An end-face coupler and its manufacturing method

Abstract

This invention discloses an end-face coupler and its manufacturing method. The end-face coupler includes a first waveguide, a second waveguide, a third waveguide, a fourth waveguide, a fifth waveguide, and a sixth waveguide. When an external optical fiber outputs an optical signal to the first waveguide, the fourth waveguide extends the first waveguide. The fifth and sixth waveguides evolve the optical signal transmitted in the end-face coupler along the vertical direction, so that the mode field of the optical signal gradually concentrates and distributes in the first waveguide before being transmitted to the second waveguide, reducing the loss of the optical signal transmitted to the second waveguide. The fourth, fifth, and sixth waveguides are formed by etching grooves in the lower cladding, followed by depositing doped silicon dioxide in the grooves and on the lower cladding and performing chemical mechanical polishing. The first, second, and third waveguides are formed by deposition followed by etching. The advantages are low coupling loss and simple manufacturing process.

Description

Technical Field

[0001] This invention relates to end-face couplers, and more particularly to an end-face coupler and its manufacturing method. Background Technology

[0002] High-refractive-index-difference silica-based / silicon-based planar optical waveguides, with their large tolerance and low temperature drift, are ideal materials for fabricating waveguide devices such as wavelength division multiplexers and optical switches, and have been widely used in the manufacture of optical waveguide devices in data centers, backbone networks, and 5G fronthaul. However, the height of high-refractive-index-difference silica waveguides is only 3–4 μm, while the mode field diameter of optical fibers is approximately 9 μm. If optical waveguide devices fabricated using high-refractive-index-difference silica waveguides are directly coupled to optical fibers, the coupling loss will be relatively high due to the large mode field mismatch. Insertion loss is a core performance indicator for all optical waveguide devices; therefore, researchers have proposed using end-face couplers to reduce the coupling loss between optical fibers and optical waveguide devices fabricated using high-refractive-index-difference silica waveguides.

[0003] Existing end-face couplers are mainly based on waveguide grating structures, multi-layer conical structures, or grayscale mask structures. End-face couplers based on waveguide grating structures are planar structures, which are simple to manufacture, but have limited height expansion capabilities and relatively high coupling loss. End-face couplers based on multi-layer conical structures and grayscale mask structures can both achieve height mode field expansion and have lower coupling loss, but their manufacturing processes are complex. Summary of the Invention

[0004] One of the technical problems to be solved by the present invention is to provide an end-face coupler with low coupling loss and simple manufacturing process.

[0005] The technical solution adopted by the present invention to solve one of the above-mentioned technical problems is as follows: an end-face coupler, comprising an upper cladding layer, a lower cladding layer, and a waveguide core layer, wherein the upper cladding layer is located above the lower cladding layer, and the waveguide core layer is disposed between the upper cladding layer and the lower cladding layer and is enclosed by the upper cladding layer and the lower cladding layer; the waveguide core layer comprises a first waveguide, a second waveguide, and a third waveguide; the materials of the first waveguide, the second waveguide, and the third waveguide are all doped silicon dioxide; the third waveguide is a single-mode waveguide; and the first waveguide is used for... Coupled with an external optical fiber, the optical signal transmitted through the external optical fiber is connected to the end-face coupler. The second waveguide is used to evolve the mode field of the optical signal transmitted in the end-face coupler in the horizontal plane along a direction perpendicular to the optical signal transmission direction, so that the optical signal mode can be matched with the third waveguide. The third waveguide is used to output the optical signal to the back-end optical waveguide device. The waveguide core layer also includes a fourth waveguide, a fifth waveguide, and a sixth waveguide. The materials of the fourth waveguide, the fifth waveguide, and the sixth waveguide are all doped silicon dioxide. The fifth and sixth waveguides are located below the first waveguide. The fourth waveguide extends the first waveguide to reduce mode field mismatch between the end-face coupler and the external optical fiber. The fifth and sixth waveguides evolve the optical signal transmitted in the end-face coupler along the vertical direction, so that the mode field of the optical signal gradually concentrates and distributes in the first waveguide along the optical signal transmission direction. The fourth, fifth, and sixth waveguides are formed by etching grooves in the lower cladding, followed by depositing doped silicon dioxide in the grooves and on the lower cladding and performing chemical mechanical polishing. After the fourth, fifth, and sixth waveguides are formed, the first, second, and third waveguides are formed by depositing doped silicon dioxide on the lower cladding, the fourth, fifth, and sixth waveguides to form a doped silicon dioxide layer. A portion with the same shape as the first, second, and third waveguides is retained in the doped silicon dioxide layer at the corresponding position, while the other portions are etched away.

[0006] Compared with the prior art, the advantage of the end-face coupler of the present invention lies in the additional provision of a fourth, fifth, and sixth waveguide in the waveguide core layer. The materials of the fourth, fifth, and sixth waveguides are all doped with silicon dioxide. These waveguides are located below the first waveguide and, together with the first, second, and third waveguides, form the core structure of the end-face coupler. When the external optical fiber outputs an optical signal to the first waveguide, the fourth waveguide extends the first waveguide and couples with it to the external optical fiber. This extends the height of the end face coupled to the optical fiber to 5–7 μm, resulting in a higher match with the optical fiber mode field (approximately 6–9 μm). In other words, the end-face mode field of the end-face coupler and the optical fiber mode field have a larger overlap integral, thereby reducing the mode field mismatch between the end-face coupler and the external optical fiber. When the first and fourth waveguides are coupled to the optical fiber, the optical signal simultaneously enters and is transmitted through the first and fourth waveguides. The fifth and sixth waveguides then couple the optical signal transmitted in the end-face coupler along… The optical signal undergoes a vertical evolution, causing the mode field of the optical signal to gradually concentrate and distribute in the first waveguide before being transmitted to the second waveguide, reducing the loss of the optical signal transmitted to the second waveguide. The second waveguide then evolves the mode field of the optical signal transmitted in the end-face coupler in the horizontal plane along a direction perpendicular to the optical signal transmission, so that the optical signal mode matches the third waveguide, enabling transmission to the back-end optical waveguide device through the third waveguide. In addition, the fourth, fifth, and sixth waveguides are formed by etching grooves in the lower cladding layer, followed by depositing doped silicon dioxide in the grooves and on the lower cladding layer and performing chemical mechanical polishing. The first, second, and third waveguides are formed by depositing doped silicon dioxide on the lower cladding layer, the fourth waveguide, the fifth waveguide, and the sixth waveguide to form a doped silicon dioxide layer, followed by etching. That is, the end-face coupler of the present invention only uses two etching processes in its manufacturing process. Therefore, the end-face coupler of the present invention has low coupling loss and a simple manufacturing process.

