Patent ID: 8562194
Filing Date: 2013-10-22
Classification: G02B

Abstract:
1. A wavelength conversion unit comprising a wavelength conversion member that transmits a part of incident excitation light and converts a part of the excitation light into wavelength-converted light having a wavelength different from a wavelength of the excitation light to emit the wavelength-converted light, wherein the excitation light has an intensity distribution in which an intensity is maximum at a center and decreases as getting apart from the center, and a thickness of the wavelength conversion member at a portion into which light at the center of the intensity distribution of the excitation light enters is larger than those at any other portions, wherein the wavelength conversion member has a rotationally symmetric shape, the excitation light enters the wavelength conversion member so that light at the center of the intensity distribution travels along a central axis of the wavelength conversion member, and the wavelength conversion member has a thickness such that an intensity of the excitation light having passed along the central axis of the wavelength conversion member is generally equal to an intensity of the excitation light having passed through the wavelength conversion member via a point on at least one circular circumference having the center at the central axis inside a region irradiated with the excitation light, wherein the excitation light that enters the wavelength conversion member has an intensity distribution approximated to a Gaussian distribution, and the thickness of the wavelength conversion member coincides with a transmission intensity uniforming thickness function on the central axis and the circular circumference, where the transmission intensity uniforming thickness function is a function of the thickness of the wavelength conversion member with which an intensity distribution of the excitation light having passed through the wavelength conversion member becomes constant in the range of a predetermined distance from the central axis of the wavelength conversion member, and wherein the transmission intensity uniforming thickness function is represented by the following expression: where x is a distance from the central axis, d(x) is a thickness of the wavelength conversion member at the distance x, d 0 is a thickness of the wavelength conversion member on the central axis, α is an absorption coefficient that is a ratio that the excitation light is absorbed by the wavelength conversion member per unit thickness, and w is a radius of the irradiated region.