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.

Aiming at the problem of the deterioration of the contact performance caused by the wear debris generated during the fretting wear of the electrical connector, low-frequency fretting wear experiments were carried out on the contacts of electrical connectors, the accumulation and distribution of the wear debris were detected by the electrical capacitance tomography technology; the influence of fretting cycles, vibration direction, vibration frequency and vibration amplitude on the accumulation and distribution of wear debris were analyzed; the correlation between characteristic value of wear debris and contact resistance value was studied, and a performance degradation model based on the accumulation and distribution of wear debris was built. The results show that fretting wear and performance degradation are the most serious in axial vibration; the characteristic value of wear debris and contact resistance are positively correlated with the fretting cycles, vibration frequency and vibration amplitude; there is a strong correlation between the sum of characteristic value of wear debris and the contact resistance value; the prediction error of ABC-SVR model of fretting wear performance degradation of electrical connectors constructed by the characteristic value of wear debris is less than 6%. Therefore, the characteristic value of wear debris in contact subareas can quantitatively describe the degree of fretting wear and the process of performance degradation.

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.

Electrical connectors are the basic components of the electric system in automobiles, aircrafts and ships to realize the current and electrical signal transmission. In the aviation electrical system, the electrical connectors are indispensable supporting devices accessories, which play important roles in connecting electrical system, monitoring and controlling equipment, and provide a guarantee for the reliable transmission of electrical signals between the aviation equipment and system. Whether aviation electrical connectors work reliably directly affects the safety and reliability of the entire aircraft aviation system. The random vibration of aircraft caused by turbulence during flight is one of the main factors affecting the contact performance of the electrical connectors. In this paper, the contacts of the circular four-slot three-pin electrical connectors were chosen as the research specimens. The theoretical model of the contact force for contacts of electrical connectors was established. The test method for contact force measurement was determined. According to the test scheme, the detecting device for the contact force and contact resistance of the electrical connectors was designed, and the turbulence test of the electrical connectors was carried out. Through the analysis of the test data, the influence rule of the turbulence degree, flight speed and flight height on the contact force and contact resistance of the aviation electrical connectors was obtained.

An electrical capacitance tomography (ECT) method was used to detect fretting wear behavior of electrical connectors. The specimens used in this study were contacts of type-M round two-pin electrical connectors. The experiments consisted of running a series of vibration tests at each frequency combined with one g levels. During each test run, the measured capacitance per pair of electrodes was monitored as a performance characteristic, which is induced by the wear debris generated by the fretting wear of electrical connectors. The fretted surface is examined using scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) analysis to assess the surface profile, extent of fretting damage and elemental distribution across the contact zone and then compared to the capacitance values. The results exhibit that with the increase of the fretting cycles or the vibration frequency, the characteristic value of the wear debris between the contacts of electrical connector gradually increases and the wear is more serious. Measured capacitance values are consistent with SEM and EDS analysis.

Under the condition of inadequate torque management, contact failure could occur in the interconnecting connector. Contact failure reduces the local immunity and degrades the electromagnetic properties of the equipment. It has been shown in previous reports that connector contact failure causes the parasitic inductance and radiated electromagnetic noise to increase. However, there is not enough discussion about the effects of connector torque fluctuation on the surrounding electromagnetic environment. Thus, in this study, the effects of a changing connector torque value on the circuit response and near field at the contact boundary were investigated. Based on these results, we discuss the influence of torque fluctuation on the electromagnetic environment surrounding the connector.

Coaxial connectors are extensively used in electrical systems and the degradation of the connector can alter the signal that is being transmitted and leads to faults, which is one of the major causes of low communication quality. In this work, the failure features caused by the degraded connector contact surface were studied. The relationship between the DC resistance and decreased real contact areas was given. Considering the inductance properties and capacitive coupling at high frequencies, the impedance characteristics of the degraded connector were discussed. Based on the transmission line theory and experimental measurement, an equivalent lump circuit of the coaxial connector was developed. For the degraded contact surface, the capacitance was analyzed, and the frequency effect was investigated. According to the high frequency characteristics of the degraded connector, a fault detection and location method for coaxial connectors in RF system was developed using a neural network method. For connectors suffering from different levels of pollution, their impedance modulus varies continuously. Considering the range of the connector's impedance parameters, the fault modes were determined. Based on the scattering parameter simulation of a RF receiver front-end circuit, the S11 and S21 parameters were obtained as feature parameters and Monte Carlo simulations were conducted to generate training and testing samples. Based on the BP neural network algorithm, the fault modes were classified and the results show the diagnosis accuracy was 97.33%.

