Four-mode mode division multiplexing / demultiplexing device based on Y-branch and multimode interference coupler

Abstract

The present invention discloses a four-mode mode division multiplexing / demultiplexing device based on Y-branching and multimode interference couplers. The device includes a four-mode multiplexer and a four-mode demultiplexer. The four-mode multiplexer and the four-mode demultiplexer multiplex four transmission modes through a four-mode bus waveguide. The four-mode multiplexer and the four-mode demultiplexer are mirror-symmetric structures, each composed of a dual-mode Y-waveguide, a four-mode Y-waveguide, a 2×2 single-mode input paired interferometer (MMI) type, and a 2×2 multimode input general interferometer (MMI) type basic unit. The present invention achieves four-mode multiplexing and demultiplexing by controlling the mode phase in the Y-waveguide and the MMI multimode coupler. The four-mode mode division multiplexer and demultiplexer have low loss, wide bandwidth, compact size, and wide manufacturing tolerance.

Description

Technical Field

[0001] The present invention belongs to the technical field of multimode silicon-based photonics multimode mode division multiplexing / demultiplexing, and in particular relates to a four-mode mode division multiplexing / demultiplexing device based on Y branches and multimode interference couplers. Background Art

[0002] Compared to traditional copper wire electrical interconnects, on-chip optical interconnects based on SOI (silicon-on-insulator) offer significant potential advantages in data transmission. Currently, several multiplexing technologies are being used to expand the data capacity of photonic communications: WDM (Wave-Division Multiplexing) and PDM (Polarization Division Multiplexing). Complementary to this, MDM (Mode-Division Multiplexing) offers another dimension to on-chip optical interconnect multiplexing, further increasing the data capacity of on-chip optical communications. Mode-division multiplexing (MDM) devices are the core components of MDM systems, used to excite, multiplex, and demultiplex various transmission modes. An ideal MDM device should meet the requirements of low crosstalk, low insertion loss, wide optical bandwidth, good manufacturing tolerances, and compact size. A variety of MDM devices have been proposed, including asymmetric directional couplers, adiabatic couplers, asymmetric Y-branches, cascaded asymmetric Y-branches, and MMI (multimode interference couplers).

[0003] However, these devices do not fully meet the requirements of an ideal mode-division multiplexing device. Although asymmetric directional couplers offer a wide bandwidth, their manufacturing tolerances are very tight, requiring precise control of the coupling length and waveguide width, and are difficult to scale to accommodate more modes. Adiabatic couplers, asymmetric Y-branches, and cascaded asymmetric Y-branches are large, making them unsuitable for high-density integration. Mode-division multiplexers that utilize only MMIs, while offering high bandwidth and compact size, are constrained by the cascaded phase shifters, limiting their manufacturing tolerances. Summary of the Invention

[0004] In order to solve the above problems existing in the prior art, the present invention provides a four-mode mode division multiplexing and demultiplexing multiplexer based on Y-branches and multimode interference couplers. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0005] In a first aspect, an embodiment of the present invention provides a four-mode mode division multiplexing demultiplexer based on a Y-branch and a multimode interference coupler, wherein the four-mode mode division multiplexing demultiplexer includes a four-mode multiplexer and a four-mode demultiplexer, wherein the four-mode multiplexer and the four-mode demultiplexer implement multiplexing of four conduction modes through a four-mode bus waveguide, and the four-mode multiplexer and the four-mode demultiplexer are mirror-symmetric structures to each other; the four-mode multiplexer includes:

[0006] The first to fourth single-mode input waveguides are used to respectively receive the power of incident light to respectively excite a fundamental mode, a second-order mode, a first-order mode, and a third-order mode in the four-mode bus waveguide;

[0007] a first 2×2 single-mode input paired interferometer MMI, configured to generate a second-order image of the fourth single-mode input waveguide and a second-order image of the third single-mode input waveguide according to the power of the incident light;

[0008] a second 2×2 single-mode input paired interferometry MMI, configured to generate a second-order image of the second single-mode input waveguide and a second-order image of the first single-mode input waveguide according to the power of the incident light;

[0009] a first dual-mode Y-type waveguide, configured to perform optical power synthesis after respectively performing a π / 2 phase delay on the second-order image of the fourth single-mode input waveguide and the second-order image of the third single-mode input waveguide;

[0010] A second dual-mode Y-type waveguide is used to perform optical power combination after performing a π / 2 phase delay on the second-order image of the second single-mode input waveguide and the second-order image of the first single-mode input waveguide;

[0011] a 2×2 multimode input general interferometer MMI, configured to generate a second-order image of the main waveguide of the first dual-mode Y-type waveguide and a second-order image of the main waveguide of the second dual-mode Y-type waveguide, respectively, based on a result of optical power synthesis of the first dual-mode Y-type waveguide and a result of optical power synthesis of the second dual-mode Y-type waveguide;

[0012] a third dual-mode Y-type waveguide, configured to decompose the second-order image output from the upper output end of the 2×2 multi-mode input general interferometer MMI into a fundamental mode, perform equal-path and equal-phase control on the fundamental mode, and perform π / 2 phase delay control on the second-order image output from the lower output end of the 2×2 multi-mode input general interferometer MMI;

[0013] a fourth dual-mode Y-type waveguide, configured to combine the optical power of the fundamental mode after phase control by the third dual-mode Y-type waveguide;

