JP2004272949A - Optical head and optical information recording/reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a quantum noise of a light source to be sufficiently lowered by changing over an intensity filter in accordance with the result of a discrimination which is made for discriminating disks having the different kind of laser powers at the recording and reproducing operation. <P>SOLUTION: A transmitted light quantity varying means is furnished for changing the light quantity reached to the optical information recording medium from the semiconductor laser in accordance with the identification information of the kind of the optical information recording medium. It is characterized that when the above identification information shows a 1st optical information recording medium, the light emitted from the semiconductor laser is used as it is, and when the identification information shows a 2nd optical information recording medium, a D range of the recording and reproducing of the light power emitted from the objective lens is arranged to be expanded without changing the D range of the light power emitted from the semiconductor laser by means of reducing the light quantity emitted from the semiconductor laser by the 2nd transmitted light quantity varying means in the process of recording operation. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical head and an optical information recording / reproducing apparatus used for optical information processing or optical communication.
[0002]
[Prior art]
2. Description of the Related Art In recent years, digital versatile discs (DVDs) have attracted attention as large-capacity optical information recording media because they can record digital information at a recording density approximately six times that of compact discs (CDs).
[0003]
However, with the increase in the capacity of information, a higher density optical information recording medium has been demanded. Here, in order to achieve higher density than DVD (wavelength 660 nm, numerical aperture (NA) 0.6), it is necessary to shorten the wavelength of the light source and increase the NA of the objective lens. For example, when a blue laser of 405 nm is used and an objective lens of NA 0.85 is used, a recording capacity five times that of DVD is achieved. In addition, in order to obtain twice the recording density by increasing the output of a blue laser in recent years, a multi-layer disc having a plurality of recording / reproducing layers has been developed in addition to a so-called single-layer disc having a single recording / reproducing layer. Has been done. For example, if a disk having two recording layers, such as a DVD dual-layer disk, becomes possible, it is possible to achieve a storage capacity about 10 times that of a DVD.
[0004]
However, in the optical information recording / reproducing apparatus for recording / reproducing a high-density optical disk using the above-described blue laser, the reproduction margin is very strict, so that the quantum noise of the light source becomes a problem. Therefore, an optical head that can suppress the noise of a semiconductor laser and perform high-quality reproduction with low noise while suppressing the optical disk surface power low to prevent deterioration of the optical disk and data erasure, etc. Proposed in reference 1.
[0005]
Here, an example of the above-described conventional optical head will be described with reference to the drawings. FIG. 5 is a schematic diagram showing a configuration of a conventional optical head. Here, 161 is a light source, 162 is an intensity filter, 163 is a beam splitter, 164 is a collimator lens, 165 is a mirror, 166 is an objective lens, 167 is an optical disk, 168 is a multi-lens, and 169 is a photodiode.
[0006]
The light source 161 is a GaN-based blue-emitting semiconductor laser that outputs coherent light for recording and reproduction to the recording layer of the optical disk 167. The intensity filter 162 is an element on which an absorption film is formed, and is provided so as to be able to be taken in and out. The beam splitter 163 is an optical element for separating light, the collimator lens 164 is a lens that converts divergent light emitted from the light source 161 and reflected by the beam splitter 163 into parallel light, and a mirror 165 converts incident light. The objective lens 166 is a lens for condensing light on the recording layer of the optical disc 167, and the multi-lens 168 is a lens for condensing light on the photodiode 169. The photodiode 169 receives light reflected by the recording layer of the optical disc and converts the light into an electric signal.
[0007]
The operation of the optical head thus configured will be described. Here, the intensity filter 162 is inserted in the optical path at the time of reproduction, and is out of the optical path at the time of recording. The light emitted from the light source 161 is partially absorbed by the absorption film of the intensity filter 162 at the time of reproduction, so that the light amount is attenuated. At the time of recording, the intensity filter 162 is out of the optical path. Not attenuated. Next, the light transmitted through the intensity filter 162 (light emitted from the light source at the time of recording) is reflected by the beam splitter 163 and is converted by the collimator lens 164 into parallel light. The collimated light is reflected by the mirror 165 and is collected on the optical disk 167 by the objective lens 166.
[0008]
Next, the light reflected from the optical disk 167 passes through the objective lens 166, is reflected by the mirror 165, passes through the collimator lens 164, passes through the beam splitter 163, and is focused on the photodiode 169 by the multi-lens 168. . The photodiode 169 outputs a focus error signal indicating a focused state of light on the optical disk 167 using an astigmatism method, and outputs a tracking error signal indicating a light irradiation position.
[0009]
A focus control unit (not shown) controls the position of the objective lens 166 in the optical axis direction based on the focus error signal so that the light is always focused on the optical disk 167 in a focused state. A tracking control unit (not shown) controls the position of the objective lens 166 based on the tracking error signal so that the light is focused on a desired track on the optical disc 167. Further, the photodiode 169 reproduces information recorded on the optical disk 167.
[0010]
With such a configuration, at the time of reproduction, the power of the light source is set to a power at which the quantum noise is sufficiently reduced, and the reproduction is performed while suppressing the surface power of the board to a low power at which deterioration of the optical disk and erasure of data do not occur. At the time of recording, recording can be performed using the power of the light source as it is.
[0011]
[Patent Document 1]
JP 2000-195086 A
[0012]
[Problems to be solved by the invention]
However, in the optical head having the above configuration, it is necessary to insert and remove an intensity filter when switching between recording and reproduction, and when recording is performed instantly after address reproduction, the speed at which the intensity filter is inserted and removed becomes a problem. . For example, a next-generation high-density optical disk having a higher density than a DVD requires switching of about 100 ns. However, the switching can be performed in the above-mentioned time not only by mechanical insertion and removal as in the conventional example but also by using a liquid crystal element or the like. It is difficult.
[0013]
In addition, the performance of semiconductor lasers has been improved every day, and if the recording sensitivity is one type of optical information recording medium, a quantum laser with sufficiently reduced quantum noise at the time of reproduction can be obtained, especially without performing attenuation by an intensity filter at the time of reproduction. can do. However, when trying to record and reproduce optical information recording media having different recording sensitivities, for example, a single-layer disc and a double-layer disc, respectively, with the same head, the reproduction and recording of a double-layer disc is about twice as large as that of a normal single-layer disc. Although power is required, it has been difficult to reduce quantization noise during reproduction of a single-layer disc while securing the recording power of a two-layer disc.
