The study asks whether large side openings can make on-chip hollow-core waveguides accessible to diffusing matter while retaining light guidance. Two-photon-polymerized photonic scaffolds reach 80% cladding openness, with measured transmission bands and selected air propagation losses of 0.42–0.93 dB/mm at 68% openness; a resonator model supports anti-resonant confinement and Bloch-mode formation. Experiments demonstrate rapid dye entry, Rhodamine 6G absorption spectroscopy and transmission of quantum-dot single photons. The effective light–liquid interaction volume is calculated to be about 1

A PAPER YOU CAN EXPLORE

A hollow waveguide with wide-open walls brings light and molecules together. Step inside the geometry that makes it possible.

Huang et al. · Nature Communications · 2026

THE CENTRAL IDEA

A path for light. An invitation to matter.

Optical waveguides usually enclose their light. Here, thin polymer membranes are separated by large gaps. The resulting photonic scaffold holds light in a hollow core while letting its surroundings enter from the sides.

The paper demonstrates air- and liquid-filled waveguides, fast molecular access, absorption measurements and the transmission of single photons.

01 / THE LIGHT EXPERIMENT

How open can a waveguide be?

Open the walls. Change the light. Discover why the thin membranes matter as much as the gaps.

TRY THE GEOMETRY

Empty space. Engineered walls.

All four walls open together. Corner rails connect the separated membrane sections.

68% open · gap 11.22 µm · membrane 5.28 µm

FIND A GUIDING WINDOW

Between membrane resonances: the beam stays confined.

Light interferes inside the thin walls. Away from a membrane resonance, those walls reflect it back into the hollow core. Near a resonance, light can escape.

Resonance positions follow the paper’s Eq. 1, using a constant polymer refractive index of 1.5 and air of 1.0. Curve shape, beam brightness and particle paths are illustrative. Opening fraction describes membrane opening area, not the whole device’s void percentage.

Thin walls reflect.

Membrane interference produces broad guiding windows between resonances. Change the wall thickness to move those windows.

Short gaps connect.

The wide hollow core gives light a shallow reflection angle. It diffracts little across each short opening.

Repetition organizes.

The repeating structure supports Bloch modes: light patterns that repeat along the scaffold. Simulated stop bands are extremely narrow.

WHAT THE PAPER MEASURED

Selected Type I scaffolds with 68% opening guided light in air with measured losses of 0.42–0.93 dB/mm (22 and 26 µm cores, Table 1). Transmission was also demonstrated at 80% opening.

MADE WITH TWO-PHOTON LITHOGRAPHY

Write the walls. Leave the core empty.

A focused laser cures tiny volumes of photoresist. Repeated three-dimensional writing forms the raised supports, corner rails and thin membranes. Development removes uncured material, leaving an open scaffold.

The authors used two-photon polymerization on a GT2 Nanoscribe with IP-Dip2 resist. The waveguides were written horizontally, layer by layer, above silicon substrates.

02 / THE MATTER EXPERIMENT

A shorter way in.

A closed capillary admits molecules through its ends. Open side walls give them access all along the light’s path.

0.00 min · none of the measured milestones reached.

WATCH THE DYE ARRIVE

Seconds from the sides. Hours from the ends.

Incoming dye absorbs the 527 nm probe light. Falling transmission reveals how quickly molecules enter the illuminated region.

Measured time to 13.5% transmission T = e−2

Different tested core sizes; equal optical interaction length. The animation illustrates access routes and measured milestones, rather than interpolating measured transmission.

A baffled chamber suppressed disturbances from dye injection. The supplementary material shows the chamber that made the comparison possible.

ANOTHER ROLE FOR THE SCAFFOLD

Keep the beam. Remove the scaffold.

Light spreads in free liquid. Guiding keeps the beam narrow, concentrating the light–liquid interaction in a small effective volume.

Switch views to compare a guided beam with a freely spreading Gaussian beam starting at the same waist.

Calculated equivalent interaction volumes in water at 527 nm over 5 mm. These are optical interaction volumes, not reservoir or total sample volumes.

1.41 nL effective light–liquid interaction volume

03 / THE MOLECULE EXPERIMENT

Read a molecule through its missing light.

Rhodamine 6G molecules absorb green light. Add more dye and watch the transmitted light fall.

64.8% transmission · 0.188 AU absorbance

BEER–LAMBERT, DIRECTLY

More molecules. Less transmitted light.

Guided light overlaps directly with the liquid in the hollow core. That lets the familiar Beer–Lambert relation connect absorption to concentration without first determining a complicated mode profile.

At 527 nm, the measured molar absorptivity is ε = 7.681 µM−1 m−1. This calculator uses a 9.8 mm optical path and the measured linear relation.

Scaffold: 0.0731 µM. Bulk reference: 0.0705 µM. Based on 1,000 blank measurements.

04 / AT THE SINGLE-PHOTON SCALE

One photon at a time.

Light emitted by a quantum dot was transmitted through a Type II scaffold. The measured antibunching signal—g(2)(0) = 0.35 —is below 0.5, the signature of predominantly single-photon emission.

The scaffold transports these photons. Its broad transmission window includes several quantum-dot emission lines, including one near the caesium D1 line at 894 nm.

A future opening: accessible hollow cores could bring single photons into contact with atomic vapours for hybrid quantum interfaces.

WHAT THE GEOMETRY MAKES POSSIBLE

Light has a pathway. Matter has a way in.

The paper brings two needs together: optical confinement and access to the material surrounding the waveguide. Fast exchange, compact absorption sensing and single-photon transmission all emerge from the same open architecture.

Explore the idea. Read the paper.

THE SOURCE

Photonic scaffolds as ultrahigh-openness on-chip hollow-core waveguides for quantum photonics and optofluidics

Wenqin Huang, Diana Pereira, Matthias Zeisberger, Hala Said, Esteban Gómez-López, Jun Sun, Oliver Benson and Markus A. Schmidt.

Nature Communications 17 (2026). Published 28 July 2026.

Source figures © The Authors 2026, used under CC BY 4.0. Figures are resized for display with scientific content unchanged. Interactive diagrams are conceptual teaching illustrations; calculated and measured quantities are identified where used.