Visible to Longwave-infrared imaging via an inverse-designed monolithic lens

Abstract

Chromatic aberrations impose a fundamental barrier on optical design, confining most imaging systems to narrow spectral bands with fractional bandwidths typically limited to $Δλ/λ< 1$. Here we report a monolithic, inverse-designed potassium bromide (KBr) lens that achieves broadband, near-achromatic focusing from 0.45 to 14 $μ$m, a continuous spectral span covering the visible, near-, mid-, and long-wave infrared. This corresponds to a fractional bandwidth of 1.9, approaching the theoretical limit of 2, while maintaining a nearly constant focal length across the entire range. The 19-mm-diameter, 22.5-mm-focal-length optic enables a single compact platform for hyperspectral imaging, mid-IR microscopy, super-resolution, imaging through scattering media, and simultaneous multi-band and long-range imaging. Coupling the KBr lens with a conventional refractive element further yields a hybrid telescope that extends these capabilities. By uniting inverse design with scalable manufacturing, this approach provides a route toward broadly deployable ultra-broadband imagers for biomedicine, climate and environmental monitoring, and space-based sensing.

Figures (7)

• Figure 1: Focusing and imaging from the visible (Vis) to the long-wave infrared using a single lens. (a) A 19-mm-diameter, single-point diamond-turned potassium bromide (KBr) ultra-broadband lens (nominal focal length 22.5 mm) images the same scene seamlessly from the visible (Vis) to the long-wave infrared (LWIR). The inset shows a micrograph of the microstructured surface, and (b) a photograph of the lens. (c) Simulated focal length, extracted from the peak of the on-axis point-spread function (PSF), remains nearly constant across the full spectral range. (d) Simulated and measured PSFs in representative bands from Vis to LWIR exhibit close agreement, confirming the lens’s achromatic response. (e–l) Representative images acquired in each band demonstrate diffraction-limited performance with minimal chromatic variation. Detector parameters and experimental details are provided in the Supplementary Information.
• Figure 2: Simultaneous two-band imaging. (a) The UBB lens images a heated soldering iron simultaneously in the visible and LWIR bands. A double-side-polished silicon wafer serves as a dichroic beamsplitter, reflecting visible light toward the CMOS sensor and transmitting thermal radiation to the LWIR detector, both positioned at identical image distances. The resulting co-registered (b) Vis and (c) LWIR images confirm diffraction-limited fidelity and spatial alignment across more than three octaves of the electromagnetic spectrum. See Supplementary Video 1 for combined Vis-LWIR video imaging. (d) Simultaneous SWIR-LWIR imaging with two identical KBr lenses of the same Air Force (AF) resolution target placed about 206 cm away from both cameras. (e) LWIR image with a person holding the AF target and (f) the SWIR image of the same target, showing much higher resolution. See Supplementary Video 2 for combined SWIR-LWIR video imaging.
• Figure 3: Broadband long-range imaging across visible to LWIR bands. Long-range, multi-spectral imaging was performed using the dual-camera configuration shown in Fig. \ref{['fig:dual_band']}d. Test objects—including an AF resolution chart and an NRL logo—were back-illuminated by natural sunlight or halogen lamps. (a) Imaging of the AF target at a distance of 15.75 m, captured in (left to right) the visible–SWIR, visible, and NIR bands, and the NRL logo in the visible–SWIR and LWIR bands. (b) AF target imaged at 17 m in the visible–SWIR and LWIR bands. (c) NRL logo and AF target imaged simultaneously in the visible–SWIR band at 41 m. (d) Two halogen lamps (inset photograph) acting as quasi-point sources at 81 m are distinctly resolved in both the visible–SWIR (left) and LWIR (right) bands. (e) Frame from Supplementary Video 3 showing LWIR imaging of an aircraft from the NRL rooftop, where the two hot engines are clearly resolved.
• Figure 4: Hyperspectral and super-resolution imaging across the visible–near-infrared spectrum. A reflective target was illuminated with narrowband light from a tunable supercontinuum laser, and images were recorded through the single KBr lens without refocusing across wavelengths (constant object and image distances). (a) Photograph of the experimental setup. (b) Representative hyperspectral images selected from 46 wavelength channels spanning $400–850$ nm. (c) Demonstration of super-resolution capability: the difference between the 400 nm and 410 nm images reveals a central feature $<$ 0.2 mm wide, corresponding to an effective angular resolution of $\approx$ 1.6 mrad.
• Figure 5: Broadband hyperspectral imaging across SWIR–MWIR–LWIR bands using a single KBr lens. A single KBr lens was used to perform hyperspectral imaging across the short-, mid-, and long-wave infrared regimes. (a) Experimental setup for LWIR imaging of an AF resolution target back-illuminated by a calibrated hot plate. Wavelength-resolved images acquired with narrowband filters centered at (b) 8 $\mu$m and (c) 10 $\mu$m (bandwidth = 500 nm) exhibit high sharpness and contrast. (d) Setup for MWIR hyperspectral imaging of the same target. Corresponding images were captured at (e) 2.8 $\mu$m (bandwidth = 56 nm), (f) 3.01 $\mu$m (15 nm), (g) 3.5 $\mu$m (500 nm), (h) 3.91 $\mu$m (21 nm), (i) 4.5 $\mu$m (500 nm), and (j) 5.0 $\mu$m (500 nm). (k) Setup for SWIR hyperspectral imaging of a heated soldering iron, with images acquired at center wavelengths of (l) 1.6 $\mu$m, (m) 1.5 $\mu$m, (n) 1.4 $\mu$m, and (o) 1.3 $\mu$m (bandwidth = 10 nm for all cases). Across all measurements, the same KBr lens produced diffraction-limited performance and maintained consistent focus from 1.3 $\mu$m to 10 $\mu$m.