KR20070019426A - Laser projection display system provided with a pair of optical elements for decreasing speckle - Google Patents

Abstract

 The display system 100 of the present invention includes a light source unit 110 for emitting a light beam of a predetermined wavelength, an illumination lens unit 120 for focusing the emitted light beam, an optical modulator 130 for modulating the focused light beam, Specification for reducing speckle of parallel light including a first projection lens unit 140 for converting a modulated light beam into parallel light, and a pair of transmissive optical elements that are symmetrical with each other and rotated at a predetermined angle about an axis of symmetry. The closure portion 150 includes a second projection lens unit 160 for magnifying and projecting parallel light having reduced speckle on the screen. The pair of transmissive optical elements have a thickness of 2 mm and a refractive index of 1.5, and are inclined at an angle ranging from 45 ° to 60 ° with respect to the horizontal axis, and reciprocate in a range of about 5.7 °.

Laser, Projection, Display, Transmissive, Optical, Speckle, Light Modulation

Description

Laser projection display system provided with a pair of optical elements for decreasing speckle}

1 is a schematic block diagram of a laser projection display system according to a preferred embodiment of the present invention;

FIG. 2 is a schematic view of a pair of optical elements installed in the speckle reduction portion of FIG. 1; FIG.

3 is a schematic view showing a state in which the pair of optical elements of FIG. 2 rotate;

4 is a partially enlarged view of the optical device of FIG. 3;

5 is a schematic block diagram of a laser projection display system of the prior art;

6 is a schematic diagram of the projection display system of FIG. 5; And

7 is a schematic cross-sectional view of a transmissive diffraction grating installed in the wavefront modulator of FIGS. 5 and 6.

<Explanation of symbols for main parts of drawing>

100: display system 110: light source

120: illumination lens unit 130: light modulator

140: first projection lens unit 150: speckle reduction unit

151, 152: transmissive optical element 151a, 152a: coated surface

160: first projection lens unit 170: driving unit

180: screen

The present invention relates to a laser projection display system, and more particularly to a laser projection display system that can reduce the speckle with a simple configuration.

Laser Projection Display is a device that connects to small handheld devices such as mobile phones, PDAs, and mini laptop displays, and displays them on a wall or even ceiling. When the small LPD module is applied, the multi-contents contained in the mobile phone or PDA can be greatly enlarged anywhere. Therefore, the screen is small when viewed by the mobile phone or PDA. You can see it on the screen, and you can easily present it with a PDA without having to connect the projector to the notebook.

Since the laser projection display uses a coherent beam, speckle is generated by the interference phenomenon. The speckle scatters due to the roughness of the surface when the coherent laser beam is reflected from the object surface. It is a random interference pattern in which the incoming light enters the human eye and forms in the retina. When speckle appears in the image, the eye becomes tired.

Many techniques for reducing or eliminating speckles in optical systems with such laser projection displays are currently known. For example, "Method and Apparatus for Reducing Laser Speckles" has been filed on October 4, 2001, filed with International Patent Application PCT / US2001 / 31418, which is shown in FIGS. 5-6.

As shown in Figs. 5 and 6, the prior art display system 40 includes a display optical system 42 and a display electronic system 44. As shown in Figs.

The display optical system 42 includes a laser source 46, an illumination optical system 48, a grating fluorescent valve 50, a Schlieren optical system 52, a wave modulator 54, a projection / scanning optical system 56 and a display. A screen 58 is included, and the display electronic system 44 is electrically connected to the laser source 46, the grating fluorescent valve 50, and the projection / scanning optical system 56.

The laser source 46 emits laser light.

The illumination optical system 48 includes a diverging lens 74, a collimating lens 76 and a cylindrical lens 78, focusing the laser illumination on the grating valve 50.

