Illuminator and projection image display employing it

An illuminator comprising two light source sections (101, 102), a rod integrator (1), and a relay lens system (4) for introducing a light flux emitted from the rod integrator (1), wherein the rod integrator (1) is a columnar optical element having an incident end face (130F) and an exit end face (130B). One pair of opposite side faces out of four side faces are formed so that the planes face each other in parallel while the other pair of opposite side faces form a taper face where the planes face each other while inclining at a specified angle such that the opposite side faces recede from the incident end face (130F) toward the exit end face (130B). Lights from the two light source sections (101, 102) are converged to the vicinity of the incident end face (130F) of the rod integrator (1).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application of the Patent Cooperation Treaty application PCT/JP2003/012865, filed on Oct. 8, 2003, and entitled ILLUMINATOR AND PROJECTION IMAGE DISPLAY EMPLOYING IT, which claims priority to Japanese Application Nos. 2002-295547, filed on Oct. 9, 2002, 2003-142489, filed on May 20, 2003, and 2003-325810, filed on Sep. 18, 2003.

TECHNICAL FIELD

The present invention relates to illuminators and projection image display devices using the same.

BACKGROUND ART

Conventionally, projection image display devices, by which a small light valve displaying an image in response to a video signal is illuminated and the image is magnified and projected using a projection lens, are known as a method for displaying large-screen videos. Some light valves use a transmissive type or a reflective type liquid crystal panel and some light valves use a digital mirror device, which is an aggregation of micro-mirrors, and projection image display devices using these have been put into practical use. The following is a description of a conventional projection image display device.

FIG. 21is a conceptual diagram of an optical system showing a projection image display device that uses a conventional columnar optical element (hereafter, “rod integrator”), and a light valve. In this drawing, reference numeral2is a lamp, reference numeral3is an elliptical concave mirror, reference numeral4is a relay lens system, reference numeral5is a field lens, reference numeral6is a transmissive light valve, reference numeral7is a projection lens, and reference numeral15is a rod integrator made of a glass material.

The following is a description of the operation. The light-emitting center of the lamp2is arranged in the vicinity of a first focal point of the elliptical concave mirror3. After the light flux emitted from the lamp2is reflected by the elliptical concave mirror3, the light is converged in the vicinity of a second focal point of the elliptical concave mirror3. The incident face of the rod integrator15is arranged in the vicinity of the second focal point. The light flux of the incident light is totally reflected as appropriate by side surfaces in the longitudinal direction of the rod integrator15and emitted by the rod integrator15.

The following is a description of the fundamental operation of the conventional rod integrator15.FIG. 22is a top view of the operation of an incident light ray andFIG. 23is a lateral view of the operation of an incident light ray. In these drawings, the light ray, which is incident at an angle θ, is totally reflected as appropriate by side surfaces in the longitudinal direction of the rod integrator15. The light ray is transmitted while maintaining its angle, and the light is emitted at an angle θ. Accordingly, if the maximum value of the converging angle of the elliptical concave mirror3is 30° for example, a light ray of a maximum 30° corresponding to this is emitted from the rod integrator15.

Furthermore, if the angles of the incident light rays are different, the number of times the light is totally reflected as appropriate by the side surfaces in the longitudinal direction of the rod integrator15is different. Since these are merged at the exit face, the light rays are superimposed at the exit face even when there is an uneven illumination distribution at the incident face. A result of this is that it is possible to obtain an illumination light flux at the exit face of the rod integrator15that has superior uniformity and that has a form that is approximately equivalent to a desired illumination range. Note, however, that since better uniformity can be achieved with a larger the number of reflections, a sufficient length of the rod integrator15obviously has to be ensured.

Furthermore, the light flux emitted from the rod integrator15illuminates the transmissive light valve6via a relay lens system4, which is configured by at least one lens, and a field lens5. The transmissive light valve6displays an image based on an electric signal that is output from a drive circuit (not shown). The image displayed on the transmissive light valve6is magnified by a projection lens7and projected onto a screen (not shown).

Furthermore, there is a strong demand to make the projected images of such projection image display devices brighter, and projection image display devices have been disclosed that use a plurality of light sources. For example, methods are disclosed such as in Patent Document 1, in which emitted light fluxes from a plurality of light sources are synthesized using a light guiding means such as an optical fiber, and a method in which light sources are arranged in predetermined positions and reflected light is synthesized by a reflective mirror and a reflective prism or the like.

Further still, in Patent Document 2 below, there is one light source, but a tapered portion is formed in the rod integrator that continuously increases in cross section from the incident end face to the exit end face. By controlling the tapering angle of the tapered portion, this structure achieves a desired value in the parallelism of the converged light flux from the lamp.

To increase the brightness in the configuration of the conventional projection image display devices shown above, methods are employed such as raising the lamp power consumption, and using a lamp that is almost a point light source, for example an extra-high pressure mercury lamp with an electrode distance of 1.3 mm or less, and increasing the rate of light convergence to increase the brightness.

However, when using the above two methods, increasing the power consumption while keeping the same electrode distance considerably shortens the life of the light source. Furthermore, leaving the power consumption the same and further shortening the distance between electrodes also results in considerable shortening of the life of the light source. Accordingly, how to further increase device brightness without shortening the life of the light source is an issue in configurations with a single light source such as in Patent Document 2.

On the other hand, a method disclosed in Patent Document 1, which attempts to increase brightness by using a plurality of light sources, is a synthesizing method in which the converging angles of light rays emitted from light source portions, which are made of a light source and an elliptical concave mirror, are left unchanged for emission. For example, when the light fluxes from two light source portions are synthesized, light rays emitted from the elliptical concave mirror with a converging angle of about 15° will have a maximum divergence angle of about 30° that is synthesized and emitted.

For this reason, although it seems to possible to realize a condenser lens to be used at a stage following the synthesizing portion made of a reflective mirror or reflective prism, when trying to achieve a sufficient condensing ratio with the elliptical concave mirror for the converging angle of about 15°, it is necessary that the positions of the first and second focal points of the elliptical concave mirror are sufficiently distanced, and that the elliptical concave mirrors themselves are large, and therefore there is the problem that the device cannot be miniaturized.

Furthermore, presently it is common to use elliptical concave mirrors with a converging angle of approximately 30°, which gives importance to improving brightness and device miniaturization, but when using two of these, the maximum divergence angle corresponding to the converging angle of the light rays reflected from synthesizing portions made of a reflective mirror or reflective prism is about 60°, and it is difficult and impractical to achieve a condenser lens to be used at a stage following the synthesizing portion.

