CN111399328B - Illuminating device and projection display system - Google Patents

Abstract

The present invention discloses an illumination device, comprising a light source unit including a plurality of light sources emitting light beams of different wavelengths; a collimating lens for collimating a plurality of light beams of different wavelengths outputted from the light source unit at different angles, and emitting a plurality of parallel light beams of different wavelengths; and a diffractive optical element disposed on the output light path of the collimating lens, and for transforming the light paths of the parallel light beams of different wavelengths, and emitting each parallel light beam parallel to the optical axis. The illumination device provided in the present application utilizes the collimating lens and the diffractive optical element to transform the light paths of the light beams emitted by the light source unit, thereby realizing the transformation of the diffuse light beams of different wavelengths into a plurality of mutually parallel light beams, which are outputted parallel to the optical axis, so as to meet the uniformity of the color and brightness of the illumination light beam. The present application also provides a projection display system having the above-mentioned beneficial effects.

Description

Illuminating device and projection display system

Technical Field

The present invention relates to the field of projection technology, and in particular to an illumination device and a projection display system.

Background Art

Projection display technology is a technology that uses optical systems and projection space to magnify and display images. It is widely used in our lives, and common projection display devices include projectors, laser TVs, etc. With the rapid development of wearable devices, augmented reality devices (AR) and virtual reality devices (VR) with projection display systems as core components are becoming increasingly miniaturized and lightweight.

The projection display system is generally composed of an illumination device and an imaging device, and the output display of the image is realized through the combination of optical devices. In order to realize the projection of color images in the projection display system, it is often necessary to set up multiple independent light sources of different wavelengths in the illumination device to provide the illumination beam. At the same time, it is also necessary to configure multiple lenses, dichroic mirrors, color combining prisms and other optical components to process the illumination light, and obtain multiple parallel beams of light to improve the uniformity of the displayed image in color and brightness, thereby ensuring that the projected image has better uniformity and the display effect. However, placing multiple lenses, dichroic mirrors, color combining prisms and other optical components also requires a large space, which hinders the further miniaturization and lightweighting of the projection display system.

Summary of the invention

The object of the present invention is to provide a lighting device and a projection display system, which simplifies the structure of the lighting device and is conducive to the miniaturization and lightness of the lighting 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 including a plurality of light sources emitting light beams of different wavelengths;

A collimating lens for collimating the multiple light beams of different wavelengths to emit multiple parallel light beams of different wavelengths;

A diffraction optical element is arranged on the output light path of the collimating lens and is used to transform the light paths of the parallel light beams of different wavelengths and output parallel light beams of different wavelengths 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 adhered 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 comprises a first light source arranged on the optical axis and having a center line parallel to the optical axis, and further comprises 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 are respectively used to emit light beams of three different wavelengths;

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

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

The first diffraction transmission grating transmits a parallel light beam having the same wavelength as the light beam emitted by the third light source without diffraction, and diffracts a parallel light beam having the same wavelength as the light beam emitted by the second light source, and emits a parallel light beam parallel to the optical axis of the first diffraction transmission grating;

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

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

The light source unit comprises a first light source arranged on the optical axis and having a center line parallel to the optical axis, and further comprises 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 are respectively used to emit light beams of three different wavelengths;

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

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

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

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

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

The present application also provides a projection display system, comprising:

The lighting device as described in any one of the above items is used to output a parallel lighting beam;

An imaging device receives the parallel illumination light beam output by the illumination device and outputs a display projection image.

In an optional embodiment of the present application, the imaging device includes a polarizer, a fly-eye lens, a first condenser, and a polarization beam splitter prism arranged in sequence along the optical path of the light emitted by the illumination device, and the first condenser is arranged on one side of the first side surface of the polarization beam splitter prism;

It also includes a second condenser arranged on a side of a second side adjacent to the first side of the polarization beam splitter prism, an image source arranged on a side of the second condenser away from the polarization beam splitter prism; a 1/4 wavelength plate arranged on a side of a third side facing the second side of the polarization beam splitter prism and parallel to the image source; and a reflector arranged on a side of the 1/4 wavelength plate away from the polarization beam splitter prism.

