Differential phase-shift keying (DPSK) modulation format has been widely employed in high speed long haul
transmission systems. The DPSK modulation format is a promising technique to increase the system performance, for
example: extending the transmission distance, reducing the OSNR requirement and suppressing the nonlinearity. So the
optical signal performance monitoring is quite necessary and indispensible for this modulation format. In this paper, a
chromatic dispersion (CD) monitoring method for DPSK signals has been demonstrated using an optical delay
interferometer with imperfect phase adjustment. We found the eye diagrams shown inclination with the combination
effect of phase error and residual CD. This method can not only be used for CD monitoring but also can discriminate
dispersion polarity. The CD monitoring range could cover from -425 to +425ps/nm of 10 GHz NRZ-DPSK system.
We demonstrate dispersion monitoring of differential phase-shift keying (DPSK) modulated optical transmission system
by measuring RF components of detected optical signal. The results show that this scheme can realize dispersion
monitoring up to 4320ps/nm and sensitivity up to 15.5(ps/nm)/dBm. The effect of OSNR on the performance of the
monitoring system are studied and discussed.
We fabricate and demonstrate a long-period grating (LPG) by periodically tapering a section of standard single-mode
fiber using resistive filament heating. The obtained LPG has a large peak transmission attenuation of -30.31 dB with only
22 periods in a 1.0-cm long optical fiber. Such a LPG exhibits unique characteristics for sensing applications. The
bending and strain sensitivities are 1.74 nm•m and 1.11 pm/με, respectively. The polarization dependent loss is large, up
to 11.65dB, caused by asymmetric index profile in the cross section of the tapered LPG.
Fractal compression is an attractive compression method with the ability of high compression ratio. But there are also some problems that has not been well solved yet. The wavelet-based fractal compression method proposed in this paper can not only make up its weakness, such as long encoding time, but also bring out its merits, such as high compression ratio.