JPH01273239A - Optical reproducing pickup - Google Patents

Abstract

PURPOSE:To efficiently condense reflected light rays from a recording medium so that the reproducing output of an optical reproducing pickup can be improved with a small optical system by making the cross-sectional area of one end of a 2nd waveguide smaller than that of the one end of a 1st waveguide, with the one ends of the waveguides being provided adjacent to each other and faced to an optical recording medium. CONSTITUTION:A laser beam from a laser diode 36 is emitted from one end 38A of the 1st optical waveguide 38 faced to an optical recording medium 31 after it is propagated through the waveguide 38 and the medium 31 is irradiated by the emitted beam. The reflected light rays of the laser beam from the medium 31 are made incident and efficiently condensed to the one end 39A of the 2nd optical waveguide 39 which is faced to the medium 31, has a larger cross-sectional area than the one end 38A has, and is provided adjacent to the one end 38A and made incident on a photodetector 37 after passing through the 2nd optical waveguide 39. Since the reflected light rays from the recording medium are efficiently condensed by the small optical system which does not required any lens, etc., in such way, the reproducing output of this pickup can be extremely improved and the optical pickup can easily be incorporated in a light-weight slider 33.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical reproducing pickup for optical discs.

[Summary of the invention]

The present invention provides an optical reproduction pink-up for optical discs, including a first optical waveguide having one end facing a recording medium and a light source disposed at the other end, and a first optical waveguide having one end adjacent to one end of the first optical waveguide and the other end facing the recording medium. By having a second optical waveguide disposed with a photodetector, and making the cross-sectional area of one end of the second optical waveguide larger than the cross-sectional area of one end of the first optical waveguide, the light beam can be placed on the lightweight slider of the optical reproducing pickup. In addition to achieving high-speed access and narrow trunks, this system also aims to improve reproduction output and suppress the influence of returned light to prevent instability in the oscillation of the laser diode, which is the light source.

[Conventional technology]

FIG. 9 shows an example of a conventional optical head for a magneto-optical disk.

In the figure, (1) is a magneto-optical disk that is a recording medium, and (2) is a laser light source.The light beam from the laser light source (2) is transmitted through a grating (3), a lens system (4), a polarizer ( 5), beam splitter (6) and objective lens (
7) and is focused onto the magneto-optical disk (1). The returning light beam reflected from the magneto-optical disk (1) is reflected in a 90° direction by a beam splinter (6), passes through a 1/2 wavelength plate (8), and is connected to a polarizing beam splinter (9) and a Funa L-diode (10). ) and (11), differential detection is performed to obtain a reproduced signal. Note that (12) and (13) are cylindrical lenses.

Recently, as shown in FIG.
6) and protection fj! (17) A magneto-optical disk (
11 is irradiated with a recording laser beam (18), and a slider-shaped magnetic head (21) similar to a magnetic disk head is placed from the side opposite to the irradiated surface, and the signal to be recorded is transferred to the magnetic head ( 21) A magneto-optical recording method has also appeared in which recording is performed manually using a magnetic field modulation method. Reproduction is performed using a laser beam as described with respect to the optical head in FIG.

In addition, a branched optical waveguide is used as an optical head for recording and reproduction, with a semiconductor laser serving as a light source placed at the end of one branched waveguide, and a photodetector placed at the end of the other branched waveguide. death,
The tip of the common waveguide is made to face the recording medium, the emitted light from the semiconductor laser is made to enter the recording medium from one branch waveguide through the common waveguide, and the reflected light from the recording medium is made to enter the recording medium from the tip of the common waveguide to the other branch waveguide. A structure has been proposed in which a reproduced signal is obtained by guiding the signal into a branch waveguide and making it incident on a photodetector (JP-A-60-59547, JP-A-60-9548, JP-A-61 -66238). Furthermore, there is also an optical head in which a semiconductor laser and photodetectors are integrally formed on the same substrate, and the emitted light from the semiconductor laser is incident on the recording medium, and the reflected light is received by the photodetectors on both sides. known (see Japanese Patent Application Laid-Open No. 192032/1983).

[Problem to be solved by the invention]

By the way, in the magneto-optical recording system using the magnetic field modulation method shown in FIG. 10, which uses the optical head mechanism shown in FIG. 9 and the slider-shaped magnetic head (21), the objective lens (7) for focusing the laser and the magnetic It is necessary to drive the heads (21) at the same time, which complicates the mechanism and makes high-speed access difficult.

On the other hand, today's magnetic disk systems using thin-film magnetic heads use thin-film formation technology on lightweight sliders.

Because the head is created using photolithography technology, it is lightweight and achieves high-speed access (20m5). However, the track density is limited to 30007Pl mainly due to the signal level during reproduction.

In addition, when using a branched optical waveguide, mode conversion, in which the direction of the polarization plane of light changes, is likely to occur, and the reflected light from the recording medium enters the branched waveguide on the semiconductor laser side and returns to the semiconductor laser. There is a problem that the oscillation becomes unstable.

The present invention solves the above-mentioned problems and provides an optical reproducing pickup that can be formed on a lightweight slider to achieve high-speed access and narrow tracks, improve reproduction output, and suppress the influence of return light. It is.

[Means to solve the problem]

The optical reproducing pickup of the present invention includes a first optical waveguide (38) having one end (38^) facing the recording medium (31) and a light source (36) disposed at the other end (38B), and one end (39A) facing the recording medium (31). A photodetector ( 37 ) is provided with a second optical waveguide (39).

The first and second optical waveguides (38) and (39) are ion-exchanged glass waveguides or 'l' i-diffused LiN
It can be formed using a bO3 waveguide or the like.

This optical reproduction pick amplifier can be used as an optical reproduction pickup for optical discs such as read-only CDs (compact discs), write-once optical discs that can be recorded only once, rewritable optical discs that can be erased and written to, and the like. Examples of the W-shaped optical disk include (i) an optical disk that utilizes changes in optical properties due to phase changes in materials; (11) Optical disks that utilize the magneto-optical effect, that is, rotation of the plane of linearly polarized light; optical disks that record using the floating magnetic field of the medium without a bias magnetic field; disks that use a bias magnetic field, such as those that use an auxiliary magnetic field (DC magnetic field); This includes optical discs that record using a magnetic field modulation method, optical discs that record using a magnetic field modulation method, etc.

[Effect]

According to the above configuration, the light emitted from the light source (36) is the first
The reflected light that passes through the optical waveguide (38) and directly enters the recording medium (31) from one end (38A) is then reflected by the recording medium (31) and passes through the second optical waveguide (39).
The light enters from A), is propagated, and enters the photodetector (37), from which a reproduced signal is obtained.

In the second optical waveguide (39), the cross-sectional area of one end (39A) facing the recording medium (31) is larger than that of the first optical waveguide (38).
) is wider than that of one end (38^) of the recording medium (38^).
The reflected light from 1) is efficiently focused and the reproduction output is improved. At the same time, the amount of reflected light returning to the first optical waveguide (38) is small, thereby preventing the oscillation of the laser diode serving as the light source (36) from becoming unstable.

Since the optical reproducing pickup of the present invention is constructed using an optical waveguide instead of a conventional large lens system, it can be formed on a lightweight slider and high-speed access can be obtained. Further, the first waveguide (38) has one end (38A
) is formed to have a small cross-sectional area, so a narrow track can be achieved.

〔Example〕

Embodiments of the optical reproducing pickup according to the present invention will be described below with reference to the drawings.

1 to 3 show an example of an optical reproducing pickup according to the present invention. In FIG. 1, (31) is a recording medium such as a magneto-optical disk, (32) is its recording track, (33)
is a lightweight slider, and an optical reproducing pickup (34) according to the present invention is formed on its end face (33^). As shown in FIGS. 2 and 3, the optical reproducing pickup (34) is mounted on a head substrate such as an end surface (33A) of a slider (33).
A semiconductor laser diode (36) that oscillates at a wavelength of 0.7 to 0.8 μm and serves as a light source, for example, and a P
A photodetector (37) consisting of an IN photodiode or an avalanche photodiode, etc., one end (38A) facing the magneto-optical disk (31) and the other end (38B) facing or facing the laser diode (36), and a laser diode. a first optical waveguide (38) that makes the emitted light from the diode (36) directly enter the surface of the magneto-optical disk (31);
9^) faces the magneto-optical disk (31) and the first
is adjacent to one end (38^) of the optical waveguide (38), and the other end (
A second optical waveguide (39) is provided so that the second optical waveguide (39B) is in contact with or facing the photodetector (37) and guides the light reflected by the magneto-optical disk (31) to the photodetector (37). The first optical waveguide (38) becomes thinner (width W becomes smaller) toward one end (38^) facing the magneto-optical disk (31).
It is formed in a tapered optical waveguide, and its magneto-optical disk (3
1) Opposed to 61i! (38A) is formed so that the cross-sectional area is small.

The second optical waveguide (39) has a cross section 1f at one end (39^) facing the magneto-optical disk (31)! (32) is the first leading wave dlr (38) (7) One end (38A) (
DlfHmfa (S 1 ) is formed so as to be larger than DlfHmfa (S 1 ). In this example, the second optical waveguide (39) is formed with a width W2 larger than the width W1 of one end (38A) of the first optical waveguide (38).

The light emitted from the laser diode (36) is linearly polarized light with a polarization plane parallel to the active layer, and the polarization ratio representing the degree of linear polarization is 80 to 100.

This laser is guided into an optical waveguide without mode conversion.

The first and second optical waveguides (38) and (39) are respectively constituted by ion exchange waveguides in which, for example, soda glass is immersed in a KNO* melt by converting ions and Na+ ions. Here, the width and depth of one end of the optical waveguide are adjusted so that the electric field distribution becomes a single mode, that is, a Gaussian distribution within the optical waveguide (38) (39).

Others, first and second optical waveguides (38) and (39)
For example, the waveguide can be constructed by a 1×1 diffusion LiNbOx waveguide formed by diffusing Ti into a LiNbOi crystal substrate. (50) indicates a glass substrate or a LiNbO3 crystal substrate for making a thermal ion exchange waveguide or a Ti diffusion waveguide.

On the other hand, the laser diode (36) is linearly polarized light with a sufficient polarization ratio, but in order to maximize the reproduced signal as described later, the first optical waveguide (38) and the second optical waveguide (39) Metal-clad mode filters (40) and (41), which serve as a polarizer and an analyzer, respectively, are provided on the way. These metal clad type mode filters (40) and (41) are shown in FIG. 5 (cross-sectional view taken along the line A-A in FIG. 2) and FIG. A buffer layer (4) made of an insulating layer such as 5i (h) is formed on the first optical waveguide (38) and the second optical waveguide (39), respectively.
2) Through (43) a metal layer (44), e.g.
) (45) is deposited and formed. The metal clad mode filter (40) serving as a polarizer and the metal clad mode filter (41) serving as an analyzer are formed so that the angle between them is 45° or a predetermined angle close to 45°. . That is, for example, as shown in FIG. 5, the metal clad mode filter (40) serving as a polarizer has its metal layer (44) and buffer layer (42) on the reference plane (substrate (
The metal clad mode filter (41), which is formed at an angle α to the plane parallel to (50) (51) and serves as an analyzer, has its metal layer (45) and buffer layer as shown in FIG. (43) is formed at an angle β with respect to the reference plane (51), and at that time α+β−45° or α+β=
The angle is 45°. Note that (52) shows a sputtered film of soda glass in the case of a thermal ion exchange waveguide, where metal In (44) (45) is formed on the optical waveguide (3B) (39). This results in I' E mode transmission and '1' M mode absorption.

In the metal clad mode filter (40) serving as a polarizer, the buffer ltm (42) is set to 5t (h) so that the TE mode does not suffer loss and the film thickness is increased to T.
Since the M mode loss is reduced, it is preferable to form the layer with a thickness of about 0.2 .mu.m.

Note that the laser diode (36) uses a metal clad mode filter (not shown) in which the active layer sandwiched between the p-type cladding layer and the n-type cladding layer serves as a polarizer.
40) so that it is inclined at the same angle α as the inclination angle α,
In line with this, the first optical waveguide (38) also has its surface (38a
) may be formed so as to be inclined at an angle α over the entire length. Also, a second optical waveguide (39)
Metal-clad mode filter (41) that also serves as an analyzer
The surface (39a) may also be configured to be inclined at an angle β over the entire length. This optical reproducing pick amplifier can be used as an optical reproducing pickup for a rewritable optical disk or the like that utilizes the above-mentioned magneto-optic effect.

In the optical reproducing pickup having such a configuration, the light emitted from the laser diode (36) passes through the first optical waveguide (38).
), propagates through a metal clad mode filter (40) which is a polarizer, and is incident on the surface of the magneto-optical disk (31). The polarization plane of the reflected light reflected by the magneto-optical disk (31) is different from the polarization plane of the incident light.
Depending on the direction of recording magnetization (e.g. upward magnetization, downward magnetization), hook 〇.

The 0-reflection light that causes Kerr rotation of angle -θ is the magneto-optical disk (
The spacing t between 31) and the tip of the pickup is 1A1
11 or less, one end (3
9A) and enters a metal clad mode filter (41) which serves as an analyzer. Here, if the sum of angle α and angle β shown in Figs. ) at angle ±θ is CO3' (φ+θ) −cos' (ψ−θ)−
-2sin (2ψ) Proportional to sin(2θ). t
In order to maximize the k edge, it is necessary to set it to around ψ-45°. Therefore, as mentioned above, in the metal clad mode filters (40) and (41), the metal ji
l (44) (45), buffer layer (42)
Add angles α and β to (43) so as to satisfy α+β−45° or α+β−45°, respectively.

The respective metal clad mode filters (40) and (
41) may be configured.

And the metal clad mode filter of the analyzer (41)
The reflected light that has passed through is received by a photodetector (3'/), from which, for example, differential detection is performed and a reproduced signal is extracted.

According to the optical reproducing pickup having such a configuration, the magneto-optical disks (
31), and the cross-sectional area (S2) of one end (398) of the second optical waveguide (39) is made adjacent to the first optical waveguide (38).
Since it is formed wider than the cross-sectional area (Sl) of one end (38A) of the magneto-optical disk (31), the reflected light from the magneto-optical disk (31) can be efficiently focused, and the reproduction output can be improved. In addition, since the cross section m (St>) of one end of the first optical waveguide (38) is small, the amount of light reflected from the magneto-optical disk (31) returning to the first optical waveguide (38) is small (therefore, the amount of light returning to the first optical waveguide (38) is small. It is possible to prevent the oscillation of the laser diode (36) from becoming unstable due to the influence of light.In addition, the first optical waveguide (38) is formed in a tapered shape, and the cross-sectional area (Sl) of one end is equal to that of the second optical waveguide (38). Since it is smaller than that of the optical waveguide (39), the recording track can be made narrower.

Furthermore, the respective first and second optical waveguides (38) and (3
9) The mode conversion in which the direction of the polarization plane changes is small.

In addition, as mentioned above, the optical waveguide (3B) <39) and the metal clad mode filters (40) (41) make the optical system smaller than before, so the lightweight slider (33) It can be formed on the end face (33A).

Therefore, high-speed access can be achieved.

7 and 8 show other examples of the present invention. In this example, the metal clad mode filters (40) and (41) are omitted, and one end (38^) is the same as in FIG. 2. Medium (5
5) and the other end (38B) is a laser diode (38B).
6), and one end (398) is adjacent to one end (38A) of the first optical waveguide (38) and one end (38A) of the first optical waveguide (38) is arranged. ) cross section +
It has a second optical waveguide (39) having a cross-sectional area (St) wider than 1jl (St) and having a photodetector (37) arranged at the other end (39B).

Optical playback pickups with this configuration are suitable for optical discs such as read-only CL), write-once optical discs that can be recorded only once,
Optical playback of rewritable optical discs, etc.

Can be used for backups.

〔Effect of the invention〕

According to the optical reproducing pickup of the present invention, the 881 and the second
By arranging one end of each of the optical waveguides facing the recording medium adjacent to each other, and making the cross-sectional area of one end of the second optical waveguide larger than the curved area of one end of the first optical waveguide, the reflection from the recording medium can be reduced. Light can be efficiently focused from one end of the second optical waveguide, and reproduction output can be greatly improved.

Furthermore, since the cross-sectional area of one end of the first optical waveguide is small, the amount of reflected light returning to the first optical waveguide is small, and instability of oscillation of the laser diode as a light source can be prevented.

Furthermore, since the cross-sectional area of one end of the first optical waveguide is small, the recording track can be made narrower. Furthermore, since the optical system can be made smaller by using a °C optical waveguide instead of a conventional large lens system, it becomes possible to form the optical system on a lightweight slider and achieve high-speed access.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an example of an optical reproducing pickup according to the present invention arranged on a lightweight slider, Fig. 2 is a plan view showing an example of the optical reproducing pink amplifier, and Fig. 3 is a perspective view of the optical reproducing pickup. Figure 4 is a perspective view of the end face of the optically regenerating pink amplifier, Figure 5 is a sectional view taken along line A-A in Figure 2, f
Fig. f16 is a sectional view taken along the line B-B in Fig. 2, Fig. 7 is a plan view showing another example of the optical reproducing pink amplifier according to the present invention, and Fig. 8 is a perspective view of the end face of the optical reproducing pick amplifier. FIG. 9 is a block diagram showing an example of a conventional optical head, and FIG. 10 is a block diagram showing a magnetic field modulation type magneto-optical recording system. (31) (55) is a recording medium, (36) is a laser diode, (37) is a photodetector, (38) is a first optical waveguide, (39) is a second optical waveguide, (40) (41
) is a metal clad mode filter.

Claims (1)

[Scope of Claims] A first optical waveguide having one end facing a recording medium and a light source disposed at the other end; one end adjacent to the one end of the first optical waveguide and one end of the first optical waveguide. An optical reproducing pickup comprising a second optical waveguide having a cross-sectional area larger than the area of the second optical waveguide and having a photodetector arranged at the other end.