JPH04212107A - Waveguide type photodetecting device and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve the detection sensitivity of a focusing error signal by arranging a light refracting element on the optical path of a photodetector in front of the incident direction. CONSTITUTION:Guided light (a) which is guided into a waveguide path 11 is made incident on the light refracting element 12, then, separately received by two photodetectors 10a and 10b on left and right sides. That means, the light which is guided so as to be made incident on an insensitive part between two photodetectors 10a and 10b among the guided light (a) can be also guided into the left and right photodetectors 10a and 10b. Thus, the width of the insensitive part between the photodetectors 10a and 10b can be effectively made zero.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a waveguide-type photodetection device in which light guided through an optical waveguide is received by a plurality of light-receiving elements, and a method for manufacturing the same.

2. Description of the Related Art A conventional waveguide type photodetecting device includes, for example, one shown in FIG. That is, a buffer layer 2 made of a thermal oxide film is formed on a substrate 1 made of Si, and an optical waveguide layer 3 is laminated on the surface of this buffer layer 2. A focusing beam splitter 4 and a focusing grating coupler 5 are formed on the optical waveguide layer 3. Further, two light receiving elements 6a to 6d are disposed on the lower surface side of the optical waveguide 3, adjacent to each other on the left and right sides.

These light receiving elements 6a to 6d are connected to an amplifier circuit 7. A laser light source 8 is located at the end face of the optical waveguide 3.
is provided. Further, an optical disk 9 as an optical information recording medium is provided above the condensing grating coupler 5.

In such a configuration, the light emitted from the laser light source 8 is guided into the optical waveguide 3, passes through the focusing beam splitter 4, is emitted upward by the focusing grating coupler 5, and is directed toward the surface of the optical disc 9. The light is irradiated onto the surface, thereby recording information and the like. Further, the reflected light from the optical disk 9 is guided into the optical waveguide 3 by being coupled to the condensing grating coupler 5 again. Then, the guided light is split into two by a condensing beam splitter 4,
Light receiving elements 6a, 6b, 6c, 6 provided two on each side
The light is focused between the distances Δx and Δy of d. In this case, the distance Δ between the light receiving element 6a and the light receiving element 6b
The beams guided during the distance x and the distance Δy between the light receiving element 6c and the light receiving element 6d are respectively detected by the light receiving elements located on the left and right sides, and the resulting light amount is sent to the amplifier circuit 7. , a focus error signal Fo, a track error signal Tr, and a reproduction signal W can be obtained by performing arithmetic processing on the mutual sum signal, difference signal, etc. as necessary.

Problems to be Solved by the Invention When a plurality of light receiving elements 6a to 6d (here, two on the left and right) as described above are formed on the substrate 1, the distance Δx between the light receiving elements 6a and 6b is , and the distance Δy between the light-receiving element 6c and the light-receiving element 6d cannot both be set to 0, and require a minimum distance of several μm or more. The structure is such that the light incident on the portions having the intervals Δx and Δy is not received by any of the light receiving elements 6a and 6b (or the light receiving elements 6c and 6d) located on both sides thereof. Therefore, when detecting a focus error signal that detects subtle positional fluctuations of the focal point, the intervals Δx and Δy become insensitive areas for signal detection, which causes a decrease in the detection sensitivity of the focus error signal. It had become.

Means for Solving the Problem Therefore, in order to solve such problems, claim 1
In the described invention, an optical waveguide for guiding light emitted from a light source is formed on a substrate, and a waveguide type is provided with a plurality of light receiving elements for receiving guided light guided within the optical waveguide. In the photodetection device, two of the light receiving elements are set as one set, and a light refraction element is provided on the incident optical path in front of each set of light receiving elements to branch and guide the guided light to each light receiving element.

In the invention according to claim 2, in the invention according to claim 1, the equivalent refractive index of the optical waveguide and the optical refraction element are N1 and N, respectively.
2, and when the changes in the equivalent refractive index with respect to the wavelength change of the guided light are ΔN1 and ΔN2, so as to satisfy the following relationship,
The optical waveguide and the optical refraction element were formed.

In the invention according to claim 3, there is provided an optical waveguide for guiding the light emitted from the light source on the substrate, a plurality of light receiving elements for receiving the guided light guided in the optical waveguide, and a plurality of light receiving elements for receiving the guided light guided within the optical waveguide. The waveguide optical system that defines the optical path and the light receiving element are combined into one
When forming a light refraction element which branches and guides the guided light for each light reception element on the incident optical path in front of each set of light reception elements, the planar shape of the waveguide optical system and the light refraction element is determined. were formed simultaneously by the same process.

Effect The invention as claimed in claim 1 allows the distance between the two light receiving elements to be "effectively" infinitely small or zero by arranging the light refraction element on the optical path in front of the light receiving element. .

According to the invention as set forth in claim 2, the path of the guided light and the light receiving position do not change even when the wavelength of the incident light changes.

According to the third aspect of the invention, the positional accuracy between the waveguide and the photodetection system can be improved.

Embodiment First, a first embodiment of the invention as claimed in claim 1 will be described based on FIG. Note that in this embodiment, the light receiving element 10a,
The structure of the waveguide type photodetector in other parts can be any form, such as the same as that described in the prior art (see Fig. 8). Since this is possible, the explanation here will be omitted.

An optical waveguide 11 is formed on a substrate (not shown),
In this optical waveguide 11, two light receiving elements 10a and 10b are arranged close to each other with an interval Δ. A light refraction element 12 is disposed on the optical path in front of these optical waveguides 11. This light refractive element 12 is formed in such a manner that two triangular so-called planar prisms have their vertices P in contact with each other.

In such a configuration, the guided light a guided into the optical waveguide 11 enters the light refraction element 12.

As a result, the guided light a, except for the light incident on the point P, is divided into two in the direction indicated by the above-mentioned arrow, and distributed to the left and right two light receiving elements 10a and 10b to be received.

By providing the light refraction element 12 on the optical path just before the light receiving elements 10a and 10b, the guided light a can be guided so that it enters the insensitive portion between the two light receiving elements 10a and 10b. Since the light that has been transmitted can also be guided to the two left and right light receiving elements 10a and 10b, the width of the insensitive portion (area of interval Δ) of the light receiving elements 10a and 10b, which has been a problem in the past, can be effectively reduced to 0. can do.

Therefore, this can significantly improve the detection sensitivity of the device.

In this case, the light refraction portion of the light refraction element 12 can be realized by forming its equivalent refractive index to be different from the equivalent refraction index of the surrounding optical waveguide 11. Specifically, it is possible to form only the material of the light refraction part with another material, to dope the original optical waveguide 11 with another material, or to dope a part of the material forming the original optical waveguide 11 with another element. It can be manufactured using well-known techniques such as replacing the optical waveguide 11 with the optical waveguide 11, providing a loading layer below or above the optical waveguide 11, or changing the thickness of the optical waveguide 11.

Next, the second embodiment will be explained based on FIG. 2.

This is a modification of the shape of the light refractive element 12. That is, here, the planar prism shape of the light refraction element 12 is formed only in the vicinity of the interval Δ between the light receiving elements 10a and 10b, so that its refraction angle is large. As a result, the distance Δ between the light receiving elements 10a and 10b
The optical path does not change significantly in areas other than the vicinity of , and the thickness of the light refractive element 12 in the waveguide direction can be reduced.

Next, the third embodiment will be explained based on FIG. 3.

Here, we avoid point connections where two planar prisms touch at their vertices, and connect their connected parts to points PQ in the figure.
It is formed with a constant width W shown in between.

As a result, a dead part is formed by the width W, but since the width W can be made narrower than the interval Δ between the light receiving elements 10a and 10b, the two light receiving elements 10a
, 10b, while effectively reducing the width of the dead part between the two vertices, it is possible to eliminate the difficulty in manufacturing the structure in which the two vertices touch, and to eliminate the manufacturing deviation from perfect point contact. It is possible to prevent light scattering at that part due to

Next, the fourth embodiment will be explained based on FIG. 4.

Here, the light refractive elements 12 are not formed in the shape of a planar prism as in the past, but are instead formed in the shape of convex lenses each having a light condensing property. As a result, the focused light is guided to the light receiving elements 10a, 10b, so the light receiving area of the light receiving elements 10a, 10b can be reduced accordingly, which is advantageous for high-speed response. be able to.

Next, the fifth embodiment will be described based on FIGS. 5(a) and 5(b). While the light refractive element 12 described so far has a case where its equivalent refractive index is larger than the equivalent refractive index of the surrounding optical waveguide 11, here, on the contrary, the equivalent refractive index of the light refractive element 12 is larger than the equivalent refractive index of the surrounding optical waveguide 11. An example is shown in which the smaller one is smaller. That is, in FIGS. 5(a) and 5(b), since the equivalent refractive index of the light refractive element 12 is smaller than the equivalent refractive index of the surrounding optical waveguide 11, the shape of the light refractive element 12 is changed to the first shape. In contrast to the embodiments 1 to 3, the planar prism shape is thickest at the center, which is the branching point of the optical path, so that the same effect is achieved. In addition, a concave lens shape corresponding to the fourth embodiment is also possible. With these, it is possible to further improve the degree of freedom in the arrangement positions of the light receiving elements 10a, 10b and the light refraction element 12, depending on the incident direction and focusing state of the guided light a.

As described above, the configurations shown in the first to fifth embodiments are applicable not only to two light receiving elements, but also to a structure in which a large number of light receiving elements are arranged in an array. A light refraction section can be provided corresponding to the insensitive portion.

Next, the sixth embodiment will be explained based on FIG. 6.

In all of the embodiments described so far, the light refractive element 12 distributes light symmetrically to the two light receiving elements, but here, the light refractive element 12 having an asymmetric structure is used to distribute the light between the two light receiving elements 10a. , 10b. Along with this, one of the light receiving elements 10a, 10b
The location of the will also change. As a result, the two light receiving elements 10a and 10b can be arranged with a large distance between them, and the manufacturing method thereof can be made easier accordingly.

Next, an embodiment of the invention according to claim 2 will be described. In this example, when the equivalent refractive index of the optical waveguide 11 and the light refractive element 12 are respectively N1 and N2, and the changes in the equivalent refractive index with respect to the wavelength change of the guided light a are respectively ΔN1 and ΔN2, the following conditional expression is satisfied. An optical waveguide 11 and a light refraction element 12 are formed as shown in FIG.

By forming each part so as to satisfy such a conditional expression, the refraction angle at the light refraction element 12 does not change even if the wavelength of the light incident on the light receiving elements 10a, 10b changes. Therefore, even if the wavelength of the guided light a changes, the path of the guided light a and the light receiving positions of the light receiving elements 10a and 10b do not change, and the fluctuation of the detection signal can be reduced.
This makes it possible to further improve the stability of the detection sensitivity of the device. In other words, even if the wavelength of the guided light a changes, the guided wave path from the light refraction element 12 to the light receiving elements 10a and 10b does not change.
Waveguide characteristics such as waveguide loss of the optical waveguide 11 and the light receiving element 10a
, 10b, furthermore, the coupling efficiency to the light receiving elements 10a, 1
It is possible to avoid fluctuations in signal output characteristics due to differences in waveguide paths due to local variations in sensitivity of 0b and the like.

Next, an embodiment of the invention according to claim 3 will be described. This embodiment describes an example of a method for manufacturing a waveguide type photodetector. That is, the light refraction element 12 and the planar shape of the waveguide optical system that determines the optical path leading to the light refraction element 12 are simultaneously formed in the same process.

FIG. 7 shows the planar shape of the device obtained by the manufacturing method. On the optical waveguide 11, there are two light receiving elements 10a, 10b, 10c, 10d on the left and right sides and a light refractive element 1.
In addition to 2, a coupling element 14 (such as a grating coupler) is provided. Two waveguide condenser lenses 15 as a waveguide optical system are disposed on the optical path between the coupling element 14 and the light refraction element 12. As a result, the light coupled into the optical waveguide 11 from the outside by the coupling element 14 is separated into two directions by the waveguide condenser lens 15, and is transmitted to the light receiving element 1 via the light refraction element 12.
Various signals can be detected by being detected at 0a, 10b, 10c, and 10d.

In this case, the waveguide condenser lens 15 and the light refraction element 12 can be formed simultaneously in the same process and with the same film structure. That is, in order to produce the planar shape of such a structure, for example, photolithography technology can be used.

Therefore, by using this technique and performing photolithography with the light refraction element 12 and the waveguide condensing lens 15 as patterns on one photomask, the positional error between them can be made extremely small. This is because the pattern position accuracy within one photomask is usually one or more orders of magnitude higher than the mask position accuracy for patterns formed by other masks when exposing this photomask.

As described above, the light refractive element 12 and the waveguide condenser lens 1
5 and 5 at the same time in the same process, or when forming these separately or when aligning the light receiving elements 10a, 10b, 10c, 10d and the waveguide condenser lens 15 without providing the light refraction element 12. Compared to this, the relative position accuracy between the guided light condensing position and its detection system is increased, so the accuracy of light detection such as a focus error signal can be improved.

Note that, as long as the steps for simultaneously determining the planar shapes of the light refractive element 12 and the waveguide condensing lens 15 are the same and are performed at the same time, it is not necessary that the processing steps of their film structures are the same. That is, instead of using the waveguide condenser lens 15 and the light refraction element 12 having the same film cross-sectional structure as described above, a combination with a grating structure, a waveguide mirror structure, etc. is also possible. These are patterned into a planar shape using the same photolithography, and then the waveguide optical system and the light refractive element 12 are formed using a mechanical mask or the like.
This can be achieved by etching only one of them, laminating a film on only one with the premise of lift-off, or providing a loading layer on only one in advance.

Effects of the Invention The invention described in claim 1 is characterized in that an optical waveguide for guiding light emitted from a light source is formed on a substrate, and a plurality of light receiving elements are configured to receive the guided light guided within the optical waveguide. In the provided waveguide type photodetection device, two of the light receiving elements are
Since a light refraction element is provided on the incident optical path in front of each set of light receiving elements to branch and guide the guided light to each light receiving element, the distance between the two light receiving elements can be set as "effectively" as possible. This allows the detection sensitivity of focus error signals to be significantly improved compared to conventional methods.

The invention according to claim 2 is the invention according to claim 1,
The equivalent refractive indices of the optical waveguide and the optical refraction element are N1 and N2, respectively.
Since the optical waveguide and the optical refraction element are formed so as to satisfy the following relationship, where the changes in the equivalent refractive index with respect to the wavelength change of the guided light are respectively ΔN1 and ΔN2, the guided light received by the light receiving element is It is possible to reduce fluctuations in the detection signal due to wavelength fluctuations of the wave light, thereby further improving the stability of the zero point and sensitivity of the present device.

The invention according to claim 3 includes: an optical waveguide for guiding light emitted from a light source on a substrate; a plurality of light receiving elements for receiving the guided light guided within the optical waveguide; a waveguide optical system that defines an optical path; and a light refraction element that divides and guides the guided light onto an incident optical path in front of each set of light-receiving elements, with the two light-receiving elements forming a set. When forming the waveguide optical system and the light refractive element, the planar shapes of the waveguide optical system and the light refractive element were simultaneously formed in the same process, so that fluctuations in the relative position of the light receiving element formed in the optical waveguide can be extremely reduced. Since the positional accuracy between the waveguide and the photodetection system can be improved, the detection accuracy of the present device can be improved, and the uniformity during mass production can be increased.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a first embodiment of the invention as claimed in claim 1, Fig. 2 is a block diagram showing a second embodiment thereof, and Fig. 3 is a block diagram showing a third embodiment thereof. , FIG. 4 is a block diagram showing the fourth embodiment, FIG. 5 is a block diagram showing the fifth embodiment, FIG. 6 is a block diagram showing the sixth embodiment, and FIG. 7 is a block diagram showing the sixth embodiment. FIG. 8 is a block diagram showing an embodiment of the invention as claimed in claim 3, and FIG. 8 is a block diagram showing a conventional example. 10... Light receiving element, 11... Optical waveguide, 12... Light refractive element,
15... Waveguide optical system, a... Waveguide optical applicant Ricoh Co., Ltd.

Claims (3)

[Claims] 1. A waveguide type in which an optical waveguide is formed on a substrate to guide light emitted from a light source, and a plurality of light receiving elements are provided to receive the guided light guided within the optical waveguide. In the photodetecting device, two of the light receiving elements are set as one set, and a light refraction element is provided on the incident optical path in front of each set of light receiving elements to branch and guide the guided light for each light receiving element. Features of waveguide type photodetection device. 2. When the equivalent refractive index of the optical waveguide and the light refractive element are respectively N1 and N2, and the change in the equivalent refractive index with respect to the wavelength change of the guided light is respectively ΔN1 and ΔN2, the following relationship is satisfied. 2. The waveguide type photodetecting device according to claim 1, wherein the optical waveguide and the photorefraction element are formed. 3. An optical waveguide for guiding light emitted from a light source on a substrate, a plurality of light receiving elements for receiving the guided light guided within the optical waveguide, and defining an optical path of the guided light. and a light refraction element that divides and guides the guided light for each light receiving element on an incident optical path in front of each set of light receiving elements, with the two light receiving elements forming a set. A method for manufacturing a waveguide type photodetecting device, characterized in that the planar shapes of the waveguide optical system and the photorefractive element are simultaneously formed in the same process.