Wavelength cross-connect circuit

Abstract

This provides a wavelength cross-connect circuit that enables wider bandwidth operation. [Solution] This circuit comprises the 1st to Nth λ N drops an optical signal of any one wavelength among the wavelengths and produces diffraction modes for wavelengths other than the one wavelength only on the shorter wavelength side of that one wavelength. λ M first optical waveguides, each having wavelength drop filters formed in series in order of increasing wavelength, and each N λ N second optical waveguides, each having wavelength drop filters arranged in series in ascending order of wavelength, M drop ports of wavelength drop filters that drop optical signals of the same wavelength in M ​​first optical waveguides, and N drop ports of wavelength drop filters that drop optical signals of the same wavelength in N second optical waveguides are connected in one-to-one pairs in one or more combinations. λ It has M input N output optical switches.

Description

[Technical Field]

[0001] This invention relates to a wavelength cross-connect circuit. [Background technology]

[0002] A Wavelength Cross-Connect (WXC) (Optical Cross-Connect (OXC)) is an optical switching device that allows switching of optical signal paths for each wavelength. It is used in ROADM (Reconfigurable Optical Add-Drop Multiplexing) systems for optical fiber communication, and conventionally consists of multiple 1×N Wavelength-Selective Switches (WSS). Conventional Wavelength-Selective Switches achieve wavelength division and multiplexing using diffraction gratings and spatial beam manipulation using LCOS (Liquid Crystal On Silicon) or MEMS (Micro Electro Mechanical System), resulting in large devices with slow operating speeds of around milliseconds.

[0003] In recent years, optical switching functions that allow for flexible switching of connection relationships have been explored in order to increase the capacity and reduce the power consumption of connections between electronic devices such as CPUs (Central Processing Units) and GPUs (Graphics Processing Units). Integrated and high-speed wavelength cross-connect technology is required, and silicon photonics technology, which enables the realization of optical integrated circuits using minute optical waveguides with CMOS (Complementary Metal-Oxide-Semiconductor) prototype lines, is considered promising.

[0004] Existing wavelength division multiplexing circuits that can be realized using optical waveguides include, for example, arrayed waveguide gratings (AWG), Mach-Zehnder interferometers, and ring resonators, which utilize high-order diffraction, interference, and resonance phenomena, as shown in Non-Patent Document 2. However, they have the problem that the free spectral range (FSR) is limited due to the periodic spectral characteristics caused by adjacent orders.

[0005] As a wavelength division multiplexing circuit operating in a wideband, a wavelength selective coupler is used in which a nanoscale periodic structure is introduced into the sidewalls of two adjacent silicon optical waveguides, and only wavelengths that satisfy the first-order Bragg condition are coupled in the opposite direction to the other optical waveguide. In this case, the adjacent order is far apart and there is no RSR limitation. By combining this wavelength selective coupler with an optical waveguide and an optical switch, a wavelength cross-connect circuit operating in a wideband can be constructed (for example, Patent Document 1, Non-Patent Documents 2 to 4). This conventional wavelength cross-connect circuit will be described in detail later.

[0006] While the wavelength cross-connect circuits described in Patent Document 1 and Non-Patent Documents 2 to 4 achieve broadband operation in the C+L band, as described in Non-Patent Document 4, further expansion to a wider bandwidth is desired to accommodate future increases in transmission capacity. Specifically, operation across the "entire communication wavelength band" (i.e., O, E, S, C, L, and U bands) is desired.

[0007] In this wavelength cross-connect circuit, when we examined the factors limiting the operating bandwidth, we found that wavelength-selective couplers have two limiting factors: (1) coupling to higher-order modes and (2) coupling to spatial modes. Therefore, bandwidth limitations remain even with the structural design of the wavelength-selective coupler. Consequently, it is difficult to extend the operating bandwidth to the entire communication wavelength band. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent No. 6708338 [Non-patent literature]

[0009] [Non-Patent Document 1] N. Saha, G. Brunetti, A. di Toma, MN Armenise, and C. Ciminelli, Silicon Photonic Filters: A Pathway from Basics to Applications. Adv. Photonics Res. 2300343 (2024). [Non-Patent Document 2] K. Ikeda, K. Suzuki, R. Konoike, H. Kawashima, "Silicon Photonics Wavelength Selective Switch with Unlimited Free Spectral Range," J. Lightwave Technol. 38, 3268-3272 (2020). [Non-Patent Document 3] K. Ikeda, R. Konoike, K. Suzuki, H. Kawashima, "2 × 2 16-ch silicon photonics wavelength-selective switch based on waveguide gratings," Opt. Express 28, 26861-26869 (2020). [Non-Patent Document 4] K. Ikeda, R. Konoike, K. Suzuki, "Large-Scale and Multiband Silicon Photonics Wavelength Cross-Connect Switch With FSR-Free Grating-Assisted Contra-Directional Couplers," J. Lightwave Technol. 42, 4310-4316 (2024) [Overview of the project]

Problems to be Solved by the Invention

[0010] Therefore, an object of the present invention is to provide, according to one aspect, a novel wavelength cross-connect circuit capable of wider-band operation.

Means for Solving the Problems

[0011] The wavelength cross-connect circuit according to the present invention includes: (A) M first optical waveguides in which N wavelength drop filters each dropping an optical signal of any one of the wavelengths from the first to the Nth wavelengths and generating a diffraction mode for wavelengths other than the one wavelength only on the short wavelength side of the one wavelength are each formed in series in the order of increasing wavelength; (B) N second optical waveguides in which N wavelength drop filters each dropping an optical signal of any one of the wavelengths from the first to the Nth wavelengths and generating a diffraction mode for wavelengths other than the one wavelength only on the short wavelength side of the one wavelength are each formed in series in the order of increasing wavelength; and (C) M drop ports of the wavelength drop filters that drop optical signals of the same wavelength among the N wavelength drop filters formed in each of the M first optical waveguides, and N drop ports of the wavelength drop filters that drop optical signals of the same wavelength as the above-mentioned same wavelength among the N wavelength drop filters formed in each of the N second optical waveguides are connected one-to-one and in one or a plurality of combinations, and N M-input N-output optical switches. λ , λ , λ , λ , λ , λ , λ λ λ λ λ λ λ

Advantages of the Invention

[0012] According to one aspect, a wavelength cross-connect circuit capable of wider-band operation can be obtained.

