An end face coupler based on inclined sidewall etching and a manufacturing method thereof

Abstract

This invention discloses an end-face coupler based on inclined sidewall etching and its manufacturing method. The end-face coupler includes a first waveguide core layer and a second waveguide core layer. The first waveguide core layer includes a first waveguide and a second waveguide. The first waveguide has a cuboid structure, and the dimensions of the second waveguide gradually decrease along the optical signal transmission direction. The second waveguide core layer includes a third waveguide with a first groove, a fourth waveguide with a second groove, and a fifth waveguide with both the third and fourth grooves. The third waveguide and the first groove are both square pyramids, and the fourth waveguide and the second groove are both triangular pyramids. The first waveguide core layer is formed by inductively coupled plasma etching (ICP-CPE), and the second waveguide core layer is formed by ICP-CPE and plasma-enhanced chemical vapor deposition (PECVD). The advantage is that it has high coupling efficiency while having low requirements for manufacturing process, achieving a balance between high coupling efficiency and low manufacturing cost.

Description

Technical Field

[0001] This invention relates to end face couplers, and more particularly to an end face coupler based on inclined sidewall etching and its manufacturing method. Background Technology

[0002] With the rapid development of the information age, the digital transformation of traditional industries and social life has accelerated, leading to an explosive growth in data traffic. This trend poses unprecedented challenges to the transmission efficiency, stability, and security of communication networks. Traditional electrical communication, due to inherent problems such as high power consumption, difficulty in heat dissipation, and transmission latency, is unable to meet the ever-increasing data processing demands. Therefore, optical communication, with its significant advantages in transmission rate, data capacity, and latency, has become a research focus.

[0003] In recent years, to achieve longer-distance, higher-speed, and larger-capacity optical communication systems while reducing cost, size, and power consumption, researchers have proposed optical integration techniques. Silicon dioxide planar waveguides, as an advantageous platform for photonic integration, are not only compatible with complementary metal-oxide-semiconductor (CMOS) fabrication processes but also offer lower losses, higher stability, and more mature fabrication processes compared to silicon and silicon nitride waveguides. Therefore, silicon dioxide planar waveguides are widely used in the fabrication of photonic integrated devices.

[0004] In optical communication systems, the optical interconnect between optical chips and optical fibers is crucial. However, the significant size difference between silica waveguides and single-mode fibers means that direct connection can lead to mode mismatch and substantial coupling loss. Furthermore, due to the small waveguide mode field size, direct coupling requires high alignment precision; even a small misalignment can cause a significant deterioration in the quality of the coupled optical signal. To address these issues, researchers have proposed end-face couplers. End-face couplers control the waveguide mode field by altering the waveguide structure at the chip-fiber connection point, achieving mode field matching with the fiber and thus improving coupling efficiency. Currently, low-loss, compact, and simple-to-fabricate end-face couplers have become a research hotspot.

[0005] With in-depth research on fiber-to-chip end-face couplers, researchers have proposed several main structures, including inverted conical structures, subwavelength grating structures, multi-material auxiliary structures, and forward conical structures. End-face couplers based on inverted conical structures, subwavelength grating structures, and multi-material auxiliary structures mainly focus on silicon and silicon nitride platforms, reducing the effective refractive index by compressing the waveguide's lateral dimensions to achieve mode expansion. Therefore, although end-face couplers based on inverted conical structures, subwavelength grating structures, and multi-material auxiliary structures have high coupling efficiency, they require extremely high precision photolithography equipment, and errors generated during fabrication significantly affect coupling efficiency. End-face couplers based on forward conical structures mainly focus on silicon dioxide and polymer platforms, achieving mode field matching with the fiber by increasing the waveguide size in both the lateral and longitudinal dimensions. Many research-designed end-face couplers based on forward conical structures possess high coupling efficiency, but their manufacturing processes are complex and dependent on high-precision equipment. For example, Li et al. proposed a high-efficiency, large-accuracy end-face coupler based on grayscale lithography in the paper "Xiaoyu Li, Shengtao Yu, Chengqun Gui, Chengliang Sun, Sheng Liu, 3Dtrapezoidaledge coupler with high efficiency and tolerance based on Silicon-on-Insulator, Optical Materials, Volume 143, 2023, 114223, ISSN 0925-3467". This end-face coupler utilizes grayscale lithography to realize its three-dimensional structure, exhibiting excellent coupling efficiency at the connections with optical fibers and waveguides. However, the grayscale lithography process required is complex, necessitating precise exposure control and placing high demands on lithography equipment and materials. Chinese patent application number CN202210362195.9 proposes a multi-layer positive conical structure (i.e., an end-face coupler based on a positive conical structure). This multi-layer positive conical structure couples light from an optical fiber to a conical structure, and gradually transitions from the upper conical shape to the final waveguide. Although theoretically its coupling efficiency with the optical fiber is high, in actual manufacturing, the etching of the upper conical waveguide is easily over-etched, which affects the lower conical waveguide, resulting in structural damage to the end-face coupler and reduced coupling efficiency.

[0006] The coupling efficiency of these existing end-face couplers all depends on the precision of the manufacturing process. High precision in the manufacturing process requires high precision in the manufacturing equipment and high performance in the materials. However, high precision in the manufacturing equipment and high performance in the materials lead to high manufacturing costs. Therefore, it is difficult for existing end-face couplers to balance high coupling efficiency and low manufacturing cost. Summary of the Invention

[0007] One of the technical problems to be solved by the present invention is to provide an end face coupler based on inclined sidewall etching that has high coupling efficiency, low manufacturing process requirements, and can balance high coupling efficiency and low manufacturing cost.

[0008] The technical solution adopted by the present invention to solve one of the above-mentioned technical problems is as follows: an end-face coupler based on inclined sidewall etching, comprising a first waveguide core layer and a second waveguide core layer, wherein the second waveguide core layer is located above the first waveguide core layer, the first waveguide core layer comprises a first waveguide and a second waveguide, the first waveguide being a cuboid structure and the second waveguide being a conical structure, the dimensions of the second waveguide gradually decreasing along the optical signal transmission direction, and the second waveguide core layer comprising a third waveguide with a downwardly recessed first groove, a fourth waveguide with a downwardly recessed second groove, and a third waveguide with a third groove and a second... The fifth waveguide has four grooves, with the third groove extending vertically through it. Both the third and first grooves are square pyramids. The fourth waveguide is a triangular frustum. The second groove is a triangular pyramid. The fifth waveguide has a cuboid structure. The third groove is a square pyramid, and the fourth groove is a triangular frustum. The first and second grooves are connected, as are the third and fourth grooves. The dimensions of both the third and fourth waveguides gradually decrease along the optical signal transmission direction. The first waveguide is used for coupling with an external optical fiber to transmit the optical signal from the external fiber. The third waveguide is connected to the end-face coupler. It serves two purposes: firstly, to extend the first waveguide and reduce mode mismatch between the first waveguide and the external optical fiber; secondly, to cooperate with the fourth waveguide to gradually reduce the constraint on the optical signal transmitted in the end-face coupler. This allows the optical field to gradually distribute within the first waveguide during propagation, reducing transmission loss. The second waveguide enables mode conversion between the first waveguide and the external single-mode waveguide, allowing the optical signal transmitted in the first waveguide to be transmitted through it to the external single-mode waveguide. An external single-mode waveguide, wherein the first, second, third, and fourth grooves are used to prevent the fifth waveguide from coupling with the first and third waveguides, avoiding optical signal transmission to the fifth waveguide and reducing optical signal transmission loss in the end-face coupler; the first waveguide core layer is formed by etching a rectangular waveguide using inductively coupled plasma etching (ICP); the second waveguide core layer is formed by depositing an upper cladding on the first waveguide core layer using plasma-enhanced chemical vapor deposition (PECVD), then firstly using ICP to obliquely etch the upper cladding to form grooves in the upper cladding that match the structural shape of the third and fourth waveguides; then using ICP to deposit a third waveguide with a first groove and a fourth waveguide with a second groove in the grooves, and a fifth waveguide with a third and fourth groove on the cladding.

[0009] Compared with the prior art, the advantage of the end-face coupler based on inclined sidewall etching of the present invention is that the end-face coupler is formed by a first waveguide core layer and a second waveguide core layer. The second waveguide core layer is located above the first waveguide core layer. The first waveguide core layer includes a first waveguide and a second waveguide. The first waveguide has a cuboid structure, and the second waveguide has a conical structure. The dimensions of the second waveguide gradually decrease along the optical signal transmission direction. The second waveguide core layer includes a third waveguide with a downwardly recessed first groove, a fourth waveguide with a downwardly recessed second groove, and a fifth waveguide with the third groove and the fourth groove. The third groove extends vertically through the fifth waveguide. The first waveguide, third waveguide, and first groove are all pyramidal, the fourth waveguide is frustum-shaped, the second groove is a frustum-shaped, and the fifth waveguide is a cuboid structure. The third groove, first groove, and second groove are vertically joined to form a pyramidal shape. The first groove is connected to the second groove, and the third groove is connected to the fourth groove. The dimensions of the third and fourth waveguides gradually decrease along the optical signal transmission direction. When the external optical fiber transmits the optical signal to the end-face coupler, the first waveguide couples with the external optical fiber, connecting the optical signal transmitted by the external optical fiber to the end-face coupler. The third waveguide reduces the distance between the first waveguide and the external optical fiber. The mode mismatch in the external optical fiber ensures that the optical signal transmitted through the external fiber can enter the end-face coupler with low loss. Simultaneously, the cooperation of the third and fourth waveguides gradually reduces the constraint on the optical signal transmitted in the end-face coupler. This allows the optical field to gradually distribute within the first waveguide during propagation after entering the end-face coupler, reducing transmission loss. The second waveguide acts as a mode converter; the optical signal transmitted in the first waveguide is transmitted to the external single-mode waveguide through the second waveguide. Furthermore, the first, second, third, and fourth grooves prevent the fifth waveguide from coupling with the first and third waveguides. This invention avoids the transmission of optical signals to the fifth waveguide, further reducing the transmission loss of optical signals in the end-face coupler. The first waveguide core layer is etched using an inductively coupled plasma etching process with relatively low current process requirements. The second waveguide core layer is etched using an inductively coupled plasma etching process with relatively low current process requirements to form a groove, without affecting the first waveguide core layer. It is then deposited using the currently mature plasma-enhanced chemical vapor deposition method. Thus, the end-face coupler based on inclined sidewall etching of the present invention has high coupling efficiency while having low manufacturing process requirements, achieving a balance between high coupling efficiency and low manufacturing cost.

[0010] Furthermore, the thickness direction of the first waveguide is along the vertical direction, the length direction of the first waveguide is defined as the horizontal direction, and the width direction is defined as the front-back direction. The plane that makes the first waveguide symmetrical front-back is called the first symmetry plane. The second waveguide is located to the right of the first waveguide. The cross-section of the second waveguide along the horizontal direction is an isosceles trapezoid. This isosceles trapezoid is symmetrical about the first symmetry plane, and its lower base is located to the left of its upper base. The left end face of the second waveguide has the same dimensions as the right end face of the first waveguide. The left end face of the second waveguide and the right end face of the first waveguide are integrally formed and joined together, and the two completely overlap. The upper end face of the second waveguide is aligned with the upper end face of the first waveguide. The end faces are located on the same plane, and the lower end face of the second waveguide is on the same plane as the lower end face of the first waveguide. The third waveguide is located above the first waveguide, and the third waveguide has an upper end face, a lower end face, a left end face, a right end face, a front end face, and a rear end face that are distributed and connected sequentially in the directions of up, down, left, right, front, and rear. The upper end face of the third waveguide is an isosceles trapezoid, which is symmetrical about the first symmetry plane, and its lower base is located to the left of its upper base. The lower end face of the third waveguide is a triangle, which is symmetrical about the first symmetry plane. The left end face of the third waveguide is an isosceles trapezoid, which is symmetrical about the first symmetry plane, and its upper base is... Located below its lower base, the right end face of the third waveguide is triangular, and this triangle is symmetrical about the first plane of symmetry. The front and rear ends of the third waveguide are both quadrilaterals, and are symmetrical about the first plane of symmetry. The lower end face of the third waveguide is integrally formed and joined with the upper end face of the first waveguide, and the left side of the lower end face of the third waveguide completely coincides with the left side of the upper end face of the first waveguide. The right end face of the third waveguide is located to the left of the plane containing the right end face of the first waveguide, and there is a distance between them. The first groove has an upper end face, a lower end face, and a lower end face arranged in an up, down, left, right, front, and rear orientation and joined sequentially. The first groove comprises an end face, a left end face, a right end face, a front end face, and a rear end face. The upper end face of the first groove is an isosceles trapezoid, which is symmetrical about the first plane of symmetry, and its lower base is located to the left of its upper base. The lower end face of the first groove is a triangle, which is symmetrical about the first plane of symmetry. The left end face of the first groove is an isosceles trapezoid, which is symmetrical about the first plane of symmetry, and its upper base is located below its lower base. The right end face of the first groove is a triangle, which is symmetrical about the first plane of symmetry. The front end face and the rear end face of the first groove are both quadrilaterals, which are symmetrical about the first plane of symmetry.The upper end face of the first groove is on the same plane as the upper end face of the third waveguide; the left end face of the first groove is on the same plane as the left end face of the third waveguide; the right end face of the first groove is on the same plane as the right end face of the third waveguide; the lower end face of the first groove is above the lower end face of the third waveguide, and there is a distance between them; the front end face of the first groove is behind the front end face of the third waveguide, and there is a distance between them; the rear end face of the first groove is in front of the rear end face of the third waveguide, and there is a distance between them; the fourth waveguide is located to the right of the third waveguide, and the fourth waveguide has an orientation of up, front, back, left, and right. The fourth waveguide comprises an upper end face, a front end face, a rear end face, a left end face, and a right end face, which are distributed and sequentially connected. The upper end face of the fourth waveguide is an isosceles trapezoid, which is symmetrical about the first plane of symmetry, with its lower base to the left of its upper base. The left end face of the fourth waveguide is a triangle, which is also symmetrical about the first plane of symmetry. The right end face of the fourth waveguide is a triangle, which is also symmetrical about the first plane of symmetry. The front end face and the rear end face of the fourth waveguide are both quadrilaterals, which are also symmetrical about the first plane of symmetry. The upper end face of the fourth waveguide is on the same plane as the upper end face of the third waveguide. The left end face of the fourth waveguide is connected to the upper end face of the third waveguide. The right end face of the third waveguide is integrally formed and joined together, and the two are completely overlapped. The front end face of the fourth waveguide is located on the same plane as the front end face of the third waveguide, and the rear end face of the fourth waveguide is located on the same plane as the rear end face of the third waveguide. The right end face of the fourth waveguide is located between the plane containing the left end face and the plane containing the right end face of the second waveguide. The lower side of the front end face of the fourth waveguide slopes upward from left to right. The second groove has an upper end face, a front end face, a rear end face, and a left end face that are distributed and joined in sequence according to the upper, front, rear, and left orientations. The upper end face of the second groove is triangular, and this triangle is symmetrical about the first symmetry plane. The left end face of the second groove is triangular, and this triangle is... The second groove is symmetrical about the first symmetry plane. Both the front and rear faces of the second groove are triangular. The front and rear faces of the second groove are symmetrical about the first symmetry plane. The upper face of the second groove is on the same plane as the upper face of the fourth waveguide. The left face of the second groove is on the same plane as the left face of the fourth waveguide. The left face of the second groove is integrally formed and joined with the right face of the first groove, and the two completely overlap. The right end of the second groove extends directly above the second waveguide. The front face of the second groove is on the same plane as the front face of the first groove. The rear face of the second groove is on the same plane as the rear face of the first groove.The fifth waveguide is located above the third and fourth waveguides. The length of the fifth waveguide is along the left-right direction, the width is along the front-back direction, and the thickness is along the top-bottom direction. The fifth waveguide is symmetrical about the first symmetry plane. The left end face of the fifth waveguide is on the same plane as the left end face of the third waveguide, and the right end face of the fifth waveguide is on the same plane as the right end face of the second waveguide. The width of the fifth waveguide is greater than the bottom length of the left end face of the third waveguide. The bottom end face of the fifth waveguide is integrally formed and connected to the top end face of the third and fourth waveguides.

