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We investigated the influence of a high-power optical transmission on an optical connector by focusing on the fiber withdrawal phenomenon. Along with the curvature radius and the convex vertex eccentricity, fiber withdrawal is one of the key factors in obtaining good connections in single-core optical connectors that use a cylindrical ferrule. When the fiber fixed to the ferrule by adhesive, fiber withdrawal is generated by creep as the adhesive undergoes shear due to the temperature increase of the optical connector. In this paper, we examine the relationship between the optical loss power and fiber withdrawal in order to clarify the conditions leading to fiber withdrawal during high-power optical transmission. We confirm that the shear stress created by the axial compressive force deliberately imposed to achieve reliable physical contact in the optical connector greatly encourages fiber withdrawal. In addition, we clarify that fiber withdrawal under high-power optical transmission depends significantly on the initial fiber position in the connector plug, regardless of the connector temperature increase. We also investigate the long-term reliability of optical connectors for high-power optical transmission. We subject optical connectors to 90 °C, which corresponds to the glass transition temperature of the adhesive, for 500 hours, and measure the optical and mechanical properties. The measured values of both properties remain excellent, and we clarify that although some slight fiber withdrawal occurs during high-power optical transmission, optical connectors with zirconia ferrules do not allow the transmission performance to degrade.

We propose an optical switch that rotates an MCF set in a cylindrical ferrule. We show the loss characteristics and examine the factor of the excess loss focusing on an offset between the each core.

We investigated the conditions that cause a connector damage during a high-power transmission in an optical connector with house dust on its endface. In this paper, to examine the connector conditions that cause the connector damage, we focused on optical characteristics, such as insertion loss and return loss, dust attachment pattern, and optical power. We show the relationship between the connector damage and the MFD of the fiber used in telecommunication network when house dust is used as a contaminant. Moreover, we show the threshold value of the input power level needed for damage to occur to a connector with house dust on its endface when that power is interrupted completely. We also describe the operating procedure for a secure high-power transmission, where the procedure consists of connector cleaning, connector endface observation, and insertion and return loss measurements. We show that it becomes possible to completely remove dust, which we could not remove with a cleaner alone, by using an air duster in combination with a cleaner. We also show that an optical connector cleaned with our proposed procedure, which exhibited an insertion loss of less than 0.5 dB and a return loss exceeding 45 dB, tolerated a high optical power of 5 W.

We experimentally investigate the cutoff wavelength shortening effect that occurs when the cladding diameter is reduced. The influence of coating thickness, and thus, cladding diameter, on the transmission loss is also discussed. We derive an empirical model of cutoff wavelength and transmission loss as a function of the cladding diameter and coating thickness. The empirical model reveals that a further reduction in the cladding diameter of step index type bending-loss insensitive fiber (BIF) is possible. The validity of the proposed BIF design is confirmed using a 70-μm cladding diameter BIF and jumper cords. This BIF enables us to construct optical fiber networks with higher reliability.

Bending-loss insensitive fiber (BIF) has proved an essential medium for constructing the current fiber to the home (FTTH) network. By contrast, the progress that has been made on holey fiber (HF) technologies provides us with novel possibilities including non-telecom applications. In this paper, we review recent progress on hole-assisted type BIF. A simple design consideration is overviewed. We then describe some of the properties of HAF including its mechanical reliability. Finally, we introduce some applications of HAF including to high power transmission. We show that HAF with a low bending loss has the potential for use in various future optical technologies as well as in the optical communication network.

We investigated the measurement conditions for measuring multipath interference (MPI) occurring between fundamental and higher order modes. We considered the sampling interval as a function of the free spectral range (FSR) as a measurement condition. We also investigated the effect of randomized polarization states when measuring the MPI characteristics. We then confirmed the MPI characteristic, which we measured using three methods with a suitable sampling interval over FSR value and a suitable number of repetitions of randomized polarization states. Furthermore, we describe the MPI characteristic of bending loss insensitive fibers (BIFs) with offset connections and tight bends. We discuss the MPI degradation factor in an access network employing BIF.

The characteristics of hole-assisted fiber (HAF) are investigated both numerically and experimentally in terms of its applicability as a bending-loss insensitive fiber (BIF). We show that HAF with the desired mode-field diameter (MFD), bending-loss and cutoff wavelength characteristics can be roughly designed by taking a few specific structural parameters into consideration. We also show that an optical cord composed of adequately designed HAF realizes satisfactory transmission performance with respect to its multi-path interference (MPI) characteristics. These results reveal that a hole-assisted type BIF will be beneficial for realizing easy and economical installation and maintenance in future access networks.

We investigate the design and characteristics of a single-mode and low bending loss HAF both numerically and experimentally. An air filling fraction S is introduced to enable us to design a HAF with desired characteristics more easily. We show that we can expect to realize a single-mode and low bending loss HAF by considering the S dependence of the bending loss α b and cutoff wavelength λ c as well as their relative index difference Δ dependence. We also show that the mode-field diameter (MFD) and chromatic dispersion characteristics of the single-mode and low bending loss HAF can be tailored by optimizing the distance between the core and the air holes. We also investigate the usefulness of the fabricated HAFs taking the directly modulated transmission and multipath interference (MPI) characteristics into consideration. We show that the designed HAF has sufficient applicability to both analog and digital transmission systems. Our results reveal that the single-mode and low bending loss HAF is beneficial in terms of developing a future fiber to the home (FTTH) network as well as for realizing flexible optical wiring.

We discuss the applicability of photonic crystal fiber (PCF) with a uniform air-hole structure to high-speed and wide-band transmission over conventional telecommunication bands. We design the PCF to maximize the effective area by utilizing the macro-bending losses of the fundamental and first higher order modes (HOM) and clarify that a single-mode and low bending loss PCF can realize the largest effective areas of 133 and 157 mum2 for transmission over the 1260-1625 nm (O ~ L bands) and 1460-1625 nm (S ~ L bands) wavelength ranges, respectively. We then investigate the impact of the designed PCF on nonlinearity reduction over a wide wavelength range and show that the PCF helps to increase the maximum channel power in a wavelength division multiplexing system. We also discuss the distributed Raman amplification (DRA) characteristics of PCF with a large effective area. Our results show that we can expect to improve the signal to noise ratio with DRA in spite of the low nonlinearity of the designed PCF. Dispersion compensating fiber (DCF) with a conventional W-shaped index profile is designed to compensate for the relatively large dispersion of the PCF, and we show that the designed DCF can extend the dispersion compensation bandwidth from 1340 nm to 1650 nm for a 40 Gbit/s transmission. Finally, we clarify the applicability of the large effective area PCF with the uniform air-hole structure as a high-speed and wide-band transmission medium.

In this paper, we describe Raman amplification characteristics and the potential for distributed Raman amplification (DRA) transmission in silica core photonic crystal fiber (PCF). We measured the Raman gain spectra of PCFs at different pump wavelengths, and confirmed that the pump wavelength dependence of the Raman gain coefficient of PCF agrees well with that of silica glass. DRA transmission performance in the 850 and 1580 nm wavelength regions was also examined individually using 6.0 and 12.7 km long PCFs. Finally, we clarified numerically that the signal-to-noise ratio (SNR) can be improved over a wide wavelength region by using silica core PCF and DRA. Our results show that silica core PCF has potential as a DRA transmission medium over an arbitrary wavelength region.

The applicability of few-mode fiber (FMF) as a single-multi-single (SMS) sensor is investigated. We examine experimentally the wavelength shift and/or visibility characteristics in an FMF based SMS sensor by changing the external temperature and longitudinal strain individually. We investigate numerically the temperature sensitivity of the fabricated sensor by considering the temperature dependence of the effective refractive index difference. Our results show that an FMF based SMS sensor can be used to measure the relative variation in temperature and strain simultaneously, and whose sensitivity can be tailored easily by designing two LP modes in an FMF.

Photonic crystal fibers (PCF) with a silica–air microstructure have received increasing attention in recent years. In this paper, we analyze the loss properties of PCF and report our progress on low loss PCF. We show that the loss performance of PCF is dominated by scattering loss and OH− absorption loss. We show that the PCF scattering loss depends on both the roughness of the hole interior surface and the power distribution in the fiber cross-section. By employing appropriate polishing, etching and dehydration processes, we succeeded in obtaining a PCF with an OH− absorption loss as low as 0.4 dB/km at 1.38 μm and another PCF with a loss of 0.28 dB/km at a wavelength of 1.55 μm, which are the lowest values to the best of our knowledge.

This paper describes the distributed Raman amplification (DRA) transmission characteristic in an optical fiber both numerically and experimentally. The paper clarifies the relationship between optical fiber parameters and DRA transmission performance with regard to the signal-to-noise ratio (SNR) characteristics and nonlinear impairments. These relationships can be successfully discussed, taking account of various fiber parameters, including Raman gain efficiency, the attenuation coefficient at signal and pump wavelengths, the Rayleigh scattering coefficient, and the nonlinear refractive index, as a function of the relative index difference in an optical fiber. An example of an optimum fiber design for a DRA-based dense-wavelength-division-multiplexing (DWDM) transmission system is also discussed.

We describe the ultrawide-band single-mode transmission performance of a photonic crystal fiber (PCF) in the 850 to 1550 nm wavelength range. We confirmed that the fabricated PCF achieves a single-mode operation over the 850 to 1550 nm wavelength range by measuring the mode-field diameter (MFD) and modal delay characteristics. The 10-Gb/s-based wavelength-division multiplexing (WDM) signals with a total capacity of 190 Gb/s were successfully transmitted over a 5.2-km low-loss PCF utilizing the 850, 1310, and 1550 nm regions simultaneously. Our experimental results show that an endlessly single-mode PCF provides an ultrawide-band of more than 160 THz for future optical communication systems.

A systematic optical emission spectroscopy (OES) study was carried out to enhance the deposition rate of microcrystalline silicon (μc-Si:H) with conventional r.f. plasma-enhanced chemical vapor deposition (r.f. PECVD). Among the various plasma parameters, the combination of total pressure, r.f. power, electrode distance and cathode heating was effective to promote the deposition rate without deteriorating the film crystallinity. Strong correlations among the OES intensity, SiH, intensity ratio, I H α / I Si* , deposition rate and Raman intensity ratio, I μc-Si / I a-Si were confirmed in the case of r.f. SiH 4 and H 2 PECVD. A relatively high deposition rate was achieved of ∼5 A/s in the μc-Si:H film growth by optimizing the deposition parameters. The effects of higher pressure, higher r.f. power, inter electrode distance and cathode heating (SiH 4 gas heating) are demonstrated in the growth of μc-Si:H from strong H 2 -diluted SiH 4 by a conventional r.f. glow discharge.

We demonstrate some specific features of hydrogenated chlorinated crystalline silicon with nanometer sized crystallites (nc-Si:H(Cl)) film fabricated from a H2-diluted dichlorosilane, SiH2Cl2 by radio frequency (RF) plasma-enhanced chemical vapor deposition (PECVD). Contrary to the conventional SiH4 based nc-Si:H growth, the crystallization occured from the initial growth stage on glass without incubation of an amorphous layer. Best crystallinity was obtained at substrate temperature, Ts of 200°C with a 10–20 nm-sized c-Si particles. The crystallinity increased with an increase in the pressure to ∼525 mTorr in the flow rate of SiH2Cl2, Fr(SiH2Cl2):Fr(H2)=3:100 (sccm) condition. In addition, the SiH2Cl2 based nc-Si:H(Cl) film had smaller optical absorption in the visible range than that of the SiH4 based nc-Si:H. The growth mechanism is discussed to better comprehend some specific features in terms of the gas phase and surface reactions in comparison with that in SiH4 and H2 system.

We describe the applicability of photonic crystal fiber (PCF) with an enlarged effective area Aeff to a distributed Raman amplification (DRA) transmission. We investigate the DRA transmission performance numerically over a large Aeff PCF taking account of the signal-to-noise ratio (SNR) improvement RSNR in the S, C, and L bands. We show that an RSNR of 3dB can be expected by utilizing DRA with a maximum pump power of 500mW when the Aeff of the PCF is 230µm2.

We achieve a 2.5-dB improvement in the power penalty in a 10-Gb/s-based distributed Raman amplification transmission at 850 nm using a silica-based low-loss photonic crystal fiber (PCF). The experimental results agree well with a signal-to-noise ratio improvement model. The model indicates the negligible influence of double Rayleigh backscattering in the fabricated PCF

A technique is proposed for evaluating power coupling coefficient distribution in a multi-core fiber. The longitudinal crosstalk characteristic in a two-core fiber is successfully evaluated using a bi-directional OTDR waveform simply obtained with one core.

The impact of multi-core crosstalk on far-field pattern (FFP) measurement is clarified numerically and experimentally. We show that the neighboring core angle against the scanning plane greatly affects the FFP and mode-field diameter characteristics.

In this letter, we describe a novel method for evaluating the cutoff wavelength in a single-mode fiber based on far-field pattern (FFP) measurement under different launch conditions. We show that the proposed method can be applied not only to conventional fiber but also to a special fiber with superior bending loss performance. We also discuss the relationship between the FFP measurement conditions and the measurement accuracy of the proposed method.

The reliability of a pure silica core single-mode fiber with long-term exposure to continuous wave (CW) high-power laser light is reported. It is found that the optical loss in the 0.6-1.6-/spl mu/m region and the Raman spectrum remain unchanged after 1900 h of exposure to 8-W CW laser light at 1.48 /spl mu/m. The nonbridging oxygen hole center concentration generated by 1900 h of exposure is estimated to be below our detection limit of 2/spl times/10/sup 12/ cm/sup -3/.

In this letter, we describe numerically the relationship between optical fiber parameters and the transmission performance of distributed Raman amplification (DRA) in terms of signal-to-noise ratio characteristics and nonlinear impairment. In our calculation, we fully considered the dopant dependence of the optical fiber parameters with regard to DRA transmission performance. Our calculated results show that an optimization of the relationship between the relative index difference and the effective area makes it possible to design an optical fiber that efficiently utilizes DRA.

We have demonstrated a distributed Raman amplification at 850 nm for the first time utilizing a low loss photonic crystal fibre. Power penalty has been improved by 1.6 dB in 6.0 km transmission. (2 pages)

We have succeeded in reducing the PMD of PCF to 10% of its initial value by periodic bidirectional twisting without loss increasing and structural deformation. A PCF with PMD of 0.03 ps/rkm has been obtained.

We describe the dopant dependence of Raman gain in germanium- and fluorine-doped optical fibers. We clarify, both theoretically and experimentally, the effective Raman gain characteristic in an optical fiber, which is closely related to the fiber's refractive-index profile and electromagnetic field profile. We also show that this experimentally determined relationship can be used to evaluate the effective Raman gain characteristic in a germaninum- or a fluorine-doped optical fiber with an arbitrary index profile.

A photonic crystal fibre (PCF) with polarisation mode dispersion (PMD) of 0.03 ps/rkm was obtained by unidirectional twist. The work was also successful in reducing the PMD of the PCF to 10% of its initial value by periodic bidirectional twisting without loss increasing and structural deformation.

Low temperature growth of hydrogenated chlorinated crystal silicon [µc-Si:H(Cl)] films from dichlorosilane (SiH2Cl2) by conventional rf glow discharge (13.56 MHz) is investigated. The role of chlorine and hydrogen in crystal formation is discussed in terms of studies on gas phase and surface chemistry through film deposition, plasma diagnostics and in situ monitoring of the surface reaction. The electron temperature in the SiH2Cl2/H2 plasma significantly depends on not only pressure but also substrate temperature. The surface termination species depend on substrate temperature and hydrogen flow rate. The growing top surface is mainly terminated by chlorine as SiCl n (n=1, 2). Specific features of crystal formation at low temperatures from SiH2Cl2/H2 plasma are demonstrated and compared with those from SiH4/H2.

A novel microwave discharge utilizing a spokewise antenna was applied for the fast deposition of hydrogenated microcrystalline silicon (µc-Si:H) film from SiH4 and Ar without the H2 dilution method. Systematic deposition studies were employed with total pressure, H2 dilution ratio and flow rate of SiH4, Fr[SiH4], as variables, combined with optical emission spectroscopy (OES) and Langmuir probe characterizations. It was found that the deposition rate exhibits a maximum at 40–50 mTorr at the axial distance of 10 cm from the quartz glass plate and the film crystallinity strongly depend on the total pressure. Correlation among OES signal intensity, SiH, the intensity ratio, I Hα /I Si* , deposition rate and film crystallinity were demonstrated. By combining the SiH4 depletion and lower pressure conditions, a high deposition rate of 40 Å/s was achieved in µc-Si:H growth with high crystallinity and photosensitivity from SiH4 and Ar plasma.

The crystallinity at the initial growth stage of hydrogenated microcrystalline silicon (µc-Si:H) was greatly improved on Corning #7059 glass substrate with dichlorosilane (SiH2Cl2) as the starting gas using conventional (13.56 MHz) capacitively coupled plasma-enhanced chemical vapor deposition system. Deposition studies examined film thickness, substrate temperature, total pressure, electrode distance and H2-dilution conditions as variables. Through Raman spectroscopy, atomic force microscopy (AFM), spectroscopic ellipsometry, X-ray diffraction (XRD) and Mie scattering measurements, it was found that ∼20 nm sized crystalline Si particles were formed in the plasma region, resulting in the enhanced crystallization from the initial growth stage. The growth kinetics of µc-Si:H from SiH2Cl2, compared with that from SiH4, is described.

Optical wiring conditions are investigated numerically and experimentally with a viewpoint of MPI induced transmission performance degradation. We reveal the impact of the interval of the bending portion on MPI degradation for the first time.