JP2002352460A - Optical disk drive - Google Patents

Abstract

[PROBLEMS] To remove laser light source noise in an optical disk device. SOLUTION: The light receiving surface of a light source monitoring light receiver is divided into an upper side and a lower side, and further divided into an odd number. The laser light source power control is performed by the output of the laser light source noise canceling light receiving element composed of the combination of the laser light source and the light receiving element for laser light source power control composed of the combination in which the lower light receiving element and the upper light receiving element are alternately selected. It is configured to be made by the output of the element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk apparatus for reproducing information by irradiating an optical disk with a laser beam, and more particularly to a technique for removing a noise component caused by a fluctuation of a laser beam from a reproduced signal. .

[0002]

2. Description of the Related Art In recent years, the recording density of information on an optical disk has become higher, and accordingly, the S / N ratio required for reproducing information has been increased.
It is difficult to secure a ratio (signal-to-noise ratio). A reproduced signal obtained by irradiating an optical disk with a laser beam contains various noise components. The noise included in the reproduced signal can be classified into the following three types, focusing on the cause of occurrence. (1) Disk noise caused by roughness and unevenness of the surface of an optical disk (2) Circuit noise generated in a circuit including a light receiver and an amplifier (3) Laser light source noise (LD) caused by a laser diode (LD) as a light source noise)

[0003] Circuit noise includes photodetector (PD) amplifier noise that depends on the design of the first-stage amplifier of the photodetector, shot noise caused by fluctuations in electrons in the photocurrent of the photodetector, and first-stage current-voltage conversion amplifier of the photoreceiver. Thermal noise (thermal noise) caused by the conversion resistance of the above. Thermal noise can be determined theoretically.

[0004] Laser light source noise is noise caused by fluctuations in the wavelength and power of laser light, and is caused by a change in the light emission mode caused by a temperature change, return light, or the like. Among them, the most dominant is the quantum noise caused by the fluctuation of the electrons in the current flowing through the laser diode.

In recent years, techniques for removing laser light source noise have been developed. The optical disk device includes a reproduction signal receiver for receiving a return light from the optical disk to generate a reproduction (RF) signal and a light source for monitoring a laser light source and generating an automatic power control (APC) signal. A monitoring light receiver is provided. A laser light source noise cancel (LNC) signal is taken out from the light source monitoring light receiver to remove the laser light source noise included in the reproduction signal.

A conventional apparatus and method for removing laser light source noise will be described with reference to FIG. This example is disclosed in Japanese Patent Application No. Hei 10-124 of Japanese Patent Application No. 8-276008 filed on Oct. 18, 1996 by the same application as the present applicant.
No. 919 gazette. Please refer to the publication for details.

As shown in the figure, the optical system of the optical disk apparatus of this embodiment comprises a laser diode 11, a collimator lens 12, a polarizing beam splitter 13, a quarter-wave plate 14, an objective lens 15, and a condenser lens 16, which are light sources. It has a reproduction signal light receiver 17 and a light source monitor light receiver 18. The laser light from the laser diode 11 is
Is split into two by the half mirror 13A of the polarizing beam splitter 13. One branch light is deflected by the half mirror 13A and received by the light source monitoring light receiver 18. The other split light passes through the half mirror 13A, and reaches the information recording surface of the optical disc 20 via the quarter-wave plate 14 and the objective lens 15. Light from the information recording surface of the optical disk is deflected by the half mirror 13A of the polarization beam splitter 13, and passes through the condenser lens 16 to the reproduction signal light receiver 17
Is received by the

The output signal of the light source monitoring light receiver 18 should fluctuate in level according to the fluctuation of the wavelength and power of the laser light. That is, the output signal of the light source monitoring light receiver 18 should have the same phase as the laser light source noise included in the output signal of the reproduction signal light receiver 17. Therefore, laser light source noise is removed from the reproduction signal by canceling the output signal of the light source monitoring light receiver 18 from the output signal of the reproduction signal light receiver 17.

An example of the cancel operation will be described. The output signal of the reproduction signal light receiver 17 is supplied to the adder via the current-voltage converter and the amplifier. Light source monitor receiver 18
Is passed through the current-voltage converter and the amplifier, and the phase is inverted by the phase inverter and supplied to the adder.
As the output of the adder, a reproduced signal from which laser light source noise has been removed is obtained.

As described above, the noise contained in the reproduced signal includes not only laser light source noise but also circuit noise such as photodetector amplifier noise. In a conventional optical disk device,
The laser light source power is controlled using the laser light source noise canceling signal output from the light source monitoring light receiver 18. It is not always compatible with ensuring the operation of canceling laser light source noise and suppressing circuit system noise.

