JPH0554424A - Optical recording/reproducing device - Google Patents

Abstract

PURPOSE:To provide an optical recording/reproducing device by which nearly constant reproduced signals such as MTF, etc., are obtained without being affected by the wave length fluctuation of a light source. CONSTITUTION:A recording medium 48 is irradiated with the light beam from a light source 41 by way of a reflection surface 46 or transmission surfaces 44 and 45 in order to record or reproduce information. At this time, at least one of above stated reflection surface 46 or transmission surfaces 44 and 45 is provided with a thin film structure 61, as a result, the light quantity change caused by wave length fluctuation of the light irradiated on the above stated recording media 48 is compensated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus for recording / reproducing information on / from an optical recording medium such as an optical disk or a magneto-optical disk.

[0002]

2. Description of the Related Art As an optical recording / reproducing device, the present applicant has proposed a device shown in FIGS. 7A and 7B in Japanese Patent Application Laid-Open No. 3-104033. This optical recording / reproducing apparatus uses a reflective surface and a transmissive surface of an optical member arranged between a recording medium and a signal detection system in order to compensate a phase difference change with respect to a wavelength change of light incident on the signal detection system. Each is provided with a thin film structure.

In FIG. 7A, the light from the semiconductor laser 11 is collimated by the collimator lens 12, is shaped into a beam by the shaping prism 13, and is further transmitted through the beam splitters 14 and 15, as shown in FIG. 7B. On total reflection mirror
It is started up with 16, and the objective lens 17 is used for the magneto-optical disk.
Focused on 18. On the other hand, the reflected light from the magneto-optical disk 18 is reflected by the beam splitters 15 and 14 through the opposite paths, and the light reflected by the beam splitter 15 is
After the polarization direction is rotated by 45 ° by the 1/2 wavelength plate 19, it is converged by the condenser lens 20 and guided to the magneto-optical signal detection optical system 21. The magneto-optical signal detection optical system 21 includes a polarization beam splitter 22 that separates incident light into a P-polarized component and an S-polarized component.
And photodetectors 23 and 24 for receiving the separated P-polarized component and S-polarized component, respectively.
The reproduced signal of the information recorded on the magneto-optical disk 18 is obtained by detecting the output difference of the.

The light reflected by the beam splitter 14 is split into transmitted light and reflected light by the beam splitter 15 and is guided to the error signal detection optical system 25. The error signal detection optical system 25 includes a critical angle prism 26, a photodetector 27 for focus error detection having a two-divided light receiving area, a tracking error detection having a four-divided light receiving area, and a beam of the beam due to an inclination of the optical axis. The photodetector 28 for offset detection is configured to allow the light transmitted through the beam splitter 15 to enter the photodetector 27 through the critical angle prism 26, and the reflected light to enter the photodetector 28, thereby the photodetector. The focus error signal is detected based on the outputs of 27 and 28, and the tracking error signal is detected based on the output of the photodetector 28.

In such an optical recording / reproducing apparatus, the wavelength dependence of the phase difference of the returning light incident on the magneto-optical signal detecting optical system 21 is substantially zero within the fluctuation range of the wavelength of the light emitted from the semiconductor laser 11. Thus, the total reflection mirror 16 and the beam splitter 15 are provided with thin-film structures 31 and 32, respectively, which cancels the wavelength dependence of the phase difference in the total reflection mirror 16 and the beam splitter 15.

That is, the thin film structure 31 of the total reflection mirror 16
8A, for example, as shown in FIG. 8A, the phase difference δ ₁ at which the phase difference becomes zero at the initial wavelength (830 nm) is wavelength-dependent, and the thin film structure 32 of the beam splitter 15 has a beam splitter.
Since 15 is rotated by 90 ° with respect to the total reflection mirror 16, the same wavelength difference δ ₂ as in the total reflection mirror 16 in which the phase difference becomes zero at the initial wavelength (830 nm) as shown in FIG. 8B. By providing the dependence, the wavelength dependence of the phase difference δ ₃ of the return light incident on the magneto-optical signal detection optical system 21 is made substantially flat with the phase difference being zero as shown in FIG. 8C. The phase differences δ ₁ , δ ₂ and δ ₃ are respectively obtained by subtracting the phase of the S polarization component from the phase of the P polarization component.

[0007]

However, in the above-mentioned optical recording / reproducing apparatus, even if the phase difference change due to the wavelength change can be compensated, the change in the reflectance and the transmittance with respect to the change in the wavelength does not occur. I can't compensate. For this reason, when the transmittance of the beam splitter or the like changes due to the wavelength fluctuation of the light source, the amount of light emitted from the objective lens or the like changes and the recording state on the recording medium changes. In particular, when the output light of the light source is reflected by the beam splitter and received by the front monitor, and the output is fed back to the light source to control the light amount, when the reflected light at the beam splitter decreases due to wavelength fluctuation, Since the transmitted light guided to the objective lens increases and the reflected light that is the monitor light decreases, the emitted light from the light source increases more and more, and the light amount changes by about a square.

