JP3089103B2 - Optical disk player - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk player capable of recording and reproducing information not only on an optical disk having a normal recording density but also on a high-density disk by using laser beams of different wavelengths.

[0002]

2. Description of the Related Art In recent years, an optical disk player capable of writing and reading information on and from an optical disk at a higher density has been developed.

FIG. 1 shows an example of an optical system of an optical disk player for performing such high-density recording and reproduction. Laser beams having different wavelengths are emitted from a light source 1. Here, the wavelength from the light source 1 is, for example, 780 n
m and 630 nm.

[0004] Outgoing light of two wavelengths from the light source 1 is cut off by a filter 2 at one wavelength. That is, when recording and reproducing information on a high-density disc, a long wavelength of 780 nm is cut.

The outgoing light having a short wavelength of 630 nm that has passed through the filter 2 is separated by the diffraction grating 3 into zero-order light and ± first-order light that is diffracted light.

The outgoing light separated by the diffraction grating 3 is
After passing through the beam splitter 4, the light is focused on the optical disk 6 by the objective lens 5.

[0007] The reflected light from the optical disk 6 is returned to the cylindrical lens 7 side by the beam splitter 4 and then condensed on the photodetector 8 via the cylindrical lens 7.

[0008] Of the reflected light condensed on the photodetector 8, the reproduced RF signal is obtained from the zero-order light having a short wavelength of 630 nm. Further, the tracking error signal is similarly obtained by the difference of ± 1 order light having a short wavelength of 630 nm by the three-beam method. Further, the focus error signal is similarly obtained by the 0th-order light having a short wavelength of 630 nm by the astigmatism method.

FIG. 2 shows another example of the optical system of the above-mentioned optical disk player. Outgoing lights having different wavelengths from a light source 1 pass through a beam splitter 4 and are condensed on an optical disk 6 by an objective lens 5. Is done. As described above, the wavelength from the light source 1 is, for example, two wavelengths of 780 nm and 630 nm.

The reflected light from the optical disk 6 is turned back to the dichroic mirror 9 by the beam splitter 4. The reflected light turned back to the dichroic mirror 9 is separated by the dichroic mirror 9 into a long wavelength of 780 nm and a short wavelength of 630 nm. The long wavelength is returned to the photodetector 8b for error signal detection through the cylindrical lens 7. The short wavelength passes through the dichroic mirror 9 and is focused on a photodetector 8a for detecting an RF signal.

The reproduced RF signal is obtained from an RF photodetector 8a. The tracking error signal and the focus error signal are obtained by the photo detector 8b. As a tracking error detection method, for example, a push-pull method is used. As a detection method of the focus error signal, for example, an astigmatism method is used.

[0012]

As described above, the conventional optical system of the optical disk player shown in FIG.
According to the recording density of the signal of the optical disk 6 to be recorded / reproduced, only the emission light of the corresponding wavelength from the light source 1 is left, and the emission light of other wavelengths is cut by the filter 2.

In the optical system of the optical disk player shown in FIG. 2, reflected light of two wavelengths from the optical disk 6 is separated by a dichroic mirror 9 and received by photodetectors 8a and 8b provided individually. .

For this reason, in the optical system of the optical disk player shown in FIG. 1, the output light of a wavelength not corresponding to the optical disk 6 to be recorded / reproduced by the filter 2 is cut by the filter 2, so that the cut out light is It is completely wasted. Further, since the outgoing light that has passed through the filter 2 is divided into three by the diffraction grating 3, there is a problem in that the amount of received reproduction RF signal to be detected by the photodetector 8 and each amount of focus / tracking error signal decreases. Was.

In the optical system of the optical disk player shown in FIG. 2, reflected light from the optical disk 6 is separated by a dichroic mirror 9 for each wavelength, and each reflected light is separated by a photodetector 8a for RF detection and an error signal detection The photodetector 8b is configured to condense light to the photodetector 8a and the photodetector 8b.
It is necessary to perform position adjustment with b. Since this position adjustment requires extremely high precision when the photodetector 8a and the photodetector 8b are incorporated into the optical system, the assembling work is complicated.

