Secure Optical Communication Research Articles

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.

Electro-optic chaotic system based on the reverse-time chaos theory and a nonlinear hybrid feedback loop.

A novel electro-optic chaos source is proposed on the basis of the reverse-time chaos theory and an analog-digital hybrid feedback loop. The analog output of the system can be determined by the numeric states of shift registers, which makes the system robust and easy to control. The dynamical properties as well as the complexity dependence on the feedback parameters are investigated in detail. The correlation characteristics of the system are also studied. Two improving strategies which were established in digital field and analog field are proposed to conceal the time-delay signature. The proposed scheme has the potential to be used in radar and optical secure communication systems.

Maximizing the security of chaotic optical communications.

The practical application of chaotic optical communications has been limited by two aspects: the difficulty in concealing the time delay - a critical security parameter in feedback chaotic systems, and the difficulty of significantly enlarging the key space without complicating the implementation. Here we propose an architecture to break the above limits. By introducing a frequency-dependent group delay module with frequency tuning resolution of 1 MHz into the chaotic feedback loop, we demonstrate excellent time delay concealment effect, and an additional huge key space of 1048 can be achieved at the same time. The effectiveness is proved by both numerical simulation and experiment. Besides, the proposed scheme is compatible with the existing commercial optical communication systems, thus pave the way for high-speed secure optical communications.

High-frequency reverse-time chaos generation using an optical matched filter.

The optical reverse-time chaos is realized by modulating a binary pseudo-random bit sequence onto an optical carrier, and then driving an optical matched filter. The filter is demonstrated experimentally by using two fiber Bragg gratings and a Fourier-domain programmable optical processor. The complexity relationship between the binary input sequence and the output chaos signal is studied. This approach could be a novel way to generate a high speed repeatable and controllable optical chaos signal, which has the potential to be used in optical secure communication systems.

Single-channel 40 Gbit/s digital coherent QAM quantum noise stream cipher transmission over 480 km.

We demonstrate the first 40 Gbit/s single-channel polarization-multiplexed, 5 Gsymbol/s, 16 QAM quantum noise stream cipher (QNSC) transmission over 480 km by incorporating ASE quantum noise from EDFAs as well as the quantum shot noise of the coherent state with multiple photons for the random masking of data. By using a multi-bit encoded scheme and digital coherent transmission techniques, secure optical communication with a record data capacity and transmission distance has been successfully realized. In this system, the signal level received by Eve is hidden by both the amplitude and the phase noise. The highest number of masked signals, 7.5 x 10(4), was achieved by using a QAM scheme with FEC, which makes it possible to reduce the output power from the transmitter while maintaining an error free condition for Bob. We have newly measured the noise distribution around I and Q encrypted data and shown experimentally with a data size of as large as 2(25) that the noise has a Gaussian distribution with no correlations. This distribution is suitable for the random masking of data.

Generations of multi-channel high-quality chaotic signals based on a ring system composed of polarization rotated coupled 1550 nm vertical-cavity surface-emitting lasers

Optical chaos based on semiconductor laser (SL) has attracted much attention due to its potential application in various fields such as secure optical communication, chaotic radar, fast physical random bit generation, etc. By introducing external perturbations such as optical feedback, optical injection or optoelectronic feedback, SL can be driven into chaotic dynamic state. In general, an obvious time-delay signature (TDS) can be observed in a chaotic SL system with optical feedback, which is undesirable in some applications. So far, several schemes have been reported on the suppression of the TDS in chaotic SL systems, which are mostly based on external cavity feedback systems or mutually coupled systems. In this work, a novel scheme for suppressing TDS to generate multi-channel high-quality chaotic signals is proposed and numerically simulated based on a ring system composed of three unidirectionally polarization-rotated coupled 1550 nm vertical-cavity surface-emitting lasers (1550 nm-VCSELs). In this scheme, the output from the first 1550 nm-VCSEL passes through an optical circulator (OC), a Faraday rotator (FR) and a variable attenuator (VA), and then is injected into the second 1550 nm-VCSEL. The output from the second (third) 1550 nm-VCSEL passes through a similar path mentioned above, and then is injected into the third (first) 1550 nm-VCSEL. The polarization direction and the strength of injection light are controlled by the FR and VA, respectively. Adopting the spin flip model (SFM), the polarization-resolved dynamical characteristics of the three VCSELs in the ring system are analyzed. By the aid of self-correlation function (SF) and mutual information (MI), the influences of the coupled strength and frequency detuning on the TDS of polarization-resolved chaotic signal output from the three VCSELs are discussed. The results show that through selecting suitable coupling strength and frequency detuning, both the X-polarization component (X-PC) and Y-polarization component (Y-PC) in the three VCSELs can simultaneously be lased with comparative output powers, and the TDSs of these polarization components can also be effectively suppressed. Furthermore, we investigate the cross-correlation among the six-channel chaotic signals output from these VCSELs, and determine the region of coupled parameters for generating six-channel chaotic signals, within which satisfied is the weak cross-correlation between two signals from different VCSELs. Theoretically, the six-channel chaotic outputs can be used as physical entropy sources to generate six-channel random number sequences. By further merging the above two channel random bit sequences with weak cross-correlation, more channel random bit sequences with higher rate can be obtained. We hope this work can provide an effective guidance for multi-channel high-rate random bit generation.

