A performance comparison between a recently proposed novel technique known as fast orthogonal frequencydivision multiplexing (FOFDM) and conventional orthogonal frequency-division multiplexing (OFDM) is undertaken over unamplified, intensity-modulated, and direct-detected directly modulated laser-based optical signals. Key transceiver parameters, such as the maximum achievable transmission capacity and the digital-to-analog/analog-to-digital converter (DAC/ADC) effects are explored thoroughly. It is shown that, similarly to conventional OFDM, the least complex and bandwidth efficient FOFDM can support up to ∼20 Gb/s over 500 m worst-case multimode fiber (MMF) links having 3 dB effective bandwidths of ∼200 MHz × km. For compensation of the DAC/ADC roll-off, a power-loading (PL) algorithm is adopted, leading to an FOFDM system improvement of ∼4 dB. FOFDM and conventional OFDM give similar optimum DAC/ADC parameters over 500 m worst-case MMF, while over 50 km single-mode fiber a maximum deviation of only ∼1 dB in clipping ratio is observed due to the imperfect chromatic dispersion compensation caused by one-tap equalizers.
There has been an increased interest in enhancing the security of optical communications systems and networks. All-optical cryptography methods have been considered as an alternative to electronic data encryption. In this paper we propose and verify the use of a novel all-optical scheme based on cryptographic keys applied on the spectral signal for encryption of the M-QAM modulated data with bit rates of up to 200 gigabits per second.
The ever-growing demand for optical network security can be addressed by data encryption at different network layers. In this work, we consider all-optical cryptography technique that applies a spectral phase change and delay encoding on spectrum slices of a specified WDM channel. In this case we have investigated a novel approach where signals are double encrypted to achieve an enhanced degree of security. Simulation results indicate that such double cyphering scheme can be applied to high data-rate M-QAM signals propagating in metro/regional networks.
We investigate the application of a new all-optical cryptography technique to wavelength division multiplexing (WDM)-compatible differential phase-shift keying (DPSK) signals. The technique uses current optical band-pass optical filters with narrow bandwidths to divide a given input WDM-compatible signal into several spectral slices, which are submitted to two cryptographic key stages. The first one impresses amplitude encoding, whereas the second imposes delay variations to each spectral slice. The technique performance is assessed by evaluating the encrypted and decrypted signals bit error rates. Computer simulations suggest that encrypted DPSK signals may be properly recovered even after being propagated through typical metropolitan area network distances. 1
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