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Ultra-contrast ratio optical encoder using photonic crystal waveguide
Materials Letters 251 (2019) 144–147
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Ultra-contrast ratio optical encoder using photonic crystal waveguide R. Rajasekar a,b,⇑, R. Latha a,c, S. Robinson a,c,⇑ a
Department of Electronics and Communication Engineering, India Krishnasamy College of Engineering and Technology, Cuddalore, India c Mount Zion College of Engineering and Technology, Pudukkottai, India b
a r t i c l e
i n f o
Article history: Received 3 April 2019 Received in revised form 25 April 2019 Accepted 10 May 2019 Available online 11 May 2019 Keywords: Encoder Defects Photonic crystal Microstructure
a b s t r a c t In recent year, ultra-compact and high-speed optical logic devices are extremely attractive for the scientific community and optical computing. In this paper, 2 1 encoder is proposed and designed using twodimensional photonic crystal based microstructure. This logic device is constructed by point and line defects in a triangular lattice with silicon rod embedded in air host. The encoder performances are analyzed by using Finite Difference Time Domain method. The numerical results reveal that the designed micro device is capable of working accurately for different logic states. The proposed device is operated at 1520 nm, and it provides a high contrast ratio of 25.82 dB, the excellent response time of 0.2833 ps and a bit rate of around 3.52 Tbps. Hence, it is highly suitable for an optical signal processor and photonic integrated circuits. Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction In recent year, the micro-optical components are primarily required for all optical communication systems and the optical signal processor [1]. In recent days, the photonic crystal based logic devices are highly suitable for optical computing due to their attractive features such as low loss, low power consumption, easy fabrication and high thermal stability [2]. The photonic crystal (PC) based optical encoder is one of the key devices in the optical signal processor that frequently designed with compact size and high processing speed [3–11]. For this reason, the 2D PC based encoders were developed by several mechanisms such as interference, self-collimation and Kerr effect where interference effect is designed with high data rate, high output power, low input power and high contrast ratio [4,9]. Hence, the interference effect is accounted for the proposed optical encoder design. In the literature, the PC based encoders were designed through Photonic Crystal Ring Resonators (PCRR) and waveguides. Generally, the ring resonators performance are realized with high power consumption, minimum contrast ratio, low output power, very slow response time and high footprint owing to more numbers of ring resonators [10]. Alternatively, photonic crystal waveguide
⇑ Corresponding authors. E-mail addresses: [email protected] (R. Rajasekar), mail2robinson@gmail. com (S. Robinson). https://doi.org/10.1016/j.matlet.2019.05.040 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
structure was offered good contrast ratio, high output power, low delay time and design with very small dimension [10]. Recently, all optical encoders are realized by different shapes of waveguides which connected from input ports to output ports. Such kinds of waveguides are called L-shaped waveguide [4], Yshaped waveguides [5] and T-shaped waveguides [11]. These waveguides corners are gradually changed which in turn reduce the normalized output power and contrast ratio of the logic device. Moreover, the aforementioned encoders were designed with any one shape of the waveguide. However, in this present work, the optimized L-shaped and Y-shaped waveguide are integrated to design the proposed encoder. In addition, the coupling rods and corner rod are employed to optimize the waveguide corners in turn realize the encoder with very high normalized output power, high contrast ratio and fast response time. 2. Design and operating principle of 2 1 encoder Generally, the encoder is processed 2N input with N outputs. The 2 1 encoder has two inputs and one output. This logic device digital circuit and its truth table are shown in Fig. 1(a). This device has two binary inputs [10] and [01] whose corresponding outputs are 0 and 1, respectively. In this device, the input combinations [00] and [11] equivalent outputs are treated as irrelevant [12]. The proposed logic device platform is composed of an array of 37 31 rods in air medium. The rods are made of silicon, and its refractive index is 3.45, the lattice constant a = 0.580 mm and radius of the rod r = 0.11 mm.
R. Rajasekar et al. / Materials Letters 251 (2019) 144–147
145
The Fig. 1(b) represents the schematic structure of 2 1 encoder. The proposed optical device is composed of two input waveguides and one output waveguide. The bottom input and output waveguide follow L-shaped and Y-shaped, respectively. These waveguide structures are designed through line defects. Based on the encoder outputs top waveguide is not coupled with output waveguide whereas the bottom input and output waveguide is connected through coupling rods which primarily used to improve the signal transmission from input to output. The coupling rods are created by changing the rod radius and refractive index. The coupling rods radius is 30 nm and its refractive index is 3.26. The Y shaped branches has one corner rod kept with the radius of 40 nm with refractive index of 3.26 which is used to reduce the reflection losses and improve the output power of an encoder. 3. Result and discussions The input signals are applied from input ports X0 and X1 and its output received at port ‘‘A” of the encoder. The proposed device input power is 1 mW, and the operating wavelength of 1520 nm is used to carry out the simulations.
