Nicholas G. Usechak

Semi-analytic technique for analyzing mode-locked lasers

A semi-analytic tool is developed for investigating pulse dynamics in mode-locked lasers. It provides a set of rate equations for pulse energy, width, and chirp, whose solutions predict how these pulse parameters evolve from one round trip to the next and how they approach their final steady-state values. An actively mode-locked laser is investigated using this technique and the results are in excellent agreement with numerical simulations and previous analytical studies.

FM mode-locked fiber lasers operating in the autosoliton regime

A high-repetition-rate ytterbium fiber laser, harmonically mode-locked using a phase modulator, is investigated experimentally, numerically, and analytically. Experimental results agree well with numerical simulations using the measured parameter values. By employing a few approximations, our model is cast in terms of a Ginzberg-Landau equation. This equation has known analytic solutions that agree well with the results of the full model in the appropriate limit. Pulse stability is also investigated numerically with an emphasis on the role of third-order dispersion.

Photodiode array for characterizing optical fibers

An innovative approach is proposed and demonstrated for measuring the attenuation of light in optical fibers. The technique utilizes a silicon device containing a v-groove that positions the fiber and detector array along the v-groove. The detectors within the v-groove are designed to partially surround the fiber in order to maximize the coupling of scattered light from the fiber into each detector.

Lasing of surface-polished polycrystalline Ho: YAG (yttrium aluminum garnet) fiber

A polycrystalline 1.5% Ho: YAG fiber with a diameter of 31 µm was prepared. Surface roughness from grain boundary grooving was reduced by polishing, which decreased the fiber scattering coefficient from 76 m-1 to 35 m-1. Lasing tests were done on this fiber with a SF57 Schott glass cladding. Lasing was confirmed by spectrum narrowing with threshold pump power lower than 500 mW and a slope efficiency of 7%. To our knowledge, this is the first lasing demonstration from a small diameter polycrystalline ceramic fiber.

Pulse switching and stability in FM mode-locked fiber lasers

We investigate the dynamics of the pulse switching mechanism in FM mode-locked fiber lasers for what we believe to be the first time. Two completely different pulse switching mechanisms are identified.

An analytic technique for investigating mode-locked lasers

We present an analytic theory capable of predicting pulse parameters in mode-locked lasers in the presence of dispersion and nonlinearity. Excellent agreement is obtained between this approach and full numerical solutions.