Fiber-Optic Gyros - Northrop Grumman Electronic Systems ...

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Fiber-Optic Gyros:
The Vision Realized
Dr. George A. Pavlath

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Dr. George A. Pavlath
Fiber-Optic Gyro Director
Northrop Grumman, Electronic Systems, Navigation Systems Division
Dr. Pavlath is a world–recognized expert with 20 years of experience in fiber
optics gyros (FOGs) and their components. He has led Northrop Grumman’s
development effort in fiber-optic gyros from research and development,
through product development, production transfer, and production support.
His directorate has successfully completed numerous contracts with the
United States Army, United States Navy, and the United States Air Force.
Dr. Pavlath has worked on fiber-optic gyros and their components since
1975. At Northrop Grumman, he is responsible for all fiber-optic gyro programs
including research and development, product development, factory
process and test equipment development, production transfer, and support of
the ongoing production activity.
He has led his directorate in the development of low accuracy FOGs for cannon–launched
applications, medium accuracy FOGs for attitude and heading
reference systems (AHRS) and tactical missile applications, and the LN–200
family – which is in production. His directorate led in the development of
high accuracy FOGs for inertial navigation of aircraft and missiles and also
for shipboard gyrocompass and fire control applications. He has also led in
the development of fiber optic components, integrated optic components,
light sources, photodetectors, assembly techniques, and automatic manufacturing
technology for component fabrication and fiber-optic gyro assembly.
Dr. Pavlath received his Doctorate degree in Applied Physics from Stanford
University and his Bachelor of Science degree in Physics from the California
Institute of Technology.
Dr. Pavlath has 21 issued patents on fiber-optic gyros and their components
and assembly processes. Ten additional patents are pending. He has also
published 15 papers on fiber-optic gyros.

ABSTRACT
Over thirty five years have elapsed since the fiberoptic
gyro was proposed by Vali and Shorthill. In
those decades, fiber-optic gyros have matured. They
are competing head to head in tactical, navigation and
strategic applications with existing technologies such
as mechanical gyros and ring laser gyros and they are
winning. Northrop Grumman has produced the
majority of fiber-optic gyros and fiber-optic-gyrobased
inertial products in the world. This paper will
cover the various Northrop Grumman fiber-optic gyro
products, the platforms they are used on, and it will
provide production and top level system data.
INTRODUCTION
It has been nearly 100 years since the discovery of
the Sagnac effect 1 , which enabled optical rotation
sensors. The Sagnac effect lay fallow for six decades
awaiting the development of technology to permit the
design and manufacture of products that could use it.
The first application of the Sagnac effect was the ring
laser gyro that was first demonstrated in the 1960s by
Macek and Davis 2 and entered production in the late
1970s. The enabling technology for this was the laser.
The development of the fiber-optic gyro required
its own enabling technology, namely low loss, single
mode, optical fibers that became available in the mid
1970s. Vali and Shorthill 3 first proposed the fiber-optic
gyro in 1975. It took researchers around the world
about a dozen years to resolve the many technical
issues with the fiber-optic gyro. The reader is referred
to the following paper 4 by this author for an overview
of these issues and their resolutions.
Over thirty years have now elapsed since Vali and
Shorthill proposed the fiber-optic gyro. Fiber-optic
gyros and inertial products utilizing them have been in
production for over a decade. Inertial products
utilizing fiber-optic gyros are in high volume
production and are used everywhere from under the
sea to outer space and in most places in between. The
vision of Vali and Shorthill has been realized.
Northrop Grumman Navigation Systems Division
has manufactured well in excess of 70,000 fiber-optic
gyros used in a wide variety of inertial products. These
products include rate gyros, inertial measurement units
(IMU), and inertial navigation systems (INS).
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1
NAVIGATION SYSTEMS DIVISION
HERITAGE
Northrop Grumman’s Navigation System Division
was formed from several predecessor entities that have
a rich and varied heritage in inertial products and in
fiber-optic gyros. Figure 1 shows the time lines of the
various predecessor entities beginning in 1980.
Figure 1. Northrop Grumman Navigation
Systems Division’s Heritage
A portion of Navigation Systems Division comes
from the purchase of Litton Industries by Northrop
Grumman in 2001. These legacy Litton entities were
Guidance and Control Systems (USA), Aero Products
(USA), Litef (Germany), and Lital (Italy). Another
portion of the division started as the Northrop
Grumman Precision Products Division which became
the Fibersense Technology Corporation in 1994 and
was subsequently purchased by Northrop Grumman.
FIBER-OPTIC GYRO PRODUCT
DEVELOPMENT AT NAVIGATION
SYSTEMS DIVISION
Guidance and Control Systems, Litef, Lital, and
Precision Products/Fibersense have been in the inertial
product business since the 1960s. The legacy Litton
divisions manufactured INS and IMUs. The Northrop
Grumman Precision Products divisions manufactured
inertial instruments and IMUs.
The development of the fiber-optic gyro at
Navigation Systems Division begins with the
acquisition of the Stanford fiber optics program from
Atlantic Richfield Corporation by Guidance and
Control Systems in 1982. Figure 2 depicts the
timelines for the various fiber-optic-gyro-based inertial
products.

