Meta-hologram-based authentication scheme employing a speckle pattern fingerprint

A concept for an optical holographic security tag is proposed and demonstrated. When illuminated with a laser beam, the image scattered from the tag projects a Quick Response code which encodes identifying information. The image also carries pseudorandom speckle noise, from which a unique speckle pattern "fingerprint" is derived. We show numerically that the tag is unclonable without access to a secret key - the starting conditions of the design algorithm. However, given the key, it is straightforward to reproduce a tag exhibiting the expected fingerprint. Several tags have been realized, implemented as plasmonic meta-holograms, and characterized experimentally. The robustness of the tag to fabrication error and its resilience to counterfeiting are studied in detail and demonstrated experimentally.

Continuous wave amplified spontaneous emission in phase-stable lead halide perovskites

Sustained stimulated emission under continuous-wave (CW) excitation is a prerequisite for new semiconductor materials being developed for laser gain media. Although hybrid organic-inorganic lead-halide perovskites have attracted much attention as optical gain media, the demonstration of room-temperature CW lasing has still not been realized. Here, we present a critical step towards this goal by demonstrating CW amplified spontaneous emission (ASE) in a phase-stable perovskite at temperatures up to 120 K. The phase-stable perovskite maintains its room-temperature phase while undergoing cryogenic cooling and can potentially support CW lasing also at higher temperatures. We find the threshold level for CW ASE to be 387 W cm^-2 at 80 K. These results indicate that easily-fabricated single-phase perovskite thin films can sustain CW stimulated emission, potential at higher temperatures as well, by further optimization of the material quality in order to extend the carrier lifetimes.

High Quality 3D Photonics using Nano Imprint Lithography of Fast Sol-gel Materials

A method for the realization of low-loss integrated optical components is proposed and demonstrated. This approach is simple, fast, inexpensive, scalable for mass production, and compatible with both 2D and 3D geometries. The process is based on a novel dual-step soft nano imprint lithography process for producing devices with smooth surfaces, combined with fast sol-gel technology providing highly transparent materials. As a concrete example, this approach is demonstrated on a micro ring resonator made by direct laser writing (DLW) to achieve a quality factor improvement from one hundred thousand to more than 3 million. To the best of our knowledge this also sets a Q-factor record for UV-curable integrated micro-ring resonators. The process supports the integration of many types of materials such as light-emitting, electro-optic, piezo-electric, and can be readily applied to a wide variety of devices such as waveguides, lenses, diffractive elements and more.

3D whispering-gallery-mode microlasers by direct laser writing and subsequent soft nanoimprint lithography

We demonstrate the realization of 3D whispering-gallery-mode (WGM) microlasers by direct laser writing (DLW) and their replication by nanoimprint lithography using a soft mold technique ("soft NIL"). The combination of DLW as a method for rapid prototyping and soft NIL offers a fast track towards large scale fabrication of 3D passive and active optical components applicable to a wide variety of materials. A performance analysis shows that surface-scattering-limited Q-factors of replicated resonators as high as 1×10⁵ at 635 nm can be achieved with this process combination. Lasing in the replicated WGM resonators is demonstrated by the incorporation of laser dyes in the target material. Low lasing thresholds in the order of 15  kW/cm² are obtained under ns-pulsed excitation.

Standoff detection of explosives and buried landmines using fluorescent bacterial sensor cells

A standoff detection scheme for buried landmines and concealed explosive charges is presented. The detection procedure consists of the following: Live bacterial sensor strains, genetically engineered to produce a dose-dependent amount of green fluorescent protein (GFP) in the presence of explosives' vapors, are encapsulated and spread on the suspected area. The fluorescence produced by the bacteria in response to traces of the explosive material in their microenvironment is remotely detected by a phase-locked optoelectronic sampling system. This scheme enables fast direct access to a large minefield area, while obviating the need to endanger personnel and equipment. Moreover, the employment of phase locking detection efficiently isolates the bacterial sensors' fluorescent output from the background optical signals. This facilitates the application of bacterial sensors in an outdoor environment, where control of background illumination is not possible. Using this system, we demonstrate standoff detection of 2,4-DNT both in aqueous solution and when buried in soil, by sensor bacteria either in liquid culture or agar-immobilized, respectively, at a distance of 50 m in a realistic optically noisy environment.