By canceling the output signal of the light source monitoring light receiver 18 from the output signal of the reproduction signal light receiver 17, the circuit design or optical design is performed so that the laser light source noise can be completely removed from the reproduction signal. Designing may result in increased circuit noise.
If the increase in the circuit noise is larger than the decrease in the laser light source noise due to the cancel operation, the noise increases as a result.

In the above-described example, the output signal from the light source monitoring light receiver 18 is used for two operations of laser light source power control and laser light source noise cancellation. There has been proposed an example in which two signals, a signal and a signal for canceling laser light source noise, are extracted and processed by separate circuit systems.

A description will be given with reference to FIG. In this example, the light receiving section of the light source monitoring light receiver 18 is divided into three. As shown, the light receiving surface is divided into an upper region A and a lower region B by a line parallel to the x-axis, and the lower region B is further divided by a line parallel to the y-axis into a left region B1 and a right region B1. Area B2. When the laser beam is applied to the center of the light receiving section, the circular spot S is applied so as to straddle three regions A, B1, and B2 as shown in the figure.

The output signal from the area A is used for laser light source power control, and the output signal from the area B is used for laser light source noise cancellation. Regions A, B, B1, B2
Output signals from the light receiving elements of a, b, b1,
Assuming that b2, the alignment in the x-axis direction uses the control signal (b1-b2), and the alignment in the y-axis direction uses the control signal (ab). When the spot of the laser beam is located at the center of the light receiving surface, the control signal (b1-b) in the x-axis direction
2) and the control signal (ab) in the y-axis direction are both zero.

[0015]

The respective areas A, B, B1,.
The current signal output from the light receiving element B2 is converted into a voltage signal by the current-voltage converter. The current-to-voltage converter for the laser light source noise canceling signal is connected immediately after the light receiver to increase the signal-to-noise (SN) ratio. However, the conversion gain of the current-voltage converter varies depending on the manufacturing process of the integrated circuit, and has a variation of 20% or more.

Therefore, when the laser light source power control signal and the laser light source noise canceling signal are used for the alignment of the photodetector, the alignment accuracy is reduced due to the variation of the current-voltage conversion gain.

In the conventional apparatus described with reference to FIG.
When the position of the spot of the laser beam applied to the light receiving surface of the light receiver changes due to temperature fluctuation, aging, or the like, the amount of light received in each region of the light receiving surface changes. As a result, the accuracy of the laser light source power control deteriorates, and the cancellation of the laser light source noise does not reach the target value.

For example, as shown in FIG. 4B, when the position of the laser spot moves in the negative direction of the y-axis, the amount of light received in the area A decreases and the amount of light received in the area B increases. The signal decreases, and the accuracy of the laser light source power control deteriorates. Although not shown, when the position of the laser spot moves in the positive direction of the y-axis, the amount of received light in the region A increases and the amount of received light in the region B decreases, so that the laser light source noise canceling signal decreases and the laser light source Noise canceling performance is degraded.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide an optical disk device capable of improving the performance of laser light source noise cancellation without lowering the alignment accuracy of the light receiver.

Accordingly, it is an object of the present invention to provide an optical disk apparatus capable of improving the performance of laser light source noise cancellation without deteriorating the accuracy of laser light source power control.

[0021]

According to the present invention, a laser light source for outputting a laser beam, a light receiving device for a reproduction signal for receiving a signal light from an optical disk and generating a reproduction signal, and a laser light from the laser light source are provided. A light source monitoring light receiver for detecting the laser light source noise, based on the reproduction signal from the reproduction signal light receiver using the output signal of the light source monitoring light receiver. The light receiving surface of the light source monitoring light receiver is divided into an upper light receiving element and a lower light receiving element by a single line parallel to the x-axis. The light receiving element and the lower light receiving element are further divided into an odd number of light receiving elements by an even number of lines parallel to the y-axis, and the laser light source noise is canceled by the upper light receiving element and the lower light receiving element. The control of the laser light source power is performed by the output of the laser light source noise canceling light receiving element constituted by an alternately selected combination, and the laser constituted by the alternately selected combination of the lower light receiving element and the upper light receiving element. It is configured to be performed by the output of the light source power control light receiving element.

Further, the alignment of the light source monitoring light receiver is performed using an output signal of the laser light source power control light receiving element.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIG. FIG. 1A shows a light receiving surface of a light source monitoring light receiver of the optical disk device of the present invention. The light receiving surface of the light source monitoring light receiver of this example is divided into an upper region and a lower region by one line parallel to the x-axis, and each region is further divided by two lines parallel to the y-axis. It is divided into three areas. Therefore, the light receiving surface is composed of the upper three light receiving elements A1, B1, C1 and the lower three light receiving elements A2, B2, C2. When the center of the light receiving surface is irradiated with the laser beam, the circular spot S is formed into six areas A1, B1, C1, A2, and B as shown in the figure.
2, irradiation is performed so as to straddle C2.

