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 Φ0 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).
Highlights
Integrated photonics is an enabling technology for important application fields, such as telecommunication [1, 2], optical signal processing [3] and various types of photonic sensing [4]
We experimentally demonstrate an interrogation procedure of a ring-resonator ultrasound sensor using a fiber Mach-Zehnder interferometer (MZI)
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 Φ0 on the circle arc periodically traced in the plane of the two orthogonal interrogator voltages, as the principal sensor signal
Summary
Integrated photonics is an enabling technology for important application fields, such as telecommunication [1, 2], optical signal processing [3] and various types of photonic sensing [4]. The lab-on-chip approach to chemical sensing and particle identification benefits strongly from integrated photonics. This is demonstrated for example by recent advances in excitation and collection of spontaneous Raman scattering near silicon nitride waveguides [5] and in optical trapping and Raman spectroscopy of micro-particles using a dual-beam trap made from composite silicon oxide-nitride waveguides [6]. For amplitudes of the ultrasound-induced resonance-wavelength modulation smaller than the bandwidth of the spectrum incident on the RR, the signal is proportional to the applied ultrasound pressure. A complete mathematical description of the operation of the interrogator, resulting in the interrogation procedure we apply, is given in Appendix A
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