JPH0923022A - Photoelectric converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To separate optical signals having a plurality of wavelengths from each other with a small-sized simple structure and, at the same time, to convert the optical signals into electric signals one wavelength by one wavelength by forming an optical waveguide having a double heterojunction by interposing a core layer between first and second clad layers and outputting the electric signals corresponding to the light having a plurality of wavelengths through the clad layers. SOLUTION: A photoelectric converter is constituted of an n-type InP substrate 1, an n-type Inp clad layer 2 formed on the substrate 1, multiple quantum well layers 3 formed on the clad layer 2 as cores, and a p-type clad layer 4 formed on the quantum well layers 3. Because of the quantum well layers 3 formed between the clad layers 2 and 4, a double heterojunction is formed. Therefore, the quantum well layers 3 constitute an optical waveguide. Optical signals having a plurality of wavelengths are made incident to the optical waveguide from one end 5a and advance through the optical waveguide toward the other end 5b.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photoelectric conversion device for converting an optical signal in which lights of a plurality of wavelengths are multiplexed into an electric signal, and in particular, an optical signal is separated into wavelengths and converted into electric signals. The present invention relates to a photoelectric conversion device.

[0002]

2. Description of the Related Art Currently, photoelectric conversion devices are used in various fields including optical communication. For example, in the field of optical communication, laser light of a single wavelength has been conventionally used as an optical signal. However, in recent years, optical signals in which lights of a plurality of wavelengths are multiplexed have come to be used in order to transmit more information.

Conventionally, in the case of converting an optical signal in which lights of a plurality of wavelengths are multiplexed into an electric signal, the following photoelectric conversion device has been used. FIG. 11 shows a configuration example of a conventional photoelectric conversion device. That is, first, the light of each wavelength is separated by the wavelength separating means, and then the plurality of photoelectric conversion units having no wavelength dependence are respectively converted into electric signals.

[0004]

However, the above-mentioned conventional photoelectric conversion device has the following problems. Since the wavelength separation means optically separates the wavelengths, the device tends to be large. The photoelectric conversion device requires not only the wavelength separating means but also a number of photoelectric conversion units corresponding to the number of wavelengths. Therefore, the number of parts increases and the structure tends to be complicated.

Further, there is a problem that an optical coupling means is required between the wavelength separation means and the photoelectric conversion unit.
In view of the above problems, an object of the present invention is to provide a photoelectric conversion device which has a small and simple structure and can separate optical signals of a plurality of wavelengths and simultaneously convert them into electrical signals for each wavelength.

[0006]

Means for Solving the Problems To solve the above problems, the present invention is characterized by taking the following means. The invention device according to claim 1, which is a photoelectric conversion device that converts light of a plurality of wavelengths into electric signals, respectively, and includes a core layer formed of a semiconductor including a plurality of core portions having different energy band gaps, and the core. A first clad layer formed of a semiconductor on the upper side of the layer, and a second clad layer formed of a semiconductor on the lower side of the core layer, wherein the core layer includes the first clad layer and the By being sandwiched between the second cladding layers, an optical waveguide having a double heterojunction is formed, and an electric signal obtained by converting light of a plurality of wavelengths is output via the first cladding layer or the second cladding layer. It is characterized by being done.

In the invention device according to claim 2, the energy band gaps of the first cladding layer and the second cladding layer are larger than any of the energy band gaps of the plurality of core portions of the core layer. And

In the invention device according to claim 3, the plurality of core portions of the core layer are sequentially formed in the light traveling direction of the optical waveguide, and the plurality of core portions propagate light. It is characterized in that it has an energy band gap that decreases stepwise in the direction.

In the invention device according to claim 4, the plurality of core portions of the core layer are sequentially formed in the light traveling direction of the optical waveguide, and the plurality of core portions propagate light. It is characterized by including a quantum well layer whose thickness changes stepwise in the direction.