[0014]
The present invention has been made in view of such conventional problems, and discriminates discs of different types in laser power during recording and reproduction, and switches the intensity filter based on the discrimination result. Accordingly, the object is to suppress the quantum noise of the light source sufficiently low.
[0015]
As a result, an object of the present invention is to extend the D range for recording and reproducing the optical power emitted from the optical head without changing the D range for recording and reproducing the optical power emitted from the semiconductor laser.
[0016]
Further, when a disc having high recording sensitivity, that is, a disc having a small laser power at the time of recording, for example, a dual-layer disc and a single-layer disc and two types of discs are interchangeably recorded and reproduced, the power output from the laser in the case of a single-layer disc The purpose is to extend the laser life by switching the intensity filter during recording so that the majority of the time is small.
[0017]
[Means for Solving the Problems]
The optical head of the present invention irradiates the optical information recording medium with light emitted from a semiconductor laser through an objective lens, guides reflected light from the optical information recording medium to a photodetector, An optical head that reads out the signal of the optical information recording medium, further comprising a transmitted light amount varying unit that changes an amount of light reaching the optical information recording medium from the semiconductor laser according to the identification information of the type of the optical information recording medium, wherein the identification information is When the identification information is the second optical information recording medium, the light emitted from the semiconductor laser is used as it is. By reducing the amount of light emitted from the semiconductor laser, the light power emitted from the objective lens can be changed without changing the output width of the optical power emitted from the semiconductor laser. Characterized in that so as to widen the output range of the recording and reproduction.
[0018]
Further, the transmission light amount varying means is configured to combine a liquid crystal element and a polarization hologram.
[0019]
Further, the transmission light amount varying means has a configuration in which a liquid crystal element and a polarization beam splitter are combined.
[0020]
Further, the transmission light amount varying means is adapted to enter and exit the optical path of the emitted light of the semiconductor laser.
[0021]
Further, the light source is a semiconductor laser capable of emitting light in a wavelength range from green to ultraviolet.
[0022]
Further, the light source is a semiconductor laser capable of emitting light in a blue wavelength region.
[0023]
An optical information recording / reproducing apparatus according to the present invention includes an optical head according to any one of the above, a discriminating unit for identifying a type of the optical information recording medium, and a semiconductor for controlling a beam light amount of light emitted from a semiconductor laser of the optical head. A laser driving circuit, and a transmission light amount variable circuit for attenuating the light amount of the beam of the emitted light from the semiconductor laser by the transmission light amount changing means of the optical head, wherein the transmission light amount variable circuit uses the transmission light amount changing means. Accordingly, when the identification information by the discriminating means is the first optical information recording medium, the light emitted from the semiconductor laser is used as it is, and the identification information by the discriminating means is the second optical information recording medium. In this case, the light quantity emitted from the semiconductor laser is reduced by the transmitted light quantity varying means, so that the optical power emitted from the semiconductor laser is reduced. Characterized in that so as to widen the output range of the recording and reproducing of the optical power emitted from without the objective lens varying the output width over.
[0024]
Further, the identification information of the optical information recording medium by the determination means is the number of recording layers of the optical information recording medium.
[0025]
Further, the discriminating means distinguishes an optical information recording medium having one recording layer and an optical information recording medium having two recording layers among types of recording layers of the optical information recording medium. .
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0027]
(Embodiment 1)
In the first embodiment, an example of the optical disk device of the present invention will be described.
[0028]
FIG. 1 is a configuration diagram of the optical disk device according to the first embodiment.
[0029]
In FIG. 1, reference numeral 1 denotes a light source, for example, a semiconductor laser. 2 is a beam splitter, 3 is a light beam attenuating optical element corresponding to a transmitted light amount varying means, 4 is a diffraction grating, 5 is a polarization beam splitter, 6 is a collimator lens, 7 is a mirror, 8 is an objective lens, and 9 is optical information recording. Medium (or disk), 10 is a first condenser lens, 11 is a second condenser lens, 12 is a first photodetector, 13 is a second photodetector, 14 is a third light A detector, 15 is a light amount control circuit corresponding to the semiconductor laser drive circuit, 16 is an optical element control circuit corresponding to the transmitted light amount variable circuit, and 17 is a quarter wavelength plate.
[0030]
Here, the condensing optical system is composed of a collimator lens 6 and an objective lens 8, the light quantity control means is composed of a first photodetector 12 and a light quantity control circuit 15, and the optical element control means is , The second photodetector 13 and the optical element control circuit 16, and the polarization splitting means includes the polarization beam splitter 5 and the 波長 wavelength plate 17. Reference numeral 18 denotes a command circuit for controlling the optical disk device, 19 a comparator circuit for disc discrimination, and 20 a reflectance detection means corresponding to discrimination means for disc discrimination.
[0031]
Here, the light source 1 is a light source composed of a GaN-based semiconductor laser element (wavelength: 405 nm) and outputting coherent light for recording and reproduction to the recording layer of the optical information recording medium 9. The beam splitter 2 is an optical element having a transmittance of 90% and a reflectance of 10%. The light beam attenuating optical element 3 is an optical element whose transmittance is changed by an external signal by a liquid crystal element and a polarization hologram. The diffraction grating 4 is a grating formed by patterning a desired pattern on a glass surface using photolithography and etching the same. The characteristics thereof are such that the 0th-order diffraction efficiency is approximately 90% and the ± 1st-order diffraction efficiency is approximately 10%. . The polarization beam splitter 5 is an optical element that transmits 90% of linearly polarized light emitted from the light source 1, reflects 10% of the linearly polarized light, and reflects 100% of linearly polarized light in a direction orthogonal to the linearly polarized light emitted from the light source 1.
[0032]
The collimator lens 6 is a lens that converts divergent light emitted from the light source 1 into parallel light. The mirror 7 is an optical element that reflects incident light and directs the light toward the optical information recording medium 9. The objective lens 8 is a lens that focuses light on the recording layer of the optical information recording medium 9. The first condenser lens 10 is a lens that condenses a part of the light emitted from the light source 1 and transmitted through the light beam attenuation optical element 3 to the second photodetector 13. The second condenser lens 11 is a lens that condenses the light reflected by the optical information recording medium 9 on the third photodetector 14. The first, second, and third photodetectors 12, 13, and 14 receive light and convert the light into an electric signal.
