Various optical fiber connectors have been developed during the 40 years since optical fiber communications systems were first put into practical use. This paper describes the key technologies for optical connectors and recent technical issues.

In this study, we discuss a structure that realizes a wideband polarization splitter comprising fiber 1 with a single core and fiber 2 with circular pits, which touch the top and bottom of a single core. The refractive index profile of the W type was adopted in the core of fiber 1 to realize the wideband. We compared the maximum bandwidth of BW-15 (bandwidth at an extinction ratio of -15dB) for the W type obtained in this study with those (our previous results) of BW-15 for the step and graded types with cores and pits at the same location; this comparison clarified that the maximum bandwidth of BW-15 for the W type is 5.22 and 4.96 times wider than those of step and graded types, respectively. Furthermore, the device length at the maximum bandwidth improved, becoming slightly shorter. The main results of the FPS in this study are all obtained by numerical analysis based on our proposed MM-DM (a method that combines the multipole method and the difference method for the inhomogeneous region). Our MM-DM is a quite reliable method for high accuracy analysis of the FPS composed of inhomogeneous circular regions.

A single-polarization single-mode (SPSM) photonic crystal fiber (PCF) based on double-hole unit core is proposed in this paper for application to cross-talk free polarization splitter (PS). Birefringence of the PCF is obtained by adopting double-hole unit cells into the core to destroy its symmetry. With an appropriate cladding hole size, single x- or y-polarized PCF can be achieved by arranging the double-hole unit in the core along the x- or y-axis, respectively. Moreover, our proposed SPSM PCF has the potential to be applied to consist a cross-talk free PS. The simulation result by employing a vectorial finite element beam propagation method (FE-BPM) demonstrates that an arbitrary polarized incident light can be completely separated into two orthogonal single-polarized components through the PS. The structural tolerance and wavelength dependence of the PS have also been discussed in detail.

The fabricated 1.55 µm high power superluminescent light emitting diodes (SLEDs) with 115 mW maximum output power and 3 dB bandwidth of 50 nm, using active multi-mode interferometer (MMI), showed high coupling efficiency of 66% into single-mode fiber, which resulted in maximum fiber-coupled power of 77 mW.

Phase performance in a temperature sensor using a conventional single-mode step-index fiber is studied. Two modes are excited in a so called single-mode fiber when the wavelength of a laser source is shorter than the one suggested by the specification of a fiber. The phase shift due to the temperature change of a step-index fiber is analyzed. The intensity fluctuation by the interference of two modes is observed in the experiment and estimated in the computer simulation.

An 80 Gbit/s conventional and carrier-suppressed return-to-zero optical time-division multiplexing signal transmission over a 208 km standard single-mode fiber was experimentally demonstrated. This was achieved by using mid-span optical phase conjugation based on four-wave mixing in semiconductor optical amplifiers. In addition, it was confirmed that the transmitted carrier-suppressed return-to-zero optical signal's carrier phase-relation was held.

In this letter, we describe the conditions for measuring the nonlinear refractive index n2 when using the self-phase modulation-based cw dual-frequency method. We clarify the appropriate measurement conditions for dispersion-shifted and conventional single-mode fibers both numerically and experimentally. We also show experimentally that the evaluated n2 values for conventional single-mode fiber depend on the signal wavelength separation.

A photonic crystal fibre has an array of microscopic air holes running along its length. The periodicity of the array is broken by a deliberate "defect" that acts as a waveguide core. Light is confined to this core by the holes. Although some designs of photonic crystal fibre guide light by total internal reflection and so can be considered analogues of conventional optical fibres, their properties can be strikingly different. Other designs guide light by photonic bandgap confinement and represent a totally new type of fibre.

A photonic crystal fibre has an array of microscopic air holes running along its length. The periodicity of the array is broken by a deliberate "defect" that acts as a waveguide core. Light is confined to this core by the holes. Although some designs of photonic crystal fibre guide light by total internal reflection and so can be considered analogues of conventional optical fibres, their properties can be strikingly different. Other designs guide light by photonic bandgap confinement and represent a totally new type of fibre.

A model for estimating the bending loss of 1.3 µm zero-dispersion single-mode fibers at 1.58 µm from the value at 1.55 µm is investigated experimentally and theoretically. An approximated equation for estimating the bending loss ratio of 1.58 µm to 1.55 µm is proposed, which provides good agreement with the experimental results.

This paper describes the fabrication of micro-pipes and their applications to splicing parts and optical switches using single-mode fibers. Micro-pipes having almost the same inner diameter of bare fiber (125 µm) and lengths of around 5 mm are successfully mass-produced by using micromachining technology. We fabricate various kinds of metal pipes such as Au, Cu, Ni, and an FeNi alloy by selecting the appropriate electro-plating bath. We use an Au micro-pipe having a small slitted portion running along its axis (slitted micro-pipe) to splice single-mode fibers. We also use an FeNi alloy micro-pipe to construct a single-mode fiber switch. These new single-mode fiber devices employing micro-pipes show excellent optical and mechanical characteristics. Splicing losses are in the range of 0.2-0.4 dB. The developed 1 2 latching type single-mode fiber switches exhibit a low insertion loss of 0.35 dB, a minimum switching speed of 2 ms with a driving power of 9 mW, and stable operation for more than 108 switchings without damage. A practical application of the developed switch for testing optical devices is also demonstrated.

This paper describes the design, characteristics, and applications of newly developed latching-type 1 2 and 1 8 single-mode fiber switches. These switches have been successfully fabricated using micromachine technology. To reduce insertion loss and light reflection, an index-matching oil is injected into the switches. The fabricated 1 2 switches exhibit a low insertion loss of 0.31 dB, high return loss of 51 dB, relatively fast switching speed of 2 ms, and low driving power of 9 mw. Switching operation is stable over 108 switching times. A practical 1 8 single-mode fiber switch was also constructed using seven 1 2 switches cascaded in three stages. The fabricated 1 2 and 1 8 switches have been applied to an NTT multichannel video distribution FTTH system to enhance system reliability.

The multichannel distortions of direct modulated laser diode were studied from the view point of rate equations. A novel technique for compensating the composite second order distortion (CSO) was proposed. Meanwhile, the related calibration procedures were indicated. After the compensation, 10 dB improvement in CSO was obtained