CN116540355A - Optical multimode interference coupler based on strip-shaped ridge waveguide mixed structure - Google Patents
Optical multimode interference coupler based on strip-shaped ridge waveguide mixed structure Download PDFInfo
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- 230000003287 optical effect Effects 0.000 title claims abstract description 164
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 37
- 229910052710 silicon Inorganic materials 0.000 claims description 37
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- 238000000034 method Methods 0.000 description 10
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- 238000010168 coupling process Methods 0.000 description 4
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Classifications
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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
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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
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference
- G02F1/212—Mach-Zehnder type
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/21—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference
- G02F1/225—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour by interference in an optical waveguide structure
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
Abstract
The invention provides an optical multimode interference coupler based on a strip-shaped ridge waveguide mixed structure, and relates to the field of integrated optics. The coupler is integrally formed, and sequentially comprises the following components from the input direction to the output direction of a signal: a single-mode input waveguide with a ridge structure, a tapered graded input waveguide, a multimode waveguide with a strip structure, a tapered graded output waveguide with a ridge structure and a single-mode output waveguide. The ridge structure waveguide includes a ridge waveguide and a slab region waveguide; the width of the ridge waveguide of the single-mode input waveguide is equal to the width of the minimum ridge waveguide of the tapered graded input waveguide; the sum of the maximum ridge waveguide widths of the tapered graded input waveguide is less than the width of the multimode waveguide; the sum of the maximum ridge waveguide widths of the tapered graded output waveguide is less than the width of the multimode waveguide; the minimum ridge waveguide width of the tapered graded output waveguide is equal to the ridge width of the single mode output waveguide. Based on the coupler, the structure of the electronic component is formed without using a traditional gradual change conversion structure.
Description
Technical Field
The invention relates to the technical field of integrated optics, in particular to an optical multimode interference coupler based on a strip-shaped ridge waveguide mixed structure.
Background
In modern optical communication systems, with the continuous increase of the demand for optical functions, a large number of optical switch modulation units are required to be used on an optical chip at the same time to realize complex optical routing and optical information processing functions. A typical application is high speed electro-optical switch arrays.
In the existing optical switch modulation unit, a strip-shaped optical beam splitter and a strip-shaped optical beam combiner are often connected with a ridge-shaped modulation arm waveguide by utilizing a conversion transition structure of the strip-shaped waveguide and the ridge waveguide. Therefore, a large number of conversion structures of the stripe waveguide and the ridge waveguide are required inside the optical chip.
Because the length of the conversion structure is longer, the size of the optical device and the whole area of the optical chip are increased under the condition that a large number of transition conversion structures are required to be repeatedly used, so that the integration level of the system chip is reduced.
Disclosure of Invention
(one) solving the technical problems
Aiming at the defects of the prior art, the invention provides an optical multimode interference coupler based on a strip-shaped ridge waveguide mixed structure, which solves the problem of lower integration level of a system chip in the prior art.
(II) technical scheme
In order to achieve the above purpose, the invention is realized by the following technical scheme:
in a first aspect of the invention, an optical multimode interference coupler based on a hybrid structure of a strip-shaped ridge waveguide is provided,
the optical multimode interference coupler sequentially comprises the following components from the input direction to the output direction of a signal: a single-mode input waveguide with a ridge structure, a conical gradual change input waveguide with a ridge structure, a multimode waveguide with a strip structure, a conical gradual change output waveguide with a ridge structure and a single-mode output waveguide with a ridge structure;
all ridge structured waveguides include ridge waveguides and slab waveguides;
the ridge waveguide width of the single-mode input waveguide is equal to the minimum ridge waveguide width of the tapered graded input waveguide;
the sum of the maximum ridge waveguide widths of the tapered graded input waveguide is less than the width of the multimode waveguide;
the sum of the maximum ridge waveguide widths of the tapered graded output waveguide is less than the width of the multimode waveguide;
the minimum ridge waveguide width of the tapered graded output waveguide is equal to the ridge width of the single mode output waveguide.