[0014] a fifth dual-mode Y-type waveguide, configured to decompose the second-order image output from the lower output end of the 2×2 multi-mode input general interferometer MMI into a fundamental mode, perform equal-path and equal-phase control on the fundamental mode, and perform π / 2 phase delay control on the second-order image output from the upper output end of the 2×2 multi-mode input general interferometer MMI;

[0015] a sixth dual-mode Y-type waveguide, configured to combine the optical power of the fundamental mode after phase delay by the fifth dual-mode Y-type waveguide;

[0016] The four-mode Y-type waveguide is used to continue optical power synthesis of the optical power synthesis result of the sixth dual-mode Y-type waveguide and the optical power synthesis result of the fourth dual-mode Y-type waveguide and input the optical power synthesis result into the four-mode bus waveguide to achieve simultaneous transmission of the fundamental mode, the first-order mode, the second-order mode and the third-order mode.

[0017] In one embodiment of the present invention, the first single-mode input waveguide is used as the input end, and the second-order image generated by the second 2×2 single-mode input paired interferometer MMI is equal in phase after phase shifting, and the second-order image generated by the 2×2 multi-mode input general interferometer MMI is equal in phase after phase shifting, so as to excite the fundamental mode in the four-mode bus waveguide; the second single-mode input waveguide is used as the input end, and the second-order image generated by the second 2×2 single-mode input paired interferometer MMI is equal in phase after phase shifting, so as to excite the four-mode bus waveguide. second-order mode; taking the third single-mode input waveguide as the input end, the second-order image generated by the first 2×2 single-mode input paired interference type MMI is equal in phase after phase shift, and the second-order image generated by the 2×2 multi-mode input general interference type MMI is equal in phase after phase shift, so as to excite the first-order mode in the four-mode bus waveguide; taking the fourth single-mode input waveguide as the input end, the second-order image generated by the first 2×2 single-mode input paired interference type MMI is equal in phase after phase shift, and the second-order image generated by the 2×2 multi-mode input general interference type MMI is equal in phase after phase shift, so as to excite the third-order mode in the four-mode bus waveguide.

[0018] In one embodiment of the present invention, the input / output ports of the first 2×2 single-mode input paired interferometry MMI and the second 2×2 single-mode input paired interferometry MMI are both designed with a gradient waveguide. By changing the length of the gradient waveguide, a phase difference of π / 2 is achieved at each port.

[0019] In one embodiment of the present invention, the input / output ports of the first 2×2 single-mode input paired interferometry MMI and the second 2×2 single-mode input paired interferometry MMI are located at ±We1 / 6, where We1 is the effective width of the first 2×2 single-mode input paired interferometry MMI and the second 2×2 single-mode input paired interferometry MMI after taking into account the Goos-Hahnchen shift;

[0020] The lengths of the first 2×2 single-mode input paired interferometry MMI and the second 2×2 single-mode input paired interferometry MMI are Lπ1 / 2, where Lπ1 is the beat length of the fundamental mode and the first-order mode in the first 2×2 single-mode input paired interferometry MMI and the second 2×2 single-mode input paired interferometry MMI.

[0021] In one embodiment of the present invention, the input / output end of the 2×2 multimode input general interferometer MMI is designed with a gradient waveguide, which is aligned with the edge of the main waveguide of the 2×2 multimode input general interferometer MMI.

[0022] In one embodiment of the present invention, the length of the 2×2 multi-mode input general interferometer MMI is 3Lπ2, where Lπ2 is the beat length of the fundamental mode and the first-order mode in the 2×2 multi-mode input general interferometer MMI.

[0023] In one embodiment of the present invention, the main waveguides of the first to sixth dual-mode Y-type waveguides support two conduction modes, the fundamental mode and the first-order mode, and the branch waveguides of the first to sixth dual-mode Y-type waveguides support one conduction mode, the fundamental mode; the third dual-mode Y-type waveguide and the fourth dual-mode Y-type waveguide are mirror-symmetrical structures, and the fifth dual-mode Y-type waveguide and the sixth dual-mode Y-type waveguide are mirror-symmetrical structures; the upper branch composed of the third dual-mode Y-type waveguide and the fourth dual-mode Y-type waveguide and the lower branch composed of the fifth dual-mode Y-type waveguide and the sixth dual-mode Y-type waveguide form a phase difference of π / 2.

[0024] In one embodiment of the present invention, the width of the main waveguide of the four-mode Y-type waveguide is the same as the width of the four-mode bus waveguide, and the main waveguide of the four-mode Y-type waveguide supports four conduction modes: fundamental mode, first-order mode, second-order mode and third-order mode; the width of the branch waveguide of the four-mode Y-type waveguide is the same as the width of the main waveguide of the first dual-mode Y-type waveguide to the sixth dual-mode Y-type waveguide, and the branch waveguide of the four-mode Y-type waveguide supports two conduction modes: fundamental mode and first-order mode.

[0025] In one embodiment of the present invention, the cross-sections of the first to fourth single-mode input waveguides, the first 2×2 single-mode input paired interferometry MMI, the second 2×2 single-mode input paired interferometry MMI, the first to sixth dual-mode Y-type waveguides, the 2×2 multi-mode input general interferometry MMI, and the four-mode Y-type waveguide are all rectangular.

