JPH043341A - Optical pickup device - Google Patents

Abstract

PURPOSE:To accurately read data by setting the direction of the occurrence of astigmatism of a light spot formed on the surface of an information recording medium to a specific angle to the tangential direction of a track and always approximately equalizing the focus positions of a track error signal and a data signal. CONSTITUTION:An optical pickup device is provided where the light emitted from a semiconductor laser is condensed by an objective lens to form a light spot 8 and the surface of an optical disk is irradiated to record and reproduce information. In this device, the direction of occurrence of astigmatism of the light spot 8 formed on the surface of the optical disk is set to about 45 deg. to the tangential direction of tracks 9. Thus, the diameters of the light spot 8 in the tracking direction of an arrow X and the jitter direction of an arrow Y are always equalized regardless of the occurrence of astigmatism. Consequently, the focus positions of the track error signal and the data signal are always approximately equalized.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical pickup device that records and reproduces information using light emitted from a laser light source such as a semiconductor laser.

2. Description of the Related Art An example of the configuration of a conventional optical pickup device will be described with reference to FIG. Light emitted from a semiconductor laser l as a laser light source is made into parallel light by a collimating lens 2, passes through a beam splitter 3, and is focused by an objective lens 4, and is deposited onto the surface of an optical disc 5 as an optical information recording medium by approximately 1 μm. A light spot is formed, and information is recorded using this light spot. In addition, the reflected light from the optical disc 5 is
It passes through the objective lens 4 again, becomes parallel light, is reflected by the beam splitter 3, is condensed by the condenser lens 6, and is received by the light receiving element 7, which reproduces information, focuses error signals, and track error signals. etc. are detected.

In this case, astigmatism occurs until the light emitted from the semiconductor laser 1 is detected by the light receiving element 7, but the main causes are astigmatism difference of the semiconductor laser 1 and the difference in collimating lens 2. Astigmatism, astigmatism of the objective lens 4, etc. can be considered. When a light spot with such astigmatism is detected by the light receiving element 7, the following phenomenon occurs.

FIG. 8 shows the astigmatism of the light spot 8 formed by being focused by the objective lens 4. As a result, the track error signal is at its maximum at the focal point A, which is the focus position, and the data signal is at its maximum (C/N
is the maximum) at the focal point B, which is the focus position. In this case, if the interval between the focal points A and B (this interval is called astigmatism) is ΔAs, for example, ΔAs=0.5
FIG. 9 shows how the track error signal T and the data signal change in μm with respect to defocus.

The peak of the tracking error signal T occurs at the position where the optical spot 8 in the tracking direction 8 occurs at the most narrowed position. Here, the peak position of the data signal relative to the peak position of the track error signal T is
This means that there is a deviation by an astigmatism difference ΔAs=0.5 μm.

Problems to be Solved by the Invention In the above-described apparatus, the depth of focus of the objective lens 4 is generally about ±1.0 μm, so the depth of focus is always ±1.0 μm from the position of the focal point on the surface of the optical disc 5. The recording surface of the optical disc 5 must be within μm. Further, the light receiving element 7 is assembled so that the track error signal T is maximized, or the data signal or C/N is maximized.

Now, assuming that the position of the light receiving element 7 is adjusted so that the track error signal T is maximized, when the optical spot 8 has an astigmatism difference ΔAs, the data signal D (the peak of C/N) Since the assembly is performed with the focus shifted by ΔAs, there is a possibility that the data signal will be out of the depth of focus range, which may significantly increase the C/N drop. On the other hand, if the light receiving element 7 is assembled at a position where the data signal is at its maximum, the C/N ratio will be improved but the detection sensitivity of the track error signal T will be reduced.

Means for Solving the Problem Therefore, in order to solve such problems, claim 1
In the described invention, in an optical pickup device that records and reproduces information by condensing light emitted by a laser light source with an objective lens to form a light spot and irradiating it onto the surface of an optical information recording medium, The direction of occurrence of astigmatism of the light spot formed on the surface of the optical information recording medium was set to be approximately 45° with respect to the tangential direction of the track.

In addition, in the invention as claimed in claim 2, the light emitted by the laser light source is focused by an objective lens to form a light spot, and the light spot is irradiated onto the surface of the optical information recording medium to record and reproduce information. In the pickup device, an arc-shaped elongated hole centered on the optical axis of the objective lens is formed in a mounting portion of a holding member that holds the objective lens.

According to the invention as claimed in claim 1, by making the direction in which the astigmatism of the light spot occurs at approximately 45 degrees with respect to the tangential direction of the track, even if astigmatism exists, the tracking direction and the jitter direction can be maintained. The diameter of the optical spot is always the same, and as a result, the focus positions of the tracking error signal and data signal can always be made approximately the same, making it possible to perform highly reliable tracking control and to accurately transmit data information. It becomes possible to read.

