Kramers-Kr\"onig approach to the electric permittivity of the vacuum in a strong constant electric field

We study the electric permittivity of the QED vacuum in the presence of a strong constant electric field, motivated by the analogy between the dynamically-assisted Schwinger effect in strong-field QED and the Franz-Keldysh effect in semiconductor physics. We develop a linear-response theory based on the non-equilibrium in-in formalism and the Furry-picture perturbation theory, with which and also utilizing the Kramers-Kr\"onig relation, we calculate the electric permittivity without assuming weak fields and low-frequency probes. We discover that the electric permittivity exhibits characteristic oscillating dependence on the probe frequency, which directly reflects the change of the QED-vacuum structure by the strong field. We also establish a quantitative correspondence between the electric permittivity and the number of electron-positron pairs produced by the dynamically-assisted Schwinger effect.Comment: 25 pages, 6 figure

Atom probe microscopy of zinc isotopic enrichment in ZnO nanorods

We report on atomic probe microscopy (APM) of isotopically enriched ZnO nanorods that measures the spatial distribution of zinc isotopes in sections of ZnO nanorods for natural abundance natZnO and 64Zn and 66Zn enriched ZnO nanorods. The results demonstrate that APM can accurately quantify isotopic abundances within these nanoscale structures. Therefore the atom probe microscope is a useful tool for characterizing Zn isotopic heterostructures in ZnO. Isotopic heterostructures have been proposed for controlling thermal conductivity and also, combined with neutron transmutation doping, they could be key to a novel technology for producing p-n junctions in ZnO thin films and nanorods. © 2017 Author(s)

Design, Simulations, and Optimizations of Mid-infrared Multiple Quantum Well LEDs

We use eight-band k·p energy band structure model to help design novel GaInSb/AlGaInSb mid-infrared multiple quantum well (MQW) structures with an emitting mid-infrared waveband of 4-5 µm. Simulation results suggest that the number of quantum wells has little influence on the spontaneous emission rate and gain because of no strong coupling between quantum wells and they just simply follow scaling laws. The SiLENSe software module from STR-soft is used to investigate injection efficiency of the designed MQW structures. Simulation results indicate that the MQW structures offer better carrier confinement i.e. higher carrier injection efficiency compared with traditional bulk active regions which are currently used for mid-infrared LEDs and sensors. Experimental investigations show that the MQW LEDs with a seven wells structure show an increase of a factor 2 in wall plug efficiency and output power compared with conventional bulk LEDs at the same wavelength

Semiconductor Integrated Optics for Switching Light

The nonlinear integrated Mach-Zehnder was also configured as an asymmetric device. For the AMZI device of length around 0.5 cm, the input intensities required to switch are around 2×109 W cm-2, which implies optical pulse energies of ..

Active polarisation control of a quantum cascade laser using tuneable birefringence in waveguides

We discuss the design, modelling, fabrication and characterisation of an integrated tuneable birefringent waveguide for quantum cascade lasers. We have fabricated quantum cascade lasers operating at wavelengths around 4450 nm that include polarisation mode converters and a differential phase shift section. We employed below laser threshold electroluminescence to investigate the single pass operation of the integrated device. We use a theory based on the electro-optic properties of birefringence in quantum cascade laser waveguides combined with a Jones matrix based description to gain an understanding of the electroluminescence results. With the quantum cascade lasers operating above threshold we demonstrated polarisation control of the output. © 2013 Optical Society of America

High power gaas/algaas mode-locked lasers

This work shows preliminary results from Colliding-Pulse Mode-Locked lasers in a GaAs/AlGaAs highpower material structure, where COMD limits the output power to 40mW. Results of gain and absorption spectra, measured to model the mode-locking operation of the devices, are also presented. ©2009 IEEE

Synchronization of optically coupled resonant tunneling diode oscillators

We experimentally investigate the synchronous response of two fiber-optic coupled optoelectronic circuit oscillators based on resonant tunneling diodes (RTDs). The fiber-optic synchronization link employs injection of a periodic oscillating optical modulated signal generated by a master RTD-laser diode (LD) oscillator to a slave RTD-photodetector (PD) oscillator. The synchronous regimes were evaluated as a function of frequency detuning and optical injection strength. The results show the slave RTD-PD oscillator follows the frequency and noise characteristics of the master RTD-LD oscillator resulting in two oscillators with similar phase noise characteristics exhibiting single side band phase noise levels below -100 dBc/Hz at 1 MHz offset from the carrier frequency. Optical synchronization of RTD-based optoelectronic circuit oscillators have many applications spanning from sensing, to microwave generation, and data transmission. © 2013 SPIE

Non-absorbing mirrors in mode-locked lasers

We present results from GaAs/AlGaAs colliding-pulse mode-locked lasers with a repetition rate of 20GHz and wavelength of 830nm. Devices with and without non-absorbing mirrors are compared in terms of output power characteristics and mode-locking operation. ©2010 IEEE

Optoelectronic oscillator topologies based on resonant tunneling diode fiber optic links

We investigate optoelectronic oscillator (OEO) configurations based on a laser diode driven by resonant tunnelling diode (RTD) optical waveguide photo-detector (PD) oscillators, with an optical fiber feedback loop carrying a fraction of the laser diode optical output that is re-injected into the OEO through the optical waveguide of the RTD-PD. In the configurations reported here, we take advantage of the RTD negative differential resistance to provide electrical highbandwidth. The optical fiber loop acts as a high quality optical energy storage element with low transmission loss. The RTD based OEO can produces stable and low-phase noise microwave signals with attractive applications in photonics and communication systems, mainly in fiber-optic based communication links since the RTD-OEO can be accessed both optically and electrically. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE)

Polarization control of a quantum cascade laser

By integrating a polarization mode converter we have obtained significant amounts of Transverse Electrical light from a quantum cascade laser. First results indicate up to around 18%TE light in an elliptically polarized output