Optical communication - LETI Innovation Days

Transcription

Silicon Photonics Technologies for Green Photonics
LETI Annual review 2013
Jean-Marc FEDELI
© CEA. All rights reserved
Source: IBM
Optical communication everywhere?
Optical communication
Optical
technology
InP
Si
InP
Si
Electrical communication
VCSEL
Si
VCSEL
(Si)
(Si)
(Si)
(Si)
The rationale of silicon photonics is the fabrication of complex optical
devices on cm² chips at low cost with low power consumption.
Green photonics= reduction of the energy /bit from tens of pJ/bit to tens of
fJ/bit
The 2000 decade: the search of Gbit/s
2002: Low loss strip waveguide 0,8 - 3dB/cm (MIT)
2003: Low loss rib waveguide 0,1dB/cm (IEF-LETI)
2003: 1 GHz Capacitive Si MZ Modulator (Intel)
2004: 10 GHz Capacitive Si MZ Modulator (Intel)
2004: 30 GHz MSM Ge photodiode (IEF-LETI)
2005: µdisc hybrid laser (INL-LETI-Gent University)
2006: FP hybrid laser (UCSB)
2007: 40 G Depletion Si MZ Modulator (Intel)
2007: 40 GHz Vertical PIN Ge Photodiode (IBM,IEF-LETI)
2009: 90 GHz Lateral PIN Ge Photodiode (IEF-LETI)
2010: 50G Depletion Si MZ Modulator (Surrey University-LETI)
…
|3
The 2010 decade: the quest of the holy fJ/bit
WDM OOK transceiver as example
|4
Reduction of the power of the receiver
Increase of the sensitivity of the PD (A/W)
Reduction of the TIA noise
Reduction of the dissipated power of the TIA
|5
Lateral PIN Ge photodiodes performances
Dark current median, mean and best values (769 dies per wafer)
Photodiodes
Wafer
Median (nA)
@-1V
Mean (nA)
Best (nA)
Yield
Responsivity @1550nm under
zero bias
Wi=0.5µm
1
196
310
<1
97.6%
2
48
208
<1
98%
~0.5A/W
Wi=0.7µm
1
2
27.7
20
53
27.5
<1
<1
97.1%
97.5%
~0.6A/W
Wi=1µm
1
17.7
29
~1
98.8%
2
8.7
21.4
<1
97.3%
~0.8A/W
Variation of the dark current due to the threading dislocations and to the
alignment tolerance
Reduction in responsivity with smaller Wi due to absorption in doped
region
Opto-electric Bandwidth of Ge PD
Extrapolated from
measurements by single pole fit
1550nm 50GHz modulated laser + 50GHz network analyzer
Zero bias bandwidth
Higher bandwidth due to reduction of
the intrinsic region width during the
implantations
Reduction of the sensitivity due to
absorption in doped regions
Ok for 10Gb/s, 25Gb/s and 40Gb/s
Improvement in sensitivity
Classic PIN photodiodes with low bias
Responsivity limited by quantum efficiency : 1 photon => 1 electron
Sensitivity or minimum detectable power of a receiver (photodiode + TIA)
inversely proportional to the responsivity of the photodiode
∝
Sensitivity limited by the noise of the TIA if the dark current of the photodiode
is below 1µA (typically with available TIAs)
At 40Gbps and BER = 1e-12, max sensitivity ~ -22.5dBm (with negligible
photodiode noise)
How to overcome the TIA noise limit?
Increase of the photodiode responsivity
To go beyond the quantum efficiency, gain is mandatory
1 photon gives rise to multiple electrons
This can be achieved by using avalanche photodiodes
Waveguide Ge APD
PIN 0.5A/W nominal responsivity
40Gbps @0V
Gain over 30
Gain-Bandwidth product over 200GHz
Breakdown voltage ~-8.6V
40
-3dB Bandwidth (GHz)
35
30
25
20
15
10
5
0
5
10
15
20
Gain
25
30
35
40
Reduction of optical losses in passive devices.
Losses due to performances in fabrication
Selection of low loss designs
Reduction of overall losses with design tricks
Reduction of the couplers insertion losses
| 10
Silicon waveguides
SiO2
Si
SiO2
Substrate
SiO2
Si
SiO2
Substrate
loss ≈ 2 dB/cm for 500nm x
220nm strip waveguide
Lower loss with larger width
Loss due to the roughness of
the edges
Low radius of curvature
Loss from 0.1dB/cm for
rib waveguide due to
reduction of the
roughness of the edges
Larger radius of
curvature
Transition from wide to regular width before turns
Transition rib-strip
Reduction of insertion loss of grating
couplers
Move from uniform grating to
cSi grating
apodized grating
Introduce Bragg mirror to reflect
the transmitted light
cSi grating
pSi layer
IC
aSi grating with aSi mirrors layers
Filter devices with TO actuation
Intensity (a. u.)
Ring uniformity
9.00E-007
8.50E-007
8.00E-007
7.50E-007
7.00E-007
6.50E-007
6.00E-007
5.50E-007
5.00E-007
4.50E-007
4.00E-007
3.50E-007
3.00E-007
2.50E-007
2.00E-007
1.50E-007
1.00E-007
5.00E-008
0.00E+000
∆λ=3nm/10mW
Group B #8 P0mW
Group B #8 P2mW
Group B #8 P4mW
Group B #8 P6mW
Group B #8 P8mW
Group B #8 P10mW
1526 1528 1530 1532 1534 1536 1538 1540 1542 1544
LETI 200mm
• Range λresmax - λresmin = 2.1119 nm
• Std deviation = 0.593 nm
The TO tuning is necessary for ring
resonator to get rid of fabrication
non-uniformity
Sensitivity to the Si thickness is
higher than width sensitivity
Wavelength (nm)
Uniformity : correlation with waveguide geometry
Correlation between Si thickness variation and
resonance wavelength variation of RR on 300mm wafer
Si Thickness range ≈ 6.5nm
Resonant wavelength range ≈ 7nm
Decrease the range of uniformity of Si thickness to reduce or even avoid the tuning
Reduction of power for modualtion
| 15
PN carrier depletion MZM
Self-aligned carrier depletion modulator in
220nm Silicon-on-insulator
Waveguide 220nm X 400nm
100nm slab height
2um buried oxide layer
1um top cladding oxide
Thomson, D.J.; Gardes, F.Y.; Fedeli, J.-M.; Zlatanovic, S.; Youfang
Hu; Kuo, B.P.P.; Myslivets, E.; Alic, N.; Radic, S.; Mashanovich, G.Z.;
Reed, G.T.; "50-Gb/s Silicon Optical Modulator," Photonics
Technology Letters, IEEE , vol.24, no.4, pp.234-236, Feb.15, 2012
Optical microscope image of
fabricated device
VpiLpi =2.3V.cm
DC extinction ratio in excess of 10 dB
with 6V drive
Optical loss of 4.5dB/mm
50Gbit/s with a 3.1dB extinction ratio
PIPIN carrier depletion MZM
Self-aligned carrier depletion modulator on
fabricated device
L=1.8mm => C ~0.5 pF
Vpp = 7 V
Energy/bit ~ 6 pJ/bit
100nm slab height
VpiLpi = 3.5V.cm
40G with ER 6 dB
Optical loss of 2dB/mm
Melissa Ziebell , Delphine Marris-Morini, Gilles Rasigade, Jean-Marc Fédéli ,
Eric Cassan, David Bouville and Laurent Vivien, “ 40Gbit/s low-loss silicon optical
modulator based on a pipin diode”, Optics Express Vol. 20, Issue 10, pp. 10591-10596 (2012)
Reduction of power for modulator
Drive the modulator in push-pull mode (voltage reduction)
Reduction of capacitance of depletion device
Slow-wave device for reducing the length (corrugated waveguide or PC
devices
Ring Modulators
Ring Assisted MZI
Improvement of the efficiency (X10) Vpi.Lpi
MZM Hybrid modulator
Capacitive modulator ( capacitance increases )
EAM Hybrid modulator
Ge EAM modulators (QCSE or FK)
Targets : ~100 fJ/bit for longer off-chip distances, 10’s of fJ/bit for dense off-chip connections
and a few fJ/bit for global onchip connections.
D. A. B. Miller, Proc. IEEE 97(7), 1166–1185 (2009).
Energy/bit = 1/4 C(Vpp)2
D.A.Miller “ Energy consumption in optical modulators for interconnects” OExpress, 12 March 2012, Vol 20 N°S2
| 18
SW PN carrier depletion modulator
Self-aligned carrier depletion modulator in
fabricated device
100nm slab height
A. Brimont, D. J. Thomson, P. Sanchis, J. Herrera, F.Y.
Gardes, J. M. Fedeli, G. T. Reed, and J. Martí, "High
speed silicon electro-optical modulators enhanced via
slow light propagation," Opt. Express 19, 20876-20885
(2011)
500µm long CMOS compatible slow wave
modulator
Group index of only ~11
Modulator ring PIPIN
10 Gbit/s ring modulator
Ring radius of 50 µm => C ~0.08 pF
Energy/bit ~ 0.7 pJ/bit
PIPIN diode integrated in a 50µm radius ring resonator.
VpLp product of 3V.cm for both TE and TM input light.
Insertion loss lower than 1 dB
10 GBit/s operations were demonstrated with 5.6 and 5.1 dB Extinction Ratio.
Rasigade, G.; Ziebell, M.; Marris-Morini, D.; Brimont, A.; Campo, A.M.G.; Sanchis, P.; Fedeli, J.; Duan, G.; Cassan, E.; Vivien, L.; , "10-Gb/s Error-Free
Silicon Optical Modulator for Both TE and TM Polarized Light," Photonics Technology Letters, IEEE , vol.23, no.23, pp.1799-1801, Dec.1, 2011
RAMZI PIPIN carrier depletion modulator
Self-aligned carrier depletion modulator on
100nm slab height
fabricated device
Bandwidth of 19 GHz,
Data transmission at 20Gbit/s
with extinction ratio of 2.6dB,
over a RF/optical interaction
length of only 200µm
Gutierrez, A.M.; Brimont, A.; Rasigade, G.; Ziebell, M.; Marris-Morini, D.; Fedeli, J.-M.; Vivien, L.; Marti, J.; Sanchis, P.; , "Ring-Assisted
Mach–Zehnder Interferometer Silicon Modulator for Enhanced Performance," Lightwave Technology, Journal of , vol.30, no.1, pp.9-14,
Jan.1, 2012
Ge/SiGe QCSE devices
Bias from 0 to 5V :
Extinction Ratio (ER) > 6 dB
for 20 nm range
Energy to charge the device
Energy/bit = 1/4C(Vpp)2
Energy dissipation of photocurrent
Energy/bit = 1/B (IphVbias)
C ~ 62 fF
Energy/bit = 70 fJ/bit
(for a voltage swing of 1 V , 20 GHz,
0.5 mW input power)
22
The 2010 decade: High efficiency hybrid lasers
| 23
Hybrid Laser concept
Gain III-V Heterostructure
Si-circuit supports all optical functions
Top view
DBR
III-V/Si active region
N-contact
P-contact
Si waveguide
Surface-grating coupler
Mode transformer
Feed-back
R>90%
R~50%
InP
Gain region
To fiber
Si waveguide
Side view
Power vs current of a Fabry-Perot hybrid laser
at 1.3 µm (InGaAlAs/InP)
Threshold current of 12mA at room temperature for 500 µm devices
Maximum out power at 20°C: 10 mW at CW conditions and 16 mW for I
= 150 mA at pulse conditions
Operating up to 80° at CW conditions
Still reflections in the III-V/Si waveguide transition areas
State of the art on hybrid III-V/Si lasers (Feb 2013)
III-V Lab/CEA LETI
CEA
LETI
Monolithic InP
lasers
Intel/UCSB
Type
Si FP
Si RRs
Si FP
Si DBR
Si DBR
Si DFB
Si DBR
DFB
SG
DBR
Silicon
waveguide
thickness (nm)
440
440
440
500
500
500
500
/
/
Ith (mA) at 20°C
30
21
12
40
45
25
65
< 20
< 20
0.1
0.1
0.1
0.1
0.1
0.05
0.15
> 0.25
> 0.25
18
10
10
14
30
5.4
11
30
20
/
45
/
>20
/
40
40
40
35
Tunability (nm)
/
45
/
/
/
/
/
/
40
T° max operation
60°C
60°C
90°C
60°C
90°C
50°C
45°C
90°C
90°C
Active gain
material (MQW)
InGaAsP
InGaAsP
InGaAlAs
InGaAsP
InGaAlAs
InGaAsP
InGaAsP
Wavelength (µm)
1.55
1.55
1.3
1.55
1.3
1.55
1.55
η (mW/mA) at
20°C
Pmax (mW) at
20°C
SMSR (dB)
InGaAsP/ InGaAsP/
InGaAlAs InGaAlAs
1.3-1.55
1.55
Green hybrid III-V/Si lasers
Increase of the power efficiency and decrease of threshold
current:
Improve the III-V/Si taper transition efficiency
Decrease the cavity losses: III-V waveguide losses, Bragg mirror losses, etc.
Improve the thermal management
Use of materials with better temperature behaviour
InGaAlAs MQW at 1.3 µm
QD materials (Comb laser)
Use of smaller cavity length (around 100µm)
Smaller DFB
Ring laser cavity
Page 27
Microring hybrid laser
25 C
30 C
…
70 C
Threshold down to 0.5mA, but reduction of the efficiency
Racket design in order to add the power of clockwise and counterclockwise modes
3.75µm radius disk, 60 nm coupling distance
Photonic-Electronic Integration
| 29
Rationale of Photonic- Electronic Integration
Reduction of the length of electric connections between
active photonic device and driving electronic device.
Reduction of resistance and capacitance for higher RF performances
Reduction of power consumption
Feedback loops for the control of the photonic building
blocks
Reduction of the cost and the number of components with
high volume manufacturing
Metallic Photonic Electronic Connection
Die to Die connection (D2D) by wire bonding
D2D with stud bumping (low number of pins)
D2D with Flip-chip technology (high number of pins)
D2D with Cu pillars (reduction of the size and Pb free)
Cu-Cu bonding
Front side W2W fabrication with direct bonding
W2W direct bonding of the electronic wafer and the photonic wafer without
metallizations
Removal of the SOI substrate
Fabrication of the electrical connections between photonic active devices
and electronic drivers
Si rib waveguide
Germanium
AWG on CMOS
Germanium PD
Si waveguide
TIA
Acknowledgements
European projects:
Collaborative program with
More information on Silicon Photonics can be found in the new bible:
Thank you for your attention
2010: Energy/bit > 10 pJ/bit
2020:energy/bit << 100fJ/bit
| 34
Si Photonics various building blocks
Passive devices (Waveguides,
splitters, cavities, gratings,
couplers,..)
Rib, Strip, horizontal slot,
vertical slot, multilayers
waveguides
SiOx, SiNx, cSi, aSi, InP on Si,
SiGe, … and a mix of
Photodetectors
Ge on Si
InGaAs on Si
Si implanted
Modulators
Si capacitive,
Si carrier injection, Si depletion
SiGe/Ge
Ge
InP on Si
Polymer
Strain
Laser sources
InP on Si
Ge
nc Si
Driving electrical power
http://silicon-photonics.ief.u-psud.fr/
Simulation for TB=0.05 ns
(data rate =20 Gbit/s)
U(t)
U
TB
0
VπL π
t
Static power dissipated in the device is negligible
as reverse current is very low.
C(U)
0.3 fF/µm
Capacitance depends on the voltage.
It has been approximated by its average value
between 0 and U volts.
0.1 fF/µm
5V U
Power modulator
. calculation of P = f x C x V^2
With C = 0.2 fF/µm, L = 4000 µm, V = 4 V et f = 10 GHz :
Pmax=128 mW.
At 40 GHz, Pmax= 512 mW. (charge+discharge).
With random signal, it will divided by 2.
In push-pull , voltage /2: P/4 .
Energy/bit= CV2/4

Optical communication - LETI Innovation Days

Transcription

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