next generation optical amplifiers requirements, bottlenecks, possible resolutions (approach...

Next Generation Optical Amplifiers Next Generation Optical Amplifiers

requirements, bottlenecks, possible resolutionsrequirements, bottlenecks, possible resolutions

(Approach concerned on Cost, Footprint , Functionality(Approach concerned on Cost, Footprint , Functionalityrather than Efficiency, utilizing nano-photonics)rather than Efficiency, utilizing nano-photonics)

Namkyoo Park

Nanoscale Energy Conversion and Information Processing DevicesSeptember 24 th, 2006

Photonic Systems LaboratorySchool of EE, Seoul National University

http://[email protected]

Photonic Systems Lab School of EECS, S.N.U.


Research Topics in PSL : Research Topics in PSL : PastPast / Present / Present

Photon Generation Raman Amplifier Erbium Amplifier Thulium Amplifier nano-Photonics : Er / Raman based Si Amplifier / Laser) This presentation

Photon Transport Transient control & amplified transmission line design Polarization Mode Dispersion tolerant transmission format Multi-level Optical Transmission

Photon Control – Coding, Detection, Logic Optical Coding (CDMA, Noise reduction) Super-resolution Techniques (2D / 3D Imaging) Surveillance system for FTTH network Distributed / Multi-port Temperature sensor Semiconductor Amplifier & SOA based Logic Gates

Integration with / Applications to IT, BT & NT Tunable Optical devices (including Photonic Crystals, MEMS) Application to Medical-Photonics (3-D Tomography)


The First MileThe First MileThe First MileThe First Mile

BackboneBackbone Continent to Continent Continent to Continent Coast to Coast all over Coast to Coast all over

Fiber at 10 Gbps & upFiber at 10 Gbps & up

BackboneBackbone Continent to Continent Continent to Continent Coast to Coast all over Coast to Coast all over

Fiber at 10 Gbps & upFiber at 10 Gbps & up

MetroMetro City to City-Town to Town City to City-Town to Town all over Fiber all over Fiber at 1Gbps 10 Gbpsat 1Gbps 10 Gbps

MetroMetro City to City-Town to Town City to City-Town to Town all over Fiber all over Fiber at 1Gbps 10 Gbpsat 1Gbps 10 Gbps

AccessAccess To the optically Fibered To the optically Fibered World “First Mile / Last Mile” World “First Mile / Last Mile” 56kbps 1 Gbps56kbps 1 Gbps

AccessAccess To the optically Fibered To the optically Fibered World “First Mile / Last Mile” World “First Mile / Last Mile” 56kbps 1 Gbps56kbps 1 Gbps

LANLAN Desktop to Desktop – Desktop to Desktop – Floor to Floor Floor to Floor 10 Mbps 1 Gbps10 Mbps 1 Gbps

LANLAN Desktop to Desktop – Desktop to Desktop – Floor to Floor Floor to Floor 10 Mbps 1 Gbps10 Mbps 1 Gbps Jonathan Thatcher, OFC2002, Tutorial Sessions(2002)Jonathan Thatcher, OFC2002, Tutorial Sessions(2002)

Network Evolution – Market Calls for METRO and BelowNetwork Evolution – Market Calls for METRO and Below

Long Haul More of the same (higher speed, more wavelength, longer reach…)

Metro/Access will shape the next wave of innovative components Tunable, intelligent, distributed amplification

The “siliconization” of photonics Drive scalable manufacturing and cost efficiency Push optics further into the network and ensure sustainable growth of the industry


Network Evolution – Challenges in TechnologyNetwork Evolution – Challenges in Technology

OITDA2000


Network Evolution – Challenges : Met for METRO netwoNetwork Evolution – Challenges : Met for METRO networkrk

Now in the Market ! (2002)Now in the Market ! (2002)


Network Evolution – Beyond Metro : How far Network Evolution – Beyond Metro : How far ??

You will need more photons forYou will need more photons forYour desktop PC / ProcessorsYour desktop PC / Processors

Electronics-photonics must converge !