Optionally, the ridge waveguide of the single-mode input waveguide is the same size as the ridge waveguide of the single-mode output waveguide;
the ridge waveguide of the tapered graded input waveguide and the ridge waveguide of the tapered graded output waveguide are the same size.
Optionally, the multimode waveguide is located in a middle region of the optical multimode interference coupler; the tapered graded input waveguide and the tapered graded output waveguide are respectively positioned at two sides of the multimode waveguide and are directly connected with the multimode waveguide.
Optionally, if the optical multimode interference coupler is a 1×2 coupler, the number of single-mode input waveguides, tapered graded input waveguides and multimode waveguides is 1, and the number of tapered graded output waveguides and single-mode output waveguides is 2;
the 2 tapered graded output waveguides and the 2 single-mode output waveguides are all distributed up and down symmetrically about a transverse central axis of the multimode waveguide.
Optionally, if the optical multimode interference coupler is a 2×1 coupler, the number of single-mode input waveguides and tapered graded input waveguides is 2, and the number of multimode waveguides, tapered graded output waveguides and single-mode output waveguides is 1;
the 2 tapered graded input waveguides and the 2 single-mode input waveguides are all distributed vertically symmetrically about a transverse central axis of the multimode waveguide.
Optionally, the thickness of the slab region waveguide is adjusted according to the thickness of the top silicon layer of the optical multimode interference coupler; the ridge waveguide width of all ridge waveguides is adjusted according to the thickness of the top silicon layer of the optical multimode interference coupler;
specifically, the thickness of the top silicon layer is 3 μm, and the thickness of the slab region waveguide is 1.3 μm; the minimum ridge waveguide width of the tapered graded input waveguide is 2.2 μm; the tapered graded input waveguide has a maximum ridge waveguide width of 2.5 μm.
Optionally, in the optical multimode interference coupler, the multimode waveguide has a length of 70 μm; the length of the ridge waveguide of the graded output waveguide is 10 μm.
(III) beneficial effects
The invention provides an optical multimode interference coupler based on a strip-shaped ridge waveguide mixed structure. Compared with the prior art, the method has the following beneficial effects:
the invention provides an optical multimode interference coupler based on a strip-shaped ridge waveguide mixed structure, which is integrally formed and sequentially comprises the following components from the input direction to the output direction: a single-mode input waveguide with a ridge structure, a conical gradual change input waveguide with a ridge structure, a multimode waveguide with a strip structure, a conical gradual change output waveguide with a ridge structure and a single-mode output waveguide with a ridge structure; all ridge structured waveguides include ridge waveguides and slab waveguides; the ridge waveguide width of the single-mode input waveguide is equal to the minimum ridge waveguide width of the tapered graded input waveguide; the sum of the maximum ridge waveguide widths of the tapered graded input waveguide is less than the width of the multimode waveguide; the sum of the maximum ridge waveguide widths of the tapered graded output waveguide is less than the width of the multimode waveguide; the minimum ridge waveguide width of the tapered graded output waveguide is equal to the ridge width of the single mode output waveguide. Based on the processing, the ridge-shaped transmission waveguide is directly connected with the strip-shaped multimode waveguide interface, and based on the multimode excitation principle of the multimode interference coupler, the optical signals in the ridge-shaped single-mode waveguide are excited at the interface of the strip-shaped multimode waveguide, and meanwhile, the conversion of the multimode excitation and the waveguide structure in the waveguide is completed, the traditional gradual change-shaped strip-shaped ridge waveguide conversion structure is not needed, the length of electronic components is effectively reduced, and the integration level of the components is improved.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a schematic diagram of a prior art 1×2 port coupler;
FIG. 2 is a schematic diagram of an electro-optical switching unit based on MZI according to the present invention;
fig. 3 is a schematic structural diagram of an electro-optical switch unit according to the present invention;
FIG. 4 is a schematic diagram of a conventional slab rib waveguide transition structure according to the present invention;
FIG. 5 is a schematic diagram of a structure of a MZI optical switch unit according to the present invention after connection with a single-mode transmission waveguide;
FIG. 6 is a schematic diagram of an optical multimode interference coupler based on a hybrid configuration of a strip-shaped ridge waveguide according to the present invention;
FIG. 7 is a top view of a 1×2 optical multimode interference coupler according to the present invention;
FIG. 8 is a cross-section of a ridge waveguide of a 1X 2 coupler provided by the present invention;
FIG. 9 is a cross-sectional view of a 1×2 coupler strip multimode waveguide provided by the present invention;
fig. 10 is a schematic diagram of a 1×1MZI optical switch based on a hybrid structure of a strip ridge waveguide according to the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention are clearly and completely described, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The embodiment of the invention provides the optical multimode interference coupler based on the strip-shaped ridge waveguide mixed structure, so that the traditional conversion structure between the strip-shaped waveguide and the ridge waveguide is avoided, and the problem of lower integration level of a system chip in the prior art is solved.
