| 摘要 |
A beam splitter formed by laminating a plurality of optical films on a glass substrate having a refractive index of 1.51+/-0.10. The optical films are first, second, third, fourth, and fifth layers laminated in this order from the glass substrate. The first layer has a refractive index of 1.44+/-0.10 and an optical film thickness of 0.05-0.15; the second layer has a refractive index of 1.68+/-0.10 and an optical film thickness of 0.01-0.10; the third layer has a refractive index of 1.44+/-0.10 and an optical film thickness of 0.50-0.60; the fourth layer has a refractive index of 2.23+/-0.10 and an optical film thickness of 0.25-0.35; and the fifth layer has a refractive index of 1.44+/-0.10 and an optical film thickness of 0.25-0.35. The optical film thickness means a relative value represented by nxd/ lambda where n denotes a refractive index; d denotes an actual film thickness, and lambda denotes a wavelength deciding the center of a wavelength band. The beam splitter can reduce the polarization dependency of a branching ratio with a beam incident angle of 22.5 DEG .
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