Edge coupler and electronic equipment
By designing a conductive inverted cone structure and appropriate refractive index distribution in the core layer of the edge coupler, the problems of existing edge coupler coupling efficiency and footprint are solved, and more efficient fiber-to-chip optical coupling is achieved.
Patent Information
- Application Number
- CN202311572934.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-11-23
- Publication Date
- 2025-05-23
AI Technical Summary
Existing edge couplers cannot meet the requirements of higher coupling efficiency and low footprint.
An edge coupler is designed, and the core layer includes a conductive first inverted cone and a second inverted cone through which light rays gradually widen and shrink, thereby improving coupling efficiency. The refractive index of the core layer is disposed between the first cladding layer and the second cladding layer and is smaller than the refractive index of the transition layer to reduce refractive index mismatch.
Through this design, the optical coupling efficiency of fiber to chip is improved, and the footprint is reduced, meeting the requirements of higher coupling efficiency and lower footprint.
Smart Images
Figure CN120028918A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of photonics, and in particular to an edge coupler and electronic equipment. Background Art
[0002] Since optical interconnection is an important issue for transmitting light in silicon photonic integrated circuits, fiber-to-chip optical interconnection is crucial in application scenarios such as data centers and optical transmission systems. There are two main types of fiber-to-chip optical coupling: out-of-plane coupling (grating coupler) and in-plane coupling (edge coupler). Grating couplers have the advantages of small size and flexible coupling position, but due to the diffraction characteristics of the grating, they have the disadvantages of narrow bandwidth, polarization sensitivity, and low coupling efficiency (below 3dB). With the advantage of flexible coupling position, grating couplers are generally used for wafer-level testing. In the in-plane coupling mode, the optical fiber is usually placed on the end face of the wafer and horizontally aligned with the Si waveguide through the edge coupler. The edge coupler has the disadvantages of large footprint, fixed coupling position, and more stringent requirements on the coupling end face, but it has a large working bandwidth, no polarization dependence, and has a relatively high coupling efficiency compared to the grating coupler. With these advantages, edge couplers play an indispensable role in silicon photonic circuits.
[0003] However, existing edge couplers still cannot meet the requirements of higher coupling efficiency and lower footprint. Summary of the invention
[0004] The invention discloses an edge coupler and electronic equipment, which are used for improving coupling efficiency.
[0005] In order to achieve the above object, the present invention provides the following technical solutions:
[0006] In a first aspect, an edge coupler is provided, the edge coupler comprising a substrate, a transition layer being provided on the substrate, a first cladding being provided on a side of the transition layer facing away from the substrate, a core layer being provided on a side of the first cladding facing away from the transition layer, and a second cladding being provided on a side of the core layer facing away from the first cladding; along a light propagation direction, the core layer sequentially comprises a first inverted cone and a second inverted cone which are conductive, and the width of the first inverted cone gradually increases, while the width of the second inverted cone gradually decreases; along a vertical direction, a projection of the second inverted cone at least partially overlaps with the transition layer; a refractive index of the core layer is greater than a refractive index of the first cladding and a refractive index of the second cladding, and is less than a refractive index of the transition layer.
[0007] The light is coupled in from the narrow end of the first inverted cone in the core layer, and the width of the first inverted cone gradually increases to gradually widen the narrow optical path of the optical fiber and accommodate more light that is gradually coupled in. When the light enters the second inverted cone, the width of the second inverted cone gradually narrows, and the amount of light accommodated by the second inverted cone decreases. The light is emitted downward and coupled into the transition layer in the vertical direction, and is coupled to the downstream waveguide structure by the transition layer. The refractive index contrast between the core layer and the first cladding is smaller than the refractive index contrast between the transition layer and the first cladding. The optical mode in the core layer and the optical modes in the first cladding and the second cladding will not produce excessive refractive index mismatch, which is beneficial to improving the coupling efficiency.
[0008] Optionally, the core layer is made of silicon nitride, the first cladding layer and the second cladding layer are both made of silicon dioxide, and the transition layer is made of silicon.
[0009] Optionally, the core layer further includes a sub-wavelength grating formed at one end of the first inverted cone away from the second inverted cone; along the propagation direction of light, the width of the sub-wavelength grating gradually increases, and the sub-wavelength grating overlaps with a portion of the length of the first inverted cone to form a transition section.
[0010] Optionally, the number of periods of the sub-wavelength grating is between 150 and 200, the length of a single period is between 300 nm and 500 nm, and the duty cycle is between 40% and 60%.
[0011] Optionally, along the light propagation direction, the width of the transition layer gradually decreases to form a third inverted cone.
