JP2761791B2 - Optical recording device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording apparatus that reproduces and records information on a recording medium while adjusting the focal position of a laser beam spot according to a focus error signal. More specifically, the present invention relates to a technique for detecting the intensity of a laser beam reflected from a recording medium and generating a focus error signal.

[Conventional technology]

FIG. 3 shows a general configuration of a conventional optical recording apparatus. The optical recording device includes a light source 21 for emitting a laser beam, a collimator lens 22 for converting the laser beam into a parallel beam,
It includes an objective lens 24 for focusing a parallel laser beam on the optical recording medium 23 and irradiating a laser beam spot.
The objective lens 24 is driven in a direction perpendicular to the optical recording medium 23 to adjust the focal position of the laser beam spot. This focus position adjustment is performed via a servo system using a focus error signal, and so-called focusing control is performed. The optical recording device is further equipped with a beam splitter
25, and separates reflected light from the optical recording medium 3 from incident light. The separated reflected light is focused by a focusing lens 26 and further split into two optical paths by a polarizing beam splitter 27. The first light receiving element 28 is provided on one of the divided optical paths.
And outputs a first detection signal according to the intensity of the received light. A second light receiving element 29 is arranged on the other of the divided optical paths, and similarly outputs a second detection signal according to the intensity of the received light. The focus error signal described above is generated by processing the first and second detection signals. The optical distance of the first light receiving element 28 and the optical distance of the second light receiving element 29 are different from each other with respect to the division surface of the polarizing beam splitter 27, and the focal position of the laser beam spot exactly matches the surface of the recording medium 23. Then, the intensity of the light received by both light receiving elements is set to be equal. Therefore, the position error of the focal point of the laser beam spot with respect to the surface of the recording medium 23 can be monitored by taking the difference between the detection signals of the two light receiving elements.

FIG. 4 schematically shows the configuration and arrangement of general light receiving elements 28 and 29. First light receiving element arranged in one optical path
Numeral 28 has a central light receiving surface A and a peripheral light receiving surface C, and each has a primary detection signal S _A according to the amount of light received by the reflected laser beam.
And outputs the S _C. The second light receiving element 29 arranged on the other optical path has the same structure, has a central light receiving surface B and a peripheral light receiving surface D, and also has a primary detection signal S _B depending on the amount of light received by the reflected laser beam. And _SD .

Conventionally, for example, a simple difference method has been adopted to process these primary detection signals to generate a focus error signal. In this method, a focus error signal is obtained based on a difference between a pair of primary detection signals S _A and S _B output from a central light receiving surface. By the way, the absolute value of the signal difference S _A -S _B changes due to a change in the laser beam output or the reflectance of the recording medium surface. When this change occurs, the loop gain of the servo system for focusing changes and the operation of the servo system becomes unstable. For this reason, an automatic gain control circuit (hereinafter referred to as AG
The signal difference S _A -S _C was normalized by the signal sum S _A + S _B representing the overall intensity of the reflected laser beam. That is, the AGC circuit generates an actual focus error signal by performing an operation of (S _A -S _B ) ÷ (S _A + S _B ).

[Problems to be solved by the invention]

However, the conventional simple difference method described above has a problem that an accurate focus error signal cannot be obtained.
That is, in this method, since only the primary detection signal obtained from the central light receiving surface of the light receiving element is used, focus error information included in the primary detection signal obtained from the peripheral light receiving surface is discarded, and the actual laser beam The spot focus position cannot be monitored faithfully. This problem is particularly remarkable when a magneto-optical recording medium that records and reproduces information by utilizing the magnetic Kerr effect is used as the recording medium. The polarization plane of the laser beam spot reflected from the surface of the magneto-optical recording medium rotates according to the content of information due to the magnetic Kerr effect.
Due to the influence of the Kerr rotation angle, the division ratio of the polarization beam splitter fluctuates, and so-called magneto-optical blur occurs. Since the influence of this magneto-optical fringe mainly appears on the peripheral light receiving surface, a focus error signal generation method taking this point into consideration is required.

As such a method, for example, a density difference method has been proposed. Density difference method is primary detection signal S _A to the logic of S _D type S _A /
Processing is performed according to (S _A + S _C ) −S _B / (S _B + S _D ) to generate a focus error signal. However, the arithmetic processing by the density difference method cannot be executed by a single AGC circuit unlike the conventional simple difference method, and there is a problem that an expensive AGC circuit must be used twice.

In view of the above-described problems of the simple difference method and the density difference method, the present invention generates a focus error signal by processing a detection signal including a primary detection signal output from a peripheral light receiving surface with a single AGC circuit. It is a first object to provide a more improved system for this purpose.

The focus error signal generation method taking into account the primary detection signal output from the peripheral light receiving surface is suitable for automatic focus tracking control of a laser beam spot via a servo loop because an accurate and faithful focus error signal can be obtained. However, it is not necessarily suitable for the initial alignment of the focal position of the laser beam spot. Therefore, the present invention provides an improved focus error signal generation method capable of continuously and smoothly performing an initial focusing operation of a focus position of a laser beam spot and an automatic focus following operation after the focusing. This is the purpose of 2.

[Means to solve the problem]

In order to achieve the first object of the present invention, the optical recording device has an optical member for dividing a laser beam reflected by a recording medium into two optical paths. One light receiving element is disposed in one of the divided optical paths, has a central light receiving surface A and a peripheral light receiving surface C, and outputs primary detection signals S _A and S _C according to the amount of light received by the reflected laser beam. I do.
Further, the other light receiving element is disposed at an optical distance different from that of the one light receiving element in the other divided optical path. The other light receiving element also outputs each primary detection signals S _B and S _D in response to the received light amount of the reflected laser beam which has a central light receiving surface B and the peripheral light receiving surface D as well. Further, an AGC circuit having a pair of differential input terminals is provided, and arithmetic processing is performed on the secondary detection signal X input to one input terminal and the secondary detection signal Y input to the other input terminal. And outputs a focus error signal XY / X + Y. Distribution means is continued between the light receiving element and the AGC circuit, and distributes the primary detection signals S _A , S _B , S _C and S _D to a pair of differential input terminals of the AGC circuit according to a predetermined logical expression. A predetermined secondary detection signal X
And Y are synthesized. The following formula is used as the predetermined logical formula.

X = S _A + (2K−1) S _B + 2KS _D Y = S _B + (2K−1) S _A + 2KS _C (where K is a correction constant) As is clear from this logical expression, the sum of the secondary detection signals is obtained. X
+ Y is proportional to the sum of the primary detection signals S _A + S _B + S _C + S _D. That is, X + Y = 2K (S _A + S _B + S _C + S _D ).

In order to achieve the above-described second object of the present invention, the optical recording apparatus includes a pair of light receiving elements and a single AGC circuit similar to the optical recording apparatus for achieving the first object. Distributing means is connected between the light receiving element and the AGC circuit, and the primary detection signals S _A , S _B , S _C and S _D according to a selectable logical expression.
Is distributed to a pair of differential input terminals of the AGC circuit to synthesize the secondary detection signals X and Y. Switching means is connected to control the distributing means, so that different logical expressions are selected during the initial focusing operation of the laser beam spot focal position and during the automatic focus following operation after the focusing. I have. That is, the distributing means distributes the primary detection signal in accordance with the following logical expression (1) during the initial focusing operation of the focal position, and performs the following logical expression (in the automatic focusing operation after the focusing). The primary detection signal is distributed according to 2).

[Operation] According to the first aspect of the present invention, the primary detection signals S _A to S _D output from the central light receiving surface and the peripheral light receiving surface of the pair of light receiving elements are distributed according to a predetermined logical formula to form a pair of two light receiving elements. It is converted into the next detection signals X and Y. A pair of secondary detection signals are arithmetically processed by a single AGC circuit to obtain a focus error signal. An accurate and faithful focus error signal is generated by a single AGC circuit based on the position detection signals obtained from all the light receiving surfaces. In addition, since the signal sum of the secondary detection signals is proportional to the signal sum of the primary detection signals, that is, the total amount of received light, an extremely complete AGC operation can be performed.

