公开(公告)号：JPH0887724A

公开(公告)日：1996-04-02

申请号：JP22132394

申请日：1994-09-16

Applicant: IBM JAPAN

Inventor： FUKUZAWA TADASHI ,  KUNO TEIJI ,  WATABE HIROSHI ,  TAKAHASHI YASUYUKI ,  OZAWA KOJI

IPC: G11B5/455 ,  G01B11/14 ,  G02B27/00 ,  G02B27/28 ,  G11B5/60 ,  G11B33/10

Abstract: PURPOSE: To maintain a high measuring accuracy by making a measuring error due to an optical elastic phenomenon minimum by providing the polarization eliminator through which light reaching reflection member and light reflected from reflection parts pass in between optical lens member and the reflection member. CONSTITUTION: When light in a linear polarization state by passing through a polarizer 503 passes through a 1/4λ plate 570, it becomes a circular polarization state and receives multiple interfering actions reflected respectively from surfaces of a glass disk 23 and a head 21. These reflected lights are restored to linear polarization states by passing through again the 1/4λ plate 570. The direction of the linear polarization at this time is a direction rotated by 90 deg. from an original direction, at first, the direction of the linear polarization perpendicular to this paper plane becomes a linear polarized light having the polarization direction horizontal to the paper by passing through the 1/4λplate twice. Then, lights whose polarization directions are rotated by 90 deg. in such a way pass through again ojective lens system 507 to reach finally an optical detecting part 515 via an analyzer 513. Moreover, the polarizer 501 and the analyzer 513 are arranged in a form in which transmission polarization axes of them are orthogonal to each other.