This PDF file contains the front matter associated with SPIE Proceedings Volume 11031, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Sub-wavelength gratings, segmented resonant-less structures with geometries featuring scales considerably smaller than the wavelength of light, have enabled an attractive technological concept to locally control light guiding properties in planar silicon chip architectures. This concept has allowed for additional degrees of freedom to tailor effective mode index, modal confinement, waveguide dispersion, as well as anisotropy, thereby providing a vital route towards high performing devices with engineered optical properties. Sub-wavelength integrated nanophotonics has opened up new horizons for realization of key building components that afford outstanding device performances, typically beyond those achieved by conventional design strategies, yet favorably benefiting from the sub-100-nm pattern resolution of established semiconductor manufacturing tools in nanophotonic foundries. The distinctive features of sub-wavelength grating structures are considered essential for future generation of chip-scale applications in optical communications and interconnects, biomedicine, as well as quantum-based technologies. In this work, we report recent advances in the development of high-performance on-chip nanophotonic waveguides and devices engineered with the sub-wavelength grating metamaterial structures. In particular, we discuss recent achievements of low-loss waveguides with controlled chromatic dispersion, high-efficiency fiber-to-chip surface grating couplers, micro-ring resonators, and grating-assisted waveguide filters, implemented on the mature silicon-on-insulator technology.

In this paper, a novel surface-emitting superluminescent diode fabricated by applying full on-wafer processing is presented. The surface-emission is achieved via mirrors etched by using an inductively coupled plasma process. This geometry allows to deflect in-plane guided and amplified optical modes perpendicular to the chip surface. The out-coupling window is anti-reflection coated, while at the other end of the waveguide a high-reflecting coating was deposited. In this way the device uses double-pass amplification, increasing efficiency, and light is emitted from a single spot. The light propagation and out-coupling in the proposed concept are first theoretically analyzed. Moreover, in order to simulate the optical output power, a rate equation-based frequency-resolved model accounting for non-ideal facet reflectivities and lasing onset is introduced. Finally, the measured L-I and spectral characteristics of fabricated InGaAs/GaAs superluminescent diodes emitting at a peak wavelength of 960nm are presented and compared to simulation results. At room temperature, pulsed output powers up to ∼ 125mW with a FWHM of 14nm and a wall-plug efficiency higher than 10% were achieved.

The design of 2D metasurface integrated with strip waveguide in SOI to achieve high coupling efficiency for 3.8 µm wavelength is presented. The metasurface design has been achieved using a commercial FDTD and the high coupling efficiency has been achieved by systematically optimizing the radius of circularly shaped unit cells and period between them by performing 3D FDTD simulations. The effective coupling efficiency is the performance metric in our case and it is defined as the ratio of the light coupled into strip waveguide to the difference of the light illuminated on the surface and the light reflected back due to interface. The effective coupling efficiency achieved for the designed 2D metasurface integrated with waveguide is ~98% in the in-plane waveguide for the out-of-plane surface illumination. The achieved bandwidth of the structure is 1µm. We believe our design is a good alternative for conventionally employed grating coupler and inverse taper. The integrated design also helps mitigate inefficient coupling using mid-IR fibers currently available and is consistent with the available lithography using 400 nm thick SOI for mid-IR applications. The monolithic integration can also be achieved using standard multi-project wafer (MPW) run.

We discuss recent progress on plasmonic and metasurface optoelectronic devices on silicon. Emphasis is placed on devices for sub-bandgap hot-carrier photodetection and high-speed intensity modulation. Surface-normal structures are of particular interest. We also discuss recent work on exceptional point waveguides, wherein the modal evolution traces out adiabatic and anti-adiabatic parametric paths around an exceptional point, and in combination with a gain saturation nonlinearity, leads to non-reciprocity.

