Multimode optically adiabatic silica glass submicron taper

Silica nanofibers fabricated by tapering optical fibers have attracted considerable interest as an ultimate platform for high-efficiency light-matter interactions. While previously demonstrated applications relied exclusively on the low-loss transmission of only the fundamental mode, the implementation of multimode tapers that adiabatically transmit several modes has remained very challenging, hindering their use in various emerging applications in multimode nonlinear optics and quantum optics. Here, we report the first realization of multimode submicron tapers that permit the simultaneous adiabatic transmission of multiple higher-order modes including the LP02 mode, through introducing deep wet-etching of conventional fiber before fiber tapering. Furthermore, as a critical application, we demonstrate "fundamental-to-fundamental" all-fiber third-harmonic generation with high conversion efficiencies. Our work paves the way for ultrahigh-efficiency multimode nonlinear and quantum optics, facilitating nonclassical light generation in the multimode regime, multimode soliton interactions and photonic quantum gates, and manipulation of the evanescent-field-induced optical trapping potentials of atoms and nanoparticles.

Increasing of the Signal-To-Noise Ratio in Precision Spectroscopy

Is considered the possibility of increasing the signal / noise ratio in one of the main methods of laser spectroscopy without Doppler broadening – the method of saturated absorption. The colliding beam of laser radiation in a multimode regime is expected to be used. Interaction of counter propagating modes with different frequencies will increase the number of gas atoms effectively interact with the field and, consequently, the value of a narrow resonance line shape. It is shown that the photon noise, which is essentially unavoidable, signal / noise ratio can be increased in a time where – the number of modes. For other noise (power fluctuations of the radiation, noise, photo detector, etc.) the magnitude of the signal / noise ratio may increase again