CN109031870B

CN109031870B - Fluorescence conversion system

Info

Publication number: CN109031870B
Application number: CN201810924149.7A
Authority: CN
Inventors: 田有良; 李巍; 刘显荣; 张勇
Original assignee: Hisense Co Ltd
Current assignee: Hisense Co Ltd
Priority date: 2015-06-30
Filing date: 2015-06-30
Publication date: 2021-03-30
Anticipated expiration: 2035-06-30
Also published as: CN106324958B; CN108761984A; CN109031870A; CN108761984B; CN106324958A

Abstract

The invention discloses a fluorescence conversion system, which comprises a laser excitation light source, a fluorescence wheel, a first lens assembly and a second lens assembly, wherein the first lens assembly and the second lens assembly are respectively positioned on the front surface and the back surface of the fluorescence wheel; the laser excitation light source also penetrates through the fluorescent wheel and is emitted out through the second lens component; the distance between the second lens component and the first lens component is larger than the equivalent focal length of the first lens component, so that the technical problem of light attenuation generated after the laser excitation light source passes through the second lens component is solved.

Description

Fluorescence conversion system

Technical Field

The invention relates to the technical field of laser projection light sources, in particular to a conversion system for generating fluorescence by utilizing laser excitation.

Background

At present, laser is applied to the field of projection display because of the advantages of high brightness, strong monochromaticity, wide color gamut, and the like, but because the cost of laser is high and the image speckle phenomenon caused by laser is serious, the current commercial laser light source is mainly a mixed light source of laser and an LED light source or fluorescence.

Fig. 1 shows a schematic diagram of an optical system for laser excitation of fluorescence, which includes a laser array 11 for emitting laser light, and the blue laser is a relatively low-cost blue laser, and is a blue laser that is usually used. The principle of fluorescence generation is to use the high energy of laser to excite the fluorescent powder to emit fluorescence. When the blue laser light reaches the wavelength conversion member 13, the wheel-shaped surface of the wavelength conversion member 13 has a reflection part and a transmission part (not shown in the figure), wherein the reflection part is coated with phosphor, a lens assembly 131a is arranged in front of the incident surface, and the lens assembly 131a has dual functions of focusing and collimating. When the laser beam enters the wavelength conversion member 13, the laser beam can be converged to a small spot, and when the wavelength conversion member 13 rotates to the position of the reflection portion, the blue laser spot is irradiated onto the phosphor in the reflection portion of the wavelength conversion member 13 to excite the fluorescence. The excited fluorescence is reflected by the wheel-shaped surface and penetrates through the lens assembly 131a, and because the divergence angle of the fluorescence is large, the fluorescence is collimated after passing through the lens assembly 131a and is converted into a parallel light beam to be emitted. When the wavelength conversion member 13 is rotated to the transmission part position, the blue laser spot is allowed to transmit through the wavelength conversion member 13, and since the light travels in a straight line, the blue light is focused by the lens assembly 131a and then is also diverged, so that the blue laser reaches the back surface of the wavelength conversion member 13 and needs to be collimated by the lens assembly 131b again according to the reversible optical path, and travels as a parallel light beam.

When the laser beam is incident on the surface of the wavelength conversion member for fluorescence excitation, theoretically, the laser beam should be converged at the focal point of the lens assembly 131a, where the energy is most concentrated and the light energy density is the greatest, so that the excitation efficiency of fluorescence is also the highest. However, in practical applications, due to the reason of processing the optical lens, aberration occurs in the image formed by the convex lens, and as shown in fig. 2, the light beam passing through the convex lens is refracted and then is not converged at one point (theoretical focal point), but is in a propagation path that gradually converges and diverges. In order to maximize the fluorescence excitation efficiency of the wavelength conversion member, the wavelength conversion member is disposed at the smallest laser spot position after passing through the lens unit 131a in order to obtain the most concentrated excitation energy, and the smallest laser spot position at this time is usually not the theoretical focal plane position, but is located before the theoretical focal point position, and is called positive aberration, and also has negative aberration, but mostly positive aberration.

When the wavelength conversion component is applied to a product, a skilled person finds that a relatively serious light attenuation phenomenon occurs after blue laser passes through the wavelength conversion component and the lens component.

There is a need to solve the problem of light decay of blue light in the wavelength converting member system described above.

