Asia Pacific Optical Conference

1. InP-based monolithically
integrated 1310/1550nm
diplexer/triplexer
a a a b
C. Silfvenius , M. Swillo , J. Claesson , N. Akram
a c,d a,c,d
E. Forsberg , M. Chacinski and L. Thylén
a) PhoXtal Communications AB, Kista, Sweden
b) University College VestFold, Tønsberg, Norway
c) Royal Institute of Technology (KTH), Kista, Sweden
d) Kista Photonics Research Center (KPRC), Kista, Sweden
APOC 2008, October 29, Paper 7135-65

2. 2
Outline
• Motivation
• Aim
• Seamless Photonics
• Fabrication
• Integrated Chip Overview
– Wide Gain Active Material
– WDM Coupler
– DFB Laser
– Waveguide Photodiode
• P2P and PON arrays
• Summary

3. 3
Motivation
Reduce cost of optics using integration and few
fabrication steps:
• Already demand for high bandwidth internet services
• IPTV will drive bandwidth demand further
• Acceptance of FTTH is the next broadband step
• The cost of optics is still a large part of FTTH network cost
and obstacle for mass deployment

4. 4
Aim
– Replace Bulk Optics and Hybrid Optics
– DFB, PD and WDM-filter in one InP Chip

5. 5
Seamless Photonics

Electrical bias defines material properties instead of different materials

No reflective interfaces

Low cost process (few process steps)

High yield due to simplified fabrication process

Absorbing material between devices reduce optical/electrical crosstalk

Reduces oxidation issue in Al-containing compounds
p-cladding
Grating
SCH-MQW
“Seamless Photonics” Laser Chip and integrated
n-cladding access waveguide”
p-cladding
Grating
SCH-MQW
Typical Integrated Photonic Chip with Butt-Joint
n-cladding between laser and access waveguide

6. Integrated Chip Overview:
Facet free 1550 DFB
Single mode waveguides
Diplexer chip
1310 PD 1Gbps
IR camera image of
Access ports single mode
WDM coupler

7. 7
Wide gain and accepted losses
Typical DFB spectrum Wide gain 1310/1550nm spectrum
>200nm wavelength separation reduces
Cross Gain Modulation (XGM) and Four
Wave Mixing (FWM)
Acceptable power losses in
Accepted power losses in wide gain integrated
existing semiconductor lasers semiconductor lasers

8. 8
Wide gain
• Subbands at different energies
• Different quantum well effective
bandgaps (1310+1550nm)
• Control of carrier transport in MQW
>200nm FWHM measured

9. 9
Wide gain (simulated in inset)
• Gain shifted from nominal 1250-1600nm (inset) to
• 1400-1800nm due to low p-doping (large figure)
• Low p-doping results in self-heating and carrier leakage before inverting 1310nm QW

10. 10
WDM coupler (as cleaved, no AR)
• 8dB port separation expected for used zerogap coupler
• 10dB port separation measured at 1580nm (and 1310nm)
• 30dB port separation theoretical limit
• Δn = 3.2x10-5/mA

11. 11
Diplexer chip MMI-coupler simulation
• Detector requires both TE and TM coupling
• 10-30dB multiplexing (split) depending on coupler design
1550nm TE 1550nm TM
1310nm TE 1310nm TM

12. 12
Simulated MMI coupler -40ºC to +80ºC: Temperature independent
1310nm
18-22dB
from -40º 1550nm 15-18dB
to +80ºC from -40º
<0.5dB ' to +80ºC
insertion <2.5dB
loss insertion
loss
Coupler extinction ratio and insertion loss

13. 13
Minor effect of diplexing
• Biased coupler power
• Blue: 1580nm only
• Red: 1580 and 1310nm (1mW each).
• Small effect on FP spectrum (small change in refractive index)

14. 14
1310 and 1550nm DFB lasers share fabrication
• Same basic structure
• Same ridge etch depth
• Same grating layer
• Same spacer layer
• Different grating periods
• Different waveguide widths

15. 15
Extracted DFB-laser data
300um cavity, as cleaved, with 1550nm DFB grating, at 30mA
DFB laser parameter extraction using Laser Parameter Extractor [LAPAREX, Tokyo University]

16. 16
1310nm and 1550nm WGPD (no AR)
• Including coupling losses from fiber to WGPD
• Unbiased photo diodes
• 0.31 A/W @ 1310nm (400uA at 1.3mW power in fiber)
• 0.52 A/W @ 1550nm (450uA at 0.78mW power in fiber)
• Limited by optical power sources

17. 17
1 Gbps eye-diagram

1dBm 1532nm from cleaved fiber

As cleaved chip facet (no AR coating)

200ps RC constant

Noise form coupling imperfection

18. 18
Pig-tail of P2P-diplexer (8 channel) package prototype
Carrier 8-Channel V-groove
8-Channel diplexer chip 8-Channel fiber ribbon

19. 19
Summary
• All fundamental properties demonstrated
– WDM multiplexing
– 1310nm and 1550nm WGPD
– 1555nm DFB laser threshold
– 1310nm and 1580nm diplexing in same waveguide
• Low p-doping (undoped SCH+MQW) limited carrier
inversion level at electrical bias in this batch
• Device performance is in accordance with models.
info@phoxtal.com

20. 20
Acknowledgement
• Royal Institute of Technology, Kista, Sweden
• University College Vestfold, Norway
• CIP Technologies, Ipswich, UK
• ACREO AB, Kista, Sweden
• VINNOVA, Stockholm, Sweden,
• Innovationsbron, Stockholm, Sweden

21. 21
WDM coupler and AR vs -47dB optical crosstalk
(assuming -3dB loss for internal laser per pass in coupler to avoid unintentional lasing)
Additional filter needed as function of AR-coating and
WDM coupler performance
Additional filter to reduce optical crosstalk to 47dB
35
30 30% AR
4% AR
1% AR
25
0.5% AR
0.1% AR
20
0.05% AR
15
10
5
0
0 5 10 15 20 25 30
WDM Coupler Multiplexing [dB]
10dB zero gap coupler (current batch): 30dB coupler
0.1% AR coating for -47dB crosstalk 20dB MMI coupler (typical coupler): (theoretical limit):
or 4% AR and additional 17dB filter 1% AR coating for -47dB crosstalk 4% AR coating for
-47dB crosstalk
or 4% AR and additional 7dB filter
no additional filter