Optical device and optical transceiver

Abstract

To provide an optical device that realizes removal of a higher-order mode and conversion of a propagation direction by a single configuration.SOLUTION: The optical device includes a photoelectric conversion element that is mounted on a substrate, and a single-mode fiber that guides light input to or output from the photoelectric conversion element to a first direction vertical or obliquely upward to the substrate, or from the first direction. The single-mode fiber has a bending part that bends with a prescribed radius of curvature, and the bending part changes 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.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to optical devices and optical transceivers. [Background technology]

[0002] With the development of the Internet, traffic volume continues to increase, especially at large-scale data centers. With the introduction of the fifth generation mobile communication system (abbreviated as "5G") and then the sixth generation mobile communication system (abbreviated as "6G"), it is expected that a data-driven society utilizing artificial intelligence (AI), machine learning, the Internet of Things (IoT) that connects various sensors, autonomous driving, etc. will spread at an accelerated pace. In the future, by 2030, there is a demand for low-cost, low-power, and high-density implementation technology for high-speed, single-core bidirectional optical links using single-mode fiber (SMF) over distances of less than 10 km.

[0003] When an optical signal having a wavelength in the 1 μm band is transmitted through an SMF in which the chromatic dispersion becomes zero at 1.3 μm (hereinafter referred to as "1.3 μm SMF"), higher-order modes are generated in the transmission path, and the transmission quality deteriorates due to inter-mode interference. A configuration is known in which a higher-order mode removal filter is formed with a curved waveguide formed in a planar lightwave circuit on a substrate, and this mode filter is placed between a photodetector and an SMF (see, for example, Patent Document 1). Research has been reported that evaluates a general SMF as a curved fiber mode filter for 1060 nm data transmission (see, for example, Non-Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-189252 [Non-patent literature]

[0005] [Non-Patent Document 1] Boxuan Zhang, Xiaodong Gu, Susumu Kinoshita and Fumio Koyama, "Bending-Fiber Mode Filter Evaluation for 1060 nm Data Transmission in Conventional Single-Mode Fiber," Proceedings of the 2022 Symposium on Electronics, Vol. 1, C-3 / 4-59, September 2022 Summary of the Invention [Problem to be solved by the invention]

[0006] In optical transmission using SMF, in addition to removing higher-order modes, a configuration is required to convert the optical path from the vertical direction to the horizontal direction or vice versa between a photoelectric conversion element having a light receiving / emitting surface parallel to the substrate. One object of the present disclosure is to provide an optical device that realizes the removal of higher-order modes and the conversion of the propagation direction with a simple configuration. [Means for solving the problem]

[0007] In one embodiment, the optical device comprises: A photoelectric conversion element mounted on a substrate; a single mode fiber that guides light input to and output from the photoelectric conversion element in a first direction perpendicular to or obliquely upward from the substrate, or from the first direction; having The single mode fiber has a bent portion that is bent at a predetermined radius of curvature, and the bent portion converts the propagation direction of the light between the first direction and a second direction different from the first direction, and radiates a higher-order mode. Effect of the Invention

[0008] An optical device that can eliminate higher-order modes and change the transmission direction with a simple configuration is realized. [Brief description of the drawings]

[0009] [Figure 1]FIG. 1 is a schematic diagram of an optical device according to a first embodiment. [Diagram 2] FIG. 1 is a diagram illustrating an example of a photoelectric conversion element used in an optical device. [Diagram 3] FIG. 4 is a schematic diagram of an optical device according to a second embodiment. [Figure 4] FIG. 13 is a schematic diagram of an optical device according to a third embodiment. [Figure 5A] FIG. 13 is a schematic diagram of an optical device according to a fourth embodiment. [Figure 5B] FIG. 1 is a schematic diagram of a V-groove that holds an SMF. [Figure 6] FIG. 13 is a schematic diagram of an optical device according to a fifth embodiment. [Figure 7] FIG. 1 is a block diagram of an optical transceiver using an optical device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In the embodiment, the SMF optically connected to the photoelectric conversion element mounted on the substrate is bent at a predetermined curvature radius to function as a direction converter that converts the light propagation direction between the vertical and horizontal directions, and also functions as a high-order mode filter that removes high-order modes. The SMF is used to build a single-core bidirectional optical link with a transmission rate of 100 Gbps or more. In 5G, 100 5G antenna base stations are required within a cell with a radius of 2 km. In 6G, the use of even higher frequency bands and a reduction in cell radius are expected. If the cell radius of 6G is 20 m, 10,000 6G cells or antenna base stations are required within a cell with a radius of 2 km. In 6G, a transmission rate of 1 Tbps or more, which is even higher than 100 Gbps, is expected.

