JP5048160B2 - Transmission screen and projection display device - Google Patents

Description

  The present invention includes a transmissive screen in which a Fresnel optical member that folds image light emitted from a projector toward an observer and a light diffusing member that diffuses the image light, and the transmissive screen are mounted. The present invention relates to a projection display device.

Unlike a CRT (Cathode Ray Tube) or a PDP (Plasma Display Panel), the projection display device is a non-luminous display device.
As shown in FIG. 25, the conventional projection display apparatus includes an illumination optical system 2 that illuminates the light valve 3, a light valve 3 that adjusts the amount of light according to an image signal, and generates image light. The projector 1 includes a projection optical system 4 that irradiates the image light generated by the above and projects the image on the transmission screen 6.

The projection display device includes a rear projection type that projects image light from the back of the transmissive screen 6 when viewed from the observer, and a front projection type that projects image light from the front of the transmissive screen 6 when viewed from the observer. And classified.
As shown in FIG. 25, the transmissive screen 6 used in the rear projection type projection display device includes a Fresnel lens screen 7 that is a Fresnel optical member that folds the image light emitted from the projector 1 toward the observer side, and It comprises a light diffusing member 10 that spreads image light by giving a divergence angle.

Since the Fresnel lens 9 constituting the Fresnel lens screen 7 is generally made with a period (for example, 1/10 of a pixel) finer than that of the projection pixel, the thickness direction is very thin (for example, the thickness including the prism portion is small). 100 microns).
Further, the Fresnel lens screen 7 includes a Fresnel lens substrate 8 for holding a Fresnel lens 9 having a very thin thickness direction.
The Fresnel lens substrate 8 is often made of a resin such as PMMA, MS, or PC, or glass, and the Fresnel lens 9 is often formed directly on the Fresnel lens substrate 8.
FIG. 25 shows an example of a light exit surface side Fresnel lens in which the Fresnel lens 9 is formed on the light exit surface side of the Fresnel lens screen 7, but as shown in FIG. 26, the Fresnel lens 9 enters the Fresnel lens screen 7. There is also an example of a light incident surface side Fresnel lens formed on the light surface side.

The light diffusing member 10 includes at least a lens element 11 and a light diffusing sheet 12, and is generally called a lenticular screen.
In the example of FIG. 25, the reflecting mirror 5 is mounted. However, as shown in FIG. 26, there is a case where the reflecting mirror 5 is not mounted.

When the image light emitted from the projector 1 is observed through the transmissive screen 6, the surface unevenness of the light diffusing member 10 or the internal refractive index distribution, phase distribution and transmittance distribution have fluctuations larger than the wavelength of the image light. Countless bright and dark spots (glare) are perceived randomly.
This bright and dark spot is generally called speckle or scintillation and causes image degradation.

Patent Document 1 below discloses an example in which a speckle interference reducing micro lenticular lens is disposed on the light source side of the Fresnel lens screen 7 in order to reduce speckle.
By disposing the speckle interference reducing micro lenticular lens, the image light irradiated from the projector 1 is given a divergence angle θv, and the image light having the divergence angle θv is given to the Fresnel lens screen 7 and the lens element 11. While propagating the distance, it spreads in proportion to the propagation distance t0 and illuminates the light diffusion sheet 12 on the light source side from the black stripe layer.
As described above, the image light emitted from the projector 1 is spread while propagating the distance between the Fresnel lens screen 7 and the lens element 11 by the micro lenticular lens for speckle interference reduction. When the propagation distance t0 is short, It is necessary to increase the divergence angle θv given by the micro lenticular lens for speckle interference reduction.

As shown in FIG. 26, when the Fresnel lens 9 is formed on the light incident surface side of the Fresnel lens screen 7, the speckle interference reducing micro lenticular lens cannot be disposed on the light incident surface side of the Fresnel lens screen 7. Therefore, it is necessary to dispose a speckle interference reducing micro lenticular lens on the light exit surface side of the Fresnel lens screen 7.
The thickness of the lens element 11 is at most several hundred microns, and since the Fresnel lens substrate 8 of the Fresnel lens screen 7 bears most of the propagation distance t0, the propagation distance t0 is from 3 mm to 1/10. If it is 300 microns, a divergence angle θv of 10 times is required.

The image light emitted from the projector 1 spreads in proportion to the divergence angle θv. However, since all the image light is preserved by the energy conservation law, there arises a problem that the image light becomes dark by the spread amount.
In general, a projector screen that is “bright and has a wide viewing angle” is desired. However, the two are in a trade-off relationship based on the law of conservation of energy, and the image light cannot be expanded by ignoring this distribution.

Note that, as described above, the speckle phenomenon originates from the unevenness of the surface of the light diffusing member 10 or fluctuations in the internal refractive index distribution, phase distribution and transmittance distribution, and image light transmitted through the fluctuation structure, that is, The wavefront of the image light is disturbed by the fluctuation structure, and as a result, bright and dark spots are formed.
The characteristic length of this fluctuation structure (for example, the fluctuation period when it fluctuates regularly) becomes a problem.

