Semiconductor lasers: What's next?
description
Transcript of Semiconductor lasers: What's next?
Semiconductor lasers: What's next?
Grigorii Sokolovskii
Ioffe Institute, St Petersburg, Russia
Outline• Applications of semiconductor lasers. ‘Revolution’ of light.
• Basic principles of laser operation (only to remind).
• Absorption and gain in semiconductors, inversion of population and conditions for it's achievement.
• Rate equations. Lasing threshold. Laser efficiency.
• Modulation of the laser signal. Gain clamping.
• Fiber-optical applications. DFB and DBR lasers. VCSELs and VECSELS
• Waveguide in LD structure. Modes of the waveguide.
• Beam-propagation (‘beam-quality’) parameter M2 and how to measure it. Achieving maximum power density with LDs.
• Interference focusing of LD beams.
• What’s next? New applications and problems to solve.
Applications of LDs
• Telecoms• Data reading/recording• Laser printing• Pumping of the solid-state and fiber lasers • ‘Direct’ applications: cutting/drilling/welding • Biology and medicine
$7B → $1T
Applications of LDs
• Telecoms• Data reading/recording• Laser printing• Pumping of the solid state and fiber lasers• ‘Direct’ applications: drilling/cutting etc• Biomedicine
1. Surface and edge-emitting(e.g. VCSELs, VECSELs, GCSELs, etc and ‘striped’ LDs)
2. Broad and narrow area Broad: high power, poor beam quality;Narrow: low power, better beam quality
Types of LDs
LDs for Mid-IR (1600-5000 nm)
0
10
20
30
40
50
60
70
80
1300 1500 1700 1900 2100 2300 2500 2700
Wavelength, nm
Sp
ectr
al d
ensi
ty
W
/nm
LED22
LED20f=500 Hz
LED18
In Mid Infrared spectral range 1600-5000 nm lies strong absorption bands of such
important gases and liquids as:
CH4 , H2O, CO2, CO, C2H2, C2H4, C2H6,
CH3Cl, OCS, HCl, HOCl, HBr, H2S, HCN, NH3 , NO2 , SO2 , glucose and
many others.
Optical tweezers
Waveguide: light in matter
‘Inverse’ waveguide: matter in light – optical tweezers
Laser projectors
Microvision SHOWWX Laser Pico Projector
MacWorld 2010 Best of Show award
Samsung H03 Pico Pocket Sized LED Projector
Aiptek PocketCinema T30
Basic principles of laser operation
Gain + Feedback
0( ) xS x S e
Basic principles of laser operation
Lasing threshold
0( ) xS x S e 2 20 0(2 ) LS L R S e S
1lnout R
L threshold out in
Spontaneous and stimulated emission
E1
E2
E1
E2
Spontaneous Stimulated Absorption
dSAn
dt dS
BSndt
dSBSn
dt
Basic principles of laser operation
‘Negative’ temperature
2
1
E
kTn
en
Gain: inversion of population
Basic principles of laser operation
E1
E2
T
n
3- & 4-level systems
E1
E2
E3
E1
E2
E3
E4
Laser diodes: Some basics
Vibronic laser
E1
E2
E3
E4
Ev
Ec
Eg
Diode laser
Ec – conduction bandEv – valence bandEg – energy gap
QWs and QDs are the ‘artificial atoms’ :)
Laser diodes: Some basics
ElectronsElectrons
Photon
CurrentCurrentCurrentCurrent
Quantum Dot or Quantum Well
Conduction band
Valence bandValence band HolesHoles CurrentCurrentCurrentCurrent
NN--typetype PP--typetypeNN--typetype PP--typetype
Light generation and absorption in semiconductors
‘Golden’ rule of Quantum mechanics: 22
fW f H i
2( ) (1 )absorbtion v cW B M S E f f
2( 1) ( )(1 )radiation v cW B M S E f f
Absorption probability:
Radiation probability:
2 2( ) (1 ) ( )( )radiation absorption c v c vW W W B M E f f SB M E f f
( ) ( ) ( )sp stW E r E Sr E 2
( ) ( ) (1 )sp c vr E B M E f f 2
( ) ( )( )st c vr E B M E f f
The total radiation probability:
Light generation and absorption in semiconductors
What is the condition for stimulated emission?
