The All-fiber MZI Structure for Optical DPSK Demodulation and Optical PSBT Encoding

Guillaume Ducournau, Olivier Latry, Mohamed Ketata

Since the beginning of optical telecommunications, the most simple modulation format has been employed in optical links. This format is called OOK (On Off Keying). With the increases in bit rates, number of optical channels in Dense Wavelength Division Multiplexing (DWDM) configuration, and the augmentation of power in each channel, new modulation formats have been studied in the last years. Today, in order to increase the quality of optical links, tendency is to modify the modulation scheme used to encode information in light signals. Particularly, the Differential Phase Shift Keying (DPSK) format presents an increased tolerance to non-linear effects in optical fibers, justifying the interest for using this format in optical communications links. In the past two years, some studies investigated the possibilities to transmit 40 Gbps data rates on the deployed 10 Gbps links. An interesting solution consists in using the Phase Shaped Binary Transmission (PSBT) modulation format. With this technique, the system upgrade costs from 10 Gbps to 40 Gbps are reduced, justifying the use of PSBT. In this paper, we present two applications of Mach-Zehnder Inteferometers (MZIs), used in optical communication links. We first review the principles of the Differential Phase Shift Keying (DPSK), a phase modulation scheme, and its interest in optical communications. After that, we also focus on a recently introduced modulation format: the all-optical Phase Shaped Binary Transmission (PSBT).

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