J. E. Sipe

Tilted fiber phase gratings

A detailed theoretical treatment is presented of bound-mode to bound-mode Bragg reflection and bound-mode to radiation-mode coupling loss in a tilted optical-fiber phase grating. Numerical predictions of the effects of grating tilt on the spectral characteristics of such a grating are calculated. These predictions are compared with experimentally measured spectra of strong gratings written by ultraviolet irradiation of deuterium-sensitized fiber with grating tilt angles ranging from 0° to 15°. Good agreement is obtained between the theoretical predictions and the experimental results.

Optical properties of photosensitive fiber phase gratings

The authors measure and calculate the optical properties of strong ( delta n/n approximately 10/sup -3/) in-core optical fiber phase gratings written by the UV laser sidewriting technique. A pronounced fine structure on the main reflection peak is observed and explained, along with a short wavelength loss associated with radiation mode coupling, modulated by cladding effects. >

Phenomenological treatment of surface second-harmonic generation

A phenomenological treatment of surface second-harmonic generation that can be applied to a host of geometries of interest is presented. We consider four standard experimental geometries and show that the expressions for the surface second-harmonic generated power can all be written in one compact form, from which the dependence of the signal on polarization, angle of incidence, and other experimental parameters can be extracted. The bulk second-harmonic generation is also included with this formalism, as we show explicity for one geometry.

Nanoscale porous silicon waveguide for label-free DNA sensing

Porous silicon (PSi) is an excellent material for biosensing due to its large surface area and its capability for molecular size selectivity. In this work, we report the experimental demonstration of a label-free nanoscale PSi resonant waveguide biosensor. The PSi waveguide consists of pores with an average diameter of 20nm. DNA is attached inside the pores using standard amino-silane and glutaraldehyde chemistry. Molecular binding in the PSi is detected optically based on a shift of the waveguide resonance angle. The magnitude of the resonance shift is directly related to the quantity of biomolecules attached to the pore walls. The PSi waveguide sensor can selectively discriminate between complementary and non-complementary DNA. The advantages of the PSi waveguide biosensor include strong field confinement and a sharp resonance feature, which allow for high sensitivity measurements with a low detection limit. Simulations indicate that the sensor has a detection limit of 50nM DNA concentration or equivalently, 5pg/mm2.

Propagation through nonuniform grating structures

We consider linear propagation through shallow, nonuniform gratings, such as those written in the core of photosensitive optical fibers. Though, of course, the coupled-mode equations for such gratings are well known, they are often derived heuristically. Here we present a rigorous derivation and include effects that are second order in the grating parameters. While the resulting coupled-mode equations can easily be solved numerically, such a calculation often does not give direct insight into the qualitative nature of the response. Here we present a new way of looking at nonuniform gratings that immediately does yield such insight and, as well, provides a convenient starting point for approximate treatments such as WKB analysis. Our approach, which is completely within the context of coupled-mode theory, makes use of an effective-medium description, in which one replaces the (in general, nonuniform) grating by a medium with a frequency-dependent refractive index distribution but without a grating.

Nonlinear Schrödinger solitons in a periodic structure

It is demonstrated theoretically that a nonlinear medium with a spatially periodic refractive index can support solitons of the nonlinear Schrodinger equation.

III – Gap Solitons

This chapter describes the gap solitons. Gap solitons are electromagnetic field structures that can exist in a nonlinear optical medium if there is also a periodic variation in the linear optical properties over a length scale on the order of the wavelength of light. The chapter outlines coupled-mode theory, leading to the nonlinear coupled-mode equations and describes the three sets of solutions to the coupled-mode equations, including stationary solutions, solitary-wave solutions, and soliton solutions. The chapter investigates the relationship between these solitons and the solitary-wave solutions and also the relationship with regular fiber solitons. The numerical solutions show that periodic nonlinear media exhibit self-pulsations that become chaotic at high intensities. The issues involved in trying to generate gap solitons are discussed and experimental schemes to detect gap solitons in the laboratory are outlined in the chapter.

Third order optical nonlinearity of graphene

We perform a perturbative calculation of the third order optical conductivities of doped graphene, using approximations valid around the Dirac points and neglecting effects due to scattering and electron–electron interactions. In this limit analytic formulas can be constructed for the conductivities. We discuss in detail the results for third harmonic generation, the Kerr effect and two-photon carrier injection, parametric frequency conversion, and two-color coherent current injection. We find a complicated dependence on the chemical potential and photon energies. The linear dispersion causes resonances over a wide range of photon energies, and it is possible to obtain large optical nonlinearities by tuning the chemical potential.

Long-period fiber gratings as band-rejection filters

Optical fiber communication systems that use optical amplifiers are increasingly seeking high-performance devices that function as spectrally-selective band-rejection filters. For example, ASE filters that improve erbium amplifier performance and band-rejection filters in Raman lasers/amplifiers1 must have low insertion losses and low back-reflections. In addition, they must be relatively inexpensive to mass-produce and should be compact after packaging. While bulk-optic filters and short-period Bragg gratings2,3 can be used for some of the applications, all the aforementioned requirements are rarely met. In this paper, we present a novel class of photoinduced, long-period fiber gratings that function as highly-efficient band-rejection filters.

Ultra-low power generation of twin photons in a compact silicon ring resonator

We demonstrate efficient generation of correlated photon pairs by spontaneous four wave mixing in a 5 μm radius silicon ring resonator in the telecom band around 1550 nm. By optically pumping our device with a 200 μW continuous wave laser, we obtain a pair generation rate of 0.2 MHz and demonstrate photon time correlations with a coincidence-to-accidental ratio as high as 250. The results are in good agreement with theoretical predictions and show the potential of silicon micro-ring resonators as room temperature sources for integrated quantum optics applications.