularly polarized light and transmitting polarized light in other polarization states. Where i is not equal to j. M reflective liquid crystals in the ith reflective liquid crystal and the jth reflective liquid crystal are used for transmitting the second circularly polarized light, and the m 1/2 wave plates are electrified.

Similarly, in the case where the jth 1/2 wave plate is not energized, the jth 1/2 wave plate is also used to convert the second circularly polarized light into the first circularly polarized light. The jth reflective liquid crystal can be used to reflect the first circularly polarized light and transmit polarized light of other polarization states. Alternatively, the jth reflective liquid crystal may be used to transmit the first circularly polarized light. After the jth reflective liquid crystal transmits the first circularly polarized light, the reflective liquid crystal after the jth reflective liquid crystal may reflect the first circularly polarized light according to the method described above.

Specifically, the reflective liquid crystal may be configured according to actual needs, and the embodiments of the present application do not limit the reflective liquid crystal to reflect circularly polarized light.

Therefore, at least two 1/2 wave plates can be respectively electrified according to the frequency greater than the visual frequency limit of human eyes, the polarization of polarized light is modulated by the 1/2 wave plate, the polarization selectivity of at least two reflective liquid crystals is utilized, the reflective liquid crystals are not required to be switched in a time sequence, the polarized light in different polarization states can be reflected on the reflective liquid crystals at different distances from the display, and the AR light field display of a plurality of depth layers is realized.

As shown in fig. 7, the optical imaging system may further include: a lens group 701 and a display 702. The lens group 701 is located between 1/4 wave plate 602 and reflection unit 603. The components are arranged in sequence according to the display, the polaroid, the 1/4 wave plate, the lens group and the at least two reflecting units. Wherein the 1/2 wave plate located in each reflection unit is closer to the lens group than the reflection type liquid crystal. Understandably, the 1/2 wave plate located in each reflection unit is closer to the lens group than the reflection type liquid crystal. It can be understood that at least two reflection units may be combined into one reflection module, and the 1/4 wave plate and the reflection module are respectively located at two sides of the lens group. And at least two 1/2 wave plates and at least two reflective liquid crystals in at least two reflective units contained in the reflective module are alternately arranged in sequence.

The display is configured to emit video light toward the polarizer, the video light configured to cause the polarizer to transmit light of a first polarization.

Further, different optical elements may be included for the lens groups to achieve transmission or reflection of polarized light of different polarization states. For example, in one implementation, as shown in fig. 8, the lens group 701 may include a half-mirror prism 7011 and an imaging lens 7012. The components are arranged in sequence according to the display, the polaroid, the 1/4 wave plate, the half-transmitting and half-reflecting prism, the imaging lens and the at least two reflecting units. Wherein: a half-transmitting and half-reflecting prism 7011 for transmitting 1/4 wave plate transmitted circularly polarized light; an imaging lens 7012 for transmitting the circularly polarized light transmitted by the half-mirror prism; the half-mirror 7011 also reflects the circularly polarized light reflected by the target reflecting unit.

It should be noted that the half-mirror prism is used to transmit half of the incident light and reflect the other half. The effective optical path of the present application is only illustrated in the figure, and in practical applications, the transflective prism is used for transmitting the circularly polarized light transmitted by the 1/4 wave plate, and understandably the circularly polarized light transmitted by the 1/4 wave plate is reflected by the transflective prism. The semi-transparent semi-reflecting prism is also used for reflecting part of the circularly polarized light reflected by the target reflective liquid crystal, and understandably, part of the circularly polarized light reflected by the target reflective liquid crystal is transmitted out by the semi-transparent semi-reflecting prism.

In another implementation, as shown in fig. 9, the lens group 701 may include a half mirror 7013, all surfaces of which are curved. The components are arranged in sequence according to the display, the polaroid, the 1/4 wave plate, the half-transparent mirror and the at least two reflection units. Wherein: a half mirror 7013 for transmitting 1/4 the circularly polarized light transmitted by the wave plate; the half mirror 7013 is further configured to reflect circularly polarized light reflected by the target reflecting unit, where the circularly polarized light is first circularly polarized light or second circularly polarized light.

For specific explanation of the display, the polarizer, the 1/4 wave plate, the half mirror, the half prism, the imaging lens, and the reflective liquid crystal, reference may be made to the above description of the optical imaging system shown in fig. 2 to 5, and details of the embodiments of the present application are not repeated herein.

The optical imaging system according to the above embodiments may be applied to a head-mounted display device, for example, an AR device. The AR device may be an AR helmet, AR glasses, or viewing glasses. The viewing glasses may be AR devices with a rectangular virtual display screen. Of course, the viewing glasses may also be AR devices with a circular virtual display screen or a circular arc with cut edges. Therefore, real world information and virtual world information are seamlessly integrated through the AR equipment, namely, entity information (visual information, sound, taste, touch and the like) which is difficult to experience in a certain time space range of the real world originally is overlapped after being simulated through scientific technologies such as computers, virtual information is applied to the real world and is perceived by human senses, and the sensory experience beyond reality is achieved.

