technology today 2005 issue 4 - Raytheon

Raytheon’s Optical Phased Array Technology Enhances Mission Assurance
FOR NEXT-GENERATION LASER COMMUNICATIONS
A new generation of Raytheon technologies
is empowering the extension of
communications into the vastly increased
bandwidth domain of the optical spectrum.
Reliable communications is key to accomplishing
most Department of Defense
(DoD) missions. Raytheon has long been a
leading provider of state-of-the-art radio
frequency (RF) and microwave communication
systems for the DoD, ranging from
miniature tactical radios to large strategic
satellite systems. These communications
systems provide the warfighter with a situational
awareness that greatly enhances
Mission Assurance. At Raytheon, we are
leveraging our technology base and
Raytheon’s Mission Assurance focus to help
the DoD implement ultra-high bandwidth
optical communications systems.
The U.S. government recently set forth a
far-reaching vision for an “internet in the
sky,” a mesh network of ad-hoc laser communication
(lasercom) links to bring ultrahigh
bandwidth to warfighters anywhere
on the globe. As part of this Transformational
Communications Architecture (TCA), a new
constellation of geosynchronous satellites
was envisioned, interconnected via high
bandwidth optical links between the satellites
and an Airborne Network Layer of
high-flying assets. This network is illustrated
in the figure on page 17, and a brief
overview was presented in technology
today 2005 issue 2.
The figure illustrates only the simplest network
involving satellite and airborne nodes.
Growing bandwidth demand will require
an evolution to a mesh network including
air-to-air links among the aircraft, as well
as additional links to lower-level assets. The
mesh network provides more efficient use
of resources, much higher reliability, and
lends itself to all-optical operations. Mesh
networks are adaptable to multiple classes
of service, and the mesh connectivity provides
redundancy and a higher probability
that data will reach its destination, even
with degraded inter-node connections.
When a node is lost, or the path to it is
degraded, the link can be reestablished by
rerouting around that node. Such optical
path diversity is important because of
potential atmospheric impairments on
16 2005 ISSUE 4 RAYTHEON TECHNOLOGY TODAY
free-space optical spans. Aboard high-altitude
unmanned aerial vehicles and satellites,
multi-node lasercom will enable ad
hoc networking among users and enhance
future military communications. Such a mesh
network, however, must support multiple
links at each node, a requirement that is
difficult to meet with conventional
mechanically based lasercom terminals.
Although the government needs simultaneous
connectivity to multiple assets and
desires multiple links per node, there was
no a priori technical solution that fit the
constraints of conventional laser beam control
and practical size, weight, and power
(SWaP) concerns. With conventional optomechanical
systems based on telescopic
beam directors, a separate beam control
system is required at each end of a link,
and the requirement of multiple simultaneous
links for each air and space node
results in unacceptable SWaP levels.
Raytheon worked with the customer at the
TCA-planning level and showed how lightweight
optical phased array (OPA) technology
has the potential to enable multiple
simultaneous high-bandwidth links between
each satellite and the network of aircraft,
and among the air-based network nodes,
without exceeding practical SWaP limits.
This resulted in a new spiral development
program to prepare Raytheon’s OPA-based
lasercom technology for TCA. We are
presently working towards an effective solution
to a greatly enhanced customer vision.
This vignette and the ensuing developmental
efforts offer a good illustration of the
four pillars of Mission Assurance in action:
Mission Enhancement, Mission Definition,
Mission Support and Mission Execution.
Mission Enhancement for TCA was
achieved through applying Raytheon OPA
technology to a new business area. (technology
today 2005 issue 2 briefly describes
what OPAs are and how they work.)
Whereas conventional beam control technologies
using gimbaled telescopes would
allow the simultaneous formation of a few
high-bandwidth lasercom links within a single
theatre, the new OPA-based architecture
allows the simultaneous formation of
many high-bandwidth links over the entire
globe, and even extending to low earth
orbit constellations, thereby providing a path
to realizing a greatly enhanced mission
vision. The figure compares schematically
the theatre-sized area for which multiple
simultaneous links would be possible with
prior technologies and the full global capability
possible with the Raytheon approach.
The OPA technology allows multiple simultaneous
links to multiple theatres, as well as
multiple simultaneous links between theatres.
Mission Definition phases are now
underway. Raytheon personnel have been
collaborating with government counterparts
to establish how the new enhanced
mission should best be accomplished. The
flexibility of OPA-based satellite terminals
not only enables the desired multiple simultaneous
links per node, but also offers mission
options unforeseen in the original
TCA. Raytheon’s terminal architecture is
modular and reconfigurable. Our approach
uses OPAs as building blocks to adaptively
configure an array of redundant transmit
and receive apertures for each node. The
multiplicity of transmit and receive apertures
not only supports the requirement for
multiple simultaneous links, but also allows
programmable bandwidth allocation for
each link. These new mission options must
be folded into broadened concepts of
operations (CONOPS) for TCA, which, in
turn, involves continuing interaction with
established customer working groups.
Raytheon’s OPA-based design features precision
steering with full beam agility without
any moving parts and minimal SWaP.
Owing to their high performance and small
SWaP, OPAs are well suited for applications
requiring multiple independent apertures.
In addition to the advantages of affordability,
low weight, high reliability with no moving
parts and completely independent
steering of multiple beams, OPAs also provide
an unprecedented degree of flexible
link dynamics. The ability of OPAs to combine,
fan out and independently steer
arrays of beams enables a multi-access,
bandwidth-on-demand capability. The programmable
nature of the new terminals
offers the potential of a changing number
of asymmetric links according to the actual
bandwidth needs of the users, rather than