If the transmittance between the light source and the recording medium changes due to such a cause, it is considered that the MTF of the reproduced signal is adversely affected. Here, the MTF of the reproduction signal represents a signal amplitude ratio when two signals of different frequencies are recorded on the recording medium and the signals of the two different frequencies are reproduced, and this mainly means that information is recorded on the recording medium. It is affected by the light intensity when recording.

The present invention has been made by paying attention to such a problem, and an optical system properly configured so that a reproduction signal such as MTF can be always almost constant without being influenced by the wavelength fluctuation of the light source. An object of the present invention is to provide a recording / reproducing apparatus.

[0010]

In order to achieve the above object, according to the present invention, an optical system for irradiating a recording medium with light from a light source through a reflecting surface and / or a transmitting surface to record or reproduce information. In the recording / reproducing apparatus, a thin film structure is provided on at least one of the reflecting surface or the transmitting surface,
This compensates for the change in the light amount due to the wavelength change of the light irradiated on the recording medium.

[0011]

1A and 1B show a first embodiment of the present invention. In this embodiment, after the light from the semiconductor laser 41 is collimated by the collimator lens 42, it is beam-shaped by the shaping prism 43, transmitted through the beam splitter 44, and separated by the beam splitter 45 into transmitted light and reflected light. ,
As shown in FIG. 1B, the transmitted light is raised by a total reflection mirror 46 and condensed on a magneto-optical disk 48 by an objective lens 47 to record information. In reproducing information, similarly, the light from the semiconductor laser 41 is condensed on the magneto-optical disk 48, and the reflected light passes through the reverse path to the beam splitter 45.
The light reflected by the beam splitter 45 is rotated by 45 ° by the 1/2 wavelength plate 49, and then the light reflected by the beam splitter 45 is converged by the condenser lens 50 and guided to the magneto-optical signal detection optical system 51. .. The magneto-optical signal detection optical system 51 converts the incident light into P
A polarization beam splitter 52 for separating a polarized light component and an S polarized light component, and photodetectors 53, 54 for receiving the separated P polarized light component and S polarized light component are provided.
By detecting the output difference between 53 and 54, the magneto-optical disk 48
The reproduction signal of the information recorded in is obtained.

Further, of the return light from the magneto-optical disk 48, the light reflected by the beam splitter 44 is split by the beam splitter 45 into transmitted light and reflected light and guided to the error signal detection optical system 55. The error signal detection optical system 55 includes a critical angle prism 56, a photodetector 57 for focus error detection having a two-divided light receiving area, a tracking error detection having a four-divided light receiving area, and a beam formed by tilting the optical axis. It is configured with a photodetector 58 for offset detection, and the transmitted light from the beam splitter 45 is incident on the photodetector 57 via the critical angle prism 56, and the reflected light is incident on the photodetector 58, and the photodetector is detected. The focus error signal is detected based on the outputs of 57 and 58, and the tracking error signal is detected based on the output of the photodetector 58. A semiconductor laser
Of the light emitted from 41, the light reflected by the beam splitter 45 is received by the front monitor 59, and the emitted light amount of the semiconductor laser 41 is controlled based on the output thereof.

In the above structure, the beam splitters 44 and 45 have wavelength dependency of transmittance in the vicinity of the initial wavelength (830 nm). For example, place the beam splitter 44 on the glass material BK7 with Ti.
When the dielectric multilayer film of O ₂ and SiO ₂ is formed by vapor-depositing nine layers, and the beam splitter 45 is formed by vapor-depositing a dielectric multilayer film similar to the beam splitter 44, The spectral characteristics obtained by multiplying both are the wavelength
The transmittance T becomes, for example, 50% at 830 nm, and there is wavelength dependency in the vicinity thereof as shown in FIG. 2A. Therefore, in this embodiment, the beam splitters 44 and 45 shown in FIG. 2A are used.
In order to cancel the wavelength dependence of the transmittance obtained by multiplying both of them, the total reflection mirror 46 is provided with the thin film structure 61. This thin film structure 61 is a dielectric multilayer film of, for example, TiO ₂ and SiO _2.
The layers are formed by vapor deposition, so that the reflectance R becomes 100% near the initial wavelength of 830 nm as shown in FIG. 2B.

