2012: MU-type multicore fiber connector - Semantic Scholar · MU-type multicore fiber connector ......

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MU-type multicore fiber connector Ryo Nagase*, Katsuyoshi Sakaime*, Kengo Watanabe** and Tsunetoshi Saito** *Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan +81-47-478-4303 [email protected] **Furukawa Electric, Co., Ltd., 6, Yawata-Kaigandori, Ichihara, Chiba 290-8555 Japan +81-436-42-1725 [email protected] Abstract 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 the MU- type connector plug housing and realized an average attenuation of 0.13 dB and an average return loss of 46.8 dB. Keywords: Multicore fiber; Optical connector; MU-type optical connector. 1. Introduction Optical communication traffic continues to increase, however, the transmission capacity of conventional single-mode fiber has now reached around 100 Tbps, which is assumed to be the maximum value [1]. Multi-core fiber (MCF) is one of the most promising candidates for achieving ultra-wide-band optical transmission in the near future [2]. Optical connectors are essential for constructing optical networks. They are unique in that they require resistance from an external force. They should usually allow some component deformation of around tens of microns and so better than 1 m accuracy is required. Optical connectors used in telecommunication systems have a ‘floating mechanism’ to eliminate the influence of deformation on connection stability. No MCF connector has yet been realized because of the design difficulty involved in the precise alignment of each core under a floating mechanism. In this paper we describe the design principle and connection characteristics of a newly developed MCF connector attached to 7- core single-mode fiber. 2. Multicore fiber connector structure 2.1 Fundamentals of optical connectors Single-mode optical connectors require an attenuation of less than 0.5 dB and a return loss of 40 dB or more. To realize these requirements with the butt joint mechanism, the fiber core offset should be less than 1 m. There are four conditions for achieving this requirement. (a) Precise fiber fixing to the center of the ferrule (b) Precise ferrule alignment with good repeatability (c) Suppression of Fresnel reflection at the connection point (d) Suppression of the influence of housing deformation caused by external force Low-cost zirconia ferrule manufacturing technology has been established for single-mode simplex connectors. This is a solution for the above-mentioned condition (a). We can use a zirconia ferrule for the MCF connector if there is precise alignment of the rotation angle around the ferrule axis. A precise ferrule alignment technique with a split sleeve was also established for condition (b). We can use the same technique for the MCF connector. For condition (c), physical contact (PC) connection technology has been established to achieve a return loss of 50 dB or more. We can use PC technology for the MCF connector, however, the specifications of the ferrule endface geometry must be reconsidered because some cores are not located in the center of the fiber. Optical connectors are usually operated by hand, so we sometimes have to consider an external force of tens of newtons interacting with the fiber cables. If such a force interacts with a small sized optical connector, the plug housing will be deformed by more than 10 m, which is far greater than the alignment tolerance. To solve this problem (condition (d)), a ferrule ‘floating mechanism’ has been widely used. 2.2 Design principle of MCF connector To connect MCFs, we have to precisely align the rotation angle of the ferrule. In this paper, we use single-mode 7-core MCFs. The outer diameter of the MCF is 204 m, the core center to center distance is 45 m, and the MFD of each core at 1550 nm wavelength are 10.4 to 10.8 m. Figure 1 is a photograph of an MCF endface. In Figure 1, the 3 dots around the bright cores are the markers that distinguish the core IDs. Figure 1. Single-mode 7-core MCF Using this MCF, the allowed angular misalignment is 1.27 degrees when the allowable offset is 1 m at the outer cores. Our target was set at an angular misalignment of 0.5° on the assumption that the lateral misalignment (offset) cannot be disregarded. 823 International Wire & Cable Symposium Proceedings of the 61st IWCS Conference

Transcript of 2012: MU-type multicore fiber connector - Semantic Scholar · MU-type multicore fiber connector ......

