KR100280183B1 - Optical disk device using acoustooptic modulation - Google Patents

Abstract

The present invention provides an optical disk device; The laser diode driver IC (Integrated Circuit) applies a multi-stage current to continuously generate a laser beam of a predetermined size in the laser diode of the optical disk device; The laser diode continuously generates a laser beam under control of the laser diode driver IC; The laser beam changing means changes the diffraction angle of the laser beam generated in the laser diode and the amount of light of the laser beam, and switches the laser beam at high speed; The control means is characterized by controlling the laser diode driver IC so that the laser beam is continuously generated at the laser diode, and controlling the laser beam to be switched at high speed by the laser beam changing means. Therefore, in the present invention, the laser diode driver IC always irradiates the laser beam, and can switch the laser beam at high speed in an acousto-optic modulator at high speed, thereby replacing the expensive laser diode driver IC with a low-cost laser diode driver. Can be replaced by IC to provide a low-cost optical pickup device

Description

Optical disk device using acoustooptic modulation

The present invention relates to an optical disk device, and more particularly, to adjust a reflection amount of a laser beam through an acoustic-optic modulator without reflecting a laser beam through a mirror. At the same time, there is provided an optical disk apparatus using an acousto-optic modulation for irradiating a laser beam to a disc by switching the laser beam at a high speed in the acoustooptic modulator without switching the laser beam in the laser diode driver IC.

In general, optical recording media such as compact discs (CDs), digital video discs (DVDs), etc., floppies are magnetic recording media having a diameter of several inches and a thin thickness of 1.2 mm but having a capacity within 2 megabytes. Hundreds of megabytes of data storage capacity, which is hundreds of times larger than a disk, has a reflective surface that reflects light as a data recording layer, and is composed of a combination of pits formed concave on the reflective surface. As a storage medium for storing information, the development of a compact disk having such a large capacity and the development of an optical disk device for reading data stored at high density with high precision and high speed without reading errors and writing data to the disk It is going on steadily.

In addition, such an optical disk device has been developed with the development of a device capable of playing / recording a mixture of various types of disks (CD, DVD, etc.), and thus, a user can use an arbitrary disk together through one optical disk device. Can be played back / recorded.

Discs are usually divided into CDs and DVDs, CDs are divided into CD / R and CD / RW, and DVDs are divided into DVD / R and DVD / RW. In addition, DVD is divided into DVD-S and DVD-D according to recording of information. Here, the CD is divided into a product that contains only audio information and video information and audio information, and the DVD is a DVD-S in which only one information is recorded in a single layer on one track, and one Two pieces of information on the track are divided into DVD-Ds recorded simultaneously in dual layers.

The configuration of such an optical disk device (3-beam type) is shown in FIG. First, the laser diode driver IC (Integrated Circuit) 2 which receives the control signal of the encoder 1 is configured to drive the laser diode 3 which generates the laser beam.

The laser diode 3 is configured to generate a laser beam having a wavelength of 780 nm in the case of a CD and a laser beam having a wavelength of 650 nm in the case of a DVD according to the driving of the laser diode driver IC 2. Here, when the laser diode 3 reads the data of the disc 9 under the control of the laser diode driver IC 2, the laser diode 3 generates a laser beam of at least 5 mW up to 12 mW, and transmits the data to the disc 9. When recording, a laser beam of about 70 mW is generated.

The grating 4 separates one laser beam generated and emitted from the laser diode 3 into three laser beams for performing tracking servo.

A beam splitter 5 reflects and transmits three laser beams separated in the grating 4.

The collimate lens 6 converts three laser beams in the form of divergent light split by the grating 4 into balanced light when irradiated through the beam splitter 5.

The mirror 7 changes the direction of the laser beam such that the balanced light that has passed through the collimating lens 6 is irradiated onto the disk 9.

The objective lens 8 collects a laser beam whose direction is changed in the mirror 7 and irradiates the disk 9.

