Experimental OFDM transmission performance analysis in a SOA - fiber cavity laser.

In this article, we present an experimental study of OFDM transmission using a specific bi-directional fiber cavity laser based on a semiconductor optical amplifier. We show that in the presence of sinusoidal modulation, its frequency response presents resonances relative to the optical cavity modes. We investigate first the performance of the system in terms of Error Vector Magnitude (EVM) for different configurations relative to the frequency position of the OFDM sub-carriers with respect to the frequency interval of the resonant modes. The obtained results show a significant improvement in the OFDM transmission EVM by increasing the OFDM subcarriers per frequency interval. We then analyze the impact of inter-symbol interference and inter-frame interference on the system's performance due to the round-trip echo and propose a pre-compensation method that added a small percentage of the previous symbol inversed before transmitting it inside the cavity where a decrease in the EVM is obtained respectively from 21.4% to 9.6% and from 26.8% to 13.2% for 4-QAM and 16-QAM data transmission.

SOA-MZI photonic sampler with a post-distortion linearization technique.

We present a post-distortion linearization technique for a semiconductor optical amplifier Mach-Zehnder interferometer (SOA-MZI) photonic sampler. The sampling source is an active mode-locked laser producing 12.6 ps-width pulses with a repetition frequency of 10 GHz. The mathematical model for the linearization technique is presented and then evaluated for the quasi-static regime, i.e. sampling continuous-wave signals, and for the dynamic regime, i.e. sampling sinusoidal signals. A significant improvement in terms of total harmonic distortion (THD) equal to 23.4 dB is observed for a modulation index equal to 80% in the quasi-static regime, matching the highest observed THD improvement in the dynamic regime.

Two cascaded SOAs used as intensity modulators for adaptively modulated optical OFDM signals in optical access networks.

Detailed theoretical and numerical investigations of the transmission performance of adaptively modulated optical orthogonal frequency division multiplexed (AMOOFDM) signals are undertaken, for the first time, in optical amplification and chromatic dispersion (CD) compensation free single mode fiber (SMF) intensity-modulated and direct-detection (IMDD) systems using two cascaded semiconductor optical amplifiers in a counterpropagating configuration as an intensity modulator (TC-SOA-CC-IM). A theoretical model describing the characteristics of this configuration is developed. Extensive performance comparisons are also made between the TC-SOA-CC and the single SOA intensity modulators. It is shown that, the TC-SOA-CC reaches its strongly saturated region using a lower input optical power much faster than the single SOA resulting in significantly reduced effective carrier lifetime and thus wide TC-SOA-CC bandwidths. It is shown that at low input optical power, we can increase the signal line rate almost 115% which will be more than twice the transmission performance offered by single SOA. In addition, the TC-SOA-CC-IM is capable of supporting signal line rates higher than corresponding to the SOA-IM by using 10dB lower input optical powers. For long transmission distance, the TC-SOA-CC-IM has much stronger CD compensation capability compared to the SOA-IM. In addition the use of TC-SOA-CC-IM is more effective regarding the capability to benefit from the CD compensation for shorter distances starting at 60km SMF, whilst for the SOA-IM starting at 90km.