A broadband polarization control type power beam splitter based on SOI

Abstract

The application provides a broadband polarization control type power splitter based on SOI, which comprises a substrate, a silicon waveguide layer, a silicon nitride waveguide layer and a cladding layer, the silicon waveguide layer comprises an input waveguide, a subwavelength grating, an input tapered waveguide, a first reverse tapered waveguide and a second reverse tapered waveguide, a narrow strip waveguide, a third reverse tapered waveguide, an intermediate output waveguide and an S-shaped bending waveguide, the input waveguide is connected with the input tapered waveguide, the input tapered waveguide is connected with the first reverse tapered waveguide and the second reverse tapered waveguide through the subwavelength grating and is connected with two S-shaped bending waveguides, and the input tapered waveguide is connected with the narrow strip waveguide, the third reverse tapered waveguide and the intermediate output waveguide, the silicon nitride waveguide layer comprises a long strip waveguide, and light is input from the input waveguide and is output from the S-shaped bending waveguide or the intermediate output waveguide. The application realizes the functions of regulating the incident light of different polarization states and power splitting of one polarization state, has a large bandwidth, a high extinction ratio, a small insertion loss and a compact size.

Description

Technical Field

[0001] This invention belongs to the field of optical communication technology, specifically relating to a broadband polarization-controlled power beam splitter based on SOI. Background Technology

[0002] Silicon-on-insulator (SOI) is a promising platform. Its high refractive index contrast makes SOI-based devices highly effective at confining light, which is beneficial for reducing the size of optical waveguide devices and improving the integration density of photonic integrated circuits (PICs). In PICs, power beamsplitters, as a key component, have been widely used for optical power distribution. In recent years, many structures for designing power beamsplitters have been reported, including Y-branch, directional couplers, and multimode interference couplers. However, these schemes are highly sensitive to wavelength and polarization state, limiting their application in optical communication. To address this issue, one approach is to add polarization management devices, such as polarization beamsplitters or polarizers, before the power beamsplitter to ensure the separation of the two polarization states, but this is not conducive to further improving high-density photonic integration. Another approach is to simultaneously implement power beam splitting and polarization control functions in a single optical device, which helps simplify the structure and reduce the size of photonic integrated chips. Therefore, how to realize a small-size, wide-bandwidth, low-insertion-loss, and high-extinction-ratio polarization-controlled power beamsplitter is a pressing problem to be solved.

[0003] In recent years, subwavelength gratings (SWGs) have attracted much attention from researchers. Composed of alternating periods of high- and low-refractive-index materials with spacing much smaller than a wavelength, they can be considered as homogeneous media, thus their equivalent refractive index can be adjusted by changing the duty cycle. This structure provides new degrees of freedom for the design of power beamsplitters. SWGs can also provide strong, flat dispersion, a characteristic that enhances the bandwidth of devices. In addition, a silicon-on-nitride low-refractive-index enhancement waveguide (ALIG) structure has been proposed, consisting of silicon waveguides and silicon nitride waveguides; in which the TE mode is confined in a thin bottom silicon layer, and the TM mode is guided in a thick upper silicon nitride layer. Thanks to the independent control characteristics of the two modes, this structure can be used to construct polarization-controlled devices. Currently, there are no reports on polarization-tunable power beamsplitters that combine SWGs and ALIGs. Therefore, this invention proposes a broadband polarization-controlled power beamsplitter based on SOI, which can achieve the desired high-performance polarization-controlled power beamsplitter by simultaneously utilizing SWGs and ALIGs. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a broadband polarization-controlled power beam splitter based on SOI. This invention can solve the technical problems of large device size, high loss, narrow bandwidth, low extinction ratio, and lack of ability to simultaneously achieve polarization control and power beam splitting.

[0005] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0006] This invention provides a broadband polarization-controlled power beamsplitter based on SOI. The power beamsplitter includes, from bottom to top, a substrate, a silicon waveguide layer, a silicon nitride waveguide layer, and a cladding. The silicon waveguide layer includes an input waveguide, a subwavelength grating, an intermediate output waveguide, and two sets of S-shaped curved waveguides. The subwavelength grating includes a first subwavelength grating, a second subwavelength grating, and a third subwavelength grating and a fourth subwavelength grating arranged in a mirror-symmetric manner. An input tapered waveguide is located between the first and second subwavelength gratings, and a... A first reverse tapered waveguide is formed between the first and fourth subwavelength gratings, and a second reverse tapered waveguide is formed between the second and fourth subwavelength gratings. The input waveguide is connected to the input tapered waveguide, which is connected to the first and second reverse tapered waveguides via the first and second subwavelength gratings. The input tapered waveguide is also connected to the intermediate output waveguide. The first and second reverse tapered waveguides are respectively connected to two sets of S-shaped curved waveguides. The silicon nitride waveguide layer includes elongated waveguides distributed above the input waveguide, subwavelength gratings, and intermediate output waveguide. Light enters through the input waveguide and exits from either the S-shaped curved waveguide or the intermediate output waveguide.

[0007] Furthermore, the present invention also includes a narrow strip waveguide and a third reverse tapered waveguide; the narrow strip waveguide and the third reverse tapered waveguide are distributed between the input tapered waveguide and the intermediate output waveguide, and the input waveguide, the input tapered waveguide, the narrow strip waveguide, the third reverse tapered waveguide and the intermediate output waveguide are connected in sequence.

[0008] Furthermore, the input tapered waveguide is tapered along the direction of light transmission; the first reverse tapered waveguide, the second reverse tapered waveguide, and the third reverse tapered waveguide are all tapered against the direction of light transmission.

[0009] Furthermore, the input waveguide, input tapered waveguide, first reverse tapered waveguide, second reverse tapered waveguide, third reverse tapered waveguide, narrow strip waveguide, intermediate output waveguide, S-shaped curved waveguide, and subwavelength grating all have the same thickness.

[0010] Furthermore, the first and second subwavelength gratings have the same structure and are mirror-symmetrical about the input waveguide centerline; the third and fourth subwavelength gratings have the same structure and are distributed outside the first and second subwavelength gratings, mirror-symmetrical about the input waveguide centerline.

[0011] Furthermore, the introduction of a subwavelength grating between the input tapered waveguide and the first and second reverse tapered waveguides can enhance mode coupling and reduce losses introduced by mode changes.

[0012] Furthermore, the two sets of S-shaped curved waveguides are mirror-symmetric about the input waveguide centerline.

[0013] Furthermore, the first and second subwavelength gratings have the same structure and are arranged vertically along the direction of light transmission; the third and fourth subwavelength gratings have the same structure and are arranged vertically along the direction of light transmission.

[0014] Furthermore, the substrate is a silicon dioxide substrate, and the cladding is a silicon dioxide cladding.

[0015] Furthermore, in the subwavelength grating structure, the high-refractive-index material is silicon, and the low-refractive-index material is silicon dioxide.

[0016] Beneficial effects

[0017] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0018] This invention integrates polarization control and power beam splitting into a single device, eliminating the need for cascading polarization control and power beam splitting devices. A subwavelength grating is used to enhance mode coupling between the input tapered waveguide and the reverse tapered waveguide, achieving efficient power beam splitting in the TE mode. For the introduced low-refractive-index enhancement waveguide structure, the TE mode can be well confined within the first silicon waveguide layer, while the TM mode is confined within the second silicon nitride waveguide layer, thus realizing polarization control. Furthermore, the polarization-controlled power beam splitter of this invention can be interconnected with other optical devices for use in polarization multiplexing systems, optical switches, modulators, etc. As an integrable, miniaturized device, this invention possesses the characteristics and advantages of low insertion loss, wide operating bandwidth, low loss, and high extinction ratio. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of the SOI-based broadband polarization-controlled power beam splitter of the present invention.

