JPH11126363A - Optical information recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform the recording or the reproducing of information with respect to recording mediums in which the optimum ratio of a pupil radius to the radius of a light beam at the time the beam is in a specific intensity is different by providing a means changing the light distribution quantity for the pupil in accordance with the recording mediums in the optical path between a light emitting means emitting the light beam and the recording mediums. SOLUTION: The recording or the reproducing of information is performed with respect to the recording mediums in which the optical A/W of a pupil radius W to the radius A of the light beam at the time the light intensity of the beam becomes 1/e<2> is different. A transmissivity-distribution filter 15 is constituted with an element whose light transmissivity is electrically controlled so as to become 1 when it is always insertingly arranged in the optical path between a beam shaping prism 4 and a polarizing beam splitter 5. Then, the uniformized state of the light quantity distribution which the pupil diameter is more improved than in the case the transmissivity is changed in a step state by constituting a device so that the change of the transmissivity of the transmissivity-distribution filter 15 gradually becomes higher from the area of the central part of the film to the area of the peripheral part of the film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus, which is suitable for reproducing information from various optical disks such as a magneto-optical disk and a disk on which pits are formed or for recording information on these disks. Optical information recording and reproducing apparatus.

[0002]

2. Description of the Related Art Generally, a light quantity distribution on a pupil plane of an objective lens for condensing a light beam on a recording surface of a recording medium has a great influence on a spot shape to be condensed, and affects the performance of an optical pickup device. .

FIG. 8 shows A / w representing the ratio of the pupil radius (W) to the radius (A) when the intensity of the light beam emitted from the laser diode becomes 1 / e ^2, and the laser beam emitted from the laser diode. FIG. 4 is a light quantity distribution diagram showing a relationship between coupling efficiency, a light quantity distribution on a pupil plane, and a spot shape representing a ratio of a light quantity incident on an entrance pupil to a total light quantity. In FIG. 1, a light beam 2 emitted from a laser diode 1 is focused on a recording surface of a recording medium 3 on which information pits are formed by an objective lens 4.

Now, when the A / W is large, the coupling efficiency also increases, and the light amount distribution shown in FIG. At this time, in the light amount distribution on the pupil plane, as shown in FIG. 8E, the light amount ratio of the peripheral part to the central part in the pupil diameter becomes low. in this case,
As shown in FIG. 8 (f), the diameter of the light spot focused on the recording surface of the recording medium becomes large, and the MT in the high frequency region is increased.
F (modulation transfer function) decreases. That is, the resolution required for reproduction is reduced.

Therefore, in order to prevent a reduction in resolution required for reproduction, an optical system is configured so that A / W is reduced. As a result, the coupling efficiency is reduced as shown in FIG. 8A, and the light amount distribution on the pupil plane is such that the ratio of the light amount at the peripheral portion to the central portion within the pupil diameter is increased as shown in FIG. 8B. , The light quantity distribution becomes substantially uniform. Therefore, FIG.
As shown in (c), the diameter of the light spot focused on the recording surface of the recording medium is reduced, and the resolution required for reproduction is increased.

As described above, by reducing the A / W, the light amount distribution within the pupil diameter represented by the equation (1) can be made relatively flat, and the light spot on the recording surface of the recording medium can be optimized. ing.

In equation (1), x and y are coordinates normalized by the pupil radius, A is the pupil radius, and Wx and Wy are the light beam intensities of 1
The pupil diameter light amount distribution when the radius is / e ² is shown. Pupil diameter light intensity distribution = exp [−2 * ((A / Wx) * x) ² −2 * ((A / Wy) * y) ² ] (1)

However, for example, a high-density magneto-optical disk recording / reproducing apparatus which is being developed at present has problems such as loss of light quantity of a light beam due to a separation optical element such as a beam splitter, reliability at the time of emitting high power of a laser diode, Coupling efficiency is high (A / W is about 0.8) due to a decrease in the sensitivity of the photodetector due to the short wavelength of the light beam.
It is configured to be. This high-density magneto-optical recording / reproducing apparatus employs a magnetically induced super resolution (MSR) system for reproduction and a magnetic field modulation recording system for recording even if the A / W is large. Therefore, the deterioration of the shape of the light spot on the recording surface of the recording medium due to the large A / W is not a problem.

FIG. 9 shows a specific configuration of an optical pickup of a magneto-optical disk recording / reproducing apparatus which is a conventional optical information recording / reproducing apparatus.

The collimator lens 8 shown in FIG. 9 converts the light beam 2 having a wavelength of 650 nm emitted from the laser diode 1 into parallel light, and the beam shaping prism 4 shapes the light beam 2 into a circular shape. The polarization beam splitter 5
It transmits a light beam 2 emitted from a laser diode 1 and reflects a light beam reflected from a magneto-optical disk.
The objective lens 6 is a condenser lens having an NA of 0.6,
The light beam 2 is focused on the recording surface of the magneto-optical disk 7.

The λ / 2 plate 9 has a disk substrate thickness of 0.6 m.
The wavefront of the light beam 2 reflected from the magneto-optical disk 7 is rotated by 45 °. The condenser lens 10 condenses the light beam 2, and the cylindrical lens 12 generates astigmatism in the incident light beam 2. Polarizing beam splitter 12
Transmits the P-polarized light of the light beam 2 whose wavefront is rotated by 45 ° and reflects the S-polarized light. The photodetector 13 is a detector that receives the light beam 2 and converts it into an electric signal, and includes four divided light receiving elements A, B, C, and D.
The light detector 14 is a detector that receives the light beam 2 and converts the light beam 2 into an electric signal, and includes one light receiving element E.

The operation of the conventional optical information recording / reproducing apparatus based on the above configuration will be described. After the light beam 2 emitted from the laser diode 1 is converted into parallel light by the collimator lens 8, the elliptical shape of the light beam 2 is shaped into a circle by the beam shaping prism 4. The shaped light beam 2 passes through the polarizing beam splitter 5 and is focused on the recording surface of the magneto-optical disk 7 by the objective lens 6. At this time, since the A / W is set to be large, the light amount distribution on the pupil plane has a peripheral light amount (rim int) as shown in FIG.
and the light spot focused on the recording surface of the magneto-optical disk 7 is increased.

The polarization plane of the light beam 2 focused on the recording surface of the magneto-optical disk 7 is rotated by the direction of magnetization that changes according to the information recorded on the magneto-optical disk 7. Light beam 2 reflected from magneto-optical disk 7
Is reflected by the polarizing beam splitter 5 and λ / 2
The light is incident on the plate 9.

The light beam 2 has its wavefront rotated by 45 ° by the λ / 2 plate 9, is input to the polarization beam splitter 12 through the condenser lens 10 and the cylindrical lens 11, and is separated into P-polarized light and S-polarized light. . P-polarized light is photodetector 1
The light receiving elements A, B, C, and D are irradiated with light, and each of these light receiving elements outputs an electric signal corresponding to the amount of light irradiated. On the other hand, the S-polarized light is applied to the light receiving element E of the photodetector 14, and this light receiving element outputs an electric signal corresponding to the amount of light applied.

For each of the electric signals thus obtained, (A + B + C + D) -E is calculated to obtain an information reproduction signal, and ((A + B)-(C + D)) is calculated to obtain a tracking error signal by the push-pull method. ((A + C)-
By calculating (B + D)), focus error signals can be obtained by the astigmatism method.

[0016]

The conventional optical information recording / reproducing apparatus needs to read out a weak signal due to the magneto-optical effect when reproducing information recorded on the magneto-optical disk. At the time of recording, since a higher light intensity on the disk surface is required, it is necessary to increase the A / W to increase the coupling efficiency as much as possible and to increase the light use efficiency.

However, for a disk which directly detects intensity modulation of light and reads information, for example, a digital video disk, etc., which has physically deformed information pits, the light utilization efficiency is magneto-optical. Is not so important as compared to the above, and rather, the A / W must be reduced to optimize the shape of the light spot.

