JPH10188331A - Optical pickup and disk device having the same - Google Patents

Abstract

(57) Abstract: A laser beam having an anamorphic prism for shaping the cross-sectional shape of a laser beam is provided. A laser beam LB emitted from a semiconductor laser is shaped using an anamorphic prism. Prism 33 is made of two types of glass material 33
A and 33B are combined, and a glass material 33A having a small refractive index is arranged on the incident side of the beam LB, and a glass material 33B having a large refractive index is arranged on the emitting side. Thus, when the wavelength of the beam LB changes, the deviation of the direction of the beam LB emitted from the prism 33 from the design value becomes very small. Therefore, at the time of recording, the recording pattern hardly wobbles with respect to the track, recording jitter and unerased residue can be reduced, and the recording pattern is suitable for high-density recording with a narrow track pitch.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup and a disk device having the same. More specifically, the present invention relates to an optical pickup or the like in which an anamorphic prism for shaping the cross-sectional shape of a laser beam is formed of a combination of two types of glass materials to reduce the deflection of the laser beam during recording. .

[0002]

2. Description of the Related Art FIG. 4 shows the structure of a general optical pickup for an optical disk.

A laser beam LB as divergent light emitted from a semiconductor laser 101 is transmitted to a collimator lens 102.
The light is then shaped into parallel light, and then passes through the polarizing film 103a of the polarizing beam splitter 103 to pass through the quarter-wave plate 1
04. And this laser beam is 1/4
The wavelength plate 104 converts the linearly polarized light (P-polarized light) into circularly polarized light,
Thereafter, the light is irradiated onto the recording surface of the optical disk 110 via the objective lens 105.

The laser beam reflected from the recording surface of the optical disk 110 is １ ／
The light is incident on the wave plate 104. Then, this laser beam is converted to linearly polarized light (S-polarized light) from circularly polarized light by the quarter-wave plate 104.
After that, the light is reflected by the polarizing film 103a of the polarizing beam splitter 103, and is incident on the photodetector 107 via the condenser lens 106.

The laser beam LB emitted from the semiconductor laser 101 is divergent light as described above, and its intensity generally has a Gaussian distribution with an angle as a parameter as shown in FIG. As shown, the active layer 10
Divergence angle θ _{H in the} direction parallel to 1a and active layer 101a
And the divergence angle θ _{V in the} direction perpendicular to In FIG. 5, a curve a indicates a radiation characteristic in a direction parallel to the active layer, and a curve b indicates a radiation characteristic in a direction perpendicular to the active layer. The divergence angle is defined as the full width at 50% of the peak intensity.

The semiconductor laser 101 actually mass-produced
Has an aspect ratio of about 2 to 3.6. When the semiconductor laser 101 having a large aspect ratio is used, the optical disc 1
The reading performance greatly changes between the direction parallel to the ten tracks and the direction perpendicular to the ten tracks. Therefore, the direction parallel to the track is the shortest mark length of the recording data, and the direction perpendicular to the track is the L of the laser beam in consideration of the track pitch.
It is necessary to shape the sectional shape of B.

Now, a triangular prism 12 as shown in FIG.
0 has a function of enlarging or reducing the diameter of the laser beam LB. In the figure, the diameter of the laser beam LB increases when the laser beam LB passes in the direction a, and decreases when the laser beam LB passes in the direction b. The magnification is determined by the refractive index of the glass material (glass material) constituting the triangular prism 120 and the apex angle and incident angle of the prism 120.

