Physical contact (PC) optical connectors realize long-term stability by maintaining contact with the optical fiber even during temperature fluctuations caused by the microscopic displacement of the ferrule endface. With multicore fiber (MCF) connectors, stable PC connection conditions need to be newly investigated because MCFs have cores other than at the center. In this work, we investigated the microscopic displacement of connected ferrule endfaces using the finite element method (FEM). As a result, by using MCF connectors with an apex offset, we found that the allowable fiber undercut where all the cores make contact is slightly smaller than that of single-mode fiber (SMF) connectors. Therefore, we propose a new equation for determining the allowable fiber undercut of MCF connectors. We also fabricated MCF connectors with an allowable fiber undercut and confirmed their reliability using the composite temperature/humidity cyclic test.

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.

Multi-core fiber (MCF) is one of the most promising candidates for achieving ultra-wideband optical transmission in the near future. To build a network using MCF, a high-performance and reliable MCF connector is indispensable. We have developed an SC-type optical connector for MCF and confirmed its excellent optical performance, mechanical durability, and environmental reliability. To put the communication system using MCF into practical use, it is necessary to establish a procedure for measuring the initial connection characteristics. Fan-in / fan-out (FIFO) devices are indispensable for measuring the connection characteristics of MCF connectors. To measure the return loss of the MCF connector, it is necessary to remove the influence of reflection at the FIFO itself and at the connection points with the FIFO. In this paper, we compare four types of return loss measurement procedures (three usual method and a new method we proposed) and find that most stable measurement method involves using our new method, the OCWR method without FIFO. The OCWR method without FIFO is considered to be the most advantageous when used for outgoing inspection of connectors. The reason is that it eliminates the measurement uncertainty caused by the FIFO and enables speedy measurement.

We describe a physical-contact (PC) multicore fiber (MCF) connector with good optical characteristics. To achieve stable physical-contact connection, we clarify the relationship between connector-end deformation and compression force with spherical polished ferrule end structures using finite element analysis and actual measurements. On the basis of the obtained relationship, we demonstrate a design approach that shows the physical-contact condition of all the cores of a multicore fiber with a simplex connector. In addition, we clarify the design criteria for low-loss connection by employing a rotational angle alignment structure, and devise an SC-type rotational MCF connector with high alignment accuracy. Based on our designs for PC and low-loss connection, we demonstrate an MCF connector with PC connection that provides a sufficiently high return loss exceeding 50dB and a sufficiently low connection loss of below 0.2dB for all the cores of a 7-core single-mode MCF.

The required packaging density has increased and it would be difficult to employ the conventional assembly technique to produce optical circuit boards with multi-fiber connectors. So we designed an MTPIPE (MT ferrules with Pre-Installed Pre-polished End fibers) connector that can be assembling easily and that does not need a polishing process. It is suitable for use with optical circuit boards and compatible with MT or MPO connectors. We propose MTPIPE which allows us to assemble optical fiber circuit boards easily, reliably and at low cost.

We have developed a 7-core-fiber connector. To maintain both the ferrule floating mechanism and precise alignment around the ferrule axis, we employed Oldham's coupling mechanism inside an MU-type connector plug housing and realized an average attenuation of 0.13dB and an average return loss of 48.2dB.

We propose a new fiber endface sealing technique for the optical connection of holey fibers (HFs). We experimentally investigate the optimum sealing condition for physical contact using a carbon dioxide (CO2) laser. We use this technique to fabricate an HF connector, and achieve low splice loss and a high return loss when splicing with a conventional SMF connector. With hole-assisted fiber (HAF), the obtained splice and return losses are almost the same as those obtained with the conventional method. In particular, with photonic crystal fiber (PCF), we obtained a minimum splice loss of 0.2 dB and a return loss exceeding 50 dB at wavelengths of 1.31 and 1.55 µm.

