Secure Optical Communication Research Articles

Investigation of the Effect of Intra-Cavity Propagation Delay in Secure Optical Communication Using Chaotic Semiconductor Lasers

The influence of intra-cavity propagation delay in message encoding and decoding using chaotic semiconductor lasers is numerically investigated. A message is encoded at the transmitter laser by a chaos shift keying scheme and is decoded at the receiver by comparing its output with the transmitter laser. The requisite intra-cavity propagation delay in achieving synchronization of optical chaos is estimated by cross-correlation analysis between the transmitter and receiver lasers’ output. The effect of intra-cavity propagation delay on the message recovery has been analyzed from the bit error rate performance. It is found that despite the intra-cavity propagation delay magnitude being less, it has an impact on the quality of message recovery. We also examine the dependency of injection rate, frequency detuning, modulation depth and bit rate on intra-cavity propagation delay and associated message recovery quality. We found that the communication performance has been adequately improved after incorporating intra-cavity propagation delay correction in the synchronization system.

Cryptography in coherent optical information networks using dissipative metamaterial gates

All-optical encryption of information in fibre telecommunication networks offers lower complexity and far higher data rates than electronic encryption can deliver. However, existing optical layer encryption methods, which are compatible with keys of unlimited length, are based on nonlinear processes that require intense optical fields. Here, we introduce an optical layer secure communication protocol that does not rely on nonlinear optical processes but instead uses energy redistribution of coherent optical waves interacting on a plasmonic metamaterial absorber. We implement the protocol in a telecommunication optical fibre information network, where signal and key distribution lines use a common coherent information carrier. We investigate and demonstrate different encryption modes, including a scheme providing perfect secrecy. All-optical cryptography, as demonstrated here, exploits signal processing mechanisms that can satisfy optical telecom data rate requirements in any current or next-generation frequency band with bandwidth exceeding 100 THz and a switching energy of a few photons per bit. This is the first demonstration of an optical telecommunications application of metamaterial technology.

Physical secure optical communication based on private chaotic spectral phase encryption/decryption.

We propose and demonstrate a novel physical, secure high-speed optical communication scheme based on synchronous chaotic spectral phase encryption (CSPE) and decryption (CSPD). The CSPE is performed by a module composed of two dispersion components and one phase modulator (PM) between them, and the CSPD is carried out by a twin module with reverse dispersions and inverse PM driving signals. The PM driving signals of the CSPE and CSPD modules are privately synchronized chaotic signals that are independently generated by local external-cavity semiconductor lasers subject to common injection. The numerical results indicate that with the CSPE, the original message can be encrypted as a noise-like signal, and the timing clock of the original message is efficiently hidden in the encrypted signal. Based on the private synchronization of the chaotic PM driving signals, only the legal receiver can decrypt the message correctly, while the eavesdropper is not able to intercept a useful message. Moreover, the proposed scheme can also support secure symmetric bidirectional high-speed WDM transmissions. This work shows a prospective way to implement high-speed secure optical communications at the physical layer.

A Novel Optical Frequency-Hopping Scheme Based on a Flexible Structure for Secure Optical Communications

A novel optical frequency-hopping scheme based on a flexible structure for secure optical communications is proposed and demonstrated. In the proposed scheme, critical users' data are divided into a lot of segments, and these segments are transmitted by different optical wavelengths in time domain. In other words, one channel optical carrier carries different users' data segments. A flexible structure was demonstrated and used in optical frequency-hopping system to simplify the structure and decrease the cost of the security system. In this paper, the viability of a four-wavelength-frequency-hopping secure optical communication system with a 25-Gb/s error-free transmission through a 32-km single-mode fiber and a 8-km dispersion compensation fiber was demonstrated and verified by simulation tools.

Effect of External Perturbation and System Parameters on Optical Secure Communication Models

Abstract Chaotic signals are regarded as secure carriers for communication due to its high sensitivity to parameter and initial condition perturbations. This paper studies the problem of optical secure communication modeled by the perturbed nonlinear Schrödinger equation. First, we prove that the chaotic signal can be easily produced from the optical soliton signal when external perturbations are executed to the Schrodinger equation. Chaos synchronization is then proved to be accomplished between the derived system and the original system which are different in the first-order derivative terms. Furthermore, we analyze the effects of system parameters on the chaos synchronization. Numerical results show that smaller differences can lead to more rapid synchronization. We also find that changing system parameters can affect the speed of chaos synchronization.