Brief Description of the Drawings

[0013] [Figure 1] FIG. 1 is a diagram showing a circuit diagram of a wavelength cross-connect circuit as a premise. [Figure 2] FIG. 2 is a diagram showing a configuration example of a wavelength selective coupler. [Figure 3] FIG. 3 is a diagram showing the relationship between the period of unevenness and wavelength in a wavelength selective coupler. [Figure 4] FIG. 4 is a diagram showing a configuration example of a wavelength cross-connect circuit according to the present embodiment. [Figure 5] FIG. 5 is a diagram showing an operation example of the wavelength cross-connect circuit according to the present embodiment. Embodiments for Carrying Out the Invention

[0014] [Regarding the Premises and Basic Concept of the Embodiment] A circuit diagram of a wavelength cross-connect circuit serving as a premise is shown in FIG. 1. This wavelength cross-connect circuit is the same as the circuit disclosed in Patent Document 1 and the like. FIG. 1 shows an example of a circuit for selecting optical signals of each wavelength from wavelength division multiplexed signals of four wavelengths λ1 to λ4 and switching paths.

[0015] In the example of FIG. 1, in the optical waveguide 601, a wavelength selective coupler 201 for dropping and adding light of wavelength λ1 (also referred to as wavelength division and multiplexing), a wavelength selective coupler 301 for dropping and adding light of wavelength λ2, a wavelength selective coupler 401 for dropping and adding light of wavelength λ3, and a wavelength selective coupler 501 for dropping and adding light of wavelength λ4 are formed in series.

[0016] Also, in the optical waveguide 602, a wavelength selective coupler 202 for dropping and adding light of wavelength λ1, a wavelength selective coupler 302 for dropping and adding light of wavelength λ2, a wavelength selective coupler 402 for dropping and adding light of wavelength λ3, and a wavelength selective coupler 502 for dropping and adding light of wavelength λ4 are formed in series.

[0017] Furthermore, the optical waveguide 603 has a wavelength-selective coupler 204 for dropping and adding light of wavelength λ1, a wavelength-selective coupler 304 for dropping and adding light of wavelength λ2, a wavelength-selective coupler 404 for dropping and adding light of wavelength λ3, and a wavelength-selective coupler 504 for dropping and adding light of wavelength λ4, all formed in series.

[0018] The optical waveguide 604 has a wavelength-selective coupler 205 for dropping and adding light of wavelength λ1, a wavelength-selective coupler 305 for dropping and adding light of wavelength λ2, a wavelength-selective coupler 405 for dropping and adding light of wavelength λ3, and a wavelength-selective coupler 505 for dropping and adding light of wavelength λ4, all connected in series.

[0019] Furthermore, wavelength-selective couplers 201, 202, 204, and 205 are connected to a 4-input, 4-output optical switch circuit 203. Specifically, one drop port of wavelength-selective coupler 201 is connected to the second port from the left of the optical switch circuit 203, and the other drop port is connected to the second port from the right of the optical switch circuit 203. Also, one drop port of wavelength-selective coupler 202 is connected to the first port from the left of the optical switch circuit 203, and the other drop port is connected to the first port from the right of the optical switch circuit 203. In addition, one drop port of wavelength-selective coupler 204 is connected to the fourth port from the left of the optical switch circuit 203, and the other drop port is connected to the fourth port from the right of the optical switch circuit 203. Furthermore, one drop port of wavelength-selective coupler 205 is connected to the third port from the left of the optical switch circuit 203, and the other drop port is connected to the third port from the right of the optical switch circuit 203.

[0020] Wavelength-selective couplers 301, 302, 304, and 305 are connected to a 4-input, 4-output optical switch circuit 303. Specifically, one drop port of wavelength-selective coupler 301 is connected to the second port from the left of the optical switch circuit 303, and the other drop port is connected to the second port from the right of the optical switch circuit 303. Also, one drop port of wavelength-selective coupler 302 is connected to the first port from the left of the optical switch circuit 303, and the other drop port is connected to the first port from the right of the optical switch circuit 303. Furthermore, one drop port of wavelength-selective coupler 304 is connected to the fourth port from the left of the optical switch circuit 303, and the other drop port is connected to the fourth port from the right of the optical switch circuit 303. In addition, one drop port of wavelength-selective coupler 305 is connected to the third port from the left of the optical switch circuit 303, and the other drop port is connected to the third port from the right of the optical switch circuit 303.

[0021] Wavelength-selective couplers 401, 402, 404, and 405 are connected to a 4-input, 4-output optical switch circuit 403. Specifically, one drop port of wavelength-selective coupler 401 is connected to the second port from the left of the optical switch circuit 403, and the other drop port is connected to the second port from the right of the optical switch circuit 403. Also, one drop port of wavelength-selective coupler 402 is connected to the first port from the left of the optical switch circuit 403, and the other drop port is connected to the first port from the right of the optical switch circuit 403. Furthermore, one drop port of wavelength-selective coupler 404 is connected to the fourth port from the left of the optical switch circuit 403, and the other drop port is connected to the fourth port from the right of the optical switch circuit 403. In addition, one drop port of wavelength-selective coupler 405 is connected to the third port from the left of the optical switch circuit 403, and the other drop port is connected to the third port from the right of the optical switch circuit 403.

[0022] Wavelength-selective couplers 501, 502, 504, and 505 are connected to a 4-input, 4-output optical switch circuit 503. Specifically, one drop port of wavelength-selective coupler 501 is connected to the second port from the left of the optical switch circuit 503, and the other drop port is connected to the second port from the right of the optical switch circuit 503. Also, one drop port of wavelength-selective coupler 502 is connected to the first port from the left of the optical switch circuit 503, and the other drop port is connected to the first port from the right of the optical switch circuit 503. Furthermore, one drop port of wavelength-selective coupler 504 is connected to the fourth port from the left of the optical switch circuit 503, and the other drop port is connected to the fourth port from the right of the optical switch circuit 503. In addition, one drop port of wavelength-selective coupler 505 is connected to the third port from the left of the optical switch circuit 503, and the other drop port is connected to the third port from the right of the optical switch circuit 503.

[0023] Then, as shown in Figure 1 within each optical switch circuit, by connecting the first port on the left and the second port on the right of optical switch circuit 203, the first port on the left and the first port on the right of optical switch circuit 303, the first port on the left and the fourth port on the right of optical switch circuit 403, and the first port on the left and the third port on the right of optical switch circuit 503, the following signal splitting and path switching become possible.

[0024] In other words, when wavelength division multiplexed signals of four wavelengths λ1 to λ4 are input from the left end of the optical waveguide 602, the optical signal of wavelength λ1 is dropped by the wavelength selective coupler 202, input to the first left port of the optical switch circuit 203, and output from the second right port. Then, the optical signal of wavelength λ1 is input to the drop port of the wavelength selective coupler 201, dropped into the optical waveguide 601, and output from the right end of the optical waveguide 601.

[0025] Furthermore, the optical signal with wavelength λ2 is dropped by the wavelength-selective coupler 302, input to the first left port of the optical switch circuit 303, and output from the first right port. Then, the optical signal with wavelength λ2 is input to the drop port of the wavelength-selective coupler 302 and dropped again into the optical waveguide 602. Here, it is added to wavelength-division multiplexed signals of wavelengths λ3 and λ4. The optical signal with wavelength λ3 is dropped by the wavelength-selective coupler 402, and the optical signal with wavelength λ4 is also dropped by the wavelength-selective coupler 502, so as a result, the optical signal with wavelength λ2 is output from the right end of the optical waveguide 602.

[0026] Furthermore, the optical signal with wavelength λ3 is dropped by the wavelength-selective coupler 402, input to the first port on the left of the optical switch circuit 403, and output from the fourth port on the right. Then, the optical signal with wavelength λ3 is input to the drop port of the wavelength-selective coupler 404, dropped into the optical waveguide 603, and output from the right end of the optical waveguide 603.

[0027] Furthermore, the wavelength λ4 optical signal is dropped by the wavelength-selective coupler 502, input to the first left port of the optical switch circuit 503, and output from the third right port. Then, the wavelength λ4 optical signal is input to the drop port of the wavelength-selective coupler 505, dropped into the optical waveguide 604, and output from the right end of the optical waveguide 604.

[0028] Furthermore, even if wavelength division multiplexed signals are simultaneously input to any other optical waveguide, the desired wavelength of optical signals can be output to the desired optical waveguide by connecting the other available ports of the optical switch circuits 203 to 503. Moreover, such wavelength cross-connect circuits are not limited to 4 wavelengths, 4 inputs, and 4 outputs, but can be adapted for other numbers of wavelengths and ports.

[0029] Figure 2 shows a specific example of the configuration of a wavelength-selective coupler used in such a wavelength cross-connect circuit. The wavelength-selective coupler includes an optical waveguide 701 corresponding to one of the optical waveguides 601 to 604, and an optical waveguide 702 on the drop port side, which is located in close proximity to the optical waveguide 701. Over the length L (e.g., 500 μm) of the wavelength-selective coupler, diffraction grating structures are formed on both sides of the optical waveguides 701 and 702. The diffraction grating structure has irregularities as shown in Figure 2, and the period Λ of these irregularities is determined by the following equation according to the wavelength λ of the optical signal to be dropped and added.

number

[0030] Here, n1(λ) represents the effective refractive index at wavelength λ of the mode propagating through optical waveguide 701, and n2(λ) represents the effective refractive index at wavelength λ of the mode propagating through optical waveguide 702. Thus, the period Λ varies depending on the size of each waveguide and the wavelength λ, but for the assumed wavelength, it is, for example, 351 to 386 nm. In this way, diffraction grating irregularities are formed in optical waveguides 701 and 702 at a period that satisfies the Bragg condition, which means that at the desired operating wavelength, the fundamental modes of each other undergo directional coupling in opposite directions.

[0031] The convexity on both sides of optical waveguide 701 is shifted by a phase of π. Similarly, the convexity on both sides of optical waveguide 702 is also shifted by a phase of π, but the phase of the convexity is the same on the adjacent sides of optical waveguides 701 and 702. In Figure 2, to make the presence of convexity easier to understand, the height ΔW1 of the convexity on the side of optical waveguide 701 is shown as being the same throughout, but it is adjusted to be a smooth curve (e.g., a Gaussian curve) where it is 0 at both ends of length L and ΔW1 in the middle. Similarly, the height ΔW2 of the convexity on the side of optical waveguide 702 is shown as being the same throughout, but it is adjusted to be a smooth curve (e.g., a Gaussian curve) where it is 0 at both ends of length L and ΔW2 in the middle. Note that ΔW1 is, for example, 40 nm and ΔW2 is, for example, 60 nm.

[0032] The width W1 of the optical waveguide 701 is, for example, 350 nm, the width W2 of the optical waveguide 702 is, for example, 450 nm, and W1 < W2. Also, the distance G between the optical waveguide 701 and the optical waveguide 702 is, for example, 250 nm, and typically, G < W1 < W2. Since the distance G is determined under the condition that the fundamental modes of each other are close enough to be coupled, the magnitude relationship among G, W1, and W2 may not be G < W1 < W2. Note that the thicknesses of the optical waveguides 701 and 702 are, for example, 220 nm.