The lighting device provided by the present invention comprises a light source unit including a plurality of light sources emitting light beams of different wavelengths; a collimating lens for collimating the plurality of light beams of different wavelengths and emitting a plurality of parallel light beams of different wavelengths; and a diffraction optical element arranged on the emitting light path of the collimating lens and for transforming the light path of each parallel light beam of different wavelengths and emitting each parallel light beam of different wavelengths parallel to the optical axis.

In the lighting device provided in the present application, there are multiple light sources emitting diffuse light beams of different wavelength bands in the light source unit, and it is impossible to set all the light sources on the optical axis. Then, after the diffuse light beams of each wavelength are collimated by the collimating lens, the diffuse light beams emitted by the light source not located on the optical axis form parallel light beams forming a certain angle with the optical axis after passing through the collimating lens. At this time, the diffraction optical element is used to deflect the direction of each parallel light beam to be parallel to the optical axis, thereby realizing the parallel emission of each parallel light beam of different wavelengths, and obtaining illumination light beams in which parallel light beams of various colors are emitted parallel to the optical axis, providing support for the color uniformity and brightness uniformity of the projected display image, simplifying the structure of the lighting device, and facilitating the development of miniaturization and lightweight of the lighting device and display system.

The present application also provides a projection display system having the above-mentioned beneficial effects.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present invention or the technical solutions of the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

FIG1 is a schematic diagram of the structure of a lighting device provided in an embodiment of the present application;

FIG2 is a schematic diagram of light source distribution of a light source unit provided in an embodiment of the present application;

FIG3 is a schematic diagram of light source distribution of another light source unit provided in an embodiment of the present application;

FIG4 is a schematic diagram of the optical path structure of another lighting device provided in an embodiment of the present application;

FIG5 is a schematic diagram of the optical path structure of another lighting device provided in an embodiment of the present application;

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

DETAILED DESCRIPTION

In order to enable those skilled in the art to better understand the scheme of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

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

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

A collimating lens 20 for collimating a plurality of light beams with different wavelengths output at different angles from the light source unit 10 to emit a plurality of parallel light beams with different wavelengths;

The diffraction optical element 30 is arranged on the outgoing light path of the collimating lens 20 and is used for transforming the light paths of the parallel light beams of different wavelengths so as to emit the parallel light beams parallel to the optical axis.

Specifically, as shown in Fig. 1, three light sources are arranged on the light source substrate 14 of the light source unit 10 of Fig. 1, namely, light source 1 11, light source 2 12 and light source 3 13, and the three light sources respectively emit three different wavelengths of light. Among them, light source 2 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 of the present application coincide with each other, 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 FIG1 , a collimating lens 20 composed of two lenses is arranged on the optical path of the light source 1 11, the light source 2 12 and the light source 3 13 in FIG1 , and the function of the collimating lens 20 is to convert the diffused light beams emitted by the three light sources into three parallel light beams. As shown in FIG1 , FIG1 shows the diffused light beams of the light source 1 11, the light source 2 12 and the light source 3 13 incident on the collimating lens 20, and the parallel light beams of the light beams exiting the collimating lens 20 with solid lines. Because the optical path of the diffused light beams entering the collimating lens 20 is relatively complicated, FIG1 only connects the incident light beam and the exiting light beam in the collimating lens 20 with dotted lines to roughly represent the light beam transmission path, which does not represent the actual transmission path of the light beam. As can be seen from FIG1 , after the diffused light beam of the light source 1 11 passes through the collimating lens 20, a parallel light beam is formed, and a certain angle is formed between the parallel light beam and the optical axis; similarly, after the diffused light beam of the light source 3 13 passes through the collimating lens 20, a parallel light beam is also formed with a certain angle to the optical axis. The second light source 12 is located on the optical axis, and the center line of the diffuse light beam emitted by it coincides with the optical axis. Correspondingly, the parallel light beam after passing through the collimating lens 20 is parallel to the optical axis.