[0012] Optionally, along the light propagation direction, two ends of the second inverted cone are aligned one by one with two ends of the transition layer in a vertical direction.
[0013] Optionally, a shielding object is provided on a side of the transition layer away from the light output end, and the refractive index of the shielding object is lower than the refractive index of the transition layer.
[0014] Optionally, the shielding object is made of silicon dioxide.
[0015] Optionally, a groove is formed on the substrate, and the shielding object is filled in the groove.
[0016] Optionally, the depth of the groove is between 10 μm and 50 μm.
[0017] In a second aspect, an electronic device is provided, comprising: an optical fiber, an optical chip and an edge coupler as described in any of the above technical solutions, wherein the light output end of the optical fiber is optically coupled with the light input end of the core layer, and the light output end of the transition layer is optically coupled with the waveguide light input end of the optical chip.
[0018] Compared with the prior art, the advantages of the electronic device are the same as those of the above-mentioned edge coupler, which will not be described in detail here. BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Figure 1 A schematic diagram of the structure of an edge coupler provided in an embodiment of the present application;
[0020] Figure 2 for Figure 1 Top view of the middle core layer and transition layer;
[0021] Figure 3 express Figure 1 Schematic diagram of the first step of the edge coupler preparation method shown;
[0022] Figure 4 express Figure 1 A schematic diagram of the second step of the edge coupler preparation method shown;
[0023] Figure 5 express Figure 4 A top view of the third inverted cone;
[0024] Figure 6 express Figure 1 The third step schematic diagram of the edge coupler preparation method shown;
[0025] Figure 7 express Figure 1 The fourth step schematic diagram of the edge coupler preparation method shown;
[0026] Figure 8 express Figure 1 A schematic diagram of the fifth step of the edge coupler preparation method shown;
[0027] Fig. 9 express Figure 7 A top view of the sub-wavelength grating 152 in the core layer 15;
[0028] Fig.10 express Figure 7 A top view of the inverted cone section 151 in the middle core layer 15;
[0029] Fig.11 express Figure 7 A top view of the sub-wavelength grating 152 and the inverted cone segment 151 in the middle core layer 15;
[0030] Fig.12 Show Figure 7 Schematic diagram of the projection relationship between the inverted cone section 151 in the core layer 15 and the transition layer 13 and the waveguide structure 33 in the vertical direction. DETAILED DESCRIPTION
[0031] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0032] The edge coupler provided by the embodiment of the present application includes a substrate 11, a transition layer 13 is provided on the substrate 11, a first cladding 14 is provided on the side of the transition layer 13 facing away from the substrate 11, a core layer 15 is provided on the side of the first cladding 14 facing away from the transition layer 13, and a second cladding 16 is provided on the side of the core layer 15 facing away from the first cladding 14; the core layer 15 includes an inverted cone segment 151 (a solid line structure between reference lines a and b), and along the light propagation direction P, the inverted cone segment 151 includes a conductive first inverted cone 1511 and a second inverted cone 1512 in sequence, and the first inverted cone 1511 is connected to the first inverted cone 1512. The width of the first inverted cone 1511 gradually increases along the propagation direction of the light (modal propagation direction), and the width of the second inverted cone 1512 gradually decreases. The first inverted cone 1511 and the second inverted cone 1512 can be directly connected and conducted, or can be connected and conducted through a rectangular waveguide section 1513 located therebetween; along the vertical direction, the projection of the second inverted cone 1512 at least partially overlaps with the transition layer 13; the refractive index of the core layer 15 is greater than the refractive index of the first cladding layer 14 and the refractive index of the second cladding layer 16, and is less than the refractive index of the transition layer 13. The "vertical direction" refers to the direction perpendicular to the substrate 11.
[0033] The light emitted by the optical fiber 21 is coupled into the core layer 15 through the narrow end of the first inverted cone 1511. The optical fiber 21 may be a standard optical fiber (SMF-28). The width of the first inverted cone 1511 gradually increases to gradually widen the narrow optical path of the optical fiber 21 and accommodate more light that is gradually coupled in. When the light enters the second inverted cone 1512, the width of the second inverted cone 1512 gradually narrows, and the amount of light accommodated by the second inverted cone 1512 decreases. The light is emitted downward and coupled into the transition layer 13 in the vertical direction, and is coupled by the transition layer 13 to the waveguide structure 33 of the downstream optical chip and other structures. The waveguide structure 33 may be made of the same material as the transition layer 13.
