JPH058495B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for optically recording signals on an optical recording medium.

BACKGROUND TECHNOLOGY AND PROBLEMS When optically recording a signal by irradiating a beam modulated with a signal onto an optical recording medium such as an optical disk or an optical card, conventional methods have been used to record the signal on the optical recording medium. In order to improve the recording density, the diameter of the spot-like recording traces formed by beam irradiation on the recording medium has been made as small as possible.

However, the smaller the diameter of this recorded trace, the more sophisticated focusing and tracking servo means and error correction and correction means become necessary.

On the other hand, if an attempt is made to simplify the focusing and tracking servo means and the error correction and modification means, it is necessary to increase the diameter of the recorded trace.

In this case, increasing the diameter of the recording trace in the recording track direction can be easily achieved by increasing the relative movement and irradiation distance of the beam with respect to the recording medium.

However, in order to increase the diameter of the recording trace in the direction perpendicular to the recording track direction, the power of the beam from the light source must be increased in proportion to the square of the diameter, but this requires increasing the output optical power of the laser light source. has its own limitations, so it is currently difficult to realize.

OBJECT OF THE INVENTION In view of the above, the present invention provides a method for increasing the optical power of a beam from a single laser light source.
The present invention attempts to propose an optical signal recording method that can substantially increase the diameter of a spot-like recording trace formed on an optical recording medium by beam irradiation in a direction substantially perpendicular to the recording track direction. .

SUMMARY OF THE INVENTION The optical signal recording method according to the present invention is characterized in that the optical signal is modulated with the same signal onto an optical recording medium in a direction substantially perpendicular to the recording track direction thereof, and is focused by an objective lens. A signal is recorded by irradiating at least two beams in parallel, each consisting of a first beam having optical power and a second beam obliquely incident on the optical axis of the first beam and the objective lens, respectively. and the distance d between each spot of the first and second beams on the optical recording medium is d≦2dl (however, dl=0.61λ/NA, where λ is the wavelength of the above beam, and NA is the distance of the objective lens. numerical aperture).

According to the present invention, spot-shaped recording traces formed on an optical recording medium by beam irradiation can be detected in a direction substantially perpendicular to the recording track direction without increasing the optical power of the beam from a single laser light source. It is possible to obtain an optical signal recording method in which the diameter can be substantially increased.

Embodiment An embodiment of the present invention will be described in detail below with reference to the drawings. First, referring to FIG. 1, a first example of an optical signal recording device to which the method of the present invention is applied is shown.
This will be explained with reference to the figures. A semiconductor laser light source _1a , a collimator lens 2a, a polarizing beam splitter 3, and an objective lens (condensing lens) are arranged on a certain axis AX1.
4 are arranged one after another, and an optical recording medium 5 is arranged at right angles to this axis _AX1 . In this way, the diverging laser beam from the light source 1a is made into a parallel beam by passing through the collimator lens 2a, and this parallel beam (plane wave beam) enters the objective lens 4 through the polarizing beam splitter 3, and from this the focused beam BMa irradiates the recording surface of the optical recording medium 5. Let SPa be the spot of this beam BMa on the recording surface of the optical recording medium 5.

Also, the reflective surface (plane) of the polarizing beam splitter 3
An axis AX ₂ perpendicular to the axis AX ₁ is provided in a plane perpendicular to 3a. Furthermore, this axis AX ₁ and axis AX ₂
Another semiconductor laser light source 1b and a collimator lens _2b are sequentially disposed on an axis _AX3 that forms a small angle θ toward the axis _AX1 with respect to the axis AX2.
In this way, the diverging laser beam from the light source 1b (its polarization direction is orthogonal to the polarization direction of the diverging laser beam from the light source 1a) is made into a parallel beam by passing through the collimator lens 2b, and this parallel beam is After being reflected by the reflective surface 3a of the polarizing beam splitter 3, it enters the objective lens 4,
The focused beam BMb from this is the optical recording medium 5
incident on the recording surface of The spot of this beam BMb on the recording surface of the optical recording medium 5 is designated as SPb.

Further, both semiconductor laser light sources 1a and 1b are driven with the same signal current, so the beams BMa and BMb are optically modulated with the same signal. Further, each of the beams BMa and BMb has a power exceeding the recordable threshold.

When the distance between both spots SPa and SPb is d, this distance d is d≦2dl (however, dl=0.61λ/NA, where λ is the wavelength of the laser beam from both laser light sources 1a and 1b, and NA is (numerical aperture of the objective lens). dI is called the Airy distribution, and due to the existence of the objective lens 4, the distribution of optical power with respect to the distance from the center of the beam incident on the recording medium 5 becomes an Airy distribution as shown in FIG. Corresponds to the distance at the minimum value. The horizontal axis in FIG. 7 represents distance as a multiple of dl. In this case, the recording track direction is perpendicular to the paper surface.

