Kotaro Koike

Design of Low-Loss Graded-Index Plastic Optical Fiber Based on Partially Fluorinated Methacrylate Polymer

As a promising candidate of optical home network, a novel Gigabit Ethernet prepared by inexpensive partially fluorinated polymer-based graded-index plastic optical fiber (GI POF) was proposed. Poly (2,2,2-trifluoroethyl methacrylate) (P3FMA) was selected as a base material for the GI POF because of its high transparency, low material dispersion, and low cost. The transmission characteristics were investigated, and it was clarified that the newly developed GI POF has low-loss (71 dB/km at 650 nm), high humidity stability, and high-bandwidth (4.86 GHz for 50-m transmission) property. Moreover, 1.25-Gbps data transmission over 50 m was demonstrated by P3FMA-based GI POF.

Poly(styrene)-based graded-index plastic optical fiber for home networks

We investigated poly(styrene) (PSt)-based graded-index plastic optical fiber (GI-POF) with low loss and high bandwidth for home networks. To install the GI-POF in home networks, the attenuation must be below 200 dB/km at a 670-680 nm wavelength, and the bandwidth must be over 2.0 GHz for the 50 m fiber. In this study, we selected a dibenzothiophene (DBT) as a dopant to PSt, and we fabricated PSt-DBT-based GI-POF. We confirmed that the PSt-DBT-based GI-POF has high bandwidth (4.4 GHz) for 50 m fiber and low loss (166-193 dB/km) at a 670-680 nm wavelength and obtained the GI-POF that satisfied the requirements for home networks.

High-Bandwidth Graded-Index Plastic Optical Fiber With Low-Attenuation, High-Bending Ability, and High-Thermal Stability for Home-Networks

The graded-index plastic optical fiber (GI-POF) is expected to be a communication medium for the next-generation optical home network because of its simple-to-use connection, installation, and high bandwidth. In spite of the expectation, we had a problem that a typical GI-POF using poly (methyl methacrylate) (PMMA) had high transmission loss in the expected communication wavelength band (VCSEL: 670-680 nm) for home networks; the required values of being below 200 dB/km could not be achieved. We, therefore, propose poly (2, 2, 2-trichloroethyl methacrylate) (PTCEMA) as a base material for the GI-POF. A PTCEMA-based GI-POF was fabricated, and its characteristics were evaluated. The PTCEMA is a prominent material in terms of its transparency and heat-resistant property. Our results demonstrated that the fabricated fiber surpassed the desired characteristics for the home network pertaining to attenuation and heat resistance. Specifically, the attenuation in the wavelength band (670-680 nm) was 104-136 dB/km, and the glass transition temperature (Tg) was 102°C in the core center where the Tg was at its lowest. Moreover, we confirmed that our PTCEMA-based GI-POF had sufficient mechanical strength and low bending loss. These results indicate that our novel GI-POF can be a candidate for home networks.

Low Loss and High Bandwidth Polystyrene-Based Graded Index Polymer Optical Fiber

Polystyrene (PS) was selected as a costless polymer matrix for graded index polymer optical fibers (GI POFs) with low attenuation at a wavelength of 670 nm. However, fabricated PS-based GI POFs showed attenuation of more than 300 dB/km. This high attenuation PS-based GI POF had a quite broad molecular weight distribution. In contrast, a PS-based GI POF with a narrow molecular weight distribution showed low attenuation of around 160 dB/km. This is because the refractive index of PS, different from general polymers, is greatly affected by the molecular weight. The PS-based GI POF showed the high thermal stability of this low loss performance at a temperature of 70°C , despite the low glass transition temperature caused by plasticization. The measured refractive index profile was near optimum (g=2.5), and a high bandwidth of 5.8 GHz for a 50 m length was obtained.

Temperature dependence of Brillouin frequency shift in polymers controlled by plasticization effect

The temperature-dependence coefficient of Brillouin frequency shift (BFS) in perfluorinated graded-index polymer optical fibers is known to change drastically, because of the glass transition, at a certain critical temperature (Tc), above which the BFS becomes more sensitive to temperature. In this paper, we demonstrate that the Tc value can be adjusted by varying the dopant concentration, which is originally used to form the graded-index profile in the core region. Furthermore, we show that the temperature sensitivity of the BFS is enhanced in the presence of dopant probably because the temperature sensitivity of Youngs modulus is increased. The results indicate a big potential of the temperature sensors based on Brillouin scattering with an extremely high sensitivity in a specific desired temperature range.

Dependence of Brillouin frequency shift on temperature in poly(pentafluorostyrene)-based polymer optical fibers estimated by acoustic velocity measurement

Poly(pentafluorostyrene) (PPFS), which can be easily synthesized and has a low optical loss window at 850nm, is a promising alternative for a costly perfluorinated polymer as a base material of polymer optical fibers (POFs). To investigate the potential of a PPFSPOF as a Brillouin-based temperature sensing fiber, the Brillouin frequency shift and its temperature dependence of PPFS were measured using an ultrasonic pulse-echo technique. The temperature coefficient, which determines the sensitivity of the temperature sensing, was approximately !7.1MHz/K independently of the molecular weight and was nearly identical to that in perfluorinated POFs.

Dependence of Brillouin frequency shift on water absorption ratio in polymer optical fibers

We studied the dependence of the Brillouin frequency shift (BFS) on the water-absorption ratio in poly(methyl methacrylate)-based polymer optical fibers (POFs) to clarify the effect of the humidity on POF-based Brillouin sensors. The BFS, deduced indirectly using an ultrasonic pulse-echo technique, decreased monotonically as the water absorption ratio increased, mainly because of the decrease in the Youngs modulus. For the same water absorption ratio, the BFS change was larger at a higher temperature. The maximal BFS changes (absolute values) at 40, 60, and 80 °C were 158, 285, and 510 MHz, respectively (corresponding to the temperature changes of ∼9 °C, ∼16 °C, and ∼30 °C). Thus, some countermeasure against the humidity is indispensable in implementing strain/temperature sensors based on Brillouin scattering in POFs, especially at a higher temperature. On the other hand, Brillouin-based distributed humidity sensors might be developed by exploiting the BFS dependence on water absorption in POFs.

Evaluation of Brillouin frequency shift and its temperature dependence in poly(pentafluorostyrene)-based polymer optical fibers by ultrasonic pulse-echo technique

Poly(pentafluorostyrene) (PPFS), which can be easily synthesized and has a low optical loss window at 850 nm, is a promising alternative for a costly perfluorinated polymer as a base material of polymer optical fibers (POFs). To investigate the potential of a PPFS-POF as a Brillouin-based temperature sensing fiber, the Brillouin frequency shift and its temperature dependence of PPFS were estimated using an ultrasonic pulse-echo technique. The temperature coefficient, which determines the sensitivity of the temperature sensing, was approximately –7.1 MHz/K independently of the molecular weight and was nearly identical to that in perfluorinated POFs.