JP2023127130A - Waveguide type orbital angular momentum generation device, and orbital angular momentum multiplexing system - Google Patents

Abstract

To provide a waveguide type orbital angular momentum generation device and orbital angular momentum multiplexing system that do not need power consumption other than light, and are high in compatibility with a small system and existing optical fiber system.SOLUTION: A waveguide type orbital angular momentum generation device 1 comprises: a dielectric nanopillar 10 that develops an orbital angular momentum on an axis 11 of MD/MQ; and a nanowire optical waveguide 20 that has an area facing the dielectric nanopillar 10, and transports incident light to the dielectric nanopillar 10. In the dielectric nanopillar 10, the axis 11 of the MD/MQ crosses with respect to an optical path axis 21 of the nanowire optical waveguide 20, and is spaced with a first distance (D1) apart from the optical path axis 21 of the nanowire optical waveguide 20.SELECTED DRAWING: Figure 1

Description

The present invention relates to a waveguide type optical vortex generator and an optical vortex multiplexing system.

Various optical elements used in optical networks include lasers, modulators, multiplexing elements, optical switches, and the like. An optical integrated circuit is one in which various functions essential for optical communication are integrated on a single chip. Compared to single-function optical devices, it is possible to reduce implementation costs, power consumption, and size, so many modules have been put into practical use and are dominating the current optical market.
In a typical optical integrated circuit, the mode of propagating light is fixed to TE mode (Transverse Electric mode)/TM mode (Transverse Magnetic mode) (hereinafter, "/" is expressed as "or"). Therefore, various devices integrated on optical circuits are designed to operate in those modes.

In optical communication technology, the future increase in signal multiplexing resources will lead to a dramatic increase in communication capacity. Optical vortices, which correspond to the orbital angular momentum of light, carry information on the helical period of the wavefront, so theoretically infinite channel multiplexing is possible, and since it is highly compatible with existing multiplexing technology, it has been widely used. It can become a key technology for capacity transmission. Therefore, in recent years, attempts have been made to apply optical vortices to communications.

15 and 16 are diagrams illustrating circularly polarized light and optical vortices when the light direction shown in FIG. 14 is irradiated. The z-axis in FIGS. 15 and 16 is the irradiation direction (z-axis) of the Light direction in FIG. 14.
The circularly polarized light (right-handed circularly polarized light) shown on the left side of the upper diagram of FIG. 15 propagates as the electric field and magnetic field describe a spiral. When this circularly polarized light is combined with the optical vortex (m=0; plane wave) shown on the upper right side of FIG. 15, circularly polarized light is observed when looking at the magnetic field Hz distribution shown on the lower side of FIG. 15.

The circularly polarized light (right-handed circularly polarized light) shown on the left side of the upper diagram of FIG. 16 propagates as an electric field and a magnetic field draw a spiral. When this circularly polarized light is combined with the optical vortex (m=-1) shown in the upper right of FIG. 16, the distribution of the magnetic field Hz shown in the lower diagram of FIG. Hz distribution, circularly polarized light with an optical vortex ("optical vortex light") is observed. The above m indicates the helical number of the optical vortex, and m=0, 1, 2, 3,... (the opposite direction is indicated by "-").

A supplementary explanation will be given of circularly polarized light and optical angular momentum (OAM).
In circularly polarized light, each electromagnetic field is spiral. Circularly polarized light includes only right-handed circularly polarized light (CW) and left-handed circularly polarized light (CCW). Circularly polarized light is necessary to exploit the properties of topological photonics.

The optical vortex has a spiral equiphase surface. In addition to the left and right optical vortices, the optical vortex can have a multi-helix structure. Therefore, theoretically infinite channels are possible.

Patent Document 1 includes a first layer and a second layer opposite to the first layer, the first layer includes a plurality of first structures each having optical anisotropy, and the second layer includes a plurality of first structures each having optical anisotropy. , describes an optical element that, when reflecting light incident from the first layer, reflects the light while maintaining the polarization state of the light between the time of incidence and the time of reflection. Paragraph [0258] of Patent Document 1 states, "The light LT2 is emitted as an optical vortex. An optical vortex is light that has a singular point and whose equiphase plane forms a spiral surface." It is stated that.

Among the optical vortex generating devices that have been published in research, there is a device that uses a spatial phase modulator (for example, “Tsinghua University” Y. Wang et al., Sci. Rep. 6, 22512 (2016)). Furthermore, waveguide-type optical vortex generators include devices that include a star coupler, an array waveguide, and an optical coupler. (For example, “University of California, Davis,” T.Su et al., Opt. Express, 20(9), 9396 (2012)).

