JPH01286155A - Magneto-optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To simplify and miniaturize the constitution and to improve the S/N and also to increase the recording density by specifying the grating direction of diffraction gratings of two kinds of recording signal detection and tracking signal detection respectively provided on the same substrate for receiving and diffracting the reflected light from a recording surface. CONSTITUTION:The reflected light from a magneto-optical recording medium due to the irradiation of light of a light source is polarized by a magneto-optical effect according to the recording information to become recording signal detecting light through waveguide paths 8a and 8b corresponding to the two kinds of diffraction gratings 6a and 6b having their different grating directions provided on the substrate, so as to be incident upon photo detectors 11a to 11d. Other diffraction gratings having their diffracting directions different from the gratings 6a and 6b with photo detectors 7a with 10a and 7b with 10b are also provided on this substrate to receive tracking signal detecting light. By this constitution of using three different kinds of diffraction gratings in diffracting direction, the diffracting direction can easily be set up, and the intensity distribution of the emitting light from the light source can be met in the tracking direction in the small size and simple constitution, thus promoting the S/N and the recording density.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a magneto-optical information recording and reproducing device that uses a magneto-optical recording method such as a magneto-optical disk, a magneto-optical card, a magneto-optical tape, etc.・Related to a magneto-optical information recording/reproducing device that is lighter in weight, more stable, and has improved light utilization efficiency, and which can reduce the overall size of the device, shorten access time, and improve reliability.

(Prior art) Information is recorded using the magneto-optical recording method, which uses the thermal effect of laser light to write minute magnetic domains into a magnetic thin film formed on the recording surface of a magneto-optical recording medium. Magneto-optical information recording and reproducing devices are known that use magneto-optical effects such as the Kerr effect and the Faraday effect to read out and reproduce information.

Incidentally, as an optical pickup section in this magneto-optical information recording/reproducing device, a combination of a bulk type optical element (for example, a lens, a prism, an analyzer, etc.), a light source, and a photodetector has conventionally been used.

However, an optical pickup section configured using a conventional bulk type optical element has the disadvantage that the device configuration is complicated and the optical pickup section as a whole becomes large and heavy.

For this reason, in a magneto-optical information recording/reproducing device equipped with an optical pickup section constructed using bulk optical elements, the entire optical pickup section is large and heavy, making high-speed access impossible and the device configuration complicated. As a result, assembly and adjustment are time-consuming, which increases production costs. Furthermore, since it is composed of a combination of many optical components, it has insufficient mechanical stability and is susceptible to deterioration over time.

Therefore, in order to solve these problems, we have developed an integrated structure in which the magneto-optical recording signal detection optical system of the optical pickup section and the focus and tracking error detection optical system are mounted on the same substrate that forms the optical waveguide. A magneto-optical information recording and reproducing device that uses a waveguide element in the optical pickup section and can make the device smaller, lighter, and more efficient has been proposed by Manjin Mizude (for example, Japanese Patent Publication No. 61-268047,
Tokuhara No. 62-066834).

Here, FIGS. 8 and 9 show an example of an optical pickup section in a conventional magneto-optical information recording/reproducing apparatus using the above-mentioned waveguide element in the optical pickup section, and FIG. 8 is a schematic side view of the optical pickup section. The configuration diagram and FIG. 9 each show a schematic plan configuration diagram of a waveguide element used in the optical pickup section.

In FIG. 8, this optical pickup unit includes a light source 311 made of a semiconductor laser or the like, and an objective lens (concentrator) that focuses the emitted light from the light source 311 onto the information recording surface of a magneto-optical recording medium 312 such as a magneto-optical disk. The structure includes a light lens (optical lens) 315 and a waveguide element 313 that detects reflected light from the recording surface of the magneto-optical recording medium 312. In order, a waveguide element 313 and an objective lens 315 are arranged side by side on the same optical axis with a predetermined interval between them. Also,
On the back side of the magneto-optical recording medium 312 is an electromagnetic coil 312 that applies a bias magnetic field when recording or erasing information.
A is installed. Here, the waveguide element 313
As shown in FIGS. 8 and 9, a buffer layer 317 is formed on a substrate 316 made of a semiconductor, metal, insulator, etc.
and an optical waveguide layer 318 are laminated in this order, and are arranged substantially perpendicular to the optical axis of the light emitted from the light source 311.

Furthermore, an opening 316a for transmitting light is provided in the light irradiation portion of the substrate 316.

Further, on the upper surface side of the optical waveguide layer 318, there is a grating coupler 320 as a diffraction grating that couples reflected light from the magneto-optical recording medium 312 to the optical waveguide layer 318.
is loaded so as to face the objective lens 315.

The grating coupler 320 is a surface relief grating having linear gratings at approximately equal intervals, and has two grating regions 320a and 320b whose grating extending directions are perpendicular to each other. still,
With respect to these grating regions 320a and 320b, the vibration direction of the light emitted from the light source 311, that is, the direction of the polarization plane is the ninth
It is set in the direction shown in the figure.

