Four-channel optical add-drop multiplexer based on dual racetrack
micro-ring resonators
Danning Wu
n
, Yuanda Wu
n
, Yue Wang, Junming An, Xiongwei Hu
R&D Center of Optoelectronics, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
article info
Article history:
Received 11 April 2015
Received in revised form
20 May 2015
Accepted 11 June 2015
Available online 13 June 2015
Keywords:
Silicon-on-insulator (SOI)
Si photonic wire waveguide
Micro-ring resonator (MRR)
OADM
abstract
In this paper we report on a four-channel optical add-drop multiplexer based on dual racetrack micro-
ring resonators in submicron SOI rib waveguides. The free spectral range (FSR) is about 18.6 nm. The
device can add/drop four optical channels in half C-band. When the device acts as an optical drop
multiplexer, the channel spacing is about 1.5 nm, maximum extinction ratio is 23.75 dB, the minimum
insertion loss 9.94 dB and the maximum adjacent channels crosstalk is 12.12 dB. When the device acts
as an optical add multiplexer, the maximum extinction ratio is 28.72 dB and the minimum insertion loss
7.35 dB. The fabricated device has effectively and perfectly realized the signals upload and download.
& 2015 Elsevier B.V. All rights reserved.
1. Introduction
Optical networks are developing towards the direction of large
capacity, high speed, and intelligent all optical networks. Optical
add-drop multiplexer (OADM), which allow the flexible provi-
sioning addition and extraction of dense wavelength-division-
multiplexing (DWDM) signals, are key components of all optical
networks. Thus several schemes based on different technology
have been proposed, such as fiber Bragg grating [1], array wave-
guide grating [2], micro-electromechanical systems (MEMS) [3],
micro-ring resonators (MRR) [4,5], etc. However, the OADM based
on MEMS and array waveguide grating are normally large-di-
mension devices. The OADM based on fiber Bragg grating should
be integrated with Circulator which increases the insertion loss in
the device. MRRs can provide a compact, narrow-band filtering,
highly-integration, fully CMOS-compatible interconnection sys-
tem. OADM can be modulated by using the thermo-optic effect
[6,7] or electro-optic effect [8,9] to achieve the reconfigurable
function.
Optical networks normally requires a band pass filter with a flat
peak, while the resonance peak of single MRR is the Lorentz line with
a sharp peak. The resonance peak of dual micro-ring resonator with a
flat peak is extremely suitable for all op tical networks. Compared
with the traditional single MRRs, the racetrack micro-ring resonators
have long coupling regions and larger coupling efficiency , which can
decrease the difficulty of fabrication process. Furthermore, the rib
wa v eguide has a less sidew all area compar ed to a strip wa v eguide
with similar dimensions, which can reduce the transmission loss in
the wavegui de. Finally , a dual racetrack resonator with rib wa veguide
structure is chosen in our design.
This paper is arranged as follows. In Section 2, the design and
fabrication of the add-drop MRRs and the OADM are reported. In
Section 2.1, the structure of single-mode waveguide is given. In
Section 2.2, the coupling coefficient and the calculation method is
introduced, and the relationship between coupling coefficient and
coupling gap is analyzed. In Section 3, the performance of dual
racetrack micro-ring resonator is analyzed theoretically, and the
selection of basic parameters are mentioned. In section 4, the
design and fabrication of the OADM are described in details. In
Section 5, the performance of the OADM is reported, including
working as an optical drop/add multiplexer are respectively given
in Sections 5.1 and 5.2. In Section 6, the conclusion draw from the
experiment and the possible improvement method is introduced.
2. Design and fabrication
2.1. Waveguide description
When there exists multiple modes in the waveguide, different
modes are coupled with each other during transmission, which
leads to the distortion of the signals. Therefore, the single-mode
transmission condition will be of vital importance in the
Contents lists available at ScienceDirect
journal homepage: www.elsevier.com/locate/optcom
Optics Communications
http://dx.doi.org/10.1016/j.optcom.2015.06.028
0030-4018/& 2015 Elsevier B.V. All rights reserved.
n
Correspondence to: Institute of Semiconductors, Chinese Academy of Sciences,
No. 35, Tsinghua East Road, Beijing, China. Fax: þ 86 01082305052.
E-mail addresses: wudanning@semi.ac.cn (D. Wu),
wuyuanda@red.semi.ac.cn (Y. Wu).
Optics Communications 354 (2015) 386–391