JPS59207035A - Position error detector of optical disc - Google Patents

Abstract

PURPOSE:To detect directly the position of an optical track and to prevent the time delay between detection signals by constituting a device with a means, which separates a converged radiated light to two beams which can be separated from each other by natural characteristics, and a means which detects intensities of separated beams independently of each other and generating an error signal of position related to detection signals. CONSTITUTION:A laser light source 12 inclines the plane of polarization of a luminous flux at about 45 deg. to the horizontal. The luminous flux 100 is irradiated to a double refracting prism 13, and horizontally polarized components are refracted at an angle different from that of vertically polarized components. Luminous fluxes 101 and 102 which are emitted from the prism 13 and are separated from each other with respect to angle are shown in the figure D. These luminous fluxes polarized at right angles form focused light spots 40 and 41 individually on the surface of a disc 11 as they are. A pit 44 passes focused light spots 40 and 41 by the rotation of the disc 11. Luminous fluxes 101 and 102 are modulated when they are reflected from the disc 11, and they are deviated from the axis of a lens by a splitter 4 after being returned. Reflected luminous fluxes 101 and 102 are reflected by a polarizing beam splitter 6 and are converged onto photodetectors 8 and 9 respectively.

Description

Detailed Description of the Invention (1) Technical Field The present invention relates to an error detection device for positioning a head on a recording track of an optical disk. The present invention relates to an optical position error detection device that forms a beam, collects reflected light or transmitted light, and detects a positional error in the lateral direction between a light spot within a target and the target.

The device is useful for automatic positioning or for displaying the positional error between a light spot and its target in magnitude and direction. It is also used to detect the absolute position error in the radial direction of a light spot (irrespective of whether it is focused or not) that exists on a spiral or concentric bit pattern that is recorded data on a rotating optical disk. Useful. Such position error detection devices either rotate the reading light spot and align it radially with the centerline or optical track of the optically detectable data bit to obtain maximum signal modulation with respect to the read data; Necessary for servo control devices when radially positioning the writing spot when recording data.

(2) Prior Art In the past, there have been a variety of methods for detecting a focused spot of light with respect to a curved pattern, or optical track, of optical data pits arranged in a recording arrangement on a rotating optical disk. For example, in the first method, three convergent light points that are linearly aligned and spatially separated are used, and the convergent light points are placed on a surface (in this case, a disk) as the focal point of the converged light beam. A two-dimensional distribution of light intensity occurs at or near that point.

FIG. 1 is a schematic diagram showing a conventional method. That is, the three focused light spots as described above have a light spot centerline 60 that is angularly offset with respect to the centerline 43 of the optical track. Focused light spot 1 is located slightly inside the optical track center line, focused light spot 2 is located on the track center line when data is read only, and focused light spot 3 is located slightly outside the optical track center line nYJ It is located at The light transmitted through or reflected from the disc is focused such that a real image of the disc and focused light spots 1.2 and 3 are formed. Another (
A photodetector 101 detects a change in the intensity of the focused light when there is a position error. 2. Each output from the two photodetectors is MI7ed and a signal containing the direction and magnitude of the tracking error is generated. Using the technique described above, the photodetector at the focal point of spots 1 and 3 will detect spots 1 and 3.
and 3 are lined up on the track in addition to horizontally analyzing the track, so it is possible to detect certain data pit paths at different times. Therefore, the components of the photodetector output signal have a relative phase shift that limits the ability to generate a useful error signal upon subtraction of the signals. To overcome this difficulty, the photodetector signal must be processed by subtracting mj by phase shifting, time integration or low pass filtering. If low-pass filtering is used, as is commonly done, the cutoff frequency of this filter must be less than or equal to the lowest frequency of the data. Due to this requirement, tracking servo control
Undesirable limitations may be imposed on both the II device and data channel bands. Another drawback of this technique is that at the photodetector position the light spots of the inner IIj and outer DI are in close proximity to each other with the n central image, so that the photodetector elements are very small and close to each other. It must be closely placed and at the actual image position of the disk. Further, the focused light spots on the disk surface must be spatially dispersed in order for their images to be separated and detected independently. This key point 1
This often results in an undesirable arrangement in which the focused light spots partially overlap each other on the recording surface of the disk. Also, because a diffraction grating is used to form the three beams and it is impractical for the reflected beam to retransmit through the grating in a double-pass J configuration, new constraints are placed on the design of the optical system.

