Polarization insensitive end face coupling device based on deposited silicon and preparation method of polarization insensitive end face coupling device

Abstract

The invention belongs to the technical field of integrated optics, and discloses a polarization insensitive end face coupling device based on a silicon waveguide and a preparation method, and the polarization insensitive end face coupling device comprises a substrate layer, a lower cladding, a silicon waveguide layer and an upper cladding along a third direction; wherein the silicon waveguide layer sequentially comprises a mode field adiabatic evolution section, a first mode conversion section, a second adiabatic evolution section, a third adiabatic evolution section, a fourth mode conversion section and a convergence section along a first direction. The waveguide segments are deposited on the lower cladding and are connected with each other. According to the invention, the coupling loss is reduced, and low-loss transmission between the silicon waveguides with different thicknesses is realized; low polarization dependent loss is realized through mode field conversion; when the material of the silicon waveguide layer is deposited silicon, a bottom layer device can be effectively protected from being damaged as a back-end process; and potential simplification, expansion and optimization schemes can be provided for other devices.

Description

Technical Field

[0001] This invention belongs to the field of integrated optical technology, and more specifically, relates to a polarization-insensitive end-face coupling device based on deposited silicon and its fabrication method. Background Technology

[0002] In modern high-density photonic integrated systems, silicon-based photonic platforms have become one of the mainstream technologies in fields such as optical interconnects, optical sensing, and optical computing due to their mature manufacturing processes, high integration, and compatibility with CMOS processes. However, due to the high refractive index contrast, the mode field size of silicon waveguides is much smaller than that of standard single-mode fibers, leading to severe mode field mismatch during light coupling between the chip and the fiber, resulting in high insertion loss (IL). Therefore, designing and implementing a low insertion loss end-face coupling structure is crucial for improving the optical coupling efficiency of silicon photonic chips and the overall system performance. Although various silicon-based end-face coupling schemes have been proposed, such as tilted grating couplers and inverted conical couplers, these structures are often sensitive to operating modes, especially with different responses to different polarization states, which introduces high polarization dependent loss (PDL) and affects the applicability of the device. In recent years, constructing waveguide layers by depositing silicon materials has become an effective way to improve mode field matching and reduce coupling loss. This helps to simultaneously adapt to TEO and TMO modes while maintaining a low PDL. However, how to further optimize its structural parameters and balance low insertion loss and low polarization sensitivity over a wide spectral range remains a key issue that urgently needs to be addressed in the design of current silicon photonic end couplers. Summary of the Invention

[0003] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a polarization-insensitive end-face coupling device based on silicon waveguide and a fabrication method, which aims to solve the technical problems of poor versatility and high insertion loss of existing devices.

[0004] To achieve the above objectives, this invention provides a polarization-insensitive end-face coupling device based on a silicon waveguide. It defines a first direction, a second direction, and a third direction that are perpendicular to each other in a spatial coordinate system. Along the third direction, from bottom to top, the device includes a substrate layer, a lower cladding layer deposited on the substrate layer, a silicon waveguide layer deposited on the lower cladding layer, and an upper cladding layer. The top layer height of the lower cladding layer is defined as h0 = 0. Along the third direction, the silicon waveguide layer has heights h1, h2, and h3 from bottom to top. The upper cladding layer is fabricated on the silicon waveguide layer and is connected to the lower cladding layer, completely enclosing the silicon waveguide layer and forming a low-high-low refractive index distribution. The silicon waveguide layer includes, in sequence along the first direction: a mode field adiabatic evolution section, a first mode conversion section, a second adiabatic evolution section, a third adiabatic evolution section, a fourth mode conversion section, and a convergence section; The mode field adiabatic evolution section includes a waveguide with a height of h0 to h2, the width of which gradually increases from the first end face along the first direction to the second end face; The first mode conversion segment includes a ridge waveguide with heights from h0 to h2, a bottom height of h1, and a ridge height of h2. It completely overlaps with the mode field adiabatic evolution segment on the second end face. The bottom width gradually widens from the second end face along the first direction to the third end face, and the ridge width gradually narrows from the second end face along the first direction to the third end face. The second adiabatic evolution section includes a ridge waveguide with heights from h0 to h2, a bottom height of h1, and a ridge height of h2. It completely overlaps with the first mode conversion section on the third end face. The bottom width remains unchanged from the third end face along the first direction, and the ridge width gradually widens from the third end face along the first direction to the fourth end face, so that the bottom and ridge have the same width on the fourth end face. The third adiabatic evolution section includes a ridge waveguide with a height of h0 to h3, a bottom height of h2, a ridge height of h3, which completely overlaps with the second adiabatic evolution section on the fourth end face. The bottom width gradually increases from the fourth end face along the first direction to the fifth end face, and the ridge width gradually increases from the fourth end face along the first direction to the fifth end face. The fourth mode conversion segment includes a ridge waveguide with heights from h0 to h3, a bottom height of h2, a ridge height of h3, and is completely overlapped with the third adiabatic evolution segment on the fifth end face. The bottom width remains unchanged from the fifth end face along the first direction, and the ridge width gradually narrows from the fifth end face along the first direction to the sixth end face. The convergence segment includes a ridge waveguide with heights from h0 to h3, a bottom height of h2, and a ridge height of h3. Its bottom partially overlaps with the fourth mode conversion segment on the sixth end face, and its ridge completely overlaps with the fourth mode conversion segment on the sixth end face. The bottom width gradually narrows from the sixth end face along the first direction to the seventh end face, and the ridge width gradually narrows from the sixth end face along the first direction to the seventh end face, achieving the same width for the bottom and ridge on the seventh end face.

[0005] The present invention also provides a method for fabricating the above-mentioned polarization-insensitive end-coupled device based on silicon waveguide, comprising: S1. Deposit silicon dioxide on the substrate layer to form a lower cladding layer; S2. Deposit silicon waveguide material with a height of h3 on the lower cladding layer and coat its upper surface with photoresist, and form it by multiple mask overlays. S3. After removing the photoresist, the silicon waveguide layer is formed, and silicon dioxide is deposited on the silicon waveguide layer to form the upper cladding layer.

[0006] In summary, compared with the prior art, the technical solutions conceived in this invention have the following beneficial effects: 1. The silicon waveguide polarization-insensitive end-face coupler based on mode conversion of the present invention changes the effective refractive index by changing the geometry of the waveguide, thereby enabling mode matching between the optical fiber and the ridge waveguide, and between different sections of the ridge waveguide, reducing coupling loss and realizing low-loss transmission between waveguides of different thicknesses. 2. Based on a multilayer waveguide structure, this invention effectively achieves coupling of the fundamental mode, improves the coupling efficiency of the base film, and achieves lower polarization-dependent loss through mode field conversion; 3. The method for fabricating a polarization-insensitive end-face coupler based on silicon waveguides used in this invention, when the silicon waveguide material is deposited silicon, uses a method of depositing amorphous silicon at a temperature below 450 degrees Celsius to fabricate the silicon-based waveguide, which can effectively protect the underlying silicon-based devices from damage.

