We investigated the property of conversion between phase modulation (PM) and amplitude modulation (AM) in optical
fiber transmission link due to chromatic dispersion (CD) for the purpose of clock information generation. As a result, a
novel all-optical clock recovery (CR) scheme from 10 Gbps
non-return-to-zero differential phase-shift-keying (NRZ-DPSK)
signal has been demonstrated experimentally. We introduce a chromatic dispersion induced clock tone from the
NRZ-DPSK signal and feed it into a free-running semiconductor optical amplifier (SOA) based fiber ring laser to
achieve an injection mode-locking. The generated mode-locked pulse is the corresponding regenerated clock of the
original signal. Since no special component is required for NRZ-DPSK demodulation, our proposed method is very
promising because of its simple configuration and higher stability. In experiments, 20km standard single mode fiber is
employed to accumulate CD and generate PM-AM conversion hence regenerate clock tone of the NRZ-DPSK signal.
The recovered clock signal with the extinction ratio over 15 dB and the root-mean-square timing jitter of 720 fs is
achieved under 231-1 pseudorandom binary sequence
NRZ-DPSK signals measurement. We also demonstrated a similar
CR system by using a chirped fiber Bragg grating (CFBG) as the dispersion device. With the same operation principle, it
is quite convenient and promising to extend our configuration to implement all-optical CR for NRZ-DPSK signal with
data rate up to 40Gbps.
We present a new simultaneous differential phase-shift keying (DPSK) payload and subcarrier-multiplexed (SCM) label generation technique using a single dual-electrode Mach-Zehnder modulator (DE-MZM). We conduct simulations to verify the feasibility of the new SCM labeling scheme and examine the mutual interference between the DPSK payload and the SCM label. By selecting the subcarrier at half of the payload bit-rate frequency, we can significantly suppress the SCM label induced-power penalty to the DPSK payload. Moreover, we apply the SCM label generated by the proposed labeling technique to chromatic dispersion monitoring for DPSK systems. Simulation results show that by detecting radio frequency power of both the clock tone and the SCM label, the monitoring range is greatly improved.
We evaluate the performance of the externally modulated optical minimum shift keying (MSK) signal. The tolerance against fiber dispersion, linear crosstalk, self phase modulation (SPM), and stimulated Brillouin scattering (SBS) threshold for MSK is studied and compared with that of 50% duty cycle return-to-zero differential phase shift keying (RZ-DPSK) and 50% duty cycle RZ on-off-keying (RZ-OOK), via both experiment and simulation. Simulation results show that the MSK signal has the widest tolerance against SPM and the smallest linear crosstalk among these formats. Experimental results agree with the simulation on negative penalty against SPM tolerance and show widest tolerance against dispersion tolerance for MSK. The measured SBS threshold of both MSK and RZ-DPSK is more than 10 dB higher than that of an RZ-OOK system.
We systematically compare the transmission performance of three different modulation formats—return-to-zero (RZ), chirped RZ (CRZ), and vestigial sideband RZ—on an economically possible transmission link using standard single-mode fiber (SSMF) and all erbium-doped fiber amplifiers. This link is composed of wavelength-division multiplexed channels at 10 Gbit/s over 24×100-km amplifier spans without using new types of fibers or Raman amplifiers. The generation of each modulation format in the experiments is optimized for more reasonable comparison, and their optical characteristics are investigated by comparison with simulation results. Optimum input powers into SSMF and dispersion compensation fiber for each modulation format signal were explored, and their transmission performance was compared. In our cost-effective transmission link, the CRZ signal showed the lowest input power and best performance among all the formats investigated.
In today's high-bit-rate WDM systems, it is essential to monitor the residual chromatic dispersion (CD) to ensure that it does not exceed the designed tolerance. Among the schemes for CD monitoring reported so far, inband subcarrier tone method is relatively simple and effective for CD monitoring. However, this technique may be influenced by both polarization mode dispersion (PMD) and the chirp fluctuation of the external modulator. In this paper, we investigate the effect of PMD and chirp on CD monitoring and show that the presence of PMD and chirp induces significant CD monitoring errors. To tackle this problem, we propose a CD monitoring technique to
suppress the influence caused by PMD and chirp fluctuation. In the proposed CD monitoring scheme, two RF tones are added at the transmitter. The light is coupled into an apriori known dispersion offset and then split into two branches in the monitoring module. A fiber Bragg grating filter which can remove one sideband is inserted before the photodetector of one branch. The PMD effect is eliminated by optically sideband filtering and RF power ratio detection, and the monitoring error induced by the small chirp fluctuation can be suppressed using two RF tones and a dispersion offset. The operational principle is analyzed and the experimental investigation is presented. Experimental results show that this technique can accurately monitor the accumulated CD without being affected by the PMD and small chirp fluctuation.
Conference Committee Involvement (1)
Optical Transmission, Switching, and Subsystems IV
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