The splicing / cylindrical lens 10 converts the laser beam reflected from the disk 9 into astigmatism for performing Focus Servo.

The photodiode integrated circuit 11 is divided into four and converts the laser beams received by the separate auxiliary photodiodes into electrical signals to track the main photodiodes and tracks for reading data. In the drawing, reference numeral 12 is a monitor photodiode that receives a laser beam transmitted from the beam splitter 5 and outputs a signal for performing APC (Optical Power Control) and OPC (Optimum Power Control).

Referring to the operation of the optical disk device, first, a laser beam is generated and radiated from the laser diode 3 under the control of the laser diode driver IC 2, which is separated into three beams in the grating 4 and then the beam. It enters into the splitter 5. The laser beam incident on the beam splitter 5 is reflected and transmitted to the balanced light in the collimated lens 6, and the three laser beams changed to the balanced light in the collimated lens 6 are transmitted to the mirror 7. This is reflected by the objective lens 8. Then, the objective lens 8 condenses three laser beams and irradiates the pits of the disk 9.

In addition, the laser beam irradiated and reflected on the pit of the disk is passed through the objective lens 8, the mirror 7, the collimated lens 6, the beam splitter 5, and the connection / cylindrical lens 10 to the photodiode IC. It is received by (11).

When the data is written on the surface of the disc 9, a laser beam of intensity (about 70 mW) that can be recorded by the control of the laser diode driver IC 2 and the encoder 1 is generated in the laser diode 3 Through the above path, the surface of the disk 9 is irradiated to form pits on the surface of the disk 9.

However, according to the conventional optical disk device, the following problems occur.

First, since the laser diode driver IC needs to switch the current applied to the laser diode at a high speed as shown in the I-T graph of FIG. 2, an expensive laser diode driver IC capable of high speed switching is used.

Second, noise is generated in the laser beam generated from the laser diode by the high frequency current generated at the high speed switching.

Therefore, the present invention is to solve such problems, the first object of the present invention is that the laser diode driver IC always irradiates the laser beam, and the laser beam at a high speed in the Acousto-Optic Modulator By switching, an expensive laser diode driver IC is replaced with a low cost laser diode driver IC to provide a low-cost optical pickup device.

In addition, the second object of the present invention is that the high speed switching of the laser beam is not performed by the current control in the laser diode driver IC, and the high speed switching of the laser beam is performed by the voltage control in the acousto-optic modulator. It is to provide an optical disk device with low noise because no noise is generated.

1 is a block diagram showing a configuration of a general optical disk device,

2 is an I-T graph showing that a conventional laser diode driver IC applies current to a laser diode when writing data to a disc.

3 is a block diagram showing the configuration of an optical disk apparatus using acoustooptic modulation according to the present invention;

4 is a functional diagram showing the operation of the acoustooptic modulator applied to the present invention,

5 is an R-Is graph showing the change of reflectance according to the acoustic wavelength intensity of the acoustooptic modulator applied to the present invention.

<Description of the code | symbol about the principal part of drawing>

1, 100: encoder 2, 200: laser diode driver IC

3, 300: laser diode 400: acousto-optic modulator

A feature of the present invention for achieving the above objects is that the laser diode driver IC (Integrated Circuit) applies a multi-stage current to continuously generate a laser beam of a predetermined size in the laser diode of the optical disk device; The laser diode continuously generates a laser beam under control of the laser diode driver IC; The laser beam changing means changes the diffraction angle of the laser beam generated in the laser diode and the amount of light of the laser beam, and switches the laser beam at high speed; The control means is to control the laser diode driver IC so that the laser beam is continuously generated at the laser diode, and to control the laser beam to be switched at high speed in the laser beam changing means.

Here, the laser beam changing means is an acoustic-optic modulator for controlling the laser beam by giving acoustic wave vibration to a predetermined medium.