Because the three parallel beams formed by the light beams emitted by the light source 1 11, the light source 2 12 and the light source 3 13 through the collimating lens 20 are not parallel, they will converge and overlap in space after the collimating lens 20, and then continue to diverge and transmit in three different directions. In FIG1, a diffractive optical element 30 is arranged on the optical path after the three parallel beams of light exit the collimating lens 20, so that the transmission direction of the parallel beams corresponding to the light source 1 11 and the light source 3 13 is deflected, and the angle between them and the optical axis is reduced to close to or even equal to 0, while the parallel light corresponding to the light source 2 12 continues to be transmitted parallel to the optical axis; that is to say, the three parallel beams of different colors formed by the light beams emitted by the light source 1 11, the light source 2 12 and the light source 3 13 through the collimating lens 20 are all approximately transmitted parallel to the optical axis after the diffractive optical element 30 acts, which ensures that after the lighting device provides illumination for the image source, the output display image has better uniformity in color and brightness.

It should be noted that the light source unit 10 in the present application includes multiple light sources, and LED light sources are generally more commonly used, although laser light sources and other types of light sources are certainly not excluded.

Compared with laser light sources, LED light sources emit light with a larger divergence angle. However, the light beam collimated by a collimating lens can greatly reduce the divergence angle of the light beam. Accordingly, the divergence angle of the light beam is reduced, which can reduce the difficulty of the diffraction optical element 30 for light beam conversion, thereby reducing the design difficulty of the diffraction optical element 30, and the arrangement requirements in the light source unit 10 are also reduced accordingly. For example, when the diffraction optical element 30 adopts a diffraction grating, because the collimating lens reduces the divergence angle of the light beam, 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 achieved. Of course, the present application does not exclude the use of a volume grating as an implementation of the diffraction optical element 30.

Of course, for the arrangement of the light sources in the light source unit 10, FIG1 only uses three light sources of different colors as an example for explanation, and the three light sources in FIG1 are arranged in a straight line. In practical applications, the present application does not limit the number and arrangement of light sources. In currently common lighting devices, it is more common to use light sources of three colors: red, green and blue. Therefore, for the light source unit, the light sources included may be a red light source, a blue light source and a green light source. The light sources may be arranged in the manner shown in FIG1 , or in an L-shaped manner as shown in FIG2 , or in a herringbone arrangement.

As mentioned above, for the light source unit, in addition to only including light sources of the 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 and is not limited to the three colors of red, green and blue. Of course, there can also be only light sources of the three colors of red, green and blue, but multiple light sources of each color are provided, as shown in FIG3 , which is a schematic diagram of the light source distribution of another light source unit provided in an embodiment of the present application. In FIG3 , the center of the light source substrate 14 is taken as the center, and the distribution diverges in all directions, and light sources of various colors are alternately arranged, so as to further enhance the illumination brightness of the output light beam of the lighting device.

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

Optionally, the diffractive optical element 30 does not necessarily have to be an independently arranged optical element, and may be arranged in a holographic film layer on the exit surface of the collimating lens 20 .

Compared with the technical solution in the current conventional lighting device that changes the light path of the light source through multiple lenses, dichroic mirrors, color combining prisms and other optical elements with complex structures and large space occupied, so that the lighting device outputs parallel light beams mixed with various colors, the lighting device in the present application utilizes the characteristics of the diffraction device for light path conversion, and adopts diffraction optical elements to replace multiple lenses, dichroic mirrors, color combining prisms and other diffraction optical elements. Its structure is simpler, occupies a smaller space area, can better simplify the internal structure of the lighting device, and can reasonably arrange the distribution of the light source according to actual needs, which is conducive to the development of miniaturization and lightweight lighting devices.

As mentioned above, there are many different options for the diffractive optical element 30 in the present application. The following will describe some of the options 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 .

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

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

Referring to FIG1 , the first light source in the light source unit 10 is equivalent to the light source 2 12 in FIG1 , and the second light source and the third light source are respectively equivalent to the light source 1 11 and the light source 3 13 in FIG1 . In the subsequent embodiments, the first light source, the second light source, and the third light source have the same corresponding relationship with the light source 1 11, the light source 2 12, and the light source 3 13, which will not be described one by one. After the light beams emitted by the three light sources pass through the collimating lens 20 and are incident on the diffraction transmission grating 30, transmission diffraction occurs, so that the light beams of the second light source and the third light source are deflected and finally emitted 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.

Accordingly, when actually selecting and designing the diffraction transmission grating 30, the diffraction transmission grating 30 can be made to diffract only light waves of a specific wavelength, while light waves of other wavelengths are directly transmitted. The light waves of the specific wavelength that the diffraction transmission grating 30 can diffract can also be the light waves emitted by the second light source and the third light source, thus avoiding the diffraction transmission grating 30 from having unnecessary influence on the light beam located on the optical axis.

Furthermore, for the same diffraction transmission grating 30, it is necessary to diffract light of multiple specific wavelengths and make the light rays deflect in a direction parallel to the optical axis. This greatly increases the difficulty of grating design and processing, increases the cost of using the diffraction transmission grating 30, and to a certain extent reduces the effect of deflecting each light beam with different wavelengths in the direction of the optical axis.

To this end, based on the above embodiment, as shown in FIG4 , FIG4 is a schematic diagram of the 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 a first diffraction transmission grating 31 and a second diffraction transmission grating 32;

The first diffraction transmission grating 31 does not diffract the parallel light beam with the same wavelength as the light beam emitted by the third light source, but diffracts the parallel light beam with the same wavelength as the light beam emitted by the second light source, and emits a parallel light beam parallel to the optical axis of the first diffraction transmission grating 31;

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

In the present 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 a light wave of a specific wavelength in a targeted manner, which can greatly reduce the design difficulty and design cost of the diffraction grating, while improving the accuracy of the optical path conversion.

For the diffraction optical element 30, in addition to the diffraction transmission grating, a reflection transmission grating can also be used. Specifically, as shown in FIG5, FIG5 is a schematic diagram of the optical path structure of an illumination device provided in another embodiment of the present application. The illumination device includes a light source unit 10, a collimating lens 20 and a diffraction optical element, and the diffraction optical element is a diffraction reflection grating 33;

The light source unit 10 includes a first light source arranged on the optical axis and having a center line parallel to the optical axis, and 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 are respectively used to emit light beams of three different wavelengths;

The diffraction reflection grating 33 reflects the parallel light beam with the same wavelength as the light emitted by the first light source without diffraction, and diffracts the parallel light beam with the same wavelength as the light emitted by the second light source and the third light source, and emits parallel light beams parallel to the optical axis of the diffraction reflection grating 33.

As shown in FIG5 and FIG1, the diffraction reflection grating 33 has a function similar to that of the diffraction transmission grating. The diffraction reflection grating 33 can only diffract light waves of a specific wavelength, while light waves of other wavelengths are not diffracted. The difference is that the diffraction outgoing light beam generated by the diffraction reflection grating 33 and the incident light beam are located on the same side of the diffraction reflection grating 33, while the non-diffracted light beam is directly reflected.

Obviously, for the diffraction reflection grating 33, only the light beams emitted by the second light source and the third light source can be diffracted, while light beams in other wavelength bands are reflected.

Similar to the diffraction transmission grating 33, 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;

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

The second diffraction reflection grating reflects the parallel light beam with the same wavelength band as the second light source without diffraction, and diffracts the parallel light beam with the same wavelength band as the third light source, and emits a parallel light beam parallel to the optical axis of the second diffraction reflection grating.

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 production cost, and improve the accuracy of optical path conversion, and will not be repeated here.

The present application also provides an embodiment of a projection display system, as shown in FIG6 , which is a schematic diagram of the optical path structure of the projection display system provided in an embodiment of the present application, and the system may include:

An illumination device for outputting an illumination parallel light beam, wherein the illumination device may be the illumination device provided by any of the above embodiments;

The imaging device 40 is used to receive the parallel illumination light beam output by the illumination device and output a display projection image.

Specifically, the imaging device 40 may include:

A polarizer 41, a fly-eye lens 42, a first condenser 43, and a polarization beam splitter prism 44 are sequentially arranged along the optical path of the outgoing light of the illumination device, wherein the first condenser 43 is arranged on one side of the right-angle side surface of the polarization beam splitter prism 44;

It also includes a second condenser 45 arranged on the other right-angled side of the polarization beam splitter prism 44, an image source 46 arranged on the side of the second condenser 45 away from the polarization beam splitter prism 44; a 1/4 wavelength plate 47 arranged opposite to the hypotenuse surface of the polarization beam splitter prism 44 and parallel to the image source 46; and a reflector 48 arranged on the side of the 1/4 wavelength plate 47 away from the polarization beam splitter prism.

