Expanding RNA editing toolkit using an IDR-based strategy.

RNA base editors should ideally be free of immunogenicity, compact, efficient, and specific, which has not been achieved for C > U editing. Here we first describe a compact C > U editor entirely of human origin, created by fusing the human C > U editing enzyme RESCUE-S to Cas inspired RNA targeting system (CIRTS), a tiny, human-originated programmable RNA-binding domain. This editor, CIRTS-RESCUEv1 (V1), was inefficient. Remarkably, a short histidine-rich domain (HRD), which is derived from the internal disordered region (IDR) in the human CYCT1, a protein capable of liquid-liquid phase separation (LLPS), enhanced V1 editing at on-targets as well as off-targets, the latter effect being minor. The V1-HRD fusion protein formed puncta characteristic of LLPS, and various other IDRs (but not an LLPS-impaired mutant) could replace HRD to effectively induce puncta and potentiate V1, suggesting that the diverse domains acted via a common, LLPS-based mechanism. Importantly, the HRD fusion strategy was applicable to various other types of C > U RNA editors. Our study expands the RNA editing toolbox and showcases a general method for stimulating C > U RNA base editors.

Origin of thermally activated Er3+ emission in GeGaSe films and waveguides.

The origin of the dead or active emission from Er in various Er-doped films has been unclear. Here we took Er-doped GeGaSe as examples and investigated the correlation between the intensity of the photoluminescence (PL) spectra, the content of the activated Er ions, and the intensity of the absorption spectra in the waveguides. We found the linear correlation between the content of Er ions, photoluminescence, and absorption intensity. This provides clear evidence that thermal annealing can promote the conversion of Er metals into Er ions, and such a conversion is essential for practical applications, in which the number of the activated Er ions rather than the nominal Er contents in the materials plays an important role in achieving emission and thus effective optical amplification and lasing.

On-chip Er-doped Ta2O5 waveguide amplifiers with a high internal net gain.

We designed and fabricated a double-layered structure Er3+:Ta2O5 waveguide and investigated its optical amplification performance in C band. The pump laser threshold for zero gain at 1533 nm was 2.5 mW, and the internal net gain was ∼4.63 dB/cm for a lunched pump power of 36.1 mW at 980 nm and signal input power of -30.0 dBm (1 µW). The relationship between the internal gain and the signal input power was also investigated, and a large internal net gain of 10.58 dB/cm was achieved at a signal input power of ∼-47.1 dBm. The results confirm the potentials of the use of Ta2O5 as a host material for optical waveguide amplification.

Formation of nanochannels in sapphire with ultrashort Bessel pulses.

We explore, both by numerical simulations and experimentally, the flexibility in controlling Bessel beam parameters by re-imaging it into transparent material with a demagnifying collimator for the formation of high-aspect ratio nanochannels. Analysis of nanochannels produced by in-house precision-made axicon with 275 fs pulses in sapphire reveals the intensity threshold of ∼7.2 × 1013 W/cm2 required to create the cylindrical microexplosion. We estimate that the maximum applied pressure during the process was 1.5 TPa and that the resulting density of compressed sapphire in the nanochannel's shells are ∼1.19 ± 0.02 times higher than the pristine crystal, and higher than what was achieved before in spherical microexplosion with Gaussian pulses.

Real-time change of optical losses in chalcogenide waveguides induced by light illumination.

We prepared several GeGaSe waveguides with different chemical compositions and measured the change of optical losses induced by light illumination. Together with some experimental data in As2S3 and GeAsSe waveguides, the results showed that maximum change of the optical loss can be observed in the waveguides under bandgap light illumination. The chalcogenide waveguides with close to stoichiometric compositions have less homopolar bonds and less sub-bandgap states, and thus are preferential to have less photoinduced losses.

Integrated microwave photonic true-time delay with interferometric delay enhancement based on Brillouin scattering and microring resonators.

True-time delays are important building blocks in modern radio frequency systems that can be implemented using integrated microwave photonics, enabling higher carrier frequencies, improved bandwidths, and a reduction in size, weight, and power. Stimulated Brillouin scattering (SBS) offers optically-induced continuously tunable delays and is thus ideal for applications that require programmable reconfiguration but previous approaches have been limited by large SBS gain requirements. Here, we overcome this limitation by using radio-frequency interferometry to enhance the Brillouin-induced delay applied to the optical sidebands that carry RF signals, while controlling the phase of the optical carrier with integrated silicon nitride microring resonators. We report a delay tunability over 600 ps exploiting an enhancement factor of 30, over a bandwidth of 1 GHz using less than 1 dB of Brillouin gain utilizing a photonic chip architecture based on Brillouin scattering and microring resonators.

Design and fabrication of As2Se3 chalcogenide waveguides with low optical losses.

In this paper, we report the fabrication and characterization of chalcogenide-based planar waveguides for possible applications in broadband light sources and/or biochemical sensing. ${{\rm Ge}_{11.5}}{{\rm As}_{24}}{{\rm Se}_{64.5}}$Ge11.5As24Se64.5 film as bottom cladding followed by another layer of ${{\rm As}_2}{{\rm Se}_3}$As2Se3 was deposited on a thermally oxidized silicon wafer using thermal evaporation, and the waveguides were patterned directly on the ${{\rm As}_2}{{\rm Se}_3}$As2Se3 layer by UV exposure followed by inductively coupled plasma dry etching. The device structure was optimized by using commercial software (COMSOL Multiphysics) based on complete vector finite components, and the fundamental mode of the waveguide was calculated. By optimizing the geometry of the waveguide, the zero dispersion wavelength was shifted to a short wavelength (at $\sim{2}.{3}\;\unicode{x00B5} {\rm m}$∼2.3µm), which facilitates supercontinuum generation with shorter wavelength pump source. The insertion loss of the rib waveguides with different widths was measured using the cut-back method, and the best propagation loss at 1550 nm was 1.4 dB/cm.

Greater than 50% inversion in Erbium doped Chalcogenide waveguides.

We report Er-doped Ge-Ga-Se films and waveguides deposited using co-thermal evaporation and patterned with plasma etching. Strong photoluminescence at 1.54 µm with intrinsic lifetime of 1 ms was obtained from deposited films with 1490 nm excitation. Erbium population inversion up to 50% was achieved, with a maximum of ~55% possible at saturation for the first time to the author's knowledge, approaching the theoretical maximum of 65%. Whilst gain was not achieved due to the presence of upconversion pumped photoinduced absorption, this nonetheless represents a further important step towards the realization of future chalcogenide Erbium doped waveguide amplifiers at 1550 nm and in the Mid-infrared.

Internal gain in Er-doped As2S3 chalcogenide planar waveguides.

Low-loss erbium-doped As2S3 planar waveguides are fabricated by cothermal evaporation and plasma etching. Internal gain in the telecommunications band is demonstrated for the first time in any chalcogenide glass and additionally in a thin film planar waveguide amplifier configuration.

Hybrid waveguide from As2S3 and Er-doped TeO2 for lossless nonlinear optics.

The fabrication and characterization of loss-compensated dispersion-engineered nonlinear As(2)S(3) on Er:TeO2 waveguides is reported for the first time, to the best of our knowledge. The hybrid waveguide is a strip loaded structure made from an Er-doped TeO2 slab and an etched As(2)S(3) strip. Almost complete loss compensation is demonstrated with 1480 nm pumping and a fully lossless waveguide with high nonlinear coefficient can be achieved with higher 1480 nm pump power.