Origin of high propagation loss in electrospun polymer nanofibers

Yuya Ishii,Mitsuo Fukuda,Ryohei Kaminose,Shota Satozono

doi:10.1063/1.4884217

Abstract

We evaluate optical propagation loss (α) in electrospun poly(methyl methacrylate) (PMMA) nanofibers with different wavelength (λ) and determine the origin of the loss. Aligned single electrospun nanofibers composed of PMMA and a small amount of an organic dye are fabricated with an average diameter of approximately 640 nm. After cladding seven fiber samples, α is evaluated to be 26–62 dB cm−1 at wavelengths 590−680 nm. Moreover, α depended linearly on λ−4, and from the fitting functions we determined the ratio of the following two possible losses for α: loss at the interface between the fiber-core and cladding because of non-uniformity within the fibers (αun), and loss because of excess light scattering in the fibers resulting from density inhomogeneity of PMMA (αsc). For the fibers, αun is evaluated to be 6.9–22 dB cm−1, which represents 19%–50% of α at λ of 650 nm with α ∼ αun + αsc. Thus, we conclude that the high α in these fibers originates from both their poor uniformity and density inhomogeneity. Furthermore, a quantitative investigation of uniformity in the individual fibers revealed that the root mean square roughness ranges from 5.5 nm to 9.0 nm and the theoretical value of αun was ∼1 dB cm−1 showing reasonable agreement with experimental data. These findings hold for low-loss polymer nanofiber waveguides, which have high aspect ratio and fine patterning even in three dimensions.

Highlights

Several groups have demonstrated using poly(methyl methacrylate) (PMMA) as a core material optical waveguiding in electrospun polymer nanofibers and reported the propagation loss to be higher than orders of 10 dB cm−1.10,23 this value is more than 104 times higher than that of a well-studied graded-index PMMA-based optical fiber with a diameter of 0.5 mm,[24] the origin of such high loss has been unclear
We evaluate propagation loss in electrospun PMMA nanofibers at different wavelengths and determine the origin of the high propagation loss
PMMA was chosen as a core material because it shows high transparency in the visible range and is well-studied as a core material in the field of thick polymer optical fibers.[25]

Summary

Introduction

Nanofibers, which are fibers with diameters less than 1 μm, are attracting considerable attention owing to unique optical interactions that arise from their subwavelength size including guiding,[1,2,3,4,5,6,7] confinement,[8] and amplification.[9,10] These properties make them promising candidates for applications in small optical devices such as waveguides,[1,2,3,4,5,6,7] light sources,[11,12] sensors,[13] resonators,[14] gratings,[15] and switches,[16] and the fibers are applicable to the field of plasmonics[17] and optomechanics.[18,19] Electrospun polymer fibers have nanometer diameters and high aspect ratios, making them well-suited for use in such optical devices.

Results

Conclusion