Other prior art techniques move the read beam sinusoidally across the track, as described in U.S. Pat. No. 4,063,287. The signal modulation fluctuations obtained here contain tracking error information. However, this technique requires complicated optical and mechanical structures, and requires lowering the strength of the read signal in order to obtain tracking error information.

Still other prior art techniques have involved pregrooved embossed disks or grooved molded disks with data pits written in or between the grooves. One reading light beam undergoes phase modulation due to the occurrence of a tracking error, or the three-light point method described above is used to follow a pre-formed groove. The disadvantages of this technique are read signal degradation and complicated media manufacturing techniques.

Further, in US Pat. No. 4,067,044, the photodetector signal of the read light beam is modulated by undulating the track in a sinusoidal manner. However, this has the disadvantage that the read signal deteriorates because tracking errors are intentionally introduced.

(3) 41 of the present invention! Summary The present invention is an improved light beam positioning error detection device.
It consists of two separate or partially overlapping focused light spots on the surface of an optical disc, which can be separated at different locations due to the inherent properties of wavelength or polarization. According to the present invention, there are advantages of blowing. i.e. directly detecting the position of the optical track without reference to external morphology;
There is no time delay between the two photodetector signals used to form the tracking error signal, the times between track centerline 43 and light spot centerline 45 in FIG. 3A! Sensitivity to 'z error [yaw] is essentially small, and reflected or transmitted light beams can be easily separated and detected. Another advantage is that the read signal of the -order data can be directly generated by combining the output signal of the corresponding photodetector from the X light spot. The data read signal thus generated is less sensitive to tracking errors than the signal obtained from a corresponding single read light spot.

(4) Description of Embodiments FIG. 2 is a schematic diagram for explaining the present invention in detail. In the figure, an optical disc 11 made of a rigid material is mounted rotatably about a shaft 31, which is driven by a motor (not shown). Optical system housing 10
has a constant gap with respect to the surface of the optical disc 11, and is moved in the half f) direction with respect to the rotation axis 31 of the optical disc 11. In this way, the housing 10
can be positioned on any optical track on 1.

The optical track on an optical disk can be a series of optically detectable data bits arranged side by side along a centerline, or it can be a preformed groove or other curved configuration that can be used as a reference.

The optically detectable data bits consist of local changes in the recording medium that are detectable by the reading beam. Such data bits can be created during the manufacture of the optical disc, or they can be recorded optically by modulating a focused laser beam.

The optical disc 11 can be of a reflective type or a transmissive type. During data reading, incident light is then reflected from or transmitted through the optical disc. In either case, the light beam focused on the surface of the optical disk interferes with the optical recording medium and is then converged, and the intensity of the light beam is detected by a photodetector. As shown in FIG. 1, the presence of optically detectable data bits 44 causes light to be amplitude or phase modulated as reflected from or transmitted through the optical disc. This optical modulation of the reading beam is converted by a photodetector into an amplitude modulation of an electrical signal, which makes it possible to take out the take. Signal modulation is defined here as signal amplitude between wave height and wave height, and the signal change JJ is maximum when it comes to the focused light point on the optical disk or the center of the optical track, and otherwise Decrease. This reduction in signal-related modulation resulting from tracking errors also serves as a means of detecting such errors. In this way, the optical track becomes a standard means for detecting tracking errors.

The present invention utilizes two reading light beams that form two focused light spots 40 and 41 on the surface of the optical disc 11.

