JP2015037017A - Light guide system and drive control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve reductions in cost and size of a light guide system while reducing speckle noise recognized by an observer.SOLUTION: According to an embodiment, a light guide system includes: a light source 101, 102 or 103 that generates and emits coherent light; and a light pipe 110 that guides the coherent light. An emission intensity of the light source 101, 102 or 103 can be switched to a plurality of levels during an ON-period of the light source 101, 102 or 103. At least a part of an internal surface of the light pipe 110 is formed so as to reflect the coherent light diffusely.

Description

  The embodiment relates to an optical system using coherent light as a light source.

  In recent years, lasers have attracted attention as light sources for projectors. By using a laser as a light source, light utilization efficiency and color reproducibility can be improved. On the other hand, since laser light has high coherence, speckle noise (for example, two-dimensional interference fringes and three-dimensional scintillation) is a problem.

  Conventionally, a diffusion plate for changing a position (speckle pattern) where speckle noise occurs has been proposed. This diffusion plate can change the speckle pattern at high speed by transmitting the laser light from the laser light source while rotating at high speed. As a result, it becomes difficult for the viewer to recognize speckle noise.

  However, in order to introduce the diffusion plate, a mechanism, components, circuits, and the like for rotating the diffusion plate are required. Furthermore, it is necessary to arrange a member (for example, a cross prism) for synthesizing a plurality of colors of illumination light, and it is necessary to secure a space for rotating the diffusion plate. That is, the introduction of the diffusion plate not only increases the cost and power consumption of the light guide system, but also makes it difficult to reduce the size of the light guide system.

JP 2010-60912 A

  The embodiment aims to reduce speckle noise recognized by the viewer while reducing the cost and size of the light guide system.

  According to the embodiment, the light guide system includes a light source that generates and emits coherent light, and a light pipe that guides the coherent light. The light emission intensity of the light source is switched to a plurality of levels in each ON period of the light source. At least a part of the inner surface of the light pipe is formed so as to diffusely reflect coherent light.

Explanatory drawing of the mode of light interference at the time of projecting a laser beam on a display apparatus. Explanatory drawing of the speckle noise which arises when a laser beam is projected on a display apparatus. Explanatory drawing of the speckle noise which arises when a laser beam is projected on a display apparatus. The figure which illustrates the light guide system of a comparative example. The figure which illustrates the light guide system which concerns on 1st Embodiment. 4 is a timing chart illustrating an ON period and an OFF period of each laser diode and an LCOS (Liquid Crystal on Silicon) type imager in an RGB sequential optical system. The timing chart which illustrates the emitted light intensity at the time of making a laser diode emit CW light. The timing chart which illustrates the light emission intensity at the time of performing light emission intensity control of a laser diode. The timing chart which illustrates the light emission intensity at the time of performing light emission intensity control of a laser diode. Explanatory drawing of the relationship between the emitted light intensity of a laser diode, and the emission angle of a laser beam.

  Hereinafter, embodiments will be described with reference to the drawings. Hereinafter, the same or similar elements as those already described are denoted by the same or similar reference numerals, and redundant description is basically omitted.

  When coherent light such as laser light is used as the projector light source, speckle noise may be a problem. Specifically, as illustrated in FIG. 1, when laser light is projected onto a display device such as a screen, the reflected light (or scattered light) interfere with each other.

  The speckle noise illustrated in FIG. 2 may occur due to light interference. That is, a planar bright and dark stripe pattern is projected on the display image, and the image quality of the display image is greatly deteriorated. Furthermore, speckle noise illustrated in FIG. 3 may be generated due to light interference. That is, a three-dimensional light / dark pattern (which corresponds to flickering of a spotted pattern called scintillation) occurs in the space between the display device and the viewer. As a result, since a large number of bright spots are distributed in the space, it is difficult for the viewer to focus on the display image for a long period of time.

  In order to reduce such speckle noise, a light guide system illustrated in FIG. 4 may be employed. The light guide system shapes laser light emitted from the three color laser light sources into parallel light by a collimator lens, and combines the shaped light by the cross prism 104. The combined light (RGB sequential light) passes through the diffusion plate 106 rotated by the motor 105. As the diffusion plate 106 rotates, the speckle pattern when the synthesized light is projected onto the display device changes. If the speed of the change in the speckle pattern is sufficiently higher than the recognition speed of the viewer's eyes, it will be difficult for the viewer to recognize the speckle noise.

