Direct answer
A fiber optic rotary joint transfers optical signals between continuously rotating and stationary structures. Review maximum loss over rotation and rotational variation for every physical pass, with wavelength, fiber, speed, direction and mounting recorded. Static loss or cable torsion testing cannot replace rotating-interface verification.
A rotating interface differs from a twisting cable
Moog's engineering white paper defines a FORJ across a continuously rotating interface. A cord qualified for specified bending or torsion does not thereby acquire continuous optical rotation capability.
Applications include rotating platforms, cable reels and internal equipment links. Draw stationary and rotating structures first, identifying the joint, each pigtail and its restraint. Otherwise, “moving optical cable” hides several different acceptance objects.
This guide addresses passive optical interconnection. Electronic processing or optical/electrical conversion requires separately defined power, protocol and latency requirements.
Count passes and channels separately
Moog distinguishes a physical optical pass from a communication channel. Multiplexing can make their counts different. An “eight-channel” RFQ therefore needs a port map rather than an assumption of eight independent fibers crossing the interface.
| Item | Required definition | Not a substitute for |
|---|---|---|
| Physical pass | Corresponding fibers across the rotating interface | Logical service count |
| Communication channel | Direction, multiplexing and endpoints | Connector cavity count |
| Maximum insertion loss | Worst value under approved rotation conditions | One stationary reading |
| Rotational variation | Defined loss change within the test interval | Maximum loss or service life |
| Active function | Conversion or electronic processing scope | Passive-joint evidence |
Number each physical path and attach the communication map. Bidirectional services also need wavelength pairing and direction-specific test coverage. Equal pass counts do not establish compatibility with the multiplexers or transceivers.
Maximum loss and variation answer different questions
Moog's FO300 page separates maximum insertion loss over full rotation from insertion-loss variation. Use that distinction when drafting requirements, without copying its limits into unrelated products.
For invented arithmetic, assume a pass measures 2.1 dB minimum and 2.8 dB maximum over a full revolution under one reference and wavelength. Peak-to-peak variation is 0.7 dB. The worst rotating loss used in the path budget is 2.8 dB, not 0.7 dB.
These are not sample results or evidence of repeated-cycle stability. Retain sampling, time or angle information so a later review can locate an anomaly by angle, revolution and pass.
Conditions to retain in the report
| Condition | Suggested record | Review purpose |
|---|---|---|
| Optical setup | Fiber, wavelength, launch and references | Applicable measurement boundary |
| Rotation | Speed, direction, revolutions and sampling | Motion coverage |
| Per-pass results | Identifier, maximum loss, variation and trace | Visibility of individual failures |
| Mounting | Flange, drive coupling, restraint and pigtails | Installed mechanical condition |
| Environment | Temperature, sealing configuration and test stage | Comparable configurations |
| System | Transceivers and complete path budget | Equipment suitability |
The FO190 page distinguishes dry and fluid-filled speed conditions and identifies LED-based optical values. Keep configuration and launch conditions with each extracted figure.
Mounting also deserves joint mechanical and optical review. Moog's white paper discusses side loading that can increase rotating loss. A bare-joint result cannot automatically replace installed-system verification. Life and environmental tests need separately approved cycles and before/during/after measurements.
Procurement FAQ
- Can a torsion-qualified cord rotate continuously? Its approved angle and cycles still apply; torsion qualification does not establish FORJ functionality.
- Are communication channels equal to passes? Multiplexing can change the relationship. Provide both maps.
- Does low variation mean low loss? No. Review variation and worst rotating loss separately.
- Is one direction or wavelength sufficient? Cover the approved application's directions and wavelengths.
- Does bare-joint testing replace equipment testing? Mounting, pigtails and drive conditions may differ. Define installed verification separately.
Related products and reading
- Industrial equipment interconnects
- Harsh-environment assembly scope
- Cable torsion test review
- Complete-path loss budget
Product links describe configuration scopes. Suitability, supply and parameters require project-specific confirmation.
Contact an engineer
Prepare endpoint drawings, path requirements or existing test records and contact an engineer to discuss assembly configuration and verification scope.
Sources and review date
- Moog FORJ engineering white paper
- Moog FO300 parameter definitions
- Moog FO190 test and operating conditions
Sources checked on 2026-10-23. References describe general technology or specific third-party configurations, not ARRANEX performance, certification or supply. Purchasing checklists are editorial recommendations; assumed examples are not test results.
Sources checked: 2026-10-23