external source end-fire mesures.pdf · external source end-fire principle light coupling in/out :...
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External sourceEnd-Fire
Principle
KTH
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External sourceEnd-Fire
Principle
Light source :• Tuneable source, laser• Broadband source, white light, LED, super-luminescent LED, ...
Light input or output :• Optical fiber, single mode• Free space
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External sourceEnd-Fire
Principle Light coupling in/out :• Microscope objective, free space• Tapered, microlensed fiber
Tapered / Lensed Fiber
DTS0080 OZ Optics reserves the right to change any specifications without prior notice. 29-Nov-04
Figure 1: Laser Shaped Lensed Fiber (End Detail)
Working Distance
"WD"
Fiber with Acrylate Coating
Ø250 micron or Ø400 micron
Stripped Fiber
Ø125 micron
Strip Length
"SL"
Taper Angle
“ ” Spot Diameter
Radius of Curvature“R”
"SD"
Figure 2: Polished Lensed Fiber (End Detail)
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External sourceEnd-Fire
Principle
Figure 6. Polarization control using, a) multiple wave plates and, b) usingmultiple coiled fiber.
Newport App. Note 20
Polarisation in/out :• Polarisation maintaining fibers• Polarisation control• Polarisation analysis• Polariser, /2 and /4 retarding plates• Coiled fibers• Often reduced to a TE/TM control / analysis
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External sourceEnd-Fire
Principle Sample :• Access waveguide
- Deep / shallow etched ridge waveguide
• Taper access waveguide / PhC waveguide• PhC device
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External sourceEnd-Fire
Principle Sample :• Access waveguide
• Deep / shallow etched ridge waveguide
• Taper access waveguide / PhC waveguide• PhC device
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External sourceEnd-Fire
Principle Imaging set-up if working in free space can be convenient• Si CCD• IR Vidicon• IR InGaAs CCD
Detector• Si• InGaAs• + spectrometer
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External sourceEnd-Fire
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Waveguides
End-Fire
Transmission spectrum, ideal case
InP-based W3: W 1 mKTH
waveguide transmission band
waveguide mini stop-band
but more commonly :
0.21 0.22 0.23 0.24 0.25 0.26 0.27 0.28
W3 (L=30 a) in GaAsTra
nsm
issi
on (
arb.
unit
s)
u=a/
Waveguide
Mini stopband
due to internal reflections and cavity fringes
W3
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End-Fire
Examples, device characterisation
L~18 μm
1st PhC 2nd PhC 3rd PhC
B12 B23
Input port
Throughport
1 2 3 4 5
Wavelength [nm]
Tra
nsm
itte
d p
ower
[d
B]
Band edge of WG2WG1
(1)(2)(3)(4)(5)
WG2
A. Shinya et al., Opt. Exp., 14, 12394, (2006) Y. Sugimoto et al., J. Sel. Area. Comm., 23, 1308, (2005)
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Measurement of R,T and propagation losses
Cut-back method
TI S
L
S
I= Te L
LnS
I
= Ln(T) L
S
I
dB
=10.log10 T( )Ln(10)
L
AdB / cm =10 cm 1
Ln(10)= 4.34
cm 1L
Tran
smis
sion
(dB
)
slope : losses in dB/L units
insertion losses in dB
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Measurement of R,T and propagation losses
Cut-back method, examples
S. J. McNab et al., Opt. Exp., 11, 2927, (2003)
SOI
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End-Fire
Transmission spectrum, parasitic reflections
Due to internal reflections and cavity fringes :• at the cleaved facets• at the tapers• inside the PhC structure• ...
Undesirable for the device performance but let's make use of them for characterisation
r,t r,t r,t r,t
cavity 1
cavity 2 cavity 3 cavity 4
cavity 5 ...
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TFP =T 2
1+ R2e 2 L 2Re L cos(4 nL
)
Measurement of R,T and propagation losses
Hakki-Paoli methodFabry-Perot cavityfringes equally spaced in energy
Energy
Tran
smis
sion
high R
low R
R,T R,Tpropagation losses
n,L
• u2 = inverse of the fringe contrast Pmax/Pmin
• does not require quantitative measurement
u =TminTmax
=PminPmax
f (u) = ln1 u
1+ u
= ln(R) L
Tmin =T
1+ Re L
2
Tmax =T
1 Re L
2
Tmax
Tmin
L
f(u) slope : losses
in 1/L units
ln(R)
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Measurement of R,T and propagation losses
Example
A. Talneau et al., Appl. Phys. Lett., 82, 2577, (2003)
InPThe method has also been used in the case of several coupled cavities with Fourier filteringExact theoretical model is missing
FIG. 3. 120 rows long W1–PCW with taper access: �a� transmitted powerspectrum, �b� spectral power on the 1484–1500 nm window, �c� unfiltered�thin line� and filtered �bold line� transmitted power with a filter suited toC1 cavity, and �d� taper reflection and propagation losses as a function ofwavelength.