[0007] Furthermore, the first waveguide is a cuboid structure, its thickness is along the vertical direction, and its length is along the optical signal transmission direction in the end-face coupler. The length direction of the first waveguide is defined as the left-right direction, and its 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, and it is an isosceles trapezoidal structure. The second waveguide is symmetrical front-back about the first symmetry plane, and its cross-section along the horizontal plane is... An isosceles trapezoid, the lower base of which is located to the left of its upper base, and both extending in the front-to-back direction. The second waveguide has its length along the left-to-right direction, its thickness along the top-to-bottom direction, and its width along the front-to-back direction. The upper end face of the second waveguide is on the same plane as the upper end face of the first waveguide, and the lower end face of the second waveguide is on the same plane as the lower end face of the first waveguide. The width of the left end of the second waveguide is equal to the width of the right end 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 completely overlap. The third waveguide... The third waveguide is located to the right of the second waveguide. The third waveguide has a cuboid structure and is symmetrical about the first plane of symmetry. Its length is along the left-right direction, its thickness along the top-bottom direction, and its width along the front-back direction. The upper end face of the third waveguide is on the same plane as the upper end face of the second waveguide, and the lower end face of the third waveguide is on the same plane as the lower end face of the second waveguide. The width of the third waveguide is equal to the width of the right end of the second waveguide. The left end face of the third waveguide is parallel to the right end face of the second waveguide. The four waveguides are integrally formed and completely overlap; the fourth waveguide is an isosceles trapezoidal structure, and the fourth waveguide is symmetrical about the first symmetry plane. The cross-section of the fourth waveguide along the vertical plane is an isosceles trapezoid, with the lower base of the isosceles trapezoid located above its upper base, both extending in the front-back direction, and the length of its upper base is greater than the width of the first waveguide. The left end face of the fourth waveguide is on the same plane as the left end face of the first waveguide, and the upper end face of the fourth waveguide is fixedly connected to the lower end face of the first waveguide and is in a fitted state; the length direction of the fourth waveguide is along the left-right direction.The fifth waveguide is located to the right of the fourth waveguide. The fifth waveguide has a trapezoidal gradient structure and is symmetrical about the first symmetry plane. It 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 sequentially in the directions of top, bottom, left, right, front, and rear. The upper end face of the fifth waveguide is an isosceles trapezoid, symmetrical about the first symmetry plane, with its lower base to the left of its upper base. The length of its lower base is equal to the length of the lower base of the right end face of the fourth waveguide, and its upper base is less than the width of the first waveguide. The lower end face of the fifth waveguide is an isosceles triangle, symmetrical about the first symmetry plane. The left end face of the fifth waveguide is an isosceles trapezoid, symmetrical about the first symmetry plane, with its upper base below its lower base. The right end face of the fifth waveguide is an isosceles triangle, and this isosceles triangle is symmetrical about the first symmetry plane. The front end face and rear end face of the fifth waveguide are both quadrilaterals, and the front end face and rear end face of the fifth waveguide are symmetrical about the first symmetry plane. The front end face of the fifth waveguide is on the same plane as the front end face of the fourth waveguide, the rear end face of the fifth waveguide is on the same plane as the rear end face of the fourth waveguide, the upper end face of the fifth waveguide is on the same plane as the upper end face of the fourth waveguide, the lower end face of the fifth waveguide is on the same plane as the lower end face of the fourth waveguide, the left end face of the fifth waveguide is integrally formed with the right end face of the fourth waveguide and completely overlaps, and the upper end face of the fifth waveguide is fixedly connected to the lower end face of the first waveguide and is in a fitted state. 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 sixth waveguide is located to the right of the fifth waveguide. The sixth waveguide has a triangular pyramidal structure and is symmetrical about the first plane of symmetry. It has an upper end face, a front end face, a rear end face, and a left end face, arranged in a top, front, rear, and left orientation and connected sequentially. The upper end face of the sixth waveguide is an isosceles triangle, symmetrical about the first plane of symmetry. The left end face of the sixth waveguide is also an isosceles triangle, symmetrical about the first plane of symmetry. Both the front and rear end faces of the sixth waveguide are triangular. The waveguide is symmetrical about the first symmetry plane. The upper surface of the sixth waveguide is on the same plane as the upper surface of the fifth waveguide. The upper surface of the sixth waveguide is fixedly connected to and in contact with the lower surface of the first waveguide. The front surface of the sixth waveguide is on the same plane as the front surface of the fifth waveguide. The rear surface of the sixth waveguide is on the same plane as the rear surface of the fifth waveguide. The left surface of the sixth waveguide is integrally formed with and completely overlaps the right surface of the fifth waveguide. The right surface of the sixth waveguide is on the same plane as the right surface of the first waveguide. The length of the sixth waveguide is along the left-right direction.

[0008] Furthermore, both the upper cladding layer and the lower cladding layer are made of silicon dioxide, and the refractive index of the doped silicon dioxide is 0.45% to 2.5% higher than that of silicon dioxide.

[0009] Furthermore, the first waveguide has a thickness H1 = 3.5 μm and a width W1 = 11.3 μm; the fourth waveguide has a bottom length W = 1.2 μm on its left end face; the fourth waveguide has a thickness H = 5.4 μm along its vertical direction; the second waveguide has a length L3 = 380 μm; the third waveguide has a length L4 = 100 μm; the fifth waveguide has a length L1 = 600 μm; the sixth waveguide has a length L2 = 800 μm; the fourth waveguide has a length L5 = 100 μm; and the sixth waveguide has an angle β = 73.3° between its rear end face and the horizontal plane.

