Wavelength converting element and system for recording and reproducing optical information

摘要

In a wavelength converting element, an oscillation line at a predetermined wavelength is excited on the basis of excited light having a predetermined wavelength. Frequencies of the excited light and light on the oscillation line are mixed with each other in a nonlinear optical medium to generate light having a sum frequency. The wavelength converting element has resonators for the oscillation line and the excited light. A system for recording and reproducing optical information has a first light source capable of being directly modulated, and a second light source for emitting light having a wavelength shorter than that of a light beam emitted from the first light source. The first beam from the first light source is superposed on the short wavelength light from the second light source to record and reproduce the optical information. This system uses an overwrite recording system in which a writing operation of data is performed by emitting and superposing a modulated light beam from the first light source on the short wavelength light, and data indicative of value "0" are equivalently written to a memory medium by erasing data therefrom in this writing operation.