1 Broadband Multifunctional Plasmonic Polarization Converter based on Multimode Interference Coupler

2025-04-30 0 0 5.74MB 7 页 10玖币

侵权投诉

Broadband Multifunctional Plasmonic Polarization

Converter based on Multimode Interference Coupler

Hamed Pezeshki, Bert Koopmans, and Jos J. G. M. van der Tol

Abstract—We propose a multifunctional integrated plasmonic-

photonic polarization converter for polarization demultiplexing

in an indium-phosphide membrane on silicon platform. Using a

compact 1×4 multimode interference coupler, this device can

provide simultaneous half-wave plate and quarter-wave plate

(HWP and QWP) functionalities, where the latter generates

two quasi-circular polarized beams with opposite spins and

topological charges of l=±1. Our device employs a two-section

HWP to obtain a very large conversion efﬁciency of ≥91% over

the entire C to U telecom bands, while it offers a conversion

efﬁciency of ≥95% over ∼86% of the C to U bands. Our

device also illustrates QWP functionality, where the transmission

contrast between the transverse electric and transverse magnetic

modes is ≈0 dB over the whole C band and 55% of the C

to U bands. We expect this device can be a promising building

block for the realization of ultracompact on-chip polarization

demultiplexing and lab-on-a-chip biosensing platforms. Finally,

our proposed device allows the use of the polarization and

angular momentum degrees of freedom, which makes it attractive

for quantum information processing.

Index Terms—Plasmonics, Polarization converter, half-wave

plate, quarter-wave plate, Photonic integrated circuit, Indium

phosphide.

INDIUM-PHOSPHIDE (InP) membrane on silicon (IMOS)

is a promising platform for the fabrication of low cost

and large scale passive and active photonic integrated circuits

(PICs) [1], [2], due to its compatibility with complemen-

tary metal oxide semiconductor (CMOS) processes. The high

refractive index difference (n ≈2) between its core and

cladding enables large scale integration of photonic devices

[3] and photonics-electronics convergence on a single chip

[4]. However, the large refractive index difference makes it

harder to obtain polarization independence in photonic devices

[5]. Meanwhile, control over the polarization in PICs for

polarization-independent operations of chips and for functions

like polarization (de)multiplexing and polarization switching,

is of great importance [6]. Hence, the development of an

integrated polarization converter (PC) with a small footprint

to support polarization diversity, as well as to convert the

polarization state of light in PICs at will, have attracted a

lot of attention during recent decades.

So far, several design proposals have been made, based on

either mode evolution or mode interference. PCs based on

This work is part of the Gravitation program ‘Research Centre for Integrated

Nanophotonics’, which is ﬁnanced by the Netherlands Organization for

Scientiﬁc Research (NWO). (Corresponding author: Hamed Pezeshki.)

H. Pezeshki and Bert Koopmans are with the Department of Applied

Physics, Eindhoven University of Technology, Eindhoven, 5612 AZ, Nether-

lands (email: h.pezeshki@tue.nl).

H. Pezeshki, Bert Koopmans, and Jos J. G. M. van der Tol are with

the Eindhoven Hendrik Casimir Institute, Center for Photonic Integration,

Eindhoven University of Technology, Eindhoven, 5600 MB, Netherlands.

mode evolution implement adiabatic mode conversion between

the two polarization states of a waveguide mode [7], [8],

and are typically long (≥100 µm). In contrast, shorter PCs

use the interference between two orthogonal beating modes,

propagating through a symmetry-broken waveguide [9], [10].

The majority of the proposed PCs based on mode interference

were developed with slanted waveguides [11] and narrow

trenches [12]. However, such approaches entail either a large

footprint or a complex fabrication process [13].

It has been demonstrated that a plasmonic metal layer can

overcome the above-mentioned challenges by enhancing the

birefringence between the two beating modes using surface

plasmon polaritons (SPPs), as well as offering a simple fabri-

cation process. Early works on designs of integrated half-wave

plates (HWPs) based on metal layers, show that large ohmic

losses [9], caused by SPPs, can be decreased by placing a

low-refractive index thin spacer layer at the metal-dielectric

interface [10], [14]. Komatsu et al. [14] and Caspers et al.

[10] presented HWPs with insertion losses (ILs) of ∼5 and >

2 dB for the device lengths of 11 and 5 µm, respectively.

Later on, other groups reported SPP-based HWPs with a

high polarization conversion efﬁciency (PCE) of 97% with

an IL of ∼2 dB. Despite works done so far, broadband and

multifunctional operation has not been addressed sufﬁciently

yet.

There have also been some reports on the integrated quarter-

wave plates (QWPs) using a plasmonic metal layer. Gao et al.

[15] theoretically presented an integrated hybrid QWP based

on plasmonics at λ0=1.55 µm, where the PC’s length was 1.5

µm. Liang et al. [16] theoretically showed a QWP with one-

way angular momentum conversion at λ0=1.55 µm, by placing

a L-shaped metal layer with a length of 2.8 µm on a square

photonic waveguide with a minimum birefringence, which is

attached to a 2.4 µm long rectangular photonic waveguide with

high birefringence. However, as shown in this paper, a better

strategy would be to place the metal layer on a rectangular

birefringence waveguide to further boost the birefringence for

a shorter length of the metal layer. This, in turn, results in

lower absorption loss (i.e. heat dissipation) by the metal layer,

which is crucial for the performance efﬁciency of devices on

a photonic chip. Moreover, there have been some reports on

the design of an integrated QWP based on aluminum gallium

arsenide (AlGaAs) with an ellipticity of 0.67 at λ0=1.55

µm [17] as well as with graphene in Terahertz regime [18]

by launching linearly polarized light at 45◦. Both designs

have very long converter sections of ∼53 µm and 145 µm,

respectively. However, in the latter case, they achieved active

adjustment of the polarization state of light through variation

arXiv:2210.11353v1 [physics.optics] 20 Oct 2022

of the graphene’s Fermi level. Despite several works done so

far on both integrated HWP and QWP, design of a broadband

multifunctional PC, to provide both polarization and angular

momentum degrees of freedom has not been investigated.

In this paper, we introduce a multifunctional PC with an

ultrabroad operational wavelength range. After ﬁrst designing

a compact and efﬁcient 1×4 multimode interference coupler

(MMI), our proposed HWP is designed as a two-section PC

to achieve optimum conversion efﬁciency and to improve

fabrication tolerance as demonstrated in [19]. According to

results obtained with a ﬁnite-difference time-domain (FDTD)

method [20], the proposed HWP offers a PCE of ≥91% over

the C to U telecom bands, while PCE is ≥95% over ∼86%

of this wavelength range. This implies that our HWP presents

a polarization extinction ratio (PER) of better than 13 dB in

the above-mentioned range, with a maximum of 38.4 dB at

λ0= 1.563 µm.

By taking advantage of the mirror symmetry in a MMI, we

then propose two QWPs, which are mirrored to each other,

presenting quasi-circular polarized beams with opposite spins

(due to the transverse spin angular momentum, SAM) based on

only one device, one input polarization, and one incoming light

beam direction. Our QWPs function efﬁciently by offering a

transmission contrast of ≈0 dB between the transverse electric

and transverse magnetic (TE0and TM0) modes over the

wavelength range of λ0=1.53 to 1.61 µm, covering the whole

C band and moreover 55% of the C to U telecom bands. The

longitudinal electric ﬁeld component of the generated quasi-

circular polarized beams carry longitudinal orbital angular

momentum (OAM) with topological charges of l=±1. Having

two quasi-circular polarized beams simultaneously on a chip

can be potentially attractive not only for on-chip telecom

applications such as mode/polarization-(de)multiplexing [21],

on-chip magneto-plasmonics [22], [23], as well as quantum

information processing [24], but also for biosensing appli-

cations including circular dichroism spectroscopy [25] and

nanoparticle movement [26] using a longitudinal OAM.

I. DESIGN STRUCTURE AND CONSIDERATIONS

We propose a device based on the IMOS platform to provide

different polarizations: linear TE0and TM0modes, as well

as two quasi-circular polarized beams with opposite spins.

It is composed of a 1×4 MMI for dividing a TE0-polarized

light into four output waveguides, as well as a PC section

for performing HWP and QWP functionalities (see Fig. 1).

The output waveguide 1 (O1) is connected to a rectangular

waveguide and outputs a TE0mode. To obtain the quasi-

circular polarized beams with opposite spins, we designed two

plasmonic QWPs on top of the O2 and O3 waveguides, which

are mirrored relative to each other. These created states will

exist over propagation lengths that are much smaller than the

TE0-TM0beat length of ∼77.5 µm for a ∆nTE0-TM0∼0.02.

The advantage of our approach over the previous approaches

is that we illustrate QWPs with opposite spins using one

device, without reversing the direction of light propagation.