[0010] The second technical problem to be solved by the present invention is to provide a method for manufacturing an end-face coupler that can produce an end-face coupler with low coupling loss and with a simple manufacturing process.

[0011] The technical solution adopted by the present invention to solve the second technical problem mentioned above is: a method for manufacturing an end-face coupler, comprising the following steps:

[0012] Step 1: Prepare a quartz substrate as the lower cladding layer;

[0013] Step 2: Coat the upper surface of the quartz substrate with photoresist, which completely covers the upper surface of the quartz substrate;

[0014] Step 3: Using photolithography, a pattern consistent with the overall cross-section of the fourth waveguide, the fifth waveguide, and the sixth waveguide is prepared in the photoresist of Step 2, and the photoresist outside the pattern is removed by developing.

[0015] Step 4: Use inductively coupled plasma etching process to etch the lower cladding layer. At this time, the part of the lower cladding layer without photoresist is etched away, and a preset groove is etched in the lower cladding layer. The inclination angle of the sidewall of the etched groove is equal to the angle β between the rear end face of the sixth waveguide and the horizontal plane.

[0016] Step 5: Deposit doped silicon dioxide in the groove and on the lower cladding layer using plasma-enhanced chemical vapor deposition. At this time, the groove is filled with doped silicon dioxide, and the first doped silicon dioxide layer is formed on the lower cladding layer.

[0017] Step 6: Perform chemical mechanical polishing from the first doped silicon dioxide layer downwards until a lower cladding layer of the preset thickness and the overall structure of the fourth waveguide, the fifth waveguide and the sixth waveguide are obtained;

[0018] Step 7: Deposit doped silicon dioxide material on the lower cladding layer, the fourth waveguide, the fifth waveguide, and the sixth waveguide to form a second doped silicon dioxide layer;

[0019] Step 8: Coat the upper surface of the second doped silicon dioxide layer with photoresist, which completely covers the upper surface of the second doped silicon dioxide layer;

[0020] Step 9: Based on the structures of the first waveguide, the second waveguide, and the third waveguide, and the positional relationship between the first waveguide, the second waveguide, and the third waveguide and the fourth waveguide, the fifth waveguide, and the sixth waveguide, a pattern consistent with the overall structure formed by the first waveguide, the second waveguide, and the third waveguide is prepared in the photoresist of step 8 using photolithography, and the photoresist outside the pattern is removed using development.

[0021] Step 10: The portion of the second doped silicon dioxide layer not covered by photoresist is etched away using an inductively coupled plasma etching process, and the remaining portion forms the first waveguide, the second waveguide, and the third waveguide.

[0022] Step 11: Deposit silicon dioxide on the lower cladding, the first waveguide, the second waveguide, and the third waveguide to form an upper cladding.

[0023] Compared with existing technologies, the manufacturing method of the end-face coupler of the present invention has the advantage of forming the first, second, third, fourth, fifth, and sixth waveguides through a two-stage etching process, which simplifies the manufacturing process. Furthermore, in the resulting end-face coupler, the fourth, fifth, and sixth waveguides, together with the first, second, and third waveguides, form the core structure of the end-face coupler. When the external optical fiber outputs an optical signal to the first waveguide, the fourth waveguide extends the first waveguide and couples with it to the external optical fiber. This extends the height of the end face coupled to the optical fiber to 5–7 μm, resulting in a higher matching degree with the optical fiber mode field (approximately 6–9 μm). In other words, the end-face mode field of the end-face coupler and the optical fiber mode field have a larger overlap integral, thereby reducing the overlap between the end-face coupler and the optical fiber mode field. When the mode field of the external optical fiber is mismatched, the optical signal will simultaneously enter and be transmitted in the first and fourth waveguides when coupled to the optical fiber. The fifth and sixth waveguides evolve the optical signal transmitted in the end-face coupler along the vertical direction, so that the mode field of the optical signal gradually concentrates and distributes in the first waveguide before being transmitted to the second waveguide, reducing the loss of the optical signal transmitted to the second waveguide. The second waveguide then evolves the mode field of the optical signal transmitted in the end-face coupler in the horizontal plane along the direction perpendicular to the optical signal transmission, so that the optical signal mode matches the third waveguide, and can be transmitted to the back-end optical waveguide device through the third waveguide. Thus, the manufacturing method of the end-face coupler of the present invention can produce an end-face coupler with low coupling loss while having a simple manufacturing process.

[0024] Furthermore, in step 4, when etching the lower cladding layer using inductively coupled plasma etching, the RF power is 1950W, the bias power is 220W, the etching gas is CF4, the protective gas is C4F8, the CF4 flow rate is 100sccm, and the C4F8 flow rate is 20sccm. Attached Figure Description

[0025] Figure 1 The three-dimensional waveguide core layer of the end-face coupler of the present invention Figure 1 ;

[0026] Figure 2 The three-dimensional waveguide core layer of the end-face coupler of the present invention Figure 2 ;

[0027] Figure 3 The three-dimensional waveguide core layer of the end-face coupler of the present invention Figure 3 ;

[0028] Figure 4 Top view of the waveguide core layer of the end-face coupler of the present invention. Figure 1 ;

[0029] Figure 5This is a front view of the waveguide core layer of the end-face coupler of the present invention;

[0030] Figure 6 Top view of the waveguide core layer of the end-face coupler of the present invention. Figure 2 ;

[0031] Figure 7 for Figure 6 Side view at midsection 1;

[0032] Figure 8 for Figure 6 Side view at section 2;

[0033] Figure 9 This is a diagram showing the fit between the waveguide core layer and the optical fiber in the end-face coupler of the present invention.

