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In this paper, photonic crystal ring resonators with hexagonal lattice structure are used to design a four-channel optical demultiplexer. The structure size, the average transfer coefficient, the quality factor, and the channel spacing are equal to 424.5 µm², 95.8%, 1943, and 2 nm, respectively. The average crosstalk is also computed to be −18.11 dB. In this study, the plane wave expansion (PWE) and finite-difference time-domain (FDTD) methods are used, respectively, to characterize the photonic bandgap and to investigate the optical behavior of the structure. The proposed design can be used in dense wavelength division multiplexing (DWDM) systems.
1 23
Optical Review
ISSN 1340-6000
Volume 24
Number 4
Opt Rev (2017) 24:605-610
DOI 10.1007/s10043-017-0353-8
Four-channel optical demultiplexer
based on hexagonal photonic crystal ring
Vahid Fallahi, Mahmood Seifouri, Saeed
Olyaee & Hamed Alipour-Banaei
1 23
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Four-channel optical demultiplexer based on hexagonal photonic
crystal ring resonators
Vahid Fallahi
Mahmood Seifouri
Saeed Olyaee
Hamed Alipour-Banaei
Received: 10 March 2017 / Accepted: 29 June 2017 / Published online: 5 July 2017
ÓThe Optical Society of Japan 2017
Abstract In this paper, photonic crystal ring resonators
with hexagonal lattice structure are used to design a four-
channel optical demultiplexer. The structure size, the
average transfer coefficient, the quality factor, and the
channel spacing are equal to 424.5 lm
, 95.8%, 1943, and
2 nm, respectively. The average crosstalk is also computed
to be -18.11 dB. In this study, the plane wave expansion
(PWE) and finite-difference time-domain (FDTD) methods
are used, respectively, to characterize the photonic bandgap
and to investigate the optical behavior of the structure. The
proposed design can be used in dense wavelength division
multiplexing (DWDM) systems.
Keywords Demultiplexer Photonic crystal Bandgap
Ring resonator FDTD
1 Introduction
Wavelength division multiplexing is a technique which
uses optical fiber to carry many separate and independent
optical channels. To increase the bandwidth of communi-
cation, wavelength division multiplexing is used. By
reducing the channel spacing, one can increase the
transmission capacity of wavelength division multiplexed
systems [1]. There are several platforms on which WDM
can be designed and fabricated, one of which is the use of
photonic crystals (PhCs) [2].
Photonic crystals can provide an optical medium in
which the refractive index changes periodically [3,4]. The
most important feature that reveals the practical signifi-
cance of photonic crystals is the photonic bandgap (PBG).
The photonic bandgap determines the energy or frequency
range, for which light propagation in photonic crystals is
not allowed, so that by creating some defects, the light
within the structure can be controlled [5]. Moreover, PhCs
can enable compact and efficient photonic devices and also
their large-scale integration. What sets photonic crystals
apart from the conventional integrated optical circuits is
their ability to interact with light on a wavelength scale,
thus allowing the creation of devices, components, and
circuits that are several orders of magnitude smaller than
currently possible [6].
The photonic crystals are applicable with or without
controlled defects in the structure [79]. Among various
defects, ring resonators are more taken into consideration
due to their specific characteristics including ease of design
and higher sensitivity compared to other known defects
[10]. The above characteristics in ring resonators are the
main basis for designing and manufacturing photonic
crystal-based devices such as optical filters [1114], optical
switches [15], optical logic gates [16,17], optical sensors
[18], and optical demultiplexers [1922].
So far, numerous papers have been presented on
designing optical demultiplexers based on photonic crystal
using linear defects, which have low transfer coefficients
and high crosstalks [2327], while such problems can
easily be overcome using ring resonators. In recent years,
ring resonators have received considerable attention due to
&Mahmood Seifouri
Faculty of Electrical Engineering, Shahid Rajaee Teacher
Training University, Tehran, Iran
Nano-photonics and Optoelectronics Research Laboratory
(NORLab), Shahid Rajaee Teacher Training University,
Tehran, Iran
Department of Electronics, Tabriz Branch, Islamic Azad
University, Tabriz, Iran
Opt Rev (2017) 24:605–610
DOI 10.1007/s10043-017-0353-8
Author's personal copy
their high transmission efficiency, high quality factor, low
crosstalk, and flexibility in selecting an appropriate wave-
length. So far, various ring resonators have been presented
for designing optical demultiplexers, including square
resonators [20,28,29], quasi-shaped resonators
[19,30,31], X-shaped resonators [32], and octagonal res-
onators [33].
In this paper, four hexagonal photonic crystal ring res-
onators with hexagonal lattice are theoretically used to
design a four-channel optical demultiplexer with average
channel spacing of 2 nm. The channel spacing of the
proposed design is comparatively much narrower than
those of the previously proposed structures. Moreover, the
values for the transfer coefficient, the quality factor, and
the crosstalk of our design are improved with respect to
other structures in the literature and this makes our device
justifiable to be used as an efficient demultiplexer in
DWDM systems.
