Resonant grating polarizers made with silicon nitride, titanium dioxide, and silicon: Design, fabrication, and characterization Kyu J. Lee,1 Jerry Giese,1,2 Laura Ajayi,1,3 Robert Magnusson,1,* and Eric Johnson4 1

Department of Electrical Engineering, University of Texas at Arlington, Box 19016, Arlington, Texas 76019, USA 2 Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA 3 Sikorsky Aircraft, 6900 Main Street, Stratford, Connecticut 06615, USA 4 Department of Electrical & Computer Engineering, Clemson University, South Carolina 29634, USA * [email protected]

Abstract: We present the design, fabrication, and characterization of guided-mode resonance (GMR) linear polarizers that operate in the optical communications C-band near a wavelength of 1550 nm. We provide theoretical and experimental spectra using resonant elements fashioned in three material systems. In particular, we investigate silicon nitride resonant gratings and titanium dioxide gratings on glass substrates as well as siliconon-quartz gratings. These materials exhibit very low losses and are capable of high diffraction efficiencies and extinction ratios; thus, high-power laser applications may be enabled. We present the methods applied to fabricate these GMR devices as well as means to ascertain their fabricated physical parameters. We quantify increased polarizer bandwidth with increased grating refractive-index modulation. The numerical results obtained with the fabricated-device parameters agree well with the experimental measured spectra. ©2014 Optical Society of America OCIS codes: (050.1970) Diffractive optics; (050.6624) Subwavelength structures; (220.4241) Nanostructure fabrication; (230.5440) Polarization-selective devices.

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#205807 - $15.00 USD (C) 2014 OSA

Received 30 Jan 2014; revised 18 Mar 2014; accepted 2 Apr 2014; published 9 Apr 2014 21 April 2014 | Vol. 22, No. 8 | DOI:10.1364/OE.22.009271 | OPTICS EXPRESS 9271

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1. Introduction Polarizers are important components for many engineered optical systems. They can filter light with random polarization components to a state of desired polarization. The wire-grid polarizer (WGP) is based on the one-dimensional subwavelength grating and has been of wide interest as reported during the past several decades due to its compact size and integration capability [1–5]. However, because WGPs comprise metals, they are absorptive and can only be used in low-power applications. For high-power applications with lossy device materials, optical absorption causes the material’s temperature to increase and thermal damage can occur. This increase in temperature also changes the material’s refractive index [6,7], which may change the functionality of the device. Therefore, lossless materials are preferred in high-power applications. Multilayer, all-dielectric polarizers are widely used in optics and can be fabricated using thin-film technology; however, these dielectric multilayer polarizers work only under oblique incidence [8]. In this paper, we report new types of polarizers that employ nanophotonic resonance effects, which enable the polarizers to operate at arbitrary input angles and, notably, at normal incidence. We utilize quasi-guided, or leaky, waveguide modes arising on subwavelength periodic films. The attendant guided-mode resonance (GMR) occurs as the input light couples to leaky eigenmodes [9,10]. GMR devices are advantageous because they are relatively simple and applicable for fabrication using low-loss materials. Previously, we reported GMR polarizers consisting of an amorphous silicon (a-Si) 1-D grating on a glass substrate [11,12]. At a wavelength of 1550 nm, a-Si has an extinction coefficient of ~10−2 [13], which is relatively high compared to typical dielectric materials. Nevertheless, successful polarizers are achievable in this medium. Here, we present GMR polarizers operating at normal incidence based on nearly lossless dielectric materials such as silicon nitride (Si3N4) and titanium dioxide (TiO2). In addition, we demonstrate the bandwidth dependency of GMR polarizers on the refractive indices of the device materials with three different values. To realize a wide-bandwidth polarizer, we apply a silicon thin film, which has a high refractive index and relatively low loss at a wavelength of ~1550 nm. 2. Design of GMR polarizers To find the polarizer design parameters, we use a metaheuristic optimization algorithm known as particle swarm optimization (PSO), which is an effective method in electromagnetic design problems [14,15]. We use PSO in conjunction with rigorous coupledwave analysis to find the optimal design parameters [16]. Since Si3N4 and TiO2 are nearly lossless materials, we apply them as thin-film materials during the design step. Additionally, we apply Si for a wideband polarizer application. 2.1 GMR polarizers designed with Si3N4 thin films Figure 1 illustrates the resultant Si3N4 GMR polarizer design configuration and parameters as well as its calculated transmittance spectra for TE and TM polarizations. The Si3N4 thin film can be prepared by plasma-enhanced chemical vapor deposition (PECVD), and its refractive index is 1.80 at a wavelength of 1550 nm. This design has only a single Si3N4 layer (Si3N4 will be partially etched) and a two-part grating profile with a grating ridge width of 433 nm. The polarizer has high transmittance for TM polarization and low transmittance for TE polarization in the 1550-nm wavelength band. It has a ~4-nm bandwidth (T>97% for TM, and T95%) for TE polarization and low transmittance (97% over a ~260-nm wavelength range (~1445–1700 nm). For TE polarization, the polarizer shows T97% and T

Resonant grating polarizers made with silicon nitride, titanium dioxide, and silicon: design, fabrication, and characterization.

We present the design, fabrication, and characterization of guided-mode resonance (GMR) linear polarizers that operate in the optical communications C...
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