JPH0581698A - Wavelength switching optical pickup - Google Patents

Abstract

PURPOSE:To use a single pickup with a normal disk as well as four times higher density disk by selecting long and short wavelength laser beams, which are generated by a laser diode and a second harmonics generating (SHG) element, respectively, through the use of corresponding liquid crystal shutters. CONSTITUTION:A dichromic mirror 7 separates a long wavelength laser beam 3, generated by a laser diode 1, and a short wavelength laser beam 6 which has a 1/2 wavelength and generated by an SHG element 5. And the separated laser beams 3 and 6 are selected by a first liquid crystal shutter 13a and a second liquid crystal shutter 13b, respectively and irradiate a disk 12 to perform recording and reproducing of information. Having this constitution, an optical pickup is provided which is used with a normal disk as well as a four times higher density disk by highly reliable long and short wavelength laser beams selected by liquid crystal shutters.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength switching type optical pickup for recording / reproducing information with laser beams having different wavelengths.

[0002]

2. Description of the Related Art Compacts commonly used in homes
The wavelength of light emitted from an optical pickup used in a disc player or a laser disc player is 7
It is 80 nm. Also, the pitch of the tracks on which the signals of the compact disc and the laser disc are recorded is 1.
It is 6 μm. Further, the laser light used in the document file device and the magneto-optical disk device, which have started to spread as industrial information storage devices, is 780 nm or 8 nm.
It is 30 nm, and the track pitch of the optical disks used in these devices is generally 1.6 μm.

On the other hand, recently, research and development of waveguides have progressed,
By the second harmonic generation element (abbreviated as SHG element), 4
Blue laser light of 15 nm or the like has come to be able to output at a practical level. Along with this, research and development of a high-density optical disc having a track pitch of about 0.8 μm, which is half that of conventional optical discs, was conducted, and a prototype example was announced (199
There is also a Denpai Newspaper with 0.6.22: by Japan Colombia).

[0004]

DISCLOSURE OF THE INVENTION Presently available compact discs, 5.25-inch write-once optical discs,
5.25 inch rewritable optical disc is based on the standard,
There are many commercialized products, and even if a new optical disc with a quadruple density with half the track pitch and half the linear velocity of the conventional one is released, the current standard will disappear soon or the product will It doesn't stop circulating.

That is, there is a period in which an optical disk having a current recording density and an optical disk having a quadruple density coexist. This is clear when looking at the history of conventional floppy disk products. In that case, it is necessary to record / reproduce optical disks of different standards with a single drive, although it has been commercialized as a floppy disk drive.

Here, FIGS. 4 and 5 show the conventional 1.6 μm.
FIG. 3 shows a side view and a front view when reproducing an optical disc having a track pitch with laser light having a wavelength of 415 μm. In FIG. 4, the broken line is the long-wavelength laser light 3 of the conventional drive device, and the wavelength is 780 nm to 830 nm. Since this is as designed, recording / playback is possible. On the other hand, the solid line is the short-wavelength laser light 6 having a wavelength of 415 nm, which is half that of the conventional one, and the tracking locus 36 follows an irregular path as shown in FIG. It becomes impossible to track. This is because the beam diameter is too small compared to the recording track width. From these, it is understood that it is impossible to record / reproduce an optical disk for a 780-830 nm laser beam by using the 415 nm short-wavelength laser beam 6.

Next, FIG. 6 is a schematic diagram when reproducing a high density optical disc having a track pitch of 0.8 μm with a long wavelength laser beam 3 having a wavelength of 780 to 830 nm. In this case, the optical disc for 415 nm has pit 37
Tracking becomes unstable because the groove depth is different from that for 780 to 830 nm and because the beam diameter is too large. Also, the pit 37 for 415 nm has a 780 to 830 n
It is a clear fact that m laser light cannot be used for reproduction.