[0026] In a second aspect, an embodiment of the present invention provides a mode interference amplitude equalizer, which includes a plurality of cascaded four-mode mode division multiplexing / demultiplexing devices based on Y branches and multimode interference couplers as described above.

[0027] Beneficial effects of the present invention:

[0028] The four-mode mode division multiplexing / demultiplexing device based on Y-branches and multimode interference couplers proposed in the present invention can realize multiplexing and demultiplexing of four transmission modes: the four-mode multiplexer and four-mode demultiplexer in the four-mode mode division multiplexing / demultiplexing device are mirror-symmetrical structures, and are both composed of dual-mode Y-type waveguides, four-mode Y-type waveguides, 2×2 single-mode input paired interference type MMIs, and 2×2 multi-mode input general interference type MMI basic units. The four-mode multiplexer composed of the dual-mode Y-type waveguides, four-mode Y-type waveguides, 2×2 single-mode input paired interference type MMIs, and 2×2 multi-mode input general interference type MMIs is used to achieve response differences of different phases, so as to excite corresponding modes at different input ports and multiplex them in the four-mode bus waveguide. Finally, the four-mode demultiplexer composed of the dual-mode Y-type waveguides, four-mode Y-type waveguides, 2×2 single-mode input paired interference type MMIs, and 2×2 multi-mode input general interference type MMIs respectively parses the four transmission modes and outputs them from the corresponding single-mode output waveguides to realize mode demultiplexing. In general, the four-mode mode division multiplexing / demultiplexing device proposed in the present invention is based on the large process tolerance of Y-type waveguides and MMI multimode couplers. By controlling the single-mode phase, this type of device has the characteristics of low loss, large bandwidth, small size and large manufacturing tolerance. It can also be flexibly expanded to multiplex / demultiplex higher-order modes according to design ideas, thereby improving the system capacity of on-chip integrated optical communications.

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 1 is a schematic structural diagram of a four-mode mode division multiplexing / demultiplexing device based on Y-branches and multimode interference couplers provided by an embodiment of the present invention;

[0031] Figure 2a to Figure 2d Schematic diagram of the fundamental mode, first-order mode, second-order mode, and third-order mode excited in a four-mode bus waveguide by the structure proposed by the present invention;

[0032] Figure 3 This is a schematic diagram of the implementation process of the structure provided by the embodiment of the present invention, taking the fourth single-mode input waveguide as the fundamental mode input as an example to illustrate the present invention. DETAILED DESCRIPTION

[0033] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0034] See Figure 1 An embodiment of the present invention provides a four-mode mode division multiplexing / demultiplexing / demultiplexing device based on a Y-branch and a multimode interference coupler. The four-mode mode division multiplexing / demultiplexing device includes a four-mode multiplexer and a four-mode demultiplexer. The four-mode multiplexer and the four-mode demultiplexer multiplex four transmission modes via a four-mode bus waveguide. The four-mode multiplexer and the four-mode demultiplexer are mirror-symmetric structures. The four-mode multiplexer includes:

[0035] The first to fourth single-mode input waveguides are used to respectively receive the power of incident light to respectively excite a fundamental mode, a second-order mode, a first-order mode, and a third-order mode in the four-mode bus waveguide;

[0036] a first 2×2 single-mode input paired interferometry MMI, configured to generate a second-order image of the fourth single-mode input waveguide and a second-order image of the third single-mode input waveguide according to the power of the incident light;

[0037] a second 2×2 single-mode input paired interferometry MMI, configured to generate a second-order image of the second single-mode input waveguide and a second-order image of the first single-mode input waveguide according to the power of the incident light;

[0038] The first dual-mode Y-type waveguide is used to perform optical power combination after the second-order image of the fourth single-mode input waveguide and the second-order image of the third single-mode input waveguide are phase-delayed by π / 2 respectively;

[0039] The second dual-mode Y-type waveguide is used to perform optical power combination after the second-order image of the second single-mode input waveguide and the second-order image of the first single-mode input waveguide are phase-delayed by π / 2 respectively;

[0040] a 2×2 multi-mode input general interference MMI, wherein the input end of the 2×2 multi-mode input general interference MMI is connected to the main waveguide output end of the first dual-mode Y-type waveguide and the main waveguide output end of the second dual-mode Y-type waveguide, and is used to generate a second-order image of the main waveguide of the first dual-mode Y-type waveguide and a second-order image of the main waveguide of the second dual-mode Y-type waveguide respectively based on the optical power synthesis result of the first dual-mode Y-type waveguide and the optical power synthesis result of the second dual-mode Y-type waveguide;

[0041] A third dual-mode Y-type waveguide is used to decompose the second-order image output from the upper output end of the 2×2 multi-mode input general interference type MMI into a fundamental mode, perform equal path and equal phase control on the fundamental mode, and perform π / 2 phase delay control on the second-order image output from the lower output end of the 2×2 multi-mode input general interference type MMI;

[0042] a fourth dual-mode Y-type waveguide, configured to combine the optical power of the fundamental mode after phase control by the third dual-mode Y-type waveguide;

[0043] a fifth dual-mode Y-type waveguide for decomposing the second-order image output from the lower output end of the 2×2 multi-mode input general interferometric MMI into a fundamental mode, performing equal-path and equal-phase control on the fundamental mode, and performing π / 2 phase delay control on the second-order image output from the upper output end of the 2×2 multi-mode input general interferometric MMI;

[0044] a sixth dual-mode Y-type waveguide, configured to combine the optical power of the fundamental mode after phase delay by the fifth dual-mode Y-type waveguide;

[0045] The four-mode Y-type waveguide is used to continue optical power synthesis with the optical power synthesis result of the sixth dual-mode Y-type waveguide and the optical power synthesis result of the fourth dual-mode Y-type waveguide, and input the optical power synthesis result into the four-mode bus waveguide to achieve simultaneous transmission of the fundamental mode, the first-order mode, the second-order mode and the third-order mode.

