Quantum Photonics 2025

Optical multiplexer for quantum cryptography

A very compact optical multiplexer has been developed for a source that generates indistinguishable, polarization-encrypted photons for quantum key distribution. It contains a photonic chip that forms the central signal combiner in the source and is actively thermally controlled using temperature probes and thermoelectric elements. The optical input is provided via lithographic microlenses that couple the light into the waveguide channels, while the output is provided via a coupled fiber.

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Entangled photon source for tap-proof quantum communication

Scientists at the Fraunhofer IOF in Jena have developed a stable, space-suitable source for entangled photons. Such connected or "entangled" photons should in future be used in secure encryption technologies (such as in so-called "Quantum Key Distribution", or QKD for short). In the photon source, a nonlinear, periodically poled crystal (ppKTP) is pumped from two sides in the arrangement of a Sagnac interferometer. The resulting spontaneous parametric fluorescence (Spontaneous Down Conversion, SPDC) in the crystal generates polarization-entangled photons in the transmitter and receiver channels. The source is under continuous development and is one of the most powerful hardware solutions in quantum communication.

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Addressing optics for quantum computers

At Fraunhofer IOF, within the research project "Advanced quantum computing with trapped ions" (AQTION), a laser-optical setup was realized that allows to manipulate ions in the ion trap of a quantum computer. In a quantum computer, which uses the so-called "ion QuBits" as memory units, the ions are held in electromagnetic traps and can be controlled by means of laser beams thanks to the addressing optics of Fraunhofer IOF.

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Double beam displacer entangled photon pair source

Millions of photon pairs per second: The emerging field of quantum technologies with applications in quantum computing and quantum communication are largely based on photonic quantum sources. To realize these applications, we require the use of small and efficient entangled photon sources. Here, we show an engineering example of a compact and high performant entangled photon source. It can operate at millions of photon pairs per second per milliwatt of laser pump power, while its broadband light spectrum allows multiplexing capabilities. The source architecture has been tested for entanglement distribution over intercity fiber networks in Germany for applications in quantum cryptography.

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Compact Entangled Photon Source towards Space QKD

The entangled photon source (EPS) is a robust and compact system designed for secure quantum communication in space applications. Utilizing a Sagnac loop interferometer, the source is encapsulated within 180 mm x 85 mm x 42 mm, occupying less than one standard unit. This miniature yet effective system designed for low earth orbit Cubesat and ensures resilience in challenging space environments.

Beam displacer EPS toward space qualification

Researchers at Fraunhofer IOF built an optomechanical compact breadboard demonstrator (15 cm x 15 cm) of a dual beam displacer EPS including the polarization aligning of the input pump light and the output collimator to distribute the entangled photons to the other systems inside a satellite for LEO orbit. The current device serves as baseline to build the Engineering Model for facing the vibrations and TVAC tests as part of the space qualification roadmap up to TRL 6 in the framework of the QUDICE project funded by the EU. The physical principle of this source relies on the Mach- Zehnder interferometer formed by the beam displacer and beam combiners. In which nonlinear crystals with perpendicular optical axis are located over the arms to produce Polarized entangled photons.

OGS Model

Model of an optical ground station (OGS) for laser and quantum communication with satellites. The ground station has an 80 cm mirror telescope, optimized for 810 and 1550 nm (low losses, polarization-maintaining). Follow-up optics can be mounted on two Nasmyth ports on the telescope axes or set up in the Coudé laboratory under the telescope.

MIR SPDC source – FastGhost

Compact Mid-Infrared light source for the Fast Ghost project. A 40mm long PPLN nonlinear crystal is pump by a 405nm CW laser. The pump beam is single-mode fiber-coupled and collimated to propagate through the crystal. A photon-pair is generated via SPDC, one photon in the MIR spectral range (3.4 - 4 um) while the visible photon is found around (450 - 460 nm). A customized dichroic mirror (Chroma) splits the three beams in two paths: First, it reflects the MIR light to the first arm of the source and allows the signal and the pump to pass through, to be later reflected by a mirror to the fiber coupler. Before reaching the fiber coupler, the photons in both arms are spectrally filtered out. The MIR and VIS photons are fiber coupled to be sent to different imaging schemes, such as Quantum Ghost Imaging, where the imaging performance shows an improvement in SNR compared to classical implementations. This improvement is due to the temporal correlations between the photon pairs, which enable noise reduction by triggering detection in a very narrow time window.

