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T-shaped channel drop filter based on photonic crystal ring resonator
G Model IJLEO-54760; No. of Pages 4
ARTICLE IN PRESS Optik xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
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T-shaped channel drop filter based on photonic crystal ring resonator Hamed Alipour-Banaei a , Mahsa Jahanara b,∗ , Farhad Mehdizadeh c a
Department of Electronics, College of Engineering, Tabriz Branch,Islamic Azad University, Tabriz, Iran Department of Electrical Engineering, College of Engineering, Ahar Branch, Islamic Azad University, Ahar, Iran c Young Researchers and Elite Club, Urmia Branch, Islamic Azad University, Urmia, Iran b
a r t i c l e
i n f o
Article history: Received 21 September 2013 Accepted 25 May 2014 Available online xxx Keywords: Photonic crystal Ring resonator Filter Quality factor Band gap
a b s t r a c t Photonic crystal ring resonators are promising candidates for realizing all optical filters with acceptable transmission efficiency and quality factor values. In this paper, by putting a12-fold quasi crystal at the middle of on 7 × 7 square cavity we created a ring resonator structure and designed a T-shaped channel drop filter. The drop wavelength of our filter is at 1551 nm, with transmission efficiency and quality factor equal to 90% and 387. Our structure is composed of dielectric rods immersed in air. Because in this kind of structures the dominant band gap is in TM mode, all of our simulations have been done in TM mode. The total footprint of our filter is 242.4 m2 , which makes it suitable for all optical integrated circuits. © 2014 Elsevier GmbH. All rights reserved.
1. Introduction Photonic crystals (PhCs) are the best platforms for designing all optical devices suitable for all optical integrated circuits. The periodic distribution of refractive index in these artificial structures results in a forbidden wavelength region for propagation of light; this forbidden wavelength region is called photonic band gap (PBG) [1–3]. By use of PBG we can control the behavior of light inside PhCs in very small spaces. For this reason, designing ultra-compact devices based on PhC suitable for optical integrated circuits is feasible. Optical reflectors [4], optical band rejection filters [5] are some examples of proposed devices using PBG property of PhCs. Considering the ever increasing trend toward optical communication networks based on fiber optics communications, we understand the significant importance of all optical devices. The optimum goal for optics and photonics engineers is having a complete optical network without any electronics. Reaching this goal needs all optical devices such as optical filters, optical demultiplexers, optical switches and etc. Optical filters are one of the most important building blocks of optical communication networks which play a crucial role in wavelength division multiplexing (WDM) technologies. Optical filters can be used for separating nearly spaced optical channels from each other in WDM applications. Recently different mechanisms have been proposed for performing filtering behavior based on PhC structures. Defect
∗ Corresponding author. E-mail address: [email protected] (M. Jahanara).
structures [6], resonant cavities [7,8] coupled waveguides [9] and ring resonators [10] are some examples of proposed filtering mechanisms. PhC ring resonators (PhC) are composed of two waveguides namely bus and drop waveguides and a resonant ring located between them. At a certain wavelength – resonant wavelength – optical waves in bus waveguide will drop to drop waveguide through the resonant ring. Djavid et al. [11] proposed a T-shaped channel drop filter based on PhCRRs and investigated the effect of different parameters on switching wavelength. They found that dielectric constant of the inner rods and coupling rods are suitable parameters for tuning the filter. Multichannel-Drop filter using PhCRR is the most recent work done by Djavid and Abrishamian [12]. Mahmoud et al. [13,14] proposed another channel drop filter based on X-shaped ring resonator structure. Kumar et al. [15] found that ring dimensions and crystal parameters play important role in resonance behavior of rig resonator. Optical demultiplexers [16], optical switches [17], optical logic gates [18], and optical bends and power splitters [19] are other devices designed based on PhCRRs. In this paper we are going to propose a novel T-shaped channel drop filter based on PhCRR. In the core part of the resonant ring we employed a 12-fold quasi crystal. The 12-fold quasi crystal structure is very similar to circle, so creates very smooth and sharp output spectrum at the output port of the filter. 2. Theoretical methods and design Currently numerical methods are the best solutions for studying optical properties of phc-based devices. Plane wave expansion (PWE) method [20] is a powerful and high speed numerical method
http://dx.doi.org/10.1016/j.ijleo.2014.06.056 0030-4026/© 2014 Elsevier GmbH. All rights reserved.
Please cite this article in press as: H. Alipour-Banaei, et al., T-shaped channel drop filter based on photonic crystal ring resonator, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.056
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Fig. 1. The band structure of the fundamental structure.
used for calculating the band structure and extracting the photonic band gap (PBG) properties of PhC structures. However this method is not suitable for studying the propagation of optical waves inside PhC-based devices. Finite difference time domain (FDTD) [21] has been proposed for studying and analyzing electromagnetic problems such as simulating the photonic crystal based devices. The fundamental platform used for designing the proposed filter is 33 × 20 square lattice of dielectric rods immersed in air. The effective refractive index of dielectric rods is 3.46. And the radius of dielectric rods is R = 0.19 × a, where a is the lattice constant of the PhC structure. The band structure diagram of the PhC with aforementioned values is depicted in Fig. 1. Fig. 1 shows that our structure has three PBG, two PBGs in TM mode (dark blue area) and one in TE mode (dark red area). The TM PBGs are in 0.29 < a/ < 0.43 and 0.72 < a/ < 0.75 range and the TE PBG is in 0.83
Fig. 2. The schematic diagram of the filter.
Fig. 3. Output spectrum of the filter.
has 3 ports; input port (A), forward transmission port (B) and output port (C). optical waves enter the structure through port A and exit it from port B, however at the desired wavelength the optical wavelengths drop to drop waveguide through the resonant ring and travel toward port C. in order to improve the transmission efficiency and the performance of the resonant ring we introduced four scattering rods at the corners of the square and one at the upper corner of the output waveguide. The radius and the refractive index of these scattering rods are the same as the initial structure. The total footprint of the filter is 242.4 m2 . 3. Simulation and results Finite difference time domain (FDTD) [20] was used for studying optical properties of PhCs. Obtaining accurate results from FDTD simulations require choosing proper values for mesh sizes and time step of the FDTD calculations. Therefore we choose mesh sizes to be x = z = a/16. Considering a = 623 nm in our structure we have x = z = 38.9 nm. In addition, the time step value will be obtained using courant condition (s) where c is the velocity of light in free space. So we have t = 0.027 ns. Obtaining accurate results from FDTD calculations requires 3D simulations which are very complex and time consuming; therefore we used effective refractive method to reduce 3D simulations to 2D one with minimum errors [21]. The other crucial parameter that we should consider in our simulations is the boundary condition, for this purpose we used perfectly matched layer (PML) [22] boundary condition surrounding our structure. The thickness of PML is assumed to be 500 nm. The transmission spectrum of the filter is shown in Fig. 3. In this Figure the normalized transmission of the structure at port B and C are depicted with blue and green curves. At = 1551 nm the normalized transmission efficiency of port B will drop to 10% and the normalized transmission efficiency of port C will rise up to 90%. The bandwidth and quality factor of the output spectrum are 4 nm and 387 respectively. The distribution of the optical wave inside the structure for two different wavelengths is shown in Fig. 4. Fig. 4(a) shows that at = 1551 nm the optical waves due to dropping function of the resonant ring will drop to the drop waveguide and travel toward port C however at = 1560 nm optical waves will not drop to the drop waveguide and only will travel toward port B because their central wavelengths do not coincide with the drop wavelength of the structure. Now we are going to investigate the effect of different parameters on the output spectrum of the filter. First parameter we are going to investigate is the refractive index of dielectric rods. In order to separate the effect of refractive index from other parameters, we assume all other parameters such as radius of rods, radius of core rods and lattice constant of core to be constant. Then obtain the output spectra of the filter for different
Please cite this article in press as: H. Alipour-Banaei, et al., T-shaped channel drop filter based on photonic crystal ring resonator, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.056
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Fig. 6. The output spectra of the proposed filter for different radiuses of fundamental structure rods. Table 2 Significant parameters of the proposed filter for different radiuses of dielectric rod. Radius
(nm)
(nm)
Q
T. E.a (%)
a
1538.5 1541.3 1544.5 1547.7 1551 1555
4.5 4.4 4.3 4.3 4 4.3
341 350 359 359 387 361
92 91 90 88 89 88
0.170 a 0.175a a 0.180a a 0.185a a 0.190a a 0.195a a a
Fig. 4. Distribution of optical power at (a) = 1550 nm and (b) = 1560 nm.
