We show that the generalized nonlinear Schrödinger equation (GNLSE) with quartic dispersion supports infinitely many multipulse solitons for a wide parameter range of the dispersion terms. These solitons exist through the balance between the quartic and quadratic dispersions with the Kerr nonlinearity, and they come in infinite families with different signatures. A traveling wave ansatz, where the optical pulse does not undergo a change in shape while propagating, allows us to transform the GNLSE into a fourth-order nonlinear Hamiltonian ordinary differential equation with two reversibilities. Studying families of connecting orbits with different symmetry properties of this reduced system, connecting equilibria to themselves or to periodic solutions, provides the key to understanding the overall structure of solitons of the GNLSE. Integrating a perturbation of them as solutions of the GNLSE suggests that some of these solitons may be observable experimentally in photonic crystal waveguides over several dispersion lengths.

We model and experimentally investigate second harmonic generation in silica microfibers and loop resonators, in which the second order nonlinearity arises from the glass-air surface dipole and bulk multipole contributions. In the loop resonator, the recirculation of the pump light on resonance is used to increase the conversion. The effect of the loop parameters, such as coupling and loss, is theoretically studied to determine their influence on the resonance enhancement. Experimentally, microfibers were fabricated with diameters around 0.7 μm to generate the intermodally phase matched second harmonic with an efficiency up to 4.2 × 10⁻⁸ when pumped with 5 ns 1.55 μm pulses with a peak power of 90 W. After reconfiguring the microfiber into a 1 mm diameter loop, the efficiency was resonantly enhanced by 5.7 times.

We investigate the interaction between fundamental and third harmonic fields in a nonlinear waveguide. We develop a method for evaluating the maximum efficiency of third harmonic (upconversion) and one-third harmonic (downconversion) generation by considering the solitonic behavior of the interaction. This method can be used to engineer waveguide parameters and identify the input power that enables maximum conversion efficiency to be achieved.

We describe a high-gain optical parametric amplifier (OPA) and optical parametric generator (OPG) system pumped by a fiber chirped-pulse amplification source based on novel large-mode-area fiber components. 45-nJ OPG thresholds and 34% pump–signal conversion efficiencies are obtained for $\sim 4‐\mathrm{ps}$ pulses. OPA gains in excess of 75 dB and pump–signal conversion efficiencies of $\sim 39\%$ (external) are demonstrated. Furthermore, we show that injection seeding of such high-gain parametric devices by use of a low-power continuous-wave beam results in high-power $\left(>18‐\mathrm{kW}\right)$ picosecond pulses with a time–bandwidth produce of $\sim 0.65$, some ten times less than from a free-running OPG. Using such an approach, we obtain 2.7-ps 50-nJ pulses at $1.310 \mathit{\mu }\mathrm{m}$.