  Optical isolators are an essential component of photonic systems. Current
integrated optical isolators have limited bandwidths due to stringent
phase-matching conditions, resonant structures, or material absorption. Here,
we demonstrate an ultra-broadband integrated optical isolator in thin-film
lithium niobate photonics. We use dynamic standing-wave modulation in a tandem
configuration to break Lorentz reciprocity and achieve isolation. We measure an
isolation ratio of 15 dB and insertion loss below 0.5 dB for a design
wavelength of 1550 nm. In addition, we experimentally show that this isolator
can simultaneously operate at visible and telecom wavelengths with comparable
performance. Isolation bandwidths ~100 nm can be achieved simultaneously at
both visible and telecom wavelengths. Our device's large bandwidth, high
flexibility, and real-time tunability can enable novel non-reciprocal
functionality on integrated photonic platforms.