c v c v gF F E E E
1 10 0
1 exp 1 expc v
c c v v
f fE F E F
kT kT
( ) 0str E 2
( ) ( )( ) 0st c vr E B M E f f
Inversion of population:
c v gF F E
Inversion of population
http://britneyspears.ac/physics/fplasers/fplasers.htm
gvc EFF
Forward-biased p-n-junction is both the source for the inversion of population and for the name of the “laser diodes”
Stimulated and spontaneous emission rate: 3D
ћω=E
r
rst
rsp
fce
fvh
ρ(E)
-ρ(E)
T↑
Eg
)1()(~)( vcsp ffEEr
))((~)( vcst ffEEr
kTFE
fcc
c
exp1
1
kTFE
fvv
v
exp1
1
gEEE ~)(
Density of states: Low-Dimensional vs 3D
Bulk semiconductor
Quantum Well
Quantum Wire
Quantum Dot
32
3 2 2
2( )
2D g
d mE E E
2 02( ) ( )D QW
mE n h E E
12
1 20
2 1( )
2QWW
D
n mE
E E
0 0( ) 2 ( )D QDE n E E
Evolution of the threshold current density: from 3D to Low-Dimensional
Density of states: Low-Dimensional vs 3D
Bulk semiconductor
~1 kA/cm2
Quantum Well
~100 A/cm2
Quantum Wire???
Quantum Dot
~10 A/cm2
3D
E
rst
0( ) 2 ( )QD QDE n E E
QDs vs 3D
Lower threshold
Lower temperature dependence of the laser parameters
But: at low QD density threshold may NOT be reached
Narrow spectrum for IDENTICAL QDs
But: broad spectrum for inhomogeneously broadened QDs
QD
k0nf
kz
kx
nc
ns
nf fkxf
kxf
φc
φs
220
22fzx nkkk mfk csx 22
mm
xfm
z Nkknkk 0)(22
0)(
fmcs nNnn ,
Laser diodes: The waveguide
Eg ↓ ↔ n↑
.
.
x
k0nf
z
k0ns k0nc
x
k0nf
z
k0ns k0nc
Modes of the waveguide
.
.
Composing Rate Equations
The simplest model
red
J
J is the average pump current densityn is the average carrier concentration in the active regionS is the average photon concentration (average intensity)
Carriers, steady-state:
Pump rate = Recombination rate
Carriers, time-dependent:
red
J
dt
dn
SngN
cn
ed
J
dt
dn
effs
)(
stsp Srred
J
dt
dn
Bn
nBnr s
ssp
1,2
gainrst ~ )(ng
N
cr
effst
Composing Rate Equations
rS
p
Photons, steady-state:
Total radiation probability = Recombination rate
Photons, time-dependent:
p
Sr
dt
dS
pstsp
SSrr
dt
dS
pseff
SnSng
N
c
dt
dS
)(
SnnAn
ed
J
dt
dn
SnSnnA
dt
dS
ts
pst
Г - confinement factorβ - spontaneous emission factornt - transparency concentrationA - linear gain coefficientτs - spontaneous recomb. timeτp - photon lifetime
Lifetimes
Bns
1
Spontaneous: Photon lifetime:
p
S
dt
dS
τs ~ 1 ns if n ~ nt, then: p
t
eSS
0
c
LNt eff
r
2 22
0
2
0)( ReSeStS inp
eff
Lc
LN
r
RLN
cin
effp
1ln
11 τp ~ 1 ps
L ↑ → τp ↑αin ↑ → τp ↓R ↑ → τp ↑
Rate Equations for QD LD
Ws
WE
E
WW
E
EW nf
nf
n
ed
J
t
n
''0
Es
EE
G
GGE
EW
E
EEE
WE nf
nf
nf
nf
n
t
n
''''00
Gs
GE
G
GtrGGG
EG nf
nSnnAf
n
t
n
')('0
p
p
Gs
GtrG
SnSnnA
t
S
)(
GS
ES
τWG
τWE
τE
τG
…where f is the filling factor
5ML InAs
Steady-state solution of the Rate Eqs
0
0
SnnAn
ed
J
dt
dn
SnSnnA
dt
dS
ts
pst
st
spt
n
ed
JSnnA
nSSnnA
0
sspt
sp
n
ed
Jn
ed
JnnA
n
ed
JS
pt
s
Ann
ed
Jn
1
pt
s
p
An
edJ
edS
S
1
0
Steady-state solution of the Rate Eqs
pt
s
Ann
ed
Jn
1
pt
s
p
An
edJ
edS
S
1
0J
J
S
Jth
n
Jth
nth
β↑
β↑nt
