Ultrasound detection is performed by measuring laser reflection off a surface plasmon resonance cavity which is integrated at a single-mode fiber end facet. It shows a total noise (or laser RIN) equivalent pressure of 9.7 KPa (or 5.2 KPa) over 0–20 MHz, a 6-dB angular detection range as large as 70° near 10 MHz, a detection bandwidth larger than 125 MHz, and a stable performance for over 20 min without feedback in ambient conditions. Its small form factor, fiber-optic integration, almost omnidirectional responsivity and large bandwidth are favorable for in vivo applications and high resolution imaging.