[0011] Conventional third-generation (3G) to fourth-generation (4G) base stations are installed in or near telecommunications carrier buildings, and these base stations are connected to the network. When installing 5G or 6G base stations, a so-called optical fronthaul is introduced, in which optical fiber is extended from a 3G or 4G (for convenience, LTE is also included) base station or a telecommunications carrier's building. There is a demand to build an efficient optical fronthaul using SMF, which has a longer transmission distance and lower cost than multimode fiber (MMF).

[0012] In SMF, when the transmission wavelength is shorter than the cutoff wavelength, higher-order modes are transmitted in addition to the fundamental mode. The cutoff wavelength is the shortest wavelength at which only a single mode can propagate. When higher-order modes are included, the signal waveform deteriorates due to inter-modal interference, so a higher-order mode filter is required to remove higher-order modes. The higher the bit rate of transmission, the more pronounced the waveform deterioration becomes, so removing higher-order modes becomes essential.

[0013] When using a conventional mode filter composed of 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 to the mode filter. This increases the optical coupling loss between the optical fiber and the mode filter, and also increases the number of parts. To solve this problem, in the embodiment, a simple and low-cost configuration is realized by using "mode filtering optical coupling" that uses bending of the optical fiber to remove higher-order modes.

[0014] The specific configuration and method of delay control of the embodiment will be described below with reference to the drawings. The embodiment shown below is an example for embodying the technical idea of ​​the present disclosure, and does not limit the disclosed contents. The size, positional relationship, etc. of the components shown in each drawing may be exaggerated to facilitate understanding of the invention. The same components or functions may be given the same names or symbols, and duplicate explanations may be omitted.

[0015] (First embodiment) FIG. 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 mounted on a substrate 12, and an SMF 11 that guides light input to or output from the photoelectric conversion element 15 from or toward a first direction perpendicular or obliquely upward from the surface of the substrate 12. The photoelectric conversion element 15 is electrically connected to wiring formed on the substrate 12 by, for example, a bonding wire 14, but may also be wire-bonded to an electric chip such as a driver or a transimpedance amplifier (TIA) that is provided adjacently on the substrate 12. The SMF 11 includes a bending portion 110 that bends with a predetermined curvature radius, and the bending portion 110 converts the propagation direction of light between a first direction perpendicular or obliquely upward from the substrate and a second direction different from the first direction, and radiates a high-order mode. The second direction is, for example, a direction parallel to the substrate 12.

[0016] In the coordinate system of FIG. 1, a plane parallel to the surface of the substrate 12 is the XY plane, and a direction perpendicular to the substrate 12 is the Z direction. The bending section 110 converts the propagation direction of light between a first direction (Z direction) perpendicular to the substrate and a second direction in the XY plane, and radiates a higher mode and propagates a fundamental mode. The first direction does not need to be strictly 90° with respect to the surface of the substrate 12, and includes a direction of 90°±10° depending on the manufacturing error of the substrate 12 and the photoelectric conversion element 15, the bending state of the SMF 11, and the like. Similarly, the second direction does not need to be strictly parallel to the surface of the substrate 12, and includes a direction of 180°±10° with respect to the surface of the substrate 12, and includes a direction of 180°±10° depending on the manufacturing error of the substrate 12, the bending state of the SMF 11, the holding state, and the like.

[0017] The diameter of SMF 11, i.e., the outer diameter of cladding 112, is typically 125 μm, and the diameter of core 111 is 7 μm to 10 μm. SMF has a step-index (SI) type refractive index profile, and pulses propagating through small-diameter, high-refractive-index core 111 are less likely to spread, enabling longer-distance transmission compared to MMF.

