Non-reciprocal light transmission device based on optical nonlinearity and PT symmetry principle

Abstract

The invention discloses a non-reciprocal light transmission device based on optical nonlinearity and PT symmetry principles, and relates to the technical field of nonlinear photonics. The low-refractive-index broadband low-pass filter comprises a low-refractive-index dielectric interlayer, a first rectangular metal cavity and a second rectangular metal cavity are formed in the two sides of the low-refractive-index dielectric interlayer respectively, a loss dielectric block is embedded in the first rectangular metal cavity, and a gain dielectric block is embedded in the second rectangular metal cavity. The gain coefficient of the gain medium block is greater than the loss coefficient of the loss medium block. According to the invention, the self-bias modulation of the system is realized only by changing the intensity of an optical signal without any external modulation mechanism, so that a relatively high forward and reverse transmission ratio is obtained; secondly, the unique design principle of PT symmetry is effectively utilized, an optical gain-loss material is introduced, a non-Hermite system is formed, lossless total transmission and directional reflection of light can be achieved under linear response, and effective non-reciprocal light transmission can be achieved 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] In terms of the transmission characteristics of light, non-reciprocal transmission is one of the hottest research areas today. It means that the propagation of light waves in non-reciprocal media is no longer restricted by the Lorentz reciprocity theorem, making its forward and reverse propagation properties different, and it is expected to achieve unidirectional transmission of signals. Non-reciprocal optical transmission devices are indispensable components in integrated photonic systems and play an indispensable and important role in the preparation of photonic devices such as optical isolators, optical amplifiers, and beam splitters.

[0003] At present, there are two main methods to achieve nonreciprocal optical transmission: one is to analogize the surface mode in the quantum Hall effect in a nonreciprocal photonic crystal to obtain a unidirectional light wave. The problem is that the isolator designed based on the photonic crystal structure is very large and has no outstanding advantages over commercial devices; the other is to use the asymmetric dispersion relationship of the light wave mode on the surface of the magneto-optical medium to obtain a unidirectional effect, such as surface plasma under a magnetic field, but most of the research remains in the theoretical stage. The fundamental problem is that the magnetic field under experimental conditions cannot reach the distribution shape and intensity in the theoretical calculation. In addition, the loss of magnetic materials may make it difficult to observe its unidirectional effect in the experiment, so it is difficult to verify experimentally; in addition to the above-mentioned nonreciprocal elements based on linear effects, the third-order nonlinear effect of the material can also be used to achieve it, but the device design requires the construction of an asymmetric structure and the fine adjustment of the structural parameters, which poses certain challenges to experimental processing. In addition, there are still certain limitations in terms of insertion loss, bandwidth, and nonreciprocal intensity range. For this reason, 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 light transmission device based on optical nonlinearity and PT symmetry principle, which can effectively improve the forward and reverse transmission ratio and realize non-reciprocal unidirectional light transmission with higher transmittance.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solutions: 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, a first rectangular metal cavity and a second rectangular metal cavity are respectively arranged on both sides of the low-refractive index medium interlayer, a loss medium block is embedded in the first rectangular metal cavity, a gain medium block is embedded in the second rectangular metal cavity, the gain coefficient of the gain medium block is greater than the loss coefficient of the loss medium block, and is used to form 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] Furthermore, the first rectangular metal cavity and the second rectangular metal cavity are arranged in a mirror-symmetrical manner along the center of the low-refractive index medium interlayer.

[0008] Furthermore, the background medium and the low-refractive-index medium interlayer 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.

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

[0010] Furthermore, the materials of the gain medium block and the loss medium block are both set to be silicon dioxide, silicon or arsenic trisulfide.

[0011] Furthermore, the thickness of the first rectangular metal cavity and the second rectangular metal cavity is set to 250-500 nm, and the thickness of the low refractive index medium interlayer is set to 100-200 nm.

[0012] Furthermore, the relative dielectric constant of the gain dielectric block is 2.2+0.08i, and the relative dielectric constant of the loss dielectric block is 2.2-0.06i.

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

[0014] The present invention has at least the following beneficial effects:

[0015] Firstly, the present invention does not require any external modulation mechanism, such as no external strong magnetic field, and no elaborate design of asymmetric device structure. It only realizes self-bias modulation of the system by changing the intensity of the optical signal, 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, which can realize lossless total transmission and directional reflection of light under linear response, and realize effective non-reciprocal optical transmission under nonlinear response. It has great application prospects in the field of optical communication and optical transmission.

[0016] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a three-dimensional schematic diagram of the overall structure of the transmission device of the present invention;

[0018] Figure 2It is a schematic top view of the overall structure of the transmission device of the present invention;

[0019] Figure 3 The transmission and reflection spectra of the present invention under linear conditions under forward and reverse incidence;

[0020] Figure 4 It is a schematic diagram of the relationship between the incident light power and the forward and reverse transmittance of the present invention under nonlinear conditions when the incident wavelength is 997nm.

[0021] Reference numerals:

[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 following will be combined with the drawings in the embodiments of the present disclosure to clearly and completely describe the technical solutions 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 ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0024] The present invention designs a metal waveguide device based on the special principle of parity-time (PT) symmetry based on optical nonlinear effects. By adjusting the gain / loss coefficient of the dielectric layer, the time reversal symmetry is broken to achieve efficient non-reciprocal transmission of light. The biggest advantage of using this principle to realize non-reciprocal optical transmission devices such as optical isolators is that no external modulation mechanism is required, such as strong magnetic fields, dynamic time-space parity modulation, etc., and there is no need to finely design an asymmetric structure. The self-bias modulation of the system is achieved only by changing the intensity of the optical signal, thereby obtaining a higher forward and reverse transmission ratio. It has great application prospects in the field of optical communication and optical transmission.

[0025] See also Figure 1 and Figure 2 As shown, the present invention provides a technical solution: a non-reciprocal optical transmission device based on optical nonlinearity and PT symmetry principle, applied to near-infrared band, comprising a low-refractive index medium interlayer 1, a first rectangular metal cavity 2 and a second rectangular metal cavity 3 are respectively arranged on both sides of the low-refractive index medium interlayer 1, a loss medium block 4 is embedded in 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 limitation on this, and it 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, and the low-refractive index medium materials are set to be air, vacuum or silicon dioxide. The low-refractive index medium interlayer 1 can be set to be any one of air, vacuum or silicon dioxide. This embodiment does not make specific limitations 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 show 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 medium block 5 needs to be slightly larger than the loss coefficient of the loss medium block 4. The relative dielectric constant of the gain medium block 5 is 2.2+0.08i, and the relative dielectric constant of the loss medium block 4 is 2.2-0.06i, where i is an imaginary unit. The third-order nonlinear polarization rate of the medium block is 4.4*10 -20 m 2 / V 2 .

[0032] Furthermore, the gain medium block 5 and the loss medium 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 medium 6 are made of air, the gain dielectric block 5 is silicon dioxide, and its relative dielectric constant is 2.2+0.08i, the loss dielectric block 4 is silicon dioxide, and its relative dielectric constant is 2.2-0.06i, where i is an imaginary unit, and the third-order nonlinear polarizability of the gain dielectric block 5 and the loss dielectric block 4 is 4.4*10 -20 m 2 / V 2 .

[0035] This embodiment implements non-reciprocal optical transmission based on optical nonlinearity and PT symmetry principle, including 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 light 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 to form 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, when the incident light wavelength is the resonance 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 total transmission and directional reflection of light;

[0038] Step 2: Use 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 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 principle are as follows: the thickness of the first rectangular metal cavity 2 and the second rectangular metal cavity 3 is a=250nm, the length is l=400nm, the width is w=400nm, the thickness of the low refractive index medium interlayer 1 is b=100nm, the gain medium block 5 and the loss medium block 4 are the same size, with a length of l1=200nm and a width of w1=40nm.

[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. 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 does not require any external modulation mechanism and only realizes the self-bias modulation of the system by changing the intensity of the optical signal, 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, which can not only realize lossless total transmission and directional reflection of light under linear response, but also realize effective non-reciprocal optical transmission under nonlinear response, and has great application prospects in the field of optical communication and optical transmission.

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

[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 also be a centered element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be a centered element at the same time. The terms "vertical", "horizontal", "up", "down", "left", "right" and similar expressions used herein are only for illustrative purposes and are not intended to be the only implementation method.

[0046] Although 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 the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

[0047] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

Claims

1. A non-reciprocal optical transmission device based on optical nonlinearity and PT symmetry principle, applied to 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 arranged on both sides of the low refractive index dielectric interlayer (1); a loss dielectric block (4) is embedded in the first rectangular metal cavity (2); a gain dielectric block (5) is embedded in 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), so as 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).

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 arranged in a mirror-symmetrical manner along the center of the low-refractive index medium interlayer (1).

3. The non-reciprocal optical transmission device based on optical nonlinearity and PT symmetry principle according to claim 2, characterized in that: 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.

4. The non-reciprocal optical transmission device based on optical nonlinearity and PT symmetry principle according to claim 2, 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.

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

6. The non-reciprocal optical transmission device based on optical nonlinearity and PT symmetry principle according to claim 5, 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.

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

8. The non-reciprocal optical transmission device based on optical nonlinearity and PT symmetry principle according to claim 7, 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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