CN105572921B

CN105572921B - Magnetic control alternative right-angle output light path switch based on photonic crystal T-shaped waveguide

Info

Publication number: CN105572921B
Application number: CN201610086377.2A
Authority: CN
Inventors: 欧阳征标; 吴昌义; 金鑫
Original assignee: Shenzhen University
Current assignee: Shenzhen University
Priority date: 2016-02-15
Filing date: 2016-02-15
Publication date: 2021-02-19
Anticipated expiration: 2036-02-15
Also published as: WO2017152653A1; CN105572921A

Abstract

The invention discloses a magnetic control alternative right-angle output light path switch based on a photonic crystal T-shaped waveguide, which comprises a photonic crystal T-shaped waveguide with a TE forbidden band; the light path switch also comprises an input end (1), two output ends (2, 3), a background silicon medium column (4), an isosceles right triangle defect medium column (5) and a defect medium column (6), and also comprises an electromagnet (7) for providing a bias magnetic field; the left end of the photonic crystal T-shaped waveguide is an input end (1), and output ends (2 and 3) are respectively positioned at the right end and the upper end of the photonic crystal T-shaped waveguide; the photonic crystal waveguide inputs TE light from a port (1), and an output signal is output from a port (2) or a port (3). The invention has small structure volume, convenient integration and high efficiency, and can realize the switching function of the magnetic control alternative optical path of the TE carrier optical signal.

Description

Magnetic control alternative right-angle output light path switch based on photonic crystal T-shaped waveguide

Technical Field

The invention relates to a magnetic control alternative light path gating switch, in particular to a magnetic control alternative right-angle output light path gating switch based on a photonic crystal technology.

Background

The traditional magnetic control alternative optical path gating switch applies a geometric optics principle, so that the size is large, and the traditional magnetic control alternative optical path gating switch cannot be used for optical path integration. The combination of magneto-optical materials and novel photonic crystals has led to the proposal of many photonic devices, the most important property of which is the gyromagnetic non-reciprocity of electromagnetic waves under a bias magnetic field, so that the magnetic photonic crystals not only have optical rotation characteristics, but also have larger transmission bandwidth and higher propagation efficiency. Photonic crystal based devices, such as magnetically controlled optical path gated switches, have photonic crystal waveguides constructed by introducing line defects. The optical switch is the most basic component of optical communication and optical computation, has wide application value, and the compact optical switch is the basic unit of an integrated optical circuit chip.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide a photonic crystal magnetic control alternative optical path gating switch which is small in structure volume, high in efficiency, short in distance and convenient to integrate.

The purpose of the invention is realized by the following technical scheme.

The invention relates to a magnetic control alternative right-angle output light path switch based on a photonic crystal T-shaped waveguide, which comprises a photonic crystal T-shaped waveguide with a TE forbidden band; the light path switch also comprises an input end 1, two

output ends

2 and 3, a background silicon medium column 4, an isosceles right triangle defect medium column 5 and a defect medium column 6, and the light path switch also comprises an electromagnet (7) for providing a bias magnetic field; the left end of the photonic crystal T-shaped waveguide is an input end 1, and the two

output ends

2 and 3 are respectively positioned at the upper end and the lower end of the photonic crystal T-shaped waveguide; the defective dielectric column 6 is positioned at the central intersection of the T-shaped waveguide; the 4 isosceles right triangle defect medium columns 5 are respectively positioned at four crossed corners of the T-shaped waveguide; the photonic crystal waveguide inputs TE light from a port 1, and an output signal is output from a port 2 or a port 3.

The light path switch further comprises an electromagnet coil 7, a lead 8, a polarity-controllable current source 9 and an electronic switch 10; the other end of the electromagnet (7) is connected with the other end of the polarity-controllable current source (9) through a lead (8); the polarity-controllable current source (9) is connected with an electronic switch (10).

The photonic crystal is a two-dimensional tetragonal lattice photonic crystal.

The photonic crystal is composed of a high-refractive-index dielectric material and a low-refractive-index material; the high-refractive-index medium material is silicon or a medium with a refractive index larger than 2; the low-refractive-index medium is air or a medium with a refractive index smaller than 1.4.

