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Surface grating couplers are diffractive periodic structures that enable efficient coupling of light between optical fibers and planar waveguides. Conventional grating couplers have polarization specific and limited wavelength operation, because of the intrinsic radiation angle dependency on both wavelength and polarization. In this Letter, we propose, to the best of our knowledge, the first polarization-independent surface fiber-chip grating coupler, behaving as a wavelength splitter for the O and C communication bands. Polarization insensitivity is achieved by subwavelength segmentation of the silicon gratings, together with a novel design to allow the dual wavelengths to propagate along two opposite directions in the chip. For the TE and TM polarizations, coupling efficiencies around −4.5 dB are achieved at both 1310 nm and 1550 nm, with an average 1-dB bandwidth of ~45 nm and ~60 nm, respectively. This grating coupler concept can be used as a part of transceivers to increase the data rate of wavelength-division-multiplexing (WDM) systems for fiber-to-the-home (FTTH) network services.

The generation of collimated steerable beams of light is a fundamental function in optics needed in many applications, including free-space optical communications, remote sensing, and light detection and ranging. Implementing large-aperture light emitters directly on a photonic integrated chip without using external optics and expensive alignment systems is an outstanding challenge in integrated photonics. Here, the experimental demonstration of a new integrated antenna array architecture that uses a compact feeding circuit is reported. The design is based on an apodized Bragg deflector working as a low-loss (

The engineering of subwavelength grating metamaterials has become an essential design strategy in silicon photonics. The lithographic segmentation of integrated waveguides at the subwavelength scale enables the synthesis of on-chip metamaterials and provides control over optical properties such as mode delocalization, wavelength dispersion, and anisotropy. At the near-infrared wavelengths of the 1.55-μm telecom band, a range of subwavelength-based devices with unprecedented performance has been demonstrated, including couplers, filters, and polarization-handling structures. In this invited paper, we review the foundations of anisotropic subwavelength grating metamaterials and discuss our latest advances in five new subwavelength-enhanced devices: a millimeter-long optical antenna that is evanescently coupled to diffractive lateral segments, thereby achieving a record far-field beam width of 0.1º in silicon; a multi-line integrated Bragg filter also using lateral loading segments, which produces 20 non-uniformly spaced spectral notches with a 3-dB linewidth as low as 210 pm; a low-loss curved wavelength demultiplexer; a segmented multi-mode interference coupler based on novel bricked subwavelength gratings, yielding a 1-dB bandwidth exceeding 140 nm; and a suspended waveguide platform with low propagation loss at mid-infrared wavelengths. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Beam splitters are core components of photonic integrated circuits and are often implemented with multimode interference couplers. While these devices offer high performance, their operational bandwidth is still restrictive for sensing applications in the mid-infrared wavelength range. Here we experimentally demonstrate a subwavelength-structured 2 × 2 multimode interference coupler with high performance in the 3.1 − 3.7 µ m range, doubling the bandwidth of a conventional device.

Silicon photonics is playing a key role in areas as diverse as high-speed optical communications, neural networks, supercomputing, quantum photonics, and sensing, which demand the development of highly efficient and compact light-processing devices. The lithographic segmentation of silicon waveguides at the subwavelength scale enables the synthesis of artificial materials that significantly expand the design space in silicon photonics. The optical properties of these metamaterials can be controlled by a judicious design of the subwavelength grating geometry, enhancing the performance of nanostructured devices without jeopardizing ease of fabrication and dense integration. Recently, the anisotropic nature of subwavelength gratings has begun to be exploited, yielding unprecedented capabilities and performance such as ultrabroadband behavior, engineered modal confinement, and sophisticated polarization management. Here we provide a comprehensive review of the field of subwavelength metamaterials and their applications in silicon photonics. We first provide an in-depth analysis of how the subwavelength geometry synthesizes the metamaterial and give insight into how properties like refractive index or anisotropy can be tailored. The latest applications are then reviewed in detail, with a clear focus on how subwavelength structures improve device performance. Finally, we illustrate the design of two ground-breaking devices in more detail and discuss the prospects of subwavelength gratings as a tool for the advancement of silicon photonics.