[0033] As schematically shown in FIG. 2, the optical signal with wavelength λ input from the left side of the optical waveguide 701 is dropped to the optical waveguide 702 and output to the left side of the optical waveguide 702. Also, the optical signal with wavelength λ input from the left side of the optical waveguide 702 is dropped to the optical waveguide 701 and output to the left side of the optical waveguide 701. Further, the optical signal with wavelength λ input from the right side of the optical waveguide 702 is dropped to the optical waveguide 701 and output to the right side of the optical waveguide 701. Also, the optical signal with wavelength λ input from the right side of the optical waveguide 701 is dropped to the optical waveguide 702 and output to the right side of the optical waveguide 702. Note that if there are optical signals of other wavelengths when dropping, the optical signals of other wavelengths only pass through, and the optical signal of the dropped wavelength is added to the optical signals of other wavelengths.

[0034] The wavelength cross-connect circuit as shown in FIG. 1 adopts a wavelength-selective coupler such that the optical waveguide 701 corresponds to the optical waveguides 601 to 604, and a wider-band operation is realized compared to that described in the prior art. However, it is difficult to expand the wavelength cross-connect circuit of FIG. 1 to the entire communication wavelength band (for example, from about 1260 nm to 1675 nm).

[0035] FIG. 3 shows the relationship between the wavelength λ [nm] and the period Λ [nm] of the diffraction grating. Note that the characteristics in the case where the width W1 of the optical waveguide 701 is 350 nm and the width W2 of the optical waveguide 702 is 450 nm are shown. Note that the thicknesses are both 220 nm.

[0036] Line a represents the relationship between wavelength λ and period Λ at which fundamental mode coupling occurs in optical waveguides 701 and 702. Above line b represents the region at which coupling occurs between the fundamental mode and spatial mode in optical waveguide 701. Furthermore, line c represents the relationship between wavelength λ and period Λ at which coupling occurs between the fundamental mode of optical waveguide 701 and the first-order mode of optical waveguide 702. However, this coupling does not occur when the fundamental mode optical signal is input to optical waveguide 702. Furthermore, above line d represents the region at which coupling occurs between the fundamental mode and spatial mode in optical waveguide 702. However, this coupling does not occur when the fundamental mode optical signal is input to optical waveguide 701.

[0037] If we focus on the region above line a and assume a wavelength-selective coupler with a diffraction grating structure of a specific period Λ, then when an optical signal with a wavelength below the wavelength on line a corresponding to that specific period Λ passes through, it will affect the coupling with spatial modes and higher-order modes for wavelengths below the wavelength on line a. In other words, it is impossible to secure a range of wavelengths across the entire communication wavelength band that does not affect wavelengths other than the wavelength on line a (more generally, where diffraction, interference, and resonance do not occur).

[0038] On the other hand, if we focus on region A below line a and assume a wavelength-selective coupler with a diffraction grating structure of a specific period Λ, we can see that when an optical signal with a wavelength greater than or equal to the wavelength on line a corresponding to the specific period Λ passes through, it is not affected by coupling with spatial modes or higher-order modes. Therefore, it is possible to secure a range of wavelengths across the entire communication wavelength band that does not affect wavelengths other than the wavelength on line a in any way (more generally, where diffraction, interference, and resonance do not occur).

[0039] Thus, the wavelength-selective coupler shown in Figure 2 is a wavelength drop filter (more precisely, a wavelength add-drop filter) that drops only the optical signal of the specific operating wavelength, by generating diffraction modes for wavelengths other than the specific operating wavelength only on the wavelength side shorter than the specific operating wavelength, and not generating diffraction modes on the wavelength side longer than the specific operating wavelength. Furthermore, by modifying such a wavelength drop filter to allow only optical signals with wavelengths greater than or equal to its operating wavelength to pass through, a wavelength cross-connect circuit capable of broadband operation than the wavelength cross-connect circuit shown in Figure 1 can be realized.

[0040] [Specific circuit example in this embodiment] Figure 4 shows an example of the configuration of a wavelength cross-connect circuit according to this embodiment. Here, an example is shown in which wavelength division multiplexed signals of four wavelengths λ1 to λ4 can be processed, with M=4 input optical waveguides and N=4 output optical waveguides, but the number of wavelengths N λ The number of input optical waveguides M and the number of output optical waveguides N can be set arbitrarily. In this embodiment, it is assumed that the relationship λ1 < λ2 < λ3 < λ4 holds.

[0041] The wavelength cross-connect circuit according to this embodiment includes input optical waveguides 1 to 4, output optical waveguides 5 to 8, optical switches 101 to 104, and a control unit 150 that controls the optical switches 101 to 104.

[0042] The input optical waveguide 1 has the following connections in series: a wavelength-selective coupler 11 that drops an optical signal with wavelength λ1 to the drop port 16 side, a wavelength-selective coupler 12 that drops an optical signal with wavelength λ2 to the drop port 17 side, a wavelength-selective coupler 13 that drops an optical signal with wavelength λ3 to the drop port 18 side, and a wavelength-selective coupler 14 that drops an optical signal with wavelength λ4 to the drop port 19 side.

[0043] The input optical waveguide 2 has the following connections in series: a wavelength-selective coupler 21 that drops an optical signal with wavelength λ1 to the drop port 26 side, a wavelength-selective coupler 22 that drops an optical signal with wavelength λ2 to the drop port 27 side, a wavelength-selective coupler 23 that drops an optical signal with wavelength λ3 to the drop port 28 side, and a wavelength-selective coupler 24 that drops an optical signal with wavelength λ4 to the drop port 29 side.

[0044] The input optical waveguide 3 has the following connections in series: a wavelength-selective coupler 31 that drops an optical signal with wavelength λ1 to the drop port 36 side, a wavelength-selective coupler 32 that drops an optical signal with wavelength λ2 to the drop port 37 side, a wavelength-selective coupler 33 that drops an optical signal with wavelength λ3 to the drop port 38 side, and a wavelength-selective coupler 34 that drops an optical signal with wavelength λ4 to the drop port 39 side.

