Photodetector

Abstract

To provide a photodetector that is advantageous for miniaturization. [Solution] A first electrode 21 is formed on one side of a core 14a of a multi-mode optical waveguide 14, and a second electrode 22 is formed on the other side. The positions at which the first electrode 21 and the second electrode 22 contact the side surfaces of the core 14a are determined to be positions where the power of light propagating through the multi-mode optical waveguide 14 is minimized due to multi-mode interference. A photocurrent detector 13 applies a voltage between the first electrode 21 and the second electrode 22. When light propagates through the multi-mode optical waveguide 14, electrons and holes are excited within the multi-mode optical waveguide 14, increasing the electrical conductivity of the core 14a and causing a photocurrent to flow.

Description

[Technical Field]

[0001] The present invention relates to a photodetector. [Background technology]

[0002] Photodetectors that detect light passing through an optical waveguide have been proposed (see Non-Patent Documents 1 and 2). The photodetector in Non-Patent Document 1 has a P-doped region and an N-doped region that sandwich a slab region that constitutes a rib-type optical waveguide in a direction perpendicular to the propagation direction of light, and a pair of electrodes connected to these P-doped region and N-doped region, respectively. This structure forms a PIN photodiode, which is reverse-biased via the pair of electrodes. The photodetector in Non-Patent Document 1 is a two-photon absorption type that detects light in the optical waveguide by generating electron-hole pairs excited by light propagating through the optical waveguide and causing a photocurrent to flow in the PIN photodiode.

[0003] In the photodetector of Non-Patent Document 2, a PIN photodiode is formed by sandwiching a rib-type optical waveguide between a P-doped region and an N-doped region, and the PIN photodiode is reverse-biased. In Non-Patent Document 2, a photonic crystal optical waveguide is used to enhance the effect of two-photon absorption to detect light.

[0004] Meanwhile, a Mach-Zehnder interferometer (MZI) type optical switch is known (see Patent Document 1), which includes channel-type first and second optical waveguides with different core doping levels, a first electrode in contact with one side of the core of the first optical waveguide, a second electrode in contact with one side of the core of the second optical waveguide, and intermediate conductors in contact with the other side of each core. In the optical switch described in Patent Document 1, a voltage is applied to the first and second electrodes to pass current through each of the serially connected cores, generating different amounts of heat depending on the doping levels, thereby changing the refractive index of the cores through the thermo-optic effect. This changes the optical path length of the first and second optical waveguides, thereby performing switching. The first and second optical waveguides are multimode, and to reduce optical loss, the first and second electrodes and the intermediate conductors are in contact with the side surfaces at positions where the power of the propagating light is minimized due to the multimode interference phenomenon. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2022-52551 [Non-patent literature]

[0006] [Non-Patent Document 1] I.-W. Hsieh, H. Rong, and M. Paniccia, “Two-photon-absorption-based optical power monitor in silicon rib waveguides,” in Proc. IEEE 7th Int. Conf. Group IV Photon., 2010, pp. 326-328. [Non-patent document 2] Ryo Hayakawa, Norihiro Ishikura, Hong C. Nguyen, Toshihiko Baba, “Two-photon-absorption photodiodes in Si photonic-crystal slow-light waveguides,” Appl. Phys. Lett. 102, 031114 (2013). Summary of the Invention [Problem to be solved by the invention]

[0007] Incidentally, many optical circuits are configured with a channel-type optical waveguide that confines light three-dimensionally. When an attempt is made to connect a photodetector configured with a rib-type optical waveguide as in Non-Patent Document 1 to an optical circuit using such a channel-type optical waveguide, the mode converter between the channel-type optical waveguide and the rib-type optical waveguide becomes large, resulting in an increase in the size of the photodetector. Similarly, when an attempt is made to connect a detector configured with a photonic crystal optical waveguide as in Non-Patent Document 2 to a channel-type optical waveguide, the mode converter becomes large, resulting in an increase in the size of the photodetector.