Here, the light spots marked mJ may partially overlap, as shown in the schematic diagrams of FIGS. 3A and 3B, or may be separated. These light spots have their centers aligned with the radial axis 45
and this axis is perpendicular to the track centerline 43. Each light spot 40 and 41 is associated with a separate photodetector, which detects only the focused light from its beam and generates a separate signal q. Due to this variation of each photodetector, a portion of j is the data bit.
It is determined by the area of the corresponding focused light spot 4o or 41 based on 44. When the center of the focused light spot 40 or 41 is equidistant from the track center Fr9.43, the tracking error becomes zero. Thus, data bit 44
acts equally on the focused light spots 4o and 41, and the two photodetector signals obtained as the optical disc rotates are equally modulated. This state of zero tracking error exists whether the light spots partially overlap or are separated, as shown in FIGS. 3A and 3B, respectively.

Figures 4A, 4D, and 4G are schematic diagrams showing three tracking error states, Figures 4B, and 4E, respectively.
Figures 4C, 4F and 4I are diagrams showing the photodetector signal modulation (vertical) for each focused light spot as a function of tracking error stiffness (horizontal axis). Figure 1111 is a diagram showing tracking error No. 18 (vertical axis) as a function of tracking error distance (horizontal axis) for the conditions of Figures 4A, D, and G; First, 4th A
In the figure, in the case of a tracking error, the data bits 44 and therefore the track center line 43 coincide with the center line 47 of the focused light spot pattern. Because of the tracking error, the photodetector output signal is equally modulated as shown at 142 in FIG. 4B.

In this figure, curves 140 and 141 show the modulation of photodetector PI3 as a function of tracking error distance for light spots 40 and 41. Curves 140, 141, etc. are at symmetrical positions with respect to the center line 47 of the focused light spot pattern. Fourth
Only point 142 in Figure B corresponds to the zero tracking error condition of Figure 4A, and all other points lying between curves 140 and 141 correspond to non-zero tracking error conditions.

For any given tracking error condition, the tracking error signal is obtained by subtracting the modulation of photodetector 1n for focused spot 41 from the modulation of the photodetector signal for focused spot 40. For the zero tracking error condition of Figure 4A, the two signal modulations are equal (
4B, and the resulting tracking error signal is zero, as shown at 46 in FIG. 4C.

Curve 150 is the trajectory of many possible tracking error signals for many possible tracking error conditions.

If the optical track is a prefabricated trench, groove, or other substrate configuration that does not contain data bits, the tracking error signal is obtained by subtracting the amplitudes of the two photodetector signals that are not modulated by data.

? The n4D diagram shows 91. of the center line 47 of the optical track. fll
Indicates the state in which The track center line 43 is the focused light point 40
As shown at 143 in FIG. 4E, the modulation of the corresponding photodetector signal begins to decrease. The track centerline is shifted toward the focused light spot 41, as shown at 144 in FIG. 4E, increasing the modulation of the corresponding photodetector signal. If the amplitude 143 or 6144 is subtracted here, a negative tracking error signal is generated as shown at 48 in FIG. 4F.

FIG. 4G shows a state in which the track center line 43 is inside the center line 47 of the focused light spot pattern. Track center line 43
is shifted toward the focused light spot 40, increasing the modulation of the photodetector signal for that light spot. Track center line 43
is shifted away from the focused light spot 41, reducing the modulation of its associated photodetector signal. The tracking error signal is the modulation of the photodetector signal by the light point 41 again this time.
obtained by subtracting from that by 0, and 50 in Figure 4I.
A positive immortal occurs as shown in . By considering many possible tracking error conditions, the tracking error signal 150 can be plotted as a function of tracking error distance as shown in FIGS. 4C, 4F, and 41. This curve has the good property that the slope is maximum and changes sinusoidally as the optical track passes through the state of zero tracking error. Thus, the tracking error signal is given by the sign of the tracking error signal, and the magnitude of the tracking error is proportional to the magnitude of the tracking error signal within the linear region of curve 150.

The present invention utilizes either of two different inherent properties of light to form focused light spots 40 and 41 to separate and conveniently detect reflected or transmitted light. One embodiment of the invention uses mutually perpendicularly polarized beams as the inherent separation characteristic.

