Fiber-based Radio Frequency Dissemination for Branching Networks with Passive Phase Noise Cancellation

0.34 MB·English

by  Y. Bai

Fiber-based Radio Frequency Dissemination for Branching Networks
with Passive Phase Noise Cancellation
Y. Bai,1,3 B. Wang,1,2,∗, C. Gao,1,2 J. Miao,1,3, X. Zhu,1,3, and L. J. Wang1,2,3,4∗
1Joint Institute for Measurement Science, Beijing 100084, China
2Department of Precision Instruments, Tsinghua University, Beijing 100084, China
3Department of Physics, Tsinghua University, Beijing 100084, China
4National Institute of Metrology, Beijing 100013, China
∗Corresponding author: [email protected], [email protected]
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1
0 CompiledJanuary15,2015
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We demonstrate a new fiber-based radio frequency dissemination scheme for branching networks. Without
n any phase controls on RFsignals or usages of active feedback locking components, the highlystable reference
a frequencysignalcanbedeliveredtoseveralremotesitessimultaneouslyandindependently. Relativefrequency
J stability of 6×10−15/s and 7×10−17/104s is obtained for 10km dissemination. The proposed low cost and
scalable method can be applied to some large-scale frequency synchronization networks. (cid:13)c 2015 Optical
4
SocietyofAmerica
1 OCIS codes: 120.3930, 120.3940,060.2360.

]
s
c
Over the past two decades, highly stable dissemina- schemes is how to compensate the fiber induced phase
i
t tion of time and frequency signals via optical-fiber links fluctuation. To our knowledge, including the recently
p
o has developed considerably and shown broad applica- demonstratedopticalfrequencydisseminationtechnique
. tion prospects [1–3]. Different schemes, such as optical for branching optical-fiber network [24], almost all ex-
s
c frequency dissemination [4,5],radio frequency (RF) dis- isting schemes are developed based on the active phase
i semination [6,7], and optical frequency comb signal dis- locking method proposed in 1994 by Ma et al [1]. The
s
y semination [8,9] have been proposedand demonstrated, costandreliabilityaremainlimitingfactorsforthelarge-
h respectively. However, almost all of these schemes have scale application of conventional active fiber-based fre-
p
a common “point-to-point” structure, as shown in Fig- quency dissemination schemes.
[
ure1(a),namelythereisonlyonereceivesitecorrespond-

1 ing to single transmit site. Despite of its high stability,
v
the limited accessibility largely limits further develop-
1
mentofthefiberbasedfrequencydisseminationtechnol-
3
3 ogy.
3 To overcomethis mainly drawback,fiber-basedmulti-
0 access ultrastable radio and optical frequency dissemi-
.
1 nation schemes have been proposed and demonstrated
0 [10–15]. Using this method, highly synchronized RF
5 modulation signal or the optical signal itself can be re-
1
covered at any arbitrary points along the fiber link, as
:
v shown in Figure 1(b). To extend the frequency dissemi-
i
X nationdistance,cascadedfrequencydisseminations(Fig-
ure1(c))havebeendemonstrated[16].Alongwithdevel-
r Fig. 1. (Color online) Topological structure dia-
a opmentsofrelatedtechnologiesandimprovementsofob-
gram of different fiber based frequency dissemination
servation accuracy, more and more large scale scientific
schemes. (a)The conventional point-to-point dissemina-
and engineering facilities such as radio astronomicalob-
tion scheme. (b)Muti-access at an arbitrary point along
servation [17–19] and deep space navigation (DSN) net-
the fiber link.(c)Cascade dissemination scheme with re-
work[20,21]requiredisseminationofreferencefrequency
lay stations. (d)Branching fiber network dissemination
signalsfromacertaincentersitetomultipleremotesites
scheme.
overabranchingfiber network,asshowninFigure1(d).
Take the Square Kilometer Array (SKA) project as an Inthisletterweproposeanddemonstrateanewfiber-
example, which represents one of the largest and most basedRF disseminationscheme for branching networks.
challenging timing and synchronization network today Usingthe passivephasenoisecancelationmethod,with-
[22]. Thousands of antennas are quasi-randomly distrib- out any phase controls on RF signals or usages of feed-
uted in a broadly symmetric array around the core, at backlockingcomponents,thehighlystablereferencefre-
where the reference clock ensemble is located [23]. The quency signal can be delivered to remote sites simulta-
key challenge of all fiber based frequency dissemination neously and independently. For 10 km distance dissemi-
1
PD MIXER
E E
A 1 4
OSC
E
B
2
E
3
C D E C Laser C
Monitor
Remote
WDM
Site C
E
A
3f
Laser A 2km 3km 5km
EDFA
Remote
H Maser
Site E
circulator
E Fiber
ref
f Laser B Link
Local
Remote
E
B Site
Site D
Fig. 2. (Color online)Schematic diagram of the fiber based radio frequency dissemination scheme for branching
networks with the passive phase noise cancellation method.
nation, relative frequency stability of 6×10−15/s and tively.Afterpassingafibercouplerandacirculator,two
7 × 10−17/104s is obtained. This simple and scalable modulated laser signals are coupled into the same fiber
scheme can be used to construct the frequency synchro- link and delivered to all remote sites.
nization network of DSN and SKA. The structures of remote sites are almost the same
Figure 2 shows the schematic diagram of the passive exceptthewavelengthsoflasermodules.Here,wechoose
frequency dissemination for branching network experi- the remote site C to explainthe concept. At remote site
ment. As a laboratorial demonstration, the branching C, a wavelength division multiplexer (WDM) is used to
network consists of one local site, three remote sites (C, separate two received laser signals. The disseminated rf
D, E), and three fiber spools with lengths of 2km, 3km signalscanbe recoveredbytwohighspeedphoto-diodes
and 5 km. Consequently, remote sites C, D, E are 2km, (PD). They can be expressed as
5kmand10kmawayfromthelocalsite,respectively.For
the convenience of relative frequency stability measure- E1 =V1cos(3ωt+3φ0+3φp), (1)
ment, the whole system is locatedatthe same lab.Con-
sidering the requirements of status monitor and error E2 =V2cos(ωt+φ0+φp), (2)
diagnose in practical applications, we also add an addi- where φ represents the fiber link induced phase fluc-
p
tional monitor part. The optical power and RF wave- tuation for the 1GHz signal E . As mentioned above,
B
forms of all remote sites can be monitored at the center E and E have certain triple relationships for both
A B
station. frequency and phase, and they are disseminated in the
At local site, the 100MHz frequency signal of a com- same fiber simultaneously. Consequently, the fiber link
mercial Hydrogen maser is employed as the reference inducedphasefluctuationforthe3GHzsignalE is3φ .
A p
frequency of whole branching network. It can be ex- The recovered frequency signal E2 is used to modulate
pressed as E = V cos(ω t + φ ). Two phase- the amplitude of another laser C, whose wavelength is
ref ref ref ref
locked dielectric resonant oscillators (PDRO) with fre- 1550nm.Themodulatedlasersignalissentbacktolocal
quencies of 3 GHz and 1 GHz are phase locked to E , site and return to remote site C again with the help of
ref
and can be expressed as EA = VAcos(3ωt+3φ0) and two fiber circulators.After detected by another PD, the
EB = VBcos(ωt+φ0), respectively. The frequency and recovered1 GHz frequency signal can be expressed as
phase of E and E have certain triple relationships.
A B
Theyareusedtomodulatethe amplitude oflaserAand E3 =V3cos(ωt+φ0+3φp). (3)
B, whose wavelengths are 1542nm and 1547nm, respec-
BysimplymixingdownthesignalsE1 andE3,wecan
2
(cid:7206)(cid:19492)(cid:20161)(cid:10679)(cid:13697)(cid:13580)(cid:12138)(cid:5951)(cid:3374)
obtain a 2 GHz signal
Transmitting side Client 1
active compensation
E4 =V4cos(2ωt+2φ0). (4) Client side passive
compensation
We can see the fiber induced phase fluctuation φ has
p Client 2
been passively compensated.
Time keeping
To distinguish the round trip signals of each remote point 1
site, the laser modules’ wavelengths inside remote sites
D and E are chosen as 1552nm and 1555nm, respec-
Time keeping Coordinated Client 3
tively. Thanks to the mature dense wavelength division point 2 point
multiplexing (DWDM) technology, laser carriers’ wave-
lengths can be as near as 0.4 nm. This will significantly Time keeping
point 3
reduce the chromatic dispersion impact on the dissemi-
Client 4
nation stability and expand the quantity of remote sites
to dozens or even hundreds.
Client N

-12
10
Fig. 4. (Color online) Schematic diagram of a regional
-13 time and frequency synchronization network.
10
n
o
ti -14
a10 As a primary application example, we take a brief in-
vi
e troduction of the Beijing regional time and frequency
D
n 10-15 synchronizationnetworkwhichisunderconstruction.As
a
All C free running showninFig.4,thesynchronizationnetworkcanbesep-
C compensated arated into three parts - time keeping stations, coordi-
-16
10 D free running
D compensated nating station and client sites. The time keeping points
E free running aretheinstituteswhichmaintainthenationalorregional
E compensated
-17
10 official times. Using the conventional active compensa-
0 1 2 3 4
10 10 10 10 10
tion scheme [7], a time keeping station can perform fre-
Averaging Time (s) quencycomparison,andtransmititstime-frequencysig-
nal to a central coordinating station. Here, the received
Fig.3.(Coloronline)Measuredrelativefrequencystabil-
time-keeping signals can be compared in real time to
ities of frequency signals at three remote sites C, D and
generate a coordinated time-frequency signal. Then the
E with and without phase noise passively compensated.
coordinatedfrequency canbe disseminatedbackto each
time keeping stations and forward to all user clients
Through mixing EA and EB at local site, we can get via the proposed passive compensation method. As one
Emix = Vmixcos(2ωt + 2φ0). To measure the dissemi- transmittingmodule canbe linkedwith multiple remote
nation stability of the compensated fiber link, we just sites,theexpansionoffuturedisseminationchannels(ex-
measure the relative frequency stability of Emix and E4 pansion of the clients) will not have significant impact
and analyze the phase error. We also compare EA and on the coordinating station’s basic structure.
E1 to measure dissemination stability of the free run- Insummary,wehavedemonstratedanewfiber-based,
ning fiber link. Similar procedures are taken for remote radiofrequencydisseminationschemeforbranchingnet-
sites D and E. In order to verify that all remote sites work. Using the method, stable, distributed RF signals
are independent and the proposed scheme is feasible for can be simultaneously and independently disseminated
theapplicationofbranchingnetworks,allthesemeasure- to many different remote sites from one central sta-
ments are carried out simultaneously. Figure 3 shows tion. Some scientific construction projects are expected
the measuredAllan Deviation results. Using the passive to benefit from this method.
phase noise cancelation method, dissemination stability We acknowledge funding supports from the National
of6×10−15/sand7×10−17/104sisachievedforremote Key Scientific Instrument and Equipment Development
site E (10km away from the local site). While for the Projects (No.2013YQ09094303).
free-running fiber link, it has dissemination stability of
6×10−13/s and 6×10−14/104s, respectively. We also
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