We investigate two different approaches for imprinting orbital angular momentum (OAM) on different spectral components of a broadband ultraviolet beam with wavelength 350-500 nm for application in quantum optical coherence tomography. Two different approaches using a spiral phase plate (SPP) are studied to achieve this goal. The first approach involves using only a SPP, calibrated for a particular wavelength, for broadband application. However, this approach leads to the presence of unmodulated components in the output beam. In the second approach, combination of SPP and grating is used to remove the unmodulated part and to filter out the imprinted OAM beam.
ACKNOWLEDGEMENTS
This work is supported by Villum Fonden (Villum Investigator project Table-Top Synchrotrons, No. 00037822) and Horizon Europe, the European Union’s Framework Programme for Research and Innovation, under Grant Agreement No. 101070062 (SEQUOIA). Views and opinions expressed are however those of the authors only and do not necessarily reflect those of the European Union. The European Union cannot be held responsible for them.
Traditional spontaneous parametric down-conversion (SPDC) generally has a broad spectral band, while quantum optical coherence tomography (QOCT) aims to achieve an ultra-broadband joint spectrum to ensure good axial resolution. Ultra-broadband supercontinuum (SC) sources enable axial resolutions of approximately 1 µm in OCT. This study investigates the impact of ultra-broadband SPDC using an SC source to generate entangled photon pairs within the 700-1000 nm range. By examining the tuning capabilities and dimensional design of the Beta Barium Borate (BBO) crystal, we explore the combination of the OCT SC source and SPDC for QOCT. The findings contribute to future developments in QOCT.
UV supercontinuum based on gas filled anti resonant hollow core fibers is demonstrated to have passed a major milestone by providing spectral properties comparable to those of plasma arc lamps, namely a broad, flat, low noise, and stable spectrum. The primary advancement is the use of pump modulation which flattens the spectrum by more than 20dB. As proof of concept, results from scatterometry measurements, with both UV supercontinuum and plasma arc lamps are shown to produce comparable results. However, UV supercontinuum can meet additional requirements making it suitable for many cutting-edge UV metrology applications such as imaging and spectroscopy.
Single photon sources are a key element for quantum computing, quantum key distribution (QKD) and quantum communications. In particular, producing single photons at telecommunications wavelengths is valuable for QKD protocols and would enable realizing the quantum internet. The preferred method for their generation has long been spontaneous down conversion in bulk crystals, which suffers from connection loss to fiber networks. In-fiber spontaneous four-wave mixing provides a viable alternative as a photon pair source due to being compatible with existing fiber networks.
We present an all-fiber photon pair source based on degenerate four-wave mixing in a 400 m Highly-Nonlinear fiber, with signal and idler wavelengths generated at 1552.5 nm and 1557 nm respectively. The source consists of CW pump laser operating at 1554.75 nm, which is slightly detuned from the zero group velocity dispersion wavelength into the normal dispersion regime. After pair generation in the highly-nonlinear fiber, three arrayed waveguide gratings are employed to spatially separate signal and idler, and provides a 120 dB pump power reduction. Firstly the source is modelled and experimentally characterized in the well known classical regime of stimulated four-wave mixing. The effect of fiber cooling on spontaneous Raman scattering is modelled and characterized, and a 30% reduction in spontaneous emission is found when cooling the fiber to -77°C. In the low power regime the coincidence to accidental count ratio is simulated and measured. An increase in the coincidence to accidental count ratio is observed when cooling the fiber.
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