JPS6292134A - Optical recording and reproducing device - Google Patents

Abstract

PURPOSE:To improve the recording density of information on a recording medium and to increase the data transfer speed by producing a beam light from a light source having plural wavelengths. CONSTITUTION:A recording/reproducing/erasing signal 31 is fed to a distributor 15 from a recording/reproducing/erasing system control circuit 23 and distributed into three signals, they are all fed to a laser drive circuit 15, a laser 1 is driven to form a beam light 32 having three kinds of wavelengths lambdaa-lambdac. The beam light 32 is shaped into a collimated light showing a true circle via a collimate lens 2 and a shaping prism 3. The shaped light beam passes through the 1st AO modulator 4 applying amplitude modulation to the beam light of wavelength lambdaa, the 2nd AO modulator 5 applying amplitude modulation to the beam light of wavelength lambdab, and the 3rd AO modulator 6 applying amplitude modulation to the beam light of wavelength lambdac. The three AO modulators are controlled respectively by using three signals divided from the recording/reproducing/ erasing signal 31 by the distributor 16.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an optical recording device, and particularly to an optical recording device 4 suitable for increasing information recording density.

[Background of the invention]

The general structure of the optical head of a conventional optical recording device is described, for example, in the document "Optical System for Optical Discs (Precision Instruments Vol. 50, No. 12,
Figure 2 shows what is introduced in ``Pine Forest''. In this optical head, light from a laser diode 1 is converted into a perfectly circular parallel beam by a collimating lens 2 and a shaping prism 3, and is then transmitted through a polarizing beam splitter (PBS) 150 to 7. /4
The light passes through the plate 15 and is focused by the objective lens 152 onto the surface of the recording film on the recording medium 153 for recording, reproduction, or erasing.

In addition, focusing and tracking of the beam light, furthermore,
In order to reproduce the signal, the reflected light from the recording film surface is returned to the PBS 150 via the λ/4 plate 151, and at this time,
Since the reflected light has a phase shift of λ/2 from the incident light, PBSL5
0 and enters the photodetector 154.

The performance of an optical recording device as a recording device is usually evaluated in terms of information recording capacity, that is, recording density, data transfer rate, data access time, and the like. However, when a conventional optical head is used, there are drawbacks in terms of information recording density and data transfer speed, as will be described later.

In conventional optical heads, because of this structure, the recording surface density of information depends on the diameter of the beam light on the recording film surface, and this diameter can be minimized by perfectly focusing the beam.

However, in this narrowing down, the wavelength of the beam light becomes the lower limit value, and it is physically impossible to narrow down the light beam below that value. For example, when a normal semiconductor laser is used as a light source, the lower limit of narrowing down the beam light is about 800 nm. Therefore, when a conventional optical head is used, the recording surface density of information is determined by the wavelength of the beam used.

Further, the data transfer speed depends on the recording linear density of information in the track direction and the recording/reproducing/erasing speed.

If the recording linear density of information is P (m-') and the recording, reproducing, and erasing time is τ (s), the number of bits b (s-1) during recording, reproducing, and erasing per unit time is b =1/τ
(1) If the moving speed of the recording medium is ν (m/s), then
2) Yan □ p τ (]), From equation (2), b=p・ν (3) Therefore, the number of bits during recording, reproduction, and erasing per unit time is the recording linear density of information in the track direction It is proportional to the product of P and the moving speed ν of the recording medium.

Since the number of bits during recording, reproduction, and erasing per unit time is equivalent to the data transfer rate, the data transfer rate is equal to the product of the recording linear density of information in the track direction and the moving speed of the recording medium. Therefore, in order to increase the data transfer rate, it is necessary to increase the recording linear density of information in the track direction or to increase the moving speed of the recording medium. However, increasing the linear density of information in the track direction is nothing but increasing the recording surface density, and as described above, the limit is determined by the wavelength of the beam light. Also, in order to increase the moving speed of the recording medium, from equation (2), recording and reproduction,
It is necessary to shorten the erasing time τ. This time τ
depends on the characteristics of the recording film, and shortening the time requires increasing the sensitivity of the recording film.

In this way, when using conventional optical heads, in order to improve information recording density and data transfer speed, it is necessary to shorten the wavelength of the beam light and increase the sensitivity of the recording film, which is a practical solution. The current situation is that no progress has been made in improving the performance of the Naganaka two due to lack of proper measures.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical recording device that increases the recording density of information on a recording medium and improves the data transfer speed.

[Summary of the invention]

In order to increase the recording density of information on a recording medium, the volumetric density is improved not only in the surface direction but also in the depth direction of the recording medium. As a solution to this problem, a film structure of the recording medium as shown in FIG. 3 can be considered. That is, the recording film is the first layer 16.
By stacking layers from layer 0 to layer 0 161 with the protective film 165 in between, the recording density is improved by n times at once. Also,
The protective film 165 prevents heat conduction between the recording films because most of the materials normally used as the recording film change their properties when heated by the thermal energy of the beam light and function as an information recording film. , to prevent previous records, etc.
It is best to use one that has a heat insulating function.

However, in the case of such a multilayer recording film, it is impossible to record, reproduce, and erase information using the functions of conventional optical recording devices. That is, a means is required for irradiating each of the multilayered recording films with a light beam whose beam diameter is selectively narrowed down. Therefore, as a means of achieving this, we devised a method in which each recording film is irradiated with a light beam using light beams with different wavelengths. This is because the focal length f of the light beam changes in the form fCk'-λ/NA (4) depending on the wavelength λ of the light beam and the numerical aperture NA of the objective lens. In fact, if the wavelengths of each light beam are selected so that their focal lengths f are the same, then by controlling the focusing of a light beam of one wavelength with one objective lens, the light beams of all wavelengths can be focused. is focused on the target recording film of each layer. Therefore, selectively
It is possible to irradiate a light beam with a sufficiently narrowed beam diameter.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. In this embodiment, an optical recording apparatus that records, reproduces, and erases information on a recording medium having three layers of recording films will be described.

A recording, reproducing, and erasing signal 31 is applied to the distributor 16 from the recording, reproducing, and erasing system control circuit 23 of the optical recording device.
The signals are divided into three signals, all of which are applied to the laser drive circuit 15, and the laser 1 is driven to produce three different wavelengths λa,
A light beam 32 having λb and λC is generated. This light beam 32 is transmitted through a collimating lens 2. The light passes through a shaping prism 3 and is shaped into perfectly circular parallel light. This shaped light beam.

A first AO modulator 4 that amplitude modulates the beam light of wavelength λa, and a second AO modulator 4 that amplitude modulates the beam light of wavelength λb.
The light beam passes through an O modulator 5 and a third A, O modulator 6 which amplitude modulates the beam light of wavelength λC. These three A○ modulators are.

The recording, reproduction, and erasing signals 31 are divided into three by the distributor 16, and each is controlled by the signal.

This situation will be explained using FIG. 4. Figure 4 (a)
is an example of the recording, reproducing, and erasing signal 31, and in this case, the recording signal is considered. This recording signal is high level (1)
It is a digital signal that takes two values: and low level (0), and when sampled with a synchronization signal, it becomes a signal sequence of 1 or 0. In this example, there are 9 signal sequences, 1101001
It shows a signal of 1.1. The distributor 16 in FIG. 1 distributes this signal train into three signal trains. That is,
The recording signal A is converted into a signal string as shown in FIG. 4(b), and the recording signal A corresponding to the first synchronization signal is 1 as the first bit, and the recording signal B is 1 as the second bit. The third bit of the recording signal C becomes 0. On the other hand, these three signal trains are applied to the laser drive circuit 15, and the laser drive circuit 15 performs an OR'm operation on the three signals and outputs a laser drive signal. Therefore, in this example, the laser 1 is driven by a pulse train as shown in FIG. 4(c), and generates a light beam of the same pulse train. As mentioned above, the three recording signals A, B, and C generated by the distributor 16 are the first, second, and third recording signals A, B, and C, respectively.
○Drive the modulator. Therefore, the light beams of three wavelengths λa, λb, and λC generated by the laser are selectively recorded by the first, second, and third A○ modulators to have an amplitude O when the recording signal is O, respectively. If the signal is 1, the amplitude is modulated to 1. therefore,
The light beam 33 that has passed through the third A○ modulator 6 in FIG. 1 has three wavelengths λa, λb, and λC coexisting as three independent signals as shown in FIG. 4(b). There is.