[0034] The refractive index contrast between the core layer 15 and the first cladding layer 14 is smaller than the refractive index contrast between the transition layer 13 and the first cladding layer 14. The optical mode in the core layer 15 and the optical mode in the first cladding layer 14 will not produce too large a refractive index mismatch. Similarly, the optical mode in the core layer 15 and the optical mode in the second cladding layer 16 will not produce too large a refractive index mismatch. The waveguide structure 33 and the transition layer 13 are made of the same material. Therefore, the light in the transition layer 13 can enter the waveguide structure 33 with lower light loss. Thus, it is beneficial to improve the coupling efficiency.
[0035] For example, the material of the core layer 15 is silicon nitride, the material of the first cladding 14 and the material of the second cladding 16 are both silicon dioxide, and the material of the transition layer 13 is silicon. In the C-band 1.55 μm, which is a common communication band, the refractive index contrast between silicon and silicon dioxide is high, and the refractive index difference is about 2. In the case where the material of the first cladding 14 and the material of the second cladding 16 are both silicon dioxide, if the material of the core layer 15 is still silicon with a larger refractive index, the optical mode of the core layer 15 will have a large refractive index mismatch with the optical mode in the first cladding 14 and the optical mode in the second cladding 16, which will reduce the coupling efficiency. However, if the core layer 15 is changed to silicon nitride with a smaller refractive index than silicon, the refractive index contrast with silicon dioxide can be reduced, and the situation that the optical mode of the core layer 15 has a large refractive index mismatch with the optical mode in the first cladding 14 and the optical mode in the second cladding 16 can be alleviated, and the coupling efficiency is improved.
[0036] Specifically, the refractive index difference between silicon nitride and silicon dioxide at 1.55 μm in the C-band, a commonly used communication band, is about 0.55. A smaller refractive index difference means that it will be easier to achieve effective refractive index matching between the waveguide mode and the optical fiber mode, which will improve the coupling efficiency.
[0037] In order to balance small footprint and high coupling efficiency, materials other than silicon such as lithium niobate are sometimes used as the medium for propagating light in edge couplers. The lithium niobate edge coupler is designed using the LNOI platform. The disadvantage is that lithium niobate is not well compatible with the current more mature CMOS process. In the embodiment of the present application, silicon nitride used in the core layer 15 is a commonly used mask, passivation and strain engineering material in CMOS foundries, which has good compatibility with CMOS processes.
[0038] In a specific embodiment, the core layer 15 also includes a sub-wavelength grating (SWG) 152 formed at one end of the first inverted cone 1511 away from the second inverted cone 1512; along the light propagation direction P, the width of the sub-wavelength grating 152 gradually increases, and the sub-wavelength grating 152 overlaps with a partial length of the first inverted cone 1511 to form a transition section T, and the transition section T specifically refers to the structure between line c and line d.
[0039] The sub-wavelength grating 152 (SWG) can suppress reflection and diffraction effects. Its effective combination with the first inverted cone 1511 is beneficial for coupling light from the optical fiber 21 into the first inverted cone 1511. The sub-wavelength grating 152 is part of the core layer 15 and is also made of silicon nitride. The refractive index of silicon nitride is smaller than that of silicon. Compared with the sub-wavelength grating made of silicon, only a shorter length is needed to couple the light from the optical fiber 21 into the first inverted cone 1511.
[0040] In a specific embodiment, the number of periods of the sub-wavelength grating 152 is between 150 and 200, such as 150, 160, 170, 180, 190 and 200, etc., the length of a single period is between 300nm and 500nm, such as 300nm, 320nm, 350nm, 360nm, 380nm, 400nm, 430nm, 450nm, 480nm and 500nm, etc., and the duty cycle is between 40% and 60%, such as 40%, 50% and 60%. The above parameters can ensure that the sub-wavelength grating 152 can efficiently couple the optical fiber of the optical fiber 21 into the first inverted cone 1511 with a shorter length.
[0041] In a specific embodiment, along the light propagation direction P, the width of the transition layer 13 gradually decreases to form a third inverted cone, so that as the width of the second inverted cone 1512 gradually decreases, the emitted light gradually increases, and the third inverted cone can also accommodate more light, which is beneficial to improving coupling efficiency.
[0042] In a specific embodiment, a shielding material 12 is provided on the side of the transition layer 13 away from the light output end, and the refractive index of the shielding material 12 is lower than the refractive index of the transition layer 13 to prevent the light emitted by the optical fiber 21 from directly entering the transition layer 13, causing light loss, which is not conducive to improving the coupling efficiency.
