Subwavelength grating auxiliary type ultra-wideband dual-mode power beam splitting waveguide device based on silicon nitride photon platform

Abstract

The invention provides a subwavelength grating structure ultra-wideband dual-mode power beam splitting waveguide device based on a silicon nitride photon platform, which mainly comprises an input waveguide, a multi-mode interference area and an output waveguide, and adopts a subwavelength grating structure. The input waveguide, the output waveguide and the multimode interference area are all made of silicon nitride materials, and a silicon dioxide material is used as a cladding layer. The period of the sub-wavelength grating structure is smaller than the effective wavelength of light in the silicon nitride material, and the sub-wavelength grating structure has a specific duty ratio. Through collaborative design of a sub-wavelength grating structure and all parts, the beam splitter can support TE1 and TE0 dual-mode transmission at the same time, efficient power beam splitting and beam combining of optical signals are achieved within the ultra-large bandwidth of 1260-1600 nm, insertion loss and the power unbalance degree are reduced, and finally flexible application of the beam splitter in an optical communication system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of optical communication and integrated photonic devices, and particularly provides a sub-wavelength grating assisted ultra-wideband dual-mode power splitting waveguide device based on a silicon nitride photonic platform, which is applicable to mode division multiplexing optical communication systems and high-density photonic integrated circuits. Background Art

[0002] The design of traditional integrated photonic devices mainly follows the "single-mode condition", enabling them to support only fundamental mode transmission. The multimode interference coupler (MMI) is a commonly used power splitting device in integrated optoelectronic devices, with advantages such as low loss, large bandwidth, good tolerance, and high splitting uniformity. It is the cornerstone for constructing various complex functional systems. The input and output waveguides of traditional MMI also operate in the fundamental mode, and their multiplexing performance needs to be further improved. Currently, the on-chip integrated refractive index engineering of sub-wavelength gratings (SWGs) has developed rapidly, and this structure has been widely applied to structures such as fiber-to-chip coupling, wavelength multiplexing, and polarization diversity. Benefiting from the advantages of sub-wavelength gratings in on-chip optical interconnection, the present invention considers realizing a high-performance dual-mode MMI coupler by introducing an SWG structure based on the self-imaging effect of MMI, and comprehensively optimizing aspects such as chip size, insertion loss, modal crosstalk, and splitting ratio. At the same time, the silicon nitride material has the characteristic of ultra-low loss, which enables the energy loss of optical signals in both modes to be extremely small during transmission. In photonic integrated circuits, low loss means that signals can be transmitted over longer distances, reducing signal attenuation and avoiding the need for optical amplification, thereby improving the efficiency and performance of the entire system.

[0003] In summary, the present invention designs a sub-wavelength grating assisted ultra-wideband dual-mode power splitting waveguide device based on a silicon nitride photonic platform, achieving high-performance and large-bandwidth dual-mode operation. It is expected to provide a new solution for optical communication and optical information processing, and also open up a new path for the development of quantum optics and photonic integration technologies. Summary of the Invention

[0004] The present invention proposes a sub-wavelength grating assisted ultra-wideband dual-mode power splitting waveguide device based on a silicon nitride photonic platform. Through the collaborative design of sub-wavelength gratings and multimode interference structures, the device has the characteristics of dual-mode compatibility, low insertion loss, ultra-wideband operation, and a compact structure. Further, it can be applied to mode splitting scenarios in optical communication systems and photonic integrated circuits. It solves the technical problems in traditional technologies such as that the multimode interference coupler only supports fundamental mode transmission, has a limited working bandwidth, insufficient flexibility in mode regulation, and an overly large device size.

[0005] To solve the above technical problems, the present invention provides the following technical solutions:

[0006] A sub-wavelength grating-assisted ultra-wideband dual-mode power splitting waveguide device based on a silicon nitride photonics platform, which consists of input and output tapered waveguides and a multimode interference region that are completely symmetric in the left-right, front-back directions. The input end is a straight waveguide that enters the multimode interference region of the periodic grating structure through a tapered waveguide, and then reaches the tapered waveguide and straight waveguide at the output end.

[0007] The input and output tapered waveguides and the multimode interference region are integrated with a sub-wavelength grating structure with a constant period. The widths of the input and output tapered waveguides gradually change linearly along the light propagation direction. The starting width is adapted for single-mode transmission, and the ending width matches the mode distribution of the multimode interference field. The geometric dimensions of the multimode interference region satisfy the self-imaging phase conditions of the TE0 and TE1 modes. The spacing between the input and output tapered waveguides is calculated and optimized based on the theory of dual-mode interference.