Fig. 1. The 2 1 encoder (a) Digital circuit and truth table (b) Schematic layout.
Case 1: The input signal X0 is ON and X1 is OFF as a result, the output A is OFF. For this logic condition the optical signal is coupled at top input waveguide only and there is no signal is received at output port as clearly shown in Fig. 2(a). In this state, the logic device output power level is accounted as 0.004 Pi for logic ‘‘0” function which clearly shown in Fig. 3(a). Hence, the output A is assumed as OFF state for this logic condition.
Fig. 2. Optical signal distribution of 2 1 encoder (a) X0 = 1, X1 = 0 and A = 0 and (b) X0 = 0, X1 = 1 and A = 1.
Fig. 3. Output response of 2 1 encoder (a) X0 = 1, X1 = 0 and A = 0 and (b) X0 = 0, X1 = 1 and A = 1.
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R. Rajasekar et al. / Materials Letters 251 (2019) 144–147
Case 2: When X0 = 0 and X1 = 1, in turn, the optical signal coupled from input waveguide to output waveguide as shown in Fig. 2(b). In this logic condition the output power of 1.53 Pi is received at the output port A as clearly explain in Fig. 3(b). Thus, A is considered as ON state for the proposed encoder. The time evaluation curve is shown normalized power level for different logic functions. It is used to compute the parameter of contrast ratio, response time and bit rate. The proposed encoder is provided high normalized power of 1.53 Pi where Pi is input power for logic ‘‘1” and 0.004 Pi for logic ‘‘0”. Therefore, the contrast ratio is 25.82 dB. The response time is defined as the device to take time to reach maximum power at simulation. In this device, the average delay time of cT = 85 lm where c is a speed of light in air. Hence, the response time of an encoder is 0.2833 ps. The data rate is depending on response time of a signal and it offers a bit rate of 3.52 Tbps.
encoder. Primarily, the CR varies with these parameters as clearly shown in Fig. 4(a)–(c). The coupling rod radius of 30 nm, corner rod radius of 40 nm (Fig. 4(a)) whose refractive index of 3.26 (Fig. 4(b)) and operating wavelength of 1520 nm (Fig. 4(c)) are provided high CR than compared to other values. In addition, the impact of output power of the encoder without and with optimization is shown in Fig. 4(d). It is observed that the optimized logic device is providing high normalized output power and good CR than the encoder without optimization. Table 1 shows the functional parameters of proposed encoder are compared with other optical encoders. From this analysis, the 2 1 encoder is designed with a low dimension, good response
Table 1 The performance comparison of proposed encoder with reported 2D PC based encoders.
3.1. Optimization of contrast ratio The Contrast Ratio (CR) is a significant parameter for logic devices and it calculated as CR = 10log (P1/P0) where P1 and P0 indicates that logic ‘‘100 and ‘‘0” normalized output power. The operating wavelength, coupling rods radius, corner rod radius and its refractive index values are directly influence the CR of an optical
***
Reference
Dimension (mm2)
Response Time (ps)
Contrast Ratio (dB)
[3] [4] [5] [6] [7] [8] Present work
3795 880 625 240.5 218.2 795.6 343
1.4 0.2
3.71 7.3 11.80 9.54 5.7 9.24 25.82
*** ***
1 1.8 0.2833
Not Discussed.
Fig. 4. Contrast ratio of the optical encoder (a) by changing radius of corner and coupling rod (b) by changing refractive index of rod (c) by changing of wavelength (d) with and without optimization.
R. Rajasekar et al. / Materials Letters 251 (2019) 144–147
time and high contrast ratio than compared to other encoders. Hence, it could be suitable for real-time applications in photonic integrated circuits. 4. Conclusion The proposed photonic crystal based 2 1 encoder is designed by line and point defects which are mainly employed to reduce their coupling loss and improve the device performance. The contrast ratio, response time and bit rate of the proposed devices are 25.82 dB, 0.2833 ps and 3.52 Tbps, respectively. Hence, it is suitable for high speed of photonic integrated circuits and optical computing. Declaration of Competing Interest None declared. References [1] A. Salmanpour, S. Mohammadnejad, A. Bahrami, Photonic crystal logic gates: an overview, Opt. Quant. Electron. 47 (2015) 2249–2275.
