polymer waveguide based optical interconnects for high-speed on-board communications

Jian Chen 0 of 36

Polymer Waveguide Based Optical Interconnects

for High-Speed On-Board Communications

Jian Chen

Centre for Photonic Systems, University of Cambridge, UK

Supervisor: Prof. Ian H. White

Email: [email protected] 06/2016

Jian Chen 1 of 36Jian Chen 1 of 36

Outline

• Introduction to Optical Interconnects

• Multimode Polymer Waveguides

• Bandwidth Studies

• Theoretical Modelling

• Experimental Results

Refractive Index Engineering

Launch Conditioning

Waveguide Layout

• High-Speed Data Transmission

• Link Simulation

• Experimental Demonstration

40 Gb/s NRZ

56 Gb/s PAM-4

• Conclusions


Outline







Launch Conditioning

Waveguide Layout


• Link Simulation


40 Gb/s NRZ

56 Gb/s PAM-4

• Conclusions

Jian Chen 3 of 36

Why Optical Interconnects?

Growing demand for data communications link capacity in:

- data centres

- supercomputers

need for high-capacity short-reach interconnects operating at > 25 Gb/s

Optics better than copper at high data rates (bandwidth, power, EMI, density)

E.Varvarigos, Summer School on Optical Interconnects, 2014.K. Hiramoto, ECOC 2013.


Board-level Optical Interconnects

Various approaches proposed:

free space interconnects

fibres embedded in substrates

waveguide-based technologies

M. Schneider, et al., ECTC 2009.

Jarczynski J. et al., Appl. Opt, 2006.R. Dangel, et al., JLT 2013.

Siloxane

waveguidesInterconnection

architectures

Board-level OE

integration PCB-integrated

optical units

Basic waveguide

components

Our work:

Polymer waveguides


Outline







Launch Conditioning

Waveguide Layout


• Link Simulation


40 Gb/s NRZ

56 Gb/s PAM-4

• Conclusions

Jian Chen 6 of 36

Multimode Polymer Waveguides

- Siloxane Polymer Materials

• low intrinsic attenuation (0.03–0.05 dB/cm at 850 nm)

• good thermal and mechanical properties (up to 350 °C)

• low birefringence;

• fabricated on FR4, glass or silicon using standard techniques

• offer refractive index tunability

- Multimode Waveguide

• Cost-efficiency: relaxed alignment tolerances

assembly possible with pick-and-place machines

50 μm core

top cladding

bottom cladding

Substrate

suitable for integration on PCBs

offer high manufacturability

are cost effective

- typical cross section used: 50×50 μm2

- 1 dB alignment tolerances: > ±10 μm

Jian Chen 7 of 36

Opto-electronic PCB Integration

N. Bamiedakis et al., IEEE Trans. Compon. Packag. Manuf. Technol., 2013.

enabling direct integration onto PCBs using conventional electronics manufacturing

assembly possible with pick-and-place machines

Jian Chen 8 of 36

Technology Development

increase data rate over each channel

N. Bamiedakis, et al., ECOC, P.4.7, 2014.

waveguide link

Finisar, Xyratex

24 channels x 25 Gb/s

K. Shmidtke et al., IEEE JLT, vol.

31, pp. 3970-3975, 2013.

4 channels x40 Gb/sM. Sugawara et al., OFC, Th3C.5,

2014.

Fujitsu Laboratories Ltd.

1 channel x40 Gb/s

Cambridge University

- Numerous waveguide technology demonstrators:

- Continuous bandwidth improvement of VCSELs:

- 850 nm VCSELs:

57 Gb/s (2013)

64 Gb/s (OFC 2014, Chalmers - IBM)

71 Gb/s (PTL 2015, Chalmers - IBM)

their highly-multimoded nature raises important concerns about their bandwidth limitations and

their potential to support very high on-board data rates (e.g. >100 Gb/s)?

D. M. Kuchta, et al., IEEE JLT, 2015.


Outline







Launch Conditioning

Waveguide Layout


• Link Simulation


40 Gb/s NRZ

56 Gb/s PAM-4

• Conclusions

Jian Chen 10 of 36

Bandwidth Studies - 1

- Bandwidth limitation in multimode waveguides mainly due to multimode dispersion:

different waveguide modes exhibit different group refractive indices ngr

they therefore exhibit different “transit” times along a particular waveguide length

- Bandwidth investigated with both frequency and time domain measurements

- frequency response measurements

measure amplitude of a high-frequency sine wave over the WG

- time domain measurements

measure pulse dispersion after transmission over the WG

0 0.25 0.5 0.75 1 1.25-0.5

0

0.5

1

1.5

2

Time (ps)