As shown in FIG. 7, the laser beam LB is a
And the exit direction is perpendicular to the exit surface, the vertex angle of the prism 120 is φ, the incident angle of the laser beam LB is θa, and the refractive index of the glass material forming the prism 120 is n. Then, the magnification β of the laser beam LB becomes as shown in Expression (1). β = cos θb / cos θa (1) The relationship between the incident angle θa and the refraction angle θb is based on Snell's law.
It is expressed by equation (2). sin θa = nsin θb (2) Thus, since θb = φ, the magnification β is
It is expressed by equation (3). β = cosφ / √ (1-n ² sin ² φ) (3)

Incidentally, the wavelength of the laser beam LB emitted from the semiconductor laser 101 changes at ambient temperature. The glass material constituting the prism 120 is a laser beam LB.
When the wavelength changes, the refractive index changes. Accordingly, when the wavelength of the laser beam LB deviates from the design wavelength, the refraction angle θb changes, and the direction of the laser beam LB that has passed through the prism 120 deviates from the design value.

When the wavelength of the laser beam LB emitted from the semiconductor laser 101 changes by Δλ and the refractive index of the glass material forming the prism 120 changes by Δn, the relationship between the incident angle θa and the refraction angle θb ′ becomes ( 4) It is expressed by the equation. FIG.
The broken line indicates the progress of the laser beam LB as in FIG. 7, and the solid line in the diagram indicates that the wavelength of the laser beam LB is Δλ.
5 shows the state of progress of the laser beam LB after the incident surface when the laser beam LB only changes. sinθa = (n + Δn) sinθb ′ (4)

In this case, the deflection Δθb of the refracted light on the incident surface
Is expressed by Expression (5), and the emission angle θc of the laser beam LB emitted from the prism 120 is expressed by Expression (6). Δθb = θb-θb '= sin - (sinθa / n) -sin - {sinθa / (n + Δn)} ··· (5) θc = sin - {(n + Δn) sinΔθb} ··· (6)

FIG. 9 shows the configuration of an optical pickup of a phase change disk device using an anamorphic prism having the same configuration as the above-described triangular prism 120.

A laser beam LB as divergent light emitted from a semiconductor laser 201 is applied to a collimator lens 202.
Then, the light is shaped into parallel light, and then the cross-sectional shape is shaped by an anamorphic prism (triangular prism) 203.

The laser beam shaped by the prism 203 is incident on a grating (diffraction grating) 204, and the grating 204 forms three beams.
In this case, a main beam Bm of zero-order light and side beams Bs1 and Bs2 of primary light for tracking are formed.

The laser beam emitted from the grating 204 enters a polarizing beam splitter 205.
The laser beam transmitted through the polarizing film 205a of the polarizing beam splitter 205 is converted to linearly polarized light (P-polarized light) by the quarter-wave plate 206, and then the objective lens 20 is rotated.
Irradiation is performed on the recording surface of the phase-change disk 220 via the.

In this case, the recording surface of the disk 220
As shown in FIG. 10A, a spot SPm formed by the main beam Bm and a spot Sm formed by the side beams Bs1 and Bs2.
Ps1 and SPs2 are formed. As will be described later, the tracking error signal is generated by the DPP method (Differential Push Pull m).
ethod) to get spots SPs1, SP2
Are formed at positions shifted from the spot SPm by half the track pitch in the radial direction.

The laser beam reflected from the recording surface of the disk 220 is incident on the quarter-wave plate 206 via the objective lens 207. This laser beam is converted to linearly polarized light (S-polarized light) from circularly polarized light by the quarter-wave plate 206, and then reflected in order by the polarizing film 205 a and the reflecting surface 205 b of the polarizing beam splitter 205. Then, the laser beam emitted from the polarizing beam splitter 205 enters the photodetector 210 via the condenser lens 208 and the multi-lens 209. Multi lens 209
Is composed of a combination of a concave lens and a cylindrical lens. The reason for using the cylindrical lens is to obtain a focus error signal by a known astigmatism method.

As shown in FIG. 10B, the photodetector 210 includes a four-division photodiode section 210M and two two-division photodiode sections 210S ₁ and 210S ₂ . Photodiode section 210M, 210
S ₁ and 210S ₂ include the above-described disk 220, respectively.
SPm, SPs1, SPs2 formed on the recording surface of
SPm ', S by laser beam reflected by
Ps1 'and SPs2' are formed.