[0034] Figure 10 This is a flowchart of the manufacturing method of the end-face coupler of the present invention;

[0035] Figure 11 Electron microscope images of grooves with different opening widths in the manufacturing method of the end face coupler of the present invention;

[0036] Figure 12 This is a diagram showing the groove etching depth under different opening widths in the manufacturing method of the end face coupler of the present invention;

[0037] Figure 13 The end face of the end face coupler of the present invention is along Figure 9 Light field distribution diagram of the YZ section;

[0038] Figure 14 The end face of the end face coupler of the present invention is along Figure 9 Light field distribution diagram of the XZ section;

[0039] Figure 15 The figure shows the simulation results of the transmission spectrum of the end-face coupler of the present invention. Detailed Implementation

[0040] This invention discloses an end-face coupler, and the end-face coupler of this invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0041] Example 1: As Figures 1 to 4As shown, an end-face coupler includes an upper cladding layer, a lower cladding layer, and a waveguide core layer. The upper cladding layer is located above the lower cladding layer, and the waveguide core layer is disposed between and enclosed by the upper and lower cladding layers. The waveguide core layer includes a first waveguide 004, a second waveguide 005, and a third waveguide 006. The materials of the first waveguide 004, second waveguide 005, and third waveguide 006 are all doped silicon dioxide. The third waveguide 006 is a single-mode waveguide. The first waveguide 004 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 coupler, the second waveguide 005, is used to evolve the mode field of the optical signal transmitted in the end-face coupler in the horizontal plane along a direction perpendicular to the optical signal transmission direction, so that the optical signal mode can be matched with the third waveguide 006. The third waveguide 006 is used to output the optical signal to the back-end optical waveguide device. The waveguide core layer also includes a fourth waveguide 001, a fifth waveguide 002, and a sixth waveguide 003. The materials of the fourth waveguide 001, the fifth waveguide 002, and the sixth waveguide 003 are all doped silicon dioxide. Located below the first waveguide 004, the fourth waveguide 001 extends the first waveguide 004 to reduce mode field mismatch between the end-face coupler and the external optical fiber. The fifth waveguide 002 and the sixth waveguide 003 evolve the optical signal transmitted in the end-face coupler along the vertical direction, so that the mode field of the optical signal gradually concentrates and distributes in the first waveguide 004 along the optical signal transmission direction. The fourth waveguide 001, the fifth waveguide 002, and the sixth waveguide 003 form grooves in the lower cladding through an etching process, and then further enhance the mode field distribution in the grooves and on the lower cladding. After depositing doped silicon dioxide and performing chemical mechanical polishing, the first waveguide 004, the second waveguide 005, and the third waveguide 006 are formed by depositing doped silicon dioxide on the lower cladding, the fourth waveguide 001, the fifth waveguide 002, and the sixth waveguide 003 to form a doped silicon dioxide layer. The doped silicon dioxide layer retains a portion with the same shape as the first waveguide 004, the second waveguide 005, and the third waveguide 006 at the corresponding position, while the other portions are etched away.

[0042] In this embodiment, the fourth waveguide 001, the fifth waveguide 002, and the sixth waveguide 003 are combined with the first waveguide 004, the second waveguide 005, and the third waveguide 006 to form the core structure of the end-face coupler. When the external optical fiber outputs an optical signal to the first waveguide 004, the fourth waveguide 001 extends the first waveguide 004 and couples with it to the external optical fiber. This extends the height of the end face coupled to the optical fiber to 5-7 μm, resulting in a higher match with the optical fiber mode field (approximately 6-9 μm). This means the end-face mode field of the end-face coupler and the optical fiber mode field have a larger overlap integral, thereby reducing the mode field mismatch between the end-face coupler and the external optical fiber and lowering coupling loss. When the first waveguide 004 and the fourth waveguide 001 are coupled to the optical fiber, the optical signal simultaneously enters and is transmitted through both waveguides. The fifth waveguide 002 and the sixth waveguide 003 evolve the optical signal transmitted in the end-face coupler along the vertical direction, allowing the optical signal to be transmitted along the vertical direction. In the direction of transmission, the mode field of the optical signal gradually concentrates and distributes in the first waveguide 004 before being transmitted to the second waveguide 005, reducing the transmission loss of the optical signal in the second waveguide 005. The second waveguide 005 then evolves the mode field of the optical signal transmitted in the end coupler in the horizontal plane along the direction perpendicular to the optical signal transmission, so that the optical signal mode matches the third waveguide 006, and can be transmitted to the back-end optical waveguide device through the third waveguide 006. In addition, the fourth waveguide 001, the fifth waveguide 002, and the sixth waveguide 003 are formed by etching grooves in the lower cladding layer, and then depositing doped silicon dioxide in the grooves and on the lower cladding layer and performing chemical mechanical polishing. The first waveguide 004, the second waveguide 005, and the third waveguide 006 are formed by depositing doped silicon dioxide on the lower cladding layer, the fourth waveguide 001, the fifth waveguide 002, and the sixth waveguide 003 to form a doped silicon dioxide layer, and then using an etching process. Only two etching processes are used, and the manufacturing process is simple.