1.25 Gbits/s-message experimental transmission utilising chaos-based fibre-optic secure communications over 143 km

Chaotic optical secure communications (COSC) are a kind of fast-speed hardware encryption technique at the physical layer. Concerning the practical applications, high-speed long-haul message transmission is always the goal to pursue. In this paper, we report experimentally a scheme of long-haul COSC, where the bit rate reaches 1.25 Gbits/s and the transmission distance up to 143 km. Besides, a distinct advantage of low-cost is guaranteed with the off-the-shelf optical components, and no dispersion compensating fibre (DCF) or forward-error correction (FEC) is required. To the best of our knowledge, this is the first experimental evidence of the longest transmission distance in the COSC system. Our results show that high-quality chaotic synchronisation can be maintained both in time- and frequency-domain, even after 143 km transmission; the bandwidth of the transmitter is enlarged by the external optical injection, which leads to the realisation of 2.5 Gbits/s-message secure transmission up to 25 km. In addition, the effects of device parameters on the COSC are discussed for supplementary detail.

1.25 Gbits/s-message experimental transmission utilising chaos-based fibre-optic secure communications over 143 km

Chaotic optical secure communications (COSC) are a kind of fast-speed hardware encryption technique at the physical layer. Concerning the practical applications, high-speed long-haul message transmission is always the goal to pursue. In this paper, we report experimentally a scheme of long-haul COSC, where the bit rate reaches 1.25 Gbits/s and the transmission distance up to 143 km. Besides, a distinct advantage of low-cost is guaranteed with the off-the-shelf optical components, and no dispersion compensating fibre (DCF) or forward-error correction (FEC) is required. To the best of our knowledge, this is the first experimental evidence of the longest transmission distance in the COSC system. Our results show that high-quality chaotic synchronisation can be maintained both in time- and frequency-domain, even after 143 km transmission; the bandwidth of the transmitter is enlarged by the external optical injection, which leads to the realisation of 2.5 Gbits/s-message secure transmission up to 25 km. In addition, the effects of device parameters on the COSC are discussed for supplementary detail.

Optical chaotic secure algorithm based on space laser communication

The traditional drive response synchronization control method has the poor robustness, which results in the low security performance of the optical chaotic secure communication. To address this problem, an optical chaotic secure algorithm based on space laser communication is proposed in this paper. With the advantage of space laser communication and full consideration of the influence of complex environment on signal transmission of laser wireless communication, a laser wireless communication channel model is built. Based on this, a hybrid self-synchronization chaotic system model is proposed. It can reduce the information needed for transmission, and only need to transmit a small amount of error correction signals on the channel to achieve synchronization of the receiving and the transmitting system, which greatly suppress the drawback of the traditional method. On the basis of chaotic synchronization, the erbium-doped fiber laser is used for information transmission. Different encryption techniques are used to achieve optical chaotic secure communication within the allowable range of error. Numerical simulation results show that the proposed algorithm has good security and robustness, and can realize the secure communication for different signals.

Confidentiality analysis of optical code-based secure optical communication system

A theoretical model is proposed to analyze the time-domain spectral phase en/decoding and evaluate the unconditional security of the optical code-based secure optical communication systems with DPSK modulation. The confidentiality of the systems with and without bit-by-bit code scrambling technique is investigated. It mathematically proves that the system without code scrambling lacks confidentiality and the system employing code scrambling can realize unconditionally secure transmission. Furthermore, encoding only within the central band of the spectrum is sufficient for perfect secrecy, and the secrecy rate can be potentially improved. It allows the system to operate in the burst mode for code generation and encoding and thus have an idle time for rearm.

OpSecure: A Secure Unidirectional Optical Channel for Implantable Medical Devices