[0046] In the embodiment of the present invention, the first to fourth single-mode input waveguides are all single-mode inputs, that is, they have only one conduction mode, such as Figure 1 The transmission modes corresponding to the first single-mode input waveguide to the fourth single-mode input are fundamental mode, second-order mode, first-order mode and third-order mode respectively.

[0047] In the embodiment of the present invention, a π / 2 phase shifter is designed at each position where a π / 2 phase delay is required.

[0048] In the embodiment of the present invention, the first single-mode input waveguide is used as the input end, and the second-order image generated by the second 2×2 single-mode input paired interferometer MMI is equal in phase after phase shifting, and the second-order image generated by the 2×2 multi-mode input general interferometer MMI is equal in phase after phase shifting, so as to excite the fundamental mode in the four-mode bus waveguide; the second single-mode input waveguide is used as the input end, and the second-order image generated by the second 2×2 single-mode input paired interferometer MMI is equal in phase after phase shifting, so as to excite the second-order mode in the four-mode bus waveguide. ; Taking the third single-mode input waveguide as the input end, the second-order image generated by the first 2×2 single-mode input paired interference type MMI is equal in phase after phase shift, and the second-order image generated by the 2×2 multi-mode input general interference type MMI is equal in phase after phase shift, so as to excite the first-order mode in the four-mode bus waveguide; Taking the fourth single-mode input waveguide as the input end, the second-order image generated by the first 2×2 single-mode input paired interference type MMI is equal in phase after phase shift, and the second-order image generated by the 2×2 multi-mode input general interference type MMI is equal in phase after phase shift, so as to excite the third-order mode in the four-mode bus waveguide.

[0049] In this embodiment of the present invention, the input / output ports of the first 2×2 single-mode input paired interferometry MMI and the second 2×2 single-mode input paired interferometry MMI are each designed with a gradient waveguide. The gradient waveguide is used to input / output the incident light or outgoing light at the corresponding port while satisfying the adiabatic approximation. By varying the length of the gradient waveguide, a phase difference of π / 2 can be achieved at each port. For example, the first 2×2 single-mode input paired interferometry MMI and the second 2×2 single-mode input paired interferometry MMI each form a second-order self-image (i.e., a second-order image) at the corresponding port via the gradient waveguide. By varying the length of the gradient waveguide, a phase difference of π / 2 can be achieved at the corresponding port.

[0050] In the embodiment of the present invention, the input / output ports of the first 2×2 single-mode input paired interferometry MMI and the second 2×2 single-mode input paired interferometry MMI are located at ±We1 / 6, where We1 is the effective width of the first 2×2 single-mode input paired interferometry MMI and the second 2×2 single-mode input paired interferometry MMI after taking into account the Goos-Hahnchen shift. The lengths of the first 2×2 single-mode input paired interferometry MMI and the second 2×2 single-mode input paired interferometry MMI are Lπ1 / 2, and Lπ1 is the beat length of the fundamental mode and the first-order mode in the first 2×2 single-mode input paired interferometry MMI and the second 2×2 single-mode input paired interferometry MMI. The calculation formula for Lπ1 is expressed as:

[0051] Lπ1=π / (β0-β1)≈4n r We1 2 / 3λ0;

[0052] where β0 and β1 are the waveguide propagation constants of the fundamental mode and the first-order mode in the first 2×2 single-mode input paired interferometry MMI and the second 2×2 single-mode input paired interferometry MMI, respectively. r is the relative nodal constant, and λ0 is the wavelength in vacuum.

[0053] In this embodiment of the present invention, the input / output ports of the 2×2 multimode input generalized interferometry (MMI) are designed with tapered waveguides aligned with the edges of the 2×2 multimode input generalized interferometry (MMI)'s main waveguides. Similarly, the tapered waveguides are used to input / output light at the current input / output port in a manner that satisfies the adiabatic approximation.

[0054] In the embodiment of the present invention, the length of the 2×2 multimode input general interferometer MMI is 3Lπ2, where Lπ2 is the beat length of the fundamental mode and the first-order mode in the 2×2 multimode input general interferometer MMI. The calculation formula of Lπ2 is expressed as:

[0055] Lπ=π / (β2-β3)≈4n r We2 2 / 3λ0;

[0056] where β2 and β3 are the waveguide propagation constants of the fundamental mode and the first-order mode in the 2×2 multimode input general interferometer MMI, respectively, and We2 is the effective width of the 2×2 multimode input general interferometer MMI after considering the Goos-Hahnchen shift.

