JP2003121791A - Illumination device using a plurality of beams and image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make uniform the intensity distribution of an illumination device using light beams from a plurality of lasers. SOLUTION: The illumination device 15 concerned with a grating light valve 20 divides the light beams from the plurality of the lasers into a plurality of beams having equal intensity. The divided beams having the equal intensity are spatially shifted by using birefringence and beams having no coherence are put one over another to obtain illumination light having a uniform intensity distribution. As a means for intensity division, a style using multiple reflection and a style using polarization are available, but the former style can increase the number of beam divisions and is advantageous in cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for realizing a uniform intensity distribution in an illuminator using a plurality of laser beams.

[0002]

2. Description of the Related Art In an image display device called a projection display, a liquid crystal panel or a D is used as a spatial modulator.
MD (Digital Micromirror Device) and the like have been used, but recently, a display using an active drive type grating (diffraction grating) by a micromachine technology has been developed and attracted attention. The name of the diffraction grating type element used is "Grating light valve (Grating
Light Valve) "(hereinafter abbreviated as" GLV "), which is capable of displaying a clear (seamless) clear and bright image without using a conventional spatial modulator and uses micromachine technology. It has the features that it can be produced at low cost and that it can operate at high speed.

To form an image using this GLV,
Of the diffracted light, Schlieren filtering that blocks the 0th order light and transmits only the ± 1st order light is necessary.

FIG. 13 shows a Schlieren filter optical system a.
It shows the main part of. Light from a light source (not shown) is condensed by the cylindrical lens L0 and G
The LV is irradiated, and the diffracted light is transmitted through the lens L1, the schlieren filter F, and the lens L2 in this order and emitted.

The rays "lt (+1), lt shown in FIG.
“(0), lt (−1)” represents the diffracted light by GLV, “lt (+1)” is the + 1st-order diffracted light, and “lt
“(0)” indicates the 0th order (diffracted) light and lt (−1) indicates the −1st order diffracted light, and only the 0th order light is blocked by the Schlieren filtering.

A reflection type element is used as the GLV, and has a structure in which a large number of minute ribbons called membranes are arranged in parallel on a substrate with an air gap. Then, of the GLV states, in the first state (when the pixels are turned off), the phases of all ribbons are aligned,
± 1st order diffracted light is not generated (only reflected light), but in the second state (when the pixel is lit), every other ribbon is attracted to the substrate side by the electrostatic force to form a reflection type diffraction grating. ± 1st order diffracted light is generated. And this ±
In order to select only the first-order diffracted light, it is necessary to perform spatial filtering (Schlieren filtering) in the Fourier plane of GLV.

Here, in order to increase the filtering contrast, it is necessary to sufficiently narrow the angular range of the incident light in the diffraction direction. This is because if the incident light beam has a spread, the light beam incident value on the filtering surface can be spread, so that leakage light occurs at the time of extinction.

FIG. 14 shows only the GLV, the lens L1, and the schlieren filter surface F of the optical system a, taken out and shown conceptually as to how ± 1st order diffracted light is selected by filtering. (However, the GLV is shown as a transmissive element for convenience of illustration.)

When a laser such as a laser display is used as a light source for such an optical system, speckle (or speckle noise) is generated.
Is a problem. Speckle is a phenomenon caused by coherent light from a laser whose phase is aligned and scattered by random phase planes, causing disturbed wavefronts from adjacent regions of an object to interfere on the observation plane. Is. Further, a technique for reducing speckle noise that appears as a granular light intensity distribution is indispensable. In particular, it is a problem in a laser display that speckles occur between the screen and the eyes of the observer, that is, the retina.

Regarding the uniformity of illumination, various methods have been proposed because they are generally required for an illumination optical system. For example, the following methods can be mentioned.

(A) Method by beam scanning (scanning) (B) Method by conversion of intensity distribution.

First, for (A), for example, in order to obtain a uniform intensity distribution from a Gaussian beam (a beam whose light intensity distribution follows a Gaussian distribution), as shown in FIG.
There is a method of arranging a plurality of beams in parallel (five in this example) and performing beam scanning in a direction inclined with respect to the direction of parallelization instead of beam scanning. In the figure, the beams indicated by the five circles are arranged from diagonally upper left to diagonally lower right. For individual beams,
As shown in the lower left of each, they have a Gaussian distribution. The beam scanning direction is defined so as to go from the left side to the right side of the figure as indicated by the arrows, so that the distribution curve of each beam ( It is possible to obtain an intensity distribution (shown by the solid line) that is a combination of the broken lines. Incidentally, this method is generally well used in applications such as laser processing and exposure where uniformity of the integrated value of the exposure amount is required. Since interference occurs when adjacent coherent beams overlap with each other, the intensity distribution becomes non-uniform, but if uniformization of the total exposure amount is required, all beams must be spatially overlapped. Since there is no (each beam can be placed apart as shown in the figure), there is no problem even with such a method.

Regarding (B) above, for example, a method of converting the intensity distribution by using an aspherical cylindrical lens can be considered, and by making full use of an optical design technique, profile conversion is performed on an input beam having a Gaussian distribution. Is performed to obtain a uniform intensity distribution.

For such illumination or exposure, there are a form using a laser beam originating from a plurality of different light sources, and a form generating a plurality of beams by performing intensity division on the laser light. The following will be described below, which is known as an elemental technology for realizing the latter.

(1) Intensity division by polarized light (2) Intensity division by multiple reflection.

First, the case of using the polarized light of (1) will be described. At that time, it is assumed that the incident laser light is linearly polarized light.

As in configuration example b shown in FIG. 16, a laser beam from a light source (not shown) is made incident on an optical system in which a λ / 2 wavelength plate (half wavelength plate) and a birefringent crystal are arranged. Think about the case. In addition, "lt1" in the figure is incident light,
"Lt2" indicates the transmitted light of the wave plate, and "lt3" indicates the transmitted light of the birefringent crystal. For these lights, as shown in the lower part of the figure, the polarization state (polarization direction) is indicated by a double-headed arrow. Are shown respectively.

When a laser beam (“lt2” in the figure) whose polarization direction is rotated by a λ / 2 wave plate into an appropriate direction is incident on the birefringent crystal cut in the appropriate direction, they are orthogonal to each other. The polarized light (that is, the two polarized light having an orthogonal relationship) is spatially separated. Therefore, by appropriately adjusting the polarization direction, a beam having two polarizations having the same intensity (see "lt3" in the figure) can be generated. Here, for the sake of convenience of description, the method of separating into two linearly polarized light beams orthogonal to each other has been described, but the present invention is not limited to this, and circularly polarized light of clockwise and counterclockwise polarized light may be used. Dielectric crystals, liquid crystals, etc. are known as optical materials having birefringence, but materials that have a high transmittance for the wavelength used and a sufficient separation angle with a practical thickness should be used. It is preferable to select it.

As a polarizing optical element produced for such a purpose, there is a Savart plate invented by Bio-Savart, which is a uniaxial optical element cut out at an azimuth of 45 ° with respect to an optical axis. The crystal was polished as a parallel plate. Light incident perpendicularly to the Savart plate is split into polarized light (ordinary ray and extraordinary ray) orthogonal to each other by birefringence. For both rays, the propagation direction in the crystal (that is, the propagation direction of the energy flow) Since the direction of the pointing vector indicating) is different, the rays are separated as they propagate through the crystal. However, when the incident light ray is vertically incident, the normal direction of the wavefront is always perpendicular to the Savart plate both in the crystal and after the emergence. Therefore, the vertically incident light ray has two polarizations that are orthogonal to each other. It will be separated into two and emitted in the same direction.

At this time, the shift amount of the two polarizations (or the positional shift amount, which will be referred to as "d") is given by the following equation.

[0021]

[Equation 1]

The meanings of the symbols used in the above equation are as follows.

[0023] t; in the crystal for two orthogonal polarization separation angle n _o;; crystal thickness φ uniaxial crystal extraordinary refractive index theta;; uniaxial ordinary refractive index n _e of the crystals of the Savart plate The angle between the normal to the plane of incidence and the optical axis.

For example, in order to maximize the separation angle, θ =
When using calcite as a uniaxial crystal at 45 °,
By substituting the numerical values of n _o = 1.658 and n _e = 1.486 into the above equation, tan φ = 0.1 as a tangent term.
To get 09. Therefore, when t = 10 mm (millimeter), it is possible to obtain separated outgoing light rays with a shift amount of d = 1.09 mm.

Various types of elements such as a Wollaston prism are known as elements for polarization separation using birefringence. Incoming light and outgoing light (ordinary ray and extraordinary ray) are known.
When it is necessary to match all the directions of the above, it is preferable to use a Savart plate or its improved product. Regarding the Savart plate, an example of using this as a single unit and, as a modification thereof, a stack of several Savart plates and the like are often used, but the function is the same (henceforth, Then, the concept of "Savart plate" shall include a plurality of configurations.). Although calcite is mentioned in the above numerical examples, it is expensive because it is a natural birefringent material, and it is difficult to mine a large quality material. Therefore, in order to reduce the cost, it is necessary to use an inexpensive crystal such as artificial quartz.

Next, the division method using the above-mentioned multiple reflection (2) will be described.

FIG. 17 shows an example of the structure of the multiple reflection plate c.

On one surface (the left surface in the figure) of the parallel plate, a total reflection coating (intensity reflectance is "R") is applied except for a window W for incidence of light rays. On the other hand, the opposite surface (the right surface in the figure) is provided with a plurality of divided regions according to the number and position of multiple reflections. In this example, the areas divided into six are coated with different intensity reflectances (these are respectively referred to as “R ₁ , R ₂ , ..., R ₆ ”) (which will be described later). As described above, since "R ₆ = 0" is set, the number of divisions shown in the figure is 5.)

The six rays "lt_n" (n =
0, 1 to 5) respectively indicate outgoing rays, and the subscript “n” corresponds to the number of reflections on the outgoing surface side.

To simplify the explanation, assuming that the window W has no intensity loss (reflectance 0), the emission intensity of each beam (incident intensity is "1") is as follows. Like

[0031] - emitted after being reflected once by intensity = "1-R _1" beam in "lt_1" (exit surface of the beam shown in "lt_0" (beams emitted without reflection on the emission surface side) Beam intensity = “R · R ₁ · (1-
R ₂ ) ”・ The intensity of the beam shown in“ lt — ₂ ”(the beam emitted after being reflected twice on the emission surface side) =“ R ² · R ₁ · R ₂ · (1
-R ₃ ) ”・ The intensity of the beam shown in“ lt — ₃ ”(the beam emitted after being reflected three times on the emission surface side) =“ R ³ · R ₁ · R ₂ · R ₃ ·
(1-R ₄ ) ”・ The intensity of the beam shown in“ lt — ₄ ”(the beam emitted after being reflected four times on the emitting surface side) =“ R ⁴ · R ₁ · R ₂ · R ₃ ·.
R ₄ · (1−R ₅ ) ”・ The intensity of the beam shown in“ lt — ₅ ”(the beam emitted after being reflected five times on the emitting surface side) =“ R ⁵ · R ₁ · R ₂ · R ₃ ·. ”
R ₄ · R ₅ · (1-R ₆ ) ”.

That is, the intensity of the beam emitted after N times of reflection is obtained by multiplying the Nth power of R by the product of the reflectance over the area that has been reflected up to that time and the transmittance of the emission area. Equal to one.

Now, assuming that six beams are generated,
In order to minimize the loss, it is preferable to AR coat the 6th region, but in the calculation shown below, “R
₆ = 0 ”and assume that“ R = 1 ”. If absorption and scattering inside the parallel plate can be ignored, the following equation can be obtained from the equivalence relation that the sum of the intensities of all beams is equal to 1.

[0034]

[Equation 2]

Further, since the purpose is to make the intensities of all beams equal, the following formula is given (that is, the values of the respective terms on the left side of the formula [2] are all equal). .

[0036]

[Equation 3]

That is, since the beams have the same intensity (1/6) in the formula [2], the reflectance is sequentially obtained using the formula [3], and finally Get the expression.

[0038]

[Equation 4]

Each reflection film having such a reflectance may be designed for a desired wavelength and incident angle, and may be formed through a film forming process on a parallel plate. For that purpose, masking and reflection coating operations are required. It can be implemented in a relatively inexpensive way as it only needs to be repeated. Regarding the thickness of the parallel plate, the interval between the multiple reflection lights should be set sufficiently with respect to the incident beam diameter.

When a plurality of lasers are used without depending on the equal intensity division of the beam as described above (for example, when it is desired to realize a high output laser in a laser display etc. in response to a request for high brightness). To achieve this, it is necessary to combine the beams from the lasers in a compact and efficient manner. Further, the use of a plurality of lasers is effective because each laser light has an incoherent relationship, which leads to a reduction in the contrast of the speckle noise described above.

[0041]

By the way, what is required of an illuminating device using a laser as a light source is that the uniformity of illumination is high, parallel light can be obtained, and there is no speckle noise (or it is inconspicuous). However, in the case of conventional lighting devices, among these items,
In particular, there is a problem in that a sufficiently satisfactory characteristic with respect to uniformity cannot be obtained, or the burden of labor required for obtaining a desired characteristic is large.

For example, in the above-mentioned method (A), if a laser beam is spatially combined, a gap (a low portion in the intensity distribution) is inevitably generated between the beams. It is difficult to divide a linear region by a large number of parallel lights and illuminate them simultaneously. Further, in the method (B), when an aspherical lens or the like is used, it can be understood from the fact that it is generally technically difficult to design, manufacture, and evaluate an aspherical cylindrical lens. Alternative technologies are needed.

If the uniformity is poor, it leads to a decrease in efficiency.
This may cause problems such as high brightness, and may bring about an adverse effect such that the display device or the like cannot have a sufficient dynamic range.

Therefore, an object of the present invention is to realize uniform intensity distribution in an illuminating device using light beams from a plurality of lasers.

[0045]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention divides a light beam from a plurality of lasers into a plurality of beams having equal intensities, and then uses birefringence to spatially divide the beams. It is configured such that a uniform light intensity distribution can be obtained by shifting the positions and overlapping them.

Therefore, according to the present invention, with respect to a plurality of divided beams having the same intensity, the beams are spatially shifted by using birefringence, and the beams having no coherence are superposed on each other. With this, it is possible to obtain illumination light having a uniform intensity distribution.

[0047]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to an optical configuration for using light rays from a plurality of lasers and obtaining illumination light having a uniform light intensity distribution. For example, in application to an image display device, a front projection (front projection) type laser display, a rear projection (rear projection) type laser display, and the like are listed.
In addition, it can be widely used for an image device including printing or recording, such as a laser printer or a recording device for recording digital image data on a movie film. Of course, it is possible to contribute to the improvement of accuracy and the like by applying it when uniform illumination light is required in applications such as processing such as laser fusion and laser annealing, and measurement.

The basic principle of the present invention will be described before describing the specific structure of the lighting apparatus according to the present invention.

First, it is assumed that light beams from a plurality of lasers are used. This is effective not only for high brightness but also for reduction of speckle noise. In addition, it is preferable that the laser beams are matched so that they have almost the same intensity.

Then, it is a basic matter to have a means for splitting into a plurality of beams having the same intensity, and after splitting, the beams are spatially shifted using one or a plurality of times of birefringence and then overlapped. is there. That is, with respect to a plurality of parallel beams, the beams are spatially shifted by utilizing birefringence and intensity-divided so that adjacent coherent beams spatially overlap with each other. By that,
A uniform intensity distribution can be generated. Uniform illumination can be performed by irradiating a linear region such as GLV with such illumination light, but it is not limited to one-dimensional illumination (linear illumination) and can be applied to two-dimensional uniform illumination. Is.

Regarding the homogenizing method by superimposing beams, it is necessary to consider the conditions required for superimposing. In the following description, a Gaussian beam is mainly assumed, but it is needless to say that the following idea can be applied to laser light having a more general intensity distribution.

FIGS. 1 and 2 show examples of the intensity distribution when a plurality of incoherent Gaussian beams having the same intensity are spatially juxtaposed.

In these figures, the Gaussian beam
Beam radius (e at peak intensity) ^-2When
value. Between the center of each beam when) is set to "1"
When changing the distance (this is referred to as "S")
The horizontal axis shows the relative coordinates in the beam arrangement direction.
(Beam radius is "1".)
I am taking a degree.

In FIG. 1, from the state where the beam center interval is S = 2, S = 1.5, S = 1.4, S = 1.3, S = 1.
It shows the degree of overlap in the case of gradually narrowing. In this figure, the sum of the intensities of the nine beams is shown by a solid line, and the intensities of the individual beams are shown by a broken line to distinguish the distributions of the two.

Further, in FIG. 2, the beam center interval is S =
It shows the situation when the state is gradually narrowed from the state of 2 to the state of S = 1 in 0.2 steps, and the graph curve (intensity distribution curve) of each state is shown together. is there.

As can be seen from the figure, the total intensity distribution is made uniform by the superposition of the beams.
When the value is 1.5 or more, the nonuniformity of the intensity becomes gradually noticeable between the beams. That is, there is a tendency that the difference between peaks and valleys in the intensity distribution increases as the S value increases.

Further, when the S value is small, the uniformity in the central portion is improved. However, as the S value becomes smaller,
The width of the uniform portion (width in the horizontal axis direction of the graphs shown in FIGS. 1 and 2) tends to be relatively narrow, and therefore, in the distribution curve indicating the strength sum, the strength of the skirt portion is relatively small. It can be seen that it increases (because the width of the uniform portion becomes narrower, the proportion of the bottom portion becomes relatively larger). Since what is actually used is mainly a uniform portion in the intensity distribution, if the S value is too small, it may cause a decrease in light utilization efficiency.

From the above consideration, it is understood that the S value with respect to the beam radius is practically desirable in the range of about 1 to 1.5. It should be noted that S = 1 and S = 1.5 are tentative values for beam superposition, and therefore, in practice, values near them may be used.

Further, for illumination applications such as laser displays, for example, non-uniformity of intensity distribution due to interference is not desirable. Therefore, within an S value range of about 1 to 1.5, three adjacent left and right lines are provided. It is desirable to prevent interference between the beams. For example, the center distances of the coherent beams among the plurality of beams are all set to be 5 times or more the radius of the Gaussian beam (corresponding to the beam width of four peaks) and separated.

In the illumination optical system according to GLV, since the illumination area is limited to the linear area on the GLV, it is impossible to spatially shift the beams and superimpose them by scanning as in the method (A). Therefore, for example, the following matters are required for the right and left three beams (a total of seven beams including oneself) centering on a certain beam and adjacent to the beam.

(I) Use of orthogonal polarization states (linear polarization) or right-handed and left-handed circularly polarized beams (II) Use beams from different lasers (beams of different origins) (III) A combination of (I) and (II).

As a result, it is possible to prevent interference between the beams.

In addition, there is a problem of speckle in application to a laser display and the like, and also in reducing the contrast of speckle, the above (I) to (III)
Is effective. That is, by overlapping different laser beams and orthogonally polarized beams, different speckle patterns can be averaged to reduce the speckle contrast. In that case, since it is necessary to make beams having no coherence to overlap each other as much as possible, for example, as described above, incoherence of seven adjacent beams is not only uniform, It is also necessary to reduce speckle contrast.

It should be noted that it is preferable to use a plurality of beams as much as possible for higher brightness, but in order to reduce the speckle contrast as much as possible, these beams are intensity distribution conversion system (in the present invention, the intensity distribution is made uniform. It is desirable to combine the light before it enters the optical system). That is, if the combined beam is regarded as one beam, it is possible to consider the homogenization of the intensity distribution in the same manner as described above. For example, in application to a laser display or the like, an illumination area is used. It is desirable to have as many incoherent beams as possible superimposed on every point in.

Based on the above matters, a concrete example of the beam configuration is as follows.

For example, p-polarized light, s for beams from two different lasers (first laser, second laser)
In the form assuming polarization (in the case of (III) above, utilizing light from different lasers and different polarization),
When the Nth beam is p-polarized by the first laser, the following is obtained.

N + 4th beam = p polarization from the first laserN + 3rd beam = s polarization from the second laserN + 2nd beam = s polarization from the first laserN + 1th beam = second P-polarized light from laser-N-1st beam = p-polarized light from second laser-N-2nd beam = s-polarized light from first laser-N-3rd beam = s-polarized light from second laser N-4th beam = p-polarized from the first laser.

In this arrangement, p-polarized light by the first laser, which is the N-th beam, is the center, and "N
+1 ”th beams are adjacent to each other, and N + 2 to N +
Each of the fourth beams is located, and on the opposite side thereof, the "N-1" th beam is adjacent to the Nth beam, and each of the N-2 to N-4th beams. Is located. Therefore, it can be seen that the three adjacent beams (N + 1 to N + 3, N-1 to N-3) of the Nth beam do not interfere with the central beam (Nth beam). The N-4th beam and the N + 4th beam may interfere with the central beam, but if the beams are spatially separated from each other and the beams are substantially separated from each other, the interference is reduced. The impact is minor.

The arrangement of the beam groups as described above, that is, the arrangement of a plurality of beams obtained after the birefringence has a spatial periodicity, and the incoherent relationship between two beams having a coherent relationship. By arranging a plurality of beams each having a center beam, and by arranging the center beam so that the beams within one cycle adjacent to the center beam do not interfere with the center beam, uniform and high efficiency and a speckle contrast can be obtained. It is possible to configure an illumination optical system that is sufficiently suppressed.

The above-mentioned beam configuration is only an example, and the relationship between adjacent beams may change depending on the distance between incident beams and the amount of birefringence of the crystal. The form is possible. That is,
Basically, a configuration is used in which three adjacent beams are arranged in parallel by using polarized light beams having the orthogonal relationship from the same laser and one set of polarized light beams (polarized light having the orthogonal relationship) from different lasers. Good. In the above example, a periodic arrangement is adopted in which the interval between the Nth beam (center beam) and the N + 4th or N-4th beam is repeated as one cycle, and the center beam and another beam immediately adjacent to the center beam are arranged. One unit of a beam group constituted by p-polarized light from a laser, s-polarized light from the same laser as the central beam, and s-polarized light from another laser is used. Regarding one cycle of the beam arrangement, it is needless to say that the beam groups of various arrangements can be used (for example, three beam arrangements adjacent to the left side or the right side, or a certain beam itself and adjacent to the left side or the right side thereof). The beams are appropriately exchanged for a total of four beam arrangements including the three beams to be used.). In short, it is important to arrange a certain number of beams centered around a certain beam so that interference with the beam at the center does not occur as much as possible, and that speckle contrast is reduced and uniform illumination is possible. Is.

Further, by using a larger number of lasers, for example, the number of beams, which is one unit of intensity division by a parallel plate or the like, may be increased. Are preferably overlapped as much as possible.

Next, in the illumination optical system according to GLV,
Points to note regarding schlieren filtering are explained. In this optical system (see FIG. 13), in order to perform Schlieren filtering, it is necessary to pay sufficient attention to the angle of the ray after the intensity distribution conversion, and in order to obtain a sufficiently high contrast after Schlieren filtering, it is necessary to use GLV. It is practically desirable to make the incident angle of ± 0.3 degrees or less.

For example, considering the structure shown in FIG. 3, an LD (laser diode) as a semiconductor laser array is used.
The light beam emitted from the array (or LD array bar) 1 is collimated by using the microlens array 2, and thereafter, the light is emitted to the GLV 5 through the birefringent crystal 3 and then the cylindrical lens 4. The LD array 1 has a large number of emitters (emission sources or radiation sources) arranged in a line on the same substrate. In the lower part of the figure, the intensity distribution of each beam (assuming a Gaussian beam) after being emitted from each emitter and passing through the microlens array 2 (see the broken line position in the figure),
Distribution immediately after passing through the birefringent crystal 3 (distribution at the position of the broken line in the figure, the distribution curve shown by the solid line shows the intensity distribution for p-polarized light, and the distribution curve shown by the alternate long and short dash line shows the intensity distribution for s-polarized light. , And the intensity distribution on the irradiation surface (linear region) of GLV5 is conceptually shown.

Since the light rays from the respective emitters of the LD array 1 are incoherent to each other, the light rays collimated by the microlens array 2 are used in the vertical direction (orthogonal to the optical axis) of the figure by using the birefringent crystal 3. The intensity distribution can be made uniform to some extent only by shifting them in the direction of (1) and overlapping them.

However, in applications such as laser displays using GLV, such a configuration is not sufficient when considering Schlieren filtering.

In order to increase the output of the LD array, the light emitting region of the LD array is required to have a size of several tens μm (microns) to several hundreds μm in the direction of the active layer. Here, the width of the light emitting region of the emitter is assumed to be 50 μm.
And The focal length of the micro lens array is 1.5 mm
(Mm), the light source after collimation has a size of ± 0.
It has a distribution width of about 95 °. Therefore, the configuration example as shown in FIG. 3 is unsuitable as an optical system for a GLV laser display from the viewpoint of contrast (in order to reduce the ray angle, the entire beam is expanded and the divergence angle is increased). I have to hold back.)

Further, in the configuration of FIG. 3, each point in the illuminated area is illuminated only by light rays from a small number of emitters (that is, when the target point of irradiation is specified, the number of emitters contributing to the brightness at that point). However, there is still a problem from the viewpoint of reducing speckle contrast.

Therefore, when an LD array is used, further improvement is required. For example, in order to suppress the incident angle to the GLV, the entire beam is sufficiently expanded and the divergence angle is made small before the light is condensed by the birefringent crystal 3 and the cylindrical lens 4. In the case of the numerical example described above, the beam may be expanded four times in order to make the angular magnification about ¼. Also, to reduce the speckle contrast,
As will be described later, a plurality of LDs are arranged in a direction perpendicular to the plane of FIG.
It is necessary to arrange the arrays side by side, or to use a plurality of LD arrays so as to obtain one beam by polarization coupling.

Next, a concrete means (optical means) for obtaining the above-mentioned configuration of the beam group will be described.

As described above, the methods for dividing the light intensity include (1) a method using polarized light and (2) a method using multiple reflection. Therefore, a method combining both methods will be shown below.

In the configuration example 6 shown in FIG. 4, one incident beam “lb” is emitted from the laser light source (not shown) as the multiple reflection plate 7.
(The configuration is as described in FIG. 17.)
After being divided into six beams of equal intensity by, the beam is further transmitted through the λ / 2 wave plate 8 and further transmitted through the birefringent crystal 9 to be output.

That is, the incident beam to the present optical system is assumed to be parallel light sufficiently collimated in consideration of the above-mentioned schlieren filtering, and the parallel light (laser light) is reflected by the multiple reflection plate 7. Is divided into a plurality of parallel beams (in the figure, an example of a beam group consisting of six beams is shown). Then, the beam group is further incident on the birefringent crystal 9 as linearly polarized light having an appropriate orientation by the λ / 2 wavelength plate 8, where it is divided into two orthogonal polarized lights and emitted. Therefore, as shown in the drawing, adjacent beams (for example, the light beam "lt_
Since "p" and "lt_s") are polarized in a mutually orthogonal relationship, they do not interfere with each other. However, every other beam (for example, the ray “lt_p
1 ”and“ lt_p2 ”) have the same polarization state, and therefore interference between the beams results in a non-uniform intensity distribution.

As described above, in order to make the intensity distribution uniform in the case of assuming a Gaussian beam, at least a shift amount for overlapping three adjacent beams without interference (see FIG. 1 and FIG. 2). It is a shift amount in the horizontal axis direction and corresponds to the S value).

Therefore, as shown in FIG. 5, light beams from a plurality of lasers are made to enter a multi-reflecting plate to be equally divided into a plurality of beams, and these beams further include a birefringent crystal. A structure is adopted in which the optical system is shifted and then superposed.

That is, in this example, two light beams from different lasers (in FIG. 5, marked with "" and "") are used, and each light beam is reflected by the multiple reflection plate 7. After being divided, after passing through the λ / 2 wave plate 8, the light passing through the birefringent crystal 9 becomes p-polarized light or s-polarized light. 2), and the birefringent crystal 9 shifts the light into p-polarized light and s-polarized light so that 2 × 6 × 2 = 24 beams can be obtained. When the emitted lights are arranged in order from the top of FIG. 6, for example, “p, p, s, s”
("," Indicates the respective laser light derived from
“P” indicates p-polarized light, and “s” indicates s-polarized light. It can be seen that the beam arrangement with (1) as one cycle is repeated.
Therefore, for example, if the beam of "p" is set at the center position, "s" or "
A "p" beam comes in, and on both sides (second adjacent area)
The beam of "s" is located. Further, since the beam of "p" or "s" is further located on both sides (third adjacent area), the beam concerned and the three beams adjacent to both sides thereof with respect to the central beam (p). It is clear that it does not interfere.

As described above, in FIG. 5, the three adjacent right and left beams are orthogonal to the rays from different lasers.
An example of a configuration realized by a combination of polarized lights is shown (the same arrangement as the beam arrangement shown in the above range N to N-4 is periodically repeated), and a certain beam is concerned. Therefore, the beams do not interfere with each other in a range within a predetermined number of beams, and the beams can be overlapped in the range.

As described above, regarding the intensity division by polarization, the intensity division by multiple reflection, and the use of light from a plurality of lasers, it must be noted in the combination thereof whether a gap is generated between beams. It is not. That is, even if only the multiple reflection plate is used, a gap is inevitably generated between the plurality of beams generated by this, so it is necessary to use birefringence in order to densely arrange the beams spatially. Is. Further, when beams from a plurality of lasers are used, it is necessary to polarize and combine the laser beams to fill the gap.

Further, in order to efficiently make the intensity distribution uniform, a large number of beams are required as described above. However, if the purpose is to increase the number of beams, it is more cost effective to use multiple reflection. Also, the degree of freedom in design is high.
That is, separation by birefringence is limited to separation into two orthogonal polarizations, but of course, it is also possible to use a plurality of Savart plates and arrange them in multiple stages.

FIG. 6 shows the Savart plate in multiple stages (two in this example).
10 shows a configuration example 10 arranged in a tier), in which two laser beams are transmitted through the λ / 2 wave plate 11 and the Savart plate 12, and then further transmitted through the λ / 2 wave plate 13 and the Savart plate 14. Then they are overlaid. In the lower part of the figure, the polarization state (polarization direction) at the position indicated by the broken line is indicated by a double-headed arrow (only one of the laser beams is shown).
The light deflected through the λ / 2 wave plate 11 is shifted and separated into two orthogonal polarizations by the Savart plate 12, and further, these are polarized by passing through the λ / 2 wave plate 13 before being orthogonalized by the Savart plate 14. Since it is shift-separated into two polarized lights of 4 beams, 4 beams can be obtained for each beam.

In this example, among the beams emitted from the Savart plate 14, those originating from the first laser light are distinguished by "", those originating from the second laser light are distinguished by "", and p-polarized When s-polarized light is distinguished by “p” and “s”, for example, “p, s,
It can be seen that the beam arrangement for "p, s" is repeated (therefore, there is a relationship in which three beams adjacent to a certain beam as the center do not interfere with the central beam).

However, the increase in the thickness and number of Savart plates is
Since it is not so attractive from a practical point of view, a configuration that combines multiple reflection and birefringence as shown in FIG. 5 is considered to be the most effective means for practical use. Of course, in the case where higher output is required, in addition to this, use of a plurality of laser beams including polarization multiplexing is still effective.

For example, FIG. 7 shows a constitutional example 15 of the illuminating device in the case of using two or more lasers in order to increase the brightness (note that the multireflecting plate 7 and the subsequent constitutions are birefringent. Cylindrical lens 1 after crystal 9
9, except that GLV20 is placed,
The configuration is the same as that of FIG. ).

In this example, the light lb1 from the first laser is used.
And the light lb2 from the second laser is applied to the apex angle portion of the prism mirror 18 via the polarization beam splitter (PBS) 16, and the light whose optical path is changed by the reflection on the mirror is incident on the multiple reflection plate 7. To be done. Also, the light lb3 from the third laser and the light lb from the fourth laser
4 is irradiated onto the prism mirror 18 via the polarization beam splitter (PBS) 17, and the light whose optical path is changed by the mirror is incident on the multiple reflection plate 7. Therefore, in the relationship with FIG. 5, one of the prism mirrors 18 corresponds to the beam of and the other corresponds to the beam of.

Beams may be combined (before being incident on the intensity distribution conversion system) by using polarization combining by such a polarization beam splitter, combining by a mirror, or the like. Of course, after combining light beams from three or more different lasers, the beams may be incident on the multiple reflection plate as in the above case, but in that case, incoherent light beams should be overlapped with each other. Therefore, in order to reduce the speckle contrast, it is desirable to perform multiple reflection and further division by birefringence after the beams are combined in the same manner as in the configuration of FIG.

In FIG. 7, for convenience of explanation, it is assumed that two or more lasers are arranged on the same plane.
Various forms are possible in which a plurality of lasers are arranged side by side in a direction perpendicular to the plane of the drawing. In addition, in FIG.
In order to illuminate the GLV 20 (the linear region thereof), the light after passing through the birefringent crystal is condensed using the cylindrical lens 19 in the preceding stage. And, combining means such as a beam splitter can be appropriately combined and used.

The laser light source used in the present invention is not limited to a specific one, and various lasers can be envisioned. However, when a laser light having a Gaussian distribution is kept in mind, for example, a solid laser, A fiber laser or a laser utilizing its wavelength conversion can be used. In particular, when using a fiber laser, the output power is compact and the V-groove array formed on the substrate (silicon substrate or the like) can be used to passively align the emitting end (that is,
Since the relative positional relationship of each beam can be set), it is suitable as the laser light source of the present invention.

Further, there are a mode in which a plurality of lasers are individually arranged in parallel and a mode in which a plurality of laser beams are obtained like a semiconductor laser array. In the latter case,
For example, the use of an LD array collimated by a microlens array may be used. In this case, it is desirable that the intensity of each emitter of the semiconductor laser has a Gaussian distribution. In the case of an emitter in a broad area (the width of the light emitting region is set to several tens to several hundreds of μm), the non-uniformity due to the multimode intensity distribution and the spread of light rays at the time of multiple reflection poses a problem. Therefore, it is necessary to make a correction (for example, by appropriately setting the reflectance of each coating region in the multiple reflection plate to make correction). Therefore, although designing and manufacturing become complicated accordingly, averaging itself by superimposing the beams described above is a generally accepted principle, so that a distribution outside the Gaussian distribution (for example, the distribution function is “exp (−x ^k ) ”(k ≠ 2)
In the case of), or to the use of a light source having an irregular intensity distribution, it can be expected to work to some extent. Further, when a large number of lasers are used in a parallel arrangement, the effect of averaging between individuals can also be obtained, so that the sum of intensities of all lasers is within a range that is practically or practically acceptable. You don't have to stick to the Gaussian distribution.

[0098]

EXAMPLES Next, specific examples will be described.

First, eight lasers of the second harmonic (wavelength 532 nm) of the YAG laser were used, the outputs of the lasers were all equal, and the beam diameter (diameter) was 1 mm.
And The light from the eight lasers is polarized and combined, and when two laser lights are combined into one, four beams can be obtained. Therefore, as shown in the configuration of FIG. 7, the first to fourth beams lb1 to lb4 may be arranged in the same plane, but here, of the four beams,
Two of them (hereinafter referred to as "beam 3" and "beam 4") are arranged so as to be irradiated from a direction perpendicular to the paper surface of FIG. FIG. 7 shows the remaining two beams (hereinafter referred to as “beam 1” and “beam 2”).
As in the above, the layout should be within the page.

In the following, only the beams 1 and 2 will be described for simplification of the description (∵ the basic contents are the same even if the beams 3 and 4 are appropriately replaced in the following description). .).

When utilizing birefringence, a Savart plate is used so that the center distance between the beams after exiting the Savart plate is 1.3 mm (S = 1.
This corresponds to the case of 3. ), Design for a combination of multiple reflectors and Savart plates.

Regarding the beam group after being emitted from the Savart plate, the ordinary ray of the beam 1, the extraordinary ray of the beam 1, and the ordinary ray of the beam 2 are arranged so that the thickness of the Savart plate can be reduced to reduce the cost. Rays and extraordinary rays of beam 2 are arranged in this order.

First, the beam 1 and the beam 2 are adjusted to have a parallel relationship with a beam interval of 2.6 mm after being reflected by the prism mirror 18. Since each beam diameter is 1 mm, the loss on the apex angle side of the prism mirror can be sufficiently suppressed even if chamfering near the apex angle is included.

If calcite is used as the Savart plate, the thickness for obtaining the polarization separation amount of 1.3 mm can be calculated from the above [Formula 1], and about 11.3 mm is obtained. The optical axis of the Savart plate is assumed to be inclined by 45 ° with respect to the normal to the incident surface.

Next, moving to the design of a multiple reflection plate, each beam emitted after reflection inside the reflection plate is shifted with a beam interval d = 5.2 mm (= 1.3 mm × 4). There is a need. When the thickness of the base plate forming the parallel plate is “t” and the refractive index is “n”, Snell's law and a simple geometrical relation give the following formula.

[0106]

[Equation 5]

FIG. 8 shows a main part of deriving the above equation, where "a" indicates the incident angle and "b" indicates the refraction angle. The second equation of the above equation is obtained because the length of the line segment connecting the points P1 and P2 in the figure multiplied by cosa is equal to d.

When the above equations are combined and solved for t, the following equation is obtained.

[0109]

[Equation 6]

Incidentally, FIG. 9 shows an example of the relation of the [Equation 6], in which the incident angle "a" (unit: degr
ee (°)) and the vertical axis represents the thickness “t” (unit: mm) to show the relationship between the two.

As a base material, BK7 (n = 1.519
47) and the thickness t = 10 mm,
It can be seen from the numerical calculation that the incident angle a should be approximately 24.7 ° (see FIG. 9). The refraction angle at this time is b≈1.
5.96 °. Although there is an error in the actual substrate thickness, this can be compensated by adjusting the incident angle of light to the substrate.

In consideration of the above geometrical relationships, in order to finally obtain six beams of equal intensity, each region of the multiple reflection plate may be subjected to a reflection coating treatment as shown in FIG. That is, for the incident surface side shown on the left side of the figure,
The light incident window W (width 5.7) is divided into two regions.
2 mm), its reflectance R ₀ = 0%, and the reflectance R of the total reflection surface (width 28.6 mm) R = 100%. The width of each region is set to 5.
70 mm, and with respect to each reflectance, R ₁ ≈83.3%, R _{2 as} calculated by the above [Formula 4].
= 80%, R ₃ = 75%, R ₄ ≈66.7%, R ₅ = 50
%, And R ₆ is 0%.

In FIG. 10, each region is formed with a gap of 0.04 mm (in the figure,
The gap is exaggerated. ).

In this example, the height (width) of the finally obtained illumination area is the beam interval × the number of beams = 5.2 mm.
X6 = 31.2 mm, which is long enough to illuminate the GLV.

FIG. 11 schematically shows an example of the intensity distribution of outgoing light.

The ordinary ray and the extraordinary ray of each of the beams 1 and 2 have a spatially shifted arrangement, and a curve (Gaussian distribution) showing their respective intensity distributions is shown in FIG. Differentiate by the difference.

The spacing between the peaks of adjacent beams is 1.3 mm, and the spacing between the peaks of the same type is 5.2 mm (= 1.3 mm ×).
4).

FIG. 12 shows an outline of the configuration of an application example 21 to an image display device using GLV.

The light from the laser light source 22 is an intensity distribution conversion system 23 described above (an optical system including a multi-reflecting plate, a birefringent crystal and the like, which is shown as a single lens as a representative in the figure). .), And the spatial modulator 24
(Eg GLV). The light diffracted by the spatial modulator is the lens 25 and the Schlieren filter 2
6. After passing through the lens 27, the light passes through the projection lens system 28, reaches the galvanometer mirror 29, and further reaches the screen 30. Illustration and description of the drive control means such as the GLV and the galvanometer mirror are omitted.

In the above description, each beam is considered to be a beam by polarization multiplexing, but for the polarization-multiplexed beam, the reflectances of the entire area of the multiple reflection plate are p-polarized and s-polarized. If they are not equal to each other, a beam of equal intensity cannot be emitted. In general, the larger the incident angle, the greater the polarization dependency with respect to the accuracy required for the coating. Therefore, it is desirable to make the incident angle to the multiple reflection plate as small as possible. However, as can be seen from the graph curve shown in FIG. 9, when the incident angle (a) is made smaller, the board thickness (t) of the base becomes thicker. Therefore, it is necessary to seek a compromise between the two and set the incident angle within a range that does not hinder practical use. On the other hand, it should be noted that the smaller the incident angle, the narrower the width of each region (reflection region). In reality, since it is necessary to allow some margin between the regions, the incident angle cannot be made too small. To increase the distance between the incident surface and the reflective surface,
Instead of applying reflective coating on both sides of a parallel plate, it is possible to use separate bases for each side to create separate structures and adjust each member, but for accuracy Considering the circumstances such as the need for adjustment and the increase in the number of parts, polarization multiplexing is avoided as much as possible, and for example, a large number of beams with the same polarization state are arranged in parallel along the direction perpendicular to the paper surface of FIG. Arrangement method is desirable.

Further, from the viewpoint of miniaturization, there may be mentioned a configuration in which coating is applied to both sides of the birefringent crystal, but multiple reflection in the birefringent crystal is complicated and difficult to design. In consideration of the moisture resistance and temperature resistance of the crystal, it is difficult to perform coating a plurality of times, and it is not very practical.

In the above embodiment, all the beams used are harmonics (S
Since it is the second harmonic due to HG), sufficient collimation is possible. In other words, all the beams can be made parallel to each other (the degree of parallelism is high).
It is possible to obtain good characteristics even in the contrast after the schlieren filtering according to the above.

When a plurality of lasers are used and the outputs of the lasers greatly differ, the intensity distribution becomes nonuniform after all the beams are combined. Therefore, in order to correct this, for example, the output of each laser can be electrically adjusted by itself, or a means for adjusting the intensity is provided outside each laser, for example, It is desirable to take measures to adjust the intensity of laser transmitted light. Examples of such output adjusting means provided outside include a mode in which a half-wave plate and a polarizer are combined when the laser light is linearly polarized light.

In the above description, a case has been described in which a one-dimensional spatial modulator such as GLV is assumed and uniform illumination is performed on a linear region, but a two-dimensional spatial modulator or the like is described. The present invention can also be applied to lighting. That is, in addition to the multiple reflection plate provided for one-dimensional illumination, another multiple reflection plate may be used so that multiple reflection is performed even in the direction perpendicular to the paper surface of FIGS. 5 and 7. For example, extension to two dimensions is easy (beams can be superposed with a planar spread). Of course, this is the same even if it expands two-dimensionally by using another Savart plate whose orientation is changed.

