  Many precision applications in the mid-infrared spectral range have strong
constraints based on quantum effects that are expressed in particular noise
characteristics. They limit, e.g., sensitivity and resolution of mid-infrared
imaging and spectroscopic systems as well as the bit-error rate in optical
free-space communication. Interband cascade lasers (ICLs) are a class of
mid-infrared laser exploiting interband transitions in type-II band alignment
geometry. They are currently gaining significant importance for mid-infrared
applications from <3 {\mu}m to >6 {\mu}m wavelength, enabled by novel types of
high-performance ICLs such as ring-cavity devices. Their noise-behavior is an
important feature that still needs to be thoroughly analyzed, including its
potential reduction with respect to the shot noise limit. In this work, we
provide a comprehensive characterization of {\lambda} = 3.8 {\mu}m-emitting,
continuous-wave ring-ICLs operating at room temperature. It is based on an
in-depth study of their main physical intensity noise features, such as their
bias-dependent intensity noise power spectral density (INPSD) and relative
intensity noise (RIN). We obtain shot-noise-limited statistics for Fourier
frequencies above 100 kHz. This is an important result for precision
applications, e.g. interferometry or advanced spectroscopy, which benefit from
exploiting the advantage of using such a shot-noise limited source, enhancing
the setup sensitivity. Moreover, it is an important feature for novel quantum
optics schemes including testing specific light states below the shot noise
level, such as squeezed states.
