Nonlinear phase-matched van der Waals crystals integrated on optical fibres

Area of Science:

• Photonics and Laser Technology
• Materials Science
• Quantum Optics

Background:

• All-fiber laser systems require high optical nonlinearity for classical and quantum applications.
• Previous efforts in exploiting second-order optical nonlinearity in fiber lasers yielded modest conversion efficiencies.

Purpose of the Study:

• To demonstrate all-fiber integration of twist-phase-matched rhombohedral boron nitride (rBN) flakes for enhanced nonlinear optical functionalities.
• To achieve efficient second-harmonic generation (SHG) and spontaneous parametric downconversion (SPDC) in integrated fiber devices.

Main Methods:

• Integration of rBN flakes on optical fiber end facets.
• Local and global optimization of interflake twist angles for phase-matching.
• Fabrication of an all-fiber frequency-doubling ultrafast laser using a graphene/rBN heterostructure.

Main Results:

• Achieved ~4.1% SHG conversion efficiency.
• Demonstrated an SPDC coincidence rate of ~90.
• Successfully designed an all-fiber laser capable of simultaneous mode-locking and intracavity SHG.

Conclusions:

• Established a novel route for high-efficiency, second-order nonlinear functionalities in all-fiber lasers.
• The integrated rBN crystals pave the way for advanced devices like optical parametric oscillators and entangled photon sources.