JP2542366B2 - Optical information recording / reproducing method - Google Patents

Description

The present invention relates to an optical information recording / reproducing method. The present invention is preferably applied to a method for recording information on a card-shaped or disk-shaped optical information recording medium and reproducing the information recorded on the medium.

[Background of the Invention]

2. Description of the Related Art Conventionally, various types of media such as a disc, a card, and a tape have been known as forms of a medium for recording information using light and reading the recorded information. Of these, an optical information recording medium formed in a card shape (hereinafter referred to as an “optical card”)
(Hereinafter referred to as ")" is expected to be in great demand as a medium with a large storage capacity that is small, lightweight and convenient to carry.

Information is recorded on the above-mentioned optical card as an optically detectable recording bit string by scanning a preset recording track on the optical card with a light beam which is modulated according to the recording information and focused into a minute spot. It

Reproduction of information recorded on the optical card is performed by scanning the above-described recording bit string with a light beam having a constant power level at which information is not written on the optical card.

The scanning of the optical beam with respect to the optical card during such information recording / reproduction is performed by the relative movement of the optical card and the optical beam.

In such optical information recording / reproducing, a semiconductor laser is often used as a light source for a light beam in order to reduce the size and cost of the device. Stray light generated by reflection from components returns to the semiconductor laser and tends to generate noise, and this noise is the S / N of the reproduced signal.
The problem of deteriorating the ratio has been pointed out in the past.

In an optical information recording / reproducing apparatus in which a disc-shaped recording medium is used, in order to eliminate the influence of such returning light, conventionally, a combination of a 1/4 wavelength plate and a polarization beam splitter or an optical device such as a Faraday rotator is used. Optical isolator, or by suppressing the mode fluctuation of the laser to reduce noise by constantly returning a certain level of light from the surface of the optical component medium to the laser side, or by adding a high frequency superposition circuit to the laser. Methods such as suppressing noise have been taken.

However, among these methods, the method using an optical isolator is expensive in material, and in particular, a recording medium having a plastic protective layer attached to the medium surface for medium surface protection such as an optical card is used. In the case of such a device, it is not practical because the protective layer easily disturbs the polarization state of light. Further, the method of returning the light of a certain level to the laser side is not effective when a component for giving the returning light is necessary or when the reflectance of the medium changes depending on the place. Further, the method of adding the high frequency superimposing circuit has the disadvantages that the circuit is expensive and that the exposure amount is reduced by the duty ratio of the pulse because of high frequency pulse lighting.

As a countermeasure against such a problem, a method in which a recording / reproducing light beam is obliquely incident on the medium surface of the optical card (hereinafter referred to as “axis off-axis method”) is particularly useful for an optical card. , Drexera Technology ·
Corporation (Drexler Technology Corporation)
In the technical disclosure to the applicant.

7 and 8 are views for explaining the configuration of an example of an optical information recording / reproducing apparatus using the above-mentioned off-axis system.
The drawing is a perspective view, and FIG. 8 is a side sectional view.

A light beam emitted from a light source 11 such as a semiconductor laser is collimated by a collimator lens 12 and divided into three beams by a diffraction grating 13. These beams are imaged on the information recording surface of the optical card 1 by the objective lens 14,
Beam spots S ₁ , S ₂ , and S ₃ are formed, respectively. Here, the optical card 1 is moved in the direction of arrow R by a driving means (not shown), and is scanned by the beam spot in the direction in which the tracking track 1a and the clock track 1b of the optical card 1 extend.

The reflected light of the beam spots S ₁ , S ₂ and S ₃ is again the objective lens 14
Is reflected by the mirror 15 and is projected by the condenser lens 16 onto the sensors 17, 18 and 19 placed on the focal plane, respectively.

With this off-axis method, the returning light from the surface of the recording medium is effectively reduced. In particular, when an optical card is used as an optical information recording medium, the plastic protective layer attached to protect the recording surface of the optical card is liable to be distorted by the strain produced during the production or use of the optical card. Often exhibits birefringence, making optical return light isolation difficult. In this case, the off-axis method is an extremely effective means.

However, in the off-axis type device shown in FIGS. 7 and 8, the semiconductor laser from the optical card 1 is further added.
It may be possible to reduce the return light to 11. That is, when the optical card 1 having pits recorded by using the light beam is used as an optical information recording medium, the reflected light from the information pits reverses the light beam incident path at the time of reproducing information and the semiconductor laser May reach 11 and cause noise. Since the noise of the semiconductor laser is likely to be generated even if the returning light is extremely weak, it is important to reduce the returning light as much as possible for reproducing high quality information.

[Object of the Invention]

Therefore, an object of the present invention is to reduce the returning light from the optical information recording medium to the light source side in the optical information recording / reproducing method, thereby reducing the noise generated in the light source.

[Outline of Invention]

According to the present invention, in order to achieve the above-mentioned object, the recording medium is scanned by irradiating the heat mode recording type recording medium with a light beam in a spot shape and modulating the light beam according to an information signal. Information is recorded by forming a pit train on the surface, and the pit train of the recording medium on which the information has been recorded is scanned while irradiating the pit train with a light beam in a spot shape to detect light reflected from the recording medium surface. In the optical information recording / reproducing method that reproduces information by means of the optical information recording / reproducing method, the information is reproduced from the direction tilted in the scanning direction of the light beam spot at the time of information recording, with the irradiation position of the light beam spot irradiated on the recording medium as the base point. An optical information recording / reproducing method is provided, which comprises irradiating a recording medium with a beam.

〔Example〕

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a partial side sectional view showing an information recording state in one embodiment of the method of the present invention. The apparatus used in this example is the same as the apparatus shown in FIGS. 7 and 8 above.

In FIG. 1, the recording light beam 20 which is incident on the objective lens 14 from the light source side passes through a position parallel to and away from the optical axis of the objective lens. Then, after passing through the objective lens 14, it is condensed to form a spot on the recording surface of the optical card 1 located on the focal plane. As shown in the figure, the light beam is directed in the surface normal direction of the optical card 1, that is, the objective lens.
The light enters the optical card 1 obliquely with respect to the optical axis direction of 14.

To form a row of information pits on the optical card 1, use a light beam
20 is modulated according to the recorded information and the optical card 1
May be moved in the direction of arrow A or B with respect to the light beam spot at an appropriate speed.

2 (a) and 2 (b) show the optical card 1 in FIG.
Information pits 21 formed on the optical card 1 when the light beam spot irradiation is performed while moving the arrow mark in the direction of arrow A.
FIG. 3 is a plan view and a sectional view of FIG.

Similarly, FIGS. 3A and 3B show information pits 21 formed on the optical card 1 when the optical beam spot irradiation is performed while moving the optical card 1 in the direction of arrow B in FIG. FIG. 3 is a plan view and a sectional view of FIG.

In FIGS. 2 (a) and (b) and FIGS. 3 (a) and (b), the arrow shown by the broken line indicates the direction in which the light beam spot is relatively scanned on the optical card surface.

As described above, the optical card 1 used in this embodiment is a so-called heat mode recording medium in which pits are formed on the recording surface by the thermal energy of the light beam.
An example of such a heat mode recording type optical card is the Drexson laser card manufactured by Drexera Technology Corporation. In a heat mode recording type recording medium, when the light beam spot scans the recording surface, the amount of heat accumulated varies depending on the position along the scanning direction, so the shape of the pits formed gradually changes along the scanning direction. Is allowed to do. That is, the second
As shown in FIGS. (A), (b) and FIGS. 3 (a), (b), the pit 21 has a deeper depth and a steeper slope at the end of writing than at the beginning of writing, and a large width. It has been found that such a tendency hardly depends on the incident angle of the light beam on the optical card 1 and its direction.

4 and 5 are side sectional views showing an information reproducing state in an embodiment of the method of the present invention. Also in this embodiment, the same device as the device shown in FIG. 7 and FIG. 8 is used as in FIG.

In FIGS. 4 and 5, the objective lens 14 is seen from the light source side.
The reproduction light beam 22 incident on the optical axis passes through a position parallel to the optical axis of the objective lens and away from the optical axis, is condensed, and is incident on the recording surface of the optical card 1 on the focal plane of the lens 14. To do. The incident angle of the incident light beam is approximately θ ₁ . The optical card 1 is moved in the direction of arrow A at a predetermined speed.

Thus, when the light beam is incident on the position other than the information pit 21 of the optical card 1, the reflected light from the optical card 1 is almost specularly reflected and again enters the objective lens 14 as shown in FIG. Then, it advances to the sensor side and is detected. Along with the movement of the optical card 1, a light beam is made incident on the position of the information pit 21, and at this time, the incident light beam is scattered by the pit as shown in FIG. The light enters the light detection optical system in a state different from that in the case of FIG. Thus, the information pit 21 is detected and the information is reproduced.

By the way, in this embodiment, as shown in FIG. 5, the slope 21a on the arrow A side of the information pit 21 is steep, while the slope 21b on the arrow B side is gentle. That is, in the optical card 1 of this embodiment, the recording light beam spot is made to scan in the direction of arrow A at the time of recording information. The maximum angle θ ₂ formed by the slope 21b of the information pit 21 with the optical card surface is smaller than the above θ ₁ . Therefore, as shown in FIG.
The scattered light (shown by the dotted line) of the light beam incident on the information pit 1 does not go backward in the incident direction, and there is no returning light on the semiconductor laser side.

The behavior of the returning light at the time of such reproduction is independent of the moving direction of the optical card 1. That is, the optical card 1 is the arrow B
It is clear that the scattered light behaves similarly when moving in the direction of.

FIG. 6 is a side sectional view in the information reproducing state shown for comparison, and shows the same portion as FIG.

In the case of this figure, the slope 21c on the arrow A side of the optical card 1 is gentle, while the slope 21d on the arrow B side is steep. That is, the optical card 1 in the case of this figure is one in which the recording light beam spot is scanned in the direction of arrow B at the time of recording information. Further, the maximum angle θ ₃ formed by the slope 21d of the information pit 21 and the optical card surface is larger than the above θ ₁ . Therefore, as shown in FIG. 6, the scattered light of the light beam incident on the information pit 21 sometimes goes backward in the incident direction. It is obvious that the behavior of the returning light at the time of such reproduction is the same whether the optical card 1 is moving in the direction of arrow A or moving in the direction of arrow B.

From the above description, in the method of the present invention, when the same optical system is used for recording and reproduction, the recording light beam is obliquely incident on the surface normal of the recording medium as shown in FIG.
In addition, recording is performed in a state where the relative movement direction of the recording medium with respect to the light beam spot at the time of recording coincides with the projection component of the incident direction of the light beam on the surface of the recording medium. By lowering the irradiation energy of the beam and scanning the surface of the recording medium with the same arrangement as at the time of recording, reproduction can be performed in the state as shown in FIG. 5 regardless of the scanning direction, and returning light can be removed. I understand.

In the above embodiments, the light beam is made incident on the recording medium in a direction oblique to the surface normal to the recording medium. However, in the present invention, the light beam incident direction at the time of recording may be perpendicular to the recording medium surface. Good. Further, in the above embodiments, the information pit has been described as having its depth changed along the scanning direction, but even if the information pit is formed by a change in the refractive index of the medium, it may be optically equivalent. For example, the present invention can be applied.

Although the above-mentioned embodiments relate to the case where the optical card is used as the optical information recording medium, the present invention is similarly applied to the case where the recording medium other than the optical card such as a disc or a tape is used as the recording medium. What will be obtained will be apparent from the above description.

〔The invention's effect〕

According to the present invention as described above, the returning light from the optical information recording medium to the light source side can be remarkably reduced at a low cost by an extremely simple means without adding a special member, and thus, the light source. Suppresses noise generation in
It is possible to improve the accuracy and reliability of reproduction of optical information.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an information recording state in the method of the present invention. 2 (a) and 3 (a) are plan views of the information pit, and FIGS. 2 (b) and 3 (b) are cross-sectional views thereof, respectively. 4 and 5 are side sectional views showing the information reproducing state in the method of the present invention. FIG. 6 is a side sectional view showing an information reproducing state for comparison. FIG. 7 is a perspective view of the optical information recording / reproducing apparatus.
The figure is a sectional side view thereof. 1 …… Optical card, 11 …… Semiconductor laser, 13 …… Diffraction grating, 17,18,19 …… Sensor, 21 …… Information pit.

Claims (1)

(57) [Claims] 1. A heat mode recording type recording medium is scanned while irradiating it with a light beam in a spot shape, and the light beam is modulated in accordance with an information signal to form a pit row on the surface of the recording medium, thereby forming information of information. Optical information recording / reproducing for recording information and reproducing information by detecting light reflected from the surface of the recording medium by scanning while irradiating the pit row of the recording medium on which the information has been recorded with a light beam in a spot shape. In the method, when reproducing information, the recording medium is irradiated with a light beam from a direction inclined to the scanning direction of the light beam spot at the time of information recording, with the irradiation position of the light beam spot irradiated on the recording medium as a base point. A method for recording and reproducing optical information.