Disclosure of Invention

The invention provides a fluorescence conversion system, wherein the distance between a second lens assembly on the back of a fluorescence wheel and a first lens assembly on the front of the fluorescence wheel is set to be larger than the equivalent focal length of the first lens assembly, so that the technical problem of light attenuation generated after a laser excitation light source passes through the second lens assembly is solved.

The invention is realized by the following technical scheme:

a fluorescence conversion system comprises a laser excitation light source, a fluorescence wheel, a first lens assembly and a second lens assembly, wherein the first lens assembly and the second lens assembly are respectively positioned on the front surface and the back surface of the fluorescence wheel; the laser excitation light source is incident to the fluorescent wheel through the first lens assembly, the fluorescent wheel is excited to emit fluorescent light, and the fluorescent light is reflected by the fluorescent wheel and then is emitted through the first lens assembly; the laser excitation light source also penetrates through the fluorescent wheel and is emitted out through the second lens assembly; the distance between the second lens component and the first lens component is larger than the equivalent focal length of the first lens component;

further, the distance d1 between the first lens assembly and the front face of the fluorescent wheel is smaller than the equivalent focal length F of the first lens assembly;

further, the distance between the second lens assembly and the first lens assembly is greater than two times d1 and less than or equal to three times d 1;

furthermore, the first lens component comprises an aspheric lens and an aspheric lens, and the second lens component comprises an aspheric lens and an aspheric lens or the second lens component comprises an aspheric lens;

furthermore, the first lens component is an aspheric lens, and the second lens component is an aspheric lens;

further, the equivalent focal length of the second lens assembly is equal to the equivalent focal length of the first lens assembly;

further, the laser excitation light source is blue laser;

further, the fluorescent wheel comprises a reflecting part and a transmitting part, wherein fluorescent powder is coated on the reflecting part and is used for being excited by blue laser to emit fluorescent light, and the transmitting part is used for transmitting the blue laser;

furthermore, the fluorescence conversion system also comprises a relay lens and an optical axis conversion lens, wherein the second lens component, the relay lens and the optical axis conversion lens form a relay loop of the laser excitation light source, and blue laser and fluorescence are combined after passing through the relay loop;

further, a light combining member is provided in front of the fluorescent wheel, and is configured to combine the blue laser light and the fluorescent light and output the combined light to the light guide member.

The technical scheme of the invention at least has the following beneficial technical effects or advantages:

the wavelength conversion system provided by the technical scheme of the invention comprises a laser excitation light source, a fluorescent wheel, a first lens assembly and a second lens assembly which are respectively positioned on the front surface and the back surface of the fluorescent wheel, wherein the light attenuation phenomenon of laser is reduced by setting the distance between the second lens assembly and the first lens assembly to be larger than the equivalent focal length of the first lens assembly. This is because, in practice, the fluorescent wheel is located at the smallest laser spot of the first lens assembly, rather than the theoretical focal plane position, and in the case of positive aberrations, the smallest spot position is closer to the first lens assembly than the focal position. The reason why the laser generates light decay is found by the research of the technical staff that the second lens component is located at the focal plane position of the first lens component or is very close to the focal plane position in the prior art, although laser spots at the positions are not focused at one point in practice, the spot area is not the minimum, but still has higher light energy density, and the higher the light spot energy density is, dust is easily adsorbed, so that more dust is accumulated on the optical lens located at the position, the penetration efficiency of the optical lens is reduced, and the problem of light attenuation is caused. In the embodiment of the scheme of the invention, when the distance between the second lens component and the first lens component is larger than the equivalent focal length of the first lens component, the second lens component through which laser passes is far away from the focal plane position of the first lens component, so that the spot density of the received laser is smaller, and the phenomenon that dust is easy to accumulate to finally cause light attenuation due to large light energy density can be greatly reduced.

According to the technical scheme, the position of the fluorescent wheel back lens assembly is changed, additional dust removal or dust prevention components are not needed, and the arrangement of other optical components is not influenced, so that the problem of laser light attenuation caused by dust accumulation due to the fact that the second lens assembly is located at a position with high optical density can be solved.

Drawings

FIG. 1 is a diagram of a prior art fluorescence conversion system;

FIG. 2 is a schematic of the optical path for aberration formation in the prior art;

FIG. 3 is a schematic structural diagram of a fluorescence conversion system according to an embodiment of the present invention;

FIG. 4 is a schematic plane view of a fluorescent wheel according to an embodiment of the present invention;

FIG. 5 is an enlarged schematic view of a fluorescence conversion member and a lens assembly according to an embodiment of the present invention;

fig. 6A,6B, and 6C are schematic diagrams illustrating changes in laser spot size according to embodiments of the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, the present invention will be described in further detail with reference to the accompanying drawings, and it is apparent that the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The embodiment of the invention provides a fluorescence conversion system, as shown in fig. 3, which includes a laser excitation light source 11, a fluorescence wheel 13, and a first lens assembly 131a and a second lens assembly 131b respectively located at two sides of the fluorescence wheel. The fluorescent wheel 13, as shown in fig. 4, includes a reflection portion 136 and a transmission portion 135, the reflection portion 136 is coated with fluorescent powder, and the coating of the fluorescent powder is not limited to one color, nor to a certain circumferential angle, and is related to the color matching of the light source. The embodiment of the present invention merely illustrates an optical system in which the phosphor is excited to convert into fluorescence. The transmission part is made of transparent materials and can transmit the laser excitation light source. The luminescent wheel 13 has a rotating shaft and a driving motor, and is capable of performing a rotational motion so that the laser excitation light source sequentially strikes the positions of the transmission section 135 and the reflection section 136 in time series.

The laser excitation light source 11 irradiates the fluorescent wheel through the first lens assembly 131a, and the first lens assembly 131a has the dual functions of focusing and collimating the transmitted light beam. The first lens assembly 131a may include an aspheric lens and a super-spherical lens as shown in fig. 3, wherein the inner super-spherical lens is disposed near the fluorescence wheel, the reason for disposing the two lenses is that the lens assembly receives the fluorescence reflected by the fluorescence wheel except for passing through the laser excitation light source, and since the divergence angle of the fluorescence is large, it is difficult to collect and collimate the light beam with a large divergence angle by using one lens, and thus the combination of the two lenses can better collect the fluorescence with a large divergence angle.

The first lens component 131a may also be an aspheric lens, but it needs to design optical parameters capable of receiving a large divergence angle and collimating the light beam, so that the aspheric curvature requirement is large, the design and processing difficulty is large, and the cost is high. For cost reasons, a lens combination of two lenses is usually used in practical applications.

The first lens component is composed of two lenses, so the equivalent focal length of the first lens component can be calculated by using the focal lengths of the two lenses, the equivalent focal length is F1= (F1 x F2)/(F1 + F2-Delta), wherein F1 and F2 are the theoretical focal lengths of the two lenses in the lens component respectively, F is the calculated theoretical equivalent focal length, and Delta is the lens spacing. Other complex calculation methods exist in the prior art, and only one calculation method is illustrated here.

In the embodiment of the present invention, the laser excitation light source is a blue laser, and the blue laser is focused by the first lens assembly 131a and then converged into a small spot to irradiate onto the fluorescent wheel 13, specifically, when the blue laser irradiates the reflection portion 136 of the fluorescent wheel 13, the phosphor on the surface thereof is excited to emit fluorescent light. The excited fluorescence is reflected by the surface of the fluorescent wheel and passes through the first lens assembly 131a in the direction opposite to the propagation direction of the blue laser, and the first lens assembly 131a collimates the fluorescence with a large divergence angle, so as to obtain a parallel or approximately parallel fluorescent light beam. When the blue laser light is irradiated to the transmission section 135 of the fluorescent wheel 13, the blue laser light is transmitted out and reaches the second lens group 131 b. In the embodiment of the present invention, the second lens assembly 131b includes a super-spherical lens and an aspheric lens as shown in fig. 3, wherein the super-spherical lens is located at the inner side, and the aspheric lens is located at the outer side (both marked in the figure), and is symmetrical to the arrangement of the two lenses in the first lens assembly 131 a. However, the aspheric lens of the second lens assembly 131b and the aspheric lens of the first lens assembly 131a are different in surface type because the distance between the two lenses and the fluorescent wheel is different, and the two lenses are not completely symmetrical light paths, and the angle of diffusion of the light beam received by the aspheric lens of the second lens assembly 131b is larger than the angle of emission of the aspheric lens of the first lens assembly 131a, that is, the constraint capability of the aspheric lens of the second lens assembly on the light is stronger. If the two surface types are the same, the optical path is restored by symmetry with respect to the fluorescent wheel, but this arrangement is very easy to cause the aspherical lens receiving surface of the second lens component 131b to be located near the focal plane of the first lens component 131 a.

In order to make the light path of the blue laser beam after passing through the first lens assembly 131a and the fluorescent wheel still propagate as a parallel beam, the equivalent focal lengths of the second lens assembly 131b and the first lens assembly 131a are equal, so that the blue laser beam can be subjected to light path convergence and inverse light path collimation, and the laser beam is ensured to still emit as a parallel beam.

The second lens element 131b may be a single aspheric lens, and in this case, the first lens element 131a may be a combination of a single aspheric lens and a super-spherical lens, or may be a single aspheric lens. As already mentioned, the aspheric lens is costly, and thus a combination of two lenses is generally used.

As shown in fig. 5, F1 is the equivalent focal length of the first lens component 131a, and is only schematically indicated in the figure, in practical applications, due to aberration, the distance d1 from the front surface of the fluorescent wheel to the first lens component 131a is smaller than the equivalent focal length of the first lens component 131a, and the light spot at the equivalent focal position is also smaller than the light spot size received by the front surface of the fluorescent wheel. Since the fluorescent wheel is located at the position of the minimum spot of the blue laser light, the light beam can be considered to be converged at the position, so that F2 is the equivalent focal length of the second lens assembly 131b and refers to the distance from the fluorescent wheel to the principal point of the second lens assembly 131 b. When F1= F2, that is, the equivalent focal lengths of the two lens assemblies are set to be equal, according to the principle that light travels along a straight line and the optical path is reversible, the blue laser beam is converged on the fluorescent wheel by the first lens assembly 131a, then is emitted from the fluorescent wheel, and is collimated into a parallel beam or an approximately parallel beam by the second lens assembly 131b for inverse optical path transformation.

In the embodiment of the present invention, the distance between the second lens element 131b and the first lens element 131a is greater than the equivalent focal length of the first lens element 131a, which means that the distance D between the inner lens piece of the second lens element 131b and the principal point plane of the first lens element 131a is greater than the equivalent focal length F1 of the first lens element 131 a. Therefore, the lens of the second lens component 131b can no longer be located at the focal plane position of the first lens component 131a, and since this focal plane is not a measurable constant value in practice, D is set to be greater than F1, it can also be considered that the second lens component 131b is no longer located at or near the focal plane of the first lens component 131a, so that the laser spot received by the second lens component 131b, whether the laser spot received by the inner aspheric lens or the laser spot received by the outer aspheric lens, becomes large, and the light energy density becomes small, thereby greatly alleviating the phenomenon that the light attenuation of the laser beam passing through the second lens component is finally caused by the easy accumulation of dust due to the large light energy density received by the second lens component.

In one implementation, the distance D between the second lens assembly 131b and the first lens assembly 131a is greater than two times the distance D1 from the first lens assembly 131a to the front surface of the fluorescent wheel and less than or equal to three times D1. Fig. 6A is a schematic diagram of a laser spot when the second lens assembly 131B is located at the focal plane of the first lens assembly 131a, and fig. 6B and fig. 6C are schematic diagrams of a laser spot when the second lens assembly is away from the focal plane of the first lens assembly 131a, where D =2.5 × D1 and D =3 × D1, respectively.

If D is too large, although the optical density of the received laser spot is reduced, the diffusion angle of the laser beam is also very large because the area of the laser spot is increased along with the distance by a multiple, the efficiency of collecting the laser beam is reduced, the design requirement on the lens surface shape of the second lens group is higher, the position or the volume of an optical component of the whole optical path framework can be changed, and the design cost is increased.

By contrast, in the focal plane or the plane very close to the focal plane, the laser spot is the imaging plane of the laser spot according to the lens imaging principle, and at this time, the schematic diagram shown in fig. 6A, which is the imaging of the laser spots one by one, can be observed through the apparatus, where the imaging laser spot is related to the arrangement of the laser array, and this figure is only used as a schematic diagram. The laser spot is very small, so the light energy density is large, and dust is easily adsorbed and accumulated at the position with large energy density, so the optical penetration efficiency of the optical lens, i.e. the second lens component 131b, is reduced, and the attenuation of the blue laser beam transmitted through the second lens component is caused. When the second lens component 131B is far from the focal plane position of the first lens component 131a, as shown in fig. 6B and 6C, compared with fig. 6A, the farther the distance is, the greater the divergence degree of the spot is, and the light energy density of the spot is smaller, so that the phenomenon of light attenuation of the blue laser can be greatly reduced.