JP 2004-171011 A (paragraph numbers [0040] to [0051], FIG. 11)

  Since the conventional projection display device is configured as described above, if a micro lenticular lens for reducing speckle interference is arranged, speckle can be reduced by giving a divergence angle θv to the image light emitted from the projector 1. Although it can be reduced, there is a problem that if the image light is given a large divergence angle θv, the image light becomes dark.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a transmissive screen and a projection display device that can reduce speckles while maintaining the brightness of image light. .

  A transmissive screen according to the present invention includes a Fresnel optical member that receives image light emitted from a light emitter and emits the image light in a predetermined direction, and a light diffusion member that diffuses the image light in order. In the transmissive screen, the light diffusing member includes at least a light diffusing sheet having a light diffusing layer having a concavo-convex shape formed thereon, or a light diffusing bead having a refractive index different from that of the sheet medium. The light diffusing sheet is composed of at least one of the light diffusing sheets, and the incident surface of the Fresnel optical member has a refracting surface that refracts image light emitted from a light emitter and a reflecting surface that reflects image light refracted by the refracting surface. A structure having a plurality of total reflection prisms arranged in a saw-tooth shape and periodically having a shape formed by connecting curved surfaces or flat surfaces on the light output surface side of the Fresnel optical member. A unit period of a shape formed by connecting the curved surface or the plane is longer than a wavelength of light forming image light and smaller than a projection pixel forming image light, and an uneven shape forming the light diffusion member, Or it is equal to or less than the characteristic length of the particle size of the light diffusion beads.

  According to the present invention, a transmissive screen that sequentially includes a Fresnel optical member that receives image light emitted from a light emitter and emits the image light in a predetermined direction, and a light diffusion member that diffuses the image light. The light diffusing member is a light diffusing sheet in which a light diffusing layer having a concavo-convex shape is formed on at least a surface, or a light diffusing bead having a refractive index different from that of the sheet medium is disposed. Total reflection comprising at least one of the sheets, and having a refracting surface for refracting the image light irradiated from the light emitter and a reflecting surface for reflecting the image light refracted by the refracting surface on the incident surface of the Fresnel optical member A plurality of prisms are arranged in a saw blade shape, and the light exit surface side of the Fresnel optical member has a structure periodically having a shape formed by connecting curved surfaces or flat surfaces, The unit period of the shape formed by connecting the planes is longer than the wavelength of the light that forms the image light and smaller than the projection pixel that forms the image light, and the concave-convex shape that forms the light diffusion member, or the light Since it is configured to be equal to or less than the characteristic length of the particle size of the diffusion beads, there is an effect that speckle can be reduced while maintaining the brightness of the image light.

It is a block diagram which shows the projection type display apparatus by Embodiment 1 of this invention. It is explanatory drawing which shows the overlap result of an interference fringe. It is explanatory drawing explaining an optical invariant. It is explanatory drawing which shows the schematic diagram of an optical system, and the relationship of a screen. It is explanatory drawing which shows the schematic diagram of an optical system, and the relationship of a screen. 3 is an explanatory view showing the inside of a light diffusion sheet 12. FIG. 3 is an explanatory view showing the inside of a light diffusion sheet 12. FIG. 3 is an explanatory view showing the inside of a light diffusion sheet 12. FIG. 3 is an explanatory view showing the inside of a light diffusion sheet 12. FIG. It is a block diagram which shows the other projection type display apparatus by Embodiment 1 of this invention. It is a block diagram which shows the other projection type display apparatus by Embodiment 1 of this invention. It is explanatory drawing which shows the manufacturing method of the transmissive screen 6 of FIG. It is explanatory drawing which shows the manufacturing method of the transmissive screen 6 of FIG. It is explanatory drawing which shows the manufacturing method of the transmissive screen 6 of FIG. It is a block diagram which shows the projection type display apparatus by Embodiment 2 of this invention. It is explanatory drawing which shows the path | route of the light beam in case the spatial frequency modulation member 22 is the sawtooth prism 22a. It is explanatory drawing which shows the path | route of the light beam in case the spatial frequency modulation member 22 is the sawtooth prism 22a. It is explanatory drawing which shows the image light which propagates the spatial frequency modulation member. 3 is an explanatory diagram schematically showing a relationship between an optical axis of a projection optical system 3 of a projector 1 and a Fresnel lens screen 7 of a transmissive screen 6. FIG. The light beams A and B are explanatory views showing the incident angle θ. 2 is a perspective view illustrating a configuration example of a light diffusing member 10. FIG. 2 is a perspective view illustrating a configuration example of a light diffusing member 10. FIG. 2 is a perspective view illustrating a configuration example of a light diffusing member 10. FIG. 2 is a perspective view illustrating a configuration example of a light diffusing member 10. FIG. It is a block diagram which shows the conventional projection type display apparatus. It is a block diagram which shows the conventional projection type display apparatus. It is a block diagram which shows the conventional projection type display apparatus. It is a block diagram which shows the conventional projection type display apparatus.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a projection display apparatus according to Embodiment 1 of the present invention. In the figure, a projector 1 is a light emitter that emits image light, and the projector 1 adjusts the amount of light according to an image signal. The light valve 3 that generates image light, the illumination optical system 2 that illuminates the light valve 3, and the projection optics that irradiates the image light generated by the light valve 3 and projects the image on the transmission screen 6 It consists of a system 4.
The transmission screen 6 includes a Fresnel lens screen 7 and a light diffusing member 10.
The Fresnel lens screen 7 of the transmissive screen 6 is a Fresnel optical member that receives the image light emitted from the projector 1 and emits the image light in a predetermined direction.
The Fresnel lens screen 7 includes a Fresnel lens base 8 and a Fresnel lens 9, and the Fresnel lens 9 having a very thin thickness direction is held by the Fresnel lens base 8.