As described above, the conventional optical information recording / reproducing apparatus cannot read or record information from a magneto-optical disk and a digital video disk having different optimum A / Ws.

The present invention has been made in view of the above points, and has as its object to provide an optical information recording / reproducing apparatus capable of reproducing or recording information from recording media having different optimum A / Ws. .

[0020]

According to the optical information recording / reproducing apparatus of the present invention, A / W as the ratio of the pupil radius to the radius when the light intensity becomes 1 / e ² is optimized. An optical information recording / reproducing apparatus for reproducing or recording information from a different recording medium, wherein a light quantity distribution variable to change a pupil light quantity distribution according to the recording medium in an optical path between a light emitting means for emitting a light beam and the recording medium It is characterized by having means.

According to a second aspect of the present invention, there is provided an optical information recording / reproducing apparatus, wherein the light amount distribution changing means is a movable light amount limiting filter, and the light amount limiting filter is inserted or not inserted into an optical path. Is characterized in that the pupil light amount distribution is changed by

According to a third aspect of the present invention, the optical information recording / reproducing apparatus is characterized in that the light quantity distribution varying means of the first aspect is a light quantity distribution variable element capable of electrically controlling the light quantity distribution.

The optical information recording / reproducing apparatus according to the fourth aspect is characterized in that the light transmittance of the light quantity distribution varying means according to the first to third aspects is higher in the peripheral part than in the central part.

An optical information recording / reproducing apparatus according to a fifth aspect is characterized in that the light transmittance of the fourth aspect is changed so as to gradually increase from a central portion to a peripheral portion.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a specific structure of an optical information recording / reproducing apparatus according to the present invention will be described below with reference to FIG. 9, the same components as those in FIG. 9 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

The optical information recording / reproducing apparatus shown in FIG. 1 is configured to be able to reproduce information or record information from a magneto-optical disk 7 and a digital video disk 3 in which two 0.6 mm thick disk substrates are bonded together. I have.

In the figure, the transmittance distribution filter 15
When the digital video disk 3 is reproduced or recorded, the beam shaping prism 4 and the polarization beam splitter 5
When the magneto-optical disk 7 is inserted into the optical path between the optical disk and the optical disk 7 for reproduction or recording, the transmittance distribution filter 15 is retracted outside the optical path.

The transmittance distribution filter 15 is provided in the central region 1.
5a and a peripheral region 15b.
The light transmission rate t with respect to the peripheral region 15b of FIG. The light transmittance t is obtained from the jitter simulation graph of FIG. 3 showing the relationship between A / w and jitter when the light transmittance is changed.

As is clear from the graph of FIG. 3, in the present invention, the A / W is set to 0.8 so as to be optimal for recording or reproducing on the magneto-optical disk. The inner light amount distribution is a light amount distribution with a small peripheral light amount ratio as shown in FIG. 3A, and the jitter when reproducing or recording the digital video disc 3 is deteriorated to about 6.3%. In order to improve the jitter while keeping t = 1, it is necessary to make A / w smaller than 0.7 and obtain a light amount distribution having a peripheral light amount ratio as large as possible, such as the light amount distribution within the pupil diameter shown in FIG. In this case, recording and reproduction on the magneto-optical disk 7 cannot be performed.

Assuming that t = 0.75, the light amount distribution within the pupil diameter is
As shown in FIG. 3B, the light amount distribution substantially has a large peripheral light amount ratio, and the jitter can be suppressed to about 5.75%. As described above, the transmittance distribution filter 1
5, the transmittance t of the central region 15a is preferably 0.75, and the diameter of the central region 15a when the pupil diameter is 1 is preferably 0.65.

Next, another embodiment of the specific structure of the optical information recording / reproducing apparatus of the present invention will be described with reference to FIG. 9, the same components as those in FIG. 9 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

In the figure, the transmittance distribution filter 16 is composed of a central region 16a and a peripheral region 16b, and the transmittance t of light of the central region 16a to the peripheral region 16b is the same as that of the transmittance distribution filter 15. 0.75,
The diameter of the central region 16a when the pupil diameter is 1 is 0.65.
It is configured so that

The transmittance distribution filter 16 is always inserted and arranged in the optical path between the beam shaping prism 4 and the polarizing beam splitter 5, so that when the magneto-optical disk 7 is reproduced or recorded, t = 1. And when the digital video disc 3 is reproduced or recorded, t = 0.75
And an element whose transmittance is electrically controlled such as a liquid crystal element or an electrochromic element.

In the above two embodiments, since the transmittance changes of the transmittance distribution filters 15 and 16 change stepwise, the jitter at the time of reproducing or recording the digital video disc 3 is sufficiently lower than in the prior art. Not really. Therefore, as shown in FIG. 5, the transmittance change of the transmittance distribution filter 15 or 16 is configured to gradually change from the central region to the peripheral region so that the transmittance change is reduced. The uniform state of the light amount distribution within the pupil diameter is improved as compared with the case where the light intensity distribution changes stepwise. Therefore,
Jitter is also improved over the above two embodiments.

FIG. 6 is a circuit block diagram showing a specific configuration for obtaining an information reproduction signal tracking error signal and focus error signal when reproducing or recording the digital video disk 3. 9, the same components as those in FIG. 9 are denoted by the same reference numerals. The method of obtaining an information reproduction signal, a tracking error signal, and a focus error signal when reproducing or recording the magneto-optical disk 7 is the same as the conventional method, and a description thereof will be omitted.

In the figure, the summing amplifier 21 has (A +
C) signal and the (B + D) signal are added, and an (A + C) + (B + D) signal is output as an information reproduction signal. The differential amplifier 22 subtracts the (A + C) signal and the (B + D) signal and generates (A + C) as a focus error signal based on the astigmatism method.
C)-(B + D) signal is output. The heterodyne arithmetic circuit 23 receives the addition amplifier 21 and the differential amplifier 22 as inputs, detects a phase difference, and outputs a tracking error signal.

FIG. 7 is a block diagram showing the overall configuration of the optical information recording / reproducing apparatus of the present invention. In the figure, the same components as those in FIG. 1 are denoted by the same reference numerals.

In FIG. 1, a spindle motor 31 is
A recording medium 40 such as a magneto-optical disk or a digital video disk is rotated. The optical pickup head 33 optically reproduces or records information on a recording medium. The signal demodulator 37 demodulates the signal reproduced by the optical pickup 33. The RAM 36 is a memory for temporarily storing the signal for demodulation. The ECC circuit corrects an error in the demodulated signal. Focus servo / Track servo circuit 35
Controls the tracking and focus of the optical pickup head 33 by the tracking error signal and the focus error signal demodulated by the signal demodulator 37. The head access control circuit 34 controls the movement of the optical pickup head 33 so as to search for a desired address. The controller 32 is an interface circuit 3 such as SCSI.
9. ECC circuit 38, signal demodulator 37, head access control circuit 34, focus servo / track servo circuit 35, and spindle motor 31 are controlled.

The operation will be described based on the above configuration. The controller 32 rotates the spindle motor 31 to rotate the recording medium 40. On the other hand, the signal demodulator 37 demodulates the reproduction signal obtained from the recording medium 40 by the optical pickup 33, and converts the demodulated information signal into an E signal.
In addition to sending to the CC circuit 38, the focus error signal and the tracking error signal are sent to the focus servo / track servo circuit 35 via the controller 32. Focus servo / track servo circuit 3 receiving the focus error signal and the tracking error signal
5 transmits a drive signal corresponding to the error signal to the optical pickup head 33.
Drives an objective lens (not shown) according to the error signal.

The information signal input to the ECC circuit 38 is
An error signal is corrected based on a control signal from the controller 32 and sent to an external computer (not shown) via the interface circuit 39. When searching for a desired address, the controller 32 sends the target address information to the head access control circuit 34 and receives the target address information.
Transmits a drive signal corresponding to a target to the optical pickup head 33.
, The optical pickup head 33 moves to the target address.

[0041]

According to the optical information recording / reproducing apparatus according to the first aspect, different recording media in which the ratio A / W as the ratio of the pupil radius to the radius when the light intensity becomes 1 / e ² is optimum are used. When reproducing or recording information, the pupil light amount distribution is changed according to the recording medium, so that information can be reproduced or recorded from various recording media having different A / Ws.

In the optical information recording / reproducing apparatus according to the second aspect, since the pupil light quantity distribution is changed by the movable light quantity limiting filter by the light quantity distribution varying means of the first aspect, the A / W is simple. Information can be reproduced or recorded from various recording media different from each other.

In the optical information recording / reproducing apparatus according to the third aspect, since the light quantity distribution varying means of the first aspect electrically controls the light quantity distribution, the A / W can be performed without employing a complicated mechanism.
Information can be reproduced or recorded from various recording media different from each other.

In the optical information recording / reproducing apparatus according to the fourth aspect, since the light transmittance of the light quantity distribution varying means of the first to third aspects is higher in the peripheral part than in the central part, it is simple. With a simple filter configuration, information can be reproduced or recorded from various recording media having different A / Ws.

In the optical information recording / reproducing apparatus according to the fifth aspect, the light transmittance of the fourth aspect is changed so as to gradually increase from the central portion to the peripheral portion. It has effects such as becoming.

[Brief description of the drawings]

FIG. 1 is an optical block diagram showing a specific configuration of an embodiment of an optical information recording / reproducing apparatus of the present invention.

FIG. 2 is an optical block diagram showing a specific configuration of another embodiment of the optical information recording / reproducing apparatus of the present invention.

FIG. 3 is a graph showing a jitter simulation of the optical information recording / reproducing apparatus of the present invention.

FIG. 4 is a plan view showing a specific configuration of an example of a transmittance distribution filter of the optical information recording / reproducing apparatus of the present invention.

FIG. 5 is a plan view showing a specific configuration of another example of the transmittance distribution filter of the optical information recording / reproducing apparatus of the present invention.

FIG. 6 is a circuit block diagram showing a specific circuit configuration for obtaining various servo error signals and information reproduction signals of the optical information recording / reproducing apparatus of the present invention.

FIG. 7 is a circuit block diagram showing an overall circuit configuration of the optical information recording / reproducing apparatus of the present invention.

FIG. 8 is a diagram illustrating a light quantity distribution characteristic.

FIG. 9 is an optical block diagram showing a configuration example of a conventional optical information recording / reproducing apparatus.

[Explanation of symbols]

Reference Signs List 1 laser diode (light emitting means), 3 digital video disk (recording medium), 6 objective lens (optical means), 7 magneto-optical disk (recording medium), 15 transmittance distribution filter (light quantity distribution variable means), 16 transmittance distribution Filter (light intensity distribution variable means)

Claims (5)

[Claims] 1. An optical information recording / reproducing apparatus for reproducing / recording information from different recording media in which A / W as a ratio of a pupil radius to a radius when the light intensity becomes 1 / e ² is optimal. A light emitting unit that emits a light beam; and an optical unit that guides the light beam to the recording medium. The pupil light amount distribution according to the recording medium in an optical path between the light emitting unit and the recording medium. An optical information recording / reproducing apparatus comprising a light amount distribution varying means for changing. 2. The light quantity distribution varying means is a movable light quantity limiting filter, and changes a pupil light quantity distribution by inserting or not inserting the light quantity limiting filter in an optical path. 2. The optical information recording / reproducing apparatus according to 1. 3. The optical information recording / reproducing apparatus according to claim 1, wherein said light quantity distribution variable means is a light quantity distribution variable element capable of electrically controlling a light quantity distribution. 4. The optical information recording / reproducing apparatus according to claim 1, wherein a light transmittance of the light amount distribution varying means is higher at a peripheral portion than at a central portion. 5. The optical information recording / reproducing apparatus according to claim 4, wherein the light transmittance changes so as to gradually increase from the central portion to the peripheral portion.