This light beam 33 passes through the first PBS 7, the -λ1 plate 10, the second (7) PBS8, -λ2 plate 11, and the third (47) PBS-λ8 plate 12, and is focused by the objective lens 13 onto the recording film. The light is focused on. The distance relationship between the objective lens 13 and each recording film at this time will be explained using FIG. 5. The recording film layers 24 .
．． 25.26 distances f1, f2. If f8 is selected as follows, the light beams 41, 42, and 43 of each wavelength λa, λb, and λC are focused on each layer 24, 25, and 26 of the recording film, and recording can be performed independently.

Also, if the distance between each layer of the recording film 11Fld s, d2 is created as follows. distance f1 from objective lens 1
3 in the vertical direction, that is, by performing focus control only on the light beam of wavelength λa, it is possible to appropriately narrow down the light beam for all wavelengths.

On the other hand, in order to perform playback, focus, and tracking control, it is necessary to extract the reflected light, sense the intensity of the reflected light, and perform signal processing.
The explanation will be given again using FIG. 1. In this case as well, the light beams of three types of wavelengths λa, λb, and λC pass through the objective lens 13° and the three AO modulators 9, 8.7 as reflected lights, and are divided into 1 parts, and the reflected light 44. Reflected light of wavelength λ-45. A method of extracting three wavelength light beams by using PBS in the photodetectors 17, 18, and 19 will be explained. λ
The light beam of wavelength a passes through the 1λ3 plate as emitted light, is reflected by the third PBS, and is separated from light beams of 5 and 4 wavelengths.

Therefore, at this point, the optical beam t1 of λa needs to be phase-converted by one λa. Further, the phase shift Δλ when light with a wavelength λ passes through the −λ0 plate is as follows. Using equation (7), the conditions for separating the light beam of wavelength λa are as follows. Furthermore, since the light beam with the wavelength λb passes through the -λ2 plate one more time than the light beam with the wavelength λa, 2 4λl114 λb 4λb. Since the light beam having the wavelength λC passes through the -λ1 plate one more time, it becomes 2 4λc 4λc 4λC. By rearranging equations (8), (9), and (10), we can obtain λ, λ2.
If λ8 is expressed using λa, λb, and λC, λ32=
2 λaz−λcZ J . However, in order for this formula to have meaning, λC〉
The following condition is required: λb>λa>−λc (13).

In this way, for three wavelengths λa, λb, λC, λ
l, λ2. By selecting λ3, it is possible to extract each of the aforementioned three light beams of three wavelengths λa, λb, and λC.

A reproduction signal 51, a focus error signal 54 . Tracking error signals 57 are output respectively. Also, a reproduced signal 52. which changes depending on the recorded state read out by the detector 18 with a light beam of wavelength λ5. Focus error signal 55 that changes due to focus shift
．． A tracking error signal 58 that changes due to tracking deviation, a reproduced signal 53 read out by the detector 19 with a light beam of wavelength λ8. Focus error signal 56. Tracking error signals 59 are each output. These focus error signals and tracking error signals are input to the focus circuit 20 and the tracking circuit 21, and each focus actuator drive signal 61
A tracking actuator drive signal 62 is applied to the focus and tracking actuator 27 to move the objective lens 13 and perform focus control and tracking control. Note that focus error signals and tracking error signals for all wavelengths are not necessary, and if focus control can be performed for one wavelength, focus control for three wavelengths can be performed. Furthermore, since the optical axes of the three wavelengths coincide with each other in tracking control, it is sufficient to perform tracking control for one wavelength.

Now, the reproduced signal 51.52 input to the signal processing circuit
．． Regarding 53, for example, consider the case where information recorded using the recording signal shown in FIG. 4(b) is reproduced. FIG. 6 shows a perspective view of a recording medium recorded with the recording signal of FIG. 4(b). In FIG. 6, the state recorded in LL 1 +7 is indicated by diagonal lines. The recording signal A in FIG. 4(b) is irradiated as a light beam with a wavelength λa as described above,
It is recorded on the recording film 24 shown in FIG. Similarly, recording signal B
is recorded on the recording film 25, and the recording signal C is recorded on the recording film 26. If the reflectance of the shaded area in FIG. 6 recorded as 1 is greater than other areas, if the reproduced signal is extracted as reflected light, 1. If the intensity is high, 1.
If the reflected light intensity directly corresponds to the recorded information, and is shaped according to the reflected light intensity taken into the detector and extracted as a pulse signal, each wavelength λ, λ1 . Detector 17, 18° 19 for λ0
The output signals from are recording signals A and B, respectively.

C, and the reproduced signal is correctly extracted. This signal is processed by the signal processing circuit 22 shown in FIG. 1, in contrast to the 1-distributor 16, by extracting information one by one from the three signals and sequentially outputting the information, as shown in FIG. 4(a). A reproduced signal equal to the recorded signal is obtained.

Up to this point, we have ignored the disadvantages of stacking the recording films of the recording medium. Below, we will consider this point and provide possible solutions. By stacking recording films, the lower part,
That is, the beam light intensity decreases in a portion away from the beam irradiation surface.

Therefore, a light beam having a distribution in which the light intensity monotonically increases with respect to the wavelength as shown in FIG. 7 is effective. In other words, the beam of light λa, which has a short wavelength, is focused on the first recording film near the surface and performs recording reproduction, whereas the light beam of λb, which has a longer wavelength, passes through the first recording film. Then, the beam light having the longest wavelength λC passes through the first and second recording films, and then finally reaches the third recording film. The beam light of wavelength λb is reflected or absorbed by the first recording film, and the beam light of wavelength λC is reflected or absorbed by the second and second recording films, and the light beam is reflected or absorbed by the first recording film. Since the beam light intensity decreases as the wavelength becomes longer, if the beam light intensity is distributed to compensate for this, the intensity of the beam light with wavelengths λb and λC irradiated to the second and third recording films will be maintained. can.

Further, contrary to the above-mentioned method, a method of adjusting the wavelength transmittance of the recording film itself is also effective. That is, it is sufficient that each recording film has wavelength dependence of transmittance as shown in FIG.

The first recording film reflects and absorbs a beam of wavelength λa,
It is capable of recording and reproducing information, and transmits beam light of wavelengths λa and λb so that the beam light is irradiated onto the second and third recording films. The second recording film has wavelength dependence of transmittance as shown by the solid line, and reflects and absorbs the beam light of wavelength λb.
A beam of light having a wavelength λC is transmitted so that information can be recorded and reproduced and the beam of light is irradiated onto the third recording film. The third recording film has a wavelength dependence of transmittance as shown by the dashed-dotted line, and the third recording film reflects and absorbs the beam light of wavelength λC, and is capable of recording and reproducing information. Has wavelength dependence of transmittance. By giving the recording film itself such transmittance dependence, it is possible to effectively irradiate the recording film with the beam light even at a distance from the surface irradiated with the beam light.

According to one aspect of the present invention, as shown in FIG.
Recording, reproduction, and recording of information on recording media with a layered recording film structure.
and erasing becomes possible, and the recording density increases by the number of laminated recording films, making it possible to obtain an information recording medium with an extremely large recording capacity. Also, as shown in Figure 4,
In order to have a configuration in which the recording signal is divided and recorded, or the divided and reproduced signals are combined into one reproduction signal, the recording and reproduction synchronization Ts determined depending on the recording sensitivity of the recording film is conventionally By increasing the number of signal divisions, or in other words, the number of recording film layers, while keeping the same conditions.

It is possible to reduce the period Tz of recording and reproduction signals as an optical recording device, and to obtain an optical recording device with an extremely short data transfer rate.

FIG. 9 is a diagram illustrating another embodiment. In this example as well, three recording films are stacked, and information can be recorded, reproduced, and recorded independently on each recording film. Whereas the film was irradiated with a beam of light using one objective lens, in the fifth embodiment, three recording films at different positions on the recording medium were irradiated with a beam of light using separate objective lenses. The difference is that

That is, the beam light 34 having three wavelengths λa, λb, and λC is split into 1/3 by a half mirror 91 that reflects 1/3 of the amount of light, and enters the AO modulator 6. Here, only the beam of wavelength λC is transmitted, the optical path is changed by the PBS 95, the beam passes through the 1/4 person board 101 for the wavelength λC, and is focused onto the recording film 26 by the objective lens 104. Further, the reflected light passes through the objective lens 104, the 1/4 person plate 101, and the PBS 95, and enters the detector 98, where reproduction, focus error, and tracking error signals are detected. Furthermore, half mirror 92
The beam light passing through the half mirror 91 is divided into 1/2 parts, and each part enters the A○ modulators 4 and 5. A
In the O modulator 5, only the beam light of wavelength λb is transmitted, and the PBS 94 and the 1/4 person board 10 for the wavelength λb are transmitted.
0. The objective lens 103 focuses the light onto the recording film 25, and the detector 97 detects the reflected light. The beam light having the wavelength λa is similarly focused onto the recording film 24, and the reflected light is detected by the detector 96. In this way, according to this embodiment as well, information can be recorded, reproduced, and erased independently on each multilayer recording film.

