Photoelectric integrated chip with efficient mode spot conversion

Abstract

The application provides a photoelectric integrated chip with efficient mode spot conversion, comprising a silicon substrate, a laser chip, a mode spot converter and a photoelectric modulation module, the laser chip is flip-chip arranged on the top surface of the silicon substrate, the mode spot converter comprises an outer cladding layer, an upper waveguide layer and a lower waveguide layer, the upper waveguide layer comprises a plurality of parallel ridge waveguides, a tapered waveguide and a connecting waveguide, the plurality of ridge waveguides are connected between the chip optical waveguide and the wide end of the tapered waveguide, the connecting waveguide is connected between the narrow end of the tapered waveguide and the photoelectric modulation module, the lower waveguide layer is arranged in a tapered shape, the lower waveguide layer is located below the plurality of ridge waveguides, and the outer cladding layer surrounds the outer periphery of the upper waveguide layer and the lower waveguide layer. The mode field of the laser chip or the mode field of the photoelectric modulation module is converted through the mode spot converter, so that the mode spot converter structure has good matching and high coupling efficiency is obtained.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optoelectronic integrated chip, and particularly relates to an optoelectronic integrated chip with efficient mode spot conversion. BACKGROUND

[0002] Lithium niobate material is widely used in the field of electro-optic modulation due to its superior electro-optic coefficient. In order to solve the problems of large size and power consumption, low integration and high manufacturing cost of traditional bulk lithium niobate electro-optic modulator, electro-optic devices based on lithium niobate thin film have attracted more and more attention. However, since lithium niobate material cannot be directly used for light source preparation, the current integrated optoelectronic modulation system still uses an external III-V material laser chip as a light source. The mainstream of on-chip integration of active modules based on thin film lithium niobate includes flip-chip based on end-face butt coupling, micro-transfer printing and wafer bonding. Among them, micro-transfer printing and wafer bonding both involve processing the structure of the laser chip, which provides a high threshold for manufacturers without active device technology accumulation and certification. Further, the current wafer bonding-based method can only achieve an on-chip output power of less than 2mW, which cannot meet the power requirements of actual applications in the short term. In contrast, the flip-chip based on end-face butt coupling integrates high-power laser chips that have been tested for stability, which is an effective way to meet the current industrial demand. This process can reduce the precision requirements of the flip-chip equipment to a certain extent by designing a suitable mode spot conversion structure.

[0003] In order to realize the flip-chip on-chip integration of active laser chips, the light output height of the laser chip needs to be strictly aligned with the light output height of the lithium niobate thin film waveguide. This requires the area where the laser chip is placed to be etched to the silicon substrate layer below the lithium niobate thin film. However, all current dry etching processes cannot achieve high-precision processing of lithium niobate material, and mechanical processing cannot achieve such high-precision accurate processing. Therefore, considering the large inclination of 60-70° of the etched lithium niobate material, the laser chip cannot be placed close to the lithium niobate waveguide structure, and the high reflection of the large inclination leads to very low coupling efficiency. Based on the above difficulties, it is particularly important to design related structures suitable for flip-chip on-chip integration of thin film lithium niobate material and efficient mode spot conversion devices for device integration. SUMMARY

[0004] The purpose of the present application is to provide an optoelectronic integrated chip with efficient mode spot conversion.

[0005] In order to achieve the object of the present application, the present application provides a photoelectric integrated chip with efficient mode spot conversion, comprising a silicon substrate, a laser chip, a mode spot converter and a photoelectric modulation module, the laser chip, the mode spot converter and the photoelectric modulation module are arranged on the silicon substrate along the light path direction, and the mode spot converter is connected between the laser chip and the photoelectric modulation module; the laser chip comprises a chip substrate and a chip optical waveguide, the chip optical waveguide is arranged on the bottom surface of the chip substrate, the laser chip is flip-chip arranged on the top surface of the silicon substrate, and the chip optical waveguide is located between the chip substrate and the silicon substrate; the mode spot converter comprises an outer cladding layer, an upper waveguide layer and a lower waveguide layer, the upper waveguide layer comprises a plurality of parallel ridge waveguides, a tapered waveguide and a connecting waveguide, the plurality of ridge waveguides are connected between the chip optical waveguide and the wide end of the tapered waveguide, the connecting waveguide is connected between the narrow end of the tapered waveguide and the photoelectric modulation module, the lower waveguide layer is arranged in a tapered shape, the lower waveguide layer is located below the plurality of ridge waveguides, and the outer cladding layer surrounds the outer periphery of the upper waveguide layer and the lower waveguide layer.

