High Power, High Brightness Laser Diode Technology Berthold Schmidt ISLC 2008, Sorrento September...

High Power, High Brightness Laser Diode Technology

Berthold Schmidt

ISLC 2008, Sorrento

September 2008

222

My special thanks to

Boris Sverdlov, Nobert Lichtenstein,Susanne Pawlik & Gunnar Stolze (Bookham)

John Marsh, Iulian Petrescu-Prahova,Chris Baker, Stewart McDougal,

Steve Gorton (Intense)

Reinhart Poprawe (ILT Aachen)Toby Strite, Victor Rossin, Erik Zucker (JDS Uniphase)

Friedhelm Dorsch (Trumpf)

Bernd Witzigmann (ETH Zürich)Christoph Harder (Harder & Partner)

Stefan Heinemann (Fraunhofer Institut USA - Visotek)David Roh (Coherent)

Volker Krause (Laserline)

Ed Wolak, Jim Harrison, Michael Atchely(Newport Spectra)

the IEEE publishing organization .... and many more.

33

Introduction·Global photonic market view·Fields of application·Underlying technologies

·Materials for High Power Laser (HPL) Diodes

Component design for high power fiber laserand direct diode systems

·Epitaxial desin g·Waveguide design·Chip reliability and quality assessment (life testing)·S ysem t d esgn i aspecs t

Summary and outlook

44

World wide photonics market

Market segments and estimated revenuesCircled: Major application areas of High Power Laser Diodes

55

Projected Market Growth till 2015

66

HPL Applications at a glance

·material processing, analysis, measurement Production technology

Optical communication • Data transmission, Optical amplification

Defence & Aerospace

Information Technology • Optical storage, printing, marking, display

·Aesthetics (Skin treatment,..), surgery, Medicaltherapy (PDD -Photodynamic disinfection-, PDT -therapy-,..), ophthalmology, Cancer treatment

·Communication (inter satellite,..), distance measurement, countermeasure,

target designation, Illumination, LIDAR,...

77

Production Technologies:Geometric scalin of material rocessing p g

1970 1980 1990 2000 2010Year

Which Laser for which Application?

Source: Prof. Dr. Reinhart Poprawe, ILT (AKL 2008)

102

100

10-2

10-4

10-6

-810

Drilling

Hard Materials

Engraving Tuning Marking

Micro joiningElectronics

Sheet Metal

Cutti ngMicro welding

FormingWeld ing

Electron ics Microelectronics

Semi finished Prod ucts

Optoelectronics Micro Lithography

Communication Data Processing Optical Memories

Surface TechnologyFunctional Surfaces

Micro processing

Light weight structures Automotive

Ship Building

Selective Laser

Computer chips

Remote

Hybrid

Melting

Pol ish ing

Bio-photonics

LIBS

EUV/13nm

88

Application example: welding of thin foils

Foils-Polypropylen (PP) transparent and blackthickness 100 µm

Microfluidic device- PMMA or PP sealingfoil (75 µm)

P= 1,4 –5,9 Wv= 50 to 250 mm/sd0= 70 µmdweld seam = 150 to 500 µm


Application example: laser polishing

Materials: 1.2343, 1.2344, 1.2316

Initial state:mille, d eroe, d dgrinded Sharp edge

maintained

1 mm

2002 2008Ra = 0,35 µm Ra = 0,09 µm

24 µ m)


9

101010

Application Examle p SLM of ZrO2-based Ceramics

10 mm

·Zirconium oxide (ZrO2): max. bending strength, resistance to wear and tensile strength

·Principle of Selective Laser Melting (SLM): Ceramic powder is fully molten (no sintering)

·Potential Application: Production of full-ceramic dental prostheses

SLM demo parts


1111

Optical Communication:E ary l driver for high power laser dioes d

Under the Ocean On the Ground

Optical communication for inter satellite, “submarine” and terrestrial areas. Supporting phone, internet and TV related digital data traffic.

g

In Space

1212

Defence and homeland security applications:slowly evolving

Laser countermeasure system against heat-seeking missilesExample: Directional Infrared Countermeasure D istance measu rement(DIRCM)

from Northrop Grumman (public Information)

,Target designation

Laser area defence system (LADS from Raytheon)(public Information)

- Laser fuses- Illumination- Detection of chemicals

1313

Information technology:optical storage, printing, display

CTP Printing - Computer to plate (CTP)Prinng ti

- Digital printing

- Display (RGB) technology - Rear projection TV

14

Medical applications:

Surgery Before After

Skin Treatment: Tattoo / Hair Removal

- Acne treatment

- Photodynamic Therapy (PDT)- Photodynamic Disinfection

(PDD)- Dental

Before After

Hair removal

Ophtalmology

15

Why choosing high power laser systemsamong other production technologies

·Processing Speed·Process Accuracy·Process Consistency·... cost (reduced cost of consumables)·Uptime (Reliability)·System flexibility·Compactness·Greener Processing (low environmentalimpact)·Enabling new fields of application

161616





Summary and outlook

1717

HPL Applications: underlin y g technoloies g

·Optical Pumping: DPSSL, fibre Laser Production technology

(Er/Y), Disk Laser, Direct Diode LaserSystems

Optical communication • DFB laser diodes, EDFAs, Ramanamplifiers

Defence & Aerospace

Information Technology • Red and short wavelength diodes, directdiode systems, SHG (frequency doubling)

Medical & Life science • Low energy, direct diode, DPSSL, fibrelaser

·– pumpng, rec t oe snge YAGiDidi d ( i lelement, stacks), DPSSL, fibre laser,

1818

Laser Market Development by Laser Type

1.400

1.200

1.000

800

600

400

200

0

Laser Type


World Market 2007

Extrapolation of current trends to 2010

Including new applications / markets 2010

19

Underlying technologies:Erbium doped fibre amplifier (EDFA)

3 level energy sysem t when pumped with 980nm light 2

level system when pumped with 1480nm light

20www.bookham.com

Why High Power 980nm Pumps?

Typical 3-stage EDFA

E rbiu mDoped Fiber

DispersionCompensating

Fiber

GainFlattening ErbiumErbiFilter Doped Fiber Doped Fiber

um

Isolator & filter Coupler Isolator

Input Coupler

980 Pumps:·A vn : d a tage

1480 Pumps (now 980nm !):·Advantage:

Output

·Low noise figure (3 level)·Low heat load·High laser efficiency·Low cost coupler

·Un-cooled operation

·Disadvantage·Lower optical

power conversion efficiency

·higher optical conversion efficiency

·Disadvantage·Increased noise figure·More expensive coupler·High heat load, expensive cooling

High power 980 pumps enable low cost EDFAs

www.bookham.com

14xy Pump laser for Raman amplifier

Features—* Coupling to optical phonons in the glass

—* max. gain at frequency shift of 13 THz in silica (60-1 00nm)

—* broad (but not particularly flat) gain spectrumAdvantaes

g

—* Effect present in all fibers (using installed fibers)

—* Gain at any wavelength only limited by pump

source —* Low noise figure because of low ASE

—* Distributed amplification

0.0E+00

4.0E-04

8.0E-04

6.0E-04

2.0E-04

Raman Gain @ pump wavelength 1455 nm

1450 1500 15501600 1650

Wavelength (nm)

Disadvantages

—* Fast response time (no upper state lifetime

buffer) —* Pump fluctuations -> gain fluctuations ->

noise

—* Polarization dependent gain

—* High pump powers required (>200 mW)

22

Laser system desin g principles

transversally p um p ed rodlaser

INNOSLAB laser

fibre laser end-pumped

thin fibre ldisk laser

aser “Y” -pumped

All based on the same design principle requiring

·Mirrors (Cavity)·Gainmedium·Pump source

Extension...amplifier technology


www.bookham.com

Fibre laser pumping scheme

CP-active fiberMulti-mode pumpsFiber

com b i ne r

FBG FBG

Multi-mode pumps

Cladding pumped fiber: Yb / Er in SiO2Emission wavelength: 1.08 / 1 .53umPump wavelength at 915, 960, 975 nmPump source: Broad area single emitters / Bars Output power: ~100W -> xxkW

Fiber laseroutput optic

CP-active fiber

Single Mode Pump“Seed laser” ~1 064nm

Fiber laseroutput optic

Multi-mode pumps

Filter

Presentation title TRUMPF abbreviation - 2007/03/25 24Presentation title TRUMPF abbreviation - 2007/03/25 24Presentation title TRUMPF abbreviation - 2007/03/25 24

Rod- and Disklaser �Lamp pumped Rodlaser

Beam quality

Efficiency '

Arc lampsRod

�Diode pumped Disklaser

Laser-diodes

Disk

Beam quality

Efficiency

Presentation title TRUMPF abbreviation - 2007/03/25 25Presentation title TRUMPF abbreviation - 2007/03/25 25

Disklaser: TruDisk

TruDisk 1000 TruDisk 8002


Design of a disklaser (8 kW)

Resonator

Parabolic Mirror

Outcoupler

Bending prisma

Laser beam

Actually: 20 passes of the pump light through the disk!

Pumping of a Disk

1 Disk

1Pump- Beam

C avy it

End-mi rror

4

5

1

8

7

2

6

3

Presentation title TRUMPF abbreviation - 2007/03/25 27

Presentation title TRUMPF abbreviation - 2007/03/25 28Presentation title TRUMPF abbreviation - 2007/03/25 28Presentation title TRUMPF abbreviation - 2007/03/25 28

> 5 kW Output Power per Disk

6000 70

0 2000 4000 6000 80000

5000

4000

3000

2000

1000

60

50

40

30

20

10

0

Pump Power Pp (W)


TruDisk 10003 –4 disk resonator

14000

12000

10000

8000

6000

4000

2000

0

70%

60%

50%

40%

30%

20%

10%

0%

0 5000 10000 15000 20000

Pump Power Pp [W]

303030

Fiber, Disk or Direct Diode Laser?

1000Ha rd en ing

Polymer weldingB razi ng

Sold eri ng

‘SM’

fiber

Welding, sintering, surface treatment

Cladding

D ee-en etration p p

we l ding Metal cutting

Non-Metal cutting

Marking

Drilling

100

10

1

Pri nti ng

1 10 100 1000 10000

Sources:

•P. Loosen, Fraunhofer Inst. Aachen

Laser output power (W)

3131

Fiber, Disk or Direct Diode Laser? .... many applications don’t needhighest beam quality (diffraction limited beam).

Sources:

·P. Loosen, Fraunhofer Inst. Aachen·C. Harder LEOS 2006

Laser output power (W)1 10 100 1000 10000

1000HardeningPolymer welding

CladdingB r a z i n g

D ee-en etration p p

we l ding Metal cutting

200um0.22,

60um,0.22 100

Sold eri ng

Welding, sintering, surface treatment

10

P50um .0.22

ri nti ng

Non-Metal cutting

Marking

Drilling1

‘SM’

fiber

1 500um,0.22

3232

2w0

f

BPP = θ · w0

Developing trends for Lasersand their applications

2003 20081.000

100

0.1

10

1

1 10 100 1.000 10.000

Printingtherm. marking

Diode lasers(2003)

F#4 focusingoptics (NA 0,12)

soldering

lamp pumpedNd :YAG-laser

plastics welding

selective laser powder remelting

CO2-laser

brazing

metal s e e h t cutting

DPSSL

transformationhardening

melting,cleaning

deep penetration welding metals

Laser Power P [W]


3333

Introduction·Global photonic market view·Fields of application·Underlying technologies·Materials for High Power Laser (HPL) Diodes



Summary and outlook

3434

Materials for Semiconductor Laser Processing

3535

Wavelength Range for major industrial applications /technologies requiring (red / MIR) HPL

DPSS

Med ical

Med ical

Med ical

Printing

Opticalstorage

TelcoPumps

TelcoPumps

Display,...

Laser TV Pumps & SHG

LIDAR

Fiber Laser Pumps

FiberLaserSeeds

Direct Diode Applications

Nd YAG Replacement

600nm 700nm 800nm 900nm 1000nm 1100nm 1400nm 1600nm

GaP Capability GaAs Capability InP Capability

3636

Pearls of Laser History

MOPA, SEDFB, α-DFB Tunable l

Quantum Dots,Quantum Cascade Lasers, new materials,new process technologiesnew integration technologies intercavity Lasers (SHG) monolithic Integration

asersFBG-StabilizationFlared / Taper Design Efficiency I mprovements New Waveguide Designs Materials

Laser bars / Stacks

1917 1950s 1960s 1970s 1980s 1990s 2000s 2010s

Herbert Nelson, RCA Liquid Phase Epitaxy 1962

3737





Summary and outlook

3838

System Design Requirements

Majority of diode based laser systemshave common d esgn i requiremens: t

·Efficient coupling into

passive optics elements or

an optical fiber (with low NA)

·High wall plug efficiency (low power consumption)·Good system reliability·Cost competitive·Simple to use (cooling, turn on time, robustness,...)

From a diode perspective this relates to various designobjectives....

3939

Laser diode design targets

Common design requirements for high power laser(HPL) diodes:

·High output power·High brightness·High wall-plug and coupling efficiency(low power consumption)·High reliability + robust·Design capable for high volume manufacturing

4040

Challenges for the design of HPL

Output Power , Capacity

Robustness for Volume Manufacturing

Subsystem Design (Cost, Brightness, Reliability)

Chip Reliability (Bulk / Facet) – Quality assessment

Epitaxial Structure

Waveguide Design

4141

Challenges for the design of HPL:Wall-plug efficiency – Broad area single emitter laser

Output Power, Capacity

Key measure for high power laser diodes:

η =

WPh I I

ν η ν η ν η ν η

( )

d th dth

− ⎞

= − −⎛ ⎛

h I

⎜ ⎝ 1 ⎠ ⎟qIV qV I(wall-plug efficiency)

Others: defect density, material properties (i.e. expansion match)

Epitaxy

Design parameters:·bandgap profile, carrier

confinement·d/gamma, confinement factors·doping

profi le,·growth

processKey characteristics:·internal losses,·internal quantum

efficiency,·series resistance, laser

voltage·thermal resistance

Waveguide characteristics:·Optical

Confinement,·Vertical far f ield,·Coupling efficiency,

...

www.bookham.com

Similar laser structures with varying η ηWP

0 2 4 6 8 10

12

14

0.7

0.

6

0.5

0.40.3

0.2

0.1

0.0

WPE 1WPE 2P 1P 2

4

2

6

0

14

12

10

8

current (A)

• Device characteristics show importance of a balanced desin aroach:g pp

– Similar differential quantum efficiency

– different terminal (operating) voltages=> different doping profiles impacting wall-plug efficiency (5-6%)

434343

Differential quantum efficiency

·

η i − − injection efficiency, defined as fraction of injected carriers which are converted into optical radiation by the stimulated emission;

− physical effects controlling it are not very well established;− difficulty: carrier loss rate increases with increase of carrier

concentration (quasi-Fermi level separation), but both stabilize at threshold

=

η η ηd i ln 1 1 2

()

R R

⎛

⎜

⎝

1+

2 α i L ⎞ ⎟

1⎠

·

α − d i s t r i b u t e d l o s s α = α + α + α

i , i FC scatt. coupl.