The T-shaped waveguide is a structure formed by removing a middle transverse row and a middle vertical row of dielectric columns from the photonic crystal.

And four background medium columns 4 at the crossed corners of the T-shaped waveguide are respectively deleted with one corner to form isosceles right-angle triangular defect medium columns, and the isosceles right-angle triangular defect medium columns 5 are triangular columns.

The background silicon medium column 4 is square.

The square silicon medium column rotates anticlockwise by 41 degrees along the z axis of the axial direction of the medium column.

The defect medium column 6 is a ferrite square column with a square shape, the magnetic conductivity of the ferrite square column is anisotropic and is controlled by a bias magnetic field, and the direction of the bias magnetic field is along the axial direction of the ferrite square column.

The port 2 is arranged at right angles to the port 3.

Compared with the prior art, the invention has the following advantages:

(1) the structure volume is small, the switching time response is fast, the optical transmission efficiency is high, and the large-scale optical path integration is suitable;

(2) the magnetic control alternative optical path switch of the TE optical signal can be realized in a short-range and high-efficiency manner, so that the integration is convenient, and the practical value is great;

(3) by applying the property that the photonic crystal can be scaled in equal proportion and changing the lattice constant in equal proportion, the function of the magnetic control alternative optical path gating switch with different wavelengths can be realized;

(4) the high-contrast high-isolation high-speed pulse laser has high contrast and high isolation, simultaneously has a wider working wavelength range, can allow pulses with certain spectral width, or Gaussian light, or light with different wavelengths to work, or light with multiple wavelengths to work simultaneously, and has practical significance.

Drawings

Fig. 1 is a schematic structural diagram of a magnetic control alternative right-angle output optical path switch based on a photonic crystal T-shaped waveguide.

In the figure, an input end 1, an output end 2, an output end 3, a background silicon medium column 4, a defect medium column 5, a defect medium column 6, a defect medium column, a defect

Fig. 2 is another structural schematic diagram of the magnetic control alternative right-angle output optical path switch based on the photonic crystal T-shaped waveguide.

In the figure, the electromagnet 7 has a wire 8 with controllable polarity, a current source 9 and an electronic switch 10

FIG. 3 is a parameter distribution diagram of a magnetic control alternative right-angle output optical path switch structure based on a photonic crystal T-shaped waveguide.

FIG. 4 is a waveform diagram of the magnetic control alternative right-angle output optical path switch based on the photonic crystal T-shaped waveguide.

Fig. 5(a) is a switch contrast diagram of the forbidden band frequency of the magnetron alternative right-angle output optical path switch of the photonic crystal T-shaped waveguide in example 1.

Fig. 5(b) is a diagram of the frequency isolation of the forbidden band of the switch of the magnetically controlled alternative right-angle output optical path of the photonic crystal T-shaped waveguide in embodiment 1.

Fig. 6(a) is a switch contrast diagram of the forbidden band frequency of the magnetron alternative right-angle output optical path switch of the photonic crystal T-shaped waveguide in example 2.

Fig. 6(b) is an isolation diagram of the forbidden band frequency of the switch of the magnetron alternative right-angle output optical path of the photonic crystal T-shaped waveguide in embodiment 2.

Fig. 7(a) is a switch contrast diagram of the forbidden band frequency of the magnetron alternative right-angle output optical path switch of the photonic crystal T-shaped waveguide in example 3.

Fig. 7(b) is an isolation diagram of the forbidden band frequency of the switch of the magnetron alternative right-angle output optical path of the photonic crystal T-shaped waveguide in embodiment 3.

Fig. 8 is a schematic diagram of the optical field distribution of the magnetic control alternative right-angle output optical path switch based on the photonic crystal T-shaped waveguide.

Detailed Description

As shown in fig. 1, the structure schematic diagram of the magnetic control alternative right-angle output optical path switch based on the photonic crystal T-shaped waveguide (with the offset circuit and the offset coil removed) of the present invention includes a photonic crystal T-shaped waveguide with a TE forbidden band, and the optical path switch further includes an input terminal 1, two

output terminals

2 and 3, a background silicon dielectric pillar 4, an isosceles right-angled triangle defect dielectric pillar 5, and a defect dielectric pillar 6; the device has the advantages that initial signal light enters from a left port 1, a port 2 outputs light waves, and a port 3 isolates the light waves; the left end of the photonic crystal T-shaped waveguide is an input end, the port 2 and the port 3 are respectively positioned at the right end and the upper end of the photonic crystal T-shaped waveguide, the port 2 and the port 3 are in a right-angle layout, TE light is input into the photonic crystal waveguide through the port 1, an output signal is output from the port 2 or the port 3, namely the port 1 is selectively connected with the

ports

2 and 3. The shape of the background silicon medium column 4 is square, the direction of the optical axis is vertical to the paper surface and is outward, the isosceles right triangle defect medium column 5 is, four background medium columns 4 at the crossed corners of the T-shaped waveguide delete one corner respectively to form the isosceles right triangle defect medium column, the isosceles right triangle defect medium column is of a triangular column shape, 4 isosceles right triangle defect medium columns 5 are respectively positioned at the four crossed corners of the T-shaped waveguide, and the direction of the optical axis is the same as that of the background medium column; the defect medium column 6 is positioned at the central intersection of the T-shaped waveguide, the defect medium column 6 is a ferrite square column, the shape of the ferrite square column is square, the direction of an optical axis is perpendicular to the paper surface and faces outwards, the magnetic permeability of the ferrite square column is anisotropic and is controlled by a bias magnetic field, and the direction of the bias magnetic field is along the axial direction of the ferrite square column. As shown in fig. 2, the structure of the magnetic control alternative right-angle output optical path switch based on the photonic crystal T-type waveguide of the present invention (including a bias circuit and a bias coil) includes an electromagnet 7 (electromagnet coil) for providing a bias magnetic field, the other end of the electromagnet 7 is connected to the other end of the polarity-controllable current source 9, and the optical path switch further includes a wire 8, the polarity-controllable current source 9, and an electronic switch 10; one end of the electromagnet 7 is connected with one end of a polarity-controllable current source 9 through a lead 8; the polarity-controllable current source 9 is connected to an electronic switch 10. A structural schematic diagram of the optical path switch adopts a Cartesian rectangular coordinate system: the positive direction of the x axis is horizontal to the right; the positive direction of the y axis is vertically upward in the paper surface; the positive z-axis direction is out of the plane of the paper.

As shown in fig. 3, the relevant parameters of the device are:

d₁either a (lattice constant)

d₂0.3a (side length of square silicon column)

d₃0.2817a (side length of square defect column)

d₄0.3a (isosceles right triangle defect column waist length)

d₅1.2997a (distance from the hypotenuse of the defect post to the center of the defect post)

d₆1.577a (waveguide width and length)

The photonic crystal is a tetragonal lattice, the lattice constant is a, the side length of a dielectric column is 0.3a, when the square silicon dielectric column of the photonic crystal rotates anticlockwise by 41 degrees in the axis direction (z axis) of the reference dielectric column, a plane wave expansion method is adopted to obtain a TE forbidden band structure in the photonic crystal, the TE forbidden band of the photonic crystal is 0.3150-0.4548 (omega a/2 pi c), light waves of any frequency in the middle of the photonic crystal are limited in a waveguide, and after the square lattice dielectric column rotates anticlockwise by 41 degrees in the axis direction (z axis), a wider forbidden band range is obtained.

The silicon dielectric waveguide used in the invention needs to delete one row and one column of dielectric columns to form the guided wave waveguide. The waveguide plane is perpendicular to the axis of the dielectric pillar in the photonic crystal. By introducing a ferrite square column (square defect column 6) at the central intersection of the photonic crystal T-shaped waveguide, the side length is 0.28a, and the distance from the hypotenuse surface of the 4 isosceles right triangle defect dielectric columns 5 to the axis of the ferrite column (square defect dielectric column 6) is 1.2997 a. The optical axis of the ferrite square column is consistent with the optical axis direction of the background medium column.