[0045] The input optical waveguide 4 has the following connections in series: a wavelength-selective coupler 41 that drops an optical signal with wavelength λ1 to the drop port 46 side, a wavelength-selective coupler 42 that drops an optical signal with wavelength λ2 to the drop port 47 side, a wavelength-selective coupler 43 that drops an optical signal with wavelength λ3 to the drop port 48 side, and a wavelength-selective coupler 44 that drops an optical signal with wavelength λ4 to the drop port 49 side.

[0046] Furthermore, the input optical waveguides 1 to 4 form part of the through ports of the wavelength-selective coupler, and it can be said that the through ports of the wavelength-selective coupler are connected in series. Also, the optical waveguide 701 of the wavelength-selective coupler shown in Figure 2 corresponds to the input optical waveguides 1 to 4, and the optical waveguide 702 corresponds to the optical waveguides on the drop ports 16 to 19, 26 to 29, 36 to 39 and 46 to 49 side.

[0047] The output optical waveguide 5 has the following connections in series: a wavelength-selective coupler 51 into which an optical signal with wavelength λ1 is dropped from the drop port 56 side; a wavelength-selective coupler 52 into which an optical signal with wavelength λ2 is dropped from the drop port 57 side; a wavelength-selective coupler 53 into which an optical signal with wavelength λ3 is dropped from the drop port 58 side; and a wavelength-selective coupler 54 into which an optical signal with wavelength λ4 is dropped from the drop port 59 side.

[0048] The output optical waveguide 6 has the following connections in series: a wavelength-selective coupler 61 into which an optical signal with wavelength λ1 is dropped from the drop port 66 side; a wavelength-selective coupler 62 into which an optical signal with wavelength λ2 is dropped from the drop port 67 side; a wavelength-selective coupler 63 into which an optical signal with wavelength λ3 is dropped from the drop port 68 side; and a wavelength-selective coupler 64 into which an optical signal with wavelength λ4 is dropped from the drop port 69 side.

[0049] The output optical waveguide 7 has the following connections in series: a wavelength-selective coupler 71 into which an optical signal with wavelength λ1 is dropped from the drop port 76 side; a wavelength-selective coupler 72 into which an optical signal with wavelength λ2 is dropped from the drop port 77 side; a wavelength-selective coupler 73 into which an optical signal with wavelength λ3 is dropped from the drop port 78 side; and a wavelength-selective coupler 74 into which an optical signal with wavelength λ4 is dropped from the drop port 79 side.

[0050] The output optical waveguide 8 has the following connections in series: wavelength-selective coupler 81 into which the optical signal with wavelength λ1 is dropped from the drop port 86 side; wavelength-selective coupler 82 into which the optical signal with wavelength λ2 is dropped from the drop port 87 side; wavelength-selective coupler 83 into which the optical signal with wavelength λ3 is dropped from the drop port 88 side; and wavelength-selective coupler 84 into which the optical signal with wavelength λ4 is dropped from the drop port 89 side.

[0051] Furthermore, the output optical waveguides 5 to 8 form part of the through ports of the wavelength-selective coupler, and it can be said that the through ports of the wavelength-selective coupler are connected in series. In addition, the optical waveguide 701 of the wavelength-selective coupler shown in Figure 2 corresponds to the output optical waveguides 5 to 9, and the optical waveguide 702 corresponds to the optical waveguides on the drop ports 56 to 59, 66 to 69, 76 to 79, and 86 to 89.

[0052] Furthermore, it is also possible to use input optical waveguides 1 to 4 as output optical waveguides and output optical waveguides 5 to 8 as input optical waveguides. That is, in the wavelength-selective couplers formed in input optical waveguides 1 to 4, optical signals of a specific operating wavelength input from the optical waveguide on the drop port side are dropped into input optical waveguides 1 to 4. Similarly, in the wavelength-selective couplers formed in output optical waveguides 5 to 8, optical signals of a specific operating wavelength input from output optical waveguides 5 to 8 are dropped into the optical waveguide on the drop port side.

[0053] The optical switch 101 connects the drop ports 16, 26, 36, and 46 of wavelength-selective couplers 11, 21, 31, and 41 to the drop ports 56, 66, 76, and 86 of wavelength-selective couplers 51, 61, 71, and 81 in one-to-one and one or more combinations, according to instructions from the control unit 150.

[0054] Furthermore, the optical switch 102 connects the drop ports 17, 27, 37, and 47 of wavelength-selective couplers 12, 22, 32, and 42 to the drop ports 57, 67, 77, and 87 of wavelength-selective couplers 52, 62, 72, and 82 in one-to-one and one or more combinations, according to instructions from the control unit 150.

[0055] Furthermore, the optical switch 103 connects the drop ports 18, 28, 38, and 48 of the wavelength-selective couplers 13, 23, 33, and 43 to the drop ports 58, 68, 78, and 88 of the wavelength-selective couplers 53, 63, 73, and 83 in one-to-one and one or more combinations, according to instructions from the control unit 150.

[0056] Furthermore, the optical switch 104 is configured to connect the drop ports 19, 29, 39, and 49 of wavelength-selective couplers 14, 24, 34, and 44 with the drop ports 59, 69, 79, and 89 of wavelength-selective couplers 54, 64, 74, and 84 in one-to-one and one or more combinations, according to instructions from the control unit 150.

[0057] The control unit 150 also stores control data for configuring the connection relationships between all input and output ports in each wavelength channel of the wavelength division multiplexed signal, and controls the switching of each optical switch according to the connection relationship specified from the outside.

