PhD and Postdocs Openings

Wir sind immer auf der Suche nach motivierten und ambitionierten Doktoranden für unsere Experimente mit Quanten-Emittern, nanophotonischen Schaltungen und supraleitenden Einzelphotonen-Detektoren. Bei Interesse meldet Euch gerne bei Prof. Schuck.

Aktuell bieten wir außerdem zwei Doktorandenstellen 1/2 und eine Postdoc-Stelle an!

We always seek motivated and ambitious PhD candidates for our experiments with quantum emitters, nanophotonic circuits and superconducting single-photon detectors. If you are interested please get in touch with Prof. Schuck.

Currently, we are also offering two doctoral positions 1/2 and one postdoc position!

Bachelor-, Master- & Doktorarbeiten

Wir haben immer spannende Themen für Abschlussarbeiten: meldet Euch bei Prof. Schuck!
We always have exciting topics for thesis projects: contact Prof. Schuck!

Themen für Bachelor & Master Arbeiten / Topics for Bachelor and Master theses:

• Optical characterization of colloidal quantum dots at cryogenic temperatures

  In this project, we will use established techniques for integrating colloidal quantum dots,
  that are attractive candidates for realizing a single-photon source, with nanophotonic
  waveguides and characterize the spectral properties of their optical emission. As excitonic
  signatures are difficult to observe at room temperatures we will translate adequately pre-
  characterized chips into cryogenic measurement stations and record optical spectra of such
  quantum dots at 1 Kelvin temperatures.

• Integration of colloidal quantum dots in photonic crystal cavities

  We have recently developed a new generation of highly performant photonic crystal
  resonators for our photonic integrated circuit platforms. In this project, we will investigate
  the quality factors of these devices and integrate colloidal quantum dots into optimal
  resonators in order to observe the Purcell effect, which should force the emission of single
  photons from quantum dots into the cavity mode and control the coherence properties of
  such quantum emitters. We will further be interested in the statistical properties of the
  quantum dot emission, which should be analyzed by performing a so-called Hanbury-Brown-
  Twiss experiment to reveal quantum optical properties in a highly integrated photonic
  system.

• Lifetime measurements of SWCNTs

  Defects in single-walled carbon nanotubes (SWCNTs) can be used as single-photon sources.
  In collaboration with colleagues at the Ruhr-University Bochum we will investigate custom
  engineered SWCNTs, analyze their optical properties first in confocal microscopy and then
  attempt their integration with nanophotonic waveguides. We will particularly be interested
  in their photostability, perform lifetime measurements and investigate the possibility of
  generating emission at technologically relevant telecommunication wavelengths. In a second
  step we plan on performing measurements with custom-designed superconducting
  nanowire single-photon detectors that should allow to resolve extremely fast optical
  processes due to superior timing accuracy.

• Realization of a nanophotonic integrated optical phase shifter based on photo- switchable molecules

  In this project, we will investigate molecules for realizing an optical switch that switches light
  with light. Molecules from the azobenzol-family can exist in two isomer-states, exhibiting
  different refractive indices if embedded in suitable host systems (such as polymers). Light at
  one wavelength can then be used to switch between the isomer states inducing refractive
  index changes for light at another wavelength. If such molecules are integrated with
  nanophotonic waveguides in a Mach-Zehnder interferometer configuration the refractive
  index changes will translate to effective phase shifts allowing to switch between the
  interferometer outputs. We will here try out the integration of such molecules, and investigate
  their switching behaviour as a function of concentration, wavelengths, etc. for finding optimal
  configurations.

• Optimization of fabrication of subwavelength-grating metamaterial waveguides

  Photonic integrated waveguides are typically made of only one core material (e.g., silicon,
  silicon nitride, or tantalum pentoxide) on top of an insulator layer (silicon dioxide). This
  material choice imposes a refractive-index contrast that limits the design space of
  nanophotonic devices. Subwavelength grating (SWG) metamaterials are periodic structures
  with such a small period that diffraction or Bragg reflection effects are prevented, thereby
  enabling diffractionless light propagation. Thus, SWG waveguides can be modelled as
  equivalent homogeneous waveguides with tailorable refractive indices. Owing to the small
  features that are required, the fabrication of these structures is challenging. While some
  SWG waveguides have already been developed in the Münster Nanofabrication Facility
  (MNF), the fabrication process is not optimized, and their performance has not yet been
  sufficiently tested. In this Bachelor project, the student will have to write the mask layouts
  for test chips, refine the fabrication recipes for silicon nitride SWG structures, and assess the
  performance of the devices experimentally.

