阅读说明：本技术 基于对称三波导与亚波长结构的偏振无关的功率分配器 (Polarization-independent power divider based on symmetrical three-waveguide and sub-wavelength structure ) 是由 肖金标 杨楠 于 2019-09-09 设计创作，主要内容包括：本发明公开了一种基于对称三波导与亚波长结构的偏振无关的功率分配器,该功率分配器从下至上依次为硅基衬底(8)、掩埋氧化层(9)、硅波导层(11)和上包层(10),硅波导层(11)由右路直通通道(2)、中路直通通道(3)和左路直通通道(4)构成对称三波导定向耦合器结构(7),对称三波导定向耦合器结构(7)的一侧设置有输入通道(1),另一侧设置有右输出通道(5)和左输出通道(6),且各个通道表面均附有亚波长光栅结构；定向耦合器结构(7)将输入的不同偏振光进行3dB功率分配。该功率分配器有效降低了现有功率分配器的插入损耗和反射损耗,改善了器件的功分比,缩短了器件的尺寸。(The invention discloses a power divider which is based on a symmetrical three-waveguide and has no relation with polarization of a sub-wavelength structure, the power divider sequentially comprises a silicon-based substrate (8), a buried oxide layer (9), a silicon waveguide layer (11) and an upper cladding (10) from bottom to top, the silicon waveguide layer (11) forms a symmetrical three-waveguide directional coupler structure (7) by a right path through channel (2), a middle path through channel (3) and a left path through channel (4), one side of the symmetrical three-waveguide directional coupler structure (7) is provided with an input channel (1), the other side of the symmetrical three-waveguide directional coupler structure is provided with a right output channel (5) and a left output channel (6), and the surface of each channel is attached with a sub-wavelength grating structure; the directional coupler structure (7) performs 3dB power distribution on input light with different polarizations. The power divider effectively reduces the insertion loss and the reflection loss of the existing power divider, improves the power dividing ratio of a device, and shortens the size of the device.)

1. A polarization-independent power divider based on a symmetric three-waveguide and a subwavelength structure is characterized in that: this power distributor adopts the silicon-on-insulator platform to make, and power distributor bottom is silicon-based substrate (8), and silicon-based substrate (8) upper surface is for burying oxide layer (9), has silicon waveguide layer (11) at burying oxide layer (9) upper surface distribution, and silicon waveguide layer (11) cover has upper cladding (10), wherein:

the silicon waveguide layer (11) comprises an input channel (1), a right through channel (2), a middle through channel (3), a left through channel (4), a right output channel (5) and a left output channel (6), and all the channels are made of silicon waveguides;

the right through channel (2), the middle through channel (3) and the left through channel (4) are arranged in parallel and aligned to form a symmetrical three-waveguide directional coupler structure (7), and the widths of the left through channel (4) and the right through channel (2) are kept consistent;

an input channel (1) is arranged on one side of the symmetrical three-waveguide directional coupler structure (7), and the input channel (1) is connected with one end of the middle-path through channel (3);

a right output channel (5) and a left output channel (6) are arranged on the other side of the symmetrical three-waveguide directional coupler structure (7), the right output channel (5) is connected with one end of the right through channel (2), the left output channel (6) is connected with one end of the left through channel (4), the right side surface of the right output channel (5) is aligned with the right side surface of the right through channel (2), and the left side surface of the left output channel (6) is aligned with the left side surface of the left through channel (4);

the left side surface of a right through channel (2), the right side surface of a left through channel (4) and the left and right side surfaces of a middle through channel (3) in the symmetrical three-waveguide directional coupler structure (7) are all provided with sub-wavelength grating structures;

tapered sub-wavelength grating structures are attached to the left side and the right side of the input channel (1) to form a transition structure, and the sum of the widths of the tapered sub-wavelength grating structures and the input channel (1) in the transition structure is equal to the sum of the widths of the intermediate path through channel (3) and the sub-wavelength grating structures attached to the left side and the right side of the intermediate path through channel;

the left side surface of the right output channel (5) and the right side surface of the left output channel (6) are provided with conical sub-wavelength grating structures, the sum of the widths of the conical sub-wavelength gratings on the right output channel (5) and the left side surface of the right output channel is equal to the sum of the widths of the conical sub-wavelength gratings on the right through channel (2) and the left side surface of the right through channel, and the sum of the widths of the conical sub-wavelength gratings on the left output channel (6) and the right side surface of the left output channel is equal to the sum of the widths of the conical sub-wavelength gratings on the left through channel (4) and the;

the sub-wavelength grating structure and the conical sub-wavelength grating structure are both composed of high-refractive-index material layers and low-refractive-index material layers alternately; and if the length of the high-refractive-index material along the channel direction is a and the period formed by the high-refractive-index material and the low-refractive-index material is lambada, the duty ratio is defined as f ═ a/lambada, and the sub-wavelength grating structure and the conical sub-wavelength grating structure have the same period and duty ratio.

