POLDI The Optical Micro-Angle-Sensor

POLDI is advICo‘s patented optical sensor for the measurement of rotational angles utilizing polarized light measured by polarization sensitive photo diodes. It's size and concept allows for a higher resolution in smaller spaces at a lower cost than previously possible.

The sensor signal in the form of polarized light is read transmissively or reflectively. The light source, a conventional LED, emits light that is polarized by passing through an unstructured polarization foil placed on an axis or a cogwheel. The rotational angle is thus equal to the angle of polarization.

The sensor itself consists of 4 photo diodes. Each diode has a dedicated polarization filter with a polarization angle set 45° in relation to the neighbouring filters and diodes (0°, 45°, 90°, 135°). A quadrature signal is created and sensor currents vary according to the angle difference over cos²(φ). The sensor can be manufactured using standard CMOS technology, and can be integrated with an ADC and other functions, which allows realization of single-chip servo electronics containing all but motor and LED.

Precise alignment, which often greatly increases the cost of operation for traditional types of angle sensors, is not required. Shock, vibration, or magnetic fields do not affect the operation of POLDI. Measurements are easily made from a distance since the sensor merely measures the polarization of light – e.g. laser light. Environments in which other angle sensors come short is no match for POLDI. The sensor can be miniaturized – precision is not affected.


  • Measurement of absolute rotation (polarization) angle (180° -periodic)
  • Accuracy: better than 12 bit or 0.02° (resolution as desired)BMWi-Logo
  • Very fast measurements
  • Minimal size
  • Minimal weight
  • Lower cost
  • No physical contact between sensor and polarization filter – no wear and tear
  • On- and off-axis measurements
  • Shock- and vibration tolerant
  • Long distance measurement
  • Transmissive and reflective setups
  • Insensitive to tilt angle and linear displacements in all 3 dimensions (x, y, z)
  • Extension to 360° periodicity by additional light/dark field or other simple measures


Multitudes of applications

Robotics, medicine, toys, automotive, cameras, production control, etc.


Broad patent protection (DE, US, CN, JP granted / EU filed)