The grating fluorescent valve 50 modulates laser illumination to form diffracted or reflected beams for the linear pixel array. At this time, the laser light 72 is a linear pixel array along a focus line forming a diffracted ray or reflected ray R including a diffraction order of ₊₁ and _-1 , D ₊₁ and D _-1 for each pixel. Is modulated by

The Schlieren optical system 52 includes first and second relay lenses 82 and 84 and a stop 80, which distinguishes the reflected light from the diffracted light rays for passing through the Schlieren optical system 52, By the stop 80, the diffracted light beam comprising D ₊₁ and D _-1 is passed and the reflected light beam R is stopped.

The wave modulator 54 includes a transmissive grating having a lattice contour at least partially perpendicular to the line image and modulates phase through the line image bandwidth.

The projection / scanning optical system 56 includes a projection lens 86 and a scanning mirror 88, which screens 58 to project a line image onto the screen 58 and to form a two-dimensional image on the screen 58. Scan the line image to.

The display optical system 42 having the above-described configuration reduces the speckle by causing the wavefront modulator 54 to change the phase of the laser illumination to generate multiple speckle patterns. Here, the wavefront modulator 54 requires a permeable diffraction grating having a lattice-shaped outline 110 formed to be inclined at about 45 ° on one surface as shown in FIG. 7.

However, the permeable diffraction grating required for the wavefront modulator 54 having the above-described configuration is difficult and complicated to form a lattice on one surface, which makes the manufacturing process difficult and takes a long time.

In addition, since the laser is diffracted through the diffraction grating, there is a problem that not only the image quality is lowered but also the light efficiency is lowered.

The present invention was devised to solve the above-mentioned problems of the prior art, and an object of the present invention is to reduce the speckle by using a pair of transmissive optical elements having a simple configuration, which is not only easy to manufacture, but also deteriorates image quality and light efficiency. It is to provide a display system that is not.

In order to achieve the above object of the present invention, the present invention provides a light source unit for emitting a light beam of a predetermined wavelength, an illumination lens unit for focusing the emitted light beam, an optical modulator for modulating the focused light beam, and modulation A first projection lens unit for converting the converted light beam into parallel light, a speckle reduction unit for reducing the speckle of parallel light by converting the length of the optical path of the parallel light with time, and parallel light with reduced speckle It provides a laser projection display system having a pair of optical elements for reducing the speckle, characterized in that it comprises a second projection lens portion for enlarging and projecting on the screen.

The display system of the present invention can form a speckle reduction portion to include a pair of transmissive optical elements that are symmetrical with each other and rotate at a predetermined angle about an axis of symmetry.

Here, the pair of transmissive optical elements may be formed to have a thickness of 2 mm and a refractive index of 1.5.

In addition, the pair of transmissive optical elements may be installed at an angle of 45 ° to 60 ° with respect to the horizontal axis, or may be inclined at an angle of 45 ° to 60 ° with respect to the horizontal axis, and may be reciprocated in a range of about 5.7 °. Can be installed.

In addition, the pair of transmissive optical elements may be formed of glass.

In addition, the pair of transmissive optical elements may coat the incident surface of the parallel light with a coating material having excellent transmittance.

Hereinafter, a laser projection display system having a pair of optical elements for reducing speckle according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 1, the display system 100 according to an exemplary embodiment of the present invention includes a light source unit 110, an illumination lens unit 120, an optical modulator 130, a first projection lens unit 140, The speckle reduction unit 150, the second projection lens unit 160, the screen unit 170, and the driving unit 180 are included.

The light source unit 110 emits a light beam of a predetermined wavelength.

The illumination lens unit 120 is for focusing the light beam emitted from the light source unit 110 to the light modulator 130, and may include a plurality of lenses such as a diverging lens, a collimating lens, a cylindrical lens, and the like. Although not shown in the examples, it includes a zoom lens that increases and collimates the width of the light beam, a beam shaper element, and a lens that enables X-direction line beam illumination after Y-direction enlargement and collimation.

The optical modulator 130 modulates the focused light beam and sends it to the first projection lens unit 140. In this embodiment, a one-dimensional diffraction type optical modulator is used.