Fig. 5. The output spectra of the proposed filter for different values of refractive index.
Transmission efficiency.
decreases, so the quality factor increases. The transmission efficiency is approximately constant for different values of refractive index. Fig. 6 shows the output spectra of the filter for different radiuses of dielectric rods. In this part we supposed all other parameters such as refractive index, lattice constant and radius of core rods are constant. According to Fig. 6 by increasing the radius we observe a red shift in the output wavelength of the proposed filter. The detailed specification of the output wavelengths for different radiuses is listed in Table 2. After studying effect of fundamental structure we are going to investigate the effect of core parameters on the output wavelength of the filter. Fig. 7 shows the output spectra for different radiuses of core rods. Like previous parameters increasing the radius of core rods results in a red shift in the output wavelength of the filter. The transmission efficiency for different radiuses of the core rods remains constant. The detailed specification of the output wavelengths for different radiuses of core rods is listed in Table 3. Finally the output spectra for different lattice constant of core structure are shown in Fig. 8. Unlike the refractive index and radius of the rods,
values of refractive index. The output spectra of the filter for six different values of refractive indices are shown in Fig. 5. According to Fig. 5 by increasing the refractive index we observe a red shift in the output wavelength of the proposed filter. The detailed specification of the output wavelengths for different refractive indices is listed in Table 1. By increasing the refractive index the bandwidth Table 1 Significant parameters of the proposed CDF for different values of n.
a
n
(nm)
(nm)
Q
T.E.a (%)
3.4 3.42 3.44 3.46 3.48 3.5
1546.3 1547.9 1549.4 1551.1 1552.6 1554.1
4.3 4.2 4.2 4 3.8 3.7
351 368 369 387 408 420
90 90 90 90 89 89
Transmission efficiency.
Fig. 7. The output spectra of the proposed filter for different radiuses of core rods.
Please cite this article in press as: H. Alipour-Banaei, et al., T-shaped channel drop filter based on photonic crystal ring resonator, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.056
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Table 3 Significant parameters of the proposed filter for different radiuses of core rod. Radius
(nm)
(nm)
Q
T.E.a (%)
a
1545.7 1546.9 1548.3 1549.6 1551 1552.5
3.5 3.7 3.8 4 4 4.1
441 418 407 387 387 378
90 89 89 89 89 89
0.170 a 0.175a a 0.180a a 0.185a a 0.190a a 0.195a a a
Transmission efficiency.
respectively. The total footprint of the filter is 242.4 m2 , so it is suitable for integrated optical circuits. We studied the impact of different parameters on the output wavelength of the filter. The results obtained from our simulations show that the resonant wavelength of the filter depends on refractive index, radius of fundamental structure rods, radius of core structure and the lattice constant of the core structure. Increasing the radius of fundamental and core structure rods and the refractive index results in a red shift in the output spectra of the filter, however increasing the lattice constant of the core results in a blue shift in the output spectra of the filter. References
Fig. 8. The output spectra of the proposed filter for different lattice constants of core structure. Table 4 Significant parameters of the proposed filter for different lattice constants of core structure. Radius a
0.50 a 0.51a a 0.52a a 0.53a a 0.54a a 0.55a a a
(nm)
(nm)
Q
T.E.a (%)
1566.3 1562.4 1558.3 1554.6 1551.1 1547.6
4 4.1 4.2 4.3 4.2 4.2
391 381 371 370 369 368
96 95 93 91 89 88
Transmission efficiency.