In this work, the authors present their recent progress in the development of a platform for the mid-infrared wavelength range, based on suspended silicon waveguides with subwavelength metamaterial cladding. The platform has some intrinsic advantages, which make it a very promising candidate for sensing applications in the molecular fingerprint region. Specifically, it can cover the full transparency window of silicon (up to a wavelength of 8 μm), only requires one lithographic etch-step and can be designed for strong light-matter interaction. Design rules, practical aspects of the fabrication process and experimental results of a complete set of elemental building blocks operating at two very different wavelengths, 3.8 and 7.7 μm, are discussed. Propagation losses as low as 0.82 dB/cm at λ0 = 3.8 μm and 3.1 dB/cm at λ0 = 7.7 μm are attained for the interconnecting waveguides.

Silicon photonic waveguides patterned at the subwavelength level behave as metamaterials whose optical properties, including refractive index, dispersion and anisotropy can be tuned by judiciously designing the subwavelength geometry. Over the past years, the added design freedom afforded by these structures has enabled a wide variety of novel high performance devices, ranging from high efficiency fibre-to-chip couplers, to on-chip polarization and mode management, and ultra-broadband waveguide couplers covering several optical communication bands. In this invited keynote talk we will revisit the physical foundations of these structures, explore some of the latest advances in the field with applications in both telecommunications and sensing, and discuss some of the outstanding challenges to move these structures from research labs to large-scale commercialisation.

Periodic silicon waveguides with a pitch that is below half the effective wavelength of light support diffraction-less Bloch modes. These modes propagate as through a homogeneous, artificial-core metamaterial waveguide whose optical characteristics can be engineered by lithographic patterning. Subwavelength gratings (SWGs) provide designers with unique tools to control the refractive index, dispersion and birefringence of the equivalent metamaterial, yielding improved device performance. Based on this approach many high-performance optical devices have been designed and experimentally demonstrated in the last years. In this paper we will review the fundamentals of SWG engineering and present some of our latest findings.

Subwavelength engineered metamaterial waveguides and devices are considered as fundamental building blocks for the next generation of integrated photonic circuits. Here we present an overview of recent advances in this surging field.

We propose a novel polarization-independent grating coupler working as a wavelength splitter for both 1310 nm and 1550 nm using subwavelength grating structures on a 500-nm-thick SOI platform. This low-cost and efficient dual-band grating coupler can be used for wavelength-division-multiplexing systems in fiber-to-the-home networks.

Integrated photonic biosensors have demonstrated low bulk detection limits down to 1e−7 refractive index units. Nevertheless, most rely on expensive optical sources, such as DFB lasers. Here, we experimentally demonstrate that with adequate sensor design comparable detection limits are achievable with a low-cost Fabry-Perot laser. European Union’s Horizon 2020, Marie Skłodowska-Curie grant agreement No 713721; Ministerio de Econom ́ıa y Competitividad (FEDER), Proyecto TEC2016-80718-R; Programa Operativo FEDER Andalucía 2014-2020 (UMA18-FEDERJA-219); Severo Ochoa program from Spanish MINECO, Grant No. SEV-2017-0706, Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

OSA Advanced Photonics Congress ¿ Integrated Photonics Research, Silicon and Nanophotonics, Washington, DC United States, 13–16 July 2020, In this invited talk we review the latest advances in the surging field of photonic subwavelength metamaterials. These structures can provide enhanced, device-specific material properties and find widespread application in silicon photonics, We acknowledge funding through Universidad de Málaga, Ministerio de Economía y Competitividad (TEC2016- 80718-R, CDTI SNEO-20181232, RTI2018-097957-B-C33), Ministerio de Educación, Cultura y Deporte (FPU16/06762, FPU16/03401, FPU17/00638), Proyecto I+D+i en el marco del Programa Operativo FEDER Andalucía 2014-2020 (UMA18-FEDERJA-219), Czech Science Foundation (Project 190062S), Alcyon Photonics (8.06/5.59.5045), the Community of Madrid – FEDER funds (S2018/NMT-4326), the Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant No. 734331

The mid-infrared (MIR) wavelength region contains unique absorption fingerprints of many molecules and substances. Therefore, the main application area in the MIR can be sensing. Si and Ge are transparent in this range (Si up to 8 μm, and Ge up to 15 μm) and due to their excellent electrical and optical properties and CMOS compatibility they can offer suitable platforms for the realisation of compact MIR sensors. However, claddings used for the telecom wavelength range are usually not suitable at longer wavelengths due to high absorption, so alternative solutions need to be investigated. In this paper we present our recent results on suspended Si and Ge devices (waveguides, couplers and detectors) that can exploit full transparency ranges of Si and Ge., 2020 22nd International Conference on Transparent Optical Networks (ICTON), July 19-23, 2020, Bari, Italy

2020 Photonics North (PN), Niagara Falls, ON, Canada, 26-28 May 2020, Subwavelength structures are enabling a host of high-performances devices in the silicon photonic platform. Here we review our progress in the field, with an emphasis on the auspicious anisotropic properties of these structures for applications ranging from broadband on-chip GRIN-lenses, to zero-birefringence waveguides and polarization splitters.

Subwavelength metamaterial structures in silicon waveguides open new degrees of freedom to control on-chip light propagation. They have been applied to many silicon photonic devices such as fiber-chip couplers, waveguide crossings, microspectrometers, ultra-fast optical switches, athermal waveguides, evanescent field sensors, polarization rotators and colorless interference couplers [1]. Here we report a demonstration of a metamaterial coupler and an InAs-on-InP quantum dash buried heterostructure laser optimized for mutual integration by direct facet-to-facet coupling with -1.2 dB coupling efficiency, coupled laser relative intensity noise (RIN) of -150 dB/Hz and 152 kHz linewidth. We further demonstrate the design of multi-line spectral notch filters based on narrow linewidth metamaterial Bragg filters synthesized using the layer-peeling method., 2020 Photonics North (PN), May 26-28, 2020, Niagara Falls, ON, Canada

Enabled by technological improvements, photonic devices and circuits are becoming increasingly more complex. Non-trivial geometries are designed to reduce device footprint, improve performance, and introduce novel functionalities. However, the number of design variables required to properly represent these geometries quickly grows, limiting the effectiveness of classical design approaches. Moreover, parameters are often strongly interdependent, restricting the use of sequential optimizations or independent parameter sweeps. Although several optimization techniques can be effective for multi-parameter design, they commonly allow to optimize for a single or a handful designs and the optimization process needs to be repeated if new performance criteria are introduced. In contrast to classical design approaches, the influences of the design parameters remain hidden as well as the general behavior of the design space. In this paper we present an extension of our recent work on the application of machine learning pattern recognition to the design of multi-parameter photonic devices. In particular, we propose using a combination of local optimization based on the adjoint method and the use of dimensionality reduction. Adjoint optimization is used multiple times to generate a small set of different designs with high performance. Dimensionality reduction is applied to analyze the relationship between these degenerate designs and identify a lower-dimensional design sub-space that includes all alternative good designs. This sub-space can be mapped for any performance criteria thus enabling informed decisions based on the relative priorities of all relevant performance specifications. As a proof of concept, we demonstrate a ten-parameter design of an integrated photonic power splitter using silicon-on-insulator technology. We identify a region of possible high performance design solutions and select two design candidates either maximizing the splitter efficiency or minimizing back-reflection., Integrated Photonics Platforms: Fundamental Research, Manufacturing and Applications, April 6-10, 2020, Online Only, France, Series: Proceedings of SPIE

Integrated photonics devices, based in subwavelength grating (SWG) metamaterials, have shown unprecedented performance in a wide variety of situations. Since their proposal and first experimental demonstration in 2010 designers have made use of the new degrees of freedom provided by these structures to design advanced devices with improved capabilities. The extended design space provided by SWG structures has been successfully used to engineer the refractive index, the dispersion and, more recently, the waveguide birefringence, thus allowing novel advanced device design. In this invited talk we will review some of the advances made by our group in the field., Smart Photonic and Optoelectronic Integrated Circuits XXII, February 1-6, 2020, San Francisco, United States, Series: Proceedings of SPIE

Silicon photonics has emerged as an intense field of research due to its unique capabilities to integrate photonics and electronics into the same platform using standard semiconductor fabrication facilities. Subwavelength grating (SWG) structures, i.e. periodic nanostructured waveguides with a pitch below half the wavelength of light, allow the lossless propagation of Bloch-Floquet modes which closely resemble propagation through a homogenous waveguide with optical properties (refractive index, dispersion, birefringence) that can be tailored to fulfill specific design goals. SWG engineering is now routinely used for novel and advanced device design. Fiber-chip couplers, polarization and mode multiplexers, multimode interference couplers (MMIs), lenses, and bragg filters have been successfully designed in our group based in these concepts. In this invited talk we will review some of our last advances in the field., High Contrast Metastructures IX, February 2-6, 2020, San Francisco, United States, Series: Proceedings of SPIE