ptth A
nn
1
thsp
ts
th ned
An
edJ
1
Lasing Threshold
0 0.2 0.4 0.6 0.8 1
5
10
Thickness, f
Thr
esho
ld, J
thsp
ts
th ned
An
edJ
1
RLN
cin
effp
1ln
11
0 5 103 0.01 0.015
1
2
3
4
5
Inverse Length, 1/L
Thr
esho
ld, J
R↑R↑
0 200 400 600 800
1
2
3
4
5
Length, L
Thr
esho
ld, J
R↑
Lasing Threshold
Threshold vs Temperature
100 200 3000
1
2
Temperature, T
Thr
esho
ld, J
100 200 3000.1
1
10
Temperature, T
Thr
esho
ld, J
0
expT
JT
)(0 TfT
Laser efficiency
thp
ii JJed
SJJ
~~
electrons
photons
J
J
i
total
active
~ Pumping efficiency
Internal quantum efficiency
32
2
CnBnAn
Bni
Ev
Ec
Ev
Ec Ev
Ec
Evv
free-carriers Auger
Laser efficiency
thp
i JJed
S
~ RL
V
N
cSP
eff
1ln
1
2
121
thp
ieff
JJedRL
V
N
cP
~1
ln1
2
121
RLN
cin
effp
1ln
11
d
VJJWLI
th
in
i II
RL
RLe
P
1
ln1
1ln
1~
2
121
outin
outi
in
i
th
d
RL
RL
IIe
P
~
2
11
ln1
1ln
1~
2
121
differential efficiency:
R↑
I
P
Ith
ηd
Laser efficiency
serial
thd
serial Ire
I
IIe
Ire
I
P
21
21
R
Lin
id1
ln1~
21
Measuring IQE:
L
1/ηd
i~2
Riin1ln~2
Lasing efficiency:
I
P
Ith
U
rserial↑
I
P
Ith
η(1/2)
rserial↑
Turn-on delay
t
J
Jth
t
S
t
S
Δt
SnnAn
ed
J
dt
dn
SnSnnA
dt
dS
ts
pst
s
ts e
ed
Jtn
1)(
thntn )(
J
J
JJ
Jt th
sth
s
ln
?
Turn-on delay
J
J
JJ
Jt th
sth
s
ln
If J = 2Jth, τs = 1 ns: Δt = 0.7 ns t
J
Jth
Non-return-to-zero (NRZ) modulation
t
S
Δt
t
J
Jth
t
S
RZ modulation
Turn-on delay of QD LDs
J
J
JJ
Jt th
sth
s
ln
J/Jth
Δt
Cτp
Non-QD laser diode:
pth
s CJ
Jt
QD LD:
SngN
cn
de
J
dt
dn
effs
)(
speff
nSSng
N
c
dt
dS
)(
)(),()(
)(),()(
)(),()(
00
00
00
tnJntnntn
tSStSStS
tJJtJJtJ
)( 00 nSgSgN
cn
de
Jn
effs
speff
nSnSgSg
N
cS
)( 00
Small-signal moduation
0)(
0)(
SngN
cn
ed
J
SnSng
N
c
effs
pseff
SngN
cn
de
J
dt
dn
effs
)(
speff
nSSng
N
c
dt
dS
)(
)exp()()(
)exp()()(
)exp()(
tibtS
tiatn
tijtJ
)( 00 nSgSg
N
cn
de
Jn
effs
speff
nSnSgSg
N
cS
)( 00
de
jbg
N
caSg
N
ci
effeffs
00
1
01
00
bg
N
ciaSg
N
c
effpseff
gN
cAAS
effs
,1
0 0
1g
N
c
effp
p
AS
02
0
Small-signal moduation
))(exp()()(22
0
20
Bp iB
de
j
ide
jb
de
jbg
N
caSg
N
ci
effeffs
00
1
01
00
bg
N
ciaSg
N
c
effpseff
222220
20
)()(
B )()(22
0
arctgB
Amplitude-freq. response of photons
gN
cAAS
effs
,1
0 0
1g
N
c
effp
p
AS
02
0
1
1/2
B(
)
I1
I2>I
1
222220
20
)()(
B
0
1AS
s
p
AS
02
0
Amplitude-freq. response of photons
-3
-2
-1
0
1
B(
)
)()(22
0
arctgB
0
1AS
s
p
AS
02
0
Phase-frequency response of photons
))(exp()()(22
0
AiAde
j
i
i
de
ja
de
jbg
N
caSg
N
ci
effeffs
00
1
01
00
bg
N
ciaSg
N
c
effpseff
222220 )(
)(
A2
)()(22
0
arctgA
Amplitude-freq. response of carriers
A(
)
222220 )(
)(
A
0
1AS
s
p
AS
02
0
Amplitude-freq. response of carriers
-3
-2
-1
0
1
A(
)
2)()(
220
arctgA
0
1AS
s
p
AS
02
0
Phase-frequency response of carriers
-3
-2
-1
0
1
2 B()
A()
B(
), A
()
π/2
π/2 shift in the phase-frequency responses means the energy flow between the photons and carriers (similar to the kinetic and potential energy in pendulum) which is called ‘relaxation oscillations’.
2)()(
220
arctgA
)()(22
0
arctgB
Phase-frequency response
0 0.5 1 1.5 2 2.5 3 3.5 40
1
2
3
4
5
6
время, нс
кон
цен
трац
ия,
о.е
.
n(t)
S(t)
Relaxation oscillations
NB: no relaxation oscillations in QD lasers!
Typical explanations: 1) QD LDs are too fast; 2) QD LDs are too slow
Eye-diagram
Eye-diagram
Gain clamping (gain saturation)
Laser diodes at extremely high pumping: pulsed vs CW
I
P
IthI
CW
pulsed
I
P
Ith
CW
pulsed
Gain clamping
ptr
tr
SNSSNNA
dt
dS
NSSNNA
ed
J
dt
dN
)1()(
)1()(
edNJ
S
S
A
edJJ
edS
ANN
S
S
ANN
thth
pth
p
ptrth
pth
,1
1,
1
1
22
th
pthth JJ
AedA
AJJ
AedNN
Quasi-analytical:
Asymptotical:
2 4 6 8 10 12 140
5
10
15
20
25
30
(I-Ith)/Ith
Concentration
.
N
ε=0
S
ε=0
pp
ASS 0
01
Gain clamping
SSngN
cn
de
J
dt
dn
effs
1)(
speff
nSSSng
N
c
dt
dS
1)(
J
S
Jth
0 5 10 15 20 25 30
20
10
0
10
20
частота, ГГц
откл
ик,
дБ
=0, =0
=21023
,
=21023
, =110-4
=0
pp
ASS 0
01
Gain clamping
Frequency, GHz
Res
pons
e,
dB
Application to the fiber optical communications
Application to the fiber optical communications
Double power: Double distance?
0
lg10P
PdB Typical attenuation: -20dB km
kmdB
dBL 100
/2.0
20
km
kmdB
dB
kmdB
dBPP
kmdB
PP
PL 115/2.0
3.0210
/2.0
2lglg10
/2.0
2lg10
)2( 00
kmPL 100)( if:
kmPL 200)100(
Wavelength / Time Division Multiplexing
Wavelength Selection
Gain Chip:
• 4mm length, 5µm wide waveguide
• 10 layers InAs QDs, grown on GaAs substrate
• waveguide angled at 5o
• facets AR coated: Rangled < 10-5
Rfront ~ 2 ·10-3
Distributed feedback (DFB) laser diodes
p-InP
n-InP
p-InP
n-InP
p-InP
n-InP
p-InP
p-InP
p-InP
n-InP
Distributed Bragg reflector (DBR) LDs
Diffraction grating in a waveguidex
k0nf
z
k0ns k0nc
mm
xfm
z Nkknkk 0)(22
0)(
x
z
k0Nm
Diffraction grating in a waveguide
N
Nkkz
20
x
z
k0Nm
x
z
k0Nm
1st order
2
k
zzz kkkk )1(
zzz kkkk 2)2(
2nd order
Distributed feedback/2
выход выход
Расстояние
Ам
пли
туда
022
2
Ez
E
n z n n z( ) cos( ) 1 02 ( ) cos( )z z 1 02
0 0 n c n c/ /
Р.Ф.Казаринов, Р.А.Сурис, ФТП, 1972, т.6(7), с. 1359-1365.H.Kogelnik, C.V.Shank, Journal of Appl. Phys, 1972, v.43(5), pp.2327-2335.
)2cos(42 022 zki
n c k n i 1 0 1 2
E z R z e S z ei z i z( ) ( ) ( ) 0 0
dR
dzi R ikS
dS
dzi S ik R *
202
2
0
0nc
Distributed feedback
202
2
00n
c
dR
dzi R ikS
dS
dzi S ik R * k n i 1 0 1 2
Vertical-cavity surface-emitting lasers VCSELs
(AlGa)Oxy
0 1000 2000 3000 4000 50000,0
0,2
0,4
0,6
0,8
1,0
Radial distance [nm]
Nor
mal
i zed
op
tica
l fie
ld in
tens
ity
Cu
rren
t de
nsit
y p
rofi
les
E2LP01
J
0 1 2 3 4 5 6 70.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
ou
tpu
t p
ow
er [
mW
]
current [mA]
0.0
0.5
1.0
1.5
2.0
2.5
3.0
vo
ltag
e [V
]
SML InGaAs QD VCSELCW RT, single-modeaperture 3.5 m
960 964 968-80
-70
-60
-50
-40
-30 31
2
Vertical-extended-cavity surface-emitting lasers (VECSELs)
A.Mooradian, “High brightness cavity-controlled surface emitting GaInAs lasers operating at 980 nm”, Proceedings of the Optical Fiber Communications Conference, 17-22 March 2001
• Power• Beam quality• Spectral quality
LD ‘bar’
Problems of LDs
Broad-stripe LD
Power density &intensity gradient
Optical confinement
dxxE
dxxEf
2
0
2
)(
)(
Double confined
Separately confined
Modes of the waveguide.
.
x
k0nf
z
k0ns k0nc
x
k0nf
z
k0ns k0nc
mm
xfm
z Nkknkk 0)(22
0)(
Optical confinement
dxxE
dxxEf
2
0
2
)(
)(
2f
Managing mode structure with optical confinement
.
Higher power does not meanhigher power density… :(
Power density and LD power
‘Not impossible’ near-field distribution of the broad-stripe LD
Higher power: • Higher modes• Spots (filaments)• Astigmatism
Multi-moded and ‘spotted’ (filamented) radiation is difficult (and sometimes impossible) to focus!
Multimode LDs
Propagation of the Gaussian beam
exp(-r2/w2).
. .
Gaussian beams
Coordinate
Gaussian exp(-r2/w2) is the most dense distribution. Therefore, Gaussian beams are the beams of the highest ‘quality’.
Even the ‘ideal’ power density is limited due to the quantum mechanical uncertainty principle ΔpΔx=h
2
20
0 1)(
w
zwzw
2201)(
z
wzzR
NAw
0
exp(-r2/w2)
.
. .
2
00
wz
Beam waist size on the level of 1/e2 (86%)
Propagating beam size (beam diameter)
Wavefront curvature
Raleigh range (distance of √2-fold increase of diameter of the beam)
Gaussian beams
LD beams: From multi-mode to quasi-Gaussian
exp(-2r2/w2)
.. .
.
M2 – beam propagation parameter
Second moment properties
dxdyyxI
dxdyyxIxxx
),(
),(202
Definition of the second moment (or variance):
Leads to a universal, rigorous parabolic propagation rule:2
020
20
2 )()( zzz xx
which holds for any arbitrary real beam (Gaussian or non-Gaussian, spatially coherent or incoherent) in free space
• Can develop such a universial propagation rule only for the second-moment beam width definition
• Actually holds true for propagation through arbitrary paraxial optical systems as well
A.E.Siegman, How to (Maybe) Measure Laser Beam Quality, OSA Annual Meeting, 1998
Second-moment-based beam width definition
xxw 2
For a zero-mode Gaussian beam the standard deviation is related to the Gaussian spot size w by
Therefore for arbitrary real beams similar beam width definitions can be adopted:
These second-moment-based beam widths will propagate exactly quadratically with distance in free space. For any arbitrary beam (coherent or incoherent), one can then write using the second-moment width definition
A.E.Siegman, How to (Maybe) Measure Laser Beam Quality, OSA Annual Meeting, 1998
xxw 2
z
zwwM
)(02
20
2
,0
4,
2,0
2, )()( zz
wMwzw
yxyxyxyx
using this width definition,
Basic properties of the M2 parameter
M2 is a “times-diffraction-limited” parameter based on measured near and far field second-moment beam widths
M2=1 for a zero-mode Gaussian beams
Arbitrary real beam widths can then be fully described by six parameters:
A.E.Siegman, How to (Maybe) Measure Laser Beam Quality, OSA Annual Meeting, 1998
220000 ,,,,, yxyxyx MMzzww
Requires time-averaged intensity measurements only.NO phase or wavefront measurements!
0
2
w
wM measured
2
2
2
2
2 1)(
MM w
zMwzw
2
2
22
1)(zM
wzzR M
NA
Mw
M 2
2
2
22
2
M
wz M
M
2M
Quasi-Gaussian beams
Beam waist size on the level of 1/e2 (15%)
Propagating beam size
Wavefront curvature
Raleigh range
exp(-2r2/w2)
.. .
.
1000 500 0 500 10000
50
100
wM z 0.1 1( )
wM z 0.1 3( )
wM z 0.1 10( )
z
wM 0 0.1 10( )
wM 0 0.1 1( )10
Focusing of the quasi-Gaussian beams
exp(-2r2/w2)
.. .
.
How to measure M2 parameter?
follows:
1000 500 0 500 10000
50
100
wM z 0.1 1( )
wM z 0.1 3( )
wM z 0.1 10( )
z
wM 0 0.1 10( )
wM 0 0.1 1( )10
22
201
220
2
2
NAB
NAzB
NAzwAM
NA
Mw
M 2
2 with
Measurable: beam diameter as a function of propagation length:
221
2220
220
220
222 2)( 22 zBzBANAzNAzzNAzwzzNAwzwMM
4
2
21
22
2
10
2
BABM
BBz
BNA
How to measure M2 parameter?
M2 is different at fast and slow axis!
1000 500 0 500 10000
50
100
wM z 0.1 1( )
wM z 0.1 3( )
wM z 0.1 10( )
z
wM 0 0.1 10( )
wM 0 0.1 1( )10
Cylindrical lens No.1(Fast axis corrector)
Cylindrical lens No.1(Fast axis corrector)
Cylindrical lens No.2(Slow axis corrector)Cylindrical lens No.2(Slow axis corrector)
Measuring lensMeasuring lens
CCDCCD
How to measure M2 in your lab?
1. Use house-built setup with any CAL or CAD software(e.g. MicroCal Origin)
2. Use specialist hard- and soft-ware (e.g. DataRay)
Approx. time for one laser: 3 hrs (when you’ve got some experience)
Approx. time for one laser: 15 mins
Standard:ISO 11146
Measuring M2 parameter
0 1 2
0,5
1,0
1,5
10
20
30
40
50
60
Pow
er, W
Current, A
M 2 p
aram
eter
0 1 2
0,5
1,0
1,5
0
3
6
9
12
15
Pow
er, W
Current, A
M 2 p
aram
eter
Fast axis
Slow axis
M2 varies with current!
For broad-stripe laser diodes,M2 at slow axis is an order ofmagnitude higher comparingto that at slow axis…
M2 can be NOT measurable!
100 um high-power LD, 1.06 um
Don’t call it ‘Gaussian’ before you are sure…
Light emitting diode Lumiled, 0.63 um 350 mA, M2=500
Don’t overestimate the M2 parameter of the ‘nasty’ LD beams…
Narrow stripe LD, 1.06 um, 100 mA, M2=4
Interference focusing (Generation of Bessel beams)
Prism: interference of plane waves
Conical lens (axicon): interference of conical waves
J. Durnin // J. Opt. Soc. Am. 1987, A 4, P. 651-654B.Ya.Zel’dovich, N.F.Pilipetskii // Izvestia VUZov, Radiophysics, 1966, 9(1), P.95-101
vg
vg vg
vg cos2(x)
J02(x)
Bessel beams vs Gaussian beamsAxicon
Bessel beams are ideal for optical tweezers, micromanipulation and lab-on-a-chip applications
vgvg vg
Lense
distance
pow
er d
ensi
ty
distance
pow
er d
ensi
ty
Bessel beams are typically generated with vibronic lasers
VCSEL DO-701d, Innolume GmbH, axicon 1700, I=1 mА
G.S.Sokolovskii et al. // Tech Phys Lett, 2008, 34(24) 75-82
Main problem: Low coherence???
Interference focusing with Laser Diodes
Interference focuing with High-power Laser Diodes
Main problem: Poor beam quality
Radiation wavelength λ = 1.06 µm. Axicon apex angle 1700. Central lobe size d0 = 10 µm.
