Fiber-Optic Acoustic Sensors (FOAS)
Northrop Grumman has applied its expertise in fiber-optic technology to develop a line of Fiber-Optic Acoustic Sensors (FOAS). FOAS originated in 1981 as part of a major effort to develop both fiber-optic gyroscope and fiber-optic hydrophone sensor technologies. This effort, which has required investment of over $140 million, has established Northrop Grumman as the world leader in optical acoustic sensor technology and exclusive manufacturer of Department of Defense fiber-optic acoustic sensor array systems.
FOAS Description and Capabilities
The arrays themselves comprise only passive fiber-optic elements, and contain very few parts and no electronics. One remote transmit/receive station houses all the necessary optoelectronics. The data are transmitted on a few single mode fibers, over distances of more than 100 kilometers.
Northrop Grumman can produce fiber-optic acoustic sensor arrays for a variety of applications. Northrop Grumman builds three FOAS systems: hull arrays like the Light Weight Wide Aperture Array (LWWAA) currently on USS Virginia-Class Submarines, towed arrays for submarine and other applications, and fixed bottom arrays for deep ocean and shallow/littoral water surveillance.
Advantages of Fiber-Optics
Over the past 15 years, Northrop Grumman and the U.S. Navy have made significant strides in developing fiber-optic sensor technology for passive acoustic monitoring. This work has focused on demonstrating the advantages of fiber-optics over conventional piezoceramic sensor arrays.
One of the primary advantages of fiber-optic acoustic arrays is their simplicity. Ceramic acoustic arrays require power, complex electronics and signal processing to be located close to the sensor to overcome resistance losses.
Ceramic arrays also have numerous connectors and mechanical joints that reduce their reliability. The electronic processing elements of a fiber-optic array are located in a dry or controlled environment on a submarine or on shore. Their location allows them to be accessed for maintenance purposes and technological refresh, which is not possible with legacy ceramic arrays.