We design perfectly vertical grating couplers with minimum feature sizes above 100 nm, high coupling efficiencies up to 75%, and low back reflection of -20 dB over 100 nm bandwidth, using a machine learning method., Integrated Photonics Research, Silicon and Nanophotonics 2020 , July 13-16, 2020, Washington, DC

Over the past two decades, integrated photonic sensors have been of major interest to the optical biosensor community due to their capability to detect low concentrations of molecules with label-free operation. Among these, interferometric sensors can be read-out with simple, fixed-wavelength laser sources and offer excellent detection limits but can suffer from sensitivity fading when not tuned to their quadrature point. Recently, coherently detected sensors were demonstrated as an attractive alternative to overcome this limitation. Here we show, for the first time, to the best of our knowledge, that this coherent scheme provides sub-nanogram per milliliter limits of detection in C-reactive protein immunoassays and that quasi-balanced optical arm lengths enable operation with inexpensive Fabry–Perot-type lasers sources at telecom wavelengths., Horizon 2020 Framework Programme (EuroNanoMed 3-H2020 DrNanoDAII); Ministerio de Economía y Competitividad (2019/PCI 2019-2, CTQ2017-86994-R, SEV-2017-0706); Junta de Andalucía, Proyectos Excelencia-Retos (P18-RT-1453, P18-RT-793); Fondos Europeos de Desarrollo Regional (CTQ2016-75870-P, PID2019-104293GB-I00, RD16/0006/0012, TEC2016-80718-R, UMA18-FEDERJA-007, UMA18-FEDERJA-219); H2020 Marie Skłodowska-Curie Actions (713721).

Integrated optical antennas are key components for on-chip light detection and ranging technology (LIDAR). In order to achieve a highly collimated far field with reduced beam divergence, antenna lengths on the order of several millimeters are required. In the high-index contrast silicon photonics platform, achieving such long antennas typically demands weakly modulated gratings with lithographic minimum feature sizes below 10 nm. Here, we experimentally demonstrate a new, to the best of our knowledge, strategy to make long antennas in silicon waveguides using a metamaterial subwavelength grating (SWG) waveguide core loaded with a lateral periodic array of radiative elements. The mode field confinement is controlled by the SWG duty cycle, and the delocalized propagating mode overlaps with the periodic perturbations. With this arrangement, weak antenna radiation strength can be achieved while maintaining a minimum feature size as large as 80 nm. Using this strategy, we experimentally demonstrate a 2-millimeter-long, single-etched subwavelength-engineered optical antenna on a conventional 220 nm SOI platform, presenting a measured far-field beam divergence of 0.1° and a wavelength scanning sensitivity of 0.13°/nm.

In recent years, sensing and communication applications have fueled important developments of group-IV photonics in the mid-infrared band. In the long-wave range, most platforms are based on germanium, which is transparent up to ∼15-µm wavelength. However, those platforms are limited by the intrinsic losses of complementary materials or require complex fabrication processes. To overcome these limitations, we propose suspended germanium waveguides with a subwavelength metamaterial lateral cladding that simultaneously provides optical confinement and allows structural suspension. These all-germanium waveguides can be fabricated in one dry and one wet etch step. A propagation loss of 5.3 dB/cm is measured at a wavelength of 7.7 µm. These results open the door for the development of integrated devices that can be fabricated in a simple manner and can potentially cover the mid-infrared band up to ∼15 µm.

Silicon photonics provides wafer-scale fabrication of densely integrated photonic circuits that are enabling breakthrough applications in datacom, artificial intelligence, and healthcare. The sub-micrometer mode size of silicon waveguides makes efficient coupling to conventional single mode fibers extremely challenging. While advanced surface grating couplers can achieve sub-decibel coupling efficiencies, their operation relies on diffraction phenomena, which intrinsically limit the operational bandwidth. Here a novel type of surface coupler is experimentally demonstrated that overcomes the efficiency-bandwidth limitation of conventional diffraction gratings by harnessing zero-order radiation from a subwavelength metamaterial waveguide to a tilted silicon prism. The device achieves a coupling efficiency above 80% to an SMF-28 fiber in a record 1-dB bandwidth beyond 90 nm, opening new venues for highly efficient broadband fiber-to-chip surface coupling in silicon photonics.

Nanophotonics finds ever broadening applications requiring complex components with many parameters to be simultaneously designed. Recent methodologies employing optimization algorithms commonly focus on a single performance objective, provide isolated designs, and do not describe how the design parameters influence the device behaviour. Here we propose and demonstrate a machine-learning-based approach to map and characterize the multi-parameter design space of nanophotonic components. Pattern recognition is used to reveal the relationship between an initial sparse set of optimized designs through a significant reduction in the number of characterizing parameters. This defines a design sub-space of lower dimensionality that can be mapped faster by orders of magnitude than the original design space. The behavior for multiple performance criteria is visualized, revealing the interplay of the design parameters, highlighting performance and structural limitations, and inspiring new design ideas. This global perspective on high-dimensional design problems represents a major shift in modern nanophotonic design and provides a powerful tool to explore complexity in next-generation devices., Machine learning is increasingly used in nanophotonics for designing novel classes of complex devices but the general parameter behavior is often neglected. Here, the authors report a new methodology to discover and visualize optimal design spaces with respect to multiple performance objectives.

Metamaterial engineered waveguide structures are emerging as fundamental building blocks for integrated photonics. Here we present an overview of our recent advances in this field, including fiber-chip couplers, ultra-broadband beam splitters, nanophotonic waveguides with engineered anisotropy and integrated Bragg filters., 2019 IEEE Photonics Conference (IPC), September 29 - October 3, 2019, San Antonio, TX, USA

Silicon-on-insulator (SOI) is the dominant platform in near-infrared silicon photonics. However, the high absorption of SiO2 at wavelengths above 4 μm limits the range at which this material can be used in the midinfrared wavelengths (2 – 20 μm). In this paper we review our recent investigation on suspended devices, building on our previous work based on suspended silicon devices with sub-wavelength grating (SWG) lateral cladding at 3.8 μm, followed by our more recent results at 7.67 μm. This platform which uses the well-known fabrication techniques of SOI, only requires a single lithographic etch step and it allows the use of the whole transparency range of the waveguide core material. Due to this, it could be a good candidate for sensing applications since the design covers a very large wavelength range. As the bottom cladding of the waveguide is air, the waveguide can be designed so that the mode is squeezed to increase the evanescent field proportion and therefore the interaction with a surrounding analyte., 2019 21st International Conference on Transparent Optical Networks (ICTON), July 9-13, 2019, Angers, France

The atmospheric-transmission window and the fingerprint region of many substances overlaps with the long-wave infrared band. This has enabled the emergence of a new path for photonic integrated circuits, which could exploit the potential applications of this wavelength range, including chemical and bio sensing. In this work we review our latest advances in the suspended silicon platform with subwavelength grating lateral cladding at 7.7-μm wavelength. Suspended waveguides only require one lithographic etch step and can be specifically designed to maximize sensitivity when used as sensors. Waveguides with propagation loss of 3.1±0.3 dB/cm are demonstrated, as well as bends with less than 0.1 dB/bend. Suspended waveguides based on shifted Bragg grating lateral cladding are also reported, with propagation loss of 5.1±0.6 dB/cm. These results prepare the ground for the development of a platform capable of covering the entire mid-infrared band., 2019 21st International Conference on Transparent Optical Networks (ICTON), July 9-13, Angers, France

Integrated nanophotonic component design processes are often constrained by computational resources. Advances in simulation and optimization tools have allowed more efficient exploration of larger design spaces. These developments reduce the time-consuming and intuition-limited effort of encoding physical insights into the design structure. However, we argue that efficient optimization is only part of the solution to tackle larger multi-parameter design spaces. Finding patterns in such a space can be more valuable than identifying the individual optima alone. This is particularly true when transitioning from simulation to real device fabrication, where considerations such as tolerance to fabrication imperfections, bandwidth, etc. take an important role but are ignored at the optimization stage. The elucidation of patterns in a complex design space enables efficient identification of designs addressing these additional considerations. As an example, in this presentation we demonstrate how limited data collected from the optimization process of a multisegment vertical grating coupler can be used to identify such patterns through the application of machine learning techniques. The identified patterns, some more interpretable than others, can be used in multiple ways: from speeding up the remaining optimization process itself to gaining insight into the properties of an interesting subset of designs. Together those insights offer a significantly clearer picture of the design space and form the basis for making much more informed decisions on the final designs to be fabricated., Integrated Optics: Devices, Materials, and Technologies XXIII, February 2-7, 2019, San Francisco, USA, Series: Proceedings of SPIE; no. 10921

Silicon photonics is one of the most promising candidates to achieve lab-on-a-chip systems. Making use of the evanescent-field sensing principle, it is possible to determine the presence and concentration of substances by simply measuring the variation produced by the light-matter interaction in the real part of the mode effective index (in the near-infrared band), or in its imaginary part in a specific range of wavelengths (in the mid-infrared band). Regardless of which is the operating wavelength range, it is essential to select the proper sensing waveguide in order to maximize the device sensitivity. In this work we will review the potential of diffractionless subwavelength grating waveguides (SWG) for sensing applications by demonstrating their powerful capability to engineer the spatial distribution of the mode profile, and thereby to maximize the light-matter interaction. Among other things, we will demonstrate that the SWG waveguide dimensions used until now in the near-infrared are not optimal for sensing applications. In the mid-infrared band, due to the unacceptable losses of silicon dioxide for wavelengths longer than 4 μm, an additional effort is required to provide a more convenient platform for the development of future applications. In this regard, we will also show our recent progress in the development of a new platform, the suspended silicon waveguide with subwavelength metamaterial cladding. A complete set of elemental building blocks capable of covering the full transparency window of silicon (λ < ∼8.5 μm) will be discussed.

In this work we will review the enormous potential of subwavelength grating waveguides for sensing applications in the near and mid-infrared bands, demonstrating the capability to engineer the mode profile to maximize the light-matter interaction., Optical Sensors, 2019, San Jose, California, USA

OECC / PSC, Fukuoka, Japan, Japan, 7-11 July 2019, Subwavelength grating metamaterials are enabling a new generation of high-performance silicon photonic devices. Here we discuss the fundamental physics along with some of the latest advances in this rapidly expanding field., Funding: Ministerio de Economía y Competitividad, Programa Estatal de Investigación Orientada a los Retos de la Sociedad (cofinanciado FEDER) – TEC2016-80718-R, TEC2015-71127-C2-1-R (FPI BES-2016-077798) and IJCI-2016-30484; Community of Madrid – S2018/NMT-4326, Marie Sklodowska-Curie –734331, Universidad de Málaga, Czech Science Foundation – 1900062S.

Recent developments of photonic integrated circuits for the mid-infrared band has opened up a new field of attractive applications for group IV photonics. Grating couplers, formed as diffractive structures on the chip surface, are key components for input and output coupling in integrated photonic platforms. While near-infrared optical fibers exhibit large mode field diameters compared to the wavelength, in the long-wave regime commercially available single-mode optical fibers have mode field diameters of the order of the operating wavelength. Consequently, an efficient fiber-chip surface coupler designed for the long-wave infrared range must radiate the power propagating in the waveguide with a higher radiation strength than a conventional grating coupler in the near-infrared range. In this article, we leverage the short electrical length required for long-wave infrared couplers to design a broadband all-dielectric micro-antenna for a suspended germanium platform at 7.67 µm. The design methodology is inspired by fundamental grating coupler equations, which remain valid even when the micro-antenna has only two or three diffractive elements. A simulated coupling efficiency of ~ 40% is achieved with a 1-dB bandwidth broader than 430 nm, which is almost twice the typical fractional bandwidth of a conventional grating coupler. In addition, the proposed design is markedly tolerant to fiber tilt misalignments of ±10°. This all-dielectric micro-antenna design paves the way for efficient fiber-chip coupling in long-wavelength mid-infrared integrated platforms.

The use of subwavelength grating structures in silicon waveguides have fuelled the development of integrated optical components with superior performance. By a judicious lithographic patterning of the grating, the optical properties of the synthesized metamaterial can be accurately tailored. In this work, we review our latest advances in subwavelength-grating-engineered silicon and germanium planar devices.

Existing OPAs are typically based on 2D rectangular arrays or 1D linear arrays. Both approaches present a limited field-of-view (FOV) due to the presence of the grating lobes when the element spacing is larger than λ/2. To address the need for an increased steering range, we propose a new design strategy of an OPA system utilizing a 2D circular phased array, with a substantially increased FOV. We present a circular OPA using a demonstrated antenna element design, with an 820-element array. A steering range ΩSR calculated as a solid angle of 0.51π sr, and an angular beamwidth of 0.22°, was achieved. The array exhibits a sidelobe suppression larger than 10 dB, and a FOV of 2π sr. Although the performance is limited by the far field pattern of the individual antenna we chose, our circular OPA achieved, to the best of our knowledge, the largest steering range reported to date compared to the state-of-the-art integrated optical phased arrays reported in literature.