Wavefront Sensor is a device for measurement of phase aberrations of an optical wavefront. Although an amplitude splitting interferometer such as the Michelson interferometer could be called a wavefront sensor, the term is normally applied to instruments that do not require an unaberrated reference beam to interfere with. They are commonly used in adaptive optics systems, lens testing and increasingly in ophthalmology.

Optical systems are normally aligned by centering the energy distribution in various apertures. However, the use of both irradiance and phase information can in many cases greatly simplify this process, and can provide information for closed-loop alignment and control of an optical system. This can be accomplished by using a wavefront sensor for alignment and performance testing.

While wavefront sensors are commonly used for adaptive optics, they have many other applications. The modern wavefront sensor is compact, rugged, and insensitive to vibration, and has fully integrated data acquisition and analysis. Furthermore, even wave fronts of broadband sources that cannot normally be tested with interferometers can be measured with Shack-Hartmann wavefront sensors. The instrument also provides information about the optical system performance, including peak-to-valley (PV) wavefront deviation, RMS wavefront error, the modulation transfer function (MTF), and the point spread function (PSF). Since the difference of two wavefronts is easily computed, the effect of individual optical elements on a complex optical system can be examined.

Types of Optical Wavefront Sensors

  • Shack-Hartmann Wavefront sensor
  • Wavefront curvature sensor
  • Pyramid wavefront sensor
  • Common path interferometer
  • Foucault knife-edge test Sensor
  • Multilateral shearing interferometer
  • Ronchi optical watester
  • Shearing Interferometer

The Shack-Hartman Wavefront Sensor is the most common wavefront sensor used today due to its simplicity and manufacturability. Using an array of miniature lenses called “lenslets,” the sensor splits light into a number of small beams which is then focused onto a CCD camera. As the incident wavefront is aberrated by the lenslet, the focused spot on the CCD camera moves. Through simple geometry using the displacement of the focused spot and the focal length of the lenslet, the local tilt of the wavefront is calculated by the control system—typically, a computer and the control algorithm software. The control system then calculates the shape required to compensate the wavefront and sends the information to the wavefront corrector.