CN111399328A - A lighting device and projection display system - Google Patents

Abstract

The invention discloses an illuminating device, comprising a light source unit including a plurality of light sources emitting light beams of different wavelengths; the light source unit is used for collimating the light beams of different wavelengths outputted at different angles in the light source unit, and emitting the light beams of different wavelengths. A collimating lens for parallel beams; a diffractive optical element arranged on the outgoing optical path of the collimating lens, used to transform the optical paths of parallel beams of different wavelengths, and emit parallel beams of parallel light with the optical axis. The lighting device provided in this application uses a collimating lens and a diffractive optical element to convert the light path of the light beam emitted by the light source unit, thereby realizing the conversion of each diffused light beam with different wavelengths into multiple parallel light beams, which are output parallel to the optical axis. , to meet the uniformity of illumination beam color and brightness. The present application also provides a projection display system with the above beneficial effects.

Description

A lighting device and projection display system

technical field

The present invention relates to the technical field of projection, in particular to a lighting device and a projection display system.

Background technique

Projection display technology is a technology that uses optical systems and projection space to amplify and display images. It has a wide range of applications in our lives, and common projection display devices such as projectors and laser TVs. With the rapid development of wearable devices, augmented reality (AR) and virtual reality (VR) devices with projection display systems as their core components tend to be smaller and lighter.

The projection display system is generally composed of an illumination device and an imaging device, and the output display of the image is realized by the combination of optical devices. To realize the projection of color images in the projection display system, it is often necessary to set up multiple independent light sources with different wavelengths in the lighting device to provide illumination beams. At the same time, it is also necessary to configure multiple lenses, dichroic mirrors, color combining prisms, etc. Optical components, etc. process the illumination light to obtain multiple parallel beams that are parallel to each other, so as to improve the uniformity of the displayed image in terms of color and brightness, so as to ensure better uniformity of the projected image and ensure the display effect. However, optical components such as multiple lenses, dichroic mirrors, and dichroic prisms also need to occupy a large space, which hinders the further miniaturization and weight reduction of the projection display system.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an illuminating device and a projection display system, which simplifies the structure of the illuminating device and is beneficial to the miniaturization and weight reduction of the illuminating device and the display system.

In order to solve the above technical problems, the present invention provides a lighting device, comprising:

a light source unit comprising a plurality of light sources emitting light beams of different wavelengths;

A collimating lens for collimating multiple beams of different wavelengths and emitting multiple parallel beams of different wavelengths;

The diffractive optical element is arranged on the outgoing optical path of the collimating lens, and is used to transform the optical paths of the parallel light beams with different wavelengths, and emit parallel light beams with different wavelengths that are all parallel to the optical axis.

In an optional embodiment of the present application, the diffractive optical element is any one of a blazed grating, a surface relief grating, a holographic lens or a volume grating.

In an optional embodiment of the present application, the diffractive optical element is a holographic film layer attached to the exit surface of the collimating lens.

In an optional embodiment of the present application, the diffractive optical element is a diffraction transmission grating;

The light source unit includes a first light source disposed on the optical axis and the center line of which is parallel to the optical axis, and at least a second light source and a third light source disposed deviating from the optical axis; wherein the first light source, the third light source The second light source and the third light source are respectively used to emit light beams with three different wavelengths;

The diffraction transmission grating transmits and does not diffract the parallel beams with the same wavelength band as the first light source, and diffracts the parallel beams with the same wavelength band as the second light source and the third light source. The diffraction transmission grating is parallel to the optical axis of the light beam.

In an optional embodiment of the present application, the diffraction transmission grating includes a first diffraction transmission grating and a second diffraction transmission grating;

Wherein, the first diffraction transmission grating transmits and does not diffract the parallel light beams with the same wavelength band as the third light source, and diffracts the parallel light beams with the same light wavelength band emitted by the second light source, and emits the same wavelength as the third light source. a parallel beam with the optical axis parallel to the diffraction transmission grating;

The second diffraction transmission grating transmits and does not diffract the parallel beams with the same wavelength band as the second light source, and diffracts the parallel beams with the same wavelength band emitted by the third light source. A parallel beam with the optical axis parallel to the transmission grating.

