JPH05242514A - Optical recording method - Google Patents

Abstract

PURPOSE:To omit a shaping prism and to reduce the size, weight and price of an optical head by irradiating a recording track with an elliptic optical spot so that the minor axis of an ellipse is inclined from the scanning direction of the tracks. CONSTITUTION:The optical axis of a laser beam radiated from a laser diode 11 is allowed to coincide with that of a collimeter lens 13 and an elliptic optical spot 35 is made incident upon a recording track 33a of a magneto-optical disk 31 to form its image. In this case, the minor axis of the elliptic spot 35 is inclined from the scanning direction Ts of the track 33a to irradiate only the track 33a so that the spot 35 is not made incident upon its adjacent tracks 33b, 33c. The inclination of the spot 35 can simply be adjusted by rotating the diode 11 in the optical axis direction of the projected beam. Thereby a shaping prism can be omitted or simplified and the size, weight and price of the optical head can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording method for optically reading and writing information by irradiating an optical recording medium such as an optical disk, a magneto-optical disk and an optical card with a spot of a laser beam.

[0002]

2. Description of the Related Art FIG. 2 is an explanatory diagram showing an optical system of an optical head in a conventional magneto-optical recording system.

The laser beam from the laser diode 11 is collimated by a collimator lens 13 into a parallel light beam, passes through a shaping prism 15 and a polarizer 17, and then a beam splitter 1.
After passing through 9, is converged by the objective lens 21, enters the magneto-optical disk 31, is reflected as information light containing information (at the time of reading), is reflected by the beam splitter 19, and is passed through the analyzer 23 to the detection system 25. Upon incidence, the detection system 25 detects an information signal. Further, the detection system 25 detects the error signals in the tracking direction and the focusing direction to move the objective lens 21 to an actuator (not shown).
Then, the laser beam is driven in the tracking direction Tr and the focusing direction to form a laser beam as a perfect circular light spot 35 on the target recording track 33a of the magneto-optical disk 31, as shown in FIG. Now, as an example, the track width of the recording tracks 33a, 33b, 33c is about 1.2 μm, and the pitch width is about 1.6 μm.

By the way, the laser beam from the semiconductor laser 11 is output as a divergent beam having different divergence in a direction parallel to the bonding surface of the semiconductor laser 11 and a direction perpendicular thereto, and the beam shape is an ellipse. There is.
Therefore, in the optical system of FIG. 2, this elliptical beam is shaped into a perfect circle by the shaping prism 15. Assuming that the shaping prism 15 is not used in the optical system of FIG. 2, the light spot 35 irradiated on the magneto-optical disk 31 is as shown in FIG.
It becomes like (B). 4C is a sectional view of the recording track 33 in the tracking direction.

When the elliptical light spot 35 as shown in FIG. 4B is irradiated, the target recording track 33 is formed.
Even the recording tracks 33b and 33c adjacent to a are spot-irradiated, and this portion (indicated by diagonal lines in the drawing) causes crosstalk, which adversely affects tracking servo and read / write operations. If the elliptical light spot 35 shown in FIG. 4B is tilted 90 degrees and becomes elongated in the jitter direction, tracking servo will not cause any problems, but the resolution will deteriorate during reading, and in particular, C / The N ratio cannot be secured. Under such circumstances, in the conventional optical recording method, a beam shaping prism is used to correct the elliptic characteristic originally possessed by the semiconductor laser to a perfect circle to perform tracking servo, read and write operations.

However, the beam shaping prism has the following drawbacks and has a problem. (1) Complex and expensive. (2) Assembling workability is poor because delicate position adjustment is required. (3) Since the area occupied by the optical head is large and the weight is large, it becomes an obstacle to downsizing and conversion of the optical head.

As the laser beam shaping element, in addition to the obliquely incident one prism type shown in FIG.
There are methods such as combining two prisms and a horizontal incidence method using a cylindrical lens, but the situation is the same in both cases.

Although it has been reported that a shaping prism for correcting a laser beam in an optical information processing apparatus is manufactured at low cost (Japanese Utility Model Publication No. 61-18492), a shaping prism for correcting a perfect circle is also reported. It is not a basic solution in terms of requiring.

[0009]

SUMMARY OF THE INVENTION The present invention provides an optical recording method capable of obtaining excellent tracking servo and read / write characteristics by using a laser beam without using a shaping prism.

[0010]

The optical recording method of the present invention comprises:
In an optical recording method for reading / writing information by spot-irradiating a laser beam from a laser diode by an optical system on a recording track on which information is recorded,
Without correcting the elliptical beam from the laser diode to a perfect circle, the ellipticity is corrected as it is or at a low correction rate, and at the neutral point in the tracking direction, the spot-irradiated elliptical light spot is recorded on the adjacent recording tracks. It is characterized in that the elliptical light spot is irradiated onto the recording track by inclining the minor axis of the ellipse with respect to the scanning direction of the recording track so that the light is not substantially incident.

[0011]

1 is an explanatory view showing an embodiment of an optical system used in an embodiment of the present invention, in which the shaping prism 15 is omitted in FIG. 2 and an optical axis of a laser beam emitted from a laser diode 11 is shown. 2 is the same as that of FIG. 2 except that the optical axis of the collimator lens 13 and the optical axis of the collimator lens 13 are aligned.

Since the shaping system 15 (see FIG. 2) is not used in the optical system of FIG. 1, an elliptical shape is formed on the recording track 33 of the magneto-optical disk 31 as shown in FIGS. The light spot 35 of is incident and imaged. Figure 3
In (A) and (B), the light spot 35 is the recording track 33a.
The state where the light spot 35 is incident on the center of the track, that is, the state at the neutral point in the tracking direction is shown. In this state, the light spot 35 does not substantially enter the adjacent recording tracks 33b and 33c. Spot irradiation is performed with the minor axis of the ellipse 35 being inclined with respect to the scanning direction Ts of the recording track 33a. Adjacent recording tracks 33b, 33
When the amount of light incident on c increases, crosstalk occurs as shown in FIG. 2A shows a state in which the light spot 35 is tilted 45 degrees to the right, and FIG. 2B shows a state in which the light spot 35 is tilted 45 degrees to the left.

In order to tilt the light spot 35 in this way,
As shown by the arrow R in FIG. 1, the laser diode 11
Can be performed by rotating in the optical axis direction of the emission beam, and the size of the tilt angle can be easily adjusted.
By tilting the elliptical light spot 35, it is possible to suppress crosstalk and spread in the jitter direction and perform tracking, read, and write operations without problems.
Generally, the ellipticity of the laser beam is about 1: 2 to 1: 3, though it depends on the laser diode.
By adjusting the inclination according to the individual situation, it is possible to prevent crosstalk.

If there are circumstances such as a large ellipticity and a narrow recording track pitch, a shaping prism may be used in the present invention. But even in this case,
Instead of making a perfect circle, the correction rate is kept low and the laser diode is adjusted to control the inclination of the ellipse to irradiate the magneto-optical disk with an elliptical light spot. In this case, the structure, combination, and arrangement of the shaping prism can be simplified, which contributes to cost reduction, size reduction, and weight reduction.

The optical recording method of the present invention is suitable for a magneto-optical drive apparatus, an optical disk apparatus, etc., which uses a laser diode to seek a target recording track to read and write information.

[0016]

According to the present invention, an expensive shaping prism used for correcting the ellipticity of a beam peculiar to a laser diode can be omitted, or the correction factor can be reduced to simplify the shaping prism to obtain an elliptical shape. By irradiating the light spot with an inclination with respect to the recording track, tracking servo, read, and write operations can be reliably performed, and the resolution at the time of reading does not deteriorate.

Since the use of the shaping prism can be omitted or simplified, the following operational effects can be obtained. (1) The cost of parts can be reduced without using a complicated and expensive shaping prism for beam correction.

(2) It is not necessary to finely adjust the position of the shaping prism and the angle can be easily adjusted only by the laser diode, so that the number of assembling steps can be reduced. (3) By omitting the shaping prism, the size and weight of the optical head can be reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of an optical system used in an embodiment of an optical recording system of the present invention.

FIG. 2 is an explanatory diagram showing an optical system in a conventional optical recording system.

3A and 3B are explanatory views showing the irradiation state of a light spot in the present invention. FIG. 6C is a sectional view of a recording track in the tracking direction Tr.

FIG. 4A is an explanatory diagram showing a conventional irradiation state of a light spot. FIG. 3B is an explanatory diagram showing a light spot irradiation state when the laser beam is not shaped.
FIG. 6C is a sectional view of a recording track in the tracking direction Tr.

[Explanation of symbols]

 11 laser diode 13 collimator lens 15 shaping prism 17 polarizer 19 beam splitter 21 objective lens 23 analyzer 25 detection system 31 magneto-optical disk 33a, 33b, 33c recording track 35 light spot

Claims (1)

[Claims] 1. An optical recording method for reading / writing information by spot-irradiating a laser beam from a laser diode onto a recording track on which information is recorded by an optical system, wherein an elliptic beam from the laser diode is a perfect circle. The ellipticity is corrected as it is or with a low correction rate without performing correction so that the ellipse-shaped light spot irradiated with the spot does not substantially enter the adjacent recording tracks at the neutral point in the tracking direction. An optical recording method characterized by irradiating an elliptical light spot on the recording track by inclining the minor axis with respect to the scanning direction of the recording track.