From the above, in the case of a drive device using a 415 nm laser beam, it is impossible to record / reproduce an optical disk having a track pitch of 1.6 μm,
In the case of a drive device using a 780-830 nm laser beam, it is impossible to record / reproduce an optical disc having a track pitch of 0.8 μm.

[0009]

In a wavelength switching type pickup for recording / reproducing information by laser beams of different wavelengths, a laser diode for emitting a long wavelength laser beam,
SHG element for generating short-wavelength laser light having a half wavelength of long-wavelength laser light, first dichroic mirror for separating long-wavelength laser light and short-wavelength laser light and guiding them to different optical paths, and long-wavelength laser A pair of liquid crystal shutters for selectively transmitting and blocking light and short-wavelength laser light, and a second for guiding long-wavelength laser light and short-wavelength laser light to the same optical path
Of the dichroic mirror, and two systems of photosensors for signal conversion of the return lights of the long-wavelength laser light and the short-wavelength laser light, respectively.

[0010]

By the above means, it is possible to select and emit the laser beam to be used for the conventional optical disc and the optical disc of 4 times higher density, and to record / reproduce.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of a wavelength switching type pickup according to the present invention. In the figure, 1 is a laser diode,
A laser beam having a long wavelength of 830 nm is emitted. 2 is a driver for driving the laser diode 1, 3 is a wavelength of 830n
m is a long-wavelength laser light, 4 is a collimator lens for collimating the long-wavelength laser light 3, and 5 is an SHG element for newly generating short-wavelength laser light having a wavelength of 415 nm, which is half the long-wavelength laser light 3. Is a first dichroic mirror that transmits a short wavelength laser beam 3 having a wavelength of 415 nm, 7 transmits a long wavelength laser beam 3 and reflects a short wavelength laser beam 6 at an angle of 45 ° with respect to the traveling direction of the laser beam. It is installed, and the traveling direction of the short wavelength laser light 6 changes by 90 °.

Reference numeral 8 is a first reflection mirror installed at an angle of 45 ° with respect to the traveling direction of the short-wavelength laser light 6, and the traveling direction of the short-wavelength laser light 6 changes by 90 °.
Reference numeral 9 is a first polarization beam splitter, 10 is a second polarization beam splitter, and 11 is a first 1 for the long wavelength laser light 3.
/ 4λ plate, 12 is the second ¼λ for the short wavelength laser light 6
Plate, where the long-wavelength laser light 3 is the first polarization beam splitter 9 and the first ¼λ plate 11, and the short-wavelength laser light 6 is the second polarization beam splitter 10 and the second 1 / λ plate 11.
Each laser beam passes through the 4λ plate 12 and is circularly polarized.

Reference numeral 13a denotes a first liquid crystal shutter, 13b denotes a second liquid crystal shutter, and one of the first liquid crystal shutter 13a and the second liquid crystal shutter 13b is provided with a first liquid crystal shutter for transmitting a laser beam. The liquid crystal shutter 13a and the second liquid crystal shutter 13b are turned on / off to transmit the laser light.
Cut off. A second dichroic mirror 14 transmits the long-wavelength laser light 3 and reflects the short-wavelength laser light 5, and is installed at an angle of 45 ° with respect to the traveling direction of the laser light. No. 6 changes its traveling direction by 90 °. 15 is 45 with respect to the traveling direction of the short-wavelength laser light 6.
It is a second reflection mirror installed at an angle of °.

Reference numeral 16 is an objective lens, and 17 is an optical disc on which information is recorded. An actuator (not shown) keeps the distance between the objective lens 16 and the optical disc 17 constant. 1
Reference numeral 8 is a first detection lens for the long wavelength laser light 3, 19 is a first half mirror for splitting the long wavelength laser light 3 into two directions,
Reference numeral 20 is a first tracking photosensor for detecting a tracking error signal and RF signal, 21 is a first cylindrical lens, 22 is a first focusing photosensor for detecting a focus error signal, and 23 is an R
A first amplifier that generates an F signal, 24 is a second amplifier that generates a tracking error signal, and 25 is a third amplifier that generates a focus error signal.