[0033]
The operation of the optical head thus configured will be described with reference to FIG. The linearly polarized light emitted from the light source 1 enters the first beam splitter 2. The light reflected by the beam splitter 2 enters the first photodetector 12, and the transmitted light enters the light beam attenuating optical element 3. Here, the light incident on the first photodetector 12 is converted into an electric signal, which becomes an electric signal for monitoring the amount of light emitted from the light source 1, and this signal is input to the light amount control circuit 15 and the optimum light amount (The light amount of the light source 1 is controlled by the light amount control means). Next, when the optical information recording medium 9 is a single-layer disk, the amount of light transmitted through the beam splitter 2 and incident on the light beam attenuating optical element 3 is attenuated to about 50%, In that case, the light quantity is not attenuated (this will be described later in detail). Most of the light transmitted through the light beam attenuating optical element 3 is transmitted by the diffraction grating 4 and partly diffracted.
[0034]
Light transmitted through the diffraction grating 4 (both transmitted light and diffracted light) is incident on the polarization beam splitter 5. The light reflected by the polarization beam splitter 5 is incident on the first condenser lens 10 and is incident on the second photodetector 13 by the condenser lens 10. The light transmitted through the polarization beam splitter 5 is incident on a collimator lens 6. Here, the signal output from the second photodetector 13 is such that the light quantity of the light emitted from the light source 1 is controlled by the first photodetector 12 and the light quantity control circuit 15. This is a signal obtained by monitoring the transmittance of the attenuation optical element 3. Therefore, this signal is input to the optical element control circuit 16 and is controlled by the optical element control circuit 16 so that the transmittance of the light beam attenuating optical element 3 is optimized (optical element control means controls the light beam attenuating optical element 3). Is controlled). The light incident on the collimator lens 6 is collimated by the collimator lens 6. The light transmitted through the collimator lens 6 is converted into circularly polarized light by the quarter-wave plate 17, reflected by the mirror 7, travels in a direction bent by 90 degrees from the traveling direction, and collected on the optical information recording medium 9 by the objective lens 8. Is lighted.
[0035]
Next, the light reflected from the optical information recording medium 9 is transmitted through the objective lens 8, reflected by the mirror 7, converted into linearly polarized light orthogonal to the outward path by the ４ wavelength plate 17, and transmitted through the collimator lens 6. Then, the light is reflected by the polarization beam splitter 5, condensed by the second condenser lens 11, and made incident on the third photodetector 14. The third photodetector 14 outputs a focus error signal indicating a focus state of light on the optical information recording medium 9 and outputs a tracking error signal indicating a light irradiation position. In this case, for example, a phase error method is used for a read-only optical information recording medium, and a tracking error signal is obtained by a three-beam method using a sub-beam created by the diffraction grating 4 for a recording optical information recording medium. Focus control means (not shown) controls the position of the objective lens 8 in the optical axis direction based on the focus error signal so that light is always focused on the optical information recording medium 9 in a focused state. . Further, a tracking control means (not shown) controls the position of the objective lens 8 based on the tracking error signal so that the light is focused on a desired track on the optical information recording medium 9. Further, information recorded on the optical information recording medium 9 is also obtained from the third photodetector 14.
[0036]
Here, the control of the light beam attenuation optical element 3 of the present invention will be described in detail. FIG. 2 shows three typical examples of the relationship between the output of the GaN-based semiconductor laser device and the quantization noise of the laser. In recent years, increasing the output of GaN-based semiconductor lasers has been actively reported, and those having a peak output exceeding 50 mW have been reported. When the peak output exceeds 50 mW, 50 mW × 25% = 12.5 mW as the peak value of the output power from the objective lens even in a general head optical transmittance, that is, an optical head having a laser output efficiency of about 25%. Can be obtained, and recording and reproduction of a so-called two-layer disc can be performed. At that time, the output from the objective lens of about 0.8 mW or less is required as the reproduction power of the dual-layer disc from the viewpoint of preventing the deterioration of the reproduction light.
[0037]
These required powers are values specific to an optical information recording / reproducing system using an objective lens with a NA of 0.85 and an optical disk corresponding thereto using a laser beam having a wavelength of 405 nm. In an optical information recording / reproducing system having a short NA and a large NA, the energy density of a spot on the optical disk is high, so that the optical information recording / reproducing system has a small optical disk compared to a conventional system having a wavelength of 780 nm and an NA of 0.45 as in a conventional MD system. Will be recorded and played back. In the case of the present embodiment, the recording power on the optical disk is 6 mW, the reproducing power is 0.4 mW, and the recording power on the optical disk is 2 in the single-layer disk based on our various experimental results. The reproducing power was set at 12 mW and the reproducing power was set at 0.8 mW. The recording / reproducing power of the double-layer disc is about twice that of the single-layer disc because the transmittance of the layer (hereinafter referred to as L0 layer) on the side near the objective lens of the double-layer disc is about 50%. Because it was set.
[0038]
When the output power from the objective lens is about 0.8 mW, the output light from the GaN-based semiconductor laser includes about 2.5 to 4.0 mW as shown in FIG. Output is required. In this case, the amount of quantization noise of the semiconductor laser is -125 dB / Hz as shown in FIG. 2 (this is a representation of the quantization noise in relative noise intensity and is also abbreviated as RIN. See: Optical Disc Technology: Radio Technology Co., Ltd.) p41), which is a level sufficient for reproduction. By switching the output of the semiconductor laser, recording / reproduction on a two-layer disc is possible.
[0039]
On the other hand, the case where a single-layer disc is recorded / reproduced by the above-mentioned optical head will be examined. As described above, the single-layer disc is recorded and reproduced with the optical output from the objective lens which is about half that of the double-layer disc. That is, recording on a single-layer disc becomes possible with a peak value of the output power from the objective lens of 12 mW × 50% = 6 mW. At this time, the output from the objective lens of about 0.4 mW or less is required as the reproduction power of the single-layer disc from the viewpoint of preventing the deterioration of the reproduction light, but the output power from the objective lens should be about 0.4 mW. In this case, the output light from the light source 1 needs to have an output of about 1.2 to 2.0 mW as shown in FIG. 2 including the variation in the efficiency of the optical head. In this case, the amount of quantization noise of the semiconductor laser greatly exceeds -125 dB / Hz as shown in FIG. 2 and is about -115 to -125 dB / Hz, and it is difficult to reproduce a single-layer disc by a normal method.
