JP2009086365A - Image display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image display device in which the contrast ratio of a displayed image is improved and high gradation of the image is achieved with a simple configuration. <P>SOLUTION: The image display device comprises: a light source; a light source driving part which drives the light source to emit a luminous flux having an intensity corresponding to an image signal while enhancing the response of the light source by supplying a prescribed bias electric current to the light source; and a scanning part which scans the luminous flux emitted from the light source, wherein the image display device projects and displays the image corresponding to the image signal on a prescribed region, wherein the image display device further comprises a light intensity reducing means which is disposed between the light source and a prescribed region on the optical path of the luminous flux, reduces the intensity of the luminous flux and reduces the luminance of the image projected and displayed on the prescribed region, and the light source driving part can increase the intensity of the luminous flux emitted from the light source so that the maximum intensity of the luminous flux reduced with the light intensity reducing means may become a prescribed intensity in the prescribed region. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image display device, and more particularly, a light source and a light beam having an intensity corresponding to an image signal are emitted by driving the light source while improving a light source responsiveness by supplying a predetermined bias current to the light source. The present invention relates to an image display device that includes a light source driving unit that causes the light source to scan and a scanning unit that scans a light beam emitted from the light source, and projects and displays an image according to an image signal in a predetermined area.

  Conventionally, as described in Patent Document 1, a light source and a predetermined bias current are supplied to the light source, thereby improving the response of the light source and driving the light source to obtain an intensity corresponding to the image signal. There is known an image display device that includes a light source driving unit that emits a light beam and a scanning unit that scans the light beam emitted from the light source, and projects and displays an image according to an image signal in a predetermined area.

In this image display device, the responsiveness of the light source is improved by supplying a bias current close to the threshold current of the light source to the light source in advance.
Japanese Patent Laid-Open No. 2004-9492

  However, the conventional image display apparatus has a problem that the contrast ratio of the image to be displayed is lowered by the supply of the bias current. That is, the minimum luminance of the displayed image is limited by the light emission of the light source by supplying the bias current, and as a result, the contrast ratio of the displayed image is lowered.

  In addition, since the brightness of the image to be displayed is controlled by the magnitude of the drive current supplied to the light source, if the light emission intensity of the light source changes due to a slight increase or decrease of the drive current, the desired image gradation is set. In order to obtain it, it was necessary to improve the supply accuracy of the drive current to the light source.

  SUMMARY An advantage of some aspects of the invention is that it provides an image display apparatus that can improve the contrast ratio of an image to be displayed with a simple configuration and can achieve higher gradation of the image.

  In order to achieve the above object, according to the first aspect of the present invention, an image signal is generated by driving the light source while improving the responsiveness of the light source by supplying a predetermined bias current to the light source and the light source. In an image display device that includes a light source driving unit that emits a light beam having an intensity corresponding to the light source and a scanning unit that scans the light beam emitted from the light source, and projects and displays an image according to the image signal in a predetermined area. A light intensity reducing unit disposed on an optical path of the light flux between the light source and the predetermined area, and reducing the intensity of the light flux to reduce the luminance of an image projected and displayed on the predetermined area; The drive unit can increase the intensity of the light beam emitted from the light source so that the maximum intensity of the light beam reduced by the light intensity reducing unit becomes a predetermined intensity in the predetermined region.

  According to a second aspect of the present invention, in the first aspect of the present invention, the light intensity reducing means includes an ND filter and / or a reflection film of the scanning unit.

  According to a third aspect of the present invention, in the first or second aspect of the invention, the light intensity reducing means includes a light diffusing member that diffuses the light flux, and a part of the diffused light flux is effective. It is characterized in that the intensity of the light beam is reduced by the light intensity.

  The invention according to claim 4 is the light dividing member according to any one of claims 1 to 3, wherein the light intensity reducing means divides the light beam emitted from the light source into two or more light beams. The scanning unit scans one of the light beams divided by the light dividing member.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the light intensity reducing means includes a diaphragm that blocks a part of the light beam emitted from the light source. Features.

  According to a sixth aspect of the present invention, in the invention according to any one of the first to fifth aspects, the light source is provided corresponding to each of the three primary colors, and the light beams emitted from these light sources are combined. A multiplexer is provided, and the multiplexer is combined with reducing the intensity of the light beam emitted from the light source, thereby causing the multiplexer to function as the light intensity reducing means.

  According to a seventh aspect of the present invention, in the sixth aspect of the present invention, the dichroic that extracts the luminous flux of each color from the light source provided corresponding to each of the three primary colors in the multiplexer, and multiplexes these luminous fluxes. An optical element is provided, and the light intensity reducing means is provided on the optical path of the light beam between the dichroic optical element and the light source.

  The invention according to claim 8 is the invention according to any one of claims 1 to 7, wherein the multiplexer includes an optical fiber, and the optical axis of the optical fiber is shifted, thereby the multiplexer. Is made to function as the light intensity reducing means.

  According to a ninth aspect of the present invention, in the invention according to any one of the first to eighth aspects, the light source driving unit is configured to reduce the bias current during at least a predetermined period of the invalid scanning period in which image display is not performed. The supply to the light source is stopped or reduced.

  According to a tenth aspect of the present invention, in the image display device according to any one of the first to ninth aspects, the light modulated in accordance with the image signal is scanned in a two-dimensional direction by the optical scanning device. It is a retinal scanning image display device that projects an image on at least one of the retinas and displays the image.

  According to the first aspect of the present invention, a light source and a predetermined bias current are supplied to the light source, thereby improving the response of the light source and driving the light source to emit a luminous flux having an intensity corresponding to the image signal. A light source driving unit that scans a light beam emitted from the light source, and a light beam between the light source and the predetermined region in an image display device that projects and displays an image according to an image signal on the predetermined region A light intensity reduction unit is provided on the road to reduce the intensity of the light beam and reduce the brightness of the image projected and displayed on the predetermined area. The light source driving unit has the maximum intensity of the light beam reduced by the light intensity reduction unit. Since the intensity of the light beam emitted from the light source can be increased so that the predetermined intensity in the predetermined area can be increased, the image signal can be reduced by reducing the influence of light emission of the light source due to the bias current by the light intensity reducing means. The contrast ratio of the corresponding projected display image can be improved, and the intensity of the light beam emitted from the light source by the light source driving unit is increased in advance according to the amount of light intensity reduced by the light intensity reducing means, thereby allowing the light source to It is possible to reduce the change in the light emission intensity with respect to increase / decrease of the supplied drive current, and as a result, it is possible to realize high gradation of the projected display image without increasing the supply accuracy of the drive current to the light source.

  According to the second aspect of the present invention, the light intensity reducing means includes the ND filter and / or the reflection film of the scanning unit. The effect of the light emission can be reduced, and the contrast ratio of the projected display image corresponding to the image signal can be improved.

  According to the third aspect of the present invention, the light intensity reducing means includes the light diffusing member that diffuses the light flux, and reduces the intensity of the light flux because a part of the diffused light flux becomes the effective light intensity. The influence of light emission of the light source due to the bias current can be reduced, and the contrast ratio of the projected display image corresponding to the image signal can be improved.

  According to the fourth aspect of the present invention, the light intensity reducing means includes a light dividing member that divides the light beam emitted from the light source into two or more light beams, and the scanning unit is one of the light beams divided by the light dividing member. Since one of them is scanned, the light beam emitted from the light source by the light dividing member is divided into a plurality of parts, and one of them is scanned by the scanning unit, thereby reducing the influence of light emission of the light source due to the bias current, The contrast ratio of the projected display image corresponding to the image signal can be improved.

  According to the fifth aspect of the present invention, the light intensity reducing means includes a stop that blocks a part of the light beam emitted from the light source, so that the influence of light emission of the light source due to the bias current is reduced by passing through the stop. The contrast ratio of the projected display image according to the image signal can be improved.

