Silicon optical chip-optical fiber coupled spot-size conversion chip based on femtosecond laser processing and preparation method thereof

Abstract

The invention discloses a femtosecond laser processing-based silicon optical chip-optical fiber coupled spot-size conversion chip and a preparation method thereof, the femtosecond laser processing-based silicon optical chip-optical fiber coupled spot-size conversion chip comprises a silicon optical chip, a spot-size converter and an optical fiber array, one end of the spot-size converter is aligned with the optical fiber array, and the other end of the spot-size converter is aligned with the silicon optical chip; preparing a waveguide in the waveguide layer in the quartz glass by using a femtosecond laser direct writing system; grinding the end surfaces of the cladding, the waveguide layer and the optical fiber by using abrasive paper with different mesh numbers in sequence, polishing by using a polishing agent, immersing in a beaker filled with absolute ethyl alcohol for cleaning, and drying after cleaning; and placing on a platform with a 45-degree inclination angle, and controlling the three-axis displacement platform to enable the femtosecond laser focus to scan in an end face coupling area of the optical fiber and the first waveguide array according to a designed path so as to obtain the thickness and the cross section width of the waveguide. According to the invention, the silicon optical chip and the optical fiber array can realize spot-matched optical signal transmission, the performance is reliable and stable, and the industrialization development of the silicon optical technology can be realized.

Description

Technical Field

[0001] The present invention relates to the field of silicon photonic devices, and in particular to a silicon photonic chip-fiber coupled mode spot conversion chip based on femtosecond laser processing and a preparation method thereof. Background Art

[0002] With the continuous development of integrated circuits, traditional electronic integrated circuits are gradually reaching their limits in terms of bandwidth and energy consumption. As the integration of electronic circuits continues to increase, metal wires are becoming thinner and the spacing between wires is shrinking. On the one hand, this increases the resistance and ohmic losses of the wires, leading to increased system energy consumption. On the other hand, it increases the capacitance between the metal wires, causing increased crosstalk between the wires, which in turn affects the high-frequency performance of the chip.

[0003] Compared with electronic integrated circuits or electrical interconnection technologies, silicon photonic integrated circuits and optical interconnections exhibit lower transmission loss, wider transmission bandwidth, smaller time delay, and stronger resistance to electromagnetic interference.

[0004] Silicon photonic devices utilize the fundamental particles of light to perform various functions. They have a wide range of applications in optical communications, optical computing, optical sensing, and optical imaging. Currently, pure silicon photonic devices can be used as independent functional modules. However, because silicon photonics itself lacks the flexibility to control optical switches and cannot serve as storage units similar to microelectronic devices, pure silicon photonic devices cannot achieve complete information processing functions on their own and still require the assistance of electronic devices. Therefore, a perfect pure "silicon photonic chip" is still in the conceptual stage and has not yet formed a practical system. Strictly speaking, the current "silicon photonic chip" should refer to an optoelectronic fusion chip that integrates silicon photonic devices or silicon photonic functional units. There are still problems such as the inability to integrate light sources at high density and integrate low-loss, high-speed optoelectronic modulators.

[0005] In the field of semiconductor silicon photonics chip technology, the development of silicon photonics chips has become crucial for achieving high-speed, high-density optical communications and optical computing. However, the small mode spot size of silicon-based silicon photonics integrated chips poses challenges such as high insertion loss and high alignment accuracy when coupled with single-mode optical fibers, presenting a major bottleneck restricting the industrialization of silicon photonics. Effective coupling between optical fibers and silicon photonic chips has always been a challenging issue. The mode field mismatch between the optical fiber and the silicon photonic chip results in energy transmission losses, limiting the performance of optical communications and optical computing systems.

[0006] Traditional fabrication methods use grating couplers or diffraction gratings to couple optical fibers to silicon photonic chips, but these methods have several limitations. First, their fabrication process is complex and expensive, requiring sophisticated photolithography and etching techniques. Second, these methods lack the flexibility to adjust the mode spot size, making them unable to meet the mode field matching requirements of different application scenarios. Summary of the Invention

[0007] Based on the above phenomenon, the present invention proposes a mode spot conversion chip based on silicon photonic chip-fiber coupling processed by femtosecond laser and a preparation method thereof to improve the coupling of optical fiber to silicon photonic chip.

