TWI408416B - Polarization beam splitter and optical system - Google Patents

Abstract

A polarization beam splitter (PBS), including a first prism, a second prism, an alignment layer and a cholesteric liquid crystal layer (CLC layer), is provided. The first prism has two first surfaces adjacent to each other, and a first slanted surface that forms a first included angle with the two first surfaces respectively. The second prism has two second surfaces adjacent to each other, and a second slanted surface that forms a second included angle with the two second surfaces respectively, and the second slanted surface is opposite to the first slanted surface. The alignment layer is disposed on the first slanted surface of the first prism. The CLC layer is disposed between the alignment layer and the second slanted surface of the second prism.

Description

Polarizing beam splitter and optical system

The present invention relates to a polarizing beam splitter and an optical system, and more particularly to a Polarization Beam Splitter (PBS) and an optical system that utilize a cholesteric liquid crystal layer to generate polarized light.

Polarizing beamsplitters have been widely used in a variety of optical systems to provide polarized light having a particular polarization direction that is required for use in optical systems. For example, liquid crystal projectors currently on the market use polarizing beamsplitters to convert the light generated by the light source into polarized light that can be utilized by the liquid crystal light valve to utilize the polarized light to project an image.

In general, polarizing beamsplitters can be designed such as: Wire-Grid Polarizer (WGP), Thin-Film Polarizer (TFP), Polymer Film Polarizer (Polymer-Film) Polarizer, PFP), etc. However, the conventional polarization beam splitter has a complicated structure and high manufacturing cost, which is disadvantageous for the related development of the polarization beam splitter.

In view of this, the present invention proposes a polarization beam splitter having a simple structure and capable of utilizing a cholesteric liquid crystal layer to cause polarized light.

The present invention further provides an optical system having the above-described polarizing beam splitter that produces polarized image light.

Based on the above, the present invention provides a polarizing beam splitter comprising: a first germanium, a second germanium, an alignment layer, and a cholesteric liquid crystal layer. The first turn has two adjacent first faces, and a first bevel that forms a first angle with the two first faces, respectively. The second turn has two adjacent second faces, and a second bevel that forms a second angle with the two second faces, respectively, and the second bevel faces the first bevel. The alignment layer is disposed on the first slope of the first turn. The cholesteric liquid crystal layer is disposed between the alignment layer and the second slope of the second crucible.

In an embodiment of the invention, the cholesteric liquid crystal layer has a thickness of between 0.5 micrometers (μm) and 2 micrometers.

In an embodiment of the invention, the cholesteric liquid crystal layer comprises: a polymer material and a plurality of cholesteric liquid crystal molecules. A plurality of cholesteric liquid crystal molecules are distributed in the polymer material. The above polymer material may be an ultraviolet curable polymer material.

In an embodiment of the invention, the alignment layer has an alignment pattern.

In an embodiment of the invention, the polarization beam splitter further includes: a multilayer film disposed on the cholesteric liquid crystal layer, and the multilayer film is located between the cholesteric liquid crystal layer and the second slope.

The present invention further provides an optical system comprising: a polarization beam splitter, a first display panel, a second display panel, and a light source. The polarizing beam splitter includes: a first germanium, a second germanium, an alignment layer, and a cholesteric liquid crystal layer. The first turn has two adjacent first faces, and a first bevel that forms a first angle with the two first faces, respectively. The second turn has two adjacent second faces, and a second bevel that forms a second angle with the two second faces, respectively, and the second bevel faces the first bevel. The alignment layer is disposed on the first slope of the first turn. The cholesteric liquid crystal layer is disposed between the alignment layer and the second slope of the second crucible. The first display panel is disposed parallel to one of the two first faces of the first turn. The second display panel is disposed parallel to one of the two second faces of the second turn, and the first display panel is adjacent to the second display panel. The light source provides light and is incident on the polarizing beam splitter, the light having a first polarization state and a second polarization state. The light incident on the first pupil having the first polarization state is reflected by the cholesteric liquid crystal layer and proceeds to the first display panel, and the light having the first polarization state is converted into the first image having the second polarization state by the first display panel. Light, the first image light returns to the first 稜鏡, passes through the cholesteric liquid crystal layer and is emitted by the second ;; and, the light incident on the first 稜鏡, having the second polarization state passes through the cholesteric liquid crystal layer and the second 稜鏡And traveling toward the second display panel, the light having the second polarization state is converted into the second image light having the first polarization state by the second display panel, and the second image light is returned to the second image and is reflected by the cholesteric liquid crystal layer. From the second line.

The invention further provides an optical system comprising: a polarizing beam splitter and a light source. The polarizing beam splitter comprises: a bismuth-based liquid crystal reflective panel, an alignment layer, and a cholesteric liquid crystal layer. The alignment layer is disposed on the 矽-based liquid crystal reflective panel. The cholesteric liquid crystal layer is disposed on the alignment layer. The light source provides light, incident on the polarizing beam splitter, and the light has a first polarization state and a second polarization state. When light is incident on the polarizing beam splitter, the 矽-based liquid crystal reflective panel converts the light into image light, and the image light has a first polarization state or a second polarization state. Further, the quinone-based liquid crystal reflective panel emits image light having a first polarization state or a second polarization state through the cholesteric liquid crystal layer.

The present invention further provides an optical system comprising: a transmissive liquid crystal panel, a first polarization beam splitter, a second polarization beam splitter, and a light source. The transmissive liquid crystal panel has a first surface and a second surface that face each other. The first polarization beam splitter is disposed on the first surface of the transmissive liquid crystal panel. The first polarization beam splitter includes: a first alignment layer and a first cholesteric liquid crystal layer. The first alignment layer is disposed on the first surface, and the first cholesteric liquid crystal layer is disposed on the first alignment layer. The second polarization beam splitter is disposed on the second surface of the transmissive liquid crystal panel. The second polarization beam splitter includes: a second alignment layer and a second cholesteric liquid crystal layer. The second alignment layer is disposed on the second surface, and the second cholesteric liquid crystal layer is disposed on the second alignment layer. The light source provides light having a first polarization state and a second polarization state, and the light is incident on the first polarization beam splitter, the transmissive liquid crystal panel, and the second polarization beam splitter from the first surface side. The light of the first polarization state passes through the first polarization beam splitter, and the light having the first polarization state is converted into the image light having the second polarization state via the transmissive liquid crystal panel. The image light having the second polarization state is emitted through the second polarization beam splitter.

In summary, the polarizing beam splitter of the present invention employs a cholesteric liquid crystal layer, so that light entering the cholesteric liquid crystal layer can produce a polarizing effect. The cholesteric liquid crystal layer can be formed on the substrate by a spin coating method, so that the production of the polarization beam splitter is relatively easy and simple. Further, by controlling the thickness of the cholesteric liquid crystal layer, polarized light of a desired wavelength can be obtained. The optical system of the present invention employs the above-described polarization beam splitter, which simplifies the related processes of the optical system.

The above described features and advantages of the present invention will be more apparent from the following description.

Polarizing beam splitter

1 is a schematic diagram of a polarization beam splitter in accordance with a preferred embodiment of the present invention. Referring to FIG. 1 , the polarization beam splitter 200 includes a first crucible 210 , a second crucible 220 , an alignment layer 230 , and a cholesteric liquid crystal layer 240 . The first crucible 210 has two adjacent first faces 212 and a first slope 214 that forms a first angle θ1 with the two first faces 212, respectively. The second turn 220 has two adjacent second faces 222 and a second slope 224 that forms a second angle θ2 with the two second faces 222, respectively, and the second slope 224 faces the first slope 214. The alignment layer 230 is disposed on the first slope 214 of the first crucible 210. The cholesteric liquid crystal layer 240 is disposed between the alignment layer 230 and the second slope 224 of the second crucible 220.

Referring to FIG. 1, the polarization beam splitter 200 adopts the polarization property of the cholesteric liquid crystal layer 240, so that polarized light can be obtained. In more detail, the cholesteric liquid crystal layer 240 may include a polymer material 242 and a plurality of cholesteric liquid crystal molecules 244, and a plurality of cholesteric liquid crystal molecules 244 are distributed in the polymer material 242. Further, the polymer material 242 is, for example, an ultraviolet curable polymer material. It is worth noting that the cholesteric liquid crystal molecules 244 in the cholesteric liquid crystal layer 240 have an asymmetric nematic phase, which causes polarization of light after passing through the cholesteric liquid crystal layer 240. When the polymer material 242 is cured by irradiation with ultraviolet light, the cholesteric liquid crystal molecules 244 in the cholesteric liquid crystal layer 240 can be maintained in an asymmetrical nematic state.

