ZERO ZERO-BIREFRINGENCE POLYMERS FOR OPTICAL DEVICES
A. Tagayaa,b, Y. Koikea,b
aKoike Photonics Polymer Project, ERATO-SORST, Japan Science and Technology Agency, E-building, Shinkawasaki Town Campus, 144-8 Ogura, Saiwai-ku, Kawasaki 212-0054, Japan
bFaculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kouhoku-ku, Yokohama 223-0061, Japan
Optical polymers are widely used as key materials for various optical devices, for example, lenses, optical disks and functional films for liquid crystal displays, due to their ease of processing, light weight, high transparency, and low cost. However, they tend to exhibit birefringence in processes such as injection molding, extrusion and drawing. The caused birefringence degrades the performance of optical devices that require fine focusing by lenses or maintaining the polarization state of incident light.
In the case of a typical thermoplastic polymer used in ordinary optical polymer devices, the major types of birefringence are orientational birefringence and photoelastic birefringence. The random copolymerization method and the anisotropic molecule dopant method have been proposed to realize optical polymers that exhibit no orientational birefringence for any orientation of the polymer main chains, and demonstrated. In addition, elimination of photoelastic birefringence has been demonstrated by both the methods. However, simultaneous compensation of the orientational birefringence and the photoelastic birefringence by means of the methods has not been demonstrated.
We define polymers as zero zero-birefringence polymers that exhibit no birefringence with any orientation of the polymer main chains and in elastic deformation (i.e., both the orientational birefringence and the photoelastic birefringence are zero). Furthermore, we demonstrated that zero zero-birefringence polymers can be realized in a system that is composed of more than three components, in which at least one of the components exhibits the opposite orientational birefringence effect and the opposite photoelastic birefringence effect to those of the other components, and explained the methods to design the zero zero-birefringence polymers. A ternary copolymer [poly(MMA/3FMA/BzMA = 52.0/42.0/6.0(w/w/w))] and a binary copolymer including an anisotropic dopant [poly(MMA/3FMA = 85.0/15.0(w/w)) containing 2.8 wt % of trans-stilbene] were designed by the methods and fine adjustment of the composition, and synthesized. We confirmed that these polymers exhibited close to zero birefringence in the oriented state and in elastic deformation. These methods are applicable to other polymers composed of other monomers and anisotropic dopants.