  Advances in quantum computing are a rapidly growing threat towards modern
cryptography. Quantum key distribution (QKD) provides long-term security
without assuming the computational power of an adversary. However,
inconsistencies between theory and experiment have raised questions in terms of
real-world security, while large and power-hungry commercial systems have
slowed wide-scale adoption. Measurement-device-independent QKD (MDI-QKD)
provides a method of sharing secret keys that removes all possible detector
side-channel attacks which drastically improves security claims. In this
letter, we experimentally demonstrate a key step required to perform MDI-QKD
with scalable integrated devices. We show Hong-Ou-Mandel interference between
weak coherent states carved from two independent indium phosphide transmitters
at $431$ MHz with a visibility of $46.5 \pm 0.8\%$. This work demonstrates the
feasibility of using integrated devices to lower a major barrier towards
adoption of QKD in metropolitan networks.