The invention device according to claim 5 is characterized in that the thickness of the quantum well layers of the plurality of core portions increases stepwise in the direction in which the light of the optical waveguide advances. In the invention device according to claim 6, the first cladding layer is divided into a plurality of parts for each of the plurality of core parts, and a space between the parts is filled with a substance having a low electric conductivity, and each of the parts is divided. Is characterized by having an electrode.

In the invention device according to claim 7, the first clad layer and the core layer are provided for each of the plurality of core portions.
It is characterized in that it is divided into a plurality of parts, a space between the parts is filled with a substance having a low electric conductivity, and each part has an electrode.

According to an eighth aspect of the present invention, the photoelectric conversion device further includes electrodes formed on the first cladding layer for each of the plurality of core portions and electrically isolated from each other. And The invention device according to claim 9, wherein the photoelectric conversion device further includes a drive device that subtracts a predetermined ratio of an electric signal output from another predetermined electrode from an electric signal output from a predetermined electrode. Characterize.

According to a tenth aspect of the present invention, the other predetermined electrode is determined in an order closer to the predetermined electrode according to the traveling direction of the light of the optical waveguide, and the core corresponding to the predetermined electrode. It is characterized in that it is determined based on the light absorption coefficient characteristic of the part.

The invention apparatus according to claim 11 is characterized in that the predetermined ratio is 1 or less. In the photoelectric conversion device according to any one of claims 1 to 5, when light having a plurality of wavelengths is incident, the light is guided to a plurality of core portions having different energy band gaps in the core layer, and the light is guided therethrough. It is converted into an electric signal for each light of the wavelength defined by the energy band gap. In the photoelectric conversion device according to any one of claims 3 to 5, in particular, the wavelength λ1 defined by the energy band gaps of two adjacent core portions.
Light having a wavelength between λ2 and λ2 (λ1 <λ <λ2) has a wavelength λ
2 is selectively converted into an electric signal in the core portion corresponding to 2.

Therefore, it becomes possible for one photoelectric conversion device to detect the change in the intensity of the light of each wavelength in the wavelength-multiplexed light. The photoelectric conversion device of the present invention does not require the wavelength separation element required in the conventional photoelectric conversion device, and can be composed of one photoelectric conversion element. Further, the optical coupling means between the wavelength separation means and the photoelectric conversion unit is unnecessary. Therefore, the number of parts of the photoelectric conversion device as a whole is reduced, and the structure is simplified.

According to another aspect of the photoelectric conversion device of the present invention, the first cladding layer or the first cladding layer and the core layer is divided into a plurality of portions for each of the plurality of core portions. Therefore, the electrodes formed in the respective portions can be reliably separated electrically. According to another aspect of the photoelectric conversion device of the present invention, each of the plurality of core portions further includes electrodes formed on the first cladding layer and electrically isolated from each other. Therefore, the electric signal converted for each wavelength can be reliably extracted from the electrode.

In the photoelectric conversion device according to any one of claims 9 to 11, a predetermined ratio of an electric signal output from another predetermined electrode is subtracted from an electric signal output from a predetermined electrode. It further has a drive unit. Therefore, the wavelength crosstalk can be corrected, and the error in the intensity detection of the light of each wavelength due to the wavelength crosstalk can be reduced.

[0018]

FIG. 1 is a sectional view of a first embodiment of a photoelectric conversion device of the present invention. This photoelectric conversion device has an n-I
An nP substrate 1, an n-InP cladding layer 2 formed on the substrate 1, a multiple quantum well layer 3 as a core formed on the cladding layer, and a multiple quantum well layer 3 formed on the multiple quantum well layer 3. It is composed of the p-InP clad layer 4. A double heterojunction is formed so that the multiple quantum well layer 3 as a core is sandwiched between the n-InP cladding layer 2 and the p-InP cladding layer 4. Therefore, the multiple quantum well layer 3 constitutes an optical waveguide. An optical signal having light of a plurality of wavelengths is incident from one end 5a of this optical waveguide, travels through the optical waveguide formed by the multiple quantum well layer 3, and proceeds toward the other end 5b.