Unexamined Japanese Patent Publication No. 2018-84679

The optical vortex generators announced to date have the following issues.
When a spatial phase modulator is used, the system becomes large, so it is not practical for optical fiber systems.
Furthermore, it is difficult to create a passive device that does not require power consumption other than optical input. For example, existing optical vortex generators that are integrated with a star coupler, arrayed waveguide, and optical coupler generally require the integration of a heater, etc. to adjust the phase difference between the arrayed waveguides, and consumes electricity.

The present invention was made in view of these circumstances, and since phase adjustment is not required, power consumption other than optical input is not required, and the present invention is a small system that is highly compatible with existing optical fiber systems. An object of the present invention is to provide a waveguide type optical vortex generator and an optical vortex multiplexing system.

In order to solve the above-mentioned problems, a waveguide type optical vortex generator according to the present invention is a waveguide type optical vortex generator, which is a nano-sized high refractive index device that generates an optical vortex on the axis of MD or MQ. a thin wire optical waveguide having a region facing the nano-sized high refractive index dielectric and transporting incident light to the nano-sized high refractive index dielectric; The refractive index dielectric is characterized in that the MD or MQ axis intersects with the optical path axis of the thin wire optical waveguide and is spaced a predetermined first distance from the optical path axis of the thin wire optical waveguide. do.

According to the present invention, it is possible to provide a waveguide type optical vortex generator and an optical vortex multiplexing system that do not require power consumption other than optical input, are small, and have high compatibility with existing optical fiber systems.

1 is a perspective view showing the structure of a waveguide type optical vortex generator according to an embodiment of the present invention. FIG. 3 is a diagram schematically showing Magnetic multipoles and Radiation multipoles in Dipoles and Quadrupoles in the waveguide type optical vortex generator of the present invention. FIG. 3 is a diagram showing, for each wavelength, the characteristics of light including MD and MQ that appear on the MD/MQ axis of the dielectric nanopillar of the waveguide type optical vortex generator of the present invention. FIG. 2 is a top view showing the structure of a waveguide type optical vortex generator that exhibits MD in the waveguide type optical vortex generator of the present invention. FIG. 2 is a side view showing the structure of a waveguide type optical vortex generator that exhibits MD in the waveguide type optical vortex generator of the present invention. FIG. 6 is a diagram showing magnetic field vectors of the waveguide type optical vortex generator shown in FIGS. 4 and 5. FIG. 6 is a diagram showing the electric field Ey distribution of the waveguide type optical vortex generator shown in FIGS. 4 and 5. FIG. 6 is a diagram showing the magnetic field Hy distribution of the waveguide type optical vortex generator shown in FIGS. 4 and 5. FIG. FIG. 2 is a top view showing the structure of the waveguide type optical vortex generator that exhibits MQ in the waveguide type optical vortex generator of the present invention. FIG. 2 is a side view showing the structure of a waveguide type optical vortex generator that exhibits MQ in the waveguide type optical vortex generator of the present invention. 11 is a diagram showing magnetic field vectors of the waveguide type optical vortex generator shown in FIGS. 9 and 10. FIG. 11 is a diagram showing the electric field Ey distribution of the waveguide type optical vortex generator shown in FIGS. 9 and 10. FIG. 11 is a diagram showing the magnetic field Hy distribution of the waveguide type optical vortex generator shown in FIGS. 9 and 10. FIG. FIG. 3 is a perspective view illustrating light direction irradiation. FIG. 15 is a diagram illustrating circularly polarized light and a light vortex when the light direction shown in FIG. 14 is irradiated. FIG. 15 is a diagram illustrating circularly polarized light and a light vortex when the light direction shown in FIG. 14 is irradiated.

Embodiments of the present invention will be described in detail below with reference to the drawings.
(Explanation of principle)
When light is incident on a nano-sized dielectric with a high refractive index, a phenomenon called Mie resonance occurs at a specific wavelength, and the light scattered by Mie resonance under certain conditions has a vortex state (Magnetic Quadrupole).

The leakage of light from a thin Si optical waveguide, which is widely used in existing optical circuits, is used as incident light to a nano-sized high refractive index dielectric. This makes it possible to emit spiral light from an existing optical device that operates only with TE/TM mode light. At this time, if the MD/MQ axis of the nano-sized high refractive index dielectric material and the optical path axis of the Si wire optical waveguide are aligned, the light emitted from the nano-sized high refractive index dielectric material is not spiral-shaped. Therefore, it is necessary to shift the axis.

(Embodiment)
FIG. 1 is a perspective view showing the structure of a waveguide type optical vortex generator according to an embodiment of the present invention.
The waveguide type optical vortex generator 1 includes a dielectric nanopillar 10 that generates an optical vortex on the MD/MQ axis 11, and is arranged apart from the dielectric nanopillar 10, and transports incident light to the dielectric nanopillar 10. A thin wire optical waveguide 20 is provided.

The MD/MQ axis 11 of the dielectric nanopillar 10 is in a direction intersecting (orthogonal here) to the optical path axis 21 of the thin optical waveguide 20, and is at a predetermined distance (D1) from the optical path axis 21 of the thin optical waveguide 20. Separated. That is, the MD/MQ axis 11 of the dielectric nanopillar 10 is shifted from the optical path axis 21 of the thin optical waveguide 20 in the intersecting direction and the distance from each other. Further, the dielectric nanopillar 10 is spaced apart from the surface 20a of the thin wire optical waveguide 20 by a predetermined distance (D2). Therefore, at least a portion of the dielectric nanopillars 10 overlap with each other at a predetermined distance (D2) from the surface 20a of the thin optical waveguide 20 on one side in the width direction of the thin optical waveguide 20 (it is sufficient if there are opposing regions).

<Dielectric nanopillar 10>
- Basic structure The dielectric nanopillar 10 is a nano-sized high refractive index dielectric.
The dielectric nanopillar 10 is nanosized because it uses a phenomenon called Mie resonance at a specific wavelength.
The dielectric nanopillar 10 is a high refractive index dielectric material such as Si, InP, GaP, AlAs, or GaAs. The dielectric nanopillar 10 has a high refractive index (3.0 or more) at the wavelength where MD/MQ occurs.

- Arrangement The dielectric nanopillar 10 is arranged vertically apart from the thin optical waveguide 20.
The dielectric nanopillar 10 is disposed on one side in the width direction of the thin optical waveguide 20 at a distance of a first distance (D1) from the optical path axis 21 of the thin optical waveguide 20. Light is incident from the direction (lateral to the MD/MQ axis 11).

In the region facing the dielectric nanopillar 10, the dielectric nanopillar 10 and the thin optical waveguide are separated by a second distance (D2), and the second distance (D2) is 5 nm to 100 nm (more preferably 10 nm to 50 nm). be.

- Rotational symmetry The dielectric nanopillar 10 has rotational symmetry, and the axis of rotational symmetry is the axis 11 of MD/MQ.

- MQ expression The radius of the dielectric nanopillar 10 is smaller than the first distance (D1), and MQ is expressed on the axis 11 of MD/MQ.
The first distance (D1) is 50 nm above and below 450 nm, and expresses MQ on the axis 11 of MD/MQ.

The axis 11 of MD/MQ developed in the dielectric nanopillar 10 is separated from the optical path axis 11 of the thin optical waveguide 20 by a radius of the dielectric nanopillar 10 or more.

<Thin optical waveguide 20>
The thin wire optical waveguide 20 transports the incident light to the dielectric nanopillar 10. In the thin optical waveguide 20 , light leaks (seeps) to the dielectric nanopillar 10 in a region facing the dielectric nanopillar 10 .

The thin wire optical waveguide 20 is made of a material that is transparent at a wavelength where MD/MQ is expressed, such as Si, Si ₃ N ₄ , PMMA (acrylic resin), diamond, or the like.
Note that the thin wire optical waveguide 20 is not a necessary condition for a high refractive index.
The thin wire optical waveguide 20 may be straight or curved.

<Three-dimensional structure of waveguide type optical vortex generator 1>
In order to realize the three-dimensional structure shown in FIG. 1, the waveguide type optical vortex generator 1 has a transparent member with a small refractive index (for example, SiO ₂ glass, etc.) interposed as a spacer on the thin wire optical waveguide 20. The dielectric nanopillars 10 are positioned and arranged.

2 and 3 are diagrams explaining MD and MQ.
FIG. 2 is a diagram schematically showing Magnetic multipoles and Radiation multipoles in Dipoles and Quadrupoles in the electromagnetic field and incident light direction k of the dielectric nanopillar 10 shown on the right side of FIG. Radiation multipoles refer to the shape in which light is emitted, and Dipoles' radiation multipoles emit light in a donut shape. Quadrupoles Radiation multipoles have a shape that combines four donut shapes.