147
[2] J.D. Joannopoulos, R.D. Meade, J.N. Winn, Photonic Crystal: Modeling of Flow of Light, Princeton University Press, Princeton, NJ, 1995. [3] H. Alipour-Banaei et al., Application of self-collimated beams to realization of all optical photonic crystal encoder, Phys. E 75 (2016) 77–85. [4] F. Mehdizadeh, M. Soroosh, H. Alipour-Banaei, Proposal for 4-to-2 optical encoder based on photonic crystals, IET Optoelectron. 11 (2016) 29–35. [5] S. Naghizade, H. Khoshsima, Low input power an all optical 4 2 encoder based on triangular lattice shape photonic crystal, J. Opt. Commun. (2018), https://doi.org/10.1515/joc-2018-0019. [6] I. Ouahab, R. Naoum, A novel all optical 4 2 encoder switch based on photonic crystal ring resonators, Optik 127 (2016) 7835–7841. [7] E.G. Anagha, A. Rajesh, D. Saranya, Design of an all optical encoder using 2D photonic crystals, in: 2nd International Conference on Inventive Systems and Control Proc, IEEE, 2018, pp. 55–59. [8] H. Seif-Dargahi, Ultra-fast all-optical encoder using photonic crystal-based ring resonators, Photon Netw. Commun. 36 (2018) 272–277. [9] T.S. Mostafa, N.A. Mohammed, E.S.M. El-Rabaie, Ultracompact ultrafastswitching-speed all-optical 42 encoder based on photonic crystal, J. Comput. Electron. 18 (2019) 279–293. [10] F. Parandin, High contrast ratio all-optical 42 encoder based on twodimensional photonic crystals, Opt. Laser Technol. 113 (2019) 447–452. [11] S. Naghizade, S. Mohammadi, H. Khoshsima, Design and simulation of an all optical 8 to 3 binary encoder based on optimized photonic crystal OR gates, J. Opt. Commun. (2018), https://doi.org/10.1515/joc-2018-0034. [12] S. Liu, M. Li, X. Yu, C.Z. Li, H. Liu, Biomacromolecular logic gate, encoder/ decoder and keypad lock based on DNA damage with electrochemiluminescence and electrochemical signals as outputs, Chem. Commun. 51 (2015) 13185–13188.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Ultra-contrast ratio optical encoder using photonic crystal waveguide R. Rajasekar a,b,⇑, R. Latha a,c, S. Robinson a,c,⇑ a
Department of Electronics and Communication Engineering, India Krishnasamy College of Engineering and Technology, Cuddalore, India c Mount Zion College of Engineering and Technology, Pudukkottai, India b
a r t i c l e
i n f o
Article history: Received 3 April 2019 Received in revised form 25 April 2019 Accepted 10 May 2019 Available online 11 May 2019 Keywords: Encoder Defects Photonic crystal Microstructure
a b s t r a c t In recent year, ultra-compact and high-speed optical logic devices are extremely attractive for the scientific community and optical computing. In this paper, 2 1 encoder is proposed and designed using twodimensional photonic crystal based microstructure. This logic device is constructed by point and line defects in a triangular lattice with silicon rod embedded in air host. The encoder performances are analyzed by using Finite Difference Time Domain method. The numerical results reveal that the designed micro device is capable of working accurately for different logic states. The proposed device is operated at 1520 nm, and it provides a high contrast ratio of 25.82 dB, the excellent response time of 0.2833 ps and a bit rate of around 3.52 Tbps. Hence, it is highly suitable for an optical signal processor and photonic integrated circuits. Ó 2019 Elsevier B.V. All rights reserved.
1. Introduction In recent year, the micro-optical components are primarily required for all optical communication systems and the optical signal processor [1]. In recent days, the photonic crystal based logic devices are highly suitable for optical computing due to their attractive features such as low loss, low power consumption, easy fabrication and high thermal stability [2]. The photonic crystal (PC) based optical encoder is one of the key devices in the optical signal processor that frequently designed with compact size and high processing speed [3–11]. For this reason, the 2D PC based encoders were developed by several mechanisms such as interference, self-collimation and Kerr effect where interference effect is designed with high data rate, high output power, low input power and high contrast ratio [4,9]. Hence, the interference effect is accounted for the proposed optical encoder design. In the literature, the PC based encoders were designed through Photonic Crystal Ring Resonators (PCRR) and waveguides. Generally, the ring resonators performance are realized with high power consumption, minimum contrast ratio, low output power, very slow response time and high footprint owing to more numbers of ring resonators [10]. Alternatively, photonic crystal waveguide
⇑ Corresponding authors. E-mail addresses: [email protected] (R. Rajasekar), mail2robinson@gmail. com (S. Robinson). https://doi.org/10.1016/j.matlet.2019.05.040 0167-577X/Ó 2019 Elsevier B.V. All rights reserved.