The technical scheme in the embodiment of the application aims to solve the technical problems, and the overall thought is as follows:
in the application scene under the thick silicon platform, the single-mode waveguide of ridge structure can realize the ultra-low loss light transmission, and the beam splitter of bar structure can accomplish the light beam splitting function under compact size.
In practical applications, it is often desirable to use both a single mode transmission waveguide in the form of a ridge and a multimode waveguide in the form of a strip. For example, in an electro-optical switch based on mach-zehnder phase shift modulation, two stripe-shaped 1×2 optical splitters, two ridge-shaped modulation arm waveguides, and two input and output transmission waveguides are included. At the junction of the strip waveguide and the ridge waveguide, a waveguide structure conversion is required.
The prior art scheme is a transition conversion structure based on a gradual change structure, but the length size of a unit device can be increased, and particularly when a phase shift modulation switch array is used in a large scale, the gradual change transition type strip-shaped ridge waveguide conversion structure is required to be used in a large scale.
The invention provides an optical multimode interference coupler based on a strip-shaped ridge waveguide mixed structure, which directly connects a ridge-shaped transmission waveguide with a strip-shaped multimode waveguide interface, and based on the multimode excitation principle of the multimode interference coupler, enables optical signals in a ridge-shaped single-mode waveguide to be at the interface of the multimode waveguide of the strip-shaped structure, simultaneously completes multimode excitation in the waveguide and conversion of the waveguide structure, does not need to use a traditional graded strip-shaped ridge waveguide conversion structure, effectively reduces the length of an electronic unit device and improves the integration level of the device.
In order to better understand the above technical solutions, the following detailed description will refer to the accompanying drawings and specific embodiments.
First, the basic concept in the present invention will be described.
Currently, in the field of silicon-based photonics, optical couplers based on the principle of multimode interference coupling are widely applied to various optical functional structures.
Wherein the multimode interference coupling principle is to use the transmission effect between different modes in a multimode optical waveguide: the propagation constants of different optical modes are different, so that multimode interference superposition of different phases can occur at different distances along the propagation direction, different interference patterns are further formed, and the optical beam splitting effect of different output ports is realized.
The core region of the multimode interference coupler is a wide waveguide in terms of waveguide structure, which internally supports different optical mode transmissions. The core region may be in a strip-like configuration or in a ridge-like configuration. Typically, there are also a number of input and output waveguides on either side of the wide waveguide core region, which are responsible for connecting the wide waveguide core region and the single-mode transmission waveguides outside the coupler. Referring to fig. 1, fig. 1 is a schematic diagram of a 1×2 port coupler according to the prior art. For a typical 1 x 2 port coupler, two configurations are shown in fig. 1.
An electro-optical switch is an optical routing device widely used in communication systems. For example, an optical switching unit based on MZI (Mach-Zehnder Interferometer ) is a 1×1 port structure, and an electrical Mach-zehnder modulation arm waveguide, an optical beam splitter, and an optical beam combiner are used therein. Referring to fig. 2, fig. 2 is a schematic diagram of an MZI-based electro-optical switching unit according to the present invention.
In the prior art, electro-optical switch units based on the principle of free carrier dispersion are widely used in high-speed optoelectronic integrated chips. In order to perform carrier doping with different concentrations and types on the modulation arm waveguides in the electro-optical switch unit, the two modulation arm waveguides often have a ridge structure. And in order to realize electro-optical modulation in the electro-optical switching unit, a 1×2 optical beam splitter and a 2×1 optical beam combiner are respectively arranged at both sides of the modulation arm waveguide. Wherein, the 1 x 2 beam splitter and the 2 x 1 beam combiner can be realized by a multimode interference coupler with 1 x 2 ports.
