A novel photonic security system is described using 2-D spatial codes based on both optical phase and amplitude information. This security system consists of an optical interferometric encoding subsystem that rapidly reads and encodes the 2-D complex-valued spatial code, forming a wideband frequency modulated optical beam and a colinear optical reference beam. After appropriate coherence coding of this beam pair, the light is launched into a low probability of intercept communication channel such as an optical fiber or a narrow beamwidth free-space optical link. At the remote code receiving and data processing site, the received light beam pair is first coherently decoded. Then, a high speed photodetector via optical heterodyne detection generates an encoded wideband radio frequency signal that contains the original 2-D code. Decoding is implemented in parallel via two independent systems. One decoder uses a Fourier transforming lens to reconstruct an electronic image interferogram of the complex-valued user code. This image interferogram is sent to a high speed electronic image processor for verification purposes. The other decoder is a high speed coherent acousto-optic time integrating correlator that optically determines matchmismatch between the received encoded signal and the code signal generated by the electronic database. Improved security to the overall communication network is added by using various keycodes such as a time varying keycode that determines the exact spatial beam scanning sequence required for both proper encoding and decoding of the 2-D code information. This paper describes preliminary experiments using a simple 1-D amplitude modulated spatial code.
A novel photonic security system is described using 2-D spatial codes based on both optical phase and amplitude information. This security system consists of an optical interferometric encoding subsystem that rapidly reads and encodes the 2-D complex-valued spatial code, forming a wideband frequency modulated optical beam and a colinear optical reference beam. After appropriate coherence coding of this beam pair, the light is launched into a low probability of intercept communication channel such as an optical fiber or a narrow beamwidth free-space optical link. At the remote code receiving and data processing site, the received light beam pair is first coherently decoded. Then, a high speed photodetector via optical heterodyne detection generates an encoded wideband radio frequency signal that contains the original 2-D code. Decoding is implemented in parallel via two independent systems. One decoder uses a Fourier transforming lens to reconstruct an electronic image interferogram of the complex-valued user code. This image interferogram is sent to a high speed electronic image processor for verification purposes. The other decoder is a high speed coherent acousto-optic time integrating correlator that optically determines matchmismatch between the received encoded signal and the code signal generated by the electronic database. Improved security to the overall communication network is added by using various keycodes such as a time varying keycode that determines the exact spatial beam scanning sequence required for both proper encoding and decoding of the 2-D code information. This paper describes preliminary experiments using a simple 1-D amplitude modulated spatial code.
We propose a method for secure wireless transmission of encrypted information. By use of an encryption key, an image or document is optically encrypted by optical heterodyne scanning and hence encryption is performed on the fly. We call this technique optical scanning cryptography. The output of the heterodyne encrypted signal is at radio frequency and can be directly sent through an antenna to a secure site for digital storage to be prepared for decryption. In the secure site, an identical optical scanning system to that used for encryption is used, together with a decryption key, to generate an electrical signal. The electrical signal is then processed and sent to a computer to be used for decryption. Utilizing the stored information received from the encryption stage and the electrical information from the secure site, a digital decryption unit performs a decryption algorithm. If the encryption key and the decryption key are matched, the decryption unit will decrypt the image or document faithfully. The overall cryptosystem can perform the incoherent optical processing counterpart of the well-known coherent double-random phase-encoding technique. We present computer simulations of the idea.
The optical network supporting emerging bandwidth-intensive services has become the cornerstone of the 5G era. However, the development of optical fiber eavesdropping and quantum computing has brought huge security challenges to traditional cryptography. As an effective approach to improving optical layer transmission security, all-optical logic gate encryption has important research significance. This paper proposes a high-speed coherent optical encryption and decryption system based on phase encoding with all-optical logic gates. The system ingeniously designs the phase encoding and decoding scheme between two quadrature phase-shift keying (QPSK) signals, which doubles the encryption and decryption efficiency. In addition, the integration of physical-layer key distribution (PLKD) and physical-layer encryption (PLE) contributes to a reduction in overall system complexity. By adopting real-time signal processing in an all-optical domain, the single-wavelength rate of system security communication can reach 100 Gbps. The system is also applicable to other phase-modulated signals and provides a feasible scheme to enhance transmission security in wavelength division multiplexing (WDM) optical networks featuring high speed, low latency, and high flexibility.
In conventional optical communication systems, the transmission signals are regular digital signals. Due to the openness of optical fiber networks, it is rather easy for eavesdroppers to obtain the transmission signals from the public fiber-link and then intercept the message directly. To address this crucial security challenge, in this work we propose a high-speed secure optical communication system in virtue of physical random temporal encryption based on private physical random phase modulation and phase-to-intensity conversion. The proposed physical random temporal encryption is performed by a module composed of a phase modulator (PM) and a chirped fiber Bragg grating (CFBG), and the corresponding decryption is achieved with a similar module composed of an inverse-phase driven PM and an oppositedispersion CFBG. By distributing a constant-amplitude random-phase signal to the local semiconductor lasers deployed in the encryption module and decryption module, a pair of synchronized physical random PM driving signals that are not exchanged on public link can be independently generated, which guarantees the receiver end can correctly decrypt the original transmission message. Our numerical results demonstrate that with the proposed encryption scheme, the regular transmission signal is encrypted as a noise-like signal that can greatly enhance the security of message, and moreover, based on the private synchronized physical random phase modulation, the privacy of encryption and decryption are guaranteed, which prevents the eavesdroppers from intercepting transmission message. This work provides a promising strategy for the implement of high-speed high-security physical-layer optical communication.
In this thesis, Quantum Key Distribution and quantum communication methods based on high-dimensional spatial coding of light are developed. Their security is based on the fundamental quantum nature of light and profits from the highdimensional Hilbert spaces offered intrinsically by imaging optics. An overview of classical information theory and quantum information is given to introduce the field of quantum cryptography. The advantages of larger dimensional alphabets and the security of the standard two-bases BB84 protocol is shown. The spatial states used for encoding are introduced. An analytic expression for the upper bound on the mutual information for these states is derived, including multiphoton states, detector noise and beam broadening. High-dimensional encoding of single photons is experimentally realized, reaching 10.5 bit per received photon. The dependence of the mutual information on the number of detector pixels is discussed and the experimental values are compared with the theoretical upper bound. It was shown that a standard error-correcting LDPC code is sufficient to achieve practically error-free communication. By adding a second mutually unbiased basis, a large-alphabet QKD system is experimentally realized and characterized. The security of this BB84-like protocol is analyzed in terms of intercept-resend and collective attacks. The key rate after postprocessing is analyzed under realistic circumstances, including finite key length. Finally, a new quantum communication method is demonstrated, which is based on encoding information into wavefronts decomposed over guided modes of a multimode fiber. At the end a step back is made and the similarities and differences of several quantum authentication and quantum cryptography schemes as well as Quantum Data Locking are discussed. This involves comparison of the characteristics of the classical channel, the quantum channel and the necessary dimension of the Hilbert space.
Secure optical communication systems based on general bent sequences have been described which encode/decode information with arrays of fiber Bragg gratings (FBG). A broadband pulse coming from an optical source will be split into a series of separated pulses when it reaches the encoding FBG array. These pulses have different spectrums and different time delays. Because it is difficult for an attacker to recover the original pulse if he doesn't know the exact structure of the encoding FBG array, one can say that the information from the optical source has been encrypted. The coded signal will be recovered by the decoding FBG array having the inverse structure of the encoding FBG array. Because various structures of encoding FBG arrays could generate different reflected pulses to ensure the security of communication in the unsafe channels, grating tuning techniques are used broadly to increase the modes of the systems. Some models of the systems will be introduced and their security will be discussed. Bent sequence is generated by a general class of bent functions to charge the modes of FBG arrays in order to increase the security of our systems because of its excellent characteristics in cryptology. That makes the optical communication system safe against the interception. Simulation and discussion will be included and the applicability of the system in the future has been prospected.
Optical communications have been widely deployed all over the world. In state-of-the-art optical communication systems, security and high capacity are the most important factors to be considered. As the rapid development of quantum computing, traditional computational complexity based encryption faces unprecedented challenges. To guarantee the unconditional security, quantum key distribution (QKD) has been proposed and now is attracting increasing attentions. Classical optical communications have been exponentially growing for decades. The telecommunications industry is always in favor of high-speed, long-haul, and cost-efficient optical transports. Lots of advanced techniques have been applied to meet the requirements, e.g., multi-dimensional multiplexing, advanced modulation formats, coherent detection, forward error correction (FEC) coding, constellation shaping, and adaptive coding. In this dissertation, I will investigate continuous-variable QKD (CV-QKD) protocols to enable unconditional security and study the reliable classical advanced optical transmission systems. In a dynamic fiber-optic transmission system, the system performance can be improved by the proposed self-adaptive coding approach. We also experimentally and numerically compare the mutual information (MI) performances of regular/probabilistically shaped/geometrically shaped (PS/GS)-8/16/32 quadrature amplitude modulation (QAM) formats. Therefore, the industry can select the best shaping scheme accordingly in a specific situation. Furthermore, we propose a novel hybrid PS/GS scheme, which can minimize non-Gray mapping penalty as well as be tolerant to the implementation penalty. In addition, free-space optical (FSO) communication systems are also studied here. We emulate the outdoor atmospheric turbulence by indoor turbulence emulator, which is based on split-step beam propagation method (SSBPM). Turbulence mitigation methods, including adaptive optics (AO), channel coding, spatial offset, and Huffman coding, are proposed and experimentally demonstrated to enable high-speed FSO communications. At the end, we propose novel four-state and eight-state CV-QKD systems, where the phase noise can be effectively mitigated, and power fluctuation caused by turbulence can be accurately monitored. Thereafter, beyond 1 Gb/s CV- QKD systems can be realized by controlling phase noise, leveraging reconciliation efficiency, monitoring power fluctuation, and multiplexing quantum channels.