  The cosmic infrared background (CIB) contains emissions accumulated over the
entire history of the Universe, including from objects inaccessible to
individual telescopic studies. The near-IR (~1-10 mic) part of the CIB, and its
fluctuations, reflects emissions from nucleosynthetic sources and
gravitationally accreting black holes (BHs). If known galaxies are removed to
sufficient depths the source-subtracted CIB fluctuations at near-IR can reveal
sources present in the first-stars-era and possibly new stellar populations at
more recent times. This review discusses the recent progress in this newly
emerging field which identified, with new data and methodology, significant
source-subtracted CIB fluctuations substantially in excess of what can be
produced by remaining known galaxies. The CIB fluctuations further appear
coherent with unresolved cosmic X-ray background (CXB) indicating a very high
fraction of BHs among the new sources producing the CIB fluctuations. These
observations have led to intensive theoretical efforts to explain the
measurements and their properties. While current experimental configurations
have limitations in decisively probing these theories, their potentially
remarkable implications will be tested in the upcoming CIB measurements with
the ESA's Euclid dark energy mission. We describe the goals and methodologies
of LIBRAE (Looking at Infrared Background Radiation with Euclid), a
NASA-selected project for CIB science with Euclid, which has the potential for
transforming the field into a new area of precision cosmology.