In the polarization beam splitter 200, the thickness t of the cholesteric liquid crystal layer 230 is, for example, between 0.5 μm and 2 μm. Here, it is to be noted that when the thickness t of the cholesteric liquid crystal layer 230 is thicker, the cholesteric liquid crystal layer 230 can filter out light having a longer wavelength. On the contrary, when the thickness t of the cholesteric liquid crystal layer 230 is thinner, the cholesteric liquid crystal layer 230 can filter out light having a shorter wavelength. By controlling the thickness t of the cholesteric liquid crystal layer 230, the cholesteric liquid crystal layer 230 can filter out the polarized light of various wavelengths required.

In addition, in the polarization beam splitter 200, the alignment layer 230 has, for example, an alignment pattern (not shown). The alignment pattern on the alignment layer 230 can be used to control the tilt angle of the cholesteric liquid crystal molecules 244. More specifically, by forming the cholesteric liquid crystal layer 240 by the spin coating method on the alignment layer 230, the tilting angle of the cholesteric liquid crystal molecules 244 and the thickness t of the cholesteric liquid crystal layer 240 can be simultaneously controlled. In this way, the cholesteric liquid crystal layer 240 can be filtered to polarize light of a specific wavelength.

In addition, referring again to FIG. 1, the material of the first crucible 210 or the second crucible 220 is, for example, a transparent organic material or a transparent glass. For the first crucible 210, the first angle formed by the two first faces 212 and the first bevel 214 may be 45 degrees. For the second turn 220, the second angle formed by the two second faces 222 and the second slope 224 may be 45 degrees. In other words, the first 稜鏡 210 or the second 稜鏡 220 is, for example, a 形状 shaped as an isosceles right triangle.

2 is a schematic diagram of another polarization beam splitter in accordance with a preferred embodiment of the present invention. Referring to FIG. 2, the polarization beam splitter 200a is substantially the same as the polarization beam splitter 200, and the same components are denoted by the same reference numerals, and the same content will not be repeated.

Referring to FIG. 2, the polarization beam splitter 200a further includes a multilayer film 250 disposed on the cholesteric liquid crystal layer 240, and the multilayer film 250 is located between the cholesteric liquid crystal layer 240 and the second slope 224. The multilayer film 250 protects the cholesteric liquid crystal layer 240 and enhances the transmittance of polarized light passing through the cholesteric liquid crystal layer 240. In addition, the multilayer film 250 can also increase the wavelength range of light that the polarization beam splitter 200a can filter.

In the above embodiment, since the polarization beam splitters 200, 200a each have the cholesteric liquid crystal layer 240, the optical characteristics of the cholesteric liquid crystal layer 240 can be used to generate polarized light. In particular, by using the cholesteric liquid crystal layer 240 in combination with the first crucible 210 and the second crucible 220, polarizing beamsplitters 200, 200a having a relatively simple structure can be fabricated.

Furthermore, before the cholesteric liquid crystal layer 240 is uncured, a specific thickness of the cholesteric liquid crystal layer 240 may be formed on the first inclined surface 214 of the first crucible 210 or the second inclined surface 224 of the second crucible 220 by spin coating. That is, the thickness of the cholesteric liquid crystal layer 240 can be easily controlled, and the wavelength band of the desired polarized light can be obtained.

Light Learning system

3 is a schematic diagram of an optical system in accordance with a preferred embodiment of the present invention. Referring to FIG. 3, the optical system 300 includes the above-described polarization beam splitter 200, a first display panel 310, a second display panel 320, and a light source 330. The polarization beam splitter 200 can be referred to the above description, and will not be repeated here.

Referring to FIG. 3 , the first display panel 310 is disposed parallel to one of the two first faces 212 of the first crucible 210 . The second display panel 320 is disposed parallel to one of the two second faces 222 of the second crucible 220 , and the first display panel 310 is adjacent to the second display panel 320 . Light source 330 provides light 332 that is incident on polarization beam splitter 200, which has a first polarization state 332a and a second polarization state 332b.

Referring to FIG. 3, in the optical system 300, the light ray 332 having the first polarization state 332a incident on the first pupil 210 is reflected by the cholesteric liquid crystal layer 240 and travels to the first display panel 310. Light ray 332 having a first polarization state 332a is converted by first display panel 310 into a first image ray M1 having a second polarization state 332b. The first image ray M1 returns to the first ridge 210, passes through the cholesteric liquid crystal layer 240, and is emitted by the second ridge 220.