The rest of the paper is organized as follows: In Sect. 2,
the band-gap structure is described. Sect 3focuses on the
demultiplexer design. In Sect. 4, simulation and results
obtained are presented and discussed, and finally, the
conclusions are presented in Sect. 5.
2 Band-gap structure
First, to design the proposed optical demultiplexer, a 59 9
21(The number of rods in xand zdirections are 59 and 21,
respectively) structure with a hexagonal lattice of dielectric
rods immersed in air is used. To determine the physical
structural parameters of our proposed demultiplexer, one
requires to calculate the gap map diagrams of the design. It
should be mentioned that a bandgap appropriate for optical
telecommunication system is considered in the design.
Hence, for a good design, it is better to use the gap map
diagrams. The photonic bandgap is extracted using PWE
calculations. Subsequently, to obtain the gap map dia-
grams, the band structure is calculated at various values of
the photonic crystal parameters, namely the refractive
index, the rod radius, and the lattice constant [34]. This is
presented in Fig. 1. As can be seen in Fig. 1a, by
increasing the refractive index, the photonic bandgap shifts
towards lower frequencies. Furthermore, as can be seen in
Fig. 1b, by increasing the R/aratio, the photonic bandgap
shifts towards lower frequencies.
For obtaining the best results, the gap map diagrams are
considered. By considering the gap map diagrams, appro-
priate parameters for designing the proposed structure can
be obtained [34]. Thus, for our structure, the refractive
index, the dielectric rod radius, and the lattice constant are
taken to be, n=4.1 [13,32], R=106 nm, and
a=610 nm, respectively. As far as the refractive index of
4.1 of our structure is concerned, there are high-refractive
index composite materials for enabling THz optical com-
ponents [35], and germanium with a refractive index of 4.1
is also a suitable material that is widely used in advanced
semiconductor processes [36]. Based on the above values,
the photonic bandgap is obtained, as shown in Fig. 2.As
can be seen in the figure, the structure contains two
Fig. 1 Gap map diagrams: variation of PBG versus arefractive index
and bR/aratio
Fig. 2 Band structure of the fundamental structure
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photonic bandgaps in transverse magnetic (TM) modes and
transverse electric (TE) modes, amongst which the pho-
tonic bandgap in the TM mode is suitable. This is because
TM mode includes appropriate telecommunication chan-
nels. The values for the TM mode lie between 0.256 Ba/k
B0.45 which is equivalent to the wavelength range of
1355 nm BkB2382 nm.
3 Demultiplexer design
The proposed four-channel optical demultiplexer is
designed through eliminating some of the dielectric rods
and using 4 hexagonal ring resonators for the purpose of
filtering the proposed wavelengths. The general schematic
of the ring resonators used in the structure is shown in
Fig. 3.
To improve the wavelength selectivity, we have
introduced four scattering rods for each hexagonal ring,
which are highlighted with black color in Fig. 3.We
have called the radius of these scattering rods Rs. The
diffraction losses in the resonators [32]. The four
scattering rods with the radius of R
=115 nm are used
in each resonator. The structure has one input port and
four output ports for obtaining the wavelength of the
corresponding telecommunication channels. Moreover,
to have a better control over the wavelength selectivity
of the rings, we have introduced other defects in the
hexagonal rings, having rods with diameter larger than
that of the outer rods. The proposed four-channel
demultiplexer is shown in Fig. 4. The radii of the inner
rods equal to R
=180 nm, R
=182 nm,
=184 nm, and R
=186 nm, for the first, second,
third, and fourth channels, respectively.
4 Simulation and results
For accurate modeling of the demultiplexer, we need 3D
simulation, but this requires a great amount of computa-
tional time. Subsequently, we have used the effective
index approximation method of PhCs, and with this
approximation, we have used 2D rather that 3D simula-
tions [32].
The 2D-FDTD method is used to simulate the proposed
structure. To use this method, the structure should be
meshed precisely. Thus, the meshing size of the structure is
Dx=Dz=a/16, which equals Dx=Dz=38.1 nm,
based on the lattice constant a=610 nm. Due to the time
step formula Dt1=cffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
r, the time step for
calculation equals DtB0.0244.
The output spectra of the demultiplexer are presented
in Fig. 5. As can be observed from the figure, this
demultiplexer can separate four channels with central
wavelengths equal to k=1583 nm, k=1585.5 nm,
k=1587.2 nm, and k=1589 nm. Furthermore, the
transfer coefficient, the quality factor, and the spectral
width of each channel is presented in Table 1. For better
understanding of WDM, Fig. 6is presented and according
Fig. 3 Schematic of hexagonal ring resonator
Fig. 4 Sketch of the proposed demultiplexer
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to which, the light propagates through channels 1 and 3 at
the wavelengths of k=1583 nm and k=1587.2 nm,
respectively. In addition, the crosstalk of each channel is
presented in Table 2.
In our structure, the average channel spacing, quality
factor, and structure transfer coefficient equal to 2 nm,
1943, and 95.8%, respectively. Besides, the minimum and
maximum crosstalks are -14 and -27 dB, respectively.
Fig. 5 Output spectra of the
demultiplexer. aLinear and
bdB scale
Table 1 Simulation results of the proposed demultiplexer
Channel Central wavelength (nm) Resonant rod (nm) Spectral width (nm) Quality factor Transmission (%)
Channel 1 1583 180 0.7 2261.5 100
Channel 2 1585.2 182 0.8 1981.5 96.5
Channel 3 1587.2 184 0.9 1763.5 94
Channel 4 1589 186 0.9 1765.5 93
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Compared to other defects including point-defect or
line-defect PC cavities, ring resonators offer scalability
in size, flexibility in mode design due to their multi-
mode nature, and adaptability in structure design
because of numerous design parameters. The design
parameters can be the radius of the scatters, coupling
rods, and the dielectric constant of the structure. In
addition, one of the advantages of ring resonators is
their flexible design of backward and forward dropping.
Owing to the above-mentioned reasons, here, we have
considered ring resonator-based demultiplexers [37].
Table 3compares the results of our demultiplexer with
other reported ones.
According to the above table, our four-channel demul-
tiplexer has a narrower channel spacing when compared to
the reported structures [19,20,2833], so it is very suit-
able for DWDM systems. Our structure has also an
appropriate transfer coefficient, quality factor, and cross-
talk, while previously reported demultiplexers have some
restrictions to all or some of the above-mentioned
5 Conclusion
In this paper, a four-channel optical demultiplexer is
proposed based on photonic crystal hexagonal ring res-
onator. The proposed structure has an average transfer
coefficient and quality factor above 95.8% and 1943,
respectively. Besides, its minimum and maximum
crosstalks are -14 and -27 dB, respectively. Moreover,
the structure size is about 424.5 lm
. In addition to
having suitable transfer coefficient and quality factor,
this structure has a channel spacing of 2 nm, which is
much narrower than those of the previously reported
structures. Hence, it is highly suitable to be used in
DWDM systems. The proposed structure has also a
simple design.
Fig. 6 Electric field distribution of proposed demultiplexer.
ak1=1583 nm and bk3=1587.2 nm
Table 2 Crosstalk values of the proposed demultiplexer (dB)
Channel 1 Channel 2 Channel 3 Channel 4
Channel 1 -14.2 -15 -15
Channel 2 -21.2 – -16 -16.5
Channel 3 -25.5 -17 – -15
Channel 4 -27 -22 -14 –
Table 3 Comparison of the proposed demultiplexer with reported one
Reference Ring resonator
width (nm)
spacing (nm)
Number of
Proposed DMUX Hexagonal 0.82 2 1943 95.8 -18.1 4 424.5
[20] Square 1.8 4.2 825 81 8 490.68
[19] Quasi-shaped 1.35 3.13 1224 96.2 -24.5 4
[29] Square 0.3 3 5969 90 -16.5 2 681.36
[33] Octagon-shaped 0.47 2.66 3409 98 -26.1 4
[32] X-shaped 1.7 3 1234 53 -15.4 4 422.4
[30] Quasi-shaped 2.8 8 608.3 90 -29 3 317
[28] Square 30 28 — 85 4
[31] Quasi-shaped 2.75 6.1 567 95 3 294.25
Opt Rev (2017) 24:605–610 609
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Compliance with ethical standards
Conflict of interest On behalf of all authors, the corresponding
author states that there is no conflict of interest.
1. Mukherjee, B.: WDM optical communication networks: progress
and challenges. IEEE J. Sel. Areas Commun. 18(10), 1810–1824
2. Song, B.S., Noda, S., Asano, T.: Photonic devices based on in-
plane hetero photonic crystals. Science 300(5625), 1537 (2003)
3. Sukhoivanov IA, Guryev IV (2009) Photonic crystals: physics
and practical modeling. 152. Springer
4. Sakoda, K.: Optics of photonic crystals. Opt. Rev. 6(5), 381–392
5. Foresi, J.S., Villeneuve, P.R., Ferrera, J., Thoen, E.R., Stein-
meyer, G., Fan, S., Joannopoulos, J.D., Kimerling, L.C., Smith,
H.I., Ippen, E.P.: Photonic-bandgap microcavities in optical
waveguides. Nature 390(6656), 143–145 (1997)
6. Krauss, T.F., Wilson, R., Baets, R., Bogaerts, W., Kristensen, M.,
Borel, P.I., Frandsen, L.H., Thorhauge, M., Tromborg, B.,
Lavrinenko, A., De La, R.M.: Photonic integrated circuits using
crystal optics (PICCO). In: Proceedings of 11th European Con-
ference on Integrated Optics (ECIO’03), 115–120 (2003)
7. Mehdizadeh, F., Soroosh., M., Alipour-Banaei, H.: Proposal for
4-to-2 optical encoder based on photonic crystals. IET Opto-
electronics (2016)
8. Xu, H., Huang, X., Wang, X., Zhou, C., Zhong, R.: Multi-channel
photonic crystal drop filter with cascaded stubs. IET Optoelec-
tronics (2016)
9. Li, X., Shen, H., Li, T., Liu, J., Huang, X.: T-shaped polarization
beam splitter based on two-dimensional photonic crystal
waveguide structures. Opt. Rev. 23(6), 950–954 (2016)
10. Mehdizadeh, F., Alipour-Banaei, H., Serajmohammadi, S.:
Channel-drop filter based on a photonic crystal ring resonator.
J. Opt. 15(7), 075401 (2013)
11. Almasian, M.R., Abedi, K.: Performance improvement of wave-
length division multiplexing based on photonic crystal ring res-
onator. Optik. Int. J. Light Electron Opt. 126(20), 2612–2615 (2015)
12. Hsiao, F.-L., C. Lee.: A nano-ring resonator based on 2-D
hexagonal-lattice photonic crystals. in optical MEMS and
nanophotonics. IEEE/LEOS International Conference on (2009)
13. Rezaee, S., Zavvari, M., Alipour-Banaei, H.: A novel optical filter
based on H-shape photonic crystal ring resonators. Optik. Int.
J. Light Electron Opt. 126(20), 2535–2538 (2015)
14. Shinya, A., Mitsugi, S., Kuramochi, E., Notomi, M.: Ultrasmall
multi-port channel drop filter in two-dimensional photonic crystal
on silicon-on-insulator substrate. Opt. Express 14(25),
12394–12400 (2006)
15. Serajmohammadi, S., Alipour-Banaei, H., Mehdizadeh, F.: All
optical decoder switch based on photonic crystal ring resonators.
Opt. Quant. Electron. 47(5), 1109–1115 (2015)
16. Alipour-Banaei, H., Serajmohammadi, S., Mehdizadeh, F.: All
optical NOR and NAND gate based on nonlinear photonic crystal
ring resonators. Optik. Int. J. Light Electron Opt. 125(19),
5701–5704 (2014)
17. Isfahani, B.M., Tameh, T.A., Granpayeh, N., Javan, A.R.M.: All-
optical NOR gate based on nonlinear photonic crystal microring
resonators. JOSA B. 26(5), 1097–1102 (2009)
18. Hsiao, F.-L., Lee, C.: Novel biosensor based on photonic crystal
nano-ring resonator. Procedia Chem. 1(1), 417–420 (2009)
19. Mehdizadeh, F., Soroosh, M., Alipour-Banaei, H.: An optical
demultiplexer based on photonic crystal ring resonators. Optik.
Int. J. Light Electron Opt. 127(20), 8706–8709 (2016)
20. Venkatachalam, K., D.S. Kumar., S. Robinson.: Investigation on
2D photonic crystal-based eight-channel wavelength-division
demultiplexer. Photonic Network Communications. 1–11 (2016)
21. Liu, C.-Y.: Fabrication and optical characteristics of silicon-
based two-dimensional wavelength division multiplexing splitter
with photonic crystal directional waveguide couplers. Phys. Lett.
A375(28), 2754–2758 (2011)
22. Yata, M., Fujita, M., Nagatsuma, T.: Photonic-crystal diplexers
for terahertz-wave applications. Opt. Express 24(7), 7835–7849
23. Bouamami, S., Naoum, R.: New version of seven wavelengths
demultiplexer based on the microcavities in a two-dimensional
photonic crystal. Optik. Int. J. Light Electron Opt. 125(23),
7072–7074 (2014)
24. Gupta, N.D., Janyani, V.: Dense wavelength division demulti-
plexing using photonic crystal waveguides based on cavity res-
onance. Optik. Int. J. Light Electron Opt. 125(19), 5833–5836
25. Rostami, A., Banaei, H.A., Nazari, F., Bahrami, A.: An ultra
compact photonic crystal wavelength division demultiplexer
using resonance cavities in a modified Y-branch structure. Optik.
Int. J. Light Electron Opt. 122(16), 1481–1485 (2011)
26. Rostami, A., Habibiyan, H., Nazari, F., Bahrami, A., Banaei,
H.A: A novel proposal for DWDM demultiplexer design using
resonance cavity in photonic crystal structure. in Communica-
tions and Photonics Conference and Exhibition (ACP). Asia IEEE
27. Rostami, A., Nazari, F., Banaei, H.A., Bahrami, A.: A novel
proposal for DWDM demultiplexer design using modified-T
photonic crystal structure. Photonics Nanostruct. Fundam. Appl.
8(1), 14–22 (2010)
28. Djavid, M., Monifi, F., Ghaffari, A., Abrishamian, M.S.:
Heterostructure wavelength division demultiplexers using pho-
tonic crystal ring resonators. Optics Commun. 281(15),
4028–4032 (2008)
29. Ghorbanpour, H., Makouei, S.: 2-channel all optical demulti-
plexer based on photonic crystal ring resonator. Front Optoelec-
tron. 6(2), 224–227 (2013)
30. Mansouri-Birjandi, M.A., Rakhshani, M.R.: A new design of
tunable four-port wavelength demultiplexer by photonic crystal
ring resonators. Optik. Int. J. Light Electron Opt. 124(23),
5923–5926 (2013)
31. Rakhshani, M.R., Mansouri-Birjandi, M.A.: Design and simula-
tion of wavelength demultiplexer based on heterostructure pho-
tonic crystals ring resonators. Physica E 50, 97–101 (2013)
32. Alipour-Banaei, H., Mehdizadeh, F., Serajmohammadi, S.: A
novel 4-channel demultiplexer based on photonic crystal ring
resonators. Optik. Int. J. Light Electron Opt. 124(23), 5964–5967
33. Alipour-Banaei, H., Serajmohammadi, S., Mehdizadeh, F.:
Optical wavelength demultiplexer based on photonic crystal ring
resonators. Photon Netw. Commun. 29(2), 146–150 (2015)
34. Alipour-Banaei, H., Mehdizadeh, F., Hassangholizadeh-Kashti-
ban, M.: A novel proposal for all optical PhC-based demulti-
plexers suitable for DWDM applications. Opt. Quant. Electron.
45(10), 1063–1075 (2013)
35. Ung, B., Dupuis, A., Stoeffler, K., Dubois, C., Skorobogatiy, M.:
High-refractive-index composite materials for terahertz waveg-
uides: trade-off between index contrast and absorption loss. JOSA
B28(4), 917–921 (2011)
36. Lu, M.F., Liao, S.M., Huang, Y.T.: Ultracompact photonic crystal
polarization beam splitter based on multimode interference. Appl.
Opt. 49(4), 724–731 (2010)
37. Robinson, S., Nakkeeran, R.: Photonic crystal ring resonator-
based add drop filters: a review. Opt. Eng. 52(6), 060901 (2013)
610 Opt Rev (2017) 24:605–610
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... The design provides the maximum transmission efficiency, spectral width, and Crosstalk are all 100%, 0.7nm, and -27dB. Mehdizadeh et al. [27] designed the four-channel demultiplexer. ...
... From the literature survey [22][23][24][25][26][27][28][29][30][31], we clearly observe that the existing reported work in the PC demultiplexer employs line defect waveguides, point defects, and resonant cavities in the shapes of a circular, hexagonal, x-shaped, quasi-circular, flower shape, square shape, or octagonal. Many of the reported papers in PC DWDM demultiplexer do not fulfil the requirements of ITU-T G.694.1. ...
... The demultiplexer is designed to drop the odd and even channels separately to reduce the Crosstalk between the adjacent channels. The proposed design provides minimum Crosstalk of -64dB and maximum Crosstalk of -44dB, which is much less than the reported paper [22][23][24][25][26][27][28][29][30][31][32]. According to Fig. 6, the transmission spectrum in dB for an eight-channel demultiplexer is shown to determine the Crosstalk between the channels. ...
Full-text available
In this work, an eight-channel Dense Wavelength Division Multiplexing (DWDM) demultiplexer is designed with a 2D Photonic Crystal (PC) Triangular lattice. The proposed demultiplexer consists of a centre bus waveguide, an isosceles trapezium resonant cavity, and an eight circular ring cavity (CR1, CR2, CR3, CR4, CR5, CR6, CR7, and CR8). The point defect resonant cavity consists of seven rods to drop different wavelengths from eight cavities, each of eight drop waveguides. The design is very simple for realistic systems. The Finite Difference Time Domain (FDTD) and Plane Wave Expansion Method (PWE) methods are used to determine the proposed design's band structure and transmission spectrum. The resonant wavelengths are 1.5441μm, 1.5443μm 1.54449μm 1.5447μm 1.5449μm 1.5551μm 1.5553μm, and 1.5555μm respectively. The proposed device provides a high-quality factor, transmission efficiency, and low Crosstalk. The device's footprint is 451.2 μm2 easily incorporated into a Photonic Integrated Circuits (PIC).
... In this figure, it is clear that the wavelengths 1.5604, 1.5614, 1.5625, and 1.5534 µm are extracted from the input waveguide and transferred to the output waveguide via four cavities. By comparing with reported works, our demultiplexer possesses higher quality factor values than those of references [12][13][14][15][16][17][18][19]. The level of diaphone is certainly better than the one obtained in [12][13][14][15][16][17][18][19] (see Table 6). ...
... By comparing with reported works, our demultiplexer possesses higher quality factor values than those of references [12][13][14][15][16][17][18][19]. The level of diaphone is certainly better than the one obtained in [12][13][14][15][16][17][18][19] (see Table 6). ...
The wavelength demultiplexing is a particularly important function in integrated optics and can be realized using photonic crystals. The aim is to extract accurately the wavelengths in a data flux. In this work, we investigate a new topologies of wavelength demultiplexing based on two-dimensional photonic crystals constituted of dielectric rods spread in a square network. The studied demultiplexer is based on optical filters with optimized parameters in order to extract four different wavelengths in the vicinity of frequencies corresponding to communication windows. It was found that the crosstalk between the structure channels of the demultiplexer are in the range of –19.19 and –44.1 dB and the channel spacing is equal to 0.96 nm. The simulation results presented in this paper are performed and analyzed using the FDTD method.
... Besides, impressive features such as photonic bandgap (PBG) [3,4], slow light [5,6], self-collimation [7,8], and super prism [9,10] have enhanced PCs-based applications. Some attempts have been made for realizing all-optical devices based on PC structures such as filters [11,12], demultiplexers [13][14][15], flip-flops [16,17], analog-to-digital converters [18][19][20], decoders [21][22][23], and encoders [24][25][26]. ...
Full-text available
In this study, a novel two-dimensional photonic crystal-based structure, including 70 and 90 rods along the x and z directions, has been proposed for multiplying two-bit numbers. The fundamental rods are made of silicon, and the lattice constant is equal to 608 nm. The structure consists of six cross-connection waveguides, and the nonlinear rods have been placed inside them. Dependence of the refractive index to the applied optical intensity for nonlinear rods helps to have the desired interferences and activate the correct output ports. The finite difference time domain and the plane-wave expansion methods are used to simulate the optical wave propagation throughout the structure and calculation of the band diagram. Time analysis of the structure shows the delay time is just around 6.5 ps that is proper to optical processing. Also, the contrast ratio is equal to 2.72 dB. The obtained results demonstrate the capability of the presented structure to be using for optical applications.
... The presence of a very suitable band-gap in these structures causes them to be able to limit and control the propagation of light waves inside extremely compact spaces. Today, considering these features of photonic crystals, many basic elements needed to realize all-optical networks such as optical filters [19][20][21], optical sensors [22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39], optical logic gates [40][41][42][43][44][45][46][47], optical multiplexers and demultiplexers [48][49][50][51][52], optical discretizers, and so on have been designed that can be used in integrated optical structures. Signal processing is a critical step in communication networks that requires a discrete digital signal as input. ...
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Today, one of the most important objectives concerned with integrated optical circuits is to realize all-optical networks. High transmission speed and efficiency and no interference between optical and electronic signals encourage us to manufacture all-optical devices. In the present paper, photonic analog-to-digital converters that are one of the key structures required in integrated optical circuits have been investigated. One of the advantages of these converters is the generation of binary codes, which leads to faster data transfer. In all the proposed designs, a power and wavelength discretizer and a coder have been used to find the optimal structure with the best specifications. The optical discretizer located at the input and designed as a combination of rods and ring resonators is strongly influenced by the input power due to nonlinear effects. The coder structure that consists of input and output ports can be controlled by controlling such elements as radius and refractive index and sometimes creating cavities in the structure. Reviewing the relevant literature can make it clear that a delay time of 5 ps and a footprint of 1520 μm can be achieved by controlling the resonance modes. By creating a cavity in the proposed design, an operation speed of 1 Ts and a footprint of 42 µm² can be achieved, causing significant improvements compared to previous designs. For better transmission, additional GaN ring resonators can be placed in the structure so that it can support the sampling rate of 220 GS/s with a resolution of 880KS. By adjusting the coupling coefficients in the structures, the threshold level can also be adjusted. These coefficients depend on the radius and refractive index. The improved optical ADC operation and switching speed and the reduced power consumption can be realized by adjusting them. In structures where the binary code “11” is generated, a sampling time of 1.5 ps can be achieved using a number of optical switches. Such converters are designed with a square and triangular topology using dielectric rods in the air (or air rods in dielectric) with a certain lattice constant and filling ratio. The Finite-difference time-domain (FDTD) method is used to simulate these structures.
... They separate the multiplexed channels in accordance with their central wavelengths. Channel drop/add filters are very crucial elements that can be employed as multichannel demultiplexers/multiplexers (Alipour-Banaei et al. 2015;Fallahi et al. 2017Fallahi et al. , 2019 and optical drop/add units (Qiang et al. 2007;Vegas Olmos et al. 2010) for wavelength division multiplexing systems. They can be also used as optical sensors. ...
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Three optical multi-color filters are modelled in the current work. They are composed of defective photonic crystals of two layers A and B and a defect layer C which is selected as silver Ag. The three multi-color filters have the structures (ABA)(ABAC) N (ABA), (ABAC) N ABA, and (ABAC) N (BAB). The transmission spectra of the filters are investigated for different values of coupled defects (N). It is found that the three filters have several filtering channels. These channels are directly related to the number of coupled defects. In the multi-color filters (ABA)(ABAC) N (ABA), (ABAC) N ABA, and (ABAC) N (BAB), the number of filtering channels is equal to N + 1, N and N − 1, respectively. With the increase of N, the resonant peaks are blue shifted. These filters can be used effectively in pre-amplification , radio tuning to a specific frequency, tone control in audio systems, equalization and signal processing circuits.
In advanced optical communication systems, a photonic crystal (PC) based channel drop filter (CDF) and dense wavelength division multiplexer (DWDM) demultiplexer are essential components in the design of a complete DWDM system, which offers a high transmission data rate. In the present work, a novel PC, CDF filter and demultiplexer based on a ring resonator with a super ellipse shape is designed and analyzed. To design a high-performance device, the performance parameters of the proposed components, such as transmission efficiency, spectral line width, channel spacing, Q -factor and crosstalk, are investigated. The proposed CDF is designed to drop a resonant wavelength with a high quality factor of 3955, and the ring resonator design is extended to the demultiplexer. The demultiplexer is designed to drop the four resonant wavelengths of 1579.8 nm, 1582 nm, 1583.6 nm and 1574.9 nm, respectively. The observed high quality factor (3955), bandwidth (0.4 nm) and transmission efficiency (90%) of the proposed demultiplexer will support high-performance DWDM systems
We have proposed a controllable topological add-drop filter (ADF) by utilizing the one-way transmission property and resonant coupling effect of topological photonic states in magneto-optical photonic crystal (MOPC) system. The ADF is symmetrically constructed by a central ring resonator (RR) with each side a MO microcavity and a topological waveguide formed by MOPC/Al 2 O 3 PCs. The topological waveguide supports one-way transmission and the microcavity is used to adjust resonant frequency and improve filtering performance. Based on the symmetry of structure and the adjustability of magnetic field, the input and output ports can be reconfigured conveniently to realize the dropping and adding functions of the ADF. Such an ADF possesses merits of nearly perfect filtering performance, convenient adjustability of resonance mode, and strong robustness against various defects. Moreover, we further design an optical demultiplexer consisting of two PCRRs which is able to separate two different resonant modes independently and efficiently. These results hold promise in many fields such as optical communications and wavelength-division multiplexing.
Optical decoders are one of the necessary building blocks that are required for realizing optical computation and optical processing systems. Photonic crystals have great potentials for designing different kinds of optical devices. They also have been used for designing different kinds of optical decoders. In this paper, we are going to present a comprehensive review of different mechanisms, methods and structures that have been proposed for designing photonic crystal-based optical decoders. All the proposed structures can be divided in two main categories: threshold switching-based decoders and beam interference-based structures. So many structure have been proposed using threshold switching but only there is one 1-to-2 optical decoder that was designed using beam interference.
In the present paper, a four-channel optical demultiplexer (DMUX) based on two-dimensional photonic crystal has been presented. In this optical demultiplexer, filtering and wavelength separation were performed using point defects between the output and input waveguides. To design the optical demultiplexer, a 31 × 21 resonance filter with a lattice constant (Λ) of 0.54 μm and the radius of the dielectric rods of 0.2Λ was first designed, and then it was expanded to obtain a four-channel 31 × 41 demultiplexer. The output wave spectrum was measured for four channels in the range of 1541.5 nm to 1557.6 nm. The average quality factor of 2567, the average crosstalk of − 25 dB, and the transmission coefficient of higher than 97% were obtained.
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In this paper, eight-channel wavelength-division demultiplexer (WDDM) is proposed and designed using two-dimensional photonic crystal (2DPC) ring resonator whose corresponding functional parameters such as transmission efficiency, resonant wavelength, Q factor are investigated. The proposed structure consists of bus waveguide, dropping waveguide and square ring resonators. Eight different channels are dropped by altering the cavity size and radius of the defect rods. The plane-wave expansion (PWE) and finite-difference time-domain (FDTD) methods are employed to analyse the photonic band gap (PBG) of periodic and non-periodic structure and to arrive normalized transmission spectra, respectively. The resonant wavelengths of eight-channel demultiplexers are 1496.9, 1502.3, 1506.9, 1512.3, 1515.0, 1520.4, 1525.3 and 1530.6 nm. The average transmission efficiency, Q factor and spectral width of proposed demultiplexer are 81%, 825 and 1.8 nm, respectively. The mean channel spacing is about 4.2 nm. The size of the demultiplexer is small; hence, it can be utilized for photonic integrated circuits (PIC).
