| 摘要 |
The present invention provides a light emitting/receiving composite unit ( 1 ) for emitting and receiving lights, which includes a light source ( 3 ), an optical splitting unit ( 4 ) for splitting returning lights to the composite unit ( 1 ) into a plurality of lights, a polarizing unit ( 5 ) for increasing and decreasing quantity of lights transmitted therefrom corresponding to polarization state of the returning lights, and an optical receiving unit ( 6 ) which has a plurality of photo-detecting elements ( 6 <SUB>-</SUB> 1 to 6 <SUB>-</SUB> 4 ) for detecting the lights transmitted through the polarizing unit ( 5 ), which are unitedly integrated into one unit. Also, the present invention provides a displacement detection apparatus of grating interference type, which includes thus unitedly integrated composite unit ( 1 ), and an external optical system of an objective unit having a reflection type diffraction grating RG, a reflecting unit (R 1 a, R 1 b) for reflecting lights from the composite unit ( 1 ) to the reflection type diffraction grating RG, a polarizing unit (WP 1 a, WP 1 b) for changing polarization state of diffracted lights from the reflection type diffraction grating RG, and a reflecting unit (R 2 a, R 2 b) for reflecting lights transmitted through the polarizing unit (WP 1 a, WP 1 b) to cause the reflected lights go backward.
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