[0040]
Therefore, in the present embodiment, after discriminating the type of the optical information recording medium 9 from a single-layer disc or a double-layer disc (the discrimination method will be described in detail separately), in the case of a two-layer disc, the light beam attenuating optical element 3 For the control, the light output from the light source 1 is set so as not to be attenuated. On the other hand, when the optical information recording medium 9 is a single-layer disk, the light beam attenuating optical element 3 is set so that the light output from the light source 1 is about 50%. Set to control. In other words, when recording / reproducing a single-layer disc, the laser output efficiency of the optical head is reduced to about 12.5%, so that the output from the light source 1 can be reduced to a 2-layer disc even if the objective lens output during reproduction is 0.4 mW. The output of about 2.5 to 4.0 mW is required in the same manner as in the case of the reproduction, and the amount of quantization noise of the semiconductor laser is smaller than -125 dB / Hz, which is a level sufficient for the reproduction.
[0041]
When performing recording, the light beam attenuating optical element 3 is controlled in the same state as the reproduction state, that is, the output of the light source 1 is directly controlled by the light amount control circuit 15 while the output from the light source 1 is limited to about 50%. By performing the modulation, it is possible to instantly start recording from the reproduction state or change from the recording state to the reproduction state. That is, a wide D range (dynamic range: output width) corresponding to the recording / reproducing light of each of the single-layer disc and the double-layer disc without changing the D range of recording and reproduction of the optical power emitted from the semiconductor laser. The emitted light can be output from the objective lens 8.
[0042]
However, if recording is continuously performed with the output from the light source 1 being limited to about 50% during recording on a single-layer disc, the output from the light source 1 will continue to be recorded with the same output as recording on the dual-layer disc. Is not preferable from the viewpoint of the life of the battery. Therefore, in this embodiment, the optical element control circuit 16 controls the transmittance of the light beam attenuating optical element 3 to the maximum after the recording of the single-layer disc is started. That is, the output from the light source 1 is controlled by the optical element control circuit 16 and the light amount control circuit 15 so as to be reduced to about 50% as compared with the case at the start of recording. Immediately before shifting from the recording state to the reproduction state, the optical element control circuit 16 controls the transmittance of the light beam attenuating optical element 3 to be about 50% again.
[0043]
That is, after the output from the light source 1 is in the same state as that at the start of recording, the state shifts to the reproduction state. As a result, the light output of the light source 1 can be extended by reducing the maximum output time at the time of recording on the single-layer disc, and the laser output efficiency of the optical head is always reduced to about 12.5% when reproducing the single-layer disc. That is, even if the output of the objective lens at the time of reproduction is set to 0.4 mW, the amount of quantization noise of the semiconductor laser is smaller than -125 dB / Hz and can be set to a level sufficient for reproduction.
[0044]
Next, the operation of determining the reflectivity of the optical disk will be described in detail. The output of the light source 1 is set to 1.2 mW and the transmittance of the light beam attenuating optical element 3 is set to 100% by the command circuit 18 in advance. In the case of such a set value, the amount of light emitted from the objective lens 8 is about 0.3 mW, and the permissible amount of reproduction is 0.4 mW or less when the optical information recording medium 9 is a single-layer disk. I won't let you. Then, the light beam is made to follow the information track of the optical information recording medium 9 by a known optical disk device technique, and the light reflected from the optical information recording medium 9 is received by the photodetector 14.
[0045]
The signal output from the photodetector 14 is compared and determined by the comparator circuit 19 with the reference voltage of the reference voltage generation circuit 22. The reference voltage is the output voltage of the photodetector 14 obtained by reflected light when the optical information recording medium disk 9 is a two-layer disk and the reflected light when the optical information recording medium 9 is a single-layer disk. Since the output voltage is set to an intermediate voltage value between the obtained output voltages, the output of the comparator circuit 19 is a low-level signal when a two-layer disc is mounted, and is a high-level signal when a single-layer disc is mounted. A signal is obtained. As a result, the type of the optical information recording medium 9 can be identified. The output signal of the comparator circuit 19 is input to the command circuit 18, and the above-described recording / reproducing operation is performed. The command circuit 18 also controls the spindle motor 28 and the like.
[0046]
Also, as a reflectance discriminating means for another optical disk, the objective lens 8 is reciprocated up and down (note that an ordinary optical disk system performs auto-focusing by an objective lens driving device not shown in the drawings, but this objective lens The objective lens 8 can be driven up and down by a driving device.) There is also a method of identifying the number of recording layers of the optical information recording medium 9 by counting the number of fluctuations of the output voltage obtained from the optical information recording medium 9.
[0047]
Further, as another optical disk discriminating means, an area for recording the type of the disk is provided in a part of the recording area of the optical information recording medium 9, and before the disk is produced and handed over to the user, the area is recorded in this area. There is also a method of storing information relating to the type of disk, particularly the reflectance. The optical disc device can identify the type of the optical information recording medium 9 by obtaining identification information on the type of the optical information recording medium 9 in this area when the optical information recording medium 9 is inserted.
[0048]
As described above, the light beam attenuating optical element 3 is used in the optical head, and after discriminating between the single-layer disc and the double-layer disc, the transmittance from the light source 1 is reduced to about 50% only during recording and reproduction of the single-layer disc. Thus, while the power of the light source is set to a power at which the quantum noise is sufficiently reduced during reproduction for both the dual-layer disc and the single-layer disc, the board power is set to a low level that does not cause deterioration of the optical information recording medium 9 or data erasure. Reproduction can be performed with the power suppressed. Further, it is necessary to take some time after the identification of the type of the optical information recording medium 9 for switching the transmittance, but since switching between recording and reproduction does not particularly require element operation, recording is performed immediately after address reproduction. It becomes possible. Further, since the transmittance is switched by an external electric signal, it is easy to reduce the size of the optical head.
[0049]
In the case of recording on a single-layer disc, the maximum output time of the light source 1 is reduced by changing the transmittance from the light source 1 from about 50% to about 100% during the recording operation, thereby reducing the time of the light source 1. A longer life can be achieved.
[0050]
Although the present embodiment has described the present invention in the case of two types of single-layer and two-layer discs, the present invention relates to compatible recording / reproducing of three types of single-layer, two-layer and three-layer discs. Can be applied. However, as a prerequisite at that time, it is expected that the recording / reproducing power on the optical recording medium 9, that is, the recording power is set to 24 mW and the reproducing power is set to 1.6 mW for the triple-layer disc, which is twice as large as the double-layer disc. Therefore, the output of the semiconductor laser needs to be about 100 mW. The amount of quantization noise of this 100 mW laser is expected to shift the characteristic shown in FIG. 2 to the high output side as it is, that is, the RIN (relative noise intensity) becomes -125 dB / Hz or less in the region of 5 mW or more. become. Therefore, by using a function of setting an arbitrary transmittance by the optical element control circuit 16 of the light beam attenuation optical element 3, the transmittance from the light source 1 is 25% in the case of a single-layer disc, and the transmittance is 25% in the case of a two-layer disc. Reduces the transmittance of the light source to 50%, thereby increasing the power of the light source during reproduction for any of the three-layer disc, the two-layer disc, and the optical information recording medium 9 of the one-layer disc, and ensuring that the quantum noise is sufficient. The reproduction can be performed while the power of the board is suppressed to a low power that does not cause deterioration of the optical information recording medium or data erasure while setting the power to be low.
