An intensity-flattened phase shifter based on unidirectional radiation resonance state and its application

Abstract

The present invention provides a phase shifter with flat intensity based on unidirectional radiation resonance states and its application, belonging to the fields of optoelectronics, optical communications, and wireless communications. The phase shifter comprises an upper dielectric layer, a lower dielectric layer, and a photonic crystal layer located between the upper and lower dielectric layers. The photonic crystal layer contains holes and slots periodically arranged along one or two dimensions. The photonic crystal layer structure has topological protection properties, forming a resonant cavity. Light passing through the photonic crystal layer is topologically protected, generating multiple resonant states in the resonant cavity. The light radiates from the upper surface of the photonic crystal layer to the upper dielectric layer, and from the lower surface of the photonic crystal layer to the lower dielectric layer. The resonant state with a wave vector of k has a unidirectional radiation characteristic, radiating only toward the upper or lower surface of the photonic crystal layer. This phase shifter utilizes highly directional radiation resonance states to achieve phase modulation while maintaining a flat intensity response.

Description

Technical Field

[0001] The invention relates to an intensity-invariant phase shifter based on a unidirectional radiation resonance state, and belongs to the fields of optoelectronics, optical communications and wireless communications. Background Art

[0002] Phase shifters are essential components for various optoelectronic applications and can be widely used in optical modulation, wavefront manipulation, and beam control. Traditional phase shifters generally produce dynamic phase modulation by changing the refractive index through thermo-optical or electro-optical effects, or achieve static phase control through geometric structure distribution. Traditional phase shifters have low modulation efficiency, high insertion loss, and are not conducive to integration. The use of optical resonators can improve modulation efficiency, but because intensity and phase follow the Kramers-Kronig relationship, phase changes are accompanied by drastic changes in intensity, which is not conducive to many application scenarios. Therefore, phase shifters with independent intensity and phase responses play an important role. Summary of the Invention

[0003] The purpose of the present invention is to provide an intensity-flat phase shifter based on a unidirectional radiation resonance state, which uses a highly directional radiation resonance state to achieve phase modulation and maintain a flat intensity response. The phase shifter can be widely used in light modulation, wavefront manipulation, beam control, etc. It can be used as a core component in applications such as optical phased arrays, planar metalenses, and optical antennas. It can also be used in fields such as three-dimensional projection, lidar, and optical detection and sensing.

[0004] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] A phase shifter with flat intensity based on unidirectional radiation resonance states comprises an upper dielectric layer, a lower dielectric layer, and a photonic crystal layer (PhC layer) located between the upper and lower dielectric layers; the photonic crystal layer contains holes and slots periodically arranged along one or two dimensions; the photonic crystal layer structure has topological protection properties, forming a resonant cavity; light passing through the photonic crystal layer is topologically protected, generating multiple resonant states in the resonant cavity, and radiating toward the upper surface of the photonic crystal layer to the upper dielectric layer, and toward the lower surface of the photonic crystal layer to the lower dielectric layer, wherein the resonant state with a wave vector of k has a unidirectional radiation characteristic, radiating only toward the upper or lower surface of the photonic crystal layer.

[0006] Preferably, the relationship among the refractive index n1 of the upper dielectric layer, the refractive index n2 of the photonic crystal layer and the refractive index n of the lower dielectric layer is n2>n1, n2>n3.

[0007] Preferably, the cross-sectional shape of the structural portion between the holes and grooves of the photonic crystal layer is bilaterally symmetrical or asymmetrical, and vertically asymmetrical.

[0008] The invention discloses an application of an intensity-flattened phase shifter based on a unidirectional radiation resonance state, which is used as a core component of an electro-optic modulation phase shifter or a thermo-optic modulation phase shifter.

[0009] Compared with the prior art, the present invention has the following positive effects:

[0010] 1. The phase shifter proposed in the present invention can achieve phase modulation by using a resonant state of highly directional radiation while maintaining a flat intensity response.

[0011] 2. The phase shifter proposed in this invention utilizes perpendicular input / output relative to the transverse plane (xy plane), avoiding the insertion loss associated with planar coupling devices. Furthermore, the phase shifter is a unidirectional surface-emitting phase shifter, utilizing the directional radiation characteristics of the resonant state to avoid wasted radiation losses, improve energy utilization, and reduce losses. Compared with traditional phase shifters, it provides more concentrated energy and halves insertion loss.

[0012] 3. The phase shifter proposed in the present invention utilizes the resonance state to enhance the phase modulation efficiency, and can change the resonance state quality factor by designing the period, duty cycle, and height, thus being flexible.

