For example, in a projector for image display such as a DLP™ projector and a liquid crystal projector and a photo mask exposure apparatus, a high intensity discharge lamps (HID lamp) such as a xenon lamp and an extra-high pressure mercury lamp has been used so far. As an example, the principle of such a projector is shown in FIG. 17 (reference: Japanese Patent Application Publication No. 2004-252112 etc.).
As described above, light from a light source (Spa), which is made up of a high intensity discharge lamp etc., is inputted into an incident end (PmiA) of a light homogenizing unit (FmA), and is outputted from an emission end (PmoA) by, for example, using a condensing unit (not shown), which is made up of a concave reflection mirror, a lens, etc. Here, for example, an optical guide can be used as the light homogenizing unit (FmA), which is also called a rod integrator, a light tunnel, etc., and may be formed of a prism, which is made from light transmittant material such as glass, resin, etc. In such an light homogenizing unit (FmA) the light inputted into the incident end (PmiA) is repeatedly and totally reflected on a side face of the light homogenizing unit (FmA) according to the same principle as that of an optical fiber, and the light propagates inside the light homogenizing unit (FmA) such that the illuminance on the emission end (PmoA) is sufficiently homogenized even if distribution of the light inputted into the incident end (PmiA) has unevenness.
Although, in the above description, the optical guide is formed by a prism, which is made from light transmittant material such as glass, resin, etc., it may be formed of a hollow prism in which the inside thereof is formed of a reflection mirror such that a reflection light is repeated on an inner face similarly and the light propagates therein so that a similar function thereto is achieved.
An illumination lens (Ej1A) is arranged so that a quadrangle image of the emission end (PmoA) is formed on a two-dimensional light amplitude modulation element (DmjA), whereby the two-dimensional light amplitude modulation element (DmjA) is illuminated by light outputted from the emission end (PmoA). However, in FIG. 17, a mirror (MjA) is arranged between the illumination lens (Ej1A) and the two-dimensional light amplitude modulation element (DmjA). And the two-dimensional light amplitude modulation element (DmjA) modulates light on a pixel to pixel basis according to an image signal so that the light is directed so as to enter the projection lens (Ej2A), or light is directed so as not to enter there, whereby an image is displayed on a screen (Tj).
Incidentally, the above-described two-dimensional light amplitude modulation element is also called a light valve, and in the case of the optical system shown in FIG. 17, a DMD™ (Digital Micromirror Device) is generally used as the two-dimensional light amplitude modulation element (DmjA).
The so-called fly eye integrator may also be used as the light homogenizing unit, instead of the above-described optical guide. FIG. 18 shows the principle of a projector using this light homogenizing unit, as an example (reference: Japanese Patent Application Publication No. 2001-142141 etc.).
Light from a light source (SjB), which is made up of a high intensity discharge lamp etc., is inputted, as approximately parallel light flux, into an incident end (PmiB) of the light homogenizing unit (FmB), which is made up of a fly eye integrator, and is outputted from an emission end (PmoB), by using a collimator unit (not shown), which is made up of a concave reflection mirror, a lens, etc. Here, the light homogenizing unit (FmB) is made up of a combination of an upstream fly eye lens (F1B) on an incident side, a downstream fly eye lens (F2B) on a light emission side, and an illumination lens (Ej1B). The upstream fly eye lens (F1B) and the downstream fly eye lens (F2B) are respectively formed by arranging, in vertical and horizontal directions, many quadrangle lenses whose focal distance is the same as one another and whose shape is the same as one another.
Each lens of the upstream fly eye lens (F1B), and each lens of the downstream fly eye lens (F2B) which corresponds to and is located downstream of each lens of the upstream fly eye lens (F1B), form a optical system called Koehler illumination, so that many Koehler illumination optical systems are aligned in a matrix in a plane. Generally, such a Koehler illumination optical system is made up of two lenses, wherein when an upstream fly eye lens collects light and illuminates an object face (face to be illuminated), the upstream lens does not form an image of a light source on the object face, but forms an image of the light source on a center face of a downstream lens, whereby the object face is uniformly illuminated by arranging the downstream lens so as to form a quadrangle contour image of the upstream fly eye lens on the object face. The downstream lens functions so as to prevent a phenomenon in which an illuminance of a circumference part of the quadrangle object face falls depending on the size, if the downstream lens is not provided and a light source is not a perfect point light source but has a limited size, whereby it is possible to form a uniform illuminance on even the circumference part of the quadrangle object face by the downstream lens, independent of the size of the light source.
Here, since the optical system shown in FIG. 18 is configured based on approximately parallel light flux, which is inputted into the light homogenizing unit (FmB), an interval between the upstream fly eye lens (F1B) and the downstream fly eye lens (F2B) is set so as to become equal to those focal distances, so that an image of the object face of the uniform illumination of a Koehler illumination optical system is formed at infinity. However, since an illumination lens (Ej1B) is arranged downstream of the downstream fly eye lens (F2B), the object face can be pulled near on the focal plane of the illumination lens (Ej1B) from the infinity. Since the Koehler illumination optical systems arranged in a matrix in a plane are parallel to an incident light axis (ZiB) and light flux is approximately axisymmetrically inputted therein with respect to each central axis so that the output light flux is also approximately axisymmetrical, and outputs of all the Koehler illumination optical systems are imaged on the same object face on the focal plane of the illumination lens (Ej1B) because of the nature of lens, i.e., a Fourier transform of a lens, in which light rays entering a lens face at the same angle as one another, are refracted so as to be directed to the same point on a focal plane without depending on the incidence position on the lens face.