[0018] The SMF 11 is deflected by approximately 90° at the bent portion 110, so that the end face 115 of the fiber faces the light receiving and emitting surface of the photoelectric conversion element 15 mounted on the substrate 12. A lens 13 may be disposed between the end face 115 of the fiber and the photoelectric conversion element 15. When the photoelectric conversion element 15 is a vertical cavity surface emitting laser (VCSEL), the light emitted from the photoelectric conversion element 15 is focused by the lens 13 onto the core 111 at the position of the end face 115. When the photoelectric conversion element 15 is a light receiving element such as a photodiode, the light emitted from the core 111 at the end face 115 is focused by the lens 13 onto the light receiving surface of the light receiving element.

[0019] The SMF generally used in optical communications is the 1.3 μm band zero dispersion SMF of ITU-T standard G652, but the limit value of the bending radius of this SMF is about 30 mm. If this SMF is bent at a bending radius of 30 mm or less and the direction is changed by 90 degrees, there is a concern that bending loss will increase and physical damage will occur. It may be desirable to use a low bending loss SMF recommended by ITU-T as G657 as the SMF 11 having the bending portion 110, but in the embodiment, an SMF with a bending loss difference between the fundamental mode and higher order modes of a certain level or more is used instead of a low bending loss SMF.

[0020] In order to propagate fundamental mode light with low loss and effectively remove higher-order modes at bending section 110, it is desirable that the difference in bending loss between the fundamental mode and the higher-order mode is sufficiently large. The difference in bending loss between the fundamental mode and the higher-order mode is, for example, 15 dB or more, preferably 18 dB or more, and more preferably 20 dB or more. As a result of extensive research by the inventors, it has been found that if a low bending loss fiber is used, the bending loss of the higher-order mode also becomes small, making it difficult to effectively remove the higher-order mode at bending section 110. Therefore, an SMF is used, which has a large bending loss for the higher-order mode and a negligible bending loss for the fundamental mode.

[0021] In Non-Patent Document 1, calculations using G652 SMF show that by increasing the bending radius to more than 6 mm, the bending loss of the fundamental mode, LP01 mode, is reduced to a negligible level. However, if the bending radius is increased to more than 7 mm, the loss of the higher order mode, LP11 mode, also decreases, and it is not possible to ensure a bending loss difference of 15 dB or more, preferably 18 dB or more, and more preferably 20 dB or more between the LP11 mode and the L01 mode. In actual specifications, the limit value of the bending radius of G652 SMF is 30 mm, so there is a risk of the fiber breaking if the bending radius is set to 7 mm.

[0022] As a result of calculations using various SMFs, the inventors found that by bending the SMF within a certain range of bending radii, the bending loss difference between the LP11 mode and the LP01 mode can be made 15 dB or more, preferably 18 dB or more, and more preferably 20 dB or more. In particular, when an SMF having bending resistance to the fundamental mode is used, the bending loss difference between the fundamental mode (LP01 mode) and the higher-order mode (LP11) can be made 20 dB or more by setting the bending radius to 3 mm or more and 7 mm or less. Even with an SMF having bending resistance to the fundamental mode, if the bending radius is smaller than 3 mm, the bending loss of the fundamental mode increases, the loss difference with the higher-order mode becomes smaller than 15 dB, and the fiber becomes more likely to be physically damaged.

[0023] By using such an SMF while bending it with a bending radius of 3 mm or more and 7 mm or more, the propagation direction of light can be converted between two different directions, for example, between the vertical direction and the horizontal direction with respect to the substrate, and a higher-order mode can be emitted at the bending 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 higher-order mode occurs in the 1.3 μm SMF. In the configuration of FIG. 1, an SMF 11 is used in which the bending loss of the higher-order mode is 15 dB or more larger than the bending loss of the fundamental mode. By using this SMF 11 while bending it with a bending radius of 3 mm or more and 7 mm or less, the propagation direction can be converted, the higher-order mode can be removed, and the fundamental mode can be transmitted with low loss.

[0024] FIG. 2 is a schematic diagram of a light emitting element 150 as an example of the 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. When used in the 1.3 μm band, the light emitting element 150 may be formed of a GaAlAs-based material or an InGaAs-based material. In the VCSEL, an n-type multilayer film reflecting mirror 152, an active layer 153, and a p-type multilayer film reflecting mirror 154 are 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 constriction layer 159 may be inserted between the active layer 153 and the p-type multilayer film reflecting mirror 154 to enhance the gain distribution in a region located below the light emitting surface 157. In this case, the distance between the active layer 153 and the current confinement 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 confinement layer 159 .

