Semiconductor Nanostructures for Photonic Systems of the Future

1
Nanotechnology International Forum 2008
Semiconductor Nanostructuresfor Photonic Systems
of the Future
Prof. Dieter Bimberg Institute of Solid State
Physics and Center of Nanophotonics Technische
Universität Berlin
2
Contents

• Change of Paradigms Quantum Dots as Giant Atoms
  in a Dielectric Matrix
• High Speed QD-Lasers and Amplifiers for the 100 G
  Ethernet
• QD VCSELs for the Terabus
• A Glimpse to the Future Security in
  Communication Quantum Cryptography
• Higher Brightness for Upconversion, Welding
• New Wavelengths, ...

3
Introduction

• Matter is classified
• Gas discrete electronic states
• Liquid very dense discrete electronic states
• Solid energy bands

4
Quantum Dots Definition
A Quantum Dot resembles electronically an atom in
a dielectric cage

• Conditions
• Lateral extensions in all three directions of
  space smaller than the de Broglie wavelength of
  the charge carriers
• Not too small ? otherwise no bound state
• Not too large energy difference
  betweensublevels gt kT at 300 K

5
Pyramids classical ? quantum
Chefren Pyramide
PbSe quantum dots on asemiconductor surface
G. Springholz et al.,Science 282, 734 (1998)

• Size relations
• Base length 1010 times larger - volume 1030
  times larger !

6
Zero-dimensional Systems are Differentto 3-, 2-
and 1- Dimensional Systems
Impact of
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Contents

• Change of Paradigms Quantum Dots as Giant Atoms
  in a Dielectric Matrix
• High Speed QD-Lasers and Amplifiers for the 100 G
  Ethernet
• QD VCSELs for the Terabus
• A Glimpse to the Future Security in
  Communication Quantum Cryptography
• Higher Brightness for Upconversion, Welding
• New Wavelengths, ...

8
Evolution of Network Traffic
x 30 in 5 years
2000
2006

• Increase of traffic from 2001 to 2006 by a factor
  of 30? A factor of 1000 every ten years !

9
Higher Speed Study Group (HSSG)

• For standardization of 100G Ethernet

• IEEE 802.3ba HSSG Objectives Criteria
• Provide Physical Layer specifications which
  support 40 / 100 Gb/s operation
• Bandwidth requirements for computing and
  networking applications are growing at different
  rates. These applications have different cost /
  performance requirements, which necessitates two
  distinct data rates, 40 Gb/s and 100 Gb/s.
• HSSG is predicting that the standard will be
  completed in 2010.

10
Mode-Locked QD Lasers for 100 G Ethernet

• Advantages of QD gain medium
• Broadband gain medium (30 50 nm ground state,
  gt80 nm incl. excited state)
• Ultrafast carrier dynamics (10-100 fs components
  of carrier relaxation)
• Low noise gain medium (record low RIN -160 dB/Hz)
  
• High temperature stability (T0 inf. below 75
  C)
• Low threshold current density (lt 10 A/cm2 per dot
  layer)

11
Threshold Current Densities of Semiconductor
Lasers
after Ledentsov et al., IEEE J. Sel. Top. Quantum
El. 6, 439 (2000)
12
Mode-Locked QD Lasers for 1000 GbE

• Advantages of QD gain medium
• Broadband gain medium (30 50 nm ground state,
  gt80 nm incl. excited state)
• Ultrafast carrier dynamics (10-100 fs components
  of carrier relaxation)
• Low noise gain medium (record low RIN -160 dB/Hz)
  
• High temperature stability (T0 inf. below 75
  C)
• Low threshold current density (lt 10 A/cm2 per dot
  layer)
• Translate into superior operation as mode-locked
  devices
• Ultra-short pulse generation (400 fs)
• Very high (80 GHz) / very low (5 GHz) monolithic
  MLL repetition rate
• Very low timing jitter (lt 200fs) for passive
  mode-locking
• Temperature stable mode-locking operation up to
  70C

13
Mode-Locked QD Lasers for 1000 GbE

• Advantages of QD gain medium
• Broadband gain medium (30 50 nm ground state,
  gt80 nm incl. excited state)
• Ultrafast carrier dynamics (10-100 fs components
  of carrier relaxation)
• Low noise gain medium (record low RIN -160 dB/Hz)
  
• High temperature stability (T0 inf. below 75
  C)
• Low threshold current density (lt 10 A/cm2 per dot
  layer)
• Translate into superior operation as mode-locked
  devices
• Ultra-short pulse generation (400 fs)
• Very high (80 GHz) / very low (5 GHz) monolithic
  MLL repetition rate
• Very low timing jitter (lt 200fs) for passive
  mode-locking
• Temperature stable mode-locking operation up to
  70C
• Making QD mode-locked devices ideal candidates
  for
• High-speed, ultra-short pulse, low noise optical
  pulse sources for OTDM / WDM

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Short, high power pulses from QD MLL
InGaAs QD passive MLL at 1280 nm
InAs/InP QD passive MLL at 1550 nm
Thompson et al., SQDA Rennes, 2008
Lu et al., Opt. Expr. 16 (14), 2008

• QD MLL yield shorter pulses than any other
  semiconductor gain medium due to their broad gain
  spectrum
• 2.25 W pulse peak power, 360 fs Fourier-limited
  pulse width w/o compression
• ? Ideal gain medium for high-speed time division
  multiplexing!

