Marian Florescu

Designer disordered materials with large, complete photonic band gaps.

We present designs of 2D, isotropic, disordered, photonic materials of arbitrary size with complete band gaps blocking all directions and polarizations. The designs with the largest band gaps are obtained by a constrained optimization method that starts from a hyperuniform disordered point pattern, an array of points whose number variance within a spherical sampling window grows more slowly than the volume. We argue that hyperuniformity, combined with uniform local topology and short-range geometric order, can explain how complete photonic band gaps are possible without long-range translational order. We note the ramifications for electronic and phononic band gaps in disordered materials.

Complete band gaps in two-dimensional photonic quasicrystals

Princeton Center for Theoretical Sciences, Princeton University, Princeton, New Jersey 08544, USA(Dated: July 22, 2010)We introduce a novel optimization method to design the first examples of photonic quasicrystalswith substantial, complete photonic band gaps (PBGs): that is, a range of frequencies over whichelectromagnetic wave propagation is forbidden for all directions and polarizations. The methodcan be applied to photonic quasicrystals with arbitrary rotational symmetry; here, we illustrate theresults for 5- and 8-fold symmetric quasicrystals. The optimized band gaps are highly isotropic,which may offer advantages over photonic crystals for certain applications.

Photonic bandgap materials: towards an all-optical micro-transistor

We describe all-optical transistor action in photonic bandgap (PBG) materials doped with active atoms and analyse the advantages of this system over other all-optical transistor proposals. In the presence of a PBG material, a coherent laser beam with the frequency slightly detuned from the resonant atomic transition frequency can drive a collection of two-level atoms to an almost totally inverted state, a phenomenon strictly forbidden in ordinary vacuum. By varying the laser field intensity in the neighbourhood of a threshold value, it is possible to drive the atomic system through a transition from states in which the atoms populate preferentially the ground level to almost totally inverted states. In this process, the atomic system switches from a passive medium (highly absorptive) to a active medium (highly amplifying). The large differential gain exhibited by the atomic medium is very robust with respect to nonradiative relaxation and dephasing mechanisms. The switching action in a PBG material is not associated with operation near a narrow cavity resonance with conventional trade-off between switching time and switching threshold intensity. Rather it is associated with an abrupt discontinuity in the engineered broad-band electromagnetic density of states of the PBG material. We demonstrate all-optical transistor action in PBG materials by analysing the absorption spectrum of a second probe laser beam and we show that the probe beam experiences a substantial differential gain by slight intensity modulations in the control laser field. Under certain conditions, the fluctuations in the number of totally inverted atoms that contribute to the amplification process are strongly diminished (the statistics of the excited atoms becomes sub-Poissonian), which, in turn, determines a very low-noise regime of amplification.

Isotropic band gaps and freeform waveguides observed in hyperuniform disordered photonic solids

Recently, disordered photonic media and random textured surfaces have attracted increasing attention as strong light diffusers with broadband and wide-angle properties. We report the experimental realization of an isotropic complete photonic band gap (PBG) in a 2D disordered dielectric structure. This structure is designed by a constrained optimization method, which combines advantages of both isotropy due to disorder and controlled scattering properties due to low-density fluctuations (hyperuniformity) and uniform local topology. Our experiments use a modular design composed of Al2O3 walls and cylinders arranged in a hyperuniform disordered network. We observe a complete PBG in the microwave region, in good agreement with theoretical simulations, and show that the intrinsic isotropy of this unique class of PBG materials enables remarkable design freedom, including the realization of waveguides with arbitrary bending angles impossible in photonic crystals. This experimental verification of a complete PBG and realization of functional defects in this unique class of materials demonstrate their potential as building blocks for precise manipulation of photons in planar optical microcircuits and has implications for disordered acoustic and electronic band gap materials.

Photonic band gap in isotropic hyperuniform disordered solids with low dielectric contrast

We report the first experimental demonstration of a TE-polarization photonic band gap (PBG) in a 2D isotropic hyperuniform disordered solid (HUDS) made of dielectric media with a dielectric index contrast of 1.6:1, very low for PBG formation. The solid is composed of a connected network of dielectric walls enclosing air-filled cells. Direct comparison with photonic crystals and quasicrystals permitted us to investigate band-gap properties as a function of increasing rotational isotropy. We present results from numerical simulations proving that the PBG observed experimentally for HUDS at low index contrast has zero density of states. The PBG is associated with the energy difference between complementary resonant modes above and below the gap, with the field predominantly concentrated in the air or in the dielectric. The intrinsic isotropy of HUDS may offer unprecedented flexibilities and freedom in applications (i. e. defect architecture design) not limited by crystalline symmetries.

Optical cavities and waveguides in hyperuniform disordered photonic solids

Using finite difference time domain and band structure computer simulations, we show that it is possible to construct optical cavities and waveguide architectures in hyperuniform disordered photonic solids that are unattainable in photonic crystals. The cavity modes can be classified according to the symmetry (monopole, dipole, quadrupole,etc.) of the confined electromagnetic wave pattern. Owing to the isotropy of the band gaps characteristic of hyperuniform disordered solids, high-quality waveguides with freeform geometries (e.g., arbitrary bending angles) can be constructed that have no analogue in periodic or quasiperiodic solids. These capabilities have implications for many photonic applications.

Single photons on demand from 3D photonic band-gap structures

We describe a practical implementation of a (semi-deterministic) photon gun based on stimulated Raman adiabatic passage pumping and the strong enhancement of the photonic density of states in a photonic band-gap material. We show that this device allows deterministic and unidirectional production of single photons with a high repetition rate of the order of 100 kHz. We also discuss specific 3D photonic micro-structure architectures in which our model can be realized and the feasibility of implementing such a device using Er3+ ions that produce single photons at the telecommunication wavelength of 1.55 μm.

Thermal emission from finite photonic crystals

We present a microscopic theory of thermal emission from finite-sized photonic crystals and show that the directional spectral emissivity and related quantities can be evaluated via standard bandstructure computations without any approximation. We then identify the physical mechanisms through which interfaces modify the potentially super-Planckian radiation flow inside infinite photonic crystals, such that thermal emission from finite-sized samples is consistent with the fundamental limits set by Planck’s law. As an application, we further demonstrate that a judicious choice of a photonic crystal’s surface termination facilitates considerable control over both the spectral and angular thermal emission properties.

Single photons on demand from tunable 3D photonic band-gap structures

In this article we propose to build a (semi-)deterministic photon gun by modifying the spontaneous decay in a photonic band-gap material. We show that such a device allows for deterministic and unidirectional single-photon emission with a repetition rate of the order of 100 kHz. We describe a specific realization of the 1D band-gap model by means of a 3D photonic-crystal heterostructure and the feasability of implementing such a device using Er3+ ions that produce single photons at the telecommunication wavelength of 1.55,μm, important for many applications.

Local self-uniformity in photonic networks

The interaction of a material with light is intimately related to its wavelength-scale structure. Simple connections between structure and optical response empower us with essential intuition to engineer complex optical functionalities. Here we develop local self-uniformity (LSU) as a measure of a random networks internal structural similarity, ranking networks on a continuous scale from crystalline, through glassy intermediate states, to chaotic configurations. We demonstrate that complete photonic bandgap structures possess substantial LSU and validate LSUs importance in gap formation through design of amorphous gyroid structures. Amorphous gyroid samples are fabricated via three-dimensional ceramic printing and the bandgaps experimentally verified. We explore also the wing-scale structuring in the butterfly Pseudolycaena marsyas and show that it possesses substantial amorphous gyroid character, demonstrating the subtle order achieved by evolutionary optimization and the possibility of an amorphous gyroids self-assembly.