Design of Mid-IR $\hbox {Er}^{3+}$ -Doped Microsphere Laser

A mid-IR lasing system based on a tapered fiber coupled to an Er³⁺-doped microsphere has been modeled and numerically investigated. In order to design and optimize the device performance, a dedicated 3-D numerical code exploiting the coupled mode theory and the rate equations model has been developed. The main energy level transitions among the Er³⁺ ions, the most relevant secondary ion-ion interactions, the amplified spontaneous emission, and the fiber-microsphere coupling phenomena have been taken into account. In order to optimize the lasing performance, several parametric simulations have been carried out. The obtained numerical results show that a laser threshold of about 55 mW and an output power of about -17.8 dBm can be obtained by using small microspheres.