JPH06349086A - Focusing servo mechanism for optical recording device having light source of short wavelength - Google Patents

Abstract

PURPOSE:To stabilize servo operation and to contrive interchangeability of a disk even in a disk having a wide track pitch by applying an offset signal corresponding to a tracking pitch to a focusing error signal. CONSTITUTION:An offset signal generating circuit selects an offset value corresponding to a track pitch of a disk to be an object from an output of the reference voltage generating circuit 22 having an offset value corresponding to plural track pitches by a multiplexer 23. This offset value is added to a focusing servo signal by an adder circuit 21. Therefore, by adding a simple offset generating circuit to a focusing servo mechanism, tracking servo can be stably applied to a disk having a wide track pitch, and interchangeability with a current optical recording device is kept.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention reduces the light spot diameter on a recording medium by shortening the wavelength of a light source,
The present invention relates to a focusing servo mechanism of a short wavelength light source optical recording device for increasing the recording density.

[0002]

2. Description of the Related Art Conventionally, in an optical recording device, 1.6 μm
Information is recorded / reproduced by applying a focusing servo and a tracking servo to an optical disc having a track pitch to focus a laser beam on the recording medium on the optical disc surface to about 1 μm. In this optical recording device, as shown in FIG. 4, a laser beam emitted from a semiconductor laser 1 and passing through a collimator lens 2 and a prism 3 is focused on a recording medium of an optical disc 5 by an objective lens 4. Then, the reflected light from the optical disk 5 is branched into two through the two prisms 3 and 6, one of which is guided to the reading photodiode 8 through the condenser lens 7 and the other of which is to the focusing error signal detection system 9. Lead. Then, a servo signal is generated based on the error signal obtained from the focusing error signal detection system 9 and the objective lens actuator 10 is driven to stably focus on the recording medium.

The focusing error signal detection system 9 divides the reflected light from the disk 5 captured by the objective lens 4 through a condenser lens 11 and a cylindrical lens 12 into four as shown in FIG. Photodiode 13
It is designed to be incident on. FIG. 5 shows the case where the disk 5 is too close to the objective lens 4 (a1) and the case where it is focused (b).
1) and (c1) when it is too far. The hatched portions Sa, Sb, Sc in (a2), (b2), and (c2) represent the light intensity distribution on the four-division photodiode 13 in each case.

Each output of the four-division photodiode 13 is
A focusing error signal which is input to the focusing error calculator 14 shown in FIG. 6 and which is the basis of the focusing servo is obtained. This focusing error signal becomes zero at the time of focusing. Then, the focusing error signal is sent to the automatic gain control (AGC) circuit 1
By passing through 5, the effect of fluctuations in light quantity is eliminated,
The phase compensation circuit 16 compensates this according to the characteristics of the objective lens actuator 10, and then the drive amplifier 1
The objective lens actuator 10 is driven by 7.

Next, the principle of tracking error signal detection will be described with reference to FIG. Generally, the push-pull method is used to detect the tracking error signal. This method is obtained from each output of the four-division photodiode 13. When there is a light spot at the center of the track guide groove (land portion) 18 as shown in FIG. As shown in a2), the light intensity distribution Sa on the four-division photodiode 13 becomes bilaterally symmetrical,
When the light spot is deviated from the center of the track guide groove 18 as shown in FIGS. 7- (b1) and 7- (c1),
As shown in FIGS. 7- (b2) and 7- (c2), the light intensity distributions Sb and Sc on the four-division photodiode 13 are shown.
Is asymmetric. Therefore, a tracking error signal can be obtained by passing each output of the four-division photodiode 13 to the tracking error calculator 19 shown in FIG.

In the above optical recording apparatus, it is possible to reduce the light spot diameter on the recording medium by shortening the wavelength of the light source, and to reduce the minimum recording mark length and the track pitch. As a result, it has been conventionally performed to increase the recording density of the optical recording device.

[0007]

However, when attempting to record / reproduce on / from a current disc having a wide track pitch in the above-mentioned short wavelength light source optical recording device, the spot diameter becomes smaller than that of the land portion 18 of the track, and the stability is stable. It will not be possible to obtain accurate tracking. This will be described with reference to FIG. 9 assuming a situation in which the objective lens 4 traverses the guide groove with only the focusing servo applied. Figure 9-
When the wavelength of the light source is long and the light spot diameter is sufficiently larger than the width of the land portion 18 as in the state shown in (a), the tracking error signal has a smooth sine wave shape, so that the value is zero. The center of the light spot and the center of the land portion 18 can be aligned by performing the servo operation so that However, as shown in FIG. 9- (b), when the light spot diameter becomes smaller than the width of the land portion 18 due to the shortening of the wavelength of the light source, the tracking error signal becomes zero while the light spot is on the land portion 18. Therefore, a step is formed in the tracking error signal. For this reason, even if the servo is applied so that the tracking error signal becomes zero, indeterminacy occurs by the width of the step portion, and the servo cannot be operated stably.

The present invention has been devised in order to solve such a problem, and its main purpose is to operate a tracking servo stably in a short wavelength light source optical recording apparatus to make a wide track. It is an object of the present invention to provide a focusing servo mechanism of a short wavelength light source optical recording device which can record / reproduce even an optical disc having a pitch and realize compatibility with the existing disc.

