Optical waveguides – With optical coupler – Movable coupler
Reexamination Certificate
2002-04-10
2004-08-24
Healy, Brian (Department: 2874)
Optical waveguides
With optical coupler
Movable coupler
C385S015000, C385S026000, C385S031000, C385S036000, C385S039000, C385S073000, C359S211200, C359S212100, C359S223100, C359S226200, C359S831000, C359S833000, C359S837000
Reexamination Certificate
active
06782160
ABSTRACT:
BACKGROUND OF THE INVENTION
A communication cable—sometimes called an “umbilical cord”—allows for the reliable communication of data and the transfer of power between a base station and a remote apparatus. For example, such a cable allows for the transfer of data between a surface vessel and a manned submersible, and another such cable allows for the transfer of data between the submersible and a remote-controlled exploration robot. These same cables also respectively allow the surface vessel to provide electric power to the submersible, and the submersible to provide power to the robot.
Because a communication cable is often prone to twisting and tangling—a cable that connects a surface vessel to a manned submersible can be more than a mile long—the cable is often formed from cable segments that are connected with rotary couplers. Each coupler serially connects two cable segments, and helps prevent twisting and tangling by allowing one segment to rotate freely with respect to the other segment. Moreover, for many of these applications it is required to deploy and retrieve the cable via a rotating stowage drum fixed to either the base or remote vessel.
And because a cable segment is typically formed from one or more bundles of filaments that each carry a different signal, a rotary coupler is designed to connect each filament from one cable segment to the same filament in the other segment. The filaments are typically electrically conductive wires, optical fibers, or a combination of both wires and fibers.
An electrical rotary coupler—one that interconnects cable segments that include only conductive wires—is typically rugged enough for use in harsh environments such as water, is relatively inexpensive, and has a relatively high connection density (the number of wire connections per unit of cross-sectional area). Because an electrical signal can propagate between conductors that merely touch one another, an electrical rotary coupler typically includes a metal slip-ring assembly that maintains the respective electrical connections between the wires of the cable segments as one segment rotates with respect to the other segment. Because the slip-ring assembly is made out of metal, the electrical coupler is relatively rugged. That is, the coupler can withstand the jarring, pressure, and other effects that are often characteristic of harsh environments. Furthermore, because it has a simple design, the electrical coupler is relatively easy to manufacture, and is thus relatively inexpensive. And because adding slip rings—typically one ring per cable wire—to the assembly increases the length, but not the width, of the coupler, the coupler's connection density can be relatively high.
But unfortunately, an optical rotary coupler—one that interconnects cable segments that include at least some optical fibers—is typically more sensitive and expensive, and has a lower connection density, than an electrical rotary coupler. Optical signals cannot propagate between optical fibers merely because they touch. Therefore, an optical coupler typically includes a delicate and complex optical assembly that maintains the fibers in one cable segment in optical alignment with the corresponding fibers in the other cable segment as one cable segment rotates with respect to the other. Unfortunately, because the optical assembly is delicate, jarring, pressure, and other environmental effects may adversely affect it such that the fibers become misaligned. If this misalignment becomes to large, one must remove the coupler and recalibrate it, repair it, or replace it. Furthermore, because the optical assembly is complex, it is often difficult to manufacture, and thus is often expensive. In addition, because the complexity, and thus the cost, of the optical assembly often increase as the number of fibers increases, the coupler's connection density and connection capacity—the total number of filaments that the optical coupler can interconnect—are often relatively low.
GENERAL OVERVIEW OF A DOVE PRISM
Referring to
FIG. 1
, a conventional dove prism
10
is typically derived from a lower portion of a conventional right-angle prism (not shown), and has sides
12
and
14
, a ceiling
16
, a base
18
which may or may not have a reflective coating, and ends
20
and
22
that are at equal angles, typically 45°, to the base
18
. When an image
24
is incident to the end
20
as shown, the prism
10
projects an inverted mirror image
26
from the end
22
. It is well known that as the prism
10
rotates through an angle &thgr; about a center axis
28
, the projected image
26
rotates through an angle −2&thgr; about the axis, or twice as far as the prism in the opposite direction. For example, if the prism
10
rotates 90° in a counterclockwise direction, then the projected image
26
rotates 180° in a clockwise direction. And if the prism
10
rotates 180° such that the base
18
is at the top of the prism, the projected image
26
rotates a full 360°. Thus, for every full revolution of the prism
10
, the projected image
26
rotates two full revolutions. Furthermore, it is well known that as the incident image
24
rotates through an angle &thgr; about the axis
28
, the projected image
26
rotates through an angle −&thgr;, or as far as the image
24
in the opposite direction.
Referring to
FIGS. 2-5
, the properties of the prism
10
of
FIG. 1
are explained with reference to a reference plane
40
and a collimated light beam
42
, which is incident to the end
20
of the prism, is projected from the end
22
, and is parallel to the ceiling
16
and base
18
before it enters and after it exits the prism. The prism has a perpendicular height H between the ceiling
16
and base
18
, and a length L along the length of the base
18
. The prism
10
also has an index of refraction that allows the prism to have the characteristics described below.
FIGS. 2-4
illustrate how a 180° revolution of the prism
10
about the axis
28
in one direction results in a 360° revolution of the projected portion of the beam
42
about the same axis in the other direction.
FIG. 2
is a side view of the prism
10
in its 0° position (the base
18
is coincident with the reference plane
40
) and the light beam
42
. The incident portion of the light beam
42
is a height Ha from the base
18
, and the end
20
refracts the beam to a reflection point
44
, which is a distance La from the end
20
and a distance Lb from the end
22
. The end
22
refracts the reflected portion of the beam
42
such that the projected portion of the beam is a height Hb from the base
18
.
FIG. 3
is a view of the prism
10
from the end
22
, where the prism is in its 0° position, the broken-line circle represents the incident portion of the beam
42
, and the solid circle represents the projected portion of the beam. Assuming that the incident portion of the beam
42
is stationary, as the prism
10
rotates about the axis
28
in a clockwise direction, the projected portion of the beam rotates at about the axis in a counterclockwise direction at twice the rotational rate of the prism. The directions of these respective rotations are represented by the broken-line arrows. Conversely, as the prism
10
rotates about the axis
28
in a counterclockwise direction, the projected portion of the beam rotates about the axis in a clockwise direction at twice the rotational rate of the prism. The directions of these respective rotations are represented by the solid-line arrows.
FIG. 4
is a side view of the prism
10
in its 180° position (the ceiling
16
is coincident with the reference plane
40
) and parallel to the light beam
42
. Because the projected portion of the beam
42
is in the same position with respect to the reference plane
40
as it was when the prism
10
was in its 0° position, it is evident that the projected portion has undergone a full revolution about the axis
28
in response to the half revolution of the prism
10
. Specifically, because the incident portion of the beam
42
has remained the height Ha above
Townsend VanWinkle T.
Varley Robert J.
Grayheal Jackson Haley LLP
Healy Brian
Lockheed Martin Corporation
Petkovsek Daniel
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