In an optional embodiment of the present application, the diffractive optical element is a diffraction reflection grating;

The light source unit includes a first light source disposed on the optical axis and the center line of which is parallel to the optical axis, and at least a second light source and a third light source disposed deviating from the optical axis; wherein the first light source, the third light source The second light source and the third light source are respectively used to emit light beams with three different wavelengths;

The diffraction reflection grating reflects the parallel light beam with the same wavelength band as the light source emitted by the first light source without diffracting, and diffracts the parallel light beam with the same wavelength band as the light source emitted by the second light source and the third light source, A parallel light beam parallel to the optical axis of the diffraction reflection grating is emitted.

In an optional embodiment of the present application, the diffraction reflection grating includes a first diffraction reflection grating and a second diffraction reflection grating;

Wherein, the first diffraction reflection grating reflects the parallel light beam with the same wavelength band as the third light source without diffracting, and diffracts the parallel light beam with the same light wavelength band emitted by the second light source. the parallel light beam with the optical axis parallel to the first diffraction reflection grating;

The second diffraction reflection grating reflects and does not diffract the parallel light beam with the same wavelength band as the light emitted by the second light source, and diffracts the parallel light beam with the same light wavelength band emitted by the third light source. The three diffraction reflection gratings are parallel beams with parallel optical axes.

In an optional embodiment of the present application, the light source unit includes a plurality of light sources disposed on a light source substrate, wherein each of the light sources is arranged in an L-shape, a zigzag arrangement, or the light source The substrate is any arrangement in which the center point is centrally symmetrical, wherein the light source substrate is perpendicular to the optical axis of the collimating lens.

The application also provides a projection display system, comprising:

As described in any one of the above, an illumination device for outputting a parallel beam of illumination;

The illuminating parallel light beam output by the illuminating device is received, and the imaging device displaying the projected image is output.

In an optional embodiment of the present application, the imaging device includes a polarizer, a fly-eye lens, a first condensing lens, and a polarizing beam splitting prism sequentially arranged along an optical path of the light emitted by the illuminating device, and the first condensing lens arranged on one side of the first side surface of the polarizing beam splitter prism;

It also includes a second condensing lens arranged on one side of the second side adjacent to the first side of the polarizing beam splitting prism, and an image source disposed on the side of the second condensing lens away from the polarizing beam splitting prism; A 1/4 wavelength plate arranged on the side of the third side of the second side of the polarizing beam splitter prism and parallel to the image source; a reflector arranged on the side of the 1/4 wavelength plate away from the polarizing beam splitting prism .

An illuminating device provided by the present invention includes a light source unit including a plurality of light sources emitting light beams of different wavelengths; a collimating lens used for collimating the multiple beams of different wavelengths and emitting multiple parallel beams of different wavelengths A diffractive optical element that is arranged on the outgoing optical path of the collimating lens, and is used to transform the optical path of each parallel beam of different wavelengths, and the output is parallel to the optical axis of each beam of parallel light of different wavelengths.

In the lighting device provided in this application, there are multiple light sources that emit diffused beams of different wavelength bands in the light source unit, and all the light sources cannot be arranged on the optical axis. After the diffused beam emitted by the light source located on the optical axis passes through the collimating lens, a parallel beam forming a certain angle with the optical axis is formed. At this time, the diffractive optical element is used to deflect the direction of each parallel beam to be parallel to the optical axis. Furthermore, the parallel beams of different wavelengths can be output in parallel to each other, and the illumination beams with parallel beams of various colors emitted parallel to the optical axis are obtained, which provides support for the color uniformity and brightness uniformity of the projected display image, and simplifies the structure of the lighting device. It is beneficial to the development of miniaturization and light weight of lighting devices and display systems.

The present application also provides a projection display system with the above beneficial effects.

Description of drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the following will briefly introduce the accompanying drawings used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only For some embodiments of the present invention, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without creative efforts.

