Andrea Di Falco

Andrea Di Falco

Andrea joined the Microphotonic Group in 2006. Since 2012 Andrea heads the Synthetic Optics research group in St Andrews. More details about this exciting new field can be found by following the link below.

Click here to go to the Synthetic Optics website


Contact Details:

Room 342
School of Physics and Astronomy
University of St Andrews
St Andrews
KY16 9SS
Tel: +44 (0)1334 463165
Fax: +44 (0)1334 463104
E-mail: adf10(at)



Propagation Losses of Slotted Photonic Crystal Waveguides

A. Di Falco, M. Massari, M. G. Scullion, S. Schulz, F. Romanato, T. F. Krauss

IEEE Photonics Journal 4 (5) 1536-1541 (2012).

We have fabricated and characterized a set of slotted photonic crystal (SPhC) waveguides in silicon-on-insulator (SOI) with a length of up to 300 mu m and slot widths ranging between 115 and 145 nm. We observe an upper limit for the loss of 11 dB/cm.

[show abstract] [hide abstract] [download pdf] [view at publisher's website] [show citation] [hide citation] DOI: 10.1109/JPHOT.2012.2211342

Lifetime statistics of quantum chaos studied by a multiscale analysis

A. Di Falco, T. F. Krauss, A. Fratalocchi

Applied Physics Letters 100 (18) 184101 (2012).

In a series of pump and probe experiments, we study the lifetime statistics of a quantum chaotic resonator when the number of open channels is greater than one. Our design embeds a stadium billiard into a two dimensional photonic crystal realized on a silicon-on-insulator substrate. We calculate resonances through a multiscale procedure that combines energy landscape analysis and wavelet transforms. Experimental data is found to follow the universal predictions arising from random matrix theory with an excellent level of agreement.

[show abstract] [hide abstract] [download pdf] [view at publisher's website] [show citation] [hide citation] DOI: 10.1063/1.4711018

Bidirectional Optical Sorting of Gold Nanoparticles

M. Ploschner, T. Cizmar, M. Mazilu, A. Di Falco, K. Dholakia

Acs Nano Letters 12 (4) 1923-1927 (2012).

We present a generic technique allowing size-based all-optical sorting of gold nanoparticles. Optical forces acting on metallic nanoparticles are substantially enhanced when they are illuminated at a wavelength near the plasmon resonance, as determined by the particle’s geometry. Exploiting these resonances, we realize sorting in a system of two counter-propagating evanescent waves, each at different wavelengths that selectively guide nanoparticles of different sizes in opposite directions. We validate this concept by demonstrating bidirectional sorting of gold nanoparticles of either 150 or 130 nm in diameter from those of 100 nm in diameter within a mixture.

[show abstract] [hide abstract] [download pdf] [view at publisher's website] [show citation] [hide citation] DOI: 10.1021/nl204378r

Electron-beam patterned self-assembled monolayers as templates for Cu electrodeposition and lift-off

Z. She, A. Di Falco, G. Hahner, M. Buck

Beilstein Journal Of Nanotechnology 3 101-113

Self-assembled monolayers (SAMs) of 4'-methylbiphenyl-4-thiol (MBP0) adsorbed on polycrystalline gold substrates served as templates to control electrochemical deposition of Cu structures from acidic solution, and enabled the subsequent lift-off of the metal structures by attachment to epoxy glue. By exploiting the negative-resist behaviour of MBP0, the SAM was patterned by means of electron-beam lithography. For high deposition contrast a two-step procedure was employed involving a nucleation phase around −0.7 V versus Cu2+/Cu and a growth phase at around −0.35 V versus Cu2+/Cu. Structures with features down to 100 nm were deposited and transferred with high fidelity. By using substrates with different surface morphologies, AFM measurements revealed that the roughness of the substrate is a crucial factor but not the only one determining the roughness of the copper surface that is exposed after lift-off.

[show abstract] [hide abstract] [download pdf] [view at publisher's website] [show citation] [hide citation] DOI: 10.3762/bjnano.3.11

Gain assisted nanocomposite multilayers with near zero permittivity modulus at visible frequencies

C. Rizza, A. Di Falco, A. Ciattoni

Applied Physics Letters 99 221107

We have fabricated a nano-laminate by alternating metal and gain medium layers, the gain dielectric consisting of a polymer incorporating optically pumped dye molecules. From standard reflection-transmission experiments, we show that, at a visible wavelength, both the real and the imaginary parts of the permittivity ε∥ attain very small values and we measure, at λ = 604 nm, |ε∥| = 0.04 which is 21.5% smaller than its value in the absence of optical pumping. Our investigation thus proves that a medium with a permittivity with very small modulus, a key condition promising efficient subwavelength optical steering, can be actually synthesized.

