JP3085594B2 - Information recording / reproducing method and apparatus therefor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for irradiating a recording track formed on the surface of an optical recording medium with a light spot and changing the physical characteristics of the irradiation position to record information.
The present invention relates to an information recording / reproducing method for reproducing information based on light reflected from a recording track and an apparatus therefor.

[0002]

2. Description of the Related Art An information recording / reproducing apparatus using a write-once optical disk, a magneto-optical disk, or a phase-change optical disk as a recording medium has an advantage of a large storage capacity, and in recent years, the capacity has been further increased.

As a technique for such a large capacity, for example, as disclosed in Japanese Patent Application Laid-Open No. 1-184726, one recording track is determined by a ternary bit position and the presence or absence of a bit per channel bit. , Two-channel binary data can be recorded to increase the data recording capacity.

[0004]

However, such a conventional apparatus has the following disadvantages.

[0005] That is, while the recording track pitch in the conventional apparatus is about 1.6 (μm),
The recording track pitch of the conventional device described above is about 2.0 (μ
m), and the recording track pitch becomes large, so that the effect of increasing the storage capacity per recording surface cannot be obtained much.

An object of the present invention is to solve the inconvenience of the conventional device, and an object of the present invention is to provide an information recording / reproducing method capable of increasing the storage capacity per recording surface and an apparatus therefor.

[0007]

SUMMARY OF THE INVENTION According to the present invention, a recording track formed on the surface of an optical recording medium is irradiated with a light spot to change the physical characteristics of the irradiated position to record information. In an information recording / reproducing method for reproducing information based on reflected light from a light source, a wavelength of a light source for forming a light spot is changed in multiple stages according to the content of a recording signal of at least 2 bits, and recording formed by the light spot is performed. While changing the diameter of the pits in multiple steps, the objective lens that narrows the light spot in response to the change in the wavelength of the light source is moved in the direction of the optical axis, while the light from the recording track is reflected with the light source set to the maximum wavelength. The level of a reproduced signal formed based on light is inspected to determine the recording pit width, and the recorded signal is reproduced based on the result of the determination.

A recording track formed on the surface of an optical recording medium is irradiated with a light spot to change the physical characteristics of the irradiated position to record information, and the information is recorded on the basis of reflected light from the recording track. In an information recording / reproducing apparatus for reproducing, a light source means for generating light of a plurality of wavelengths, and a focusing servo control means for controlling a focal position of an objective lens for focusing light generated by the light source means on a surface of an optical recording medium; Light source control means for switching the wavelength of light generated by the light source means in multiple stages in accordance with the content of a recording signal of at least 2 bits; and reflection from a recording track with the light source means generating light of the maximum wavelength. Recording pit diameter determining means for inspecting the level of a reproduced signal formed based on light to determine a recording pit width; A reproduction data forming means for forming playback data on the basis of, those having a focal length correction means for offsetting the amount of control of the focusing servo control means in response to the wavelength of the light generated from the light source means. Further, the light source means includes a plurality of light emitters respectively generating light of a plurality of wavelengths, and is arranged on the same optical axis so as to face each light emitter and emit light from each light emitter. It consists of a deflecting prism that selectively reflects and deflects on its optical axis. Further, the light source means includes:
A non-linear optical element rotatably provided, a luminous body for generating light incident on the non-linear optical element, and a rotation angle of the non-linear optical element set according to the wavelength of the generated light; Wavelength switching means for switching the wavelength of the oscillating light generated from the light.

[0009]

[0010]

[0011]

[0012]

[0013]

Therefore, data of 2 bits or more can be recorded on one recording track, and the recording position of each recording pit does not change in the arrangement direction of the recording tracks, so that the recording track pitch does not increase. The data recording capacity per recording surface can be increased.

[0014]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 shows an optical disk drive according to one embodiment of the present invention. In this case, a write-once optical disc is used as a recording medium.

In FIG. 1, an optical disk 4 is detachably mounted on a turntable 3 fixed to a rotating shaft 2 of a spindle motor 1.
The optical pickup device for recording / reproducing data on / from the recording surface is divided into a fixed optical system 5 and a movable optical system 6.
The carriage 7 of the moving optical system 6 is provided with a seek mechanism 8 for moving the moving optical system 6 in the radial direction of the optical disk 4.

Next, the optical system of the optical pickup device will be described. In this optical pickup device, a push-pull method is used as a tracking error detection method, and a knife edge method is used as a focusing error detection method.