structure was offered good contrast ratio, high output power, low delay time and design with very small dimension [10]. Recently, all optical encoders are realized by different shapes of waveguides which connected from input ports to output ports. Such kinds of waveguides are called L-shaped waveguide [4], Yshaped waveguides [5] and T-shaped waveguides [11]. These waveguides corners are gradually changed which in turn reduce the normalized output power and contrast ratio of the logic device. Moreover, the aforementioned encoders were designed with any one shape of the waveguide. However, in this present work, the optimized L-shaped and Y-shaped waveguide are integrated to design the proposed encoder. In addition, the coupling rods and corner rod are employed to optimize the waveguide corners in turn realize the encoder with very high normalized output power, high contrast ratio and fast response time. 2. Design and operating principle of 2 1 encoder Generally, the encoder is processed 2N input with N outputs. The 2 1 encoder has two inputs and one output. This logic device digital circuit and its truth table are shown in Fig. 1(a). This device has two binary inputs [10] and [01] whose corresponding outputs are 0 and 1, respectively. In this device, the input combinations [00] and [11] equivalent outputs are treated as irrelevant [12]. The proposed logic device platform is composed of an array of 37 31 rods in air medium. The rods are made of silicon, and its refractive index is 3.45, the lattice constant a = 0.580 mm and radius of the rod r = 0.11 mm.
R. Rajasekar et al. / Materials Letters 251 (2019) 144–147
145
The Fig. 1(b) represents the schematic structure of 2 1 encoder. The proposed optical device is composed of two input waveguides and one output waveguide. The bottom input and output waveguide follow L-shaped and Y-shaped, respectively. These waveguide structures are designed through line defects. Based on the encoder outputs top waveguide is not coupled with output waveguide whereas the bottom input and output waveguide is connected through coupling rods which primarily used to improve the signal transmission from input to output. The coupling rods are created by changing the rod radius and refractive index. The coupling rods radius is 30 nm and its refractive index is 3.26. The Y shaped branches has one corner rod kept with the radius of 40 nm with refractive index of 3.26 which is used to reduce the reflection losses and improve the output power of an encoder. 3. Result and discussions The input signals are applied from input ports X0 and X1 and its output received at port ‘‘A” of the encoder. The proposed device input power is 1 mW, and the operating wavelength of 1520 nm is used to carry out the simulations.
Fig. 1. The 2 1 encoder (a) Digital circuit and truth table (b) Schematic layout.
Case 1: The input signal X0 is ON and X1 is OFF as a result, the output A is OFF. For this logic condition the optical signal is coupled at top input waveguide only and there is no signal is received at output port as clearly shown in Fig. 2(a). In this state, the logic device output power level is accounted as 0.004 Pi for logic ‘‘0” function which clearly shown in Fig. 3(a). Hence, the output A is assumed as OFF state for this logic condition.
Fig. 2. Optical signal distribution of 2 1 encoder (a) X0 = 1, X1 = 0 and A = 0 and (b) X0 = 0, X1 = 1 and A = 1.
Fig. 3. Output response of 2 1 encoder (a) X0 = 1, X1 = 0 and A = 0 and (b) X0 = 0, X1 = 1 and A = 1.
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R. Rajasekar et al. / Materials Letters 251 (2019) 144–147
Case 2: When X0 = 0 and X1 = 1, in turn, the optical signal coupled from input waveguide to output waveguide as shown in Fig. 2(b). In this logic condition the output power of 1.53 Pi is received at the output port A as clearly explain in Fig. 3(b). Thus, A is considered as ON state for the proposed encoder. The time evaluation curve is shown normalized power level for different logic functions. It is used to compute the parameter of contrast ratio, response time and bit rate. The proposed encoder is provided high normalized power of 1.53 Pi where Pi is input power for logic ‘‘1” and 0.004 Pi for logic ‘‘0”. Therefore, the contrast ratio is 25.82 dB. The response time is defined as the device to take time to reach maximum power at simulation. In this device, the average delay time of cT = 85 lm where c is a speed of light in air. Hence, the response time of an encoder is 0.2833 ps. The data rate is depending on response time of a signal and it offers a bit rate of 3.52 Tbps.
encoder. Primarily, the CR varies with these parameters as clearly shown in Fig. 4(a)–(c). The coupling rod radius of 30 nm, corner rod radius of 40 nm (Fig. 4(a)) whose refractive index of 3.26 (Fig. 4(b)) and operating wavelength of 1520 nm (Fig. 4(c)) are provided high CR than compared to other values. In addition, the impact of output power of the encoder without and with optimization is shown in Fig. 4(d). It is observed that the optimized logic device is providing high normalized output power and good CR than the encoder without optimization. Table 1 shows the functional parameters of proposed encoder are compared with other optical encoders. From this analysis, the 2 1 encoder is designed with a low dimension, good response
Table 1 The performance comparison of proposed encoder with reported 2D PC based encoders.