Optical metasurfaces composed of designed Mie-resonant semiconductor nanoparticles arranged in a plane offer unique opportunities for controlling the properties of light fields [1]. Such metasurfaces can impose a spatially variant phase shift onto an incident light field, thereby providing control over its wave front with high transmittance efficiency. They can also e.g. act as polarizing optical elements, exhibit tailored nonlinear optical properties, or manipulate spontaneous emission processes of nanoscale emitters integrated in the metasurface architecture. However, the optical response of most semiconductor metasurfaces realized so far was permanently encoded into the metasurface structure during fabrication. Recently, a growing amount of research is concentrating on obtaining dynamic control of their optical response, with the aim of creating metasurfaces with functionalities that can be tuned, switched or programmed on demand. This talk will provide an overview of our recent advances in actively tunable Mie-resonant semiconductor metasurfaces. In particular, by integrating silicon metasurfaces into a liquid-crystal (LC) cell, we can tune their linear-optical transmittance and reflectance spectra by application of a voltage [2]. In our work, we utilize a LC photoalignment material [3] during the assembly of the LC metasurfaces, leading to a drastic improvement of the tuning performance and reproducibility. Based on this method, we demonstrate electrical tuning of LC-infiltrated dielectric metasurfaces at near-infrared and visible wavelengths. We show that these metasurfaces can be tuned into and out of the so-called Huygens’ regime of spectrally overlapping electric and magnetic dipolar resonances, which is characterized by near-unity resonant transmission, by application of an external voltage. In particular, we demonstrate tuning of the metasurface transmission from nearly opaque to nearly transparent at 1070 nm. Furthermore, making use of the strong modulation of the metasurface response in combination with patterned electrodes, we experimentally demonstrate a transparent metasurface display device operating in the visible spectral range. However, while the integration of silicon metasurfaces into nematic LC cells represents an efficient and versatile tuning approach showing large resonance shifts and strong tuning contrast, the switching times that can be achieved based on this approach are limited. Thus, as an alternative tuning mechanism allowing for ultrafast operation, we consider the transient changes of the optical properties of semiconductor materials when optically pumped by femtosecond laser pulses. These changes can lead to pronounced changes of the resonance condition for semiconductor metasurfaces at an ultrafast time scale. Our recent progress in ultrafast switching and tuning of semiconductor metasurfaces based on different material platforms and different physical mechanisms occurring at an ultrafast time scale will be discussed [4,5]. Furthermore, strategies to translate ultrafast tuning of metasurface resonances to ultrafast control of more complex metasurface functionalities such as wavefront shaping will be outlined. [1] I. Staude & J. Schilling, Nature Photon. 11, 274 (2017). [2] A. Komar et al., Appl. Phys. Lett. 110(7), 071109 (2017). [3] I. I. Rushnova et al., Opt. Commun. 413, 179 (2018). [4] M. R. Shcherbakov et al., Nano Lett. 15, 6985 (2015). [5] M. R. Shcherbakov et al., Nat. Commun. 8, 17 (2017).

Backside illumination enables an increase in photoactive area and numerical aperture of Ge-on-Si photodetectors for SWIR applications. The transparency of silicon in the infrared range (λ > 1.1 μm) allows a nearly lossless propagation of incoming light through the Si substrate and an application of various optical microstructures on the rear side of the Si substrate. Moreover, an aluminum front contact covering the whole top area serves as a mirror which extends the optical propagation of the detectable SWIR light through the absorbing layers and hence increases the quantum efficiency.

We developed back-illuminated Ge-on-Si photodiodes to apply such microstructures. Especially the usage of light trapping structures to increase the quantum efficiency of the photodiodes shows great potential. Among the different microstructures we chose black silicon (b-Si) as a promising light trapping candidate. After the fabrication, photodiodes with different configurations were evaluated. The obtained results show a strong increase of the quantum efficiency due to both, the existence of an Al mirror and the application of b-Si.

We report several PECVD silicon nitride photonic building blocks required for the implementation of a CMOS-compatible photonic integrated circuit technology platform operating in the 850 nm and 600 nm wavelength domain. In particular, for the 850 nm wavelength region we discuss a low-loss broadband 1x2 power splitter and a loop mirror. In the 600 nm wavelength region, we present new results on an optically pumped integrated dye-doped polymer laser that couples its light directly into a silicon nitride waveguide. Moreover, we discuss design considerations for a waveguide based gas sensing concept detecting target gas specific absorption changes in a thin dye-doped polymer cladding layer.

Low-cost, mass-produced biosensing systems needing minimal sample preparation and user intervention are required for many applications, ranging from food safety, water quality and security to personal and preventative medicine and rapid point-of-care diagnostics. Optical techniques have traditionally played a major role in quantitative chemical analysis and remain the mainstay of detection in “lab-on-chip” systems, but the degree of optical functionality integrated within these systems remains limited. Mid-infrared (MIR) absorption spectroscopy at wavelengths between 2.5 µm and 25 µm is widely used for quantitative analysis of biochemical species, as the fundamental vibrations of many biomolecules take place at these frequencies, offering the potential for label-free biosensing through analysis of molecular “fingerprints. However, while telecommunications applications have caused a revolution in photonic materials, devices and integration in the near-infrared, progress in biosensing systems has been hampered by the lack of integrated photonic platforms which can operate over the MIR wavelength region. Improvements in MIR sources and detectors combined with increasing demand for biochemical information to improve understanding of biological systems and to target medical treatment more effectively are driving research into materials and processes for MIR waveguide biosensors. Progress on new materials and approaches for high-sensitivity waveguide evanescent spectroscopies in the MIR which would enable new opportunities for sensitive, selective, label-free biochemical analysis will be described.