[0043] In a specific embodiment, the material of the shielding material 12 is silicon dioxide, which not only has a lower refractive index than the silicon of the transition layer 13, but also facilitates the stable combination of the two. A buried oxide layer 11a is provided between the substrate 11 and the transition layer 13, and the buried oxide layer 11a can also be made of silicon dioxide, so it is convenient to use the SOI process to manufacture the above edge coupler. The buried oxide layer 11a and the shielding material 12 are both made of silicon dioxide, which is conducive to the stable combination of the two.
[0044] In a specific embodiment, a groove U is formed on the substrate 11, and a shielding material 12 is filled in the groove U. On the one hand, the bonding area between the shielding material 12 and the substrate 11 can be increased to improve the bonding stability. On the other hand, the shielding of the light spot formed by the light emitted from the optical fiber 21 can be increased, thereby further reducing the possibility of the light being directly coupled into the transition layer 13.
[0045] In a specific embodiment, the depth of the groove U is between 10 μm and 50 μm, and can be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, etc. The depth range of the groove U can ensure that the light spot formed by the light emitted by the optical fiber 21 is effectively shielded, and ensure that the substrate 11 has sufficient thickness.
[0046] The following is an introduction to the method for preparing the edge coupler with reference to the accompanying drawings. It should be noted that the dimensions in the following preparation process are examples and are not intended to be limiting.
[0047] refer to Figure 3 , specifically, the description is given based on the 220nm SOI (Silicon-On-Insulator) process as an example.
[0048] The substrate 11 is made of silicon and serves as a back substrate with a thickness of 700 μm. A buried oxide layer 11a is formed on the substrate 11. The buried oxide layer 11a is made of silicon dioxide and has a thickness of 3 μm. A transition layer 13 is formed on the surface of the buried oxide layer 11a away from the substrate 11. The transition layer 13 is made of silicon and has a thickness of 220 nm.
[0049] refer to Figure 4 , the transition layer 13 is etched to a depth of 220 nm to prepare a third inverted cone.
[0050] refer to Figure 5 The top view of the third inverted cone is shown. Along the light propagation direction, the width of the third inverted cone gradually increases. The length L of the third inverted cone is between 100 μm and 150 μm. The side inclination angle is 90°. The narrow end width W Si1 The width of the wide end is 0.13μm and the width of the wide end is 0.45μm.
[0051] refer to Figure 6 , the buried oxide layer 11a and the substrate 11 are etched to form a groove U, and the etching depth of the groove U is between 10 μm and 50 μm.
[0052] refer to Figure 7 , silicon dioxide is deposited in the groove U, the portion where the buried oxide layer 11a is etched, and the portion where the transition layer 13 is etched, the deposited silicon dioxide covers the entire transition layer 13, the portion below the plane where the top surface of the transition layer 13 is located forms a shield 12, and the portion above the plane where the top surface of the transition layer 13 is located forms a first cladding layer 14, and after the deposition is completed, CMP (chemical mechanical polishing) is performed on the top surface of the first cladding layer 14 to flatten the top surface of the first cladding layer 14, and at the same time, the over-deposited portion is ground off to control the thickness of the first cladding layer 14, and the deposition thickness of the first cladding layer 14 is controlled to be 0.18μm.
[0053] refer to Figure 8 , deposit silicon nitride to form the core layer 15. After the deposition is completed, the top surface of the core layer 15 is subjected to CMP (chemical mechanical polishing) to grind the top surface of the core layer 15 flat. At the same time, the over-deposited part is ground off to control the thickness of the core layer 15. The deposition thickness of the core layer 15 is controlled to be 0.3 μm. Then the core layer 15 is etched to form Figure 2 The structure shown in , comprises a sub-wavelength grating 152 and an inverted cone segment 151, and the detailed description thereof may be referred to the foregoing text.
[0054] Fig. 9 Show Figure 2 A top view of the mid-subwavelength grating 152, with a width w at its narrow end g1 The width w of the wide end is 0.5 μm. g2 is 0.7 μm, the number of periods is between 150 and 200, and the width of the transition zone is w b The length of a single period T is between 300nm and 500nm, and the duty cycle is between 40% and 60%.
[0055] refer to Fig.10 The side inclination angle of the inverted cone section 151 is 90°, and the width w of the narrow end of the first inverted cone 1511 and the second inverted cone 1512 is SiN1 The width w of the wide end is 0.2 μm. SiN2 The cross-sectional area of the rectangular waveguide section 1513 is 1×0.3 μm. 2 , length L w 5μm.
[0056] Fig.11 The positional relationship between the inverted cone segment 151 and the sub-wavelength grating 152 is shown. Fig.12 Show Figure 7 Schematic diagram of the projection relationship between the inverted cone section 151 in the core layer 15 and the transition layer 13 and the waveguide structure 33 in the vertical direction.