On the other hand, the light ray 332 incident on the first pupil 210 and having the second polarization state 332b travels through the cholesteric liquid crystal layer 240 and the second buffer 220 to the second display panel 320. Light ray 332 having a second polarization state 332b is converted by second display panel 320 into a second image ray M2 having a first polarization state 332a. The second image light M2 returns to the second crucible 220, is reflected by the cholesteric liquid crystal layer 240, and is emitted by the second crucible 220.

The optical system 300 may further include a projection lens 340 disposed on the optical path of the first image light M1 and the second image light M2. In other words, the optical system 300 illustrated in FIG. 3 is, for example, a two-panel liquid crystal panel type liquid crystal projector that can project an image.

In other embodiments, the polarization beam splitter 200 in the optical system 300 can also be replaced with the polarization beam splitter 200a of FIG. 2, so that the optical system 300 can filter light having a larger wavelength range or make a cholesteric liquid crystal layer. 240 is better protected.

4 is a schematic view of another optical system in accordance with a preferred embodiment of the present invention. Referring to FIG. 4, the optical system 400 includes a polarization beam splitter 410 and a light source 420. The polarization beam splitter 410 includes a ruthenium-based liquid crystal reflective panel 412, an alignment layer 414, and a cholesteric liquid crystal layer 416. The alignment layer 414 is disposed on the 矽-based liquid crystal reflective panel 412, and the cholesteric liquid crystal layer 416 is disposed on the alignment layer 414.

4, the light source 420 provides light 422, incident on the polarizing beam splitter 410, and the light 422 has a first polarization state 422a and a second polarization state 422b. When the light ray 422 is incident on the polarization beam splitter 410, the 矽-based liquid crystal reflective panel 412 converts the light ray 422 into the image light ray M, and the image light ray M has a first polarization state 422a or a second polarization state 422b (shown as A polarization state 422a). Moreover, in the embodiment illustrated in FIG. 4, the 矽-based liquid crystal reflective panel 412 causes the image light M having the first polarization state 422a to exit through the cholesteric liquid crystal layer 416. In other embodiments, the 矽-based liquid crystal reflective panel 412 causes the image ray M having the second polarization state 422b to exit through the cholesteric liquid crystal layer 416.

Similarly, in the optical system 400, the material, the thickness of the cholesteric liquid crystal layer 416, the alignment pattern (not shown) of the alignment layer 414, and the like are described in the related content of FIG. 1, and will not be repeated herein. It is worth mentioning that by controlling the thickness of the cholesteric liquid crystal layer 416 and the tilting angle of the cholesteric liquid crystal molecules 244, the cholesteric liquid crystal layer 416 can be filtered out of the polarized light of different wavelengths required.

Referring to FIG. 4, the optical system 400 further includes a projection lens 430 disposed on the optical path of the emitted image light M having the first polarization state 422a. In other words, the optical system 400 illustrated in FIG. 4 is, for example, a reflective liquid crystal projector that can project an image.

5A and 5B are schematic views of two other optical systems in accordance with a preferred embodiment of the present invention. In the embodiment of FIG. 5A, the polarization beam splitter 410 may further include a protective layer P disposed on the cholesteric liquid crystal layer 416. The protective layer P protects the cholesteric liquid crystal layer 416 from damage caused by moisture or external force. The material of the protective layer P is, for example, glass or other protective material. In the embodiment of FIG. 5B, the polarizing beam splitter 410 has a multilayer film F disposed on the cholesteric liquid crystal layer 416. The multilayer film F can provide additional optical effects of the polarizing beam splitter 410, such as increasing the wavelength range of light that the polarizing beam splitter 410 can filter, or increasing the overall transmittance of the polarizing beam splitter 410.

As apparent from the above, the cholesteric liquid crystal layer 416 can be directly formed on the bismuth-based liquid crystal reflective panel 412, and an optical system 400 capable of projecting the polarized image light M can be obtained.

Figure 6 is a schematic illustration of yet another optical system in accordance with a preferred embodiment of the present invention. Referring to FIG. 6 , the optical system 500 includes a transmissive liquid crystal panel 510 , a first polarization beam splitter 520 , a second polarization beam splitter 530 , and a light source 540 .

