8 things you should know about Fibre Optic Slip Rings (FORJ)



1. Technology
A quick patent search will throw up innumerable FORJ patents, both two- and multi-channel. Only a few of these designs have been put into production, however. Our slip rings use technologies which facilitate both dual-port (2-channel) and multi-port (multi-channel) FORJs, thus offering our clients a high performance product.To get more news about how does a fiber optic slip ring work, you can visit grandslipring.com official website.

2. Key parameters
The function of a FORJ is to transmit power and/or data between two or more optic fibre cables, while leaving them free to rotate relative to each other. It is thus essential that the device have a very low insertion loss, very little insertion loss variation (wow) and a high return loss, all parameters that characterise the amount of reflection generated by the FORJ itself, and hence its quality.
3. Single- or multi-channel
A single-channel FORJ has a very simple mechanical design which makes it very reliable and durable, compact and able to rotate at high speed.
It is also important to note that a single-fibre FORJ can transmit tens (and even hundreds) of data channels and, even when combined with a multiplexer, is much cheaper than a multi-channel FORJ.

However, if your application really needs a two-channel solution, Servotecnica offers co-axial FORJs which satisfy the most stringent requirements while maintaining a reasonable cost and compact size. Furthermore, our design does away with black spots.

Multi-channel FORJs necessarily have a much more complex mechanical design. They also require accurate optical alignment to maintain good performance in all the three key areas discussed above. Inadequate alignment or poor optical design not only compromise the key optical performance parameters, they also create new problems such as losses at high wavelengths, high PDL (polarisation dependent loss), high PMD (polarisation mode dispersion) and crosstalk (this is discussed further below). The multi-channel design of our slip rings can align up to 12 standard channels, in addition to a large number of personalisation options.
4. Singlemode vs. multimode
The very small fibre core (9 micron) of single-mode fibres keeps the optical bands in their purest form, a mathematically perfect Gaussian profile. The bandwidth capacity of single-mode fibres is much larger than that of multi-mode fibres. Their bandwidth is also much less dependent on the length of the fibre itself, and can easily be extended. Overall, multi-mode systems still have a cost advantage over single-mode systems. However, the gap between them is coming down as single-mode solutions grow in popularity.

5. Size
Size matters - as the history of passive fibre optic components demonstrates. In reality, ever smaller solutions have driven innovation.
It is not uncommon to combine fibre transmission with electric slip rings, RF rotary joints or fluid rotary joints, with the FORJ at the centre of the system; this ensures that its diameter is a deciding factor in sizing the system as a whole.
6. Fibre or female connector (pigtail or receptacle)
A FORJ may terminate in a free fibre (pigtail) or female connector (receptacle) at both ends of the device. In general, versions with a fibre pigtail have more repeatable optical characteristics, since they do away with the uncertainties inherent in joining connectors to each other. Furthermore, in the pigtail version, defective connectors can be easily reconditioned or re-terminated, while a similar defect in the receptacle version can easily be irreparable.

This is why we at Servotecnica generally recommend the pigtail version to the majority of our customers. However, for applications which do not permit the use of fixed fibre terminations on the device, our series R FORJs offer female connectors in the FC and ST formats. It is also possible to mix and match pigtails and receptacles in a single custom solution.
7. Through hole
Nearly all standard commercially available FORJs are supplied without through holes and, if they are present, they are not really passive FORJs , since they replace the output fibre with a photographic detector. Designing a passive FORJ with a through hole is very complex and challenging. Servotecnica offers a variety of passive models with through hole for a wide range of applications.

8. Fluid filling
FORJs are widely used in underwater applications, where waterproofing and pressure equalisation are critical factors. Filling the FORJ with fluid not only makes pressure compensation possible, but also provides lubrication and the correct index of refraction.