The development of methods for the rapid analysis of pathogenic bacteria or viruses is of crucial interest in the clinical diagnosis of infectious diseases. In the last decade, optical resonators integrated with microfluidic layers arose as promising tools for biological analysis, notably thanks to their ability to trap objects with low powers, beneath the damage threshold of biological entities, and with a small footprint. Moreover, the resonant nature of optical cavities allows for the simultaneous acquisition of information on the trapped objects, thanks to the feedback effect induced by the specimen on the trapping field itself.
Here we report on the trapping and on the Gram-type differentiation of seven types of living bacteria in an optofluidic system based on an optical cavity consisting in a large hole in a 2D silicon photonic crystal membrane. The hollow nature of the resonant cavity results in a large overlap between the confined field and the hollow volume, allowing for a maximum interaction between the trapping field and the trapped cell. The optical cavity was excited at the resonance wavelength and the shift induced by the trapped bacteria was analysed. To test the trapping capabilities of our structure, we investigated seven types of bacteria, featuring different morphologies, Gram-types and mobilities (presence or absence of flagella). The analysis of the resonance shift yielded Gram typing in a label-free and not destructive way, due to differences in the refractive index and in the deformability of the cell wall. In particular, Gram negative bacteria showed a larger shift.
Antibiotic resistance kills an estimated 700,000 people each year worldwide and experts predict that this number could hit 10 million by 2050. Rapid diagnostics would play an essential role in the fight against this alarming phenomenon by improving the way in which antibiotherapy is used, notably by stopping the unnecessary use of antibiotics. Clinical microbiology has relied on culture as the standard method for characterizing pathogens over the past century. This process is time-consuming and requires large biomasses. In this context, single-cell monitoring would be a significant breakthrough compared to Petri dishes culture. A first step was achieved by the demonstration of single bacterium trapping by optical tweezers and integrated photonics. Here, the nondestructive real-time state monitoring of a single alive trapped bacterium is demonstrated. In order to achieve this, a two-laser setup was developed to simultaneously trap and monitor a single bacterium in the near-field of a nanobeam microcavity. While the first laser is used to excite the optical field tweezing the bacterium, the second laser probes the cavity resonance spectrum. The bacterium optical interaction with the resonant cavity mode allows to assess the bacterium state in real time when subjected to an antibacterial agent (antibiotics, alcohol, temperature). Confronted to standards culture-based methods, this optical label-free approach yields relevant information about bacterial viability, without time-consuming culture or staining.
Those results evidence that on-chip devices operating at telecom wavelength may greatly enhance the monitoring of bacteria in the near future leading to major improvements in health care diagnosis and patient treatments.
The possibility of using integrated photonics to scale multiple optical components on a single monolithic chip offers transformative advantages in fields such as communications, computing, bioengineering, and sensing. However, today’s integrated photonic circuits are rudimentary compared to the complexity of modern electronic circuits. Any advancements to efficiently integrate new photonic functionalities bring us closer to replicate the enormous impact of electronic integrated circuits.
Slow light propagation in chip-integrated nanophotonic structures with engineered band dispersion is a highly promising approach for controlling the relative phase of light and for enhancing optical nonlinearities on a chip. A primary goal in this field is to achieve devices with large, approximately constant group index (n_g) over the largest possible bandwidth, thereby enabling multimode and pulsed operation. We present an experimental record high group-index-bandwidth product (GBP) in genetically optimized coupled-cavity-waveguides (CCWs) designed by L3 photonic crystal nanocavities. The resulting designs were realized in SOI buckling-free suspended slabs with CCWs integrating up to 800 coupled nanocavities. The samples were characterized by measuring the CCW transmission, the mode dispersion through Fourier-space imaging, and ng via Mach-Zehnder interferometry. Various nanocavity designs were investigated, with theoretical n_g ranging from 37 to 100. Record high GBP = 0.47 was demonstrated over a bandwidth of 19.5 nm with a homogeneous flat-top transmission profile (variations lower than 10 dB) and losses below 56 dB/ns. Our results open the path towards building enhanced slow-light-based devices such as of slow-light-enhanced spectroscopic interferometers and single-photon buffers.
We report on the first experimental demonstration of resonant optical trapping of dielectric particles in a two-dimensional hollow photonic crystal cavity. The cavities are implemented in an optofluidic chip consisting of a silicon-on-insulator substrate and an ultrathin microfluidic membrane, Resonant optical trapping of 500 nm polystyrene beads is achieved using less than 120 μW optical power in the cavity for trapping times reaching over ten minutes.
