All-optical modulation format conversion from NRZ-OOK to RZ-QPSK using parallel SOA-MZI OOK/BPSK converters

Area of Science:

• Optical communications
• Photonic integrated circuits

Background:

• Non-return-to-zero on-off-keying (NRZ-OOK) and return-to-zero quadrature-phase-shift-keying (RZ-QPSK) are crucial modulation formats in optical networks.
• Efficient all-optical conversion between these formats is essential for flexible network operation.

Purpose of the Study:

• To propose and experimentally demonstrate a novel all-optical modulation format conversion from NRZ-OOK to RZ-QPSK.
• To evaluate the performance of the converted RZ-QPSK signal in terms of receiver sensitivity and dispersion tolerance.

Main Methods:

• The proposed scheme utilizes parallel Mach-Zehnder interferometric (MZI) OOK/binary-phase-shift-keying (BPSK) converters integrated with semiconductor optical amplifiers (SOAs).
• Experimental demonstration at a symbol rate of 10.7 Gsymbol/s.
• Numerical simulations based on carrier rate equations were performed for verification.

Main Results:

• The converted RZ-QPSK signal exhibited comparable receiver sensitivity in both decoded channels.
• A significant dispersion tolerance of up to +295 ps/nm was achieved for the converted signal.
• Experimental results were corroborated by numerical simulations.

Conclusions:

• The proposed all-optical NRZ-OOK to RZ-QPSK conversion scheme is effective and practical.
• The demonstrated method offers robust performance suitable for high-speed optical communication systems.