| The nonlinear optical phenomena of second harmonic generation (SHG), also known as frequency doubling, in optical fibers was thought to be forbidden due to their amorphous nature. In 1986, it was discovered that if an intense infrared (IR) light from a Nd:YAG laser at 1.064 μm was sent through a telecommunication optical fiber for a period of time, green light at 532 nm, the second harmonic of the input IR light, was generated. This optical phenomenon is due to the interaction of the IR light with the electrons inside the optical fiber Germanium-doped silica core. Several models have been developed to describe this phenomenon, and they all require the knowledge of actual values of certain physical properties of the optical fiber such as conductivity σ dc, electron lifetime in the conduction band τR, electron mean free path le, and electron drift mobility μ D. We have succeeded in measuring σdc, l e and μD in optical fiber preforms (OFP) supplied by Naval Research Laboratory. Well-established methods for analyzing amorphous semiconductors were used. These methods are the three-electrode configuration, photoinjection of carriers by a continuous-wave (cw) laser, and time of flight techniques. The three-electrode configuration technique was used to measure the conductivity and characterizing the dielectric relaxation process of the optical fiber preforms, the cw photoinjection for the electron scattering mean free path, and time of flight technique (photoexcitation and photoinjection) for the drift mobility in optical fiber preform cores. The measured values for these physical properties are σdc ≈ 10−20 Ω −1 cm−1, le = 21 and 46 ± 3 Å by positive and negative cw photoinjection methods, respectively, μD = 44 ± 3 and 53 ± 4 cm2 V−1 s−1 by photoexcitation and photoinjection methods, respectively. |