Fig. 10 is a first structural example of a head-mounted display device provided in an embodiment of the present application, and as shown in fig. 10, the head-mounted display device may include at least one processor 1001, a memory 1002, a communication interface 1003, a communication bus 1004, and an optical imaging system 1005.

The following specifically describes each constituent component of the head-mounted display device with reference to fig. 10:

the processor 1001 is a control center of the head-mounted display device, and may be a single processor or a collective term for a plurality of processing elements. In a specific implementation, for example, the processor 1001 may include a Central Processing Unit (CPU) or multiple CPUs such as the CPU0 and the CPU1 shown in fig. 10. The processor 1001 may also be an Application Specific Integrated Circuit (ASIC), or one or more integrated circuits configured to implement embodiments of the present application, such as: one or more microprocessors (DSPs), or one or more Field Programmable Gate Arrays (FPGAs).

Taking the processor 1001 as an example of one or more CPUs, the processor 1001 may cause the display included in the optical imaging system 1005 to display an image by running or executing image data stored in the memory 1002 in the head-mounted display device, so that the optical imaging system 1005 presents a virtual image of the image displayed by the display.

In a particular implementation, as an embodiment, the head mounted display device may include multiple processors, such as processor 1001 and processor 1006 shown in fig. 10. Each of these processors may be a single-Core Processor (CPU) or a multi-Core Processor (CPU). A processor herein may refer to one or more devices, circuits, and/or processing cores for processing data (e.g., computer program instructions).

The memory 1002 may be, but is not limited to, a read-only memory (ROM) or other type of static storage device that may store static information and instructions, a Random Access Memory (RAM) or other type of dynamic storage device that may store information and instructions, an electrically erasable programmable read-only memory (EEPROM), a magnetic disk storage medium or other magnetic storage device, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. The memory 1002 may be self-contained and coupled to the processor 1001 via a communication bus 1004. The memory 1002 may also be integrated with the processor 1001. The memory 1002 is used for storing image data and is controlled by the processor 1001 to execute the image data.

The optical imaging system 1005 may be coupled to the memory 1002 and the processor 1001 via a bus to facilitate the display of image content stored by the memory 1002. In practical applications, the head-mounted display device may not include a memory, and may be directly connected to other devices through the communication interface to obtain the image data. The optical imaging system 1005 may be the optical imaging system described in any one of fig. 3 to fig. 5 and fig. 7 to fig. 9, and for the specific explanation, reference may be made to the description of the optical imaging system, which is not repeated herein in this embodiment of the present application.

The communication interface 1003 is used for communicating with other devices or communication networks, and the communication interface 1003 may include a receiving unit implementing a receiving function and a transmitting unit implementing a transmitting function.

The communication bus 1004 may be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, an Extended ISA (EISA) bus, or the like. The bus may be divided into an address bus, a data bus, a control bus, etc. For ease of illustration, only one thick line is shown in FIG. 10, but this is not intended to represent only one bus or type of bus.

The device structure shown in fig. 10 does not constitute a limitation of head mounted display devices and may include more or fewer components than shown, or some components may be combined, or a different arrangement of components.

Fig. 11 is a second structural example of a head-mounted display device according to an embodiment of the present application. As shown in fig. 11, the head mounted display device may include at least one processor 1101, memory 1102, communication interface 1103, communication bus 1104, optical imaging system 1105, and display 1106. The processor is used for controlling the display to display the image. The optical imaging system 1105 may be any of the optical imaging systems described above with respect to fig. 2-9. It should be noted that the display in the optical imaging system may belong to a head-mounted display device. For a detailed explanation, reference may be made to the above description of the optical imaging system, and the embodiments of the present application are not described herein again. The head-mounted display device shown in fig. 10 and 11 is only schematically illustrated, and is not limited thereto.

The above description is only an embodiment of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions within the technical scope of the present disclosure should be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. An optical imaging system, comprising: polarizer, polarization converter, 1/4 wave plate, first reflective liquid crystal and second reflective liquid crystal, wherein:

the polaroid is used for transmitting the first polarized light;

the polarization converter is used for transmitting the first polarized light or converting the first polarized light into second polarized light;

the 1/4 wave plate is used for converting the polarized light output by the polarization converter into circularly polarized light, the polarized light output by the polarization converter is the first polarized light or the second polarized light, and the circularly polarized light is the first circularly polarized light or the second circularly polarized light;

the first reflective liquid crystal is for reflecting the circularly polarized light, or for transmitting the circularly polarized light and the second reflective liquid crystal is for reflecting the circularly polarized light.

2. The optical imaging system of claim 1, wherein the polarization converter comprises twisted nematic liquid crystals.

3. The optical imaging system of claim 2,

the polarization converter is specifically configured to transmit the first polarized light when the polarization converter is powered on, and convert the first polarized light into the second polarized light when the polarization converter is not powered on.

