JP2777481B2 - Optical head structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for transmitting and receiving information to and from an optical card or an optical disk as an optical information recording medium. The present invention relates to an optical head structure used for an optical information recording medium provided in a plurality of rows via extending guide tracks.

[0002]

2. Description of the Related Art A conventional optical head 21 for exchanging information with, for example, an optical card 3 as an optical information recording medium.
Some are shown schematically in FIG. In the figure, a collimator lens 5 for converting the emitted light 4 to parallel light is provided in the optical path of the emitted light 4 from the laser diode 2.
A diffraction grating 6 for converting the main beam for focusing error detection and a pair of sub-beams for tracking error detection into three beams, and a beam splitter 7 for distributing the outgoing light 4 and the reflected light from the optical card 3. And an objective lens 10 for condensing each beam toward the optical card 3 are arranged in this order. The reflected light from the optical card 3 is turned to the right in the drawing by the beam splitter 7 and taken out as the error detection light 11. The detection light 11 is provided in the optical path of the detection light 11. A detection lens 12 for condensing light toward a photodetector 14 comprising a multi-division photodiode of a type and a cylindrical lens 13 for detecting a focusing error by an astigmatism method are arranged in this order.

As shown in FIG. 5, the optical card 3 has a data track 15 for recording and reproducing optical information along a conveying direction of the optical card 3 via a guide track 17 extending at a side edge thereof. Are provided in a plurality of rows. When transmitting and receiving information to and from the optical card 3, the spotlight 4 for focusing error detection by the main beam is applied to the data pit 16 provided on the data track 15.
The spot light beams 4b and 4c for tracking error detection by a pair of sub-beams are respectively radiated so as to irradiate “a” so as to straddle each boundary between the data track 15 and the guide tracks 17 on both sides thereof. The data pits 16 are reflected by the focusing error detection light 11a, which is the reflected light of the focusing error detection spot light 4a.
And the information obtained from is read by the photodetector 14,
When the optical head 21 is relatively advanced in the longitudinal direction of the data track 15, a pair of tracking error detection spot lights 4b
The tracking error detection light 11b which is the reflected light of 4c
The tracking control is performed by detecting the light amount difference between the two at 11c by the photodetector 14.

In the optical head 21 having the above-described structure, when information is transmitted / received to / from a certain data track 15, each track row is transmitted / received so as to transmit / receive the next information to / from a predetermined adjacent data track 15. There is a case where the optical head 21 is moved in a transverse direction. At this time, by counting the number of data tracks 15 or guide tracks 17 that cross, the optical head 21 can be moved to a predetermined data track 15 position. When crossing the data track 15, each spot light 4a
In the direction in which b.4c crosses the track row as shown by the arrow, it moves as shown by the imaginary line in FIG. At this time, the tracking error detection value based on the light amount difference between the two tracking error detection lights 11b and 11c is, for example, as shown in FIG.
However, in the section where both the tracking error detection spot lights 4b and 4c move on the data track 15, the flat portion indicated by the imaginary line in the figure where the difference between the two detection values becomes 0 is shown in FIG. 18 results.

However, due to a difference in the manufacturing accuracy of the optical card 3 or the like, various causes such as birefringence in the protective layer on the card surface, unevenness of the data track 15, or reflected light noise, stray light, or inclination of the card, cause As shown by the solid line in FIG.
May occur. When this noise 19 increases,
As described above, counting the number of tracks may cause a count error.

[0006]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, a main object of the present invention is to provide a tracking error for counting the number of tracks when an optical head crosses a plurality of tracks. An object of the present invention is to provide an optical head structure capable of minimizing generation of noise in detection light.

[0007]

SUMMARY OF THE INVENTION According to the present invention, there is provided a data track for recording / reproducing optical information and a guide track for detecting a tracking error extending along a side edge of the data track. When moving an optical head for transmitting and receiving information to and from the provided optical information recording medium in a direction across each of the track rows to transmit and receive information to and from a predetermined data track, An optical head structure of a type in which the number of tracks up to the predetermined data track is counted and the optical head is moved with a change in tracking error detection light caused by a tracking error detection spot light crossing a track row, A compensating plate for reducing noise included in the tracking error detection light in the optical path of the light emitted from the optical head; Is achieved by providing an optical head structure, characterized in that provided is inclined a predetermined small angle the optical axis relative to the polarization plane of the emitted light.

[0008]

In this way, noise generated in the tracking error detection signal by various causes such as birefringence in the protective layer on the card surface, unevenness of the data track, reflected light noise, stray light, and inclination of the card is reduced. It is possible,
The noise can be removed from the tracking error detection signal used for counting the number of tracks when the optical head moves across the track row.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a preferred embodiment of the present invention. FIG. 1 is a schematic view showing the structure of an optical head 1 to which the present invention is applied. The same parts as those in FIG. 4 of the above-described conventional example are denoted by the same reference numerals, and detailed description thereof will be omitted. As shown in FIG. 1, a diffraction grating 6 and a beam are provided in the optical path of the outgoing light 4 from the laser diode 2 toward the optical card 3 and provided after the collimator lens 5 for making the outgoing light 4 parallel. Between the splitter 7 and a compensator 8 which is an optical element for changing a phase between polarization planes orthogonal to each other, for example, a λ / 2 plate, is provided. As shown in FIG. 2, the compensating plate 8 emits light 4 traveling in the direction of arrow A along its optical axis 8a.
Is provided so as to be inclined at a predetermined small angle with respect to the polarization plane 9. The beam splitter 7 and the optical card 3
And a detection lens 12 and a cylindrical lens 13 provided in the optical path of the detection light 11 turned to the side by the beam splitter 7 with the reflected light of the optical card 3. The photodetector 14 for detecting each error has the same configuration as the conventional example.

