Optical device and optical transceiver

Abstract

The invention relates to an optical device and an optical transceiver. An optical device includes: a photoelectric conversion element provided on a substrate; and a single-mode optical fiber configured to guide light input to the photoelectric conversion element from a first direction and output from the photoelectric conversion element toward the first direction, the first direction being perpendicular or obliquely upward with respect to the substrate. The single mode fiber has a bent portion bent at a predetermined radius of curvature. The curved portion converts a propagation direction of light between a first direction and a second direction different from the first direction, and radiates a high order mode.

Description

Technical Field

[0001] The embodiments discussed herein relate to optical devices and optical transceivers. Background Art

[0002] Due to the development of the Internet, data traffic continues to increase in large-scale data centers, etc. With the introduction of the fifth-generation mobile communication system ("5G" system) and further the sixth-generation mobile communication system ("6G" system), it is expected that the data-driven society using artificial intelligence (AI), machine learning, the Internet of Things (IoT) for connecting various sensors, autonomous driving, etc. will expand at an accelerated pace. It is necessary to achieve technology for implementing a high-speed single-core bidirectional optical link using a single-mode optical fiber (SMF) at a distance of less than 10km at low cost, low power consumption and high density by 2030.

[0003] In the case of transmitting an optical signal with a wavelength in the 1 μm band through an SMF in which dispersion becomes zero at 1.3 μm (hereinafter also referred to as a "1.3 μm SMF"), a higher-order mode is generated in the transmission path, and the transmission quality is degraded due to inter-mode interference. For example, it is known from Japanese Patent Publication No. 2021-189252 that a high-order mode elimination filter is formed by a curved waveguide formed in a planar lightwave circuit on a substrate and the mode elimination filter is set between a photodetector and the SMF. For example, research on evaluating ordinary SMF as curved fiber mode filter for 1060nm data transmission has also been reported in: Boxuan Zhang, Xiaodong Gu, Susumu Kinoshita and Fumio Koyama, “Bending-Fiber Mode Filter Evaluation for 1060nm Data Transmission in Conventional Single-Mode Fiber”, Electronic Lecture Proceedings 1, C-3 / 4-59, September 2022.

[0004] In light transmission using SMF, in addition to eliminating high-order modes, a structure is required to convert the light path from vertical to horizontal or from horizontal to vertical between the SMF and a photoelectric conversion element having a light receiving surface and a light emitting surface parallel to the substrate. Summary of the invention

[0005] Therefore, an aspect of an embodiment is to provide an optical device capable of eliminating a high-order mode and converting a propagation direction of light using a simple configuration.

[0006] According to one aspect of the embodiment, an optical device includes: a photoelectric conversion element, which is arranged on a substrate; a single-mode optical fiber, which is configured to guide light input to the photoelectric conversion element from a first direction and output from the photoelectric conversion element toward the first direction, the first direction being vertical or obliquely upward relative to the substrate, wherein the single-mode optical fiber has a curved portion curved with a predetermined radius of curvature, and the curved portion converts a propagation direction of light between the first direction and a second direction different from the first direction, and radiates a higher-order mode.

[0007] The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.

[0008] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a schematic diagram of an optical device according to a first embodiment;

[0010] Figure 2 is a diagram illustrating an example of a photoelectric conversion element used in an optical device;

[0011] Figure 3 is a schematic diagram of an optical device according to a second embodiment;

[0012] Figure 4 is a schematic diagram of an optical device according to a third embodiment;

[0013] Figure 5A is a schematic diagram of an optical device according to a fourth embodiment;

[0014] Figure 5B is a schematic diagram of a V-groove for holding SMF;

[0015] Figure 6 is a schematic diagram of an optical device according to a fifth embodiment; and

[0016] Figure 7 is a block diagram of an optical transceiver using optical devices. DETAILED DESCRIPTION

[0017] Preferred embodiments of the present invention will be described with reference to the accompanying drawings.

[0018] In an embodiment, a single-mode optical fiber (SMF) optically connected to a photoelectric conversion element provided on a substrate is bent at a predetermined radius of curvature and used, thereby playing the role of a direction converter configured to convert the direction of light propagation between the vertical direction and the horizontal direction, and also serving as a high-order mode filter configured to eliminate high-order modes. SMF is used to construct a single-core bidirectional optical link with a transmission rate of 100Gbps or higher. In a 5G system, 100 5G antenna base stations are required in a cell with a radius of 2km. In a 6G system, it is expected to use a higher frequency band and a reduced cell radius compared to a 5G system. If it is assumed that the cell radius of the 6G system is 20m, 10,000 6G cells or 6G antenna base stations are required in a cell with a radius of 2km. In a 6G system, the expected transmission rate is higher than 100Gbps, that is, the transmission rate is 1Tbps or higher.

