Optical gain around 1.5 µm in erbium-doped waveguide amplifiers

The development in the field of erbium-doped integrated waveguide amplifiers for the generation of broadband and high-speed optical amplification around 1.5−1.6 μm is discussed and current and future potential applications are explored. In erbium-doped amorphous aluminium oxide on a silicon wafer, an internal net gain per unit length of 2.0 dB/cm at the wavelength of 1533 nm and internal net gain over a bandwidth of 80 nm has been demonstrated. Spiral-waveguide amplifiers of different lengths and erbium concentrations have been studied and an internal net gain of 20 dB in the small-signal-gain regime has been achieved. Currently, a highly promising crystalline host material, potassium double tungstate, which provides high emission cross sections to rare-earth ions and has generated an internal net gain per unit length of > 1000 dB/cm when exploiting the ytterbium transition at 1 μm, is doped with erbium ions and tested for amplification around 1.5−1.6 μm.