In the optical head 1 having the above structure, when information is transmitted / received to / from the data pits 16 on the data track 15 of the optical card 3, for example, the data track 1
The spot lights 4a, 4b, and 4c reach the terminal portion of the spot No. 5. Next, when the optical head 1 is moved to transmit / receive information to / from another data track, as shown in FIG.
Move across the data track 15.

Therefore, as shown by the solid lines in FIG. 5, the spotlights 4b and 4c for detecting both tracking errors are located on the respective boundaries between the data track 15 and the guide tracks 17.
Is located before the start of movement, the difference between the two tracking error detection light beams 11b and 11c is 0, and when the light beam starts to move across the track row as described above,
The upper spot light 4b in FIG.
7 and the lower spot light 4c moves onto the data track 15. When the spot lights 4b and 4c further move, both spot lights 4b and 4c are completely moved onto the data track 15, and this state continues for a while. And both spot lights 4b
When 4c starts to be applied to the guide tracks 17 on both sides of the next data track 15, the detection value changes and is again located on the boundary line, and an equilibrium state where the difference between the two detection lights 11b and 11c becomes zero can be achieved. In this way, both detection lights 11b
Since the light amount difference between the light-emitting elements 11c changes, the tracking error detection value changes as shown in FIG.

Incidentally, due to various causes as shown in the conventional example, as shown by the solid line in FIG.
The noise 19 may occur where it should be. According to the present invention, the noise 19 can be reduced by rotating the compensator 8 provided as described above so that the optical axis 8a is inclined with respect to the polarization plane 9 of the emitted light 4. become able to. Therefore, if the compensating plate 8 is fixed at an angle that minimizes the noise 19, the flat portion 18 can be reliably detected without being affected by the noise 19, that is, If the flat portion 18 is counted when the optical head 1 moves, the number of data tracks 15 crossing can be reliably counted, and the optical head 1 can be positioned on a predetermined data track 15.

In this embodiment, the compensator 8 is connected to the diffraction grating 6
The beam splitter 7 is provided between the laser diode 2 and the objective lens 10 in the optical path of the emitted light 4 and may be arranged at an arbitrary position. Further, the structure for detecting each error and reading data is not limited to the embodiment.

[0014]

As described above, according to the optical head structure of the present invention, when the optical head is moved in a direction crossing the track row, the number of tracks is counted based on the change in the tracking error detection light, and The head can be moved to a predetermined data track,
In this case, noise included in the tracking error detection light can be reduced due to various causes such as birefringence in the card, so that the optical head can be reliably moved without causing a counting error. In addition, the servo control of tracking is stabilized, and the above-mentioned effects can improve the access speed of the optical head and reduce the error rate at the time of information transfer. Further, by stabilizing the servo, it is possible to realize a high-performance and highly-reliable optical head such as improved shock resistance and vibration resistance.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing an optical head structure according to the present invention.

FIG. 2 is a perspective view for explaining a main part of the present optical head structure.

FIG. 3 is a diagram showing a change in a tracking error detection value in the present optical head structure.

FIG. 4 is a diagram schematically showing a conventional optical head structure.

FIG. 5 is an explanatory diagram showing a moving direction of a tracking error detection spot light.

FIG. 6 is a diagram showing a change in a tracking error detection value in a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical head 2 Laser diode 3 Optical card 4 Outgoing light 4a Focusing error detection spot light 4b / 4c Tracking error detection spot light 5 Collimator lens 6 Diffraction grating 7 Beam splitter 8 Compensator 8a Optical axis 9 Polarization plane 10 Objective lens 11 Detection light 11a Focusing error detection light 11b / 11c Tracking error detection light 12 Detection lens 13 Cylindrical lens 14 Photodetector 15 Data track 16 Data pit 17 Guide track 18 Flat portion 19 Noise 21 Optical head

Claims (1)

(57) [Claims] An information is transmitted / received to / from an optical information recording medium in which a plurality of data tracks for optical information recording / reproduction and guide tracks for tracking error detection extending on the side edges thereof are alternately provided in a plurality of rows. Error caused by the tracking error detection spot light traversing each track row when the optical head is moved in a direction crossing each track row to transfer information to and from a predetermined data track. An optical head structure of a type in which the number of tracks up to the predetermined data track is counted based on a change in detection light and the optical head is moved, wherein the tracking error detection light is included in an optical path of light emitted from the optical head. In order to reduce the noise included in the light, the compensator adjusts the optical axis of the compensator to a predetermined small angle with respect to the polarization plane of the emitted light. The optical head structure, characterized in that provided is inclined an angle.