Patent ID: 9612480
Date: 2017-04-04
CPC Classifications: G02B,G02F

Claim:
1. A method of producing a phase device operating at least at one wavelength (λ), the phase device including a cell containing a liquid crystal which has a helical structure and is inserted between two alignment layers each having rubbing axes, and means for applying a voltage to said cell, said helical structure having a number of helix turns k, and said liquid crystal having a twist angle θ defined between the rubbing axes of the two alignment layers, the method comprising the following steps: determining a compensation angle ε satisfying the following equation: with: N the integer closest to said compensation angle ε being an angle for minimizing a residual ellipticity of the liquid crystal and making a rotation amplitude of the light beam which passes through the liquid crystal to be equal to an integer multiple of 2π; determining the twist angle θ=2kπ−ε based upon the compensation angle ε; where Δn: the birefringence of the liquid crystal; d: the thickness of the liquid-crystal cell; λ: the wavelength of the light beam which passes through the liquid-crystal cell; and rubbing one of the faces along an alignment direction of said liquid-crystal molecules based upon the twist angle: θ=2kπ−ε.