In FIG. 1, signal light output from a light source 10 capable of switching the wavelength of output light in three stages is converted into parallel light by a coupling lens 11, and half of the light amount is converted by a half mirror 12. The light is reflected and guided to the deflecting prism 13 of the moving optical system 6, further reflected by the deflecting prism 13 and made incident on the objective lens 14, condensed by the objective lens 14 and formed on the recording surface of the optical disc 4. Is done. The signal light transmitted through the half mirror 12 is received by a light receiving element 15 for detecting the output level of the light source 10.

The reflected light from the optical disk 4 is transmitted through the objective lens 14 and converted into substantially parallel light, then reflected again by the deflecting prism 13 and guided to the fixed optical system 5, and a half of the light flux is half. The light passes through the mirror 12.

In this way, the reflected light from the optical disk 4 that has passed through the half mirror 12 is focused by the lens 16 and almost half of the light is reflected by the split mirror 17 forming a knife edge, and is reflected in the tracking direction. The light receiving element 1 for tracking error detection, the light receiving surface of which is divided into two in the radial direction of the optical disc 4
8 is incident.

The remaining portion of the light beam converged by the lens 16 is incident on a light receiving element 19 for detecting a focusing error, the light receiving surface of which is divided into two by a dividing line parallel to the ridge line of the dividing mirror 17. .

Then, a tracking error signal is obtained based on the difference between the light receiving signals output from the two divided light receiving surfaces of the light receiving element 18, and the light receiving output from the two divided light receiving surfaces of the light receiving element 19 is obtained. A focusing error signal is obtained based on the difference between the signals. Further, a reproduction signal from the optical disc 4 is obtained based on the sum of the light receiving signals of the light receiving elements 18 and 19. Also, the objective lens 14
Is provided with an objective lens moving mechanism (not shown) for moving the objective lens 14 in the tracking direction and the focusing direction.

In the present embodiment, 2
Data of one information channel is recorded on one recording track. That is, two bits of data can be recorded per one channel bit of the recording pit.

That is, as shown in FIG. 2A, data of two information channels of a recording signal are arranged bit by bit, and four types of recording modes corresponding to the contents of each data are determined for each channel bit. . For example, when the first channel is data 0 and the second channel is data 0, the recording mode is determined to be 0, and the first channel is data 1 and the second
If the channel is data 0, it is determined that the recording mode is 1, the first channel is data 0, and the second channel is data 1
In the case of, the recording mode is determined to be 2, and when the first channel is the data 1 and the second channel is the data 1, the recording mode is determined to be 3 (see FIG. 3B).

Then, as shown in FIG. 3C, when the recording mode is 1, the recording pit of the channel bit is formed by 800 (nm) light, and when the recording mode is 2, the recording pit is formed. The recording pit of the channel bit is set to 600 (n
m), and when the recording mode is 3, the recording pit of the channel bit is formed by 400 (nm) light. When the recording mode is 0, no recording pit is formed in the channel bit.

Here, the diameter d of the light spot formed on the recording surface of the optical disk 4 is expressed by the following equation (I).

D = K · λ / NA (I)

Here, λ is the light wavelength, NA is the numerical aperture of the objective lens 14, and K is a constant.

Therefore, as the wavelength becomes larger, the diameter of the light spot formed on the recording surface of the optical disk 4 becomes larger. Therefore, for each recording mode, as shown in FIG. The shape of the direction changes.

In this way, two bits of data can be recorded per channel bit for one recording track.

On the other hand, when this recording track is followed by using the light spot having the maximum diameter at the time of recording, the reflected light level decreases as the dimension in the width direction of the recording pit increases. The reproduction signal level fluctuates as shown in FIG. That is, the reproduction signal level LV0 in the recording mode 0 portion becomes maximum,
Reproduction signal level L from channel bits in recording mode 3
V1, the reproduction signal level LV2 from the recording mode 2 channel bit, and the reproduction signal level LV3 from the recording mode 1 channel bit decrease in this order.

Therefore, a threshold VT3 smaller than the reproduction signal level LV0 and larger than the reproduction signal level LV1, a threshold VT2 smaller than the reproduction signal level LV1 and larger than the reproduction signal level LV2, and a reproduction signal level LV3 smaller than the reproduction signal level LV2. By comparing the levels of the reproduced signals with the threshold value VT1 larger than the threshold value VT1, the recording mode of the reproduced channel bits can be determined based on the combination of the logical levels of the signals SS1, SS2, and SS3 obtained from the comparison result. Note that the determination timing can be formed in synchronization with the channel bit timing.

