Waveplate overview
Waveplates are made from birefringent materials, most commonly crystal quartz. Birefringent materials have slightly different indices of refraction for light polarized in different orientations. As such, they separate incident unpolarized light into its parallel and orthogonal components.
Fast Axis and Slow Axis
Light polarized along the fast axis encounters a lower index of refraction and travels faster through waveplates than light polarized along the slow axis. The fast axis is indicated by a small flat spot or dot on the fast axis diameter of an unmounted waveplate, or a mark on the cell mount of a mounted waveplate.
Retardation
Retardation describes the phase shift between the polarization component projected along the fast axis and the component projected along the slow axis. Retardation is specified in units of degrees, waves, or nanometers. One full wave of retardation is equivalent to 360°, or the number of nanometers at the wavelength of interest. Tolerance on retardation is typically stated in degrees, natural or decimal fractions of a full wave, or nanometers. Examples of typical retardation specifications and tolerances are:
λ/4 ± λ/300 (Quarter waveplate)
λ/2 ± 0.003λ (Half waveplate)
λ/2 ± 1°
430nm ± 2nm
The most popular retardation values are λ/4, λ/2, and 1λ, but other values can be useful in certain applications.
Waveplate type:
Multiple order waveplate
Multiple order waveplate means the retardance of a light path will undergo a certain number of full wavelength shifts in addition to the fractional design retardance. The thickness of multi order waveplate is always around 0.5mm. Compared with zero order waveplate, multi order waveplate is more sensitive to wavelength and temperature changes. However, they are less expensive and widely used in many applications where the increased sensitivities are not critical.
Features:
- Low temperature bandwidth
- Low wavelength bandwidth
- High damage threshold
- Low cost
Dual wavelength waveplate
Dual wavelength waveplate is a single retardation plate with dual-wavelength AR coating
Features:
- Provide specific retardance at two different wavelengths
Achromatic waveplate
Achromatic waveplate is similar to zero order waveplate except that the two plates are made from different birefringent crystals. Since the dispersion of the birefringence of two materials is different, it is possible to specify the retardation values at a broad wavelength range. So, the retardation will be less sensitive to wavelength change. In other words, it can be used at a broadband wavelength range.
Features:
- Good temperature banwidth
- Very broad wavelength bandwidth
- Cemented and air spaced available
Cemented zero order waveplate
Cemented zero order waveplate is constructed by two quartz plates with their fast axis crossed, the two plates are cemented by UV epoxy. The difference in thickness between the two plates determines the retardation. Zero order waveplates offer a substantially lower dependence on temperature and wavelength change than multi order waveplates.
Features:
- Cemented by Epoxy
- Thickness 1.5~2mm
- Double Retardation Plates
- Broad Spectral Bandwidth
- Wide Temperature bandwidth
- AR coated and Mounted
Optically Contacted zero order waveplate
Optically Contacted zero order waveplate is constructed by two quartz plates with their fast axis crossed, the two plates are constructed by optically contacted method, the optical path is epoxy free. The difference in thickness between the two plates determines the retardation. Zero order waveplates offer a substantially lower dependence on temperature and wavelength change than multi order waveplates.
Features:
- Optically Contacted,no glue
- Double Retardation Plates
- Broad Spectral Bandwidth
- Wide Temperature bandwidth
- Hight Damage Threshold
Air spaced zero order
Air spaced zero order waveplate is constructed by two quartz plates installed in a mount, to form a air gap between the two quartz plates. The difference in thickness between the two plates determines the retardation. Zero order waveplates offer a substantially lower dependence on temperature and wavelength change than multiorder waveplates.
Features:
- Mounted, no glue
- Broad Spectral Bandwidth
- Wide Temperature bandwidth
- Hight Damage Threshold
True Zero Order Waveplate
Cemented true zero order waveplate
- Cemented by glue
- Good temperature bandwidth
- Wide wavelength bandwidth
- Moderate damage threshold
- Excellent retardation performance
Single plate true zero order waveplate
- Good temperature bandwidth
- Wide wavelength bandwidth
- High damage threshold
- Only 1310nm, 1550nm available