JPH0283829A - Optical pickup - Google Patents

Abstract

PURPOSE:To obtain an accumulated-type optical pickup which can be substituted for a non-accumulated type optical pickup by providing a means to divide the light from a grating coupler into 3, and to converge the reflected light from an optical disk to photodetectors divided into 6. CONSTITUTION:After light 15 emitted from a semiconductor laser 1 is passed through a waveguide 2, it is emitted to an external part as a parallel light 16 with a grating coupler 5. Light 16 transmits a transparent plate 8, is divided into 3 by Fresnel lenses 9a, 9b and 9c, three beams are converged to the pit recorded onto an optical disk. The reflecting light from an optical disk transmits the transparent plate 8 again and is converged to a photodetectors 13 divided into 6 through a Fresnel lens 11 and a grating lens 12. Thereafter, in the same way as the conventional non-accumulated type optical pickup. A tracking error signal is detected by the 3-beam method and a focus error signal is detected by the astigmatism. When the high speed focus is desired, the electronic circuit is kept as it is only by changing the optical pickup to the accumulated-type, and therefore, the spread is promoted.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an optical pick-up amplifier used in optical disk devices, etc., and more specifically, to an integrated optical pick-up amplifier capable of high-speed access. be.

[Conventional technology]

FIG. 4 is a schematic diagram showing the configuration of an optical pink-up using a conventional optical member. In the figure, 1 indicates a semiconductor laser as a light source. Light 26 emitted from the semiconductor laser 1 passes through a diffraction grating 21. After being divided into three parts, the light is focused on the bit 20 recorded on the optical disk 19 by the objective lens 23. 3
Among the divided lights, the central main beam 27, which is the 0th-order diffracted light, is used to read the bit information (F signal and focus error signal), and the sub-beams 28 on both sides, which are the ±1st-order diffracted lights, are used as the tracking error signal. are used for reading.

The reflected light from the optical disk 19, which is divided into three parts, is split by a beam splitter 22, passes through a cylindrical lens 24, and is received by light receiving elements 25a and 25b.

At this time, in the reflected light corresponding to the main beam 27, the focal length of the vertical light 27a and the focal length of the horizontal light 27b are made different by the cylindrical lens 24.

Further, FIG. 5 is an enlarged plan view of the light receiving elements 25a and 25b, and the reflected light corresponding to the main beam 27 is detected by the central four-divided light receiving elements 13a, 13b, 13c, and 13d, and the reflected light corresponding to the sub beam 28 is detected. The reflected light is detected by the light-receiving elements 13e13f on both sides, and based on the detection signals from each light-receiving element, the calculation as shown in FIG.
A focus error signal, an HF signal, and a tracking error signal are output. In other words, in such an optical system,
The astigmatism method is used to read the focus error signal.
A three-beam method is used to read the tracking error signal.

The method of reading an error signal in optical pink-up having the above-mentioned configuration is used in most of the CD players currently on the market, and is the mainstream in optical disc devices. However, since such an optical pink-up is constructed by combining conventional optical members, it has the drawbacks of being bulky and heavy, and requiring a long access time.

In order to eliminate these drawbacks, an integrated optical big amplifier in which optical members are integrated on one substrate has been devised. Figure 6 shows, for example, "Optical integrated circuitization of optical disk pickup" (IEICE Technical Report 0QE85-721985)
FIG. 2 is a perspective view showing the configuration of an integrated optical pink-up disclosed in 2003. In the figure, reference numeral 4 denotes a Si substrate, and a waveguide 2 is formed on the Si substrate 4 via a buffer layer 3, and a grating coupler 5. A beam splinter 312-divided light receiving element 33 is integrated.

Further, a semiconductor laser 1 serving as a light source is coupled to the end face of the waveguide 2 by an end face direct coupling method.

When light from the semiconductor laser 1 enters the waveguide 2, the light 15 is guided through the waveguide 2, then emitted to the outside by the grating coupler 5, and concentrated on the bit 20 recorded on the optical disk 19. be illuminated. The reflected light 16 from the optical disk 19 enters the waveguide 2 and passes through the beam splinter 31.
The light 32 is separated into two directions by the light receiving element 33, and the separated light 32 is received by each light receiving element 33. In such an optical pickup, the tracking error signal of the optical disk is detected based on the push-pull method, and the focus error signal is detected based on the Foucault method, and these error signals and the HF signal that is pit information are detected. is obtained by calculations as shown in FIG.

[Problem to be solved by the invention]

By the way, commercially available CD players or CDRO
When trying to replace an M driver non-integrated optical pickup with an integrated optical pickup like the one described above, since the signal calculation methods of the two optical big amplifiers are different (see Figures 5 and 6), the peripheral It is necessary to change the electronic circuit at the same time, and there is a drawback that the configuration becomes complicated.

