title: Miniature photonic-crystal hydrophone optimized for ocean acoustics.
abstract: This work reports on an optical hydrophone that is insensitive to hydrostatic pressure, yet capable of measuring acoustic pressures as low as the background noise in the ocean in a frequency range of 1 Hz to 100 kHz. The miniature hydrophone consists of a Fabry-Perot interferometer made of a photonic-crystal reflector interrogated with a single-mode fiber and is compatible with existing fiber-optic technologies. Three sensors with different acoustic power ranges placed within a sub-wavelength sized hydrophone head allow a high dynamic range in the excess of 160 dB with a low harmonic distortion of better than -30 dB. A method for suppressing cross-coupling between sensors in the same hydrophone head is also proposed. A prototype was fabricated, assembled, and tested. The sensitivity was measured from 100 Hz to 100 kHz, demonstrating a sound-pressure-equivalent noise spectral density down to 12 μPa/Hz(1/2), a flatband wider than 10 kHz, and very low distortion.
authors.affiliation: EL Ginzton Laboratory, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305, USA. okilic@stanford.edu
authors.forename: Onur
authors.initials: O
authors.lastname: Kilic
authors.forename: Michel J F
authors.initials: MJ
authors.lastname: Digonnet
authors.forename: Gordon S
authors.initials: GS
authors.lastname: Kino
authors.forename: Olav
authors.initials: O
authors.lastname: Solgaard
mesh_terms: D000162:Acoustics / Q000295:instrumentation*; D004548:Elasticity; D007834:Lasers; D008904:Miniaturization; D008962:Models, Theoretical; D009791:Oceanography / Q000295:instrumentation*; D009792:Oceans and Seas; D055100:Optical Fibers; D055095:Optics and Photonics; D011312:Pressure; D012623:Seawater; D012825:Silicon; D013696:Temperature; D014159:Transducers
chemical_list: D012825:Silicon