Steven E. Golowich

Control of orbital angular momentum of light with optical fibers

We present a fiber-based method for generating vortex beams with a tunable value of orbital angular momentum from -1ℏ to +1ℏ per photon. We propose a new (to our knowledge) method to determine the modal content of the fiber and demonstrate high purity of the desired vortex state (97% after 20 m, even after bends and twists). This method has immediate utility for the multitude of applications in science and technology that exploit vortex light states.

On the scalability of ring fiber designs for OAM multiplexing

The promise of the infinite-dimensionality of orbital angular momentum (OAM) and its application to free-space and fiber communications has attracted immense attention in recent years. In order to facilitate OAM-guidance, novel fibers have been proposed and developed, including a class of so-called ring-fibers. In these fibers, the wave-guiding region is a high-index annulus instead of a conventional circular core, which for reasons related to polarization-dependent differential phase shifts for light at waveguide boundaries, leads to enhanced stability for OAM modes. We review the theory and implementation of this nascent class of waveguides, and discuss the opportunities and limitations they present for OAM scalability.

Long-Wave Infrared Hyperspectral Remote Sensing of Chemical Clouds: A focus on signal processing approaches

This paper focusses on the signal processing approaches necessary to achieve the three main tasks of gas-phase remote sensing: detection of a plume, identification of its constituent gases, and quantification of the amounts present. A tutorial introduction to the radiance phenomenology is given that drives the models on which exploitation algorithms are based which is followed by the fundamental aspects of the data-exploitation problem, develop algorithms that can successfully exploit data from many different sensors, and discuss the many challenges that remain open to the signal processing community. Results using real hyperspectral data sets are also presented.

Asymptotic theory of strong spin–orbit coupling in optical fiber

The spin-orbit coupling of light propagating in optical fiber can be dramatically enhanced by the presence of a high-contrast interface in the refractive index profile, even for modes that are highly paraxial. The resulting modes have spatial and polarization structures that depart greatly from the weak coupling form, and, in particular, are neither orbital nor spin angular momentum eigenstates. We explain the physical origins of this strong-coupling regime with a vector geometric theory of diffraction expansion.

Multimode Communications Using Orbital Angular Momentum

In this chapter, we provide a comprehensive review of multimode communications using OAM. The fundamentals of OAM are introduced first followed by the techniques for OAM generation, multiplexing/demultiplexing, and detection. We then present recent research efforts to free-space communication links and fiber-based transmission links using OAM multiplexing together with optical signal processing using OAM (data exchange, add/drop, multicasting, monitoring, and compensation). Future challenges of OAM communications are discussed at the end.

Fibers Supporting Orbital Angular Momentum States for Information Capacity Scaling

A novel mode-division-multiplexing scheme would be provided by fibers supporting stable orbital angular momentum states. We present a new class of air-core fibers that achieves this goal through enhancement of vector propagation effects.

Impact of fiber design on polarization dependence in microbend gratings.

Polarization dependence in microbend gratings is an inherent problem. We formulate simple analytical expressions to describe it, and demonstrate their effectiveness via a comparison with experimental results on a standard transmission fiber. The ability to control polarization dependence with fiber design potentially enables replacing UV-LPGs within low-cost, tunable microbend gratings.

Scattering Resonances of Microstructures and Homogenization Theory

Scattering resonances are the eigenvalues and corresponding eigenmodeswhich solve the Schrodinger equation

Complex mode amplitude measurement for a six-mode optical fiber

H\psi=E\psi

Performance limits of LWIR gaseous plume quantification

for a Hamiltonian, H, subject to the condition of outgoing radiation at infinity. We consider the scattering resonance problem for potentials which are rapidly varying in space and are not necessarily small in a pointwise sense. Such potentials are of interest in many applications in quantum, electromagnetic, and acoustic scattering, where the environment consists of microstructure, e.g., rapidly varying material properties. Of particular interest in applications are high contrast microstructures, e.g., large pointwise variations of material properties.We develop a perturbation theory for the scattering resonances and eigenvalues of such high contrast and oscillatory potentials. The expansion is proved to be convergent in a norm which encodes the degree of oscillation in the microstructure. Next, we consider the concrete example of two-dimensional microstructure potentials. These corres...