Further, the photo detectors 8a and 8b
The dichroic mirror 9 for separating the reflected light for each wavelength is required, which hinders the cost reduction of the apparatus.

The present invention has been made in view of such circumstances, and provides an optical disk player capable of preventing a light quantity loss by arranging a phase grating and reducing the cost of the apparatus. With the goal.

[0018]

According to the present invention, there is provided an optical disk player comprising: a first optical disk having a wavelength of λ1;
A light source that emits light and a second light having a wavelength of λ2, a photodetector that receives reflected light from an optical disc, and a light detector that is interposed between the light source and the photodetector and has a wavelength of λ2.
A phase element for setting the phase difference to be given to the first light to 2mπ (m is an integer) when the relationship of 1 <λ2 is satisfied, and calculating the tracking error by calculating the intensity of ± 1st order light of the second light. A signal is detected, and a reproduction RF signal is obtained by the zero-order light of the first light.

[0019]

In the optical disk player of the present invention, a phase diffraction grating is interposed between the light source and the photodetector in order to transmit one of the two wavelength lights emitted from the light source and diffract the other.

This phase diffraction grating has a phase difference of 2 with respect to the first light having the wavelength λ1 when the wavelength satisfies λ1 <λ2.
mπ (m is an integer). The tracking error signal is detected based on the difference of ± 1st order light of the second light having the wavelength λ2, and the reproduced RF signal is obtained by the 0th order light of the first light.

Therefore, unlike the related art, it is not necessary to cut out the emission light of the wavelength from the uncorresponding light source with a filter in accordance with the recording density of the signal of the optical disk.
There is no loss of light quantity.

Further, since the light reflected from the optical disk is received by a single photodetector, the position can be easily adjusted, so that the work of assembling the photodetector can be simplified. Furthermore, a single photodetector can be used, and a relatively expensive dichroic mirror conventionally used is not required.

[0023]

Embodiments of the present invention will be described below in detail with reference to the drawings. In the drawings described below, portions common to FIGS. 1 and 2 are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 3 shows an optical system according to an embodiment of the optical disk player of the present invention. A light source 1 emits laser beams having different wavelengths. The light source 1 is S
FG (Sum Frequecy Generation) is used,
Any two wavelengths λ1 and λ2 (λ1 <λ2) are emitted. After the light emitted from the light source 1 passes through the collimator 10, the phase diffraction grating 11 gives a phase difference of 2mπ (m: integer) to the short wavelength λ1.

The light emitted through the phase diffraction grating 11 is focused on the optical disk 6 by the objective lens 5 through the beam splitter 4.

The reflected light from the optical disk 6 passes through the objective lens 5 and then is split by the beam splitter 4 into the imaging lens 1.
It is folded back to two sides. The reflected light passing through the imaging lens 12 is
The light is condensed on a photodetector 8 through a cylindrical lens 7.

FIG. 4 shows details of the photodetector 8 and RF
2 shows an arithmetic circuit for detecting a signal and an error signal. As shown in the figure, the photodetector 8 is provided with three detection surfaces 8A, 8B and 8C.
A three-beam method is used for detecting a tracking error signal. The difference between the light receiving amounts of the detection surfaces 8A and 8C is obtained by the operation of the operational amplifier 17.

The focus error signal is detected by an astigmatism method. A focus error signal is obtained by calculating the diagonal sum of the four divided surfaces of the detection surface 8B by the operation of the operational amplifiers 13 and 15, and further obtaining the output difference of the operational amplifiers 13 and 15 by the operation of the operational amplifier 14.

The reproduced RF signal is obtained by adding the operation outputs of the operational amplifiers 13 and 15 by the operational amplifier 16. Next, the operation of the optical disk player having such a configuration will be described.

From the light source 1, a wavelength λ1 that differs depending on the SFG
And λ2 (λ1 <λ2).

Here, the function of SFG utilizes a parametric interaction in a nonlinear optical crystal.
By mixing the signal light with a laser beam having a strong angular frequency ω2, the angular frequency of the signal can be converted to ω1 + ω2 = ω3.

The outgoing lights of wavelengths λ 1 and λ 2 from the light source 1 are collimated by the collimator lens 10 and then enter the phase diffraction grating 11. The phase diffraction grating 11 gives a phase difference of 2mπ (m: integer) to the wavelength λ1, which is a short wavelength.

The outgoing light that has passed through the phase diffraction grating 11 is split into three beams: a zero-order light traveling straight through the phase diffraction grating 11 and ± first-order lights having a predetermined diffraction angle.

The outgoing light that has passed through the phase diffraction grating 11 passes through the beam splitter 4 and is then focused on the optical disk 6 by the objective lens 5.

The light reflected from the optical disk 6 is reflected by the beam splitter 4 toward the imaging lens 12. The reflected light condensed by the imaging lens 12 passes through the cylindrical lens 7 and is condensed on the photodetector 8.

As shown in FIG. 4, the reflected light from the photodetector 8 is focused on the 0th-order light on the detection surface 8B and on ± 8th-order light on the detection surfaces 8A and 8C. The reproduced RF signal is supplied to the operational amplifiers 13 and 15 as described above.
Are added by the operational amplifier 16 to obtain the calculation output.

By the way, the photodetector 8 has a wavelength λ.
When the zero-order lights of 1 and λ2 overlap, the wavelength λ
It is necessary to consider the allowable range of the adverse effects of 2.

In FIG. 5, each curve represents the signal recorded on the disk for the wavelength λ1, the wavelength λ1,
This shows a signal reproduced with light of λ2. The signal can be read at the wavelength λ1, and cannot be read at the wavelength λ2. In this case, the photo detector 8
In the above, the signal is the sum of the two signals.

Here, when the deterioration of the reproduction RF signal exceeds the allowable range, a measure can be easily taken by attaching an optical film for cutting the second light to the detection surface 8B so as to fall within the allowable range. be able to.

A three-beam method is used for detecting a tracking error signal. The difference between the light receiving amounts of the detection surfaces 8A and 8C is obtained by the operation of the operational amplifier 17.

The focus error signal is detected by an astigmatism method. A focus error signal is obtained by calculating the diagonal sum of the four divided surfaces of the detection surface 8B by the operation of the operational amplifiers 13 and 15, and further obtaining the output difference of the operational amplifiers 13 and 15 by the operation of the operational amplifier 14.

Subsequently, the light emitted from the light source 1 is λ and λ / 2.
The case of the two wavelengths will be described. In the configuration of the optical system in FIG. 3, the light source 1 has a second harmonic generation (SHG).
Has been adopted.

Thus, the light source 1 emits light having two wavelengths, a fundamental wave having a wavelength λ (hereinafter, referred to as light source light) and a second harmonic having a wavelength λ / 2 (hereinafter, referred to as SH light).

The light emitted from the light source 1 is collimated by the collimator lens 10 and then enters the phase diffraction grating 11. Here, the phase diffraction grating 11 shifts the phase by π with respect to the light source light having the wavelength λ.

For SH light having a wavelength of λ / 2, the phase difference is 2π, that is, the phase to be shifted = 0.

The SH light passes through the phase diffraction grating 11 as it is. The light from the light source is SH emitted from the phase diffraction grating 11.
The light is emitted as two light beams having a target angle with respect to the light. The outgoing light that has passed through the phase diffraction grating 11 passes through the beam splitter 4 and is condensed on the optical disk 6 by the objective lens 5.

The light reflected from the optical disk 6 is reflected by the beam splitter 4 toward the imaging lens 12. The reflected light condensed by the imaging lens 12 passes through the cylindrical lens 7 and is condensed on the photodetector 8.

As shown in FIG. 4, the state of collection of the reflected light in the photodetector 8 is such that the SH light having the wavelength λ / 2 is collected on the central detection surface 8B. The light source light having the wavelength λ is focused on the detection surfaces 8A and 8C.

As described above, the tracking error signal and the focus error signal are detected by the three-beam method and the astigmatism method.

As described above, in this embodiment, the phase diffraction grating 11 is interposed between the light source 1 and the photodetector 8 in order to reduce the phase difference between the two wavelengths emitted from the light source 1 to zero.

