Wideband slow light in photonic crystal slab waveguide based on geometry adjustment and optofluidic infiltration Morteza Janfaza and Mohammad Ali Mansouri-Birjandi* Faculty of Electrical and Computer Engineering, University of Sistan and Baluchestan (USB), P.O. Box 98164-161, Zahedan, Iran *Corresponding author: [email protected] Received 9 July 2013; revised 24 September 2013; accepted 21 October 2013; posted 22 October 2013 (Doc. ID 193514); published 21 November 2013
In this paper, a photonic crystal slab waveguide with wideband slow light, large group index (ng ), and very low group velocity dispersion (GVD) has been presented. The structure is designed by shifting the first row of the air holes adjacent to the waveguide center in the longitudinal direction, and optofluidic infiltration in the second row. By applying optimized parameters for the two rows, a flexible control of ng 17.5 < ng < 133 with large bandwidth (2 nm < Δλ < 23 nm) is obtained. The GVD decreased at the range of 10−22 s2 ∕m. Numerical simulations are performed by the three-dimensional plane-wave expansion method. © 2013 Optical Society of America OCIS codes: (130.5296) Photonic crystal waveguides; (230.5298) Photonic crystals; (230.7400) Waveguides, slab; (260.2030) Dispersion. http://dx.doi.org/10.1364/AO.52.008184
1. Introduction
Slow light tools in photonic crystal slab waveguides (PhCSWs) are highly welcomed for different fields of all-optical device design, such as optical switches, memories and buffers [1–3], quantum computing [4], all-optical signal processing systems [5], and enhanced light–matter interaction [6]. There are six major mechanisms for slowing down the velocity of light, including electromagnetic induced transparency (EIT), coherent population oscillation (CPO), stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS), soliton collision, and photonic crystal waveguides (PhCWs) [7]. Slow light in PhCWs has a wider bandwidth compared with EIT and CPO mechanisms [8]. Among various types of PhCWs, W1 slab waveguides made by removing one single row of air holes from a PhC lattice have been investigated in detail more than other types of waveguides [9–11]. 1559-128X/13/348184-06$15.00/0 © 2013 Optical Society of America 8184
APPLIED OPTICS / Vol. 52, No. 34 / 1 December 2013
Upon the appearance of distortion in an optical pulse due to high group velocity dispersion (GVD) of slow light in PhCSWs, the bandwidth of the guided mode and applications of the device will be decreased. Therefore, maximizing the bandwidth and minimizing the GVD seems to be necessary in PhCSWs. In recent years, several techniques have been presented to decrease the dispersion and control of the GVD in PhCWs. Most of these methods are based on adjusting the geometry of the waveguide. By making adjustments in some parameters, such as the width of the waveguide [12,13], the shape of the holes in the photonic crystal (PhC) lattice [14–16], and the diameter and the position of the holes adjacent to the waveguide center [17–19], the GVD can reach about zero. Infiltrating optofluidics in the first two rows adjacent to the PhCW center [20] and using a slot at the center of the PhCW [21,22] can also lead to near-zero GVD. In this paper, besides geometry adjustment, optofluidics are used to obtain low GVD. Optofluidics is a
new branch of photonics originated by the combination of optics and microfluidics [23,24]. In this method, optical fluids are injected into some holes of the PhC assuming that holes have voids that can be filled easily with fluids. Thanks to technology, one can control optofluidic properties and fabricate photonic devices in both micro and nano scales. The flexibility in configuration of the PhC devices by changing the refractive index of the fluid and the pattern of the regions under the optofluidic infiltration is another advantage of optofluidics. In this study, the suggested structure has a W1 linear defect inside the triangular lattice of air holes in a silicon substrate. To obtain high group index (ng ) and a low GVD, the first row of the holes adjacent to the waveguide center (row 1 in Fig. 1) is shifted in the x direction, and the second row (row 2 in Fig. 1) is infiltrated with an optical fluid of refractive index nf . The magnitude of shifting is Δx, and various refractive indices (nf ) for optofluid are considered. In the fabrication point of view, changing the position of the holes is more controllable than changing their diameters since the effect of time and temperature has more influence on the diameter of the holes in comparison to their position. Changing the position of the holes will result in less error (
