JP6827965B2 - Display device - Google Patents

Description

An embodiment of the present invention relates to a display device that uses laser light for rear illumination.

A transmissive display device such as a liquid crystal display device includes a lighting device that irradiates the back surface of a display panel with light. A lighting device has been proposed in which red LEDs, green LEDs, and blue LEDs are arranged along an incident surface of a light guide plate, and light is mixed in the light guide plate to extract white light (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2006-236951

When a semiconductor laser (Laser Modede) that emits laser light having high color purity is used as a light source instead of an LED, the color gamut that can be expressed by a display device is expanded. However, laser light has greater coherence than light emitted from LEDs. When laser light is used for the back lighting, speckles (bright and dark spots) are easily visible.

In particular, when the laser light directed toward the end face of the light guide plate and the laser light reflected by the end face and returned are overlapped, the speckle is easily visible because the laser light has the same wavelength emitted from the same semiconductor laser. An object of the present disclosure is to provide a high-quality display device using laser light for rear illumination.

The display device according to one embodiment includes a plurality of light sources, a light guide plate, and a display panel. Each light source consists of a semiconductor laser that emits laser light. The light guide plate irradiates light emitted from a plurality of light sources. The display panel transmits the light emitted from the light guide plate and displays an image.

The light guide plate has an exit surface, a reflection surface, and an end surface. The exit surface faces the display panel. The reflective surface is located on the opposite side of the exit surface. The end face connects the exit surface and the reflection surface. The end face includes a first incident surface, a first end face, and a second end face. The first incident surface faces a plurality of light sources. The first end face and the second end face are orthogonal to the first incident surface.

The plurality of light sources are arranged in a row between the first end surface and the second end surface at positions facing the first incident surface. The first light source located on the first end face side among the plurality of light sources is arranged on an extension line of the first end face. The second light source located on the second end face side of the plurality of light sources is arranged on the extension line of the second end face.

FIG. 1 is a perspective view showing a schematic configuration of a display device common to each embodiment. FIG. 2 is a cross-sectional view showing a cross-sectional structure of the display panel and the lighting device shown in FIG. FIG. 3 is a plan view schematically showing the lighting device according to the present embodiment. FIG. 4 is a diagram schematically showing the output characteristics of a low-efficiency laser diode. FIG. 5 is a plan view schematically showing a lighting device according to a modified example of the present embodiment. FIG. 6 is a plan view schematically showing a lighting device according to a comparative example for comparison with the present embodiment.

Some embodiments will be described with reference to the drawings. It should be noted that the disclosure is merely an example, and those skilled in the art can easily conceive of changes as appropriate while maintaining the gist of the invention are naturally included in the scope of the present invention. In addition, the drawings may be represented schematically as compared with actual embodiments in order to clarify the description, but the drawings are merely examples and do not limit the interpretation of the present invention. In each figure, the reference numerals may be omitted for the same or similar elements arranged consecutively. Further, in the present specification and each figure, components exhibiting the same or similar functions as those already described may be designated by the same reference numerals, and duplicate detailed description may be omitted.

Further, in the present specification, "α includes A, B or C", "α contains any of A, B and C", and "α is one selected from the group consisting of A, B and C". Unless otherwise specified, the expression "including" does not exclude the case where α includes a plurality of combinations of A to C. Furthermore, these expressions do not exclude cases where α contains other elements. In each embodiment, a liquid crystal display device DSP is disclosed as an example of the display device. However, each embodiment does not preclude the application of the individual technical ideas disclosed in each embodiment to other types of display devices.

As the other type of display device, for example, a display device having a mechanical display cell such as a Micro Electro Mechanical System (MEMS) shutter is assumed. The liquid crystal display device DSP can be used in various devices such as smartphones, tablet terminals, mobile phone terminals, personal computers, television image receiving devices, in-vehicle devices, game devices, and wearable terminals.

FIG. 1 is a perspective view showing a schematic configuration of the liquid crystal display device DSP of the present embodiment. For convenience of explanation of the embodiment, as shown in FIG. 1, the left-right direction, the front-back direction, and the up-down direction are defined. The vertical direction is, for example, the thickness direction of the liquid crystal display device DSP. When the liquid crystal display device DSP is arranged at an angle, the vertical direction does not always coincide with the gravity direction. The left side is an example of the first side, and the right side is an example of the second side opposite to the first side. The right side may be the first side and the left side may be the second side.

The liquid crystal display device DSP includes a display panel PNL, a lighting device (backlight) BL that irradiates the back surface of the display panel PNL, a control module CTR that controls the operation of the display panel PNL and the lighting device BL, and a display panel PNL. The drive IC chip 4 for driving the control module CTR and the flexible circuit boards FPC1 and FPC2 for transmitting the control signal of the control module CTR to the display panel PNL and the lighting device BL are provided.

The display panel (liquid crystal cell) PNL is arranged between the first substrate (array substrate) SUB1, the second substrate (opposing substrate) SUB2 facing the first substrate SUB1, and the first and second substrates SUB1 and SUB2. It also has a liquid crystal layer LC. The liquid crystal layer LC is an example of an electro-optical layer that is driven by electricity and selectively transmits light. The electro-optical layer may be the above-mentioned MEMS shutter, electrophoresis element, or the like. The display panel PNL has a display area DA for displaying an image. The display panel PNL has a plurality of pixels PX arranged in a matrix on the front, back, left, and right in the display area DA.

The drive IC chip 4 is mounted on, for example, the first substrate SUB1. The drive IC chip 4 may be mounted on a control module CTR or the like. The flexible circuit board FPC1 connects the first board SUB1 and the control module CTR. The flexible circuit board FPC2 connects the lighting device BL and the control module CTR.

The control module CTR sequentially receives one frame of image data for display in the display area DA from the main board or the like of an electronic device on which the liquid crystal display device DSP is mounted. This image data includes information such as the display color of each pixel PX. The control module CTR supplies a signal for driving each pixel PX to the drive IC chip 4 based on the received image data. Further, the control module CTR supplies a signal for controlling lighting or extinguishing to the lighting device BL.

The illuminating device BL irradiates polarized white light toward the back surface of the display panel PNL. White light, which is a mixture of red laser light, green laser light, and blue laser light, is an example of laser light containing two or more colors. In the example shown in FIG. 1, the lighting device BL has a light guide plate LG arranged so as to be vertically overlapped on the display panel PNL, and first and second light source groups LS1 and LS2 facing each other with the light guide plate LG interposed therebetween. It has. Either one of the first and second light source groups LS1 and LS2 may be omitted.

FIG. 2 is a cross-sectional view showing a cross-sectional structure of the display panel PNL and the lighting device BL. As shown in FIG. 2, the light guide plate LG includes a first main surface (exit surface) 31 facing the first substrate SUB1 and a second main surface (reflection surface) 32 on the side opposite to the first main surface 31. , And an end surface 30 between the first and second main surfaces 31 and 32.

The first and second light source groups LS1 and LS2 face the end surface 30 of the light guide plate LG. The second main surface 32 is inclined so as to increase in thickness as the distance from the first and second light source groups LS1 and LS2 increases. The polarized laser light emitted by the first and second light source groups LS1 and LS2 enters the end surface 30 of the light guide plate LG, propagates in the light guide plate LG while being reflected by the second main surface 32, and propagates in the light guide plate LG, and the first main surface 31 Emit from.

The light guide plate LG preferably has low birefringence from the viewpoint of maintaining the polarization direction of the polarized laser light passing through the inside thereof. The phase difference of the light guide plate LG is, for example, one-fourth or less of the main wavelength of the incident laser light. The light guide plate LG is formed of, for example, a polymer having an absolute birefringence of 3 × 10 ^-3 or less, which is composed of a mixture or a copolymer of a positive birefringent substance and a negative birefringent substance.