Free carrier absorption

αp = 7 - 14⋅10-1 8p; α n = 3 - 6 ⋅ 10-18n

4444

Bandgap engineering example:Graded Index carrier confinement (GRICC)

0 . 5 1 . 0

InGaAs/AlGaAs GRICC design

·provides efficient0.8carrier confinement

·stable control of vertical waveguide·low internal losses

-1

(below 1cmreported)-1.0

Hole Quasi-Fermi Level

-1.5

Valence Band

-2.0

Vertical Position (a. u.)B. Schmidt et al. Proceedins g of SPIE Vol. 5248, SPIE, Bellinham g , WA, 2003, 42-54.

0.0

-0.5

Electron Quasi-Fermi Level

Conduction Band

0.6

0.4

0.2

0.0

4545

Low loss laser waveguides:strong guided structures

The main idea - to minimize overlap between optical mode and regions of high doping to reduce internal absorption losses

Very strong confinement undoped waveguide

M. Gokhale et al., JQE, v.33, p.2236 (1997)

4646

Low loss waveguides:Shifting mode into n material2. A symmerc t i wavegues

id

Mode maximum shifted from the QW position: lower FC absorption in QW-1

Values of aFC as low as 0.4 cmwere reported

Free carrier absorption in p material is higher than in n material: - higher absorption cross section;- higher doping for comparable conductivity required;=> The design idea is to shift optical mode from p- to n-type material

In addition higher order modes can be suppressed

M. Buda et al., JSTQE, v.3, p.173 (1997) C.M. Stikley et al., SPIE Proc., v.6104, (2006)

4747

Minimizing laser diode voltageLaser voltage V = Vj +IRs+ Vhb:

*

*·Vj - voltage on pn junction; stabilizes at threshold:

V j = F n − F p

·V hb - voltage drop on (isotype) heterojunctions throughout laser

structure:usually minimized by graded hetero-interfaces

·R s - series resistance: compromise has to be found to reconcile requiremens t of l ow d opng i f or high ηd and high d opng i f or l ow R s

M. Kanskar et al., Electron Lett, v.41, (2006)

4848

Example: Multi-mode single emitter diodefor fiber laser pumping

·793nm pump wavelength for Thulium based fiber lasers·Waveguide with ~90 um aperture·3.5 mm chip length·Achieving around 10-11 W roll over at 25 C (CW)·High wall plug efficiency

4949






Epitaxial Structure

Waveguide Design

5050

Optical Waveguide & Substrate modes: GaN* laser diodeGaN SiC Al2O3

Strain % 0.0 3.4 16

Refr. Index 2.52 2.75 1.78

SNOM

Simulation

GaN-Substrate, dtot = 100μm

2 µmPotential Impact ofSubstrate Modes:

vertical section

. . .

- otical lossp

- gain oscillations

*Source: Prof. B. Witzigmann et al., IEEE JQE 2007

www.bookham.com

Challenges for the design of HPL:Waveguide Design – single mode ridge laser

Output Power, Volume

SQW - GRICC Structure InGaAs/AlGaAs intensity profile

gain profile

Waveguide Design impacted by

·length scaling,·spatial hole burning,·local heating,·carrier injection·refractive index step (etch

depth),=> slow axis diverence linear ower near field attern

g , p ,p

52

2D simulation (*) of GaAs-based high-powerSM-Laser Diodes

- Most often 1 – 2D simulation- Solving wave equation with

changing parameters, i.e. at increased drive currents (time consuming)

- Input Parameters often not fully explored

Pictures: Boundaries and simulation domains for modeling high power laser diodes.

*Source: Prof. B. Witzigmann, ETH-Zurich

Wave guiding impacted by free carriers, etch depthand temperature...

Ridge

High waveguide stability is essential for every laser diode used for telecom-

Active region and non-telecom applications

Influenced by> Refractive index step > free carrier density> temperature variations

(thermal blooming,..)

B.Schmidt et al., Proceedings ISLC 2002

Temperatureinduced index change

53

545454

(significant higher relative increase of optical losses of 1st, 2nd and.. order modes as compared to the zero order mode)

=> suppression of coherent coupling with higher order modes (higher linear power)

Lateral Waveguide stabilizationfor high power spatial SM laser diodes

High power SM operation

> Linear Powers up to 1.9W achieved (*) > Low divergence leaky waveguide> Stabilization of fundamental mode

by increasing losses of higher order modes

* Wenzel et al., “Fundamental-Lateral Mode Stabilized RWG Lasers”, IEEE Phot. Tech. Let., Vol.20, No.3, 2008

5555

Length scaling

Both electrical and thermal resistance of the chip are inversely proportionalto the its waveguide active area;

broad area laser

V. Gaontsev et al. Proc. o SPIE v. 6104 2006 p, f (injected current (mA)

56

5670.1

2

3 4 5 6 7 12

3 4 5 6 7 10

( )zg

Asymmetric power/current distribution along the wavguidePower distribution inside laser cavityOptical intensity distri

0.8

0.6

0.4

0.2

0.0

1.0

Rfront= 0.1%Rback = 100%

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

cavity length (a.u.)

0.0

2520

15105

0

front facet reflectivity (percent)

=>> refractive index and gain profile changes along laser cavity

Δ F * z ⇒ N z ⇒( ) ( )

( )z*

)VΔ F

+ j z z

( ) (

ρ

( )z= +R R

spstim

j

(zRstimΓ( )

z g

=

hcS) [ ( )

( ) ]

P z P z+ + −

facetRate equations refl

ed

Voltage on laser

e

I = ∫ L j z d z

0 ( )

www.bookham.com

Challenges for the design of HPL:Waveguide Design – single mode ridge laser

0 500 1000 1500 2000 2500inected current mA j

()

Output Power, Volume

1600

1400

1200

1000

-200

400

200

800

600

0

junction side up CW-operation= °T 2 5 C

G03

G05

G07

G06

G08 >100MW/cm2

Waveguide DesignLength Scaling, Spatial hole burning, local heating, Carrier injection Refractive index, slow axis divergence

585858






Epitaxial Structure

Waveguide Design

5959

Long term reliability & COMD protection

Catastrophic Optical Mirror Damage (COMD)

Free carrier absorption

Stimulated

E m i s s i o n A b s o r p t i o n :e-h

Non-rad iativerecombinationvia surface states

Facet Degradation leads to formation surface states Surface states cause non-radiative recombination

Non-radiative recombination leads to a local increase of current injection This leads to an increase of the local temperatureWhich causes a further shrinkage of the bandgap and thus an

increase of free carriers

Additional generation of e-h pairs leads to further absorptionof stimulated laser light causing an acceleration of the thermal run away .... COMD

6060

Avoiding COMD

Avoid or reduce formation of non-radiative recombination states ·E2

-> Cleaving in high vacuum and in-situ passivation of the cleaved surface

·Use of InGaAsP based barrier materials -> reduced oxidation (“Al-free”) -> re-growth covering cleaved facets possible

Remove formation of non-radiative recombination states ·“Cleaving on air” -> Dry etching in vacuum -> in-situ nitridation or sulphation

·“Cleaving on air” -> low energy hydrogen plasma or ion beam cleaning -> in situ passivation (ZnSe, Si,...)

M. Gasser, E.E. Latta, "Method for mirror passivation of semiconductor laser diodes," U.S. Patent No. 5063173 M. Hu, L.D. Kinney, M.

Pessa, et al.,"Aluminium-free 980-nm laser diodes for Er-doped optical fiber amplifiers," SPIE 1995, vol. 2397, 333-341

K. Hausler, N. Kirstaedter, "Method and device for passivation of the resonator end faces of semiconductor lasers based on III-V semiconductor material," U.S. Patent No. 7033852

L .. K Lindsrom, t et al."Meo th d to obtan i contamnaon i ti free laser mirrors and passivaon tiof these," U .. S Patent No. 6812152

H. Kawanishi, et al."Semiconductor laser device with a sulfur-containing film provided between the facet and the protective film," U.S. Patent No. 5208468 E.C.

Onyiriuka, M.X. Ouyang, C. E. Zah, "Passivation of semiconductor laser facets," U.S. Patent No. 6618409P. Ressel et al. "Novel Passivation Process for the Mirror Facets of Al-Free Active-Region High-Power Semiconductor Diode Lasers," PTL 2005, vol. 17, no. 5,

962-964

www.bookham.com

Long term reliability & COMD protection

E2 by Bookham: Stress test of first generation 980nm SM laser diodes

330

310

290

270

250

230

210

1901990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007

Time (years)

626262

Avoiding COMD

Reduce number of free carriers at the laser facet

·Reduce direct carrer i injecon ti without changng i the bandgap (at wafer level process)

Front section isolation

·NAM (non absorbing mirrors) to reduce absorption, diffusion and thermalized carriers (at wafer level process)

Zn diffusion

Etching and subsequent re-growth of a III-V window Si-

doped and disordered windows

Vacancy induced windows (QWI)

B. Schmidt et al., US Patent 6782024 - High power semiconductor laser diode

H.0. Yonezu, M. Ueno, T. Kamejima and I. Hayashi, "An AIGaAs Window Structure Laser," JQE 1979, vol. 15, no. 8, 775-781J. Ungar, N. Bar-Chaim and I. Ury, "High-Power GaAlAs Window Lasers," EL 1986, vol. 22, no. 5, 279-280R .. L Thornon, t D .. F W ec, l h R .. D B urnam, h T L. Paoli and P .. S Cross, "High power (2.1 W) 10-srpe t i AlGas Alaser arrays with Si disorere d d facet windows,"

Appl Phys Lett 1986, vol. 49, no. 23, 1572-1574S. Yamamura, K. Kawasaki, K. Shigihara, Y. Ota, T. Yagi and Y. Mitsui, "Highly Reliable Ridge Waveguide 980nm Pump Lasers Suitable for Submarine and Metro

Application," OFC 2003, vol. 1, 398-399J.H. Marsh, C.J. Hamilton, "Semiconductor laser," U.S. Patent No. 6760355

