This application is based on application Nos. 10-337671 and 11-077460 filed in Japan, the content of which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an optical head and an optical head device, and more particularly to an optical head which is suited to be used for high-density recording/reading/erasing of information to or from an optical recording medium and an optical head device using this optical head.
2. Description of Related Art
In the art of optical memories which optically record and read information, in recent years, with speed-up of computer processing and development of multimedia, high-density devices which are capable of recording an extremely large volume of information are demanded, and in order to comply with the demand, a near field optical recording technique is suggested. In a conventional optical memory using a laser beam, the recording density is limited depending on the diffraction limit of light, and such an optical memory can record and read marks of sizes at least light wavelength (several hundred nanometers). A recently proposed optical memory which uses near field optics radiates light to a recording medium (optical disk) for recording/reading with the optical head and the recording medium arranged at an interval of only some dozen nanometers. At this time, the optical memory uses a fiber probe with a minuscule aperture smaller than light wavelength and a solid immersion lens. Thereby, in spite of the diffraction limit, it becomes possible to record and read minuscule marks of some dozen nanometers.
In a conventional memory which uses propagated light, such as a CD, a DVD, an MO or the like, a convergent lens, a mirror, a prism and other optical elements are installed in the optical head, and the optical head is large and heavy. It is, therefore, difficult to adopt an air floating method based on the air lubricating principle, which is generally adopted in magnetic recording heads, in such an optical memory. In the above-mentioned optical head using a solid immersion lens, although the solid immersion lens itself is small and light, it is necessary to further use a convergent lens, which indispensably increases the size and weight.
Lately, xe2x80x9cObjective Lenses for DVD and Near Field Optical Disk Pickupxe2x80x9d ODF""98, Tokyo, Jun. 16, 1998 suggests an SIM (solid immersion mirror) which does not require a convergent lens. This SIM converges light by performing refraction once and reflection twice in a prism. Since this eliminates the necessity of using a convergent lens, an optical head using this SIM is small and light. However, because the SIM uses a coaxial optical system, the design is strongly limited. Also, since a direction of light incident to the SIM is perpendicular to a recording surface, a mirror for bending optical path of incident light is required. Accordingly, vibration and shift of the mirror must be adjusted, which obstructs reduction of the size and weight of the optical head device.
An object of the present invention is to provide a small and light optical head.
Another object of the present invention is to provide an optical head device of which optical system can be designed freely.
Another object of the present invention is to provide an optical head device in which light has only a small loss.
Another object of the present invention is to provide a near field optical head which is suited to make a gap from a recording medium by an air floating method.
Another object of the present invention is to provide an optical head which is capable of correcting spherical aberration when a parallel bundle of rays is incident thereto.
Another object of the present invention is to provide an optical head which is capable of using a divergent bundle of rays as incident light thereto.
Another object of the present invention is to provide an optical head which is capable of recording, reading and erasing information at a higher density by reducing the diameter of a near field light beam.
Another object of the present invention is to provide an optical head device which is strong against external vibration and shock.
Another object of the present invention is to provide an optical head device which records, reads and erases information by use of either one selected from near field light and propagated light.
Another object of the present invention is to provide an optical head device which uses a non-coaxial optical system.
In order to attain the objects, an optical head device according to the present invention comprises: a first light source which emits light; and a prism which receives the light emitted from the first light source as first incident light, reflects the first incident light inside at least once and emits the first incident light in a direction different from a direction in which the first incident light was incident thereto.
A prism according to the present invention comprises: an incident section which receives incident light; a first surface which reflects the incident light received by the incident section in the prism; and a second surface through which the light reflected by the first surface is emergent from the prism for reading of information.
Another prism according to the present invention comprises: an incident section which receives incident light; a first surface which reflects the incident light received by the incident section in the prism; a second surface which reflects the light reflected by the first surface in the prism in a direction which is different from a direction in which the incident light was received by the incident section; and a third surface through which the light reflected by the second surface is emergent from the prism for reading of information.
Another prism according to the present invention uses near field light occurring on an emergent surface for recording, reading and erasing of information, and the prism comprises an internal reflective surface which reflects light which was incident to the prism inside and converges the light on a vicinity of the emergent surface. In this prism, a non-coaxial optical system is formed.
According to the present invention, light of a specified wavelength which was incident to a prism through an incident section is reflected inside at least once and is converged on an emergent surface. Then, the light effuses through the emergent surface as near field light (in other words, optical near field). By use of this near field light, recording, reading and erasing of information are carried out. According to the present invention, an optical head can be composed of only a prism. Accordingly, the optical head is small and light and has a simple optical system. Also, an air floating method can be adopted in making a gap between the optical head and a recording medium.
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