With this arrangement, the magneto-optical disk 48
Light incident on the beam splitters 44 and 45,
Transmittance T and reflectance R with respect to the total reflection mirror 46
The wavelength dependence of the multiplied light becomes constant at a specified value as shown in FIG. 2C. Therefore, even if the oscillation wavelength of the semiconductor laser 41 fluctuates due to temperature change or the like, the amount of light for recording, erasing and reproducing information can be made substantially constant without being affected by it.
Further, by providing the thin film structure 61 in this way, it is not necessary to strictly suppress the wavelength dependence for each individual beam splitter, so that the degree of freedom in design can be increased,
In addition, the design time can be shortened, so that the device can be made inexpensive.

FIG. 3 shows a second embodiment of the present invention. In this embodiment, after the light from the semiconductor laser 65 is collimated by the collimator lens 66, it is beam-shaped by the shaping prism 67, and further transmitted through the beam splitters 68 and 69, and then is transmitted through the objective lens 70 onto the magneto-optical disk 71. Focus and record information. In reproducing information, similarly, the light from the semiconductor laser 65 is condensed on the magneto-optical disk 71, and the reflected light is reflected by the beam splitters 69 and 68 through the opposite paths, and the beam splitter
The polarization direction of the light reflected by 69 is 45 ° by the half-wave plate 72.
After rotating, it is converged by the condenser lens 73 and guided to the magneto-optical signal detection optical system 74. The magneto-optical signal detection optical system 74 has a polarization beam splitter 75 that separates incident light into P-polarized component and S-polarized component, and photodetectors 76 and 77 that receive the separated P-polarized component and S-polarized component. In this configuration, the reproduction signal of the information recorded on the magneto-optical disk 71 is obtained by detecting the output difference between the photodetectors 76 and 77.

Further, of the return light from the magneto-optical disk 71, the light reflected by the beam splitter 68 is guided to the error signal detection optical system 78. The error signal detection optical system 78 includes a critical angle prism 79 and a photodetector 80 for detecting focus and tracking errors having a four-divided light receiving area, and reflects light reflected by the beam splitter 68 through the critical angle prism 79. The light is incident on the photodetector 80, and the focus error signal and the tracking error signal are detected based on the output thereof.

In the above structure, the beam splitter 68
Is formed by vapor-depositing five dielectric multilayer films of TiO ₂ and SiO ₂ on the glass material BK7, its spectral characteristics show a transmittance T ₁ of, for example, 70% at a wavelength of 830 nm, and the vicinity thereof is shown in FIG. 4A. It has such wavelength dependence. Therefore, in this embodiment, in order to cancel the wavelength dependence of the transmittance T ₁ of the beam splitter 68 shown in FIG. 4A, the beam splitter 69 is provided with a thin film structure 81.
To provide. This thin film structure 81 is made of, for example, Zr on glass material BK7.
A dielectric multilayer film of O ₂ and SiO ₂ is formed by vapor deposition of 15 layers, which allows the beam splitter 69 to have a wavelength of 83 nm as shown in FIG. 4B.
It has wavelength dependence such that the transmittance T ₂ becomes 70% at 0 nm.

With this arrangement, the magneto-optical disk 71
The wavelength dependence of the light incident on the light, that is, the wavelength dependence of the light multiplied by the respective transmittances T ₁ and T ₂ of the beam splitters 68 and 69 is
As shown in FIG. 4C, it becomes constant with a specified value. Therefore, even if the oscillation wavelength of the semiconductor laser 65 fluctuates due to a temperature change or the like, the amount of light incident on the magneto-optical disk 71 can be made substantially constant without being affected by it, and the same as in the first embodiment. The effect can be obtained.

FIG. 5 shows a third embodiment of the present invention. This embodiment is similar to the semiconductor laser of the second embodiment.
Light emitted from 65 and reflected by the beam splitter 68 is received by the front monitor 82, and the amount of light emitted from the semiconductor laser 65 is controlled based on the output thereof. As described above, when the emitted light amount of the semiconductor laser 65 is controlled using the front monitor 82, if the emitted light has no wavelength fluctuation, the incident light amount on the magneto-optical disk 71 is set to a desired value in recording, erasing and reproducing. It can be controlled to be constant.

However, when the beam splitter 68 is formed by vapor-depositing seven dielectric multilayer films of TiO ₂ and SiO ₂ on, for example, a glass material BK7, its spectral characteristic is the transmittance at a wavelength of 830 nm.
T ₁ is, for example, 60%, and there is wavelength dependence in the vicinity thereof as shown in FIG. 6A. Therefore, if the wavelength of the semiconductor laser 65 fluctuates, the amount of light incident on the magneto-optical disk 71 also changes as shown in FIG.
It changes depending on the wavelength dependency of the transmittance T ₁ of the beam splitter 68 shown in FIG. On the other hand, the light incident on the front monitor 82 is the light reflected by the beam splitter 68, and
Since it has a characteristic opposite to that of A, if the emitted light amount of the semiconductor laser 65 is controlled based on its output, the light amount fluctuates by about the square, and the transmitted light T ₁ ′ at the beam splitter 68 in that case is changed. The wavelength dependence becomes as shown in FIG. 6B.

