| 摘要 |
PROBLEM TO BE SOLVED: To provide an optical pickup which executes focus error detection in constitution of the grating patterns of an optical waveguide element, is small in the area of a photodetecting part and is small in size and low in cost. SOLUTION: The light beam emitted from a semiconductor laser is reflected by a forward path and backward path separation film 18 of the optical waveguide device and is condensed via an optical system to an information recording medium. The reflected light beam transmits the forward path and backward path separation film and arrives at a grating (element) 20, from which part of the light beam is inputted and coupled to a waveguide layer 16. The remaining light beam arrives at a photodetecting part 30. The grating pattern to maximize the coupling efficiency to the waveguide layer 16 when the information recording medium exists in a near position and the grating pattern to maximize the coupling efficiency when the information recording medium exists in a far position are formed at the element 20. The focus error signal based on the S-shape characteristic obtained by taking a differential signal of the respective regions from the photodetecting output from the photodetecting parts subjected to region division in correspondence to thereto is formed. |
