CN116256842A - Polarization beam splitting rotator - Google Patents
Polarization beam splitting rotator Download PDFInfo
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- CN116256842A CN116256842A CN202310262442.2A CN202310262442A CN116256842A CN 116256842 A CN116256842 A CN 116256842A CN 202310262442 A CN202310262442 A CN 202310262442A CN 116256842 A CN116256842 A CN 116256842A
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
- G02B6/1228—Tapered waveguides, e.g. integrated spot-size transformers
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/122—Basic optical elements, e.g. light-guiding paths
- G02B6/125—Bends, branchings or intersections
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/126—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind using polarisation effects
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
- G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
- G02B6/13—Integrated optical circuits characterised by the manufacturing method
- G02B6/136—Integrated optical circuits characterised by the manufacturing method by etching
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Abstract
The invention discloses a polarization beam splitting rotator, which comprises: the silicon waveguide layer comprises a partially etched adiabatic tapered waveguide structure, an asymmetric directional coupling structure and a double asymmetric directional coupling structure, wherein the partially etched adiabatic tapered waveguide structure is connected with the asymmetric directional coupling structure, and the asymmetric directional coupling structure is also connected with the double asymmetric directional coupling structure. The invention adopts a partially etched adiabatic tapered waveguide structure to realize mode hybridization and meet process compatibility; an asymmetric directional coupling structure is adopted to realize the mode evolution of a larger bandwidth and increase the manufacturing tolerance; and adopting a double asymmetric directional coupling structure to filter residual modes to realize high polarization extinction ratio. The invention can balance the indexes of process compatibility, manufacturing tolerance, polarization extinction ratio and the like of the polarization beam splitting rotator, and improve the practicability of the polarization beam splitting rotator.
Description
Technical Field
The invention relates to the technical field of optical communication, in particular to a polarization beam splitting rotator.
Background
Silicon-based photonic devices on insulators are attractive because of their complementary metal oxide semiconductor (cmos) compatible fabrication technology and compact dimensions, but because of the nature of the cmos process and the material itself, there is a strong birefringence of the device on the insulator, thus causing different polarization modes to produce different responses in the loop, which can greatly degrade system performance due to polarization mode dispersion and loss. To address the polarization sensitivity problem, polarization independence is achieved, typically using polarization diversity techniques based on polarization beam-splitting rotators.
The difficulty of polarization treatment is mainly polarization mode conversion, and three modes for realizing polarization mode conversion are mainly adopted at present: firstly, through using different materials on the vertical structure to realize the asymmetry of refractive indexes in the vertical direction, hybrid supermodes can be generated in a certain width area, and polarization mode conversion can be realized when the polarization ratio is close to 50%; secondly, the refractive indexes in the horizontal direction and the vertical direction are symmetrically broken through an asymmetric coupling structure, so that hybrid supermodes are formed between waveguides, and polarization mode conversion is realized in the polarization separation process through a polarization mode coupling effect; thirdly, a Y-branch structure is used, and the conversion among multiple polarization modes is realized by utilizing the polarization mode classification principle.
However, the above manner may cause that the existing polarization beam splitter rotator is difficult to achieve balance in terms of indexes such as process compatibility, manufacturing tolerance, polarization extinction ratio, and the like, so that the practicability of the polarization beam splitter rotator is low.
Disclosure of Invention
The invention mainly aims to provide a polarization beam splitting rotator, which aims to solve the problems of balancing indexes such as process compatibility, manufacturing tolerance, polarization extinction ratio and the like of the polarization beam splitting rotator and improve the practicability of the polarization beam splitting rotator.
To achieve the above object, the present invention provides a polarization beam-splitting rotator including:
the silicon waveguide layer comprises a partially etched adiabatic tapered waveguide structure, an asymmetric directional coupling structure and a double asymmetric directional coupling structure, wherein the partially etched adiabatic tapered waveguide structure is connected with the asymmetric directional coupling structure, and the asymmetric directional coupling structure is also connected with the double asymmetric directional coupling structure.
Optionally, the partially etched adiabatic tapered waveguide structure includes:
an input waveguide having a first width;
the method comprises the steps of partially etching an adiabatic taper waveguide, wherein the length of the partially etching adiabatic taper waveguide is a first length, the partially etching adiabatic taper waveguide comprises a first etched part and a first unetched part, the width of the first etched part is a second width, the etching depth is a preset depth, and the width of the first unetched part is gradually changed from the first width to a third width;
the input waveguide is connected with a side face of the first unetched part, which has the width of the first width, in the partially etched adiabatic tapered waveguide.
Optionally, the asymmetric directional coupling structure comprises:
the waveguide comprises a second etched part and a second unetched part, wherein the width of the second unetched part is a third width, the length of the second unetched part is a second length, the width of the second etched part is a second width, the etching depth is a preset depth, and the length of the second unetched part is a third length;
the width of the gradual change taper waveguide gradually changes from a fourth width to a fifth width, and the length of the gradual change taper waveguide is a fourth length;
the partially etched waveguide is arranged opposite to the gradual change taper waveguide, and the distance between the partially etched waveguide and the gradual change taper waveguide is a preset distance.
Optionally, the dual asymmetric directional coupling structure includes:
the upper end comprises an S-shaped bent waveguide and a first adiabatic tapered waveguide, the width of the S-shaped bent waveguide is a fifth width, the width of the first adiabatic tapered waveguide is gradually changed from the fifth width to the first width, the length of the first adiabatic tapered waveguide is a fifth length, and the S-shaped bent waveguide is connected with the side face of the first adiabatic tapered waveguide, the width of which is the fifth width;
the lower end comprises a second adiabatic tapered waveguide, a first tapered waveguide, an S waveguide, a second tapered waveguide and a 90-degree waveguide, wherein the width of the second adiabatic tapered waveguide is gradually changed from a third width to the first width, the length is a sixth length, the width of the first tapered waveguide is gradually changed from the sixth width to a seventh width, the length is a seventh length, and the width of the second tapered waveguide is gradually changed from an eighth width to a ninth width, and the length is an eighth length.
The upper end is opposite to the lower end.
Optionally, the first graded waveguide and the S waveguide in the lower end are located at one side of the second adiabatic graded tapered waveguide, the second graded waveguide and the 90 ° waveguide are located at the other side of the second adiabatic graded tapered waveguide, the S waveguide is connected to a side with the width of the seventh width in the first graded waveguide, and the 90 ° waveguide is connected to a side with the width of the ninth width in the second graded waveguide.
Optionally, a side surface with the third width in the first unetched part of the partially etched adiabatic tapered waveguide in the partially etched adiabatic tapered waveguide structure is connected with the partially etched waveguide in the asymmetric directional coupling structure, the partially etched waveguide in the asymmetric directional coupling structure is connected with a side surface with the third width in the second adiabatic graded tapered waveguide at the lower end in the double asymmetric directional coupling structure, and a side surface with the fifth width in the graded tapered waveguide in the asymmetric directional coupling structure is connected with a side surface of the curved waveguide at the upper end in the double asymmetric directional coupling structure.
Optionally, the input waveguide is configured to receive an input optical signal, and the partially etched adiabatic tapered waveguide is configured to perform mode hybridization on a mode of the optical signal that meets a preset condition.
Optionally, the partially etched waveguide and the tapered waveguide are used for performing mode evolution on the mode of the optical signal after mode hybridization.
Optionally, the second adiabatic tapered waveguide, the first tapered waveguide, the S-waveguide, the second tapered waveguide, and the 90 ° waveguide may be used to filter out other residual modes in the optical signal that are not target modes after mode hybridization and mode evolution.
Optionally, the S-shaped curved waveguide and the first adiabatic tapered waveguide are configured to output an optical signal of a target mode obtained after mode filtering.
The polarization beam splitting rotator provided by the invention comprises: the silicon waveguide layer comprises a partially etched adiabatic tapered waveguide structure, an asymmetric directional coupling structure and a double asymmetric directional coupling structure, wherein the partially etched adiabatic tapered waveguide structure is connected with the asymmetric directional coupling structure, and the asymmetric directional coupling structure is also connected with the double asymmetric directional coupling structure. The invention adopts a partially etched adiabatic tapered waveguide structure to realize mode hybridization and meet process compatibility; an asymmetric directional coupling structure is adopted, so that mode evolution with larger bandwidth is realized and manufacturing tolerance is increased; and adopting a double asymmetric directional coupling structure to filter residual modes to realize high polarization extinction ratio. The invention can balance the indexes of process compatibility, manufacturing tolerance, polarization extinction ratio and the like of the polarization beam splitting rotator, and improve the practicability of the polarization beam splitting rotator.
Drawings
FIG. 1 is a schematic perspective view of a polarization beam splitter rotator according to a first embodiment of the present invention;
FIG. 2 is a schematic perspective view of a lower cladding layer and a silicon waveguide layer of a polarization beam splitter rotator according to a first embodiment of the present invention;
FIG. 3 is a schematic plan view of a polarization beam splitter rotator according to a first embodiment of the present invention;
FIG. 4 is a schematic cross-sectional view of the invention at A-A' of FIG. 2;
FIG. 5 is a schematic cross-sectional view of the present invention at B-B' of FIG. 2;
FIG. 6 is a schematic diagram of effective refractive indices corresponding to a stripe waveguide and a partially etched waveguide of the present invention at different widths;
FIG. 7 is a schematic diagram showing simulated distribution of optical field transmission of an optical signal in TM0 mode through a polarization beam splitter rotator according to the present invention;
FIG. 8 is a schematic diagram showing simulated distribution of optical field transmission of TE0 mode optical signals through a polarization beam-splitting rotator according to the present invention;
FIG. 9 is a schematic diagram of transmission efficiency of a Cross port (upper port) of a polarization beam splitter rotator of the present invention at different polarization mode inputs;
FIG. 10 is a schematic diagram of transmission efficiency of a Through port (lower port) of a polarization beam splitter rotator according to the present invention under different polarization mode inputs;
fig. 11 is a schematic plan view of a polarization beam splitter rotator according to a second embodiment.
