| 摘要 |
PURPOSE: To inexpensively remove zero order diffracted light signals by using a spatial optical modulator which is aligned with a linearly polarized light, the axis of polarization of the linearly polarized light and the major axis of molecules and a linearly polarized light detecting element which is provided with an orthogonal relation with the major axis of the polarization of the zero order diffracted light. CONSTITUTION: A 90 deg. twisted nematic type liquid crystal element is used as the spatial optical modulator 403. Parallel laser beams 401 linearly polarized in a Y-axis direction are modulated by the spatial optical modulator 403. In such a case, the orientation direction of the major axis of the molecules of the surface on the linearly polarized light incident side of the twisted nematic type liquid crystal element aligns to the Y-axis direction. The first order diffracted light 409 is also polarized to the linearly polarized light and is intersected with the polarization direction of the zero order diffracted light 407 when the wavelengthλof the incident light, the thickness (d) of the liquid crystal layer and the refractive index difference between the major axis and minor axis of the liquid crystal molecules are so selected that the relative phase differenceϕattains odd timesπradian. At this time, the zero order diffracted light 407 is removed by installing the linearly polarized light detecting element 411 so as to intersect orthogonally with the polarization axis of the zero order diffracted light 407. In addition, the complete taking-out of the components of the first order diffracted light 409 is possible as well.
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