[0043] Example 2: This example is basically the same as Example 1, except that: in this example, as Figures 5 to 9As shown, the first waveguide 004 has a cuboid structure. The thickness of the first waveguide 004 is along the vertical direction, and its length is along the direction of optical signal transmission in the end-face coupler. The length direction of the first waveguide 004 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 004 symmetrical front-back is called the first symmetry plane. The second waveguide 005 is located to the right of the first waveguide 004. The second waveguide 005 has an isosceles trapezoidal structure and is symmetrical about the first symmetry plane. The cross-section of the second waveguide 005 along the horizontal plane is an isosceles trapezoid. The lower base of the isosceles trapezoid is located to the left of its upper base, and both extend in the front-to-back direction. The length direction of the second waveguide 005 is along the left-to-right direction, the thickness direction is along the up-to-down direction, and the width direction is along the front-to-back direction. The upper end face of the second waveguide 005 is on the same plane as the upper end face of the first waveguide 004, and the lower end face of the second waveguide 005 is on the same plane as the lower end face of the first waveguide 004. The width of the left end of the second waveguide 005 is equal to the width of the right end of the first waveguide 004. The left end face of the second waveguide 005 and the right end face of the first waveguide 004 are integrally formed and completely overlap; the third waveguide 006 Located to the right of the second waveguide 005, the third waveguide 006 is a cuboid structure. The third waveguide 006 is symmetrical about the first plane of symmetry. Its length is along the left-right direction, its thickness along the top-bottom direction, and its width along the front-back direction. The upper end face of the third waveguide 006 is on the same plane as the upper end face of the second waveguide 005, and the lower end face of the third waveguide 006 is on the same plane as the lower end face of the second waveguide 005. The width of the third waveguide 006 is equal to the width of the right end of the second waveguide 005. The left end face of the third waveguide 006 is parallel to the right end face of the second waveguide 005. The surfaces are integrally formed and completely overlapped; the fourth waveguide 001 is an isosceles trapezoidal structure, and the fourth waveguide 001 is symmetrical about the first symmetry plane. The cross-section of the fourth waveguide 001 along the vertical plane is an isosceles trapezoid, and the lower base of the isosceles trapezoid is located above its upper base. Both extend in the front-back direction, and the length of its upper base is greater than the width of the first waveguide 004. The left end face of the fourth waveguide 001 and the left end face of the first waveguide 004 are located in the same plane. The upper end face of the fourth waveguide 001 and the lower end face of the first waveguide 004 are fixedly connected and in a fitted state; the length direction of the fourth waveguide 001 is along the left-right direction.The fifth waveguide 002 is located to the right of the fourth waveguide 001. The fifth waveguide 002 has a trapezoidal gradient structure and is symmetrical about the first symmetry plane. It 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 order of top, bottom, left, right, front, and rear. The upper end face of the fifth waveguide 002 is an isosceles trapezoid, symmetrical about the first symmetry plane, with its lower base to the left of its upper base. The length of its lower base is equal to the length of the lower base of the right end face of the fourth waveguide 001, and its upper base is less than the width of the first waveguide 004. The lower end face of the fifth waveguide 002 is an isosceles triangle, symmetrical about the first symmetry plane. The left end face of the fifth waveguide 002 is an isosceles trapezoid, symmetrical about the first symmetry plane, with its upper base below its lower base. The right end face of the fifth waveguide 002... The face of the fifth waveguide 002 is an isosceles triangle, and this isosceles triangle is symmetrical about the first symmetry plane. The front and rear faces of the fifth waveguide 002 are both quadrilaterals, and the front and rear faces of the fifth waveguide 002 are symmetrical about the first symmetry plane. The front face of the fifth waveguide 002 is on the same plane as the front face of the fourth waveguide 001, the rear face of the fifth waveguide 002 is on the same plane as the rear face of the fourth waveguide 001, the upper face of the fifth waveguide 002 is on the same plane as the upper face of the fourth waveguide 001, the lower face of the fifth waveguide 002 is on the same plane as the lower face of the fourth waveguide 001, the left face of the fifth waveguide 002 is integrally formed with the right face of the fourth waveguide 001 and completely overlaps, and the upper face of the fifth waveguide 002 is fixedly connected to the lower face of the first waveguide 004 and is in a fitted state. The length of the fifth waveguide 002 is along the left-right direction, the width is along the front-back direction, and the thickness is along the top-bottom direction.The sixth waveguide 003 is located to the right of the fifth waveguide 002. The sixth waveguide 003 has a triangular pyramidal structure and is symmetrical about the first plane of symmetry. It has an upper end face, a front end face, a rear end face, and a left end face, arranged in the top, front, back, and left orientations and connected sequentially. The upper end face of the sixth waveguide 003 is an isosceles triangle, and this isosceles triangle is symmetrical about the first plane of symmetry. The left end face of the sixth waveguide 003 is also an isosceles triangle, and this isosceles triangle is symmetrical about the first plane of symmetry. Both the front and rear end faces of the sixth waveguide 003 are triangular. The first symmetry plane is symmetrical front to back. The upper end face of the sixth waveguide 003 is on the same plane as the upper end face of the fifth waveguide 002. The upper end face of the sixth waveguide 003 is fixedly connected to the lower end face of the first waveguide 004 and is in a close fit. The front end face of the sixth waveguide 003 is on the same plane as the front end face of the fifth waveguide 002. The rear end face of the sixth waveguide 003 is on the same plane as the rear end face of the fifth waveguide 002. The left end face of the sixth waveguide 003 is integrally formed with the right end face of the fifth waveguide 002 and completely overlaps with it. The right end face of the sixth waveguide 003 is on the same plane as the right end face of the first waveguide 004. The length of the sixth waveguide 003 is along the left-right direction.

[0044] In this embodiment, both the upper and lower cladding layers are made of silicon dioxide, and the refractive index of the doped silicon dioxide is 0.45% to 2.5% higher than that of the silicon dioxide.

[0045] In this embodiment, the thickness H1 of the first waveguide 004 is 3.5 μm, the width W1 is 11.3 μm, the bottom length of the left end face of the fourth waveguide 001 is W = 1.2 μm, the thickness H of the fourth waveguide 001 along the vertical direction is 5.4 μm, the length L3 of the second waveguide 005 is 380 μm, the length L4 of the third waveguide 006 is 100 μm, the length L1 of the fifth waveguide 002 is 600 μm, the length L2 of the sixth waveguide 003 is 800 μm, the length L5 of the fourth waveguide 001 is 100 μm, and the angle β between the rear end face of the sixth waveguide 003 and the horizontal plane is 73.3°.

[0046] In this embodiment, the mode field matching of the end-face coupler mainly includes three parts. The first part is the matching of the fiber and the end face: by filling the groove formed by etching with doped silicon oxide to form the fourth waveguide 001, and simultaneously depositing the first waveguide 004, the height (dimension along the vertical direction) of the end face of the end face coupler (the end face formed by the left end face of the first waveguide 004 and the fourth waveguide 001) can be extended to 5-7 μm, resulting in a higher matching degree with the fiber mode field (approximately 6-9 μm), that is, the end face mode field and the fiber mode field have a larger overlap integral. The second part is the longitudinal mode field compression evolution, which mainly utilizes the gradual change in groove depth formed by inclined etching to achieve a gradual change in the height (dimension along the vertical direction) of the end face coupler, thereby achieving a gradual change in the mode field in height. The third part is the transition from a wide waveguide mode field to a conventional waveguide mode field by slowly reducing the width (dimension along the front-back direction) of the end face coupler. The fourth waveguide 001, the fifth waveguide 002, and the sixth waveguide 003 all adopt a gradient structure. The grooves with inclined surfaces that match the fourth waveguide 001, the fifth waveguide 002, and the sixth waveguide 003 are obtained by etching at an angle. Then, the grooves are filled to obtain the fourth waveguide 001, the fifth waveguide 002, and the sixth waveguide 003. This reduces coupling loss and simplifies the manufacturing process.

[0047] The present invention also discloses a method for manufacturing the above-mentioned end-face coupler. The manufacturing method of the end-face coupler of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0048] Example: Figure 10 As shown, a method for manufacturing an end-face coupler includes the following steps:

[0049] Step 1: Prepare a quartz substrate as the lower cladding layer;

[0050] Step 2: Coat the upper surface of the quartz substrate with photoresist, which completely covers the upper surface of the quartz substrate;

[0051] Step 3: Using photolithography, a pattern with the same cross-section as the overall structure of the fourth waveguide 001, the fifth waveguide 002, and the sixth waveguide 003 is prepared in the photoresist of Step 2, and the photoresist outside the pattern is removed by developing.

[0052] Step 4: Use inductively coupled plasma etching process to etch the lower cladding. At this time, the part of the lower cladding without photoresist is etched away, and a preset groove is etched in the lower cladding. The tilt angle of the sidewall of the etched groove is equal to the angle β between the rear end face of the sixth waveguide and the horizontal plane.

[0053] Step 5: Deposit doped silicon dioxide in the groove and on the lower cladding using plasma-enhanced chemical vapor deposition. At this time, the groove is filled with doped silicon dioxide, and the first doped silicon dioxide layer is formed on the lower cladding.

[0054] Step 6: Starting from the first doped silicon dioxide layer, perform chemical mechanical polishing downwards until a lower cladding layer of the preset thickness and the overall structure of the fourth waveguide 001, the fifth waveguide 002 and the sixth waveguide 003 are obtained;

[0055] Step 7: Deposit doped silicon dioxide material on the lower cladding, fourth waveguide 001, fifth waveguide 002 and sixth waveguide 003 to form a second doped silicon dioxide layer;

[0056] Step 8: Coat the upper surface of the second doped silicon dioxide layer with photoresist, which completely covers the upper surface of the second doped silicon dioxide layer;

[0057] Step 9: Based on the structure of the first waveguide 004, the second waveguide 005, and the third waveguide 006, and the positional relationship between the first waveguide 004, the second waveguide 005, and the third waveguide 006 and the fourth waveguide 001, the fifth waveguide 002, and the sixth waveguide 003, a pattern consistent with the overall structure formed by the first waveguide 004, the second waveguide 005, and the third waveguide 006 is prepared in the photoresist of step 8 using photolithography, and the photoresist outside the pattern is removed using development.

[0058] Step 10: The portion of the second doped silicon dioxide layer without photoresist coverage is etched away using an inductively coupled plasma etching process, and the remaining portion forms the first waveguide 004, the second waveguide 005, and the third waveguide 006.

[0059] Step 11: Deposit silicon dioxide on the lower cladding, the first waveguide 004, the second waveguide 005 and the third waveguide 006 to form the upper cladding.

[0060] In this embodiment, considering that in the actual manufacturing process, when the lithography linewidth is large, the mask tip width cannot infinitely approach 0, the tip will actually be arc-shaped or square, and a step will be generated during etching, so the height of the sixth waveguide is not completely gradual to 0. Therefore, the groove shape is inconsistent with the required shape (tip) of the right end of the sixth waveguide. Therefore, in step 4, a corresponding margin space is preset for the groove to adapt to the existing lithography process and reduce the precision requirements of the existing lithography process. After depositing doped silicon dioxide, the doped silicon dioxide in the margin space is removed by chemical mechanical polishing to form the fourth waveguide 001, the fifth waveguide 002 and the sixth waveguide 003, so that the tip height of the sixth waveguide can transition to close to 0, ensuring the manufacturing precision of the sixth waveguide 003. Generally, the height of the margin reserved in the groove is the tip width * tanβ, where the tip width refers to the tip width of the formed mask, which is appropriately selected according to the actual lithography machine.

[0061] In this embodiment, the thickness H1 of the first waveguide 004 is 3.5 μm, the width W1 is 11.3 μm, the bottom length W of the left end face of the fourth waveguide 001 is 1.2 μm, the thickness H of the fourth waveguide 001 along the vertical direction is 5.4 μm, the distance L3 between the right end of the sixth waveguide 003 and the plane containing the right end face of the second waveguide 005 is 380 μm, the length L4 of the third waveguide 006 is 100 μm, the length L1 of the fifth waveguide 002 is 600 μm, the length L2 of the sixth waveguide 003 is 800 μm, the length L5 of the fourth waveguide 001 is 100 μm, and the angle β between the rear end face of the sixth waveguide 003 and the horizontal plane is 73.3°.

[0062] In this embodiment, when etching the lower cladding using inductively coupled plasma etching in step 4, the RF power is 1950W, the bias power is 220W, the etching gas is CF4, the protective gas is C4F8, the CF4 flow rate is 100sccm, and the C4F8 flow rate is 20sccm.

[0063] In this embodiment, when plasma-enhanced chemical vapor deposition is used to deposit doped silicon dioxide in the groove and on the upper cladding, not only is an integral structure of the fourth waveguide 001, the fifth waveguide 002 and the sixth waveguide 003 formed in the groove, but also the first doped silicon dioxide layer is formed on the upper cladding. Then, the first doped silicon dioxide layer is removed by chemical mechanical polishing, which can avoid the large stress introduced by the large area of ​​thick film during the formation of the second doped silicon dioxide layer, thus avoiding warping and cracking.

[0064] In this embodiment, electron microscope images of the grooves with different opening widths are shown below. Figure 11 As shown, the groove etching depth diagrams for different opening widths are as follows: Figure 12 As shown; Analysis Figure 11 and Figure 12 It is understood that the manufacturing method of the end face coupler of the present invention can form a groove that matches the overall structure of the fourth waveguide 001, the fifth waveguide 002 and the sixth waveguide 003 with high precision by tilting etching, without the need for additional operations.

