faheem freqstandardsinhollowfiber
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Portable, robust optical
Frequency standards in hollow
optical fiber
Mohammad Faheem,
Rajesh Thapa, Ahmer Naweed,
Greg Johnson, and
Kristan Corwin
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Motivation
Develop high accuracy Portable WavelengthStandards for Telecommunication
Industry.
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Outline
roadening Me!hanisms and "aturation
"pe!tros!op#
$ntrodu!tion
Fre%uen!# measurement.
&'perimental "et(up
Results
Future )or*
+reious )or*
-imitations
Our Approa!h
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Oer iew
C/0/
?
frequency
Fre%uen!# measurement Fre%uen!# !om1
-aser
23 Torr
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"our!es
Coupler
Fi1er
4emultiple'er
Output Fi1ers
( Channel adjustment in )4M 562/2(6272 nm8 s#stem.
( Cali1ration o9 waelength measurement dei!es.
)aelength 4iision Multiple'
"eparation 1etween
!hannel is 6 nm
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Re!ipe 9or a )aelength "tandard
Atomi! or mole!ular a1sorption lines
( A1solute 9re%uen!# re9eren!e.
( er# sta1le under !hanging enironmental
!onditions
( Good re9eren!es in the 6233 nm region
Good re9eren!es in 6233 nm region
»A!et#lene 56263(62:3 nm8
» 0#drogen !#anide 562;3(6272 nm8
» Ru1idium 56273(62
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A!et#lene 5 Also !alled &th#ne8
0 C C 0
( Colorless and e'tremel# 9lamma1le- 23 transition lines, spa!ed 1# 73(=3 G0> e'tending 9rom
6262nm(62:3 nm
Anti(s#mmetri! C( 0 1ond "tret!hing
C C0 0
"tret!hing i1rations
C0
CC
C0
ν6
ν/
"#mmetri! C( 0 1ond "tret!hing
ν;
ν6?ν; lies in 6.2 m region
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4oppler roadening
m
kT
c
wo Doppler 2ln2
2=δ
$mportant roadening $n $R "pe!tros!op#
A1sorption sample
$O $
>
z w
oe I I )(α −=
@ @is the a1sorption !o99i!ient
22
2
)2/()(2/
4 γ π γ
ε α
+−
=
wwmc
Ne
oo
A1sorption 5eers law8
+ower roadening
s
power
P
P S
S
=
+= 1γ δ
Laser spectroscopy by Wolfgang Demtroder
C/0/ at room temp. B 233 M0> .max2~ power δ
3 233 6333 6233 /333
(;
(/
(6
3
A r 1 i t r a r # A ' i s
Fre%uen!# in M0>
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$mportant 1roadening near $R spe!tros!op#
+ressure 1roadening
and shi9t
∫ ∞
−=+=∆0
))(cos1(2 RdR Rwherev N wbb η σ σ γ
-ine "hi9t
RdR Rwherev N s sessure ))((sin0
Pr η σ σ δ ∫ ∞
==
Transit(Time roadening
)2ln(2)/(4 d vtt =δ
Transit time TdD
Laser spectroscopy by Wolfgang Demtroder
C/0/ 1roadening +5638 B 66.7 M0>DTorr
-ine roadening
C/0/ line shi9t +5638 B 3./< M0>DTorr
233 K0> 9or 3.
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"aturation "pe!tros!op#
• &liminates 4oppler width• Re%uires high +ower 5T#pi!all# ;33 m)
9or a!et#lene8
• 4ominant -ine width
+ressure 1roadening 5B66 M0>DTorr 8Transit(time 1roadening 5!oheren!e
time 1etween laser and mole!ules8+ower roadening
• "ignal "i>e
4epends linearl# on pressure4epends linearl# on sample length
M6M/
- a s e r
Cell
."
4et.
+ump eam +ro1e eam
63E
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Fre%uen!# Measurement
Fre%uen!# C#!lesDse!ond
4e9inition o9 time Caesium 6;; atom
Opti!al 9re%uen!# ((((( $n hundreds o9 T0>
$ts eas# to measure in T0>
+hoto 4ete!tor (((((( $n :3(633 G0>
)hat we need to do
Mode -o!*ing Fre%uen!# Com1
4uration o9 < 6
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Time(Fre%uen!# Corresponden!e
2∆φ
τr .t = 1/f r
t
E(t) ∆φ
0 9 n n 9 r ? 9 o
I (f )
f
9 r
9 o
fr Laser repetition rate
fo Offset D. J. Jones, et al. Science 288, 63 !2""" )
Fourier transform of periodic signal discrete frequency components.
