JPH11337868A - Optical element, optical device, illumination device, image display device including the same, and exposure device - Google Patents

Abstract

(57) [Problem] To provide an optical element, an optical device, an illumination device, an image display device, and an exposure device for reducing spatial coherence or speckle. An inclined 45 degrees relative to the incident light optical axis, the first optical element (first beam splitter having a first plurality of half-mirror surface 4a to dispose in parallel and regular intervals d ₁ from each other A stack 4), a half-wave plate 5 for rotating the polarization direction of the reflected light on the first plurality of semi-transmissive mirror surfaces 4a by 90 degrees, and the reflected light on the first plurality of semi-transmissive mirror surfaces 4a Inclined at 45 degrees to the axis, parallel to each other and at a constant distance d
_{A second} optical element (second beam splitter stack 6) having a second plurality of semi-transmissive mirror surfaces 6a provided in 2
And the first and second plurality of semi-transmissive mirror surfaces 4a, 6a
Partial reflection and partial transmission of light incident on the mirror are sequentially performed, and branch light composed of a plurality of light beams having a constant optical path length difference is sequentially emitted from the second plurality of semi-transmissive mirror surfaces 6a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element, an optical device, an illuminating device, an image display device and an exposing device having the same, and more particularly, to spatial coherence or speckle of coherent light emitted from a coherent light source. TECHNICAL FIELD The present invention relates to an optical element, an optical device, an illuminating device, an image display device including the same, and an exposing device which reduce the amount of light.

[0002]

2. Description of the Related Art As an apparatus having a coherent light source such as a semiconductor laser, for example, laser light of three colors of red, green and blue is intensity-modulated, and the intensity-modulated laser light is horizontally and vertically projected on a screen. A scanning type image display device that displays an image such as a television image by scanning the image, a device that irradiates an image display element such as a liquid crystal with a laser beam as an illumination light source and displays an image based on the projected image, or on a mask. There is an exposure apparatus for manufacturing a semiconductor device that projects and exposes the pattern on a semiconductor substrate. The coherent light source provided in these devices is used by utilizing features such as high monochromaticity of the emitted coherent light, but the coherent light having high coherence is scattered by a rough surface or an uneven medium. A problem peculiar to coherent light called speckle, which has an irregular intensity distribution, occurs, which is one of factors that hinder its application. Hereinafter, speckle, which is a problem unique to coherent light, will be described with reference to FIGS. 13 and 14 which are schematic power spectrum diagrams of coherent light.

In general, coherent light emitted from a coherent light source such as a semiconductor laser has a single mode power spectrum as shown in FIG. Coherence degree of this coherent light | g
(Τ) | is the Fourier transform G of the power spectrum
(Τ) is given as | g (τ) | = | G (τ) / G (0) |, as shown in FIG. For example, as shown in FIG. 13, _assuming that the full width at half maximum of the power spectrum is ν _s , the full width at half maximum τ _s of the coherence degree depends on the function form of the power spectrum, but is approximately (τ _s 〜1 / ν _s ). Can be These τ _s and l _c = cτ _s (c is the speed of light in the medium through which the light propagates) are called the respective coherence times or coherence lengths. This is because when coherent light emitted from a coherent light source is branched into two and an optical path passing through one is made longer than the other optical path by l, the light is branched if l is equal to or smaller than l _c . 2
Light interfere with each other with great coherence,
If l is equal to or greater than l _c , it means that the two split lights have low coherence and no interference occurs.

When such a coherent light source is used, for example, in an image display device, on an image plane, for example, on a viewer's retina, contributions from an object plane, for example, points and areas of a screen are aggregated to form an image. Can be considered to form. Since the object surface generally has irregularities with a depth of about the wavelength or more, light beams having complicated phase relations overlap on the image surface. Therefore, if these light beams are coherent with each other, interference occurs, and a complex light and dark pattern, so-called speckle, occurs, which is one factor that significantly impairs the image quality of the image display device. In order to reduce this speckle, it is important to make these light beams incoherent with each other, and two reduction methods are conceivable.

The first reduction method is a method of making the power spectrum width of the coherent light emitted from the coherent light source sufficiently large, that is, making the coherence length sufficiently small. However, this method is not preferable because the property of high monochromaticity of coherent light is lost.

A second reduction method is a method in which a coherent light source having a certain coherent length is branched into a plurality of light beams, and a light path length difference of at least about the coherent length is given to each other, and then they are merged or arranged again. According to this reduction method, non-coherence occurs between the light beams. Therefore, as the number of split light beams increases, the spatial coherence of the combined or arranged coherent light can be reduced. As a specific known example, bundling a plurality of optical fibers with both ends aligned, giving an optical path length difference longer than the coherence length of the coherent light source incident on the length of each optical fiber, and allowing coherent light to enter from one end There is a method in which coherent light beams emitted from the other ends are made incoherent with each other, and the spatial coherence of the entire light beam to be merged or arranged again is reduced.

However, the method of reducing speckles by bundling a plurality of optical fibers has the following problems. For example, when 31 optical fibers are bundled and the difference in length between them is 1 cm, the difference in length between the shortest optical fiber and the longest optical fiber is 30 cm.
For example, a large volume is required to accommodate a bundle of 31 optical fibers having both ends aligned, for example, in an image display device, which is a hindrance in downsizing the image display device. Further, since the aperture ratio of the bundle of 31 optical fibers having both ends aligned is 1 or less, a loss occurs when the incident coherent light is coupled to the optical fiber.

Japanese Unexamined Patent Publication (Kokai) No. 63-101815 proposes an illuminating device in which a large number of element mirrors are provided as a means for generating an optical path length difference. In this method, light is made to enter the element mirror group almost perpendicularly and is reflected almost perpendicularly, and both the incident light flux and the outgoing light flux are condensed by a lens, and their optical axes are slightly shifted, and only the reflected light is reflected. The optical axis is bent by 45 degrees by a mirror.
In this case, mirrors and lenses are required as optical elements as the minimum constituent elements, and highly accurate arrangement of these optical elements together with the element mirror group is required. Also,
The element mirror group has a configuration in which a large number of mirror surfaces are stacked, and its manufacture requires many man-hours.

