Single-mode and High-speed Intracavity Metal Aperture VCSEL
High-speed VCSEL Photonics for Datacenter Networks
with Transverse Coupled Cavity Effect
H. R Ibrahim1,2, A. Hassan1, M. Ahmed2 and F. Koyama1

Fumio Koyama
Institute of Innovative Research4259-R2-22Nagatsuta, Midori-ku, Yokohama 226-8503, JapanTokyo
Instituteof Technology
2
Faculty of Science,
Minia University,
Egypt4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan
Email: koyama@pi.titech.ac.jp1

Institute of Innovative Research, Tokyo Institute of Technology

Abstract We present a novel design of intracavity metal-aperture VCSELs toward high-speed andsingle-mode operations. The intracavity metal contact causes the transverse resonance which provides
A VCSEL
is a key component in hyper-scale datacenter and supercomputer networks because of its
the modulation bandwidth enhancement. The small-signal modulation bandwidth can be double with alarge mode-field
diameter
10µwhichm and single-mode
operations.
fascinating
properties[1,of2],
provideshigh-speed operations, low power consumption, small footprint,
wafer-scaletesting, low-cost packaging, easeof fabricationarrays.
optics (CPO) has beenIntroduction
by MOCVD
with 4 pairs ofinto
top p-type
DBR.Co-packaged
The
Verticalcavityattention
surface emitting(VCSELs)andactive
includes three
850 nm quantum
attracting
muchin lasers
datacenter
edgeregion
computingnetworks
since CPO brings optics much closer
have exhibited the advantages of low cost, easewells (3QWs). In order to form cavity structures,to switch
ASICs into
in arrays,a singleso thatpowershaped
consumption
couldby beof fabrication
smallpackage,
footprint, waferrectangularmesas were formed
dry- saved by reducing the reach [3].
scale
testing,
andlowpower
consumption[1,2].
etching
process
andfollowed
bywet-oxidation
In particular, a VCSEL solution gives us high-speed and low-power consumption, which will meet
Therefore, VCSELs are attracting much attention
process. The size of an active region oxidation
requirements
CPO.
We started
the NICT
project
high-speed
and low-power consumption CPO
for use inindata
center networks.
The network
apertureis 9 x 10towardm, as shownin Fig.1(b) which
trafficin
data
centers
isincreasing
rapidlyandislarge
enoughforhighreliabilities.
Polyamidetransceivers based on VCSEL array and multi-core fiber (MCF), which could deliver advantages on power
hence the development of high speed VCSELs iswas used for planarization and passivation.
consumptions
andThecapacity
densityperofmodule.
thisdeposited
paper, toweformpresent
a key issue.
modulation
bandwidth
AuGe/Ni/AuInwas
n-type our recent activity on high-speed
VCSELs is typically less than ~ 20 GHz due toelectrodes. The p-type electrode (Au/Zn/Au)
transverse-coupled-cavity(TCC) VCSEL array[4, 5] for co-packaged optics as shown in Fig. 1. A singlethe limited intrinsic carrier-photon resonancewere deposited with a rectangular aperture.
(CPR)
[3].
Therefore,manyefforts
have
been
Finally,
8 pairs inof Fig.
dielectric
Ta2O
5/SiO2 weremode 1060nm metal-aperture VCSELs array shown
2 isdeveloped,
which offers high-density I/Odone to push the modulation bandwidth ofdeposited above the surface of the mesas as aplatformVCSELs
withfurthera multi-core
fiber.
Figure3shows
thescalinginCPO
transceivercapacity per module. By
into the mm-wave band [4-14]
top hybrid DBR. We found that two lateral
However,
therestill
remaindifficulties
inboundaries
cause
thetransverse
resonanceasfurther increase in the modulation speed of VCSEL and in a number of MCF, we expect a possibility ofincreasing the modulation bandwidth of singleshown in Fig. 1(c). A key parameter is theultrahighcapacityof beyond
1 Tbps. distance d-W between two boundaries, which
mode
VCSELs inCPO
comparison
with multi-mode

5 the transverseshould be 0
1.5-2 µm to observe
coupled cavity effect, we found.

8Ib=9.0 mA

Intensity (a.u)

1000

6.4
3.2

800
600
400
200

1.60.8020Metal (p-contact)

24

NFP at 9mA

OxideAperture
25G-NRZd2µmd3240

44485256

50G-NRZ

Data Rate per ChannelGb/s

-4

04

800
600

100G
(50G-PAM4)
400
200

9 µm

Fig. 3 Scaling toward Tbps capacitytransceivers.
0-28-24-20-16-12-8

Y Direction

Oxide Aperture: 10μm9μm NFP at 9mA at X and y Direction

Acknowledgement This work was supported by NICT (#0010101). The author acknowledges theDevice Structure(b)(c)
collaboratorsofillustrates
the Beyond
5G structure
programtheir contributions.
Figure 1 (a)the schematicof for
Fig.1. (a) Schematic (b) top-view of infrared image of oxide
the fabricated single-mode MA-VCSEL. The/'65479#18
aperture ofü9 x10µm and(c) the physical pictureof theReferences
device is fabricated on a half-VCSEL wafer growntransverseü
resonance.
!(*
1. K. Iga, "Vertical-cavity surface-emitting laser: Its conception and evolution," Jpn. J. Appl. Phys. 47(1R),ü .&:> 3 mW
1-10 (2008).
ü 0.3"
2. F. Koyama, "Recent advances of VCSEL photonics,"
J. Lightw.8μm8μm)+Technol. 24(12),,)%42
4502-4513 (2006). 25
ü -$(>
3. D. Kuchta et al., "Multi-Wavelength Optical Transceivers Integrated on Node (MOTION)," OFC 2019,
M4D.6 (2019).
4. H. Dalir, and F. Koyama, "29GHz directly modulated 980nm vertical-cavity surface emitting lasers withbow-tie shape transverse coupled cavity," Appl. Phys. Lett., vol. 103, 091109-1-4, Aug. 2013.Appl. Phys.
Lett. 103, 091109 (2013).
5. H. Ibrahim, A. M. A. Hassan, X. Gu, S. Shinada, M. Ahmed, F. Koyama, "1060nm Single-mode Metalaperture VCSEL Array with Transverse Resonance and Low Power Consumption below 50 fJ/bit,"
ECOC 2021, Tu3D.5 (2021).
236

Ib=9.0 mA

1000

0.4

28X Direction

Intensity (a.u)

5µm

In this paper, we propose and demonstrate
intracavity metal aperture VCSELs (MA-VCSEL)
with a rectangular shaped oxide aperture. The
fabrication process is exactly the same as
intracavity- contact VCSELs. We found that the
intracavity
metal contact causes the transverse
1FFP at 9mA
resonance 1which provides
the modulation(a)bandwidth enhancement. We demonstrate theFig. 1 CPO
transceiver
based onenhancementof the modulation
bandwidthFig.
and 2 Metal aperture transverse
10 µm
single-mode operation thanks to the opticalVCSEL
array and MCF.
coupled cavity VCSEL.
transverse coupled cavity effect. The mode-field
diameter could be increased to 10 µm with stablesingle-mode operations.

Transceiver CapacityTb/s

VCSELs, although single-mode VCSELs offer alonger link length of MM fibers thanks to narrower
spectral widths. Also, the poor reliability has
been a limiting factor for single-mode, small oxide
aperture VCSELs.