[0008] The present invention has been made in view of the above circumstances, and has as its object to provide a photodetector that is advantageous for miniaturization. [Means for solving the problem]

[0009] The photodetector of the present invention comprises a multi-mode optical waveguide having a core covered with cladding and having light incident from one end, and an electrode section formed in the same plane as the multi-mode optical waveguide, the electrode section having a first electrode in contact with one side of the core and a second electrode in contact with the other side of the core at a position where the optical intensity of light propagating through the multi-mode optical waveguide is minimum, and connected to a photocurrent detection section that applies a voltage between the first electrode and the second electrode and detects a photocurrent flowing between the first electrode and the second electrode via the core. [Effects of the Invention]

[0010] According to the photodetector of the present invention, the first and second electrodes are formed in the same plane as the multi-mode optical waveguide and are in contact with each side of the core at a position where the optical intensity of light propagating through the multi-mode optical waveguide is minimum, and an electrode section is provided that is connected to a photocurrent detection section that detects the photocurrent that flows between the first and second electrodes via the core when a voltage is applied between the first and second electrodes. This makes it possible to configure a compact photodetector for many optical circuits. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 2 is an explanatory diagram illustrating a configuration of a photodetector according to an embodiment. [Figure 2] FIG. 10 is an explanatory diagram showing the results of a simulation of light propagation in a multi-mode optical waveguide. [Figure 3] 3 is a cross-sectional view showing a cross section of a photodetector at a position where a first electrode and a second electrode are in contact with a core of a multi-mode optical waveguide. FIG. [Figure 4] 10 is a cross-sectional view showing a cross section of a photodetector at a position where the first electrode and the second electrode are not in contact with the core of a multi-mode optical waveguide. FIG. [Figure 5] FIG. 10 is an explanatory diagram showing an example in which a photodetector is incorporated into a ring optical waveguide of a tunable wavelength laser. [Figure 6] FIG. 2 is an explanatory diagram showing the configuration of a ring optical waveguide including a photodetector. [Figure 7] 1 is a cross-sectional view showing a cross section of a photodetector at a position where the first electrode, the second electrode, and the intermediate electrode are in contact with the core of a multi-mode optical waveguide in a ring optical waveguide. [Figure 8] 10 is a cross-sectional view showing a cross section of a photodetector at a position where the first electrode, the second electrode, and the intermediate electrode are not in contact with the core of a multi-mode optical waveguide in a ring optical waveguide. FIG. [Figure 9] 10 is a graph showing the relationship between the output intensity of the SOA and the current flowing between the first electrode and the second electrode measured when an applied voltage of 0.5 V is set. [Figure 10] 10 is a graph showing the relationship between the output intensity of the SOA and the current flowing between the first electrode and the second electrode measured when the applied voltage is 1.0 V. [Figure 11] 10 is a graph showing the sensitivity of a photodetector. DETAILED DESCRIPTION OF THE INVENTION

[0012] 1, a photodetector 10 of this embodiment includes a photodetector 12 and a photocurrent detection unit 13. The photodetector 12 includes a multi-mode optical waveguide 14, mode converters 15 and 16, and an electrode unit 17, and single-mode optical waveguides 18 and 19 are connected to one end and the other end of the multi-mode optical waveguide 14 via the mode converter 15. In this photodetector 10, for example, light is incident on the multi-mode optical waveguide 14 from the single-mode optical waveguide 18 via the mode converter 15, and the photodetector 10 detects the light propagating through the multi-mode optical waveguide 14 as a photocurrent corresponding to the light intensity.

[0013] In this example, the multi-mode optical waveguide 14, mode converters 15 and 16, and single-mode optical waveguides 18 and 19 are configured as channel-type optical waveguides that confine light three-dimensionally. The multi-mode optical waveguide 14 is an optical waveguide that is wider than a single-mode optical waveguide with a single guided mode and has multiple guided modes. The single-mode optical waveguides 18 and 19 are configured as optical waveguides with a single guided mode.

[0014] Mode converters 15 and 16 are tapered optical waveguides whose width gradually increases toward multi-mode optical waveguide 14, and adiabatically change the guided mode between multi-mode optical waveguide 14 and single-mode optical waveguides 18 and 19. This suppresses loss of light when propagating from single-mode optical waveguide 18 to multi-mode optical waveguide 14 and from multi-mode optical waveguide 14 to single-mode optical waveguide 19.

[0015] Generally, channel-type optical waveguides are used in optical circuits, but if a photodetector is configured with a rib-type optical waveguide as in Non-Patent Document 1 and connected to a channel-type optical waveguide, the mode converter becomes large, and the length of the optical waveguide of the photodetector becomes 10 mm or more, resulting in an increase in size. Also, if a detector is configured with a photonic crystal optical waveguide as in Non-Patent Document 2 and connected to a channel-type optical waveguide, the mode converter also becomes large, and the length of the optical waveguide of the photodetector becomes about 300 μm, resulting in an increase in size.

[0016] In contrast, in photodetector 12 of this example, because it is a channel-type optical waveguide as described above, the length of mode converters 15 and 16 can be about several μm, and the total length of the optical waveguide including multi-mode optical waveguide 14 and mode converters 15 and 16 can be about 20 μm. In this way, photodetector 12 can be configured to be compact and space-saving.

[0017] The multi-mode optical waveguide 14, the mode converters 15 and 16, and the single-mode optical waveguides 18 and 19 are configured as silicon optical waveguides. That is, the cores of the multi-mode optical waveguide 14, the mode converters 15 and 16, and the single-mode optical waveguides 18 and 19 are formed of silicon (Si), and the cladding covering the cores is formed of silicon dioxide (SiO2). The materials constituting these optical waveguides are not limited to these, and SiGe, Ge, InP, InGaAsP, etc. can also be used for the core, and SiON, SiN, etc. can also be used for the cladding. The core and cladding may also be formed of other inorganic or organic materials.

[0018] The electrode section 17 has a first electrode 21 and a second electrode 22 that are conductive, and electrode terminals 24 and 25. The first electrode 21 has a contact end 21a formed at its tip that contacts one side of the core 14a of the multi-mode optical waveguide 14. The second electrode 22 has a contact end 22a at its tip that contacts the other side of the core 14a.

[0019] The position where the contact end 21a of the first electrode 21 contacts the side surface of the core 14a is determined to be a position where the power (electrical power) of light propagating through the multimode optical waveguide 14 is minimized by multimode interference. Similarly, the position where the contact end 22a of the second electrode 22 contacts the side surface of the core 14a is determined to be a position where the power (electrical power) of light propagating through the multimode optical waveguide 14 is minimized by multimode interference.

[0020] As shown in the simulated image in Figure 2, within multimode optical waveguide 14, light propagating periodically converges and diverges repeatedly due to multimode interference. The position where this light converges is the position where the optical power is minimum, and contact ends 21a and 22a contact the side surface of core 14a at this position. Note that in Figure 2, the intensity of the magnetic field component Hy of the light propagating through multimode optical waveguide 14 is indicated by shading. Magnetic field component Hy is the component of the magnetic field perpendicular to the substrate on which multimode optical waveguide 14 is formed.

[0021] In this example, as shown in FIG. 1, the first electrode 21 and the second electrode 22 each have five contact ends 21a and 22a that contact each side of the core 14a. That is, the first electrode 21 and the second electrode 22 each contact the core 14a at five locations. The number of contact ends 21a and 22a, i.e., the number of locations where the first electrode 21 and the second electrode 22 contact the core 14a, may be one or more. From the perspective of reducing light loss due to contact between the first electrode 21 and the second electrode 22, it is preferable that the number of locations where the first electrode 21 and the second electrode 22 contact the core 14a be as few as possible. Furthermore, the first electrode 21 and the second electrode 22 do not necessarily need to contact the side of the core 14a at opposing positions (at the same node positions), and the number of locations where the first electrode 21 and the second electrode 22 contact the side of the core 14a may differ.

[0022] The width of contact with the core 14a at each contact position of the first electrode 21 and the second electrode 22 (the length of each of the contact ends 21a, 22a in the light propagation direction) is preferably small from the viewpoint of reducing light loss, and is preferably 400 nm or less.

[0023] In this example, the first electrode 21 and the second electrode 22 are heavily doped with Si. The dopants for the first electrode 21 and the second electrode 22 are selected so that the junctions between the core 14a and the first electrode 21 and the second electrode 22 do not form PN junctions. That is, the first electrode 21, the second electrode 22, and the core 14a are prevented from becoming semiconductors with different polarities (P-type or N-type). In this example, since the core 14a exhibits a slight P-type polarity, the first electrode 21 and the second electrode 22 are made into P-type semiconductors by doping Si with B (boron). The type of dopant is not particularly limited. The first electrode 21 and the second electrode 22 may also be formed of, for example, a conductive metal.

[0024] The electrode terminals 24, 25 are provided at the bases of the first electrode 21 and the second electrode 22. The first electrode 21 and the second electrode 22 are electrically connected to the photocurrent detection unit 13 via these electrode terminals 24, 25. The electrode terminals 24, 25 are made of, for example, aluminum (Al).