Page 1: 2012: MU-type multicore fiber connector - Semantic Scholar · MU-type multicore fiber connector ... axis, we employed Oldham's coupling mechanism inside the MU-type connector plug

MU-type multicore fiber connector

Ryo Nagase*, Katsuyoshi Sakaime*, Kengo Watanabe** and Tsunetoshi Saito**

*Chiba Institute of Technology, 2-17-1 Tsudanuma, Narashino, Chiba 275-0016, Japan +81-47-478-4303 [email protected]

**Furukawa Electric, Co., Ltd., 6, Yawata-Kaigandori, Ichihara, Chiba 290-8555 Japan +81-436-42-1725 [email protected]

Abstract 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 the MU-type connector plug housing and realized an average attenuation of 0.13 dB and an average return loss of 46.8 dB.

Keywords: Multicore fiber; Optical connector; MU-type optical connector.

1. Introduction Optical communication traffic continues to increase, however, the transmission capacity of conventional single-mode fiber has now reached around 100 Tbps, which is assumed to be the maximum value [1]. Multi-core fiber (MCF) is one of the most promising candidates for achieving ultra-wide-band optical transmission in the near future [2].

Optical connectors are essential for constructing optical networks. They are unique in that they require resistance from an external force. They should usually allow some component deformation of around tens of microns and so better than 1 m accuracy is required. Optical connectors used in telecommunication systems have a ‘floating mechanism’ to eliminate the influence of deformation on connection stability. No MCF connector has yet been realized because of the design difficulty involved in the precise alignment of each core under a floating mechanism.

In this paper we describe the design principle and connection characteristics of a newly developed MCF connector attached to 7-core single-mode fiber.

2. Multicore fiber connector structure 2.1 Fundamentals of optical connectors Single-mode optical connectors require an attenuation of less than 0.5 dB and a return loss of 40 dB or more. To realize these requirements with the butt joint mechanism, the fiber core offset should be less than 1 m. There are four conditions for achieving this requirement.

(a) Precise fiber fixing to the center of the ferrule

(b) Precise ferrule alignment with good repeatability

(c) Suppression of Fresnel reflection at the connection point

(d) Suppression of the influence of housing deformation caused by external force

Low-cost zirconia ferrule manufacturing technology has been established for single-mode simplex connectors. This is a solution for the above-mentioned condition (a). We can use a zirconia ferrule for the MCF connector if there is precise alignment of the rotation angle around the ferrule axis.

A precise ferrule alignment technique with a split sleeve was also established for condition (b). We can use the same technique for the MCF connector.

For condition (c), physical contact (PC) connection technology has been established to achieve a return loss of 50 dB or more. We can use PC technology for the MCF connector, however, the specifications of the ferrule endface geometry must be reconsidered because some cores are not located in the center of the fiber.

Optical connectors are usually operated by hand, so we sometimes have to consider an external force of tens of newtons interacting with the fiber cables. If such a force interacts with a small sized optical connector, the plug housing will be deformed by more than 10 m, which is far greater than the alignment tolerance. To solve this problem (condition (d)), a ferrule ‘floating mechanism’ has been widely used.

2.2 Design principle of MCF connector To connect MCFs, we have to precisely align the rotation angle of the ferrule. In this paper, we use single-mode 7-core MCFs. The outer diameter of the MCF is 204 m, the core center to center distance is 45 m, and the MFD of each core at 1550 nm wavelength are 10.4 to 10.8 m. Figure 1 is a photograph of an MCF endface. In Figure 1, the 3 dots around the bright cores are the markers that distinguish the core IDs.

Figure 1. Single-mode 7-core MCF

Using this MCF, the allowed angular misalignment is 1.27 degrees when the allowable offset is 1 m at the outer cores. Our target was set at an angular misalignment of 0.5° on the assumption that the lateral misalignment (offset) cannot be disregarded.

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We designed the MCF connector based on the following assumptions:

(1) Existing mechanical interface

The first priority with optical connectors is intermateability. Considerable investment and a long period of development is needed to develop a new mechanical interface that achieves intermateability between the devices of different vendors. We selected an existing interface that was standardized in the IEC 61754 series.

(2) Small size

The new MCF connector should have the same or greater packaging density than conventional optical connectors. On the other hand, there is some possibility of using an MCF connector for the high-speed optical transceivers. In this regard, small form factor (SFF) connectors are recommended.

(3) Symmetrical structure

The plug housing will be deformed not only via interaction with an external force but also by interaction with the internal force that is produced by the spring used for PC connection. To realize stable connection for all the cores in an MCF, uniform pressure is recommended for every outer core.

There are two types of SFF connectors, one type has only one cantilever for a latch (e.g. the LC connector) and the other type has 2 cantilevers that are arranged symmetrically (e.g. the MU connector). To realize stable MCF connection, we recommend using the latter type because it will deform symmetrically when mated.

To satisfy all the above assumptions, we selected the MU connector (IEC 61754-6) for the MCF connector interface.

To design the MU type MCF connector, we rearranged the basic conditions mentioned above as follows:

(a) Precise fiber fixing

We designed a press fit flange to fix the MCF to the ferrule at a fixed angle. We can align the angle of the flange after the MCF has been glued to the ferrule and polished. It is very difficult to align the fiber angle while gluing the fiber.

(b) Precise ferrule alignment

No change is required for the ferrule - split sleeve alignment mechanism for MCFs.

(c) PC connection

The optical interface specification (IEC 61755-3-1) allows an endface spherical radius apex offset of 70 m. The allowable apex offset will be 25 m for MCF because the outer cores are located 45 m from the center. In this paper we followed the IEC 61755-3-1 specifications for all the ferrule endface dimensions except for the apex offset of 25 m. The optical interface of MCFs should be reconsidered in the future.

(d) Floating mechanism

An MU connector has 0.1 mm gap in each of the directions between the ferrule flange and plug housing. This gap allows a ferrule rotation of 10° which value cannot satisfy the allowable tolerance of 0.5°. To realize an angle tolerance of 0.5°, we used an MU-

type PANDA fiber connector structure, which incorporates Oldham’s coupling mechanism [3].

2.3 MU-type MCF connector structure Figure 2 shows the design principle of our MCF connector, which incorporates Oldham’s coupling mechanism. The coupling device shown in Fig. 2 can float in a vertical direction inside the plug housing. The ferrule can float from the coupling device in a horizontal direction. Therefore, the ferrule can float from the plug housing by the same distance as a normal MU plug, but it cannot rotate around the ferrule axis. The flange can be pressed into the ferrule in any direction after the fiber has been glued to the ferrule.

Figure 2. Ferrule alignment mechanism

We manufactured MCF connectors with smaller dimensional tolerances for each part than a conventional PANDA fiber connector. The ferrule was glued to the MCF and polished, and then we observed the core arrangement direction with a microscope and adjusted the flange direction as shown in Fig. 3. Figure 4 shows the directional relationship between the plug housing and the core arrangement.

Figure 3. Ferrule alignment procedure

Coupling deviceZirconia tip Flange

Ferrule floating from plug housing

Plug housing

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(1) Aligning fiber cores to the reference line on the monitor

(2) Press fitting the flange into the ferrule parallel to the guide

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Figure 4. MCF direction in connector plug

Figure 5 shows one example of ferrule endface geometry. We used an SCP-241 type ferrule polisher (NTT-AT). In this example, the spherical radius of the endface was 16.3 mm, the endface spherical radius apex offset was 14.9 m, and the fiber undercut was -0.043 m (protrusion). In this sample, the maximum apex offset for each core of 59.9 m (14.9+45 m) satisfied the allowable apex offset of 70 m specified in IEC 61755-3-1.

Figure 5. Ferrule endface geometry of MCF connector

3. Connection Characteristics of MCF Connector We attached MCF connectors to 7-core fibers and measured the connection characteristics. We used a fiber bundle type fan-out [4] to launch a 1550 nm wavelength optical signal into each core. We measured all the connection points for the same core ID combination.

3.1 Attenuation Figure 6 shows the attenuation measurement setup. Using an 8-ch optical switch and a fan-out, optical signals were injected individually into each core. After measuring the reference powers for all the cores, we measured the attenuation of the connection point for each core using an optical switch. The switching repeatability was better than 0.01 dB.

Figure 6. Attenuation measurement setup

Figure 7(a) shows an attenuation histogram for 11 random connection points. There were 5 mating cycles each for the 7 cores. The average attenuation was 0.13 dB. The distribution of cores 2-7 (Fig. 7(b)) was slightly worse than for core 1 (center core; Fig. 7(c)). There appears to be some ferrule rotation, but we believe that we can improve it.