[0008] The technical solution adopted is: a silicon photonic chip-fiber coupled mode spot conversion chip based on femtosecond laser processing, including a silicon photonic chip, a mode spot converter and a fiber array. One end of the mode spot converter is aligned with the fiber array, and the other end is aligned with the silicon photonic chip.

[0009] The spot converter includes a substrate, a waveguide layer, and a cladding, with their port cross-sections aligned. The cladding is located above the substrate and wraps around the waveguide layer. The waveguide layer contains several waveguides fabricated by femtosecond laser direct writing, and several parallel waveguides form a waveguide array.

[0010] The waveguide includes a first waveguide, a second waveguide and a transition waveguide; one side of the transition waveguide is the first waveguide, and the other side is the second waveguide;

[0011] A plurality of parallel first waveguides form a first waveguide array; a plurality of parallel second waveguides form a second waveguide array;

[0012] The first waveguide array is optically coupled and aligned with the optical fiber array; specifically, the first waveguide is optically coupled and aligned with the optical fiber in the corresponding optical fiber array;

[0013] The second waveguide array is optically coupled to the silicon photonic chip; specifically, the second waveguide is optically coupled to the core layer of the corresponding silicon photonic chip.

[0014] Furthermore, the cross-sectional width of the first waveguide is smaller than the cross-sectional width of the second waveguide.

[0015] Furthermore, the cross-sectional width of the first waveguide is 2 μm; the cross-sectional width of the second waveguide is 9 μm.

[0016] Furthermore, the first waveguide and the second waveguide are connected by a transition waveguide whose cross-sectional width increases linearly from small to large; the cross-sectional width of the end of the transition waveguide with a small cross-sectional width is the same as the cross-sectional width of the first waveguide; the cross-sectional width of the end of the transition waveguide with a large cross-sectional width is the same as the cross-sectional width of the second waveguide.

[0017] Furthermore, under the premise of maintaining the same laser power and laser repetition frequency, a laser scanning speed of 3 mm / s was used to prepare the first waveguide, a laser scanning speed of 3 mm / s to 0.1 mm / s was used to prepare the transition waveguide, and a laser scanning speed of 0.1 mm / s was used to prepare the waveguide in the second waveguide array.

[0018] Furthermore, the optical fiber array includes a plurality of V-shaped grooves and optical fibers, one optical fiber is fixed in each V-shaped groove, and the cover plate fixes the plurality of optical fibers on the substrate.

[0019] Furthermore, each optical fiber of the optical fiber array corresponds to the first waveguide one-to-one, and each optical fiber is coupled to the corresponding first waveguide by femtosecond laser welding.

[0020] A method for preparing a silicon photonic chip-fiber coupled mode spot conversion chip based on femtosecond laser processing, the preparation steps are as follows:

[0021] Step 1: Using a femtosecond laser direct writing system, waveguides in the waveguide layer are prepared in quartz glass. Maintaining the same laser power and laser repetition rate, a laser scanning speed of 3 mm / s is used to prepare the waveguides in the first waveguide array, a laser scanning speed ranging from 0.1 mm / s to 3 mm / s is used to prepare the transition waveguides, and a laser scanning speed of 0.1 mm / s is used to prepare the waveguides in the second waveguide array.

[0022] Step 2: Use sandpaper of different mesh sizes to polish the cladding, waveguide layer, and end faces of the optical fibers in the optical fiber array, and polish them with a polishing agent. Then, immerse the cladding, waveguide layer, and end faces of the optical fibers in a beaker of anhydrous ethanol for cleaning and drying.

[0023] Step three: Place the cladding, waveguide layer, and end face of the optical fiber on a platform with a 40-50 degree inclination angle, control the three-axis displacement platform, and scan the femtosecond laser focus along the periphery of the optical fiber core layer and the end face coupling area of the first waveguide to obtain the thickness and cross-sectional width of the waveguide.

[0024] In step 1, the waveguides in the waveguide layer are spaced apart from each other by a distance h1 based on the center position; the optical fibers in the optical fiber array are spaced apart from each other by a distance h2 based on the center position; h1 = h2 = 128 μm.

[0025] In step 2, the cladding, waveguide layer and end faces of the optical fiber are polished using 100 mesh, 320 mesh, 800 mesh, 1000 mesh, 1500 mesh and 2000 mesh sandpaper in sequence, and the cladding, waveguide layer and end faces of the optical fiber are polished using 8000 mesh polishing agent.

[0026] The beneficial effects of the present invention are as follows: 1. The coupling method between the planar optical waveguide chip and the silicon photonic chip is planar evanescent wave coupling. It is only necessary to etch the cladding layers of the planar optical waveguide chip and the silicon photonic chip so that the waveguide structure on the silicon photonic chip can generate evanescent wave coupling with the planar optical waveguide chip to transmit optical signals. This method is simpler to operate than the cross-section coupling method and the grating coupling method, and does not require precise control of angles and cross-section alignment.

[0027] 2. The planar optical waveguide chip is transformed from a narrow-distance input waveguide to a wide-distance output waveguide, with the optical fiber array and the silicon photonic chip coupled at both ends respectively. The optical signal of the silicon photonic chip can be transmitted through the optical fiber for communication, thereby realizing optical signal transmission with mode matching between the silicon photonic chip and the optical fiber array.

[0028] 3. The coupling method between the silicon photonic chip and the planar optical waveguide chip is evanescent wave coupling, which is simple to operate. It only requires the planar optical waveguide chip to be directly attached to the waveguide surface of the silicon photonic chip. The contact area is large without increasing the size of the overall system. The performance is reliable and stable, and it can better realize the industrial development of silicon photonic technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of a mode spot conversion chip for silicon photonic chip-fiber coupling;

[0030] Figure 2 is a cross-sectional view of the present invention;

[0031] Figure 3 is the input light field mode spot intensity distribution diagram;

[0032] Figure 4 is the intensity distribution diagram of the output light field mode;

[0033] Figure 5 This is a top view of the waveguide in the mode spot conversion chip;

[0034] Figure 6 is a schematic cross-sectional view of the coupling between the optical fiber and the first waveguide;

[0035] Figure 7 Schematic diagram of the placement of the silicon photonic chip-fiber coupled mode conversion chip during femtosecond laser direct writing;

[0036] Figure 8 Schematic diagram of the femtosecond laser direct writing system. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is described in detail below. The embodiments of the present invention are only for illustrating a specific structure, and the scale of the structure is not limited by the embodiments.

[0038] like Figures 1 to 8 As shown, a pattern spot conversion chip based on femtosecond laser processing of silicon photonic chip-fiber coupling includes a silicon photonic chip 1, a pattern spot converter 2 and a fiber array 3. One end of the pattern spot converter 2 is aligned with the fiber array, and the other end is aligned with the silicon photonic chip.

[0039] The pattern converter 2 includes a substrate 21, a waveguide layer 22, and a cladding layer 23, the port cross sections of which are aligned. The cladding layer 23 is located above the substrate 21 and wraps around the waveguide layer 22. The waveguide layer 22 contains a plurality of waveguides 4 prepared by femtosecond laser direct writing, and the plurality of parallel waveguides 4 form a waveguide array.

[0040] The waveguide 4 includes a first waveguide 41, a second waveguide 42 and a transition waveguide 43; one side of the transition waveguide 43 is the first waveguide 41, and the other side is the second waveguide 42;

[0041] A plurality of parallel first waveguides form a first waveguide array; a plurality of parallel second waveguides form a second waveguide array;

[0042] The first waveguide array is optically coupled and aligned with the optical fiber array 3; the first waveguide 41 is optically coupled and aligned with the optical fiber 31 in the corresponding optical fiber array;

[0043] The second waveguide array is optically coupled to the silicon photonic chip; the second waveguide 42 is optically coupled to the core layer 11 of the corresponding silicon photonic chip 1 .

[0044] The cross-sectional width of the first waveguide 41 is 2 μm; the cross-sectional width of the second waveguide 42 is 9 μm. The first and second waveguides 41 and 42 are connected by a transition waveguide 43 whose cross-sectional width increases linearly from small to large. The cross-sectional width of the end of the transition waveguide 43 with the smaller cross-sectional width is the same as the cross-sectional width of the first waveguide 41; the cross-sectional width of the end of the transition waveguide 43 with the larger cross-sectional width is the same as the cross-sectional width of the second waveguide 42.

[0045] Under the premise of maintaining the same laser power and laser repetition frequency, a laser scanning speed of 3 mm / s was used to prepare the first waveguide, a laser scanning speed of 3 mm / s to 0.1 mm / s was used to prepare the transition waveguide, and a laser scanning speed of 0.1 mm / s was used to prepare the waveguide in the second waveguide array.

