  Understanding the atmospheres of exoplanets is a milestone to decipher their
formation history and potential habitability. High-contrast imaging and
spectroscopy of exoplanets is the major pathway towards the goal. Directly
imaging of an exoplanet requires high spatial resolution. Interferometry has
proven to be an effective way of improving spatial resolution. However, means
of combining interferometry, high-contrast imaging, and high-resolution
spectroscopy have been rarely explored. To fill in the gap, we present the
dual-aperture fiber nuller (FN) for current-generation 8-10 meter telescopes,
which provides the necessary spatial and spectral resolution to (1) conduct
follow-up spectroscopy of known exoplanets; and (2) detect planets in
debris-disk systems. The concept of feeding a FN to a high-resolution
spectrograph can also be used for future space and ground-based missions. We
present a case study of using the dual-aperture FN to search for biosignatures
in rocky planets around M stars for a future space interferometry mission.
Moreover, we discuss how a FN can be equipped on future extremely large
telescopes by using the Giant Magellan Telescope (GMT) as an example.
