This PDF file contains the front matter associated with SPIE Proceedings Volume10537, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Over the past 30 years silicon photonics has evolved into a volume technology supporting mainstream commercial applications. Though we have seen a proliferation of new approaches, the attributes required for commercial success remain the same as they were three decades ago: volume manufacturability, optical power efficiency, and high-signalling bandwidth. Comparing to the evolution of the silicon microelectronics industry several decades earlier however, in the history of silicon photonics we see one key difference: for electronic Integrated circuit design, reductions in process node geometry have generally always contributed to advancing the goals of the product, leading to a conclusion that smaller is better. In contrast, for silicon photonics, reducing process geometries have introduced complexities that can inversely impact manufacturability, optical power efficiency and fiber-optic packaging. As microelectronics races to progressively smaller nodes the industry faces a question: what makes for a leading photonics platform? Perhaps bigger is better!

The first generation of silicon photonic products is now commercially available. While silicon photonics possesses key economic advantages over classical photonic platforms, it has yet to become a commercial success because these advantages can be fully realized only when high-volume testing of silicon photonic devices is made possible. We discuss the costs, challenges, and solutions of photonic chip testing as reported in the recent research literature. We define and propose three underlying paradigms that should be considered when creating photonic test structures: Design for Fast Coupling, Design for Minimal Taps, and Design for Parallel Testing. We underline that a coherent test methodology must be established prior to the design of test structures, and demonstrate how an optimized methodology dramatically reduces the burden when designing for test, by reducing the needed complexity of test structures.

A self-aligned dry etching method was proposed and verified theoretically to enhance the magnitude and simultaneously improve the uniformity of the tensile strain in a germanium (Ge) wave-guide (WG), with the help of tensile-stressed SiN stressor at the WG sidewalls. The SiN-strained germanium-on-insulator (GOI) WG was also experimentally demonstrated. Significant tensile strain was observed in the Ge material via micro-Raman measurements. This method could potentially facilitate a Ge photodetector with its optical detection range extended further towards longer wavelength and to be comparable with that of state-of-the-art InGaAs detectors.

The superior confinement of light provided by the high refractive index contrast in Si/SiO₂ waveguides allows the use of sub-micron photonic waveguides. However, when downscaling waveguides to sub-micron dimensions, propagation losses become dominated by sidewall roughness scattering. In a previous study, we have shown that hydrogen annealing after waveguide patterning yielded smooth silicon sidewalls. Our optimized silicon patterning process flow allowed us to reduce the sidewall roughness down to 0.25 nm (1σ) while maintaining rectangular Strip waveguides. As a result, record low optical losses of less than 1 dB/cm were measured at telecom wavelengths for waveguides with dimensions larger than 350 nm. With Rib waveguides, losses are expected to be even lower. However, in this case the Si reflow during the H₂ anneal leads to the formation of a foot at the bottom of the structure and to a rounding of its top. A compromise is thus to be found between low losses and conservation of the rectangular shape of the Rib waveguide. This work proposes to investigate the impact of temperature and duration of the H₂ anneal on the Rib profile, sidewalls roughness and optical performances. The impact of a Si/SiO₂ interface is also studied. The introduction of H₂ thermal annealing allows to obtain very low losses of 0.5 dB/cm at 1310 nm wavelength for waveguide dimensions of 300-400 nm, but it comes along an increase of the pattern bottom width of 41%, with a final bottom width of 502 nm.