[0008] Furthermore, the period of the sub-wavelength grating structure is 300 - 350 nm, and the duty cycle is 60% - 70%. And the grating period is less than 50% of the effective wavelength when the working wavelength propagates in the silicon nitride medium, reducing the transmission loss of the sub-wavelength grating, and thus meeting the requirements of the sub-wavelength grating structure.

[0009] Furthermore, the starting width of the input tapered waveguide is 2.0 - 2.5 μm, and the ending width expands to 4.5 - 5.5 μm. The output tapered waveguide adopts a symmetric structure design, and its gradual change length is 18 - 22 μm, which can adiabatically transform the modes of the dual-mode, improve the mode field matching between the light field at the end and the multimode interference region, and reduce the insertion loss of the device.

[0010] Furthermore, the geometric dimensions of the multimode interference region satisfy: the length L is 236 μm (the acceptable range is 230 - 240 μm), and the width W is 10 - 12 μm, so as to achieve the self-imaging phase matching conditions of the TE0 and TE1 modes and meet the requirements of dual-mode operation.

[0011] Furthermore, the working wavelength of the device covers the range of 1260 - 1600 nm, and simultaneously supports the transmission of TE0 and TE1 modes. The insertion loss of the TE0 mode is less than 0.8 dB, and the insertion loss of the TE1 mode is less than 1 dB. The power imbalance of the TE0 mode is less than 1.2 dB, and the power imbalance of the TE1 mode is less than 1.5 dB. The mode crosstalk suppression ratio is about -18 dB, reducing the crosstalk between the output waveguides.

[0012] The ultra-wideband dual-mode power splitting waveguide device based on the silicon nitride photonics platform and its design method of the present invention have the following advantages:

[0013] 1. The power splitting waveguide device provided by the present invention combines the collaborative design of the SWG and MMI structures, and has the advantages of ultra-wideband coverage (1260 - 1600 nm), dual-mode compatible transmission (TE0 and TE1), low insertion loss (TE0 < 0.8 dB, TE1 < 1 dB), and high power balance (TE0 < 1.2 dB, TE1 < 1.5 dB), breaking through the technical bottlenecks of traditional multimode interference couplers that only support the fundamental mode, have limited bandwidth, and low efficiency.

[0014] 2. The sub-wavelength grating-assisted waveguide design method provided by the present invention significantly reduces the mode conversion loss and crosstalk (the suppression ratio reaches -18 dB) through the precise regulation of the grating period (300 - 350 nm) and duty cycle (60% - 70%), combined with the linear gradient optimization of the tapered waveguide (starting width 2.0 - 2.5 μm, ending width 4.5 - 5.5 μm), and at the same time realizes the compactness of the device size, which is suitable for the batch preparation of large-scale photonic integrated chips.

[0015] 3. The device provided by the present invention can be seamlessly integrated into high-speed optical communication systems, mode division multiplexing networks, and quantum optical chips. Through the high-efficiency splitting of dual modes and the ultra-wideband signal processing ability, it significantly improves the system capacity and transmission flexibility, providing a key solution for high-density optical interconnection, multi-dimensional multiplexing technology, and next-generation photonic integrated circuits. Brief Description of the Drawings

[0016] Figure 1 It shows a schematic structural diagram of the present invention.

[0017] Figure 2 It shows a schematic diagram of the design process of the present invention.

[0018] Figure 3 It shows the optical field distribution diagram of the TE0 mode of the present invention.

[0019] Figure 4 It shows the optical field distribution diagram of the TE1 mode of the present invention.

[0020] Figure 5 It shows the power imbalance diagram of the TE0 mode of the present invention.

[0021] Figure 6 It shows the power imbalance diagram of the TE1 mode of the present invention.

[0022] Figure 7 It shows the insertion loss diagram of the TE0 mode of the present invention.

[0023] Figure 8 It shows the insertion loss diagram of the TE1 mode of the present invention. Detailed Description of the Invention

[0024] To better understand the purpose, structure, and function of the present invention, the following further details an ultra-wideband dual-mode power splitting waveguide device based on a silicon nitride photonic platform and assisted by a subwavelength grating, in conjunction with the device.

[0025] As Figure 1 shown in the structural diagram of an ultra-wideband dual-mode power splitting waveguide device based on a silicon nitride photonic platform and assisted by a subwavelength grating, it consists of input and output tapered waveguides and a multimode interference region that are completely symmetric in the left-right, front-back directions. The input end is a straight waveguide that enters the multimode interference region of the subwavelength grating structure through a tapered waveguide, and then to the tapered waveguide and straight waveguide at the output end. The overall height of the device is equal. The TE-polarized light incident from a straight waveguide at the input end passes through the tapered waveguide and the multimode interference region successively, and is split into two output waveguides.

[0026] The present invention discloses the process of device structure design:

[0027] 1. Selection of waveguide layer and cladding materials: Silicon nitride (Si3N4) is selected as the waveguide layer material with a thickness of 400 nm and a refractive index of 2.0; silicon dioxide (SiO2) is selected as the cladding material with a thickness of 2 μm and a refractive index of 1.44.

[0028] 2. Design of the input linear tapered waveguide in the structural schematic diagram as Figure 1 shown: The starting width is 2.0 μm, linearly tapering along the light propagation direction with a tapering length of 18 - 22 μm, and the end width expands to 5.0 μm; the linear tapering design of the tapered waveguide helps to achieve a smooth transition from single-mode transmission to the multimode interference region.

[0029] 3. Design of the output tapered waveguide in the structural schematic diagram as Figure 1 shown: A symmetric tapered structure is adopted, with a starting width of 5.0 μm, linearly tapering along the light propagation direction with a tapering length of 18 - 22 μm, and the end width is reduced to 2.0 μm; the symmetric structure design helps to achieve effective coupling and output of optical signals.

[0030] 4. Design of the multimode interference region in the structural schematic diagram as Figure 1 shown: An integrated subwavelength grating structure with a period of 340 nm and a duty cycle of 64% is adopted; the length of the multimode interference region is 236 μm and the width is 10.8 μm; the period of the subwavelength grating structure is less than 50% of the effective wavelength of the working wavelength in the silicon nitride medium, meeting the self-imaging phase conditions of the TE0 and TE1 modes.

[0031] The present invention uses simulation software to obtain the following parameters:

[0032] 1. Power imbalance: As Figure 5, as shown in the power imbalance diagram in Figure 6, the average power imbalance of the TE0 mode is 0.5 dB, and the maximum average power imbalance is less than 0.2 dB. The average power imbalance of the TE1 mode is 0.5 dB, and the maximum power imbalance is less than 1.5 dB, far better than the index requirements.

[0033] 2. Insertion loss: As Figure 7 , as shown in the insertion loss diagram in Figure 8, in the TE0 mode, in the wavelength range of 1260 - 1600 nm, the average insertion loss is 0.3 dB, and the maximum insertion loss is 0.8 dB; TE1 mode: in the wavelength range of 1260 - 1600 nm, the average insertion loss is 0.7 dB, and the maximum insertion loss is 1 dB.

[0034] 3. Mode crosstalk suppression ratio: In the wavelength range of 1260 - 1600 nm, the mode crosstalk suppression ratio is about -18 dB, indicating that the device has good mode isolation performance.

[0035] As Figure 2 shown in the schematic diagram of the design process of the present invention, the design of the multimode interference (MMI) region of the present invention is based on the self-imaging phase matching principle. Its core is to determine the geometric dimensions that meet the self-imaging conditions of the TE0 and TE1 dual modes through calculation, and finally achieve the optical field distribution diagram as Figure 3 , as shown in Figure 4. The specific calculation process is as follows:

[0036] 1. Effective refractive index calculation The equivalent refractive index n of the SWG structure eff is approximately calculated through the effective medium theory (EMT):

[0037]

[0038] where f is the grating duty cycle, and this value is used for subsequent propagation constant and mode coupling analysis.

[0039] 2. Propagation constant and phase difference calculation:

[0040] The propagation constants of the TE0 and TE1 modes are respectively:

[0041]

[0042] where W is the MMI width and λ is the center wavelength. The calculated propagation constant difference is:

[0043]

[0044] 3. MMI length design:

[0045] The self-imaging length L π is determined by the phase difference condition (β0 - β1)L = π:

[0046]

[0047] To support both TE0 and TE1 modes simultaneously, the general interference condition gives:

[0048]

[0049] As Figure 2 shown, through FDTD simulation verification and optimization, the actual value of 236 μm can meet the self-imaging conditions of TE0 and TE1 modes in the full wavelength range of 1260 - 1600 nm.

[0050] 4. Optimization of grating period and duty cycle:

[0051] The SWG period needs to meet the sub-wavelength condition Calculated with the shortest wavelength λ = 1260 nm:

[0052]

[0053] The present invention optimizes the grating period through a simulation software, and determines that 340 nm is the optimal period, which can not only meet the requirements of the sub-wavelength grating but also achieve efficient mode coupling.

[0054] The present invention verifies through a simulation software and determines that a duty cycle of 64% is the optimal value, at which time the insertion loss and mode crosstalk suppression ratio of the device both reach the best performance.

[0055] The device of the present invention can be applied to high-speed optical communication systems, such as 100G / 400G optical transmission networks; in a mode division multiplexing network, by achieving efficient dual-mode beam splitting, the system capacity and transmission flexibility can be significantly improved.

[0056] The device of the present invention can be applied to quantum optical chips for realizing efficient mode beam splitting and quantum state manipulation; in the fields of quantum communication and quantum computing, by achieving efficient dual-mode beam splitting, it can provide a key solution for quantum information processing.

[0057] It can be understood that the present invention is described through simulation design. Those skilled in the art know that, without departing from the spirit and scope of the present invention, various changes or equivalent replacements can be made to these features and parameter examples. Additionally, under the teaching of the present invention, these features and parameter examples can be modified to adapt to specific situations without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited by the specific parameter designs disclosed herein, and all parameter designs falling within the scope of the claims of this application belong to the scope protected by the present invention.

Claims

1. A sub-wavelength grating-assisted ultra-wideband dual-mode power beam splitting waveguide device based on a silicon nitride photonic platform, characterized in that: It consists of a completely symmetrical input and output tapered waveguide and a multimode interference region. The input end is a straight waveguide that passes through a tapered waveguide into the multimode interference region of a periodic grating structure, and then to the tapered waveguide and straight waveguide at the output end. The input and output tapered waveguides and the multi-mode interference region have integrated sub-wavelength grating structures with constant periods; the widths of the input and output tapered waveguides linearly change along the direction of light propagation, the width at the starting end is adapted to single-mode transmission, and the width at the end matches the mode distribution of the multi-mode interference field; the geometric dimensions of the multi-mode interference region meet the self-imaging phase conditions of the TE0 and TE0 modes, and the spacing between the input and output tapered waveguides is designed based on dual-mode interference theoretical calculation and simulation optimization.

2. The sub-wavelength grating-assisted ultra-wideband dual-mode power beam splitting waveguide device based on silicon nitride photonic platform according to claim 1, characterized in that: A sub-wavelength grating structure with a constant period is integrated in the multi-mode interference region, wherein the grating period is less than 50% of the effective wavelength of the working wavelength in the silicon nitride medium, and the duty cycle is kept constant.

3. The sub-wavelength grating-assisted ultra-wideband dual-mode power beam splitting waveguide device based on silicon nitride photonic platform according to claim 1, characterized in that: The linear tapered waveguide at the input end, the tapered waveguide at the output end, and the multi-mode interference region are all made of silicon nitride, and the cladding is made of silicon dioxide.

4. The sub-wavelength grating-assisted ultra-wideband dual-mode power beam splitting waveguide device based on silicon nitride photonic platform according to claim 1, characterized in that: The sub-wavelength grating structures are arranged in parallel in the multi-mode interference region, the duty cycle thereof is constant within the range of 60%-70%, and the grating period is 300-350nm.

5. The sub-wavelength grating-assisted ultra-wideband dual-mode power beam splitting waveguide device based on silicon nitride photonic platform according to claim 1, characterized in that: The input and output end tapered waveguide has a starting width of 2.0-2.5 μm and a terminating width of 4.5-5.5 μm. The output tapered waveguide adopts a symmetrical structure design and a gradual length of 18-22 μm.

6. The sub-wavelength grating-assisted ultra-wideband dual-mode power beam splitting waveguide device based on silicon nitride photonic platform according to claim 1, characterized in that: The geometric dimensions of the multi-mode interference region satisfy: a length L of 230-240 μm and a width W of 10-12 μm, so as to achieve the self-imaging phase matching conditions of the TE0 and TE1 modes.

7. The sub-wavelength grating-assisted ultra-wideband dual-mode power beam splitting waveguide device based on silicon nitride photonic platform according to claim 1, characterized in that: The device has an operating wavelength covering the range of 1260-1600nm and supports both TE0 and TE1 mode transmission. The insertion loss of TE0 mode is less than 0.8dB, and the insertion loss of TE1 mode is less than 1dB; the power imbalance of TE0 mode is less than 1.2dB, and the power imbalance of TE1 mode is less than 1.5dB; the mode crosstalk suppression ratio is about -18dB.

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