[0019] Conventional base stations of the third generation mobile communication system ("3G" system) to the fourth generation mobile communication system ("4G" system) are installed in or near the buildings of communication carriers, and these base stations are connected to the network. When the base stations of the 5G system or 6G system are installed, the so-called optical fronthaul is introduced, in which the optical fiber is extended from the base station of the 3G system or 4G system (including LTE for convenience) or from the building of the communication carrier as a starting point. Compared with multimode fiber (MMF), SMF with a longer transmission distance and lower cost is required for efficient optical fronthaul.

[0020] In SMF, when the transmission wavelength becomes shorter than the cutoff wavelength, in addition to the fundamental mode, a higher-order mode is transmitted. The cutoff wavelength is the shortest wavelength that can propagate only in a single mode. When a higher-order mode is included in the transmission, signal waveform degradation occurs due to inter-mode interference, and therefore, a higher-order mode filter is required to eliminate the higher-order mode. Because the signal waveform degradation becomes more significant as the bit rate of the transmission becomes higher, it is necessary to eliminate the higher-order mode.

[0021] In the case of a conventional mode filter formed by a planar lightwave circuit, a light emitting element or a light receiving element is optically connected to an optical fiber using a lens or the like, and the optical fiber is fused and spliced ​​with the mode filter. The optical coupling loss between the optical fiber and the mode filter increases, and the number of components increases. In order to solve this problem, in one embodiment, a simple and low-cost construction is achieved by eliminating high-order modes through "mode filter optical coupling" by utilizing the bend (or bending) of the optical fiber.

[0022] Hereinafter, the specific structure and method of delay control according to the embodiment will be described with reference to the accompanying drawings. The following embodiments are examples for realizing the technical concepts of the present disclosure, and the present disclosure is not limited to these examples. In order to facilitate understanding of the present disclosure, the size, positional relationship, etc. of the constituent elements shown in the accompanying drawings may be exaggerated. Constituent elements with the same structure or function are referred to by the same name or figure mark, and their redundant description may be omitted.

[0023] <First Embodiment>

[0024] Figure 1 1 is a schematic diagram of an optical device 10 according to a first embodiment. The optical device 10 includes a photoelectric conversion element 15 disposed on a substrate 12, and an SMF 11 for guiding light input to the photoelectric conversion element 15 from a first direction and light output from the photoelectric conversion element 15 to the first direction, the first direction being relative to the front surface ( Figure 1 The photoelectric conversion element 15 is electrically connected to an interconnect formed on the substrate 12, for example, via a bonding wire 14, but may be wire-bonded to an electronic chip such as a driver, a transimpedance amplifier (TIA), etc., which is disposed on the substrate 12 adjacent to the photoelectric conversion element 15. The SMF 11 has a curved (or bent) portion 110 that is curved (or bent) with a predetermined radius of curvature, and the curved portion 110 converts the propagation direction of light between a first direction that is vertical or obliquely upward relative to the substrate 12 and a second direction that is different from the first direction, and radiates a high-order mode. For example, the second direction is a direction parallel to the substrate 12.

[0025] exist Figure 1 In the coordinate system, the plane parallel to the front surface of the substrate 12 is defined as the XY plane, and the direction perpendicular to the substrate 12 is defined as the Z direction. The curved portion 110 converts the propagation direction of light between a first direction (Z direction) perpendicular to the substrate 12 and a second direction in the XY plane, radiates a higher-order mode, and propagates a fundamental mode. Depending on the manufacturing errors of the substrate 12 and the photoelectric conversion element 15, the bending (or bending) state of the SMF 11, etc., the first direction does not necessarily have to be exactly 90° relative to the front surface of the substrate 12, but includes a direction of 90°±10° relative to the front surface of the substrate 12. Similarly, depending on the manufacturing errors of the substrate 12, the bending state and the holding state of the SMF 11, etc., the second direction does not necessarily have to be completely parallel to the front surface of the substrate 12, but includes a direction of 180°±10° relative to the front surface of the substrate 12.

[0026] The diameter of the SMF 11 (i.e., the outer diameter of the cladding 112) is generally 125 μm, and the diameter of the core 111 is in the range of 7 μm to 10 μm. The SMF 11 has a step-index (SI) type refractive index profile, so that a pulse propagating through the core 111 having a small diameter and a high refractive index has a small spread, and therefore, long-distance transmission is feasible compared to a multimode fiber (MMF).

