O-band end face coupler based on silicon nitride multi-conical waveguide

Abstract

The utility model discloses an O wave band end face coupler based on a silicon nitride multi-cone waveguide. The O wave band end face coupler is characterized in that a waveguide layer is composed of three double-cone input waveguides, two double-cone waveguides, a single-cone waveguide and a straight waveguide connected with the single-cone waveguide; according to the utility model, through the introduction of the multi-conical structure of the biconical input waveguide, the biconical waveguide and the single-conical waveguide, the mode mismatch between the waveguides and the optical fiber is effectively reduced, so that the loss caused by mode adaptation is reduced, the efficient optical coupling between the optical fiber and a chip is realized, and the structure between the waveguides is compact; only single exposure and etching are needed, the process complexity is reduced, the coupling loss in the O wave band is low, and the bandwidth is large.

Description

Technical Field

[0001] This utility model relates to the field of end-face coupler technology, specifically to an O-band end-face coupler based on a silicon nitride multi-tapered waveguide. Background Technology

[0002] Optical communication occupies a crucial position in the field of high-speed data transmission. As the initial band for optical communication, the O-band has the least signal distortion caused by optical dispersion compared with other bands, and is widely used in optical communication and optical interconnection scenarios.

[0003] Silicon photonics technology has been a hot research field that has been booming for the past two decades. With the exponential growth of data transmission volume, silicon photonic transceiver modules have significant advantages over traditional discrete transceiver devices. One of the key issues for the widespread application of silicon photonic chips is the coupling between optical fibers and silicon photonic chips.

[0004] Research has shown that current end-face couplers are mainly developed based on the C-band, which results in significant coupling loss and low efficiency in the O-band. Therefore, it is necessary to design end-face couplers specifically for the O-band.

[0005] Silicon nitride (SiN) materials exhibit optical transparency from the visible to the mid-infrared bands. Its refractive index falls between that of silicon and silicon dioxide. The manufacturing process is mature and compatible with CMOS. Furthermore, SiN's stable chemical structure provides strong damage resistance, enabling high-power laser transmission.

[0006] A search of existing technologies revealed that Yuanjian Wan et al. published an article titled "O-Band Low Loss and Polarization Insensitivity Edge Coupler" at the 2024 Conference on Lasers and Electro-Optics Pacific Rim (CLEO-PR). This paper designed a dual-layer, dual-tip end-face coupler suitable for the O-band, achieving a coupling loss of 1.52 dB in TE mode. However, its coupling loss is relatively high, and the multi-layer structure is difficult to fabricate, resulting in high implementation costs.

[0007] In their paper "O-Band Fiber-to-Chip Edge Coupler for High NAFiber Based on a CMOS Compatible SOI Platform," published at the 2022 Optical Fiber Communications Conference and Exhibition (OFC), Min Teng et al. designed an end-face coupler with a dual-tip silicon nitride structure. By using silicon nitride and silicon transitions at different heights, power is converted into silicon waveguides, achieving a coupling loss of less than 1.9 dB in the O-band. However, the fabrication is difficult and the coupling loss is high, making it difficult to apply on a large scale.

[0008] Essam Berikaa et al. published "Misalignment-Tolerant Ultra-Broadband Edge Coupler Based on 10 Inverse Tapers" in Photonics North in 2021, proposing a 10-tip inverted tapered edge coupler that can achieve a coupling loss of 0.72dB at 1310nm. However, it requires high processing precision, advanced manufacturing processes, and high cost. To address this, an O-band edge coupler based on silicon nitride multi-tapered waveguides was proposed. Utility Model Content

[0009] The main purpose of this utility model is to provide a solution that can effectively address the problems in the background art.

[0010] To achieve the above objectives, the technical solution adopted by this utility model is as follows: an O-band end-face coupler based on silicon nitride multi-conical waveguides, comprising an upper cladding layer, a waveguide layer, a lower cladding layer, and a substrate layer from top to bottom. The waveguide layer is characterized by being composed of three biconical input waveguides, two biconical waveguides, a single-conical waveguide, and a straight waveguide connected to the single-conical waveguide. The waveguide layer is axially symmetrical, and the middle waveguide of the biconical input waveguide, the single-conical waveguide, and the straight waveguide are on the same axis. The optical signal is coupled to the biconical waveguide via the biconical input waveguide, and then coupled to the single-conical waveguide. Each waveguide achieves mode field matching through a multi-conical gradient structure and finally enters the straight waveguide for output in TEO mode.

