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SF Connector Optical Interface for Parallel Optical Module

- Dense multi-fiber connection technique for multi-channel optical modules with a receptacle to reduce its size and power dissipation -

1. Introduction

To reduce the size and cost of optical communication systems for high-capacity optical communication networks and large-scale data processing systems such as the high-end routers employing high-speed optical data transmission to replace the conventional electrical transmission, improvement in density and working cost for large-scale complex optical fiber wiring in the systems is required. That has created a high demand for a compact multi-fiber optical connector that allows high-density optical fiber connection as an important component for optical fiber wiring. NTT has developed an SF connector that can offer such connection as well as high-reliability by using a PC connection.

Here, we describe an SF connector optical interface for parallel (multi-channel) optical modules used for high-speed optical data transmission as an application of this SF connector technology, taking advantage of the design features of the SF connector, including lack of ferrule, small and thin form factor, and ease of connection and disconnection.

Plugged in(a) Plugged in

Disconnected(b) Disconnected

Figure 1. Structure of SF connector optical interface

Before plug insertionBefore plug insertion

Plug is attached to receptaclePlug is attached to receptacle

Plug is locked(completed connection)Plug is locked(completed connection)

Figure 2. Application example of SF connector optical interface (Parallel optical module)

2. Features of SF connector optical interface for parallel modules

The SF connector optical interface developed by the NTT laboratories comprises an SF connector plug with optical fibers (normally multi-mode fibers) and a receptacle that is installed in the module body. The receptacle has micro-holes for precise positioning the ends of the fibers in relation to optical devices.

This optical interface brings the ends of the fibers into a position very close to the optical devices, thus implementing an efficient optical coupling between the optical fiber and optical device without using a micro-lens. Furthermore, the SF connector plug is thin, allowing the receptacle to also be thin. That allows the receptacle to be mounted on the top of the module, thus reducing the footprint of the module by about a half of conventional modules.

  [Features]  
Optical interface

SF connector
Close fiber placement
Using an SF connector, which does not have ferrules, for a parallel (multichannel) optical module makes it possible to position the tip of each fiber in close proximity to a surface-type photosemiconductor device such as a surface-emitting laser [VCSEL] or photodiode{PD}.
Precise alignment
When the SF connector plug is inserted into the receptacle, the tip of each optical fiber fits into a microhole and is guided into position against the surface-type photosemiconductor device with high precision.
Microholes
The center axes of the microholes in the receptacle are aligned with the optical axes of the photosemiconductor devices for positioning.
Tilting mechanism
Using the flexibility of the LCP base to tilt the receptacle makes it easy to connect or disconnect the optical fiber (SF connector plug).
Thin receptacle
The thinness of the plug allows the receptacle to also be thin. Even when the receptacle is placed on the top (or on the bottom) of the optical module body, the overall height of the module is small enough for practical use and the overall footprint of the optical module can be reduced.
Small and thin
The 16-core SF optical connector is small and thin (9 mm by 4 mm by 26 mm when connected), about 1/4 the size of existing PC connection type multicore connectors.
No ferrules
The PC connection is achieved by means of the elastic force of the fiber itself, so springs and ferrules are not needed, allowing a reduction in both size and cost.
Other merits
  • Implementing a PC connection without ferrules allows multicore connection (1 to 10 cores).
  • Because a PC connection is used, stable low loss and low reflection can be maintained.

3. Technical Details

3.1 Overview of NTT technology

Electrical data transmission is increasingly being replaced by high-speed parallel optical data transmission to achieve faster data transmission between circuit boards within units of equipment and between units of equipment in large-scale data processing systems such as high-end routers and servers. The factors that are important in implementing the parallel optical modules that send and receive the optical signals for such optical transmission include the ability to attach and remove the optical fibers to facilitate mounting on the circuit boards, a smaller module footprint to increase mounting density, and reduced power dissipation to reduce the heat burden on the module itself and on the air-conditioning system.

