A large-bandwidth optical splitter with adjustable splitting ratio based on subwavelength gratings

Abstract

The application discloses a large-bandwidth silicon-based optical splitter with adjustable splitting ratio based on a subwavelength grating structure. The device comprises a first-stage 1*2 multimode interference coupler (I), a thermal phase shifter (II) and a second-stage 2*2 multimode interference coupler (III). A first input waveguide is connected with two arms of the thermal phase shifter through the first-stage 1*2 multimode interference coupler, the two arms of the thermal phase shifter are connected with the second-stage 2*2 multimode interference coupler respectively, and the second-stage 2*2 multimode interference coupler is connected with a first output waveguide and a second output waveguide respectively. The thermal phase shifter comprises two phase-shifting areas composed of a subwavelength grating wide waveguide and a silicon continuous wide waveguide, and a metal electrode is arranged above the two phase-shifting areas. The application realizes the large-bandwidth optical splitter with adjustable splitting ratio, and has the advantages of high performance, simple process and easy expansion.

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic devices, specifically designing a wide-bandwidth optical beam splitter with adjustable splitting ratio based on a subwavelength grating. Background Technology

[0002] Optical distribution networks are a crucial component of fiber optic network systems, providing optical transmission channels and enabling bidirectional transmission of optical signals. Optical beamsplitters are the most critical devices in optical distribution networks, used to distribute power between different transmission paths. Unequal beam splitting schemes are currently the mainstream fast pre-linking solution for optical distribution networks, showing great application potential in the industry market. Therefore, optical beamsplitters with freely adjustable splitting ratios are particularly important. Existing adjustable splitting ratio optical beamsplitters are based on Mach-Zehnder interferometer structures. By heating one arm of the Mach-Zehnder interferometer, the refractive index of the waveguide is changed, introducing a phase difference and thus altering the output optical power. However, this structure exhibits significant wavelength sensitivity, supporting only a wavelength range of 80–100 nm. To cover the entire optical communication band, cascading is required, greatly increasing the complexity of the devices and the difficulty of adjusting the splitting ratio. Summary of the Invention

[0003] The purpose of this invention is to address the shortcomings of existing technologies by proposing a high-bandwidth optical beamsplitter with adjustable splitting ratio based on a subwavelength grating. This invention utilizes a subwavelength grating structure to realize a high-bandwidth multimode interference coupler and a thermally modulated phase shifter, thereby achieving the high-bandwidth characteristics of the adjustable-split-ratio optical beamsplitter while reducing structural complexity and the difficulty of splitting ratio control.

[0004] This invention comprises a two-stage coupler and a thermally modulated phase shifter. The first-stage coupler is a subwavelength grating 1×2 multimode interference coupler, and the second-stage coupler is a 2×2 multimode interference coupler. The thermally modulated phase shifter includes two identical, centrally symmetrical phase-shifting regions. The first input waveguide is connected to the two arms of the thermally modulated phase shifter (II) via the first-stage 1×2 multimode interference coupler (I). The two arms of the thermally modulated phase shifter (II) are then connected to the second-stage 2×2 multimode interference coupler (III), which is subsequently connected to the first output waveguide and the second output waveguide.

[0005] The first-stage 1×2 multimode interference coupler (I) adopts a subwavelength grating structure, which greatly expands the device's supported bandwidth. Specifically, it includes an input transition waveguide, a first subwavelength grating multimode interference region, a first output transition waveguide, and a second output transition waveguide. The signal light input from the input waveguide will be split into two beams of signal light with equal phase and intensity by the aforementioned multimode interference coupler, and then input to the two arms of the thermally modulated phase shifter, respectively.

[0006] The thermally tunable phase shifter includes a first phase shifting region (a) and a second phase shifting region (b). The lower waveguide arm of the first phase shifting region is composed of a subwavelength grating wide waveguide, including a third input transition waveguide, a subwavelength grating wide waveguide, and a fifth output transition waveguide. The upper waveguide arm of the first phase shifting region is composed of a continuous silicon wide waveguide, including an input tapered waveguide with gradually increasing width, a continuous silicon wide waveguide, and an output tapered waveguide with gradually decreasing width, wherein the width of the continuous silicon wide waveguide is equal to that of the subwavelength grating wide waveguide. The upper waveguide arm of the second phase shifting region has the same structure as the lower waveguide arm of the first phase shifting region, and the lower waveguide arm of the second phase shifting region has the same structure as the upper waveguide arm of the first phase shifting region. The two centrally symmetrical phase shifting regions can eliminate the initial phase difference and loss difference between the two waveguide arms of the thermally tunable phase shifter. Therefore, in the initial state, the two signal beams output by the thermally tunable phase shifter have equal phase and intensity.

[0007] Above the two phase-shifting regions are metal heating electrodes with identical structure and parameters. When a current is introduced to heat the electrodes, the two wide waveguides symmetrically positioned on both sides of the electrodes will rise in temperature by an equal amount. The effective refractive index change of the subwavelength grating wide waveguide is less than that of the continuous silicon wide waveguide, thus introducing a phase difference between the two waveguide arms. Heating the first metal electrode with injected current can introduce a positive phase change into the two waveguide arms, while heating the second metal electrode with injected current can introduce a negative phase change. The phase difference between the two signal beams output from the phase-shifting region structure during the heating process is wavelength insensitive. The two signal beams are then input to a second-stage 2×2 multimode interference coupler.

[0008] The second-stage 2×2 multimode interference coupler (III) employs a subwavelength grating structure, specifically including a first input transition waveguide, a second input transition waveguide, a second subwavelength grating multimode interference region, a third output transition waveguide, and a fourth output transition waveguide. The first, second, third, and fourth input transition waveguides have the same structure, parameters, and function. The first and second input transition waveguides are symmetrically distributed around the middle of the starting end of the multimode interference region, while the third and fourth output transition waveguides are symmetrically distributed around the center of the ending end of the multimode interference region. The signal light input via the first and second input transition waveguides will be split and interfered in the multimode interference region, resulting in two signal lights of different intensities being output via the third and fourth output transition waveguides.

[0009] Because the first-stage 1×2 multimode interference coupler, the second-stage 2×2 multimode interference coupler, and the thermally modulated phase shifter are all wavelength-insensitive devices, the adjustable beam splitter is also wavelength-insensitive and can cover the entire optical communication band from 1260 to 1660 nm.

[0010] The beneficial effects of this invention are:

[0011] The adjustable splitting ratio, high-bandwidth optical beam splitter based on a subwavelength grating employs a subwavelength grating structure with low wavelength sensitivity, supporting the entire optical communication band; it also has low additional loss and can be cascaded to achieve multi-stage controllable beam splitting.

[0012] The large-bandwidth optical beam splitter with adjustable splitting ratio based on subwavelength grating has a simple structure, the waveguide structure only requires one etching, it is compatible with CMOS technology, and does not require additional manufacturing processes.

[0013] The adjustable splitting ratio wide-bandwidth optical beam splitter based on a subwavelength grating has a simple splitting ratio control method, requires low operating current, and has high reliability. Attached Figure Description

[0014] Figure 1 A schematic diagram of the large bandwidth optical beam splitter with adjustable splitting ratio based on a subwavelength grating according to the present invention is provided.

[0015] Figure 2 A schematic diagram of the structure of the first-stage subwavelength grating 1×2 multimode interference coupler of the present invention is given;

[0016] Figure 3 A schematic diagram of the structure of the second-stage subwavelength grating 2×2 multimode interference coupler of the present invention is given;

[0017] Figure 4 A schematic diagram of the structure of the first phase-shifting region of the thermally adjustable phase shifter of the present invention is provided;

[0018] Figure 5 A cross-sectional schematic diagram of the first phase-shifting region of the thermally adjustable phase shifter of the present invention is provided;

[0019] Figure 6 The transmission spectra of the beam splitter under different splitting ratios are given.

[0020] In the figure: I, First-stage subwavelength grating 1×2 multimode interference coupler; II, Thermally tuned phase shifter; III, Second-stage subwavelength grating 2×2 multimode interference coupler; 21, First phase shifting region; 22, Second phase shifting region; 11, Input transition waveguide; 12, First subwavelength grating multimode interference region; 13, First output transition waveguide; 14, Second output transition waveguide; 31, First input transition waveguide; 32, Second input transition waveguide; 33, Second subwavelength grating multimode interference region; 34, Third output transition waveguide; 35, Fourth output transition waveguide; 211, Input tapered waveguide; 212, Third input transition waveguide; 213, Continuous silicon wide waveguide; 214, Subwavelength grating wide waveguide; 215, Output tapered waveguide; 216, Fifth output transition waveguide; 41, First metal heating electrode; 42, Second metal heating electrode. Detailed Implementation

[0021] The invention will be further described below with reference to the accompanying drawings and an implementation example of an end-face coupler for a silicon waveguide array covering SU-8 cladding based on refractive index modulation.

[0022] like Figure 1 , Figure 2 , Figure 3 As shown, this invention consists of a two-stage coupler and a thermally modulated phase shifter. The first-stage coupler is a first-stage subwavelength grating 1×2 multimode interference coupler (I), and the second-stage coupler is a second-stage subwavelength grating 2×2 multimode interference coupler (III). The thermally modulated phase shifter (II) includes two identical, centrally symmetrical phase-shifting regions. The first input waveguide is connected to two arms at one end of the thermally modulated phase shifter (II) via the first-stage 1×2 multimode interference coupler (I). The two arms of the thermally modulated phase shifter (II) are then connected to the second-stage 2×2 multimode interference coupler (III), which in turn is connected to the first output waveguide and the second output waveguide.

[0023] like Figure 2 As shown, the first-stage subwavelength grating 1×2 multimode interference coupler (I) adopts a subwavelength grating structure, which greatly expands the device's supported bandwidth. Specifically, it includes an input transition waveguide 11, a first subwavelength grating multimode interference region 12, a first output transition waveguide 13, and a second output transition waveguide 14. The signal light input to the input waveguide will be split into two beams of signal light with equal phase and intensity by the aforementioned multimode interference coupler, and then input to the two arms of the thermally modulated phase shifter (II) respectively.

[0024] The thermally adjustable phase shifter includes a first phase shift region 21 and a second phase shift region 22.

[0025] The lower waveguide arm of the first phase-shifting region 21 includes a subwavelength grating wide waveguide 214, specifically comprising a third input transition waveguide 212, a subwavelength grating wide waveguide 214, and a fifth output transition waveguide 216. The upper waveguide arm of the first phase-shifting region 21 includes a continuous silicon wide waveguide 213, specifically comprising an input tapered waveguide 211 with gradually increasing width, a continuous silicon wide waveguide 213, and an output tapered waveguide 215 with gradually decreasing width, wherein the continuous silicon wide waveguide 213 has the same width as the subwavelength grating wide waveguide 214.

[0026] The upper waveguide arm of the second phase shift region 22 has the same structure as the lower waveguide arm of the first phase shift region 21, and the lower waveguide arm of the second phase shift region 22 has the same structure as the upper waveguide arm of the first phase shift region 21.

[0027] The two centrally symmetrical second phase shift regions 22 and the first phase shift region 21 can eliminate the initial phase difference and loss difference between the two waveguide arms of the thermally modulated phase shifter. Therefore, in the initial state, the two signal beams output by the thermally modulated phase shifter have equal phase and intensity.

[0028] Both the second phase-shifting region 22 and the first phase-shifting region 21 are equipped with metal heating electrodes of identical structure and parameters. When a current is introduced to the metal heating electrodes, the two wide waveguides symmetrically positioned on both sides of the metal heating electrodes will rise in temperature by the same amount. The effective refractive index change of the subwavelength grating wide waveguide 214 is less than the effective refractive index change of the continuous silicon wide waveguide 213, thereby introducing a phase difference between the two waveguide arms. Heating the first metal heating electrode 41 by injecting current can introduce a positive phase change to the two waveguide arms, and heating the second metal heating electrode 42 by injecting current can introduce a negative phase change to the two waveguide arms. The phase-shifting region structure makes the phase change difference between the two output signal beams during the heating process wavelength insensitive. The two signal beams are then input into a second-stage 2×2 multimode interference coupler.

[0029] like Figure 3 As shown, the second-stage 2×2 multimode interference coupler (III) adopts a subwavelength grating structure, specifically including a first input transition waveguide 31, a second input transition waveguide 32, a second subwavelength grating multimode interference region 33, a third output transition waveguide 34, and a fourth output transition waveguide 35. The first input transition waveguide 31, the second input transition waveguide 32, the third output transition waveguide 34, and the fourth output transition waveguide 35 have the same structure, parameters, and function. The first input transition waveguide 31 and the second input transition waveguide 32 are symmetrically distributed around the middle of the starting end of the second subwavelength grating multimode interference region, and the third output transition waveguide 34 and the fourth output transition waveguide 35 are symmetrically distributed around the middle of the ending end of the second subwavelength grating multimode interference region. After the signal light input through the first input transition waveguide 31 and the second input transition waveguide 32 is split, interference will occur in the second subwavelength grating multimode interference region 33, thereby outputting two signal lights with different intensities through the third output transition waveguide 34 and the fourth output transition waveguide 35.