[show abstract] [hide abstract] [download pdf] [view at publisher's website] [show citation] [hide citation] DOI: 10.1063/1.3665414

Optical metasurfaces with robust angular response on flexible substrates

A. Di Falco, Y. Zhao, A. Alu

Applied Physics Letters 99 163110

We have fabricated optical metasurfaces on flexible substrates that show an optical response independent on the polarization and angles of incidence of light. The realized devices operate as ultrathin selective filters at visible frequencies, with a bandwidth of ∼200 nm, and their response is robust to membrane bending for possible integration in conformal optical devices.

[show abstract] [hide abstract] [download pdf] [view at publisher's website] [show citation] [hide citation] DOI: 10.1063/1.3655332

Slotted photonic crystal cavities with integrated microfluidics for biosensing applications

M. G. Scullion, A. Di Falco, T. F. Krauss

Biosensors And Bioelectronics 27 (1) 101-105 (2011).

We demonstrate the detection of dissolved avidin concentrations as low as 15 nM or 1 μg/ml using functionalized slotted photonic crystal cavities with integrated microfluidics. With a cavity sensing surface area of approximately 2.2 μm2, we are able to detect surface mass densities of order 60 pg/mm2 corresponding to a bound mass of approximately 100 ag. The ultra-compact size of the sensors makes them attractive for lab-on-a-chip applications where high densities of independent sensing elements are desired within a small area. The high sensitivity over an extremely small area is due to the strong modal overlap with the analyte enabled by the slotted waveguide cavity geometry that we employ. This strong overlap results in larger shifts in the cavity peak wavelength when compared to competing approaches.

[show abstract] [hide abstract] [download pdf] [view at publisher's website] [show citation] [hide citation] DOI: 10.1016/j.bios.2011.06.023

Valve controlled fluorescence detection system for remote sensing applications

T. D. James, M. G. Scullion, P. C. Ashok, A. Di Falco, K. Dholakia, T. F. Krauss

Microfluidics And Nanofludics 1-8

We demonstrate a microfluidics-based fluorescence detection device where the filters, source, detector, and electronically controlled valves are embedded into a Polydimethylsiloxane (PDMS)-based microfluidic chip. The device reported here has been specifically designed for chlorophyll a fluorescence sensing in autonomous systems, such as oceanic applications. In contrast to a monolithic approach, the modular approach made the fabrication of this device simpler and cheaper. For fluorescence detection, an InGaN/GaN LED is used as the excitation source to specifically excite chlorophyll a; a metal-dielectric Fabry–Perot filter was used to extinguish out-of-band excitation. A simple Si photodiode is used as detector and provided with a thermally evaporated CdS emission filter to block the excitation source. This filter combination provides an excellent solution to the difficult problem of combining high-rejection excitation and emission filters in an integrated thin-film format. Furthermore, the metal-dielectric filter provides a much broader angular response than a comparable multilayer Bragg mirror, which is a key advantage in the integrated format. We use a novel paraffin wax-based valve design affords low power single-use actuation, between 0.5 and 1 J per actuation and withstands 0.6 bar differential pressure, which provides better performance than its previously reported counterparts. The remote valve-controlled operation of the fluorescence detection system is demonstrated, illustrating the measurement of a chlorophyll a solution, with a detection limit of 340 μM and subsequent valve-controlled flushing of the measurement reservoir.

[show abstract] [hide abstract] [download pdf] [view at publisher's website] [show citation] [hide citation] DOI: 10.1007/s10404-011-0818-1

High Efficiency Interface for Coupling Into Slotted Photonic Crystal Waveguides

M. G. Scullion, T. F. Krauss, A. Di Falco

Photonics Journal, IEEE 3 (2) 203-208 (2011).

We investigate the mechanism of coupling light into slotted photonic crystal waveguides. We identify two alternative approaches for improving the coupling efficiency, based on engineered mode dispersion and on resonant mechanisms. For the optimized geometry, we calculate a loss figure of 0.3 dB over 100-nm bandwidth per interface and demonstrate a corresponding experimental value of 1.5 dB over 78-nm bandwidth per interface.

[show abstract] [hide abstract] [download pdf] [view at publisher's website] [show citation] [hide citation] DOI: 10.1109/JPHOT.2011.2125785

Luneburg lens in silicon photonics

A. Di Falco, S. C. Kehr, U. Leonhardt

Optics Express 19 (6) 5156-5162 (2011).

The Luneburg lens is an aberration-free lens that focuses light from all directions equally well. We fabricated and tested a Luneburg lens in silicon photonics. Such fully-integrated lenses may become the building blocks of compact Fourier optics on chips. Furthermore, our fabrication technique is sufficiently versatile for making perfect imaging devices on silicon platforms.

