Sam A. Berry

Investigation of the role of the lateral photo-Dember effect in the generation of terahertz radiation using a metallic mask on a semiconductor.

Pulses of coherent terahertz radiation can be efficiently generated by a lateral diffusion current after ultrafast generation of photo-carriers near a metal interface on the surface of a semiconductor, this is known as the lateral photo-Dember effect. We investigate how the emission depends on the pump spot position, size, power and how it is affected by the application of an applied external bias. We study the role of the metallic mask and how it suppresses emission from the carriers diffusing under it due to a reduction of available radiation states both theoretically and experimentally.

Multiple double-metal bias-free terahertz emitters

We demonstrate multiplexed terahertz emitters that exhibits 2 THz bandwidth that do not require an external bias. The emitters operate under uniform illumination eliminating the need for a micro-lens array and are fabricated with periodic Au and Pb structures on GaAs. Terahertz emission originates from the lateral photo-Dember effect and from the different Schottky barrier heights of the chosen metal pair. We characterize the emitters and determine that most terahertz emission at 300 K is due to band-bending due to the Schottky barrier of the metal.

Fluence and polarisation dependence of GaAs based Lateral Photo-Dember terahertz emitters.

We characterise THz output of lateral photo-Dember (LPD) emitters based on semi-insulating (SI), unannealed and annealed low temperature grown (LTG) GaAs. Saturation of THz pulse power with optical fluence is observed, with unannealed LTG GaAs showing highest saturation fluence at 1.1 ± 0.1 mJ cm(-2). SI-GaAs LPD emitters show a flip in signal polarity with optical fluence that is attributed to THz emission from the metal-semiconductor contact. Variation in optical polarisation affects THz pulse power that is attributed to a local optical excitation near the metal contact.

External cavity diode laser based upon an FBG in an integrated optical fiber platform

An external cavity diode laser is demonstrated using a Bragg grating written into a novel integrated optical fiber platform as the external cavity. The cavity is fabricated using flame-hydrolysis deposition to bond a photosensitive fiber to a silica-on-silicon wafer, and a grating written using direct UV-writing. The laser operates on a single mode at the acetylene P13 line (1532.83 nm) with 9 mW output power. The noise properties of the laser are characterized demonstrating low linewidth operation (< 14 kHz) and superior relative intensity noise characteristics when compared to a commercial tunable external cavity diode laser.

Multiple lateral photo-Dember terahertz emitters illuminated by a cylindrical micro-lens array

We demonstrate a terahertz multiple emitter design based on the lateral photo-Dember effect and illuminated with a cylindrical micro-lens array. The multiple emitter produces an average of 5.2 times the output power of a single lateral photo-Dember emitter and is capable of reaching bandwidth comparable to that of a single commercial photoconductive antenna.

A metamolecule antenna for coplanar waveguides.

We report on a metamolecule antenna, based on a fish-scale design but augmented with two split-ring resonators (SRRs) placed within the fish-scale loops. The properties of the antenna resonator, with and without additional SRRs, were examined using finite element method simulations (COMSOL Multiphysics). The simulation findings were subsequently confirmed experimentally, using a vector network analyser coupled to an antenna-loaded coplanar waveguide (CPW). The addition of SRRs to the fish-scale meta-molecule leads to a demonstrably large increase in microwave-absorption. It is shown that the fish-scale/SRR/CPW combination performs as a microwave antenna. Simulations of the antenna gain and far-field emission are presented and discussed.

Determination of spatio-spectral properties of individual modes within multimode waveguides using spectrally resolved near-field scanning optical microscopy

Near-field scanning optical microscopy (NSOM) is used to measure the relative group velocity and relative amplitude of modes in a multimode waveguide with an incoherent broadband light source. A spectrally resolving NSOM probe was used to observe localized spectral interference in the multimode waveguide. Fourier analysis was used to identify temporal delays. The modes can be further identified by their temporally discriminated spatial profile which is based on the product of their fields. This data provide the relative amplitude and phases of the modes.

Taking large optical quantum states out of the lab: engaging pupils and the public on quantum photonics sciences

Novel research-inspired outreach activities allow scientists and members of the public to engage in a conversation, increasing the public’s understanding and interest in scientific research. This paper reviews outreach and public engagement initiatives undertaken by researchers from the University of Southampton’s Optical Engineering and Quantum Photonics Group during a 5-year research program grant entitled Building Large Optical Quantum States. The activities have been supported by a UK Engineering and Physical Sciences Research Council program grant and institutional, national and international professional organizations. The paper discusses activities and hand-outs that have been developed to increase the visibility and public understanding of integrated-photonics fabrication and testing facilities, including a cleanroom-based process for the design and fabrication of quantum outreach chips. More than 1,000 of these chips have been distributed to children, parents and government officials in public events and the activities have contributed towards the authors’ research group receiving the 2017 South East England Physics Network Highly Commended Award for Best Research Group. This paper also discusses the impact of these activities and lessons learned.

Dataset for Terahertz focusing and polarization control in large-area bias-free semiconductor emitters

We show that, when large area multiplex terahertz semiconductor emitters that work on diffusion currents and Schottky potentials are illuminated by ultrashort optical pulses, can radiate a directional electromagnetic terahertz pulse which is controlled by the angular spectrum of the incident optical beam. Using the lens that focuses the incident near infrared pulse, we have demonstrated THz emission focusing in free space, at the same point where the optical radiation would focus. We investigated the beam waist and Gouy phase shift of the THz emission as a function of frequency. We also show that the polarization profile of the emitted THz can be tailored by the metallic patterning on the semiconductor, demonstrating radial polarization when a circular emiter design is used. Our techniques can be used for fast THz beam steering and mode control for efficiently coupling to waveguides without the need for THz lenses or parabolic mirrors.

Developing PPLN Waveguides for Quantum Rubidium Atom Traps in Space

We demonstrate single mode zinc-indiffused MgO:PPLN ridge waveguides with insertion losses of <1.3 dB (2 cm device length), developed towards rubidium atom traps. We will report on fabrication, modal engineering, loss, and second harmonic generation.