A monolithic microcavity laser with simultaneous upconversion and frequency-doubled lasing via crystal-in-glass...

Area of Science:

• Integrated Photonics
• Materials Science
• Nonlinear Optics

Background:

• Developing multifunctional micro-nano light sources is crucial for integrated photonics.
• Existing materials often struggle to combine different light emission mechanisms efficiently.
• Whispering gallery mode (WGM) microcavities offer high quality factors for light manipulation.

Purpose of the Study:

• To demonstrate a novel crystal-in-glass composite structure for multifunctional micro-nano light sources.
• To achieve dual-mode optical responses including upconversion (UC) lasing and frequency-doubled lasing within a single microcavity.
• To explore the potential for tunable lasers and on-chip nonlinear photonic systems.

Main Methods:

• Fabrication of Er³⁺/Yb³⁺-codoped glass-ceramic (GC) WGM microcavities incorporating Ba₂TiGe₂O₈ (BTG) crystals.
• Utilizing a low-phonon-energy germanate glass matrix for UC gain and BTG microcrystals for second harmonic generation (SHG).
• Employing tapered fiber near-field coupling and femtosecond free-space pumping for excitation and measurement.

Main Results:

• Achieved green (550 nm) and red (660 nm) UC lasing with low thresholds (13.31 μW and 12.97 μW) in a 30-μm-diameter microcavity.
• Demonstrated ultrabroadband frequency-doubling response from 900 to 1200 nm due to the random quasi-phase-matching (RQPM) mechanism in BTG GC.
• Successfully achieved simultaneous output of UC lasing and frequency-doubled lasing within the single microcavity.

Conclusions:

• The developed crystal-in-glass composite enables multifunctional light sources for integrated photonics.
• The hybrid material design allows for cooperative optical field manipulation.
• This work provides a foundation for tunable lasers and advanced on-chip nonlinear photonic systems.