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1980 1990 2000 2010
FOG R&D
G&CS
FOG R&D
Litef
MOG
LN-200
Development
LCR-92/93
Development
Dev
uFORS Dev
LN-25x
Development
Dev
Dev
FOG 200
2
LN-200
LCR-92/93
LTN-101e
Development
Atlas V
uFORS
ATFLIR
LFK-95
EKV
LLN-G1/GX/GY
LISA 200
LN-25x
LN-260
LTN-101e
LTR-97
LN-270
Figure 2. Fiber-Optic-Gyro-Based Inertial Product Timelines Grouped by Product Category
In 1985, development of resonant fiber-optic gyros
began at Litef in Germany and was followed by the
development of interferometric fiber-optic gyros in
1987.
Development of fiber optic IMUs began
simultaneously at Guidance and Control Systems and
at Litef in 1988. Guidance and Control developed the
LN-200 and Litef developed the LCR-92/93 family of
IMUs. Both were in production by 1992. In 1995, Lital
began using the LN-200 in its LISA 200 family of
Attitude and Heading Reference Systems (AHRS).
In 1998, Fibersense started the development of the
IMU 600 for precision pointing applications and the
IMU 200 for missile defense applications.
Development of fiber optic inertial navigation
systems started at Guidance and Control Systems in
Dev
IMU
AC
INS
Land
Nav
Ship
Nav
Gyros
1995 on the LN-251 INS product. The LN-251 entered
production in 2001 and is now in high rate production.
Navigation Systems Division began development
of the LN-260 product in 2005. This fiber-optic gyro
inertial navigation system was specifically designed
for the F-16 fighter aircraft and it was recently selected
for this aircraft by the U.S. Air Force.
In 2003, Navigation Systems Division began
development of the LTN-101E INS product for the
commercial airline market using fiber-optic gyros. The
LTN-101E is scheduled to be certified on Airbus
aircraft in 2008.
Litef started the development of the LTR-97 in
1997. This unit is a fiber-optic gyro vertical
gyro/directional gyro replacement for the commercial
airline market, which began production in 1999.
Commercial

A land navigation version of the LN-251,
designated the LN-270, began development in 2003.
The LN-270 provides position and pointing
information to land based artillery and to forward
observation vehicles.
Litef began the development of its fiber optic land
navigation systems in 1994 is producing three
versions, the LLN-G1, the LLN-GX, and the
LLN-GY. Production of these units began in 1995.
Litef started development of the LFK-95 in 1995.
It is a commercial ship’s navigator product that was
first produced in 1997.
Fibersense developed a single axis FOG 200
product and also single axis gyros for space programs
starting in 1998.
Litef started development of its uFORS line of
single axis, fiber-optic gyro rate sensors in 1990. Four
major subfamilies exist with performance ranging
from 1 to 36° per hour.
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3
FIBER GYRO ARCHITECTURE
The fiber-optic gyros used in Northrop Grumman
fiber optic inertial products share many design
characteristics. Figure 3 is a generic schematic of the
optical circuit of a typical Northrop fiber-optic gyro.
The gyro optical circuit is reciprocally configured 5 and
utilizes a multifunction integrated optic chip (MIOC)
manufactured in LiNbO3 using proton exchange
technology 6 to create the polarizing waveguides. The
MIOC contains a polarizer, a Y junction coupler, and
an electro-optic phase modulator.
The light source is a broadband light source 7,8,9,10
the wavelength of which varies from product to
product. Typical wavelengths are in the 800 nm and
the 1500 nm bands where optical fibers and optical
components are readily available. Some products use a
single light source per gyro axis, while other products
share a single light source between two or three axes.
A semiconductor photodetector is used to convert the
light exiting the gyro into an electrical signal so it can
be processed to measure the rotation rate.
All of Northrop’s fiber-optic gyros are operated in
a closed loop mode using variants of the dual loop,
digital serrodyne technique pioneered by Arditty and
Lefevre 11 .
Figure 3. Optical Schematic of a Typical Northrop Fiber-Optic Gyro

