Eta100 L Ultra: Optical Hydrophone


Optical Microphone – World’s first microphone without any moving parts

XARION’s Eta100 L Ultra is a robust, long-lasting optical hydrophone designed for ultrasound sensing in rugged environments. Using patented technology, the Eta100 L Ultra sensor is immune to electromagnetic interference, damage or de-calibration from high pressure amplitudes and allows measurements at elevated temperatures up to 100°C. Covering a 50 kHz to 10 MHz frequency range and pressure amplitudes in the kPa to MPa range, it offers highly versatile ultrasound detection in liquids within a small form factor.
This makes the Eta100 L Ultra the perfect ultrasound sensor for military and civil applications in high electromagnetic fields, or for the characterization of ultrasound transducers with high sound pressures that could potentially destroy other hydrophones.



  • Suitable for temperatures up to 100°C, resilient to decalibration by high pressure amplitudes
  • High versatility through small footprint and 10 MHz measurement bandwidth
  • Fiber-coupled optical hydrophone
  • Immunity to electromagnetic interference


Ultrasound Measurements


Ultrasound Field Characterization
The small size and the linear frequency response make the Optical Microphone the perfect tool for precise measurements of time signals, frequency distributions and acoustic field maps of ultrasound emitters such as air-coupled ultrasonic piezos.
Measurements in High Electromagnetic Field
All-optical components in the sensor head as well as the optical fiber cabling are insensitive to strong electromagnetic fields. Thus, sound can be recorded in applications that are out of reach for classical microphones due to strong EM- or radioactive fields.
Ultra-high Sound Pressure Levels
The Eta100 Ultra was designed to measure extremely high sound pressure levels (up to 180dB SPL). All our microphones are immune to damage by excessive acoustic pressure levels.


XARION’s patent-protected sensor technology platform offers substantial advantages:


  • Extreme ultrasound frequency range from 10 Hz up to 2 MHz in air, 20 MHz in liquids
  • Acoustic and ultrasound detection greater by a factor of 10 than present state-of-the art
  • Transducer principle with a perfectly linear frequency response. Although the enclosure needs to be carefully designed to minimize its influence on the sound field, the transducer itself is not frequency dependent
  • Sound detection in air and liquids
  • Qualification for ultra-high sound pressure levels (up to 190 dB SPL)
  • Since no moving inert mass is involved, the Optical Microphone has a true temporal impulse response.
  • Inherent phase match in array configurations
  • No metallic parts and glass fiber-coupled, hence operational in high electromagnetic fields.


Listening to Ultrasound with a Laser
All-optical highly sensitive akinetic sensor for ultrasound detection and photoacoustic imaging
Characterization of polymer-based piezoelectric micromachined ultrasound transducers for short-range gesture recognition applications
Development of an innovative measurement system for audible noise monitoring of overhead lines
Optical microphone hears ultrasound


Demonstration of Frequency Bandwidth

✔The Optical Microphone is able to detect the entire acoustic frequency bandwidth which is transmitted through air
✔High frequencies often contain significant process-quality information
✔Hence, disturbing background noise (low frequencies) can be separated from process information (high frequencies)




For the detection of sound waves, conventional microphones use membranes or other moving parts as intermediaries between the incoming acoustic and the resulting electrical quantity. For acoustic ultrasound sensors based on piezoelectric crystals, the approach is similar: the acoustic wave mechanically deforms the crystal. In contrast, the patented idea behind XARION’s Optical Microphone is to exploit another, completely different property of sound: the fact that sound changes the speed of light!   In a rigid Fabry-Pérot laser interferometer consisting of two miniaturized mirrors, sound pressure changes the refractive index of the air. This alters the optical wavelength and the light transmission which consequently leads to the respective electrical signal. In contrast to conventional microphones, the Optical Microphone is the world’s first microphone without any moving parts. No mechanically movable or physically deformable parts are involved. By consequence, the sensors exhibit a compelling frequency bandwidth, free from mechanical resonances. The sensor principle is highly sensitive. In fact, refractive index changes below 10-14 can be detected with this technology. This corresponds to pressure changes as small as 1 µPa.


Eta100 L Ultra: Optical Hydrophone Datasheet
XARION Ultrasound Field Characterization Information Brochure

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