The atom marks the ultimate scaling limit of Moore’s law, which is why atomic scale devices have attracted significant research interests from the electronics industry. To allow efficient co-integration of electronics and photonics, key components such as photodetectors [1] and modulators [2] should match the footprint of electronic devices. Here we demonstrate the first atomic-scale plasmonic photodetector where atoms rather than electrons are responsible for the device operation. The concept is based on a so-called electro-chemical metallization (ECM) cell where an atomic-scale conductive filament is partially dissolved through a plasmonic-thermal effect. To realize this new type of photodetectors, three different disruptive technologies have been combined into one single fabrication process. First, a 3-D photonic technology based on a modified self-aligned approach of local-oxidation of silicon (LOCOS) has been developed for silicon-on-insulator (SOI) substrates. This is an important step as it enables the integration of tip-based atomic-scale plasmonics within a low-loss bus photonic waveguide. Second, vertical 3-D adiabatic plasmonic couplers have been fabricated using two e-beam lithography steps and a lift off process. The resulting metal-insulator-metal (MIM) waveguide that houses the ECM cell consists of a silver and a platinum contact separated by a gap of 20 nanometers. Finally, the atomic scale junction has been realized by electroforming a silver filament inside the ECM cell. To investigate the operation principle of this photodetector, a 3-D axis-symmetrical finite element method (FEM) model has been implemented that is able to self-consistently simulate the device resistance as a function of the applied voltage and temperature. The electrochemical growth and dissolution of a conductive filament between two electrodes is modeled analogously to the work of Refs. [3] and [4]. The current through the device is approximated as a tunneling current whose dependence on the filament state can be derived from ab initio quantum transport calculations. The microscopic nature of the device is also taken into account by considering an electrical double layer at the metal-insulator interfaces that accurately describes the electrostatic potential distribution within the ECM device. The incorporation of first-principles results [5] allowed us to significantly reduce the number of free parameters. Two light-matter interaction mechanisms have been identified and investigated, namely the optical force acting on individual filament atoms and the heating through electromagnetic dissipation in the metal. An atomistic study based on real-time time-dependent density-functional theory revealed that the optical forces are not strong enough to move single atoms, which leaves the optically-induced temperature as the main driving force behind the filament dissolution. In this paper we will show through accurate device simulations that this is indeed what is happening: the variation of the temperature at the metal-insulator interfaces strongly affect the electron transfer rates between these two regions, which explains the observed device behavior. Quantitative agreement between simulation and experiments will be demonstrated, thus opening up the possibility of future computer-aided designs of atomic-scale photodetectors. References [1] Emboras et al. doi:10.1021/acsnano.8b01811 [2] Emboras et al. doi:10.1021/acs.nanolett.5b04537 [3] Menzel. doi:10.1007/s10825-017-1051-2 [4] Lin et al. doi:10.1109/IEDM.2012.6479107 [5] Ducry et al. doi:10.1109/IEDM.2017.8268324

In the past few years we went from the ability to miniaturize a handful of optical components to being able to print massive optical circuits on a microelectronic chip composed of thousands of optical components. These optical circuits enable one to control the flow of light in unprecedented ways and are opening the door to applications that only a decade ago were unimaginable. The idea for guiding light on silicon chip originated in the 1980s but only in the early 2000s the viability of the platform was demonstrated. I will describe the challenges that silicon photonic faced in its infancy, and the work that helped overcome these challenges. I will also discuss the current state of art of silicon photonics, where larger and more complex systems are now putting higher demands and setting up new challenges for the technology.

Here we experimentally characterize photonic crystal nanolasers where the first endhole of the mirror has been systamatically shifted. FDTD simulations of similar passive cavities are done in order to find the expected evolution of the quality factor. We find that the predicted increase in the quality factor of the equivalent passive cavities leads to a decrease in the threshold power of the active nanolasers as expected. The maximum output power for varying endhole shifts has also been investigated and shifting the holes to optimize quality factor leads to lower maximum output power, when measuring from the top. The mirror of the photonic crystal cavity is further investigated as the mirror phase and penetration depth into the mirror are determined as a function of the endhole shift.

Refractive index engineering represents a powerful technique to design devices with advanced characteristics in the silicon-on-insulator platform. The use of subwavelength grating waveguides (SWG), in which subwavelength periodicities in both longitudinal direction and transversal direction are exploited, has shown to be a simple way to tune the desired refractive index. In this work is theoretically carried out the design of different SWG based Bragg grating filters for TE and TM polarization optimized at wavelength 1550 nm and assuming a minimum feature size of 100 nm. The main novelty of the proposed topology is the utilization of wide waveguides, which allow us to effectively control the size of the band gap. Additionally, the resultant quasi-2D structure can be efficiently analyzed by using simpler 2D simulators. Bragg grating filter optimized for TE polarization achieves a band-gap of 100 nm and radiation losses below -20 dB. In contrast, TM polarized waves are able to achieve radiation losses as low as -35 dB and band gap of 18 nm.

Integrated circuits constitute a complex mosaic, where materials with different characteristics, grown or deposited in different ways and at different temperatures, are linked together in various geometries. It is well known that during and after processing of these devices, mechanical stresses develop in the layers. These stresses may be due to thermal steps, intrinsic stresses, which are inherent in the formation process of the film, or due to the geometry of the material. For example, high stresses are present in the substrate at film edges. The presence of local residual stress has an important effect on the electrical properties of electronic devices, in particular on the reliability and the lifetime of the semiconductor components.

The present work focuses on the optical investigation of the thermomechanical stress of semiconductor materials used to realize new LED modules for front lighting application. Blue LEDs, based on gallium nitride (GaN) on sapphire, are bonded to a silicon carrier using gold silicon. Afterwards the sapphire is removed. The GaN on silicon devices are soldered by eutectic AuSn soldered on copper substrates, with different thicknesses. In the solder process different AuSn solder layer are achieved by varying the bond force. Raman spectroscopy is used to investigate the influence of the assembly process and assembly material on the local stress in the semiconductor. By that the physical, mechanical and chemical properties of the interconnect material can be analyzed. A model is developed to simulate the thermomechanical stress in the GaN LED assemblies. The Raman results validate the computational model. The phenomena are evaluated at room temperature, at -50°C and at 180°C.

