Circular polarizers are used throughout the optics industry for a wide range of applications including 3D glasses and displays, OLED displays, VR and AR headset components, and many more.  AxoScan is widely used throughout the industry for testing circular polarizers. Several common applications are shown below, but feel free to contact us to discuss your particular application.

Testing Polarization States

AxoScan directly measures the output polarization states of circular polarizers. The results are typically displayed on the Poincaré sphere or as ‘polarizance ellipticity’ values, as shown below.

Since there are not many materials that directly create circularly polarized light, circular polarizers are commonly manufactured from a linear polarizer followed by one or more retarders (waveplates). But these devices are inherently non-achromatic and often work well at only one wavelength. A few measurement examples of different types of circular polarizers are shown below.

Predicting Polarization States for a Retarder

The classic way of creating circular polarization is to use a quarter-wave retarder following a linear polarizer at 45° orientation. It is straightforward to show that this combination will create good circular polarization for wavelengths where the retardation is very close to 90°. 

But many modern circular polarizer designs employ stacks of 2, 3 or even 5 retarders all at different orientation angles to create circular polarization states with less wavelength variation.  Manufacturers of these complex devices use the AxoScan to measure the full Mueller matrix of these retarder stacks before they are laminated to a linear polarizer. They then use the polarization ray tracing functions in our Spectral Viewer software to calculate how well the device will create circular polarization for various input linear polarization states.

The example below shows the measured retardance and elliptical fast-axis states of a two-layer retarder.

From the retardance spectrum, it is not clear that this device would make a useful circular polarizer. But by using the polarization ray tracing function in the Spectral Viewer software, we find that vertically-oriented (90°) linear polarization will be transformed into nearly-circular polarization across the entire 400 to 650 nm range by this retarder.

Analyzing the Subcomponents of a Circular Polarizer

Once a circular polarizer has been manufactured, testing may show that the created polarization states are not as circular as desired. In that case, manufacturers and end-users can use our Multi-Layer Analysis Software Package (MLSP) to determine the optical properties of the individual components comprising the circular polarizer.

In the example shown below, a two-layer retarder stack following a linear polarizer is analyzed. From the measured Mueller matrices, the software is able to calculate the orientation angles of the polarizer and two retarders well as the retardation magnitude of both retarders. Comparing these values to the nominal design lets manufacturers understand what went wrong in the manufacturing process.

Predicting Reflectance from a Mirror or OLED Panel

When circular polarization reflects from a mirror, the electric field continues to rotate in the same direction (conserving angular momentum), however the propagation direction reverses.  This results in right-hand circular polarization changing to left-hand circular upon reflection, and vice versa. As shown below, this means that a circular polarizer placed in front of a mirror can be used to fully attenuate the light reflected from the mirror.

This property is important for OLED displays. Without a circular polarizer placed in front, the reflective metallic surface of the OLED would result in a dull gray appearance when the display should be black. But by placing a high-quality circular polarizer on the front of the display, extremely dark black states can be achieved.

However, this property only works if the generated polarization state is perfectly circular. Elliptical states will not be fully attenuated after reflection as shown below.

Using our Circular Polarizer Viewer software, users can measure the Mueller matrix of a circular polarizer across a full range of wavelengths, tilt angles, and rotation angles. From the Mueller matrix data, the software calculates the percent reflectance and color coordinate of the reflected light for each tilt and rotation angle.