4. The optical imaging system of claim 1, wherein the polarization converter comprises a liquid crystal variable phase retarder and a zero-order 1/4 wave plate, wherein:

the liquid crystal variable phase retarder is used for converting the first polarized light into elliptical polarized light;

the zero-order 1/4 wave plate is used for converting the elliptically polarized light into the first polarized light or the second polarized light.

5. The optical imaging system of any of claims 1-4, wherein the first and second reflective liquid crystals are cholesteric liquid crystals.

6. The optical imaging system according to any of claims 1 to 5, wherein the first reflective liquid crystal is disposed on a parallel aligned liquid crystal cell and the second reflective liquid crystal is disposed on a parallel aligned liquid crystal cell.

7. The optical imaging system of any of claims 1-6, further comprising the display, the display configured to emit video light toward the polarizer, the video light configured to cause the polarizer to transmit the first polarization light.

8. The optical imaging system of any one of claims 1-7, further comprising a lens group comprising a half-mirror prism and an imaging lens, wherein:

the half-transmitting and half-reflecting prism is used for transmitting the circularly polarized light transmitted by the 1/4 wave plate;

the imaging lens is used for transmitting the circularly polarized light transmitted by the semi-transparent semi-reflective prism;

the semi-transmitting and semi-reflecting prism is also used for reflecting the circularly polarized light reflected by the first reflection type liquid crystal or the second reflection type liquid crystal.

9. The optical imaging system of any one of claims 1-7, further comprising a lens group comprising a transflective mirror, all surfaces of which are curved, wherein the transflective prism is configured to transmit the circularly polarized light transmitted by the 1/4 wave plate and to reflect the circularly polarized light reflected by the first reflective liquid crystal or the second reflective liquid crystal.

10. An optical imaging system, comprising: a polarizer, 1/4 wave plates, and at least two reflecting units comprising one 1/2 wave plate and one reflective liquid crystal, wherein:

the polaroid is used for transmitting the first polarized light;

the 1/4 wave plate is used for converting the first polarized light into first circularly polarized light;

a target reflection unit in the at least two reflection units is used for reflecting circularly polarized light, when no other reflection unit exists between the target reflection unit and the 1/4 wave plate, a 1/2 wave plate in the target reflection unit is used for transmitting the first circularly polarized light or converting the first circularly polarized light into a second circularly polarized light, a reflective liquid crystal in the target reflection unit is used for reflecting the first circularly polarized light transmitted from a 1/2 wave plate in the target reflection unit or reflecting the second circularly polarized light converted by a 1/2 wave plate in the target reflection unit, and the circularly polarized light is the first circularly polarized light or the second circularly polarized light;

1/2 wave plates within the target reflection unit serve to transmit the circularly polarized light or convert the polarization state of the circularly polarized light when other reflection units exist between the target reflection unit and the 1/4 wave plates;

any one of the reflection units located between the 1/4 wave plate and the target reflection unit is used for transmitting the circularly polarized light, and the any one of the reflection units satisfies the following conditions:

if the reflection-type liquid crystal in the reflection unit can transmit the circularly polarized light received by the reflection unit, the 1/2 wave plate in the reflection unit is used for transmitting the circularly polarized light;

if the reflection-type liquid crystal in the reflection unit cannot transmit the circularly polarized light received by the reflection unit, the 1/2 wave plate in the reflection unit is used for converting the polarization state of the circularly polarized light, so that the reflection-type liquid crystal transmits the converted circularly polarized light.

11. The optical imaging system of claim 10, wherein the 1/2 wave plate includes twisted nematic liquid crystals.

12. The optical imaging system of claim 11,

the 1/2 wave plate, in particular for transmitting the first circularly polarized light or the second circularly polarized light, with the 1/2 wave plate energized;

the 1/2 wave plate is specifically configured to convert the first circularly polarized light to the second circularly polarized light or to convert the second circularly polarized light to the first circularly polarized light when the 1/2 wave plate is not powered.

13. The optical imaging system of any of claims 10 to 12, wherein each of the at least two reflective liquid crystals is a cholesteric liquid crystal.

14. The optical imaging system according to any one of claims 10 to 13, wherein each of the at least two reflective liquid crystals is disposed in a parallel aligned liquid crystal cell.

15. The optical imaging system of any of claims 10-14, further comprising the display, the display configured to emit video light toward the polarizer, the video light configured to cause the polarizer to transmit the first polarization light.

16. The optical imaging system of any of claims 10-15, further comprising a lens group comprising a half-mirror prism and an imaging lens, wherein:

the semi-transmitting and semi-reflecting prism is also used for reflecting the circularly polarized light reflected by the target reflecting unit.

17. The optical imaging system of any of claims 10-15, further comprising a lens group comprising a half mirror, all surfaces of the half mirror being curved; wherein:

the half-transmitting and half-reflecting prism is used for transmitting the circularly polarized light transmitted by the 1/4 wave plate and is also used for reflecting the circularly polarized light reflected by the target reflecting unit.

18. A head-mounted display device, comprising: the optical imaging system of any one of claims 1-9 or the optical imaging system of any one of claims 10-17, and a processor and a display, the processor for controlling the display to display an image.