Directional asymmetries due to write‐laser mode hopping during optical recording

The wavelength of semiconductor lasers generally increases with increased output power due to changes in laser gain with current and temperature. Time‐resolved studies of the optical spectrum during the write‐pulse train clearly depicted the quasirandom mode hopping that occurred. In optically dispersive systems, the wavelength shifts caused significant write‐spot displacements down at the recording surface and affected mark lengths. Thermal modeling studies successfully duplicated the salient features of this effect and provided explanations for some of the experimental observations.