Auto

corr

ela

tion T

race A

mplit

ude

B2B - x= +0.0 m

Data

Gauss fit

Sech fit

Lore fit

Data FWHM = 0.25 psGaus FWHM = 0.18 psSech FWHM = 0.16 psLoren FWHM = 0.12 ps

R2 Gaus = 0.999

R2 Sech = 1.000

R2 Loren =

0.988

0 10 20 30 40 50 60-0.2

0

0.2

0.4

0.6

0.8

1

1.2

Time (ps)

Auto

corr

ela

tion T

race A

mplit

ude

Sp2 SI WG#3 In:x10, Out: x16- x= +0.0 m

Data

Gauss fit

Sech fit

Lore fit

Data FWHM = 19.99psGaus FWHM = 14.00psSech FWHM = 12.68psLoren FWHM = 10.31ps

R2 Gaus =

0.998

R2 Sech =

0.995

R2 Loren =

0.982

input pulse output pulse

∆tin ∆tout

frequency

0

0

|Hin(f

) |(d

B)

-3

in

dBf 3

frequency

0

0

|Ho

ut(f)

|(d

B)

-3

out

dBf 3

Jian Chen 11 of 36

Overfilled

Restricted

Input pulse Output pulse


Mode propagation in waveguide

Bandwidth Studies - 2

1. Refractive index (RI) engineering

2. Launch conditioning and input offsets

3. Waveguide layout and waveguide components

T. Ishigure, Summer

School on Optical

Interconnects, 2014.

Overfilled

Restricted



Mode propagation in waveguide Mode propagation in waveguideMode propagation in waveguideInput pulse Output pulse Input pulse Output pulse

90° crossing 90° bend S bend Y splitter

elementary waveguide

components in complex

interconnection architectures

- Bandwidth studies on

Jian Chen 12 of 36

Waveguide Modelling

1. Calculate waveguide modes for different waveguide geometries and index step

Δn (FIMMWAVE Mode Solver);

e.g. cross section used: 20x20 µm2 or 60×60 µm2; index step difference Δn 0.005 to 0.03 at 850 nm.

2. Calculate effective and group refractive indices for all waveguide modes;

3. Calculate mode power coefficient for a specific launch condition;

4. Find normalised transfer function from impulse response.

f

0

0 1/ td 2/ td

|H(f

)/ H

(0)|

(dB

)

-3

f3dB

~0.6/ td

L

time tmin tmax

1/N

1

δ(t)

0

td

MM WG

y

zh

h(t) : impulse responseH(f) : frequency response

Jian Chen 13 of 36

Simulation Results

- Model to check reference BW values

- width: 20 µm to 60 µm, square cross section

- step index profile assumed, ∆n : 0.005 to 0.03

- uniform mode loss profile

- no mode mixing inside the waveguide

BW for overfilled launch condition

“worst-case” value

BW for a well-aligned SMF input

“best-case” value

h=w core

cladding

Δn =n1-n0

n1

n0

-∞w

130

140

140

140

140

140

140

150

150

150

150

150

150

150

150

160

16

0160

160

160

160

160

160

170

170

170

170

170

170

170

180

180

180

180

180

180

180

190

190

Bandwidth-Length Product-h/w=1.00-SMF Z-Gap RIX 1 -form Input

n

(n

1-n

0)

Waveguide width (m)20 25 30 35 40 45 50 55 60

0.005

0.01

0.015

0.02

0.025

0.03*values in GHz×m

- values greatly vary ! e.g. from ~10 GHz×m to 150 GHz×m for a 50×50 µm2, ∆n=0.02

step-index profile

w/2

nclad

position

-w/2

ncore∆n

Jian Chen 14 of 36

1 m Long Spiral Waveguide

- 1 m long multimode spiral waveguide

- cross section 32×50 µm2, ∆n ~ 0.02

- sample fabricated on 8’’ inch Si substrate

- input/output facets exposed with dicing saw

- no polishing steps undertaken32 µm

50

µm

- Frequency response investigated under different launch conditions:

~ 4 µm 50 µm 50 µm

100 µm

exciting increasing number of waveguide modes at waveguide input

4/125 µm SMF

restricted launch

typical (no mode mixer)

50/125 µm MMF

quasi-overfilled (mode mixer)

