JP2000251314A - Optical pickup and optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve optical characteristics with a simple constituting when first and second light sources are used selectively for accessing an optical recording medium by providing an astigmatism correction means common to laser beams emitted from the first and second light sources. SOLUTION: An optical integrated element 4 emits selectively laser beams of wavelength corresponding to respective optical disks 2A, 2B toward the optical disks 2A, 2B, and corresponding photodetectors receive return beams. A collimating lens 5 is a parallel planar transparent planar member and is arranged in the optical path of the laser beam tilting obliquely to the optical axis of the laser beam. The collimating lens 5 has an astigmatic amount equal to the astigmatism of the laser beam, and the tilt, the plate thickness, etc., are selected so as to impart astigmatism in the direction canceling the astigmatism of the laser beam. Thus, the collimating lens 5 corrects the astigmatism of the laser beams of different wavelengths.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup and an optical disk device, for example, a DVD (Digital Video).
o Disk) and an optical disk device for reproducing a compact disk. The present invention corrects the aberrations of a plurality of laser beams by one astigmatism correction unit, so that when a plurality of light sources are selectively used to access an optical recording medium, the optical characteristics can be improved by a simple configuration. Be able to improve.

[0002]

2. Description of the Related Art Conventionally, in a compact disk player, which is an optical disk apparatus, an optical pickup irradiates a laser beam onto an information recording surface of the compact disk and processes the result of receiving the return light to record the information on the compact disk. It reproduces various types of data.

As such an optical pickup, a type in which a light emitting element and a light receiving element are individually arranged and a type using an optical integrated element in which a light emitting element and a light receiving element are integrated have been proposed. In the latter, the overall shape can be made smaller and the reliability can be improved as compared to the former.

In such an optical pickup, a laser diode is arranged such that the deflection surface of the laser beam forms an angle of approximately 45 degrees with respect to the scanning direction of the laser beam, thereby providing any astigmatism of the laser beam. Without increasing the jitter, it is possible to prevent an increase in jitter due to deterioration of optical characteristics.

[0005]

When an optical integrated device is used, the overall shape can be reduced in size and simplified, so that an optical pickup using the optical integrated device can be used in an optical disk apparatus for reproducing DVDs. It would be convenient if it could be constructed. Further, it is considered that such a DVD optical disk device is convenient if a compact disk can be reproduced.

In this case, the light emitting element and the light receiving element for the DVD and the light emitting element and the light receiving element for the compact disk are integrated to constitute an optical integrated element, thereby forming an optical disk apparatus capable of reproducing the compact disk and the DVD. It is considered possible.

However, in a compact disc,
The pit depth is λ / 8 wavelength, whereas the pit depth is λ / 4 wavelength in DVD,
In an optical disk device for reproducing a DVD, it is difficult to detect a tracking error signal by the same method as a compact disk.
It is necessary to generate a tracking error signal by the ase detection method. In the DPD method, it is necessary to dispose a laser diode such that the laser beam deflection surface is parallel or perpendicular to the laser beam scanning direction.

In order to effectively use the internal space of the optical integrated device, it is desirable to arrange the laser diode so that the deflection surface of the laser beam is parallel or perpendicular to the scanning direction of the laser beam.

However, in this case, there is a problem in the optical disc device that the optical characteristics are deteriorated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and when a plurality of light sources are selectively used to access an optical recording medium, the optical characteristics can be improved with a simple configuration. A pickup and an optical disk device using the optical pickup are proposed.

[0011]

According to the first or fifth aspect of the present invention, there is provided an optical pickup or an optical disk device, wherein the first and second embodiments are applied to an optical pickup or an optical disk apparatus.
Are arranged such that the deformation directions of the beam cross-sectional shape of the laser beam due to astigmatism substantially match, and the optical system uses an optical system common to the laser beams emitted from the first and second light sources. And a common astigmatism correction unit for the laser beams emitted from the first and second light sources.

According to the structure of claim 1 or 5,
The first and second light sources are arranged so that the deformation directions of the beam cross-sectional shape of the laser beam due to astigmatism substantially match, and the optical system is shared by the laser beams emitted from the first and second light sources. If the laser beam emitted from the first and second light sources has a common astigmatism correction means, the laser light emitted from the plurality of light sources by the simple astigmatism correction means The astigmatism of the beam can be corrected collectively, and the optical characteristics can be improved by a simple configuration.

[0013]

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

(1) Configuration of Embodiment FIG. 1 is a cross-sectional view showing an optical system of an optical disk device according to an embodiment of the present invention. This optical disc device 1
The data recorded on the optical disk 2A which is a VD and the data recorded on the compact disk 2B are reproduced.

Here, the compact disc 2B can reproduce recorded data by processing return light obtained by irradiating a laser beam onto the information recording surface through a transparent substrate having a thickness of 1.2 [mm]. This is an optical disk that has been made. On the other hand, the DVD 2A can reproduce the recorded data by processing the return light obtained by irradiating the information recording surface with a laser beam through a transparent substrate having a thickness of 0.6 [mm]. It is an optical disk.

In the optical disk device 1, the optical pickup 3 is arranged so as to be movable in a radial direction of the optical disk by a predetermined thread mechanism. The optical pickup 3 converts the laser beam emitted from the optical integrated device 4 into an astigmatism correction plate 5, a collimator lens 6, an aperture 7,
The optical disc 2A or 2B is irradiated through the objective lens 8 and the return light obtained from the optical disc 2A or 2B is reflected by the optical integrated element 4 through the objective lens 8, the aperture 7, the collimator lens 6, and the astigmatism correction plate 5. Incident on.

The optical disc device 1 processes the result of receiving the return light in the optical integrated device 4 to generate a tracking error signal, a focus error signal, and a reproduction signal. The optical disk device 1 moves the objective lens 8 based on the tracking error signal and the focus error signal to perform tracking control and focus control, and processes a reproduction signal to reproduce data recorded on the optical disks 2A and 2B.

Here, the optical integrated device 4 is formed by integrating a light emitting element and a light receiving element for a compact disk and a light emitting element and a light receiving element for a DVD into a package. In the optical integrated device 4, semiconductor laser diode chips constituting these light emitting devices are arranged at a distance of about 100 [μm] in the radial direction of the optical disks 2A and 2B.
Under control of a system controller (not shown), these two semiconductor laser diode chips are selectively driven in accordance with the optical disks 2A and 2B, thereby directing a laser beam having a wavelength corresponding to each of the optical disks 2A and 2B to the optical disks 2A and 2B. To selectively emit light, and return light is received by a corresponding light receiving element.

The astigmatism correction plate 5 is a parallel plate transparent plate member, and is disposed in the optical path of the laser beam at an angle to the optical axis of the laser beam. The astigmatism correction plate 5 has an astigmatism amount equal to the astigmatism of the laser beam, and its inclination, plate thickness, and the like are set so as to give astigmatism in a direction to cancel the astigmatism of the laser beam. It is made to be selected. Thereby, the astigmatism correction plate 5 corrects the astigmatism of the laser beams having different wavelengths.

The collimator lens 6 converts the laser beam transmitted through the astigmatism correction plate 5 into a substantially parallel light beam and emits it.

The aperture 7 has a circular opening formed at the center by depositing a dielectric film on a transparent plate member. In the aperture 7, a dielectric film is formed in a portion surrounding the opening, and the dielectric film selectively blocks light having a wavelength of 780 [nm] which is a wavelength of a laser beam for a compact disk. Wavelength 6 which is the wavelength of the beam
The filter is configured to transmit 50 [nm] light. As a result, the aperture 7 transmits the laser beam for compact disc by shaping the beam shape according to the beam diameter determined by the aperture, while transmitting the laser beam for DVD without changing the beam shape at all. It has been made like that.

The objective lens 8 is an aspherical plastic lens formed by injection molding of a transparent resin, and a DVD which is incident by substantially parallel light beams by selecting the refractive index of the transparent resin and the shape of each lens surface. The laser beams for the information recording surfaces of the corresponding optical disks 2A and 2B can be focused on the laser beam for compact disks and the laser beam for compact disks. Thus, the objective lens 8 is provided with a so-called 2D laser beam corresponding to a DVD laser beam and a compact disc laser beam.
It is designed to constitute a focusing lens.

Further, the objective lens 8 is provided with an optical disk 2A, 2
The actuator is configured to be movable in the radial direction of B and in the direction along the optical axis, so that the actuator can be driven in accordance with a tracking error signal and a focus error signal to perform tracking control and focus control.

In this tracking control, when reproducing the compact disk 2B, the objective lens 8 is movable by the actuator by offsetting in the radial direction of the optical disk 2B by the distance that the light emitting elements are arranged apart in the optical integrated element 4. In this way, deterioration of the characteristics of the optical system when reproducing the compact disk 2B is prevented.

The matrix operation circuit 9 includes the optical integrated device 4
The received light output result is subjected to matrix calculation processing to obtain a tracking error signal TE whose signal level changes according to the tracking error amount, a focus error signal FE whose signal level changes according to the focus error amount, and a pit row. To generate a reproduction signal RF whose signal level changes. At this time, the matrix operation circuit 9
These tracking error signals and the like are generated for DVD and compact disc, respectively.

FIG. 2A is a plan view showing the optical integrated device 4 as viewed from the direction of emission of the laser beam, and FIG.
FIG. 4 is a cross-sectional view showing the optical integrated device 4 in a cross-section in the circumferential tangent direction of the optical disks 2A and 2B. Optical integrated device 4
Is an optical system 1 in which a prism 14 and semiconductor laser diode chips 15A and 15B are arranged on a semiconductor substrate 17.
After the optical system 16 is housed in the package 18 and wired, a lid glass 19 serving as a transparent sealing member is formed.
It is created by sealing.

Here, the semiconductor laser diode chip 1
The laser beams 5A and 15B are arranged at a distance of about 100 [μm] in the radial direction of the optical disks 2A and 2B, and have a laser beam for DVD with a wavelength of 650 [nm] corresponding to a DVD and a wavelength 7 for a compact disk.
An 80 [nm] compact disk laser beam is emitted toward the prism 14. The semiconductor laser diode chips 15A and 15B are provided on the optical disc 2A,
On the light receiving surface of 2B, the deflection surface is arranged so as to be parallel to the scanning direction of the laser beam or to be in a direction orthogonal to the scanning direction. Further, as the semiconductor laser diode chips 15A and 15B, for example, those having substantially the same amount of astigmatism generated by sorting are arranged in pairs,
Furthermore, they are arranged so that the deformation directions of the beam cross-sectional shape of the laser beam due to astigmatism substantially match. As a result, in the optical disc apparatus 1, the astigmatism of each of the laser beams emitted from these two light sources can be corrected by one astigmatism correction plate 5, and when reproducing a DVD, the DPD method is used. The tracking error signal can be detected.

The prism 14 is an optical element for separating a laser beam and return light, and is formed in a substantially rectangular shape having a slope on one side. The prism 14 reflects the laser beams emitted from the semiconductor laser diode chips 15A and 15B on the inclined surface and emits the laser beams toward the collimator lens 5, and also returns the incident light by reversely following the optical path of the laser beam. Guide inside from the slope.

The return light incident from the slope enters the lower surface of the prism 14, where it transmits about 50% of the light, and reflects the remaining amount of return light toward the upper surface. Further, the prism 14 reflects the return light toward the lower surface by approximately 100% on the upper surface, and emits the return light reflected on the upper surface from the lower surface.

For this reason, the prism 14 has a mirror surface formed on the upper surface by vapor deposition, and return light emitted from an inclined surface side (hereinafter referred to as a front side) of the lower surface and a side remote from the inclined surface (hereinafter referred to as a rear side). The beam splitter surface and the anti-reflection surface are formed on the lower surface on the front side by the same vapor deposition process so that the light amount ratio of the light source becomes approximately 1: 1.

In the semiconductor substrate 17, the prism 14
The light receiving surfaces 25A and 26A for DVD and the light receiving surfaces 25B and 26B for compact disk are formed at the portions where the return light from the laser beam for DVD and the return light from the laser beam for compact disk are incident.

In FIG. 3, as shown in a partially enlarged view of these light receiving surfaces, the optical integrated element 4 is placed on the semiconductor substrate 17 in the just-focused state by the return light transmitted through the prism 14 in this manner. The semiconductor laser diode is designed so that the beam spot formed has a substantially focal line shape on the rear side and an elliptical shape having a major axis in a direction orthogonal to the extension direction of the rear side focal line on the front side. The directions of the chips 15A and 15B, the size of the prism 14, and the like are selected.

The light receiving surfaces 25B and 26B on the compact disk side are formed in a substantially rectangular shape side by side in the circumferential tangential direction of the compact disk, and are divided in the radial direction of the compact disk by the dividing lines extending in the circumferential tangential direction. Formed. The light receiving surfaces 25B and 26B receive the beam spot formed on each light receiving surface by dividing the beam spot formed on each light receiving surface into four in the radial direction of the compact disk in the just tracking state. Are respectively output. In the following, the small light receiving surface divided in this manner is denoted by the symbol m on the outside on the front side.
And p, the inside on the front side is indicated by reference numerals n and o. Also, for the outside on the rear side, the code q
And t, the inside on the rear side is indicated by symbols r and s.

On the other hand, the light receiving surfaces 25A and 26A on the DVD side are similarly formed in a substantially rectangular shape along the circumferential tangent direction of the optical disk 2A, respectively.
6A is formed in the same manner as the rear-side light receiving surface 26B for the compact disk.

On the other hand, the light receiving surface 25A on the front side
In addition to the configuration of the front-side light receiving surface 25B for the compact disk, the light receiving surface is further divided into two in the circumferential tangential direction of the optical disk. Thus, in the semiconductor substrate 17, a tracking error signal can be generated by the so-called DPD method. In the following, the DV divided in this way is
For the small light-receiving surface on the D side, the outside on the front side, and on the slope side, the symbols a and d indicate the inside on the front side,
The slope side is indicated by reference numerals b and c. The outside of the front side and the side farther from the slope are denoted by reference signs e and h, and the inside of the front side and the side farther than the slope are denoted by reference signs f and g. For the outside on the rear side,
The inside on the rear side of the reference numerals i and l is indicated by reference numerals j and k.

The semiconductor substrate 17 performs a current-to-voltage conversion process on the light receiving results of each of the divided light receiving surfaces a to t, performs an arithmetic process, and outputs the result.
The calculation output is further processed to generate a tracking error signal, a focus error signal, and a reproduction signal.

That is, in the case of a compact disc, a difference signal is generated between the inner light receiving surface and the outer light receiving surface on the front and rear light receiving surfaces 25B and 26B, respectively. Is subtracted by (m + p + r + s)-(n + o
+ Q + t). Also, the front and rear light receiving surfaces 25B and 26
In B, a difference signal is generated between the inner peripheral light receiving surface and the outer peripheral light receiving surface, respectively, and the difference signal is added on the front side and the rear side to obtain (m + n + s + t).
Generate a tracking error signal represented by-(o + p + q + r). Front and rear light receiving surfaces 2
In 5B and 26B, a reproduction signal represented by (m + n + o + p + q + r + s + t) is generated by adding all the light reception results.

On the other hand, on the DVD side, similarly, (a + d + e + h + j + k)-(b + c + f + g)
+ I + 1), a focus error signal represented by (a)
+ B + c + d + e + f + g + h + i + j + k + 1). On the other hand, as shown in FIG. 4, with respect to the tracking error signal TE for DVD, the inner circumferential side and the outer circumferential side of the optical disc 2A are respectively divided for each group of the light receiving surfaces divided in the arrangement direction of the light receiving surfaces 25A and 26A. Are added by the adder circuits 42A to 42D, respectively, to thereby detect the amount of received light on the inner peripheral side and the outer peripheral side for these groups. Further, the phase comparison circuits 43A and 43
In B, the light receiving results on the inner and outer circumferences are compared in phase for each group, and then added by the adder circuit 44 to generate the tracking error signal TE.

(3) Operation of the Embodiment In the above configuration, the optical disc apparatus 1 (FIG. 1) uses the optical pickup 3 to irradiate the optical discs 2A and 2B with a laser beam, receive the return light thereof, and The information recorded on the optical disks 2A and 2B is reproduced by processing the result of receiving the return light by the signal processing circuit.

That is, in the optical disk device 1, the optical pickup 3 emits a laser beam from the optical integrated element 4, and this laser beam is converted into a substantially parallel light beam by the collimator lens 6, and then passes through the aperture 7 and passes through the objective lens. 8 and is focused on the information recording surfaces of the optical disks 2A and 2B by the objective lens 8. The return light obtained by the irradiation of the laser beam is received by the objective lens 8 and is incident on the optical integrated element 4, and the optical integrated element 4 obtains the result of receiving the return light.

In the optical disk device 1, a tracking error signal TE is generated from the result of receiving the return light, and the servo lens is used to move the objective lens 7 by the servo circuit so that the tracking error signal TE has a predetermined signal level.
A tracking control is performed by moving in the radial directions of A and 2B. Similarly, a focus error signal is generated,
The objective lens 7 is moved up and down so that the focus error signal becomes a predetermined signal level, thereby controlling the focus.

That is, when the optical disk loaded in the optical disk device 1 is the DVD 2A, in the optical disk device 1, in the optical integrated element 4, the semiconductor laser diode chips 15A and 15B (arranged in the radial direction of the optical disks 2A and 2B). In FIG. 3), a laser beam is selectively emitted from the semiconductor laser diode chip 15A for DVD.
A is irradiated. Also, the return light from the DVD 2A is transmitted through the prism 14 to the DVD light receiving surfaces 25A and 26A.
Is received by the

On the other hand, when the optical disk loaded in the optical disk device 1 is the compact disk 2B, the optical disk device 1 uses the semiconductor laser diode chip 15
A laser beam is selectively emitted from the semiconductor laser diode chip 15B of the compact disk out of A and 15B (FIG. 3), and this laser beam is irradiated on the compact disk 2B. The return light from the compact disk 2B is received by the light receiving surfaces 25B and 26B for the compact disk via the prism 14.

Further, these light reception results are processed by the matrix operation circuit 9 to generate a reproduction signal RF, a tracking error signal TE, and a focus error signal FE for a compact disk and a DVD, respectively.

In accessing the optical disks 2A and 2B by selectively emitting each laser beam in this manner, in the optical disk device 1, the astigmatism correction plate 5 which is a transparent plate member of a parallel flat plate is used for the laser beam. The astigmatism correcting plates 5 are disposed obliquely in the optical path, and the astigmatism of the laser beam is corrected.

In the correction of the astigmatism, in the optical disk device 1, the deflection surface on the disk surface is parallel or perpendicular to the scanning direction of the laser beam, and the deformation direction of the beam cross-sectional shape of the laser beam due to the astigmatism. And the semiconductor laser diode chips 15A and 15B having substantially the same amount of astigmatism are arranged in a pair so that two astigmatism correction plates 5 are commonly used. By correcting the astigmatism of the laser beam, the optical characteristics can be improved with a simple configuration.

Thus, in the optical disk device 1,
The semiconductor laser diode chips 15A and 15B can be arranged such that the deflection surface of the laser beam is parallel or perpendicular to the scanning direction of the laser beam, and for a DVD, a tracking error signal can be generated by the DPD method. The internal space of the optical integrated device can be effectively used to prevent the optical integrated device 4 from being enlarged.

(3) Effects of the Embodiment According to the above configuration, a common optical system is provided by selectively irradiating a laser beam from a semiconductor laser diode chip, which is a light source, spaced apart in the radial direction of an optical disc. When the laser beam is condensed on the optical disk, the aberration of these laser beams is corrected by one astigmatism correction unit, so that the optical characteristics can be improved with a simple configuration.

(4) Other Embodiments In the above-described embodiment, a case has been described in which the parallel plate-like transparent plate-like members are arranged obliquely to constitute astigmatism correction means. However, the present invention is not limited thereto, and a cylindrical lens, a hologram, a Fresnel lens, and the like may be arranged to constitute the astigmatism correction unit. When a coupling lens or the like is used, the coupling lens or the like may be provided with astigmatism generating means.

In the above embodiment, the case where the objective lens is displaced in conjunction with the switching of the laser beam has been described. However, the present invention is not limited to this, and the entire optical system may be displaced. If sufficient characteristics can be obtained for practical use, the displacement may be omitted.

In the above embodiment, the DVD
A case has been described in which the light receiving surface is configured exclusively for the optical disk and the compact disk. However, the present invention is not limited to this, and can be widely applied to a case where the light receiving surface is commonly configured.

In the above-described embodiment, the case of reproducing a compact disk and a DVD has been described. However, the present invention is not limited to this, and is widely applied to, for example, a case of accessing a compact disk and a CD-R. be able to.

In the above-described embodiment, the case of accessing two types of optical disks has been described. However, the present invention is not limited to this, and can be widely applied to the case of accessing a plurality of types of optical disks.

Further, in the above-described embodiment, the case where the optical pickup is constituted by the optical integrated device in which the light emitting element and the light receiving element are integrated has been described. However, the present invention is not limited to this, and the light emitting element and the light receiving element are not limited to this. The present invention can also be widely applied to a case where the and are arranged separately.

[0055]

As described above, according to the present invention, an optical recording medium is accessed by selectively using a plurality of light sources by correcting aberrations of a plurality of laser beams by one astigmatism correcting means. In this case, the optical characteristics can be improved with a simple configuration.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an optical disk device according to an embodiment of the present invention.

FIGS. 2A and 2B are a plan view and a cross-sectional view showing an optical integrated device applied to the optical disk device of FIG.

FIG. 3 is a plan view showing a light receiving surface of the optical integrated device of FIG.

FIG. 4 is a block diagram for explaining generation of a tracking error signal by the optical integrated device of FIG. 2;

[Explanation of symbols]

1 ... optical disk device, 2A, 2B ... optical disk, 3
… Optical pickup, 4… optical integrated device, 5… astigmatism correction plate, 5… collimator lens, 6… aperture, 7… objective lens, 14… prism, 15
A, 15B: Semiconductor laser diode chip, 25
A, 25B, 26A, 26B .......... Light receiving surface

Claims (10)

[Claims] An optical pickup for irradiating an optical recording medium with a laser beam, receiving return light obtained from the optical recording medium, and outputting a light receiving result, wherein first and second light emitting laser beams with different wavelengths. A second light source, a light receiving element for receiving return light obtained from the optical recording medium, and condensing the laser beams emitted from the first and second light sources on the optical recording medium, An optical system for guiding return light obtained from a recording medium to the light receiving element, wherein the first and second light sources are arranged such that a deformation direction of a beam cross-sectional shape of the laser beam due to astigmatism substantially matches. Wherein the optical system is an optical system common to the laser beams emitted from the first and second light sources, and before the light beams are emitted from the first and second light sources. Optical pickup and having an astigmatism correction means common to the laser beam. 2. The optical pickup according to claim 1, wherein said astigmatism correction means is a parallel plate transparent member. 3. The optical pickup according to claim 1, wherein the first and second light sources have substantially the same amount of astigmatism. 4. The optical pickup according to claim 1, wherein said first and second light sources and said light receiving element are integrally housed in one package. 5. An optical disk apparatus for reproducing information recorded on the optical disk by irradiating the optical disk with a laser beam, receiving return light obtained from the optical disk, and processing a result of the light reception. First and second light sources for emitting the laser beam, a light receiving element for receiving return light obtained from the optical recording medium, and optical recording of the laser beam emitted from the first and second light sources. An optical system for converging light on a medium and guiding return light obtained from the optical recording medium to the light receiving element, wherein the first and second light sources have a beam cross-sectional shape of the laser beam due to astigmatism. The optical system is arranged so that the deformation directions are substantially coincident with each other, and the optical system is configured to emit light common to the laser beams emitted from the first and second light sources. An optical disc device, which is a scientific system and has astigmatism correction means common to the laser beams emitted from the first and second light sources. 6. The optical disk device according to claim 5, wherein said astigmatism correction means is a parallel plate transparent member. 7. The optical disk device according to claim 5, wherein the first and second light sources have substantially the same amount of astigmatism. 8. The optical disk device according to claim 5, wherein said first and second light sources and said light receiving element are housed integrally in one package. 9. The light receiving element divides a light receiving surface into a first direction corresponding to a scanning direction of the laser beam and a second direction orthogonal to the first direction. 6. The optical disk device according to claim 5, wherein a light receiving result of the light receiving surface is output. 10. The apparatus according to claim 5, wherein the first and second light sources have a deflecting surface set in parallel with or perpendicular to the scanning direction of the laser beam. An optical disk device as described in the above.