In this case, when all of the signals SS1, SS2 and SS3 are at the logical H level, the recording mode 0
Can be determined, and when all of the signals SS1, SS2, and SS3 are at the logical L level, it can be determined that the recording mode is 1, and the signal SS1 is at the logical H level and the signal S
When S2 and SS3 are at the logic L level, it can be determined that the mode is the recording mode 2, and when the signals SS1 and SS2 are at the logic H level and the signal SS3 is at the logic L level, it can be determined that the mode is the recording mode 3. .

As described above, in this embodiment, two bits of data can be recorded / reproduced per channel bit for one recording track. Therefore, the recording capacity of the optical disc 4 can be doubled at the same recording track pitch as the conventional apparatus, for example, about 1.6 (μm).

The focal length f of the objective lens 14
Is expressed as in the following equation (II).

(1 / f) = (n−1) · ((1 / r1) − (1 / r2)) (II)

Here, n is the refractive index of the material of the objective lens 14, and r1 and r2 are the radii of curvature of the objective lens 14.

On the other hand, as described above, when the wavelength of the light output from the light source 10 is changed, the focal length f changes because the refractive index changes. In this case, as the wavelength becomes longer, the focal length f changes to a larger value.

Therefore, in this embodiment, at the time of recording,
The focusing actuator that moves the objective lens 14 in the focal direction by the objective lens moving mechanism is moved so that the fluctuation of the focal length f of the objective lens 14 according to the recording mode can be eliminated (described later).

FIG. 3 shows an example of the light source 10.

Referring to FIG.
Numeral 2 is for generating 830 (nm) light, and the semiconductor laser element 23 is for generating 670 (nm) light.

The semiconductor laser element 21 and the prisms 24 and 25 are located on the output optical axis XL1 of the light source 10, and the prism 24 is provided with the semiconductor laser element 23 from a direction orthogonal to the optical axis XL1. Output light is incident,
The light of 415 (nm) obtained by converting the output light of the semiconductor laser element 22 by the second harmonic generator 26 enters the prism 25 from a direction orthogonal to the optical axis XL1.

In the prism 24, a reflection film that reflects light of 670 (nmm) and transmits other light is formed on the incident surface of the output light of the semiconductor laser 23,
In the prism 25, the light of 415 (nm) is reflected on the incident surface of the output light of the second harmonic generator 26,
A reflection film that transmits other light is formed.

Therefore, when only the semiconductor laser element 21 is turned on, 83 output from the semiconductor laser element 21 is output.
The signal light of 0 (nm) passes through the prisms 24 and 25 and is output to the output optical axis XL1 of the light source 10.

When only the semiconductor laser element 23 is turned on, 670 (n) output from the semiconductor laser element 23 is output.
The signal light of m) is reflected by the prism 24, and then passes through the prism 25, and is output to the output optical axis XL1 of the light source 10.

When only the semiconductor laser element 22 is turned on, 830 (n) output from the semiconductor laser element 22 is output.
The signal light of m) is converted to 415 by the second harmonic generator 26.
(Nm), and the 415 (nm) signal light is reflected by the prism 25 and output to the output optical axis XL1.

In this way, the wavelength of the signal light output from the light source 10 is set to 830 (nm), 670 (nm), 41
It can be set to any one of 5 (nm).

FIG. 4 shows a control system of the optical disk drive according to one embodiment of the present invention when the device shown in FIG. 3 is used as the light source 10.

In the figure, the light receiving surface 18 of the light receiving element 18
The light receiving signal Pa output from a is applied to the plus input terminal of the subtractor 31 and the input terminal of the adder 32,
Light receiving signal P output from light receiving surface 18b of light receiving element 18
b is the minus input terminal of the subtractor 31 and the adder 32
And the light receiving surface 19 of the light receiving element 19
The light receiving signal Pc output from a is input to the plus input terminal of the subtractor 33 and the input terminal of the adder 32.
Light receiving signal P output from light receiving surface 19b of light receiving element 19
d is the minus input terminal of the subtractor 33 and the adder 32
Has been added to the input end.

The subtractor 31 subtracts the light receiving signal Pb from the light receiving signal Pa, and the result of the subtraction is used as a tracking error signal ET as a tracking servo controller 34.
Has been added to The subtractor 33 subtracts the light receiving signal Pd from the light receiving signal Pc, and the result of the subtraction is applied to the focusing servo control unit 35 as a focusing error signal EF. The adder 32 calculates the sum of the light receiving signals Pa, Pb, Pc, and Pd.
The calculation result is applied to the signal reproducing unit 36 as a reproduced signal RF.