[0020] Figure 2 This is a schematic diagram of the silicon waveguide layer structure of the SOI-based broadband polarization-controlled power beam splitter of the present invention.

[0021] Figure 3 This is a schematic cross-sectional view of the input waveguide of the SOI-based broadband polarization-controlled power beam splitter of the present invention.

[0022] Figure 4 A schematic diagram of the optical path transmission simulation results for the polarization-controlled power beam splitter of this invention, which inputs TE mode light;

[0023] Figure 5 A schematic diagram of the optical path transmission simulation results for the polarization-controlled power beam splitter of this invention, which inputs TM mode light;

[0024] Figure 6 A schematic diagram of insertion loss and extinction ratio in the 1450–1650 nm band when TE mode and TM mode light are input into the polarization-controlled power beam splitter of this invention;

[0025] The labels in the attached diagram are:

[0026] 1. Input waveguide; 2. Input tapered waveguide; 3. Reverse tapered waveguide; 3-1. First reverse tapered waveguide; 3-2. Second reverse tapered waveguide; 3-3. Third reverse tapered waveguide; 4. Narrow strip waveguide; 5. Intermediate output waveguide; 6. S-shaped bend waveguide; 6-1. First S-shaped bend waveguide; 6-2. Second S-shaped bend waveguide; 7. Subwavelength grating; 7-1. First subwavelength grating; 7-2. Second subwavelength grating; 7-3. Third subwavelength grating; 7-4. Fourth subwavelength grating; 8. Long strip waveguide; 9. Silica substrate; 10. Silica cladding. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] like Figures 1-3 As shown, this embodiment of the invention provides a broadband polarization-controlled power beam splitter based on SOI. The power beam splitter includes a silicon dioxide substrate 9, a silicon waveguide layer, a silicon nitride waveguide layer, and a silicon dioxide cladding layer distributed from bottom to top. Figure 3 In the middle, the top layer and the bottom layer represent the silicon dioxide substrate 9 and the silicon dioxide cladding 10, respectively, which are used to protect the silicon waveguide layer and the silicon nitride waveguide layer in between.

[0030] Specifically, the silicon waveguide layer includes an input waveguide 1, a subwavelength grating 7, a narrow strip waveguide 4, a third reverse tapered waveguide 3-3, an intermediate output waveguide 5, and two sets of S-shaped curved waveguides 6 (a first S-shaped curved waveguide 6-1 and a second S-shaped curved waveguide 6-2). The subwavelength grating 7 includes a first subwavelength grating 7-1 and a second subwavelength grating 7-2 that are mirror-symmetrical, and a third subwavelength grating 7-3 and a fourth subwavelength grating 7-4 that are mirror-symmetrical. The input tapered waveguide 2 is located between the first subwavelength grating 7-1 and the second subwavelength grating 7-2; the first reverse tapered waveguide 3-1 is located between the first subwavelength grating 7-1 and the third subwavelength grating 7-3; and the second reverse tapered waveguide 3-2 is located between the second subwavelength grating 7-2 and the fourth subwavelength grating 7-4. Input waveguide 1 is connected to input tapered waveguide 2. Input tapered waveguide 2 is connected to first reverse tapered waveguide 3-1 and second reverse tapered waveguide 3-2 through first subwavelength grating 7-1 and second subwavelength grating 7-2, respectively. Input tapered waveguide 2 is also connected to narrow strip waveguide 4, third reverse tapered waveguide 3-3 and intermediate output waveguide 5 in sequence. First reverse tapered waveguide 3-1 and second reverse tapered waveguide 3-2 are connected to first S-shaped curved waveguide 6-1 and second S-shaped curved waveguide 6-2, respectively. First S-shaped curved waveguide 6-1 is used to receive the light transmitted by first reverse tapered waveguide 3-1 and output it. Second S-shaped curved waveguide 6-2 is used to receive the light transmitted by second reverse tapered waveguide 3-2 and output it. The silicon nitride waveguide layer includes a strip waveguide 8, which is located in the second layer. That is, the strip waveguide 8 is distributed above the input waveguide 1, the subwavelength grating 7, and the intermediate output waveguide 5, and the width of the strip waveguide 8 remains constant. In application, light is input through the input waveguide 1 and output from either the S-shaped curved waveguide 6 or the intermediate output waveguide 5.

[0031] In this embodiment, refer to Figures 1-2 The input tapered waveguide 2 is tapered along the direction of light transmission, and the first reverse tapered waveguide 3-1, the second reverse tapered waveguide 3-2 and the third reverse tapered waveguide 3-3 are all tapered against the direction of light transmission.

[0032] In this embodiment, the input waveguide 1, input tapered waveguide 2, first reverse tapered waveguide 3-1, second reverse tapered waveguide 3-2, third reverse tapered waveguide 3-3, narrow strip waveguide 4, intermediate output waveguide 5, first S-shaped curved waveguide 6-1, second S-shaped curved waveguide 6-2 and subwavelength grating 7 have the same thickness.

[0033] In this embodiment, the first subwavelength grating 7-1 and the second subwavelength grating 7-2 have identical structures and are arranged perpendicularly along the direction of light transmission. The third subwavelength grating 7-3 and the fourth subwavelength grating 7-4 have identical structures and are arranged perpendicularly along the direction of light transmission. The first subwavelength grating 7-1 and the second subwavelength grating 7-2 are mirror-symmetric about the centerline of the input waveguide 1. The third subwavelength grating 7-3 is distributed outside the first subwavelength grating 7-1, and the fourth subwavelength grating 7-4 is distributed outside the second subwavelength grating 7-2. The third subwavelength grating 7-3 and the fourth subwavelength grating 7-4 are mirror-symmetric about the centerline of the input waveguide 1. The first S-shaped curved waveguide 6-1 and the second S-shaped curved waveguide 6-2 are mirror-symmetric about the centerline of the input waveguide 1.

[0034] Application principle of this invention:

[0035] In the SOI-based broadband polarization-controlled power beam splitter of this invention, the TE mode is confined to the first layer (silicon waveguide layer), and the TM mode is confined to the second layer (silicon nitride waveguide layer). The TE and TM modes propagate independently in the two separate layers, and their propagation in these independent layers does not affect each other. The entire device is surrounded by a silicon dioxide cladding.

[0036] For the input TE mode, which propagates in the silicon waveguide layer, the mode cannot be effectively supported when the width of the input tapered waveguide 2 narrows. Therefore, it transitions to the subwavelength grating region. Then, the mode seeks other high refractive index regions to support its own mode field, and is further coupled to the adjacent first reverse tapered waveguide 3-1 and second reverse tapered waveguide 3-2 through the subwavelength grating. Finally, it is output from the first S-shaped curved waveguide 6-1 and the second S-shaped curved waveguide 6-2, respectively, and the power of the two output ports is equal.

[0037] The input TM mode is confined in the second layer of silicon nitride waveguide. Thanks to the connection between the narrow strip waveguide 4 and the third reverse tapered waveguide 3-3, the TM mode can be output from the middle output waveguide 5 with low loss to achieve polarization control. At the same time, the transmission process of the TM mode is not affected by the first layer of silicon waveguide.

[0038] Example 2

[0039] The purpose of this embodiment is to verify the technical effect of the present invention. The parameters of the power beam splitter in Embodiment 1 are limited, and a simulation experiment is conducted.

[0040] This embodiment uses the finite-difference time-domain method for calculation and analysis. The main parameters used in the simulation calculation include: the thickness of the silicon waveguide is 220nm; the period of the subwavelength grating 7 is 244nm and the duty cycle is 0.5; the length of the input tapered waveguide 2 is 1μm and the width gradually narrows from 500nm to 250nm; the length of the first reverse tapered waveguide 3-1 and the second reverse tapered waveguide 3-2 is 2.9μm and the width gradually widens from 255nm to 500nm; the length of the narrow strip waveguide 4 is 2.4μm and the width is 250nm; the length of the third reverse tapered waveguide 3-3 is 1.5μm and the width gradually widens from 250nm to 500nm. The spacing between the input tapered waveguide 2 and the first reverse tapered waveguide 3-1 and the second reverse tapered waveguide 3-2 is 260 nm; the thickness of the silicon dioxide substrate 9 and the silicon dioxide cladding 10 is 3 μm; the lateral offset of the first S-shaped curved waveguide 6-1 and the longitudinal offset of the second S-shaped curved waveguide 6-2 are 6 μm and 2 μm, respectively.

[0041] When light is input from input waveguide 1 in TE mode, the calculated optical field transmission mode is as follows: Figure 4 As shown, the optical energy is input from the input waveguide 1, passes through the input tapered waveguide 2, undergoes a slight change in the optical mode distribution, and is coupled into the first reverse tapered waveguide 3-1 and the second reverse tapered waveguide 3-2, and finally output from the first S-shaped curved waveguide 6-1 and the second S-shaped curved waveguide 6-2, respectively.

[0042] When light is input from input waveguide 1 in TM mode, the optical field transmission mode is calculated as follows: Figure 5 As shown, the TM mode is completely unaffected by the first silicon waveguide layer, always propagating within the second silicon nitride waveguide layer, and ultimately outputting from the middle output waveguide 5.

[0043] Specifically, when light is input into this polarization-controlled power beam splitter in TE and TM modes, the transmission spectrum obtained is as follows: Figure 6 As shown, insertion loss TE (insertion loss TM) represents the total energy of the first S-shaped curved waveguide 6-1, the second S-shaped curved waveguide 6-2, and the intermediate output waveguide 5 when inputting in TE mode (TM mode); extinction ratio TE represents the ratio of the energy of the first S-shaped curved waveguide 6-1 and the second S-shaped curved waveguide 6-2 to the energy of the intermediate output waveguide 5 when inputting in TE mode; extinction ratio TM represents the ratio of the energy of the intermediate output waveguide 5 to the energy of the first S-shaped curved waveguide 6-1 and the second S-shaped curved waveguide 6-2 when inputting in TM mode. Figure 6 It can be seen that in the wavelength range of 1450nm to 1650nm of the input light, the device insertion loss is about 0.3dB, the extinction ratio is more than 15dB, and the bandwidth is more than 190nm.

[0044] In summary, the SOI-based broadband polarization-controlled power beam splitter provided by this invention can achieve the functions of separating different polarization states and power beam splitting. Moreover, it has low insertion loss, high extinction ratio, and balanced power beam splitting within a 190nm operating bandwidth, possessing the main characteristics of a polarization-controlled power beam splitter. As an SOI-based broadband polarization-controlled power beam splitter, it has stronger functionality than existing technologies and can be applied to polarization multiplexing systems, optical switches, modulators, and coherent optical communications.

[0045] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A broadband polarization-controlled power beam splitter based on SOI, characterized in that, The power beam splitter comprises, from bottom to top, a substrate, a silicon waveguide layer, a silicon nitride waveguide layer, and a cladding layer; The silicon waveguide layer includes an input waveguide (1), a subwavelength grating (7), an intermediate output waveguide (5), and two sets of S-shaped curved waveguides (6); the subwavelength grating (7) includes a first subwavelength grating (7-1), a second subwavelength grating (7-2), a third subwavelength grating (7-3), and a fourth subwavelength grating (7-4); the first subwavelength grating (7-1) and the second subwavelength grating (7-2) form an input tapered waveguide (2), the first subwavelength grating (7-1) and the third subwavelength grating (7-3) form a first reverse tapered waveguide (3-1), and the second subwavelength grating (7-2) and the fourth subwavelength grating (7-4) form a second reverse tapered waveguide (3-2); The input waveguide (1) is connected to the input tapered waveguide (2). The input tapered waveguide (2) is connected to the first reverse tapered waveguide (3-1) and the second reverse tapered waveguide (3-2) through the first subwavelength grating (7-1) and the second subwavelength grating (7-2). The input tapered waveguide (2) is connected to the intermediate output waveguide (5). The first reverse tapered waveguide (3-1) and the second reverse tapered waveguide (3-2) are respectively connected to two sets of S-shaped curved waveguides (6). The silicon nitride waveguide layer includes a strip waveguide (8), which is distributed above the input waveguide (1), the subwavelength grating (7) and the intermediate output waveguide (5); It also includes a narrow strip waveguide (4) and a third reverse conical waveguide (3-3). The narrow strip waveguide (4) and the third reverse tapered waveguide (3-3) are distributed between the input tapered waveguide (2) and the intermediate output waveguide (5), and the input waveguide (1), the input tapered waveguide (2), the narrow strip waveguide (4), the third reverse tapered waveguide (3-3) and the intermediate output waveguide (5) are connected in sequence; Among them, the subwavelength grating (7) has a period of 244nm and a duty cycle of 0.5; the input conical waveguide (2) has a length of 1μm and a width that gradually narrows from 500nm to 250nm; the first reverse conical waveguide (3-1) and the second reverse conical waveguide (3-2) have a length of 2.9μm and a width that gradually widens from 255nm to 500nm; the narrow strip waveguide (4) has a length of 2.4μm and a width of 250nm; the third reverse conical waveguide (3-3) has a length of 1.5μm and a width that gradually widens from 250nm to 500nm; the interval between the input conical waveguide (2) and the first reverse conical waveguide (3-1) and the second reverse conical waveguide (3-2) is 260nm; the lateral offset of the first S-shaped curved waveguide (6-1) and the longitudinal offset of the second S-shaped curved waveguide (6-2) are 6μm and 2μm, respectively.

2. The broadband polarization-controlled power beam splitter based on SOI according to claim 1, characterized in that, The input tapered waveguide (2) is tapered along the direction of light transmission; The first reverse tapered waveguide (3-1), the second reverse tapered waveguide (3-2), and the third reverse tapered waveguide (3-3) are all tapered in the opposite direction of light transmission.

3. The broadband polarization-controlled power beam splitter based on SOI according to claim 1, characterized in that, The input waveguide (1), input tapered waveguide (2), first reverse tapered waveguide (3-1), second reverse tapered waveguide (3-2), third reverse tapered waveguide (3-3), narrow strip waveguide (4), intermediate output waveguide (5), S-shaped curved waveguide (6) and subwavelength grating (7) have the same thickness.

4. The broadband polarization-controlled power beam splitter based on SOI according to claim 1, characterized in that, The first subwavelength grating (7-1) and the second subwavelength grating (7-2) have the same structure and are mirror-symmetrical about the centerline of the input waveguide (1); The third subwavelength grating (7-3) and the fourth subwavelength grating (7-4) have the same structure. The third subwavelength grating (7-3) and the fourth subwavelength grating (7-4) are distributed outside the first subwavelength grating (7-1) and the second subwavelength grating (7-2), and are mirror-symmetrical about the centerline of the input waveguide (1).

5. The broadband polarization-controlled power beam splitter based on SOI according to claim 1, characterized in that, The two sets of S-shaped curved waveguides (6) are mirror-symmetric about the centerline of the input waveguide (1).

6. The broadband polarization-controlled power beam splitter based on SOI according to claim 1, characterized in that, The first subwavelength grating (7-1), the second subwavelength grating (7-2), the third subwavelength grating (7-3), and the fourth subwavelength grating (7-4) are all arranged vertically along the direction of light transmission.

7. The broadband polarization-controlled power beam splitter based on SOI according to claim 1, characterized in that, The substrate is a silicon dioxide substrate, and the cladding is a silicon dioxide cladding.

8. The broadband polarization-controlled power beam splitter based on SOI according to claim 1, characterized in that, The high-refractive-index material in the subwavelength grating (7) structure is silicon, and the low-refractive-index material is silicon dioxide.

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