Reference numeral 26 is a second detection lens for the short wavelength laser light 6, and 27 is a second detection lens for dividing the short wavelength laser light 6 into two directions.
Half mirror, 28 is a second tracking photo sensor for detecting a tracking error signal and an RF signal, 2
Reference numeral 9 is a second cylindrical lens, 30 is a second focusing photosensor for detecting a focus error signal, 31 is a fourth amplifier for generating an RF signal, and 32 is a fifth amplifier for generating a tracking error signal. , 33 is a sixth amplifier for generating a focus error signal.

Next, the operation will be described with reference to FIG. In the figure, a laser diode 1 emits a long-wavelength laser light 3 of 830 nm, passes through a collimator lens 4, and the long-wavelength laser light 3 becomes parallel light. When the long wavelength laser light 3 reaches the SHG element, a short wavelength laser light 6 of 415 nm, which is half the original wavelength, is newly emitted. Subsequently, the long-wavelength laser light 3 and the short-wavelength laser light 6 reach the first dichroic mirror 7, the long-wavelength laser light 3 passes through the first dichroic mirror 7, and the short-wavelength laser light 6 is the first dichroic light. It is reflected by Mira 7. The long-wavelength laser light 3 transmitted through the first dichroic mirror 7 is transmitted through the first polarization beam splitter 9 and the first ¼λ plate 11 and is circularly polarized, and reaches the first liquid crystal shutter 13a. On the other hand, the short-wavelength laser 6 which is changed by 90 ° by the first dichroic mirror 7 and is reflected at a right angle is subsequently changed by 90 ° by the first reflection mirror 8 and is then reflected by the second dichroic mirror 8. Circularly polarized light is transmitted through the polarization beam splitter 10 and the second ¼λ plate 12, and reaches the second liquid crystal shutter 13b.

Here, the first liquid crystal shutter 13a and the second liquid crystal shutter 13a
The liquid crystal shutter 13b is selectively turned on / off to perform transmission / blocking. Turn on the first liquid crystal shutter 13a,
When transmitting the long-wavelength laser 3, the long-wavelength laser light 3
Passes through the second dichroic mirror 14 and reaches the objective lens 16 and the optical disc 17. The long-wavelength laser light 3 reflected by the optical disk 17 is the objective lens 16, the second dichroic mirror 14, the first liquid crystal shutter 13a, and the first liquid crystal shutter 13a.
After passing through the 1/4 λ plate 11, the first polarization beam splitter 9 is reflected, and the first polarization beam splitter 9 changes its direction by 90 °.

The long-wavelength laser light 3 passes through the detection lens 18, reaches the first half mirror 19, a part of the long-wavelength laser light 3 goes straight, and the rest is reflected. The long-wavelength laser light 3 traveling straight is divided into two first tracking photosensors 2
The RF signal is generated by the first amplifier 23 and the tracking error signal is generated by the second amplifier 24. On the other hand, the reflected long-wavelength laser light 3 passes through the first cylindrical lens 21, reaches the first focusing photosensor 22 divided into four, and the third amplifier 25 generates a focusing error signal. The tracking error signal and the focusing error signal described above are fed back to an actuator (not shown) supporting the objective lens 16 to adjust the position of the objective lens 16. Further, the RF signal is processed as information.

On the other hand, when the second liquid crystal shutter 13b is turned on and the short-wavelength laser light 6 is transmitted, the short-wavelength laser light 6 changes its direction by 90 ° by the second reflection mirror 15, and further by the dichroic mirror 14. The direction is changed by 90 °, the light passes through the objective lens 16, and reaches the optical disc 17. Optical disc 1
The short-wavelength laser light 6 reflected by 7 passes through the objective lens 16 and is reflected by the second dichroic mirror 14 after changing its direction by 90 °, and then by the second reflecting mirror 15 after being changed by 90 °. , The second liquid crystal shutter 13b, the second 1
The second polarization beam splitter 1 passing through the / 4 λ plate 12
It reaches 0. The short-wavelength laser light 6 whose direction is changed by 90 ° by the second polarization beam splitter 10 is the second detection lens 26.
To reach the second half mirror 27. The short-wavelength laser light 6 partially passes through the half mirror 27 and the rest is reflected.

