Fiber optic gyros are a mature product and have been in production for nearly three decades. Over 200,000 have been delivered to customers. This paper will review the recent improvements that have been made to fiber optic gyros and the systems that use them at Northrop Grumman Corporation. These improvements reduce gyro noise, improve bias and scale factor errors, reduce cost, and improve reliability in inertial measurement units (IMUs), inertial navigation systems (INS), and marine navigation systems.
Fiber optic gyros are a great success story for a new inertial measurement technology that successfully transitioned from the laboratory in 1975 to production in 1992. This paper will review their research, advanced development, product development, and production transfer. The focus of the paper will be this cycle from Stanford University to Northrop Grumman.
This paper will review the technical developments that brought the fiber optic gyro from the laboratory to production.
Selected Northrop Grumman fiber optic gyro based products will be then reviewed at a high level. Finally, potential
future developments in fiber optic gyros that are being examined by researchers around the world will be reviewed.
Over thirty five years have elapsed since the fiber optic gyro was proposed by Vali and Shorthill. In those
decades, fiber gyros have matured. They are competing head to head with existing technologies such as
mechanical gyros and RLGs in tactical, navigation and strategic applications and are winning. Northrop
Grumman has produced the majority of fiber optic gyros and fiber optic gyro based inertial products in the
world. This paper will cover the various Northrop fiber gyro products, the platforms they are used on, as well
as production and top level system data.
Research and development of fiber optic gyros began in the mid 1 970s and focused on improving the
gyro's sensitivity to rotation and reducing noise. Next, bias performance was addressed. By the early
1980s, fiber gyros were achieving bias errors of 0.01 O/ in a laboratory environment. Scale factor
performance was initially addressed at McDonnell Douglasi in the late 1 970s by the use of a closed-loop
fiber gyro which employed acousto-optic frequency shifters. Good performance was achieved but this
approach was not productionized.
In the mid 1980s, Thomson CSF developed a fiber gyro which used a double closed-loop technique
employing a digital phase ramp and an electro-optic phase modulator2. Derivatives of this approach
have been adopted by most gyro producers in the world. This technique has enabled fiber gyros to have
high scale factor linearity and has significantly improved scale factor stability and repeatability.
Today closed-loop fiber optic gyros using derivatives of this technique are in production for many
tactical applications3 . These include tactical missiles, smart bombs, and attitude and heading reference
systems (AHRS) and require gyro bias performance of 1 to 1 0 O/ and gyro scale factor performance of
1 00 to 1 000 ppm. Closed-loop fiber gyros using derivatives of this technique are presently in
development for future inertial navigation systems4 (INS) which require bias performance in the 0.00 1
to 0.01 0/hr and scale factor performance in the 5 to 50 ppm range.
This paper will examine how this double closed-loop, digital phase ramp technique functions. An error
source unique to this type of closed-loop gyro, the deadband error, will be examined along with a
technique for eliminating it.
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