[0051]
The discrimination method at this time is to provide two kinds of reference voltages of the comparator circuit 19 and three kinds of output levels of low, middle, and high, so that the optical recording medium 9 has three kinds of one layer and two layers. It can be used for discriminating three types of discs including a layer disc.
[0052]
That is, the reference voltage is determined by the output voltage of the photodetector 14 obtained by the reflected light when the optical information recording medium disk 9 is a two-layer disk and the reflected light when the optical information recording medium 9 is a single-layer disk. The output voltage of the photodetector 14 obtained by the reflected light when the optical information recording medium 9 is a three-layer disc and the second reference voltage are provided at an intermediate voltage value of the obtained output voltage and the optical information recording medium 9. When a three-layer disc is mounted, the output of the comparator circuit 19 is a low-level signal when a three-layer disc is mounted. When a disk is mounted, the output of the comparator circuit 19 is a middle-level signal, and when a single-layer disk is mounted, a high-level signal is obtained. As a result, the type of the optical information recording medium 9 can be identified.
[0053]
(Embodiment 2)
Next, this embodiment will be described with reference to the drawings. The present embodiment is different from the above-described first embodiment in that the structure of the light beam attenuating optical element 23 is different and that the light beam attenuating optical element 23 is composed of only a liquid crystal element and does not use a polarization hologram, the characteristics of the polarization beam splitter 25, and the light source 1 Is the same as that of the first embodiment except that the mirror 27, the condenser lens 10 and the photodetector 12 are used. Therefore, in the present embodiment, components that are not particularly described are the same as those in the first embodiment, and the components denoted by the same reference numerals as those in the first embodiment are the same as those in the first embodiment unless otherwise described. Shall have the same function as.
[0054]
FIG. 3 is a configuration diagram of the optical head according to the second embodiment.
[0055]
In FIG. 3, 1 is a light source, 23 is a light beam attenuating optical element, 4 is a diffraction grating, 25 is a polarization beam splitter, 6 is a collimator lens, 27 is a mirror, 8 is an objective lens, 9 is an optical information recording medium, and 10 is A first condenser lens, 12 is a first photodetector, 14 is a second photodetector, 15 is a light amount control circuit, 16 is an optical element control circuit, and 17 is a quarter wavelength plate. Reference numeral 18 denotes a command circuit for controlling the optical disc device, 19 a comparator circuit for disc discrimination, and 20 a reflectance detecting means for disc discrimination. Reference numeral 21 denotes a light absorbing element for preventing stray light due to light reflected by the prism 25. Here, the condensing optical system is composed of a collimator lens 6 and an objective lens 8, and the light quantity control means is composed of a first photodetector 12 and a light quantity control circuit 15, which controls the optical element. The means is constituted by an optical element control circuit 16, and the polarization separation means is constituted by a polarization beam splitter 25 and a １ ／ wavelength plate 17.
[0056]
Here, the light source 1 is a light source composed of a GaN-based semiconductor laser element (wavelength: 405 nm) and outputting coherent light for recording and reproduction to the recording layer of the optical information recording medium 9. The light beam attenuating optical element 23 is a liquid crystal element and is an optical element that changes the polarization direction of the transmitted light beam according to an external signal. The diffraction grating 4 is a grating formed by patterning a desired pattern on a glass surface using photolithography and etching the same. The characteristics thereof are such that the 0th-order diffraction efficiency is approximately 90% and the ± 1st-order diffraction efficiency is approximately 10%. . The polarization beam splitter 25 is an optical element that transmits 100% of linearly polarized light emitted from the light source 1 and reflects 100% of linearly polarized light in a direction orthogonal to the linearly polarized light emitted from the light source 1.
[0057]
The collimator lens 6 is a lens that converts divergent light emitted from the light source 1 into parallel light. The mirror 27 is an optical element that reflects and transmits incident light and directs the reflected light toward the optical information recording medium 9. The mirror 27 transmits 10% of the circularly polarized light beam by the 波長 wavelength plate 17. , 90%. The objective lens 8 is a lens that focuses light on the recording layer of the optical information recording medium 9. The first condenser lens 10 is a lens that condenses the light emitted from the light source 1, transmitted through the light beam attenuation optical element 23, and transmitted through the mirror 27 to the first photodetector 12. The second condenser lens 11 is a lens that condenses the light reflected on the optical information recording medium 9 to the second photodetector 14. The first, second, and photodetectors 12 and 14 receive light and convert the light into an electric signal.
[0058]
The operation of the optical head thus configured will be described with reference to FIG. The linearly polarized light emitted from the light source 1 enters the light beam attenuation optical element 23. When the optical information recording medium 9 is a single-layer disk, the polarization direction of the light incident on the light beam attenuating optical element 23 is changed by the optical element control circuit 16, and the polarization beam splitter 25 thereafter changes the polarization direction by about 50%. Is reflected, and the remaining 50% of the light beam is transmitted. When the optical information recording medium 9 is a two-layer disk, the polarization direction is controlled so as not to change, and almost 100% of the light beam is transmitted by the polarization beam splitter 25 thereafter. This is the same as in Embodiment 1.) When the optical information recording medium 9 is a single-layer disk, the light absorbing element 21 is arranged so that the light beam reflected by the polarization beam splitter 25 does not become stray light, and absorbs the reflected light beam. .
[0059]
Most of the light transmitted through the light beam attenuating optical element 23 is transmitted by the diffraction grating 4 and partly diffracted. The light transmitted through the diffraction grating 4 (both the transmitted light and the diffracted light) is incident on the polarizing beam splitter 25. The behavior of the light beam in the polarization beam splitter 25 is as described above. The light transmitted through the polarizing beam splitter 25 is incident on the collimator lens 6. The light incident on the collimator lens 6 is collimated by the collimator lens 6. The light transmitted through the collimator lens 6 is converted into circularly polarized light by the quarter-wave plate 17, reflected by the mirror 27 at a light intensity of 90%, travels in a direction bent by 90 degrees from its traveling direction, and is recorded by the objective lens 8 with optical information. The light is focused on the medium 9. The 10% light beam transmitted through the mirror 27 is incident on the condenser lens 10 and is incident on the first photodetector 12 by the condenser lens 10. Here, the light incident on the photodetector 12 is converted into an electric signal, which becomes an electric signal for monitoring the amount of light emitted from the light source 1, and this signal is input to the light amount control circuit 15 to output the optimum amount of light. The light source 1 is controlled as described above.
[0060]
Next, the light reflected from the optical information recording medium 9 passes through the objective lens 8, is reflected by the mirror 27, is converted into linearly polarized light orthogonal to the outward path by the 波長 wavelength plate 17, and is transmitted through the collimator lens 6. Then, the light is reflected by the polarization beam splitter 25, collected by the second condenser lens 11, and made incident on the second photodetector 14. The second photodetector 14 outputs a focus error signal indicating a focus state of light on the optical information recording medium 9 and outputs a tracking error signal indicating a light irradiation position.
[0061]
In this case, for example, a phase error method is used for a read-only optical information recording medium, and a tracking error signal is obtained by a three-beam method using a sub-beam created by the diffraction grating 4 for a recording optical information recording medium. Focus control means (not shown) controls the position of the objective lens 8 in the optical axis direction based on the focus error signal so that light is always focused on the optical information recording medium 9 in a focused state. . Further, a tracking control means (not shown) controls the position of the objective lens 8 based on the tracking error signal so that the light is focused on a desired track on the optical information recording medium 9. The information recorded on the optical information recording medium 9 is also obtained from the second photodetector 14.
[0062]
The details of the control of the light beam attenuation optical element 23 are the same as in the first embodiment. As described above, using the light beam attenuating optical element 23 in an optical head, after discriminating between a single-layer disc and a double-layer disc, the transmittance from the light source 1 is reduced to about 50% only during recording and reproduction of the single-layer disc. By setting the power of the light source at the time of reproduction for both the dual-layer disc and the single-layer disc to the power at which the quantum noise is sufficiently low, the board power does not deteriorate the optical information recording medium 9 or erase data. Reproduction can be performed with low power. That is, a wide D range of emitted light corresponding to the recording / reproducing light of each of the single-layer disc and the double-layer disc can be obtained without changing the D range of recording and reproduction of the optical power emitted from the light source 1 of the semiconductor laser. be able to.
[0063]
Also, as in the case of the first embodiment, when recording is continuously performed while the output from the light source 1 is limited to about 50% at the time of recording on a single-layer disc, the output from the light source 1 is the same output as the recording on the dual-layer disc. , Which is not preferable from the viewpoint of laser life. Therefore, also in the present embodiment, the optical element control circuit 16 controls the transmittance of the light beam attenuating optical element 23 to be maximum after the recording of the single-layer disc is started. That is, the output from the light source 1 is controlled by the optical element control circuit 16 and the light amount control circuit 15 so as to be reduced to about 50% as compared with the case at the start of recording. Immediately before shifting from the recording state to the reproduction state, the optical element control circuit 16 controls the transmittance of the light beam attenuating optical element 23 to be about 50% again.
[0064]
That is, after the output from the light source 1 is in the same state as that at the start of recording, the state shifts to the reproduction state. As a result, the light output of the light source 1 can be extended by reducing the maximum output time at the time of recording on the single-layer disc, and the laser output efficiency of the optical head is always reduced to about 12.5% when reproducing the single-layer disc. That is, even if the output of the objective lens at the time of reproduction is set to 0.4 mW, the amount of quantization noise of the semiconductor laser is smaller than -125 dB / Hz and can be set to a level sufficient for reproduction.
[0065]
In addition, it is necessary to take a certain amount of time after the discrimination of the disc type, after the start of recording, and at the end of recording for switching the transmittance. However, when switching between recording and reproduction, no particular element operation is required. Recording can be performed instantaneously later. Further, since the transmittance is switched by an external electric signal, it is easy to reduce the size of the optical head.
[0066]
(Embodiment 3)
Next, this embodiment will be described with reference to the drawings. The present embodiment is different from the above-described second embodiment in that the light beam attenuating optical element itself, which was called the light beam attenuating optical element 23 in the second embodiment, is further mechanically moved in and out. 33 except that the structure of the light beam attenuating optical element 33 is different. Therefore, in the present embodiment, components that are not particularly described are the same as those in the second embodiment, and the components denoted by the same reference numerals as those in the second embodiment are the same as those in the second embodiment unless otherwise described. Shall have the same function as.
[0067]
FIG. 4 is a configuration diagram of an optical head according to the third embodiment. In FIG. 4, 1 is a light source, 33 is a light beam attenuating optical element, 4 is a diffraction grating, 25 is a polarizing beam splitter, 6 is a collimator lens, 27 is a mirror, 8 is an objective lens, 9 is an optical information recording medium, and 10 is A first condenser lens, 12 is a first photodetector, 14 is a second photodetector, 15 is a light amount control circuit, 16 is an optical element control circuit, and 17 is a quarter wavelength plate. Reference numeral 21 denotes a light absorbing element for preventing stray light due to light reflected by the prism 25. Reference numeral 18 denotes a command circuit for controlling the optical disc device, 19 a comparator circuit for disc discrimination, and 20 a reflectance detecting means for disc discrimination.
[0068]
Here, the condensing optical system is composed of a collimator lens 6 and an objective lens 8, and the light quantity control means is composed of a first photodetector 12 and a light quantity control circuit 15, which controls the optical element. The means comprises a second photodetector 14 and an optical element control circuit 16, and the polarization separation means comprises a polarization beam splitter 25 and a quarter-wave plate 17.
[0069]
Here, the light source 1 is a light source composed of a GaN-based semiconductor laser element (wavelength: 405 nm) and outputting coherent light for recording and reproduction to the recording layer of the optical information recording medium 9. The light beam attenuating optical element 33 has a liquid crystal element capable of changing the polarization direction of a transmitted light beam by an external signal, and is an element capable of mechanically moving the liquid crystal element in and out by an external signal.
[0070]
The diffraction grating 4 is a grating formed by patterning a desired pattern on a glass surface using photolithography and etching the same. The characteristics thereof are such that the 0th-order diffraction efficiency is approximately 90% and the ± 1st-order diffraction efficiency is approximately 10%. . The polarization beam splitter 25 is an optical element that transmits 100% of linearly polarized light emitted from the light source 1 and reflects 100% of linearly polarized light in a direction orthogonal to the linearly polarized light emitted from the light source 1. The collimator lens 6 is a lens that converts divergent light emitted from the light source 1 into parallel light. The mirror 27 is an optical element that reflects and transmits incident light and directs the reflected light toward the optical information recording medium 9. The mirror 27 transmits 10% of the circularly polarized light beam by the 波長 wavelength plate 17. , 90%. The objective lens 8 is a lens that focuses light on the recording layer of the optical information recording medium 9. The first condenser lens 10 is a lens that condenses the light emitted from the light source 1, transmitted through the light beam attenuation optical element 33, and transmitted through the mirror 27 to the first photodetector 12. The second condenser lens 11 is a lens that condenses the light reflected on the optical information recording medium 9 to the second photodetector 14. The first, second, and photodetectors 12 and 14 receive light and convert the light into an electric signal.
[0071]
The operation of the optical head thus configured will be described with reference to FIG. The linearly polarized light emitted from the light source 1 enters the light beam attenuating optical element 33. When the optical information recording medium 9 is a single-layer disc by the optical element control circuit 16, the light beam attenuating optical element 33 is mechanically inserted into the optical path and the liquid crystal element is simultaneously controlled, so that a light beam of about 50% light amount is emitted. It is controlled to transmit. When the optical information recording medium 9 is a two-layer disc, the light beam attenuating optical element 33 is mechanically extracted from the optical path and almost 100% of the light beam is transmitted. (The details of this are the same as in Embodiments 1 and 2.) Most of the light transmitted through the light beam attenuating optical element 33 is transmitted by the diffraction grating 4 and partly diffracted. The light transmitted through the diffraction grating 4 (both the transmitted light and the diffracted light) is incident on the polarizing beam splitter 25. The light transmitted through the polarizing beam splitter 25 is incident on the collimator lens 6. The light incident on the collimator lens 6 is collimated by the collimator lens 6. The light transmitted through the collimator lens 6 is converted into circularly polarized light by the quarter-wave plate 17, reflected by the mirror 27 at a light intensity of 90%, travels in a direction bent by 90 degrees from its traveling direction, and is recorded by the objective lens 8 with optical information. The light is focused on the medium 9. The 10% light beam transmitted through the mirror 27 is incident on the condenser lens 10 and is incident on the first photodetector 12 by the condenser lens 10. Here, the light incident on the photodetector 12 is converted into an electric signal, which becomes an electric signal for monitoring the amount of light emitted from the light source 1, and this signal is input to the light amount control circuit 15 to output the optimum amount of light. The light source 1 is controlled as described above. Next, the light reflected from the optical information recording medium 9 passes through the objective lens 8, is reflected by the mirror 27, is converted into linearly polarized light orthogonal to the outward path by the 波長 wavelength plate 17, and is transmitted through the collimator lens 6. Then, the light is reflected by the polarization beam splitter 25, collected by the second condenser lens 11, and made incident on the second photodetector 14. The second photodetector 14 outputs a focus error signal indicating a focus state of light on the optical information recording medium 9 and outputs a tracking error signal indicating a light irradiation position. In this case, for example, a phase error method is used for a read-only optical information recording medium, and a tracking error signal is obtained by a three-beam method using a sub-beam created by the diffraction grating 4 for a recording optical information recording medium. Focus control means (not shown) controls the position of the objective lens 8 in the optical axis direction based on the focus error signal so that light is always focused on the optical information recording medium 9 in a focused state. . Further, a tracking control means (not shown) controls the position of the objective lens 8 based on the tracking error signal so that the light is focused on a desired track on the optical information recording medium 9. The information recorded on the optical information recording medium 9 is also obtained from the second photodetector 14. The details of the control of the liquid crystal element in the light beam attenuating optical element 33 of the present embodiment are the same as those of the second embodiment of the present invention.
[0072]
As described above, the light beam attenuating optical element 33 is used in an optical head, and after discrimination between a single-layer disc and a double-layer disc, the transmittance from the light source 1 is reduced to about 50% only during recording and reproduction of the single-layer disc. By setting the power of the light source at the time of reproduction for both the dual-layer disc and the single-layer disc to a power at which the quantum noise is sufficiently reduced, the board power is set to a low level at which deterioration of the optical information recording medium or erasure of data does not occur. Reproduction can be performed with the power suppressed. That is, it is possible to obtain emission light of a wide D range corresponding to recording and reproduction light of each of the single-layer disc and the double-layer disc without changing the D range of recording and reproduction of the optical power emitted from the semiconductor laser. .
[0073]
Also, when recording is continuously performed with the output from the light source 1 limited to about 50% during single-layer disc recording as in the first and second embodiments, the output from the light source 1 is the same output as that of the dual-layer disc recording. , Which is not preferable from the viewpoint of laser life. Therefore, also in this embodiment, the optical element control circuit 16 controls the liquid crystal element of the light beam attenuating optical element 33 so that the transmittance becomes maximum after the recording of the single-layer disc is started. That is, the output from the light source 1 is controlled by the optical element control circuit 16 and the light amount control circuit 15 so as to be reduced to about 50% as compared with the case at the start of recording. Immediately before shifting from the recording state to the reproducing state, the optical element control circuit 16 controls the liquid crystal element of the light beam attenuating optical element 33 so that the transmittance becomes about 50% again. That is, after the output from the light source 1 is in the same state as that at the start of recording, the state shifts to the reproduction state. As a result, the light output of the light source 1 can be extended by reducing the maximum output time at the time of recording on the single-layer disc, and the laser output efficiency of the optical head is always reduced to about 12.5% when reproducing the single-layer disc. That is, even if the output of the objective lens at the time of reproduction is set to 0.4 mW, the amount of quantization noise of the semiconductor laser is smaller than -125 dB / Hz and can be set to a level sufficient for reproduction.
[0074]
In addition, it is necessary to take a certain amount of time after the discrimination of the disc type, after the start of recording, and at the end of recording for switching the transmittance. However, when switching between recording and reproduction, no particular element operation is required. Recording can be performed instantaneously later.
[0075]
Further, although a single lens is used as the objective lens, there is no problem even if it is a set lens having a high NA. Further, if a lens with a high NA is used, the density can be further increased, and the stability of the reproduced signal with respect to the noise of the light source becomes strict, so that the present invention is very useful.
[0076]
As described above, the present embodiment has been described by way of example. However, the present invention is not limited to the above embodiment, and can be applied to other embodiments based on the technical idea of the present invention.
[0077]
In the above embodiment, an infinite optical head is described, but a finite optical head that does not use a collimator lens may be used.
[0078]
In the above embodiment, the optical information recording medium for recording information only by light has been described. However, the same effect can be obtained by using the optical element of the present invention for an optical information recording medium for recording information by light and magnetism. Needless to say, this is obtained.
[0079]
Further, in the above-described embodiment, the case where the optical information recording medium is an optical disk has been described. However, the present invention can be applied to an optical information recording / reproducing apparatus that realizes similar functions, such as a card-shaped optical information recording medium.
[0080]
【The invention's effect】
As described above, according to the present invention, light emitted from a semiconductor laser is irradiated onto the optical information recording medium via an objective lens, and reflected light from the optical information recording medium is guided to a photodetector. An optical head for reading a signal on a recording medium, comprising: a transmitted light amount varying means for changing a light amount reaching the optical information recording medium from the semiconductor laser according to identification information of a type of the optical information recording medium; When the information is the first optical information recording medium, the light emitted from the semiconductor laser is used as it is, and when the identification information is the second optical information recording medium, the transmitted light amount is variable. Means for reducing the amount of light emitted from the semiconductor laser, thereby reducing the light emitted from the objective lens without changing the output width of the optical power emitted from the semiconductor laser. Since the output width of recording and reproduction of power is widened, the light beam from the semiconductor laser is attenuated at the time of recording and reproduction of the second optical information recording medium (single-layer disc), so that the light source at the time of reproduction of the single-layer disc is reproduced. The power is set to a value that will sufficiently reduce the quantum noise, and the transmittance will be reduced by the variable transmission light amount means to control the board power to a low power that does not cause deterioration of the optical information recording medium or data erasure. When recording on the first optical information recording medium (the disk with the largest number of layers), the transmittance by the transmitted light amount varying means is set to 100%, so that recording is performed using the power of the semiconductor laser as it is. It can be carried out.
[0081]
That is, the output light having a wide output width corresponding to the recording and reproduction light of each of the single-layer disc and the double-layer disc is output from the objective lens without changing the D range of recording and reproduction of the optical power emitted from the semiconductor laser. can do.
[0082]
In addition, when switching between recording and reproduction of a single-layer disc and recording and reproduction of a double-layer disc, switching of transmittance is not performed, so that switching can be performed immediately after address reproduction.
[0083]
In addition, in the case of a disk having high recording sensitivity, that is, a disk having a low laser power at the time of recording, the laser life is shortened by switching the intensity filter during recording so that the power output from the laser occupies most of the time. It can be extended.
[0084]
Further, since the transmittance is switched by an external electric signal, it is easy to reduce the size of the optical head.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of an optical information recording / reproducing apparatus according to the present invention.
FIG. 2 is a diagram showing the relationship between the output of a blue semiconductor laser of the present invention and quantization noise.
FIG. 3 is a schematic view showing another example of the optical information recording / reproducing apparatus of the present invention.
FIG. 4 is a schematic diagram showing another example of the optical information recording / reproducing apparatus of the present invention.
FIG. 5 is a schematic view showing an example of a conventional optical head.
[Explanation of symbols]
1 light source
2 Beam splitter
3 Light beam attenuation optical element
4 Diffraction grating
5 Polarizing beam splitter
6 Collimator lens
8 Objective lens
9 Optical information recording medium
12 Photodetector
13 Photodetector
14 Photodetector
15 Light intensity control circuit
16 Optical element control circuit
17 1/4 wavelength plate
18 Command circuit
19 Comparator circuit
20 Reflection detecting means
21 Light absorbing element
23 Optical beam attenuation optical element
25 Polarizing beam splitter
27 mirror
28 spindle motor

Claims (9)

An optical head that irradiates the optical information recording medium with an emitted light from a semiconductor laser through an objective lens, guides reflected light from the optical information recording medium to a photodetector, and reads a signal on the optical information recording medium. So,
A transmission light amount varying unit that changes a light amount reaching the optical information recording medium from the semiconductor laser according to the identification information of the type of the optical information recording medium,
When the identification information is the first optical information recording medium, the light emitted from the semiconductor laser is used as it is,
When the identification information is the second optical information recording medium, by reducing the amount of light emitted from the semiconductor laser by the transmitted light amount varying means,
An optical head characterized in that the output width of recording and reproduction of the optical power emitted from the objective lens is expanded without changing the output width of the optical power emitted from the semiconductor laser. 2. The optical head according to claim 1, wherein the transmission light amount varying means has a configuration in which a liquid crystal element and a polarization hologram are combined. 2. The optical head according to claim 1, wherein the transmission light amount varying means has a configuration in which a liquid crystal element and a polarization beam splitter are combined. 2. The optical head according to claim 1, wherein the transmitted light amount varying unit is configured to enter and exit the light emitted from the semiconductor laser in an optical path. 5. The optical head according to claim 1, wherein the light source is a semiconductor laser capable of emitting light in a wavelength range from green to ultraviolet. 6. The optical head according to claim 1, wherein the light source is a semiconductor laser capable of emitting light in a blue wavelength region. An optical head according to any one of claims 1 to 6,
Determining means for identifying the type of the optical information recording medium;
A semiconductor laser drive circuit that controls the beam light amount of the emitted light of the semiconductor laser of the optical head;
A transmission light amount varying circuit for attenuating the light amount of the light beam emitted from the semiconductor laser by the transmission light amount varying means of the optical head,
The transmitted light amount variable circuit uses a transmitted light amount variable unit,
When the identification information by the determination means is the first optical information recording medium, the light emitted from the semiconductor laser is used as it is,
When the identification information by the discriminating means is the second optical information recording medium, by reducing the amount of light emitted from the semiconductor laser by the transmitted light amount varying means,
An optical information recording / reproducing apparatus characterized in that the output width of recording and reproduction of the optical power emitted from the objective lens is expanded without changing the output width of the optical power emitted from the semiconductor laser. 8. The optical information recording / reproducing apparatus according to claim 7, wherein the identification information of the optical information recording medium by the discriminating means is the number of recording layers of the optical information recording medium. 2. The optical disc according to claim 1, wherein said discriminating means discriminates an optical information recording medium having one recording layer and an optical information recording medium having two recording layers among types of recording layers of said optical information recording medium. 8. The optical information recording / reproducing apparatus according to 7.

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