The multiple quantum well layer 3 has a non-doped multiple quantum well structure (details will be described later) in which InGaAs well layers and InGaAsP barrier layers are alternately laminated. In this structure, when light of a wavelength having energy equal to or larger than the energy gap in the quantum well structure is incident, the light is absorbed. The multi-quantum well layer 3 is composed of four multi-quantum well layers 3a, 3b, 3c and 3d having different well layer thicknesses according to the traveling direction of incident light.

Electrodes 6a, 6b, 6c and 6d are formed on the upper surface of the p-InP clad layer 4 corresponding to the multiple quantum well layers 3a, 3b, 3c and 3d, respectively. An electrode 7 is formed on the lower surface of the n-InP substrate 1.
Are formed. FIG. 2 is a diagram showing a detailed configuration of the photoelectric conversion device shown in FIG. Components that are the same as in FIG. 1 are indicated with the same reference numbers. FIG. 3 is similar to FIG.
The multiple quantum well layers 3a, 3b, 3 of the photoelectric conversion device shown in FIG.
It is an energy band figure regarding arbitrary one of c and 3d. The horizontal axis indicates the position in the thickness direction. That is, the energy levels in the n-InP clad layer 2, the multiple quantum well layer 3, and the p-InP clad layer 4 are shown from left to right.

Multiple quantum well layers 3a, 3b, 3c, 3d
2 has a multiple quantum well structure in which InGaAs well layers (black portions in the figure) and InGaAsP barrier layers are alternately laminated, as shown in FIG. The energy band gap of this barrier layer is different from that of the well layer. Therefore, in the multiple quantum well layer 3, the energy band gap changes stepwise as shown in FIG. Electrons are confined in the well layer to form a quantum well due to the gradual drop in energy level.

In FIG. 3, Ec is the lowest energy level in the conduction band, and Ev is the highest energy level in the valence band. When the crystal forming the quantum well is sufficiently thick, that is, when each well layer is thick, the energy band gap at this time is represented by Egi. On the other hand, when the crystal forming the quantum well is thin, quantum level levels 8c and 8v are formed in the well layer. In this case, the quantum level levels 8c and 8
The energy level difference from v is the actual energy band gap Egqw. In this structure, when light of a wavelength having an energy corresponding to the energy band gap Egqw or more is incident, it is absorbed and activates electrons.

4 (A), (B), (C), (D)
3A and 3B are energy band diagrams for the multiple quantum well layers 3a, 3b, 3c, and 3d of the photoelectric conversion device shown in FIG. 2, respectively. Also in this figure, as in FIG. 3, the horizontal axis indicates the position in the thickness direction. That is, from left to right, n−
The energy levels in the InP clad layer 2, the multiple quantum well layer 3, and the p-InP clad layer 4 are shown. However, w indicates the thickness of each quantum well layer, and Ea
Indicates the energy band gap. The lengths of the multiple quantum well layers 3a, 3b, 3c, and 3d in the traveling direction of light are all 100 μm, and the quantum well layer thickness w of each multiple quantum well layer is 5 nm and 6.5 nm, respectively.
8 nm and 10 nm. The energy band gap λ _Ea converted to the wavelength of light is 1.34 μm.
m, 1.41 μm, 1.48 μm, and 1.55 μm. That is, the multi-quantum well layers 3a, 3b, 3c, 3d can respectively absorb the light having the above wavelength or less.

FIG. 5 shows the multiple quantum well layers 3a, 3b, 3
It is a figure which shows the absorption coefficient with respect to the wavelength of the incident light in c and 3d. Sa, Sb, Sc and Sd are absorption coefficients of the multiple quantum well layers 3a, 3b, 3c and 3d. Further, the wavelengths λa, λb, λc, and λd are respectively set in the multiple quantum well layer 3
Wavelengths corresponding to the energy band gaps of a, 3b, 3c, 3d 1.34 μm, 1.41 μm, 1.48 μ
m, 1.55 μm. For example, the multiple quantum well layer 3c
Then, light having a wavelength of λc = 1.48 μm or less can be absorbed. The details are shown below.

In the photoelectric conversion device shown in FIG. 2, from the left end 5a of the multiple quantum well layer 3, 1.34 μm, 1.
When light with wavelengths of 41 μm, 1.48 μm, and 1.55 μm is made to enter at one time, 1.34 is obtained in the multiple quantum well layer 3a.
Light with a wavelength of μm is absorbed. The light having the remaining three wavelengths further proceeds to the multiple quantum well layer 3b, where the light having the wavelength of 1.41 μm is absorbed. The light having the remaining two wavelengths further proceeds to the multiple quantum well layer 3c, where the light having the wavelength of 1.48 μm is absorbed. The remaining 1.51 μm light travels to the multiple quantum well layer 3d and is absorbed there. As a result, 1.34μm, 1.41μ
Light having wavelengths of m, 1.48 μm, and 1.55 μm has the largest absorption at the portions of the multiple quantum well layers 3a, 3b, 3c, and 3d, and the largest photocurrents at the electrodes 6a, 6b, 6c, and 6d. Flows.

In the above example, the incident light is 1.34
4 μm, 1.41 μm, 1.48 μm, 1.55 μm
It is a multiplexed light of two different wavelengths. However, when multiple wavelengths of multiple wavelengths are incident, in the photoelectric conversion device of FIG.
light having a wavelength of 1.34 μm <λ ≦ 1.41 μm is absorbed by the multiple quantum well layer 3 b and has a wavelength of 1.41 μm.
Light having a wavelength of <λ ≦ 1.48 μm can be emitted from the multiple quantum well layer 3c.
Light having a wavelength of 1.48 μm <λ ≦ 1.55 μm is absorbed by the multiple quantum well layer 3d.

By configuring the photoelectric conversion device as described above, it becomes possible to detect the change in the intensity of the light of each wavelength in the wavelength-multiplexed light with one photoelectric conversion device. In the photoelectric conversion device of the present invention, the wavelength separation element required in the conventional photoelectric conversion device becomes unnecessary, and
It can be composed of one photoelectric conversion element. Further, the optical coupling means between the wavelength separation means and the photoelectric conversion unit is unnecessary. Therefore, the number of parts of the photoelectric conversion device as a whole is reduced, and the structure is simplified.

Next, a second embodiment of the photoelectric conversion device will be described. FIG. 6 is a configuration diagram of a second embodiment of the photoelectric conversion device according to the present invention. The present photoelectric conversion device is obtained by connecting the photoelectric conversion device shown in FIG. 2 to a driving device composed of a differential amplifier. In this photoelectric conversion device, the outputs from the electrodes 6a, 6b, 6c, 6d of the photoelectric conversion device shown in FIG. 2 are processed by the differential amplifiers A1, A2, A3, and the wavelength λa,
The accurate intensity of light of λb, λc, and λd is detected.

In the above description, when multiple lights of wavelengths λa, λb, λc, and λd are incident on the photoelectric conversion device of FIG. 2, they correspond to the intensities of light of the respective wavelengths on the electrodes 6a, 6b, 6c, and 6d. It has been shown that an electric signal can be obtained. However, the light absorption coefficients of the multiple quantum well layers 3a, 3b, 3c, 3d are tailed in the direction of larger wavelengths as shown in FIG. Therefore, when the multiplex lights of the wavelengths λa, λb, λc, and λd are incident, for example, the multiple quantum well layer 3a absorbs the light of the wavelength λa, and at the same time, the wavelengths λb, λ
Lights of c and λd are also slightly absorbed according to the characteristics of the absorption coefficient Sa. Similarly, in the multiple quantum well layer 3b, light of wavelengths λc and λd is absorbed in addition to the light of wavelength λb, and in the multiple quantum well layer 3c, light of wavelength λd is absorbed in addition to the light of wavelength λc. As described above, in the photoelectric conversion device of FIG. 2, there is wavelength crosstalk that absorbs light other than the desired wavelength.
This causes an error in the detection of the intensity of light of each wavelength. With the photoelectric conversion device to which the driving device shown in FIG. 6 is connected, the wavelength crosstalk can be reduced and the error in the intensity detection of the wavelength can be reduced. The principle will be described below.

In the multiple quantum well layer 3a, light of wavelength λa and light of wavelengths λb, λc, and λd are slightly absorbed, and the total intensity appears as an electric signal on the electrode 6a. In the differential amplifier A1, from the electric signal appearing on the electrode 6a, the intensities of the light of the wavelengths λb, λc, and λd (the electrodes 6b and 6
predetermined coefficients k1, k2, k3
The amount multiplied by is subtracted. The coefficients k1, k2, k3 are
It is determined by the characteristics of the bottom of the absorption coefficient Sa of the multiple quantum well layer 3a. For example, 0.05, 0.01, and
It is 0.005.

Similarly, in the differential amplifier A2, the intensity of light of wavelengths λc and λd (detected by the electrodes 6c and 6d, respectively) is determined from the electric signal detected by the multiple quantum well layer 3b appearing on the electrode 6b. The amount obtained by multiplying the coefficients k4 and k5 of is subtracted. The coefficients k4 and k5 are determined by the characteristics of the bottom of the absorption coefficient Sb of the multiple quantum well layer 3b, and are 0.05 and 0.01, respectively, for example.

In the differential amplifier A3, the amount obtained by multiplying the intensity of light of wavelength λd (detected by the electrode 6d) by a predetermined coefficient k6 from the electric signal detected by the multiple quantum well layer 3c appearing on the electrode 6c is obtained. Is subtracted. The coefficient k6 is determined by the characteristic of the bottom of the absorption coefficient Sc of the multiple quantum well layer 3c, and is, for example, 0.05.

In the multiple quantum well layer 3d, the wavelength λ has already been
Lights of a, λb, and λc are multiplexed quantum well layers 3a, 3b, and 3c.
The light having only the wavelength λd is absorbed. Therefore, the electric signal appearing on the electrode 6d is directly output as the intensity of the light of the wavelength λd.

In the second embodiment of the photoelectric conversion device described above, the wavelength crosstalk can be corrected in the driving device including the differential amplifier, and the error in detecting the intensity of the light of each wavelength due to the wavelength crosstalk can be reduced. be able to. The multiple quantum well layers 3a, 3b, 3c, 3d having different quantum well layer thicknesses in the photoelectric conversion device shown in FIG. 2 can be easily formed by using a region selective growth technique.

FIG. 7 is a diagram for explaining the selective region growth, FIG. 7A is a plan view of a substrate on which the selective region growth is performed,
FIG. 3B is a diagram showing the relationship between the growth width and the width W of the mask. In FIG. 7A, a quantum well layer is formed on the InP substrate. In this case, the width W of the non-mask (region where mask is not performed) region is gradually increased as shown in the figure.
Different SiO ₂ masks are used. Using such a mask, for example, metalorganic vapor phase epitaxy (MO
VPE) crystal growth is performed. According to this method, the crystal growth thickness can be changed stepwise according to the width W of the non-mask region, as shown in FIG.

The multiple quantum well layer manufactured by such a forming method has a constant absorption coefficient characteristic. However, the electrode 7 of the photoelectric conversion device and the electrodes 6a, 6b, 6c,
It is also possible to finely adjust the absorption coefficient characteristic as shown in FIG. 8 by applying a voltage to 6d (reverse bias in the case of a PN junction). At this time, when a voltage is applied to each electrode, it is necessary to reliably separate the electrodes in order to reduce interference between the electrodes. The configuration is shown in FIGS. 9 and 10 below.