Two families of photonic crystal based Terahertz Quantum Cascade Laser structures are demonstrated. The first one uses Bragg mirrors that relies on a two-dimensional photonic lattice. Single mode lasing emission is observed from the edge of the structure for particular lattice constants. Moreover mode pinning of the laser is obtained along the whole dynamic range. In the second part a vertically emitting THz Quantum Cascade Laser device that exploits in-plane resonator based on a two-dimensional photonic crystal is demonstrated. Stable single mode lasing is reported. Simulations based on block-iterative frequency-domain methods on a plane wave basis account for the observed results.
This work addresses feature size effects (the lag-effect and roughness development) in chemically assisted ion beam etching (CAIBE) etching of InP based photonic crystals. Photonic crystal fields with varying hole size and periods were etched with different etching times. The slope of the etch depth versus diameter curves (lag-curves) reveals a hole size dependence, with a critical aspect ratio higher than 25. A model for the etch rate specific to Ar/Cl2 CAIBE is proposed. We calculate the etch rate using a physico-chemical model which takes in to account the effect of Ar-ion sputtering and surface chemical reactions. In addition, it combines the aspect ratio dependence of the gas conductance of the etched holes. The origin and evolution of the bottom roughness of the etched holes is examined. The impact of the feature size dependence of the etching on the photonic crystal optical properties is then assessed by measuring the quality-factor of one dimensional Fabry Perot cavities using the Internal Light Source method, and discussed in terms of hole shape and depth. A systematic trend between the determined quality factor (Q) and the lag-effect is evidenced: Q decreases from about 250 to 60 when the hole depth drops from 5 μm to 2 μm.
Recently there has been a growing amount of attention devoted to tuneable photonic crystals (PhCs) where the optical response of PhC structures can be dynamically modified. We will show how infiltrating planar PhCs with a synthetic organic material allows the trimming and tuning of their optical properties. The potential of PhC infiltration
will be demonstrated for InP-based planar PhCs consisting of a hexagonal array of air holes (hole diameter = 200 − 400 nm; air filling factor = 0.40-0.50) etched through a planar waveguide in which light emitters (i.e. quantum wells) were embedded to enable optical measurements. The PhC pores were infiltrated with LC-K15 (5CB) nematic liquid crystals (LCs) in a specifically designed vacuum chamber, thereby changing the refractive index contrast between the holes and the semiconductor (trimming). Moreover, the possibility of tuning the optical response of PhCs by an external perturbation (i.e. temperature) was demonstrated. The change of the PhC optical properties due to infiltration and temperature tuning was studied both experimentally and theoretically. Experimental measurements were compared to theoretical calculations in order to obtain information on the in-filling efficiency, the LC refractive index, and the molecule orientation inside the holes. In the first case, optical measurements were performed as a function of
temperature, whilst the average LC director configuration was determined by comparing transmission spectra in the transverse electric and magnetic polarization directions.
Electromagnetic Bloch waves are the standard representation of the
optical field in two-dimensional photonic crystals (2D-PhCs). We
present an intuitive description of Bloch waves based on their
Fourier transform into series of electromagnetic plane waves. The
contribution of each plane wave to the global energy and group
velocity is detailed and the valid domain of this decomposition is
discussed. This approach enables a continuous description of light
propagation from the homogeneous medium to the strongly modulated
PhC case and resolves inconsistencies that result from band
folding. Finally this model provides a clear physical
understanding of the negative refraction effects observed in
We report on the temperature tuning of the optical properties of planar Photonic Crystal (PhC) microcavities. Studies were made on one and two dimensional PhCs that were etched in InP and GaAs vertical waveguides. Two dimensional (hexagonal) and one-dimensional (Fabry-Perot) cavities were optically investigated by an internal light source technique. The samples were mounted on a Peltier-stage which allowed temperature variation from T = 20 °C up to T = 76 °C. A linear dependence of the resonance wavelengths with respect to temperature is observed. A gradient of dλ/dT = 0.09 nm/°C and 0.1 nm/°C for the GaAs and InP based cavities was observed, respectively. These results are in agreement with the theoretical calculations based on the thermal dependence of the refractive index of the PhC semiconductor component.
Practical realizations of 2D (planar) photonics crystal (PhC) are either on a membrane or etched through a conventional heterostructure. While fascinating objects can emerge from the first approach, only the latter approach lends itself to a progressive integration of more compact PhC's towards monolithic PICs based on InP. We describe in this talk the various aspects from technology to functions and devices, as emerged from the European collaboration "PCIC." The main technology tour de force is deep-etching with aspect ratio of about 10 and vertical sidewall, achieved by three techniques (CAIBE, ICP-RIE, ECR-RIE). The basic functions explored are bends, splitters/combiners, mirrors, tapers, and the devices are filters and lasers. At the end of the talk, I will emphasize some positive aspects of "broad" multimode PhC waveguides, in view of compact add-drop filtering action, notably.
