An optical encoding method based on optical devices with different SHG responses

Abstract

This invention provides an optical encoding method based on optical devices with different SHG responses. The optical encoding device has distinguishable SHG intensities in three different excitation light polarization directions. The method includes the following steps: establishing an encoding mapping relationship, mapping the SHG intensity states corresponding to the three different excitation light polarization directions to multiple symbol states in a multi-level encoding; acquiring the information to be encoded, converting the information to be encoded into a symbol sequence composed of the symbol states; and sequentially illuminating the optical encoding device with the corresponding excitation light polarization directions according to the symbol sequence to generate an SHG signal carrying the encoded information. This invention utilizes a designed Me-PTCDI / 3R-MoS2 heterojunction with a strong SHG response and a simple polarization encoding method, requiring no complex external control devices, thus meeting the application requirements of flexible, miniature nonlinear optical devices.

Description

Technical Field

[0001] This invention relates to the field of nonlinear optical devices and optical information encoding technology, and specifically to an optical encoding method based on optical devices with different SHG responses. Background Technology

[0002] Second harmonic generation (SHG) is a typical second-order nonlinear optical phenomenon, essentially the generation of frequency-doubled photons after two beams of photons with the same frequency are coupled through a nonlinear medium. SHG is extremely sensitive to the lattice symmetry of materials, and can only be generated in non-centrosymmetric crystal structures. Moreover, its intensity exhibits a specific anisotropic distribution with the polarization angle of the incident light. This polarization-dependent characteristic makes it of significant application value in fields such as crystal orientation analysis, biological microscopic imaging, and nonlinear optical coding.

[0003] In recent years, photodetectors based on two-dimensional material heterojunctions have also made progress in the field of communication encryption. For example, Chinese patent CN119450252B discloses a method for communication encryption based on a two-dimensional inorganic / inorganic van der Waals heterojunction polarization photodetector. This method constructs a type II heterostructure of ReS2 and MoSe2, utilizes the in-plane anisotropy of ReS2 to achieve a response to polarized light, and establishes an encryption key based on the difference in photocurrent at different polarization angles. However, this technical solution still has the following shortcomings: First, this solution relies on photocurrent intensity as the encoding carrier, but the photocurrent of the photodetector is easily affected by factors such as ambient light fluctuations, device dark current drift, and temperature changes, making it difficult to guarantee the long-term stability and repeatability of the encoded state; Second, the device is an inorganic / inorganic heterostructure, and its polarization response originates from the in-plane anisotropy of ReS2 itself. The polarization sensitivity is limited by the intrinsic properties of the material, making it difficult to effectively control and enhance through interface engineering; Third, this solution can only achieve three-state differentiation of current amplitude, resulting in limited encoding capacity and difficulty in meeting the needs of higher-density information encoding.

[0004] Although organic / inorganic heterojunctions have been extensively studied in fields such as photodetectors, their application in enhancing SHG response and polarization coding remains limited. N,N'-dimethyl-3,4,9,10-perylenetetracarboxydiimide (Me-PTCDI) molecules exhibit a tendency for non-centrosymmetric arrangement and significant intramolecular charge transfer characteristics. Its localized Frenkel excitons possess strong oscillator strength, and efficient charge or energy transfer exists at the organic / inorganic interface, potentially leading to synergistic gains in the nonlinear optical response of the inorganic layer. Previous studies have shown that Me-PTCDI / WS2 heterojunctions can achieve a 124-fold enhancement in photoluminescence through resonant energy transfer, and the MoS2 / PTCDA system has also confirmed the epitaxial growth-promoting effect of organic molecules on inorganic surfaces, indicating a non-superimposed synergistic effect at the organic / inorganic interface. When Me-PTCDI is combined with 3R-MoS2, which also has a non-centrosymmetric structure, it is expected to break the symmetry limitations of a single component through synergistic modulation of interfacial charge transfer and molecular orientation ordering, endowing the heterojunction with unique polarization response characteristics. However, the SHG polarization characteristics of the Me-PTCDI / 3R-MoS2 heterostructure and its feasibility in optical coding have not yet been reported.

[0005] Therefore, developing an optical device based on the Me-PTCDI / 3R-MoS2 organic / inorganic heterojunction and utilizing the intensity difference of SHG signals in different polarization directions to achieve simple encoding is of great theoretical significance and practical application value. This would solve the problems of weak response intensity, single encoding dimension, and complex fabrication process in existing SHG encoding schemes.

[0006] Therefore, this invention proposes an optical encoding method based on optical devices with different SHG responses. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned shortcomings and provide an optical encoding method based on optical devices with different SHG responses.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: an optical encoding method based on optical devices with different SHG responses, wherein the optical encoding device has distinguishable SHG intensities in three different excitation light polarization directions; comprising the following method steps: Establish an encoding mapping relationship to map the SHG intensity states corresponding to the three different excitation light polarization directions to multiple symbol states in a multi-level encoding. Obtain the information to be encoded, and convert the information to be encoded into a symbol sequence composed of the symbol states; According to the symbol sequence, the optical encoding device is sequentially illuminated with the corresponding excitation light polarization direction to generate an SHG signal carrying encoded information.

[0009] Furthermore, the multi-base encoding is ternary encoding, and the specific operation process includes: Three excitation light polarization directions with distinguishable differences in SHG intensity are selected from the polarization-dependent SHG response curve of the optical encoding device, corresponding to ternary symbol states 0, 1, and 2, respectively. Establish a character mapping table, using 27 combinations of three-digit ternary numbers to cover the 26 English letters and at least one control character; The information to be transmitted is split into characters, and each character is converted into a corresponding three-digit ternary code element combination according to the character mapping table, and arranged in the transmission time sequence to form a ternary code element sequence. According to the timing of the ternary symbol sequence, the polarization direction of the excitation light is switched sequentially to the polarization direction corresponding to the current symbol state, so that the excitation light with the corresponding polarization direction illuminates the optical encoding device in time slots to complete the optical transmission of information.

[0010] Furthermore, the multi-base encoding is quaternary encoding, and the specific operation process includes: In the polarization-dependent SHG response curve of the optical encoding device, three excitation light polarization directions with distinguishable differences in SHG intensity are selected, corresponding to quaternary encoding states 1, 2, and 3 respectively. At the same time, the no-light input state is corresponding to encoding state 0, and a quaternary mapping relationship is established. The information to be transmitted is split into characters, and a quaternary strength state is assigned to each character according to the preset mapping rules; According to the timing sequence of the quaternary intensity states, the polarization direction of the excitation light is switched or the light source is turned off in sequence, so that the optical encoding device is illuminated in the corresponding state according to the time slot, thereby completing the optical transmission of information.

[0011] Furthermore, the preset mapping rules include: Each character is converted into a Morse sequence consisting of dotted symbols, dashed symbols, and spacers according to the Morse coding rules. In the timing coding process, the dot symbol is represented as a light signal continuously outputting the assigned intensity state within a unit time slot, the slash symbol is represented as a light signal continuously outputting the same intensity state within two consecutive unit time slots, and the interval symbol is represented as an output no-light state.

[0012] Furthermore, encryption steps are also included: Before splitting the information to be transmitted into characters, the characters in the information to be transmitted are scrambled and recombined according to a preset character substitution rule to generate an encrypted character sequence. The character substitution rule is pre-agreed upon by both the sending and receiving ends as an encryption key; During decoding, the receiving end reverses the encrypted character sequence obtained from demodulation according to the character substitution rules to restore the original information.

[0013] Furthermore, the character replacement rule is specifically as follows: The characters in the information to be transmitted are divided into three character groups according to preset rules. Each group corresponds to a different SHG strength level, and each character in the same group is assigned the same strength state. During cross-group permutation, the relative order of characters within each strength group remains unchanged during the permutation process. The characters in each strength group are interleaved and inserted, so that the characters of different strength groups are staggered in the arrangement, thereby forming the encrypted character sequence.

[0014] Furthermore, the optical coding device includes a substrate and a heterojunction structure formed on the substrate. The heterojunction structure is composed of a two-dimensional inorganic material layer and an organic molecular functional layer. The two-dimensional inorganic material layer is prepared by chemical vapor deposition, and the organic molecular functional layer is grown on the two-dimensional inorganic material layer by epitaxial growth.

[0015] Furthermore, the two-dimensional inorganic material layer is a uniform, wrinkle-free 3R-MoS2 layer, and the number of layers in the two-dimensional inorganic material layer is 2 to 3. The organic molecular functional layer is N,N'-dimethyl-3,4,9,10-perylenetetracarboxydiimide, and the number of layers in the organic molecular functional layer is a single layer.

[0016] Furthermore, the thickness of the two-dimensional inorganic material layer is 0.5 nm to 10 nm, and the thickness of the organic molecular functional layer is 0.5 nm to 5 nm.

[0017] Compared with the prior art, the present invention has the following beneficial effects: 1. This application is the first to discover and utilize the SHG polarization response distortion phenomenon of the Me-PTCDI / 3R-MoS2 heterojunction. The original six-fold symmetrical SHG distribution with the same intensity in each direction is distorted into an asymmetric distribution with different intensity in three directions. Based on this phenomenon, ternary or even quaternary optical encoding can be realized. The encoding state is clear, no complex external field control is required, and physical layer encryption capability is provided, providing a brand-new device solution for optical encrypted communication.

[0018] 2. Both encoding schemes provided in this application have physical layer encryption capabilities; in the ternary scheme, the mapping relationship between polarization direction and encoding state constitutes the encryption key; in the quaternary scheme, based on the polarization-intensity mapping key, character substitution rules and Morse time slot encoding rules are further superimposed to form a triple encryption mechanism; if an unauthorized receiver does not know all of the above keys at the same time, even if the SHG signal is detected, the information cannot be demodulated correctly, which significantly improves the security of the communication system.

[0019] 3. Because the Me-PTCDI / 3R-MoS2 heterojunction designed in this application has a strong SHG response and a simple polarization encoding method, it does not require complex external control devices and can meet the application requirements of flexible, miniature nonlinear optical devices. The switching speed of the excitation light polarization direction is only limited by the response speed of the electro-optic modulator, giving the encoded transmission of this scheme the potential for high-speed information communication. Attached Figure Description

[0020] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram of a single-layer Me-PTCDI / few-layer 3R-MoS2 heterojunction structure and its principle; Figure 2 This is a 100x optical microscope image of the Me-PTCDI / bilayer 3R-MoS2 heterojunction prepared in Example 1; Figure 3 This is the SHG peak diagram of the Me-PTCDI / double-layer 3R-MoS2 heterojunction; Figure 4 This is the SHG power dependence plot of the Me-PTCDI / double-layer 3R-MoS2 heterojunction; Figure 5 This is the SHG polarization response diagram of the Me-PTCDI / double-layer 3R-MoS2 heterojunction; Figure 6 It is a ternary symbol mapping table; Figure 7 It is a ternary encrypted signal diagram; Figure 8 This is the SHG polarization response diagram of the Me-PTCDI / trilayer 3R-MoS2 heterojunction prepared in Example 2; Figure 9 It is a Morse code rule diagram; Figure 10 This is a diagram of a quaternary encrypted signal and its result. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1: This example discloses a method for fabricating a two-dimensional organic / inorganic heterojunction optical coding device with SHG response. The specific fabrication steps are as follows: Step 1) Purchase a commercially available 3R-MoS2 thin film grown on a sapphire substrate by chemical vapor deposition. Confirm that the 3R-MoS2 is a bilayer with a uniform and wrinkle-free surface using optical and atomic force microscopy.

[0023] Step 2) Place the organic source material Me-PTCDI in the center of the tube furnace, and place the 3R-MoS2 substrate obtained in the previous step on one side of the organic source material. Evacuate the chamber and control the heating temperature and time under an inert atmosphere. After epitaxially growing a single layer of organic small molecule material crystals on the bilayer 3R-MoS2, the device fabrication is complete. The epitaxial growth process allows for precise control of temperature and argon flow rate, enabling the monolayer organic molecules to arrange themselves orderly on the 3R-MoS2 surface. This enhances intermolecular synergy, reduces interface defects and scattering, and improves the stability of the SHG signal.

[0024] Structural characterization and performance testing: Figure 1 This is a schematic diagram of a single-layer Me-PTCDI / few-layer 3R-MoS2 heterojunction structure and its principle.

[0025] Figure 2 Optical microscope image of the Me-PTCDI / bilayer 3R-MoS2 heterojunction prepared for this embodiment.

[0026] Figure 3 The image shows the SHG peak position diagram of the heterojunction region. A sharp SHG signal (approximately 1 nm FWHM) was detected at 532 nm using 1064 nm laser excitation, confirming the generation of the SHG process.

[0027] Figure 4 The curve shows that the SHG signal intensity increases linearly with the square of the incident laser power, verifying the second-order nonlinear nature of the SHG signal.

[0028] Figure 5The image shows the SHG polarization response of the Me-PTCDI / double-layer 3R-MoS2 heterojunction. The sixfold symmetry is broken, and the SHG intensities are significantly different in three directions at approximately 30°, 90°, and 150° (the measured intensity ratio is approximately 0.59:1:0.35). The intensities are even lower in the other directions, exhibiting an asymmetric polarization distribution.

[0029] Encoding applications: Based on the above polarization response characteristics, this embodiment further provides a specific implementation scheme for ternary optical encoding using the Me-PTCDI / double-layer 3R-MoS2 device.

[0030] In this embodiment, three excitation light polarization directions with distinguishable differences in SHG intensity are selected from the polarization-dependent SHG response curve of the device as the encoding polarization directions, and a ternary symbol mapping relationship is established: when the polarization angle is approximately 90°, the normalized SHG intensity value is 1.00, corresponding to ternary symbol state "2"; when the polarization angle is approximately 30°, the normalized SHG intensity value is 0.59, corresponding to ternary symbol state "1"; and when the polarization angle is approximately 150°, the normalized SHG intensity value is 0.35, corresponding to ternary symbol state "0". The intensity differences between the above three polarization excitation states are 0.41 and 0.24, respectively, both greater than the minimum resolution threshold of conventional spectral testing systems, enabling error-free symbol differentiation. Figure 6 The character mapping table shown converts each character into its corresponding ternary symbol combination.

[0031] like Figure 7 As shown, a specific example of encrypted transmission illustrates the following: During the encoding stage, the sending end obtains the PASSWORD information to be transmitted. After splitting it by character, it looks up the corresponding values ​​in a table: P corresponds to 121, A to 001, S to 201, W to 212, O to 120, R to 200, and D to 011. The ternary code elements of each character are then concatenated sequentially according to the transmission time order to form the ternary code element sequence 121001201201212120200011.

[0032] Subsequently, according to the timing of the ternary symbol sequence, the polarization direction of the excitation light is adjusted by rotating a half-wave plate or an electro-optic modulator, switching the polarization angle to the angle corresponding to the current symbol: when writing symbol "2", the polarization direction is adjusted to approximately 90°; when writing symbol "1", it is adjusted to approximately 30°; and when writing symbol "0", it is adjusted to approximately 150°. Each symbol state occupies an independent time slot, and the corresponding polarized light is used to illuminate the nonlinear device to complete the writing of single symbol information. By continuously switching the polarization angle of the excitation light in the time dimension, the optical timing transmission of multi-symbol, multi-character information can be completed.

[0033] During encoding and reading, the SHG signal generated by the device under polarized light excitation is separated from the fundamental frequency excitation light by a dichroic mirror. The SHG intensity value of each time slot is collected and recorded by a spectral testing system. The measured intensity is compared with a preset intensity threshold to determine the ternary symbol state of each time slot. The specific determination logic is as follows: the strongest SHG signal is obtained by excitation at a polarization angle of 90°, which is decoded as "2"; the medium SHG signal is obtained by excitation at a polarization angle of 30°, which is decoded as "1"; and the weakest SHG signal is obtained by excitation at a polarization angle of 150°, which is decoded as "0". All time slots are demodulated sequentially to obtain the ternary symbol sequence. The original plaintext PASSWORD can be recovered by looking up the character mapping table in groups of 3 symbols.

[0034] This embodiment uses ternary symbols to directly represent information. Each character corresponds to three fixed ternary symbols, fully covering the 26 English letters and one spacer control character. The encoding efficiency is better than the binary scheme, and the decoding process is simple and clear, making it suitable for high-speed optical communication scenarios.

[0035] Example 2: This example discloses a method for fabricating a two-dimensional organic / inorganic heterojunction optical coding device with SHG response. The difference from Example 1 is that a three-layer 3R-MoS2 substrate is used. The specific fabrication steps are as follows: Step 1) Purchase a commercially available 3R-MoS2 thin film grown on a sapphire substrate by chemical vapor deposition. Confirm that the 3R-MoS2 film consists of three layers (approximately 2.2 nm thick) with a uniform and wrinkle-free surface using optical and atomic force microscopy.

[0036] Step 2) The epitaxial growth process is the same as step 2 in Example 1: The organic source material Me-PTCDI is placed in the center of a tube furnace, and the 3R-MoS2 substrate is placed on one side of the organic source material. The chamber is evacuated, and the heating temperature and time are controlled under an inert atmosphere. After epitaxially growing a single layer of organic small molecule material crystal on the three layers of 3R-MoS2, the device fabrication is complete. The epitaxial growth process allows for precise control of temperature and argon flow rate, enabling the single layer of organic molecules to arrange themselves orderly on the 3R-MoS2 surface, enhancing intermolecular synergy, reducing interface defects and scattering, and improving the stability of the SHG signal.

[0037] Structural characterization and performance testing: Figure 8 The image shows the SHG polarization response of the Me-PTCDI / trilayer 3R-MoS2 heterojunction prepared in this embodiment. Consistent with the results of Example 1, the single trilayer 3R-MoS2 still exhibits a six-fold symmetric equal-intensity distribution, while the SHG intensities of the heterojunction differ significantly in three different polarization directions. This indicates that the non-six-fold symmetric polarization distortion characteristic also exists in the multilayer system. These results demonstrate that the polarization distortion phenomenon of the Me-PTCDI / 3R-MoS2 heterojunction is thickness-invariant and not limited to a specific number of 3R-MoS2 layers.

[0038] Encoding applications: Based on the above polarization response characteristics, this embodiment further provides a specific implementation scheme for quaternary optical encoding using the Me-PTCDI / trilayer 3R-MoS2 device.

[0039] Based on the polarization response characteristics of devices, this scheme proposes a time-encrypted SHG polarization optical communication coding implementation plan. It redefines the mapping rules between polarization angle and SHG encoding, and introduces a character substitution encryption mechanism and Morse time-slot coding to achieve encrypted transmission of physical layer information. In this embodiment, the preset mapping rules employ a combination of Morse coding and time-slot coding.

[0040] The three polarization directions were sorted from high to low SHG intensity, and an encoding mapping relationship was established: when the polarization angle was approximately 90°, the normalized SHG intensity value was 1.00, corresponding to encoding state "3"; when the polarization angle was approximately 150°, the normalized SHG intensity value was 0.64, corresponding to encoding state "2"; when the polarization angle was approximately 30°, the normalized SHG intensity value was 0.34, corresponding to encoding state "1"; and the state with no light input was encoded as "0". The intensity differences between the above three polarization excitation states were 0.36 and 0.30, respectively, both greater than the minimum resolution threshold of conventional spectral testing systems. The 0-state with no light background had extremely high distinguishability from the three photoinduced signal intensities, enabling error-free signal differentiation.

[0041] During the encoding and writing phase, the sending end first performs character substitution encryption: each character in the original information is assigned to three groups of strength levels, from high to low, based on its total slot length in the Morse code. Characters with shorter total slot lengths are assigned to the high-strength group, characters with intermediate total slot lengths are assigned to the medium-strength group, and characters with longer total slot lengths are assigned to the low-strength group, with characters within each group having the same strength. During cross-group substitution, the relative order of characters within each group remains unchanged. Characters from different groups are interleaved, resulting in a staggered distribution of characters from different strength groups, forming an encrypted character sequence. This character substitution rule is pre-agreed upon by both the sending and receiving ends as the encryption key.

[0042] Subsequently, the sending end based on Figure 9 Morse coding converts each character into a Morse sequence composed of dotted symbols, dashed symbols, and spacers. During timing coding, a unit time slot length is defined. A dotted symbol represents a light signal continuously outputting at a constant intensity state assigned to the character within one unit time slot. A dashed symbol represents a light signal continuously outputting at the same constant intensity state within two consecutive unit time slots. A spacer symbol represents the encoded state 0 corresponding to a lightless state outputting at least one unit time slot. The symbols are arranged sequentially, and all illuminated symbols of the same character are transmitted using the same quaternary intensity state, forming a quaternary symbol timing sequence representing the Morse sequence.

[0043] During encoding, the polarization angle is switched to the angle corresponding to the target encoding by adjusting the polarization direction of the excitation light: when writing encoding "1", the polarization direction is adjusted to about 30°; when writing encoding "2", it is adjusted to 150°; when writing encoding "3", it is adjusted to 90°; the no-signal interval corresponds to encoding "0".

[0044] During encoding and reading, the SHG signal generated by the device under polarized light excitation is separated from the fundamental frequency excitation light by a dichroic mirror. The SHG intensity value is acquired and recorded by a spectral testing system. The measured intensity is compared with a preset intensity threshold to divide the corresponding intensity interval and determine the quaternary intensity state of each unit time slot: if the time slot state is encoding state 0, it is determined to be an interval symbol; if the same non-zero intensity state continues for one unit time slot, it is determined to be a dot symbol; if the same non-zero intensity state continues for two consecutive unit time slots, it is determined to be a dash symbol. Then, based on the persistence of the intensity state in consecutive time slots, Morse decoding is performed to restore the Morse sequence and character corresponding to the encrypted character sequence; the encrypted character sequence is then restored according to the mapping rules.

[0045] like Figure 10 As shown, a specific example of encrypted transmission illustrates the process: The original plaintext to be transmitted by the sender is HELLOWORLD. The sender first performs character substitution encryption, grouping each character according to a preset strength level and then shuffling them across groups to generate the encrypted sequence RLHOWLEODL. Then, according to the Morse code and strength state assigned to each character in this sequence, the excitation light polarization direction and light source on / off are switched sequentially for timing output (30° / 150° / 90° / 150° / 150° / 30° / 90° / 150° / 30° / 90°, where each symbol is split into dot time slots, dash time slots, and interval time slots according to Morse rules). The receiver synchronously collects the SHG strength at each time node, first determines the strength state of each time slot, and then demodulates the dots, dashes, and intervals according to Morse rules to restore the encrypted sequence RLHOWLEODL. The receiver uses the strength sorting key to rearrange the encrypted sequence a second time, finally restoring the original plaintext HELLOWORLD.

[0046] Combining Examples 1 and 2, the Me-PTCDI / 3R-MoS2 heterojunction constructed in this application exhibits an asymmetric distribution characteristic in the SHG polarization response that is not present in a single component, and this characteristic can be reproduced in both bilayer and trilayer 3R-MoS2 systems. Based on this polarization-intensity differential response, multi-level optical coding can be realized, providing a new device solution for nonlinear optical encrypted communication.

[0047] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. An optical coding method based on optical devices with different SHG responses, wherein the optical coding device has distinguishable SHG intensities in three different excitation light polarization directions; characterized in that, The following methods and steps are included: Establish an encoding mapping relationship to map the SHG intensity states corresponding to the three different excitation light polarization directions to multiple symbol states in a multi-level encoding. Obtain the information to be encoded, and convert the information to be encoded into a symbol sequence composed of the symbol states; According to the symbol sequence, the optical encoding device is sequentially illuminated with the corresponding excitation light polarization direction to generate an SHG signal carrying encoded information.

2. The optical encoding method based on optical devices with different SHG responses according to claim 1, characterized in that, The multi-base encoding is a ternary encoding, and the specific operation process includes: Three excitation light polarization directions with distinguishable differences in SHG intensity are selected from the polarization-dependent SHG response curve of the optical encoding device, corresponding to ternary symbol states 0, 1, and 2, respectively. Establish a character mapping table, using 27 combinations of three-digit ternary numbers to cover the 26 English letters and at least one control character; The information to be transmitted is split into characters, and each character is converted into a corresponding three-digit ternary code element combination according to the character mapping table, and arranged in the transmission time sequence to form a ternary code element sequence. According to the timing of the ternary symbol sequence, the polarization direction of the excitation light is switched sequentially to the polarization direction corresponding to the current symbol state, so that the excitation light with the corresponding polarization direction illuminates the optical encoding device in time slots to complete the optical transmission of information.

3. The optical encoding method based on optical devices with different SHG responses according to claim 1, characterized in that, The multi-base encoding is a quaternary encoding, and the specific operation process includes: In the polarization-dependent SHG response curve of the optical encoding device, three excitation light polarization directions with distinguishable differences in SHG intensity are selected, corresponding to quaternary encoding states 1, 2, and 3 respectively. At the same time, the no-light input state is corresponding to encoding state 0, and a quaternary mapping relationship is established. The information to be transmitted is split into characters, and a quaternary strength state is assigned to each character according to the preset mapping rules; According to the timing sequence of the quaternary intensity states, the polarization direction of the excitation light is switched or the light source is turned off in sequence, so that the optical encoding device is illuminated in the corresponding state according to the time slot, thereby completing the optical transmission of information.

4. The optical encoding method based on optical devices with different SHG responses according to claim 3, characterized in that, The preset mapping rules include: Each character is converted into a Morse sequence consisting of dotted symbols, dashed symbols, and spacers according to the Morse coding rules. In the timing coding process, the dot symbol is represented as a light signal continuously outputting the assigned intensity state within a unit time slot, the slash symbol is represented as a light signal continuously outputting the same intensity state within two consecutive unit time slots, and the interval symbol is represented as an output no-light state.

5. The optical encoding method based on optical devices with different SHG responses according to claim 3, characterized in that, It also includes encryption steps: Before splitting the information to be transmitted into characters, the characters in the information to be transmitted are scrambled and recombined according to a preset character substitution rule to generate an encrypted character sequence. The character substitution rule is pre-agreed upon by both the sending and receiving ends as an encryption key; During decoding, the receiving end reverses the encrypted character sequence obtained from demodulation according to the character substitution rules to restore the original information.

6. The optical encoding method based on optical devices with different SHG responses according to claim 5, characterized in that, The character replacement rules are as follows: The characters in the information to be transmitted are divided into three character groups according to preset rules. Each group corresponds to a different SHG strength level, and each character in the same group is assigned the same strength state. During cross-group permutation, the relative order of characters within each strength group remains unchanged during the permutation process. The characters in each strength group are interleaved and inserted, so that the characters of different strength groups are staggered in the arrangement, thereby forming the encrypted character sequence.

7. The optical encoding method based on optical devices with different SHG responses according to claim 1, characterized in that, The optical coding device includes a substrate and a heterojunction structure formed on the substrate. The heterojunction structure consists of a two-dimensional inorganic material layer and an organic molecular functional layer. The two-dimensional inorganic material layer is prepared by chemical vapor deposition, and the organic molecular functional layer is grown on the two-dimensional inorganic material layer by epitaxial growth.

8. The optical encoding method based on optical devices with different SHG responses according to claim 7, characterized in that, The two-dimensional inorganic material layer is a uniform, wrinkle-free 3R-MoS2 layer, and the number of layers in the two-dimensional inorganic material layer is 2 to 3. The organic molecular functional layer is N,N'-dimethyl-3,4,9,10-perylenetetracarboxydiimide, and the number of layers in the organic molecular functional layer is a single layer.

9. The optical encoding method based on optical devices with different SHG responses according to claim 8, characterized in that, The thickness of the two-dimensional inorganic material layer is 0.5 nm to 10 nm, and the thickness of the organic molecular functional layer is 0.5 nm to 5 nm.

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