The control means is an encoder which controls the frequency of acoustic wave vibration generated by the laser beam changing means and controls the laser diode driver IC so that the magnitude of the current applied from the laser diode driver IC to the laser diode is determined.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The same reference numerals refer to the same components as in the prior art, and redundant description of the components is omitted.

3 is a block diagram showing the configuration of an optical disk apparatus using acoustooptic modulation according to the present invention.

Referring to FIG. 3, first, the encoder 100 performs general control in recording and reproducing data, and in particular, the sound generated in the acoustooptic modulator 300 by encoding of the data in data recording. Control the vibration frequency of the wave.

The laser diode driver IC 200 applies currents of several channels to the laser diode 300 such that a laser beam of a constant intensity is continuously generated from the laser diode 300 when data is recorded and reproduced.

The laser diode 300 generates a laser beam of a constant intensity when recording and reproducing data by the laser diode driver IC 200.

Acousto-Optic Modulator 400 converts the oscillation frequency of the acoustic wave to a voltage in accordance with the control signal input from the encoder 100 to the diffraction angle of the laser beam generated by the laser diode 300 and the laser beam It is provided between the collimated lens 6 and the objective lens 8 so as to change the amount of light and to switch the laser beam at high speed. Here, the acousto-optic modulator 400 is also called an acoustic wave modulator, and is provided by a diffraction grating obtained by giving an acoustic wave vibration in a medium such as tellurium glass or fused quartz to cause a periodic change in refractive index. The diffraction light intensity is modulated using the diffraction of. The acoustooptic effect occurs when the light beam passes through a transparent material such as glass, in which case the acoustic wave appears as shown in FIG. Acoustic waves are generated in the glass by a piezoelectric transducer driven by an RF signal source. A constant density change in the glass corresponding to the compression and rarity of the moving acoustic wave occurs with the change of the refractive index with respect to the propagation of the beam in the medium. Acoustic waves traveling at this change in refractive index cause the crystal diffraction X-Ray to diffract the projected light in the atomic plane, as in Bragg dispersion. For acoustic waves with strong power, most of the light projected onto the acoustooptic modulator is diffracted and deviates from the projection direction.

The light beam passing through the acoustically driven medium is refracted at an angle as shown in Equation 1 below.

here, θ : Diffraction angle, m: refraction coefficient, λ : Wavelength, d: length of acoustic wavelength.

In FIG. 1, the reflectance is shown in Equation 2 below.

Where R: reflectance, Is: acoustic wavelength intensity, L: medium length, μ : parameter, λ _o : Free space wavelength of the laser beam.

The three common modes of operation of the acoustooptic modulator are:

(1) Deflection: Under optimal conditions, the acousto-optic modulator diffracts nearly 85-90% of the projected light into one-coefficient diffraction beam. Just by turning on and off the acoustic energy power source, the acoustooptic modulator can act as a quick light deflector. Switching the see-through light with a one-coefficient diffraction beam takes place in a very short time depending on how quickly the acoustic wave field turns on and off the volume of the tellurium glass in which the laser beam is moving. By simply varying the acoustic wavelength intensity Is of the acoustooptic modulator, the laser beam can be redirected at different angles. The diffracted beam appearing in the acoustooptic modulator is in the 3.3 mrad angular range when the acoustic drive frequency is 30-50 MHz. This feature allows products such as laser printers and direct laser displays to move the laser beam quickly in space without moving parts.

(2) Modulation: The amount of laser beam diffracted into one coefficient beam depends on the amplitude of the acoustic wave diffracting the scanning laser beam. Thus, the intensity of the diffracted light beam can be modulated by modulating the power level of the acoustic wave so that electrical signals, including voice, music and television, can modulate the intensity of the light beam as part of an optical communication system.

(3) Frequency variation: This is one of the most useful features for acousto-optic modulators. This function, which changes the frequency of the laser beam to an accurate and stable amount, plays a decisive role in generating a bit-note from two light beams.

