Fan-In / Fan-Out device and optical communication system including same

Abstract

The present invention pertains to an optical waveguide device that enables signal-mode connection of cores to be connected through control of optical signal intensity fluctuation caused by MPI. This optical waveguide device is provided with: a first device end surface (50a); a second device end surface (50b); a waveguide (51); and a clad layer (52). The waveguide has a first waveguide end surface (51a) and a second waveguide end surface (51b), and guides waves of light in a plurality of modes having different orders. The waveguide has one or more bent parts (55). The clad layer has a refractive index lower than that of the waveguide. The waveguide has a waveguide length L of 5×106 [nm] to 100×106 [nm], and has a structure where an inter-mode group delay time difference Δβ1 satisfies a condition of |Δβ1|≤1 / 2×10-12[s] / L.

Description

[Technical field]

[0001] The present disclosure relates to an optical waveguide device and an optical communication system including the same. This application claims priority from Japanese Patent Application No. 2020-038906, filed on March 6, 2020, the contents of which are relied upon and incorporated herein by reference in their entirety. [Background technology]

[0002] As one type of optical waveguide device, a FIFO (Fan-in / Fan-out) device that converts the pitch of multiple aligned waveguides (cores) along the light propagation direction is known, as disclosed in, for example, Patent Document 1 and Patent Document 2. By using such a FIFO device, it becomes possible to connect, with low loss, combinations of different core pitches, for example, each core of multiple single-core optical fiber fibers (hereinafter referred to as "SCFs") arranged in parallel on the same plane to the corresponding core of a multi-core optical fiber (hereinafter referred to as "MCF").

[0003] Patent Document 1 discloses a FIFO device that has a three-dimensional waveguide structure and a mode field diameter (hereinafter, referred to as "MFD") conversion function. Patent Document 2 discloses a configuration that uses a lens to suppress connection loss between cores to be connected. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. WO2018-135411 [Patent Document 2] JP 2014-178628 A Summary of the Invention

[0005] The optical waveguide device of the present disclosure includes a first device end face, a second device end face opposite the first device end face, a waveguide, and a cladding layer. The waveguide has a first waveguide end face coinciding with the first device end face and a second waveguide end face coinciding with the second device end face, and guides light of a plurality of modes with different orders. The waveguide also has one or more bends on the optical path from the first waveguide end face to the second waveguide end face. The cladding layer has a waveguide provided inside or on the surface. The cladding layer has a refractive index lower than that of the waveguide. In particular, the waveguide has a refractive index of 5×10 6 [nm] or more 100×10 6 The waveguide has a length L of 100 nm or less, and the differential mode delay (DMD: Differential Mode Delay, hereinafter referred to as "differential mode group delay") Δβ1 between a plurality of modes satisfies the following formula: |Δβ1|≦1 / 2×10 -12 [s] / L The structure satisfies the condition given by [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a diagram for explaining a configuration example (system configuration) of an optical communication system according to the present disclosure. [Diagram 2] FIG. 2 is a diagram for explaining a configuration example (device configuration) of the optical waveguide device of the present disclosure. [Diagram 3] FIG. 3 is a diagram for explaining a control operation for the optical signal intensity fluctuation caused by MPI. [Figure 4] FIG. 4 is a graph showing the relationship between the differential mode group delay Δβ1 (absolute value) and the number of divisions N for various modulation speeds. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] [Problem that this disclosure aims to solve] The present disclosure aims to provide an optical waveguide device and an optical communication system including the same that enable single-mode connection between the cores of a pair of optical fibers to be connected by controlling an unavoidable problem in the structure of conventional FIFO devices, namely, optical signal intensity fluctuation caused by interference between lower and higher modes (multipass interference, hereinafter referred to as "MPI") within a frequency band required for signal modulation in optical signal transmission.

[0008] [Effects of this disclosure] According to the optical waveguide device disclosed herein, it becomes possible to control the optical signal intensity fluctuation caused by MPI within the frequency band required for signal modulation in optical signal transmission, thereby enabling a single-mode connection between the cores of a pair of optical fibers to be connected.

[0009] First, the structural features required for optical waveguide devices such as FIFO devices will be described.