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Measurement o9 9 r and 9 o
9 r !an 1e measured with photo(dete!tor in opti!al path
Repetition Rate
O99set
0 9 /n
I (f )
f
9 n
9 r
9 o
/9 n(9 /n /5n9 rep?9 o8 ( 5/n9 rep?9 o8 9 3
O!tae "panning
( Mi!rostru!ture 9i1er
( -aser Cait#
D. J. Jones, et al. Science 288, 63 !2""" )
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A.C>aj*ows*i,J.& ernard,A.A.Madej,R.".)inler
"el9 re9eren!e 9re%uen!# !om1
f
Hn*nown signal
#pp.Phys.$%&,'(2" !2""')
Hn*nown signal
9 o
9 r
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"olid !ore mi!rostru!ture Fi1er
Fused silica core
1.7 m
(=3
(G3
(73
(23
(:3
(;3
(/3
6/336333=33733:33
laser
spe!trum
633 m)
56 nJ8
"pe!trum roadening
/3 m)
53./ nJ8
)aelength 5nm8
R e l a t i , e + o w e r 5 d 1 8
CladdingCore
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Fre%uen!# !om1 "et(up
Fiber in Fiber outFiber Laser
10 W
1075 nm
HNLF
! "!r#forsterite Laser
$%
nonlinearcrystal
stabili&ed optical
frequency comb
ynt'esi&er
frep Loop
Filter
('ase
$etector
ynt'esi&er
f0 Loop
Filter
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Pre*ious wor+ -.a+a/awa, 0.de 1abachelerie, .#waiand -ouro/i
!J.opt.soc.#4.$5ol.73,o.725Dece4ber7&&6)
- -ong intera!tion length.
- 0igh intra!ait# power 5633 mw8.
- Fragile.- Cait# and laser lo!*ed to
resonan!e independentl#.
Cait# I
"ignal Measurement I
- Two photon R1 5= nm8 transition as
a re9eren!e.
- 0#drogen C#anide56227 nm, +5/88 as a
$ntermediate re9eren!e.
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Pressure broadening & shiftFor P(1! broadening 66.: M0>DTorr "ine shift 3./ M0>DTorr #$ect of Temp negligible e$ect%sed to calibrate ptical Spectrum
'nalyers (S')s!
Pre*ious or+ .9. Swann and S.1. :ilbert. !;S
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Saturation signal * 1 +,+easure Po-er shift 11./ ,0m-Pressure Shift 2 0>DmTorr
Pre*ious or+ I #.9>a+ows+i, #.#.0ade, P.DubeDe*elop4ent and Study of a 7. u4 ?ptical frequency Standard referenced to p!76) Saturated
absorption line in the !7@*3) o*ertone band of 739 2 A 2
Opti!s Communi!ations /;:5/33:8 /2
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4eelop high a!!ura!# porta1le waelength "tandards 9or
tele!ommuni!ation industr#.
Our Approa!h
( Cait# 1ased re9eren!es are not +orta1le.
( Transitions in the glass !ells !an not 1e 9urther
narrowed. "olution I
Hse mole!ular a1sorption inside opti!al 9i1er.
AdantagesI
- +orta1le- &as# to align- &asier to get high intensities oer long path
Through e'isting Te!hnolog# I
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&'perimental "et(up
Capa!itie
manometers
0ollow opti!al 9i1er
Gas $nlet Gas $nlet
6 m)
To a!uum pump
+ro1e +ump
562 ( ;338 m)
C/0/ mole!ules
Fiber in Fiber out
ultimately3
" O i
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"etup( Opti!s
4iode
-aser
$"O
"%uee>er
+"
"%uee>er
+"
Fi1er
63D
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Capillar# Tu1e
Too loss#
3
2
/1a
l atten
λ α
-ength 6= !m and dia ;;3 m
-aser
+ower loss
/a
l
Onl# :3E transmission
4oppler roadened signalo1sered
No saturation signal;33 733
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Capillar# tu1e
3 63 /3 ;3 :3 23 73
23
73
G3
=3
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+hotoni! andgap 9i1er
12 m
loss4 2.2 d50m
No total internal re9le!tion
raggs re9le!tion
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63(m +hotoni! andgap 9i1er
(6233(6333 (233 3 233 6333 6233
(/./(/.3
(6.=(6.7(6.:(6./(6.3
(3.=(3.7(3.:(3./
3.3
T r a n s m i s s i o n 5 a . u 8
Fre%uen!# 5M0>8
At 63 m)
+ump L +ro1e
+ro1e
Re9le!tion o9 +ump
1eam 9rom 9i1er ends
"aturation 4ip
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63(m +hotoni! andgap 9i1er
(6333 (233 3 233 6333
3.3
3./
3.:
3.7
3.=
6.3 66/ m) 5? 3.:8 =; m) 5? 3.;8
:3 m) 5? 3./8
/3 m) 5? 3.68
63 m)
F r a ! t i o n
a l A 1 s o r p t i o n
Fre%uen!# 5M0>8
(:33 (/33 3 /33 :33 733 =33(3.7
(3.2
(3.:
(3.;
(3./
(3.6
3.3
66/ m) 5( 3./8
=; m) 5( 3.68
:3 m) 5( 3.68
/3 m) 5( 3.328
63 m)
F r a ! t i o n a l A 1 s o r p t i o n
Fre%uen!# 5M0>8
"igni9i!ant signal strength at 63
and /3 m) pump powers
7.2
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)e are transit limited or pressure limited
63(m +hotoni! andgap 9i1er
733 =33 6333 6/33;2
:3
:2
23
22
73 )aelength 62;6.;6 nm
- i n e w i d t h i n M 0
>
+ressure in mTorr
N
v N
P
s pressure
α δ
σ δ = -ine width does not in!rease signi9i!antl# with pressure whi!h implies
that it is transit time limit.