With a configuration of Patent Document 2, the divergence angles at the exit end face can be controlled using a rod integrator with a tapered portion. However, in single light source configurations, this technique is for controlling the parallelism of light fluxes in both horizontal and vertical directions using tapered surfaces formed in the rod integrator in both the horizontal and vertical directions. That is, Patent Document 2 does not disclose a technique addressing the enlargement of the maximum divergence angle when using two light sources.

DISCLOSURE OF INVENTION

The present invention solves the above-described conventional problems and it is an object thereof to provide an illuminator and a projection image display device using this illuminator that can achieve high brightness and uniformity from a plurality of light source portions onto an area to be illuminated.

In order to achieve this object, an illuminator according to the present invention is provided with a light source portion including a lamp and a concave mirror; a rod integrator; and a relay lens system that guides a light flux emitted from the rod integrator; wherein the rod integrator is a columnar optical element having an incident end face at a front side and an exit end face at a back side; wherein, when a long-side direction of the exit end face is a horizontal direction and a short-side direction is a vertical direction, of four side surfaces other than the front side and the back side of the columnar optical element, one pair of opposing side surfaces is formed as tapered surfaces in which the side surfaces face each other at an inclination of a predetermined angle such that a distance between the side surfaces in the horizontal direction or the vertical direction increases from the incident end face toward the exit end face; wherein light from the light source portion is converged and irradiated onto a vicinity of the incident end face of the rod integrator; and wherein two of said light source portions are arranged in the horizontal direction or the vertical direction.

Next, a projection image display device according to the present invention is provided with a light source portion including a lamp and a concave mirror; a rod integrator; a relay lens system that guides a light flux emitted from the rod integrator; a light valve that modulates a light flux guided from the relay lens system and forms an image; and a projection lens that projects an image formed by the light valve; wherein the rod integrator is a columnar optical element having an incident end face at a front side and an exit end face at a back side; wherein, when a long-side direction of the exit end face is a horizontal direction and a short-side direction is a vertical direction, of four side surfaces other than the front side and the back side of the columnar optical element, one pair of opposing side surfaces is formed as tapered surfaces in which the side surfaces face each other at an inclination of a predetermined angle such that a distance between the side surfaces in the horizontal direction or the vertical direction increases from the incident end face toward the exit end face; wherein light from the light source portion is converged and irradiated onto a vicinity of the incident end face of the rod integrator; and wherein two of said light source portions are arranged in the horizontal direction or the vertical direction.

BEST MODE FOR CARRYING OUT THE INVENTION

With an illuminator or a projection image display device according to the present invention, it is possible to control the divergence angle of light at the exit end face using a pair of tapered surfaces of the rod integrator, and when using two or more light source portions, it is possible to make the divergence angles of light at the exit end face substantially equivalent in the horizontal and vertical directions even when the divergence angles at the incident end face are different in the horizontal and vertical directions. For this reason, it is possible to achieve a light of high brightness and uniformity. Furthermore, it is possible to achieve device miniaturization.

In the illuminator and the projection image display device according to the present invention, it is preferable that, of the four side surfaces other than the front side and the back side of the columnar optical element, one pair of opposing side surfaces is provided with a portion in which the side surfaces are parallel to each other, and the other pair of opposing side surfaces is formed as tapered surfaces in which the side surfaces face each other at an inclination of a predetermined angle such that the distance between the two side surfaces increases from the incident end face toward the exit end face. With this configuration, light reflected by the side surfaces of the pair of parallel planes is such that the divergence angle of light at the incident end face and the divergence angle of light at the exit end face are the same, and light reflected by the tapered surfaces is such that the divergence angle of light at the incident end face and the divergence angle of light at the exit end face are different. When using a total of two light source portions, this makes it possible to achieve a divergence angle of light at the exit end face that is substantially equivalent in the horizontal direction and the vertical direction even when the divergence angles of light at the incident end face are different in the horizontal direction and the vertical direction.

Furthermore, it is preferable that, parallel to the two light source portions, a further two light source portions are arranged, and of four side surfaces other than the front side and the back side of the columnar optical element, both pairs of opposing side faces are formed as tapered surfaces in which the side surfaces face each other at an inclination of a predetermined angle such that the distance between the two side surfaces increases from the incident end face toward the exit end face. When using a total of four light source portions, with this configuration it is possible to make the divergence angle of light at the exit end face substantially equivalent in the horizontal and vertical directions, and it is possible to make the divergence angle of light at the exit end face small than the divergence angle of light at the incident end face. This is particularly advantageous when a light of high brightness is desirable.

Furthermore, it is preferable that, when the two light source portions are a first light source portion and a second light source portion, the illuminator further comprises a first reflector for guiding light from the first light source portion to the incident end face of the rod integrator and a second reflector for guiding light from the second light source portion to the incident end face of the rod integrator. With this configuration, since the first and second reflector are provided, it is possible to achieve a high level of freedom in the arrangement of the two light source portions.

Furthermore, it is preferable that a maximum value in the horizontal direction and a maximum value in the vertical direction of the divergence angle of light emitted from the exit end face of the rod integrator are substantially the same. With this embodiment, there is the advantage of achieving a light of high brightness and uniformity.

Furthermore, it is preferable that, when a normal direction on the pair of parallel planes is a first direction and a direction that is perpendicular to a center line of the rod integrator and perpendicular to the first direction is the second direction, the two light source portions are arranged such that a divergence angle of light entering the incident end face of the rod integrator has a maximum value in the second direction that is larger than a maximum value in the first direction; that light corresponding to the maximum value in the second direction is reflected by the tapered surfaces of the rod integrator and light corresponding to the maximum value in the first direction is reflected by the parallel planes of the rod integrator; and that a divergence angle of light at the exit end face has a maximum value in the first direction that is substantially the same as a maximum value in the first direction at the incident end face, and the maximum value of the divergence angle of the exit end face in the second direction is smaller than the maximum value in the second direction at the incident end face. With this configuration, it is possible to achieve control such that while using the parallel surfaces of the rod integrator to keep the divergence angle of light in the vertical direction at the incident end face substantially equivalent, the tapered surfaces of the rod integrator can be used to make the divergence angle of light in the horizontal direction at the exit end face different from the divergence angle of light in the horizontal direction at the incident end face.

Furthermore, it is preferable that the first light source portion and the second light source portion are arranged such that the second light source portion is in an emission direction of the first light source portion.

Furthermore, it is preferable that the illuminator further comprises a projection lens, and that optical axes of the concave mirrors of the two light source portions and an optical axis of the projection lens are perpendicular. With this configuration, the light source portions can be made not to slant even when the installation adjustment angle is changed, thus reducing the possibility of harming the life of the light sources, and achieving increased reliability.

Furthermore, it is preferable that the first light source portion and the second light source portion are arranged such that an optical axis of a concave mirror of the first light source portion and an optical axis of a concave mirror of the second light source portion do not intersect a center line of the rod integrator. With this configuration, by providing reflector, it is possible to prevent the occurrence of areas that cannot be used by the light rays.

Furthermore, it is preferable that the first and second reflector are constituted by a reflection mirror or prism coated with a dielectric material.

Furthermore, it is preferable that, when an angle between a center line of the rod integrator and an optical axis of the concave mirror that passes through an apex of the concave mirror is an incident angle; an angle formed by a light flux emitted from a most peripheral area of an effective aperture of the concave mirror and a center line of the rod integrator at the incident end face is a maximum angle; and a difference between the maximum angle and the incident angle is a converging angle; then the incident angle is smaller than the converging angle. With this configuration, it is possible to improve the device brightness.

Furthermore, it is preferable that a ratio of the incident angle to the converging angle is in a range of at least 60% and at most 80%. With this configuration, it is possible to achieve excellent convergence efficiency.

Furthermore, it is preferable that the projection image display device according to the present invention is provided with a means for turning light that turns a light flux emitted from the rod integrator around a center line of the rod integrator and guides the light flux to the light valve in accordance with an arrangement of the light valve. With this configuration, since a means for turning light is provided, it is possible to improve the efficiency of light utilization of the light valve.

First, the structure and operation of a projection image display device according to Embodiment 1 is described usingFIG. 1.FIG. 1is a top view of a conceptual diagram of an optical system according to Embodiment 1.

As shown inFIG. 1, the projection image display device according to the present embodiment is provided with two light source portions101and102, a rod integrator1, a relay lens system4that guides the light flux emitted from the rod integrator1, a field lens5, a transmissive light valve6that modulates the light flux guided by the relay lens system4and forms an image, and a projection lens7that projects the image formed by the light valve6.

It should be noted that inFIG. 1, although an example is shown of a projection image display device, the structure from the two light source portions101and102to the relay lens system4in the order in which the light flux proceeds also may be an illuminator, which can be used independently. Furthermore, a projection lens further may be added to the illuminator. This is also true for the embodiments described below.

The light source portions101and102have the same structure and are respectively provided with a light source2, and a concave mirror3which is a condenser optical system that condenses light from the light sources2. An extra-high pressure mercury lamp, a metal halide lamp, a xenon lamp, or a white lamp such as a halogen lamp can be used as the light sources2. In the example of this diagram, the concave mirrors3are elliptical concave mirrors. Furthermore, the rod integrator1is formed with a glass material that has good heat resistance.

FIG. 2is a perspective view andFIG. 3Ais a top view of the rod integrator1.FIG. 3Bincludes a lateral view and left and right lateral views. As shown inFIG. 2, the rod integrator1is a columnar optical element provided with an incident end face130F at a front side, an exit end face130B at a back side, and four side surfaces (130T,130U,130L, and130R). Of the side surfaces that face each other, in one direction there are the side surfaces130T and130U, which are parallel planes (seeFIG. 3B). In another direction, there are opposing side surfaces130L and130R, which are planes that face each other at an inclination of a predetermined angle such that both side surfaces130L and130R become farther apart from each other from the incident end face130F toward the exit end face130B (seeFIG. 3A).

It should be noted that in this embodiment, “horizontal direction” refers to the long-side direction of the exit end face130B (the direction of arrow “a” inFIG. 2) and “vertical direction” refers to the short-side direction of the exit end face130B (the direction of arrow “b” inFIG. 2). This is also the same in embodiments below.

That is, when the rod integrator1is viewed in the vertical direction, the pair of side surfaces130T and130U are formed parallel, but when viewed in the horizontal direction, the pair of side surfaces130R and130L are arranged in a tapered shape such that they widen from the incident end face130F toward the exit end face130B.

InFIG. 1, the two light source portions of the pair of light source portions101and102, which include the lamps2and the concave mirrors3, are arranged in the horizontal direction (the direction of the arrow “a”). Furthermore, the light-emitting centers of the lamps2of the light source portions101and102are positioned in the vicinity of a first focal point of the concave mirrors3.

Each of the light source portions101and102is arranged at an incident light angle θ to the incident end face130F, and the light fluxes emitted from each of the lamps2are reflected by the concave mirrors3, then converged and irradiated onto the vicinity of the incident end face130F, that is, a second focal point of the concave mirrors3. Here, “incident light angle” refers to the angle between a center line103of the rod integrator and the optical axes of the concave mirrors3, which pass through apexes3aof the concave mirrors3. In the example shown inFIG. 1, the angle θ corresponds to the incident light angle.

It should be noted that when a reflective surface other than the concave mirror3is provided between the incident end face130F and the lamps2, “light ray intersecting the apex3aof the concave mirror3” refers to a light ray that intersects the apex3aof the concave mirror3via the reflective surface and traveling through an intersecting point of the center line103and the incident end face103F.

As described above, the incident end face130F of the rod integrator1is arranged in the vicinity of the second focal point of the concave mirror3. The incident light fluxes are totally reflected as appropriate by side surfaces of the rod integrator1in the vertical and horizontal directions and emitted from the exit end face130B of the rod integrator1.

The following is a description of the fundamental operation of the rod integrator1.

FIG. 4is a top view of the rod integrator1showing the behavior of the incident light ray.FIG. 5is a lateral view of the rod integrator1showing the behavior of the incident light ray.FIG. 4shows how the incident light ray enters the incident end face130F at a maximum angle (2θ), and is then reflected inside the rod integrator1and emitted from the exit end face130B. Here, “maximum angle” refers to the maximum angle corresponding to one of the light sources of the light entering the incident end face130F of the rod integrator1.

More specifically, “maximum angle” refers to the angle between the light flux emitted from the most peripheral area of the effective aperture of the concave mirror3(effective diameter R inFIG. 1) and the center line103of the rod integrator1at the incident end face130F. In the example shown inFIG. 1, the angle θM corresponds to the maximum angle.

Furthermore, “converging angle” here refers to the angle obtained by subtracting the incident angle from the maximum angle.

Given θMAX as the maximum angle, θE as the incident angle, and θc as the converging angle, the above relationship can be arranged in the following formula (1):
θMAX=θE+θcFormula (1)

In the example shown inFIG. 1, both the incident angle θE and the converging angle θc are θ and the maximum angle θMAX is 2θ. As shown inFIG. 4, an incident light ray at the maximum angle 2θ is emitted from the exit end face130B at an angle θ′ that is different from the maximum angle 2θ due to being totally reflected as appropriate by the pair of tapered surfaces of the rod integrator1.

