JPH07235095A - Magneto-optical reproducing pickup - Google Patents

Abstract

PURPOSE:To easily compensate a phase difference between two intrinsic modes (integral multiple of pi) and to reduce deterioration in quality of a reproducing signal due to the elliptical polarization of a light even when there are a variance in manufactured waveguides, fluctuations in an optical parameter due to temperature changes, fluctuations in the wavelengths of emitted lights, etc. CONSTITUTION:This device is provided with an optical waveguide 4 for guiding the TE mode component of a laser light emitted from a light emitting means 5 to the magneto-optical recording medium side and guiding a reflective light from the magneto-optical recording medium to the differential light detecting part 9 side and this optical waveguide 4 is provided with a phase compensating means for compensating a phase difference between the light components of TE and TM modes included in the reflective light. In this case, the phase compensating means is constituted of an optical waveguide constituted on a base plate made of an electrical optical crystal by forming a thin film having a light refractive index higher than that of this base plate, phase control electrodes (21a and 21b) for impressing a magnetic field to this optical waveguide in a direction along the TM mode and a feedback circuit 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical reproducing pickup used for reproducing information signals recorded on, for example, a magneto-optical disk, and particularly suitable for a magneto-optical reproducing pickup using an optical waveguide. Is.

[0002]

2. Description of the Related Art A conventional magneto-optical reproducing pickup using individual parts, as shown in FIG. 15, shows a predetermined light emitted from a light source section 101 having a laser light source by a laser diode and a polarizing plate. Linearly polarized light having a plane of polarization (hereinafter referred to as TE wave) is a partial beam splitter (hereinafter simply referred to as partial BS) 1
The recording medium, that is, the magneto-optical recording medium 103, is irradiated through 02, the reflected light from the magneto-optical recording medium 103 is reflected by the partial BS 102, and a pair of analyzers (45 degree detection) is used. A configuration is adopted in which the light is made incident on the photodetection elements 105a and 105b and input as electric signals (detection outputs) to the differential amplifier 106 in the subsequent stage. A differential detection circuit 107 is composed of the pair of photodetection elements 105a and 105b and the differential amplifier 106. In this case, the partial BS 102 has a characteristic of reflecting, for example, 20% of TE wave and almost 100% of TM wave of a polarization plane orthogonal to the TE wave.

In this way, the TE from the light source unit 101 is
Most of the waves (80%) are applied to the magneto-optical recording medium 103. Then, the reflected light whose polarization plane is rotated by the optical-magnetic interaction (Kerr effect) according to the recording signal magnetization of the magneto-optical recording medium 103 is again the partial BS 102.
Enter, but here the rotation due to the Kerr effect (Kerr rotation)
Almost all the TM wave components generated by are reflected.

T reflected by the partial BS 102
The M wave component is subjected to 45-degree analysis and branching by the next analyzer 104 and is incident on the pair of photodetection elements 105a and 105b. In this case, depending on the recorded information of the magneto-optical recording medium 103, that is, depending on the magnitude of the Kerr rotation, for example, the amount of incident light on one photodetecting element 105a becomes small, and the detection outputs of both are detected by the differential detection circuit. The reproduced signal can be taken out by differentially detecting by 107.

On the other hand, as a magneto-optical reproducing pickup, it is intended to reduce its size, weight and mass productivity.
A magneto-optical reproducing pickup using the so-called optical integrated technology by an optical waveguide, that is, a magneto-optical reproducing pickup that directly irradiates a magneto-optical recording medium with light emitted from the optical waveguide and detects rotation of a polarization plane of transmitted light or reflected light. Have been proposed (for example, JP-A-60-224139 and JP-A-1).
-279432 publication).

[0006]

Generally, as shown in FIG. 16, the light L propagating in the optical waveguide 111 has different propagation constants between modes corresponding to orthogonal polarization directions, and therefore exits from the waveguide. Light is generally elliptically polarized.

When the polarization of the light incident on the surface of the magneto-optical material becomes elliptical, the detected information on the rotation of the plane of polarization becomes small. If the direction of the polarized light incident on the optical waveguide is matched with one eigenmode, it is possible to pass through the waveguide while maintaining the polarization state on the outward path. However, when the reflected light from the surface of the magneto-optical material is made to enter the waveguide again, the other eigenmode component is also generated in the return path due to the rotation of the plane of polarization by the magneto-optical material, and between these two modes. Due to the phase difference of, the outgoing light is eventually elliptically polarized.

Hereinafter, a case where differential detection is performed by using analyzers whose analysis directions are inclined by ± 45 ° with respect to the polarization direction of incident light will be described with reference to FIGS. 17 and 18. Here, in the diagrams shown in FIGS. 17 and 18, the vertical axis represents the TE-mode polarization direction and the horizontal axis represents the TM-mode polarization direction. And each polarization direction (vector) of the reflected light 122 with downward magnetization.

In FIGS. 17 and 18, lines m and n extending in the directions of ± 45 ° with respect to the horizontal axis are the incident light 12
The directions of analysis of two analyzers whose inclinations are + 45 ° and −45 ° respectively with respect to the polarization direction of 3 are shown. In this example, it is assumed that TM mode light is incident on the magneto-optical recording medium.

That is, when the magnetization direction of the magneto-optical recording medium is reversed, the polarization directions of the two reflected lights 121 and 122 are rotated by + θ or −θ with respect to the horizontal axis TM due to the Kerr effect. . At this time, the output of the differential detector is
Peak to Peak (Line AA'-Line aa ')
− (Line segment BB′−Line segment bb ′).

When the reflected lights 121 and 122 propagate through the optical waveguide to be elliptically polarized lights 124 and 125, respectively, as shown in FIG. 18, line segments AA 'projected from the ellipses to the lines m and n. And the line segment aa ′ (= line segment AA′−line segment aa ′) and the difference between the line segment BB ′ and the line segment bb ′ (= line segment BB′−line segment bb ′) are respectively the line in FIG. Smaller than the difference between the line segment AA 'and the line segment aa' (= line segment AA'-line segment aa ') and the difference between the line segment BB' and the line segment bb '(= line segment BB'-line segment bb') And the detection signal drops accordingly.

The rotation angle of the plane of polarization in the magneto-optical material is θ, and the phase difference between two eigenmodes generated when light is one-way guided in the optical waveguide is ψ, and ± 4 from the incident polarization direction.
When differential detection is performed on the plane of polarization inclined by 5 °, the detection signal is proportional to cos ψsin2θ.

As a result, if the phase difference ψ is set to an integral multiple of π, there will be no signal deterioration. In this case, the phase difference ψ
Since it is proportional to the waveguide length, there is a method of adjusting it by the length of the waveguide, but it is not realistic because it requires a manufacturing accuracy of a wavelength order. Further, there is a problem that it is not possible to cope with the change of the optical parameter of the waveguide due to the temperature change and the change of the polarization state of the emitted light due to the wavelength change of the light source.

The present invention has been made in view of the above problems. An object of the present invention is, even if there are fluctuations in optical parameters due to manufacturing variations of a waveguide or temperature changes, wavelength fluctuations of emitted light, etc. It is an object of the present invention to provide a magneto-optical reproducing pickup capable of easily compensating for a phase difference between two eigenmodes (an integral multiple of π) and preventing deterioration of a reproduced signal due to elliptically polarized light.

[0015]

As shown in FIG. 1, the magneto-optical reproducing pickup according to the present invention guides the light component of the first mode of the light emitted from the light emitting means 5 to the recording medium side, The optical waveguide 4 for guiding the light reflected by the recording medium to the photodetector 9 side is provided, and the optical waveguide 4 is provided with the phase difference between the light components of the first and second modes included in the reflected light. A phase compensating means for compensation is provided and configured.

In this case, the first mode can be a vertical polarization mode or a horizontal polarization mode, and the second mode is a horizontal polarization mode when the first mode is a vertical polarization mode. Then, when the first mode is a horizontal polarization mode, it can be a vertical polarization mode.

Then, as shown in FIG. 2, the phase compensating means is constructed by forming a thin film 2 having a higher optical refractive index than the substrate 1 on a substrate 1 made of an electro-optic crystal. 4 and electric field applying means (phase control electrode 21 and feedback circuit 11) for applying an electric field to the optical waveguide 4.

Further, as shown in FIG. 6, the phase compensating means is formed by forming a thin film 43 made of an electro-optic crystal and having a higher optical refractive index than the substrate 41 on the substrate 41, as shown in FIG. The waveguide 4 and electric field applying means (phase control electrode 21 and feedback circuit 11) for applying an electric field to the optical waveguide 4 can be used.

The direction of the electric field applied by the electric field applying means may be along the first or second mode, or may be the film thickness direction of the optical waveguide 4.

As the phase compensation means, as shown in FIG. 7, the temperature control element 5 formed on the optical waveguide 4 is used.
4 may be provided, or as shown in FIG. 11, wavelength control means (wavelength tunable semiconductor laser 64, drive current source 66, and feedback circuit 65) for varying the wavelength of the light emitted from the light emitting means 64. ) May be provided and configured.

[0021]

In the magneto-optical reproducing pickup according to the present invention, the light component of the light emitted from the light emitting means 5 in the first mode is guided to the recording medium side by the optical waveguide 4 and reflected by the recording medium. Similarly, the (reflected light) is guided to the side of the photodetector 9 by the optical waveguide 4, and the reproduction signal is extracted from this photodetector 9.

At this time, the reflected light is a mixture of a light component of the first mode (for example, TE mode) and a light component of the second mode (for example, TM mode), and becomes elliptically polarized light due to the phase difference between the modes. Become. As a result, this elliptically polarized light normally causes deterioration of the reproduction signal.

However, the phase difference between the above two modes is π
It is possible to avoid the deterioration of the reproduction signal by setting the integer multiple of.

Since the magneto-optical reproducing pickup according to the present invention is provided with the phase compensating means for compensating for the phase difference between the two modes, the phase compensating means allows, for example, the phase difference between the two modes. Can be compensated to an integral multiple of π, and as a result, the reproduction signal can be prevented from deteriorating due to the elliptically polarized light.

In particular, the phase compensating means, the optical waveguide 4 formed by forming a thin film 2 having a higher optical refractive index than the substrate 1 on a substrate 1 made of an electro-optic crystal, and the optical waveguide 4. On the other hand, in the case of the electric field applying means for applying the electric field, when the electric field is applied by the electric field applying means, the refractive index component of the optical refractive index of the substrate 1 made of the electro-optic crystal changes due to the so-called Pockels effect. To do.

Specifically, by the electric field applying means,
For example, when an electric field is applied in a direction along the second mode, the substrate 1 made of an electro-optic crystal is produced due to the Pockels effect.
In the optical refractive index of, the refractive index component in the direction along the second mode changes. When an electric field is applied by the electric field applying means in the film thickness direction of the optical waveguide, the refractive index component in the film thickness direction of the optical refractive index of the substrate 1 made of an electro-optic crystal changes due to the Pockels effect.

As a result, the propagation constant of the mode having the electric field component (the mode of the optical component) changes in the direction in which the electric field is applied,
The phase difference between the two modes will change. Specifically, for example, when an electric field is applied in the film thickness direction by the electric field applying means, the propagation constant of the TM mode having an electric field component in the film thickness direction changes and the phase difference between the two modes changes. Become. Therefore, the phase difference between the two modes can be controlled by appropriately selecting the strength of the electric field generated from the electric field applying means, and the phase difference can be adjusted to an integral multiple of π.

Further, the phase compensating means is formed by forming a thin film 43 made of an electro-optic crystal on the substrate 41 and having a higher photorefractive index than the substrate 41, and the optical waveguide 4. Even when the waveguide 4 is constituted by an electric field applying means for applying an electric field, the phase difference between the two modes can be controlled by appropriately selecting the strength of the electric field generated by the electric field applying means. The phase difference can be adjusted to an integral multiple of π.

Further, when the phase compensating means is constructed by providing the temperature control element 54 formed on the optical waveguide 4, the temperature control element 54 can control the temperature of a part of the optical waveguide 4. . Therefore, the phase difference between the two modes can be controlled by appropriately changing the part of the temperature by the temperature control element 54, and the phase difference can be adjusted to an integral multiple of π.

When the wavelength control means for varying the wavelength of the light emitted from the light emitting means 64 is provided, the wavelength of the light emitting means 64 can be controlled by the wavelength control means. Therefore, by appropriately changing the wavelength of the light emitting means 64 by the wavelength control means, the phase difference between the two modes can be controlled, and the phase difference can be adjusted to an integral multiple of π.

[0031]

EXAMPLES Some examples of a magneto-optical reproducing pickup according to the present invention will be described below with reference to FIGS.

First, the magneto-optical reproducing pickup according to the first embodiment, as shown in FIGS.
For example, a height of about 0.5 mm made of KTP (z-cut plate)
On the substrate 1 of, for example, a high-refractive-index dielectric film such as Ti.
An O ₂ thin film is formed to form a waveguide layer 2 having a thickness of about 170 nm,
Furthermore, by selectively etching the waveguide layer 2 by ion milling to a depth of about 20 nm, a convex line (thickness of about 170 nm) extending along a predetermined waveguide and having a convex waveguide section is formed. ) Optical waveguide 4 formed in the shape of a so-called rib type three-dimensional optical waveguide having 3)
Is configured.

A light source, for example, a semiconductor laser (laser diode) 5 is installed on an end surface b of the optical waveguide 4 opposite to a surface (hereinafter, simply referred to as a facing surface) a facing the magneto-optical recording medium. . The active layer of the semiconductor laser 5 is connected to the outward path 6 of the optical waveguide 4 and is optically coupled to the optical waveguide 4. Further, on the way of the outward path 6 of the optical waveguide 4, linearly polarized light (TE
A mode filter 7 as a polarizer for obtaining a wave) is arranged.

Here, the convex line 3 forming the optical waveguide 4 effectively uses the laser light emitted from the semiconductor laser 5 and the light reflected by the magneto-optical recording medium (collectively referred to as guided light). It is for confining and efficiently transmitting along the optical waveguide 4. In this embodiment, the film thickness of the waveguide layer 2 and the width and height of the convex line 3 are set so that the beam width of the guided light in the film thickness direction is minimized and the single mode condition is satisfied. To be elected. For example, the wavelength λ of the laser light emitted from the semiconductor laser 5 is 63
In the case of 2.8 nm, the height and width of the convex line 3 are 170 nm and 2 μm for the TM0 mode.
By setting the beam width in the film thickness direction to 210 n
m can be realized.

The optical waveguide 4 is branched into a substantially Y shape in the middle of the outward path 6. The part branched from this outward path 6 is a part through which the light reflected by the magneto-optical recording medium passes, and constitutes the return path 8 of this optical waveguide 4. Therefore,
In the following description, this branched portion will be referred to as the return path 8.

A differential photodetection section 9 is arranged from the middle of the return path 8 to the end thereof. This differential light detection unit 9
As shown in FIG. 3, two branch paths 8 branching from the return path 8
a and 8b and first and second photodetector elements 9a, which are optically coupled to the tips of the branch paths 8a and 8b and photoelectrically convert the reflected light from the branch paths 8a and 8b, which are, for example, photodiodes. And 9b. The output terminals of these photodetectors 9a and 9b are connected to a differential amplifier 10 installed outside. The differential amplifier 10 is a circuit that differentially amplifies each detection signal from the first and second photodetection elements 9a and 9b, and is recorded on a magneto-optical recording medium from an output terminal of the differential amplifier 10. The information signal that is present is taken out. In this embodiment, a reproduction output S is obtained from its output terminal through a feedback circuit 11 described later. The first and second photodetector elements 9a
And 9b and the differential amplifier 10 in the differential amplifier circuit 1
2 will be configured.

Further, first and second signal detecting mode filters 13a and 13b are provided in the respective branch paths 8a and 8b in the differential light detecting section 9. These first and second signal detecting mode filters 13a and 13b
Is ideally provided so as to transmit a plane of polarization that forms + 45 ° and −45 ° with respect to the TE mode, for example.

The first and second signal detecting mode filters 13a and 13b are provided with, for example, grooves 14 having both side surfaces forming a required angle with each other, and the branch paths 8a and 8b pass through the side surfaces 14a and 14b, respectively. In addition, at the portion where these respective branch paths 8a and 8b communicate,
For example, it can be configured by forming a clad type mode filter. The formation of the groove 14 having the side surface of such a required angle can be performed by selecting the crystal plane of the substrate 1 and by crystallographically anisotropic etching with respect to the substrate 1, and the rib type optical waveguide is formed on the substrate 1 after the etching. By forming the TiO ₂ film 2 to be formed, it is possible to form the convex line 3 on the side surfaces 14a and 14b of the groove 14 along with the formation of the groove 14, that is, the branch lines 8a and 8b. Become.

The laser light emitted from the semiconductor laser 5 is introduced to the convex line 3 in the outward path 6 of the optical waveguide 4, and is guided to the facing surface a side by the convex line 3. At this time, the laser light is linearly polarized (TE) having a predetermined polarization plane by the mode filter 7 formed on the way.
And is guided to the facing surface a side. The laser light guided to the facing surface a side is directly applied to a magneto-optical recording medium (not shown), and its polarization plane is rotated by the optical-magnetic interaction according to the magnetization information recorded in the magneto-optical recording medium. , Is again introduced to the convex line 3 of the optical waveguide 4 as reflected light.

Since the plane of polarization of the reflected light is rotated by the optical-magnetic interaction depending on the magnetization of the magneto-optical recording medium, the TE-mode optical component and the TM-mode optical component are mixed. Become light.

The reflected light is transmitted through the signal detecting mode filters 13a and 13b of the differential light detecting section 9 provided on the return path 8 with a polarization component of + 45 ° and a polarization component of −45 °, respectively. The light is incident on the corresponding photodetector elements 9a and 9b.

Here, when the magnetization information recorded in the magneto-optical recording medium is, for example, upward magnetization, and the polarization plane of the reflected light is rotated by + θ with respect to the TE mode, the first signal detection The light component transmitted through the use mode filter 13a has a larger amount of light than the light component transmitted through the second signal detection mode filter 13b, and accordingly,
The signal level of the detection signal output from the first photodetection element 9a becomes higher than the signal level of the detection signal output from the second detection element 9b, and the differential amplifier 10 outputs, for example, a positive amplitude. A signal will be output.

On the other hand, when the magnetization information recorded on the magneto-optical recording medium is downward magnetization, and the polarization plane of the reflected light is rotated by -θ with respect to the TE mode, the first signal detection The light component transmitted through the mode filter 13a is
The amount of light is smaller than that of the light component that has passed through the second signal detection mode filter 13b, and accordingly, the signal level of the detection signal output from the first photodetection element 9a changes from the second detection element 9b. The signal level becomes lower than the signal level of the output detection signal, and the differential amplifier 10 outputs an output signal having a negative amplitude, for example.

In accordance with the polarity of the output signal output from the differential amplifier 10, recording is performed on the magneto-optical recording medium in such a manner that it is logically "0" when positive and logically "1" when negative. It is possible to convert the existing magnetization information into logical information.

In the magneto-optical reproducing pickup according to the first embodiment, as shown in FIGS. 1 and 2, SiO, for example, is formed on the waveguide layer 2 including the convex line 3 forming the rib type optical waveguide 4. _A flattening film 15 made of ₂ is formed, and one sheet, for example, an Al electrode film (hereinafter, referred to as a plus electrode film) that constitutes the plus electrode 21a and two sheets that construct the minus electrode 21b are formed on the flattening film 15. Al electrode films (hereinafter referred to as negative electrode films) are formed.

The plus electrode 21a serves as the forward path 6 of the optical waveguide 4.
The two minus electrodes 21b are formed on the portion immediately above the convex line 3 between the Y branch point and the facing surface a, and are separated from the plus electrode 21a by a predetermined distance on both sides of the plus electrode 21a. Has been formed. In this embodiment, from the side end of the plus electrode 21a to the minus electrode 21
The distance to the side edge of b is set to several μm. The positive electrode 21a and the negative electrode 21b constitute the phase control electrode 21.

In the first embodiment, the feedback circuit 11 is inserted and connected between the phase control electrode 21 and the differential amplifier 10 to make the optical waveguide 4
The electric field is applied to the convex line 3 in the film thickness direction (z direction). The configuration of this feedback circuit 11 will be described later. The z direction is the same direction as the TM mode included in the reflected light.

As described above, when an electric field is applied in the z direction, the electro-optic crystal (KTP) is produced by the Pockels effect.
The z-direction component of the photorefractive index in the substrate 1 formed in step 1 changes, and the propagation constant of the TM mode changes accordingly. Therefore, the control signal S from the feedback circuit 11 is changed.
It is possible to control the phase difference between the TE-mode optical component and the TM-mode optical component included in the reflected light based on c.

Here, the numerical values are concretely shown and the first
The configuration of the magneto-optical reproducing pickup according to the example will be described.

In the magneto-optical reproducing pickup according to the first embodiment, as the substrate 1, the Pockels constant γ33 is 36.
A substrate made of KTP of 3 pm / V and having a horizontal direction, that is, a photorefractive index (n4TE) of 1.7627 and a photorefractive index of z direction (n4TM) of 1.8656 is used on the substrate 1. After forming a TiO ₂ thin film 2 having a photorefractive index n1 = 2.5, ion milling is selectively performed to obtain a height of 1
An optical waveguide 4 is formed by forming a convex line 3 of 70 nm, and SiO having an optical refractive index n2 = 1.45 is formed on the TiO ₂ thin film 2.
₂ film 15 is formed, and A is formed at the required position on the SiO ₂ film 15.
The positive electrode 21a and the negative electrode 2 made of the 1 electrode film
By forming 1b, the magneto-optical reproducing pickup according to the first embodiment was formed. At this time, the lengths of the plus electrode 21a and the minus electrode 21b in the longitudinal direction are both 10 mm.

Then, the voltage applied to the phase control electrode 21 composed of the plus electrode 21a and the minus electrode 21b is changed to change the photorefractive index in the z direction of the substrate 1 to the respective photodetection elements 9a and 9b. As shown in FIG. 4, the change in the relative value of the output detection signal is about 10 ^{−4 as} the period D of the photorefractive index in the z direction where the relative value is maximum. In the illustrated example, the variation ΔNsZ of the optical refractive index in the z direction.
Is about -0.00003 and about +0.00008, the relative value is maximum. In FIG. 4, n3 indicates the optical refractive index of air, and the wavelength λ indicates the wavelength of the laser light emitted from the laser light source.

In this first embodiment, the control signal Sc is supplied from the feedback circuit 11 to give the optical waveguide 4 an electric field of 0.85 V / μm at maximum in the z direction, whereby the optical refractive index in the z direction is increased. Change amount ΔNsZ of 10 ⁻⁴
The maximum relative value is obtained by changing the range.

Here, the configuration of the feedback circuit 11 will be described with reference to FIG. The feedback circuit 11 has an error signal Se indicating a deviation from the voltage applied to the phase control electrode 21 so that the relative value becomes maximum.
Is used for phase compensation.

That is, the feedback circuit 11 synchronously detects the output from the differential amplifier 10 at a frequency fm which is sufficiently higher than the frequency fc of the carrier signal read from the magneto-optical recording medium, and extracts the error signal Se. The error signal Se is fed back to the phase control electrode 21.

Specifically, as shown in FIG. 5, the frequency f
The oscillator 31 that outputs a modulation signal of m and the differential amplifier 10
Of the first low-pass filter (hereinafter referred to as the first low-pass filter) that removes the modulated signal component of the frequency fm from the output of
32), a bandpass filter (hereinafter referred to as BPF) 33 having a center frequency fm for removing harmonic components of the frequency fm from the output of the differential amplifier 10, a modulation signal from the oscillator 31, and the BPF 33. , A second low-pass filter (hereinafter, referred to as a second LPF) 35 for extracting an error signal Se from the multiplication signal from the multiplier 34, and a second LP.
It is configured to have an adder 36 that adds the error signal Se from the F35 and the modulation signal from the oscillator 31 to generate the control signal Sc.

Next, the signal processing of the feedback circuit 11 will be described. First, the oscillator 31 applies a modulation signal of the frequency fm to the phase control electrode 21 so that the output of the differential amplifier 10 is modulated at the frequency fm. To Then, the output of the differential amplifier 10 is passed through the BPF 33 to remove the harmonic component of the frequency fm, and then the multiplier 34 multiplies the modulated signal from the oscillator 31, and the error signal Se is obtained through the second LPF 35.

This error signal Se is added to the modulation signal from the oscillator 31 by the adder 36 in the subsequent stage and supplied to the phase control electrode 21 as the control signal Sc. On the other hand, the output from the differential amplifier 10 is output by the first LPF 32 at the frequency f.
The modulation signal component of m is removed and is extracted as a reproduction signal.

As described above, in the magneto-optical reproducing pickup according to the first embodiment, the TiO having a higher optical refractive index than the substrate 1 is formed on the substrate 1 made of the electro-optic crystal KTP.
_{2 On} the optical waveguide 4 formed by forming the thin film 2, SiO
_The phase control electrode 21 composed of the plus electrode 21a and the minus electrode 21b is formed through the flattening film 15 composed of _2, and the control signal Sc is further supplied to the phase control electrode 21 so that Direction along the TM mode (z
Direction), an electric field is applied in the z direction of the substrate 1 due to the so-called Pockels effect.
The optical refractive index in the direction changes.

As a result, the propagation constant of the TM mode changes and the phase difference between the TE mode and the TM mode changes. Therefore, based on the control signal Sc supplied from the feedback circuit 11, the TE mode and TM
The phase difference between the modes can be controlled, and the phase difference can be
It becomes possible to adjust to an integral multiple of. As a result, it is possible to maximize the relative value of the detection signal output from each of the photodetection elements 9a and 9b, and prevent deterioration of the reproduction signal due to elliptically polarized light.

Next, a modification of the first embodiment will be described with reference to FIG. The magneto-optical reproducing pickup according to this modified example basically has substantially the same configuration as the magneto-optical reproducing pickup according to the first embodiment, but as shown in the figure, the substrate using the electro-optic crystal is not used. Instead, for example, a silicon substrate 41 is used, and an electro-optic crystal such as LN is formed on the silicon substrate 41 via an oxide film 42.
The difference is that the optical waveguide 4 is formed by forming the film (LiNbO ₃ ) 43 in a line shape (to be exact, a line shape having a Y branch) by, for example, a sputtering method. The oxide film 42 can be formed by thermally oxidizing the silicon substrate 41.

The plus electrode 21a and the minus electrode 21b are formed at the positional relationship formed in the first embodiment, with the flattening film 15 made of SiO ₂ or the like formed on the LN film 43 interposed therebetween. It

Also in the magneto-optical reproducing pickup according to this modification, as in the first embodiment, the plus electrode 21 is used.
a and a negative electrode 21b for phase control electrode 21
To the optical waveguide 4 in the direction (z) along the TM mode.
By applying an electric field in the (direction), the optical refractive index in the z direction of the optical waveguide changes due to the so-called Pockels effect.

As a result, the propagation constant of the TM mode changes and the phase difference between the TE mode and the TM mode changes. Therefore, the phase difference between the TE mode and the TM mode can be controlled based on the control signal Sc from the feedback circuit 11, and the phase difference can be adjusted to an integral multiple of π. As a result, it is possible to maximize the relative value of the detection signal output from each of the photodetection elements 9a and 9b, and prevent deterioration of the reproduction signal due to elliptically polarized light.

Next, a magneto-optical reproducing pickup according to the second embodiment will be described with reference to FIGS.
Note that the same reference numerals are given to those corresponding to those in FIGS. 1 and 2, and the duplicate description thereof will be omitted.

The magneto-optical reproducing pickup according to the second embodiment has substantially the same structure as the magneto-optical reproducing pickup according to the first embodiment, as shown in FIGS.
The configuration is different in the following points.

That is, when the height of the substrate is 0.5 mm, the optical refractive index =
The thin film forming the 1.45 glass substrate 51, the waveguiding layer and the convex line 3 is a Ta ₂ O ₅ thin film 5 having an optical refractive index of 2.05.
2. The flattening film is the SiO ₂ film 53 having an optical refractive index of 1.46, and the temperature control is performed in the forward path 6 of the optical waveguide 4 just above the convex line 3 between the Y branch point and the facing surface. The point is that a Peltier element 54 as an element is formed.

By forming the Peltier element 54, the temperature of the optical waveguide 4 below the Peltier element 54 is controlled. As a result of the experiment, when the length of the Peltier element 54 in the longitudinal direction was 10 mm, the phase difference between the TE mode and the TM mode could be changed by π by the change from 10 ° C to 30 ° C.

As shown in FIGS. 7 and 9, a current source 55 is connected to the Peltier element 54 according to the second embodiment through wiring, and the current source 55 and the differential amplifier 1 are connected.
Between 0 and 0, the value of the current I injected from the current source 55 to the Peltier element 54 is a constant value, that is, the relative value of each detection signal from the first and second photodetection elements 9a and 9b. A feedback circuit 56 that performs feedback control so as to maximize the value is inserted and connected.

This feedback circuit 56 is provided with the current source 5
A circuit that performs phase compensation using an error signal Se indicating a deviation from the current value I such that the relative value from 5 becomes maximum,
The basic configuration is as shown in FIG.
Synchronously detects the output from the carrier at a frequency fm sufficiently lower than the frequency fc of the carrier signal read from the magneto-optical recording medium,
The error signal Se is taken out and the error signal Se is fed back to the current source.

That is, the oscillator 31 applies a modulation signal of the frequency fm to the current source 55 so that the output of the differential amplifier 10 is modulated at the frequency fm. Then, the differential amplifier 10
Is passed through the second BPF 72 to remove the harmonic component of the frequency fm, the multiplier 34 multiplies the modulated signal from the oscillator 31, and the error signal Se is obtained through the LPF 73.

This error signal Se is added to the modulation signal from the oscillator 31 by the adder 36 in the subsequent stage and supplied to the current source 55 as the control signal Sc. On the other hand, the output from the differential amplifier 10 is taken out as a reproduction signal after the modulation signal component of the frequency fm is removed by the first BPF 71.

As described above, in the magneto-optical reproducing pickup according to the second embodiment, the Ta ₂ O ₅ thin film 52 having a higher optical refractive index than the substrate 51 is formed on the glass substrate 51. A Peltier element 54 is formed on the optical waveguide 4 via a flattening film 53 made of SiO _2, and a current source 5 for supplying a current I to the Peltier element 54.
Since the control signal Sc is supplied to 5 to control the temperature of a part of the optical waveguide 4, the phase difference between the TE mode and the TM mode changes.

Therefore, based on the control signal Sc supplied from the feedback circuit 56, the TE mode and T
Since the phase difference of the M mode can be controlled, the phase difference can be adjusted to an integral multiple of π. As a result, it is possible to maximize the relative value of the detection signal output from each of the photodetection elements 9a and 9b, and prevent deterioration of the reproduction signal due to elliptically polarized light.

The width of temperature change by the Peltier element 54 can be changed by appropriately selecting the waveguide length of the optical waveguide 4 and the length of the Peltier element 54 in the longitudinal direction. In this case, coarse adjustment is performed by changing the waveguide length of the optical waveguide 4, and fine adjustment is performed by changing the length of the Peltier element 54 in the longitudinal direction. From this, when the waveguide length of the optical waveguide 4 is changed, it is not necessary to fabricate the optical waveguide 4 with wavelength order accuracy, which is practical.

Next, a magneto-optical reproducing pickup according to the third embodiment will be described with reference to FIGS. 11 to 14. In addition, the same code | symbol is described about the thing corresponding to FIG. 1, and the overlapping description is abbreviate | omitted.

As shown in FIGS. 11 and 12, the magneto-optical reproducing pickup according to the third embodiment has substantially the same structure as that of the magneto-optical reproducing pickup according to the first embodiment. The configuration is different.

That is, the substrate has a height of 0.5 mm and the optical refractive index n
2 = 1.45 glass substrate 61, the thin film forming the waveguide layer and the convex line 3 is a TiO ₂ thin film 62 having a photorefractive index n1 = 2.5, and the flattening film is a photorefractive index n4 = 1.46. SiO ₂
That it is the film 63, that the phase control electrode 21 shown in the first embodiment is not formed on the optical waveguide 4, and
The tunable semiconductor laser 64 is used as the laser light source.

As a method of making the wavelength of the wavelength tunable semiconductor laser 64 tunable, at present, in addition to control by temperature and drive current, an externally installed grating TE-TM is used.
A device using a mode converter or the like has been proposed. In this embodiment, the wavelength is made variable by controlling the drive current I from the drive current source 66 by the feedback circuit 65 described later.

Here, when the waveguide length is set to 2 mm, the change in the relative value of the detection signal output from each of the photodetection elements 9a and 9b when the wavelength λ of the wavelength tunable semiconductor laser 64 is changed will be examined. Then, as shown in FIG. 13, a wavelength change of 5 nm is required to change the phase difference by π, and further, an accuracy control of 1 nm or less is required to maintain the relative value above 90% of the maximum value. Become.

These conditions can be realized by the wavelength tunable technique by the feedback circuit 65 described later, and the above conditions can be changed depending on the waveguide length.

Here, the structure of the feedback circuit 65 will be described with reference to FIG. The same reference numerals are given to those corresponding to FIG. The feedback circuit 65 is inserted and connected between the differential amplifier 10 and the drive current source 66 for supplying the drive current I to the variable wavelength semiconductor laser 64, and the relative value from the drive current source 66 is maximized. Error signal S indicating a deviation from a large current value I
This is a circuit for phase compensation using e, and its basic configuration is almost the same as that of the feedback circuit according to the first embodiment.

That is, the output from the differential amplifier 10 is synchronously detected at a frequency fm which is sufficiently higher than the frequency fc of the carrier signal read from the magneto-optical recording medium, an error signal Se is taken out, and this error signal Se is outputted as a drive current. Feedback to the source 66.

That is, the oscillator 31 supplies the drive current source 66 with the modulation signal of the frequency fm so that the output of the differential amplifier 10 is modulated with the frequency fm. Then, the output of the differential amplifier 10 is passed through the BPF 33 to remove the harmonic component of the frequency fm, and then the multiplier 34 multiplies the modulated signal from the oscillator 31, and the error signal Se is obtained through the second LPF 35.

This error signal Se is added to the modulation signal from the oscillator 31 by the adder 36 in the subsequent stage and supplied to the drive current source 66 as the control signal Sc. On the other hand, the differential amplifier 1
The first LPF 32 removes the modulated signal component of the frequency fm from the output from 0, and outputs it as a reproduction signal.

As described above, in the magneto-optical reproducing pickup according to the third embodiment, the optical waveguide formed by forming the TiO ₂ thin film 62 having a higher optical refractive index than the glass substrate 61 on the glass substrate 61. A wavelength tunable semiconductor laser 64 is used as a laser light source for
Since the control signal Sc is supplied to the drive current source 66 for supplying the drive current I to 4 to variably control the wavelength of the laser light emitted from the wavelength tunable semiconductor laser 64, the TE mode and the TM mode are provided. The phase difference between them will change.

Therefore, based on the control signal Sc supplied from the feedback circuit 65, the TE mode and T
Since the phase difference of the M mode can be controlled, the phase difference can be adjusted to an integral multiple of π. As a result, it is possible to maximize the relative value of the detection signal output from each of the photodetection elements 9a and 9b, and prevent deterioration of the reproduction signal due to elliptically polarized light.

[0087]

As described above, according to the magneto-optical reproducing pickup of the present invention, the light component of the first mode of the light emitted from the light emitting means is guided to the recording medium side, and the recording medium is used. An optical waveguide for guiding the reflected light to the photodetector side is provided, and the optical waveguide is provided with phase compensating means for compensating for the phase difference between the light components of the first and second modes contained in the reflected light. Since it is provided, the phase difference between the two eigenmodes can be easily compensated (an integral multiple of π) even if there are variations in optical parameters due to manufacturing variations of the waveguide, temperature changes, or wavelength variations of the emitted light. Therefore, it is possible to prevent the reproduction signal from deteriorating due to the elliptically polarized light.

Further, in the invention, in the above structure, the phase compensating means is formed by forming a thin film having a higher optical refractive index than the substrate on a substrate made of an electro-optic crystal, Since the optical waveguide is constituted by the electric field applying means for applying an electric field, the phase difference between the two modes can be controlled by appropriately selecting the strength of the electric field generated by the electric field applying means. The phase difference can be adjusted to an integral multiple of π. As a result, it is possible to prevent the reproduction signal from deteriorating due to the elliptically polarized light.

Further, in the invention, in the above structure, the phase compensating means is formed by forming a thin film having a higher photorefractive index than the substrate on a substrate made of an electro-optic crystal, Since the optical waveguide is constituted by the electric field applying means for applying an electric field, the phase difference between the two modes can be controlled by appropriately selecting the strength of the electric field generated by the electric field applying means. The phase difference can be adjusted to an integral multiple of π. As a result, it is possible to prevent the reproduction signal from deteriorating due to the elliptically polarized light.

Further, according to the present invention, in the above structure, the phase compensating means is constituted by providing the temperature control element formed on the optical waveguide, so that a part of the waveguide is formed by the temperature control element. Since the temperature can be controlled, the phase difference between the above two modes can be controlled. As a result, the phase difference can be adjusted to be an integral multiple of π, and the reproduction signal can be prevented from deteriorating due to the elliptically polarized light.

Further, according to the present invention, in the above structure, the phase compensating means is provided with the wavelength control means for varying the wavelength of the light emitted from the light emitting means. The wavelength of the light emitting means can be controlled, and the phase difference between the two modes can be controlled. As a result, the phase difference can be adjusted to be an integral multiple of π, and the reproduction signal can be prevented from deteriorating due to the elliptically polarized light.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a magneto-optical reproducing pickup according to a first embodiment.

FIG. 2 is a sectional view of an essential part of the magneto-optical reproducing pickup according to the first embodiment.

FIG. 3 is a configuration diagram showing a differential light detection unit.

FIG. 4 is a characteristic diagram showing a dependency of a relative value of a photo detection signal from two photo detection elements on a change in a refractive index of a substrate (z direction).

FIG. 5 is a block diagram showing a configuration of a feedback circuit connected to the magneto-optical reproducing pickup according to the first embodiment.

FIG. 6 is a sectional view of an essential part of a magneto-optical reproducing pickup according to a modification of the first embodiment.

FIG. 7 is a configuration diagram showing a magneto-optical reproducing pickup according to a second embodiment.

FIG. 8 is a sectional view of an essential part of a magneto-optical reproducing pickup according to a second embodiment.

FIG. 9 is a perspective view of essential parts of a magneto-optical reproducing pickup according to a second embodiment.

FIG. 10 is a block diagram showing a configuration of a feedback circuit connected to the magneto-optical reproducing pickup according to the second embodiment.

FIG. 11 is a configuration diagram showing a magneto-optical reproducing pickup according to a third embodiment.

FIG. 12 is a sectional view of an essential part of a magneto-optical reproducing pickup according to a third embodiment.

FIG. 13 is a characteristic diagram showing laser light wavelength dependence in relative values of photodetection signals from two photodetection elements.

FIG. 14 is a block diagram showing a configuration of a feedback circuit connected to the magneto-optical reproducing pickup according to the third embodiment.

FIG. 15 is a configuration diagram showing a magneto-optical reproducing pickup according to a conventional example.

FIG. 16 is an explanatory diagram showing elliptically polarized light emitted from an optical waveguide.

FIG. 17 is a vector diagram showing respective polarization directions of reflected light with upward magnetization and reflected light with downward magnetization from the magneto-optical recording medium.

FIG. 18 is a vector diagram showing signal deterioration due to elliptically polarized light of two reflected lights.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Substrate (KTP) 2 Waveguide layer (TiO ₂ ) 3 Convex line 4 Optical waveguide 5 Semiconductor laser 6 Outgoing path 7 Mode filter 8 Return path 8a and 8b Branching path 9 Differential light detector 9a and 9b First and second Photodetector 10 Differential amplifier 11 Feedback circuit 12 Differential detection circuit 13a and 13b Signal detection mode filter 14 Grooves 14a and 14b Side surface 15 Flattening film (SiO ₂ ) 21 Phase control electrode 21a Positive electrode 21b Negative electrode 31 Oscillator 32 First LPF 33 BPF 34 Multiplier 35 Second LPF 36 Adder 41 Silicon Substrate 42 Oxide Film (Thermal Oxide Film: SiO ₂ ) 43 LN Film (LiNbO ₃ ) 51 Glass Substrate 52 Waveguide Layer (Ta ₂ O) ₅₎ 53 planarization film (SiO ₂₎ 54 Peltier element 55 current source 56 feedback circuit 1 glass substrate 62 waveguide layer (TiO ₂₎ 63 planarization film (SiO ₂₎ 64 variable wavelength semiconductor laser 65 feedback circuit 66 drive current source 71 and 72 first and second BPF 73 LPF

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Sasaki 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation

Claims (8)

[Claims] 1. An optical waveguide is provided, which guides the light component of the first mode of the light emitted from the light emitting means to the recording medium side, and guides the light reflected by the recording medium to the photodetector side, A magneto-optical reproducing pickup characterized in that the optical waveguide has a phase compensating means for compensating for the phase difference between the respective light components of the first mode and the second mode contained in the reflected light. 2. The first mode is a vertical polarization mode or a horizontal polarization mode, and the second mode is the first polarization mode.
2. The magneto-optical reproducing pickup according to claim 1, wherein the vertical polarization mode is a horizontal polarization mode, and the first mode is a horizontal polarization mode, the vertical polarization mode. . 3. The phase compensating means comprises an optical waveguide formed by forming a thin film having a higher optical refractive index than the substrate on a substrate made of an electro-optic crystal, and an electric field is applied to the optical waveguide. 3. The magneto-optical reproducing pickup according to claim 1 or 2, which is comprised of an electric field applying means for applying. 4. The phase compensating means, wherein the optical waveguide is formed by forming a thin film made of an electro-optic crystal on the substrate and having a higher optical refractive index than the substrate; 3. The magneto-optical reproducing pickup according to claim 1 or 2, comprising an electric field applying means for applying an electric field. 5. The magneto-optical reproducing pickup according to claim 3, wherein the direction of the electric field applied by the electric field applying means is a direction along the first or second mode. 6. The magneto-optical reproducing pickup according to claim 3, wherein the direction of the electric field applied by the electric field applying means is the film thickness direction of the optical waveguide. 7. The magneto-optical reproducing pickup according to claim 1, wherein the phase compensating means has a temperature control element formed on the optical waveguide. 8. The magneto-optical reproducing pickup according to claim 1, wherein the phase compensating means has a wavelength control means for varying the wavelength of the light emitted from the light emitting means.