For example, in Dipoles, there is a magnetic multipole in the center of the donut-shaped radiation multipole. "m" shown in the magnetic multipoles is the direction in which the optical vortex is emitted, and corresponds to the axis of the incident light direction k of the dielectric nanopillar 10 shown on the right side of FIG. Further, "Current" shown in the Magnetic multipoles is a current flowing around in the circumferential direction of the dielectric nanopillar 10, which generates the electric field E of the dielectric nanopillar 10 shown on the right side of FIG. A light vortex is created by the current flowing in circles.

FIG. 3 is a diagram showing, for each wavelength, the characteristics of light including MD and MQ developed in the MD/MQ axis 11 of the dielectric nanopillar 10 of the waveguide type optical vortex generator 1, and FIG. The total extinction cross section is shown as _{the exl} /σ _geom ratio. In the figure, σ is the cross-sectional area and σ_ext is the extinction cross-section. σ_geom is the cross-sectional area of the geometric nanostructure, and dividing by σ_geom normalizes σ_ext.
As shown in FIG. 3, the wavelength band in which MQ appears is narrow, and when viewed as a whole wavelength, MD is dominant.

As shown in FIG. 3, by adopting the structure of the waveguide-type optical vortex generator 1 shown in FIG. At the wavelength of Mie resonance (near λ=2200 um), an optical vortex (Magnetic Quadrupole) is generated.

Hereinafter, the operation of the waveguide type optical vortex generator 1 configured as described above will be explained.
(Explanation of principle)
The present inventors are able to operate only with TE/TM mode light by utilizing the leakage of light from the thin optical waveguide 20 as incident light to a nano-sized high refractive index dielectric (dielectric nanopillar 10). We have discovered that it is possible to emit spiral light from existing optical devices. At this time, it has also been found that when the MD/MQ axis 11 of the nano-sized high refractive index dielectric material and the optical path axis 21 of the thin wire optical waveguide 20 are aligned, the emitted light does not become spiral-shaped. For this reason, it is essential to shift the MD/MQ axis 11 of the nano-sized high refractive index dielectric material and the optical path axis 21 of the thin wire optical waveguide 20.

Here, "shifting the MD/MQ axis 11 of the nano-sized high refractive index dielectric material and the optical path axis 21 of the thin wire optical waveguide 20" means that the nano-sized The MD/MQ axis 11 of the high refractive index dielectric is spaced a predetermined distance (D1) to one side in the width direction of the thin wire optical waveguide 20, and is also separated upwardly from the surface 20a of the thin wire optical waveguide 20 by a predetermined distance (D2). Refers to the arrangement. Further, the MD/MQ axis 11 of the nano-sized high refractive index dielectric material is arranged to intersect with the optical path axis 21 of the thin wire optical waveguide 20 .

[MD expression structure]
4 and 5 are diagrams showing the structure of the waveguide type optical vortex generator 1 that exhibits MD, FIG. 4 is a top view thereof, and FIG. 5 is a side view thereof (Crosssectional view). It is.

<Dielectric nanopillar 10>
The dielectric nanopillar 10 is a nano-sized high refractive index dielectric made of Si-metamaterial.
The dielectric nanopillar 10 is a cylindrical high refractive index dielectric with a radius r of 300 nm (FIG. 4) and a height of 300 nm (FIG. 4).

<Thin optical waveguide 20>
The thin wire optical waveguide 20 is a Si thin wire optical waveguide having a line width of 500 nm (lengths from the optical path axis 21 to the ends 22 and 23, 250 nm and 250 nm) (FIG. 4) and a line thickness of 220 nm (FIG. 5) and a rectangular parallelepiped cross section.

<Arrangement of dielectric nanopillar 10 and thin optical waveguide 20>
As shown in FIG. 4, the dielectric nanopillar 10 has a cylindrical central axis O (MD/MQ axis 11) with a radius r located a predetermined distance ( D1: 180 nm), and as shown in FIG. be done. In FIG. 4, when viewed from above, the portion where the dielectric nanopillar 10 of radius r overlaps the thin optical waveguide 20 is the "region facing the nano-sized high refractive index dielectric".

