The New Generation of Fiber Optic Rotary Joints

Be it in the industrial sector or in the military – the desire to transfer ever-higher data volumes with increasing data rates is becoming greater and greater.

In the radar sector, the trend of building in the transmitter including the signal generation directly to the rotating antenna platform and controlling it through a rapid, interference-free, optical data connection is gaining increasingly in significance. As well as digital signals, it is necessary as a matter of urgency to transmit analogue video and audio signals interference-free and potential-free over wide distances.

SPINNER has recognized this trend and determined the requirements for the next generation of radar systems early on. From the identifi ed requirements, the standards for two development projects have been derived. The first project deals with the optimization of our single channel rotary joint, which has been used in the field for years.

The developmental objectives were to fundamentally improve the optical parameters of insertion loss and deviation during rotation. The second project deals with the development of the smallest 6 channel fiber optic rotary joint available on the global market. Both the single channel rotary joint and the 6 channel rotary joint are available as products in the portfolio. The fiber optic rotary joints have passed stringent qualification tests.

To develop the fi ber optic rotary joints, SPINNER has been able to fall back on more than 20 years of experience in the field of optical transmission systems. As a signifi cant supplier of complex optical systems, we have the necessary knowledge to optimize the critical assembly processes. We are proficient in the packaging of integrated circuits, which is needed to adjust and fix the optical components with micrometer precision.

It goes without saying that critical optical components are assembled in the clean room. All parts of these fiber optic rotary joints are produced on precision machinery. This guarantees a consistently highquality for these low-maintenance, fiber optic rotary joints with first-classtechnical data. As a leading manufacturer of RF rotary joints, SPINNER can offer combinations of RF rotary joints, contact rings, media feed-through and fiber optic rotary joints, together with gigabit LAN transmissions.

For more than 10 years, pre-combined RF and fiber optic rotary joints from SPINNER have been integrated successfully into the systems of our customers. We have the experience and knowledge to carry out all critical manufacturing and assembly steps independently. Below, detailed information about the single channel and 6 channel rotary joints will be provided:

Single Mode Single Channel Fiber Optic Rotary Joint BN 549397

The single mode single channel fiber optic rotary joint was consistently trimmed to a low insertion loss with a concurrently high refl ection loss. Over the entire range of usage temperatures between -32 °C and +71 °C with the two optical transmission bands at 1310 nm and 1550 nm, the insertion loss is a maximum of 1 dB with an equivalent variation of ±0.25 dB.

The return loss is 55 dB. The excellent optical parameters are achieved through the use of fi ber optic collimators combined with an optimized software-controlled adjustment technique and special adhesive technology.

A fiber optic collimator is a component, with which the light that is lead into a single mode fiber is expanded using a lens. The expanded light ray can be transmitted via a concealed distance of several millimeters with virtually no loss. As part of the adjustment, the light rays radiated by the collimators are aligned with regards the mechanical rotating shaft.

The coupling losses between two fiber optic collimators depend in principle on the mutual angle malpositioning. By using special ball bearings combined with high-precision mechanical parts, the necessary angle rigidity of the rotary joint is guaranteed. The selected optical compensation of the collimators even enables operation of the rotary joint in the wavelength range of 1270 nm to 1650 nm.

As most commercially available optical transmission and receiver components are equipped with an LC connection, the portfolio rotary joint has LC-APC connectors. If required, other optical connector systems are available. The BN 549357 is available off the shelf. For aeronautic applications, a variation was developed with the BN 549399, which can be operated between -55 °C and +85 °C. A special fiber is used for this.

Single Mode 6 Channel Fiber Optic Rotary Joint BN 549599

Multi-channel fiber optic rotary joints are used wherever several analogue or digital signals need to be transmitted in a non-contacting manner at the same time for rotating applications without reciprocal influence. To do this, the optical signal must be transmitted off set from the mechanical rotating shaft.

A known property of the Dove prism is used to solve this technical problem: if a rotating image is shown through a Dove prism, which rotates with half the angular speed, then a still image is shown on the stator. With the help of a transmission, the relative movement between the rotor and a wave, containing the Dove prism, isrealized.

The quality of a multi-channel fiber optic rotary joint depends decisively on the adjustment of the prism, the packaging of integrated circuits and the quality of the transmission unit. SPINNER has more than 10 years of experience in the development, manufacturing and assembly of such transmission units, including the integration of Dove prisms.

The processes have been continually improved in the last few years. Several hundred multi-channel rotary joints with SPINNER transmission units are already in use.

To be able to fulfill the requirement of our customers for as small a multichannel rotary joint as possible with up to six channels, SPINNER has developed the smallest multi-channel fiber optic rotary joint for single mode fibers currently on the market. The core of the rotary joint is a transmission unit with integrated Dove prism.

To transmit the optical signals, we use collimators for the single channel rotary joint. To cover as many fields of use as possible in the civil and military sectors, the rotary joints have been optimized for a temperature range of -40 °C to +85 °C.

Over the entire range of usage temperatures and with the two optical transmission bands at 1310 nm and 1550 nm, the insertion loss is a maximum of 4.5 dB with an equivalent variation of ±0.75 dB. In the temperature range of -30 °C to +50 °C, we guarantee a maximum insertion loss of no more than 3 dB.

The return loss is 55 dB. All compensations of the optical components are designed as broadband, so that the rotary joint can be operated in the wavelength range of 1270 nm to 1650 nm. The fiber optic conductors have LC-APC connectors as standard. The new 6 channel fiber optic rotary joint represents a milestone in technical innovation in terms of its size. The table summarizes the most important specifications of the rotary joints.

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