Versatile SESAM Platform for 1560 nm Operation Based on Strain-Free, InP-based MBE Growth

Ultrafast fiber and solid-state lasers at 1560 nm find extensive applications in ultrafast spectroscopy, optical clocks, and telecommunications. Passive mode-locking is often achieved using semiconductor saturable absorber mirrors (SESAMs) [1], which must be meticulously designed to ensure reliable self-starting and continuous wave mode-locked operation. While state-of-the-art SESAMs are grown on GaAs, the lack of suitable lattice-matched absorber materials for the 1.5 μm range leads to reliance on highly strained InGaAs layers with the consequence of defect formation and high non-saturable losses. We report on our strain-free SESAMs grown on InP with bulk, unstrained iron-doped InGaAs absorbers, thus enhancing optical quality and durability and enabling precise tuning of relaxation times [2]. In addition to the benefit for fiber lasers [3], here we demonstrate that this approach also provides the higher reflectivity and lower losses required for solid-state lasers.