In this paper, we present a new type of optical fiber, called universal fiber, which can be used for both multimode and single mode transmissions. The fiber is a multimode fiber that has an LP01 mode field diameter approximately matched to that of standard single mode fiber. First, we will present the universal fiber design concept and discuss design tradeoffs for both single mode and multimode operations. Then we will show characterizations of a preliminary experimental fiber and present system testing results with 110 m, 150 m and 2700 m system reach using 100G SR4, 40G sWDM multimode and 100G CWDM4 single mode transceivers, respectively, which demonstrate both multimode and single mode transmission capabilities of universal fiber.
Radiation pressure and photon momentum in negative-index media are no different than their counterparts in ordinary (positive-index) materials. This is because the parameters responsible for these properties are the admittance √ε /μ and the group refractive index n<sub>g</sub> of the material (both positive entities), and not the phase refractive index n =√με , which is negative in negative-index media. One approach to investigating the exchange of momentum between electromagnetic waves and material media is via the Doppler shift phenomenon. In this paper we use the Doppler shift to arrive at an expression for the radiation pressure on a mirror submerged in a negative-index medium. In preparation for the analysis, we investigate the phenomenon of Doppler shift in various settings, and show the conditions under which a so-called “inverse” Doppler shift could occur. We also argue that a recent observation of the inverse Doppler shift upon reflection from a negative-index medium cannot be correct, because it violates the conservation laws.
In a recent paper we explored the novel reflection properties of several conical optical elements using
numerical simulations based on Maxwell's equations. For example, in the case of a hollow metallic cone having
an apex angle of 90°, a circularly-polarized incident beam acquires, upon reflection, the opposite spin angular
momentum in addition to an orbital angular momentum twice as large as the spin, whereas a 90° cone made of a
transparent material in which the incident light suffers two total internal reflections before returning, may be
designed to endow the retro-reflected beam with different mixtures of orbital and spin angular momenta. In the
present paper we introduce an approximate analysis based on the Jones calculus to elucidate the physics
underlying the reflection properties, and we point to the strengths and weaknesses of the approach.
The classical theory of electromagnetism is based on Maxwell's macroscopic equations, an energy
postulate, a momentum postulate, and a generalized form of the Lorentz law of force. These seven postulates
constitute the foundation of a complete and consistent theory, thus eliminating the need for physical models of
polarization P and magnetization M - these being the distinguishing features of Maxwell's macroscopic equations.
In the proposed formulation, P(r,t) and M(r,t) are arbitrary functions of space and time, their physical properties
being embedded in the seven postulates of the theory. The postulates are self-consistent, comply with special
relativity, and satisfy the laws of conservation of energy, linear momentum, and angular momentum. The Abraham
momentum density p<sub>EM</sub>(r,t)=E(r, t)×H(r,t)/c<sup>2</sup> emerges as the universal electromagnetic momentum that does not
depend on whether the field is propagating or evanescent, and whether or not the host media are homogeneous,
transparent, isotropic, linear, dispersive, magnetic, hysteretic, negative-index, etc. Any variation with time of the
total electromagnetic momentum of a closed system results in a force exerted on the material media within the
system in accordance with the generalized Lorentz law.
Electromagnetic waves carry the Abraham momentum, whose density is given by p<sub>EM</sub> = S(r,t)/c<sup>2</sup>. Here
S(r, t) = E(r, t)×H(r, t) is the Poynting vector at point r in space and instant t in time, E and H are the local
electromagnetic fields, and c is the speed of light in vacuum. The above statement is true irrespective of whether the
waves reside in vacuum or within a ponderable medium, which medium may or may not be homogeneous, isotropic,
transparent, linear, magnetic, etc. When a light pulse enters an absorbing medium, the force experienced by the
medium is only partly due to the absorbed Abraham momentum. This absorbed momentum, of course, is
manifested as Lorentz force (while the pulse is being extinguished within the absorber), but not all the Lorentz force
experienced by the medium is attributable to the absorbed Abraham momentum. We consider an absorptive/
reflective medium having the complex refractive index n<sub>2</sub>+i κ<sub>2</sub>, submerged in a transparent dielectric of refractive
index n<sub>1</sub>, through which light must travel to reach the absorber/reflector. Depending on the impedance-mismatch
between the two media, which mismatch is dependent on n<sub>1</sub>, n<sub>2</sub>, κ<sub>2</sub>, either more or less light will be coupled into the
absorber/reflector. The dependence of this impedance-mismatch on n<sub>1</sub> is entirely responsible for the appearance of
the Minkowski momentum in certain radiation pressure experiments that involve submerged objects.
In a recent paper, W. She, J. Yu and R. Feng reported the slight deformations observed upon transmission
of a light pulse through a short length of a silica glass nano-filament. Relating the shape and magnitude of these
deformations to the momentum of the light pulse inside and outside the filament, these authors concluded that,
within the fiber, the photons carry the Abraham momentum. We present an alternative evaluation of force and
momentum in a system similar to the experimental setup of She et al. Using precise numerical calculations that take
into account not only the electromagnetic momentum inside and outside the filament, but also the Lorentz force
exerted by a light pulse in its entire path through the nano-waveguide, we conclude that the net effect should be a
pull (rather than a push) force on the end face of the nano-filament.
We propose a method of optical data storage that exploits the small dimensions of metallic nano-particles
and/or nano-structures to achieve high storage densities. The resonant behavior of these particles (both individual and in
small clusters) in the presence of ultraviolet, visible, and near-infrared light may be used to retrieve pre-recorded
information by far-field spectroscopic optical detection. In plasmonic data storage, a femtosecond laser pulse is focused
to a diffraction-limited spot over a small region of an optical disk containing metallic nano-structures. The digital
information stored in each bit-cell modifies the spectrum of the femtosecond light pulse, which is subsequently detected
in transmission (or reflection) using an optical spectrum analyzer. We present theoretical as well as preliminary
experimental results that confirm the potential of plasmonic nano-structures for high-density optical storage applications.
The Bloch modes of a periodic slit array in a metallic slab are identified, then used to
investigate the transmission of light through sub-wavelength slits residing in a finite-thickness slab.
Specifically, the Bloch mode method is used here to study Fabry-Perot-like resonances within
individual slits, in conjunction with the onset of surface plasmon polariton (SPP) resonances and in
the vicinity of the Wood anomalies. Although the results largely agree with our earlier numerical
simulations obtained with the Finite-Difference-Time-Domain (FDTD) method, there are
indications that the FDTD method has difficulty with convergence at and around resonances; the
points of agreement and disagreement between the two methods are discussed in the present paper.
When the period <i>p</i> of the slit array is comparable to (or somewhat below) the incident wavelength
λ<sub>o</sub>, the Bloch mode method requires only the 10-20 lowest-order modes of the slit array to achieve
stable solutions; we find the Bloch mode method to be an effective tool for studying dielectric-filled
apertures in highly conductive hosts.
Two formulations of the Lorentz law of force in classical electrodynamics yield identical results for the total force (and total torque) of radiation on a solid object. The object may be surrounded by the free space or immersed in a transparent dielectric medium such as a liquid. We discuss the relation between these two formulations and extend the proof of their equivalence to the case of solid objects immersed in a transparent medium.
Optically-pumped vertical external cavity semiconductor lasers offer the exciting possibility of designing kW-class solid state lasers that provide significant advantages over their doped YAG, thin-disk YAG and fiber counterparts. The basic VECSEL/OPSL (optically-pumped semiconductor laser) structure consists of a very thin (approximately 6 micron thick) active mirror consisting of a DBR high-reflectivity stack followed by a multiple quantum well resonant periodic (RPG) structure. An external mirror (reflectivity typically between 94%-98%) provides conventional optical feedback to the active semiconductor mirror chip. The "cold" cavity needs to be designed to take into account the semiconductor sub-cavity resonance shift with temperature and, importantly, the more rapid shift of the semiconductor material gain peak with temperature. Thermal management proves critical in optimizing the device for serious power scaling. We will describe a closed-loop procedure that begins with a design of the semiconductor active epi structure. This feeds into the sub-cavity optimization, optical and thermal transport within the active structure and thermal transport though the various heat sinking elements. Novel schemes for power scaling beyond current record performances will be discussed.