In the mixture, a polymer having a positive intrinsic birefringence and a polymer having a negative intrinsic birefringence are mixed in an appropriate ratio, so that the birefringences cancel each other out when the polymer is oriented, and the birefringence is macroscopically expressed. I won't let you. Alternatively, the mixture offsets the birefringence of the polymer by adding small molecules with rod-like molecular shapes and polarizability anisotropy to the polymer.

In the copolymer, a monomer having a positive intrinsic birefringence and a monomer having a negative intrinsic birefringence are copolymerized at an appropriate ratio to cancel the anisotropy in one polymer chain. As such a polymer, for example, those described in paragraphs [0043] to [0052] of Japanese Patent No. 5263771 can be used.

As shown in FIG. 2, the display panel PNL further includes a sealing material 3 for bonding the first and second substrates SUB1 and SUB2, and a polarizing plate PL attached to the upper surface of the second substrate SUB2. .. The liquid crystal layer LC is sealed between the first and second substrates SUB1 and SUB2 inside the sealing material 3.

The lighting device BL according to the present embodiment irradiates polarized laser light. Therefore, the polarizing plate is not arranged on the lower surface of the first substrate SUB1, and the polarizing plate PL is arranged only on the upper surface of the second substrate SUB2. Since there is only one polarizing plate, when the transparency of the first and second substrates SUB1 and SUB2 is increased, a so-called transparent liquid crystal device in which the background of the liquid crystal display device DSP can be seen through can be obtained.

The lighting device BL may irradiate unpolarized laser light, and the display panel PNL may be configured to include two polarizing plates. In the example shown in FIG. 2, the liquid crystal display device DSP further includes a prism sheet PS and a diffusion sheet DS arranged between the light guide plate LG and the first substrate SUB1.

The prism sheet PS aligns the optical paths of the laser light emitted from the illumination device BL in the vertical direction. The diffusion sheet DS diffuses the laser beam that has passed through the prism sheet PS in the left-right direction to widen the viewing angle. From the viewpoint of maintaining the degree of polarization, the prism sheet PS and the diffusion sheet DS are preferably made of a low birefringence material similar to the light guide plate LG.

FIG. 3 is a plan view schematically showing the lighting device BL according to the present embodiment. The end surface 30 of the light guide plate LG has a rear end surface 33 facing the first light source group LS1, a front end surface 34 facing the second light source group LS2, a left end surface 35, and a right end surface 36. The rear end surface 33 extends in the left-right direction. The front end surface 34 extends parallel to the rear end surface 33. The left end surface 35 and the right end surface 36 are both orthogonal to the rear end surface 33 and the front end surface 34.

The rear end surface 33 is an example of a first incident surface, and the front end surface 34 is an example of a second incident surface. The left end surface 35 is an example of the first end surface, and the right end surface 36 is an example of the second end surface. The first light source group LS1 includes a plurality of semiconductor lasers 20 arranged in a row at equal intervals along the rear end surface 33 of the light guide plate LG. Similarly, the second light source group LS2 includes a plurality of semiconductor lasers 20 arranged in a row at equal intervals along the front end surface 34. The semiconductor laser 20 is an example of a plurality of light sources composed of a semiconductor laser.

The first and second light source groups LS1 and LS2 are a pair of first color light sources that emit light of the first color, a second color light source that opposes the light of the second color, and a third color that emits light of the third color. Includes a light source. The first to third light sources are, for example, semiconductor lasers 20 corresponding to the three primary colors.

The first and second light source groups LS1 and LS2 are configured by chaining unit light sources in which a second color light source, a first color light source, a third color light source, and a first color light source are arranged in this order. In other words, in the first and second light source groups LS1 and LS2, the second light source and the third light source are alternately arranged between the first light sources arranged in a row.

In the example shown in FIG. 3, the first color is green, the second color is red, and the third color is blue. The first and second light source groups LS1 and LS2 are a red semiconductor laser R that emits red light, a first green semiconductor laser G1 that emits green light, a blue semiconductor laser B that emits blue light, and a first that emits green light. The unit light source RGBG in which the two green semiconductor lasers G2 are arranged in this order is formed in a chain. The first color may be red, or the first color may be blue.