The light receiving elements A1, B2 and C1 are for controlling the laser light source power, and the light receiving elements A2, B1 and C2 are for canceling the laser light source noise. In this example, the laser light source power control signal is extracted from the upper light receiving elements A1 and C1 and the lower light receiving element B2, and the laser light source noise canceling signal is similarly output from the upper light receiving element B1 and the lower light receiving element A2. , C2. Each light receiving element A1, B1, C
The output signals of 1, A2, B2, and C2 are respectively a1, b
1, c1, a2, b2, and c2. The laser light source power control signal APC and the laser light source noise canceling signal LNC are represented by the following equations.

[0025]

APC = a1 + b2 + c1 LNC = a2 + b1 + c2

FIG. 1B shows the amount of light received by each light receiving element when the spot S of the laser light is deviated from the center of the light receiving surface.
According to this example, even if the spot S of the laser beam deviates from the center of the light receiving surface, the level of the laser light source power control signal and the laser light source noise canceling signal change little.
For example, when the spot of the laser beam moves in the negative direction of the y-axis, the amount of light received by the upper light receiving element decreases, and the amount of light received by the lower light receiving element increases. However, since both signals include the signal of the upper light receiving element and the signal of the lower light receiving element, the decrease in the amount of light received by the upper light receiving element and the increase in the amount of light received by the lower light receiving element cancel each other. After all, the fluctuation of the signal level is small.

The six light receiving elements on the light receiving surface of the laser light source monitoring light receiver of this embodiment are arranged such that the output of each light receiving element satisfies the following equation when the spot of the laser light is arranged at the center of the light receiving surface. Is set.

[0028]

## EQU2 ## b2 = a1 + c1 b1 = a2 + c2

That is, when the spot of the laser beam is located at the center of the light receiving surface, the sum a1 + c1 of the outputs of the upper laser light source power controlling light receiving element is equal to the output b2 of the lower laser light source power controlling light receiving element. The output b1 of the upper laser light source noise canceling light receiving element is equal to the sum a2 + c2 of the outputs of the lower laser light source noise canceling light receiving element. The alignment of the light source monitoring light receiver uses the laser light source power control signals a1, b2, and c1.

[0030]

## EQU3 ## Ex = c1-a1 Ey = a1 + c1-b2

Ex and Ey are control signals used for alignment of the light source monitoring light receiver in the x-axis direction, respectively.
This is a control signal used for alignment of the light source monitoring light receiver in the axial direction. When the spot of the laser beam is located at the center of the light receiving surface, the control signal Ex in the x-axis direction and the control signal Ey in the y-axis direction are both zero.

According to the present invention, only the laser light source power control signal is used and the laser light source noise canceling signal is not used in the alignment of the light source monitoring light receiver as expressed by the equation (3). Therefore,
The accuracy of alignment of the light source monitoring light receiver can be ensured.

In this example, the laser light source noise canceling current signals a2, b1, and c2 are not used for alignment, but are used only for laser light source noise canceling. Only the sum of the laser light source noise canceling current signals a2, b1, and c2 is required. Therefore, according to this example, the current signals a2, b1, and c2 output from the laser light source noise canceling light receiving elements A2, B1, and C2 are converted into voltage signals by one common current-voltage converter.

According to this embodiment, the three laser light source noise canceling current signals a2, b1, and c2 are converted into voltage signals by one common current-to-voltage converter. Since the number of pads can be reduced, it is possible to improve the frequency characteristics caused by the capacitance reduction.

A second embodiment of the present invention will be described with reference to FIG. FIG. 2A shows another example of the light receiving surface of the light source monitoring light receiver of the optical disk device of the present invention. The light receiving surface of the light source monitoring light receiver of this example is divided into an upper region and a lower region by one line parallel to the x-axis, and each region is further divided by four lines parallel to the y-axis. It is divided into five areas. Therefore, the light receiving surface includes the upper five light receiving elements A1, B1, C1,
D1, E1 and the lower five light receiving elements A2, B2, C2,
D2 and E2. When the center of the light receiving surface is irradiated with the laser beam, the circular spot S is divided into six areas A as shown in the figure.
The irradiation is performed so as to straddle 1, B1, C1, A2, B2, and C2.

The light receiving elements A1, B2, C1, D2, and E1 are for controlling the power of the laser light source, and the light receiving elements A2, B1,.
C2, D1, and E2 are for laser light source noise cancellation. Each light receiving element A1, B1, C1, D1, E1, A2,
Output signals of B2, C2, D2, and E2 are respectively a1, b
1, c1, d1, e1, a2, b2, c2, d2, e2
And The laser light source power control signal APC and the laser light source noise canceling signal LNC are represented by the following equations.