[0046] The optical fiber array 3 includes a plurality of V-shaped grooves 32 and optical fibers 31 . An optical fiber is fixed in each V-shaped groove, and the cover plate fixes the multiple optical fibers on the substrate.

[0047] Each optical fiber 31 of the optical fiber array corresponds to a first waveguide 41 one by one, and each optical fiber is coupled to the corresponding first waveguide by femtosecond laser welding.

[0048] A method for preparing a silicon photonic chip-fiber coupled mode spot conversion chip based on femtosecond laser processing, the preparation steps are as follows:

[0049] Step 1: Use a femtosecond laser direct writing system to prepare waveguides in the waveguide layer in quartz glass. Maintaining the same laser power and laser repetition rate, use a laser scanning speed of 3 mm / s to prepare the waveguides in the first waveguide array, use a laser scanning speed ranging from 3 mm / s to 0.1 mm / s to prepare the transition waveguides, and use a laser scanning speed of 0.1 mm / s to prepare the waveguides in the second waveguide array. The waveguides in the waveguide layer are spaced apart by a distance h1 relative to their center positions. The optical fibers in the optical fiber array are spaced apart by a distance h2 relative to their center positions; h1 = h2 = 128 μm.

[0050] Step 2: Use 100 mesh, 320 mesh, 800 mesh, 1000 mesh, 1500 mesh, and 2000 mesh sandpaper to polish the cladding, waveguide layer, and end face of the optical fiber. Use 8000 mesh polishing agent to polish the cladding, waveguide layer, and end face of the optical fiber. Then, immerse the cladding, waveguide layer, and end face of the optical fiber in a beaker of anhydrous ethanol for cleaning and dry them after cleaning.

[0051] Step 3: Place the cladding, waveguide layer and end face of the optical fiber on a platform with a 45-degree inclination. Figure 7 As shown, the three-axis displacement platform is controlled as Figure 8 As shown, the focus of the femtosecond laser is scanned along the outer circumference of the optical fiber core layer and the end face coupling area of the first waveguide array to obtain the thickness and cross-sectional width of the waveguide.

[0052] Regarding the optical fiber array, specifically, the optical fiber array consists of several V-shaped grooves with cover plates and optical fibers. One optical fiber is fixed in the V-shaped groove, and the cover plate fixes multiple optical fibers on the substrate. In addition, each optical fiber of the optical fiber array corresponds one-to-one to a waveguide of the first waveguide array, and each optical fiber is coupled to the corresponding waveguide by femtosecond laser welding.

[0053] like Figure 3 and Figure 4 As shown in the figure, it shows a simulation example of the mode fields at the input and output ends of a femtosecond laser-written silicon photonic chip-to-fiber coupled mode conversion chip. The mode field is transformed after light enters the silicon photonic chip-to-fiber coupled mode conversion chip from a specific mode field. Within the mode conversion chip, the light first passes through the first waveguide, which serves as the input waveguide. Subsequently, the light enters the transition waveguide, whose width linearly changes from narrow to wide, causing its mode field to transform. After the mode field is adjusted, the light's mode field has been optimized to match the target waveguide. The light is output from the output end of the mode converter and enters the target waveguide. The core of the entire process lies in the fact that by precisely adjusting the geometric parameters of the waveguide, the light's mode field can smoothly transition from a larger state to a smaller state, thereby achieving efficient optical coupling.

Claims

1. A silicon photonic chip-fiber coupled mode spot conversion chip based on femtosecond laser processing, characterized in that It includes a silicon photonic chip, a spot converter and an optical fiber array, one end of the spot converter is aligned with the optical fiber array, and the other end is aligned with the silicon photonic chip; wherein, The pattern spot converter comprises a substrate, a waveguide layer and a cladding, the port cross sections of the three being aligned; the cladding is located above the substrate and wraps around the waveguide layer; the waveguide layer contains a plurality of waveguides prepared by femtosecond laser direct writing, and the plurality of parallel waveguides form a waveguide array; The waveguide includes a first waveguide, a second waveguide and a transition waveguide; one side of the transition waveguide is the first waveguide, and the other side is the second waveguide; A plurality of parallel first waveguides form a first waveguide array; a plurality of parallel second waveguides form a second waveguide array; The first waveguide array is optically coupled and aligned with the optical fiber array; specifically, the first waveguide is optically coupled and aligned with the optical fiber in the corresponding optical fiber array; The second waveguide array is optically coupled to the silicon photonic chip; specifically, the second waveguide is optically coupled to the core layer of the corresponding silicon photonic chip.

