Double-clad photonic crystal fiber coupler for compact nonlinear optical microscopy imaging

Area of Science:

• Photonics
• Optical Engineering
• Materials Science

Background:

• Photonic crystal fibers (PCFs) offer unique light manipulation properties.
• Double-clad structures enable simultaneous guiding of different modes or wavelengths.
• Nonlinear optical microscopy requires efficient beam splitting and wavelength separation.

Purpose of the Study:

• To fabricate and characterize a 1x2 double-clad PCF coupler.
• To demonstrate its utility in constructing a miniaturized nonlinear optical microscope.
• To explore its potential for compact all-fiber imaging systems.

Main Methods:

• Fabrication of a 1x2 double-clad PCF coupler using the fused tapered method.
• Characterization of optical properties, including excess loss and splitting ratio across visible and near-infrared wavelengths.
• Integration with a gradient-index lens to build a miniaturized microscope for two-photon fluorescence and second-harmonic generation imaging.

Main Results:

• The fabricated coupler exhibited low excess loss (1.1 dB) and a high splitting ratio (97/3) over the entire visible and near-infrared spectrum.
• The double-clad design successfully separated a near-infrared single-mode beam from a visible multimode beam.
• 3D nonlinear optical images were successfully acquired, demonstrating the system's imaging capabilities.

Conclusions:

• The developed double-clad PCF coupler is a high-performance optical component for laser power splitting and beam separation.
• It enables the construction of compact, all-fiber nonlinear optical microscopy systems.
• The coupler shows significant potential for applications in miniaturized endoscopy and advanced bio-imaging.