The description of the principles of the present invention is explained primarily in relation to magneto-optical media. Ferrite is a material with magnetic anisotropy, and the magnetic anisotropy of ferrite is induced by an external DC bias magnetic field. The magnetic field causes the magnetic dipoles in the ferrite to align in the same direction, thereby creating a resultant magnetic dipole moment and causing the magnetic dipoles to precess at a frequency controlled by the strength of the biasing magnetic field. The interaction with an external microwave signal can be controlled by adjusting the intensity of the bias magnetic field, so that the magnetic control alternative right-angle output light path gating switch of the photonic crystal T-shaped waveguide is realized. Under the action of a bias magnetic field, the permeability tensor of the ferrite shows asymmetry, wherein the permeability [ mu ] of the ferrite tensor is as follows:

(offset) (1)

The element of the permeability tensor is given by the following equation:

ω₀＝μ₀γH₀ (2)

ω_m＝μ₀γM_s (3)

ω＝2πf (4)

wherein, mu₀Is magnetic permeability in vacuum, gamma is gyromagnetic ratio, H₀For application of a magnetic field, M_SFor saturation magnetization, for the operating frequency, p ═ k/μ is the normalized magnetization frequency, also called the separation factor, the parameters μ and k determine the different ferrite materials, a material with a permeability tensor of this type is called gyromagnetic, and H is then assumed to be opposite in direction of bias₀And M_SThe sign will change so the direction of rotation will be opposite.

The bias magnetic field is generated by a bias electromagnet, a bias current is loaded in the bias electromagnet, the bias current is a control signal, the bias current is a positive (negative) value, one optical path is in gating (closing), and the other optical path is in gating (closing).

Determining coincidence H-H by adjusting magnitude of bias magnetic field H₀When light is output from port 3, H ═ H₀At this time, light is output from port 2. Thereby realizing the magnetic control alternative light path gating switch.

The magnetic control alternative optical path gating switch is generally realized by the following method: under a bias magnetic field, photon forbidden band and photon local characteristic of the photonic crystal are combined with gyromagnetic characteristic of a magneto-optical medium, light is rotated by a required angle by utilizing Faraday rotation effect and is output by any one of two ports, namely, the port 1 is selectively connected with the

ports

2 and 3, so that the intensity of the light output by the ports can be changed, and the effect of optical switching is realized.

Calculated by numerical scanning, d₂＝0.3a，d₃＝0.2817a，d₅1.2997a, 0.4121 normalized optical wave frequency f, and dielectric constant epsilon_rThe optical signal outputs a maximum value from port 3 and a minimum value from port 2, 12.9. When the direction of the bias magnetic field changes, H₀And M_SSuch that the annular direction of the optical signal should be changed. Therefore, the optical signal is output at a maximum from port 2 and at a minimum from port 3.

After the defect is introduced into the silicon dielectric pillar array waveguide, the incident signal port is located at the position of the left port 1 shown in fig. 1, and the TE optical signal is located at the port 1. The optical signal is transmitted in the waveguide formed by the dielectric column array of the silicon dielectric column 4, after the TE optical signal reaches the defect position of the defect dielectric column 6, the TE optical signal passes through all the optical signals, and finally the TE optical signal is output at the position of the output port 2; the TE optical signal is hardly outputted at the output port 3 position. At the same time, insertion loss in the waveguide is small. At this time, port 2 is in the on state and port 3 is in the off state. When the direction of the bias magnetic field changes, the incident signal port is located at the position of the left port 1 shown in fig. 1, and the TE optical signal is located at the port 1. The optical signal is transmitted in the waveguide formed by the dielectric column array of the silicon dielectric column 4, after the TE optical signal reaches the defect position of the defect dielectric column 6, the TE optical signal passes through all the optical signals, and finally the TE optical signal is output at the position of the output port 3; the TE optical signal is hardly outputted at the output port 2 position. At the same time, insertion loss in the waveguide is small. At this time, port 3 is in the on state and port 2 is in the off state.