According to the second aspect of the present invention, the direction of astigmatism of a light spot generated on the objective lens is determined by rotating the objective lens along the elongated hole formed in the attachment portion of the holding member. The diameter of the optical spot in the tracking direction and the jitter direction is always the same even if there is astigmatism in the optical spot due to the optical characteristics of the objective lens itself. As a result, the focus positions of the track error signal and the data signal can always be made substantially equal, so even if the objective lens includes astigmatism, it is possible to use the objective lens.

Embodiment An embodiment of the invention recited in claim 1 will be described with reference to FIGS. 1 to 3. Note that the same reference numerals are used for the same parts as in the prior art (see FIG. 7).

This embodiment is an optical pickup device that records and reproduces information by condensing light emitted by a semiconductor laser 1 with an objective lens 4 to form a light spot 8 and irradiating it onto the surface of an optical disc 5. As shown in FIG.
The angle is set to 5°.

FIGS. 2(a) to 2(C) show the surface condition of the optical disc 5, in which the optical spot 8 is located on the land 11 between the groups 10. In this case, FIG. 2(a) shows the state of the optical spot 8 at the position where the track error signal T and the data signal D (C/N) reach their peaks, and the astigmatism of the optical spot 8 is The direction in which this occurs is rotated by approximately 45 degrees with respect to the tangential direction of the track 9. This peak position corresponds to the vicinity of the circle of least confusion approximately in the middle of the astigmatism difference. In addition, FIGS. 2(b) and 2(c) show the direction in which the astigmatism of the light spot 8 occurs is rotated by approximately 45 degrees with respect to the tangential direction of the track 9 at a position defocused on the soil. .

Further, FIGS. 3A to 3C show examples in which the direction of astigmatism, the tracking direction X, and the jitter direction Y coincide with each other. In this case as well, the direction in which the astigmatism of the light spot 8 occurs is rotated by approximately 45° with respect to the tangential direction of the track 9. Note that FIG. 3(b) corresponds to the peak of the track error signal T, and FIG. 3(C) corresponds to the peak of the data signal.

As described above, by setting the direction in which the astigmatism of the light spot 8 occurs at approximately 45 degrees with respect to the tangential direction of the track 9, even if astigmatism exists, the tracking direction The diameter of the Y light spot 8 is always the same. Therefore, this causes the track error signal T
Since the focus positions of the data signal and the data signal can always be made substantially equal, highly reliable tracking control can be performed and data information can be read accurately.

Next, based on the configuration of the optical pickup device shown in FIG. This section describes how to achieve this. First, as a first example, when an astigmatism difference occurs in the light emitted from the semiconductor laser 1, the direction in which the astigmatism of the light spot 8 occurs is relative to the tangential direction of the track 9. The mounting can be realized by rotating the semiconductor laser 1 about its tip axis so that the angle is approximately 45 degrees, and adjusting the direction. As a second example, if astigmatism occurs in the collimating lens 2,
The installation is realized by rotating the collimating lens 2 about its tip axis and adjusting the direction so that the direction of astigmatism of the light spot 8 is approximately 45 degrees with respect to the tangential direction of the track 9. can do.

Next, an embodiment of the invention according to claim 2 is shown in FIGS. 4 and 5.
This will be explained based on the diagram. FIG. 4 shows an example of the configuration of the optical pickup optical system 12. A galvanomirror 14 for deflecting light is placed on the bottom surface 13 of the optical system. An objective lens actuator 15 serving as an objective lens holding member is attached to cover the lens from above. This objective lens actuator 15 holds the objective lens 4 at its upper part, and has a mounting part 16 formed on the outer surface of its lower part. Three arcuate long holes 17 are formed in this attachment portion I6.

FIG. 5 shows the mounting portion 16 of the objective lens actuator 15.
This is a view from the bottom side.

In this case, the arc-shaped elongated holes 17 are formed at three locations at approximately 120 degrees each with the optical axis of the objective lens 4 as the center. Fixing screws 18 are inserted into those elongated holes 17, respectively.
By passing it through, the objective lens actuator 15 is stably attached to the bottom surface 13.

In such a configuration, a method for attaching the objective lens 4 will be described. The direction in which the astigmatism of the objective lens 4 occurs is
The attachment of the objective lens 4 is determined by the direction. Therefore,
In this embodiment as well, the optical spot 8 formed on the surface of the optical disc 5 is similar to the embodiment described above (see FIG. 1).
The objective lens actuator 15 is rotated around the optical axis of the objective lens 4 so that the direction in which astigmatism occurs is approximately 45 degrees with respect to the tangential direction of the drag 9, and fixed at that position via the elongated hole 17. Fix using screws 18.

By forming the long arc 17 centered on the optical axis of the objective lens 4, the objective lens actuator 15 can be moved in any direction regardless of the direction in which the astigmatism of the objective lens 4 occurs. Since the position can be fixed, the direction in which astigmatism occurs can always be set at approximately 45° with respect to the tracking direction X (or Jeddah direction Y).

Therefore, even if astigmatism exists in the optical spot 8 due to the optical characteristics of the objective lens 4 itself, the diameters of the optical spot 8 in the tracking direction X and the jitter direction Y are always equal.
The focus positions of the track error signal T and the data signal can always be made substantially equal, so that even if the objective lens 4 contains astigmatism and is determined to be a defective product, the objective lens 4 can be used. becomes.

