A non-reciprocal optical transmission device based on optical nonlinearity and PT symmetry principle

Abstract

The application discloses a kind of nonreciprocal light transmission devices based on optical nonlinearity and PT symmetry principle, it is related to nonlinear photonics technical field.The present application includes low refractive index medium interlayer, the low refractive index medium interlayer is respectively provided with first rectangular metal cavity and second rectangular metal cavity at two sides, the inside of the first rectangular metal cavity is embedded with loss medium block, gain medium block is embedded in second rectangular metal cavity, and the gain coefficient of gain medium block is greater than the loss coefficient of loss medium block.The present application does not need any external modulation mechanism, and only by changing the intensity of optical signal, the self-bias modulation of the system is realized, so that a higher forward and reverse transmission ratio is obtained.Secondly, the present application effectively utilizes the unique design principle of PT symmetry, introduces optical gain-loss material, forms a non-hermitian system, which can realize lossless full transmission and directional reflection of light under linear response, and can realize effective nonreciprocal light transmission under nonlinear response.

Description

Technical Field

[0001] The present invention relates to the technical field of nonlinear photonics, and in particular to a non-reciprocal optical transmission device based on optical nonlinearity and PT symmetry principles. Background Art

[0002] Nonreciprocal transmission is a hot area of ​​research in the field of optical transmission properties. It refers to the fact that light waves propagating in nonreciprocal media are no longer constrained by the Lorentz reciprocity theorem, resulting in different forward and reverse propagation properties, potentially enabling unidirectional signal transmission. Nonreciprocal optical transmission devices are essential components in integrated photonic systems and play an essential role in the fabrication of photonic devices such as optical isolators, optical amplifiers, and beam splitters.

[0003] Currently, there are two main approaches to achieving nonreciprocal optical transmission. One is to simulate the surface modes in the quantum Hall effect in nonreciprocal photonic crystals to obtain unidirectional light waves. However, the problem is that isolators designed based on photonic crystal structures are very large and have no significant advantages over commercial devices. The other is to exploit the asymmetric dispersion relationship of light wave modes on the surface of magneto-optical media, such as surface plasmons under magnetic fields, to obtain unidirectional effects. However, most research remains at the theoretical stage. The fundamental problem is that the magnetic field under experimental conditions cannot achieve the distribution and intensity predicted by theoretical calculations. In addition, the loss of magnetic materials can make the unidirectional effect difficult to observe in experiments, making experimental verification difficult. In addition to the aforementioned nonreciprocal elements based on linear effects, the third-order nonlinear effects of materials can also be exploited. However, device design requires the construction of an asymmetric structure and the fine tuning of structural parameters, which poses certain challenges in experimental processing. In addition, there are still certain limitations in terms of insertion loss, bandwidth, and nonreciprocal intensity range. To this end, we propose a nonreciprocal optical transmission device based on optical nonlinearity and PT symmetry principles. Summary of the Invention

[0004] The purpose of the present invention is to provide a non-reciprocal optical transmission device based on optical nonlinearity and PT symmetry principles, which can effectively improve the forward and reverse transmission ratio and achieve non-reciprocal unidirectional optical transmission with higher transmittance.

[0005] To achieve the above objectives, the present invention provides the following technical solutions: a non-reciprocal optical transmission device based on optical nonlinearity and PT symmetry principles, applied to the near-infrared band, comprising a low-refractive-index dielectric interlayer, with a first rectangular metal cavity and a second rectangular metal cavity respectively disposed on either side of the low-refractive-index dielectric interlayer, a loss dielectric block embedded in the first rectangular metal cavity, and a gain dielectric block embedded in the second rectangular metal cavity, wherein the gain coefficient of the gain dielectric block is greater than the loss coefficient of the loss dielectric block, thereby achieving a gain-loss balance state;

[0006] The low-refractive-index medium interlayer, the first rectangular metal cavity and the second rectangular metal cavity are uniformly arranged in a uniform background medium.

[0007] Further, the first rectangular metal cavity and the second rectangular metal cavity are symmetrically arranged along the center of the low-refractive-index medium interlayer.

[0008] Further, the background medium and the low-refractive-index medium interlayer are both made of a low-refractive-index medium material, and the low-refractive-index medium material is air, vacuum or silicon dioxide.

