CN105572919B

CN105572919B - Magneto-optical modulator based on photonic crystal cross waveguide

Info

Publication number: CN105572919B
Application number: CN201610085962.0A
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: WO2017140142A1; CN105572919A

Abstract

The invention discloses a magneto-optical modulator based on a photonic crystal cross waveguide, which comprises a photonic crystal cross waveguide with a TE forbidden band; the modulator also comprises an input end (1), three output ends (2, 3 and 4), a background silicon medium column (5), an isosceles right triangle defect medium column (6) and a defect medium column (7), and also comprises an electromagnet (8) for providing a bias magnetic field, a modulation current source (10) and a modulation signal (11); the left end of the photonic crystal cross waveguide is an input end (1), and output ends (2, 3 and 4) are respectively positioned at the lower end, the right end and the upper end of the cross waveguide; the defective medium column (7) is positioned at the central intersection of the cross waveguide; 4 isosceles right triangle defect medium columns (6) are respectively positioned at four crossed corners of the cross waveguide; TE carrier light is input into the photonic crystal waveguide through a port (1), and amplitude-modulated light is output from any port of ports (2), (3) and (4). The invention realizes the TE carrier wave light wave signal modulator with high efficiency.

Description

Magneto-optical modulator based on photonic crystal cross waveguide

Technical Field

The invention relates to a modulator, in particular to a magneto-optical modulator based on photonic crystal cross waveguide.

Background

The conventional optical modulator generally utilizes the electro-optic effect of a crystal to modulate light, and needs a microwave modulation signal, an electro-optic crystal and an interference structure, such as a mach-zehnder interference structure. Because of the limitation of the electro-optic coefficient of the electro-optic crystal, the electro-optic crystal with longer geometric dimension needs to be adopted, so that the optical modulator has larger volume, can only be used in the traditional optical device and cannot be integrated into an optical chip. Optical modulators are key devices used to control light intensity during light emission, transmission, and reception of the overall optical communication, and are also one of the most important integrated optical devices.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a magneto-optical modulator of photonic crystal cross waveguide, which has small structure volume, high efficiency and short distance and is convenient to integrate.

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

The invention relates to a magneto-optical modulator based on a photonic crystal cross waveguide, which comprises a photonic crystal cross waveguide with a TE forbidden band; the modulator also comprises an input end 1, three

output ends

2, 3 and 4, a background silicon medium column 5, an isosceles right triangle defect medium column 6 and a defect medium column 7, and also comprises an electromagnet 8 for providing a bias magnetic field, a modulation current source 10 and a modulation signal 11; the left end of the photonic crystal T-shaped waveguide is an input end 1; the

output ends

2, 3 and 4 are respectively positioned at the lower end, the right end and the upper end of the photonic crystal cross waveguide; the defect medium column 7 is positioned at the central intersection of the cross waveguide; the 4 isosceles right-angled triangular defect medium columns 6 are respectively positioned at four crossed corners of the cross waveguide; TE carrier light is input into the photonic crystal waveguide through a port 1, and amplitude-modulated light is output from any port of

ports

2, 3 and 4.

The modulator further includes a conductor 911; one end of the electromagnet 8 is connected with the negative electrode of the modulation current source 10; the other end of the electromagnet 8 is connected with the anode of a modulation current source 10 through a lead 9, and the modulation current source 10 is connected with a modulation signal 11.

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

The photonic crystal is composed of a high-refractive-index material and a low-refractive-index material, and the high-refractive-index 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 cross waveguide is a structure formed by removing a middle transverse row and a middle vertical row of dielectric columns from the photonic crystal.

The background medium columns 5 at the cross corners of the cross waveguide are respectively deleted with one corner to form isosceles right triangle defect medium columns, and the isosceles right triangle defect medium columns 6 are triangular columns.

The background silicon dielectric column 5 is square.

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

The defect medium column 7 is a ferrite square column, the shape of the defect medium column is square, 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 4 is a modulation output terminal.

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

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

(2) the integration is convenient and efficient, the TE carrier wave light wave signal modulator can be realized in a short distance, and the TE carrier wave light wave signal modulator has great practical value;

(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 magneto-optical modulator of the photonic crystal cross waveguide 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 wide 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 diagram of a structure of a magneto-optical modulator based on a photonic crystal cross waveguide according to the present invention.

In the figure: input end 1, output end 2, output end 3, output end 4, background silicon medium column 5, isosceles right triangle defect medium column 6, defect medium column 7

Fig. 2 is another structural diagram of the magneto-optical modulator based on photonic crystal cross waveguide according to the present invention.

In the figure: electromagnet 8, wire 9, current source 10, modulation signal 11

Fig. 3 is a structural parameter distribution diagram of a magneto-optical modulator based on a photonic crystal cross waveguide.