Furthermore, on the upper surface side of the optical waveguide M318, each grating region 320a of the grating coupler 320,
A waveguide lens beam splitter 32 constituted by two waveguide lenses, each adjacent to the waveguide lens 320b.
1a and a waveguide lens 321b are loaded.

Further, in the substrate 316 of the waveguide element 313, each grating region 320a of the grating coupler 320 is disposed in contact with the end portion of the optical waveguide layer 318.

Photodetectors 322 and 32 for detecting the light diffraction-guided from 320b and collected by the waveguide lens beam splitter 321a and the waveguide lens 321b, respectively.
3 are buried. Here, the photodetector 322 is
four photodetectors 322a, 322b, 322c,
322d, as shown in Figure 9, 2
two photodetectors 322a and 322b and 322c and 322
Two sets, each with d as one set, are installed at a predetermined distance apart.

Now, in the optical pickup section having the configuration shown in FIGS. 8 and 9, the light emitted from the light source 311 is transmitted through the opening 31 formed in the substrate 316 of the waveguide element 313.
6 a and is focused on the information recording surface of the magneto-optical recording medium 312 by the objective lens 315 .

The return light (reflected light) reflected by the information recording surface of the magneto-optical recording medium 312 passes through the objective lens 315 again and enters the waveguide element 313.

The light incident on the waveguide element 313
The light is diffracted by each grating region 320a, 320b of a grating coupler 320 loaded on the leading waveguide layer 318 of the optical waveguide layer 318, and is coupled to the optical waveguide layer 318.

The guided light from one grating region 320b of the grating coupler 320 is focused onto the photodetector 323 by the waveguide lens 321b, and the waveguide light from the other grating region 320b
The guided light from a is passed through the waveguide lens beam splinter 321
The light is divided into two parts by a, and the light is focused at the center of each set of photodetectors 322a and 322b and 322c and 322d of the photodetector 322.

Here, each photodetector 322a, 32 of the photodetector 322
2b.

Each output from 322c, 322d at bj C#
d, and the output from the photodetector 323 is e.

The recording signal ΔS recorded on the magneto-optical recording medium 312 is as follows.

Δ5=e−(a+b+c+d), and the focusing signal ΔF is detected by ΔF=(
a+d)-(b+c), and the tracking signal ΔT is detected by ΔT
=(a+b)-(c+d) Detected by:

By the way, in the optical pickup section having the configuration shown in FIGS. 8 and 9, the recording track direction on the magneto-optical recording medium 312 must be set in the direction C in FIG. The direction of the plane of polarization must be set in the direction C in FIG. 9, as described above. Therefore, in this case, in the track direction shown in FIG.
direction) and the direction of the polarization plane (the ninth direction) are different directions.

However, when a semiconductor laser or the like is used as the light source 311, the intensity distribution of the light from the light source 311 is not a perfect circle but an ellipse that is long in the direction of the polarization plane (9th diagram direction). If the wavefront directions do not match, the light intensity distribution of the spot light focused on the track will be tilted at an angle with respect to the track, which will cause pit distortion during recording and playback. This may cause problems in formation or reading.

Therefore, in the optical pickup section having the configuration shown in FIGS. 8 and 9, the light source 311 is used.

Either a light source with a perfect circular light intensity distribution must be used, or only the central part of the light emitted from the light source 311 must be used, which may limit the number of usable light sources or reduce light utilization efficiency. A problem occurs.

In addition, in the optical pickup section having the configuration shown in FIGS. 8 and 9, when the light intensity distribution of the light source forms an ellipse shape with a long axis in the direction of the polarization plane as described above, a spot focused on the track Since the light intensity distribution of the light is tilted at an angle with respect to the track, there is a high possibility that the tracking signal will not be detected correctly. When the recording medium 312 is tilted, the light intensity distribution on the recording surface of the magneto-optical recording medium 312 becomes a distribution that is further expanded in the tilt direction, making it impossible to detect the center position of the optical axis, and normal Another problem is that accurate tracking control is no longer performed.

(Purpose) The present invention has been made in view of the above circumstances, and is capable of aligning the major axis direction of the light intensity distribution of the light emitted from the light source with the track direction of the magneto-optical recording medium, and improving the shape of the recording pits. The optical pickup section has an optical pickup section configured to have a shape along the track direction, which increases recording density, increases light utilization efficiency, improves the S/N ratio of read signals, and reduces tracking errors. can be prevented, and
It is an object of the present invention to provide a magneto-optical information recording and reproducing device that can reduce the size of the entire device, shorten access time, and improve reliability.