The Finite-Difference Time-Domain (FDTD) method is often a viable alternative to other computational methods used for the design of sub-wavelength components of photonic devices. We describe an FDTD based grid refinement method, which reduces the computational cell size locally, using a collection of nested rectangular grid patches. On each patch, a standard FDTD update of the electromagnetic fields is applied. At the coarse/fine grid interfaces the solution is interpolated, and consistent circulation of the fields is enforced on shared cell edges. Stability and accuracy of the scheme depend critically on the update scheme, space and time interpolation, and a proper implementation of flux conditions at mesh boundaries. Compared to the conformal grid refinement, the method enables better efficiency by using non-conformal grids around the region of interest and by refining both space and time dimensions, which leads to considerable savings in computation time. We discuss the advantages and shortcomings of the method and present its application to the problem of computation of a quality factor of a 3-D photonic crystal microcavity.
We propose the general idea of constructing an ultra-compact optical pickup based on photonic crystals. A few optical components necessary for various functions of an optical head are designed and analyzed.
Uniform, nonuniform and adaptive mesh refinement FDTD approaches to solving 3D Maxwell's equations are compared and contrasted. Specific applications of such schemes to optical memory, nanophotonics and plasmonics problems will be illustrated.
Modeling of high-power diodes poses several numerical problems. They require algorithms capable of capturing accurately the fast temporal and spatial dynamics in a broad spectral range. Another problem is how to reconcile vastly different time scales of various physical processes involved. We present an outline of a semiconductor laser simulation engine that incorporates both the first-principles many body gain calculations, and the carrier and heat transport simulation into an interactive computer laser model.
A general scheme for the determination of vital operating characteristics of semiconductor lasers from low intensity photo-luminescence spectra is outlined and demonstrated. A fully microscopic model for the optical properties is coupled to a drift-diffusion model for the mesoscopic charge and field distributions to calculate luminescence and gain spectra in barrier-doped laser material. Analyzing experiments on an optically pumped multi quantum-well structure it is shown that the electric fields arising from the charges of ionized dopants lead to strongly excitation dependent optical properties like significant differences between luminescence and gain wavelengths.
We present a comparison of experimental and microscopically based model results for optically pumped vertical external cavity surface emitting semiconductor lasers. The quantum well gain model is based on a quantitative ab-initio approach that allows calculation of a complex material susceptibility dependence on the wavelength, carrier density and lattice temperature. The gain model is coupled to the macroscopic thermal transport, spatially resolved in both the radial and longitudinal directions, with temperature and carrier density dependent pump absorption. The radial distribution of the refractive index and gain due to temperature variation are computed. Thermal managment issues, highlighted by the experimental data, are discussed. Experimental results indicate a critical dependence of the input power, at which thermal roll-over occurs, on the thermal resistance of the device. This requires minimization of the substrate thickness and optimization of the design and placement of the heatsink. Dependence of the model results on the radiative and non-radiative carrier recombination lifetimes and cavity losses are evaluated.
A general scheme for the determination of vital operating characteristics of semiconductor lasers from low intensity photo-luminescence spectra is outlined and demonstrated. A fully microscopic model for the calculation of optical properties is coupled to a drift diffusion model for the mesoscopic charge and electric field distributions to calculate photo-luminescence and gain spectra in barrier-doped semiconductor laser material. Analyzing experiments on an optically pumped multi quantum-well structure it is demonstrated that the electric fields arising from the space charges of ionized dopants contribute to strongly excitation dependent optical properties, such as significant shifts of the luminescence versus peak gain wavelengths.