A new optical fan-out adapter is proposed and fabricated by applying the jacket removing system with a CO2 laser. The fan-out adapter has both the multi-fiber connection function and the fiber separating function for single-fiber connections. In order to remove the jacket of a fiber ribbon to connectorize and fabricate the fan-out adapter, the optimum conditions of the laser power P and the scan speed V are clarified for the jacket removing. Based on the optimum conditions, the fan-out adapter was fabricated successfully. Individual fibers could be taken out from the MT connector of the fan-out adapter. The connection losses of the fabricated fan-out adapter were comparable with the values of commercially available MT connectors and SC connectors. The length of the fabricated fan-out adapter was 27 mm, including 2 MT connectors. This result clarifies that the size of the connection with a fan-out can be reduced dramatically by the proposed fan-out adapter.

We propose and demonstrate a new type of field installable optical connector that enables us to realize physical contact connection without polishing the fiber endface by using a sharpened fiber endface and the compression force of buckled fiber. We confirmed that all the assembled connectors achieved physical contact connection without the fiber endface being polished, and provided good optical performance with a low insertion loss of 0.08 dB and a high return loss of over 49 dB.

Various types of optical connector with a precise alignment mechanism and long-term reliability have been researched, developed and improved during about 30 years since practical optical communication systems were first introduced in Japan in 1981. The main issues related to optical fiber connector development changed from performance improvement to miniaturization, cost reduction and ease of field assembly when optical communication systems expanded from optical trunk networks to optical access networks. Various different key technologies for optical connectors have been developed to meet these requirements, and a large number of optical connectors are currently being used for the flexible and efficient construction, maintenance and operation of optical access networks. This paper describes the structure, features, and basic technologies of the optical connectors employed in optical access networks in Japan and their standardization and future prospects.

Field assembly of optical connectors is demanded because of the wide use of optical fiber in telecommunications systems. We propose a new assembling techniques that enable us to assemble connectors anywhere quickly and cost effectively. The key points are an adhesive technique and a polishing technique. In this report, we focus mainly on our a new polishing machine, which is suitable for optical connector ends machining on-site. The machine which is small and light weight can finish optical connector ends easily in a short time with enough low cost.

We have developed an optical connector assembly method that allows the rapid on-site installation of an optical connector. To simplify this on-site assembly process we fabricated built-in parts that enable us to install the optical connector using pre-assembled optical connector parts. Moreover, we have established an advanced method for applying a solidifying agent that adheres to the inner wall of a ferrule flange. With our assembly method, we can complete on-site optical connector installation, other than the polishing process, in two steps, namely bonding agent application and fiber insertion.

Optical connectors for printed circuit board interfaces are required for the implementation of reliable high-density multi-fiber connection. We developed a 16-fiber fiber physical contact (FPC) connector with an MU connector coupling mechanism and a compact shutter to meet this requirement. In the FPC connector, two arrays of fibers are aligned in micro-holes without ferrules. A micro-hole array is a key component as regards the optical characteristics of the FPC connector. We developed a 16-ch micro-hole array composed of injection molded zirconia ceramics. The 16-fiber FPC connectors with a zirconia ceramic micro-hole array had an insertion loss of less than 0.3 dB with an average value of 0.07 dB and a return loss of over 45 dB. The optical characteristics remained stable in environmental and mechanical tests.

Plastic ferrules for single-mode (SM) MU-type simplified receptacles are fabricated with a precise injection-molding technique using a liquid crystalline polymer (LCP). The fabricated plastic ferrules exhibit an eccentricity of < 0.6 µm and outer diameter variation of 1 µm. MU-type simplified plugs incorporating the plastic ferrules have an average insertion loss of 0.13 dB and a return loss of > 46 dB. The plastic ferrules exhibit good resistance in 500-cycle mating tests, and in vibration and impact tests as well. The initial optical characteristics are maintained during a temperature and humidity cycling test and a heat-cycling test.

