Azusa Inoue

Low loss graded index polymer optical fiber with high stability under damp heat conditions

A low loss graded index polymer optical fiber (GI POF) with a wide wavelength range around 650 nm is fabricated using a copolymer of methyl methacrylate and pentafluorophenyl methacrylate as a polymer matrix. Dopant hydrophobicity similar to that of the polymer matrix is an important factor in maintaining the low loss of the GI POF. No loss increment is observed under damp heat conditions of 75°C and 85% relative humidity when using 9-bromo phenanthrene as the high refractive index dopant required to form the GI profile. The copolymer based GI POF can provide an inexpensive premise network with long-term stability.

Deformable Mirror for Mechanical Q-Switching of Laser-Diode-Pumped Microchip Laser

A piezoelectrically deformable output-mirror was used for the mechanical Q-switching of a laser-diode-pumped Nd3+:YVO4 microchip laser. A unimorph structure consisting of a piezoelectric polymer and a polymeric multilayered mirror on a flexible polymer substrate was vibrated to periodically change the laser-cavity loss under the application of an AC voltage of 250 V. It yielded Q-switched pulses with a duration of 16 ns at a repetition rate of 1.338 kHz for a pump power of 284 mW and a cavity length of 16 mm. The average power and peak power were 1.1 mW and 52 W, respectively.

Evaluation of modal noise in graded-index silica and plastic optical fiber links for radio over multimode fiber systems

We have evaluated and compared modal noise induced in a graded-index silica multimode fiber (GI-MMF) link and a graded-index plastic optical fiber (GI-POF) link with the misaligned fiber connections. In radio over fiber (RoF) systems using these optical fibers, modal noise appears as unwanted amplitude modulation in the received signal, and results in degradation of the RoF transmission performance. In this work, we have evaluated the modal noise induced in GI-MMFs and GI-POFs with its same core diameter of 50 μm. Our results show that GI-POFs have an inherently higher tolerance to misaligned connection and less modal noise than GI-MMFs in terms of both the error-vector magnitude and the speckle pattern of the transmitted signals.

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.

High-Speed Graded-Index Plastic Optical Fibers and Their Simple Interconnects for 4K/8K Video Transmission

We developed a consumer-friendly interface graded-index plastic optical fiber (GI POF) cable with the ballpoint-pen interconnects for uncompressed 4K/8K video transmission of 120 Gb/s. Since the material dispersion of perfluorinated GI POF is smaller than that of silica multimode fiber (MMF) at 850-nm wavelength, the bandwidth achieved by GI POF is higher than that of silica MMF. Moreover, it is confirmed that by using GI POF with larger-scale microscopic polymer heterogeneities, serious noise problems observed in silica MMF are much improved by GI POF, which is achieved by resulting stronger mode coupling. This suggests that thinner 4K/8K cables can be feasible by using multilevel transmission through the low-noise GI POFs. The high-speed and low-noise GI POF is paving the way for consumer applications of 4K/8K optical interface toward the 2020 Tokyo Olympics and Paralympics.

Intrinsic transmission bandwidths of graded-index plastic optical fibers

We theoretically demonstrate that microscopic heterogeneous properties can enhance the transmission bandwidths of graded-index plastic optical fibers (POFs) for short-haul communication networks. The heterogeneities of the POF cores are quantitatively correlated with mode couplings by modifying the coupled power equation with consideration of the spatial correlation characteristics of the heterogeneities. Using the modified theory, we clarify that the larger fluctuation size and/or amplitude results in higher bandwidth because of greater forward scattering and/or higher scattering efficiency, respectively. This suggests that the multimode fiber bandwidths can depend on the macroscopically observed index profiles as well as on the microscopic material properties.

Reflection noise reduction effect of graded-index plastic optical fiber in multimode fiber link

We experimentally demonstrate that a graded-index plastic optical fiber (GI POF) can significantly reduce reflection noise in a multimode fiber link with a vertical-cavity surface-emitting laser (VCSEL). By directly observing beams backreflected to the VCSEL, we show that the noise reduction effect is closely related to random mode coupling because of light scattering by microscopic heterogeneities in the GI POF core material. This suggests that intrinsic mode coupling can lower the self-coupling efficiency of the light backreflected to the VCSEL cavity through beam quality degradation. Using GI POFs, low-cost radio-over-fiber systems for indoor networks can be realized without optical isolators or fiber end-face polishing.

Efficient group delay averaging in graded-index plastic optical fiber with microscopic heterogeneous core

Intrinsic mode coupling in a graded-index plastic optical fiber (GI POF) is investigated using the developed coupled power theory for a GI POF with a microscopic heterogeneous core. The results showed that the intrinsic material properties can induce random power transitions between all the guided modes, whereas the structural deformation of microbending results in nearest-neighbor coupling. It was numerically demonstrated that efficient group-delay averaging due to intrinsic mode coupling brings the pronounced bandwidth enhancement in fibers with much shorter length than the case of glass multimode fibers.

Polymeric saturable-absorber mirror for passive Q-switching of a laser-diode-pumped Nd3+:YVO4 microchip laser.

A polymeric multilayered mirror doped with a saturable dye worked as a passive Q-switch of a laser-diode-pumped Nd(3+):YVO4 microchip laser. The multilayered mirror consisted of alternately spin-coated layers of polyvinylcarbazole (PVK) and cellulose acetate on a glass substrate. A dye of bis-(dimethylaminodithiobenzil)-nickel was doped in one of the layers of PVK, providing the repetitively Q-switched pulses. The pulse width and repetition rate were 4 ns and 68 kHz, respectively, for a laser-cavity length of 5 mm, and the average and the peak power were 40 mW and 156 W, respectively, for the highest pump power of 435 mW. The dependence of the Q-switched characteristics on the pump power and on the concentration of the doped dye is described.

A surface-emitting distributed-feedback dye laser fabricated by spin-coating organic polymers

A distributed-feedback dye laser was fabricated by use of alternate spin-coating of a high and a low refractive-index polymer. The laser was emitted from the surface of the dye-doped polymeric multilayer at the designed wavelength.