[0057] In the embodiment of the present invention, the main waveguides of the first dual-mode Y-type waveguide to the sixth dual-mode Y-type waveguide support two conduction modes, the fundamental mode and the first-order mode, and the branch waveguides of the first dual-mode Y-type waveguide to the sixth dual-mode Y-type waveguide support one conduction mode, the fundamental mode; the third dual-mode Y-type waveguide and the fourth dual-mode Y-type waveguide are mirror-symmetrical structures, and the fifth dual-mode Y-type waveguide and the sixth dual-mode Y-type waveguide are mirror-symmetrical structures; the third dual-mode Y-type waveguide and the fourth dual-mode Y-type waveguide, the fifth dual-mode Y-type waveguide and the sixth dual-mode Y-type waveguide respectively constitute a phase difference of π / 2, and here the curvature radius of the S-type branch waveguide of the third dual-mode Y-type waveguide to the sixth dual-mode Y-type waveguide can be changed so that the upper branch composed of the third dual-mode Y-type waveguide and the fourth dual-mode Y-type waveguide and the lower branch composed of the fifth dual-mode Y-type waveguide and the sixth dual-mode Y-type waveguide constitute a phase difference of π / 2. The phase points of the second-order image of the main waveguide of the first dual-mode Y-type waveguide have a phase difference of π / 2, and the phase points of the second-order image of the main waveguide of the second dual-mode Y-type waveguide have a phase difference of -π / 2.

[0058] In the embodiment of the present invention, the width of the main waveguide of the four-mode Y-type waveguide is the same as the width of the four-mode bus waveguide, and the main waveguide of the four-mode Y-type waveguide supports four conduction modes: fundamental mode, first-order mode, second-order mode and third-order mode; the width of the branch waveguide of the four-mode Y-type waveguide is the same as the width of the main waveguide of the first dual-mode Y-type waveguide to the sixth dual-mode Y-type waveguide, and the branch waveguide of the four-mode Y-type waveguide supports two conduction modes: fundamental mode and first-order mode.

[0059] In the embodiment of the present invention, the cross-sections of the first to fourth single-mode input waveguides, the first 2×2 single-mode input paired interferometry MMI, the second 2×2 single-mode input paired interferometry MMI, the first to sixth dual-mode Y-type waveguides, the 2×2 multi-mode input general interferometry MMI, and the four-mode Y-type waveguide are all rectangular.

[0060] In the embodiment of the present invention, the four-mode bus waveguide is used to simultaneously transmit the fundamental mode, the first-order mode, the second-order mode and the third-order mode. Its length is designed by extending, bending, etc. according to actual applications.

[0061] The process of exciting the fundamental mode, first-order mode, second-order mode, and third-order mode in the four-mode bus waveguide through the four-mode multiplexer in the embodiment of the present invention is as follows:

[0062] First single-mode input waveguide (fundamental mode) → second 2×2 single-mode input paired interferometric MMI → excite the second-order image of the single mode with a phase difference of π / 2 → introduce -π / 2 into the Y branch of the second dual-mode Y-type waveguide → in-phase (phase difference 0) at the main waveguide of the second dual-mode Y-type waveguide → output Y-branch fundamental mode → 2×2 multi-mode input general interferometric MMI outputs the second-order image of the fundamental mode with a phase difference of π / 2 → introduce -π / 2 into the upper branch composed of the third and fourth dual-mode Y-type waveguides, and the lower branch composed of the fifth and sixth dual-mode Y-type waveguides → in-phase synthesis at the main waveguide of the four-mode Y-type waveguide and feed into the four-mode bus waveguide, and excite the fundamental mode in the four-mode bus waveguide as shown in FIG. Figure 2a As shown;

[0063] Second single-mode input waveguide (second-order mode) → second 2×2 single-mode input paired interferometric MMI → excite the second-order image of the single mode with a phase difference of π / 2 → introduce π / 2 into the Y branch of the second dual-mode Y-type waveguide → reverse phase (phase difference π) at the main waveguide of the second dual-mode Y-type waveguide → output the first-order mode of the Y branch → 2×2 multi-mode input general interferometric MMI outputs the second-order image of the first-order mode with a phase difference of π / 2 → introduce -π / 2 into the upper branch composed of the third and fourth dual-mode Y-type waveguides and the lower branch composed of the fifth and sixth dual-mode Y-type waveguides → synthesize in phase at the main waveguide of the four-mode Y-type waveguide and feed into the four-mode bus waveguide, and excite the second-order mode in the four-mode bus waveguide as shown in FIG. Figure 2c As shown;

[0064] The third single-mode input waveguide (first-order mode) → the first 2×2 single-mode input paired interferometric MMI → excites the second-order image of the single mode with a phase difference of π / 2 → the Y branch of the first dual-mode Y-type waveguide introduces -π / 2 → in-phase (phase difference 0) at the main waveguide of the first dual-mode Y-type waveguide → outputs the Y-branch fundamental mode → the 2×2 multi-mode input general interferometric MMI outputs the second-order image of the fundamental mode with a phase difference of π / 2 → introduces π / 2 at the upper branch composed of the third and fourth dual-mode Y-type waveguides, and the lower branch composed of the fifth and sixth dual-mode Y-type waveguides → in-phase synthesis (phase difference π) at the main waveguide of the four-mode Y-type waveguide and feeds into the four-mode bus waveguide, and excites the first-order mode in the four-mode bus waveguide. Figure 2b As shown;

