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One of the most critical elements in a data center transceiver is the optoelectronic modulator. In a silicon-based optoelectronic modulator, the ultimate performance depends on the orientation and positioning of its pn junction(s). In comparison to a conventional, lateral pn junction, a vertical pn junction improves energy efficiency by having a stronger overlap with the resonant optical signal. Adding to this design philosophy, we present two new designs of vertical junction modulators: (i) a double vertical junction, which doubles the interaction length, and (ii) a staggered double vertical junction, which further increases the interaction length by adding a lateral component to the double junction design. In this work, we provide a comprehensive numerical comparison of microring/disk modulators between the conventional, lateral pn junction and our vertical pn junction designs. We demonstrate how our new double vertical junction configurations offer the most promising power performance characteristics, with an energy-efficiency improvement by over a factor of 4. Our work may pave the way for new, energy-efficient silicon modulators in next-generation information processing and communications.

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.

To review and analyze the clinical outcomes of thermal therapy (≤1.4°C increase in core body temperature) in patients with heart failure (HF). A systematic review and meta-analysis regarding the effects of thermal therapy on HF was done by searching PubMed, Ovid Medline, Ovid Embase, Scopus, and internal databases up to date (2019). Improvement in the New York Heart Association (NYHA) class: Ten studies with 310 patients showed significant improvement in NYHA class. Only 7 among 40 patients remained in Class IV and 99 patients in Class III from 155 patients. Increased patients in lower classes indicate that more patients showed improvement. Sixteen studies on 506 patients showed an overall improvement of 4.4% of left ventricular ejection fraction (LVEF). Four studies reported improved endothelial dysfunction by 1.7% increase in flow-mediated dilation (FMD) on 130 patients. Reduction in blood pressure: Thermal therapy reduced both systolic blood pressure (SBP) and diastolic blood pressure by 3.1% and 5.31%, respectively, in 431 patients of 15 studies. Decrease in cardiothoracic ratio (CTR): Eight studies reported an average of 5.55% reduction of CTR in a total of 347 patients. Improvement in oxidative stress markers: Plasma brain natriuretic peptide (BNP) levels significantly decreased (mean difference of 14.8 pg/dL) in 303 patients of 9 studies. Improvement of quality of life: Among 65 patients, thermal therapy reduced cardiac death and rehospitalization by 31.3%. A slight increase in core body temperature is a promising, noninvasive, effective, and complementary therapy for patients with HF. Further clinical studies are recommended.

We report on a two-dimensional optical phased arrays with circular configurations to effectively suppress the grating sidelobes down to 10 dB, while enlarging the steering range to 0.24π and narrowing the angular beamwidths to 0.5°.

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

Integrated optical antennas are relevant devices for the development of next-generation LIDAR systems. Here we experimentally demonstrate a new topology to implement long antennas in silicon-on-insulator platform. The designed 2-millimeter-long antenna presents a measured far-field beam divergence of 0.1° and a wavelength sensitivity of 0.13°/nm., 2021 IEEE 17th International Conference on Group IV Photonics (GFP), December 7-10, 2021, Malaga, Spain

We present an open-source deep artificial neural network (ANN) model for the accelerated design of polarization-insensitive subwavelength grating (SWG) couplers on the silicon-on-insulator platform. Our model can optimize SWG-based grating couplers for a single fundamental-order polarization, or both, by splitting them counter-directionally at the grating level. Alternating, SWG sections are adopted to reduce the reflections (loss) of standard, single-etch devices—further accelerating the design time by eliminating the need to process a second etch. The model of this device is trained by a dense uniform dataset of finite-difference time-domain (FDTD) optical simulations. Our approach requires the FDTD simulations to be made up front, where the resulting ANN model is made openly available for the rapid, software-free design of future standard photonic devices, which may require slightly different design parameters (e.g., fiber angle, center wavelength, and polarization) for their specific application. By transforming the nonlinear input–output relationship of the device into a matrix of learned weights, a set of simple linear algebraic and nonlinear activation calculations can be made to predict the device outputs 1830 times faster than numerical simulations, within 93.2% accuracy of the simulations.

We present a compact silicon-based surface grating antenna design with a high diffraction efficiency of 89% (-0.5 dB) and directionality of 0.94. The antenna is designed with subwavelength-based L-shaped radiating elements in a 300-nm silicon core, maintaining high efficiency with a compact footprint of 7.6 µm × 4.5 µm. The reflectivity remains below -10 dB over the S, C and L optical communication bands. A broad 1-dB bandwidth of 230 nm in diffraction efficiency is achieved with a central wavelength of 1550 nm.

We experimentally demonstrate, to the best of our knowledge, the first microdisk-based silicon-photonic mode-division (de)multiplexer circuit, which is compatible with wavelength-division multiplexing for high aggregate bandwidth on-chip optical communications. This circuit uses waveguide-wrapped microdisk resonators, featuring low levels of intermodal crosstalk and insertion loss within an ultracompact footprint. In addition, the proposed device presents an increased free spectral range, allowing for 530 combined data channels. Furthermore, the microdisk structure naturally supports vertically oriented depletion-type pn junctions, which have been shown to reach subfemtojoule-per-bit modulation efficiencies. The high modulation efficiency, compactness, and wide free spectral range of waveguide-wrapped microdisk resonators present the potential for higher bandwidth and lower energy consumption in next-generation data processing and communication applications.