6363

Effect of front section isolation *( )Standard Contact

Truncated Contact

Reduction of current injection into front section (reduced local heating)

Reduction of free carriers (impact on the gain profile)

*Source: Prof. B. Witzigmann, ETH-Zurich

6464

Avoiding COMD: QWI (quantum well intermixing)

·Uncoated 830 nm lasers·Test conditions: Initial CW measurement followed by a pulsed L-I

NAM45 nm shift

NAM0 nm shift

0 250 500 750 1000 1250 1500 1750Current (mA) Increase of the bandgap close

to the facet region

Reduction of free carriers Reduction of local absorption

350

300

250

200

150

100

50

0

NAM65 nm shift

QWIregions

Transparentoutput

waveguide

ConventionalLaser

6565

QWI process concept

As-grown bandgap Intermixed bandgap

Al

Ga

AlGaAs GaAs AlGaAs AlGaAs

QWI allows bandgap tuning in selected areas of the chip

6666

QWI Process StepsIntense QWI technology enables high power/brightness lasers to be produced

in a manufacturing environment·Dielectric caps are deposited on surface of wafer·W aer f i s anneae l d·Quantum wells intermix with adjacent material altering the bandgap wavelength·Wavelength change depends on properties of dielectric cap

QWI works in a variety of materials and wavelength s·808 nm SQW material used in this work

Photoluminescence spectra160

140

120

Intermixing cap Suppressing cap100

80

60

QW

20

0

700 720 740 760 780800 820 840 860

Wavelength, nm

40

Suppressed Intermixed

High TemperatureAnneal

6767

Life testing array with 64 single emitters(QWI – technology)

64 emitter life testEach device operates at 808nm with >200mW output power, room temp.

68


–

Epitaxial Structure

Waveguide Design


Chip Reliability (Bulk / Facet)

Quality assessment


Output Power,

Capacity

696969

Quality assessment andlife test strategies

Challenge for quality control of high power laser diodesfor industrial laser systems

·No clear industrial standards defined, yet.(in comparison to Telcordia standards for fibre networks -GR-468-)

·Different system requirements in different industries(from commodity to space application)

·Comparison of varying technologies for similar applications

Single emitter high power laser diodes (spatial multi-mode or single

mode) 1 cm High Power Laser bars with varying fill factors“Mini-Bars” and related devices

Differn e t worin d g to describe reliability (FIT, MTBF, MTTF, end of life,...)

·Additional influence factors

Mounting (Indium or hard solder (AuSn, SnAg, SnAgCu,...))

Cooling (passive cooling, active cooling (TEC, micro-channel, macro-

channel) Environment (hermetic, non-hermetic, ....)Operating regime (CW, quasi CW, pulsed)

Cost of life test equipment and test

7070

Classical life test strategy:single emitter devices

Assumptions·Known failure modes

·Laser diode lifetime follows “bath tube” curve·Infant mortality rate is vanishing or can be screened out by burn-in

·Constant failure rate (intrinsic period) is determined by sudden death (or a short wear out period followed by sudden death)·Wear out is expece t d to kick in after guaranee t d d evce i life time

a kbT)∝ x y −

·Constant failure rate can be described by: FR

I P e x p ( E

tonset

Example: Reliability testing of 980nm telecom chip

·Stress cells with different conditions (acceleration of failure rate)·high number of stress cells and devices·similar failure mode as at “field condition”·failure rate for each condition (must be constant)

·Determination of the acceleration factors in the reliability model with maximum likelihood approach (Ea , x , y)

·Prediction of reliability at use conditions: 30 - 500 FIT

0 500 1000 1500 2000Current (mA)

www.bookham.com

1200

1400 25 °C

Testi ng

1000

85 °C800

600 Use400

200

0

45 °C

°65 C

727272

Challenge of qualifying industrial devices

·High Power (single emitter) Laser Diodes are expected to operatecloser to 1 – 5kFIT at standard operating condition (in comparison tobelow 100FIT for telecom “submarine” applications)

·Acceleration of failure rates is more challenging since devicesoperate closer to the thermal roll over point at standard operatingcondition

·Cost of life testing can be significant if devices have to be tracked insitu and separately operated / cooled for conditions ranging from(10-20A, 25°-75°C heat sink temperatures)

·Operating conditions might vary severely (CW, quasi CW, pulsed)

7373

Central life test philosophy

er

– 0.15 or 0.22NA

– Rth= 2.2oC/W– rae pow10W t d

74 © 2008 JDSU. All rights reserved. SSDLTR June 2008

Example: JDSU L4 module performance & testing

·Fiber-coupled package– 105 μm diameter

– 50% wall plug 00 5 10

15 2025

Current (A)

·Laser chip InAlGaA

s–– 880-1000nm

– 100μm aperture 20

– 4.1mm cavity– AuSn solder 15

25 75%ex-ace

f

tex-fiber

15C

45%

30%

60%

15%

0%

10

5

10%

5%

0%

-5%

·Packae Testg

– 10W, 12A – T case = 35oC– 14 lasers– 0 failures -10%

0 1000 2000 3000 4000, , , ,

Time (hours)


