IEEE PHOTONICS TECHNOLOGY LETTERS, VOL. 27, NO. 2, JANUARY 15, 2015 201
Ultracompact TE-Pass Polarizer Based
on a Hybrid Plasmonic Waveguide
Zhoufeng Ying, Guanghui Wang, Member, IEEE, Xuping Zhang, Member, IEEE,
Ying Huang, Member, IEEE, Ho-Pui Ho, and Yixin Zhang
Abstract—An ultracompact and broadband TE-pass polarizer
based on a hybrid plasmonic waveguide is proposed on the
silicon-on-insulator platform. The optimized design has an active
region as small as 0.8 µm, which is the shortest polarizer reported
until now, and exhibits high polarization-dependent transmission
imposing a TM mode cutoff while leaving the TE mode almost
unaffected. Finite-difference time-domain simulation reveals an
insertion loss <1 dB and an extinction ratio of 19 dB. The
extinction ratio could be further improved to 25 dB over 300-nm
bandwidth, with an insertion loss of 2.5 dB.
Index Terms— Integrated optics, surface plasmons, polarizer,
waveguide.
I. INTRODUCTION
P
OLARIZATION dependent performance in integrated
optics has attracted much interest in recent years. The
silicon-on-insulator (SOI) waveguide, possibly one of the
most studied device platform, is intrinsically of high polar-
ization dependence because of the high index contrast at the
silicon-air and silicon-silica interfaces. Indeed, polarization-
selective devices are essential in SOI platform, such as
polarizer [1]–[4], polarization beam splitter [5]–[7] and polar-
ization rotator [8]–[11]. A number of integrated polarizer
schemes within the SOI platform have been reported in
the literature, e.g., utilizing shallowly etched SOI ridge
waveguide [2], hybrid plasmonic waveguide (HPW) [4] and
horizontal nanoplasmonic slot waveguide (HNSW) [3]. How-
ever, as a polarizer, the shallowly etched SOI ridge waveguide
based polarizer has a long device length of 1mm,whichmakes
this design not attractive in terms of compactness on chip.
The HPW is another promising option for polarizer because
the device offers very tight optical confinement with high
polarization dependence [12]. The authors of [4] proposed a
compact TE-pass polarizer with high extinction ratio and low
Manuscript received July 10, 2014; revised October 17, 2014; accepted
October 20, 2014. Date of publication October 27, 2014; date of current
version December 24, 2014. This work was supported by the National Natural
Science Foundation of China under Grant 61205111 and Grant 61308118.
(Corresponding author: Guanghui Wang.)
Z. Ying, G. Wang, X. Zhang, and Y. Zhang are with the Institute of
Optical Communication Engineering, Nanjing University, Nanjing 210093,
China (e-mail: yjcyzf@gmail.com; wangguanghui@nju.edu.cn; xpzhang@
nju.edu.cn; zyixin@nju.edu.cn).
Y. Huang is with the Institute of Microelectronics, Agency for
Science, Technology and Research, Singapore 117685 (e-mail:
huangy@ime.a-star.edu.sg).
H.-P. Ho is with the Department of Electronic Engineering, Chinese
University of Hong Kong, Hong Kong (e-mail: hpho@ee.cuhk.edu.hk).
Color versions of one or more of the figures in this letter are available
online at http://ieeexplore.ieee.org.
Digital Object Identifier 10.1109/LPT.2014.2365029
insertion loss based on HPW. In the device, only the TM mode
has a large propagation loss, thus providing the required
polarization dependence. However, this design needs a longer
active region for TM to attenuate, with the length of 8μm.
In contrast, the authors of [1] proposed a complementary
structure, which only permits the hybrid plasmonic mode to go
through while all other modes are in cutoff state. Nevertheless,
the length and the insertion loss of the polarizer are not
satisfactory, as it is fundamentally difficult for a HPW with
only one metal strip to achieve perfect mode cut-off and small
insertion loss at the same time. The HNSW design offers most
promise as reported in ref. [3], where TM mode cut-off is
achieved by optimizing the structural parameters of the active
region, while taking advantage of taper coupling. This leads
to a large loss for the TM mode while the TE mode is well
guided with minimal changes. The total length of the device
is 3μm, which is the shortest reported until now, as far as we
know. However due to the use of taper coupling, the insertion
loss is still as large as 4dB in simulation.
In this letter, we propose a new ultracompact and broadband
TE-pass polarizer based on the HPW scheme. Instead of being
used as an attenuator, the HPW acts as a bridge for the
selective coupling of TE mode between two silicon dielectric
waveguides (DWs). Meanwhile the TM mode is in cutoff state.
We notice that direct coupling is better than taper coupling,
due to the very high excitation efficiency of HPW with the
help of plasmonic assisted coupling mechanism [13]. Recent
theoretical and experimental works also demonstrated the
extraordinary efficiency of direct coupling between DWs and
surface plasmonic waveguides [14], [15]. Without the taper
region, insertion loss has been greatly reduced and the device
becomes much shorter. Moreover, other device performance
parameters such as wavelength dependence and transmis-
sion bandwidth are also improved significantly. Overall the
ultracompact and SOI compatible polarizer reported herein
has an insertion loss less than 1dB and an active region
as short as 0.8μm. Since no taper region is needed, the
proposed device is the shortest polarizer ever reported until
now.
II. S
TRUCTURE AND PRINCIPLE
Fig. 1 shows the three dimensional schematic of the
proposed TE-pass polarizer as well as the cross sections of
the input/output silicon DWs and the HPW. The device will
be fabricated on a standard SOI wafer with two DWs acting
as the input and output ports. In order to achieve perfect
1041-1135 © 2014 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission.
See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.