Design of the multiple-beam liquid crystal diffractive optical element

This paper presents a novel light modulator based on the technologies of liquid crystal diffractive optical elements (LCDOE) for a recordable optical pickup head with switching capability on single-beam data writing and multiple-beam data retrieving. The method of Dammann's phase grating was adopted on the LCDOE pattern design for generating seven diffracted orders. The diffraction pattern was etched on transparent conducting glass substrate to act as the electrodes of the modulator and the LCDOE was made by the fabrication processes of liquid crystal devices. The experimental results show that the multiple-beam LCDOE has the function of generating seven diffracted beams with equal light intensities while applying a voltage to the device. By adjusting the amplitude of the voltage, that accordingly changes the difference between the refractive indices of the ordinary and the extra-ordinary rays, the diffraction efficiency can be properly optimized. The switching capability is controllable by turning the voltage on or off. Besides, the polarization-selective effect is verified and an advanced multiple-beam pickup design in integrated type is also proposed.