(2016, rev. 2019)
First of all, I composed the piece for solo five-string violin, with a viola C-string, and had a premiere by Takao Hyakutome in II Edición Festival ME_MMIX in 2014. After that, I arranged it for normal violin for Sirga Festival 2016 and I then revised it for string quartet with various rhythms and timbres. The title means the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringence. So all of the strings play double stopping and these notes go to the different intervals or different directions. Each string has scordatura and in each section, different strings are used as two principal strings which are related to overtones and the other theory. As the effects, the sounds more reflect and have more variety with natural harmonics.