JP3023119B2 - Optical disk drive - Google Patents

Description

Description of the Invention [Object of the Invention] (Field of Industrial Application) The present invention relates to an optical disk apparatus for optically recording information on an information recording medium and optically reproducing the recorded information. Things.

(Prior Art) Currently, semiconductor lasers are mostly used as light sources for optical heads of optical disk devices using optical information recording media. The spread angle of light emitted from a semiconductor laser is almost anisotropic (aspect ratio ≠ 1) in most cases. In order to efficiently guide the emitted light from the semiconductor laser to the information recording surface of the optical disk and to record information on the optical disk with high density, the emitted light of the semiconductor laser is used after being shaped into an isotropic circular beam. .

A Littrow type prism is often used for beam shaping. Japanese Patent Publication No. 61-53775 discloses that when the refractive index of the glass used for the beam shaping prism is selected according to the aspect ratio of the spread angle of the semiconductor laser, the reflection loss at the entrance surface of the beam shaping prism can be significantly reduced. It states in detail what can be done.

However, when the oscillation wavelength of the semiconductor laser changes due to wavelength dispersion in glass, the emission angle of the beam emitted from the beam shaping prism changes, and the position of the light spot condensed as a minute spot on the optical disk by the focusing lens is changed. Fluctuations occur. When the glass having a high refractive index is used when the aspect ratio of the semiconductor laser is large, the wavelength dispersion is large, so that the position variation of the light spot also becomes large. Here, the position variation of the light spot occurs in a direction along the bonding surface of the semiconductor laser. In the conventional optical head, since the bonding surface of the semiconductor laser is arranged or configured to be parallel or perpendicular to the track on the optical disk, it appears as time-axis jitter or track deviation. Since the oscillation wavelength of the semiconductor laser fluctuates when the oscillation output changes, in the operation of the optical disk, when the operation mode changes from the reproduction mode to the recording mode and from the recording mode to the reproduction mode, the oscillation wavelength instantly becomes 3 to 5 nm. Because of the wavelength shift, the control of the position of the light spot is reduced.

(Problems to be Solved by the Invention) As described above, in the conventional optical head incorporating the beam shaping prism, when the oscillation wavelength of the semiconductor laser changes, the light spot on the optical disc is caused by the wavelength dispersion of the beam shaping prism. It moves in the tangential direction or the direction off the track. When the oscillation wavelength changes slowly, PLL control (PHASE
LOCK LOOP), the tracking control can control the position fluctuation of the light spot in the off-track direction. However, the fluctuation of the oscillation wavelength that occurs when switching the operation mode of the optical disk device where the output of the semiconductor laser changes greatly is instantaneous. Because of the fluctuation of the oscillation wavelength of 3 to 5 nm, it cannot be controlled by the control system described above, and there is a problem that the information is erroneously read when the information recorded on the optical disk is reproduced.

The present invention is a novel and useful optical spot position change on the optical disk due to the instantaneous change in the oscillation wavelength of the semiconductor laser caused by the change in the information recording and reproduction on the optical disk. It is an object to provide an optical disk device.

[Structure of the Invention] (Means for Solving the Problems) In an optical disc device according to the present invention, in an optical disc that rotates so that the linear velocity becomes faster toward the outer periphery, the movement of the light beam in the tangential direction of the track becomes greater toward the outer periphery. Focusing on the fact that the influence on the time axis is small, the movement of the light spot on the optical disk caused by the wavelength dispersion of the beam shaping prism is set in a rotatable drum so that the movement is in the tangential direction of the track at the outer periphery. An optical system required for an optical head was incorporated to realize a compact and highly reliable optical disk device.

(Operation) In the optical disk device of the present invention, when an optical system required as an optical head is incorporated in a rotatable drum, and a track can be selected by rotation of the rotatable drum, the optical disk device can be used for the inside and outside of the optical disk. The projected image of the semiconductor laser on the optical disk rotates around the circumference. That is, the relative positional relationship with the track on the optical disk changes. At the inner periphery of the recording area of the optical disc, the angle formed by the tangent direction of the track of the projected image of the semiconductor laser bonding surface becomes larger, and at the outer periphery of the recording area, the angle formed by the tangent direction of the track becomes smaller. When a laser and a beam shaping prism are incorporated in a rotatable drum (that is, a light-transmitting optical system including a semiconductor laser is arranged on the rotation center side of the optical disc), a light spot on the optical disc caused by wavelength dispersion of the beam shaping prism Moves in the tangential direction of the track at the outer peripheral portion, and the time axis jitter can be reduced.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment according to the present invention. FIG. 1 is a configuration diagram of an optical disk device according to the present invention. An optical system in which all necessary optical systems are incorporated in a rotatable drum (5) is integrated with an access mechanism, and a straight line passing through the center of rotation of the optical disk (100) and the optical axis of the focusing lens (1) ( A) and a straight line (B) passing through the optical axis of the focusing lens (1) and the rotation center of the rotatable drum (5) are the optical disc (10).
This is arranged and configured to be orthogonal at the center of the information recording area of (0). In order to explain the effects of the above arrangement and configuration, the configuration of the optical system in the rotatable drum (5) will be described with reference to FIG. 2 along the light transmission path.

FIG. 2 is a configuration diagram of an optical head according to the present invention.
When describing the configuration of the optical system according to the light transmission path,
The light beam emitted from the semiconductor laser (103) is converted into parallel light by the collimator lens (104) and enters the combined optical unit (105). The incident surface from the collimator lens (104) of the optical unit (105) is
It functions as a beam shaping prism for converting a light beam having an anisotropic intensity distribution emitted from 03) into an isotropic light beam. The light incident on the optical unit (105) passes through a beam splitter (105a) for splitting the reflected light from the optical disk into a receiving optical system, and is totally reflected on a reflecting surface (105b) whose end source is polished to 45 degrees. And rotating drum (10
The light is deflected by the converging lens arranged on the upper surface of 2) to form a minute light spot on the medium surface of the optical disk.

The light reflected on the medium surface of the optical disk is reflected again by the beam splitter (105a) via the focusing lens and the reflecting surface (105b) of the optical unit (105). Optical unit (10
At the output end to the light receiving optical system of 5), a half-wave plate (105c) and a condenser lens (105d) are integrally provided. The half-wave plate (105c) rotates the polarization plane of the light beam reflected by the beam splitter (105a) by 45 degrees, and divides the light beam into two by a polarization beam splitter (108a) described later. The light emitted from the condenser lens (105d) is reflected by the reflecting mirror (107) while being converged, and is reflected by the polarizing beam splitter (108).
a) and the two photodetectors (108b, 108c) are incident on the integrated detection unit (108). Two photodetectors (108b, 10
In FIG. 8c), the glass portion is lengthened with respect to the light transmitted through the polarizing beam splitter (108a) so as to provide an optical path difference so as to be positioned before and after the converging point of the condensed beam.
Each of the photodetectors (108b, 108c) is composed of a light receiving surface divided into three parts. The difference between the light receiving outputs on both sides is obtained from the light receiving output at the center, and the difference between the two light detectors (108b, 108c) is obtained. Thus, a change in the shape of the light beam on the light receiving surface is detected to detect the light spot condensing state on the medium surface of the optical disk (focus error detection). Further, from the sum of the sums of the three divided photodetectors (108b, 108c), emboss information previously formed on the optical disc and information recorded as a change in reflectance are obtained. Can obtain information recorded on a magneto-optical recording medium or the like. In this embodiment, the tracking error detection for controlling the pit train on the optical disk can be obtained by detecting wobbled pits provided in advance in the optical disk in an embossed manner. That is, the total output of the photodetectors (108b, 108c) is sampled in the wobbled pit portion, and the tracking error is detected by comparing the respective signal amplitudes. Also, as described above, coils (12a, 12b) are mounted at two locations on the outer peripheral portion of the rotating drum (5) for rotational driving.

The optical system described above, as shown in FIG. 2, uses the center of rotation (A) of the rotating drum (5) and the optical axis (B) of the focusing lens (1) for condensing the light beam on the optical disk. When the rotatable drum (5) is divided into two parts by a straight line (X) connecting the light transmitting optical system and the light receiving optical system to one side and the other side, respectively. And the light receiving system can be configured stably. Further, the optical system is efficiently arranged in a space formed by the support rod (101) provided through the rotating drum (5) and the outer shape of the rotating drum (5), and the light transmitting optical system By locating the optical axis and the optical axis of the light receiving optical system on the same plane (the optical system is not a two-stage configuration), it is possible to reduce the thickness of the rotating drum (5) and to provide an overall thin optical head. .

The bonding surface of the semiconductor laser (103) is projected at an angle of about 45 degrees with respect to the straight line (X). That is, since it is a line segment orthogonal to the dashed line indicating the optical axis of the light emitted from the semiconductor laser (103), it forms an angle of approximately 45 degrees with the straight line (X) on the optical axis of the focusing lens. Will be. The angle between them is defined as an acute angle (the same applies hereinafter). In the arrangement and configuration shown in FIG. 1, in the center of the information recording area of the optical disk (100), the bonding surface of the semiconductor laser (103) has an angle of approximately 45 degrees with respect to the track on the optical disk (100). Will be projected. Further, since the light transmitting optical system including the semiconductor laser (103) is arranged on the rotation center side of the optical disk (100), the rotatable drum (5) rotates and the light is transmitted to the outer peripheral side of the optical disk (100). When the spot is located, the angle changes so that the angle becomes smaller.

On the other hand, when the oscillation wavelength of the semiconductor laser (103) changes, the light spot on the optical disc (100) moves due to the wavelength dispersion of the optical unit (105) having a beam shaping function.
The amount of movement of the light spot is shown in equation (1).

M = cosβ / cosα nλ * sinβ = sinα, (nλ + Δλ * Δn) sinβ = s
inα λ: oscillation wavelength of semiconductor laser [nm] Δλ: wavelength variation [nm] nλ: refractive index, Δn: refractive index variation [/ nm] F: focal length of focusing lens [mm] M: beam shaping rate α: beam Angle of incidence on the shaping surface β: Emission angle When the glass constituting the optical unit (105) is BK7, λ = 830 nm, M = 2, F = 3 mm, nλ = 1.510206, Δn = 1.845 * 10 ⁻⁵ / nm Δd = 4.2356 * 10 ^-2 * Δλ [μm] (2) When the oscillation wavelength of the semiconductor laser (103) changes by 5 nm, the light spot on the optical disk (100) moves by 0.212 μm.

FIG. 3 shows the relative relationship between the moving direction of the light spot due to wavelength fluctuation and the track on the optical disk (100) at the position (inner circumference, center, outer circumference) of the information recording area of the optical disk (100). Here, the moving direction of the light spot is a direction along the projected image of the bonding surface of the semiconductor laser.

The movement amount of the light spot due to the wavelength fluctuation is determined by the wavelength fluctuation amount Δλ as shown in Expression (2), regardless of the position (inner circumference, center, outer circumference) of the information recording area of the optical disc (100). However, the angle between the moving direction of the light spot (the direction along the projected image of the bonding surface of the semiconductor laser) and the track direction changes depending on the position (inner circumference, center, outer circumference) of the information recording area of the optical disc (100). . The angle is large on the inner peripheral side and smaller on the outer peripheral side. In other words, the influence on the off-track direction is great on the inner circumference side, and the influence on the time axis direction is great on the outer circumference side. However, for example, in an optical disc rotating at a constant angular velocity (constant rotation speed), the influence on the time axis jitter due to the movement of the light beam in the time axis direction is smaller at the outer peripheral portion. This is because the bit length, which is a unit of information recording, is longer because the linear velocity is higher at the outer periphery. Also,
At the center, the angle between the direction of movement of the light spot (the direction along the projected image of the junction surface of the semiconductor laser) and the track direction is approximately 45 degrees, and the effect of the movement of the light spot is off-track and in the time axis direction. Compared to the conventional 0.71.

According to the optical disk apparatus described above, the movement of the light spot on the optical disk that causes the wavelength dispersion of the beam shaping prism and the fluctuation of the oscillation wavelength of the semiconductor laser is controlled by information recording / recording.
The optical disk device can be reduced to such an extent that reproduction is not affected, and a highly reliable optical disk device can be provided as a whole.

In the detection optical system in the above embodiment, focus error detection and magneto-optical signal detection were performed using a half-wave plate, a polarizing beam splitter, and two sets of photodetectors. However, the present invention is not limited to this configuration. The same effect can be obtained by using other known detection systems according to the optical disk used without any problem, for example, a light receiving optical system using a telephoto lens that has an optical system shorter than the focal length by arranging a concave lens in the detection optical system. Is obtained. The main point of the present invention is to obtain a novel effect by characterizing the positional relationship between the light transmitting optical system and the optical disk, and to configure the other parts in various ways without departing from the gist of the present invention. Can be.

