Table 3.
Summary of performance characteristics of optical ultrasound detectors.
| Sensor | Geometry | Detection direction | Diameter (μm) | Sensitivity (kPa) | Bandwidth (MHz) |
|---|---|---|---|---|---|
| FP etalon [36] | Cylindric cavity | Forward | 6–10 | 15 | 20 |
| FP etalon [37] | Concave cavity | Forward | 125 | 0.4 | 20 |
| FP etalon [38] | Dual cladding | Forward | — | — | — |
| FP etalon [38] | Dual cladding | Sideway | — | — | — |
| FP etalon [39] | Planoconcave cavity | Forward | 5.2 | 0.093 | 40 |
| Microring [41] | Ring | Forward | 100 | 0.23 | 75 |
| Microring [40] | Ring | Sideway | ~800 | 0.352 | 250 |
| FBG [42] | Cylindric grating | Sideway | -/(270 in length) | 0.44 | 10 |
| FBG [43] | Cylindric grating | Forward | -/(1500 in length) | 9 nε/Hz1/2 | — |
Noise equivalent pressure (NEP), the acoustic pressure with which signal-to-noise ratio equals 1, is used as the criterion to evaluate detectors. Forward refers to the axial direction of the optical fiber while sideway refers to the radial direction.