JP2000089160A - Optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical device in which speckle noise reduction is effectively conducted, highly efficient illumination is conducted in a polarization conversion and which is used for the projector that uses a spatial optical modulation element having a laser as a light source. SOLUTION: The device is provided with a laser light source which outputs S polarized light beams, a polarized beam splitter 11 which conducts separation of linear polarized light, an optical fiber 12 which transmits light beams to an output section from an input section, and condensing lenses 13 and 14 which make incident the emitted light beams from the output section of the fiber 12 on the input section of the fiber 12. An optical loop is made up with the fiber 12, the polarized beam splitter 11 and the lenses 13 and 14. The S polarized light beams from the layer light source are led to the optical loop through the beam splitter 11 and S polarized light beam are finally outputted from the beam splitter 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device,
In particular, the present invention relates to an optical device using a laser with reduced speckle noise as a light source.

[0002]

2. Description of the Related Art When constructing a projector (laser image display device) using a laser as a light source, there are roughly two constitutional methods. One method is to scan a laser beam at a point spot on a screen and modulate the laser intensity (there is also a method of performing the same scanning and modulation on a linear laser beam that is one-dimensionally modulated). In this method, light modulation must be performed at a speed similar to that of an input video signal. For this reason, there are drawbacks such as an inevitable increase in size of the device and poor efficiency. As another method, like a projector using a discharge lamp and a spatial light modulator,
There is a method of combining a laser and a spatial light modulator. Although this method is basically the same as a projector using a discharge lamp, it has a specific problem when a laser is used as a light source.

When a laser is used as a light source, there is a problem that speckle noise is generated on a screen in either of the above two configurations. This is because when light emitted from a light source with high spatial coherence is scattered and reflected on a rough surface or transmitted through a rough surface, light scattered by minute irregularities on the rough surface interferes in an irregular phase relationship. Thus, a random interference pattern is generated on the screen. In particular, when a laser light source is used, the coherence is very high, and the contrast of speckle on the screen is high. When a projector using a laser as a light source is configured, speckle noise appears to be superimposed on an input image, which leads to deterioration of image quality.

Heretofore, several methods for reducing speckle noise have been proposed. Methods for reducing speckle noise can be basically classified into the following five methods. 1) A method of controlling coherency spatially. 2) A method of controlling coherency over time. 3) Spatial sampling method. 4) Spatial averaging method. 5) A method of performing digital image processing.

[0005] Of these, methods of controlling spatial coherence which are often used include a method using a light guide such as an optical fiber, a method of passing light through a rotating ground glass, and a method of using a random retardation plate. Famous. Among them, a method using an optical fiber is particularly convenient and is often used.

When laser light is passed through an optical fiber, the light propagates inside the optical fiber while causing total reflection. The optical path length when passing through the fiber varies depending on the angle of incidence of the laser beam on the fiber. As a result, at the fiber emission portion, light emitted from the laser at different times is added, and the spatial coherence degree is reduced. It is also effective to vibrate the optical fiber to increase the change in the optical path length and increase the superposition effect.

As described above, the method of reducing speckle using an optical fiber is simple, but has a problem.
That is, when the laser light passes through the optical fiber, the degree of polarization is reduced. Laser light is characterized by a very high degree of polarization. It is possible to guide the light to the element with high efficiency by utilizing the high degree of polarization of the laser. Thereby, when an element that modulates using polarized light, such as liquid crystal, is used as a spatial light modulation element in a projector, the illumination efficiency can be increased. However, by passing the laser light through an optical fiber to reduce speckle, the degree of polarization is reduced, and thus the illumination efficiency is reduced.

[0008] As a method of eliminating the decrease in the degree of polarization,
As shown in FIG. 8, after an optical fiber 12, a polarizing beam splitter (hereinafter referred to as PBS) 11, a reflecting mirror 18, and a λ / 2 retardation plate 1
There is a method of arranging 9 so that polarized light is aligned in one direction. This is a method often used in projectors that use non-polarized light as a light source, such as a discharge lamp, and is called polarization conversion.

In FIG. 8, when the P-polarized light is passed through the optical fiber 12, the degree of polarization is reduced and the light is output as a mixture of P-polarized light and S-polarized light. This light is condensed by the condenser lens 13 and input to the PBS 11. The PBS 11 has a property of transmitting the P-polarized light component and reflecting the S-polarized light component. Reflected S
The polarized light component is reflected by the reflecting mirror 18 and the λ / 2 retardation plate 19
And is output as P-polarized light. As a result, all output lights are unified to P-polarized light. However, according to this method, there is a problem that the beam diameter of the light is more than doubled.

Now, a spatial light modulator such as a liquid crystal panel,
Consider illuminating a laser beam that has passed through an optical fiber. In the optical system, the following theorem holds with the configuration shown in FIG. S1 × θ1 = S2 × θ2 where S1 is the size (area) of the object, S2 is the size (area) of the image, θ1 is the divergence angle (solid angle) of light emitted from the object, and θ2 is the angle of light incident on the image ( Solid angle).

When the size of the spatial light modulator and the divergence angle θ1 of the light emitted from the object are constant, if the size of the object is doubled, the angle θ2 of the light incident on the image is doubled. When the above-described polarization conversion is used, the size of the object can be considered to be doubled by doubling the beam diameter of the light, so that the angle of the light incident on the spatial light modulator is also doubled. Become. As a result, problems such as a decrease in lighting efficiency and an increase in the number of constituent devices arise.

[0012]

As described above, in the case of constructing a projector using a spatial light modulator using a laser as a light source, if an attempt is made to reduce speckle using an optical fiber, the degree of polarization may decrease. There were problems such as a reduction in lighting efficiency.

[0013] The present invention solves this problem, and by a relatively simple method, it is possible to effectively reduce speckle noise and to perform polarization conversion capable of high-efficiency illumination. It is an object to realize an optical device that can be used for a projector using a light modulation element.

[0014]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a laser light source means for oscillating a single linearly polarized light mode, a polarizing beam splitter means for separating linearly polarized light, a light input unit and an output unit. Having a light guiding means for propagating light from the input part to the output part, and a condensing optical system for making light emitted from the output part of the light guiding means incident on the input part of the light guiding means. Providing the polarizing beam splitter means in the condensing optical system, forming an optical loop with the light guiding means, the polarizing beam splitter means and the condensing optical system, and outputting the output of the laser light source means to the polarizing beam splitter. Means for introducing linearly polarized light from the polarizing beam splitter means.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an optical device according to the present invention will be described in detail with reference to the accompanying drawings. An object of the present invention is to realize both effective speckle noise reduction using an optical fiber and polarization conversion that enables highly efficient illumination. FIG. 1 shows a configuration of an optical device according to an embodiment of the present invention. In FIG. 1, reference numeral 11 denotes a polarizing beam splitter (P
BS) and 12 are optical fibers, and 13 and 14 are condenser lenses. The feature of this configuration is that only one polarization beam splitter 11 is used.

The operation of the optical device will be described with reference to FIG. The laser beam input here is assumed to be S-polarized light with respect to the polarization beam splitter. Since the laser light has a very high degree of polarization, most of the light is reflected by the polarization beam splitter 11 (FIG. 2A). The reflected light is incident on the optical fiber 12 by the condenser lens 13 and travels while totally reflecting inside the optical fiber. At this time, the degree of spatial coherence decreases due to the superposition of light. In addition, part of the S-polarized light is changed to P-polarized light (Fig. 2-
b).

In this way, the laser light emitted from the optical fiber emitting portion has a reduced spatial coherence degree and includes S-polarized light and P-polarized light (FIG. 2C). The light emitted from the optical fiber 12 spreads, but is made closer to parallel light by the condenser lens 14. And again the polarizing beam splitter 11
Is incident on. In the polarization beam splitter 11, S-polarized light is reflected and P-polarized light is transmitted. For this reason, the reflected S-polarized light travels in the direction in which it is first incident, and travels to the next optical element of the projector device. The transmitted P-polarized light is again incident on the optical fiber 12 (FIG. 2D). The P-polarized light that has entered the optical fiber 12 again changes to P + S polarized light while passing through the optical fiber 12. The S-polarized light is emitted by the polarization beam splitter 11.