The wavefront division phase modulation member 21 is a member that spatially finely divides the wavefront of the image light emitted from the Fresnel lens screen 7 and modulates the phase of the wavefront (a member that tilts the wavefront or gives an optical path length difference). The surface shape of the wavefront division phase modulation member 21 is composed of a curved surface such as a convex lens shape, a concave lens shape, or a sinusoidal shape, or a planar surface such as a lattice shape or a saw blade shape, for example. But you can.
The light diffusing member 10 is a member that diffuses image light whose wavefront phase is modulated by the wavefront division phase modulating member 21, and the light diffusing member 10 is composed of at least a lens element 11 and a light diffusing sheet 12, and generally includes a lenticular screen, be called.

Next, the operation will be described.
First, the reason why a phenomenon called speckle or scintillation is seen on the transmissive screen 6 will be described.
When the surface of the object has rough unevenness with respect to the light wavelength scale, an image of coherent illumination light scattered, transmitted, and reflected on the surface of the object appears.
This is made by superimposing a large number of amplitude distributions (not intensity distributions) generated from different scattering points, and can be explained by interference due to coherence of the light source.

Here, for simplification of description, the superposition of monochromatic waves E _jk represented by the following equation (1) is considered.
E _j (r, t) = Re [E _jk expi (kr−ωt + δ _jk )] (1)
However, k is a wave number, r is a position, ω is an angular frequency, t is time, and δ is a phase.
For example, as shown in the following equation (2), when two monochromatic waves overlap at a certain point, the time average <E ² > of the intensity of the monochromatic wave is expressed by the following equation (3).
E = E ₁ + E ₂ (2)
<E ² > = <E ₁ ² > + <E ₂ ² > +2 <E ₁ E ₂ > (3)
The time average <E ² > of the intensity of the monochromatic wave is added with an interference term as shown in the following formula (4), that is, 2 <E ₁ E ₂ >. The intensity changes due to the phase difference.
2 <E ₁ E ₂ > = ΣE _1k E _2k cos (δ _2k −δ _1k ) (4)
However, Σ is an addition symbol to be added up from k = 1 to 3.

On the other hand, for example, speckle may be observed when observing light from a distant celestial body from the ground.
The difference between the light from the celestial body and the laser light source will be described. The spectrum of the light from the celestial body is continuous and incoherent, and the spectrum of the laser light source is monochromatic and coherent.
As shown in FIG. 2, there is an incoherent monochromatic light source having a slit d and a finite size D. The upper end of the monochromatic light source is virtually the first light source 31, and the lower end of the monochromatic light source is virtually assumed. Consider a case where light is emitted from the first light source 31 and the second light source 32 as the second light source 32.
Since the light from the first light source 31 passes through different optical paths, a solid interference fringe is formed, and the light from the second light source 32 similarly forms a broken interference fringe.
If the difference D between the positions of the monochromatic light sources is small at the origin of each interference fringe, the deviation of the origin of the interference fringe is also small.

Since the first light source 31 and the second light source 32 have no correlation with each other, the superposition of the solid-line interference fringes and the broken-line interference fringes is not an amplitude but simply an intensity superposition.
When the slit interval d is small, the period of the interference fringes becomes conversely large, so that the deviation of the origin of the interference fringes is smaller than the period. For this reason, as a result of the addition of the strengths, they are strengthened like a one-dot chain line stripe.
On the other hand, when the slit interval d is large, the period of the interference fringes becomes conversely small, so that the deviation of the origin of the interference fringes is larger than the period. For this reason, as a result of the addition of strength, the peaks and valleys cancel each other out and become uniform.

A wavefront from a monochromatic light source having a finite size D has an inclination of size D / z and has coherence if the optical path length difference is equal to or less than 1λ at a position separated by the slit interval d.
Dd / z ≦ λ (5)
Further, the length d for maintaining the coherence is expressed by the following formula (6).
d ≦ λz / D to λF (6)
However, F is an F number and represents the reciprocal F to z / D of the spread of the light beam. Therefore, the narrower the beam spread (the larger the F number), the longer the length d that maintains coherence.