On the other hand, inFIG. 5, an incident light ray at the angle θ″ is maintained and emitted at the same angle θ″ as the incident angle due to being totally reflected as appropriate by the pair of parallel side surfaces of the rod integrator1.

InFIGS. 2 and 3for example, when the effective horizontal length of the exit end face of the rod integrator1is 7.6 mm, with a tapering angle of approximately 1.63734°, a length of 56.18624 mm, and five reflections at the side surfaces in the longitudinal direction, and using quartz (refractive index nd=1.45874) with good heat resistance and optical properties for the glass material of the rod integrator1, then incident light with a maximum angle 2θ of 60° inFIG. 4can be emitted at approximately 30°. Furthermore, inFIG. 5, incident light at 30° can be maintained and transmitted at an angle of 30°.

More specifically, when the incident angle of each of the concave mirrors is 30° as described above, according to formula (1), the maximum angle of the concave mirrors3is 60°. When two concave mirrors3are arranged in the horizontal direction as in the configuration inFIG. 1, light is incident at the exit end face130F of the rod integrator1at the maximum angle of 120°, but the maximum emission angle of the exit end face130B can be set to approximately 60°.

On the other hand, when viewed in the vertical direction, the maximum value of the angle of incident light at the incident end face even when two concave mirrors3are arranged is no different from when there is a single concave mirror3. The maximum value is 60°, with the angle being maintained and transmitted while light is reflected between the parallel surfaces to be emitted at 60°.

In this way, even when the maximum value of the angles at the incident end face130F of light incident to the rod integrator1is 120° in the horizontal direction and 60° in the vertical direction, the emission angle at the exit end face130B can be set to approximately 60° in both the horizontal and vertical directions.

In other words, even when the maximum value in the horizontal direction of the converging angle of the light flux incident at the incident end face130F is larger than the maximum value in the vertical direction, the divergence angle of the light flux emitted from the exit end face130B can be set such that the maximum value in the horizontal direction and the maximum value in the vertical direction are approximately equal.

Furthermore, color display can be achieved by arranging in the vicinity of the emission portion of the rod integrator1a color wheel (not shown inFIG. 1) constituted by dichroic filters that allow the transmission of at least the three primary colors red, blue, and green, and that rotates to separate white light on a time-division basis.

It should be noted that a property of the thin films used in coating the dichroic mirrors that constitute the color wheel is that they usually are rated to support an incident angle of 30°, so that in this case, the desired angle of the incident angle of the concave mirrors3is 30°.

Further still, if the angles of the incident light rays are different, the number of times the light is totally reflected as appropriate on the respective pairs of side surfaces in the horizontal direction and vertical direction of the rod integrator1will be different. And since they are merged at the exit face, the light rays are superimposed at the exit face even when there is an uneven illumination distribution at the incident face. A result of this is that it is possible to obtain an illumination light flux at the exit end face130B of the rod integrator1that has superior uniformity and that has a form that is approximately equivalent to a desired illumination range.

However, although it is generally true that better uniformity can be achieved with a larger number of reflections, it must be emphasized that it is necessary to determine the form of the rod integrator1giving consideration to the fact that the maximum exit angle depends on the taper angle and the number of reflections of the incident light rays.

The following is a description of determining the form of the rod integrator1usingFIG. 6.FIG. 6is a top view of the rod integrator1. In determining the form of the rod integrator1, although the details will be described in order with reference to the formulae, it is necessary to determine the number of reflections on the tapered surfaces130R and130L of the incident light ray with the maximum angle of the light incident on the incident end face130F (hereafter, “number of reflections”) and derive a tapering angle θT and a horizontal length L′ of the incident end face130F.

Further still, values for a horizontal length L of the exit end face130B, the maximum angle of the light source θMAX, and a refractive index nd of the rod integrator1are required, but these are constants. This is because the length L is determined according to such factors as the form of the light valve, the maximum angle θMAX is determined by the incident angle of each light source portion, and the refractive index nd is determined by the material that constitutes the rod integrator. Furthermore, the value for the emission angle θE is also required, but this value is a requirement determined according to the maximum angle θMAX, so this too is a constant.

InFIG. 6, if the emission angle immediately after refraction of the incident light on the incident end face130F with the maximum angle θMAX (degrees) is given as θ′MAX (degrees), the following formula (2) is true according to Snell's law:
1×sin θMAX=nd×sin θMAX′  Formula (2)

Furthermore, if the emission angle immediately before refraction of the incident light on the exit end face130B with the maximum angle θMAX is given as θ′E (degrees), and the emission angle immediately after refraction on exit end face130B is given as θE (degrees), the following formula (3) is also true according to Snell's law:
1×sin θE=nd×sin θ′EFormula (3)

Furthermore, as shown inFIG. 6, when the initial incident angle θR1(degrees) is set with the normal lines of the reflective surfaces130R and130L as a reference, θR1can be expressed by the following formula (4):
θR1=90−(θ′MAX−θT)  Formula (4)

Furthermore, as shown inFIG. 6, when the incident angle θRn (degrees) for the number of reflections n (n=2, 3, 4, . . . ) is set with the normal lines of the reflective surfaces130R and130L as reference, θRn can be expressed by the following formula (5):
θRn=θR1+2×θT×(n−1)  Formula (5)

When θR1is eliminated from the formulae (4) and (5), the following formula (6) can be obtained:
θRn=90−(θ′MAX−θT)+2×θT×(n−1)  Formula (6)

On the other hand, the reflective angle θ′E before refraction at the exit end face130B is expressed by the following formula (7):
θ′E=90−θRn−θTFormula (7)

The following formula (8) can be obtained by transforming the formula (7):
θRn=90−θT−θ′EFormula (8)

Since θRn in both formula (6) and (8) are equivalent, the following formula (9) can be found, enabling θT to be obtained:
θT=(θ′MAX−θ′E)/2nFormula (9)

On the other hand, keeping in mind that before and behind illumination optical systems as known in the art, the product of the surface area of the illumination area and the solid angle of the illuminating light is constant, the length L′ (mm) in the horizontal direction of the incident end face130F can be expressed as follows since similarly the product of the surface area of the exit face of the rod integrator1and the emission angle of the illuminating light is equivalent to the product of the surface area of the transmissive light valve6and the solid angle of the illuminating light.
π×L′×V×sin θMAX×sin θV=π×L×V×sin θE×sin θV

Note that V (mm) is the length in the vertical direction of the rod integrator, θV (degrees) is the maximum incident angle in the vertical direction, and L (mm) is the length in the horizontal direction of the exit end face130B.