[0065] Fourth single-mode input waveguide (third-order mode) → first 2×2 single-mode input paired interferometric MMI → excite the second-order image of the single mode with a phase difference of π / 2 → introduce π / 2 into the Y branch of the first dual-mode Y-type waveguide → invert the phase (phase difference π) at the main waveguide of the first dual-mode Y-type waveguide → output the first-order mode of the Y branch → 2×2 multi-mode input general interferometric MMI outputs the second-order image of the first-order mode with a phase difference of π / 2 → introduce π / 2 into the upper branch composed of the third and fourth dual-mode Y-type waveguides and the lower branch composed of the fifth and sixth dual-mode Y-type waveguides → synthesize in phase (phase difference π) at the main waveguide of the four-mode Y-type waveguide and feed into the four-mode bus waveguide, and excite the third-order mode in the four-mode bus waveguide as shown in FIG. Figure 2d shown.

[0066] Take single fundamental mode input as an example, Figure 3As shown, the single fundamental mode is input into the fourth single-mode input waveguide (corresponding to the third-order mode); the first 2×2 single-mode input paired interferometer MMI is fed through the gradient waveguide, and the second-order image of the fourth single-mode input waveguide is formed in the first 2×2 single-mode input paired interferometer MMI with a phase difference of π / 2; the second-order image of the fourth single-mode input waveguide is input into the first dual-mode Y-type waveguide, and the main waveguide of the first dual-mode Y-type waveguide is a dual-mode waveguide, that is, it supports two conduction modes, the fundamental mode and the first-order mode, and the Y branch is a fundamental mode waveguide. The width of the two Y branches is equal to the cross-section of the main waveguide. By changing the gradient The length of the waveguide is introduced into the lower Y-branch waveguide of the first dual-mode Y-type waveguide, and a phase difference of π / 2 is introduced relative to the upper Y-branch waveguide, so that the phase difference of the second-order image output by the first 2×2 single-mode input paired interferometric MMI is accumulated to π after passing through the Y branch of the first dual-mode Y-type waveguide. Then, according to the working principle of the Y branch, when the phase difference between the upper and lower Y branches is π, the first-order mode is excited in the main waveguide of the first dual-mode Y-type waveguide; the output of the main waveguide of the first dual-mode Y-type waveguide is fed into the 2×2 multi-mode input general interferometric MMI, and the output of the 2×2 multi-mode input general interferometric MMI is fed into the output of the 2×2 multi-mode input general interferometric MMI. The output end forms a second-order image of the first dual-mode Y-type waveguide with a phase difference of π / 2. Specifically, the upper output end of the 2×2 multi-mode input general interference type MMI is connected to the Y branch of the third dual-mode Y-type waveguide. Through the Y branch, the second-order image of the first-order mode of the upper Y branch is decomposed into the fundamental mode in the Y branch, and the second-order image of the first-order mode of the upper Y branch is reproduced through the symmetrical lower Y branch. Similarly, the lower output end of the 2×2 multi-mode input general interference type MMI is connected to the Y branch of the fifth dual-mode Y-type waveguide. Through the Y branch, the second-order image of the first-order mode of the upper Y branch is decomposed into the fundamental mode in the Y branch. mode, and reproduce the second-order image of the first-order mode of the upper Y-branch through the symmetrical lower Y-branch. Finally, by changing the S-waveguide curvature radius of the third to sixth dual-mode Y-type waveguides, a π / 2 phase difference is introduced in the upper branch composed of the third dual-mode Y-type waveguide and the fourth dual-mode Y-type waveguide, and the lower branch composed of the fifth dual-mode Y-type waveguide and the sixth dual-mode Y-type waveguide. The two dual-mode Y-type waveguides are synthesized at the main waveguide of the four-mode Y-type waveguide, where the phase difference of the second-order image is π / 2. According to the working principle of the Y-branch waveguide, the third-order mode can be excited in the main waveguide, thereby exciting the third-order mode in the four-mode bus waveguide.

[0067] Furthermore, if Figure 1 As shown, the four-mode demultiplexer and the four-mode multiplexer are mirror-symmetric structures with respect to the four-mode bus waveguide. The specific structure of the four-mode demultiplexer is described in detail in the four-mode multiplexer and will not be further described here. Ultimately, after passing through the four-mode multiplexer, the four-mode bus waveguide, and the four-mode demultiplexer, the fundamental mode, second-order mode, first-order mode, and third-order mode are output from the first through fourth single-mode output waveguides of the four-mode demultiplexer, respectively. The cross-sections of the first through fourth single-mode output waveguides are all rectangular.

[0068] It should be noted that since the four-mode demultiplexer and the four-mode multiplexer are mirror-symmetrical structures, in actual applications, either the left or right side can be used as the input side, i.e., the four-mode multiplexer, and the corresponding other side will be used as the output side, i.e., the four-mode demultiplexer. Figure 1 The diagram shows the case where the left side is used as a four-mode multiplexer and the right side is used as a four-mode demultiplexer.