By the way, no matter what kind of optical path length difference is used, since the coherence length of the coherent light emitted from the coherent light source having the single mode power spectrum is generally sufficiently long, sufficient spatial coherence can be obtained. There are limits to reduction. For example, when a semiconductor laser having a single mode power spectrum is used as a coherent light source for an image display device, a typical coherence length of the semiconductor laser is 1
m, and a large volume is required in order to generate such a difference in optical path length, which is an obstructive factor in reducing the size of the image display device.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical device, an optical device, an illuminating device, an image display device and an exposing device having the same, which reduce spatial coherence or speckle and are small. To provide.

[0011]

In order to solve the above-mentioned problems, in the optical element according to the first aspect of the present invention, the optical element is inclined at substantially 45 degrees with respect to the optical axis of the incident coherent light, and is arranged parallel to each other at a constant interval. It has a plurality of semi-transmissive mirror surfaces to be provided, sequentially performs partial reflection and partial transmission of coherent light incident on the plurality of semi-transparent mirror surfaces, and is composed of a plurality of light beams having a constant optical path length difference in sequence. Which is characterized by emitting branched light.

The optical element according to the second aspect of the present invention has a first plurality of semi-transmissive mirror surfaces which are inclined at substantially 45 degrees with respect to the optical axis of the incident coherent light, and which are arranged parallel to each other and at regular intervals. The first optical element and a second optical element that is inclined at an angle of about 45 degrees with respect to the optical axis of the reflected light of the incident coherent light on the first plurality of semi-transmissive mirror surfaces, and is disposed parallel to each other at a constant interval. A second optical element having a plurality of semi-transmissive mirror surfaces, and partially reflecting and partially coherent light incident on the first plurality of semi-transparent mirror surfaces and the second plurality of semi-transmissive mirror surfaces And transmission sequentially,
The second plurality of semi-transmissive mirror surfaces sequentially emit branched light composed of a plurality of surface-developed light beams having a constant optical path length difference.

[0013] In the optical element according to the third aspect of the present invention, the first plurality of optical elements are arranged at an angle of about 45 degrees with respect to the optical axis of the coherent light having linear polarization and arranged in parallel with each other and at a constant interval. 1 / rotates the polarization direction of incident coherent light reflected by the first plurality of semi-transmissive mirror surfaces by 90 degrees.
A two-wavelength plate and a second plurality of coherent light beams which are inclined at an angle of about 45 degrees with respect to the optical axis of reflected light of the incident coherent light beam on the first plurality of semi-transmissive mirror surfaces, and which are disposed parallel to each other and at regular intervals. And a second optical element having a semi-transmissive mirror surface, and partially reflecting and partially transmitting coherent light incident on the first plurality of semi-transparent mirror surfaces and the second plurality of semi-transmissive mirror surfaces. Are sequentially performed, and branch light composed of a plurality of surface-developed light beams having a constant optical path length difference is sequentially emitted from the second plurality of semi-transmissive mirror surfaces.

In the optical device according to the present invention, the coherent light source for emitting at least coherent light and the optical axis of the incident coherent light are disposed at an angle of approximately 45 degrees and parallel to each other at a constant interval. An optical element having a plurality of semi-transmissive mirror surfaces to perform partial reflection and partial transmission of incident coherent light sequentially on the plurality of semi-transparent mirror surfaces, and a plurality of optical elements each having a certain constant optical path length difference. And a branch light composed of the above light beams is emitted.

In the optical device according to the present invention, a coherent light source that emits at least coherent light and an optical axis of the incident coherent light are disposed at an angle of approximately 45 degrees and parallel to each other at a constant interval. First
A first optical element having a plurality of semi-transmissive mirror surfaces, and an optical axis of reflected light of the incident coherent light at the first plurality of semi-transmissive mirror surfaces, which is inclined substantially 45 degrees and parallel to each other and And a second optical element having a second plurality of semi-transmissive mirror surfaces disposed at regular intervals, and the light is incident on the first plurality of semi-transmissive mirror surfaces and the second plurality of semi-transmissive mirror surfaces. Partial reflection and partial transmission of coherent light are sequentially performed, and branch light composed of a plurality of surface-developed light beams having a constant optical path length difference is sequentially emitted from the second plurality of semi-transmissive mirror surfaces. It is characterized by.

In the optical device according to the ninth aspect of the present invention, the coherent light source for emitting coherent light having at least linearly polarized light and the optical axis of the incident coherent light are inclined approximately 45 degrees and are parallel and constant to each other. A first optical element having a first plurality of semi-transmissive mirror surfaces arranged at intervals, and a direction in which the polarization direction of incident coherent light reflected by the first plurality of semi-transmissive mirror surfaces is rotated by 90 degrees 1 A half-wave plate, and a second obliquely inclined at an angle of 45 degrees with respect to the optical axis of the reflected light of the incident coherent light on the first plurality of semi-transmissive mirror surfaces, and arranged in parallel and at a constant interval. A second optical element having a plurality of semi-transmissive mirror surfaces; a first plurality of semi-transmissive mirror surfaces;
A part of the coherent light incident on the plurality of semi-transmissive mirror surfaces is sequentially reflected and partially transmitted, and from the second plurality of semi-transmissive mirror surfaces, a plurality of luminous fluxes having a constant optical path length difference are sequentially developed on a plurality of surfaces. The branched light composed of the above is emitted.