increasing the lattice constant of the core results in a blue shift in the output wavelength of the proposed filter. And the transmission efficiency will decrease by increasing the lattice constant of the core structure. The detailed specification of the output wavelengths for different lattice constant of core structure is listed in Table 4. 4. Conclusion In this paper we proposed a T-shaped channel drop filter based on PhCRR. We employed a 12 fold quasi crystal structure as the core of our ring resonator. Our proposed filter has a resonant wavelength at 1551 nm with transmission efficiency equal to 90%. The bandwidth and quality factor the filter is 4 nm and 387
[1] K. Sakoda, Optical Properties of Photonic Crystals, Springer-Verlag, Berlin, 2001. [2] F. Mehdizadeh, H. Alipour-Banaei, Band gap management in two dimensional photonic crystal thue-morse structures, J. Opt. Commun. 34 (2013) 61–65. [3] Z. Wu, K. Xie, H. Yang, Band gap properties of two-dimensional photonic crystals with rhombic lattice, Optik 123 (2012) 534–536. [4] F. Mehdizadeh, H. Alipour-Banaei, Z. Daie-Kuzekanani, All optical multi reflection structure based on one dimensional photonic crystals for WDM communication systems”, Optoelectronics Adv. Mater-Rapid Commun 6 (2012) 527–531. [5] H. Alipour-Banaei, F. Mehdizadeh, A proposal for anti-uvb filter based on onedimensional photonic crystal structure, Digest J. Nanomater. Biostruct. 7 (2012) 361–367. [6] A.A. Rostami, H.F. Nazari, H. Alipour-Banaei, Proposal for an ultracompact tunable wavelength-division-multiplexing optical filter based on quasi-2D photonic crystals, J. Opt. 12 (2010) 015405. [7] H. Alipour-Banaei, H. Mehdizadeh, Significant role of photonic crystal resonant cavities in WDM and DWDM communication tunable filters, Optik (2012), http://dx.doi.org/10.1016/j.ijleo.2012.07.029. [8] A.E. Akosman, M. Mutlu, H. Kurt, E. Ozbay, Dual-frequency division demultiplexer based on cascade photonic crystal waveguides, Phys. B (2012), 1621616/j.physb.26122622624. [9] H. Alipour-Banaei, M. Hassangholizadeh-Kashtiban, F. Mehdizadeh, WDM and DWDM optical filter based on 2D photonic crystal Thue-Morse structure, Optik (2013), http://dx.doi.org/10.1016/j.ijleo.2013.03.027. [10] A. Taalbi, G. Bassou, M.Y. Mahmoud, New design of channel drop filters based on photonic crystal ring resonators, Optik (2012), http://dx.doi.org/10.1016/ j.ijleo.2012.01.045. [11] M. Djavid, A. Ghaffari, F. Monifi, M.S. Abrishamian, T-shaped channel-drop filters using photonic crystal ring resonators, Physica E 40 (2008) 3151–3154. [12] M. Djavid, M.S. Abrishamian, Multi-channel drop filters using photonic crystal ring resonators”, Optik 123 (2011) 167–170. [13] M.Y. Mahmoud, G. Bassou, A. Taalbi, Z.M. Chekroun, Optical channel drop filter based on photonic crystal ring resonators”, Opt. Commun. 285 (2012) 368–372. [14] M.Y. Mahmoud, G. Bassou, A. Taalbi, A new add-drop filter based on two dimensional photonic crystal ring resonator, Optik 124 (2013) 2864–2867. [15] V.D. Kumar, T. Srinivas, A. Selvarjan, Investigation of ring resonators in photonic crystal circuits, Photonics Nanostruct-Fundam. Appl. 2 (2004) 199–206. [16] M.R. Rakhshani, M.A.M. Birjandi, Design and simulation of wavelength demultiplexer based on heterostructure photonic crystals ring resonators, Physica E 50 (2013) 97–101. [17] T. Ahmadi-Tame, B.M. Isfahani, N. Granpayeh, A.M. Javan, Improving the performance of all optical switching based on nonlinear photonic crystal micro ring resonator, Int. J. Electron. Commun. (AEU) 65 (2011) 281–287. [18] P. Andalib, N. Granpayeh, All optical ultracompact photonic crystal AND gate based on nonlinear ring resonators, J. Opt. Soc. Am. B 26 (2009) 10–16. [19] A. Ghaffari, F. Monifi, M. Djavid, M.S. Abrishamian, Photonic crystal bends and power splitters based on ring resonators, Opt. Commun. 281 (2008) 5929–5934. [20] S.G. Johnson, J.D. Joannopoulos, Block-iterative frequency-domain methods for Maxwell’s equations in a plane wave basis, Opt. Express 8 (2001) 173–190. [21] S.D. Gedney, Introduction to Finite-Difference Time-Domain (FDTD) Method for Electromagnetics, Morgan&Claypool, Lexington KY, 2010. [22] Min Qiu, Effective index method for heterostructure-slab-wave-guide-based two-dimensional photonic crystals, Appl. Phys. Lett. 81 (2002) 1163–1165.