[0065] To verify the performance of this invention, the end-face coupler was simulated using the finite-difference time-domain method. During the simulation, a single-mode fiber was used to connect to the end face of the end-face coupler. The dimensions of the end-face coupler are as follows: W = 1.2 μm, H = 5.4 μm, β = 73.3°, H1 = 3.5 μm, W1 = 11.3 μm, L1 = 600 μm, L2 = 800 μm, L3 = 380 μm, L4 = 100 μm, L5 = 100 μm. The end face of the end-face coupler of this invention is connected to the TE single-mode optical field input from the fiber. Figure 9 The light field distribution diagram of the YZ section is as follows Figure 13As shown; the end face of the end face coupler of the present invention along Figure 9 The light field distribution diagram of the XZ section is as follows Figure 14 As shown. Figure 13 and Figure 14 As can be seen, the end-face coupler of the present invention can achieve mode field broadening or shrinking in the width direction (along the front-to-back direction) and height direction (along the up-and-down direction), and can achieve a mode field of 10μm*8μm, which is close to the mode field of an optical fiber. By monitoring the TE single-mode component power at the right single-mode waveguide (third waveguide 006), the transmission spectrum simulation results of the end-face coupler of the present invention are shown in the figure below. Figure 15 As shown. Analysis Figure 15 It can be seen that the normalized loss of the end face coupler of the present invention is less than 0.29 dB / facet, and the coupling loss is low.

[0066] In summary, the end-face coupler of the present invention can extend the height of the end face coupling with the optical fiber to 5-7 μm, achieving a higher matching degree with the optical fiber mode field (approximately 6-9 μm), exhibiting lower coupling loss. Furthermore, its manufacturing method requires only two etching processes, simplifying the manufacturing process. Moreover, chemical mechanical polishing can be used to remove the excess portion formed within the grooves due to the wide linewidth during photolithography, resulting in the formation of the fourth, fifth, and sixth waveguides with high dimensional accuracy. This eliminates the need for high-precision photolithography during the deep groove etching process, significantly reducing costs. Therefore, the end-face coupler and its manufacturing method of the present invention not only combine low coupling loss and a simple manufacturing process but also offer low cost advantages, demonstrating significant effectiveness and broad application prospects.

Claims

1. An end-face coupler, comprising an upper cladding layer, a lower cladding layer, and a waveguide core layer, wherein the upper cladding layer is located above the lower cladding layer, and the waveguide core layer is disposed between and enclosed by the upper and lower cladding layers, the waveguide core layer comprising a first waveguide, a second waveguide, and a third waveguide, wherein the first, second, and third waveguides are all made of doped silicon dioxide, and the third waveguide is a single-mode waveguide; the first waveguide is used for coupling with an external optical fiber to access an optical signal transmitted through the external optical fiber into the end-face coupler; the second waveguide is used for evolving the mode field of the optical signal transmitted in the end-face coupler in a horizontal plane perpendicular to the optical signal transmission direction, so that the optical signal mode can match the third waveguide; and the third waveguide is used for outputting an optical signal to a downstream optical waveguide device, characterized in that... The waveguide core layer further includes a fourth waveguide, a fifth waveguide, and a sixth waveguide. The fourth, fifth, and sixth waveguides are all made of doped silicon dioxide. The fourth, fifth, and sixth waveguides are located below the first waveguide. The fourth waveguide extends the first waveguide, reducing mode field mismatch between the end-face coupler and the external optical fiber. The fifth and sixth waveguides evolve the optical signal transmitted in the end-face coupler along the vertical direction, causing the mode field of the optical signal to gradually concentrate and distribute in the first waveguide along the optical signal transmission direction. The fifth and sixth waveguides are formed by etching grooves in the lower cladding layer, followed by depositing doped silicon dioxide in the grooves and on the lower cladding layer and performing chemical mechanical polishing. After the fourth, fifth, and sixth waveguides are formed, the first, second, and third waveguides are formed by depositing doped silicon dioxide on the lower cladding layer, the fourth, fifth, and sixth waveguides to form a doped silicon dioxide layer. A portion of the doped silicon dioxide layer with the same shape as the first, second, and third waveguides is retained at the corresponding position, while the other portions are etched away.