In this case, the four-division photodiode section 21
The detection signals of the four diodes Da to Dd constituting 0M are defined as Sa to Sd, and the two-division photodiode unit 210S
The detection signals of the two diodes De and Df forming ₁ are denoted by Se and Sf, and the two-division photodiode unit 210
Two photodiodes Dg constituting the S _2, when the detection signal of Dh Sg, and Sh, reproduction signal Sp, a tracking error signal E _T, the focus error signal E _F, respectively obtained by the following calculation. That is, the reproduction signal S
The arithmetic expression of p is Sp = Sa + Sb + Sc + Sd.
The equation for calculating the tracking error signal E _T is given by E _T =
[(Sa + Sd)-(Sb + Sc)]-K [(Se-S
f) + (Sg-Sh)]. Here, K indicates that the objective lens 207 moves and the photodiode units 210M, 2M
10S _1, the spot is formed on the 210S ₂ SPm ', S
Ps1 ', SPs2' even if the offset occurs in the position of the DC component of the tracking error signal E _T is set to a value such that constant.

Returning to FIG. 9, the grating 20
4 and reflected by the polarizing film 205a of the polarizing beam splitter 205, the front APC
(AutoPower Control) is incident on the photodetector 211. Detection signal laser power detection output S _PC next to the photodetector 211, it is used to control the laser power.

[0021]

In the optical pickup shown in FIG. 9 using an anamorphic prism 203 having the same structure as the triangular prism 120 shown in FIG. 7, a laser beam LB emitted from a semiconductor laser 201 is used. Is changed by the environmental temperature, the direction of the laser beam LB emitted from the prism 203 deviates from the design value (see the solid line in FIG. 8).

In a semiconductor laser actually mass-produced,
When the output power changes from 5 mW to 30 mW, the wavelength becomes about 5 n.
It is known to change by m. When the apex angle φ of the prism 203 is 38.1 °, the incident angle θa of the laser beam LB is 69.4 °, and the glass material forming the prism 203 is BK7 (the Abbe number is 64.1) (incident angle θ
a, the vertex angle φ is shown in FIG. 8), and the wavelength changes by about 5 nm, and the direction of the laser beam LB emitted from the prism 203 is inclined by 0.11 mrad from the initial value. Therefore, when the focal length of the objective lens 207 is 2.6 mm, the spots SPm, SPs1, SPs on the recording surface of the disk 220
s2 (see FIG. 10A) will move, for example, by about 0.3 μm in the radial direction.

There is no problem as long as the frequency of the movement of the spots SPm, SPs1, SPs2 is within the band that the tracking servo follows. However, in the phase change disk device, the laser power of the laser beam LB emitted from the semiconductor laser 201 is set to “1” of data (shown in FIG. 11A),
The modulation is performed at a high speed of several tens of MHz according to the change of “0” (shown in FIG. 11B).
Data is recorded on 20 recording surfaces. At this time, the temperature near the active layer of the semiconductor laser 201 changes at high speed, and the wavelength of the emitted laser beam LB changes at high speed. Therefore, on the recording surface of the disc 220, the spot SP
m, SPs1, and SPs2 move at a high speed, for example, in the radial direction, and the recording pattern for the track is wobbled as shown in FIG. 12B. This has a negative effect on the recording / reproducing characteristics as the track pitch becomes narrower for higher density. FIG. 12A shows an ideal recording pattern along a track.

In view of the above points, according to the present invention, in a device having an anamorphic prism for shaping the cross-sectional shape of a laser beam, the deflection of the laser beam at the time of recording is reduced, and the invention is applied to high density recording. It is an object to provide a suitable optical pickup or the like.

[0025]

An optical pickup according to the present invention has an anamorphic prism for shaping the cross-sectional shape of a laser beam. The anamorphic prism has a wavelength of an incident laser beam. Is constituted by a combination of a plurality of types of glass materials so as to reduce the deflection of the emitted laser beam due to the change of the laser beam. For example, an anamorphic prism is composed of a combination of two types of glass materials, a glass material having a small refractive index is arranged on the laser beam incident side, and a glass material having a large refractive index is arranged on the emission side thereof.