Fig. 4 is a sine waveform diagram of the bias magnetic field of the magneto-optical modulator based on the photonic crystal cross waveguide.

FIG. 5 is a graph of the relationship between the values of permeability μ, k for a magneto-optical modulator based on photonic crystal cross waveguide varying with a bias magnetic field in a period according to the present invention.

Fig. 6 is a modulation curve diagram of a magneto-optical modulator based on a photonic crystal cross waveguide.

Fig. 7(a) is a modulation graph of the magneto-optical modulator of the photonic crystal cross waveguide in embodiment 1.

Fig. 7(b) is a modulation sensitivity chart of the magneto-optical modulator of the photonic crystal cross waveguide in embodiment 1.

Fig. 8(a) is a modulation graph of the magneto-optical modulator of the photonic crystal cross waveguide in embodiment 2.

Fig. 8(b) is a modulation sensitivity chart of the magneto-optical modulator of the photonic crystal cross waveguide in embodiment 2.

Fig. 9(a) is a modulation graph of the magneto-optical modulator of the photonic crystal cross waveguide in embodiment 3.

Fig. 9(b) is a modulation sensitivity chart of the magneto-optical modulator of the photonic crystal cross waveguide in embodiment 3.

Fig. 10 is a schematic diagram of the optical field distribution of the magneto-optical modulator of the photonic crystal cross waveguide of the present invention.

Detailed Description

As shown in fig. 1, the magneto-optical modulator based on photonic crystal cross waveguide according to the present invention has a schematic structural diagram (with a bias circuit and a bias coil removed), and includes a photonic crystal cross waveguide with a TE forbidden band, an input terminal 1, three

output terminals

2, 3, 4, a background silicon dielectric pillar 5, an isosceles right triangle defect dielectric pillar 6, and a defect dielectric pillar 7; in the device, the left end of the photonic crystal cross waveguide is an input end 1, and

output ends

2, 3 and 4 are respectively positioned at the lower end, the right end and the upper end of the photonic crystal cross waveguide; TE carrier light is input into the photonic crystal waveguide from a port 1, and amplitude-modulated light is output from any port of

ports

2, 3 and 4; the shape of a background silicon medium column 5 is square, the direction of an optical axis is vertical to the paper surface and faces outwards, an isosceles right triangle defect medium column 6 is formed, one corner of the background medium column 5 at the crossed corner of the cross waveguide is deleted to form the isosceles right triangle defect medium column, the isosceles right triangle defect medium column 6 is in a triangular column shape, 4 isosceles right triangle defect medium columns 6 are respectively positioned at four crossed corners of the cross waveguide, the direction of the optical axis is the same as that of the background medium column, a defect medium column 7 is positioned at the central crossed part of the cross waveguide, the defect medium column 7 is a ferrite square column and is square, and the direction of the optical axis is vertical to the paper surface and faces outwards; the ferrite square column has anisotropic magnetic permeability 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 magneto-optical modulator based on photonic crystal cross waveguide according to the present invention (including a bias circuit and a bias coil) comprises an electromagnet 8 for providing a bias magnetic field, a modulation current source 10 and a modulation signal 11, and the modulator further comprises a wire 9; one end of the electromagnet 8 is connected with the negative electrode of the modulation current source 10, and the other end of the electromagnet 8 is connected with the positive electrode of the modulation current source 10 through a lead 9; the modulation current source 10 is connected to a modulation signal 11. The modulator of the present invention employs a cartesian rectangular coordinate system as shown in fig. 1 and 3: the positive direction of the x axis is horizontal to the right; the positive direction of the y axis is vertical and upward; 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)

d₃0.2217a (Square defect medium column side length)

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) of the reference dielectric column, a wider forbidden band range is obtained.

The silicon dielectric waveguide used in the present invention requires the deletion of one row and one column of dielectric pillars to form a cross waveguide. The waveguide plane is perpendicular to the axis of the dielectric pillar in the photonic crystal. By introducing a ferrite square column (a square defective dielectric column 7) at the intersection of the centers of the cross waveguides, the side length of the ferrite square column is 0.2217a, and the distance from the hypotenuse surface of 4 isosceles right triangle defective dielectric columns 6 to the axis of the ferrite square column (the square defective dielectric column 7) 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 magneto-optical modulator of the photonic crystal cross 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 elements of the permeability tensor are 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 the saturation magnetization, for the operating frequency,p-k/μ is the normalized magnetization frequency, also called the separation factor, the parameters μ and k determining the different ferrite materials, a material with this form of permeability tensor is called gyromagnetic, H assuming the direction of bias is opposite₀And M_SThe sign will change so the direction of rotation will be opposite.

