  Hong-Ou-Mandel (HOM) interference is a quantum optics laboratory experiment
that has recently become more accessible to undergraduate students. The
experiment consists of two identical photons simultaneously entering a
non-polarizing beam splitter. The wavefunctions destructively interfere and the
photon pairs bunch at the outputs whereas classically they are equally likely
to exit different outputs. Due to the precision needed to achieve
indistinguishability, setup and alignment of this experiment is often
considered to be too difficult and time consuming to be appropriate for an
undergraduate lab, with an end goal of merely demonstrating the HOM
interference dip. Here, we present an alternative optical fiber-based apparatus
that gives a consistently reproducible experiment with interference occurring
in a fused-fiber coupler instead of a traditional beam splitter. We use a
commercially available fiber coupled biphoton source that requires minimal
alignment and increases coherence length of the interference. In addition, our
biphoton source provides direct temperature based control of the frequency
degeneracy of the photon pairs produced, allowing for students to investigate
physical properties of HOM interference such as coherence length and
interference visibility. Through use of standard opto-mechanical parts combined
with the commercially available fiber integrated biphoton source and laser, our
apparatus is a middle ground between built-from-scratch and pre-aligned setups.