FIG. 2A shows the arrangement of the spots SPa and SPb of the beams BMa and BMb, which are arranged in a direction perpendicular to the recording track direction x. Second
RM in FIG. B indicates a spot-like recording trace formed on the optical recording medium 5 by the beams BMa and BMb, and SPp in the same figure indicates a spot of the reproduction beam. This spot SPp is a neighboring record trace.
The minimum interval is set so that it does not cross over the RM.

Incidentally, as shown in Figure 3A, the beams BMa,
When the angle of the straight line connecting spots SPa and SPb of BMb with respect to the recording track direction x is significantly different from 90°, the minimum interval between adjacent recording traces RM is set as shown in Figure 2B, as shown in Figure 3B. Even if the same value is selected, the recording traces where the playback beam spots SPp are adjacent to each other
It can be seen that the reproduction resolution is lower in the case of Fig. 3 than in the case of Fig. 2, since there is a possibility of straddling the RM.

Next, as a recording medium, Te was placed on an acrylic substrate.
A metal thin film such as In, Bi, CS ₂ -Te, Te-C, TeOx, etc. is deposited, and two focused lasers are modulated by the signal from an optical signal recording device using a semiconductor laser light source as described above. Study on the recordable threshold of the optical power of the beam when irradiating the beam to form a spot-like recording trace based on the change in light reflectance due to the amorphous-to-crystalline phase transition of a metal thin film. do.

The equation of heat conduction when a metal thin film is irradiated with two beams is expressed as follows.
However, T is temperature, t is time, and U is the thermal conductivity of the metal thin film.

∂T/∂T=U▽ ² T...(1) Equation (1) is converted into a difference equation and the results of one-dimensional simulation are shown in FIGS. 4 and 5. Fourth
In both the figure and FIG. 5, the horizontal axis represents the distance from the center of the two beam spots on the metal thin film, and the vertical axis represents the temperature of the metal thin film. Fig. 4 shows the case where the distance between the centers of the two beam spots is 0, and Fig. 5 shows the case when the distance between the centers of the two beam spots is 1.2 dl. Curves a, b, c in Figures 4 and 5;
a', b', and c' sequentially show part of the process in which heat distribution is imparted to the metal thin film by the laser beam, and immediately after that, the heat in the metal thin film gradually collapses. Also, curves S and S' are curves a, b, and c, respectively;
It shows the envelope formed by connecting the highest temperature values at each distance among the countless thermal disintegration curves including a', b', and c'. Also, the straight lines L ₁ , L ₂ , L ₃ , ;L ₁ ′,
L ₂ ′ and L ₃ ′ show examples of threshold values for changes in optical properties of metal thin films, and the sensitivity is in the order of low, medium, and high, respectively, and the envelopes S and S′ on the straight line are The width corresponds to the diameter of two spot-like recording traces on the metal thin film in the direction perpendicular to the recording track.

Next, the diameter (pit diameter) in the direction perpendicular to the recording track of the two spot-shaped recording traces on the metal thin film (vertical axis) with respect to the distance between the beam spots (horizontal axis)
The relationship is shown in Figure 6. Here, the horizontal and vertical axes in FIG. 6 represent distance and diameter, respectively, as multiples of dl. In addition, in FIG. 6, the above-mentioned sensitivities L ₁ (=L ₁ ′) and L ₂
(=L ₂ ′) and L ₃ (=L ₃ ′) are used as parameters.
Further, "*" on the vertical axis in FIG. 6 indicates the pit diameter at each of the above-mentioned sensitivities L ₁ , L ₂ , and L ₃ in the case of a single beam. In Figure 6, the white circle part of the curve is the part where two beam spots overlap and become one, and the black circle part is the part where the two beam spots are separated, but the shortest point on each peripheral edge is the part of the curve. Distance d′ is d′≦
dl indicates a portion within a range where a spot-like recording trace based on the beam spot can be reproduced as one recording trace. Therefore, from Fig. 6, when the distance d between the two beam spots is in the range d≦2dl, the diameters of the two beam spots in the direction perpendicular to the recording direction are larger than the diameter of the spot of one beam. It can be seen that the condition d′≦dl is satisfied. Furthermore, if d exceeds 0.5dI,
This is effective because the spot diameter is larger than the spot diameter when d=0.

Next, another example of an optical recording device to which the present invention can be applied will be described with reference to FIG. 8 and subsequent figures.

In the apparatus shown in FIG. 8, planes parallel to the direction of the recording track and parallel to each other are provided at predetermined intervals. On the axis perpendicular to the recording surface of the optical recording medium 5 in one plane, the laser beam from the semiconductor laser light source 1a sequentially passes through the collimator lens 2a, the polarizing beam splitter 3, and the objective lens 4 into an optical system. The recording medium 5 is irradiated with light. On the axis parallel to the recording surface of the optical recording medium 5 in the other plane, the laser beam from the semiconductor laser light source 1b enters the polarizing beam splitter 3 through the collimator lens 2b, where it is polarized by 90 degrees. After the beam is perpendicular to the recording surface of the optical recording medium 5, it is focused by the objective lens 4, and the recording surface of the optical recording medium 5 is irradiated. Therefore, by selecting the spacing between the two planes parallel to each other, the two beam spots SPa and SPb on the recording surface of the recording medium 5 can be
The distance d between them can be set within the above range.

In the apparatus shown in FIG. 9, a semiconductor laser light source 1 consisting of an array of three laser semiconductor elements 1a, 1b, and 1c is provided as a laser light source, and the laser beam from the element 1a is directed against the recording surface of the optical recording medium 5. The laser beams from elements 1b and 1c on both sides are emitted at right angles, and the laser beams from elements 1b and 1c on both sides are made to have angles symmetrical to each other with respect to the laser beam from element 1a. In this way, the configuration of the optical system becomes simple, compact, and easy to adjust. Thus, the laser beams from the elements 1a, 1b, and 1c are sequentially passed through the collimator lens 2, the polarizing beam splitter 3, the quarter-wave plate 6, and the objective lens 4 to irradiate the recording surface of the optical recording medium 5. . In this case, by selecting the angles of the beams BMa, BAb, and BMc, the distance d between the beam spots SPa, SPb, and SPc on the recording surface of the recording medium 5 is set within the above range. This example also serves as a reproducing device, and the reproducing beam is obtained from the polarizing beam splitter, but if it is only a recording device, the polarizing beam splitter 3 and quarter-wave plate 6 can be omitted. It is possible.

In this case, since a semiconductor laser light source is used, there is an advantage that backtalk to the semiconductor laser light source can be avoided by providing a polarizing beam splitter and a quarter wavelength plate.

In the apparatus shown in FIG. 10, three beams are created from the beam from one semiconductor laser light source 1 using a diffraction grating, and these beams are made to enter the recording surface of the optical recording medium 5. be.

That is, a laser beam from a semiconductor laser light source 1 is made incident on a diffraction grating 7 through a collimator lens 2 to form three beams, and these beams are made to irradiate the recording surface of an optical recording medium 5 through an objective lens 4. Beam spots SPa of the three beams BMa, BMb, and BMc incident on the recording medium 5,
The distance d between SPb and SPc is set by the grating spacing of the diffraction grating 7.

In addition, in the apparatus shown in FIG. 1, the semiconductor laser light source 1b and _the collimator lens _2b are arranged on the axis _AX3 , and the beam can be The diameter of the spot in the direction orthogonal to the recording track can also be modulated by the signal.

Note that the number of beam spots on the recording surface of the recording medium 5 may be any number as long as it is two or more.

Spot-like recording traces on an optical recording medium are caused by differences in reflectance from other parts in the case of a reflective type (due to phase transition from amorphous to crystalline metal thin film, melting, etc.), and in the case of a transmission type. It is formed due to the difference in transmittance from other parts.

According to the present invention described above, without increasing the optical power of the beam from a single laser light source, the spot-like recording traces formed on the optical recording medium by beam irradiation are formed in a direction substantially perpendicular to the recording track direction. It is possible to obtain an optical signal recording method that allows the diameter of the optical signal to be substantially increased.

Effects of the Invention According to the present invention described above, without increasing the optical power of the beam from a single laser light source, the direction of the recording track of the spot-like recording trace formed on the optical recording medium by beam irradiation can be adjusted. It is possible to obtain an optical signal recording method in which the diameter in the orthogonal direction can be substantially increased.

[Brief explanation of drawings]

FIGS. 1, 8, 9, and 10 are schematic diagrams showing examples of optical recording devices to which the present invention is applied, and FIG. FIG. 3 is a pattern diagram showing spot-like recording traces on a recording medium that will be used to explain the present invention, and FIGS.
The figure is a characteristic curve diagram for explaining the present invention. BMa, BMb, BMc are beams, SPa, SPb,
SPc is a beam spot, 1, 1a, 1b, 1c are laser light sources, 2, 2a, 2b are collimator lenses, 3 is a polarizing beam splitter, 4 is an objective lens, and 5 is an optical recording medium.

Claims (1)

[Claims] 1. A first optical recording medium having optical power equal to or higher than a recordable threshold value, which is modulated with the same signal and focused by an objective lens in a direction substantially orthogonal to the recording track direction of the optical recording medium. and a second beam that is obliquely incident on the optical axis of the first beam and the objective lens, respectively, to record a signal by irradiating the first beam in parallel. And the distance d between each spot of the second beam on the optical recording medium is d≦2dl (where dl=0.61λ/NA, where λ is the wavelength of the beam and NA is the numerical aperture of the objective lens. ) An optical signal recording method characterized by being selected as follows.