11 November 2008 Monitoring techniques for phase and OSNR of DPSK/DQPSK signals
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Proceedings Volume 7136, Optical Transmission, Switching, and Subsystems VI; 71360U (2008) https://doi.org/10.1117/12.803097
Event: Asia-Pacific Optical Communications, 2008, Hangzhou, China
We review our recent achievements in the optical performance monitoring techniques such as the optical phasor monitor and optical signal-to-noise ratio (OSNR) monitor developed for differential phase-shift-keyed (DPSK) and quaternary PSK (DQPSK) signals. The optical phasor monitor is a tool that can measure the in-phase and quadrature components of the optical field of the phase-modulated signal and display the measured results on the complex plane as a phasor. We implement such a phasor monitor by using an adjustment-free differential-phase demodulator composed of a 120-degree optical hybrid (which can be realized simply by using a conventional 3x3 optical coupler), and demonstrate its plug-and-play (i.e., phase-adjustment free and wavelength/polarization-independent) operation experimentally. We also show that the proposed phasor monitor is well suited for the use in the diagnosis of DPSK/DQPSK. The OSNR monitoring is another important function to evaluate the signal quality as well as the condition of the transmission link. We have recently proposed a new technique for monitoring the 'in-band' OSNR of DPSK/DQPSK signals. This technique estimates the OSNR by analyzing the radio frequency (RF) spectrum obtained by the self-heterodyne detection. In this paper, we briefly explain its operating principle and show the experimental results. Using this technique, we could accurately monitor the OSNR of the 10-Gb/s DPSK and 20-Gb/s DQPSK signals in a 640-km long transmission link. The results also show that the performance of the proposed technique is not sensitive to the effects of chromatic dispersion and polarization-mode dispersion.
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Y. Takushima, Y. Takushima, H. Y. Choi, H. Y. Choi, Y. C. Chung, Y. C. Chung, } "Monitoring techniques for phase and OSNR of DPSK/DQPSK signals", Proc. SPIE 7136, Optical Transmission, Switching, and Subsystems VI, 71360U (11 November 2008); doi: 10.1117/12.803097; https://doi.org/10.1117/12.803097

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