(First embodiment)
As illustrated in FIG. 5, the light guide system according to the first embodiment includes a red laser diode (R-LD) 101, a green laser diode (G-LD) 102, and a blue laser diode (B-LD). ) 103 and a light pipe 110. The light guide system in FIG. 1 may be applied to, for example, a projector optical system using an LCOS imager, but is not limited thereto.

  The R-LD 101, G-LD 102, and B-LD 103 are attached to one end side of the light pipe 110. The R-LD 101, the G-LD 102, and the B-LD 103 generate and emit red laser light, green laser light, and blue laser light, respectively, during driving (ie, the ON period). The R-LD 101, the G-LD 102, and the B-LD 103 may be replaced with a coherent light source of an arbitrary method. Further, the number of coherent light sources is not limited to three.

  The R-LD 101, G-LD 102, and B-LD 103 are ON / OFF controlled by a drive circuit (not shown). Further, the R-LD 101, the G-LD 102, and the B-LD 103 also control the light emission intensity during the ON period by the drive circuit. That is, the R-LD 101, the G-LD 102, and the B-LD 103 emit light with the light emission intensity controlled by the drive circuit over the ON period controlled by the drive circuit.

  The light pipe 110 combines and guides red laser light, green laser light, and blue laser light from the R-LD 101, G-LD 102, and B-LD 103. Specifically, the light pipe 110 is formed in a three-way shape on one end side. As described above, the R-LD 101, the G-LD 102, and the B-LD 103 are attached to one end of the light pipe 110. Red laser light, green laser light, and blue laser light from the R-LD 101, G-LD 102, and B-LD 103 are guided from one end side to the other end side of the light pipe 110, and are combined in the course of light guide. . Note that the shape of one end of the light pipe 110 is not limited to a three-way shape, and may be appropriately determined according to the number of coherent light sources attached to one end of the light pipe 110, for example.

  At least a part of the inner surface of the light pipe 110 is formed so as to diffusely reflect red laser light, green laser light, and blue laser light (in short, as a rough surface). Specifically, at least a part of the inner surface of the light pipe 110 can be formed as a rough surface by using, for example, blasting.

  The red laser light, green laser light, and blue laser light guided by the light pipe 110 are irregularly reflected by the inner surface of the light pipe 110 (in other words, reflected as diffused light). Therefore, the paths of the red laser light from the R-LD 101 (the same applies to the G-LD 102 and B-LD 103) to the other end of the light pipe 110 are diversified, and the red laser light emitted at the same time also depends on the path. Path differences (for example, differences in the number of reflections) occur. That is, the red laser light emitted from the other end of the light pipe 110 (the same applies to the green laser light and the blue laser light) has various phases. Accordingly, speckle noise generated when the red laser light is projected onto the display device is reduced.

  According to the light pipe 110, the red laser light, the green laser light, and the blue laser light can be synthesized and guided at a low cost, low power consumption, and space saving compared to the light guide system illustrated in FIG. .

  As described above, according to the light pipe 110, red laser light, green laser light, and blue laser light having various phases are emitted. Therefore, speckle noise generated when these laser lights are projected onto the display device. Is alleviated. Further, speckle noise can be further reduced by controlling the emission intensity of the R-LD 101, G-LD 102, and B-LD 103 as described later.

  For example, according to the RGB sequential optical system, as illustrated in FIG. 6, any one of R-LD 101, G-LD 102, and B-LD 103 is determined in a predetermined order in each ON period of the LCOS type imager. One is turned on independently.

  For example, the R-LD 101 is independently turned on in the first ON period of the LCOS type imager, the G-LD 102 is independently turned on in the second ON period of the LCOS type imager, and the third ON period of the LCOS type imager. The B-LD 103 is independently turned ON, and the R-LD 101 is independently turned ON again in the fourth ON period of the LCOS type imager.

  In general, each of the R-LD 101, the G-LD 102, and the B-LD 103 is controlled to drive CW (Continuous Wave) as shown in FIG.

  However, in the present embodiment, each of the R-LD 101, the G-LD 102, and the B-LD 103 is configured such that the emission intensity is switched to a plurality of levels in each ON period (for example, PWM (Pulse Width Modulation) driving). Preferably it is controlled.

  As illustrated in FIG. 10, the laser diode has a characteristic that the emission angle also changes as the emission intensity changes. Therefore, for example, if the R-LD 101 (the same applies to the G-LD 102 and the B-LD 103) is controlled so that the emission intensity can be switched to a plurality of levels within each ON period, the emission angle of the red laser light is set to the ON Within a period, it switches to a several magnitude | size according to the level of light emission intensity. That is, red laser light (the same applies to green laser light and blue laser light) is irregularly reflected at various positions on the inner surface of the light pipe 110, so that speckles generated when the red laser light is projected onto the display device. The pattern will also change. Therefore, speckle noise is further reduced.

  Note that the emission intensity in each ON period of the R-LD 101 (same for G-LD 102 and B-LD 103) may be controlled to be switched to two levels as illustrated in FIG. It may be controlled to be switched to more levels as exemplified in FIG. As the number of light emission intensity levels that can be switched increases, the emission angle of laser light can be diversified, which is effective in reducing speckle noise.

  In addition, the emission intensity of the R-LD 101 (same for G-LD 102 and B-LD 103) is preferably set so that the total light amount at the time of DC conversion in each ON period of the R-LD 101 matches a desired value. Switching to a plurality of levels in each ON period. Here, the desired value is equal to the total light amount in each ON period when, for example, the R-LD 101 (the same applies to the G-LD 102 and the B-LD 103) is CW-driven.

  Furthermore, the emission intensity of the R-LD 101 (same for G-LD 102 and B-LD 103) needs to be switched at a higher speed than the recognition speed of the viewer's eyes. Specifically, the emission intensity switching frequency (for example, PWM frequency) is preferably about 1 to 2 kHz. The practical drive frequency of the R-LD 101 (the same applies to the G-LD 102 and B-LD 103) is about 180 Hz. Therefore, if a switching frequency of about 1 to 2 kHz is set, each ON period is within the ON period. The light emission intensity of the R-LD 101 can be switched about 10 to 20 times.

  As described above, the light guide system according to the first embodiment is formed such that at least a part of the inner surface irregularly reflects the laser beams of the plurality of colors in order to synthesize and guide the laser beams of the plurality of colors. A light pipe (for example, blasted) is provided. Therefore, according to the light guide system, it is possible to combine and guide light beams of a plurality of colors with low cost, low power consumption, and space saving, and occurs when the laser beams of a plurality of colors are projected onto a display device. Speckle noise is also reduced.

  Furthermore, in the light guide system according to the present embodiment, the emission intensity of each of the plurality of laser diodes that respectively generate and emit a plurality of colors of laser light can be switched to a plurality of levels in each ON period of the laser diode. Controlled. Therefore, according to this light guide system, since the emission angles of the laser light are diversified, speckle noise generated when a plurality of colors of laser light are projected onto the display device can be further reduced.

  The processing of the above embodiment can be realized by using a general-purpose computer as basic hardware. The program for realizing the processing of the above embodiment may be provided by being stored in a computer-readable storage medium. The program is stored in the storage medium as an installable file or an executable file. Examples of the storage medium include a magnetic disk, an optical disk (CD-ROM, CD-R, DVD, etc.), a magneto-optical disk (MO, etc.), and a semiconductor memory. The storage medium may be any as long as it can store the program and can be read by the computer. Further, the program for realizing the processing of the above embodiment may be stored on a computer (server) connected to a network such as the Internet and downloaded to the computer (client) via the network.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 101 ... Red laser diode, 102 ... Green laser diode, 103 ... Blue laser diode, 104 ... Cross prism, 105 ... Motor, 106 ... Diffusing plate, 110 ... Light pipe

Claims (5)

A light source for generating and emitting coherent light;
A light pipe for guiding the coherent light,
The light emission intensity of the light source is switched to a plurality of levels in each ON period of the light source,
At least a part of the inner surface of the light pipe is formed so as to diffusely reflect the coherent light,
Light guide system. The light emission intensity of the light source is switched to a plurality of levels in each ON period so that the total amount of light at the time of DC conversion in each ON period of the light source matches a desired value.
The light guide system of claim 1. At least a part of the inner surface of the light pipe is blasted,
The light guide system of claim 1. Switching the light emission intensity of a light source that generates and emits coherent light guided by a light pipe formed so that at least a part of the inner surface diffusely reflects the coherent light to a plurality of levels in each ON period of the light source. A drive control method comprising: A plurality of light sources respectively generating and emitting a plurality of colors of coherent light;
A light pipe for combining and guiding the coherent light of the plurality of colors,
The emission intensity of each of the plurality of light sources is switched to a plurality of levels in each ON period of the light source,
At least a part of the inner surface of the light pipe is formed so as to diffusely reflect the coherent light of the plurality of colors.
Light guide system.

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