Transcript No Slide Title

Monolithically Integrated Semiconductor
Components for Coarse Wavelength
Division Multiplexing
Alan Kost
Frontiers in Optics
Tucson, AZ
October 20, 2005
OUTLINE
• The need for photonic integrated circuits
• Coarse wavelength division multiplexing
- Arrayed waveguide gratings on InP
• Quantum Well Intermixing
- GaAsSb Quantum Wells
Low cost is the driver
ELECTRONIC ICs
A WDM Data Link
Components are numerous and expensive
LASER
VARIABLE
ATTENUATOR
OPTICAL
MODULATOR
OUR
PROGRAM
PHOTODIODE
l1
l1
l 1, l 2 … l n
li
ADD
l2
l2
FIBER
POWER
AMP
IN-LINE
AMP
DROP
PREAMP
lj
lm
ln
MULTIPLEXER
DE-MULTIPLEXER
AWG/SOA Concept
De-multiplexing, amplification, and equalization on one, InP chip
l = 20nm
l1
l2
l3
l4
1 to 9
Coupler
Arrayed
Waveguide
Grating (AWG)
Semiconductor
Optical Amplifiers
(SOAs)
 1 cm
9 to 4
Coupler
l1
l2
l3
l4
InP Substrate
 1 cm
Coarse Wavelength Division Multiplexing
DWDM
CWDM
• Very high throughput
(80 channels over C-Band
from 1530 to 1565 nm)
• Smaller number of channels
and correspondingly smaller
throughput
• For use in short to medium haul
networks
• For use in long haul
networks
• Compatible with less
expensive, un-stabilized
lasers and broadband filters
• Stabilized lasers and
narrow-band filters required
32 nm
50 GHz (~0.4 nm at 1.55 mm)
340 nm (1270 – 1610 nm)
l = 20 nm
l
l
ARRAYED WAVEGUIDE GRATINGS:
“HORSESHOE” TYPE
SYMMETRY LINE
l1 l2 l3 l4
L + 2L
InP
L = ml
L + L
L + 3L
L + 4L
L + 5L
l1 l2 l3 l4
Transmission
Free Spectral Range
Output
Waveguide #
1 2 3 4
1
2
3
OPTICAL PATH
LENGTH = L
4
1
L
 Small L for CWDM
FSR ~
l
l1
l2
l3
l4
An “S-SHAPED”
Arrayed Waveguide Grating
Arc
Waveguide
Array
Star Coupler
Input
Star Coupler
Output
Waveguides
The optical path difference between waveguides in the
array can be made arbitrarily small reducing the angle
subtended by the arc.
This kind of AWG has not been
previously fabricated in semiconductor
Shallow Ridge Waveguides
2.5 or 3.5 mm
InP
10
1.45 mm
0.11 mm
InGaAsP
InP
8
Bend Loss (db/cm)
0.30 mm
Fundamental
Mode
6
4
Bend radius
range for AWGs
2
First Higher
Order Mode
0
Loss = 4.5 dB/cm
0
1000
2000
3000
4000
5000
6000
Bend Radius (mm)
7000
8000
Patterned AWGs
Star Coupler
“S”
1-micron
AWG Response
Proper AWG
design should include chromatic dispersion
Channel
3
4
5
6
7
8
1
-15
-20
-25
-30
1473
Wavelength (nm)
1546
1509 ~ 7 nm (FWHM)
Channel Width
1490talk ~ - 15 1527
1562
Cross
dB or less
Yurt, Rausch, Kost, Peyghambarian, Opt. Express 13, 5535 (2005)
1580
1570
1560
1550
1540
1530
1520
1510
1500
1490
1480
1470
-35
1460
Transmitted Power (dB)
-10
L small
 Insensitivity
to dimensional
error
AWG/SOA Concept
l1
l2
l3
l4
AWG
 A passive device
SOAs
 Active devices
 1 cm
l1
l2
l3
l4
InP Substrate
Conventional Approach: Epitaxial Re-Growth
Epi-Layers for AWG
1st growth of epi-layers for AWG
SUBSTRATE
Epi-Layers for AWG
SUBSTRATE
Epi-Layers for AWG Epi-Layers for SOAs
SUBSTRATE
Selective area etch to substrate
Re-growth of epi-layers for
SOAs
Technical Problems:
• Poor morphology for re-grown layers
• Vertical misalignment of AWG and SOA
layers
• Rough AWG/SOA interface
Low
Yield
Ion-Induced Band Gap Modification
HIGH ENERGY IONS
HEAT
DEFECT
ION MASK
BARRIER
DIFFUSION
QUANTUM WELL
ABSORPTION COEFFICIENT
BARRIER
ABSORPTION
EDGE
Advantage
-No re-growth
BLUE SHIFT
PHOTON ENERGY
Disadvantage
- Constraints on layers
AMPLIFIER BANDWIDTH
SOA bandwidth is insufficient to cover all CWDM wavelengths
Useful amplification range for
Semiconductor Optical Amplifier
(or Erbium-Doped Fiber Amplifier)
340 nm (1270 – 1610 nm)
l = 20 nm
l
QUANTUM WELL INTERMIXING
TO ADJUST AMPLIFICATION RANGE
l1
l2
l3
l4
Candidates Materials
• InGaAsP
- conventional material,
limited tuning range
• GaInNAs
• GaAsSb
ABSORPTION COEFFICIENT
l1
l2
l3
l4
ABSORPTION
EDGE
BLUE SHIFT
l1
l2
l3
l4
GaSb MATERIALS FOR 1.5 MICRON DEVICES
0.5
AlSb
BAND GAP WAVELENGTH
(MICRONS)
GaAs
Candidates
1.0
AlGaSb
1.5
GaAsSb
AlGaSb
(nearly indirect band gap)
GaSb
2.0
GaSb Quantum Wells
(indirect gap)
GaAsSb Quantum Wells
Substrate
2.5
3.0
3.5
5.6 5.7 5.8 5.9 6.0 6.1 6.2
LATTICE CONSTANT IN ANGSTROMS
GaASSb/AlSb Quantum Wells
GaAsSb
Adding As +
Quantum
Confinement
X
LL
GaSb
Adding
Quantum
Confinement
Indirect
band gap
Г
G.Griffiths, K.Mohanned, S.Subbana, H.Kroemer and
J.L.Merz, Appl. Phys. Lett. 43, 1059 (1983)
GaAsSb Quantum Wells
Photoluminescence (arb. units)
Photoluminescence increases dramatically with As content
0.00
GaSb Cap
GaAsSb/AlSb
Quantum Wells
AlSb
Sb1704
15.1% As
Sb1720
1200
GaSb Substrate
9.1% As
Sb1682
1300
AlSb
18.8% As
Sb1707
Sb1690
GaAsxSb1-x
31% As
0% As
x 10
1400
1500
1600
1700
1800
Wavelength (nm)
Kost, Sun, Peyghambarian, Eradat, Selvig, Fimland, and Chow, Appl. Phys. Lett. 85, 5631 (2004).
60X
GaAsSb Quantum Wells
The shift is the largest for any quantum wells (in the telecom band)
BORON ION IMPLANTATION (~300 keV, 3x1013 cm-2)
l = 140 nm, E = 86 meV
Sun, Peyghambarian, Kost, Eradat, Appl. Phys. Lett. 86, (2005)
l = 195 nm, E = 123 meV
Summary
• AWG for CWDM
(lower cost devices)
→ Demonstrated first semiconductor AWGs
for CWDM using an flexible “S-shape”
• Band Gap Modification for Heterogeneous
Integration (enabling technology for PICs)
→ GaAsSb/AlSb quantum wells show
promise
Future Directions
• Application for CWDM AWG
- Combined wavelength and time-division
multiplexing
• New materials for intermixing
- GaInNAs
- Sb quantum wells on InP
© 1998 - 2005 Christian L. Deichert