Detecting electromagnetic radiation at the quantum limit is essential for a wide range of applications, and superconducting nanowire single-photon detectors (SNSPDs) are among the highest-performing devices for this task. However, scaling SNSPDs from few-pixel devices to large detector arrays while preserving their beneficial metrics remains challenging.
In this work, three advances toward the realization of SNSPD arrays are presented. Atomic layer deposition is employed to enable uniform superconducting niobium nitride films of only few-nanometer thickness suitable for large-area devices. To operate and read out multiple detectors with a reduced number of lines, a frequency-multiplexing scheme is investigated, in particular regarding its effect on the resetting behavior and duty cycle of the detector. Finally, efficient optical coupling from free space and optical fibers onto the active area of the detectors is achieved by directly integrating SNSPDs with free-form polymer structures.
Author(s): Emanuel Marius Knehr
Publisher: KIT Scientific Publishing
Year: 2022
Language: English
Pages: 197
City: Karlsruhe
Kurzfassung
Contents
Introduction
Superconducting nanowire single-photon detectors
Superconducting detectors
Operation principle of SNSPDs
Hotspot formation
Detection mechanism
Response dynamics
Detection metrics
Detection efficiency and spectral dependence
Dark-count rate
Maximum count rate
Other metrics
Detector materials
State-of-the-art NbN thin film deposition
SNSPD arrays
Multiplexing schemes
Frequency-multiplexed SNSPDs
Optical coupling
Free-space coupling
Fiber coupling
On-chip coupling
Summary
Atomic-layer-deposited NbN thin films
Atomic layer deposition of NbN
Properties of ALD-NbN
Film properties
Micro- and nanobridge properties
Variation of the ICP-to-sample distance
Spatial uniformity of ALD-NbN
Morphological uniformity
Compositional uniformity and crystal structure
Spread of superconducting properties
Summary
ALD-NbN SNSPDs
Detector design and fabrication
Detector design
Detector patterning
Experimental setup
Optical detector characterization
Bias and photon-rate dependence
Spectral dependence
Thickness-dependent dark and photon counts
Summary
Frequency-multiplexed SNSPDs
Array design and fabrication
Self-resetting behavior
Simulation of DC- and RF-biased detectors
Synchronized gated detection
Experimental setup
Phase-sensitive detection efficiency
Duty cycle
Matched-filter array readout
Concept
Proof-of-principle experiment
Future readout of RF-SNSPD arrays
Summary
Optical coupling
Microlens-integrated RF-SNSPD
Microlens concept and fabrication
Optical measurements of the microlens gain
Optical packaging of SNSPDs with photonic wire bonds
Detector design and fabrication
Direct laser-writing of the bonds
Optical measurements of the PWB coupling efficiency
Summary
Nanowire characterization with M-KING
Layout and fabrication
Current-dependent microwave properties
Determination of the depairing current
Noise current
Summary
Conclusions and outlook
List of Figures
List of Tables
Nomenclature
Bibliography
List of Own Publications
Peer-reviewed Journals
Conferences
Danksagung
