公开(公告)号：JPH03191805A

公开(公告)日：1991-08-21

申请号：JP12139990

申请日：1990-05-14

Applicant: IBM

Inventor： HARII JIYONASON MAMIN ,  DANIERU RUGAA

IPC: G01B9/02 ,  G01D5/26 ,  G01Q10/06 ,  G01Q20/02 ,  G01Q60/24 ,  G02B6/00

Abstract: PURPOSE: To minimize the sensitivity of a position detector to polarized light and to thermal response of an optical fiber component by providing an optical directional coupler provided with a plural of external boards. CONSTITUTION: The light from a diode laser 13 having a short coherence length is made incident to a port (a). A directional coupler 10 works as a beam splitter which directs part of the incident light to a member (cantilever) 14 through a second port (b) and a single mode optical fiber 11. Part of the light is returned to the fiber 11 by simultaneously reflecting the part at the member 14 and the adjacent split end of the fiber 11 and optically coupled with a photodetector 15 through a third port (c) so that the photodetector 15 can output a signal indicating the position of the member 14 with its amplitude based on the relative phase of the simultaneous reflection. The other part of the incident light is transmitted to another photodetector 18 from the coupler 10 through a fourth port (d). The two signals are outputted through a subtracting circuit 21 and a dividing circuit by minimizing the fluctuation of the laser intensity.