The slow light is always at the cost of the signal distortion when the periodic rectangular signal propagates in
Erbium-doped fiber (EDF), which is confirmed by the implemented simulations and measurements. A new definition of
Fundamental Harmonic Fractional Delay (FHFD) is proposed based on the fundamental harmonic phase delay with the
consideration of signal distortion to evaluate the slow light effect. The influences of signal power, modulation depth and
duty ratio on slow light effect are studied, and the relationship between Fundamental Harmonic Fractional Delay (FHFD)
and Total Harmonic Distortion (THD) is given.
Advanced modulation formats, such as DPSK, DQPSK, QAM, have become the mainstream technologies in the optical
network over 40Gb/s, the DPSK format is the fundamental of all advanced modulation formats. Optical buffers, as a key
element for temporarily storing packets in order to synchronization or contention resolution in optical nodes, must be
adapted to this new requirement. Different from other current buffers to store the NRZ or RZ format, an all-optical buffer
of storing DPSK packets based on nonlinear polarization rotation in SOA is proposed and demonstrated. In this buffer, a
section of PMF is used as fiber delay line to maintain the polarization states unchanged, the driver current of SOA is
optimized, and no amplifier is required in the fiber loop. A packet delay resolution of 400ns is obtained and storage for
tens rounds is demonstrated without significant signal degradation. Using proposed the new tunable DPSK demodulator,
bit error rate has been measured after buffering for tens rounds for 10Gb/s data payload. Configurations for First-in
First-out (FIFO) buffer or First-in Last-out (FILO) buffer are proposed based on this buffer. The buffer is easy control
and suitable for integration. The terminal contention caused by different clients can be mitigated by managing packets
delays in future all-optical network, such as optical packet switching network and WDM switching network.
A new scheme of demodulating DPSK signal is proposed based on structure of differential delay interference which is
suitable for variable bit-rate and the tuning speed is faster than the existed demodulator. The demodulation of variable
bit-rate NRZ-DPSK formats of 10Gb/s and 40Gb/s are demonstrated, the BER after demodulating is lower than 10-9. It is proved that this demodulator can be used to demodulate 10Gb/s to tens Gb/s bit rate DPSK signal. The demodulator can realize one-, half-, or quarter-bit delays for DPSK signals. Compared to other DPSK demodulators, this demodulator is tunable and the tunable speed is faster.
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