3.1. Optimization of contrast ratio The Contrast Ratio (CR) is a significant parameter for logic devices and it calculated as CR = 10log (P1/P0) where P1 and P0 indicates that logic ‘‘100 and ‘‘0” normalized output power. The operating wavelength, coupling rods radius, corner rod radius and its refractive index values are directly influence the CR of an optical
***
Reference
Dimension (mm2)
Response Time (ps)
Contrast Ratio (dB)
[3] [4] [5] [6] [7] [8] Present work
3795 880 625 240.5 218.2 795.6 343
1.4 0.2
3.71 7.3 11.80 9.54 5.7 9.24 25.82
*** ***
1 1.8 0.2833
Not Discussed.
Fig. 4. Contrast ratio of the optical encoder (a) by changing radius of corner and coupling rod (b) by changing refractive index of rod (c) by changing of wavelength (d) with and without optimization.
R. Rajasekar et al. / Materials Letters 251 (2019) 144–147
time and high contrast ratio than compared to other encoders. Hence, it could be suitable for real-time applications in photonic integrated circuits. 4. Conclusion The proposed photonic crystal based 2 1 encoder is designed by line and point defects which are mainly employed to reduce their coupling loss and improve the device performance. The contrast ratio, response time and bit rate of the proposed devices are 25.82 dB, 0.2833 ps and 3.52 Tbps, respectively. Hence, it is suitable for high speed of photonic integrated circuits and optical computing. Declaration of Competing Interest None declared. References [1] A. Salmanpour, S. Mohammadnejad, A. Bahrami, Photonic crystal logic gates: an overview, Opt. Quant. Electron. 47 (2015) 2249–2275.
147
[2] J.D. Joannopoulos, R.D. Meade, J.N. Winn, Photonic Crystal: Modeling of Flow of Light, Princeton University Press, Princeton, NJ, 1995. [3] H. Alipour-Banaei et al., Application of self-collimated beams to realization of all optical photonic crystal encoder, Phys. E 75 (2016) 77–85. [4] F. Mehdizadeh, M. Soroosh, H. Alipour-Banaei, Proposal for 4-to-2 optical encoder based on photonic crystals, IET Optoelectron. 11 (2016) 29–35. [5] S. Naghizade, H. Khoshsima, Low input power an all optical 4 2 encoder based on triangular lattice shape photonic crystal, J. Opt. Commun. (2018), https://doi.org/10.1515/joc-2018-0019. [6] I. Ouahab, R. Naoum, A novel all optical 4 2 encoder switch based on photonic crystal ring resonators, Optik 127 (2016) 7835–7841. [7] E.G. Anagha, A. Rajesh, D. Saranya, Design of an all optical encoder using 2D photonic crystals, in: 2nd International Conference on Inventive Systems and Control Proc, IEEE, 2018, pp. 55–59. [8] H. Seif-Dargahi, Ultra-fast all-optical encoder using photonic crystal-based ring resonators, Photon Netw. Commun. 36 (2018) 272–277. [9] T.S. Mostafa, N.A. Mohammed, E.S.M. El-Rabaie, Ultracompact ultrafastswitching-speed all-optical 42 encoder based on photonic crystal, J. Comput. Electron. 18 (2019) 279–293. [10] F. Parandin, High contrast ratio all-optical 42 encoder based on twodimensional photonic crystals, Opt. Laser Technol. 113 (2019) 447–452. [11] S. Naghizade, S. Mohammadi, H. Khoshsima, Design and simulation of an all optical 8 to 3 binary encoder based on optimized photonic crystal OR gates, J. Opt. Commun. (2018), https://doi.org/10.1515/joc-2018-0034. [12] S. Liu, M. Li, X. Yu, C.Z. Li, H. Liu, Biomacromolecular logic gate, encoder/ decoder and keypad lock based on DNA damage with electrochemiluminescence and electrochemical signals as outputs, Chem. Commun. 51 (2015) 13185–13188.