All-optical OR, NOT and XOR gates based on linear photonic crystal with high port-to-port isolation
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All‑optical OR, NOT and XOR gates based on linear photonic crystal with high port‑to‑port isolation Sara Esmail Kordi1 · Reza Yousefi1 · Seyed Saleh Ghoreishi1 · Habib Adrang1 Received: 8 February 2020 / Accepted: 21 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract This paper presents new structures for OR, NOT, and XOR logic gates based on a two-dimensional photonic crystal. The proposed structures are quite linear and have the same basic structure for all three gates. Isolation between input ports is one of the features that is given special attention in this study. The proposed designs reduce the leakage signal from an input port to another input port to less than 17%. The reflection to the input port is less than 30% in the worst case. The structures are designed and simulated, and then their characteristics are compared to previous works. The simulation results show that the proposed structures, despite being linear, have a smaller size, faster response time, and acceptable contrast ratio in comparison to those of the other works. The results of the tolerance study demonstrate that manufacturing tolerance must be less than 5% for the proposed gates’ working properly.
1 Introduction Logic gates and devices play an important role in modern integrated circuits. The use of all-optical logic gates has been considered significant, as part of the efforts to increase the speed of these devices. Photonic crystals, which have been used frequently in the past decades for the design of all-optical devices such as filters, switches, routers, and multiplexers [1–5], can also be used for the design of all-optical logic gates [6]. They can be very efficient in the development of all-optical logic devices due to their small size and their special feature of the presence of the photonic band gap [7]. The photonic band gap is the frequency range in which the photonic crystal does not pass any optical signal. Due to this feature, many logic gates have been proposed based on a variety of optical phenomena, such as self-collimated beam [8–10], Mach–Zehnder interferometer [11–13], various shapes of the resonant structures [14–17], wave interference phenomena [18–21] and nonlinear Kerr effects [22–25]. Nonlinear structures use the nonlinear Kerr effect, which requires the consideration of a threshold input power to take advantage of the nonlinearity [26, 27]. In some works that operate based on wave interference, the input signals need * Reza Yousefi [email protected] 1
to have the required phase difference [28, 29]. In this case, it needs additional elements to change the input phase. In some other works, ring resonators of various shapes guide the desired wavelength to the output port, but these structures are often large, which increases the response time [15, 30]. Another significant issue in designing logic gates is portto-port isolation. In practice, a percentage of the signal transfers from one input port to another. A high value of the transferred signal can cha
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