Hereinafter, the operation of the optical disk device using the acoustooptic modulation according to the present invention will be described in detail with reference to the accompanying drawings.

First, as described above, when data is written to a disk, the laser diode driver IC 200 applies a constant current to the laser diode 300 such that a 70 mW laser beam is continuously generated from the laser diode 300. A laser beam of 70 mW is generated at 300 and irradiated to the grating 4. Then, the beam is split into three beams in the grating 4 and then incident to the beam splitter 5, and the laser beam incident to the beam splitter 5 is reflected and converted into balanced light in the collimated lens 6. Irradiated with the acousto-optic modulator 400.

On the other hand, when the control signal is input to the acousto-optic modulator 400 from the time when the laser beam is irradiated from the encoder 100, the acoustooptic modulator 400 changes the frequency of the acoustic wave vibration with a voltage according to the input control signal. As shown in Equation 1, the laser beam irradiated from the collimating lens 6 corresponds to the frequency of the surface acoustic wave according to Bragg's diffraction equation so that the laser beam is diffracted, and at the same time as shown in FIG. By changing the Is, the reflectance R, that is, the amount of light of the laser beam is adjusted to switch the laser beam at high speed.

Then, the laser beam diffracted by adjusting the amount of light in the acoustooptic modulator 400 is reflected to the objective lens 8, whereby three laser beams are collected by the objective lens and irradiated onto the disk 9 to form a pit. Let's do it.

In addition, the laser beam of the intensity which can be reproduced by the control of the encoder 100 and the laser diode driver IC 200 is irradiated to the pit of the disc 9 through the above path and reflected again when the disc is reproduced. The laser beam is received by the photodiode IC 11 through the objective lens 8, the mirror 7, the collimated lens 6, the beam splitter 5, and the connection / cylindrical lens 10.

Therefore, the laser diode driver IC continuously applies a constant current to the laser diode when writing data to the disk, and the laser beam generated from the laser diode is switched at high speed by diffraction and high speed in the acousto-optic modulator to record the data, thereby inexpensive laser diode A driver IC can be used, and high frequency current noise is not generated in the laser beam generated from the laser diode by the fast switching of the laser diode driver IC.

As described above, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined by the claims below and equivalents thereof.

As described above, the optical disk apparatus using the acoustooptic modulation according to the present invention has the following advantages.

Firstly, the laser diode driver IC always irradiates the laser beam and can switch the laser beam at high speed from the Acousto-Optic Modulator to replace the expensive laser diode driver IC with a low cost laser diode driver IC. In order to provide a low-cost optical pickup device.

Second, since the high speed switching of the laser beam is not performed by the current control in the laser diode driver IC, and the high speed switching of the laser beam is performed by the voltage control in the aco-optic modulator, noise is generated by the high frequency current in the laser diode. It provides a low noise optical disk device.

Claims (3)

An optical disk device; A laser diode driver integrated circuit (IC) for applying a plurality of currents to continuously generate a laser beam of a predetermined size in the laser diode of the optical disk device; A laser diode that continuously generates the laser beam under control of the laser diode driver IC; Laser beam changing means for changing the diffraction angle of the laser beam generated in the laser diode and the amount of light of the laser beam, and switching the laser beam at high speed; And And controlling means for controlling the laser diode driver IC such that the laser beam is continuously generated in the laser diode, and controlling the laser beam to be switched at high speed in the laser beam changing means. Optical disk device to use. The method of claim 1, wherein the laser beam changing means, An optical disk apparatus using an acoustic optical modulation, characterized in that it is an acoustic-optic modulator for controlling the laser beam by giving an acoustic wave vibration to a predetermined medium. The method according to claim 1 or 2, wherein the control means, And an encoder controlling the frequency of the acoustic wave vibration generated by the laser beam changing means and controlling the laser diode driver IC to determine the magnitude of the current applied from the laser diode driver IC to the laser diode. An optical disk apparatus using an acousto-optic modulation.