Multimode Filamented Oblique
Axicon apex angle 1700
Bessel beams from the broad-stripe LD
G.S.Sokolovskii et al. // Tech Phys Lett, 2010, 36(1) 22-30
Propagation length of Bessel beams generated from Laser Diodes
Распространение Бесселева пучка, созданного аксиконом
vg
vg vg
Фокусировка Гауссова и квази-Гауссова пучков линзой
exp(-2r2/w2)
.
. .
.
2M
NA
M
2
M2LD=10-50
M2LED=200-500
Распространение Бесселева пучка, сформированного
из расходящегося Гауссова пучка
zB0 J02(r) exp(-2r2/w2) z0 zB
.
vg
vg
.
Achieving ‘non-achievable’ intensity gradients with broad-stripe LDs
Broad-stripe LD 1.06 um, М2=22, interference focal spot dia = 4 um
LED 0.63 um, М2=200, interference focal spot dia = 6 um
(Fiber axicon(Fiber axicons manufactured by Maria Farsari and colleagues, FORTH)
Fiber axicons
5000100001500020000250003000035000
40
50
60
70
80
90
100
5000100001500020000250003000035000
40 60 80 10040
50
60
70
80
90
100
NA
M
2
1
Applications of LDsWhat’s next?
• Data reading/recording• Telecoms• Laser printing• ‘Direct’ applications: cutting/drilling/welding • Pumping of other lasers and frequency conversion • Biology and medicine
$7B → $1T
Laser projectors: Green Light?
Microvision SHOWWX Laser Pico Projector
MacWorld 2010 Best of Show award
Samsung H03 Pico Pocket Sized LED Projector
Aiptek PocketCinema T30
No need for focusing!
From laser printers to 3D printing
Telecoms/Datacoms: Silicon Photonics?
On-chip Datacoms: Size matters?Energy matters!
What counts? fJ/bit!
Polariton Laser?
Automotive applications: laser ignition?
Optical tweezers: lab-on-a-chip?
Waveguide: light in matter
‘Inverse’ waveguide: matter in light – optical tweezers
‘Lab’
‘Chip-in-a-lab’ ‘Lab-on-a-chip’
‘Lab-on-a-chip’
‘Laboratory’
Lab-on-a-chip
Fluorescent microscopy: need for color?
480 500 520 540 560 580 600 620 640 660
0,01
0,1
1
10
100
0,01
0,1
1
10
100
960 1000 1040 1080 1120 1160 1200 1240 1280 1320
Fundamental Wavelength, nm
Pu
mp
Po
wer
, mW
SH
Po
wer
, mW
SH Wavelength, nm
Extracellular heat shock proteins (Hsp70) and ceramides are known to possess high adjuvant activity for cancer vaccines and low-immunogenic vaccines against dangerous infections. Hsp70 and ceramide can activate receptors of the innate immunity (TLR4) and boost protective immune response reactions against abiotic stress factors and biopathogens.
Generation of Heat-Shock Proteins and Ceramides with Laser Diodes
Laser diode
Power supply
Hsp70 Pulse duration 100 nsFrequency 10 kHzWavelength 1060 nm
LDs for Mid-IR (1600 nm - 5000 nm)
0
10
20
30
40
50
60
70
80
1300 1500 1700 1900 2100 2300 2500 2700
Wavelength, nm
Sp
ectr
al d
ensi
ty
W
/nm
LED22
LED20f=500 Hz
LED18
In Mid Infrared spectral range 1600-5000 nm lies strong absorption bands of such
important gases and liquids as:
CH4 , H2O, CO2, CO, C2H2, C2H4, C2H6,
CH3Cl, OCS, HCl, HOCl, HBr, H2S, HCN, NH3 , NO2 , SO2 , glucose and
many others.
16 μm
Thank you for your attention!• Applications of semiconductor lasers. ‘Revolution’ of light.
• Basic principles of laser operation (only to remind).
• Absorption and gain in semiconductors, inversion of population and conditions for it's achievement.
• Rate equations. Lasing threshold. Laser efficiency.
• Modulation of the laser signal. Gain clamping.
• Fiber-optical applications. DFB and DBR lasers. VCSELs and VECSELS
• Waveguide in LD structure. Modes of the waveguide.
• Beam-propagation (‘beam-quality’) parameter M2 and how to measure it. Achieving maximum power density with LDs.
• Interference focusing of LD beams.
• What’s next? New applications and problems to solve.