JPH03260920A - light detection device - Google Patents

Abstract

PURPOSE:To allow the detection of a focus error signal with a high sensitivity and to make high-speed accessing with a small size by disposing a grating coupler and an optical waveguide element on an introducing optical path of the reflected light from a optical medium. CONSTITUTION:The exit light from a semiconductor laser 26 is reflected by an optical disk 27 and is introduced into a signal detecting optical system 28. The optical waveguide element 29 is disposed on the optical path in an optical system 28. The element 29 is formed with an optical waveguide 32 via a buffer layer 31 on a substrate 30. The grating coupler 34 is formed in the position deviated from the optical axis A of the reflected light 33 from the optical disk 27 and photodetectors 35 are formed at both ends with the coupler 34 in-between. The light entering through the coupler 34 progresses in the optical waveguide 32 and is detected by the photodetectors 35. This light is sent via an amplifier 40 to the outside and the value of a focus error signal F0 is determined.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a photodetection device that records and reproduces information using an optical information recording medium such as a magneto-optical disk and detects focus error signals and the like.

Conventional Technology There are various types of conventional photodetection devices.
First, the first conventional example will be explained based on FIG. 9.

Light emitted from a semiconductor laser l serving as a laser light source is collimated by a collimator lens 2, sequentially passes through a beam shaping prism 3 and a polarizing beam splitter 4, is reflected by a reflecting mirror 5, and is focused by an objective lens 6. Magneto-optical disk 7 as an optical information recording medium
The surface of the device is irradiated with light, thereby recording or reproducing information. Further, the repulsed light from the magneto-optical disk 7 is guided into the signal detection optical system 8 via a separate lens 6, a repulsion mirror 5, and a polarizing beam splitter 4. Here, the reflected light passes through the 1/2 wavelength plate 9, is condensed by a condensing lens 10, is split into two by a polarizing beam splitter 11, and is separated into transmitted light T and reflected light. In this case, the transmitted light T is detected by the two-split light receiving element 12, whereby the tracking error signal Tr is detected. Further, the reflected light sequentially passes through a wedge prism 13 and an optical lens 14 and is guided to a four-division light receiving element 15, whereby a focus error signal Fo is detected. Furthermore, the reproduced signals MO and Rf can be detected by determining the sum and difference between the detected track error signal Tr and focus error signal F○.

Next, a second conventional example will be explained based on FIG. 10. A leading wave path 18 is formed on the substrate 16 via a buffer layer 17, and a semiconductor laser 19 is provided at the end of the leading wave path 18.
The light that has been emitted and converted from the above propagates through the leading wave path 18, passes through the grating 20 and the condensing grating coupler 21 in order, and is irradiated onto the surface of the magneto-optical disk 22 as an optical information recording medium. The information is recorded by

Further, the reflected light from the magneto-optical disk 22 is guided into the leading waveguide 18 again by the condensing grating coupler 21, divided into two parts by the grating 20, and travels through the optical detectors provided two on the left and right sides. The magneto-optical signal Rf, which is a reproduced signal, is guided to the
A focus error signal Fo and a track error signal Tr can be detected. These detected signals are then sent to the outside via the amplifier 24 to perform various controls.

Here, a general method of detecting the focus error position F○ in the conventional example as described above will be summarized and shown in FIGS. 11 to 15. FIG. 11 shows the critical angle method, using two divided light-receiving surfaces a and b of the light-receiving element 25,
It can be detected by Fo=ab. Figure 12 shows the astigmatism method, in which the light receiving surfaces are divided into four parts a, b,
Using c and d, it can be detected by Fo = (a + c) - ('b + d). Figure 13 shows the beam size method (concentric circle method), using two three-part light-receiving surfaces a, b, c, d, e, f, FO = (a + c + e) (b (10d10f) can be detected. FIG. 14 shows the Naifezi method, in which detection can be performed using two divided light-receiving surfaces a and b and F○=a−b. Figure 15 shows the Foucault method, using two two-part light-receiving surfaces a, b, c, and d.
-(a0d) (b0c) can be detected.

Problems to be Solved by the Invention In the case of the first conventional example described above, the focus error signal F
○ is detected by the Foucault method, and the track error signal Tr
is detected by the bush-pull method, and the reproduced signal is detected as a pit reading signal by taking the sum and difference of these two signals. However, in the case of such a writing and reading device, the configuration including the signal detection optical system 8 is extremely complicated and large-scale.

Therefore, as a solution to this problem, there is a device as described in the second conventional example. As a result, the number of parts can be reduced, the device can be made smaller and more integrated, and high-speed access can be performed at the time of seeking. However, once the light emitted from the semiconductor laser 19 is guided into the optical waveguide 18,
In the method of emitting light to the outside again using the condensing grating coupler 21, the loss of light becomes very large, and there is a possibility that it will not be possible to obtain a sufficiently large power during writing.

Means for Solving the Problem Therefore, in order to solve such problems, claim 1
In the invention described, information is recorded by condensing light emitted from a laser light source with an objective lens and irradiating a light spot onto the surface of an optical information recording medium, and at the same time, the reflected light from the optical information recording medium is recorded. In a photodetecting device that detects a reproduced signal or a focus error signal by guiding the reflected light from the optical information recording medium into the signal detecting optical system, the reflected light is A grating coupler was formed at a position deviated from the optical axis of the light, and a guiding waveguide element in which a light receiving element was formed on both sides of the grating coupler was disposed.

In the invention according to claim 2, the light emitted from the laser light source is focused by the objective lens and a light spot is irradiated onto the surface of the optical information recording medium to record information, and the information is recorded from the optical information recording medium. In a photodetection device that detects a regenerated signal or a focus error signal by guiding reflected light into a signal detection optical system, at least two or more types of grating couplers with different coupling widths are arranged at positions offset from the optical axis of the reflected light. A leading waveguide element having a light-receiving element formed thereon was disposed on both sides sandwiching these two couplers.

According to the invention described in claim 1, the vertical incidence coupling characteristic of the grating coupler is utilized by adjusting in advance so that the reflected light from the optical information recording medium is perpendicularly incident on the optical waveguide element when focused. Thus, it becomes possible to detect a focus error signal with excellent detection sensitivity.

According to the invention as set forth in claim 2, the defocus state can be detected in a narrow range near the focal point by using the grating coupler with a large coupling width or aperture, and the defocus state can be detected in a wide range away from the focal point by using the grating coupler with a narrow coupling width or aperture. It is possible to detect a defocus state, thereby making it possible to detect a focus error signal with high sensitivity over a wide range.

Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 5.

First, in FIGS. 1 to 3, light emitted from a semiconductor laser 26 as a laser light source is reflected by an optical disc 27 as an optical information recording medium, and is reflected by a signal detection optical system 28.
An optical waveguide element 29 is disposed on the optical path guided inside. In this guide waveguide element 29, an optical waveguide 32 is formed on a substrate 30 with a buffer layer 31 interposed therebetween. Further, a grating coupler 34 is formed at a position offset from the optical axis A of the reflected light 33 from the optical disk 27, and furthermore, light receiving elements 35 are formed at both ends of the grating coupler 34.

FIG. 3 shows the situation when the guiding waveguide element 29 is disposed within an optical system that can detect a focus error signal. In this case, the light emitted from the semiconductor laser 26 is collimated by the collimating lens 36, transmitted through the polarizing beam splitter 37, passed through the 1/4 wavelength plate 38, and condensed by the objective lens 39 to form the optical disc 27. The reflected light 33 is reflected by the polarizing beam splitter 37, and the light beam B is irradiated onto the surface of the guide waveguide element 29 disposed within the signal detection optical system 28. As a result, the light incident through the grating coupler 304 travels within the leading waveguide 32, is detected by the light receiving element 35, and is sent to the outside via the amplifier 40, so that the value of the focus error signal F○ can be determined. .

As described above, by detecting the focus error signal Fo, it is possible to check whether the focus of the light beam B focused by the objective lens 39 is located on the surface of the optical disk 27 or not. That is, when the beam is focused on the surface of the optical disk 27, the beam state of the reflected light 33 toward the optical waveguide element 29 becomes parallel, and the beam state of the reflected light 33 toward the optical waveguide element 29 becomes parallel.
When the optical disk 7 is far from the focused position, the beam state of the reflected light 33 heading toward the optical waveguide element 29 becomes a focused beam, and conversely, when the optical disk 27 is closer to the optical waveguide element 29
The beam state of the reflected light 33 heading towards the light beam 9 becomes diverging light. Therefore, it is sufficient to detect the inclination of the beam state of such reflected light 33 using the grating coupler 34.

Therefore, we will now examine how the amount of guided light C changes depending on the incident angle O of reflected light 33 on leading waveguide element 29. FIG. 4 shows its operating principle. The grating coupler 34 formed on the leading waveguide 32 has a coupling condition slightly shifted from the normal incidence (θ-0°) condition. Therefore, as shown in FIG. 4(a), when O=o', there is no waveguide coupling at the maximum amount of light, but since it has a symmetrical structure, the guided light C is guided by the same amount of light to the left and right, As shown in FIG. 5(a), a symmetrical waveform is obtained. However, as shown in FIGS. 4(b) and 4(c), the incident angle 0 deviates slightly from the vertical (θ〉O2
0<0>, the amount of guided light C guided left and right becomes unbalanced, and if we take the difference between the signals of the amount of light detected on the left and right sides, we get a figure 8 curve as shown in Figure 5(b). is obtained, and a waveform in which the signal output becomes O when θ=O° can be obtained.

Therefore, using such an operating principle, the reflected light 33 is made incident from the grating coupler 34 of the optical waveguide element 29, and the resulting guided light C is transmitted to the left and right light receiving elements 35.
By detecting the difference signal and taking the difference signal, it enters the grating coupler 34 perpendicularly at the time of focusing, so the focus error signal F○ becomes Fo=O and is not detected. lens 3
If you move too far away from or too close to 9, a difference will appear in the outputs of the left and right light receiving elements 35, so Fo≠
This means that the defocus state can be detected.

Next, a second embodiment of the present invention will be described based on FIGS. 6 to 8. In the first embodiment described above, one grating coupler 34 is formed in the leading waveguide element 29, but in this case, two grating couplers having different shapes are used. That is, the guiding waveguide element 29 includes a first grating coupler 41 as a grating coupler with a large coupling width (aperture) and a grating coupler with a small coupling width (aperture) at a position offset from the optical axis of the reflected light 33. A second nigerating coupler 42 is formed. below,
The reason why grating couplers 41 and 42 having different coupling widths (hereinafter referred to as apertures) are formed will be explained.

In the case of the first four gratings with large openings in the bonding direction as shown in FIG. 7(a), the bonding characteristics are as follows.
As shown in Figure (b), the peak width of the waveform 43 of the output signal (focus error signal) is very narrow, and the output value within that narrow region is large. Also, Figure 8 (
A second nigerating 42 with a small opening as shown in a)
In this case, the coupling characteristic becomes as shown in FIG. 8(b), and the peak width of the waveform 44 becomes wider. Therefore, by combining the first grating 41 and the second grating 42, the coupling characteristic becomes a combination of both, resulting in a waveform as shown in FIG. 6(C). It becomes 45.

Therefore, in this embodiment, by forming the first and second nigerating couplers 41 and 42 having apertures of different sizes, the detection sensitivity of the focus error signal near the in-focus point is high, and the detection sensitivity is high in the area far from the in-focus point. Although the detection sensitivity of the focus error signal becomes low, it becomes possible to perform control over the store range accordingly.

In the graphs representing waveforms 43, 44, and 4.5, the vertical axis represents the output value of the focus error signal FO, and the horizontal axis represents the defocus amount, which is expressed as df. However, the waveform d is between the objective lens 39 and the optical disk 27.
, and f indicates the focal length therebetween. Further, the guide waveguide element 29 can be bonded to the side surface of the polarizing beam splitter 37 using an adhesive 46, as shown in FIG.

Effects of the Invention The invention as set forth in claim 1 is characterized in that a grating coupler is formed at a position offset from the optical axis of the reflected light in the optical path in which the reflected light from the optical information recording medium is guided into the signal detection optical system. Since a leading waveguide element with light receiving elements formed on both sides of the grating coupler is arranged, adjustment is made in advance so that the reflected light from the optical information recording medium enters the optical waveguide element perpendicularly when focused. This makes it possible to detect focus error signals with excellent detection sensitivity by utilizing the vertical incidence coupling characteristics of the grating coupler, and also allows for miniaturization and weight reduction, resulting in high speed during seek. Access can be achieved.

Further, the invention according to claim 2 provides a light guide in which at least two or more types of grating couplers having different coupling widths are formed at a position offset from the optical axis of reflected light, and light receiving elements are formed on both sides of these two couplers. Since the waveguide element is provided, the defocus state can be detected in a narrow range near the focal point by the first grating coupler with a large coupling width or aperture, and the defocus state can be detected in a narrow range near the focal point by the first grating coupler with a large coupling width or aperture. Since the defocus state can be detected over a wide range, it is possible to detect a focus error signal with high sensitivity over a wide range.

[Brief explanation of drawings]

Fig. 1 is a front view of a guiding waveguide element showing a first embodiment of the present invention, Fig. 2 is a side view thereof, Fig. 3 is a configuration diagram showing the structure including other optical systems, and Fig. 4 is a guiding waveguide element. FIG. 5 is an explanatory diagram showing how the amount of guided light changes depending on the incident angle condition of the light incident on the element. FIG. ) is a configuration diagram showing the second embodiment of the present invention, FIG. 6(b) is a waveform diagram showing the state of guided light guided in the optical waveguide, and FIGS. 7 and 8 are the gratings. An explanatory diagram for creating a coupler, Fig. 9 is a block diagram showing the first conventional example, Fig. 10 is a block diagram showing the second conventional example, and Figs. 11 to 15 are focus error signal detection. FIG. 26... Laser light source, 27... Optical information recording medium, 2
8... Signal detection optical system, 33... Reflected light, 34...
・Grating coupler, 35... Light receiving element, 39・
・Objective lens, 41.42... Grating coupler Applicant Rico Co., Ltd. 17 8 3 ``Ittoku Sei- 4'' 41 (a) (b) To Z, J, 15 Figure (a) 137-

Claims (1)

[Claims] 1. Recording information by condensing light emitted from a laser light source with an objective lens and irradiating a light spot onto the surface of an optical information recording medium, and recording information from the optical information recording medium. In a photodetection device that detects a reproduced signal or a focus error signal by guiding reflected light into a signal detection optical system, the reflected light from the optical information recording medium is placed on an optical path guided into the signal detection optical system. . A photodetecting device comprising: a grating coupler formed at a position offset from the optical axis of the reflected light; and an optical waveguide element having light receiving elements formed on both sides of the grating coupler. 2. The light emitted from the laser light source is focused by an objective lens and a light spot is irradiated onto the surface of the optical information recording medium to record information, and the reflected light from the optical information recording medium is detected by signal detection optics. In a photodetecting device that detects a reproduced signal or a focus error signal by guiding the reflected light into the system, at least two types of grating couplers with different coupling widths are formed at a position offset from the optical axis of the reflected light, and these two couplers 1. A photodetecting device comprising an optical waveguide element having a light receiving element formed on both sides thereof.