The straight-wavelength short-wavelength laser light 6 is divided into two second parts.
To the tracking photo sensor 28, the RF signal is generated by the fourth amplifier 31, and the tracking error signal is generated by the fifth amplifier 32. On the other hand, the reflected short-wavelength laser light 6 passes through the second cylindrical lens 29, and is divided into four second focusing photosensors 3.
When reaching 0, the sixth amplifier 33 generates a focusing error signal. The obtained tracking error signal and focusing error signal are fed back to an actuator (not shown) supporting the objective lens 16 to adjust the position of the objective lens 16. Further, the RF signal is processed as information.

Next, the outline of the liquid crystal shutter will be described with reference to FIG. In the figure, when a low signal is generated by the switching signal generator 34, the second liquid crystal shutter 13b is in the off state, and the short wavelength laser light 6 is cut off. On the other hand, the low signal becomes high through the inverter 35, and the first liquid crystal shutter 13a is turned on. As a result, the long wavelength laser light 3 passes through the liquid crystal shutter 13a. As described above, the on / off operation is performed by applying the DC voltage of several V to the liquid crystal shutter. Further, the identification signal of the liquid crystal shutter on / off may be provided, for example, on the cartridge of the optical disc. Incidentally, conventionally, a mechanical shutter has been used for the liquid crystal shutter portion.

Next, FIG. 3 which is a schematic view showing the beam diameter will be described. In the figure, the diameter of the narrow wavelength laser light 3 passing through the objective lens 16 is twice the diameter of the short wavelength laser light 6. Further, the optical axes of the two types of laser light do not need to be particularly aligned.

[0023]

The wavelength switching type optical pickup of the present invention is
It is possible to record / reproduce an optical disk having a current recording density and an optical disk having a quadruple density with one unit. Further, the liquid crystal shutter is smaller and more reliable and effective than the mechanical shutter.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a wavelength switching type optical pickup.

FIG. 2 is a schematic diagram of a liquid crystal shutter.

FIG. 3 is a schematic diagram showing a diameter of a diaphragm portion of laser light.

FIG. 4 is a side view when a conventional 1.6 μm track pitch optical disc is reproduced with laser light having a wavelength of 415 nm.

FIG. 5 is a front view of a conventional 1.6 μm track pitch optical disc when being reproduced with laser light having a wavelength of 415 nm.

FIG. 6 is a schematic diagram when reproducing a high density optical disc having a track pitch of 0.8 μm with laser light having a wavelength of 780 to 830 nm.

[Explanation of symbols]

 1 laser diode 3 long wavelength laser light 5 SHG element 6 short wavelength laser light 7 first dichroic mirror 13a first liquid crystal shutter 13b second liquid crystal shutter 14 second dichroic mirror 20 first tracking photosensor 22 second First Focusing Photo Sensor 28 Second Tracking Photo Sensor 30 Second Focusing Photo Sensor

Claims (1)

[Claims] 1. A wavelength switching pickup for recording / reproducing information by laser beams of different wavelengths, a laser diode emitting a long wavelength laser beam, and a short wavelength laser beam having a half wavelength of the long wavelength laser beam. Second to generate
A harmonic generation element, a first dichroic mirror for separating long-wavelength laser light and short-wavelength laser light and guiding them to different optical paths, and a pair for selectively transmitting and blocking long-wavelength laser light and short-wavelength laser light. Liquid crystal shutter, a second dichroic mirror for guiding the long-wavelength laser light and the short-wavelength laser light to the same optical path, and two systems for signal conversion of the return light from the long-wavelength laser light and the short-wavelength laser light A wavelength switching optical pickup, comprising: