Simultaneous multichannel RZ to NRZ format conversion for LP₀₁ and LP₁₁ using a few-mode fiber Bragg grating

Area of Science:

• Optical Communications
• Photonics
• Fiber Optics

Background:

• Optical signal formats like return-to-zero (RZ) and non-return-to-zero (NRZ) are crucial in high-speed data transmission.
• Simultaneous conversion between these formats for multiple spatial modes (LP01 and LP11) presents significant technical challenges.

Purpose of the Study:

• To propose and demonstrate a novel format conversion scheme for multichannel RZ to NRZ conversion.
• To enable simultaneous conversion for both LP01 and LP11 modes using a single device.

Main Methods:

• Design of a few-mode fiber Bragg grating (FM-FBG) with comb spectra.
• Engineering the FM-FBG response spectra to align LP11 with LP01 channels based on WDM-MDM channel spacing.
• Selecting specific few-mode fiber (FMF) parameters to manage the effective refractive index difference between LP01 and LP11.
• Designing individual channel spectral responses based on the algebraic difference between RZ and NRZ spectra.

Main Results:

• Successful simultaneous RZ to NRZ format conversion for both LP01 and LP11 channels.
• Demonstration with 300-GHz-spaced RZ signals at 40 Gbit/s.
• Converted NRZ signals exhibit high Q-factors and clean, open eye diagrams, indicating high signal quality.

Conclusions:

• The proposed FM-FBG based scheme offers an efficient solution for multichannel RZ to NRZ format conversion.
• This method supports simultaneous signal processing for dual spatial modes (LP01 and LP11).
• The technique is suitable for high-speed optical communication systems requiring format flexibility.