JPH04258821A - Optical head - Google Patents

Abstract

PURPOSE:To correct the difference in wavelength between two laser beams in an optical head which records and reproduces information utilizing two laser beams. CONSTITUTION:A semiconductor laser 20 emits the laser beam with first wavelength and a conductor laser 29 emits the laser beam with second wavelength. A wavelength selecting mirror 24 synthesizes the laser beam with the first wavelength and the laser beam with the second wavelength and feeds it to an objective lens 25. A concave lens 26 is arranged between the wavelength selecting mirror 24 and a beam splitter 27 and correct the out-of-focus due to the difference in the wavelength by slightly diffusing the laser beam with the second wavelength.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a file device for optically recording and reproducing information, and more particularly to an optical head for recording and reading by focusing a light beam onto a record carrier.

0002

[Prior art] A laser beam is focused and irradiated onto a record carrier,
Optical information recording and reproducing device that records and reproduces information (
2. Description of the Related Art Optical disk devices (optical disk devices) are attracting attention as file devices that record extremely high-density, large-capacity information using focused laser light. In this optical disk device, an optical head that focuses a laser beam and irradiates it onto a record carrier and captures the reflected light from the record carrier plays an extremely important role.

Conventionally, an optical head emits only one light beam (focused light) because laser light sources are expensive and the optical system for accurately irradiating multiple beams onto the recording surface is complicated. It is. In other words, even with an optical head that performs both recording and reproduction, the number of light beams irradiated onto the recording surface is 1.
It is a book, and information is recorded and reproduced by emitting high-power light during recording, and by emitting low-power light that does not affect the recording surface during reading.

On the other hand, optical recording is not necessarily stable enough and there are defects on the recording surface, so it is necessary to verify whether recording has been performed reliably.
For this purpose, it is necessary to perform a read check operation after recording. In conventional one-beam optical heads, the same beam is used for recording and reproduction, so information must be read after recording.

On the other hand, for example, Japanese Patent Laid-Open No. 59-586
As described in the specification of No. 38, if an optical head having multiple irradiation beams is used, one beam is used for recording and the other beams are used for reproduction, so that recording and recording can be performed almost simultaneously. The recorded information can be confirmed, and the recording processing speed of the optical disc device is significantly improved.

However, as in the above example, in a multi-beam optical head, the wavelengths of the two beams are made different in order to separate the light beams, and a wavelength-selective mirror (dichroic mirror) is used to separate the two beams. Generally, a method is required to combine the two beams and separate the two beams for the reflected light.

[0007]

[Problems to be Solved by the Invention] In the above-mentioned optical head that emits a plurality of (two or more) light beams, two light beams (laser lights) with different wavelengths are focused and irradiated onto the recording surface. A lens for focusing (objective lens)
has the problem that chromatic aberration exists and the focal points of the two beams do not match. That is, even if two beams with different wavelengths are similarly incident on the objective lens, the focusing positions are different, and therefore both beams cannot be accurately focused on the recording surface.

In order to solve this problem, it is necessary to shift one laser beam from a completely parallel state (collimated beam) before entering the objective lens, but if you try to do this on the laser light source side, the adjustment will be necessary. In addition, the problem arises that the optical system for passing the beam cannot necessarily be optimally set.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical head that can eliminate such drawbacks, easily correct lens chromatic aberration, and adjust the spot positions of two light beams.

0010

[Means for Solving the Problems] The present invention provides an optical head for recording information by focusing and irradiating a record carrier with a laser beam, and for reading the recorded information.
a first semiconductor laser that emits a laser beam having a wavelength of , a second semiconductor laser that emits a laser beam of a second wavelength different from the first wavelength, and a laser beam of the first wavelength a dichroic mirror for combining the laser beam of a second wavelength; and a focusing lens for focusing the laser beam of the second wavelength combined by the dichroic mirror onto the surface of the recording carrier, respectively; a lens for correcting chromatic aberration of the focusing lens due to a wavelength shift between the first wavelength and the second wavelength incident on the dichroic mirror, and the lens mainly uses laser light of the first wavelength. It is characterized in that it is used for recording information, and a laser beam of a second wavelength is used for reading out the recorded information.