Here, the optical invariant will be described.
FIG. 3 is an explanatory diagram for explaining optical invariants.
FIG. 3 shows an example in which an object of size y ₁ forms an image of size y ₂ by the lens 41.
At this time, although the proof of the relationship between the image size and the prospective angle θ is omitted, it is expressed by the following equation (7).
y ₁ θ ₁ = y ₂ θ ₂ (7)
This relational expression indicates that the product of the image size and the prospective angle θ is invariant in the optical system, which is called an “invariant of“ Helholz-Larange ””, and is strictly established by paraxial theory. .
For example, if the size of the image is y ₂ <y ₃ <y ₄ , it can be seen that the prospective angles θ are sequentially θ ₂ > θ ₃ > θ ₄ .
That is, it can be seen that the spread of the light beam becomes smaller in inverse proportion to the lateral magnification β of the optical system.
β = y ₂ / y ₁ (8)
Since the magnification of the projector optical system is generally high, such as 50 to 100 times, the spread of the light beam becomes smaller in inverse proportion.

Next, the relationship between the optical system of the rear projection display device and the screen will be described.
FIG. 4 is an explanatory diagram showing the relationship between the schematic diagram of the optical system and the screen.
In FIG. 4, illumination light from an illumination optical system (not shown) is used to create an image with the light valve 3 of the projector 1, and this image is projected through a virtual condenser lens 43 by a virtual projection lens 42 that is a projection optical system 4. Projects to the light diffusing member 10.
At this time, when the screen size of the rear projection display device is large (for example, 1 meter square), the Fresnel lens screen 7 which is a Fresnel optical element is used as the virtual condenser lens 43.
Since the image is enlarged at a lateral magnification β = y ₂ / y ₁ of the projection optical system, the spread of the light beam (expected angle θ ₂ ) is 1 / β times, and the length d for maintaining coherence is It is represented by Formula (9).
d ≦ λFβ (9)
For example, when the magnification β of the projection optical system is 100 times, the F number F of the illumination optical system is F = 3.5, and the wavelength λ is 530 nm, the length d that maintains coherence is d <186 microns.
Since the distance d is proportional to the magnification β and the F number, the larger the F number and the lateral magnification β (the narrower the light beam spread), the larger the distance d.

The light diffusing member 10 includes, for example, a surface diffusion type in which image light is diffused by unevenness on the surface, and beads having various particle diameters having a refractive index different from that of the medium are mixed, and the beads having a particle diameter diffuse image light. There is a type of volume diffusion type.
The surface irregularities and the characteristic length of the beads are larger than the wavelength of visible light (about 380 to 780 nm), and at most 1 to 50 microns, in fact, about 5 to 20 microns is the mainstream.
When the characteristic length of the fluctuation of the surface to be illuminated (illuminated surface) is sufficiently smaller than the length d that maintains coherence, the image light is partially coherently illuminated due to spatial coherence. Since it becomes light, speckle noise, which is a bright and dark spot, is generated.
Although the proof is omitted, the discussion of the monochromatic light described above is not the amplitude but the superposition of the intensities, so that it can be applied to a light source having a bandwidth such as quasi-monochromatic light.
From the above, even for an incoherent light source, the spatial coherence of a light source with a finite size results in partially coherent illumination, and the speckle phenomenon is explained by superposition of intensity, not amplitude. Can do.
Since the laser light source is a quasi-monochromatic light source having a narrow bandwidth, speckle is observed from the above discussion even if the high coherence of the laser light source is reduced by some means.

In order to reduce the occurrence of speckle noise, which is a bright and dark spot, as is clear from the above discussion, the image light incident on the light diffusing member 10 may be spread. That is, various inclinations may be given to the incident wavefront of the light diffusing member 10.
FIG. 5 is an explanatory diagram showing the relationship between the schematic diagram of the optical system and the screen.
In FIG. 5, the wavefront division phase modulation member 21 is inserted between the virtual condenser lens 43 equivalent to the Fresnel optical element and the light diffusion member 10.
In FIG. 5, the wavefront division phase modulation member 21 is represented by a small lens for simplification of description, but it may be formed of a curved surface such as a convex lens shape, a concave lens shape, or a sinusoidal shape, or a lattice shape. It may be configured from a plane like a saw blade.
This is because the object is to spatially divide the wavefront in front of the light diffusing member 10 and to incline the wavefront or to provide an optical path length difference.

In the wavefront division phase modulation member 21 of FIG. 5, lenses having a V cross section that is long in the H direction in the shape of the wavefront division phase modulation member 21 (a cylindrical lens when the cross section is an arc) are arranged in the V direction. Although an example is shown, lenses having a long H section in the V direction in the shape of the wavefront division phase modulation member 21 are arranged in the H direction, or both of them are stacked in two layers, and the H and V cross sections are wavefront division phase modulation. You may arrange the two-dimensional microlens of the shape of the member 21. FIG.
What is important here is that the unit length of the wavefront division phase modulation member 21 needs to be smaller than the projection pixel. However, from the above discussion, it is desirable that the unit length is equal to or smaller than the characteristic length of the fluctuation structure.