Referring to FIG. 6, the transmissive liquid crystal panel 510 has a first surface 512 and a second surface 514 opposite to each other. The first polarization beam splitter 520 is disposed on the first surface 512 of the transmissive liquid crystal panel 510. The first polarization beam splitter 520 includes a first alignment layer 522 and a first cholesteric liquid crystal layer 524. The first alignment layer 522 is disposed on the first surface 512 , and the first cholesteric liquid crystal layer 524 is disposed on the first alignment layer 522 . In addition, the second polarization beam splitter 530 is disposed on the second surface 514 of the transmissive liquid crystal panel 510. The second polarization beam splitter 530 includes a second alignment layer 532 and a second cholesteric liquid crystal layer 534. The second alignment layer 532 is disposed on the second surface 514, and the second cholesteric liquid crystal layer 534 is disposed on the second alignment layer 532.

Referring to FIG. 6 , the light source 540 provides a light 542 having a first polarization state 542 a and a second polarization state 542 b , and the light 542 is incident on the first polarization beam splitter 520 and the penetrating liquid crystal from the first surface 512 side. The panel 510 and the second polarization beam splitter 530. The light ray 542 of the first polarization state 542a passes through the first polarization beam splitter 520, and the light ray 542 having the first polarization state 542a is converted to the image light ray M having the second polarization state 542b via the transmissive liquid crystal panel 510. The image light ray M having the second polarization state 542b is emitted through the second polarization beam splitter 530.

In the optical system 500, the thicknesses t1, t2 of the first or second cholesteric liquid crystal layers 524, 534 are, for example, between 0.5 micrometers and 2 micrometers. By controlling the thicknesses t1, t2 of the first or second cholesteric liquid crystal layers 524, 534, the first or second cholesteric liquid crystal layers 524, 534 can filter out the polarized light of the desired wavelength.

The first cholesteric liquid crystal layer 524 includes a polymer material 525 and a plurality of cholesteric liquid crystal molecules 526, and a plurality of cholesteric liquid crystal molecules 526 are distributed in the polymer material 525. The second cholesteric liquid crystal layer 534 includes a polymer material 535 and a plurality of cholesteric liquid crystal molecules 536, and a plurality of cholesteric liquid crystal molecules 536 are distributed in the polymer material 535. The polymer materials 525 and 535 are, for example, ultraviolet curable polymer materials.

In addition, in the optical system 500, the first alignment layer 522 or the second alignment layer 532 may respectively have an alignment pattern (not shown). The tilt angle of the cholesteric liquid crystal molecules 526, 536 can be controlled by the alignment pattern on the first or second alignment layers 522, 532.

It can be seen that the first and second cholesteric liquid crystal layers 524, 534 of the optical system 500 can be used to replace the polarizing plates conventionally disposed on both sides of the liquid crystal panel, so that the deflection state of the liquid crystal layer in the transmissive liquid crystal panel 510 can be obtained. And the image light M is projected.

In summary, the polarization beam splitter and the optical system of the present invention have at least the following feature: the polarization beam splitter uses a cholesteric liquid crystal layer, and the light is polarized by the optical characteristics of the cholesteric liquid crystal layer. Further, the thickness of the cholesteric liquid crystal layer can be easily controlled by the spin coating method, and a polarizing beam splitter that can filter polarized light of different wavelengths can be easily produced. Since the optical system has the above-described polarization beam splitter, the optical system can convert the light provided by the light source into polarized image light.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the invention, and any one of ordinary skill in the art can make some modifications and refinements without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims.

200, 200a, 410. . . Polarizing beam splitter

210. . . First

212. . . First side

214. . . First slope

220. . . Second

222. . . Second side

224. . . Second slope

230. . . Alignment layer

240, 416. . . Cholesterol liquid crystal layer

242, 417, 525, 535. . . Polymer Materials

244, 418, 526, 536. . . Cholesterol liquid crystal molecule

250, F. . . Multilayer film

300, 400, 500. . . Optical system

310. . . First display panel

320. . . Second display panel

330, 420, 540. . . light source

332, 422, 542. . . Light

332a, 422a, 542a. . . First polarization state

332b, 422b, 542b. . . Second polarization state

340. . . Projection lens

412. . . Silicon-based liquid crystal reflective panel

414. . . Alignment layer

510. . . Penetrating LCD panel

512. . . First surface

514. . . Second surface

520. . . First polarization beam splitter

522. . . First alignment layer

524. . . First cholesterol liquid crystal layer

530. . . Second polarization beam splitter

532. . . Second alignment layer

534. . . Second cholesterol liquid crystal layer

M. . . Image light

M1. . . First image light

M2. . . Second image light

P. . . The protective layer

t, t1, t2. . . Thickness of cholesteric liquid crystal layer

Θ1. . . First angle

Θ2. . . Second angle

1 is a schematic diagram of a polarization beam splitter in accordance with a preferred embodiment of the present invention.

