Low-frequency fiber optic hydrophone based on weak value amplification.

A high-sensitivity low-frequency fiber optic hydrophone based on weak value amplification (WVA) is proposed and demonstrated. A polarization maintaining (PM) fiber with a length of 0.8 m wound around a polycarbonate (PC) tube is used as the sensing element. Theoretical analysis shows that the PM fiber in a WVA measurement scheme responds to underwater acoustic pressure with unprecedented sensitivity. The prototypical hydrophone based on such a scheme can sense underwater acoustic disturbance as weak as 1.3×10-6 Pa/Hz1/2 at 10 Hz, with a flat frequency response in the low-frequency band of 0.1-50 Hz. The experimental result agrees well with the theoretical prediction to within 0.5 dB.

Measurement of Chiral Molecular Parameters Based on a Combination of Surface Plasmon Resonance and Weak Value Amplification.

A novel combination of surface plasmon resonance (SPR) and weak value amplification (WVA) is employed to measure the optical rotation angle and refractive index of chiral enantiomers such as sugars and amino acids. An extremely low optical rotation change (2.73 × 10-4 rad) is readily measurable, with a resolution of 6.75 × 10-7 rad, 1 order of magnitude higher than that obtained using weak value amplification with intensity modulation, and a refractive index change of 1.13 × 10-6 RIU is also detected, with a resolution of 1.99 × 10-9 RIU, a nearly 1-order-of-magnitude increase in sensitivity over weak measurement based on a Mach-Zehnder interferometer. The optical activity and refractive index changes of chiral molecules are determined in real time by measurements of the output light intensity variation, whereby the absolute configuration of the chiral molecule is identified through the relation between intensity and molecular orientation. The SPR-WVA combination sensing scheme fills the gap of capability for detecting the optical activity of a molecular solution, which has not been possible with conventional SPR alone.

Direct and Doppler angle-independent measurement of blood flow velocity in small-diameter vessels using ultrasound microbubbles.

This article represents an initial attempt to demonstrate the feasibility of a novel method for measuring flow velocity in small vessels, which is a direct, noninvasive, ultrasound-guided, and Doppler angle-independent method. In vitro, experiments were designed to mimic blood flow inside tubes. Harmonic ultrasound imaging was used to track the movement of microbubbles, and the mean flow velocity was calculated. In vivo, the flow velocities were measured in the central arteries of rabbit ears. This method can be used whenever the Doppler ultrasound cannot measure the velocity in small vessels because of either low sensitivity or Doppler angle limitation.