The birefringence is one of the most important properties of all kinds of optical materials. and is widely used in many basic researches and industrial fields. By utilizing high birefringent materials or waveguides, a variety of unique and interesting optical features or functions can be achieved, such as in manipulating the polarization of an optical beam in a miniaturized way and providing the organic electro-luminescence display. Crystals, liquid crystals, semiconductor, silicon, ferroelectric material and polymer can exhibit their birefringences. While polymer materials are commonly used to fabricate optical films and waveguides, most polymer materials show relatively weak birefringences, and thus they are restricted in realizing novel functional photonics devices. In the past, such a weak birefringence has been roughly characterized in experiment. There is a lack of systematic method to theoretically calculate the birefringences of polymer materials, especially at a molecular level. This restricts the research on enhancing the birefringences of polymer materials. To study the birefringences in fluorinated polymers and find the way to enhance them, the origin of the birefringence in fluorinated polymer should be investigated in depth and the birefringence should be exactly calculated. In this paper, a theoretical method is established to calculate the birefringence of polymer systematically from the monomer unit to the molecular chain. Based on this method, the limiting factor that leads to a weak birefringence in polymer material is investigated. Taking the polymethyl methacrylate(PMMA) for example, the density functional theory(DFT) is first used to study the intrinsic birefringence of PMMA, where the intrinsic birefringence value is indeed the birefringence of the monomer unit and is also a maximum birefringence of the polymer material when the molecular chains are fully oriented. In the DFT, a stable structure of the PMMA monomer unit is constructed, and the intrinsic birefringence of this PMMA monomer unit structure is calculated. The calculation result shows that the intrinsic birefringence of PMMA monomer unit can reach up to 0.0738, the dispersion curve of the average birefringence of the monomer unit is also given. Furthermore, the molecular dynamics is used to study the material birefringence of the PMMA material consisting of 20 molecular chains. The calculation results show that although the intrinsic birefringence is much larger, the material birefringence of the PMMA is only 0.00052, due to the low degree of orientation of molecular chain in the PMMA. It is found that the molecular structure and the molecular orientation of the polymer are the two main factors influencing the birefringence. The theoretical method established in this work and the calculation results provide a research basis for enhancing the birefringences of polymer materials.
While monolithic integration especially based on InP appears to be quite an expensive solution for optical devices, hybrid integration solutions using cheaper material platforms are considered powerful competitors because of the high freedom of design, yield optimization and relative cost-efficiency. Among them, the polymer planar-lightwave circuit (PLC) technology is regarded attractive as polymer offers the potential of fairly simple and low-cost fabrication, and of low-cost packaging. In our work, polymer PLC was fabricated by using the standard reactive ion etching (RIE) technique, while other active and passive devices can be integrated on the polymer PLC platform. Exemplary polymer waveguide devices was a 13-channel arrayed waveguide grating (AWG) chip, where the central channel cross-talk was below -30dB and the polarization dependent frequency shift was mitigated by inserting a half wave plate. An optical 90 0 hybrid was also realized with one 2×4 multi-mode interferometer (MMI). The excess insertion losses are below 4dB for the C-band, while the transmission imbalance is below 1.2dB. When such an optical hybrid was integrated vertically with mesa-type photodiodes, the responsivity of the individual PD was around 0.06 A/W, while the 3 dB bandwidth reaches 24 ~ 27 GHz, which is sufficient for 100Gbit/s receivers. Another example of the hybrid integration was to couple the polymer waveguides to fiber by applying fiber grooves, whose typical loss value was 0.2 dB per-facet over a broad spectral range from 1200-1600 nm.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.