The choice of lattice constant and operating wavelength can be determined in the following manner. By the formula

In which the normalized forbidden band frequency range of the tetragonal silicon structure of the present invention is

f_norm＝0.3150～0.4548 (8)

The corresponding forbidden band wavelength range is calculated as:

λ＝2.1987a～3.1746a (9)

it follows that a value of λ satisfying a wavelength range in equal proportion thereto can be obtained by changing the value of the lattice constant a without considering the dispersion or the change of the material dispersion to be small. The operating wavelength can be tuned by the dielectric column-to-column lattice constant without regard to dispersion or with negligible dispersion.

As shown in FIG. 4, by controlling the voltage, an optical power output waveform is obtained, where 0 to t₁The time interval magnetic field is-H and is output from the port 2; t is t>t₁Time-interval magnetic fieldIs H, output from port 3. Switch rise time T_rAnd a fall time T_fDepending on the speed of change of the magnetic field.

Optical switching parameters:

(1) switch rise time, fall time (the rise time and fall time of the switch of this configuration are determined by the rate of change of the magnetic field, so that a fast switching process can be achieved, typically only 1us of switching time.) referring to fig. 4.

(2) The on-off contrast is defined as:

for port 2 conduction: 10log (output power of port 2 when on/output power of port 2 when off) is 10log (P)_{Opening device}/P_{Closing device})

For port 3 conduction: 10log (output power of port 3 when on/output power of port 3 when off) is 10log (P)_{Opening device}/P_{Closing device}) Refer to fig. 5 (a).

(3) The isolation is defined as: the isolation degree is 10log (input power/output power of isolation terminal) is 10log (P)_Into/P_Partition) Refer to fig. 5 (b).

Example 1

In this embodiment, under the condition that the dispersion or material dispersion change is not considered to be small, the function of the magnetically controlled alternative optical path gating switch with different wavelengths can be realized by a method of changing the lattice constant in an equal proportion. Let parameter a be 6.1772 × 10^-3[m]，d₂＝0.3a，d₃＝0.2817a，d₅1.2997a, 9.6125, p 0.7792, 0.4121, and other parameters are not changed, so that the normalized optical wave frequency ω a/2 pi c corresponds to an optical wave of 20 GHz. The switching contrast in the forbidden band optical wave frequency range is obtained through simulation calculation, and as can be seen from fig. 5(a), the switching contrast can reach 48dB when the normalized optical wave frequency ω a/2 π c is 0.4121. In the isolation diagram of the switch in the forbidden band light wave frequency range, as can be seen from fig. 5(b), the isolation of the

ports

2 and 3 can reach 48dB, and the performance of the switch has obvious advantages compared with other optical switches. The structure has a magnetic control alternative optical path gating switch with high contrast and high isolation, thereby realizing the optical switch function.

Example 2

In this embodiment, under the condition that the dispersion or material dispersion change is not considered to be small, the function of the magnetically controlled alternative optical path gating switch with different wavelengths can be realized by a method of changing the lattice constant in an equal proportion. Let parameter a be 4.1181 × 10^-3[m]，d₂＝0.3a，d₃＝0.2817a，d₅1.2997a, μ 9.6125, p 0.7792, 0.4121, and other parameters are not changed, so that the normalized optical wave frequency ω a/2 pi c corresponds to an optical wave of 30 GHz. The switch contrast in the forbidden band light wave frequency range is obtained through simulation calculation, referring to fig. 6(a), the switch isolation diagram in the forbidden band light wave frequency range, referring to fig. 6(b), the structure has a magnetic control alternative light path gating switch with high contrast and high isolation, and therefore the optical switch function is achieved.

Example 3

In this embodiment, under the condition that the dispersion or material dispersion change is not considered to be small, the function of the magnetically controlled alternative optical path gating switch with different wavelengths can be realized by a method of changing the lattice constant in an equal proportion. Let parameter a be 3.0886 × 10^-3[m]，d₂＝0.3a，d₃＝0.2817a，d₅1.2997a, μ 9.6125, p 0.7792, 0.4121, and other parameters are not changed, so that the normalized optical wave frequency ω a/2 pi c corresponds to an optical wave of 40 GHz. As can be seen from fig. 7(a) and 7(b), when the normalized optical wave frequency ω a/2 π c is 0.4121, the optical field simulation diagram obtained by calculating with finite element software COMSOL is shown in fig. 8. It is thus observed that TE light propagates efficiently to port 2 and port 3, respectively. The structure has a magnetic control alternative optical path gating switch with high contrast and high isolation, thereby realizing the optical switch function.

The invention described above is subject to modifications both in the specific embodiments and in the field of application and should not be understood as being limited thereto.

Claims

1. A magnetic control alternative right-angle output light path switch based on photonic crystal T-shaped waveguide is characterized in that: the photonic crystal T-shaped waveguide with a TE forbidden band comprises a TE carrier optical signal input end, two output ends, at least one background silicon dielectric column, at least one first defect dielectric column and a second defect dielectric column; the light path switch also comprises an electromagnet and a polarity-controllable current source; the left end of the photonic crystal T-shaped waveguide is a TE carrier optical signal input end, the right end of the photonic crystal T-shaped waveguide is a first output end, the upper end of the photonic crystal T-shaped waveguide is a second output end, and a second defect medium column is arranged at the central intersection; four first defect medium columns are arranged at four crossed corners of the photonic crystal T-shaped waveguide; the electromagnet and the polarity-controllable current source generate a bias magnetic field, and TE carrier optical signals at the TE carrier optical signal input end are transmitted to the first output end or the second output end by setting the direction of the bias magnetic field.

2. The magnetically controlled alternative right-angle output optical path switch based on a photonic crystal T-type waveguide according to claim 1, wherein: the optical circuit switch further comprises a wire.

3. The magnetically controlled alternative right-angle output optical path switch based on a photonic crystal T-type waveguide of claim 2, wherein: one end of the electromagnet is connected with one end of the polarity-controllable current source through the lead, and the other end of the electromagnet is connected with the other end of the polarity-controllable current source.

4. The magnetically controlled alternative right-angle output optical path switch based on a photonic crystal T-type waveguide according to claim 1, wherein: the light path switch further comprises an electronic switch; the electronic switch is connected with the polarity-controllable current source.

5. The magnetically controlled alternative right-angle output optical path switch based on a photonic crystal T-type waveguide according to claim 1, wherein: the photonic crystal T-shaped waveguide is a structure formed by removing a middle transverse row and a middle vertical row of dielectric columns from a photonic crystal.

6. The magnetically controlled alternative right-angle output optical path switch based on a photonic crystal T-type waveguide according to claim 1, wherein: the second defect medium column is a ferrite square column, and the shape of the second defect medium column is square.

7. The magnetically controlled alternative right-angle output optical path switch based on a photonic crystal T-type waveguide of claim 6, wherein: the permeability of the ferrite square columns is anisotropic and is controlled by a bias magnetic field, the direction of which is along the direction of the axis of the ferrite square columns.

8. The magnetically controlled alternative right-angle output optical path switch based on a photonic crystal T-type waveguide according to claim 1, wherein: and deleting one corner of the four background silicon medium columns at the crossed corners of the photonic crystal T-shaped waveguide to form isosceles right triangle defect medium columns.

9. The magnetically controlled alternative right-angle output optical path switch based on a photonic crystal T-type waveguide according to claim 1, wherein: the isosceles right triangle defect dielectric column is silicon.

10. The magnetically controlled alternative right-angle output optical path switch based on a photonic crystal T-type waveguide according to claim 1, wherein: the isosceles right triangle defect medium column is a triangular column type.

11. The magnetically controlled alternative right-angle output optical path switch based on a photonic crystal T-type waveguide according to claim 1, wherein: the background silicon medium column is square.

12. The magnetically controlled alternative right-angle output optical path switch based on a photonic crystal T-type waveguide according to claim 1, wherein: the background silicon medium column rotates anticlockwise by 41 degrees along the Z-axis direction of the medium column axis.