[0011]

Embodiments Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, the optical head 2 is the present embodiment. In this embodiment, a laser beam is focused on the record carrier 1 and the reflected light is received. And, in this example,
Recording laser drive circuit 10 and readout laser drive circuit 1
1, a read amplifier 12, and differential amplifiers 13 and 14 are connected.

In this embodiment, semiconductor lasers 20, 29
, collimating lenses 21 and 28, polarizing beam splitter 22, λ/4 plate 23, wavelength selection mirror 24,
It includes an objective lens 25, a concave lens 26, a beam splitter 27, a photodetector 30, a half mirror 31, a lens 32, a knife edge 33, a focus error detector 34, and a track error detector 35. There is.

In this embodiment, the semiconductor laser 2
Reference numeral 9 emits a laser beam having a wavelength different from that of the laser beam emitted by the semiconductor laser 20 .

The collimating lenses 21 and 28 convert the laser beams from the semiconductor lasers 20 and 29 into parallel beams.

The polarizing beam splitter 22 sends the laser beam from the collimating lens 21 to the λ/4 plate 23 . Further, the laser beam from the λ/4 plate 23 is bent and sent to the half mirror 31.

Beam splitter 27 sends the laser beam from collimating lens 28 to concave lens 26 . Further, the laser beam from the concave lens 26 is bent and sent to the photodetector 30.

The λ/4 plate 23 changes the linear polarization state of the incident light beam into circular polarization.

The wavelength selection mirror 24 combines and separates laser beams of two wavelengths.

The concave lens 26 functions to diffuse the laser light that has passed through the beam splitter 27.

The half mirror 31 separates the laser beam from the deflection beam splitter 22.

The photodetector 30 converts the laser beam from the beam splitter 27 into an electrical signal and sends it to the readout amplifier 1.
Send to 2. The focus error detector 34 converts the laser light emitted from the half mirror and passes through the lens 32 and the knife edge 33 into an electrical signal, and converts the laser light into an electrical signal.
send to The track error detector 35 includes a half mirror 3
Converts the laser light from 1 into an electrical signal.

Next, the operation of this embodiment will be explained.

A semiconductor laser 20 that generates laser light of a first wavelength mainly for recording is connected to a recording laser drive circuit 10 and supplied with a current for light emission. The recording laser drive circuit 10 receives a recording signal 105 indicating information to be recorded on the record carrier 1, and supplies a current for power modulating the light emission of the semiconductor laser 20 in a corresponding timing pattern. The light emitted from the semiconductor laser 20 is
The collimating lens 21 converts the divergent light into a parallel beam (collimated light). The polarizing beam splitter 22 is
This is for separating the incident light flux according to the polarization state, and allows the parallel light from the collimating lens 21 to pass through as it is and enter the λ/4 plate 23. λ/4 plate 23
changes the linear polarization state of the incident light beam to circular polarization. The wavelength selection mirror 24 is for combining and separating light of two wavelengths, and transmits the laser light of the first wavelength generated by the semiconductor laser 20, and transmits the laser light of the first wavelength generated by the semiconductor laser 29. It has the property of reflecting laser light of the second wavelength.

The light beams combined by the wavelength selection mirror 24 enter the objective lens 25 and are focused by the objective lens 25 to form two light spots on the recording surface of the record carrier 1. The laser beam spot of the first wavelength from the semiconductor laser 20 records information by altering the recording surface of the record carrier 1, and is also used for detecting defocus and tracking displacement with respect to the recording surface.

The two beams reflected by the surface of the record carrier 1 pass through the objective lens 25 again, return to a parallel beam, and enter the wavelength selection mirror 24 . The laser beam of the first wavelength passes through the wavelength selection mirror 24 and returns to the λ/4 plate 23. By passing through the λ/4 plate 23, the reflected laser beam has a polarization direction of 90° compared to when it is directed toward the record carrier 1.
° (orthogonal) Changed linear polarization is corrected. The polarizing beam splitter 22 reflects this reflected light whose polarization direction has changed, and bends its optical path in a direction toward the half mirror 31. The half mirror 31 is used to separate reflected light in intensity for focus error detection and tracking error detection, and directs one of the separated lights to the track error detector 35 and directs the other light to the track error detector 35. is directed toward the focus error detector 34.

The focus error detection system includes a lens 32.
and a knife edge 33 are arranged to constitute a knife edge type focus error detection system. Note that the knife-edge type detection system is shown only as an example, and the optical head of the present invention is not limited to this configuration.

The focus error detector 34 is composed of a photodetector (photodetector) divided into at least two parts, and a focus error signal 102 is obtained by amplifying the output thereof with the differential amplifier 13. Further, the tracking error detector 35 is also constituted by a photodetecting element divided into at least two parts, and detects a tracking deviation by detecting a change in the intensity distribution of reflected light due to a tracking guide groove formed on the record carrier 1. By amplifying the output of the track error detector 35 with the differential amplifier 14, a track error signal 103 is obtained. In addition,
Since the sum signal of the output of the track error detector 35 or the focus error detector 34 indicates a change in the reflectance of the record carrier 1, by amplifying these sum signals, the reflectance on the recording surface of the record carrier 1 can be changed. It is also possible to read out information recorded in a changing form.

On the other hand, a semiconductor laser 29 that generates a laser beam of a second wavelength for reading out is connected to the reading laser drive circuit 11, and a current for emitting a constant amount of laser beam for reading is connected to the reading laser drive circuit 11. Supplied. Similar to the laser light of the first wavelength, the diverging laser light from the semiconductor laser 29 is converted into parallel light (collimated light) by the collimating lens 28 . The beam splitter 27 is for separating the light directed toward the record carrier 1 and the light reflected by the record carrier 1, but it is necessary to ensure that the optical path efficiency of the read light beam is as high as that of the recording light. Since there is no polarizing beam splitter, it may be a simple intensity-separating half mirror instead of a polarizing beam splitter. Since the reflected light is not separated based on the difference in polarization state, the λ/4 plate 23 used in the recording optical system is not particularly arranged in the reading optical system.

The laser beam of the second wavelength transmitted through the beam splitter 27 enters the concave lens 26. concave lens 2
6 is for correcting chromatic aberration between the laser beams of the first wavelength and the second wavelength in the objective lens 25. That is, when the laser beam of the second wavelength generated by the semiconductor laser 29 has a shorter wavelength than the laser beam of the first wavelength generated by the semiconductor laser 20, the focal length of the objective lens 25 is set to the second wavelength.
It is slightly shorter than the wavelength of laser light. On the other hand, in order to perform optical recording and reproduction, it is necessary that the two light beams are correctly focused on the recording surface. Therefore, it is necessary to make the short wavelength laser light slightly diffusive before it enters the objective lens 25 so as to correct the difference in focal length due to the difference in wavelength. The concave lens 26 functions to make the parallel laser beam of the second wavelength that has passed through the beam splitter 27 slightly diffusive.

Conventionally, in order to make the beam diffusive, means such as slightly shifting the adjustment of the collimating lens 28 have been considered, but this method has the disadvantage that adjustment is difficult and reproducibility is poor. The optical head of the present invention is characterized by the fact that the chromatic aberration caused by the objective lens 25 is constant, and a lens 26 having a focal length that corrects the chromatic aberration is inserted into the optical path of the laser beam of the second wavelength. . By inserting this concave lens 26, not only can chromatic aberration be easily corrected, but also the lens 2
By adjusting the position in the direction perpendicular to the optical axis of the laser beam No. 6, the position of the laser beam spot of the second wavelength on the recording surface can be adjusted.

The laser beam that has passed through the concave lens 26 is incident on the wavelength selection mirror 24 . The wavelength selection mirror 24 reflects the laser beam of the second wavelength and directs it to the objective lens 25 together with the laser beam of the first wavelength that passes through the mirror. The laser beam spot of the second wavelength focused by the objective lens 25 is positioned behind the laser beam spot of the first wavelength with respect to the traveling direction of the record carrier 1 (disk rotation direction), and the laser beam spot of the second wavelength is focused by the objective lens 25. The function is to read out the information recorded by the laser beam immediately after recording.

The light reflected from the recording surface passes through the objective lens 2.
5 and returns to the wavelength selection mirror 24. The wavelength selection mirror 24 reflects the light of the second wavelength and directs it toward the concave lens 26 . The light of the second wavelength that has passed through the concave lens 26 and returned to the original parallel beam is directed by the beam splitter 27 to a photodetector 30 . The photodetector 30 detects information recorded on the record carrier 1 by receiving the reflected light of the second wavelength laser beam that has returned through such a path.

In the configuration of this embodiment, information recorded by changes in brightness and darkness is read out by changes in reflected light intensity. However, when a magneto-optical recording medium is used as the record carrier 1, optical detection is required. By placing a polarizer or the like in front of the device 30, it is also possible to detect magneto-optical signals. A readout signal 101 is obtained by amplifying the output of the photodetector 30 with the readout amplifier 12. This readout signal 101 is obtained as a reproduction signal of the data immediately after data is recorded on the recording surface by the laser beam of the first wavelength, and reproduction can be performed almost simultaneously with recording, thereby preventing recording defects. can be detected instantly.

FIG. 2 is a diagram showing in more detail the positional relationship of the light spots on the recording surface produced by the optical head 2 shown in FIG. 1. As shown in FIG. The objective lens 25 includes a laser beam 2 having a first wavelength.
01 and a laser beam 202 having a second wavelength are focused to form a minute optical spot on the recording surface 40. At this time, by slightly shifting the angle of incidence of the first wavelength laser beam 201 and laser beam 202 on the objective lens 25, the light spots of the two laser beams are positioned slightly apart from each other on the recording surface 40. It is formed. Light spot 21 by first laser beam 201 for recording information
1 is intensity-modulated according to the information to be recorded, and the recording surface 4
Information is recorded by altering 0. Light spot 212 by second laser beam 202 for reading information
is formed behind the recording light spot 211 when viewed from the moving direction of the record carrier 1 (disc rotation direction), and reads out the information recorded by the recording light spot 211 with a slight delay time.

Since the interval between the light spots 211 and 212 determines the delay time from recording to reading, the positional relationship must be adjusted accurately. Furthermore, as a matter of course, the optical spots 211 and 212 must be placed on the same recording track. For this reason, light spot 2
The positional relationship between 11 and 212 needs to be adjusted extremely precisely.

As mentioned above, the light spots 211 and 21
The positional relationship between the two is determined by the difference in the inclination of the optical axes of the laser beams 201 and 202 that enter the objective lens 25. Therefore, by adjusting the in-plane position of the concave lens 26 in the direction perpendicular to the optical axis, the position of the optical spot 212 can be subtly adjusted by slightly changing the inclination of the laser beam 202 of the second wavelength. . The concave lens 26 is for eliminating slight chromatic aberration between two wavelengths, and has a relatively long focal length. Therefore, the movement of the concave lens 26 is reduced to the movement of the light spot 212, and extremely minute positional adjustments can be easily made.

FIG. 3 is a diagram showing an example of waveforms when recording information and reading information immediately after recording using the optical head of this embodiment. Waveform A shows changes in the recording signal 105, and waveform B shows changes in the read signal 101. Recording signal 10
5 is input, the recording laser drive circuit 10 supplies a modulation current corresponding to this to the semiconductor laser 20. The semiconductor laser 20 receives this modulation current (i.e., the recording signal 105
), and information is recorded on the record carrier 1 by emitting a laser beam having a first wavelength and an intensity corresponding to the wavelength. On the other hand, the readout laser drive circuit 11 always supplies a current for emitting light with a constant power to the semiconductor laser 29, and the semiconductor laser 29 emits laser light of the second wavelength for readout. By capturing and amplifying changes in the amount of reflected laser light of this second wavelength, a read signal 101 for reproducing a recorded signal immediately after recording is obtained. The time delay td from recording to reading is determined by the moving speed V of the record carrier 1 and the distance D between the two light spots 211 and 212,
It is given by td=D/V.

In the embodiment, a concave lens is used as the lens for correction, but if the wavelength or the chromatic aberration of the objective lens is different, it is also possible to use a convex lens.

In this way, the optical head of this embodiment has the following features:
a first semiconductor laser that emits a laser beam with a first wavelength; a second semiconductor laser that emits a laser beam with a second wavelength different from the first wavelength; and lasers with the first and second wavelengths. A dichroic mirror that combines light, a focusing lens that focuses the two laser beams combined by the dichroic mirror, and a laser beam of the second wavelength placed before it enters the dichroic mirror. The lens is equipped with a lens for correcting chromatic aberration of the focusing lens due to the difference between the first and second wavelengths, and by inserting the chromatic aberration correction lens, the focal point (focusing position) due to the difference between the two wavelengths can be easily adjusted. Discrepancies can be eliminated.

Furthermore, not only can it be easily realized to accurately focus the two beams on the recording surface, but also the relative position of the second beam in the recording surface direction (beam lateral direction) with respect to the first beam can be easily realized. A two-beam (multiple beam) irradiation head that can be easily adjusted and is highly practical can be obtained.

[0042]

As explained above, the present invention provides an optical head that emits a plurality of beams with different wavelengths, and a lens for correcting chromatic aberration between the different wavelengths is attached to the optical path of the laser beam of the second wavelength. By arranging the chromatic aberration, it is possible to easily obtain an optical head in which chromatic aberration is corrected.

Furthermore, by moving the position of the lens for correcting chromatic aberration, it is possible to easily and accurately adjust the positional relationship between the two light beam spots. By using the optical head of the present invention, it is expected that reproduction immediately after recording can be easily realized, and an optical disc device that is highly reliable and capable of high-speed processing will be realized.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing in detail the positional relationship of light spots on a recording surface by the optical head shown in FIG. 1;

FIG. 3 is a diagram showing an example of waveforms when recording information and reading information immediately after recording with the optical head of FIG. 1;

[Explanation of symbols]

1 Record carrier 2 Optical head 10 Recording laser drive circuit 11 Readout laser drive circuit 12 Readout amplifier 13,14 Differential amplifier 20 Semiconductor laser 21 Collimating lens 22 Polarizing beam splitter 23　λ/4 plate 24 Wavelength selection mirror 25 Objective lens 26 Concave lens 27 Beam splitter 28 Collimating lens 29 Semiconductor laser 30 Photodetector

Claims (1)

[Claims] Claims: 1. An optical head for recording information by focusing and irradiating a record carrier with laser light and reading the recorded information, a first semiconductor that emits a laser light having a first wavelength. a laser; a second semiconductor laser that emits a laser beam of a second wavelength different from the first wavelength; and a laser beam for combining the laser beam of the first wavelength and the laser beam of the second wavelength. a dichroic mirror, a focusing lens for focusing laser beams of a second wavelength synthesized by the dichroic mirror onto the recording carrier surface, and a laser beam of the first wavelength that is incident on the dichroic mirror; a lens for correcting chromatic aberration of the focusing lens due to wavelength shift between the second wavelengths, the laser beam of the first wavelength is mainly used for recording information, and the laser beam of the second wavelength is used for recording information; An optical head that uses light to read recorded information.