[0069] In summary, the four-mode mode division multiplexing demultiplexer based on Y-branch and multimode interference coupler proposed in the embodiment of the present invention can realize the multiplexing and demultiplexing of four transmission modes: the four-mode multiplexer and the four-mode demultiplexer in the four-mode mode division multiplexing demultiplexer are mirror-symmetrical structures, both of which are composed of dual-mode Y-type waveguide, four-mode Y-type waveguide, 2×2 single-mode input paired interference type MMI and 2×2 multi-mode input general interference type MMI basic units. A four-mode multiplexer consisting of a single-mode input paired interferometric MMI and a 2×2 multimode input general interferometric MMI achieves phase-dependent response differences, stimulating corresponding modes at different input ports and multiplexing them in a four-mode bus waveguide. Finally, a four-mode demultiplexer consisting of a dual-mode Y-waveguide, a four-mode Y-waveguide, a 2×2 single-mode input paired interferometric MMI, and a 2×2 multimode input general interferometric MMI resolves the four transmission modes and outputs them from the corresponding single-mode output waveguides for mode demultiplexing. In summary, the proposed four-mode mode division demultiplexer leverages the wide process tolerances of the Y-waveguide and MMI multimode coupler and, through single-mode phase control, achieves low loss, wide bandwidth, compact size, and wide manufacturing tolerances. Furthermore, it can be flexibly expanded to multiplex / demultiplex higher-order modes based on design considerations, thereby increasing the system capacity of on-chip integrated optical communications.

[0070] In a second aspect, an embodiment of the present invention provides a mode interference amplitude equalizer, which includes a plurality of cascaded four-mode mode division multiplexing / demultiplexing devices based on Y branches and multimode interference couplers according to the first aspect.

[0071] As for the embodiment of the second aspect, since it is basically similar to the embodiment of the first aspect, the description is relatively simple, and the relevant parts can be referred to the partial description of the embodiment of the first aspect.

[0072] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0073] Although the present invention is described herein in conjunction with various embodiments, those skilled in the art may understand and implement other variations of the disclosed embodiments by reviewing the specification and accompanying drawings in the process of implementing the claimed invention. In the specification, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude multiple components or steps. The fact that certain measures are described in different embodiments does not mean that these measures cannot be combined to produce good results.

[0074] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A four-mode mode division multiplexing / demultiplexing device based on Y-branch and multimode interference coupler, characterized in that: The four-mode mode division multiplexing demultiplexer includes a four-mode multiplexer and a four-mode demultiplexer, wherein the four-mode multiplexer and the four-mode demultiplexer realize multiplexing of four conduction modes through a four-mode bus waveguide, and the four-mode multiplexer and the four-mode demultiplexer are mirror-symmetrical structures to each other; the four-mode multiplexer includes: The first to fourth single-mode input waveguides are used to respectively receive the power of incident light to respectively excite a fundamental mode, a second-order mode, a first-order mode, and a third-order mode in the four-mode bus waveguide; a first 2×2 single-mode input paired interferometer MMI, configured to generate a second-order image of the fourth single-mode input waveguide and a second-order image of the third single-mode input waveguide according to the power of the incident light; a second 2×2 single-mode input paired interferometry MMI, configured to generate a second-order image of the second single-mode input waveguide and a second-order image of the first single-mode input waveguide according to the power of the incident light; a first dual-mode Y-type waveguide, configured to perform optical power synthesis after respectively performing a π / 2 phase delay on the second-order image of the fourth single-mode input waveguide and the second-order image of the third single-mode input waveguide; A second dual-mode Y-type waveguide is used to perform optical power combination after performing a π / 2 phase delay on the second-order image of the second single-mode input waveguide and the second-order image of the first single-mode input waveguide; a 2×2 multimode input general interferometer MMI, configured to generate a second-order image of the main waveguide of the first dual-mode Y-type waveguide and a second-order image of the main waveguide of the second dual-mode Y-type waveguide, respectively, based on a result of optical power synthesis of the first dual-mode Y-type waveguide and a result of optical power synthesis of the second dual-mode Y-type waveguide; a third dual-mode Y-type waveguide, configured to decompose the second-order image output from the upper output end of the 2×2 multi-mode input general interferometer MMI into a fundamental mode, perform equal-path and equal-phase control on the fundamental mode, and perform π / 2 phase delay control on the second-order image output from the lower output end of the 2×2 multi-mode input general interferometer MMI; a fourth dual-mode Y-type waveguide, configured to combine the optical power of the fundamental mode after phase control by the third dual-mode Y-type waveguide; a fifth dual-mode Y-type waveguide, configured to decompose the second-order image output from the lower output end of the 2×2 multi-mode input general interferometer MMI into a fundamental mode, perform equal-path and equal-phase control on the fundamental mode, and perform π / 2 phase delay control on the second-order image output from the upper output end of the 2×2 multi-mode input general interferometer MMI; a sixth dual-mode Y-type waveguide, configured to combine the optical power of the fundamental mode after phase delay by the fifth dual-mode Y-type waveguide; The four-mode Y-type waveguide is used to continue optical power synthesis of the optical power synthesis result of the sixth dual-mode Y-type waveguide and the optical power synthesis result of the fourth dual-mode Y-type waveguide and input the optical power synthesis result into the four-mode bus waveguide to achieve simultaneous transmission of the fundamental mode, the first-order mode, the second-order mode and the third-order mode.

2. The four-mode mode division multiplexing / demultiplexing device based on Y-branch and multimode interference coupler according to claim 1, characterized in that: Taking the first single-mode input waveguide as the input end, the second-order images generated by the second 2×2 single-mode input paired interferometer MMI are phase-shifted and equal in phase, and the second-order images generated by the 2×2 multi-mode input general interferometer MMI are phase-shifted and equal in phase, thereby exciting the fundamental mode in the four-mode bus waveguide; taking the second single-mode input waveguide as the input end, the second-order images generated by the second 2×2 single-mode input paired interferometer MMI are phase-shifted and equal in phase, and the second-order images generated by the 2×2 multi-mode input general interferometer MMI are phase-shifted and equal in phase, thereby exciting the second-order mode in the four-mode bus waveguide; The third single-mode input waveguide is used as the input end, and the second-order image generated by the first 2×2 single-mode input paired interferometric MMI is equal in phase after phase shift, and the second-order image generated by the 2×2 multi-mode input general interferometric MMI is phase shifted by a phase difference π, so as to excite the first-order mode in the four-mode bus waveguide; Taking the fourth single-mode input waveguide as the input end, the phase difference π after the second-order image phase shift generated by the first 2×2 single-mode input paired interference type MMI is the phase difference π after the second-order image phase shift generated by the 2×2 multi-mode input general interference type MMI, so as to excite the third-order mode in the four-mode bus waveguide.

3. The four-mode mode division multiplexing / demultiplexing device based on Y-branch and multimode interference coupler according to claim 1, characterized in that: The input / output ports of the first 2×2 single-mode input paired interferometer MMI and the second 2×2 single-mode input paired interferometer MMI are both designed with gradient waveguides. By changing the length of the gradient waveguide, a phase difference of π / 2 is achieved at each port.

4. The four-mode mode division multiplexing / demultiplexing device based on Y-branch and multimode interference coupler according to claim 1, characterized in that: The input / output ports of the first 2×2 single-mode input paired interferometry MMI and the second 2×2 single-mode input paired interferometry MMI are located at ±We1 / 6, where We1 is the effective width of the first 2×2 single-mode input paired interferometry MMI and the second 2×2 single-mode input paired interferometry MMI after taking into account the Goos-Hahnchen shift; The lengths of the first 2×2 single-mode input paired interferometry MMI and the second 2×2 single-mode input paired interferometry MMI are Lπ1 / 2, where Lπ1 is the beat length of the fundamental mode and the first-order mode in the first 2×2 single-mode input paired interferometry MMI and the second 2×2 single-mode input paired interferometry MMI.

5. The four-mode mode division multiplexing / demultiplexing device based on Y-branch and multimode interference coupler according to claim 1, characterized in that: The input / output end of the 2×2 multi-mode input general interference type MMI is designed with a gradient waveguide, and the gradient waveguide is aligned with the edge of the main waveguide of the 2×2 multi-mode input general interference type MMI.

6. The four-mode mode division multiplexing / demultiplexing device based on Y-branch and multimode interference coupler according to claim 1, characterized in that: The length of the 2×2 multi-mode input general interference type MMI is 3Lπ2, where Lπ2 is the beat length of the fundamental mode and the first-order mode in the 2×2 multi-mode input general interference type MMI.

7. The four-mode mode division multiplexing / demultiplexing device based on Y-branch and multimode interference coupler according to claim 1, characterized in that: The main waveguides of the first to sixth dual-mode Y-type waveguides support two conduction modes, the fundamental mode and the first-order mode, and the branch waveguides of the first to sixth dual-mode Y-type waveguides support one conduction mode, the fundamental mode; the third dual-mode Y-type waveguide and the fourth dual-mode Y-type waveguide are mirror-symmetrical structures, and the fifth dual-mode Y-type waveguide and the sixth dual-mode Y-type waveguide are mirror-symmetrical structures; the upper branch composed of the third dual-mode Y-type waveguide and the fourth dual-mode Y-type waveguide and the lower branch composed of the fifth dual-mode Y-type waveguide and the sixth dual-mode Y-type waveguide form a phase difference of π / 2.

8. The four-mode mode division multiplexing / demultiplexing device based on Y-branch and multimode interference coupler according to claim 1, characterized in that: The width of the main waveguide of the four-mode Y-type waveguide is the same as the width of the four-mode bus waveguide, and the main waveguide of the four-mode Y-type waveguide supports four conduction modes: fundamental mode, first-order mode, second-order mode, and third-order mode; the width of the branch waveguides of the four-mode Y-type waveguide is the same as the width of the main waveguides of the first to sixth dual-mode Y-type waveguides, and the branch waveguides of the four-mode Y-type waveguide support two conduction modes: fundamental mode and first-order mode.

9. The four-mode mode division multiplexing / demultiplexing device based on Y-branch and multimode interference coupler according to claim 1, characterized in that: The cross-sections of the first single-mode input waveguide to the fourth single-mode input waveguide, the first 2×2 single-mode input paired interferometry MMI, the second 2×2 single-mode input paired interferometry MMI, the first dual-mode Y-type waveguide to the sixth dual-mode Y-type waveguide, the 2×2 multi-mode input general interferometry MMI, and the four-mode Y-type waveguide are all rectangular.

10. A mode interference amplitude equalizer, characterized in that: The mode interference amplitude equalizer includes a plurality of cascaded four-mode mode division multiplexing / demultiplexing devices based on Y branches and multimode interference couplers as described in any one of claims 1 to 9.

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