The tracking servo control section 34 forms a tracking control signal ST for changing the tracking error to 0 based on the input tracking error signal ET. Has been added to

Tracking actuator driver 37
Is a tracking actuator for moving the objective lens 14 in the tracking direction in the objective lens moving mechanism based on the input tracking control signal ST,
A drive current is supplied.

The focusing servo control unit 35 controls the focusing control signal S for changing the focusing error to 0 based on the input focusing error signal ET.
The focusing control signal SF is applied to one input terminal of an adder 38.

The signal reproducing section 36 receives the reproduced signal RF.
Is used to detect a recording mode for each channel bit of a recording signal recorded on the optical disc 4 based on
The detection data is applied to the decoder 39.

The decoder 39 outputs 2 bits for each channel bit based on the input recording mode data.
To form reproduction data RD1 and RD2 of two information channels, and these reproduction data RD1 and RD2 are
It is added to the decoders 40 and 41, respectively.

The decoders 40 and 41 detect and correct errors contained in the reproduced data RD1 and RD2 using the error correction code added to the input reproduced data RD1 and RD2. The output data is applied to the control unit 42 as reproduction data RD1a and RD2a.

The encoders 43 and 44 add a predetermined error correction code to the recording data output from the control unit 42. The output data is transmitted to the encoder 45 as recording signals of two information channels. Have been added.

The encoder 45 forms the recording mode data RM of each channel bit based on the recording signals of the two information channels. The recording mode data RM is transmitted to the focal length correcting section 46 and the semiconductor laser. It is added to the drive control unit 47.

When the recording mode is set by the control unit 42, the focal length correction unit 46 corrects a focusing servo error due to a change in the focal length of the objective lens 14 based on the recording mode data RM. The correction signal FC is applied to the other input terminal of the adder 38. Further, when the playback mode is set by the control unit 42, the focal length correction unit 46 sets the value of the correction signal FC to 0.

The adder 38 outputs the focusing control signal S
F and the correction signal FC are added, and the addition result is applied to the focusing actuator driving unit 48 as a focusing control signal SFc.

The focusing actuator driving section 48
Is based on the input focusing control signal SFc,
In the objective lens moving mechanism, a drive current is supplied to a focusing actuator that moves the objective lens 14 in the front-back direction of the optical axis.

Light receiving signal Pe output from light receiving element 15
Are added to the semiconductor laser drive control unit 47. When the reproduction mode is set by the control unit 42, the semiconductor laser drive control unit 47 drives and turns on the semiconductor laser element 21 and sets the level of the light receiving signal Pe at that time to a predetermined value at the time of reproduction. Semiconductor laser device 2
1 is controlled. When the recording mode is set by the control unit 42, the encoder 45
Semiconductor lasers 21, 22, 2 corresponding to the designated recording mode based on the recording mode data RM added from
3 is driven to light, and the level of the drive signal is controlled so that the level of the light receiving signal Pe at that time becomes a predetermined value at the time of recording. That is, when the recording mode 0 is set, all the semiconductor laser elements 21, 22,
When the recording mode 1 is set, the semiconductor laser device 21 is turned on and the recording mode 2 is turned off.
Is set to drive the semiconductor laser element 23, and when the recording mode 3 is set, the semiconductor laser element 22 is driven to light.

The position detector 49 detects the position of the moving optical system 6 moved by the seek mechanism 8, and the detection signal is applied to the seek motor control unit 50 as a position detection signal SP.

The seek motor control unit 50 drives the seek motor 51 which is the drive source of the seek mechanism 8 so that the value of the position detection signal SP becomes a value corresponding to the target position commanded by the control unit 42. Things.

The speed detector 52 detects the rotation speed of the spindle motor 1, and the detection signal is applied to the spindle motor control unit 53 as a speed detection signal SV.

The spindle motor control section 53 drives the spindle motor 1 so that the value of the speed detection signal SV becomes a value corresponding to the target speed commanded by the control section 42.

The host interface circuit 54
This is for exchanging various data with a host device using this optical disk drive as an external storage device.

With the above configuration, when the optical disk 4 is mounted on the optical disk drive, the spindle motor control unit 53
As a result, the spindle motor 1 is rotated at a predetermined rotation speed, and data recording / reproducing operation on the optical disk 4 by the optical pickup device becomes possible.

