JPH0589547A - Pickup for magneto-optical medium - Google Patents

Abstract

PURPOSE:To attain miniaturization and reduction of the weight of a pickup for a magneto-optical medium and to improve an S/N of a detected signal. CONSTITUTION:Laser beams emitted from an LD 15 and propagated through an optical waveguide 5 are converged on an optical disk 10 via an FGC 29 and a condenser lens. A hologram optical element 43 diffracting a returning light from the magneto-optical disk on the optical waveguide 5 is provided and at the same time, photodetectors 20a-20d detecting zero-order light and photo-detectors 22-25 detecting + or - first-order light are formed respectively, on the substrate 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical medium pickup for recording and / or reproducing information using a magneto-optical medium, and more particularly to an integrated magneto-optical medium pickup.

[0002]

2. Description of the Related Art In recent years, in information recording technology represented by magnetic recording such as floppy disks and magnetic tapes, demands for high density, large capacity and high speed have been increasing. In order to meet the demand, research on magneto-optical information recording technology using a magneto-optical medium that enables high density and large capacity
Development is actively done.

A pickup for a magneto-optical medium, which is a key component in this magneto-optical information recording technique, requires a magneto-optical signal differential detection optical system in addition to a focusing or tracking error detection optical system. Required, and downsizing is difficult. On the other hand, in order to access desired information on the magneto-optical medium at high speed, it is important to reduce the size and weight of the pickup itself.

In order to solve such a problem, a waveguide type differential detection device in which a pickup is integrated by using an optical waveguide, a grating element or the like has been proposed. For example, 1988 Electronic Information Communication The one disclosed in "Optical IC for magneto-optical disk pickup" at the autumn conference of the academic society is known. The pickup will be described below.

Light emitted from a laser diode (hereinafter referred to as LD) is collimated by a collimating lens which is three-dimensionally arranged with respect to the optical waveguide, and is reflected by a half mirror provided on the optical waveguide. The light reflected by the half mirror is condensed by the objective lens and is applied to the magneto-optical disk. Then, the return light reflected from the magneto-optical disk passes through the objective lens again by rotating the polarization direction by ± θ by the Kerr effect, corresponding to the bit information 0 and 1 recorded as the magnetization direction on the disk. Trifocal focusing grating coupler (hereinafter FG
(C) is irradiated.

This trifocal FGC is for the TM component in the center,
Condensing FGCs for TE components are arranged at both ends, and P-polarized incident light is TM guided light by the central TM FGC, and S-polarized incident light is TE guided light by the TE FGCs at both ends. It is introduced into the optical waveguide and each guided light is condensed at three different positions. When the reflected light as described above is incident on the trifocal FGC, the TE / TM mode guided light power is inverted and increased / decreased according to the polarization rotation ± of the incident light. Information is read from the magneto-optical disk by detecting this with a photodiode arranged at each condensing point and taking a differential between the TE guided light output and the TM guided light output. In addition, the focusing and tracking error signals are detected by the two TE waveguides for both ends.
The Foucault method or the push-pull method is performed using the output of the divided photodiode.

Further, in Japanese Laid-Open Patent Publication No. 62-146444, a magneto-optical medium in which optical elements such as a grating and a lens are integrated into a base body for guiding a laser beam by using a curved surface to reduce the size and weight. Pickups are disclosed.

[0008]

In the technique disclosed in the above-mentioned paper, the LD, the collimator lens and the objective lens are three-dimensionally arranged, so that the pickup cannot be further miniaturized. That is, L
Since the laser light emitting side from D to the magneto-optical disk is spatially separated from the signal detecting side, it is difficult to realize a small and thin pickup. Further, since the optical elements are three-dimensionally arranged in this way, it is difficult to adjust the positions of the LD, the collimator lens and the objective lens.

Further, as described above, the light reflected from the magneto-optical disk is divided by the trifocal FGC into two components, TE and TM, which are orthogonal to each other, and coupled to the optical waveguide. Separating the guided component is achieved by the difference in the pitch of the FGC formed on the optical waveguide, but with this method, one component cannot be guided and escapes as reflected or scattered light. That is, F for TE
The light of TM component is cut by the GC and the light of TE component is cut by the FGC for TM, and about half of the total reflected light amount is cut, resulting in poor light utilization efficiency. Also, T
The difference in pitch between the FGC for E and TM is very small.
Since it is about 4%, the separation of the TE component and the TM component becomes incomplete. In this way, the utilization efficiency of light is poor and TE component and TM
Due to incomplete separation of the components, the detected signal is S /
N is considerably deteriorated.

The pickup disclosed in Japanese Patent Laid-Open No. 62-146444 requires a technique for integrally molding a wide variety of aspherical surfaces with high precision. Difficult and difficult to create easily.

The present invention has been made in order to solve the above-mentioned problems, and is smaller in size, lighter in weight, easier to manufacture, and has a good S / N of a detected signal. Is intended to provide.

[0012]

In order to solve the above problems, a magneto-optical medium pickup of the present invention comprises a waveguide layer and
A laser diode for guiding a laser beam to the waveguide layer, and an optical element formed on the waveguide layer for emitting the guided light in the waveguide layer toward the magneto-optical medium and rotating the polarization plane by 45 °. A separating optical element for separating the return light from the magneto-optical medium into light for detecting a servo signal and light for detecting a magneto-optical signal of the medium; and a photodetector for detecting each of the separated lights. It is characterized in that the respective constituent elements are formed on the same substrate.

[0013]

By forming the optical element integrally on the same substrate and dividing the return light from the magneto-optical medium into a system for detecting the magneto-optical signal of the medium and a system for detecting the servo signal,
The return light from the magneto-optical medium is efficiently used.

[0014]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a perspective view showing an outline of a magneto-optical medium pickup according to the present invention, and FIG. 2 is a side view of the magneto-optical medium pickup shown in FIG. The configuration of the magneto-optical medium pickup according to the present invention will be described below with reference to FIGS.

On the Si substrate 1, there is formed a SiO ₂ film which becomes a clad layer of the optical waveguide by thermally oxidizing the surface, and # 7059 glass manufactured by Corning Co. is deposited on the surface by sputtering or the like. Thus, the optical waveguide 5 is formed. A predetermined gap 1 is formed on the optical waveguide 5.
A transparent substrate 7 having a concave cross section is provided so that 3 exists. The thickness of the gap 13 and the transparent substrate 7 is set arbitrarily. The transparent substrate 7 is omitted in FIG.

On the front left and right of the Si substrate 1, respectively,
Divided photodetectors 20a, 20 for detecting the guided light reflected from the magneto-optical disk 10 and propagating through the optical waveguide 5.
b and 20c and 20d are formed. Photodetectors 22, 23 and 24, 25 are formed on the left and right sides of the rear portion of the Si substrate 1, respectively.

An incident FG is provided at the center of the front part on the optical waveguide 5.
C27 is formed, and the laser light emitted from the LD 15 described later is made to enter the optical waveguide 5. Optical waveguide 5
A beam splitter 28 and an FGC 29 for emission are formed in the upper rear center, and the guided light emitted from the LD 15 is emitted to the outside of the optical waveguide 5. Further, multilayer films 31 and 33 having a polarization separation function are formed on the left and right sides of the optical waveguide 5 above the photodetectors 22 and 24, respectively. This multilayer film is designed to have an analyzer function of transmitting 100% of P-polarized light and reflecting 100% of S-polarized light with respect to incident light. This multilayer film 3
The multilayer films 31 and 33 and the photodetectors 22 and 24 are arranged so that the P-polarized light transmitted through the light detectors 1 and 33 is detected by the photodetectors 22 and 24, respectively. FG for injection described above
A 1 / 2λ plate is arranged on C29, and the plane of polarization of the light emitted from the optical waveguide 5 via the emission FGC 29 is rotated by 45 °.

On the left and right sides of the back surface of the transparent substrate 7, the S-polarized light reflected by the multilayer films 31 and 33 is received,
In addition, a reflective film is formed so as to reflect the S-polarized light toward the photodetectors 23 and 25. Although this reflection film is not shown, reflection points are shown by P1 and P2 in FIG. A hologram optical element (hereinafter, referred to as HOE) 43 is formed on the rear surface of the rear surface of the transparent substrate 7 so as to correspond to the emission FGC 29 described above, and diffracts the return light from the magneto-optical disk 10. In the HOE 43, the 0th-order light is incident on the FGC 29, and the 1st-order light and the -1st-order light are respectively generated in the multilayer films 31 and 3.
3 is adjusted so as to be incident.

An objective lens 47 is attached to the surface of the transparent substrate 7 at a position corresponding to the HOE 43, and the laser light emitted from the emission FGC 29 is applied to the magneto-optical disk 1.
Focus to 0. A recess 7a is formed at the center of the front surface of the transparent substrate 7, and an LD is formed in the recess 7a.
15 is attached. This LD is arranged so as to irradiate the above-mentioned incident FGC 27 with laser light.

Next, the function of this pickup will be specifically described along the light path. As shown in FIG. 2, LD1
The laser light emitted from 5 passes through the transparent substrate 7 and is guided into the optical waveguide 5 by the incident FGC 27. The laser light guided into the optical waveguide 5 is guided while repeating total reflection in the waveguide, and is emitted upward by the emission FGC 29.

The light emitted from the LD 15 and guided through the optical waveguide 5 is TE mode light, and its electric vector oscillates in the direction of the arrow in the figure. As described above, since the 1 / 2λ plate 30 is provided on the emission FGC 29, the polarization direction of the light incident on the HOE 43 is rotated by 45 ° as shown in the figure. Laser light emitted upward from the emission FGC 29 and having its polarization plane rotated by 45 ° is HO.
It is focused on the surface of the magneto-optical disk 10 via E43, the transparent substrate 7 and the objective lens 47. Then, the light condensed on the surface of the magneto-optical disk 10 is reflected by rotating the polarization direction by ± θ by the Kerr effect, corresponding to the bit information 0 and 1 recorded as the direction of magnetization on the magneto-optical disk. To be done.

As shown in FIG. 4, the reflected light from the magneto-optical disk enters the HOE 43 through the objective lens and the transparent substrate. The light incident on the HOE 43 is diffracted into 0th order light and ± 1st order light. As mentioned above, the ± 1st order light is HOE4.
With the configuration of No. 3, the light is diffracted so as to be perpendicular to the traveling direction of the guided light, and goes toward the multilayer films 31, 33, respectively. In the figure, since the ± 1st order light behaves in the same way, the multilayer film 3
It is shown for the primary light guided to 1.

The primary light guided to the multilayer film 31 is 1 / 2λ
The polarization plane is inclined by 45 ° by the plate. In this multilayer film 31, of the polarized light inclined at 45 °, P
Only polarized light is transmitted, and the transmitted light is detected by the photodetector 22. On the other hand, the S-polarized light reflected by the multilayer film 31 is reflected by the reflective film (P1) and detected by the photodetector 23.

As described above, the polarized light inclined by 45 ° undergoes the polarization rotation of ± θ corresponding to the bit information due to the Kerr effect in the magneto-optical disk 10. By receiving the polarization rotation in this way, the power of the P component light or the power of the S component light increases (see FIG. 5). Therefore, the magneto-optical signal is detected by taking the difference between the signals detected by the photo detectors 22 and 23.

The 0th-order light from the HOE 43 is emitted by the FGC for emission.
The beam splitter 2 is guided by 29 to the optical waveguide 5.
It is divided by 8 and directed to the photodetectors 20a, 20b and photodetectors 20c, 20d (see FIG. 1). In these photodetectors, the focus error signal and the tracking error signal are detected by the Foucault method / push-pull method as in the conventional case.

As described above, the magneto-optical signal can be efficiently detected by not using the optical waveguide 5 for the detection of the magneto-optical signal but by using the polarization separating element by reflection and transmission to obtain the differential. .. On the other hand, a part of the reflected light from the magneto-optical disk 10 returns to the optical waveguide 5 and is used to obtain a servo signal. In order to obtain the focus and tracking error signals for servo, the LD 15, FGCs 27, 29 and the photodetectors 20a to 20d are required to have a precise positional relationship, but these are integrated on one substrate, so they are assembled. There is no need for adjustment. Further, by forming the photodetectors 22 to 25 for detecting the magneto-optical signal on the same substrate, the number of parts can be reduced. This photodetector only needs to receive the amount of light without waste, and does not require strict position adjustment.

Next, the manufacturing process of the pickup shown in this embodiment will be described with reference to FIGS. First, a photodetector is formed on a Si substrate, and then a SiO ₂ film serving as a clad layer of a waveguide is formed by thermal oxidation. Corning 7059 glass, which serves as a waveguide, is formed thereon by sputtering. Further, a multilayer film having a polarization separation function is formed above the photodetector for receiving P-polarized light. Next, incident and emitted FGCs are formed in accordance with the positions of the photodetectors for servo signal detection. This is first S on the waveguide
After forming the i ₃ N ₄ layer by sputtering, a resist is applied, a grating is drawn by an electron beam method and developed, and then the Si ₃ N ₄ layer is removed by reactive ion etching and the resist is dropped to form an FGC.

FIG. 7 shows a manufacturing process of the transparent substrate 7 mounted on the silicon substrate 1 shown in FIG. The transparent substrate on which the HOE is formed is HOE
It is manufactured by injection molding of plastic resin using a mold that is a replica of. A recess for mounting the LD at the time of injection molding is formed on the transparent substrate, and a gold thin film pattern for wiring of the LD is formed on the surface of the recess by vapor deposition. Finally, the objective lens is attached to the opposite surface of the transparent substrate on which the HOE is formed with a transparent adhesive.

The transparent substrate is attached to a predetermined position on the silicon substrate. In this method, an LD is attached to a transparent substrate, wiring is performed, and the transparent substrate is brought onto a silicon substrate while the LD emits light. In that state, the focused spot on the objective lens is observed, and the position of the transparent substrate is adjusted so that the aberration is minimized. Therefore, an adhesive is poured between the transparent substrate and the silicon substrate to fix them.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made.
For example, it can be modified as shown in FIG.
This is to attach the LD stem 15b to the silicon substrate 1,
By fixing the LD 15 to this, the laser light is directly coupled into the waveguide 5 from the end face of the waveguide. This eliminates the need for adjusting the adhesion of the transparent substrate to the silicon substrate. Other configurations are the same as those in the above-described embodiment.

Further, a replica of a Fresnel type lens which becomes an objective lens is formed in a mold for molding a transparent substrate. As a result, as shown in FIG. 9, after the transparent substrate 7 is molded, this portion becomes the objective lens 47a, and it is not necessary to bond a new lens.

[0032]

As described above, according to the present invention,
It is not necessary to dispose the LD, the collimator lens and the objective lens in three dimensions, and the pickup itself can be made smaller and thinner. Further, it is not necessary to adjust the position between the optical elements such as the LD and the collimator lens. Also,
In order to efficiently use the return light from the magneto-optical medium,
The system for detecting the magneto-optical signal of the magneto-optical medium and the system for detecting the servo signal are separated. That is, in the process of detecting the light reflected from the magneto-optical medium, since the loss of the light quantity is eliminated, a detection signal with a good S / N can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing an outline of a magneto-optical medium pickup according to the present invention.

FIG. 2 is a side view of the magneto-optical medium pickup shown in FIG.

FIG. 3 is a diagram showing a polarization state after passing through a 1 / 2λ plate.

FIG. 4 is an enlarged view showing a light path of an emission FGC portion in the magneto-optical medium pickup shown in FIG.

FIG. 5 is a graph showing the intensities of the P component and the S component detected by the photodetector when the polarization rotation of ± θ is received corresponding to the bit information.

6A and 6B are views for sequentially explaining a manufacturing process on the Si substrate side in the magneto-optical medium pickup shown in FIG.

7A to 7C are views for sequentially explaining a manufacturing process on the transparent substrate side in the magneto-optical medium pickup shown in FIG.

8 is a side view showing a modified example of the magneto-optical medium pickup shown in FIG.

FIG. 9 is a diagram showing a modified example of a condenser lens attached to a transparent substrate.

[Explanation of symbols]

1 ... Si substrate, 5 ... Optical waveguide, 10 ... Magneto-optical disk,
15 ... LD, 20a to 20d, 22 to 25 ... Photodetector,
30 ... 1 / 2λ plate, 43 ... Holographic optical element.

Claims (1)

[Claims] 1. A waveguide layer, a laser diode which guides laser light to the waveguide layer, and a waveguide light which is formed on the waveguide layer and is emitted in the waveguide layer toward a magneto-optical medium. And an optical element for rotating the plane of polarization by 45 °, a separating optical element for separating the return light from the magneto-optical medium into light for detecting a servo signal and light for detecting a magneto-optical signal of the medium, and the separated light And a photodetector for detecting each of the above, and a pickup for a magneto-optical medium in which each of the components is formed on the same substrate.