FIG. 1 is a schematic structural diagram of a lighting device according to an embodiment of the application;

FIG. 2 is a schematic diagram of a light source distribution of a light source unit according to an embodiment of the present application;

3 is a schematic diagram of a light source distribution of another light source unit provided by an embodiment of the present application;

4 is a schematic diagram of an optical path structure of another lighting device provided by an embodiment of the present application;

5 is a schematic diagram of an optical path structure of another lighting device provided by an embodiment of the present application;

FIG. 6 is a schematic diagram of an optical path structure of a projection display system provided by an embodiment of the present application.

Detailed ways

In order to make those skilled in the art better understand the solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, but not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

As shown in FIG. 1, FIG. 1 is a schematic structural diagram of a lighting device according to an embodiment of the present application, and the lighting device may include:

a light source unit 10 comprising a plurality of light sources emitting light beams of different wavelengths;

a collimating lens 20 for collimating multiple beams of different wavelengths outputted at different angles in the light source unit 10 and emitting multiple parallel beams of different wavelengths;

The diffractive optical element 30 is provided on the outgoing optical path of the collimating lens 20, and is used to transform the optical path of each parallel beam of different wavelengths, and to emit each parallel beam parallel to the optical axis.

Specifically, as shown in FIG. 1 , the light source substrate 14 of the light source unit 10 in FIG. 1 is provided with three light sources, namely light source one 11 , light source two 12 and light source three 13 , and the three light sources respectively emit light of three different wavelengths. light. The second light source 12 is arranged on the optical axis.

It should be noted that the optical axes of the collimating lens 20 and the diffractive optical element 30 in the optical path in this application are coincident, and the optical axis referred to in this embodiment is also the optical axis of the collimating lens 20 and the diffractive optical element 30 .

As shown in FIG. 1 , a collimating lens 20 composed of two lenses is arranged on the optical paths of the light source 1 11 , the light source 2 12 and the light source 3 13 in FIG. 1 . The function of the collimating lens 20 is to diffuse the light emitted by the three light sources. The beam is converted into three parallel beams. As shown in FIG. 1 , in FIG. 1 , the light source one 11 , light source two 12 and light source three 13 are shown in solid lines as the diffused light beams entering the collimating lens 20 and the parallel light beams exiting the collimating lens 20 , because the diffused light beams The optical path of the light entering the collimating lens 20 is relatively complicated. In FIG. 1 , the incident light and the outgoing light in the collimating lens 20 are only connected by dotted lines to roughly represent the beam transmission path, not the actual transmission path of the light beam. It can be seen from FIG. 1 that after the diffused beam of light source 1 11 passes through the collimating lens 20, a parallel beam is formed, and the parallel beam forms a certain angle with the optical axis; A parallel beam at an angle to the optical axis is also formed. The second light source 12 is located on the optical axis, the center line of the diffused beam emitted by the light source coincides with the optical axis, and the corresponding parallel beam passing through the collimating lens 20 is parallel to the optical axis.

Because the light beams emitted by the light source 1 11 , the light source 2 12 and the light source 3 13 are not parallel among the three parallel beams formed by the collimating lens 20 , they will converge and overlap in space after the collimating lens 20 , and then continue to the third beam. Divergent transmission in different directions. In FIG. 1, a diffractive optical element 30 is arranged on the optical path after the three parallel beams exit the collimating lens 20, so that the transmission directions of the parallel beams corresponding to the light source one 11 and the light source three 13 are deflected, and the angle between the optical axes decreases. It is as small as close to or even equal to 0, and the parallel light corresponding to the second light source 12 continues to transmit parallel to the optical axis; that is to say, the light beams emitted by the light source one 11, the light source two 12 and the light source three 13 pass through the collimating lens 20 to form three different beams. The color-parallel light beams are transmitted approximately parallel to the optical axis after the diffractive optical element 30 acts, which ensures that the output display image is more uniform in color and brightness after the illumination device provides illumination for the image source.

It should be noted that the plurality of light sources included in the light source unit 10 in the present application are generally LED light sources, and of course, laser light sources and other types of light sources are not excluded.

