High-capacity free-space chaotic secure communication system based on orbital angular momentum multiplexing

Abstract

This invention discloses a high-capacity free-space chaotic secure communication system based on orbital angular momentum multiplexing. The system generates a chaotic carrier signal via a main laser in the encrypted transmitter using a conventional optical feedback structure. Optical information is then encrypted by hiding it within the chaotic optical carrier through intensity modulation. Two information streams are modulated into two vortex beams with different spatial topological charges in the OAM multiplexing module using a spatial light modulator. After multiplexing by a beam combiner, these beams enter the free-space link for transmission. After transmission through the free-space link, opposite single-order phase plates are loaded onto the spatial light modulator in the OAM demultiplexing module to demodulate the corresponding link's optical field modes. In the synchronization receiving module, local chaotic synchronization is achieved using a one-way injection-locking mechanism. The original information is then obtained by subtracting the information-carrying chaotic optical carrier from the local synchronization chaotic signal, ultimately completing secure communication.

Description

Technical Field

[0001] This invention belongs to the field of optical communication technology, and more specifically, relates to a high-capacity free-space chaotic secure communication system based on orbital angular momentum reuse. Background Technology

[0002] Chaotic signals generated based on the nonlinear dynamics of lasers have characteristics such as sensitivity to initial conditions and broadband noise. They can mask information in broadband chaotic optical carriers to achieve secure optical transmission, which is one of the important technologies to enhance the information security of the physical layer of optical communication systems.

[0003] However, due to the inherent relaxation oscillation phenomenon in semiconductor lasers, the effective bandwidth of chaotic lasers generated by external cavity semiconductor lasers via conventional optical feedback is only a few GHz. The limited chaotic carrier bandwidth restricts the transmission rate and transmission capacity of chaotic secure optical communication.

[0004] Currently, scholars at home and abroad have proposed many schemes to improve the effective bandwidth of chaotic lasers. For example, Uchida et al. (Optics Express, 2015, 23(2):1470-1490) used optical feedback ECSL as the master laser and obtained a chaotic signal with an effective bandwidth of 26 GHz in the end slave laser based on the method of cascading injection of multiple slave lasers; Wang Yuncai et al. of Taiyuan University of Technology disclosed a time-delay-free, spectrum-flat, broadband photonic integrated chaotic semiconductor laser (patent name: time-delay-free, spectrum-flat, broadband photonic integrated chaotic semiconductor laser, patent number: CN 104158085). B), the lasers generated by the left and right lasers are transmitted to the non-isolated bidirectional amplification chip via optical waveguides to achieve mutual injection perturbation. The backscattering of light by the erbium-doped passive optical waveguide achieves random perturbation of the left and right lasers. Under the action of mutual injection perturbation and random perturbation, the left laser outputs a chaotic laser with no time delay, flat spectrum, and wide bandwidth. Li Nianqiang et al. from Soochow University proposed that a chaotic laser with an effective bandwidth of nearly 40 GHz was generated by using the four-wave mixing effect introduced through a high-order nonlinear fiber (Optics Letters, 2020, 45(7): 1750-1753). These schemes can generate broadband complex high-quality chaotic lasers by controlling the intensity, phase, frequency, polarization and other dimensions of the chaotic laser. However, these schemes have problems such as complex structure and high cost, and are difficult to apply to existing communication systems. At the same time, there are currently no literature or patent reports on improving the transmission capacity of chaotic optical communication systems by controlling the spatial dimension of chaotic lasers. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high-capacity free-space chaotic secure communication system based on orbital angular momentum multiplexing. While ensuring the security of optical information spatial link transmission, it utilizes the spatial dimension of chaotic carriers to improve the transmission capacity of the chaotic communication system.

[0006] To achieve the above-mentioned objectives, the present invention provides a high-capacity free-space chaotic secure communication system based on orbital angular momentum multiplexing, characterized in that it includes: an encrypted transmitter, an OAM multiplexing module, an OAM demultiplexing module, and a synchronous receiver;

[0007] The encrypted transmitter includes: a main laser DL, an optical fiber coupler FC1, a polarization controller PC1, a tunable optical attenuator VOA1, an optical fiber mirror M1, an optical isolator ISO1, a Mach-Zehnder modulator MZM, an arbitrary waveform generator AWG, an erbium-doped fiber amplifier EDFA, and a tunable optical attenuator VOA2.

[0008] The laser signal generated by the DL is split into two paths by the FC1 according to the set beam splitting ratio. One path passes through the PC1 and is input to the VOA1. After being attenuated by the VOA1, it is reflected back to the DL by the M1. The other path outputs a chaotic optical carrier. The chaotic optical carrier passes through the ISO1 and enters the MZM. At the same time, the information generated by the AWG is modulated onto the chaotic optical carrier through the MZM to obtain a chaotic optical carrier carrying information. Finally, the chaotic optical carrier is amplified by the EDFA and attenuated by the VOA2 before being input to the OAM multiplexing module.

[0009] The OAM multiplexing module includes a polarization controller PC2, an optical fiber coupler FC2, an optical fiber collimator COL1 / COL2, a linear polarizer LP1 / LP2, an optical fiber delay line DL, a beam splitter BS1 / BS2 / BS3, a 45-degree reflector M2, and a reflective spatial light modulator SLM1 / SLM2.

[0010] After the chaotic optical carrier enters the OAM multiplexing module, the polarization of the beam is first adjusted by PC2, and then the information-carrying chaotic optical carrier is divided into two links according to the set beam splitting ratio by FC2. In the first link, the optical signal is first collimated into a spatial Gaussian beam by COL1, and then the polarization of the spatial beam is adjusted by LP1 to be aligned with the long axis of the liquid crystal molecules in SLM1. Subsequently, it is transmitted to SLM1 through BS1 and modulated into a vortex beam carrying a -3rd order topological charge. The modulated vortex beam is then reflected back to BS1 after passing through SLM1, and then through BS1... The beam is reflected to M2, then transmitted to BS3 and combined with the beam output from the second link. The optical signal in the second link is first delayed by DL to reduce the correlation between the two information paths, and then transmitted through COL2, LP2 and BS2 in sequence before being input to SLM2. It is then modulated by SLM2 into a vortex beam carrying a +1 order topological charge. This vortex beam is then reflected to BS3 after passing through SLM2 and BS2, and then combined with the beam output from the first link. The multiplexed vortex beam is then transmitted in the free space link and enters the OAM demultiplexing module.

[0011] The OAM demultiplexing module includes a beam splitter BS4, a spatial light modulator SLM3 / SLM4, a 45-degree reflector M3 / M4 / M5, and an optical fiber collimator COL3 / COL4.

[0012] After transmission through the free-space link, the multiplexed vortex beam is first split into two paths by BS4. One path passes through SLM3 to demodulate the output beam of the first link in the OAM multiplexing module. The demodulated Gaussian beam then passes through M4 and COL3 before entering the optical fiber and being transmitted to the first synchronous receiving module, thus achieving optical field demodulation of the output beam of the first link. The other path passes through M3 and is reflected to SLM4 to demodulate the output beam of the second link in the OAM multiplexing module. The demodulated Gaussian beam then passes through M5 and COL4 before entering the optical fiber and being transmitted to the second synchronous receiving module, thus achieving optical field demodulation of the output beam of the second link.

[0013] The synchronous receiving end includes two synchronous receiving modules with identical structure and function. The first synchronous receiving module includes an optical fiber isolator ISO2, a small signal amplifier AEDFA1, a 2×2 optical fiber coupler FC3, tunable optical attenuators VOA3 / VOA4 / VOA5, a polarization controller PC3, a slave laser SL1, and photodetectors PD1 / PD2. The second synchronous receiving module includes an optical fiber isolator ISO3, a small signal amplifier AEDFA2, a 2×2 optical fiber coupler FC4, tunable optical attenuators VOA6 / VOA7 / VOA8, a polarization controller PC4, a slave laser SL2, and photodetectors PD3 / PD4.

[0014] In the first synchronization receiving module, the collimated optical signal is compensated for spatial transmission impairment by AEDFA1 after passing through ISO2, and then proportionally split into two paths by FC3. One path is injected unidirectionally into SL1 through VOA3 and PC3. At this time, SL1 generates a local synchronization chaotic signal, which is received by PD2 after passing through FC3 and VOA5. The other path is received by PD1 after passing through VOA4. Finally, the signals received by the two photodetectors are subtracted to obtain the original optical signal transmitted in the first link.

[0015] Similarly, the second synchronous receiving module obtains the original optical signal transmitted by the second link.

[0016] The objective of this invention is achieved as follows:

[0017] This invention relates to a high-capacity free-space chaotic secure communication system based on orbital angular momentum multiplexing. The system utilizes a main laser in the encrypted transmitter to generate a chaotic carrier signal via a conventional optical feedback structure. Optical information is then encrypted by hiding it within the chaotic optical carrier through intensity modulation. Two information streams are modulated into two vortex beams with different spatial topological charges in the OAM multiplexing module via a spatial light modulator. After multiplexing by a beam combiner, these beams enter the free-space link for transmission. After transmission through the free-space link, opposite single-order phase plates are loaded onto the spatial light modulator in the OAM demultiplexing module to demodulate the corresponding link's optical field modes. In the synchronization receiving module, a one-way injection-locking mechanism is used to achieve local chaotic synchronization. The original information is then obtained by subtracting the information-carrying chaotic optical carrier from the local synchronization chaotic signal, ultimately completing secure communication.

