| 摘要 |
PROBLEM TO BE SOLVED: To obtain the interference image input device which has a short optical path, can be constituted compact, and precisely machined and assembled, and can obtain an interference image of desired wavelength. SOLUTION: The interference image input device has an image forming lens 21, a polarizer 22, birefringent plates 23 and 24, an analyzer 25, and an area photodetecting element 26 arranged in the travel direction X of light. The birefringent plates 23 and 24 have their crystal axes crossed orthogonally to the optical axis in a vertical plane, and continuously vary in each thickness difference from the lower sides to the upper sides, so that transmitted light is given a phase difference according to the thickness difference. |