Two pillars of information revolution: Si IC & Two pillars of information revolution: Si IC & photonicsphotonics

WDM

vsvs

“A chip that can transfer data using laser light”, NYT, 20060918 By Intel and UC-Santa Barbara

“$6 million project to develop silicon-based laser”, 20060804 By MIT, the Microphotonics Center from US DoD Using nanocrystalline silicon as an sensitizer for Er

“Electronics-photonics must converge”, MIT, 20050520 By MIT from 3-year study


Status of Photonics – Compared to ElectronicsStatus of Photonics – Compared to Electronics

Electronics : Vacuum tube Transistor IC VLSI Common User

$’s per 0.1M 100’s M Gb Memory

TO OPEN THE PHOTONIC AGE, compatible to that of semiconductor industry,

Need Cost reduction

Need Smaller Footprint

Need Integrated functionality

Need optical power lines (amplification function)

25% of the material cost is in the package

Another 25% is in the assembly

Beyond automation and off-shore assembly

Packaging really hasn’t advanced much until recently Costly 70’s-era technology Poor signal integrity Poor Thermal properties

Need : New materials, Athermal designs, and Packaging standards

OpticalSub-Assembly

Electronics Sub-Assembly

Zolo Technologies


Challenges and PromisesChallenges and Promises

Challenges in achieving Photonic Age -- if it comes ^^; Cost 10’s of $ Footprint Size of PCMCIA Functionality More than Serial integration

Promises made to meet above challenges, with some technologies OEIC mostly for active devices Compound semiconductor PLC mostly for passive devices Silica, Polymer MEMS mostly for switching devices Silicon, Glass, etc.. EDWA mostly for amplification devices Silica Hybrids Si-Photonics Plasmonics Ph-Xtals ….. ….

How far do we need to go ?

Is it really possible to meet these Promises ?

Let’s sit back and look at the status of Silica based technologies (EDWA / PLC )


Si Photonics – Optical Communication in the Si Photonics – Optical Communication in the ChipChipLeveraging the astronomical Si processing technology for photonicsPhotonics based on Si-based materials and Si-compatible processesPassives, Modulators, Detectors but still missing Photon Generators

0.5 m bend

0.5 m splitter

0.5 m bend0.5 m bend

0.5 m splitter0.5 m splitter


Discrete

Gain

PLC

Loss

Discrete components

??????

Integration

EDFA

EDWA

What are we missing ? - Functionality / SizeWhat are we missing ? - Functionality / Size

For Photonics, there is lack of optical power lines which is compatible to that of electrical PCB

For Increased data rates, we need more photon (per bit) : Photon generator (amplifier, laser)

For SOA, with its strong electron - electron interaction and high noise figure

For EDWA, true integration is impossible after certain level (e.g. Splitting OA) : Only serial

??????

Integration /Functionality

Cost

PLC

EDA

PLC + EDA

High Power DFB

Not allowed by physics


Challenges in Amplifier TechnologyChallenges in Amplifier Technology

Gbps/user Gbps/user need more photons/bit, but not with $1K/unit nor at current size !! need more photons/bit, but not with $1K/unit nor at current size !!

OITDA2000


1962Proposal for optical amplifier first published J.E. Geusic and H.E.D. Scovil at ATT

Stimulated Raman scattering first observed E. Woodbury and Won Ng

1964 optical fiber amplifier demonstrated E. Snitzer using Nd doping for 1060-nm signals

1966 Proposal for glass light waveguides By K.C. koa and G. A. Hockman

1970

First continuous operation of diode laser at room temperature simultaneously demonstrated

Hayashi and M. panish at ATT.

and Z.I. Alferov at loffe institute(USSR)

Mass production of quality optical fiber Corning

1976 First major trial of commercial lightwave system Atlanta, Georgia(USA), without optical amplifiers

1983 First demonstration of doped single-mode fiber By ATT

1984First demonstration of 1550-nm operation Without optical amplifiers

5 wavelength CWDM in 1310-nm range By Toshiba, using 5-nm spacing

1987First EDFAs simultaneously developed R.J. mears, D. Payne. et al at university of Southa

mpton, and E. Desurvire, et al, at ATT

1989

Diode-pumped EDFA demonstrated By m. Nakazawa

First commercial EDFA introduced By Oki Electric

First commercial SOA introduced By BT&D Technologies (now Agilent)

1993 First major installation of optical amplifiers By MCI

1996 First installation of EDFAs into undersea links TPC-5 and TAT-12,13

1999 First EDWAs introduced MOEC and Teem Photonics

Amplifier evolution before millenniumAmplifier evolution before millennium


20 30 40 50 60 70 80 90 100 110 1200 100

1.0

3.0

4.0

2.0

Rel

ativ

e C

ost

(A

.U.)

