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A new optical steganography scheme is proposed that transmits a stealth optical code-division multiple-access (OCDMA) signal through a public binary phase-shift keying (BPSK) channel. Polarization beam splitters and arrayed waveguide gratings are used to implement a spectral-polarization coding (SPC) system with an incoherent optical source. We employ a Walsh–Hadamard code as the signature code of the user who wants to transmit stealth information using the system. A free space optical link applied to this system maintains the polarization states of light during propagation. The secret data are extracted using correlation detection and balanced subtraction in the OCDMA decoder of the intended receiver, and the other signal from the public channel is reduced by the OCDMA decoder. At the demodulator of the public channel, BPSK demodulation eliminates the stealth signal so that the public channel is not affected by the stealth signal. The two signals cannot interfere with each other. The results of this study show that our proposed optical steganography system is highly secure. The stealth signal can be favorably hidden in the public channel when the average source power of the stealth signal, public noise, and public signal are −5, −3, and 0 dBm, respectively. [ABSTRACT FROM AUTHOR]

Purpose – The purpose of this paper is to propose a new optical steganography framework that can be applied to public optical binary phase-shift keying (BPSK) systems by transmitting a stealth spectrum-amplitude-coded optical code-division multiple-access signal through a BPSK link. Design/methodology/approach – By using high-dispersion elements, the stealth data pulses temporally stretch and the amplitude of the signal decreases after stretching. Thus, the signal can be hidden underneath the public signal and system noise. At the receiver end, a polarizer is used for removing the public BPSK signal and the stealth signal is successfully recovered by a balanced detector. Findings – In a simulation, the bit-error rate (BER) performance improved when the stealth power increased. Research limitations/implications – The BER performance worsens when the noise power become large. Future work will consider increasing the system performance during high-noise power situation. Practical implications – By properly adjusting the power of the amplified spontaneous emission noise, the stealth signal can be hidden well in the public channel while producing minimal influence on the public BPSK signal. Originality/value – In conclusion, the proposed optical steganography framework makes it more difficult for eavesdroppers to detect and intercept the hidden stealth channel under public transmission, even when using a dispersion compensation scheme. [ABSTRACT FROM AUTHOR]

This study proposes novel three-dimensional (3D) matrices of wavelength/time/spatial code for code-division multiple-access (OCDMA) networks, with a double balanced detection mechanism. We construct 3D carrier-hopping prime/modified prime (CHP/MP) codes by extending a two-dimensional (2D) CHP code integrated with a one-dimensional (1D) MP code. The corresponding coder/decoder pairs were based on fiber Bragg gratings (FBGs) and tunable optical delay lines integrated with splitters/combiners. System performance was enhanced by the low cross correlation properties of the 3D code designed to avoid the beat noise phenomenon. The CHP/MP code cardinality increased significantly compared to the CHP code under the same bit error rate (BER). The results indicate that the 3D code method can enhance system performance because both the beating terms and multiple-access interference (MAI) were reduced by the double balanced detection mechanism. Additionally, the optical component can also be relaxed for high transmission scenery. [ABSTRACT FROM AUTHOR]

This study presents a hybrid analog/digital (A/D) mechanism of two-dimensional (2-D) structure of wavelength-hopping and time-spreading coding optical code-division multiple-access (OCDMA) system for future generation communication and network technologies. The 2-D method increases the maximum permissible number of simultaneous base stations (BSs) and security using a finite bandwidth of optical broad-band light source (BLS). In the proposed system, we can employ low-cost BLS which can mitigate the sampling rate of optical switch (OSW) and has the advantage of power saving. The performance enhancement is using the time-spreading method by a Mach-Zehnder modulator (MZM) with switch function to suppress the phase-induced intensity noise (PIIN) effect of the wavelength domain and the receiver structure is equipped with balanced detectors in order to suppress the multiple-access interference (MAI). In addition, the hybrid OCDMA network is equipped using a dual input MZM for the choice which time analog or digital signals to be transmitted and the advantage of these two kinds of signals can transmit by the same coder/decoder (codec) mechanism and recover by different type filters in the receiver end. The numerical evaluation results demonstrate that, for analog and digital signals under PIIN- and MAI-limited conditions, the proposed system outperforms a conventional multi-wavelength and time-spreading OCDMA scheme. Hence, enhancing the confidentiality of the asynchronous networks of codeword assignments and integratable hardware designs for the scheme with a MZM, an optical switch (OSW), arrayed-waveguide grating (AWG) and fiber Bragg gratings (FBGs) in hybrid A/D 2-D OCDMA system is proposed. [ABSTRACT FROM AUTHOR]

