Long period grating-based fiber coupler to whispering gallery mode resonators

Area of Science:

• Photonics and Optical Engineering
• Materials Science

Background:

• Whispering gallery mode resonators (WGMs) offer high sensitivity for various applications.
• Efficiently coupling light into WGMs, especially silica-based ones, remains a challenge for practical implementation.

Purpose of the Study:

• To develop a novel and robust method for coupling light into high-Q silica whispering gallery mode resonators.
• To demonstrate the practical utility of this coupling technique for optical sensing.

Main Methods:

• Utilizing long period fiber gratings (LPGs) to selectively excite fiber cladding modes.
• Implementing partial fiber tapering to enhance the evanescent field overlap with WGMs.
• Employing a taper size approximately one order of magnitude larger than standard fiber tapers for increased robustness.

Main Results:

• Successfully demonstrated light coupling to high-Q silica microspheres and microbubbles.
• Observed clear transmission dips at the fiber output upon resonance.
• Showcased the ability to address multiple resonators along a single fiber by cascading LPGs with different periods.

Conclusions:

• The proposed LPG-based method provides a robust and practical approach for light coupling to silica WGMs.
• This technique enhances the feasibility of using WGMs in real-world optical sensing and device applications.
• Wavelength-selective addressing of multiple resonators offers advanced functionalities for integrated photonic systems.