Optical frequency combs are poised to have an enormous impact on many areas of science and technology, including time and frequency metrology, precision measurement, telecommunications, and spectroscopy. I will describe our recent research on frequency combs based on microresonators pumped by a single frequency pump field. Such chip-based combs offer great promise for creating devices that are highly integrated, stable, and can operate from the visible to mid-infrared regimes.

Dear Technical Committee, Prof. Josè Azaña and I have gladly accepted the invitation by Dr. Pavel Cheben to present an Invited Talk at the Integrated Optics: Design, Devices, Systems and Applications of the SPIE Optics and Optoelectronics Symposium. Best regards, Daniel Onori Abstract: The key goal for next-generation RF signal transceivers for communication, radar, and surveillance systems is a chip-scale implementation able to provide the highest performance in terms of total frequency range of operation (i.e., from 0.5 to 40 GHz and beyond), dynamic range, and linearity. Unfortunately, microwave technology is revealing unable to achieve the target performance with the desired level of compactness. In fact, its intrinsic bandwidth constraints impose the need of components that prevent a chip-scale integration, such as RF filter banks and multiple crystal oscillators. The generation and detection of RF signals through photonic coherent architectures results extremely attractive due to the promising wide bandwidth and large tunability that could be achieved with these technologies. When implemented in integrated-waveguide formats, photonic devices also present significantly reduced footprint with respect to conventional RF components. However, in order to reduce the interference noise introduced by optical sources exploited in the schemes, current solutions rely on technologies or components that prevent a monolithic on-chip integration. For instance, self-heterodyning schemes use tunable RF synthesizers for the electro-optical generation of the required coherent optical tones, while injection locking techniques, used to cancel the interference noise between the optical sources, stem from optical circulators, that cannot be integrated on chip. In this talk, we will review recent work on a novel noise cancelling architecture used to suppress the interference noise introduced by the lasers that feed the system and preserve the integrity of the processed signals during the operation. The solution overcomes the mentioned main drawbacks of the previously proposed scheme, enabling the realization of RF transceivers with high-performance and reduced footprint. Considering the commercial and integration potential of silicon photonics technology, we will discuss the advantages of a chip-scale implementation of this new design in terms of performance, reliability, and cost.

Based on magnetooptic Fourier modal method (MOaRCWA) simulations, both in 2D in 3D, we have studied the magnetoplasmons in plasmonic nanostructures, such as InSb within the THz spectral region. One of only few possibilities how to impose nonreciprocity in guiding subwavelength structures is to apply an external magnetic field (mainly in the Voigt configuration). In such a case, one-way (nonreciprocal) propagation of SP is not only possible but may bring many interesting phenomena in connection with magnetoplasmons (MSP). We have developed an efficient 2D and 3D numerical technique based on MO aperiodic rigorous coupled wave analysis – MOaRCWA. In our in-house tool, the artificial periodicity is imposed within a periodic 1D and 2D RCWA methods, in the form of the complex transformation and / or uniaxial perfectly matched layers. We have combined the MOaRCWA simulations with (quasi)analytical predictions in order to study MSP performance of plasmonic nanostructures with highly-dispersive polaritonic InSb material, in the presence of external magnetic field. Here, Voigt MO effect can be used to impose nonreciprocity (one-way propagation) bringing new interesting phenomena in connection with MSP. We have successfully applied our 2D and 3D numerical MOaRCWA technique to several interesting structures, such as THz a novel type of one-way structure, designed as a combination of the InSb and 3D hybrid dielectric-plasmonic slot waveguide, and others.

Subwavelength gratings (SWG) are periodic structures which behave as controllable homogeneous metamaterials. SWGs are extremely interesting when they are used in platforms with a limited choice of material refractive indices, enabling the design of a myriad of high-performance devices. Here we present a novel technique to gain control over the intrinsic anisotropy of the synthesized metamaterial. We show that tilting the silicon segments in a SWG structure mainly affects the in-plane (TE) modes, with little impact on the out-of-plane (TM) modes. Moreover, we present a methodology to quickly but accurately calculate the modes of a tilted periodic structure modeling the structure as a rotated uniaxial crystal which can be solved with an anisotropic mode solver. Measurements on a set of fabricated tilted SWG waveguides validate our simulation results. By using the presented technique, we design a polarization beam splitter based on a 2x2 multimode interferometer. The design is based on the optimization of the tilting angle to tone the beat length of the TE modes to be a half of the beat length of the TM modes.

Plasmonics-based waveguiding structures can deliver unprecedented degrees of wave-matter interaction, enhancing linear and nonlinear optical processes such as spectroscopy, sensing and signal processing, all within small form-factors and staggering device density. However, the main obstacle to a wider adoption has always been the excessive losses that scale poorly with optical confinement / localization [1-6]. Also in this work we demonstrate how can one utilize composite plasmonic waveguides with unparalleled alleviation of the loss-confinement tradeoff to achieve record Purcell factors within plasmonic waveguides [6]. Also I this talk we plan to discuss a novel class of nanoscale devices that address unmet performance demands for applications in data communications [1-6]. The performance of emerging generations of high-speed, integrated electronic circuits is increasingly dictated by interconnect density and latency as well as by power consumption. To alleviate these limitations, data communications using photons has been deployed, where photonic circuits and devices are integrated on platforms compatible with conventional electronic technologies. Within the dominant platform; namely Si, dielectric waveguides confine light via total internal reflection. This imposes bounds on minimizing device dimensions and density of integration. Those bounds arise due to the diffraction limit and the cross-coupling between neighbouring waveguides. Nanoscale Plasmonic waveguides provide the unique ability to confine light within a few nanometers and allow for near perfect transmission through sharp bends as well as efficient light distribution between orthogonally intersecting junctions. With these structures as a building block, new levels of optoelectronic integration and performance metrics for athermal transceivers with achievable bandwidths in excess of 500 Gbps as will be overviewed in this talk. In addition opportunities for the role that 2D materials may pay in propelling these record performance metrics even further will be projected [2]. 4. References [1] W. Ma and Amr S. Helmy, "Asymmetric long-range hybrid-plasmonic modes in asymmetric nanometer-scale structures," J. Opt. Soc. Am. B, Vol. 31, pp. 1723-1729 (2014). [2] C. Lin, Amr S. Helmy. "Dynamically reconfigurable nanoscale modulators utilizing coupled hybrid plasmonics." Scientific Reports 5, 12313 (2015). [3] . Lin, R. Grassi, T. Low and Amr S. Helmy. "Multilayer black phosphorus as a versatile mid-infrared electro-optic material" ACS Nano Lett. 5, 12313 (2016). [4] Herman M. K. Wong, and Amr S. Helmy, Performance Enhancement of Nano-Scale VO2 Modulators using Hybrid Plasmonics, IEEE J. Light. Technolo., vol. 36, pp797-808, (2018) [5] Y. Su, P. Chen, C Lin and Amr. S. Helmy, Highly sensitive wavelength-scale amorphous hybrid plasmonic detectors, OSA Optica, Vol. 4, No. 10, 1259-1262, (2017). [6] Y. Su, P. Chen, C Lin and Amr. S. Helmy, (2018). Submitted

New optical materials for hybrid photonic integration on silicon platform have become a hot research topic aiming at providing additional functionalities. In this regard, functional oxides are a very interesting class of materials due to their singular properties. Material engineering is commonly employed to tune and manipulate such properties at will, thus being functional oxides often used to build active reconfigurable elements in complex systems. Transparent oxides with moderate refractive indexes are targeted for hybrid integration due to the rewarding benefits envisioned. Yttria-Stabilized Zirconia (YSZ) is a chemically stable oxide¹ with a transparency range that spans from the visible to the mid-IR², with a refractive index around 2.1, which makes this functional oxide interesting for the development of low-loss waveguides when grown over a low contrast substrate. While these optical properties are very interesting for various applications, including on-chip optical communications and sensing, YSZ has remained almost unexplored in photonics up to now. Nevertheless, this complex functional oxide shows interesting optical properties such as low-moderate propagation losses of 2 dB/cm at telecom wavelengths³.

In our work, we explore the deposition of erbium doped YSZ by pulsed layer deposition (PLD) on a multilayer approach providing outstanding luminescence in correspondence with C-band of telecommunication window (λ=1530 nm) and in the visible range by means of up-conversion processes. The optical properties of active layers of Er-doped YSZ grown on waveguides in different platforms and under resonant pumping will be discussed in this paper, as well as their propagation losses. Based on the preliminary study of these active hybrid systems, we envision light amplification functionalities based on rare-earth doped functional oxides.

Silicon photonics has been the subject of intense research efforts. In order to implement complex integrated silicon photonic devices and systems, a wide range of robust building blocks is needed. Waveguide couplers are fundamental devices in integrated optics, enabling different functionalities such as power dividers, spot-size converters, coherent hybrids and fiber-chip coupling interfaces, to name a few. In this work we propose a new type of nanophotonic coupler based on sidewall grating (SIGRA) concept. SIGRAs have been used in the Bragg regime, for filtering applications, as well as in the sub-wavelength regime in multimode interference (MMI) couplers. However, the use of SIGRAs in the radiation regime has been very limited. Specifically, a coarse wavelength division multiplexer was proposed and experimentally validated. In this work we study the use of SIGRAs in the diffractive regime as a mean to couple the light between a silicon wire waveguide mode and a continuum of slab waveguide modes. We also propose an original technique for designing SIGRA based couplers, enabling the synthesis of arbitrary radiation field profile by Floquet- Bloch analysis of individual diffracting elements while substantially alleviating computational load. Results are further validated by 3D FDTD simulations which confirm that the radiated field profile closely matches the target design field.

The performance and functionality of integrated photonic devices can be enhanced by using complex structures controlled by a large number of design variables. However, the optimization of such high-dimensional structures is challenging, often limiting their realization. Global optimization algorithms and artificial neural networks are increasingly used to tackle these problems. Although these are exciting new developments, the outcome is a single optimized design meeting particular performance objectives selected upfront. The influences of the various design parameters remain hidden. Here we report on our strategy of using machine learning pattern recognition techniques to create a methodology for building the global performance map of a high-dimensional design space. As an example and demonstration, we study the design of a vertical grating coupler consisting of silicon and subwavelength metamaterial segments. We show how the relationship between designs with comparable primary performance can be clearly revealed by identifying the minimum number of characterizing parameters that defines the subspace of good designs, significantly scaling down the complexity of the problem. Moreover, the subspace can be identified using only a small number of good design solutions. We reveal design areas with comparable fiber coupling efficiency but with significant differences in other performance criteria, such as back-reflections, tolerance to fabrication uncertainty and minimum feature size. This novel approach provides the designer with a global perspective of the design space, enabling informed decisions based on the relative priorities of all relevant performance specifications and figures-of-merits for a particular application. Insights from the mapping exercise also inspired new design structures with enhanced characteristics.