The sagged fiber (SF) connector that has been developed by NTT is a multi-fiber connector that is suitable for a high-density multiple optical fiber connection and wiring and features high-performance (low loss and low reflectivity), small form, and low cost. (See Fig. 3 for the basic structure (a) and a photograph (b).) We used the SF connector to develop a new type of optical interface that is compact and makes it possible to connect and disconnect optical fibers to the optical module. The basic structure of this interface is shown in Fig. 1. Use of this interface can be expected to produce an optical module that is smaller and consumes less power.

3.2 Advantages of NTT technology

  • Can be applied to multi-channel optical modules (ex. 4ch, 12ch, 24ch)
  • Allows high-density arrangement of optical devices and optical fibers (ex. 0.127 mm, and 0.25 mm pitch)
  • Simplifies packaging of the optical modules and optical fibers because the fibers can be connected after the module is mounted on the circuit board
  • That feature also allows compact optical fiber wiring, without excess fiber length
  • The high-efficiency optical coupling between optical fiber and optical device (VCSEL or PD) helps reduce power dissipation of the optical module

3.3 Explanation of NTT technology

The optical interface comprises a receptacle that is designed to fit on the optical module and an SF connector plug to which multi-mode optical fibers are fixed. Connection between the optical module and the optical fibers is accomplished by inserting the SF connector plug into the receptacle by hand. The module and fibers can be connected and disconnected repeatedly. The main features of the structure and mechanism of this interface are described below.

The receptacle has micro-holes for positioning the optical fibers. The axis of each micro-hole is the same as the optical axis of each optical device (VCSEL or PD). The SF connector plug has a compact and simple structure, without the ferrules used by ordinary optical connectors. When the plug is inserted into the receptacle, the end of each fiber fits in its corresponding micro-hole, thus correctly positioning the fiber relative to the optical device. In this way, an efficient optical coupling between the fiber and the device is achieved without using a micro-lens.

The SF connector plug is thin, so the receptacle can also be designed to be thin. That allows the receptacle to be mounted on the top of the optical module while staying within the practical range for the overall height of the module. The receptacle and the optical module share the same footprint so that the entire optical module, including a connector part, has a reduced footprint. The receptacle part can be tilted upward to facilitate the insertion or removal of the plug (Fig. 4).

NTT has used this optical interface to make a prototype a 12-channel parallel optical module. The performance and functions of the prototype module have been demonstrated. The footprint of the module, including the optical connector with fiber connected, was reduced to as small as one half that of existing modules (Fig. 5). [Ref. (1), (2)].

3.4 Figures and tables

Basic structure of SF connector

Inside micro-holeInside micro-hole
Figure 3(a). Basic structure of SF connector

Appearance of 16-fiber SF connectorFigure 3(b) Appearance of 16-fiber SF connector

Example of using the optical interface

Example of using the optical interface 2When connectiong/disconnection

Figure 4. Example of using the optical interface
(Appearance of 12-channel optical module)

An application example of SF connector optical interfaceFigure 5. An application example of SF connector optical interface
(12-channel optical module)

3.5 Refference

  • (1)
    Author/Editor :Masasru Kobayashi, Shuichiro Asakawa and Ryou Nagase
    Title/Journal Name: Proceedings of the Nagoya IEICE General Conference
    Publisher: The Institute of Electronics, Information and Communication Engineers(IEICE)
    Article/Paper Title: SF Optical Connector utilizing Short Micro-Hole
    Volume No./issue : C-5-9, p.7, Nagoya, Japan, Mar.
    Publication year: 2007
  • (2)
    Author/Editor :Ryou Nagase ,Shuichiro Asakawa, Masaru Kobayashi and Yoshiteru Abe
    Title/Journal Name: IEICE Technical Report
    Publisher: The Institute of Electronics, Information and Communication Engineers(IEICE)
    Article/Paper Title: 16-fiber Type SF connector for on-board optical wiring
    Volume No./issue : EMD2008-115, vol. 108, no. 404, pp. 11-14, Yokohama, Japan, Jan.
    Publication year: 2009
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