Reconfigurable high-order mode pass filter for mode-division multiplexing

Area of Science:

• Photonics and Optical Engineering
• Integrated Optics
• Waveguide Technology

Background:

• Mode division multiplexing (MDM) optical systems require effective mode filters to reduce modal crosstalk.
• Filtering lower-order modes in optical systems presents a significant challenge.

Purpose of the Study:

• To propose and demonstrate a reconfigurable higher-order mode pass filter for MDM systems.
• To enable dynamic switching between higher-order and fundamental mode filtering functionalities.

Main Methods:

• A reconfigurable filter structure comprising two tunable mode converters and a directional coupler (DC) was designed.
• The structure was implemented on a three-mode planar waveguide platform.
• Simulations were performed to evaluate filter performance across the C-band.

Main Results:

• The proposed filter achieved high performance for second-order mode (TE2) transmission with low excess loss (~0.61 dB at 1.550 μm).
• Extinction ratios of ≥24 dB (TE0 & TE2) and ≥25 dB (TE1 & TE2) were maintained across the entire C-band (1.530-1.565 μm).
• The device demonstrated negligible polarization dependence, with similar results for TM polarization.

Conclusions:

• The reconfigurable mode filter offers a versatile solution for MDM systems, capable of filtering specific higher-order modes or the fundamental mode.
• The demonstrated performance, including high extinction ratios and low loss, supports its application in advanced optical communication systems.
• The dynamic tunability of the filter opens possibilities for flexible optical signal processing and routing.