Mode spot conversion chip for photon chip-optical fiber coupling and preparation method thereof

Abstract

The invention relates to the field of photonic devices, and discloses a spot-size conversion chip for photonic chip-optical fiber coupling, which comprises a substrate, a waveguide layer, a cladding, and a first waveguide array and a second waveguide array which are respectively arranged at two ends of the cladding, the cladding is positioned above the substrate and wraps the waveguide layer, and port sections of the cladding, the waveguide layer and the cladding are aligned; the waveguide layer comprises a plurality of waveguides prepared by femtosecond laser direct writing; the first waveguide array is matched with an optical fiber array, and optical coupling alignment is carried out on the first waveguide array and optical fibers in the optical fiber array; the second waveguide array is matched with a photon chip, and the waveguide in the second waveguide array is optically coupled with the waveguide in the photon chip. According to the invention, only the cladding layers of the planar optical waveguide chip and the silicon optical chip need to be etched, so that the waveguide structure on the silicon optical chip and the planar optical waveguide chip can generate evanescent wave coupling for optical signal transmission, and the mode is simpler and more convenient to operate than a section coupling mode and a grating coupling mode; and accurate angle control and section alignment are not needed.

Description

Technical Field

[0001] The present invention belongs to the field of photonic devices, and in particular relates to a mode spot conversion chip for photonic chip-fiber coupling 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 technology, photonic integrated circuits and optical interconnection exhibit lower transmission loss, wider transmission bandwidth, smaller time delay, and stronger anti-electromagnetic interference capability.

[0004] Photonic devices are devices that use the elementary 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 photonic devices can be used as independent functional modules. However, because photons themselves are difficult to flexibly control optical switches and cannot serve as storage units similar to microelectronic devices, pure photonic devices cannot achieve complete information processing functions on their own and still require the help of electronic devices. Therefore, the perfect pure "photonic chip" is still in the conceptual stage and has not yet formed a practical system. Strictly speaking, the current "photonic chip" should refer to an optoelectronic fusion chip that integrates photonic devices or 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 photonic chip technology, the development of photonic chips has become crucial for achieving high-speed, high-density optical communications and optical computing. However, the small mode spot size of silicon-based photonic integrated chips poses challenges in coupling with single-mode optical fibers, such as high insertion loss and high alignment accuracy. This is one of the major bottlenecks restricting the industrialization of silicon photonics. Effective coupling between optical fibers and photonic chips has always been a challenging problem. The mode field mismatch between the optical fiber and the photonic chip results in energy transmission losses, limiting the performance of optical communication and optical computing systems.

[0006] Traditional fabrication methods use grating couplers or diffraction gratings to achieve fiber-to-chip coupling, 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] Technical problem to be solved: How to improve the coupling of optical fiber to photonic chip.

[0008] Technical solution:

[0009] On the one hand, the present invention provides a spot conversion chip for photonic chip-fiber coupling, comprising: a substrate, a waveguide layer, a cladding, and a first waveguide array and a second waveguide array arranged at both ends thereof, wherein: the cladding is located above the substrate, wrapping the waveguide layer, and the port cross-sections of the three are aligned; the waveguide layer contains multiple waveguides prepared by femtosecond laser direct writing; the first waveguide array is matched with an optical fiber array, which is optically coupled and aligned with the optical fibers in the optical fiber array; the second waveguide array is matched with a photonic chip, and the waveguides therein are optically coupled with the waveguides in the photonic chip.

[0010] Furthermore, the cross-sectional width of the waveguides of the first waveguide array is smaller than the cross-sectional width of the waveguides of the second waveguide array.

[0011] Furthermore, the waveguides of the first waveguide array are connected to the waveguides of the corresponding second waveguide array 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 waveguide of the first waveguide array, and 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 waveguide of the second waveguide array.

[0012] Furthermore, under the premise of maintaining the same laser power and laser repetition frequency, a higher laser scanning speed is used to prepare the waveguides in the first waveguide array, a laser scanning speed that changes from high linearity to low is used to prepare the transition waveguides, and a lower laser scanning speed is used to prepare the waveguides in the second waveguide array.

[0013] Furthermore, the optical fiber array is composed of a cover plate with a V-shaped groove and optical fibers. One optical fiber is fixed in the V-shaped groove, and the cover plate fixes multiple optical fibers on the substrate.

[0014] Furthermore, each optical fiber of the optical fiber array corresponds one-to-one to a waveguide of the second waveguide array, and each optical fiber is coupled to the corresponding waveguide by femtosecond laser welding.

