Ultraviolet writing of channel waveguides in proton-exchanged LiNbO₃

We report on a direct ultraviolet (UV) writing method for the fabrication of channel waveguides at 1.55 µm in LiNbO3 through UV irradiation of surface and buried planar waveguides made by annealed proton exchange and reverse proton exchange. A systematic study of the guidance properties as a function of the UV writing conditions is presented

A two-way photonic interface for linking Sr+ transition at 422 nm to the telecommunications C-band

We report a single-stage bi-directional interface capable of linking Sr+ trapped ion qubits in a long-distance quantum network. Our interface converts photons between the Sr+ emission wavelength at 422 nm and the telecoms C-band to enable low-loss transmission over optical fiber. We have achieved both up- and down-conversion at the single photon level with efficiencies of 9.4% and 1.1% respectively. Furthermore we demonstrate noise levels that are low enough to allow for genuine quantum operation in the future.Comment: 5 pages, 4 figure

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.Comment: 14 pages; 4 figure

Direct-UV-written buried channel waveguide lasers in direct-bonded intersubstrate ion-exchanged neodymium-doped germano-borosilicate glass

We report a technique for producing single-mode buried channel waveguide lasers in neodymium-doped SiO2:GeO2:B2O3:Na2O (SGBN) glass. Direct bonding forms the basis of this process, providing a buried waveguide layer in the photosensitive SGBN material into which channel confinement can be directly written with a focused UV beam. Characterization of a 7.5-mm-long device was performed using a Ti:Sapphire laser operating at 808 nm and the resultant 1059 nm channel waveguide laser output exhibited single-mode operation, milliwatt-order lasing thresholds, and propagation losses of <0.3 dB cm–1

Media 6: Nanoscale roughness micromilled silica evanescent refractometer

Originally published in Optics Express on 26 January 2015 (oe-23-2-1005

Optimizing resolution in an integrated blazed chirped Bragg grating spectrometer

We present an investigation into the resolution of blazed chirped Bragg grating spectrometers. These are dispersive spectrometers that diffract light out of a waveguide at a wavelength dependent angle, whilst focusing the light. The spectral resolution is found to be inversely proportional to grating length; previously used fabrication schemes limited the grating length (and hence resolution) when creating compact devices. We propose and implement a solution to this problem by varying the blaze angle of a Bragg grating along its length. Initial results show the fabrication of longer gratings (while preserving focal length) and an increase in FWHM resolution from 0.57 nm to 0.52 nm. This increase in resolution is thought to be limited by the appearance of aberrations which can be corrected for in future devices

Germanium-on-silicon waveguides operating at mid-infrared wavelengths up to 8.5 μm

We report transmission measurements of germanium on silicon waveguides in the 7.5–8.5 μm wavelength range, with a minimum propagation loss of 2.5 dB/cm at 7.575 μm. However, we find an unexpected strongly increasing loss at higher wavelengths, potential causes of which we discuss in detail. We also demonstrate the first germanium on silicon multimode interferometers operating in this range, as well as grating couplers optimized for measurement using a long wavelength infrared camera. Finally, we use an implementation of the “cut-back” method for loss measurements that allows simultaneous transmission measurement through multiple waveguides of different lengths, and we use dicing in the ductile regime for fast and reproducible high quality optical waveguide end-facet preparation