[0025] A p-side anode electrode 155 is provided on the surface of p-type multilayer film reflecting mirror 154, and an n-side cathode electrode 156 is provided on the back surface of substrate 151. The surface exposed in the opening of anode electrode 155 serves as light emitting surface 157. The size of light emitting surface 157 may be designed so that the mode field diameter of the emitted light is 7 to 10 μm, which matches the core diameter of SMF 11.

[0026] When a GaAlAs-based material is used, the substrate 151 may be an n-type GaAs substrate, and the multilayer reflective mirrors 152 and 154 may be formed of a distributed Bragg reflector (DBR) in which GaAs and AlAs with different refractive indices are alternately laminated. 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 GaInNAs well layer and a GaAs barrier layer, or the like. The current confinement layer 159 may be formed of an oxide of AlAs. The 1.3 μm VCSEL may be formed of an InP-based material instead of a GaAs-based material.

[0027] Since the VCSEL emits light in a direction perpendicular to the substrate 12, as described below, when the optical device 10 is applied to an optical transceiver, a direct modulation method is adopted. The output light is directly modulated by controlling the on / off of the current injected from the anode electrode 155 and the cathode electrode 156 of the light emitting element 150 to the active layer 153. The modulation current of the light emitting element 150 may be controlled to be turned on and off while a predetermined bias current is applied between the anode electrode 155 and the cathode electrode 156.

[0028] Light emitted from the light-emitting element 150 is focused by the lens 13 onto the core 111 at the end face 115 of the SMF 11. If 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 multiple modes. Even if the light-emitting element 150 oscillates in a single mode, light that is incident on the SMF 11 at a wavelength shorter than the cutoff wavelength of the SMF 11 may contain higher-order modes, but the higher-order modes are emitted at the bend 110, and the modulated light in the fundamental mode is propagated in a direction parallel to the substrate 12. This makes it possible to suppress inter-mode interference and maintain a good waveform of the signal light.

[0029] Second embodiment FIG. 3 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 has a photoelectric conversion element 15 mounted on a substrate 12, and an SMF 11 that guides light input to and output from the photoelectric conversion element 15 from a first direction perpendicular to or obliquely upward from the surface of the substrate 12, or toward the first direction. The photoelectric conversion element 15 is electrically connected to wiring formed on the substrate 12 by, for example, a bonding wire 14, but may also be wire-bonded to an electric chip such as a driver or a transimpedance amplifier (TIA) that is provided adjacently on the substrate 12. The SMF 11 has a bending portion 110 that bends with a predetermined radius of curvature. The bending portion 110 converts the propagation direction of light between a first direction perpendicular to or obliquely upward from the substrate, and a second direction different from the first direction (for example, a direction parallel to the substrate), and radiates a high-order mode.

[0030] An end face 115 of the SMF 11 and an input / output light surface of the photoelectric conversion element 15 are optically coupled by a butt joint 120. When the photoelectric conversion element 15 is a VCSEL, its light output surface 157 and the end face 115 of the SMF 11 are directly optically coupled by a butt joint 120. If there is no misalignment between the central axis (optical axis) of the core 111 of the SMF 11 and the center of the light output surface 157 of the VCSEL, even if the distance in the Z direction between the end face 115 of the SMF 11 and the light output surface 157 of the VCSEL 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 output surface 157, as long as the distance between the end face 115 of the SMF 11 and the light output surface 157 of the VCSEL is 60 μm or less, the optical coupling is performed with a coupling loss of 2 dB or less.

[0031] The optical device 10A of the second embodiment has a simple configuration in which the number of parts is reduced and the SMF 11 itself has a bent portion 110, and can convert the propagation direction of light between vertical and horizontal directions with respect to the substrate 12 and remove higher-order modes.

[0032] Loss is calculated using a model in which the opposite end face of SMF 11 is optically coupled via a butt joint to the light-receiving surface of optical device 10A equipped with a PD in the configuration of Figure 3. For comparison, loss is calculated for a model in which a VCSEL and a normal 1.3 μm SMF are optically coupled via a lens, the SMF is fused to a mode filter in a planar lightwave circuit, the output side of the mode filter is connected to another SMF, and the model is optically coupled to the light-receiving surface of the PD via a lens.

