Ultra-fast Optical Signal Processing For Digital Communications Using All-Optical Nonlinear Interactions In Semiconductor Optical Waveguides

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In optical communications, clock recovery, optical time demultiplexing, and 3R regeneration are known as optical signal processing. Ultra-fast optical signal processing techniques are mandatory in future high-speed network and transmission systems to allow effective use of the large optical fiber bandwidth and the light speed capabilities.

One solution is all-optical signal processing that avoids the bottleneck of slow electronics. All-optical modulation can be achieved through nonlinearties in semiconductor waveguides like EAM or SOA. Those waveguides have fast and strong nonlinearties that are appropriate for ultra-fast processing. In addition, semiconductors require reasonable optical power to operate and they can be integrated with other semiconductor devices. 

In this work, we demonstrated a several new techniques for optical signal processing, such as ultrafast optical clock recovery. We use the fast and nonlinear time-dependent loss/gain saturation in EAM/SOA to perform all-optical timing extraction. This in turn is used for optical clock recovery from data rates up to 160 Gbit/s. Simulation results shows that the technique has a potential to recover optical clock up to 640 Gbit/s.

Also we demonstrated all-optical logic AND gate using nonlinear transmission of EAM. The gate shows successful operation at 10 Gbit/s with a 2^31-1 PRBS data and it has potential for higher speeds.

We also demonstrated optical time division demultiplexing from 40 Gbit/s with simultaneous clock recovery using cross-absorption saturation inside a single EAM. The system shows an error free operation using a 2^31-1 PRBS. Also, it shows successful operation with burst-mode data propagating in a fiber-optic recirculating loop up to a distance of 10,000 Km. 

The optical 3R regeneration is also demonstrated at 10 Gbit/s using a single EAM. The all-optical timing extraction inside EAM is used for retiming, while the nonlinear transmission of EAM is used for reshaping. Meanwhile, wavelength conversion and re-amplification are performed at the same time. 

FWM is well known by its ultrafast operation and has been widely investigated by other groups in SOA's and optical fibers. Here, we showed that FWM in EAM has unique characteristics, like wide detuning range and enhancement of conversion efficiency with reverse bias. Also, we demonstrated FWM demultiplexing from 80 Gbit/s with simultaneous clock recovery using co-propagation inside a single EAM.