Experimental investigations on the dynamical characteristics of pulse packages in a monolithically integrated amplified feedback laser

Under suitable external perturbation such as optical feedback, optical injection or optoelectronic feedback, semiconductor lasers can be driven to realize diverse dynamic outputs including period-one, period-two, multi-period, pulse packages（PPs), chaos, etc., which have potential applications in optical secure communications, microwave photonics, lidar, high speed random signal generation, etc.. For the PPs dynamics, most of previous relevant investigations are usually based on a system composed of discrete elements. In this work, we experimentally investigate the PP dynamical characteristics in a three-section monolithically integrated amplified feedback laser（AFL) composed of a distributed feedback（DFB) laser section, a phase（P) section, and an amplified feedback（A) section. For the AFL, the sections P and A act as a compounded feedback cavity in which the feedback phase and strength can be varied by adjusting the current in section P（IP) and the current in section A（IA), respectively. Via the power spectrum and self-correlation function curve of the time series output from the AFL, the influences of IP and IA on repeated frequency（PP) and regularity of PPs are analyzed in detail. The results indicate that, for the section DFB, whose current（IDFB) is biased at a relatively large level, the AFL can realize two-mode oscillation. After further choosing appropriate IP and IA, the AFL can behave as the dynamical state of PPs. Under IDFB=86.15 mA and IP=96.00 mA, through varying IA in a range of 6.50-10.50 mA, there exist two separated regions for IA to make the AFL operate at PPs. For the region with relatively small value of IA, both PP and the secondary maximum（) of self-correlation curve characterizing the regularity of PPs monotonically decrease with the increase of IA. However, for the region with relatively large value of IA, with the increase of IA, PP first decreases and then fluctuates in a tiny range, but first increases, and further reaches an extreme value, and then decreases. Under IDFB=86.15 mA and IA=9.00 mA, the output characteristics of PPs are significantly affected by IP. With IP increasing from 90.5 mA to 96.5 mA, PP first decreases, and then increases after reaching a minimal value, meanwhile shows an approximately opposite variation trend. Finally, for IDFB=86.15 mA, the mapping of PPs in the parameter space of IP and IA is given and the evolution regularities of PPs are also presented.

Secure coherent optical multi-carrier system with four-dimensional modulation space and Stokes vector scrambling.

A secure enhanced coherent optical multi-carrier system based on Stokes vector scrambling is proposed and experimentally demonstrated. The optical signal with four-dimensional (4D) modulation space has been scrambled intra- and inter-subcarriers, where a multi-layer logistic map is adopted as the chaotic model. An experiment with 61.71-Gb/s encrypted multi-carrier signal is successfully demonstrated with the proposed method. The results indicate a promising solution for the physical secure optical communication.

The Blue LED Nobel Prize: Historical context, current scientific understanding, human benefit

The Blue LED Nobel Prize: Historical context, current scientific understanding, human benefit

Experimental demonstration of the real-time online fault monitoring technique for chaos-based passive optical networks

In this paper, a real-time online fault monitoring technique for chaos-based passive optical networks (PONs) is proposed and experimentally demonstrated. The fault monitoring is performed by the chaotic communication signal. The proof-of-concept experiments are demonstrated for two PON structures, i.e., wavelength-division-multiplexing (WDM) PON and Ethernet PON (EPON), respectively. For WDM PON, two monitoring approaches are investigated, one deploying a chaotic optical time domain reflectometry (OTDR) for each transmitter, and the other using only one tunable chaotic OTDR. The experimental results show that the faults at beyond 20km from the OLT can be detected and located. The spatial resolution of the tunable chaotic OTDR is an order of magnitude of centimeter. Meanwhile, the monitoring process can operate in parallel with the chaotic optical secure communications. The proposed technique has benefits of real-time, online, precise fault location, and simple realization, which will significantly reduce the cost of operation, administration and maintenance (OAM) of PON.

Experimental demonstrations of Y-00 cipher for high capacity and secure optical fiber communications

Quantum Enigma Cipher is an epoch-making concept in the cryptography that may break the Shannon limit of the cryptography. Yuen-2000 (Y-00) protocol is a first generation toward the Quantum Enigma ...

Experimental Investigation of Improving the Performance of the Chaotic Optical Communication with Chaos-Masking through Wavelength Mismatch

In this paper, the wavelength mismatch between the message and the chaotic carrier in the chaotic optical communication with chaos-masking has been experimentally investigated. The results show that the decryption performance of the receiver can be improved when the message wavelength is greater than that of the chaotic carrier. When the wavelength offset is set to 0.12 nm, high-speed secure optical communication with a message of 2.5 Gbits/s is achieved.

Control of optical orbital angular momentum by Vogel spiral arrays of metallic nanoparticles

In this Letter, we experimentally demonstrate structured light carrying multiple values of orbital angular momentum (OAM) in the farfield scattering region of Vogel spiral arrays of metallic nanoparticles. Using Fourier-Hankel mode decomposition analysis and interferometric reconstruction of the complex amplitude of scattered waves, we show the ability to encode well-defined numerical sequences, determined by the aperiodic spiral geometry, into azimuthal OAM values, in excellent agreement with analytical scattering theory. The generation of azimuthal sequences of OAM values by light scattering from engineered aperiodic surfaces is relevant to a number of device applications for secure optical communication, classical cryptography, and quantum cryptography.

Secure optical communication using stimulated Brillouin scattering in optical fiber

We propose to encrypt/decrypt high-speed optical signal using stimulated Brillouin scattering (SBS) effect in optical fiber for the first time. The broadened SBS gain or loss distorts the amplitude and phase of the optical signal so as to realize all-optical encryption. The corresponding SBS loss or gain with the same bandwidth and amplitude recovers the distorted signal to implement optical decryption. The encryption/decryption keys could be the SBS gain amplitude, bandwidth, central wavelength and the spectral shape, which are configurable and can be flexibly controlled by the users. The operation principle of the SBS based encryption and decryption is explained in detail. Complete encryption and error-free decryption for a 10.86-Gb/s on-off-keying signal has been experimentally demonstrated using broadband SBS amplification and absorption. The immunity of the proposed encryption method to the eavesdropper's attack is also analyzed. The SBS based secure optical communication is compatible with the current optical communication systems.

Scrambled coherent superposition for enhanced optical fiber communication in the nonlinear transmission regime

Coherent superposition of light waves has long been used in various fields of science, and recent advances in digital coherent detection and space-division multiplexing have enabled the coherent superposition of information-carrying optical signals to achieve better communication fidelity on amplified-spontaneous-noise limited communication links. However, fiber nonlinearity introduces highly correlated distortions on identical signals and diminishes the benefit of coherent superposition in nonlinear transmission regime. Here we experimentally demonstrate that through coordinated scrambling of signal constellations at the transmitter, together with appropriate unscrambling at the receiver, the full benefit of coherent superposition is retained in the nonlinear transmission regime of a space-diversity fiber link based on an innovatively engineered multi-core fiber. This scrambled coherent superposition may provide the flexibility of trading communication capacity for performance in future optical fiber networks, and may open new possibilities in high-performance and secure optical communications.