[0015] On the other hand, the present invention provides a method for preparing a spot conversion chip for photonic chip-fiber coupling, which includes the following steps: step 1, using a femtosecond laser direct writing system to prepare waveguides in a waveguide layer in quartz glass, maintaining the same laser power and laser repetition frequency, using a higher laser scanning speed to prepare the waveguides in the first waveguide array, using a laser scanning speed that changes from high linearity to low to prepare the transition waveguides, and using a lower laser scanning speed to prepare the waveguides in the second waveguide array; step 2, using sandpaper of different mesh sizes to polish the end faces of the cladding, waveguide layer and optical fiber, and polishing with a polishing agent, then immersing the cladding, waveguide layer and end face of the optical fiber in a beaker of anhydrous ethanol for cleaning, and drying them after cleaning; step 3, placing the cladding, waveguide layer and end face of the optical fiber on an inclined platform, controlling the three-axis displacement platform so that the femtosecond laser focus scans the end face coupling area between the optical fiber and the second waveguide array according to the designed path to obtain the thickness and cross-sectional width of the waveguide.

[0016] Furthermore, in step 1, all waveguides in the waveguide layer are spaced apart from each other by a distance of 127 μm from the center position of the optical fiber in the optical fiber array based on the center position.

[0017] Technical effects:

[0018] 1. The coupling method between the planar optical waveguide chip and the silicon photonic chip is planar evanescent wave coupling. It only requires etching 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.

[0019] 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.

[0020] 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

[0021] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0022] Figure 1Schematic diagram of a mode spot conversion chip for photonic chip-fiber coupling;

[0023] Figure 2 Schematic diagram of cladding and waveguide layer;

[0024] Figure 3 is the input light field mode spot intensity distribution diagram;

[0025] Figure 4 is the intensity distribution diagram of the output light field mode;

[0026] Figure 5 This is a top view of the waveguide in the mode spot conversion chip;

[0027] Figure 6 is a schematic cross-sectional view of the waveguide coupling portion between the optical fiber and the second waveguide array;

[0028] Figure 7 Schematic diagram of the placement of the spot conversion chip for photonic chip-fiber coupling during femtosecond laser direct writing;

[0029] Figure 8 Schematic diagram of the femtosecond laser direct writing system. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0031] The mode spot conversion chip for photonic chip-fiber coupling provided in this embodiment is as follows: Figure 1-8 Shown, including:

[0032] A substrate, a waveguide layer, a cladding, and a first waveguide array and a second waveguide array at both ends thereof, wherein:

[0033] First, the cladding is located above the substrate, which wraps around the waveguide layer. The waveguide layer contains multiple waveguides prepared by femtosecond laser direct writing, and the port cross-sections of the three are aligned.

[0034] Second, the first waveguide array is matched with an optical fiber array, which is optically coupled and aligned with the optical fibers in the optical fiber array; the second waveguide array is matched with a photonic chip, and the waveguides therein are optically coupled with the waveguides in the photonic chip. Furthermore, the cross-sectional width of the waveguides in the first waveguide array is smaller than the cross-sectional width of the waveguides in the second waveguide array. Furthermore, the waveguides in the first waveguide array are connected to the waveguides in the corresponding second waveguide array by a transition waveguide whose cross-sectional width increases linearly from small to large. The cross-sectional width of the transition waveguide at the end with the smaller cross-sectional width is the same as the cross-sectional width of the waveguides in the first waveguide array, and the cross-sectional width of the end with the larger cross-sectional width is the same as the cross-sectional width of the waveguides in the second waveguide array. Specifically, for the first waveguide array, the second waveguide array, and the transition waveguide, while maintaining the same laser power and laser repetition frequency, a higher laser scanning speed is used to prepare the waveguides in the first waveguide array, a laser scanning speed that decreases linearly from high to low is used to prepare the transition waveguides, and a lower laser scanning speed is used to prepare the waveguides in the second waveguide array.

[0035] In addition, regarding the optical fiber array, specifically, the optical fiber array consists of a cover plate with a V-shaped groove and an optical fiber. One optical fiber is fixed in the V-shaped groove, and the cover plate fixes multiple optical fibers on the substrate. Moreover, each optical fiber of the optical fiber array corresponds one-to-one to a waveguide of the second waveguide array, and each optical fiber is coupled to the corresponding waveguide by femtosecond laser welding.

[0036] The method for preparing a spot conversion chip for photonic chip-fiber coupling provided in this embodiment includes the following steps:

[0037] 1. Femtosecond laser direct writing system Figure 8 As shown, it is prepared in quartz glass Figure 2 The waveguides in the waveguide layer shown. Maintaining the same laser power and laser repetition rate, the waveguides in the first waveguide array were fabricated using a higher laser scanning speed, the transition waveguides were fabricated using a laser scanning speed that shifted from high linearity to lower speed, and the waveguides in the second waveguide array were fabricated using a lower laser scanning speed. All waveguides in the waveguide layer were spaced 127 μm apart from each other, based on their center positions. The spacing between the centers of the optical fibers in the optical fiber array is 127 μm.

[0038] Second, use 100-, 320-, 800-, 1000-, 1500-, and 2000-grit sandpaper to polish the cladding, waveguide, and fiber end faces. Use 8000-grit polishing compound to polish the cladding, waveguide, and fiber end faces. Submerge the cladding, waveguide, and fiber end faces in a beaker of anhydrous ethanol. Clean the sample using an ultrasonic cleaner for 15 minutes. Dry the sample after cleaning.