Based on this relationship, L′ can be determined using the following formula (10):
L′=L×sin θE/sin θMAX  Formula (10)

In this way, by determining the tapering angle θT and the length L′ in the horizontal direction of the incident end face130F, the length H (mm) in the longitudinal direction of the rod integrator1is determined with the following formula (11):
H=(L−L′)/2 tan θTFormula (11)

As described above, if the length L, the number of reflections n, the maximum angle θMAX, and the emission angle θE are determined, it is possible to derive the length U, the tapering angle θT, and the length H in the longitudinal direction, and thus it is possible to determine the form of the rod integrator1.

It should be noted that, as described above in regard to the form of the rod integrator1, it is possible to derive theoretical values by substituting desired numerical values in the above-described formulae. However, adjustments may be required for the theoretical value of the length H when consideration is given to the elliptical form of the concave mirror3, the tubular shape of the lamp2, the light distribution properties of the lamp, and the intensity distribution of the arc.

Furthermore, the calculated values have a tolerance range. It is preferable that θT (degrees) in formula (9) is in the following range:
[(θ′MAX−θ′)/2n]−1≦θT≦[(θ′MAX−θ′)/2n]+1

Furthermore, it is preferable that θT (degrees) is within the range of ±5′ (minutes) of the calculated value. Within this range, production is possible within the tolerance of polishing.

The following is a description of calculation examples using the above-described formulae. For example, presently it is common to use elliptical concave mirrors with a converging angle (incident angle) of approximately 30°, which gives importance to improving brightness and miniaturization. For this reason, two such elliptical concave mirrors are used for the rod integrator1according to the calculation examples. In this case, the maximum angle θMAX according to formula (1) is 60°. Given that the required value for the emission angle θE is 30°, a tapering angle θT of 1.63734° is found based on the formulas (2) to (9).

On the other hand, given that, in accordance with the size of the light valve, the length L of the side surface in the horizontal direction of the exit end face130B is 7.6 mm, based on the formula (10) it is possible to determine a length L′ of the incident end face130F of 4.38786 mm.

Furthermore, based on the formula (11), it is possible to determine a length H of 56.1862490 mm.

However, note that this was calculated using 5 as the number of reflections and with the refractive index nd of the rod integrator1as 1.45874.

The following tables show changes in the tapering angle θT, the length L′, and the length H when the number of reflections n and the maximum angle θMAX are changed. Table 1 shows the results of calculating the tapering angle θT from θMAX and the number of reflections n. Table 2 shows the results of calculating the length L′ of the incident end face130F from θMAX and the exit end face length L. Table 3 shows the results of calculating the length H by varying the number of reflections n and the maximum angle θMAX using the tapering angle θT, the length L of the exit end face130B, and the length L′ of the incident end face130F.

In these calculations, the nd of the rod integrator1is taken to be 1.45874 and the emission angle θE at the exit end face130B is taken to be

The light flux emitted from the rod integrator1determined in this way illuminates the transmissive light valve6via a relay lens system4, which is configured by at least one lens, and a field lens5.

The transmissive light valve6displays an image based on an electric signal that is output from a drive circuit (not shown). The image displayed on the transmissive light valve6is magnified by the projection lens7and projected onto a screen (not shown).

With the present embodiment, it is possible to achieve control such that while the divergence angle of light in the vertical direction of the exit end face130B is kept approximately equivalent to the divergence angle of light in the vertical direction of the incident end face130F (seeFIG. 5), the divergence angle of light in the horizontal direction of the exit end face130B is different from the divergence angle (maximum angle) of light in the horizontal direction of the incident end face130F (seeFIG. 4).

In this way, for example, in regard to light with a maximum angle at the incident end face130F of 60° (2θ inFIG. 4) and a divergence angle of 30° in the vertical direction with respect to the center line103(see θ″ inFIG. 5), it is possible to set the divergence angle of light in the horizontal direction of the exit end face130B (θ′ inFIG. 4) and the divergence angle of light in the vertical direction (θ″ inFIG. 5) to the same angle of 30°.

Accordingly, the divergence angle of light emitted from the exit end face130B when using two light sources has a maximum angle in the horizontal direction and a maximum angle in the vertical direction that is the same angle of 60°, and it is possible to obtain a light having high brightness and uniformity. In regard to brightness, it is possible to achieve a brightness that is approximately 1.7 to 1.8 times that achievable with a single light source portion. Furthermore, by alternating the use of single light source portions, the time until the light source of each light source portion expires is increased, and therefore it is possible to achieve approximately double the light source life compared to a device with one light source.

It should be noted that the present embodiment was described using an example of a projection image display device, but if using a device provided with at least, in the direction in which light proceeds, the structure from the light source2to the relay lens system4as an illuminator, it is possible to achieve an illuminator that can emit a light having high brightness and uniformity.

FIG. 7is a conceptual diagram of an optical system of a projection image display device according to Embodiment 2. The same reference numerals are used for items with the same structure as in the projection image display device according to Embodiment 1 shown inFIG. 1, and detailed description of such items is omitted here. Compared to the structure shown inFIG. 1, the arrangement of the two light source portions101and102is different in the structure shown inFIG. 7and a first reflector48and a second reflector49are provided.

In the present embodiment, synthesizing prisms48and49are used as the first and second reflector. The synthesizing prisms48and49are formed from a glass material with excellent heat resistance and their reflective surfaces are coated with a multi-layer dielectric film with an excellent reflectance ratio.

It is also possible to use a reflective mirror coated with a multi-layer dielectric film. However, when using a reflective mirror or prism on which aluminum or silver is deposited, it is necessary to insert a filter that removes ultraviolet light at a stage preceding the synthesizing portion.

The first reflector48guides light from the light source portion102to the incident end face130F of the rod integrator1and the second reflector49guides light from the light source portion101to the incident end face130F of the rod integrator1. When viewed from above, the first reflector48and the second reflector49are arranged such that they form a “>”-shape opening toward the side opposite to the incident end face130F of the rod integrator1(which is substantially a V shape when viewed from the incident end face130F). By being arranged in this way, the inclination angles of the reflective surfaces of the first reflector48and the second reflector49are half of the maximum angle.

In the present embodiment, by using the first reflector48and the second reflector49, there is a greater level of freedom in arranging the light source portions101and102, and in the example ofFIG. 7, the light source portions101and102are arranged opposing each other in the horizontal direction. That is, both light sources2and concave mirrors3face each other in the horizontal direction. The light fluxes emitted from the light sources2are reflected by the concave mirrors3, then respectively reflected by the first reflector48and the second reflector49. The reflected light is converged and irradiated at angles θ, which are equivalent with respect to the center line103of the rod integrator, in the vicinity of the incident end face130F, that is, in the vicinity of the second focal point of the concave mirrors3.

