2,464 research outputs found
Slow waves in locally resonant metamaterials line defect waveguides
In the past decades, many efforts have been devoted to the temporal
manipulation of waves, especially focusing on slowing down their propagation.
In electromagnetism, from microwave to optics, as well as in acoustics or for
elastic waves, slow wave propagation indeed largely benefits both applied and
fundamental physics. It is for instance essential in analog signal computing
through the design of components such as delay lines and buffers, and it is one
of the prerequisite for increased wave/matter interactions. Despite the
interest of a broad community, researches have mostly been conducted in optics
along with the development of wavelength scaled structured composite media,
that appear promising candidates for compact slow light components. Yet their
minimum structural scale prevents them from being transposed to lower
frequencies where wavelengths range from sub-millimeter to meters. In this
article, we propose to overcome this limitation thanks to the deep
sub-wavelength scale of locally resonant metamaterials. In our approach,
implemented here in the microwave regime, we show that introducing coupled
resonant defects in such composite media allows the creation of deep
sub-wavelength waveguides. We experimentally demonstrate that waves, while
propagating in such waveguides, exhibit largely reduced group velocities. We
qualitatively explain the mechanism underlying this slow wave propagation and
first experimentally demonstrate, then numerically verify, how it can be taken
advantage of to tune the velocity, achieving group indices ng as high as 227
over relatively large bandwidths. We conclude by highlighting the three
beneficial consequences of our line defect slow wave waveguides in locally
resonant metamaterials: the deep sub-wavelength scale, the very large group
indices and the fact that slow wave propagation does not occur at the expense
of drastic bandwidth reductions
Progress towards photonic crystal quantum cascade laser
The work describes recent progress in the design, simulation, implementation and characterisation of photonic crystal (PhC) GaAs-based quantum cascade lasers (QCLs). The benefits of applying active PhC confinement around a QCL cavity are explained, highlighting a route to reduced threshold current operation. Design of a suitable PhC has been performed using published bandgap maps; simulation results of this PhC show a wide, high reflectivity stopband. Implementation of the PhC for the device is particularly difficult, requiring a very durable metallic dry etch mask, high performance dry etching and a low damage epilayer-down device mounting technique. Preliminary shallow etched PhC QCLs demonstrated the viability of current injection through the metal etch mask and the device mounting technique. Development of the etch mask and dry etching have demonstrated a process suitable for the manufacture of deep etched PhC structures. All the necessary elements for implementing deep etched PhC QCLs have now been demonstrated, allowing for the development of high performance devices
Substrate Integrated Bragg Waveguide: an Octave-bandwidth Single-mode Functional Transmission-Line for Millimeter-Wave and Terahertz Applications
We demonstrate an air-core single-mode hollow waveguide that uses Bragg
reflector structures in place of the vertical metal walls of the standard
rectangular waveguide or via holes of the so-called substrate integrated
waveguide. The high-order modes in the waveguide are substantially suppressed
by a modal-filtering effect, making the waveguide operate in the fundamental
mode over more than one octave. Numerical simulations show that the propagation
loss of the proposed waveguide can be lower than that of classic hollow
metallic rectangular waveguides at terahertz frequencies, benefiting from a
significant reduction in Ohmic loss. To facilitate fabrication and
characterization, a proof-of-concept 20 to 45 GHz waveguide is demonstrated,
which verifies the properties and advantages of the proposed waveguide. A zero
group-velocity dispersion point is observed at near the middle of the operating
band. This work offers a step towards a novel hybrid transmission-line medium
that can be used in a variety of functional components for broadband
millimeter-wave and terahertz applications.Comment: 11 pages, 9 figures, journal articl
Electrically-pumped, broad-area, single-mode photonic crystal lasers
Planar broad-area single-mode lasers, with modal widths of the order of tens of microns, are technologically important for high-power applications and improved coupling efficiency into optical fibers. They may also find new areas of applications in on-chip integration with devices that are of similar size scales, such as for spectroscopy in microfluidic chambers or optical signal processing with micro-electromechanical systems. An outstanding challenge is that broad-area lasers often require external means of control, such as injection-locking or a frequency/spatial filter to obtain single-mode operation. In this paper, we propose and demonstrate effective index-guided, large-area, edge-emitting photonic crystal lasers driven by pulsed electrical current injection at the optical telecommunication wavelength of 1550nm. By suitable design of the photonic crystal lattice, our lasers operate in a single mode with a 1/e^2 modal width of 25μm and a length of 600μm
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