(Structure) In order to achieve the above object, in the present invention, in a magneto-optical information recording and reproducing apparatus that uses a magneto-optical recording method, an optical pickup unit includes a light source and a light source that outputs light from the light source to record information on a magneto-optical recording medium. The system comprises an optical system that focuses light on a surface, a diffraction grating that diffracts reflected light from the information recording surface of the magneto-optical recording medium, and a photodetector that detects diffracted light from the diffraction grating. The grating and the photodetector are mounted on the same substrate on which an optical waveguide is formed, and the diffraction grating has a separate configuration for recording signal detection and tracking signal detection, and the diffraction grating for recording signal detection is It has two types of diffraction gratings with different grating directions.

The diffraction grating for tracking signal detection has a grating direction different from each grating direction of the two types of diffraction gratings for detecting recording signals, and the track direction of the information recording surface of the magneto-optical recording medium and the direction of the polarization plane of the light emitted from the light source are substantially the same.

In the magneto-optical information recording and reproducing device having the above configuration,
The diffraction grating of the waveguide element used in the optical pickup section is configured to be separated for recording signal detection and tracking signal detection, and the recording signal detection diffraction grating includes two types of diffraction gratings with different grating directions. The diffraction grating for detecting the tracking signal has two diffraction gratings for detecting the recording signal.
Since the grating direction is different from each grating direction of the seed diffraction grating, the direction of the polarization plane of the light emitted from the light source is highly arbitrary, and the track direction of the information recording surface of the magneto-optical recording medium and the direction from the light source are increased. The direction of the polarization plane of the emitted light can be made almost the same, and the long axis direction of the light intensity distribution of the spot light focused on the recording surface can be made to follow the track direction. Become.

Hereinafter, the present invention will be explained in detail based on illustrated embodiments.

FIG. 1 is a schematic side configuration diagram of an optical pickup section of a magneto-optical information recording/reproducing apparatus showing an embodiment of the present invention, and FIG. 2 is a schematic plan configuration diagram of a waveguide element used in the optical pickup section. Show each.

In FIG. 1, this optical pickup unit includes a light source 1 made of a semiconductor laser or the like, and a condenser lens (1) that focuses the emitted light from the light source 1 onto the information recording surface of a magneto-optical recording medium 4 such as a magneto-optical disk. It consists of a condenser lens) 3 and a waveguide element 2 that detects reflected light from the recording surface of the magneto-optical recording medium 4, and between the light source 1 and the magneto-optical recording medium 4,
Starting from the light source 1, a waveguide element 2 and a condensing lens 3 are arranged side by side on the same optical axis with a predetermined interval between each other.

Furthermore, an electromagnetic coil 14 is installed on the back side of the magneto-optical recording medium 4 for applying a bias magnetic field when recording or erasing information.

In the optical pickup having the above configuration, the light emitted from the light source 1 is transmitted through the light transmission section of the waveguide element 2, which will be described later, and is focused onto the information recording surface of the magneto-optical recording medium 4 by the condenser lens 3. be done. Then, the returned light that is reflected from the recording surface of the magneto-optical recording medium 4 and has its plane of polarization rotated by a small angle due to the magneto-optic effect is again focused through the condenser lens 3 and enters the waveguide element 2 .

Here, as shown in FIGS. 1 and 2, the waveguide element 2 is formed by sequentially forming a buffer layer 15 and an optical waveguide layer 5 on an opaque substrate 10, so that light emitted from It is arranged so as to be substantially perpendicular to the optical axis of the emitted light.

Furthermore, the transparent substrate 10 is provided with an opening 13 as the aforementioned light transmitting section.

On the upper surface side of the optical waveguide layer 5 of the waveguide element 2, there are grating couplers 6a, 6b which are divided into a plurality of parts and are formed as a diffraction grating for coupling the reflected light from the magneto-optical recording medium 4 to the optical waveguide layer 5. 7a and 7b are loaded so as to face the condensing lens 3, and on the optical waveguide layer 5 are guided light beams that have been diffraction-guided by grating couplers indicated by reference numerals 6a and 6b in the figure, respectively. two waveguide prism lenses 8a that refract and condense the
8b is loaded.

Further, reference numeral 9 in FIGS. 1 and 2 indicates a light-shielding groove formed in the waveguide layer 5, and the light-shielding groove 9 is.

The guided light from grating couplers 6a and 6b is
It is provided so as not to be incident on the grating coupler indicated by reference numeral 7a.

Further, in the opaque substrate 10, a pair of photodetectors 11a and llb are provided for detecting the light diffracted and guided from the grating couplers 6a and 6b and focused by the waveguide prism lenses 8a and 8b. Two sets of photodetectors 11 using a lie and a lid as a set are arranged, and on the sides of the grating couplers 7a, 7b in the opaque substrate 10, there is a photodetector 11 from the grating couplers 7a, 7b. Photodetectors 10a and 10b are respectively provided for detecting the guided light.

Therefore, in the optical pickup section using the waveguide element 2 having the above configuration, the light is reflected from the information recording surface of the magneto-optical recording medium 4, passes through the condensing lens 3, and is directed in two directions by the grating couplers 6a and 6b, respectively. The two waveguide lights that have been diffracted and coupled and guided to the optical waveguide layer 5 are refracted and focused by the waveguide prism lenses 8a and 8b, respectively, and are transmitted to the photodetectors 11a, llb, and 11 of each set of the photodetector 11, respectively.
The light is focused on the lc and lid. Incidentally, the focusing position of the light focused on the photodetectors 11a, llb, lie and lid of each set of the photodetector 11 is the same as that of the photodetector 11a, llb, llc of each set when the optical pickup is focused. Each photodetector is arranged so that the light is focused at a midpoint between 11d and 11d.
At the time of focusing, the photodetectors 11a and 11b, and ll
The outputs of c and lid have the same size.

Further, the return light incident on the grating couplers 7a, 7b is diffraction-coupled to the optical waveguide layer 5 by the grating couplers 7a, 7b, guided through the optical waveguide N5, and incident on the photodetectors 10a, 10b, so that the amount of incident light increases. Detected.

In addition, in FIG. 1 and FIG. 2, symbols 12a, 12b, 1
2c.

12d, 12e, 12f are the respective photodetectors 11a, l
lb, llc, lid.

These are extraction electrodes for extracting the outputs of 10a and 10b, and each electrode is connected to a detection circuit (not shown).

Next, the structure and function of each component of the optical pickup section and waveguide element 2 shown in FIGS. 1 and 2 will be explained in more detail.

The light source 1 used in the optical pickup section is preferably one with good coherence and linear polarization, such as a semiconductor laser, but various other laser light sources such as gas lasers, solid-state lasers, and dye lasers may also be used. Can be used. Further, the polarization plane direction of the light emitted from the light source 1 is set to the direction A in FIGS. 1 and 2 (the direction perpendicular to the plane of the paper in FIG. 1).

Further, the overall arrangement of the optical pickup section is determined so that the track direction of the magneto-optical recording medium 4 is A' (force direction perpendicular to the plane of the paper in FIG. 1).

Note that a collimating lens may be disposed between the light source 1 and the waveguide element 2 to make the light beam directed toward the condenser lens 3 a parallel light beam, and the optical system of the optical pickup may be an infinite system (parallel light beam system).

The condensing lens 3 of the optical pickup section is a condensing lens such as a normal convex lens in the illustrated example, but there are other condensing lenses.
Optical systems consisting of Fresnel lenses, Fresnel zone plates, aspheric lenses, distributed index lenses, spherical lenses, other lenses, and combinations thereof can be used.

Next, as the constituent material of the opaque substrate 10 of the waveguide element 2, semiconductors, metals, opaque insulators, etc. can be used, but in this embodiment, a semiconductor substrate of Si, GaAs, etc. is used. When a semiconductor substrate is used as the opaque substrate 10 in this way, a photodetector such as a photodiode can be directly formed in the substrate by means such as impurity diffusion or ion implantation. The advantage is that other electronic circuits can be formed in the same way.

Furthermore, if the substrate used is a substrate made of another material, an α-3L photodiode, a thin film transistor, or the like can be formed on the leading waveguide layer S.

Next, the buffer N1 is laminated on the opaque substrate 10.
5. The optical waveguide layer 5 is made of glass using a method such as a vacuum deposition method, a sputtering method, a CVD method, a crystal growth method, or a thermal oxidation method. Si, N,, Nb, O,, Ta,
O.

A dielectric layer such as is formed. In addition, it can also be formed by coating an organic material such as a polymer on a substrate or by laminating it by other methods, and also by impurity diffusion method,
It can also be formed by a method such as an ion exchange method or an ion implantation method.

Here, the buffer layer 15 is for reducing the loss of light passing through the leading waveguide layer 5, and for this reason, the buffer layer 15
The refractive index of the optical waveguide layer 5 must be lower than that of the optical waveguide layer 5. Note that if light loss is not considered, the buffer layer 15 may not be provided.

Next, the opaque substrate 10 is provided with an opening 13 through which light from the light source 1 passes. Methods for forming this opening include dry etching, wet etching, cutting, polishing, and ion milling. In addition, it is also possible to make a part of the opaque substrate 10 transparent by thermal oxidation, laser annealing, polishing, etc., in place of the opening. They can also be used together.

Next, grating couplers 6a and 6b loaded on the optical waveguide layer 5 serve as photodetectors 11a and llb for detecting recording signals and focusing error signals.

11c, is provided to guide the light through the lid by diffraction, and as shown in FIG. 2, the grating coupler 6
The lattice directions of the grating coupler a and the grating coupler 6b are different from each other, for example, directions substantially perpendicular to each other. Incidentally, the angles formed by the mutual lattice directions do not necessarily have to be right angles, and can be arbitrarily set to some extent.