As a result, it is not easy to convert to an integrated optical pickup, and there is a problem in that the conversion to an integrated optical pickup is not promoted.

The present invention has been made in view of such circumstances, and includes a means for dividing light from a grating coupler into three parts,
By being equipped with a means for focusing the reflected light from the optical disk onto the six-divided light receiving element, even integrated optical pickups can detect signals using the same calculation method as in non-integrated optical pickups. The purpose of the present invention is to provide an integrated optical pink-up that requires only replacing the optical pickup without changing the circuit.

[Means to solve the problem]

The optical pickup according to the present invention includes a light source, a waveguide that guides light from the light source, a grating coupler that emits the light guided by the waveguide toward an optical disk, and receives reflected light from the optical disk. In an optical pink-up in which a light-receiving element is integrated, the light-receiving element is a six-segment type light-receiving element, and means for dividing the light emitted from the grating coupler into three and focusing it on three points on the optical disk; a condensing means for condensing the reflected light from the optical disk onto the six-divided light receiving element; and a condensing means provided in an optical path between the condensing means and the six-divided light receiving element to condense light only in one direction. It is characterized by comprising means having a function of emitting light.

[Effect]

In the optical pickup of the present invention, the light emitted from the grating coupler is divided into three parts and emitted to the optical disc, and the reflected light from the optical disc is focused on the light receiving element divided into six parts.

Therefore, in the present invention, similarly to the conventional non-integrated optical pickup, the tracking error signal is detected by the three-beam method, and the focus error signal is detected by the astigmatism method.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below based on drawings showing embodiments thereof.

FIG. 1 is a diagram showing the configuration of a first embodiment of the optical pink-up according to the present invention, and FIG. 1 (al indicates a plan view thereof, and the first equivalent) shows a cross-sectional view thereof. Note that in FIG. 1 (al), components that are not integrated on the substrate 4 are not shown.

In the figure, 4 indicates a substrate made of n-type Si, and the substrate 4
A waveguide 2 made of Corning #7059 is formed through a buffer layer 3 made of SiO□ to prevent loss of guided light, and a semiconductor laser 1 serving as a light source is connected to the end face of the waveguide 2. combined. Note that the waveguide 2 is not formed in a part of the region on the side opposite to the side where the semiconductor laser 1 is arranged. A grating coupler 5 made of SiN is provided on the − side of the waveguide 2 opposite to the coupling side of the semiconductor laser 1, and is made of SiN and emits the light 15 guided through the waveguide 2 to the outside. Note that this grating coupler 5 is
The shape of the grating coupler 5 is designed so that the emitted light 16 from the grating coupler 5 becomes parallel light.

In the direction of light emission from grating coupler 5, BK
A transparent plate 8 consisting of 7 is provided so as to be perpendicular to its optical axis. The front surface of the transparent plate 8 (the surface opposite to the waveguide 2) is provided with a device that divides the light incident on the transparent plate 8 into three parts and focuses the light on three points on an optical disk (not shown). Three-divided Fresnel lenses 9a, 9b, and 9c are provided, and on the back surface of the transparent plate 8 (the surface on the waveguide 2 side), the reflected light from the optical disk is transferred onto a six-divided light receiving element 13, which will be described later. An off-axis Fresnel lens 11 is provided to condense light into the center. Note that the three-split Fresnel lenses 9a, 9b, and 9c are designed so that their focal points are slightly shifted in the direction perpendicular to the optical axis. The material of these Fresnel lenses 9a, 9b, 9c, and 11 is Corning #7059.

Fig. 2 is a sectional view showing the vicinity of the six-divided light receiving element 13, and Fig. 2 fal is a sectional view seen from the same direction as bl, and the second opening is a sectional view taken from a direction perpendicular to this direction. A cross-sectional view is shown. The light-receiving element 13, which has the same configuration as a conventional non-integrated optical pickup in plan view (see FIG. 5), is a p-n junction formed by partially doping an n-type Si substrate 4 with p-type impurities. Consists of 43. A grating lens 12 corresponding to a cylindrical lens is provided on the buffer layer 3 above the light receiving element 13. The grating lens 12 has a chirp shape whose period becomes shorter as it moves away from the center, and is obtained by etching the waveguide 2. In addition, 14 in the figure
Reference numerals a and 14b denote an upper electrode and a lower electrode of the light receiving element 13, which are made of AI and Au, respectively.

Next, the operation will be explained.

Light 15 emitted from the semiconductor laser 1 is guided through the waveguide 2 and then emitted to the outside as parallel light 16 by the grating coupler 5 . The light 16 emitted to the outside passes through the transparent plate 8
is transmitted through the Fresnel lenses 9a and 9b.

It is divided into three parts at 9c. Three beams divided into three (0
The main beam 17a at the center, which is the second-order diffracted light, and the sub-beams 18a on both sides, which are the ±1st-order diffracted lights, are respectively focused on bits recorded on the optical disk. The reflected light from the optical disk passes through the transparent plate 8 again and passes through the Fresnel lens 11. The light passes through the grating lens 12 and is focused on the light receiving element 13 .

Similar to the conventional non-integrated optical pink-up, the reflected light 17b corresponding to the main beam 17a is detected by the four-divided light-receiving element in the center, and the reflected light 18b corresponding to the sub-beam 18a is detected by the two-divided peripheral light receiving element. It is detected by a light receiving element, and the main beam is used to calculate an HF signal as pit information and a focus error signal, and the sub beam 18 is used to calculate a tracking error signal (see FIG. 5).

As described above, the arithmetic processing in the optical pick-up amplifier of the present invention is exactly the same as in conventional non-integrated optical pickups, so when high-speed access is desired in conventional CD players, etc., there is no need to replace peripheral electronic circuits. , it would be sufficient to simply convert the optical big amplifier to an integrated type.

FIG. 3 is a sectional view showing a second embodiment of the optical pickup according to the present invention, and in FIG. 3, the same numbers as in FIG. 12 indicate the same members. In this embodiment, another grating 7 is provided in the optical path between the grating coupler 5 and the transparent Fi 8 on its front surface (the surface opposite to the waveguide 2) to divide the parallel output light 16 into three. A transparent plate 6 is arranged. Therefore, since the Fresnel lens for condensing light onto the optical disk does not need to have a three-division function, unlike the first embodiment described above, a single Fresnel lens 10 is provided on the front surface of the transparent plate 8. It is provided. The materials of the grating 7 and the transparent plate 6 are Corning #7059. It is BK7.

In the second embodiment, parallel emitted light 16 from the grating coupler 5 is diffracted by a grating 7 fabricated on a transparent plate 6, and the 0th-order and ±1st-order diffracted lights are used as three beams. The light divided into 3 beams is passed through a Fresnel lens 10.
The light is focused on the bits of the optical disk. The optical path of the reflected light from the optical disk and the arithmetic processing for detecting each signal are the same as those in the first embodiment, so the explanation thereof will be omitted.

Compared to the first embodiment, this second embodiment requires an extra grating 7 to diffract the parallel emitted light 16 from the grating coupler 5, but it requires a Fresnel lens to condense the light onto the optical disk. Since the aperture can be made wider, it has the advantage of excellent light collection characteristics.

Note that in both of the above two embodiments, the grating coupler 5
Although the emitted light is parallel light, it is needless to say that the same configuration is possible even if the light emitted from the parallel light is convergent light.

〔Effect of the invention〕

As detailed above, according to the present invention, when high-speed access is desired in a commercially available CO player, etc., it is sufficient to simply change the optical pink amplifier to an integrated type (or to use the conventional electronic circuit for signal calculation as it is). Therefore, when developing an optical disk device that requires high-speed access, you can achieve the required high-speed access by simply changing the optical pickup in a conventional optical disk device. As a result, the present invention has excellent effects such as promoting the spread of integrated optical pickups.

[Brief explanation of the drawing]

FIG. 1 is a plan view and a cross-sectional view showing the structure of a first embodiment of an optical pink-up according to the present invention, and FIG. 2 is a cross-sectional view near the light receiving element of the first and second embodiments of an optical pickup according to the present invention. figure,
FIG. 3 is a cross-sectional view showing the configuration of a second embodiment of the optical pink amplifier of the present invention, and FIG. 4 is a perspective view showing the configuration of a non-integrated optical pink-up used in a general optical disk device. , FIG. 5 is an enlarged plan view of the vicinity of a six-divided light receiving element, and FIG. 6 is a perspective view showing the configuration of a conventional integrated optical pickup. 1... Semiconductor laser 2... Waveguide 4... Substrate 5... Grating coupler 9a, 9b, 9c,
10.11... Fresnel lens 12... Grating lens 13... Light receiving element

Claims (1)

[Claims] 1. A light source, a waveguide that guides light from the light source, a grating coupler that emits the light guided by the waveguide toward an optical disk, and a grating coupler that receives reflected light from the optical disk. In an optical pickup having integrated light-receiving elements, the light-receiving element is a six-segment type light-receiving element, and means for dividing the light emitted from the grating coupler into three and focusing the light on three points on the optical disk; a condensing means for condensing the reflected light from the optical disk onto the six-divided light receiving element; and a condensing means provided in an optical path between the light condensing means and the six-divided light receiving element to condense the light in only one direction. What is claimed is: 1. An optical pickup comprising: means having an effect of causing