JP2862127B2 - Optical head device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device used for an information input / output device for recording and reproducing information using light, and more particularly to an optical head device utilizing a super-resolution phenomenon for condensing light. It is about.

[0002]

2. Description of the Related Art To improve the recording density of an optical disk device, it is necessary to reduce the diameter of a light spot formed on a recording medium by an optical head device. The light spot diameter is determined by the wavelength of the light source and the numerical aperture of the condenser lens. However, there is still an unsolved problem in shortening the wavelength of a semiconductor laser. There is a limit from. Therefore, use of the super-resolution phenomenon as a means for reducing the light spot diameter by a method other than these methods is being studied. The super-resolution is a method of obtaining a spot diameter equal to or larger than a normal diffraction limit by changing the amplitude or phase distribution of a light beam incident on a condenser lens.

FIG. 5 shows a conventional optical head device utilizing the super-resolution phenomenon. The divergent beam from the laser diode 51 is converted into parallel light by a collimating lens 52, the light intensity at the center is attenuated by a light shielding band 53, passes through a polarizing beam splitter 55, passes through a quarter-wave plate 54, and is condensed by a condenser lens 56. The light is focused on the recording surface 57. At this time, since the light intensity distribution of the light beam incident on the condenser lens 56 is changed, the light intensity on the recording surface of the optical disk 57 is smaller than the normal spot diameter as shown by the solid line in FIG. The distribution has side lobes. The reflected light from the optical disk 57 having the information signal is
The light is again reflected by the polarization beam splitter 55 through the condenser lens 56 and the quarter-wave plate 54 and guided to the signal detection system 58, where the reproduced signal and the servo signal are detected.

[0004]

The above-mentioned conventional optical heads utilizing the super-resolution phenomenon are all constituted by a group of bulk optical elements. Therefore, the production requires a complicated process such as mutual alignment and bonding, and requires a large number of assembly steps. In addition, the number of components is large,
It is difficult to reduce the weight. As means for solving these problems, attempts have been made to integrate an optical element group using a thin film waveguide. A condensing grating coupler as shown in FIG. 7 has been proposed in Japanese Patent Application Laid-Open No. 3-15003 as a thin film waveguide that utilizes the super-resolution phenomenon for a grating coupler for inputting and outputting a light beam. In this condensing grating coupler, an optical waveguide 73 is provided on a substrate, and a condensing grating coupler 71 is formed on the surface thereof. However, no grating is formed on a central portion 72 of the grating coupler, and the grating is flat.

For this reason, coupling occurs only in the peripheral portion where the grating is formed, and the light intensity distribution on the grating opening surface is not uniform, so that the super-resolution phenomenon can be used. However, in this structure, since the super-resolution phenomenon occurs two-dimensionally, ring-shaped side lobes are two-dimensionally generated around the spot of the condensed light. Crosstalk is likely to occur due to side lobes also affecting the direction.

Therefore, the problems to be solved by the present invention are:
An object of the present invention is to reduce the size and weight of an optical head device and to reduce the number of manufacturing steps, and to reduce the occurrence of crosstalk when utilizing the super-resolution phenomenon.

[0007]

An object of the present invention is to provide a light intensity (or phase) modulating means extending in a direction perpendicular to a tangential direction of a track of an optical disk on a grating coupler for guiding reflected light from the optical disk to an optical waveguide. This can be solved by arranging and making available the super-resolution phenomenon by this modulation means.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical head device according to the present invention comprises a light source and an optical head for changing the intensity or phase of light from the light source.
Adjusting means , condensing means for condensing light from a light source on an optical disk, and thin-film optical waveguide for guiding reflected light from the optical disk
Means for dividing the light reflected from the optical disc and
Gratings that guide the waveguide means in different directions
Comprising a Ppura, a pair of light receiving element for receiving the light guided by the thin film optical waveguide means and coupled to said grating coupler, wherein the light modulation means the Gureti
It is arranged linearly at the center of the optical coupler and extends in the direction perpendicular to the tangential direction of the track of the optical disk.

Since the optical head according to the present invention is constructed as described above, the conventional optical head composed of a group of bulk optical elements is integrated on a thin film waveguide, and is integrally formed by planar technology. This eliminates the need for complicated processes such as mutual alignment and bonding. In particular, an element that changes the amplitude or phase of a light beam to obtain a super-resolution phenomenon conventionally required complicated optical axis adjustment with an objective lens, but it can be easily performed by integrally forming this with a grating coupler. Become. Further, since the number of elements to be configured is reduced and the devices can be integrated on a plane, the device can be reduced in size and weight. Furthermore, since the region where the side lobes caused by the super-resolution phenomenon occur is limited in the track tangential direction, crosstalk due to the side lobe wraparound is less likely to occur.

[0010]

Next, embodiments of the present invention will be described in detail with reference to the drawings. [First Embodiment] FIGS. 1A and 1B show a first embodiment of the present invention.
It is the top view and side view which show Example of this. This optical head device includes a laser diode 11 as a light source, a condenser lens 14 for condensing light emitted from the laser diode 11 on the surface of the optical disk 15, and photodiodes 16a and 16b for receiving reflected light of the optical disk 15. Optical disk 1
5 are coupled to the optical waveguide 17 formed on the substrate 18 and condensed under the photodiodes 16a and 16b, the grating couplers 12a and 12b, the grating coupler 12a and the grating coupler 1
Light-shielding band 13 of appropriate width provided in the divided area between
And Here, the grating coupler 12a
And 12b are gratings engraved on the surface of the optical waveguide 17 into a shape close to a straight line, and are formed by etching or molding. Further, the photodiodes 16a and 16b are provided on the optical waveguide 17, and although not shown, a grating coupler is engraved below the photodiode, so that return light condensed below the photodiode is converted to a photo-diode. Guided by a diode.

The light beam emitted from the laser diode 11 passes through the grating coupler 12a and the grating coupler 12b and enters the condenser lens 14. At this time, as shown in FIG. 2, the light intensity distribution of the light beam incident on the condenser lens 14 is a distribution in which the vicinity of the center is attenuated by the light shielding band 13 in the X direction and a Gaussian distribution in the Y direction. Therefore, the intensity distribution of the light spot condensed on the optical disk 15 by the condenser lens 14 has a distribution with side lobes due to the super-resolution phenomenon only in the X direction. As shown in FIG. 2, if the X direction is the tangential direction of the track and the Y direction is the perpendicular direction of the track, it is possible to read an information signal recorded at a high density by a light spot reduced by the super-resolution phenomenon, Since there is no side lobe in the track vertical direction, crosstalk from adjacent tracks is less likely to occur.

As an element for dividing the grating coupler, an element that changes the phase may be used instead of the light-shielding band 13 if the above condition is satisfied. The grating couplers 12a and 12b are formed so as to be focused on the photodiodes 16a and 16b, respectively. Therefore, the reflected light from the optical disk 15 passes through the condenser lens again, and
2a and the grating coupler 12b guide the light to the optical waveguide 17 and split the wavefront into two parts, respectively, the photodiode 16a and the photodiode 16b.
Focused below. Since the light incident on the photodiode 16a and the photodiode 16b is split into two at the center, a reproduction signal and a servo signal are detected based on the sum signal and the difference signal.

[Second Embodiment] FIGS. 3A and 3B show
It is the top view and side view which show the 2nd Example of this invention. This optical head device has a laser diode 31 as a light source.
An optical waveguide 37 formed on a substrate 38 for guiding light emitted from the laser diode 31;
A condensing grating coupler 33 for condensing the divergent guided light from 1 on the surface of an optical disc 35, and a division region 34 of an appropriate width for dividing the condensing grating coupler 33 at the center.
And photodiodes 36a and 36b for receiving reflected return light from the optical disk 35, and splitting the reflected return guided light from the optical disk 35 into two photodiodes 36a and 36b.
And a grating beam splitter 32 that condenses the light to the beam 36b. Focusing grating coupler 33
Is formed in an off-axis concentric pattern so as to converge the divergent guided light to one point on the surface of the optical disk 35. I have. The grating beam splitter 32 is a grating that is close to a straight line whose direction changes at the center. These gratings 32,
Reference numeral 33 denotes a cutout formed on the surface of the optical waveguide by etching. In this embodiment, the substrate 3
8, silicon (Si) is used, and photodiodes 36a and 36b are formed in the substrate.

The light emitted from the laser diode 31 is guided to an optical waveguide 37 coupled to the end face, passes through a grating beam splitter 32, and is condensed on a surface of an optical disk 35 by a condensing grating coupler 33. At this time, the light intensity distribution on the opening surface of the condensing grating coupler 33 has no coupling in the divided region 34, and therefore, as shown in FIG. The distribution is attenuated, and the distribution in the Y direction is an exponential function reflecting the attenuation due to the diffraction of the guided light. Therefore, the intensity distribution of the light spot converged on the surface of the condenser lens 35 is a distribution with side lobes due to the super-resolution phenomenon only in the X direction, and a sinc function (sink function) reflecting an exponential function distribution in the Y direction. Function).

As shown in FIG. 4, if the X direction is the tangential direction of the track and the Y direction is the perpendicular direction of the track, it is possible to read an information signal recorded at a high density by a light spot reduced by the super-resolution phenomenon. Can be. In this embodiment, as shown in FIG. 4, side lobes also occur in the track vertical direction, but crosstalk from an adjacent track hardly occurs because the side lobes are relatively weaker than the X-direction side lobe caused by the super-resolution phenomenon. Has become. The reflected return light incident on the condensing grating coupler 33 is again guided to the optical waveguide 37 and guided to the photodiodes 36a and 36b by the grating beam splitter 32 divided at the center. That is, the reflected light from the optical disk 35 is split into two wavefronts and collected on the photodiode 36a and the photodiode 13b, respectively.
A reproduction signal and a servo signal can be obtained from the sum signal and the difference signal.

[0016]

As described above, the optical head device according to the present invention irradiates the optical disk with the light emitted from the light source via the grating coupler formed on the optical waveguide and having the optical modulation means at the center. Since the reflected light is guided to the thin film optical waveguide by this grating coupler and collected on two light receiving elements, the miniaturization and weight reduction of the optical head device utilizing the super-resolution phenomenon and simplification of the manufacturing process are realized. it can. Further, since the light modulating means provided at the center of the grating coupler extends in the direction perpendicular to the tangential direction of the optical disk track, recording / reproduction with less crosstalk can be realized.

[Brief description of the drawings]

FIG. 1 is a plan view and a side view of a first embodiment of the present invention.

FIG. 2 is an operation explanatory diagram of the first embodiment of the present invention.

FIG. 3 is a plan view and a side view of a second embodiment of the present invention.

FIG. 4 is an explanatory diagram of the operation of the second embodiment of the present invention.

FIG. 5 is a diagram showing a configuration of a conventional optical head device utilizing a super-resolution phenomenon.

FIG. 6 is a diagram showing a change in light intensity distribution due to a super-resolution phenomenon.

FIG. 7 is a perspective view of a conventional condensing grating coupler using a super-resolution phenomenon and configured using a thin film waveguide.

[Explanation of symbols]

 11, 31, 51 Laser diode 12a, 12b Grating coupler 13, 53 Light-shielding band 14, 56 Condensing lens 15, 35, 57 Optical disk 16a, 16b, 36a, 36b Photodiode 17, 37, 73 Optical waveguide 18, 38 Substrate 32 Grating beam splitters 33, 71 Condensing grating coupler 34 Division area 52 Collimating lens 54 Quarter-wave plate 55 Polarization beam splitter 58 Signal detection system 72 Central part

Claims (2)

(57) [Claims] 1. A light source and the intensity or phase of the light from the light source
Light modulating means for changing the light intensity, light condensing means for condensing light from a light source on an optical disk, and guiding light reflected from the optical disk.
The thin-film optical waveguide means that waves and the reflected light from the optical disc are separated.
Split and lead to the thin film optical waveguide means in different directions
A grating coupler, the optical head device provided with a pair of light receiving element for receiving the light guided by the thin film optical waveguide means and coupled to said grating coupler, said light modulating means is a grating coupler
An optical head device, which is linearly arranged at the upper center and extends in a direction perpendicular to a tangential direction of a track of an optical disk. 2. A light source, and light from the light source is guided on a plane.
Thin film optical waveguide means, and the thin film optical waveguide means
Light from the optical disk
Condensing grating that guides the reflected light again to the thin-film optical waveguide means.
A coupling coupler and the thin film optical waveguide means.
The light guided by the focusing grating coupler is
Grating that splits and focuses light in different directions
A beam splitter and the grating beam splitter.
A pair of light receiving elements for receiving the light guided by the
An optical head device comprising:
The coupler changes the intensity distribution of light focused on the optical disk.
Light modulating means for converting the light
An optical head device extending in a direction perpendicular to a tangential direction of a track of the optical disk.