JPH04149830A - Optical information recording/reproducing device - Google Patents

Abstract

PURPOSE:To improve light using efficiency by setting the length of a grating coupler to a value longer than the beam diameter of an incident laser beam and allowing the end face of the coupler to coincide with that of the incident beam. CONSTITUTION:An optical integration detecting element 14 is arranged in an optical path formed between a semiconductor laser 10 and an optical disk 13. The element 14 is constituted by laminating an optical waveguide 17 on a substrate 14 through a buffer layer 16, forming the grating coupler 18 on the upper surface of the waveguide 17 and arranging photodetectors 19a to 19c on the lower face of the waveguide 17. The length of the coupler 18 is set to a value longer than the beam diameter of an incident beam inputted from the laser 10 into the coupler 18 and the end face of the coupler 18 is set so as to approximately coincide with that of the incident beam. Thereby, light radiated by decoupling and light reflected on the surface of the coupler 18 are together converged by an objective lens 12 and applied to the surface of the disk 13 to record information. Thus, the light using efficiency can be improved.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an optical information recording/reproducing device.

BACKGROUND OF THE INVENTION FIG. 5 shows an example of a conventional optical information recording/reproducing apparatus. A leading waveguide 3 is laminated on a Si substrate 1 with a buffer layer 2 interposed therebetween. On this leading waveguide 3, a waveguide beam splitter 4 and a condensing grating coupler 5 are provided.
and is provided.

An optical disk 6 as an optical information recording medium is provided above the condensing grating coupler 5. Also,
Two photodetectors 78 to 7d are provided on the left and right sides of the optical waveguide 3, respectively. These photodetectors 7a~
7d is connected to the amplifier circuit 8 so that a signal can be taken out to the outside. Furthermore, a semiconductor laser 9 as a laser light source is attached to the end face of the optical waveguide 3.

In such a configuration, the light emitted from the semiconductor laser 9 is coupled to the end face of the optical waveguide 3 and travels through the optical waveguide 3 as guided light. The guided light passes through a waveguide beam splitter 4 and a condensing grating coupler 5.
The light is diffracted by the light beam, travels upward in the air, and is irradiated onto the surface of the optical disc 6. And optical disc 6
The reflected light enters the condensing grating coupler 5 again and is coupled to the optical waveguide 3 to become guided light.

The guided light is split into two parts by a waveguide beam splitter 4 and received by photodetectors 7a to 7d. In this case, the amount of light received on each light receiving surface of the photodetectors 7a to 7d is A-'.
D, the reproduction signal S output by the amplifier circuit 8
, focus error signal Fo, track error signal Tr
becomes as follows. That is, S=A+B+C+D Fo= (A+D) (B+C)Tr= (
C+D)-(A+B). Note that the focus error signal can be detected using the Foucault method, and the tracking error signal can be detected using the bush-pull method.

Problems to be Solved by the Invention In the case of the conventional device as described above, the light emitted from the semiconductor laser 9 is irradiated onto the surface of the optical disk 6 via the condensing grating coupler 5, and the light reflected from the optical disk 6 is reflected from the optical disk 6. The light is again guided to the optical waveguide 3 via the condensing grating coupler 5. Therefore, the diffraction efficiency (coupling efficiency) of the condensing grating coupler 5 affects the light utilization efficiency in performing light pickup.

Here, an example will be given and explained. The input and output coupling efficiencies of the condensing grating coupler 5 are 20% and 50%, respectively, which is poor efficiency. At this time, estimating the light utilization efficiency, if the excitation efficiency of the guided light from the semiconductor laser 9 to the optical waveguide 3 is a/I O0%, the transmittance of the waveguide beam splitter 4 is 50%, so the light reaches the optical disk 6. The amount of light Pw (%) that reaches the signal detection system and the amount of light Po (%) that reaches the signal detection system are: Pw=aX0.5X0.2 =O, lxaxloo-(1) Po=PwX0.5X0.5XR =0.025XaXRX100- (2) This is the reflectance of the R binary disc.

In these formulas (1) and (2), even if a==1, Pw=10%, Po=0.625% (R=25%)
is a small value.

In the optical pickup used for optical disk memory,
It is necessary to increase the amount of light that reaches the optical disk 6 and the amount of light that reaches the signal detection system as much as possible, but as described above, in the conventional configuration, there is a limit to obtaining the maximum amount of light.

Means for Solving the Problems Therefore, in order to solve such problems, in the present invention, the light emitted from the laser light source is made into parallel light by a coupling lens, and this parallel light is focused by an objective lens. In an optical information recording and reproducing device that records and reproduces information by irradiating an optical information recording medium, the optical information recording and reproducing apparatus includes a leading waveguide formed on a substrate in an optical path between the laser light source and the optical information recording medium, and this optical guide. An optical integrated detection element including a grating coupler formed on the upper surface of the waveguide and a photodetector provided on the lower surface of the optical waveguide is disposed, and the length of the grating coupler is the same as that of the grating. The grating coupler was set to be longer than the beam diameter of the incident beam from the laser light source, and the end face of the grating coupler and the end face of the incident beam were set to substantially coincide with each other.

During the outgoing path of the light emitted from the laser light source toward the optical information recording medium, the length of the grating coupler is set to be longer than the beam diameter of the incident beam from the laser light source, which causes a decoupling phenomenon. In addition, on the return path of the light reflected by the optical information recording medium toward the photodetector, the end face of the grating coupler and the end face of the incident beam of light reflected from the optical information recording medium substantially coincide with each other. This setting makes it possible to prevent the decoupling phenomenon. Therefore, this results in approximately 1 of the light transmitted through the coupling lens.
00% to reach the optical information recording medium, and moreover, it is possible to efficiently guide the reflected light from the optical information recording medium into the leading waveguide, making it possible to create a device with higher light utilization efficiency than before. Obtainable.

Example An embodiment of the present invention will be described based on the drawings.

This figure shows the overall configuration of the present device shown in FIG. 1. Light emitted from a semiconductor laser 10 as a laser light source is converted into parallel light by a coupling lens 11, and this parallel light is passed through an objective lens 1.
2, the optical disc 1 is used as an optical information recording medium.
In the optical information recording and reproducing apparatus that records and reproduces information by irradiating the semiconductor laser 10 and the optical disk 13, an optical integrated detection element 14 is provided in the optical path between the semiconductor laser 10 and the optical disk 13
is installed. In this optical integrated detection element 14, an optical waveguide 17 is laminated on a substrate (Si substrate) 15 with a buffer layer 16 interposed therebetween. A grating coupler 18 is formed on the upper surface of this optical waveguide 17. Further, on the lower surface of the guide waveguide 17, two photodetectors 19a to 19d are arranged on the left and right sides. In this case, the optical waveguide 17 has a curved condensing mirror surface divided into two parts from the center to the end so that the guided light is detected separately by the photodetectors 19a to 19d. 'L7a
, 17b.

Here, as shown in FIG.
The beam diameter is set to be longer than the beam diameter φ of 0, and is set so that the end surface 18a of the grating coupler 18 and the end surface 20a of the incident beam 2o substantially coincide with each other.

In this case, the length of the grating coupler 18 is set so that the beam emitted to the outside is decoupled.
It is longer than the beam diameter φ of the incident beam 2o incident from the semiconductor laser 10.

In such a configuration, the light emitted from the semiconductor laser 10 is converted into parallel light by the coupling lens 11, and the parallel light enters the grating coupler 18 formed on the optical integrated detection element 14. A part of this incident light is reflected by the surface of the grating coupler 18 or the interface of the substrate 15, and the other light is guided into the optical waveguide 17 by the grating coupler 18. The guided light is emitted into the air again from another position (different from the incident position) of the grating coupler 18 (this phenomenon is called decoupling). The light emitted by decoupling in this way is combined with a part of the light reflected on the surface of the grating coupler 18 to be sent to the objective lens 12.
heading towards. The light focused by the objective lens 12 is irradiated onto the surface of the optical disk 13, thereby making it possible to record information.

Further, the reflected light from the optical disk 13 is reflected by the objective lens 12.
When the light enters the grating coupler 18 again through the light, a part of the light is guided and coupled into the optical waveguide 17. At this time, since the wave is guided where there is no grating coupler 18, the phenomenon of decoupling does not occur.

The guided light guided into the optical waveguide 17 as in 2.
Condensing mirror surfaces 17a, 1 formed on the optical waveguide 17
It is divided into two parts at 7b and goes in the direction of photodetectors 198 to 19d. In this case, when the optical disk 13 and the objective lens 12 are in focus, the respective focal points P and Q of the light spot formed by dividing into two are
9b and between the photodetectors 19c and 19d. On the other hand, when the optical disc 13 and the objective lens 12 are out of focus and move away from each other, the focal points P and Q
is shifted in the direction of the photodetector 19a and in the direction of the photodetector 19d. Furthermore, when the focus is moved out of focus, the focal points P and Q are shifted in the direction of the photodetector 19b and the photodetector 19c.

Therefore, by detecting the positional deviation of such focal points P and Q, it is possible to detect the focus error signal Fo, the track error signal Tr, and the reproduction signal S using the same method as described in the prior art. .

As described above, during the outgoing path of the light emitted from the semiconductor laser 10 toward the optical disk 13, the length T of the grating coupler 18 is changed at the grating coupler 18.
is the beam diameter φ of the incident beam 20 that enters the optical waveguide 17
Since the length is set longer than that of the grating coupler 18, the decoupling phenomenon can be utilized, and the light reflected by the optical disk 13 is reflected from the end surface 18a of the grating coupler 18 and the optical disk 13 on the return path toward the photodetectors 19a to 19d. The end face 20a of the incident light beam 20 is set to substantially coincide with the end face 20a of the incident light beam 20, thereby making it possible to prevent a decoupling phenomenon. Therefore, this allows the coupling lens 1
It is now possible to allow almost 100% of the light that has passed through the optical disc 13 to reach the optical disc 13, and moreover, it is possible to efficiently guide the reflected light from the optical disc 13 into the optical waveguide 17. Utilization efficiency can be further increased.

Next, a specific example of this device will be described. Semiconductor laser 1
The wavelength λ of the beam emitted from 0 is 790 nm.

Grating coupler: After forming a SiN layer, a grating is made by photolithography, grating height = 0.02 μm, pitch = 0.94 μm Optical waveguide: 5iON sputtered film n-1,557, d = 1.5 μm Buffer layer , Sl○, thermal oxide film n=1.460. d=1.0 μm where n is the refractive index, d is the film thickness, the beam diameter of the parallel light at the coupling lens 11 was set to 4 mm, and the length of the grating coupler 18 was set to 8 mm.

When the light emitted from the semiconductor laser 10 enters the grating coupler 18 at an incident angle of 45'', the guided light guided into the optical waveguide 17 via the grating coupler 18 is guided as TE mode light. , the guided light is emitted again via the grating coupler 18 and is made incident on the surface of the optical disk 13. At this time, it is reflected and decoupled by the grating coupler 18, and the waveguide light is reflected and decoupled by the grating coupler 18.
The beam diameter of the light directed toward is expanded by about 6 mm due to decoupling, so that on the surface of the optical disc 13,
We were able to reach almost 100% of the light.

In the embodiments described so far, one end surface of the grating coupler 18 and the end surface 20a of the incident beam 20 from the semiconductor laser 10 are set to almost completely match, but this is not necessarily the case. Without,
The positions of these end faces may be slightly shifted. However, in this case, the coupling efficiency to the optical waveguide 17 will decrease slightly, but it is sufficient to obtain an appropriate coupling efficiency desired in terms of design.

Next, a modification of this embodiment will be explained based on FIGS. 3 and 4.

As shown in FIG. 3, since the incident beam 20 is actually round, even if the end surface 20a on one side of the incident beam 2o is made to slightly protrude beyond the end surface 18a of the grating coupler 18, the same result as in the embodiment described above can be achieved. effect can be obtained.

In addition, as shown in FIG. 4, the grating coupler 18
Even if the shape of the end face 18a on one side of the beam is made round to match the shape of the beam, the same effect as in the embodiment described above can be obtained.

Effects of the Invention The present invention provides a light beam that records and reproduces information by converting light emitted from a laser light source into parallel light using a coupling lens, condensing this parallel light using an objective lens, and irradiating it onto an optical information recording medium. In the information recording/reproducing device, an optical waveguide formed on a substrate in an optical path between the laser light source and the optical information recording medium, a grating coupler formed on the upper surface of the optical waveguide, and the optical waveguide. an optical integrated detection element having a photodetector located on a lower surface, and the length of the grating coupler is longer than the beam diameter of the incident beam incident on the grating coupler from the laser light source. Moreover, since the end face of the grating coupler and the end face of the incident beam are set to substantially coincide with each other, the length of the grating coupler is fixed at the grating coupler during the outgoing path of the light emitted from the laser light source toward the optical information recording medium. Since it is set longer than the beam diameter of the incident beam from the laser light source, it is possible to utilize the decoupling phenomenon, and
On the return path of the light reflected by the optical information recording medium towards the photodetector, the end face of the grating coupler and the end face of the incident beam of the light reflected from the optical information recording medium are set to approximately match. Decoupling phenomenon can be prevented. Therefore, this makes it possible to allow approximately 100% of the light transmitted through the coupling lens to reach the optical information recording medium, and also to efficiently guide the reflected light from the optical information recording medium into the optical waveguide. This makes it possible to obtain a device with higher light utilization efficiency than before.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of the present invention, FIG. 2 is a plan view of the optical integrated detection element, and FIG. 3 is a plan view showing the situation when the position of the incident beam is changed. FIG. 4 is a plan view showing how the end face shape of the grating coupler is changed, and FIG. 5 is a perspective view showing a conventional example. 10...Laser light source, 11...Coupling lens, 12...
- Objective lens, 13... Optical information recording medium, 14... Optical integrated detection element, 15... Substrate, 7... Optical waveguide,... Grating coupler, 8a... End surface, 20... Incident beam, 20a...end face, φ...beam diameter Applicant Rico Co., Ltd.

Claims (1)

[Claims] In an optical information recording and reproducing apparatus that records and reproduces information by converting light emitted from a laser light source into parallel light using a coupling lens, condensing this parallel light using an objective lens, and irradiating it onto an optical information recording medium, the above-mentioned An optical waveguide formed on a substrate in an optical path between a laser light source and the optical information recording medium, a grating coupler formed on an upper surface of the optical waveguide, and a grating coupler provided on a lower surface of the optical waveguide. an optical integrated detection element having a photodetector, the length of the grating coupler is longer than the beam diameter of the incident beam incident on the grating coupler from the laser light source, and An optical information recording/reproducing apparatus characterized in that the incident beam is set to substantially coincide with an end face of the incident beam.