[0025] The photocurrent detection unit 13 is composed of a power supply circuit that applies a voltage to the core 14a between the first electrode 21 and the second electrode 22 via electrode terminals 24 and 25, and a detection circuit that detects the photocurrent that flows between the first electrode 21 and the second electrode 22 via the core 14a. When light propagates within the multi-mode optical waveguide 14 while a voltage is applied between the first electrode 21 and the second electrode 22 by the photocurrent detection unit 13, a photocurrent flows between the first electrode 21 and the second electrode 22. This occurs because electrons and holes are excited by light absorption within the multi-mode optical waveguide 14, which increases the electrical conductivity between the first electrode 21 and the second electrode 22 and causes a photocurrent to flow. The excitation of electrons and holes at this time includes not only excitation of electrons and holes due to two-photon absorption but also excitation of electrons and holes due to one-photon absorption, allowing for high sensitivity detection even with weaker light. Furthermore, the electrical conductivity increases or decreases depending on the intensity of light propagating through the multi-mode optical waveguide 14. The photocurrent detector 13 detects this flowing photocurrent. The voltage applied between the first electrode 21 and the second electrode 22 is not particularly limited, but can be, for example, 1.0 V or less.

[0026] Figures 3 and 4 show cross sections of the photodetector 12. Figure 3 shows a cross section at a position where the first electrode 21 and the second electrode 22 are in contact with the core 14a, and Figure 4 shows a cross section at a position where the first electrode 21 and the second electrode 22 are not in contact with the core 14a. Note that hatching indicating cross sections is omitted in Figures 3 and 4.

[0027] The Si core 14a is embedded in a cladding 34 made of SiO2. A first electrode 21 and a second electrode 22, doped with Si, are formed on the same plane as the core 14a. Electrode terminals 24 and 25 are formed on the upper layers of the bases of the first electrode 21 and the second electrode 22, respectively. As shown in FIG. 3, contact ends 21a and 22a of the first electrode 21 and the second electrode 22 are in contact with the side surfaces of the core 14a, and the other portions are not in contact with the side surfaces of the core 14a, as shown in FIG. 4. The thickness of the core 14a is approximately 0.2 μm.

[0028] According to the above configuration, when detecting light, the photocurrent detection unit 13 applies a voltage to the core 14a between the first electrode 21 and the second electrode 22. In this state, light enters the multi-mode optical waveguide 14 from the single-mode optical waveguide 18 via the mode converter 15 and propagates through the multi-mode optical waveguide 14. As a result, the electrical conductivity of the core 14a increases between the first electrode 21 and the second electrode 22, causing a photocurrent to flow. The electrical conductivity of the core 14a between the first electrode 21 and the second electrode 22 increases or decreases depending on the intensity of light propagating through the multi-mode optical waveguide 14. Therefore, the greater the intensity of the propagating light, the greater the photocurrent that flows. This photocurrent is then detected by the photocurrent detection unit 13. Therefore, the photodetector 12 can detect light, including its intensity.

[0029] 5 shows an example of a photodetector configured to detect light in a ring optical waveguide provided in an external resonator type tunable laser 40. The tunable laser 40 in this example changes wavelength by utilizing the Vernier effect, and is composed of annular ring optical waveguides 41 and 42, three bus optical waveguides 43 to 45 optically coupled by the ring optical waveguides 41 and 42, a loop mirror 46, heaters 47 and 48, an SOA (Semiconductor Optical Amplifier) ​​51, and a spot size converter 52. The cores of the ring optical waveguides 41 and 42 are heated by the heaters 47 and 48, which shifts the resonance wavelengths of the ring optical waveguides 41 and 42, thereby controlling the wavelength of the laser light output by the tunable laser 40.

[0030] The ring optical waveguides 41 and 42 are provided with photodetectors 54 and 55, respectively. Photocurrent detection units 56 and 57 are connected to the photodetectors 54 and 55, which constitute photodetectors 58 and 59, respectively. The ring optical waveguide 41 and the ring optical waveguide 42 have the same configuration except for the length of the optical waveguide. The photodetectors 54 and 55 also have the same configuration. For this reason, the following will describe the photodetector 54 provided in the ring optical waveguide 41, and a detailed description of the photodetector 55 provided in the ring optical waveguide 42 will be omitted.

[0031] 6, the ring optical waveguide 41 is formed in a ring shape with straight portions. The ring optical waveguide 41 is composed of multi-mode optical waveguides 61 and 62 provided as a pair of opposing straight portions, mode converters 63 and 64 connected to the front and rear of each multi-mode optical waveguide 61 and 62, respectively, and single-mode optical waveguides 65 and 66 connected to the multi-mode optical waveguides 61 and 62 via the mode converters 63 and 64. The multi-mode optical waveguides 61 and 62 have multiple waveguide modes, while the single-mode optical waveguides 65 and 66 have a single waveguide mode.

[0032] The single-mode optical waveguide 65 is disposed adjacent to and optically coupled to the bus optical waveguide 44, and the single-mode optical waveguide 66 is disposed adjacent to and optically coupled to the bus optical waveguide 45. As a result, light of a wavelength that resonates in the ring optical waveguide 41 is input from the bus optical waveguides 44 and 45 to the single-mode optical waveguides 65 and 66, and the light from the single-mode optical waveguides 65 and 66 is incident on the multi-mode optical waveguides 61 and 62 via the mode converters 63 and 64.

[0033] The multimode optical waveguides 61 and 62 form part of the photodetector 54. In addition to the multimode optical waveguides 61 and 62 and mode converters 63 and 64, the photodetector 54 also has an electrode unit 70. The electrode unit 70 has a first electrode 71, a second electrode 72, an intermediate electrode 73, and electrode terminals 75 and 76, all of which are conductive.

[0034] The materials forming the core and cladding of the ring optical waveguide 41 are the same as those of the multi-mode optical waveguide 14 and the single-mode optical waveguides 18 and 19 in the above examples. The materials forming the first electrode 71, the second electrode 72, the intermediate electrode 73, and the electrode terminals 75 and 76 are also the same as those of the first electrode 21, the second electrode 22, and the electrode terminals 24 and 25 in the above examples.

[0035] The first electrode 71 has a contact end 71a formed at its tip in contact with the outer peripheral side surface (the side surface on the left in the figure) of the core 61a of the multi-mode optical waveguide 61. The second electrode 72 has a contact end 72a formed at its tip in contact with the outer peripheral side surface (the side surface on the right in the figure) of the core 62a of the multi-mode optical waveguide 62.

[0036] One end of the intermediate electrode 73 serves as a second electrode for the core 61a of the multi-mode optical waveguide 61, and a contact end 73a formed at one end thereof contacts the inner peripheral side surface of the core 61a (the side surface on the right in the figure). The other end of the intermediate electrode 73 serves as a first electrode for the core 62a of the multi-mode optical waveguide 62, and a contact end 73b formed at the other end contacts the inner peripheral side surface of the core 62a (the side surface on the left in the figure). This connects the core 61a and the core 62a in series between the first electrode 71 and the second electrode 72.

[0037] As in the above example, the positions at which the contact ends 71a, 72a, 73a, 73b contact the side surfaces of the corresponding cores 61a, 62a are determined to be positions at which the power of light propagating through the multimode optical waveguides 61, 62 is minimized by multimode interference. The first electrode 71, the second electrode 72, and the intermediate electrode 73 may each contact the cores 61a, 62a at one or more locations, but the fewer the number of locations, the better from the viewpoint of reducing light loss.

[0038] Furthermore, as in this example, when the resonant wavelength of the ring optical waveguide 41 is changed, i.e., when the wavelength propagating through the multimode optical waveguides 61 and 62 is changed, the position where the power of the light propagating through the multimode optical waveguides 61 and 62 is minimized due to multimode interference may shift slightly depending on the wavelength of the light, and the positions where the first electrode 71, the second electrode 72, and the intermediate electrode 73 contact each other may shift from the minimum position. From the viewpoint of minimizing the shift from the minimum position and reducing optical loss, it is preferable to reduce the number of points where the first electrode 71, the second electrode 72, and the intermediate electrode 73 contact each of the cores 61a and 62a. The number of points where the first electrode 71, the second electrode 72, and the intermediate electrode 73 contact each of the cores 61a and 62a may vary.

[0039] Similar to the photocurrent detection unit 13 in the above example, the photocurrent detection unit 56 is composed of a power supply circuit that applies a voltage between the first electrode 71 and the second electrode 72 via electrode terminals 75, 76, and a detection circuit that detects the photocurrent flowing between the first electrode 71 and the second electrode 72.

[0040] Fig. 7 shows a cross section of the photodetector 54 at a position where the first electrode 71, the second electrode 72, and the intermediate electrode 73 are in contact with the cores 61a, 62a. Fig. 8 shows a cross section of the photodetector 54 at a position where the first electrode 71, the second electrode 72, and the intermediate electrode 73 are not in contact with the cores 61a, 62a. Note that hatching indicating the cross section is omitted in Figs. 7 and 8.