Photonic crystals have seen major advances in the past few years in the optical range. The association of in-plane waveguiding and two-dimensional (2D) photonic crystals (PCs) in thin-slab or waveguide structures leads to good 3D confinement with easy fabrication. Such structures, much easier to fabricate than 3D PCs, open many exciting opportunities in optoelectronic devices and integrated optics. We review the basics of these structures, with emphasis on basic properties and loss performance, as well as modeling tools, which show that 2D PCs etched through waveguides supported by substrates are a viable route to high-performance PC-based photonic integrated circuits (PICs). A companion paper by Benisty et al. in these proceedings illustrates further high performance building blocks and integrated devices.
We are progressively approaching the physical limits of microcavity LEDs (MC-LEDs) for high brightness, high efficiency LEDs. They are promising high efficiency devices and they offer the very attractive prospect of full planar fabrication process. However, to compete with other high efficiency LED schemes, they need to approach or surpass the 50 % efficiency mark. We first explore the limits of planar MC-LEDs in both the GaAlInAsP and GaInAlN materials systems, and show that the single-step extraction limit is in the 40 % range at best, depending on the materials system used, with the largest part of the non-extracted light being emitted into guided modes. The waveguided light can itself be extracted by photon recycling, when the internal quantum efficiency is high. Otherwise, another extraction scheme for that light is provided by various photonic-crystal-assisted extraction schemes. Simple photonic crystals (PCs) appear to lack the omnidirectional extraction properties required. However, more rotation-invariant PCs like Archimedean tilings allow to obtain such extraction with added efficiencies already in the 10% range. We discuss the further improvements to such structures.
Microcavity light emitting diodes (MCLEDs) are planar emitting devices that can achieve large brightness increase compare to conventional LEDs. We designed and fabricated a GaAs/AlxGa1-xAs surface-emitting MCLED emitting at 880 nm. Two InGaAs quantum wells are included in a (lambda) -Al0.3Ga0.7As cavity between two Al0.1Ga0.9As/Al0.8Ga0.2As Bragg mirrors. The top n-doped Bragg mirror has 4 pairs, the bottom one is p-doped like the substrate and has 20 pairs. The detuning between the source emission wavelength and the Fabry Perot wavelength is -20 nm. It is optimum for an extraction into air. By inserting the bonded MCLED device into an integration sphere we measured a maximum external quantum efficiency of 14% at 10 mA. An epoxy lens is placed on top of the device and the external quantum efficiency is increased up to 20.5% at 10 mA. These values are in good agreement with theoretical calculations if the internal quantum efficiency of the structure is equal to 85%. Additional calculations and measurements are performed and lead to a good physical understanding of the MCLED.
Microcavity light emitting diodes (MCLEDs) present several interesting features compared to conventional LEDs such as narrow linewidth, improved directionality and high efficiency. We report here on MCLEDs with a top emitting geometry. The MCLED layers were grown using molecular beam epitaxy on GaAs substrates. They consist of a 3-period Be- doped distributed Bragg reflector (DBR) centered at 950 nm wavelength, a cavity containing three InGaAs quantum wells and a 15-periods Si-doped DBR. Different values for the wavelength detuning between spontaneous emission line and Fabry-Perot cavity mode were explored, between -40 nm and +10 nm. Devices sizes ranged from 420 X 420 micrometers 2 to 22 X 22 micrometers 2. As expected from simulations, the higher efficiencies are obtained when the detuning is in the -20 to 0 nm range. The devices exhibit then up to 10% external quantum efficiency, measured for a 62 degree(s) collection half-angle. After correction for the surface shadowing due to the grid p-contact, the efficiency increases to 14% and is practically independent of device size.
We report on the MBE growth of nominally 2 and 3 monolayers (ML) thick InAs quantum wells embedded in GaAs. The structures presented were grown using different substrate temperatures and growth interruption times. They were characterized by high resolution x-ray diffraction and low temperature photoluminescence (PL) measurements. The PL spectrum for the 3 ML sample was dominated by a strong electron-hole pair recombination at 1.262 eV, with a full width at half maximum (FWHM) of 39 meV. For a nominally 2 ML InAs quantum well the main PL peak was shifted to higher energies. The PL emission from a second 2 ML thick film having a growth interruption at the InAs/GaAs interface exhibited a large shift to lower energies and a broader linewidth. The evolution from 2 to 3 dimensional growth mode is reflected in the PL spectra and the x-ray diffraction patterns. The spectral positions of the PL peaks are in good agreement with estimates of the subband energies from a 3-band Kane model including the effects of strain.