[0027] The direction of the SMF 11 is converted by about 90° at the curved portion 110, and the end face 115 of the optical fiber is opposite to the light receiving surface and the light emitting surface of the photoelectric conversion element 15 provided on the substrate 12. The lens 13 may be provided between the end face 115 of the optical fiber and the photoelectric conversion element 15. In the case where the photoelectric conversion element 15 is a vertical cavity surface emitting laser (VCSEL), the light emitted from the photoelectric conversion element 15 is converged by the lens 13 on the core 111 at the position of the end face 115. In the case where the photoelectric conversion element 15 is a light receiving element (such as a photodiode, etc.), the light emitted from the core 111 at the end face 115 is converged by the lens 13 on the light receiving surface of the light receiving element.

[0028] The SMF commonly used in optical communications is a 1.3 μm band zero-dispersion SMF specified under G652 of the ITU-T standard, but the limit value of the bending radius (or bend radius) of this SMF is about 30 mm. When the bending radius of the SMF is set to 30 mm or less and the direction is converted by 90°, there is a problem of increased bending loss and physical damage. It may seem desirable to use the low bending loss SMF recommended under G657 of the ITU-T standard as the SMF 11 having the bent portion 110, but in an embodiment, an SMF having a certain degree or greater bending loss difference between the fundamental mode and the higher-order mode is used instead of using a low bending loss SMF.

[0029] In order to propagate the light of the fundamental mode with low loss in the curved portion 110 and effectively eliminate the higher order modes, it is desirable that the bending loss difference between the fundamental mode and the higher order modes is sufficiently large. For example, the bending loss difference between the fundamental mode and the higher order modes is 15 dB or more, preferably 18 dB or more, and more preferably 20 dB or more. As a result of extensive studies conducted by the present inventors, it was found that when a low bending loss optical fiber is used, the bending loss of the higher order mode is also reduced, making it difficult to effectively eliminate the higher order mode through the curved portion 110. Therefore, the embodiment uses an SMF having a large bending loss for the higher order mode and a negligible small bending loss for the fundamental mode.

[0030] In Boxuan Zhang, Xiaodong Gu, Susumu Kinoshita and Fumio Koyama, "Bending-Fiber Mode Filter Evaluation for 1060nm Data Transmission in Conventional Single-Mode Fiber", Electronic Lecture Proceedings 1, C-3 / 4-59, September 2022, when calculations are performed using the SMF specified in G652, the bending loss for the LP01 mode as the fundamental mode is reduced to a negligible level by making the bending radius greater than 6 mm. However, when the bending radius is greater than 7 mm, the bending loss for the LP11 mode as the higher-order mode is also reduced, and the bending loss difference between the L11 mode and the LP01 mode cannot be fixed to 15 dB or more, preferably 18 dB or more, and more preferably 20 dB or more. In actual specifications, the limit value of the bending radius of the SMF specified in G652 is set to 30 mm. Therefore, when the bending radius is set to 7 mm, the optical fiber may break.

[0031] The present inventors found through calculations using various SMFs that the bending loss difference between the LP11 mode and the LP01 mode can be 15 dB or more, preferably 18 dB or more, and more preferably 20 dB or more by bending and using an SMF with a bending radius within a certain range. Specifically, in the case of using an SMF that is bend-resistant relative to the base mode, by setting the bending radius within a range of greater than or equal to 3 mm and less than or equal to 7 mm, the bending loss difference between the base mode (LP01 mode) and the higher-order mode (LP11 mode) can be 20 dB or more. Even in the case of an SMF that is bend-resistant relative to the base mode, when the bending radius becomes less than 3 mm, the bending loss of the base mode increases, and the bending loss difference between the base mode and the higher-order mode becomes less than 15 dB, and the possibility of physical damage to the optical fiber increasing.

[0032] By using such an SMF bent (or curved) with a bending radius (or bending radius) of 3 mm or more and 7 mm or more, the propagation direction of light can be converted between two different directions (i.e., between a direction perpendicular to the substrate 12 and a direction parallel to the substrate 12), for example, a high-order mode can be radiated at the bent portion 110. The cutoff wavelength of the 1.3 μm band SMF is 1.26 μm. In optical transmission in the T band where the communication wavelength is shorter than 1.26 μm, a high-order mode is generated in the 1.3 μm band SMF. Figure 1In the configuration shown, the SMF 11 used has a bending loss of a higher order mode that is 15 dB or more greater than the bending loss of the fundamental mode. By bending and using the SMF 11 having a bending radius within a range of 3 mm or more and 7 mm or less, the propagation direction can be converted and the higher order mode can be eliminated, so that the fundamental mode can be transmitted with a small loss.

[0033] Figure 2 1 is a schematic diagram of a light emitting element 150 as an example of a photoelectric conversion element 15 used in the optical device 10. The light emitting element 150 is, for example, a VCSEL that emits light in a direction perpendicular to the substrate 12. In the case where the VCSEL is used together with the 1.3 μm band SMF 11, the light emitting element 150 may be formed of a GaAlAs-based material or an InGaAs-based material. The VCSEL includes an n-type multilayer film reflector 152, an active layer 153, and a p-type multilayer film reflector 154 stacked in a direction perpendicular to the substrate 151, and a resonator (cavity) is formed in a direction perpendicular to the substrate 151. A current limiting layer 159 may be inserted between the active layer 153 and the p-type multilayer film reflector 154 to increase the gain distribution in the region below the light emitting surface 157. In this case, the distance (or interval) between the active layer 153 and the current limiting layer 159 is adjusted by the spacer layer 158 so that the antinode of the standing wave is located in the active layer 153, and the node of the standing wave is located in the current limiting layer 159.

[0034] A p-type anode electrode 155 is provided on the front surface of the p-type multilayer film reflector 154, and an n-type cathode electrode 156 is provided on the rear surface of the substrate 151. The surface exposed in the opening of the anode electrode 155 serves as a light emitting surface 157. The size of the light emitting surface 157 may be designed to fall within the range of 7 μm to 10 μm so that the mode field diameter of the emitted light matches the core diameter of the SMF 11.

[0035] In the case of using GaAlAs-based materials, the substrate 151 may be formed of an n-type GaAs substrate, and the multilayer film reflectors 152 and 154 may be formed of distributed Bragg reflectors (DBRs) in which GaAs and AlAs having different refractive indices are alternately stacked. The active layer 153 is formed of a multiple quantum well (MQW) having a GaAs well layer and an AlGaAs barrier layer, an MQW having a GaAsSb well layer and a GaAs barrier layer, an MQW having a GaInNA well layer and a GaAs barrier layer, etc. The current limiting layer 159 may be formed of an oxide of AlAs. The 1.3 μm band VCSEL may be formed of an InP-based material instead of using a GaAs-based material.

[0036] Since the VCSEL emits light in a direction perpendicular to the substrate 12, a direct modulation method is adopted when the optical device 10 is applied to an optical transceiver, as will be described later. The output light is directly modulated by controlling the on and off states of the current injected into the active layer 153 from the anode electrode 155 and the cathode electrode 156 of the light emitting element 150. In the light emitting element 150, in a state where a predetermined bias current is applied between the anode electrode 155 and the cathode electrode 156, the modulation current can be controlled to be on and off states.

[0037] The light emitted from the light emitting element 150 is converged by the lens 13 on the core 111 at the end surface 115 of the SMF 11. When the injection current is increased to increase the output power of the light emitting element 150, the light emitting element 150 is more likely to oscillate in a multi-mode. Even when the light emitting element 150 oscillates in a single mode, the light incident to the SMF 11 at a wavelength shorter than the cutoff wavelength of the SMF 11 may include a high-order mode, but the high-order mode is radiated at the bent portion 110, and the modulated light of the fundamental mode propagates in a direction parallel to the substrate 12. Therefore, inter-mode interference is reduced, and the waveform of the signal light can be maintained in a satisfactory state.

[0038] <Second Embodiment>

[0039] Figure 3 1 is a schematic diagram of an optical device 10A according to a second embodiment. In the second embodiment, the lens 13 is omitted, and the SMF 11 and the photoelectric conversion element 15 are optically coupled by a butt joint. The optical device 10A includes a photoelectric conversion element 15 disposed on a substrate 12, and an SMF 11 configured to guide light input to the photoelectric conversion element 15 from a first direction and output from the photoelectric conversion element 15 to the first direction, the first direction being perpendicular to the front surface of the substrate 12 or obliquely upward from the front surface of the substrate 12. For example, the photoelectric conversion element 15 is electrically connected to an interconnect formed on the substrate 12 via a bonding wire 14, but may be wire-bonded to an electronic chip such as a driver, a transimpedance amplifier (TIA), etc. disposed on the substrate 12 adjacent to the photoelectric conversion element 15. The SMF 11 has a curved (or bent) portion 110 that is curved (or bent) with a predetermined radius of curvature, and the curved portion 110 converts a propagation direction of light between a first direction perpendicular to the substrate 12 or diagonally upward relative to the substrate 12 and a second direction different from the first direction (for example, a direction parallel to the substrate 12), and radiates a higher-order mode.