[0057] refer to Figure 1 In the structure of the middle edge coupler, silicon dioxide is deposited as the second cladding layer 16, and after the deposition is completed, CMP (chemical mechanical polishing) is performed on it to control its thickness.
[0058] In silicon photonic integrated circuits, optical interconnection is the key to achieving efficient data transmission. Improving the coupling performance of the coupler is an important part of optical interconnection. Reducing the loss of light coupling into the optical chip can achieve more efficient data transmission, which is of great significance to the realization of integrated high-speed silicon-based interconnection optical chips and the promotion of optical interconnection.
[0059] The processing technology of silicon and silicon nitride materials used is compatible with mature CMOS technology, and silicon reserves are abundant and cheap. The size of the device is also consistent with the mature processing technology of the foundry, and the preparation cost is low. At the same time, the introduction of silicon nitride inverted cone makes it easier to achieve effective refractive index matching between waveguide mode and fiber mode, which will significantly reduce coupling loss and improve the performance of silicon photonic chips while maintaining low cost.
[0060] The inverted cone profile adopts a basic linear profile, which is easy to implement technically, has a small preparation error, and has low processing difficulty and cost. At the same time, the grating segment length of 200nm of the sub-wavelength grating 152 meets the current process node of 8-inch process grating manufacturing. The device can be successfully manufactured using the foundry's mature deposition and etching processes.
[0061] Based on the same inventive concept, the embodiment of the present application further provides an electronic device, which includes: an optical fiber 21, an optical chip, and the edge coupler provided in the above embodiment, the light output end of the optical fiber 21 is optically coupled with the light input end of the core layer 15, and the light output end of the transition layer 13 is optically coupled with the waveguide light input end of the optical chip. The beneficial effects of the electronic device can refer to the edge coupler mentioned above.
[0062] refer to Figure 1 In the optical chip, the waveguide structure 33 can be made of the same silicon dioxide material as the buried oxide layer 11a, the chip substrate 31 below the buried oxide layer 11a and the substrate 11 of the edge coupler can be made of the same silicon material, and the waveguide structure 33 can be made of a silicon dioxide layer flush with the second cladding layer 16 above.
[0063] Obviously, those skilled in the art can make various changes and modifications to the embodiments of the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.
Claims
1. An edge coupler, It is characterized in that The invention comprises a substrate, a transition layer is provided on the substrate, a first cladding is provided on a side of the transition layer away from the substrate, a core layer is provided on a side of the first cladding away from the transition layer, and a second cladding is provided on a side of the core layer away from the first cladding; Along the light propagation direction, the core layer includes a first inverted cone and a second inverted cone in sequence, and the width of the first inverted cone gradually increases, while the width of the second inverted cone gradually decreases; In the vertical direction, the projection of the second inverted cone at least partially overlaps with the transition layer; The refractive index of the core layer is greater than the refractive index of the first cladding layer and the refractive index of the second cladding layer, and is less than the refractive index of the transition layer.
2. The edge coupler according to claim 1, It is characterized in that The material of the core layer is silicon nitride, the material of the first cladding layer and the material of the second cladding layer are both silicon, and the material of the transition layer is silicon.
3. The edge coupler according to claim 2, It is characterized in that The core layer further includes a sub-wavelength grating formed at an end of the first inverted cone away from the second inverted cone; Along the propagation direction of the light, the width of the sub-wavelength grating gradually increases, and the sub-wavelength grating overlaps with a portion of the length of the first inverted cone to form a transition section.
4. The edge coupler according to claim 3, It is characterized in that The number of periods of the sub-wavelength grating is between 150 and 200, the length of a single period is between 300 nm and 500 nm, and the duty cycle is between 40% and 60%.
5. The edge coupler according to claim 1, It is characterized in that Along the light propagation direction, the width of the transition layer gradually decreases to form a third inverted cone.
6. The edge coupler according to claim 2, It is characterized in that A shielding object is provided on a side of the transition layer away from the light output end, and the refractive index of the shielding object is lower than the refractive index of the transition layer.
7. The edge coupler according to claim 6, It is characterized in that The material of the shielding object is silicon dioxide.
8. The edge coupler according to claim 7, It is characterized in that The substrate is formed with a groove, and the shielding object is filled in the groove.
9. The edge coupler according to claim 8, It is characterized in that The depth of the groove is between 10 μm and 50 μm.
10. An electronic device, It is characterized in that include: An optical fiber, an optical chip, and an edge coupler as described in any one of claims 1 to 9, wherein the light output end of the optical fiber is optically coupled with the light input end of the core layer, and the light output end of the transition layer is optically coupled with the waveguide light input end of the optical chip.