The moving optical system 6 is moved by the seek mechanism 8.
When the semiconductor laser drive control unit 47 is operated in the reproduction mode while moving the laser beam to the predetermined initial position, the reflected light from the recording surface of the optical disc 4 is obtained. Is set, the operation of the focusing servo control unit 35 is started. Thereby, the focusing servo control operation by the focusing servo control unit 35 is performed, and the focus position of the objective lens 14 is controlled so as to coincide with the recording surface of the optical disc 4.

When the control of the focusing servo control unit 35 is locked, the control unit 42 starts the operation of the tracking servo control unit 34, whereby the tracking servo control operation by the tracking servo control unit 34 is performed. The laser beam follows the recording track.

When the control of the tracking servo control unit 34 is locked, an appropriate reproduction signal RF is input to the signal reproduction unit 36, so that the control unit 42
6 is started. As a result, the detection data of the recording mode for each channel bit of the reproduction signal RF is output from the signal reproduction unit 36, and the reproduction data RD1 and RD2 of the two information channels are output from the decoder 39. It is applied to the decoders 40, 41.

Thus, the control unit 42 supplies the reproduced data RD1a and RD2a of the two information channels to the decoder 4
0, 41, and when there is a request from the host device, the control unit 42 controls the reproduction data RD1a, R
D2a is output via the host interface circuit 54 in a state where the information D2a is collected into one information channel by a predetermined method.

At the time of data recording, the control unit 42
With the focal length correction unit 46 and the semiconductor laser drive control unit 47 set to the recording mode, the recording data input via the host interface circuit 54 is appropriately distributed to two information channels, and the recording of those information channels is performed. The data is output to encoders 43 and 44.

As a result, the recording signals of the two information channels are added to the encoder 45 from the encoders 43 and 44, whereby the encoder 45 outputs the signals based on the input recording signals of the two information channels. The recording mode data RM of each channel bit is formed and output to the focal length correction unit 46 and the semiconductor laser drive control unit 47.

As a result, the semiconductor laser drive control unit 4
7 indicates that when the recording mode 0 is set by the recording mode data RM, all the semiconductor laser elements 21 and
When the recording mode 1 is set, the semiconductor laser element 21 is turned on. When the recording mode 2 is set, the semiconductor laser element 23 is turned off.
To drive the semiconductor laser element 22 when the recording mode 3 is set, and at the same time, control the level of the drive signal so that the level of the light receiving signal Pe becomes a predetermined value at the time of recording. I do.

The focal length correcting section 46 forms a correction signal FC for correcting a focusing servo error due to a change in the focal length of the objective lens 14 based on the recording mode data RM, and outputs the correction signal FC to the adder 38. I do.

Thus, even if the focal length f of the objective lens 14 fluctuates according to the wavelength of the signal light at the time of recording, the focusing actuator is driven so as to follow the fluctuation, and as a result, the focusing servo control unit The in-focus state of the objective lens 14 by the servo control 35 is maintained.

FIG. 5 shows another example of the light source 10.
In this figure, the same parts as those in FIG. 3 and corresponding parts are denoted by the same reference numerals.

In the figure, between the output surface of the semiconductor laser device 21 and the prism 24, between the output surface of the semiconductor laser device 23 and the prism 24, and between the second harmonic generator 26 and the prism 25. Has a semiconductor laser element 21
Liquid crystal shutters 27, 28, and 29 for blocking the output light of the semiconductor laser element 23 and the output light of the second harmonic generator 26 are provided.

FIG. 6 shows an example of a control system of the optical disk drive when the light source of FIG. 5 is used. In the same figure, the same parts as those in FIG.
The same reference numerals are given.

In the figure, the recording mode data RM output from the encoder 45 is
Has been added to When the reproduction mode is set by the control unit 42, the liquid crystal shutter control unit 55 turns on (opens) the liquid crystal shutter 27 and turns off (shields) the liquid crystal shutters 28 and 29. When the recording mode is set by the control unit 42, the encoder 45
The liquid crystal shutters 27, 28, 2 correspond to the designated recording mode based on the recording mode data RM added from the
9 is controlled. That is, when the recording mode 0 is set, all the liquid crystal shutters 27, 28, and 29 are turned off. When the recording mode 1 is set, the liquid crystal shutter 27 is turned on and the liquid crystal shutters 28 and 29 are turned on. When the recording mode 2 is set, the liquid crystal shutter 28 is turned on and the liquid crystal shutters 27 and 29 are turned off.
Is set, the liquid crystal shutter 29 is turned on and the liquid crystal shutters 27 and 28 are turned off.

When the recording mode is set by the control unit 42, the semiconductor laser drive control unit 47 controls the semiconductor laser 2 corresponding to the designated recording mode based on the recording mode data RM added from the encoder 45.
1, 22, and 23 are driven to light, and the level of the drive signal is controlled so that the level of the light receiving signal Pe at that time becomes a predetermined value at the time of recording. That is, when the recording mode 0 is set, all the semiconductor laser elements 21, 22, and 23 are turned off. When the recording mode 1 is set, the semiconductor laser element 21 is driven to be turned on, and the recording mode 2 is set. When the recording mode 3 is set, the semiconductor laser element 23 is turned on.

Therefore, in the recording mode 0, no signal light is output from the light source 10. In the case of the recording mode 1, the liquid crystal shutter 27 is turned on, the liquid crystal shutters 28 and 29 are turned off, and the semiconductor laser element 21 is turned on.
The light of wavelength 830 (nm) output from the light source 1 passes through the liquid crystal shutter 27 and the prisms 24 and 25, and
It is output as a signal light of 0.

In the recording mode 2, the liquid crystal shutter 28 is turned on and the liquid crystal shutters 27 and 29 are turned on.
Is turned off and the semiconductor laser element 23 is driven to be lit, so that the wavelength 6 output from the semiconductor laser element 23 is
70 (nm) light passes through the liquid crystal shutter 28, is reflected by the prism 24, passes through the prism 25, and
Is output as a signal light.

In the recording mode 3, the liquid crystal shutter 29 is turned on and the liquid crystal shutters 27 and 28 are turned on.
Is turned off and the semiconductor laser element 22 is driven to be lit, so that 415 output from the second harmonic generator 26 is output.
(Nm) is reflected by the prism 25 and output as signal light of the light source 10.

FIG. 7 shows still another example of the light source 10. This is an optical parametric oscillator using a nonlinear optical element.

In the figure, a semiconductor laser device 61
830 (nm) light, and the output light is applied to the second harmonic generator 62. From the second harmonic generator 62, the light of 415 (nm) is converted into parallel light through the collimator lens 63, and then enters the BBO crystal 65 through the oscillation mirror 64 as excitation light.
The oscillated light of the BBO crystal 65 is output via an oscillating mirror 66, and is output as a signal light of the light source 10 via a filter 67. The BBO crystal 65 is fixed to a rotatable turntable 68.

As shown in FIG. 8, when the excitation light LA1 is incident on the BBO crystal 65, the angle between the excitation light LA2 output from the BBO crystal 65 and the optical axis LL of the BBO crystal 65 is θ. Then, the relationship between the wavelength of the oscillation light LA3 output from the BBO crystal 65 and the angle θ is, for example, as shown in FIG.

Therefore, in this case, when the angle θ is set to the value θ1, oscillation light having a wavelength of 400 (nm) is obtained, and when the angle θ is set to the value θ2, oscillation light having a wavelength of 500 (nm) is obtained. When the angle θ is set to the value θ3, the wavelength becomes 600
(Nm) oscillation light is obtained. (References: Hideo Suzuki, "Optical Parametric Oscillation", 1991 17th Winter Seminar, "Wavelength Conversion of Laser Light-Fundamentals and Recent Perspectives-" (sponsored by The Optical Society of Japan).

That is, in this case, when the recording mode 1 is set, the rotational position of the turntable 68 is positioned so that the angle θ becomes the value θ3, and when the recording mode 2 is set. In this case, the rotation position of the turntable 68 is positioned so that the angle θ becomes the value θ2, and when the recording mode 3 is set, the rotation position of the turntable 68 is changed so that the angle θ becomes the value θ1. When the positioning is performed, light of a desired wavelength can be output from the light source 10.

In this case, if a filter that blocks light having a wavelength of 700 (nm) or more is used as the filter 67, for example, light of an unnecessary wavelength component can be blocked.

In this case, B is used as the nonlinear optical element.
Although a BO crystal is used, other nonlinear optical elements such as a KTP crystal and an LBO crystal can also be used.
Further, since the wavelength can be continuously changed, the light spot diameter can also be continuously changed.

FIG. 10 shows a control system of the optical disk drive when the light source 10 shown in FIG. 7 is used. In the figure, the same parts as those in FIG. 4 and corresponding parts are denoted by the same reference numerals.