According to the second aspect of the present invention, the distributing means distributes the primary detection signal in accordance with the above-described logical expression (1) during the initial adjustment operation of the focal position of the laser beam spot, so that the focus error is obtained by a so-called simple error method. A signal is generated. Since the focus error signal has no polarity reversal in a portion other than the focal point, the initial adjustment of the focal position can be performed extremely smoothly. Subsequently, after the initial alignment has been performed, the distribution means selects a different logical expression (2) and enters the automatic focus tracking operation. As described above, the focus error signal synthesized according to the logical expression (2) is faithful and accurate, and the AGC circuit can be operated stably.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1A is a schematic circuit diagram showing a configuration of a focus error signal circuit built in an optical recording apparatus according to the present invention. The other optical components are the same as those shown in FIG. 3 and will not be described in detail. As shown in the figure, the focus error signal circuit has a first light receiving element 1 arranged on one optical path divided by a polarizing beam splitter (not shown). The light receiving element 1 has a central light receiving surface _A and outputs a primary detection signal S _A according to the amount of received reflected laser beam. Further, to output a primary detection signal S _C depending on the amount of received similarly reflected laser beam has a peripheral light receiving surface C so as to surround the central light receiving surface A. The second light receiving element 2 is arranged on the other of the divided optical paths. The optical path length of the light receiving element 2 with respect to the division plane of the polarization beam splitter is arranged so as to be different from that of the light receiving element 1. Similarly, the light receiving element 2 has a central light receiving surface B and a peripheral light receiving surface D surrounding it. From the central light receiving surface B is output detection signal S _B corresponding to the received light amount of the reflected laser beam, a primary detection signal S _D corresponding to the received light amount of the reflected laser beam from the peripheral light receiving surface D is outputted. The focus error signal circuit further includes an AGC circuit 3. AGC circuit 3
Has a pair of differential input terminals, and computes XY / X + Y for a secondary detection signal X input to one input terminal and a secondary detection signal Y input to the other input terminal. , And outputs a focus error signal FES.

Distributing means 4 is connected between the pair of light receiving elements 1 and 2 and the AGC circuit 3. The distribution means 4 is for distributing the primary detection signals S _A , S _B , S _C and S _D in accordance with a predetermined logical formula and synthesizing predetermined secondary detection signals X and Y. The distribution means 4
_A shunt circuit 5 for shunting the primary detection signal S _A at a ratio of 1.0 to 0.5 is provided. And also it has a doubler circuit 6 for doubler primary detection signal S _C at a ratio of 1.5. Furthermore, the primary detection signal
And a doubler circuit 8 for the doubler and shunt circuit 7 for diverting a ratio of the S _B 1.0: 0.5 a primary detection signal S _D in a ratio of 1.5. In addition, there are provided switches 9 to 12 for switching the divided or constant-multiplied primary detection signal and adders 13 to 16 for adding the divided, constant-multiplied or switched primary detection signal.

The above-mentioned distribution means 4 is for switching the above-mentioned logical expressions (1) and (2) to synthesize a pair of secondary detection signals X and Y, and the embodiment shown in FIG. The case where the constant K is set to 0.75 is shown. By setting K = 0.75, the shunt ratio and the constant magnification ratio can be set to an integral multiple of each other, and there is an advantage that the circuit configuration can be simplified. In the state shown in FIG. 1A, the four switches 9 to 12 constituting the switching means are controlled so as to select the logical expression (2), and the focus error signal generated in accordance with the logical expression (2) The automatic focus tracking operation of the laser beam spot is executed by FES.

On the other hand, in the state shown in FIG. 1B, the four switches 9 to 12 are switched so as to select the logical expression (1). The initial adjustment of the beam spot focal position is performed.

Next, the operation of the above-described focus error signal circuit will be described in detail. As shown in FIG. 1A, in the automatic focus following operation after the initial focus position adjusting operation is completed,
One component of the primary detection signal S _A shunted by the shunt circuit 5 is input to the addition circuit 13. Further, one component of the primary detection signal S _B, which is shunted by the shunt circuit 7 is input to the adder 14 via the switch 12. Further, the primary detection signal _SD multiplied by the multiplication circuit 8 is also input to the addition circuit 14. The output of the adder circuit 14 is connected to the input of the adder circuit 13 as a result, to one input terminal of the AGC circuit 3 secondary detection signal _{X = S A + 0.5S B +} 1.5S D is applied.

The other components of the primary detection signal S _B, which is shunted by shunt circuit 7 adder circuit together is input to the adder circuit 16
The output of 16 is connected to the other input terminal of the AGC circuit. The other component of the primary detection signal S _A shunted by the shunt circuit 5 is input to the addition circuit 15 via the switch 11, and the primary detection circuit S _C is multiplied by the doubling circuit 6.
Are also input to the adding circuit 15. The output of the addition circuit 15 is connected to the addition circuit 16 via the switch 10. As a result, the secondary input signal Y = S is applied to the other input terminal of the AGC circuit 3.
_B + 0.5S _A + 1.5S _C is input. Generally, the signal difference XY in the AGC circuit 3 is (S _A -S _B ) -K [(S _A + S _C )-(S _B +
S _D )], and a faithful and accurate focus error signal can be output in consideration of not only the center detection signal but also the peripheral detection signal. Also, since the signal sum X + Y is 2K (S _A + S _B + S _C + S _D ) and is proportional to the total light amount of the reflected laser beam received by the pair of light receiving elements 1 and 2, a stable AGC operation over a wide range Processing can be performed.

Next, with reference to FIG. 1B, a description will be given of the initial focus position adjusting operation before the automatic focus tracking operation is started. Shunt circuit 5
One component of the primary detection signal S _A shunted is input to the addition circuit 13, and the other component is also returned to the common input terminal of the addition circuit 13 via the switch 11. As a result, secondary detection signal X becomes that the primary detection signal S _A to 1.5 times. Further, one component of the primary detection signal S _B, which is shunted by shunt circuit 7 is applied to a summing circuit 16, and the other component is also refluxed through the switch 12 is applied to the same summing circuit 16. Consequently other secondary detection signal Y is assumed that the 1.5-fold primary detection signal S _B. At this time, switch 9
And 10 are open, the primary detection signal output from the peripheral light receiving surface of each light receiving element is not input to the AGC circuit 3. In the AGC circuit 3, the difference between the secondary detection signals is 2K (S _A -S
_B ), and the signal sum becomes X + Y = 2K (S _A + S _B ). The AGC circuit 3 divides the signal difference by the signal sum and outputs a focus error signal FES according to a so-called simple difference method.
According to the focus error signal, an initial adjusting operation of the focus position is performed.

Finally, the features of the focus error signal generation method according to the present invention will be described in detail with reference to FIGS. 2A and 2B.
FIG. 2A is a graph showing a change in the focus error signal FES obtained in the state shown in FIG. 1A, and FIG.
3 is a graph showing a change in a focus error signal FES obtained in the state shown in FIG. B. In each of the graphs, the focus error signal is indicated by a solid line, the horizontal axis indicates the amount of error based on the focal point, and the vertical axis indicates the magnitude of the focus error signal. A dotted line indicates a change in the sum of the secondary detection signals. First, at the time of initial adjustment of the focus position, that is, at the time of focus-in, the focus error signal shown in FIG. 2B is used. This error signal has a gentle slope without polarity inversion except at the focal point. Therefore, it is suitable for smoothly drawing the laser beam spot to the focal point. At this time, the sum of the secondary detection signals X + Y is not simply a sum of the pair of central primary detection signals S _A and S _B but is increased by a factor of 1.5 by the above-mentioned reflux. The reason why the sum of the secondary detection signals is increased in advance in this way is to prevent the signal sum from fluctuating greatly at the time of switching of the logical formula, and to prevent the AGC circuit from rampaging for a moment.

After the focus-in, an automatic focus following operation is performed using the error signal shown in FIG. 2A. Since the focus error signal shown in FIG. 2A is obtained by utilizing the density difference between the central detection signal and the peripheral detection signal, it is possible to monitor the error amount very faithfully and accurately near the focal point. In particular, it is effective when there is magneto-optical flare generated when using a magneto-optical medium. Further, since the gain, that is, the inclination of the error signal near the focal point shown in FIG. 2A is substantially equal to the gain near the focal point of the error signal shown in FIG. 2B, the servo system is unstable even if the logical expression is switched. This is preferable because it does not occur. In addition, in the state shown in FIG. 2A, since the sum of the secondary detection signals is proportional to the sum of all the primary detection signals, it has a constant value over a wide range centered on the focal point. AGC circuit does not run out and AGC is wide
Processing is possible. Finally, when switching from the state shown in FIG. 2B to the state shown in FIG. 2A, the value of the secondary signal sum is 1.5.
It fluctuates from (S _A + S _B ) to 1.5 (S _A + S _B + S _C + S _D )
Since the ratio is increased by a factor of 1.5 in the state shown in FIG. 2B in advance, the fluctuation of the signal sum accompanying the switching can be reduced.

〔The invention's effect〕

As described above, according to the present invention, all the primary detection signals output from the central light receiving surface and the peripheral light receiving surface of the pair of light receiving elements are distributed according to a predetermined logical formula to synthesize a pair of secondary detection signals. Since the focus error signal is generated by a single AGC circuit, there is an effect that a faithful focus error signal can be obtained with a simple structure. In addition, by switching the logical expression for primary detection signal distribution at the time of focus-in and after the focus-in, it is possible to effectively perform the initial focus position adjustment and the subsequent automatic focus tracking operation effectively. is there.

[Brief description of the drawings]

FIG. 1A is a schematic block diagram of a focus error signal circuit built in the optical recording apparatus according to the present invention, showing an automatic focus following operation, and FIG. Show. 2A is a graph showing a change in a focus error signal obtained in the operation state shown in FIG. 1A, and FIG. 2B is a graph showing a change in a focus error signal obtained in the operation state also shown in FIG. 1B. FIG. 3 is a block diagram showing a general optical configuration of an optical recording apparatus, and FIG.
The figure is a schematic plan view showing the configuration and arrangement of a pair of light receiving elements. DESCRIPTION OF SYMBOLS 1 ... 1st light receiving element, 2 ... 2nd light receiving element 3 ... AGC circuit, 4 ... Distribution means 5 ... Dividing circuit, 6 ... Constant magnification circuit 7 ... Dividing circuit, 8 ... Constant Doubler circuit 9-12 Switch, 13-16 Adder circuit 21 Laser beam source 23 Recording medium 24 Objective lens 27 Polarizing beam splitter

Continuation of the front page (56) References JP-A-2-94118 (JP, A) JP-A-61-156536 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 7 / 09 G11B 7/08

Claims (4)

(57) [Claims] 1. An optical recording apparatus for recording / reproducing information on / from a recording medium while adjusting a focal position of a laser beam spot according to a focus error signal, wherein the laser beam reflected by the recording medium is divided into two optical paths. An optical member, one light-receiving element that has a central light-receiving surface A and a peripheral light-receiving surface C arranged in one optical path and outputs primary detection signals S _A and S _C according to the amount of light received by the reflected laser beam, each primary detection signals S _B and S _D in response to the received light amount of the reflected laser beam which has the other are arranged at different optical distances from the one light receiving element in the optical path central light receiving surface B and the peripheral light receiving surface D The other light-receiving element for output, and a secondary detection signal X having a pair of differential input terminals and input to one input terminal and a secondary detection signal input to the other input terminal An AGC circuit for performing arithmetic processing on the signal Y and outputting a focus error signal XY / X + Y; a primary detection signal S _A , connected between the light receiving element and the AGC circuit, according to the following logical equation: S _B , S _C, and S _D are distributed to a pair of differential input terminals, and predetermined secondary detection signals X and Y are combined to convert the secondary detection signal sum X + Y to the primary detection signal sum S _A +
An optical recording apparatus having a distribution means for making the ratio proportional to S _B + S _C + S _D. X = S _A + (2K-1) S _B + 2KS _D Y = S _B + (2K-1) S _A + 2KS _C (where K is a correction constant) 2. The optical recording apparatus according to claim 1, wherein said distribution means synthesizes the secondary detection signals X and Y in accordance with the logical formula in which a correction value K = 0.75 is substituted. 3. An optical recording apparatus for recording and reproducing information on a recording medium while adjusting a focal position of a laser beam spot according to a focus error signal, wherein a laser beam reflected by the recording medium is divided into two optical paths. An optical member, one light-receiving element that has a central light-receiving surface A and a peripheral light-receiving surface C arranged in one optical path and outputs primary detection signals S _A and S _C according to the amount of light received by the reflected laser beam, each primary detection signals S _B and S _D in response to the received light amount of the reflected laser beam which has the other are arranged at different optical distances from the one light receiving element in the optical path central light receiving surface B and the peripheral light receiving surface D The other light-receiving element to be output, and a secondary detection signal X having a pair of differential input terminals and input to one input terminal and a secondary detection signal input to the other input terminal An AGC circuit that performs arithmetic processing on Y and outputs a focus error signal XY / X + Y; a primary detection signal S _A , connected between the light receiving element and the AGC circuit and according to a selectable logical expression A distributing means for distributing S _B , S _C and S _D to a pair of differential input terminals and synthesizing the secondary detection signals X and Y; An optical recording apparatus comprising: a switching unit for selecting a different logical expression during an automatic focus following operation after the focusing operation. An optical recording apparatus which distributes a primary detection signal according to (1) and distributes the primary detection signal according to the following logical formula (2) during an automatic focus following operation after the alignment. 4. The optical recording apparatus according to claim 3, wherein said distribution means distributes the primary detection signal according to the following logical expressions (1) 'and (2)'.