Fibre optic rotary joints
Princetel MJ2 series fibre optic rotary joint
Two-channel multimode fibre optic rotary joint for LED light sources, 20 mm in diameter, at 1310/850 or 1310/1550 nm, up to 100 rpm and -40 to +72 °C, IP60 (IP65 optional).
Key specifications
| Speed (max) | 100 rpm |
|---|---|
| Ingress protection | IP60 (IP65 optional) |
| Temperature | -40–72 °C |
| Fibre channels (max) | 2 |
| Rated life (revolutions) | 100–200 million |
| Fibre | multimode (LED sources) |
| Wavelength | 1310/850 or 1310/1550 |
| Insertion loss | <4 ch1, <6 ch2 |
| Size | 20 mm dia. x 65 mm |
Summarised in our own words from Princetel, Inc.'s published data; series maxima, individual models vary. Last checked 2026-10-30. Source 1
Notes on this data
Princetel recommends ZJn or MXn for laser sources.
Specify Motion is not affiliated with Princetel, Inc.. Princetel and MJ2 series are used only to identify the product. Comparisons use published figures; always confirm against the current datasheet.
Typical applications
Alternatives that meet or exceed these figures
Engineers often come to us with a Princetel part number and leave with an alternative that is easier to source, quicker to deliver or a better fit for the machine. These 2 series from our supply network are the closest match on published figures.
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 | MJ2 series | FR Series Fiber Optic Rotary Joint |
|---|---|---|
| Speed | 100 rpm | 2,000 rpm meets or exceeds |
| Fibre channels | 2 | 50 meets or exceeds |
Hybrid units combining fibre optic channels with power and signal circuits, used on electro-optical pod systems.
| Published maximum | MJ2 series | Fiber Optic Integrated Electrical Slip… |
|---|---|---|
| Circuits | — | 70 |
| Current per circuit | — | 30 A |
| Speed | 100 rpm | 500 rpm meets or exceeds |
| Fibre channels | 2 | — |
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.
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 Princetel MJ2 series
Send these with your enquiry and an engineer can confirm the right MJ2 series 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
Princetel MJ2 series: frequently asked questions
What is the Princetel MJ2 series?
Two-channel multimode fibre optic rotary joint for LED light sources, 20 mm in diameter, at 1310/850 or 1310/1550 nm, up to 100 rpm and -40 to +72 °C, IP60 (IP65 optional). Published series figures include speed 100 rpm, temperature -40 °C, temperature 72 °C, fibre channels 2. It is made by Princetel, Inc.; Specify Motion can help source it or propose an equivalent.
Who makes the Princetel MJ2 series?
The Princetel MJ2 series is made by Princetel (Princetel, Inc.) and is listed here for engineers comparing options. Specify Motion is not affiliated with Princetel, Inc.; brand names are used only to identify the product.
What is the speed of the Princetel MJ2 series?
The published series maximum speed is 100 rpm. Individual models and sizes in the MJ2 series 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 Princetel MJ2 series?
Yes. On published figures, FR Series Fiber Optic Rotary Joint and Fiber Optic Integrated Electrical Slip Ring are the closest match 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
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