[0018] Meanwhile, the high-capacity free-space chaotic secure communication system based on orbital angular momentum reuse of the present invention also has the following beneficial effects:

[0019] (1) The free space OAM multiplexing chaotic secure communication scheme designed in this invention can effectively encrypt and decrypt information, ensuring the security and privacy of information between the two parties in communication;

[0020] (2) Compared with conventional broadband chaotic signal generation schemes, this scheme combines OAM spatial multiplexing technology for the first time, which makes full use of the spatial dimension of the chaotic carrier and improves the transmission capacity of the chaotic secure communication system. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of a specific implementation of the high-capacity free-space chaotic secure communication system based on orbital angular momentum reuse according to the present invention.

[0022] Figure 2 This is an architecture diagram of another specific implementation of the present invention, a high-capacity free-space chaotic secure communication system based on orbital angular momentum reuse;

[0023] Figure 3 (a) is the time-domain waveform diagram of the encrypted information; (b) is the time-domain waveform diagram of the original information and the legitimate decryption information of the synchronous receiver 1; (c) is the time-domain waveform diagram of the original information and the legitimate decryption information of the synchronous receiver 2; (d) is the eye diagram of the encrypted information; (e) is the eye diagram of the legitimate decryption information of the synchronous receiver 1; and (f) is the eye diagram of the legitimate decryption information of the synchronous receiver 2. Detailed Implementation

[0024] The specific embodiments of the present invention will now be described with reference to the accompanying drawings to enable those skilled in the art to better understand the invention. It should be particularly noted that in the following description, detailed descriptions of known functions and designs that might obscure the main content of the invention will be omitted here.

[0025] Example

[0026] Figure 1 This is a schematic diagram of the high-capacity free-space chaotic secure communication system based on orbital angular momentum reuse, as per the present invention.

[0027] In this embodiment, as Figure 1 As shown, the present invention discloses a high-capacity free-space chaotic secure communication system based on orbital angular momentum multiplexing, comprising: an encrypted transmitter, an OAM multiplexing module, an OAM demultiplexing module, and a synchronous receiver;

[0028] The encrypted transmitter includes: main laser DL, fiber coupler FC1, polarization controller PC1, tunable optical attenuator VOA1, fiber mirror M1, optical isolator ISO1, Mach-Zehnder modulator MZM, arbitrary waveform generator AWG, erbium-doped fiber amplifier EDFA, and tunable optical attenuator VOA2.

[0029] The laser signal generated by the DL is split into two paths by the FC1 according to the set beam splitting ratio of 2:8. 20% of the light from one path passes through the PC1 and is then input to the VOA1. After being attenuated by the VOA1, it is reflected back to the DL by the M1. The other path outputs 80% of the light as a chaotic optical carrier. The chaotic optical carrier passes through the ISO1 and enters the MZM. At the same time, the information generated by the AWG is modulated onto the chaotic optical carrier through the MZM to obtain a chaotic optical carrier carrying information. Finally, the chaotic optical carrier is amplified by the EDFA and attenuated by the VOA2 before being input to the OAM multiplexing module.

[0030] The OAM multiplexing module includes a polarization controller PC2, an optical fiber coupler FC2, an optical fiber collimator COL1 / COL2, a linear polarizer LP1 / LP2, an optical fiber delay line DL, a beam splitter BS1 / BS2 / BS3, a 45-degree reflector M2, and a reflective spatial light modulator SLM1 / SLM2.

[0031] After the chaotic optical carrier enters the OAM multiplexing module, the polarization of the beam is first adjusted by PC2, and then the information-carrying chaotic optical carrier is split into two links according to the set beam splitting ratio of 5:5 by FC2. In the first link, the optical signal is first collimated into a spatial Gaussian beam by COL1, and then the polarization of the spatial beam is adjusted by LP1 to be aligned with the long axis of the liquid crystal molecules in SLM1. Subsequently, it is transmitted to SLM1 through BS1 and modulated into a vortex beam carrying a -3rd order topological charge. The modulated vortex beam is then reflected back to BS1 after passing through SLM1, and then through B... S1 is reflected to M2, and then the beam is transmitted to BS3 to be combined with the beam output from the second link. The optical signal in the second link is first delayed by DL to reduce the correlation between the two information paths, and then transmitted through COL2, LP2 and BS2 in sequence before being input to SLM2. It is then modulated by SLM2 into a vortex beam carrying a +1 order topological charge. This vortex beam is then reflected to BS3 after passing through SLM2 and BS2, and then combined with the beam output from the first link. The multiplexed vortex beam is then transmitted in the free space link and then enters the OAM demultiplexing module.