[show abstract] [hide abstract] [download pdf] [view at publisher's website] [show citation] [hide citation] DOI: 10.1364/OE.19.005156

Flexible metamaterials at visible wavelengths

A. Di Falco, M. Ploschner, T. F. Krauss

New Journal Of Physics 12 113006

We report on the fabrication and characterization of plasmonic structures on flexible substrates (Metaflex) and demonstrate the optical properties of a single layer of Metaflex. The layer exhibits a plasmonic resonance in the visible region around 620 nm. We show experimental and numerical results for both nano-antennas and fishnet geometries. We anticipate the use of Metaflex as a building block for flexible metamaterials in the visible range.

[show abstract] [hide abstract] [download pdf] [view at publisher's website] [show citation] [hide citation] DOI: 10.1088/1367-2630/12/11/113006

Electro-optic modulation in slotted resonant photonic crystal heterostructures

J. H. Wulbern, J. Hampe, A. Petrov, M. Eich, J. D. Luo, A. K. Y. Jen, A. Di Falco, T. F. Krauss, J. Bruns

Applied Physics Letters 94 (24) 241107 (2009).

Two dimensional photonic crystal waveguides in high index materials enable integrated optical devices with an extremely small geometrical footprint on the scale of micrometers. Slotted waveguides are based on the guiding of light in low refractive index materials and a field enhancement in this particular region of the device. In this letter we experimentally demonstrate electro-optic modulation in slotted photonic crystal waveguides based on silicon-on-insulator substrates covered and infiltrated with nonlinear optical polymers. A photonic crystal heterostructure is used to create a cavity, while simultaneously serving as an electrical connection from the slot to the metal electrodes that carry the modulation signal.

[show abstract] [hide abstract] [download pdf] [view at publisher's website] [show citation] [hide citation] DOI: 10.1063/1.3156033

Integrated polymer microprisms for free space optical beam deflecting

C. Reardon, A. Di Falco, K. Welna, T. F. Krauss

Optics Express 17 (5) 3424 (2009).

We demonstrate beam deflection and multiple channel communication in free space optical communications using microprisms integrated directly onto an array of vertical cavity surface emitting lasers (VCSELs). The design and fabrication of such a transmitter is presented, and shown to achieve beam deflection of up to 10° in a planar configuration. A location discovery application, for use within a distributed network, is put forward and analysed.

[show abstract] [hide abstract] [download pdf] [view at publisher's website] [show citation] [hide citation] DOI: 10.1364/OE.17.003424

Chemical sensing in slotted photonic crystal heterostructure cavities

A. Di Falco, L. O'Faolain, T. F. Krauss

Applied Physics Letters 94 (6) 63503 (2009).

We fabricated slotted photonic crystal waveguides and cavities supporting resonant modes in air. Their peculiar geometry enables the detection of refractive index changes in a given analyte with high sensitivity because of the large overlap between the optical mode and the analyte. This yields a high figure of merit for the sensitivity of the device and we are able to report values of S=Delta lambda/Delta n over 1500. By applying a photonic crystal heterostructure to the slotted geometry, we are able to create high quality-factor cavities essential for realizing low detection limits up to Q=50 000.

[show abstract] [hide abstract] [download pdf] [view at publisher's website] [show citation] [hide citation] DOI: 10.1063/1.3079671

Dispersion control and slow light in slotted photonic crystal waveguides

A. Di Falco, L. O'Faolain, T. F. Krauss

Appl. Phys. Lett. 92 083501

Slotted photonic crystal waveguides combine the ability to confine light in air with the dispersion control available from photonic crystals. Here, we study the dependence of their dispersion properties on geometry, especially the slot width, and demonstrate slow light operation with group indices in excess of 100.

[show abstract] [hide abstract] [download pdf] [view at publisher's website] [show citation] [hide citation] DOI: 10.1063/1.2885072

Other Members of the Group


Group Leader

Thomas Krauss



Post-Grad Students

Research Technicians

Andrea Di Falco

William Whelan-Curtin (Liam O'Faolain)



Christopher Reardon

Marcello Ferrera

Abdul Shakoor

Annett Klemm

Bryan O'Regan

Christian Schuster

Emiliano Rezende Martins

Kapil Debnath

Mark Scullion

Peter Reader-Harris

Steve Balfour

Callum Smith


Project Students


Former Group Members


George Robb

Armando Ricciardi

Arran Gillies

Christian Reimer

Daryl Beggs

Dominik Szymanski

Douglas McRobbie

Fengqiao Dong

Isabella Rey

Juntao Li

Khaled Mnaymneh

Karl Welna

Maria Dienerowitz

Marco Grande

Maria Kotlyar

Martin Ploschner

Marcel Spurny

M. Umar Khan

Paolo Cardile

Pedro Damas

Praveen Ashok

Rob Marchington

Sebastian Schulz

Simone Portalupi

Stephen Moore

Tim James

Tom White

Yikun Liu