Silicon photonic platforms are becoming more and more mature with competitive devices suitable for increasing needs of HPC (High Performance Computing) systems and datacenters. Compared to bulk III-V technologies, Si photonic technologies are suffering from the lack of integrated light source. Several works have been done in the past years to integrate laser on silicon using III-V direct bonding on top of patterned silicon. These demonstrations were using a CMOS compatible process for the silicon part but all the process steps following the introduction of the III-V material were done with small wafer diameter III-V fabrication lines. With such integrations, the cost advantage of silicon photonics based on the use of CMOS platforms and large wafer format is no more valid. In this paper we present the integration of a hybrid III-V/Si laser using a fully CMOS compatible 200mm technology. The laser is integrated in a mature photonic platform. The additional process modules required for this integration will be deeply described. These modules are localized silicon thickening using damascene process, Bragg reflector patterning with DUV lithography, III-V patterning and ohmic contact formation with no lift-off and without noble metal. This integration is compatible with a multi metal levels planar BEOL, mandatory for photonic circuit design. The first DFB lasers fabricated with this new platform are operating at 1310nm with a threshold current around 60mA, a SMSR larger than 45dB and more than 1.5mW optical power in the output waveguide. New laser designs, specifically adapted for this new process, will be introduced and fabricated.

Subwavelength pho¬tonics has seen tremendous progress, particularly in nanostructured engineered materials: metamateri¬als, metallic and dielectric subwavelength structures and subwavelength engineered waveguides. The novel optical properties found in these structures, along with the capability, through advanced fabrication techniques, to control their optical responses with unprecedented accuracy, has opened new prospects for controlling and manipulating light in planar waveguide circuits, at subwavelength scale. Since the first demonstrations of an optical waveguide with a periodic subwavelength grating metamaterial core at National Research Council of Canada, metamaterial SWG waveguides have attracted a strong research interest in academia and industry because of their unique potential to control light propagation in planar waveguides. The subwavelength metamaterial waveguides have been adopted by industry for fiber-chip coupling and subwavelength engineered structures in general are likely to become key building blocks for the next generation of integrated photonic circuits. In this invited talk we will present an overview of recent advances in implementations of these structures in silicon photonics, including high-efficiency fiber-chip couplers, ultra-broadband surface grating couplers and multimode interference (MMI) devices, and grating filters for near- and mid-infrared operation.

We introduce our 200 mm Si-SiN photonics platform for high-speed and energy-efficient optical transceiver. We present the fabrication process as well as wafer level characterizations in the O-band of Si and SiN photonic components such as waveguides, grating fiber couplers and Si-SiN interlayer adiabatic transitions. We demonstrate a low thermo-optic coefficient of the SiN layer and a large optical bandwidth for the hybrid Si-SiN photonic devices. This enhanced Si-SiN platform is of great importance for the realization of CWDM transceivers for which low temperature sensitivity and large bandwidth are needed.

In this paper, we discuss a back-end CMOS fabrication process for the large-scale integration of 2D materials on SOI (siliconon-insulator) platform and present a complete theoretical study of the change in the effective refractive index of 2D materialsenabled silicon nitride waveguide structures. The chemical vapour deposition (CVD) and liquid exfoliation fabrication methods are described for the fabrication of graphene, WS₂ and MoS₂ thin films. Finite-difference frequency-domain (FDFD) approach and the Transfer Matrix Method were used in order to mathematically describe these structures. The introduction of thin films of 2D material onto Si₃N₄ waveguide structures allows manipulation of the optical characteristics to a high degree of precision by varying the Fermi-level through the engineering of the number of atomically thin layers or by electrical tuning, for example. Based on the proposed tuning approach, designs of graphene, WS₂ and MoS₂ enabled Si₃N₄ micro-ring structures are presented for the visible and NIR range, which demonstrate versatility and desirable properties for a wide range of applications, such as bio-chemical sensing and optical communications.

Silicon nitride has received a lot of attention during the last ten years, for applications such as bio-photonics, tele/datacom, optical signal processing and sensing. In this paper, firstly an updated review of the state of the art of silicon nitride photonics integration platforms will be provided. Secondly, our developments on a moderate confinement Si₃N₄ platform in the near-infrared will be presented. Finally, our steps towards establishing a Si₃N₄ based platform for broadband operation spanning from visible to mid-infrared wavelengths will be introduced.