15
80 GHz QD MLL in QD SOA
Output after SOA 15 increase of pulse width
only
Input 80 GHz QD mode-locked laser

• 80 GHz mode-locking frequency little alteration
  of the pulse input
• Fits to 100 Gb/s Ethernet

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Double-pulse pump-probe measurement
Recovery ofground state

• Two 150 fs pulses with 5 ps delay
• Investigation of gain recovery after first pulse
  DG1 and second pulse DG2
• Complete gain recovery of the ground state for
  high current density
• Implementation of QD SOAs in 100G Ethernet viable

S. Dommers, D. Bimberg et al., Appl. Phys.Lett.,
90 (2007)
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QD SOA-based Ultrafast Digital Signal Processing

• Bulk/QW-SOA interdependence of refr. index and
  gain ? patterning effects
• QD-SOA gain and refractive index are decoupled
  in regime of maximum gain
• phase changes are not accompanied by amplitude
  changes
• ? PEF-free amplification
• Condition ngtno ? gconst., trecltlt tpulseltlt Tp

• QD based SOAs enable ultrahigh bit rate
  amplification (gt100 Gb/s) without patterning
• ultrafast optical switching in nonlinear
  interferometer with QD SOAs

A. Uskov, D. Bimberg, IEEE PTL 16, 1265 (2004)
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High-Gain Quantum Dot SOAs at 1.3 µm

• Self-assembled QD at 1.3 µm
• 15-fold stacked InGaAs QD layers for maximum gain
• Deep mesa waveguide, width 4 µm, length 4 mm
• Untilted, anti-reflection coated facets for
  improved coupling efficiency

• Experimental chip gain up to 26 dB
• Theoretical unsaturated gain 40 dB
• Signal-to-ASE ratio lt 25 dB
• Comparison to simulation shows good
• agreement, influence of gain saturation

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Contents

• Change of Paradigms Quantum Dots as Giant Atoms
  in a Dielectric Matrix
• High Speed QD-Lasers and Amplifiers for the 100 G
  Ethernet
• QD VCSELs for the Terabus
• A Glimpse to the Future Security in
  Communication Quantum Cryptography
• Higher Brightness for Upconversion, Welding
• New Wavelengths, ...

20
Optics for Interconnects
A. F. Benner et al., IBM

• Bandwidth is driven by IC scaling and increase in
  computational power
• Intel, IBM, Fujitsu, NEC, ... work on high-speed
  VCSEL devices

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980 nm VCSELs for Short Distance Optical
Interconnects
A.F.J. Levi, Stanford, April 2005, www.usc.edu/ale
vi
Memory-Access Performance Gap
Optical interconnects can fill this gap
J. A. Kash et al, OFC06, OFA3, 2006
VCSEL ARRAY
Terabus, IBM 4x12 VCSEL _at_ 20 Gb/s, 985 nm
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Work on 20 Gbit/s VCSEL
next year
Mutig, ..., Bimberg,El. Lett. 2008
NEC 7 InGaAs/GaAsP strain-compensated QWs,
Proton implanted, oxide confined
Agilent 2 Flip-Chip, 4x12 array
TU Berlin 1 Sub-monolayer grown active region
UCSB 4 Deep oxidation, thick tapered aperture,
bottom emitting, SM
Finisar 6 Proton implanted, thick tapered
aperture
NEC 5 TJ-VCSEL
Cha 8 Two apertures, InGaAs
NEC 3 Proton implanted, oxide confined
1 F. Hopfer et al., ISLC 2006, WC3 2 Chao-Kun
Lin et al., JSTQE, 13 (5) 2007 3 K. Fukatsu et
al., IPRM 2007 4 Y.-C. Chang et al., EL, 43
(19) 2007
5 T. Anan et al., VCSEL symposium, Tokyo Dec.
2007 6 R. H. Johnson et al., CLEO/QELS 2008,
CPDB2 7 H. Hatakeyama et al., CLEO/QELS 2008,
CMW3 8 P. Westbergh et al., EL, 44 (15) and
ISLC 2008
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Novel Concept for gtgt40 Gb/s Modulation Single
Cavity EOM VCSEL

• Keep drive current constant
• Modulate the mirror transmission

N. Ledentsov et al., Proc. of the IEEE, Vol. 95,
No. 9, pp. 1741-1756 (2007)
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Contents

• Change of Paradigms Quantum Dots as Giant Atoms
  in a Dielectric Matrix
• High Speed QD-Lasers and Amplifiers for the 100 G
  Ethernet
• QD VCSELs for the Terabus
• A Glimpse to the Future Security in
  Communication Quantum Cryptography
• Higher Brightness for Upconversion, Welding
• New Wavelengths, ...

25
Cyber Security Issue

• Annual U.S. businesses losses because of
  computer-related crimes is 67.2 billion (FBI
  estimation).
• Risk of terrorist invasion in strategic military
  and civil systems (nuclear and chemical plants,
  access to military information and technologies)
• 13,723 computer crimes were committed in Russia
  in the calendar year 2004 (Information Center of
  the Ministry of Internal Affairs of the Russian
  Federation).

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Ensure Secure Data Transmission
Classical cryptographyKey based on
factorisation in prime numbers
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Ensure Secure Data Transmission
Today use of two data channels - fast channel
encrypted signal - slow channel key for
decryption
Quantum cryptography Key based on q-bits or
entangled states
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Single Photon Source (SPS)
Ideal SPS
The ideal light source for a quantum
key-distribution system emits one and only one
photon in each time interval T1/R (photon
gun).
Classical light source described by Poissonian
Statistics probability of producing n
photons (µ - average photon number per pulse)
A Poisson distribution of the number of photons
per pulse from strongly attenuating light pulse
shows no photons in most time slots and two
photons in a small number.
Non-classical (quantum) light source is needed!
29
Basic Properties of Quantum Mechanics

• Position and momentum can not be determined
  independently
• Measurement perturbs the system
• Notion of trajectory no longer valid
• Quantum states Qbits - can not be duplicated
• (non-cloning theorem)
• Measurement of the polarization of a single
  photon destroys the initial polarization

Signal transmission security benefits
from quantum mechanics!
30
Single Photon Emitter
Novosibirsk
Berlin
The novelty
Oxide
aperture
A
Oxide aperture size

• Current confinement by oxide aperture
• Real single dot excitation

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Single Photon Emitter
Novosibirsk
Berlin
Emission of linearly polarized photons !

• Only exciton recombination is observed
• 870 pA (1.65 V) 0.2 photons / injected
  electron-hole-pair

A. Lochmann, D. Bimberg et al., Proc. ICPS-28,
Vienna, late news session, Austria (2006) and
phys. stat. sol. (c) 4, No. 2, 547 (2007)
32
Single Photon Emitter
Novosibirsk
Berlin
Hanbury-Brown Twiss Experiment Proof of
nondeterministic (Single Photon) Light Source
A. Lochmann, D. Bimberg et al., Proc. ICPS-28,
Vienna, late news session, Austria (2006) and
phys. stat. sol. (c) 4, No. 2, 547 (2007)
33
Single Photon RC-LED
Complex Nanophotonics Device

• Double-DBR periodicity, photonic crystal to
  prohibit tilted modes
• Single photon source with gt90 efficiency
• Fast (lt0.1 ns)
• Double-DBR RC-LED first time demonstrated 11/2008

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Contents

• Change of Paradigms Quantum Dots as Giant Atoms
  in a Dielectric Matrix
• High Speed QD-Lasers and Amplifiers for the 100 G
  Ethernet
• QD VCSELs for the Terabus
• A Glimpse to the Future Security in
  Communication Quantum Cryptography
• Higher Brightness for Upconversion, Welding
• New Wavelengths, ...

35
Background
What we have learned No photonic devices no
fast and secure data transmission
But! 34 of world-wide semiconductor-laser sales
in datacom only !
Diffusion into new fields of application

• Optical memories (blue ray, ...)
• Scanner
• Printer
• Pump laser
• Material treatment
• VCSEL mouse
• Automobile (MOST 3)

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Semiconductor Lasers of High Brilliance
What we have learned No photonic devices no
fast and secure data transmission
But! 34 of world-wide semiconductor-laser sales
in datacom only !
Diffusion into new fields of application

• Optical memories (blue ray, ...)
• Scanner
• Printer
• Pump laser
• Material treatment
• VCSEL mouse
• Automobile (MOST 3)

other3
material treatment6
military/aviation 6
printer10
pump laser 49
medicine 26
Source Laser Marketplace
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Semiconductor Lasers of High Brilliance

• Conventional
• angle of aperture typ. 45

Brilliance (number of photons per solid angle)
is decisive for optical power density at working
point
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Structure of German Center of ExcellenceSemicond
uctor Nanophotonics

• Mainstream nanophotonic materials research on
  InP, GaAs, GaN
• Advanced numerical modelling
• Advanced device design
• Device RD following mainstream system demands
• Goal Impact on the development of a
  multi-billion market

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Gain Synergy
!!! RD in different fields of nano-photonic
applications is conducted by non-interacting
physicists and engineers (uncorrelated). !!!
There are no modular design sets for
nano-photonics like for electronics (logics,
memories, micro processors), ... ! Setting up
such sets is difficult as one has to include all
different kind of scales in time and space
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Our New Center of ExcellenceSemiconductor
Nanophotonics
internationalcooperations
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Our New Center of ExcellenceSemiconductor
Nanophotonics
localcooperations