[0011] The third groove has an upper end face, a lower end face, a left end face, a right end face, a front end face, and a rear end face, arranged in an up-down-left-right-front-rear orientation and connected sequentially. The upper end face of the third groove is an isosceles trapezoid, which is symmetrical about the first plane of symmetry, and its lower base is located to the left of its upper base. The lower end face of the third groove is an isosceles triangle, which is symmetrical about the first plane of symmetry. The left end face of the third groove is an isosceles trapezoid, which is symmetrical about the first plane of symmetry, and its upper base is located below its lower base. The right end face of the third groove is an isosceles triangle, which is symmetrical about the first plane of symmetry. The front end face and the rear end face of the third groove... All end faces are quadrilaterals. The front and rear faces of the third groove are symmetrical about the first symmetry plane. The upper end face of the third groove is on the same plane as the upper end face of the fifth waveguide. The lower end face of the third groove is on the same plane as the lower end face of the fifth waveguide. The left end face of the third groove is on the same plane as the left end face of the fifth waveguide. The lower base length of the left end face of the third groove is equal to the upper base length of the left end face of the first groove. The front end face of the third groove is on the same plane as the front end face of the first groove. The rear end face of the third groove is on the same plane as the rear end face of the first groove. The right end face of the third groove is on the same plane as the right end face of the second groove.

[0012] The fourth groove is located to the right of the third groove. The fourth groove has an upper end face, a front end face, a rear end face, a left end face, and a right end face, arranged in a top, front, back, left, and right orientation and connected sequentially. The upper end face of the fourth groove is an isosceles trapezoid, which is symmetrical about the first plane of symmetry, with its lower base to the left of its upper base. The left end face of the fourth groove is an isosceles triangle, also symmetrical about the first plane of symmetry. The right end face of the fourth groove is an isosceles triangle, also symmetrical about the first plane of symmetry. The front and rear faces of the fourth groove are both quadrilaterals, and the front and rear faces of the fourth groove are symmetrical about the first symmetry plane. The upper face of the fourth groove is on the same plane as the upper face of the third groove. The left face of the fourth groove is integrally formed with the right face of the third groove and the two completely overlap. The front face of the fourth groove is on the same plane as the front face of the third groove. The rear face of the fourth groove is on the same plane as the rear face of the third groove. The lower side of the front face of the fourth groove slopes upward from left to right.

[0013] The second technical problem to be solved by the present invention is to provide a manufacturing method for an end face coupler based on inclined sidewall etching. This manufacturing method can produce an end face coupler with high coupling efficiency using a manufacturing process with lower requirements, so that the end face coupler can achieve a balance between high coupling efficiency and low manufacturing cost.

[0014] The technical solution adopted by this invention to solve the second technical problem mentioned above is: a manufacturing method for an end-face coupler based on inclined sidewall etching, comprising the following steps:

[0015] Step 1: Prepare a quartz wafer as a substrate;

[0016] Step 2: Deposit waveguide material on the upper surface of the wafer using plasma-enhanced chemical vapor deposition to form the first waveguide layer. The thickness of the first waveguide layer along the vertical direction is equal to the thickness of the first waveguide.

[0017] Step 3: Uniformly coat the upper surface of the first waveguide layer with a layer of photoresist, which completely covers the upper surface of the first waveguide layer;

[0018] Step 4: Using photolithography, a pattern with the same cross-section as the overall structure formed by the first waveguide and the second waveguide is prepared in the photoresist of step 3, and the photoresist outside the pattern is removed by developing.

[0019] Step 5: The first waveguide layer is etched using an inductively coupled plasma etching process. At this time, the part of the first waveguide layer without photoresist coverage is etched away, and the remaining part forms the first waveguide and the second waveguide.

[0020] Step 6: Deposit a lower cladding layer on the first waveguide and the second waveguide using plasma-enhanced chemical vapor deposition, the lower cladding layer completely covering the first waveguide and the second waveguide;

[0021] Step 7: Uniformly coat a layer of photoresist on the upper surface of the lower cladding layer, so that the photoresist completely covers the upper surface of the lower cladding layer;

[0022] Step 8: Based on the positional relationship between the third waveguide and the fourth waveguide and the first waveguide and the second waveguide, a pattern consistent with the upper surface of the overall structure formed by the third waveguide and the fourth waveguide is prepared on the photoresist in step 7 using photolithography. The photoresist in the area where the pattern is located is removed using development.

[0023] Step 9: The lower cladding layer is etched at an angle using an inductively coupled plasma (ICP) etching process. At this time, the part of the lower cladding layer that is not covered by photoresist is etched away. An inclined groove with the front and rear sidewalls is etched in the lower cladding layer. The shape of the groove is consistent with the overall structure formed by the third waveguide and the fourth waveguide.

[0024] Step 10: Deposit waveguide material in the groove and on the lower cladding using plasma-enhanced chemical vapor deposition to form the second waveguide core layer;

[0025] Step 11: Deposit an upper cladding layer on the fifth waveguide, in the first groove, in the second groove, in the third groove, and in the fourth groove using plasma-enhanced chemical vapor deposition.

[0026] Compared with the prior art, the manufacturing method of the end-face coupler based on inclined sidewall etching of the present invention has the advantage of forming the first waveguide core layer by etching with the current inductively coupled plasma etching process, which has lower process requirements. After forming the groove by etching with the current inductively coupled plasma etching process, the first waveguide core layer is not affected. Then, the second waveguide core layer is deposited using the currently mature plasma-enhanced chemical vapor deposition method. The first waveguide core layer and the second waveguide core layer constitute the end-face coupler. The second waveguide core layer is located above the first waveguide core layer. The first waveguide core layer includes a first waveguide and a second waveguide. The first waveguide has a cuboid structure, and the second waveguide has a conical structure. The dimensions of the second waveguide core layer gradually decrease along the direction of optical signal transmission. It includes a third waveguide with a downward-recessed first groove, a fourth waveguide with a downward-recessed second groove, and a fifth waveguide with both a third and fourth groove. The third groove extends vertically through the fifth waveguide. The third waveguide and the first groove are both square pyramidal, the fourth waveguide is a triangular frustum, the second groove is a triangular pyramidal, and the fifth waveguide is a cuboid structure. The third groove is a square pyramidal, and the fourth groove is a triangular frustum. The first and second grooves are connected, as are the third and fourth grooves. The dimensions of the third and fourth waveguides gradually decrease along the direction of optical signal transmission. When the external optical fiber transmits the optical signal to the end-face coupler, the first waveguide and the external... The optical fiber coupling connects the optical signal transmitted through the external optical fiber to the end-face coupler. The third waveguide reduces the mode mismatch between the first waveguide and the external optical fiber, ensuring that the optical signal transmitted through the external optical fiber can enter the end-face coupler with low loss. Simultaneously, the cooperation of the third and fourth waveguides gradually reduces the constraint on the optical signal transmitted in the end-face coupler, causing the optical field to gradually distribute in the first waveguide during propagation after entering the end-face coupler, reducing transmission loss. The second waveguide acts as a mode converter; the optical signal transmitted in the first waveguide is transmitted to the external single-mode waveguide through the second waveguide. Furthermore, the first, second, third, and fourth grooves prevent the fifth waveguide from interfering with the first and third waveguides. The waveguide generates coupling, thereby preventing the optical signal from being transmitted to the fifth waveguide and further reducing the transmission loss of the optical signal in the end-face coupler. The first waveguide core layer is formed by etching using the inductively coupled plasma etching process, which has relatively low process requirements. The second waveguide core layer is etched using the inductively coupled plasma etching process, which also has relatively low process requirements, to form a groove without affecting the first waveguide core layer. Then, it is deposited using the currently mature plasma-enhanced chemical vapor deposition method. Thus, the manufacturing method of the end-face coupler based on inclined sidewall etching of the present invention can produce an end-face coupler with high coupling efficiency using a manufacturing process with relatively low requirements, so that the end-face coupler can achieve a balance between high coupling efficiency and low manufacturing cost.

[0027] Furthermore, in step 9, when the cladding is etched at an angle using inductively coupled plasma (ICP) etching, the RF power is 1950W, the bias power is 220W, and the etching gases are CF4 and C4F8, with a volume ratio of CF4 to C4F8 of 5:1. Attached Figure Description

[0028] Figure 1 This invention relates to a three-dimensional end-face coupler based on inclined sidewall etching. Figure 1 ;

[0029] Figure 2 This invention relates to a three-dimensional end-face coupler based on inclined sidewall etching. Figure 2 ;

[0030] Figure 3 This invention relates to a three-dimensional end-face coupler based on inclined sidewall etching. Figure 3 ;

[0031] Figure 4 This is an exploded view of the end-face coupler based on inclined sidewall etching according to the present invention;

[0032] Figure 5 This is a front view of the end-face coupler based on inclined sidewall etching according to the present invention;

[0033] Figure 6 This is a left view of the end face coupler based on inclined sidewall etching according to the present invention;

[0034] Figure 7 This is a top view of the end face coupler based on inclined sidewall etching according to the present invention;

[0035] Figure 8(a) shows the relationship between etching depth and groove opening width in the inclined etching process of the lower cladding layer using inductively coupled plasma etching in the manufacturing method of the end face coupler based on inclined sidewall etching of the present invention.

