JPH04332921A - Optical recording/reproducing device - Google Patents

Abstract

PURPOSE:To enable a tracking error signal to be detected stably in a multi-beam system optical recording/reproducing device which performs recording and reproduction of information in parallel. CONSTITUTION:A beam interval of laser beam is set so that either two beams out at least four or more laser beams 18 and 19 which are emitted from a semiconductor laser array 1 are focused at and emitted to an edge portion of different sides of same or different guide grooves and remaining beam are focused on and emitted onto each separate land portion and tracking error signal detection is performed by the twin-spot method using a focusing spot 19A which is emitted to the edge portion of the above guide groove.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] This invention relates to an optical recording and reproducing device that optically records and reproduces information, and particularly relates to an optical recording and reproducing device that has a plurality of light emitting sources and records and reproduces information in parallel. be.

0002

2. Description of the Related Art Conventionally, optical means such as laser beams have been used to record information on a rotating disk-shaped information recording medium.
Optical recording and reproducing devices that record and reproduce information concentrically or spirally are known, but with the development and spread of information equipment such as electronic computers, the amount of information handled has increased, and optical recording and reproducing devices have There is a demand for improvement in the amount of information that can be recorded and reproduced (transfer rate). In order to improve this transfer rate, for example, as shown in Japanese Patent Application Laid-Open No. 1-312747, an array type semiconductor laser that emits multiple laser beams is used to irradiate multiple information tracks with the laser beam. There is a method of recording and reproducing information in parallel. The configuration of this conventional example will be explained below using the drawings.

FIG. 7 is a diagram showing a conventional optical recording/reproducing apparatus. Reference numeral 1 denotes a semiconductor laser array, which here emits four laser beams, of which 2 is the central two laser beams, and 3 is the two laser beams at both ends. A collimator lens 4 , a beam splitter 5 , and an objective lens 6 are sequentially arranged in the laser beam emission direction of the semiconductor laser array 1 . A focused spot 2A and focused spots 3A of the two laser beams 3 at both ends are formed. Among these, the two central focused spots 2A are formed on the flat part 8 (hereinafter referred to as land part) of the information recording medium 7, and the two focused spots 3A at both ends are provided on the information recording medium 7. It is formed on the guide groove 9. The laser beam reflected by the information recording medium 7 is reflected by the beam splitter 5, and further separated by the composite prism 10 into reflected light and transmitted light. Of these, the reflected light enters the photodetector 12 via the lens 11, and in the direction of the transmitted light there are a first prism 13, a second prism 14, etc.
are arranged, and the reflective surfaces 13A and 14A of each prism
Photodetectors 15 and 16 are respectively arranged in the transmission direction.

Next, the operation will be explained. FIG. 8 is a plan view showing the arrangement of condensed spots 2A and 3A on the surface of the information recording medium 7, and the two spots 3A at both ends are on the guide grooves 9 provided in advance on the information recording medium 7.
The two central spots 2A are arranged on the land portion 8 between the guide grooves 9 at a predetermined interval. By recording and reproducing information in parallel using these four spots 2A and 3A, it is possible to improve the information transfer rate, but each condensed spot 2A and 3A is always arranged as shown in FIG. To achieve this, this conventional example uses the following means.

Due to the difference in the angle of incidence of the four laser beams 2 and 3 that entered the first prism 13, only one of the two laser beams 3 at both ends is transmitted through the reflective surface 13A, and the light is The light enters the detector 15. In addition, the remaining three laser beams 2 reflected by the reflective surface 13A,
3 is incident on the second prism 14, but due to the difference in incidence angle, the remaining laser beam 3 of the two laser beams 3 at both ends is transmitted through the reflective surface 14A.
The light is incident on the photodetector 16. The two photodetectors 15 and 16 are two-split photodetectors each consisting of two light-receiving surfaces. Here, the two laser beams 3 at both ends are both beams irradiated onto the guide groove 9 of the information recording medium 7. Therefore, by using a well-known tracking error detection method called the so-called push-pull method, it is possible to determine whether the two laser beams 3 at both ends are tracking correctly on the respective predetermined guide grooves 9, and if they are not tracking correctly. Correction control is performed by a variable mechanism (not shown).

