arXiv subjects

James A. Grieve

Publications and source records attributed to James A. Grieve.

24 records · Page 2Linked to original sources

arXiv2018

Tunable interferometers on a flexible polymer chip

To facilitate the implementation of large scale photonic quantum walks, we have developed a polymer waveguide platform capable of robust, polarization insensitive single mode guiding over a broad range of visible and near- infrared wavelengths. These devices have considerable elasticity, which we exploit to enable tuning of optical behaviour by precise mechanical deformations. In this work, we investigate pairs of beamsplitters arranged as interferometers. These systems demonstrate stable operation over a wide range of phases and reflectivities. We discuss device performance, and present an outlook on flexible polymer chips supporting large, reconfigurable optical circuits.

physics.app-ph↗

arXiv2018

Mechanically tunable integrated beamsplitters on a flexible polymer platform

We report the development of a monolithic, mechanically tunable waveguide platform based on the flexible polymer polydimethyl siloxane (PDMS). Such devices preserve single mode guiding across a wide range of linear geometric distortions. This enables the realization of directional couplers with tunable splitting ratios via elastic deformation of the host chip. We fabricated several devices of this type, and verified their operation over a range of wavelengths, with access to the full range of input/output ratios. The low cost and relative ease of fabrication of these devices via a modified imprint lithographic technique make them an attractive platform for investigation of large scale optical random walks and related optical phenomena.

physics.optics↗

arXiv2017

SpooQySats: cubesats to demonstrate quantum key distribution technologies

Satellite-based QKD offers the potential to share highly secure encryption keys between optical ground stations all over the planet. SpooQySats is a programme for establishing the space worthiness of highly-miniaturised, polarization entangled, photon pair sources using CubeSat nanosatellites. The sources are being developed iteratively with an early version in orbit already and improved versions soon to be launched. Once fully developed, the photon pair sources can be deployed on more advanced satellites that are equipped with optical links. These can allow for very secure uplinks and downlinks and can be used to establish a global space-based quantum key distribution network. This would enable highly secure symmetric encryption keys to be shared between optical ground stations all over the planet.

quant-ph↗

arXiv2016

Correcting for accidental correlations in saturated avalanche photodiodes

In this paper we present a general method for estimating rates of accidental coincidence between a pair of single photon detectors operated within their saturation regimes. By folding the effects of recovery time of both detectors and the detection circuit into an "effective duty cycle" we are able to accomodate complex recovery behaviour at high event rates. As an example, we provide a detailed high-level model for the behaviour of passively quenched avalanche photodiodes, and demonstrate effective background subtraction at rates commonly associated with detector saturation. We show that by post-processing using the updated model, we observe an improvement in polarization correlation visibility from 88.7% to 96.9% in our experimental dataset. This technique will be useful in improving the signal-to-noise ratio in applications which depend on coincidence measurements, especially in situations where rapid changes in flux may cause detector saturation.

quant-ph↗

arXiv2015

The thick-crystal regime in photon pair sources

We present comprehensive measurement data on the pump and collection beam parameters necessary to achieve high collection efficiency ($89.0 \pm 1.7 \%$) together with high brightness when a single $β$-Barium Borate crystal is operated in the thick-crystal regime and pumped with a narrow linewidth laser source. Spectral analysis of the collinear, non-degenerate photons suggest that the effective interaction length within the crystal is dominated by the collection beam mode and the use of longer crystals with increased spatial walk-off does not necessarily lead to a reduced collection efficiency. This result is an important consideration for optical designers who seek to develop practical photon pair sources.

physics.optics↗

arXiv2015

Extreme environmental testing of a rugged correlated photon source

Experiments in long distance quantum key distribution have motivated the development of ruggedised single photon sources, capable of producing useful correlations even when removed from the warm, nurturing environment found in most optics laboratories. As part of an ongoing pro- gramme to place such devices into low earth orbit (LEO), we have developed and built a number of rugged single photon sources based on spontaneous parametric downconversion. In order to evalu- ate device reliability, we have subjected our design to various thermal, mechanical and atmospheric stresses. Our results show that while such a device may tolerate launch into orbit, operation in orbit and casual mishandling by graduate students, it is probably unable to survive the forcible disassembly of a launch vehicle at the top of a ball of rapidly expanding and oxidising kerosene and liquid oxygen.

quant-ph↗