Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Reexamination Certificate
1999-03-17
2001-04-17
Epps, Georgia (Department: 2873)
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
C349S202000, C369S109010
Reexamination Certificate
active
06218655
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical pickup for recording or reproducing information on or from information recording media such as CD and DVD by irradiating a light beam onto the information recording media.
2. Description of the Related Art
Conventionally, an optical pickup to be used for reproduction and the like from an information recording medium such as DVD is constituted so that a main-beam is irradiated in order to detect information pits on a recording track and a plurality of sub-beams are irradiated onto predetermined positions for various objects such as a tracking information detection by means of the a so-called three-beam method and an operation of a cross talk canceller in order to suppress cross talk from adjacent tracks. For this reason, it is generally performed that a light beam is diffracted by a diffraction grating to produce diffracted lights which are irradiated as sub-beams.
Recently, in order to realize the diffraction grating for use in an optical pickup, a liquid crystal panel has been utilized. Namely, a split form of the liquid crystal panel is formed as a grating pattern, and the diffracted light can be irradiated as sub-beams by giving a phase difference due to a refractive index change to the light beam passing through the liquid crystal panel according to a birefringence effect of the liquid crystal.
In such a liquid crystal panel, a desired diffraction efficiency can be obtained by setting the split form suitably, and the phase change to be given to the light beams can be adjusted by controlling an applied voltage to the liquid crystal panel. Moreover, it is comparatively easy to perform switched control between the irradiation of only a main-beam irradiation and three beams or the like. Therefore, when the liquid crystal panel is used as the diffraction grating, it is possible to provide an optical pickup which is effective for recording on or reproduction from DVD and the like.
However, it is not easy to operate the conventional optical pickup utilizing the liquid crystal panel with changing the irradiated positions of the main-beam and sub-beams. Namely, the distances of beam spots of the main-beam and sub-beams change in inverse proportion to a grating pitch of the diffraction gratings. While the phase difference can be changed by controlling the applied voltage to the liquid crystal panel, the distances of the beam spots should be fixed because the grating pitch is preset as the split form.
In addition, it is conceivable to provide and suitably switch two kinds of liquid crystal panels on which the diffraction grating are formed with different pitches. However, if the optical pickup is constituted in such a manner, it is not easy to adjust the orientation of the liquid crystals relative to the light beams and the positioning of the liquid crystal panels, and thus this causes a rise in the cost.
SUMMARY OF THE INVENTION
The present invention has been achieved with such points in view, and its object is to provide an optical pickup using a liquid crystal panel as a diffraction grating and having a simple structure in which an irradiation state and a positional relationship of a main-beam and sub-beams can be readily controlled.
According to one aspect of the present invention, there is provided an optical pickup for irradiating a light beam onto an information recording medium and receiving a light reflected by the medium, including: a light source for emitting a light beam; a liquid crystal panel for diffracting the light beam to produce a main beam and a plurality of sub-beams to be irradiated on the medium, the liquid crystal panel including a first area in which a first group of grating patterns with predetermined pitches is formed and a second area in which a second group of grating patterns having the predetermined pitches is formed, the first group of grating patterns and the second group of grating patterns being arranged on a plane with a gap area formed between the first area and the second area so as to form an integrated grating pattern; and a control unit for applying a first voltage to the first area to control a refractive index of the first area and applying a second voltage to the second area to control a refractive index of the second area, thereby to control a diffraction characteristic of the integrated grating pattern.
In accordance with the optical pickup thus configured, the light beam from the light source passes through the integrated grating pattern of the liquid crystal panel and is diffracted. Here, the liquid crystal panel includes the first area and second area, and the first and the second groups of grating patterns are formed in the first and second areas, respectively. These groups of grating patterns are arranged on a plane with a gap area formed therebetween. The pitch of the grating patterns in the first area may be equal to the pitch of the grating patterns in the second area. Here, the pitch of the grating patterns is a spatial period with which the phase change to be given to the light beam is repeated, and when basic patterns are repeatedly arranged, the grating patterns are formed.
The light beam passed through the liquid crystal panel is divided into the main-beam and the sub-beams as diffracted light, and they are irradiated onto the information recording medium. At this time, the control unit varies the first voltage to be applied to the first area and the second voltage to be applied to the second area so as to control the refractive indexes of both the areas. Namely, the phase difference is given to the light beams passed through the first and second areas, and the diffraction efficiency and diffraction angle of the diffracted lights can be controlled by the voltages applied to the first and the second areas.
Therefore, the irradiation state of the sub-beams can be changed with respect to the main-beam, and the control can be made so that the phase change by diffracting the light beams is given by one or both of the first and second areas. Since the pitch can be varied, the relative irradiated positions of the sub-beams can be changed without complicating the structure of the optical pickup. As a result, the optical pickup, which has the simple structure and can easily control the diffraction characteristic, is provided.
The control unit may operate by selecting one of a first mode for applying both the first voltage and second voltage and a second mode for applying either one of the first voltage and second voltage. By this, the control unit controls the first voltage to be applied to the first area and the second voltage to be applied to the second area. In the first mode, both the first voltage and second voltage are applied. In the second mode, one of the first voltage and second voltage is applied. Therefore, in the first mode, the light beam is diffracted by the integrated grating pattern formed by the grating patterns of the second area. In the second mode, the light beam is diffracted by the integrated grating pattern of the first and second areas. Thus, the pitch in the first mode and the second mode may be altered, and as a result the irradiated positions of the sub-beams on the information recording medium may be appropriately controlled.
The control unit may operate by selecting one of a first mode for applying both the first voltage and second voltage, a second mode for applying either one of the first voltage and second voltage, and a third mode for applying neither the first voltage nor second voltage. By this, the first and second modes as well as the third mode can be selected, and in the third mode, neither the first voltage nor the second voltage is applied by the control unit. Therefore, in the third mode, the liquid crystal panel does not serve as the diffraction grating, and only the main-beam is irradiated onto the information recording medium. As a result, the optical pickup can be operated by switching between the recording/reproduction using the 1 beam and the recording/reproduction using the 3 beams.
Prefe
Ogasawara Masakazu
Ohtaki Sakashi
Tateishi Kiyoshi
Epps Georgia
Ladas & Parry
Pioneer Electronic Corporation
Schwartz Jordan M.
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