This makes it attractive for applications that require both spins

simultaneously on a single chip. Finally, to obtain a TM0

mode, we designed a plasmonic HWP, as a top cladding on

the O4 waveguide. The proposed HWP is a two-section PC

which consists of a combination of a QWP and a three quarter-

wave plate (TQWP). We chose this approach to achieve our

objectives of highly efﬁcient conversion efﬁciency over an

ultrabroad wavelength range, as well as enhanced fabrication

tolerance, as demonstrated in [19]. Using this approach, the

length of the converter is two times that of a single-section

HWP.

The MMI section has a length and a width of lMMI = 36 µm

and wMMI = 9 µm, respectively. In order to have an ultralow

loss 1×4 MMI, we provide the coupling between the MMI

section and the input as well as the output waveguides using

linear tapers with a length and a width of ltaper = 8 µm and

wtaper = 2 µm, respectively, creating a smooth mode transitions

between the input, MMI, and output sections. Fig. 1b shows

the top view of the PC section in which the center-to-center

distances between the O1(2) and O4(3) waveguides are d1−4

= 6.75 and d2−3= 2.4 µm, respectively. The QWPs devices

on the O2 and O3 waveguides have a plasmonic cladding

with a length of lQWP = 1.48 µm to transform a TE0mode

into quasi-circular polarized beams with two opposite spins.

The designed HWP, with a total length of lHWP = 6.8 µm, is

designed as a top cladding on the O4 waveguide to transform a

TE0mode to a TM0mode. The input and O1 waveguides have

a width of wWG-1 = 0.34 µm, while the O2 to O4 waveguides

are linked with waveguides with a different width of wWG-2

= 0.4 µm to minimize the birefringence in end parts of the

waveguides, i.e. ∆nTE0-TM0∼0.02. The height of all photonic

components are equal to hWG = 0.39 µm. The width and height

of all the plasmonic metal layers, as well as the height of silica

(SiO2) spacer layer are the same in the O2 to O4 waveguides,

i.e. wML = 0.03 µm, hML = 0.03 µm, and hSL = 0.02 µm,

respectively (see Fig. 1c). As indicated in Fig. 1, the materials

for the waveguides and MMI, substrate and the spacer layer

beneath the plasmonic components are InP and SiO2, whose

parameters come from [27], and the material for the plasmonic

components is gold [28].

We evaluate the performance of the proposed HWP in

section II-B based on PCE (ηin percent) and insertion loss

(ILHin dB). For an input TE0mode, we have:

η= (PO4

TM /(PO4

TM +PO4

TE )) ×100,(1)

ILH=−10 ×log(PO4

TM /P I4

TE ),(2)

where PI4

TE and PO4

TE are the TE0mode powers at the input

and output of the O4 waveguide, while PO4

TM is the TM0

mode power at the output of the O4 waveguide. Note that

in calculating IL using Eq. 2, the splitting loss by the MMI is

neglected.

In section II-C, we assess the presented QWP function

according to the transmission contrast, TC, (CTin dB) between

the beating TE0and TM0modes and insertion loss (ILQin

dB). Since both QWPs are identical and just mirrored relative

to each other, we will just illustrate the results for the O2

waveguide, where CTand ILQare deﬁned as:

文档加载中……请稍候！
如果长时间未打开，您也可以点击刷新试试。

下载文档到电脑，查找使用更方便

10 玖币 0人已下载

立即下载

摘要：

1BroadbandMultifunctionalPlasmonicPolarizationConverterbasedonMultimodeInterferenceCouplerHamedPezeshki,BertKoopmans,andJosJ.G.M.vanderTolAbstractWeproposeamultifunctionalintegratedplasmonic-photonicpolarizationconverterforpolarizationdemultiplexinginanindium-phosphidemembraneonsiliconplatform.Usin...

展开>> 收起<<

1 Broadband Multifunctional Plasmonic Polarization Converter based on Multimode Interference Coupler.pdf

共7页,预览2页

还剩页未读，继续阅读

声明：本站为文档C2C交易模式，即用户上传的文档直接被用户下载，本站只是中间服务平台，本站所有文档下载所得的收益归上传人(含作者)所有。玖贝云文库仅提供信息存储空间，仅对用户上传内容的表现方式做保护处理，对上载内容本身不做任何修改或编辑。若文档所含内容侵犯了您的版权或隐私，请立即通知玖贝云文库，我们立即给予删除！

1 Broadband Multifunctional Plasmonic Polarization Converter based on Multimode Interference Coupler

相关推荐

开通VIP享超值会员特权

作者详情

相关内容

热门标签

举报选择: