  Broadband temporal modes of pulsed optical fields have been recently
recognized as very promising for photonic quantum information processing and
time-frequency metrology. Exploiting their full potential demands efficient and
flexible tools for their manipulation. Among the tools demonstrated
surprisingly the most basic, a single-mode temporal filter, is missing. In this
work, we propose an experimentally feasible approach to realize a genuine
single-mode temporal filter that is based on the concept of temporal cavity, a
device with temporal mode-dependent resonances in the basis of frequency comb
modes. This functionality is achieved as temporal-domain analogy of
spatial-mode cleaner cavities. This device will enable robust temporal mode
filtering and detection, opening new prospects in time-frequency metrology and
multidimensional quantum information processing.
