Interrogation of a ring-resonator ultrasound sensor using a fiber Mach-Zehnder interferometer

Abstract

We experimentally demonstrate an interrogation procedure of a ring-resonator ultrasound sensor using a fiber Mach-Zehnder interferometer (MZI). The sensor comprises a silicon ring resonator (RR) located on a silicon-oxide membrane, designed to have its lowest vibrational mode in the MHz range, which is the range of intravascular ultrasound (IVUS) imaging. Ultrasound incident on the membrane excites its vibrational mode and as a result induces a modulation of the resonance wavelength of the RR, which is a measure of the amplitude of the ultrasound waves. The interrogation procedure developed is based on the mathematical description of the interrogator operation presented in Appendix A, where we identify the amplitude of the angular deflection Φ on the circle arc periodically traced in the plane of the two orthogonal interrogator voltages, as the principal sensor signal. Interrogation is demonstrated for two sensors with membrane vibrational modes at 1.3 and 0.77 MHz, by applying continuous wave ultrasound in a wide pressure range. Ultrasound is detected at a pressure as low as 1.2 Pa. Two optical path differences (OPDs) of the MZI are used. Thus, different interference conditions of the optical signals are defined, leading to a higher apparent sensitivity for the larger OPD, which is accompanied by a weaker signal, however. Independent measurements using the modulation method yield a resonance modulation per unit of pressure of 21.4 fm/Pa (sensor #1) and 103.8 fm/Pa (sensor #2).

On-chip silicon Mach–Zehnder interferometer sensor for ultrasound detection

“…The sensor is robust with respect to possible wavelength misalignment to a maximum sensitivity point, as this can be compensated by simply increasing the optical power without inducing nonlinear effects (see below). The wide FWHM of the sensitivity branches (≈400 pm), compared to a FWHM ≈ 100 pm for Si RR sensors [8,9] is of additional help here.…”

“…Recently, RRs made in polymer and silicon-on-insulator (SOI) platforms have been used to sense ultrasound [6][7][8][9]. For the polymer RRs, located on a rigid substrate, the optoelastic effect leads to ultrasound induced resonancewavelength modulation.…”

“…In [7] an all-optical photoacoustic imaging is presented using a polymer RR sensor. The RR sensor in SOI [8,9] developed at our department is located on a membrane sensitive to ultrasound waves, such that periodic membrane deflection at the ultrasound frequency leads to the sensor signal via transduction to the RR. This sensor has a high sensitivity owing to a high quality factor and a NEP as small as 0.4 Pa. Interrogating the sensor requires some care in view of the limited predictability of the quality factor and the resonance wavelengths due to inherent variability of the fabrication and nonlinear effects already occurring at moderate optical power, leading to bistability of the resonances [10].…”

On-chip interrogator based on Fourier transform spectroscopy

“…Photonic based sensors find nowadays a wide range of applications. Acoustic and ultrasound sensors [1,2], pressure sensors [3], biochemical and gas sensors [4,5] are examples of sensors based on optical technology. They are low cost, immune to electromagnetic radiation, and operate under a wide range of temperatures.…”

“…In this paper, we focus our attention on photonic sensors whose transmission or reflection spectra have a peak (or dip) in their lineshape. Examples are sensors based on fiber Bragg gratings (FBGs) [5,6] or on integrated ring resonators [1,2,4]. For these sensors, it is possible to build large and multi-purpose sensor arrays by wavelength multiplexing the spectrum of the sensors [6,7].…”