Abstract
We present a compact integrated photonics interrogator for a ring-resonator (RR) ultrasound sensor, the so-called MediGator. The MediGator consists of a special light source and an InP Mach-Zehnder interferometer (MZI) with a 3 ×3 multi-mode interferometer. Miniaturization of the MZI to chip size enables high temperature stability and negligible signal drift. The light source has a -3 dB bandwidth of 1.5 nm, a power density of 9 dBm/nm and a tuning range of 5.7 nm, providing sufficient signal level and robust alignment for the RR sensor. The mathematical procedure of interrogation is presented, leading to the optimum MZI design. We measure the frequency response of the sensor using the MediGator, giving a resonance frequency of 0.995MHz. Further, high interrogation performance is demonstrated at the RR resonance frequency for an ultrasound pressure range of 1.47 - 442.4 Pa, which yields very good linearity between the pressure and the resulting modulation amplitude of the RR resonance wavelength. The measured signal time traces match well with calculated results. Linear fitting of the pressure data gives a sensor sensitivity of 77.2 fm/Pa. The MediGator provides a low detection limit, temperature robustness and a large measurement range for interrogating the RR ultrasound sensor.
Highlights
Integrated photonics sensors are contributing to many fields, including chemical sensing [1,2,3,4], temperature sensing [5, 6], and ultrasound detection [7, 8]
We present a compact integrated photonics interrogator for a ring-resonator (RR) ultrasound sensor, the so-called MediGator
Using the characteristics of the fabricated RR sensor, we arrived at the final design of the Mach-Zehnder interferometer (MZI) and the light source and fabricated these MediGator components, of which we present the characterization
Summary
Integrated photonics sensors are contributing to many fields, including chemical sensing [1,2,3,4], temperature sensing [5, 6], and ultrasound detection [7, 8]. The arrayed waveguide grating is suitable for high speed, but its resolution is too low for RR ultrasound sensors Another method is the so-called modulation method, using a narrow linewidth tunable laser and a high speed photodetector [9,10,11]. Due to the large footprint of the fiber circuit, the environmental phase drift of the MZI is hard to control, making this fiber interrogator unsuited for long-time measurements It requires pre-measurement at high ultrasound pressure for a circle fitting procedure with the measured signals, adding complexity in using the fiber interrogator [14]. The light source comprises a pump laser, an Er-doped fiber and a tunable FBG It provides a spectrum with high power density, large tuning range and suitable bandwidth.
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