The ability to integrate optical phased arrays (OPA) on a single silicon-photonics substrate offers a plethora of new opportunities in various fields, including projection and imaging. In this paper, we will discuss some of the trade-offs in the design of OPAs and their application. We investigate OPA receivers which can form and electronically steer a “gazing beam” in a desired direction. We will discuss various architectural and systems choices and present a one-dimensional (1D) OPA and a two dimensional (2D) OPA, as examples. We will demonstrate how an optical heterodyning approach can be used to improve the sensitivity of such OPA and form images directly from the surface of a silicon nano-photonic chip without any lens, additional optical components, or moving parts. We will discuss the design details of a 1D OPA RX camera with a field of view in excess of 60 with a gazing beam width of 0.74 based on a heterodyning architecture. We will also investigate the details of the design of a heterodyne 2D OPA lensless camera which can image with the gazing beam width of 0.75 and the ability to image a field of view of roughly 8 in azimuth and elevation. We will also discuss the concept and implementation of coherent imagers that can be used as highly precise 3D imagers. As an example, we will show 3D imaging at the distance of 0.5m with a resolution of 15um.

Coherent Ising machines are a type of optical accelerators that can solve different optimization tasks by encoding the problem in the connection matrix of the network. So far, experimental realizations have been limited to time multiplexed solutions, in which one nonlinear node is present in a feedback loop. In Hewlett Packard Labs, we investigate the implementation of a spatially multiplexed solution, with an array of nominally identical nonlinear nodes. As this avoids the need for a long delayline, this makes the system more suitable for integration and hence mass production. HPE investigated two material platforms with good bulk nonlinearity properties: a-Si and GaAs. For the CMOS compatible a-Si platform, HPE demonstrated a design approach that allows to fabricate 1000 component all-optical computational circuits in a scalable way. In addition, to be able to do layout of Ising machines with ~1000 components, HPE developed highly capable photonic layout that will help across interconnects, sensors, and computation. In the GaAs platform, we focused on reducing the energy per elementary operation down to 1 fJ. The optical gates are designed with a bus-waveguide connectivity using a multi-level layered architecture design that allows waveguide connectivity between optical gates. This allows to separate computation and communication into their own dedicated layers increasing overall performance. Finally, we will highlight how both drastic automation at the layout stage and a tight integration between the electronic control layer (used for tuning of resonances and phase-shifters) and the photonic layer are key to achieve actual scalability to larger circuits.

Due to ever increasing demand for information bandwidth, and with electronics approaching their performance limit, there has been a renewed interest in using optical logic for computing and signal processing over the past decade. System advantages that the optical schemes promise over the conventional electrical schemes including but not limited to: significant reduction of gate latency, ultra-low energy consumption, and simplified layout architecture. For example, adding is the fundamental operation for computation. However, though it has a concise layout, a conventional electrical carry-ripple adder will be too slow for many-bit addition due to excessive carry propagation delay. Thus, modern microprocessors all have to use much more complicated structures such as parallel prefix adders to obtain satisfactory performance while they come with inevitable power penalty. The greater the number of bits, the more complex and power hungry the adder will become. In this paper, we propose a silicon photonics based architecture of carry-ripple adder, which utilizes the particular merit of light that interference, for future high-speed and low-power consumption optical computing. In our proposed carry-ripple adder, the critical path will be built with optical switch and optical signals will be modulated to carry information. As all of the optical switches could operate simultaneously, the unpleasant accumulated gate latency from the electrical approach will be removed. Silicon photonic based optical switches are promising candidates to implement the adder due to their compact sizes, which could significantly reduce the capacitances and energy-consumption.