In a thick silicon platform, the performance of the strip-shaped structure optical beam splitter based on the multimode interference coupling principle is often better than that of the strip-shaped structure optical beam splitter based on the ridge-shaped structure, so in order to form an electro-optical switch based on the MZI, a modulation arm waveguide of the ridge-shaped structure needs to be used in combination with the strip-shaped structure optical beam splitter, and a schematic diagram of the modulation arm waveguide is shown in fig. 3. Fig. 3 is a schematic structural diagram of an electro-optical switching unit according to the present invention.
As can be seen from fig. 3, when the electro-optical switching unit includes both a modulation arm waveguide with a ridge structure and a multimode interference coupler with a stripe structure, a transition structure is often required between the stripe waveguide and the ridge waveguide to realize the transition of different optical waveguide structures. In the present invention, the transition structure between the stripe waveguide and the ridge waveguide is referred to as a stripe ridge transition structure.
The conventional strip-shaped ridge waveguide conversion structure is a transition waveguide structure based on adiabatic gradual change, the structure of which is shown in fig. 4, and fig. 4 is a schematic diagram of a conventional strip-shaped ridge waveguide conversion structure provided by the invention.
In a thick silicon platform, the optical beam splitter with a strip structure and the waveguide modulation arm with a ridge structure have good optical transmission characteristics, and in order to realize the optical switch unit based on the MZI modulation principle, a transition structure of the strip waveguide and the ridge waveguide is required to be used for connecting the strip optical beam splitter, the optical beam combiner and the ridge modulation arm waveguide.
In addition to the need for a switching structure using a strip waveguide and a ridge waveguide inside the MZI electro-optical switching cell, a single mode ridge waveguide in a thick silicon platform can achieve ultra low loss optical transmission. Thus, in addition to the electro-optical switching unit, a ridge optical waveguide is used as an optical path transmission structure, and the external interfaces of the optical switching unit are a 1×2 optical beam splitter and a 2×1 optical combiner. As shown in fig. 5, fig. 5 is a schematic structural diagram of an MZI optical switch unit provided by the present invention after being connected to a single-mode transmission waveguide.
Because the optical beam splitter and the optical beam combiner adopt high-efficiency strip structures, when the MZI optical switch unit is connected with the low-loss thick silicon ridge transmission waveguide, the input/output port of the optical switch unit can also face the problem of the conversion of the strip waveguide and the ridge waveguide, and the conversion structure of the strip waveguide and the ridge waveguide is also required.
In summary, in the application scenario under the thick silicon platform, the ridge single-mode waveguide can realize ultra-low loss optical transmission, and the strip-shaped optical beam splitter can complete the optical beam splitting function under the compact size. In practical applications, it is often desirable to use both a ridged single-mode transmission waveguide and a bar-shaped optocoupler multimode waveguide. For example, in an electro-optical switch based on mach-zehnder phase shift modulation, two stripe-shaped 1×2 optical splitters, two ridge modulation arm waveguides, and two input and output transmission waveguides are included.
Therefore, waveguide structure conversion is required at the junction of the strip waveguide and the ridge waveguide, and the conventional scheme is a transition conversion structure based on a gradual change structure, but the conversion structure required by the scheme can increase the length size of a unit device, and particularly in the case of using a phase shift modulation switch array on a large scale, the gradual change transition type strip ridge waveguide conversion structure can be used in a large amount.
In order to avoid using a conversion structure of a stripe waveguide and a ridge waveguide, the present invention provides an optical multimode interference coupler based on a stripe ridge waveguide hybrid structure, referring to fig. 6, fig. 6 is a schematic structural diagram of an optical multimode interference coupler based on a stripe ridge waveguide hybrid structure.
