1. Technical Field
The present invention relates to an illumination device and a projector.
2. Related Art
A projector has been hitherto known as one of display devices (for example, see JP-A-2009-216843). For example, the projector modulates light from an illumination device using a light modulation device to form an image and projects the image onto a screen using a projection lens or the like.
As a light source of the illumination device, various light sources are used, and a coherent light source which emits light (coherent light) having coherence may be used. The coherent light source includes a solid-state light source using a laser diode (LD) or a super luminescence diode (SLD), a short-arc lamp light source, and the like. For example, in a projector using a laser light source, it is possible to sufficiently expand a color reproduction range since the wavelength band of the laser light source is narrow, and to achieve reduction in size or to reduce the number of constituent components.
On the other hand, if display is performed by a projector using a coherent light source, an observer who observes an image may recognize so-called speckle. Speckle is a pattern in which bright points and dark points are distributed in a striped pattern or a spotted pattern due to interference of light, gives a sense of glare to the observer, and gives a sense of discomfort during image viewing. For this reason, a technique which makes speckle be less recognizable (hereinafter, “reduces” speckle) is expected to be devised.
As one of techniques for reducing speckle, JP-A-2009-216843 suggests a technique which rotates a spot formed on a pupil plane of a projection lens around an optical axis on the pupil plane. According to the technique of JP-A-2009-216843, the angular distribution of light rays entering respective points on a screen temporally changes, and the pattern of speckle temporally changes. As a result, the observer observes speckle in a superimposed (integrated) manner, and speckle is reduced.
In the above-described technique, in the course of effectively reducing speckle, there is room for improvement. For example, according to a method which moves a pupil image on a pupil plane, since there is no change in the pattern of the pupil image itself, it is not possible to sufficiently reduce speckle. Since it is necessary to increase the effective pupil (effective diameter) of the projection lens, an increase in the size of the projection lens and an increase in cost occur.