[0033] In the comparative example, the configuration is VCSEL → lens → SMF → mode filter → SMF → transmission line → SMF → mode filter → SMF → lens → PD. The components used are two lenses, four SMFs, and two mode filters.

[0034] 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 splice loss is 0.1 dB). In the configuration of the comparative example, the total loss on the transmitting side is 2.4 dB.

[0035] On the receiving side of the comparative example, the coupling loss between the SMF and the light receiving surface of the PD 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 splice loss is 0.1 dB). With the configuration of the comparative example, the total loss at reception is 1.9 dB.

[0036] On the other hand, the optical device 10A of the second embodiment has a configuration of VCSEL→SMF (butt joint)→transmission line→SMF (butt joint)→PD. The only components are the two SMFs 11 having the bent portions 110.

[0037] On the transmitting side of the optical device 10A, the coupling loss at the butt joint 120 between the VCSEL and SMF is 1.0 dB, the bending loss for the fundamental mode at the bending section 110 is 0.5 dB, and the total loss is 1.5 dB. This is an improvement of 0.9 dB compared to the loss of 2.4 dB on the transmitting side of the comparative configuration.

[0038] On the receiving side of optical device 10A, the coupling loss at the butt joint between SMF and PD is 0.5 dB, and the bending loss for the fundamental mode at bending section 110 is 0.5 dB, for a total loss of 1.0 dB. This represents an improvement of 0.9 dB compared to the loss of 1.9 dB on the receiving side of the comparison configuration. Combining the transmitting and receiving sides, a loss improvement of 1.8 dB and a reduction of six parts were achieved.

[0039] The optical device 10A of the second embodiment realizes the change of direction of optical transmission and the removal of higher-order modes with a simpler configuration. Note that the optical device 10 of the first embodiment has a larger number of parts than the second embodiment due to the use of the lens 13, but the number of parts is reduced by four compared to the configuration of the comparative example, and the same level of loss improvement effect as the second embodiment can be obtained.

[0040] Third embodiment FIG. 4 is a schematic diagram of an optical device 10B according to a third embodiment. In the third embodiment, a fixed bending fiber is used, which is fixed to a predetermined bending radius by relaxing stress through heat treatment. The fixed bending fiber is used to convert the light emission direction in a silicon photonics circuit, and the limit value of the bending radius is about 2.5 mm. In the existing fixed bending fiber, the loss difference between the higher mode and the fundamental mode is about 0.1 dB at a bending radius of 3 mm, and the fundamental mode and the higher mode cannot be separated. In the third embodiment, a fixed bending fiber is used, but the loss characteristics are adjusted so that the difference between the bending loss of the higher mode and the bending loss of the fundamental mode is 15 dB or more. As an adjustment method, the trench-type index profile of the existing low-loss fixed bending fiber is changed to a step-type index profile in the third embodiment, and the mode field diameter is adjusted so that the bending loss has the desired characteristics.

[0041] The optical device 10B has a photoelectric conversion element 15 mounted on a substrate 12, and an SMF 11B that guides light input to and output from the photoelectric conversion element 15 from or to a first direction perpendicular or obliquely upward from the surface of the substrate 12. The SMF 11B is a fixed bending fiber whose index profile is adjusted and whose stress is relieved by heat treatment to fix it to a predetermined radius of curvature. The photoelectric conversion element 15 is electrically connected to wiring formed on the substrate 12 by, for example, a bonding wire 14, but may also be wire-bonded to an electric chip such as a driver or a transimpedance amplifier (TIA) provided adjacently on the substrate 12. The SMF 11B has a bending portion 110B that is fixed to a predetermined radius of curvature. The bending portion 110B converts the propagation direction of light between a first direction perpendicular or obliquely upward from the substrate and a second direction different from the first direction (for example, a direction parallel to the substrate), and radiates a high-order mode.

[0042] By using a fixed-bend fiber with stress relief and an adjusted index profile, the possibility of physical damage or failure of the SMF 11B can be reduced, and the reliability of the optical coupling can be maintained. The optical device 10B, like the optical devices 10 and 10A, changes the light propagation direction by approximately 90°, radiates a higher-order mode at the bent portion 110B, and propagates the fundamental mode with low loss.

[0043] (Fourth embodiment) 5A is a schematic diagram of an optical device 10C according to a fourth embodiment. In the fourth embodiment, the SMF 11 is held by a fiber guide block 18. The fiber guide block 18 has an upper surface 182, a front surface 184 adjacent to the photoelectric conversion element 15, and a curved corner portion 183 connecting the upper surface 182 and the front surface 184. The fiber guide block 18 is formed with a groove 181 that extends from the upper surface 182 through the corner portion 183 to at least a part of the front surface 184. By fitting the SMF 11 into the groove 181, a bent portion 110 that bends with a predetermined radius of curvature is formed in the SMF 11, and the SMF 11 can be aligned with respect to the photoelectric conversion element 15 with high accuracy.

[0044] The corners 183 of the fiber guide block 18 are curved so that the SMF 11 has a bent portion 110 with a predetermined radius of curvature. The radius of curvature of the bent portion 110 of the SMF 11 is set to a value that makes the difference between the bending loss of the higher-order mode and the bending loss of the fundamental mode 15 dB or more, preferably 18 dB or more, and more preferably 20 dB or more. This allows the fundamental mode of light input to and output from the photoelectric conversion element 15 to be transmitted with low loss, and allows the higher-order mode to be radiated from the SMF 11.

[0045] In order to adjust the height of the fiber guide block 18, a support layer 17 may be formed on the substrate 12. The support layer 17 is made of an adhesive, resin, an insulator, or the like. By adjusting the thickness of the support layer 17 to 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 by a butt joint 120.

[0046] 5B is a schematic diagram of a groove 181 that holds the SMF 11. The groove 181 illustrated in FIG. 5B is a V-groove, but may be a groove with a semicircular or U-shaped cross section. By fitting the SMF 11 into the groove 181, the SMF 11 is stably held and a bent portion 110 with a designed radius of curvature is formed. This converts the propagation direction of light between a first direction perpendicular to the substrate 12 and a second direction parallel to the substrate 12, while emitting a higher-order mode and transmitting a fundamental mode with low loss.

[0047] Fifth embodiment 6 is a schematic diagram of an optical device 10D according to a fifth embodiment. In the fifth embodiment, a photoelectric conversion element array 15 mounted on a substrate 12 is ARR On the other hand, a fiber array 11 carrying a plurality of SMFs 11 ARR Fiber array 11 ARR has a fiber holder 192 that holds a plurality of SMFs 11. A plurality of grooves that individually hold a plurality of SMFs 11 at predetermined intervals are formed in the fiber holder 192, and the SMFs 11 are held in the grooves of the fiber holder 192.

[0048] The fiber holder 192 is arranged so that the end face of each SMF 11 is connected to the photoelectric conversion element array 15 ARR The SMFs 11 are fixed to the substrate 12 so as to face the corresponding photoelectric conversion elements of the SMFs 11. Optical coupling between each SMF 11 and the corresponding photoelectric conversion element may be achieved by a butt joint. ARR and photoelectric conversion element array 15 ARR A microlens array for focusing light may be disposed between the first and second electrodes.

[0049] The portion of the SMF 11 held by the fiber holder 192 extends almost perpendicular to the substrate 12, and is deflected by about 90° by the bending portion 110 to extend in a direction parallel to the substrate 12. Each SMF 11 may be a fixed-bend fiber whose index profile has been adjusted in advance and whose curvature radius has been fixed in a predetermined state in which stress has been relieved by heat treatment. In this case, damage to each SMF 11 at the bending portion 110 can be suppressed, and the higher-order modes can be radiated, allowing the fundamental mode to propagate with low loss.

[0050] A fiber guide block 19 may be disposed on the substrate 12 in order to stably hold the portion of the SMF 11 that extends parallel to the substrate 12. A support layer 17 may be formed on the substrate 12 in order to adjust the height of the fiber guide block 19. ARR Each of the photoelectric conversion elements is electrically connected to an electric circuit chip 20 mounted on the substrate 12. The photoelectric conversion element array 15ARR and the electric circuit chip 20 may be connected by a bonding wire or by wiring formed on the substrate 12.

