Electro-optic spatial light modulator from an engineered organic layer

ARTICLE https://doi.org/10.1038/s41467-021-26035-y OPEN Electro-optic spatial light modulator from an engineered organic layer 1234567890():,; Ileana-Cristina Benea-Chelmus 1 ✉, Maryna L. Meretska Larry R. Dalton 2 & Federico Capasso 1 ✉ 1, Delwin L. Elder 2, Michele Tamagnone 1, Tailored nanostructures provide at-will control over the properties of light, with applications in imaging and spectroscopy. Active photonics can further open new avenues in remote monitoring, virtual or augmented reality and time-resolved sensing. Nanomaterials with χ(2) nonlinearities achieve highest switching speeds. Current demonstrations typically require a trade-off: they either rely on traditional χ(2) materials, which have low non-linearities, or on application-specific quantum well heterostructures that exhibit a high χ(2) in a narrow band. Here, we show that a thin film of organic electro-optic molecules JRD1 in polymethylmethacrylate combines desired merits for active free-space optics: broadband record-high nonlinearity (10-100 times higher than traditional materials at wavelengths 1100-1600 nm), a custom-tailored nonlinear tensor at the nanoscale, and engineered optical and electronic responses. We demonstrate a tuning of optical resonances by Δλ = 11 nm at DC voltages and a modulation of the transmitted intensity up to 40%, at speeds up to 50 MHz. We realize 2 × 2 single- and 1 × 5 multi-color spatial light modulators. We demonstrate their potential for imaging and remote sensing. The compatibility with compact laser diodes, the achieved millimeter size and the low power consumption are further key features for laser ranging or reconfigurable optics. 1 Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA. 2 Department of Chemistry, University of Washington, Seattle, WA, USA. ✉email: ; NATURE COMMUNICATIONS | (2021)12:5928 | https://doi.org/10.1038/s41467-021-26035-y | www.nature.com/naturecommunications 1 ARTICLE R NATURE COMMUNICATIONS | https://doi.org/10.1038/s41467-021-26035-y ecent advances in both traditional and novel electro-optic materials that exhibit a χ(2) nonlinearity have resulted into an unprecedented richness of active photonic devices, that find applications in communications1–3, electric field metrology4,5, dynamic beam steering6, and quantum science7. Multi-pixel, largearea spatial light modulators (SLMs) are a prerequisite to achieve massively parallel dynamic and reconfigurable control over the diverse properties of light. They promise to revolutionize applications in industry and fundamental science. In reconfigurable photonics, multipixel optical components can control light ondemand, but they need to be compact and consume minimal power per pixel. In massively parallel remote sensing8, high-speed SLMs can generate parallel optical channels that scan the environment in three dimensions, but operation at high speeds is mandatory to resolve small changes in the position and velocity of objects within a short timeframe. In the area of ultrafast optics, SLMs can manipulate femtosecond pulses through pulse-pickers, but must accommodate a broad optical bandwidth and switching speeds commensurate with the repetition rate of these lasers, typically around few MHz to GHz. In fundamental science, SLMs play a crucial role e.g., in the sorting and reconfiguration of cold atoms for quantum simulation9, and reaching higher speeds can access entirely new physics. In industry applications, such as selfdriving cars10, high-speed SLMs can monitor a scene if they are compatible with low-power electronic circuits, chip-based laser diodes that typically have a broad linewidth and low foot-print packaging. Among all existing SLM technologies, SLMs that employ electric tuning enabled by χ(2) materials are outstanding candidates to reach high speeds in parallel multipixel architectures. They are intrinsically compatible with massively parallel radio-frequency (RF) electronic circuits that promise to deliver the necessary electrical controls by hybrid electronic-optical integration. In this case, the SLM is essentially a two-dimensional array of free-space electro-optic modulators. Commercial SLMs instead use bulky digital micro-mirror arrays11 or liquid crystals12, which not only limit them to around 10 kHz but also do not employ nanostructures. Few state-of-the art SLM demonstrations address the quest for ever-higher speed by making use of narrow-band surface plasmon resonances in rather complex prism-based schemes using χ(2) nonlinear materials13, but the nano-scale engineering of the individual pixels remains unexplored and the employed nonlinearity is rather low. Flat lens technology around metasurfaces14 is a powerful platform that permits engineering of the properties of light at a sub-wavelength scale in an extremely compact device. Static single-pixel metasurfaces have addressed multiple needs (focussing, polarization control15, or correcting optics16) or multipixel metasurfaces (next-generation biodevices17). Consequently, an ideal platform for high-speed SLMs combines highperformance χ(2) materials with nanostructures. Current demonstrations of monolithic metasurfaces from χ(2) materials typically trade off an operation around a sharp resonance in materials with moderate but broadband χ(2) effect e.g., in lithium niobate18,19 or colloidal nonlinear nanocubes20 against an efficient χ(2) effect in application-specific engineered III–V heterostructures, which is however narrowband and located around its bandgap6. While many demonstrations are single-pixel, few exciting multifunctional metasurfaces with multiple electronic controls have emerged experimentally6,21,22 and theoretically23. Important to mention are also metasurfaces based on transparent conductive oxides22,24–26 that have enabled SLMs recently27, gate-tunable low-dimensional materials28 or phase change materials such as e.g., GST29–33 that are excellent candidates in scenarios, where high switching speeds are not required. Microelectromechanical34,35 or thermo-optically controlled36 systems are ideal for low speed applications that do not require pixel-level control. 2 Custom-engineered organic nonlinear molecules instead overcome this bandwidth-nonlinearity limitation since they have electro-optic coefficients that are 10–100 times higher than standard materials (up to r33 = 560 pmV−1 in bulk layers and 200 pmV−1 in nanoplasmonic gaps of gold electrodes37), over the entire band from 1100 to 1600 nm (see Supplementary Note 7). They are anticipated to deliver high-end SLMs, owing to their terahertz-compatible bandwidth (up to 2.5 THz38), high index of refraction and recently reported long-term thermal and chemical stability39. Only little work studies such molecules beyond silicon photonic circuits (where they reach highest electro-optic couplings4 and integration with complementary metal-oxidesemiconductor (CMOS) electronics40) for large-area electro- (...truncated)