JPH0240576Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention is a method for recording information such as video and audio signals from an information medium, such as a disk-shaped information medium, on which information tracks consisting of an array of uneven surfaces are recorded. The present invention relates to an optical pickup device that irradiates the information medium with a light beam and detects the reflected light to obtain a main information signal, a tracking information signal of the light beam, and a focus information signal of the light beam.

[Technical background of the invention]

so-called optical video disc, optical
To read information recorded on a disc-shaped information medium such as a DAD (digital audio disk) with an information track consisting of a row of uneven surfaces formed by rows of convex or concave surfaces called pits, etc. irradiates the information track with a light beam such as a laser beam, detects the reflected light with a light receiving element, and thereby generates a main information signal corresponding to the recorded information and tracking control of the light beam on the information track. A tracking information signal and a focus information signal for the focusing control are obtained. An optical pickup device is used to read and detect such information.

For example, the following optical pickup devices for the above-mentioned DAD have conventionally been used.

That is, in the first example, the optical system is configured as shown in FIG. Light emitted from a semiconductor laser 1 serving as a light source of a light beam is converted into a parallel beam by a collimating lens 2 and enters a polarizing prism 3. The laser beam incident on the polarizing prism 3
It is reflected by the polarizing film 3a inside the polarizing prism 3, and further reflected by the other surface of the polarizing prism 3.
The light is focused through the objective lens 5 into a spot with a diameter of about 1 to 1.5 μm. The light reflected by the recording surface of the disk 6, which is an information medium, passes through the objective lens 5 again and returns to the polarizing film 3a along the same path as the outward path. Due to the action of the λ/4 plate 4, the polarization direction of the disk reflected light is changed so that it is perpendicular to the outgoing path, so it passes through the polarizing film 3a and does not return to the semiconductor laser 1, but instead enters the critical angle prism 7 for focus detection. incident on . The light incident on the critical angle prism 7 is reflected three times within the prism 7, and then enters, for example, a 4-segment pin photodiode (hereinafter referred to as "4-segment PD") 8 as a 4-segment light receiving element. .

FIG. 2 shows a circuit for processing the detection signal of the four-division PD 8 in this first example.

In FIG. 2, the four photodiodes constituting the four-part PD 8 are Da, Db, Dc, and Dd, and the radial direction of the disk 6, that is, the radial direction r, and the tangential direction of the information track, that is, the tangential direction t, are as shown in the figure. It shall correspond to the direction. (The direction perpendicular to the surface of the disk 6 in FIG. 1 is defined as the Z direction.) Then, each photodiode Da
If the outputs of ~Dd are respectively Sa~Sd, then adder 9 adds the outputs Sa and Sb of photodiodes Da and Db, and adds outputs Sc and Sd of photodiodes Dc and Dd in adder 10, A differential amplifier 11 takes the difference between the two, and a low-pass filter 12 takes out the DC component to obtain a focus information signal S _F. On the other hand, the outputs Sa and Sc of the photodiodes Da and Dc are added in an adder 13, the outputs Sb and Sd of the photodiodes Db and Dd are added in an adder 14, and the outputs of the adders 13 and 14 are added in an adder 15. The main information signal RF is obtained by adding the signals. Further, a subtracter 16 takes the difference between the outputs of adders 13 and 14. The first pulse generator 17 receives the main information signal which is the output of the adder 15.
The rising zero cross is detected with the average light intensity of RF received as a reference (zero level), and in synchronization with it, the first sampling pulse _S1 is generated, and the second pulse generator 18 generates the main information signal RF as described above. It detects the falling zero cross according to the reference of and generates the second sampling pulse _S2 in synchronization with it. 1st
The sample and hold circuit 19 samples and holds the output of the subtracter 16 with the first sampling pulse _S1 , and the second sample and hold circuit ₂₀ samples and holds the output of the subtracter 16 with the second sampling pulse S2. , hold output S ₃ , S ₄ respectively
get. Both sample and hold circuits 19, 2
The hold outputs S ₃ and S ₄ of 0 are given to a subtracter 21, and the difference between them is output as a tracking information signal _ST .

That is, in this first example, the focus information signal S _F is detected using a critical angle prism, and a four-part PD
This is done by extracting the DC component of the signal (Sa+Sb)-(Sc+Sd) based on the photodiode outputs Sa to Sd of 8. Such a focus information detection method is generally called a critical angle method.

Also, in this first example, the tracking information signal
S _T is detected using each of the photodiode outputs Sa to Sd above.
This is done by sampling the signal (Sa + Sc) - (Sb + Sd) based on Sa + Sb + Sc + Sd at the rising zero cross and falling zero cross of the main information signal RF, respectively, and taking the difference between the two. Such a tracking information detection method is called a heterodyne method or the like.

In the second example, the optical system is constructed as shown in FIG. In FIG. 3, the same parts as those in FIG. Further, the light passes through the λ/4 plate 4 and is focused onto the recording surface of the disk 6 by the objective lens 5. The reflected light from the disk 6 passes through the objective lens 5, the λ/4 plate 4, and the collimating lens 2, is reflected and polarized within the polarizing prism 3, and is divided into four parts through the cylindrical lens 22.
It enters PD8.

The output of the 4-division PD8 is processed by an arithmetic processing circuit (not shown) from each photodiode output Sa to Sd to obtain Sa + Sb + Sc + Sd, which is used as the main information signal RF, and from (Sa + Sc) - (Sb + Sd), the focus information is obtained. A signal S _F is obtained, and a tracking information signal S _T is obtained from (Sa + Sb) - (Sc + Sd).

Cylindrical lens 2 in this second example
The detection method of the focus information signal S _F using 2 is called the astigmatism method, and the tracking information signal S _T is determined by the difference between the sums of two adjacent photodiodes.
This detection method is called the push-pull method.

By the way, in the case of the first example above, since the critical angle method is used to detect the focus information signal S _F , the light amount is reduced by the critical angle prism, and furthermore, the change in the reflection coefficient with respect to the angle change near the critical angle is gradual. There is a problem that the sensitivity tends to be low in
In addition, in the case of the second example above, the tracking information signal S _T
Since the push-pull method is used for detection, if the disk 6 is tilted (due to warping, etc.)
There was a problem in that the spot position moved on the PD8, which had an adverse effect and made the tracking operation unstable, and the control went out of order due to differences in pit depth.

Moreover, in the first and second examples above, both
Sa+Sb+Sc+Sd, (Sa+Sb)-(Sc+Sd), (Sa+
There was also the problem that the arithmetic processing circuit system became complicated because three types of calculations, Sc) - (Sb + Sd), were required.

[Purpose of invention]

An object of the present invention is to provide an optical pickup device that can detect focus information and tracking information with high accuracy and sensitivity with a simple configuration, and is resistant to tilting of the surface of a recording medium.

[Summary of the idea]

The present invention is characterized in that it uses the astigmatism method to detect focus information and the heterodyne method to detect tracking information, making many parts of the calculation process common.

[Example of idea]

FIG. 4 shows a schematic configuration of the main parts of an optical system according to an embodiment of the present invention, and FIG. 5 shows a configuration of a signal processing circuit.

As shown in FIG. 4, in the astigmatism method used in this embodiment, a reflected beam is condensed by a collimator lens 2, passes through a cylindrical lens 22, and is then received by a four-part PD 8. Here, 4-division PD8
The dividing line that divides the photodiodes Da, Db and Dc, Dd corresponds to the radial direction r, and the dividing line that divides the photodiodes Da, Dd and Db, Dc corresponds to the tangential direction t, and the cylinder of the cylindrical lens 22. It is arranged so that the axial direction of the surface is inclined at 45 degrees to the above-mentioned dividing line and corresponds to the direction connecting photodiodes Da and Dc.

In addition, as shown in Fig. 5, the above-mentioned 4-division PD8 has photodiodes Da and Dc connected in series to add and synthesize their outputs Sa and Sc, and photodiodes Db and Dd connected in series to output both. Sb and
Perform additive synthesis of Sd. These added and combined signals Sa + Sc and Sb + Sd are processed by subtracters 2 and 3 to obtain the difference between them, ie (Sa + Sc) - (Sb + Sd), and an adder to obtain the sum of the two, ie (Sa + Sc) - (Sb + Sd). 24 respectively.
A DC component of the output of the subtracter 23 is extracted by a low-pass filter 25 and becomes a focus information signal _SF . The output of the adder 24 is directly derived as the main information signal RF, while the output from the first and second pulse generators 26,
27 is also given. The first pulse generator 26 generates a first sampling pulse S ₅ in synchronization with the point where the input signal crosses the output level of the adder 24 from below to above when the average light amount is received, that is, the rising zero cross.
The second pulse generator 27 outputs a second sampling pulse _S6 in synchronization with a similar falling zero cross. The first sampling pulse _S5 is applied to a first sample and hold circuit 28, and the first sample and hold circuit 28 samples and holds the output of the subtracter 23 using the first sampling pulse _S5 . Similarly, the second sample hole circuit 29 receives the second sampling pulse.
_S6 is given, and the output of the subtracter 23 is sampled and held. The outputs S ₇ and S ₈ of the first and second sample and hold circuits 28 and 29 are given to a subtracter 30, and the difference between the two S ₇ -S ₈ is determined, and this is output as the tracking information signal _ST . .

Next, the operation of the above configuration will be explained in detail.

In FIG. 4, when the diffracted reflected light from the disk recording surface enters the collimating lens 2 as a parallel beam, the collimating lens 2 and the cylindrical lens 22 create a focal line FLa that is parallel to the axis of the cylindrical surface of the cylindrical lens 22 and a focal line that is perpendicular to it. caustic line of direction
FLb are formed at a predetermined distance from each other. A four-division PD 8 is arranged at a position where the cross section of the light beam forms a circle between these two focal lines FLa and FLb. Therefore, the light rays as shown by solid lines in FIG. 4 enter the photodiodes Da and Dc in the same positional relationship as they entered the collimating lens 2. On the other hand, the fourth
The light rays shown by the broken lines in the figure are from the collimating lens 2.
The positional relationship of the incident light is reversed at the focal line FLa, and the light enters the photodiodes Db and Dd in the opposite direction. That is, the light flux that has entered the collimator lens 2 enters the four-part PD 8 in a line-symmetrical relationship with respect to a line parallel to the axis of the cylindrical surface of the cylindrical lens 22. In this astigmatism method, as the laser beam incident on the disk surface is out of focus, the outputs of two sets of photodiodes Da, Dc and Db, Dd in the cross direction, that is, in the direction parallel to the above-mentioned axis and in the direction orthogonal to it. Using the _fact that a DC signal difference (Sa + Sc) - (Sb + Sd) occurs between the
Detection is performed. Therefore, when the cylindrical lens 22 is inserted and a circular spot is formed on the 4-part PD 8 (that is, when there is no focus error), and when the cylindrical lens 22 is not inserted (of course, when a circular spot is formed) ) (Sa + Sc) - (Sb + Sd) based on the output of the 4-division PD 8 does not change depending on the time (if the cylindrical lens 22 is not inserted, there will be no change due to defocus). In addition, as will be explained later, the tracking information signal _ST by the heterodyne method will also be detected as (Sa + Sc) - (Sb + Sd), so even if we consider Sa + Sb + Sc + Sd to obtain the main information signal RF, (Sa + Sc) and (Sb+Sd) is common, so photodiodes Da to Dd are connected in advance.
In other words, Da and Dc are connected in series and Db and
By connecting Dd in series, two sets of combined outputs (Sa+Sc) and (Sb+Sd) can be directly obtained. Here, if the center position of the light beam focused by the optical system deviates from the center position of the 4-division PD8, the tracking information signal S _T
The main information signal RF component Sa + Sb + Sc + Sd will be mixed into the signal (Sa + Sc) - (Sb + Sd) to obtain , but this will not become a problem due to the operation of the circuit described later.

In addition, by adopting the astigmatism method, it is not greatly affected by the polarization state of the laser beam unlike the critical angle method, and there is no need to set a critical angle, making it easy to align the optical axis. There is also an advantage.

Next, signal processing will be explained in detail.

In FIG. 5, the signal (Sa
The DC signal difference and the AC signal difference between +Sc) and (Sb+Sd) are taken out at the same time, and the DC signal difference is separated and extracted by the low-pass filter 25 and output as a focus information signal _SF , and the AC signal difference is tracked as follows. Used to obtain information signal _ST . The tracking information signal S _T is obtained by the adder 24 (Sa
+Sc) and (Sb+Sd) addition signal, that is, the first sampling pulse synchronized with the rise of the sum signal
The output of the subtracter 23 (AC signal difference) is sampled and held using S ₅ and a second sampling pulse S ₆ synchronized with the fall of the summation signal, and the signal S ₇
and S ₈ are obtained, and the subtracter 30 calculates the difference between these signals S ₇ and S ₈ . The above summation signal is used as the main information signal RF.

In this case, if the center position of the reflected light flux (detection light flux) deviates from the center of the 4-division PD8, the main information signal RF component will be mixed into the tracking information signal _ST , but as described above, the tracking information signal _ST Since the main information signal RF is sampled in synchronization with the point that crosses the level corresponding to the average light intensity, the main information signal RF component mixed into the sampled signal will also be at a constant level corresponding to the average light intensity, and the tracking information signal S _T It will not have any negative impact on.

In addition, in the above configuration, the output of the 4-division PD8 performs the same calculation when obtaining the focus information signal S _F and when obtaining the tracking information signal S _T , so each photodiode Da to Dd is The signals are added and combined into two sets of signals in the 4-part PD8 section. Therefore, the output of the 4-division PD8 can be reduced to half that of the conventional system, and the circuit configuration is significantly simplified.

Of course, in this case, since the astigmatism method is used to detect focus information, there is no reduction in detection sensitivity as in the critical angle method described above, and a simple configuration with high sensitivity can be realized.

Note that the present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with various modifications without changing the gist thereof.

[Effect of idea]

According to the present invention, it is possible to provide an optical pickup device that can detect focus information and tracking information with high precision and high sensitivity with an extremely simple configuration, and is resistant to tilting of the recording medium surface.

[Brief explanation of drawings]

1 and 2 are schematic perspective views of an optical system and a block diagram of a signal processing system, respectively, for explaining a first example of a conventional device, and FIG. 3 is a diagram for explaining a second example of a conventional device. FIG. 4 is a schematic perspective view of an optical system for explaining an embodiment of the present invention, and FIG. 5 is a block diagram of a signal processing system in the same embodiment. 2...Collimating lens, 8...4-split type pin
Photodiode (four-division PD), 22... Cylindrical lens, 23, 30... Subtractor, 24...
...Adder, 25...Low pass filter, 26,2
7... Pulse generator, 28, 29... Sample hold circuit.

Claims (1)

[Scope of utility model registration request] A light beam is irradiated onto an information medium on which information is recorded having an information track consisting of an array of uneven surfaces, and the reflected light is detected to obtain a tracking information signal and a focus information signal of the light beam on the information medium. In an optical pickup device for reading a main information signal recorded on the information track, a four-division type light receiving element is divided into two in each direction corresponding to the information track direction and a direction perpendicular thereto, and receives the reflected light. , an optical system for condensing the reflected light near the light-receiving surface of the light-receiving element, and an axial direction of the cylindrical surface in the direction of 45 degrees with respect to both dividing lines of the light-receiving element within the optical path of this optical system. The cylindrical lenses arranged in correspondence and the output of each unit light-receiving element of the above-mentioned 4-segment light-receiving element are crosswise divided into two with respect to the arrangement.
A combining circuit that adds and combines the two sets of combined outputs of the combining circuit, an adding circuit that obtains the main information signal by adding the two sets of combined outputs of the combining circuit, and a first difference detection that takes the difference between the two sets of combined outputs of the combining circuit. a DC detection circuit that extracts the DC component of the output of the first difference detection circuit to obtain a focus information signal; and an information signal output of the adder circuit that increases the average value of the information signal level in an upward direction and a downward direction. a synchronous sampling circuit for obtaining first and second sampling values by sampling the output of the first difference detection circuit in synchronization with the respective timings of the difference detection; 1. An optical pickup device comprising: a second difference detection circuit that obtains a tracking information signal by calculating a difference between sampling values.