Instant and efficient second-harmonic generation and downconversion in unprepared graded-index multimode fibers

Area of Science:

• Nonlinear Optics
• Materials Science
• Optical Fibers

Background:

• Second-harmonic generation (SHG) is a key nonlinear optical process.
• Previous SHG experiments in optical fibers required extensive preparation.
• Developing efficient, instantaneous nonlinear processes in fibers is desirable.

Purpose of the Study:

• To investigate SHG and downconversion in germanium-doped graded-index multimode silica fibers.
• To determine conversion efficiencies and temporal characteristics of these nonlinear processes.
• To assess the feasibility of using unprepared fibers for rapid nonlinear frequency conversion.

Main Methods:

• Excitation of germanium-doped graded-index multimode silica fibers at 1064 nm.
• Measurement of second-harmonic generation conversion efficiencies.
• Observation of accompanying downconversion phenomena.
• Assessment of the temporal dynamics of the nonlinear processes.

Main Results:

• Achieved relatively high SHG conversion efficiencies of approximately 6.5%.
• Observed instantaneous frequency-doubling behavior.
• Demonstrated effective downconversion alongside SHG.
• Reported among the highest efficiencies in unprepared fibers, requiring no lengthy preparation.

Conclusions:

• Germanium-doped graded-index multimode silica fibers offer efficient and instantaneous nonlinear frequency conversion.
• These fibers present a significant advancement over traditional methods requiring hours of preparation.
• The observed high efficiencies and rapid response make these fibers promising for practical nonlinear optical applications.