[0039] Third, the cladding, waveguide layer and end face of the optical fiber are as follows Figure 7Place it on an inclined platform as shown, and control it as Figure 8 The three-axis displacement platform shown in the figure makes the focus of the femtosecond laser move as shown in the figure. Figure 6 The path shown scans the end-face coupling region between the optical fiber and the second waveguide array. The results show that all waveguides are 5 μm thick, the cross-sectional width of the waveguides in the second waveguide array, which serve as output waveguides, is 9 μm, the cross-sectional width of the transition waveguide, which linearly narrows from wide to narrow, is 9 μm at the widest end and 2 μm at the narrowest end, and the cross-sectional width of the waveguides in the first waveguide array, which serve as input waveguides, is 2 μm. The input light wavelength is 1.25 μm to 1.65 μm.

[0040] like Figure 2 and Figure 3 Figure 2 shows a simulation example of the input and output mode fields of a photonic chip-to-fiber coupled spot conversion chip using femtosecond laser direct writing. The spot conversion process occurs when light enters the photonic chip-to-fiber coupled spot conversion chip from a specific mode field. Within the spot conversion chip, the light first passes through a straight waveguide, which serves as the input waveguide. Subsequently, the light enters a transition waveguide, whose width linearly changes from narrow to wide, causing its mode field to shift. After mode field adjustment, the light's mode field is optimized to match the target waveguide. Light is output from the output of the spot converter and enters the target fiber. The core of this process lies in precisely adjusting the waveguide's geometric parameters to enable the light's mode field to smoothly transition from a larger state to a smaller state, thereby achieving efficient optical coupling.

[0041] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0042] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A mode spot conversion chip for photonic chip-fiber coupling, characterized in that: include: A substrate, a waveguide layer, a cladding, and a first waveguide array and a second waveguide array at both ends thereof, wherein: The cladding is located above the substrate, wrapping around the waveguide layer, and the port cross sections of the three are aligned; The waveguide layer contains multiple waveguides prepared by femtosecond laser direct writing; The first waveguide array is matched with an optical fiber array and is optically coupled and aligned with the optical fibers in the optical fiber array; The second waveguide array is matched with the photonic chip, and the waveguides therein are optically coupled with the waveguides in the photonic chip.

2. The mode spot conversion chip for photonic chip-fiber coupling according to claim 1, characterized in that: The cross-sectional width of the waveguides of the first waveguide array is smaller than the cross-sectional width of the waveguides of the second waveguide array.

3. The mode spot conversion chip for photonic chip-fiber coupling according to claim 1, characterized in that: The waveguides of the first waveguide array are connected to the waveguides of the corresponding second waveguide array 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 waveguide of the first waveguide array, and 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 waveguide of the second waveguide array.

4. The mode spot conversion chip for photonic chip-fiber coupling according to claim 1, characterized in that: Under the premise of maintaining the same laser power and laser repetition frequency, a higher laser scanning speed is used to prepare the waveguides in the first waveguide array, a laser scanning speed that changes from high linearity to low is used to prepare the transition waveguide, and a lower laser scanning speed is used to prepare the waveguides in the second waveguide array.

5. The mode spot conversion chip for photonic chip-fiber coupling according to claim 1, characterized in that: The optical fiber array consists of a cover plate with a V-shaped groove and optical fibers. One optical fiber is fixed in the V-shaped groove, and the cover plate fixes multiple optical fibers on the substrate.

6. The mode spot conversion chip for photonic chip-fiber coupling according to claim 5, characterized in that: Each optical fiber of the optical fiber array corresponds one-to-one to a waveguide of the second waveguide array, and each optical fiber is coupled to the corresponding waveguide by femtosecond laser welding.

7. The method for preparing a mode spot conversion chip for photonic chip-fiber coupling according to any one of claims 1 to 6, characterized in that: The method comprises the following steps: Step 1: Using a femtosecond laser direct writing system to prepare waveguides in a waveguide layer in quartz glass, while maintaining the same laser power and laser repetition frequency, a higher laser scanning speed is used to prepare the waveguides in the first waveguide array, a laser scanning speed that is changed from high linearity to low is used to prepare the transition waveguides, and a lower laser scanning speed 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 fiber, and polish them with a polishing agent. Then, immerse the cladding, waveguide layer, and end faces of the optical fiber in a beaker of anhydrous ethanol to clean them and dry them after cleaning. Step three: Place the cladding, waveguide layer, and end face of the optical fiber on an angled platform, and control the three-axis displacement platform so that the focus of the femtosecond laser scans the end face coupling area between the optical fiber and the second waveguide array along the designed path to obtain the thickness and cross-sectional width of the waveguide.

8. The method for preparing a spot conversion chip for photonic chip-fiber coupling according to claim 7, characterized in that: In step 1, all waveguides in the waveguide layer are spaced apart from each other with their center positions as a reference, and the spacing between the center positions of the optical fibers in the optical fiber array is 127 μm.

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