6 and 7 are explanatory views showing the inside of the light diffusion sheet 12.
FIG. 6 shows an example in which light diffusion beads 52 of various particle diameters having different refractive indexes are arranged in the light diffusion sheet medium 51 as the light diffusion sheet 12.
Here, for simplification of explanation, a case where a plane wave having a small spread is incident on the light diffusion sheet 12 is considered.
When the length d that maintains coherence is sufficiently larger than the particle diameter of the light diffusing beads 52 (for example, the length d that maintains coherence is 200 microns and the particle size of the light diffusing beads 52 is 20 microns) On the wavefront of the image light transmitted through the diffusion sheet 12, speckles that are bright and dark spots are observed.

On the other hand, FIG. 7 shows an example in which the wavefront division phase modulation member 21 is disposed in front of the light diffusion sheet 12.
Here, for simplification of description, a case where the wavefront division phase modulation member 21 has a grating structure with a period p is considered.
Note that the period p is sufficiently larger than the wavelength λ and smaller than or equal to the particle diameter of the light diffusion beads 52.
In this case, the optical path length of the image light transmitted through the wavefront division phase modulation member 21 is caused by the grating structure. However, as described above, since the image light does not spread, the length d that maintains coherence is small. Although the wavefront of the image light is spatially divided, there is a difference in the optical path length of each wavefront after the division, and the pattern of bright and dark spots changes.

In FIG. 7, the surface shape of the wavefront division phase modulation member 21 is a shape in which planes are connected. However, in FIGS. 8 and 9, the surface shape of the wavefront division phase modulation member 21 is a curved surface. The connected shape is shown.
The wavefront of the image light is spatially divided by the length of the wavefront division phase modulation member 21, and an inclination and a phase difference are given to the wavefront.
In this case, as is clear from the above discussion, there is an effect that the length d for maintaining coherence is reduced.
In addition, since the wavefront of the image light is divided into wavefronts of length p, the bright and dark speckle pattern changes.

When the surface shape of the wavefront split phase modulation member 21 is a curved surface (see FIG. 8), unlike the case where the surface shape of the wavefront split phase modulation member 21 is a flat surface, the wavefront is divided because it is inclined. The wave fronts are superposed.
That is, in addition to providing the wavefront with an inclination or phase difference, the wavefront peaks and valleys cancel each other out and are made uniform by averaging them by superimposing various wavefronts.

  On the other hand, when the length of the wavefront division phase modulation member 21 is relatively large with respect to the fluctuation structure (the light diffusion beads 52 having different refractive indexes are arranged in the light diffusion sheet medium 51) (see FIG. 9), the light diffusion member 10 can spread the image light incident on the light beam 10 (because various inclinations can be given to the incident wavefront of the light diffusing member 10). It can be seen that there is no averaging effect due to the superposition of.

As described above, if the wavefront division phase modulation member 21 is arranged between the Fresnel lens screen 7 and the light diffusing member 10, speckles can be reduced. In practice, however, the screen is composed of a plurality of optical members. Therefore, it is necessary to consider so as not to deteriorate the function of each optical member.
The transmission screen 6 includes at least a Fresnel lens screen 7 and a light diffusing member 10. The Fresnel lens screen 7 is selected according to the characteristics of the projector 1, and the light diffusing member 10 has a viewing angle and a screen brightness. Therefore, they are designed and manufactured separately and are often selected independently. That is, the Fresnel lens screen 7 and the light diffusing member 10 may be considered separately.

Here, as shown in FIG. 1, a case where a light incident surface side Fresnel lens is used as the Fresnel lens 9 of the Fresnel lens screen 7 is considered.
In this case, the light incident surface side total reflection / refractive mixed Fresnel lens 61 (a total reflection prism having a refraction surface that refracts image light and a reflection surface that reflects image light refracted by the refraction surface, and refracts image light) Fresnel lens in which a refraction prism having a refracting surface is formed at one pitch), a light incident surface side total reflection type Fresnel lens 62 (a refracting surface that refracts image light, and image light refracted by the refracting surface. Fresnel lens having a reflecting surface to be reflected) or a light incident surface side partial total reflection type Fresnel lens 63 (a non-incident surface that is blocked by the front Fresnel prism and is not directly irradiated with image light is substantially the same as the Fresnel lens substrate 8. One of the Fresnel lenses formed in parallel).

In the example of FIG. 1, the wavefront division phase modulation member 21 is disposed on the light exit surface side of the Fresnel lens substrate 8, but as shown in FIG. 10, the Fresnel lens substrate 8 is disposed between the Fresnel lens 9 and the Fresnel lens substrate 8. The wavefront division phase modulation member 21 may be disposed on the surface.
In addition, as shown in FIG. 11, the wavefront division phase modulation member 21 may be disposed on the light incident surface side of the light diffusion member 10.

The image light changes its traveling direction in proportion to the difference in refractive index of the boundary surface, but the transmission screen 6 in FIG. 1 uses the boundary surface with air, and the transmission screen 6 in FIG. 10 is a Fresnel lens screen. 7 is different from the transmission screen 6 of FIG. 10 in that a boundary surface with the Fresnel lens 9 is used.
In the case of the transmissive screen 6 of FIG. 1, for example, it can be realized by bonding the wavefront division phase modulation member 21 formed on a thin transparent substrate to the Fresnel lens substrate 8. The transmission type screen 6 in FIG. 1 has a feature that the boundary surface is air and the light is largely inclined due to the difference in refractive index from the medium.

The transmissive screen 6 of FIG. 10 can be formed by a manufacturing method as shown in FIGS.
For example, the wavefront division phase modulation member 21 is formed on the Fresnel lens substrate 8 (see FIG. 12).
On the other hand, in the Fresnel lens 9, a photo-curing resin 72 is poured into a metal mold 71 engraved with a lens shape (see FIG. 12), and the Fresnel lens substrate 8 is pressed and photo-cured (see FIG. 13).
Thereafter, the Fresnel lens 9 is formed on the light incident surface side of the Fresnel lens screen 7 by releasing from the mold 71 (see FIG. 14).
In the case of the transmissive screen 6 of FIG. 13, the refractive index difference between the Fresnel lens 9 and the wavefront split phase modulation member 21 is expected to be smaller than that of the case where the other party is air because the other is a medium. That is, it is difficult to give a large inclination or phase difference to the wavefront of the image light.

When the image light propagation distance t0 is short, as described above, it is necessary to increase the image light divergence angle θv, and the Fresnel lens substrate 8 of the Fresnel lens screen 7 bears most of the image light propagation distance t0. .
However, when the wavefront division phase modulation member 21 is arranged in front of the Fresnel lens substrate 8 as in the transmission screen 6 of FIG. 10, the wavefront division phase modulation member 21 can also carry the propagation distance t0. There is an advantage that it is not necessary to increase the divergence angle θv of the image light.

  As apparent from the above, according to the first embodiment, the wavefront division phase modulation member 21 that divides the wavefront of the image light emitted from the Fresnel lens screen 7 and modulates the phase of the wavefront is provided as the light diffusion member. Since it is configured to be arranged in front of 10, the effect of reducing speckles while maintaining the brightness of the image light is achieved.

Embodiment 2. FIG.
In Embodiment 1 described above, the wavefront division phase modulation member 21 that divides the wavefront of the image light and modulates the phase of the wavefront is arranged in front of the light diffusion member 10, but as shown in FIG. Further, a spatial frequency modulation member 22 is disposed on the light exit surface side (observer side) of the light diffusion member 10 so that the spatial frequency modulation member 22 modulates the spatial frequency of the image light diffused by the light diffusion member 10. It may be.
The surface shape of the spatial frequency modulation member 22 is similar to the surface shape of the wavefront split phase modulation member 21, for example, having a curved surface such as a convex lens shape, a concave lens shape, and a sinusoidal shape, a lattice shape, and a saw shape. It is composed of a blade-like plane.

In the example of FIG. 15, a light incident surface side Fresnel lens is employed as the Fresnel lens 9 of the Fresnel lens screen 7.
For example, either the light incident surface side total reflection / refractive mixed Fresnel lens 61, the light incident surface side total reflection Fresnel lens 62, or the light incident surface side partial total reflection Fresnel lens 63 is employed.
In the example of FIG. 15, a saw blade prism 22 a as shown in FIG. 16 is adopted as the spatial frequency modulation member 22.
When the saw blade prism 22a is employed as the spatial frequency modulation member 22, for example, the first light beam 81 incident obliquely is sawtooth prism 22a, depending on the apex angle and refractive index of the saw blade prism 22a. It is refracted at the boundary and bent toward the observer.
A part of the light beam (second light beam 82) is totally reflected internally at the boundary surface of the sawtooth prism 22a, refracted from the opposite boundary surface, and greatly bent in an oblique direction.

As shown in FIG. 17, when the light beam is incident substantially in the direction of the observer, the fifth light beam 85 is bent in the direction of the observer, but the third light beam 83 and the fourth light beam 84 are saw blades. Total internal reflection at the boundary surface of the prism 22a.
Thereafter, the fourth light beam 84 is refracted from the opposite boundary surface and bent largely in an oblique direction, while the third light beam 83 is greatly bent along the adjacent saw-toothed prism 22a, and the original direction. Return to the side opposite the observer.

Here, paying attention to the third light beam 83, the third light beam 83 is totally incident on the boundary surface of the saw-toothed prism 22 a and reenters the light diffusing member 10.
It is assumed that the third light beam 83 re-enters the light diffusing member 10 and is scattered by the light diffusing member 10, for example, to be bent in the direction of the observer like a fifth light beam 85.
Since the third light beam 83 crosses at least one of the saw blade prisms 22a, the image is blurred by one of the saw blade prisms 22a. That is, when the unit length q of the sawtooth prism 22a is appropriately reduced (at least sufficiently smaller than the projected pixel), the sawtooth prism 22a functions as a low-frequency transmission filter, and increases the spatial frequency high frequency. It has the effect of reducing.

FIG. 18 is an explanatory diagram showing image light propagating through the spatial frequency modulation member 22.
Part of the image light that has passed through the lens element 11 (the light absorbing portion 91 and the unit lens 92) and entered the light diffusion sheet 12 is returned to the original direction by the spatial frequency modulation member 22, and part of the image light is observed. It is emitted in the direction of the person.
At this time, the image light emitted in the direction of the observer propagates through several spatial frequency modulation members 22 having a length q.
Note that the thickness of the light diffusion sheet 12 needs to be several times the length q in order to prevent the problem that the image is blurred while the image light propagates through the light diffusion sheet 12.
Specifically, the size of the projection pixel is 1 mm, the period of the lens element 11 is 50 to 100 microns, the thickness of the light diffusion sheet 12 is 20 to 40 microns, and the length q of the spatial frequency modulation member 22 is 5 to 20 microns. Degree. Both are sufficiently longer than the wavelength λ (0.3 to 0.7 microns).

Speckle noise in which countless bright and dark spots (glaring) are recognized in a disorderly manner is recognized as very small spots, although it depends on the fluctuation of the illuminated surface.
By arranging the spatial frequency modulation member 22 on the observer side of the light diffusing member 10 as in the second embodiment, it becomes possible to average bright and dark spots with high frequency at the spatial frequency.
For example, if the image light is designed to propagate about three sawtooth prisms 22a that are the spatial frequency modulation members 22, the image will not blur more than that (four or more). Only speckle noise can be selectively averaged with little effect on low frequencies.

Embodiment 3 FIG.
In the first and second embodiments, the transmission screen 6 on which the wavefront division phase modulation member 21 or the spatial frequency modulation member 22 is mounted has been described. However, the transmission screen 6 is rarely used alone. Yes, it is used in combination with the projector 1.
As shown in FIG. 25, a conventional rear projection display device typified by a rear projector has the optical axis of the projection optical system 3 and the center of the transmission screen 6 substantially matching each other, so that the depth of the projection display device can be reduced. In order to reduce the thickness or reduce the size, the reflecting mirror 5 is used to fold the image light.
In order to achieve further reduction in thickness, there is also a projection display device in which the projector 1 projects image light at an oblique steep angle with respect to the transmission screen 6 as shown in FIG.

For example, when a laser light source having a large coherence is used as the illumination light source, the laser light source emits light with a small divergence angle from a small area, so that the illumination optical system 2 and the projection optical system 4 can be reduced in size. There is.
It goes without saying that if the internal illumination optical system 2 is reduced in size, the projection display apparatus as a whole becomes thinner or more easily reduced in size. In other words, a method of projecting at an oblique steep angle is suitable for the transmission screen 6 described above.
Of course, as shown in FIGS. 27 and 28, the reflecting mirror 5 may be disposed in the middle of the optical path, and the reflecting mirror 5 may be configured to bend and reduce the size of the image light. The upper and lower sides of the transmission screen 6 are not limited to the example shown in the figure.

The difference between FIG. 25 and FIG. 26 seems to be that the projector 1 is simply tilted, but if it is simply tilted, a square object may be projected into a trapezoid, and this is not the case.
FIG. 19 is an explanatory diagram schematically showing the relationship between the optical axis of the projection optical system 3 of the projector 1 and the Fresnel lens screen 7 of the transmissive screen 6.
Of the Fresnel lens 9 of the Fresnel lens screen 7, the light exit surface side Fresnel lens 9 a having a prism on the light exit surface has the center of rotation at the center of the screen, and this center of rotation substantially coincides with the optical axis of the projection optical system 10.
On the other hand, the light incident surface side Fresnel lens 9 b having a prism on the light incident surface side has a rotation center outside the screen, and this rotation center substantially coincides with the optical axis of the projection optical system 10.
That is, the spread angle from the optical axis of the light incident surface side Fresnel lens 9b is θ, and this spread angle θ corresponds to the incident angle θ to the Fresnel lens screen 7, and from the optical axis of the light exit surface side Fresnel lens 9a. Larger than the spread angle. That is, as shown in FIG. 20, the light beam B including the optical axis has a small incident angle θ and the light beam A off the optical axis has an incident angle θ as compared to the light beam A and the light beam B that form a screen of the same size. You can see that it ’s big.

As apparent from FIG. 20, the Fresnel lens screen 7 is a collimating lens that deflects the image light emitted from the projection optical system 10 to the light diffusion sheet 12 that is an imaging surface, and is considered to be a field lens. Can do.
In order to deflect extreme oblique projection light in the normal direction of the screen, it is necessary to greatly change the traveling direction of the image light. If this is performed using only the refraction phenomenon of image light, energy loss due to Fresnel reflection and color separation due to the light dispersion phenomenon become problems.