  According to the sixth aspect of the present invention, the light source is provided corresponding to each of the three primary colors, the multiplexer is provided for combining the light beams emitted from these light sources, and the light beam emitted from the light source in the multiplexer. Since the multiplexer functions as a light intensity reducing means by reducing the intensity of the light, the influence of the light emission of the light source due to the bias current can be reduced by passing through the multiplexer. The contrast ratio of the projected display image can be improved.

  According to the seventh aspect of the present invention, the multiplexer includes a dichroic optical element that extracts the light beams of the respective colors from the light sources provided corresponding to the three primary colors and combines the light beams, and this dichroic optical device. Since the light intensity reducing means is provided on the optical path of the light beam between the element and the light source, the intensity of the light beam emitted from the light source having the highest intensity of the bias light emission among the three primary color light sources can be intensively reduced. As a result, the influence of light emission of the light source due to the bias current of the entire light source can be efficiently reduced.

  According to the eighth aspect of the present invention, the multiplexer includes the optical fiber, and the optical axis of the optical fiber is shifted so that the multiplexer functions as the light intensity reducing means. Only a part of the light beam is output to the optical fiber. As a result, the influence of light emission of the light source due to the bias current can be reduced, and the contrast ratio of the projected display image corresponding to the image signal is improved. be able to.

  According to the ninth aspect of the present invention, the light source driving unit stops or reduces the supply of the bias current to the light source for at least the predetermined period of the invalid scanning period in which image display is not performed. The range of the drive current supplied to the light source can be expanded by increasing the intensity of the light beam emitted from the light source in advance by the light source drive unit according to the amount of light intensity reduction. It is possible to realize adjustment, and it is possible to reduce as much as possible the increase in power consumption caused by increasing the intensity of the light beam emitted from the light source by the light source driving unit in advance.

  According to the invention described in claim 10, the contrast ratio of the projected display image according to the image signal can be improved, and the gradation of the projected display image can be increased without increasing the supply accuracy of the drive current to the light source. Can be provided.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the following description, as an example of an image display device, light that has been modulated in accordance with an image signal is scanned in a two-dimensional direction by an optical scanning device, whereby an image is projected onto at least one retina of a user. The case where the present invention is applied to a retinal scanning image display apparatus to be displayed will be described as an example. However, the present invention is not limited to this, and light scanning such as an optical scanning image display apparatus is performed. Thus, the present invention can be applied to other image display devices that display images.

[1. First Embodiment]
[1.1 Outline of image display device configuration]
First, an outline of the configuration of the image display apparatus 1 of the present embodiment will be described with reference to the drawings. FIG. 1 is an explanatory diagram showing a schematic configuration of the image display apparatus according to the first embodiment of the present invention, and FIG. 2 is a diagram for explaining a light beam scanning mode by the optical scanning unit of the image display apparatus of the present embodiment. FIG.

  As shown in FIG. 1, the image display device 1 includes a light beam generator 20 that generates and emits a light beam whose intensity is modulated in accordance with an image signal S supplied from the outside. Between the observer's eyes 10, there is provided an optical scanning unit that two-dimensionally scans a light beam emitted from a light source described later included in the light beam generator 20. The optical scanning unit includes a collimating optical system 61 that collimates the light beam generated and emitted by the light beam generator 20 through the optical fiber 100, and the light beam collimated by the collimating optical system 61. A horizontal scanning unit 70 that scans relatively fast in the horizontal direction for image display, and a vertical scan that scans light beams scanned in the horizontal direction by the horizontal scanning unit 70 relatively slowly in the vertical direction Section 80, a first relay optical system 75 provided between the horizontal scanning section 70 and the vertical scanning section 80, and a light beam (hereinafter referred to as "scanning") two-dimensionally scanned in the horizontal and vertical directions in this way. And a second relay optical system 90 for causing the pupil 12 to enter the pupil 12.

  As shown in FIG. 1, the light beam generator 20 is provided with a signal processing circuit 21 that generates signals and the like that are elements for displaying an image. The signal processing circuit 21 outputs a horizontal synchronizing signal 23 used in the horizontal scanning unit 70 and a vertical synchronizing signal 24 used in the vertical scanning unit 80, respectively. Furthermore, the signal processing circuit 21 generates and outputs the image signals 22a to 22c of blue (B), green (G), and red (R) based on the image signal S supplied from the outside, Bias current supply signals 27 a to 27 c for supplying a bias current to lasers 34, 35, and 36 to be described later that are light sources are generated and output to laser drivers 31, 32 and 33 to be described later. The bias current supply signals 27a to 27c may be output from the signal processing circuit 21 by being superimposed on the blue (B), green (G), and red (R) image signals 22a to 22c.

  Further, the luminous flux generator 20 includes a light source unit 30 that converts the three image signals (B, R, G) 22a to 22c output from the signal processing circuit 21 into luminous fluxes, and these three luminous fluxes into one luminous flux. And a light combining unit 40 for generating an arbitrary light beam.

  The light source unit 30 includes a B laser 34 that generates a blue light beam, a G laser 35 that generates a green light beam, and an R laser 36 that generates a red light beam as a plurality of light sources respectively corresponding to the three primary colors. I have. These B laser 34, G laser 35, and R laser 36 function as a light source that emits a light beam having an intensity corresponding to an image signal, and can be configured as, for example, a semiconductor laser or a solid-state laser with a harmonic generation mechanism. Is possible. In addition, when a semiconductor laser is used, the drive current can be directly modulated to modulate the intensity of the light beam. However, when a solid-state laser is used, each laser is provided with an external modulator to modulate the intensity of the light beam. There is a need.

  The light source unit 30 includes a B laser driver 31 that drives the B laser 34, a G laser driver 32 that drives the G laser 35, and an R laser driver 33 that drives the R laser 36. The B laser driver 31, the G laser driver 32, and the R laser driver 33 are respectively supplied to the B laser 34, the G laser 35, and the R laser 36 based on the bias current supply signals 27a to 27c output from the signal processing circuit 21, respectively. In response to the image signal S during the effective scanning period in which the optical scanning unit scans the light beam and displays an image while improving the responsiveness of each laser 34, 35, 36 by supplying a predetermined bias current. Are supplied sequentially to the B laser 34, the G laser 35, and the R laser 36 in units of pixels, so that the B laser 34, the G laser 35, and the R laser 36 are respectively supplied. Is a light source driving unit that emits a luminous flux having an intensity corresponding to the image signal S.

  The light combining unit 40 includes collimating optical systems 41, 42, and 43 that are provided so as to collimate a light beam incident from the light source unit 30 into parallel light, and B lasers 34 and G that are light sources provided corresponding to the three primary colors, respectively. The light beams of each color collimated by the collimating optical systems 41, 42 and 43 are taken out from the laser 35 and the R laser 36, and combined with dichroic mirrors 44, 45 and 46 which are dichroic optical elements for combining these light beams. A coupling optical system 47 that guides the light beam to the optical fiber 100 is provided. The light beams emitted from the lasers 34, 35, and 36 are collimated by the collimating optical systems 41, 42, and 43, respectively, and then incident on the dichroic mirrors 44, 45, and 46, respectively. Thereafter, the light beams are selectively reflected and transmitted with respect to the wavelength by these dichroic mirrors 44, 45, and 46 to reach the coupling optical system 47, and are collected by the coupling optical system 47 and output to the optical fiber 100. . At this time, the light combining unit 40 functions as a multiplexer that combines the light beams emitted from the B laser 34, the G laser 35, and the R laser 36, which are light sources.

  The horizontal scanning unit 70 and the vertical scanning unit 80 scan in the horizontal direction and the vertical direction to form a scanning light beam so that the light beam incident from the optical fiber 100 can be projected as an image.

  The horizontal scanning unit 70 swings the reflecting surface of the scanning element 71 based on the scanning element 71 having a reflecting surface for scanning the light beam in the horizontal direction and the horizontal synchronization signal 23 output from the signal processing circuit 21. And a horizontal scanning drive circuit 72 for generating a drive signal. As the scanning element 71, a galvanometer mirror or the like can be used. The vertical scanning unit 80 drives the scanning element 81 based on the scanning element 81 having a reflection surface for scanning the light beam in the vertical direction and the vertical synchronization signal 24 output from the signal processing circuit 21. And a drive circuit 82. As the scanning element 71 and the scanning element 81, for example, a galvano mirror can be used. The scanning element 71 and the scanning element 81 can be driven by any driving method such as piezoelectric driving, electromagnetic driving, and electrostatic driving as long as the reflecting surface is swung (rotated) so as to scan the light beam. There may be.

  Further, as described above, the first relay optical system 75 that relays the light beam between the horizontal scanning unit 70 and the vertical scanning unit 80 is provided, and the light beam scanned in the horizontal direction by the scanning element 71 is the first light beam. The light beam passes through the first relay optical system 75, is scanned in the vertical direction by the scanning element 81, and enters the second relay optical system 90 as a scanning light beam scanned two-dimensionally.

  That is, as shown in FIG. 2A, the scanning element 71 that swings at a relatively high speed is swung by the horizontal scanning drive circuit 72 to reciprocate the incident light beam in the horizontal direction X. Then, the scanning light scanned in the horizontal direction by the scanning element 71 enters the vertical scanning unit 80 via the first relay optical system 75. The scanning element 81 of the vertical scanning unit 80 is swung in a sawtooth shape by the vertical scanning drive circuit 82 and scans the incident light beam in the vertical direction Y. Then, the scanning light beam in the effective scanning range Z scanned in the vertical direction by the scanning element 81 enters the pupil 12 of the user via the second relay optical system 90.

  In FIG. 2B, the scanning element 71 and the swing range W of the scanning element 81 (range consisting of the vertical swing range W1 and the horizontal swing range W2) and the effective scanning range Z (the vertical effective scanning range Z3 and the horizontal effective range). A range of the scanning range Z5) is shown, and the luminous flux is emitted at the timing of the range Z (hereinafter referred to as “effective scanning range Z”) in the swing range W by the scanning element 71 and the scanning element 81. When the light beam is emitted from the generator 20, the light beam is scanned in the effective scanning range Z by the horizontal scanning unit 70 and the vertical scanning unit 80. As a result, the light flux for one frame is scanned. This scanning is repeated for each frame image. As shown in FIG. 2B, the locus of the light beam scanned by the horizontal scanning unit 70 and the vertical scanning unit 80 is virtually shown when it is assumed that the light beam is always emitted from the light beam generator 20. Yes. In the following description, a range Z1 excluding the effective scanning range Z in the swing range W is referred to as an “invalid scanning range Z1” (see FIG. 2B).

  As shown in FIG. 1, the second relay optical system 90 includes lens systems 91 and 94 having positive refractive power. The scanning light beams emitted from the vertical scanning unit 80 are converted into convergent light beams by the lens system 91 so that the respective light beams have their center lines parallel to each other. Then, the lens system 94 converts the light beams into substantially parallel light beams, and the center line of these light beams is converted to converge on the pupil 12 of the observer. In this way, the light beam is incident on the pupil 12 of the observer and the image is projected on the retina 14, and the light beam is incident on the pupil 12 of the observer and the image is projected on the retina 14. A virtual image can be viewed in front of the pupil 12 of the eye 10.

  In this embodiment, the light beam incident from the optical fiber 100 is scanned in the horizontal direction by the horizontal scanning unit 70 and then scanned in the vertical direction by the vertical scanning unit 80. The arrangement with the vertical scanning unit 80 may be exchanged, and after the vertical scanning unit 80 scans in the vertical direction, the horizontal scanning unit 70 may scan in the horizontal direction.

[1.2. Laser drive method]
Next, a method for driving the lasers 34, 35, and 36 in this embodiment will be described.

  First, the characteristics of the lasers 34, 35 and 36 will be described with reference to the drawings. FIG. 3 is a diagram showing the relationship between the drive current supplied to each of the lasers 34, 35, and 36, which is the light source of the image display device 1 of the present embodiment, and the amount of light emitted. The drive current values are shown in FIG.

  As shown in this figure, each of the lasers 34, 35, and 36 has a characteristic in which the amount of emitted light suddenly rises when a driving current Iop exceeding a specific threshold current Ith is supplied. With this driving current, there is almost no change in the amount of light emission. Therefore, in the image display apparatus 1 according to the present embodiment, a driving current Iop that is equal to or higher than the threshold current Ith is supplied to each laser 34, 35, 36, and a light beam for displaying an image is emitted from each laser 34, 35, 36. Like to do.

  Since each of the lasers 34, 35, and 36 uses a semiconductor laser or the like as described above and includes a capacitance component, there is a delay time from the start of flowing the drive current Iop equal to or higher than the threshold current Ith to the start of light emission.

  FIG. 4 is a diagram illustrating an example of an equivalent circuit of each laser 34, 35, 36. As shown in this figure, each of the lasers 34, 35, and 36 is considered to be equivalent to a circuit in which a parasitic capacitance Cp and a parasitic resistance Rp are connected in parallel to a laser diode LD connected in series with a parasitic resistance Rs. be able to.

Therefore, as shown in FIG. 5, when the drive current Iop is changed from 0 to the threshold current Ith at time t = 0, a part of Iop is used to charge Cp. The effective current I _LD useful for light emission rises with a time constant Cp · Rs (assuming that Rp >> Rs is normally established), and it takes time to reach a desired current value. As described above, there is a delay until the light emission is started after the drive current Iop is supplied to each of the lasers 34, 35, and 36.

  In order to suppress this light emission delay, generally, a bias current Ib having the same current value as or slightly lower than the threshold current Ith is supplied to each of the lasers 34, 35, and 36, respectively. The responsiveness of each laser 34, 35, 36 is configured to be improved.

  However, the supply of the bias current Ib causes each of the lasers 34, 35, and 36 to emit light slightly, so that the contrast ratio of the projected display image corresponding to the image signal S decreases. That is, as shown in FIG. 3, the light emission amount Lth slightly higher than the light emission amount Lb by the bias current Ib becomes the light emission amount of each laser 34, 35, 36 for displaying the minimum luminance of the image, and the light emission amount Lop1 is set as the image. If the light emission amount of each of the lasers 34, 35, and 36 for displaying the maximum luminance of the light is contrast ratio Lop1 / Lth, the light emission for displaying the minimum luminance of the image without supplying the bias current Ib. Compared with the case where the amount is smaller than Lth, the contrast ratio is lowered.

  Therefore, in the image display apparatus 1 of the present embodiment, the light source is arranged on the optical path of the light beam between the lasers 34, 35, and 36 that are light sources and the retina 14 in the observer's eye 10 to reduce the intensity of the light beam. As shown in FIG. 1, an ND (neutral density) filter 50, which is an example of light intensity reducing means for reducing the minimum luminance of an image projected and displayed on the retina 14 as a predetermined region, is connected to a dichroic mirror 44 and a coupling optical system. 47, and the ND filter 50 reduces the contrast ratio.

  FIG. 6A is a diagram illustrating an example of the relationship between the drive current and the light emission amount in each of the lasers 34, 35, and 36 when the ND filter 50 is not provided. In FIG. 6A, the vertical axis represents the light emission amount and the horizontal axis represents the drive current value.

  In each of the lasers 34, 35, and 36, the light emission amount Lth when the threshold current Ith is applied is the light emission amount Lop1 when the maximum value Iop1 of the drive current necessary for projecting and displaying an image on the retina 14 of the observer is applied. When the comparison is relatively large, the minimum luminance of the image is increased, and the contrast ratio Loop1 / Lth of the image projected and displayed on the retina 14 of the observer is relatively decreased.

  On the other hand, in each of the lasers 34, 35, and 36, the light emission amount Lth when the threshold current Ith is applied is the light emission amount when the maximum value Iop1 of the drive current necessary for projecting and displaying an image on the retina 14 of the observer is applied. When it is relatively small compared to Loop 1, the contrast ratio Lop1 / Lth of the image projected and displayed on the retina 14 of the observer is relatively large.

  Therefore, in the image display device 1 of the present embodiment, the ND filter 50 is disposed on the optical path of the light beam between the lasers 34, 35, and 36 serving as the light source and the retina 14 of the observer to reduce the intensity of the light beam. In this way, the contrast ratio is improved. For example, when the ND filter 50 has a transmittance characteristic of 50%, as shown in FIG. 6A, when the lasers 34, 35, and 36 as the light sources emit light with the light emission amount Lth, the retina of the observer The luminous flux incident on 14 becomes a luminous flux having a half intensity compared to the light emission amount Lth, and the minimum luminance of the displayed image can be reduced to a half.

  The ND filter 50 is a neutral density filter that does not depend on the optical color (wavelength) and exhibits the same transmittance with respect to the light beams of R (red), G (green), and B (blue). By disposing the ND filter 50 on the optical path of the light beam between the lasers 34, 35, and 36 that are light sources and the retina 14 in the observer's eye 10, the ND filter 50 is emitted from the lasers 34, 35, and 36. The intensity of the light beam can be reduced without depending on the wavelength of the light beam, and the minimum luminance of the image projected and displayed on the retina 14 can be reduced.

  In order to adjust the minimum luminance of the image to be displayed, the light intensity reducing means may be configured so that the light transmittance can be changed. For example, the ND filter 50 may be arranged such that a plurality of ND filters 50 having different light transmittances are arranged in a turret or the like, or a plurality of ND filters 50 having the same light transmittance are prepared, and the ND filters 50 are stacked to change the light transmittance. Or

  By the way, when the light intensity reducing means is arranged on the optical path of the light flux in this way, the intensity of the light flux reaching the retina 14 of the observer is lowered. Therefore, simply arranging the light intensity reducing means on the optical path of the light flux Not only the minimum luminance of the image projected and displayed on the retina 14 but also the maximum luminance is reduced. For example, as shown in FIG. 6A, when the drive current Iop1 is supplied to each laser 34, 35, and 36 to emit light with the light emission amount Lop1, the maximum brightness of the image projected and displayed on the retina 14 is conventionally obtained. However, the maximum brightness of the image is not achieved by the light intensity reducing means. FIG. 6A shows an example in which an ND filter 50 for reducing the light intensity by 50% is arranged. In the conventional case, in the drive current Iop1 for setting the maximum luminance of the image projected and displayed on the retina 14, When it passes through the ND filter 50, it indicates that the brightness of the projected image is halved.

  Therefore, in this image display device 1, each of the laser drivers 31, 32, and 33 serving as the light source driving unit is configured so that the maximum intensity of the light beam reduced by the ND filter 50 becomes a predetermined intensity in the retina 14 of the observer. The intensity of the light beam emitted from the lasers 34, 35, 36 can be increased.

  That is, when the ND filter 50 is disposed, the minimum luminance and the maximum luminance of the image projected and displayed on the retina 14 are reduced. In order to increase the reduced maximum luminance to a predetermined luminance, the light intensity of the ND filter 50 is increased. By increasing the intensity of the light beam emitted from each laser 34, 35, 36 in advance by each laser driver 31, 32, 33 in accordance with the amount of reduction, the contrast ratio of the image to be projected and displayed can be improved as a result. it can. In addition, the current range of the drive current Iop supplied to each of the lasers 34, 35, and 36 can be expanded, and as a result, the gradation of the projected display image can be increased.

  For example, as shown in FIG. 6B, when the ND filter 50 that reduces the light intensity by 50% is disposed, each laser driver 31, 32, 33 applies about 2 of the drive current Iop1 to each laser 34, 35, 36. By supplying the double drive current Iop2 and increasing the light emission amount of each of the lasers 34, 35, and 36 as the light source from Loop1 to 2Lop1, the maximum luminance of the image projected and displayed on the retina 14 can be set to a predetermined luminance. it can. On the other hand, the light beam incident on the retina 14 of the observer passes through the ND filter 50 and has a half intensity (the light emission amount at this time) as compared with the light emission amount Lth in each of the lasers 34, 35, and 36 as the light source. Is 1/2 Lth), and the minimum luminance of the displayed image can be reduced to ½. Accordingly, the contrast ratio in this case is doubled to 2Lop1 / Lth, compared to when the ND filter 50 is not disposed. FIG. 6B is a diagram illustrating an example of the relationship between the drive current and the light emission amount in each of the lasers 34, 35, and 36 when the ND filter 50 is provided.

  Moreover, since the maximum value of the drive current supplied from the laser drivers 31, 32, and 33 to the lasers 34, 35, and 36 is increased from Iop1 to Iop2, it is supplied to the lasers 34, 35, and 36 that are light sources. The range of the drive current can be expanded (in FIG. 6B, it can be expanded from ΔI1 (= Iop1−Ith) to ΔI2 (= Iop2−Ith)), and as a result, an image projected and displayed on the retina 14 of the observer Higher gradation can be realized.

  For example, as shown in FIG. 6B, if the laser drivers 31, 32, and 33 can control the supply of drive current to the lasers 34, 35, and 36 for each ΔIa, as shown in FIG. , 35, and 36, the range of drive current supplied to ΔI2 which is approximately twice ΔI1 is increased, so that the number of gradations of an image to be projected is changed from ΔI1 / ΔIa to ΔI2 / ΔIa. As a result, the number of gradations of an image to be projected and displayed is about twice (= (ΔI2 / ΔIa) / (ΔI1 / ΔIa).

  As described above, in the image display device 1 according to the present embodiment, the ND filter 50 is disposed on the optical path of the light beam between the lasers 34, 35, and 36 serving as the light sources and the retina 14 of the observer, thereby providing contrast. The ratio can be improved, and the range of the drive current supplied to each of the lasers 34, 35, and 36, which are light sources, can be expanded to achieve higher gradation of the image to be projected and displayed.

[1.3 Position of ND filter]
Next, the arrangement position of the ND filter 50 will be described with reference to FIG.

  As shown in FIG. 1, in the present embodiment, the ND filter 50 is disposed at a position between the dichroic mirror 44 and the coupling optical system 47.

  Thus, since the ND filter 50 is provided between the dichroic mirror 44 and the coupling optical system 47 on the optical path of the light beam, the intensity of one light beam immediately after the three primary color light beams are combined in the dichroic mirror 44. Can be reduced by one ND filter 50, and the intensity of the luminous flux can be efficiently reduced without providing a plurality of ND filters 50.

  Further, the ND filter 50 replaces the position between the dichroic mirror 44 and the coupling optical system 47 described above, and the light flux between the lasers 34, 35, 36 serving as the light source and the dichroic mirrors 44, 45, 46. It may be provided on the optical path, more preferably on the optical path of the light beam between the B laser 34 and the dichroic mirror 44.

  Here, the intensity of light emission by supplying the bias current of the B laser 34 is generally much higher than the intensity of light emission by the bias currents of the other G lasers 35 and R lasers 36. Therefore, by providing the ND filter 50 on the optical path of the light beam between the B laser 34 and the dichroic mirror 44, the light beam emitted from the B laser 34 having the highest light emission intensity due to the bias current among the three primary color light sources. The intensity can be reduced intensively, and as a result, the intensity of light emission by the bias current of each of the lasers 34, 35, and 36 as the light source can be efficiently reduced.

  The ND filter 50 is not limited to the position described above, but is a position between the collimating optical system 61 and the horizontal scanning unit 70, a position between the first relay optical system 75 and the vertical scanning unit 80, and a second relay optical. It may be arranged at a position between the system 90 and the retina 14 of the observer. In short, if the ND filter 50 can reduce the intensity of the light beam emitted from each laser 34, 35, 36, the light beam between the laser 34, 35, 36 and the retina 14 of the observer on the optical path. You may arrange | position in arbitrary places.