Two-dimensional polaritons have emerged as powerful tools to manipulate light at atomic scales in materials such as graphene, transition metal dichalcogenides, and atomically-thin metal films. In this talk, we will review recent experimental advances in this front and discuss fundamental properties of these excitations, including their in/out-coupling to light and their potential for applications in sensing, nonlinear optics, and quantum physics.

Bragg-grating-based distributed-feedback waveguide resonators, with a discrete phase shift introduced inside the Bragg grating, exhibit within their grating reflection band a Lorentzian-shaped resonance line with an ultranarrow linewidth. If the phase shift is π/2, the resonance is located at the center of the reflection band, i.e., at the Bragg wavelength, where the grating reflectivity is maximum, hence the resonance linewidth is minimum. Alternatively, the required π/2 phase shift is often introduced by a distributed change in effective refractive index, e.g. by adiabatically widening the waveguide. Despite careful design and fabrication, the experimentally observed resonance wavelength deviates from the designed one. Besides deviations owing to fabrication errors, a fundamental, systematic shift towards shorter wavelengths occurs. We show theoretically and experimentally that the decay of light intensity during propagation from the phase-shift center into both sides of the Bragg grating due to (i) reflection by the periodic grating and (ii) the adiabatic refractive-index change causes an incomplete accumulation of designed phase shift by the oscillating light, thereby systematically shifting the resonance to a shorter wavelength. Calculations are performed based on the characteristic-matrix approach. Experimental studies are carried out in distributed-feedback channel-waveguide resonators in an amorphous aluminum oxide thin film on silicon with a distributed phase shift introduced by adiabatic widening of the waveguide according to a sin² function. Calculations and experiments show good agreement. Considering in the design the overlap integral between distributed phase shift and light intensity provides a performance that is much closer to the desired value.

Optical waveguide devices based on adiabatic mode evolution have large bandwidth and fabrication tolerances, but they have longer device lengths in general. We define a suitable adiabaticity parameter for optical waveguides and derive the formulae for engineering the adiabaticity along the waveguide. The fast quasiadiabatic dynamics (FAQUAD) protocol can then be applied to redistribute adiabaticity over the length of the device, speeding up mode evolution in adiabatic waveguide devices. By homogeneously distributing the adiabaticity along the length of the devices, shortcuts to adiabaticity are found for adiabatic waveguide devices, resulting in significant length reductions from the conventional designs. Devices on silicon, including mode (de)multiplexers, polarization splitter-rotators and 3 dB couplers using the FAQUAD approach are discussed. The FAQUAD approach leads to devices that are compact, broadband, and have good fabrication tolerances.

In this study, a high speed two-dimensional photodetector array (2D-PDA) was fabricated for the receipt of transmission signals from multi-core and few-mode fibers. With respect to the multi-core fiber (MCF) designs, the same square-shaped or triangular alignment arrangement as that used in a 19–32 MCF was applied to the 2D-PDA design layout. For a high-density integration with narrow gaps, the typical photodetector’s (PD) pixel size was set within the range of 10 m. The measured 3dB bandwidths were obtained from 20–26.5 GHz for all the pixels. No defects were observed in the pixels. With the constant gap between the pixels, the crosstalk due to the electromagnetic field from a neighboring pixel or wiring was measured using a lightwave component analyzer in the frequency range of 0.1–50 GHz. Under the light-ON condition for all the other pixels, with the exception of a center or corner pixel, the crosstalk at the center pixel was compared with that at the corner pixel. A difference of 1.2 dB at BER = 1 × 10-4 was found between them. A larger crosstalk was observed at the center pixel than at the outer pixel. A discussion on the origin of the crosstalk in the 2D-PDA is presented further in the manuscript, along with the electromagnetic (EM) simulation results.

Here we study self-assembled of 9-diethylamino-5-benzo[α]phenoxazinone 9 . AFM, SEM, Raman imaging, studies demonstrate that such materials form micron-sized tub-like structures with rectangular shape. These microstructures show both active and passive wave guiding modes. Applying wavelengths in resonance 532 nm, and in non-resonance (785nm) with the molecular electronic absorption bands was undertaken for active and passive wave guiding studies. PL spectra capping point, the body and emerging light points were investigated. Meanwhile, Raman scattered photons were also acquired which maintain the polarized light propagation direction(s) and its interaction with tube molecules. The hollow features and tubes defect were identified using Raman imaging. These studies showing that excellent wave guiding features are present using these self-assembled micron-tube structures.

