Several waveguide solutions based on technologies from both electronics and photonics have been proposed for guiding Terahertz (THz) radiation. Hollow-core dielectric waveguides are one of the best options for guiding THz radiation since the material absorption is almost zero in the air-core. However, these waveguides are usually multimode and have dimensions in the order of a few millimeters. Here we propose a hollow-core waveguide with sub-wavelength scale metallic wires in the cladding for THz guidance. The theoretical studies show that such a hybrid cladding reflects the transverse magnetic (TM) waves and transmits the transverse electric (TE) waves, leading to a waveguide structure that only confines TM modes. The numerical simulations show a pure single mode, single polarization operation window from 0.22 THz to 0.34 THz and 14.8 dB/m propagation loss at 0.29 THz. Compared to a metallic waveguide with similar dimension, the proposed waveguide more than doubles the single mode operation bandwidth with comparable losses. We discuss the effect of optical and structural parameters of the hybrid cladding on the single mode operating window and propagation losses, and suggest methods of fabrication of the waveguide. The design principle of the proposed waveguide can be extended to the mid-inferred spectrum.
Polymer optical fibres (POF) have historically focused on applications in data transmission over short distances, using
highly multimode step-index or graded-index fibre designs. This paper will focus on a qualitatively different type of
polymer fibres - microstructured polymer optical fibres (mPOF) - which allow a wider variety of fibre designs and
optical properties to be achieved. Fibres with similar properties to conventional step- and graded-index POF can be made
for data transmission applications, as well as single-mode fibres which can be used for grating inscription and gratingbased
sensing. The use of microstructures can also be extended to longer wavelengths for the transmission of THz
radiation, and both solid-core and hollow-core mPOF-based THz waveguides have been demonstrated. Finally, the
development and extension of mPOF to form metal-dielectric structures for the manufacture of metamaterials using
fibre-drawing methods will be discussed. Such drawn-metamaterials with electric and magnetic responses at THz
frequencies have been demonstrated.
We demonstrate and optimize a microfluidic refractive index sensor with ultra-high sensitivity based on an acoustic
grating in a solid core photonic bandgap fiber. The sensitivity of the acoustic grating's resonance is 17 900 nm/RIU
which corresponds to smallest detectable changes in refractive index of 8.4×10<sup>-6</sup>.
We experimentally demonstrate novel hybrid photonic crystal fibres incorporating a single ring of high-index
inclusions surrounded by several rings of holes. These fibres are designed to exhibit large bandwidths of guidance
combined with periodic group velocity dispersion zeros. While the multimode character of these fibres limits
their use, they are an ideal platform to experimentally demonstrate the emergence of photonic bandgaps.
Many of the applications of photonic crystals and photonic crystal fibers require the periodic structure to have some type of defect. In photonic crystal fibers a point defect defines the fiber core, whereas in photonic crystals a line defect acts as a waveguide, and point defects act as cavities. The modeling of these defects usually either makes use of periodic boundary conditions, by which the defect is replicated periodically, or models a photonic crystal of finite extent. However, some applications, for example the cut-off behavior of a defect mode where the field extends very widely, require methods that can model a defect in an otherwise infinite and perfectly periodic structure. Here we present such a method. It combines the method of fictitious sources with averaging over the Brillouin zone, and we apply it to study the long-wavelength behavior of the fundamental mode of photonic crystal fibers.
In this paper we review the fabrication and characterisation techniques of m icrostructured optical fibre (M OF) tapers, their fundam ental waveguiding properties and potential applications. W e fabricate photonic crystal fibre tapers without collapsing the air-holes, and confirm this along the taper with a non-invasive probing technique. We then describe the fundam ental property of such tapers associated with the leakage of the core m ode that leads to long wavelength loss. We also revisit the waveguiding properties in another form of tapered MOF photonic wires, which transition through waveguiding regimes associated with how strongly the mode is isolated from the external environment. We explore these regimes as a potential basis for evanescent field sensing applications, in which we can take advantage of controlled airhole collapse as an extra dimension to these photonic wires.
In solid core Microstructured Optical Fibers (MOFs), guidance of light is due to a finite number of layers of holes surrounding a solid core. Because the potential barrier is finite, all modes are leaky, blurring the distinction between guided and non-guided modes. Through simulations using a multipole formulation, we clarify the definition of modal cutoff in MOFs. We establish that the fundamental mode of MOFs undergoes a transition between modal confinement and non-confinement similar to modal cutoff. An asymptotic analysis gives us a better understanding of mode properties on each side of the cutoff but also near cutoff and leads us to define a cutoff point and a cutoff region for the fundamental mode. Three operation regimes with very different mode properties can be distinguished. Only two of these are of practical interest, one with strong mode confinement and another with broader field distributions. The former is of interest for single-mode guidance with strong confinement, whereas the latter, the cutoff region, is where highly adjustable chromatic dispersion can be achieved. We provide a map of the parameter space (MOF "phase diagram") summarizing the operating regimes of MOFs, and show for a few examples how this map can be used for deterministic MOF design.
We describe a multipole theory of photonic crystal or more generally microstructured optical fibers (MOF). We review basic MOF properties such-as losses and number of modes-obtained with our method and expose considerations and results on dispersion management taking into account the losses.