In the disk device according to the present invention, the recording surface of the disk medium is irradiated with a laser beam emitted from an optical pickup to perform recording or reproduction. In the disk device, the optical pickup shapes the sectional shape of the laser beam. The anamorphic prism is composed of a combination of a plurality of types of glass materials so as to reduce the deflection of the output laser beam due to a change in the wavelength of the incident laser beam.

For example, a laser beam LB emitted from a semiconductor laser is shaped in cross section by an anamorphic prism, and is then irradiated on a recording surface of a disk medium. For example, an anamorphic prism is formed by combining two types of glass materials, and a laser beam first transmits through a glass material having a small refractive index, and then transmits through a glass material having a large refractive index.

When the wavelength of the laser beam changes, the direction of the laser beam deviates from the design value due to the change in the refractive index of the glass material on the incident side. At this time, the direction of the laser beam also deviates from the design value due to a change in the refractive index of the glass material on the emission side. In this case, since the glass material on the incident side has a small refractive index and the glass material on the outgoing side has a large refractive index, the deviation from the design value of the direction of the laser beam in the glass material on the outgoing side is very small.

For example, when data is recorded on a disk medium by the intensity of a laser beam emitted from a semiconductor laser, the temperature near the active layer of the semiconductor laser changes according to the data, and the wavelength of the laser beam also changes. However, the deviation of the direction of the laser beam emitted from the anamorphic prism from the design value due to the change in the wavelength is extremely small as described above, and the recording pattern does not wobble with respect to the track, and the disc medium is A substantially ideal recording pattern along the track is formed.

[0030]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration of a phase change disk device 10 as an embodiment.

The disk device 10 includes a spindle motor 12 for driving the phase change disk 11 to rotate at a constant angular velocity, a semiconductor laser, an objective lens,
Optical pickup 1 composed of photodetector, etc.
3 and a laser drive circuit 14 for driving the laser diode of the optical pickup 13.

The laser drive circuit 14 is supplied with a laser power detection output S _DP from the optical pickup 13, is supplied with a power control signal S _PC from a system controller described later, and is emitted from the semiconductor laser of the optical pickup 13. Control is performed so that the laser power of the laser beam LB becomes the optimum power at the time of recording and at the time of reproduction, respectively.

The recording data Dr is supplied to the laser drive circuit 14 from a channel encoder / decoder described later at the time of data writing. Therefore, at the time of data writing, the semiconductor laser of the optical pickup 13 is driven by the laser drive circuit 14 so that the laser power changes according to the recording data Dr. Thereby, the disk 1
The recording data Dr is recorded as a mark on one recording surface. The optical pickup 13 obtains a reproduction signal Sp from the disk 11 during recording and reproduction, and
The focus error signal E _F by the tracking error signal E _T and astigmatism method using the DPP method is obtained.

The disk device 10 has a CPU (cent
ral processing unit). Error signal E _T output from the optical pickup 13, is E _F is supplied to the servo circuit 15. The operation of the servo circuit 15 is controlled by a system controller described later. The servo circuit 15 controls a tracking coil, a focus coil, and an actuator 16 including a linear motor for moving the optical pickup 13 in a radial direction, and performs tracking and focus servo.
3 is controlled in the radial direction. Further, the rotation of the spindle motor 12 is controlled by the servo circuit 15 so that the disk 11 rotates at a constant angular velocity.

The disk device 10 is a system controller having a CPU (hereinafter, referred to as "syscon").
17 and a buffer memory 1 necessary for continuously inputting data and outputting discretely or vice versa.
8 is provided. The system controller 17 controls the entire system. The disk device 10 is connected to a host computer (not shown) through the system controller 17.

