Spectrally efficient optical CDMA using coherent phase-frequency coding

Spectrally Phase Coded Waveform Discrimination at 10 GHz for Narrow Band Optical CDMA within 100 GHz Spectral Window

“…However, for practical applications, there are several issues to overcome, including low spectral efficiency, large multiuser access interference (MAI) as well as others. Spectrally phase coded OCDMA has been studied in detail [4][5][6][7] and attempts have been made to overcome these problems. In spectrally phase coded OCDMA, a mode-locked laser produces phaselocked spectral lines, evenly spaced with the pulse repetition rate.…”

“…The random phase coding disturbs the phaselocked feature and spreads the pulse in time, converting the input short pulses into noise like, low intensity signals. In a receiver, the same coder is used to recover the original phase, and the noise-like signal is converted back to the original pulse signal, while waveforms from other users (i.e., MAI noise) which use different codes retain phasedisturbed, low-intensity, noise-like waveforms, which are very similar to the coded signals [4][5][6][7]. This means that decoding of a random phase coded waveform simply returns to a random coded waveform set unless the decoding is matched to the pulse.…”

“…The probability of the signal overlap at the above NB-OCDMA receiver can be reduced up to 1/5, whereas the spectral efficiency can increase up to 4 times, compared with those of a BB-OCDMA. Recently, Etemad et al studied this NB-OCDMA, where 16 spectral lines within the 80 GHz bandwidth were coded for 4×2.5 Gb/s and 6×5 Gb/s OCDMA systems, and they achieved spectral efficiencies of 0.125 bit/Hz and 0.375 bit/Hz respectively [6,7]. However, the relatively good efficiency of 0.375 bit/s in [7] was achieved by an additional polarization multiplexing, which reduces the significance of the value to half (0.1875 bit/s).…”

“…Our NB-OCDMA itself (without polarization multiplexing and/or hybrid transmission with DWDM) has a potential spectral efficiency of 0.4 bit/Hz (3.2 times of [6]). Due to narrow bandwidth, the number of available spectral chips becomes small and a relatively low contrast ratio between the signal and MAI noise is expected.…”

Photonic Arbitrary Waveform Generation Technology

“…The key aspects of this approach are to use the optical frequency comb source in three different modalities that exploit the fundamental nature of phase coherent optical frequency combs. These salient features are: 1) the short optical pulse duration generated (for OTDM formats), 2) the narrow linewidths and multiplicity of optical frequency components (for direct and coherent detection analog or digital WDM formats) and 3) the spectral phase coherence which will allow for frequency domain based coding techniques (for secure OCDMA formats) [3].…”