Abstract: A video signal is recorded in successive tracks on a recording medium together with a pilot signal, the latter having a frequency that changes cyclically with a different one of at least four frequencies in successive tracks. A field detector detects sequential fields in the frames of the video signal, and rotation of the usual rotary transducers is servo-controlled in response to the detected sequence of fields and a pulse that is generated as the transducers rotate to represent the rotational phase of those transducers. A pilot signal generator generates the pilot signal with an initial frequency determined by an initial field in the detected field sequence, and with this frequency changing as a function of the detected sequential fields.

Abstract: A semiconductor laser apparatus which detects a laser beam from a semiconductor laser element by using a light-receiving element so as to perform automatic light power control, the temperature characteristic of the power of a laser beam which is transmitted through an end face protection film of the semiconductor laser element and the detected power of the light-receiving element have inverse characteristics relative to each other, and variations in intensity of the output light due to changes in temperature are minimized.

Abstract: A semiconductor laser has a semiconductor substrate with a feature on its surface. The feature, either a projection or a groove, forms a mesa or a mesa groove having relatively sharp edges. Active layers and cladding layers are deposited on this seimconductor substrate. The cladding layer deposited directly on the semiconductor substrate has at least one slope opposite the mesa or mesa groove, on which slope no active layer is formed during epitaxial growth. The active layer immediately above the cladding layer is prevented from depositing on the slope of the cladding layer so that no etching process for removing sections of the active layer is necessary. This allows deposition of the active layers and cladding layers on the semiconductor substrate in an uninterrupted sequence of single epitaxial growth steps.