We report cylinder photon traps, prism photon traps, and SiO2/Ta2O5 antireflection films added to the active areas of short wavelength infrared detectors. The total device thickness was estimated ~3.3μm and with the p-i-n structure based on antimonide. The simulation results show that the photon traps increase the absorption of the invisible spectrum distinctly. Also, the optical measurements reveal that maximal responsivity of the detector with PTs array is 0.094A/W in the visible range and 0.64A/W in the short wavelength infrared spectrum. The responsivity in the wavelength of short-wave infrared can be increased apparently as well. Thus, the photon traps array may a potential method for antimonide-based visible to short wavelength infrared bispectral photodetector.

We show the possibility of polarization-selective amplification of a defect mode in an active photonic crystal through the excitation of surface plasmon resonance in a 2D periodic array of spheroidal metallic nanoparticles embedded in the structure. The array acts as a polarizer whose spectral characteristics depend on the shape of the nanoparticles and the periodicity of the array. The modal selectivity of the amplification is due to the strong dependence of the surface plasmon assisted light scattering by the nanoparticles on the relative orientations of their anisotropy axis and the polarization direction of the incoming light wave. We show that effective defect mode suppression, for a well-chosen polarization, can be achieved if the nanoparticles array is embedded in regions of high localization of the optical field.

1D photonic crystal waveguide resonator has been designed for mid-IR wavelengths. The distinguishing feature of periodic nature of photonic crystals helps to achieve Bragg scattering, which allows waves that meet certain criteria to pass through. Using this principle, we have designed high-Q photonic crystal waveguide cavity for wavelengths centered at 3.8 μm in silicon-on-insulator (SOI), as it is a promising material for mid-IR exhibiting low-loss for wavelengths up to 4 μ m. The design process and optimization has been achieved by performing 3D FDTD simulations using a commercial software. 400 nm thick SOI is used to design well-known L5 cavity. It consists of circularly shaped air-holes placed in Si slab. Circularly shaped cells have been preferred to achieve fabrication tolerance in contrast to other shapes. A line defect is created by removing the five holes from center. A dipole source is place at center to which the cavity is exposed. Two step iterative process has been used to optimize the design and achieve high-Q. First the radius parameter has been optimized which is followed by optimization in period. Finally, an inner air-hole sweep has been performed to maximize the Q factor. High-Q factor of 99,359 has been achieved at 3.9 μm wavelengths. Our design is consistent with the available lithography for achieving integrated mid-IR sensors in SOI. Secondly, monolithic integration can be achieved using single etch process in Multi-Project-Wafer (MPW) run. These sensors can be designed for different gas sensing applications depending upon the wavelengths of gases.

In this work, the device is integrated with two bus waveguides and three ring waveguides. The ring and the bus waveguide is designed with a width of 250nm and a height of 400nm is considered. The mid infrared wavelength of 1550nm is considered as an input source for the coupling of light from the bus waveguide to ring waveguide. The coupling between the three ring waveguides is also observed. The multimode coupling takes place in the configuration. The guided mode resonance at 1550nm is observed. The four ports are placed at the inputs and outputs of the bus waveguide. Here the three ring structure with the bus waveguide is analyzed for spectral properties, where quality factor is of main concern. If the structure has to be implemented for a lab-on-a-chip application, sensitivity plays an important role, which in turn is related to the quality factor. Hence the enhancement of the quality factor up to 3000 with three rings is achieved. Two rings are considered as sensing ring for various parameter analyses with one of the ring as reference ring. In the designed structure, the phase shift in the transmission spectrum is observed for the bio-sensing application. The sensor in the ring resonator is based on the refractive index change. The change in the refractive index of the surrounding medium will change the effective refractive index. Hence the effective refractive index along with the group index is monitored for the bio-sensing application. A thin layer on the surface of the waveguide is highly sensitive to refractive index change in the TM mode. The configuration is simulated using Lumerical FDTD as well as Lumerical Mode solutions. The integrated optical devices has a good platform in bio-sensing application, hence the designed configuration can be further incorporated for point of care device.

The demand for high speed in wireless communication is a big concern since the number of connections is increasing. The employment of higher carrier is strongly recommended and millimeter wave (mm-wave) frequency are necessary in the future. In this paper, we propose the generation and the transmission of multiband signal for millimeter-wave Radio over Fiber (RoF) system using the full spectrum of 200 -300GHz for downlink transmission of 10 Gb/s On off Keying (OOK) and 40 Gb/s Differential Quadrature Phase Shift Keying (DQPSK). An optimized Optical Flat Comb Source (OFCS) based on dual-arm Mach-Zehnder Modulator (MZM) is employed in order to generate 5 carriers with 25 GHz spacing and centered around 250 GHz. For 10 Gb/s OOK and 40 Gb/s DQPSK, the system performances are evaluated by measuring the Bit Error Rate (BER). In addition, we have studied the Error Vector Magnitude (EVM) for 40 Gb/s DQSK system.The obtained results have been done for single and multiband channels. At first, we have explored the effect of the optical fiber in the performance of our system. The optical fiber is inserted after each modulatorand after the local oscillator (LO) for path compensation.The optical delay line has an important role in reducing interference between channels. Furthermore, we discuss the performance of the system in back to back transmission in different cases such as without wireless link and with wireless link. Finally, we have studied the wireless link distances for acceptable BER below Forward Error Correction (FEC) limit BER 3.8x10^-3 and EVM for each modulation format. The transmission link length is about 2 m. The generated signal is used for short range indoor wireless systems.