[0041] For example, the cores 61a and 62a are made of Si and embedded in a cladding 77 made of SiO2. A first electrode 71, a second electrode 72, and an intermediate electrode 73 are formed by heavily doping Si on the same plane as the cores 61a and 62a. Electrode terminals 75 and 76 are formed on the upper layers of the bases of the first electrode 71 and the second electrode 72, respectively. As shown in FIG. 7, the first electrode 71 and the second electrode 72 have contact ends 71a and 72a that are in contact (bonded) with the side surfaces of the cores 61a and 62a, and the other portions are not in contact with the side surfaces of the cores 61a and 62a, as shown in FIG. 8.

[0042] Further, a heater 47 is disposed below the core of the ring optical waveguide 41, including the cores 61a and 62a, with a clad 77 sandwiched between them. As a result, when the heater 47 generates heat, the core of the ring optical waveguide 41 is heated, and the optical path length of the ring optical waveguide 41 changes due to the thermo-optic effect, and the resonant wavelength of the ring optical waveguide 41 changes.

[0043] When light propagates within the ring optical waveguide 41 while a voltage is applied between the first electrode 71 and the second electrode 72, electrons and holes are excited by the absorption of light within the multi-mode optical waveguides 61 and 62, causing a photocurrent to flow between the first electrode 71 and the second electrode 72. As a result, the light from the ring optical waveguide 41 is detected.

[0044] In the configuration of FIG. 5, the applied voltage (Vapp) to the first electrode 71 and the second electrode 72 was set to 0.5 V and 1.0 V, and the change in the current (Current) flowing between the first electrode 71 and the second electrode 72 detected by the photodetector 54 and the output intensity (Fiber Coupled Power) of the SOA 51 relative to the drive current of the SOA 51 was measured. The measurement results are shown in FIGS. 9 and 10. Note that FIG. 9 shows the change in the applied voltage (V app ) is set to 0.5V, Figure 10 shows the applied voltage (V app ) was set to 1.0 V, and the current flowing between the first electrode 71 and the second electrode 72 is a value including dark current (= dark current + photocurrent). The sensitivity of the photodetector 54 was also calculated based on the above measurement results. The calculated sensitivity of the photodetector 54 is shown in FIG.

[0045] The above measurements reveal that there is a corresponding relationship between the intensity of light propagating through the ring optical waveguide 41 and the photocurrent flowing in the photodetector 54. Furthermore, it is clear that even in areas where laser oscillation is not occurring and the light intensity is weak, sufficient photocurrent is obtained, demonstrating the high sensitivity of the photodetector 54. Furthermore, it is clear that a photocurrent is obtained that changes according to the light intensity.

[0046] In this example, two multi-mode optical waveguides 61 and 62 are provided in one ring optical waveguide 41 to form the photodetector 54, but the photodetector may also be configured by providing a multi-mode optical waveguide in only one straight portion of the ring optical waveguide 41. [Explanation of symbols]

[0047] 10. Photodetector 12, 54, 55 Photodetectors 13, 56, 57 Photocurrent detection section 14, 61, 62 Multimode optical waveguide 14a, 61a, 62a Core 15, 16 Mode converter 17, 70 Electrode section 21, 71 1st electrode 22, 72 2nd electrode 73 Intermediate electrode

Claims

1. a multimode optical waveguide having a core covered with a cladding and having light incident on one end; an electrode section formed in the same plane as the multi-mode optical waveguide, the electrode section having a first electrode in contact with one side surface of the core and a second electrode in contact with the other side surface of the core at a position where the optical intensity of light propagating through the multi-mode optical waveguide is minimum, the electrode section being connected to a photocurrent detection section that applies a voltage between the first electrode and the second electrode and detects a photocurrent that flows between the first electrode and the second electrode via the core; Equipped with 1. A photodetector comprising:

2. The first electrode, the second electrode, and the core are not semiconductors of opposite polarities.

2. The photodetector of claim 1.

3. the core is made of silicon; The cladding is made of SiO ２ It consists of The first electrode and the second electrode are made of doped silicon.

3. The photodetector according to claim 2.

4. The first electrode and the second electrode have a contact width of 400 nm or less at each position where they contact the core.

2. The photodetector of claim 1.

5. One end of the multi-mode optical waveguide is connected to a single-mode optical waveguide, and light from the single-mode optical waveguide is incident on the multi-mode optical waveguide.

2. The photodetector of claim 1.

6. The multimode optical waveguide is connected to the single-mode optical waveguide via a mode converter that adiabatically transitions modes.

6. The photodetector according to claim 5.

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