Implantable medical devices (IMDs) are opening up new opportunities for holistic healthcare by enabling continuous monitoring and treatment of various medical conditions, leading to an ever-improving quality of life for patients. Integration of radio frequency (RF) modules in IMDs has provided wireless connectivity and facilitated access to on-device data and post-deployment tuning of essential therapy. However, this has also made IMDs susceptible to various security attacks. Several lightweight encryption mechanisms have been developed to prevent well-known attacks, e.g., integrity attacks that send malicious commands to the device, on IMDs. However, lack of a secure key exchange protocol (that enables the exchange of the encryption key while maintaining its confidentiality) and the immaturity of already-in-use wakeup protocols (that are used to turn on the RF module before an authorized data transmission) are two fundamental challenges that must be addressed to ensure the security of wireless-enabled IMDs. In this paper, we introduce OpSecure, an optical secure communication channel between an IMD and an external device, e.g., a smartphone. OpSecure enables an intrinsically user-perceptible unidirectional data transmission, suitable for physically-secure communication with minimal size and energy overheads. Based on OpSecure, we design and implement two protocols: (i) a low-power wakeup protocol that is resilient against remote battery-draining attacks, and (ii) a secure key exchange protocol to share the encryption key between the IMD and the external device. We evaluate the two protocols using a human body model.

A novel double masking scheme for enhancing security of optical chaotic communication based on two groups of mutually asynchronous VCSELs

The emergence of optical chaotic secure communication has opened up an alternative path for information security. In this paper, based on two groups of mutually asynchronous vertical-cavity surface-emitting lasers (VCSELs), a novel double masking (DM) scheme for enhancing security of optical chaotic communication is proposed. We numerically analyze the synchronization characteristic of the lasers and the suppression of the time-delay signature (TDS). The self-correlation function (SF) and permutation entropy (PE) are employed to extract the TDS. Meanwhile, based on the high quality synchronization, we also investigate the communication performances of DM scheme in a long distance. Especially, the influence of the time delay due to delay fiber (DF) on the communication quality in different cases is studied. The results show that the TDS can be suppressed by the DM scheme to some certain degree. Four messages of 10 Gbit/s can be propagated in 138 km single mode fiber (SMF) after introducing the dispersion compensating fiber (DCF), bidirectionally and simultaneously. When the BER ⩽10-9 and Q factor ⩾6, the DM scheme has smaller critical value of the time shift (Δt) than the single masking (SM) system, which indicate a good level of security.

Secure Key Distribution Strategy in OFDM-PON by Utilizing the Redundancy of Training Symbol and Digital Chaos Technique

A secure key distribution scheme for orthogonal frequency division multiplexing (OFDM) passive optical network system is proposed and experimentally demonstrated. The training symbol (TS), which is used for time synchronization and channel estimation, is formed by adopting a noise-like chaotic sequence. The redundancy of the TS is utilized to embed secure keys. An experiment is performed, in which 7.64 Gb/s 16-quadrature-amplitude-modulation OFDM data and 28.4 Mb/s keys embedded in are successfully transmitted over 25 km standard single mode fiber. The results indicate a promising key distribution method for physical layer secure optical communication.

Influence of optical feedback strength and semiconductor laser coherence on chaos communications

The existence of high chaotic spiking in the dynamics of semiconductor lasers with an AC-coupled optical feedback is investigated experimentally. After chaos signal generation, the effect of attenuation feedback strength as a control parameter is studied, and the time evolution of photon density is analyzed. The chaotic instability is tested; our results exhibit monostability in dynamics. By applying different frequencies to observe the hidden regions, the chaotic dynamic results are indicated as a good candidate to hide information for satisfying the resonance phenomenon, to evaluate secure optical communication.

Chaotic optical communications over 100-km fiber transmission at 30-Gb/s bit rate

For the first time, to the best of our knowledge, we experimentally demonstrate a successful 30-Gb/s signal transmission of a duobinary message hidden in a chaotic optical carrier over 100-km fiber. Thanks to the duobinary modulation format with high spectral efficiency, the 30-Gb/s signal can be encrypted by a 10-GHz-wide chaotic carrier. A digital signal processing technique can be used to convert duobinary data into binary data on the receiver side. This proposal lowers the requirement for wideband chaos generation and synchronization in high-speed long-distance chaotic optical communications, and fiber dispersion compensation can also be simplified, which has potential to be used in high-speed long-distance secure optical communications.

Optical secure communication modeled by the perturbed nonlinear Schrödinger equation

This paper proposes an optical secure communication scheme based on chaos synchronization. Nonlinear Schrodinger equation is an important model for optical communication. Our theoretical analysis and numerical simulation show that when the nonlinear Schrodinger equation is perturbed by multiple frequencies, the optical solitons becomes chaotic despite that optical soliton is usual preferred for long-distance transmission. By taking the generated chaotic signals as communication carrier, a master slave system for optical secure communication is designed. A feedback controller is applied to the slave system. Sufficient conditions for chaos synchronization are then proved. It is discovered that the synchronization speed is closely linked with parameters of the nonlinear Schrodinger equation.

QAM Quantum Noise Stream Cipher Transmission Over 100 km With Continuous Variable Quantum Key Distribution

We report the first on-line high-speed and large-capacity secure optical communication system. This was realized by combining a quadrature amplitude modulation/quantum noise stream cipher technology where a coherent multi-level optical signal is hidden in quantum noise and a quantum key distribution technology where secure key delivery is realized with an extremely weak laser light comparable to a single photon. In our security analysis, we adopt a realistic assumption, namely, that an adversary does not have a lossless fiber. To show the advantage of this scheme, we performed a 128 QAM, 70-Gbit/s single-channel transmission over 100 km with a spectral efficiency of as high as 10.3 bits/s/Hz. This is the fastest data rate and highest spectral efficiency yet achieved in quantum cryptography with a realistic assumption.

Electro-optic intensity chaotic system with an extra optical feedback

Electro-optic (EO) delay oscillators have been widely investigated for secure optical communication. To improve complexity and security, an EO intensity chaotic system with an extra optical feedback is proposed. Simulation results show that the proposed system can improve complexity. Moreover, it can effectively suppress the time delay analysis, and the suppression can be enhanced by increasing the optical feedback strength of our system. In addition, synchronization of the communication system in a chaotic modulation encryption scheme based on the proposed system is discussed.

Conversion from Single Photon to Single Electron Spin Using Electrically Controllable Quantum Dots

Polarization is a fundamental property of light and could provide various solutions to the development of secure optical communications with high capacity and high speed. In particular, the coherent quantum state conversion between single photons and single electron spins is a prerequisite for long-distance quantum communications and distributed quantum computation. Electrically defined quantum dots have already been proven to be suitable for scalable solid state qubits by demonstrations of single-spin coherent manipulations and two-qubit gate operations. Thus, their capacity for quantum information technologies would be considerably extended by the achievement of entanglement between an electron spin in the quantum dots and a photon. In this review paper, we show the basic technologies for trapping single electrons generated by single photons in quantum dots and for detecting their spins using the Pauli effect with sensitive charge sensors.

Characteristics of chaotic output from a Gaussian apodized fiber Bragg grating external-cavity semiconductor laser

Optical chaos based on semiconductor laser (SL) has some vital applications such as optical chaos secure communication, high-speed physical random number generation, chaos lidar, etc. Among various schemes to drive an SL into chaos, the introduction of external cavity feedback is one of the most popular techniques, which can generate chaos signals with high dimension and complexity. For the chaos output from an external cavity feedback SL, a time-delay signature (TDS) and bandwidth are two key indexes to assess the chaos signal quality. In this work, according to the rate-equation model of an optical feedback SL, we theoretically investigate the characteristics of TDS and effective bandwidth (EWB) of chaotic output from a Gaussian apodized fiber Bragg grating (GAFBG) feedback SL (GAFBGF-SL). The results show that with the increase of feedback strength, the GAFBGF-SL experiences a quasi-periodic route to chaos. Through selecting the suitable feedback strength and the frequency detuning between the Bragg frequency of the GAFBG and the peak frequency of the free-running SL, the TDS of chaotic output from the GAFBGF-SL can be efficiently suppressed to a level below 0.02. Furthermore, by mapping the TDS and EWB in the parameter space of the feedback strength and the frequency detuning between the Bragg frequency of the GAFBG and the peak frequency of the free-running SL, the optimized parameter region, which is suitable for achieving chaotic signal with weak TDS and wide bandwidth, can be determined. We believe that this work will be helpful in acquiring the high quality chaotic signals and relevant applications.

128-bit spectral processing of sub-picosecond optical pulses in a standard SOI CMOS process.

Optical short pulse processors enable several systems including optical code division multiple access networks, optical secure communications, and optical pulse shapers. For instance, compact and low cost integrated solutions for optical short pulse en/de-coders with large code length and capable of processing large optical bandwidth may enable realization of Tbps communication networks. Here, we report an integrated 128-bit short pulse processor capable of signal processing on large amount of optical bandwidth, demonstrated ≈ 25 nm, using sub-ps optical short pulse signal. The chip fabricated in a commercial foundry SOI CMOS process and includes more than 500 distinct optical components and over 150,000 distinct electrical components.