Spectral filters are important building blocks for many applications in integrated photonics, including datacom and telecom, optical signal processing and astrophotonics. Sidewall-corrugated waveguide grating is typically the preferred option to implement spectral filters in integrated photonic devices. However, in the high-index contrast silicon-on-insulator (SOI) platform, designs with corrugation sizes of only a few tens of nanometers are often required, which hinders their fabrication. In this work, we propose a novel geometry to design complex Bragg filters with an arbitrary spectral response in silicon waveguides with laterally coupled Bragg loading segments. The waveguide core is designed to operate with a delocalized mode field, which helps reduce sensitivity to fabrication errors and increase accuracy on synthesized coupling coefficients and the corresponding spectral shape control. We present an efficient design strategy, based on the layer-peeling and layer-adding algorithms, that allows to readily synthesize an arbitrary target spectrum for our cladding-modulated Bragg gratings. The proposed filter concept and design methodology are validated by designing and experimentally demonstrating a complex spectral filter in an SOI platform, with 20 non-uniformly spaced spectral notches with a 3-dB linewidth as small as 210 pm.

We study the fabrication tolerance of two types of grating antennas featuring U-shape and L-shape structures. The L-shape design is found to be more fabrication tolerant, showing performance degradation of less than 2% assuming common fabrication imperfections, making it promising for optical phased array applications., 2020 IEEE Photonics Conference (IPC), September 28 - October 1, 2020, Vancouver, BC, Canada

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.

We propose the first GST-induced switching device designed with serially-coupled ring resonators. This non-volatile technique can provide greater path diversity and offer higher efficiency without any need for a constant power supply, offering an excellent alternative for conventional thermo-optic and electro-optic switching.

For next-generation on-chip optical communications, the combination of wavelength- and mode-division multi-plexing has been proposed as way to achieve high aggregate bandwidth on a single multimode silicon bus waveguide. In this application, microring resonators are used to multiplex and demultiplex the different wavelength and mode channels. The designs of the microrings ultimately determine the throughput and power consumption of the circuit. In this work, we perform a comprehensive numerical comparison of the two designs that have already been demonstrated (the point-coupled and racetrack microring resonators) with a new, waveguide-wrapped design. The proposed design reduces the size of the microring cavity, which reduces the spatial footprint and increases the free spectral range (bandwidth), without heavily increasing loss and intermodal crosstalk (power budget). We believe that efficiency improvements to next-generation optical communications circuits like these can help meet the growing global demand for bandwidth without adding to the growing cost of operating them.

Optical phased arrays (OPAs) are now at the forefront of photonic research as a key beam steering technology for myriad of photonic applications, including in light detection and ranging (LIDAR), communications, and metrology, among others. Integrated OPAs with narrow beam widths and wide-angle steering are in critical need, especially for LIDARs in autonomous vehicle, drone and airplane navigation, or satellites. In this work, we numerically study the performances of OPAs having a circular layout arrangement. Compared to recently available solutions with 1D linear or 2D rectangular arrays, the proposed circular OPAs are poised to deliver effective suppression of the grating sidelobes, while improving beam steering range and obtaining narrower beamwidths. We demonstrate 110-element circular arrays with sidelobe suppression better than 10 dB and an angular beamwidth of 0.5°. Under a monochromatic operation at a 1550 nm wavelength, such array provides a solid angle steering range of 0.21π-sr, with a perspective for performance improvement by using large number of OPA elements and operating under broader spectral range.

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.

We experimentally demonstrate a ring-assisted Mach–Zehnder interferometer (RAMZI) design with slot waveguides for bulk index sensing using sucrose solution. Devices were implemented with both directional couplers (DCs) and multimode interferometer couplers (MMIs). The RAMZI designs with DCs were found to have a sensitivity of 203.3 ± 15.3 nm/RIU, while 177.2 p 12.0 nm/ RIU was demonstrated with MMIs-coupled RAMZI. The free spectral ranges (FSRs) of DCs and MMIs-coupled RAMZI were measured to be 24.3 and 34.3 nm, respectively. The FSRs demonstrated can be as wide as 7.9 times larger than the equivalent microring resonator.

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

We have successfully fabricated electronic and photonic components on the same substrate using a standard process offered by public silicon photonics foundry service. As we adopted the standard process parameters offered by A*STAR’s Institute of Microelectronics (IME), the design and fabrication of the n- and p-regions of the electronic devices are limited to the specific parameters optimized for creating optical waveguide modulators and photodetectors. In this work, we chose to fabricate and integrate Lateral Bipolar Transistors (LBJTs) and Junction Field Effect Transistors (JFETs) transimpedance amplifiers with Ge waveguide photodetectors, as well as on-chip photonic components such as grating couplers, submicron strip waveguides and PN depletion modulators. Our experimental results shows rectifying Ge photodiode characteristics and demonstrates full integration for sensing applications.