[0013] 4. The phase shifter proposed in this invention supports both transmissive and reflective operating modes. Specifically, because the unidirectional radiative resonance state can radiate toward the upper and lower surfaces of the photonic crystal layer, the phase shifter of this invention can function as both a reflective and a transmissive phase shifter for incident light from a fixed direction. The phase shifter of this invention eliminates the need for additional reflectors and, relying solely on the design of the photonic crystal layer structure, allows radiation to be directed solely toward the upper or lower surface of the photonic crystal layer.

[0014] 5. The light output angle of the phase shifter of the present invention follows the law of reflection and the law of refraction, and the output angle is not limited, and small-angle output and large-angle output can be achieved.

[0015] 6. In order to ensure the existence of the mode in the resonant cavity, the photonic crystal layer is required to have a certain thickness (for example, a thickness of hundreds of nanometers) to support the fundamental mode of the resonant cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 FIG. 1 is a plan view of a phase shifter with flat intensity according to a first embodiment of the present invention.

[0017] Figure 2 FIG. 1 is a perspective schematic diagram of an intensity-flattened phase shifter according to a first embodiment of the present invention.

[0018] Figure 3 2 is a diagram of the upper and lower radiation ratios of the first embodiment of the present invention; wherein the horizontal axis is kx and the vertical axis is the asymmetric radiation ratio.

[0019] Figure 4The intensity diagram (i.e., Figure (a)) and phase diagram (i.e., Figure (b)) of transmission and reflection under lossy conditions of the present invention are shown; the horizontal axis is the wavelength, and the vertical axis is the normalized intensity and phase, respectively.

[0020] Figure 5 Schematic diagram of the structure of the intensity-flattened phase shifter according to the second embodiment of the present invention, wherein (a) shows the structure dimensions and (b) shows the incident angle.

[0021] Figure 6 Schematic diagram of the energy exchange port of the intensity-flattened phase shifter according to the second embodiment of the present invention.

[0022] Figure 7 Schematic diagram of energy transmission of the intensity-flattened phase shifter of the present invention.

[0023] Figure 8 These are the intensity and phase diagrams obtained by verification measurement of the intensity-flattened phase shifter according to the second embodiment of the present invention. The horizontal axis represents wavelength, and the vertical axis represents normalized intensity and phase, respectively. DETAILED DESCRIPTION

[0024] In order to make the above features and advantages of the present invention more clearly understood, embodiments are given below and described in detail with reference to the accompanying drawings.

[0025] Example 1:

[0026] An embodiment is now provided. This embodiment discloses an intensity-flattened phase shifter based on a unidirectional radiation resonance state, such as Figure 1-2 As shown. The phase shifter is composed of a photonic crystal layer 20 with a refractive index of n2 and an upper dielectric layer 10 and a lower dielectric layer 30 with a refractive index of n1 and n3, respectively, wherein n2>n1 and n2>n3. In order to facilitate the description of the phase shifter structure, a three-dimensional Cartesian coordinate system (x, y, z) is set in this embodiment. Among them, the photonic crystal layer 20 contains holes and grooves 21 arranged periodically along the xy plane. In this embodiment, it is a one-dimensional arrangement, specifically, it is periodically arranged along the x direction in the xy plane to form a one-dimensional matrix. However, the present invention is not limited to this. In some embodiments, the holes and grooves 21 can also be arranged two-dimensionally periodically in the xy plane, that is, they are periodically arranged in both the x and y directions to form a two-dimensional matrix, for example, similar to a grid.

[0027] The cross section of the structure portion 22 between the holes 21 of the photonic crystal layer 20, that is, the cross section cut out from the xz plane (or the projection on the xz plane) is a left-right asymmetric shape, as shown in FIG. Figure 1-2The photonic crystal layer 20 is an oblique trapezoid, wherein the thickness of the photonic crystal layer 20 is h and the refractive index is n2. In some embodiments, the cross-section of the structural portion 22 of the photonic crystal layer 20 may also be a bilaterally symmetrical shape, such as a standard isosceles trapezoid, but asymmetrical in both vertical directions. In other embodiments, for a two-dimensional arrangement, the cross-section of the structural portion 22 of the photonic crystal layer 20 is a cross-section cut along the xz plane (or a projection on the xz plane) and a cross-section cut along the yz plane (or a projection on the yz plane), and the shape may be bilaterally asymmetrical or bilaterally symmetrical, but not vertically symmetrical.

[0028] The structural design of this phase shifter, particularly the photonic crystal layer 20, exhibits topological protection. This means that when light passes through this structure, it is essentially unaffected by structural defects (e.g., manufacturing errors) and continues to function as intended. In other words, the structure's functionality is unaffected by the presence of structural defects, thereby increasing the robustness of the structure. This structure can form a resonant cavity in which light exists in multiple resonant states. These states can radiate toward the upper dielectric layer 10 from the upper surface of the photonic crystal layer 20, and simultaneously radiate toward the lower dielectric layer 30 from the lower surface of the photonic crystal layer 20. However, the resonant state with a wave vector of k radiates only toward the upper or lower surface, i.e., it exhibits unidirectional radiation. For ease of description, this special resonant state with unidirectional radiation is referred to as the working state.

[0029] In this embodiment, the apertures 21 of the photonic crystal layer 20 form a one-dimensional array with a period a and a duty cycle ff. By adjusting the period a, duty cycle ff, the medium refractive index n1, n2, n3, thickness h, and the shape of the apertures 21, the size and central wavelength of the phase shifter can be changed. By changing the thickness h, period a, duty cycle ff, and shape of the photonic crystal layer 20, the ratio of the energy radiated from the upper and lower surfaces in the resonant state can be adjusted, so that the working state can achieve highly directional radiation, or even unidirectional radiation, such as Figure 3 The phase shifter includes a unidirectional radiation design based on a photonic crystal layer, and is independent of the shape of the specific holes 21 forming the photonic crystal layer 20 .

[0030] This phase shifter is a surface excitation and surface emission phase shifter. It can be used as a reflective phase shifter or a transmissive phase shifter, and both have the characteristic of intensity flatness. This phase shifter has an optimal excitation angle (emission angle), and the specific value of this angle depends on the design of the photonic crystal layer. When the asymmetric radiation ratio between the upper and lower surfaces of the photonic crystal layer 20 is the largest, it is the optimal angle. At this angle, unidirectional radiation can be achieved. Within a certain range near this angle, the intensity can be flat, and the characteristics of a sharp phase change can be achieved, such as Figure 4Therefore, the phase shifter has a certain degree of robustness. When there are process errors in the actual manufacturing process, such as the difference between the actual period and the designed period, or the difference between the actual cross-sectional shape and the designed shape, the phase shifter can still operate within a certain error range because the unidirectional radiation characteristics of the resonant state are topologically protected.

[0031] Example 2:

[0032] Now another embodiment is provided, which applies the intensity-flat phase shifter based on the unidirectional radiation resonance state proposed by the present invention to a specific environment. Specifically, the phase shifter is designed on an SOI plate. The SOI plate is composed of a three-layer structure of silicon-silicon dioxide-silicon, with a bottom substrate silicon thickness of about 725 microns, a middle layer of silicon dioxide thickness of 2 microns, and a top layer of silicon thickness of 500 nanometers. The photonic crystal layer structure of the phase shifter is made on the top silicon, that is, the top silicon of the SOI plate is the photonic crystal layer of the phase shifter, the middle layer of silicon dioxide is the lower dielectric layer, and the air above is the upper dielectric layer. The holes and grooves of the photonic crystal layer are arranged periodically, and the width of one period is 825 nanometers. The cross-section between the holes and grooves of the photonic crystal layer is trapezoidal, with bottom angles of 75 degrees and 79 degrees respectively, and the width of the upper surface of the trapezoid is 473 nanometers, as shown in FIG. Figure 5 As shown in Figure (a). Figure 5 As shown in Figure (b), when the angle between the incident angle and the plane perpendicular to the paper (the vertical dotted line in the figure is the intersection of the plane and the straight surface) is around 8 degrees, a unidirectional radiation resonance state will be excited, radiating energy only to the upper surface.

[0033] In this embodiment, when the incident angle is obliquely incident at about 8°, the phase shifter has four energy input / output ports, which are defined as port 1, port 2, port 3 and port 4. Figure 6 As shown. Light is input from port 3. During the excitation process, the incident energy light enters the device from port 3. Since the coupling efficiency between the resonant cavity and the port is less than 100%, not all of the light is coupled, that is, part of it is coupled and part of it is not coupled. Part of it is coupled into the resonant state and then radiated from port 2 or port 4; the other part does not participate in the resonant state coupling and is directly reflected from port 4 or transmitted from port 2, as shown. Figure 7 As shown. Because the resonant state exhibits unidirectional radiation, in this embodiment, radiation from port 4 is disabled, leaving only directly reflected light. According to the law of conservation of energy, the sum of the energy transmitted from port 2 and the energy reflected from port 4 should equal the energy input to port 3. Since only directly reflected light passes through port 4, the reflected intensity curve is flat. Therefore, although the output of port 2 is a superposition of directly transmitted and resonantly radiated light, the intensity curve is also flat. However, port 2 incorporates the phase shift caused by resonance, so while its intensity is flat, it still exhibits phase response characteristics.

[0034] Experimental verification:

[0035] To verify the effectiveness of the phase shifter of Example 2, a confocal observation system was built for measurement. When measuring the intensity, the tunable laser output first passes through a polarizer and is focused onto the back focal plane of the microscope objective lens through a lens. The incident angle entering the phase shifter is adjusted by moving the lens to excite a unidirectional radiation resonance state with a momentum of k in the plane of the photonic crystal layer of the phase shifter. The transmitted light and the reflected light are collected by two identical objective lenses respectively, and are received by a camera or a photodetector after the magnification is appropriately adjusted by the 4f system. The wavelength is scanned and the reflection spectrum and the transmission spectrum are recorded. When measuring the phase, a Michelson interferometer is used for observation. The incident light is divided into signal light and reference light by a beam splitter, and the interference pattern of concentric and equal inclination angles is observed by a camera. The phase shift is obtained by calculating the movement of the edge ring.

[0036] Figure 8 Figure (a) shows the measured intensity plot. The experimentally measured intensity spectra at the reflection and transmission ports show no resonant peaks (or valleys), as expected for a flat reflection. In practice, due to non-radiative losses, the total reflectivity of the transmission spectrum exhibits a "dip" with a normalized depth of ~0.43. This dip can be mitigated or eliminated by improving process precision and suppressing non-radiative losses. Figure 8 Figure (b) shows the measured phase diagram. The phase shift of light in the transmission and reflection channels can be characterized by the movement of interference fringes. The concentric interference fringes were recorded with a camera, and the phase shift was extracted based on the movement of the fringes. It was confirmed that the phase of the reflected light hardly changed, while the phase of the transmitted light changed by 2π within the wavelength scanning range (1540-1556 nm), which is consistent with the design. Figure 8 As can be seen from the two figures, the test results are consistent with the theoretical results, which shows that the phase shifter designed in this embodiment is effective.

[0037] It should be noted that the present invention uses directional terms such as "upper dielectric layer," "lower dielectric layer," "upper surface," "lower surface," and "transverse plane" simply to facilitate the description of the phase shifter structure, but does not limit the orientation of the phase shifter. For example, in different implementations, the "upper dielectric layer" may be located below or laterally of the "lower dielectric layer," the "upper surface" may be located below or laterally of the "lower surface," and the "transverse plane" may be vertical or inclined. Furthermore, structures such as "upper dielectric layer," "lower dielectric layer," "upper surface," "lower surface," "transverse plane," and "hole slot" may have different names in different documents or implementations. Therefore, these structures should be defined based on their structural relationships and functions.

[0038] Although the present invention has been disclosed as above by way of embodiments, they are not intended to limit the present invention. Any appropriate modification or equivalent substitution of the technical solution of the present invention by a person skilled in the art should be included in the protection scope of the present invention. The protection scope of the present invention shall be based on that defined in the claims.

Claims

1. An intensity-flattened phase shifter based on a unidirectional radiation resonance state, characterized in that: The photonic crystal layer comprises an upper dielectric layer, a lower dielectric layer and a photonic crystal layer located between the upper dielectric layer and the lower dielectric layer; the photonic crystal layer contains holes and grooves periodically arranged along one-dimensional or two-dimensional directions; The photonic crystal layer structure has a topological protection characteristic and forms a resonant cavity; light passing through the photonic crystal layer is topologically protected, generates multiple resonant states in the resonant cavity, and radiates to the upper dielectric layer toward the upper surface of the photonic crystal layer, and radiates to the lower dielectric layer toward the lower surface of the photonic crystal layer, wherein the resonant state with a wave vector of k has a unidirectional radiation characteristic, has an asymmetric radiation ratio on the upper and lower surfaces of the photonic crystal layer, and radiates only toward the upper or lower surface of the photonic crystal layer, and the radiation ratio of the resonant state to the upper and lower surfaces is adjusted by changing the thickness, period, duty cycle and shape of the apertures of the photonic crystal layer.

2. The phase shifter according to claim 1, wherein The relationship among the refractive index n1 of the upper dielectric layer, the refractive index n2 of the photonic crystal layer and the refractive index n of the lower dielectric layer is n2>n1, n2>n3.

3. The phase shifter according to claim 1, wherein The cross-sectional shape of the structural portion between the holes and grooves of the photonic crystal layer is bilaterally symmetrical or asymmetrical, and vertically asymmetrical.

4. An application of an intensity-flattened phase shifter based on a unidirectional radiation resonance state, characterized in that: Used as the core component of an electro-optical modulation phase shifter or a thermo-optical modulation phase shifter.

Images