As shown in fig. 6, the optical multimode interference coupler is integrally formed, and sequentially includes, from a signal input to an output direction (i.e., from left to right): a single-mode input waveguide with a ridge structure, a tapered graded input waveguide with a ridge structure, a multimode waveguide with a strip structure, a tapered graded output waveguide with a ridge structure, and a single-mode output waveguide with a ridge structure.
All ridge structured waveguides include ridge waveguides and slab waveguides.
Wherein the ridge waveguide width of the single-mode input waveguide is equal to the minimum ridge waveguide width of the tapered graded input waveguide.
The sum of the maximum ridge waveguide widths of the tapered graded input waveguide is less than the width of the multimode waveguide.
The sum of the maximum ridge waveguide widths of the tapered graded output waveguide is less than the width of the multimode waveguide.
The minimum ridge waveguide width of the tapered graded output waveguide is equal to the ridge width of the single mode output waveguide.
Specifically, the ridge waveguide of the single-mode input waveguide has the same size as the ridge waveguide of the single-mode output waveguide.
The ridge waveguide of the tapered graded input waveguide and the ridge waveguide of the tapered graded output waveguide are the same size.
Specifically, the multimode waveguide is located in the middle region of the optical multimode interference coupler; the tapered graded input waveguide and the tapered graded output waveguide are respectively positioned at two sides of the multimode waveguide and are directly connected with the multimode waveguide.
If the optical multimode interference coupler is a 1×2 coupler, the number of single-mode input waveguides, tapered graded input waveguides and multimode waveguides is 1, and the number of tapered graded output waveguides and single-mode output waveguides is 2.
The 2 tapered graded output waveguides and the 2 single-mode output waveguides are all distributed up and down symmetrically about a transverse central axis of the multimode waveguide.
If the optical multimode interference coupler is a 2×1 coupler, the number of single-mode input waveguides and tapered graded input waveguides is 2, and the number of multimode waveguides, tapered graded output waveguides and single-mode output waveguides is 1.
The 2 tapered graded input waveguides and the 2 single-mode input waveguides are all distributed vertically symmetrically about a transverse central axis of the multimode waveguide.
The thickness of the slab region waveguide is adjusted according to the thickness of the top silicon layer of the optical multimode interference coupler; the ridge waveguide width of the ridge waveguide is adjusted according to the thickness of the top silicon layer of the optical multimode interference coupler.
Specifically, the thickness of the top silicon layer is 3 μm, and the thickness of the slab region waveguide is 1.3 μm; the minimum ridge waveguide width of the tapered graded input waveguide is 2.2 μm; the tapered graded input waveguide has a maximum ridge waveguide width of 2.5 μm.
In some embodiments, the multimode waveguide has a length of 70 μm and the ridge waveguide of the tapered graded output waveguide has a length l2 of 10 μm.
Referring to fig. 7, fig. 7 is a top view of a 1×2 optical multimode interference coupler provided by the present invention. As shown in fig. 7, the 1×2 optical multimode interference coupler is a single-mode input waveguide with a ridge structure, a tapered graded input waveguide with a ridge structure, a multimode waveguide with a bar structure, a tapered graded output waveguide with a ridge structure, and a single-mode output waveguide with a ridge structure in order from left to right.
Referring to fig. 8, fig. 8 is a cross section of a 1×2 coupler ridge waveguide provided by the present invention. Referring to fig. 8, first, it is necessary to determine the single mode condition of the input ridge waveguide to implement a low-loss thick silicon ridge single mode waveguide, and by using optical simulation software, the ridge waveguide width satisfying the single mode condition can be obtained under the thick silicon platform condition of 3 μm thickness, and the length of w1 is 2.2 μm in the present invention to implement a single mode ridge waveguide.
The ridge waveguide portion of the tapered input waveguide is a ridge waveguide of tapered width that widens gradually from the minimum width (2.2 μm) of the ridge waveguide to a maximum width at the arrival of the strip-shaped multimode interference coupling waveguide, having a value w2 and w2 of 2.5 μm.
Further, the length of the input tapered waveguide needs to be chosen such that the optical field completes a gradual transition in the process of being transferred from the input end of the input tapered waveguide to the output end of the input tapered waveguide, in the embodiment of the invention the length l2 of the tapered waveguide is 10 μm.
