| The capacity of all-optical communication networks increases continuously in recent years with the developments of wireless mobile network, increasing of high definition video services and the approaching of the big data era. The network transmission bit rate increases from 10 Gb/s to 40 Gb/s and beyond, in which case the conventional intensity modulation format can no longer satisfy the requirements of high-speed all-optical communication networks. The phase modulation formats are widely used in those optical networks providing higher spectrum efficiency, effectively improving the systems’ nonlinear tolerance, the intrinsic dispersion and the polarization mode dispersion tolerance. With the applications of the phase modulation formats in 40 Gb/s and beyond high speed optical communication networks, it brings in new issues to the network technologies and all-optical signal processing technologies, and it demands changes in the transmission link technologies as well.The all-optical buffer technology works as a key technology of the all-optical switching networks, should also adapt to this phase modulation formats. This Ph.D. dissertation is funded with the supporting of the National Natural Science Foundation Project "All-optical buffer, slow light and payload extraction of the 40 Gb/s and the above new modulation format". In this PhD. dissertation, the several key technologies in all-optical buffer and the associated signal processing technologies of the phase modulation formats are studied, the researches mainly focuses on:The modulation and demodulation of DPSK and QPSK signal are studied, in order to adapt the variable bit-rate in dynamic bandwidth allocation in all-optical network, a novel scheme of tunable demodulator of non-return to zero differential phase shift keying (NRZ-DPSK) signal is put forward, which can be used to demodulate variable bit-rate signal; in order to solve the problem of the high speed signal generation,20 Gb/s optical signal is generated from 10 Gb/s electrical signal by double times repetition rate, in order to synchronize the processing unit (such as all-optical buffer unit) in the network’s, a new all-optical clock recovery scheme of the NRZ-DPSK signal based on tunable demodulator is presented; the semiconductor optical amplifiers’(SOAs) properties are investigated, and a new measurement method on the SOA’s internal loss factor and the line-width enhancement factor is proposed; based on the above researches, an all-optical buffer technology for the phase modulation formats based on nonlinear polarization rotation is proposed to solve the competition and congestion packet at the switching node, and the all-optical buffer of 10 Gb/s NRZ-DPSK signal is achieved, by the demodulator in the 3rd chapter, the results of the buffered signal is analyzed, all the above work lay a basis of the bit buffer and all-optical time sequence switching.The main innovative research works of this dissertation are summarized as follows:1. A new tunable demodulator scheme for the NRZ-DPSK signals based on Fizeau interferometer is proposed. Simply by tuning the distance between the collimator and the total reflecting mirror, demodulation of 2.5 Gb/s,10 Gb/s and 40 Gb/s NRZ-DPSK signals are realized experimentally, the bit error rate (BER) after demodulation is less than 10-9. The fast demodulation of 38 Gb/s and then 39 Gb/s NRZ-DPSK signal is achieved, proving the fast tuning possibility of this demodulator.2. A novel scheme of electro-optical repetition rate multiplication based on phase modulation (PM) and differential demodulation of NRZ-DPSK signal is proposed. By using the Fizeau optical fiber interference as the differential demodulator, a short pulse with the full width at half maximum (FWHM) less than 20 ps converted from NRZ electrical signal is achieved. Adjusting the delay time of a delay combiner consisted of the polarization beam splitter (PBS), fiber delay lines and polarization beam combiner (PBC),10 Gb/s and 20 Gb/s RZ signal are obtained. Without any nonlinear active components and additional noise, it is only dependent on rising and falling edges of the electrical pulse generated by programmable pattern generator. A new scheme of clock recovery of variable bit-rate NRZ-DPSK signal based on tunable demodulator is proposed. The tunable demodulator composed by Fizeau interferometer based on free space light converts the NRZ-DPSK signal into RZ signal which includes clock component.Clock recovery of 2.5 Gb/s and 5 Gb/s NRZ-DPSK signals are achieved and the optical extinction ratio (ER) of the clock recovered is better than 10 dB, which prove that this scheme is useful for the tunability of the changed clock signal.3. As one of the key devices in all-optical signal processing, Semiconductor Optical Amplifier (SOA) was investigated. A new measurement method of the SOA’s internal loss factor is proposed without obtaining the noise figure spectra. Under the condition of considering the SOA’s internal loss and ignoring its amplified spontaneous emission (ASE) noise, the modified formula of SOA’s input-output characteristics is deduced. By fitting the practical measured input-output characteristics curves, the SOA’s internal loss coefficient, the small signal gain coefficient and the saturation output power are measured under different injection currents, which all coincide well with our theoretical prediction.4. A simple measurement scheme of the line-width enhancement factor (LEF) based on the Nonlinear Polarization Rotation (NPR) of semiconductor optical amplifier (SOA) is proposed. Considering polarization dependent gain, the relationships between the LEF and the Stokes vector was derived theoretically. It is proved that the LEF can be calculated directly from the Stokes parameters without any other assistant measurement system The results demonstrated that the LEF varies in a small range from 10.5 to 8.5 for TE mode and from 8.2 to 5.8 for TM mode respectively, when the input optical power varies from 50 μW to 1 mW and the bias current varied from 90 mA to 170 mA.5. An all-optical buffer for 10 Gb/s NRZ-DPSK signal based on nonlinear polarization rotation in SOA is presented and experimentally demonstrated. The resolution of this buffer is 0.4 μs and the depth is 90%, and ten loops buffering is realized providing a maximum buffer delay of 4 μs. The BER of the buffered packets, which is measured with above proposed tunable demodulator, is less than 10-9. The nonlinear polarization rotation effect of NRZ-DPSK signal and the gain equilibrium problem of NRZ-DPSK signal buffer are studied.
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