Sound & Bright’s various technologies were born from a research and development grant from NASA and the National Science Foundation and are now marketed worldwide.

TWM: Two-wave mixing in a photorefractive crystal

Our Ultra high Frequency and Multi-component receivers are based on photorefractive two-wave mixing. A dynamic hologram resulting from the interferences between the reference beam and the signal beam is recorded in the photorefractive crystal. The response time of the process permits to compensate the slow phase change (low frequency acoustic vibration for example) of the signal beam but not the fast change at high frequencies (>1 kHz). The diffraction of the reference beam by the dynamic hologram creates a local oscillator adapted to the signal i.e. same wavefront and same direction. Two-wave mixing in a photorefractive material is equivalent to an adaptive beam splitter. The two beams – signal and adapted local oscillator – are in perfect quadrature and are incident on the photodetector that delivers a homodyne signal.

High performances photorefractive crystals are used with reliable properties to insure an optimum two-wave mixing process. A high voltage field is applied on the photorefractive crystal in order to optimize the coupling and maintain the quadrature between the signal and the diffracted reference (adapted local oscillator). Photorefractive two-wave mixing has been extensively studied over the past 40 years and is a well-controlled process.


No high frequency limit
Large etendue interferometer
Simultaneous In-plane and Out-of-plane detection
Continuous detection laser

MCRQ: Multi-Channel Random Quadrature

Patent US7978341

Multi-channel laser interferometric method and apparatus for detection of ultrasonic motion from a surface

Patent US7864338

 Interferometric method and apparatus for linear detection of motion from a surface

Patent US7729881

Laser intensity noise rejection for interferometric apparatus


Our Multi-purpose and Thickness Gauge receivers combine the advantages of homodyne interferometry and multi-detector ability. The beam reflected by the sample rough surface has many speckle. The signal multi-speckled beam is combined with the reference beam and focused on 50 photo-detectors. Each detector collects a few speckle and delivers an homodyne signal.

Each homodyne signal is processed in parallel using a patented signal processing architecture, based on “random quadrature” demodulation scheme taking advantage of the random phase distribution inherent to speckle light. The detectors produce a time-varying analog voltage that is proportional to the rectified instantaneous surface displacement at ultrasonic frequencies.


Not laser wavelength dependent, from visible to IR
Inspection on rapidly moving object
High sensitivity on all surface types and materials
Continuous or pulsed detection laser