Parity-time-symmetric grating structure and application thereof

Abstract

The application provides a parity-time symmetric grating structure and application thereof, wherein the grating structure comprises a cover layer, a grating layer and a substrate which are stacked in sequence, wherein the cover layer and the substrate are transparent media; the grating layer is composed of ridge regions and groove regions which are periodically and alternately arranged in the transverse direction, the ridge regions and the groove regions are optical loss material and optical gain material respectively, and satisfy the parity-time symmetry condition. The application realizes the enhancement of the photonic spin Hall effect by reaching the maximum value of the reflection / transmission coefficient polarization ratio, does not need to rely on singular points, has high outgoing light signal strength, is convenient for practical detection and engineering application, and can be widely applied to the fields of reconfigurable optical switches, high-sensitivity optical sensors, polarization beam splitters, optical encoders and quantum information processing and other spin photon device fields.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano optics and optoelectronic devices technology, specifically relating to a parity-time symmetric grating structure and its applications. Background Technology

[0002] The photonic spin hall effect (PSHE) refers to the phenomenon where, when a spatially confined linearly polarized light beam passes through an interface composed of different media, photons with opposite spin directions deflect laterally in a direction perpendicular to the incident plane, splitting into left-handed and right-handed circularly polarized beams. As a typical physical phenomenon of photon spin-orbit coupling, PSHE is closely related to the refractive index gradient and can realize the spatial separation and manipulation of photon spin states, showing significant application prospects in precision measurement, novel sensing, quantum information processing, and on-chip spin photonic devices. However, since PSHE is a weak optical effect caused by photon spin-orbit interaction, the resulting spin-related displacement is typically only on the nanometer scale. How to effectively enhance this displacement and achieve flexible control has always been a research challenge in this field.

[0003] To overcome the challenge of weak PSHE displacement, researchers have proposed various enhancement schemes based on resonance mechanisms, including surface plasmon polariton (SPP), localized plasmon resonance (LSPR), and giant plasmon mode resonance (GMR). However, these schemes are limited by metal ohmic losses and mode coupling efficiency, resulting in limited enhancement of PSHE. Furthermore, their control methods are passive and limited in scope, making it difficult to meet the application requirements of flexible, dynamic, highly sensitive detection and integrated devices.

[0004] In recent years, parity-time (PT) symmetric optical structures have provided a new physical means to enhance and control PSHE (Power-Side-Earth Elevation) due to their non-Hermitian properties, which remain unchanged under joint spatial and temporal inversion operations. PT-symmetric structures consist of gain and loss media with equal real refractive indices and opposite imaginary refractive indices. These structures exhibit unique optical phenomena such as anomalous resonance enhancement and asymmetric optical transmission near the exception point (EP). This structure has been widely applied in the design and control of various optical devices, including semiconductor lasers, waveguide distributors, signal selectors, optical isolators, and optical sensors. For example, patent publication CN109244828A discloses a semiconductor laser based on a parity-time symmetric Bragg reflection waveguide, achieving mode selection and single-mode laser output by constructing a PT-symmetric periodic waveguide structure; patent publication CN113867016A proposes a PT-symmetric all-fiber optical isolator based on a Fabry-Perot resonator coupling system, utilizing the asymmetric transmission characteristics of the PT-symmetric system to achieve forward light conduction and reverse light suppression. Furthermore, existing research indicates that in PT-symmetric layered structures (such as bilayer films, multilayer films, and metamaterials), the spin shift of the PSHE can be significantly enhanced by utilizing the near-zero reflectivity and phase abrupt change near the epipolar point (EP). However, the above methods still have shortcomings: on the one hand, the PSHE enhancement effect is highly dependent on the EP, and the reflectivity at the EP is close to zero, resulting in extremely weak actual reflected signals, which is not conducive to detection and applications; on the other hand, the modulation method mainly relies on material parameters and the incident angle, lacking the ability to perform multi-dimensional modulation through structural geometric parameters. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a parity-time symmetric grating structure and its application to solve the problem of singularity dependence in existing PSHE enhancement effects.