The disk device 10 performs processing for adding an error correction code to write data supplied from the host computer through the system controller 17 and the buffer memory 18, and performs a channel encoder / write operation described later.
ECC (error correction code) for performing error correction processing on the read data supplied from the decoder
It has an encoder / decoder 19. The read data output from the ECC encoder / decoder 19 is supplied to the host computer through the system controller 17 and the buffer memory 18.

The disk device 10 performs digital modulation processing on the write data to which the error correction code has been added by the ECC encoder / decoder 19 to obtain recording data Dr, and outputs the data from a data discriminator described later. A channel encoder / decoder 20 for performing digital demodulation processing on the reproduction data Dp to obtain read data; a waveform equalizer 21 for performing waveform equalization processing on the reproduction signal Sp obtained from the optical pickup 13; A data discriminator 22 for performing a data discrimination process on the output signal of the waveform equalizer 21 to obtain reproduction data Dp. The data discriminator 22 includes a binarizing circuit, a Viterbi decoder, and the like.

Further, the disk device 10 includes a disk 11
Has an address decoder 23 for obtaining address data AD from the reproduction data Dp obtained from the data discriminator 22 corresponding to the reproduction signal Sp of the header portion of each sector. This address data AD is supplied to the system controller 17 and used for access control at the time of data writing and data reading.

The operation of the phase change disk device 10 shown in FIG. 1 will be described.

The operation at the time of writing data will be described. The write data from the host computer is supplied to the ECC encoder / decoder 19 via the system controller 17 and the buffer memory 18 and added with an error correction code, and then supplied to the channel encoder / decoder 20 to be subjected to digital modulation processing. Then, the recording data D output from the channel encoder / decoder 20
r is supplied to the laser drive circuit 14. As a result, the laser beam LB emitted from the semiconductor laser of the optical pickup 13 is subjected to light intensity modulation according to the recording data Dr, and a mark corresponding to the recording data Dr is recorded on the recording surface of the disk 11.

The operation at the time of reading data will be described. The reproduction signal Sp from the optical pickup 13 is applied to a waveform equalizer 21.
, And after that, the data is identified by the data identifier 22 to obtain reproduced data Dp. Then, the reproduced data Dp is supplied to the channel encoder / decoder 20 and subjected to digital demodulation processing.
It is supplied to the CC encoder / decoder 19 and subjected to error correction processing. The read data output from the ECC encoder / decoder 19 is supplied to the host computer via the system controller 17 and the buffer memory 18.

Next, the optical pickup 13 will be described in detail. FIG. 2 shows the configuration of the optical pickup 13.

The optical pickup 13 includes a semiconductor laser 31 for obtaining a laser beam LB, a collimator lens 32 for shaping the laser beam LB output from the semiconductor laser 31 from parallel light to divergent light, An anamorphic prism 33 for shaping the cross-sectional shape of the beam LB and a grating (diffraction grating) 34 for forming three beams are provided. In the grating 34, the main beam Bm by the zero-order light and the DPP
Beam B by primary light for tracking in the method
s1 and Bs2 are formed.

The anamorphic prism 33 is formed by bonding two types of glass materials 33A and 33B with, for example, an ultraviolet curing adhesive. In this case, a glass material 33A having a small refractive index is arranged on the incident side of the laser beam LB, and a glass material 33B having a large refractive index is arranged on the emission side thereof. For example, BK7 (refractive index n1 =
1.51385) is used, and SF 33 is used as the glass material 33B.
11 (refractive index n2 = 1.77597) is used.

By forming the prism 33 by combining the two types of glass materials 33A and 33B, when the wavelength of the laser beam LB changes, the design value of the direction of the laser beam LB emitted from the prism 33 is reduced. The deviation is very small.