The bias magnetic field is generated by a bias electromagnet, and bias current is loaded in the bias electromagnet and is a modulation signal.

The magnitude of the bias magnetic field H is adjusted by the change of an external magnetic field according to sine wave shape, so that the magnetic conductivity is changed, the intensity of light output by the

ports

2, 3 and 4 is changed, and the modulation of optical signals is realized.

Setting bias magnetic field H ═ H₀+H₁sin (nt), t epsilon (0,2 pi/n), and the value of n can be determined according to requirements. H varies according to a sinusoidal waveform law as shown in fig. 4. The sine waveform is equally divided into 20 segments in one period (called as a modulation period) and totally divided into 21 points, for the magnetic field value of each point, the magnetic permeability value is calculated, as shown in fig. 5, and the optical wave electric field amplitude of the

channels

2, 3 and 4 is calculated, as shown in fig. 6.

Let parameter d₃＝0.2217a，d₅＝1.2997a，Ms＝2.39×10⁵[A/m]. When the normalized optical wave frequency ω a/2 π c is 0.4121, referring to FIG. 6, a modulation graph, which is a modulation graph of the optical wave electric field amplitude varying with the modulation magnetic field in one period, of the

channels

2, 3, and 4, is obtained through simulation calculation, as shown in FIG. 7 (a). From the modulation curve, the modulation sensitivity, which is the derivative of the amplitude of the optical wave electric field in the channel to the amplitude of the modulation magnetic field, i.e. the slope of the modulation curve, can be found, see fig. 7 (b).

When the defects are introduced into the silicon dielectric column array waveguide, H is the magnetic field H₀+H₁At the time, the incident signal port is located at the position of the left port 1 shown in fig. 1, and the TE carrier optical signal is located at the port 1. Carrier optical signals are propagated in the waveguide formed by the dielectric column array of the silicon dielectric column 5, TE carrier optical signals completely pass through after reaching the defect position of the defect dielectric column 7, and finally the TE carrier optical signals are transmittedThe output port 4 is positioned to output, and the TE carrier optical signal is hardly output at the output positions of the

ports

2 and 3. In a magnetic field H ═ H₀-H₁At the time, the incident signal port is located at the position of the left port 1 shown in fig. 1, and the TE carrier optical signal is located at the port 1. Carrier optical signals are propagated in a waveguide formed by a dielectric column array of the silicon dielectric column 5, TE carrier optical signals all pass through after reaching the defect position of the defect dielectric column 7, and finally the TE carrier optical signals are output at the

output ports

2 and 3, and almost no TE carrier optical signals are output at the output port 4.

Therefore, the port 4 is used as a modulation output port, and the amplitude of the optical wave electric field of the port 4 channel under 21H values is plotted, i.e., a curve that the amplitude of the electric field passing through the optical wave changes with the modulation magnetic field is a modulation curve, which is shown in fig. 8 (a). The modulation sensitivity can be obtained from the modulation curve, and see fig. 8 (b). The modulation depth can also be determined from the modulation curve, where 2 (maximum electric field amplitude-minimum electric field amplitude)/(maximum electric field amplitude + minimum electric field amplitude)

As can be seen from fig. 8(b), the modulation sensitivity was 0.00181.

As can be seen from fig. 8(a), the modulation depth is 0.39356.

As can be seen from fig. 8(a), if a sinusoidal bias magnetic field is input to the modulation curve, the amplitude of the electric field at the port 4 changes approximately sinusoidally around the static operating point in the linear range, which indicates that the present study has a more ideal modulation effect.

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

Normalized forbidden band frequency range of tetragonal silicon structure therein and in the present invention

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.

Example 1

In the embodiment, under the condition of not considering dispersion or little change of material dispersion, the function of the magneto-optical modulator of the photonic crystal cross waveguide 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＝0.2217a，d₅＝1.2997a，Ms＝2.39×10⁵[A/m]，H₀＝4.79925×10⁵[A/m]，H₁＝225[A/m]. The normalized optical wave frequency ω a/2 pi c is 0.4121, and other parameters are not changed, so that the normalized optical wave frequency ω a/2 pi c corresponds to the optical wave carrier of 20 GHz. Referring to fig. 7(a), a modulation curve graph, namely a modulation curve graph, of the port 4 channel, in which the amplitude of the optical wave electric field changes with the modulation magnetic field in one period, is obtained through simulation calculation; referring to fig. 7(b), the slope of the modulation curve in the port 4 channel during one cycle, i.e., the modulation sensitivity map. This structure has a more ideal modulator function.