FIGS. 4 and 5 show the overall configuration of the optical head configured as described above. The focusing lens 1 is fixed to a lens holder 2, and the lens holder 2 is attached to the leaf springs 3a and 3b by Z
It is supported so as to be able to translate in the axial direction. Leaf spring 3a, 3b
Is fixed to the rotating drum 5 by a leaf spring fixing member 4.

A focusing coil 9 is wound around the lens holder 2, and a magnetic field is applied by a magnetic circuit 17 including a yoke 10 and a permanent magnet 11 fixed to the rotating drum 5. By the action, the focusing lens 1 is moved in the focus direction in the Z direction in the figure.

At both ends of the rotating drum 5, tracking coils 12a,
12b is fixed via bobbins 13a, 13b, and yokes 14a, 14b,
A magnetic field is applied by a magnetic circuit fixed by 15a, 15b and permanent magnets 16a, 16b, and the tracking coils 12a, 12b
The rotating drum 5 around the Z-axis in the figure is rotated by an electromagnetic action with a current supplied to the focusing lens 1, and as a result, the focusing lens 1 is moved in the tracking direction in the Z direction. In addition, the moment of inertia of the tracking coils 12a and 12b is equal to the total moment of inertia of the rotating drum 5 and all components (excluding the tracking coils 12a and 12b) driven integrally with the rotating drum 5. Is configured.

[Effects of the Invention] As described above, in the optical disk device of the present invention, an optical system required as an optical head is incorporated in a rotatable drum, and a track can be selected by rotating the rotatable drum. When configured, the projected image of the semiconductor laser on the optical disk rotates at the inner and outer circumferences of the optical disk. That is, the relative positional relationship with the track on the optical disk changes. At the center of the recording area of the optical disk, the direction along the projected image of the bonding surface of the semiconductor laser is approximately 45 degrees with respect to the tangential direction of the track. Similarly, the angle is large at the inner circumference and is larger at the outer circumference. If the semiconductor laser and the beam shaping prism are incorporated into a rotatable drum so as to be small (the rotation center side of the optical disc), the movement of the light spot on the optical disc caused by the wavelength dispersion of the beam shaping prism due to the wavelength fluctuation of the semiconductor laser. In a disk rotating at a constant speed, for example, at a constant speed due to the tangential direction of the track at the outer peripheral portion, since the linear speed is high at the outer peripheral portion, the unit length of the bit, which is a unit of recording information, is long, and the movement of the light spot to the time-axis jitter is large. The effect can be reduced, and the information recorded on the optical disk can be read without error. It is possible to provide a location.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical disk device according to an embodiment of the present invention, FIG. 2 is a configuration diagram of an optical system in a rotatable drum according to the embodiment of the present invention, and FIG. 3 is an information recording area of the optical disk. FIG. 4 is a view for explaining that the moving direction of a track and a light spot changes due to the difference in the optical head, FIG. 4 is an external view of an optical head according to the present invention, and FIG. 5 is a configuration diagram of the optical head according to the present invention. (1) Focusing lens (5) Rotatable drum (100) Optical disc (103) Semiconductor laser (104) Collimator lens (105) Optical unit

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Claims (2)

(57) [Claims] 1. A first optical system for guiding light emitted from a semiconductor laser via a converging lens to an optical disk which rotates so that a linear velocity becomes faster toward the outer periphery, and light reflected from the optical disk to a photodetector. A second optical system, and the first and second optical systems;
An optical head having a housing rotatably provided so that tracks on the optical disk can be selected, wherein the optical disk is disposed on the optical head. In this case, the tangential direction of a track located substantially at the center of the information recording area of the optical disc and the direction of a straight line passing through the optical axis of the focusing lens coincide with the rotation center of the case. A body is disposed, an angle between a direction along a projection image of the bonding surface of the semiconductor laser on the optical disc and the tangential direction is set to approximately 45 degrees, and the housing rotates toward the outer peripheral side of the optical disc. An optical disk device characterized in that the angle becomes smaller as the angle increases. 2. The optical system according to claim 1, wherein the first optical system is positioned closer to the rotation center of the optical disc than the second optical system with respect to a straight line passing through the center of rotation of the housing and the optical axis of the focusing lens. The optical disk device according to claim 1, wherein the optical disk device is incorporated in a housing.