Can compact on-chip optics collect angular information independently from many sites? Furman and colleagues fabricate ellipsoidal IP-Dip microlenses directly on optical microcavities using two-photon polymerization. Measured spectra and energy-filtered images demonstrate approximately 0.95 numerical aperture and parallel momentum-space imaging at 64 sites, including at 4.5 K. In a CdTe cavity, measured polariton condensation thresholds under microlens excitation are nearly an order of magnitude lower than in nearby regions excited with a 0.55-NA objective. Ray-tracing and transfer-matrix simul

ON-CHIP OPTICS · NATURE COMMUNICATIONS · 2026

A tiny lens on a microcavity can reveal where light is going. Print an array, and 64 places become 64 local momentum maps.

Explore the light paths. Read the measured maps. Discover what changes when a lens also focuses the excitation.

Keep where the light came from and which way it travels in the same measurement.

FOLLOW A RAY

Bring the optics to the light.

A lens printed directly on the surface collects wide-angle light before it escapes. Its Fourier plane turns direction into position.

TRY THIS ↙

Can you catch the 55° ray?

Switch from the objective to a microlens. Then move the angle slider and watch the collection limit.

In the array, each lens measures a different spatial site . The 64 maps are 64 locations; each map contains many light directions.

The microlenses work inside the cryostat. Bertrand and imaging optics still relay their Fourier-plane images to the detector.

Angular mapping follows k∥/k₀ = sin θ; ray paths and geometry are schematic. Lens pitch: 20 μm.

HOW A LENS BECOMES PART OF THE CHIP

Written in light. Designed for angles.

A tightly focused femtosecond laser writes smooth ellipsoidal lenses into photosensitive IP-Dip resin. Two-photon polymerization turns a designed optical surface into a structure directly on the microcavity.

The geometry is optimized by ray tracing to collect broad angles and preserve the Fourier plane , roughly 10–15 μm above a lens.

Only near the focus does the resin polymerize. A Photonic Professional printer uses a 785 nm laser and an NA 1.3 immersion objective.

READ THE MEASUREMENT

One image. Two kinds of space.

Across the image: different places on the chip. Within every circle: different momenta at that place.

TRY THIS ↙

Turn the rings into spots.

Move through the three measured energies. As the slice approaches the bottom of the polariton branch, the rings contract toward low momentum.

These data come from a GaAs-based polariton microcavity at 4.5 K . Polaritons combine a cavity photon with a material excitation called an exciton.

The Gaussian excitation profile makes some sites brighter than others. Ring asymmetry also reflects the horizontally polarized pump.

Energy and in-plane momentum are connected. The low-energy spots trace the minimum of the GaAs cavity’s lower polariton branch.

Numerical data from Figure 3b–d, recolored and downsampled. Contrast is scaled independently for visibility; each slider position is a separate measured slice.

RUN A VIRTUAL EXPERIMENT

Focus the excitation. Lower the threshold.

The same printed lens can focus incoming light. In a CdTe microcavity, condensation emerges with far less pulse energy.

TRY THIS ↙

Same pulse. A different response.

At 20 pJ, switch the excitation optics. Compare the emission intensity and linewidth, then increase the pulse energy.

With microlens excitation, a steeper rise in intensity and a narrower spectrum appear at much lower pulse energies. Together with the energy shift, these mark the onset of nonequilibrium polariton condensation .

This comparison covers 26 microlens sites and 26 reference positions across two cavity detunings. Two unpatterned positions did not reach condensation.

The condensate occupies intrinsic localized trap states in the CdTe cavity. This is a driven, decaying light–matter system.

The plotted points and numerical readouts are measured data from Figure 4c,d. The glowing emission is a conceptual illustration. Detection used a modified microlens with NA ≈ 1 for this sample.

FROM ONE PLATFORM TO MANY

Small optics. A wider view.

The paper tests the approach across three microcavity systems. Parallel local momentum maps open a route to studying particle flows, relaxation and coupling across many sites.

Photon modes

Room-temperature reflectivity reveals broad-angle cavity dispersion.

Parallel maps

At 4.5 K, many local exciton-polariton dispersions are recorded together.

Condensation

At 4.5 K, tightly focused excitation lowers the pulse-energy threshold.

What a Fourier plane tells us

For light in air, the normalized in-plane wavevector is k∥/k₀ = sin θ. A Fourier-plane image separates directions, while a conventional real-space image separates positions. The microlens array preserves a local angular map for each spatial position.

Printing and platform design

The IP-Dip resin has refractive index 1.52. After writing with the Photonic Professional system, unpolymerized resin is removed with solvents, leaving the lens on the cavity. This work applies two-photon polymerization to integrated optical spectroscopy.

From collection to resolution

Ray tracing in the supplement guides the ellipsoidal design. External optics relay and magnify the local Fourier planes. Lower magnification reduces wavevector resolution, while the printed polymer can alter the local optical environment and strain.

What opens next

Simultaneous access to multiple dispersion relations enables future studies of flows, relaxation and interactions between sites. Time-resolved multiplexed momentum imaging is a proposed extension of this platform.

Go from the idea to the evidence.

Multiplexed back focal plane imaging with on-chip integrated microlens array

Magdalena Furman, Marcin Muszyński, Przemysław Oliwa, Łukasz Zinkiewicz, Aleksander Bogucki, Jacek Szczytko, Piotr Wasylczyk, Wojciech Pacuski, Mateusz Król and Barbara Piętka.

Nature Communications 17, 4890 (2026). doi:10.1038/s41467-026-71297-z

Numerical data: Furman et al., Zenodo 18992306, CC BY 4.0. Figure 3 maps recolored and downsampled; contrast scaled per panel. Figure 4 point values unchanged. Article: CC BY-NC-ND 4.0. Graphical abstract: AI-generated conceptual illustration; geometry schematic. Interactive optical paths and emission illustrations are conceptual.