2. The polarization independent power splitter of claim 1 based on a symmetric triple waveguide subwavelength structure, wherein: the sum of the widths of the sub-wavelength grating structures on the left side surface of the right through channel (2) and the left side surface of the left through channel (4) and the right side surface of the left through channel is 490-500 nm, wherein the widths of the sub-wavelength grating structures on the left side surface of the right through channel (2) and the right side surface of the left through channel (4) are 200-250 nm, the periods of the sub-wavelength grating structures are 200-240 nm, and the duty ratio of the sub-wavelength grating structures is 45-50%; the sum of the widths of the intermediate path through channel (3) and the sub-wavelength grating structures on the left side surface and the right side surface of the intermediate path through channel is 510 nm-570 nm, wherein the widths of the sub-wavelength grating structures on the left side surface and the right side surface are respectively 130 nm-160 nm, the period is 200 nm-240 nm, and the duty ratio is 45% -50%.

3. The polarization independent power splitter of claim 1 based on a symmetric triple waveguide subwavelength structure, wherein: the width of the middle-path through channel (3) is the same as the width of the contact end of the input channel (1) and the middle-path through channel (3), and is 245-255 nm; the width of the right through channel (2) is the same as the width of the contact end of the output channel (5) and the right through channel (2), and is 250 nm-300 nm; the width of the left through channel (4) is the same as the width of the contact end of the output channel (6) and the left through channel (4), and is 250 nm-300 nm; the width of the right through channel (2) is the same as that of the left through channel (4).

4. The polarization independent power splitter of claim 1 based on a symmetric triple waveguide subwavelength structure, wherein: the width of the input channel (1) is transited from 245-255 nm to 490-500 nm from the contact end with the middle path through channel (3) to the far end, the sum of the width and the width of the tapered sub-wavelength grating structure in the transition structures attached to the left side and the right side is 510-570 nm, the period of the grating is 200-240 nm, and the duty ratio is 45-50%.

5. The polarization independent power splitter of claim 1 based on a symmetric triple waveguide subwavelength structure, wherein: the sum of the widths of the right output channel (5) and the tapered sub-wavelength grating structure on the left side surface of the right output channel and the sum of the widths of the left output channel (6) and the tapered sub-wavelength grating structure on the right side surface of the left output channel are 490-500 nm, wherein the right output channel (5) and the left output channel (6) are transited from 250-300 nm to 490-500 nm from the contact end with the called directional coupler structure (7) to the far end, the period of the tapered sub-wavelength grating structure attached to the surface of the right output channel is 200-240 nm, the width of the tapered sub-wavelength grating structure within 3-4 mu m is transited from 200-250 nm to 50-70 nm from the contact end with the called directional coupler structure (7) to the far end linearly within 3-4 mu m, and the duty ratio is 45-.

6. The polarization independent power splitter of claim 1 based on a symmetric triple waveguide subwavelength structure, wherein: in the parallel and aligned arrangement of the right through channel (2), the middle through channel (3) and the left through channel (4), the distance between the structure formed by the middle through channel (3) and the sub-wavelength gratings on the left and right side surfaces thereof is equal to the distance between the structure formed by the right through channel (2) and the sub-wavelength gratings on the left side surface thereof, and the distance between the structure formed by the left through channel (4) and the sub-wavelength gratings on the right side surface thereof, and the distances are all 100-150 nm.

7. The polarization independent power splitter of claim 1 based on a symmetric triple waveguide subwavelength structure, wherein: the material of the high-refractive-index material layer is silicon, and the material of the low-refractive-index material layer is silicon dioxide.

8. The polarization independent power splitter of claim 1 based on a symmetric triple waveguide subwavelength structure, wherein: the sizes of the right through channel (2), the middle through channel (3) and the left through channel (4) meet the following conditions:

1) the effective refractive indexes of TE and TM modes supported by the right through channel (2) and the left through channel (4) are equal;

2) the difference between the effective refractive indexes of TE modes supported by the middle-path through channel (3) and the right-path through channel (2) and the left-path through channel (4) distributed on the two sides is less than 0.1, and the phases are matched;

3) the difference between the effective refractive indexes of TM modes supported by the middle-path through channel (3) and the right-path through channel (2) and the left-path through channel (4) distributed on the two sides is less than 0.1, and the phases are matched;

4) lowest order even mode TE supported by a symmetric three-waveguide directional coupler structure (7)₀And TE₂Effective refractive index difference of (1) and TM supported thereby₀And TM₂Are equal.

9. The polarization independent power splitter of claim 1 based on a symmetric triple waveguide subwavelength structure, wherein: the coupling length L of the symmetrical three-waveguide directional coupler structure (7)_CSatisfies the following formula:

in the formula: lambda is the wavelength of operation and,represents the effective refractive index of the 0 th order TM or TE mode supported by the symmetrical three-waveguide directional coupler structure (7),represents the effective refractive index of the 2 nd order TM or TE mode supported by the symmetrical three-waveguide directional coupler structure (7).

10. The polarization independent power splitter of claim 1 based on a symmetric triple waveguide subwavelength structure, wherein: the silicon-based substrate (8) is a silicon wafer with standard size, the thickness of the buried oxide layer (9) is 1-3 mu m, and the buried oxide layer is made of silicon dioxide material; the upper cladding (10) is made of silicon dioxide, polymethyl methacrylate or air.

Technical Field

The invention relates to a polarization-independent power divider based on a symmetrical three-waveguide and sub-wavelength structure, and belongs to the technical field of integrated optics.

Background

Photonic Integrated Circuits (PICs) are considered to be a good choice for developing optical computing and high broadband interconnects in next generation optical networks by providing low cost solutions for optical interconnects and higher transmission rates. In recent years, in order to realize photonic integrated circuits, silicon-on-insulator (SOI) materials have attracted extensive attention and have been practically applied in many optical fields due to their cmos-compatible fabrication processes, high refractive index contrast, low-loss nanowire waveguides and small device footprint. The power divider is an important component of complex optical devices such as a mode multiplexer, an optical phase control array, an optical switch and the like. Because the refractive index contrast between the core layer and the cladding layer is high, the power divider based on the SOI platform has strong birefringence characteristics for transverse electric field modes (TE) and transverse magnetic field modes (TM) with different polarization characteristics; making most SOI-based power splitters generally polarization sensitive, which negatively impacts PIC performance. The traditional polarization-independent power divider realizes the equal coupling length of TE and TM modes by introducing a thicker silicon waveguide layer, a wider waveguide gap, a bent waveguide or a lower waveguide width; but at the same time, it brings higher design complexity and power Splitting Ratio (SR), and also leads to higher insertion loss and reflection loss. In recent years, sub-wavelength grating (SWG) structures have received much attention from researchers due to a variety of effective diffraction suppression capabilities and index processing capabilities; a new degree of freedom is provided for the design of the optical device. Therefore, it is necessary to design a power divider with a compact structure, low insertion loss, large operating bandwidth and uniform power division ratio to realize next-generation PIC.

Disclosure of Invention

The technical problem is as follows: the invention aims to provide a power divider which is based on a symmetrical three-waveguide and has no relation with polarization of a sub-wavelength structure, wherein the power divider adopts a symmetrical three-waveguide directional coupler structure consisting of a right path through channel, a middle path through channel and a left path through channel, and carries out power 3dB distribution on input different polarized lights TE (TM) so as to couple the input different polarized lights into an output channel waveguide; the scheme effectively reduces the insertion loss of the power divider, improves the power dividing ratio of the device and shortens the size of the device.

The technical scheme is as follows: the invention provides a power divider which is based on symmetrical three-waveguide and has no relation with polarization of a sub-wavelength structure, the power divider is manufactured by adopting an insulating silicon chip platform, the bottommost layer of the power divider is a silicon-based substrate, the upper surface of the silicon-based substrate is a buried oxide layer, a silicon waveguide layer is distributed on the upper surface of the buried oxide layer, and the silicon waveguide layer is covered with an upper cladding, wherein:

the silicon waveguide layer comprises an input channel, a right through channel, a middle through channel, a left through channel, a right output channel and a left output channel, and all the channels are made of silicon waveguides;

the right path through channel, the middle path through channel and the left path through channel are arranged in parallel and aligned to form a symmetrical three-waveguide directional coupler structure, and the width of the left path through channel is consistent with that of the right path through channel;

an input channel is arranged on one side of the symmetrical three-waveguide directional coupler structure and is connected with one end of the middle-path through channel;

the other side of the symmetrical three-waveguide directional coupler structure is provided with a right output channel and a left output channel, the right output channel is connected with one end of a right through channel, the left output channel is connected with one end of a left through channel, the right side of the right output channel is aligned with the right side of the right through channel, and the left side of the left output channel is aligned with the left side of the left through channel;

the left side surface of a right path straight-through channel, the right side surface of a left path straight-through channel and the left and right side surfaces of a middle path straight-through channel in the symmetrical three-waveguide directional coupler structure are all provided with sub-wavelength grating structures;

the two sides of the input channel are attached with conical sub-wavelength grating structures to form a transition structure, and the sum of the widths of the conical sub-wavelength grating structures and the input channel in the transition structure is equal to the sum of the widths of the intermediate path through channel and the sub-wavelength grating structures attached to the left and the right of the intermediate path through channel;

the left side surface of the right output channel and the right side surface of the left output channel are provided with conical sub-wavelength grating structures, the sum of the widths of the conical sub-wavelength gratings on the right output channel and the left side surface of the right output channel is equal to the sum of the widths of the conical sub-wavelength gratings on the right through channel and the left side surface of the right through channel, and the sum of the widths of the conical sub-wavelength gratings on the left output channel and the right side surface of the left output channel is equal to the sum of the widths of the conical sub-wavelength gratings on the left through channel and the;

the sub-wavelength grating structure and the conical sub-wavelength grating structure are both composed of high-refractive-index material layers and low-refractive-index material layers alternately; and if the length of the high-refractive-index material along the channel direction is a and the period formed by the high-refractive-index material and the low-refractive-index material is lambada, the duty ratio is defined as f ═ a/lambada, and the sub-wavelength grating structure and the conical sub-wavelength grating structure have the same period and duty ratio.

Wherein:

the sum of the widths of the sub-wavelength grating structures on the left side surface of the right through channel and the left through channel and the sum of the widths of the sub-wavelength grating structures on the right side surface of the left through channel and the left through channel are both 490nm to 500nm, wherein the widths of the sub-wavelength grating structures on the left side surface of the right through channel and the sub-wavelength grating structures on the right side surface of the left through channel are both 200nm to 250nm, the periods are both 200nm to 240nm, and the duty ratio is both 45% to 50%; the sum of the widths of the middle-path straight-through channel and the sub-wavelength grating structures on the left side surface and the right side surface of the middle-path straight-through channel is 510 nm-570 nm, wherein the widths of the sub-wavelength grating structures on the left side surface and the right side surface are respectively 130 nm-160 nm, the period is 200 nm-240 nm, and the duty ratio is 45% -50%.

The width of the middle straight-through channel is the same as the width of the contact ends of the input channel and the middle straight-through channel, and is 245-255 nm; the width of the right through channel is the same as the width of a contact end of the output channel and the right through channel, and is 250 nm-300 nm; the width of the left through channel is the same as that of a contact end of the output channel and the left through channel and is 250 nm-300 nm; the width of the right through channel is kept the same as that of the left through channel.

The width of the input channel is transited from 245-255 nm to 490-500 nm from the contact end with the middle path through channel to the far end, the sum of the width of the input channel and the width of the tapered sub-wavelength grating structure in the transition structures attached to the left side and the right side is 510-570 nm, the period of the grating is 200-240 nm, and the duty ratio is 45-50%.

The width sum of the right output channel (and the width sum of the tapered sub-wavelength grating structure on the left side surface of the right output channel, and the width sum of the tapered sub-wavelength grating structure on the left output channel and the right side surface of the left output channel are 490 nm-500 nm, wherein the right output channel and the left output channel are transited from 250 nm-300 nm to 490 nm-500 nm from the contact end of the directional coupler structure to the far end, the period of the tapered sub-wavelength grating structure attached to the surface of the right output channel is 200 nm-240 nm, the width of the tapered sub-wavelength grating structure is linearly transited from 200 nm-250 nm to 50 nm-70 nm from the contact end of the directional coupler structure to the far end within 3 mu m-4 mu m, and the duty ratio is.

In the parallel and aligned arrangement of the right path through channel, the middle path through channel and the left path through channel, the distance between the structure formed by the middle path through channel and the sub-wavelength gratings on the left and right side surfaces of the middle path through channel is equal to the distance between the structure formed by the right path through channel and the sub-wavelength gratings on the left side surface of the middle path through channel and the structure formed by the left path through channel and the sub-wavelength gratings on the right side surface of the left path through channel, and the distances between the structures are all 100-150 nm.

The sub-wavelength grating structure and the conical sub-wavelength grating structure have uniform period and duty ratio.

The material of the high-refractive-index material layer is silicon, and the material of the low-refractive-index material layer is silicon dioxide.

The sizes of the right through channel, the middle through channel and the left through channel meet the following conditions:

1) the effective refractive indexes of TE and TM modes supported by the right through channel and the left through channel are equal;

2) the difference of effective refractive indexes of TE modes supported by the middle-path through channel and the right-path through channel and the left-path through channel distributed on the two sides is less than 0.1, and the phases are matched;

3) the difference between the effective refractive indexes of TM modes supported by the middle through channel and the right through channel and the left through channel distributed on the two sides is less than 0.1, and the phases are matched;

4) lowest order even mode TE supported by symmetrical three-waveguide directional coupler structure₀And TE₂Effective refractive index difference of (1) and TM supported thereby₀And TM₂Are equal.

The coupling length L of the symmetrical three-waveguide directional coupler structure_CSatisfies the following formula:

in the formula: lambda is the wavelength of operation and,representing the effective refractive index of the 0 th order TM or TE mode supported by the symmetric three-waveguide directional coupler structure,representing the effective refractive index of the 2 nd order TM or TE mode supported by the symmetric three-waveguide directional coupler structure.

The silicon-based substrate is a silicon wafer with standard size, the thickness of the buried oxide layer is 1-3 mu m, and the buried oxide layer is made of silicon dioxide material; the upper cladding material is silicon dioxide, polymethyl methacrylate or air.

Has the advantages that: compared with the prior art, the technical scheme of the invention has the following beneficial effects:

1. the insertion loss is low: the most important condition met by the polarization-independent 3dB dual-mode power divider is that both TE and TM modes meet the phase matching condition; the TE polarized light and the TM polarized light are subjected to phase matching, nearly 50% of power is coupled to the through channels on two sides, and therefore insertion loss is low; if the structural parameters are further adjusted, the coupling distance of the two polarized lights is reduced, the size of the device is reduced, and the insertion loss is further reduced.

2. The power division ratio is uniform: the polarization-independent 3dB dual-mode power divider adopts a centrosymmetric design, and polarized light in TE and TM modes is input from a middle-path through channel and symmetrically coupled to two side through channels through a symmetric three-waveguide directional coupler; the power available from the left and right output channels can be highly approximately equal, resulting in an output power ratio of approximately 1.

3. The reflection loss is low: the 3dB dual-mode power divider adopts a symmetrical design, and also introduces a sub-wavelength grating structure and a three-waveguide directional coupler structure; the comprehensive use of the two structures ensures that the device performance is more stable; meanwhile, the use of a bent output waveguide can be omitted, so that the reflection loss is reduced, and the coupling efficiency is higher.

Drawings

FIG. 1 is a schematic view of a silicon waveguide layer structure in embodiment 1 of the present invention;

fig. 2 is a schematic cross-sectional structure diagram of a symmetric three-waveguide directional coupler structure in embodiment 1 of the present invention;

fig. 3 is a diagram showing the relationship between the coupling length of TE and TM modes at 1.55 μm and the change in the channel pitch in the conventional symmetric three-waveguide directional coupler structure in embodiment 1 of the present invention;

fig. 4 is a diagram showing the relationship between the coupling length corresponding to TE and TM modes at 1.55 μm and the width change of the intermediate-path through channel in the conventional symmetric three-waveguide directional coupler structure in embodiment 1 of the present invention;

fig. 5 is a diagram showing the relationship between the coupling lengths of TE and TM modes at 1.55 μm and the SWG width variation in the mid-path waveguide in the symmetric three-waveguide directional coupler structure after the SWG structure is added in embodiment 1 of the present invention;

fig. 6 is a diagram showing the relationship between the coupling lengths of TE and TM modes at 1.55 μm and the SWG period variation of a symmetric three-waveguide directional coupler structure after the SWG structure is added in embodiment 1 of the present invention;

FIG. 7 shows TE at an operating wavelength of 1.55 μm in example 1 of the present invention₀Mode and TM₀Transmission diagram of main components of the mode in the power divider;

the figure shows that: the silicon waveguide directional coupler comprises an input channel 1, a right through channel 2, a middle through channel 3, a left through channel 4, a right output channel 5, a left output channel 6, a symmetrical three-waveguide directional coupler structure 7, a silicon substrate 8, a buried oxide layer 9, an upper cladding layer 10 and a silicon waveguide layer 11.

Detailed Description

The invention is further explained below with reference to the drawings.