Laser system for excitation of fluorescent light sources on a CubeSat
Fig. 1: CubeSat during construction. © Lukas Wiese
Fig. 2: CAD rendering of the laser unit, excluding any housing and electronics.
Fig. 3: Spectral map of an ECDL after all environmental testing.
Quantum technologies have been transforming information processing, communication, sensing, and metrology by exploiting fundamental principles such as superposition and entanglement. These advances promise new capabilities in secure communication and high-precision measurements and are increasingly moving beyond laboratory environments into real-world and space-based applications.
Within this context, the QUICK3 mission (QUantum phonIsChe Komponenten für sichere Kommunikation mit Kleinsatelliten) aims to demonstrate a compact quantum light source in orbit. The mission includes a single-photon source based on fluorescent defects in hexagonal boron nitride (hBN) and an FBH-built fiber-coupled laser system to excite these emitters. The payload is integrated into a 3U (10 × 10 × 34 cm) CubeSat (see Fig. 1) and was launched aboard a Falcon 9 on June 23, 2025. In addition to exploring satellite-based quantum communication, the mission supports tests of extended quantum theories in space using a quantum light interferometer.
Our laser unit operates at 698 nm, a wavelength that, to our knowledge, has not previously been used in space applications. It is not only suitable for exciting different color centers in hBN, but also corresponds to the strontium optical clock transition – highlighting the potential of this technology to enable future space-compatible optical clocks. Developing such devices could significantly enhance timekeeping precision, improve global positioning and navigation, and enable tests of fundamental physics.
The optical design consists of a 698 nm external-cavity diode laser (ECDL) coupled through an isolator into a polarization-maintaining fiber (see Fig. 2). Precision mirrors align the beam into the fiber under single-mode conditions, yielding up to 12 mW of linearly polarized output. This straightforward layout minimizes alignment complexity and facilitates quick assembly. Miniaturization of the laser system was also facilitated by utilizing FBH’s micro-isolator technology developed for space applications.
Rather than following the traditional full space-certification path, we adopted the “new space” philosophy focused on efficient development. Commercial off-the-shelf components were purchased in sets, allowing parallel qualification. The qualification process comprised four tests: vibration and shock tests simulating the conditions of a Falcon 9 transport, a 48-hour thermal-vacuum cycle between 0 °C and 40 °C, and a 20-hour radiation exposure at 10 Gy/h, accumulating a total dose of 200 Gy – roughly fifty times the dosage expected during one year in orbit. Fig. 3 shows the spectral behavior of a laser device for different currents after the qualification: all components retained functionality as an ECDL, and no damage occurred during the tests. Following qualification, we housed the components in a titanium base to ensure alignment. Additionally, we designed a 3D-printed aluminum cover to protect the unit.
By combining a 698 nm laser wavelength with a simplified development process, the payload demonstrates that stringent space-flight requirements can be met rapidly and cost-efficiently. This approach offers a blueprint for future small-satellite quantum payloads and paves the way toward scalable and affordable satellite-based quantum communication networks.
This work is supported by the German Space Agency (DLR) with funds provided by the BMWK under grant number 50WM2166 and 50WM2261B, and with funds provided by the BMFTR under grant number 13N14906.
Publications
N. Ahmadi et al., “QUICK3 – Design of a Satellite‐Based Quantum Light Source for Quantum Communication and Extended Physical Theory Tests in Space”, Advanced Quantum Technologies 7 (2024).
S. Schwertfeger et al., “A 698 nm laser system for excitation of fluorescent quantum light sources on a CubeSat mission”, https://arxiv.org/abs/2509.21065.
M. Bursy et al., “Miniaturised Optical Isolators for Realising Micro-Integrated Photonic Modules in Quantum Technology Applications”, Proc. of 2025 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC).