Quantum networks can exploit quantum effects over long distances, for example, to enable tap-proof communication, synchronize quantum clocks, connect telescopes, or network quantum computers and increase their computational capability. To adapt the wavelength of current optical qubits to the optical fiber standard (1550 nm) and prevent high losses during information transmission, high-precision quantum frequency converters (QFC) are needed. In the project “HIFI — Highly Integrated Quantum Frequency Converter of Highest Fidelity Based on Innovative Laser, Fiber and Production Technology,” a consortium is developing such QFCs. The German Federal Ministry of Education and Research (BMBF) is funding HIFI over three years as part of the funding measure “Enabling Technologies for Quantum Technologies.”

The Fraunhofer Institute for Applied Solid State Physics IAF contributes to the project by developing special single-mode semiconductor disk lasers (SDL) as low-noise pump sources for quantum frequency conversion. These are expected to meet the strict requirements of QFCs in terms of pump power, linewidth as well as stability, thus enabling high conversion efficiency with minimal wavelength noise that would interfere with the functionality of optical qubits.

2-µm semiconductor disk lasers enable low-noise quantum frequency conversion

Dr. Marcel Rattunde, project leader of HIFI on the part of Fraunhofer IAF, emphasizes the importance of SDL development for the project: “In HIFI, a particularly low-noise type of frequency conversion is being developed. This necessitates a powerful, narrow-band laser in the range around 2.0 to 2.2 µm, which at the same time can be stabilized and spectrally tuned precisely to the application. Gallium antimonide (GaSb) based semiconductor disk lasers are the ideal light source for this purpose, because they can combine high output power with spectral tunability, single-mode emission and long-term stability.”

In HIFI, for example, Fraunhofer IAF researchers have developed a compact and spectrally single-mode SDL module based on the III-V semiconductor material system GaSb. It can be actively locked for absolute wavelength stability using a frequency comb at a wavelength of 2128 nm, achieves a high output power currently exceeding 1.5 W, and is characterized by a narrow linewidth. With this module, the frequency of optical qubits from nitrogen-vacancy centers (NV centers) in diamond, which is 637 nm, can be converted to the telecom band.

Module development and manufacturing as part of the III-V semiconductor value chain at Fraunhofer IAF

Realizing modules for applications in optoelectronics as well as high-frequency and power electronics forms an essential step in the value chain for III-V compound semiconductors. Fraunhofer IAF covers not only this step, but the entire research and development (R&D) value chain: from simulation and design of circuits or diodes, material growth, processing, realization and characterization of devices to the integration of modules into existing or self-developed application systems. The research depth of the institute enables collaborations both in the context of public research projects and individual industrial orders.

Semiconductor disk laser module of Fraunhofer IAF at LASER World of PHOTONICS 2023

At LASER World of PHOTONICS, which will take place in Munich from June 27 to 30, 2023, Fraunhofer IAF presents a single-mode SDL module in the wavelength range from 2 to 2.2 nm for quantum frequency conversion. The researchers also provide fundamental information on the institute’s R&D activities in the field of III-V optoelectronics along the semiconductor value chain. In addition, they showcase, among others, processed wafers, an avalanche photodiode, efficient control electronics for optoelectronic applications, and a Bragg reflection waveguide based on aluminum gallium arsenide (AlGaAs) as an entangled photon pair source. Fraunhofer IAF is part of the Fraunhofer joint booth 441 in hall A3.