[0010] In a FIFO device, the pitch of multiple aligned cores (waveguides) is converted along the light propagation direction, so each core usually has a bent structure. Therefore, bending loss occurs while light propagates through the cores in the FIFO device. Therefore, in order to connect a pair of optical fibers (effectively between cores in one-to-one correspondence) with low loss, it is necessary to suppress bending loss. Furthermore, in a FIFO device, the minimum pitch between adjacent cores is 50 μm or less, and increased crosstalk between adjacent cores becomes a noise factor in optical signal transmission. Therefore, it is also necessary to suppress crosstalk.

[0011] Considering the suppression of the bending loss and crosstalk mentioned above, it is effective to increase the relative refractive index difference between the core and cladding in the FIFO device (for example, the relative refractive index difference of the core based on the refractive index of the cladding at a wavelength of 589 [nm]) and strengthen the light confinement in the core. However, an increase in the relative refractive index difference Δ of the core causes a decrease in the MFD (mode field diameter) of the FIFO device, increasing the coupling loss with single mode optical fiber (SMF). Therefore, in the FIFO device, it is necessary to expand the core width (or core diameter) as the relative refractive index difference Δ of the core increases.

[0012] However, when the relative refractive index difference Δ of the core is increased and the core width is expanded, not only the fundamental mode that is desired to be guided but also higher-order modes that are not desired to be guided can be guided. In optical signal transmission, the propagation of light in these higher-order modes generally becomes a problem. That is, in optical waveguiding devices such as FIFO devices for single-mode transmission, when the structure allows the higher-order modes to be guided, the occurrence of interference (MPI) between the fundamental mode and the higher-order mode becomes a problem.

[0013] Therefore, the waveguide device disclosed herein does not actively eliminate the above-mentioned MPI, but instead ensures a single-mode connection between a pair of optical fibers to be connected by controlling to reduce the optical signal intensity fluctuations caused by MPI within the frequency band required for signal modulation.

[0014] [Description of the embodiments of the present disclosure] First, the contents of the embodiments of the present disclosure will be individually listed and described.

[0015] (1) The optical waveguide device of the present disclosure has a 25×10 9 [Hz] or more 1000×10 9The optical waveguide device is an optical device for single-mode transmission of an optical signal of wavelength λ0 modulated at a modulation rate defined by any frequency of 0.1 [Hz] or less. Specifically, in one embodiment, the optical waveguide device comprises a first device end face, a second device end face opposing the first device end face, a waveguide, and a cladding layer. The waveguide has a first waveguide end face coinciding with the first device end face and a second waveguide end face coinciding with the second device end face, and guides light of a plurality of modes with different orders. The waveguide has one or more bends on the optical path from the first waveguide end face to the second waveguide end face. The cladding layer has a waveguide provided inside or on the surface. The cladding layer has a refractive index lower than that of the waveguide. In particular, the waveguide has a refractive index of 5×10 6 [nm] or more 100×10 6 It has a waveguide length L of [nm] or less and has the following formula: |Δβ1|≦1 / (N 2Δf L) The waveguide length L is defined as the optical path length from the end face of the first waveguide to the end face of the second waveguide. In the above formula, the parameter "Δβ1" is the mode group delay time difference. The parameter "N" is an integer value that divides the oscillation period Tf of the optical frequency of the optical signal intensity fluctuation caused by MPI between multiple modes, and is a division number defined as an integer between 10 and 100. The parameter "Δf" is 25×10 9 [Hz] or more 1000×10 9 It is a modulation rate defined by any frequency below [Hz] (for example, Δf = 25 [GHz] corresponds to 25 [GBaud]).

[0016] (2) In one embodiment of the present disclosure, the bent portion preferably has a curvature radius r of 40 mm or less. Fan -In / Fan This is applicable to optical fiber (O-Out) devices and enables optical connection between optical fibers with different core pitches. However, the waveguide length L must be set to 5×10 so that bending loss is not too large (curvature radius r is not too small). 6On the other hand, in order to ensure ease of handling of the device, the waveguide length L is preferably 100×10 6 [nm] or less is preferable. 。

[0017] (3) In one embodiment, the optical communication system of the present disclosure includes at least a pair of optical fibers and an optical waveguide device (optical waveguide device of the present disclosure) having the above-described structure provided between the pair of optical fibers. By applying the optical waveguide device having the above-described structure, the cores of the pair of optical fibers can be connected in a single mode.