[0009] Further, the first rectangular metal cavity and the second rectangular metal cavity are made of the same material, and are specifically gold or silver.

[0010] Further, the gain medium block and the loss medium block are both made of silicon dioxide, silicon or arsenic trisulfide.

[0011] Further, the first rectangular metal cavity and the second rectangular metal cavity have a thickness of 250-500 nm, and the low-refractive-index medium interlayer has a thickness of 100-200 nm.

[0012] Further, the gain medium block has a relative dielectric constant of 2.2+0.08i, and the loss medium block has a relative dielectric constant of 2.2-0.06i.

[0013] Further, the gain medium block and the loss medium block have the same size, and both have a length of 200-300 nm and a width of 40-60 nm.

[0014] The present application has at least the following advantages:

[0015] Firstly, the present application does not need any external modulation mechanism, such as an external strong magnetic field or a fine design of an asymmetric device structure, and only by changing the intensity of the optical signal, the self-bias modulation of the system is realized, so that a higher forward-to-backward transmission ratio is obtained; secondly, the present application effectively utilizes the unique design principle of PT symmetry, introduces optical gain-loss materials, forms a non-Hermite system, can realize lossless full transmission and directional reflection of light under linear response, and can realize effective non-reciprocal optical transmission under nonlinear response, and has great application prospect in the field of optical communication and optical transmission.

[0016] Of course, any product implementing the present application does not necessarily need to achieve all the advantages described above. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a schematic view of the overall structure of the transmission device of the present application;

[0018] Figure 2Fig. 1 is a schematic view of the overall structure of the transmission device of the present application from the top;

[0019] Figure 3 Fig. 6 is a transmission and reflection spectrum diagram of the present application under linear conditions under forward and backward incidence;

[0020] Figure 4 Fig. 7 is a schematic view of the relationship between the incident light power and the forward and backward transmission rate of the present application under nonlinear conditions when the incident wavelength is 997 nm.

[0021] Reference signs:

[0022] 1, low refractive index medium interlayer; 2, first rectangular metal cavity; 3, second rectangular metal cavity; 4, loss medium block; 5, gain medium block; 6, background medium. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present disclosure will be clearly and completely described below with reference to the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present disclosure.

[0024] The present application designs a metal waveguide device based on the special principle of optical nonlinear effect and parity-time (PT) symmetry, breaks the time reversal symmetry by adjusting the gain / loss coefficient of the medium layer, realizes efficient non-reciprocal transmission of light, and uses the principle to realize the maximum advantage of the non-reciprocal optical transmission device such as optical isolator: without any external modulation mechanism, such as strong magnetic field, dynamic time-space parity modulation, etc., and without fine design of asymmetric structure, only by changing the light signal intensity to realize the self-bias modulation of the system, so as to obtain a higher forward and backward transmission ratio, which has great application prospect in the field of optical communication and optical transmission.

[0025] Please refer to Figure 1 and Figure 2 The present application provides a technical solution: a non-reciprocal optical transmission device based on optical nonlinear and PT symmetry principle, applied to near-infrared waveband, comprising a low refractive index medium interlayer 1, a first rectangular metal cavity 2 and a second rectangular metal cavity 3 are arranged on both sides of the low refractive index medium interlayer 1, a loss medium block 4 is embedded in the inside of the first rectangular metal cavity 2, a gain medium block 5 is embedded in the second rectangular metal cavity 3, the gain coefficient of the gain medium block 5 is greater than the loss coefficient of the loss medium block 4, and is used to form a gain-loss balance state;

[0026] The low refractive index medium interlayer 1, the first rectangular metal cavity 2 and the second rectangular metal cavity 3 are uniformly arranged in the uniform background medium 6.

[0027] According to the technical solution of this embodiment, the first rectangular metal cavity 2 and the second rectangular metal cavity 3 are arranged in mirror symmetry along the center of the low-refractive-index medium interlayer 1. The first rectangular metal cavity 2 and the second rectangular metal cavity 3 are made of the same material, specifically gold or silver. This embodiment does not make any specific restrictions on this, and can be selected according to actual conditions.