[0058] Thus, unlike the wavelength cross-connect circuit shown in Figure 1, the input optical waveguide and the output optical waveguide are separated. Then, wavelength-selective couplers corresponding to the wavelength order λ1 < λ2 < λ3 < λ4 are arranged in the input optical waveguides 1 to 4. As a result, at each wavelength-selective coupler, optical signals with wavelengths shorter than its operating wavelength (i.e., the wavelength at which fundamental mode coupling occurs) are dropped by the wavelength-selective coupler before it and do not pass through. In other words, at each wavelength-selective coupler, only optical signals with wavelengths equal to or greater than the operating wavelength pass through, so coupling with higher-order modes (e.g., the first-order mode) or spatial modes cannot occur, eliminating the limitation on the operating wavelength and enabling broadband operation.

[0059] When comparing the wavelength cross-connect circuit shown in Figure 1 with the wavelength cross-connect circuit shown in Figure 4, the maximum number of crossings on the path through which the optical signal passes is approximately doubled. However, this is still comparable to a typical wavelength cross-connect circuit (see, for example, TJ Seok et al., “Silicon photonic wavelength cross-connect with integrated MEMS switching,” APL Photonics 4, 100803 (2019)), and it is superior in terms of broadband operation.

[0060] Next, using Figure 5, an example of the operation of the wavelength cross-connect circuit according to this embodiment shown in Figure 4 will be explained.

[0061] First, we will explain a pattern in which wavelength division multiplexed signals with wavelengths λ1 to λ4 are input from the left side of the input optical waveguide 2, an optical signal with wavelength λ1 is output from the output optical waveguide 5, an optical signal with wavelength λ2 is output from the output optical waveguide 6, an optical signal with wavelength λ3 is output from the output optical waveguide 7, and an optical signal with wavelength λ4 is output from the output optical waveguide 8.

[0062] In this case, the control unit 150 instructs the connection of the third port on the left and the first port on the right of the optical switch 101, the third port on the left and the second port on the right of the optical switch 102, the third port on the left and the third port on the right of the optical switch 103, and the third port on the left and the fourth port on the right of the optical switch 104.

[0063] When the wavelength division multiplexed signal input from the left side of the input optical waveguide 2 is input to the wavelength selective coupler 21, the optical signal with wavelength λ1 is dropped, and the wavelength division multiplexed signals with wavelengths λ2 to λ4 are output to the wavelength selective coupler 22. The optical signal with wavelength λ1 is dropped to the drop port 26 of the wavelength selective coupler 21, input to the third port from the left of the optical switch 101, and output from the first port from the right of the optical switch 101. Then, the optical signal with wavelength λ1 is input to the drop port 56 of the wavelength selective coupler 51, so it is dropped by the wavelength selective coupler 51 to the output optical waveguide 5 and output to the left side of the output optical waveguide 5.

[0064] Furthermore, when wavelength division multiplexed signals with wavelengths λ2 to λ4 are input to the wavelength selective coupler 22, the optical signal with wavelength λ2 is dropped, and the wavelength division multiplexed signals with wavelengths λ3 and λ4 are output to the wavelength selective coupler 23. The optical signal with wavelength λ2 is dropped to the drop port 27 of the wavelength selective coupler 22, input to the third port from the left of the optical switch 102, and output from the second port from the right of the optical switch 102. Then, the optical signal with wavelength λ2 is input to the drop port 67 of the wavelength selective coupler 62, so it is dropped by the wavelength selective coupler 62 to the output optical waveguide 6 and output to the left side of the output optical waveguide 6.

[0065] Furthermore, when wavelength division multiplexed signals of wavelengths λ3 and λ4 are input to the wavelength selective coupler 23, the optical signal of wavelength λ3 is dropped, and the optical signal of wavelength λ4 is output to the wavelength selective coupler 24. The optical signal of wavelength λ3 is dropped to the drop port 28 of the wavelength selective coupler 23, input to the third port from the left of the optical switch 103, and output from the third port from the right of the optical switch 103. Then, the optical signal of wavelength λ3 is input to the drop port 78 of the wavelength selective coupler 73, so it is dropped by the wavelength selective coupler 73 to the output optical waveguide 7, and output to the left side of the output optical waveguide 7.

[0066] Then, when the optical signal with wavelength λ4 is input to the wavelength-selective coupler 24, the optical signal with wavelength λ4 is dropped to the drop port 29 of the wavelength-selective coupler 24, input to the third port on the left of the optical switch 104, and output from the fourth port on the right of the optical switch 104. The optical signal with wavelength λ4 is then input to the drop port 89 of the wavelength-selective coupler 84, so it is dropped to the output optical waveguide 8 by the wavelength-selective coupler 84 and output to the left side of the output optical waveguide 8.

[0067] By changing the output port of optical switches 101 to 104, any optical signal of wavelengths λ1 to λ4 can be output to any output optical waveguide.

[0068] Figure 5 also shows a pattern in which wavelength division multiplexed signals with wavelengths λ1 to λ4 are simultaneously input from the left side of the input optical waveguide 4, an optical signal with wavelength λ4 is output from the output optical waveguide 5, an optical signal with wavelength λ3 is output from the output optical waveguide 6, an optical signal with wavelength λ2 is output from the output optical waveguide 7, and an optical signal with wavelength λ1 is output from the output optical waveguide 8.

[0069] To realize this pattern, the control unit 150, simultaneously with the previously shown pattern, instructs the connection of the first left port and the fourth right port of optical switch 101, the first left port and the third right port of optical switch 102, the first left port and the second right port of optical switch 103, and the first left port and the first right port of optical switch 104.

[0070] When the wavelength division multiplexed signal input from the left side of the input optical waveguide 4 is input to the wavelength selective coupler 41, the optical signal with wavelength λ1 is dropped, and the wavelength division multiplexed signals with wavelengths λ2 to λ4 are output to the wavelength selective coupler 42. The optical signal with wavelength λ1 is dropped to the drop port 46 of the wavelength selective coupler 41, input to the first left port of the optical switch 101, and output from the fourth right port of the optical switch 101. Then, the optical signal with wavelength λ1 is input to the drop port 86 of the wavelength selective coupler 81, so it is dropped by the wavelength selective coupler 81 to the output optical waveguide 8 and output to the left side of the output optical waveguide 8.

[0071] Furthermore, when wavelength division multiplexed signals with wavelengths λ2 to λ4 are input to the wavelength selective coupler 42, the optical signal with wavelength λ2 is dropped, and the wavelength division multiplexed signals with wavelengths λ3 and λ4 are output to the wavelength selective coupler 43. The optical signal with wavelength λ2 is dropped to the drop port 47 of the wavelength selective coupler 42, input to the first left port of the optical switch 102, and output from the third right port of the optical switch 102. Then, the optical signal with wavelength λ2 is input to the drop port 77 of the wavelength selective coupler 72, so it is dropped by the wavelength selective coupler 72 to the output optical waveguide 7 and output to the left side of the output optical waveguide 7.

[0072] Furthermore, when wavelength division multiplexed signals of wavelengths λ3 and λ4 are input to the wavelength selective coupler 43, the optical signal of wavelength λ3 is dropped, and the optical signal of wavelength λ4 is output to the wavelength selective coupler 44. The optical signal of wavelength λ3 is dropped to the drop port 48 of the wavelength selective coupler 43, input to the first left port of the optical switch 103, and output from the second right port of the optical switch 103. Then, the optical signal of wavelength λ3 is input to the drop port 68 of the wavelength selective coupler 63, so it is dropped to the output optical waveguide 6 by the wavelength selective coupler 63 and output to the left side of the output optical waveguide 6.

[0073] Then, when the optical signal with wavelength λ4 is input to the wavelength-selective coupler 44, the optical signal with wavelength λ4 is dropped to the drop port 49 of the wavelength-selective coupler 44, input to the first left port of the optical switch 104, and output from the first right port of the optical switch 104. Then, the optical signal with wavelength λ4 is input to the drop port 59 of the wavelength-selective coupler 54, so it is dropped to the output optical waveguide 5 by the wavelength-selective coupler 54 and output to the left side of the output optical waveguide 5.

[0074] By changing the output port of optical switches 101 to 104, any optical signal of wavelengths λ1 to λ4 can be output to any output optical waveguide.

[0075] Although not explained here, even if wavelength division multiplexed signals are input to other input optical waveguides, it is possible to output optical signals of each wavelength to any output optical waveguide.

[0076] Although optical switches 101 to 104 are M-input, N-output optical switches, various types of optical switches can be used. Specifically, a Mach-Zehnder interference switch (see, for example, BG Lee and N. Dupuis, "Silicon Photonic Switch Fabrics: Technology and Architecture," in Journal of Lightwave Technology, vol. 37, no. 1, pp. 6-20, 1 Jan. 1, 2019, doi: 10.1109 / JLT.2018.2876828.) can be used as the unit optical switch, and multiple such switches can be combined to form the configuration. Alternatively, the system may be configured by combining multiple MEMS-type unit optical switches (see, for example, TJ Seok et al., "Large-scale broadband digital silicon photonic switches with vertical adiabatic couplers," Optica 3, 64-70 (2016)) or ring-cavity type unit optical switches (see, for example, D. Nikolova et al., "Scaling silicon photonic switch fabrics for data center interconnection networks," Opt. Express 23, 1159-1175 (2015)). Since the optical switch configuration is not the main part of this embodiment, optical switches with configurations other than those described above may also be used.

[0077] Furthermore, it is preferable that such wavelength cross-connect circuits be constructed using Si optical waveguides, SiN optical waveguides, or both, manufactured using silicon photonics technology.

[0078] Silicon photonics, based on advanced silicon technology cultivated through electronics, boasts high stability and reproducibility of material properties. Furthermore, because it can be manufactured in semiconductor manufacturing plants, it excels in mass productivity, precision, and long-term reliability.

[0079] In addition, since the wavelength selection coupler described above has a strong interaction between the waveguide modes of two adjacent waveguides with the diffraction gratings on the side surfaces of each other, it is preferable that the refractive index difference between the core and the cladding is large. Furthermore, when the refractive index difference becomes larger, the waveguide size and the grating size become on the scale of sub-micrometers, so the silicon photonics technology excellent in microfabrication is suitable.

[0080] Also, at the intersection of optical waveguides, a three-dimensional intersection of a SiN optical waveguide and a Si optical waveguide can be used. The SiN optical waveguide layer is formed on the upper layer sandwiching the Si optical waveguide layer and the SiO2 cladding layer, and is sufficiently separated in the vertical direction, for example, by 1 μm or more so that no loss or crosstalk occurs even when intersecting three-dimensionally. For the interlayer connection between the Si optical waveguide and the SiN optical waveguide, a highly efficient connection with a loss of 1 dB or less can be obtained by a directional coupler or the like.

[0081] Although the embodiments of the present invention have been described above, the present invention is not limited thereto. For example, although an example employing a wavelength selection coupler as shown in FIG. 2 has been shown, a diffraction mode for a wavelength other than the specific operating wavelength occurs only on the short wavelength side of the specific operating wavelength, and no diffraction mode occurs on the long wavelength side. Any configuration other than that shown in FIG. 2 may be used as long as it is a wavelength drop filter that drops an optical signal of a specific operating wavelength.

[0082] Also, the arrangement of each component in the wavelength cross-connect circuit shown in FIG. 4 is an example, and the arrangement may be changed as long as the connection relationship with each component is maintained. For example, although an example in which the inputs and outputs of the optical switches 101 to 104 are in the horizontal direction is shown, the inputs and outputs of the optical switches 101 to 104 may be in the vertical direction to connect the optical waveguides.

[0083] Summarizing the embodiments described above, it is as follows.

[0084] The wavelength cross-connect circuit according to the present embodiment includes (A) the first to the Nth respectively λN drops an optical signal at any one of the wavelengths and generates diffraction modes for wavelengths other than the one wavelength only on the shorter wavelength side of that one wavelength. λ (B) M first optical waveguides, each having wavelength drop filters formed in series in order of increasing wavelength, and (B) each having the first to N λ N drops an optical signal of any one wavelength among the wavelengths and produces diffraction modes for wavelengths other than the one wavelength only on the shorter wavelength side of that one wavelength. λ N second optical waveguides, each having wavelength drop filters formed in series in order of increasing wavelength, and (C) M first optical waveguides, each having N λ Among the wavelength drop filters, M drop ports of the wavelength drop filters that drop optical signals of the same wavelength, and N formed in the N second optical waveguides. λ N wavelength drop filters are connected in one-to-one pairs, with one or more combinations, to the drop ports of the N wavelength drop filters that drop optical signals of the same wavelength as the above-mentioned wavelength. λ It has M input N output optical switches.

[0085] In this configuration, for example, if a wavelength division multiplexed signal is input to one of the first optical waveguides from the side of the wavelength drop filter responsible for the shortest wavelength, the signals will be dropped by the wavelength drop filters in order of increasing wavelength. As a result, other wavelength drop filters formed in series with the same first optical waveguide will not receive optical signals with wavelengths shorter than those handled by the respective wavelength drop filters. Therefore, if the wavelength drop filters have the characteristics described above, the optical signals input to each wavelength drop filter will not be adversely affected by diffraction or other factors. Similarly, on the second optical waveguide side, no optical signals with wavelengths shorter than those handled by the respective wavelength drop filters will be input, enabling broadband operation overall.

[0086] Furthermore, N is formed in each of the M first optical waveguides mentioned above. λEach of the wavelength drop filters may include a diffraction grating structure formed on the side of the first optical waveguide and the optical waveguide on the drop port side, which is located adjacent to the first optical waveguide, according to the wavelength of the optical signal to be dropped. λ Each of these wavelength drop filters may include a diffraction grating structure formed on the side of the second optical waveguide and the optical waveguide on the drop port side, which is located adjacent to the second optical waveguide, according to the wavelength of the optical signal to be dropped. This illustrates the case where the wavelength drop filter is a wavelength selective coupler, as shown in Figure 2.

[0087] Furthermore, at least one of the first optical waveguides of the M-type is a first to N-type λ If a wavelength division multiplexed signal of the wavelength is input from the side of the wavelength drop filter responsible for the shortest wavelength, (D) the N formed in the first optical waveguide into which the wavelength division multiplexed signal is input λ Each of these wavelength drop filters drops the optical signal of the wavelength that the wavelength drop filter is responsible for, (E)N λ The optical signal dropped by each of the wavelength drop filters is input to an M-input N-output optical switch connected to the drop port of the drop filter, and from the M-input N-output optical switch, it is output to the drop port of the wavelength drop filter formed in the second optical waveguide that should output the optical signal among the N second optical waveguides, and the wavelength drop filter drops the signal into the second optical waveguide in which the wavelength drop filter is formed. Note that at least one of the N second optical waveguides is a first to Nth wavelength drop filter. λ The same processing is applied when a wavelength division multiplexed signal of a certain wavelength is input from the side of the wavelength drop filter responsible for the shortest wavelength. [Explanation of Symbols]

[0088] 1~5,6~8 optical waveguide Wavelength-selective couplers: 11-14, 21-24, 31-34, 41-44, 51-54, 61-64, 71-74, 81-84 101-104 Optical switches 150 Control Unit

Claims

1. Each of the following is the 1st to the Nth. λ N is a light signal that drops at any one of the wavelengths and generates diffraction modes for wavelengths other than the one wavelength only on the shorter wavelength side of that one wavelength. λ A first optical waveguide consisting of M wavelength drop filters, each formed in series in order of increasing wavelength, Each of the first to the Nth λ N is a light signal that drops at any one of the wavelengths and generates diffraction modes for wavelengths other than the one wavelength only on the shorter wavelength side of that one wavelength. λ N second optical waveguides, each having wavelength drop filters arranged in series in order of increasing wavelength, The N formed in each of the M first optical waveguides λ Among the wavelength drop filters, M drop ports of the wavelength drop filters that drop optical signals of the same wavelength, and the N second optical waveguides each formed in the N λ N wavelength drop filters are connected in one-to-one pairs, with one or more combinations, to the drop ports of the N wavelength drop filters that drop optical signals of the same wavelength as the aforementioned wavelength. λ A set of M-input N-output optical switches, A wavelength cross-connect circuit having [a specific feature / feature].

2. The N formed in each of the M first optical waveguides λ Each of these wavelength drop filters includes a diffraction grating structure formed on the side of the first optical waveguide and the drop port side optical waveguide located adjacent to the first optical waveguide, according to the wavelength of the optical signal to be dropped. The N wavelength drop filters respectively formed in the N second optical waveguides each have an N λ diffraction grating structure formed according to the wavelength of the optical signal to be dropped on the side surface between the second optical waveguide and the optical waveguide on the drop port side disposed close to the second optical waveguide The wavelength cross-connect circuit according to claim 1.

3. At least one of the first optical waveguides M of the first optical waveguides is the first to N λ When a wavelength division multiplexed signal of a certain wavelength is input from the side of the wavelength drop filter responsible for the shortest wavelength, The N formed in the first optical waveguide into which the wavelength division multiplexed signal is input. λ Each of these wavelength drop filters drops the optical signal of the wavelength that the wavelength drop filter is responsible for. The aforementioned N λ The optical signal dropped by each of the wavelength drop filters is input to an M-input N-output optical switch connected to the drop port of the drop filter, and from the M-input N-output optical switch, it is output to the drop port of the wavelength drop filter formed in the second optical waveguide that should output the optical signal among the N second optical waveguides, and the signal is dropped into the second optical waveguide by the wavelength drop filter. The wavelength cross-connect circuit according to claim 1.

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