Fiber bonded waveguide chip

At our booth, we will be showcasing a fiber-to-chip coupling with 12 polarization-maintaining fibers, which are connected to a waveguide chip by means of an optically adapted adhesive. The fibers were actively aligned and integrated according to their optical power and polarization. The fiber-to-chip coupling is UV-capable at 390 nm and transmits circular mode profiles with ellipticities >0.99.

4-mode LNOI interferometer

The lithium niobate waveguide chip with Mach-Zehnder interferometer, including optical and electrical packaging, forms the centrepiece of a photonic quantum computer. The waveguide chip was developed within the PhoQuant project.

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Silicon Nitride 400 nm Platform Technology for Photonic Integration

Fraunhofer IOF presents a 4-inch (100 mm) wafer, featuring integrated photonic building blocks based on 400 nm low-loss silicon nitride (SiN). Recognized for its wide transparency window, high power handling, and CMOS compatibility, SiN is a vital material in modern integrated photonics. This wafer includes essential passive components such as waveguides, grating couplers, directional couplers, MMIs, ring resonators, MZIs, and mode converters, supporting a broad spectrum of applications from quantum optics to telecom and sensing.

Manufactured in the clean room of the institute using CMOS-compatible processes, the wafer ensures consistent SiN film quality and low propagation loss. Its layout is optimized for device testing and prototyping of photonic integrated circuits (PICs), offering a scalable platform for research and industrial development. Successful tests on the 4-inch wafer can be seamlessly scaled to 12-inch wafers within the Fraunhofer IOF facilities, providing a pathway for larger-scale production and development.

Fraunhofer IOF provides foundry services focused on hybrid materials integration, enabling precise and efficient development of photonic technologies. Collaborate with us to leverage our expertise and facilities for your next innovation.

Fraunhofer IOF Process Development Kit (PDK): A Comprehensive Tool for Photonic Integrated Circuits

The Fraunhofer IOF Process Development Kit (PDK) is an indispensable tool for the development of photonic integrated circuits on the SiN 400 nm platform. It provides a detailed and structured overview of the available components essential for designing modern and efficient circuits.

The PDK includes comprehensive specifications, layout previews, and performance data for a variety of components, including waveguides, couplers, interferometers, and microring resonators. This information is crucial for the precise planning and implementation of design projects. Additionally, the document offers clear design rules to ensure that your projects meet the highest standards. Information on the process stack and meaningful test results support you in making informed decisions and maximizing the performance of your designs.

The Fraunhofer IOF PDK is a valuable resource for professionals working in photonics who wish to develop innovative solutions. It serves as a practical reference and assists you in the successful execution of your design projects. Leverage the capabilities of the Fraunhofer IOF PDK to help shape the future of photonics.

QuNET-Initiative

Telescope system for quantum communication

Together with partners from industry and business, Fraunhofer IOF is developing the physical and technical foundations of quantum communication systems and optical link technologies for use in real infrastructure as part of the QuNET initiative – specifically targeting applications in high-security networks. Here, the institute presents a Breadboard of a minaturized metal telescope as part of the transmitter and receiver system for free-space optical links for QKD. The metal-optical telescope made from an aluminum-silicon material is based on a four-mirror design with an aperture of 100 mm. It combines a topology-optimized, additively manufactured housing structure with an active tip-tilt mirror and five additional optical functional surfaces on two substrates. The manufacturing of multiple optical functional surfaces on a single substrate is made possible by ultra-precise diamond machining as a freeform surface. Further process steps such as coating and polishing produce the final high-performance optics for the telescope.

