Structural, chemical, and optical design optimization of an Fe2+-doped chalcogenide fiber for mid-infrared lasing

Optimization of an Fe²⁺-doped chalcogenide fiber is considered for mid-IR lasing. The concept of using a chalcogenide glass as a fiber matrix to support optically active Fe²⁺ ions in ZnSe crystal particles requires use of a protective shell to prevent dissolution of the ZnSe particles. Here, we investigate the effect that the shell has on optical scattering and subsequently the relative gain and loss for a range of particle size, shell thickness and loading fraction of the ZnSe particles. Scattering loss depends on the particle size and is found to be acceptably low for fiber lasing for sizes larger than a threshold size. Furthermore, upon considering collective scattering from the particle group, increasing the concentration is shown to reduce the scattering loss and to be helpful in improving the gain coefficient to scattering loss coefficient ratio. Proper optimization is expected to result in a viable Fe²⁺ mid-IR fiber laser.