[0036] Figure 8(b) shows the relationship between the etching angle and the groove opening width in the inclined etching process of the lower cladding layer using inductively coupled plasma etching in the manufacturing method of the end face coupler based on inclined sidewall etching of the present invention.

[0037] Figure 8(c) is a cross-sectional view of the groove in the inclined etching process of the lower cladding layer using inductively coupled plasma etching in the manufacturing method of the end face coupler based on inclined sidewall etching of the present invention.

[0038] Figure 8(d) is a cross-sectional view of grooves with different opening widths in the inclined etching process of the lower cladding layer using inductively coupled plasma etching process in the manufacturing method of the end face coupler based on inclined sidewall etching of the present invention.

[0039] Figure 9 This is a process flow diagram of the manufacturing method of the end face coupler based on inclined sidewall etching according to the present invention;

[0040] Figure 10 The relationship between the coupling loss between the first waveguide core layer and the second waveguide core layer obtained by the manufacturing method of the end face coupler based on inclined sidewall etching of the present invention and the coupling loss between the first waveguide core layer and the second waveguide core layer obtained by the traditional manufacturing method of the end face coupler based on vertical sidewall etching, and the minimum linewidth of the structure, are respectively.

[0041] Figure 11 The coupling loss curves of the end face coupler based on inclined sidewall etching of the present invention in TE and TM polarization states are shown.

[0042] Figure 12 This is a statistical diagram of the alignment error in the horizontal and vertical directions of the end face coupler based on inclined sidewall etching according to the present invention. Detailed Implementation

[0043] This invention discloses an end face coupler based on inclined sidewall etching. The following describes the end face coupler based on inclined sidewall etching in further detail with reference to the accompanying drawings and embodiments.

[0044] Example 1: As Figures 1 to 4As shown, an end-face coupler based on inclined sidewall etching includes a first waveguide core layer and a second waveguide core layer, with the second waveguide core layer located above the first waveguide core layer. The first waveguide core layer includes a first waveguide 1 and a second waveguide 2. The first waveguide 1 has a cuboid structure, and the second waveguide 2 has a conical structure. The dimensions of the second waveguide 2 gradually decrease along the optical signal transmission direction. The second waveguide core layer includes a third waveguide 3 with a downwardly recessed first groove 31, a fourth waveguide 4 with a downwardly recessed second groove 41, and a third waveguide 4 with a third groove 51 and a fourth waveguide 4 with a fourth groove 51. The fifth waveguide 5 of groove 52 is traversed vertically by the third groove 51. The third waveguide 3 and the first groove 31 are both square pyramidal, the fourth waveguide 4 is a triangular frustum, the second groove 41 is a triangular pyramidal, the fifth waveguide 5 is a cuboid structure, the third groove 51 is a square pyramidal, and the fourth groove 52 is a triangular frustum. The first groove 31 is connected to the second groove 41, and the third groove 51 is connected to the fourth groove 52. The dimensions of the third waveguide 3 and the fourth waveguide 4 gradually decrease along the optical signal transmission direction. The first waveguide 1 is used for coupling with an external optical fiber. The transmitted optical signal enters the end-face coupler. The third waveguide 3 serves two purposes: firstly, it extends the first waveguide 1, reducing mode mismatch between the first waveguide 1 and the external optical fiber; secondly, it works in conjunction with the fourth waveguide 4 to gradually reduce the constraint on the optical signal transmitted in the end-face coupler. This allows the optical field to gradually distribute within the first waveguide 1 during propagation after entering the end-face coupler, reducing transmission loss. The second waveguide 2 is used to achieve mode conversion between the first waveguide 1 and the external single-mode waveguide, enabling the optical signal transmitted in the first waveguide 1 to pass through... The transmission to the external single-mode waveguide is achieved through the first groove 31, the second groove 41, and the third groove 51, which prevent the fifth waveguide 5 from coupling with the first waveguide 1 and the third waveguide 3, thus avoiding the transmission of optical signals to the fifth waveguide 5 and reducing the transmission loss of optical signals in the end-face coupler. The first waveguide core layer is formed by etching a rectangular waveguide using an inductively coupled plasma etching process. The second waveguide core layer is formed by depositing an upper cladding on the first waveguide core layer using plasma-enhanced chemical vapor deposition, followed by tilting the upper cladding using an inductively coupled plasma (ICP) etching process to form grooves in the upper cladding that match the structural shape of the third waveguide 3 and the fourth waveguide 4. Then, the third waveguide 3 with the first groove 31 and the fourth waveguide 4 with the second groove 41 are deposited in the grooves using plasma-enhanced chemical vapor deposition, and the fifth waveguide 5 with the third groove 51 and the fourth groove 52 is deposited on the cladding.

[0045] In this embodiment, when the external optical fiber transmits the optical signal to the end-face coupler, the first waveguide 1 couples with the external optical fiber, connecting the optical signal transmitted through the external optical fiber to the end-face coupler. The third waveguide 3 reduces the mode mismatch between the first waveguide 1 and the external optical fiber, ensuring that the optical signal transmitted through the external optical fiber can enter the end-face coupler with low loss. Simultaneously, the cooperation of the third waveguide 3 and the fourth waveguide 4 gradually reduces the constraint on the optical signal transmitted in the end-face coupler, causing the optical field to gradually distribute in the first waveguide 1 during propagation after entering the end-face coupler, reducing the transmission loss of the optical signal in the end-face coupler. The second waveguide 2 acts as a mode converter; the optical signal transmitted in the first waveguide 1 is transmitted to the external single-mode waveguide through the second waveguide 2. Furthermore, the first groove 31, the second groove 41, the third groove 51, and the fourth groove 52 can... This design prevents coupling between the fifth waveguide 5 and the first and third waveguides 1 and 3, thus avoiding optical signal transmission to the fifth waveguide 5 and further reducing transmission loss in the end-face coupler. The first waveguide core layer is formed using an inductively coupled plasma etching process with relatively low process requirements. The second waveguide core layer is also etched using an inductively coupled plasma etching process with relatively low process requirements to form a groove, which does not affect the first waveguide core layer. The second waveguide core layer is then deposited using a mature plasma-enhanced chemical vapor deposition (PECVD) method, which simplifies the process and avoids the use of grayscale lithography. It also achieves low coupling loss even with a large linewidth in the lithography machine. Furthermore, the processes for constructing the end-face coupler are all back-end processes, which do not affect device performance and do not require chemical mechanical polishing (CMP), thus simplifying the process flow.

[0046] Example 2: This example is basically the same as Example 1, except that: in this example, as Figures 5 to 7 As shown, the thickness direction of the first waveguide 1 is along the vertical direction. The length direction of the first waveguide 1 is defined as the left-right direction, and the width direction is defined as the front-back direction. The plane that makes the first waveguide 1 symmetrical front-back is called the first symmetry plane. The second waveguide 2 is located to the right of the first waveguide 1. The cross-section of the second waveguide 2 along the horizontal direction is an isosceles trapezoid. This isosceles trapezoid is symmetrical about the first symmetry plane, and its lower base is located to the left of its upper base. The left end face of the second waveguide 2 has the same dimensions as the right end face of the first waveguide 1. The left end face of the second waveguide 2 and the right end face of the first waveguide 1 are integrally formed and joined together, and the two are completely overlapped. The upper end face of the second waveguide 2 and the upper end face of the first waveguide 1 are located in the same plane. The lower end face of the second waveguide 2 and the lower end face of the first waveguide 1 are located in the same plane.