Finally, matters common to the invention claimed in claim 1 and the invention claimed in claim 2 will be described. Here, optical disc 5
The relationship between the astigmatism difference and the wavefront aberration (RMS value) of the light spot 8 irradiated onto the surface will be explained based on FIG.

Waveform a shows the state when there is no astigmatism difference (ideal light spot), waveform A shows the state when the astigmatism difference is 0.4 μm, and waveform C shows the state when the astigmatism difference is 0.8 μm. This is what is shown. As a result, when there is no astigmatism difference, the wavefront aberration is minimized at the beam waist, and when there is an astigmatism difference, the wavefront aberration is minimized at the circle of least confusion. In this case, when in focus (defocus value is 0), as the astigmatism increases, the wavefront aberration also increases; however, at the position of defocus ±1 μm, three waveforms a.

The difference between b and c is almost small.

Therefore, the present invention is implemented in such a state (the direction in which the astigmatism of the optical spot 8 formed on the surface of the optical disc 5 occurs is set at approximately 45° with respect to the tangential direction of the track 9). As a result, the value of wavefront aberration with respect to defocus at a position of ±1 μm is almost the same regardless of the presence or absence of astigmatism, and as a result, even if the optical spot 8 includes astigmatism, the tracking error signal Since there is no focus shift between the T peak and the data signal D (C/N) peak, these signals are within the implementation range (approximately ±1 μm)
In this case, it can be used in the same way as when there is no astigmatism.

Effects of the Invention The invention described in claim 1 records and reproduces information by condensing light emitted by a laser light source with an objective lens to form a light spot and irradiating it onto the surface of an optical information recording medium. In an optical pickup device, the direction in which astigmatism occurs in a light spot formed on the surface of an optical information recording medium is set at approximately 45° with respect to the tangential direction of the track, so that astigmatism does not exist. However, the diameters of the optical spots in the tracking direction and the thick direction are always the same, and as a result, the focus positions of the tracking error signal and data signal can always be made approximately equal, making it possible to perform highly reliable tracking control. At the same time, it is possible to read data information accurately.

In addition, the invention according to claim 2 provides light for recording, reproducing, etc. of information by condensing the light emitted by a laser light source with an objective lens to form a light spot and irradiating it onto the surface of an optical information recording medium. In the pickup device, an arc-shaped elongated hole centered on the optical axis of the objective lens is formed in the attachment part of the holding member that holds the objective lens, so the objective lens can be attached to the elongated hole formed in the attachment part of the holding member. By rotating the objective lens along the axis, it is possible to rotate the direction of the astigmatism of the light spot generated on the objective lens by approximately 45 degrees with respect to the direction of the track of the optical information recording medium. Even if there is astigmatism in the spot, the diameter of the optical spot in the tracking direction and jitter direction is always the same, and the focus positions of the tracking error signal and data signal can always be made approximately the same, so the objective lens has no astigmatism. Even if a lens contains point aberration, it is possible to use the lens, thereby improving the yield of objective lenses, thereby further reducing production costs.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing an embodiment of the invention as claimed in claim 1,
Figure 2 shows the direction of occurrence of astigmatism of the light spot on the optical disk surface at approximately 45° with respect to the tangential direction of the track.
FIG. 3 is an explanatory diagram showing the spot state when the rotation state of the light spot is changed, and FIG. 4 is a perspective view showing an embodiment of the invention as claimed in claim 2. , FIG. 5 is a bottom view of the holding member that holds the objective lens, FIG. 6 is a waveform diagram showing the relationship between wavefront aberration and astigmatism with respect to defocus, and FIG. 7 is an example of a conventional optical pickup device. FIG. 8 is an explanatory diagram showing the state of the light spot focused by the objective lens, and FIG. 9 is a waveform diagram showing the relationship between the track error signal and the data signal with respect to defocus. DESCRIPTION OF SYMBOLS 1... Laser light source, 4... Objective lens, 5... Optical information recording medium, 8... Light spot, 9... Track,
15・Holding member, 16...Mounting part, I7...Elongated hole ratio Applicant Ricoh Co., Ltd. (a) (b) (C) δ Focus l (pm) Fig. 3) Waste 1tpm)

Claims (1)

[Claims] 1. An optical pickup device that records and reproduces information by condensing light emitted by a laser light source with an objective lens to form a light spot and irradiating it onto the surface of an optical information recording medium. An optical pickup device according to claim 1, wherein the direction of occurrence of astigmatism of the light spot formed on the surface of the optical information recording medium is set at approximately 45 degrees with respect to the tangential direction of the track. 2. In an optical pickup device that records and reproduces information by condensing light emitted by a laser light source with an objective lens to form a light spot and irradiating it onto the surface of an optical information recording medium, the objective lens is An optical pickup device characterized in that an arc-shaped long hole centered on the optical axis of the objective lens is formed in a mounting portion of a holding member to be held.