IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 20, NO. 3, FEBRUARY 1, 2008 187 Mass Manufacturable 180 -Bend Single-Mode Fiber Socket Using Hole-Assisted Low Bending Loss Fiber Jürgen Van Erps, Student Member, IEEE, Christof Debaes, Member, IEEE, Rahul Singh, Tomasz Nasilowski, Member, IEEE, Pawel Mergo, Jan Wojcik, Tim Aerts, Herman Terryn, Pedro Vynck, Jan Watté, and Hugo Thienpont, Associate Member, IEEE Abstract—High-efficiency low-cost field-installable 180 -bend single-mode fiber (SMF) sockets are promising new fiber con- nector components that can facilitate network element footprint reduction and allow for more comfortable connector handling in the field. We present a novel type of small-form-factor 180 coupling SMF socket component, yielding coupling losses between two side-by-side positioned fibers as low as 0.5 dB, making use of specially designed low bending loss hole-assisted fiber. The com- ponents are prototyped in a polymer using deep proton writing and show all the potentialities for low-cost fabrication in different types of plastics. Index Terms—Deep proton writing (DPW), hole-assisted fiber, low bending loss fiber, optical fiber connectors, plastics, rapid pro- totyping. I. INTRODUCTION A LTHOUGH present-day service providers bridge the last kilometers in the telecom network using copper wires, the increasing number of subscribers and the potential growth of the bandwidth demand in the coming years require a shift to all-optical full-service access networks [1]. It is clear that new fiber connector developments are one of the drivers to allow for low-cost fiber-to-the-home deployments, since the choice of connectivity has a high impact on the reduction of capital ex- penditures [2]. The connector principle we present here can po- tentially solve design issues of optical distribution frames when considering high termination densities. In optical distribution frames widely used today, single-mode fibers (SMFs) from the Manuscript received September 25, 2007; revised October 31, 2007. This work was supported in part by DWTC-IAP6, in part by Fund for Scientific Re- search-Flanders (FWO), in part by IWT, in part by the European Network of Excellence on Micro-Optics NEMO, and in part by the OZR of the Vrije Uni- versiteit Brussel. The work of J. Van Erps and C. Debaes was supported by the FWO under a research fellowship. J. Van Erps, C. Debaes, R. Singh, T. Nasilowski, P. Vynck, and H. Thienpont are with the Department of Applied Physics and Photonics, Vrije Universiteit Brussel, 1050 Brussel, Belgium (e-mail: Jurgen.Van.Erps@vub.ac.be; Christof. debaes@vub.ac.be; rahul.g.singh@gmail.com; tnasilowski@tona.vub.ac.be; hthienpo@vub.ac.be). P. Mergo and J. Wojcik are with the Laboratory of Optical Fiber Tech- nology, Marie Curie-Sklodowska University, 20-031 Lublin, Poland (e-mail: mergopaw@hermes.umcs.lublin.pl; wojcik@hermes.umcs.lublin.pl). T. Aerts and H. Terryn are with the Department of Metallurgy, Electrochem- istry and Material Science, Vrije Universiteit Brussel, 1050 Brussel, Belgium (e-mail: taerts@vub.ac.be; hterryn@vub.ac.be). J. Watté is with Tyco Electronics, 3010 Kessel-Lo, Belgium (e-mail: jwatte@tycoelectronics.com). Color versions of one or more of the figures in this letter are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/LPT.2007.912973 Fig. 1. Schematic working principle: the 180 deflection of the beam is realized by a hole-assisted low bending loss fiber. central office cable have to be patched to fibers going to the sub- scriber, i.e., optical network units. The fibers coming from the central office and from the subscriber are generally coming from below the ground, and therefore, it would be advantageous to be able to connect these two parallel positioned fibers by a socket to avoid the necessity to make a loop inside the network hub when those fibers were to be connected or spliced in-line. The spare length of fiber required because of the in-line splicing con- figurations used until now, results in storage and management problems, increasing the size of the connector cabinets, and the complexity of the tasks involved in making and changing con- nections. It would be far preferable if the connections between optical fibers could be made with a simple plug-in arrangement so that the fibers do not need to be positioned accurately in line with one another. To enable an increase of fiber density in the rack and facilitate fiber identification, we developed a novel type of fiber connector that mimics the working principle of distribution frames for copper cables, in which conductors that have to be connected can simply be inserted into side-by-side sockets using a suitable plug. This approach also enables field installability by low-cost labor force. The concept of the novel fiber socket presented here is based on bringing together the end facets of incoming and outgoing fibers at the front panel of the frame by means of a component that bends the light over 180 . To this end, we designed and fabricated a specialty low bending loss hole-assisted fiber to connect the end facets of the parallel positioned fibers, as shown in Fig. 1. For the fabrication of the 180 connector components, we use our rapid prototyping technology of deep proton writing (DPW) [3]. The concept of DPW is based on a local irradiation of a PMMA polymer substrate with a pencil-like collimated proton beam, according to a predefined pattern. The irradiation process changes the physical and chemical properties of the material in the irradiated zones. As a next step, a selective etching sol- vent is applied for the development of the irradiated regions, 1041-1135/$25.00 © 2008 IEEE