50/125 µm MMF

100/140 µm MMF

overfilled launch

1 m long spiral waveguide

Jian Chen 15 of 36

Frequency Response Measurements

- S21 response of waveguide calculated from the difference between the two recorded

responses for the waveguide and back-to-back link for the different inputs

back-to-back link waveguide link

1 m spiral waveguide

cleaved

50 μm MMF 50 μm MMF

patchcord

850 nm

VCSEL30 GHz PD

VNA RF

amplifier

MM VOA

Voltage

sourceBias

Tee

cleaved

input fibre

fibre

patchcord

mode

mixer

50 μm MMF

patchcord

850 nm

VCSEL30 GHz PD

VNARF amplifier

MM VOA

Voltage

sourceBias

Tee

fibre

patchcord

mode

mixer

4 µm SMF input (“best-case”)

~ 4 µm

N. Bamiedakis, et al., IEEE JLT, vol. 33, pp. 1-7, 2015.

“overfilled” 100 µm MMF input (“worst-case”)

100 µm

-3 dB frequency response >35 GHz for all inputs and input positions

suitable for high-speed transmission of ≥ 40 Gb/s data transmission

Jian Chen 16 of 36

Time Domain Measurements

10× lens 50 μm MMF 50 μm MMF+MM

1 m long spiral waveguide-25 -20 -15 -10 -5 0 5 10 15 20 25

-25

-20

-15

-10

-5

0

5

10

15

20

25

x (m)

y (

m)

1.515

1.517

1.519

1.521

1.523

1.525

1.527

1.529

1.531

1.532

-25 -20 -15 -10 -5 0 5 10 15 20 25-25

-20

-15

-10

-5

0

5

10

15

20

25

x (m)

y (

m)

1.5151.5161.5171.5181.5191.5201.5211.5221.5231.5241.5251.526

WG 1 WG 2(b) (c)(a)

- cross section ~35×35 µm2

- sample fabricated on 8’’ inch Si substrate

- input/output facets exposed with dicing saw

The index profile can be varied by changing the

fabrication conditions and material formulations.

Near field images- Experimental setup

- Waveguide samples with different RI profilesSI GI

Short pulse laser 1

Autocorrelator10x 16x

Cleaved 50/125 μm MMF

MM

Autocorrelator10x 16xShort pulse laser 2 + SHG

Jian Chen 17 of 36

∆tin∆tout

Input pulse Output pulse1. Short pulse generation system

(a) Ti:Sapphire laser emitting at 850 nm

(b) Femtosecond erbium-doped fibre laser at ~1574 nm

and a frequency-doubling crystal to generate pulses

at wavelength of ~787 nm

2. Matching autocorrelator to record output pulse

3. Convert autocorrelation traces back to pulse traces

curve fitting is needed to determine the shapes

of the original pulses, i.e. Gaussian, sech2 or Lorentzian.

4. Bandwidth calculation

waveguide frequency response and bandwidth estimated by comparing Fourier

transforms of input and output pulses

Bandwidth Estimation

0 0.5 1 1.5 2

x 1012

-20

-17

-14

-11

-8

-5

-2

0

Frequency (Hz)

Inte

nsity (

dB

)

Output pulse

Input pulse

3 dB

Jian Chen 18 of 36

Refractive Index Engineering - 1

SI GI

50 μm MMF: no MM 50 μm MMF: with MM 50 μm MMF: no MM 50 μm MMF: with MM

Bandwidth-length product (BLP): 30 – 60 GHz×m Bandwidth-length product (BLP): 50 – 90 GHz×m

J. Chen, et al., IEEE Optical Interconnects Conference (OIC), 2015.

1 m long spiral waveguide -25 -20 -15 -10 -5 0 5 10 15 20 25-25

-20

-15

-10

-5

0

5

10

15

20

25

x (m)

y (

m)

1.515

1.517

1.519

1.521

1.523

1.525

1.527

1.529

1.531

1.532

-25 -20 -15 -10 -5 0 5 10 15 20 25-25

-20

-15

-10

-5

0

5

10

15

20

25

x (m)

y (

m)

1.5151.5161.5171.5181.5191.5201.5211.5221.5231.5241.5251.526

WG 1 WG 2(b) (c)(a)

SI GI

Jian Chen 19 of 36

Refractive Index Engineering - 2

SI: no MM SI: with MM

GI: no MM GI: with MM

SI: no MM SI: with MM

GI: no MM GI: with MM

Coupling loss Bandwidth

- Simulation results:

J. Chen, et al., IEEE JLT, vol. 32, pp. 1-7, 2016.

Jian Chen 20 of 36

Launch Conditioning - 1

- Launch conditioning widely used in MMF links (10GbE) for BW improvement

specify position for input spot at fibre facet reduce ISI in the link

potential to use launch conditioning (restricted launches) to ensure large bandwidth

and low coupling losses in such multimode polymer waveguides

L. Raddatz, et al., IEEE JLT, vol. 16, pp. 324-331, 1998 .

Jian Chen 21 of 36

Launch Conditioning - 2

J. Chen, et al., ACP, paper AM3A.5, 2015.

-16 -12 -8 -4 0 4 8 12 16

-16

-12

-8

-4

0

4

8

12

16

Horizontal offset (m)

