JP2020020962A - Optical unit and image projection device - Google Patents

Abstract

To provide an optical unit and an image projection device that produce white light.SOLUTION: An optical unit comprises: a light source 1 that emits light in a first wavelength range; a polarization separation element 2 that separates light in a direction different with respect to the light in the first wavelength range; a phase difference plate 3 that rotates a polarization direction by 1/4 rotation with respect to the light in the first wavelength range separated by the polarization separation element 2 and transmits the light; an optical element 4 that reflects one part of the light in the first wavelength range having the polarization direction rotated by 1/4 rotation and passing through the phase difference plate 3, and transmits the other part; and a phosphor 5 that converts the other part of the light in the first wavelength range passing through the optical element 4 into light in a second wavelength range and emits the light to the optical element 4. The optical unit produces white light from one part of the light in the first wavelength range reflected by the optical element 4 and the light in the second wavelength range converted by the phosphor 5.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical unit and an image projection device.

  Patent Literature 1 discloses a configuration of an optical system using a blue light source and a color wheel.

  However, according to the method disclosed in Patent Document 1, a color wheel having a reflecting area and a phosphor area rotates to emit time-division light, and alternately alternately synthesize them in a time-division manner. That creates white light. However, the technique disclosed in Patent Document 1 involves difficulty in reducing the size of the device. Further, there is a problem that an image is not stable due to the influence of time division.

  Therefore, an object of the present invention is to provide an optical unit and an image projection device that generate white light.

  In order to achieve the above object, an optical unit according to the present invention includes a light source that emits light in a first wavelength band and a polarization separation element that separates light in different directions with respect to the light in the first wavelength band. A retardation plate that transmits the light of the first wavelength band separated by the polarization separation element by rotating the polarization direction by １ ／, and a polarization direction that is transmitted through the retardation plate and decreases the polarization direction by 1 / An optical element that reflects a part of the light of the first wavelength band rotated four times and transmits the other part, and the other part of the light of the first wavelength band that has passed through the optical element to a second wavelength band A phosphor that converts the light into light and emits the light to the optical element, and a part of the light in the first wavelength band reflected by the optical element and the second wavelength that is converted by the phosphor. White light is generated from the band light.

  According to the present invention, it is possible to provide an optical unit and an image projection device that generate white light.

FIG. 2 is a configuration diagram of an example of an optical unit according to the first embodiment. 6 is an example of a graph illustrating a relationship between characteristics of a wavelength-selective polarization beam splitter according to the first embodiment and a spectrum of a light source. 6 is an example of a graph illustrating a relationship between characteristics of the dichroic mirror according to the first embodiment and a spectrum of a light source. 4 is an example of a spectrum of light emitted from the optical unit according to the first embodiment. 7 is an example of a graph illustrating a relationship between characteristics of a wavelength-selective polarization beam splitter according to a first modification and a spectrum of a light source. FIG. 9 is a configuration diagram of an example of an optical unit according to a second embodiment. 9 is an example of a graph illustrating a relationship between characteristics of a wavelength-selective polarization beam splitter according to a second embodiment and a spectrum of a light source. 9 is an example of a graph illustrating a relationship between characteristics of a wavelength-selective polarization beam splitter according to a second modification and a spectrum of a light source. FIG. 9 is a configuration diagram of an example of an optical unit according to a third embodiment. 14 is an example of a dichroic mirror according to a third embodiment.

  An embodiment for carrying out the present invention will be described below. Note that the same members and the like are denoted by the same reference numerals and description thereof is omitted.

<< 1st Embodiment >>
An example of the optical unit 10 according to the first embodiment will be described with reference to FIG. FIG. 1 is a configuration diagram of an example of an optical unit 10 according to the first embodiment.

  The optical unit 10 is used for, for example, a lighting device of a projector (image projection device). An example of the projector includes an optical unit 10 that emits white light, a color separation unit (not shown) that separates white light into red light, green light, and blue light, and generates a projection image for each of the separated colors. It includes three light modulation elements (not shown) and a projection lens (not shown) that projects a projection image generated by the light modulation elements onto a screen (not shown). The configuration of the projector is not limited to this.

  The optical unit 10 includes a light source 1, a wavelength-selective polarization beam splitter (polarization splitting element) 2, a quarter-wave plate (phase difference plate) 3, a dichroic mirror (optical element) 4, a phosphor 5, Have. The optical path from the light source 1 to the wavelength-selective polarizing beam splitter 2 and the optical path from the wavelength-selective polarizing beam splitter 2 to the phosphor 5 are laid out orthogonally. Further, a １ ／ wavelength plate 3 and a dichroic mirror 4 are arranged on an optical path between the wavelength selection type polarization beam splitter (polarization splitting element) 2 and the phosphor 5.

  The light source 1 is configured using a solid-state light source such as an LED (light emitting diode) or an LD (laser diode), and emits light in a first wavelength band. In the following description, the light source 1 will be described as a blue light LD. Light emitted from the light source 1 is linearly polarized light having a first polarization direction. In the following description, it is assumed that P-polarized light is used for the wavelength-selective polarization beam splitter 2. The P-polarized blue light 61 emitted from the light source 1 enters the wavelength-selective polarization beam splitter 2.

  The wavelength-selective polarization beam splitter 2 separates the light of the first wavelength band into one linearly polarized light and the other linearly polarized light. The characteristics of the wavelength-selective polarization beam splitter 2 will be described with reference to FIG. FIG. 2 is an example of a graph for explaining the relationship between the characteristics of the wavelength-selective polarization beam splitter 2 according to the first embodiment and the spectrum of the light source 1. In FIG. 2, the horizontal axis indicates the wavelength, the first vertical axis on the left indicates the transmittance of the wavelength-selective polarizing beam splitter 2, and the second vertical axis on the right indicates the light intensity of the spectrum of the light source 1. It is an axis graph. Further, corresponding to the first vertical axis, the transmittance of S-polarized light is indicated by a broken line, and the transmittance of P-polarized light is indicated by a dotted line. The light intensity of the spectrum of the light source 1 is indicated by a solid line corresponding to the second vertical axis.

  As shown in FIG. 2, the blue light of the light source 1 has a light spectrum having a sharp peak near 450 nm. The wavelength-selective polarization beam splitter 2 has a characteristic of reflecting P-polarized light having a wavelength of about 500 nm or less and transmitting almost 100% of P-polarized light having a longer wavelength. Further, the wavelength-selective polarization beam splitter 2 has a characteristic of transmitting almost 100% of S-polarized light regardless of the wavelength. In other words, the wavelength-selective polarization beam splitter 2 reflects the light in the first polarization direction and transmits the light in the second polarization direction orthogonal to the first polarization direction in the light of the first wavelength band. Have the following characteristics. The wavelength-selective polarization beam splitter 2 has a property of transmitting light in a second wavelength band (yellow light described later) having a longer wavelength than the first wavelength band. Thereby, as shown in FIG. 1, the P-polarized blue light 61 that has entered the wavelength-selective polarizing beam splitter 2 from the light source 1 is reflected by the wavelength-selective polarizing beam splitter 2, and is reflected by the quarter-wave plate 3. Incident.

  The 波長 wavelength plate 3 rotates the polarization direction by ４. The circularly polarized blue light 62 transmitted through the 波長 wavelength plate 3 enters the dichroic mirror 4.

  The characteristics of the dichroic mirror 4 will be described with reference to FIG. FIG. 3 is an example of a graph illustrating the relationship between the characteristics of the dichroic mirror 4 according to the first embodiment and the spectrum of the light source 1. In FIG. 3, the horizontal axis indicates wavelength, the first vertical axis on the left indicates the transmittance of the dichroic mirror 4, and the second vertical axis on the right is a two-axis graph indicating the light intensity of the spectrum of the light source 1. . Also, the transmittance of the dichroic mirror 4 is shown by a broken line corresponding to the first vertical axis, and the light intensity of the spectrum of the light source 1 is shown by a solid line corresponding to the second vertical axis.

  As shown in FIG. 3, the dichroic mirror 4 has a characteristic of transmitting 80% of light having a wavelength of 500 nm or less and reflecting 20%. Further, light having a wavelength of 500 nm or more has a characteristic of transmitting (100% transmission).

  As a result, as shown in FIG. 1, of the blue light 62 incident on the dichroic mirror 4, a part of the blue light 63 is reflected by the dichroic mirror 4, passes through the quarter-wave plate 3 again, and selects a wavelength. Incident on the polarization beam splitter 2.

  Of the blue light 62 that has entered the dichroic mirror 4, the remaining other portion of the blue light 64 passes through the dichroic mirror 4 and enters the phosphor 5.

  The phosphor 5 converts the incident light of the first wavelength band into light of a second wavelength band having a different wavelength from the light of the first wavelength band. Here, the phosphor 5 has a yellow phosphor and converts blue light into yellow fluorescence. Further, a reflecting surface is formed on the opposite side of the surface of the phosphor 5 on which the light is incident, and reflects the light. Further, a heat dissipation member (not shown) is provided outside the reflection surface. The yellow light 71 emitted from the phosphor 5 enters the dichroic mirror 4 again. The yellow light whose wavelength has been converted by the phosphor 5 has a light spectrum having a sharp peak near 550 nm. Therefore, as shown in FIG. 3, the yellow light 71 passes through the dichroic mirror 4. The yellow light 71 that has passed through the dichroic mirror 4 again passes through the quarter-wave plate 3 and enters the wavelength-selective polarization beam splitter 2.

  The circularly polarized blue light 63 and yellow light 71 pass through the quarter-wave plate 3 again to become S-polarized blue light 65 and yellow light 72. The S-polarized blue light 65 and yellow light 72 transmitted through the 波長 wavelength plate 3 enter the wavelength-selective polarization beam splitter 2. As shown in FIG. 2, the wavelength-selective polarization beam splitter 2 has a property of transmitting almost 100% of S-polarized light regardless of the wavelength. Thus, the S-polarized blue light 65 and the yellow light 72 pass through the wavelength-selective polarization beam splitter 2.

  FIG. 4 is an example of a spectrum of light emitted from the optical unit 10 according to the first embodiment. In FIG. 4, the horizontal axis represents the wavelength, and the vertical axis represents the light intensity of the spectrum. The spectrum of the blue light 65 indicated by the solid line is light having a center wavelength of about 450 nm. The spectrum of the yellow light 72 indicated by the broken line is light having a center wavelength of about 550 nm. When these two lights are mixed, white light is obtained.

  As described above, according to the optical unit 10 according to the first embodiment, the white light 8 in which the blue light 65 and the yellow light 72 are mixed can be emitted. Further, the white light 8 emitted from the optical unit 10 is not time-divided, and can be continuous light.

  Here, as a method of generating white light using a conventional solid-state light source, a transmission type yellow phosphor is used, some blue light is transmitted through the phosphor, and other blue light is yellow light by the phosphor. There is a method in which the phosphor is emitted after being converted into a white light, and then mixed to produce white light. However, in this method, a heat radiation member for cooling the phosphor is not attached, and the temperature of the phosphor may increase. At that time, the fluorescence conversion efficiency is lower than the fluorescence conversion efficiency before the temperature rise.

  In addition, as a method of generating white light using a conventional solid-state light source, a reflective yellow phosphor is moved and blue light is emitted as it is, or the phosphor is irradiated and converted to yellow light before emitting. There is a method of creating white light using the illusion of the eye by separating blue and yellow according to time, and switching between them alternately. However, in this method, blue light and yellow light are time-divided into white light. In addition, the size of the optical system increases.

  There is also a method of producing white light using a solid-state light source of three colors RGB. However, this method increases the size of the optical system.

  On the other hand, according to the optical unit 10 of the first embodiment, it is possible to suppress the temperature rise of the phosphor 5 and increase the fluorescence conversion efficiency. Thereby, the luminous efficiency of the white light 8 of the optical unit 10 can be increased. Further, according to the optical unit 10, the size of the apparatus can be reduced as compared with a mechanism for moving the phosphor or a configuration using a plurality of light sources.

  The quarter-wave plate 3 preferably has a transmittance of 90% or more for visible light. Thereby, the amount of the white light 8 emitted from the optical unit 10 can be increased.

  Further, it is preferable that the dichroic mirror 4 has a property of transmitting 50% or more of light (blue light) in the first wavelength band. This makes it possible to increase the amount of yellow light, which has higher luminosity characteristics than blue light, and is bright.

  Although the quarter-wave plate 3 and the dichroic mirror 4 are illustrated as being configured as separate components, they may be configured as one optical component. Thereby, the number of parts of the optical unit 10 can be reduced, and the assemblability can be improved.

  In the optical unit 10 according to the first embodiment, the light source 1 emits the P-polarized blue light 61, and the wavelength-selective polarization beam splitter 2 reflects the P-polarized light in the blue light wavelength region as shown in FIG. Although the configuration has been described as having a characteristic of transmitting S-polarized light, it is not limited to such a configuration.

  FIG. 5 is an example of a graph for explaining the relationship between the characteristics of the wavelength-selective polarization beam splitter 2 according to the first modification and the spectrum of the light source 1.

  In the optical unit 10 according to the first modification, the light source 1 emits S-polarized blue light. As shown in FIG. 5, the wavelength-selective polarizing beam splitter 2 according to the first modification reflects S-polarized light having a wavelength of about 500 nm or less and transmits S-polarized light having a longer wavelength. have. The wavelength-selective polarization beam splitter 2 has a property of transmitting P-polarized light regardless of the wavelength. Other configurations are the same as those of the optical unit 10 according to the first embodiment, and a duplicate description will be omitted.

  According to the optical unit 10 according to the first modified example, similarly to the optical unit 10 according to the first embodiment, it is possible to emit white light in which blue light and yellow light are mixed. In addition, the emitted white light is not time-divided and can be continuous light.

<< 2nd Embodiment >>
An example of the optical unit 10A according to the second embodiment will be described with reference to FIGS. FIG. 6 is a configuration diagram of an example of an optical unit 10A according to the second embodiment. FIG. 7 is an example of a graph illustrating the relationship between the characteristics of the wavelength-selective polarization beam splitter 2A according to the second embodiment and the spectrum of the light source 1.

  The optical unit 10A includes a light source 1, a wavelength-selective polarization beam splitter 2A, a quarter-wave plate 3, a dichroic mirror 4, and a phosphor 5. The optical unit 10A according to the second embodiment shown in FIG. 6 has a layout different from that of the optical unit 10 according to the first embodiment shown in FIG. That is, the optical path from the light source 1 to the wavelength-selective polarizing beam splitter A and the optical path from the wavelength-selective polarizing beam splitter 2A to the phosphor 5 are laid out coaxially. Further, as shown in FIG. 7, the characteristics of the wavelength-selective polarization beam splitter 2A are different. Other configurations are the same as those of the optical unit 10 according to the first embodiment, and a duplicate description will be omitted.

  As shown in FIG. 7, the wavelength-selective polarization beam splitter 2A according to the second embodiment has a property of transmitting P-polarized light having a wavelength of about 500 nm or less and reflecting P-polarized light having a longer wavelength. Have. The wavelength-selective polarization beam splitter 2A has a characteristic of reflecting S-polarized light regardless of wavelength. In other words, the wavelength-selective polarization beam splitter 2A transmits light of the first polarization direction in light of the first wavelength band and reflects light of the second polarization direction orthogonal to the first polarization direction. Have the following characteristics. The wavelength-selective polarization beam splitter 2A has a characteristic of reflecting light in a second wavelength band having a longer wavelength than the first wavelength band.

  The P-polarized blue light 61 that has entered the wavelength-selective polarizing beam splitter 2A from the light source 1 passes through the wavelength-selective polarizing beam splitter 2A and enters the quarter-wave plate 3. The circularly polarized blue light 62 transmitted through the 波長 wavelength plate 3 enters the dichroic mirror 4. A part of the blue light 63 among the blue light 62 incident on the dichroic mirror 4 is reflected by the dichroic mirror 4 and again incident on the quarter-wave plate 3. Of the blue light 62 incident on the dichroic mirror 4, the other part of the blue light 64 passes through the dichroic mirror 4, enters the phosphor 5, and is converted into a yellow fluorescent light. The yellow light 71 emitted from the phosphor 5 passes through the dichroic mirror 4 and enters the quarter-wave plate 3 again. The circularly polarized blue light 63 and yellow light 71 pass through the quarter-wave plate 3 again to become S-polarized blue light 65 and yellow light 72. The S-polarized blue light 65 and yellow light 72 transmitted through the 波長 wavelength plate 3 enter the wavelength-selective polarizing beam splitter 2A. The wavelength-selective polarization beam splitter 2A has a characteristic of reflecting S-polarized light regardless of wavelength. Therefore, the S-polarized blue light 65 and the yellow light 72 are reflected by the wavelength-selective polarizing beam splitter 2A. The white light 8 is obtained by mixing these two lights.

  As described above, according to the optical unit 10A according to the second embodiment, the white light 8 in which the blue light 65 and the yellow light 72 are mixed can be emitted. Further, the white light 8 emitted from the optical unit 10A is not time-divided, and can be continuous light. Further, the luminous efficiency of the white light 8 of the optical unit 10A can be increased. Further, the size of the optical unit 10A can be reduced.

  The optical unit 10A according to the second embodiment has a configuration in which the light source 1 emits P-polarized blue light 61, and the wavelength-selective polarization beam splitter 2A transmits P-polarized light and reflects S-polarized light. However, the present invention is not limited to such a configuration.

  FIG. 8 is an example of a graph illustrating the relationship between the characteristics of the wavelength-selective polarizing beam splitter 2A according to the second modification and the spectrum of the light source 1.

  In the optical unit 10A according to the second modification, the light source 1 emits S-polarized blue light. As shown in FIG. 8, the wavelength-selective polarization beam splitter 2A according to the second modification transmits S-polarized light having a wavelength of about 500 nm or less and reflects S-polarized light having a longer wavelength. have. The wavelength-selective polarization beam splitter 2A has a characteristic of reflecting P-polarized light regardless of wavelength. Other configurations are the same as those of the optical unit 10A according to the second embodiment, and a duplicate description will be omitted.

  According to the optical unit 10A according to the second modification, similarly to the optical unit 10A according to the second embodiment, it is possible to emit white light in which blue light and yellow light are mixed. In addition, the emitted white light is not time-divided and can be continuous light.

<< 3rd Embodiment >>
An example of the optical unit 10B according to the third embodiment will be described with reference to FIGS. FIG. 9 is a configuration diagram of an example of an optical unit 10B according to the third embodiment. FIG. 10 is a diagram illustrating an example of the dichroic mirror 4B according to the third embodiment.

  The optical unit 10B includes a light source 1, a wavelength-selective polarizing beam splitter 2, a quarter-wave plate 3, a dichroic mirror 4B, a phosphor 5, and a dichroic mirror switching unit (transmittance changing unit) 9B. Have. Other configurations are the same as those of the optical unit 10 according to the first embodiment, and a duplicate description will be omitted.

  As shown in FIG. 10, the dichroic mirror 4B has two regions 41 and 42 having different characteristics. The first region 41 of the dichroic mirror 4B has, for example, a characteristic of transmitting 80% of light having a wavelength of 500 nm or less and reflecting 20%. Further, light having a wavelength of 500 nm or more has a characteristic of transmitting (100% transmission). The second region 42 of the dichroic mirror 4B has, for example, a characteristic of transmitting 70% of light having a wavelength of 500 nm or less and reflecting 20%. Further, light having a wavelength of 500 nm or more has a characteristic of transmitting (100% transmission).

  Returning to FIG. 9, the dichroic mirror switching unit 9B is configured as a moving device that moves the dichroic mirror 4B. An example after the movement is indicated by a two-dot chain line. The dichroic mirror switching unit 9B switches which of the two regions 41 and 42 shown in FIG. 10 is arranged on the optical path by moving the dichroic mirror 4B.

  As described above, according to the optical unit 10B according to the third embodiment, similarly to the optical unit 10 according to the first embodiment, the white light 8 in which the blue light 65 and the yellow light 72 are mixed can be emitted. Further, the white light 8 emitted from the optical unit 10B is not time-divided and can be continuous light.

  Further, the dichroic mirror switching unit 9B serves as a transmittance changing unit that changes the ratio of the blue light 64 transmitted through the dichroic mirror 4B by moving the dichroic mirror 4B and switching the areas 41 and 42 arranged on the optical path. Can work. Thus, the balance between the amounts of the blue light 65 and the yellow light 72 is changed, and the color of the white light 8 can be changed.

  Note that, in FIG. 9, the configuration of changing the characteristics of the dichroic mirror is applied to the layout of the optical unit 10 according to the first embodiment, but the present invention is not limited to this. In the layout of the optical unit 10A according to the second embodiment, a configuration for changing the characteristics of the dichroic mirror may be applied.

  Further, in the third embodiment, it has been described that the region to be irradiated with light is switched by moving the dichroic mirror 4B to change the characteristics, but the present invention is not limited to this. The dichroic mirror may be configured as a disk having fan-shaped regions having different characteristics, and the dichroic mirror switching unit may switch the dichroic mirror to switch the region irradiated with light to change the characteristics.

  Although the embodiments of the optical units 10 to 10B have been described above, the present invention is not limited to the above embodiments and the like, and various modifications may be made within the scope of the present invention described in the appended claims. Deformation and improvement are possible.

1 light source 2, 2A wavelength-selective polarization beam splitter (polarization separation element)
3 1/4 wavelength plate (phase difference plate)
4,4B dichroic mirror (optical element)
41, 42 Area 5 Phosphors 61 to 65 Blue light 71 to 72 Yellow light 8 White light 9B Dichroic mirror switching unit (transmittance changing unit)
10,10A, 10B Optical unit

JP 2012-78488 A

Claims (8)

A light source that emits light in the first wavelength band,
A polarization separation element that separates light in different directions with respect to the light of the first wavelength band,
A retardation plate that transmits the light of the first wavelength band separated by the polarization separation element by rotating the polarization direction by ４,
An optical element that transmits the retardation plate, reflects a part of the light in the first wavelength band whose polarization direction is rotated by １ ／, and transmits the other part;
A phosphor that converts the other part of the light of the first wavelength band transmitted through the optical element to light of a second wavelength band and emits the light to the optical element,
An optical unit, wherein white light is generated from a part of the light of the first wavelength band reflected by the optical element and light of the second wavelength band converted by the phosphor. An optical path from the light source to the polarization splitting element and an optical path from the polarization splitting element to the phosphor are arranged orthogonally.
The polarization separation element,
In the light of the first wavelength band, reflects light in a first polarization direction, transmits light in a second polarization direction orthogonal to the first polarization direction,
The optical unit according to claim 1, wherein the light in the second polarization direction is transmitted in the light in the second wavelength band. An optical path from the light source to the polarization separation element and an optical path from the polarization separation element to the phosphor are coaxially arranged,
The polarization separation element,
In the light of the first wavelength band, the light of the first polarization direction is transmitted, and the light of the second polarization direction orthogonal to the first polarization direction is reflected,
The optical unit according to claim 1, wherein the light in the second polarization direction reflects the light in the second polarization direction. The optical unit according to any one of claims 1 to 3, wherein the retardation plate has a transmittance of 90% or more for visible light. The optical unit according to any one of claims 1 to 4, wherein the optical element has a characteristic of transmitting 50% or more of the light of the first wavelength band. The optical unit according to claim 1, wherein the retardation plate and the optical element are configured as one optical component. The optical unit according to any one of claims 1 to 6, further comprising a transmittance changing unit that changes a ratio of the light of the first wavelength band that passes through the optical element.   An image projection apparatus comprising the optical unit according to claim 1.

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