[0009]

According to the present invention, there is provided a focusing error signal detection system, an auto gain control circuit, a phase compensation circuit, an objective lens actuator, and a drive for driving the actuator. In a focusing servo mechanism of a short wavelength light source optical recording device having an amplifier, an offset signal generating circuit for generating an offset signal of an amount corresponding to the track pitch of an optical disc, and an offset signal generated by the circuit as a focusing error signal. It is achieved by providing a focusing servo mechanism of a short wavelength light source optical recording device, which has an adding circuit for adding.

[0010]

According to the structure of the present invention, when the short wavelength light source optical recording apparatus attempts to record / reproduce on / from a disk having a wide track pitch, the offset value of the focusing servo system is adjusted according to the width of the track pitch. To change to the defocused state. As a result, the light spot diameter can be increased and the tracking servo can be operated stably.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described in detail below with reference to specific embodiments shown in the accompanying drawings. Figure 1
FIG. 4 is a block diagram showing a configuration of the present invention, in which a focusing error signal detection system 9 and an AGC are provided as in the conventional configuration.
It has a circuit 15, a phase compensation circuit 16, an objective lens actuator 10, and a drive amplifier 17 for driving the actuator 10. In addition to this, an offset signal of an amount corresponding to the track pitch of the optical disk 5 is provided. It has an offset signal generating circuit 20 for generating and an adding circuit 21 for adding an offset signal generated by the circuit to a focusing error signal.

Focusing servo signals obtained from the phase compensation circuit 16 in the same manner as the servo system shown in FIG.
The offset value generated by the offset signal generation circuit 20 is added according to the track pitch of the target disk 5. By generating a drive current for the objective lens actuator 10 in the drive amplifier 17 based on this signal, the light spot diameter can be controlled by shifting the objective lens 4 from the in-focus position. As a result, even in the short wavelength light source optical recording device, the tracking servo can be stably operated even for a disc having a wide track pitch such as a current disc.

Next, the offset signal generating circuit 20 will be described in more detail. FIG. 2 shows a first embodiment of this circuit, in which an offset value corresponding to the track pitch of the target disk 5 is multiplexed from the output of the reference voltage generating circuit 22 having offset values corresponding to a plurality of track pitches. Select with 23. This is added to the focusing servo signal by the adder circuit 21. Reference numeral 24 is a voltage follower.

FIG. 3 shows a second embodiment. In this example, the D / A converter 25 generates an offset value of the focusing servo corresponding to the track pitch of the target disk 5, and this is used as the focusing servo signal. I am adding.

Although the above embodiments have been described with respect to the analog servo system, the digital servo system can be similarly realized.

[0016]

As described above in detail, according to the present invention, by adding a simple offset generating circuit to the focusing servo mechanism which is generally used at present, the current disk can be used even in a short wavelength light source optical recording apparatus. It is possible to stably apply the tracking servo to a disc having such a wide track pitch. Therefore, it is possible to maintain compatibility with the existing optical recording device even in the optical recording device having a short wavelength light source.

[Brief description of drawings]

FIG. 1 is a block diagram of a focusing servo mechanism according to the present invention.

FIG. 2 is an explanatory diagram of the first embodiment.

FIG. 3 is an explanatory diagram of a second embodiment.

FIG. 4 is an explanatory diagram showing a configuration of a conventional optical recording device.

FIG. 5 is an explanatory diagram of an optical system that detects a focusing error signal.

FIG. 6 is a block diagram of a circuit that calculates a focusing error signal from the output of a 4-division photodiode.

FIG. 7 is an explanatory diagram of an optical system that detects a tracking error signal.

FIG. 8 is a block diagram of a circuit that calculates a tracking error signal from the output of a 4-division photodiode.

FIG. 9 is a schematic diagram illustrating a state of a tracking error signal when a light spot diameter on a recording medium is smaller than a track pitch.

[Explanation of symbols]

 1 Semiconductor Laser 2 Collimator Lens 3 Prism 4 Objective Lens 5 Optical Disc 6 Prism 7 Focusing Lens 8 Photodiode 9 Focusing Error Signal Detection System 10 Objective Lens Actuator 11 Focusing Lens 12 Cylindrical Lens 13 4 Split Photodiode 14 Focusing Error Calculator 15 Automatic gain control (AGC) circuit 16 Phase compensation circuit 17 Drive amplifier 18 Track guide groove (land part) 19 Tracking error calculator 20 Offset signal generation circuit 21 Adder circuit 22 Reference voltage generation circuit 23 Multiplexer 24 Voltage follower 25 D / A converter

Claims (1)

[Claims] 1. A focusing servo mechanism of a short wavelength light source optical recording apparatus having a focusing error signal detection system, an auto gain control circuit, a phase compensation circuit, an objective lens actuator, and a drive amplifier for driving the actuator. And a short wavelength light source light having an offset signal generating circuit for generating an offset signal of an amount corresponding to the track pitch of the optical disc and an adding circuit for adding the offset signal generated by the circuit to a focusing error signal. Focusing servo mechanism of recording device.