On-Chip Light Pulses Flip Magnetic Bits in Breakthrough for Photonic Memory

For nearly three decades, scientists have dreamed of writing magnetic data using nothing but flashes of light — no magnetic fields, no electrical currents, just ultrashort laser pulses that coax tiny magnetic moments to flip on demand. That dream, known as all-optical switching, has always come with a stubborn catch: the experiments relied on bulky free-space optics, with microscope objectives and precisely aligned laser beams that could never survive in a real data center or inside a processor. Now a team at Eindhoven University of Technology, working with LioniX International, has taken the decisive step that the field has been waiting for. Reporting in Nature Nanotechnology, they demonstrate, for the first time, all-optical switching of magnetization fully integrated within a silicon nitride photonic circuit, with the light delivered through an on-chip waveguide rather than a laboratory benchtop beamline.

The physics at the heart of the work stretches back to a landmark 1996 experiment, in which an ultrashort laser pulse was shown to demagnetize nickel on femtosecond timescales — far faster than any magnetic field pulse could. Subsequent discoveries revealed something even stranger: in certain ferrimagnetic alloys, a single pulse of circularly or even unpolarized light could deterministically reverse the magnetization entirely, toggling it from one stable state to its opposite. The most effective materials for this trick are synthetic ferrimagnets built from cobalt and gadolinium, in which two magnetic sublattices respond to the pulse’s sudden heat differently, driving the system through a transient state where exchange forces complete the reversal within picoseconds.

What has always limited the technology’s promise is integration. Optical fiber links and photonic integrated circuits already carry data across chips and between servers, but the magnetic memory elements that all-optical switching promised were still addressed with external lasers focused from above. To make the scheme practical, the writing mechanism had to live inside the same chip-scale platform that routes light in modern communications. The Eindhoven team, led by Pingzhi Li and Bert Koopmans, addressed this by fabricating a submicrometre magnetic memory element directly on top of a silicon nitride waveguide, so that femtosecond pulses traveling inside the guide could deposit their energy into the magnetic layer beneath — and flip it.

The device itself is an elegant piece of hybrid engineering. A low-loss silicon nitride waveguide, produced on a commercial photonics platform, carries trains of femtosecond pulses in its fundamental optical mode. Patterning a Co/Gd synthetic ferrimagnet directly atop the guide, the researchers shaped the magnetic layer into a Hall cross geometry narrower than one micrometre. This geometry is not arbitrary: the anomalous Hall effect, in which the voltage transverse to a current depends on the magnetization’s out-of-plane orientation, provides a purely electrical read-out. That means the state of the magnetic bit can be determined without any magneto-optical microscope, a crucial requirement for real integrated circuits where electrical addressing is the norm.

The results were striking. In the narrowest devices, with Hall crosses 500 nanometres wide, single-pulse, deterministic toggle switching was achieved — each incoming pulse flipped the magnetization to the opposite state, exactly as theory predicts for all-optical switching in a compensated ferrimagnet. The electrical read-out revealed a switching contrast of up to 90 percent, meaning nearly the full magnetic volume responded reliably to the guided pulse train. This is the first clear demonstration that light confined within a waveguide, rather than focused from free space, carries enough energy density to drive complete magnetic reversal in a device geometry compatible with photonic manufacturing.

Perhaps the most instructive finding came from scaling studies. When the researchers enlarged the Hall crosses, the switching contrast dropped and the reversal became stochastic — some pulses switched, some did not, and the reliability deteriorated with device size. Finite-element simulations of the optical absorption profile explained why: the guided mode deposits heat non-uniformly across the magnetic element, with the absorbed energy concentrated where the optical field intensity peaks. In a large device, only part of the magnetic volume reaches the energy threshold needed for reversal, leaving a partially switched region whose fate depends on how magnetic domain walls move and relax afterwards.

The authors attribute this behaviour, hypothetically, to domain-wall relaxation and thermally assisted pinning and depinning processes within the partially switched regions. After the femtosecond pulse triggers local demagnetization and subsequent reversal, the boundary between the switched and unswitched domains must sweep across the device for the toggle to complete. In small devices, that sweep happens quickly and reliably; in larger ones, domain walls encounter pinning landscapes and thermal fluctuations, and the outcome per pulse becomes a matter of chance. The lesson is unambiguous: device scaling is not an afterthought for on-chip all-optical switching — it is the critical design parameter that determines whether the switching is deterministic or erratic.

The significance of the work extends well beyond a single demonstration. Silicon nitride waveguides, of the TriPleX style used here, are a commercial low-loss platform already deployed in filters, sensors and telecommunications circuits. Combining them with magnetic memory elements opens a credible route to hybrid spintronic–photonic systems in which a single chip routes light for communication, computes optically where advantageous, and stores information in non-volatile magnetic bits written with femtosecond pulses. Because all-optical switching can occur on picosecond timescales with remarkably low pulse energies in optimized Co/Gd multilayers, the approach promises both ultrafast write speeds and the kind of energy efficiency that the semiconductor industry urgently seeks as electrical memory technologies approach their physical limits.

The application landscape is broad. Magnetic random-access memories based on spin-transfer or spin-orbit torque already occupy niches in embedded systems, but their write currents and speeds face trade-offs. Photonic writing sidesteps those constraints entirely, potentially enabling optical RAM architectures, in-memory computing accelerators, and neuromorphic spintronic devices in which light pulses act as both carriers and writers of information. The Eindhoven team’s demonstration that the writing mechanism works inside a standard photonic circuit — with electrical read-out built in — transforms what was a laboratory curiosity into an engineering platform with a clear scaling roadmap.

Challenges remain before magneto-photonic memories ship in products. The stochastic switching in larger devices must be understood and suppressed, whether through refined thermal engineering, materials optimization to lower the switching threshold, or deliberate control of domain-wall landscapes. Write speeds, endurance and integration density all need sustained attention. But the conceptual barrier has fallen: magnetization can now be switched entirely optically, on chip, with the light routed by the same waveguides that carry data. The era of fully integrated, ultrafast and energy-efficient spintronic–photonic information technology has moved from promise to platform, and the foundation stones have now been laid.

Subject of Research: On-chip all-optical switching of magnetization in integrated silicon nitride photonic circuits using femtosecond light pulses to write magnetic memory

Article Title: Demonstration of on-chip all-optical switching of magnetization in integrated photonics

Article References: Li, P., Simons, G. W. A., Zhang, T., Schrinner, P. P. J., Kamyar, S., Dekker, R., Leitao, D. C., Lavrijsen, R., Jiao, Y., & Koopmans, B. (2026). Demonstration of on-chip all-optical switching of magnetization in integrated photonics. Nature Nanotechnology. https://doi.org/10.1038/s41565-026-02281-3

Image Credits: AI Generated

DOI: 10.1038/s41565-026-02281-3

Keywords: all-optical switching, magnetization, integrated photonics, spintronics, silicon nitride waveguide, Co/Gd synthetic ferrimagnet, magnetic memory, anomalous Hall effect, femtosecond pulses, magneto-photonics, domain wall dynamics, Nature Nanotechnology