  The number of ND filters 50 is not limited, and only one or a plurality of ND filters 50 may be installed on the optical path of the light beam between the lasers 34, 35, and 36 and the retina 14 of the observer. .

[1.4 Light intensity reduction means]
In the present embodiment, the ND filter 50 has been mainly described as an example of the light intensity reducing unit. However, the light intensity reducing unit is not limited to the ND filter 50, and as described below, each laser 34, which is a light source, 35, 36 and the observer's retina 14 are disposed on the optical path of the light beam, and the intensity of the light beam is reduced to reduce the minimum luminance of the image projected and displayed on the observer's retina 14. good.

(About light intensity reduction in the photosynthesis unit)
In the image display device 1, the light combining unit 40 shown in FIG. 1 may be configured to reduce the intensity of the light beam.

  For example, the light combining unit 40 is configured to function as a light intensity reducing unit by combining the light combining units 40 while reducing the intensity of light beams emitted from the lasers 34, 35, and 36.

  That is, in the light combining unit 40, the dichroic mirrors 44, 45, and 46 are configured so as to reflect a part of the incident light in a right angle direction and transmit the remaining part of the incident light. , 36 can be combined while reducing the intensity of the light beams of the three primary colors.

  As described above, by causing the light combining unit 40 to function as a light intensity reducing unit, it is possible to reduce the influence of light emission of the light source due to the bias current by passing through the light combining unit 40, and the contrast ratio of the projected display image according to the image signal. Can be improved.

  Further, in the light combining unit 40 shown in FIG. 1, the light combining unit 40 may function as a light intensity reducing unit by shifting the optical axis of the optical fiber 100.

  For example, the coupling optical system 47 and the optical fiber 100 are not configured to be disposed on the same optical axis, but a part of the light beam emitted from the coupling optical system 47 is incident on the optical fiber 100 and the other part is light. By arranging the coupling optical system 47 and the optical fiber 100 at positions shifted from their optical axes so as not to enter the fiber 100, only a part of the light beams emitted from the coupling optical system 47. However, since the light enters the optical fiber 100, the intensity of the light beam emitted from the coupling optical system 47 is reduced.

  As described above, since the light combining unit 40 functions as the light intensity reducing means, only a part of the light beams emitted from the coupling optical system 47 is output to the optical fiber 100, and the bias current Can reduce the influence of light emission of the light source, and can improve the contrast ratio of the projected display image according to the image signal.

(Light intensity reduction by wavefront curvature modulation optical system)
In the image display device 1 described above, when the wavefront curvature of the scanned light beam (the degree of spread of the light beam) is modulated in order to change the presentation distance of the displayed image or give a sense of depth, A wavefront curvature modulation optical system that modulates the wavefront curvature is installed, but the wavefront curvature modulation optical system may be configured to reduce the intensity of the light beam.

  For example, by configuring the wavefront curvature modulation optical system 300 as shown in FIG. 7, the intensity of the light beam passing through the wavefront curvature modulation optical system 300 is reduced.

  That is, as shown in FIG. 7, the wavefront curvature modulation optical system 300 divides the light beam collimated by the collimating optical system 61 into transmitted light and reflected light reflected in the vertical direction of the transmitted light. And a convex lens 102 having a focal length f for converging the light beam reflected by the beam splitter 101 and a movable movable mirror 103 for reflecting the light beam converged on the convex lens 102 in the incident direction are arranged in parallel on the same optical axis. is doing. 7 is an explanatory diagram illustrating a configuration of the image display device 1 including the wavefront curvature modulation optical system 300, and FIG. 8 is an explanatory diagram illustrating an operation mode of the wavefront curvature modulation optical system 300.

  Then, the wavefront curvature modulation optical system 300 changes the distance between the convex lens 102 and the movable mirror 103 based on the wavefront modulation signal 26 output from the signal processing circuit 21, and enters the collimating optical system 61 to perform horizontal scanning. The wavefront curvature of the light beam traveling toward the unit 70 is changed. For example, as shown in FIG. 8, the distance between the convex lens 102 and the movable mirror 103 is changed to f−d shorter than the focal length f, so that the light enters from the collimating optical system 61 toward the horizontal scanning unit 70. The luminous flux is converted from the parallel light shown in FIG. 8A to the diffused light shown in FIG.

  Here, as shown in FIG. 8, the beam splitter 101 has a cube-like shape in which two right-angle prisms each having a dielectric multilayer film are bonded to an inclined surface 101a, and incident light is incident on the inclined surface 101a. About 50% of the incident light is reflected in the right angle direction, and the remaining about 50% of the incident light is transmitted to split the incident light into two. For this reason, 50% of the light beam incident on the beam splitter 101 from the collimating optical system 61 is reflected in the direction perpendicular to the inclined surface 101 a and passes through the convex lens 102, then is reflected by the movable mirror 103, and passes through the convex lens 102 again. After that, an additional 50% passes through the inclined surface 101a and is emitted to the horizontal scanning unit 70.

  Therefore, the light beam emitted from the beam splitter 101 to the horizontal scanning unit 70 is split by passing through the beam splitter 101, and the intensity of the light beam is compared with the intensity of the light beam incident on the beam splitter 101 from the collimating optical system 61. Reduced to 1/4.

  The horizontal scanning unit 70 and the vertical scanning unit 80 that are scanning units scan one of the light beams divided by the beam splitter 101.

  Thus, the beam splitter 101 divides the light beam emitted from each of the lasers 34, 35, and 36 serving as the light source into a plurality of parts and scans one of them with the scanning unit, thereby affecting the light emission of the light source due to the bias current. And the contrast ratio of the projected display image according to the image signal can be improved. At this time, the beam splitter 101 functions as a light splitting member that splits the light beam emitted from the light source into two or more light beams.

  Further, in the image display device 1 described above, a wavefront curvature modulation optical system 302 shown in FIG. 9 is provided as a modification of the wavefront curvature modulation optical system 300, and the intensity of the light beam is reduced in the wavefront curvature modulation optical system 302. It is good also as a structure made to do. FIG. 9 is a schematic diagram showing the configuration of the wavefront curvature modulation optical system 302, and FIG. 10 is a schematic diagram showing the configuration of the light beam selection means 220 provided in the wavefront curvature modulation optical system 302.

  As shown in FIG. 9, the wavefront curvature modulation optical system 302, which is a modified example, divides the light beams emitted from the lasers 34, 35, and 36 into four light beams A to D by the light beam generation means 210. Each of the four light beams A to D is subjected to wavefront modulation (wavefront curvatures a to d) having different curvatures, and at least one of them (for example, the light beam B having the wavefront curvature b) is selectively selected by the light beam selection means 220. The selected light beam is scanned by the horizontal scanning unit 70 and the vertical scanning unit 80.

  Here, as shown in FIG. 10, in the light beam selection unit 220, the light paths A to D incident from the light beam generation unit 210 are changed in their respective optical paths by the optical switches 231, 232, 233, and 234, and the total reflection mirror 235, the light beams synthesized by the combining mirrors 236, 237, and 238 are any of the light beams A to D only when the changed optical path is an optical path that coaxially overlaps the light beam that can pass through the slit 239. Are emitted toward the horizontal scanning unit 70 (see FIG. 9) through the slit 239.

  For example, in the example shown in FIG. 10, the light flux A having the wavefront curvature a, the light flux C having the wavefront curvature c, and the light flux D having the wavefront curvature d incident from the light flux generating means 210 are respectively transmitted by the optical switches 231, 232, 233, and 234. The optical path is changed and synthesized by the total reflection mirror 235, the synthesis mirrors 236, 237, and 238, and the optical path deviates from the axis of the light beam that can pass through the slit 239. . On the other hand, the light beam B having the wavefront curvature b is reflected by the optical switch 232 so that its optical path is reflected by the combining mirror 236 in a direction overlapping with the axis of the light beam that can pass through the slit 239. Therefore, the light beam B can pass through the slit 239 and is emitted from the wavefront curvature modulation optical system 302 toward the horizontal scanning unit 70 as the light beam B having the wavefront curvature b selected by the light beam selection unit 220.

  The light beam emitted from the wavefront curvature modulation optical system 302 toward the horizontal scanning unit 70 is one of the four light beams A to D divided by the light beam generation unit 210 and selected by the light beam selection unit 220. Therefore, the intensity of the light beam is reduced as compared with the intensity of the light beam incident on the wavefront curvature modulation optical system 302 from the collimating optical system 61. The horizontal scanning unit 70 and the vertical scanning unit 80 serving as scanning units scan one of the light beams divided by the light beam generation unit 210 and the light beam selection unit 220.

  In this way, the light beam emitted from each of the lasers 34, 35, and 36 as the light source is divided into a plurality of light beams by the light beam generation unit 210 and the light beam selection unit 220 in the wavefront curvature modulation optical system 302, and one of them is divided by the scanning unit. By scanning, the influence of the light emission of the light source due to the bias current can be reduced, and the contrast ratio of the projected display image corresponding to the image signal can be improved. At this time, the light beam generation unit 210 and the light beam selection unit 220 function as a light splitting member that splits the light beam emitted from the light source into two or more light beams.

(About light intensity reduction by diffraction grating)
In the image display apparatus 1 described above, when the exit pupil is enlarged, a diffraction grating is provided on the optical path of the light flux between the lasers 34, 35, and 36 that are light sources in the image display apparatus 1 and the retina 14 of the observer. Although it will be installed, the diffraction grating may reduce the intensity of the light beam.

  For example, the light beam that passes through the diffraction grating 54 is provided by installing the diffraction grating 54 at a position deviated from the intermediate image plane between the lens system 91 and the lens system 94 shown in FIG. The strength of can be reduced.

  That is, as shown in FIG. 11, the diffraction grating 54 is a transmission type diffraction element, and has a diffraction surface 54a in which a plurality of transmission parts and non-transmission parts are periodically arranged at a predetermined diffraction pitch. The light beam incident on the diffractive surface 54a is diffracted and diffused as multi-order diffracted light. Of the multiple orders of diffracted light diffracted by the diffraction grating 54, for example, only the 0th-order light beam is used as the light beam for projection display, and the other-order light beams are not used as the light beam for projection display. To reduce the effective light intensity. By configuring the diffraction grating 54 so that the proportion of the 0th-order light in the diffracted light is reduced, the degree of reduction in effective light intensity can be adjusted.

  Thus, by installing the diffraction grating 54, the influence of light emission of the light source due to the bias current can be reduced, and the contrast ratio of the projected display image according to the image signal can be improved. At this time, the diffraction grating 54 is an example of a light diffusion member that diffuses a light beam. The exit pupil may be enlarged by using the first-order light and the −1st-order diffracted light for projection display in addition to the 0th-order light among the multiple-order diffracted lights diffracted by the diffraction grating 54.

(Other light intensity reduction means)
As other light intensity reducing means, a diaphragm (not shown) that shields a part of the light beam emitted from each laser 34, 35, 36 is used as each laser 34, 35, 36 as a light source and the retina 14 of the observer. May be provided on the optical path of the light flux between the two.

  As described above, when the diaphragm is provided, the influence of light emission of the light source due to the bias current can be reduced by passing through the diaphragm, and the contrast ratio of the projected display image according to the image signal can be improved.

  Further, the reflective surface of the scanning element 71 or the scanning element 81 is coated with a reflective film (not shown) formed of a metal film having a low reflectance such as aluminum, so that the scanning element 71 or the scanning element 81 is formed. In addition to the original scanning function, a function of reducing the intensity of the light beam may be achieved. At this time, the reflective film of the scanning element 71 or the scanning element 81 functions as a light intensity reducing unit.

  Thus, by using the reflection film of the scanning element 71 or the scanning element 81 as the light intensity reducing means, the influence of light emission of the light source due to the bias current can be reduced without increasing the number of parts of the image display device 1. In addition, the contrast ratio of the projected display image according to the image signal can be improved.

  Further, as a light intensity reducing means, a scattering plate having a random pattern surface made of an abrasive or the like is arranged on the optical path of the light flux between each of the lasers 34, 35, and 36 serving as a light source and the retina 14 of the observer. By providing, it is good also as a structure which scatters the incident light beam.

  In this way, by arranging the scattering plate, a light beam having a wavelength larger than the width of the pattern of the scattering plate is specularly reflected, and a light beam having a wavelength smaller than the width of the pattern of the scattering plate is randomly scattered. The influence of light emission of the light source due to the bias current can be reduced, and the contrast ratio of the projected display image corresponding to the image signal can be improved.

  In addition, in this embodiment, it is good not only as a structure provided with the above-mentioned light intensity reduction means independently, but it is good also as a structure which combined several light intensity reduction means arbitrarily.

[2. Second Embodiment]
By the way, as described above with reference to FIG. 6, the laser drivers 31, 32, and 33 are previously set so that the maximum intensity of the light beam reduced by the light intensity reducing unit becomes a predetermined intensity in the retina 14 of the observer. Since the intensity of the light beam emitted from the lasers 34, 35, and 36 is increased, the power consumption of the entire image display device 1 is increased.

  Therefore, in the image display apparatus according to the second embodiment, in order to suppress the light emission delay of each of the lasers 34, 35, and 36 and improve the responsiveness in at least a predetermined range of the invalid scanning range Z1 (see FIG. 2B). In addition, the supply of the bias current Ib (see FIG. 3) supplied from the laser drivers 31, 31, 33 to the lasers 34, 35, 36, respectively, is stopped or reduced. That is, each of the laser drivers 31, 32, and 33 has a bias current Ib for improving the responsiveness of each of the lasers 34, 35, and 36 serving as a light source at least for a predetermined period of the invalid scanning period in which image display is not performed. The supply to the lasers 34, 35, 36 is stopped or reduced.

  As described above, the laser drivers 31, 32, and 33, which are light source driving units, stop or reduce the supply of the bias current to the lasers 34, 35, and 36 in a predetermined period, so that the light by the light intensity reducing unit is reduced. The drive current supplied to each laser 34, 35, 36 is increased by increasing the intensity of the light beam emitted from each laser 34, 35, 36 in advance by each laser driver 31, 32, 33 according to the intensity reduction amount. The range can be expanded. As a result, the gradation of the projected display image can be increased, and the intensity of the light beam emitted from each laser 34, 35, 36 by each laser driver 31, 32, 33 can be increased in advance. An increase in power consumption due to the increase can be reduced as much as possible. The supply of the bias current Ib can be reduced, for example, by supplying a current that is ½ of the bias current Ib. In the following description, when the supply of the bias current is stopped, it is assumed that the supply of the bias current is reduced in addition to the stop of the supply of the bias current.

  Next, a specific configuration and operation for starting and stopping the supply of the bias current Ib will be described with reference to the drawings. FIG. 12 and FIG. 13 are diagrams for explaining the timing for starting and stopping the supply of the bias current in the vertical scanning.

  As shown in FIG. 12, in the vertical range Z2 in which the effective scanning range Z is not included in the vertical swing range W1 by the scanning element 81 (hereinafter, referred to as “vertical invalid scanning range Z2”), the light beam generator 20. The light beam is not emitted from the light source and no image is displayed. Further, if the bias current Ib is supplied to each of the lasers 34, 35, 36 after shifting to the vertical effective scanning range Z 3 including the effective scanning range Z in the vertical swing range W 1, each laser 34, 35, 36 It is enough to keep the 36 responsiveness high.

