Open Microcavity Research Articles

Gain Spectroscopy of Solution‐Based Semiconductor Nanocrystals in Tunable Optical Microcavities

The lasing behavior of solution‐based colloidal quantum dots within an open microcavity is reported. The small size and wide tunability of the cavity provide single mode lasing over a wavelength range in excess of 25 nm. By extracting the lasing threshold and differential gain for the fundamental cavity mode over this spectral range, gain spectroscopy of the quantum dot solution is demonstrated. This new approach could help in the optimization of laser gain media and provides a way of constructing miniature laser arrays for on‐chip integration.

Tunable polaritonic molecules in an open microcavity system

We experimentally demonstrate tunable coupled cavities based upon open access zero-dimensional hemispherical microcavities. The modes of the photonic molecules are strongly coupled with quantum well excitons forming a system of tunable polaritonic molecules. The cavity-cavity coupling strength, which is determined by the degree of modal overlap, is controlled through the fabricated centre-to-centre distance and tuned in-situ through manipulation of both the exciton-photon and cavity-cavity detunings by using nanopositioners to vary the mirror separation and angle between them. We demonstrate micron sized confinement combined with high photonic Q-factors of 31 000 and lower polariton linewidths of 150 μeV at resonance along with cavity-cavity coupling strengths between 2.5 meV and 60 μeV for the ground cavity state.

Escape of quantum particles from an open nano-circular microcavity

When a laser is irradiated on a negative ion, it will provide a coherent, mono-energetic source of detached electrons propagating out from the location of the negative ion. The total escape probability density of the electrons when the negative ion is placed inside an open nano-circular microcavity has been studied on the basis of the semiclassical theory. It is shown that significant oscillations appear in the total escape probability density due to the quantum interference effects. Besides, our study suggests that the escape probability density depends on the laser polarization sensitively. In order to show the correspondence between the escaped probability density and the detached electron׳s escaped orbits clearly, we calculate the path length spectrum and find that each peak corresponds to the length of one detached electron׳s escaped orbit. This study provides an example where the quantum nature of the electron׳s wave function can be observed in the macroscopic world. Our study may guide the future experimental research on the escape and transport process of particles through semiconductor microjunctions.

Label-free detection of cardiac troponin I with a photonic crystal biosensor

A biosensor has been developed with a photonic crystal structure used in a total-internal-reflection (PC-TIR) configuration for label-free detection of a cardiac biomarker: Troponin I (cTnI). In contrast to a conventional optical microcavity that has a closed structure with its cavity layer sandwiched between two high-reflection surfaces, the PC-TIR configuration creates a unique open microcavity, which allows its cavity layer (sensing layer) to be easily functionalized and directly exposed to analyte molecules for bioassays. In this study, a PC-TIR sensor has been used for the label-free measurements of cardiac biomarkers by monitoring the changes in the resonant condition of the cavity due to biomolecular binding processes. Antibodies against cTnI are immobilized on the sensor surface for specific detection of cTnI with a wide range of concentrations. Detection limit of cTnI with a concentration as low as 0.1ngmL−1 has been achieved.

Detection of Myoglobin with an Open-Cavity-Based Label-Free Photonic Crystal Biosensor.

The label-free detection of one of the cardiac biomarkers, myoglobin, using a photonic-crystal-based biosensor in a total-internal-reflection configuration (PC-TIR) is presented in this paper. The PC-TIR sensor possesses a unique open optical microcavity that allows for several key advantages in biomolecular assays. In contrast to a conventional closed microcavity, the open configuration allows easy functionalization of the sensing surface for rapid biomolecular binding assays. Moreover, the properties of PC structures make it easy to be designed and engineered for operating at any optical wavelength. Through fine design of the photonic crystal structure, biochemical modification of the sensor surface, and integration with a microfluidic system, we have demonstrated that the detection sensitivity of the sensor for myoglobin has reached the clinically significant concentration range, enabling potential usage of this biosensor for diagnosis of acute myocardial infarction. The real-time response of the sensor to the myoglobin binding may potentially provide point-of-care monitoring of patients and treatment effects.

Fiber In-Line Michelson Interferometer Tip Sensor Fabricated by Femtosecond Laser

A fiber in-line Michelson interferometer tip sensor based on open micro-cavity, which is fabricated by femtosecond laser micromachining and the thin film coating technique, is proposed and demonstrated. When used in refractive index sensing, such an interferometer operates in a reflection mode of detection, and exhibits a compact sensor head, good mechanical reliability, wide operation range, and high sensitivity of 975 nm/refractive index unit at a refractive index value of 1.484.

Mathematical modeling of an open microcavity with a layer of metamaterial

We investigate the properties of an open Fabry-Perot microcavity containing a layer of metamaterial with a negative refractive index. Numerical simulation of this cavity is performed using an original program package based on the FDTD scheme, with allowance for the frequency dispersion of the media and the UPML absorbing boundary conditions. We demonstrate that waveguide eigenmodes with arbitrary profiles exist in such a cavity and the metamaterial lowers diffraction losses considerably.

Enhancing fluorescence detection with a photonic crystal structure in a total-internal-reflection configuration

In contrast to fluorescence enhancement of fluorophores embedded in a photonic crystal structure as previously reported [Appl. Phys. Lett. 75, 3605 (1999)], in this Letter we demonstrate a unique approach to forming an open microcavity using a one-dimensional photonic crystal in a total-internal-reflection geometry. This configuration opens up the possibility for enhancing fluorescence imaging and biosensing. Time-resolved fluorescence detection of fluorophores immobilized on the open cavity has been carried out. Over 20-fold fluorescence enhancement was observed.