Ultra-dense WDM-PON 6.25 GHz spaced 8×1 Gb/s based on a simplified coherent-detection scheme.

Area of Science:

• Optical communications
• Telecommunications engineering

Background:

• Passive Optical Networks (PONs) are crucial for broadband access.
• Existing PONs face limitations in capacity and reach for future demands.
• Ultra-Dense-Wavelength Division Multiplexing (UD-WDM) offers a path to increased capacity.

Purpose of the Study:

• To demonstrate a novel, cost-effective UD-WDM PON system.
• To achieve polarization-independent coherent detection without complex diversity schemes.
• To enable long-reach transmission suitable for overlaying existing PONs.

Main Methods:

• Experimental demonstration of a UD-WDM PON with 6.25 GHz channel spacing.
• Implementation of a novel coherent detection scheme using a 3x3 coupler, three photodiodes, and a common DFB laser as a free-running local oscillator (LO).
• Temperature tuning of the DFB LO for channel selection.

Main Results:

• Achieved polarization-independent coherent detection.
• Demonstrated 70 km long-reach transmission with 30 dB attenuation (> 45 dB total optical distribution network loss).
• Successfully tuned the free-running DFB LO to detect eight channels within a 2°C range.

Conclusions:

• The proposed UD-WDM PON is a novel, low-cost solution for high-capacity optical access.
• The system's long-reach capability and simple coherent detection scheme make it suitable for overlaying existing PON infrastructure.
• This technology offers a viable upgrade path for broadband networks.