The first projection lens unit 140 converts the light beam sent from the light modulator 130 into parallel light and sends it to the speckle reduction unit 150. The first projection lens unit 140 is composed of a relay lens group and a projection lens group and is disposed between the two lenses. To form an intermediate image plane.

The speckle reduction part 150 reduces the speckle of parallel light sent from the first projection lens part 140 and includes a pair of transmissive optical elements. The transmissive optical element will be described in detail below with reference to FIGS. 2 to 4.

The second projection lens unit 160 enlarges the parallel light of which speckle is reduced and projects it on the screen 180.

The driving unit 170 is connected to the speckle reduction unit 150 to drive the speckle reduction unit 150.

The speckle reduction part 150 includes a pair of transmissive optical elements 151 and 152 shown in FIGS. 2 and 3.

As shown in Fig. 2, the pair of transmissive optical elements 151 and 152 are inclined at a predetermined angle, preferably 45 ° or more, more preferably about 45 ° to 60 °, with respect to the X axis shown by a dashed line. Install symmetrically with respect to Y axis.

The transparent optical elements 151 and 152 are made of a material having excellent transparency such as glass. Herein, the refractive indexes n of the transparent optical elements 151 and 152 are all applicable when not 1. The refractive index n is set to 1.5 in this embodiment. In addition, the thickness t of the transparent optical elements 151 and 152 may be changed depending on the size of the speckle reducing unit 150 or the overall size of the display system 100. In the present embodiment, the thickness t is 2 mm.

The transmissive optical elements 151 and 152 have coating surfaces 151a and 152a formed of a predetermined coating material, preferably a coating material having excellent transmittance, on the incident surface on which the light beam is incident. Here, both surfaces of the optical elements 151 and 152 are subjected to anti-reflection coating, and the anti-reflection coating is alternately performed on materials having different indices such as magnesium oxide (MgO).

As shown in FIG. 3, the transmissive optical elements 151 and 152 having the above-described configuration are reciprocally rotated in the direction of the arrow around A and A 'by predetermined driving means (not shown). In this case, the rotation speed of the transparent optical elements 151 and 152 is preferably in the range of 1 Hz to 1500 Hz.

In FIG. 3, the transmissive optical elements 151 and 152 rotate symmetrically with respect to each other, and thus the description of the transmissive optical element 152 will be omitted based on the transmissive optical element 151.

The transmissive optical elements 151 and 152 are initially inclined at an angle of θ ₁ and then inclined at an angle of θ ₂ , where a difference in rotation angle, that is, a difference δ θ of θ ₂ −θ ₁ is about 5.7 ° (0.1 (rad). Is preferred). Here, the smaller the initial inclination angle θ ₁ is, the smaller it is, but if it is too small, the transmittance of the light beam is lowered. In addition, the initial inclination angle θ ₁ may vary depending on the degree of coating of the coating surfaces 151a and 152a formed on the transparent optical devices 151 and 152.

As shown by the dotted line, when the inclination angle of the transmissive optical elements 151 and 152 is θ ₁ , the path of the light beam is B ₁ while the inclination angle of the transmissive optical elements 151 and 152 is θ ₂ as shown by the solid line. At that time, the path of the light beam becomes B ₂ . Therefore, when the inclination angle of the transparent optical elements 151 and 152 is changed from θ ₁ to θ ₂ , the path of the light beam is changed from B ₁ to B ₂ . By changing the optical path, the light beam leaving the optical device 152 may be out of phase while maintaining the same optical path, and thus the speckle may be greatly reduced.

When the inclination angle of the transparent optical elements 151 and 152 is changed from θ ₁ to θ ₂ , the path length P of the light beam is changed from P ₁ = A to B ₁ to P ₂ = A to B ₂ , and based on the path length difference δP = P ₁ -P ₂ is obtained. This will be described in detail with reference to FIG. 4.