[0006] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0007] A parity-time symmetric grating structure includes a capping layer, a grating layer, and a substrate stacked sequentially, wherein:

[0008] Both the capping layer and the substrate are transparent media;

[0009] The grating layer consists of ridges and grooves arranged periodically and alternately in the lateral direction;

[0010] The ridge region is an optical loss material with a complex refractive index of 100%. ;

[0011] The groove region is an optical gain material with a complex refractive index of 100%. ;

[0012] In the formula, Let be the real part of the refractive index. is the extinction coefficient.

[0013] Furthermore, the geometric parameters of the grating layer are:

[0014] The grating period P = 0.34λ, where λ is the operating wavelength;

[0015] Thickness d = 0.17λ;

[0016] The duty cycle f ranges from 0.3 to 0.7.

[0017] Furthermore, the operating wavelength λ is taken as 1400nm~2200nm, and the real part of the refractive index... The value ranges from 1 to 3.5, and the extinction coefficient is... The value ranges from 0.1 to 1.0.

[0018] Furthermore, the operating wavelength λ = 1550 nm, the duty cycle f = 0.5, and the real part of the refractive index... =3, extinction coefficient =0.46.

[0019] Furthermore, the cover layer and the substrate are air.

[0020] A polarization beam splitter, comprising:

[0021] The above parity-time symmetric grating structure;

[0022] The light inlet is located on the incident light path of the grating structure;

[0023] There are two light outlets, located on the two outgoing light paths of the grating structure.

[0024] An optical sensor, comprising:

[0025] The aforementioned parity-time symmetric grating structure has a capping layer used to set the object under test;

[0026] A light source for irradiating linearly polarized light onto the grating structure at a fixed incident angle;

[0027] The detector is used to detect the spin displacement of the left-hand and right-hand circularly polarized components in the reflected light.

[0028] A reconfigurable optical switch, comprising:

[0029] The above parity-time symmetric grating structure;

[0030] A laser and a polarizer are used to irradiate linearly polarized light onto the grating structure at a fixed incident angle.

[0031] The control unit is used to control the grating period in the grating structure;

[0032] The first output port and the second output port are located on the reflected light paths corresponding to different grating periods.

[0033] Furthermore, multiple grating layers with different periods are provided, and the control unit changes the grating period by switching the grating layers in the grating structure.

[0034] Furthermore, the grating layer in the grating structure is a fiber grating, and the control unit changes the grating period by adjusting the strain or temperature.

[0035] The beneficial effects of this invention are as follows:

[0036] (1) This invention provides a parity-time symmetric grating structure. Compared with the existing PT-symmetric layered structure, which relies on near-zero reflectivity near the singular point (EP) to enhance PSHE, the reflected signal at EP is close to zero, resulting in a very low signal-to-noise ratio in actual detection, which limits its application in the field of precision measurement. This invention achieves PSHE enhancement by maximizing the polarization ratio of the reflection / transmission coefficient, without relying on EP, and the emitted light signal intensity is high, which is convenient for actual detection and engineering applications.

[0037] (2) Existing solutions mainly rely on adjusting the incident angle or material parameters, which limits the degree of freedom of control. This invention uses the grating period as an independent geometric control dimension. By changing the grating period, the peak and valley values ​​of spin displacement can be continuously switched in the incident angle domain, providing a simple and efficient control method for reconfigurable spin photonic devices.

[0038] (3) Existing enhancement schemes are usually only effective within a very narrow incident angle range; the present invention can maintain significant spin displacement within a wider incident angle range, significantly reducing the alignment accuracy requirements of the incident light angle and improving the robustness and practicality of the system.

