Novel super-continuum fiber lasers and wavelength-tunable soliton pulses

Abstract

Advances in ultrashort laser pulse technology have recently generated several new applications in fields as diverse as laser processing, medical and bio-optics, opto-electronics, etc. However, ultrashort-pulse lasers require quiet laboratory environments and water cooling which prevents their use for practical applications. Spectroscopic applications also require a wavelengthtunable ultrashort pulses. The tuning range, however, is generally limited by the gain bandwidth of the laser. Since these pulses are generated with wavelength conversion using nonlinear crystals and mechanical tuning, it is difficult to generate wideband tunable pulses. Of significant interest is the recent development of compact ultrashort-pulse fiber lasers. Since these lasers consist of fiber-optic devices, they produce stable pulses and water cooling is not required. Fiber lasers are also maintenance-free and can work wherever there is electricity. The wavelength of the output pulses, however, can only be changed within the gain bandwidth of the fiber amplifier and the bandwidth is less than 100nm. In our work, we investigate all-fiber wideband utrashort-pulse sources based on ultrashort-pulse fiber lasers and study nonlinear effects in optical fibers. Specialty fibers, such as highly nonlinear fibers and photonic crystal fibers, were recently developed. Their characteristics are determined by their structure and they have demonstrated high energy density and dispersion tunability. Using ultrashort-pulse lasers and suitable specialty fibers, we can generate ultrawideband optical spectra, referred to as a super continuum. All-fiber super-continuum sources have also been reported. However, their noise level is generally high and the super continuum is characterized by excessive fine structure. To date, no practical Figure 1. Optical spectra of wavelength-tunable soliton pulses that were generated through nonlinear effects. As the fiber input power is increased, the center wavelength is continuously red-shifted. We can tune the wavelength from 1.55 to 2.0μm.