Phase-change materials

Phase-change materials (PCMs) offer a huge contrast in their refractive index when switched between an amorphous and crystalline state, for example exhibited as the data storage medium in DVDs. Combined with integrated photonics these materials widley open the door for many applications in all-optical signal processing and computing. First prototypes of all-optical multilevel data storage, an abacus for arithmetic operations and non-volatile switches have been developed and realized in our group.
A highly vivid and interesing topic of current research are unconventional computing architectures as neural networks, for example used for pattern and speech recognition. In our group, we investigate all-optical neural networks based on the phase-change photonic platform.

Diamond Photonics for Quantum Registers

Diamond provides attractive material properties for both optical applications and mechanical devices. Especially defects in diamond offer one of the most promising platforms for spin-photonic qubits. They offer a discrete energetic level structure within diamond’s bandgap accessible with photons while also featuring long coherence times due to the low nuclear spin noise in diamond. We use Faraday cage angled etching to create free-standing photonic nanobeam resonators from single crystal diamond substrate. These resonators enable coherent coupling of the defect to our diamond photonic circuitry via the Purcell effect. Since our resonators are made of diamond, defects can be created via focused ion beam (FIB) implantation in the centers of our resonators. This allows for the fabrication of large-scale quantum registers.

Superconducting nanowires

Superconducting nanowires allow for realizing single photon detectors with high timing resolution and quantum efficiency. We demonstrate the first nanophotonic circuits that incorporate such devices on chip. By fabricating nanowire detectors directly on top of waveguides we achieve near perfect detection efficiency, high timing resolution and a miniature footprint all in the same device. The results are the first step towards fully scalable single photon circuits at telecoms wavelengths.

The fiber tapering setup

Preparation of fibers necessary for coupling light adiabatically from fiber to chip.

Coupling light efficiently from standard fiber optics to nanometer-scale on-chip waveguides remains a key challenge for Photonic-Integrated systems. One of the most efficient ways to do so is through adiabatic coupling.

Placing the fiber taper on top of a tapered waveguide allows for super-low-loss transfer of light, which is particularly interesting for single-photon and quantum computation applications.

In this setup we thin down fibers with diameters of hundreds of micrometers to diameters in the range of integrated photonic waveguide dimensions. The thinning procedure requires melting the fiber with a hydrogen flame and pulling it in a reproducible fashion. The fabrication of high-quality fiber tapers requires clean preparation, statistical optimization, and a little bit of mechanical ingenuity.

This setup is always open for contributions from students with the scope of a Projektpraktikum/Bachelor’s thesis/Master’s thesis or similar.

Contact: Mark Ulanov

Video: Shabnam Taheriniya