[0018] (4) In one aspect of the present disclosure, in the optical communication system, each of a pair of optical fibers arranged to sandwich the optical waveguide device preferably includes a single-core optical fiber (hereinafter, referred to as "SCF") or a multi-core optical fiber (hereinafter, referred to as "MCF"). In particular, when one of the pair of optical fibers includes an MCF, it becomes possible to efficiently use the wiring space in a base station or the like.

[0019] As described above, each aspect listed in the [Description of the embodiments of the present disclosure] section is applicable to each of the remaining aspects or to all combinations of these remaining aspects.

[0020] [Details of the embodiment of the present disclosure] Hereinafter, specific structures of optical waveguide devices and optical communication systems according to embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to these examples, but is indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims. In addition, in the description of the drawings, the same elements are given the same reference numerals, and duplicated descriptions are omitted.

[0021] FIG. 1 is a diagram for explaining a configuration example (system configuration) of an optical communication system according to the present disclosure. The upper part of FIG. 1 shows a general configuration example of an optical communication system according to the present disclosure. The middle part of FIG. 1 shows a configuration example of a fusion-extended optical waveguide device 50A that can be applied as a FIFO device of the optical communication system. The lower part of FIG. 1 shows a configuration example of a PLC (Planar Lightwave Circuit) type optical waveguide device 50B that can be applied as a FIFO device of the optical communication system. The FIFO device of the optical communication system according to the present disclosure may be an optical waveguide device in which optical circuits are arranged three-dimensionally.

[0022] The optical communication system includes a plurality of optical transmitters (hereinafter referred to as "TX") 10, a plurality of optical receivers (hereinafter referred to as "RX") 20, an MCF (multi-core optical fiber) 40, a pair of FIFO devices 50 (the FIFO device located between the plurality of TXs 10 and the MCF 40 is referred to as the "input side FIFO device", and the FIFO device located between the MCF 40 and the plurality of RXs 20 is referred to as the "output side FIFO device"), and a plurality of SCFs (single-core optical fibers) 30 arranged both between the plurality of TXs 10 and the input side FIFO device and between the output side FIFO device and the plurality of RXs 20. The TX 10 has a transmission ratio of 25×10 for optical signals with wavelengths of, for example, 1310 [nm] and 1550 [nm]. 9 [Hz] or more 1000×10 9 [Hz] Any of the following modulation rates Δf (e.g., 25×10 9 [Hz], 50×10 9 [Hz], 100×10 9 [Hz], 200×10 9 [Hz], 500×10 9 [Hz], 1000×10 9 Modulation is performed in increments of [Hz].

[0023] Among the multiple SCFs 30, the SCFs 30 corresponding to the multiple TXs 10 are disposed between the multiple TXs 10 and the input side FIFO device, and the SCFs 30 corresponding to the multiple RXs 20 are disposed between the multiple RXs 20 and the output side FIFO device. Optical signals are output from the multiple TXs 10, and the multiple RXs 20 receive the optical signals from the multiple TXs 10. Therefore, the multiple SCFs 30 function as a waveguide for individually propagating the optical signals from the multiple TXs 10 to the input side FIFO device, or as a waveguide for individually propagating the optical signals from the output side FIFO device to the multiple RXs 20. Each of the multiple SCFs 30 has a single core extending along a central axis and a cladding surrounding the single core.

[0024] The MCF 40 provided between a pair of FIFO devices 50 (an input FIFO device and an output FIFO device) has multiple cores extending along a central axis and a common cladding surrounding each of the multiple cores. Each of the pair of FIFO devices 50 is an optical device that connects multiple SCF 30 cores to corresponding cores of the MCF 40 in single mode, and the waveguide pitch (core pitch) is converted along the light propagation direction.

