Progress in Birefringent Material-Based Achromatic Phase Modulators

The phenomenon of birefringence is strongly related to polarization optics that leads to phase modulation. Natural birefringent materials often find applications in polarizing devices or phase modulators. Some materials can be induced with this property externally. The performance of the polarizing devices often depends on wavelength, known as chromaticity, which puts forward the need for achromatic devices in many applications. Therefore, the elimination of wavelength dependency has been an exciting research field. Phase modulators often consist of quarter-wave and half-wave retarders to provide fixed or variable phase retardations. Materials like crystalline quartz, MgF2, calcite, etc., are being widely used for designing achromatic phase retarders that provide constant phase difference among two orthogonal components of light over a wide range of wavelengths. In this chapter, birefringent networks based on waveplates of identical materials, as well as combinations of different birefringent materials, have been introduced to achieve achromatic to superachromatic behavior over other wavelength regions. Moreover, teaching new materials in designing phase retarders has also been elaborated, indicating progress in this research domain.