As a result, all the illuminance distributions in each lens face of the upstream fly eye lens (F1B) are overlaid, so that one synthesized quadrangle image, whose illuminance distribution is more uniform than that in case of one Koehler illumination optical system, is formed on the incident light axis (ZiB). The two-dimensional light amplitude modulation element (DmjB), which is an illumination object, is illuminated by light outputted from the emission end (PmoB) when a two-dimensional light amplitude modulation element (DmjB) is arranged at a position of the synthesized quadrangle image. However, the light is reflected towards the two-dimensional light amplitude modulation element (DmjB) in case of illumination, by arranging a polarization beam splitter (MjB) between the illumination lens (Ej1B) and the two-dimensional light amplitude modulation element (DmjB). And the two-dimensional light amplitude modulation element (DmjB) performs a modulation and reflection so as to or so as not to rotate the polarization direction of light by 90 degrees on a pixel to pixel basis according to an image signal, whereby only the rotated light passes through the polarization beam splitter (MjB), and enters the projection lens (Ej3B), so that an image may be displayed on a screen (Tj).
In addition, in the case of the optical system shown in FIG. 18, in general, a LCOS™ (Liquid Crystal on Silicon) is used as the two-dimensional light amplitude modulation element (DmjA) in many cases. In the case of such a liquid crystal device, since only a component of light in a specified polarization direction can be modulated effectively, although a component parallel to the specified polarization direction is usually passed therethrough as it is, only a component perpendicular to the specified polarization direction is rotated by 90 degrees with respect to the polarization direction, so that the polarized-light alignment functional device (PcB) for making all the light effectively usable is inserted, for example, downstream of the downstream fly eye lens (F2B). Moreover, a field lens (Ej2B) is inserted immediately upstream of the two-dimensional light amplitude modulation element (DmjB) so that approximately parallel light may enter the two-dimensional light amplitude modulation element (DmjB).
In addition to the reflection type of the two-dimensional light amplitude modulation element shown in FIG. 18, a transmissive liquid crystal device (LCD) may be used as the two-dimensional light amplitude modulation element in the optical arrangement which is suitable therefor (reference: Japanese Patent Application Publication No. H10-133303 etc.).
Generally, for example, a dynamic color filter such as a color wheel is arranged downstream of the light homogenizing unit in a projector in order to display a color image, and the two-dimensional light amplitude modulation element is illuminated with color sequential light flux of R, G and B (Red, Green, Blue), whereby color display is realized in time dividing manner, or a dichroic mirror or a dichroic prism is arranged downstream of the light homogenizing unit, so that the two-dimensional light amplitude modulation element, which is independently provided in each color, is illuminated with light which is separated into the three primary colors of R, G and B, and a dichroic mirror or a dichroic prism for performing color synthesis of the modulated light flux of the primary colors R, G and B is arranged. However, for ease of explanation, in FIGS. 17 and 18, these elements are omitted.
However, the high intensity discharge lamp has drawbacks such as low conversion efficiency from applied power to light power, i.e., great heat generation and/or a short life span. A solid light source such as an LED and a semiconductor laser attracts attention in recent years as an alternative light source, in which these drawbacks are solved. Although of these light sources, in the LED, heat generation thereof is small and an operating life span thereof is long as compared with those of the discharge lamp, since there is no directivity of light emitted therefrom as in such a discharge lamp, there is a problem that the usage efficiency of light is low when it is used in the above-mentioned projector or exposure apparatus, in which only light in specific direction can be used. On the other hand, a semiconductor laser has high directivity in addition to a small heat generation and a long operating life spam as in such an LED, so that there is an advantage that the usage efficiency of light is high, when it is used in the above-mentioned projector, exposure apparatus, etc. in which only light in a specific direction can be used. However, in such a semiconductor laser, there is a problem that a speckle occurs. Here, the term “speckle” means a spotty or patchy pattern which inevitably appears when projecting semiconductor laser light, or other laser or coherent light, which is generated by performing wavelength conversion of laser light (using nonlinear optical phenomena, such as a harmonic generation and an optical parametric effect). Since the speckle is a very troublesome phenomenon because of remarkably degrading image quality for use in the above-mentioned projector for watching an image, or for use in precise exposure of a pattern of a photomask on a film, which is made up of photosensitive material, many devices for an improvement thereof have been proposed for many years.
For example, Japanese Patent Application Publication No. S59-024823 discloses an influence elimination apparatus for eliminating a speckle of an output light of an optical fiber, wherein an optical element, by which a relative relation between an input end surface of the optical fiber and a laser light beam is changed in time, is provided on an optical path of a laser beam, which is generated by condensing laser light so as to input the laser beam into an input end surface of an optical fiber. The publication illustrates an example where a position of a spot, at which laser light beam is condensed, is changed in an oscillating manner within a predetermined range on an input end face of an optical fiber, as one of forms for changing in terms of time the relation between the input end face of the optical fiber and the laser light beam, and it gives an embodiment of a concrete optical system structure using an ultrasonic diffraction element, a deflecting mirror (galvanometer), an oscillating mirror, and a rotation non-parallel glass plate. In addition, the publication illustrates an example of another form for changing the relative relation between an input end face of an optical fiber and a laser light beam in terms of time where an angle of a central axis of a laser light beam to be condensed is changed in an oscillating manner within a predetermined range although a position of a spot, at which a laser light beam is condensed, is not changed on an input end face of an optical fiber. However, it does not show any embodiment of a concrete structure of an optical system.