FIG. 8is a lateral view of a conceptual diagram of an optical system according to the present embodiment. The dotted line portion shows a state in which an installation adjustment angle9is adjusted in the elevation angle direction in accordance with the position of a screen (not shown). Ordinarily, the life of a light source is shortened by the influence of heat and other factors when it is slanted in the optical axis direction. In the present embodiment, since the optical axes of the concave mirrors3of the two light source portions101and102and the optical axis of the projection lens7are arranged perpendicularly, the optical axes of the light source portions are not slanted when the installation adjustment angle9is changed.

In this way, with the present embodiment, even when the light sources2and the concave mirrors3are rotated around their optical axis by the angle of the installation adjustment angle9, the position of the optical axes does not change, and the horizontal lighting is continued without a change in the specifications. For this reason, even if the device itself is installed slanted, there is little chance of harming the life of the light source, and a highly reliable device can be achieved.

FIG. 9is a conceptual diagram showing an optical system of a projection image display device according to Embodiment 3. The same reference numerals are used for items with the same structure as in the projection image display device according to Embodiment 1 shown inFIG. 1, and detailed description of such items is omitted here. Note, however, that the light source portions101and102are shown as more concrete objects, and the concave mirrors3are shown as cross sections (same for following diagrams).

Compared to the structure shown inFIG. 1, the arrangement of the two light source portions101and102is different in the structure shown inFIG. 9and a synthesizing mirror61(first reflector) and a synthesizing mirror62(second reflector) are provided. The synthesizing mirrors61and62are reflection mirrors coated with a multi-layer dielectric film for example.

Furthermore, the structure of the rod integrator1itself is the same as in Embodiment 1, but in contrast to the arrangement in Embodiment 1, the rod integrator1of the present embodiment is rotated 90° around the center axis103.

Accordingly, when using in Embodiment 3 the definitions of “vertical direction” and “horizontal direction” as described in Embodiment 1, the horizontal direction in the paper plane inFIG. 9is the “vertical direction” and the direction that is vertical to the paper plane is the “horizontal direction.”

The light sources2and the concave mirrors3face each other in the vertical direction. Furthermore, the reflective surfaces of the synthesizing mirrors61and62respectively face the lamps2. Furthermore, the reflective surfaces of the synthesizing mirrors61and62are respectively inclined 45° in the vertical direction, and the directions of inclination of the synthesizing mirror61and the synthesizing mirror62are reversed. In this way, the light fluxes from the lamps2are turned 90° by the reflective surface of the synthesizing mirror61and the reflective surface of the synthesizing mirror62and guided to the incident end face130F of the rod integrator1.

Furthermore, the reflective surface of the synthesizing mirror61is inclined 15° (the direction of arrow “c” inFIG. 9), which is half the converging angle of the concave mirror3, in the horizontal direction, and the reflective surface of the synthesizing mirror62is inclined 15° (the direction of arrow “d” inFIG. 9), which is half the converging angle of the concave mirror3, in the horizontal direction.

FIG. 10Ashows the device shown inFIG. 9as viewed from the side of the exit end face130B of the rod integrator1. As shown in this diagram, the light source portions101and102are arranged such that the optical axis of the concave mirror3of the light source portion101and the optical axis of the concave mirror3of the light source portion102do not intersect with the center line103of the rod integrator1. That is, both of these optical axes are separated such that they are parallel, and neither of the optical axes intersects with the center line103of the rod integrator1. The arrangement of the synthesizing mirrors61and62corresponds to the arrangement of these light source portions101and102.

FIG. 10Bis a lateral view showing the vicinity of the incident end face130F of the rod integrator1. AndFIG. 13is a perspective view of an example arrangement of the synthesizing mirrors61and62that is shown in order to facilitate understanding of the arrangement of the synthesizing mirrors61and62. Using these drawings, it is evident that the light fluxes from the light source portions101and102are reflected by the inclined surfaces of the synthesizing mirrors61and62.

Due to the slant of the reflective surfaces of the synthesizing mirrors61and62and the displacement in the horizontal direction of the two lamps2on the left and right of the synthesizing mirrors61and62, the light from the lamps2is reflected by the synthesizing mirrors61and62, then converged and irradiated at incident angles θ (30°), which are equivalent with respect to the center line103, in the vicinity of the incident end face130F, that is, in the vicinity of the second focal point of the concave mirrors3.

In this case, light of a maximum angle 2θ (60°) respectively from the concave mirrors3is incident at the incident end face130F, such that light of a maximum angle of 120° is incident at the incident end face130F on rod integrator1. Since the tapered surfaces of the rod integrator1in the present embodiment are arranged in the horizontal direction, light of the maximum 120°is reflected by the tapered surfaces such that it is possible to control the maximum emission angle at the exit end face130B to approximately 60° in the same way as in Embodiment 1.

As described above, in the present embodiment, the light source portions101and102are arranged such that the optical axis of the concave mirror3of the light source portion101and the optical axis of the concave mirror3of the light source portion102do not intersect with the center line103of the rod integrator1, and the synthesizing mirrors61and62are arranged in correspondence to this. This eliminates the areas that cannot be used by light rays (hatched areas inFIG. 7) caused by the synthesizing prisms in Embodiment 2, and it is therefore possible to achieve a device that can provide an image of even better brightness and uniformity.

Furthermore, by arranging optical axes of the concave mirrors of the two light source portions vertically to the optical axis of the projection lens, the danger of light source damage is reduced even when the device is installed inclined, and like in Embodiment 2, a high reliability can be achieved.

FIG. 11is a conceptual diagram showing an optical system of a projection image display device according to Embodiment 4. The same reference numerals are used for items with the same structure as in the projection image display device according to Embodiment 1 shown inFIG. 1, and detailed description of such items is omitted here.FIG. 12shows the device shown inFIG. 11as viewed from the side of the exit end face130B of the rod integrator1. As shown inFIGS. 11 and 12, the structure from the light sources2to the rod integrator1in the order of progression of the light fluxes is the same as in Embodiment 4.

As shown inFIG. 11, the light flux emitted from the rod integrator1illuminates a reflective light valve14via a color wheel11, a relay lens system4constituted by at least one lens, a total reflection mirror12, a field lens5, and a total reflection prism13. Modulated light that forms an optical image is emitted by the light valve14. The light flux from the light valve14reaches the projection lens7via the total reflection prism13and the projection lens7projects the optical image formed by the light valve14.

