External sourceEnd-Fire

Principle

KTH

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

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)

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

External sourceEnd-Fire

Principle Sample :• Access waveguide

- Deep / shallow etched ridge waveguide

• Taper access waveguide / PhC waveguide• PhC device

External sourceEnd-Fire

Principle Sample :• Access waveguide

• Deep / shallow etched ridge waveguide

• Taper access waveguide / PhC waveguide• PhC device

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

External sourceEnd-Fire

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

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)

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

Measurement of R,T and propagation losses

Cut-back method, examples

S. J. McNab et al., Opt. Exp., 11, 2927, (2003)

SOI

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 ...

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)

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.

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

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

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

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

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

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

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

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

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

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

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)

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

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

ILSExperimental set-up

R. Ferrini et al., J. Quantum Electron., 38, 786, (2002)

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

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)

D. Labilloy et al., Phys. Rev. B, 59, 1649, (1999)

Transmission spectrum

Triangular lattice of holes in GaAs based planar waveguide

Examples

Reflectivity spectrumMake use of the cavity fringes PhC / cleaved facet

D. Labilloy et al., Phys. Rev. Lett., 79, 4147, (1997) D. Labilloy PhD dissertation

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

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)

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

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).

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

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

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

Photoluminescence

D. Ochoa et al., Phys. Rev. B, 61, 4806, (2000)

Coupled with angular resolution

Mode spectroscopy

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

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

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)

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