Ve

rtic

al o

ffse

t (

m)

40.060.080.0100.0120.0140.0160.0180.0200.0

WG 1 WG 2

-16 -12 -8 -4 0 4 8 12 16

-16

-12

-8

-4

0

4

8

12

16

Horizontal offset (m)

Ve

rtic

al o

ffse

t (

m)

40.060.080.0100.0120.0140.0160.0180.0200.0

Bandwidth >100 GHz×m

Lower bottom part: ~32 × 8 μm2

Bandwidth >100 GHz×m

Upper bottom part: ~20 × 22 μm2

19.2 cm long waveguide-25 -20 -15 -10 -5 0 5 10 15 20 25

-25

-20

-15

-10

-5

0

5

10

15

20

25

x (m)

y (

m)

1.515

1.517

1.519

1.521

1.523

1.525

1.527

1.529

1.531

1.532

-25 -20 -15 -10 -5 0 5 10 15 20 25-25

-20

-15

-10

-5

0

5

10

15

20

25

x (m)

y (

m)

1.5151.5161.5171.5181.5191.5201.5211.5221.5231.5241.5251.526

WG 1 WG 2(b) (c)(a)

≥ 100 Gb/s data

transmission

over a single

channel !

*values in GHz×m

10× lens:

SI GI

SI GI

Jian Chen 22 of 36

Waveguide Layout

Radius: 5, 6, 8, 11, 15 and 20 mm

Number of crossings: 1, 5, 10, 20, 40 and 80

A B

A B

Length: ~137 mm

Length: ~137 mm

output

input

input

output

- Mode filtering schemes: used in multimode fibre systems such as mode-selective ring

resonators and couplers.

Multimoded on-board optical interconnects using waveguide bends / crossings

- Two waveguide samples with slightly different RI profiles under a SMF (loss) and

50 μm MMF launch (loss, BW)50 μm MMF

B

Length: ~137 mmA B

WG length: 16.25 cm

reference WGs 90° bends 90° crossings

Jian Chen 23 of 36

Experimental Results - 1

- Insertion loss of the crossing and bends measured under:

- 9 μm SMF (restricted launch)

- 50 μm MMF (likely encountered in real-world systems)

- Obtained by normalising with respect to the insertion loss of reference waveguides.

InputLoss (dB/crossing)

WG A WG B

SMF 0.093 0.033

50 μm MMF 0.098 0.046

- WG A has worse crossing loss

- WG A and B have similar bending loss < 1 dB for radius R > 6 mm.

J. Chen et al., OFC, paper W1E.3, 2016.

Jian Chen 24 of 36

Experimental Results - 2

0 10 20 30 40 50 60 70 8035

40

45

50

55

60

65

Ban

dw

idth

-len

gth

pro

du

ct

(GH

zm

)

Number of crossings

WG A

WG B

0 10 20 30 40 50 60 70 800

2

4

6

8

10

12

Insert

ion lo

ss (

dB

)

Number of crossings

WG A

WG B

6 8 10 12 14 16 18 2035

40

45

50

55

60

65

Ban

dw

idth

-len

gth

pro

du

ct

(GH

zm

)

Radius (mm)

WG A

WG B

6 8 10 12 14 16 18 200

1

2

3

4

Insert

ion lo

ss (

dB

)

Radius (mm)

WG A

WG B

0 10 20 30 40 50 60 70 8035

40

45

50

55

60

65

Bandw

idth

-length

pro

duct

(GH

zm

)

Number of crossings

WG A

WG B

0 10 20 30 40 50 60 70 800

2

4

6

8

10

12

Insert

ion loss (

dB

)

Number of crossings

WG A

WG B

6 8 10 12 14 16 18 2035

40

45

50

55

60

65

Bandw

idth

-length

pro

duct

(GH

zm

)

Radius (mm)

WG A

WG B

6 8 10 12 14 16 18 200

1

2

3

4

Insert

ion loss (

dB

)

Radius (mm)

WG A

WG B

1.55× 1.25× ~1.9 dB~0.7 dB

1.25×

~1.6 dB

BW Loss

BW Loss

90° Bends vs. Straight WG

90° Crossings vs. Straight WG

R = 5 mm R = 11 mm

BLP

improvement

> 60 GHz×m

(1.55×)

> 50 GHz×m

(1.25×)