For example, as shown in FIG.
It is assumed that the vertex angles of 33B are φ1 and φ2, respectively, and the refractive indexes are n1 and n2, respectively. Consider a case where the progress of the laser beam LB is as designed as indicated by the solid line.
The exit direction of the prism 33 is assumed to be perpendicular to the exit surface. In this case, the relationship between the incident angle θd and the refraction angle θe with respect to the glass material 33A is expressed by equation (7) according to Snell's law. sinθd = n1sinθe (7)

The relationship between the incident angle θf and the refraction angle θg with respect to the glass material 33B is expressed by equation (8) according to Snell's law. Here, θf = φ1−θe. n1sinθf = n2sinθg (8)

Next, let us consider a case where the traveling state of the laser beam LB changes as shown by a broken line by changing the wavelength of the laser beam LB by Δλ. In this case, the refractive indices of the glass materials 33A and 33B are changed by Δn1 and Δn2, respectively. The relationship between the incident angle θd and the refraction angle θe ′ with respect to the glass material 33A is expressed by equation (9). sinθd = (n1 + Δn1) sinθe '(9)

In this case, the deflection Δθe of the refracted light on the incident surface of the glass material 33A is expressed by the following equation (10). Δθe = θe-θe '= sin - (sinθd / n1) -sin - {sinθd / (n1 + Δn1)} ··· (10)

The relationship between the incident angle θf ′ and the refraction angle θg ′ with respect to the glass material 33B is expressed by equation (11). (N1 + Δn1) sin θf ′ = (n2 + Δn2) sin θg ′ (11)

In this case, the deflection Δθg of the refracted light on the entrance surface of the glass material 33B is expressed by the following equation (12).
The emission angle θh of the laser beam LB emitted from 3 is
It is represented by equation (13). Δθg = θg′−θg = sin ⁻ {(n1 + Δn1) · sinθf ′ / (n2 + Δn2)} ⁻ sin− {n1 · sinθf / n2) (12) θh = sin ⁻ ｛(n2 + Δn2) sinΔθg｝ (13)

As described above, since the refractive index of the glass material 33A is small and the refractive index of the glass material 33B is large, (1)
The deflection Δθ of the refracted light on the incident surface of the glass material 33B shown in the equation 2)
g becomes very small. Therefore, the emission angle θh of the laser beam LB emitted from the prism 33 shown in Expression (13) is also very small. That is, when the wavelength of the laser beam LB changes, the deviation of the direction of the laser beam LB emitted from the prism 33 from the design value becomes very small.

For example, BK7 is used as the glass material 33A, SF11 is used as the glass material 33B, and φ1 = 47.
8 °, φ2 = 17.8 °, θd = 68.5 °,
The emission angle θh of the laser beam LB becomes substantially 0 with respect to the change of the wavelength of the laser beam LB by 5 nm.

Returning to FIG. 2, the optical pickup 1
Reference numeral 3 denotes a polarizing beam splitter 35 and a quarter-wave plate 36 which constitute an optical isolator, and an objective lens 37 for irradiating the recording surface of the disk 11 with a laser beam. In this case, the laser beam is supplied from the grating 34 to the polarization beam splitter 35 side by the optical isolator, but the reverse is prohibited. That is, the laser beam incident on the quarter-wave plate 36 from the polarization beam splitter 35 is linearly polarized light (P-polarized light), and is converted into circularly polarized light by the quarter-wave plate 36. On the other hand, the laser beam (circularly polarized light) incident on the １ ／ wavelength plate 36 from the objective lens 37 is
Is converted into linearly polarized light (S-polarized light). Therefore, this 1/4
The laser beam incident on the polarization beam splitter 35 from the wave plate 36 is reflected by the polarization film 35a, further reflected by the reflection surface 35b, and emitted to the outside.

The optical pickup 13 includes a condenser lens 38 for condensing a laser beam as parallel light reflected by the reflection surface 35 b of the polarization beam splitter 35 and emitted to the outside, and a condenser lens 38. and the laser beam from the reproducing signal Sp to be more emitted, the tracking error signal E _T, and a photodetector 40 for obtaining a focus error signal E _F, and a multi-lens 39 disposed between the condenser lens 38 and the photodetector 40 Have.

The multi-lens 39 is composed of a combination of a concave lens and a cylindrical lens. The reason for using the cylindrical lens is to obtain a focus error signal by a known astigmatism method. Also, the photodetector 40
10B, as shown in FIG. 10B, a four-division photodiode unit 40M and two two-division photodiode units 40S ₁ ,
Composed of the 40S _2.

The optical pickup 13 has a photo detector 41 for front APC.

Next, the operation of the optical pickup 13 shown in FIG. 2 will be described.

The laser beam LB as divergent light emitted from the semiconductor laser 31 is shaped into parallel light by the collimator lens 32, and then the cross-sectional shape is shaped by the anamorphic prism 33.

The laser beam shaped by the prism 33 is incident on the grating 34 and the grating 3
4 forms three beams. Then, the laser beam emitted from the grating 34 enters the polarization beam splitter 35. The laser beam transmitted through the polarizing film 35a of the polarizing beam splitter 35 is 1/4.
The light is converted from linearly polarized light (P-polarized light) to circularly polarized light by the wave plate 36, and is then irradiated onto the recording surface of the phase change disk 11 via the objective lens 37.

In this case, on the recording surface of the disk 11, as shown in FIG. 10A, a spot SPm by the main beam Bm and a spot SPm by the side beams Bs1 and Bs2.
s1 and SPs2 are formed. Since the tracking error signal is obtained by the DPP method as described later, the spot SPs1,
SPs2 is formed at a position shifted from the spot SPm by half of the track pitch in the radial direction.

The laser beam reflected from the recording surface of the disk 11 is incident on the quarter-wave plate 36 via the objective lens 37. This laser beam is a 波長 wavelength plate 3
6, the light is changed to linearly polarized light (S-polarized light) from circularly polarized light.
The light is sequentially reflected at 5b. Then, the laser beam emitted from the polarizing beam splitter 35 is incident on the photodetector 40 via the condenser lens 38 and the multi-lens 39.

The photodiode sections 40M, 40S ₁ , and 40S ₂ constituting the photo detector 40 have the configuration shown in FIG.
As shown in B, spots SPm ', SPs formed by the laser beams reflected by the spots SPm, SPs1, SPs2 formed on the recording surface of the disk 11, respectively.
1 'and SPs2' are formed.

In this case, the four-division photodiode section 40
The detection signals of the four photodiodes Da to Dd constituting M are defined as Sa to Sd, and the two-division photodiode unit 40
S 2 pieces of photodiodes De _{of 1} constituting a detection signal of Df and Se, and Sf, further bisected photodiode portion 40S 2 pieces of photodiodes ₂ constituting Dg, D
When the detection signals of h are Sg and Sh, the reproduction signal Sp, the tracking error signal E _T , and the focus error signal E
_F is obtained by the same calculation as that of the optical pickup shown in FIG.

The light is emitted from the grating 34,
The laser beam reflected by the polarizing film 35a of the polarizing beam splitter 35 is incident on the photodetector 41. A laser power detection output _SPC is obtained from the photodetector 41 as a detection signal, and is used for controlling the laser power as described above.

As described above, in the present embodiment, the anamorphic prism 33 of the optical pickup 13 for shaping the sectional shape of the laser beam is constituted by a combination of two kinds of glass materials 33A and 33B. The laser beam L emitted from the semiconductor laser 31
When the wavelength of B changes, the deviation of the direction of the laser beam emitted from the prism 33 from the design value becomes very small.

Therefore, at the time of recording, the semiconductor laser 31
Even if the temperature near the active layer changes according to the data and the wavelength of the laser beam LB changes, the recording pattern hardly wobbles with respect to the track,
In FIG. 1, an almost ideal recording pattern along the track can be formed, and recording jitter and unerased portions can be reduced. As a result, the recording and reproducing characteristics can be improved, and the recording and reproducing characteristics are suitable for high-density recording with a narrow track pitch.

