Rico Henze

Three-dimensional quantum photonic elements based on single nitrogen vacancy-centres in laser-written microstructures

To fully integrate quantum optical technology, active quantum systems must be combined with resonant microstructures and optical interconnects harvesting and routing photons in three diemsnsions (3D) on one chip. We fabricate such combined structures for the first time by using two-photon laser lithography and a photoresist containing nanodiamonds including nitrogen vacancy-centers. As an example for possible functionality, single-photon generation, collection, and transport is successfully accomplished. The single photons are efficiently collected via resonators and routed in 3D through waveguides, all on one optical chip. Our one-step fabrication scheme is easy to implement, scalable and flexible. Thus, other complex assemblies of 3D quantum optical structures are feasible as well.

An alignment-free fiber-coupled microsphere resonator for gas sensing applications

In this paper we report on the assembly of a robust sensor system consisting of a polystyrene microsphere resonator attached to an optical fiber taper. Since the sphere is only supported by the micrometer-sized fiber no further alignment is necessary. This results in a thermally and mechanically well isolated optical resonator system with quality factors as high as 6×105. The narrow resonances of whispering gallery modes supported by the polystyrene resonators shift with temperature at a rate of 3.8 GHz/K. Thus, a sensitive thermometer is established which allows to detect the surrounding gas via its characteristic thermal conductivity.In this paper we report on the assembly of a robust sensor system consisting of a polystyrene microsphere resonator attached to an optical fiber taper. Since the sphere is only supported by the micrometer-sized fiber no further alignment is necessary. This results in a thermally and mechanically well isolated optical resonator system with quality factors as high as 6×105. The narrow resonances of whispering gallery modes supported by the polystyrene resonators shift with temperature at a rate of 3.8 GHz/K. Thus, a sensitive thermometer is established which allows to detect the surrounding gas via its characteristic thermal conductivity.

On-demand positioning of a preselected quantum emitter on a fiber-coupled toroidal microresonator

The coupling of a quantum emitter to the modes of a silica toroid is presented. A fiber taper is used to manipulate and transfer a preselected diamond nanocrystal onto the toroid. Optical coupling of few nitrogen vacancy (NV) color centers contained inside the nanocrystal to the resonator modes is demonstrated by detecting the fluorescence via a tapered optical fiber coupler. A clear antibunching in the photon correlation measurement is observed indicating emission from only six NV centers residing inside the nanocrystal. The latter is confirmed by a photoluminescence spectrum at liquid helium temperature resolving individual zero phonon lines.

Fine-tuning of whispering gallery modes in on-chip silica microdisk resonators within a full spectral range

We investigate an efficient method for fine-tuning whispering gallery mode resonances in disk-type silica microresonators to reach an arbitrary frequency within the free spectral range of the system. This method is based on a post-production hydrofluoric acid etching process to precisely resize the radius of such microresonators. We show the effectiveness of this approach by tuning their resonance frequency within 10 GHz of specific hydrogen cyanide reference lines (P16, P18). This technique allows for simple and exact matching of narrow-linewidth lasers or spectroscopic lines with the high-Q resonances of on-chip silica microresonators.

Temperature independent tuning of whispering gallery modes in a cryogenic environment

A new tuning method for tuning whispering gallery modes (WGMs) in a cryogenic environment is presented. Within a home-made exchange gas cryostat the applicability of pressure tuning in microbubbles at liquid nitrogen (LN) temperature is shown. The general thermal shift and tuning behavior of borosilicate microbubbles is theoretically analyzed and compared to experimental data. We show that stress/strain tuning using compressed gas is widely unaffected by system temperature.

Design and numerical optimization of an easy-to-fabricate photon-to-plasmon coupler for quantum plasmonics

We design an on-chip single mode photon to surface-plasmon coupler. Our coupler consists of a tapered dielectric waveguide and a V-shaped plasmonic part. In contrast to other concepts designated to minimized-loss coupling into long-ranging waveguides, we focus on an easy-to-fabricate structure working in the visible spectral range. The air-cladded design provides full experimental access to the evanescent fields emerging from the plasmonic stripe guide. An adaptive finite element method for full three dimensional simulations is used combined with the Taguchi method for optimization, which makes our procedure extremely time-efficient and executable on standard personal computers.

Nanophotonics with Single Photons from NV Centers in Three-Dimensional Laser-Written Microstructures

Three dimensional quantum optical elements are built using a hybrid material consisting of nanodiamonds and a photoresist. Single photons from nitrogen-vacancy centers are routed between them and scalable on-demand fabrication of such elements is introduced.