Spiral-waveguide amplifiers in erbium-doped aluminum oxide on a silicon wafer are fabricated and characterized. Spirals of several lengths and four different erbium concentrations are studied experimentally and theoretically. A maximum internal net gain of 20 dB in the small-signal-gain regime is measured at the peak emission wavelength of 1532 nm for two sample configurations with waveguide lengths of 12.9 cm and 24.4 cm and concentrations of 1.92 × 10(20) cm(-3) and 0.95 × 10(20) cm(-3), respectively. The noise figures of these samples are reported. Gain saturation as a result of increasing signal power and the temperature dependence of gain are studied.

Single-crystalline KY 1-x-y-z Gd x Lu y Yb z (WO 4 ) 2 layers are grown onto undoped KY(WO 4 ) 2 substrates by liquid-phase epitaxy. The purpose of co-doping the KY(WO 4 ) 2 layer with suitable fractions of Gd 3? and Lu 3? is to achieve lattice-matched layers that allow us to engineer a high refractive-index contrast between waveguiding layer and substrate for obtaining tight optical mode confinement and simultaneously accommodate a large range of Yb 3? doping concentrations by replacing Lu 3? ions of similar ionic radius for a variety of optical amplifier or laser applications. Crack-free layers, up to a maximum lattice mismatch of *0.08 %, are grown with systematic variations of Y 3? , Gd 3? , Lu 3? , and Yb 3? concentrations, their refractive indices are measured at several wavelengths, and Sellmeier dispersion curves are derived. The influence of co-doping on the spectroscopy of Yb 3? is investigated. As evidenced by the experimental results, the lattice constants, refractive indices, and transition crosssections of Yb 3? in these co-doped layers can be approximated with good accuracy by weighted averages of data from the pure compounds. The obtained information is exploited to fabricate a twofold refractive-index-engineered sample consisting of a highly Yb 3? -doped tapered channel waveguide embedded in a passive planar waveguide, and a cladding-side-pumped channel waveguide laser is demonstrated.

Modal gain per unit length versus launched pump power is predicted and measured in a 47.5 at.% Yb3+‐doped potassium double tungstate channel waveguide. The highest measured gain exceeds values previously reported for rare‐earth‐ion‐doped materials by two orders of magnitude.

Nanophotonic waveguide enhanced Raman spectroscopy (NWERS) is a sensing technique that uses a highly confined waveguide mode to excite and collect the Raman scattered signal from molecules in close vicinity of the waveguide. The most important parameters defining the figure of merit of an NWERS sensor include its ability to collect the Raman signal from an analyte i.e. "the Raman conversion efficiency" and the amount of "Raman background" generated from the guiding material. Here, we compare different photonic integrated circuit (PIC) platforms capable of on-chip Raman sensing in terms of the aforementioned parameters. Among the four photonic platforms under study, tantalum oxide and silicon nitride waveguides exhibit high signal collection efficiency and low Raman background. In contrast, the performance of titania and alumina waveguides suffers from a strong Raman background and a weak signal collection efficiency respectively.

Silicon nitride Si 3 N 4-on-SiO 2 attracts increasing interest in integrated photonics owing to its low propagation loss and wide transparency window, extending from ∼400 nm to 2350 nm. Scalable integration of active devices such as amplifiers and lasers on the Si 3 N 4 platform will enable applications requiring optical gain and a muchneeded alternative to hybrid integration, which suffers from high cost and lack of high-volume manufacturability. We demonstrate a high-gain optical amplifier in Al 2 O 3 :Er 3 monolithically integrated on the Si 3 N 4 platform using a double photonic layer approach. The device exhibits a net Si 3 N 4-to-Si 3 N 4 gain of 18.1 0.9 dB at 1532 nm, and a broadband gain operation over 70 nm covering wavelengths in the S-, C-and L-bands. This work shows that rare-earth-ion-doped materials and in particular, rare-earth-ion-doped Al 2 O 3 , can provide very high net amplification for the Si 3 N 4 platform, paving the way to the development of different active devices monolithically integrated in this passive platform.