CN105572920B

CN105572920B - Double-path reverse-phase optical clock signal generator based on photonic crystal cross waveguide

Info

Publication number: CN105572920B
Application number: CN201610086342.9A
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: CN105572920A; WO2017140144A1

Abstract

The invention discloses a two-way inverse optical clock signal generator based on a photonic crystal cross waveguide, which comprises a photonic crystal cross waveguide with a TE forbidden band; the generator 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), an electromagnet (8) for providing a bias magnetic field and a rectangular wave current source (10); 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; the defective medium column (7) is positioned at the central intersection of the cross waveguide; TE carrier light is input into the photonic crystal waveguide through a port (1), and two paths of optical clock signals with opposite phases are output from a port (2) and a port (4). The invention has small structure volume and convenient integration, and can realize the TE optical double-path reverse optical clock signal generator with short distance and high efficiency.

Description

Double-path reverse-phase optical clock signal generator based on photonic crystal cross waveguide

Technical Field

The invention relates to a double-path reverse optical clock signal generator, in particular to a photonic crystal cross waveguide double-path reverse optical clock signal generator.

Background

The traditional two-way optical clock signal generator with adjustable duty ratio and mutual logical negation applies a geometrical optics principle, so that the two-way optical clock signal generator is large in size and cannot be used in 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. Tiny devices, including dual-path inverted optical clock generators, can be fabricated based on photonic crystals. The photonic crystal waveguide light path of the dual-path inverted optical clock signal generator is generally constructed by introducing line defects into the photonic crystal. The optical clock is an important component of optical communication, optical logic devices, optical information processing systems and optical computation, has wide application value, and the compact optical clock generator is an important component of an integrated wide-interest chip.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provides a photonic crystal cross waveguide two-way reverse phase optical clock signal generator which is small in structure volume, high in efficiency, short in distance and convenient to integrate.

The object of the invention is achieved by the following technical scheme.

The invention relates to a photonic crystal cross waveguide based two-way reversed-phase optical clock signal generator, which comprises a photonic crystal cross waveguide with a TE forbidden band; the generator 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 and a rectangular wave current source (10); the left end of the photonic crystal cross waveguide is an input end 1, and 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 light is input into the photonic crystal waveguide through a port 1, and two paths of optical clock signals with opposite phases are output from a port 2 and a port 4.

The generator further comprises a wire 9; one end of the electromagnet 8 is connected with one end of a rectangular wave current source 10; the other end of the electromagnet 8 is connected with the other end of a rectangular wave current source 10 through a lead 9, and the direction of a bias magnetic field provided by the electromagnet 8 changes periodically with time.

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; 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 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 one corner of the background medium column 5 at the crossed corner of the T-shaped waveguide is deleted to form an isosceles right triangle defect medium column.

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 isosceles right triangle defect medium column 6 is a triangular column.

The defect medium column 7 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.

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, the TE optical double-path reverse phase optical clock signal generator can be realized in a short-range and high-efficiency manner, and the TE optical double-path reverse phase optical clock signal generator has great practical value;

(3) by applying the property that the photonic crystal can be scaled in equal proportion and the method of changing the lattice constant in equal proportion, the generation of two-way reverse clock signals 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 structural diagram of a photonic crystal cross waveguide two-way inverted optical clock signal generator 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 a schematic diagram of another structure of a photonic crystal cross waveguide two-way inverted optical clock signal generator according to the present invention.

In the figure: electromagnet 8, lead 9 and rectangular wave current source 10

FIG. 3 is a structural parameter distribution diagram of a photonic crystal cross waveguide two-way inverse optical clock signal generator of the present invention.

FIG. 4 is a waveform diagram of an optical clock signal of a photonic crystal cross waveguide two-way inverted optical clock signal generator according to the present invention.

Fig. 5 is a logic contrast diagram of the forbidden band frequencies of the photonic crystal cross waveguide dual-channel inverted optical clock signal generator in embodiment 1.

Fig. 6 is a logic contrast diagram of the forbidden band frequency of the photonic crystal cross waveguide dual-channel inverted optical clock signal generator in embodiment 2.

Fig. 7 is a logic contrast diagram of the forbidden band frequency of the photonic crystal cross waveguide dual-channel inverted optical clock signal generator in embodiment 3.

FIG. 8 is a schematic diagram of the optical field distribution of a photonic crystal cross waveguide two-way inverted optical clock signal generator of the present invention.

