Amorphous electrically actuating submicron fiber waveguides are promising building blocks for creating novel opto‐electromechanical devices. In this study, waveguiding and electrically actuating properties of the waveguides composed of racemic poly(lactic acid) and a dye are investigated. The fibers have mean diameters of <0.4 µm, and each fiber demonstrates subwavelength waveguiding with a loss coefficient of 1.5 × 10−4–8.3 × 10−4 µm−1 at 0.63 µm wavelength. Light propagates with a near‐light speed group velocity between wavelengths of 0.59 and 0.63 µm, where the fraction of power inside the core is 0.13–0.28. The fiber mat thicknesses change in response to both the polarity and the magnitude of an applied voltage, similar to the inverse‐piezoelectric effect. The estimated values for both the apparent piezoelectric constant (29 000 × 10−12 m V−1) and Young's modulus (1.5 kPa) indicate a high degree of electricity actuation and a soft mat. Extremely small, soft, and electrically actuating waveguides can produce novel opto‐electromechanical devices.

Dye-doped submicron poly(N-vinylcarbazole) fibers having mean diameters of 290-430 nm were fabricated via electrospinning and their waveguiding properties were investigated. The middle of each fiber's length was excited with UV light and guided photoluminescence (PL) was measured at the end of each of the fibers for different propagation lengths. The spectral shapes of the guided PL differed depending on the fiber diameter because of leakage of light into the substrate. We propose a model that reproduces the PL attenuation with increasing propagation lengths and includes the temporal PL decay due to photobleaching and the size of the excitation area. The calculated propagation loss coefficient in the fibers was 6.3 3 10 23 21.4 3 10 21 mm 21 with k 5 430-500 nm. The propagation loss was inherent in the fiber itself because the reabsorption loss coefficient of the doped dye was <1.3% of the propagation loss coefficient.

No abstract

Wet-electrospun (WES) polymer micron and submicron fibers are promising building blocks for small, flexible optical fiber devices, such as waveguides, sensors, and lasers. WES polymer fibers have an inherent cylindrical geometry similar to that of optical fibers and a relatively large aspect ratio. Furthermore, WES fibers can be produced using low-cost and low-energy manufacturing techniques with large-area fabrication and a large variety of materials. However, the high propagation loss in the fibers, which is normally on the order of tens or thousands of decibels per centimeter in the visible light region, has impeded the use of these fibers in optical fiber devices. Here, the origin of propagation losses is examined to develop a comprehensive and versatile approach to reduce these losses. The excess light scattering that occurs in fibers due to their inhomogeneous density is one of the primary factors in the propagation loss. To reduce this loss, the light transmission characteristics were investigated for single WES polymer fibers heated at different temperatures. The propagation loss was significantly reduced from 17.0 to 8.1 dB cm –1 at 533 nm wavelength, by heating the fibers above their glass transition temperature, 49.8 °C. In addition, systematic verification of the possible loss factors in the fibers confirmed that the propagation loss reduction could be attributed to the reduction of extrinsic excess scattering loss. Heating WES polymer fibers above their glass transition temperature is a versatile approach for reducing the propagation loss and should be applicable to a variety of WES fibers. This finding paves the way for low-loss WES fiber waveguides and their subsequent application in small, flexible optical fiber devices, including waveguides, sensors, and lasers.

Front Cover: Electrically actuating and waveguiding amorphous polymer submicron fibers can be used to produce novel opto–electromechanical devices. The fibers are further functionalized by embedding other functional materials. This cover image represents dye‐embedded light‐emitting amorphous submicron fibers which actuate in response to the polarity of an applied voltage and guide the emitted light in the fibers. This is reported by Yuya Ishii, Taiki Nobeshima, Heisuke Sakai, Keisho Omori, Sei Uemura and Mitsuo Fukuda in article number https://doi.org/10.1002/mame.201700302.