Fibre optic rotary joints
Moog FO291 fibre optic rotary joint
Modular stacked singlemode FORJ in 2 to 9 channel builds; replacement for the legacy FO242.
Need this part, a replacement or a complete package? Our experienced UK engineering team helps you select, source and obtain the right products, with pricing, delivery coordination and after-sales support.
Pricing and availability
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Need Moog parts, a replacement or a suitable alternative? Send us a part number, or tell us what the machine needs to do. Our UK engineers will come back with the right product, pricing, lead time and delivery, whether that is the original part, a checked alternative or a complete axis.
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Spec builder
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Select every part you need and answer the questions an applications engineer would ask. Our engineers use your specification to come back with the right products, pricing and lead times. You see your summary before we ask for any details.
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What are you specifying?
Select everything you need. A motor, drive and gearbox can be specified together as one axis.
Key specifications
| Speed (max) | 100 rpm |
|---|---|
| Temperature | -40–60 °C |
| Fibre channels (max) | 9 |
Summarised in our own words from Moog Inc.'s published data; series maxima, individual models vary. Last checked 2026-10-29. Source 1 · Source 2 · Source 3
Notes on this data
Singlemode (one MM pass possible). Insertion loss up to 6.5 dB. Dimensions per data sheet. 100+ rpm.
Specify Motion is not affiliated with Moog Inc.. Moog and FO291 are used only to identify the product. Comparisons use published figures; always confirm against the current datasheet.
Moog FO291 replacement and alternative options
Use these supply-network options as a starting point for an engineering check. We can also help source the original Moog part. Published series figures do not establish an exact-model or drop-in replacement: confirm ratings, fit, interfaces and approvals for your application.
Fibre optic rotary joints that carry single-mode or multi-mode optical channels across rotation for high-bandwidth, interference-free data. Channel counts run from one to fifty.
| Published maximum | FO291 | FR Series Fiber Optic Rotary Joint |
|---|---|---|
| Speed | 100 rpm | 2,000 rpm meets or exceeds |
| Fibre channels | 9 | 50 meets or exceeds |
Hybrid units combining fibre optic channels with power and signal circuits, used on electro-optical pod systems.
| Published maximum | FO291 | Fiber Optic Integrated Electrical Slip… |
|---|---|---|
| Circuits | — | 70 |
| Current per circuit | — | 30 A |
| Speed | 100 rpm | 500 rpm meets or exceeds |
| Fibre channels | 9 | — |
Figures are the highest published for each series and are not always measured the same way. A higher figure is not automatically a better choice: mounting, duty cycle, feedback, connectors and approvals matter too. An engineer will check the fit against your application before recommending anything.
Typical applications
What a fibre optic rotary joint is
A fibre optic rotary joint, or FORJ, is the optical equivalent of a slip ring: it passes light signals between a fixed and a rotating fibre without a physical join. In a single-channel unit the two fibre ends sit on the rotation axis with collimating lenses so the beam crosses a small gap. Multi-channel units use a derotating optical element, such as a Dove prism, so several fibres can share the axis. Joints are built for single-mode or multimode fibre and can be combined with electrical slip rings.
When engineers choose a fibre optic rotary joint
Choose a FORJ when the rotating part needs very high bandwidth, immunity to electromagnetic interference or long transmission distances, as in subsea vehicles, cable reels, radar and video systems. It is passive and wear is very low because nothing touches. The trade-offs are insertion loss, which must fit the optical budget, sensitivity to contamination and a higher cost for multi-channel units. If data rates are modest and EMC is manageable, an electrical Ethernet slip ring may be simpler.
How to specify the Moog FO291
Send these with your enquiry and an engineer can confirm the right FO291 variant or an equivalent:
- Number of optical channels
- Fibre type: single-mode or multimode, core size (µm)
- Operating wavelengths (nm)
- Maximum insertion loss and loss variation during rotation (dB)
- Return loss requirement (dB)
- Connector type, such as FC, ST, LC or SC
- Speed (rpm), environment and any electrical circuits to combine
Common mistakes to avoid
- Not including the FORJ insertion loss in the full link optical budget
- Mixing single-mode and multimode fibres between the joint and the transceivers
- Leaving connectors uncapped during assembly, which contaminates the optical faces
- Specifying many channels when wavelength multiplexing would cut cost and size
Moog FO291: frequently asked questions
Can you help replace Moog FO291 or source the original?
Send the full model code, quantity and required date. Our engineers can check original-part availability and assess suitable alternatives, including supply-network options where appropriate. We confirm compatibility and any changes needed before recommending a replacement.
What is the Moog FO291?
Modular stacked singlemode FORJ in 2 to 9 channel builds; replacement for the legacy FO242. Published series figures include speed 100 rpm, temperature -40 °C, temperature 60 °C, fibre channels 9. It is made by Moog Inc.; Specify Motion can help source it or propose an equivalent.
Who makes the Moog FO291?
The Moog FO291 is made by Moog (Moog Inc.) and is listed here for engineers comparing options. Specify Motion is not affiliated with Moog Inc.; brand names are used only to identify the product.
What is the speed of the Moog FO291?
The published series maximum speed is 100 rpm. Individual models and sizes in the FO291 range vary, so check the exact variant against your duty cycle, mounting and environment, or ask our engineers to confirm the right size for you.
Is there an alternative to the Moog FO291?
We can assess suitable replacement options. On published figures, Motion Control Products FR Series Fiber Optic Rotary Joint and Motion Control Products Fiber Optic Integrated Electrical Slip Ring are options to assess from our supply network. An engineer confirms the fit against your application before recommending anything.
What is the difference between single-mode and multimode fibre optic rotary joints?
Single-mode joints carry light in one guided mode through a very small core, which suits long distances and high data rates but needs precise alignment. Multimode joints use a larger core, which is more tolerant of alignment and suits shorter links. The joint must match the fibre and transceivers already used in the system, so state the fibre type and wavelength.
Can a fibre optic rotary joint be combined with an electrical slip ring?
Yes. A common arrangement places the FORJ on the axis, with the electrical slip ring built around it in a through-bore format, so power and optical data pass through one assembly. This is widely used on cable reels, ROVs and radar. Specify the electrical circuits and optical channels together so the supplier can design one housing and sealing system.
Further reading: How to select a fibre optic rotary joint · How to select a slip ring · Slip rings
Other fibre optic rotary joints series
Engineer support
Let our experienced engineers do the hard work for you
Tell us how you use the Moog FO291: the load, speed, duty and environment. Our engineers will confirm whether it is still the right part, find it for you, or propose an alternative that fits better.
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Prefer to configure it? Use the spec builder.
How it works
From enquiry to delivery
Send a part number or describe the application. Our engineers take it from there: the right product, a clear quotation, and delivery and support arranged.
- 01Tell us what you needSend a part number, or configure the application, quantities and timing.
- 02An engineer reviews itWe check the specification and find the original part, a checked equivalent or a complete axis.
- 03Receive your quotationProducts, pricing, lead time and compatibility notes in one reply.
- 04Order and deliveryWhen you are happy, the order is placed and delivery and after-sales support are arranged.