[0040] The end face 115 of the SMF 11 and the light receiving surface and the light emitting surface of the photoelectric conversion element 15 are optically coupled through the butt joint 120. In the case where the photoelectric conversion element 15 is a VCSEL, the light emitting surface 157 of the VCSEL and the end face 115 of the SMF 11 are directly optically coupled through the butt joint 120. In the case where there is no misalignment between the center axis (optical axis) of the core 111 of the SMF 11 and the center of the light emitting surface 157 of the VCSEL, even if the distance between the end face 115 of the SMF 11 and the light emitting surface 157 of the VCSEL in the Z direction is about 100 μm, the coupling loss is several dB or less. Even if there is a misalignment of about ±1 μm between the optical axis of the SMF 11 and the optical axis of the light emitting surface 157, as long as the distance between the end face 115 of the SMF 11 and the light emitting surface 157 of the VCSEL is 60 μm or less, optical coupling can be achieved with a coupling loss of 2 dB or less.

[0041] The optical device 10A according to the second embodiment can convert the propagation direction of light between a direction perpendicular to the substrate 12 and a direction parallel to the substrate 12 and remove a high-order mode using a simple configuration in which the number of components is reduced and the SMF 11 itself has the bent portion 110 .

[0042] exist Figure 3 In the configuration of the second embodiment shown, the loss can be calculated using a model in which the opposite end faces of the SMF 11 are optically coupled to the light-receiving surface of the optical device 10A on which a photodiode is disposed through a butt joint. For comparison purposes, the loss is calculated for a model of a control example having the following: a VCSEL and a conventional 1.3 μm band SMF are optically coupled via a lens, the SMF is fused and spliced ​​to a mode filter of a planar lightwave circuit, the SMF is connected to another SMF on the emission side of the mode filter, and is optically coupled to the light-receiving surface of a photodiode via a lens.

[0043] In the comparative example, the configuration includes VCSEL→lens→SMF→mode filter→SMF→transmission path→SMF→mode filter→SMF→lens→photodiode. The components used include two lenses, four SMFs and two mode filters.

[0044] The coupling loss between the VCSEL and the SMF is 1.0 dB, and the coupling loss at the connection between the mode filter and the two SMFs is 1.4 dB (the loss of the mode filter itself is 0.3 dB, the coupling loss of the SMF on both sides of the mode filter is 1.0 dB, and the splicing loss is 0.1 dB). In the construction of the control example, the total loss on the transmission side is 2.4 dB.

[0045] On the receiving side of the control example, the coupling loss between the SMF and the light-receiving surface of the photodiode is 0.5 dB, and the coupling loss at the connection between the mode filter and the two SMFs is 1.4 dB (the loss of the mode filter itself is 0.3 dB, the coupling loss of the SMF on both sides of the mode filter is 1.0 dB, and the splicing loss is 0.1 dB). In the configuration of the control example, the total loss on the receiving side is 1.9 dB.

[0046] In contrast, the optical device 10A according to the second embodiment has a configuration including VCSEL→SMF (butt joint)→transmission path→SMF (butt joint)→photodiode. The components used are only two SMFs 11 having a bent portion 110 .

[0047] On the transmission side of the optical device 10A, the coupling loss at the butt joint 120 between the VCSEL and the SMF is 1.0 dB, the bending loss for the fundamental mode at the bent portion 110 is 0.5 dB, and the total loss is 1.5 dB. Compared with the total loss on the transmission side of the control example, the total loss on the transmission side is improved by 0.9 dB, that is, the total loss on the transmission side is 2.4 dB.

[0048] On the receiving side of the optical device 10A, the coupling loss at the butt joint between the SMF and the photodiode is 0.5 dB, the bending loss for the fundamental mode at the bent portion 110 is 0.5 dB, and the total loss is 1.0 dB. Compared with the total loss of the receiving side of the control example, the total loss of the receiving side is improved by 0.9 dB, that is, the total loss of the receiving side is 1.9 dB. When the transmitting side and the receiving side of the optical device 10A are combined, the loss improvement effect is 1.8 dB, and six components can be reduced compared with the control example.

[0049] The optical device 10A according to the second embodiment can convert the direction of light transmission and eliminate high-order modes using a simple configuration. In the optical device 10 according to the first embodiment, the number of components is greater than that of the second embodiment due to the use of the lens 13, but four components can still be reduced compared to the configuration of the control example, and the loss improvement effect obtainable in the first embodiment is similar to the loss improvement effect obtainable in the second embodiment.

[0050] <Third Embodiment>

[0051] Figure 4is a schematic diagram of an optical device 10B according to a third embodiment. The third embodiment utilizes a fixed bend (fixed bend) optical fiber, which is fixed to a predetermined bending radius by relaxing stress through heat treatment. The fixed bend optical fiber is used to convert the light emission direction in a silicon photonic circuit, and the limit value of the bending radius is about 2.5 mm. In the existing fixed bend optical fiber, when the bending radius is 3 mm, the bending loss difference between the high-order mode and the fundamental mode is about 0.1 dB, and the fundamental mode and the high-order mode cannot be separated. In the third embodiment, although a fixed bend optical fiber is used, the loss characteristics are adjusted so that the bending loss difference between the high-order mode and the fundamental mode becomes greater than or equal to 15 dB. As an adjustment method, in the third embodiment, the groove-type refractive index distribution of the existing low-loss fixed bend optical fiber is changed to a step-type refractive index distribution, and the mode field diameter is adjusted so that the bending loss becomes the desired characteristic.

[0052] The optical device 10B includes a photoelectric conversion element 15 disposed on a substrate 12 and an SMF 11B configured to guide light input to the photoelectric conversion element 15 and output from the photoelectric conversion element 15 to the first direction, the first direction being perpendicular to the front surface of the substrate 12 or obliquely upward from the front surface of the substrate 12. The SMF 11B is a fixed bend optical fiber whose refractive index profile is adjusted and whose radius of curvature is fixed to a predetermined radius of curvature by relaxing stress through heat treatment. For example, the photoelectric conversion element 15 is electrically connected to an interconnect formed on the substrate 12 via a bonding wire 14, but may be wire-bonded to an electronic chip such as a driver, a transimpedance amplifier (TIA), etc. disposed on the substrate 12 adjacent to the photoelectric conversion element 15. The SMF 11B includes a curved (or bent) portion 110B having a fixed predetermined radius of curvature. The curved portion 110B converts the propagation direction of light between a first direction perpendicular to the substrate 12 or obliquely upward relative to the substrate 12 and a second direction different from the first direction (e.g., a direction parallel to the substrate 12), and radiates a high-order mode.

[0053] The use of a fixed-bend optical fiber with relaxed stress and adjusted refractive index profile can reduce the possibility of physical damage or failure of SMF 11B and maintain the reliability of optical coupling. Similar to optical devices 10 and 10A, optical device 10B converts the propagation direction of light by about 90°, radiates high-order modes at the bent portion 110B, and propagates the fundamental mode with low loss.

[0054] <Fourth Embodiment>

[0055] Figure 5A1 is a schematic diagram of an optical device 10C according to a fourth embodiment. In the fourth embodiment, the SMF 11 is held by the fiber guide block 18. The fiber guide block 18 has a top surface 182, a front surface 184 adjacent to the photoelectric conversion element 15, and a curved corner portion 183 connecting the top surface 182 and the front surface 184. The fiber guide block 18 is formed with a groove 181 extending from the top surface 182 through the corner portion 183 to at least a portion of the front surface 184. By fitting the SMF 11 into the groove 181, a curved portion 110 curved with a predetermined radius of curvature is formed on the SMF 11, and the SMF 11 can be accurately positioned and aligned relative to the photoelectric conversion element 15.

[0056] The corner portion 183 of the fiber guide block 18 is curved so that the SMF 11 includes a curved portion 110 having a predetermined radius of curvature. The radius of curvature of the curved portion 110 of the SMF 11 is set to a value such that the bending loss difference between the high-order mode and the fundamental mode becomes greater than or equal to 15 dB, preferably greater than or equal to 18 dB, and more preferably greater than or equal to 20 dB. Therefore, the fundamental mode of light input and output from the photoelectric conversion element 15 can be transmitted with low loss, and the high-order mode can be radiated from the SMF 11.

[0057] The support layer 17 may be formed on the substrate 12 to adjust the height of the fiber guide block 18. The support layer 17 is formed of an adhesive, a resin, an insulator, etc. By matching the thickness of the support layer 17 with the height of the photoelectric conversion element 15, the SMF 11 held by the fiber guide block 18 and the photoelectric conversion element 15 can be optically coupled through the butt joint 120.

[0058] Figure 5B FIG. 1 is a schematic diagram of the groove 181 for holding the SMF 11. Figure 5B The groove 181 shown in FIG. 1 is a V-shaped groove, but may be a groove having a semicircular or U-shaped cross section. By fitting the SMF 11 into the groove 181, the SMF 11 can be stably held, and the curved portion 110 having a designed curvature radius can be formed. Therefore, the propagation direction of light is converted between a first direction perpendicular to the substrate 12 and a second direction parallel to the substrate 12, a high-order mode is radiated, and the fundamental mode is transmitted with low loss.

[0059] <Fifth Embodiment>

[0060] Figure 6 FIG. 1 is a schematic diagram of an optical device 10D according to a fifth embodiment. In the fifth embodiment, an optical fiber array 11 carrying a plurality of SMFs 11 ARR Optically coupled to the photoelectric conversion element array 15 provided on the substrate 12 ARR Fiber Array 11 ARRAn optical fiber holder 192 for holding a plurality of SMFs 11 is included. The optical fiber holder 192 is formed with a plurality of grooves for individually holding a plurality of SMFs 11 at predetermined intervals, and the SMFs 11 are held in the grooves of the optical fiber holder 192.

[0061] The optical fiber holder 192 is fixed to the substrate 12 so that the end face of each SMF 11 is aligned with the photoelectric conversion element array 15. ARR Each SMF 11 and the corresponding photoelectric conversion element are opposite. Each SMF 11 and the corresponding photoelectric conversion element can be optically coupled through a butt joint. Alternatively, a microlens array for converging light can be arranged on the optical fiber array 11. ARR and photoelectric conversion element array 15 ARR between.

[0062] A portion of the SMF 11 held by the fiber holder 192 extends in a direction substantially perpendicular to the substrate 12, changes direction at about 90° at the bent portion 110, and extends in a direction parallel to the substrate 12. Each SMF 11 may be a fixed curved optical fiber whose refractive index profile has been pre-adjusted and fixed to a predetermined radius of curvature in a state where stress is relaxed by heat treatment. In this case, damage to each SMF 11 at the bent portion 110 can be reduced, and a high-order mode can be radiated to propagate the fundamental mode with low loss.

[0063] In order to stably hold the portion of the SMF 11 extending in a direction parallel to the substrate 12, a fiber guide block 19 may be provided on the substrate 12. A support layer 17 may be formed on the substrate 12 for adjusting the height of the fiber guide block 19. Photoelectric conversion element array 15 ARR Each photoelectric conversion element in the array 15 is electrically connected to a circuit chip 20 provided on the substrate 12. ARR The and circuit chips 20 may be connected to each other through bonding wires, or may be connected to each other through interconnects formed on the substrate 12 .

[0064] <Example of application to optical transceiver>

[0065] Figure 7 1 is a block diagram of an optical transceiver 100 using an optical device according to an embodiment. The optical transceiver 100 includes a transmission-side optical device 10T and a reception-side optical device 10R provided on a substrate 12. The transmission-side optical device 10T includes a light emitting element 15 VC and light coupled to the light emitting element 15 VC SMF 11. SMF 11 relative to the light emitting element 15 VCThe bent portion 110 is provided on the light imaging side of the substrate 12. The bent portion 110 serves as a vertical-to-horizontal converter 117 configured to convert the propagation direction of light between the vertical direction and the horizontal direction relative to the substrate 12, and also serves as a mode filter 118 that eliminates a high-order mode. In the mode filter 118, the difference in bending loss between the high-order mode and the fundamental mode is 15 dB or more, preferably 18 dB or more, and more preferably 20 dB or more.

[0066] The receiving side optical device 10R includes a light receiving element 15 PD and light coupled to the light receiving element 15 PD The SMF 11 is located relative to the light receiving element 15. PD The bent portion 110 is provided on the light imaging side of the substrate 12. The bent portion 110 serves as a vertical-to-horizontal converter 117 configured to convert the propagation direction of light between the vertical direction and the horizontal direction relative to the substrate 12, and also serves as a mode filter 118 that eliminates a high-order mode. In the mode filter 118, the difference in bending loss between the high-order mode and the fundamental mode is 15 dB or more, preferably 18 dB or more, and more preferably 20 dB or more.

[0067] The optical transceiver 100 has a transmission IC 20T connected to a transmission-side optical device 10T and a reception IC 20R connected to a reception-side optical device 10R. The transmission IC 20T is an example of a circuit chip 20 and includes, for example, a drive light emitting element 15. VC The transmitting IC 20T including the driver circuit generates and outputs a signal for directly modulating the light emitting element 15 based on a data signal input from a large scale integrated circuit (LSI) such as a digital signal processor (DSP). VC The modulated driving signal.

[0068] The receiving IC 20R is an example of the circuit chip 20 and includes a circuit chip 21 that receives light from the light receiving element 15. PD The output photocurrent is converted into a voltage signal by the TIA and amplified. The voltage signal output from the TIA is provided to the DSP and other LSIs.

[0069] In the optical transceiver 100, the direction of the transmission path is converted between the vertical direction and the horizontal direction on each side of the transmission side and the receiving side, and the high-order mode is eliminated by propagating the fundamental mode with low loss. Therefore, inter-mode interference can be reduced, and the waveform of the optical signal can be maintained. The entire optical transceiver 100 can be accommodated in a housing together with the substrate 12. Since the direction of the SMF 11 is converted by about 90° at the curved portion 110 having a small bending radius ranging from 3 mm to 7 mm, the size of the optical transceiver 100 including the housing can be reduced.