4 is an exaggerated change in the inclination angle in order to explain the change in the optical path length according to the change in the inclination angle, and in practice, the change in the inclination angle is considerably smaller than the change in the inclination angle of about 5.7 °.

In FIG. 4, when the inclination angle is changed to θ ₂ , for example, the optical path length P and the optical path length difference δP = P ₁ -P ₂ are obtained through the following equations.

,

,

If the refractive index of the optical element n = 1.5, t = 2mm, θ ₁ = 0.5 (rad) and θ ₂ = 0.6 (rad) in the present embodiment, the results shown in Table 1 on the basis of Equations 1 to 4 above Is obtained.

 θ (rad)  sin θ  sin θ '  cos θ  cos θ '  P (mm)  δP (mm) θ ₁ = 0.5  0.479  0.340  0.878  0.948  1.631    0.063 θ ₂ = 0.6  0.565  0.376  0.825  0.926  1.694

In general, when the amount of change in the optical path length per unit becomes 1 times the wavelength of the light beam in one pixel time, the speckle is completely removed. Based on Table 1, it can be seen that the speckle is sufficiently reduced since the amount of change in the optical path length per unit time is 1/2 times the wavelength of the light beam during one pixel time. This is because the interference of the coherent beam emitted from the image plane occurring in the retina of the human eye is completely reversed from constructive interference to destructive interference at all points on the retina for 1 pixel time, thereby affecting the time integration effect of visual cells. This is because the distortion of the amount of light due to the interference is eliminated.

The laser projection display system including a pair of optical elements for reducing speckles has been described above with reference to a preferred embodiment of the present invention, but modifications, changes, and various modifications can be made without departing from the spirit of the present invention. It is apparent to those skilled in the art that examples are possible.

According to the display system of the present invention, the speckle of the light beam is reduced by using a pair of transmissive optical elements having a predetermined refractive index, which is simple in construction, so that the optical element, the speckle reduction portion, or the display system can be reduced. The manufacturing process is very easy and the manufacturing time can be greatly reduced.

In addition, since the optical element has a high transmittance and can also increase the transmittance by changing the coating surface, the light efficiency is greatly improved compared to the prior art.

Claims (8)

A light source unit for emitting a light beam of a predetermined wavelength; An illumination lens unit for focusing the emitted light beam; An optical modulator for modulating the focused light beam; A projection lens unit for converting the modulated light beam into parallel light and enlarging the projected light onto a screen; And And a pair of optical elements for reducing speckle, wherein the speckle reduction portion reduces the speckle of the parallel light by converting the length of the optical path of the parallel light with time. A light source unit for emitting a light beam of a predetermined wavelength; An illumination lens unit for focusing the emitted light beam; An optical modulator for modulating the focused light beam; A first projection lens unit for converting the modulated light beam into parallel light; A speckle reduction unit for reducing the speckle of the parallel light by converting a length of the optical path of the parallel light with time; And And a second projection lens unit configured to magnify the parallel light having the reduced speckle and project the same to a screen, wherein the laser projection display system comprises a pair of optical elements for reducing speckle. The display system according to claim 1 or 2, wherein the speckle reduction part comprises a pair of transmissive optical elements that are symmetrical with each other and rotate in a predetermined angle about an axis of symmetry. The display system according to claim 3, wherein the pair of transmissive optical elements have a thickness of 2 mm and a refractive index of 1.5. The display system as claimed in claim 3, wherein the pair of transmissive optical elements are inclined at an angle in a range of 45 ° to 60 ° based on a horizontal axis. The display system of claim 3, wherein the pair of transmissive optical elements are inclined at an angle ranging from 45 ° to 60 ° with respect to a horizontal axis and installed to reciprocate in a range of about 5.7 °. 4. A display system according to claim 3, wherein the pair of transmissive optical elements is glass. The display system according to claim 7, wherein the transmissive optical element is coated with a coating material having excellent transmittance on the incident surface of the parallel light.

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