Additional

loss~1.9 dB ~0.7 dB

No. crossings = 10

BLP

improvement

~50 GHz×m

(1.25×)

Additional

loss~1.6 dB

90° Bends

90° Crossings

BW increases but loss degrades

design trade-off

J. Chen et al., OFC, paper W1E.3, 2016.


Outline







Launch Conditioning

Waveguide Layout


• Link Simulation


40 Gb/s NRZ

56 Gb/s PAM-4

• Conclusions


Link Simulation Studies

400 500 600 700 800 900 1000

0

0.2

0.4

0.6

0.8

1

1900 2000 2100 2200 2300 2400 2500

0

0.5

1

1.5

2

2.5

3

Gaussian:

VCSEL

Gaussian

Channel:

Waveguide

4th order

Bessel filter

Receiver:

PIN + TIA

T T T…

…

……

……

T T…

…

……

……

T

Decision

Feed Forward EqualiserDecision Feedback

Equaliser

NRZ PAM-4

or

Output

Transmitter Channel Receiver Equalisation

Gaussian Response Gaussian Response 4th order Bessel Response

VCSEL:

Wavelength: 850nm

Bandwidth: 25 GHz

Output power: 10 dBm

RIN: -130 dB/Hz

Waveguide:

Loss: 0.06 dB/cm

Bandwidth: 35GHz m

Couling loss: 3 dB

PIN photodiode + TIA

Cut-off frequency: 22GHz

Responsivity: 0.4 A/W

Sensitivity: -5.5 dBm

Minimum Mean Square

Error (MMSE) equalizer

consists of 7-tap FFE and

5-tap DFE

System Margin

N D N D N D-4-202468

1012141618202224

1.5 m1 m0.5 mPow

er

penalty (

dB

o)

System Margin

RIN

Waveguide Loss

ISI Penalty

Multilevel Penalty

PAM-4

FEC (10-3, 10

-12)

RIN Penalty

Waveguide Loss

ISI Penalty

Multilevel Penalty

Total Link

Power Budget

VCSEL Launching Power

Receiver Sensitivity

Power budget analysis

- Link model based on characteristics of actual components

- System simulation model

40 Gb/s NRZ

56 Gb/s PAM-4


NRZ vs. PAM-4

- NRZ-based links for > 40 Gb/s require bandwidth of link components

>25 GHz and therefore impose stringent requirements on:

performance of active optoelectronic devices (VCSELs, PDs)

driving electronic circuits

transmission of RF signals on the board: EMI, short-link lengths required

- Alternative way of achieving high-speed on-board

interconnect by relaxing component and link requirements:

use of spectral-efficient modulation schemes such as

Pulse Amplitude Modulation (PAM): - makes full use of component bandwidth

- relaxed specifications for electronic, photonic and RF board design

PAM-4 schemes currently considered for use in short-reach MMF-based links

In this work, the use of NRZ and PAM-4 in waveguide-based interconnects is

assessed via simulation and experiments.

cost and complexity issues arise 40 Gb/s NRZ

0.5m

56 Gb/s NRZ 56 Gb/s PAM-4

1m

1.5m

-10 -5 0 5 10

-1

0

1

Time (ps)

Norm

alis

ed A

mplit

ude

-5 0 5

-1

0

1

Time (ps)

Norm

alis

ed A

mplit

ude

-10 0 10

-1

0

1

Time (ps)

Norm

alis

ed A

mplit

ude

-10 -5 0 5 10

-1

0

1

Time (ps)

Norm

alis

ed A

mplit

ude

-5 0 5

-1

0

1

Time (ps)

Norm

alis

ed A

mplit

ude

-10 0 10

-1

0

1

Time (ps)

Norm

alis

ed A

mplit

ude

-10 -5 0 5 10

-1

0

1

Time (ps)

Norm

alis

ed A

mplit

ude

-5 0 5

-1

0

1

Time (ps)

Norm

alis

ed A

mplit

ude

-10 0 10

-1

0

1

Time (ps)

Norm

alis

ed A

mplit

ude

40 Gb/s NRZ

0.5m

56 Gb/s NRZ 56 Gb/s PAM-4

1m

1.5m

-10 -5 0 5 10

-1

0

1

Time (ps)N

orm

alis

ed A

mplit

ude

-5 0 5

-1

0

1

Time (ps)

Norm

alis

ed A

mplit

ude

-10 0 10

-1

0

1

Time (ps)

Norm

alis

ed A

mplit

ude

-10 -5 0 5 10

-1

0

1

Time (ps)

Norm

alis

ed A

mplit

ude

-5 0 5

-1

0

1

Time (ps)

Norm

alis

ed A

mplit

ude

-10 0 10

-1

0

1

Time (ps)

Norm

alis

ed A

mplit

ude

-10 -5 0 5 10

-1

0

1

Time (ps)

Norm

alis

ed A

mplit

ude

-5 0 5

-1

0

1

Time (ps)

Norm

alis

ed A

mplit

ude

-10 0 10

-1

0

1

Time (ps)

Norm

alis

ed A

mplit

ude


Power Budget Analysis

N D N D N D-2

0

2

4

6

8

10

12

14

1.5 m1 m0.5 mPo

we

r p

en

alty (

dB

o)

System Margin

RIN

Waveguide Loss

ISI Penalty

NRZ

N D N D N D-2

0

2

4

6

8

10

12

14

1.5 m1 m0.5 mPo

we

r p

en

alty (

dB

o)

System Margin

RIN

Waveguide Loss

ISI Penalty

NRZ

N: no equalisation; D: 7 taps T-spaced FFE + 5 taps T-spaced DFE.

- Non-return-to-zero (NRZ):40 Gb/s 56 Gb/s

N D N D N D-4-202468

1012141618

1.5 m1 m0.5 mPow

er

penalty (

dB

o)

System Margin

RIN

Waveguide Loss

ISI Penalty

Multilevel Penalty

PAM-4

FEC (10-5, 10

-15)

N D N D N D-4-202468

1012141618

1.5 m1 m0.5 mPow

er

penalty (

dB

o)

System Margin

RIN

Waveguide Loss

ISI Penalty

Multilevel Penalty

PAM-4

FEC (10-3, 10

-12)

N: no equalisation; D: 7 taps T-spaced FFE + 5 taps T-spaced DFE.

- Pulse amplitude modulation (PAM-4):

56 Gb/s PAM-4 waveguide link:

- feasible for 0.5 m with large power

margins ( > 4 dB)

-1 m feasible with a power margin of

2.3 dB for a BER 10-5 and 4.6 dB for a

BER 10-3

40 Gb/s NRZ waveguide link:

- feasible up to 1.5 m

56 Gb/s NRZ waveguide link:

- feasible for 0.5 m

- not feasible unless equalisation

employed for 1 m long

Jian Chen 29 of 36

40 Gb/s NRZ data transmission - 1

- free-space launch to maximise

received power

- ~9 dB total insertion loss

- multimode variable optical attenuator

employed at spiral output to adjust

received power levels

- back-to-back link also tested

- open eye diagrams up to 40 Gb/s

- some eye closure due to limited

bandwidth of active devices

present in both waveguide and back-

to-back link

waveguide link

back-to-back link

Bias

Tee

Waveguide

Sample

50 μm

MMF

patchcord

Oscilloscope

Voltage

Source

Pattern

GeneratorVOA

A B

Cleaved

50 μm

MMF

850 nm

VCSEL

16 16

Photodiode

Bias

Tee

Voltage

Source

Pattern

Generator

850 nm

VCSEL

VOA

50 μm

MMF

patchcord

Oscilloscope

Photodiode

Cleaved

50 μm

MMF

RF

Amplifier

RF

Amplifier

25 Gb/s 36 Gb/s 40 Gb/s

Back-to-back

link

Waveguide

link

-3 dBm

19.5 mV/div

8 ps/div

-2 dBm

23 mV/div

5 ps/div

-0.5 dBm

33 mV/div

5 ps/div

Received optical power

Voltage scale:

Time scale:

Jian Chen 30 of 36

40 Gb/s NRZ data transmission - 2

- error-free (BER<10-12)

40 Gb/s data transmission

- power penalty for 10-9 BER:

~ 0.5 dB for 25 Gb/s

~ 1.2 dB for 40 Gb/s

N. Bamiedakis, et al., IEEE JLT, vol. 33, pp. 1-7, 2015

record data transmission

over such long MM waveguide (1 m)

link power-limited rather than BW-limited

Bias

Tee

Waveguide

Sample

50 μm

MMF

patchcord

Oscilloscope

Voltage

Source

Pattern

GeneratorVOA

A B

Cleaved

50 μm

MMF

850 nm

VCSEL

16 16

Photodiode

Bias

Tee

Voltage

Source

Pattern

Generator

850 nm

VCSEL

VOA

50 μm

MMF

patchcord

Oscilloscope

Photodiode

Cleaved

50 μm

MMF

RF

Amplifier

RF

Amplifier

Jian Chen 31 of 36

56 Gb/s PAM-4 data transmission - 1

Back-to-back link

Waveguide link

Bias

Tee

850 nm

VCSEL

VOA

50 μm

MMF

patchcord

Cleaved

50 μm

MMF

Voltage

Source

Pattern

Generator 6 dB

Data

XData

Electrical

delay

RF

combiner

DSA

module

Bias

Tee

Waveguide

Sample

50 μm

MMF

patchcord

DSA

moduleVOA

Cleaved

50 μm

MMF850 nm

VCSEL

16 16 Voltage

Source

Pattern

Generator 6 dB

Data

XData

Electrical

delay

RF

combiner

Back-to-back link

Waveguide link

Bias

Tee

850 nm

VCSEL

VOA

50 μm

MMF

patchcord

Cleaved

50 μm

MMF

Voltage

Source

Pattern

Generator 6 dB

Data

XData

Electrical

delay

RF

combiner

DSA

module

Bias

Tee

Waveguide

Sample

50 μm

MMF

patchcord

DSA

moduleVOA

Cleaved

50 μm

MMF850 nm

VCSEL

16 16 Voltage

Source

Pattern

Generator 6 dB

Data

XData

Electrical

delay

RF

combiner

waveguide link back-to-back link

- back-to-back link also setup and tested

- recorded 28 Gbaud eye diagrams (56 Gb/s)

Back-to-back link Waveguide link

~35.7 ps ~35.7 ps

7.5 ps/div 7.5 ps/div

- open eye diagrams

- minimal signal degradation due

to insertion of polymer

waveguide in the link

Jian Chen 32 of 36

56 Gb/s PAM-4 data transmission - 2

Back-to-back link

Waveguide link

Bias

Tee

850 nm

VCSEL

VOA

50 μm

MMF

patchcord

Cleaved

50 μm

MMF

Voltage

Source

Pattern

Generator 6 dB

Data

XData

Electrical

delay

RF

combiner

DSA

module

Bias

Tee

Waveguide

Sample

50 μm

MMF

patchcord

DSA

moduleVOA

Cleaved

50 μm

MMF850 nm

VCSEL

16 16 Voltage

Source

Pattern

Generator 6 dB

Data

XData

Electrical

delay

RF

combiner

Back-to-back link

Waveguide link

Bias

Tee

850 nm

VCSEL

VOA

50 μm

MMF

patchcord

Cleaved

50 μm

MMF

Voltage

Source

Pattern

Generator 6 dB

Data

XData

Electrical

delay

RF

combiner

DSA

module

Bias

Tee

Waveguide

Sample

50 μm

MMF

patchcord

DSA

moduleVOA

Cleaved

50 μm

MMF850 nm

VCSEL

16 16 Voltage

Source

Pattern

Generator 6 dB

Data

XData

Electrical

delay

RF

combiner

waveguide link back-to-back link

- estimation of BER performance based on Q-factor analysis

- histograms of recorded eye diagrams at different received optical power levels

- Q-factor for each eye in PAM-4 signal estimated BER estimated

- 1 m waveguide link:

-10-5 BER threshold achieved

- power penalty ~ 1dB due to

insertion of the waveguide

record 56 Gb/s data

transmission over a 1 m long

multimode interconnect

N. Bamiedakis et al., CLEO, paper STu4F.5, 2015.


Outline







Launch Conditioning

Waveguide Layout


• Link Simulation


40 Gb/s NRZ

56 Gb/s PAM-4

• Conclusions


Conclusions

• Multimode polymer waveguides constitute an attractive technology for use in board-

level optical interconnects

• Theoretical model of bandwidth estimation of MM WGs developed

depends on launch conditions, WG parameters, etc.

• Frequency and time domain measurements on 1 m long spiral waveguides conducted

BLP > 100 GHz×m across a large range of offsets 100 Gb/s per waveguide possible

• Bandwidth performance of multimode WGs can be enhanced using

refractive index engineering, launch conditions, waveguide layout, etc. agree with model

• Record 40 Gb/s NRZ and 56 Gb/s PAM-4 over 1 m long waveguide demonstrated

advanced modulation formats employed on board-level optical interconnects.

- Dow Corning

- EPSRC UK

Acknowledgements:


References

[1] J. Chen, “Polymer Waveguide Based Optical Interconnects For High-speed On-board Communications ”, Ph.D. Thesis, University of Cambridge, June 2016.

[2] J. Chen, N. Bamiedakis, P. Vasil’ev, R. V Penty, and I. H. White, “Low-Loss and High-Bandwidth Multimode Polymer Waveguide Components Using Refractive

Index Engineering,” in Conference on Lasers and Electro-Optics (CLEO), p. SM2G.7, San Jose, USA, June 2016.

