Low-loss optical fibers are essential for laser applications and fiber-optic communications. This paper reviews the history and technology for reducing the transmission loss of optical fibers. For today’s optical fibers, the key technology for reducing loss is to reduce the Rayleigh scattering loss. Pure-silicacore fiber (PSCF) with low Rayleigh scattering has been developed, with a record-low loss of 0.1484 dB/km at 1570 nm. Commercial PSCF has low loss less than 0.17dB/km at 1550 nm, whereas the loss of standard single mode fiber with a Ge-doped core is about 0.19dB/km. We also introduce lownonlinearity fibers with an effective area larger than 130 μm2. Low-loss and low-nonlinearity fibers, which can effectively improve the optical signal-to-noise ratio, should be best suited for large capacity and long-haul transmissions in near future. Evolutional fibers such as hollow-core fiber are anticipated to ultimately realize low loss and low nonlinearity.

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Multi-core fibers, which are the strong candidates for enabling future high-density transmission system, have receiving great interest to meet the increase of the internet traffic demand. This manuscript includes their designing approach, manufacturing technique, recent characteristics and perspective. Also, their reliabilities, splicing technique and applications are summarized.

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Laser technologies are extensively used in the various fields such as material processings, medical treatments, and measurements. Especially, the developments of the high power laser with excellent beam quality such as fiber lasers have advanced in the laser machining fields, which are for the production line of the automotive body and the lithium ion battery. In the fields, the laser power transmission technologies by using laser delivery fi bers are indispensable and the higher reliability is increasingly required. In this report, we introduce the overview about the preparation methods, which are a laser polishing and an end-cap structure, for the optical fi ber end face and the connector technology that is a cladding mode stripper. These technologies can be expected to support the reliability of the laser delivery fi bers.

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Photonic crystal fiber (PCF) has an array of the air hole that surrounds the core region. PCF is classified into two types by the difference of the principle of the optical guide mechanism. One is called index guiding type PCF, that confines the light into the core by lower effective refractive index of the cladding region. The other type is called PBGF (photonic band gap fiber), that has the optical guide mechanism based on the photonic band gap effect. In this report, we discuss the properties of various types of PCF, namely endlessly single mode (ESM) fiber, high birefringence polarization maintaining fiber, bending insensitive hole assisted fiber and double cladding fiber with air holes. We also discuss the property of PBGF.

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We reviewed the basics of optical fiber splicing and introduced advanced splicing technologies. The splicing technologies of optical fibers are indispensable to the evolution of such optical fiber applications as optical communications, optical fiber components, and optical fiber sensors. In this paper, we review the theories of the splicing loss of optical fibers, the basics of arc-fusion splicing technologies, and such recent advances on arc-fusion splicers as a new high-performance splicer for telecom optical fibers and a new splicer applicable to a wide range of specialty fibers. The basics of optical connector technologies are reviewed as well as recent advances on optical fiber connectors such as optical fiber connectors for FTTH and optical interconnections.

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Fluoride glasses, in spite of only 80 years old, have been widely developed with many kind of different compositions so far, because of its attractive properties, for example, high transparency in wide spectral range between visible and mid-infrared, and low phonon energy property that enhances the emission of many active ions. Many researchers have been challenging to make fluoride glass optical fibers, however, fluoride glasses are generally weak at humidity and have difficulty of glass formation due to crystallization or high susceptibility of viscosity to temperature, thus a fluoride glass is still one of the most difficult glass-system to draw optical fibers. In this paper, with surveying fluoride glasses and fibers, I introduce the waterproof fluoride glass (fluoroaluminate glass system) and fiber that we developed. The waterproof fluoride glass fiber is expected to use for multi-color visible lasers and midinfrared fiber lasers.

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Lock-in amplifier is a useful instrument for recovering small signals buried in noise. This paper describes the principle and an application example of the lock-in amplifier. In addition, it offers some advice on the selection and usage of signal amplifier.

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