At this time, the axis 11 of MD/MQ developed in the dielectric nanopillar 10 is spaced a predetermined distance (D1: 180 nm) from the optical path axis 21 of the thin optical waveguide 20 toward the end 22 in the width direction of the thin optical waveguide 20, And they are orthogonal.
Therefore, as shown in FIGS. 1, 4, and 5, in the waveguide type optical vortex generator 1, the dielectric nanopillar 10 is placed on the surface 20a of the thin optical waveguide 20 at a predetermined distance (D1: 180 nm) and are arranged above at a predetermined distance (D2: 50 nm). In other words, in the waveguide type optical vortex generator 1, a part of the bottom 10a of the dielectric nanopillar 10 is vertically spaced apart on the surface 20a shifted from the optical path axis 21 of the thin wire optical waveguide 20, and The nanopillar 10 receives light leaking from the thin wire optical waveguide 20 at the bottom 10a.

When producing circularly polarized light using an MD producing structure, there is a margin in the design value of the predetermined distance (D1: 180 nm). D1: 180 nm is close to the lower limit, and D1: up to about 300 nm is acceptable.
The dielectric nanopillar 10 must be configured to float a predetermined distance (D2) from the thin optical waveguide 20. Therefore, the predetermined distance (D2) does not hold true at 0, and although it does hold true at the predetermined distance (D2: 100 nm), the efficiency is poor because the light leaking into the dielectric nanopillar 10 decreases, and the predetermined distance (D2: 50 nm) is close to the upper limit. Further, the lower limit value is (D2: 10 nm).

<MD expression>
The waveguide type optical vortex generator 1 generates an optical vortex by inputting light into a nano-sized high refractive index dielectric (dielectric nanopillar 10) from a Si thin wire optical waveguide (thin wire optical waveguide 20).

First, incident light (wavelength: 1551 nm) is transported to the dielectric nanopillar 10 through the thin optical waveguide 20 . Then, light is incident on the dielectric nanopillar 10 from the lateral direction.

When TE-mode (having Hy, Ex, and Ez components) is input into the Si thin wire optical waveguide (thin wire optical waveguide 20), the dielectric nanopillar 10 has a magnetic field vector (H vector (Hx, Hz)) (Fig. 6). , Ey (FIG. 7), and Hy (FIG. 8).

FIG. 6 is a diagram showing the magnetic field vector (H vector (Hx, Hz)) of the waveguide type optical vortex generator 1 shown in FIGS. 4 and 5. FIG. FIG. 6 is a simulation result of a magnetic field vector when viewed upward from the center of the thin optical waveguide 20 shown by the broken line a in FIG. 5, for example, from a height of 1 μm. The x-axis and z-axis in FIG. 6 are the x-axis and z-axis in FIG. 4.
In the distribution of the magnetic field vector (H vector (Hx, Hz)) shown in FIG. 6, the magnetic field vector rotates just above the dielectric nanopillar 10, indicating that the light is circularly polarized.

FIG. 7 is a diagram showing the electric field Ey distribution of the waveguide type optical vortex generator 1 shown in FIGS. 4 and 5. FIG. FIG. 7 is a simulation result of a magnetic field vector when viewed upward from the center of the thin optical waveguide 20 shown by the broken line a in FIG. 5, for example, from a height of 1 μm. The x-axis and z-axis in FIG. 7 are the x-axis and z-axis in FIG. 4.
As shown in FIG. 7, looking at the distribution of the electric field Ey, it can be seen that circularly polarized light is emitted from the MD/MQ axis 11 of the dielectric nanopillar 10 at the 1 μm point. This is the circularly polarized light and optical vortex (m=0; plane wave) in FIG. 14, that is, the emission of circularly polarized light.

FIG. 8 is a diagram showing the magnetic field Hy distribution of the waveguide type optical vortex generator 1 shown in FIGS. 4 and 5. FIG. FIG. 8 is a simulation result of the magnetic field vector when viewed upward from the center of the thin wire optical waveguide 20 shown by the broken line a in FIG. 5, for example, from a height of 1 μm. The x-axis and z-axis in FIG. 8 are the x-axis and z-axis in FIG. 4.
As shown in FIG. 8, looking at the distribution of the magnetic field Hy, it can be seen that circularly polarized light is emitted from the MD/MQ axis 11 of the dielectric nanopillar 10 at the 1 μm point.

As described above, as shown in FIGS. 6 to 8, the waveguide type optical vortex generator 1 is in a state where only circularly polarized light is generated.

