Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2002-03-11
2004-03-02
Edun, Muhammad (Department: 2655)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S112270, C369S110010, C369S044230
Reexamination Certificate
active
06700855
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical disc drive which writes and/or reads signals to and/or from an optical disc by radiating a light to the latter, and more particularly to an optical disc drive adapted to transmit a light used to write and/or read signals to and/or from an optical disc through a polarization maintaining optical fiber.
BACKGROUND ART
Heretofore, optical discs such as ROM (read-only memory) type optical discs represented by CD (compact disc) and RAM (random-access memory) type optical discs represented by phase-change disc and magneto-optical disc, have widely been used as recording medium to store information including image, sound, character data, etc.
For such optical discs, it has been actively tried to increase the recording density for an increased storage capacity. Along with this trend, various attempts have been made to adapt the optical disc drives for successful write and/or read of signals to and/or from such higher recording density optical discs.
Recently, it has been proposed to apply the flying head technique already implemented in the hard disc drive to the optical disc drive in order to attain a higher recording density of the optical disc.
In this optical disc drive, an objective lens to converge a light on an optical disc is mounted on a slider to form a head and a light emitted from a light source is guided to the head through an optical fiber. In the optical disc drive, the head is scanned over the optical disc while being floated above the optical disc, and a spot of the light converged by the objective lens is radiated onto the optical disc to write and/or read signals to and/or from the optical disc.
An optical disc drive which writes and/or reads signals to and/or from an optical disc should desirably be compatible with all types of optical discs. However, when a magneto-optical disc is used in an optical disc drive which uses an optical fiber for transmission of a light, there will take place such problems as will be described in the following.
When the magneto-optical disc as a recording medium is used in the optical disc drive since signal detection is effected by the use of the Kerr effect that the polarization axes of the linearly polarized light are rotated under the effect of the magnetic field, it is necessary to transmit the light while keeping the light polarized. However, ordinary optical fibers show a random birefringence caused by a disturbance etc. having taken place during manufacture. Hence, a phase difference will take place between electric field vibration components of a light allowed to travel through the optical fiber and will cause a complex change in polarized state of the light.
The polarization maintaining optical fiber has already been known as an optical fiber capable of transmitting a light while maintaining the polarized state of the light. The polarization maintaining optical fiber has a waveguide structure having an advanced phase axis and retarded phase axis (two axes difference in refractive index) perpendicular to each other. In the waveguide structure of the optical fiber, a linearly polarized light incident along any one of the axes can be transmitted while the polarized state is being maintained.
However, even in case a light is guided through such a polarization maintaining optical fiber, when a magneto-optical disc is used as a recording medium with the conventional optical disc drive, the return light from the magneto-optical disc will be incident at a Kerr rotation angle upon the polarization maintaining optical fiber, and thus a phase difference will be caused between the field vibration components of the return light guided through the polarization maintaining optical fiber and will adversely affect the detection of signals.
DISCLOSURE OF THE INVENTION
Accordingly, the present invention has an object to overcome the above-mentioned drawbacks of the prior art by providing an optical disc drive compatible with all types of optical discs including magneto-optical discs.
The above object can be attained by providing an optical disc drive including means for rotating an optical disc, a light source to emit a light used for write and/or read of signals to and/or the optical disc, a head having installed therein an objective lens which converges the light emitted from the light source and being scanned over the optical disc being rotated by the rotating means to radiate the light converged by the objective lens to the optical disc, means for receiving a return light being a part of the light radiated from the head to the optical disc and which is reflected from the optical disc and detecting signals from the return light, and means for guiding the light emitted from the light source to the head and the return light from the optical disc to the signal detecting means.
In the above optical disc drive according to the present invention, the light transmitting means includes a polarization maintaining optical fiber and phase difference generating means to cancel out a phase difference between electric field vibration components generated when the light going towards the head or the return light going towards the signal detecting means is guided through the polarization maintaining optical fiber by the phase difference generated by the phase difference generating means or multiply the phase difference by an integer multiple of &pgr;.
In this optical disc drive, an installed optical disc is rotated by the disc rotating means, and a light used to write and/or read signals to and/or from the optical disc is emitted from the light source.
The light emitted from the light source is guided to the head by the light transmitting means including the polarization maintaining optical fiber and phase difference generating means. The head is scanned over the optical disc being rotated by the disc rotating means, and the light guided through the light transmitting means from the light source is converged by the objective lens and radiated to the optical disc.
A return light being a part of the light radiated from the head to the optical disc and reflected from the optical disc and which carries signals written on the optical disc, is guided by the light transmitting means to the signal detecting means. The signal detecting means thus receives the return light to detect the signals.
In the above optical disc drive according to the present invention, in case a magneto-optical disc from which signals are detected by the use of the Kerr effect is used as an optical disc, a return light from the magneto-optical disc will be incident in an off-axis manner upon the polarization maintaining optical fiber of the light transmitting means. Thus, in the return light guided through the polarization maintaining optical fiber, there will take place a phase difference between electric field vibration components depending upon the birefringence of the polarization maintaining optical fiber. In this optical disc drive, however, the phase difference between the field vibration components, having taken place in the light guided through the polarization maintaining optical fiber, is canceled out by a phase difference generated by the phase difference generating means or is multiplied by an integer multiple of &pgr;, so that the signals written on the magneto-optical disc can be detected properly.
That is, since it is possible to predict a distribution of refractive indices of the birefringence in the polarization maintaining optical fiber, magneto-optical signals can properly be detected by allowing the phase difference generating means to generate a predetermined phase difference in a light going towards the bead or a return light going towards the signal detecting means by means of the phase difference generating means correspondingly to a phase difference between field vibration components of the light, generated due to a birefringence of the polarization maintaining optical fiber and thus canceling out a phase difference between field vibration components, generated when the light is guided through
Edun Muhammad
Sonnenschein Nath & Rosenthal LLP
Sony Corporation
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