2 is a schematic diagram of another polarization beam splitter in accordance with a preferred embodiment of the present invention.

3 is a schematic diagram of an optical system in accordance with a preferred embodiment of the present invention.

4 is a schematic view of another optical system in accordance with a preferred embodiment of the present invention.

5A and 5B are schematic views of two other optical systems in accordance with a preferred embodiment of the present invention.

Figure 6 is a schematic illustration of yet another optical system in accordance with a preferred embodiment of the present invention.

200. . . Polarizing beam splitter

210. . . First

212. . . First side

214. . . First slope

220. . . Second

222. . . Second side

224. . . Second slope

230. . . Alignment layer

240. . . Cholesterol liquid crystal layer

242. . . Polymer Materials

244. . . Cholesterol liquid crystal molecule

t. . . Thickness of cholesteric liquid crystal layer

Θ1. . . First angle

Θ2. . . Second angle

Claims (7)

A polarizing beam splitter comprising: a first cymbal having two adjacent first faces, and a first bevel forming a first angle with each of the first faces; a second cymbal, a second inclined surface having two adjacent sides, and a second inclined surface respectively forming a second angle with the two second surfaces, wherein the second inclined surface faces the first inclined surface; an alignment layer is disposed on a first inclined surface of the first crucible; a cholesteric liquid crystal layer disposed between the alignment layer and the second inclined surface of the second crucible; and a multilayer film disposed on the cholesteric liquid crystal layer, and the A multilayer film is positioned between the cholesteric liquid crystal layer and the second slope. The polarizing beam splitter of claim 1, wherein the cholesteric liquid crystal layer has a thickness of between 0.5 micrometers and 2 micrometers. The polarizing beam splitter of claim 1, wherein the cholesteric liquid crystal layer comprises: a polymer material; and a plurality of cholesteric liquid crystal molecules, wherein the cholesteric liquid crystal molecules are distributed in the polymer material. The polarizing beam splitter of claim 3, wherein the polymer material comprises: an ultraviolet curable polymer material. The polarizing beam splitter of claim 1, wherein the alignment layer has an alignment pattern. An optical system comprising: a polarizing beam splitter comprising: a first weir, having two adjacent first faces, and a first bevel forming a first angle with each of the first faces; a second weir, a second inclined surface having two adjacent sides, and a second inclined surface respectively forming a second angle with the two second surfaces, wherein the second inclined surface faces the first inclined surface; an alignment layer is disposed on a first inclined surface of the first crucible; a cholesteric liquid crystal layer disposed between the alignment layer and the second inclined surface of the second crucible; and a multilayer film disposed on the cholesteric liquid crystal layer And the multilayer film is disposed between the cholesteric liquid crystal layer and the second inclined surface, and is disposed parallel to one of the two first faces of the first cymbal; a second display panel is parallel Provided in one of the two second faces of the second turn, and the first display panel is adjacent to the second display panel; a light source provides a light incident on the polarizing beam splitter, The light has a first polarization state and a second polarization state, wherein the first edge is incident The light having the first polarization state is reflected by the cholesteric liquid crystal layer and travels toward the first display panel, and the light having the first polarization state is converted by the first display panel into a first polarization state. a first image light, the first image light returns to the first pupil, passes through the cholesteric liquid crystal layer, and is emitted by the second cymbal, and The light incident on the first pupil having the second polarization state travels through the cholesteric liquid crystal layer and the second pupil to the second display panel, and the light having the second polarization state is used by the second The display panel is converted into a second image ray having the first polarization state, and the second image ray is returned to the second ridge, reflected by the cholesteric liquid crystal layer, and emitted by the second ridge. The optical system of claim 6, wherein the cholesteric liquid crystal layer has a thickness of between 0.5 μm and 2 μm.