METHOD AND APPARATUS FOR WRITING A SIGNAL INFORMATION TRACK ON A DISC

摘要

Apparatus and process for writing video information in the form of a frequency-modulated signal upon a disc member and for retrieving the recorded information. The disc member (10) formed by the writing apparatus is also described. The apparatus includes a laser (30) as a source of write light beam (29) and a write optical system for directing the focused beam to a moving disc member. The member comprises a substrate carrying a light responsive coating (26) at least on one surface. The write optical system includes an optical modulator (44) that charges the intensity of the write laser beam with respect to a predetermined threshold intensity sufficient to form a first type of indicia in the coating and a feedback apparatus that stabilises the operating level of said modulator. The read optical system includes a light sensing circuit (158) for changing the intensity-modulated reflected-light beam to a corresponding electrical signal. A triangular frequency modulator (Figure 14C) for driving a Pockels cell (68), for obtaining a sinusoidal-shaped light-modulation output signal from the linear polariser (70) and a bias circuit (264) employed for removing the second harmonic intermodulation distortion of the modulated write beam, are described.