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1. Polarization-insensitive 1D grating coupler based on a zero-birefringence subwavelength corelet waveguide

   https://doi.org/10.1364/OL.459306  

   Zhang, Bohan ; Schiller, Mark ; Al Qubaisi, Kenaish ; Onural, Deniz ; Khilo, Anatol ; Naughton, Michael J. ; Popović, Miloš A. ( June 2022 , Optics Letters)

   Grating coupler devices provide efficient, foundry-compatible vertical fiber-to-chip coupling solutions in integrated photonic platforms. However, standard grating coupler designs are highly polarization sensitive, which hinders their adoption. We present a new, to the best of our knowledge, type of 1D polarization-insensitive grating coupler (PIGC) that is based on a zero-birefringence subwavelength “corelet” waveguide. We demonstrate a PIGC for coupling in the telecommunications O-band in a 45-nm-node monolithic silicon-on-insulator (SOI) CMOS electronic-photonic platform, with measured insertion losses of 6.7 and 6.1 dB to transverse electric and transverse magnetic polarizations, respectively, and a ±1-dB polarization dependent loss bandwidth of 73 nm.
2. High-resolution and compact serpentine integrated grating spectrometer

   https://doi.org/10.1364/JOSAB.423968  

   Brand, Michael ; Zhang, Bohan ; Onural, Deniz ; Al Qubaisi, Kenaish ; Popović, Miloš ; Dostart, Nathan ; Wagner, Kelvin ( June 2021 , Journal of the Optical Society of America B)

   Integrated astrophotonic spectrometers are integrated variants of conventional free-space spectrometers that offer significantly reduced size, weight, and cost and immunity to alignment errors, and can be readily integrated with other astrophotonic instruments such as nulling interferometers. Current integrated dispersive astrophotonic spectrometers are one-dimensional devices such as arrayed waveguide gratings or planar echelle gratings. These devices have been limited to${10}^4$resolving powers and$<<\#comment/>1000$spectral bins due to having limited total optical delay paths and 1D detector array pixel densities. In this paper, we propose and demonstrate a high-resolution and compact astrophotonic serpentine integrated grating (SIG) spectrometer design based on a 2D dispersive serpentine optical phased array. The SIG device combines a 5.2 cm long folded delay line with grating couplers to create a large optical delay path along two dimensions in a compact integrated device footprint. Analogous to free-space crossed-dispersion high-resolution spectrometers, the SIG spectrometer maps spectral content to a 2D wavelength-beam-steered folded-raster emission pattern focused onto a 2D detector array. We demonstrate a SIG spectrometer with$\sim <\#comment/>100\mathrm{k}$resolving power and$\sim <\#comment/>6750$spectral bins, which are approximately an order of magnitude higher than previous integrated photonic designs that operate over a wide bandwidth, in amore »display='inline'>0.4mm2footprint. We measure a Rayleigh resolution of$1.93\pm <\#comment/>0.07\mathrm{G}\mathrm{H}\mathrm{z}$and an operational bandwidth from 1540 nm to 1650 nm. Finally, we discuss refinements of the SIG spectrometer that improve its resolution, bandwidth, and throughput. These results show that SIG spectrometer technology provides a path towards miniaturized, high-resolution spectrometers for applications in astronomy and beyond.

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3. Vernier optical phased array lidar transceivers

   https://doi.org/10.1364/OE.451578  

   Dostart, Nathan ; Zhang, Bohan ; Brand, Michael ; Al Qubaisi, Kenaish ; Onural, Deniz ; Feldkhun, Daniel ; Popović, Miloš ; Wagner, Kelvin ( June 2022 , Optics Express)

   Optical phased arrays (OPAs) which beam-steer in two dimensions (2D) are currently limited to grating row spacings well above a half wavelength. This gives rise to grating lobes along one axis which limit the field of view (FOV), introduce return signal ambiguity, and reduce the optical efficiency in lidar applications. We demonstrate a Vernier transceiver scheme which uses paired transmit and receive phased arrays with different row periodicities, leading to mismatched grating lobe angular spacings and only a single aligned pair of transmit and receive lobes. This permits a return signal from a target in the desired lobe to be efficiently coupled back into the receive OPA while back-scatter from the other grating lobes is rejected, removing the ambiguity. Our proposal goes beyond previously considered Vernier schemes in other domains like RF and sound, to enable adynamic Vernierwhere all beam directions are simultaneously Vernier aligned, and allow ultra-fast scanning, or multi-beam, operation with Vernier lobe suppression. We analyze two variants of grating lobe suppressing beam-steering configurations, one of which eliminates the FOV limitation, and find the conditions for optimal lobe suppression. We present the first, to the best of our knowledge, experimental demonstration of an OPA Vernier transceiver, including gratingmore »lobe suppression of 6.4 dB and beam steering across 5.5°. The demonstration is based on a pair of 2D-wavelength-steered serpentine OPAs. These results address the pervasive issue of grating lobes in integrated photonic lidar schemes, opening the way to larger FOVs and reduced complexity 2D beam-steering designs.

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4. Hyperuniform disordered waveguides and devices for near infrared silicon photonics

   https://doi.org/10.1038/s41598-019-56692-5  

   Milošević, Milan M. ; Man, Weining ; Nahal, Geev ; Steinhardt, Paul J. ; Torquato, Salvatore ; Chaikin, Paul M. ; Amoah, Timothy ; Yu, Bowen ; Mullen, Ruth Ann ; Florescu, Marian ( December 2019 , Scientific Reports)

   We introduce a hyperuniform-disordered platform for the realization of near-infrared photonic devices on a silicon-on-insulator platform, demonstrating the functionality of these structures in a flexible silicon photonics integrated circuit platform unconstrained by crystalline symmetries. The designs proposed advantageously leverage the large, complete, and isotropic photonic band gaps provided by hyperuniform disordered structures. An integrated design for a compact, sub-volt, sub-fJ/bit, hyperuniform-clad, electrically controlled resonant optical modulator suitable for fabrication in the silicon photonics ecosystem is presented along with simulation results. We also report results for passive device elements, including waveguides and resonators, which are seamlessly integrated with conventional silicon-on-insulator strip waveguides and vertical couplers. We show that the hyperuniform-disordered platform enables improved compactness, enhanced energy efficiency, and better temperature stability compared to the silicon photonics devices based on rib and strip waveguides.
5. Ultra-low-power nonvolatile integrated photonic switches and modulators based on nanogap-enhanced phase-change waveguides

   https://doi.org/10.1364/OE.411254  

   Zhang, Jieying ; Zheng, Jiajiu ; Xu, Peipeng ; Wang, Yanqun ; Majumdar, Arka ( November 2020 , Optics Express)

   We propose a nanogap-enhanced phase-change waveguide with silicon PIN heaters. Thanks to the enhanced light-matter interaction in the nanogap, the proposed structure exhibits strong attenuation (Δα = ∼35 dB/µm) and optical phase (Δn_eff = ∼1.2) modulation atλ = 1550 nm when achieving complete phase transitions. We further investigate two active optical devices based on the proposed waveguide, including an electro-absorption modulator and a 1 × 2 directional-coupler optical switch. Finite-difference time-domain simulation of the proposed modulator shows a high extinction ratio of ∼17 dB at 1550 nm with an active segment of volume only ∼0.004λ³. By exploiting a directional coupler design, we present a 1 × 2 optical switch with an insertion loss of < 4 dB and a compact coupling length of ∼ 15 µm while maintaining small crosstalk less than −7.2 dB over an optical bandwidth of 50 nm. Thermal analysis shows that a 10 V pulse of 30 ns (1×1 modulator) and 55 ns (1×2 switch) in duration is required to raise the GST temperature of the phase-change waveguide above the melting temperature to induce the amorphization; however, the complete crystallization occurs by applying a 5 V pulse of 180 ns (1×1 modulator) and a 6 V pulse of 200 ns (1×2 switch),more »respectively.

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