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Juejun (JJ) Hu
Chalcogenide Glasses for Integrated Photonics
Juejun (JJ) Hu
Materials Science & Engineering, MIT
Juejun (JJ) Hu
Materials
Devices
Systems
Infrared glass
Phase change
materials
Infrared gas
sensorsTunable
metasurfaces
2D material
integration
Optical
isolator
Micro-CPV Board-level
interconnect
Mini-
spectrometer
Research @ PMAT
Flexible
photonics
Juejun (JJ) Hu
Tian Gu
Hongtao Lin
Lan Li
Derek Kita
Jerome Michon
Qingyang Du
Sarah Geiger
Gufan Yin
Duanhui Li
Skylar Deckoff-Jones
Haya Alhummiany
Yifei Zhang
Hanyu Zheng
Huikai Zhong
Roger Fang
PMAT @
Funding support
Collaborators
Kathleen Richardson
Nanshu Lu
Jing Kong
Daniel Hewak
Juejun (JJ) Hu
2-D materials
Monolithic photonic integration on 2-D materials
Flexible planar photonics
Integration with nanomembranes and elastomers
Glass photonic integration
ChGs are uniquely poised for multi-material integration
Introduction
Chalcogenides (ChGs): an emerging optical material
Juejun (JJ) Hu
Introduction
Chalcogenides (ChGs): an emerging optical material
2-D materials
Monolithic photonic integration on 2-D materials
Flexible planar photonics
Integration with nanomembranes and elastomers
Glass photonic integration
ChGs are uniquely poised for multi-material integration
Juejun (JJ) Hu
Amorphous compounds ofchalcogens (S, Se and Te) covalently bonded to other elements
Adv. Mater. 25 (2013): 3050-3054; Opt. Express 18 (2010): 26720-26727.
ChG lenses ChG fibers ChG Microspheres ChG Metaswitch
Juejun (JJ) Hu
Wide IR transparency makes ChGs ideal materials for
infrared sensing
Juejun (JJ) Hu
ChG mid-infrared photonics
Sci. Tech. Adv. Mater. 15, 014603 (2014)
OE 21, 29927 (2013); OE 23, 19969 (2015)
Opt. Mater. Express 4, 1617 (2014)
Opt. Lett. 35, 3324 (2010)
Juejun (JJ) Hu
As
S Se
As2Ch3
Glass
Crystal
Property Range
Refractive
index2.3 – 2.8
Nonlinear
index
0.2 – 1.2
[10-17 m2/W]
Optical
band gap
1.6 – 2.3
[eV]
Glass
transition
80 – 220
[°C]
M. A. Popescu, Non-crystalline
chalcogenides, Springer (2001).
Index-matching, insulating
optical adhesive in stacked
solar cells
Nat. Mater. 13, 593 (2014)
ChG properties can be tuned over a wide range
via composition engineering
Juejun (JJ) Hu
ChGs exhibit large optical Kerr nonlinearity
MaterialNonlinear index
n2 (10-20 m2/W)
TPA
a2 (10-12 m/W)
FOM
( n2/a2l )
Silica (SiO2) 2.2 ‒ ‒
c-Si 440 8.4 0.4
a-As2S3 290 < 0.01 > 10
a-As2Se3 1200 1.0 2
Data quoted for l = 1550 nm: Opt. Express 15, 9205 (2007)
2-10 micron
supercontinuum
generation in ChG
waveguides
Opt. Lett. 41, 958
(2016)
Juejun (JJ) Hu
Phase change chalcogenide alloys
✓ Index change: Dn = 2.6
× Loss: k = 0.06 (22000 dB/cm)
Dn
k
The classical GST phase
change alloys are lossy
Juejun (JJ) Hu
Broadband low-loss phase change alloys
✓ Index change: Dn = 1.8
× Loss: k < 0.001
Dn
k
1 2FOM , FOMn k
k k
D D
FO
M2
/ 10
FO
M1
/ 10
GST GSS4T1
Data from V.
Liberman & J.
Chou @ LL
Juejun (JJ) Hu
Non-volatile switching by phase change alloys
Amorphous
Crystalline
Optical loss in GST limits
insertion loss and switching
contrast ratio
Juejun (JJ) Hu
Non-volatile switching by phase change alloys
Amorphous
Crystalline
Transparent phase change
material enables high-
contrast, low-loss switching
Juejun (JJ) Hu
2-D materials
Monolithic photonic integration on 2-D materials
Flexible planar photonics
Integration with nanomembranes and elastomers
Glass photonic integration
ChGs are uniquely poised for multi-material integration
Introduction
Chalcogenides (ChGs): an emerging optical material
Juejun (JJ) Hu
Introduction
Chalcogenides (ChGs): an emerging optical material
2-D materials
Monolithic photonic integration on 2-D materials
Flexible planar photonics
Integration with nanomembranes and elastomers
Glass photonic integration
ChGs are uniquely poised for multi-material integration
Juejun (JJ) Hu
Photonic integration necessarily involve different
materials
Source Modulator DetectorWaveguide
Isolator
III-V
semiconductor
Electro-
optic crystal
Photonic
glass
SemiconductorMagneto-
optical
garnet
Juejun (JJ) Hu
V
Glass
waveguide
Optical crystal
Polymer
2-D material
Semiconductor
Glass-based multi-material integration
Rubber
Ceramics & Metal
Juejun (JJ) Hu
ChGs for multi-material photonic integration
Epitaxy-free deposition?
Low deposition temperature?
Cl
F
At
Br
I
P
N
Bi
As
Sb
S
O
Po
Se
Te
Al
B
Tl
Ga
In
Si
C
Pb
Ge
Sn
Chalcogenide
glass (ChG)
have weaker
interatomic
bonds than
those in oxides
Juejun (JJ) Hu
Epitaxy-free deposition
Low deposition temperature
Versatile microfabrication
?
?
?
ChGs for multi-material photonic integration
2 µm
Waveguide loss:
0.5 dB/cm
Cavity Q-factor:
1.2 × 106
Opt. Lett. 41, 3090-
3093 (2016).
Ge23Sb7S70
glass waveguide
Juejun (JJ) Hu
Epitaxy-free deposition
Low deposition temperature
Versatile microfabrication
?
?
?
Tailorable optical properties?
ChGs for multi-material photonic integration
Juejun (JJ) Hu
2-D materials
Monolithic photonic integration on 2-D materials
Flexible planar photonics
Integration with nanomembranes and elastomers
Glass photonic integration
ChGs are uniquely poised for multi-material integration
Introduction
Chalcogenides (ChGs): an emerging optical material
Juejun (JJ) Hu
Introduction
Chalcogenides (ChGs): an emerging optical material
Flexible planar photonics
Integration with nanomembranes and elastomers
Glass photonic integration
ChGs are uniquely poised for multi-material integration
2-D materials
Monolithic photonic integration on 2-D materials
Juejun (JJ) Hu
2-D materials in photonics
Nat. Photonics 8, 899-907 (2014)
✓ Light emission and detection
✓ Optical modulation
✓ Saturable absorption
✓ Optical nonlinearity
✓ Magneto-optical activity
✓ Tunable plasmonics
Juejun (JJ) Hu
Photonic integration of 2-D materials relies on
hybrid transferNature 474, 64-67 (2011)
Fabricated device 2-D layer transfer
Hybrid transfer:
× 2-D layer rupture at pattern
edges
× Weak evanescent interaction
× Limited throughput and
integration capacity
Monolithic integration:
✓ Improved yield and
throughput
✓ Flexible 2-D layer placement
✓ Superior alignment accuracy
× Material degradation
Juejun (JJ) Hu
Thick dielectric growth on graphene is difficult
due to its inert surface
Nano Lett. 10, 3572-3576 (2010)
Dielectric
deposition
× Mobility degradation
× ALD dielectrics: low
throughput for optical
devices
Juejun (JJ) Hu
Chalcogenide glass-on-2D-material photonics
ChG maintains the structural
and optoelectronic properties
of graphene
Juejun (JJ) Hu
Chalcogenide glass-on-2D-material photonics
MoS2
Black
phosphorus
InSeHexagonal
BN
Juejun (JJ) Hu
Chalcogenide glass-on-2D-material photonics
Black
phosphorus
30 nm
Ge23Sb7S70
glass film
The multifunctionalChG material
✓ Broadband light
guiding medium
✓ Passivation layer
for 2-D materials
✓ Gate dielectric
arXiv:1703.01666
Juejun (JJ) Hu
Broadband on-chip waveguide polarizer
Strong birefringence due to optical
anisotropy of graphene and
waveguide modal symmetry
arXiv:1703.01666
Juejun (JJ) Hu
Insertion loss Contrast ratio Length
Nat. Photonics 5, 411 (2011) 5 dB 23.6 dB 2100 mm
Our device 0.8 dB 23 dB 400 mm
Broadband on-chip waveguide polarizer
Juejun (JJ) Hu
Broadband on-chip waveguide polarizer
Octave-spanning broadband performance
Bandwidth with > 20 dB
contrast ratio:
❖ Experiment: 0.98 mm
& 1.55 mm
❖ Theory: 0.94 – 2.5 mm
arXiv:1703.01666
Juejun (JJ) Hu
Graphene as an energy-efficient transparent
heater
✓ Vanishing parasitic
optical loss
✓ Minimal thermal mass
✓ Large spatial overlap
between heating zone
and optical mode
Juejun (JJ) Hu
Graphene as an energy-efficient transparent
heater
Heating
efficiency:
10 nm/mW
t = 14 ms
Low-loss, broadband, energy-efficient transparent electrode
FOM 1.5 mW μsP t
Juejun (JJ) Hu
Waveguide-integrated mid-IR detector
Pauli blocking
Broadband mid-IR response with a peak responsivity of 250 mA/W
arXiv:1703.01666
Juejun (JJ) Hu
The first graphene mid-IR waveguide modulator
ChG functions simultaneously as an infrared-transparent
gate dielectric and the light guiding medium
arXiv:1703.01666
Juejun (JJ) Hu
The first graphene mid-IR waveguide modulator
arXiv:1703.01666
TheoryExperiment
8 dB/mm modulation depth at 2.05 mm wavelength
Juejun (JJ) Hu
Chalcogenide glass-on-2D-material photonics
&
The multifunctional ChG
✓ Direct deposition on 2-D
materials without surface
modification
✓ Broadband light guiding
medium
✓ 2-D material passivation
✓ Gate dielectric
2-D materials
✓ Large-area, catalyst-free
growth on semiconductor
substrates
✓ Broadband operation
✓ Unique optical functions
✓ Optoelectronic properties
readily tuned by gating
Juejun (JJ) Hu
2-D materials
Monolithic photonic integration on 2-D materials
Flexible planar photonics
Integration with nanomembranes and elastomers
Glass photonic integration
ChGs are uniquely poised for multi-material integration
Introduction
Chalcogenides (ChGs): an emerging optical material
Juejun (JJ) Hu
Introduction
Chalcogenides (ChGs): an emerging optical material
Glass photonic integration
ChGs are uniquely poised for multi-material integration
Flexible planar photonics
Integration with nanomembranes and elastomers
2-D materials
Monolithic photonic integration on 2-D materials
Juejun (JJ) Hu
Flexible photonics: the next-generation photonic technology
Manufacturing
Integration & packaging
Applications
Roll-to-roll
manufacturing
Packaging in space-
constrained settings
Wearable devices
Bio-integration
Photonic tuning
Juejun (JJ) Hu
Transfer printing of flexible devices is limited in
yield and integration capabilities
SOI Handle wafer
PI precursor
Polymer
PDMS
device
Si nano-membrane
Handle wafer
PI
AuSiPI
Image courtesy of Dr. N. Lu @ UT Austin
Juejun (JJ) Hu
Elastomer/glass thermal expansion mismatch
Glass
PDMS
Material CTE (ppm/°C)
PDMS (elastomer) 310
Ge23Sb7S70 glass 21
Material CTE (ppm/°C)
PDMS (elastomer) 310
Ge23Sb7S70 glass 21
SU-8 epoxy 52
SU-8 epoxy effectively releases
thermal stress
Juejun (JJ) Hu
Making stretchable photonics out of rigid glass
Grating
coupler
Resonator
Devices on locally stiffened
islands interconnected by
serpentine waveguides
Juejun (JJ) Hu
Stretchable glass device fabrication
Non-
deformedStretched
Juejun (JJ) Hu
Stretchability of serpentine waveguides
Serpentine waveguides are robust against repeated stretching
0% elongation
36% elongation
▪ Before 3000 cycles @ 42%
▪ After 3000 cycles @ 42%
Juejun (JJ) Hu
Strain-optical coupling in waveguide devices
00
Leff
L
eff
it t g io i i
d dLL
n n
nn
ll
Light into waveguide
Optical resonator 0
eff
N L N Zn
l
Resonant condition:
Stress-induced resonance shift:
Juejun (JJ) Hu
Strain-optical coupling in waveguide devices
Can we correlate the resonant wavelength shift with local strain?
00
Leff
L
eff
it t g io i i
d dLL
n n
nn
ll
Juejun (JJ) Hu
Strain-optical coupling in waveguide devices
Length change X-section change Photoelasticity
Summing over all stress components
Can be derived from mechanical simulations
i
i
nn
D
i
A B B
B A B
B B An
C
C
C
where
Shear stress has no contribution
Two parameters!
00
Leff
L
eff
it t g io i i
d dLL
n n
nn
ll
Juejun (JJ) Hu
Predicting strain-optical coupling
Substrate stiffening
decreases local
strain by 25-fold
Juejun (JJ) Hu
Flexible waveguide integrated photodetectors
Metal-semiconductor-
metal (MSM) detector
InGaAs
Metal Metal
0+–
V
Juejun (JJ) Hu
Flexible waveguide integrated detector fabrication
❖ Fully leverages standard semiconductor fabrication processes
Juejun (JJ) Hu
Optical
input
Modeling of detector performance at 1550 nm
SU-8 top cladding
SU-8 bottom cladding
GeSbS
InGaAs
2 mm
❖ 80% quantum efficiency
❖ 10% reflection and scattering
❖ 10% transmitted (not absorbed)
Juejun (JJ) Hu
Nanopositioner
Polarization
controller
CCD & lamp
Microscope
Motion stages
Tunable laserOptical fiber
Computer
control
Power meter
Nanopositioner
Optical fiber
Device
Bright field
illumination
Semiconductor
parameter analyzer
Micro-probe
Electrical cable
Juejun (JJ) Hu
Detector response to waveguide input
Laser power
250 mW
Dark
At 5 V bias:
❖ Dark current ~ 1 nA
❖ Photo current 120 mA
Responsivity: 0.35 A/W
Quantum efficiency: 30%
Juejun (JJ) Hu
Mechanical testing
5 V bias
The device can withstand sub-millimeter bending without
performance degradation
Juejun (JJ) Hu
2-D materials
Monolithic photonic integration on 2-D materials
Flexible planar photonics
Integration with nanomembranes and elastomers
Glass photonic integration
ChGs are uniquely poised for multi-material integration
Introduction
Chalcogenides (ChGs): an emerging optical material
Juejun (JJ) Hu
V
Glass
waveguide
Optical crystal
Polymer
2-D material
Semiconductor
Glass-based multi-material integration
Rubber
Ceramics & Metal
Juejun (JJ) Hu
Si, LiNbO3, InP,
polymer…ChGs, 2-D crystals, &
other emerging optical
materials
Questions?