Compared with the laser light source, the LED light source has a larger divergence angle of the emitted light. However, the beam collimated by the collimating lens can greatly reduce the divergence angle of the beam. Correspondingly, the divergence angle of the light beam is reduced, which can reduce the difficulty of beam conversion by the diffractive optical element 30 , thereby reducing the design difficulty of the diffractive optical element 30 , and the arrangement requirements in the light source unit 10 are correspondingly reduced. For example, when the diffractive optical element 30 uses a diffraction grating, because the collimating lens reduces the beam divergence angle, even if a one-dimensional grating is used, the light sources in the light source unit 10 are not arranged in a straight line, and the conversion of the light path can be well realized. . Of course, the present application does not exclude the implementation of the volume grating as the diffractive optical element 30 .

Of course, for the arrangement of the light sources in the light source unit 10 , FIG. 1 only takes three light sources of different colors as an example for illustration, and the three light sources are arranged in a straight line in FIG. 1 . In practical applications, the present application does not limit the number and arrangement of the light sources. Among the current common lighting devices, light sources with three colors of red, green and blue are relatively common. Therefore, in the light source unit, the included light sources may be red light sources, blue light sources and green light sources. The arrangement of the light sources may be as shown in FIG. 1 , may also be arranged in an L-shaped manner as shown in FIG. 2 , or may be arranged in a zigzag manner.

As mentioned above, for the light source unit, in addition to only including the light sources of three colors of red, green and blue, it can also include more than three light sources, wherein the color of each light source can be set according to actual needs, Not limited to red, green and blue. Of course, there may be only three light sources of red, green and blue, but there are multiple light sources of each color, as shown in FIG. In FIG. 3 , the center of the light source substrate 14 is taken as the center, and the light sources of various colors are alternately arranged around the light source substrate 14 to further improve the illumination brightness of the output beam of the lighting device.

In addition, the diffractive optical element 30 in the present application may specifically be one of any components that can realize light diffraction, such as a blazed grating, a surface relief grating, and a holographic lens.

Optionally, the diffractive optical element 30 is not necessarily an independent optical element, and specifically, a holographic film layer may also be provided on the exit surface of the collimating lens 20 .

Compared with the current conventional lighting device, the light path of the light source is changed by using multiple lenses, dichroic mirrors, and optical elements with complex structure and large space occupation, so that the lighting device outputs parallel beams of various colors. In other words, the lighting device in this application utilizes the feature of diffractive devices to convert the light path, and uses diffractive optical elements to replace diffractive optical elements such as multiple lenses, dichroic mirrors, and dichroic prisms, which has a simpler structure and occupies a space area. Smaller, the internal structure of the lighting device can be better simplified, and the distribution of light sources can be reasonably arranged according to actual needs, which is beneficial to the development of miniaturization and light weight of the lighting device.

As previously mentioned, there are many different options for the diffractive optical element 30 in this application. The following will describe some of these situations with specific embodiments.

In an optional embodiment of the present application, the lighting device may include a light source unit 10 , a collimating lens 30 and a diffractive optical element 30 .

Wherein, the light source unit 10 includes a first light source disposed on the optical axis and the center line of the emitted light beam is parallel to the optical axis, and also includes at least a second light source and a third light source disposed offset from the optical axis; wherein, the first light source and the second light source and the third light source are respectively used to emit light beams with three different wavelengths;

The diffractive optical element 30 is a diffractive transmission grating; the diffractive transmission grating 30 transmits and does not diffract the parallel light beam with the same wavelength band as the light emitted by the first light source, and diffracts the parallel light beam with the same wavelength band as the light emitted by the second light source and the third light source, A parallel light beam parallel to the optical axis of the diffraction transmission grating 30 is emitted.

Referring to FIG. 1 , the first light source in the light source unit 10 corresponds to the second light source 12 in FIG. 1 , while the second light source and the third light source correspond to the first light source 11 and the third light source 13 in FIG. The first light source, the second light source and the third light source, and the light source one 11, the second light source 12, and the third light source 13 also have the same corresponding relationship, which will not be described one by one. After the light beams emitted by the three light sources are incident on the diffraction transmission grating 30 through the collimating lens 20, transmission diffraction occurs, so that the light beams of the second light source and the third light source are deflected, and finally exit approximately parallel to the optical axis.

Obviously, for the first light source, when its light passes through the diffraction transmission grating 30, it is directly transmitted and continues to propagate along the original light path direction.

Correspondingly, when the diffraction transmission grating 30 is actually selected and designed, the diffraction transmission grating 30 can only be capable of diffracting light waves of a specific wavelength, while the light waves of other wavelengths are directly transmitted, and the diffraction transmission grating 30 can generate light waves of a specific wavelength that are diffracted. That is, it can be the light waves emitted by the second light source and the third light source, which can avoid unnecessary influence of the diffraction transmission grating 30 on the light beam located on the optical axis.

Further, for the same diffraction transmission grating 30, it is necessary to diffract a plurality of light rays with specific wavelengths, so that the light rays are all deflected in the direction parallel to the optical axis, which greatly increases the difficulty of designing and processing the grating. , on the basis of increasing the use cost of the diffraction transmission grating 30 , the effect of deflecting the light beams with different wavelengths toward the optical axis direction will also be reduced to a certain extent.

To this end, based on the above-mentioned embodiment, as shown in FIG. 4 , FIG. 4 is a schematic diagram of an optical path structure of another lighting device provided in an embodiment of the present application. In another specific embodiment of the present application, the diffraction transmission grating 30 further includes the first diffraction transmission grating 31 and the second diffraction transmission grating 32;

Among them, the first diffraction transmission grating 31 transmits and does not diffract the parallel light beams with the same wavelength band as the third light source, and diffracts the parallel light beams with the same light wavelength band emitted by the second light source, and exits the optical axis of the first diffraction transmission grating 31 parallel parallel beams;

The second diffraction transmission grating 32 transmits and does not diffract the parallel light beam with the same wavelength band as the second light source, and diffracts the parallel light beam with the same light wavelength band emitted by the third light source, and emits a light beam parallel to the optical axis of the second diffraction transmission grating 32. parallel beam.

In this embodiment, a diffraction transmission grating is provided for each light source that is not located on the optical axis. Accordingly, each diffraction transmission grating can only diffract light waves of a specific wavelength in a targeted manner. The design difficulty and design cost of the diffraction grating are greatly reduced, and the precision of the optical path conversion is improved at the same time.

For the diffractive optical element 30, in addition to a diffraction transmission grating, a reflection transmission grating can also be used. Specifically, as shown in FIG. 5 , FIG. 5 is a schematic diagram of an optical path structure of an illumination device provided by another embodiment of the present application. The lighting device includes a light source unit 10, a collimating lens 20 and a diffractive optical element, and the diffractive optical element is a diffractive reflection grating 34;

The light source unit 10 includes a first light source arranged on the optical axis and the center line of which is parallel to the optical axis, and also includes at least a second light source and a third light source arranged offset from the optical axis; wherein the first light source, the second light source and the third light source The light sources are respectively used to emit light beams of three different wavelengths;

The diffraction reflection grating 34 reflects and does not diffract the parallel light beams with the same wavelength band as the first light source, and diffracts the parallel light beams with the same light wavelength band as the second light source and the third light source, and emits light from the diffraction reflection grating 34 Parallel beams with parallel axes.

As shown in FIG. 5 and FIG. 1 , for the diffraction reflection grating 34, similar to the function of the diffraction transmission grating, the diffraction reflection grating 34 can only diffract light waves of a specific wavelength, while the light waves of other wavelengths are not diffracted. The difference is that the diffraction reflection grating 34 produces a diffracted outgoing light beam and an incident light beam on the same side of the diffraction reflection grating 34, while the undiffracted light beam is directly reflected.

Obviously, for the diffraction reflection grating 34, only the light beams emitted by the second light source and the third light source can be diffracted, while the light beams of other wavelength bands are reflected.

Similar to the diffraction transmission grating 34, in another optional embodiment of the present application, the diffraction reflection grating may also include a first diffraction reflection grating and a second diffraction reflection grating;

Wherein, the first diffraction reflection grating reflects and does not diffract the parallel light beam with the same wavelength band as the third light source, and diffracts the parallel light beam with the same light wavelength band emitted by the second light source, and exits the optical axis of the first diffraction reflection grating. parallel parallel beams;

The second diffraction reflection grating reflects and does not diffract the parallel light beam with the same wavelength band as the second light source, and diffracts the parallel light beam with the same light wavelength band emitted by the third light source. parallel beam.