The multimode waveguide of the strip structure is the core structure within the multimode interference coupler. Referring to fig. 9, fig. 9 is a cross-sectional view of a 1×2 coupler strip multimode waveguide provided by the present invention. The length and width of the strip multimode waveguide need to be determined at a top silicon layer thickness of 3 μm.
In an embodiment of the invention, the width w3 of the strip multimode waveguide is 8 μm to ensure that a sufficient number of optical modes are supported within the multimode waveguide region. Further, it is necessary to optimize the length of the bar-shaped multimode waveguide so as to maximize the optical transmission efficiency of the 1×2 coupler. In the present embodiment of the invention, the length l3 of the multimode waveguide is 70 μm.
At present, the multimode interference coupler based on the thin silicon platform can realize the light beam splitting effect of different ports in a small size, but is limited by the distribution of the optical mode field in the thin silicon waveguide and the etching roughness of the side wall of the waveguide, and the optical waveguide based on the thin silicon platform is difficult to realize the ultra-low loss light transmission.
An optical device under a thin silicon mesa having a top silicon layer thickness of 100nm to 300nm; whereas the thickness of the top silicon layer of thick silicon mesa-based optics may be above 2 μm.
Based on the optical device under the thick silicon platform, the binding property of the mode field in the waveguide is weaker than that of the device under the thin silicon platform, the sensitivity of the optical loss to the sidewall roughness is lower than that of the thin silicon material, and particularly the ridge waveguide under the thick silicon platform can realize the ultra-low loss optical transmission.
Therefore, the optical multimode interference coupler based on the strip-shaped ridge waveguide mixed structure is provided by the invention. It is applied to optical components of thick silicon platforms.
The optical multimode interference coupler based on the strip-shaped ridge waveguide mixed structure provided by the invention can be a 1 x 2 optical coupler. The 1 x 2 optical coupler may be an optical splitter based on multimode interference coupling effects within the multimode waveguide. The strip waveguide and the ridge waveguide are simultaneously used in the optical beam splitter.
The core area of the beam splitter is a multimode waveguide with a strip structure, and two sides of the core area are a tapered graded waveguide with a ridge structure and an input/output single-mode waveguide. At the interface of the core region and the tapered graded waveguide, the cross section of the waveguide is abrupt, i.e. the use of a conventional graded-section bar-shaped ridge transition structure is avoided.
The 1X 2 optical beam splitter of the strip-shaped ridge waveguide mixed structure has the functions of optical power beam splitting and waveguide structure conversion. Specifically, the thickness of the top silicon layer of the optical beam splitter is 3 μm, the thickness of the slab region waveguide of the ridge waveguide is 1.3 μm, so as to realize a low-loss single-mode waveguide, the input end of the optical beam splitter is connected with the low-loss ridge input waveguide, and the output end is connected with the ridge electro-optic modulation arm waveguide.
Similarly, the structure of the 1×2 optical splitter based on the strip-shaped ridge waveguide hybrid structure can also be used for realizing a 2×1 port optical splitter, and the optical signal can be input from the dual port side of the multimode interference coupler and output from the single port side only by exchanging the input port with the output port, so that the beam combining effect can be realized.
Similarly, for a 2×1 optical combiner with a hybrid structure of strip-shaped ridge waveguides, the thicknesses of the waveguides of the top silicon layer and the slab waveguide are the same as those of the optical splitter, the input end of the 2×1 optical combiner is connected with the ridge electro-optical modulation arm waveguide, and the output end is connected with the ridge output waveguide with low loss.
In some embodiments, when the optical multimode interference coupler based on the strip-shaped ridge waveguide hybrid structure provided by the invention is used for realizing a 2×1 port optical combiner, the multimode interference coupler corresponding to the optical combiner should be dual-port input, and two paths of signal light are simultaneously input from one side of the dual-port of the multimode interference coupler, and interference output of two paths of optical signals can be realized by adjusting the relative amplitude and phase difference value between the two paths of signal light.