[0025] For example, the optical waveguide device 50A shown in the middle of FIG. 1 can be applied to the pair of FIFO devices 50. The optical waveguide device 50A has a structure in which the end portions of a plurality of SCFs 30, each having a core 31 and a clad 32, are fused in a bundled state, and the arrangement (pitch) of the cores at an end face 300 of the fused end portion is extended so as to match the arrangement (pitch) of the cores in the MCF 40. The MCF 40 also has a plurality of cores 41 and a common clad 42, and each core 41 of the MCF 40 and each core 31 of the plurality of SCFs 30 are optically connected (for example, fusion-spliced) at an end face (substantially the end face 300 of the SCF 30) of the optical waveguide device 50A. Among the plurality of SCFs 30 constituting the optical waveguide device 50A, the cores 31 of the SCFs 30 located at the periphery in the cross section of the fused portion are formed with a bent portion having a smaller radius of curvature r than the bent portion provided in the core of the SCF 30 located at the center in the cross section of the fused portion. In this optical waveguide device 50A, each core 31 is integrally surrounded by the cladding 32 of the SCF 30. In the case of this optical waveguide device 50A, the position where the pitch of adjacent cores 31 in the fused portion of the SCF 30 begins to change corresponds to the first device end face, and the position of the end face 300 of the SCF 30 corresponds to the second device end face. The waveguide length L of this optical waveguide device 50A is preferably 10 to 100 mm to suppress excess loss due to abrupt core diameter fluctuations in the extended portion. The upper limit of the waveguide length is 80×10 6 [nm], 60×10 6 [nm], 40×10 6 [nm], or 20×10 6 [nm] is also acceptable.

[0026] Also, a PLC-type optical waveguide device 50B shown in the lower part of FIG. 1 can be applied to a pair of FIFO devices 50. The optical waveguide device 50B has a first device end face to which an end face 300 of each SCF 30, each having a core 31 and a cladding 32, is fixed, and a second device end face to which an end face 400 of the MCF 40 is fixed. Between the first device end face and the second device end face, an intra-device core (a waveguide in the optical waveguide device 50B) for single-mode connection of the core 31 of each SCF 30 to the corresponding core 41 of the MCF 40 is formed near the surface or inside the cladding layer. The cross-sectional shape of the intra-device core may be any of a circle, a semicircle, and a rectangle. In particular, when the intra-device core is a rectangular waveguide having a rectangular cross section, for example, a rectangular waveguide is formed on an underlayer of the cladding layer, and then an upper layer of the cladding layer is provided so as to cover the rectangular waveguide. The waveguide length L of this optical waveguide device 50B is preferably 5 to 20 mm from the viewpoint of ease of handling.

[0027] FIG. 2 is a diagram for explaining in detail an example of a PLC type optical waveguide device 50B as a configuration example (device configuration) of an optical waveguide device according to the present disclosure.

[0028] A PLC-type optical waveguide device 50B shown in the upper part of Fig. 2 has a first device end face 50a to which an end face 300 (see the lower part of Fig. 1) of an SCF 30, each having a core 31 and a cladding 32, is fixed, and a second device end face 50b to which an end face 400 (see the lower part of Fig. 1) of an MCF 40 is fixed. Between the first device end face 50a and the second device end face 50b, a core (waveguide) 51 for single-mode connection of each of the cores 31 of the SCF 30 to the corresponding cores 41 of the MCF 40 is formed near the surface or inside the cladding layer 52. A first end face (first waveguide end face) 51a of the core 51 coincides with the first device end face 50a, and a second end face (second waveguide end face) 51b of the core 51 coincides with the second device end face 50b. The core 51 has at least one bent portion 55 provided between the first end face 51a and the second end face 51b, and the bent portion 55 has a radius of curvature r of 40 mm or less. The relative refractive index difference of the core 51 with respect to the cladding layer 52 and the width of the core 51 are appropriately determined according to the SCF 30 and the MCF 40. The lower limit of the relative refractive index difference of the core 51 with respect to the cladding layer 52 is, for example, 0.25%, 0.30%, or 0.35%. The upper limit is, for example, 0.6%, 0.7%, or 0.8%. The lower limit of the width of the core 51 is, for example, 6.5 μm, 7.0 μm, or 7.5 μm. The upper limit is, for example, 8.0 μm, 8.5 μm, or 9.0 μm. With this configuration, light of a plurality of modes with different orders is guided through the core 51. The waveguide length L of the core 51 is set to 5×10 6 On the other hand, in order to ensure ease of handling of the device, the waveguide length L is preferably 20×10 6 It is preferable that the thickness is less than [nm].

