Nov. 30, 1999

NTT Confirms Plan to Introduce Single-Fiber Optic Connectors into Future Network Systems
- All SC fiber optic connectors to be replaced by MU type connectors -

Original is written in Japanese. Translated by NTT-AT.

For years, NTT has been promoting the development of low-cost fiber-optic connector technologies to contribute to economical and flexible network construction. Incorporating the results of these efforts, NTT has confirmed plan to introduce single-fiber optic connectors into its future network systems. NTT group companies will adopt the new connectors in accordance with this policy.

Based on the policy, the MU (Miniature Unit coupling) fiber-optic connector, which features compact size, high packaging density, and high performance, will be used in place of the various types of single-fiber connectors in the current lineup including SC (Single Coupling) and DS (Fiber optic connector for Digital System) connectors.

NTT has implemented the following action plan to put this policy into effect:

Actively introduce MU connectors into all network systems.

Allow open access to fiber-optic connector specifications, and establish a system for compatibility certification

Promote the widespread use of newly developed, low-cost MU fiber-optic connector technologies.

Background

Demand for fiber optic connectors is increasing as a result of the rapid expansion of the optical communications market that accompanied advancements in network technologies, such as Fiber-to-the-Home (FTTH), DWDM, and IP over photonic networks. DWDM (dense wavelength division multiplexing) is a fiber-optic transmission technique that employs large volumes of optic fibers that simultaneously utilize multiple signals of varying light wavelengths to transmit data. “Fiber optic connectors” -- plugs used for joining optical fibers -- are critical interface parts that ensure the reliability and flexibility of optical networks. Low cost is also important because network systems require large numbers of connectors.

NTT has already developed and introduced into networks SC, DS and MU fiber optic connectors. SC connectors are used for cable connections and DS for connections between equipment. MU connectors, which have small plugs, were developed mainly for high-density connections. Small, low-cost connector will be required for the economical and flexible construction of future networks. NTT has thus encouraged further developments in cost-reducing technologies for the MU, a unit ideally suited to high packaging density.

MU fiber optic connectors

The MU fiber optic connector (see Figure 1) is the smallest single-fiber connector in the world, and also exhibits the highest performance. It was developed in 1993 by NTT’s R&D division for dense packaging systems based on technologies of SC connector, the world’s most commonly used system. MU has already been listed as a standard by several worldwide standardization organizations, including IEC (International Electrotechnical Commission) and JIS (Japanese Industrial Standards). MU connectors provide more than double the packaging density when compared with the SC connector. Another important advantage of MU is its wide range of applications, from cable connections to internal plug-in type connections similar to DS connectors. Over a million MU plugs have already been installed in the networks of NTT group companies where high-density packaging is required. The range of applications for MU technology is expected to expand rapidly as photonic network systems continue to become more advanced.

Low-cost technologies and future promotion plan for the MU connectors

NTT has developed new technologies that bring about cost reductions in both parts and assembly for MU connectors. These technologies have substantially reduced the manufacturing cost, to the point that it is now possible to manufacture MU connectors more inexpensively than SC connectors. This means that the stage has been set for all SC fiber optic connectors in current applications to be replaced by MU connectors. Given the explosive increase in demand for fiber optic network traffic, NTT group companies will promote the adoption of the low-cost, compact, high-density, high-performance MU as their single-fiber optic connector of choice, and at the same time encourage the de-facto standardization of this technology.

The specific elements of the action plan are as follows:

Expand applications of MU connectors into all network systems

NTT group companies will actively employ MU throughout their network systems. MU should be adopted in various applications in existing systems, as well as in newly introduced systems, with consideration for the costs involved.

Allow open access to fiber-optic connector specifications

NTT’s specification for the MU system will be made openly available. NTT will also establish a system in the near future to certify compatibility between fiber-optic connectors.

Promote the widespread use of new MU fiber-optic connector technologies

MU fiber-optic technologies, including the newly developed low-cost MU, will be openly disseminated through such means as technology transfers. At the same time, NTT will actively promote the use of this technology as a global de-facto standard that will contribute to the construction of worldwide fiber-optic networks.

NTT plans to carry out a full-scale introduction of this technology, while promoting a shift from SC to MU connectors, as a way of accelerating the economical and efficient construction of next-generation optic fiber networks.

Meanwhile, MT (Mechanically Transferable) fiber optic connectors, which are used for connecting fiber ribbons, have been developed and introduced into commercial networks, and are used mainly for connections between multi-fiber cables. NTT also has developed low-cost technologies intended to lower the cost of FTTH to that of its metal counterpart, while at the same time making the systems easier to operate. MT connectors are expected to be widely used for multi-fiber connections in future.

Appendix

Essential low-cost technologies of MU fiber optic connectors

Low-cost plug and adapter

The structure of the conventional MU plug was re-designed to increase cost competitiveness by reducing the cost of parts and assembly (see Figure). First, the company actively promoted the replacement of several metal parts with a single plastic part to reduce the total number of components. Further cost reductions were attained through the adoption of a plastic adapter. In addition, NTT was successful in reducing assembly costs by developing pre-assembled parts that take into account applications involving automatic assembly or field assembly.

Simplified MU receptacle

This simplified MU receptacle, which features a greatly simplified connection construction, was developed to substantially reduce connection costs. The previous “plug - adapter - plug” connection format was replaced with a “plug - simple receptacle” connection, in order to simplify the parts configuration and reduce the cost of assembly .

Low-cost polishing technique

A new polishing machine was developed to reduce the cost of the ferrule polishing -- which is one of the more expensive elements of fiber optic connector production -- to about one third of the previous level. In the case of the MU connector, the ferrule area to be polished is roughly one tenth that of conventional connectors. This machine was designed to take advantage of the smaller polishing area, thus establishing the optimum polishing conditions. The polishing process has thus be reduced to only two steps from the former three-step process, and expensive abrasives such as diamond slurries are no longer required. As a result, the polishing cost can be reduced to less than one third compared with conventional methods.

Polishing techniques for fiber-optic connectors

The ferrule is an important part of fiber-optic connector; it holds the 10 micrometer diameter core portion of each optic fiber securely in place for connection when two connectors are joined together, and also maintains contact between the two fibers by applying constant pressure. The MU and SC fiber optic connectors employ ferrules with diameter of 1.25 mm and 2.50 mm, respectively. In either case, the end surface of each ferrule has to be polished meticulously for the connector assembly. The cost of the polishing process comprised a large part of the total assembly cost, and so a low-cost polishing technique had been long sought after.