We experimentally demonstrate the security vulnerability in the temporal phase coding single-user differential phase-shift
keying (DPSK) and code-shift keying (CSK) OCDMA systems with a DPSK demodulator. In the experiment, we
build up the 2.5Gbit/s DPSK- and CSK-OCDMA systems. In the systems, we use two 31-chip 640 Gchip/s
superstructured fiber Bragg grating encoders for the signal encoding. In the receiving side, we remove the decoders and
utilize the DPSK demodulator to detect the encoded signals directly. We successfully achieve the error-free BER
performance and obtaine the clear open eye diagrams using the detection without the proper decoding. It indicates the
existence of the eavesdropping vulnerability in the both systems. Furthermore, we also discuss the principle of DPSK
demodulation attack.
We propose and experimentally demonstrate a reconfigurable two-dimensional (temporal-spectral) time domain spectral
phase encoding (SPE) scheme for coherent optical code-division-multiple-access (OCDMA) application. The time-domain
SPE scheme is robust to wavelength drift of the light source and is very flexible and compatible with the fiber
optical system. In the proposed scheme, the ultra-short optical pulse is stretched by dispersive device and the SPE is
done in time domain using high speed phase modulator. A Fiber Bragg Gratings array is used for generating the two-dimensional
wavelength hopping pattern while the high speed phase modulator is used for generating the spectral phase
pattern. The proposed scheme can enable simultaneous generation of the time domain spectral phase encoding and
DPSK data modulation using only a single phase modulator. In the experiment, the two-dimensional SPE codes have
been generated and modulated with 2.5-Gb/s DPSK data using a single phase modulator. Transmission of the 2.5-Gb/s
DPSK data over 49km fiber with BER<10-9 has been demonstrated successfully. The proposed scheme exhibits the
potential to simplify the architecture and improve the security of the OCDMA system.
We have proposed and experimentally demonstrated an ultrafast optical pulse repetition rate multiplication technique
from a relatively slow optical pulse source at 1550nm based on reconfigurable time domain spectral amplitude/phase
filtering operation. In the proposed technique, a pair of dispersive fibers and a high speed electro-optical modulator
driven by a 40GHz pulse pattern generator that can be rapidly programmed are used to control the repetition rate. In the
experiment, repetition rate multiplication from 10GHz to a high speed repetition rate of 20GHz and 40GHz has been
successfully achieved by the proposed time domain spectral amplitude/phase filtering.
We demonstrate the security improvement using ±π/2-phase-shifted SSFBG encoder in time-spreading OCDMA.
Compared with conventional 0/π-phase-shifted SSFBG encoder, ±π/2-phase-shifted SSFBG encoder conceals code
pattern well in the encoded waveform. We also theoretically analyze and experimentally investigate the influence of
input pulse and the experimental measurement matches the calculated result very well.
In this paper, the recent progresses in the optical code division multiple access (OCDMA) technology for the future
optical access networks are reviewed including OCDMA/WDM system configuration, en/decoding devices, OCDMA
prototype, and demonstrations.
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