Cost-effective fiber-to-lithium niobate chip coupling using a double-side irradiation self-written waveguide

Area of Science:

• Photonics
• Materials Science
• Optical Engineering

Background:

• Integrated lithium niobate (LN) chips are crucial for advanced photonic devices like electro-optical modulators.
• High coupling loss between optical fibers and LN waveguides is a major obstacle for practical applications.
• Existing solutions like lensed fibers or taper structures can increase design and fabrication complexity.

Purpose of the Study:

• To propose and demonstrate a novel method for reducing fiber-to-LN chip coupling loss.
• To alleviate the stringent alignment requirements associated with traditional end-fire coupling.
• To offer a cost-effective and flexible solution for optical interconnects in integrated photonics.

Main Methods:

• Utilizing self-written waveguides (SWWs) induced by light irradiation to bridge the mode-field mismatch between single-mode fibers (SMFs) and LN waveguides.
• Applying double-side irradiation for SWW formation.
• Characterizing coupling loss between a SMF (4.4 µm MFD) and a sub-micrometer LN rib waveguide.

Main Results:

• Achieved a significant reduction in coupling loss from -14.27 dB to -5.61 dB.
• Demonstrated the effectiveness of SWWs in overcoming mode-field mismatches.
• Showcased the potential for simplified alignment procedures.

Conclusions:

• Self-written waveguides offer a promising solution for efficient fiber-to-LN chip optical coupling.
• The proposed method can lead to more cost-effective and flexible integrated photonic systems.
• This technique addresses a key challenge in the practical implementation of LN-based photonic devices.