Key Technologies For All-Optical Networks Based On Semiconductor Optical Amplifiers: Research And Applications

All-optical signal processing techniques play an important role in future high-speed, large capacity and highly trustworthy all-optical networks. All-optical signal processing based on semiconductor optical amplifiers (SOAs) has attracted considerable attention during the past years due to their features such as small footprint, low power consumption, and potential photonic integration with other optical components. In this dissertation, the key techniques in all-optical networks are studied based on SOA nonlinear polarization rotation (NPR) effect and cross-phase modulation (XPM) effect. Base on such nonlinearities, many useful applications have been applied, such as all-optical wavelength conversion (WC), all-optical 2R regeneration, all-optical On-Off Keying (OOK) to Polarization-Shift Keying (PolSK) format conversion, all-optical up-conversion, tunable birefringent Lyot filter and simultaneously multi-channel Optical Time Domain Multiplexing (OTDM) system demultiplexing.We have proposed and demonstrated a simultaneous inverted and non-inverted polarization-insensitive WCs with 2R regeneration based on SOA-NPR effect, at the frist time. We have characterized the NPR effect with linear polarization maintenance arising in polarization-insensitive SOAs in terms of probe and pump power, bias current, pump polarization, and wavelength. The step-like nonlinear power transfer function for 2R regeneration, during the pump-signal-induced NPR arising in SOAs, is obtained by calculated the measured results. The complementary WC with 2R regeneration is achieved at the two output ports of a single polarization beam splitter (PBS). The polarization switching phenomena is measured by complementary output powers of the probe light with respect to the pump light injection after passing through the PBS. Therefore, both the inverted and non-inverted WC can be achieved simultaneously by properly setting the binary power level of the pump light. The temporal waveforms, optical spectrum and bit error rate (BER) are further measured. The results have shown simultaneous power penalty reductions of 1.2 dB for inverted WC and 0.8 dB for non-inverted WC at a lOGb/s BER of 10-9 compared to the back-to-back result which has loaded the amplified spontaneous emission (ASE) noise source. Thus simultaneous inverted and non-inverted WCs with 2R regeneration based on SOA-NPR effect are approved. Moreover, this technique features polarization-insensitive and can be applied for the whole C-band.The NPR with linear polarization maintenance is applied to perform OOK to PolSK format conversion in conjunction with WC function, where the power fluctuation caused by the SOA cross gain modulation (XGM) is successfully mitigated using two cascaded SOAs. The power fluctuation of the converted PolSK signal is reduced to less than 0.6 dB, compared with 10 dB fluctuation in single SOA scheme. The power to polarization conversion is accomplished through the NPR effect. The extinction ratio (ER) of polarization modulation is maintained at larger than 30 dB which is measured after a polarizer. This technique can be applied in the whole C-band.We have proposed and experimentally demonstrated a tunable fiber-optical Lyot birefringent comb filter with independent tuning of the channel spacing and wavelength using NPR in an SOA, at the frist time. The filter configuration is based on sandwiching a fiber-optic programmable differential group delay line (DGDL) and a SOA between two polarizers. The channel spacing of the filter can be tuned by adjusting the programmable DGDL. The switching time of the programmable DGDL is around 250μs, while the tunable range is±45ps. Using the NPR effect in the SOA, we have proposed an optically controlled technique to continuously verify the phase shift. The phase shift from 0 toπbetween the transverse electric (TE) and the transverse magnetic (TM) components of the input probe beam can be adjusted by varying the power of the pump light from-10 dBm to 17 dBm. Hence fast and continuously wavelength tuning of the filter can also be achieved. The wavelength tuning range is up to 50% of the arbitrary channel spacing (or FSR) when the pump power is increased from-10 dBm to 17 dBm.We have proposed and experimentally demonstrated a novel structure of a cascadable photonic serial-to-parallel converter (SPC) based on the XPM effect in a SOA for simultaneous multiple-channel OTDM demultiplexing. The serial signal and the half rate clock signal are injected into an SOA as probe and pump, respectively. The two channels of the probe signals are set at the rise and fall slopes of the pump clock pulse, respectively. As the XPM effect arises in an SOA, the probe channel which interacts mainly with the leading edge of the pump pulse has a negative XPM-induced chirp and the spectrum has only red-shifted components, while the neighbouring channel which interacts with the trailing edge has a positive chirp and its spectrum is shifted towards blue. Thus the two channels are separated in frequency domain. Then a two channel narrow bandpass filter can be used to select each channel. Consequently, the simultaneous 1:2 serial-to-parallel conversion is achieved. A proof-of-concept experiment is carried out to demonstrate error-free operation of simultaneous two-channel demultiplexing for a 20 Gbit/s OTDM signal. A subsequent array waveguide grating (AWG) is used to symmetrically filtering the optical spectra. The red-shifted signal has an ER of 9.65 dB while the blue-shifted one has an ER of 9.1 dB. In the BER test, error-free 20 Gb/s simultaneous two-channel OTDM demultiplexing is experimentally demonstrated. The red-shifted signal has a power penalty of 1 dB while the blue-shifted one has 2 dB. The proposed SPC features cascadability, compact structure, symmetrically filtering, high-speed operation, and simultaneous two-channel operation.