In addition, in FIG. 2, grating coupler 6a,
6b is arranged as shown, even if the intensity distribution of the return light from the magneto-optical recording medium 4 changes during tracking of the optical pickup, detection of the magneto-optical recording signal is not affected. .

In other words, the light intensity distribution is perpendicular to direction A in Figure 2 (
Grating couplers 6a, 6 in the plan view of FIG.
Since the distribution is symmetrical with respect to the symmetry axis direction of b), the arrangement of the grating couplers 6a and 6b as shown in the second @ is not easily affected by tracking.

Further, the grating couplers 7a and 7b are provided to diffraction-guide the light to the photodetectors 10a and 10b for detecting tracking error signals, and the optical system of the optical pickup unit is connected to the magneto-optical recording medium. Even if the intensity distribution of the returned light within the recording surface changes due to an inclination with respect to 4, it is arranged at a position where there is relatively little influence.

Here, although the grating couplers 6a, 6b and the grating couplers 7a, 7b are linear gratings at equal intervals in the illustrated embodiment, they do not necessarily have to be at equal intervals, and may be formed by chirp-to-gelating or other non-uniform gratings. It is also applicable to interval gratings. Furthermore, it is also possible to apply a grating in which the grating itself has a light condensing function.

Further, each grating is usually of a one-surface relief type, but the cross-sectional shape can be arbitrary, and gratings such as a refractive index distribution modulation type and a one-volume phase type can also be applied. Note that these gratings can be formed by a method such as a diffusion method or an embedding method.

Incidentally, in order to prevent the diffracted light from the grating couplers 6a, 6b from entering the grating couplers 7a, 7b, a light shielding groove 9 is provided in the optical waveguide layer 5, or a light shielding groove 9 is provided in the grating coupler 6a, 6b.
It is necessary to set the shape of 6b.

The light-shielding groove 9 can be formed by removing a predetermined position of the optical waveguide layer 5 by etching or the like to form a groove, and in order to improve the light-shielding property,
A metal or the like may be vapor-deposited into the groove 9, or an opaque substance may be filled in the groove.

Note that even if the light shielding groove 9 is not provided, the basic operation of the optical pickup is not affected much, so the light shielding groove 9 does not need to be provided, except that the S/N ratio of the detection signal is slightly lowered.

Next, although the waveguide prism lenses 8a and 8b are of the loaded mode index lens type in the illustrated embodiment, they may also be of the refractive index gradient type lens, or may have an aspherical shape. Although it is a lens type, it is not limited to an aspherical lens type, and other shapes may be used, such as Fresnel lens type, geodemic lens type, Luneburg lens type, grating lens type, etc. can.

The waveguide prism lenses 8a and 8b may be formed by forming a film using a vacuum evaporation method, a sputtering method, a CVD method, a coating method, or the like, and then selectively etching it, or by forming it by a lift-off method or the like. be done.

In addition to loading the waveguide prism lenses 8a and 8b into the optical waveguide layer 5, the waveguide prism lenses 8a and 8b can be directly loaded into the optical waveguide layer 5 by a method such as an ion exchange method, an impurity diffusion method, an ion implantation method, or an embedding method. It can also be formed. Note that various materials such as dielectrics, metals, semiconductors, organic substances, etc. can be used as materials for forming the waveguide prism lenses 8a and 8b.

The configuration and structure of the optical pickup section of the magneto-optical information recording medium according to the present invention in the embodiment shown in FIGS. 1 and 2 has been described above, but next.

A method of detecting recording signals and various error signals in the optical pickup section shown in FIGS. 1 and 2 will be described.

First, the polarization plane direction of the light emitted from the light source 1 is set in the direction A in FIG.

Return light emitted from the light source 1, focused by the condensing lens 3 onto the information recording surface of the magneto-optical recording medium 4, and reflected from the information recording surface of the magneto-optical recording medium 4 is used to record information on the magneto-optical recording medium 4. Due to the magneto-optical effect (magnetic Kerr effect or Faraday effect) caused by the magnetic field of information recording magnetization at the reflection position of the surface, the plane of polarization is rotated by a minute angle (±θk).

Here, the information when the above minute angle is +θ is "1", -
Let rQJ be the information in the case of θ.

In addition, each photodetector 11a, llb, of the photodetector 11,
llc.

Let the outputs of the lid be a, b, Q, and d, respectively, and the photodetector 1
When the outputs of 0a and 10b are respectively e and f, the recording signal ΔS is defined as Δ5=(a+b)−(c+d).

Here, a detection circuit (not shown) is provided so that the recording signal ΔS when the optical pickup is focused becomes ΔS=0 when the rotation angle θk of the polarization plane of the return light from the magneto-optical recording medium 4 is 0. Adjust the circuit constants.

Now, if the recorded information at the reading position of the magneto-optical recording medium 4 is "1", the polarization plane of the returned light is rotated by a minute angle +θ in FIG. 2. Therefore, among the grating couplers 6a and 6b, the diffraction efficiency toward the leading waveguide layer 5 on the grating coupler 6a side is higher than that on the grating coupler 6b side, and each photodetector 11a, llb,
The relationship between the outputs of llc and lid is a + b > c
+d, and the recording signal ΔS becomes ΔS>0.

Furthermore, when the recorded information is "1", the polarization plane of the returned light is rotated by a small angle -θ in FIG. The diffraction efficiency to the grating coupler 6a side is higher than that of each photodetector 11a,
The relationship among the outputs of llb, lie, and lid is a + b < c + d, and the recording signal ΔS is ΔS<0.

Therefore, by determining the positive or negative sign of the recording signal ΔS, it is possible to detect the binarized recording information.

Next, in the detection of the focusing error signal, each of the photodetectors 11a and llb of the photodetector 11 as described above.

When the outputs of 11c and lid are respectively a, b, Q, and d, the focusing error signal ΔF is defined as ΔF=(a+d)−(b+c).

In addition, the circuit constants are adjusted so that the relationship between the outputs of the photodetectors 11a, llb, lie, and lld when the optical pickup is at the in-focus position is as follows: a=b and c=d. The focusing error signal ΔF at the position is set so that ΔF=0.

Now, in FIGS. 1 and 2, when the optical pickup approaches the magneto-optical recording medium 4 from the in-focus position, the flux of the return light from the magneto-optical recording medium 4 becomes more divergent than when it is focused. Therefore, each photodetector 11a, llb, ll
The relationship between the outputs of c and lld is as follows.

a) b and d>c Therefore, the focusing error signal ΔF is.

ΔF>0 becomes.

On the contrary, when the optical pickup moves away from the magneto-optical recording medium 4 from the in-focus position, the flux of the return light from the magneto-optical recording medium 4 becomes more focused than when it was focused.
Each photodetector 11a, llb, llc.

The relationship between the lid output is a (b and d < c Therefore, the focusing error signal ΔF is ΔF<0 becomes.

Therefore, the focusing error signal ΔF is ΔF=O
The condenser lens 3, the condenser lens 3 and the waveguide element 2, or the entire optical pickup are controlled by a focusing control actuator (not shown) so that the light source 1
Autofocusing becomes possible by moving the light emitted from the lens in the optical axis direction.

Next, in detecting the tracking error signal, the outputs of the photodetectors 10a and 10b are converted to e and f, respectively, as described above.
Then, the tracking error signal ΔT is defined as ΔT=e−f.

Here, at the time of one focus, the tracking error signal ΔT is ΔT=
If the circuit constants are set so that 0, the tracking error signal ΔT becomes ΔT>O or ΔT<0 when the focused position deviates from the track of the magneto-optical recording medium 4.

Therefore, the tracking error signal T is ΔT>O or ΔT<.

When , a tracking control actuator (not shown) moves the condenser lens 3 or the condenser lens 3 and the waveguide in a direction perpendicular to the track direction of the magneto-optical recording medium 4 so that ΔT=O. Auto-tracking becomes possible by moving the element 2 or the entire optical pickup.

The above is based on the optical pickup in the embodiment shown in FIG. 1 and FIG. The method of detecting the recording signal and each error signal has been explained, but next, the grating coupler 6a
, 6b, 7a, and 7b will be explained in more detail.

FIG. 3 shows a schematic enlarged side view of essential parts of the waveguide element 2 shown in FIG. 2, and shows a part of the grating G of the grating coupler.

Now, consider a case where this grating G is inclined at an angle θ with respect to the incident light.

Here, let the central wave number of the incident wave from the light source be k, the grating vector be K, the propagation constant of the waveguide mode of the leading waveguide layer be β, the order of the grating be N, and the refractive index of air be n. The condition for increasing the diffraction efficiency of the grating G is the following formula (1)% Formula % Therefore, in order to obtain high diffraction efficiency, the order N of the grating should be set to N=±1, and N=±1.
When it is set to 1, the amount of diffracted light that is not coupled to the waveguide is reduced, and the light utilization efficiency is increased. Note that the case where N=-1 is better.

In addition, when θ=0, the light coupled to the optical waveguide layer is coupled in both directions A and B in Fig. 3, but if θ is slightly increased, the value of the grating vector changes to A. It becomes possible to couple only in the direction and only in the B direction. In this case, the emitted light from the light source and the returned light from the magneto-optical recording medium can be combined in opposite directions,
The S/N ratio in information detection can be increased compared to the case where θ=0.

Therefore, in practice, the waveguide element 2 may be arranged at a slight inclination in a direction parallel to the plane of the paper with respect to the other light source 1 of the optical pickup and the condenser lens 3 in FIG. In this case, the grating couplers 7a and 7b for tracking signal detection connect the light to the optical waveguide Ji15 in opposite directions.

The grating pitch of each grating will be different.

Next, another embodiment of the magneto-optical information recording/reproducing apparatus according to the present invention will be described.

FIG. 4 shows another embodiment of the waveguide element 2 used in the optical pickup section of the magneto-optical information recording and reproducing apparatus according to the present invention. The grating couplers 6a and 6b for detecting recorded signals of the waveguide element shown in FIG. 2 are constructed almost in the same way as the waveguide element, but the grating couplers 6a and 6b of the waveguide element shown in FIG. hand,
Grating couplers 6a, 6 in this embodiment
The structure of the structure 2b differs in that it is constructed using a condensing grating coupler and that the waveguide prism lenses 8a and 8b are omitted.

That is, in the waveguide element shown in FIG. 4, since the grating couplers 6a and 6b for recording signal detection themselves have light focusing ability, the waveguide prism lens 8 shown in FIG.
a and 8b can be omitted.

Therefore, in the waveguide element shown in FIG. 4, the cost can be reduced compared to the waveguide element shown in FIG. 2.

Note that the other configurations are the same as those shown in FIG. 2.

Next, FIG. 5 shows yet another embodiment of the waveguide element 2 used in the optical pickup section of the magneto-optical information recording and reproducing apparatus according to the present invention, and the configuration of the waveguide element 2 in this embodiment is also shown. The structure is almost the same as the waveguide element shown in FIG. 2, but in this embodiment, waveguide concave mirrors 8c and 8d are used instead of the waveguide prism lenses 8a and 8b shown in FIG. is provided.

These waveguide concave mirrors 8c and 8d are formed by creating concave grooves in the same manner as the light shielding groove 9 of the leading waveguide submersible 5 described above, and if high reflectivity is required, A.
A metal with high reflectivity such as g, Au, A1, etc. is loaded on the groove surface.

Now, in the waveguide element shown in FIG. 5, the optical waveguide N5 is diffracted by the grating couplers 6a and 6b.
The guided light is totally reflected by the waveguide concave mirrors 8c and 8d and optically detected! E equipment 11a and Hb and 11c and l
The light is focused at the intermediate position of each ID.

Here, since the waveguide concave mirrors 8c and 8d are used instead of the waveguide prism lens, the focusing error signal ΔF has the opposite sign from that of the embodiment shown in FIG. If this is taken into consideration, detection can be performed using the same method as in the case described above, and autofocusing can also be performed in the same manner.

Note that the waveguide element having the configuration shown in FIG. 5 has the advantage that the entire element can be configured smaller than that shown in FIG. 2.

Next, another embodiment of the optical pickup section of the magneto-optical information recording/reproducing apparatus according to the present invention will be described with reference to FIG.

FIG. 6 shows a schematic side view of the configuration of the optical pickup, and shows the optical pickup section in this embodiment.

In addition to the configuration of the optical pickup section shown in FIGS. 1 and 2, a collimating lens 1 is provided between the light source 1 and the waveguide element 2.
9, dielectric medium 16, optical fiber 17, condensing lens 18
is newly inserted, and each of the above elements has an integrated structure. Furthermore, in the optical pickup section shown in FIG. 6, an example is shown in which Fresnel lenses are applied to the condensing lens 3 and the collimating lens 19.
It can be similarly applied to other types of lenses. Note that the collimating lens 15 is not necessarily required. Further, as the optical fiber 17,
A polarization-maintaining optical fiber is preferable.

In addition to the waveguide element shown in FIG. 2, waveguide elements used in the optical pickup section shown in FIG. 6 include those shown in FIG.
The waveguide element shown in FIG. 5 can also be applied in the same manner.

As mentioned above, the optical pickup section having the configuration shown in FIG. 6 has high reliability because the entire optical system is integrated.
Further, since the optical fiber 17 is used, the light source 1 can be arranged freely, so there is an advantage that the degree of freedom in the type and arrangement of the light source 1 is increased. .

Next, still another embodiment of the optical pickup unit will be described with reference to FIG. 7.

FIG. 7 shows a schematic side view of the optical pickup section,
The basic configuration of the optical pickup section in this embodiment is almost the same as the configuration of the optical pickup section shown in FIGS. 1 and 92, but in the optical pickup section with the configuration shown in FIG. As the substrate 10 of the element 2, a transparent glass, dielectric, polymer, or other transparent substrate is used.

Therefore, in the optical pickup section having the configuration shown in FIG.
ie.

The lid is loaded on the optical waveguide layer S as a detector consisting of an α-SL type photodiode or the like. Furthermore, since the substrate 1O is made of a transparent substrate, there is no need to provide an opening for transmitting the light from the light source 1.
It is similar to that shown in FIG. In addition to the planar configuration of the waveguide element shown in FIG. 2, the configurations shown in FIGS. 4 and 5 are also applicable.

As described above, in the optical pickup section having the configuration shown in FIG. 7, since the substrate 10 of the waveguide element 2 is made of a transparent substrate,
This eliminates the need for the step of providing an opening for transmitting the light from the light source 1, and has the advantage that the substrate can be easily produced and costs can be reduced.

(Effects) Various embodiments of the magneto-optical pickup section and waveguide element in the magneto-optical information recording and reproducing apparatus according to the present invention have been described above.According to the present invention, the diffraction grating (grating coupler) of the optical pickup section and a photodetector that detects the diffracted light from this diffraction grating are integrated onto the same substrate that forms the optical waveguide, making it possible to reduce the size and weight of the optical pickup section. , downsizing the entire device, shortening access time, improving reliability,
Manufacturing costs can be reduced.

Further, according to the present invention, the diffraction grating has a separate structure for detecting a magneto-optical recording signal and for detecting a tracking signal, and the diffraction grating for detecting a recording signal has two types with different grating directions. The diffraction grating for detecting the tracking signal has a different grating direction from the grating directions of the two types of diffraction gratings for detecting the recording signal, so the direction of the polarization plane of the light emitted from the light source is Setting flexibility is increased, and the track direction of the information recording surface of the magneto-optical recording medium and the polarization plane direction of the light emitted from the light source can be made to substantially match. Therefore, the light intensity distribution of the spot light focused on the recording surface (usually.

It is possible to make the long axis direction of the elliptical distribution whose long axis is in the direction of the polarization plane to be along the track direction.

Therefore, according to the present invention, since the long axis direction of the light intensity distribution of the light emitted from the light source can be aligned with the track direction of the magneto-optical recording medium, the shape of the light spot during information recording can be made longer in the track direction. It is possible to increase the recording density of information. Also, when reading, a larger signal component is obtained, so the S/N ratio is increased,
Reliability during signal reading is improved.

Further, according to the present invention, since the long axis direction of the light intensity distribution of the light emitted from the light source can be aligned with the track direction of the magneto-optical recording medium, the optical system of the optical pickup unit can be aligned with the track direction of the magneto-optical recording medium. Even when the optical axis is tilted, the influence on tracking signal detection is reduced, and a decrease in the S/N ratio can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a schematic side configuration diagram of an optical pickup section showing an embodiment of the magneto-optical information recording/reproducing apparatus according to the present invention, and FIG. 2 is a diagram showing an embodiment of a waveguide element used in the optical pickup section. 3 is a schematic plan view of the waveguide element; FIG. 3 is a schematic enlarged side view of the waveguide element used to explain the grating coupler of the same waveguide element; FIGS.
The figures are schematic plan configuration diagrams of waveguide elements showing different embodiments of the waveguide element used in the optical pickup section of the magneto-optical information recording and reproducing apparatus according to the present invention, and FIGS. 6 and 7 are according to the present invention. FIG. 8 is a schematic side view of the optical pickup section showing different embodiments of the optical pickup section of the magneto-optical information recording/reproducing device; FIG. 9 is a schematic plan view of a waveguide element, which is an example of a conventional waveguide element used in the optical pickup section shown in FIG. 8. 1... Light source, 2... Waveguide element, 3... Condensing lens (objective lens), 4... Magneto-optical recording medium,
5... Optical waveguide layer, 6a, 6b... Diffraction grating for recording signal detection, 7a, 7b... Diffraction grating for tracking signal detection, 8a, 8b... Waveguide prism lens, 8c, 8d... waveguide concave mirror, 9...
... Light shielding groove, 10 ... Substrate, 10a. 10b, lla, llb, llc, lid”
Photodetector, 13--Aperture, 14--Magneto-optical recording electromagnetic coil, 15--Buffer layer, 16--
・Dielectric medium, 17...optical fiber, 18...
Condensing lens, 19... Collimating lens. Figure 1 1m

Claims (1)

[Claims] In a magneto-optical information recording and reproducing apparatus that uses a magneto-optical recording method, an optical pickup section includes a light source, an optical system that focuses light from the light source onto an information recording surface of a magneto-optical recording medium, and a magneto-optical recording medium. It is equipped with a diffraction grating that diffracts reflected light from the information recording surface and a photodetector that detects the diffracted light from the diffraction grating, and the diffraction grating and the photodetector are formed on the same substrate on which an optical waveguide is formed. The diffraction grating has a separate configuration for recording signal detection and tracking signal detection, and the recording signal detection diffraction grating has two types of diffraction gratings with different grating directions, and The diffraction grating for tracking signal detection is characterized in that it has a grating direction different from each grating direction of the two types of diffraction gratings for detecting recorded signals, and the grating direction is different from the track direction of the information recording surface of the magneto-optical recording medium. A magneto-optical information recording/reproducing device characterized in that the polarization plane direction of the light emitted from the light source substantially coincides with that of the light emitted from the light source.