Optical connectors for printed circuit board interfaces are required for the implementation of high-density multi-fiber connection. We have developed a fiber physical contact (FPC) connector to meet this requirement. The FPC connector has to ensure reliability when bare fibers are used. Moreover, the FPC connector must employ an established coupling mechanism and provide higher density connection. To meet these requirements, we developed a 16-fiber FPC connector that utilizes the MU connector coupling mechanism and a shutter. We connect the 16 fibers in the housing of the duplex MU connector. We developed compact shutters that open only when they come into contact with each other. Moreover, the developed FPC connector enables us to clamp the fibers to a plug without adhesive. This structure can greatly boost the production yield. We confirmed that the developed FPC connector has an easy connection operation and good optical performance, and we verified that the shutters open properly.

Various optical fiber connectors have been developed during the 20 years since optical fiber communications systems were first put into practical use. As the domain of optical fiber communication systems expanded from trunk lines to subscriber lines and customer premises the main focus changed from performance improvement to miniaturization and cost reduction. This paper describes the technical background, recent trends in standard optical connectors, and recent issues related to photonic connection technologies.

We have developed a fiber physical contact (FPC) connector for the high-density connection of optical fibers. This connector individually aligns multiple bare fibers in micro-holes without ferrules and realizes physical contact by using the buckling force of the fibers themselves. The fiber endfaces must be tapered to allow the fibers to be inserted into the micro-holes. The endfaces must also be polished so that they realize physical contact (PC) with excellent optical performance. For each process, we examined the required shape and processing condition of the fiber endface for the FPC connector. As regards tapering, we determined the processing condition for achieving a target tapering angle and developed a non-breaking process with the optical fibers bent. In terms of polishing, we revealed that it is important for the fiber endface angle error to be less than 0.7 degrees if we are to achieve excellent optical performance. These results allowed us to fabricate an FPC connector that exhibited excellent levels of optical performance.

We examined the creep properties and hazard rates of plastic ferrules to ensure the long-term reliablity of optical fiber connections. The endface deformation ΔL had to be smaller than 3 µm to keep the insertion-loss and return-loss fluctuation to acceptable levels in the worst case of random concatenation of similarly deformed plastic ferrules. From the fluctuation data, we estimated the time-to-failure tf at which the ΔL value became 3 µm. We estimated the acceleration parameters, median lifetimes ξ, and hazard rates λ by using tf values based on Weibull statistics. The ξ values decreased rapidly with increasing temperature and relative humidity. We found we could expect small λ values of < 0.1 FIT (FIT=10-9/hour) and of 1 FIT for 20 years in a normal atmosphere (25C/50%RH) and in a more severe case of 25C/90%RH, respectively.

We examined the creep properties and hazard rates of plastic split alignment sleeves to ensure the long-term reliablity of optical fiber connections. It required a gauge retention force Fr of more than 200 gf to suppress the fluctuation in the insertion loss of a plastic sleeve. From the fluctuation data, we estimated the time-to-failure tf at which the Fr value became 200 gf. We estimated the acceleration parameters, median lifetimes ξ, and hazard rates λ by using the tf values based on the Weibull statistics. The ξ values decreased rapidly with increasing temperature and relative humidity. Small λ values of < 0.01 FITs and of 1 FITs were expected for 20 years in a normal atmosphere (25C/50%RH) and in a more severe case of 25C/90%RH or 45C/50%RH.

We successfully fabricated split alignment sleeves for single-mode operation with the injection-molding technique using both thermosetting epoxy resin and thermoplastic polyetherimide (PEI) resin. The relationship between the surface smoothness and the connection-loss characteristics of these injection-molded plastic sleeves was investigated. We made two-dimensional contour maps of the outer and inner surfaces of the plastic sleeves using the measured surface roughness. There were many contour lines on both the outer and inner surfaces of the PEI sleeve. In contrast, the epoxy sleeves had very smooth surface profiles. An offset Δr was estimated by using the inner-surface roughness data of the sleeve-ferrule contact regions. The connection loss of the sleeve increased as the Δr value increased. The measured losses agree fairly well with the theoretical losses estimated by using the Δr values. The PEI sleeves exhibited large Δr values, and one-third of them had large connection losses of > 0.5 dB. In contrast, the epoxy sleeves had very small Δr values of < 0.6 µm, and exhibited an average loss of < 0.1 dB.