[0047] The third waveguide 3 is located above the first waveguide 1. The third waveguide 3 has an upper end face, a lower end face, a left end face, a right end face, a front end face, and a rear end face, arranged in the directions of top, bottom, left, right, front, and rear, and connected sequentially. The upper end face of the third waveguide 3 is an isosceles trapezoid, which is symmetrical about the first plane of symmetry, and its lower base is located to the left of its upper base. The lower end face of the third waveguide 3 is a triangle, which is also symmetrical about the first plane of symmetry. The left end face of the third waveguide 3 is an isosceles trapezoid, which is also symmetrical about the first plane of symmetry. The bottom is located below the lower bottom. The right end face of the third waveguide 3 is triangular, and the triangle is symmetrical about the first symmetry plane. The front end face and rear end face of the third waveguide 3 are both quadrilaterals, and the front end face and rear end face of the third waveguide 3 are symmetrical about the first symmetry plane. The lower end face of the third waveguide 3 is integrally formed and connected with the upper end face of the first waveguide 1, and the left side of the lower end face of the third waveguide 3 completely coincides with the left side of the upper end face of the first waveguide 1. The right end face of the third waveguide 3 is located to the left of the plane where the right end face of the first waveguide 1 is located, and there is a distance between the two.

[0048] The first groove 31 has an upper end face, a lower end face, a left end face, a right end face, a front end face, and a rear end face, which are arranged and connected sequentially in the directions of top, bottom, left, right, front, and rear. The upper end face of the first groove 31 is an isosceles trapezoid, which is symmetrical about the first plane of symmetry, and its lower base is located to the left of its upper base. The lower end face of the first groove 31 is a triangle, which is symmetrical about the first plane of symmetry. The left end face of the first groove 31 is an isosceles trapezoid, which is symmetrical about the first plane of symmetry, and its upper base is located below its lower base. The right end face of the first groove 31 is a triangle, which is symmetrical about the first plane of symmetry. The front end face of the first groove 31 and... All rear faces are quadrilaterals. The front and rear faces of the first groove 31 are symmetrical about the first symmetry plane. The upper face of the first groove 31 is on the same plane as the upper face of the third waveguide 3. The left face of the first groove 31 is on the same plane as the left face of the third waveguide 3. The right face of the first groove 31 is on the same plane as the right face of the third waveguide 3. The lower face of the first groove 31 is above the lower face of the third waveguide 3, and there is a distance between them. The front face of the first groove 31 is behind the front face of the third waveguide 3, and there is a distance between them. The rear face of the first groove 31 is in front of the rear face of the third waveguide 3, and there is a distance between them.

[0049] The fourth waveguide 4 is located to the right of the third waveguide 3. The fourth waveguide 4 has an upper end face, a front end face, a rear end face, a left end face, and a right end face, arranged in the directions of top, front, back, left, and right, and connected sequentially. The upper end face of the fourth waveguide 4 is an isosceles trapezoid, which is symmetrical about the first plane of symmetry, with its lower base to the left of its upper base. The left end face of the fourth waveguide 4 is a triangle, which is also symmetrical about the first plane of symmetry. The right end face of the fourth waveguide 4 is a triangle, which is also symmetrical about the first plane of symmetry. The front and rear end faces of the fourth waveguide 4 are both quadrilaterals. The front and rear faces of the fourth waveguide 4 are symmetrical about the first symmetry plane; the upper face of the fourth waveguide 4 is on the same plane as the upper face of the third waveguide 3; the left face of the fourth waveguide 4 is integrally formed and connected with the right face of the third waveguide 3, and the two are completely overlapped; the front face of the fourth waveguide 4 is on the same plane as the front face of the third waveguide 3; the rear face of the fourth waveguide 4 is on the same plane as the rear face of the third waveguide 3; the right face of the fourth waveguide 4 is located between the plane where the left face of the second waveguide 2 is located and the plane where the right face of the second waveguide 2 is located; the lower side of the front face of the fourth waveguide 4 slopes upward from left to right.

[0050] The second groove 41 has an upper end face, a front end face, a rear end face, and a left end face that are distributed and connected in the directions of top, front, back, and left. The upper end face of the second groove 41 is triangular and is symmetrical about the first plane of symmetry. The left end face of the second groove 41 is also triangular and is symmetrical about the first plane of symmetry. The front and rear ends of the second groove 41 are both triangular and are symmetrical about the first plane of symmetry. The upper end face of the second groove 41 is on the same plane as the upper end face of the fourth waveguide 4. The left end face of the second groove 41 is on the same plane as the left end face of the fourth waveguide 4. The left end face of the second groove 41 is integrally formed and connected to the right end face of the first groove 31, and the two completely overlap. The right end of the second groove 41 extends directly above the second waveguide 2. The front end face of the second groove 41 is on the same plane as the front end face of the first groove 31. The rear end face of the second groove 41 is on the same plane as the rear end face of the first groove 31.

[0051] The fifth waveguide 5 is located above the third waveguide 3 and the fourth waveguide 4. The length of the fifth waveguide 5 is along the left-right direction, the width is along the front-back direction, and the thickness is along the top-bottom direction. The fifth waveguide 5 is symmetrical about the first symmetry plane. The left end face of the fifth waveguide 5 is on the same plane as the left end face of the third waveguide 3, and the right end face of the fifth waveguide 5 is on the same plane as the right end face of the second waveguide 2. The width of the fifth waveguide 5 is greater than the bottom length of the left end face of the third waveguide 3. The bottom end face of the fifth waveguide 5 is integrally formed and connected to the top end face of the third waveguide 3 and the fourth waveguide 4.

[0052] The third groove 51 has an upper end face, a lower end face, a left end face, a right end face, a front end face, and a rear end face, which are arranged and connected sequentially in the directions of top, bottom, left, right, front, and rear. The upper end face of the third groove 51 is an isosceles trapezoid, which is symmetrical about the first plane of symmetry, and its lower base is located to the left of its upper base. The lower end face of the third groove 51 is an isosceles triangle, which is symmetrical about the first plane of symmetry. The left end face of the third groove 51 is an isosceles trapezoid, which is symmetrical about the first plane of symmetry, and its upper base is located below its lower base. The right end face of the third groove 51 is an isosceles triangle, which is symmetrical about the first plane of symmetry. The front end face of the third groove 51... Both the front and rear faces are quadrilaterals. The front and rear faces of the third groove 51 are symmetrical about the first symmetry plane. The upper face of the third groove 51 is on the same plane as the upper face of the fifth waveguide 5. The lower face of the third groove 51 is on the same plane as the lower face of the fifth waveguide 5. The left face of the third groove 51 is on the same plane as the left face of the fifth waveguide 5. The length of the lower base of the left face of the third groove 51 is equal to the length of the upper base of the left face of the first groove 31. The front face of the third groove 51 is on the same plane as the front face of the first groove 31. The rear face of the third groove 51 is on the same plane as the rear face of the first groove 31. The right face of the third groove 51 is on the same plane as the right face of the second groove.

[0053] The fourth groove 52 is located to the right of the third groove 51. The fourth groove 52 has an upper end face, a front end face, a rear end face, a left end face, and a right end face that are distributed and connected sequentially in the directions of top, front, back, left, and right. The upper end face of the fourth groove 52 is an isosceles trapezoid that is symmetrical about the first plane of symmetry, and its lower base is located to the left of its upper base. The left end face of the fourth groove 52 is an isosceles triangle that is symmetrical about the first plane of symmetry. The right end face of the fourth groove 52 is an isosceles triangle that is symmetrical about the first plane of symmetry. The front and rear faces of the fourth groove 52 are both quadrilaterals, and the front and rear faces of the fourth groove 52 are symmetrical about the first symmetry plane. The upper face of the fourth groove 52 is on the same plane as the upper face of the third groove 51. The left face of the fourth groove 52 is integrally formed with the right face of the third groove 51, and the two completely overlap. The front face of the fourth groove 52 is on the same plane as the front face of the third groove 51. The rear face of the fourth groove 52 is on the same plane as the rear face of the third groove 51. The lower side of the front face of the fourth groove 52 slopes upward from left to right.

[0054] In this embodiment, the left end faces of the first waveguide 1 and the third waveguide 3 constitute the coupling region between the external optical fiber and the end-face coupler. The first waveguide 1 and the third waveguide 3 form a two-layer structure, expanding the cross-sectional area of ​​the coupling region in two dimensions and reducing the mode mismatch between the coupling region and the optical fiber. When the optical signal is coupled into the end-face coupler, during transmission within the end-face coupler, the dimensions of the third waveguide 3 and the fourth waveguide 4 gradually decrease along the incident direction of the optical signal in both dimensions, thus gradually reducing the constraint on the transmitted optical signal. Therefore, during the propagation of the optical signal after entering the end-face coupler, the optical field gradually distributes to the first waveguide 1. The second waveguide 2 serves as the mode conversion region of the end-face coupler. The width of the second waveguide 2 (its dimension along the front-to-back direction) gradually decreases along the incident direction of the optical signal to the width of a single-mode waveguide, enabling it to connect with the single-mode waveguide. In this mode conversion region, the mode field area of ​​the optical signal decreases in the lateral direction and is eventually transmitted to the single-mode waveguide. Thus, the end-face coupler achieves the function of efficiently transmitting the optical signal output from the external optical fiber to the single-mode waveguide.