[0006] Further, the ridge waveguides are arranged in a tapered shape, the wide end of the ridge waveguide is connected with the chip optical waveguide, and the narrow end of the ridge waveguide is connected with the wide end of the tapered waveguide.

[0007] Further, the height of the lower waveguide layer at the wide end is greater than the height of the lower waveguide layer at the narrow end.

[0008] Further, the width of the lower waveguide layer at the wide end is greater than the distance between the outermost two ridge waveguides.

[0009] Further, the distance between the upper waveguide layer and the lower waveguide layer in the height direction is between 200nm and 800nm.

[0010] Further, the photoelectric modulation module comprises a single-mode waveguide and a modulation electrode, the single-mode waveguide and the modulation electrode are arranged on the silicon substrate, and the single-mode waveguide is connected with the connecting waveguide.

[0011] Further, the two side angles of the single-mode waveguide are between 60° and 70°, and the two side angles of the narrow end of the tapered waveguide are between 50° and 70°.

[0012] Further, the chip substrate further comprises a chip electrode arranged on the bottom surface, the silicon substrate further comprises a metal connecting layer arranged on the top surface, and the chip electrode is connected with the metal connecting layer.

[0013] Further, the top surface of the silicon substrate is provided with a height limiting structure, and the chip substrate is connected with the height limiting structure.

[0014] The beneficial effect of the present application is that by means of the flip of the laser chip, in combination with the cladding surrounding the outer periphery of the upper waveguide layer and the lower waveguide layer, and the waveguide structure of the upper waveguide layer and the lower waveguide layer, and then connecting the photoelectric modulation module with the mode spot converter, the conversion of the mode field of the laser chip or the mode field of the photoelectric modulation module is realized through the mode spot converter, the gradual change of the taper and size makes the mode spot converter structure have good matching and obtain high coupling efficiency, and through the spacing arrangement of the upper and lower waveguide layers, the freedom of adjusting the spacing can provide better optimization conditions for different types of outgoing light spots to improve the coupling efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 is a plan view of the optical-electric integrated chip embodiment of the present application.

[0016] Figure 2 is a structural view of the optical-electric integrated chip embodiment of the present application.

[0017] Figure 3 is a flip view of the laser chip in the optical-electric integrated chip embodiment of the present application.

[0018] Figure 4 is a structural view of the mode spot converter in the optical-electric integrated chip embodiment of the present application.

[0019] Figure 5 is an electric field distribution view of the mode spot converter in the optical-electric integrated chip embodiment of the present application.

[0020] Figure 6 is a manufacturing flow view of the optical-electric integrated chip embodiment of the present application.

[0021] Figure 7 is a coupling loss view of the optical-electric integrated chip embodiment of the present application under different butt joint position deviations.

[0022] Figure 8 is an electric field distribution view of the mode spot converter in another optical-electric integrated chip embodiment of the present application.

[0023] The present application will be further described below in combination with the drawings and embodiments. DETAILED DESCRIPTION

[0024] REFERENCE Figures 1 to 4 The optical-electric integrated chip comprises a silicon substrate 101, a laser chip 110, a mode spot converter 120 and a photoelectric modulation module 130, the laser chip 110, the mode spot converter 120 and the photoelectric modulation module 130 are arranged on the silicon substrate 101 along the light path direction X, and the mode spot converter 120 is connected between the laser chip 110 and the photoelectric modulation module 130.

[0025] Specifically, the laser chip 110 includes a chip substrate 113 and a chip optical waveguide 111, the chip optical waveguide 111 is arranged on the bottom surface of the chip substrate 113, two chip electrodes 112 are also arranged on the bottom surface of the chip substrate 113, the two chip electrodes 112 are located on both sides of the chip optical waveguide 111, two metal connecting layers 103 and two height limiting structures 102 are arranged on the top surface of the silicon substrate 101, the two height limiting structures 102 are located outside the two metal connecting layers 103 and are higher than the two metal connecting layers 103, the laser chip 110 is flip-chip arranged on the top surface of the silicon substrate 101, the chip substrate 113 is connected with the height limiting structure 102, the chip electrode 112 is connected with the metal connecting layer 103 and forms an electrical conduction connection, and then the chip optical waveguide 111 is located between the chip substrate 113 and the silicon substrate 101.

