| Summary: | Fast, energy-efficient, and compact manipulation of multimode optical signals is required for technologies ranging from brain imaging to quantum control, yet remains an open goal for present-day spatial light modulators (SLMs), active metasurfaces, and optical phased arrays. Here, we develop wavelength-scale, high-finesse photonic crystal cavity arrays as a solution to this problem.
Specifically, we demonstrate nanosecond- and femtojoule-order spatial light modulation enabled by four key advances: (i) near-unity vertical coupling to high-finesse microcavities through inverse design, (ii) scalable fabrication of photonic crystal circuits by optimized, 300 mm full-wafer processing, (iii) picometer-precision resonance alignment using automated, closed-loop “holographic trimming”, and (iv) out-of-plane cavity control via a high-speed µLED display. Combining each, our approach weds the latest advances in incoherent and coherent optics to open a previously inaccessible regime of programmability: near-complete spatiotemporal control with a >MHz modulation bandwidth per diffraction-limited mode. Simultaneously operating wavelength-scale modes near the space- and time-bandwidth limits, this work approaches the fundamental limits of multimode optical control.
In developing this technology, we also analyze the fundamental limits of light-matter interaction in these remarkable optical microcavities that continue to drive modern science. Operated in reverse, our device constitutes a high-spatial-resolution focal plane array. Surprisingly, we discover that the fundamental limits of these sensors are ultimately dictated by refractive index variations induced by statistical temperature fluctuations. We present the first theoretical and experimental characterization of the associated thermal noise limits in wavelength-scale microcavities, develop a new class of optical sensors operating at this fundamental limit, and analyze noise cancellation techniques to enable continued development in quantum optical measurement, precision sensing, and low-noise integrated photonics.
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