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.

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 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.

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.

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 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.

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.

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.

This paper describes the optical characteristics and static fatigue reliability of a zirconia alignment sleeve, which is a component part of an optical connector with zirconia ferrules. This combination of sleeve and ferrules hardly generates any wear debris during connector insertion and removal cycles. This has reduced the cleaning frequency of the ferrule endface during cycles and greatly improved the return loss stability of the optical connectors. The zirconia alignment sleeve enables stable return loss characteristics to be achieved over a wide temperature range as it has the same thermal expansion coefficient as the zirconia ferrule. Furthermore, the gauge retention force for the zirconia alignment sleeve is defined with a view to its practical use. This force must be between 2.0 and 3.9 N to allow stable optical connections to be made under various mechanical and environmental conditions. We also clarify the conditions for a proof test by which to prevent the occurrence of static fatigue fractures in the sleeve, and we confirm the validity of the test. The static fatigue parameters for zirconia ceramics and derived from the static fatigue theory for brittle materials and fracture testing. We use these static fatigue parameters to predict the lifetime of a zirconia sleeve under working stress. An appropriate stress level for the proof test which eliminates weak sleeves, is about 3 times greater than working stress. The strength of the sleeve as demonstrated in the proof test is confirmed by accelerative stress aging. The performance of this sleeve is superior to that of a conventional copper alloy sleeve and the proof test confirms its reliability; under 0.1 FIT for 20 years of use.

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.

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.

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.

Failure probability of a split ceramic alignment sleeve in an optical fiber connector has been predicted based on slow crack growth theory. Applying the theory to split zirconia ceramic alignment sleeves, a failure probability of 104 for 20 years is predicted and the value is expected to decrease to almost zero when an appropriate proof test is introduced.

Fiber physical contact (FPC) is proposed and demonstrated as a new method designed to enable fibers to be connected easily with a small structure while maintaining high optical performance. FPC is performed by mating two bare optical fibers in a micro sleeve and fixing them to a holder while they are buckled. Buckling is a phenomenon whereby a long column is bent by compression along its length. PC connection is realized by the buckling force of the fibers themselves and does not require any springs. Optical fiber buckling is studied both theoretically and experimentally. The buckling force, which is determined by an initial span between the optical fiber holding points, remains constant when the span is changed and is useful as the PC force. The buckling amplitude which is determined by the span reduction must be so small that it does not cause excess radiation loss. A suitable span is about 7 mm. This generates a 0.7 N. The allowed span reduction is 0.1 mm. This results in a buckling amplitude of 0.64 mm which prevents radiation losses of above 0.1 dB for 1.31 µm light. Based on a study of fiber buckling, we demonstrate the optical performance for FPC connection with a 0.126 mm diameter micro sleeve in which optical fibers are mated and with polished fiber end faces. The insertion loss is under 0.3 dB and the average return loss is 50 dB for 1.31 µm light. These values are stable in the 20 to 70 temperature range. We confirm that FPC connection realizes high optical performance with a small simple structure.

The increasing number of channels in dense wavelength division multiplexing (DWDM) systems has led to the need for wiring involving a large number of optical fibers in the system racks. We have developed a novel scalable optical fiber wiring system designed to realize as many as 10,000-fiber shuffled interconnections without fiber congestion. We propose a scheme for constructing a large-scale shuffler capable of permuting interconnected fibers that employs plural optical fiber sheets, and for arranging optical fibers without congestion in racks. We constructed a 16,384-fiber shuffler system with sixty-four 256-fiber shuffler sheets and 16-fiber fiber physical contact (FPC) connectors for a 128128 switch system with 1128 planar lightwave circuit (PLC) type thermo-optic switches (TOSW). Input here the part of summary.

This paper presents a design approach for developing MU-type single-mode miniature optical connectors featuring 1. 25 mm diameter zirconia ferrules. They are smaller and have a higher packaging density than conventional optical connectors. The ferrule pitch is 1/2, the plug volume 2/5 and the cross-sectional area 2/5 that of the SC connector. The aim of our approach is to reduce the ferrule size and to realize durable connectors. With 10/125 SM fibers, these MU connectors produced an average insertion loss of 0. 07 dB and an average return loss of 49. 4 dB, and there was no degradation during or after mechanical and environmental tests.

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.

A photonic inter-module connector for near-future electronic switching systems is demonstrated through the use of silica-based 88 optical switches. A small-scale switch matrix is sufficient because the near-future systems will consist of a limited number of modules. If an active module is affected by a fatal fault or accident, a stand-by module must quickly take its place. The experimental photonic inter-module connector can switch 156-Mbit/s photonic interconnections between seven subscriber-line-concentrator modules and eight circuit-switching modules.

The statistical properties of insertion losses and return losses for optical connectors are investigated theoretically using the probability theory and the Monte Carlo simulation. Our investigation is focused on an orientation method for reducing insertion loss by which a fiber-core center is adjusted in a region of within a certain angle to the positioning key direction. It is demonstrated that the method can significantly improve insertion losses, and that an adjusting operation angle of 90 degrees is sufficient to realize an insertion loss of less than 0.5 dB with 99% cumulative probability. Good agreement was obtained between the theoretical distribution and the experimental results for single-mode fiber connection. Consequently, it is indicated that the statistical distributions of insertion losses and return losses of optical connectors in the field can be predicted theoretically from the values measured in the factory by connection to a master connector.