Dual-Polarization Two-Port Fiber-Optic Gyroscope

106 Pages·2017·3.588 MB·English

by  Zinan Wang (auth.)

Springer Theses
Recognizing Outstanding Ph.D. Research
Zinan Wang

Dual-Polarization
Two-Port Fiber-
Optic Gyroscope
Springer Theses
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Zinan Wang
Dual-Polarization Two-Port
Fiber-Optic Gyroscope
Doctoral Thesis accepted by
Peking University, China
123
Author Supervisor
Dr. ZinanWang Prof. ZhengbinLi
Data Center(Beijing) State Key Laboratoryof AdvancedOptical
Agricultural Bank of China Communication SystemsandNetworks,
Beijing Departmentof Electronics
China PekingUniversity
Beijing
China
ISSN 2190-5053 ISSN 2190-5061 (electronic)
SpringerTheses
ISBN978-981-10-2835-9 ISBN978-981-10-2836-6 (eBook)
DOI 10.1007/978-981-10-2836-6
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’
Supervisor s Foreword
Gyroscopes are sensors for measuring angular velocity, which are widely used for
industrial and militarily applications, such as motion attitude control, antenna
locking, inertial guidance, navigation, and building deformation detection. The
fiber-optic gyroscope has developed rapidly in recent 30 years. Especially, the
interferometric fiber-optic gyroscope (IFOG) is the mostly popular and the most
maturetype.HighersensitivityandlowercostaretwodevelopinggoalsforIFOGs.
There is a generally used model for designing IFOGs, which is called the
“minimal scheme.” The “minimal scheme” has obvious advantages as it ensures
reciprocity between light paths in the IFOG, but it also has limitations. In IFOGs
based on the conventional “minimal scheme,” two couplers are required to ensure
reciprocity. The two couplers may be replaced by circulators, Y-junction waveg-
uides,orotherfunctionallysimilardevices,butthenumberofopticaldevicescannot
bereducedtoone.This“two-coupler”structure isusedtoensurebothpolarization
reciprocity and coupler reciprocity. In this case, the free port of the coil coupler is
definedasanonreciprocalport,anditisgenerallynotfeasibleforsignaldetection.
It is well known that optical fiber supports the propagation of two orthogonal
polarization modes, so sensing with two polarizations is the natural potential of
IFOG. Similar to the polarization multiplexing in the field of optical fiber com-
munication, the simultaneous use of two polarization states will bring additional
signal, also bring new features. In Zinan Wang’s thesis, dual-polarization two-port
IFOGisinvestigated.Itisprovedthatpolarizationerrorcanbecompensatedwhen
two polarizations are simultaneously used in an IFOG. The polarization nonre-
ciprocity errors on two orthogonal polarizations have opposite signs, so that the
fluctuation errors can be compensated by direct adding up two signals. As long as
the two polarizations are balanced in power and incoherent, the PN errors can
naturally compensate each other. They can be outputted at the same port, and thus
light intensities are directly superimposed at the photodetector, in optical domain.
This superimposition process is a convenient way to achieve polarization fluctua-
tion error compensation, and we call it optical compensation.
v
vi Supervisor’sForeword
Intheopticallycompensateddual-polarizationIFOG,absolutereciprocityisnot
required, as the nonreciprocal errors are eliminated by the compensation mecha-
nism. One of its special features is that the nonreciprocal port and reciprocal port
are theoretically similar, both of which have error compensation mechanism and
canobtainstableangularvelocityoutput.Therefore,twopossiblebeneficialdesigns
areavailable:oneistwo-portdetection,andthetwosignalscanbeprocessedjointly
bypropertwo-channelalgorismsforfurthernoisereduction.Anotherapplicationis
toachieveasinglecouplerIFOG,withaverysimplestructureandverylowcostto
achieve stable performance.
So,wecanseethatZinanWang’sthesisbringsanewsolutiontothepolarization
fluctuation problem in IFOGs, and breaks through the limit of the conventional
“minimal scheme,” where polarization errors are suppressed by polarization fil-
tering. The “minimal scheme” eliminates one polarization of light and keeps the
otherforrotationsensing,andthenapolarizerandseveralpolarizationcomponents
areusedintheconventionalIFOGs.Ontheotherhand,thedual-polarizationIFOG
suppressespolarizationerrorsbymutualcompensationwithtwopolarizationsofthe
light in optical domain. Its structure can be built up with normalsingle mode fiber
components.Differentfromthesinglepolarizationrequirementoftheconventional
structure,thedual-polarizationIFOGrequirestwopolarizationswhicharebalanced
in power and mutually incoherent.
Mathematical models and experimental verifications of the optically compen-
sated dual-polarization IFOG are presented in Zinan Wang’s thesis. These new
findings will have important impacts in the field of IFOG designing. In principle,
thedual-polarizationIFOGhasmanyadvantages.Itrelaxestheabsolutereciprocity
requirements and it has two feasible detection ports. The research group in Peking
University is still conducting further researches to make it practical. In the long
term, when dual-polarization IFOG has accumulated enough designing experience
and engineering optimization skills, it will achieve higher accuracy and stability
while requiring less complexity and cost. Therefore, the dual-polarization IFOG
will definitely promote the IFOG development for broader applications.
Beijing, China Prof. Zhengbin Li
November 2016
Abstract
Gyroscopes arerotation sensors.Theyare widely usedfor many purposes,suchas
motion attitude control, inertial guidance, navigation, antenna orientation, building
deformation detection. Fiber-optic gyroscopes (FOG) are constructed based on the
Sagnac effect, and they have been developing fast during the past three decades.
The interferometric fiber-optic gyroscope(IFOG)isthemost mature kind ofFOG,
and it hasbeen most intensivelystudied.Conventionally,the “minimalscheme”is
regardedasthebasicmodelfordesigningIFOGs.Itacquiresonepolarizerandtwo
couplers for assuring both polarization reciprocity and coupler reciprocity. The
basicfeatureofthe“minimalscheme”isthatonlyonepolarizationisremained,and
only one port is used for detection.
Inthisdissertation,dual-polarizationtwo-portIFOGisinvestigated.Itisshowed
that polarization error can be compensated when two polarizations are used
simultaneously. The polarization nonreciprocity (PN) errors on two orthogonal
polarizations have opposite signs, so that the errors can be compensated by direct
adding up two signals in optical domain or in electric domain. A mathematical
model is established for studying the error compensation mechanism. Simulation
and experiment are both applied for observing its inner process and the effective-
ness for noise suppression. Furthermore, the basic requirements for PN error
compensation are provided.
Based on the theory model, a dual-polarization IFOG with a depolarized fiber
loopisproposed.InthisIFOGconfiguration,PNerrorcompensationisachievedin
optical domain. Both theory analysis and experimental results show that no
polarizer or polarization maintaining device are required when applying optical
compensation. In addition, the fiber loop is constructed by ordinary single mode
fiber, so the total cost of the IFOG is promising to be suppressed. The
dual-polarization IFOG with optical compensation is an alternative way for IFOG
designing besides the principle of the “minimal scheme.”
Furthermore, another specific feature of the dual-polarization IFOG is discov-
eredthatitsnonreciprocalportisfeasible.OpticalcompensationsuppressesthePN
error at the nonreciprocal port in the same way as at the reciprocal port.
Beneficially,bothtwoportscanobtaintableoutput.Inthiscase,two-channelsignal
vii
viii Abstract
processing algorithms can be applied for further noise suppression. The syn-
chronous difference method is applied as an example to prove the potential per-
formance improvement by two-port sensing. As the nonreciprocal port is feasible,
two couplers are no longer necessary. In this dissertation, we propose and test an
ultra-simple dual-polarization IFOG where only one coupler is used. In this way,
the restriction of the “minimal scheme” is broken through.
At last, an engineering prototype of the dual-polarization IFOG is tested. It
obtains a bias stability of 1 (cid:1) 10−2 °/h in a 20-hour room temperature test. In the
turntable test, it achieves a scale factor nonlinearity of 150 ppm. This test proves
that the optical compensation theory is valid and the dual-polarization two-port
IFOG is applicable.
In conclusion, this dissertationhas studied a basic structure of dual-polarization
two-port IFOG. The mechanism of PN error compensation and the corresponding
mathematicalmodelareprovided.Experimentsarealsoappliedtoverifythetheory
model. The dual-polarization two-port IFOG breaks through the restriction of the
“minimalscheme.”ItalsobringsnewpossibilityforIFOGstoreachlowercostand
higher sensitivity.
(cid:3) (cid:3)
Keywords Fiber-optic gyroscope Polarization nonreciprocity error Optical
(cid:3) (cid:3)
compensation Dual polarization Two-port detection
Parts of this thesis have been published in the following journal articles:
[1] Z. Wang, Y. Yang, Y. Li, X. Yu, Z. Zhang, and Z. Li. Quadrature demod-
ulationwithsynchronousdifferenceforinterferometricfiber-opticgyroscopes.
Opt Express, 2012, 20: 25421–25431
[2] Z. Wang, Y. Yang, P. Lu, Y. Li, D. Zhao, C. Peng, Z. Zhang, and Z. Li.
All-Depolarized Interferometric Fiber-Optic Gyroscope Based on Optical
Compensation. IEEE Photon J, 2014, 6: 7100208
[3] Z. Wang, Y. Yang, P. Lu, C. Liu, D. Zhao, C. Peng, Z. Zhang, and Z. Li.
Optically compensated polarization reciprocity in interferometric fiber-optic
gyroscopes. Opt Express, 2014, 22: 4908–4919
[4] Z. Wang, Y. Yang, P. Lu, R. Luo, Y. Li, D. Zhao, C. Peng, and Z. Li.
Dual-polarization interferometric fiber-optic gyroscope with an ultra-simple
configuration. Opt Lett, 2014, 39: 2463–2466
[5] Y. Yang, Z. Wang, and Z. Li. Optically compensated dual-polarization
interferometric fiber-optic gyroscope. Opt Lett, 2012, 37: 2841–2843
[6] Y. Yang, Z. Wang, C. Peng and Z. Li. Unbiasedness of simultaneous inde-
pendent measurement. Meas Sci Technol, 2012, 23: 085005
[7] Y. Yang, Z. Wang, C. Peng and Z. Li. Multidimensional gray-wavelet pro-
cessing in interferometric fiber-optic gyroscopes. Meas Sci Technol, 2013,
24: 115203
[8] Y. Li, Z. Wang, Y. Yang, C. Peng, Z. Zhang, and Z. Li. A multi-frequency
signal processing method for fiber-optic gyroscopes with square wave mod-
ulation. Opt Express, 2014, 22: 1608–1618
[9] Y. Li, Z. Wang, C. Peng, Z. Li. Signal subspace analysis for decoherent
processes during interferometric fiber-optic gyroscopes using synchronous
adaptive filters. Appl Optics, 2014, 53: 6853–6860
ix