It is worth noting that the optical multimode interference coupler based on the strip-shaped ridge waveguide mixed structure provided by the invention realizes the high-efficiency 1×2 optical coupler capable of being directly connected with the ridge single-mode waveguide on a thick silicon optical platform of 3-micron SOI for the first time, and has breakthrough progress. The optical multimode interference coupler can achieve 99.6% optical transmission efficiency equivalent to that of a pure strip coupler under the light wavelength of 1550nm, and meanwhile, compared with a ridge waveguide coupler, the efficiency of 94.2% is remarkably improved.
Referring to fig. 10, fig. 10 is a schematic diagram of a 1×1MZI optical switch based on a hybrid structure of a strip-shaped ridge waveguide according to the present invention. As shown in fig. 10, a 1×2 multimode interference coupler of a 1×1MZI optical switch comprising a hybrid structure of two stripe ridge waveguides is an optical splitter and an optical combiner in the MZI optical switch, respectively.
In a high-speed MZI electro-optical switch unit taking electro-optical modulation as a basic principle on a thick silicon optical platform, a modulation arm waveguide is a ridge waveguide, and a high-efficiency optical beam splitter and an optical beam combiner are strip waveguides. Therefore, using a 1×2 multimode interference coupler based on a hybrid strip-shaped ridge waveguide structure as a beam splitter and a beam combiner in an MZI electro-optical switch can avoid the use of a conventional graded transition strip-shaped ridge waveguide structure.
As shown in fig. 10, in the 1×1MZI optical switch based on the stripe ridge waveguide hybrid structure provided by the present invention, the 4 waveguide conversion regions coexist, which are the junction of the ridge input waveguide and the 1×2 optical beam splitter, the junction of the 1×2 optical beam splitter and the ridge electro-optic modulation arm waveguide, the junction of the ridge electro-optic modulation arm waveguide and the 2×1 optical beam combiner, and the junction of the 2×1 optical beam combiner and the ridge output waveguide. The optical coupler with the strip-shaped ridge waveguide mixed structure is adopted, and the 4 waveguide conversion areas do not need to use a traditional strip-shaped ridge waveguide gradual change conversion structure, so that high-efficiency optical signal transmission in the MZI optical switch is ensured on the premise of effectively shortening the size of the device.
In summary, compared with the prior art, the method has the following beneficial effects:
1. the invention provides an optical multimode interference coupler based on a strip-shaped ridge waveguide mixed structure, which is characterized in that a ridge-shaped transmission waveguide is directly connected with a strip-shaped multimode waveguide interface, and based on the multimode excitation principle of the multimode interference coupler, an optical signal in a ridge-shaped single-mode waveguide is enabled to finish multimode excitation and waveguide structure conversion in the waveguide at the interface of the multimode waveguide of the strip-shaped structure, a traditional gradual change-shaped ridge waveguide conversion structure is not needed, the length of an electrical unit device is effectively reduced, and the integration level of the device is improved.
2. The invention provides an optical multimode interference coupler based on a strip-shaped ridge waveguide mixed structure, which solves the problem of transition between a strip-shaped waveguide and a ridge waveguide in a thick silicon optical platform. The method utilizes the idea of expanding and exciting the mode field of an optical signal in a multimode waveguide, and completes the conversion of an optical waveguide structure in the input section and the output section of the multimode waveguide, namely, the strip multimode waveguide is directly connected with the ridge input-output waveguide to realize the high-efficiency multimode interference coupler. Light beam splitting and light beam combining in the waveguide in the thick silicon platform are realized, and a traditional gradual change conversion structure between the strip waveguide and the ridge waveguide can be avoided.
It is noted that the length and width of the multimode waveguide of the strip structure in the optical multimode interference coupler of the invention follow the multimode interference principle, and the working wavelength can cover the common infrared band range.
3. The invention provides an optical multimode interference coupler based on a mixed structure of a strip-shaped ridge waveguide, which reduces the structural complexity of an optical unit device with both the strip-shaped ridge waveguide and the ridge waveguide, and can effectively reduce the size of the device under the condition of ensuring high-efficiency optical signal transmission.
