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Polymer liquid crystals

Polymer liquid crystals (PLCs) are a class of materials that combine the properties of polymers with those of liquid crystals. A liquid crystal polymer can be seen as a network of conventional LC molecules that are linked together by polymerization.

The main advantage of these materials compared to inorganic crystals such as calcite or quartz is that it is inexpensive technology and can be easily shaped in any wanted geometry such as microlenses or wedges. The disadvantage is the lower optical quality due to enhanced scattering and defects. The use of PLC, as many other plastic optical components, is ideal for applications where low-cost robust  birefringent elements are needed with modest quality requirements.

The polymerized liquid crystal forms a positive uniaxial birefringent material with an ordinary index of about 1.5 and an extraordinary index between 1.6 to 1.7 depending on the LC. The maximal birefringence that can be obtained is about n_e-n_o= 0.2. Note that with this technology we are limited to a maximal thickness of 0.2 mm.

Birefringent wedges and Wollaston prisms

Birefringent wedges are useful for separating the two polarization component of light.

When combining two wedges one can obtain a Wollaston prism, which double the splitting angle compared to the simple prism.

Actually we are able to manufacture prisms with splitting angles from 0° to 0.5°. Prism size (active area) can be comprise between 5x5mm and 20x20mm. Such prisms can be used for applications such as Differential Interference Contrast (DIC) microscopy.

Ask a polaroptic engineer for more information: info@arcoptix.com

Molding technique

With the unique molding technique developed by ARCoptix we are capable to manufacture on demand uniaxial birefringent elements of any geometry (diffractive elements, cylindrical or toroidal lenses...). However the maximal thickness of the elements should not exceed 0.2mm. This technology offers the possibility to combine ordinary diffractive optical element design with an additional degree of freedom:Polarization!

The molding (or replication) technique can essentially be divided in three steps:

1) Fabrication of the master. The master should be the copy of the wanted diffractive-refractive one wants to obtain with LC polymer. Master are usually realized by using ordinary photolithographic methods.

2) Fabrication of a PDMS stamp. A PDMS stamp can be obtain by casting the master with degassed liquid PDMS. The PDMS becomes solid by thermal polymerization.

3) Fabrication of the birefringent LC element. The liquid LC polymer is sandwiched between a substrate with an alignment layer and the PDMS stamp. When The LC is nicely aligned the LC molecules are linked together by UV curing. When removing the PDMS one obtain a plastic birefringent diffractive-refractive element.

Replication technique for LC polymer elements

Birefringent microlens arrays 

A Birefringent lens produces two different focal points for the two polarization components as demonstrated in the figure below. ARCoptix can fabricate such birefringent microlenses arrays made of polymer nematic LC on demand. For more information: info@arcoptix.com.

Birefringent microlenses shows different focal points for each polarization component Birefringent microlenses realized with the LC polymer molding technique.