Due to the growth of the number of communication devices over the last decades, the millimeter wave (mm-wave) band has been strong interest. In fact, this band offers a massive bandwidth and highest speed. However, in order to obtain the highest receiver sensitivity, it's necessary to generate the millimeter wave signals with low phase noise. In this paper, we propose the photonic generation of mm-wave signals with three methods. The generation is based on an optical frequency comb source (OFCS) from which five carriers are selected for 40 Gb/s Differential Quadrature Phase Shift Keying (DQPSK) modulation. At the level of the photo-detector, the optical local oscillator (LO) beats the mm-wave modulated signal. In the first case, the optical LO is distributed and emitted from an independent laser. In the second case, the optical LO which is a comb line is lumped. Finally, the optical LO is in an Optical Phase Locked Loop (OPLL) with the OFCS. Furthermore, we compare the performance of the 40 Gb/s DQPSK mm-wave generation and transmission system in the band of 200 - 300 GHz. We discuss their back-to-back (b-to-b) and over 10 km Single Mode Fiber (SMF) in term of Bit Error Rate (BER), Quality factor (Q factor), Signal to Noise Ratio (SNR) for single channel and for multiband channels in the band of 200 - 300 GHz. The system using the phase locked LO source has the high receiver sensitivity since the OPLL assured his phase stabilization. The 250 GHz channel has the best results for single band and multiband generation.

Optical spectrum analysis has been widely used in numerous areas such as optical network performance monitoring, materials analysis and medical research. Although there are many kinds of spectrometers, on-chip spectrometer could be a promising alternative with apparent size and weight advantages,. Silicon-on-Insulator(SOI) waveguide technology offers means to miniaturize the different parts of the spectrometer, even if often at the cost of performance and scalability. In this work, a cascaded waveguide structure was proposed for a spectrometer, with a spectral range from 1150nm to 1550nm, which corresponds to the second overtone region of the NIR absorption, and a resolution of 2 nm for performing spectrum derivation. The spectrometer is realized by a SOI cascaded Mach-Zehnder Interferometer and four SOI arrayed waveguide gratings. The cascaded MZI based coarse wavelength division de-multiplexers was employed for the first stage of the spectrometer and was used to disperse the signal into four channels. The output signals of the four channels are further dispersed into eight channels by the second stage AWG structures. We further implemented the thermo-optic modulation to achieve a higher spectral resolution. The output channel wavelengths of the spectrometer are modulated (with a wavelength shift 2 nm) by the embedded heater to obtain the first order derivative spectra of the input optical signal. We present the theory, modeling, and experimental demonstration of the thermally tuned spectrometer. With respect to the computer simulation and device characterization results, the 400nm spectral range and the 2nm resolution have been demonstrated.

This article focuses on the analysis of the effect of long-time thermal load on the total losses of the selected fiber-optic couplers which have been thermal stressed for the thirty weeks at temperature 100 °C ± 5 °C. A total of six couplers with 10:90, 1:99 and 50:50 dividing ratio were tested. Measurements were made for two wavelengths (1310 nm and 1550 nm). The results obtained show how long-term thermal stresses affect the total losses of the optical couplers. This information could be interest for the practical implementations of the optical couplers.

In this paper, we describe the design and modeling of novel long-range hybrid plasmonic waveguides that consist of both plasmonic thin films and nano-scale structures of a high refractive index material (such as silicon), with a material of low refractive index (such as silicon di-oxide) lying in the region between the nano-scale structures and the plasmonic thin film. We have employed complex geometry of silicon nanostructures in the vicinity of a plasmonic thin film. The effective refractive index and the corresponding propagation length obtained for these plasmonic waveguides and hybrid plasmonic waveguides were obtained using a full-vector finite difference eigen mode solver. In our simulations, different structural parameters of the the hybrid plasmonic waveguides were varied, and the effect of these parameters ⎯ on the propagation length and effective mode area ⎯ was analyzed. We describe the design of novel hybrid plasmonic waveguides that have a propagation length greater than 1 mm and also have a low effective mode area. The waveguides being proposed by us can be fabricated with relative ease using the standard lithography processes.

We present the design and modeling of novel electro-optic modulators and switches that have large extinction ratios, such that these electro-optic modulators and switches operate at the optical communication wavelength range (around 1550 nm). Firstly, we describe the design of an electro-optic modulator based on a tunable slotted ring resonator, having two pairs of partially overlapping graphene layers above and below of the slotted ring (in some portion of the circumference). We demonstrate that the transmission of light through the through port can be modulated by the application of voltage across the graphene layers. Secondly, we discuss the design of electro-optic switches using phase change materials either in a micro disk resonator or in a photonic crystal slab waveguide. These devices are based on the shift in the resonant frequency of a micro disk resonator and on the shift in the photonic bandgap of the photonic crystal slab waveguide, respectively, when its refractive index changes upon the application of voltage across the phase change material. A three dimensional finite-difference time-domain modeling software (Lumerical FDTD) was used for optical modeling and a commercial device modeling software (Lumerical DEVICE) was for the electrical modeling. The proposed electro-optic modulators and electro-optic switches can be used in optoelectronics, as well in the telecom wavelength range.