[0029] When the core 51 is formed on the surface of the cladding layer 52, the core 51 has a semicircular or rectangular cross section. When the core 51 is formed inside the cladding layer 52, the core 51 has a circular or rectangular cross section. In either case, the width of the core 51 is given as the maximum width along a direction perpendicular to the longitudinal direction of the core 51 in a plan view obtained when the core 51 is projected onto the surface of the cladding layer 52. When the core 51 is provided inside the cladding layer 52, the core 51 and an over cladding may be stacked in this order on an under cladding, or a laser beam may be irradiated onto the cladding layer 52 to draw in the cladding layer 52.

[0030] As shown in the lower part of FIG. 2, in general, when light of a predetermined wavelength is input from one end face 510a of a waveguide 510 provided with a bent portion 550 of a curvature radius r, low-order mode and high-order mode light are generated in the process of the input light propagating by the waveguide length L toward the other end face 510b. At this time, MPI occurs between the low-order mode and the high-order mode propagating in the core 51. The occurrence of this MPI becomes a problem during signal modulation in optical signal transmission (optical signal intensity fluctuations due to MPI occur within the frequency band required for signal modulation). For this reason, the optical waveguide device (corresponding to a pair of FIFO devices 50) disclosed herein is designed to enable single-mode connection between a pair of optical fibers whose cores are optically connected to each other.

[0031] Fig. 3 is a diagram for explaining the control operation of the optical signal intensity fluctuation caused by MPI. The upper part of Fig. 3 shows the frequency dependence of the optical signal intensity caused by MPI, and this frequency characteristic is characterized by the oscillation period Tf of the optical signal intensity caused by MPI with respect to the optical frequency.

[0032] In this disclosure, the effect of the lower-order mode and higher-order mode interference (MPI) on the optical communication (modulation) system is quantified as the "fluctuation rate of optical signal intensity fluctuation" shown in the middle and lower parts of Figure 3, and the condition under which this "fluctuation rate of optical signal intensity fluctuation" caused by MPI does not cause a problem within the frequency band required for signal modulation is defined as follows.

[0033] In an optical waveguide device having a waveguide length L [mm], the group delay time difference between a lower mode and a higher mode, i.e., the inter-mode group delay time difference Δβ1 [s / nm], and the oscillation period Tf [Hz] (upper part of Figure 3) with respect to the optical frequency of the frequency dependence of the optical signal intensity fluctuation caused by MPI are related by the following first relational expression: Tf [Hz] = 1 / (|Δβ1|·L) is established.

[0034] Here, the group delay time β1 of each mode is expressed by the following formula (1):

number

[0035] In order to prevent this optical signal intensity fluctuation caused by MPI from becoming noise during signal modulation, the oscillation period Tf [Hz] of the MPI with respect to the optical frequency must be sufficiently larger than the frequency band 2Δf required for signal modulation (Δf is the rate of the modulation speed, 25 [GHz] or more). Specifically, as shown in the middle part of FIG. 3, the oscillation period Tf [Hz] is modulated within a frequency range divided by an integer N (the frequency band 2Δf required for modulation is set within Tf / N), and the fluctuation rate of the optical signal intensity fluctuation caused by MPI can be arbitrarily suppressed by increasing the division number N as shown in the lower part of FIG. 3. In addition, in the middle part of FIG. 3, the vertical axis indicates normalized intensity with the fluctuation width of the optical signal intensity set to 1 (maximum intensity is set to 0.5, minimum intensity is set to -0.5). In other words, the modulation speed Δf is expressed by the following second relational expression for the oscillation period Tf with respect to the optical frequency and its division number N: 2×Δf[Hz]≦Tf[Hz] / N This means that the effect of MPI on the optical signal intensity fluctuation is limited to the range of (f0-Δf) [Hz] or more and (f0+Δf) [Hz] or less, centered on the frequency f0. In other words, the maximum fluctuation range A max The fluctuation of the optical signal strength is expressed as the fluctuation range A min This means that the optical signal intensity fluctuation is treated as

[0036] For example, as shown in the lower part of Fig. 3, when the number of divisions N is 10, the maximum fluctuation rate of optical signal strength fluctuations caused by MPI is 31%. When the number of divisions N is 20, the maximum fluctuation rate is 16%. When the number of divisions N is 50, the maximum fluctuation rate is 6%. When the number of divisions N is 100, the maximum fluctuation rate of optical signal strength fluctuations caused by MPI is 3%.

[0037] Furthermore, by substituting the first relational expression above into the second relational expression above, the following equation is obtained: |Δβ1|≦1 / (N 2Δf L) Here, "L" is the waveguide length, "Δβ1" is the mode group delay time difference, "N" is the number of divisions defined as an integer between 10 and 100 that divides the oscillation period Tf for the optical frequency, and "Δf" is 25×10 9[Hz] or more 1000×10 9 The modulation rate is defined as any frequency below 2×10 [Hz] (for example, Δf=25[GHz] corresponds to 25[GBaud]). -12 In an optical waveguide device that satisfies [s] / L, the modulation speed Δf = 25 × 10 9 For a signal of 10 [Hz], the division number can be increased to 10 or more, and the intensity fluctuation of the modulated signal can be suppressed to 31% or less of the maximum optical signal intensity fluctuation caused by MPI.

[0038] Fig. 4 is a graph showing the relationship between the differential mode group delay time Δβ1 (absolute value) and the number of divisions N for each of the various modulation speeds described above. The prepared optical waveguide device is a FIFO device having a core with a rectangular cross section and an SI (Step Index) type refractive index profile that allows higher-order modes as a waveguide. The upper part of Fig. 4 shows the relationship between Δβ1 (absolute value) and the number of divisions N in an optical waveguide device having a waveguide length L of 10 mm, and the lower part of Fig. 4 shows the relationship between Δβ1 (absolute value) and the number of divisions N in an optical waveguide device having a waveguide length L of 40 mm.

[0039] Specifically, in the prepared FIFO devices, the relative refractive index difference Δ of the core with respect to the cladding layer is 0.5% for Sample 1 (FIFO device as an embodiment of the present disclosure) and Comparative Example 1, and 0.7% for Sample 2 (FIFO device as an embodiment of the present disclosure) and Comparative Example 2. The core width is 8 μm for Sample 1 and Comparative Example 1, and 8.5 μm for Sample 2 and Comparative Example 2. In all the prepared FIFO devices, the minimum core pitch is 35 μm, and the curvature radius r of the bent portion provided in the core is 20 mm. The core waveguide length L is 10 mm for Sample 1 and Sample 2 (upper part of FIG. 4), and 40 mm for Comparative Example 1 and Comparative Example 2 (lower part of FIG. 4). An optical signal with a wavelength λ0=1310 [nm] is input to this FIFO device.

[0040] In the FIFO device having the above-mentioned structure, the theoretical bending loss is approximately 0 dB / mm in all the prepared FIFO devices. The measured crosstalk is -40 dB or less for Sample 1 and Comparative Example 1, and -50 dB or less for Sample 2 and Comparative Example 2. In addition, regarding the mode group delay time difference Δβ1, the group delay time β1 of the low-order mode (fundamental mode) is 4.904 × 10 -18 [s / nm], Sample 2 and Comparative Example 2 were 4.914 × 10 -18 The group delay time β1 of the highest mode guided in the waveguide is 4.905×10 -18 [s / nm] (primary), Sample 2 and Comparative Example 2 are 4.919 × 10 -18 [s / nm] (second order). In this case, the absolute value of the differential mode group delay time Δβ1 is 5.211×10 -22 [s / nm](=|(4.904-4.905)|×10 -18 ), and Sample 2 and Comparative Example 2 are 4.717 × 10 -21 [s / nm](=|(4.914-4.919)|×10 -18 ).

[0041] In the upper and lower parts of FIG. 4, graphs G510A and G510B show the relationship between the number of divisions N and Δβ1 (absolute value) when the modulation speed Δf is 25 [GHz], graphs G520A and G520B show the relationship between the number of divisions N and Δβ1 (absolute value) when the modulation speed Δf is 50 [GHz], and graphs G530A and G530B show the relationship between the number of divisions N and Δβ1 (absolute value) when the modulation speed Δf is 100 [GHz]. Graphs G540A and G540B show the relationship between the number of divisions N and Δβ1 (absolute value) when the modulation speed Δf is 200 [GHz], graphs G550A and G550B show the relationship between the number of divisions N and Δβ1 (absolute value) when the modulation speed Δf is 500 [GHz], and graphs G560A and G560B show the relationship between the number of divisions N and Δβ1 (absolute value) when the modulation speed Δf is 1 [THz]. Graph G410 shows the relationship between the number of divisions N and Δβ1 (absolute value) for a FIFO device having the structure of sample 1, and it can be confirmed that the formula: |Δβ1|≦1 / (N·2Δf·L) is satisfied in all cases where the modulation speed Δf is from 25 [GHz] to 1 [THz]. Graph G420 shows the relationship between the number of divisions N and Δβ1 (absolute value) for a FIFO device having the structure of Sample 2, and it can be confirmed that the formula: |Δβ1|≦1 / (N·2Δf·L) is satisfied when the modulation speed Δf is from 25 [GHz] to 100 [GHz]. On the other hand, in a FIFO device having the structure of Comparative Example 1 (graph G430) in which the waveguide length L exceeds 20 mm, the modulation speed Δf is limited to 200 [GHz], and in a FIFO device having the structure of Comparative Example 2 (graph G440), the modulation speed Δf is limited to 25 [GHz]. The theoretical coupling loss between the connected optical fiber and the FIFO device is less than 0.05 [dB] for Sample 1 and Comparative Example 1, and less than 0.08 [dB] for Sample 2 and Comparative Example 2.