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6333 /333 ;333 :333
-(
-%
"
+ump?+ro1e
+ro1e onl#
Mi!helsonNs 9ringes
A r 1 i t r
a r # H n i t
Fre%uen!# 5M0>8
/3(m +hotoni! andgap 9i1er
3 /3 :3 73 =3 6333.3
3./
3.:
3.7
3.=
6.3
F r a ! t . T r a n s m i s s
i o n
Time 5s8
2 m core6 72 cm lengthFiber 8lls to mTorr in * 12 s
2 9m6 : cm long P5F at 1;1.2 nm
6733 6=33 /333 //333.63
3.62
3./3
3./2
3.;3
3.;2
3.:3
3.:2
F)0M /
A r 1 i t r a r # u n i t s
Fre%uen!# in M0>
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/33 :33 733 =33 6333
//
/:
/7
/=
;3
;//3 m FF
- i n e ) i d t h 5 M 0 > 8
+ressure 5mTorr8
/3(m +hotoni! andgap 9i1er
+ressure limited
Transit limited
Fa!tor o9 ; !hange in pressure gies a 9a!tor o9
6./ !hange in line width
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/33 :33 733 =33 6333 6/33/3
/2
;3
;2
:3
:2
23
22
73
63 m +F
/3 m +F
- i n e w i d t h i n M 0 >
+ressure in mTorr
)2ln(2)/(4 d vtt =δ
63(m, /3( m +F data Comparison
To redu!e Transit time roadeningI
in!rease 9i1er hole si>e(or( 9ind a heaier mole!ule
(or( 4e!rease the elo!it# o9 mole!ule 1#
!ooling
Transit Time
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"ignal strengthI
• optimal 9i1er length 9or pressure
Noise
• $nter9eren!e 5pro1e with stra#Dre9le!ted pump8
• laser intensit# noise
-inewidthI 5target 6 M0>8
• transit time 1roadening
• pressure(1roadeningTo narrow the transition, we mustI
» redu!e transit(time 1roadening» redu!e the pressure
» lengthen the 9i1er
Hltimate limits
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( O1sered saturated a1sorption 9eatures in photoni!
1andgap 9i1er 9or 9irst time.
( "igni9i!ant a1sorption 9ra!tion o1sered at lowpower 5 /3 m)8, with /; M0>(wide 9eature.
( Con9irmed transit time 1roadened, /3 m produ!e
narrower 9eature than 63 m 9i1ers
Con!lusions
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Future +lan
Near(termI Ma*e more porta1le, redu!e noise.uild 9re%uen!# Com1 9or a1solute measurement.O1sere dependen!e o9 di99erent 1roadening
me!hanisms.O1sere the shi9ts in +hotoni! 1andgap 9i1ers.
-onger(termI "eal the 9i1er 9illed with gas. 5Greg Johnson8
Narrow the transition&'plore larger photoni! 1andgap 9i1ers&'plore other gases.
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Than* Pou
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+hotoni! andgap 9i1ers
$nde'
guiding
0ollow Core guiding
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"aturated a1sorption 9eature width
(6333 (233 3 233 6333(3.63
(3.3=
(3.37
(3.3:
(3.3/
3.33
3.3/
1" mW
%" mW
F r a ! t i o n a l A 1 s o r p t i o n
Fre%uen!# 5M0>8
12 m
Transit time 1roadeningI Naieestimate
t dD B6D23 M0>
+ressure 1roadeningI
66 M0>DTorr Q 6./ Torr 6;./ M0>
* /2 +,
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$mportant roadening $n $R "pe!tros!op#
4oppler roadeningMole!ules are in motion when the# a1sor1energ#. This !auses a !hange in
the 9re%uen!# o9 the in!oming radiation.
+ressure 1roadening
+rodu!e 1# the shi9ts o9 energ# leels 1#intera!tion o9 radiating atom with near 1#
parti!les
Transit time roadeningThe intera!tion time o9 mole!ules with the
radiation 9ield is small with thespontaneous li9e time o9 e'!ited leels
+ower roadeningMole!ules a1sor1 energ# 9rom intense laser.
This !auses a energ# shi9t !ausing 1roadening.
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