JPS63183635A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To obtain an optical pickup which is miniature and operated with high efficiency and safely, by providing an opening for allowing the light of light a source to transmit through, a diffraction grating, an optical splitter for splitting a diffracted light into plural luminous fluxes, etc. on an opaque substrate for forming an optical waveguide. CONSTITUTION:A divergent luminous flux of a P polarized light from a semicon ductor laser 11 passes through a waveguide element 13 and an opening part 16a of an opaque substrate 16 for forming a waveguide layer 18 and transmits through a grating coupler 20 on the substrate 16 without being diffracted and becomes a circularly polarized light by a 1/4 wavelength plate 14, and condensed to an optical disk 12 by an objective lens 15. A reflected light from the disk 12 goes to S polarized light by the wavelength plate 14, diffracted by the coupler 20 and excites the layer 18, and the reflected light and an incident light are separated and become plural luminous fluxes by a beam splitter 21 on a sub strate 22, and made incident on photodetectors 22a-22d on the substrate 22. By a miniature constitution in which each necessary part has been installed onto the substrate, an access can be shortened and an operation of an optical pickup can be executed with high efficiency and stability.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to an optical information recording and reproducing device that detects or records information by irradiating light onto the recorded information surface of a recording medium, and particularly relates to an optical information recording and reproducing device that is small, efficient, and capable of detecting or recording information. The present invention relates to an optical information recording/reproducing device that can operate stably.

(Prior Art) FIG. 22 shows an example of an optical pickup device in a general optical information recording/reproducing device.

In the figure, a diverging beam emitted from a semiconductor laser 1 is separated by a diffraction grating 2 into, for example, three beams. After these light beams pass through the polarizing beam splitter 3,
It passes through the 1/4 wavelength plate 4 and becomes circularly polarized light, which is then passed through the objective lens 5.
The light is focused on the information recording surface of the optical disc 6 as a recording medium.

The light beam reflected from the information recording surface of the optical disk 6 passes through the objective lens 5 and then roughly passes through the 1/4 wavelength plate 4 to become linearly polarized light, and enters the polarizing beam splitter 3 again. Here, the polarizing beam splitter 3 functions as a light splitter, reflects the reflected light from the information recording surface, separates it from the incident light by 11i+i, and guides it through the cylindrical lens 7 to the photodetector 8.

In addition to being processed as an information reading signal, the signal detected by the photodetector 8 is used as an autofocusing signal that always focuses the light from the light source on the information recording surface, or as an autofocusing signal that always focuses the light from the light source on the information recording surface. It is processed as a tracking signal that adjusts the position of the optical pickup so that it is focused on the track row.

However, such conventional optical pickup devices use many bulk optical components such as the cubic polarizing beam splitter 3, making the entire device large and heavy. This results in long access times, high production costs, and poor mechanical stability.

As a proposal to solve such problems, for example, as described in Japanese Patent Laid-Open No. 61-92439, a light source is provided on the substrate and the light from the light source is focused onto the recording medium. A monolithic structure that includes a lattice-shaped collimating element and a crating-type condensing element, a lattice-shaped beam splitting element that separates the reflected light beam from the recording medium, and a beam separating and condensing element that focuses the separated light onto a photodetector. As described in Japanese Patent Application Laid-Open No. 61-178740, a light splitter that separates the reflected light from the recording medium from the incident light is arranged perpendicular to the optical axis. There are some that are formed from a diffraction grating.

However, in the former case, since the semiconductor laser that is the light source is directly coupled to the leading waveguide, it is not possible to increase the coupling efficiency to the leading waveguide (around 3%), and the light utilization rate is significantly reduced. . Therefore, light with sufficient power does not reach the information recording surface, making it impossible to perform recording and reproduction with a high S/N ratio. In particular, this method can hardly be used in information recording because it requires a large recording power. In addition, if the oscillation wavelength of the semiconductor laser that is the light source fluctuates due to the so-called mode pop phenomenon caused by temperature characteristics, it will be directly affected, and the convergent light on the information recording surface will deviate from the information track array. However, there is a problem in that it is not possible to accurately record and reproduce information.

Furthermore, even in the latter case, since the reflected light from the recording information surface is diffracted toward the photodetector by the diffraction grating, if the oscillation wavelength from the semiconductor laser that is the light source fluctuates due to the mode pop phenomenon, the light will be diffracted accordingly. As a result, the position of the convergent light on the photodetector changes, making it difficult to stably record and reproduce information.

(Purpose) Therefore, an object of the present invention is to provide an optical information recording/reproducing device which is small in size, operates efficiently and stably, and is equipped with a optical pickup.

(Structure) In order to achieve the above object, an optical information recording/reproducing apparatus according to the present invention includes a converging optical system that converges light from a light source onto an information recording surface of a recording medium, and a converging optical system that converges light from a light source onto an information recording surface of a recording medium. a diffraction grating that diffracts the reflected light so as to separate it from the incident light; a light splitter that splits the diffracted light from the diffraction grating into a plurality of light beams; and detecting the output of each light beam emitted from the light splitter. The diffraction grating, the optical splitter, and the optical detection element are installed on the same substrate that forms the optical waveguide, and the substrate includes:
It is characterized by being made of an opaque material and having an opening that equalizes the light from the light source.

In an optical information recording/reproducing device having such a configuration, the diffracted light from the diffraction grating that diffracts the reflected light from the information recording surface, and each luminous flux output from the splitting diffraction grating that splits this diffracted light into multiple luminous fluxes. is designed to propagate through the substrate forming the leading wavepath.

Embodiments of the present invention will be described in detail below with reference to the drawings.

In FIGS. 1 and 2, between the semiconductor laser 11 as a light source and the optical disk 12 as a recording medium,
In order from the semiconductor laser 11 side, the waveguide element 13.1/4
A wavelength plate 14 and an objective lens 15 are arranged in parallel with each other at a predetermined interval.

The waveguide element 13 includes a buffer layer 17 and a waveguide layer 18 on an opaque substrate 16 such as a semiconductor, metal, or insulator.
are sequentially stacked by vacuum evaporation, sputtering, CVD, etc., and are arranged substantially perpendicular to the optical axis.

This waveguide element 13 is configured to constitute a single mode optical waveguide as an optical waveguide layer. That is, only the fundamental mode is allowed to propagate in the optical waveguide, and is not affected at all by wavelength changes of about several nanometers.

The buffer layer 17 and the waveguide layer 18 may be made of glass, S:02, Si3N4, Nb2O5, Ta205, or the like. Transparent materials such as electric bodies and organic materials such as polymers are used. The buffer layer 17
is provided to reduce optical waveguide loss in the waveguide layer 18, and its refractive index is equal to that of the waveguide layer 18.
It needs to be smaller than that on the side. However, if waveguide loss is not a problem, it is not necessary to provide the above-mentioned barrier layer 17.

Roughly speaking, an opening 16a for transmitting light is formed in the light irradiation portion of the opaque substrate 16. Possible means for forming this opening 16a include dry or wet etching, polishing, ion milling, and the like.

A grating coupler 20 serving as a diffraction grating is mounted on the upper surface side of the waveguide layer 18 so as to face the 174-wavelength plate 14 . This grating coupler 20 is a surface relief type grating having linear gratings at equal intervals, and has an extremely low diffraction efficiency for the light emitted from the semiconductor laser 11, that is, the P-polarized light vibrating in the direction of FIG. It has extremely high diffraction efficiency for S-polarized light that is reflected light from the information recording surface.

Therefore, the emitted light from the semiconductor laser 11 passes through the grating coupler 20, and the reflected light from the information recording surface is diffracted and coupled into the waveguide by the grating coupler 20.

Further, on the upper surface side of the waveguide layer 18, adjacent to the grating coupler 20, two grating beam splitters 21 each having equally spaced linear gratings as a split diffraction grating are mounted. Each grating beam splitter 21 has a grating extending direction set in a different direction, and has a function of splitting the diffracted light from the grating coupler 20 into two light beams. Each of the divided light beams is then directed toward a photodetector, which will be described later. In this case, the light in the waveguide is condensed into a beam by the objective lens 15, so the point of convergence on the photodetector is the emission point of the semiconductor laser 11 (indicated by the output point X in FIG. 1) and the optical This will occur at a position that is equivalent to the actual position. If the grating beam splitter 21 has a convergence function, the distance to the convergence point can be further reduced.

Additionally, in the opaque substrate 16, the end portion (
The photodetector 22 is placed in contact with the fabric edge (in the drawing).
One is buried. As particularly shown in FIG. 3, each of these photodetectors 22 is made up of two sets separated by a predetermined distance, and each set includes two detection bodies 22a, 22b and 2.
2c and 22d are arranged in parallel. When each of the detection bodies 22a, 22b, 22c, and 22d is made of a semiconductor such as 3i, a photodiode formed by diffusion in the substrate can be used. Furthermore, if the opaque substrate 16 is made of an insulator or metal, a photodiode layer laminated on the upper surface side of the waveguide 1118 can be used. By embedding the photodetector 22 in the substrate in this way, the photodetector 22 can be formed monolithically, which is convenient, and there is no need to polish the end face when installing the photodetector 22, as in the conventional case. . The optical signal detected by this photodetector 22 is
The signals are processed as recording/reading signals, autofocus signals, and tracking signals.

In such an embodiment, the diverging light beam emitted from the semiconductor laser 11 passes through the aperture 16a of the waveguide element 13, enters the grating coupler 20, and is diffracted by the grating coupler 20 into a P polarization number. After that, the light passes through the quarter-wave plate 14 to become circularly polarized light, and is focused by the objective lens 15 onto the information recording surface of the optical disc 12 as a recording medium. As described above, by allowing the emitted light from the semiconductor laser 11 to pass through the opening 16a of the opaque substrate 16, the substrate is no longer limited to a transparent body, and weight reduction, cost reduction, and improvement in processability can be achieved. This makes it possible to select a substrate with good durability and integration.

The light beam reflected from the information recording surface of the optical disk 12 passes through the objective lens 15 to become a condensed light beam, and further passes through the 174-wavelength plate 14 to become S-polarized light and enters the grating coupler 20 again.

At this time, the diffraction efficiency of the grating coupler 20 is extremely high, and as shown by arrow B in FIG.
8 to excite the guided light to separate the reflected light from the information recording surface from the incident light. In this case, since a single mode optical waveguide is configured, only the fundamental mode is propagated in the optical waveguide, and the light diffracted by the grating coupler 20 is propagated in a direction almost parallel to the grating surface. It happens. This guided light is separated into two light beams by a grating beam splitter 21, and each light beam is directed toward a photodetector 22. When the optical disc 12 is at a predetermined reference position, one of the light beams is directed toward the center of the detection bodies 22a and 22b, and the other light beam is directed toward the center of the detection bodies 22c and 22d. There is.

When the respective output signals from the detection bodies 22a, 22b, 22c, and 22d are a, b, c, and d, the force force and the error signal Δf are calculated as follows: Δf−(a+d)−(b+c). That is, when the optical disc 12 is at a predetermined reference position, a-b, c-d, and Δf=Q
becomes. When the optical disk 12 approaches the pickup side, the light beam shifts as shown in FIG. 3(a), and a>b
, c<d, and Δf>Q is calculated. When the optical disk 12 moves away from the pickup side, the light beam deviates as shown in FIG. 3(b), so that a<b, c>d, and Δf<Q is calculated. Therefore, the focus error direction is known depending on the sign of Δf, and always Δf
The objective lens 15 is moved in the optical axis direction by an actuator (not shown) so that the autofocus 117 is controlled.

On the other hand, the tracking error signal Δt is Δt−(a+b
)−(c+d). In other words, if the spot on the information recording surface is on an information track such as a bit string, Δ becomes even more,
If it deviates from the information track, Δt>O or Δt<Q
becomes. Therefore, the direction of the tracking error is determined by the sign of Δt, and the objective lens 15 is always moved in the direction perpendicular to the track by an actuator (not shown) so that the angle becomes Δ1-0, thereby performing auto-tracking control.

Also, a read signal S of information recorded on the optical disc 12
is determined by the sum of all outputs, that is, S-a+b+c+d.

The embodiment shown in FIG. 4 uses a micro Fresnel lens 35 as an objective lens, and a waveguide element 33.
A micro Fresnel lens 35 and a quarter wavelength plate 34 are superimposed and bonded to a grating coupler 30 mounted above. In this way, the overall size can be further reduced.

Note that, as shown in FIG. 5, if the waveguide element 43 is made to enter at a predetermined angle θ with respect to the optical axis, all of the guided light can be made to proceed in the direction of arrow B.
Guided light attempting to travel in the opposite direction can be completely eliminated. In this case, the lattice constant may be determined so as to satisfy the following equation.

nksinθ+qK=Nk Here, k-2π/λ λ; optical wavelength '-2π/d d: lattice constant n; air refractive index N; waveguide equivalent refractive index q; If the above equation is satisfied, Coupling efficiency can be improved, and there is no need for light to travel in the opposite direction.

The embodiment shown in FIG. 6 uses ill! instead of the grating splitter 21 in the above embodiment. A prism 51 is mounted thereon. The thin film prism 51 is, for example,
It is formed by depositing a material such as iO2 having a higher refractive index than the waveguide layer 18.

Even in this case, the same functions and effects as in the above embodiment can be obtained due to the refraction effect of the thin film prism 51.

Furthermore, the embodiment shown in FIG. 7 uses a micro Fresnel lens 65 as an objective lens, and the waveguide element 13 is used in the opposite manner to the above embodiment, and the back opening 16a of the waveguide element 13 is The 1/4 wavelength plate 14 and the micro Fresnel lens 65 are bonded together in a superimposed manner. In this way, the overall size can be further reduced.

Further, the embodiment shown in FIG. 8 achieves miniaturization by integrally forming a micro Fresnel lens 75 on the back side of the waveguide element 13.

In the embodiment shown in FIG. 9, a mirror 8o is arranged between the waveguide element 13 and the semiconductor laser 11 to bend the optical axis, thereby making it possible to reduce the size in the vertical direction.

In the embodiment shown in FIG. 10, a collimating lens 9o formed of a Fresnel lens is disposed between the waveguide element 13 and the semiconductor laser 11, thereby making it possible to converge and read a finer spot.

The embodiment shown in FIG. 6 can be applied when the reflected return light becomes a convergent beam, and when the convergence of the reflected return light is weak or the reflected return light becomes a parallel beam. Sometimes it is necessary to provide a condensing means for guided light. The embodiment shown in FIG. 11 is a thin film waveguide lens 10.
This thin film waveguide lens 101 has a planar entrance surface and a spherical or aspherically curved exit surface.

In this way, the luminous flux can be divided and condensed at the same time.

Further, as shown in FIG. 12, a thin film waveguide lens 111
It is also possible to form curves on both sides of the spherical or aspherical surfaces with different curvatures.

This has the advantage of facilitating lens power adjustment and aberration correction, especially when the refractive index difference between the 11I waveguide lens and the waveguide section is limited. It is valid.

In the embodiment shown in FIG. 13, a thin film waveguide Fresnel lens 121 is used instead of the thin film waveguide lens. Even in this case, the same operation and effect as in the above embodiment can be obtained. Note that such a thin film waveguide lens or thin film waveguide Fresnel lens may be of a refractive index distribution type in addition to a thickness distribution type. In this case, it can be formed by diffusing a material having a different refractive index from that of the waveguide onto the waveguide.

Furthermore, as in the embodiment shown in FIG. 14, even if a grating coupler 130 formed of a curved grating is used, the convergence of the light beam can be strengthened.

In the embodiment shown in FIG.
As the grating 40, an asymmetric structure having a serrated blazed grating cross section is adopted. In this way, the reflected return light coming from the direction can be made to travel in the direction of arrow B in the waveguide layer 18, and the light detection efficiency can be improved.

In each of the embodiments described above, a surface relief type grating is used as the grating coupler, but the grating coupler is not limited to this, and various general gratings such as a volume phase type and an amplitude type can be used. can do.

FIG. 16 and FIG. 17 show an embodiment in which the present invention is applied to a pickup device that does not use a quarter-wave plate. It has the same configuration as the example. Although the semiconductor laser 210 is used as the light source, a He-Ne laser or other normal lasers may also be used. Between the semiconductor laser 211 and the magneto-optical disk 212 as a recording medium, a waveguide element 213 and an objective lens 215 are arranged in parallel at a predetermined distance from the semiconductor laser 211 side.

The waveguide element 213 is formed by laminating a buffer 1m 217 and a waveguide 11218 in order on an opaque substrate 216 made of semiconductor, gold paint, insulator, etc. by vacuum evaporation, sputtering, CVD, etc. They are arranged almost orthogonally. This waveguide element 213 is configured to constitute a single mode optical waveguide as an optical waveguide layer. In other words, only the fundamental mode is propagated in the leading wavepath, and is not affected by wavelength changes of several nanometers at all.

The buffer layer 217 and the waveguide WJ218 are made of glass, Si 02 , Si3N4, Nb2O.
Transparent materials such as dielectric materials such as 5 or D2Q5 and organic materials such as polymers are used.

The buffer 1ii217 is provided to reduce optical waveguide loss in the waveguide layer 218,
Its refractive index needs to be smaller than that on the waveguide layer 218 side. However, if waveguide loss is not a problem, it is not necessary to provide the buffer layer 217. Further, it is also possible to install the buffer 11217 on the upper surface side of the waveguide layer 218, and in this case, waveguide loss can be further reduced.

Furthermore, an opening 216a for transmitting light is formed in the light-irradiated portion of the opaque substrate 216. Possible methods for forming the opening 216a include dry or wet etching, polishing, ion milling, and the like. Further, as a modification example in which the opening 216a is not formed, it is conceivable to make a part of the opaque substrate 216 transparent by thermal oxidation, laser annealing, polishing, or the like. It is also possible to use a transparentization process in combination.

A grating coupler 220 serving as a diffraction grating for coupling external light to the waveguide layer 218 is mounted on the upper surface of the waveguide layer 218 so as to face the objective lens 215 .

This grating coupler 220 is a surface relief grating having linear gratings at equal intervals.

A part of the light emitted from the semiconductor laser 211 is transmitted as is, and the remaining light is diffracted into the waveguide, and
A part of the reflected light from the information recording surface is diffracted and coupled into the waveguide, and the remaining light is transmitted.

Note that the grating coupler 220 does not necessarily have to be a uniformly spaced grating, and may also be a chirved grating or other grating.

Furthermore, the grating coupler 220 does not need to be a linear grating; it may be curved to provide light condensing properties, or the grating direction may be partially changed to provide a light splitting function. Furthermore, it is not necessary to form the grating coupler 220 into a surface relief type, and the cross-sectional shape of the grating coupler 220 can be arbitrarily determined. Furthermore, it is also possible to employ a refractive index distribution modulation type grating or a volume phase type grating. Such a grating can be formed by various methods such as a diffusion method and an embedding method. On the other hand, when an acousto-optic element such as LiNbO3 is used for the waveguide layer or buffer layer, a grating using surface acoustic waves can be employed.

Further, on the upper surface side of the waveguide layer 218, adjacent to the grating coupler 220, two waveguide lens beam splitters 221 each having equally spaced linear gratings as a splitting diffraction grating are mounted. Each waveguide lens beam splitter 221 has a function of splitting the diffracted light from the grating coupler 220 into two light beams and a function of directing each of the divided light beams toward a photodetector to be described later. Types of the waveguide lens beam splitter 221 include a mode index type and a gradient index type. When the waveguide lens beam splitter 221 is to have a lens function, in addition to the usual aspherical type, a Fresnel lens type, a geodisic lens type, a Fresnel lens type, etc. can be considered. Further, when the grating coupler 220 has a light condensing property or a split grating, the waveguide lens beam splitter 221 does not necessarily need to be installed.

Further, four photodetectors 222 are embedded in the opaque substrate 216 so as to be in contact with the end portions (the cloth ends in the drawing) of the waveguide layer 218. Each of these photodetectors 22
2, as particularly shown in FIG.
, 222b, 222c, and 222d are arranged in parallel. As each of the detection bodies 222a, 222b and 222c, 222d, a photodite or the like can be used. When the opaque substrate 216 is made of a semiconductor substrate such as Si or QaAs, the photodetector 222 can be formed into the substrate by various methods such as diffusion, ion implantation, etching, and oxidation. can. By embedding the photodetector 222 in the substrate in this way, the photodetector 222 can be formed monolithically, which is convenient.
There is no need to polish the end face when installing it, as is the case with conventional methods. Furthermore, when the opaque substrate 216 is made of an insulator or metal, a photodiode or the like stacked on the upper surface of the waveguide layer 218 can be used as the photodetector 222. The optical signal detected by this photodetector 222 is processed as a recording/reading signal, an autofocus signal, and a tracking signal to obtain uX<.

In such an embodiment, the diverging light beam emitted from the semiconductor laser 211 passes through the aperture 21 of the waveguide element 213.
6a and enters the grating coupler 220,
A part of the emitted light is transmitted as is, and the remaining light is diffracted and coupled into the waveguide layer 218. The light transmitted through the grating coupler 220 is
The objective lens 215 focuses the light onto the information recording surface of the optical disk 212 as a recording medium. As described above, by allowing the emitted light from the semiconductor laser 211 to pass through the opening 216a of the opaque substrate 216, the substrate is no longer limited to a transparent body, and weight reduction, cost reduction, and improvement in processability can be achieved. This makes it possible to select a substrate with good durability and integration.

The light beam reflected from the information recording surface of the optical disc 212 is
The light beam passes through the objective lens 215 and becomes a condensed light beam, and enters the grating coupler 220 again. And some of the reflected light from this information recording surface is a waveguide! The remaining light is diffracted and coupled into grating coupler 218 and transmitted through grating coupler 220 . That is, due to the diffraction effect of the grating coupler 220, the first
As shown by arrow C in FIG. 6, guided light is excited in the waveguide layer 218 to extract modulated reflected light from the information recording surface. In this case, since a single mode optical waveguide is configured, only the fundamental mode is propagated in the optical waveguide, and the light diffracted by the grating coupler 220 is propagated in a direction substantially parallel to the grating surface. It happens. This guided light is separated into two beams by a grating beam splitter 221, and each beam is directed toward a photodetector 222. When the optical disk 212 is at a predetermined reference position, one of the light beams is directed toward the center portions of the detection bodies 222a and 222b, and the other light beam is directed toward the detection bodies 222c and 222d.
is oriented towards the central part of the An information read signal is obtained from the sum of all outputs, and a luminous flux is generated when the optical disk 212 approaches or moves away from the pickup side and when the spot irradiated on the information recording surface deviates from the information track such as a bit string. Autofocus control and autotracking control are performed based on the deviation (see FIGS. 3(a) and 3(b)).

In this embodiment as well, the waveguide element 213 can be used with the front and back sides reversed, and it is also possible to arrange the waveguide element 213 between the objective lens 215 and the optical disk 212. The waveguide element 213 can be used with the front and back sides reversed. Furthermore, if a collimation lens is installed between the semiconductor laser 211 as a light source and the waveguide element 213, the light incident on the waveguide element 213 can be made close to parallel light. In this way, the optical axis can be adjusted easily and accurately, and a finer spot convergence operation and reading operation can be performed.

In the embodiments shown in FIGS. 18 and 19, the present invention is applied to a pickup using a magneto-optical disk as a recording medium. Between the semiconductor laser 311 as a light source and the magneto-optical disk 312 as a recording medium, a waveguide element 313 and an objective lens 315 are arranged side by side on the optical axis at a predetermined interval from the semiconductor laser 311 side. ing. Further, the magneto-optical disk 312
On the back side, there is an electromagnet 312a that generates a bias magnetic field.
is installed. As the light source, in addition to semiconductor lasers, He--Ne lasers and other normal lasers can also be used. Preferably, the light emitted from the light source is linearly polarized. The electromagnet 312a applies a magnetic field for recording and erasing information,
Permanent magnets can also be used.

The waveguide element 313 is formed by laminating a buffer ff1317 and a waveguide layer 318 in order on an opaque substrate 316 made of semiconductor, metal, insulator, etc. by vacuum evaporation, sputtering, CVD, etc. They are arranged so that they are almost perpendicular to each other. This waveguide element 313 is configured to constitute a single mode optical waveguide as an optical waveguide layer. In other words, only the fundamental mode is propagated in the leading wavepath, and several W
It is completely unaffected by slight wavelength changes.

The materials of the buffer layer 317 and waveguide layer 318 include glass, Si 02 , Si3N4, Nb2O5
Alternatively, transparent materials such as dielectric materials such as Ta205 and organic materials such as polymers are used.

The barrier layer 317 is provided to reduce optical waveguide loss in the waveguide layer 318, and its refractive index needs to be smaller than that on the waveguide layer 318 side. However, if waveguide loss is not a problem, it is not necessary to provide the buffer layer 317. Furthermore, it is also possible to install a loose layer 317 on the upper surface side of the waveguide layer 318, and in this way, waveguide loss can be further reduced.

Furthermore, an opening 316a for transmitting light is formed in the light-irradiated portion of the opaque substrate 316. Possible methods for forming the opening 316a include dry or wet etching, polishing, ion milling, and the like. Further, as a modification example in which the opening 316a is not formed, it is conceivable to make a part of the opaque substrate 316 transparent by a method such as thermal oxidation, laser annealing, or polishing. It is also possible to use a transparentization process in combination.

On the upper surface side of the waveguide layer 318, a grating coupler 320 serving as a diffraction grating that couples external light to the waveguide 1i11318 is provided on the objective lens 315.
It is mounted so as to face the

This grating coupler 320 is a surface relief grating having linear gratings at equal intervals,
Two gratings 11 [3
2C1a and 320b. For each of these grating regions 320a and 320b, the vibration direction of the emitted light from the semiconductor laser 311 is set in the first Ql1 diagonal direction (straight line). That is, the angle θ between the polarization plane of the incident light and the grating extending direction of both grating regions 320 a and 320 b is set to be 45°.

Note that each of the grating regions 320 a and 320 b of the grating coupler 320 does not necessarily have to be a regularly spaced grating, and a chirved grating or other grating can also be employed. Further, the grating coupler 320 does not need to be a linear grating,
It is also possible to have a curved shape to provide light condensing properties, or to partially change the grating direction to provide a light splitting function. If such light focusing and splitting functions are provided, the focusing beam splitter 321a and waveguide lens 321b, which will be described later,
It is also possible to omit these functions by combining the functions of . Furthermore, it is not necessary to form the grating coupler 320 into a surface relief type, and the cross-sectional shape of the grating coupler 320 can be arbitrarily determined. Furthermore, it is also possible to employ a refractive index distribution modulation type grating or a volume phase type grating. Such a grating can be formed by various methods such as a diffusion method and an embedding method.

On the other hand, when an acousto-optic element such as LiNbO3 is used for the waveguide layer or buffer layer, a grating using surface acoustic waves can be employed.

Further, on the upper surface side of the waveguide layer 318, a condensing beam splitter 321a and a waveguide consisting of two waveguide lenses are arranged adjacent to each grating region 1320a, 320b of the grating coupler 320. A lens 321b is mounted. The condensing beam splitter 3218 has a planar light incident surface facing the grating region 320a, and a partially cylindrical or non-cylindrical curved light emitting surface on the opposite side. It has a function of splitting the diffracted light from the grating coupler 320 into two light beams and a condensing function. Each light beam split by the condensing beam splitter 321 is directed toward a photodetector to be described later. on the other hand,
The waveguide lens 321b has a planar entrance surface facing the grating region 320b, and a partially cylindrical or non-cylindrical curved exit surface on the opposite side.・Grating coupler 32
It has the function of condensing diffracted light from zero. The light beam converged by this waveguide lens 321b is also directed toward a photodetector to be described later. in this case,
The light within the waveguide has already been condensed into a condensing beam by the objective lens 315, and the light immediately after diffraction is directed to the semiconductor laser 311.
The sword will be ejected so as to occur at a position optically equivalent to the emitting point (indicated by the number X in Figure 18).

These condensing beam splitter 321a and waveguide lens 321b may be installed by depositing a material made of TlO2 or the like having a higher refractive index than the waveguide layer 318 on the waveguide layer 318 by photolithography. Alternatively, only the lens portion may be changed to have a high refractive index in a lens pattern by impurity diffusion, ion exchange, proton exchange, or the like.

Furthermore, photodetectors 322 and 323 are embedded in the opaque substrate 316 so as to be in contact with the end portions (right edge and upper edge in FIG. 19) of the waveguide layer 318. The photodetector 322 is composed of four detecting bodies, and as particularly shown in FIG. 19, two sets of detecting bodies are installed separated by a predetermined distance. Each set is configured by arranging two detection bodies 322a, 322b and 322c, 322d in parallel. Each detection object 322
For a, 322b, 322c, and 322d, photodye totes or the like can be used. The photodetector 322 is configured such that the opaque substrate 316 is made of, for example, Si or Ga.
If it is made of a semiconductor substrate such as As, it can be formed by various methods such as diffusion, ion implantation, etching, and oxidation into the substrate. When the photodetector 322 is embedded in the substrate as in this embodiment, the photodetector 322
22 can be formed monolithically, which is convenient, and when installing the photodetector 322, there is no need to polish the end face as in the conventional case.

Furthermore, when the opaque substrate 316 is made of an insulator or metal, a photodiode or the like stacked on the upper surface side of the waveguide B518 can be used as the photodetector 322. The optical signal detected by the photodetector 322 is processed as a recording/reading signal, an autofocus signal, and a tracking signal, as will be described later. On the other hand, the photodetector 323 is
It is composed of one detection object, and this photodetector 323
The detected optical signal is processed as a recording read signal, as will be described later. Each of these photodetectors 322, 323 can be installed by laminating a photoelectric exchange material such as amorphous silicon on the waveguide layer 318.

In such an embodiment, the diverging light beam emitted from the semiconductor laser 311 passes through the aperture 31 of the waveguide element 313.
6a and enters the grating coupler 320,
A portion of the light passes through the grating coupler 320 while being diffracted, and is focused into a spot on the information recording surface of the magneto-optical disk 312 by the objective lens 315. In this case, as described above, if the emitted light from the semiconductor laser 311 is made to pass through the opening 316a of the opaque substrate 316, the substrate is not limited to a transparent body, and the weight can be reduced.
It is possible to reduce costs and improve processability, as well as improve durability and
It becomes possible to select a substrate with good integration performance.

The light irradiated onto the information recording surface of the magneto-optical disk 312 is
When recording, the information recording surface is locally heated to a high temperature, and a bias magnetic field applied thereon magnetizes the inside of the information recording surface in the direction of the magnetic field. In the case of deletion, the opposite is true.

On the other hand, when reading information, the plane of polarization of the light reflected from the information recording surface is 1. Based on the so-called Kerr effect or Faraday effect, it is rotated by a minute angle depending on the recorded information. That is, the polarization plane of the reflected light is rotated by a predetermined angle with respect to the information "1" recorded on the magneto-optical disk 312. If this rotation angle is 10, the plane of polarization of the reflected light will be rotated to -θ with respect to information "0". The light reflected in such a rotated state of the polarization plane passes through the objective lens 315 again, enters the grating coupler 320 of the waveguide element 313, and is guided by the diffraction action of each grating area [320a, 320b] of the grating coupler 320. The light is guided and coupled into the waveguide layer 318 and the photodetector 32
2 and 323, respectively.

As described above, due to the information "1" recorded on the magneto-optical disk 312, the polarization plane of the reflected light is +θ.

When the light is rotated by 45°, the angle θ between the polarization plane of the incident light and the grating extension direction of the light incident on one grating region 320a of the grating coupler 320 becomes slightly larger than the original 45°. Therefore, the diffraction efficiency in the grating region [200a is reduced, and the intensity of the diffracted light beam is reduced.

On the other hand, for the light incident on the other grating region 320b of the grating coupler 320, the 8 degrees θ between the incident light polarization plane and the grating extending direction becomes slightly smaller than the initial 45 degrees, so the diffraction efficiency increases. do. This increases the intensity of the light beam after being diffracted by the grating region 320b.

Furthermore, the light beam after being diffracted by the grating region 320a is diffracted and guided into the waveguide layer 318 and received by the photodetector 322,
Output a from 2d, respectively.

b, c, and d are obtained. These outputs a, b, c.

The sum of d (a+b+c+d) will be lower than the initial value due to the decrease in light intensity as described above.

On the other hand, the light beam diffracted by the grating region 320b is diffracted and coupled into the waveguide layer 318 and received by the photodetector 323, from which an output e is obtained. This output e will be increased from the beginning due to the increase in light intensity as described above.

Therefore, the differential output S of each of these outputs is 5-
e−(a+b+c+d) is increased by rotating the polarization plane of the reflected light by +θ with respect to the information “1” recorded on the magneto-optical disk 321.

Furthermore, when the polarization plane of the reflected light is rotated by -θ due to the information rOJ recorded on the magneto-optical disk 312, one grating area 130 of the grating coupler 320
For the light incident on 0a, the angle θ between the incident light polarization plane and the grating extension direction is slightly smaller than the original 45°. Therefore, the diffraction efficiency in the lattice region Ig 320a is increased, and the intensity of the diffracted light beam is increased. Therefore, each detection body 322a, 322b of the photodetector 322
, 322c, 322d, respectively.

The sum of c and d (a+b+c÷d>) will be increased from the beginning due to the increase in light intensity as described above.

On the other hand, the light incident on the other grating area 14!320b of the grating coupler 320 has diffraction efficiency because the capacitance θ between the incident light polarization plane and the grating extension direction is slightly larger than the initial 45°. decreases. As a result, the intensity of the light beam after being diffracted by the grating region 320b is reduced. Therefore, the output e from photodetector 322
is lower than the initial value due to the decrease in light intensity as described above. Therefore, the differential output S of each of these outputs, that is, 5=e−(a+b+c+d)lt, is reduced by rotating the polarization plane of the reflected light by −θ1 with respect to the information rOJ recorded on the magneto-optical disk 312. It happens.

For this reason, if the circuit is set so that it becomes S-O with respect to the reference setting direction, when the information is "1", S>○, and when the information is "○", , Sho. This allows information to be read.

In addition, the deviation of the light flux that occurs when the magneto-optical disk 312 approaches or moves away from the pickup side and when the spot irradiated on the information recording surface deviates from the information track such as a pit row (Fig. 3 (a), (see (b)), autofocus control and autotracking control are performed. Autofocus control and autotracking control are performed by operating the objective lens 315 or operating the entire waveguide element 313 and light source 311 using an actuator (not shown).

FIG. 20 shows a second embodiment in which the present invention is applied to a pickup using a magneto-optical disk as a recording medium. In this embodiment, grating coupler 4
As 20, a uniformly spaced linear grid is adopted as a whole. The grating extension direction of this grating coupler 420 is 4
They are set to form an angle of 5°.

Roughly speaking, a waveguide lens beam splitter 421 is installed near the grating coupler 420, and the waveguide lens beam splitter 421 has a function of splitting and condensing diffracted light. TE-7M mode splitters 430 and 431 are installed to split the light beam into TE mode light and 7M mode light. Here, the TE mode light is an electric field component parallel to the waveguide (component parallel to the plane of the paper in Figure 20), and 7
The M-mode light is an electric field component perpendicular to the waveguide (component in the direction perpendicular to the plane of the paper in FIG. 20).

As the TE-7M mode splitters 430 and 431, surface relief type or volume phase type gratings are used, and these TE-TM mode splitters 430t3 and 431 are respectively installed in the direction of splitting and outputting the diffracted light. ing. Further, the TE-TM mode splitter 430 is set to satisfy the Bragg reflection condition to reflect the 7M mode light. Furthermore, between the two TE-7M mode splitters 430 and 431, a TE-7M mode splitter 430
A photodetector 433 is mounted and installed so as to receive light reflected from. Note that the TE mode light is configured to pass through the TE-7M mode splitter 430 and reach the photodetector 422.

In such an embodiment, when the light reflected from the magneto-optical disk and whose plane of polarization is rotated according to the information is diffracted by the grating coupler 420, this diffracted light is transmitted by the waveguide lens beam splitter 421. The light beam is split into two light beams, and each of these light beams becomes convergent light that is focused toward the photodetector 422. Each of these convergent lights is transmitted to TE-TM mode splitters 430 and 43
1, the light is split into TE mode light and TM mode light, and then enters photodetectors 422 and 433. In this case, the output e from the photodetector 433 and the other photodetector 422
The difference R4 from the sum of the outputs (a+b+c+d) is increased or decreased depending on the read information, and takes a positive value or a negative value. This result information is detected.

In addition, deviations in the light flux occur when the magneto-optical disk 412 approaches or moves away from the pickup side and when the spot irradiated on the information recording surface deviates from the information track such as a bit string (Fig. 3 (a), ( Autofocus control and autotracking control are performed from (see b)). Autofocus control and autotracking control are performed by actuating the objective lens or the entire structure including the waveguide element 432 and the light source using an actuator (not shown).

By the way, TE propagates within the waveguide layer 418.

TM modes can range from fundamental mode (0-order mode) to high-order modes (1st-order or higher), but the ease of design of grating coupler 420 and TE-TM mode splitters 430 and 431 and improvement of coupling efficiency are important. For this purpose, it is preferable to guide only TE mode light and TM mode light, which are fundamental mode light. For this purpose, it is possible to appropriately select the layer thickness of the waveguide layer 418.

In each of the embodiments described above, linearly polarized light, circularly polarized light, or circularly polarized light may be used as the light emitted from the light source. Further, in order to obtain a small spot diameter, it is preferable to use as coherent light as possible, but incoherent light may also be used.

Generally, the efficiency of a grating coupler has polarization angle dependence, so the opening of the light to be guided and coupled is changed based on the angle formed between the polarization direction of the incident light and the direction of the grating. Although this angle setting can be made arbitrarily, we will consider below what kind of case is most preferable.

The diffraction efficiency of the grating coupler to the waveguide layer is η,
If the efficiency of the condensing lens system is t, the light reflectance of the optical information recording medium is R1, the output light power of the light source is P, and the proportionality constant is C, then
The power P of light coupled through the waveguide layer is given by P=CtR(1-η)ηP. In this case, the value of η that maximizes P is:
Assuming that C, t, R, and P are constant, it is given by dP /dη-〇. Therefore, by setting dP/dη-Ct R(1-2η)P10, we obtain η=0.5. In other words, if the diffraction efficiency η of the grating coupler is selected to be 50%, the power of the light coupled to the waveguide layer can be maximized and good signal detection operation can be performed. Conceivable.

Furthermore, the diffraction efficiency of a grating coupler varies greatly depending on the grating shape, refractive index difference, and the like. If the diffraction efficiency of the grating coupler is relatively high, if the direction of the grating and the polarization direction of the incident light are set around 45 degrees, η = 5 as described above.
Almost 0% can be obtained. This can be applied to all the embodiments described above.

However, when recording information on an optical information medium, the above η
It is preferable to make the light intensity on the information recording surface as large as possible by making it as small as possible. Therefore, an embodiment can be considered in which the installation angle of the grating coupler with respect to the incident light can be adjusted to make the diffraction efficiency η variable.

Next, the optical axis of the grating coupler G and the light source is
Consider the case where it is tilted as shown in FIG. In this case, the center frequency of the light emitted from the light source is KI,
K is the grating direction vector. , β is the propagation constant of the guided mode in the waveguide layer.

The angle between the incident light and the vertical direction of the grating is θ, and the wave number of the grating is N (N-±0.±1°±2.±3
．． ), the condition for high diffraction efficiency η is given by β0NKG=±KIsinθ. If the NKG is set to a condition where either one of these signs holds true, the coupling strength of the incident light in either the E direction or the F direction of the waveguide layer will change depending on the set condition. Become stronger. and,
The reflected light from the optical information recording medium has a stronger coupling strength in the direction opposite to the incident light. Therefore, by installing the waveguide layer at an angle with respect to the optical axis of the light from the light source, the incident light and the reflected light can be coupled in different waveguide directions. If a photodetector is installed in the direction where there is a lot of reflection, it is possible to reduce the intensity of the light coupled from the incident light and increase the coupling strength of the reflected light, increasing the S/N ratio of the information signal. can. This can be applied to all embodiments.

(Effects) As described above, the optical information recording/reproducing device according to the present invention has the diffraction grating, the optical splitter, and the optical detection element installed on the same substrate forming the optical waveguide. The pickup can be made smaller, the access time can be shortened and costs can be reduced, and moreover, recording and reproduction can be performed efficiently and stably. Further, in the present invention, an opaque substrate is used as the substrate, and an opening is formed in the substrate to transmit the emitted light emitted from the light source, so various substrate materials can be used without being limited to transparent materials. By using a material that is durable, inexpensive, and has good processability, it becomes possible to select a substrate with good durability and integration.

[Brief explanation of the drawing]

1 and 2 are a schematic side view and a schematic plan view of an optical pickup device according to an embodiment of the present invention, and FIGS. 3(a) and 3(b) are schematic diagrams showing the optical detection operation. 4 and 5 are schematic partially enlarged side configuration diagrams of an optical pickup device according to another embodiment of the present invention, and FIG. 6 is a schematic diagram of an optical pickup device according to still another embodiment of the present invention. Figures 7 to 10
11 to 14 are schematic plan configuration diagrams of an optical pickup device according to still another embodiment of the present invention, and FIG. 16 is a schematic partially enlarged side configuration diagram of an optical pickup device according to still another embodiment of the present invention, and FIGS. 16 and 17 are schematic side configuration diagrams of an optical pickup device according to still another embodiment of the present invention. FIG. 18 and FIG. 19 are a schematic side view and a schematic plan configuration diagram of an optical pickup device according to another embodiment of the present invention, and FIG. A schematic planar configuration diagram of an optical pickup device in another embodiment, FIG. 21 is a side view illustrating the principle of an embodiment in which the waveguide layer is inclined, and FIG. 22 is a schematic side configuration diagram of a general optical pickup device. It is a diagram. 11.211,311...Semiconductor laser, 12°21
2.312... optical disc, 13,213,313.
413...Waveguide element, 14...1/4 wavelength plate, 1
5.35.65.75, 215.315...Objective lens, 20.30,220,320.420...Grating coupler, 22,222,322°422.4
33... Photodetector. Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 9 Figure 20 Figure 12 Figure 13 Figure 1 To Figure 1 - Figure 13 Figure 16 Figure 18 Figure 12a Figure 20Figure 21

Claims (1)

[Claims] 1. A converging optical system that converges light from a light source onto an information recording surface of a recording medium, and a diffraction system that diffracts reflected light from the information recording surface of the recording medium so as to separate it from incident light. lattice and
A light splitter that splits the diffracted light from the diffraction grating into a plurality of light beams, and a photodetector element that detects the output of each light beam emitted from the light splitter, the diffraction grating and the light splitter and the photodetecting element are installed on the same substrate that forms the optical waveguide, and the substrate is made of an opaque material and has an opening that allows light from the light source to pass through. An optical information recording/reproducing device characterized by: 2. The optical information recording/reproducing device according to claim 1, wherein the substrate is formed to constitute a single mode optical waveguide.