Ultra-sensitive pressure sensor using double stage racetrack silicon micro resonator

Abstract

Three layouts of add-drop double stage racetrack microring resonators (ADSRMRR) located on the centre of the flexible silicon diaphragm were introduced as microscale optomechanical pressure sensors. The light propagation through all of the proposed ADSRMRR layouts were simulated using the signal flow graph method and the variational finite difference time domain (varFDTD) analysis. To achieve optimum transmission, a formula was derived for a critical coupling coefficient in the presence of the coupling loss factor for each coupling region. The pressure was measured from a wavelength shift in the output drop port signals considering the change in the optical length of the ADSRMRR due to the diaphragm shear stress. The pressure sensitivity of 48.5 pm/kPa, 42.4 pm/kPa and 33.2 pm/kPa with the limit of detection of 4.1 × 10−2 kPa, 4.7 × 10−2 kPa and 6.0 × 10−2 kPa were measured for the symmetric-large layout, the asymmetric and the symmetric-small layout of ADSRMRR pressure sensor, respectively. We introduced the ratio of the total optical length rather the sum of the resonant mode numbers (R-ratio) as a key factor in designing of the microscale Vernier based-pressure sensors. It is found that, using an ADSRMRR layout with a higher R-ratio provides a higher sensitivity with a lower detection limit, which are required in altitude sensors in satellites, aircraft, and weather balloons.