CN112859477B

CN112859477B - Mach-Zehnder interferometer based on nano antenna

Info

Publication number: CN112859477B
Application number: CN202110229598.1A
Authority: CN
Inventors: 杨可扬; 夏军
Original assignee: Southeast University
Current assignee: Southeast University
Priority date: 2021-03-02
Filing date: 2021-03-02
Publication date: 2022-04-05
Anticipated expiration: 2041-03-02
Also published as: CN112859477A

Abstract

The invention discloses a Mach-Zehnder interferometer based on a nano antenna. The interferometer comprises a lower substrate (1), a modulator (2), a birefringent material (3) and an upper substrate (4); the modulator (2) is positioned on the lower substrate (1); the birefringent material (3) is filled between the lower substrate (1) and the upper substrate (4) and wraps the modulator (2); the phase shifter (2-1) of the modulator (2) is a sub-wavelength nano antenna (2-2) array; when light passes through the nano antenna (2-2), Mie resonance occurs, and phase retardation is obtained while high forward scattering rate is achieved, and the phase retardation is controlled by the refractive index of the birefringent material; the output intensity modulation of the interferometer is achieved by modulating the refractive index of the birefringent material. Compared with the traditional Mach-Zehnder interferometer, the Mach-Zehnder interferometer has the advantages of higher modulation efficiency, higher working speed, compatibility with a CMOS (complementary metal oxide semiconductor) process, contribution to integration of devices and cost saving.

Description

Mach-Zehnder interferometer based on nano antenna

Technical Field

The invention relates to a Mach-Zehnder interferometer, in particular to a Mach-Zehnder interferometer based on a nano antenna.

Background

In current photonic integrated circuits, the propagation of light is controlled by a network of 2 x 2 optical analog gates. As a fundamental component of programmable photonic integrated circuits, the most common on-chip implementation of 2 x 2 optical gates is the mach-zehnder interferometer; meanwhile, the modulation of the light intensity is realized by a Mach-Zehnder modulator derived from a Mach-Zehnder interferometer. Most of the phase modulation functions of the current mach-zehnder interferometers are realized by thermo-optic materials, that is, the refractive index of the materials is changed through temperature change, and then the phase change of light passing through the materials is changed.

However, mach-zehnder interferometers based on thermo-optic materials have certain drawbacks: on one hand, the heating process needs more time; on the other hand, heating itself consumes more energy and introduces thermal crosstalk. Therefore, programmable photonic integrated circuits used in optical computing and other fields need new materials and techniques to further improve their performance. Although electro-optic materials such as lithium niobate currently exist as new solutions, there is still no satisfactory demand in terms of process compatibility and miniaturization.

Light can generate Mie resonance in the nano antenna with certain material and geometric parameter characteristics, and the forward scattering rate of the light is improved, so that the one-dimensional nanoparticle chain has the function of guiding light wave transmission. If the nano-antenna is wrapped by a birefringent material such as liquid crystal, the amount of phase retardation caused by mie resonance changes when the refractive index characteristics of the birefringent material change. Therefore, the phase modulation can be realized by modulating the refractive index of the birefringent material through voltage and further controlling the Mie resonance, and finally the output intensity modulation of the interferometer is realized. The Mach-Zehnder interferometer realized based on the principle can improve the performance of the programmable photonic integrated circuit, such as size, speed, process compatibility and the like.

Disclosure of Invention

The technical problem is as follows: aiming at the problems in the prior art, the invention provides a Mach-Zehnder interferometer based on a nano antenna, which realizes dynamic regulation and control of optical phase based on the Mie resonance phenomenon of light in the nano antenna, and further realizes the Mach-Zehnder interferometer beneficial to miniaturization of a programmable photonic integrated circuit.

The technical scheme is as follows: the Mach-Zehnder interferometer based on the nano antenna comprises a lower substrate (1), a modulator, a birefringent material and an upper substrate; the modulator is positioned on the lower substrate; the birefringent material is filled between the lower substrate and the upper substrate and wraps the modulator; the phase shifter of the modulator is a sub-wavelength nano antenna array; when light passes through the nano antenna, the Mie resonance occurs, the phase retardation is obtained while the forward scattering rate is high, and the phase retardation is controlled by the refractive index of the birefringent material; the output intensity modulation of the interferometer is achieved by modulating the refractive index of the birefringent material.

