Fig. 1: Ultrafast pulse amplification on a chip.
a Photograph of the chip, hosting several amplifiers. Low-energy chirped pulses are amplified 50-fold. The output pulse is a high-peak power, nearly time-bandwidth-limited femtosecond pulse. b After temporally stretching (chirping) the input pulse, it is coupled to the amplifier chip, where it is gradually amplified and compressed, avoiding strong nonlinearities until passing the output section. c Composite photograph of an amplifier structure consisting of large mode-area (LMA) gain waveguides folded into a small 15 mm2-scale footprint. The waveguides are defined in a silicon nitride (Si3N4) layer, where within the area of the gain waveguides, an active thulium-doped alumina layer (Tm3+:Al2O3) is used as a top cladding; in the input and output sections, a silica (SiO2) cladding is used. d Layer structure in the LMA gain waveguide section. Intensity contours of the optical mode illustrate that most of the power is propagating in the gain layer for optimal amplification. e Same as (d) but for the bent waveguide sections. The mode is strongly confined to the Si3N4-core, enabling low-loss propagation through the bends.