As shown in FIG6 , the mixed parallel light beam emitted by the lighting device is incident on the polarizer 41; the polarizer 41 polarizes the incident parallel light beam to form S-polarized light; the fly-eye lens 42 performs homogenization on the incident S-polarized light and emits it to the first condenser 43; the first condenser 43 refracts the S-polarized light homogenized by the fly-eye lens 42 and enters the polarization beam splitter prism 44; the polarization beam splitter 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 polarization beam splitter prism 44 and emits it to the image source 46; the image source 46 is used to provide image information, which can be specifically an LCOS image source 46 and modulate the received S polarized light into P polarized light and reflect it back to the second condenser, and transmit it through the second condenser and the polarization splitter prism to the 1/4 wavelength plate 47. The 1/4 wavelength plate 47 receives the P polarized light modulated and reflected by the image source 46 and emits it 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. The P polarized light modulated twice by the 1/4 wavelength plate 47 is converted into S polarized light and reflected by the polarization splitter prism 44 to realize projection output.

It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the term "includes", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or equipment comprising a series of elements are inherent to the elements. In the absence of more restrictions, the elements limited by the sentence "comprising one..." do not exclude the presence of other identical elements in the process, method, article or equipment comprising the elements. In addition, the above-mentioned technical solution provided in the embodiment of the present application is consistent with the corresponding technical solution in the prior art in principle, and the part is not described in detail, so as to avoid too much redundancy.

The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core ideas of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims (6)

1. A lighting device, comprising:

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

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

the diffraction optical element is arranged on an emergent light path of the collimating lens and used for carrying out light path conversion on the parallel light beams with different wavelengths, and emergent parallel light beams with different wavelengths, which are parallel to an optical axis;

The diffractive optical element is a diffraction transmission grating;

The light source unit comprises a first light source which is arranged on the optical axis and emits a central line parallel to the optical axis, and at least comprises a second light source and a third light source which are arranged offset 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 does not diffract the transmission of the parallel light beams with the same light wave band as the first light source, diffracts the parallel light beams with the same light wave band as the second light source and the third light source, and emits the parallel light beams parallel to the optical axis of the diffraction transmission grating;

The diffraction transmission grating comprises a first diffraction transmission grating and a second diffraction transmission grating;

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

The second diffraction transmission grating does not diffract the transmission of the parallel light beams with the same light wave band as the second light source, diffracts the parallel light beams with the same light wave band as the third light source, and emits the parallel light beams parallel to the optical axis of the second diffraction transmission grating;

or, the diffractive optical element is a diffraction reflection grating;

The light source unit comprises a first light source which is arranged on the optical axis and emits a central line parallel to the optical axis, and at least comprises a second light source and a third light source which are arranged offset 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 and does not diffract the parallel light beams with the same light wave band as the first light source, diffracts the parallel light beams with the same light wave band as the second light source and the third light source, and emits the parallel light beams parallel to the optical axis of the diffraction reflection grating;

the light source unit comprises a plurality of light sources arranged on a light source substrate, wherein each light source is arranged in an L-shaped mode, a Y-shaped mode or any mode of symmetrical arrangement with the light source substrate as a central point.

2. The illumination device of claim 1, wherein the diffractive optical element is any one of a blazed grating, a surface relief grating, a holographic lens, or a bulk 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 diffraction reflection grating comprises a first diffraction reflection grating and a second diffraction reflection grating;

The first diffraction reflection grating reflects and does not diffract the parallel light beams with the same light wave band as the third light source, diffracts the parallel light beams with the same light wave band as the second light source, and emits the parallel light beams parallel to the optical axis of the first diffraction reflection grating;

The second diffraction reflection grating reflects and does not diffract the parallel light beams with the same light wave band as the second light source, diffracts the parallel light beams with the same light wave band as the third light source, and emits the parallel light beams parallel to the optical axis of the second diffraction reflection grating.

5. A projection display system, comprising:

The illumination device according to any one of claims 1 to 4 for outputting an illumination parallel beam;

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

6. The projection display system of claim 5, wherein the imaging device comprises a polarizer, a fly-eye lens, a first condenser lens, and a polarization beam splitter prism sequentially disposed along the light path of the light rays emitted from the illumination device, the first condenser lens being disposed on one side of a first side of the polarization beam splitter prism;

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