Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2000-04-17
2004-03-02
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S112170
Reexamination Certificate
active
06700854
ABSTRACT:
BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to an optical storage apparatus in which by radiating light to a storage medium with information stored therein and receiving the light subjected to a polarized state change in the storage medium, the information stored in the storage medium is read based on the polarized state change.
(ii) Description of the Related Art
As one type of the storage medium in which the information is read based on the change of the polarized state as described above, optical disks such as a magnetic optical (MO) disk have been noted, this type of high capacity storage medium is small-sized, light-weighted, and portable, and further possibilities of high densification and capacity enlargement have been pursued.
In a conventional optical disk drive in which the optical disk is accessed, the optical disk is irradiated with light, and the information stored in the optical disk is read by picking up the reflected light whose polarized state is changed in accordance with the information stored in the optical disk. Specifically, the light reflected by the optical disk is split from the light of a forward path to be radiated to the optical disk by a beam splitter, and further separated into both P, S polarized component beams crossing at right angles to each other by a Wollaston prism, and the beams are incident upon and received by two divided light receiving elements. The received light signal is subjected to a pre-processing by an analog circuit, and subsequently to a signal extraction processing, so that the information is read out.
Here, in the reflected light from the optical disk, besides the change of the polarized state by the intrinsic action of the stored information, a phase change is also generated between both P, S polarized components by the birefringence of the protective layer of the optical disk medium, and further the birefringence is nonuniform over the entire surface of the optical disk and also fluctuates even in one track. Furthermore, the optical system for guiding the reflected light from the optical disk to the light receiving element is provided with a polarized beam splitter, a reflective mirror, and other optical elements in which a phase deviation is possibly generated between both P, S polarized components of the reflected light from the optical disk.
This phase deviation between both P, S polarized components appears as the “surge” of the DC component of the regenerated signal obtained in the stage of pre-processing by an analog circuit after the light receiving element receives light. Even in the optical system, if the phase deviation is generated, the “surge” is remarkably largely emphasized, and there is a possibility that the range of signals able to be handled in a signal extraction processing circuit is exceeded. In this case, there is a problem that correct information (signal) cannot be extracted.
In recent years, because of further capacity enlargement, there has been a tendency to record the information in a region finer than ever with a high density and to regenerate the information by the irradiation with light more intense than ever. In this case, the surge of the DC component of the regenerated signal tends to increase further in proportion to the intensity of the irradiation light.
A conventional method for solving the problem comprises: sorting the components which possibly cause the phase deviations between both P, S polarized components from the components constituting the optical system; or combining the phase deviation directions of a plurality of components causing the phase deviations in the optical system in order to mutually compensate for the phase deviations in the entire optical system.
However, in this method, the process of sorting the components or combining the directions is required, it is difficult to save costs, and the necessity of radiating further intense light to read the information cannot be handled.
Moreover, instead of the above-described method of sorting the components or selecting the combination, a method of disposing a phase plate immediately before the Wollaston prism on the optical path of the reflected light from the optical disk is proposed. This phase plate is an optical component which is disposed and inclined with respect to an optical axis, so that the thickness of the optical axis direction of the phase plate is changed. In accordance with the change of the thickness, that is, an inclination angle, the phase between both P, S polarized components can be adjusted. By disposing the phase plate and adjusting the inclination in each optical system, product dispersions are suppressed while the surge of the regenerated signal DC component can be controlled to provide a low level in any product.
However, in the above-described method of disposing the phase plate and adjusting the inclination angle to adjust the phase deviation between both P, S polarized components in the optical system, when the phase plate inclination is adjusted to adjust the phase deviation, the optical path ahead of the phase plate changes by the light refraction action of the phase plate. It cannot be monitored simply by changing the phase plate inclination whether or not the phase deviation is compensated. Additionally, it cannot be monitored whether or not the phase deviation is compensated until the position of the light receiving element or the like starts to be readjusted with the adjustment of the phase plate inclination. When the phase compensation Is insufficient, a process of readjusting the phase plate inclination and further readjusting the position of the light receiving element or the like to perform the monitoring needs to be repeated. A precise adjustment is abandoned, or the cost increase for the adjusting operation is abandoned and the above-described operation needs to be repeated many times as occasion demands.
SUMMARY OF THE INVENTION
In consideration of the above-described situations, an object of the present invention is to provide an optical storage apparatus including a constitution which can easily compensate for the phase deviation by an optical system between both P, S polarized components of the light subjected to a polarized state change in a storage medium, and a phase compensation amount adjustment method in the optical storage apparatus.
To attain the above-described object, according to the present invention, there is provided an optical storage apparatus in which by radiating light to a storage medium with information stored therein and receiving the light subjected to a polarized state change in the storage medium, the information stored in the storage medium is read based on the polarized state change.
The optical storage apparatus comprises a phase plate disposed in an optical path in which the light reciprocates so that a forward light emitted from a light source is radiated to the storage medium and a backward light subjected to the polarized state change in the storage medium reaches a light receiving element. The phase plate is disposed to compensate for a phase deviation between both P, S polarized components of the backward light.
In the constitution of the optical storage apparatus of the present invention, the light reciprocates by the phase plate. Therefore, when a phase plate inclination is adjusted, the optical path of the light which passes by the phase plate only once changes, but with respect to the light which again passes by the phase plate in a reverse direction, the change of the optical path is canceled. Therefore, by reciprocating the phase plate, even when the phase plate inclination is adjusted, the position of the light receiving element disposed after the phase plate does not need to be adjusted, the degree of phase compensation by the adjustment of the phase plate inclination can immediately be monitored, the adjustment of the phase plate inclination is remarkably facilitated, and a precise adjustment can be performed. Additionally, since the adjusting operation efficiency is high, cost reduction can be re
Kataoka Masahiko
Mizuishi Kazuyuki
Saito Hidenori
Fujitsu Limited
Greer Burns & Crain Ltd.
Tran Thang V.
Vuong Bach
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