Abstract

Distributed feedback (DFB) was first incorporated in dye lasers in 1971,^1–3 in solid-state lasers in 1973,⁴ and in a gas laser in 1979,^5–8 i.e., an optically pumped 496-μm CH₃F laser with a periodic metal waveguide. All these DFB lasers operate on the principle of linear periodic modulations of refractive-index waveguide cross section and/or gain. Therefore, they are called linear DFB lasers. The first theories on this type of DFB lasers were restricted to small modulations.^9,10 In principle, theories on linear DFB lasers are based on complex Mathieu and Hill equations.¹¹ Recently a theory was developed¹² which also permits the treatment of strong modulations on the basis of matrix methods.¹³ This theory provides dispersion relations, resonance conditions, and threshold gains of the DFB laser modes. The dispersion relations are characteristic for infinite DFB laser structures, while resonance frequencies and threshold gains of the modes are related to the finite structures.

© 1984 Optical Society of America