Can a compact, three-dimensional metasurface produce broadband circularly polarized terahertz reflection? Chaudhary and colleagues print L-shaped polymer resonators by two-photon polymerization and metallize them with approximately 200 nm of gold. Reflection-mode terahertz time-domain measurements and electromagnetic simulations support quarter-wave operation over a reported 0.75–1.30 THz band, with axial ratio below 3 dB and approximately 54% fractional bandwidth. The structure balances orthogonal reflected fields and their relative phase. Its performance depends on illumination alignment: th

A surface of tiny, 3D-printed resonators turns a linearly polarized terahertz wave into a rotating electric field. The secret is a quarter of a cycle.

Inside the research of Chaudhary et al. · Advanced Photonics Research · 2026

Two fields. One beautiful turn.

A wave’s electric field can point back and forth along a line—or sweep around a circle. Give two perpendicular components equal strength and a 90° delay, and the field rotates.

Turn this line into a circle.

Start with the timing. A quarter-cycle delay gives the field room to turn.

Then match the amplitudes. A circle needs equal x and y components.

The tip moves back and forth along a line. Set a quarter-cycle delay.

For the two orthogonal components, Eₓ = Aₓ cos(t) and Eᵧ = Aᵧ cos(t + δ). The sliders set the phase difference δ and amplitude ratio Aᵧ/Aₓ. A 90° phase difference and equal amplitudes give an ideal circle.

The axial ratio compares the ellipse’s long and short axes: 0 dB is a circle; a straight line has an infinite ratio. These are calculated teaching values. The actual metasurface’s phase and amplitude response depends on frequency.

Polarization is a direction in time. Watch the small end-on view: it shows how the electric field changes at a single point.

A quarter-wave plate sets the timing. The printed surface creates a relative delay between the two reflected components.

Print the shape. Give it a golden skin.

Two-photon polymerization builds raised, Γ-shaped polymer resonators. A thin gold coating turns their 3D geometry into a reflective terahertz metasurface.

Write a solid shape inside liquid resin.

A focused 780 nm femtosecond laser writes the resonator in IP-Q resin on a 725 µm-thick, high-resistivity silicon substrate.

Small structures, collective control.

At 1 THz, a free-space wavelength is about 300 µm. The 218 µm cell spacing makes each engineered resonator smaller than that wavelength. A 60 × 60 array repeats the shape over approximately 13.1 mm × 13.1 mm.

The resonator height is 75 µm; the silicon substrate is 725 µm thick. Two-photon polymerization makes the structure. Terahertz waves are its operating signal.

The gold-coated 3D shape supports resonant responses that engineer the amplitudes and relative phases of the reflected components across a broad frequency range.

A circle, across a band of frequencies.

The researchers measured the reflected terahertz field and compared it with electromagnetic simulations. Explore their measured and simulated field trajectories.

Measured operating band

Fractional bandwidth

Reported measured axial ratio in the band

Follow the field’s tip.

Each panel plots the reflected electric-field components against each other. The solid red curve is simulated; the dotted curve with circles is experimental. Reflection-mode time-domain spectroscopy measures the two perpendicular reflected components relative to a metal mirror.

Near the centre of the band, the field traces a circle closely. The simulated and experimental trajectories agree.

The trajectories become more elliptical toward the band edges and nearly circular in the centre. Original plotting scales and normalization are retained.

A compact way to shape the unseen.

Polarization adds another degree of freedom to terahertz spectroscopy, imaging and communications. A printed, reflective quarter-wave surface offers a route toward compact polarization components in this part of the spectrum.

The work demonstrates the fabrication and broadband polarization conversion. Those applications motivate the design; the device is a passive structure whose response comes from its geometry.

Broadband Reflective Terahertz Quarter-Wave Metasurface Enabled by Two-Photon Polymerization 3D-Printing

Anjali Chaudhary · Anju Sajan · Rohit Chikkaraddy · Sunil Kumar · Ravendra Kumar Varshney · Miguel Navarro-Cía

Advanced Photonics Research 7, e70225 (2026) · doi:10.1002/adpr.70225

Figures reproduced from the article under CC BY 4.0. Figure 3 panels are cropped and resized; other source figures are resized. Interactive diagrams are explanatory schematics. The graphical abstract is an AI-generated conceptual illustration.

The article also reports supplementary analyses of gold coating, resonator height, reflected energy and the Jones matrix. Supplementary information ↗

Research, made explorable.