In the illumination device according to the fifteenth aspect, a coherent light source for emitting at least coherent light;
An optical element having a plurality of semi-transmissive mirror surfaces that are arranged at an angle of approximately 45 degrees with respect to the optical axis of the incident coherent light and that are arranged parallel and at a constant interval to each other, and a fly-eye lens that is constituted by a plurality of element lenses And an optical integrator composed of a condenser lens and a partial constant reflection and partial transmission of coherent light incident on a plurality of semi-transmissive mirror surfaces. The optical system is characterized in that the N light fluxes transmitted through the optical integrator are transmitted, and the contrast of speckle on the irradiated surface emitted and emitted from the optical integrator is reduced to 1 / ^N1 / ² .

In the illumination device according to the sixteenth aspect, a coherent light source for emitting at least coherent light;
A first optical element having a first plurality of semi-transmissive mirror surfaces that are inclined at an angle of approximately 45 degrees with respect to the optical axis of the incident coherent light and are disposed parallel to each other and at a constant interval;
A second plurality of semi-transmissive mirror surfaces which are inclined approximately 45 degrees with respect to an optical axis of reflected light of the incident coherent light on the first plurality of semi-transmissive mirror surfaces, and which are arranged parallel to each other and at a constant interval. A second optical element having a first plurality of semi-transmissive mirror surfaces and a second plurality of optical integrators each including a fly-eye lens and a condenser lens each including a plurality of element lenses. N light beams having a constant difference in optical path length, which are generated by sequentially performing partial reflection and partial transmission of the coherent light incident on the semi-transmissive mirror surface, are transmitted through the optical integrator and emitted from the optical integrator. The contrast of the speckle on the irradiated surface to be irradiated is reduced to 1 / ^N1 / ² .

In the illumination device according to the seventeenth aspect, the coherent light source that emits coherent light having at least linearly polarized light and the optical axis of the incident coherent light are inclined approximately 45 degrees and are parallel and constant with each other. A first optical element having a first plurality of semi-transmissive mirror surfaces arranged at intervals, and a direction in which the polarization direction of incident coherent light reflected by the first plurality of semi-transmissive mirror surfaces is rotated by 90 degrees 1 A half-wave plate, and a second obliquely inclined at an angle of 45 degrees with respect to the optical axis of the reflected light of the incident coherent light on the first plurality of semi-transmissive mirror surfaces, and arranged in parallel and at a constant interval. Optical integrator including a second optical element having a plurality of semi-transmissive mirror surfaces, a fly-eye lens including a plurality of element lenses, and a condenser lens A constant optical path length generated by sequentially performing partial reflection and partial transmission of coherent light incident on the first plurality of semi-transmissive mirror surfaces and the second plurality of semi-transmissive mirror surfaces. The method is characterized in that N light beams having a difference are transmitted through an optical integrator, and the contrast of speckle on an irradiated surface emitted and emitted from the optical integrator is reduced to 1 / ^N1 / ² .

According to a twenty-third aspect of the present invention, there is provided an image display device including any one of the above-described illumination devices according to the fifteenth, sixteenth, and seventeenth aspects. Further, in the exposure apparatus according to the twenty-fourth aspect, the above-described fifteenth and one aspects are described.
It is characterized by comprising any one of the lighting devices according to the sixth and the 17th inventions.

The operation of the above means will be described below. According to the optical element and the optical device of the present invention, the incident coherent light is split into a plurality of light fluxes having substantially the same light intensity, and the split light fluxes sequentially have a constant optical path length difference. Thus, spatial coherence or speckle can be efficiently reduced. Also,
In the illumination device using the optical device of the present invention, since the light beam is split into N non-coherent light beams emitted from the optical device, the contrast of speckle can be reduced to approximately 1 / N ^1/2. it can. Further, the optical element of the present invention is smaller than a conventional optical element, for example, in which optical fibers are bundled, so that the optical device and the illuminating device can be reduced in size, and an image display device and an exposing device equipped with the illuminating device Can also be reduced in size. In the image display device of the present invention, it is possible to obtain a high-quality image by reducing the spatial coherence or speckle, and in the exposure device of the present invention, it is possible to perform high-quality exposure of a pattern on a mask. Become.

By the way, when the incident coherent light has a plurality of different wavelengths, for example, when a multi-mode semiconductor laser is used as the coherent light source, the following operation can be obtained. This will be described with reference to FIGS.

FIG. 1 is a schematic power spectrum diagram of a multi-mode laser beam. Each mode of the power spectrum is represented by c _0/2 , where L is the cavity length of the semiconductor laser.
They are arranged at regular intervals represented by nL (c ₀ is the speed of light in a vacuum, and n is the refractive index of the semiconductor laser medium). The coherence degree | g (t) | of such a multimode laser beam is as shown in the schematic power spectrum diagram shown in FIG. Therefore, in the case of multimode laser light, the maximum of the coherence degree appears periodically,
The full width at half maximum τ _t of each local maximum waveform is approximately τ _t １ ／ 1 / ν
_t (v _t is the full width at half maximum of the envelope of the power spectrum). τ _t is generally sufficiently smaller than the coherence time τ _s １ ／ 1 / ν _s when a single longitudinal mode of width ν _s stands. Also, since the coherence time τ _c is generally defined by the following equation 1, it can be said that τ _t is smaller than the coherence time.

[0024]

(Equation 1)

Therefore, when a semiconductor laser that emits multi-mode laser light is used as the coherent light source, it is not necessary to increase the optical path length difference to about τ _c , and the optical path length difference that avoids the maximum coherence degree is not required. Should be generated. That is, utilizing the periodicity of the coherence, the optical path length difference is calculated as c ((n−1) τ _d + τ _t /
2) or _{c (nτ d -τ t / 2} ) within the range (although, c is the light beam, n represents by the natural numbers), can be effectively reduced spatial coherence.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention can be applied to an optical element, an optical device, an illuminating device, an image display device and an exposure device having the same, which handle coherent light emitted from a coherent light source such as a semiconductor laser. .
Hereinafter, embodiments to which the present invention is applied will be described with reference to FIGS.

