Can miniature optics printed directly on a single-mode fiber tailor both bright-centered and vortex Bessel beams? The authors fabricate a three-segment polymer photonic structure using two-photon lithography and experimentally demonstrate zeroth-order and high-order beams, including topological charges up to 20. Analytical relations connect printed geometry to beam width and diffraction-free distance. Many beam characterizations use structures printed on cover glass; the polymer may constrain operation in harsh environments.

A tiny 3D-printed structure turns an optical fiber into a source of precisely shaped light. From a bright point to a hollow ring.

Light usually spreads as it travels. A Bessel beam holds its central pattern over an extended distance. This paper brings the optics that create it onto the end of a single optical fiber.

Three steps. One print.

Two-photon lithography writes a polymer structure directly onto the fiber tip. Each segment gives the light a different job.

Align the input

A tapered waveguide narrows the Gaussian-like fiber output and makes the next stage tolerant of small alignment offsets.

Make a ring. Add a twist.

An inverse taper transforms the light into an annulus. An optional spiral phase plate adds a helical wavefront for higher-order beams.

Bring it into focus

A microlens, placed one focal length away, transforms the annular beam into a Bessel pattern: a bright center or a dark central node.

A point. A ring. A choice of geometry.

Slide the beam order to open a dark center. Then change the lens and annulus to explore how the beam’s dimensions respond.

Shape the light

Order zero: a bright central peak surrounded by concentric rings.

How to read this model. The transverse field follows Jℓ²(2πRr / λf). Higher orders carry a helical phase and have zero intensity on the axis. Brightness is normalized separately for each pattern; the image is not a power comparison.

λ = 0.94 µm · annular width Δ = 4 µm. FWHM at ℓ = 0: 0.36λf/R. For ℓ > 0, the displayed diameter spans the first bright ring. Estimated length D ≈ f²λ/(RΔ). Controls explore designs; the printed device itself is fixed.

Small device. Structured light.

The authors fabricated and characterized these structures, including devices on fiber tips. These are selected measured results from the paper.

High-order beams demonstrated

A spiral phase element enabled orders up to 20. Adjusting geometry also produced different orders with the same annular diameter.

A fine central spot, on fiber

The demonstrated fiber-mounted zeroth-order device produced this measured FWHM at a wavelength of 1.06 µm.

Measured transmission loss

The measured structure loss points to efficient conversion. Most systematic beam characterization used structures printed on cover glass.

A longer useful focus

One measured Bessel beam extended about 230 µm, compared with a roughly 50 µm two-sided Rayleigh range for a Gaussian beam of comparable 3.4 µm width. Other device geometries reached approximately 1 mm.

Complex light. Delivered through a fiber.

The advance is a versatile way to build beam-shaping optics at the point where light leaves a fiber. The authors demonstrated two-dimensional trapping of microbeads, putting the shaped light to work.

Compact, tailored beams could support miniature imaging probes, fiber-based sensing and optical manipulation. Their helical phase also creates opportunities for communication systems that use light’s orbital angular momentum.

3D-printed fiber-based zeroth- and high-order Bessel beam generator

Innem V. A. K. Reddy · Andrea Bertoncini · Carlo Liberale

Optica 9, 645–651 (2022) · DOI: 10.1364/OPTICA.453839