Bandwidth (nm)

Nortel Networks,1999

Amplifier – Bandwidth and CostAmplifier – Bandwidth and Cost

Gain media (whatever)Pump laser diode

PumpMUX

Tap Tap

Photodiode

Photodiode

IsolatorIsolator

DGFF


Amplifiers – Any challenges left ?Amplifiers – Any challenges left ?

Optical Amplifier now 40 + year old, mature technology

Researchers have touched most issues on amplifiers Gain flattening Transient Temperature Power Conversion efficiency Noise, Scattering, Fiber structure, Host materials, Co-Dopants

Various types of OAs have been commercialized, by numerous vendors EDFA TDFA Raman Hybrid EDWA SOA (bulk, QW, QD)

Not much issues left for OAs, especially for LH, trunk line applications (personal opinion)

Let’s sit back and look at the Technology / Bottlenecks of OA for Metro and beyond


Photonics : Different material / structure for each function, with high losses

1st Generation of Integration : Parallel (Laser, Detector, VOA arrays)

2nd Generation of Integration : Serial (ILM, Router, Receiver..)

Amplifier : 10-20 components with intensive package SERVING JUST ONE FUNCTION

NOT have been integrated with any other functional devices

Size reduction achieved to reasonable level to Metro, but not yet enough

Cost reduction achieved to reasonable level to Metro, but not yet enough

Is it possible to achieve above requirements with EDWA ?

Status of Amplifier – for Metro and beyond, to FTTHStatus of Amplifier – for Metro and beyond, to FTTH

x N

Pump LDIsolators

PD

Er-doped Waveguide Gain Block Array

Hybrid integrated activesPhotodiode Pump laser die

Yields ? Delivery ?

For N=8 : 80 1 part


The current status of EDWAThe current status of EDWA

Exactly the same schematic as that of an EDFA

Efforts on the amplifying section only : > 10 M$ to make the cheapest part cheaper

Larger than the smallest available conventional EDFA

Need every component in one plane : severely restricts further reduction in size

Integration no more than an addition : Amplifying splitter = AMP + splitter


Story behind the Limitation - CostStory behind the Limitation - Cost

For EDFA & EDWA, optical excitation occurs through direct photon absorption Very small absorption cross section (210-21 cm2)

Requires a long interaction length btw pump and signal Efficiency, Size Narrow absorption band – requires finely tuned lasers

Requires an expensive pump LD with wavelength (temperature) control Cost

Cost-centered view of an EDA

Pump laser diodePump laser diode

$1.53m0.98m0.80m0.66m

4F9/2

4I9/2

4I13/2

4I11/2

4I15/2

Er Er energy level diagramenergy level diagram

Energy level determined by QM


Splitting Section

Amplifying Section

Reflecting mirror

Half MUX/ DMUX

Story behind the Limitation - StructureStory behind the Limitation - Structure

PLC and EDWA shares the same platform but the real integration is Difficult

Limited to serial integration Marginal reduction in the footprint with lower chip yield

Point amplification impossible Series of resistors and filters adds in system noise

Photonic Lightwave circuit without optical power line, EDWA as a mimic of EDFA

Serial Integration : Lower Yield 2-D Structure : Point Access Impossible


Story behind the Limitation - MaterialStory behind the Limitation - Material

PLC is a stabilized, patterned fiber arrays using the same material

Mode size limitation dictates the minimum device size (much bigger than memory chip)

Wafer uniformity affects the yield of the chip higher index for smaller device size

To keep the Er numbers same within smaller volume, concentration have to be much higher

Increased Er concentration much lower ( ~ x 2 ) PCE from the quenching process


Faults of Integrated Amplifiers proposed so far Faults of Integrated Amplifiers proposed so far

EDFA on a substrate Similar properties under similar conditions

competes against established products with only an incremental advantage Can never be integrated with anything else

can never truly “siliconize” photonics

Still requires an expensive pump LD Transfers the control over the final price of the device to LD suppliers The better you are, the worse this problem gets!

The smaller you get, you lose more pump power from Er quenching Dictates the smallest possible size of EDWA Not different at all when compared to EDFA again

Current OA technology not enough to support for metro – access network Cost Too high Photon Price, dictated by Electrical – Optical – Optical pumping Footprint Limited by Erbium on Silica wafer Functionality Limited by 2-D structure

Any solutions… ?Any solutions… ?


Compound Semiconductor Bandgap - electrical : fast, strong interaction modulation, switching Strong interaction Smaller device size Energy source (electrical pump) independent from signal plane Feedback structure : LED FP, DFB but at much increased cost Bandgap engineering Wider, adjustable bandgap Difficulties in pigtailing Cost Differences in refractive index with fiber AR coating for SOA

Silica base Rare Earth Atomic level - optical : slow, weak interaction amplification without crosstalk Weak interaction Larger device size, Low efficiency Energy source (optical pump) requires waveguide Feedback structure : Fiber laser but no modulation capability Bandgap engineering None Compatibility in Pigtailing

Next generation Optical Amplifier – photon wavelength converter Eliminate an expensive LD source : just need to provide inversion COST Require dimensional separation of Pump and Signal plane FUNCTIONALITY Need stronger interaction mechanism for the excitation FOOTPRINTS

Contemplations on Photon GeneratorsContemplations on Photon Generators


Si-Photonic Optical Amplifier ?Si-Photonic Optical Amplifier ?


Pump photonsInteracting medium

Conversion mechanism

Signal photons

Signal photons

SiO 2

(host matrix)

Si nanoclustersEr ions

20 nm

Nanocrystal-Si sensitized EDWANanocrystal-Si sensitized EDWA

Amplifier is Wavelength Converter in its nature

Why do we use expensive coherent photons ?


Material propertiesMaterial properties

1.30 1.35 1.40 1.45 1.50 1.55 1.60 1.65102

103

104

105

0 10 20 30 4010-2

10-1

100

Inte

nsit

y (a

.u.)

Wavelength (m)

with 477 nm pump with 980 nm pump

Time (msec)

PL

Int

ensi

ty (

a.u.

)

Continuous excitation spectra from IR to UV: anything bluer than green works!

No need of Frequency control (or cooling)

>100 times Er3+ luminescence intensity even with half the photon flux

nc-Si completely dominates excitation (100 x larger with 477nm than 980nm)


SRSO / Er layer depositionSRSO / Er layer deposition

Deposition process ECR – PECVD (electron cyclotron resonant plasma enhanced chemical deposition) Silicon rich silicon oxide to construct silicon nanocluster Silicon contents control : Ar , SiH4, O2 (automated MFC) Evaporation / sputtering Er

Microwave

Sampleholder

SiH4, O2 gas(99.999%)

Ar gas(99.9999%)

Arplasma

Er Target(with negative bias)

Load lockChamber

TMP

Sampleholder


Silicon nanocrystal controlSilicon nanocrystal control

Silicon nanocrystal Controlled by RTA annealing condition / silicon contents

Best energy coupling condition to Er ions

Size control : Quantum energy state of nanocrystal

State control : Crystal or amorphous


Bulk performance measurementBulk performance measurement

PL measurement PL intensity and lifetime for various pump wavelength (980nm for Er, 477nm for NC-Er)

Activity of silicon nanocluster and Er, coupling efficiency

RBS measurement Atomic composition estimation for layer depth


Waveguide characterization (amplification)Waveguide characterization (amplification)

Butt-coupled tapered fibers for signal input and output

15mm linear array of commercial, 470 nm LEDs

Need to clear the fibers and cover glass: 2mm separation between LED and waveguide, pump only center 5mm portion of the waveguide

Ridge WaveguideW 8 m x L 11 mm

LED arrayW 1,000 m x L 5 mm

H 2 mm


Wavelength-dependence of signal changeWavelength-dependence of signal change

1515 1520 1525 1530 1535 1540 1545

-3

-2

-1

0

1

2

3

Sig

nal C

hange (

dB

/cm

)

Wavelength (nm)

Laser on (24W/cm2)

Laser on (16W/cm2) LED on Pump off

Signal change: Itrans(P)/Itrans(0): typical inversion curves for Er3+

With LED pump: low pump density due to unoptimized alignment

lower inversion, optical gain at 1545 nm

Simulation of high LED pump power with 477 nm laser:

full inversion with 3 dB/cm optical gain at 1533 nm

1532 1533

1292 1294

Sig

nal

Inte

nsit

y (a

.u.)

Wavelength (nm)

LED On LED Offa)

Wavelength (nm)

Sig

nal

Inte

nsit

y


Numerical Assessment / DesignNumerical Assessment / Design

Parameters from experimental results Much larger effective excitation cross-section and signal absorption cross-section Emission cross-section from PL measurement Absorption cross-section from McCumber relation

Simulation scheme (top pumped NC-Si EDWA) 2-D propagation equations (with 10x10x400 segments) 1500 ~ 1610 nm with 1nm resolution


Population inversion characteristics of NC-Si ErPopulation inversion characteristics of NC-Si Er

Much larger pump absorption cross-section than signal emission cross-section Over 50% inversion with small # of pump photons (Left-shift of red region in below figures) Top pumping scheme Large doping area than conventional EDF

Doping area confined to the center of the fiber core for high inversion (conventional EDF) Large doping area Enhancement of overlap factor with signal high gain per length

Pump intensity (dBm/cm2)

Sig

nal

inte

nsi

ty (

dB

m/c

m2 )

Inversion of conventional EDFA Inversion of NC-Si EDWA

Pump intensity (dBm/cm2)

Sig

nal

inte

nsi

ty (

dB

m/c

m2 )

Populationinversion


Device Structure & FeasibilityDevice Structure & Feasibility

Performance comparison 4 cm EDWA without coupling loss NC-Si EDWA with type A core (7x7 μm2) Type A core EDWA with bottom mirror (100% reflection)

Large gain by reusing of wasted pump power

Adiabatic designed large core (type B, 100x7 μm2) Saturation gain enhancement by increasing pump collection area Small signal gain enhancement by overlap factor enhancement

Type A w/ mirror


High intensity visible (blue) pump LED

Chip LED for illumination application (Cree)

Max 25W/cm2 (hard contact)

Easy to align (waveguide width 50um < LED 250um)

LED Die-Bonding pattern Emission of LED Array(0.3x3 cm)

7mW(at 20mA) x 64 Chip size : 300um x 300 um Array size : 0.03(cm) x 3(cm) Total Power : 5W/cm2

Optimization : Pump LEDs Optimization : Pump LEDs


Gain: 2.4dB/cmPL : 93000LT : 6.3 ms

Optimization : Material Composition Optimization : Material Composition

x 17

x 12

Estimated result

Gain: 0.2dB/cmPL : 8000

LT : 9.3 ms

Experimental result

Evaporation Sputtering


Schematic of a SRSO based VCPAC (pump WDM removed)

Pump light

SRSO wafer

LED Pump array

VCPAC Splitter (Splitting section = Amplifying section)

Amplifying Splitter

Examples & Implications in the applicationsExamples & Implications in the applications

Splitting SectionPump WDMs

Pump & Signal

Amplifying Section

Amplifying Section

Ultra-compact, low-costUltra-compact, low-cost True integration for Active PLCTrue integration for Active PLC

Totally NEW concept, Reduced Complexity & Higher Chip Yield !Totally NEW concept, Reduced Complexity & Higher Chip Yield !


Much things you can do with NANO Si !!That’s a good news for Photonics Engineers

Summary Summary

# of Am

plifier W

orldw

ide

# of nan

o-particle W

orldw

ide

# of Am

plifier E

ngin

eers

next generation optical amplifiers requirements, bottlenecks, possible resolutions (approach...

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gbps access

gbps metro city

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