Figure 7. Attenuation measurement result

Opticalswitch

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N 55 Ave. 0.09 dB S.D. 0.060dB Min. 0.02 dB Max. 0.26 dB

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3.2 Return Loss Figure 8 shows the return loss measurement setup. We used optical continuous wave reflectometry (OCWR). The OCWR, optical switch and fan-out were connected by PC connectors with a return loss of around 50 dB.

Figure 8. Return loss measurement setup

Figure 9 shows the return loss histogram of 6 MCF connector plugs for 7 cores. These values include the excess return loss of 2 connection points, the optical switch and fan-out. We confirmed that all the cores of each connection point formed physical contact (PC) connections.

Figure 9. Return loss measurement result

3.3 Mating cycles Figure 10 shows the test result of 500 mating cycles. The attenuation for each core was measured after every 10 mating cycles. If the attenuation had changed by more than 0.2 dB, the ferrule endface was cleaned with an OPTIPOP connector cleaner and re-measured. We confirmed that there was no deterioration after 500 mating cycles.

Figure 10. Mating cycle test result

3.4 Temperature Dependence Figure 11 shows the temperature dependence of the MCF connector in a temperature cycling range of -10 to 60 for 144 hours. We confirmed that the loss variation was small enough for practical use.

Figure 11. Temperature dependence

4. Conclusions We have developed an MU-type multi-core fiber connector that includes Oldham’s coupling mechanism to maintain both a ferrule floating mechanism and precise alignment around the ferrule axis. It features a low average attenuation of 0.13 dB for random connection. We also confirmed that physical contact connection was realized for all cores.

5. Acknowledgments This work was supported by the National Institute of Information and Communications Technology (NICT) program “R&D of Innovative Optical Communication Infrastructure”.

6. References [1] T. Morioka, “New generation optical infrastructure

technologies: EXAT initiative towards 2020 and beyond,” in 14th OptoElectronics and Communications Conference, 13-17 (July, 2009).

[2] K. Imamura, K. Mukasa and R. Sugizaki, “Trench assisted multi-core fiber with large Aeff over 100 m2 and low attenuation loss,” in Proc. ECOC2011, Mo. 1. LeCervin. 1 (Sep., 2011).

[3] R. Nagase and S. Mitachi, "MU-type PANDA fiber connector," in Proc. Symposium on Optical Fiber Measurements, Boulder, U.S., pp. 53-56, Oct. 1996.

[4] K. Watanabe, T. Saito, K. Imamura and M. Shiino, “Development of fiber bundle type fan-out for multicore fiber,” in Proc. OECC2012, 5C1-2 (July, 2012).

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N 42 Ave. 46.8 dB S.D. 1.74 dB Min. 43.4 dB Max. 49.3 dB

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Ryo Nagase received B.E., M.E. and Ph. D. degrees in precision engineering from Tohoku University, Sendai, Japan, in 1983, 1985, and 1998, respectively. From 1985 to 2009, He has been engaged in research and development of optical fiber connectors in NTT Laboratories. From Oct., 2009, he is a professor of precision engineering at Chiba Institute of Technology, Chiba, Japan. His current interests are microscopic deformation and optical remote-sensing technology.

[email protected]

Katsuyoshi Sakaime received B.E. degree from Chiba Institute of Technology, Chiba, in 2012. He is a student at the Graduate School of Engineering, Chiba Institute of Technology.

Kengo Watanabe received B.E. and M.E. degrees from Tohoku University, Sendai, in 2008 and 2010, respectively. He joined Furukawa Electric co., Ltd. in 2010. Since then, he has been engaged in R&D of optical connectors for telecommunication.

[email protected]

Tsunetoshi Saito received B.E. and M.E. degrees from Tohoku University, Sendai, in 1994 and 1996, respectively. He joined Furukawa Electric Co., Ltd. in 1996. Since then, he has been engaged in R&D of optical components and connectors for telecommunication.

[email protected]

827 International Wire & Cable Symposium Proceedings of the 61st IWCS Conference