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Fibre optic single mode rotary joint
| Details |
Inventors: Snow, James W.; Smith, Graham A. J.; Channer, Geoffrey H.; Purdy, John W.;
Assignee: Focal Technologies Incorporated (Dartmouth, CA)
Primary Examiner: Healy; Brian
Assistant Examiner:
Attorney, Agent or Firm: Jones, Tullar & Cooper
The invention is a rotary joint for singlemode optical fibers, having a fixed and a rotating part to permit the transmission of optical signals across a rotational interface (such as a winch or turret) with minimal insertion loss and, in particular, low reflections (good return loss). There is no need of conversion to electrical signals; the device is passive. It may be use an oil of refractive index matched to that of the glass fibers and to that of fiber tapers or lenses used to expand the beam emitted from one fiber and contract it for transmission into the other fiber. The device is bidirectional. By use foil, through precision techniques for building and mounting the optical and mechanical components, and by use of advanced bearings, both the insertion loss and unwanted reflections (return loss) can be minimized, thereby making it suitable for use with singlemode fiber. Insertion loss can be further reduced in conjunction with index-matching fluid by using optical elements (lenses, tapers, fibers) having angled or curved facets rather than perpendicular facets. Oil filling has the further advantage of pressure compensation allowing the device to operate at any ambient pressure. Lenses having curved surfaces can be accommodated by the use of fluid having a refractive index different from that of the lens material. |
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DETAILED DESCRIPTION The present invention provides a rotary joint for optical fibers without the need to convert to electrical signals.
It is designed for use with singlemode fiber but can also be used with the less difficult case of multimode fiber.
In particular the return loss performance is improved over previously reported rotary joints, and the devices can be operated at any ambient pressure.
To achieve these results, an object of the present invention is to provide a rotary assembly wherein a subassembly containing one optical fiber is made rotatable on the same axis as, and in relation to, a subassembly containing a second optical fiber, and a subsystem for transmission of light from either fiber to the other with minimal loss, including an optically clear oil.
The light transmission system between the fibers may include lenses of several types.
The refractive index of the oil may be matched to that of the lenses or may be different depending on the type of lenses used.
The presence of the oil has the added advantage of providing pressure compensation, so that the device can be operated at any water depth.
Procedures are presented for the precision (sub-micron) alignment of the optical parts and machining of the mechanical parts, to achieve the control over dimensions that is required to provide good loss performance with singlemode fiber.
Another object of the invention is to provide a rotary joint wherein optical fiber tapers are used to expand the beam from one fiber and subsequently contract it into the other, thereby achieving, without the use of lenses, a reduction in optical losses associated with dimensional variations.
By deleting the fiber to lens interface, this also gives improved return loss, especially with an index-matching fluid between the faces.
Still another object of the invention is to incorporate tapered bearings and precision sleeve bearings for the rotating assembly, to achieve reduced optical losses through improved concentricity between the rotating and stationary assemblies
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