2. The end-face coupler according to claim 1, characterized in that... The first waveguide is a cuboid structure. The thickness of the first waveguide is along the vertical direction, and the length is along the transmission direction of the optical signal in the end coupler. The length direction of the first waveguide is defined as the left-right direction, and the width direction of the first waveguide 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 second waveguide is an isosceles trapezoidal structure and is symmetrical about the first symmetry plane. The cross-section of the second waveguide along the horizontal plane is an isosceles trapezoid, with the lower base of the trapezoid located to the left of its upper base and extending in the front-back direction. The length of the second waveguide is along the left-right direction, the thickness is along the up-down direction, and the width is along the front-back direction. The upper end face of the second waveguide is on the same plane as the upper end face of the first waveguide, and the lower end face of the second waveguide is on the same plane as the lower end face of the first waveguide. The width of the left end of the second waveguide is equal to the width of the right end 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 completely overlap. The third waveguide is located to the right of the second waveguide. The third waveguide has a cuboid structure and is symmetrical about the first symmetry plane. The length of the third waveguide is along the left-right direction, the thickness is along the up-down direction, and the width is along the front-back direction. The upper end face of the third waveguide is on the same plane as the upper end face of the second waveguide, and the lower end face of the third waveguide is on the same plane as the lower end face of the second waveguide. The width of the third waveguide is equal to the width of the right end of the second waveguide. The left end face of the third waveguide is integrally formed with the right end face of the second waveguide and completely overlaps with it. The fourth waveguide is an isosceles trapezoidal structure, symmetrical about the first symmetry plane. The cross-section of the fourth waveguide along the vertical plane is an isosceles trapezoid, with the lower base of the trapezoid located above its upper base. Both bases extend in the front-to-back direction, and the length of the upper base is greater than the width of the first waveguide. The left end face of the fourth waveguide is on the same plane as the left end face of the first waveguide. The upper end face of the fourth waveguide is fixedly connected to the lower end face of the first waveguide and is in a fitted state. The length of the fourth waveguide is along the left-to-right direction. The fifth waveguide is located to the right of the fourth waveguide. The fifth waveguide has a trapezoidal gradient structure and is symmetrical about the first symmetry plane. It 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 sequentially in the directions of top, bottom, left, right, front, and rear. The upper end face of the fifth waveguide is an isosceles trapezoid, symmetrical about the first symmetry plane, with its lower base to the left of its upper base. The length of its lower base is equal to the length of the lower base of the right end face of the fourth waveguide, and its upper base is less than the width of the first waveguide. The lower end face of the fifth waveguide is an isosceles triangle, symmetrical about the first symmetry plane. The left end face of the fifth waveguide is an isosceles trapezoid, symmetrical about the first symmetry plane, with its upper base below its lower base. The right end face of the fifth waveguide is an isosceles triangle, and this isosceles triangle is symmetrical about the first symmetry plane. The front end face and rear end face of the fifth waveguide are both quadrilaterals, and the front end face and rear end face of the fifth waveguide are symmetrical about the first symmetry plane. The front end face of the fifth waveguide is on the same plane as the front end face of the fourth waveguide, the rear end face of the fifth waveguide is on the same plane as the rear end face of the fourth waveguide, the upper end face of the fifth waveguide is on the same plane as the upper end face of the fourth waveguide, the lower end face of the fifth waveguide is on the same plane as the lower end face of the fourth waveguide, the left end face of the fifth waveguide is integrally formed with the right end face of the fourth waveguide and completely overlaps, and the upper end face of the fifth waveguide is fixedly connected to the lower end face of the first waveguide and is in a fitted state. 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 sixth waveguide is located to the right of the fifth waveguide. The sixth waveguide has a triangular pyramidal structure and is symmetrical about the first plane of symmetry. It has an upper end face, a front end face, a rear end face, and a left end face, arranged in a top, front, rear, and left orientation and connected sequentially. The upper end face of the sixth waveguide is an isosceles triangle, symmetrical about the first plane of symmetry. The left end face of the sixth waveguide is also an isosceles triangle, symmetrical about the first plane of symmetry. Both the front and rear end faces of the sixth waveguide are triangular. The waveguide is symmetrical about the first symmetry plane. The upper end face of the sixth waveguide is on the same plane as the upper end face of the fifth waveguide. The upper end face of the sixth waveguide is fixedly connected to the lower end face of the first waveguide and is in a close fit. The front end face of the sixth waveguide is on the same plane as the front end face of the fifth waveguide. The rear end face of the sixth waveguide is on the same plane as the rear end face of the fifth waveguide. The left end face of the sixth waveguide is integrally formed with the right end face of the fifth waveguide and completely overlaps. The right end face of the sixth waveguide is on the same plane as the right end face of the first waveguide. The length of the sixth waveguide is along the left-right direction.

3. An end-face coupler according to claim 2, characterized in that... Both the upper cladding layer and the lower cladding layer are made of silicon dioxide, and the refractive index of the doped silicon dioxide is 0.45% to 2.5% higher than that of silicon dioxide.

4. An end-face coupler according to claim 2, characterized in that... The first waveguide has a thickness H1 = 3.5 μm and a width W1 = 11.3 μm. The fourth waveguide has a bottom length W = 1.2 μm on its left end face and a thickness H = 5.4 μm along the vertical direction. The second waveguide has a length L3 = 380 μm. The third waveguide has a length L4 = 100 μm. The fifth waveguide has a length L1 = 600 μm. The sixth waveguide has a length L2 = 800 μm. The fourth waveguide has a length L5 = 100 μm. The angle β between the rear end face of the sixth waveguide and the horizontal plane is 73.3°.

5. A method for manufacturing the end-face coupler according to any one of claims 1 to 4, characterized in that... Includes the following steps: Step 1: Prepare a quartz substrate as the lower cladding layer; Step 2: Coat the upper surface of the quartz substrate with photoresist, which completely covers the upper surface of the quartz substrate; Step 3: Using photolithography, a pattern consistent with the overall cross-section of the fourth waveguide, the fifth waveguide, and the sixth waveguide is prepared in the photoresist of Step 2, and the photoresist outside the pattern is removed by developing. Step 4: The lower cladding layer is etched using inductively coupled plasma etching (ICP-CED). During this process, the portion of the lower cladding layer not covered by photoresist is etched away, and a pre-defined groove is etched into the lower cladding layer. The inclination angle of the sidewall of the etched groove is equal to the angle β between the rear end face of the sixth waveguide and the horizontal plane. Step 5: Doped silicon dioxide is deposited in the groove and on the lower cladding layer using plasma-enhanced chemical vapor deposition (PECVD). The groove is filled with doped silicon dioxide, and the first doped silicon dioxide layer is formed on the lower cladding layer. Step 6: Perform chemical mechanical polishing from the first doped silicon dioxide layer downwards until a lower cladding layer of the preset thickness and the overall structure of the fourth waveguide, the fifth waveguide and the sixth waveguide are obtained; Step 7: Deposit doped silicon dioxide material on the lower cladding layer, the fourth waveguide, the fifth waveguide, and the sixth waveguide to form a second doped silicon dioxide layer; Step 8: Coat the upper surface of the second doped silicon dioxide layer with photoresist, which completely covers the upper surface of the second doped silicon dioxide layer; Step 9: Based on the structures of the first waveguide, the second waveguide, and the third waveguide, and the positional relationship between the first waveguide, the second waveguide, and the third waveguide and the fourth waveguide, the fifth waveguide, and the sixth waveguide, a pattern consistent with the overall structure formed by the first waveguide, the second waveguide, and the third waveguide is prepared in the photoresist of step 8 using photolithography, and the photoresist outside the pattern is removed using development. Step 10: The portion of the second doped silicon dioxide layer not covered by photoresist is etched away using an inductively coupled plasma etching process, and the remaining portion forms the first waveguide, the second waveguide, and the third waveguide. Step 11: Deposit silicon dioxide on the lower cladding, the first waveguide, the second waveguide, and the third waveguide to form an upper cladding.

6. A method for manufacturing an end-face coupler as described in claim 5, characterized in that... In step 4, when etching the lower cladding layer using inductively coupled plasma etching, the RF power is 1950W, the bias power is 220W, the etching gas is CF4, the protective gas is C4F8, the CF4 flow rate is 100sccm, and the C4F8 flow rate is 20sccm.

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