[0055] In this embodiment, the first waveguide 1 has a length of 900 μm, a width W of 10 μm, and a thickness H of 3.5 μm. The distance L3 between the left and right end faces of the second waveguide 2 is 200 μm, and the length W3 of the right end face of the second waveguide 2 along the front-back direction is 3.5 μm. The distance H2 between the upper and lower end faces of the third waveguide 3 is 7 μm, the distance L1 between the left and right end faces of the third waveguide 3 is 500 μm, the length of the upper base of the left end face is 10 μm, the angle β between the upper base of the left end face and the waist is 105°, and the angle β between the bottom of the right end face and the waist is 75°. The distance between the upper and lower surfaces of the first groove 31 is 2 μm, and the distance between its left and right surfaces is 500 μm. The length of the upper base of the left surface of the first groove 31 is 10 μm, and the angle between the upper base of the left surface and the waist is 105°. The angle between the bottom of the right surface of the first groove 31 and the waist is 75°. The distance L2 between the left and right surfaces of the fourth waveguide 4 is 400 μm, and the angle between the bottom of the left surface of the fourth waveguide 4 and the waist is 75°. The length W2 of the bottom of the right surface is 1 μm, and the angle between the bottom of the right surface and the waist is 75°. The angle between the bottom of the left surface of the second groove 41 and the waist is 75°. The fifth waveguide 5 has a length of 1100 μm, a width W1 of 40 μm, and a thickness H1 of 5 μm. The distance between the upper and lower surfaces of the third groove 51 is 5 μm. The angle between the lower bottom of the left end face and the waist is 75°. The angle between the lower bottom of the right end face and the waist is also 75°. The bottom length of the right end face of the fourth groove 52 is 1 μm, and the angle between the bottom of the right end face and the waist is 75°.

[0056] The present invention also discloses the above-mentioned method for manufacturing an end face coupler based on inclined sidewall etching. The following describes in further detail the method for manufacturing an end face coupler based on inclined sidewall etching of the present invention with reference to the accompanying drawings and embodiments.

[0057] Example 1: A method for manufacturing an end-face coupler based on inclined sidewall etching, comprising the following steps:

[0058] Step 1: Prepare a quartz wafer as a substrate;

[0059] Step 2: Deposit waveguide material on the upper surface of the wafer using plasma-enhanced chemical vapor deposition to form the first waveguide layer. The thickness of the first waveguide layer along the vertical direction is equal to the thickness of the first waveguide 1.

[0060] Step 3: Uniformly coat a layer of photoresist on the upper surface of the first waveguide layer, so that the photoresist completely covers the upper surface of the first waveguide layer;

[0061] Step 4: Using photolithography, a pattern with the same cross-section as the overall structure formed by the first waveguide 1 and the second waveguide 2 is prepared in the photoresist of step 3, and the photoresist outside the pattern is removed by developing.

[0062] Step 5: The first waveguide layer is etched using an inductively coupled plasma etching process. At this time, the part of the first waveguide layer without photoresist coverage is etched away, and the remaining part forms the first waveguide 1 and the second waveguide 2.

[0063] Step 6: Deposit a lower cladding layer on the first waveguide 1 and the second waveguide 2 using plasma-enhanced chemical vapor deposition. The lower cladding layer completely covers the first waveguide 1 and the second waveguide 2.

[0064] Step 7: Apply a layer of photoresist evenly to the upper surface of the lower cladding layer, so that the photoresist completely covers the upper surface of the lower cladding layer;

[0065] Step 8: Based on the positional relationship between the third waveguide 3 and the fourth waveguide 4 and the first waveguide 1 and the second waveguide 2, a pattern consistent with the upper surface of the overall structure formed by the third waveguide 3 and the fourth waveguide 4 is prepared on the photoresist in step 7 using photolithography. The photoresist in the area where the pattern is located is removed using development.

[0066] Step 9: Use inductively coupled plasma (ICP) etching process to etch the lower cladding layer at an angle. At this time, the part of the lower cladding layer without photoresist is etched away, and the grooves with inclined front and rear sidewalls are etched in the lower cladding layer. The shape of the grooves is consistent with the overall structure formed by the third waveguide 3 and the fourth waveguide 4.

[0067] Step 10: Deposit waveguide material in the groove and on the lower cladding using plasma-enhanced chemical vapor deposition to form the second waveguide core layer;

[0068] Step 11: The upper cladding is deposited on the fifth waveguide 5, in the first groove 31, in the second groove 41, in the third groove 51 and in the fourth groove 52 using plasma-enhanced chemical vapor deposition.

[0069] Example 2: This example is basically the same as Example 1, except that in this example, in step 9, when the cladding is etched at an angle using inductively coupled plasma (ICP) etching, the RF power is 1950W, the bias power is 220W, the etching gas is CF4 and C4F8, and the volume ratio of CF4 to C4F8 is 5:1.

[0070] In this embodiment, because the volume ratio of CF4 to C4F8 is 5:1 during the etching process, the content of C4F8 in the etching gas is increased based on the current etching gas. This increases the concentration of CFx (X represents the number of F atoms) groups generated after the decomposition of C4F8, which will form a protective layer on the sidewall of the groove. The upper protective layer of the groove sidewall is thinner and easier to be etched, while the lower protective layer is thicker and prevents etching, thus making it easy to form a groove structure that is wider at the top and narrower at the bottom. Meanwhile, when the lengths of the upper and lower bottom surfaces of the first groove 31 and the third groove 51 are relatively large, the reaction is sufficient, and the etching rate is mainly limited by the reaction formula, resulting in little change in the etching depth within a certain width range. Therefore, the distance between the upper and lower surfaces of the first groove 31 and the third groove 51 does not change significantly. However, when the bottom length of the upper surface of the second groove 41 and the fourth groove 52 is relatively small, the inclined sidewall etching reduces the contact area between the reactants and the etching gas, resulting in insufficient reaction and slowing down the etching rate. In addition, the discharge of reaction products is restricted, and the small bottom length of the upper surface of the second groove 41 and the fourth groove 52 will filter out ions incident at large angles, reducing the number of effective ions participating in the etching. Ultimately, this leads to a decrease in the etching rate and depth, resulting in the second groove 41 and the fourth groove 52 with reduced groove depth and inclined sidewalls.

[0071] To verify the performance of the manufacturing method of the end face coupler based on inclined sidewall etching of the present invention, the etching process of the manufacturing method of the end face coupler based on inclined sidewall etching of the present invention was verified. The relationship between the etching depth and the groove opening width in the inclined etching process of the cladding layer using inductively coupled plasma etching (ICP-CPE) in the manufacturing method of the end face coupler based on inclined sidewall etching of the present invention is shown in Figure 8(a); the relationship between the etching angle and the groove opening width in the inclined etching process of the cladding layer using ICP-CPE in the manufacturing method of the end face coupler based on inclined sidewall etching of the present invention is shown in Figure 8(b); the cross-sectional view of the groove in the inclined etching process of the cladding layer using ICP-CPE in the manufacturing method of the end face coupler based on inclined sidewall etching of the present invention is shown in Figure 8(c); and the cross-sectional views of the groove with different opening widths in the inclined etching process of the cladding layer using ICP-CPE in the manufacturing method of the end face coupler based on inclined sidewall etching of the present invention are shown in Figure 8(d).

[0072] Analysis of Figure 8(a) shows that when the groove opening width is less than 4 μm, the etching depth is linearly related to the groove opening width; as the groove opening width increases, the etching depth increases. When the groove opening width is greater than 4 μm but less than 6 μm, the rate of increase in etching depth gradually slows down and tends to level off as the groove opening width increases. When the groove opening width is greater than 6 μm, the etching depth remains stable with no significant change as the groove opening width increases. Analysis of Figure 8(b) shows that, under certain etching process parameters, the etching depth does not change significantly with changes in the groove opening width. From Figures 8(c) and 8(d), it can be seen that the manufacturing method of the end face coupler based on inclined sidewall etching of the present invention can form the required inclined sidewall groove through an inclined etching process.

[0073] The coupling loss between the first and second waveguide core layers obtained by the manufacturing method of the end-face coupler based on inclined sidewall etching of the present invention and the coupling loss between the first and second waveguide core layers obtained by the conventional manufacturing method of the end-face coupler based on vertical sidewall etching, respectively, are related to the minimum linewidth of the structure as follows: Figure 9 As shown; Analysis Figure 9 It can be seen that when the minimum linewidth of the structure is less than 0.3 μm, the coupling loss between the upper and lower waveguides of the vertically etched structure and the tilted etched structure is similar with the increase of the minimum linewidth, and there is no significant change. When the minimum linewidth of the structure is greater than 0.3 μm, the coupling loss between the upper and lower waveguides of the vertically etched structure increases significantly with the increase of the linewidth, while the coupling loss between the upper and lower waveguides of the tilted etched structure does not change significantly. Therefore, the end face coupler of the tilted etched structure has lower requirements for the process.

[0074] The coupling loss curves of the end-face coupler based on tilted sidewall etching of the present invention in the TE and TM polarization states are shown in the figure below. Figure 10 As shown, analysis Figure 10 It can be seen that the end face coupler based on inclined sidewall etching of the present invention has good performance in different polarization states. The coupler can achieve a minimum loss of 0.456dB in TE mode, a minimum loss of 0.467dB in TM mode, and a minimum related polarization loss of 0.009dB.

[0075] The alignment error statistics of the end face coupler based on inclined sidewall etching of the present invention in the horizontal and vertical directions are shown in the figure below. Figure 11 As shown, analysis Figure 11 It can be seen that the end face coupler based on inclined sidewall etching of the present invention has a 1dB alignment tolerance of ±2.5um in the vertical direction and ±1.8um in the horizontal direction. The end face coupler structure based on inclined sidewall etching of the present invention has excellent performance in terms of alignment tolerance.

[0076] In summary, an end-face coupler based on inclined sidewall etching and its manufacturing method are disclosed. The first waveguide 1 is coupled to an external optical fiber, allowing the optical signal transmitted through the external fiber to enter the end-face coupler. The third waveguide 3 extends the first waveguide 1, reducing the mode mismatch between the first waveguide 1 and the external optical fiber, ensuring that the optical signal transmitted through the external fiber can enter the end-face coupler with low loss. Simultaneously, the cooperation of the third waveguide 3 and the fourth waveguide 4 gradually reduces the constraint on the optical signal transmitted in the end-face coupler, causing the optical field to gradually distribute within the first waveguide 1 during propagation after entering the end-face coupler, reducing transmission loss. The second waveguide 2 acts as a mode converter, transmitting the optical signal transmitted in the first waveguide 1 to the external single-mode waveguide. Furthermore, the first groove 31, the second groove 41, and the third groove 5... 1. This design prevents coupling between the fifth waveguide 5 and the first and third waveguides 1 and 3, thus avoiding optical signal transmission to the fifth waveguide 5 and further reducing optical signal transmission loss in the end-face coupler. The first waveguide core layer is formed using an inductively coupled plasma etching process with relatively low process requirements. The second waveguide core layer is also etched using an inductively coupled plasma etching process with relatively low process requirements to form a groove, which does not affect the first waveguide core layer. It is then deposited using the currently mature plasma-enhanced chemical vapor deposition method, which has simple process requirements. It not only avoids the use of grayscale lithography but also achieves low coupling loss even with a large linewidth in the lithography machine process. At the same time, the processes for constructing the end-face coupler are all back-end processes, which do not affect device performance and do not require chemical mechanical polishing (CMP), simplifying the process flow.

Claims

1. An end-face coupler based on inclined sidewall etching, characterized in that... The system includes a first waveguide core layer and a second waveguide core layer, with the second waveguide core layer located above the first waveguide core layer. The first waveguide core layer includes a first waveguide and a second waveguide. The first waveguide has a cuboid structure, and the second waveguide has a conical structure. The dimensions of the second waveguide gradually decrease along the optical signal transmission direction. The second waveguide core layer includes a third waveguide with a downwardly recessed first groove, a fourth waveguide with a downwardly recessed second groove, and a fifth waveguide with both the third and fourth grooves. The third groove extends vertically through the fifth waveguide. The third waveguide and the first groove are both square pyramidal, the fourth waveguide is a triangular frustum, the second groove is a triangular pyramidal, the fifth waveguide is a cuboid structure, the third groove is a square pyramidal, the fourth groove is a triangular frustum, the first groove is connected to the second groove, and the third groove is connected to the fourth groove. The dimensions of the third and fourth waveguides gradually decrease along the optical signal transmission direction. The first waveguide is used for coupling with an external optical fiber, connecting the optical signal transmitted through the external optical fiber to the end-face coupler. The third waveguide... The first waveguide is used to extend the first waveguide and reduce the mode mismatch between the first waveguide and the external optical fiber. It also works in conjunction with the fourth waveguide to gradually reduce the constraint on the optical signal transmitted in the end-face coupler. This allows the optical field to gradually distribute within the first waveguide during propagation after the optical signal enters the end-face coupler, reducing transmission loss. The second waveguide is used to achieve mode conversion between the first waveguide and the external single-mode waveguide, enabling the optical signal transmitted in the first waveguide to be transmitted to the external single-mode waveguide. The first, second, third, and fourth grooves are used to prevent the fifth waveguide from coupling with the first and third waveguides, avoiding optical signal transmission to the fifth waveguide and reducing optical signal transmission loss in the end-face coupler. The first waveguide core layer is formed by etching a rectangular waveguide using inductively coupled plasma etching. The second waveguide core layer is formed by depositing an upper cladding on the first waveguide core layer using plasma-enhanced chemical vapor deposition, then first using inductively coupled plasma (ICP) etching to etch the upper cladding at an angle, forming a groove in the upper cladding that matches the structural shape of the third and fourth waveguides. Then, using plasma-enhanced chemical vapor deposition, a third waveguide with the first groove and a fourth waveguide with the second groove are deposited in the grooves, and a fifth waveguide with the third and fourth grooves is deposited on the cladding.

2. The end-face coupler based on inclined sidewall etching according to claim 1, characterized in that... The thickness direction of the first waveguide is vertical. The length direction of the first waveguide is defined as horizontal, and the width direction is defined as front-back. The plane that makes the first waveguide symmetrical front-back is called the first symmetry plane. The second waveguide is located to the right of the first waveguide. The cross-section of the second waveguide in the horizontal direction is an isosceles trapezoid. This isosceles trapezoid is symmetrical about the first symmetry plane, and its lower base is located to the left of its upper base. The left end face of the second waveguide has the same dimensions as the right end face of the first waveguide. The left end face of the second waveguide and the right end face of the first waveguide are integrally formed and joined together, and the two completely overlap. The upper end face of the second waveguide is located in the same plane as the upper end face of the first waveguide. The lower end face of the second waveguide is located in the same plane as the lower end face of the first waveguide. The third waveguide is located above the first waveguide. The third waveguide has an upper end face, a lower end face, a left end face, a right end face, a front end face, and a rear end face, arranged in an up-down-left-right-front-rear orientation and sequentially connected. The upper end face of the third waveguide is an isosceles trapezoid, symmetrical about the first plane of symmetry, with its lower base to the left of its upper base. The lower end face of the third waveguide is a triangle, symmetrical about the first plane of symmetry. The left end face of the third waveguide is an isosceles trapezoid, symmetrical about the first plane of symmetry, with its upper base to the left of its upper base. Below its bottom edge, the right end face of the third waveguide is triangular, and this triangle is symmetrical about the first symmetry plane. The front end face and rear end face of the third waveguide are both quadrilaterals, and the front end face and rear end face of the third waveguide are symmetrical about the first symmetry plane. The lower end face of the third waveguide is integrally formed and joined with the upper end face of the first waveguide, and the left side of the lower end face of the third waveguide completely coincides with the left side of the upper end face of the first waveguide. The right end face of the third waveguide is located to the left of the plane containing the right end face of the first waveguide, and there is a distance between the two. The first groove has an upper end face, a lower end face, a left end face, a right end face, a front end face, and a rear end face, which are arranged and connected sequentially in the directions of top, bottom, left, right, front, and rear. The upper end face of the first groove is an isosceles trapezoid, which is symmetrical about the first plane of symmetry, and its lower base is located to the left of its upper base. The lower end face of the first groove is a triangle, which is symmetrical about the first plane of symmetry. The left end face of the first groove is an isosceles trapezoid, which is symmetrical about the first plane of symmetry, and its upper base is located below its lower base. The right end face of the first groove is a triangle, which is symmetrical about the first plane of symmetry. The front end face and the rear end face of the first groove... All surfaces are quadrilaterals. The front and rear faces of the first groove are symmetrical about the first symmetry plane. The upper face of the first groove is on the same plane as the upper face of the third waveguide. The left face of the first groove is on the same plane as the left face of the third waveguide. The right face of the first groove is on the same plane as the right face of the third waveguide. The lower face of the first groove is above the lower face of the third waveguide, and there is a distance between them. The front face of the first groove is behind the front face of the third waveguide, and there is a distance between them. The rear face of the first groove is in front of the rear face of the third waveguide, and there is a distance between them. The fourth waveguide is located to the right of the third waveguide. The fourth waveguide has an upper end face, a front end face, a rear end face, a left end face, and a right end face, arranged and connected sequentially in the directions of top, front, back, left, and right. The upper end face of the fourth waveguide is an isosceles trapezoid, symmetrical about the first plane of symmetry, with its lower base to the left of its upper base. The left end face of the fourth waveguide is a triangle, symmetrical about the first plane of symmetry. The right end face of the fourth waveguide is a triangle, symmetrical about the first plane of symmetry. The front and rear end faces of the fourth waveguide are both quadrilaterals. The front and rear faces of the fourth waveguide are symmetrical about the first symmetry plane; the upper face of the fourth waveguide is on the same plane as the upper face of the third waveguide; the left face of the fourth waveguide is integrally formed and joined with the right face of the third waveguide, and the two completely overlap; the front face of the fourth waveguide is on the same plane as the front face of the third waveguide; the rear face of the fourth waveguide is on the same plane as the rear face of the third waveguide; the right face of the fourth waveguide is located between the plane containing the left and right faces of the second waveguide; and the lower side of the front face of the fourth waveguide slopes upward from left to right. The second groove has an upper end face, a front end face, a rear end face, and a left end face that are distributed and connected sequentially in the directions of top, front, back, and left. The upper end face of the second groove is triangular and is symmetrical about the first plane of symmetry. The left end face of the second groove is also triangular and is symmetrical about the first plane of symmetry. The front and rear ends of the second groove are both triangular and are symmetrical about the first plane of symmetry. The upper end face of the second groove is on the same plane as the upper end face of the fourth waveguide. The left end face of the second groove is on the same plane as the left end face of the fourth waveguide. The left end face of the second groove is integrally formed and connected to the right end face of the first groove, and the two completely overlap. The right end of the second groove extends directly above the second waveguide. The front end face of the second groove is on the same plane as the front end face of the first groove. The rear end face of the second groove is on the same plane as the rear end face of the first groove. The fifth waveguide is located above the third and fourth waveguides. The length of the fifth waveguide is along the left-right direction, the width is along the front-back direction, and the thickness is along the top-bottom direction. The fifth waveguide is symmetrical about the first symmetry plane. The left end face of the fifth waveguide is on the same plane as the left end face of the third waveguide, and the right end face of the fifth waveguide is on the same plane as the right end face of the second waveguide. The width of the fifth waveguide is greater than the bottom length of the left end face of the third waveguide. The bottom end face of the fifth waveguide is integrally formed and connected to the top end face of the third and fourth waveguides. The third groove has an upper end face, a lower end face, a left end face, a right end face, a front end face, and a rear end face, arranged in an up-down-left-right-front-rear orientation and connected sequentially. The upper end face of the third groove is an isosceles trapezoid, which is symmetrical about the first plane of symmetry, and its lower base is located to the left of its upper base. The lower end face of the third groove is an isosceles triangle, which is symmetrical about the first plane of symmetry. The left end face of the third groove is an isosceles trapezoid, which is symmetrical about the first plane of symmetry, and its upper base is located below its lower base. The right end face of the third groove is an isosceles triangle, which is symmetrical about the first plane of symmetry. The front end face and the rear end face of the third groove... All end faces are quadrilaterals. The front and rear faces of the third groove are symmetrical about the first symmetry plane. The upper end face of the third groove is on the same plane as the upper end face of the fifth waveguide. The lower end face of the third groove is on the same plane as the lower end face of the fifth waveguide. The left end face of the third groove is on the same plane as the left end face of the fifth waveguide. The lower base length of the left end face of the third groove is equal to the upper base length of the left end face of the first groove. The front end face of the third groove is on the same plane as the front end face of the first groove. The rear end face of the third groove is on the same plane as the rear end face of the first groove. The right end face of the third groove is on the same plane as the right end face of the second groove. The fourth groove is located to the right of the third groove. The fourth groove has an upper end face, a front end face, a rear end face, a left end face, and a right end face, arranged in a top, front, back, left, and right orientation and connected sequentially. The upper end face of the fourth groove is an isosceles trapezoid, which is symmetrical about the first plane of symmetry, with its lower base to the left of its upper base. The left end face of the fourth groove is an isosceles triangle, also symmetrical about the first plane of symmetry. The right end face of the fourth groove is an isosceles triangle, also symmetrical about the first plane of symmetry. The front and rear faces of the fourth groove are both quadrilaterals, and the front and rear faces of the fourth groove are symmetrical about the first symmetry plane. The upper face of the fourth groove is on the same plane as the upper face of the third groove. The left face of the fourth groove is integrally formed with the right face of the third groove and the two completely overlap. The front face of the fourth groove is on the same plane as the front face of the third groove. The rear face of the fourth groove is on the same plane as the rear face of the third groove. The lower side of the front face of the fourth groove slopes upward from left to right.

3. A method for manufacturing an end-face coupler based on inclined sidewall etching as described in claim 1 or 2, characterized in that... Includes the following steps: Step 1: Prepare a quartz wafer as a substrate; Step 2: Deposit waveguide material on the upper surface of the wafer using plasma-enhanced chemical vapor deposition to form the first waveguide layer. The thickness of the first waveguide layer along the vertical direction is equal to the thickness of the first waveguide. Step 3: Uniformly coat the upper surface of the first waveguide layer with a layer of photoresist, which completely covers the upper surface of the first waveguide layer; Step 4: Using photolithography, a pattern with the same cross-section as the overall structure formed by the first waveguide and the second waveguide is prepared in the photoresist of step 3, and the photoresist outside the pattern is removed by developing. Step 5: The first waveguide layer is etched using an inductively coupled plasma etching process. At this time, the part of the first waveguide layer without photoresist coverage is etched away, and the remaining part forms the first waveguide and the second waveguide. Step 6: Deposit a lower cladding layer on the first waveguide and the second waveguide using plasma-enhanced chemical vapor deposition, the lower cladding layer completely covering the first waveguide and the second waveguide; Step 7: Uniformly coat a layer of photoresist on the upper surface of the lower cladding layer, so that the photoresist completely covers the upper surface of the lower cladding layer; Step 8: Based on the positional relationship between the third waveguide and the fourth waveguide and the first waveguide and the second waveguide, a pattern consistent with the upper surface of the overall structure formed by the third waveguide and the fourth waveguide is prepared on the photoresist in step 7 using photolithography. The photoresist in the area where the pattern is located is removed using development. Step 9: The lower cladding layer is etched at an angle using an inductively coupled plasma (ICP) etching process. At this time, the part of the lower cladding layer that is not covered by photoresist is etched away. An inclined groove with the front and rear sidewalls is etched in the lower cladding layer. The shape of the groove is consistent with the overall structure formed by the third waveguide and the fourth waveguide. Step 10: Deposit waveguide material in the groove and on the lower cladding using plasma-enhanced chemical vapor deposition to form the second waveguide core layer; Step 11: Deposit an upper cladding layer on the fifth waveguide, in the first groove, in the second groove, in the third groove, and in the fourth groove using plasma-enhanced chemical vapor deposition.

4. The manufacturing method of an end-face coupler based on inclined sidewall etching as described in claim 3, characterized in that... In step 9, when the cladding is etched at an angle using inductively coupled plasma (ICP) etching, the RF power is 1950W, the bias power is 220W, and the etching gases are CF4 and C4F8, with a volume ratio of CF4 to C4F8 of 5:1.

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