Waveplates, Wave Plate

Waveplates (retardation plates or phase shifters) are made from optical materials  with precise thickness such as quartz, calcite or mica, which exhibit birefringence. The velocities of the extraordinary and ordinary rays through the birefringent materials vary inversely with their refractive indices. The difference in velocities gives rise to a phase difference when the two beams recombine. In the case of an incident linearly polarized beam this is given by α=2πd (n_e-n_o) / λ， where α is phase difference; d is thickness of waveplate; n_e,n_o-refractive indices of extraordinary and ordinary rays respectively; λ is wavelength). At any particular wavelength the phase difference is determined by the thickness of the waveplate.                

Low-order waveplate
The properties of low-order waveplate are much better than the multi-order waveplate because of its thinner thickness (less than 0.5mm). Better temperature (38°C), wavelength (1.5nm) and incident angle (4.5°) bandwidth and high damage threshold make it widely used in common application. 

Zero-order waveplate
Zero-order waveplate is constructed of two multi-order waveplates with their axis crossed. Thus, it performs as a zero-order waveplate because of the effect of two plates counteracting each other. It has wide temperature bandwidth and wavelength bandwidth properties. The damage threshold must be considered (about 10kW/cm2) when use the zero-order waveplates, because they are cemented.                      

Cemented True Zero-Order Waveplate                     

The true zero-order waveplate means that the thickness of waveplate is very thin (less than 0.1mm) which make them excellent in temperature, wavelength and incident angle (about 20º) bandwidth. Therefore, they are excellent choice for the highly accurate application. This kind of waveplate is cemented with a block of glass which is limited to low and medium power application.                

Half (λ/2) Waveplate
After passing through the λ/2 waveplate, the linearly polarized light is still linearly polarized, however, there is angle difference (2θ) between the vibration plane of the combined vibration and the vibration plane of the incident polarized light. If θ=45°, the vibration plane of the exit light is perpendicular to the vibration plane of the incident light, that is, when θ=45°, the λ/2 waveplate can change the polarization state by 90°.

Quarter (λ/4) Waveplate
When the angle between the incident vibration plane of polarized light and the optical axis of the waveplate is θ=45°, the light passing through the λ/4 waveplate is circularly polarized. Otherwise, after passing through the λ/4 waveplate, a circularly polarized light will be linearly polarized. A λ/4 waveplate has equal effect with a λ/2 waveplate when it allows the light to pass through twice.

WISOPTIC Specifications - Waveplates

Multiple Order – In multiple order waveplates, the total retardation is the desired retardation plus an integer. The excess integer portion has no effect on the performance, in the same way that a clock showing noon today looks the same as one showing noon a week later – although time has been added, it still appears the same.

Although multiple order waveplates are designed with only a single birefringent material, they can be relatively thick, which eases handling and system integration. The high thickness, though, makes multiple order waveplates more susceptible to retardation shifts caused by wavelength shift or ambient temperature changes.

Multiple order waveplates are ideal for use with monochromatic light that deviates less than 1% of the waveplate’s design wavelength.

Zero Order – In zero order waveplates, the total retardation is the desired value without excess. For example, Zero Order Quartz Waveplates consist of two multiple order quartz waveplates with their axes crossed so that the effective retardation is the difference between them.

Zero order retarders offer high performance over wider wavelength or temperature ranges.