The Miniaturised Multi‑Laser Engine (mu‑MLE) project, funded by the German Federal Ministry of Education and Research under the “KMU‑Innovativ: Photonik” programme (grant 13N14956), ran from 1 June 2020 to 31 May 2023. It was a consortium of three small and medium‑sized enterprises—Innolume GmbH (Dortmund), Carl Zeiss Microscopy GmbH (Jena) and TOPTICA Photonics AG (Gräfelfing)—supported by the Ferdinand‑Braun‑Institut and the Leibniz Institute for High‑Frequency Technology (FBH Berlin). The project was initially coordinated by Dr. Patrick Leisching and Thomas Klos of TOPTICA, later taken over by Dr. Reto Häring and Chris Kugler. The consortium defined system and sub‑component specifications jointly, iterating them throughout the project.

Technically, the effort focused on semiconductor laser development, optomechanical integration, and compact electronics. New semiconductor material was engineered to provide frequency‑doubled diode lasers at 1092 nm and 1188 nm, achieving higher output power and extended lifetime. P‑I characteristics measured on Innolume chips showed linear operation up to 1000 mA drive and 500 mW output; beyond 500 mW the curves became strongly nonlinear, making calibration difficult for the developed electronics. Amplifier modules were designed in collaboration with TOPTICA; measured results met almost all specifications, with only a slight reduction in polarization‑extinction ratio, which was deemed acceptable for demonstrator testing. The optomechanical design achieved the target module size for four wavelengths, and a realistic price point was set for a 100 mW, six‑wavelength module with two frequency‑doubled lasers, acknowledging the increased complexity of power supply, heat management and integration.

System‑level goals included an external‑fiber output, a lifetime exceeding 5000 h, and coverage of the “yellow gap” wavelengths. Application‑driven specifications for fluorescence microscopy and flow‑cytometry demanded specific output powers, noise levels, modulation bandwidths, and stability under varying environmental conditions. Zeiss and TOPTICA evaluated the demonstrators against these criteria; all but a few minor deviations were satisfied. The electronics architecture comprised a main board driving three lasers and one frequency‑doubled module, with temperature control loops and interface circuitry, and an optional expansion board. The first demonstrator delivered 50 mW external‑fiber power across four laser lines, including a 561 nm frequency‑doubled output. Subsequent iterations expanded to six lines, adding a second frequency‑doubled laser at 594 nm. The final 6‑line demonstrator was integrated into a Zeiss microscope system for end‑to‑end validation.

Overall, the project produced a compact, high‑performance laser platform that bridges the wavelength gap in the visible spectrum, offers high output power with low noise, and meets stringent lifetime and size requirements. The collaborative framework enabled rapid iteration of specifications, shared expertise in semiconductor physics, optomechanics, and system integration, and culminated in a demonstrator ready for deployment in advanced microscopy, flow‑cytometry, and quantum‑optics applications.