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Opening of Quantum Photonics 2025 with Institute Director Prof. Andreas Tünnermann

Opening speech of the 1st edition of Quantum Photonics, moderated by the Director of the Fraunhofer IOF, Prof. Dr. Tünnermann, State Secretary Mario Suckert and the CEO of Messe Erfurt, Michael Kynast.

Date: May 13, 2025

Time: 10:00 a.m. to 10:30 a.m.

Where: Hall 2

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Chip-Scale Quantum Optics: Overcoming Challenges to Unlock Market Potential

Speaker: Dr. Sebastian W. Schmitt

The integration of quantum optical components on chips enables ultra-secure communication, precise sensing, and faster AI. Fraunhofer IOF develops innovative solutions for scalable, CMOS-compatible technologies.

Integrating quantum optical building blocks at the chip level paves the way for bringing the benefits of quantum optics to the consumer market, enabling advancements such as ultra-secure communication, high-precision sensing, faster AI processing, and next-generation medical diagnostics in everyday applications. With the quantum technology market projected to reach billions in value over the coming years, scalable on-chip solutions will be key to driving widespread adoption and commercialization.

However, integrating quantum optical components at this scale presents significant challenges in material selection and fabrication, requiring high-purity materials, precise nanofabrication techniques, and seamless integration with existing semiconductor technologies to maintain quantum coherence and efficiency. PIC activities at Fraunhofer IOF strategically address these challenges, beginning with precise calculations of waveguide coupled mode dynamics, followed by component development and layout design, and culminating in high-precision fabrication within a 300 nm cleanroom environment.

The talk will explore solution approaches for enabling the preparation and modulation of quantum states of light through advancements in modern materials science and nanotechnology. Specifically, we will focus on devices for the generation and modulation of signal and idler photons with different frequencies and polarizations within CMOS-compatible platform technologies such as Silicon Nitride (Si3N4), Lithium Niobate (LiNbO3) and Barium Titanate (BaTiO₃).

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“The QuNET Initiative: Highly secure communication through quantum physics”

• Speaker: Prof. Fabian Steinlechner
• May 13, 2025
• 1:30 p.m. to 1:40 p.m.

"Ad-hoc hybrid heterogeneous metropolitan-range quantum key distribution network”

• Speaker: Dr. Thorsten Albert Goebel
• May 13, 2025
• 1:40 p.m. to 2 p.m.

"Telescopes for QKD – based on metal optics”

• Speaker: Dr. Nils Heidler
• May 13, 2025
• 3 p.m. to 3:20 p.m.

"Quantum Microscopy in the mid-Infrared”

• Speaker: Dr. Valerio Gili
• May 14, 2025
• 1:40 p.m. to 2 p.m.

Quantum imaging protocols have been emerging in the last decades as powerful tools to move beyond the limitations imposed by classical optics on existing imaging systems, and unlock quantum-enhanced capabilities, in terms of resolution, enhanced signal-to-noise ratio, lowlight illumination-enabled reduced phototoxicity, and the possibility to exploit quantum frequency correlations to perform imaging in wavelength ranges where detection technology is underdeveloped using standard CMOS silicon camera technology. Focusing on the last of the above-mentioned four directions to pursue a “quantum advantage” in imaging systems, we present our latest progress in “two-color” quantum imaging schemes, based on frequency 
correlations of photon-pairs generated through Spontaneous Parametric Down-conversion (SPDC), to access the mid-infrared spectral region with enhanced detection efficiency for biomedical applications. We further discuss technical implementation bottlenecks through Quantum Imaging with Undetected Light (QIUL) and discuss feasibility and scalability towards 
market uptake. 

"Photonics Packaging for Quantum Technologies”

• Speakers: Michael Reibe, Marcus Babin
• May 14, 2025
• 1:20 p.m. to 1:40 p.m.

Photonic packaging is a key technology for building capable quantum systems beyond their laboratory stages. This talk explores how we utilize different packaging technologies, including active fiber coupling and microlens array alignment, to develop integrated photonic systems, such as addressing units for ion quantum computing and optical multiplexers for quantum communication.