The phase diffraction grating 11 has a wavelength of λ1 <λ.
When the relationship is 2, the phase difference is 2mπ (m is an integer) with respect to the first light having the wavelength λ1. The tracking error signal is detected based on the difference of ± 1st order light of the second light having the wavelength λ2, and the reproduced RF signal is obtained by the 0th order light of the first light.

Therefore, unlike the conventional case, it is not necessary to cut out, by the filter 2, the outgoing light of the wavelength from the light source 1 which does not correspond to the recording density of the signal of the optical disk, so that there is no loss of light amount.

Further, since the light reflected from the optical disk is received by the single photodetector 8, the position can be easily adjusted, and the work of assembling the photodetector 8 can be simplified.

Furthermore, a single photodetector 8 can be used, and the relatively expensive dichroic mirror 9 conventionally used is not required.

Although the present embodiment has been described in connection with the case where the phase diffraction grating 11 is used to transmit one of the two wavelengths of light emitted from the light source 1 and diffract the other, the present embodiment is not limited to this. The object that does not have a lattice structure may be applied as long as the object gives a phase difference of 2mπ.

In this embodiment, the photodetector 8
Although the description has been made on the assumption that the intensities of the reflected lights converged on the detection surfaces 8A and 8C are equal, the detection surfaces 8A and 8C are not limited to this example.
If the intensities of the reflected lights condensed on C are different, at the time of calculation for obtaining a tracking error, by multiplying one of the signals by a coefficient, the intensities of the reflected lights are equivalently made equal.

[0057]

As described above, in the optical disk player of the present invention, one of the two wavelengths of light emitted from the light source is transmitted and the other is diffracted,
A phase diffraction grating was interposed between the light source and the photodetector.

When the wavelength is in a relationship of λ1 <λ2, the phase diffraction grating has a phase difference of 2 with respect to the first light having the wavelength λ1.
mπ (m is an integer). The tracking error signal is detected based on the difference of ± 1st order light of the second light having the wavelength λ2, and the reproduced RF signal is obtained by the 0th order light of the first light.

Therefore, unlike the related art, it is not necessary to cut out the emission light of the wavelength from the uncorresponding light source by the filter in accordance with the recording density of the signal of the optical disk.
There is no loss of light quantity.

In addition, since the light reflected from the optical disk is received by a single photodetector, the position can be easily adjusted, so that the work of assembling the photodetector can be simplified.

Further, since a single photodetector can be used, and a relatively expensive dichroic mirror conventionally used is not required, the cost of the apparatus can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an optical system of a conventional optical disk player capable of high-density recording and reproduction.

FIG. 2 is a diagram showing another example of an optical system of a conventional optical disc player capable of high-density recording and reproduction.

FIG. 3 is a diagram showing a configuration of an optical system according to an embodiment of the disc player of the present invention.

FIG. 4 is a diagram showing a photodetector of FIG. 3 and an arithmetic circuit for detecting various signals.

FIG. 5 is a diagram for explaining a case where reflected lights of different wavelengths are collected on the photodetector of FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light source 4 Beam splitter 5 Objective lens 6 Optical disk 7 Cylindrical lens 8 Photodetector 10 Collimator lens 11 Phase diffraction grating 12 Imaging lens

Continuation of the front page (56) References JP-A-3-62326 (JP, A) JP-A-1-176339 (JP, A) JP-A-1-267845 (JP, A) JP-A-63-317932 (JP) , U) (58) Fields surveyed (Int. Cl. ⁷ , DB name) G11B ^7/ 09-7/095 G11B 7/135 JOIS

Claims (1)

(57) [Claims] A light source that emits a first light having a wavelength of λ1 and a second light having a wavelength of λ2; a photodetector that receives light reflected from an optical disc; and a light detector that is interposed between the light source and the photodetector. A phase element that sets a phase difference to be given to the first light to 2mπ (m is an integer) when λ1 <λ2, and performs tracking by calculating the intensity of ± first-order light of the second light. An optical disk player comprising: detecting an error signal; and obtaining a reproduction RF signal by the 0th-order light of the first light.