[0051] (Example of application to optical transceivers) 7 is a block diagram of an optical transceiver 100 using the optical device of the embodiment. The optical transceiver 100 includes a transmitting optical device 10T and a receiving optical device 10R mounted on a substrate 12. The transmitting optical device 10T includes a light emitting element 15. VC And this light emitting element 15 VC The SMF 11 includes a light emitting element 15. VCThe bending section 110 is disposed on the optical imaging side of the substrate 12. The bending section 110 functions as a vertical-horizontal converter 117 that converts the propagation direction of light between the vertical direction and the horizontal direction with respect to the substrate 12, and also functions as a mode filter 118 that removes higher-order modes. In the mode filter 118, the difference between the bending loss for the higher-order mode and the bending loss for the fundamental mode is 15 dB or more, preferably 18 dB or more, and more preferably 20 dB or more.

[0052] The receiving optical device 10R includes a light receiving element 15 PD And this photodetector 15 PD The SMF 11 includes a light receiving element 15. PD The bending section 110 is disposed on the optical imaging side of the substrate 12. The bending section 110 functions as a vertical-horizontal converter 117 that converts the propagation direction of light between the vertical direction and the horizontal direction with respect to the substrate 12, and also functions as a mode filter 118 that removes higher-order modes. In the mode filter 118, the difference between the bending loss for the higher-order mode and the bending loss for the fundamental mode is 15 dB or more, preferably 18 dB or more, and more preferably 20 dB or more.

[0053] The optical transceiver 100 includes a transmitting IC 20T connected to a transmitting optical device 10T, and a receiving IC 20R connected to a receiving optical device 10R. The transmitting IC 20T is an example of an electric circuit chip 20, and may include, for example, a light emitting element 15. VC The transmission IC 20T including the driver circuit drives 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 A modulated drive signal that directly modulates the input signal is generated and output.

[0054] The receiver IC 20R is an example of the electric circuit chip 20, and includes a light receiving element 15 PD The photocurrent output from the TIA is converted to a voltage signal and amplified. The voltage signal output from the TIA is supplied to a DSP and other LSIs.

[0055] In the optical transceiver 100, the direction of the transmission line is converted between vertical and horizontal on both the transmitting and receiving sides, and the fundamental mode is propagated with low loss to eliminate higher-order modes. This makes it possible to suppress interference between modes and maintain the waveform of the optical signal. The entire optical transceiver 100 together with the substrate 12 may be housed in a casing. In the bending section 110, the direction of the SMF 11 is converted by about 90° with a small bending radius of 3 mm to 7 mm, so that the optical transceiver 100 including the casing can be made compact.

[0056] Although the higher-order mode removal configuration of the optical device 10 has been described based on a specific configuration example, the present disclosure is not limited to the above-mentioned configuration example. The configurations of each embodiment may be combined. In all embodiments, an SMF whose stress has been relieved by heat treatment may be used, or a fiber array in which multiple SMFs 11 are arranged may be used. Even if the photoelectric conversion element 15 operates at a wavelength equal to or less than the cutoff wavelength of the SMF 11 or a higher-order mode occurs in the transmission path, the higher-order mode can be removed by the bending portion 110 to maintain the quality of the optical signal.

[0057] In response to the above disclosure, the following remarks are presented: (Appendix 1) A photoelectric conversion element mounted on a substrate; a single mode fiber that guides light input to and output from the photoelectric conversion element in a first direction perpendicular to or obliquely upward from the substrate, or from the first direction; having The single mode fiber has a bent portion that is bent at 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. Optical devices. (Appendix 2) The second direction is a direction parallel to the substrate. 2. The optical device of claim 1. (Appendix 3) The radius of curvature of the bent portion is 3 mm or more and 7 mm or less. 3. The optical device of claim 1 or 2. (Appendix 4) A difference between the bending loss of the higher mode and the bending loss of the fundamental mode in the bending portion is 15 dB or more. 4. An optical device according to any one of claims 1 to 3. (Appendix 5) the photoelectric conversion element is a vertical cavity surface emitting laser or a photodiode having a light receiving surface parallel to the substrate; 5. An optical device according to any one of claims 1 to 4. (Appendix 6) The single mode fiber is a fixed bending fiber that is fixed to the predetermined radius of curvature in a state where the stress is relieved by heat treatment. 6. An optical device according to any one of claims 1 to 5. (Appendix 7) The single mode fiber and the photoelectric conversion element are butt-jointed. 7. An optical device according to any one of claims 1 to 6. (Appendix 8) a lens disposed between the photoelectric conversion element and an end face of the single mode fiber; having the lens focuses the light emitted from the photoelectric conversion element onto the core of the single mode fiber, or focuses the light emitted from the core of the single mode fiber onto a light receiving surface of the photoelectric conversion element. 7. An optical device according to any one of claims 1 to 6. (Appendix 9) The single mode fiber is an optical fiber for use in the 1.3 μm band, The photoelectric conversion element operates in a wavelength band of 1.26 μm or less, which is the cutoff wavelength of the single mode fiber. 9. An optical device according to any one of claims 1 to 8. (Appendix 10) a fiber guide block mounted on the substrate for guiding the single mode fiber; 10. The optical device of claim 1, wherein the fiber guide block has a curved corner portion that holds the bent portion of the single mode fiber. (Appendix 11) a fiber holder for holding a plurality of the single mode fibers; a photoelectric conversion element array having an arrangement of a plurality of the photoelectric conversion elements; each of the plurality of single mode fibers has the bent portion; 11. An optical device according to any one of claims 1 to 10. (Appendix 12) An optical device according to any one of claims 1 to 11; an electric circuit mounted on the substrate for inputting and outputting electric signals between the photoelectric conversion element and the electric circuit; An optical transceiver having (Appendix 13) The electric circuit generates a drive signal for driving the photoelectric conversion element, and the photoelectric conversion element outputs an optical signal directly modulated by the drive signal. 13. The optical transceiver of claim 12. [Explanation of symbols]

[0058] 10, 10A, 10B, 10C, 10D Optical Devices 10T Transmitting Optical Device 10R Receiver Optical Device 11 Single mode fiber (SMF) 11 ARR Fiber Array 11D fixed bend fiber 12 Substrate 13 Lens 15 Photoelectric conversion element 15 VC Light emitting element 15 PD Light receiving element 15 ARR Photoelectric conversion element array 17 Support layer 18, 19 Fiber guide block 20 Electrical Circuit Chip 20T transmitting IC 20R receiving IC 100 Optical Transceiver 110 Bending section 111 cores 112 Clad 115 End face 117 Vertical-horizontal converter 118 Mode Filter 120 Butt Joint 157 Light exit surface 181 Groove 192 Fiber Holder

Claims

1. A photoelectric conversion element mounted on a substrate; a single mode fiber that guides light input to and output from the photoelectric conversion element in a first direction perpendicular to or obliquely upward from the substrate, or from the first direction; having the single mode fiber has a bent portion that is bent at a predetermined radius of curvature, 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. Optical devices.

2. The second direction is a direction parallel to the substrate.

10. The optical device of claim 1 .

3. The radius of curvature of the bent portion is 3 mm or more and 7 mm or less. The optical device according to claim 1 .

4. A difference between the bending loss of the higher mode and the bending loss of the fundamental mode at the bending portion is 15 dB or more.

10. The optical device of claim 1 .

5. the photoelectric conversion element is a vertical cavity surface emitting laser or a photodiode having a light receiving surface parallel to the substrate; 10. The optical device of claim 1 .

6. The single mode fiber is a fixed bending fiber that is fixed to the predetermined radius of curvature in a state where the stress is relieved by heat treatment.

10. The optical device of claim 1 .

7. The single mode fiber and the photoelectric conversion element are butt-jointed.

10. The optical device of claim 1 .

8. The single mode fiber is an optical fiber for use in the 1.3 μm band, The photoelectric conversion element operates in a wavelength band of 1.26 μm or less, which is the cutoff wavelength of the single mode fiber.

10. The optical device of claim 1 .

9. An optical device according to any one of claims 1 to 8; an electric circuit mounted on the substrate for inputting and outputting electric signals between the photoelectric conversion element and the electric circuit; An optical transceiver having

10. The electric circuit generates a drive signal for driving the photoelectric conversion element, and the photoelectric conversion element outputs an optical signal directly modulated by the drive signal.

10. The optical transceiver of claim 9.

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