  
  Only with prior clean room experience or an additional 2-3 months for training at the
  MNF!

• Design of adiabatic transitions for strong integrated Bragg reflectors

  Integrated Bragg reflectors are periodic photonic waveguides that reflect the propagating
  light. These structures are pivotal to creating on-chip spectral filters and Fabry-Pérot cavities.
  Many implementations involve small corrugations in the sidewalls of the waveguides, which
  leads to narrow bandwidths. However, when wider bandgaps are required, strong periodic
  variations need to be applied to the optical waveguides. These variations induce high
  scattering due to the mismatch between the unperturbed waveguide and the Bragg
  waveguide. As a consequence, to reduce optical loss, transitions must be carefully designed.
  In this Bachelor project, firstly, the student will have to simulate different types of
  transitions and evaluate their performance; then, experimental characterization in an optical
  measurement setup will be performed.

• Implementation of new electromagnetic simulation capabilities for nanophotonic inverse design

  In addition to designing nanophotonic circuit components using conventional methods, we
  work on fully automated inverse design algorithms to find abstract structures enabling novel
  functionalities. With computational efficiency being a critical aspect, we employ our own
  Python/C++-based backend to simulate the electromagnetic field distribution needed in
  specific stages of the iterative design process. The simulation backend is not yet feature-
  complete and certain capabilities (such as adaptive mesh refinement in specific regions of
  the simulation cell, a time-domain simulation routine, and advanced sources for interfacing
  with quantum emitters) would broaden the range of devices that can be optimized using our
  inverse-design tool. Please note that good programming skills are essential for this project.

• Optimization of Superconducting Nanowire Single Photon Detectors

  We typically fabricate Superconducting Nanowire Single Photon Detectors (SNSPDs) from
  Niobium-Titanium alloys, which we sputter deposit on our nanophotonic chips. In this
  project, we will test the influence of the material composition (the niobium-to-titanium ratio)
  on the detector performance. The student will learn how to design SNSPDs and characterize
  them in electronic transport measurements, at cryogenic temperatures and extract
  fundamental superconducting properties. The project will involve practical work on our
  cryostats to set up experiments and perform measurements, device fabrication will be
  carried out by a supervisor but students may accompany the process as observers.

• Low noise Superconducting Nanowire Single Photon Detectors

  Superconducting Nanowire Single Photon Detectors (SNSPDs) intrinsically feature very low
  levels of unwanted dark counts (noise), i.e. the detector produces an output signal even
  though no signal was incident. This is a very attractive feature that enables many new
  applications, but it is often difficult to reach the intrinsic dark count level of an SNSPD as
  stray light and black body radiation produce too much unwanted background that is
  indistinguishable from intrinsic dark counts. In this project, we will design an encapsulation
  for a waveguide-integrated SNSPD that should shield the detector from such noise. The
  design will be aided by electromagnetic simulations, which will play an important role in this
  project, while fabrication work will be carried out by a supervisor but students may
  accompany the process as observers.

• Optimization of Total Internal Reflection Couplers for Photonic Integrated Circuits

  Efficient in- and out-coupling of light onto a chip is crucial for the functionality of photonic
  integrated circuits. This project focuses on the utilization of 3D-printed total internal
  reflection couplers to achieve this objective. The primary aim is to enhance the performance
  of the coupler, specifically tailored for the 1550 nm telecom wavelength on a Silicon-on-
  insulator (SOI) platform.
  The project includes the simulation of the coupling through the structure onto the chip to
  achieve enhanced performance, with a particular emphasis on minimizing losses.
  Furthermore, the investigation includes the characterization of the coupler's properties post-
  fabrication, enabling a dynamic development process and the formulation of conclusions.
  The ultimate goal is to gain valuable insights towards the optimization of total reflection
  couplers for photonic integrated circuits.

• Developing a characterization stage for integrated photonic circuits

  Optical characterization is a critical aspect in the analysis of nanophotonic circuits. By
  measuring wavelength-dependent transmission, the optical properties can be evaluated to
  determine if the circuit is functional and meets its intended properties as per the design.
  The objective of this project is to expand a currently developed setup with several new
  features. Existing setups provide efficient in- and out-coupling of signals to the chip for a
  fixed distance of 127 μm between the couplers on the chip. An additional, independent fiber
  for in- and out-coupling will provide more flexibility for nanophotonic circuit design, opening
  the door for the analysis of more complex chip designs. Electrical circuits can be employed to
  characterize resistances and I-V curves of devices on the same stage. The properties of
  devices may be temperature dependent, and to study this influence, Peltier elements can be
  utilized to control the temperature.