In the figure, the semiconductor laser drive control unit 4
7 drives and turns on the semiconductor laser element 61 when the reproduction mode is set by the control unit 42;
The drive signal level of the semiconductor laser element 61 is controlled so that the level of the light receiving signal Pe at that time becomes a predetermined value at the time of reproduction. Further, when the recording mode is set by the control unit 42, when the recording mode data RM added from the encoder 45 is other than the recording mode 0, the semiconductor laser element 61 is driven to be turned on and the received light signal Pe at that time is changed. The level of the drive signal is controlled so that the level becomes a predetermined value at the time of recording.

The step motor 71 drives the rotary table 68 of the light source 10 to rotate. The step motor control unit 72 sets the angle θ to the value θ 3 when the reproduction mode is set by the control unit 42. Step motor 7
1 is driven. When the recording mode is set by the control unit 42, the recording mode 0 and the recording mode 1 are determined by the recording mode data RM added from the encoder 45.
Is designated, the step motor 71 is driven so that the angle θ becomes the value θ3, and the recording mode data RM
When the recording mode 2 is designated by
Is driven to the value θ2, and when the recording mode 3 is designated by the recording mode data RM, the step motor 71 is driven so that the angle θ becomes the value θ1.

With the above configuration, when the optical disk 4 is mounted on the optical disk drive, data can be recorded / reproduced on / from the optical disk 4 by the optical pickup device in the same manner as in the above-described embodiment. At this time, the control unit 42 sets the reproduction mode in the step motor control unit 72, whereby the step motor control unit 72 drives the step motor 71 so that the angle θ becomes the value θ3. At the same time, the operation of the focusing servo control unit 35 starts, and the focusing servo control unit 35
Is in the locked state, the operation of the tracking servo control unit 34 is started, and the laser beam follows the recording track.

When the control of the tracking servo control unit 34 is locked, an appropriate reproduction signal RF is input to the signal reproduction unit 36. Therefore, if necessary, the control unit 42
Starts the operation of the signal reproducing unit 36 and outputs the reproduced data RD1a and RD2a of the two information channels to the decoders 40 and 4
1, the reproduced data RD1a, RD2a
Into a single information channel in a predetermined manner,
Output through the host interface circuit 54.

At the time of data recording, the control unit 42
With the focal length correction unit 46 and the semiconductor laser drive control unit 47 set to the recording mode, the recording data input via the host interface circuit 54 is appropriately distributed to two information channels, and the recording of those information channels is performed. The data is output to encoders 43 and 44.

As a result, the recording signals of the two information channels are added to the encoder 45 from the encoders 43 and 44, whereby the encoder 45 outputs the signals based on the input recording signals of the two information channels. The recording mode data RM of each channel bit is formed and output to the focal length correction unit 46 and the semiconductor laser drive control unit 47.

Thus, the semiconductor laser drive control unit 4
Reference numeral 7 controls the level of the drive signal in accordance with the recording mode data RM so that the semiconductor laser element 61 is lit and driven in modes other than the recording mode 0 so that the level of the light receiving signal Pe becomes a predetermined value at the time of recording. .

At the same time, the step motor control unit 72
Is the recording mode data R added by the encoder 45.
When the recording mode 0 and the recording mode 1 are designated by M, the step motor 71 is driven so that the angle θ becomes the value θ3, and when the recording mode 2 is designated by the recording mode data RM, the angle θ becomes When the stepping motor 71 is driven to the value θ2 and the recording mode 3 is designated by the recording mode data RM,
The step motor 71 is driven so that the angle θ becomes the value θ1.

As a result, the signal light having the wavelength corresponding to the recording mode is focused on the optical disc 4, and recording pits having a width corresponding to the recording mode are formed on the recording track.

In the above-described embodiment, the present invention is applied to an optical disk apparatus using a write-once optical disk as a recording medium. However, other optical disks, for example, a magneto-optical disk or a phase-change optical disk are used as a recording medium. The present invention can be similarly applied to an optical disk device.

Further, in the above-described embodiment, the case where the GaAs type semiconductor laser device which is relatively easy to use is described, but other light emitting devices can be used as the light source. Further, in the above-described embodiment, the wavelength of the light source is switched between three levels so that quaternary values can be expressed and 2-bit data can be recorded per channel bit. The amount is not limited to this. For example, if the type of light source is switched to seven levels so that eight values can be expressed, three bits of data can be recorded per one channel bit.