[0011] Preferably, the waveguide layer is one or more silicon nitride thin films.

[0012] Preferably, the thickness of the silicon nitride thin film is 300 nm.

[0013] Preferably, the distance between the widest point in the center of the biconical waveguide and the tip of the single-conical waveguide, and the distance between the middle waveguide end of the biconical input waveguide and the tip of the single-conical waveguide, are the same.

[0014] Preferably, the waveguide width of the biconical input waveguide, biconical waveguide, and single-conical waveguide varies with the length.

[0015] The present invention has the following advantages: by introducing a multi-conical structure of double-conical input waveguide, double-conical waveguide and single-conical waveguide, the mode mismatch between waveguide and optical fiber is effectively reduced, thereby reducing the loss caused by mode adaptation, realizing efficient optical coupling between optical fiber and chip, and the structure between waveguides is compact; only a single exposure and etching is required, which reduces the complexity of the process, and the coupling loss in the O-band is low and the bandwidth is large. Attached Figure Description

[0016] Figure 1 This is a three-dimensional structural schematic diagram of the present invention;

[0017] Figure 2 This is a top view of the present invention;

[0018] Figure 3 This is the optical field transmission diagram of this utility model;

[0019] Figure 4 This is a graph showing the relationship between transmittance and wavelength of this utility model.

[0020] Legend: 1. Upper cladding; 2. Waveguide layer; 3. Lower cladding; 4. Substrate layer; 5. Biconical input waveguide; 6. Biconical waveguide; 7. Single-conical waveguide; 8. Straight waveguide. Detailed Implementation

[0021] To make the technical means, creative features, objectives and effects of this utility model easier to understand, the present utility model will be further described below in conjunction with specific embodiments.

[0022] like Figure 1-4As shown, the O-band end-face coupler based on silicon nitride multi-conical waveguides comprises, from top to bottom, an upper cladding layer 1, a waveguide layer 2, a lower cladding layer 3, and a substrate layer 4. Its key feature is that the waveguide layer 2 is composed of three biconical input waveguides 5, two biconical waveguides 6, a single-conical waveguide 7, and a straight waveguide 8 connected to the single-conical waveguide 7. The waveguide layer 2 is axially symmetrical, and the middle waveguide of the biconical input waveguide 5, the single-conical waveguide 7, and the straight waveguide 8 are on the same axis. The optical signal passes through the biconical input waveguides... Waveguide 5 is coupled to a biconical waveguide 6, which is then coupled to a single-conical waveguide 7. Each waveguide achieves mode field matching through a multi-conical gradient structure and finally enters a straight waveguide 8 to output in TEO mode. The introduction of the multi-conical structure of the biconical input waveguide 5, biconical waveguide 6, and single-conical waveguide 7 effectively reduces mode mismatch between the waveguide and the fiber, thereby reducing the loss caused by mode adaptation, achieving efficient optical coupling between the fiber and the chip, and the structure between the waveguides is compact with low coupling loss in the O-band.

[0023] In one embodiment, the waveguide layer 2 is one or more layers of silicon nitride thin film, and the thickness of one layer of silicon nitride thin film is 300nm; the fabrication process is simple and only requires a single exposure and etching.

[0024] In one embodiment, the spacing between the upper waveguide, middle waveguide, and lower waveguide tip of the biconical input waveguide 5 is 1650 nm, and the spacing between the widest points in the center is 550 nm.

[0025] In one embodiment, the waveguide widths of the biconical input waveguide 5, biconical waveguide 6, and single-conical waveguide 7 vary with their lengths. Specifically, the waveguide widths of the biconical input waveguide 5 and biconical waveguide 6 first widen and then narrow again with the length, while the waveguide width of the single-conical waveguide 7 widens with the length. The waves are then output through the connected straight waveguide 8. The specific changes are as follows:

