Eli Yablonovitch (born 15 December 1946) is an American physicist and engineer who, along with Sajeev John, founded the field of photonic crystals in 1987.

In addition to pioneering photonic crystals, he was the first to recognize that a strained quantum-well laser has a significantly reduced threshold current compared to its unstrained counterpart.

[3] During his post-graduate studies, Yablonovitch worked on nonlinear optics with carbon dioxide lasers.

[4] While working at Exxon, Yablonovitch derived the 4 (n squared) factor as the theoretical limit for light trapping in photovoltaics.

His research topics include silicon photonics, telecommunications, optical antennas, new applications of photovoltaics, and searching for a low-voltage replacement for the transistor.

[4] In 2001, Yablonovitch co-founded Luxtera Inc., a semiconductor company that makes electro‑optical systems using silicon photonics, manufactured with CMOS processes.