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.
We study the spectroscopic properties of thin films of potassium ytterbium gadolinium double tungstates, KYb0.57Gd0.43(WO4)2, and potassium ytterbium lutetium double tungstates, KYb0.76Lu0.24(WO4)2, specifically at the central absorption line near 981 nm wavelength, which is important for amplifiers and lasers. The absorption cross-section of both thin films is found to be similar to those of bulk potassium rare-earth double tungstates, suggesting that the crystalline layers retain their spectroscopic properties albeit having >50 at.% Yb3+ concentration. The influence of sample temperature is investigated and found to substantially affect the measured absorption cross-section. Since amplifiers and lasers typically operate above room temperature due to pump-induced heating, the temperature dependence of the peak-absorption cross-section of the KYb0.57Gd0.43(WO4)2 is evaluated for the sample being heated from 20 °C to 170 °C, resulting in a measured reduction of peak-absorption cross-section at the transitions near 933 nm and 981 nm by ~40% and ~52%, respectively. It is shown that two effects, the change of Stark-level population and linewidth broadening due to intra-manifold relaxation induced by temperature-dependent electron-phonon interaction, contribute to the observed behavior. The effective emission cross-sections versus temperature have been calculated. Luminescence-decay measurements show no significant dependence of the luminescence lifetime on temperature.
A low-loss and broadband multimode interference (MMI)-based wavelength multi/demultiplexer in Si 3 N 4 /SiO 2 technology for erbium-doped lasing and amplifying applications is presented. The structural parameters of a 2 × 1 Si 3 N 4 MMI multi/demultiplexer are optimized to minimize losses. The design and analysis of the MMI multi/demultiplexer are carried out using a hybrid approach, which combines a modified effective index method, the 2D film mode matching method, and the 2D beam propagation method, with lower impact in the computing requirements and simulation time than 3D methods. Simulated total losses of 0.19 and 0.23 dB at 980 and 1550 nm, respectively were obtained for the optimized MMI multi/demultiplexer. The measurements of our fabricated couplers, with 110 nm thick Si 3 N 4 layer, show good agreement with our design. As multiplexers, the average losses of the MMI were measured to be 0.4 ± 0.3 dB for both 976 and 1550 nm wavelengths, and less than 1 dB across the whole C-band. As demultiplexers, the measured average extinction ratio of the fabricated MMI was found to be 21.4 ± 1.2 and 26.3 ± 0.8 dB for pump and signal wavelengths, respectively. Index Terms-Beam propagation and laser couplers, integrated optoelectronics, multi/demultiplexer, multimode interference (MMI), silicon nitride (Si 3 N 4 ).
Abstract:We report on the optical-gain properties of channel waveguides patterned into lattice-matched KGd x Lu y Er 1-x-y (WO 4 ) 2 layers grown onto undoped KY(WO 4 ) 2 substrates by liquid phase epitaxy. A systematic investigation of gain is performed for five different Er 3+ concentrations in the range of 0.75 to 10at.% and different pump powers and signal wavelengths. In pump-probe-beam experiments, relative internal gain, i.e., signal enhancement minus absorption loss of light propagating in the channel waveguide, is experimentally demonstrated, with a maximum value of 12 ± 5 dB/cm for signals at the peakemission wavelength of 1534.7 nm.
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