IMU PRODUCTS
Figure 4 shows the LN-200 IMU which consists of
three fiber-optic gyroscopes, three micromachined
silicon accelerometers and a microprocessor. It senses
acceleration and rotation about three orthogonal axes
and outputs temperature compensated incremental
angles and incremental velocities.
The IMU is 3.5 inches in diameter and is 3.35
inches high. It weighs approximately 750 grams. It
utilizes an RS-485 digital bus to interface with the
using platform. This product family has been in
production for over 14 years and over 13,000 IMUs
have been sold.
Figure 5 shows typical fiber-optic gyro bias and
scale factor yields from the production line.
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Frequency
Frequency
80
70
60
50
40
30
20
10
0
80
70
60
50
40
30
20
10
0
4
Figure 4. LN-200 IMU
-90 -60 -30 0 30 60
Gyro SF Residuals (ppm)
Figure 5. Typical LN-200 Fiber-Optic Gyro Bias and Scale Factor Yields

The LN-200 is used in a wide variety of
applications including torpedoes, missiles, fixed and
rotary wing aircraft, radars, targeting pods, spacecraft,
surveying systems, camera stabilization, and in many
other applications.
The LN-200 is also used as a building block for
other inertial systems. One such system is the LISA
200 AHRS manufactured in Europe. It is shown in
Figure 6 below. The unit is approximately 7 × 4 × 4.5
inches in size and weighs 4.5 pounds. It contains both
digital input/out (ARINC 429, Military Standard 1553,
and RS-422/485) along with an analog synchro output
(ARINC 407). Approximately 300 systems have been
delivered to customers.
Figure 7 shows the LCR 92 and LCR 93 AHRS
units also manufactured in Europe. The two systems
are externally identical and they both utilize three
fiber-optic gyros. The LCR 92 uses a bubble level for
sensing local level while the LCR 93 uses three silicon
MEMS accelerometers. Both digital and synchro
outputs are provided. Over 5,500 LCR systems have
been delivered to many customers and production is
ongoing.
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Figure 6. LISA 200 AHRS system
5
Figure 7. LCR 92/93 AHRS Products
The IMU 600 is a high performance unit which is
used for precision pointing applications. It uses three
fiber-optic gyros and three quartz accelerometers in a
non-orthogonal configuration to reduce the volume
occupied. The IMU is 5.4 × 7.5 × 2.7 inches and weighs
approximately 3.25 pounds. It uses an RS-485 serial
interface and outputs uncompensated incremental
angles and velocities. Compensation for thermal
sensitivity is performed in the computer of its host
vehicle. Figure 8 shows the IMU 600. Over 200 IMU
600s have been delivered.
Figure 9 shows scale factor data from the
calibration verification for approximately 140 IMU
600s. The scale factor is well within the specification.
The last IMU product that will be described is the
IMU 200, which is shown in Figure 10. It utilizes three
fiber-optic gyros and three quartz accelerometers. The
IMU weighs approximately three pounds and utilizes
an RS-485 serial interface. Approximately 30 have
been delivered. It is primarily used in very high
reliability missile applications.
Figure 8. The High Performance
IMU 600