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Measurement of R,T and propagation losses
Hofstetter methodthe Hofstetter method generalises the Hakki-Paoli method to the higher orders of the Fourier transform of the transmission spectrum
D. Hofstteter et al., Opt. Lett., 22, 1381, (1997) and IEEE J. Quant. Elect., 34, 1914, (1998)
W3
Amplitude decay of the harmonic n
Ar = attenuation after n single passes
Ar,n = Re-n L R,T R,Tpropagation losses
n,L
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Measurement of R,T and propagation losses
Hofstetter method
D. Hofstteter et al., Opt. Lett., 22, 1381, (1997) and IEEE J. Quant. Elect., 34, 1914, (1998)
W3
A = R.T 2e CPhLCPhe R Lr1 +Lr 2( )
after division by a reference waveguide
ln(Ar/ACPh) = - ln T2 + ( CPh- r)LCPh
T = 0.99
CPh r = 84 dB/cm
r = 6.2 dB/cm
CPh = 90.2 dB/cm
1-T = 0.01
T T
r, Lr1 r, Lr2CPh, LCPh
RR
L
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Measurement of R,T and propagation losses
Hofstetter methodInternal reflections lead to multiple cavities
Lr1Lr2Lr
W1 • harmonics 1 and 4 : Lr1
• harmonics 2 and 5 : Lr2
• harmonics 3 and 6 : Lr
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Dispersion curve
Fabry-Perot fringes and k-space sampling
R,T R,T
n( ),L
Fabry-Perot fringes equally spaced in energy ?
TFP =T 2
1+ R2 2Rcos(4 nL
)TFP =
T 2
1+ R2 2Rcos(2kL)
Note: sampling in k, exact k values are more difficult to determine
resonances equally spaced in k k = /L
n=cst = kc/n
Transmission Wavevector k
Ener
gy
k
Transmission Wavevector k
Ener
gy
k
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Une manière plus visuel de décrire cela consiste déveloper les images des miroirs, ce qui donne un objet de période 2L donc une périodicité en 2 /2L= /L
Echantillonage
L
G
2L
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0.7 0 0.5 0.4 0.3 0.2 0.1
Transmission
TE K TE M
Reduced wavevector
u=a/
0 0.40.30.20.1
k = Cst. . .
180 nm
200
220
240
260
280
300 nm
15 rows
0.5 0.9Transmission
0 0.50.5
u=a/
0.32
0.20
0.24
0.22
0.26
0.28
0.30
0.180.18
0.32
0.20
0.24
0.22
0.26
0.28
0.30
Reduced energy
TE Bandgap
Dispersion curve measurement
D. Labilloy et al., Phys. Rev. B, 59, 1649, (1999)GaAs, internal light source
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Dispersion curve measurement
M. Notomi et al., Phys. Rev. Lett., 87, 253902, (2001)
-10
0
1514 1516λ (nm)
1518
T (
dB)
-5
0
1480 1500Wavelength: λ (nm)
(a)wd =
1.0W
0
20
40
60
80
100
1460 1480 1500 1520Wavelength: λ (nm)
0
10
1420 1460 1500λ (nm)
wd=0.65W
wd=1.0W
wd=1.0W
1520
(b)
5
Tra
nsm
ittan
ce: T
(dB
)
Gro
up in
dex:
n g
n g
ld
Si membrane
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Dispersion curve measurement
Y. Vlasov et al., Nature, 438, 65, (2005)
Mach-Zehnder interferometer
Figure 1 | SEM images of a passive unbalanced Mach–Zehnderinterferometer using photonic crystal waveguides. a, Input section of theh i l id h i h d d ili b
Figure 3 | Active electrically tunable MZI with lateral electrical contacts tophotonic crystal waveguides. a, Time averaged magnetic field energy
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Optical cavities, high quality factor
Measurement of the cavity requires coupling to a probe which affect the Q
• Intrinsic Q = Qint, unloaded cavity, coupling only to free space radiation and material losses, defects• Coupling Q = Qprobe, additional losses due to the measurement• Measured Q = Qmeas, loaded cavity
1
Qmeas
=1
Qint
+1
Qprobe
In OutCoupling
Losses
Waveguide
Cavity
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Optical cavities, high quality factor
Y. Akahane et al., Opt. Exp., 13, 1202, (2005)
(a)
(b)
Inte
nsity
(ar
b. u
nits
)
1584 1585 1586 1587 1588 1589
Wavelength (nm)
Δλ
T2
T1
(a)
(b)
Inte
nsity
(ar
b. u
nits
)
1584 1585 1586 1587 1588 1589
Wavelength (nm)
Δλ
T2
T1
(a)
(b)
Inte
nsity
(ar
b. u
nits
)
1584 1585 1586 1587 1588 1589
Wavelength (nm)
Δλ
T2
T1
Inte
nsity
(ar
b. u
nits
)
1584 1585 1586 1587 1588 1589
Wavelength (nm)
Δλ
T2
T1
T =T2T1
Qint =Qmeas
T
s+1
s-1
s-2Port 1(input)
Propagation constant β
d2d1
1/τin
1/τva1
Port 2(through)
Waveguide
Cavity
s+1
s-1
s-2Port 1(input)
Propagation constant β
d2d1
1/τin
1/τva1
Port 2(through)
Waveguide
Cavity
Transmission
Emission
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420 nm (=a)
A B CABC
Waveguide
(b)(a)
Cavity
420 nm (=a)
A B CABC
Waveguide
(b)(a)
Cavity
Optical cavities, high quality factor
Y. Akahane et al., Opt. Exp., 13, 1202, (2005)
Qtotal = 88,000Qv = 100,000
1586.2 1586.4 1586.6Wavelength (nm)
Inte
nsity
(ar
b. u
nits
)
18 pm
Qtotal = 88,000Qv = 100,000
1586.2 1586.4 1586.6Wavelength (nm)
Inte
nsity
(ar
b. u
nits
)
18 pm
E. Kuramochi et al., Appl. Phys. Lett., 88, 041112, (2006)
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Internal sourceILS
Goal, a versatile technique that: • does not require the full fabrication of device with access waveguides etc...• allows the light source to be injected where needed• allows quantitative measurements
D. Labilloy et al., Phys. Rev. Lett., 79, 4147, (1997)Historically, among the first actually quantitative transmission measurements on 2D PhC
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ILSPrinciple: Insert light emitters inside the planar waveguide
• Quantum wells• "bad" quantum dots (large emission band)
R. Ferrini et al., J. Quantum Electron., 38, 786, (2002)
And make use of lithographic tuningTa ( ) =I2( )I1( )
T(u =a)
D. Labilloy et al., Phys. Rev. Lett., 79, 4147, (1997)
D. Labilloy PhD dissertation
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ILSExperimental set-up
R. Ferrini et al., J. Quantum Electron., 38, 786, (2002)
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ILSExperimental set-up,as usual real life is a bit more complex
H. Benisty et al., J. Quantum Electron., 38, 770, (2002)
Cleaved
facet
Air
2 3 1
microscope optical axis
secondary source
cleaved
facet
(a)
ZX
laser excitation
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a
TE polarization
1 row
0
0.5
1
0.15 0.2 0.25 0.3 0.35
- 10 rows
TE
Energy (reduced units u = a / )
Tra
nsm
issi
on
0
0.5
1
0.15 0.2 0.25 0.3 0.35
280
0
0.5
1
0.15 0.2 0.25 0.3 0.35
300
0
0.5
1
0.15 0.2 0.25 0.3 0.35
320
0
0.5
1
0.15 0.2 0.25 0.3 0.35
340
0
0.5
1
0.15 0.2 0.25 0.3 0.35
360
0
0.5
1
0.15 0.2 0.25 0.3 0.35
380
0
0.5
1
0.15 0.2 0.25 0.3 0.35
400
0
0.5
1
0.15 0.2 0.25 0.3 0.35
420
0
0.5
1
0.15 0.2 0.25 0.3 0.35
440
0
0.5
1
0.15 0.2 0.25 0.3 0.35
480460
0
0.5
1
0.15 0.2 0.25 0.3 0.35InP/(Ga,In)(As,P) QW =1.55μm f=30%
Transmission spectrumExamples
R. Ferrini et al., J. Quantum Electron., 38, 786, (2002)
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D. Labilloy et al., Phys. Rev. B, 59, 1649, (1999)
Transmission spectrum
Triangular lattice of holes in GaAs based planar waveguide
Examples
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Reflectivity spectrumMake use of the cavity fringes PhC / cleaved facet
D. Labilloy et al., Phys. Rev. Lett., 79, 4147, (1997) D. Labilloy PhD dissertation
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DiffractionMeasurement of light diffration at the PhC interface