The nano antenna adopts various geometric forms of nanospheres, nano bricks or nano columns.

The birefringent material employs liquid crystal.

The liquid crystal can work in an electrically driven mode or in an optically driven mode.

The lower substrate is a pixilated driving circuit.

The phase shifter is provided with a hybrid tapered coupler, so that the loss of the waveguide structure in the transmission process is reduced.

The interferometer is used to modulate the intensity of the input light.

The interferometer implements a 2 x 2 optical gate.

Has the advantages that: compared with the prior art, the invention has the following remarkable characteristics: firstly, the phase modulation method based on the Mie's resonance principle has higher modulation efficiency, can obtain the required phase modulation amount within a shorter modulation distance, and is beneficial to the miniaturization of a programmable photonic integrated circuit; secondly, a birefringent material which responds to external bias quickly is adopted, so that the working speed of the device is greatly improved compared with that of a traditional thermo-optic material; and finally, the manufacture of the nano antenna is compatible with the existing CMOS process, thereby being beneficial to reducing the manufacture cost.

Drawings

Fig. 1 is a schematic diagram of a mach-zehnder interferometer based on a nano-antenna.

Fig. 2 is a schematic top view of the structure of the modulator portion of a mach-zehnder interferometer based on nanoantennas.

Fig. 3 is a schematic diagram of the geometrical parameters of the modulator and the nano-antenna structure.

Fig. 4 is a schematic top view of the modulator portion.

Fig. 5 is a schematic top view of the structure of the modulator portion of a nano-antenna based 2 x 2 optical gate.

FIG. 6 is a schematic top view of the structure of the modulator portion of a nanopillar-based Mach-Zehnder interferometer.

FIG. 7 is a schematic diagram of the geometrical parameters of a nanorod phase shifter structure.

Fig. 8 is a schematic top view of a phase shifter incorporating a hybrid tapered coupler.

Fig. 9 is a schematic diagram of the operation principle of the hexagonal optical gate network according to the present invention.

The figure shows that: the antenna comprises a lower substrate 1, a modulator 2, a birefringent material 3, an upper substrate 4, a phase shifter 2-1 and a nano antenna 2-2.

Detailed Description

The technical solution of the present invention will be described in detail with reference to the accompanying drawings and the detailed description.

Example 1

Fig. 1 is a schematic diagram of a mach-zehnder interferometer based on a nano-antenna. The liquid crystal display device is composed of an upper substrate 1, a modulator 2, a birefringent material 3, and a lower substrate 4. The modulator is prepared on the lower substrate, and the birefringent material is filled between the upper substrate and the lower substrate and wraps the whole modulator structure.

Liquid crystals are used as the birefringent material. The liquid crystal can be driven electrically. The lower substrate is a pixilated liquid crystal driving circuit. The modulator can be fabricated using CMOS compatible 193nm lithography and reactive ion etching methods. The upper substrate is made of a total reflection metal material. The lower surface of the upper substrate is coated with an alignment layer for alignment of liquid crystal molecules. The orientation mode can adopt rubbing orientation or light orientation.

The modulator portion is schematically shown in figure 2 in a top view. The basic structure and interference principle of the integrated waveguide Mach-Zehnder interferometer are the same as those of the known integrated waveguide Mach-Zehnder interferometer. Monochromatic light is input into a waveguide from any coupling input port, passes through the 3dB directional coupler 1, is divided into two paths of light with equal intensity, one path of light is modulated in phase when passing through the phase shifter, and then passes through the 3dB directional coupler 2 to obtain two paths of output light which is coupled and output to a subsequent light path. The intensity transmission coefficient of the two output lights is determined by the phase difference of the two lights after phase modulation.