The reproduction signal is detected by independently detecting the signals of each of the laser beams 2 and 3 by a photodetector 12 having at least four light-receiving surfaces.

[0007]

[Problems to be Solved by the Invention] As described above, the conventional optical recording and reproducing apparatus performs tracking error detection using the push-pull method using the two laser beams 3 at both ends, and therefore has the following problems. there were.

FIG. 9 is a plan view of the optical system for explaining the problems in the push-pull method.
, 17B corresponds to the photodetector 15 or 16 in FIG. In FIG. 9,
The dotted line indicates the case where the objective lens 6 is displaced in the X direction indicated by the arrow in the figure in order for the condensing spots 3A at both ends (only one is shown) to follow the predetermined guide groove 9. In this case, even though the focused spot 3A is correctly located on the guide groove 9, the optical axis of the laser beam reflected by the information recording medium 7 is shifted from the original optical axis due to the displacement of the objective lens 6. Therefore, the laser beam pattern on the two-split photodetector 17 surface moves as shown by the broken line in FIG. In the push-pull method, the differential output from the two light-receiving surfaces 17A and 17B of the two-split photodetector 17 is used as the tracking error signal, so movement of the laser beam pattern causes the tracking error signal to change, i.e. There is a problem in that a tracking offset occurs, and as a result, it becomes impossible to correctly follow the guide groove 9.

Furthermore, in the conventional example, the two condensing spots 3A at both ends are irradiated onto the guide groove 9, and the two central condensing spots 2A are irradiated onto the land portion 8. Information is recorded and reproduced using the two condensed spots 2A and 3A, but the condensed spot 3A irradiated onto the guide groove 9 is affected by diffraction from the guide groove 9, so it is reflected by the guide groove 9. The amount of light of the laser beam is smaller than the amount of light of the laser beam reflected by the land portion 8. In other words, there was a problem in that the signal levels of the four laser beams were not uniform.

Further, in order to detect a tracking error signal from the two laser beams 3 at both ends at the same time as detecting the reproduction signal, two prisms 13 are used.
, 14, and in order to transmit only the desired laser beam through the reflective surfaces 13A and 14A of each prism, highly accurate angle adjustment is required.

Furthermore, the two condensing spots 3A at both ends are arranged on the guide groove 9, and the two condensing spots 2A at the center are arranged on the guide groove 9.
Since A is arranged on the land portion 8, an information recording medium 7 in which a guide groove 9 is formed to match such a condensing spot arrangement is required. Along with the change, the information recording medium 7 must also be changed. The above also means that information recording media that are already in circulation for optical recording and reproducing devices that record and reproduce information using a single laser beam cannot be used in the configuration shown in this conventional example. However, there were problems in that usable information recording media were limited or not available.

The present invention was made to solve the above-mentioned problems, and has already been used for optical recording and reproducing devices that record and reproduce information using a single beam without requiring high-precision adjustment of the optical system. A plurality of laser beams should be correctly irradiated onto a predetermined land portion or an information track of a guide groove portion of an information recording medium in circulation, and the signal level of the plurality of laser beams reflected by the information recording medium should be uniform. The purpose is to obtain an optical recording/reproducing device. Another object of the present invention is to obtain an optical recording/reproducing device that can detect a plurality of laser beams with high precision and can also obtain a tracking error signal with a high signal-to-noise ratio (SN ratio).

[0013]

[Means for Solving the Problems] An optical recording/reproducing apparatus according to the present invention is characterized in that a condensed spot formed by any two of at least four or more laser beams is focused on a single laser beam on an information recording medium. or on different side edges of two different guide grooves, each beam is such that a focused spot formed from the remaining laser beams is focused and irradiated onto each separate land portion of the information recording medium. The guide groove is provided with a means for detecting a tracking error signal from reflected light from edges on different sides of the guide groove and performing tracking adjustment. Further, the above two laser beams are laser beams at both ends of the semiconductor laser array. Further, the two laser beams are the two laser beams at the center of the semiconductor laser array. Further, all the laser beams of the semiconductor laser array have optical output necessary for recording or erasing information. Further, the remaining laser beams of the semiconductor laser array have an optical output necessary for recording or erasing information, and the reflectance at the output end face of the two laser beams is such that the reflection rate at the output end face of the remaining laser beams is It is designed to be higher than the average rate. Further, in the photodetector that separately detects each laser beam of the semiconductor laser array reflected by the information recording medium, the width of the plurality of light receiving surfaces corresponds to the unequal intervals of the laser beams of the semiconductor laser array. It is something that

[0014]

[Operation] The optical recording/reproducing apparatus of the present invention detects tracking errors by the twin spot method using two condensed spots irradiated on the edges of different sides of the guide groove, so that the objective lens Even if the information is displaced, each of the plurality of laser beams for recording and reproducing information can correctly follow a predetermined information track. Also, twin
By increasing the reflectance at the output end face of the laser beam used to detect tracking error signals using the spot method,
Less affected by returned light. Furthermore, by making the width of the light receiving surface of the photodetector for detecting the laser beam correspond to the laser beam interval of the semiconductor laser array, it is possible to detect laser beams that are irregularly spaced.

[0015]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to FIGS. 1 to 4. FIG. 1 is an overall view showing this embodiment, and the same components as those in FIG. 7 are denoted by the same reference numerals, and the explanation thereof will be omitted. In the figure, the semiconductor laser array 1 has a total of six laser beams, four laser beams 18 in the center and two laser beams 19 at both ends.
This shows what emits the beam. The focused spots 18A of the four laser beams 18 at the center are arranged on land portions of the information recording medium 7, and the focused spots 19A of the two laser beams 19 at both ends are located on different sides of the guide grooves 9. placed at the edge. 20 is a focusing lens, 21 is a photodetector, and at least the number of laser beams, in this embodiment, at least six light receiving surfaces 21A.
21F, and light receiving surfaces 21A and 21F.
F connects the laser beams 19 at both ends to the light receiving surface 21.
B to 21E are arranged so as to receive the central laser beam 18, respectively. The outputs of the light receiving surfaces 21A and 21F are connected to a differential amplifier 22. Differential amplifier 2
The output of No. 2 is connected to a tracking servo circuit 23, and the output of the tracking servo circuit 23 is connected to an objective lens drive mechanism 24. Note that the focusing servo circuit and its driving mechanism for focusing the objective lens 6 with respect to the information recording medium 7 are not covered by this invention, and are therefore not shown.

The operation of this invention will be explained. Six laser beams 18, 1 emitted from the semiconductor laser array 1
9 is condensed and irradiated onto the surface of the information recording medium 7 by the objective lens 6. FIG. 2 is a plan view showing the arrangement of condensed spots on the surface of the information recording medium 7. As shown in FIG. The information recording medium 7 used is one that is already on the market for optical recording and reproducing devices that record and reproduce information using one laser beam, and has land portions 8 and guide grooves 9 that correspond to one information track alternately. It is being formed. Here, the track pitch is P,
Let the width of the land portion 8 be w. In Fig. 2, the condensing spot 18
A and 19A are shown by solid lines, and the positions before and after one rotation of the information recording medium 7 are shown by broken lines. The six focused spots 18A and 19A are on a straight line and have an inclination of i with respect to the guide groove. Four focused spots in the center 1
8A are equally spaced apart by d1, and are arranged on adjacent land portions 8 spaced apart by track pitch P, respectively. Therefore, the distance d1 between the focused spots 18A and the track pitch P of the information recording medium 7 is d1 = P/sin i

There is the relationship (1). On the other hand, the two condensing spots 19A at both ends are arranged at the edges of different guide grooves 9 on different sides. The distance q from the center of the land portion 8 to the edge sandwiched between the adjacent guide groove 9 and the adjacent land portion 8 is calculated using the track pitch P and the width w of the land portion 8 as follows: q=P−w/2

(2), the spot interval d2 between the two condensing spots 19A at both ends and the central condensing spot 18A adjacent thereto is d2 = q/sin i

(3) becomes. As described above, in this embodiment, the central condensing spots 18A except for the two at both ends have the same spot spacing and are sequentially arranged on adjacent land portions 8, whereas the two condensing spots at both ends The spot spacing between each of the center condensing spots 18A is different from that between the center condensing spots 18A, and the spacing between the center condensing spots 18A is such that the spots 19A are arranged at the edge of the guide groove 9. By the way, in an optical recording/reproducing apparatus that uses the semiconductor laser array 1 to form a plurality of focused spots on the surface of the information recording medium 7 using the same optical system, the intervals between the focused spots are determined by the laser beams of the semiconductor laser array 1. It corresponds to the beam spacing. In other words, if the lateral magnification of the optical system when looking from the light source side, that is, the object point side, to the condensed spot side, that is, the image point side, is M, then the distance of the laser beam interval of the light source multiplied by the lateral magnification M is the distance of the condensed spot. This will be the interval. Therefore, if the focused spot intervals on the surface of the information recording medium 7 are not equal as shown in FIG. 2, the laser beam intervals in the semiconductor laser array 1 cannot be equal. FIG. 3 is a perspective view of the semiconductor laser array 1 used in this embodiment, in which the same active layer 2
5 to 6 laser beams 18 and 19 are emitted. According to the above explanation, the laser beam spacing L1 between the four laser beams 18 at the center of the semiconductor laser array 1 can be calculated as L1 = d1 /M using the lateral magnification M of the optical system, the focused spot spacing d1, and equation (1).
=P/(M*sin i)
(4)
becomes. Similarly, the interval L2 between the two laser beams 19 at both ends and their respective adjacent laser beams is calculated using the condensed spot interval d2 and equations (2) and (3): L2 = d2 /M
=q/(M*sin i
) = (P-w/2)
/(M*sin i) (5). In equations (4) and (5), the factor M*sin
i can be considered as a constant of the optical system, and therefore, the information track pitch P of the information recording medium 7 and the laser beam interval L1
On the other hand, the laser beam interval L2 depended on the track pitch P and the width w of the land portion 8 (P-w/
It is sufficient if it corresponds to 2). In the above-described arrangement in which the information recording medium 7 and the focused spots 18A and 19A are irradiated, the central four focused spots 18A that are irradiated onto the land portion 8 are used for recording and reproducing information.

Next, the operation of the two converging spots 19A irradiated onto the edge of the guide groove 9 will be explained. The two focused spots 19A at both ends are used for tracking error detection, and tracking error detection is performed by the well-known twin spot method. FIG. 4 is a diagram for explaining the principle of the twin beam method. When the information recording medium 7 shifts in the direction A shown by the arrow in the diagram due to its eccentricity, the edge of the guide groove 9 is irradiated. The two condensing spots 26A and 26B at both ends (for convenience of explanation, the reference numeral 19A has been changed to 26A and 26B) may cross the guide groove 9 or cross the land depending on the direction of the deviation. The area 8 will be irradiated. Since the guide groove 9 has a lower reflectance than the land portion, the amount of reflected light of the focused spots 26A and 26B changes differently with respect to the amount of displacement A. The amounts of reflected light from these focused spots 26A and 26B are detected separately by light receiving surfaces 21A and 21F of photodetector 21 shown in FIG. The differential amplifier 22 subtracts the signals detected on the two light receiving surfaces 21A and 21F, and generates a tracking error signal (TE) as shown in FIG. Point B of the tracking error signal (TE) is a state in which the four central focused spots 18A are correctly located on the land portion 8, that is, a state in which there is no tracking deviation,
The tracking servo circuit 23 and the objective lens drive mechanism 24 move the objective lens 6 so that it is always at point B as shown in FIG.
By performing the corrective displacement in the X direction shown in , each focused spot 18A is always irradiated onto a predetermined information track. The twin spot method based on the above-mentioned principle is well known as a method in which tracking offset occurs very little with respect to the displacement of the objective lens 6. The reflected light from the four central focused spots 18A irradiated onto the predetermined information track of the land portion 8 is reflected by the light receiving surface 2 of the photodetector 21.
1B to 21E are detected separately, and the information is reproduced.

In addition to the tracking error detection and correction described above, it is necessary to detect and correct focusing errors caused by surface wobbling of the information recording medium 7. This method may be performed using any of the known methods such as the astigmatism method and the knife edge method, so it will not be described here.

Example 2. In the first embodiment described above, the focusing spots for tracking error detection using the twin beam method are the spots at both ends, and the focusing spots other than the spots at both ends are used for recording and reproducing information. However, the following configuration is used. You can also use it as FIG. 5 is a perspective view of a semiconductor laser array 1 in another embodiment of the invention, and FIG. 6 is a plan view showing the arrangement of condensed spots on the information recording medium 7 surface. Among the six laser beams emitted from the semiconductor laser array 1, the two central laser beams 27 are emitted with a laser beam spacing L3 from each other, and the focused spots 27A on the surface of the information recording medium 7 are spaced with a spot spacing of d2. Thus, it is arranged at the edges of two guide grooves sandwiching one land portion 8. Next, the laser beams 28 on both sides of the two central laser beams 27 are emitted with a laser beam interval L2 from the adjacent central laser beam 27, and the laser beams 28 are separated by twice L1. . Furthermore, the two laser beams 29 at both ends are separated from the adjacent laser beam 28 by a laser beam interval L1.
It emits with. Focusing spots 28A and 29A corresponding to the other four laser beams 28 and 29 excluding the two central laser beams 27 are all arranged on the land portion 8 of the information recording medium 7. The adjacent focused spots 28A and 29A have an interval of d1 and are arranged on adjacent land portions 8 with a track pitch of P. The distance between the condensed spots 28A is twice d1, and they are arranged across one land. From the above explanation and the focused spot arrangement shown in FIG. 6, each spot interval d1
, d2 and d3 are calculated in the same way as in Example 1. d1 = P/sin i

(6) d2 = (P
-w/2)/sin i
(7) d3 = w
/sin i
(8) becomes. Also, 2*d2 +d3 = (2P
−w)/sin i+w/sin i
=2P/s
in i
=2d1
(9) holds true. Furthermore, each laser beam interval of the semiconductor laser array 1 corresponding to each spot interval is also calculated as in Example 1 using the lateral magnification M of the optical system to obtain L1.
=d1/M=P
/(M*sin i)
(10) L
2 = d2 /M =
(P-w/2)/(M*sin i)
(11) L3 = d3
/M = w/(M*
sin i)
(12) is obtained as follows. Furthermore (10)~
From formula (12), 2*L1 =
2*L2 +L3
The identity (13) is derived. In this embodiment, tracking error detection is performed using the twin spot method using the two central condensed spots 27A placed on the edge of the guide groove, and the two central condensed spots 27A placed on the land portion 8 Needless to say, information is recorded and reproduced in the other four focused spots 28A and 29A, except for 27A.

Example 3. In Examples 1 and 2 above, each laser beam of the semiconductor laser array 1 was designed to be able to emit laser light output sufficient to perform a recording operation or a recording operation accompanied by an erasing operation on the information recording medium 7. However, the two laser beams 19 or 2 used for tracking error detection using the twin spot method are
7 does not need to perform a recording operation, so it may be possible to emit at least a reproducible optical output. In the case of the semiconductor laser array described here, each laser element has the same structure, so the maximum optical output of the laser beam can be controlled by changing the reflectance of the reflective film applied to the output end face. This is common. For example, in order to obtain an optical output of 30mW or more required for recording operation, 4 to 16
% reflectance is selected, and if it is sufficient to obtain the optical output of about 5 mW necessary for reproduction operation, a reflectance of 16% or more is selected. Therefore, by forming only the emission portions of the two laser beams 19 or 27 used for tracking error detection into a reflective film with a high reflectance, it is possible to limit the maximum optical output to the reproduction optical output. Increasing the reflectance of the output end face as described above reduces the generation of return optical noise induced by the laser beam reflected by the information recording medium 7 and the like returning to the semiconductor laser array 1, and reduces the SN
A characteristic effect is that a tracking error signal with a high ratio (signal-to-noise ratio) can be obtained.

Example 4. In the first and second embodiments described above, the photodetector 21 is divided into at least the number of laser beams so as to receive each laser beam separately. It may be a split-type photodetector with light-receiving surface widths at uneven intervals corresponding to the beam spacing, and the detection of each laser beam is more accurate than a photodetector with equally spaced light-receiving surface widths. can be done.

[0022]

As described above, according to the present invention, the focused spots of any two of the plurality of laser beams are located on the same side of the information recording medium or on different sides of the two guide grooves. Using a semiconductor laser array arranged with a predetermined laser beam interval, two The tracking error signal is detected by the twin spot method from the reflected light from the edges on different sides, and information is recorded and reproduced using multiple focused spots illuminated on different land parts. When correcting tracking deviation by displacing the objective lens, there is no tracking offset, and since all information is recorded and reproduced on the land, a uniform signal level can be obtained, and the optical system is highly efficient. This has the effect of providing an optical recording/reproducing device that does not require precise assembly and adjustment.

In addition, by increasing the reflectance of the output end faces of the two laser beams used for tracking error detection and limiting the operation to the optical output for reproduction, the laser beams return to the semiconductor laser array 1 again and the induced This has the effect of suppressing the generation of return optical noise caused by the noise and obtaining a tracking error signal with a high S/N ratio.

Furthermore, since the width of the light-receiving surface of the split-type photodetector corresponds to the laser beam spacing of the semiconductor laser array, the laser beam detection is improved even though the laser beam spacing is uneven. It has the effect of being precise.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram showing an optical system of an optical recording/reproducing apparatus according to a first embodiment of the present invention.

FIG. 2 is a plan view showing the arrangement of condensing spots according to Example 1 of the present invention.

FIG. 3 is a perspective view showing a semiconductor laser array according to Example 1 of the present invention.

FIG. 4 is a characteristic diagram of an optical system, a reflected light amount curve, and a tracking error signal for explaining the principle of the twin spot method according to the first embodiment of the present invention.

FIG. 5 is a perspective view showing a semiconductor laser array according to Example 2 of the present invention.

FIG. 6 is a plan view showing the arrangement of condensing spots according to Example 2 of the present invention.

FIG. 7 is a plan view showing an optical system of a conventional optical recording/reproducing device.

FIG. 8 is a plan view showing the arrangement of condensing spots in a conventional example.

FIG. 9 is an explanatory diagram showing the displacement of an optical system and a light spot on a photodetector to explain the problems of the conventional push-pull method.

[Explanation of symbols] 1 Semiconductor laser array 6 Objective lens 7 Information recording medium 8 Land part 9 Guide groove 18 Laser beam 18A Light focus spot 19 Laser beam 19A Light focus spot 21 Photodetector 22 Differential amplifier 26A　Light focus spot 26B Light focus spot 27 Laser beam 27A　Light focus spot 28 Laser beam 28A　Light focus spot 29 Laser beam 29A Light focus spot

Claims (6)

[Claims] Claim 1: At least four or more laser beams are focused and irradiated onto the surface of an information recording medium provided with a guide groove using a semiconductor laser array, and the reflected light is used for photodetection having a plurality of light receiving surfaces. An optical recording/reproducing system configured to perform tracking control by detecting each component separately, and to record and reproduce information in parallel by condensing the remaining laser beam onto the land at regular intervals. In the apparatus, the condensed spots formed by any two of the at least four laser beams are located at edges on different sides of a single or two different guide grooves of the information recording medium. The beam spacing of each beam is such that a focused spot formed from the remaining laser beams is focused and irradiated on each separate land portion of the information recording medium, and An optical recording/reproducing device characterized by comprising means for detecting a tracking error signal from light reflected from an edge and performing tracking adjustment. 2. The optical recording/reproducing apparatus according to claim 1, wherein the two laser beams are laser beams at both ends of the semiconductor laser array. 3. The optical recording/reproducing apparatus according to claim 1, wherein the two laser beams are two central laser beams of the semiconductor laser array. 4. The optical recording/reproducing apparatus according to claim 1, wherein all the laser beams of the semiconductor laser array have optical output necessary for recording or erasing information. 5. The remaining laser beam of the semiconductor laser array has an optical output necessary for recording or erasing information, and the reflectance at the emission end face of the two laser beams is such that the remaining laser beam has an optical output necessary for recording or erasing information, and 2. The optical recording/reproducing device according to claim 1, wherein the reflectance is higher than the reflectance at the output end face. 6. In the photodetector that separately detects each laser beam of the semiconductor laser array reflected by the information recording medium, the width of a plurality of light receiving surfaces is unequally spaced from the laser beams of the semiconductor laser array. The optical recording and reproducing apparatus according to claim 1, characterized in that the optical recording and reproducing apparatus corresponds to the interval.