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Bias Error (deg/hr)
Scale Factor Error (PPM)
0.10
0.08
0.06
0.04
0.02
0.00
100
80
60
40
20
0
6
Gyro 1
Gyro 2
Gyro 3
100 110 120 130 140 150 160 170 180 190 200 210
Gyro 1
Gyro 2
Gyro 3
IMU SNE
40 60 80 100 120 140 160 180
IMU Serial Number
Figure 9. FOG-600 IMU Bias and Scale Factor Error at Calibration Verification
for Over 100 IMUs

INS PRODUCTS
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Figure 10. The IMU 200
Inertial navigation systems use their gyros and
accelerometers to compute current position and
velocity from a given starting position. Northrop
Grumman’s Navigations Systems Division has built
inertial navigation systems since the 1960s. Its early
systems used mechanical platforms with floated and
dry tuned mechanical gyros. Strapdown systems,
utilizing ring laser gyros (RLGs) which required
mechanical dithering, started production in the 1980s.
Zero lock gyros required no mechanical dither and
they replaced RLGs at Navigation Systems Division in
the 1990s.
Development of inertial grade fiber-optic gyros
started in the mid-1980s and production of fiber-optic
gyro based inertial navigations systems started in
2001. The first fiber-optic-gyro-based INS product
was the LN-251 system shown in Figure 11. Its
officially designation is the AN/ZSN-1.
Figure 11. LN-251 Fiber Optic INS
7
The LN-251 contains a 12 channel Selective
Availability Anti-Spoofing Module (SAASM) GPS
receiver in a tightly coupled configuration. It
propagates three position solutions: free inertial, GPS
only, and blended INS/GPS. It utilizes digital
interface: RS-422/485 and dual Military Standard
1553 digital buses.
Over 400 LN-251 and LN-270 systems have been
produced and delivered. Figure 12 shows the
distribution of free inertial performance at Acceptance
Test Procedure in the factory. The mean of the
distribution is 0.7 nautical miles per hour (nmph) with
a standard deviation of 0.3 nmph. The systems are
available in 0.8, one, two, and five nmph navigation
performance ranges.
Figure 12. Free Inertial Navigation
Performance at ATP for the LN-251/LN-270
Systems
Figure 13 depicts the LN-260, which is a variant
of the LN-251, developed for use on the F-l6. It
implements the full interface requirements of SNU-84
and has the required analog and mechanical interfaces
for the F-16.
The LN-260 system has been flight tested on a
Northrop Grumman Sabreliner, where it was used to
stabilize the Synthetic Aperture Radar (SAR) antenna.
Figure 14 shows the SAR image of Fort McHenry
taken during the flight test. The system satisfies all
SAR requirements.
Figure 15 depicts the flight test data from a F-16
aircraft. The aircraft was pulling nine gravities in tight
turns. The radial position error rate for this flight was
0.44 nmph, well under the 0.8 nmph specification.

Latitude (deg)
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33.05
33
32.95
32.9
32.85
32.8
32.75
32.7
32.65
Figure 13. LN-260 INS/GPS
F16[1] C015.1539.00015.BNG016.bd01.mat
32.6
32.55
-99 -98.8 -98.6 -98.4 -98.2 -98 -97.8 -97.6 -97.4
Longitude (deg)
COMMERCIAL PRODUCTS
8
Figure 14. Synthetic Aperture Radar Image of
Fort McHenry Obtained Using the LN-260 to
Stabilize and Navigate the SAR Antenna
Figure 15. LN-260 Flight Test Trajectory (left) on an F-16 and
Radial Position Error Rate Versus Time (right)
The LTN-101E (Figure 16) uses fiber-optic gyros
in a four MCU package for use on commercial
transport aircraft. The LTN-101E also uses navigation
grade silicon MEMS accelerometers. It performs both
a navigation function and an air data function and
integrates with an external GPS receiver.
The graph on the left of Figure 17 shows the free
inertial position error during a 15 hour static
laboratory navigation test. The green line indicates the
two nautical mile per hour (nmph) performance
requirement and the red line is the radial position error
rate (1.69 nmph) for the first hour of testing. The
graph on the right in Figure 17 shows the free inertial
position error for a flight test that lasts over 10 hours.
The LTN-101E readily meets its free inertial
performance requirements.
The LTN-101E is in development and
qualification and will start production in 2007. It will
be DO-178 certified.
Another fiber-optic gyro product for commercial
transport aircraft is the LTR-97. This a replacement for
an old mechanical direction gyro/vertical gyro
(DG/VG) system used on older transport aircraft. It
provides synchro outputs for pitch, roll, and heading,
analog outputs for pitch and roll, and discrete outputs.
It is DO-178A certified. Over 300 systems have been
delivered to date and production is ongoing.

