Wavelength agile switching in photonic integrated circuits

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Wavelength agile switching in photonic integrated circuits
Citation for published version (APA):
Rohit, A. (2012). Wavelength agile switching in photonic integrated circuits. [Phd Thesis 1 (Research TU/e /
Graduation TU/e), Electrical Engineering]. Technische Universiteit Eindhoven. https://doi.org/10.6100/IR735600
DOI:
10.6100/IR735600
Document status and date:
Published: 01/01/2012
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Wavelength Agile Switching in Photonic
Integrated Circuits
PROEFSCHRIFT
ter verkrijging van de graad van doctor aan de
Technische Universiteit Eindhoven, op gezag van de
rector magnificus, prof.dr.ir. C.J. van Duijn, voor een
commissie aangewezen door het College voor
Promoties in het openbaar te verdedigen
op donderdag 11 oktober 2012 om 16.00 uur
door
Abhinav Rohit
geboren te Patna, India
Dit proefschrift is goedgekeurd door de promotor:
prof.dr. H.J.S. Dorren
Copromotor:
dr. K.A. Williams
iii
This Ph.D. thesis has been approved by a committee with the follow-
ing members:
prof.dr. R.V. Penty, University of Cambridge, UK
prof.dr.ir. D.van Thourhout, Universiteit Gent, Belgium
prof.dr. M.J. Wale, Eindhoven University of Technology, The Nether-
lands
Acataloguerecordis availablefromtheEindhoven University of Tech-
nology Library
Wavelength Agile Switching in Photonic Integrated Circuits
Author: Abhinav Rohit
Eindhoven University of Technology, 2012.
ISBN: 978-90-386-3245-2
NUR 959
Keywords: Optical fibre communication / Optical switches / Pho-
tonic integrated circuits / Semiconductor optical amplifiers / Tunable
filters / Optical resonators / Silicon on insulator technology
The work described in this thesis was performed in the Faculty of
Electrical Engineering of the Eindhoven University of Technology and
was financially supported by the Dutch Technology Foundation, Stift-
ing voor Technische Wetenschappen (STW).
Copyright c 2012 by Abhinav Rohit
(cid:13)
All rights reserved. No part of this publication may be reproduced,
stored in a retrieval system, or transmitted in any form or by any
means without the prior written consent of the author.
Typeset using LATEX, printed in The Netherlands

Summary
Essay on the Wavelength Agile Switching
in Photonic Integrated Circuits
In the last decade, photonic integration has been considered as a suit-
able candidate to provide scalable, monolithically integrated solution
toaccomplish wavelength agileswitching circuits forfuturebandwidth
demands. Though many prototypes have been proposed before, none
of them have demonstrated the system level complexity that is re-
quired of them. This thesis focuses on two approaches, namely wave-
length selective switches (WSS) and resonant tunable switches, for
achieving wavelength agile networking. The thesis aims at reducing
the existing substantial gap between the system-level requirements
and the demonstrated circuit-level competence.
Wavelengthagileswitchingelementsaretheessentialbuildingblocks
foranintegratedwavelength agilenetworking. Acompact, scalable re-
configurable WSS design using semiconductor optical amplifier (SOA)
gated cyclic arrayed waveguide grating (AWG) is proposed. The cir-
cuit is realized on an active-passive re-grown InP wafer. A first ex-
perimental demonstration to increase end-to-end capacity by using
waveband multiplexing for multi-wavelength routing is shown. Power
penalties less than 1.0 dB is measured. Time and wavelength mul-
tiplexed data is routed dynamically for guard times as low as 2 ns.
For the first time, a dynamic label-controlled remote reconfiguration
is demonstrated using an on-chip optical label detection scheme and
signal gating using the same SOA array. This enables on-the-fly re-
configuration without external read-out circuitry.
ii
The experimentally verified WSS architecture is combined with a
preceding space switch to realize the first monolithically integrated
4 4 space and wavelength cross-connect. It combines a broadcast
×
and select stage with the four WSSs. The cross-connect is designed
to achieve simultaneous routing of any wavelength from a given in-
put port to any given output port. For compact design, two different
SOA lengths are used. Using longer SOAs for both stages will result
in higher signal extinction with greater on-chip loss compensation, al-
beit at the cost of larger footprint and energy consumption. To meet
the system-level routing requirements, the circuit is thoroughly char-
acterized. Multi-path simultaneous routing is demonstrated for both
co- and counter-propagating data with under 1.0 dB power penalty.
For the first time, simultaneous multipath routing of three 40 Gb/s
input signal is demonstrated with less than 0.2 dB power penalty for
multiple routed channels. Dynamic routing through the integrated
cross-connect is presented employing multiple hops with less than 2
ns switching to perform the full circuit assessment. The scalability of
the current architecture may ultimately be limited by the on-chip loss
compensation for the broadcast network, and the crosstalk introduced
due to the waveguide crossings in the shuffle network.
The Silicon-on-Insulator (SOI) integration platform is exploited
to achieve further increase in the switch density due to an increased
index contrast. Cascaded ring-based tunable switches allow simulta-
neous enhancement of both bandwidth and switch extinction which is
not possible using first-order single ring based switches. SOI technol-
ogy seems more mature for high yield and uniformity due to CMOS-
process compatibility and the availability of commercial foundry ser-
vice. Nevertheless, nanometer-scale fabrication error across the chip
makes the realization of large switch fabric extremely challenging. Re-
silient fifth-order resonant switch is designed for relaxed tolerances.
Detailed theoretical study shows that fabrication tolerances are re-
laxed considerably through the combination of moderate size direc-
tional couplers of up to 20 µm, moderate 350 GHz free spectral range
resonator design and the use of fifth order resonance. The detailed ex-
perimental analysis confirms the theory with 3-dB bandwidth greater
than 100 GHz measured with extinction ratio better than 30 dB. The
iii
first study on wavelength misalignment tolerance between 10 Gb/s
routed data and the resonant wavelength of the switch element is pre-
sented. Low power penalty routing is achievable for signal detuning
up to 50 GHz.
±
The designed fifth-order broadband switch is used to create an on-
chip crossbar switch matrix. In order to evaluate the operation of
the fabricated cross-bar switch with sufficient connectivity and band-
width, proof-of-principlerouting experiments are performed. Thermal
tuning is used for switching. Micro-heater arrays are fabricated which
provides the wide-tuning range, and compensate for the inter-switch
spectral misalignment. A novel matrix addressing wiring scheme is
investigated to reduce the number of electrodes. Static as well as dy-
namic high speed 10 Gb/s optical signal routing is performed for 1 4
×
and 2 2 configuration. A worst case power penalty of less than 1.5
×
dB is measured. This is highly promising for future high-bandwidth
integrated wavelength agile switch fabrics.