The first and second green semiconductor lasers G1 and G2 are arranged alternately. The red semiconductor laser R is arranged between the first and second green semiconductor lasers G1 and G2 on the left side of the first green semiconductor laser G1. The blue semiconductor laser B is arranged between the first and second green semiconductor lasers G1 and G2 on the right side of the first green semiconductor laser G1. That is, the red semiconductor laser R and the blue semiconductor laser B are arranged alternately with the first or second green semiconductor lasers G1 and G2 emitting green light.

The green laser light emitted by the first green semiconductor laser G1 and the green laser light emitted by the second green semiconductor laser G2 may have the same main wavelength or different main wavelengths. When the main wavelengths are different, the main wavelength of the green laser light emitted by the second green semiconductor laser G2 may be closer to red or closer to blue than the first green semiconductor laser G1. The difference between the main wavelengths of the first and second green semiconductor lasers G1 and G2 is, for example, about several tens of nm.

In the following description, among the plurality of semiconductor lasers 20 included in the first and second light source groups LS1 and LS2, the one located on the leftmost side (the left end surface 35 side viewed from the right end surface 36) is the first light source 21. Alternatively, it is called the first semiconductor laser 21, and the one located on the far right side (the right end surface 36 side as viewed from the left end surface 35) is called the second light source 22 or the second semiconductor laser 22. In the liquid crystal display device DSP of the present embodiment, the first semiconductor laser 21 intersects the plane X on which the left end surface 35 of the light guide plate LG is extended, and the second semiconductor laser 22 intersects the plane Y on which the right end surface 36 of the light guide plate LG is extended. One of the features is that it intersects with.

That is, in a plan view, at least a part of the housing of the first semiconductor laser 21 located on the leftmost end surface 35 side is arranged on the extension line of the left end surface 35. At least a part of the housing of the second semiconductor laser 22 located on the rightmost end surface 36 side is arranged on the extension line of the right end surface 36. In the example shown in FIG. 3, the center position of the emitted light of the first semiconductor laser 21 is arranged on the extension line of the left end surface 35, and the center position of the emitted light of the second semiconductor laser 22 is arranged on the extension line of the right end surface 36. ing.

The second semiconductor laser 22 has substantially the same arrangement and function as the first semiconductor laser 21. Therefore, the first semiconductor laser 21 will be described in detail as a representative, and the overlapping description of the second semiconductor laser 22 will be omitted. FIG. 6 is a plan view schematically showing a lighting device BL according to a comparative example for comparison with the present embodiment.

As in the comparative example shown in FIG. 6, when the first semiconductor laser 21 does not intersect the plane X extending the left end surface 35 of the light guide plate LG, the laser light emitted from the first semiconductor laser 21 is emitted. Is reflected on the left end surface 35. The reflected laser light returns to the light guide plate LG as if the virtual semiconductor laser 24 is at a position folded around the left end surface 35.

In the virtual semiconductor laser 24 and the actual semiconductor lasers 21 and 23, the intervals between the green semiconductor lasers G1 and VG1 are wider than the intervals between the red semiconductor lasers R and VR, and the intervals between the blue semiconductor lasers B and VB are even wider. Therefore, in the vicinity of the left end surface 35, the ratio of the red laser light increases relatively, and the light emitted from the light guide plate LG becomes reddish.

In addition, laser light has a large coherence. For example, when the laser light from the red semiconductor laser R toward the inside of the light guide plate LG and the laser light reflected by the left end surface 35 and returned are overlapped, the laser light of the same wavelength emitted from the same first semiconductor laser 21 is emitted. Therefore, speckle is likely to occur. Since the optical path difference is short, it is difficult for phase shifts to occur, and it is difficult for speckles to be reduced.

On the other hand, in the lighting device BL according to the present embodiment shown in FIG. 3, the center of the first semiconductor laser 21 intersects the plane X extending the left end surface 35 of the light guide plate LG. If the first semiconductor laser 21 is a red semiconductor laser R or a blue semiconductor laser B, in the virtual semiconductor laser 24 and the actual semiconductor lasers 21 and 23, the green semiconductor laser VG1, the red semiconductor laser R, the green semiconductor laser G1, and the blue The semiconductor lasers B are lined up at equal intervals.