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A T-shaped polarization beam splitter based on two-dimensional photonic crystal is proposed, which is composed of three waveguides: one input and two output. Unpolarized beams incident from the input port will be separated into two different polarization modes and outputted individually by two different coupling structures. Simulation results can be obtained by the finite-difference time-domain (FDTD) method. In the normalized frequency range of 0.3456 < \(\omega \alpha /2\pi {}c\) < 0.37, multiple frequencies can obtain high transmission efficiency simultaneously for both TE and TM modes. And the degree of polarization is very closed to 1 for both output ports at this frequency range. When the normalized frequency \(f=0.3534 \omega \alpha /2\pi {}c\), the transmission efficiency, respectively, is 88 % and \(91\) % for TE modes and TM modes. The extinction ratio is all 30dB for both modes. The polarization beam splitter attains the requirement we expected by analyzing simulation results.
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A compact diplexer is designed using a silicon photonic-crystal directional coupler of length comparable to the incident wavelength. The diplexer theoretically and experimentally exhibits a cross state bandwidth as broad as 2% of the operation frequency, with over 40-dB isolation between the cross and bar ports. We also demonstrate 1.5-Gbit/s frequency-division communication in the 0.32- and 0.33-THz bands using a single-wavelength-sized diplexer, and discuss the transmission bandwidth. Our study demonstrates the potential for application of photonic crystals as terahertz-wave integration platforms.
Abstract A 4-channel wavelength division demultiplexer based on photonic crystal structures suitable for WDM communication applications is proposed. In order to improve the wavelength selectivity we introduce four scattering rods above and under the X-shaped ring resonators in the proposed structure. It is shown that the PBG of the structure is tuned for communication systems in both TE and TM modes but the results demonstrated that just the first PBG in TM mode is suitable for WDM applications, so all the simulations will be done
An eight-channel drop filter based on two-dimensional photonic crystal is proposed. A five-cascaded stub is used to receive 100% reflection feedback. The geometric parameters on the transmission spectra of the bus waveguide output port are investigated. The Fabry-Perot fibre grating theory is used to explain the influences. On the basis of the 100% reflector, a channel drop filter is designed according to the wavelength spacing in the coarse wavelength division multiplexing system. Numerical simulations demonstrate that each channel exhibits over 93% transfer efficiency.
In this study, an all optical 4-to-2 encoder have been proposed which has four input and three output ports. The proposed structure can generate a 2-bit binary code considering which input port is active. For realising the proposed structure first the authors proposed and designed a BUFFER and an OR gate. Then combined these basic gates to realise the proposed encoder. The maximum switching delay and footprint for the proposed structure are about 200 fs and 880 μm2, respectively.
In this paper, an ultra-narrow band channel drop filter (CDF) based on two-dimensional photonic crystal ring resonator (2D PCRR) with hexagonal lattice of silicon rods is proposed and designed. For this purpose, the influences of variation of the radius of the quad rods on corners of X-shaped PCRR, on the performance characteristics of channel drop filter such as drop efficiency, and quality factor have been investigated. Calculation results show that the efficiency of 100% and quality factor of nearly 1500 at operating wavelength of 1550 nm can be achieved. Consequently the channel bandwidth and channel spacing are reduced to 1 nm and 10 nm respectively, which will be suitable for coarse wavelength division multiplexing (CWDM) optical network systems with 10 nm channel spacing. Simulations have been performed using 2D finite difference time-domain (2D FDTD) calculations.
Photonic crystal based ring resonators are promising structures used for designing optical filters suitablefor optical communication networks. In this work we use an H-shaped resonant ring for designing anoptical filter. The proposed filter consists of two upper and lower waveguides coupled through an H-shaped resonator which is designed for coupling of an identical wavelength from upper waveguide tothe lower one. We use numerical methods such as plane wave expansion and finite difference timedomain for performing our simulations and studying the optical properties of the proposed structure.The transmission efficiency and quality factor of our filter is about 100% and 221 relatively.
Improving transmission efficiency, quality factor, channel spacing and crosstalk levels are the top priorities in designing optical demultiplexers, suitable for wavelength division multiplexing applications. In this paper, we proposed a novel structure for designing optical demultiplexer based on photonic crystal ring resonator. For performing wavelength selection task, we used four ring resonators. The resonance wavelength of the ring resonators depends on the dimensions of the ring core; therefore, we chose two different values for the lattice constant of the ring resonators core section. The channel spacing of the structure is about 3 nm, the minimum transmission efficiency is more than 95 %, the overall quality factor is more than 2,600, and finally the crosstalk levels are better than \(-\) 19 dB.