Integrated optical single photon source "on demand" based on time multiplexing
Final Report Abstract
The project goal was the development of an integrated optical, efficient single photon source by exploiting a time multiplexing scheme to provide true single photons “on demand” with a high probability of triggered single photon generation and strongly suppressed multi-photon contributions. The time multiplexed source is based on integrated optical circuits realized in LiNbO3. Initial research activities included the modelling of such sources to identify the potential and challenges of the time multiplexing scheme. With purely stochastic models the impact of the losses of the components, which are as expected strongly determine the performance, could be quantitatively analysed. These modelling results provided the guideline for the technological development towards the practical implementation. A key challenge was to minimize losses at interfaces between the different components – in particular at waveguide-fiber interfaces. We developed an apparatus for a precise alignment of the fiber-waveguide coupling with a subsequent permanent fixing the connection via UV-curing glue. This fiber pigtailing can be routinely applied to achieve coupling efficiencies well above 80 % between a (polarisation maintaining) single mode fiber and the Ti-indiffused LiNbO3 waveguides. A `plug&play´ source was developed which exploits type II phase-matched parametric downconversion (PDC) in a Ti-indiffused periodically poled LiNbO3 (PPLN) waveguide. The PDC chip was pigtailed with single mode fibers. Together with a commercial fiber optic polarization beam splitter and isolators for pump suppression a heralded single photon source with high heralding efficiency (>54%) and brightness of B≈1.4·107 pairs/(s mW nm). The purity of the heralded photons was determined from joint spectral intensity and g(2)(0) measurements to be P≈0.69. For the implementation of the time multiplexing scheme electro-optic switches are required. The in-house development of integrated switches based on directional couplers with ∆βreversal electrode structures initially caused problems because the fabrication of durable gold electrodes failed. Although this problem could be solved by using aluminum electrodes, further experiments were performed with a commercial fiber-optic switch. This switch was implemented in a low loss fiber loop. The limited funding prevented the detailed experimental investigation of the time multiplexing. But despite of limited resources we could already apply our PDC source and the electro-optic switch in a feed-forward experiment, where we observed the expected improvement. Further quantitative studies and the implementation of the full time-multiplexing scheme are ongoing.
Publications
- Filtering is not enough for pure, efficient photon pair
E. Meyer-Scott, N. Montaut, J. Tiedau, L. Sansoni, H. Herrmann, T. J. Bartley, and C. Silberhorn
- High efficiency ‘plug & play’ source of heralded single photons
N. Montaut, L. Sansoni, E. Meyer-Scott, R. Ricken, V. Quiring, H. Herrmann, C. Silberhorn