Example 2

In the embodiment, under the condition of not considering dispersion or little change of material dispersion, the function of the magneto-optical modulator of the photonic crystal cross waveguide 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＝0.2217a，d₅＝1.2997a，Ms＝2.39×10⁵[A/m]，H₀＝7.5696×10⁵[A/m]，H₁＝135[A/m]. The normalized optical wave frequency ω a/2 pi c is 0.4121, and other parameters are not changed, so that the normalized optical wave frequency ω a/2 pi c corresponds to the optical wave carrier of 30 GHz. Referring to fig. 8(a), a modulation curve graph, namely a modulation curve graph, of the port 4 channel, in which the amplitude of the optical wave electric field changes with the modulation magnetic field in one period, is obtained through simulation calculation; referring to FIG. 8(b), of the modulation profile in the port 4 channel during one cycleSlope, i.e. modulation sensitivity map. This structure has a more ideal modulator function.

Example 3

In the embodiment, under the condition of not considering dispersion or little change of material dispersion, the function of the magneto-optical modulator of the photonic crystal cross waveguide 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＝0.2217a，d₅＝1.2997a，Ms＝2.39×10⁵[A/m]，H₀＝10.38505×10⁵[A/m]，H₁＝135[A/m]. The normalized optical wave frequency ω a/2 pi c is 0.4121, and other parameters are not changed, so that the normalized optical wave frequency ω a/2 pi c corresponds to the optical wave carrier of 40 GHz. Referring to fig. 9(a), a modulation curve graph, namely a modulation curve graph, of the port 4 channel, in which the amplitude of the optical wave electric field changes with the modulation magnetic field in one period, is obtained through simulation calculation; referring to fig. 9(b), the slope of the modulation curve in the port 4 channel, i.e., the modulation sensitivity map, is measured over one cycle. This structure has a more ideal modulator function.

As can be seen from fig. 10, the finite element software COMSOL is used to perform calculation to obtain the optical field simulation diagram, and as can be seen from fig. 10(a), (b), (c), and (d), the TE carrier light is modulated and propagated to the port 2, the port 3, and the port 4.

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 magneto-optical modulator based on photonic crystal cross waveguide is characterized in that: the photonic crystal cross waveguide with a TE forbidden band comprises a TE carrier light input end, three signal output ends, a first defect medium column, at least one second defect medium column and at least one background silicon medium column; the modulator also comprises an electromagnet, a modulation current source and a modulation signal; the left end of the photonic crystal cross waveguide is a TE carrier wave light input end, the lower end of the photonic crystal cross waveguide is a first signal output end, the right end of the photonic crystal cross waveguide is a second signal output end, the upper end of the photonic crystal cross waveguide is a third signal output end, and a first defect medium column is arranged at the central intersection; second defect medium columns are arranged at four crossed corners of the photonic crystal cross waveguide; the second defect medium column is an isosceles right triangle defect medium column; the electromagnet and the modulation current source generate a bias magnetic field, the electric field amplitude of the light wave at the signal output end changes along with the change of the modulated bias magnetic field in a modulation period, and the TE carrier optical signal at the TE carrier optical input end is transmitted to the first signal output end, the second signal output end and the third signal output end.

2. A photonic crystal cross waveguide based magneto-optical modulator according to claim 1, wherein: the modulator further comprises a wire.

3. A photonic crystal cross waveguide based magneto-optical modulator according to claim 2, wherein: one end of the electromagnet is connected with the negative electrode of the modulation current source, and the other end of the electromagnet is connected with the positive electrode of the modulation current source through the lead.

4. A photonic crystal cross waveguide based magneto-optical modulator according to claim 1, wherein: the modulation current source is connected with the modulation signal.

5. A photonic crystal cross waveguide based magneto-optical modulator according to claim 1, wherein: the photonic crystal cross waveguide is a structure formed by removing a middle transverse row and a middle vertical row of dielectric columns from a photonic crystal.

6. A photonic crystal cross waveguide based magneto-optical modulator according to claim 1, wherein: the first defect medium column is a ferrite square column, and the shape of the first defect medium column is square.

7. A photonic crystal cross waveguide based magneto-optical modulator according to 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. A photonic crystal cross waveguide based magneto-optical modulator according to claim 1, wherein: and deleting one corner of the four background silicon medium columns at the crossed corners of the photonic crystal cross waveguide to form isosceles right triangle defect medium columns.

9. A photonic crystal cross waveguide based magneto-optical modulator according to claim 1, wherein: the isosceles right triangle defect dielectric column is silicon.

10. A photonic crystal cross waveguide based magneto-optical modulator according to claim 1, wherein: the isosceles right triangle defect medium column is a triangular column type.

11. A photonic crystal cross waveguide based magneto-optical modulator according to claim 1, wherein: the background silicon medium column is square.

12. A photonic crystal cross waveguide based magneto-optical modulator 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.

13. A photonic crystal cross waveguide based magneto-optical modulator according to claim 1, wherein: the third signal output end is a modulation output end.