Please cite this article in press as: H. Alipour-Banaei, et al., T-shaped channel drop filter based on photonic crystal ring resonator, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.056
ARTICLE IN PRESS Optik xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
T-shaped channel drop filter based on photonic crystal ring resonator Hamed Alipour-Banaei a , Mahsa Jahanara b,∗ , Farhad Mehdizadeh c a
Department of Electronics, College of Engineering, Tabriz Branch,Islamic Azad University, Tabriz, Iran Department of Electrical Engineering, College of Engineering, Ahar Branch, Islamic Azad University, Ahar, Iran c Young Researchers and Elite Club, Urmia Branch, Islamic Azad University, Urmia, Iran b
a r t i c l e
i n f o
Article history: Received 21 September 2013 Accepted 25 May 2014 Available online xxx Keywords: Photonic crystal Ring resonator Filter Quality factor Band gap
a b s t r a c t Photonic crystal ring resonators are promising candidates for realizing all optical filters with acceptable transmission efficiency and quality factor values. In this paper, by putting a12-fold quasi crystal at the middle of on 7 × 7 square cavity we created a ring resonator structure and designed a T-shaped channel drop filter. The drop wavelength of our filter is at 1551 nm, with transmission efficiency and quality factor equal to 90% and 387. Our structure is composed of dielectric rods immersed in air. Because in this kind of structures the dominant band gap is in TM mode, all of our simulations have been done in TM mode. The total footprint of our filter is 242.4 m2 , which makes it suitable for all optical integrated circuits. © 2014 Elsevier GmbH. All rights reserved.
1. Introduction Photonic crystals (PhCs) are the best platforms for designing all optical devices suitable for all optical integrated circuits. The periodic distribution of refractive index in these artificial structures results in a forbidden wavelength region for propagation of light; this forbidden wavelength region is called photonic band gap (PBG) [1–3]. By use of PBG we can control the behavior of light inside PhCs in very small spaces. For this reason, designing ultra-compact devices based on PhC suitable for optical integrated circuits is feasible. Optical reflectors [4], optical band rejection filters [5] are some examples of proposed devices using PBG property of PhCs. Considering the ever increasing trend toward optical communication networks based on fiber optics communications, we understand the significant importance of all optical devices. The optimum goal for optics and photonics engineers is having a complete optical network without any electronics. Reaching this goal needs all optical devices such as optical filters, optical demultiplexers, optical switches and etc. Optical filters are one of the most important building blocks of optical communication networks which play a crucial role in wavelength division multiplexing (WDM) technologies. Optical filters can be used for separating nearly spaced optical channels from each other in WDM applications. Recently different mechanisms have been proposed for performing filtering behavior based on PhC structures. Defect
∗ Corresponding author. E-mail address: [email protected] (M. Jahanara).
structures [6], resonant cavities [7,8] coupled waveguides [9] and ring resonators [10] are some examples of proposed filtering mechanisms. PhC ring resonators (PhC) are composed of two waveguides namely bus and drop waveguides and a resonant ring located between them. At a certain wavelength – resonant wavelength – optical waves in bus waveguide will drop to drop waveguide through the resonant ring. Djavid et al. [11] proposed a T-shaped channel drop filter based on PhCRRs and investigated the effect of different parameters on switching wavelength. They found that dielectric constant of the inner rods and coupling rods are suitable parameters for tuning the filter. Multichannel-Drop filter using PhCRR is the most recent work done by Djavid and Abrishamian [12]. Mahmoud et al. [13,14] proposed another channel drop filter based on X-shaped ring resonator structure. Kumar et al. [15] found that ring dimensions and crystal parameters play important role in resonance behavior of rig resonator. Optical demultiplexers [16], optical switches [17], optical logic gates [18], and optical bends and power splitters [19] are other devices designed based on PhCRRs. In this paper we are going to propose a novel T-shaped channel drop filter based on PhCRR. In the core part of the resonant ring we employed a 12-fold quasi crystal. The 12-fold quasi crystal structure is very similar to circle, so creates very smooth and sharp output spectrum at the output port of the filter. 2. Theoretical methods and design Currently numerical methods are the best solutions for studying optical properties of phc-based devices. Plane wave expansion (PWE) method [20] is a powerful and high speed numerical method
http://dx.doi.org/10.1016/j.ijleo.2014.06.056 0030-4026/© 2014 Elsevier GmbH. All rights reserved.