Embodiment 1 In this embodiment, a laser light source, which is a coherent light source, and a first optical element which emits a branched light composed of a plurality of light beams from the laser light emitted from the laser light source A half-wave plate that rotates the polarization direction of the split light composed of a plurality of light beams by 90 degrees, and a second optical element that emits a plurality of branched lights that are spread out from the split light composed of the plurality of light beams FIG. 3 is a schematic external perspective view of an optical device having a first beam splitter stack 4 and a second beam splitter stack, which are first optical elements, from the + x-axis direction in FIG.
A description will be given with reference to FIG. 4 which is a schematic plan view of the second beam splitter stack 6 which is the optical element of FIG.

The laser light emitted from the laser light source 2 is converted into a parallel light by the collimator lens 3 and is converted into the first parallel light.
To the first beam splitter stack 4 which is an optical element of the first embodiment. At this time, the incident laser light has linear polarization, and is arranged such that the vibration surface of the electric field is parallel to the z-axis shown in FIG. The first beam splitter stack 4 is approximately 4 ° with respect to the optical axis of the incident laser light.
Half-mirror surface 4a of s ₁ or to 5 degree inclined (in FIG. 3 5) is one that is juxtaposed on the optical axis at a predetermined interval length d _1.

First, the incident laser beam is partially reflected and partially transmitted by the s ₁ semi-transmissive mirror surface 4a of the first beam splitter stack 4 in order, and the light amount is substantially reduced. It is split into equal s ₁ light beams. Each of the optical axes of the light beams branched into s ₁ is bent by approximately 45 degrees in the + y direction. Next, the luminous flux bent at 45 ° + y-axis direction and branched into s ₁ light beams is １ ／ wavelength plate 5
Is transmitted, the polarization direction is rotated by 90 degrees (the electric field oscillates in the x-axis direction), and is incident on a second beam splitter stack 6 as a second optical element. In the second beam splitter stack 6, s ₂ (five in FIG. 3) semi-transmissive mirror surfaces 6a inclined at approximately 45 degrees with respect to the optical axis of the incident light are separated by a fixed interval d _2. They are arranged side by side on the optical axis, and their functions are almost equivalent to those of the first beam splitter stack 4. Next, the s ₁ branched light flux is subjected to partial reflection and partial transmission of the incident laser light sequentially by the s ₂ semi-transmissive mirror surfaces 6 a of the second beam splitter stack 6, and the light amount Are approximately equal (s ₁
× s ₂ ) light beams. That is, the luminous flux of _one laser beam emitted from the laser beam source 2 is (s ₁ × s
₂ ) It is possible to provide a small-sized optical element that splits the laser beam into laser beams and develops and emits them on the xy plane in the + z-axis direction, and sequentially from the second plurality of semi-transmissive mirror surfaces 6a. It is possible to emit a branched light composed of (s ₁ × s ₂ ) surface-developing light beams having a constant optical path length difference.

The first and second optical elements, ie, the first and second optical elements
For example, the laser beam emitted from the laser beam source 2 has a wavelength of 650 nm, and the semi-transmissive mirror surfaces 4a and 6a of the first and second beam splitter stacks 4 and 6 are manufactured. The case where the numbers s ₁ and s ₂ are 5 will be described with reference to FIGS. 5 and 6 which are schematic perspective views.

First, five first to fifth parallel glass substrates 7a, 7b, 7c, 7d, 7e having a refractive index n _s = 1.51 with respect to a wavelength of 650 nm of a laser beam are prepared. A 95 nm-thickness Si ₃ N ₄ film is formed on the surface of the first parallel glass substrate 7a bonded to the second parallel glass substrate 7b, and the second parallel glass substrate 7b is bonded to the third parallel glass substrate 7c. 95 nm thick Si
₃ N ₄ film, SiO ₂ film of 30 nm thickness, 140 nm thickness
The Si ₃ N ₄ film is formed, third fourth order thickness 95nm the bonding surface between the parallel glass substrate 7d of the Si ₃ N ₄ film of parallel glass substrate 7c, the film thickness 50 nm SiO ₂ film,
A 140 nm-thick Si ₃ N ₄ film is formed, and a 95 nm-thick Si ₃ N ₄ film and a 130 n-thick film are sequentially formed on the surface of the fourth parallel glass substrate 7 d bonded to the fifth parallel glass substrate 7 e.
An SiO ₂ film having a thickness of m and a Si ₃ N ₄ film having a thickness of 140 nm are formed, and an Al film having an appropriate thickness is further formed on the fifth parallel glass substrate 7e.

Next, as shown in FIG. 5, the first to fifth parallel glass substrates 7a, 7b, 7c, 7d, 7
e is laminated with a transparent adhesive having a refractive index substantially equal to these refractive indices and laminated, and a cut line indicated by a dotted line in the drawing (a line of approximately 45 degrees as viewed from the surface of the laminated line). Cut and polish this cut surface. Next, as shown in FIG. 6, if the cut block is cut along a cutting line shown by a dotted line in the drawing and the cut surface is polished, S-polarized light having a wavelength of 650 nm incident at 45 degrees (incident surface) is obtained. 19%, 25%, linearly polarized light having an electric field component perpendicular to
The first beam splitter stack 4 having the reflectivities of 33%, 50% and 90% is completed. Further, the second beam splitter stack 6 having the same configuration as the first beam splitter stack 4 can also be manufactured through the same steps as the above-described steps. Further, the first beam splitter stack 4 thus manufactured and the second
The optical device can be completed by integrally assembling the beam splitter stack 6, the half-wave plate 5, the laser light source 2, and the collimator lens 3.