[0042] As described above, the optical waveguide device of the present disclosure achieves low bending loss, low crosstalk, and even low coupling loss, and the mode group delay difference Δβ1 satisfies the formula: |Δβ1|≦1 / (N·2Δf·L). This indicates that the degradation of the optical signal caused by lower-order mode and higher-order mode interference (MPI) is not significant. Therefore, it does not pose a problem in the optical communication system of the present disclosure. [Explanation of symbols]

[0043] 10...TX (optical transmitter), 20...RX (optical receiver), 30...SCF (single-core optical fiber), 31...core, 32...clad, 300...end face, 40...MCF (multi-core optical fiber), 41...core, 42...common clad, 400...end face, 50...FIFO device, 50A, 50B...optical waveguide device (FIFO device), 50a...first device end face, 50b...second device end face, 51...core (waveguide), 51a...first end face (first waveguide end face), 51b...second end face (second waveguide end face), 52...clad layer, 55...bent portion.

Claims

1. a first device endface; a second device end face opposite the first device end face; a waveguide having a first waveguide end face coinciding with the first device end face and a second waveguide end face coinciding with the second device end face, through which light of a plurality of modes having different orders is guided, the waveguide having one or more bends provided on an optical path from the first waveguide end face to the second waveguide end face; a cladding layer having a refractive index lower than that of the waveguide; Equipped with The waveguide is 5×10 defined as the optical path length from the first waveguide end face to the second waveguide end face ６ [nm] or more 100×10 ６ [nm] or less of a waveguide length L, The group delay time difference Δβ1 between the multiple modes is |Δβ1|≦2×10 －１２ [s] / L having a structure satisfying the condition given by Fan-In / Fan-Out device.

2. a first device endface; a second device end face opposite the first device end face; a waveguide having a first waveguide end face coinciding with the first device end face and a second waveguide end face coinciding with the second device end face, through which light of a plurality of modes having different orders is guided, the waveguide having one or more bends provided on an optical path from the first waveguide end face to the second waveguide end face; a cladding layer having a refractive index lower than that of the waveguide; Equipped with The waveguide is 5×10 defined as the optical path length from the first waveguide end face to the second waveguide end face ６ [nm] or more 100×10 ６ [nm] or less of a waveguide length L, a division number N defined as an integer value that divides the oscillation period Tf of the optical frequency of the optical signal intensity fluctuation caused by the MPI between the multiple modes and is an integer between 10 and 100, and 25×10 ９ [Hz] or more 1000×10 ９ For a modulation speed Δf defined at any frequency of 0.1 Hz or less, the group delay time difference Δβ1 between the multiple modes is |Δβ1|≦1 / (N·2Δf·L) having a structure satisfying the condition given by Fan-In / Fan-Out device.

3. The waveguide length is 20×10 ６ [nm] or less, The Fan-In / Fan-Out device according to claim 2.

4. The bent portion has a radius of curvature r of 40 mm or less. A Fan-In / Fan-Out device according to any one of claims 1 to 3.

5. At least one pair of optical fibers having cores connected in a single mode; disposed between the pair of optical fibers; A Fan-In / Fan-Out device according to any one of claims 1 to 4, An optical communication system comprising:

6. Each of the pair of optical fibers includes a single-core optical fiber or a multi-core optical fiber.

6. The optical communication system according to claim 5.

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