Experimental realization of a high-contrast grating based broadband quarter-wave plate

Mehmet Mutlu,Mutlu Gokkavas,Gokhan Kurt,Ahmet E Akosman,Ekmel Ozbay

doi:10.1364/oe.20.027966

Abstract

Fabrication and experimental characterization of a broadband quarter-wave plate, which is based on two-dimensional and binary silicon high-contrast gratings, are reported. The quarter-wave plate feature is achieved by the utilization of a regime, in which the proposed grating structure exhibits nearly total and approximately equal transmission of transverse electric and transverse magnetic waves with a phase difference of approximately π/2. The numerical and experimental results suggest a percent bandwidth of 42% and 33%, respectively, if the operation regime is defined as the range for which the conversion efficiency is higher than 0.9. A compact circular polarizer can be implemented by combining the grating with a linear polarizer.

Highlights

High-contrast gratings (HCGs), which are near-wavelength binary grating structures consisting of a high-index grating material surrounded by low-index materials [1], have attracted significant interest since the numerical [2] and experimental [3] demonstration of their diffractionfree, broadband, and high-reflectivity regimes
We have shown that a two-dimensional HCG structure with optimized geometrical parameters can be utilized for implementing a broadband circular polarizer [18]
The proposed HCG geometry is optimized such that, in the close neighborhood of λ0 = 1.55 μm, the conditions |TTM| |TTE| and ∠ (TTM) − ∠ (TTE) π/2 are satisfied simultaneously, which result in the transmission of a right-hand circularly polarized (RCP, +) and left-hand circularly polarized (LCP, −) wave assuming that the structure is illuminated by a normally incident plane wave that is linearly polarized with a polarization plane angle of 45◦ and −45◦ with respect to the x-axis on the xy-plane, respectively

Summary

Introduction

High-contrast gratings (HCGs), which are near-wavelength binary grating structures consisting of a high-index grating material surrounded by low-index materials [1], have attracted significant interest since the numerical [2] and experimental [3] demonstration of their diffractionfree, broadband, and high-reflectivity regimes. Thereafter, the extraordinary and intriguing properties of HCGs have been exploited to design and build various optical elements such as high-Q Fabry-Perot resonators [4], top mirrors in vertical-cavity surface-emitting lasers [5, 6], one- and two-dimensional hollow-core low-loss optical waveguides [7], slow-light waveguides [8], planar focusing reflectors and lenses [9, 10], monolithic cavity mirrors [11], saturable absorbers [12], resonant cavity-enhanced absorbers [13], polarizing beam-splitters [14], polarization-independent reflectors [15], and unidirectional transmission devices [16]. We have shown that a two-dimensional HCG structure with optimized geometrical parameters can be utilized for implementing a broadband circular polarizer [18]. The optimized geometrical parameters have been suggested by benefiting from the periodic dielectric slab waveguide interpretation, which is studied rigorously in [19]. The spectral transmission results obtained from the rigorous coupled-wave analysis [20] and finite-difference time-domain (FDTD) simulations (FDTD Solutions, Lumerical Inc.) have suggested that an operation percent bandwidth of 54% and 51% can be achieved, respectively, under the assump-

Methods

Results

Conclusion