In the above-described embodiment, the wavelength of the light source is changed discretely (in multiple stages). However, if an optical parametric oscillator is used, the wavelength of the light source can be changed continuously. There is a possibility that an analog signal can be directly recorded on a computer.

In the above-described embodiment, the diameter of the light spot is changed by changing the wavelength of the light focused on the optical disk. However, the method of changing the diameter of the light spot is not limited to this.

The configuration of the optical pickup and the optical system are not limited to those of the above-described embodiment.

[0108]

As described above, according to the present invention,
Since two or more bits of data can be recorded on one recording track, and the recording position of each recording pit does not fluctuate in the arrangement direction of the recording tracks, the recording track pitch does not increase. The data recording capacity can be increased.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an optical disk drive according to one embodiment of the present invention.

FIG. 2 is a waveform chart for explaining the recording / reproducing principle of the embodiment.

FIG. 3 is a schematic configuration diagram illustrating an example of a light source.

FIG. 4 is a block diagram illustrating a control system of an apparatus using the light source of FIG. 3;

FIG. 5 is a schematic configuration diagram showing another example of the light source.

FIG. 6 is a block diagram illustrating a control system of a device using the light source of FIG. 5;

FIG. 7 is a schematic configuration diagram showing still another example of the light source.

FIG. 8 is an explanatory diagram for explaining the wavelength of oscillation light of the light source in FIG. 7;

FIG. 9 is a graph illustrating the relationship between the angle and the wavelength of oscillation light.

FIG. 10 is a block diagram illustrating a control system of an apparatus using the light source of FIG. 7;

[Explanation of symbols]

 Reference Signs List 10 light source 21, 22, 23, 61 semiconductor laser element 24, 25 prism 26, 62 second harmonic oscillator 27, 28, 29 liquid crystal shutter 36 signal reproduction unit 39 decoder 42 control unit 45 encoder 46 focal length correction unit 47 semiconductor laser Control unit 55 Liquid crystal shutter control unit 63 Collimating lens 65 BBO crystal 64, 66 Oscillating mirror 67 Filter 68 Turntable 71 Step motor 72 Step motor control unit

Claims (4)

(57) [Claims] 1. A recording track formed on the surface of an optical recording medium is irradiated with a light spot to change the physical characteristics of the irradiation position to record information, and the information is recorded on the basis of light reflected from the recording track. In the information recording / reproducing method for reproducing information, the wavelength of the light source forming the light spot is changed in multiple steps according to the content of the recording signal of at least 2 bits, and the diameter of the recording pit formed by the light spot is changed in multiple steps. In addition, the objective lens that narrows the light spot in response to the change in the wavelength of the light source is moved in the direction of its optical axis, while the reproduction signal formed based on the reflected light from the recording track with the light source set to the maximum wavelength. An information recording / reproducing method characterized by inspecting the recording pit width by inspecting the level of the information and reproducing the recording signal based on the result of the determination. 2. A recording track formed on the surface of an optical recording medium is irradiated with a light spot to record information by changing physical characteristics of an irradiation position, and the information is recorded on the basis of reflected light from the recording track. In an information recording / reproducing apparatus for reproducing, a light source means for generating light of a plurality of wavelengths, and a focusing servo control means for controlling a focal position of an objective lens for focusing light generated by the light source means on a surface of an optical recording medium; Light source control means for switching the wavelength of light generated by the light source means in multiple stages in accordance with the content of a recording signal of at least 2 bits; and reflection from a recording track with the light source means generating light of the maximum wavelength. A recording pit diameter determining means for inspecting the level of a reproduced signal formed based on light to determine a recording pit width, and based on a determination result of the recording pit diameter determining means. Information recording means for forming reproduction data based on the information, and a focal length correction means for offsetting a control amount of the focusing servo control means according to a wavelength of light generated from the light source means. Playback device. 3. The light source means comprises: a plurality of light emitters for respectively generating light of a plurality of wavelengths; and light from each of the light emitters arranged on the same optical axis facing each light emitter. 3. An information recording / reproducing apparatus according to claim 2, comprising a deflecting prism for selectively reflecting light and deflecting the light on its optical axis. 4. The non-linear optical element according to claim 1, wherein the light source means includes a non-linear optical element rotatably provided, a luminous body for generating light incident on the non-linear optical element, and a non-linear optical element according to a wavelength of the generated light. 3. The information recording / reproducing apparatus according to claim 2, further comprising wavelength control means for setting a rotation angle and switching a wavelength of oscillation light generated from the nonlinear optical element.