The principles of the first diffraction reflection grating and the second diffraction reflection grating in this embodiment are similar to the principles of the first diffraction transmission grating and the second diffraction transmission grating in the above-mentioned embodiment, which can reduce the difficulty of preparing the grating, reduce the manufacturing cost, and improve the optical path. The conversion precision is not repeated here.

The application also provides an embodiment of a projection display system, as shown in FIG. 6 , which is a schematic diagram of an optical path structure of the projection display system provided by the embodiment of the application, and the system may include:

An illuminating device for outputting a parallel beam of illumination, wherein the illuminating device may be the illuminating device provided in any of the above-mentioned embodiments;

The imaging device 40 for receiving the illuminating parallel light beam output by the illuminating device and outputting the projected image.

Specifically, the imaging device 40 may specifically include:

A polarizer 41, a fly-eye lens 42, a first condenser 43, and a polarizing beam splitter prism 44 are arranged in sequence along the light path of the light emitted by the lighting device, and the first condenser lens 43 is arranged on the right-angle side of the polarizing beam splitter prism 44;

Also includes a second condensing mirror 45 arranged on one side of another right-angled surface of the polarizing beam splitting prism 44, an image source 46 disposed on the side of the second condensing mirror 45 away from the polarizing beam splitting prism 44; The 1/4 wavelength plate 47 arranged parallel to the image source 46; the reflecting mirror 48 arranged on the side of the 1/4 wavelength plate 47 away from the polarizing beam splitter prism.

As shown in FIG. 6 , the mixed parallel beam emitted by the illumination device is incident on the polarizer 41; the polarizer 41 polarizes the incident parallel beam to form S-polarized light; The first condenser 43, the first condenser 43 refracts the S-polarized light homogenized and exited by the fly-eye lens 42 into the polarizing beam splitter prism 44, and the polarizing beam splitting prism 44 reflects the S-polarized light refracted by the first condenser 43 to the second condenser 45. , the second condenser 45 refracts the S-polarized light reflected by the polarizing beam splitting prism 44 and emits it to the image source 46, and the image source 46 is used to provide image information, specifically an LCOS image source 46 and converts the received S-polarized light modulation into P The polarized light is reflected back to the second condenser, and transmitted through the second condenser and the polarizing beam splitter prism to the 1/4 wavelength plate 47, and the 1/4 wavelength plate 47 receives the P-polarized light modulated and reflected by the image source 46 and exits to the reflector 48, The reflector 48 reflects the polarized light modulated by the 1/4 wavelength plate 47 back to the 1/4 wavelength plate 47 , and the P polarized light modulated twice by the 1/4 wavelength plate 47 is converted into S polarized light and reflected by the polarization beam splitting prism 44 Implement projection output.

It should be noted that, in this document, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any relationship between these entities or operations. any such actual relationship or sequence exists. Moreover, the terms "comprising", "comprising" or any other variation thereof are intended to encompass a non-exclusive inclusion such that elements inherent to a process, method, article or apparatus of a list of elements are included. Without further limitation, an element qualified by the phrase "comprising a..." does not preclude the presence of additional identical elements in a process, method, article or apparatus that includes the element. In addition, parts of the above technical solutions provided in the embodiments of the present application that are consistent with the implementation principles of the corresponding technical solutions in the prior art are not described in detail, so as to avoid redundant descriptions.

The principles and implementations of the present invention are described herein by using specific examples, and the descriptions of the above embodiments are only used to help understand the method and the core idea of the present invention. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, several improvements and modifications can also be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims (10)

1. An illumination device, comprising:

a light source unit including a plurality of light sources emitting light beams of different wavelengths;

the collimating lens is used for collimating the light beams with different wavelengths and emitting a plurality of parallel light beams with different wavelengths;

and the diffraction optical element is arranged on an emergent light path of the collimating lens and used for carrying out light path transformation on each beam of parallel light with different wavelengths and emitting each beam of parallel light with different wavelengths parallel to the optical axis.

2. The illumination device of claim 1, wherein the diffractive optical element is any one of a blazed grating, a surface embossed grating, a holographic lens, or a volume grating.

3. The illumination device of claim 1, wherein the diffractive optical element is a holographic film layer attached to the exit surface of the collimating lens.

4. The illumination device of claim 1, wherein the diffractive optical element is a diffractive transmission grating;

the light source unit comprises a first light source which is arranged on an optical axis and emits light with a central line parallel to the optical axis, and at least comprises a second light source and a third light source which are arranged in a way of deviating from the optical axis; the first light source, the second light source and the third light source are respectively used for emitting light beams with three different wavelengths;

the diffraction transmission grating transmits the parallel light beams with the same light wave band as that emitted by the first light source without diffraction, and diffracts the parallel light beams with the same light wave band as that emitted by the second light source and the third light source to emit the parallel light beams parallel to the optical axis of the diffraction transmission grating.

5. The illumination device of claim 4, wherein the diffractive transmission grating comprises a first diffractive transmission grating and a second diffractive transmission grating;

the first diffraction transmission grating transmits parallel light beams with the same light wave band as the light wave band emitted by the third light source without diffraction, diffracts the parallel light beams with the same light wave band emitted by the second light source, and emits the parallel light beams parallel to the optical axis of the first diffraction transmission grating;

the second diffraction transmission grating transmits the parallel light beams with the same light wave band as that emitted by the second light source without diffraction, diffracts the parallel light beams with the same light wave band as that emitted by the third light source, and emits the parallel light beams parallel to the optical axis of the third diffraction transmission grating.

6. The illumination device of claim 1, wherein the diffractive optical element is a diffractive reflective grating;

the light source unit comprises a first light source which is arranged on an optical axis and emits light with a central line parallel to the optical axis, and at least comprises a second light source and a third light source which are arranged in a way of deviating from the optical axis; the first light source, the second light source and the third light source are respectively used for emitting light beams with three different wavelengths;

the diffraction reflection grating reflects parallel light beams with the same light wave band as the light wave band emitted by the first light source without diffraction, and diffracts the parallel light beams with the same light wave band as the light wave bands emitted by the second light source and the third light source to emit parallel light beams parallel to the optical axis of the diffraction reflection grating.

7. The illumination device of claim 6, wherein the diffractive reflection grating comprises a first diffractive reflection grating and a second diffractive reflection grating;

the first diffraction reflection grating reflects parallel light beams with the same light wave band as the light wave band emitted by the third light source without diffraction, and diffracts the parallel light beams with the same light wave band emitted by the second light source to emit parallel light beams parallel to the optical axis of the first diffraction reflection grating;

the second diffraction reflection grating reflects parallel light beams with the same light wave band as the light wave band emitted by the second light source without diffraction, and diffracts parallel light beams with the same light wave band emitted by the third light source to emit parallel light beams parallel to the optical axis of the third diffraction reflection grating.

8. The illumination device according to any one of claims 1 to 7, wherein the light source unit includes a plurality of light sources disposed on a light source substrate, wherein each of the light sources is arranged in any one of an L-type arrangement, a delta-type arrangement, or a centrosymmetric arrangement with the light source substrate as a center point, and wherein the light source substrate is perpendicular to an optical axis of the collimating lens.

9. A projection display system, comprising:

an illumination device as claimed in any one of claims 1 to 8 for outputting an illuminating parallel beam;

and the imaging device is used for receiving the illumination parallel light beams output by the illumination device and outputting and displaying a projection image.

10. The projection display system according to claim 9, wherein the imaging device includes a polarizer, a fly-eye lens, a first condenser lens, and a polarization splitting prism, which are arranged in this order along the optical path of the outgoing light from the illumination device, the first condenser lens being arranged on one side of the first side of the polarization splitting prism;

the image source is arranged on one side of the second side surface, which is adjacent to the first side surface of the polarization splitting prism, of the second condenser lens; the 1/4 wavelength plate is arranged on one side of the third side face opposite to the second side face of the polarization beam splitter prism and is parallel to the image source; and the reflecting mirror is arranged on the side, facing away from the polarization splitting prism, of the 1/4 wavelength plate.

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