| 摘要 |
The present invention provides an optical module having a window structure, which is easy to manufacture, has high reliability, has a small polarized light extinction ratio, and the plane of linear polarization of transmitted light is kept constant. The optical module of the present invention has a housing, and a junction having a light transmissive window structure, which is fixed to the housing, and which utilizes a sapphire plate. The sapphire window is constituted such that the following expressions (1) through (4) are established between an angle ~ formed by the C axis of the sapphire, and the plane of polarization of light, and an angle .theta. formed by the C axis of the sapphire and the optical axis. In the following expressions, .omega. is the principal refractive index of sapphire, .epsilon. is the secondary refractive index, .lambda. is the wavelength of transmitted light, and d is the thickness of the window plate. (see formula I) (2) .delta. = 2.pi.d (.omega. - n).lambda. (see formula II) (4) -30 .gtoreq. +20log (tan.beta.)
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