FIG. 9 is a sectional view of a third embodiment of the photoelectric conversion device of the present invention, and FIG. 10 is a sectional view of the fourth embodiment of the photoelectric conversion device of the present invention. Together, the same components as in FIG. 2 are indicated with the same reference numbers. In the photoelectric conversion device of FIG. 9, the cladding layer 4 on the upper side of the multiple quantum well layer 3 is divided for each of the electrodes 6a, 6b, 6c, 6d, and a space between them is filled with a substance having low electric conductivity. There is. The substance is polyimide, and I is doped with iron as an impurity.
An nP crystal or the like can be applied. In addition, VB1, VB2, VB
3, VB4 are voltages applied to the electrodes 6a, 6b, 6c, 6d.

In the photoelectric conversion device of FIG. 10, the multiple quantum well layer 3 and the cladding layer 4 on the upper side of the multiple quantum well layer 3 have electrodes 6a and 6a.
It is divided into b, 6c, and 6d, and a space between them is filled with a transparent material having a low electric conductivity. As the substance, the above-mentioned polyimide, I doped with iron as an impurity
An nP crystal or the like can be applied.

In the embodiment of the photoelectric conversion device of the present invention described above, the case where the optical waveguide is composed of multiple quantum well layers is shown. However, in the photoelectric conversion device of the present invention, the optical waveguide is not limited to the multiple quantum well layer, and any component whose energy band gap changes stepwise with respect to the traveling direction of light can be applied.

[0040]

As described above, the present invention has the following effects. In the photoelectric conversion device according to any one of claims 1 to 5, when light having a plurality of wavelengths is incident, the light is guided to a plurality of core portions having different energy band gaps in the core layer, and the light is guided therethrough. It is converted into an electric signal for each light of the wavelength defined by the energy band gap.

Therefore, it becomes possible for one photoelectric conversion device to detect the change in the intensity of the light of each wavelength in the wavelength-multiplexed light. The photoelectric conversion device of the present invention does not require the wavelength separation element required in the conventional photoelectric conversion device, and can be composed of one photoelectric conversion element. Further, the optical coupling means between the wavelength separation means and the photoelectric conversion unit is unnecessary. Therefore, the number of parts of the photoelectric conversion device as a whole is reduced, and the structure is simplified.

In the photoelectric conversion device according to the sixth or seventh aspect, the first cladding layer, or the first cladding layer and the core layer are divided into a plurality of portions for each of the plurality of core portions. Therefore, the electrodes formed in the respective portions can be reliably separated electrically. According to another aspect of the photoelectric conversion device of the present invention, each of the plurality of core portions further includes electrodes formed on the first cladding layer and electrically isolated from each other. Therefore, the electric signal converted for each wavelength can be reliably extracted from the electrode.

In the photoelectric conversion device according to any one of claims 9 to 11, a predetermined ratio of an electric signal output from another predetermined electrode is subtracted from an electric signal output from a predetermined electrode. It further has a drive unit. Therefore, the wavelength crosstalk can be corrected, and the error in the intensity detection of the light of each wavelength due to the wavelength crosstalk can be reduced.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a first embodiment of a photoelectric conversion device of the present invention.

FIG. 2 is a diagram showing a detailed configuration of the photoelectric conversion device shown in FIG.

FIG. 3 is a multiple quantum well layer 3 of the photoelectric conversion device shown in FIG.
It is an energy band diagram regarding arbitrary one of a, 3b, 3c, and 3d.

4 is a multiple quantum well layer 3 of the photoelectric conversion device shown in FIG.
It is an energy band diagram regarding a, 3b, 3c, and 3d.
(A) is a part of the multiple quantum well layer 3a, (B) is a part of the multiple quantum well layer 3b, (C) is a multiple quantum well layer 3c.
Part (D) is an energy band diagram relating to the part of the multiple quantum well layer 3d.

FIG. 5 is a diagram showing absorption coefficients with respect to wavelengths of incident light in the multiple quantum well layers 3a, 3b, 3c, 3d.

FIG. 6 is a configuration diagram of a second embodiment of a photoelectric conversion device according to the present invention.

FIG. 7 is a diagram for explaining area selective growth.
(A) is a plan view of a substrate on which region selective growth is performed, (B)
FIG. 6 is a diagram showing a relationship between a growth width and a mask width W.

FIG. 8 is a diagram illustrating fine adjustment of the absorption coefficient of a multiple quantum well layer by applying a voltage between electrodes.

FIG. 9 is a cross-sectional view of a third embodiment of the photoelectric conversion device of the present invention,

FIG. 10 is a cross-sectional view of a fourth embodiment of the photoelectric conversion device of the present invention.

FIG. 11 is a diagram showing a configuration example of a conventional photoelectric conversion device.

[Explanation of symbols]

 1 n-InP substrate 2 n-InP clad layer 3, 3a, 3b, 3c, 3d multiple quantum well layer 4 p-InP clad layer 5a optical waveguide entrance end 5b optical waveguide exit end 6, 6a, 6b, 6c, 6d electrode 7 electrode A1, A2, A3 differential amplifier

Claims (11)

[Claims] 1. A photoelectric conversion device for converting light of a plurality of wavelengths into electric signals, the core layer formed of a semiconductor including a plurality of core portions having different energy band gaps, and a core layer above the core layer. A first clad layer formed of a semiconductor; and a second clad layer formed of a semiconductor below the core layer, wherein the core layer includes the first clad layer and the second clad. By being sandwiched between the layers, a double heterojunction optical waveguide is formed, and electric signals corresponding to light of a plurality of wavelengths are output via the first cladding layer or the second cladding layer. And a photoelectric conversion device. 2. The energy band gap of the first cladding layer and the second cladding layer is larger than any energy band gap of the plurality of core portions of the core layer. Photoelectric conversion device. 3. The plurality of core portions of the core layer are sequentially formed in the light traveling direction of the optical waveguide, and the plurality of core portions are stepwise in the light traveling direction. The photoelectric conversion device according to claim 2, wherein the photoelectric conversion device has an energy band gap that becomes extremely small. 4. The plurality of core portions of the core layer are sequentially formed in a light traveling direction of the optical waveguide, and the plurality of core portions have a thickness in a light traveling direction. 3. The photoelectric conversion device according to claim 2, wherein the photoelectric conversion device includes a quantum well layer that changes stepwise. 5. The photoelectric conversion device according to claim 4, wherein the thickness of the quantum well layers of the plurality of core portions increases in a stepwise manner in the light traveling direction of the optical waveguide. 6. The first clad layer is divided into a plurality of parts for each of the plurality of core parts, and an electrical conductivity lower than that of the first clad layer is provided between the parts. The photoelectric conversion device according to any one of claims 1 to 5, wherein the photoelectric conversion device is filled with a substance having, and has an electrode for each portion. 7. The first clad layer and the core layer are divided into a plurality of parts for each of the plurality of core parts, a space between the parts is transparent, and the electric conductivity of the first clad layer is larger than that of the first clad layer. The photoelectric conversion device according to any one of claims 1 to 5, wherein the photoelectric conversion device is filled with a substance having a low electric conductivity and has an electrode for each of the portions. 8. The electrode according to claim 1, further comprising electrodes formed on the first cladding layer for each of the plurality of core portions and electrically isolated from each other. The photoelectric conversion device described. 9. The apparatus further comprises means for subtracting the electric signal output from the second electrode by a coefficient smaller than 1 from the electric signal output from the first electrode of the electrodes. The photoelectric conversion device according to claim 8. 10. The second electrodes are arranged in the order closer to each other in the light traveling direction of the optical waveguide from the first electrode, and based on the light absorption coefficient characteristic of the core portion corresponding to the first electrode. The photoelectric conversion device according to claim 8, wherein the photoelectric conversion device is a specified electrode. 11. The light according to claim 1, wherein the light having the plurality of wavelengths is a transmission signal.
The photoelectric conversion device according to the item.