If the loss inside the optical fiber 12 and the insertion loss at the part where the light enters the optical fiber 12 are low, the incident S
The polarized light is finally output as S-polarized light. In addition, since laser light that travels inside the optical fiber 12 many times is present, the superposition of light can be increased, and a great effect can be achieved in reducing speckle.

FIG. 3 shows another embodiment of the present invention.
In this embodiment, P-polarized light is used when a laser beam is incident on the optical device. The basic operation is the same. In this case, the emitted light is P-polarized light. Further, as shown in FIG. 4, by vibrating the optical fiber 12 with the vibrating device 17, it is possible to change the propagation path of the light in the optical fiber 12 and obtain a larger speckle reduction.

In the present invention, even if the intermediate portion of the optical fiber is vibrated, the insertion loss and the like do not change, so that effective speckle reduction can be performed in combination with the vibration of the optical fiber.

As the optical fiber, in addition to a glass material and a plastic material, a material made of a liquid can be used. This uses a liquid having a high transmittance for the core. Optical fiber using such a liquid,
It is considered that the insertion loss can be reduced because the core diameter is large, and it is advantageous in the operation of vibrating the optical fiber described above. It is also effective to provide an antireflection film in order to prevent an increase in insertion loss due to reflection at the entrance and exit of the optical fiber.

[0022]

FIG. 5 is a block diagram showing a monochromatic laser image display device using the optical device of the present invention. In FIG. 5, 1
Is an optical device of the present invention, 11 is a polarizing beam splitter, 1
2 is an optical fiber, 13, 14, 15, and 16 are condenser lenses, 17 is a vibration device, 20 is a laser light source, and 25 is an LCD.
A panel, 26 is a projection lens, 27 is a screen, and 28 is a fly-eye lens.

The laser light from the laser light source 20 passes through the condenser lens 13 and is input to the polarization beam splitter 11 as S-polarized light. Since the configurations of the polarization beam splitter 11, the optical fiber 12, and the condenser lenses 14 and 15 are the same as those shown in FIG. 1, the operation is as described in FIG. As a result, the light traveling toward the fly-eye lens 28 is output as S-polarized light with reduced speckle. The fly-eye lens 28 has a function of making spatial illumination unevenness uniform. The output S-polarized light of the optical device 1 with uniform illuminance is condensed by the condenser lens 16 and illuminated on the LCD panel 25, and the light transmitted through the LCD panel 25 is projected on the screen 27 by the projection lens 26. .

FIGS. 7 and 6 show the effect of speckle reduction according to this embodiment. The wavelength of the laser light used for the measurement is visible light of 0.4 μm to 0.7 μm. FIG. 6 shows a screen 2 when the laser light from the laser light source 20 is directly input to the fly-eye lens 28 without passing through the optical device 1.
7 shows the light intensity distribution on the screen of FIG. 7, and FIG. 7 shows the light intensity distribution on the screen of the screen 27 when the light is input to the fly-eye lens 28 through the optical fiber 12 of the optical device 1. In each case, the horizontal axis indicates the position on the screen, and the vertical axis indicates the normalized light intensity (up to 255). By comparing FIG. 6 and FIG. 7, it can be clearly seen that the intensity variation is smaller when the light passes through the optical device 1. Comparing this with a value obtained by dividing the variance by the average (Spectra contrast) results in a significant improvement from 0.612 to 0.423.

The longer the length of the optical fiber 12 used in the apparatus, the greater the probability of light superposition and the greater the effect of speckle reduction, but the greater the loss inside the optical fiber 12. The length of the optical fiber 12 is selected from all lengths from a length that can be physically bent to a length of several tens of meters in consideration of both the effect of reducing speckle and the loss. However, even if the length is not so long, by vibrating the optical fiber 12 with the vibrating device 17, a greater speckle reduction effect can be achieved.

As described above, according to the optical device of the present invention,
A laser beam with a high degree of polarization from which speckle has been removed can be efficiently obtained. The device uses only one optical fiber and one polarizing beam splitter. In particular, only one relatively expensive polarizing beam splitter is needed.
This is advantageous in terms of cost. Further, regarding the polarization conversion, since the spot size of the laser beam does not increase, efficient illumination is possible.