Optical signal modulation is presently done using Si pn junctions which cause phase shifting due to Soref effect and, put in a Mach-Zehnder configuration, produce interference and generate amplitude modulation. The drawback of pn junctions is the relatively low phase shifting efficiency which consequently inflicts high power consumptions on the electrical driver. An alternative device to pn junctions was developed and consists of introducing capacitive structures within the optical waveguide. The proposed device has the same cross-section foot-print but is much shorter due to improved efficiencies. Typical pn-junctions can generate phase shifts of < 20°/mm for given implantation conditions and the capacitive structure developed produces shifts of > 60°/mm for the same implantation conditions. The device is made up of crystal Si, a thin SiO2 capacitor dielectric and poly-Si. Benchmarking the two phase shifters with respect to insertion losses, we observe that the proposed device is promising. Another material exhaustively used in CMOS technologies is Si3N4. In the data-communication bandwidths, the index contrast between Si3N4 (n = 1.95) and SiO2 (n=1.45) is smaller than that with Si (n = 3.5). Thus, nitride waveguides have lower optical mode confinements and are thus less sensitive to insertion losses caused by line edge roughness and wavelength shifting incurred by process variations. Moreover, the temperature induced index variations are 5 times les in Si3N4 than Si. Therefore, the use of nitride to fabricate devices in silicon photonics looks advantageous. However, high speed electro-optic devices are challenging in Si3N4. Consequently, a co-integration of both materials is essential. We developed a fabrication method and associated devices which allow to transfer the signal to and fro Si and Si3N4. We present some devices in each layer to illustrate the benefits.

Silicon modulators based on the carrier depletion mechanism are extensively used in recent years for high-speed data transmission. Lateral PN junctions are the most common electro-optical phase shifters for silicon Mach-Zehnder modulators (MZMs) due to its ease of fabrication. They have a relatively high DC V_πL_π of around 2.5 V.cm in the Oband. An alternative approach is to design and optimize vertical PN junctions for lower DC V_πL_π, which is currently lacking in the literature for silicon MZMs that operates using carrier depletion mechanism in the O-band. In this work, we look into the design and optimization of silicon phase shifters based on vertical PN junctions for high-modulationefficiency with V_πL_π ≤ 1 V.cm, while meeting the stringent low loss budget of ≤ ∼1 dB/mm for data communication in the O-band. This is achieved by varying the offsets of the vertical PN junction with respect to different doping concentrations (2e¹⁷/cm³ – 3e¹⁸/cm³ ) near the depletion region. Different types of doping schemes are explored and optimized. Our optimized vertical PN junction designs are predicted to give low DC V_πL_π of 0.26–0.5 V.cm for low DC reverse bias of ≥ –2V and low propagation loss of ≤ ∼1dB/mm, resulting in α.V_πL_π = 1.7 for the best designs, which to the best of our knowledge, is the lowest α.V_πL_π at the O-band to date. Electrical and optical modeling are based on our in-house proprietary software that is able to perform both optical and electrical simulations without loss of data fidelity.

Optical phased array (OPA) is considered as promising device in LiDAR application. We implemented a 1x16 silicon OPA consisting of an array of p-i-n electro-optic phase shifters and thermo-optic tunable grating radiators capable of two-dimensional beam-steering. The OPA was fabricated with CMOS-compatible process using SOI wafer. The p-i-n electro-optic phase shifters were formed in OPA channels for transversal beam-steering. With an array pitch of 2 μm, we attained transversal steering up to 45.6° at 1550 nm wavelength. For longitudinal beam-steering, we employed thermo-optic tunable grating radiators with p-i-n junction. The i-region covers whole radiator array and the p- and n-doped regions are placed on the both sides of the radiator array. This structure can provide fairly uniform heating of the radiator region, shifting the overall radiation field in longitudinal direction by the thermo-optic effect. As a result, a longitudinal beam-steering up to 10.3° was achieved by forward-biasing with a power consumption of 178 mW. This result proves a possibility of wide two-dimensional beam-steering with one-dimensional OPA without using tunable light source. We confirmed that the longitudinal tuning range obtained above is corresponding to near 100 nm wavelength tuning. Our device scheme can be a cost-effective solution of the OPA and also be a solution of self-adjustment for fluctuation of the wavelength-dependent performances.

Quantum dot comb sources integrated with silicon photonic ring-resonator filters and modulators enable the realization of optical sub-components and modules for both inter- and intra-data-center applications. Low-noise, multi-wavelength, single-chip, laser sources, PAM4 modulation and direct detection allow a practical, scalable, architecture for applications beyond 400 Gb/s. Multi-wavelength, single-chip light sources are essential for reducing power dissipation, space and cost, while silicon photonic ring resonators offer high-performance with space and power efficiency.

