Optical element, laser light source, and two-dimensional image forming apparatus Number:7,522,792 from the United States Patent and Trademark Office (PTO) owispatent

Title: Optical element, laser light source, and two-dimensional image forming apparatus

Abstract: An optical element (10) according to the present invention is provided with a plurality of waveguides (11).about.(13) and a plurality of light path coupling parts (21), (22) coupling adjacent waveguides so as to optically couple said plural waveguides serially, wherein the paths for transmitting lights through the plural waveguides are curved at the optical path coupling parts, thereby the optical elements which is converted the incident laser light into the emitted light having uniform cross-sectional light intensity distribution can give a compact structure, further a laser light source that employs the optical element, and a two-dimensional image forming apparatus that employs the laser light source can also give a compact structure.

Patent Number: 7,522,792 Issued on 04/21/2009 to Sugita,   et al.

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Inventors:	Sugita; Tomoya (Osaka, JP), Mizuuchi; Kiminori (Osaka, JP), Kasazumi; Ken'ichi (Osaka, JP), Morikawa; Akihiro (Osaka, JP)
Assignee:	Panasonic Corporation (Osaka, JP)
Appl. No.:	10/582,341
Filed:	December 9, 2004
PCT Filed:	December 09, 2004
PCT No.:	PCT/JP2004/018361
371(c)(1),(2),(4) Date:	June 09, 2006
PCT Pub. No.:	WO2005/057271
PCT Pub. Date:	June 23, 2005

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Foreign Application Priority Data

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Dec 10, 2003 [JP]			2003-411442

Current U.S. Class:	385/50 ; 385/32; 385/39
Current International Class:	G02B 6/26 (20060101); G02B 6/42 (20060101)
Field of Search:	385/32,50,133,31,36,39,129 372/6

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References Cited [Referenced By]

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U.S. Patent Documents

6324330	November 2001	Stites
6741394	May 2004	Tanitsu et al.
2003/0031029	February 2003	Kawaai et al.

Foreign Patent Documents

	58-48013		Mar., 1983		JP
	59-180519		Oct., 1984		JP
	6-51236		Feb., 1994		JP
	7-306304		Nov., 1995		JP
	07307273		Nov., 1995		JP
	08111107		Apr., 1996		JP
	2002-40327		Feb., 2002		JP
	2002-268000		Sep., 2002		JP
	2003-57514		Feb., 2003		JP
	3410813		Mar., 2003		JP

Primary Examiner: Wood; Kevin S
Assistant Examiner: Bedtelyon; John M
Attorney, Agent or Firm: Steptoe & Johnson LLP

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Claims

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The invention claimed is:

1. A laser light source comprising: a semiconductor laser which emits a laser light; and an optical element which-transmits the laser light, said optical element comprising: a plurality of waveguides transmitting the laser light; and a plurality of light path coupling parts which couple adjacent waveguides and optically couple said plural waveguides serially, the plurality of light path coupling parts comprising: a reflection plane which reflects and refracts laser light passing through the waveguides, wherein optical path length L from a light input surface of the waveguides to a light output surface of the waveguides satisfies the following equation: L.gtoreq.W/tan(sin.sup.-1(sin(.theta./2)/n)), wherein W is a width of the waveguide, n is a refractive index inside the waveguide, and .theta. is a minimum beam spread angle of the semiconductor laser.

2. The laser light source as defined in claim 1, further comprising: a convex lens or a plano-convex lens is located in an optical path between the semiconductor laser and the optical element and makes a spread angle of laser light incident to the optical element smaller than a spread angle of laser light emitted from the semiconductor laser.

3. The laser light source as defined in claim 1, further comprising: a cylindrical lens is located in the path between said semiconductor laser and said optical element.

4. The laser light source as defined in claim 3, wherein the cylindrical lens is a plano-concave lens.

5. The laser light source as defined in claim 1, wherein a light incident surface of the optical element is in a curved configuration with a curvature.

6. The laser light source as defined in claim 1, wherein said plurality of waveguides is an odd number of waveguides, and said odd number of waveguides are overlapping with each other in parallel with the light transmission direction of said waveguides.

7. The laser light source as defined in claim 1, wherein external surfaces other than a light input surface and a light output surface of the waveguides and said light path coupling parts are coated with a reflection film reflecting the transmitting light.

8. The laser light source as defined in claim 1, wherein said light path coupling parts comprise inclined surfaces which are inclined with respect to a plane vertical to the light transmission direction and are integrated with said waveguides at one or both ends of adjacent waveguides.

9. The laser light source as defined in claim 1, wherein said waveguides comprise a hollow structure in which gas or liquid, and Brownian particles, are sealed.

10. The laser light source as defined in claim 9, wherein said Brownian particles are colloid particles.

11. A two-dimensional image forming apparatus comprising: a laser light source emitting a laser light comprising: a plurality of waveguides transmitting a light; and a plurality of light path coupling parts which couple adjacent waveguides and optically couple said plurality of waveguides serially, the plurality of light path coupling parts comprising: a reflection plane which reflects and refracts laser light passing through the waveguides; a space optical modulation part that modulates the laser light emitted from the laser light source; and an illumination optical system for illuminating the laser light that is outputted from the laser light source to the space light modulation part, wherein an optical path length L from a light input surface of the waveguides to a light output surface of the waveguides satisfies the following equation: L.gtoreq.W/tan(sin.sup.-1(sin(.theta./2)/n)), wherein W is a width of the waveguide, n is a refractive index inside the waveguide, and .theta. is a minimum beam spread angle of the laser light source.

12. The two-dimensional image forming apparatus as defined in claim 11 further comprising: a projection optical system which projects the laser light that is emitted from the space. optical modulation part.

