OPTICAL INFORMATION READER

摘要: PURPOSE:To eliminate the use of an optical system which converts form luminous flux to reduce weight a reader and at same time facilitate positioning photodetector, by obtaining focusing error signal from variation reflection factor level close critical angle after combining diffraction grating with parallel plate. CONSTITUTION:When beams 17 are made incident vertically on 1st boundary surface 13 plate 13, transmit through 2nd 13b 15 be diffracted there. The beam 18 is again travels straight reach point P. constant decided so that P equal total reflection. Therefore totally reflected photodetector 11. if theta larger than thetaS; while transmits partially 13a smaller. When disk 7 gets objective lens 6, light turned into dispersed fluxes. Then has semicircular only 11b. While focused when goes further away 6. 11a.