Aperiodic arrays of active nanopillars for radiation engineering

We engineer aperiodic nanostructures for enhanced omnidirectional light extraction and coupling of 1.55 μm radiation to distinctive optical resonances carrying of orbital angular momentum (OAM) using light emitting Si-based materials. By systematically studying nanopillar arrays with varying pillar separations and increasing degree of rotational symmetry in Fourier space, we show that omnidirectional extraction is achieved with circularly symmetric Fourier space, leading to best light emission enhancement from planar devices such as LEDs or lasers. To demonstrate the potential of active aperiodic structures with azimuthally isotropic k-space, we fabricate nanopillar arrays of erbium doped silicon-rich nitride using electron beam lithography and reactive ion etching. Experimental results obtained using leaky-mode photoluminescence spectroscopy prove over 10 times extraction enhancement at 1.55 μm from aperiodic golden angle spirals (GA spirals), in good agreement with design based on analytical Bragg scattering and finite difference time domain calculations. In addition, by imaging Er radiation in direct and reciprocal space, we demonstrate that GA spiral arrays support angularly isotropic emission patterns and distinctive optical resonances with a well-defined azimuthal structure carrying OAM. These findings offer unique opportunities for the engineering of novel active structures that leverage isotropic emission patterns and structured light for secure optical communication, sensing, imaging, and light sources on a Si platform.

Secure Optical Communication System Based on Dynamic Strong Dispersion Control

An novel solution for secure optical communication system based on dynamic strong dispersion control is proposed. Firstly, the theoretical principle of dynamic strong dispersion control and the system structure, especially the composition of encryption part and decryption part, are presented. Secondly, the feasibility and performance of the secure system are verified by numerical analyzing in a 40 Gb/s simulation system. Lastly, the huge application potential of this system in various fields is pointed out.

Chaotic optical cryptographic communication using a three-semiconductor-laser scheme

In this paper, a secure optical chaos-based communication scheme is proposed. A semiconductor laser (SL) subjected to polarization-rotated optical feedback serves as the drive laser (DL), and two identical or near-identical SLs act as the transmitter laser (TL) and receiver laser (RL). The TL and the RL receive identical polarization-rotated optical injection from the DL. Two channels are used, and the TM mode of the DL, after being rotated by 90°, serves as the perturbation quantity. The communication performance is numerically studied. More importantly, the high fidelity and high degree of privacy of the proposed scheme are verified in detail, and the failure of two potential attacker scenarios is demonstrated, even if the attacker can get access to both channels simultaneously.

40 Gb/s, secure optical communication based upon fast reconfigurable time domain spectral phase en/decoding with 40 Gchip/s optical code and symbol overlapping

We propose and experimentally demonstrate a 40 Gb/s secure optical communication system with on-off-keying (OOK) modulation format by using a time domain spectral phase en/decoding scheme, which employs a highly dispersive element and high-speed phase modulator for introducing significant symbol overlapping for both the encoded and incorrectly decoded noiselike signals to enhance the information security against eavesdropping using a power detector. The influence of dispersion and chip modulation rate on the symbol overlapping of the incorrectly decoded signal has been analytically investigated and experimentally verified. Security enhancement for 40 Gb/s OOK data using fast reconfigurable 40 Gchip/s optical codes with code lengths of up to 1024 has been demonstrated and compared with a 10 Gb/s system.

Rapid programmable/code-length-variable, time-domain bit-by-bit code shifting for high-speed secure optical communication

We propose and experimentally demonstrate a time-domain bit-by-bit code-shifting scheme that can rapidly program ultralong, code-length variable optical code by using only a dispersive element and a high-speed phase modulator for improving information security. The proposed scheme operates in the bit overlap regime and could eliminate the vulnerability of extracting the code by analyzing the fine structure of the time-domain spectral phase encoded signal. It is also intrinsically immune to eavesdropping via conventional power detection and differential-phase-shift-keying (DPSK) demodulation attacks. With this scheme, 10 Gbits/s of return-to-zero-DPSK data secured by bit-by-bit code shifting using up to 1024 chip optical code patterns have been transmitted over 49 km error free. The proposed scheme exhibits the potential for high-data-rate secure optical communication and to realize even one time pad.