Design and analysis of photonic crystal biperiodic waveguide structure based optofluidic-gas sensor

We present a photonic crystal (PhC) biperiodic waveguide (BPW) structure for both gas and fluid sensing based on modulation of refractive index (RI) of supercavities. The proposed structure has been designed by creating a BPW in silicon (Si) substrate with triangular array of air holes. This BPW structure consists of an array of supercavities and only the resonant wavelength is allowed to pass through the waveguide while the rest of the wavelengths are reflected by the structure. The principle of sensing is based on the shift of the resonance wavelength of supercavities when infiltrated by any liquid or gas. The transmission spectra of sensor have been analyzed numerically by finite difference time domain (FDTD) method. The proposed design can be utilized as a gas sensor or fluid sensor by selectively filling the holes of supercavities. For gas sensing application, the sensitivity of the sensor has been found to be 610 nm per refractive index unit (RIU) with minimum detection limit of 0.0001 RIU. Sensitivity of 300 nm/RIU with wider RI detection range of 1.0–1.5 is obtained when the structure is used as a fluid sensor.