[3] J. Chen, N. Bamiedakis, P. Vasil’ev, R. V Penty, and I. H. White, “Bandwidth Enhancement in Multimode Polymer Waveguides Using Waveguide Layout for

Optical Printed Circuit Boards,” in Optical Fiber Communication Conference and Exposition (OFC), p. W1E.3, Anaheim, USA, March 2016.

[4] N. Bamiedakis, J. Chen, R. V. Penty, and I. H. White, “High-Bandwidth and Low-Loss Multimode Polymer Waveguides and Waveguide Components for High-

Speed Board-Level Optical Interconnects,” in Photonics West conference, Proceeding of SPIE, vol. 9753, pp. 975304–1–9, San Francisco, USA, February 2016.

[Invited paper]

[5] J. Chen, N. Bamiedakis, P. Vasil’ev, T. Edwards, C. Brown, R. Penty, and I. White, “High-Bandwidth and Large Coupling Tolerance Graded-Index Multimode

Polymer Waveguides for On-board High-Speed Optical Interconnects,” Journal of Lightwave Technology, vol. 34, no. 12, pp. 2934–2940, November 2015.

[Invited paper]

[6] J. Chen, N. Bamiedakis, P. Vasil’ev, R. V Penty, and I. H. White, “Restricted Launch Polymer Multimode Waveguides for Board-level Optical Interconnects with

> 100 GHz × m Bandwidth and Large Alignment Tolerance,” in Asia Communications and Photonics Conference (ACP), p. AM3A. 5, Hong Kong, China,

November 2015.

[7] J. Chen, N. Bamiedakis, P. Vasil’ev, T. J. Edwards, C. T. A. Brown, R. V. Penty, and I. H. White, “Graded-Index Polymer Multimode Waveguides for 100 Gb/s

Board-Level Data Transmission,” in European Conference on Optical Communication (ECOC), no. 0613, Valencia, Spain, September 2015.

[8] N. Bamiedakis, J. Wei, J. Chen, P. Westbergh, A. Larsson, R. Penty, and I. White, “56 Gb/s PAM-4 Data Transmission Over a 1 m Long Multimode Polymer

Interconnect,” in Conference on Lasers and Electro-optics (CLEO), p. STu4F.5, San Jose, USA, May 2015.

[9] J. Chen, N. Bamiedakis, T. J. Edwards, C. T. A. Brown, R. V Penty, and I. H. White, “Dispersion Studies on Multimode Polymer Spiral Waveguides for Board-

Level Optical Interconnects,” in Optical Interconnects Conference (OIC), p. MD2, San Diego, USA, April 2015.

[10] R. V. Penty, N. Bamiedakis, J. Chen, and I. H. White, “Bandwidth Studies on Multimode Polymer Waveguides for High-Speed Board-Level Optical

Interconnects,” in Photonics West conference, Proceeding of SPIE, pp. 9368–2, San Francisco, USA, February 2015. [Invited paper]

[11] N. Bamiedakis, J. Chen, P. Westbergh, J. S. Gustavsson, A. Larsson, R. V. Penty, and I. H. White, “40 Gb/s Data Transmission Over a 1 m Long Multimode

Polymer Spiral Waveguide for Board-Level Optical Interconnects,” Journal of Lightwave Technology, vol. 33, no. 4, pp. 882–888, November 2014.

[12] N. Bamiedakis, J. Chen, R. V. Penty, I. H. White, P. Westbergh, and A. Larsson, “40 Gb/s Data Transmission over a 1 m Long Multimode Polymer Spiral

Waveguide,” in European Conference on Optical Communication (ECOC), p. P.4.7, Cannes, France, September 2014.

[13] N. Bamiedakis, J. Chen, R. V Penty, and I. H. White, “Bandwidth Studies on Multimode Polymer Waveguides for ≥25 Gb/s Optical Interconnects,” IEEE

Photonics Technology Letters, vol. 26, no. 20, pp. 2004–2007, July 2014.

[14] J. Chen, N. Bamiedakis, R. V. Penty, I. H. White, P. Westbergh, and A. Larsson, “Bandwidth and Offset Launch Investigations on a 1.4 m Multimode Polymer

Spiral Waveguide,” in European Conference on Integrated Optics (ECIO), p. P027, Nice, France, June 2014.

[15] J. Chen, N. Bamiedakis, R. V. Penty, I. H. White, P. Westbergh, and A. Larsson, “Bandwidth Studies on a 1.4 m Long Multimode Polymer Spiral Waveguide,”

in Semiconductor and Integrated OptoElectronics Conference (SIOE), Cardiff, UK, April 2014.

Jian Chen 36 of 36

Thank you !