Fiber optic connectivity systems: Expanded Beam Optical

Our webtalk about the new Expanded Beam Optical (EBO) technology and the possibilities it offers for various applications raised very high interest. This also shows the number of questions we received after the live webtalk. That’s why we use the opportunity to interview our expert Wolfgang Rieger in a short Q&A session around the EBO principle.

Why did Expanded Beam Connectors until today not find more widespread market adoption?
As explained already during the live webtalk, former expanded beam connectors had some disadvantages (higher insertion loss, quite expensive technology). However the EBO Technology eliminates now these disadvantages, what will make the Expanded Beam concept very attractive for a lot of applications.

Is it imaginable, that the EBO technology will be integrated into active networking equipment – i.e. optical transceiver ports?
Yes, optical transceivers suffer also from contaminations with dust & dirt. We have also here concrete interest from the market, especially with regard to future 400G & 800G applications.

EBO applies the principle of expanding the beam. How much is the beam expanded in relation to the fiber core?
The beam diameter in the contact zone is about 70µm in case of Singlemode and about 200 µm in case of Multimode. However the beam diameter is not the right parameter to get a conclusion about the “in-sensivity” – it is the enlarged area which needs to be considered. I made a calculation for Singlemode and the effective area is about 60 times bigger than the Singlemode core – what means it is 60 times less sensitive.

Are there also other connector designs already available than those shown during the presentation?
Rosenberger OSI is working on projects with different companies to integrate the EBO technology into other connector designs. And also 3MTM is working on additional developments – even on additional ferrule designs.

It was developed and patented by the company 3M^TM and has therfore the name 3M^TM EBO. EBO stands for Expanded Beam Optical. With regard to this new technology Rosenberger Optical Solutions & Infrastructure (Rosenberger OSI) entered already in an early stage into a close cooperation with 3M^TM. The Expanded Beam priciple is implemented here in a complete new way and with a precision not known until know.

By means of a new delevoped EBO ferrule the light beam is at first expanded. Afterwords on a curved surface it is divirted by 90 degrees and aligned parallel by total internal reflection. The effect is comparable to that of a collimating deflection mirror. In the opposite connector (the bottom part of the illustration) the principle is reversed and the light is coupled back into the fibre. This principle is implemented with the EBO ferrule shown here. This is a precision injection-moulded part. In the rear area it has grooves for fibre positioning instead of holes as we know it from classical PC-type connectors. The clieved fibres are bonded  via an automated process. No polishing of fibre ends are required, what is a very unique feature. Among many others the EBO ferrule offers thus two main advantages: first it realizes an absolute new optical principle with highest precision and second it allows the possibility to automize the termination process to an extend, which was until today in case of fiber optic connectors not possible.

The illustration above shows a terminated EBO ferrule. At a defined distance from the ferrule, a so-called clamping, the collet, is attached here (Figure 1). This assembly is then inserted into a so-called cassette, which is an important part of the fibre connector (Figure 2). As already indicated the fibers are capted here with a suspension what finally supports the mating process. This mating process is shown here in 3 phases. You can see how the EBO ferrules slide over each other and finally make the optical contact. The cassette can be seen as an ideal building block for integrating the EBO technology into many other connector environments with relatively little effort.

What kind of performance can be expect from this fibre optic connectivity system?
The "Expanded Beam" concept offers impressive values in the areas of insertion loss (IL) and return loss (RL) (see illustration). It is quite close to the one of classical PC or APC-connectors. The maximum insertion loss specified for the EBO system is 0.7 dB for singlemode and 0.3 dB for multimode. The typical values are in the range of 0.3 - 0.4 dB for singlemode and approx. 0.2 dB for multimode. And also the return loss is in a range how it is required for today's and future high-speed applications.

But what is perhaps even more important: this system is characterised by excellent repeatability and stability over many mating cycles (see figure below). The upper diagram shows the change in insertion loss and the lower diagram the return loss, both over 100 mating cycles.