We measure the transmission characteristics of hollow-core photonic crystal fiber (HC-PCF) gas cells with ferrule- and fusion-spliced configurations, and near- and far-field images of the HC-PCF are observed. Results show that the center of mass (COM) of the far-field image varies with the laser frequency and temperature, and the moving COM relates to the oscillatory transmission. Using a model of the spatial interference, we first demonstrate that mainly the modes with asymmetric phase distribu
