The purpose of this paper is to clear the practicality of an optical waveguide device for magneto optical disk head. This device is made on the Si substrate with photo-diodes for magneto optical signals detection. An incident. light beam to this device is convert.ed into TE and TM modes by its optical coupler, and these mode are separated corresponding to their polarization by its thin fUm bi-prism. The optical coupler consists of a prism and a resin layer with an edge portion. The edge portion, precisely defined by a photolithography process, produces stable coupling efficiency. This coupler structure also reduces sensitivity of the incident angle and coupling dependence on the polarization direction. In addition, a taper region is made around the thin film bi-prism to obtain high transmission efficiency. These waveguide technologies realize an integrated unit for a Mini-Disc head. As the evaluation results of a pickup, the CNR of 3T signal (resonance bandwidth: 10kHz) is 45dB.

An integrated magnetooptical (MO) pickup is developed with an optical waveguide device that can detect the MO signal. In this pickup, the optical waveguide device is mounted in a package with a laser diode and a photodiode for servo signal detection, so all optical functions are integrated into a unit except a light converging function. The optical waveguide device is constructed with a prism coupler, a thin-film bi-prism and four PIN photodiodes, on a 1 mm×2 mm Si substrate. The optical utilization efficiency and the extinction ratio of the device are more than 50% and 1 : 10, respectively. The carrier-to-noise ratio of the signal reproduced with this pickup reaches up to 45 dB.