[0030] Because the first-stage 1×2 multimode interference coupler, the second-stage 2×2 multimode interference coupler, and the thermally modulated phase shifter are all wavelength-insensitive devices, the adjustable beam splitter is also wavelength-insensitive and can cover the entire optical communication band from 1260 to 1660 nm. Example

[0031] A silicon nanowire waveguide based on silicon-on-insulator (SOI) material was selected. Its core layer is made of silicon with a thickness of 220 nm, a refractive index of 3.478 at 25℃, and a refractive index temperature coefficient of 1.84 × 10⁻⁶.-4 / K; the lower cladding is a 3μm thick silicon dioxide insulating layer with a refractive index of 1.444; the upper cladding is a 2μm thick silicon dioxide insulating layer with a refractive index of 1.444. In this embodiment, all connecting waveguides have a width of 500nm, each subwavelength grating structure has a period of 200nm, a duty cycle of 50%, and the input waveguide receives TE mode signal light.

[0032] The first-stage 1×2 subwavelength grating multimode interferometer has a multimode interference region width of 4 μm and a length of 5.6 μm; the input transition waveguide length is 10 μm, the maximum width of the subwavelength grating structure is 1.9 μm, and the minimum width of the input tapered waveguide is 50 nm; the output transition waveguide length is 10 μm, the maximum width of the subwavelength grating structure is 1.6 μm, the minimum width of the output tapered waveguide is 50 nm, and the output transition waveguide spacing is 2.1 μm.

[0033] The second-stage 2×2 subwavelength grating multimode interferometer has a multimode interference region width of 3.4 μm and a length of 17 μm; the transition waveguide length is 10 μm; the maximum width of the subwavelength grating structure is 1.3 μm; the minimum width of the tapered waveguide is 50 nm; and the transition waveguide spacing is 2.1 μm.

[0034] The subwavelength grating wide waveguide and silicon wide waveguide of the thermally modulated phase shifter are both 0.75 μm wide and 70 μm long, with a waveguide spacing of 2.1 μm and a transition waveguide length of 5 μm; the metal heating electrode is 2.1 μm wide and 50 μm long, and is disposed above the silicon dioxide cladding. Example

[0035] Beam Splitter 1: There is an existing tunable beam splitter with a waveguide-type Mach-Zehnder interferometer structure. By heating one arm of the Mach-Zehnder interferometer, the refractive index of the waveguide is changed, introducing a phase difference and thus changing the output optical power. However, it can only support a wavelength range of 80nm and cannot cover the all-optical communication band of 1260-1660nm.

[0036] Beam splitter 2: There is a planar optical waveguide type optical beam splitter that can cover the all-optical communication band of 1260-1660nm, but it can only achieve a specific splitting ratio, such as 1:1 splitting, and its splitting ratio is fixed and cannot be adjusted. Example

[0037] like Figure 4 As shown, based on the specific structure of Embodiment 1, the beam splitter of the present invention specifically achieves large-bandwidth beam splitting ratio control as follows:

[0038] The signal light input from the input waveguide passes through a first-stage 1×2 subwavelength grating multimode interferometer and is split into two beams of equal phase and intensity, which are then input into the thermally modulated phase-shifting region. Without applying a control current, the phase difference between the two output beams from the thermally modulated phase shifter is 0. After interference in the second-stage 2×2 multimode interferometer coupler, the two output beams have equal intensity, resulting in a splitting ratio of 50:50. Applying a control current to the metal electrodes of the first phase-shifting region to heat the waveguide causes a phase difference that increases with temperature between the two output beams. After interference in the second-stage 2×2 multimode interferometer coupler, the intensity of the signal light output from the first output waveguide is greater than that output from the first output waveguide. When the phase difference equals π / 2, the splitting ratio is 100:0. When a regulating current is applied to the metal electrode of the second phase-shifting region to heat the waveguide, the two signal lights output by the thermally modulated phase shifter will have a phase difference that decreases with temperature. After interference occurs in the second-stage 2×2 multimode interference coupler, the light intensity of the signal light output from the first output waveguide is less than that of the signal light output from the first output waveguide. When the phase difference is equal to -π / 2, the splitting ratio is 0:100.

[0039] The above embodiments are used to explain and illustrate the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A high-bandwidth optical beamsplitter with adjustable splitting ratio based on a subwavelength grating, characterized in that, By utilizing a subwavelength grating structure, a high-bandwidth multimode interference coupler and a thermally modulated phase shifter are realized, thereby achieving the high-bandwidth characteristics of an adjustable beam splitter, while reducing structural complexity and the difficulty of beam splitting ratio control. This high-bandwidth optical beam splitter consists of two-stage couplers and a thermally modulated phase shifter. The first-stage coupler is a first-stage subwavelength grating 1×2 multimode interference coupler (I), and the second-stage coupler is a second-stage subwavelength grating 2×2 multimode interference coupler (III). The thermally modulated phase shifter (II) includes two centrally symmetrical phase shifting regions with identical structures. The first input waveguide is connected to two arms at one end of the thermally modulated phase shifter (II) through the first-stage 1×2 multimode interference coupler (I). The two arms of the thermally modulated phase shifter (II) are then connected to the second-stage subwavelength grating 2×2 multimode interference coupler (III), and the second-stage subwavelength grating 2×2 multimode interference coupler (III) is then connected to the first output waveguide and the second output waveguide, respectively. The thermally adjustable phase shifter includes a first phase shift region (21) and a second phase shift region (22); The lower waveguide arm of the first phase-shifting region (21) includes a subwavelength grating wide waveguide (214), specifically including a third input transition waveguide (212), a subwavelength grating wide waveguide (214), and a fifth output transition waveguide (216); the upper waveguide arm of the first phase-shifting region (21) includes a continuous silicon wide waveguide (213), specifically including an input tapered waveguide (211) with gradually increasing width, a continuous silicon wide waveguide (213), and an output tapered waveguide (215) with gradually decreasing width, wherein the width of the continuous silicon wide waveguide (213) is equal to that of the subwavelength grating wide waveguide (214).

2. The large-bandwidth optical beam splitter with adjustable splitting ratio based on a subwavelength grating according to claim 1, characterized in that... The first-stage subwavelength grating 1×2 multimode interference coupler (I) adopts a subwavelength grating structure, specifically including an input transition waveguide (11), a first subwavelength grating multimode interference region (12), a first output transition waveguide (13), and a second output transition waveguide (14). The signal light input to the input transition waveguide (11) will be split into two beams of signal light with equal phase and intensity by the first subwavelength grating multimode interference region (12), and then input to the two arms of the thermally modulated phase shifter (II) respectively.

3. A large-bandwidth optical beam splitter with adjustable splitting ratio based on a subwavelength grating according to claim 2, characterized in that... The upper waveguide arm of the second phase shift region (22) has the same structure as the lower waveguide arm of the first phase shift region (21), and the lower waveguide arm of the second phase shift region (22) has the same structure as the upper waveguide arm of the first phase shift region (21).

4. A large-bandwidth optical beam splitter with adjustable splitting ratio based on a subwavelength grating according to claim 3, characterized in that... The two centrally symmetrical second phase shift regions (22) and the first phase shift region (21) can eliminate the initial phase difference and loss difference between the two waveguide arms of the thermally modulated phase shifter. Therefore, in the initial state, the two signal beams output by the thermally modulated phase shifter have equal phase and intensity.

5. A large-bandwidth optical beam splitter with adjustable splitting ratio based on a subwavelength grating according to claim 4, characterized in that... The second phase-shifting region (22) and the first phase-shifting region (21) are both provided with metal heating electrodes with the same structure and parameters. When current is introduced to the metal heating electrodes, the two wide waveguides on both sides of the metal heating electrodes will rise to the same temperature. The effective refractive index change of the subwavelength grating wide waveguide (214) is less than the effective refractive index change of the continuous silicon wide waveguide (213), thereby introducing a phase difference between the two waveguide arms. By injecting current to heat the first metal heating electrode (41), a positive phase change is introduced to the two waveguide arms. By injecting current to heat the second metal heating electrode (42), a negative phase change is introduced to the two waveguide arms. The phase-shifting region structure makes the phase change difference between the two output signal lights during the heating process wavelength insensitive. Then the two signal lights will be input into the second-stage subwavelength grating 2×2 multimode interference coupler.

6. A large-bandwidth optical beamsplitter with adjustable splitting ratio based on a subwavelength grating according to claim 5, characterized in that... The second-stage subwavelength grating 2×2 multimode interference coupler (III) adopts a subwavelength grating structure, specifically including a first input transition waveguide (31), a second input transition waveguide (32), a second subwavelength grating multimode interference region (33), a third output transition waveguide (34), and a fourth output transition waveguide (35); the first input transition waveguide (31), the second input transition waveguide (32), the third output transition waveguide (34), and the fourth output transition waveguide (35) have the same structure, parameters, and function; the first input transition waveguide (31) The second input transition waveguide (32) is symmetrically distributed at the middle of the starting end of the second subwavelength grating multimode interference region, and the third output transition waveguide (34) and the fourth output transition waveguide (35) are symmetrically distributed at the middle of the ending end of the second subwavelength grating multimode interference region. After the signal light input through the first input transition waveguide (31) and the second input transition waveguide (32) is split, it will interfere in the second subwavelength grating multimode interference region (33), thereby outputting two signal lights with different intensities through the third output transition waveguide (34) and the fourth output transition waveguide (35).

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