Preferably, in order to achieve the purpose of efficient excitation of fluorescence and reduce light loss of blue laser in the transmission process, the laser excitation light source further forms a small light spot with uniform energy after beam shrinking and homogenizing by the beam shaping device 111 and then enters the surface of the fluorescent wheel, in a specific embodiment, the laser excitation light source beam first reaches the light combining part 12, the light combining part 12 is configured to transmit the blue laser, and after transmission, the laser excitation light source beam is focused by the first lens component 131a and then irradiates the surface of the reflective part 136 of the fluorescent wheel with the reduced light spot. The light combining component can adopt a dichroic mirror, and light with corresponding wavelength can be selectively transmitted and reflected through coating, so that the light output effects of blue transmission, red reflection and green reflection are realized. And, the excited fluorescence also reaches the light combining part 12 after passing through the first lens assembly 131a, and if the fluorescence is green fluorescence and red fluorescence, the dichroic mirror may be set to reflect both the green and red fluorescence.

And, further, after passing through the second lens assembly 131b, the blue laser beam also passes through the relay lens 132 and the optical axis conversion mirror 133, and after optical axis conversion and convergence, returns to the light combining component 12 again, and after being transmitted by the light combining component 12, the blue laser beam is consistent with the output direction of the reflected fluorescence, and reaches the light guiding component, such as a light rod, or after being filtered and output by the color filter wheel 14, enters the light rod. The second lens assembly 131b, the relay lens 132 and the optical axis conversion lens 133 form a blue light relay loop, which forms a blue light collecting optical path as an output source of blue light in the whole laser and fluorescence mixed light source. Therefore, if the blue light is attenuated after passing through the relay loop, the attenuation of the blue light component in the whole laser mixed light source is caused, so that the brightness of the laser mixed light source is reduced, meanwhile, the proportion of each primary color is unbalanced due to the attenuation of the blue light component, so that the color temperature is shifted, and the display quality of a laser projection image is also reduced.

In the embodiment of the invention, the distance between the lens component in the blue light relay loop and the first lens component on the front surface of the fluorescent wheel is set to be larger than the equivalent focal length of the first lens component, so that the lens of the second lens component can be prevented from being positioned on the equivalent focal plane or the position close to the equivalent focal plane of the first lens component, a larger laser spot can be received, the light energy density is smaller, the dust accumulation condition is reduced, the attenuation degree of blue light after passing through the relay loop is reduced, and for the whole laser light source system, the problems of blue light attenuation degree, color temperature shift and light source brightness reduction are also reduced.

While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

Claims

1. A fluorescence conversion system comprises a laser excitation light source, a fluorescence wheel, a first lens assembly and a second lens assembly, wherein the first lens assembly and the second lens assembly are respectively positioned on the front surface and the back surface of the fluorescence wheel;

laser excitation light is incident to the fluorescent wheel through the first lens assembly, and the fluorescent wheel is excited to emit fluorescent light; the laser excitation light also penetrates through the fluorescent wheel and is emitted out through the second lens assembly;

the distance between the second lens assembly and the first lens assembly is larger than the equivalent focal length of the first lens assembly;

wherein the distance from the front surface of the fluorescent wheel to the first lens assembly is less than the equivalent focal length of the first lens assembly,

and the distance between the second lens component and the first lens component refers to the distance between the inner side lens piece of the second lens component and the principal point plane of the first lens component.

2. The fluorescence conversion system according to claim 1, wherein the fluorescence wheel includes a reflection portion on which a phosphor is coated, and the laser excitation light excites the phosphor of the reflection portion to emit fluorescence.

3. The fluorescence conversion system according to claim 1 or 2, wherein the fluorescence wheel includes a transmission portion that can transmit the laser excitation light.

4. The fluorescence conversion system of claim 1, wherein a distance between a second lens assembly and the first lens assembly is greater than two times a distance between the first lens assembly and the face of the fluorescent wheel and less than or equal to three times the distance between the first lens assembly and the face of the fluorescent wheel.

5. The fluorescence conversion system of claim 1, wherein the first lens assembly comprises a piece of aspheric lens and a piece of aspheric lens, the second lens assembly comprises a piece of aspheric lens and a piece of aspheric lens or the second lens assembly comprises a piece of aspheric lens.

6. The fluorescence conversion system of claim 1, wherein the first lens component is a piece of aspheric lens and the second lens component is a piece of aspheric lens.

7. The fluorescence conversion system of claim 1, wherein an equivalent focal length of the second lens assembly is equal to an equivalent focal length of the first lens assembly.

8. The fluorescence conversion system of claim 1 or 5, wherein the optical paths of the second lens assembly and the first lens assembly are asymmetrically arranged with respect to the fluorescence wheel.