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Description

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CLAIM OF PRIORITY

This application claims priority under 35 USC 371 to International Application No. PCT/JP2004/018361, filed on December 9, 2004, which claims priority to Japanese Patent Application No. 2003-411442, filed on December 10, 2003, each of which is incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to an optical element, a laser light source, and a two-dimensional image forming apparatus and, more particularly, to an optical element that converts an incident light to an emitted light that has a uniform emitted light intensity distribution, a laser light source employing the optical element, and a two-dimensional image forming apparatus employing the laser light source.

BACKGROUND ART

Up to now, the laser light source is mainly applied in the fields of measurements, optical communication, optical discs, and the like which utilize the collecting characteristics of laser light as well as high coherency. However, the research and developments of laser light sources are eminent and small-sized high output lasers represented by semiconductor lasers are advancing in their practical uses, and there are such as multi-mode semiconductor lasers which can accomplish outputs of several watts order in semiconductor lasers.

Accompanying by such miniaturizations and high outputting of such laser light sources, developments of applications using laser light sources of miniaturized and capable of high outputting and developments of apparatuses used therein are activated.

High output light sources are expected to be applied in various uses such as in picture display apparatuses, illumination apparatuses, and semiconductor exposure apparatuses, and particularly, high output laser light sources are sought to become capable of realizing a high color purity degree sharpness image in a laser display using high laser outputs of RBG three original colors utilizing its high mono-color characteristics. In addition, it is also expected to apply a miniaturized high output laser light source to an illumination light source that is of low power consumption and has a lengthy lifetime. Further, the high output laser light sources are also applied to laser processing where minute configuration processing by the high output lasers is being realized.

In the applications using such high output laser light sources, in addition to that the mono-color characteristics and high output characteristics of the laser light are utilized, there is a large request for a uniform cross-section intensity distribution, and there have conventionally methods for satisfying the same.

For example, in patent Documents No. 1 and No. 2, those which form the output lights from the laser light sources having a Gaussian light intensity distribution so as to have a uniform light intensity distribution using devices or optical systems which make the light quantity uniform and which are called as a homogenizer are disclosed. Further, in patent Documents No. 3 and No. 4, those which form the output lights from the laser light sources so as to have a uniform light intensity distribution using optical elements which are called as integrators. Patent Document No. 1: Japanese Unexamined Patent Publication No. 07-306304 Patent Document No. 2: Japanese Patent No. 3410813 Patent Document No. 3: Japanese Unexamined Patent Publication No. 2002-40327 Patent Document No. 4: Japanese Unexamined Patent Publication No. 2003-57514

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

In the prior art patent references No. 1 to No. 3 as described above, since it is required to properly enlarge the cross-sectional area of the output light before the output light from the laser light source is incident to the optical element or the optical system, the optical system including the laser light source becomes complicated and the device area is increased. Further, when the output light from the laser light source is incident to the optical element after the cross-sectional area of the output light is increased, the outer circumferential part of the beam of the output light is cut out, thereby resulting in a loss on light quantity.

In the patent reference No. 4, though the cross-sectional area of the output light is not required to be broadened, in order to output the light from the laser light source with making the light intensity uniform, the length in the light transmission direction of the rod integrator has to be made long, thereby resulting in a large device area.

Further, when a laser light source having a high interference is employed as a light source, the light emitted from the optical element that has made the light quantity uniform as described above generates minute irregular noises due to minute interfering patterns specific to laser light characteristics which are called as speckle noises. As a method to remove these speckle noises, a method of vibrating a screen, a method of making the light pass through a dispersion plate to give random phases to the laser light temporarily and spatially, and the like have bee adopted. However, the method of vibrating the screen cannot fix the screen, and the method employing such as a dispersion plate resulted in reduction in the light quantity used for the video image projection as well as an increase in the device size.

The present invention is directed to solving the above-described problems and has an object to provide a compact optical element that converts the incident light to an emitted light that has a uniform output light intensity distribution, a laser light source that employs the optical element, and a two-dimensional image forming apparatus that employs the laser light source.

Measures to Solve the Problems

In order to solve the above-described problems, according to one embodiment of the present invention, an optical element comprises: a plurality of waveguides transmitting a light; a plurality of light path coupling parts coupling adjacent waveguides so as to optically couple said plural waveguides serially, and the paths for transmitting lights through the plural waveguides are curved at least one part of said optical path coupling parts.

Thereby, the incident laser light can be converted into the emitted light having uniform cross-sectional light intensity distribution by quite compact optical elements.

Such an an optical element may include an odd number of waveguides are provided as said plural waveguides, and said odd number of waveguides are disposed overlapping with each other in parallel with respect to the light transmission direction of said waveguides.

Thereby, the advancing direction of the light incident to the optical element and the advancing direction of the light that is outputted from the optical element can be made the same direction, and therefore, the device structure for mounting the optical elements can be simplified.

Such an an optical element may also include external surfaces other than the light incident surface and the light output surface of the waveguide path comprising said waveguides and said light path coupling parts are coated by a reflection film reflecting the transmitting light.

Thereby, it is possible to transmit the light incident into inside the waveguide with efficiently reflecting the same.

In such an optical element said light path coupling parts may have inclined surfaces which are inclined with respect to the plain vertical to the light transmission direction and are integrated with said waveguides at either or both of said adjacent waveguides.

Thereby, it is possible to reduce a number of parts in the light path coupling parts.

Such an an optical element also may include waveguides of a hollow structure in which either of gas or liquid and Brownian particles are sealed.

Thereby, it is possible to reduce speckle noises that are generated in a laser light source having a high coherency.

In such an optical element said Brownian particles may colloid particles.

Thereby, it is possible to make appropriately random the phase of the light incident to the waveguide.

In such an optical element the distance along the light transmission path from the light incident surface to the light output surface may satisfy the following equation (1): L.gtoreq.W/tan(sin.sup.-1(sin (.theta./2)/n)) (1)

W: width of the waveguide

n: refractive index inside the waveguide

.theta.: the minimum beam spread angle possessed by the semiconductor laser.

Thereby, it is possible to produce an optical element that can convert the incident laser light to an output light having a uniform cross-sectional light intensity distribution in a size that is to the minimum within the required.

The present invention also may include a laser light source comprising a semiconductor laser and an optical element which emits the laser light which is emitted from said semiconductor laser with transmitting the same, wherein said optical element includes a plurality of waveguides transmitting light, and a plurality of light path coupling parts coupling adjacent waveguides so as to optically couple said plural waveguides serially, and the path of the light for transmitting the light through the plural waveguides are curved at said optical path coupling part.

Thereby, it is possible to provide a quite compact laser light source that outputs an output light having a uniform cross-sectional light distribution intensity.

Such an optical element may also include a convex lens or a plano-convex lens which is disposed on an optical path between the semiconductor laser and the optical element and makes the spread angle of the laser light incident to the optical element smaller than the spread angle of the laser light that is emitted from the semiconductor laser.

Thereby, it is possible to realize a light source making the cross-sectional light intensity distribution uniform which can convert the spread angle of the light emitted from the optical element to an arbitrary angle. As a result, since the spread angle of the output light from the optical element can be made small, it is possible to make the light emitted from the optical element one that is easy in being handled.

In the present invention, a laser light source may include a cylindrical lens disposed on a light path between said semiconductor laser and said optical element.

Thereby, it is possible to convert the elliptical shape light beam that is outputted from the semiconductor laser to a light beam having a circular shape that is easy to handle. Further, even when the cross-sectional configurations of the respective waveguides are designed to be in a rectangular shape having an arbitrary aspect ratio, a laser light source having an arbitrary output beam aspect ratio that can accomplish a uniform output light cross-sectional intensity distribution with a short optical path length efficiently by selecting the curvature of the cylindrical lens can be obtained, thereby the design of the configuration of the optical element is made without any inhibition.

In the laser light source the cylindrical lens may be a plano-concave lens.

Therefore, it is possible to broaden the spread angle only in one axis direction of the light that is incident to the optical element, and as a result, the entire optical length of the optical element that is required for making uniform the output light cross-sectional intensity distribution can be reduced.

And, in the laser light source the light incident surface of the optical element may be in a curved configuration having curvature.

Thereby, it is not needed to dispose a lens on an optical path between the semiconductor laser and the optical element, and therefore, a compact laser light source is obtained.

The present invention is also embodied in a two-dimensional image forming apparatus comprising: a laser light source emitting a laser light; a space optical modulation part that modulates a laser light emitted from the laser light source; and an illumination optical system for illuminating the laser light that is outputted from the laser light source to the space light modulation part, wherein said laser light source has a plurality of waveguides transmitting a light, and a plurality of light path coupling parts coupling adjacent waveguides so as to optically couple said plural waveguides serially, and the paths for transmitting lights through the plural waveguides are curved at said optical path coupling parts.

Thereby, it is possible to provide, as a laser light source used in a two-dimensional image forming apparatus, one which is quite a compact laser light source that outputs an output light having a uniform cross-sectional light distribution intensity.

The two-dimensional image forming apparatus may include a projection optical system which projects the laser light that is emitted from the space optical modulation part.

Thereby, quite a compact two-dimensional image formation system which has quite simple parts constructions can be realized.

Effects of the Invention

According to an optical element of the present invention, since the optical element comprises a plurality of waveguides transmitting a light and a plurality of light path coupling parts coupling adjacent waveguides so as to optically couple said plural waveguides serially, and the paths for transmitting lights through the plural waveguides are curved at the optical path coupling parts, thereby it is possible to make the size the optical elements quite small and to obtain the effects which can be converted into the emitted light having uniform cross-sectional light intensity distribution by the optical element.

Further, since the plural waveguides have hollow structure, and either of gas or liquid and Brownian particles are sealed in the hollow of the waveguides, it is possible to reduce speckle noise that are generated in a laser light source having a high coherency.

According to a laser light source of the present invention, since the laser light source has integrated a semiconductor laser with the optical element, and has employed lens which collects or diffuses the laser light on an optical path between the laser light source and the semiconductor laser, it is possible to convert the spread angle of the light emitted from the optical element or to broaden the spread angle only in one axis direction of the incident light so that the cross-section light intensity distribution is made uniform, whereby it is possible to obtain the laser light source having a beam shape that is easy to handle.

Further in the laser light source, by having a lens which collects or diffuses the laser light before the optical element and selecting the curvature of the lens, it is possible to realize the laser light source which can accomplish a uniform output light cross-sectional intensity distribution with a short optical path length efficiently and can have an arbitrary output beam aspect ratio, thereby it is possible to increase the degree of freedom in designing the optical element.

In addition, according to a two-dimensional image forming apparatus of the present invention, since the two-dimensional image forming apparatus employs the laser light source, it is possible to obtain a effect that quite a compact two-dimensional image formation system which has quite simple parts constructions can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 are a cross-sectional view (FIG. 1(a)) and a perspective view (FIG. 1(b)) for explaining an optical element according to a first embodiment of the present invention.

FIG. 2 is a diagram for geometrically illustrating a light transmission path of the semiconductor laser light transmitting through a simple rod shaped waveguide.

FIG. 3 is a diagram for explaining a function of the optical element according to the first embodiment, where FIG. 3(a) shows variation of the light intensity distribution in a free space of the laser light, while FIGS. 3(b) and 3(c) show the manner of the light intensity distribution in the waveguide being made uniform.

FIG. 4 are diagrams illustrating other examples of combinations of waveguides in the optical element according to the first embodiment of the present invention.

FIG. 5 is a diagram illustrating a light path coupling part in cross-section that is constituted by waveguides in an optical element according to the second embodiment of the present invention.

FIG. 6 is a perspective view for illustrating an optical element according to the third embodiment of the present invention.

FIG. 7 are a perspective view (FIG. 7(a)) and a cross-sectional view (FIG. 7(b)) illustrating a laser light source according to a fourth embodiment of the present invention.

FIG. 8 is a side view illustrating a laser light source according to a fifth embodiment of the present invention.

FIG. 9 are a perspective view (FIG. 9(a)) and a cross-sectional view (FIG. 9(b)) illustrating a laser light source according to a sixth embodiment of the present invention.

FIG. 10 is a diagram for explaining an illumination apparatus according to a seventh embodiment of the present invention.

FIG. 11 is a diagram illustrating a two-dimensional image forming apparatus according to an eighth embodiment of the present invention.

DESCRIPTION OF NUMERALS

3 reflection film 10, 10a, 10b, 10c, 10d, 15, 30, 40, 50, 60 optical element 11, 11a, 11b, 11c, 11d, 12, 12a, 12b, 12c, 12d, 13, 13a, 13b, 13c, 13d, 16, 17, 18,31, 32, 33, Wg waveguide 21, 22 optical coupling parts 16a, 17a, 17b, 18b inclined surface 19a, 19b light passing region.tau.s 41, 51, 61, Ld semiconductor laser 52 plano-convex lens 62 cylindrical lens 70 lens 72 liquid crystal panel 81 projector lens 82 screen 140, 150, 160, 170 laser light source 200, 270 lighting system 300 two-dimensional image forming apparatus L1, L1a, L2, L2a, L3 laser light

BEST MODE TO EXECUTE THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1

In this first embodiment, an optical element that has made the device size quite small by using plural waveguides and light path coupling parts which optically serially couples the waveguides.

FIG. 1 are diagrams for explaining an optical element according to a first embodiment of the present invention, FIG. 1(a) shows a cross-sectional view and FIG. 1(b) shows a perspective view.

The optical element 10 shown in FIG. 1 has first to third waveguides 11 to 13 having rectangular configurations comprising glass material transmitting incident light, and optical coupling parts 21, 22 coupling the respective waveguides 11 to 13 optically serially.

In this optical element 10, second and third waveguides 12 and 13 are successively stacked on the first waveguide 11 so that the light propagation directions in theses waveguides are parallel to each other, and the first waveguide 11 and the second waveguide 12 positioned thereon, and the second waveguide 12 and the third waveguide 13 positioned thereon are adhered to each other at their respective confronting surfaces by such as adhesion, respectively.

Here, an end surface of the second waveguide 12 that is perpendicular to its light propagation direction and an end surface of the third waveguide 13 that is perpendicular to its light propagation direction are positioned in the same plain as the light emitting surface of the first waveguide 11. Further, the other end surface of the second waveguide 12 that is perpendicular to its light propagation direction and the other end surface of the third waveguide 13 that is perpendicular to its light propagation direction are positioned in the same plain as the light incident surface of the first waveguide 11.

Further, at the side of the light emitting surface of the first waveguide 11, a rectangular prism 21 serving as a light path coupling part which optically couples the first waveguide and the second waveguide, and this rectangular prism 21 is disposed straddling the end surfaces of these waveguides so that the light emitted from the light emission end surface of the first waveguide 11 is reflected thereby to be incident to the one end surface of the second waveguide 12. Further, at the side of the light incident surface of the first waveguide 11, a rectangular prism 22 serving as a light path coupling part which optically couples the second waveguide and the third waveguide, and this rectangular prism 22 is disposed straddling the end surfaces of these waveguides so that the light emitted from the side of the other surface of the second waveguide 12 is reflected thereby to be incident to the other end surface of the third waveguide 13.

Further, at the side surface and at the upper and lower end surfaces of the waveguides 11 to 13 and at the external surface of the rectangular prism, a reflection film 3 is provided so as to effectively carry out light confinement in the respective waveguides. These reflection films 3 comprise a metal film such as aluminum material.

Functions and effects will be described.

First of all, an operation of an optical element 10 according to the first embodiment will be briefly described.

When a light is incident to the light incident surface of the first waveguide 11, the incident light transmits through the first waveguide 11 and the rectangular prism 21 to be incident to the second waveguide 12. The light incident to the second waveguide 12 transmits through the waveguide 12 and the rectangular prism 22 to be incident to the third waveguide 13. The light incident to the third waveguide 13 is emitted from an end surface of the third waveguide 13.

Hereinafter, that the incident light can be converted into the output light having a uniform cross-section intensity distribution in the optical element 10 of this embodiment will be described.

For example, a case where a laser light is employed for the incident light is considered. While generally a laser light has a cross-sectional light intensity distribution of a Gaussian distribution, when the laser light is propagated through the waveguide with being subjected to multi-reflections, the reflected laser lights are mixed. Thereby, the light intensity distributions in arbitrary surfaces which are perpendicular to the light transmission directions in the waveguides 11, 12, and 13 are gradually made uniform in the plains as it becomes far from the light incident surface. Accordingly, by setting the lengths in the light transmission direction of the waveguides at appropriate values, the cross-sectional light intensity distribution of the laser light that is incident to the waveguide 11 can be made uniform at the light output end surface of the waveguide 13.

In quite general semiconductor lasers (such as AlGaAs series, AlGaInP series, or GaN series), the aspect ratio and the spread angle of the output lights are different. Accordingly, when a waveguide having a cross-section aspect ratio of approximately 1 is employed, a required waveguide distance may be short in order to make the cross-sectional intensity distribution uniform in the direction in which the spread angle of the light emitted from the semiconductor laser is larger, but the distance is required to be long in the direction in which the spread angle is smaller.

Conventionally, there is proposed a device which utilizes a rod shaped integrator waveguide as shown in patent reference No. 4 as a method of making the cross-section intensity distribution uniform, but it is required to make the rod length larger than several 10s mm in the light transmission direction in order to realize a perfect uniform cross-section light intensity distribution.

To the contrary, in the first embodiment of the present invention, first to third waveguides 11 to 13 are disposed overlapping, and these waveguides 11 to 13 are optically coupled so that the output light from the first waveguide is incident to the second waveguide and the output light from the second waveguide is incident to the third waveguide by using prisms 21 and 22. Thereby, the total of the lengths of these three waveguides 11 to 13 become the wave guiding distance of the light required to make the cross-sectional light intensity distribution uniform. Therefore, it is possible to shorten the lengths in the light transmission direction of the respective waveguides and to greatly shorten the length of the entire device.

The method for concretely determining the lengths of the waveguides will be described.

In the optical element 10 of the first embodiment, since the lengths in the light propagation direction of the waveguide is a main factor which determines the size of the device, a design which can realize an as much as possible compact optical element is required.

FIG. 2 shows a diagram optically and geometrically illustrating a light transmission path of the laser light which transmits through a simple rod shaped waveguide.

FIG. 2 shows a case where a single semiconductor laser is disposed adjacent the light incident surface of the waveguide so that the output light from the single semiconductor laser is incident to inside of one waveguide as a case where the size in the light transmission direction of the optical element is lengthened to the maximum.

In the figures, Ld designates a semiconductor laser, and Wg designates a waveguide comprising transparent material having a refractive index n. .theta.1 designates a spread angle of laser light L1 in the waveguide Wg, which is represented by a half-value entire angle of the light intensity distribution. Here, the width of waveguide Wg in spread direction of the laser light is W, and the length from the light incident surface to the light emitting end surface of the waveguide Wg, i.e., the length of the waveguide is made L.

In the arrangements of the semiconductor laser and waveguide shown in FIG. 2, the laser light L1 incident to the waveguide Wg is reflected by the side surface of the waveguide Wg. Accordingly, there can be seen a light intensity distribution that is obtained by overlapping on the light intensity distribution that is obtained by reflecting the former light intensity distribution at the side wall portion of the waveguide Wg. FIG. 3 shows a manner in which the light intensity distribution is made uniform by the reflection of the laser light at the side surface of the waveguide.

FIG. 3(a) shows a light intensity distribution in a case where the laser light transmits in a free space where there is no waveguide present, FIG. 3(b) shows a state of light intensity distributions being overlapped with each other at the side surface of the waveguide in a case where the laser light transmits in a waveguide, and FIG. 3(c) shows the light intensity distribution that is obtained by the above-described overlapping of the light intensity distribution. In FIG. 3, Ld denotes a semiconductor laser, and Wg denotes a waveguide comprising transparent material having refractive index n. Further, .theta.2 designates a spread angle of the semiconductor laser light in a free space, and .theta.3 designates a spread angle of laser light in the waveguide Wg having a refractive index n.

As shown in FIG. 3(a), the light emitted from the semiconductor laser which propagates in the free space is broadened in a spread angle .theta.2 with its propagation. In this way, while the spatial spreading of the light emitted from the semiconductor laser Ld increases in the free space, its intensity distribution does not change, and its cross-sectional intensity distribution keeps to maintain a Gaussian distribution type intensity distribution.

More particularly, in any of the plain D that is perpendicular to the light propagation direction in the vicinity of the semiconductor laser Ld, the plain F that is perpendicular to the light propagation direction that is apart from the semiconductor laser Ld, and the plain E that is perpendicular to the light propagation direction located between these two positions, the light intensity distribution is in a Gaussian distribution.

On the other hand, the light emitted from the semiconductor laser Ld which propagates through the waveguide Wg is totally reflected by side walls of the waveguides Wg as shown in FIGS. 3(b) and 3(c).

More particularly, the light intensity distribution of the laser light that is incident to the waveguide Wg has a Gaussian distribution in a plain D' that is perpendicular to the light propagation direction in the vicinity of the semiconductor laser Ld, while as the laser light advances along the light propagation direction from the light incident surface with repeating multiple refection of the laser lights in the waveguide, the light intensity distribution of the laser light is gradually made uniform in the cross-section (plain E' that is perpendicular to the light propagation direction) of the waveguide, and it is made uniform in a plain F' that is perpendicular to the light propagation direction that is apart from the semiconductor laser Ld.

In this case, the spread angle .theta.3 of the laser light thai is incident into the waveguide Wg of refractive index n becomes: .theta.3=2.times.sin.sup.-1((sin(.theta.2/2))/n)

Assuming the width of the waveguide Xg is W, when the incident light beam into the waveguide Wg reaches a position where the distance from the incident surface is W/(2.times.tan(sin.sup.-1(sin(.theta./2)/n))), a part of the light intensity distribution starts to be reflected at the side surfaces of the waveguide Wg. Further, when the incident light beam exceeds this position, the intensity distribution of the light gradually increases, and until the light reaches the light emitting surface of the waveguide Wg, a light intensity distribution that is obtained by overlapping a light intensity distribution when a light propagates in a free space with one as shown FIG. 3(a) that is obtained by reflecting the light intensity distribution at a portion corresponding to the sidewall of the waveguide, is observed (FIG. 3(b)).

Then, in order that substantial light intensity distribution (FIG. 3(c)) is made sufficiently uniform, it is preferable the length of the waveguide Wg is made sufficiently long, and the number of times of total reflection is increased. However, in view of device fabrication and use, an as much as possible compact laser light source is desired.