[0039] (4) The present invention can significantly enhance incident light of both horizontal polarization (H) and vertical polarization (V), and simultaneously supports reflection mode and transmission mode. The maximum spin displacement can approach the theoretical limit (half beam waist), providing a core component for designing multifunctional and multipurpose spin photonic devices.

[0040] (5) The present invention adopts a one-dimensional grating structure, and its fabrication process is highly compatible with standard micro-nano processing technology (such as electron beam lithography, inductively coupled plasma etching, etc.). The control unit can be directly integrated, which is convenient to interface with existing photonic chip platforms. It has good industrialization prospects and can be widely used in the field of spin photonic devices such as reconfigurable optical switches, high-sensitivity optical sensors, polarization beam splitters, optical encoders and quantum information processing. Attached Figure Description

[0041] Figure 1 This is a diagram of the parity-time symmetric grating structure of the present invention;

[0042] Figure 2 This is a graph showing the variation of the spin displacement of the grating structure of the present invention with the incident angle;

[0043] Figure 3 This is a schematic diagram of the reconfigurable optical switch structure of the present invention.

[0044] Figure label:

[0045] 1-Laser; 2-Polarizer; 3-Raster layer; 4-Control unit;

[0046] 5 - First output port; 6 - Second output port. Detailed Implementation

[0047] Embodiments of the present invention are described in detail below. Examples of the embodiments are shown in the accompanying drawings, wherein similar or identical reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0048] I. Parity-Time Symmetric Grating Structure

[0049] 1. Structural parameters

[0050] like Figure 1 The parity-time symmetric grating structure shown comprises, from top to bottom, a capping layer, a grating layer, and a substrate. Both the capping layer and the substrate are transparent media; in this embodiment, air is used.

[0051] The grating layer consists of ridge regions (denoted as L) and groove regions (denoted as G) arranged periodically and alternately in the lateral direction. The ridge regions are optical loss materials, and the groove regions are optical gain materials.

[0052] In this embodiment:

[0053] 1) The geometric parameters of the grating layer are set as follows:

[0054] The period P = 0.34λ, where λ is the working wavelength, which can be adjusted between 1400nm and 2200nm. In this embodiment, λ = 1550nm is taken, so P = 527nm.

[0055] Thickness d = 0.17λ (corresponding to approximately 263.5 nm);

[0056] The duty cycle (i.e., the ratio of ridge width w to period P) f ranges from 0.3 to 0.7. In this embodiment, f = 0.5 is taken, that is, ridge width = groove width = P / 2.

[0057] 2) The complex refractive indices of the gain material and the loss material are respectively:

[0058] Gain material (slot area): ;

[0059] Consumable materials (ridge area): ;

[0060] Among them, the real part of the refractive index The value ranges from 1 to 3.5; in this embodiment, it is taken as... =3, extinction coefficient The value range is 0.1 to 1.0, and in this embodiment, it is taken as... =0.46 to reflect broadband enhancement characteristics. Furthermore, this material parameter satisfies the parity-time symmetry condition. = (That is, the two are conjugates).

[0061] 2. Working conditions and performance

[0062] A linearly polarized Gaussian beam is used as the incident light, with a beam waist. =30λ, with the angle of incidence The light is irradiated onto the surface of the grating structure. The spin displacement in the reflected light is calculated using rigorous coupled-wave analysis (RCWA) combined with angular spectrum theory.

[0063] like Figure 2 As shown in (a), under horizontal polarization, when the grating period P takes values ​​of 0.33λ, 0.34λ, and 0.35λ, the spin shift... With the angle of incidence The variation curve shows obvious peak and valley characteristics, and the peak position shifts towards lower incident angles as the period increases. For example, when P increases from 0.33λ to 0.35λ, the peak incident angle shifts from about 38.8° to about 6.8°, realizing a continuous switching of the spin displacement peak and valley positions.

[0064] like Figure 2 As shown in (b), under vertical polarization, when P takes values ​​of 0.34λ, 0.342λ, and 0.345λ, the increase in period also leads to spin displacement. The peak value shifts towards lower incident angles. Furthermore, when the extinction coefficient... When the value is set to 0.46, a broadband enhanced response greater than 10λ can be obtained in the low incident angle range (approximately 2.8°~11.6°).

[0065] Note: and The symbols "+" and "-" in the diagram indicate the direction of reflected circularly polarized light, where "+" indicates left-handed circular polarization and "-" indicates right-handed circular polarization. For left-handed photon spin Hall shift, This represents the right-hand spin Hall displacement. and The symbols “H” and “V” in the diagram represent the direction of the incident ray polarized light, where “H” is the horizontal direction and “V” is the vertical direction.

[0066] The above results show that the parity-time symmetric grating structure proposed in this invention can achieve spin displacement enhancement close to the theoretical limit (half-waist) without relying on singular points, and can flexibly switch the peak and valley positions of spin displacement by adjusting the grating period P, while also possessing wide incident angle enhancement characteristics.

[0067] II. Application

[0068] 1. Polarization beam splitter

[0069] This invention includes a parity-time symmetric grating structure, wherein an entrance is provided in the incident light path of the grating structure, and the incident light is ensured to have a fixed incident angle. An injection grating structure is provided; two light exit ports are set in the reflected light path.

[0070] In use, linearly polarized light is incident through the light inlet; then, based on the grating structure of this invention, the incident light is separated into left-handed circularly polarized light and right-handed circularly polarized light that are spatially separated; finally, the two circularly polarized lights are emitted from the two light outlets respectively.

[0071] 2. Optical Sensors

[0072] It includes a light source, a detector, and the parity-time symmetric grating structure proposed in this invention, wherein:

[0073] The light source is used to fix the angle of incidence. Linearly polarized light is irradiated onto the grating structure;

[0074] The detector is placed in the reflected light path of the grating structure to detect the spin displacement of the left-hand and right-hand circularly polarized components in the reflected light.

[0075] In use, the sample to be tested is placed in the cover layer of the grating structure (i.e., the upper surface of the grating layer), thereby changing the refractive index of the cover layer; when the refractive index of the cover layer changes, the spin displacement of the reflected light also changes accordingly; based on this, the properties of the sample to be tested can be detected by detecting the change in the spin displacement.

[0076] 3. Reconfigurable optical switch

[0077] like Figure 3 The reconfigurable optical switch shown is equipped with the parity-time symmetric grating structure proposed in this invention, and also includes a laser 1, a polarizer 2, a control unit 4, and a first output port 5 and a second output port 6. Wherein:

[0078] Laser 1 emits linearly polarized light, which is then polarized by polarizer 2 at a fixed incident angle. Illumination is directed onto the grating structure.

[0079] Control unit 4 is used to adjust the grating period P in the grating structure. In specific engineering implementation:

[0080] 1) Two or more grating layers 3 with different periods P can be set in the device. The control unit 4 is used as a position adjustment mechanism to adjust the position of each grating layer 3 so that the grating layers 3 with different periods P enter the grating structure in turn; that is, by switching different grating layers 3, the grating period P of the grating structure can be adjusted.

[0081] 2) The grating layer 3 adopts a fiber optic grating, and the control unit 4 adjusts the grating period P by means of mechanical stretching (strain) and heating (temperature);

[0082] In addition to the two methods listed above, other feasible grating period control methods can also be applied to this invention.

[0083] The first output port 5 and the second output port 6 are located on the reflected light paths of the grating structures corresponding to different periods P, respectively.

[0084] Working principle:

[0085] According to the grating equation, the grating period P directly determines the diffraction efficiency distribution of each diffraction order, thus affecting the ratio of the reflection coefficients of horizontally polarized to those of vertically polarized diffraction. or As the period P changes, the polarization ratio changes accordingly, causing spin shifts in the left-hand and right-hand circularly polarized components of the reflected light. and The sign or size of the grating changes. Therefore, by adjusting the grating period P, it is possible to achieve a fixed incident angle. This allows for the change of the position of the reflected light path.

[0086] Work process:

[0087] When the control unit 4 sets the grating period P to a first value (0.33λ in this embodiment), the spin displacement of the reflected light... or With a large positive value, the reflected light enters the first output port 5, corresponding to the "on" state of the optical switch.

[0088] When the control unit 4 sets the grating period P to the second value (0.35λ in this embodiment), the spin displacement becomes negative or approaches zero at the same incident angle, and the corresponding reflected light enters the second output port 6, corresponding to the "off" state of the optical switch.

[0089] By adjusting the grating period P as described above, optical path switching between the two output ports can be achieved. This reconfigurable optical switch has advantages such as fast response speed, high extinction ratio, and simple control method, and can be widely used in signal routing, optical interconnection, and reconfigurable optical networks in optical communication systems.

[0090] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0091] This invention is not limited to the above-described embodiments. Any obvious improvements, substitutions, or modifications that can be made by those skilled in the art without departing from the essence of this invention are within the scope of protection of this invention.

Claims

1. A parity-time symmetric grating structure, characterized in that: It includes a capping layer, a grating layer, and a substrate stacked in sequence, wherein: Both the capping layer and the substrate are transparent media; The grating layer consists of ridges and grooves arranged periodically and alternately in the lateral direction; The ridge region is an optical loss material with a complex refractive index of 100%. ; The groove region is an optical gain material with a complex refractive index of 100%. ; In the formula, Let be the real part of the refractive index. is the extinction coefficient.

2. The parity-time symmetric grating structure according to claim 1, characterized in that: The geometric parameters of the grating layer are: The grating period P = 0.34λ, where λ is the operating wavelength; Thickness d = 0.17λ; The duty cycle f ranges from 0.3 to 0.

7.

3. The parity-time symmetric grating structure according to claim 2, characterized in that: The operating wavelength λ is taken to be 1400nm~2200nm, and the real part of the refractive index is... The value ranges from 1 to 3.5, and the extinction coefficient is... The value ranges from 0.1 to 1.

0.

4. The parity-time symmetric grating structure according to claim 2, characterized in that: The operating wavelength λ = 1550 nm, duty cycle f = 0.5, and real part of refractive index. =3, extinction coefficient =0.

46.

5. The parity-time symmetric grating structure according to claim 1, characterized in that: The cover layer and substrate are made of air.

6. A polarization beam splitter, characterized in that: include: The parity-time symmetric grating structure according to any one of claims 1 to 5; The light inlet is located on the incident light path of the grating structure; There are two light outlets, located on the two outgoing light paths of the grating structure.

7. An optical sensor, characterized in that: include: The parity-time symmetric grating structure according to any one of claims 1 to 5 has a cover layer for setting the object to be measured; A light source for irradiating linearly polarized light onto the grating structure at a fixed incident angle; The detector is used to detect the spin displacement of the left-hand and right-hand circularly polarized components in the reflected light.

8. A reconfigurable optical switch, characterized in that: include: The parity-time symmetric grating structure according to any one of claims 1 to 5; A laser (1) and a polarizer (2) are used to irradiate linearly polarized light onto the grating structure at a fixed incident angle; The control unit (4) is used to control the grating period in the grating structure; The first output port (5) and the second output port (6) are located on the reflected light paths corresponding to different grating periods.

9. The reconfigurable optical switch according to claim 8, characterized in that: The system has multiple grating layers (3) with different periods. The control unit (4) changes the grating period by switching the grating layers (3) in the grating structure.

10. The reconfigurable optical switch according to claim 8, characterized in that: The grating structure uses fiber optic grating for the grating layer (3), and the control unit (4) changes the grating period by adjusting the strain or temperature.

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