[0070] Although the configuration of the optical device 10 for eliminating high-order modes is described above based on a specific configuration example, the present disclosure is not limited to the configuration example. The configurations of the embodiments may be arbitrarily combined. In each embodiment, an SMF in which stress is relaxed by heat treatment may be used, or an optical fiber array in which a plurality of SMFs 11 are arranged may be used. Even when the photoelectric conversion element 15 operates at a wavelength shorter than or equal to the cutoff wavelength of the SMF 11 or a high-order mode is generated in the transmission path, the high-order mode can be eliminated by the bent portion 110, and the optical signal quality can be maintained.

[0071] According to the embodiments, an optical device capable of eliminating a high-order mode and converting a propagation direction of light using a simple configuration can be provided.

[0072] The above description uses terms such as "determine", "identify", etc. to describe the implementation, however, such terms are abstractions of the actual operations performed. Therefore, as is apparent to those skilled in the art, the actual operations corresponding to these terms may vary depending on the implementation.

[0073] Although the embodiments are numbered, for example, "first," "second," "third," "fourth," or "fifth," the ordinal numbers do not imply priority of the embodiments. Many other variations and modifications will be apparent to those skilled in the art.

[0074] All examples and conditional language described herein are intended for teaching purposes to assist the reader in understanding the inventions and concepts contributed by the inventors to promote technological development, and should be interpreted as not being limited to such specific examples and conditions, and the organization of this example in the specification is not involved in showing the advantages and disadvantages of the invention. Although the embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions and modifications may be made thereto without departing from the spirit and scope of the present invention.

Claims

1. An optical device, comprising: A photoelectric conversion element is disposed on a substrate; as well as a single-mode optical fiber that guides light input to the photoelectric conversion element from a first direction and light output from the photoelectric conversion element toward the first direction, the first direction being vertical or obliquely upward relative to the substrate, wherein the single-mode optical fiber has a curved portion curved with a predetermined radius of curvature, and The bent portion converts a propagation direction of the light between the first direction and a second direction different from the first direction, and radiates a higher-order mode.

2. The optical device according to claim 1, wherein: The second direction is a direction parallel to the substrate.

3. The optical device according to claim 1, wherein: The predetermined radius of curvature of the curved portion is within a range of greater than or equal to 3 mm and less than or equal to 7 mm.

4. The optical device according to any one of claims 1 to 3, wherein: A difference between a bending loss of a high-order mode and a bending loss of a fundamental mode in the bent portion is greater than or equal to 15 dB.

5. The optical device according to any one of claims 1 to 3, wherein: The photoelectric conversion element is a vertical cavity surface emitting laser or a photodiode whose light receiving surface is parallel to the substrate.

6. The optical device according to any one of claims 1 to 3, wherein: The single-mode optical fiber is a fixed curved optical fiber fixed to the predetermined curvature radius in a state where stress is relaxed by heat treatment.

7. The optical device according to any one of claims 1 to 3, wherein: The single-mode optical fiber and the photoelectric conversion element are optically coupled via a butt joint.

8. The optical device according to any one of claims 1 to 3, further comprising: a lens disposed between the photoelectric conversion element and the end face of the single-mode optical fiber, The lens focuses the light emitted from the photoelectric conversion element on the core of the single-mode optical fiber, or focuses the light emitted from the core of the single-mode optical fiber on the light receiving surface of the photoelectric conversion element.

9. The optical device according to any one of claims 1 to 3, wherein: The single-mode optical fiber is an optical fiber for the 1.3 μm band, and The photoelectric conversion element operates in a wavelength band less than or equal to 1.26 μm which is a cutoff wavelength of the single-mode optical fiber.

10. The optical device according to any one of claims 1 to 3, further comprising: an optical fiber guide block, which is disposed on the substrate and guides the single-mode optical fiber, The optical fiber guide block has a bending angle portion for holding the bent portion of the single-mode optical fiber.

11. The optical device according to any one of claims 1 to 3, further comprising: an optical fiber holder, the optical fiber holder holding a plurality of single-mode optical fibers; as well as A photoelectric conversion element array, the photoelectric conversion element array comprising an array of a plurality of photoelectric conversion elements, Wherein, each of the plurality of single-mode optical fibers has the bent portion.

12. An optical transceiver, comprising: The optical device according to any one of claims 1 to 11; as well as A circuit is provided on the substrate and inputs and outputs an electric signal between the photoelectric conversion element and the circuit.

13. The optical transceiver according to claim 12, wherein: The circuit generates a drive signal for driving the photoelectric conversion element, and The photoelectric conversion element is directly modulated by the driving signal and outputs an optical signal.

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