That is, on the first semiconductor laser 21 side, the virtual red semiconductor laser VR shown in FIG. 6 does not exist in the virtual semiconductor laser 24. Therefore, the RGBG unit light sources are arranged in a chain over the virtual semiconductor laser 24 and the actual semiconductor lasers 21 and 23. According to this embodiment, since the first semiconductor laser 21 is arranged on the left end surface 35 at a position where the laser light is hard to be reflected, the laser light of the same wavelength emitted from the same first semiconductor laser 21 It is possible to suppress the occurrence of speckle due to.

By the way, even in the lighting device BL according to the comparative example, it is difficult to visually recognize the speckle at the center of the light guide plate LG. The wavelength of the semiconductor laser 23 in the center varied, for example, by about ± 5 to 6 nm due to individual differences. In order to more reliably suppress the generation of speckle, it is preferable to widen the wavelength bandwidth to about ± 5 to 6 nm or more.

In this embodiment, the semiconductor laser 20 is driven by an AC power source having a frequency of 50 to 500 kHz or less. When the current that drives the semiconductor laser fluctuates at a low frequency, the junction temperature fluctuates periodically in conjunction with it. When the junction temperature fluctuates, the wavelength fluctuates periodically. Assuming that an example of the bandwidth of a semiconductor laser driven by direct current is ± 1.5 nm from the center wavelength, an example of the bandwidth of a semiconductor laser driven by low-frequency alternating current is ± 2 to 3 nm from the center wavelength.

Further, if the first and second semiconductor lasers 21 and 22 located on the outermost side are semiconductor lasers having lower luminous efficiency than the other semiconductor lasers 23 located between them, speckle can be suppressed more reliably. .. FIG. 4 is a diagram schematically showing the output characteristics of a low-efficiency laser diode. As shown in FIG. 4, the low-efficiency semiconductor laser has a larger threshold value 2 until the laser light is emitted and a smaller inclination 2 of the laser light output with respect to the input current than the high-efficiency semiconductor laser. .. That is, the current loss is large.

The rise in junction temperature is proportional to the current loss. With a low-efficiency laser diode, the temperature fluctuates greatly up and down due to the large current loss, and the wavelength range fluctuates greatly. When a low-efficiency semiconductor laser is used instead of the high-efficiency semiconductor laser, the bandwidth extends from the center wavelength to, for example, ± 5 to 6 nm.

FIG. 5 is a plan view schematically showing the lighting device BL according to the modified example of the present embodiment. The feature of the modified example shown in FIG. 5 is that the center position of the emitted light of the first semiconductor laser 21 is arranged at a position slightly deviated from the extension line of the left end surface 35. The amount of deviation between the center position of the emitted light of the first semiconductor laser 21 and the extension line of the left end surface 35 is, for example, a deviation of the housing itself of the first semiconductor laser 21 so as to hang on the extension line of the left end surface 35. Is. Even in this modification, the virtual red semiconductor laser VR overlaps with the actual red semiconductor laser R at substantially the same position.

At this time, if the actual red semiconductor laser R and the virtual red semiconductor laser VR have the brightness of one light in total, the proportion of the red laser light does not increase. If the first semiconductor laser 21 is a semiconductor laser having a lower efficiency than the other semiconductor lasers 23, not only the coherence can be reduced, but also the output can be halved to make it easier to adjust the hue.

According to the liquid crystal display device DSP of the present embodiment and its modified example configured as described above, the actual first semiconductor laser 21 and its virtual light source are arranged so as to substantially overlap each other. In particular, when the plane X extending the left end surface 35 intersects the center of the first semiconductor laser 21, the actual first semiconductor laser 21 and its virtual light source are arranged so as to overlap with each other, so that the laser is used for the back illumination. It is difficult for speckles to occur even when using light. Further, it is possible to prevent the ratio of the laser beam of a specific color from increasing relatively and the hue from becoming non-uniform.

Even if the center position of the emitted light of the first semiconductor laser 21 is displaced from the plane X on which the left end surface 35 is extended, if the output of the first semiconductor laser 21 is halved, the ratio of the laser light of a specific color Can be prevented from increasing relatively and causing uneven hue. For example, if the first semiconductor laser 21 is a semiconductor laser having a lower efficiency than the other semiconductor laser 23, the output can be adjusted to the other half. Moreover, since the wavelength range is widened, speckles are less likely to occur.

If all low-efficiency semiconductor lasers are used, speckles are less likely to occur, but power consumption will increase. In this embodiment and its modifications, only the first and second semiconductor lasers 21 and 22 at both ends use semiconductor lasers with lower efficiency than the other semiconductor lasers 23, so that the speckle does not excessively increase the power consumption. Can be suppressed.

In addition, various suitable effects can be obtained from the present embodiment and its modifications.

Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof. The configurations disclosed in each embodiment can be combined as appropriate.

20 ... semiconductor laser (an example of a light source), 21 ... a first semiconductor laser (an example of a first light source), 22 ... a second semiconductor laser (an example of a second light source), 23 ... another semiconductor laser (an example of another light source) (Example), 31 ... 1st main surface (example of exit surface), 32 ... 2nd main surface (example of reflection surface), 33 ... rear end surface (example of first incident surface), 34 ... front end surface (first) 2 incident surface), 35 ... left end surface (example of first end surface), 36 ... right end surface (example of second end surface), B ... blue semiconductor laser (example of third color light source), BL ... illumination device , DSP ... LCD display device (an example of a display device), G1 ... a first green semiconductor laser (an example of one first color light source), G2 ... a second green semiconductor laser (an example of the other first color light source), LG ... light guide plate, PNL ... display panel, R ... red semiconductor laser (an example of a second color light source).

Claims (8)

A plurality of light sources composed of semiconductor lasers that emit laser light, a light guide plate that irradiates light emitted from the plurality of light sources, and a display panel that transmits light emitted from the light guide plate and displays an image. Prepare,
The light guide plate has an exit surface facing the display panel, a reflection surface opposite to the emission surface, and an end surface connecting the emission surface and the reflection surface.
The end face includes a first incident surface facing the plurality of light sources, and a first end surface and a second end surface orthogonal to the first incident surface.
The plurality of light sources are arranged in a line between the first end surface and the second end surface at positions facing the first incident surface.
The first light source located on the first end face side of the plurality of light sources is arranged on an extension line of the first end face, and the second light source located on the second end face side of the plurality of light sources is located. A display device characterized in that the light source is arranged on an extension line of the second end surface. The display device according to claim 1, wherein the plurality of light sources are driven by an AC power source having a frequency of 500 kHz or less. The first light source and the second light source are composed of a light source having a lower luminous efficiency than another light source located between the first light source and the second light source, claim 1 or 2. The display device described in. The plurality of light sources include a pair of first color light sources that emit light of the first color, a second color light source that emits light of the second color, and a third color light source that emits light of the third color, and the first color. The invention according to any one of claims 1 to 3, wherein the light source, the second color light source, the first color light source, and the third color light source are arranged in a chain of unit light sources. Display device. The display device according to claim 4, wherein the first light source and the second light source are the second color light source or the third color light source. The first color light source is a green light source that emits green light.
The display device according to claim 4 or 5, wherein the green laser light emitted by one of the pair of green light sources included in the unit light source and the green laser light emitted by the other have different main wavelengths. The light guide plate has a second incident surface facing the first incident surface and located between the first end surface and the second end surface.
Any one of claims 1 to 6, wherein the plurality of light sources are arranged in a line between the first end surface and the second end surface at positions facing the first end surface and the second incident surface. The display device according to paragraph 1. The center position of the emitted light of the first light source is arranged at a position deviated from the extension line of the first end surface, and the center position of the emitted light of the second light source deviates from the extension line of the second end surface. The display device according to any one of claims 1 to 7, wherein the display device is arranged at a vertical position.

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