[0037]

APC = a1 + b2 + c1 + d2 + e1 LNC = a2 + b1 + c2 + d1 + e2

The laser light source noise canceling signal a2,
b1, c2, d1, e2 may be converted to a voltage signal by one common current-to-voltage converter. The ten light receiving elements on the light receiving surface of the laser light source monitoring light receiver of this example are set so that the output of each light receiving element satisfies the following equation when the spot of the laser light is located at the center of the light receiving surface. Is done.

[0039]

## EQU5 ## b2 + d2 = a1 + c1 + e1 b1 + d1 = a2 + c2 + e2

The alignment of the light source monitoring receiver is
Laser light source power control signals a1, b2, c1, d2,
Use e1.

[0041]

Ex = e1 + d2-b2-a1 Ey = a1 + c1 + e1-b2-d2

Ex and Ey are control signals used for alignment of the light source monitoring light receiver in the x-axis direction, respectively.
This is a control signal used for alignment of the light source monitoring light receiver in the axial direction. When the spot of the laser beam is located at the center of the light receiving surface, the control signal Ex in the x-axis direction and the control signal Ey in the y-axis direction are both zero.

According to another embodiment of the present invention, the light receiving surface of the light source monitoring light receiver is divided into an upper area and a lower area by one line parallel to the x-axis, and each area is further divided by y. It is divided into an odd number of regions by an even number of lines parallel to the axis. The laser light source power control light receiving element is configured by a combination of alternately selecting the upper light receiving element and the lower light receiving element, and the laser light source noise canceling light receiving element alternates the lower light receiving element and the upper light receiving element. It is constituted by the combination selected. When the spot of the laser beam is located at the center of the light receiving surface, the control signal E in the x-axis direction
The light receiving surface is divided such that the control signals Ey in the x and y axis directions are both zero.

Although the example of the present invention has been described above, the present invention is not limited to the above example, and various other examples are possible within the scope of the invention described in the claims. It will be readily understood by those skilled in the art.

[0045]

According to the optical disk apparatus of the present invention, even if the position of the spot of the laser beam applied to the light receiving surface of the light receiver changes due to temperature fluctuation, aging, etc., the laser light source power control signal and the laser light source The change in the level of the noise canceling signal has a small effect.

According to the optical disk apparatus of the present invention, even if the position of the spot of the laser beam applied to the light receiving surface of the light receiver changes due to temperature fluctuation, aging, etc., the laser light source power control signal and the laser light source noise canceling are performed. Since there is little change in the level of the application signal, the accuracy of laser light source power control is improved and the accuracy of laser light source noise cancellation is improved.

According to the optical disk apparatus of the present invention, of the laser light source power control signal and the laser light source noise canceling signal obtained from the light source monitoring light receiver, only the laser light source power control signal is transmitted to the light source monitoring light receiver. Since it is used for alignment, there is an effect that alignment can be performed with high accuracy.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram for describing a first example of a light receiving surface of a light receiver of an optical disc device of the present invention.

FIG. 2 is an explanatory diagram for describing a second example of the light receiving surface of the light receiver of the optical disc device of the present invention.

FIG. 3 is an explanatory diagram for explaining an example of an optical configuration of a conventional optical disc device.

FIG. 4 is an explanatory diagram for describing an example of a light receiving surface of a light receiver of a conventional optical disc device.

[Explanation of symbols]

11 laser diode 12 collimator lens 13 polarizing beam splitter 13A half mirror 14 quarter-wave plate 15 objective lens 16・ Condensing lens, 17 ・ ・ ・ Receiver for reproduction signal, 18 ・ ・ ・ Receiver for light source monitor, 20 ・ ・ ・
optical disk

Claims (2)

[Claims] 1. A laser light source for outputting laser light, a reproduction signal light receiver for receiving a signal light from an optical disk to generate a reproduction signal, and a light source monitoring light receiver for detecting laser light from the laser light source. And using the output signal of the light source monitoring light receiver to cancel the laser light source noise from the reproduction signal from the reproduction signal light receiver and to control the laser light source power. In the optical disc device, the light receiving surface of the light source monitoring light receiver is divided into an upper light receiving element and a lower light receiving element by one line parallel to the x-axis, and the upper light receiving element and the lower light receiving element are divided. Is further divided into an odd number of light receiving elements by an even number of lines parallel to the y-axis, and the laser light source noise is canceled by a combination in which an upper light receiving element and a lower light receiving element are alternately selected. The power of the laser light source is controlled by the output of the laser light source noise canceling light receiving element, and the laser light source power control light receiving means is constituted by a combination in which the lower light receiving element and the upper light receiving element are alternately selected. An optical disk device characterized by being configured to be made by an output of an element. 2. The optical disk device according to claim 1, wherein the alignment of the light source monitoring light receiver is performed using an output signal of the laser light source power control light receiving element.