JPH09265653A - Optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make an optical head small in size and light in weight, to reduce the manufacturing man-hour and to hardly generate cross talk at the time of utilizing a super-high resolving phenomenon. SOLUTION: A laser beam transmitted from a laser diode 11 is transmitted through grating couplers 12a, 12b and a light shielding band 13 and made incident on a condenser lens 14. At this time, the light intensity distribution of the laser beam made incident on the condenser lens 14 becomes a distribution whose neighboehood of center is attenuated by the light shielding band in X direction (the longitudinal direction of the light shielding band) and a gaussian distribution in Y direction. Consequently, the intensity distribution of a light spot converged on the surface of an optical disk 15 by the condenser lens 14 has a side lobe only in the X direction by a super-high resolving phenomenon. X direction is made to be the tangential direction of a track of the optical disk 15. The reflected returned light beam is introduced to an optical wave-guide 17 by the grating couplers 12a, 12b and converged on photodiodes 16a, 16b.

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 in an information input / output device for recording / 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 In order to improve the recording density in 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, but there is still an unsolved problem in shortening the wavelength of the semiconductor laser, and increasing the numerical aperture also increases the allowable amount of aberration. There are limits. Therefore, using a super-resolution phenomenon as a means for reducing the light spot diameter by a method other than these has been studied. Super-resolution is a method of obtaining a spot diameter that exceeds the usual diffraction limit by changing the amplitude or phase distribution of the light beam that enters the condenser lens.

A conventional optical head device utilizing the super-resolution phenomenon is shown in FIG. The diverging beam from the laser diode 51 is collimated by the collimator lens 52, the light intensity of the central portion is attenuated by the light shielding band 53, passes through the polarization beam splitter 55, passes through the quarter wavelength plate 54, and passes through the condensing lens 56 to the optical disc. 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 disc 57 is smaller than the ordinary spot diameter as shown by the solid line in FIG. The distribution is accompanied by side lobes. The reflected light from the optical disc 57 having the information signal is
The light again passes through the condenser lens 56 and the quarter-wave plate 54, is reflected by the polarization beam splitter 55, is guided to the signal detection system 58, and the reproduction signal and the servo signal are detected.

[0004]

The above-mentioned conventional optical head utilizing the super-resolution phenomenon is composed of a bulk optical element group. Therefore, manufacturing requires complicated processes such as mutual alignment and bonding, and requires a large number of assembly steps. In addition, the number of parts to configure is large, and
It is difficult to reduce the weight. As a means for solving these problems, attempts have been made to integrate optical element groups using thin film waveguides. In the thin film waveguide, a condensing grating coupler as shown in FIG. 7 has been proposed in Japanese Patent Laid-Open No. 3-15003 as a device utilizing a super-resolution phenomenon for a grating coupler for coupling an input / output of 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, but the central portion 72 of the grating coupler is flat without a grating.

Therefore, coupling occurs only in the peripheral portion where the grating is formed, and the light intensity distribution on the aperture surface of the grating is not uniform, so that the super-resolution phenomenon can be used. However, since the super-resolution phenomenon occurs two-dimensionally in this structure, a ring-shaped side lobe occurs two-dimensionally around the spot of the condensed light. Therefore, if this is directly used for the optical head, it will be perpendicular to the track. The side lobe also influences the direction, and crosstalk easily occurs.

Therefore, the problems to be solved by the present invention are as follows.
The object is to realize the reduction in size and weight of the optical head device and the reduction in the number of manufacturing steps, and to prevent crosstalk from occurring when utilizing the super-resolution phenomenon.

[0007]

SUMMARY OF THE INVENTION The above-mentioned problem is to provide a light intensity (or phase) modulating means extending on a grating coupler for guiding reflected light from an optical disk to an optical waveguide in a direction perpendicular to a tangential direction of a track of the optical disk. It can be solved by arranging and making the super-resolution phenomenon available by this modulation means.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical head device according to the present invention comprises a light source, a grating coupler arranged between the light source and an optical disc irradiated with the light from the light source, and a linear arrangement in the center of the grating coupler. A light modulating means for changing the intensity or phase of light transmitted through the grating coupler and condensed on the optical disc; a condensing means for condensing light from the light source on the optical disc; and a reflection from the optical disc. The thin film optical waveguide means for guiding the light guided by the grating coupler, and the pair of light receiving elements in the thin film optical waveguide means for receiving the light guided by the grating coupler; The modulator is characterized in that it extends in a direction perpendicular to the tangential direction of the track of the optical disc.

Since the optical head according to the present invention is constructed as described above, the conventional bulk optical element group will be integrated on the thin film waveguide and integrally formed by the planar technique. 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 has conventionally required complicated optical axis adjustment with an objective lens, but it can be easily formed by integrally forming this with a grating coupler. Become. Further, the number of elements to be configured is reduced and the devices can be integrated on a plane, so that the size and weight of the device can be reduced. Further, since the side lobe generation region caused by the super-resolution phenomenon is limited in the track tangential direction, crosstalk due to sidelobe 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.
3A and 3B are a plan view and a side view showing the embodiment of FIG. This optical head device includes a laser diode 11 as a light source, a condenser lens 14 that condenses light emitted from the laser diode 11 on the surface of an optical disc 15, and photodiodes 16a and 16b that receive reflected light from the optical disc 15. Optical disc 1
The grating couplers 12a and 12b for coupling the reflected light of No. 5 to the optical waveguide 17 formed on the substrate 18 and condensing it under the photodiodes 16a and 16b, the grating coupler 12a and the grating coupler 1
Light-shielding band 13 of appropriate width provided in the divided area between 2b
And. Here, the grating coupler 12a
Reference numerals 12b and 12b denote gratings formed on the surface of the optical waveguide 17 in 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 under the photodiodes, whereby the return light condensed under the photodiodes is 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 has 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 surface of the optical disk 15 by the condenser lens 14 becomes a distribution with side lobes only in the X direction due to the super-resolution phenomenon. As shown in FIG. 2, if the X direction is the track tangential direction and the Y direction is the track vertical direction, it is possible to read the information signal recorded at a high density by the light spot reduced by the super-resolution phenomenon, Since side lobes do not occur in the track vertical direction, crosstalk from adjacent tracks is less likely to occur.

As an element for dividing the grating coupler, an element for changing the phase may be used instead of the light-shielding band 13 as long as the above conditions are satisfied. The grating couplers 12a and 12b are patterned so as to focus light on the photodiodes 16a and 16b, respectively. Therefore, after the reflected light from the optical disk 15 passes through the condenser lens again, the grating coupler 1
2a and the grating coupler 12b guide the light to the optical waveguide 17 and divide the wavefront into two parts, which are a photodiode 16a and a photodiode 16b, respectively.
Focused below. Since the light incident on the photodiode 16a and the photodiode 16b is divided into two at the center, the reproduction signal and the servo signal are detected by their sum signal and difference signal.

[Second Embodiment] FIGS. 3A and 3B are
It is a top view and a side view showing the 2nd example of the present invention. This optical head device includes a laser diode 31 as a light source.
An optical waveguide 37 formed on the substrate 38 for guiding the light emitted from the laser diode 31, and the laser diode 3
A condensing grating coupler 33 that condenses the divergent guided light from the optical disc 35 onto the surface of the optical disc 35, and a dividing region 34 having an appropriate width that divides the condensing grating coupler 33 at the center.
, Photodiodes 36a and 36b that receive the reflected return light from the optical disc 35, and photodiode 36a that divides the reflected return guided light from the optical disc 35 into two.
And a grating beam splitter 32 for condensing the light beams 36b. Focusing grating coupler 33
Is formed in a pattern close to an off-axis concentric circle so that the divergent guided light is condensed at one point on the surface of the optical disk 35, but the pattern is not formed in the central divided region 34 and becomes flat. There is. The grating beam splitter 32 is a grating that is close to a straight line whose direction changes in the center. These gratings 32,
Reference numeral 33 is an inscription on the surface of the optical waveguide, and is formed by etching. In this embodiment, the substrate 3
Silicon (Si) is used for 8, and the photodiodes 36a and 36b are formed in the substrate.

The light emitted from the laser diode 31 is guided to the end-coupled optical waveguide 37, passes through the grating beam splitter 32, and is condensed on the surface of the optical disk 35 by the condensing grating coupler 33. At this time, in the light intensity distribution on the opening surface of the condensing grating coupler 33, since no coupling occurs in the divided region 34, as shown in FIG. 4, the center of the Gaussian distribution reflecting the input guided light is in the X direction. The distribution is attenuated, and has an exponential distribution in the Y direction that reflects the attenuation of the guided light due to diffraction. Therefore, the intensity distribution of the light spot condensed on the surface of the condenser lens 35 becomes a distribution with side lobes due to the super-resolution phenomenon only in the X direction, and the sinc function (sync) reflecting the exponential function distribution in the Y direction. Function).

As shown in FIG. 4, if the X direction is the track tangential direction and the Y direction is the track vertical direction, the information signal recorded at a high density by the light spot reduced by the super-resolution phenomenon can be read. You can In this embodiment, as shown in FIG. 4, side lobes also occur in the track vertical direction, but they are relatively weaker than the side lobes in the X direction caused by the super-resolution phenomenon, so crosstalk from adjacent tracks is less likely to occur. Has become. The reflected return light incident on the condensing grating coupler 33 is guided again 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 disc 35 is divided into two wavefronts and focused on the photodiode 36a and the photodiode 13b, respectively.
A reproduction signal and a servo signal can be obtained from these sum signal and 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 through the grating coupler formed on the optical waveguide and having the optical modulator at the center thereof. Since the reflected light is guided to the thin film optical waveguide by this grating coupler and focused on two light receiving elements, the optical head device that utilizes the super-resolution phenomenon can be made smaller and lighter, and the manufacturing process can be simplified. it can. Further, since the optical modulator provided at the center of the grating coupler extends in the direction perpendicular to the tangential line of the optical disc track, recording / reproduction with less crosstalk can be realized.

[Brief description of 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 operation explanatory diagram 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, which is configured by 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 disc 16a, 16b, 36a, 36b Photodiode 17, 37, 73 Optical waveguide 18, 38 Substrate 32 Grating beam splitter 33, 71 Condensing grating coupler 34 Divided area 52 Collimating lens 54 Quarter wave plate 55 Polarizing beam splitter 58 Signal detection system 72 Central part

Claims (4)

[Claims] 1. A light source, a grating coupler arranged between the light source and an optical disk irradiated with light from the light source, and a linearly arranged central portion of the grating coupler, which is transmitted through the grating coupler. An optical modulator that changes the intensity or phase of the light condensed on the optical disc, a condenser that condenses the light from the light source on the optical disc, and a light guided by the grating coupler of the reflected light from the optical disc. In an optical head device comprising a thin film optical waveguide means for guiding and a pair of light receiving elements coupled to the thin film optical waveguide means for receiving the light guided by the grating coupler, the optical modulator means is an optical disc. An optical head device characterized in that it extends in a direction perpendicular to the tangential direction of the track. 2. The grating coupler has a function of condensing the reflected light from the optical disc on different light receiving elements for each of the portions divided by the light modulating means. The optical head device described. 3. The light emitted from the light source is guided to the optical disk through the thin film optical waveguide means and the grating coupler, and the grating coupler also serves as the light converging means. Optical head device. 4. A beam splitter for condensing the reflected light guided in the thin-film optical waveguide means between the grating coupler and the light receiving element to each light receiving element is formed. 3. The optical head device according to item 3.