N N Elkin

Above-threshold numerical modeling of high-index-contrast photonic-crystal quantum cascade lasers

Three-dimensional above-threshold analyses of high-index-contrast (HC) photonic-crystal (PC) quantum-cascade-laser arrays (QCLA) structures, for operation at watt-range CW powers in a single spatial mode, have been performed. Threeelement HC-PC structures are formed by alternating active- antiguided and passive-guided regions along with respective metal-electrode spatial profiling. The 3-D numerical code takes into account absorption and edge-radiation losses. Rigrod’s approximation is used for the gain. The specific feature of QCLA is that only the transverse component of the magnetic field sees the gain. Results of above-threshold laser modeling in various approximate versions of laser-cavity description are compared with the results of linear, full-vectorial modeling by using the COMSOL package. Additionally, modal gains for several higher-order optical modes, on a ‘frozen gain background’ produced by the fundamental-mode, are computed by the Arnoldi algorithm. The gain spatial-hole burning effect results in growth of the competing modes’ gain with drive current. Approaching the lasing threshold for a competing higher-order mode sets a limit on the single-mode operation range. The modal structure and stability are studied over a wide range in the variation of the inter-element widths. Numerical analyses predict that the proper choice of construction parameters ensures stable single-mode operation at high drive levels above threshold. The output power from a single- mode operated QCLA at a wavelength of 4.7 μm is predicted to be available at multi-watt levels, although this power may be restricted by thermal effects.

Simulation of phase locking of two lasers with hybrid resonators

A three-dimensional numerical diffraction model of a slab laser with a hybrid resonator is developed and used for studying the phase locking of two lasers optically coupled through the edge of the output mirror. Numerical analysis of phase locking of industrial CO2 slab lasers shows that such a locking is possible for an appropriate choice of coupling parameters. It is found that the destructive effect of the active medium caused by an increase in the pump intensity can be minimised. It is shown that as the pump intensity is increased, the lateral radiation pattern of the output radiation improves while the beam is broadened in the transverse direction due to excitation of higher-order waveguide modes.