Hereinafter, the first beam splitter stack 4
Half interval length of transmission mirror surfaces 4a d ₁ and relation between the distance length d ₂ of the half-mirror surface 6a of the second beam splitter stack 6 is d ₁ = d ₂ = d, and the first beam splitter Refractive index n _s for the incident light of the stack 4 and the second beam splitter stack 6 and the transflective mirror surface 4 a
Alternatively, a case where the value of the product (n _s × d) with the interval length d of 6a is sufficiently longer than the coherence length of the laser light source 2 will be described. Of light emitted from the second beam splitter stack 6, the difference between the shortest optical path length and the longest ones are the _{(n s × d) × (} s 1 + s 2 -2). In other words, a set of (s ₁ + s ₂ −1) light fluxes in which an incoherent optical path length difference is generated on the outgoing light surface can be obtained. Then, if s ₁ = s ₂ , both the first beam splitter stack 4 and the second beam splitter stack 6 can be cut out from the same parallel glass substrate and can be manufactured. These can be manufactured without necessity.

Hereinafter, the first beam splitter stack 4
Are s ₁ semi-transmissive mirror surfaces 4 separated by a constant interval length d ₁
a, the second beam splitter stack 6 is composed of s ₂ semi-transmissive mirror surfaces 6 a separated by a fixed interval d ₂ , and the first beam splitter stack 4 and the second beam splitter stack 6 (N _s) of the refractive index n _s for the incident light and the interval d ₁ of the semi-transmissive mirror surface 4 a
× d ₁ ) is sufficiently longer than the coherence length of the incident light and d ₂ is larger than (d ₁ × s ₁ ), or ( _ns × d ₂ ) is larger than the coherence length of the incident light. A case where the length is sufficiently long and d ₁ is larger than (d ₂ × s ₂ ) will be described. In the light emitted from the second beam splitter stack 6, the respective optical path length differences are all different. In other words, a set of (s ₁ × s ₂ ) luminous fluxes having a non-coherent optical path length difference on the exit light surface can be obtained. In this case, as shown in FIG. 7 which is a schematic external perspective view of the optical device, the arrangement of the emitted light beams is not uniform in the xy plane, but as described later, the number of non-coherent light beams is small. The larger the number, the more advantageous in reducing speckle.

Embodiment 2 In this embodiment, a coherent light source constituting an optical device is
This is an example in which a plurality of independent coherent light sources are used. This will be described with reference to FIGS. 8 and 9, which are schematic perspective views of the optical device. The functions of the collimator lens, the first beam splitter stack 4 as the first optical element, the half-wave plate 5, and the second beam splitter stack 6 as the second optical element are the same as those in FIG. 4 and the case described with reference to FIG. 4 will be omitted.

As shown in FIG. 8, a pair of first beam splitter stacks 4 as a first optical element are provided with a pair of a plurality of light beams arranged so that incident light is incident side by side in the y-axis direction. A laser light source 2, which is a coherent light source, is provided. Since the laser beams emitted from the individual laser beam sources 2 are non-coherent with each other, the spatial coherence can be further reduced as compared with the optical device 1 in the case shown in the first embodiment, and the second optical element It is possible to further uniform the arrangement of the branched light beams emitted from the pair of second beam splitter stacks 6.

Further, in the optical device 1 of the present embodiment, as shown in FIG. 9, a plurality of laser light sources 2 arranged in a straight line and a collimator lens 3 arranged correspondingly thereto.
And a first beam splitter stack 4 as a first optical element. In this case, the first beam splitter stack 4 may be one, and by arranging a large number of independent laser light sources 2, the emission of the pair of second beam splitter stacks 6 as the second optical element is achieved. Spatial coherence on the surface can be sufficiently reduced.

As the light source provided in the optical device of the case shown in the first and second embodiments, a coherent light source is generally used, and the first beam splitter stack 4 and the first optical element, The difference between the optical path lengths of the light beams split by only the second beam splitter stack 6 as the second optical element or the first beam splitter stack 4 as the first optical element is 、 of the coherence length. By doing so, the spatial coherence on the emission surface can be effectively reduced. However, when a semiconductor laser is used as a coherent light source and a high-frequency signal is superimposed on the input current, the spatial coherence can be reduced by an optical path length difference shorter than the coherence length. This will be described below with reference to FIGS. 10 and 11, which are schematic power spectrum diagrams.

It is generally known that a semiconductor laser oscillating in a single mode oscillates at a plurality of frequencies as shown in FIG. 10 when a high-frequency signal is superimposed on the input current. I have. The degree of coherence can be derived by Fourier transform of the power spectrum, and FIG. 11 shows the degree of coherence as a function of the distance in vacuum (optical path length difference). In the example shown in FIG. 11, the coherence between the light beams is reduced when the optical path length difference is 0.5 mm, and is 0 until the optical path length difference becomes 4.5 mm again. However, when the optical path length difference becomes 5 mm, the coherence reaches the maximum again, and thereafter, the maximum appears periodically. In the case shown in the first and second embodiments, ( _ns × d
₁ ) or an optical path length difference in units of ( _ns × d ₂ ) is generated. When these are set to 8 mm, a light flux in a certain area and a light flux having an optical path length difference of up to approximately 4 units are obtained.
In other words, the coherence between the light beams having the optical path length differences of 8 mm, 16 mm, 24 mm, and 32 mm is almost zero. Note that a light beam having an optical path length difference of 5 units, that is, 4
Although the coherence with the light beam having an optical path length difference of 0 mm corresponds to a maximum, as shown in FIG. 10, in a semiconductor laser on which a high-frequency signal is superimposed, generally, if there is an optical path length difference of about 20 cm, The degree of coherence is sufficiently small and there is no possibility of causing a problem.

In general, the full width at half maximum of each mode of the power spectrum of a semiconductor laser on which a high frequency signal is superimposed is larger than the full width at half maximum of a power spectrum when a single mode oscillation is performed without superimposing a high frequency signal. Is known. Considering that the coherence length of a laser beam emitted from a semiconductor laser that oscillates in single mode without superimposing a high-frequency signal is generally about 3 m, the size of the optical device is reduced by superimposing a high-frequency signal. be able to.

Further, as a multi-mode coherent light source, there are various options other than superimposing a high-frequency signal on the input current of the semiconductor laser. For example, a so-called longitudinal multi-mode laser which originally oscillates at a plurality of frequencies may be used, or a so-called self-excited oscillation semiconductor laser behaves as a longitudinal multi-mode laser, so that a similar effect can be obtained.

Embodiment 3 This embodiment is an example of a lighting device provided in an image display device or an exposure device. This will be described with reference to FIG. 12 which is a schematic configuration diagram of the lighting device. Reference numeral 1 denotes an optical device of any one of the cases shown in the first and second embodiments. A plurality of light beams arranged in the xy plane are emitted from the optical device 1 in the + z-axis direction and are incident on the optical integrator 8. The optical integrator 8 is composed of a so-called fly-eye lens 8a composed of a plurality of element lenses and a condenser lens 8b. The optical integrator 8 forms a planar light source for each element lens from incident light, and irradiates each emitted light with light. It is configured to illuminate surface 9. In this case, it is desirable that the number of element lenses constituting the fly-eye lens 8a be substantially the same as or less than the number of light beams emitted from the optical device 1, and each light beam is transmitted to one or more of the element lenses of the optical integrator 8. The light is incident on the surface 9 to be irradiated. When one point on the irradiated surface 9 is viewed, the light irradiated to this point is a superposition of a plurality of non-coherent light beams emitted from the optical device 1. It is known that when illuminating with a light beam of a book, the contrast of speckle is approximately 1 / N ^1/2 , whereby the occurrence of speckle can be reduced.

In the case of the illuminating device 10 of this embodiment, there is a slight difference in the optical path length difference from the position of each light beam on the exit surface of the optical device 1 to one point on the surface 9 to be illuminated. Specifically, the distance between the optical integrator 8 and the irradiated surface 9 is sufficiently larger than the size of the emission surface, so that the distance can be neglected as compared with the optical path length difference of each branch light generated in the optical device 1. There is no problem. Further, in the illumination device 10 of the present embodiment, even if a semiconductor laser whose longitudinal mode is a multi-mode is used as the coherent light source constituting the optical device 1, there is no possibility of causing a problem.

When the illumination device 10 is used as a light source of an image display device or an exposure device, for example, the spatial coherence or speckle can be reduced, and a bundle of optical fibers is not used unlike the conventional one. The size can be reduced. Therefore, in the image display device, a high-quality image can be obtained and the size can be reduced. In the exposure device, high-quality exposure of the pattern on the mask can be performed.

[0045]

According to the optical element and the optical device of the present invention, the incident light is divided into a plurality of light beams with almost equal intensity and splits, and a difference in optical path length is generated. It is possible to provide a small optical element and a small optical device that effectively reduce the amount of light. In addition, if a multimode laser having a plurality of different wavelengths is used as the coherent light source, the optical path length difference can be optimized by using the periodic coherence degree, and the optical path length difference shorter than the coherence length can be achieved. Spatial coherence can be more effectively reduced. ADVANTAGE OF THE INVENTION According to the illuminating device of this invention, a high-precision of the relative positional accuracy of an optical device and the optical integrator comprised by the fly-eye lens and the condenser lens is not required, and the small illuminating optical system which reduces speckle is needed. Can be configured. Therefore, in the image display device and the exposure device including the illumination device, the size of the device can be reduced and the spatial coherence or speckle can be reduced.
High-quality exposure of a high-quality image or a pattern on a mask becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic power spectrum diagram of a multi-mode laser beam for explaining the operation of the present invention.

FIG. 2 is a schematic power spectrum diagram illustrating the operation of the present invention and illustrating the degree of coherence of a multi-mode laser beam.

FIG. 3 is a schematic external perspective view of the optical device according to the first embodiment of the present invention.

FIG. 4 is a schematic plan view seen from the + x-axis direction in FIG. 3;

FIG. 5 is a schematic external perspective view illustrating a method for manufacturing a beam splitter stack according to the present invention.

FIG. 6 is a schematic external perspective view illustrating a method for manufacturing a beam splitter stack according to the present invention.

FIG. 7 is a schematic external perspective view of an optical device in another case according to the first embodiment of the present invention.

FIG. 8 is a schematic external perspective view of an optical device according to a second embodiment of the present invention.

FIG. 9 is a schematic external perspective view of an optical device in another case according to the second embodiment of the present invention.

FIG. 10 is a schematic power spectrum diagram when a semiconductor laser is used as a coherent light source according to the present invention, and a high-frequency signal is superimposed on an input current thereof.

11 is a schematic power spectrum diagram showing the degree of coherence of the power spectrum of FIG.

FIG. 12 is a schematic configuration diagram of a lighting device according to a third embodiment of the present invention.

FIG. 13 is a schematic power spectrum diagram of coherent light for explaining speckle which is a problem specific to coherent light in the related art.

14 is a schematic power spectrum diagram showing a coherence degree of the power spectrum of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical device, 2 ... Laser light source, 3 ... Collimator lens, 4 ... First beam splitter stack, 4a ... Semi-transmissive mirror surface, 5 ... 1/2 wavelength plate, 6 ... Second beam splitter stack, 6A ... Semi-transmissive mirror surface, 7a ... First parallel glass substrate, 7b ... Second parallel glass substrate, 7c ...
A third parallel glass substrate, 7d... A fourth parallel glass substrate,
7e: Fifth parallel glass substrate, 8: Optical integrator, 8a: Fly-eye lens, 8b: Condenser lens, 9: Illuminated surface, 10: Illumination device

Claims (24)

[Claims] A plurality of semi-transmissive mirror surfaces that are inclined at an angle of approximately 45 degrees with respect to the optical axis of the incident coherent light and are disposed parallel to each other and at a constant interval; An optical element characterized by sequentially performing partial reflection and partial transmission of coherent light, and sequentially emitting branched light composed of a plurality of light beams having a constant optical path length difference. 2. A first optical element having a first plurality of semi-transmissive mirror surfaces that are inclined at an angle of approximately 45 degrees with respect to the optical axis of the incident coherent light and are disposed parallel to each other and at a fixed interval. A second plurality of semi-transmissive mirror surfaces that are inclined approximately 45 degrees with respect to an optical axis of reflected light of the coherent light on the first plurality of semi-transmissive mirror surfaces and are disposed parallel to each other and at a constant interval are provided. A second optical element having the first plurality of semi-transmissive mirror surfaces and the second plurality of semi-transmissive mirror surfaces sequentially performing partial reflection and partial transmission of the coherent light, An optical element which emits, from a second plurality of semi-transmissive mirror surfaces, a branched light composed of a plurality of surface-developed light beams having a constant optical path length difference. 3. A first semi-transmissive mirror surface having a first plurality of semi-transmissive mirror surfaces which are inclined at an angle of approximately 45 degrees with respect to the optical axis of the coherent light incident with linearly polarized light, and which are arranged parallel to each other and at regular intervals. An optical element, a half-wave plate for rotating the polarization direction of reflected light of the coherent light on the first plurality of semi-transmissive mirror surfaces by 90 degrees, and the first plurality of halves of the coherent light. A second optical element having a second plurality of semi-transmissive mirror surfaces that are arranged at an angle of about 45 degrees with respect to the optical axis of the reflected light on the transmissive mirror surface, and are arranged in parallel with each other at a constant interval. Performing a partial reflection and a partial transmission of the coherent light sequentially on the first plurality of semi-transmissive mirror surfaces and the second plurality of semi-transmissive mirror surfaces; , Sequentially having a constant optical path length difference Wherein the optical element to emit a branched light composed of a light beam surface extending. 4. The apparatus according to claim 1, wherein the constant optical path length difference is larger than コ of a coherence length of the coherent light. Optical element. 5. The coherent light has a plurality of different periodic wavelengths, the degree of coherence of the coherent light is represented as a function of time, the full width at half maximum of the first local maximum waveform is τ _t , When the distance between the center values of the local maximum waveform and the second local maximum waveform adjacent to the first local maximum waveform is τ _d , the constant optical path length difference σ is c ((n−1) τ _d + Τ _t / 2) ≦ σ ≦ c (nτ _d −τ
The optical element according to claim 1, wherein the optical element falls within a range satisfying a condition of ( _t / 2). (However, c is the speed of light and n is a natural number.) 6. The number of the first plurality of half-mirror surface as a _single s, constant the s ₁ single semitransparent mirror interplanar arranged at regular intervals d ₁ refractive index n ₁ Wherein the number of the second plurality of semi-transmissive mirror surfaces is s ₂ ,
The surface between the s ₂ semi-transmissive mirrors arranged at a constant distance d ₂ is made of a substance having a constant refractive index n ₂ , and n ₂ d ₂ > n ₁ d ₁ s ₁ and n ₁ d ₁ > n ₂ d ₂ s ₂
3. The method according to claim 2, wherein one of the conditions is satisfied.
Or the optical element of 3. 7. A coherent light source that emits at least coherent light, and a plurality of semi-transmissive mirror surfaces that are inclined at approximately 45 degrees with respect to the optical axis of the coherent light, and are disposed parallel to and at a constant interval from each other. An optical element, and sequentially performs partial reflection and partial transmission of the coherent light on the plurality of semi-transmissive mirror surfaces, and sequentially branches light composed of a plurality of light beams having a constant optical path length difference. An optical device that emits light. 8. A coherent light source that emits at least coherent light, and a first plurality of semi-transmissive mirror surfaces that are inclined at approximately 45 degrees with respect to the optical axis of the coherent light and that are arranged at parallel and constant intervals to each other. A first optical element having: a first optical element having an angle of approximately 45 degrees with respect to the optical axis of the reflected light of the coherent light on the first plurality of semi-transmissive mirror surfaces, and disposed in parallel with each other at a constant interval. A second optical element having a second plurality of semi-transmissive mirror surfaces, and a partial reflection of the coherent light on the first plurality of semi-transparent mirror surfaces and the second plurality of semi-transparent mirror surfaces And a partial transmission in sequence, and sequentially emits, from the second plurality of semi-transmissive mirror surfaces, a branched light composed of a plurality of surface-developed light beams having a constant optical path length difference. apparatus. 9. A coherent light source that emits coherent light having at least linearly polarized light, and a first plurality of light sources that are arranged at an angle of approximately 45 degrees with respect to the optical axis of the coherent light and that are arranged parallel to each other and at regular intervals. A first optical element having a semi-transmissive mirror surface, a half-wave plate for rotating the polarization direction of reflected light of the coherent light on the first plurality of semi-transparent mirror surfaces by 90 degrees, and the coherent light A second plurality of semi-transmissive mirror surfaces that are inclined approximately 45 degrees with respect to the optical axis of light reflected by the first plurality of semi-transmissive mirror surfaces, and are disposed parallel and at regular intervals to each other. The first plurality of semi-transmissive mirror surfaces and the second plurality of semi-transmissive mirror surfaces to sequentially perform partial reflection and partial transmission of the coherent light, Multiple A semi-transparent mirror surface, successively optical apparatus characterized by emitting a branch light composed of the light beam a plurality of surface extending with a constant optical path length difference. 10. The apparatus according to claim 7, wherein the constant optical path length difference is larger than コ of a coherence length of the coherent light. Optical device. 11. The optical device according to claim 7, wherein the coherent light has a plurality of different wavelengths. 12. The coherent light has a plurality of different periodic wavelengths, the degree of coherence of the coherent light is represented as a function of time, the full width at half maximum of the first local maximum waveform is τ _t , When the distance between the center values of the local maximum waveform and the second local maximum waveform adjacent to the first local maximum waveform is τ _d , the constant optical path length difference σ is c ((n−1) τ _d + Τ _t / 2) ≦ σ ≦ c (nτ _d −τ