[0026] After light enters the chip from the optical fiber, the width of the upper and lower waveguide tips of the biconical input waveguide 5 gradually increases from 200nm to 1850nm after 47.2mm. Similarly, the width of the middle waveguide of the biconical input waveguide 5 gradually increases from 300nm at the tip to 1800nm ​​after 47.2mm, resulting in a continuous increase in effective refractive index. The width of the rear ends of the upper and lower waveguides of the biconical input waveguide 5 gradually narrows from 1850nm to 200nm after 35.2mm of transmission, while the width of the rear end of the middle waveguide of the biconical input waveguide 5 narrows from 1800nm ​​to 100nm after 34mm of transmission. The width of the biconical waveguide 6 continuously increases. The light gradually increases from a tip width of 280nm to 2050nm after a transmission length of 34.6mm. As the effective refractive index of the biconical input waveguide 5 decreases, the effective refractive index of the biconical waveguide 6 gradually increases. Light is coupled from the biconical input waveguide 5 into the biconical waveguide 6. Similarly, the width of the rear end of the biconical waveguide 6 gradually narrows from 2050nm to 600nm after a transmission length of 12mm. The width of the single-conical waveguide 7 gradually increases from 200nm, and light is coupled into the single-conical waveguide 7. As the width of the cone continues to increase after a transmission length of 12mm until it reaches 1000nm, the same as the straight waveguide 8, light is coupled into the straight waveguide 8.

[0027] In one embodiment, the distance between the widest points of the two biconical waveguides 6 is 400 nm, and the distance between them and the tip of the single-conical waveguide 7 is 100 nm; the distance between the ends of the two biconical waveguides 6 and the tip of the single-conical waveguide 7 is 100 nm, and the distance between the middle waveguide end of the biconical input waveguide 5 and the single-conical waveguide 7 is 150 nm.

[0028] In one embodiment, a single-mode fiber with a spot diameter of 10m is coupled to a straight waveguide 8 with a waveguide width of 1m via an end-face coupler. Through 3D-FDTD simulation verification, it is calculated that the end-face coupling loss is less than 1dB in the wavelength range of 1.3mm to 1.4mm, and the coupler has a large operating bandwidth, with a 1dB operating bandwidth covering the wavelength range of 1.25-1.5m.

[0029] When this invention is used, light is introduced into the SOI chip through optical fiber coupling and then input along the double-conical input waveguide 5. After a tapered transition, the light is coupled from the double-conical input waveguide 5 to the double-conical waveguide 6, and finally coupled to the single-conical waveguide 7, and finally enters the straight waveguide 8 and is output in TEO mode.

[0030] The foregoing has shown and described the basic principles, main features, and advantages of this utility model. Those skilled in the art should understand that this utility model is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this utility model. Various changes and modifications can be made to this utility model without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claims. The scope of protection of this utility model is defined by the appended claims and their equivalents.

Claims

1. An O-band end-coupler based on silicon nitride multi-tapered waveguide, comprising from top to bottom an upper cladding layer (1), a waveguide layer (2), a lower cladding layer (3) and a substrate layer (4), characterized in that: The waveguide layer (2) is composed of three double-tapered input waveguides (5), two double-tapered waveguides (6), a single-tapered waveguide (7) and a straight waveguide (8) connected with the single-tapered waveguide (7); the waveguide layer (2) is axially symmetrical, the middle waveguide of the double-tapered input waveguide (5), the single-tapered waveguide (7) and the straight waveguide (8) are on the same axis, the optical signal is coupled to the double-tapered waveguide (6) through the double-tapered input waveguide (5), the double-tapered waveguide (6) is coupled to the single-tapered waveguide (7), the waveguides are matched in mode through multi-tapered gradual change structure, and finally enter the straight waveguide (8) to be output in the form of TE0 mode.

2. The silicon nitride based multi-tapered waveguide O-band end-coupler of claim 1, wherein: The waveguide layer (2) is one or more layers of silicon nitride film.

3. The silicon nitride based multi-tapered waveguide O-band end-coupler of claim 2, wherein, The thickness of the one layer of silicon nitride film is 300 nm.

4. The silicon nitride based multi-tapered waveguide O-band end-coupler of claim 1, wherein: The central widest part of the double-tapered waveguide (6) is the tip of the single-tapered waveguide (7), and the interval between the end of the middle waveguide of the double-tapered input waveguide (5) and the tip of the single-tapered waveguide (7) is the same.

5. The silicon nitride based multi-tapered waveguide O-band end-coupler of claim 1, wherein: The waveguide width of the double-tapered input waveguide (5), the double-tapered waveguide (6) and the single-tapered waveguide (7) changes with the length.

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