In this paper, a photonic crystal slab waveguide with wideband slow light, large group index (ng ), and very low group velocity dispersion (GVD) has been presented. The structure is designed by shifting the first row of the air holes adjacent to the waveguide center in the longitudinal direction, and optofluidic infiltration in the second row. By applying optimized parameters for the two rows, a flexible control of ng 17.5 < ng < 133 with large bandwidth (2 nm < Δλ < 23 nm) is obtained. The GVD decreased at the range of 10−22 s2 ∕m. Numerical simulations are performed by the three-dimensional plane-wave expansion method. © 2013 Optical Society of America OCIS codes: (130.5296) Photonic crystal waveguides; (230.5298) Photonic crystals; (230.7400) Waveguides, slab; (260.2030) Dispersion. http://dx.doi.org/10.1364/AO.52.008184
1. Introduction
Slow light tools in photonic crystal slab waveguides (PhCSWs) are highly welcomed for different fields of all-optical device design, such as optical switches, memories and buffers [1–3], quantum computing [4], all-optical signal processing systems [5], and enhanced light–matter interaction [6]. There are six major mechanisms for slowing down the velocity of light, including electromagnetic induced transparency (EIT), coherent population oscillation (CPO), stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS), soliton collision, and photonic crystal waveguides (PhCWs) [7]. Slow light in PhCWs has a wider bandwidth compared with EIT and CPO mechanisms [8]. Among various types of PhCWs, W1 slab waveguides made by removing one single row of air holes from a PhC lattice have been investigated in detail more than other types of waveguides [9–11]. 1559-128X/13/348184-06$15.00/0 © 2013 Optical Society of America 8184
APPLIED OPTICS / Vol. 52, No. 34 / 1 December 2013
Upon the appearance of distortion in an optical pulse due to high group velocity dispersion (GVD) of slow light in PhCSWs, the bandwidth of the guided mode and applications of the device will be decreased. Therefore, maximizing the bandwidth and minimizing the GVD seems to be necessary in PhCSWs. In recent years, several techniques have been presented to decrease the dispersion and control of the GVD in PhCWs. Most of these methods are based on adjusting the geometry of the waveguide. By making adjustments in some parameters, such as the width of the waveguide [12,13], the shape of the holes in the photonic crystal (PhC) lattice [14–16], and the diameter and the position of the holes adjacent to the waveguide center [17–19], the GVD can reach about zero. Infiltrating optofluidics in the first two rows adjacent to the PhCW center [20] and using a slot at the center of the PhCW [21,22] can also lead to near-zero GVD. In this paper, besides geometry adjustment, optofluidics are used to obtain low GVD. Optofluidics is a
new branch of photonics originated by the combination of optics and microfluidics [23,24]. In this method, optical fluids are injected into some holes of the PhC assuming that holes have voids that can be filled easily with fluids. Thanks to technology, one can control optofluidic properties and fabricate photonic devices in both micro and nano scales. The flexibility in configuration of the PhC devices by changing the refractive index of the fluid and the pattern of the regions under the optofluidic infiltration is another advantage of optofluidics. In this study, the suggested structure has a W1 linear defect inside the triangular lattice of air holes in a silicon substrate. To obtain high group index (ng ) and a low GVD, the first row of the holes adjacent to the waveguide center (row 1 in Fig. 1) is shifted in the x direction, and the second row (row 2 in Fig. 1) is infiltrated with an optical fluid of refractive index nf . The magnitude of shifting is Δx, and various refractive indices (nf ) for optofluid are considered. In the fabrication point of view, changing the position of the holes is more controllable than changing their diameters since the effect of time and temperature has more influence on the diameter of the holes in comparison to their position. Changing the position of the holes will result in less error (