Please cite this article in press as: H. Alipour-Banaei, et al., T-shaped channel drop filter based on photonic crystal ring resonator, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.056
G Model IJLEO-54760; No. of Pages 4 2
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Fig. 1. The band structure of the fundamental structure.
used for calculating the band structure and extracting the photonic band gap (PBG) properties of PhC structures. However this method is not suitable for studying the propagation of optical waves inside PhC-based devices. Finite difference time domain (FDTD) [21] has been proposed for studying and analyzing electromagnetic problems such as simulating the photonic crystal based devices. The fundamental platform used for designing the proposed filter is 33 × 20 square lattice of dielectric rods immersed in air. The effective refractive index of dielectric rods is 3.46. And the radius of dielectric rods is R = 0.19 × a, where a is the lattice constant of the PhC structure. The band structure diagram of the PhC with aforementioned values is depicted in Fig. 1. Fig. 1 shows that our structure has three PBG, two PBGs in TM mode (dark blue area) and one in TE mode (dark red area). The TM PBGs are in 0.29 < a/ < 0.43 and 0.72 < a/ < 0.75 range and the TE PBG is in 0.83
Fig. 2. The schematic diagram of the filter.
Fig. 3. Output spectrum of the filter.
has 3 ports; input port (A), forward transmission port (B) and output port (C). optical waves enter the structure through port A and exit it from port B, however at the desired wavelength the optical wavelengths drop to drop waveguide through the resonant ring and travel toward port C. in order to improve the transmission efficiency and the performance of the resonant ring we introduced four scattering rods at the corners of the square and one at the upper corner of the output waveguide. The radius and the refractive index of these scattering rods are the same as the initial structure. The total footprint of the filter is 242.4 m2 . 3. Simulation and results Finite difference time domain (FDTD) [20] was used for studying optical properties of PhCs. Obtaining accurate results from FDTD simulations require choosing proper values for mesh sizes and time step of the FDTD calculations. Therefore we choose mesh sizes to be x = z = a/16. Considering a = 623 nm in our structure we have x = z = 38.9 nm. In addition, the time step value will be obtained using courant condition (s) where c is the velocity of light in free space. So we have t = 0.027 ns. Obtaining accurate results from FDTD calculations requires 3D simulations which are very complex and time consuming; therefore we used effective refractive method to reduce 3D simulations to 2D one with minimum errors [21]. The other crucial parameter that we should consider in our simulations is the boundary condition, for this purpose we used perfectly matched layer (PML) [22] boundary condition surrounding our structure. The thickness of PML is assumed to be 500 nm. The transmission spectrum of the filter is shown in Fig. 3. In this Figure the normalized transmission of the structure at port B and C are depicted with blue and green curves. At = 1551 nm the normalized transmission efficiency of port B will drop to 10% and the normalized transmission efficiency of port C will rise up to 90%. The bandwidth and quality factor of the output spectrum are 4 nm and 387 respectively. The distribution of the optical wave inside the structure for two different wavelengths is shown in Fig. 4. Fig. 4(a) shows that at = 1551 nm the optical waves due to dropping function of the resonant ring will drop to the drop waveguide and travel toward port C however at = 1560 nm optical waves will not drop to the drop waveguide and only will travel toward port B because their central wavelengths do not coincide with the drop wavelength of the structure. Now we are going to investigate the effect of different parameters on the output spectrum of the filter. First parameter we are going to investigate is the refractive index of dielectric rods. In order to separate the effect of refractive index from other parameters, we assume all other parameters such as radius of rods, radius of core rods and lattice constant of core to be constant. Then obtain the output spectra of the filter for different
Please cite this article in press as: H. Alipour-Banaei, et al., T-shaped channel drop filter based on photonic crystal ring resonator, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.056
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Fig. 6. The output spectra of the proposed filter for different radiuses of fundamental structure rods. Table 2 Significant parameters of the proposed filter for different radiuses of dielectric rod. Radius
(nm)
(nm)
Q
T. E.a (%)
a
1538.5 1541.3 1544.5 1547.7 1551 1555
4.5 4.4 4.3 4.3 4 4.3
341 350 359 359 387 361
92 91 90 88 89 88
0.170 a 0.175a a 0.180a a 0.185a a 0.190a a 0.195a a a
Fig. 4. Distribution of optical power at (a) = 1550 nm and (b) = 1560 nm.
Fig. 5. The output spectra of the proposed filter for different values of refractive index.
Transmission efficiency.
decreases, so the quality factor increases. The transmission efficiency is approximately constant for different values of refractive index. Fig. 6 shows the output spectra of the filter for different radiuses of dielectric rods. In this part we supposed all other parameters such as refractive index, lattice constant and radius of core rods are constant. According to Fig. 6 by increasing the radius we observe a red shift in the output wavelength of the proposed filter. The detailed specification of the output wavelengths for different radiuses is listed in Table 2. After studying effect of fundamental structure we are going to investigate the effect of core parameters on the output wavelength of the filter. Fig. 7 shows the output spectra for different radiuses of core rods. Like previous parameters increasing the radius of core rods results in a red shift in the output wavelength of the filter. The transmission efficiency for different radiuses of the core rods remains constant. The detailed specification of the output wavelengths for different radiuses of core rods is listed in Table 3. Finally the output spectra for different lattice constant of core structure are shown in Fig. 8. Unlike the refractive index and radius of the rods,
values of refractive index. The output spectra of the filter for six different values of refractive indices are shown in Fig. 5. According to Fig. 5 by increasing the refractive index we observe a red shift in the output wavelength of the proposed filter. The detailed specification of the output wavelengths for different refractive indices is listed in Table 1. By increasing the refractive index the bandwidth Table 1 Significant parameters of the proposed CDF for different values of n.
a
n
(nm)
(nm)
Q
T.E.a (%)
3.4 3.42 3.44 3.46 3.48 3.5
1546.3 1547.9 1549.4 1551.1 1552.6 1554.1
4.3 4.2 4.2 4 3.8 3.7
351 368 369 387 408 420
90 90 90 90 89 89
Transmission efficiency.
Fig. 7. The output spectra of the proposed filter for different radiuses of core rods.
Please cite this article in press as: H. Alipour-Banaei, et al., T-shaped channel drop filter based on photonic crystal ring resonator, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.056
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Table 3 Significant parameters of the proposed filter for different radiuses of core rod. Radius
(nm)
(nm)
Q
T.E.a (%)
a
1545.7 1546.9 1548.3 1549.6 1551 1552.5
3.5 3.7 3.8 4 4 4.1
441 418 407 387 387 378
90 89 89 89 89 89
0.170 a 0.175a a 0.180a a 0.185a a 0.190a a 0.195a a a
Transmission efficiency.
respectively. The total footprint of the filter is 242.4 m2 , so it is suitable for integrated optical circuits. We studied the impact of different parameters on the output wavelength of the filter. The results obtained from our simulations show that the resonant wavelength of the filter depends on refractive index, radius of fundamental structure rods, radius of core structure and the lattice constant of the core structure. Increasing the radius of fundamental and core structure rods and the refractive index results in a red shift in the output spectra of the filter, however increasing the lattice constant of the core results in a blue shift in the output spectra of the filter. References
Fig. 8. The output spectra of the proposed filter for different lattice constants of core structure. Table 4 Significant parameters of the proposed filter for different lattice constants of core structure. Radius a
0.50 a 0.51a a 0.52a a 0.53a a 0.54a a 0.55a a a
(nm)
(nm)
Q
T.E.a (%)
1566.3 1562.4 1558.3 1554.6 1551.1 1547.6
4 4.1 4.2 4.3 4.2 4.2
391 381 371 370 369 368
96 95 93 91 89 88
Transmission efficiency.
increasing the lattice constant of the core results in a blue shift in the output wavelength of the proposed filter. And the transmission efficiency will decrease by increasing the lattice constant of the core structure. The detailed specification of the output wavelengths for different lattice constant of core structure is listed in Table 4. 4. Conclusion In this paper we proposed a T-shaped channel drop filter based on PhCRR. We employed a 12 fold quasi crystal structure as the core of our ring resonator. Our proposed filter has a resonant wavelength at 1551 nm with transmission efficiency equal to 90%. The bandwidth and quality factor the filter is 4 nm and 387
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Please cite this article in press as: H. Alipour-Banaei, et al., T-shaped channel drop filter based on photonic crystal ring resonator, Optik - Int. J. Light Electron Opt. (2014), http://dx.doi.org/10.1016/j.ijleo.2014.06.056