Tunable Doppler shift using a time-varying epsilon-near-zero thin film near 1550 nm

Cong Liu*, M. Zahirul Alam, Kai Pang, Karapet Manukyan, Joshua R. Hendrickson, Evan M. Smith, Yiyu Zhou, Orad Reshef, Hao Song, Runzhou Zhang, Haoqian Song, Fatemeh Alishahi, Ahmad Fallahpour, Ahmed Almaiman, Robert W. Boyd, Moshe Tur, Alan E. Willner

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


We experimentally investigate the tunable Doppler shift in an 80 nm thick indium-tin-oxide (ITO) film at its epsilon-near-zero (ENZ) region. Under strong and pulsed excitation, ITO exhibits a time-varying change in the refractive index. A maximum frequency redshift of 1.8 THz is observed in the reflected light when the pump light has a peak intensity of ∼140 GW/cm2 and a pulse duration of ∼580 fs, at an incident angle of 40. The frequency shift increases with the increase in pump intensity and saturates at the intensity of ∼140 GW/cm2. When the pump pulse duration increases from ∼580 fs to ∼1380 fs, the maximum attainable frequency shift decreases from 1.8 THz to 0.7 THz. In addition, the pump energy required to saturate the frequency shift decreases with the increase in pump pulse duration for <1 ps and remains unchanged for >1 ps durations. Tunability exists among the pump pulse energy, duration, and incident angle for the Doppler shift of the ITO-ENZ material, which can be employed to design efficient frequency shifters for telecom applications.

Original languageEnglish
Pages (from-to)3444-3447
Number of pages4
JournalOptics Letters
Issue number14
StatePublished - 15 Jul 2021


FundersFunder number
Defense Advanced Research Projects AgencyW911NF-18-0369
Defense Advanced Research Projects Agency


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