In the above embodiment, the anamorphic prism 33 for shaping the cross-sectional shape of the laser beam has been described as being composed of a combination of two types of glass materials 33A and 33B. And the deviation of the direction of the laser beam emitted from the prism 33 from the design value when the wavelength of the laser beam LB emitted from the semiconductor laser 31 changes may be reduced.

In the above-described embodiment, the present invention is applied to a phase change disk device. However, the present invention relates to an optical pickup having an anamorphic prism for shaping the cross-sectional shape of a laser beam. Needless to say, the present invention can be similarly applied to other disk devices such as a magnetic disk device.

[0070]

According to the present invention, an anamorphic prism for shaping the cross-sectional shape of a laser beam is constituted by a combination of a plurality of types of glass materials, for example, two types of glass materials. Can be made very small, an almost ideal recording pattern along a track can be formed on a disk medium, and recording jitter and unerased residue can be reduced. Therefore, the recording / reproducing characteristics can be improved, and it is suitable for high-density recording with a narrow track pitch.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a phase change disk device according to an embodiment.

FIG. 2 is a diagram showing a configuration of an optical pickup according to the embodiment.

FIG. 3 is a diagram illustrating a configuration example of an anamorphic prism of the optical pickup.

FIG. 4 is a diagram showing a configuration of a general optical pickup.

FIG. 5 is a diagram illustrating radiation characteristics of a semiconductor laser.

FIG. 6 is a diagram showing a divergence angle of a laser beam from a semiconductor laser.

FIG. 7 is a diagram for explaining a beam enlargement / reduction function of a triangular prism.

FIG. 8 is a diagram for explaining the progress of the laser beam when the wavelength of the laser beam changes.

FIG. 9 is a diagram illustrating a configuration example of an optical pickup using an anamorphic prism (triangular prism).

FIG. 10 is a diagram showing spots on a disc and spots on a photodetector.

FIG. 11 is a diagram showing a relationship between data and laser power.

FIG. 12 is a diagram showing an ideal recording pattern and a wobbled recording pattern.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Phase change disk device, 11 ... Phase change disk, 13 ... Optical pickup, 14 ... Laser drive circuit, 15 ... Servo circuit, 16 ... Actuator, 17 ... System Controller, 18 ...
Buffer memory, 19 ... ECC encoder / decoder, 20 ... channel encoder / decoder, 21.
..Waveform equalizers, 22 ... data discriminators, 23 ...
Address decoder, 31 ... Semiconductor laser, 32 ...
・ Collimator lens, 33 ・ ・ ・ Anamorphic prism, 33A, 33B ・ ・ ・ Glass material, 34 ・ ・ ・ Grating, 35 ・ ・ ・ Polarization beam splitter, 36 ・ ・ ・
1/4 wavelength plate, 37 ... objective lens, 38 ... condensing lens, 39 ... multi-lens, 40, 41 ... photodetector

Claims (3)

[Claims] 1. An optical pickup having an anamorphic prism for shaping a cross-sectional shape of a laser beam, wherein the anamorphic prism reduces the deflection of an output laser beam due to a change in the wavelength of an incident laser beam. An optical pickup comprising a combination of a plurality of types of glass materials. 2. The anamorphic prism is composed of a combination of two kinds of glass materials, a glass material having a small refractive index is arranged on an incident side of the laser beam, and a glass material having a large refractive index is arranged on an emission side of the laser beam. The optical pickup according to claim 1, wherein the optical pickup is disposed. 3. A disk device for performing recording or reproduction by irradiating a recording surface of a disk medium with a laser beam emitted from an optical pickup, wherein the optical pickup is an anamorphic for shaping a cross-sectional shape of the laser beam. A disk device comprising a prism, wherein the anamorphic prism is composed of a combination of a plurality of types of glass materials so as to reduce the deflection of an output laser beam due to a change in the wavelength of an incident laser beam.