Abstract text

A hologram recording and reproducing system for recording or reproducing information to or from a hologram record carrier that stores an optical interference pattern of a reference beam and a signal beam therein as a diffraction grating, includes: light producing means that generates a reference beam and a signal beam based on a coherent beam in which the coherent beam is modulated into the signal beam according to information to be recorded; interference means that allows one of the reference and signal beams to propagate axially on an optical axis as a central region light flux and allows the other of the reference and signal beams to propagate coaxially and annularly in section as an annular region light flux surrounding the one spatially separated from the other in a same direction and converges both the reference beam and the signal beam on different focal points in the optical axis respectively through an objective lens optical system to cause interference between the reference beam and the signal beam; a hologram record carrier having a hologram record layer located on a side of a near one of the different focal points to the objective lens optical system and a reflection layer located on a side of a distant one of the different focal points from the objective lens optical system; and image detecting means arranged on the optical axis and for receiving a beam returning from the hologram record layer through the objective lens optical system when the reference beam is illuminated to the hologram record layer; wherein the hologram record carrier further comprising a servo guide layer which is placed at a position either nearer to the objective lens optical system than the hologram record layer or farther than the reflection layer from the objective lens optical system. The hologram recording and reproducing system further includes a servo control system for focusing a servo beam onto the servo guide layer and for receiving a reflection light returning from the servo guide layer to photoelectrically convert it to a signal and for driving the objective lens optical system in accordance with the signal photoelectrically converted, wherein the servo beam has a wavelength different from the coherent beam wavelength and passes through the central region coaxially with the central region light flux including the optical axis.