A highly efficient asymmetric transmission device for arbitrary linearly polarized light

Highlights

• A nanophotonic optical asymmetric transmission device (NOATD) for the arbitrary linear polarization is proposed.

• Highly efficient asymmetric transmission for both TM and TE polarizations, as well as the linear polarization along the 45° as an example are demonstrated, to show the unique capability of our device.

• The NOATD can work for arbitrarily linearly polarized light, which is linear combinations of TM and TE polarization states.

• The design principle can deepen the understanding of nanophotonic asymmetric transmission devices and can be further applied to design different types of photonic devices.

Abstract

In this paper, we theoretically demonstrate a nanophotonic optical asymmetric transmission device (NOATD) for arbitrary linear polarization, which is composed of two two-dimensional (2D) square-lattice photonic crystals (PhCs) with different effective refractive indices. In this way, the NOATD achieves asymmetric transmission based on the generalized total reflection principle, which is able to realize a high forward transmittance (>0.6) and contrast ratio (>0.9) for arbitrary linearly polarized light in a broad wavelength range (>100 nm).

Introduction

Highly efficient optical asymmetric transmission devices are indispensable for optical quantum computing and information processing [[1], [2], [3], [4], [5], [6], [7], [8], [9], [10]]. Among them, nanophotonic optical asymmetric transmission devices (NOATD) have attracted broad attention as they can be integrated in photonic chips [[11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28]]. According to the working principles, there are two types of NOATDs: nonreciprocal NOATDs and reciprocal NOATDs. The nonreciprocal NOATDs work by breaking the time-inverse symmetry (breaking the Lorentz reciprocity) which requires optical nonlinearity or a magneto-optical effect [[1], [2], [3]]. In comparison, the reciprocal NOATDs break the space-inverse symmetry by diffractive asymmetric transmission [4,5]. The reciprocal NOATDs are preferable because they do not require an external magnetic field or strong incident light. A number of reciprocal NOATDs have been proposed utilizing metamaterials [6,7], photonic crystals [8,9], slab waveguides [10], surface plasmon [11], and resonant effects [12].

An ideal NOATD should have a high forward transmittance and transmission contrast ratio (defined as the ratio of the forward and backward transmittance) for arbitrary polarization states, because the polarization state is a fundamental property of light, which can be applied to encode information [29,30]. In addition, the NOATD structure should be compatible with semiconductor CMOS processes for on-chip integration. To realize this, NOATDs based on dielectric photonic crystals (PhCs) have been proposed to achieve efficient asymmetric propagation of light [26] because of the unique optical properties of PhCs that can be flexibly tuned by structure parameters and the compatibility of CMOS fabrication process. It has been demonstrated that the NOATD-based silicon PhC structures achieved polarization-independent asymmetric transmission, and the forward transmittance for TE and TM polarizations is 0.46, which is the state-of-the-art high forward transmittance [27] to the best of our knowledge. Therefore, it is necessary to further improve the forward transmittance (to be >0.5) and the contrast ratio (>0.9) to meet the stringent requirements of optical communication and quantum computing.

Herein, we theoretically demonstrate an NOATD based on a 2D PhC heterostructure, which is able to achieve asymmetric transmission of the arbitrary linearly polarized light with a high forward transmittance. The NOATD can work for arbitrarily linearly polarized light, which comprises linear combinations of TM and TE polarization states. The high forward transmittance (>0.6) and the high contrast ratio (>0.93) in the wavelength range of 1533–1634 nm with a broad bandwidth (up to 101 nm) for different linear polarizations are achieved.