Lewis D. Wright | Searcharxiv

arXiv2026

A Fibre-Integrated SPDC Heralded Single-Photon Source Using Zn-Indiffused PPLN Ridge Waveguides at Telecom Wavelengths

We report a fibre-integrated heralded single-photon source based on a commercial Zn-indiffused MgO:PPLN ridge waveguide operated in Type-0 degenerate spontaneous parametric down-conversion (SPDC). The device emits a broadband spectrum spanning approximately 70 nm across the telecom C-and L-bands, with an absolute brightness of $9.1\times 10^{9}$ pairs/(s mW). After accounting for optical losses, we determine an internal heralding efficiency of 58(5)%. The source maintains high purity, exhibiting a coincidences-to-accidentals ratio exceeding $9\times 10^{4}$ and a heralded second-order correlation of $g_{\text{h}}^{(2)}(0) = (5.53 \pm 0.46)\times 10^{-4}$. Low multi-photon noise and broadband emission demonstrate the viability of such platforms for wavelength-multiplexed quantum networking.

quant-ph↗

arXiv2023

Continuous Ultraviolet to Blue-Green Astrocomb

The characterization of Earth-like exoplanets and precision tests of cosmological models using next-generation telescopes such as the ELT will demand precise calibration of astrophysical spectrographs in the visible region, where stellar absorption lines are most abundant. Astrocombs--lasers providing a broadband sequence of ultra-narrow, drift-free, regularly spaced optical frequencies on a multi-GHz grid--promise an atomically-traceable, versatile calibration scale, but their realization is challenging because of the need for ultra-broadband frequency conversion of mode-locked infrared lasers into the blue-green region. Here, we introduce a new concept achieving a broad, continuous spectrum by combining second-harmonic generation and sum-frequency-mixing in an aperiodically-poled MgO:PPLN waveguide to generate gap-free 390-520 nm light from a 1 GHz Ti:sapphire laser frequency comb. We lock a low-dispersion Fabry-Perot etalon to extract a sub-comb of bandwidth from 392-472 nm with a spacing of 30 GHz, visualizing the thousands of resulting comb modes on a high resolution cross-dispersion spectrograph. Complementary experimental data and simulations demonstrate the effectiveness of the approach for eliminating the spectral gaps present in second-harmonic-only conversion, in which weaker fundamental frequencies are suppressed by the quadratic \{chi}^((2)) nonlinearity. Requiring only ~100 pJ pulse energies, our concept establishes a practical new route to broadband UV-visible generation at GHz repetition rates.

physics.optics↗