DQPSK (Differential Quadrature Phase Shift Keying) modulation, i.e., Differential Quadrature Phase Shift Modulation, is a new modulation technique. On the transmitter side, an optical signal with four phase states 0, π/2, π, and 3π/2 is output by differentially coding the input electrical signal stream and driving a modulator for quadrature phase shift keying modulation. On the receiving side, the differential coding is decoded by a demodulator and balanced reception is used, which improves the receiving sensitivity by 3 dB with respect to the amplitude modulation technique.

DQPSK is a phase multilevel modulation, the bit rate is twice the baud rate, so it is very suitable for 40G high-speed transmission system.DQPSK modulation has a narrow spectral width, the output spectrum is smooth, it can effectively inhibit all kinds of nonlinear effects of optical fiber, the change of phase is conducive to improve all kinds of phase-related nonlinearities (SPM, XPM, FWM), and to improve the dispersion of the chromaticity and the tolerance of polarization mode dispersion, it is the best way to improve the phase of optical fiber. Mode dispersion tolerance, is an important modulation method for long-distance high-speed high-capacity optical transmission.

Huawei provides the unique enhanced DQPSK technology (eDQPSK). Among them, eDQPSK is the introduction of chirp RZ modulation technology, which makes the system nonlinear tolerance further improved, and is the best technology for 40G ultra-long-distance transmission.

The related technical information in this chapter and the SDH equipment troubleshooting process are collected and organized by Shenzhen Optical Transmission Network Technology Company Limited (www.opticaltrans.com), please retain! Our company specializes in Huawei SDH optical transmission equipment,SDH transmission equipment sales.