The optical device according to claim 7, wherein the optical device falls within a range satisfying a condition of ( _t / 2). (However, c is the speed of light and n is a natural number.) 13. The optical device according to claim 7, wherein the coherent light source includes a plurality of independent coherent light sources. 14. The number of the first plurality of half-mirror surface as a _single s, the arranged at regular intervals d ₁ s ₁
Between the semi-transmissive mirror surfaces is made of a material having a constant refractive index n ₁ , and the number of the second plurality of semi-transmissive mirror surfaces is s ₂ ,
The surface between the s ₂ semi-transmissive mirrors arranged at a constant distance d ₂ is made of a substance having a constant refractive index n ₂ , and n ₂ d ₂ > n ₁ d ₁ s ₁ and n ₁ d ₁ > n ₂ d ₂ s ₂
9. A method according to claim 8, wherein one of the conditions is satisfied.
Or the optical device according to 9. 15. A coherent light source that emits at least coherent light, and a plurality of semi-transmissive mirror surfaces that are inclined at approximately 45 degrees with respect to the optical axis of the coherent light, and are arranged parallel to each other and at regular intervals. An optical element, an optical integrator configured with a fly-eye lens and a condenser lens configured with a plurality of element lenses, and a partial reflection and a partial transmission of the coherent light on the plurality of semi-transmissive mirror surfaces. Are sequentially transmitted, N light fluxes having successively constant optical path length differences are transmitted through the optical integrator, and the contrast of speckle on the irradiated surface emitted and emitted from the optical integrator is approximately 1 /. A lighting device characterized in that the lighting device is reduced to N ^1/2 . 16. A coherent light source that emits at least coherent light, and a first plurality of semi-transmissive mirrors that are inclined at an angle of about 45 degrees with respect to the optical axis of the coherent light, and are disposed parallel to and at a constant interval from each other. A first optical element having a surface, and being disposed at an angle of approximately 45 degrees with respect to the optical axis of the coherent light reflected by the first plurality of semi-transmissive mirror surfaces and parallel to each other at a constant interval. A second optical element having a second plurality of semi-transmissive mirror surfaces, and an optical integrator including a fly-eye lens and a condenser lens each including a plurality of element lenses; Is generated by sequentially performing partial reflection and partial transmission of the coherent light on the semi-transmissive mirror surface and the second plurality of semi-transmissive mirror surfaces. And characterized by reducing the N optical beams having an optical path length difference transmitted to the optical integrator, the contrast of the speckle on the irradiated surface to be irradiated is emitted from the optical integrator in the schematic 1 / N ^1/2 Lighting equipment. 17. A coherent light source that emits coherent light having at least linearly polarized light, and a first plurality of light sources that are inclined at substantially 45 degrees with respect to the optical axis of the coherent light, and that are arranged parallel to each other and at regular intervals. A first optical element having a semi-transmissive mirror surface, a half-wave plate for rotating the polarization direction of reflected light of the coherent light on the first plurality of semi-transparent mirror surfaces by 90 degrees, and the coherent light A second plurality of semi-transmissive mirror surfaces that are inclined approximately 45 degrees with respect to the optical axis of light reflected by the first plurality of semi-transmissive mirror surfaces, and are disposed parallel and at regular intervals to each other. And an optical integrator including a fly-eye lens and a condenser lens each including a plurality of element lenses, and the first plurality of semi-transparent lenses. The optical integrator converts N light fluxes having successively constant optical path length differences generated by sequentially reflecting and partially transmitting the coherent light on a mirror surface and the second plurality of semi-transmissive mirror surfaces. A speckle contrast on a surface to be irradiated, which is transmitted through the optical integrator and emitted from the optical integrator, is reduced to approximately 1 / N ^1/2 . 18. The method according to claim 15, wherein the constant optical path length difference is larger than コ of a coherence length of the coherent light. Lighting equipment. 19. The lighting device according to claim 15, wherein the coherent light has a plurality of different wavelengths. 20. The coherent light has a plurality of different periodic wavelengths, the degree of coherence of the coherent light is represented as a function of time, the full width at half maximum of the first local maximum waveform is τ _t , When the distance between the center values of the local maximum waveform and the second local maximum waveform adjacent to the first local maximum waveform is τ _d , the constant optical path length difference σ is c ((n−1) τ _d + Τ _t / 2) ≦ σ ≦ c (nτ _d −τ
The lighting device according to any one of claims 15, 16, and 17, wherein the value falls within a range satisfying a condition of ( _t / 2). (However, c is the speed of light and n is a natural number.) 21. The lighting device according to claim 15, wherein the coherent light source includes a plurality of independent coherent light sources. 22. The number of the first plurality of half-mirror surface as a _single s, the arranged at regular intervals d ₁ s ₁
Between the semi-transmissive mirror surfaces is made of a material having a constant refractive index n ₁ , and the number of the second plurality of semi-transmissive mirror surfaces is s ₂ ,
The surface between the s ₂ semi-transmissive mirrors arranged at a constant distance d ₂ is made of a substance having a constant refractive index n ₂ , and n ₂ d ₂ > n ₁ d ₁ s ₁ and n ₁ d ₁ > n ₂ d ₂ s ₂
2. The method according to claim 1, wherein one of the following conditions is satisfied.
18. The lighting device according to 6 or 17. 23. An image display device comprising the lighting device according to claim 15. Description: 24. An exposure apparatus comprising the illumination device according to claim 15. Description: