Analysis of frequency-doubling processes in optical fibers using Raman spectroscopy

Visible light generation in the cladding of optical fibers carrying near-infrared continuous-wave lasers due to Cherenkov-phase matched harmonic conversion

In this work, we report and analyze the cause of the surprising observation of visible light generation in the cladding of silica-based continuous-wave (CW), near-infrared fiber lasers. We observe a visible rainbow of hues in a cascaded Raman fiber laser, which we attribute to second and third harmonic conversion of the different wavelength components propagating in the core of the fiber. The light in the cladding of the fiber occurs through Cherenkov-type phase matching, and a mathematical analysis is presented to estimate the power of the harmonic light generated. We then extend this theory to visible light generation in other types of fiber lasers. Specifically, we analyze the case of a CW supercontinuum generated in standard telecom fibers, and verify our theoretical predictions with experimental results through visible spectra collected.

Widely tunable second-harmonic generation in a chalcogenide-tellurite hybrid optical fiber

When a chalcogenide-tellurite hybrid optical fiber with a high refractive index difference Δn=0.24 is pumped by an optical parametric oscillator with a pump wavelength from 1700 to 3000 nm, widely tunable second-harmonic generation (SHG) from 850 to 1502 nm is obtained. The observation of SHG is primarily due to the surface nonlinearity polarization at the core-cladding interface and the second-harmonic signal remains stable at the maximal level throughout the laser pulse irradiation.

Light-induced erasure of self-organized chi((2)) gratings in optical fibers

Self-organized chi((2)) gratings in optical fiber, prepared by irradiating the fiber with 1.06-microm light from a Q-switched mode-locked Nd:YAG laser simultaneously with its second harmonic, can be erased optically. This is accomplished by irradiating the prepared fiber with the 532-nm mode-locked Q-switched light alone, without the 1.06-microm light, or with intense green or blue light from an argon laser. The erasure is reversible, and the fiber can be reprepared as before for second-harmonic conversion. The nonexponential time dependence of the erasure process can be explained by a model involving charge separation during seeding and recombination during erasure.