Organic microcavities and photonics
The interaction between light and matter is of fundamental importance in a range of optoelectronic technologies. By modifying the electromagnetic environment around an excited state, it is possible to profoundly change its emission properties.
We have a long-standing interest in the physics of organic (carbon-based) semiconductors placed in high finesse 1-dimensional optical cavities (see figure 1). Here, two high reflectivity mirrors are placed in close proximity - usually a few hundred nanometers. The mirrors quantise the optical field within the cavity, meaning that only photons of certain energy can be confined within the structure.
Within the so-called 'strong-coupling' regime, the trapped cavity photons and the electronic states of the semiconductor in the cavity can undergo a mixing process, where the new states formed (termed cavity polaritons) are a superposition of optical and electronic states.
Fig 1: Cavity schematic.
The formation of polaritons can be identified from the cavity dispersion curve through an 'anticrossing' between photon and exciton modes (see Figure 2). At high pump-density, the polariton states in a micro cavity can undergo condensation, forming a coherent macroscopic object that can act as a source of laser light.
We are currently studying non-linear optical processes in organic microcavities and also making electrically driven polariton devices. The papers below show some examples of what can be achieved by placing organic semiconductor into various types of optical cavity.
Fig 2: White-light reflectivity from the cavity.
Optical-Mode Structure of Micropillar Microcavities Containing a Fluorescent Conjugated Polymer
Faleh L. Al-Jashaam, Rahul Jayaprakash, David M. Coles, Andrew J. Musser, Kyriacos Georgiou, David G. Lidzey*
The light emission from a series of micropillar microcavities containing a fluorescent, red-emitting conjugated polymer, is explored. Cavities are fabricated by defining two dielectric mirrors either side of a polymer active region. Focused ion beam (FIB) lithography is then used to etch pillar structures into the planar cavity having diameters between 1 and 11 µm.
The photoluminescence (PL) emission of the cavities is characterised using real space tomographic and Fourier space imaging techniques, with emission shown to be quantised into a mode structure resulting from both vertical and lateral optical confinement within the pillar. The optical confinement effects which result in a blue shift of the fundamental mode as the pillar diameter is reduced is demonstrated, with a model applied to describe the energy and distribution of the confined optical modes.
Cover article: A Nanophotonic Structure Containing Living Photosynthetic Bacteria
David Coles, Lucas C. Flatten, Thomas Sydney, Emily Hounslow, Semion K. Saikin, Alán Aspuru-Guzik, Vlatko Vedral, Joseph Kuo-Hsiang Tang, Robert A. Taylor, Jason M. Smith, and David G. Lidzey*.
This article reports what we believe to be the first demonstration of the modification of energy levels within living biological systems using a photonic structure.
Cover article: A Yellow Polariton Condensate in a Dye Filled Microcavity
Tamsin Cookson, Kyriacos Georgiou, Anton Zasedatelev, Richard T. Grant, Tersilla Virgili, Marco Cavazzini, Francesco Galeotti, Caspar Clark, Natalia G. Berloff, David G. Lidzey,* and Pavlos G. Lagoudakis*.
Advanced Optical Materials 2017, 1700203 DOI: 10.1002/adom.201700203
This article reports the observation of a polariton-condensate at room temperature in a microcavity containing the molecular dye BODIPY-Br dispersed in a polystyrene matrix. Above the condensation threshold, the structure emits monochromatic radiation at 565nm, corresponding to yellow light. Coherence measurements using a Michelson Interferometer reveal spatial coherence across the condensate, which is almost 30 microns in diameter.
Cover article: Efficient Radiative Pumping of Polaritons in a Strongly Coupled Microcavity by a Fluorescent Molecular Dye
Richard T. Grant, Paolo Michetti, Andrew J. Musser, Pascal Gregoire, Tersilla Virgili, Eleonora Vella, Marco Cavazzini, Kyriacos Georgiou, Francesco Galeotti, Caspar Clark, Jenny Clark, Carlos Silva, and David G. Lidzey*.
Advanced Optical Materials 2016, DOI: 10.1002/adom.201600337
Cover article: Photonic Crystals: Photonic Crystal Nanocavities Containing Plasmonic Nanoparticles Assembled Using a Laser-Printing Technique
Jaekwon Do, Khalid N. Sediq, Kieran Deasy, David M. Coles, Jessica Rodríguez-Fernández,*, Jochen Feldmann,* and David G. Lidzey*.
Advanced Optical Materials 1.12 p. 887 December 2013, DOI: 10.1002/adom.201370071
Cover article: Vibrationally Assisted Polariton-Relaxation Processes in Strongly Coupled Organic-Semiconductor Microcavities
Coles et al.
Advanced Functional Materials 21 (2011), 3691-3696