[0028] Furthermore, the thickness of the first rectangular metal cavity 2 and the second rectangular metal cavity 3 is set to 250 nm, the thickness of the low refractive index medium interlayer 1 is set to 100 nm, and the thickness of the metal cavity is preferably about 2.5 times the thickness of the low refractive index medium interlayer.

[0029] With respect to the technical solution of this embodiment, the background medium 6 and the low-refractive-index medium interlayer 1 are both made of low-refractive-index medium materials. The low-refractive-index medium materials are set to air, vacuum or silica. The low-refractive-index medium interlayer 1 can be set to any one of air, vacuum or silica. This embodiment does not make specific restrictions on this and can be selected according to actual conditions.

[0030] According to the technical solution of this embodiment, the materials of the gain medium block 5 and the loss medium block 4 are both set to silicon dioxide, silicon or arsenic trisulfide. Since they are doped with different quantum dots, they will exhibit different gain and loss characteristics under the irradiation of the pump laser.

[0031] Furthermore, in order to compensate for the large ohmic loss of metal in the near-infrared band, the gain coefficient of the gain dielectric block 5 needs to be slightly larger than the loss coefficient of the loss dielectric block 4. The relative dielectric constant of the gain dielectric block 5 is 2.2+0.08i, and the relative dielectric constant of the loss dielectric block 4 is 2.2-0.06i, where i is an imaginary unit. The third-order nonlinear polarization rate of the dielectric block is 4.4*10 -20 m 2 / V 2 .

[0032] Furthermore, the gain dielectric block 5 and the loss dielectric block 4 have the same size, with a length of 200 nm and a width of 40 nm. Preferably, the length is about 5 times the width.

[0033] Next, the embodiments of the present invention are described in further detail:

[0034] In this embodiment, the first rectangular metal cavity 2 and the second rectangular metal cavity 3 are made of precious metal silver, the low refractive index dielectric interlayer 1 and the background dielectric 6 are both made of air, the gain dielectric block 5 is made of silicon dioxide, and its relative dielectric constant is 2.2+0.08i, and the loss dielectric block 4 is made of silicon dioxide, and its relative dielectric constant is 2.2-0.06i, where i is an imaginary unit. The third-order nonlinear polarizability of the gain dielectric block 5 and the loss dielectric block 4 is both 4.4*10 -20 m 2 / V 2 .

[0035] This embodiment implements non-reciprocal optical transmission based on optical nonlinearity and PT symmetry principles, and includes two steps:

[0036] Step 1: Optimize the structure size by using the PT symmetry principle and the linear response of the device:

[0037] In order to compensate for the large ohmic loss of precious metals in the visible and near-infrared bands, the gain coefficient of the gain medium block 5 needs to be slightly larger than the loss coefficient of the loss medium block 4, forming a non-Hermitian system so that the entire system reaches a gain-loss balance state; when the incident light power is low (less than 0.1 MW / cm 2 ), the system is in the linear response stage, at this time the forward and reverse transmittances of the non-reciprocal optical transmission device are the same, and the forward and reverse reflectances are different; Figure 3 As shown in the figure, when the incident light wavelength is the resonant wavelength of 997nm, the forward and reverse transmittances are both 1, the forward reflectivity is 12, and the reverse reflectivity is 0.0001, achieving lossless full transmission and directional reflection of light;

[0038] Step 2: Utilize the nonlinear response of the device to achieve optical nonreciprocity:

[0039] When the incident light power is high (greater than 0.1 MW / cm 2 ), the system is in the nonlinear response stage, and the third-order Kerr nonlinear effect of the gain medium block 5 and the loss medium block 4 is excited, resulting in changes in the transmission mode under forward and reverse incidence; Figure 4 The graph shows the relationship between the incident light power and the forward and reverse transmittance of this embodiment under nonlinear conditions when the incident wavelength is 997nm. in =40MW / cm 2 The forward transmittance is 0.8 and the reverse transmittance is 0.3, achieving effective non-reciprocal unidirectional light transmission.

[0040] The working wavelength of this embodiment is the near infrared band. Figure 3 It can be seen.

[0041] The optimized structural dimensions of the non-reciprocal optical transmission device based on optical nonlinearity and PT symmetry principles are as follows: the thickness of the first rectangular metal cavity 2 and the second rectangular metal cavity 3 is a = 250 nm, the length is l = 400 nm, and the width is w = 400 nm. The thickness of the low-refractive-index medium interlayer 1 is b = 100 nm. The gain medium block 5 and the loss medium block 4 have the same size, with a length of l1 = 200 nm and a width of w1 = 40 nm.

[0042] In this embodiment, the forward and reverse transmission ratio of the non-reciprocal optical transmission device based on the optical nonlinearity and PT symmetry principle can be adjusted as the incident light power changes, such as Figure 4 As shown, when the incident light power I in In the range of 10-100 MW / cm 2 Effective non-reciprocal optical transmission can be achieved within the range.

[0043] In summary, the present invention achieves self-bias modulation of the system by simply changing the intensity of the optical signal without any external modulation mechanism, thereby obtaining a higher forward and reverse transmission ratio. Secondly, the present invention effectively utilizes the unique design principle of PT symmetry, introduces optical gain-loss materials, and forms a non-Hermitian system. It can achieve lossless full transmission and directional reflection of light under linear response, and effective non-reciprocal optical transmission under nonlinear response. It has great application prospects in the field of optical communication and optical transmission.

[0044] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0045] For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances. When an element is referred to as being "assembled on", "installed on", "fixed on" or "set on" another element, it can be directly on the other element or there can be a central element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there can be a central element at the same time. The terms "vertical", "horizontal", "up", "down", "left", "right" and similar expressions used herein are for illustrative purposes only and are not intended to be the only embodiment.

[0046] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

[0047] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that a specific feature, structure, material, or characteristic described in conjunction with that embodiment or example is included in at least one embodiment or example of the present disclosure. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

Claims

1. A non-reciprocal optical transmission device based on optical nonlinearity and PT symmetry principle, applied to the near-infrared band, comprising a low-refractive-index medium interlayer (1), characterized in that: A first rectangular metal cavity (2) and a second rectangular metal cavity (3) are respectively provided on both sides of the low-refractive-index dielectric interlayer (1); a loss dielectric block (4) is embedded in the interior of the first rectangular metal cavity (2); a gain dielectric block (5) is embedded in the interior of the second rectangular metal cavity (3); the gain coefficient of the gain dielectric block (5) is greater than the loss coefficient of the loss dielectric block (4), and is used to form a gain-loss balance state; The low-refractive-index medium interlayer (1), the first rectangular metal cavity (2), and the second rectangular metal cavity (3) are uniformly arranged in a uniform background medium (6); The first rectangular metal cavity (2) and the second rectangular metal cavity (3) are arranged in a mirror-symmetrical manner along the center of the low-refractive-index medium interlayer (1); The background medium (6) and the low-refractive-index medium interlayer (1) are both made of low-refractive-index medium materials, and the low-refractive-index medium materials are set to be air, vacuum or silicon dioxide.

2. The non-reciprocal optical transmission device based on optical nonlinearity and PT symmetry principle according to claim 1, characterized in that: The first rectangular metal cavity (2) and the second rectangular metal cavity (3) are made of the same material, specifically gold or silver.

3. The non-reciprocal optical transmission device based on optical nonlinearity and PT symmetry principle according to claim 2, characterized in that: The materials of the gain medium block (5) and the loss medium block (4) are both set to silicon dioxide, silicon or arsenic trisulfide.

4. The non-reciprocal optical transmission device based on optical nonlinearity and PT symmetry principle according to claim 3, characterized in that: The thickness of the first rectangular metal cavity (2) and the second rectangular metal cavity (3) is set to 250-500 nm, and the thickness of the low-refractive-index medium interlayer (1) is set to 100-200 nm.

5. The non-reciprocal optical transmission device based on optical nonlinearity and PT symmetry principle according to claim 4, characterized in that: The relative dielectric constant of the gain dielectric block (5) is 2.2+0.08i, and the relative dielectric constant of the loss dielectric block (4) is 2.2-0.06i.

6. The non-reciprocal optical transmission device based on optical nonlinearity and PT symmetry principle according to claim 5, characterized in that: The gain medium block (5) and the loss medium block (4) have the same size, with a length of 200-300 nm and a width of 40-60 nm.

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