In the above description, the application of the present invention has been described with respect to a projector using a laser as a light source. However, the present invention can be applied to various other uses such as a semiconductor exposure apparatus used for producing a semiconductor device. Needless to say.

[0028]

As described above, according to the first aspect of the present invention, there are provided a laser light source means for oscillating a single linearly polarized light mode, a polarization beam splitter means for separating linearly polarized light, a light input part and an output part. Having a light guiding means for propagating light from the input part to the output part, and a condensing optical system for causing light emitted from the output part of the light guiding means to be incident on the input part of the light guiding means. A beam splitter means is provided in the condensing optical system, a light guide means, a polarizing beam splitter means and an optical loop are formed by the condensing optical system, and a laser light source means output is introduced into the optical loop through the polarizing beam splitter means, The polarization beam splitter outputs linearly polarized light. As a result, the presence of laser light that can pass through the optical fiber a plurality of times increases the effect of superimposing the light, so that the speckle noise can be effectively reduced by a relatively simple method and the beam diameter can be reduced. An optical device capable of performing high-efficiency illumination that can perform polarization conversion without spreading light and that can be used for a projector using a spatial light modulator using a laser as a light source can be realized at low cost.

According to a second aspect of the present invention, the light guiding means is constituted by an optical fiber. Thus, the light guide path can be formed relatively easily and at low cost, and the target optical device can be realized at low cost.

The invention according to claim 3 of the present invention is characterized in that the light guide means is constituted by a tube whose inside is filled with a liquid and whose inner wall totally reflects light. As a result, a light guide path having a large speckle noise reduction effect can be formed relatively easily and inexpensively, and a target optical device can be realized at low cost.

The invention according to a fourth aspect of the present invention is characterized in that a vibration means for vibrating the light guide means is provided. This makes it possible to increase the speckle noise reduction effect even when the length of the light guide is relatively short.

The invention according to claim 5 of the present invention is characterized in that an antireflection film is provided on an input portion and an output portion of the light guide means. Thereby, the loss of the light guide means can be reduced, and an optical device capable of highly efficient illumination can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an optical device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining the operation of the embodiment in FIG. 1;

FIG. 3 is a schematic diagram showing a configuration of an optical device according to another embodiment of the present invention.

FIG. 4 is a schematic diagram showing a configuration of an optical device according to still another embodiment of the present invention.

FIG. 5 is a schematic diagram showing a configuration of an embodiment of a laser image display device using the present invention.

FIG. 6 is a chart showing intensity unevenness on a screen screen when an optical fiber is not passed.

FIG. 7 is a table showing intensity unevenness on a screen screen in the embodiment of FIG. 5;

FIG. 8 is a schematic diagram showing a configuration of a conventional polarization conversion.

FIG. 9 is an explanatory diagram showing a relationship between an image size and an incident angle.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical device of this invention, 11 ... Polarization beam splitter
12: Optical fiber, 13, 14, 15, 16: Condensing lens, 17: Vibrating device, 18: Reflecting mirror, 19: λ / 2 phase plate, 20: Laser light source, 25: LCD panel, 26:
Projection lens, 27 ... screen, 28 ... fly-eye lens.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Junichi Iwai 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Toruyuki Miyawaki 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation

Claims (5)

[Claims] 1. A laser light source means for oscillating a single linearly polarized light mode, a polarization beam splitter means for separating linearly polarized light, and an input part and an output part for light, and light is transmitted from the input part to the output part. A light guiding unit; and a condensing optical system that causes light emitted from an output unit of the light guiding unit to enter an input unit of the light guiding unit. The polarizing beam splitter unit is provided in the condensing optical system. Forming an optical loop with the light guiding means, the polarizing beam splitter means, and the condensing optical system, introducing the output of the laser light source means into the optical loop through the polarizing beam splitter means, An optical device for outputting linearly polarized light. 2. The optical device according to claim 1, wherein said light guiding means is an optical fiber. 3. The light guide means is filled with a liquid inside,
The optical device according to claim 1, wherein the inner wall is a tube that totally reflects light. 4. The optical device according to claim 1, further comprising a vibrating means for vibrating the light guiding means. 5. The optical device according to claim 1, wherein an antireflection film is provided on an input portion and an output portion of the light guide.