Detailed Description

As shown in fig. 1, the structural schematic diagram (deleting bias circuit and bias coil) of the photonic crystal cross waveguide two-way inverse optical clock signal generator of the present invention includes a photonic crystal cross waveguide with TE forbidden band, the generator further includes an input end 1, three

output ends

2, 3, 4, a background silicon dielectric column 5, an isosceles right triangle defect dielectric column 6 and a square defect dielectric column 7; the device has the advantages that initial signal light enters from the left port 1, the port 2 outputs light waves, and the port 3 and the port 4 isolate the light waves; the left end of the photonic crystal cross waveguide is an input end 1,

ports

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 light is input into the photonic crystal waveguide through the port 1, and two paths of optical clock signals with opposite phases are output from the port 2 and the port 4; the shape of the background silicon medium column 5 is square, the direction of an optical axis is vertical to the paper surface and faces outwards, the isosceles right triangle defect medium column 6 is, one corner of the background medium column 5 at the crossed corner of the T-shaped waveguide is deleted to form the isosceles right triangle defect medium column, the isosceles right triangle defect medium column 6 is of a triangular column shape, 4 isosceles right triangle defect medium columns 6 are respectively positioned at four crossed corners of the cross-shaped waveguide, the direction of the optical axis is the same as that of the background medium column, the defect medium column 7 is positioned at the crossed position of the center of the cross-shaped waveguide, the defect medium column 7 is a ferrite square column, the shape of the defect medium column is square, the direction of the optical axis is vertical to the paper surface and faces outwards, the magnetic permeability of the ferrite square column is anisotropic and is controlled by a bias; 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 structural schematic diagram of the bright photonic crystal cross waveguide two-way inverse optical clock signal generator (including the bias circuit and the bias coil) of the present invention includes an electromagnet 8 (electromagnet coil) for providing a bias magnetic field and a rectangular wave current source (10); the generator also comprises a lead 9, one end of the electromagnet 8 is connected with one end of a rectangular wave current source 10, the other end of the electromagnet 8 is connected with the other end of the rectangular wave current source 10 through the lead 9, and the direction of the bias magnetic field provided by the electromagnet 8 changes periodically along with time. The generator of the invention uses a cartesian rectangular coordinate system as shown in fig. 1 and 2: 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 (square silicon column side length)

d₃0.2817a (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), 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 7) at the cross of the cross waveguide, the side length is 0.28a, and the distance from the hypotenuse face of each 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 photonic crystal cross waveguide two-way reverse phase optical clock signal generator 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 relevant parameters in the matrix 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 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, bias current is loaded in the bias electromagnet, the bias current is a modulation signal, and the modulation signal is a time-varying periodic signal.

Determining coincidence H-H by adjusting magnitude of bias magnetic field H₀When light is output from port 4, H ═ H₀At this time, light is output from port 2. Thereby realizing a two-way inverted optical clock signal generator.

A two-way inverted optical clock signal generator is generally implemented by: under the periodically changing bias magnetic field, the Faraday rotation effect is utilized to make the light rotate by the required angle, and the light is alternately output by two ports, namely two paths of optical clock signals with opposite phases are output.

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 output a maximum value from port 2 and a minimum from port 4 is 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 the port 4 and at a minimum from the port 2.

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. Optical signals are transmitted in a waveguide formed by a dielectric column array of the silicon dielectric column 5, TE optical signals completely pass through the waveguide after reaching a defect position in the form of a defect dielectric column 7, and finally the TE optical signals are output at an output port 2; the TE optical signal is hardly outputted at the

output ports

3 and 4. At the same time, insertion loss in the waveguide is small. At this point port 2 is on and

ports

3 and 4 are off. 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. Optical signals are transmitted in a waveguide formed by a dielectric column array of the silicon dielectric column 5, TE optical signals completely pass through the waveguide after reaching a defective position in the form of a defective dielectric column 7, and finally the TE optical signals are output at an output port 4; the TE optical signal is hardly outputted at the

output ports

2 and 3. At the same time, insertion loss in the waveguide is small. At this point port 4 is on and

ports

2 and 3 are off.

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.

By controlling the voltage, an optical power output waveform is obtained, where T is shown in FIG. 4₁The time interval magnetic field is-H and is output from the port 2; t is₂The time interval magnetic field is H, output from port 4. Optical clock signal duty ratio is time when signal is 1/time when signal is 0 is T₁/T₂. Pulse rise time-rectangular pulse edgeThe time required to rise from 0 to 90% of the maximum output power, the pulse rise time of this configuration depends on the rate of change of the magnetic field.

By adjusting the time ratio of the positive value and the negative value of the modulation signal, the duty ratio of the output clock signal can be adjusted, and the duty ratio is equal to the ratio of the time when the modulation signal is positive to the time when the modulation signal is negative.

Optical clock parameters:

(1) the pulse rise time is the time required for the rectangular pulse edge to rise from 0 to 90% of the maximum output power, and the pulse rise time of this configuration depends on the rate of change of the magnetic field.

(2) Clock frequency being the frequency of variation of the magnetic field

(3) The logical 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 4 conduction: 10log (output power of port 4 when on/output power of port 4 when off) is 10log (P)_{Opening device}/P_{Closing device})

The isolation is defined as: the isolation degree is 10log (input power/output power of isolation terminal) is 10log (P)_Into/P_Partition)

As can be seen from fig. 6, the logical contrast ratio can reach 48dB when the normalized optical wave frequency ω a/2 pi c is 0.4121.

Example 1

In this embodiment, the function of the two-way inverse optical clock signal generator with different wavelengths can be realized by changing the lattice constant in an equal proportion without considering the dispersion or the material dispersion change. 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. Referring to fig. 5, the logic contrast in the forbidden band light wave frequency range is obtained by simulation calculation, and the structure has the advantages of high logic contrast, adjustable duty ratio and dual-path optical time of mutual logic negationClock signal generator, thus has realized the function of the two-way reverse phase optical clock signal generator.

Example 2

In this embodiment, the function of the two-way inverse optical clock signal generator with different wavelengths can be realized by changing the lattice constant in an equal proportion without considering the dispersion or the material dispersion change. 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. Referring to fig. 6, the logic contrast in the forbidden band lightwave frequency range is obtained by simulation calculation, and the structure has the functions of a high logic contrast and a two-way reverse optical clock signal generator.

Example 3

In this embodiment, the function of the two-way inverse optical clock signal generator with different wavelengths can be realized by changing the lattice constant in an equal proportion without considering the dispersion or the material dispersion change. 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. Referring to fig. 7, the logic contrast in the forbidden optical wave frequency range is obtained by simulation calculation, and the structure has the functions of a high logic contrast and a two-way reverse optical clock signal generator.

As can be seen from fig. 8, when the normalized optical wave frequency ω a/2 pi c is 0.4121, the finite element software COMSOL is used to perform calculation to obtain the optical field simulation diagram. From this, it can be seen that the TE light efficiently propagates to the port 2 and the port 4, respectively.

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 two-way opposite-phase optical clock signal generator based on photonic crystal cross waveguide is characterized in that: the photonic crystal ten-type waveguide with a TE forbidden band comprises a TE carrier optical signal input end, three signal output ends, a second defect dielectric column, at least one first defect dielectric column and at least one background silicon dielectric column; the generator further comprises an electromagnet and a rectangular wave current source; the left end of the photonic crystal ten-type waveguide is a TE carrier optical signal input end, the lower end of the photonic crystal ten-type waveguide is a first signal output end, the right end of the photonic crystal ten-type waveguide is a second signal output end, the upper end of the photonic crystal ten-type waveguide is a third signal 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 cross waveguide; the electromagnet and the rectangular wave current source generate a bias magnetic field, the direction of the bias magnetic field changes periodically along with time, a TE carrier optical signal at the TE carrier optical signal input end is transmitted to the first signal output end or the third signal output end, and two clock signals with opposite phases are output.

2. A two-way inverse optical clock signal generator based on a photonic crystal cross waveguide as claimed in claim 1, wherein: the generator further comprises a wire.

3. A two-way inverse optical clock signal generator based on a photonic crystal cross waveguide as claimed in claim 2, wherein: one end of the electromagnet is connected with one end of the rectangular wave current source, and the other end of the electromagnet is connected with the other end of the rectangular wave current source through the lead.

4. A two-way inverse optical clock signal generator based on a photonic crystal cross waveguide as claimed in 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.

5. A two-way inverse optical clock signal generator based on a photonic crystal cross waveguide as claimed in claim 1, wherein: the second defect medium column is a ferrite square column, and the shape of the second defect medium column is square.

6. A two-way inverse optical clock signal generator based on a photonic crystal cross waveguide as claimed in claim 5, 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.

7. A two-way inverse optical clock signal generator based on a photonic crystal cross waveguide as claimed in 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.

8. A two-way inverse optical clock signal generator based on a photonic crystal cross waveguide as claimed in claim 1, wherein: the isosceles right triangle defect dielectric column is silicon.

9. A two-way inverse optical clock signal generator based on a photonic crystal cross waveguide as claimed in claim 1, wherein: the isosceles right triangle defect medium column is a triangular column type.

10. A two-way inverse optical clock signal generator based on a photonic crystal cross waveguide as claimed in claim 1, wherein: the background silicon medium column is square.

11. A two-way inverse optical clock signal generator based on a photonic crystal cross waveguide as claimed in claim 1, wherein: the background silicon medium column rotates anticlockwise by 41 degrees along the Z-axis direction of the medium column axis.

12. A two-way inverse optical clock signal generator based on a photonic crystal cross waveguide as claimed in claim 1, wherein: the third signal output end is a modulation output end.