[MQ expression structure]
9 and 10 are diagrams showing the structure of the waveguide type optical vortex generator 1 that expresses MQ, FIG. 9 is a top view thereof, and FIG. 10 is a side view thereof (Crosssectional view). It is.

<Dielectric nanopillar 10>
The dielectric nanopillar 10 is a nano-sized high refractive index dielectric made of Si-metamaterial.
The dielectric nanopillar 10 is a cylindrical high refractive index dielectric with a radius r of 300 nm (FIG. 9) and a height of 300 nm (FIG. 9).

<Thin optical waveguide 20>
The thin wire optical waveguide 20 is a Si thin wire optical waveguide having a line width of 500 nm (lengths from the optical path axis 21 to the ends 22 and 23, 250 nm, 250 nm) (FIG. 9) and a line thickness of 220 nm (FIG. 10) and a rectangular parallelepiped cross section.

<Arrangement of dielectric nanopillar 10 and thin optical waveguide 20>
As shown in FIG. 9, the dielectric nanopillar 10 has a cylindrical central axis O (MD/MQ axis 11) with a radius r located a predetermined distance ( D1: 450 nm), and as shown in FIG. be done. In FIG. 9, when viewed from above, the portion where the dielectric nanopillar 10 of radius r overlaps the thin wire optical waveguide 20 is the "region facing the nano-sized high refractive index dielectric".

At this time, the axis 11 of MD/MQ developed in the dielectric nanopillar 10 is spaced a predetermined distance (D1: 450 nm) from the optical path axis 21 of the thin optical waveguide 20 toward the end 22 in the width direction of the thin optical waveguide 20, And they are orthogonal.
Therefore, as shown in FIGS. 1, 9, and 10, in the waveguide type optical vortex generator 1, the dielectric nanopillar 10 is placed on the surface 20a of the thin optical waveguide 20 at a predetermined distance (D1: 180 nm) and are arranged above at a predetermined distance (D2: 25 nm). In other words, in the waveguide type optical vortex generator 1, a part of the bottom 10a of the dielectric nanopillar 10 is vertically spaced apart on the surface 20a shifted from the optical path axis 21 of the thin wire optical waveguide 20, and The nanopillar 10 receives light leaking from the thin wire optical waveguide 20 at the bottom 10a.

The MQ expression structure has stricter design value setting conditions than the MD expression structure.
When circularly polarized light and optical vortices are produced using the MQ expression structure, the predetermined distance (D1: 450 nm) is close to the optimum value, and the vertical deviation from (D1: 450 nm) is about 50 nm.
When MQ is expressed, the efficiency is poor at the predetermined distance (D2: 50 nm) described for MD expression, and the predetermined distance (D2: 25 nm) is the upper limit. Note that the lower limit value is (D2: 10 nm) as in the case of MD expression.

<MQ expression>
The waveguide type optical vortex generator 1 generates an optical vortex by inputting light into a nano-sized high refractive index dielectric (dielectric nanopillar 10) from a Si thin wire optical waveguide (thin wire optical waveguide 20).

First, incident light (wavelength: 1410 nm) is transported to the dielectric nanopillar 10 through the thin optical waveguide 20 . Then, light is incident on the dielectric nanopillar 10 from the lateral direction to generate an optical vortex.

When TE-mode (having Hy, Ex, and Ez components) is input into the Si thin wire optical waveguide (thin wire optical waveguide 20), the dielectric nanopillar 10 has a magnetic field vector (H vector (Hx, Hz)) (FIG. 11). , Ey (FIG. 12), and Hy (FIG. 13).

FIG. 11 is a diagram showing the magnetic field vector (H vector (Hx, Hz)) of the waveguide type optical vortex generator 1 shown in FIGS. 9 and 10. FIG. 11 is a simulation result of the magnetic field vector when viewed upward from the center of the thin wire optical waveguide 20 shown by the broken line a in FIG. 10, for example, from a height of 1 μm. The x-axis and z-axis in FIG. 11 are the x-axis and z-axis in FIG. 9.
In the distribution of the magnetic field vector (H vector (Hx, Hz)) in FIG. 11, the magnetic field vector exhibits the behavior of circularly polarized light and an optical vortex just above the dielectric nanopillar 10, which indicates that it is circularly polarized light and an optical vortex. I understand.

