Patent ID: 8659818
Filing Date: 2014-02-25
Classification: G02F

Abstract:
1. An optical-path-switching apparatus comprising: a signal light source that can generate signal light having one or more types of wavelengths; two or more control light sources that can generate control light having a specific wavelength different from that of the signal light; a thermal-lens-forming optical element including a light-absorbing layer that can transmit the signal light and selectively absorb the control light; and a condensing unit that can guide the control light and the signal light to converge into the light-absorbing layer in such a way as to differentiate respective convergence points in a direction perpendicular to the optical axis, wherein the thermal-lens-forming optical element causes the control light and the signal light to converge into the light-absorbing layer and then diffuse in the traveling direction of the light in such a way as to transiently form a thermal lens due to a temperature increase locally occurring in an area where the control light is absorbed and its peripheral area in the light-absorbing layer, and the thermal lens generates a refractive index distribution in the light-absorbing layer that can change the traveling direction of the signal light so as to realize optical path switching, a first light-receiving unit and a second light-receiving unit are provided, so that straight signal light whose traveling direction has not been changed due to lack of irradiation with the control light and signal light whose optical path has been switched due to irradiation with the control light are converged or condensed by the first light-receiving unit and the second light-receiving unit that are similar to each other, a wedge-type prism is provided between the first light-receiving unit and the second-light receiving unit, wherein the wedge-type prism refracts the straight signal light whose traveling direction has not been changed due to lack of irradiation with the control light and the signal light whose optical path has been switched due to irradiation with the control light while keeping a light separation state, and further at least one of the following conditions (1) to (5) is satisfied: (1) a signal light incidence plane of the thermal-lens-forming optical element is set to be perpendicular to the direction of gravity, and the traveling directions of the signal light and the control light incident on the thermal-lens-forming optical element are set to be parallel to the direction of gravity, (2) the condensing unit causes the control light and the signal light to condense on the incidence plane of the light-absorbing layer in such a way as to differentiate respective convergence points in the direction perpendicular to the optical axis and constitute a reducing projection optical system, (3) the wedge-type prism has at least one wedge face provided at a portion corresponding to each passing position of the optical-path-switched signal light, (4) the wedge-type prism has at least one wedge face provided at a portion corresponding to each passing position of the optical path switched signal light so as to refract the optical path switched signal light in such a way as to reduce a distance between the optical axis of the optical-path-switched signal light and the optical axis of the straight signal light whose traveling direction has not been changed due to lack of irradiation with the control light, and (5) the thermal-lens-forming optical element is positioned in such a manner that, when the wedge-type prism is not provided, the straight-traveling signal light and the optical-path-switched signal light are converged or condensed to the same position by the first light-receiving unit and the second light-receiving unit.