CN114488405A - Design method of double-waveguide adiabatic mode coupler - Google Patents

Design method of double-waveguide adiabatic mode coupler Download PDF

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CN114488405A
CN114488405A CN202210129395.XA CN202210129395A CN114488405A CN 114488405 A CN114488405 A CN 114488405A CN 202210129395 A CN202210129395 A CN 202210129395A CN 114488405 A CN114488405 A CN 114488405A
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waveguide
mode coupler
adiabatic mode
mode
coupler
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CN114488405B (en
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荣巍巍
梁图禄
许一娴
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Nantong University
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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
    • 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
    • G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
    • G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0075—Arrangements of multiple light guides
    • G02B6/0078—Side-by-side arrangements, e.g. for large area displays
    • 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 discloses a design method of a double-waveguide adiabatic mode coupler, the double-waveguide adiabatic mode coupler is a bending waveguide structure and is formed by connecting a plurality of oblique line sections along the propagation direction of light beams, and a local mode coupling coefficient kappa is utilized during design12An appropriate inclination angle is selected for the length of each segment, then the oblique line segments are spliced together to form a complete device, compared with a double-waveguide adiabatic mode coupler which linearly connects an initial end and a tail end, the length of the device is shortened, and the design method is simple. Such compact adiabatic mode couplers may be a key component of photonic integrated circuit systems.

Description

Design method of double-waveguide adiabatic mode coupler
Technical Field
The invention relates to a design method of a double-waveguide adiabatic mode coupler.
Background
The heat insulation device is a connector for connecting various optical functional units in a photonic integrated circuit, and plays an important role in future large-scale photonic integrated chips. Photonic integrated circuits are moving towards higher integration levels, which includes the multi-layer meaning: (1) a single optical device has a smaller size; (2) more functional devices are integrated on a single chip. In addition, silicon photonics is one of the hot research fields of integrated optics, and silicon materials and photonics are combined together to research the manufacture and integration of various photonic functional devices on the silicon materials or the silicon materials. An adiabatic mode coupler is a common mode for realizing light splitting and light combining in an optical fiber system, and can evolve an input mode in one waveguide into a symmetric mode and an input mode in a second waveguide into an antisymmetric mode on a phase matching plane.
While the total length of the waveguide structure sweep can be simply varied linearly to achieve the desired device length for a particular transmission power when designing an adiabatic mode coupler, the device length obtained in this manner can significantly exceed the desired length. The existing design of the adiabatic mode coupler is based on the analytic solution of an equation set, is generally complex and not easy to use, and needs some assumptions and approximations, so that the accuracy is influenced to a certain extent, and the design of the adiabatic mode coupler is difficult to use for the design of a complex structure.
Disclosure of Invention
The purpose of the invention is as follows: in view of the above prior art, a design method of a dual-waveguide adiabatic mode coupler is proposed to make the designed adiabatic mode coupler compact in structure.
The technical scheme is as follows: a design method of a double-waveguide adiabatic mode coupler is characterized in that the double-waveguide adiabatic mode coupler is of a bent waveguide structure and is formed by connecting a plurality of oblique line sections along a light beam propagation direction; initial conditions of the design method include initial end widths of the two waveguides, end widths, a gap between the two waveguides, the number of diagonal segments constituting the dual-waveguide adiabatic mode coupler, and lengths of the respective diagonal segments, and the design method includes: for each diagonal segment, the local mode coupling coefficient κ at the center cross-section is calculated according to the following formula12；
Figure BDA0003502031660000011
Where c is the speed of light in vacuum, n1Is the effective index of mode 1 at the central cross section, n2Is the effective refractive index of mode 2 at the central cross section, L is the length of the ramp segment, θ is the inner sidewall tilt angle of the ramp segment, wt1、wt2Respectively the width of both ends of one of the waveguides in the diagonal line segment, e1(ym)、e2(ym) Electric field intensity, y, for mode 1 and mode 2, respectivelym(x) Respectively a waveguide sideCoordinates, Δ ε, corresponding to the electric field on the wallmThe variation of the dielectric constant on the side wall of the oblique line section; m is 1,2,3,4, which represents the inner and outer side walls of the two waveguides;
let the coupling coefficient kappa12Obtaining the inner wall inclination angle theta of the inclined line segment as 0; all the diagonal segments are spliced together to form a complete dual-waveguide adiabatic mode coupler shape.
Further, the number of diagonal stages constituting the dual-waveguide adiabatic mode coupler is 3 or more.
Has the advantages that: the double-waveguide heat-insulating mode coupler is a bent waveguide structure and is formed by connecting a plurality of oblique line sections along the propagation direction of light beams, and a local mode coupling coefficient kappa is utilized during design12An appropriate inclination angle is selected for the length of each segment, then the oblique line segments are spliced together to form a complete device, compared with a double-waveguide adiabatic mode coupler which linearly connects an initial end and a tail end, the length of the device is shortened, and the design method is simple. Such compact adiabatic mode couplers may be a key component of photonic integrated circuit systems.
Drawings
FIG. 1 is a schematic diagram of an initial end structure of a dual-waveguide adiabatic mode coupler;
FIG. 2 is a schematic diagram of the end structure of a dual-waveguide adiabatic mode coupler;
FIG. 3 is a schematic top view of a dual-waveguide adiabatic mode coupler with a straight line connecting the initial end and the terminal end;
FIG. 4 is a schematic top view of the dual-waveguide adiabatic coupler of the present invention;
FIG. 5 is a schematic diagram of a diagonal segment;
FIG. 6 is a graph of the transmission curve of the dual-waveguide adiabatic mode coupler of the example.
Detailed Description
The invention is further explained below with reference to the drawings.
This example illustrates the design process by using an adiabatic mode coupler fabricated on a silicon waveguide slab on a silicon thin film substrate.
As shown in figure 1,Fig. 2 is a schematic diagram showing the structure of the initial end and the end of the dual-waveguide adiabatic mode coupler, respectively, and the dual-waveguide adiabatic mode coupler of the required design connects the initial end and the end to transmit the energy of the initial end to the end in the shortest possible distance without loss. The substrate 2 of the structure is silica, the core 1 of the structure is silica, the cladding 3 of the structure is air, wherein the refractive index n of the silica isSiO23.455, refractive index n of siliconSi3.455, refractive index n of air Air1. In this example, the silica thickness is 2 μm, the silicon thickness h is 220nm, the initial end widths of the two waveguides are 220nm and 100nm, the end widths of the two waveguides are 160nm, the gap g between the two silicon waveguides is 100nm, and the wavelength of the light beam is 1.55 μm.
Fig. 3 shows a straight-line connected dual-waveguide adiabatic mode coupler, which typically requires a long length. In order to realize a compact adiabatic mode coupler, as shown in fig. 4, the dual-waveguide adiabatic mode coupler of the present invention has a curved waveguide structure formed by connecting a plurality of diagonal segments as shown in fig. 5 along the propagation direction of the light beam. In fig. 4, the opposite inner walls of the two waveguides are kept parallel and the opposite outer walls of the two waveguides are kept parallel, i.e. the outer side wall of the first waveguide is inclined at an angle θ1Inclined at an angle theta to the outer side wall of the second waveguide4The inner side wall of the first waveguide is inclined at an angle theta2Inclined at an angle theta to the inner side wall of the second waveguide3And (5) the consistency is achieved.
As shown in FIG. 5, for a diagonal segment, the local mode coupling coefficient κ from mode 1 to mode 2 at the center cross section12The expression is as follows:
Figure BDA0003502031660000031
where ω is the angular frequency, β1＝ωn1/c、β2＝ωn1C is the phase constant of mode 1 and mode 2, respectively, c is the speed of light in vacuum, n1Is the effective index of mode 1 at the central cross section, n2Effective refractive index at the center cross section for mode 2, e1(ym)、e2(ym) Electric field intensity, y, for mode 1 and mode 2, respectivelym(x) Respectively, the coordinates, Delta epsilon, corresponding to the electric field on the waveguide side wallmThe variation of the dielectric constant on each side wall of the oblique line section is 1,2,3 and 4, and the variation corresponds to the outer side wall of the first waveguide, the inner side wall of the second waveguide and the outer side wall of the second waveguide in sequence.
Through geometric derivation, the relationship of the inclination angle to the length L of the diagonal line segment can be derived:
tanθ2＝tanθ3＝tanθ (2)
Figure BDA0003502031660000032
wherein, wt1、wt2The widths of two ends of the second waveguide in the diagonal line segment are respectively, theta is the inner side wall inclination angle of the diagonal line segment, and theta is the width of the second waveguide2＝θ3＝θ。
Bringing formulae (2) and (3) into formula (1) gives:
Figure BDA0003502031660000033
wherein, Delta epsilonmThe variation of the dielectric constant on the oblique line section side wall, where m is 1,2,3,4, respectively corresponds to the outer side wall of the first waveguide, the inner side wall of the second waveguide, and the outer side wall of the second waveguide in sequence.
When the coupling coefficient is k12When 0, no loss is caused in the mode transmission. This example illustrates dividing the adiabatic coupler into 4 segments, each segment having a length of 0.1 μm, let κ in equation (4)12The specific shape of each diagonal segment can be obtained by obtaining the inclination angle θ of the inner side wall of each diagonal segment as 0. All the diagonal segments are spliced together to form a complete dual-waveguide adiabatic mode coupler shape.
It should be noted that the selection of the length and the inclination angle of each inclined line segment of the adiabatic mode coupler is not unique as long as equation (4) is satisfied.
The total length of the device is scanned to obtain the transmission curve of a complete dual-waveguide adiabatic mode coupler, as shown in fig. 6. Comparing the double-waveguide adiabatic mode coupler designed in this embodiment with the case where a straight line connects the initial end and the final end, as shown in fig. 6, it can be seen that the adiabatic mode coupler designed in the present invention has a length much shorter than that based on the straight line for the same power transmission. For example, at 99.5% power transfer, the total length required for the invention is 9 μm, 19 μm in the straight case. Therefore, in the case of 99.5% power transfer, the length of the straight line case is more than 2 times the length required by the present invention, indicating that the length of the adiabatic mode coupler designed by the present invention can be made very short, achieving miniaturization of the device.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (2)

1. A design method of a double-waveguide adiabatic mode coupler is characterized in that the double-waveguide adiabatic mode coupler is of a bent waveguide structure and is formed by connecting a plurality of oblique line sections along a light beam propagation direction; initial conditions of the design method include initial end widths of the two waveguides, end widths, a gap between the two waveguides, the number of diagonal segments constituting the dual-waveguide adiabatic mode coupler, and lengths of the respective diagonal segments, and the design method includes: for each diagonal segment, the local mode coupling coefficient κ at the center cross-section is calculated according to the following formula12；
Figure FDA0003502031650000011
Where c is the speed of light in vacuum, n1Is the effective index of mode 1 at the central cross section, n2Is the effective refractive index of mode 2 at the central cross section, L is the length of the ramp segment, θ is the inner sidewall tilt angle of the ramp segment, wt1、wt2Respectively the width of both ends of one of the waveguides in the diagonal line segment, e1(ym)、e2(ym) Electric field intensity, y, for mode 1 and mode 2, respectivelym(x) Respectively, the coordinates, Delta epsilon, corresponding to the electric field on the waveguide side wallmThe variation of the dielectric constant on the side wall of the oblique line section; m is 1,2,3,4, which represents the inner and outer side walls of the two waveguides;
let the coupling coefficient kappa12Obtaining the inner wall inclination angle theta of the inclined line segment as 0; all the diagonal segments are spliced together to form a complete dual-waveguide adiabatic mode coupler shape.
2. The method of designing a dual-waveguide adiabatic mode coupler of claim 1, wherein the number of slash sections constituting the dual-waveguide adiabatic mode coupler is 3 or more.
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CN115494586A (en) * 2022-10-26 2022-12-20 南通大学 Double-waveguide adiabatic coupler

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