FIG. 12 is a diagram showing the electric field Ey distribution of the waveguide type optical vortex generator 1 shown in FIGS. 9 and 10. FIG. 12 is a simulation result of a magnetic field vector when viewed upward from the center of the thin optical waveguide 20 shown by the broken line a in FIG. 10, for example, from a height of 1 μm. The x-axis and z-axis in FIG. 12 are the x-axis and z-axis in FIG. 9.
As shown in FIG. 12, looking at the electric field Ey distribution, at the 1 μm point above, the Ey distribution is divided into four parts on the MD/MQ axis 11 of the dielectric nanopillar 10, which is a characteristic of circularly polarized light and an optical vortex. You can see that it is being emitted.
Looking at the Ey distribution shown in FIG. 12, it can be seen that light in which an optical vortex is added to circularly polarized light ("optical vortex light") is generated. That is, an Ey distribution divided into four parts, which is a characteristic of the circularly polarized light and optical vortex shown in FIG. 15, is observed.

FIG. 13 is a diagram showing the magnetic field Hy distribution of the waveguide type optical vortex generator 1 shown in FIGS. 9 and 10. FIG. 13 is a simulation result of the magnetic field vector when viewed upward from the center of the thin wire optical waveguide 20 shown by the broken line a in FIG. 10, for example, from a height of 1 μm. The x-axis and z-axis in FIG. 13 are the x-axis and z-axis in FIG. 9.
As shown in FIG. 13, looking at the distribution of the magnetic field Hy, it can be seen that at least circularly polarized light is emitted from the MD/MQ axis 11 of the dielectric nanopillar 10 at the 1 μm point.

Incidentally, in the case of FIG. 1, if incident light enters the thin optical waveguide 20 from the front, the light transported in the lateral direction of the dielectric nanopillar 10 leaks at the position of the dielectric nanopillar 10, and the Circularly polarized light and a light vortex are emitted from above. The optical vortex at this time is counterclockwise when viewed from directly above the dielectric nanopillar 10. In FIG. 1, if the dielectric nanopillar 10 is placed below the thin optical waveguide 20, the direction is clockwise when viewed from directly above the dielectric nanopillar 10.

As described above, as shown in FIGS. 11 to 13 (in particular, FIG. 12), the waveguide type optical vortex generator 1 generates circularly polarized light on the MD/MQ axis 11 of the dielectric nanopillar 10 at the 1 μm point. It is also thought that the light is emitted as a four-part Ey distribution, which is a characteristic of a light vortex.

As explained above, the waveguide type optical vortex generator 1 according to the present embodiment includes the dielectric nanopillar 10 (nano-sized high refractive index dielectric) that generates an optical vortex on the MD/MQ axis 11, A thin wire optical waveguide 20 has a region facing the dielectric nanopillar 10 and transports incident light to the dielectric nanopillar 10. It is characterized in that it intersects with the optical path axis 21 of the thin wire optical waveguide 20 and is spaced apart from the optical path axis 21 of the thin wire optical waveguide 20 by a first distance (D1).

With this configuration, for example, TE/TM mode light incident on the thin wire optical waveguide 20 is transported to the dielectric nanopillar 10, and the light leaks in the lateral direction of the dielectric nanopillar 10 in a region facing the thin wire optical waveguide 20. Since the dielectric nanopillar 10 is a nano-sized dielectric with a high refractive index, when light is incident thereon, it is scattered by Mie resonance at a specific wavelength, and the scattered light has a vortex state (Magnetic Quadrupole). Circularly polarized light and an optical vortex (m=0; plane wave), that is, circularly polarized light is emitted from the MD/MQ axis 11 of the dielectric nanopillar 10 (<MD expression>), or circularly polarized light and an optical vortex (m=±1 ; a plus or minus light vortex with a helical number of 1) is emitted (<MQ expression>).

Here, <MD expression> or <MQ expression> can be selected under certain conditions. The above-mentioned certain conditions are mainly determined by the wavelength and the first distance (D1) that defines the area facing the thin wire optical waveguide 20 (the external dimensions of the component such as the radius r for this purpose). The second distance (D2) is a parameter that determines the leakage of light to the dielectric nanopillar 10. However, the second distance (D2) also slightly changes the relative distance between the optical path axis 21 of the thin wire optical waveguide 20 and the MD/MQ axis 11 of the dielectric nanopillar 10, so this is taken into consideration. The same applies to the angle at which the axis 11 of MD/MQ intersects with the optical path axis 21 of the thin optical waveguide 20.