In this case, the light incident surface side Fresnel lens 9b in which the prism is formed on the light incident surface side is suitable instead of the conventional light output surface side Fresnel lens 9a in which the prism is formed on the light output surface side. The light incident surface side Fresnel lens 9b includes, for example, the following Fresnel lens.
(1) A light incident surface side total reflection type Fresnel lens 62 that deflects a light beam incident on a prism in a light exit surface direction using total reflection on the opposite side.
(2) Light-incidence surface side partial total reflection type Fresnel lens 63 with the valley of total reflection type Fresnel lens 62 parallel to the light exit surface
(3) Total reflection type Fresnel lens 62 and a refractive type Fresnel lens that deflects the light beam incident on the prism in the direction of the light exit surface only for refraction are mixed in one prism. Lens 61
Note that the Fresnel lenses 61 to 63 may be appropriately selected in accordance with the design of the projector 1, and needless to say, three types need not be mixed in one screen.

For example, as shown in FIG. 21, the light diffusing member 10 includes a cylindrical lens 90 on the light incident surface side, and a light absorbing portion 91 formed in a stripe shape at a position corresponding to a non-condensing portion of the cylindrical lens 90. 22 and instead of the one having the cylindrical lens 90 on the light incident surface side, as shown in FIG. 22, a part of the incident light beam is totally reflected by the total reflection portion and then emitted from the light emission portion. The trapezoidal unit lenses 92 to be arranged may be arranged side by side, and the light absorbing portions 91 may be formed in stripes in the valleys of the unit lenses 92.
As a combination, as shown in FIG. 23, light absorbing portions 91 are formed in stripes at positions corresponding to non-condensing portions of the vertical and horizontal cylindrical lenses 93 in which the cylindrical lenses are vertically and horizontally arranged on the light incident surface side. As shown in FIG. 24, trapezoidal unit lenses 92 in which light absorbing portions 91 are formed in stripes in the valleys may be arranged in front and back so as to be orthogonal to each other. However, it goes without saying that the vertical and horizontal order is not limited to this.

In order to reduce the influence of external light, an antireflection layer (not shown) for reducing light reflection may be provided on the light exit surface of the light diffusion sheet 12 of the light diffusion member 10 on the surface.
In addition, an anti-glare layer (not shown) for preventing glare from appearing, an antistatic layer (not shown) for preventing dust from adhering to static electricity, and a hard coat layer (not shown) for protecting the surface (Not shown) may be provided.

In the first to third embodiments, in order to make it easy to understand the total reflection Fresnel lens and the lenticular lens screen, independent configurations are shown, but actually, these are combined as one element, for example, with an adhesive layer. It may be configured.
The projection display device using the transmission screen 6 includes a projector 1 including at least a light valve 3 that forms an image, an illumination optical system 2 that illuminates the light valve 3, and a projection optical system 4 that projects an image. The transmission screen 6 and the light diffusing member 10 are characterized in addition to, for example, a housing, a holding mechanism, an air conditioner, a speaker, a TV stand, a remote control light receiving unit, and an electric circuit. It may be included in components such as a geometric correction circuit and a color correction circuit.

  DESCRIPTION OF SYMBOLS 1 Projector (light emitter), 2 Illumination optical system, 3 Light valve, 4 Projection optical system, 5 Reflecting mirror, 6 Transmission type screen, 7 Fresnel lens screen (Fresnel optical member), 8 Fresnel lens base, 9 Fresnel lens, 9a Light exit side Fresnel lens, 9b Light entrance side Fresnel lens, 10 Light diffusing member, 11 Lens element, 12 Light diffusing sheet, 21 Wavefront division phase modulating member, 22 Spatial frequency modulating member, 22a Saw blade prism, 31 1st Light source, 32 second light source, 41 lens, 42 virtual projection lens, 43 virtual condenser lens, 51 light diffusing sheet medium, 52 light diffusing beads, 61 light incident surface side total reflection / refractive mixed Fresnel lens, 62 light incident Surface-side total reflection type Fresnel lens, 63 Incident surface side partial reflection type Fresnel lens, 71 Mold, 2 Photocuring resin, 81 1st light beam, 82 2nd light beam, 83 3rd light beam, 84 4th light beam, 85 5th light beam, 90 cylindrical lens, 91 light absorption part, 92 unit lens, 93 length and width Cylindrical lens.

Claims (2)

In a transmissive screen that sequentially includes a Fresnel optical member that emits image light emitted from a light emitter and emits the image light in a predetermined direction, and a light diffusion member that diffuses image light.
The light diffusing member is a light diffusing sheet in which a light diffusing layer having a concavo-convex shape is formed on at least a surface thereof, or a light diffusing sheet having a light diffusing bead having a refractive index different from that of a sheet medium. Consisting of at least one,
A plurality of total reflection prisms having a refraction surface that refracts image light emitted from a light emitter and a reflection surface that reflects image light refracted by the refraction surface are arranged in a saw blade shape on the incident surface of the Fresnel optical member. And
The light exit surface side of the Fresnel optical member has a structure periodically having a shape formed by connecting curved surfaces or flat surfaces,
The unit period of the shape configured by connecting the curved surface or the plane is longer than the wavelength of the light that forms the image light, smaller than the projection pixel that forms the image light, and the uneven shape that forms the light diffusion member, or A transmission type screen characterized by having a particle length equal to or less than a characteristic length of the light diffusion beads.   A projection display device comprising the transmissive screen according to claim 1.

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