Optical design and analysis of a laser expander for a blu-ray pickup head for synchronous detection of the tilt angle and displacement on the test plane

An optical design is developed for a Blu-ray pickup head with a laser expander that can synchronously detect the linear displacement and twodimensional angular tilts at the test plane. To improve the signal accuracy of the photo detector, a laser expander is used to transform the shape of the laser beam from elliptical to circular. A quadrant detector as used to detect the relative relationship between the V_A, V_B, V _C, V_D signals, can be used to measure the tilt angle and displacement at the test plane. Measurement detection and analysis is based on one normalized focus error signal (NFES) and two angular signals. The optical efficiency of the Blu-ray pickup head with laser expander is 59.29%. The optical efficiency of the currently used commercial pickup head is only 8.08%. Tolerance analysis is also considered in the performance requirements.