Accelerated life test examples

·Chip Life Test– 9 ., 3W 13A – Tcase = 70oC– Tj= 117oC– 28 lasers

– 0 failures

TimeZero

MechShock

85°C / 85% RH Damp Heat

Vibration


L4 Package qualification and robustness tests

• Reference Telcordia GR-468– ero pacage aures n u suteZ k f il if ll i

– Proves robustness of design

500G Mechanical Shock+ 20G Vibration

-10%

10%

-5%

5%

0%

18 units

0 1000 2000 30004000 5000

Time (hours)

-40°C to +85°CTemperature Cycling

-10%

10%

-5%

5%

0%

27 units

0 100 200 300 400 500

No of Cycles

10%

5%

0%

-5%

-10%12 units

Pump power trends – commercially available

10

1

L 4 6 3 9 8

L3-6 397

L3-63 96

L3-6 390

L2-6380

•

•

•

9XXnm105μm diameter fiber “Reliable” rated power

1992 1994 1996 1998 2000 20022004 2006 2008

Year

·15% annualincrease in reliable

power

·imilar trend orS f– 8XXnm–

Singlemode lasers– Multi mode lasers

– Bars


787878

Life t esng ti of laser dioe d bars

Important to understand

·cooling type·fill factor (FF) of bars

·operational mode (CW, pulsed, QCW)·expected degradation scheme(gradual degradation, sudden failure or a combination)·and expected failure mode(stress induced failure, contamination induced failure,COMD, bulk fail or combinaon,... ti )

7979

Types of coolers for hard solder bar mounting

(*)

- Passive Cooling (copper heat sink with heat exchanger -> Water or Air cooled)- A cve ti C oong li of high power bars (micro, meso or macro channel cooer l )

- Active cooling of single emitter devices (TEC and heat exchanger)

* Christoph Harder; “Chapter: Pump Diode Lasers”, Optical Fiber Telecommunications V A (Fifth Edition), Components and Subsystems, Editor: Ivan P. Kaminow, Tingye Li andAlan E. Willner, pp. 107-144.

Current (A)


Current (A)


Current (A)


Results – Compare FF = 50% to FF = 33% �Microchannel Cooler (MCC)

Rth = 0.23 C/W

L = 3.5 mm

P = 200 W (FF=50%)

P = 207 W (FF=33%)

0 50 100 150 200250

270

300 70

MCC60

240

210 Tj = 60 C 50

40180

150

30120

FF=50% Model FF=50% Data FF=33% Model FF=33% Data

90

60

30

0

20

10

0

Current (A)


Current (A)


Results – Compare FF = 50% to FF = 33% �Mesochannel Compact Heat Exchanger (MesCHE)

Rth = 0.38 C/W

L = 3.5 mm

P = 127 W (FF=50%)

P = 151 W (FF=33%)

0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0 2 2 0

50

240 60

MesCHE

160 Tj = 60 C 40

140

120

100

80

30

20FF=50% Model FF=50% Data FF=33% Model FF=33% Data

220

200

180

60

40

20

0

10

0

828282

Life testing of laser diode bars:modes of operation

Short pulse operation I ntermittent-CW operation

Optical pulse

Current (us)

Semiconductor / Mount Temp

Mechanical stress

Current (s) GaAsα = 6 ppm/ °K

Semiconductor / Mount Temp

Mechanical stress

CuWα = 6.5ppm/ °K

Optical pulse

Cu

α = 16.5ppm/ °K

- Short pulse operation with strong variations in duty cycle and pulse length(ns - ms.... ) Application oriented (highest optical stress per pulse)

- Intermittent-CW (normally ~1 .3Hz) creates highest mechanical stress

8383

Example: QCW-Stack

HERMES QCW Stack

·10 Bar QCW Stacked Diode Arrays

·200W bars @ 808nm

·250u sec x 20Hz

·Hard solder

·MIL-SPEC

3000

2500

2000

1500

1000

500

12 %9 %

Onoin life test g g

9 %

0 -5.0E+07 0.0E+00 5.0E+07 1.0E+08 1.5E+08

2.0E+08 2.5E+08 3.0E+08 3.5E+08

Number of Shots

www.bookham.com www.bookham.com Page 84www.bookham.com Page 84

0 20 40 60 80 100 120 140 010 20 30 40 50 60 70 80 90

Drive Current [A] Current [A]

• Improved optical and electrical design– Low drive current: 60W @ 63A (50%FF) / 40W @ 42A (30%FF)– High wallplug efficiency: 53% @ 60W, 57% max WP

– Improved far field pattern: 7° x 55° (90% power)

808 BAR: High Performance in CW

160 2.5 100 2.5

140 90

802.0120 2.0

70

10060

80 1.5

50 1.5

60 40

301.040 1.0

20

2010

0.5 00 0.5

www.bookham.com www.bookham.com Page 85

Burn in Time (h] Time (h]

·Multi-cell accelerated long-term aging test – Hard-pulse (1.3 Hz, 50% duty-cycle, full ON-

OFF)·Average power wear-out <1% / 1000h (gradual

degradation) – Stability of design and proven benefits of hard

solder technology

808 BAR: Reliability assessment (Intermittent operation)

1.1 1.1

0.5

0 500 1000 1500500 1000 1500 20002500 3000 35004000

1 1

0.9 0.9

0.8 0.8

0.7 0.7

0.675W / 75A 105W / 100A0.6

0.5

868686






Epitaxial Structure

Waveguide Design

8787

Various pumping/coupling schemes

end pumping with fiber combiner

laser bar lens

step mirror

End pumping with collimated bar,

Direct applications

8888

Cladding pumped active fiber (CP-fiber)

Special fibers for hih g power fiber laser

Low index coating (polymer with low index)

•Multi-mode waveguide (normally with high NA~0.46 to provide strong guiding of the pump light)

The high NA of the double clad fiber allows multiple low NA fiber ports to be coupe l d into one fiber and to maintan ithe brightness

Rare earth doped waveguide (normally 10-30um with 0.07 NA)

Coupling pump radiation into fiber laser

Pump radiation is usually supplied through multimode fibers with core diameter D = 50 - 105 mm and numerical aperture NA = 0.15 -0.22

P

end pumping with fiber combiner side pumping

In other words: it is impossible to increase radiance by combining radiation ofTh t d h p w p n i r e a p u i s l i d a g l i n s dseveral uncorrelated but otherwise identical sources

Fiber radiance

R ≅ α P( )2

D N Acore ×

Max. No. of pumps per node2

⎛ laser laserD N Aclad clad

× ⎞

⎜ ⎟pump pump ⎝ D N A

×

core c o re ⎠

Key objective: Optimize brightness per pump source!

89

90

Example: Second-Generation Fiber Pump Modules

·Characteristics

– Multiple emitters (e.., g a single mini-bar)

– Micro-optics for beam conditioning

– More power in (e.., g higher current at std voltage)

·Features

– Enhanced brightness per fiber channel

– Reduced thermal and electrical resistance (higher power at rollover)

– CoS with single-emitter economies, no smile

– Independent dropouts, reduced facet loading, enhance reliability

– Highly scalable at module level

H2 short presentation

90

91

Mini-Bar Fiber Pump Module• -

Brightness of industrial modules now exceeds 1 MW/cm2 sr

OrionTM series

- 20W, 105um core, 0.20NA 3.8cm

- 915nm, 940nm, 976nm 30 0.6

- mini-bar architecture25 0.5

20 0.4

- very high reliability15

03Specified Operating Pt

10

0.2

Power PCE

5 0.1

0 0

0 5 10 15 2025 30 35

Current (A)


92

Mini-Bar Reliability: verification of emitter independence

Multi-Stripe Modules as Ensembles of Semi-Independent Emitters:·failures are dominated by random, sudden failures of individual emitters

·the failure of an individual emitter only impacts other emitters by an increase in ensemble drivecurrent (for constant power) and warming of the other stripes on the same mini-bar

·all assumptions are consistent with test data giving over 300,000 hrs MTBEF (mean time between emitter failure) at the specified operating point

single-emitter failures

CoS: 5-element mini-bar on CT

(AuSn solder on CuW heatsink)


92

939393

Bar Based Direct Diode Laser Systems

Material Processing requires very high powers and powerdensities!

To achieve the required power levels the followingtechnologies are applied on system level:

·Bar multiplexing with passive optical elements

·Polarization combining

·Wavelength multiplexing

9494

Bar multiplexing to achieve highest opticalpower densities for direct application

Picture with courtesy of

9595

Challenges for the design of HPL:Bar Bonding – Low Smile and High Current Capability

Subsystem design

·Submount material (expansion matched)

·Robust cooler design (avoid corrosion)·Strain – Stress (reduced at all

interfaces)·low Smile (hard solder, low smile)·Passive optics design (efficient)·Fiber diameter (low core, low NA)

Picture with courtesy of

9696

Wavelength and Polarization multiplexStack 1 (interleaved 2 x 10 bars)

Output Power System: 2 X Pstack X 3 = 10kW- 12kWBPP ~ BPP (Stack) ~ 90-200 mm*mrad

λ 1 optics opticsStack 2

Polarizationcombining

λ 2 λ 3

9797

Challenes g for the desin g of HPL





Epitaxial Structure

Waveguide Design

9898

Efficient design for robust volume manufacturing:one design platform for multiple packaging formats

TO Can forsmaller arrays

Laser Array on Ceramic Carrier

Low cost Butterfly Packageforlarger arrays

MarkingModule

Laser Array

9999

Summary and outlook

45+ years of semiconductor laser development hasbrought the technology to high level in terms of

·efficiency,·achievae bl power l eves, l·waveguide design·and reliability

Current challenges are more in the interaction with thesystem design level to optimize efficiency, brightnessand robustness of those systems

Future developments will lead to a broadening of thewavelength range, strengthening of the direct diode

laser system desins g and exploration of new fields ofapplication

100

End

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High Power, High Brightness Laser Diode Technology Berthold Schmidt ISLC 2008, Sorrento September...

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Transcript of High Power, High Brightness Laser Diode Technology Berthold Schmidt ISLC 2008, Sorrento September...