Highlights: [•] A new all fiber loop vibration sensor system based on OCDMA is presented. [•] Experimental results show that this sensing system obtain accurate vibration frequency. [•] This sensor system can increase the measured point by extending the codewords length. [Copyright &y& Elsevier]

Abstract: This study proposes a novel radio-over-fiber (RoF) system using two-dimensional (2-D) optical code-division multiple-access (OCDMA) scheme using pseudorandom (PN) codes for the time-spreading and wavelength-hopping (t-spreading/λ-hopping) codes. The 2-D system is implemented using optical switches (OSWs) and arrayed-waveguide grating (AWG) routers. By constructing 2-D codes using bipolar PN codes rather than unipolar codes provides a significant increase in the maximum permissible number of active radio base stations (RBSs). In general, the phase-induced intensity noise (PIIN) generated at high optical intensities significantly degrades the performance of a conventional multi-wavelength scheme. However, the OSW-based time-spreading method employed in the current 2-D OCDMA scheme effectively suppresses the PIIN effect. Additionally, multiple-access interference (MAI) is suppressed by the use of a wavelength/time balanced detector structure in the network receivers. The numerical evaluation results demonstrate that under PIIN- and MAI-limited conditions, the proposed system outperforms a conventional multi-wavelength OCDMA scheme by using the spectral spreading scheme to suppress beating noise. Especially, the t-spreading encoder/decoder (codec) groups share the same wavelength codec and the overall complexity is reduced and system network becomes more compact. [Copyright &y& Elsevier]

Abstract: This study presents a double-spread code-division multiple-access (CDMA) scheme for radio-over-fiber (RoF) transmissions. The network coder/decoders (codecs) are implemented using arrayed-waveguide grating (AWG) routers coded with maximal-length sequence (M-sequence) codes. The effects of phase-induced intensity noise (PIIN) and multiple-access interference (MAI) on the system performance are evaluated numerically for different values of the optical modulation index (OMI) during the nonlinear electro-optical modulator (EOM) response. At low OMI optical device noise is dominant, but at high OMI nonlinear effect becomes significant. Numerical result shows that the system performance is highly sensitive to the OMI. Therefore, specifying an appropriate value of the OMI is essential in optimizing the system performance. The influence of the degree of polarization (DOP) in the system is also discussed. By employing the scrambler in front of the balanced photo-detector, the system performance can be enhanced. The high-performance, low-cost characteristics of the double-spread CDMA render the scheme an ideal solution for radio-CDMA wireless system cascaded with optical CDMA network. [Copyright &y& Elsevier]

Abstract: This paper exploits the inherent cyclic and periodic free-spectral-range (FSR) properties of arrayed-waveguide grating (AWG) routers to construct a two-dimensional (2D) time-spreading and wavelength-group-hopping embedded M-sequence code for optical multiple-access networks. In the proposed codecs (encoder/decoder), a fine arrayed-waveguide grating (AWG) is used to generate an M-sequence code pattern, which is then spread in the wavelength domain by multiple coarse AWGs. The signals produced at the output ports of the coarse AWGs are then spread in the time domain using optical delay lines. The 2D code is evaluated in terms of its correlation, bit-error-rate (BER) and cardinality characteristics. It is shown that the TS/GH embedded M-sequence code yields a significant improvement in both the BER and cardinality performance of the optical multiple-access networks compared to that obtained using conventional prime-hop code (PHC), modified prime-hop code (MPHC), Barker and Walsh-based bipolar–bipolar sequence. [Copyright &y& Elsevier]