Figure 16. LTN-101E Navigation and Air Data
System
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9
LAND NAVIGATION PRODUCTS
Figure 19 shows the land navigation version of the
LN-251 designated the LN-270. The US Army
designation for it is the AN/VSN-12. It is designed for
use in wheeled or tracked vehicles and adds odometer
aiding, the ability to use a Precision Lightweight GPS
Receiver (PLGR) external GPS receiver instead of the
embedded SAASM receiver and software unique to
land navigation. It meets all requirements of Military
Performance Specification 71185 including
specifications for gunfire shock. These systems are
typically mounted on the trunnion of the cannon and
see the full recoil of the gun firing.
Figure 17. LTN-101E Free Inertial Position Error Versus Time.
The graph on the left is a static lab test. The graph on the right is a flight test on a commercial aircraft.
Figure 18. LTR-97 DG/VG Replacement
Figure 19. LN-270 Land Navigation INS

Figure 20 shows a van test of an LN-270 system in
the San Fernando Valley area of Los Angeles. The top
graph shows the path and elevation, while the bottom
graph shows the position and altitude errors versus
distance traveled. The error limits on the graphs are
from Military Performance Specification 71185.
Figure 21 shows the LLN-GX, LLN-G1, and the
LLN-GY land navigation systems manufactured by
Northrop Grumman in Europe. The GX and the G1 are
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10
similar and they both have three fiber-optic gyros. The
GX uses two level sensors for reduced cost while the
G1 uses three accelerometers for higher accuracy. The
LLN-GY is the lowest cost of the three. It uses a single
fiber-optic gyro sensing rotation about the vertical axis
and two accelerometers. Over 1,700 of these systems
have been manufactured and delivered. Production is
ongoing.
Figure 20. LN-270 Van Test Position and Altitude (top) and North, East, and Horizontal Position
Errors (bottom).
The lines on the top graph show the performance limits in Military Performance Specification 71185.

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Figure 21. From left to right, LLN-GX, LLN-G1, and LLN-GY Land Navigation Systems
SHIP’S NAVIGATOR PRODUCTS
Northrop Grumman manufactures the LFK-95
gyrocompass and reference system for commercial
shipping. This was the world’s first marine fiber-optic
gyro based gyrocompass and was designed specifically
for high speed craft such as hydrofoils. It supports a
variety of digital and synchro interfaces for
compatibility with a broad range of watercraft. To date
650 systems have been sold to a wide range of
customers and production is ongoing. Figure 22 shows
the system. Vessels using the LFK-95 system include
ships, hydrofoils, and unmanned underwater vehicles.
Figure 22. LFK-95 Marine Gyro Compass
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FIBER OPTIC RATE SENSOR PRODUCTS
Northrop Grumman also sells many single axis
fiber-optic gyro rate sensors. These gyros are modular
and sold either standalone or combined into an IMU.
The uFORS line has been in production the
longest of any fiber optic rate sensor. To date over
7500 rate sensors and IMUs have been delivered and
the product line continues in production. Figure 23
shows the four major subfamilies in the uFORS
product line.
Each uFORS is a fully contained, single axis,
fiber-optic gyro rotation sensor. The uFORS-36 was
the first product developed and it had 36° per hour bias
accuracy. With the improvement of optical
components, the bias accuracy was improved. The
uFORS-6U was developed next with a six degrees per
hour bias accuracy followed by the uFORS-1 with a
one degree per hour bias accuracy. Scale factor
repeatability is around 1000 ppm. The units draw two
watts of power and have a digital output. The weight
of the uFORS-36 and -uFORS-6U is 0.3 lb and their
size is 0.8 × 2.5 × 4 inches. The uFORS-36m is
miniaturized uFORS-36 with a 36° per hour bias
accuracy for size critical applications.
Another single axis rate sensor product is the
FOG-200. It is available as a single axis assembly that
is fully self-contained as shown in the picture on the
left side of Figure 24. The rate sensing element can be
packaged remotely from the electronics for special
applications as shown in the middle picture of
Figure 24 for a two axis rate sensor. The right-hand
picture shows a three axis, remote sensing, rate sensor
package.