  Therefore, in particular, in the image display device of the present embodiment, the bias current Ib is supplied from the laser drivers 31, 32, 33 to the lasers 34, 35, 36 in the vertical invalid scanning range Z2 indicated by diagonal lines in FIG. It is configured to stop, thereby reducing power consumption.

  Here, the relationship between the vertical scanning by the scanning element 81 and the supply period of the bias current Ib at this time will be described with reference to FIG. The upper left diagram of FIG. 13 shows the relationship between the angle of the reflecting surface of the scanning element 81 and time, the lower left diagram shows the relationship between the start / stop of supply of bias current and time, and the upper right diagram shows FIG. Similar to b), the relationship between the effective scanning range Z and the invalid scanning range Z1 is shown.

  As shown in this figure, the laser drivers 31, 32, and 33 each have a predetermined time (timing from tc to tb) before the scanning by the vertical scanning unit 80 shifts from an invalid scanning period to an effective scanning period for displaying an image. Supply of the bias current Ib to each of the lasers 34, 35, and 36 is started, and immediately after the scanning by the vertical scanning unit 80 shifts from the effective scanning period to the invalid scanning period (timing from tf to tg), the bias current to the light source The supply of Ib is stopped.

  That is, the laser drivers 31, 32, and 33 each laser 34 when the scanning position by the vertical scanning unit 80 is in the horizontal scanning line L1 immediately before the transition from the vertical invalid scanning range Z2 to the vertical effective scanning range Z3. , 35 and 36, supply of the bias current Ib is started. The laser drivers 31, 32, and 33 are respectively connected to the lasers 34, 32 when the scanning by the vertical scanning unit 80 is in the first horizontal scanning line L2 that has shifted from the vertical effective scanning range Z3 to the vertical invalid scanning range Z2. Supply of the bias current Ib to 35 and 36 is stopped.

  As described above, since the supply of the bias current Ib is started a predetermined time before the transition to the effective scanning period of the vertical scanning, the bias current Ib is supplied to each of the lasers 34, 35, and 36 at the time of transition to the effective scanning range Z. Is supplied with high responsiveness, so that it is possible to surely prevent deterioration in the image quality of the display image due to light emission delay, and to reduce power consumption in the invalid scanning period in the vertical direction.

  In addition, since the start control and the stop control (or reduction control) for supplying the bias current Ib only need to be performed once for scanning one frame of the image, the power consumption can be reduced without complicating the processing. .

  By the way, the timing for starting the supply of the bias current Ib to each of the lasers 34, 35, 36 is a state in which the bias current Ib is supplied to each of the lasers 34, 35, 36 at the time of shifting to the effective scanning range Z and the response is high. It only has to be.

Equivalent circuit of each laser 34, 35, 36 is as shown in FIG. 4 as described above, the rise time constant Δt of effective current _{I LD} is expressed by the following equation (1).

Δt = −Cp · Rs (1)
Here, it is assumed that Rp >> Rs, which is normally established.

  Therefore, in consideration of the inherent rise time constant of each laser 34, 35, 36, it is only necessary to start the supply of the bias current Ib before Δt that shifts to the effective scanning period of the vertical scanning. Can be reduced.

  Further, the supply of the bias current Ib to the lasers 34, 35, and 36 is stopped immediately after shifting from the effective scanning range Z to the invalid scanning range Z1 (timing of te), thereby further reducing power consumption. it can.

  As described above, in the image display apparatus according to the present embodiment, each of the laser drivers 31, 32, and 33 serving as the light source driving unit is a light source when scanning by the scanning unit is at least in a predetermined period of the invalid scanning period. Since supply of the bias current to each of the lasers 34, 35, and 36 is stopped, it is possible to reduce power consumption during a predetermined period in the invalid scanning period that is not visually recognized by the user.

  Next, a modification of the image display device of the present invention will be described. In the above-described embodiment, the bias current Ib is supplied to the lasers 34, 35, and 36 that are light sources depending on whether the vertical scanning by the vertical scanning unit 80 is in the vertical invalid scanning range Z2 or the vertical effective scanning range Z3. Although the configuration is such that the start and the supply stop are performed, in this modification, the range in which the supply of the bias current Ib is stopped is further expanded. That is, in this modification, the supply of the bias current Ib to the lasers 34, 35, and 36 serving as the light sources is started and stopped according to the horizontal scanning by the horizontal scanning unit 70. Note that the image display apparatus in the above-described embodiment has the same configuration and is partially different in processing and the like. In this modification, particularly different parts will be described.

  Hereinafter, an image display device according to a modification will be specifically described with reference to the drawings. 14 and 15 are diagrams for explaining supply start and supply stop of bias current in horizontal scanning.

  As shown in FIG. 14, a light beam is emitted from the light beam generator 20 in the invalid scanning range Z1 (the region indicated by the oblique lines in FIG. 14) excluding the effective scanning range Z in the horizontal swing range W2 by the scanning element 71. No image is displayed. For this reason, if each laser 34, 35, 36 is in a highly responsive state at the time of shifting to the effective scanning range Z, the response of each laser 34, 35, 36 in most of the invalid scanning range Z1. Therefore, it is not necessary to supply the bias current Ib to the lasers 34, 35 and 36 in advance in order to ensure the performance.

  Therefore, in particular, in the image display apparatus according to the present modification, not only the vertical invalid scanning range Z2 indicated by the oblique lines in FIG. 14 but also the lasers 34 from the laser drivers 31, 32, 33 in the entire effective scanning range Z. , 35, and 36 so as not to supply the bias current Ib.

  That is, as shown in FIG. 14, in the vertical effective scanning range Z3 (see FIG. 12), the bias current from each laser driver 31, 32, 33 to each laser 34, 35, 36 in the horizontal invalid scanning range Z4. By not supplying Ib, power consumption can be further reduced.

  However, since the responsiveness of each laser 34, 35, 36 must be high at the time of shifting from the horizontal invalid scanning range Z4 to the effective scanning range Z, until a predetermined period before shifting to the effective scanning range Z. It is necessary to start supplying the bias current Ib. Note that the predetermined period here must be longer than the time Δt (see Expression (1)) corresponding to the rise time constant of each of the lasers 34, 35, and 36 described in the above embodiment.

  Here, the relationship between the horizontal scanning by the scanning element 71 and the supply period of the bias current Ib will be described with reference to FIG. In FIG. 15, the upper part shows the relationship between the angle of the reflecting surface of the scanning element 81 and the time, the middle part shows the relation between the start and stop of light emission by the light beam generator 20 and the time, and the latter part shows the bias. The relationship between the start / stop of supply of current Ib and time is shown.

  As shown in this figure, the reflecting surface of the scanning element 71 is swung by the horizontal scanning driving circuit 72 within an angle range (horizontal rocking range W2) of + θ1 to −θ1 with a predetermined position as a reference (0 degree). The light beam is emitted from the light beam generator 20 in the range where the reflection surface is ± θ2 (horizontal effective scanning range Z5).

  In this embodiment, as shown in FIG. 15, each laser driver 31, 32, 33 has a predetermined transition in which scanning by the horizontal scanning unit 70 shifts from a horizontal invalid scanning period Ta to a horizontal effective scanning period Tb in which image display is performed. Before the time Δt, supply of the bias current Ib to each laser driver 31, 32, 33 is started, and each laser is scanned when scanning by the horizontal scanning unit 70 shifts from the horizontal effective scanning period Tb to the horizontal invalid scanning period Ta. The supply of the bias current Ib to the drivers 31, 32, 33 is stopped or reduced. Note that Δt is a time corresponding to the rise time constant of each of the lasers 34, 35, and 36, and is a time derived from the above-described equation (1).