[0007] 4. The device based on silicon deposition in this invention can provide potential simplification, expansion and optimization solutions for other devices. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the structure of a polarization-insensitive end-face coupler based on deposited silicon in an embodiment of the present invention; Figure 2 This is a front view of a polarization-insensitive end-face coupler based on deposited silicon in an embodiment of the present invention. Figure 3 This is a left view of a polarization-insensitive end-face coupler based on deposited silicon in an embodiment of the present invention. Figure 4 This is a top view of a polarization-insensitive end-face coupler based on deposited silicon in an embodiment of the present invention. Figure 5 This is a schematic diagram of a polarization-insensitive end-face coupler based on deposited silicon in an embodiment of the present invention. Figure 6 The TEO mode of the polarization-insensitive end-face coupler based on deposited silicon in this embodiment of the invention is shown at the second end face. Figure 7 The image shows the optical field at the second end face of the TMO mode of the polarization-insensitive end face coupler based on deposited silicon in this embodiment of the invention. Figure 8 This is the optical field diagram of the TEO mode of the polarization-insensitive end-face coupler based on deposited silicon in this embodiment of the invention at the third end-face section; Figure 9 This is the optical field diagram of the TE1 mode of the polarization-insensitive end-face coupler based on deposited silicon in this embodiment of the invention at the fourth end-face section. Figure 10This is the optical field diagram of the TEO mode of the polarization-insensitive end-face coupler based on deposited silicon in this embodiment of the invention at the fifth end-face section; Figure 11 This is the optical field diagram of the TE1 mode of the polarization-insensitive end-face coupler based on deposited silicon in this embodiment of the invention at the sixth end-face section. Figure 12 This is the optical field diagram of the TEO mode of the polarization-insensitive end-face coupler based on deposited silicon in this embodiment of the invention at the seventh end-face section. Figure 13 This is the optical field diagram of the TE1 mode of the polarization-insensitive end-face coupler based on deposited silicon in this embodiment of the invention at the third end-face section. Figure 14 This is the optical field diagram of the TEO mode of the polarization-insensitive end-face coupler based on deposited silicon in this embodiment of the invention at the fourth end-face section; Figure 15 This is the optical field diagram of the TM0 mode of the polarization-insensitive end-face coupler based on deposited silicon in this embodiment of the invention at the fifth end-face section; Figure 16 This is the optical field diagram of the TEO mode of the polarization-insensitive end-face coupler based on deposited silicon in this embodiment of the invention at the sixth end-face section; Figure 17 This is the optical field diagram of the TM0 mode of the polarization-insensitive end-face coupler based on deposited silicon in this embodiment of the invention at the seventh end-face section; Figure 18 This refers to the mode conversion insertion loss of the polarization-insensitive end-face coupler based on deposited silicon in this embodiment of the invention. Figure 19 This is a front view of the SOI-based polarization-insensitive end-face coupler in an embodiment of the present invention; Figure 20 This is a schematic diagram of a conventional III-V heterogeneous integrated laser in an embodiment of the present invention; Figure 21 This is a schematic diagram of a III-V heterogeneous integrated laser provided in an embodiment of the present invention. Detailed Implementation

[0009] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0010] This invention provides a polarization-insensitive end-face coupling device based on a silicon waveguide. It defines a first direction, a second direction, and a third direction that are perpendicular to each other in a spatial coordinate system. Along the third direction, from bottom to top, the device includes a substrate layer 1, a lower cladding layer 2 deposited on the substrate layer 1, a silicon waveguide layer 3 deposited on the lower cladding layer 2, and an upper cladding layer 4. The top layer height of the lower cladding layer is defined as h0 = 0. Along the third direction, the silicon waveguide layer 3 has heights h1, h2, and h3 from bottom to top. The upper cladding layer 4 is fabricated on the silicon waveguide layer 3 and is connected to the lower cladding layer 2, completely enclosing the silicon waveguide layer 3 and forming a low-high-low refractive index distribution. The silicon waveguide layer 3 includes, in sequence along the first direction: a mode field adiabatic evolution section 30, a first mode conversion section 31, a second adiabatic evolution section 32, a third adiabatic evolution section 33, a fourth mode conversion section 34, and a convergence section 35. The mode field adiabatic evolution section 30 includes a strip waveguide with a height of h0 to h2, the width of which gradually increases from the first end face along the first direction to the second end face; The first mode conversion segment 31 includes a ridge waveguide with heights from h0 to h2, a bottom height of h1, and a ridge height of h2. It completely overlaps with the mode field adiabatic evolution segment 30 on the second end face. The bottom width gradually widens from the second end face along the first direction to the third end face, and the ridge width gradually narrows from the second end face along the first direction to the third end face. The second adiabatic evolution section 32 includes a ridge waveguide with a height of h0 to h2, a bottom height of h1, and a ridge height of h2. It completely overlaps with the first mode conversion section 31 on the third end face. The bottom width remains unchanged from the third end face along the first direction, and the ridge width gradually widens from the third end face along the first direction to the fourth end face, so that the bottom and ridge have the same width on the fourth end face. The third adiabatic evolution section 33 includes a ridge waveguide with a height of h0 to h3, a bottom height of h2, a ridge height of h3, and the bottom completely overlaps with the second adiabatic evolution section 32 on the fourth end face. The bottom width gradually increases from the fourth end face along the first direction to the fifth end face, and the ridge width gradually increases from the fourth end face along the first direction to the fifth end face. The fourth mode conversion segment 34 includes a ridge waveguide with heights from h0 to h3, a bottom height of h2, and a ridge height of h3. It completely overlaps with the third adiabatic evolution segment 33 on the fifth end face. The bottom width remains unchanged from the fifth end face along the first direction, and the ridge width gradually narrows from the fifth end face along the first direction to the sixth end face. The convergence segment 35 includes a ridge waveguide with heights from h0 to h3, a bottom height of h2, and a ridge height of h3. Its bottom partially overlaps with the fourth mode conversion segment 34 on the sixth end face, and its ridge completely overlaps with the fourth mode conversion segment 34 on the sixth end face. The bottom width gradually narrows from the sixth end face along the first direction to the seventh end face, and the ridge width gradually narrows from the sixth end face along the first direction to the seventh end face, so that the bottom and ridge have the same width on the seventh end face.

[0011] Example 1 This embodiment provides a working mode and fabrication parameters for a polarization-insensitive end-face coupler based on deposited silicon, such as... Figure 1-5 As shown, its specific structure includes: The structure, arranged in ascending third direction, comprises: a substrate layer 1, a lower cladding layer 2 disposed on the substrate layer 1, wherein the top layer height of the lower cladding layer 2 is defined as h0=0. In this embodiment, preferably, the substrate layer 1 is a front-end optoelectronic integrated chip. A silicon waveguide layer 3, made of deposited silicon, is disposed on the lower cladding layer 2, and its heights from bottom to top along the ascending third direction are h1, h2, and h3 respectively. Along the first direction, the silicon waveguide layer 3 structure comprises: The waveguide consists of a mode field adiabatic evolution section 30, a first mode conversion section 31, a second adiabatic evolution section 32, a third adiabatic evolution section 33, a fourth mode conversion section 34, and a convergence section 35. An upper cladding layer 4 is disposed on the surface of the silicon waveguide layer 3 and is connected to the lower cladding layer 2, completely enclosing the silicon waveguide layer 3 to form a low-high-low refractive index distribution.

[0012] The mode field adiabatic evolution section 30 is a width-gradient strip waveguide structure, including strip waveguides with heights from h0 to h2, whose width gradually increases from the first end face along a first direction to the second end face. Preferably, the effective refractive index of the mode field adiabatic evolution section 30 for the TEO mode increases from 1.455 to 2.365, such as... Figure 6 The diagram shows the mode field of the TE0 mode at the second end face. The effective refractive index for the TM0 mode increases from 1.477 to 1.647. Figure 7 The diagram shows the mode field of the TM0 mode at the second end face. The first mode conversion section 31 is an inverted conical ridge waveguide structure, including a ridge waveguide with heights from h0 to h2. Its bottom height is h1, and its ridge height is h2. It completely coincides with the mode field adiabatic evolution section 30 on the second end face. The bottom width gradually widens from the second end face along the first direction to the third end face, and the ridge width gradually narrows from the second end face along the first direction to the third end face. Preferably, the effective refractive index of the first mode conversion section 31 for the TE0 mode decreases from 2.365 to 2.333, as shown below. Figure 8 The diagram shows the mode field of the TE0 mode at the third end face. When the TM0 mode optical field is input to the first mode conversion segment 31, mode field conversion is achieved through changes in refractive index distribution and waveguide structure, transforming it into the TE1 mode, as shown below. Figure 9The diagram shows the mode field of the TE1 mode at the third end face. The second adiabatic evolution section 32 is a width-gradient ridge waveguide structure, including a ridge waveguide with heights from h0 to h2. Its bottom height is h1 and its ridge height is h2. It completely coincides with the first mode conversion section 31 on the third end face. The bottom width remains constant from the third end face along the first direction, while the ridge width gradually widens from the third end face along the first direction to the fourth end face, where the bottom and ridge have the same width. Preferably, the effective refractive index of the second adiabatic evolution section 32 for the TE0 mode increases from 2.333 to 2.671, as shown below. Figure 10 The diagram shows the mode field of the TE0 mode at the fourth end face. The effective refractive index for the TE1 mode increases from 1.915 to 2.335. Figure 11 The diagram shows the mode field of the TE1 mode at the fourth end face. The third adiabatic evolution section 33 is a width-gradient ridge waveguide structure, including a ridge waveguide with heights from h0 to h3, a bottom height of h2, and a ridge height of h3. The bottom completely overlaps with the second adiabatic evolution section 32 on the fourth end face. The bottom width gradually increases from the fourth end face along the first direction to the fifth end face, and the ridge width gradually increases from the fourth end face along the first direction to the fifth end face. Preferably, the effective refractive index of the third adiabatic evolution section 3 for the TE0 mode increases from 2.743 to 3.168, as shown below. Figure 12 The diagram shows the mode field of the TE0 mode at the fifth end face; the effective refractive index for the TE1 mode increases from 2.329 to 3.107, as shown below. Figure 13 The diagram shows the mode field of the TE1 mode at the fifth end face. The fourth mode conversion segment 34 is a width-gradient ridge waveguide structure, including a ridge waveguide with heights from h0 to h3, a bottom height of h2, and a ridge height of h3. It completely overlaps with the third adiabatic evolution segment 33 on the fifth end face. The bottom width remains constant from the fifth end face along the first direction, while the ridge width gradually narrows from the fifth end face along the first direction to the sixth end face. Preferably, the effective refractive index of the fourth mode conversion segment 34 for the TE0 mode decreases from 3.168 to 3.096, as shown below. Figure 14 The diagram shows the mode field of the TE0 mode at the sixth end face; when the TE1 mode optical field is input to the fourth mode conversion segment 34, mode field conversion is achieved through changes in refractive index distribution and waveguide structure, transforming it into the TM0 mode, as shown below. Figure 15 The diagram shows the mode field of the TM0 mode at the sixth end face. The convergence section 35 is a width-gradient ridge waveguide structure, including a ridge waveguide with heights from h0 to h3, a bottom height of h2, and a ridge height of h3. Its bottom partially overlaps with the fourth mode conversion section 34 on the sixth end face, and its ridge completely overlaps with the fourth mode conversion section 34 on the sixth end face. The bottom width gradually narrows from the sixth end face along the first direction to the seventh end face, and the ridge width also gradually narrows from the sixth end face along the first direction to the seventh end face, achieving the same width for both the bottom and ridge on the seventh end face. Preferably, the effective refractive index of the convergence section 35 for the TM0 mode decreases from 3.096 to 3.048, as shown below. Figure 16The diagram shows the mode field of the TE0 mode at the seventh end face. The effective refractive index for the TM0 mode decreases from 2.899 to 2.866. Figure 17 The diagram shown is the mode field diagram of the TM0 mode at the seventh end face.

[0013] The maximum thickness of the waveguide layer 3, made of deposited silicon, ranges from 330 nm to 500 nm. In this embodiment, after etching, h2 is preferably between 180 nm and 220 nm, and h3 is between 380 nm and 420 nm. More preferably, h2 is 200 nm and h3 is 400 nm.

[0014] It is important to note that the fabrication method used in this embodiment can employ CVD (Chemical Vapor Deposition) to deposit amorphous silicon material. Furthermore, the waveguide structure is constructed using a method that deposits amorphous silicon material, which is simple to fabricate and has low etching difficulty. It can replace the coupling portion in the front-end chip, significantly reducing the process and design complexity of the front-end optoelectronic integrated chip. Moreover, the amorphous silicon deposition process can utilize low-temperature deposition technology, requiring a substrate process temperature of less than or equal to 450 degrees Celsius, effectively protecting the functional integrity of the front-end optoelectronic integrated chip.

[0015] In this example, we consider a pure TE0, a pure TM0, or a mixed TE0 and TM0 fundamental mode. The optical output port is aligned along the first direction, the central axis along the second direction, and the first mode conversion segment is horizontally aligned upwards along the third direction. During coupling, the TE0 mode normally achieves low-loss transmission from the optical fiber to the 330nm to 500nm silicon waveguide via the optical waveguide. For the TM0 mode, due to refractive index matching, the first mode conversion segment first converts the TM0 mode to the TE1 mode. After adiabatic transmission through the second adiabatic evolution segment, the third adiabatic evolution segment couples the TE1 mode from the 180nm to 220nm thick silicon waveguide into the 330nm to 500nm thick silicon waveguide. The fourth mode conversion segment then converts the TE1 mode back to the TM0 mode, finally outputting from the convergence segment, completing the coupling. Figure 18 The figure shows the insertion loss caused by mode switching in this device. Furthermore, the thickness can be flexibly adjusted by controlling the deposition time. Combined with the aforementioned method for a polarization-insensitive end-coupled waveguide based on deposited silicon, it is possible to meet coupling requirements for different future scenarios and achieve efficient coupling.

[0016] In summary, this embodiment, based on a working method for a polarization-insensitive end-face coupled waveguide with deposited silicon and excellent back-end processes and deposition processes for deposited silicon materials, achieves integration with front-end optoelectronic chips without compromising performance. It is applicable to different front-end chips, demonstrating the versatility and flexibility of the present invention.

[0017] Example 2 This embodiment demonstrates the application of a polarization-insensitive end-face coupler on the SOI platform, and its specific structure is as follows: Figure 19 As shown, specifically: Along a third direction, it sequentially includes: a substrate layer 21, a cladding layer 22 disposed on the substrate layer 21, and a silicon waveguide layer 23 of the polarization-insensitive design provided by the present invention fabricated on the lower cladding layer 22; in this embodiment, preferably, the substrate layer 21 is a silicon substrate.

[0018] Furthermore, an upper cladding layer 24 is deposited on the aforementioned silicon waveguide layer 23 and connected to the lower cladding layer 22, completely enclosing the silicon waveguide layer 23 to achieve strong confinement of the optical field.

[0019] In this example, the optical output port is aligned along the first direction, the central axis along the second direction, and the mode conversion segment one is horizontally aligned upwards along the third direction. This device design possesses polarization insensitivity and a large bandwidth; therefore, high coupling efficiency can be achieved without the need for a polarization controller or on-chip polarization beam rotator. During coupling, the TE0 mode passes normally. For the TM0 mode, high coupling efficiency is maintained even after two mode conversions. The refractive index of the silicon waveguide layer 23 is greater than that of silicon dioxide, forming a low-high-low refractive index distribution structure. When light propagates in the first direction, it is not easily able to propagate upwards in the second or third direction, and will be completely confined around the silicon waveguide layer 23 structure, resulting in high coupling efficiency. Simultaneously, the thickness of the silicon waveguide layer 23 can be flexibly adjusted by controlling the fabrication time. Combined with the above-described method for a polarization-insensitive end-face coupled waveguide, coupling requirements for different future scenarios can be met, achieving highly efficient coupling.

[0020] In summary, this embodiment, based on a polarization-insensitive end-coupled waveguide on an SOI platform, enables simultaneous transmission of TE and TM substrate films, providing a new and efficient optical coupling scheme for polarization-insensitive systems. Furthermore, this embodiment avoids the use of polarization controllers or on-chip polarization splitters in the optical chip coupling system, which reduces additional insertion loss and eliminates the need to consider mode purity. This provides more options and fault tolerance for complex and variable scenarios in real-world environments.

[0021] Example 3 In the on-chip coupling structure of III-V heterogeneous integrated lasers, current solutions are mostly as follows: Figure 20 As shown, along the third direction, it includes, in sequence, a silicon substrate layer 51, a silicon dioxide substrate layer 52, a conventional industrial 220nm silicon waveguide layer 53, a silicon dioxide lower cladding layer 54, a conventional 400nm silicon coupling layer 55, an n-type InP layer 56, and a composite layer 57. The composite layer 57 specifically includes: a p-type InP 571 and an InP active region 572 symmetrically prepared along the central axis in the second direction, wherein the InP active region 572 is sandwiched on the central axis by the symmetrical p-type InP 571, and a gold metal electrode 573; the composite layer 57 is connected by an n-type InP layer 56.

[0022] And gold metal electrodes 58 covering the p-type InP571 and InP572.

[0023] Traditional III-V heterogeneous integrated lasers generate an optical field in the InP active region 572 by applying pressure to the metal electrodes 573 attached to the n-type InP56 and the metal electrodes 58 attached to the p-type InP571. To achieve sufficient gain and low loss, the InP active region 572 of the laser is typically thick, and the output optical field mode diameter is usually on the order of micrometers. However, the 220nm silicon layer used on traditional SOI platforms struggles to capture the light source produced by III-V heterogeneous integrated lasers. Furthermore, due to the thick core layer, the optical field produced by the laser is confined within the III-V group material, whose effective refractive index is typically close to 3.2. This is a severe mismatch with the effective refractive index of approximately 2.45 of the 220nm silicon layer, and the difference in propagation constant makes it even more difficult for the light source to couple into the waveguide layer. Therefore, it is often necessary to first couple the optical field from the laser into a conventional 400nm silicon coupling layer 55, and then achieve optical field conversion from the conventional 400nm silicon coupling layer 55 to the conventional industrial 220nm silicon waveguide layer 53 through interlayer coupling. However, this method has certain requirements for the process and also introduces additional losses.

[0024] This embodiment is based on the application of the polarization-insensitive end-face coupler waveguide described above, specifically as follows: like Figure 21 As shown, along the third direction, it includes, in sequence, a silicon substrate layer 61, a silicon dioxide substrate layer 62, a silicon waveguide layer 63, an n-type InP layer 64, and a composite layer 65; The composite layer 65 specifically includes: a p-type InP 651 symmetrically prepared along the central axis in the second direction, an InP active region 652 wherein the InP active region 652 is sandwiched on the central axis by the symmetrical p-type InP 651, and a gold metal electrode 653; the composite layer 65 is connected by an n-type InP layer 64.

[0025] And gold metal electrodes 66 covering the p-type InP651 and InP652.

[0026] Compared with the traditional method described above, in this embodiment, after the III-V heterogeneous integrated laser generates the light source, the effective refractive index of the relatively thick silicon waveguide layer is also around 3.4, which can better match the light field produced by the laser. Therefore, the light field can be directly captured by the polarization-insensitive end-face coupling device based on silicon waveguide provided by this invention and directly input into the optical system. It eliminates the need for evanescent wave coupling in traditional structures, reducing insertion loss while eliminating the interlayer alignment error problem of multilayer structures.

[0027] In summary, the polarization-insensitive end-coupled waveguide based on silicon waveguides provided in this embodiment offers an optical device solution for III-V heterogeneous integrated lasers, reducing optical coupling loss and improving the versatility of the device.

[0028] In the description of this application, it should be understood that the terms "upper", "lower", "first direction", "second direction", "third direction", "capture", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0029] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A polarization-insensitive end-coupling device based on a silicon waveguide, a first direction, a second direction, and a third direction being perpendicular to each other in a spatial coordinate system, characterized in that, comprises, in sequence from bottom to top along the third direction: a substrate layer (1), a lower cladding layer (2) deposited on the substrate layer (1), a silicon waveguide layer (3) deposited on the lower cladding layer (2), and an upper cladding layer (4); a top layer height of the lower cladding layer (2) is defined as h0=0; the waveguide layer (3) comprises, in sequence from bottom to top along the third direction, a height h1, a height h2, and a height h3; the upper cladding layer (4) is made on the silicon waveguide layer (3) and is connected with the lower cladding layer (2), completely wrapping the silicon waveguide layer (3) and forming a low-high-low refractive index distribution; wherein the silicon waveguide layer (3) comprises, in sequence along the first direction: a mode field adiabatic evolution section (30), a first mode conversion section (31), a second adiabatic evolution section (32), a third adiabatic evolution section (33), a fourth mode conversion section (34), and a converging section (35); the mode field adiabatic evolution section (30) comprises a strip waveguide with a height from h0 to h2, and a width gradually widening from a first end face to a second end face along the first direction; the first mode conversion section (31) comprises a ridge waveguide with a height from h0 to h2, a bottom height h1, and a ridge height h2, and is completely coincident with the mode field adiabatic evolution section (30) at the second end face, a bottom width gradually widening from the second end face to a third end face along the first direction, and a ridge width gradually narrowing from the second end face to the third end face along the first direction; the second adiabatic evolution section (32) comprises a ridge waveguide with a height from h0 to h2, a bottom height h1, and a ridge height h2, and is completely coincident with the first mode conversion section (31) at the third end face, a bottom width unchanged from the third end face along the first direction, and a ridge width gradually widening from the third end face to a fourth end face along the first direction, and the bottom and the ridge are of the same width at the fourth end face; the third adiabatic evolution section (33) comprises a ridge waveguide with a height from h0 to h3, a bottom height h2, and a ridge height h3, and is completely coincident with the second adiabatic evolution section (32) at the fourth end face, a bottom width gradually widening from the fourth end face to a fifth end face along the first direction, and a ridge width gradually widening from the fourth end face to the fifth end face along the first direction; the fourth mode conversion section (34) comprises a ridge waveguide with a height from h0 to h3, a bottom height h2, and a ridge height h3, and is completely coincident with the third adiabatic evolution section (33) at the fifth end face, a bottom width unchanged from the fifth end face along the first direction, and a ridge width gradually narrowing from the fifth end face to a sixth end face along the first direction; the converging section (35) comprises a ridge waveguide with a height from h0 to h3, a bottom height h2, and a ridge height h3, and is partially coincident with the fourth mode conversion section (34) at the sixth end face, and is completely coincident with the fourth mode conversion section (34) at the sixth end face, a bottom width gradually narrowing from the sixth end face to a seventh end face along the first direction, and a ridge width gradually narrowing from the sixth end face to the seventh end face along the first direction, and the bottom and the ridge are of the same width at the seventh end face.

2. The polarization-insensitive end-coupled device of claim 1, wherein, The material of the silicon waveguide layer (3) is amorphous silicon material or single crystal silicon material.

3. The polarization-insensitive end-coupled device of claim 1, wherein, The ridge width of the third adiabatic evolution section (33) is smaller than the bottom width at the fourth end face, and the ridge width of the third adiabatic evolution section (33) is smaller than the bottom width at the fifth end face.

4. The polarization-insensitive end-coupled device of claim 1, wherein, The ridge width of the fourth mode conversion section (34) on the sixth end surface is less than the bottom width.

5. The polarization-insensitive end-coupled device of claim 1, wherein, In operation, the method comprises: T1, after a pure TE0 or pure TM0 or mixed TE0 and TM0 base film is input into the first mode conversion section (31), the TE0 mode is normally transmitted and the TM0 mode is converted into a TE1 high-order mode for transmission; T2, after a TE0 mode or TE1 mode or mixed TE0 and TE1 mode is transmitted through the second mode conversion section (32) and input into the third mode conversion section (33), transmission between waveguides with different heights is realized; T3, the fourth mode conversion section (34) normally transmits the input TE0 mode and converts the TE1 mode into a TM0 mode, thereby realizing polarization-insensitive transmission.

6. A method of fabricating a polarization-insensitive end-coupling device based on a silicon waveguide according to any one of claims 1 to 5, characterized in that, The method comprises: S1, depositing silicon dioxide on the substrate layer (1) to form a lower cladding layer (2); S2, depositing a silicon waveguide material with a height of h3 on the lower cladding layer (2) and coating photoresist on the upper surface thereof, and forming the same through multiple mask etching; S3, after the photoresist is removed, the silicon waveguide layer (3) is formed.

7. The preparation method according to claim 6, when the silicon waveguide material is deposited silicon, the temperature in the deposition process in the S2 step is not more than 450 degrees Celsius.

8. The preparation method according to claim 6, after the photoresist is removed in the S3 step, the method further comprises: depositing silicon dioxide above the silicon waveguide layer (3) to form an upper cladding layer (4).

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