Back in 2002, Toshiba released its pioneer Quantum LED design.  It opened a route for electrically driven quantum light sources adapted to different spectral ranges and environments. However, several constraints of the design, like the lack of a built-in wavelength tuning mechanism, or how to surpass the large sheet resistance in nanophotonic structures, remained unsolved. Just recently, completely new approaches appeared adding new functionalities to the original design. [2,4]
We will present our own design. It is based on a vertical multijunction heterostructure where quantum light emission and tuning into photonic crystal cavities might become possible, for the first time, without constraints.  The device comprises of two separated electrical injection and electrical tuning regions in a bi-polar transistor configuration. The connection between them is purely optical and thus, it naturally avoids the sheet resistance problems that plague other approximations, especially when applied to nanophotonic devices. The first fabricated devices show single photon emission with g2(0)<0.1 at injection currents as low as 100 mA/cm2 and fully linear conversion between electrical power and single photon flux.
Z.Yuan et al Electrically Driven Single-Photon Source. Science 2002, 295, 102.
B. Alén et al “Tunable monolithic quantum light source and quantum circuit thereof” Patent pending EP/17382061.4, PCT/EP2018/052960. Date: Feb 8th 2017
J. P.Murray et al “Electrically Driven and Electrically Tunable Quantum Light Sources”. Appl. Phys. Lett. 2017, 110 (7), 071102.
P.Munnelly et al “Electrically Tunable Single-Photon Source Triggered by a Monolithically Integrated Quantum Dot Microlaser”. ACS Photonics 2017, 4 (4), 790–794.
Dilute nitride GaAsSbN is an ideal candidate to form the 1-1.15 eV lattice-matched sub-cell that would significantly enhance the performance of 3- and 4-junction solar cells. However, growth problems inherent to this quaternary alloy lead typically to a poor crystal quality that limits its applicability. Better compositional control and crystal quality have been recently reported by growing the material as a GaAsSb/GaAsN superlattice, because of the spatial separation of Sb and N that avoid miscibility problems. Moreover, these structures provide bandgap tunability trough period thickness. Here we study the performance of lattice-matched 1.15 eV GaAsSb/GaAsN type-II superlattice p-i-n junction solar cells with different period thickness and compare them with the bulk and GaAsSbN/GaAs type-I superlattice counterparts. We demonstrate carrier lifetime tunability through the period thickness in the type-II structures. However, the long carrier lifetimes achievable with periods thicker than 12 nm are incompatible with a high carrier extraction efficiency under short-circuit conditions. Only superlattices with thinner periods and short carrier lifetimes show good solar cell performance. Quantum kinetic calculations based on the non-equilibrium Green’s function (NEGF) formalism predict a change in transport regime from direct tunneling extraction to sequential tunneling with sizable thermionic emission components when passing from 6 nm to 12 nm period length, which for low carrier lifetime results in a decrease of extraction efficiency by more than 30%.
In this work we show room temperature continuous (CW) lasing at 1.5 μm in photonic crystal microcavities
with a single layer of self-assembled quantum wires (QWRs). Low threshold values in the range of 1-20 μW
(depending on the excitation type, pulsed or CW) have been measured, along high quality factors exceeding
Q=55000 using L7-type photonic crystal microcavities. Solid-source molecular beam epitaxy has been used
for the synthesis of the InP/InAs epitaxial material comprising a single layer of InAs QWRs. The main axis of
the cavity is always parallel to the QWRs, which are more than 1ìm in length along the [1-10] direction. No
lasing has been obtained for L7 cavities with axis parallel to the  (i.e., perpendicular to the direction of
the QWRs), showing the strong one-dimensional character of the QWRs inside the photonic cavity. Under
inhomogeneous pulsed excitation the lasing spectra show asymmetric lineshapes and peak splittings first in
the μeV and later in the meV ranges as the excitation power is increased.
Surface plasmon excitation using a variation of Kretschmann method based on light guiding through an optical fiber has
been extensively studied in the literature. But, due to its particularly bad propagation conditions, plastic optical fiber was
not taken into account in documented experiments. We propose a low cost sensor using this type of fiber, in which we
try to avoid the problems both through careful design and signal processing. First of all we discuss the sample fabrication
and measurement in section 2; then the results obtained are discussed in section 3, including the problems faced because
of the multimode character of the fiber, for which we propose alternative sample shapes as a mean of reducing them. As
a conclusion we propose a roadmap to design a low cost sensor based in the structures studied in this paper.