Modulation format identification enabled by the digital frequency-offset loading technique for hitless coherent...

Area of Science:

• Optical Communications
• Digital Signal Processing
• Coherent Transceiver Technology

Background:

• Hitless coherent transceivers require fast and accurate modulation format identification (MFI).
• Traditional MFI methods can introduce latency or complexity.
• Frequency-offset (FO) distribution is a potential carrier for encoding modulation format information.

Purpose of the Study:

• To propose and verify a blind and fast MFI technique for hitless coherent transceivers.
• To enable modulation format switching without performance degradation.
• To integrate MFI with frequency-offset compensation (FOC) for enhanced efficiency.

Main Methods:

• Utilizing a digital frequency-offset (FO) loading technique to encode modulation format information.
• Employing Fast Fourier Transformation based FO estimation (FFT-FOE) for non-data-aided (NDA) MFI.
• Implementing Constant Modulus Algorithm (CMA) pre-equalization at the receiver.

Main Results:

• Demonstrated high-accuracy MFI for various modulation formats (DP-QAM, TD-hybrid-QAM, SP-QAM) at 28 Gbaud.
• Achieved fast format switching with a switching block of only 2048 symbols.
• Verified no performance degradation in terms of amplified spontaneous emission (ASE) noise, laser linewidth, and fiber nonlinearity tolerance.

Conclusions:

• The proposed blind and fast MFI method is effective for hitless coherent transceivers.
• The technique integrates seamlessly with FO compensation, reducing complexity.
• Successful demonstration over 1500 km SSMF transmission validates the approach for long-haul optical networks.