By the examination on length of waveguide that is required to make the light intensity distribution of the laser light in the waveguide Wg, it is found that if the formula (1) in the following is satisfied, the light intensity distribution is made uniform: L.gtoreq.W/tan(sin.sup.-1(sin(.theta.1/2)/n)) (formula 1)

.theta.1: a spread angle of a laser output light

n: refractive index inside the waveguide

W: width of the waveguide

Accordingly, by disposing plural waveguides 11 to 13 stereoscopically overlapping to each other and serially connecting these waveguides by optical coupling parts 21 and 22, it is possible to make the size in the light propagation direction of the optical element a length that is required for making the light intensity distribution uniform, that is, a one third of the light propagation length L.

In this way, according to the optical element 10 of this first embodiment, since there are provided a plurality of waveguides which are disposed stereoscopically stacking with each other and optical path coupling parts 21,22 which optically serially couples these waveguides, it is possible to obtain an optical element which can convert the incident laser light into an emitted light having a uniform cross-sectional light intensity distribution, and having a small size in the light propagation direction.

In the above-described first embodiment, the number of stacked waveguides is three, this is not limited to three. Further, the length in the light propagation direction of the first to third waveguides 11 to 13 may be any length. In other words, in such an optical element which comprises plural waveguides which are stacked on each other as in the first embodiment, the number of lamination of waveguides and the lengths of respective waveguides can be arbitrarily determined as well as the device size can be arbitrarily varied.

Further, the advancing direction of the emitted light from the optical element can be made reverse to the advancing direction of the light incident to the optical element by setting the number of stacked waveguides an even number as well as it can be made the same as the advancing direction of the light incident to the optical element by setting the number of stacked waveguides an odd number. Therefore, it is possible to increase the degree of freedom in designing an optical element in which the light intensity distribution of the output light is made uniform.

Further, while an optical element in which plural waveguides are stacked with each other in its height direction, so that the light propagation directions in the respective waveguides are predetermined directions as in the first embodiment, the optical element may be one in which plural waveguides are overlapped with each other in its width direction or one in which plural waveguides are overlapped with each other in both of its width direction and its height direction. Further, one of the waveguides may have its light propagation direction which is different from the light propagation direction(s) of the other waveguide(s). In this case, the arrangement of waveguides in an optical element can be made one which accepts limitations on a layout in an apparatus which is provided with the optical element.

FIG. 4 shows an example that has such a stereoscopic arrangement of plural waveguides.

In FIG. 4, L1 designates an incident light incident to the waveguide, L2 designates an emitted light emitted from the waveguide.

The optical element 10a shown in FIG. 4(a) has three waveguides 11a, 12a, 13a and optical path coupling parts 21a, 22a which optically serially couples these waveguides.

In this optical element 10a, three waveguides 11a, 12a, 13a are arranged on a same plain in such a manner that the three waveguides 11a, 12a, 13a are positioned at each of the edges of a rectangular hollow three edged frame. A prism 21a which curves the light path by 90 degree is disposed between the light emitting end surface of the waveguide 11a and the light incident surface of the waveguide 12a so that these waveguides are mutually optically coupled. Further, a prism 22a which curves the light path by 90 degree is disposed between the light emitting end surface of the waveguide 12a and the light incident surface of the waveguide 13a so that these waveguides are mutually optically coupled.

The optical element 10b shown in FIG. 4(b) has three waveguides 11b, 12b, 13b and optical path coupling parts 21b, 22b which optically serially couples these waveguides, similarly as in the optical element 10 or 10a.

Here, the three waveguides 11b, 12b, 13b are arranged in their width directions, respectively, and the light emitting end surface of the waveguide 11b and the light incident surface of the waveguide 12b are positioned in the same plain, and the light emitting end surface of the waveguide 12b and the light incident surface of the waveguide 13b are positioned in the same plain. Further, a rectangular prism 21b which optically couples the waveguide 11b and the waveguide 12b is disposed straddling the light emitting end surface of the waveguide 11band the light incident side end surface of the waveguide 12b. Further, a rectangular prism 22bwhich optically couples the waveguide 12b and the waveguide 13b is disposed straddling the light emitting end surface of the waveguide 12b and the light incident side surface of the waveguide 13b.

The optical element 10c shown in FIG. 4(c) has three waveguides 11c, 12c, 13c and optical path coupling parts 21c, 22c which optically serially couples these waveguides, similarly as in the optical elements described.

Here, the waveguide 11c and the waveguide 12c are disposed adjacent to each other in their width directions. The light emitting end surface of the waveguide 11c and the light incident surface of the waveguide 12c are positioned in the same plain, and the light emitting end surface of the waveguide 12c and the light incident surface of the waveguide 13c are positioned in the same plain. Further, a rectangular prism 21c which optically couples the waveguide 11c and the waveguide 12c is disposed straddling the light emitting end surface of the waveguide 11c and the light incident side end surface of the waveguide 12c. Further, a rectangular prism 22c which optically couples the waveguide 12c and the waveguide 13c is disposed straddling the light emitting end surface of the waveguide 12c and the light incident side end surface of the waveguide 13c.

The optical element 10d shown in FIG. 4(d) has three waveguides 11d, 12d, 13d and optical path coupling parts 21d, 22d which optically serially couples these waveguides, similarly as in the optical elements described.

Here, the waveguide 11d and the waveguide 12d are disposed adjacent to each other in their width directions, and a rectangular prism 21d which optically couples the waveguide 11d and the waveguide 12d is disposed straddling the light emitting end surface of the waveguide 11d and the light incident side end surface of the waveguide 12d. Further, the waveguide 13d is disposed at the side of the light emitting end surface of the waveguide 12d so as to have a light propagation direction in the height direction of the waveguide 12d, and a prism 22d which curves the light path by 90 degree is disposed between the light emitting end surface of the waveguide 12d and the light incident surface of the waveguide 13d so as to optically couple waveguides.

