Zin Lin, Raphaël Pestourie, Charles Roques-Carmes, Zhaoyi Li, Federico Capasso, Marin Soljačić, and Steven G. Johnson. 7/19/2022. “End-to-end metasurface inverse design for single-shot multi-channel imaging.” Opt. Express, 30, 16, Pp. 28358–28370. Publisher's VersionAbstract
We introduce end-to-end inverse design for multi-channel imaging, in which a nanophotonic frontend is optimized in conjunction with an image-processing backend to extract depth, spectral and polarization channels from a single monochrome image. Unlike diffractive optics, we show that subwavelength-scale &\#x201C;metasurface&\#x201D; designs can easily distinguish similar wavelength and polarization inputs. The proposed technique integrates a single-layer metasurface frontend with an efficient Tikhonov reconstruction backend, without any additional optics except a grayscale sensor. Our method yields multi-channel imaging by spontaneous demultiplexing: the metaoptics front-end separates different channels into distinct spatial domains whose locations on the sensor are optimally discovered by the inverse-design algorithm. We present large-area metasurface designs, compatible with standard lithography, for multi-spectral imaging, depth-spectral imaging, and &\#x201C;all-in-one&\#x201D; spectro-polarimetric-depth imaging with robust reconstruction performance (&\#x2272; 10&\#x0025; error with 1&\#x0025; detector noise). In contrast to neural networks, our framework is physically interpretable and does not require large training sets. It can be used to reconstruct arbitrary three-dimensional scenes with full multi-wavelength spectra and polarization textures.
Paul Chevalier, Marco Piccardo, Arman Amirzhan, Federico Capasso, and Henry O Everitt. 7/1/2022. “Accurately Measuring Molecular Rotational Spectra in Excited Vibrational Modes.” Applied Spectroscopy, ja, Pp. 00037028221111174. Publisher's VersionAbstract
Although gas phase rotational spectroscopy is a mature field for which millions of rotational spectral lines have been measured in hundreds of molecules with sub-MHz accuracy, it remains a challenge to measure these rotational spectra in excited vibrational modes with the same accuracy. Recently it was demonstrated that virtually any rotational transition in excited vibrational modes of most molecules may be made to lase when pumped by a continuously tunable quantum cascade laser (QCL). Here we demonstrate how an infrared QCL may be used to enhance absorption strength or induce lasing of terahertz rotational transitions in highly excited vibrational modes in order to measure their frequencies more accurately. To illustrate the concepts, we used a tunable QCL to excite v3 R-branch transitions in N2O and either enhanced absorption or induced lasing on 20 v3 rotational transitions, whose frequencies between 299-772 GHz were then measured using either heterodyne or modulation spectroscopy. The spectra were fitted to obtain the rotational constants B3 and D3, which reproduce the measured spectra to within the experimental uncertainty of +/- ∼5 kHz. We then show how this technique may be generalized by estimating the threshold power to make any rotational transition lase in any N2O vibrational mode.
M.L. Meretska, F. H. B. Somhorst, M. Ossiander, Y. Hou, J. Moodera, and F. Capasso. 6/22/2022. “Measurements of the magneto-optical properties of thin-film EuS at room temperature in the visible spectrum.” Applied Physics Letters, 120, 25, Pp. 251103. Publisher's Version 5.0090533.pdf
Mikhail Mamaikin, Yik-Long Li, Enrico Ridente, Wei Ting Chen, Joon-Suh Park, Alexander Y. Zhu, Federico Capasso, Matthew Weidman, Martin Schultze, Ferenc Krausz, and Nicholas Karpowicz. 6/9/2022. “Electric-field-resolved near-infrared microscopy.” Optica, 9, 6, Pp. 616–622. Publisher's VersionAbstract
Access to the complete spatiotemporal response of matter due to structured light requires field sampling techniques with sub-wavelength resolution in time and space. We demonstrate spatially resolved electro-optic sampling of near-infrared waveforms, providing a versatile platform for the direct measurement of electric field dynamics produced by photonic devices and sub-wavelength structures both in the far and near fields. This approach offers high-resolution, time- or frequency-resolved imaging by encoding a broadband signal into a narrowband blueshifted image, lifting the resolution limits imposed by both chromatic aberration and diffraction. Specifically, measuring the field of a near-infrared laser with a broadband sampling laser, we achieve 1.2 µm resolution in space and 2.2 fs resolution in time. This provides an essential diagnostic for complete spatiotemporal control of light with metasurface components, demonstrated via a metalens as well as a meta-axicon that forms broadband, ultrashort, truncated Bessel beams in the near infrared. Finally, we demonstrate the electric field dynamics of locally enhanced hot spots with sub-wavelength dimensions, recording the full temporal evolution of the electric field at each point in the image simultaneously. The imaging modality opens a path toward hyperspectral microscopy with simultaneous sub-wavelength resolution and wide-field imaging capability.
Zhaoyi Li, Raphaël Pestourie, Zin Lin, Steven G. Johnson, and Federico Capasso. 6/9/2022. “Empowering Metasurfaces with Inverse Design: Principles and Applications.” ACS Photonics, Pp. null. Publisher's Version acsphotonics.1c01850.pdf
Ileana-Cristina Benea-Chelmus, Sydney Mason, Maryna L Meretska, Delwin L Elder, Dmitry Kazakov, Amirhassan Shams-Ansari, Larry R Dalton, and Federico Capasso. 6/6/2022. “Gigahertz free-space electro-optic modulators based on Mie resonances.” Nature Communications, 13, 1, Pp. 3170. Publisher's VersionAbstract
Electro-optic modulators are essential for sensing, metrology and telecommunications. Most target fiber applications. Instead, metasurface-based architectures that modulate free-space light at gigahertz (GHz) speeds can boost flat optics technology by microwave electronics for active optics, diffractive computing or optoelectronic control. Current realizations are bulky or have low modulation efficiencies. Here, we demonstrate a hybrid silicon-organic metasurface platform that leverages Mie resonances for efficient electro-optic modulation at GHz speeds. We exploit quasi bound states in the continuum (BIC) that provide narrow linewidth ( Q = 550 at $$łambda }_\rmres=1594$$ $łambda$ res = 1594 nm), light confinement to the non-linear material, tunability by design and voltage and GHz-speed electrodes. Key to the achieved modulation of $$\fracΔ T}T_\max =67 %$$ $Δ$ T T max = 67 % are molecules with r 33 = 100 pm/V and optical field optimization for low-loss. We demonstrate DC tuning of the resonant frequency of quasi-BIC by $$Δ }łambda }_\rmres=$$ $Δ$ $łambda$ res = 11 nm, surpassing its linewidth, and modulation up to 5 GHz ( f E O ,−3 d B = 3 GHz). Guided mode resonances tune by $$Δ }łambda }_\rmres=$$ $Δ$ $łambda$ res = 20 nm. Our hybrid platform may incorporate free-space nanostructures of any geometry or material, by application of the active layer post-fabrication.
Haig A. Atikian, Neil Sinclair, Pawel Latawiec, Xiao Xiong, Srujan Meesala, Scarlett Gauthier, Daniel Wintz, Joseph Randi, David Bernot, Sage DeFrances, Jeffrey Thomas, Michael Roman, Sean Durrant, Federico Capasso, and Marko Lončar. 5/11/2022. “Diamond mirrors for high-power continuous-wave lasers.” Nature Communications, 13, Pp. 2610. Publisher's Version s41467-022-30335-2.pdf
Zhaoyi Li, Raphaël Pestourie, Joon-Suh Park, Yao-Wei Huang, Steven G. Johnson, and Federico Capasso. 5/3/2022. “Inverse design enables large-scale high-performance meta-optics reshaping virtual reality.” Nature Communications, 13, Pp. 2409. Publisher's Version s41467-022-29973-3.pdf
Ahmed H. Dorrah and Federico Capasso. 4/22/2022. “Tunable structured light with flat optics.” Science, 376, 6591, Pp. eabi6860. Publisher's VersionAbstract
Flat optics has emerged as a key player in the area of structured light and its applications, owing to its subwavelength resolution, ease of integration, and compact footprint. Although its first generation has revolutionized conventional lenses and enabled anomalous refraction, new classes of meta-optics can now shape light and dark features of an optical field with an unprecedented level of complexity and multifunctionality. Here, we review these efforts with a focus on metasurfaces that use different properties of input light—angle of incidence and direction, polarization, phase distribution, wavelength, and nonlinear behavior—as optical knobs for tuning the output response. We discuss ongoing advances in this area as well as future challenges and prospects. These recent developments indicate that optically tunable flat optics is poised to advance adaptive camera systems, microscopes, holograms, and portable and wearable devices and may suggest new possibilities in optical communications and sensing. The development of metasurfaces has provided a route to replacing bulk optical components with thin layers of engineered materials. In a review, Dorrah and Capasso highlight some of the recent advances in wavefront shaping using multifunctional meta-optics. They focus on the ability to tune the response of the metasurface by simply tuning one or more degrees of freedom of incident light, for example, by varying its angle of incidence, polarization, wavelength, or phase. The key feature of these metasurfaces is that although they are static, they can produce a tunable response without the need for complex switching. These developments enable multifunctional and lightweight components for technologies such as augmented and virtual reality displays, drone-based sensing, and endoscopy. —ISO A review discusses methods to control the functionality of optical metasurfaces by the incident light.
Noah A. Rubin, Paul Chevalier, Michael Juhl, Michele Tamagnone, Russell Chipman, and Federico Capasso. 3/8/2022. “Imaging polarimetry through metasurface polarization gratings.” Optics Express, 30, 6, Pp. 9389-9412. Publisher's Version oe-30-6-9389.pdf
Jaewon Oh, Kangmei Li, Jun Yang, Wei Ting Chen, Ming-Jun Li, Paulo Dainese, and Federico Capasso. 3/7/2022. “Adjoint-optimized metasurfaces for compact mode-division multiplexing.” ACS Photonics. Publisher's Version acsphotonics.1c01744.pdf
Paul Chevalier, Arman Amirzhan, Jeremy Rowlette, H. Ted Stinson, Michael Pushkarsky, Timothy Day, Federico Capasso, and Henry O. Everitt. 2/24/2022. “Multi-line lasing in the broadly tunable ammonia quantum cascade laser pumped molecular laser.” Applied Physics Letters, 120, 8, Pp. 081108. Publisher's Version 5_0079219.pdf
Masoud Pahlevaninezhad, Yao-Wei Huang, Majid Pahlevani, Brett Bouma, Melissa J Suter, Federico Capasso, and Hamid Pahlevaninezhad. 2/14/2022. “Metasurface-based bijective illumination collection imaging provides high-resolution tomography in three dimensions.” Nature Photonics. Publisher's Version naturephotonicfeb2022.pdf
Arman Amirzhan, Paul Chevalier, Jeremy Rowlette, H. Ted Stinson, Michael Pushkarsky, Timothy Day, Henry O. Everitt, and Federico Capasso. 1/25/2022. “A quantum cascade laser-pumped molecular laser tunable over 1 THz.” APL Photonics, 7, 1, Pp. 016107. Publisher's Version 5.0076310.pdf
Noah A. Rubin, Zhujun Shi, and Federico Capasso. 1/3/2022. “Polarization in diffractive optics and metasurfaces.” Advances in Optics and Photonics, 13, 4, Pp. 836-970. Publisher's VersionAbstract
Polarization, the path traced by light’s electric field vector, appears in all areas of optics. In recent decades, various technologies have enabled the precise control of light’s polarization state, even on a subwavelength scale, at optical frequencies. In this review, we provide a thorough, high-level review of the fundamentals of polarization optics and detail how the Jones calculus, alongside Fourier optics, can be used to analyze, classify, and compare these optical elements. We provide a review of work in this area across multiple technologies and research areas, including recent developments in optical metasurfaces. This review unifies a large body of work on spatially varying polarization optics and may be of interest to both researchers in optics and designers of optical systems more generally.
Marco Piccardo and Federico Capasso. 12/16/2021. “Laser Frequency Combs with Fast Gain Recovery: Physics and Applications.” Laser & Photonics Reviews, Pp. 2100403. Publisher's VersionAbstract
 The dynamics of semiconductor lasers with fast gain is generally considered to suppress amplitude modulation, resulting in a frequency-modulated output. Since their first demonstration of frequency comb operation, quantum cascade lasers—ideal representatives of this class of lasers with fast gain dynamics—were indeed shown to emit frequency-modulated combs. The understanding of these frequency comb regimes has progressively evolved, being refined from simpler arguments to more advanced theories, considering the role of Kerr nonlinearity and linewidth enhancement factor. By now, the traditional frequency-modulated combs are rather well understood in quantum cascade lasers, but new types of frequency combs have emerged, reopening interesting physics questions in these lasers. Recent advancements on two open frontiers will be discussed: harmonic frequency combs, characterized by mode skipping of many free spectral ranges, and spatiotemporal structures with solitonic features, recently reported in unidirectional ring cavities. These new types of frequency combs open technological and fundamental perspectives, sprouting new interest in quantum cascade lasers.
Marco Piccardo, Vincent Ginis, Andrew Forbes, Simon Mahler, Asher A Friesem, Nir Davidson, Haoran Ren, Ahmed H Dorrah, Federico Capasso, Firehun T Dullo, Balpreet S Ahluwalia, Antonio Ambrosio, Sylvain Gigan, Nicolas Treps, Markus Hiekkamäki, Robert Fickler, Michael Kues, David Moss, Roberto Morandotti, Johann Riemensberger, Tobias J Kippenberg, Jérôme Faist, Giacomo Scalari, Nathalie Picqué, Theodor W Hänsch, Giulio Cerullo, Cristian Manzoni, Luigi A Lugiato, Massimo Brambilla, Lorenzo Columbo, Alessandra Gatti, Franco Prati, Abbas Shiri, Ayman F Abouraddy, Andrea Alù, Emanuele Galiffi, JB Pendry, and Paloma A Huidobro. 12/16/2021. “Roadmap on multimode light shaping.” Journal of Optics, 24, 1, Pp. 013001. Publisher's VersionAbstract
Our ability to generate new distributions of light has been remarkably enhanced in recent years. At the most fundamental level, these light patterns are obtained by ingeniously combining different electromagnetic modes. Interestingly, the modal superposition occurs in the spatial, temporal as well as spatio-temporal domain. This generalized concept of structured light is being applied across the entire spectrum of optics: generating classical and quantum states of light, harnessing linear and nonlinear light-matter interactions, and advancing applications in microscopy, spectroscopy, holography, communication, and synchronization. This Roadmap highlights the common roots of these different techniques and thus establishes links between research areas that complement each other seamlessly. We provide an overview of all these areas, their backgrounds, current research, and future developments. We highlight the power of multimodal light manipulation and want to inspire new eclectic approaches in this vibrant research community.
Aun Zaidi, Noah A. Rubin, Ahmed H. Dorrah, Joon-Suh Park, and Federico Capasso. 11/22/2021. “Generalized polarization transformations with metasurfaces.” Opt. Express, 29, 24, Pp. 39065–39078. Publisher's VersionAbstract
Metasurfaces are arrays of sub-wavelength spaced nanostructures, which can be designed to control the many degrees-of-freedom of light on an unprecedented scale. In this work, we design meta-gratings where the diffraction orders can perform general, arbitrarily specified, polarization transformation without any reliance on conventional polarization components, such as waveplates and polarizers. We use matrix Fourier optics to design our devices and introduce a novel approach for their optimization. We implement the designs using form-birefringent metasurfaces and quantify their behavior &\#x2013; retardance and diattenuation. Our work is of importance in applications, such as polarization abberation correction in imaging systems, and in experiments requiring novel and compact polarization detection and control.
F. Prati, L. A. Lugiato, A. Gatti, L. Columbo, C. Silvestri, M. Gioannini, M. Brambilla, M. Piccardo, and F. Capasso. 11/20/2021. “Global and localised temporal structures in driven ring quantum cascade lasers.” Chaos, Solitons & Fractals, 153, Pp. 111537. Publisher's VersionAbstract
Starting from a full set of effective Maxwell-Bloch equations for a ring quantum cascade laser in the limit of fast material dynamics we derive a new set of equations which require a considerably lower numerical load because they evolve on the time scale of the electric field. With the further assumption of laser very close to threshold the equations take the form of the generalised Lugiato-Lefever equation. Using the latter, we study the formation and stability of multi-peaked localised structures which can be regarded as portions of a global pattern and exhibit a snaking structure.
Ahmed H. Dorrah, Michele Tamagnone, Noah A. Rubin, Aun Zaidi, and Federico Capasso. 11/19/2021. “Introducing Berry phase gradients along the optical path via propagation-dependent polarization transformations.” Nanophotonics. Publisher's Version 10.1515_nanoph-2021-0560.pdf