Note that although the following description relates to operation using a reflective optical disc, a transmissive optical disc can be used with only slight changes in the optical arrangement.

FIG. 5 is a schematic diagram of a 4PA example using two light beams whose electric field polarities are perpendicular to each other. Note that Figures 5A and 5B are vector polarity diagrams at cross section A-A in Figure 5, and Figure 5C.
The figure is a polarity diagram of a light beam at cross section B--B, and FIG. 5D is an explanatory diagram of a polarized light beam at cross-section C-C. In FIG. 5, a laser light source 12 has a monochromatic linearly polarized light beam 10.
Emit 0. Laser light source 12 orients the plane of polarization of light beam 100 at approximately 45 degrees with the horizontal, as shown in FIG. 5A. Such a light beam is the same as a superposition of two component light beams of equal intensity polarization in the horizontal and vertical planes, as shown in FIG. 5B. Next, the luminous flux 100 is the Rocon (
Roch n) or Wollaston type (Wo If
as ton), where the horizontally polarized light component is refracted at a different angle than the vertically polarized light component. FIG. 5C shows the angularly separated beam 10 exiting the prism 13, i.e., the beam 10 with respect to the focused beam spot 40.
1 and a light beam 102 related to the focused light spot 41. These orthogonally polarized light beams pass through the beam splitter 4 and the objective lens 5 without being deviated, and form focused light spots 40 and 41 on the surface of the optical disk 11 separately or partially overlapping. form. As the optical disc 11 rotates, the data bits 44 are focused on the light spots 40 and 41.
It comes to pass through. Upon reflection from the optical disk 11, the light beams 101 and 102 are modulated and
After returning through the beam, it is moved off the axis of the lens by the beam splitter 4. The reflected light beams 101 and 102 directly head toward the polarizing beam splitter 6, where the light beam 101 is transmitted, but the light beam 102 is reflected. Lenses 7 and 7' focus the light onto photodetectors 8 and 9, respectively.

Next, FIG. 6 is a schematic diagram of a second embodiment using two light beams with different wavelengths. In the figure, laser light sources 20 and 21
emits monochromatic light beams 110 and 111 with different wavelengths,
The beams then pass through the beam splitters 23 and 22 without being deflected, and are combined by the dichroic beam splitter 24. The tilt of the beam splitter 24 is determined by the objective lens 25.
Adjustments are made so that the two entering beams are angularly separated. The light beam 110 forms a focused light spot 40 (not shown), and the light bundle 111 forms a focused light spot 41 (not shown). The objective lens 25 uses the same method as the objective lens 5 shown in FIG. focus on.

Depending on the type of optical disc used, the amplitude-modulated or phase-modulated light collected from the focused light spots 40 and 41 returns through the objective lens 25.

The light returning from the focused light points 40 and 41 is transmitted to the beam splitter 2.
4 through lenses 26 and 26' to photodetectors 27, respectively.
The light is received at and 28. The separation between the focused light spots 40 and 41 can be adjusted by changing the inclination of the beam splitter 24.

FIG. 7A is a schematic diagram of a third embodiment using two light beams whose electric field polarities are perpendicular to each other, and FIG. 7B is a schematic diagram of a modified embodiment thereof. In FIG. 7A, a polarizing beam splitter is used instead of a birefringent prism to separate the input beam into two angularly displaced linearly polarized output beams. That is, the light beam 120 emitted from the linearly polarized laser light source 48 passes through the amplitude beam splitter 49 and heads toward the polarized beam splitter 50 . The polarizing beam splitter splits the light beam 120 into two orthogonally polarized component light beams 121 and 12.
Divide into 2. These two light beams are directed to separate plane mirrors 51 and 52, respectively. The two beams reflected from this mirror return to the polarizing beam splitter 50 and then to the amplitude beam splitter 49. A portion of each luminous flux is
The light beam passes through the amplitude beam splitter 29, is reflected from the amplitude beam splitter 49, and is focused on the surface of the optical disk 11 by the objective lens 53, forming two focused light spots 40 and 41. Luminous flux 1 from laser light source 48
20 is 45 with respect to the main cross section of the polarizing beam splitter 5o.
If the light is linearly polarized in a plane that forms a diagonal, the intensities of the component light beams 121 and 122 will be the same. When reflected from the optical disk 11, the light beams 121 and 122 are data bits 4
4 and returns through the objective lens 53 and further reflected from the beam splitter 29. Focused light spot 40
The light returning from and 41 passes through beam splitter 55 and from lenses 58 and 56 to photodetectors 59 and 5, respectively.
The light is received at 7.