While in this first embodiment, examples in which the light paths for transmitting the light through plural waveguides are curved at all the light path coupling parts are described as shown in FIG. 1 or FIG. 4, the light path may not be curved at all the light path coupling parts, but may be serially connected at each of the light path coupling parts.

While in the first embodiment the optical element was one that optically couples between waveguides using a prism, the optical element may not be limited to those in which a prism is employed to couple between waveguides.

Embodiment 2

FIG. 5 shows an optical element according to a second embodiment of the present invention.

The optical element 15 of this second embodiment is constituted by serially coupling the respective waveguides of the optical element 10 of the first embodiment, without using a prism.

More particularly, the optical element 15 shown in FIG. 5 has a first waveguide 16 which has an end surface that is inclined by 45 degree with respect to the light propagation direction in the waveguide, a second waveguide 17 which has both end surfaces that are respectively inclined by 45 degree with respect to the light propagation direction of the waveguide, and a third waveguide 18 which has an end surface that is inclined by 45 degree with respect to the light propagation direction.

Here, the inclined surface 16a at an end side of the first waveguide 16 is a reflection plain that reflects the light propagating in the waveguide to be reflected along the waveguide height direction. The inclined surface 17b at an end side of the second waveguide 17 is a reflection plain directing downwards that reflects the light that is incident along the waveguide height direction so as to make its advancing direction be the waveguide length direction, and the inclined surface 17a at the other end side of the second waveguide 17 is a reflection plain directing upwards that reflects the light propagating in the waveguide so as to make the same emit along the waveguide height direction. The inclined surface 18b at an end side of the third waveguide 18 is a reflection plain directing downwards that reflects the light incident along the waveguide height direction so as to make its advancing direction be the waveguide length direction.

In this optical element 15, the second waveguide 17 is stacked on the first waveguide 16 so that the light propagation directions in these waveguides are parallel to each other and that the upward directing reflection plain 16a at an end side of the first waveguide 16 and the downward directing reflection plain 17b at the other end side of the second waveguide 17 confront to each other. Further, the third waveguide 18 is stacked on the second waveguide 17 so that the light propagation directions in these waveguides are parallel to each other and that the upward directing reflection plain 17a at an end side of the second waveguide 17 and the downward directing reflection plain 18b at the other end side of the third waveguide 18 confront to each other. The first waveguide 16 and the second waveguide 17 disposed thereon, and the second waveguide 17 and the third waveguide 18 disposed thereon, are respectively adhered to each other at their confronting surfaces by such as adhesion.

Here, by the upward directing reflection plain 16a of the first waveguide 16 and the downward directing reflection plain 17b of the second waveguide 17, the optical path coupling part which couples the first waveguide 16 and the second waveguide 17 is provided, and by the upward directing reflection surface 17a of the second waveguide 17 and the downward directing reflection surface 18b of the third waveguide 18 the optical path coupling part which couples the second waveguide 17 and the third waveguide 18 is provided.

Here, at the upper and lower both side surfaces of the respective waveguides 16, 17, 18 and the external surfaces of the optical coupling part, for example, a high reflection film such as a metal film comprising aluminum material is formed. Further, at the light coupling parts which couple the upper and lower waveguides, glass material constituting the two waveguides are adhered, and these adhesion plains constitute light passing regions 19a and 19b where high reflection films are not formed.

Functions and effects will be described.

The light incident to the light incident side end surface of the first waveguide 16 propagates through the first waveguide 16 and the optical coupling part, and is incident to the second waveguide 17. The light incident to the second waveguide 17 propagates through the second waveguide 17 and the optical coupling part, and is incident to the third waveguide 18. Then, the light incident to the third waveguide 18 is emitted from the light emitting side end surface.

In this second embodiment, the first to third waveguides 16 to 18 are disposed stacking with each other, and these waveguides 16 to 18 are coupled with each other by utilizing inclined surfaces which are formed by processing the end surfaces of the respective waveguides so that the light emitted from the first waveguide 16 is incident to the second waveguide 17 and the light emitted from the second waveguide 17 is incident to the third waveguide 18. Therefore, the total of the lengths of the three waveguides 16 to 18 become the light wave guiding distance that is required to make the cross-section intensity distribution uniform. Thus, it is possible to shorten the lengths of the respective waveguides in the light propagation direction as well as to shorten the length of the entire device to a great extent.

Further, since the respective waveguides are optically coupled by utilizing inclined surfaces which are formed at the end portions of the waveguides, it is also possible to reduce the part number, without using prisms which are to be required.

Embodiment 3

FIG. 6 is a perspective view illustrating an optical element according to a third embodiment of the present invention.

The optical element 30 of this third embodiment is constituted having first to third waveguides 31 to 33 having rectangular configurations comprising glass material transmitting incident light, and optical coupling parts 21, 22 coupling the respective waveguides 31 to 33 optically serially.

In this optical element 30, second and third waveguides 32 and 33 are successively stacked on the first waveguide 31 so that the light propagation directions in theses waveguides are parallel to each other, and the first waveguide 31 and the second waveguide 32, and the second waveguide 32 and the third waveguide 33 are respectively optically coupled by a rectangular prism 21 which serves as an optical path coupling part and a rectangular prism 22 which serves as an optical path coupling part, respectively.

In this third embodiment, the respective waveguides 31 to 33 are constituted by hollow structure cells comprising material which is transparent at a visible light region, respectively, and either of gas or liquid and Brownian particles are sealed in the respective waveguides.

Functions and effects will be described.

The optical element constituted as above has a compact structure and can convert the incident laser light into a light having uniform cross-sectional light intensity distribution, and further can remove speckle noises which is specific to the laser light source.

A description is detailed below.

As discussed above, speckle noises are generated when laser light of high coherency is employed and the mutual interferences of scattered lights which are reflected at respective portions of convexo-concave at the surface of the screen are their causes. There is a method of vibrating the screen or a method of passing through a scattering plate as conventional methods of reducing speckle noises which are generally known. These methods give to the laser light random phases as temporarily and spatially thereby to arise spatial and temporal variations in the speckle patterns, thereby reducing speckle patterns observed.

In this point, it is thought effective to make the waveguide constituting an optical element as a hollow cell structure and disturb the phase of the laser light in the inside the waveguide. Further, the inventors have found that, noticing the Brownian particles in gas or liquid, the Brownian particles have similar phase disturbing functions.

The Brownian particles mean particles which perform Brownian motion, that is, which behaves irregularly and at random by that gas or liquid serving as solvent, collide to those from various directions and in various speeds, and the briskness of the movements depend on the sizes of Brownian particles, temperatures, and viscosity of solvents.

For example, when the temperature is raised, the thermal movement of molecules constituting the solvents becomes active. Accordingly, by the rise of the temperature, the solvent molecules vigorously move, and accompanying therewith, the Brownian particles become active in their movements. In other words, when the solvent molecules collide with Brownian particles with being rushed, the amount of the Brownian particles being moved becomes large. Therefore, as the temperature is high, the Brownian movement becomes active.

Further, when the size of the Brownian particles is increased, the mass thereof is also increased. Thereby, the amount of the Brownian particles being moved by the solvent molecules are decreased. Further, by that the surface area of the Brownian particles is increased, a lot of particle solvent molecules are collided with each other from various directions, and their forces are cancelled with each other, thereby the forces which the Brownian particles receive is decreased. From these two reasons, when the Brownian particles are large, the Brownian movement becomes not likely occur.

In this third embodiment, as the Brownian particles, latex particles which are colloid particles (polystylene standard particles, its particle diameter is about 1 .mu.m) is employed.

Colloid generally means a nature that is presented by particles of a size of 10.sup.-9 m to 10.sup.-6 m, and it is divided into gel for which the dispersion medium of the colloid particles is solid, sol for which the dispersion medium is liquid, and aerosol for which the dispersion medium is gas. While any of these colloids present Brownian movement, it is preferable that sol for which the dispersion medium is liquid is used. In order to reduce speckle noises, colloid particles which have sizes which can disperse the transmitting light is required. To that end, those which have particle diameter of about 1 .mu.m described above is used in this third embodiment.

Particularly, in order to employ the optical element of the present invention in the visible light region, the colloid particles are preferred to be transparent in the use wavelength region. While almost all of the colloid particles are opaque to the visible light, it is possible to adjust the light transmittance and the speckle noise reduction effect by utilizing such as diluted colloid solution by controlling the colloid concentration.

Speckle noises which are observed when latex solution that is obtained by the above latex particles are dispersed in water which is filling material (solvent) is hermetically sealed in a cell structure waveguide, as laser light is irradiated thereto when it reached a settling equilibrium, and the emitted light from the waveguide is projected onto the screen are compared with speckle noises which are observed when a waveguide which comprises glass material and which is not a hollow shape is used.

In the optical element which comprises a hollow structure waveguide filled with latex solution, the phase of the laser light transmitting through the waveguide is disturbed temporary and spatially by the latex particles which conduct Brownian movement, in addition to that they are subjected to the above-described function of making the emitted light intensity distribution uniform, and the speckle noises are reduced to a great extent with relative to a case where such as a waveguide which comprises glass material and is not of a hollow shape is used.

Besides, when latex particles of about 0.8 .mu.m particle diameter are used, the particle distribution and the Brownian movement of particles become intensive because the particles are light, and the speckle noises are more effectively reduced. On the contrary, when latex particles of larger particle diameter (of about 3 .mu.m particle diameter) are used, the scattering of light become large, but the Brownian movement becomes moderate, and as a total, the effect of reducing speckle noises is reduced. However, when the temperature of the latex solution is held above 60.degree. C., the Brownian movement becomes intensive and the effect of reducing the speckle noises becomes effective.

Since the optical element 30 according to the third embodiment of the present invention is provided with a plurality of waveguides 31 to 33 having hollow structures and optical path coupling parts 21, 22 which optically serially couple the waveguides, and has hermetically sealed either of gas and liquid and Brownian particles, it has a compact structure and can convert the incident laser light into an emitted output light having a uniform cross-section light intensity distribution, and therefore, it is possible to reduce speckle noises which are specific to the laser light source itself.

While in the third embodiment three waveguide 31 to 33 are disposed stacking with each other in the waveguide height direction so that the light transmission directions in the waveguides are parallel to each other and these waveguides are serially connected by the optical path coupling parts 21, 22, the number of waveguides or the number of optical path coupling parts, or the lengths or arrangements of the waveguides are not limited to these shown in the above-described third embodiment.

While in the third embodiment rectangular prisms 21, 22 are employed at the light path coupling parts 21, 22, the coupling of the waveguides may be realized by the respective end surfaces of the waveguides being inclined with respect to the light propagation direction as shown in the second embodiment, resulting in the same effects as in the third embodiment.

Embodiment 4

FIG. 7 are diagrams illustrating a laser light source according to a fourth embodiment of the present invention, where FIG. 7(a) is a perspective view and FIG. 7(b) is a side view.

The laser light source 140 of this fourth embodiment has integrated a semiconductor laser 41 with an optical element 40 which converts the laser light emitted from the laser light source 41 to an emitted light having a light intensity distribution that is made uniform. Here, the optical element 40 is the same as the optical element 10 of the first embodiment, and has first to third waveguides 11 to 13 which are disposed stereoscopically stacking with each other and first and second optical path coupling parts 21, 22 which optically serially couples these waveguides.

Next, the function and effect will be described.

At present, among laser light sources which are widely sold out, the smallest general-use laser light source is a semiconductor laser and is used in various apparatuses and in commercial products. As discussed above, the miniaturizatio