JPH04188440A - Optical pickup apparatus - Google Patents

Abstract

PURPOSE:To obtain an optical pickup apparatus characterized by the high S/N of a signal, compact size and light weight by a constitution wherein laser light is emitted to the outside of a lightguide region with a grating coupler, the light is split with a beam splitter, the laser light is cast on a recording surface with an optical element, the reflected laser light is collected at a specified position with a diffraction element with data being included, and the data are detected. CONSTITUTION:An LGC(linear grating coupler) 20 is formed at the bottom surface of a beam splitter 10. The laser light from a semiconductor laser element 8 undergoes diffraction action with the LGC by way of a lightguide layer 6. The light is cast into the beam splitter 10. The light is further reflected from a reflecting film 16. The light which advances upward in the vertical direction through the beam splitter 10 is collected on the recording surface of an optical disk 32 with an objective lens 30. The light is reflected and becomes the signal light containing data. The light is cast into a reflection-type diffraction element 26. In the reflection-type diffraction element 26, the wave front of the incident signal light is split into two parts and reflected. The light beams are further reflected from a reflecting film 28 and collected on optical disks 34 and 36. In this way, the S/N ratio of the signal is high, and the compact configuration and the light weight can be achieved.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical pickup device for recording and reproducing information on an optical recording medium such as an optical disk, and in particular to a small and lightweight optical pickup device using an optical waveguide region. The present invention relates to a pickup device.

[Prior Art] A conventional optical pickup device is composed of individual parts such as an objective lens, a beam splitter, a semiconductor laser element, and an optical detector. In the configuration of this type of optical pickup device, each component must be kept at a constant size in order to improve operability, positioning accuracy, etc. during assembly of each component. Further, a mechanism for mutually adjusting the positions of each member is also required, which complicates the manufacturing process and limits the reduction in size and weight of the optical pickup device.

In order to overcome these drawbacks, an optical integrated pickup device has been developed that integrates components such as an optical waveguide region and a grating on the same substrate to form an optical integrated circuit. VoI.

This is proposed in the paper "Optical integrated circuit implementation of a disk pickup" published in J69-C No. 5. In such a conventional technique, as shown in FIG. An optical integrated circuit is constructed by integrating an optical grating coupler) 60, a CBS (grating beam splitter) 62, optical detectors 64 and 64, and a semiconductor laser element 8 on the front end face of the semiconductor substrate 2. In such an optical pickup device, from the semiconductor laser element 8 to the optical waveguide layer 6
The laser beam emitted to the optical disk 32 is directed by the FCC 60 toward the recording surface of the optical disk 32 installed above the device, and the laser beam reflected from the recording surface enters the optical waveguide layer 6 again by the FGC 60. After that, the light is divided by the GBS 62 and incident on each of the light detectors 64 and 64, and then a focus error and a tracking error are detected from the imaging relationship of the FGC 60.

In addition, an optical pickup device proposed to solve the above-mentioned drawbacks from another perspective without using an optical waveguide region is disclosed in Japanese Patent Laid-Open No. 1-2.
It is described in No. 60645. In this optical pick-up device, as shown in FIG. It is partially reflected by the semi-transparent reflective film 74. This reflected light is irradiated onto the recording surface of the optical disk 32 by the objective lens 30, and the laser light reflected from the recording surface is focused on the objective lens 30 while partially transmitting through the semi-transparent reflective film 74, and is transmitted through the beam splitter] The tracking error is detected by entering the divided detector 68 located below zero. Thereafter, the beam is further partially reflected by the bottom surface of the beam splitter 10, and then reflected by the reflective film 16 attached to the top surface of the beam splitter 0. This reflected light enters another divided detector 70 located behind the divided detector 68, and a focus error is detected. Of the laser beams reflected by the recording surface of the optical disk 32 and focused by the objective lens 30, the laser beams reflected by the semi-transparent reflective film 74 without transmitting to the beam splitter 10 are reflected by the semiconductor laser element 8. Together with the oscillated light, the light enters a monitoring detector 72 located behind the semiconductor laser element 8, and becomes a reproduced signal.

[Problems to be Solved by the Invention] However, both of the above two conventional examples have many practical problems.

Firstly, since the optical pickup device in the above paper is a finite optical system, the main body of the first pickup device must be driven by an actuator or the like.Also, it is necessary to lengthen the optical path to the objective lens. It is not possible to sufficiently reduce the size and weight of the device. Second,
Due to constraints such as light focusing characteristics and efficiency, FCC is a light focusing optical system.
Because the numerical aperture is small, the light cannot be focused to the diffraction limit. Thirdly, the laser beam is emitted from the semiconductor laser element, passes through the FGC and GBS twice until it irradiates the recording surface of the optical disk and the information is detected by the optical detector. Therefore, the loss of light increases. Further, it is difficult to accurately couple the active layer and the leading wave layer of the semiconductor laser element, and even if a deviation occurs in this coupling, the loss of light increases.゛And, firstly, the optical pickup device of the above-mentioned publication has the following features:
Since it is a finite optical system and requires a long optical path to the condensing optical system, it is difficult to make the optical pickup device smaller and lighter. Second, since the laser beam is divided into two types of detection systems, an error signal system and a reproduction signal system, the amount of each laser beam is halved. Further, by passing the reproduced signal light through the semiconductor laser element, the reproduced signal light is also lost. This lost reproduction signal light makes the output of the semiconductor laser light unstable, and this unstable laser light enters the split detector, causing an offset in the error signal and lowering the S/N ratio of each signal.

In general, when it comes to recording and reproducing optical discs, optical pickup devices are made smaller and lighter in order to enable high-speed access, and in order to detect playback signals with a high S/N ratio, optical losses are eliminated and the amount of light emitted onto the optical disc is reduced. needs to be controlled at a constant level. However, these requirements are not met in the above two conventional examples.

An object of the present invention is to provide an optical pickup device that has a high signal-to-noise ratio and can be made sufficiently compact and lightweight.

[Means for solving the problem] - Therefore, the optical pickup device of the present invention includes a substrate,
a semiconductor laser element provided on the substrate to emit a laser beam; an optical waveguide region provided on the substrate to guide the laser beam; and an optical waveguide region provided on the optical waveguide region to emit the laser beam to the outside of the optical waveguide region. a grating coupler,
a beam splitter provided on the optical waveguide region and splitting a part of the laser beam emitted by the grating coupler in the direction of the recording surface of the optical information recording medium;
an optical element that emits the branched laser beam onto the recording surface of the medium; a diffraction element that focuses a part of the light reflected on the recording surface of the medium split by the beam splitter at a predetermined position; The present invention is characterized by comprising an information signal detection system that is provided at the predetermined position and detects information by receiving the laser light focused by the diffraction element.

[Function] In the optical pickup device of the present invention, the laser light emitted from the semiconductor laser element is guided to the optical waveguide region, emitted outside the optical waveguide region by the grating coupler, and then recorded on the information recording medium by the beam splitter. The laser beam is branched in the direction of the surface, and an optical element irradiates this laser light onto the recording surface of the information recording medium. The laser beam reflected on the recording surface of the medium is focused at a predetermined position by a diffraction element while carrying information, and is received by an information signal detection system, whereby information is detected.

[Embodiments] Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The optical pickup device 1 of the first embodiment shown in FIGS. 1 to 3 has a semiconductor substrate 2 made of silicon in the shape of a rectangular thin plate. This semiconductor substrate 2 is attached to an optical disk 32 with longitudinal force.
is installed parallel to the tangential direction of the track. The upper surface of this semiconductor substrate 2 is coated with optically high-quality S having a refractive index of about 1.46, which is formed by thermally oxidizing the semiconductor substrate 2.
A buffer layer 4 made of iO2 is provided.

For example, on the top surface of the buffer layer 4, #705 manufactured by Corning Co., Ltd.
9 glass deposited by sputtering method etc. with a refractive index of approximately 1,
55 optical waveguide regions, ie, leading waveguide layers 6, are provided.

A semiconductor laser element 8 that emits laser light toward the rear surface of the semiconductor substrate 2 is coupled to the front surface of the semiconductor substrate 2 via the optical waveguide layer 6 . The upper surface of the leading wave layer 6 has an inclined surface 12 inclined toward the emission surface side of the semiconductor laser element 8.
A beam splitter 10 having a trapezoidal cross section is bonded to an adhesive 14.
is fixed by. The inclined surface 12 of this beam splitter 10 is inclined at a predetermined angle, which will be explained later.
A first reflective film 16 that reflects laser light is provided. A beam splitting surface 18 is formed in the center of the beam splitter 10, which is inclined at 45 degrees on the same side as the inclined surface 12, and splits laser light incident from the front into an upper direction and a rearward direction. As shown in FIG. 2, the beam splitter 10 in the area sandwiched between the inclined surface 12 and the beam splitting surface 18
An LGC (linear grating coupler) 20 is formed on the bottom surface of the semiconductor IC using semiconductor IC manufacturing techniques, such as lithography and etching techniques.

This LGC 20 has a function of emitting incident light into the beam splitter 10 toward the inclined surface 12 and converting it into a parallel light beam. The angle of the inclined surface 12 is set so as to reflect the laser beam from the LGC 20 in the horizontal direction. Below this LGC 20, a monitor detector 22 for monitoring the emitted laser light is provided in the semiconductor substrate 2. This monitor detector 22 is divided into two parts along the designed optical axis of the guided light guided through the waveguide layer 6, and the signal strength of each of these divided monitor detectors 22 is compared when assembling the optical pickup device. This is used to adjust the position of the semiconductor laser element 8. A reflection type diffraction element 26 is formed on the bottom surface of the beam splitter 10 in the projection area of the beam splitting surface 18 by a method similar to that of the LGC 20. This reflective diffraction element 26 has a function of dividing the wavefront of the incident laser beam into two along the tangential direction of the track of the optical disk 32, that is, along the extension line of the designed optical axis of the guided light. Furthermore, this reflective diffraction element 26 constitutes a diffraction element that focuses incident light on a predetermined position. A reflective film (not shown) is formed on the outside of the reflective diffraction element 26 by depositing a thin film of material such as A1 using a vacuum evaporation method. It is installed so as to reflect laser light from vertically upward toward a second reflective film 28 attached to the top surface. Further, an objective lens 30 is installed above the beam splitting surface 18 and is movable in the vertical and horizontal directions by a driving means (not shown), and an optical disk 32 is placed above the objective lens 30. In the area behind the second reflective film 28 on the semiconductor substrate 2, that is, in a predetermined position where the light incident on the reflective diffraction element 26 is focused by the reflective diffraction element 26, The first and second optical detectors 34 and 36 are formed in parallel in a direction perpendicular to the designed optical axis,
It constitutes an information signal detection system that receives the laser light focused by the reflective diffraction element 26 and detects information on the optical disc 32. Each of these optical detectors 34 and 36 is divided into two parts along the designed axis.

In the optical pickup device configured in this manner, the laser light from the semiconductor laser element 8 passes through the optical waveguide layer 6 and becomes guided light, reaching the LGC 20.

A part of the guided light that has reached the LGC 20 is diffracted and enters the monitor detector 22, where it is used as a reference signal to keep the light output of the semiconductor laser element 8 constant. The other laser light is diffracted by the LGC 20 and becomes a parallel light beam toward the first reflective film 16 toward the beam splitter 10.
It is ejected inside.

The emitted laser beam is reflected by the first reflective film °16,
The light is directed toward the rear in the horizontal direction, and is split by the beam splitter 10 into light that travels further toward the rear in the horizontal direction and light that travels upward in the vertical direction. The light traveling backward in the horizontal direction continues straight and is radiated outside the beam splitter 10 without entering any of the detectors. Light traveling vertically upwards is
The light is focused by the objective lens 30 onto the recording surface of the optical disk 32, reflected there, becomes a signal beam with information, is made parallel again through the objective lens 30, and is transmitted through the beam split surface 18 to the reflective diffraction element. 26. The reflective diffraction element 26 divides the wavefront of the incident signal light into two and focuses the light while reflecting it toward the second reflective film 28 . Each of the signal lights that have been divided into two and reflected is further reflected by the second reflective film 28 and condensed onto the first and second optical detectors 34 and 36 to form a light spot. These first and second optical detectors 34, 36 each have two
The size of the light spot and the shift in the left and right light intensities of each of the two divided optical detectors are output to a predetermined circuit to detect focus errors and tracking errors.

Next, a second embodiment of the present invention will be described using FIG. 4.

In this embodiment, the same members as in the first embodiment are denoted by the same reference numerals, and only the different parts will be described in detail. below,
The third to seventh embodiments will also be described in the same manner.

In the optical pickup device 1 of the second embodiment, a 5i-N film 40 is formed on the optical waveguide layer 6 by, for example, a plasma CVD method, and an LGC 20 and a reflective diffraction element are formed on this film in the same manner as in the first embodiment. 26. According to this embodiment, there is no need to perform precise processing on minute parts such as the beam splitter 10, and the optical waveguide layer 6 and optical detector 34 are not required to be precisely processed.
．． By manufacturing the LGC 20 and the reflective diffraction element 26 as part of forming and processing the optical pickup device 36, etc., the manufacturing process of the optical pickup device can be simplified.

Next, a third embodiment will be described using FIG. In this embodiment, the beam splitter 10 in the first embodiment is replaced with a polarization beam splitter 42 having polarization selectivity, and the optical disc 3
A /4 wavelength plate 46 is fixed with an adhesive 14 on the optical path of the reflected light from the recording surface of FIG. By adopting such a configuration, the loss of laser light at the beam splitting surface is reduced, and the S of the reproduced signal light is reduced without unnecessary laser light entering each detector.
Detection with a high /N ratio becomes possible.

The fourth embodiment shown in FIG. 6 is 1/4 of the third embodiment.
A wavelength plate 46 is fixed to the rear surface of the polarizing beam splitter 42, a mirror 48 tilted 45 degrees to the rear is fixed to a device frame (not shown), and an objective lens 30 is arranged below this mirror 48. By adopting such a configuration, similarly to the third embodiment, it is possible to detect the reproduced signal light with a high S/N ratio, and it is possible to promote thinning of the optical pickup device.

The fifth embodiment shown in FIG. 7 is a modification of the first embodiment, in which the portions of the buffer layer 4 and the optical waveguide layer 6 covering the optical detectors 34 and 36 are removed by etching by RIE or the like, and the detector window 50 is etched away. That is. According to this embodiment, it is possible to prevent the signal light incident on the optical detectors 34 and 36 from being scattered or multiple-reflected by the leading wave layer 6 and the buffer layer 4, and it is possible to prevent signal light detection errors. can.

In the sixth embodiment shown in FIG. 8, a mirror 48 tilted at 45 degrees to the rear of the beam splitter 10 in the first embodiment is fixed to an apparatus frame (not shown), and an objective lens 30 is arranged below this mirror 48. and beam splitter 10
An inclined surface 12 is disposed on the end surface of the semiconductor substrate 2, and a reflective diffraction element 26 is formed on this inclined surface 12. Further, in order to prevent the laser light from being scattered within the beam splitter 10 due to the adhesive 14 or the beam splitter 10 coming into contact with the active layer of the semiconductor laser element 8 or the optical waveguide portion of the optical waveguide layer 6, the optical waveguide layer 6 A cladding layer 52 is formed on the upper surface of the cladding layer 52, and an LGC 20 is formed on this cladding layer 52 to form an optical pickup device. This crat layer 52 can be easily formed using a material having a refractive index lower than that of the leading wave layer 6, such as 5i02, by chemical vapor deposition or the like. Further, the lattice portion of the LGC 20 formed as described above may be filled with an adhesive. According to this embodiment, the thickness of the optical pickup device can be reduced, and the miniaturization of the optical pickup device can be promoted.

The seventh embodiment shown in FIG. 9 is a modification of the sixth embodiment, in which the semiconductor laser element 8 is coupled not to the front end face of the semiconductor substrate 2 but to the rear end face. If you do this, the 6th
Unlike the embodiment, the adhesive 14, the beam splitter 10, etc. do not come into contact with the active layer of the semiconductor laser element 8 or the optical waveguide portion of the optical waveguide layer 6, and there is no need to form the cladding layer 52 on the upper surface of the waveguide layer 6. . In this case, LGC20 is the first
It is formed on the bottom surface of the beam splitter 10 as in the embodiment. In this way, the manufacturing process is simpler than in the sixth embodiment, but of course the cladding layer 52 may be formed on the upper surface of the leading wave layer 6 as in the sixth embodiment.

Further, as a configuration other than the above seven embodiments, an information signal detection system, that is, an error detection system configuration as shown in FIGS. 10 and 11 may be adopted. In this configuration, the reflective diffraction element 26 has a wavefront splitting function, the first and second optical detectors 34, 3.6 are each divided into multiple divisions, for example, into three, and - Design of guided light They are formed in series along the optical axis. and these first optical detectors 34
is placed in front of the second optical detector 36, a semi-transparent reflective film (not shown) is attached to the upper surfaces of the first and second optical detectors 34, 36, and a second optical detector is placed on the upper surface of the beam splitter 10. In addition to the reflective film 28, there is another reflective film, a third reflective film.
is fixed as a reflective film 38. In the optical pickup device fl in such a modified example, the first and second light detectors 34, 36 are arranged so that the respective light spots that the reflective diffraction element 26 connects onto the first and second light detectors 34, 36 have the same size. a second detector 34, 36 and a second and third detector 34,36;
The reflective films 28 and 38 are positioned. In this way, the focus error is measured based on the change in the light spot size between the front and the rear, and the tracking error is measured using the Bushfull method.

Further, as shown in FIG. 12, an error detection system located in front, that is, an optical detector 34 may be provided on the upper surface of the beam splitter 10. At this time, a semi-transparent reflective film (not shown) is formed on the light receiving surface of the optical detector 34.

Furthermore, the astigmatism method can also be used for the information signal detection system, that is, the error detection system. In addition to this, various other modifications are possible.

[Effects of the Invention] According to the present invention, it is possible to provide a small, lightweight pre-bias amplifier device with a high signal-to-noise ratio.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an optical pickup device according to a first embodiment of the present invention, FIG. 2 is a longitudinal sectional view of the optical pickup device in FIG. 1, and FIG. 3 is a top view of the device in FIG. 1.
FIG. 4 is a vertical cross-sectional view showing an optical pickup device according to a second embodiment of the present invention, FIG. 5 is a vertical cross-sectional view showing an optical pickup device according to a third embodiment, and FIG. 6 is a vertical cross-sectional view showing an optical pickup device according to a fourth embodiment. FIG. 7 is a vertical cross-sectional view showing the optical pickup device of the fifth embodiment; FIG. 8 is a vertical cross-sectional view showing the optical pickup device of the sixth embodiment; FIG. 9 is a vertical cross-sectional view showing the optical pickup device of the sixth embodiment. FIG. 10 is a top view showing a modification of the error detection system in the optical pickup device of the present invention, and FIG. 11 is a longitudinal cross-sectional view of the optical pickup device shown in FIG. 10. 12 is a longitudinal sectional view showing another modification of the error detection system in the optical pickup device of the present invention,
FIG. 13 is a perspective view showing a conventional optical pickup device using an optical waveguide region, and FIG. 14 is a longitudinal sectional view showing a conventional optical pickup device not using an optical waveguide region. 1... Optical pickup device, 2... Semiconductor substrate, 6
... Optical waveguide layer, 8... Semiconductor laser element, 1o...
Beam splitter, 20... Linear grating coupler (LGC), 26... Reflection type diffraction element, 3o
...Objective lens, 32...Front disk, 34...First
optical detector, 36... second optical detector. Applicant's agent Patent attorney Tsuboi 4 1＼ Figure 3 Figure 4 Figure 5 Figure 7 L 52 Class 1 layer 1. 1″-X Fig. 10 Fig. 11 Fig. 12

Claims (1)

[Scope of Claims] 1. A substrate, a semiconductor laser element provided on the substrate and emitting laser light, an optical waveguide region provided on the substrate and guiding the laser light, and a semiconductor laser device provided on the optical waveguide region, a grating coupler that emits the laser beam outside the optical waveguide region; and a grating coupler that is provided on the optical waveguide region and branches a part of the laser beam emitted by the grating coupler in the direction of the recording surface of the optical information recording medium. a beam splitter that emits the split laser light onto a recording surface of the medium, and a part of the light reflected on the recording surface of the medium that is split by the beam splitter and focuses it on a predetermined position. An optical pickup device comprising: a diffraction element; and an information signal detection system provided at the predetermined position and configured to detect information by receiving laser light focused by the diffraction element. 2. The optical pickup device according to claim 1, wherein the optical element is provided movably outside the semiconductor substrate. 3. The beam splitter is a polarizing beam splitter having a polarizing function, and the polarizing beam splitter and a quarter wavelength plate are provided on the optical path of the reflected light from the recording surface of the medium. The optical pickup device according to claim 1 or 2.