  That is, in each laser driver 31, 32, 33, scanning by the vertical scanning unit 80 is in the vertical effective scanning range Z3 (see FIG. 12), and scanning by the horizontal scanning unit 70 is horizontal ineffective within the horizontal swing range W2. Bias current to each laser 34, 35, 36 before a predetermined time (Δt in FIG. 15) (a timing indicated by “t 1” and “t 1 ′” in FIG. 15) before moving from the scanning range Z 4 to the horizontal effective scanning range Z 5. The supply of Ib is started.

  Further, in each laser driver 31, 32, 33, the scanning by the horizontal scanning unit 70 shifts from the horizontal effective scanning range Z5 to the horizontal invalid scanning range Z4 in a state where the scanning of the vertical scanning unit 80 is in the vertical effective scanning range Z3. Sometimes, the supply of the bias current Ib to each laser 34, 35, 36 is stopped.

  As a result, before the scanning by the horizontal scanning unit 70 reaches the horizontal effective scanning period Tb, the bias current Ib is supplied in advance to each of the lasers 34, 35, and 36 so that the responsiveness is improved. The power consumption in the invalid scanning range Z1 is reduced while ensuring the quality of the image displayed in the effective scanning range Z by avoiding the light emission delay of each laser 34, 35, 36. Moreover, since the supply of the bias current Ib is stopped when the scanning by the horizontal scanning unit 70 shifts from the horizontal effective scanning period Tb to the horizontal invalid scanning period Ta, the power consumption in the invalid scanning range Z1 is made as much as possible. Can be reduced.

  As a result, while the scanning position by the horizontal scanning unit 70 is in the effective scanning range Z, the power consumption can be reduced as much as possible while ensuring the responsiveness of each laser 34, 35, 36.

  Incidentally, in the above description, the relationship between the drive current of each laser 34, 35, and 36 and the light emission amount is shown in FIG. 3, but this relationship changes according to the ambient temperature as shown in FIG. FIG. 16 is a graph showing how the threshold current value fluctuates depending on the ambient temperature. Like FIG. 3, the vertical axis represents the light emission amount and the horizontal axis represents the drive current value.

  As shown in this figure, in each of the lasers 34, 35, and 36, the threshold current Ith2 at a high temperature (85 ° C.) is larger than the threshold current Ith1 at a normal temperature (25 ° C.).

  Therefore, the image display device includes, for example, a temperature measurement unit (not shown) that measures the ambient temperature of the B laser 34, the G laser 35, and the R laser 36, which are light sources, inside the light beam generator 20, and the B laser. When the ambient temperature of the B laser 34, G laser 35, and R laser 36 measured by the temperature measuring unit is higher than a predetermined temperature, the driver 31, the G laser driver 32, and the R laser driver 33 The supply of the bias current Ib to the laser 35 and the R laser 36 may be stopped.

  With this configuration, power consumption can be reduced even when the drive current necessary for light emission from the B laser 34, G laser 35, and R laser 36 increases as the ambient temperature increases. Can do.

  In the image display device described above, the B laser driver 31, the G laser driver 32, and the R laser driver 33 are bias currents for at least one of the B laser 34, the G laser 35, and the R laser 36, which are a plurality of light sources. The supply may be stopped. Generally, among the B laser 34, the G laser 35, and the R laser 36, the operating voltage of the B laser is the highest, and the driving current required for light emission is the highest, so that the supply of bias current to the B laser 34 is stopped. It is preferable to be configured to perform.

  As described above, if the supply of the bias current is stopped for the B laser 34 having a large driving current required for light emission among the plurality of light sources B laser 34, G laser 35, and R laser 36, the supply of the bias current is stopped. Since only one light source is required, power consumption can be reduced more easily than when supply of bias current is stopped for all light sources.

  As described above, some of the embodiments of the present invention have been described in detail with reference to the drawings. However, these are merely examples, and various embodiments can be made based on the knowledge of those skilled in the art including the aspects described in the section of the disclosure of the invention. The present invention can be implemented in other forms that have been modified or improved.

It is explanatory drawing which shows the image display apparatus which concerns on 1st Embodiment of this invention. It is a figure for demonstrating the scanning aspect of the light beam by the optical scanning part of an image display apparatus. It is a figure which shows the relationship between the drive current and light emission amount in a light source. It is a figure which shows an example of the equivalent circuit of a light source. It is a figure for demonstrating the starting characteristic of a light source. . It is a figure which shows the relationship between the drive current and light emission amount in a light source. It is explanatory drawing which shows the structure of the image display apparatus provided with the wavefront curvature modulation optical system. It is explanatory drawing which shows the operation | movement aspect of a wavefront curvature modulation optical system. It is a schematic diagram which shows the structure of the modification of a wavefront curvature modulation optical system. It is a schematic diagram which shows the structure of the light beam selection means with which the wavefront curvature modulation optical system was equipped. It is a schematic diagram which shows the aspect by which a light beam is spread | diffused by a diffraction grating. It is a figure for demonstrating the timing of the supply start and supply stop of the bias current in vertical scanning in the image display apparatus which concerns on 2nd Embodiment of this invention. It is a figure for demonstrating the timing of supply start and supply stop of the bias current in vertical scanning. It is a figure for demonstrating the supply start and supply stop of the bias current in horizontal scanning. It is a figure for demonstrating the supply start and supply stop of the bias current in horizontal scanning. It is a graph which shows a mode that a threshold current value is fluctuate | varied with ambient temperature.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image display apparatus 20 Light beam generator 21 Signal processing circuit 31-33 Light source drive part 34-36 Light source 50 ND filter 70 High-speed scanning part 71 Scanning element 80 Low-speed scanning part 81 Scanning element

Claims (10)

A light source, a light source driving section for driving the light source to emit a light beam having an intensity corresponding to an image signal, while supplying a predetermined bias current to the light source to improve the responsiveness of the light source, and the light source A scanning unit that scans the light beam emitted from the image display device, and projects and displays an image according to the image signal in a predetermined area.
A light intensity reducing means disposed on an optical path of the light flux between the light source and the predetermined area, and reducing the intensity of the light flux to reduce the luminance of an image projected and displayed on the predetermined area;
The light source driving unit can increase the intensity of the light beam emitted from the light source so that the maximum intensity of the light beam reduced by the light intensity reducing unit becomes a predetermined intensity in the predetermined region. Image display device.   The image display apparatus according to claim 1, wherein the light intensity reducing unit includes an ND filter and / or a reflection film of the scanning unit.   The light intensity reducing means includes a light diffusing member for diffusing the light flux, and reduces the intensity of the light flux when a part of the diffused light flux becomes an effective light intensity. Item 3. The image display device according to Item 2. The light intensity reducing means includes a light splitting member that splits a light beam emitted from the light source into two or more light beams,
The image display device according to claim 1, wherein the scanning unit scans one of the light beams divided by the light dividing member.   5. The image display device according to claim 1, wherein the light intensity reduction unit includes a diaphragm that blocks a part of a light beam emitted from the light source. The light source is provided corresponding to each of the three primary colors, and includes a multiplexer that combines the light beams emitted from these light sources,
6. The multiplexer according to claim 1, wherein the multiplexer is made to function as the light intensity reducing means by multiplexing while reducing the intensity of the light beam emitted from the light source. The image display device according to item 1.   The multiplexer includes a dichroic optical element that extracts light beams of each color from light sources provided corresponding to the three primary colors, and combines the light beams, and the dichroic optical element and the light source The image display apparatus according to claim 6, wherein the light intensity reducing means is provided on an optical path of a light beam.   8. The optical multiplexer according to claim 1, further comprising an optical fiber in the multiplexer, wherein the multiplexer functions as the light intensity reducing unit by shifting an optical axis of the optical fiber. The image display device described.   The said light source drive part stops or reduces supply of the said bias current to the said light source at least for a predetermined period among the invalid scanning periods which do not display an image. The image display device described in 1.   A retinal scanning image display device that projects an image on at least one retina of a user by scanning light modulated in accordance with an image signal in a two-dimensional direction with an optical scanning device, and displays the image. The image display device according to any one of claims 1 to 9.

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