[0026] The mode spot converter 120 includes an outer cladding layer 123, an upper waveguide layer 121 and a lower waveguide layer 122, the upper waveguide layer 121 includes a plurality of parallel extending ridge waveguides 1211, a tapered waveguide 1212 and a connecting waveguide 1213, the ridge waveguide 1211 is arranged in a rectangular cross-section in the first region, the ridge waveguide 1211 is arranged in a tapered shape, the ridge waveguide 1211 is connected with the chip optical waveguide 111 at the wide end of the first region, the narrow end of the ridge waveguide 1211 is connected with the wide end of the tapered waveguide 1212, the ridge waveguide 1211 is arranged in a gradually narrowing shape in the second region, the tapered waveguide 1212 is located at the third region, the connecting waveguide 1213 is connected between the narrow end of the tapered waveguide 1212 and the optoelectronic modulation module 130, the connecting waveguide 1213 is connected with the optoelectronic modulation module 130 at the fourth region, the lower waveguide layer 122 is arranged in a tapered shape, the lower waveguide layer 122 is located below the plurality of ridge waveguides 1211, the wide end of the lower waveguide layer 122 is located at the first region, the wide end of the lower waveguide layer 122 is close to the third region, the outer cladding layer 123 surrounds the outer periphery of the upper waveguide layer 121 and the lower waveguide layer 122, the spacing between the upper waveguide layer 121 and the lower waveguide layer 122 in the height direction Z is between 200 nm and 800 nm, the width of the wide end of the lower waveguide layer 122 is greater than the distance between the outermost two ridge waveguides 1211. The height of the wide end of the lower waveguide layer 122 is greater than the height of the narrow end of the lower waveguide layer 122, and the height of the lower waveguide layer 122 gradually decreases to 0 from the first region to the third region.

[0027] The optoelectronic modulation module 131130 includes a single-mode waveguide 131 and a modulation electrode 132, the single-mode waveguide 131 and the modulation electrode 132 are arranged on the silicon substrate 101, the single-mode waveguide 131 is connected with the connecting waveguide 1213, the two sides of the single-mode waveguide 131 are inclined at an angle between 60° and 70°, and the two sides of the narrow end of the tapered waveguide 1212 are inclined at an angle between 50° and 70°.

[0028] As Figure 5The electric field distribution of the mode spot converter 120 during light transmission is shown, and the entire electric field transition is uniform and smooth, which also confirms the high conversion efficiency. After obtaining the mode spot converter structure, we can etch the corresponding support column and solder preposition in the laser chip placement area to ensure that the laser chip exit spot has good matching with the mode spot converter structure after placement and welding and obtains high coupling efficiency.

[0029] The entire optoelectronic integrated chip is prepared based on thin film lithium niobate. The thin film lithium niobate wafer from top to bottom is 460 nm X-cut lithium niobate waveguide layer, 2 microns of SiO2 insulating layer and the lowermost silicon substrate, the outer cladding layer can be made of SiO2 material, the upper and lower waveguide layer materials are TiO2 which has a refractive index close to that of lithium niobate and can be obtained by dry etching to obtain high-quality structure, the two structures gradually change into a sharp structure at the end of the second region in the light transmission direction, the third region only has a gradual change structure with the same height as the upper waveguide layer 121, which further matches the mode spot to the maximum mode overlap with the lithium niobate waveguide mode, and the fourth region is directly contacted with the waveguide end face with a large inclination after dry etching of lithium niobate. The structure design starts with optimizing the width and height of the waveguide of the filling material in the fourth region to obtain the optimal mode spot overlap with the lithium niobate modulation structure waveguide. After optimization, the mode spot overlap at the interface between TiO2 and lithium niobate waveguide can reach more than 97%, and the high overlap mode spot machine has a similar refractive index, which can obtain high coupling efficiency. Further, by fixing the height of the first layer waveguide structure, the width, spacing and width and height of the lower structure can be optimized to obtain the structure design with the optimal overlap with the laser chip mode.

[0030] Referring to Figure 6 , the first step is to prepare a lithium niobate electro-optic modulation structure and the corresponding input and output single-mode waveguide by photolithography, dry etching, and deposition of modulation electrodes, and then depositing the upper cladding layer of lithium niobate. The second step is to remove all the materials above the SiO2 insulating layer in the flip-chip area of the laser chip corresponding to the mode spot conversion structure by photolithography and dry etching, and then to prepare the lowermost structure of the mode spot conversion structure waveguide layer on the SiO2 insulating layer by photolithography and dry etching, and then to deposit a material layer with a thickness corresponding to the mode spot conversion structure for the next step of structure preparation.