This study is aimed at clarifying the mechanism of wear process for Ag plating. The samples of different hardness Ag plating on copper alloys were prepared as coupon and embossment specimens, which simulated terminal contacts. During the sliding test, the contact resistance and the friction coefficient versus sliding distance are measured. The surface observation and surface roughness of the Ag films after wear tests were investigated. As results, the hard Ag plating film (120 Hv) exhibited higher contact resistance comparing to the soft Ag plating film (80 Hv). The soft Ag film delivered wider wear trace on coupon specimens compared to the hard one. Moreover, the observation of tribofilms formed on the Ag films after wear tests suggested that a mixed-type of adhesive and abrasive wears occurred for both of soft and hard Ag films. Furthermore, the fretting corrosion resistance of Ag plating samples with different hardness was also investigated. As results, the wear resistance of hard Ag film was stronger than that of soft Ag film.

The history of optical fiber and optical transmission technologies has been described in many publications. However, the history of other technologies designed to support the physical layer of optical transmission has not been described in much detail. I would like to highlight those technologies in addition to optical fibers. Therefore, this paper describes the history of the development of optical fiber related technologies such as fusion splicers, optical fiber connectors, ribbon fiber, and passive components based on changes in optical fibers and optical fiber cables. Moreover, I describe technologies designed to support multi-core fibers such as fan-in/fan-out devices.

Contact lubricants have been used in electric contacts such as connectors. Contact failures for down size of connector contacts with low contact force and cost down of gold plated are a serious problem to be solved. One solution is the application of lubricants to the contacts. Particularly these contacts are exposed to elevated temperature under reflow treatment in assembling processes. It is an important subject should be clarified that the deterioration phenomenon of increases in contact resistance properties under the reflow. This degradation should be induced by two causes. Namely, one is a surface contamination due to oxidation of diffused small amount of additives through gold plated layer. The other is decomposition of the coated lubricants. In this study, first of all, degradation of contact resistance properties were measured, and change of images of STM for exposure time of high temperature were observed. To clarify more in detail this degradation of the contact resistance, for both clean gold plated surface and heated clean surface were examined by using XPS and AES analysis. As results, contact resistance properties of clean surface were found to degrade for exposure at the elevated temperature. This degradation was found due to oxidation of base metal nickel and cobalt additive to gold plated surface. However, influence of the contact lubrication on the degradation of contact resistance was not recognized. The change of composition of an olefin lubricant was discussed by using STM images. Moreover, growth of oxide film on the clean surface was found as cubic law by using an ellipsometry.

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 experimentally investigate and analyze faults in optical fiber connections with refractive index matching material that have incorrectly cleaved fiber ends. We explain that incorrectly cleaved fiber ends, which are not ideal because they are uneven and not perpendicular to the fiber axis, are caused by defective optical fiber cleavers. We discover that the optical performance of field installable connections using incorrectly cleaved fiber ends might change greatly. We also infer that the significant change in insertion and return losses might be attributed to partially air-filled gaps by using scatter diagrams of measured insertion and return losses. Our experiment results reveal that the optical performance might deteriorate to more than 40dB in terms of insertion loss and less than 30dB in terms of return loss.

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.

Tin (Sn) contacts are widely applied to connector contacts. Surfaces of plated tin layer are covered with an oxide film that results in high contact resistance. However, it is possible to obtain low contact resistance by using high contact load. Current downsizing trends often make it difficult to obtain high contact loads. Therefore, it is important to conduct basic studies of the contacts resistance characteristics under low contact load conditions. In this study, relationships between contact resistance and the changes of contact traces were examined. When a platinum (Pt) hemisphere contacted to tin plated flat coupon, it was found that the hemisphere surface sank into the softer tin plated flat surface during loading resulting in a piling up tin crystal grains along the periphery of the contact trace. During this process, sudden decrease in contact resistance was observed. To clarify the phenomenon, morphology changes of contact traces were observed by AFM, SEM and EBSD. FEM analysis was also used to analyze the mechanical stress distribution in the tin plated layer. Due to the peculiar distribution of stress, the crystal grains are separated and push out the contact area. This phenomenon is very different from commonly observed decrease in contact resistance due to elastic and plastic deformation inducing mechanical fracture of the surface oxide film.

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.

A capacitive coupling wireless connector circuit is implemented with 50 µm 50 µm pads, which is a 25X reduction of pad size compared with previous wireless connectors by allowing contacting and non-contacting modes. The proposed track and charge scheme allows both contacting and non-contacting communication through PCB capacitive pads. By making the precharge level of the input VDD or VSS, instead of 1/2 VDD, the time necessary to precharge is reduced. The proposed digitally tunable comparator does not require analog voltages, reduces the power to less than 1/20 at lower frequencies compared to previous capacitive coupling receivers. A test chip successfully transmitted and received 1 Gb/s, 27-1PRBS signal at 1 mW while increasing design freedom of the wireless connectors.

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.