According to the above arrangement, however, uniform illumination in which speckle noise and interference noise are sufficiently suppressed can be realized with high efficiency by using two or more lasers. Moreover, since the structure is relatively simple, it is suitable for downsizing of the device and cost reduction. For example, by applying the above-mentioned illumination device to an image display device, a laser display or the like capable of displaying a high-quality image with excellent color reproducibility can be realized.

[0126]

As is apparent from the above description, according to the inventions according to claims 1 and 7, each beam is spatially divided by using birefringence with respect to the divided beams of equal intensity. By displacing the beams without coherence and superimposing the beams having no coherence, it is possible to obtain illumination light with excellent uniformity, so that it is possible to improve efficiency and reduce speckle. Since a relatively simple structure that does not require an aspherical cylindrical lens or the like is sufficient, it is suitable for downsizing and cost reduction.

According to the inventions of claims 2 and 8,
By using the multiple reflection plate, the number of beam divisions can be increased, which is also advantageous in terms of cost reduction.

According to the inventions of claims 3 and 4,
The group of beams can be spatially arranged regularly, and by arranging the beam at the center position so as not to interfere with another beam adjacent to it, homogenization and reduction of speckle contrast can be achieved. Is effective for. In particular, by using lights from different lasers and lights with different polarization states, various beam arrangements can be adopted, so that the degree of freedom in design is high.

According to the fifth aspect of the invention, the light collimated by the microlens array can be used after the light is emitted from the semiconductor laser array, and a compact and simple structure can be obtained.

According to the invention of claim 6, by appropriately setting the relationship between the beam radius and the center interval of the beams, non-uniformity of intensity does not occur between the beams, and after the superposition, It is possible to prevent the width of the uniform portion in the intensity distribution of 1 from being too narrow.

According to the ninth and tenth aspects of the present invention, when applied to an image display device using a GLV, it is possible to realize high brightness and improvement of contrast and image quality. Are suitable.

[Brief description of drawings]

FIG. 1 is an explanatory view of an intensity distribution obtained by overlapping Gaussian beams together with FIG. 2, and this figure shows a beam radius of 2 times, 1.5 times, and 1.4 times.
The case where the beam center intervals are 1 times, 1.3 times, and 1 time will be described.

FIG. 2 is a beam radius of 2 to 1 times 0.2.
It is a figure shown about the case where a beam center space | interval is changed in steps.

FIG. 3 is an explanatory diagram of a configuration using a semiconductor laser array and a microlens array.

FIG. 4 shows an example of the configuration of an intensity distribution conversion optical system using a multiple reflection plate and a birefringent crystal together with FIG. 5, and this figure shows the case where the number of beams is one.

FIG. 5 is a diagram showing an example when the number of beams is two.

FIG. 6 is a diagram showing an example in which the Savart plate has a multi-stage configuration.

FIG. 7 is a diagram illustrating a configuration example of a lighting device.

8 is a diagram for explaining a design example of a multiple reflection plate together with FIGS. 9 and 10, and this diagram is an explanatory diagram showing a geometrical-optical relationship regarding specifications. FIG.

FIG. 9 is a graph illustrating the relationship between the incident angle and the substrate thickness.

FIG. 10 is a diagram for explaining the reflectance of each part of the multiple reflection plate.

FIG. 11 is a diagram for explaining the intensity distribution of emitted light.

FIG. 12 is a diagram schematically showing a configuration example of an image display device.

13 is a diagram for explaining the Schlieren filter optical system together with FIG. 14, and this diagram is a perspective view schematically showing the optical system.

FIG. 14 is an explanatory diagram showing a main part of an optical system.

FIG. 15 is a diagram for explaining a homogenizing method by beam scanning.

FIG. 16 is a diagram for explaining an intensity division method using polarized light.

FIG. 17 is a diagram for explaining an intensity division method by multiple reflection.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser array, 2 ... Microlens array, 3, 9, 12, 14 ... Birefringent crystal, 5, 20 ... Grating light valve, 7 ... Multiple reflection plate, 15 ... Illumination device, 21 ... Image display device, 24 ... Spatial modulator

Claims (10)

[Claims] 1. An illumination device using a plurality of beams, which is configured to obtain a uniform intensity distribution by using the beams from a plurality of lasers, wherein the light beams from the plurality of lasers have the same intensity. An illumination device using a plurality of beams, characterized by dividing the beams into a plurality of beams, spatially shifting the beams using birefringence, and superimposing the beams. 2. A lighting device using a plurality of beams according to claim 1, wherein light beams from a plurality of lasers are divided into a plurality of beams by a multiple reflection plate, and the beams are birefringent crystal. An illuminating device using a plurality of beams, wherein the illuminating device is configured to pass through an optical system including a laser beam and superposed on each other. 3. An illuminator using a plurality of beams according to claim 1, wherein the plurality of beam arrangements obtained after birefringence have spatial periodicity and are between two beams having a coherent relationship. , A plurality of beams having an incoherent relationship are arranged, and a beam centered on a certain beam and adjacent to the beam within one period is arranged so as not to interfere with the beam at the center. Lighting device using a beam. 4. The illumination device using a plurality of beams according to claim 3, wherein the plurality of beams forming one cycle are lights from different lasers and have different polarization states. A lighting device using a plurality of beams. 5. The illumination device using a plurality of beams according to claim 1, wherein a semiconductor laser array and a microlens array are used as a laser light source. 6. The illumination device using a plurality of beams according to claim 1, wherein the intensity distribution of each of the incident beams has a Gaussian distribution, and the beams finally arranged in parallel are adjacent to each other. An illuminating device using a plurality of beams, characterized in that the center interval of the beams is defined in a range of approximately 1 to 1.5 times the Gaussian beam radius. 7. An illumination device configured to obtain a uniform intensity distribution using light beams from a plurality of lasers, and an image display device using a spatial modulator illuminated by the illumination device. The beam from the laser is split into multiple beams of equal intensity, then the beams are spatially offset using birefringence and then superposed, so that the homogenized light is applied to the spatial modulator. An image display device characterized by the above. 8. The image display device according to claim 7, wherein the light beams from the plurality of lasers are divided into a plurality of beams by a multiple reflection plate, and the beams are made into an optical system including a birefringent crystal. An image display device characterized in that it is passed through and then superposed. 9. The image display device according to claim 7, wherein a grating light valve is used as the spatial modulator. 10. The image display device according to claim 8, wherein a grating light valve is used as the spatial modulator.