Abstract

Efficient second harmonic generation in optical fibers is still a largely unexplained phenomenon.¹ In particular, neither the microscopic mechanism nor the defects or impurities that might be involved have been identified yet. We present new results that may contribute toward a solution of this problem. We modified the defect content of a Ge-doped-core fiber by subjecting it to a hydrogen and heat treatment that led directly to enhancement of the achievable second harmonic conversion efficiency. The fiber was placed in a pressure chamber with 3-atm H₂ at room temperature for 3 days and was then removed and heated at 250°C for 6 h. Strands of this fiber, 15 cm long, were prepared for second harmonic generation: each was seeded with light at 1.06 μm and 532 nm at fixed power levels for a fixed time, long enough to reach saturation of the conversion efficiency.² The conversion efficiency of the treated fiber was compared with that of untreated strands of the same fiber seeded in identical conditions. To date, an enhancement by more than a factor of 2 has been observed in such treated fibers.

© 1988 Optical Society of America