[0031] The third step is to prepare the corresponding mode spot converter by at least one step of photolithography and dry etching in the corresponding area of the mode spot conversion structure, and then to deposit the corresponding waveguide outer cladding material on it. The fourth step is to obtain the corresponding height limiting structure in the flip-chip area of the laser chip by photolithography and dry etching. The fifth step is to preposition the chip metal connection layer in the corresponding position in the flip-chip area by electroplating or thermal evaporation. The sixth step is to finally obtain stable chip-to-chip connection by melting the metal connection layer by heating, to complete the flip-chip welding of the laser chip. Since the coupling loss does not increase significantly when the mode spot conversion structure deviates in different directions, such asFigure 7 The figure shows the corresponding coupling efficiency changes of the embodiment corresponding to different direction coupling position deviations, the loss only increases 0.5dB when the X direction deviation is 0.5 microns, and the structure can significantly reduce the requirement of coupling precision

[0032] Referring to Figure 8 On the basis of the above embodiment, the upper and lower spacing of the upper and lower waveguide layers is pulled apart, and the cross section is as shown in the figure Figure 8 The upper and lower waveguide layers select SiN material, and the outer cladding material selects SiO2 material, and the simulation results show that the mode spot conversion structure also has a conversion efficiency of 90%, and the increased spacing adjustment degree can provide better optimization conditions for different types of exit light spots to improve the coupling efficiency.

[0033] As can be seen from the above, by means of flip-chip of the laser chip, and cooperating with the outer cladding surrounding the outer periphery of the upper waveguide layer and the lower waveguide layer, and the waveguide structure of the upper waveguide layer and the lower waveguide layer, and then connecting the photoelectric modulation module with the mode spot converter, and then realizing the conversion of the mode field of the laser chip or the mode field of the photoelectric modulation module through the mode spot converter, through the taper and the gradual change of the size, the mode spot converter structure has good matching and obtains high coupling efficiency, and through the spacing arrangement of the upper and lower waveguide layers, the increased spacing adjustment degree can provide better optimization conditions for different types of exit light spots to improve the coupling efficiency.

Claims

1. A high-efficiency mode-spot conversion optoelectronic integrated chip, characterized in that, The device includes a silicon substrate, a laser chip, a mode converter, and an optoelectronic modulation module. The laser chip, the mode converter, and the optoelectronic modulation module are disposed on the silicon substrate along the optical path direction, and the mode converter is connected between the laser chip and the optoelectronic modulation module. The laser chip includes a chip substrate and a chip optical waveguide. The chip optical waveguide is disposed on the bottom surface of the chip substrate, and the laser chip is flip-chip disposed on the top surface of the silicon substrate. The chip optical waveguide is located between the chip substrate and the silicon substrate. The mode converter includes an outer cladding layer, an upper waveguide layer, and a lower waveguide layer. The upper waveguide layer includes multiple ridge waveguides, a tapered waveguide, and a connecting waveguide. The multiple ridge waveguides extend in parallel and are connected between the chip optical waveguide and the wide end of the tapered waveguide. The connecting waveguide is connected between the narrow end of the tapered waveguide and the optoelectronic modulation module. The lower waveguide layer is arranged in a tapered shape and is located below the multiple ridge waveguides. The outer cladding layer surrounds the outer periphery of the upper and lower waveguide layers.

2. The optoelectronic integrated chip according to claim 1, characterized in that: The ridge waveguide is arranged in a tapered shape, with its wide end connected to the chip optical waveguide and its narrow end connected to the wide end of the tapered waveguide.

3. The optoelectronic integrated chip according to claim 1, characterized in that: The height of the lower waveguide layer at the wide end is greater than the height of the lower waveguide layer at the narrow end.

4. The optoelectronic integrated chip according to claim 1, characterized in that: The width of the lower waveguide layer at its wide end is greater than the distance between the outermost two ridge waveguides.

5. The optoelectronic integrated chip according to claim 1, characterized in that: The distance between the upper waveguide layer and the lower waveguide layer in the height direction is between 200 nm and 800 nm.

6. The optoelectronic integrated chip according to any one of claims 1 to 5, characterized in that: The optoelectronic modulation module includes a single-mode waveguide and a modulation electrode, which are disposed on the silicon substrate. The single-mode waveguide is connected to the connecting waveguide.

7. The optoelectronic integrated chip according to claim 6, characterized in that: The tilt angles of the single-mode waveguide are between 60° and 70°, and the tilt angles of the narrow ends of the tapered waveguide are between 50° and 70°.

8. The optoelectronic integrated chip according to any one of claims 1 to 5, characterized in that: A chip electrode is also disposed on the bottom surface of the chip substrate, and a metal interconnect layer is also disposed on the top surface of the silicon substrate, and the chip electrode is connected to the metal interconnect layer.

9. The optoelectronic integrated chip according to claim 8, characterized in that: A height limiting structure is provided on the top surface of the silicon substrate, and the chip substrate is connected to the height limiting structure.

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