2. The silicon photonic chip-fiber coupled mode spot conversion chip based on femtosecond laser processing according to claim 1 is characterized in that The cross-sectional width of the first waveguide is smaller than the cross-sectional width of the second waveguide.

3. The silicon photonic chip-fiber coupled mode spot conversion chip based on femtosecond laser processing according to claim 1, characterized in that The cross-sectional width of the first waveguide is 2 μm; the cross-sectional width of the second waveguide is 9 μm.

4. The silicon photonic chip-fiber coupled mode spot conversion chip based on femtosecond laser processing according to claim 1, characterized in that The first waveguide and the second waveguide are connected by a transition waveguide whose cross-sectional width increases linearly from small to large. The cross-sectional width of the end of the transition waveguide with a small cross-sectional width is the same as the cross-sectional width of the first waveguide; the cross-sectional width of the end of the transition waveguide with a large cross-sectional width is the same as the cross-sectional width of the second waveguide.

5. A silicon photonic chip-fiber coupled mode spot conversion chip based on femtosecond laser processing according to claim 1 or 4, characterized in that Under the premise of maintaining the same laser power and laser repetition frequency, a laser scanning speed of 3 mm / s was used to prepare the first waveguide, a laser scanning speed of 3 mm / s to 0.1 mm / s was used to prepare the transition waveguide, and a laser scanning speed of 0.1 mm / s was used to prepare the waveguide in the second waveguide array.

6. The silicon photonic chip-fiber coupled mode spot conversion chip based on femtosecond laser processing according to claim 1, characterized in that The optical fiber array comprises a plurality of V-shaped grooves and optical fibers, one optical fiber is fixed in each V-shaped groove, and the cover plate fixes the plurality of optical fibers on the base.

7. The silicon photonic chip-fiber coupled mode spot conversion chip based on femtosecond laser processing according to claim 1, characterized in that Each optical fiber of the optical fiber array corresponds to a first waveguide one by one, and each optical fiber is coupled to the corresponding first waveguide by femtosecond laser welding.

8. A method for preparing a spot conversion chip for a silicon photonic chip-fiber coupling based on femtosecond laser processing, using a spot conversion chip for a silicon photonic chip-fiber coupling based on femtosecond laser processing as described in claims 1-7, characterized in that The preparation steps are as follows: Step 1: Using a femtosecond laser direct writing system, waveguides in the waveguide layer are prepared in quartz glass. Maintaining the same laser power and laser repetition rate, a laser scanning speed of 3 mm / s is used to prepare the waveguides in the first waveguide array, a laser scanning speed ranging from 3 mm / s to 0.1 mm / s is used to prepare the transition waveguides, and a laser scanning speed of 0.1 mm / s is used to prepare the waveguides in the second waveguide array. Step 2: Use sandpaper of different mesh sizes to polish the cladding, waveguide layer, and end faces of the optical fibers in the optical fiber array, and polish them with a polishing agent. Then, immerse the cladding, waveguide layer, and end faces of the optical fibers in a beaker of anhydrous ethanol for cleaning and drying. Step three: Place the cladding, waveguide layer, and end face of the optical fiber on a platform with a 40-50 degree inclination angle, control the three-axis displacement platform, and scan the femtosecond laser focus along the periphery of the optical fiber core layer and the end face coupling area of the first waveguide to obtain the thickness and cross-sectional width of the waveguide.

9. The method for preparing a silicon photonic chip-fiber coupled mode spot conversion chip based on femtosecond laser processing according to claim 8, characterized in that In the step 1, the waveguides in the waveguide layer are spaced apart from each other by a distance h1 based on the center position; the optical fibers in the optical fiber array are spaced apart from each other by a distance h2 based on the center position; h1 = h2 = 128 μm.

10. The method for preparing a silicon photonic chip-fiber coupled mode spot conversion chip based on femtosecond laser processing according to claim 8, characterized in that In the step 2, the cladding, waveguide layer and end faces of the optical fiber are polished using 100 mesh, 320 mesh, 800 mesh, 1000 mesh, 1500 mesh and 2000 mesh sandpaper in sequence, and the cladding, waveguide layer and end faces of the optical fiber are polished using 8000 mesh polishing agent.

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