PHOTONICS RESEARCH GROUP
Lab-on-chip and point-of-care applications of
silicon photonics
Roel Baets
Photonics Research Group, Ghent University – IMEC
Center for Nano- and Biophotonics, Ghent University
roel.baets@ugent.be
PHOTONICS
RESEARCH GROUP
UK Silicon Photonics Workshop,
University
of Southampton, 12 Nov 2013
1
What is silicon photonics?
The implementation of high density photonic integrated
circuits by means of CMOS process technology in a CMOS fab
PHOTONICS RESEARCH GROUP
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Outline
An introduction to silicon photonics
Biosensing and gas sensing
Laser Doppler vibrometry and optical coherence tomography
Spectroscopy-on-a-chip
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Why silicon photonics
High index contrast  very compact PICs
CMOS technology  nm-precision, high yield,
existing fabs, low cost in volume
High performance passive devices
High performance Ge photodetectors
High performance modulators
Wafer-level automated testing
Hierarchical set of design tools
Light source integration (hybrid/monolithic?)
Integration with electronics (hybrid/monolithic?)
D4
D3
D2
D1
33mm
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High index contrast: a blessing and a curse
A blessing
• very small bend radii
Si
down to 1 m
• grating couplers for coupling to optical fibers
SiO2
[2um box]
with <1-2 dB coupling loss
• photonic crystals
wavelength-sized cavities with very high Q
A curse
• losses due to scattering
roughness of a few nm: a few dB/cm loss
• optical path length phase error
waveguide width error of a few nm: phase error of  after a few 100 m
• spurious reflections
CMOS technology is the only manufacturing technology
with sufficient nm-process control
3
nm without
matters
to take advantageEvery
of the blessing
suffering from the curse
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Optical Lithography by deep UV steppers

Re solution  k1
NA
light source
Deep UV
(excimer lasers)
Near UV
mask with
pattern
Visible light:
380 - 760 nm
lens
193nm
248nm
200
300
365nm
violet
blue
green
yellow
orange
red
400
500
600
700
wavelength (nm)
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Lower waveguide loss in 300mm fab with immersion litho
193nm DUV patterning
in 200mm fab
193nm immersion DUV
patterning in 300mm fab
http://www2.imec.be/content/user/Image/Press_releases/Optical%20io%20waveguide%20loss.jpg
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Industrial take-up examples in telecom/datacom
• active optical cables (eg 4x10Gb/s on parallel fibers)
• WDM transceivers (eg 4 WDM channels x 12.5 Gb/s on single fiber)
• coherent receiver (eg 100 Gb/s PM-QPSK)
• fiber-to-the-home bidirectional transceiver (eg 12 x 2.5 Gb/s)
• monolithic receiver (eg 16x20Gb/s)
• etc
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Outline
An introduction to silicon photonics
Biosensing and gas sensing
Laser Doppler vibrometry and optical coherence tomography
Spectroscopy-on-a-chip
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Microresonator biosensing
drop port
pass port
Resonator spectrum
Intensity [A.U.]
Wavelength [nm]
1575.7
Real time response
1575.5
avidin binding
1575.3
1575.1
buffer level
shift [nm]
Wavelength
shift [nm]
wavelength
resonance
input port
Concentration
measurement
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1573
1575
1577
time
wavelength
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0
5
10
15
20
25
avidin concentration
[μg/ml]
Avidin concentration
[ug/ml]
12
Microfluidics above silicon photonics
1
Fabrication of PDMS channels with soft lithography
2
PDMS (O2 plasma treatment)
Substrate + SU8 glue
3
PDMS + SU8
SOI sensors
4
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Multiplex sensing results
0.6
Serum with 82.6μg/ml anti-HSA
Serum with 128μg/ml anti-HuIgG
0.5
wavelength shift [nm]
0.4
HuIgG - αHuIgG
0.3
0.2
HSA - αHSA
0.1
BSA receptor
no receptor
0
0
-0.1
20
40
60
80
100
120
time [min]
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128 biosensor array chip
• 128 spiral resonator sensors
• One input; 128 output channels
200 m
50 m
through surface coupling gratings
2 m
• Real time detection and
monitoring of 128 independent
molecular binding reactions
O145
Ab
O55
Ab
1400
1000
800
600
400
200
1400
0
1000
800
600
400
200
20
40
60
80
100
20
60
80
200
100
400
200
1000
800
600
400
200
0
-200
0
S6
20
40
60
80
100
0
800
600
400
200
S7
O55
1000
800
600
400
200
1000
200
0
-200
0
20
40
60
80
100
0
Time (minutes)
600
400
200
0
S10
O103
1000
800
600
400
200
20
40
60
80
100
20
Time (minutes)
40
60
80
600
400
200
100
S13
600
400
200
S14
800
600
400
200
600
40
60
80
400
200
100
0
S15
O157
1200
1000
800
600
400
200
1000
200
0
0
20
40
60
Time (minutes)
80
100
0
20
40
60
Time (minutes)
80
100
S0
400
-200
100
100
600
0
80
80
800
-200
60
60
Temperature
1200
0
40
40
Time (minutes)
-200
Time (minutes)
20
1400
0
20
100
S12
800
-200
0
80
O145
1000
Time (minutes)
O157
1000
60
0
20
1400
1200
Wavelength shift (pm)
O157
800
40
-200
0
1400
1000
800
Time (minutes)
1400
1200
O103
1000
1200
-200
0
20
Time (minutes)
S11
0
-200
0
0
1400
1200
0
-200
100
Wavelength shift (pm)
800
80
1400
1200
Wavelength shift (pm)
O103
1000
60
Wavelength shift (pm)
S9
40
Time (minutes)
1400
1200
20
S8
400
0
-200
100
100
600
0
80
80
800
-200
60
60
O145
1200
0
40
40
Time (minutes)
-200
20
20
1400
1200
Wavelength shift (pm)
600
1000
Time (minutes)
O55
1200
Wavelength shift (pm)
Wavelength shift (pm)
S5
O55
800
1400
Wavelength shift (pm)
400
S4
O145
1200
1400
Time (minutes)
Wavelength shift (pm)
40
1400
0
•
600
Time (minutes)
1400
1000
800
-200
0
Time (minutes)
1200
1000
0
-200
0
1400
S3
O121
1200
0
-200
9 mm
S2
O121
1200
Wavelength shift (pm)
Wavelength shift (pm)
Output grating
Coupler array
S1
O121
1200
Wavelength shift (pm)
1400
O121
Ab
Wavelength shift (pm)
O55
Bacteria
Wavelength shift (pm)
Fluid channel
Wavelength shift (pm)
Sensor
element
Wavelength shift (pm)
Input grating
coupler
0
20
40
60
Time (minutes)
Application - multiplexed serotyping of E. coli isolates
(with Canadian Food Inspection Agency and Health Canada)
15
80
100
Selective, reversible and fast ammonia gas detection
Microporous silica layer, pores: 2nm; porosity: 45%
Functionalized for ammonia-selectivity
Application:
breath analysis
Sensitivity down to 100ppb demonstrated
N. Yebo et al, Optics Express, 20(11), pp. 11855 (2012)
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Outline
An introduction to silicon photonics
Biosensing and gas sensing
Laser Doppler vibrometry and optical coherence tomography
Spectroscopy-on-a-chip
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Laser Doppler vibrometer on silicon-on-insulator
Moving target
Polytec OFV-534 LDV sensor
head.
miniaturization
Polytec
x 10
2
1
Amplitude (m)
Doppler effect:
f opt
vtarget
2
f opt
c
On-chip LDV
-6
0
-1
-2
Y. Li et al, Optics Express, 21(11), p.13342-13350 (2013)
Y. Li et al, Photonics Technology Letters, 25(13), p.1195-1198 (2013)
Y. Li et al, Applied Optics, 52(10), p.2145-2152 (2013)
-3
0.9
0.95
1
1.05
1.1
Time (s)
1.15
1.2
1.25
1.3
Piezo stack driver; fv =11.3 Hz; Vpp = 50 V [1]
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LDV-measurement of blood pulse velocity
Blood pulse velocity: increases when blood vessels become stiffer due to arteriosclerosis
Fiber array
BPD
BPD
I1(t)
Q1(t)
Laser
PC
BPD
BPD
I2(t)
Q2(t)
os
1
hybrid
2
lens
Carotid
Artery
θ
os
2
θ
-3
Correlation (a.u.)
Velocity (m/s)
x 10
hybrid
1
SOI chip
8
6
4
2
0
-2
1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
Time (s)
Y. Li, et al, Biomedical Optics Express, 4(7), p.1229(2013)
Δt = 0.003s
Pulse velocity: 4.5 m/s
0.25
0.2
0.15
0.1
-0.05
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Time (s)
0.05
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Challenges in LDV-circuits
On-chip optical frequency shifter
• acousto-optic diffraction: very difficult on chip
• serrodyne phase modulation
phase
2
t
Spurious reflections on chip (high index contrast!)
• from grating couplers
• from MMI couplers
• from backside of chip
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Spurious reflections from grating couplers
Side view
Fresnel
reflection
Optical fiber
or
imaging lens
2nd order
reflection
Si
SiO2
Typical spurious reflection: -20dB
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Tilted focusing grating couplers (TFGCs)
φ
D. Vermeulen et al, Optics Express, p.22278 (2012)
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Reflectionless grating couplers
Back reflection (dB)
-10
-20
-30
-40
-50
0
30
60
90
120
Azimuth (degree)
150
180
Y. Li et al, Optics Letters, 37(21), p.4356 (2012)
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Optical coherence tomography
stratum corneum viable epidermis
papillary dermis
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reticular dermis
G. Yurtsever et al,
to be published
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Coupling
16 grating couplers
Phased array beam scanners
220nm Si
5µm
150nm Si
no Si
Induced refractive
index change
Phase tuners
16 thermal tuners
Waveguide
Excitation with TE mode
K. Van Acoleyen et al,
IEEE JLT, 29(23), p.3500 (2011)
Star coupler
Splitting with
Gaussian apodization
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Coupling
Efficient light collection
16 grating couplers
220nm Si
150nm Si
Scattered light
5µm
no Si
Phase tuners
correct aberrations
Waveguide
Collected light for
further processing
Star coupler
Combining in phase
light contributions
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Integrated 2D phased array beam scanners
Large technological implementation
Compact grating couplers
Compact heaters for individual phase tuning
Directional coupling to deliver equal power to each element from power line
Far field
(green circle= NA of 0.4 = +/-23)
Jie Sun, Erman Timurdogan, Ami Yaacobi, Ehsan Shah Hosseini and Michael R. Watts,
“Large-scale nanophotonic phased array”, Nature, vol. 493, p. 195-199, 2013
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Outline
An introduction to silicon photonics
Biosensing and gas sensing
Laser Doppler vibrometry and optical coherence tomography
Spectroscopy-on-a-chip
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Optical spectroscopy: fingerprint for molecular sensing
Probing the photon-electron
coupling in molecules
Probing the photon-phonon
coupling in molecules
Absorption spectra of simple molecules
Absorption spectrum of hemoglobin
Fluorescence spectrum of GFP
Raman spectrum of CCl4
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Spectroscopy-on-chip: what
Fluid or gas
Light in
waveguide
Light out
On-chip
detection
On-chip
light source
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Spectroscopy-on-chip: what
Absorption spectroscopy
Broadband
probe
D
spectro
meter
D
Laser
D
Broadband
Filter
probe
probe
Detector
D
Fluorescence spectroscopy
D
Laser
probe
spectro
meter
D
D
Raman spectroscopy
D
Laser
probe
Filter
spectro
meter
D
D
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Integrated spectrometers
spectrometer
spectrometer
E. Ryckeboer et al., Opt Express 2013
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Integrated short-wave infrared spectrometer
Covering 1500-2300nm
E. Ryckeboer et al., Opt Express 2013
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Glucose absorption spectroscopy
Objective:
Continuous Glucose Monitoring
by means of subcutaneous implant
hypoglycemia
hypoglycemia
hyperglycemia
hyperglycemia
First overtone band: 1500 - 1800 nm
Combination band: 2000 - 2500 nm
For glucose sensing in humans (3-15 mM): Largest change in transmission is 0.5 %
Required sensitivity : 0.02%
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Single-Beam up/down 14 mM experiment
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Dual beam implementation
To reference detector
To signal detector
Source with
variable
wavelength
Glucose solution
Pure water
Advantages:
Simultaneous reference measurement
Eliminate influence largest interferent (water)
Minimize influence source noise
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View of the chip
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dual-beam
Experiment
We apply 8mM, 16 mM, 24 mM and 32 mM of glucose
Wavelength dependent slow drift remains
PHOTONICS RESEARCH GROUP
Absorption dip increases with
increasing glucose concentration
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Emission spectroscopy: enhancement by waveguides
Fluorescent or
Raman-active
molecule
Guided wave
collection
Guided
wave pump
Three enhancement effects
• waveguide confinement: high pump field strength for a given pump power
• dipole couples a relatively large fraction of its emitted power into the guided mode(s) of
the waveguide (waveguide coupling factor )
• total power emitted by dipole enhanced by the vicinity of the waveguide (Purcell
enhancement factor Fp)
High refractive index contrast matters!
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Dipole emission power coupled to the waveguide modes
air
Si3N4
SiO2
Fp
Si
Conclusions
• Best enhancement for vertical dipoles coupling to TM-mode
• Better enhancement for high refractive index contrast
A Dhakal et al, ECIO 2012, Barcelona Spain
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Detection volume
Collection
• Large étendue from particle cloud:
 Resolution - sensitivity - size
compromise for the spectrometer
On-chip excitation and collection
Monochromator
Free space excitation and collection
guided mode
Channel waveguide
• Cloud couples to single waveguide mode:
smallest possible étendue!
 Optimal performance of spectrometer
• In a confocal microscope:
Fraction of the
field in the Enhancement
analyte
factor
Raman/Fluorescence
Scattering cross section
Pcoll = Ppump
2 l0
rs scat
n
On-chip spect.
Asset of waveguide based emission spectroscopy
Pcoll = PPump (GLFp )s scat r
Main assets
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Si3N4 Rib waveguides for 780 nm light
w
ncl=1.33
Si3N4
h
Assumption:
• molecules with Raman cross section ≈ 10-27 cm2 Sr-1 molecule-1
• concentration=1 mol/lit
• waveguide length = 1 cm
SiO2
[2um box]
ηmax≈10-8
(100mW of pump
generates 1nW
of single mode Stokes light)
free space: ηmax≈10-10
W (nm)
A. Dhakal et al, OSA APC, p.ST2B.5 (2013)
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Nanoplasmonic enhancement on Si3N4 waveguide
nanoparticle
SiO2
E
k
Excitation
Si3N4
Au
Au
SiO2
Collection
Enhancement of Raman
scattering scales with |E|4
F. Peyskens et al, CLEO, CM2F.5 (2013)
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Silicon photonics: extending the wavelength range
without leaving the CMOS fab
Si
SiO2
[2um box]
0.3
1.0
3.0
10.0
[m]
Ge
Si3N4
SiO2
Si
R. Soref, Nature Photonics 2010
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PECVD Si3N4 waveguides for visible and VNIR wavelengths
Waveguide loss
unclad
clad
Grating coupler loss
nitride
SiO2
Cross-section of Grating couplers
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SOI waveguide platform (400nm c-Si) for mid IR
0
-1.75
P1
-5
Normalized transmission(dB)
P2
-10
P3
P4
-15
P5
-20
P6
-24.9
-25
-30
-35
3740
3750
3760
3770
3780
Wavelength(nm)
AWG wavelength (de)multiplexer
3790
3800
3810
M. Muneeb et al., Optics Express, 21(10), p.11659 (2013)
M. Muneeb, MF1.2
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Ge-on-Si waveguides
Ge
Ge
Si
Si
Epitaxially grown Ge on Si
Ge
Si
Metal mask by negative litho
Si
Waveguide etching in RIE
Wavelength = 5.3 µm, Ge thickness = 2 µm
Wavelength = 3.74 µm, Ge thickness = 1 µm
0
-2
0
0
0.5
1
-8
-12
-14
2.5
0
y = -7.7683x + 3.877
R² = 0.9822
Length (cm)
1
2
3
4
-2
Loss (dB)
-6
-10
2
Loss = 7.8 dB/cm
-4
Loss (dB)
1.5
Loss = 3 dB/cm
-4
-6
-8
y = -2.9764x + 2.2104
R² = 0.9976
-10
Length (cm)
A. Malik, MF1.4
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Conclusion
When does silicon photonics make (a lot of) sense?
1. High volume markets with extreme performance/cost ratios
active optical cable, data centers, HPC
use-once biosensor chip
2. Extreme performance, based on nano-accuracy
coherent receiver
high performance spectrometers/filters
photonic crystal devices
3. Extreme miniaturization, based on high index contrast
intra-chip optical interconnect (match electronic scaling)
beam scanner
body implants
Silicon photonics = the implementation of PIC’s in a CMOS eco-system
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Acknowledgements
Ghent University
funding and collaborations
Photonics Research Group
professors P. Bienstman, W. Bogaerts, G. Morthier, G. Roelkens,
N. Le Thomas, D. Van Thourhout and many postdocs and PhD’s
IMEC CMOS process line
and ePIXfab www.epixfab.eu
Funding and collaborations through national and EU research projects
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