Also, the amplitude beam splitter 49 in FIG. 7A is replaced with a plane mirror 54 in FIG. 7B.

Furthermore, mirrors 51 and 52 are tilted so that beams 131 and 132 from beam splitter 50 are completely reflected by mirror 54. The advantage of this embodiment is that element 50.51.5
The light transmittance of the sub-optical system consisting of 2 and 54 is so high as to reach 100%. By the way, element 4 in Figure 7A
The transmittance by the sub-optical systems 9.50.51 and 52 is at most 25%.

In each of the embodiments shown in FIGS. 7A and 7B, the propagation direction of each output beam is independently controlled, and the position and separation of the two focused light spots on the optical disk are determined by adjusting the inclination of the mirrors 51 and 52. The orientation of the optical plane is independent of the orientation of the focused light spot on the optical disc, and the mirrors 51 and 52 are dynamically positioned (e.g. using a galvanometer). (by) the position and/or separation of the focused light spot of the optical disk operator can be actively controlled; each light beam can be approached separately within the space of the polarizing beam splitter and the six mirrors 51 and 52; Advantages include the ability to insert additional optical elements for selectively WJing the light beam and the absence of the need to use crystalline optical materials.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a conventional detection method, FIG. 2 is a schematic diagram showing the principle of the present invention, FIGS. 3A and 3B are illustrations of an optical track, and FIGS. 4A, 4D, and 4
Figure G is a schematic diagram showing three tracking error states, and Figures 4B, 4E, and 4H are graphs showing the photodetector signal change g11 (vertical axis) for each focused light point and the tracking error distance (horizontal axis). ), the characteristic diagrams shown in FIGS. 4C, 4F, and 41 are n'+7 No. 4A,
Characteristic diagrams showing the tracking error signal (vertical axis) as a function of the tracking error distance (horizontal axis) for the shape 1 shown in Figures D and G. Figure 5 uses two light beams whose electric field polarities are perpendicular to each other. 5A and 5B are vector polarity diagrams at the cross section A-A in FIG. 5, and FIG. 5C is a polarity diagram of the luminous flux at the cross section B-H in FIG.
Figure D is an explanatory diagram of a polarized light beam in cross section C-C, and Figure 6 is a schematic diagram of a second embodiment using two light beams with different wavelengths.
FIG. 7A is a schematic diagram of a third embodiment using two light beams whose electric field polarities are perpendicular to each other, and FIG. 7B is a schematic diagram of a modified embodiment thereof. 1 , 2 , 3 Focused light point, 10: Optical system housing, 11
: Optical disk, 31 Rotating shaft, 44-Data bit, 1
2.20.21.48: Laser light source, 13 prism,
4.6.24.29.50.55: Beam splitter,
5.25.53 Objective lens, 8.9.27.28
．． 57', 59: Photodetector, 51.52.54: Plane mirror. Applicant ° Yokokai Hewlett-Packard Co., Ltd. Agent 4
F Physician Hasegawa TsuguoFIG 6 FIG? A

Claims (1)

[Claims] a signal source for emitting at least two electromagnetic wave beams selectively separable by unique characteristics; means for directing each beam from said signal source to at least two light points; and said two light beams. means for energizing (reflecting or transmitting) the points; means for converging the emitted light from both energized light points; and separating means for separating the focused emitted light into at least two beams. , ... 1. A position error in an optical disk, comprising photodetecting means for independently detecting the intensity of the separated beams, and generating a position error signal related to the output signals from the 617. both photodetecting means. Detection device.