D. Labilloy PhD dissertation
Diffraction cut-off frequencies, normal incidence
In-plane source is isotropic
Forw
ard
diffr
actio
n effic
ienc
y
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Waveguides, bends and Fabry-Perot cavities
S. Olivier, J. Light. Tech., 20, 1198, (2002)
S. Olivier, Opt. Lett., 26, 1019, (2001)
0
0.2
0.4
950 970 990 1010 1030
Tran
smis
sion
u = a /
QP1b : 140
FP CavityW / a = 2.1a = 260 nm
FP = 997 nm
T = 0.048T (4 rows) = 0.05 ± 0.01
R = 0.921
Q = 150 ± 5
= 6.6 ± 0.2 nm
R. Ferrini et al., J. Quantum Electron., 38, 786, (2002)
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0
400
800
1200
0
0.04
0.08
0.12
1400 1450 1500 1550 1600
Wav
egui
de A
bsor
ptio
n (c
m-1
)C
avity Transm
ission
Wavelength (nm)
W / a = 1.7IWK5
a = 440 nm
a = 420 nm
a = 400 nm
LimitationQW or QD absorption in the waveguide
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Out of plane scattering and lossesPhenomenological model
• For data analysis out of plane scattering can be cast into a phenomenological imaginary dielectric constant in air• Intrinsic losses
1
1
2
H. Benisty et al. Appl. Phys. Lett. 76, 532, (2000).
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R. Ferrini et al., J. Opt. Soc. Am. B 20, 469, (2003)
Out of plane scattering and lossesPhenomenological model• Extrinsic losses, strongly correlated with hole shape, depth and in-plane disorder
zo
(zo) 1
2 (z)
z 2
2
Core
Bottom cladding
Top cladding
(z)
0
z
z 1
z 2
zb
2 r
d
R. Ferrini et al., Appl. Phys. Lett. 82, 1009, (2003)
10-5
10-4
10-3
10-2
10-1
0.1 1Angle a (°)
'' hole
Simple Cone
d = 4 μm
d = 2 μm
R. Ferrini et al., Opt. Lett. 31, 1426, (2006)
0
0.5
1
0
0.5
1
0.2 0.3 0.4
TE
f = 0.30
f = 0.30
Exp. '' = 0.32
'' = 0.08
'' = 0.32
'' = 0.08
u = a /
Tran
smis
sio
n
0
3.2 μ
m
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Photoluminescence
Light source inside the PhC structure• PhC defect- Point defect, optical cavity
laser
2 m(a)
laser
Front photoluminescence emission
collected lightlaser excitation
scattering
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C.J.M. Smith et al., JOSA B, 17, 2043, (2000)
laser
940 960 980 1000 1020 10400
200P
ho
tolu
min
escen
ce (
a.u
.)
wavelength (nm)
Mode spectroscopy
Photoluminescence
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Photoluminescence
D. Ochoa et al., Phys. Rev. B, 61, 4806, (2000)
Coupled with angular resolution
Mode spectroscopy
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PhotoluminescenceTime resolved
Life time modification, Purcell effect, emission enhancement and inhibition
Wen-Hao Chang et al., Phys. Rev. Lett. 96, 117401, (2006)
0 2 4 6 8 10
PL
inte
nsity
( a.
u. )
time ( ns )
QD1
QD2
QD in bulk
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PhotoluminescenceLight source inside the PhC structure• PhC defect- Line defect, waveguide
Probing the density of states singularities
E.Viasnoff-Schwoob et al., Phys. Rev. Lett., 95, 183901, (2005)
Excitation outside
Excitation inside
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PhotoluminescenceLight source inside the PhC structure• Bulk 3D PhC
CdSe nanocrystals in inverted opals
Probing the local density of states singularities, lifetime modification
P. Lodahl et al., Nature, 430, 654, (2004)
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PhotoluminescenceLight source inside the PhC structure• Bulk 2D PhC
M. Fujita et al., Science, 308, 1296, (2005)
Probing the local density of states singularities, lifetime modification