[0032] OAM demultiplexing module: includes beam splitter BS4, spatial light modulator SLM3 / SLM4, 45-degree reflector M3 / M4 / M5, and fiber collimator COL3 / COL4;

[0033] After transmission through the free-space link, the multiplexed vortex beam is first split into two paths by BS4. One path passes through SLM3 to demodulate the output beam of the first link in the OAM multiplexing module. The demodulated Gaussian beam then passes through M4 and COL3 before entering the optical fiber and being transmitted to the first synchronous receiving module, thus achieving optical field demodulation of the output beam of the first link. The other path passes through M3 and is reflected to SLM4 to demodulate the output beam of the second link in the OAM multiplexing module. The demodulated Gaussian beam then passes through M5 and COL4 before entering the optical fiber and being transmitted to the second synchronous receiving module, thus achieving optical field demodulation of the output beam of the second link.

[0034] The synchronous receiver includes two synchronous receiver modules with identical structure and function. The first synchronous receiver module includes an optical fiber isolator ISO2, a small signal amplifier AEDFA1, a 2×2 optical fiber coupler FC3, tunable optical attenuators VOA3 / VOA4 / VOA5, a polarization controller PC3, a slave laser SL1, and photodetectors PD1 / PD2. The second synchronous receiver module includes an optical fiber isolator ISO3, a small signal amplifier AEDFA2, a 2×2 optical fiber coupler FC4, tunable optical attenuators VOA6 / VOA7 / VOA8, a polarization controller PC4, a slave laser SL2, and photodetectors PD3 / PD4.

[0035] In the first synchronization receiving module, the collimated optical signal is collimated and coupled through ISO2, and then the spatial transmission impairment is compensated by EDFA2. After passing through FC3, it is proportionally split into two paths. One path is injected unidirectionally into SL1 through VOA3 and PC3. At this time, SL1 generates a local synchronization chaotic signal, which is received by PD2 after passing through FC3 and VOA5. The other path is received by PD1 after passing through VOA4. Finally, the signals received by the two photodetectors are subtracted to obtain the original optical signal transmitted in the first link.

[0036] Similarly, the second synchronous receiving module obtains the original optical signal transmitted by the second link.

[0037] In this embodiment, as Figure 2 As shown, we can use different encrypted transmitters to send two different laser beams to the OAM multiplexing module. The OAM multiplexing module multiplexes the two different laser beams into one laser beam for transmission on the free space link. Then, the OAM demultiplexing module performs demultiplexing on each beam separately. Finally, the two original optical signals are obtained through the synchronous receiver.

[0038] Next, we verified the results through experiments. As a principle verification experiment, we successfully verified the OAM multiplexing chaotic secure transmission of a dual-link rate of 20Gbps with OOK modulation format in a 2-meter free space link. Figure 3 As shown, (a) displays the encrypted signal waveform, (b) shows the original information and decryption signal waveforms of synchronous receiver 1, (c) shows the original information and decryption signal waveforms of synchronous receiver 2, (d) shows the encrypted signal eye diagram, (e) shows the decryption signal eye diagram of synchronous receiver 1, and (f) shows the decryption signal eye diagram of synchronous receiver 2. It can be seen that the encrypted information waveform exhibits a random fluctuation trend, making it impossible to distinguish the original information; the communication eye diagram is tightly closed, and the calculated encryption error rate is close to 0.5. On the other hand, under highly correlated chaotic synchronization conditions, the legitimate receiver can obtain information similar to the original signal waveform through chaotic decryption; the communication eye diagram is open, and the corresponding error rate is below 3.8 × 10⁻⁶. -3Therefore, the feasibility of the free-space OAM multiplexing chaotic secure communication scheme is verified.

[0039] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A high-capacity free-space chaotic secure communication system based on orbital angular momentum reuse, characterized in that, include: Encrypted transmitter, OAM multiplexing module, OAM demultiplexing module, and synchronous receiver; The encrypted transmitter includes: a main laser DL, an optical fiber coupler FC1, a polarization controller PC1, a tunable optical attenuator VOA1, an optical fiber mirror M1, an optical isolator ISO1, a Mach-Zehnder modulator MZM, an arbitrary waveform generator AWG, an erbium-doped fiber amplifier EDFA, and a tunable optical attenuator VOA2. The laser signal generated by the DL is split into two paths by the FC1 according to the set beam splitting ratio. One path passes through the PC1 and is input to the VOA1. After being attenuated by the VOA1, it is reflected back to the DL by the M1. The other path outputs a chaotic optical carrier. The chaotic optical carrier passes through the ISO1 and enters the MZM. At the same time, the information generated by the AWG is modulated onto the chaotic optical carrier through the MZM to obtain a chaotic optical carrier carrying information. Finally, the chaotic optical carrier is amplified by the EDFA and attenuated by the VOA2 before being input to the OAM multiplexing module. The OAM multiplexing module includes a polarization controller PC2, an optical fiber coupler FC2, an optical fiber collimator COL1 / COL2, a linear polarizer LP1 / LP2, an optical fiber delay line DL, a beam splitter BS1 / BS2 / BS3, a 45-degree reflector M2, and a reflective spatial light modulator SLM1 / SLM2. After the chaotic optical carrier enters the OAM multiplexing module, the polarization of the beam is first adjusted by PC2, and then the information-carrying chaotic optical carrier is divided into two links according to the set beam splitting ratio by FC2. In the first link, the optical signal is first collimated into a spatial Gaussian beam by COL1, and then the polarization of the spatial beam is adjusted by LP1 to be aligned with the long axis of the liquid crystal molecules in SLM1. Subsequently, it is transmitted to SLM1 through BS1 and modulated into a vortex beam carrying a -3rd order topological charge. The modulated vortex beam is then reflected back to BS1 after passing through SLM1, and then through BS1... The beam is reflected to M2, then transmitted to BS3 and combined with the beam output from the second link. The optical signal in the second link is first delayed by DL to reduce the correlation between the two information paths, and then transmitted through COL2, LP2 and BS2 in sequence before being input to SLM2. It is then modulated by SLM2 into a vortex beam carrying a +1 order topological charge. This vortex beam is then reflected to BS3 after passing through SLM2 and BS2, and then combined with the beam output from the first link. The multiplexed vortex beam is then transmitted in the free space link and enters the OAM demultiplexing module. The OAM demultiplexing module includes a beam splitter BS4, a spatial light modulator SLM3 / SLM4, a 45-degree reflector M3 / M4 / M5, and an optical fiber collimator COL3 / COL4. After transmission through the free-space link, the multiplexed vortex beam is first split into two paths by BS4. One path passes through SLM3 to demodulate the output beam of the first link in the OAM multiplexing module. The demodulated Gaussian beam then passes through M4 and COL3 before entering the optical fiber and being transmitted to the first synchronous receiving module, thus achieving optical field demodulation of the output beam of the first link. The other path passes through M3 and is reflected to SLM4 to demodulate the output beam of the second link in the OAM multiplexing module. The demodulated Gaussian beam then passes through M5 and COL4 before entering the optical fiber and being transmitted to the second synchronous receiving module, thus achieving optical field demodulation of the output beam of the second link. The synchronous receiving end includes two synchronous receiving modules with identical structure and function. The first synchronous receiving module includes an optical fiber isolator ISO2, a small signal amplifier AEDFA1, a 2×2 optical fiber coupler FC3, tunable optical attenuators VOA3 / VOA4 / VOA5, a polarization controller PC3, a slave laser SL1, and photodetectors PD1 / PD2. The second synchronous receiving module includes an optical fiber isolator ISO3, a small signal amplifier AEDFA2, a 2×2 optical fiber coupler FC4, tunable optical attenuators VOA6 / VOA7 / VOA8, a polarization controller PC4, a slave laser SL2, and photodetectors PD3 / PD4. In the first synchronization receiving module, the collimated optical signal is compensated for spatial transmission impairment by AEDFA1 after passing through ISO2, and then proportionally split into two paths by FC3. One path is injected unidirectionally into SL1 through VOA3 and PC3. At this time, SL1 generates a local synchronization chaotic signal, which is received by PD2 after passing through FC3 and VOA5. The other path is received by PD1 after passing through VOA4. Finally, the signals received by the two photodetectors are subtracted to obtain the original optical signal transmitted in the first link. Similarly, the second synchronous receiving module obtains the original optical signal transmitted by the second link.

2. The high-capacity free-space chaotic secure communication system based on orbital angular momentum reuse according to claim 1, characterized in that, The encrypted transmitter can also use two parallel encrypted transmitters to generate two different laser beams, and then the two different laser beams are multiplexed into one laser signal by the OAM multiplexing module for transmission on the free space link.

Images