Polarization insensitive multi-channel on-chip cross waveguide based on a slotted waveguide array

Abstract

The application provides a polarization-insensitive multi-channel on-chip cross waveguide based on a slot waveguide array, comprising a substrate layer, a buried layer and a waveguide layer, the waveguide layer comprising N parallel input waveguides, a width-graduated slot waveguide array and N parallel output waveguides; wherein the input waveguides, the width-graduated slot waveguide array and the output waveguides are connected end to end; N represents N cross channels, N is a positive integer, and N is greater than or equal to 2. i When a light beam is emitted from the first input waveguide, the width-graduated slot waveguide array functions as a gradient refractive index convex lens, and the light beam passes through the slot waveguide array and reaches the (N+1-i)th output waveguide (i is a positive integer, and i is less than or equal to N), thereby realizing the on-chip light beam cross function. i i The on-chip cross waveguide has the advantages of compact device structure, simple preparation process, large preparation error tolerance, expandable mode and channel number, and can be applied to a multi-dimensional hybrid multiplexing system with on-chip dense integration.​

Description

Technical Field

[0001] This invention belongs to the field of optoelectronic devices and integration technology, specifically relating to a polarization-insensitive multichannel on-chip cross waveguide based on a slot waveguide array. Background Technology

[0002] In recent years, on-chip optoelectronic integration technology has been considered a promising optical interconnect technology. To meet the exponentially increasing demand for I / O bandwidth, on-chip mode division multiplexing (MDM) and polarization multiplexing (PMD) systems for high-capacity data throughput have been proposed. Cross-waveguides are an important functional component of on-chip MDM and PDM photonic integrated circuits. Currently, the reported structural schemes for on-chip cross-waveguide devices mainly include: multimode interferometers (MMI), subwavelength structures, nanopore structures, and Maxwell's fisheye lenses. Multimode interferometer (MMI) type cross waveguides are mainly based on the self-imaging principle. However, since the self-imaging positions and performance of light with different polarizations and modes are not completely consistent and are sensitive to wavelength, the bandwidth and scalability of higher-order modes of this structure are usually limited. Cross waveguides based on subwavelength structures are designed by controlling the anisotropic refractive index of the waveguide, but it is difficult to extend to multi-channel cross applications. Nanopore structures based on reverse design methods can optimize device size to several micrometers and support multiple modes, but the optimization of these complex nanopore structures is very time-consuming and contains many fine feature dimensions that exceed the manufacturing process. Maxwell's fisheye lens type cross waveguides are based on the transformation optics principle and propose to use metasurfaces and grayscale stepped electron beam lithography to form on-chip gradient refractive index lenses to achieve cross functionality. However, the feature size of metasurfaces is very small, grayscale lithography requires a complex manufacturing process, is incompatible with complementary metal-oxide-semiconductor (CMOS) technology, and is not suitable for mass production. Summary of the Invention

[0003] In view of the shortcomings of the prior art, the present invention discloses an on-chip cross waveguide based on a slot waveguide array. By using a slot waveguide array with gradually varying width, a polarization-insensitive multi-channel on-chip cross waveguide is realized, which is compact, simple to manufacture, and can be integrated on a large scale. It aims to solve the problems of polarization sensitivity, limited number of modes and channels, and complex and incompatible fabrication processes of existing on-chip cross waveguide devices.

[0004] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0005] A polarization-insensitive multi-channel on-chip cross waveguide based on a slotted waveguide array includes a substrate layer, a buried layer, and a waveguide layer. The waveguide layer is provided with N parallel input waveguides, one width-gradient slotted waveguide array, and N parallel output waveguides. The input waveguides, the width-gradient slotted waveguide array, and the output waveguides are connected end to end. Here, N represents N cross channels, N is a positive integer, and N≥2. The beam is emitted from the i-th input waveguide, passes through the slotted waveguide array, and reaches the (N+1-i)-th output waveguide, where i is a positive integer and i≤N, realizing the on-chip beam crossing function.

[0006] A further improvement to the technical solution of the present invention is that the waveguide layer and the substrate layer are made of silicon, and the buried layer is made of silicon dioxide.

[0007] A further improvement of the technical solution of the present invention is that the slot waveguide array is composed of slot waveguides with equal period, equal length and gradually varying width.

[0008] A further improvement of the technical solution of the present invention is that the period of the slot waveguide array is less than the working wavelength, thus satisfying the subwavelength dimension.

[0009] A further improvement of the technical solution of the present invention is that: the width of the slotted waveguide array is defined according to the gradient effective refractive index distribution, and is calculated by the effective refractive index calculation formula along the y-axis direction of the waveguide. Calculate the effective refractive index n of TE polarization and TM polarization along the y-axis from the center to both edges of the waveguide. effi,TE and n effi,TM Where g is the distribution parameter, n eff,max n is the maximum effective refractive index of the slot waveguide array. eff,min Let w be the minimum effective refractive index of the slot waveguide array. The duty cycle F of the slot waveguide corresponds to the effective refractive indices for TE and TM polarization. The corresponding waveguide width is then calculated using the duty cycle formula F = Λ / w. Since the effective refractive indices for TE and TM polarization calculated at the same position on the y-axis are different, they will correspond to two different waveguide widths. Therefore, the final waveguide width is taken as their average value w. i =(Λ / F i,TE +Λ / F i,TM ) / 2, to obtain a polarization-insensitive waveguide width distribution.

[0010] A further improvement to the technical solution of this invention lies in that: according to ray optics theory, the length of the slot waveguide array is defined based on the width distribution of the slot waveguide array, and the total length LWG is determined according to formula L WG =π / g.

[0011] A further improvement of the technical solution of the present invention is that: the waveguide width of the N parallel input waveguides is greater than or equal to 0.5μm, which satisfies the propagation of transverse electric TE mode and transverse magnetic TM mode, and the spacing between adjacent input waveguides is greater than or equal to 1μm, which ensures that the beams in adjacent waveguides do not crosstalk.

[0012] A further improvement of the technical solution of the present invention is that the width and spacing parameters of the N parallel input waveguides and the N parallel output waveguides are kept consistent.

[0013] A further improvement of the technical solution of the present invention is that the polarization-insensitive multi-channel on-chip cross waveguide device based on the slot waveguide array has two axes of symmetry along the center point of the device, one horizontal and one vertical.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0015] First, a method is proposed to construct an on-chip gradient refractive index convex lens by using a slot waveguide array with gradually varying width. By rationally designing the width distribution of the slot waveguide array and optimizing its dual polarization characteristics, a polarization-insensitive multi-channel on-chip cross waveguide device is realized.

[0016] Second, the proposed device is small in size, has a simple fabrication process, is fully compatible with standard silicon photonics process platforms, has a large tolerance for fabrication errors, and can be scaled up in terms of modes and channel numbers. It can be integrated on a large scale and is expected to be applied to on-chip densely integrated multidimensional hybrid multiplexing systems. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a three-dimensional structure of a polarization-insensitive multichannel on-chip cross waveguide based on a slot waveguide array according to an embodiment of the present invention.

[0018] Figure 2 This is a schematic diagram of the planar structure and a magnified partial cross-section of a polarization-insensitive multichannel on-chip cross waveguide based on a slotted waveguide array, according to an embodiment of the present invention.

[0019] Figure 3 This is a diagram showing the effective refractive index distribution of the slotted waveguide array from the center to both sides, according to an embodiment of the present invention.

[0020] Figure 4 The effective refractive index of the waveguide varies with the waveguide duty cycle in an embodiment of the present invention;

[0021] Figure 5 This is a simulated optical field distribution diagram of an embodiment of the present invention when a 1550nm TEO mode is input into different input waveguides;

[0022] Figure 6The transmission efficiency and channel crosstalk of this invention are shown in the embodiments of the present invention when TEO mode of 1500-1600nm is input into different input waveguides;

[0023] Figure 7 This is a simulated optical field distribution diagram of an embodiment of the present invention when a 1550nm TMO mode is input into different input waveguides;

[0024] Figure 8 The transmission efficiency and channel crosstalk of this invention are shown in the embodiments of the present invention when 1500-1600nm TMO mode is input into different input waveguides;

[0025] Among them, 1. waveguide layer, 2. buried layer, 3. substrate layer, 4. input waveguide, 5. slotted waveguide array, and 6. output waveguide. Detailed Implementation

[0026] The preferred embodiments of the present invention will be described in further detail below.

[0027] like Figure 1 As shown, this embodiment is a polarization-insensitive multi-channel on-chip cross waveguide based on a slotted waveguide array, which includes a waveguide layer, a buried layer, and a substrate layer from top to bottom. Specifically, the on-chip cross waveguide device is built on an SOI platform, the waveguide layer and substrate layer are made of silicon, and the buried layer is made of silicon dioxide. The on-chip cross waveguide device can be fabricated using a standard silicon photonics fabrication process with one-step etching.

[0028] like Figure 2 As shown, the main structure of this embodiment is in the waveguide layer, including three parallel input waveguides (I1, I2, I3), one width-gradient slotted waveguide array, and three parallel output waveguides (O1, O2, O3). The center operating wavelength of the device is set to the 1550nm optical communication band (λ = 1550nm), the thickness of the waveguide layer is 220nm, the width of the input waveguide is set to 2μm to support TE and TM polarization modes, the spacing between adjacent input waveguides is set to 1μm to ensure that the beams in adjacent waveguides do not crosstalk, and the width and spacing parameters of the output waveguides are consistent with those of the input waveguides. The slotted waveguide array consists of slotted waveguides with equal period, equal length, and gradually varying width. The period is set to one-third of the wavelength (Λ = 500nm), and the widths from the center to the two edges are defined as w1, w2, ..., w... i ... (i is a positive integer), calculated based on the gradient refractive index distribution requirements of the slotted waveguide array. According to the width calculation formula, the width distribution changes from large to small from the center of the slotted waveguide array to both sides, thus meeting the requirements for constructing a gradient refractive index convex lens.

[0029] The total width (w) of the slotted waveguide arrayWG Based on the spacing of the three input waveguides being set to 9 μm, the total length (L) of the slotted waveguide array is... WG )Calculated based on the gradually varying width distribution of the slot waveguide array.

[0030] like Figure 3 As shown, according to the formula for calculating the effective refractive index of a waveguide along the y-axis... The effective refractive index (n) of the waveguide along the y-axis from the center to both edges, for TE and TM polarization, can be calculated. effi,TE and n effi,TM ), where g is the distribution parameter, n eff,max n is the maximum effective refractive index of the slot waveguide array. eff,min is the minimum effective refractive index of the slot waveguide array.

[0031] like Figure 4 As shown, the effective refractive index (n) for TE polarization and TM polarization is calculated using the finite difference method. effi,TE and n effi,TM The duty cycle F of the corresponding slot waveguide is determined, and the corresponding waveguide width is calculated using the duty cycle formula F = Λ / w. Since the effective refractive indices for TE and TM polarizations calculated at the same position on the y-axis are different, two different waveguide widths will be generated. Therefore, the final waveguide width is taken as their average value w. i =(Λ / F i,TE +Λ / F i,TM ) / 2, to obtain a polarization-insensitive waveguide width distribution. According to ray optics theory, the total length (L) of the slotted waveguide array WG According to formula L WG =π / g is used for calculation. This completes the parameter design of the polarization-insensitive multichannel on-chip cross waveguide based on a slotted waveguide array.

[0032] Figure 5 The simulated optical field distribution diagram of the embodiment of the present invention is shown when a 1550nm TE0 mode is input into three input waveguides (I1, I2, I3) respectively. It can be seen that the cross optical field of the TE polarization mode beam is well maintained. Figure 6 The transmission efficiency and channel crosstalk of this invention are measured when TEO mode of 1500-1600nm is input to three input waveguides (I1, I2, I3) respectively. Within a 100nm working bandwidth, the transmission efficiency is higher than -0.4dB and the channel crosstalk is lower than -17dB.

[0033] Figure 7 The simulated optical field distribution diagram of the embodiment of the present invention is shown when the 1550nm TM0 mode is input into the three input waveguides (I1, I2, I3) respectively. It can be seen that the cross optical field of the TM polarization mode beam is also well maintained. Figure 8To illustrate the transmission efficiency and channel crosstalk of this invention when TE0 modes at 1500-1600nm are input to the three input waveguides (I1, I2, I3) respectively, within a 100nm operating bandwidth, the transmission efficiency is higher than -0.2dB and the channel crosstalk is lower than -18dB. Thus, the function of the polarization-insensitive multi-channel on-chip cross waveguide based on a slotted waveguide array is realized.

[0034] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A polarization-insensitive multi-channel on-chip cross waveguide based on a slotted waveguide array, characterized in that: The system includes a substrate layer (3), a buried layer (2), and a waveguide layer (1). The waveguide layer (1) is provided with N parallel input waveguides (4), a slotted waveguide array (5) with a gradually varying width, and N parallel output waveguides (6). The input waveguides (4), the slotted waveguide array (5), and the output waveguides (6) are connected end to end. Here, N represents N cross channels, N is a positive integer, and N≥2. The beam exits from the i-th input waveguide (4), passes through the slotted waveguide array (5), and reaches the N+1-i-th output waveguide (6). i is a positive integer, and i≤N, thus realizing the on-chip beam crossing function. The waveguide width of the N parallel input waveguides (4) is greater than or equal to 0.5 μm, which satisfies the propagation of transverse electric TE mode and transverse magnetic TM mode. The spacing between adjacent input waveguides (4) is greater than or equal to 1 μm, which ensures that the beams in adjacent waveguides do not crosstalk. The width and spacing parameters of the N parallel input waveguides (4) and the N parallel output waveguides (6) are kept consistent; The width of the slotted waveguide array is defined according to the gradient effective refractive index distribution, and is calculated using the formula for the effective refractive index of the waveguide along the y-axis. Calculate the effective refractive index of TE polarization and TM polarization along the y-axis from the center to both edges of the waveguide. and Where g is the distribution parameter, , The maximum effective refractive index of the slot waveguide array. Let F be the minimum effective refractive index of the slot waveguide array; where the effective refractive indices for TE and TM polarization correspond to the duty cycle F of the slot waveguide, and then the duty cycle formula is used. The corresponding waveguide width is calculated. Since the effective refractive indexes for TE and TM polarizations are different at the same position on the y-axis, two different waveguide widths will be calculated. Therefore, the final waveguide width is taken as the average value. This allows for the acquisition of polarization-insensitive waveguide width distributions.

2. The polarization-insensitive multi-channel on-chip cross waveguide based on a slotted waveguide array according to claim 1, characterized in that: The waveguide layer (1) and the substrate layer (3) are made of silicon, and the buried layer (2) is made of silicon dioxide.

3. A polarization-insensitive multi-channel on-chip cross waveguide based on a slotted waveguide array according to claim 1, characterized in that: The slot waveguide array (5) is composed of slot waveguides with equal period, equal length, and gradually varying width.

4. A polarization-insensitive multi-channel on-chip cross waveguide based on a slotted waveguide array according to claim 3, characterized in that: The period of the slot waveguide array (5) is less than the operating wavelength, satisfying the subwavelength dimension.

5. A polarization-insensitive multi-channel on-chip cross waveguide based on a slotted waveguide array according to claim 2, characterized in that: According to ray optics theory, the length of the slot waveguide array is defined based on the width distribution of the slot waveguide array, with a total length L. WG According to the formula calculate.

6. A polarization-insensitive multi-channel on-chip cross waveguide based on a slotted waveguide array according to claim 1, characterized in that: The polarization-insensitive multichannel on-chip cross waveguide device based on a slotted waveguide array has two axes of symmetry along the center point of the device, one horizontal and one vertical.

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