The waveguides in the modulator are strip waveguides made of silicon material, the cross-section of which is shown in fig. 3 (a). The width W of the rectangular silicon waveguide is 400nm, and the height H is 220 nm. The phase shifter in the modulator consists of a one-dimensional nanoparticle resonator chain. As shown in FIG. 3(b), the nanoparticles and the waveguide have the same cross section, and the length L is 243nm, the period p of the nanoparticle arrangement, i.e. the distance between the central points of two adjacent nanoparticles, is 400 nm. The input light wavelength was 1650 nm. Under the geometric parameters, light generates Mie resonance in the nano particles, has high forward scattering rate, and changes the phase retardation.

The working principle of the interferometer is as follows: after the device receives the control signal, corresponding voltage is applied between the upper substrate and the lower substrate, and an electric field is formed inside the liquid crystal layer; under the action of an electric field, the director of the liquid crystal molecules is changed, and the refractive index distribution of the liquid crystal molecules is changed along with the change; the change in the external environment changes the amount of phase retardation by the mie resonance. Therefore, the modulation of the optical phase can be realized through external voltage bias, the phase difference between the two paths of input light is controlled, and the power of the two output lights is finally controlled.

Example 2

According to the Mach-Zehnder interferometer based on the nano antenna, provided by the invention, a Mach-Zehnder modulator is realized. The basic structure is the same as that described in embodiment 1, namely, it is composed of an upper substrate, a modulator, a birefringent material, and a lower substrate. The birefringent material is liquid crystal, and the lower substrate is a pixel liquid crystal driving circuit. The modulator can be fabricated using CMOS compatible 193nm lithography and reactive ion etching methods. The upper substrate is made of a total reflection metal material. The lower surface of the upper substrate is coated with an alignment layer for alignment of liquid crystal molecules. The orientation mode can adopt rubbing orientation or light orientation.

The modulator portion is schematically shown in figure 4 in a top view. Monochromatic light is coupled into the waveguide from the input port, and after passing through the 3dB beam splitter, the monochromatic light is divided into two paths of light with equal success rate, wherein one path of light is modulated in phase when passing through the phase shifter. The phase shifter in the modulator consists of a one-dimensional nanoparticle resonator chain. Light generates Mie resonance in the nano particles, and has high forward scattering rate and simultaneously changes the phase retardation. The two paths of light pass through the 3dB beam combiner and interfere with each other, and the power of the light output after the two paths of light are determined by the phase difference of the two paths of light. Finally, the output light is output through a coupling output end.

The operation principle of the Mach-Zehnder modulator based on the invention is as follows: after the device receives the control signal, corresponding voltage is applied between the upper substrate and the lower substrate, and an electric field is formed inside the liquid crystal layer; under the action of an electric field, the director of the liquid crystal molecules is changed, and the refractive index distribution of the liquid crystal molecules is changed along with the change; the change in the external environment changes the amount of phase delay caused by the mie resonance in the phase shifter. Therefore, the modulation of the optical phase can be realized through external voltage bias, so that the phase difference between two paths of light after passing through the beam splitter is controlled, and the intensity of coupled output light is finally controlled.

Example 3

According to the Mach-Zehnder interferometer based on the nano antenna, a 2 x 2 optical gate is realized. The basic structure is the same as that described in embodiment 1, namely, it is composed of an upper substrate, a modulator, a birefringent material, and a lower substrate. The birefringent material is liquid crystal, and the lower substrate is a pixel liquid crystal driving circuit. The modulator can be fabricated using CMOS compatible 193nm lithography and reactive ion etching methods. The upper substrate is made of a total reflection metal material. The lower surface of the upper substrate is coated with an alignment layer for alignment of liquid crystal molecules. The orientation mode can adopt rubbing orientation or light orientation.

The modulator portion is schematically shown in figure 5 in a top view. Monochromatic light is input into the waveguide from any coupling input port, passes through the 3dB directional coupler 1 and is divided into two paths of light with equal intensity. Each light path needs to pass through a phase shifter to modulate its phase. The phase shifter in the modulator consists of a one-dimensional nanoparticle resonator chain. Light generates Mie resonance in the nano particles, and has high forward scattering rate and simultaneously changes the phase retardation. Then the two paths of light pass through the directional coupler 2 to obtain two paths of output light and are coupled and output to a subsequent light path. The intensity transmission coefficient of the two output lights is determined by the phase difference of the two lights after phase modulation.

The working principle of the 2 x 2 optical door based on the invention is as follows: after the device receives the control signal, corresponding voltage is applied between the upper substrate and the lower substrate, and an electric field is formed inside the liquid crystal layer; under the action of an electric field, the director of the liquid crystal molecules is changed, and the refractive index distribution of the liquid crystal molecules is changed along with the change; the change in the external environment changes the amount of phase delay caused by the mie resonance in the phase shifter. The pixelated liquid crystal driving circuit of the lower substrate can realize pixelated voltage control, namely different voltages can be applied to two phase shifters in the modulator, so that the phase delays of the two phase shifters can be respectively and independently controlled. The modulation of the two optical phases can be achieved by an external voltage bias. Because the phases of the two paths of light can be modulated, the light path has two degrees of freedom, and the control of the intensity transmission coefficient and the phase difference of the two paths of coupled output light can be finally realized. Based on the principle, the intensity transmission coefficient can be designed, and the coupled light can be completely coupled to any output path by correspondingly controlling the input voltage, so that the 2 x 2 optical gate is realized.

Example 4

The modulator portion is schematically shown in figure 6 in a top view. The basic structure and interference principle of the integrated waveguide Mach-Zehnder interferometer are the same as those of the known integrated waveguide Mach-Zehnder interferometer. Monochromatic light is input into a waveguide from any coupling input port, passes through the 3dB directional coupler 1, is divided into two paths of light with equal intensity, one path of light is modulated in phase when passing through the phase shifter, and then passes through the 3dB directional coupler 2 to obtain two paths of output light which is coupled and output to a subsequent light path. The intensity transmission coefficient of the two output lights is determined by the phase difference of the two lights after phase modulation.

The waveguides in the modulator are strip waveguides made of silicon material, the cross-section of which is shown in fig. 3 (a). The width W of the rectangular silicon waveguide is 400nm, and the height H is 220 nm. The phase shifter in the modulator consists of a one-dimensional nanoparticle resonator chain. The schematic diagram of the phase shifter is shown in fig. 7, the nanoparticle is a nanopillar, the diameter D is 340nm, and the height H is also 220 nm. The period p of the nano-particle arrangement, i.e. the distance between the central points of two adjacent nano-particles, is 510 nm. The input light wavelength was 1650 nm. Under the geometric parameters, light generates Mie resonance in the nano particles, has high forward scattering rate, and changes the phase retardation.

Example 5

In order to reduce the loss of light due to geometric abrupt change or refractive index jump, the coupling efficiency is optimized by using a hybrid tapered coupler. A schematic top view of a phase shifter incorporating a hybrid tapered coupler is shown in fig. 8.

Example 6

Liquid crystals are used as the birefringent material. The liquid crystal can be driven in an optical drive manner. The modulator can be fabricated using CMOS compatible 193nm lithography and reactive ion etching methods. The upper substrate is made of glass material, so that the driving light can penetrate. The lower surface of the upper substrate is coated with an alignment layer for alignment of liquid crystal molecules. The orientation mode can adopt a photo-orientation mode, and the orientation agent adopts SD1 material.

The working principle of the interferometer is as follows: ultraviolet polarized light was used as drive light, and the drive light was incident from above the upper substrate and irradiated to the SD1 alignment layer. The orientation of the SD1 molecules was reoriented to be perpendicular to the direction of the driving light polarization. Under the action of SD1 molecules, the director changes along with the orientation of SD1 molecules, and the refractive index distribution of the liquid crystal molecules changes along with the change; the change in the external environment changes the amount of phase retardation by the mie resonance. Therefore, the modulation of the optical phase can be realized through external voltage bias, the phase difference between the two paths of input light is controlled, and the power of the two output lights is finally controlled.

Example 7

According to the Mach-Zehnder interferometer based on the nano antenna, optical gate networks in various forms such as polygons, ellipses and random irregular shapes can be realized. Wherein the polygon may comprise a triangle, a quadrangle, a hexagon, etc., and the ellipse comprises a circle, etc. Taking the hexagonal optical gate network as an example, the basic structure of the hexagonal optical gate network is the same as that described in embodiment 1, that is, the hexagonal optical gate network is composed of an upper substrate, a modulator, a birefringent material, and a lower substrate. The birefringent material is liquid crystal, and the lower substrate is a pixel liquid crystal driving circuit. The modulator can be fabricated using CMOS compatible 193nm lithography and reactive ion etching methods. The upper substrate is made of a total reflection metal material. The lower surface of the upper substrate is coated with an alignment layer for alignment of liquid crystal molecules. The orientation mode can adopt rubbing orientation or light orientation.

The basic unit of the hexagonal gate network is a 2 × 2 optical gate, and the structure of the modulator part is schematically shown in fig. 5 from the top view. Monochromatic light is input into the waveguide from any coupling input port, passes through the 3dB directional coupler 1 and is divided into two paths of light with equal intensity. Each light path needs to pass through a phase shifter to modulate its phase. The phase shifter in the modulator consists of a one-dimensional nanoparticle resonator chain. Light generates Mie resonance in the nano particles, and has high forward scattering rate and simultaneously changes the phase retardation. Then the two paths of light pass through the directional coupler 2 to obtain two paths of output light and are coupled and output to a subsequent light path. The intensity transmission coefficient of the two output lights is determined by the phase difference of the two lights after phase modulation.

The hexagonal optical gate network according to the present invention can use any port thereof as an input or output port of light, and the operation principle thereof is shown in fig. 9, taking two transmission paths as an example. In fig. 9, the rectangles in the transmission network represent 2 × 2 optical gate units. By controlling the liquid crystal in pixel form, different gate units in the network can have different coupling functions, distinguished by different colors in fig. 9, i.e. a white gate unit controls the input and output on the same side, and a black gate unit couples the input light to the output on the other side. When the working state of the liquid crystal is changed, the coupling function of the gate unit is changed, and the propagation path of light in the network is switched. According to the above principle, programming of the optical gate network can be realized by controlling the liquid crystal so that light propagates in any path in the network and any port can be used as an input or output port.

Based on the basic principle, researchers can construct optical gate networks in any forms, and the optical gate networks belong to the protection scope of the invention.

Claims

1. A Mach-Zehnder interferometer based on a nano-antenna is characterized in that: the interferometer comprises a lower substrate (1), a modulator (2), a birefringent material (3) and an upper substrate (4); the modulator (2) is positioned on the lower substrate (1); the birefringent material (3) is filled between the lower substrate (1) and the upper substrate (4) and wraps the modulator (2); the phase shifter (2-1) of the modulator (2) is a sub-wavelength nano antenna (2-2) array; when light passes through the nano antenna (2-2), the Mie resonance occurs, and the phase retardation is obtained while the forward scattering rate is high, and the phase retardation is controlled by the refractive index of the birefringent material; the output intensity modulation of the interferometer is achieved by modulating the refractive index of the birefringent material.

2. A mach-zehnder interferometer based on a nanoantenna according to claim 1, characterized in that: the nano antenna (2-2) adopts a nanosphere, a nano brick or a nano column.

3. A mach-zehnder interferometer based on a nanoantenna according to claim 1, characterized in that: the birefringent material (3) adopts liquid crystal.

4. A mach-zehnder interferometer based on a nanoantenna according to claim 3, characterized in that: the liquid crystal works in an electric driving mode or in an optical driving mode.

5. A Mach-Zehnder interferometer based on a nanoantenna as claimed in claim 4, characterized in that: the lower substrate (1) is a pixilated driving circuit.

6. A mach-zehnder interferometer based on a nanoantenna according to claim 1, characterized in that: the phase shifter (2-1) has a hybrid tapered coupler, which reduces loss of the phase shifter during transmission.

7. A mach-zehnder interferometer based on a nanoantenna according to claim 1, characterized in that: the interferometer is used to modulate the intensity of the input light.

8. A mach-zehnder interferometer based on a nanoantenna according to claim 1, characterized in that: the interferometer implements a 2 x 2 optical gate.