Figure 23. uFORS Product Line (left to right): uFORS-1, uFORS-36m, uFORS-6U, and uFORS-36
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Figure 24. FOG-200 Product Family
From left to right: FOG-200 single axis, self contained rate sensor; two axes, remote sensing rate
package; three axes, remote sensing package.
Figure 25 shows a variant of the FOG-200 that
was developed for a space launch application in which
the fiber-optic gyro had to operate through a 200 g rms
vibration environment.
Figure 25. High Vibration Environment
Version of the FOG-200 Single Axis Rate
Sensor
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SUMMARY
In the last fifteen years, Northrop Grumman
Navigation Systems Division has delivered
approximately 22,000 fiber-optic gyro based inertial
system products and 7,500 individual fiber-optic gyro
rate sensors. This represents nearly 75,000 axes of
fiber-optic gyros. The vision that Vali and Shorthill
gave the world is no longer just a vision. The vision
has been achieved. It is a reality.

REFERENCES
1
G. Sagnac, “L’ether lumineux demontre par l’effet du vent relatif d’ether dans un interferometre en rotation uniforme” C.R.
Acad. Sci., vol. 95, pp 708-710, 1913.
2
W. M. Macek and D. T. M. Davis, “Rotation rate sensing with traveling wave ring lasers”, Appl. Phys. Lett., vol. 2, pp 67-
68, 1963.
3 V. Vali and R. W. Shorthill, “Fiber Ring Interferometer”, Appl. Opt., vol. 15(5), 1099, 1976.
4
G. Pavlath, “Challenges in the development of the IFOG”, AIAA-2003-5763, AIAA Guidance, Navigation and Control
Conference, Austin, Texas, August 11-14, 2003.
5
K. Bohm, P. Russer, E. Weidel, and R. Ulrich, “Low-noise fiber-optic rotation sensing”, Opt. Lett., vol. 6(2), pp 64-66,
1981.
6
M. Papuchon and C. Puech, “Integrated Optics: a possible solution for the fiber gyroscope”, Proc. SPIE vol. 157, pp 218-
219, 1978.
7
K. Bohm, P. Marten, K. Petermann, E. Weidel, “Low-drift Fibre Gyro Using a Superluminscent Diode”, Electron. Lett., Vol
17(10), pp 352-353, 1981.
8 R. A. Bergh, B. Culshaw, C. C. Cutler, H. C. Lefevre, and H. J. Shaw, “Source statistics and the Kerr effect in fiber-optic
gyroscopes”, Opt. Lett., vol. 7(11), pp 561-565, 1982.
9 W. K. Burns and R. P. Moeller, “Polarizer Requirements for Fiber Gyroscopes with High-Birefringence Fiber and Broad-
Band Sources” J. Lightwave Tech., vol. LT-2(4), pp 430-435, 1984.
10
M. J. Digonnet, P. F. Wysocki, B. Kim, H. J. Shaw, “Broadband fiber sources for gyros”, Proc. SPIE, vol 1585, pp 371-382,
1991.
11
H. C. Lefevre, J. P. Bettini, S. Vatoux, and M. Papuchon, “Progress in Optical Fiber Gyroscopes using Integrated Optics”,
AGARD CPP-383, 9A/1-l3, 1985.
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Strategic Programs & Business Development
(SP&BD), Navigation Systems Division
One of the main functions of the SP&BD organization is to
sustain NSD’s competitive advantage in all of its product
lines by providing cutting edge technologies that supply
entirely new capabilities to the marketplace and also
enhance its current products.
Ike J. Song, Director of SP&BD
ike.song@ngc.com
For more information, please contact:
Northrop Grumman Corporation
Navigations Systems
21240 Burbank Boulevard
Woodland Hills, CA 91367 USA
1-866-NGNAVSYS (646-2879)
www.nsd.es.northropgrumman.com
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