Color display is made possible by the color wheel11arranged in the vicinity of the exit end face130B of the rod integrator1. The color wheel11is constituted by dichroic filters that allow the transmission of at least the three primary colors red, blue, and green, and rotates to separate white light on a time-division basis. A property of the thin films used in coating the dichroic mirrors that constitute the color wheel11is that they are commonly rated to support an incident angle of 30°, so that in this case, the desired angle of the incident angle is 30°.

The total reflection mirror12and the total reflection prism13are configured as means for turning light and are arranged such that the light flux emitted from the rod integrator1is turned with the center line103as the center when viewed from the direction of the center line103of the rod integrator. The angle of turning is determined to match the arrangement of the reflective light valve14and is 90° in the example ofFIG. 11.

With this configuration, the illuminating light emitted from the exit end face130B of the rod integrator1illuminates the reflective light valve14in a state in which it is turned 90°. The turning angle can be adjusted by setting the angle of the boundary with the atmosphere of the total reflection prism13that uses total reflection to guide the light flux to the reflective light valve14and the angle of the total reflection mirror12to desired angles.

The means for turning light are provided in this way to improve the convergence efficiency. For example, although there is no problem when the reflective light valve14has a sufficient surface area, that is, when it is possible to ensure a short-side length of the exit face of the rod integrator1of a sufficient length, to miniaturize the set, the light valve also must be miniaturized, and when making the converging angle of the illuminating light appropriate for an F-number of 2 using a reflective light valve with a diagonal length of 17.78 mm for example, it is necessary for the short-side length of the exit face of the rod integrator1to be approximately 6 mm. In this case, applying a tapering angle based on an approximately 6-mm short-side length of the exit face further shortens the length of the incident face and reduces the convergence efficiency.

In order to solve this issue, it is possible to improve the efficiency of light utilization of the reflective light valve greatly and achieve an illuminator that has even higher brightness and uniformity, and it is possible to achieve a projection image display device provided with this illuminator, by providing a tapering angle on the long-side length of the rod integrator and improving the convergence efficiency and by implementing a configuration in which the illuminating light is turned by the total reflection mirror12and the total reflection prism13to match the arrangement of the reflective light valve.

Note, however, that while it is widely known that before and behind illumination optical systems, the product of the surface area of the illumination area and the solid angle of the illuminating light is constant, the product of the surface area of the exit face of the rod integrator1and the emission angle of the illuminating light is of course equivalent to the product of the surface area of the transmissive light valve14and the solid angle of the illuminating light.

Furthermore, as shown inFIG. 12, the light source portions101and102are arranged such that, as in Embodiment 3, the optical axis of the concave mirror3of the light source portion101and the optical axis of the concave mirror3of the light source portion102do not intersect with the center line103of the rod integrator1, and the synthesizing mirrors61and62are arranged in correspondence to this. This makes it possible to achieve an image with higher brightness and uniformity.

When the rod integrator is rotated around the center line103and arranged as in the present embodiment, the arrangement of the two left and right lamps2also changes in accordance with the rotation angle. Even in this case, if the light source portions101and102and the synthesizing mirrors61and62shown inFIG. 12are rotated around the center line103while maintaining their positional relationship, it is possible to accommodate the arrangement of the above-described rotated rod integrator.

Furthermore, the reflective light valve14is constituted by a digital mirror device, which is an aggregation of micro-mirrors, and displays an image based on an electric signal that output from a drive circuit (not shown). The image displayed by the reflective light valve14is magnified and projected via the total reflection prism13and the projection lens7and projected onto a screen (not shown).

Each of the above-described embodiments had two light source portions, but Embodiment 5 is an example in which four light source portions are used.FIG. 14Ais a top view of a projection image display device according to Embodiment 5 andFIG. 14Bis a lateral view.

The projection image display device according to the present embodiment is provided with four light source portions201to204, a rod integrator20, a relay lens system4that guides the light flux emitted from the rod integrator20, a field lens5, a transmissive light valve6that modulates the light flux guided by the relay lens system4to form an image, and a projection lens7that projects the image formed by the light valve6. Reference numeral206indicates the center line of the rod integrator20.

The light source portions201to204have the same structure and are respectively provided with a light source200, and a concave mirror205which is a condenser optical system that condenses light from the light source2. The number of light source portions is different compared to the structure shown inFIG. 1, but the structure of each of the light source portions is the same as the light source portions inFIG. 1.

FIG. 15is a perspective view of the rod integrator20, whileFIG. 16Ais a top view andFIG. 16Bincludes a lateral view and left and right lateral views. As shown inFIG. 15, the rod integrator20is a columnar optical element provided with an incident end face230F at a front side, an exit end face230B at a back side, and four side surfaces (230T,230U,230L, and230R).

Compared with the rod integrator1of the above-described embodiments shown inFIG. 2, in which, of the two pairs of opposing side surfaces, only one pair of side surfaces,130L and130R, were formed as tapered surfaces, in the present embodiment, the two pairs of side faces are formed as tapered surfaces.

That is, the opposing side surfaces230L and230R face each other at an inclination of a predetermined angle such that both side surfaces230L and230R become farther apart from each other from the incident end face230F toward the exit end face230B (seeFIG. 16A). The same is true also for the opposing surfaces230T and230U (seeFIG. 16B).

As described above, the incident end face230F of the rod integrator20is arranged in the vicinity of the second focal point of the concave mirrors205and incident light is totally reflected as appropriate in the vertical direction and horizontal direction of the rod integrator20, and then emitted from the exit end face230B of the rod integrator20.

InFIG. 14A, the pair of two light source portions201and202are arranged in the horizontal direction (the direction of the arrow “a”). In this case, the pair of two light source portions203and204are arranged in the same way behind the paper plane. Furthermore, inFIG. 14B, the pair of two light source portions201and203are arranged in the vertical direction (the direction of the arrow “b”). In this case, the pair of two light source portions202and204are arranged in the same way behind the paper plane.

In the present embodiment, there are four light source portions, with two of these arranged in the horizontal direction and two arranged in the vertical direction.

That is, the structure of the light source portions of Embodiment 5 has two light source portions arranged in the horizontal direction or the vertical direction and a further two light source portions arranged parallel to these. In the present Embodiment 5, the light source portions are provided in accordance with the two respective pairs of tapered surfaces and there is a total of four light source portions.

The following is a description of the fundamental operation of the rod integrator20.FIG. 17is a top view of the rod integrator20showing the behavior of an incident light ray.FIG. 18is a lateral view of the rod integrator20showing the behavior of an incident light ray.

FIG. 17shows how the incident light ray enters the incident end face230F at the maximum angle (2θ), and is then reflected inside the rod integrator20and emitted from the exit end face230B. As shown inFIG. 17, an incident light ray at the maximum angle 2θ is emitted from the exit end face230B at an angle θ′ that is different from the maximum angle 2θ due to being totally reflected as appropriate by the pair of tapered surfaces230L and230R of the rod integrator20.

This is the same also inFIG. 18. An incident light ray at the maximum angle 2θ is emitted from the exit end face230B at an angle θ′ that is different from the maximum angle 2θ due to being totally reflected as appropriate by the pair of tapered surfaces230T and230U of the rod integrator20.

In other words, with the present embodiment, the incident light ray at an angle of 2θ in the horizontal direction and the incident light ray at an angle of 2θ in the vertical direction are both emitted at the exit end face230B at an angle of θ′.

Since the present embodiment, has such a large total number of four light source portions, the divergence angle of light at the exit end face can be made smaller than the divergence angle of light at the incident end face in the horizontal direction and the vertical direction as described above, which is advantageous when a light of a very high brightness is desired.

Embodiment 1 was described with an example in which the incident angle and the converging angle of the light incident at the rod integrator1were the same, but in Embodiment 6, the incident angle is smaller than the converging angle.

FIG. 19is a top view of a conceptual diagram of an optical system according to Embodiment 6. Except for the relationship between the incident angle and the converging angle, the configuration shown in this diagram is the same configuration as shown inFIG. 1of Embodiment 1, and therefore the same reference numerals asFIG. 1are used and a further description of each part is omitted.

InFIG. 19, θE is the incident angle and θc is the converging angle. In the configuration of this drawing, the incident angle θE is smaller than the converging angle θc.

The 2θ of the incident end face130F inFIG. 4is θE+θc in the present embodiment, and this becomes the angle θ′ at the exit end face130B, which is an angle that is different from the incident end face130F, just like in Embodiment 1. Furthermore, as shown inFIG. 5, the incident angle θ″ likewise is maintained and transmitted, then emitted.

For example, incident light in which the maximum angle of θE+θc is 51° (θE=21°) can be emitted with an emission angle θ′ of approximately 30°. In this case, the effective horizontal length of the exit face of the rod integrator1was set to 7.5 mm, the tapering angle to approximately 1.51848°, the length to 50.4485 mm, the number of reflections on the side surfaces in the longitudinal direction was 4, and quartz (refractive index nd=1.45859) with good heat resistance and optical properties was used for the glass material of the rod integrator1. Furthermore, when the incident angle θ″ inFIG. 5is 30°, the light is transmitted maintaining this angle, and then emitted at an angle of 30°.

Table 4 below shows calculated values of the tapering angle θT, the incident face length L′, the rod integrator length M, and the convergence efficiency normalized to a maximum value of 1, for various incident angles. The effective lengths of the exit face of the rod integrator are an effective horizontal length of 7.5 mm and an effective vertical length of 5.8 mm, and a substantially ideal relay lens system is used for the calculated values of the convergence efficiency. Furthermore, the number of reflections is set to 3, 4, and 5.

In the examples of Table 4, the converging angle θc is fixed at 30° and the incident angle θE is changed in increasing increments of 3 degrees from 15° to 30°. Except for when the incident angle θE is 30°, the relationship between the two is such that the incident angle is smaller than the converging angle. The letter E in Table 4 is the convergence efficiency. The convergence efficiency was calculated using simulation software for evaluating illumination optical systems in which optical devices such as light sources, lenses, and mirrors are modeled to determine what amount of the desired light rays reaches the screen onto which the light rays emitted from the light source are projected. The values shown in Table 4 are normalized to a maximum value of 1 for each of the settings for the number of reflections in the rod integrator.

FIG. 20shows the relationship between convergence efficiency and incident angle, using the numerical values in Table 4. The horizontal axis θ is the incident angle and the vertical axis E is the convergence efficiency.

InFIG. 19, when the θ marked on the horizontal axis is 30°, then the converging angle is also 30°, but otherwise, the incident angle θ is smaller than the converging angle. As can be seen inFIG. 20, the convergence efficiency is lowest at θ=30° on the horizontal axis, at which the incident angle and the converging angle are the same, and the greatest value is attained when the incident angle is set to θ=21°, which is 70% of the converging angle.

In other words, it is evident according to Table 4 andFIG. 20that device brightness can be improved when the incident angle is smaller than the converging angle. In this case, convergence efficiency shows particularly good values when the ratio of the incident angle θ to the converging angle is in the range of at least 60% (θ=18°) and at most 80% (θ=24°).

It should be noted that although the description here was for the case of two light sources, it also can be applied to configurations with four light sources, as in Embodiment 5.

Furthermore, in the configurations of above-described embodiments in which one pair of opposing side surfaces of the rod integrator1are parallel planes and the other pair of opposing side surfaces are planes that face each other with a predetermined angle of inclination, the rod integrator1may be configured such that at least a portion of one pair of opposing side surfaces is made of parallel planes and at least a portion of the other pair of opposing side surfaces is made of planes that face each other with a predetermined angle of inclination. This is because the emission angle can be narrowed to a desired angle and uniform illumination can be achieved by reflecting a light flux between pairs of planes that face each other with a predetermined angle of inclination. This aspect is true also for embodiments 1 through 5.

Furthermore, the exit end face130B of the rod integrator has to be polished during production. However, the end portions of the rod integrator1, that is, the four edges and four corners of the exit end face130B, are sometimes chipped during the polishing process. The size of the chipped of portions may be 0.1 mm or more.

Uniformity of illumination is adversely affected by chipping of the exit end face130B and unevenness can appear in the illumination.

For this reason, it is preferable that the form of the rod integrator is determined using a length L1in which an extra length is added to the desired standard length L of the four edges of the rod integrator. In this way, it is possible to prevent the influence caused by chipping of the four edges and four corners of the exit end face130B from adversely affecting the uniformity of illumination. The extra length is within the range of up to 0.2 mm for example. This is true also for Embodiments 1 through 5.

Furthermore, the rod integrator in the above-described embodiments was described with examples using a glass material, but it also may be a columnar optical element that is hollow with the four inner wall surfaces formed with mirrors. The incident light flux in this configuration is also totally reflected as appropriate by the mirrors of the inner wall surfaces.

INDUSTRIAL APPLICABILITY

As described above, with the present invention, since control can be achieved such that the divergence angle of light in the horizontal direction at the exit end face is different from the divergence angle of light in the horizontal direction at the incident end face, light having high brightness and uniformity can be obtained. For this reason, the present invention is useful in illuminators and projection image display devices equipped with a rod integrator.