Mode properties and characteristics of negative branch unstable ring resonators

Abstract

The unfolded single-aperture near-imaging negative branch confocal unstable ring-resonator design is considered. Diffractive properties and mode characteristics of the moderate Fresnel-number baseline-resonator design with Neq = - 10.28 are calculated using three-dimensional FFT, FHT, and virtual source codes. The FFT results are in agreement with those from positive branch unstable resonators having the same Fresnel number. Similar modeling for resonator designs where Neq is varied from - 6.6 to - 12.0 is analyzed, and good mode discrimination is found between the dominant 1 = 0 modes and higher order modes at half integral Fresnel numbers. Both FFT and FHT diffractive codes exhibit increasing loss of accuracy when applied to resonator designs as equivalent Fresnel numbers increase above Neq = 12 - 15. The virtual-code results agree well with the FFT and FHT modeling results for Neq = - 10 to - 25.