Reference numerals illustrate:
the achievement of the objects, functional features and advantages of the present invention will be further described with reference to the accompanying drawings, in conjunction with the embodiments.
Detailed Description
It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Referring to fig. 1, a first embodiment of the present invention is presented, and a polarization beam splitting rotator proposed by the first embodiment of the present invention includes:
an upper cladding layer 111, a lower cladding layer 113, and a silicon waveguide layer 112 wrapped in a cavity formed by the upper cladding layer and the lower cladding layer;
the silicon waveguide layer 112 includes a partially etched adiabatic tapered waveguide structure, an asymmetric directional coupling structure, and a dual asymmetric directional coupling structure, the partially etched adiabatic tapered waveguide structure is connected with the asymmetric directional coupling structure, and the asymmetric directional coupling structure is connected with the dual asymmetric directional coupling structure.
The upper cladding 111 and the lower cladding 113 are insulating layers and are made of silicon dioxide materials; the upper cladding layer 111 wraps the upper surface and the side surfaces of the silicon waveguide layer 112, and the lower cladding layer 113 wraps the lower surface of the silicon waveguide layer 112; it will be understood that, as shown in fig. 1 and 2, fig. 1 is a schematic perspective view of a polarization beam splitter rotator according to a first embodiment of the present invention, and fig. 2 is a schematic perspective view of a lower cladding layer and a silicon waveguide layer of the polarization beam splitter rotator according to the first embodiment of the present invention, the silicon waveguide layer 112 is embedded in the upper cladding layer 111, a lower surface of the silicon waveguide layer 112 is located on the same plane as a lower surface of the upper cladding layer 111, and both the lower surface of the silicon waveguide layer 112 and the lower surface of the upper cladding layer 111 are connected to an upper surface of the lower cladding layer 113, so that the upper cladding layer 111 and the lower cladding layer 113 completely encapsulate the silicon waveguide layer 112.
Optionally, the polarization beam splitter rotator is made of silicon-on-insulator (SOI): the lower cladding 113 material is silicon dioxide; the silicon waveguide layer 112 is a silicon material with a thickness of 220nm.
Further, as shown in fig. 3, fig. 3 is a schematic plan view of a polarization beam splitter rotator according to a first embodiment of the present invention.
Wherein the partially etched adiabatic tapered waveguide structure in the polarization beam splitter rotator comprises an input waveguide 11 and a partially etched adiabatic tapered waveguide 12.
The width of the input waveguide 11 is a first width; alternatively, the shape of the input waveguide 11 is a cube or a cuboid; when the input waveguide 11 is square in shape, the length of each side is a first width; when the input waveguide 11 is rectangular in shape, the corresponding width is the first width, and the corresponding height and length are not limited herein.
The length of the partially etched adiabatic taper waveguide 12 is a first length; referring to fig. 4, fig. 4 is a schematic cross-sectional view of a portion A-A' of fig. 3, in which an upper cladding layer 101 and a lower cladding layer 102 completely encapsulate a partially etched adiabatic tapered waveguide structure, the partially etched adiabatic tapered waveguide 12 includes a first etched portion 103 and a first unetched portion 100, an upper surface of the first etched portion 103 is etched to a corresponding etching depth, the etching depth is a preset depth, and a lower surface of the first etched portion 103 and a lower surface of the first unetched portion 100 are located on the same plane; further, a portion denoted by 100 in fig. 4 is a core region of an optical waveguide, and refractive indexes of the upper cladding 101 and the lower cladding 102 are equal or different; referring to fig. 3 and 4, the width of the first etched portion 103 is a second width, and the width of the first unetched portion 100 is gradually changed from the first width to a third width, wherein the first width is smaller than the third width; the input waveguide 11 is connected to a side of a first unetched portion 100 of the partially etched adiabatic taper waveguide 12 having a first width.
Wherein, the asymmetric directional coupling structure in the polarization beam splitting rotator comprises: a partially etched waveguide 21 and a tapered waveguide 22.
The partially etched waveguide 21 includes a second etched portion and a second unetched portion, one end of the second etched portion being in the same plane as one end of the second unetched portion, the other end of the second etched portion being not in the same plane as the other end of the second unetched portion, the second unetched portion having a third width and a second length, the second etched portion having a second width and a third length, wherein the second length is greater than the third length.
The tapered waveguide 22 tapers in width from a fourth width to a fifth width and has a fourth length.
The taper waveguide 22 is located on one side of the second unetched portion of the partially etched waveguide 21, the partially etched waveguide 21 is disposed opposite to the taper waveguide 22, and a distance between the partially etched waveguide 21 and the taper waveguide 22 is a preset distance.
Referring to fig. 5, fig. 5 is a schematic cross-sectional view of a portion B-B' in fig. 3, in which the tapered waveguide 22 is on the left side, the partially etched waveguide 21 is on the right side, the partially etched waveguide 21 includes a second etched portion 203 and a second unetched portion 200, the second unetched portion 200 has a third width and a second length, the second etched portion 203 has a second width, the etched depth has a preset depth, and the length has a third length; further, 200 is a core region of an optical waveguide, and the refractive index of the upper cladding 201 is equal to or different from that of the lower cladding 202.
Wherein, the two asymmetric directional coupling structures in the polarization beam splitting rotator include: an upper end and a lower end, the upper end being disposed opposite to the lower end, wherein the upper end includes an S-shaped curved waveguide 34 and a first adiabatic graded tapered waveguide 35, and the lower end includes a second adiabatic graded tapered waveguide 31, a first graded waveguide 32a, an S-shaped waveguide 32b, a second graded waveguide 33a, and a 90 ° waveguide 33b.
The width of the S-shaped curved waveguide 34 is a fifth width, the width of the first adiabatic tapering tapered waveguide 35 is gradually changed from the fifth width to the first width, the length is a fifth length, and the S-shaped curved waveguide 34 is connected to a side of the first adiabatic tapering tapered waveguide 35 having the fifth width.
The second adiabatic tapered waveguide 31 is tapered from the third width to the first width, and has a length of a sixth length, the first tapered waveguide 32a is tapered from the sixth width to the seventh width, and has a length of a seventh length, and the second tapered waveguide 33a is tapered from the eighth width to the ninth width, and has a length of an eighth length.
Further, the first graded waveguide 32a and the S waveguide 32b in the lower end are located at one side of the second adiabatic graded tapered waveguide 31, the second graded waveguide 33a and the 90 waveguide 33b are located at the other side of the second adiabatic graded tapered waveguide 31, the S waveguide 32b is connected to a side having a seventh width in the first graded waveguide 32a, and the 90 waveguide 33b is connected to a side having a ninth width in the second graded waveguide 33 a.
Further, in the silicon waveguide layer, the side face with the third width in the first unetched part of the partially etched adiabatic tapered waveguide 12 in the partially etched adiabatic tapered waveguide structure is connected to the partially etched waveguide 21 in the asymmetric directional coupling structure, the partially etched waveguide 21 in the asymmetric directional coupling structure is connected to the side face with the third width in the second adiabatic graded tapered waveguide 31 at the lower end in the double asymmetric directional coupling structure, and the side face with the fifth width in the graded tapered waveguide 22 in the asymmetric directional coupling structure is connected to the side face of the S-shaped curved waveguide 34 at the upper end in the double asymmetric directional coupling structure.
Further, an input waveguide 11 for receiving an input optical signal, and a partially etched adiabatic tapered waveguide 12 for mode-hybridizing a mode of the optical signal satisfying a preset condition; specifically, the width of the first unetched portion in the partially etched adiabatic tapered waveguide 12 is gradually changed from the first width to the third width, and the polarization mode conversion critical width is passed in the gradual change process, so that by designing the first length of the partially etched adiabatic tapered waveguide 12, the energy conversion of the TM0 polarization mode into the TE1 polarization mode in the partially etched adiabatic tapered waveguide 12 can be achieved, and attention needs to be paid to both a shorter coupling length and high conversion efficiency.
Further, the partially etched waveguide 21 and the tapered waveguide 22 are used for performing mode evolution on the mode of the optical signal after mode hybridization; specifically, the TE1 polarization mode in the partially etched waveguide 21 and the TE0 polarization mode in the tapered waveguide 22 satisfy the phase matching condition:
n eff1 (TE1)＝n eff2 (TE0)
wherein n is eff1 (TE 1) represents the effective refractive index of TE1 polarization mode in the partially etched waveguide 21, n eff2 (TE 0) represents the effective refractive index of the TE0 polarization mode in the graded tapered waveguide 22. It is noted that in the mode evolution process, the coupling efficiency varies periodically with the coupling length.
Further, the second adiabatic graded tapered waveguide 31, the first graded waveguide 32a, the S waveguide 32b, the second graded waveguide 33a and the 90 ° waveguide 33b can be used to filter out other residual modes in the optical signal that are not the target modes after mode hybridization and mode evolution; an S-shaped curved waveguide 34 and a first adiabatic tapered waveguide 35 for outputting an optical signal of the converted target mode; in particular, the tapered structure of S-waveguide 32b, 90 ° waveguide 33b, and its tail serves to dissipate the energy of the filtering coupling in free space; the residual TE1 and TM0 polarization modes in the second adiabatic graded tapered waveguide 31 respectively satisfy the phase matching condition with the TE0 mode in the first graded waveguide 32a and the TE1 mode in the second graded waveguide 33a, so that the energy of the residual TE1 and TM0 modes in the second adiabatic graded tapered waveguide 31 can be filtered; the energy of TE0 mode in the graded tapered waveguide 22 is finally output from the first adiabatic graded tapered waveguide 35 via the S-bend waveguide 34. The specific working process of the polarization beam splitting rotator in this embodiment is as follows:
optical signals in the operating wavelength range of the polarization beam splitter are input from the left side of the input waveguide 11.
One operating scenario is that the incoming optical signal is in TE0 mode:
when the optical signal inputted from the input waveguide 11 is TE0 mode, the TE0 mode of the adiabatic tapered waveguide 12 is not transmitted through the second adiabatic tapered output waveguide 31, and the TE0 mode is not transmitted through the second adiabatic tapered output waveguide 31, and the mode energy is not coupled into the double asymmetric directional coupling structure because the TE0 mode of the adiabatic tapered waveguide 12 does not satisfy the mode hybridization condition in the partially etched adiabatic tapered waveguide 12, so that the mode hybridization does not occur, the TE0 mode of the optical signal enters the partially etched waveguide 21, and the mode evolution condition is not satisfied, so that the TE0 mode propagates forward along the partially etched waveguide 21 and is outputted from the second adiabatic tapered output waveguide 31.
Another operating condition is that the input optical signal is in TM0 mode:
when the optical signal inputted from the input waveguide 11 is TM0 mode, the optical signal inputted from the partially etched adiabatic taper waveguide 12 is changed from TM0 mode to TE1 mode gradually because the effective refractive index of the TM0 mode satisfies the mode hybridization condition in the partially etched adiabatic taper waveguide 12. The TE1 mode optical signal then enters the partially etched waveguide 21, and because its mode effective refractive index satisfies the supermode evolution condition, the energy of the TE1 mode in the partially etched waveguide 21 is mainly limited to evolve into the energy of the TE0 mode in the graded tapered waveguide 22, and is finally output from the first adiabatic graded tapered waveguide 35 via the S-bend waveguide 34.
Because of errors in the manufacturing process, the width, etching depth and the like of the actually manufactured waveguide cannot be completely consistent with the designed dimensions, so that the TM0 mode cannot be completely changed into the TE1 mode and the TE1 mode cannot be completely changed into the TE0 mode, and therefore, the energy of the optical signals of the TM0 mode and the TE1 mode is always remained in the second adiabatic slowly-changing tapered waveguide 31 at the lower end; the second adiabatic graded tapered waveguide 31 and the first graded waveguide 32a form an ADC structure, and energy of the optical signal of the residual TE1 mode in the second adiabatic graded tapered waveguide 31 can be converted by meeting a phase matching condition and is dissipated in a free space through a tapered structure at the tail part of the S waveguide 32b so as to filter the energy of the optical signal of the residual TE1 mode; the second adiabatic graded tapered waveguide 31 and the second graded waveguide 33a form an ADC structure, and by satisfying the phase matching condition, the energy of the optical signal of the residual TM0 mode in the adiabatic graded tapered waveguide 31 can be converted, and dissipated in the free space through the tapered structure at the tail of the 90 ° waveguide 33b, so as to filter the energy of the optical signal of the residual TM0 mode.
The width and length of the partially etched adiabatic tapered waveguide 12, and the etching width and depth are designed so that the optical signal satisfying the TM0 mode can be mode-hybridized and can be completely converted into the optical signal of the TE1 mode; the length, taper width, and length of the partially etched waveguide 21 of the taper waveguide 22 are designed so as to gradually convert the optical signal of the TE1 mode in the partially etched waveguide 21 into the optical signal of the TE0 mode in the taper waveguide 22; the lengths of the second adiabatic slowly varying tapered waveguide 31 and the first graded waveguide 32a are designed to satisfy the energy conversion filtering of the optical signal of the residual TE1 mode in the second adiabatic slowly varying tapered waveguide 31; the lengths of the second adiabatic tapered waveguide 31 and the second graded waveguide 33a are designed to satisfy the energy conversion filtering of the optical signal of the TM0 mode remaining in the second adiabatic tapered waveguide 31.