Therefore, in this embodiment, in order to cancel the wavelength dependence of the transmittance T ₁ ′ of the beam splitter 68, the beam splitter 69 is provided with a thin film structure 83. The thin film structure 83 is formed by vapor-depositing 17 layers of a dielectric multilayer film of ZrO ₂ and SiO ₂ on a glass material BK7.
69, as shown in FIG. 6C, the transmittance T _{2 is about} 70 at a wavelength of 830 nm.
% To have a wavelength dependence. With this structure, the light incident on the magneto-optical disk 71, that is, the front monitor
The wavelength dependency when the emitted light amount of the semiconductor laser 65 is controlled by 82 becomes constant with a specified value as shown in FIG. 6D, and therefore the same effect as the above-described embodiment can be obtained.

It should be noted that the present invention is not limited to the above-described embodiments, but many variations and modifications are possible. For example, in the above-described embodiment, the thin film structure is provided in the optical path from the semiconductor laser to the magneto-optical disk, but this thin film structure may be provided in the optical path from the magneto-optical disk to the magneto-optical signal detecting optical system. it can. By doing so, the reflected light from the magneto-optical disk can be made constant at all times, so that the magneto-optical signal can always be detected stably. In addition, in the above-described embodiment, the initial wavelength is
Although it is set to 830 nm, the present invention can be effectively applied to the case of using light of other wavelengths, and the recording medium is not limited to the magneto-optical disc, and an optical disc, a compact disc, or other optical recording medium is used. Even in this case, the present invention can be effectively applied. Further, in the above-described embodiment, the thin film structure for compensating the light quantity change due to the wavelength variation of the light is provided on one reflecting surface or one transmitting surface, but the thin film structure is provided on two or more reflecting surfaces and / or transmitting surfaces. A body may be provided, and the plurality of thin film structures may be configured to compensate for a change in light amount due to a change in wavelength of light.

[0023]

As described above, according to the present invention, the thin film structure is formed on at least one reflecting surface or transmitting surface in the optical path for irradiating the recording medium with the light from the light source through the reflecting surface and / or the transmitting surface. Is provided to compensate for the change in the light amount due to the change in the wavelength of the light irradiated on the recording medium, so that the recording can be performed in a constant state without being affected by the change in the wavelength of the light source. In reproduction, an almost constant reproduction signal such as MTF can be obtained.
Further, by providing the thin film structure, it is not necessary to suppress the wavelength dependence of the reflectance and the transmittance of each optical component. Therefore, the degree of freedom in design can be improved and the design time can be shortened, so that the entire device can be inexpensive. You can

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining the operation of the first embodiment.

FIG. 3 is a diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram for explaining the operation of the second embodiment.

FIG. 5 is a diagram showing a third embodiment of the present invention.

FIG. 6 is a diagram for explaining the operation of the third embodiment.

FIG. 7 is a diagram for explaining a conventional technique.

FIG. 8 is a diagram for explaining the operation of FIG. 7.

[Explanation of symbols]

 41 Semiconductor laser 42 Collimating lens 43 Shaping prism 44,45 Beam splitter 46 Total reflection mirror 47 Objective lens 48 Magneto-optical disk 49 1/2 Wave plate 50 Condensing lens 51 Magneto-optical signal detection optical system 52 Polarizing beam splitter 53,54, 57,58 Photodetector 55 Error signal detection optical system 56 Critical angle prism 59 Front monitor 61 Thin film structure 65 Semiconductor laser 66 Collimating lens 67 Shaping prism 68,69 Beam splitter 70 Objective lens 71 Magneto-optical disk 72 1/2 Wave plate 73 Condenser lens 74 Opto-magnetic signal detection optical system 75 Polarizing beam splitter 76,77 Photo detector 78 Error signal detection optical system 79 Critical angle prism 80 Photo detector 81 Thin film structure 82 Front monitor 83 Thin film structure

Claims (1)

[Claims] 1. An optical recording / reproducing apparatus for recording or reproducing information by irradiating a recording medium with light from a light source through a reflecting surface and / or a transmitting surface, the wavelength variation of the light irradiating the recording medium. An optical recording / reproducing apparatus, wherein a thin film structure is provided on at least one of the reflecting surface or the transmitting surface so as to compensate for a change in light quantity.