On-chip low-leakage mode polarizer for a silicon-on-insulator platform

Abstract

The application discloses a low-leakage mode polarizer on a silicon-on-insulator platform. The polarizer mainly comprises a combined waveguide area and a leakage mode absorption area. The combined waveguide area comprises an input strip ridge waveguide, an intermediate ridge waveguide and an output strip ridge waveguide in sequence, and the intermediate ridge waveguide comprises an input tapered ridge waveguide, a polarized ridge waveguide and an output tapered ridge waveguide in sequence. The leakage mode absorption area comprises a heavily doped silicon absorption area and a black epoxy absorption area. The heavily doped silicon absorption area is symmetrically distributed on both sides of the combined waveguide area, and a Bragg grating reflection area is arranged outside the heavily doped silicon absorption area. The black epoxy absorption area is formed by opening a groove in the Si substrate under the combined waveguide area and filling black epoxy. The application realizes physical polarization on a small-size SOI platform by designing specific intermediate ridge waveguide structure parameters, and solves the problem of coupling of the TM0 mode into an optical system after leakage by the leakage mode absorption area. The application reduces the influence of leakage mode crosstalk on an optical system, has the characteristics of low loss, low leakage and high polarization extinction ratio, and meets the actual needs in the fields of optical communication and integrated optics.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of optical communication, and particularly relates to a low-leakage-mode on-chip polarizer on a silicon-on-insulator platform. BACKGROUND

[0002] As a cutting-edge communication technology, optical communication is expected to become a substitute for future electrical interconnection technology and lead the development of high-speed broadband networks due to its high information capacity, low energy consumption, high-speed transmission and reconfigurability. At present, optical communication has been widely applied to fields such as data centers, telecommunication networks and cable television, and gradually replaces traditional data transmission methods, showing strong competitiveness.

[0003] In recent years, silicon photonics chips, as a key branch of optical communication, have made remarkable progress. They have good compatibility with CMOS technology, low optical loss and high integration, and have the advantages of ultra-large scale and ultra-high precision. At the same time, the ultra-high speed and ultra-low power consumption characteristics of silicon photonics chips make them an ideal choice for high-speed and long-distance communication. By using existing semiconductor manufacturing infrastructure, silicon photonics chips achieve low-cost mass production, and with the progress of technology, the cost of mass production gradually decreases, and the application range becomes increasingly wide.

[0004] However, since silicon waveguides have a large structural birefringence, most silicon devices are polarization-sensitive. Therefore, polarization splitters, rotators, beam splitters, rotators and polarizers have become indispensable polarization processing components in the silicon-on-insulator platform.

[0005] As a key polarization processing device of the silicon optical platform, the polarizer can efficiently purify the polarization state and only allow specific polarization to pass, which is crucial for integrated optical systems. Although the traditional absorption-type polarizer can absorb the cutoff polarized light, the transmission loss of the polarized light is large, and the application scenarios are limited. The transmission loss of the reflection-type and leakage-type polarizer is low, but the cutoff polarized light is easily recoupled into the waveguide region, affecting the system performance. Therefore, developing a low-loss, low-leakage-mode polarizer has become an urgent need in the field of optical communication. SUMMARY

[0006] In order to solve the problems in the background art, the application provides a low-leakage-mode on-chip polarizer on a silicon-on-insulator platform. The polarizer adopts the principle of a leakage-type polarizer and absorbs the leakage mode through a leakage-mode absorption region. The low-leakage-mode on-chip polarizer has the characteristics of low loss, low leakage and high polarization extinction ratio, and is simple to implement, compact in structure and easy to integrate on a chip. It has strong practicality in most optical systems and has a very broad application and development scenario.

[0007] The technical scheme adopted by the application is as follows:

[0008] This invention relates to an on-chip low-leakage mode polarizer on a silicon-on-insulator platform, comprising a silicon substrate (1), a silicon dioxide cladding and a buried layer (2), a black epoxy resin layer absorption region (3) with a bottom-filled trench, and a silicon core layer (a). The silicon core layer (a) includes a combined waveguide region (b), a heavily doped silicon absorption region (4), and an outermost Bragg grating reflection region (5). Its structure, from bottom to top, consists of a silicon substrate (1), a silicon dioxide buried layer, a silicon core layer (a), and a silicon dioxide cladding. The silicon dioxide cladding and buried layer (2) are composed of the silicon dioxide buried layer and the silicon dioxide cladding.

[0009] The present invention includes a combined waveguide region (b) fabricated in a ridge shape and an absorption region for leakage modes.

[0010] The combined waveguide region (b) consists of an input strip ridge waveguide (6), an intermediate ridge waveguide (c) that provides polarization, and an output strip ridge waveguide (10). The input strip ridge waveguide (6) is connected to the input end of the intermediate ridge waveguide (c), and the output strip ridge waveguide (10) is connected to the output end of the intermediate ridge waveguide (c).

[0011] The absorption region of the leakage mode includes heavily doped silicon absorption regions (4) on both sides of the combined waveguide region (b) and a black epoxy resin absorption region (3) at the bottom. A Bragg grating reflection region (5) is also distributed outside the heavily doped silicon absorption region (4). After the signal light enters the combined waveguide region (b), the TEO mode passes through with low loss, while the TMO mode leaks to the silicon planar layer in the form of a planar mode. The planar mode leaking to the silicon planar layer will be absorbed in the leakage mode absorption region. The heavily doped silicon absorption region (4) mainly absorbs the planar modes leaking to the silicon planar layer on both sides, while the black epoxy resin absorption region (3) absorbs the radiation mode leaking to the bottom.

[0012] The input strip ridge waveguide (6) and the output strip ridge waveguide (10) serve as the input and output terminals of the polarizer, respectively, and they have the same width. The input strip ridge waveguide (6) and the output strip ridge waveguide (10) can be curved waveguides or straight waveguides.

[0013] The intermediate ridge waveguide (c) includes an input tapered ridge waveguide (7), a biasing ridge waveguide (8), and an output tapered ridge waveguide (9). It is composed of the input tapered ridge waveguide (7), the biasing ridge waveguide (8), and the output tapered ridge waveguide (9) connected sequentially. The input end of the input tapered ridge waveguide (7) serves as the signal input end of the intermediate ridge waveguide (c). The optical signal is input from the input tapered ridge waveguide (7), passes through the biasing ridge waveguide (8), and is output from the output tapered ridge waveguide (9).

[0014] The input tapered ridge waveguide (7) and the output tapered ridge waveguide (9) are of equal length and satisfy the adiabatic transmission requirements for the TE0 mode. The TE0 mode does not introduce additional losses through the input tapered ridge waveguide (7) and the output tapered ridge waveguide (9).

[0015] The polarization ridge waveguide (8) is a single-mode waveguide specifically designed for low-loss transmission of the TEO mode, but with significant loss in the TM0 mode. After the signal light enters the combined waveguide region (b), the TEO mode passes through with low loss, while the TM0 mode leaks to the silicon slab layer. By optimizing the waveguide length, full leakage of the TM0 mode is achieved, thereby obtaining a high polarization extinction ratio.

[0016] The heavily doped silicon absorption region (4) is symmetrically distributed on both sides of the combined waveguide region (b). It has a strong absorption capacity for the leaked planar mode. Optimizing the width of the heavily doped silicon absorption region (4) can make the leakage mode leakage rate less than -50dB.

[0017] The Bragg grating reflective region (5) is symmetrically distributed outside the heavily doped silicon absorption region, and the period of the Bragg grating satisfies the phase matching condition of the following formula:

[0018] N eff0 =λ / (2Λ·sinθ)

[0019] Where, N eff0 λ is the effective refractive index of the TM0 mode in the Bragg grating, λ is the polarization wavelength, Λ is the grating sawtooth period, and θ is the incident light angle. The reflective region of the Bragg grating can reflect leakage modes that have not been absorbed by the heavily doped silicon absorption region, thus enabling the reabsorption of leakage modes.

[0020] The cross-section of the Bragg grating reflective region (5) is preferably toothed.

[0021] The black epoxy resin absorption region (3) is formed by trenching and filling a silicon substrate (1) below the ridged combined waveguide region (b) with black epoxy resin. This black epoxy resin material effectively absorbs the TM0 radiation mode leaking into the silicon substrate, preventing it from being coupled back into the waveguide through substrate reflection, thus achieving high-efficiency optical performance.

[0022] The input strip ridge waveguide (6), input cone ridge waveguide (7), deflection ridge waveguide (8), output cone ridge waveguide (9) and output strip ridge waveguide (10) are formed in one step.

[0023] The beneficial effects of this invention are:

[0024] 1. This invention features a simple intermediate ridge waveguide structure for polarization, free from subwavelength, lateral coupler, and grating structures, resulting in low overall perturbation and low additional loss. Furthermore, a large polarization extinction ratio can be achieved by optimizing the length of the polarizing ridge waveguide. The overall device loss is low while maintaining a high polarization extinction ratio, meeting the application requirements of optical communication and demonstrating broad application prospects.

[0025] 2. The synergistic effect of the heavily doped silicon absorption region and the Bragg grating reflection region of the present invention can fully absorb the leakage modes that leak to both sides of the combined waveguide region. The black epoxy resin absorption region can also absorb the TMO radiation modes that leak to the substrate, thereby preventing the TMO leakage modes from being recoupled into the waveguide and effectively avoiding optical crosstalk caused by the recoupling of leakage modes.

[0026] 3. This invention allows for targeted modification of the width of the polarization ridge waveguide, thereby achieving polarization filtering of light of any wavelength and providing flexible wavelength selectivity.

[0027] 4. The on-chip combined waveguide designed in this invention has polarization function, simple structure, small size, large process tolerance, and is easy to integrate with other devices in photonic integrated circuits. Its feature size far exceeds the linewidth of existing processes, and it is manufactured using general semiconductor processes, which are simple and inexpensive. It has a high polarization extinction ratio and low additional loss, making it extremely promising for production.

[0028] This invention employs the principle of a leaky polarizer, effectively absorbing the TMO leaked mode through the leaky mode absorption region, achieving low additional loss and a high polarization extinction ratio, while simultaneously solving the TMO mode leakage problem. It boasts a large process tolerance, simple fabrication, and significant advantages such as low leakage, low loss, and a high extinction ratio. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the cross-sectional structure of the on-chip low-leakage mode deflector of the present invention.

[0030] Figure 2 This is a top view of the on-chip low-leakage mode deflector of the present invention.

[0031] Figure 3 This is a schematic diagram of the on-chip low-leakage mode polarizer of the present invention.

[0032] Figure 4 The transmittance spectra of the TEO and TMO modes of this invention are obtained through the present invention.

[0033] In the above figures, the reference numerals have the following meanings: 1. Silicon substrate; 2. Silicon dioxide cladding and buried layer; 3. Black epoxy resin absorption region; 4. Heavily doped silicon absorption region; 5. Bragg grating reflection region; 6. Input strip ridge waveguide; 7. Input tapered ridge waveguide; 8. Offset ridge waveguide; 9. Output tapered ridge waveguide; 10. Output strip ridge waveguide; a is silicon core layer; b is combined waveguide region; c is intermediate ridge waveguide. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the scope of protection of the present invention.

[0035] like Figure 1 As shown, this design utilizes a silicon-on-insulator (SiI) platform, specifically a silicon core layer containing a combined waveguide region and a leakage mode absorption region. The single-crystal silicon used has a refractive index of 3.46 and an overall thickness of 220 nm. The waveguide structure is etched to a depth of 110 nm, including a heavily doped silicon absorption region, a ridge-shaped combined waveguide region, and a Bragg grating reflection region, meeting the commonly used operating parameters of a SiI platform. The buried layer is a 2 μm thick silicon dioxide insulating layer, and the upper cladding silicon dioxide layer is also 2 μm thick with a refractive index of 1.45. Furthermore, trenches are formed in the Si substrate below the combined waveguide region and filled with black epoxy resin. Note that the black epoxy resin absorption region here only serves to absorb the TMO radiation modes leaking to the substrate; therefore, other materials with good filling properties and strong light absorption can be used instead.

[0036] like Figure 2 As shown, the ridge-shaped combined waveguide region is composed of an input strip ridge waveguide, an intermediate ridge waveguide, and an output strip ridge waveguide connected in sequence. The intermediate ridge waveguide includes an input tapered ridge waveguide, a polarizing ridge waveguide, and an output tapered ridge waveguide.

[0037] The input and output strip ridge waveguides have the same width. In this example, a straight waveguide with a width of 1.6 μm is selected as the input and output strip ridge waveguides of the system. This width can support lossless transmission in TE0 and TM0 modes, and facilitates the measurement of the performance of the on-chip polarizer in this example.

[0038] Furthermore, the width of the polarization ridge waveguide (8) is 0.1 to 1 μm, and it is a single-mode transmission waveguide that only supports TE0 mode. It has a relatively large loss for TM0 mode, thus achieving a large polarization extinction ratio. In this example, the length of the polarization ridge waveguide (8) is greater than 30 μm. Preferably, the width of the polarization ridge waveguide (8) of this invention is 0.4 μm, and the length of the polarization ridge waveguide (8) is 70 μm. Figure 3 As shown, the input TM0 mode light leaks into the silicon planar layer in a planar mode.

[0039] The input and output tapered ridge waveguides have the same length. Optimization is performed based on the widths of the input and output strip ridge waveguides and the width of the biasing ridge waveguide. In this example, the lengths of the input and output tapered waveguides are 8 μm, which is an adiabatic waveguide for the TE0 mode. Figure 3 As shown, the input tapered ridge waveguide and output tapered ridge waveguide of this length ensure that the TE0 mode polarizer does not produce mode hybridization and excessive additional losses.

[0040] like Figure 4 As shown, with the above design, within a 100nm bandwidth, the TE0 mode loss is less than 0.2dB, and the polarization extinction ratio of the TM0 mode is greater than 35dB, resulting in a polarizer with low additional loss and high polarization extinction ratio. This design has a simple structure, and its minimum feature width is much larger than the minimum linewidth of existing fabrication processes, meeting the requirements of advanced semiconductor processing technology. It is worth noting that the input and output waveguide widths can be selected according to the actual system; optimizing the tapered waveguide lengths of the input and output can yield a polarizer structure with similar performance.

[0041] After the TM0 light passes through the polarization structure in this example, it leaks into the silicon planar layer in a planar mode. These leaked modes can be recoupled into the waveguide region through reflection or scattering, leading to parasitic interference and degrading system performance. Therefore, a corresponding leaked mode absorption region was designed in this example.

[0042] The ridge-shaped combined waveguide region is symmetrically flanked by heavily doped silicon absorption regions, with a doping concentration of 2 × 10⁻⁶. 20 cm -3 The light absorption efficiency reaches 0.56 dB / μm. TM0 mode light leaking to both sides of the combined waveguide region through the polarizer ridge waveguide is fully absorbed by the heavily doped silicon absorption region. A Bragg grating reflector with 20 periods is distributed on the outermost side of the core layer, with a period of 430 nm. The leakage mode through the Bragg grating reflector is less than 20 dB, thus reflecting the light leaking from the heavily doped silicon absorption region back to it for re-absorption. The thickness of the heavily doped silicon absorption region is designed to be 45 μm, ensuring a leakage rate of less than -50 dB for the planar mode. Simultaneously, the black epoxy resin absorption region on the lower side of the combined waveguide region absorbs the TM0 radiation mode leaking to the substrate, achieving a light absorption efficiency of 0.2 dB / μm, thus ensuring low leakage of the polarizer's TM0 mode and preventing the TM0 mode from re-coupled into the waveguide.

[0043] 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. An on-chip low-leakage mode polarizer with a silicon-on-insulator platform, characterized in that... It includes a silicon substrate (1), a silicon dioxide cladding and a buried layer (2), a black epoxy resin layer absorption region (3) with a bottom-filled trench, and a silicon core layer (a); wherein the silicon core layer (a) includes a ridge-shaped combined waveguide region (b), a heavily doped silicon absorption region (4), and an outermost Bragg grating reflection region (5); its structure from bottom to top is a silicon substrate (1), a silicon dioxide buried layer, a silicon core layer (a), and a silicon dioxide cladding; The combined waveguide region (b) consists of an input strip ridge waveguide (6), an intermediate ridge waveguide (c) with a polarization function, and an output strip ridge waveguide (10) in sequence; the input strip ridge waveguide (6) is connected to the input end of the intermediate ridge waveguide (c), and the output strip ridge waveguide (10) is connected to the output end of the intermediate ridge waveguide (c); The heavily doped silicon absorption regions (4) on both sides of the combined waveguide region (b) and the black epoxy resin absorption region (3) at the bottom form the leakage mode absorption region. A Bragg grating reflection region (5) is also distributed outside the heavily doped silicon absorption region (4). After the signal light is input into the combined waveguide region (b), the TEO mode passes through with low loss, while the TMO mode leaks to the silicon plate layer in the form of a planar mode. The planar mode leaking to the silicon plate layer will be absorbed in the leakage mode absorption region. The heavily doped silicon absorption region (4) absorbs the planar modes leaking to the silicon plate layer on both sides, and the black epoxy resin absorption region (3) absorbs the radiation mode leaking to the bottom. The input strip ridge waveguide (6) and the output strip ridge waveguide (10) serve as the input and output ends of the polarizer, respectively, and they have the same width; the input strip ridge waveguide (6) and the output strip ridge waveguide (10) are either curved waveguides or straight waveguides; The intermediate ridge waveguide (c) includes an input tapered ridge waveguide (7), a biasing ridge waveguide (8), and an output tapered ridge waveguide (9); and is composed of the input tapered ridge waveguide (7), the biasing ridge waveguide (8), and the output tapered ridge waveguide (9) connected in sequence; the input end of the input tapered ridge waveguide (7) serves as the signal input end of the intermediate ridge waveguide (c), and the optical signal is input from the input tapered ridge waveguide (7), passes through the biasing ridge waveguide (8), and is output from the output tapered ridge waveguide (9); The input tapered ridge waveguide (7) and the output tapered ridge waveguide (9) are of equal length and satisfy the adiabatic transmission of the TE0 mode; the TE0 mode does not introduce additional losses through the input tapered ridge waveguide (7) and the output tapered ridge waveguide (9); The ridge waveguide (8) is a single-mode waveguide, specifically designed for low-loss transmission in TEO mode, and has significant loss in TMO mode. After the signal light enters the combined waveguide region (b), the TE0 mode passes through with low loss, while the TM0 mode leaks to the silicon slab layer; by optimizing the waveguide length, the TM0 mode is fully leaked, thereby obtaining a high polarization extinction ratio; The heavily doped silicon absorption region (4) is symmetrically distributed on both sides of the combined waveguide region (b). It has a strong absorption capacity for the leaked planar mode. The width of the heavily doped silicon absorption region (4) is optimized so that the leakage mode leakage rate is less than -50dB.

2. The on-chip low-leakage mode polarizer of a silicon-on-insulator platform according to claim 1, characterized in that, The Bragg grating reflective region (5) is symmetrically distributed outside the heavily doped silicon absorption region, and the period of the Bragg grating satisfies the phase matching condition of the following formula: N eff0 =λ / (2Λ·sinθ) Where, N eff0 λ is the effective refractive index of the TM0 mode in the Bragg grating, λ is the polarization wavelength, Λ is the grating sawtooth period, and θ is the incident light angle. The reflective region of the Bragg grating can reflect leakage modes that have not been absorbed by the heavily doped silicon absorption region, thus enabling the reabsorption of leakage modes.

3. The on-chip low-leakage mode polarizer of a silicon-on-insulator platform according to claim 2, characterized in that, The black epoxy resin absorption region (3) is made by trenching and filling the silicon substrate (1) below the ridge-shaped combined waveguide region (b) with black epoxy resin. The black epoxy resin material effectively absorbs the TMO radiation mode leaked into the silicon substrate and prevents it from being reflected back into the waveguide through the silicon substrate, thereby achieving high-efficiency optical performance.

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