Low Cost Lasers for the Next Generation Internet
using High Contrast Subwavelength Optics
Christopher Chase, Yi Rao, and Connie Chang-Hasnain
University of California, Berkeley
High Contrast Gratings on VCSELs
Introduction
Motivation
Nature Photonics, vol. 1, p. 119-122 (2007)
 High contrast grating mirrors are one layer of material, ~200 nm thick
with subwavelength bars surrounded by air.
 They are 20X thinner than conventional DBR mirrors, which can have
over 100 layers
 This makes the mirror MUCH easier to fabricate!
 While 1.55 µm VCSELs have been demonstrated, they have used
complicated, costly technological approaches
 A simple, low cost approach is still needed to solve these problems!
Power (mW)
1.55 µm VCSEL Design
HCG
n-InP + 2 n-DBR
VCSEL Performance
Air Gap
10 µm Aperture
CW
20º C
Ith=3.4 mA
30º C
40º C
50º C
Intensity (dB)
Challenges
High-Contrast
Subwavelength Grating
(HCG)
Voltage (V)
 Fiber optic communication systems using lasers as the light source
are the backbone of the internet.
 The next generation of internet applications will require even higher
capacity optical communication links.
 Generally, the system of choice will be wavelength-divisionmultiplexing (WDM).
 Current lasers for WDM systems are too EXPENSIVE for a typical
consumer.
 VCSELs are the lowest cost lasers
 Current low cost VCSELs are incompatible with WDM systems.
 WDM systems typically use 1.3 µm or 1.5 µm lasers for technical
reasons, but low cost VCSELs are not available at that wavelength
RT CW
CW
at 7.12.3*I
mAth 3.4*Ith
1.8*I
30º
2.9*Ith 4.0*Ith
th
40º C 50º C
1.2*Ith
20º
60º C
65º C
Top Contact
Wavelength (nm)
Current (mA)
Optics Express, vol. 18, pp. 15461-15466 (2010)
Oxide
capping
n-InPcapping HCG
sacrificial
sacrificial
.9 µm
 >1 mW output power under room
temperature continuous wave
operation.
1.2 µm
3 µm
45 pairs n-DBR
n-InP substrate
TunnelDBR
Bottom
Junction
i-GaAlInAs
QW/Barrier
 Lases continuous wave up to 65º C
 Devices lase in a single transverse
mode with a side mode
suppression ratio >45 dB
Proton
Implant
Bottom Contact
 Array of VCSELs with multiple
wavelengths spanning >50 nm
demonstrated
 Key challenges in VCSEL design at 1550 nm:
 Top Mirror that is 99% reflective
 Solution: Use a high contrast grating
TE
>20 dB
Intensity (dB)
 Electrical Carrier Confinement
 Solution: Use low cost proton implant to provide confinement
 Severe free carrier absorption in p-materials at 1550 nm
TM
RT CW
12 X 12 µm2 HCG
 Solution: Minimize amount of p-materials by replacing them
with a tunnel junction and n-materials.
Current (mA)
ISLC 2010, Kyoto, Japan, 2010, pp. 11-12
Summary
195 nm
40 µm
 Demonstrated first electrically-driven HCG VCSEL at 1550 nm
2 µm
Acknowledgements
 NSF GRF, IGERT, and CIAN NSF ERC under grant #EEC-0812072
 Operates up to 65º C with >1 mW output power at room temperature,
approaching commercial performance requirements
 Demonstrated VCSELs emitting at multiple wavelengths on the
same chip using HCGs
 Promising approach to achieve low cost 1550 nm VCSELs for WDM
systems for the next generation internet.
©2011 University of California - Berkeley, Department of Electrical Eng. and Computer Sci., cchase@eecs.berkeley.edu