4. The optical multimode interference coupler with the strip-shaped ridge waveguide mixed structure provided by the invention avoids the traditional transition conversion structure between the strip-shaped multimode interference coupler and the ridge transmission waveguide, and realizes a low-loss thick silicon 1X 2 optical beam splitting device and a 2X 1 optical beam combining device in a compact area.
In addition, the optical beam splitter and the optical beam combiner in the Mach-Zehnder electro-optical switch unit are formed based on the strip-shaped ridge mixed waveguide structure, so that the direct conversion of the waveguide structure is realized among the optical beam splitter, the optical beam combiner and the electro-optical modulation arm waveguide, and meanwhile, the input end and the output end of the Mach-Zehnder electro-optical switch unit are directly connected with the ridge-shaped low-loss waveguide, so that the traditional transition conversion structure between the strip-shaped waveguide and the ridge-shaped waveguide is avoided.
It is noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus 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 apparatus. 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 apparatus that comprises the element.
The above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (7)
1. An optical multimode interference coupler based on a strip-shaped ridge waveguide mixed structure is characterized in that,
the optical multimode interference coupler is integrally formed, and sequentially comprises the following components from the input direction to the output direction of a signal: a single-mode input waveguide with a ridge structure, a conical gradual change input waveguide with a ridge structure, a multimode waveguide with a strip structure, a conical gradual change output waveguide with a ridge structure and a single-mode output waveguide with a ridge structure;
all ridge structured waveguides include ridge waveguides and slab waveguides;
the ridge waveguide width of the single-mode input waveguide is equal to the minimum ridge waveguide width of the tapered graded input waveguide;
the sum of the maximum ridge waveguide widths of the tapered graded input waveguide is less than the width of the multimode waveguide;
the sum of the maximum ridge waveguide widths of the tapered graded output waveguide is less than the width of the multimode waveguide;
the minimum ridge waveguide width of the tapered graded output waveguide is equal to the ridge width of the single mode output waveguide.
2. The optical multimode interference coupler of claim 1, wherein,
the ridge waveguide of the single-mode input waveguide and the ridge waveguide of the single-mode output waveguide have the same size;
the ridge waveguide of the tapered graded input waveguide and the ridge waveguide of the tapered graded output waveguide are the same size.
3. The optical multimode interference coupler of claim 1, wherein the multimode waveguide is located in a middle region of the optical multimode interference coupler; the tapered graded input waveguide and the tapered graded output waveguide are respectively positioned at two sides of the multimode waveguide and are directly connected with the multimode waveguide.
4. The optical multimode interference coupler of claim 1, wherein if the optical multimode interference coupler is a 1 x 2 coupler, the number of single-mode input waveguides, tapered graded input waveguides, and multimode waveguides are all 1, and the number of tapered graded output waveguides, single-mode output waveguides are all 2;
the 2 tapered graded output waveguides and the 2 single-mode output waveguides are all distributed up and down symmetrically about a transverse central axis of the multimode waveguide.
5. The optical multimode interference coupler of claim 1, wherein if the optical multimode interference coupler is a 2 x 1 coupler, the number of single-mode input waveguides, tapered graded input waveguides, and single-mode output waveguides are all 2, and the number of multimode waveguides, tapered graded output waveguides, and single-mode output waveguides are all 1;
the 2 tapered graded input waveguides and the 2 single-mode input waveguides are all distributed vertically symmetrically about a transverse central axis of the multimode waveguide.
6. The optical multimode interference coupler of any one of claims 4 or 5, wherein the slab waveguide thickness is adjusted according to the thickness of the top silicon layer of the optical multimode interference coupler; the ridge waveguide width of the ridge waveguide is adjusted according to the thickness of the top silicon layer of the optical multimode interference coupler;
specifically, the thickness of the top silicon layer is 3 μm, and the thickness of the slab region waveguide is 1.3 μm; the minimum ridge waveguide width of the tapered graded input waveguide is 2.2 μm; the maximum ridge waveguide width of the tapered graded input waveguide is 2.5 μm; the multimode waveguide has a width of 8 μm.
7. The optical multimode interference coupler of claim 6, wherein in the optical multimode interference coupler, the multimode waveguide has a length of 70 μιη; the length of the ridge waveguide of the graded output waveguide is 10 μm.
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