Subwavelength Lattice Research Articles

Subwavelength lattice optics by evolutionary design.

This paper describes a new class of structured optical materials—lattice opto-materials—that can manipulate the flow of visible light into a wide range of three-dimensional profiles using evolutionary design principles. Lattice opto-materials are based on the discretization of a surface into a two-dimensional (2D) subwavelength lattice whose individual lattice sites can be controlled to achieve a programmed optical response. To access a desired optical property, we designed a lattice evolutionary algorithm that includes and optimizes contributions from every element in the lattice. Lattice opto-materials can exhibit simple properties, such as on- and off-axis focusing, and can also concentrate light into multiple, discrete spots. We expanded the unit cell shapes of the lattice to achieve distinct, polarization-dependent optical responses from the same 2D patterned substrate. Finally, these lattice opto-materials can also be combined into architectures that resemble a new type of compound flat lens.

Suspended SOI waveguide with sub-wavelength grating cladding for mid-infrared.

We present a new type of mid-infrared silicon-on-insulator (SOI) waveguide. The waveguide comprises a sub-wavelength lattice of holes acting as lateral cladding while at the same time allowing for the bottom oxide (BOX) removal by etching. The waveguide loss is determined at the wavelength of 3.8 μm for structures before and after being underetched using both vapor phase and liquid hydrofluoric acid (HF). A propagation loss of 3.4 dB/cm was measured for a design with a 300 nm grating period and 150 nm holes after partial removal (560 nm) of BOX by vapor phase HF etching. We also demonstrate an alternative design with 550 nm period and 450 nm holes, which allows a faster and complete removal of the BOX by liquid phase HF etching, yielding the waveguide propagation loss of 3.6 dB/cm.

Multistability and switching in a superconducting metamaterial.

The field of metamaterial research revolves around the idea of creating artificial media that interact with light in a way unknown from naturally occurring materials. This is commonly achieved using sub-wavelength lattices of electronic or plasmonic structures, so-called meta-atoms. One of the ultimate goals for these tailored media is the ability to control their properties in situ. Here we show that superconducting quantum interference devices can be used as fast, switchable meta-atoms. We find that their intrinsic nonlinearity leads to simultaneously stable dynamic states, each of which is associated with a different value and sign of the magnetic susceptibility in the microwave domain. Moreover, we demonstrate that it is possible to switch between these states by applying nanosecond-long pulses in addition to the microwave-probe signal. Apart from potential applications for this all-optical metamaterial switch, the results suggest that multistability can also be utilized in other types of nonlinear meta-atoms.

High-Rotational Symmetry Lattices Fabricated by Moiré Nanolithography

This paper describes a new nanofabrication method, moiré nanolithography, that can fabricate subwavelength lattices with high-rotational symmetries. By exposing elastomeric photomasks sequentially at multiple offset angles, we created arrays with rotational symmetries as high as 36-fold, which is three times higher than quasiperiodic lattices (≤12-fold) and six times higher than two-dimensional periodic lattices (≤6-fold). Because these moiré nanopatterns can be generated over wafer-scale areas, they are promising for a range of photonic applications, especially those that require broadband, omnidirectional absorption of visible light.

OPTICAL PROPERTIES OF PHOTONIC CRYSTAL FIBERS WITH A FIBER CORE OF ARRAYS OF SUBWAVELENGTH CIRCULAR AIR HOLES: BIREFRINGENCE AND DISPERSION

We propose a kind of novel photonic crystal flbers (PCFs) based on a flber core with arrays of subwavelength circular air holes, achieving the ∞exible control of the birefringence or the dispersion property of the PCFs. A highly birefringent (HB) PCF is achieved by employing arrays of subwavelength circular air hole pairs in the flber core, which are arranged as a conventional hexagonal lattice structure with a subwavelength lattice constant. The HB-PCF is with uniform and ultrahigh birefringence (up to the order of 0.01) in a wavelength region from 1.25m to 1.75m or even a larger region, which, to the best of our knowledge, is the best birefringence property of the PCFs. A dispersion-∞attened (DF) PCF with near-zero dispersion is achieved by employing arrays of subwavelength circular air holes in the flber core arranged as a conventional hexagonal lattice structure with a subwavelength lattice constant, which contributes negative waveguide dispersion to the PCF. The proposed design of the DF-PCF provides an alternate approach for the dispersion control of the PCF. Besides the high birefringence and the ∞attened near-zero dispersion, the proposed PCFs with a flber core of arrays of subwavelength circular air holes have the potential to achieve a large mode area single mode PCF.

State-dependent, addressable subwavelength lattices with cold atoms

We discuss how adiabatic potentials can be used to create addressable lattices on a subwavelength scale, which can be used as a tool for local operations and readout within a lattice substructure, while taking advantage of the faster timescales and higher energy and temperature scales determined by the shorter lattice spacing. For alkaline-earth-like atoms with nonzero nuclear spin, these potentials can be made state-dependent, for which we give specific examples with 171Yb atoms. We discuss in detail the limitations in generating the lattice potentials, in particular non-adiabatic losses, and show that the loss rates can always be made exponentially small by increasing the laser power.

Optical interaction between a dielectric tip and a nanometric lattice: implications for near-field microscopy

We make a theoretical analysis of the interaction of the field transmitted by a subwavelength tip and a two-dimensional subwavelength lattice. Such a model provides a new insight into the resolution achievable by near-field microscopy and confirms the experimental results obtained recently. In the present model the probe, characterized by its electric dipolar susceptibility, is assumed to be locally spherical, and the representation of the sample is based on a discrete description of the matter. This permits separation of the electric field detected by the probe after reflection into two different parts that describe both the continuum character and the corrugation of the surface. Numerical results performed on a two-dimensional lattice are similar to those obtained by atomic force microscopy and exhibit specific behavior such as a strong dependence on the polarization of the incident field.