In a possible embodiment, the upper and lower cladding materials are silicon dioxide, the silicon waveguide layer is a silicon material, and the thickness is 220nm, forming the body of the polarization beam splitter rotator;
the first width of the input waveguide 11 is 0.5um; the width of the first unetched portion of the partially etched adiabatic tapered waveguide 12 tapers from a first width of 0.5um to a third width of 0.8um; the second width of the first etched portion of the partially etched adiabatic tapered waveguide 12 is 0.2um and the etch depth is 0.15um. As shown in fig. 6, by scanning the effective refractive index of each mode corresponding to the different widths of the first etched portion of the partially etched adiabatic tapered waveguide 12, it can be known that the critical width w≡0 mode to TE1 mode is approximately 0.6um, and at the same time, when the etching depth of the partially etched adiabatic tapered waveguide 12 and the narrow waveguide width are within the target value ±10nm error, the corresponding effective refractive index can also be seen from fig. 6; the first length of the partially etched adiabatic taper waveguide 12 is set to 47.7um, and it is found through simulation that the conversion rate of the optical signal of TM0 polarization mode to the optical signal of TE1 polarization mode by the partially etched adiabatic taper waveguide 12 is greater than 98%.
The second unetched portion of the partially etched waveguide 21 has a third width of 0.8um and a length of 25.2um; the width of the second etched portion in the partially etched waveguide 21 is 0.2um, the etching depth is 0.15um, and the length is 23.2um; the width of the tapered waveguide 22 is gradually changed from the fourth width 0.382um to the fifth width 0.422um, and the length is 21.2um; the distance between the partially etched waveguide 21 and the tapered waveguide 22 is a preset distance of 0.2um.
The second adiabatic tapered waveguide 31 tapers from a third width of 0.8um to a first width of 0.5um, and has a length of 17um; the first graded waveguide 32a is graded from a sixth width of 0.385um to a seventh width of 0.3um, with a length of 11.6um; the second graded waveguide 33a is graded from an eighth width of 0.7um to a ninth width of 0.6um, with a length of 17um. The tapered structure of S-waveguide 32b, 90 ° waveguide 33b, and its tail serves to dissipate the energy of the filtering coupling in free space; the width of the S-shaped curved waveguide 34 is a fifth width of 0.422um, and the first adiabatic tapered waveguide 35 tapers from the fifth width of 0.422um to the first width of 0.5um, and has a length of a fifth length of 10um.
Under the condition of the implementation case, through 3D-FDTD scanning calculation and analysis, a light field transmission simulation distribution diagram of a TM0 mode with 1550nm and a TE0 light source through a polarization beam splitting rotator can be obtained, as shown in fig. 7 and 8. The transmission performance of the overall structure of the present invention is shown in fig. 9 and 10, and is the transmission efficiency of the Cross port (upper port) and the Through port (lower port) under different polarization mode inputs. Under the TM0 polarization mode input condition, the loss is lower than 1dB in the bandwidth of 1480nm-1620nm, and the extinction ratio is higher than 20dB in the bandwidth of 1450nm-1650 nm; in the C-band (1535-1565 nm) range, the polarization extinction ratio is greater than 25dB and the loss is less than 0.25dB. Under the condition of TE0 polarization mode input, the extinction ratio is more than 22dB and the loss is lower than 0.2dB in the bandwidth of 1450nm-1650 nm.
The polarization beam splitting rotator of the embodiment uses a conventional SOI material, adopts a partially etched adiabatic slowly-changing tapered waveguide structure, breaks the symmetry in the horizontal and vertical directions at the same time, and has asymmetry under the condition that the upper cladding and the lower cladding are the same, so that mode hybridization is realized, and the large-scale silicon-based photoelectric integration through a CMOS process is satisfied; an asymmetric directional coupling structure is formed by adopting a gradual change waveguide, so that the device realizes the mode evolution with larger bandwidth and increases the manufacturing tolerance; the double asymmetric directional coupling structure is formed through the graded waveguide, and meanwhile, the residual TM0 and TE1 are subjected to coupling filtering, so that the device can realize high polarization extinction ratio under the condition of large manufacturing error. The polarization beam splitting rotator has the excellent performances of CMOS process compatibility, high polarization extinction ratio, large manufacturing tolerance, large bandwidth and the like, balances the indexes of the polarization beam splitting rotator such as process compatibility, manufacturing tolerance, polarization extinction ratio and the like, and improves the practicability of the polarization beam splitting rotator.
Further, referring to fig. 11, a second embodiment of the present invention is proposed, and a polarization beam splitting rotator proposed by the second embodiment of the present invention includes:
the first section, which includes the input waveguide and the partially etched adiabatic taper waveguide, is the same as the first embodiment and is not described here.
A second section, in which the partially etched waveguide in the first embodiment is replaced with a partially etched adiabatic tapered waveguide, and the tapered waveguide is kept unchanged;
and a third section in which the S-shaped curved waveguide and the first adiabatic graded tapered waveguide at the upper end (Cross end) in the first embodiment are replaced with a waveguide having a rectangular parallelepiped shape, and the first adiabatic graded tapered waveguide at the lower end (Through end) is replaced with an S-shaped curved waveguide and an adiabatic graded tapered waveguide.
In particular implementations, optical signals within the operating wavelength range of the polarization beam splitter rotator are input from the left side of the input waveguide.
One operating scenario is that the incoming optical signal is in TE0 mode:
when the optical signal input from the input waveguide is TE0 mode, the optical signal passes Through the partially etched adiabatic taper waveguide in the first section, the effective refractive index of the optical signal in TE0 mode does not meet the mode hybridization condition in the partially etched adiabatic taper waveguide, so that mode hybridization does not occur, the optical signal in TE0 mode enters the partially etched adiabatic taper waveguide in the second section, and propagates forward along the partially etched adiabatic taper waveguide to the third section, and is output from the adiabatic ramp taper waveguide from the S-shaped curved waveguide at the lower end (Through end) because the mode evolution condition is not met when the optical signal in TE0 mode is transmitted in the adiabatic ramp taper waveguide in the third section, and the mode energy is not coupled into the double asymmetric directional coupling structure.
Another operating condition is that the input optical signal is in TM0 mode:
when the optical signal inputted from the input waveguide is TM0 mode, the optical signal inputted from the TM0 mode is changed from TM0 mode to TE1 mode by passing through the partially etched adiabatic taper waveguide in the first section, since the effective refractive index of the TM0 mode satisfies the mode hybridization condition in the partially etched adiabatic taper waveguide. The TE1 mode optical signal then enters the partially etched adiabatic tapered waveguide in the second segment, and since its mode effective refractive index satisfies the supermode evolution condition, it mainly limits the energy evolution of TE1 mode in the partially etched adiabatic tapered waveguide in the second segment to the energy of TE0 mode in the graded tapered waveguide and is output via the upper end (Cross end) cuboid shaped waveguide in the third segment.
Because the manufacturing process has errors, the width, etching depth and the like of the actually manufactured waveguide cannot be completely consistent with the designed size, so that the TM0 mode cannot be completely changed into the TE1 mode and the TE1 mode cannot be completely changed into the TE0 mode, and the energy of optical signals of the TM0 mode and the TE1 mode is always remained in the adiabatic slowly-changing tapered waveguide at the lower end in the third section; an ADC structure is formed by an S-shaped bent waveguide at the lower end (Through end) in the third section, an adiabatic slowly-varying tapered waveguide and a first gradual-varying waveguide, and the energy of the residual TE1 mode optical signal in the adiabatic slowly-varying tapered waveguide can be converted by meeting the phase matching condition and is dissipated in a free space Through a tapered structure at the tail part of the S-shaped waveguide so as to filter the energy of the residual TE1 mode optical signal; the S-shaped bent waveguide, the adiabatic slowly-varying tapered waveguide and the second gradual-varying waveguide form an ADC structure, the energy of the optical signal of the residual TM0 mode in the adiabatic slowly-varying tapered waveguide can be converted by meeting the phase matching condition, and the energy of the optical signal of the residual TM0 mode can be filtered by dissipating the optical signal in the free space through the tapered structure at the tail part of the 90-degree waveguide.
The width and length of the partially etched adiabatic tapered waveguide in the first section, and the etching width and depth are designed to satisfy that the optical signal of TM0 mode can be mode hybridized and can be completely evolved into the optical signal of TE1 mode; the length, width, and length of the partially etched adiabatic taper waveguide in the second segment are designed to gradually convert the TE1 mode optical signal in the partially etched adiabatic taper waveguide to the TE0 mode optical signal in the tapered taper waveguide; the lengths of the adiabatic slowly varying tapered waveguide and the first gradually varying waveguide in the third section are designed to meet the requirement of filtering out the energy conversion of the optical signal of the residual TE1 mode in the adiabatic slowly varying tapered waveguide; the lengths of the adiabatic tapered waveguide and the second tapered waveguide are designed to satisfy the energy conversion filtering of the optical signal of the TM0 mode remaining in the adiabatic tapered waveguide.
The polarization beam splitting rotator has the excellent performances of CMOS process compatibility, high polarization extinction ratio, large manufacturing tolerance, large bandwidth and the like, balances the indexes of the polarization beam splitting rotator such as process compatibility, manufacturing tolerance, polarization extinction ratio and the like, and improves the practicability of the polarization beam splitting rotator.
It should be noted that, in this document, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or system that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or system. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article, or system that comprises the element.
The foregoing embodiment numbers of the present invention are merely for the purpose of description, and do not represent the advantages or disadvantages of the embodiments.
From the above description of the embodiments, it will be clear to those skilled in the art that the above-described embodiment method may be implemented by means of software plus a necessary general hardware platform, but of course may also be implemented by means of hardware, but in many cases the former is a preferred embodiment.
The foregoing description is only of the preferred embodiments of the present invention, and is not intended to limit the scope of the invention, but rather is intended to cover any equivalents of the structures or equivalent processes disclosed herein, or any application, directly or indirectly, in the field of other related technology.
Claims (10)
1. A polarization beam splitter rotator, the polarization beam splitter rotator comprising:
the silicon waveguide layer comprises a partially etched adiabatic tapered waveguide structure, an asymmetric directional coupling structure and a double asymmetric directional coupling structure, wherein the partially etched adiabatic tapered waveguide structure is connected with the asymmetric directional coupling structure, and the asymmetric directional coupling structure is also connected with the double asymmetric directional coupling structure.
2. The polarization beam splitter rotator of claim 1, wherein the partially etched adiabatic tapered waveguide structure comprises:
an input waveguide having a first width;
the method comprises the steps of partially etching an adiabatic taper waveguide, wherein the length of the partially etching adiabatic taper waveguide is a first length, the partially etching adiabatic taper waveguide comprises a first etched part and a first unetched part, the width of the first etched part is a second width, the etching depth is a preset depth, and the width of the first unetched part is gradually changed from the first width to a third width;
the input waveguide is connected with a side face of the first unetched part, which has the width of the first width, in the partially etched adiabatic tapered waveguide.
3. The polarization beam-splitting rotator of claim 1, wherein the asymmetric directional coupling structure comprises:
the waveguide comprises a second etched part and a second unetched part, wherein the width of the second unetched part is a third width, the length of the second unetched part is a second length, the width of the second etched part is a second width, the etching depth is a preset depth, and the length of the second unetched part is a third length;
the width of the gradual change taper waveguide gradually changes from a fourth width to a fifth width, and the length of the gradual change taper waveguide is a fourth length;
the partially etched waveguide is arranged opposite to the gradual change taper waveguide, and the distance between the partially etched waveguide and the gradual change taper waveguide is a preset distance.
4. The polarization beam splitter rotator of claim 1, wherein the dual asymmetric directional coupling structure comprises:
the upper end comprises an S-shaped bent waveguide and a first adiabatic tapered waveguide, the width of the S-shaped bent waveguide is a fifth width, the width of the first adiabatic tapered waveguide is gradually changed from the fifth width to the first width, the length of the first adiabatic tapered waveguide is a fifth length, and the S-shaped bent waveguide is connected with the side face of the first adiabatic tapered waveguide, the width of which is the fifth width;
the lower end comprises a second adiabatic tapered waveguide, a first tapered waveguide, an S waveguide, a second tapered waveguide and a 90-degree waveguide, wherein the width of the second adiabatic tapered waveguide is gradually changed from a third width to the first width, the length is a sixth length, the width of the first tapered waveguide is gradually changed from the sixth width to a seventh width, the length is a seventh length, and the width of the second tapered waveguide is gradually changed from an eighth width to a ninth width, and the length is an eighth length.
The upper end is opposite to the lower end.
5. The polarization beam splitter rotator of claim 4 wherein the first graded waveguide and the S waveguide in the lower end are located on one side of the second adiabatic graded tapered waveguide, the second graded waveguide and the 90 waveguide are located on the other side of the second adiabatic graded tapered waveguide, the S waveguide is connected to a side of the first graded waveguide having the seventh width, and the 90 waveguide is connected to a side of the second graded waveguide having the ninth width.
6. The polarization beam splitter rotator of any one of claims 1 to 5, wherein a side of the first unetched portion of the partially etched adiabatic tapered waveguide in the partially etched adiabatic tapered waveguide structure having the third width is connected to the partially etched waveguide in the asymmetric directional coupling structure, the partially etched waveguide in the asymmetric directional coupling structure is connected to a side of the second adiabatic graded tapered waveguide in the lower end of the double asymmetric directional coupling structure having the third width, and a side of the graded tapered waveguide in the asymmetric directional coupling structure having the fifth width is connected to a side of the curved waveguide in the upper end of the double asymmetric directional coupling structure.
7. The polarization beam splitter rotator of claim 2, wherein the input waveguide is configured to receive an input optical signal and the partially etched adiabatic tapered waveguide is configured to mode-hybridize to a mode of the optical signal that satisfies a predetermined condition.
8. The polarization beam splitter rotator of claim 3, wherein the partially etched waveguide and the tapered waveguide are configured to mode evolve a mode of the mode-hybridized optical signal.
9. The polarization beam splitter rotator of claim 4, wherein the second adiabatic tapered waveguide, the first graded waveguide, the S-waveguide, the second graded waveguide, and the 90 ° waveguide are configured to filter out other residual modes of the optical signal that are not the target modes after mode hybridization and mode evolution.
10. The polarization beam splitter rotator of claim 4, wherein the S-bend waveguide and the first adiabatic tapered waveguide are configured to output an optical signal of a target mode obtained by mode filtering.
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