| 摘要 |
An optical path switching method according to the present invention comprises converging and irradiating, on a light absorption layer film provided in a thermal lens forming element ( 1, 2, 3 ) including at least the light absorption layer film, each of a control light ( 121, 122, 123 ) having a wavelength selected from a wavelength band which is absorbed by the light absorption layer film and a signal light ( 110, 111, 112 ) having a wavelength selected from a wavelength band which is not absorbed by the light absorption layer film. Arrangement of the light absorption layer film is adjusted such that at least the control light focuses within the light absorption layer film. A thermal lens is reversibly formed according to a distribution of refraction index created by a temperature increase generated in and around an area of the light absorption layer film in which the control light is absorbed, such that, according to whether or not the control light is irradiated, the converged signal light is output either as is in its converged form or after its spread angle is changed and a mirror ( 61, 62, 63 ) including a hole and reflecting means, the signal light output from the thermal lens forming element is either passed through the hole or reflected by the reflecting means to change the optical path.
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