FIG. 10 is an explanatory diagram of another embodiment. In this example, to divide the three wavelengths λa, λb, and λC, a deflection prism is used instead of the AO modulator in the example of FIG. 9. When the beam light 34 is passed through the polarizing prism 1.10,
Since the deflection angle differs depending on the wavelength, it is divided into beams of each wavelength.Furthermore, the beam of wavelength λa is converted by the deflection prism 111 so that the optical path is perpendicular to the recording medium 14, and the beam of wavelength λb is converted. A similar operation is performed by the deflection prism 112. The rest of the configuration is the same as that of the example shown in FIG. 9, and in this example as well, recording, reproduction, and erasing can be performed independently on the multilayer recording film.

FIG. 11 is an explanatory diagram of another embodiment.

In this embodiment, when recording information, the beam light of the white laser 120 that generates beam light of all wavelengths is shaped into parallel perfect circular light by the collimating lens 121, which is a completely achromatic lens, and then passed through the optical filter 122. incident. The wavelength transmittance of the optical filter 122 changes according to the recording signal 130, and the output light of the optical filter 122 is intensity-modulated at each wavelength.

The intensity modulation of this light beam will be explained with reference to FIG. For example, when 10 n-bit signals as shown in FIG. 12 are input to the optical filter 122 as the recording signal 130, the optical filter 122 outputs a light intensity distribution corresponding to the signals as shown in FIG. Generates a beam of light with . This beam light whose intensity has been changed is sent to the optical path converter 123 in FIG.
The beam enters the recording medium, travels straight, and is focused into the recording medium by the objective lens 125. At this time, since the focal length differs depending on the wavelength, the beam light of each wavelength is focused in the depth direction in the recording medium, and information is recorded. Furthermore, during reproduction, the optical filter 122 transmits the beam light of all wavelengths, and the beam light is irradiated into the recording medium in the same manner as during recording. Depending on the recording state of information in the recording medium, the reflected light with different light intensities at each wavelength passes through the objective lens 125 and passes through the optical path converter 123.
The optical path is converted by a photodetector] 26, and a reproduced signal 131 corresponding to each wavelength is generated.

In this way, in this embodiment, multiple pieces of information can be recorded in the depth direction of the recording medium, and a large-capacity recording device can be obtained.

〔Effect of the invention〕

According to the present invention, since information can be easily recorded, reproduced, and erased on a recording medium having a multilayer recording film, it is possible to provide an optical recording device with a high recording density and a short data transfer rate. .

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of an embodiment of the present invention, Fig. 2 is an explanatory diagram of a conventional column, Fig. 3 is a structural diagram of a recording medium targeted by the present invention, and Fig. 4 is an illustration of the signal processing of the present invention. Example diagrams, FIG. 5 is a detailed view of the objective lens portion of the embodiment of the present invention, FIG. 6 is a perspective view of the recording medium targeted by the present invention, and FIG. 7 is an explanation of the intensity of the light source used in the present invention. It is a diagram. 1...Laser, 4,5.6...AO modulator,
7゜8.9... PBS, 10, 11.12... Wave plate, 13... Objective lens, 14... Recording medium, 24
...first recording film, 25...second recording film, 26.
...Third recording film. Agent Patent Attorney Katsuma Ogawa 1・' ・ 4 figures (C)

Claims (1)

[Claims] 1. In an optical recording and reproducing apparatus that records, reproduces, and erases information on a recording medium by irradiating a beam of light onto the recording medium, the beam of light is emitted from a light source having a plurality of wavelengths. An optical recording and reproducing device characterized in that it generates. 2. The optical recording and reproducing apparatus according to claim 1, characterized in that the beam light has a high light intensity on the long wavelength side. 3. In the recording medium having a multilayer recording film, the light transmittance of the recording film on the incident side of the beam light is larger on the longer wavelength side, and the recording film is farther from the incident side of the beam light. 2. The optical recording and reproducing apparatus according to claim 1, wherein the wavelength at which the light transmittance increases becomes lower as the wavelength increases.