Further, in the waveguide type optical vortex generator 1, the dielectric nanopillars 10 (nano-sized high refractive index dielectric) have rotational symmetry, and the axis of rotational symmetry is the MD/MQ axis 11. Since the nano-sized high refractive index dielectric material has rotationally symmetrical MD/MQ axis 11, the environment in which light vortices occur becomes isotropic in the axial direction, and the vortex-like light exits along MD/MQ axis 11. By concentrating it, we can expect to increase the efficiency of light vortex production. Further, there is an advantage that disturbance factors caused by structural anisotropy can be eliminated, and the design can be simplified. Note that the nano-sized high refractive index dielectric may be any structure as long as it has rotational symmetry, and includes structures such as a conical structure and a sphere, in addition to the above-mentioned pillar structure.

In this way, the waveguide-type optical vortex generator 1 can generate vortex-like light by shifting the MD/MQ axis 11 of the dielectric nanopillar 10 and the optical path axis 21 of the thin optical waveguide 20.
The waveguide-type optical vortex generator 1 does not require power consumption other than optical input, and can provide a small-sized waveguide-type optical vortex generator that is highly compatible with existing optical fiber systems.

This makes it possible to realize a waveguide-type optical vortex generator that can be integrated on topological silicon photonic integrated circuits (TPICs). Since optical vortices theoretically have no multiplexing restrictions, they are a powerful elemental technology for optical vortex communication technology for large-capacity transmission. An example of application to an optical vortex multiplexing system is to integrate nanostructures that express MD, MQ, and even large m-order optical vortices on one or more waveguides through which signal light propagates. By doing so, a plurality of optical vortex signals corresponding to the nanostructures can be emitted from the surface. By combining these optical vortex signals using lenses etc. integrated on this device, it is possible to function as an optical vortex multiplexing system using free space or various optical fibers as transmission paths.

The waveguide type optical vortex generator 1 can be applied to optical circuits with topological characteristics. The waveguide type optical vortex generator 1 can be formed on a semiconductor substrate (silicon, InP, etc.) and has excellent compatibility with semiconductor lasers and multi-core fibers, which are key components for large-capacity transmission. We can also expect improved compatibility with optical communications.

In particular, it is suitable when circularly polarized light is used to operate a topological photonic crystal (PhC) and an optical vortex is used as a multi-dimensional element. The above-mentioned Topological Photonic Crystal is a photonic structure in which the inside is an insulator with an energy gap, but the edges are in a metal state with no band gap.

The present invention is not limited to the above-described embodiments, and includes other modifications and applications without departing from the gist of the present invention as set forth in the claims.

1 Waveguide type optical vortex generator 10 Dielectric nanopillar (nano-sized high refractive index dielectric)
10a Bottom of dielectric nanopillar 11 MD/MQ axis (MD or MQ axis)
20 Si thin wire optical waveguide (thin wire optical waveguide)
20a Surface of thin optical waveguide 21 Optical path axis D1 First distance D2 Second distance

Claims (6)

A waveguide type optical vortex generator,
A nano-sized high refractive index dielectric material that expresses an optical vortex on the axis of MD (Magnetic Dipole) or MQ (Magnetic Quadrupole),
a thin wire optical waveguide having a region facing the nano-sized high refractive index dielectric and transporting incident light to the nano-sized high refractive index dielectric,
The nano-sized high refractive index dielectric is arranged such that the MD or MQ axis intersects with the optical path axis of the thin wire optical waveguide and is spaced a predetermined first distance from the optical path axis of the thin wire optical waveguide. A waveguide type optical vortex generator characterized by the following. In a region facing the nano-sized high refractive index dielectric, the nano-sized high refractive index dielectric and the thin wire optical waveguide are separated by a predetermined second distance;
The waveguide type optical vortex generator according to claim 1, wherein the second distance is 5 nm to 100 nm. The waveguide type optical vortex generator according to claim 1, wherein the nano-sized high refractive index dielectric has rotational symmetry, and the axis of rotational symmetry is the MD or MQ axis. The waveguide-type optical vortex according to claim 3, wherein when the MQ is expressed on the axis of the MD or MQ, the radius of the nano-sized high refractive index dielectric is smaller than the first distance. Generator. The waveguide type optical vortex generator according to claim 1, wherein when the MQ is expressed on the axis of the MD or MQ, the first distance is 50 nm above and below 450 nm. An optical vortex multiplexing system in which a large number of optical vortex signals are spatially synthesized by arranging a plurality of waveguide type optical vortex generators according to any one of claims 1 to 5.