The challenges associated with the photonic packaging of silicon devices is often underestimated and remains technically challenging. In this paper, we review some key enabling technologies that will allow us to overcome the current bottleneck in silicon photonic packaging; while also describing the recent developments in standardisation, including the establishment of PIXAPP as the worlds first open-access PIC packaging and assembly Pilot Line. These developments will allow the community to move from low volume prototype photonic packaged devices to large scale volume manufacturing, where the full commercialisation of PIC technology can be realised.

Publisher’s Note: This conference presentation, originally published on 14 March 2018, was withdrawn on 6 April 2020 per author request.

A hybrid integrated single-wavelength laser with silicon micro-ring reflector is demonstrated theoretically and experimentally. It consists of a heterogeneously integrated III-V section for optical gain, an adiabatic taper for light coupling, and a silicon micro-ring reflector for both wavelength selection and light reflection. Heterogeneous integration processes for multiple III-V chips bonded to an 8-inch Si wafer have been developed, which is promising for massive production of hybrid lasers on Si. The III-V layer is introduced on top of a 220-nm thick SOI layer through low-temperature wafer-boning technology. The optical coupling efficiency of >85% between III-V and Si waveguide has been achieved. The silicon micro-ring reflector, as the key element of the hybrid laser, is studied, with its maximized reflectivity of 85.6% demonstrated experimentally. The compact single-wavelength laser enables fully monolithic integration on silicon wafer for optical communication and optical sensing application.

This presentation will give an overview over germanium photonic devices that are monolithically integrated into a Si CMOS process and then focus on our current work on single photon detectors and Ge modulators. Due to the quasi direct bandgap behavior of Ge and its compatibility with Si CMOS technology, germanium photonic devices have been developed successfully. Ge photodetectors perform similar to III-V photodetectors and are preferred when very low dark currents are not needed. Ge modulators show promise for high speed devices with ultra-low power consumption. Ge photodetectors and modulators are already used in commercially available products, however, new applications and increased performance requirements call for better materials quality and new designs. Ge lasers have been demonstrated and more development is needed to determine the application space. These lasers are at the early stages of development and show great potential for a large number of applications.

Doping and Sn-alloying are very important in Ge research, since they can be used to drive this material into direct gap conditions. Both perturbations have similar effects on the optical dielectric function: they redshift and broaden the critical point structures, and they also reduce the strength of the optical transitions. On the other hand, there are some fundamental differences between them, since doping leads to Pauli blocking of transitions, which does not occur when Ge is substituted by an iso-electronic impurity such as Sn. Quite recently we documented the existence of special phase-filling singularities in the dielectric function of n-type Ge associated with optical transitions to states at the Fermi level. We also developed a theoretical formalism that allows us to compute this contribution to the dielectric function, and clearly distinguish between the phase-filling and alloying aspects of the dopant contribution to the dielectric function. Here we use these advanced tools to carry out a systematic comparison of the dielectric function of doped Ge with that of Sn-alloyed Ge.

Mid-infrared (mid-IR) silicon photonics is becoming a prominent research with remarkable potential in several applications such as in early medical diagnosis, safe communications, imaging, food safety and many more. In the quest for the best material platform to develop new photonic systems, Si and Ge depart with a notable advantage over other materials due to the high processing maturity accomplished during the last part of the 20th century through the deployment of the CMOS technology. From an optical viewpoint, combining Si with Ge to obtain SiGe alloys with controlled stoichiometry is also of interest for the photonic community since permits to increase the effective refractive index and the nonlinear parameter, providing a fascinating playground to exploit nonlinear effects. Furthermore, using Ge-rich SiGe gives access to a range of deep mid-IR wavelengths otherwise inaccessible (λ ~2-20 μm). In this paper, we explore for the first time the limits of this approach by measuring the spectral loss characteristic over a broadband wavelength range spanning from λ = 5.5 μm to 8.5 μm. Three different SiGe waveguide platforms are compared, each one showing higher compactness than the preceding through the engineering of the vertical Ge profile, giving rise to different confinement characteristics to the propagating modes. A flat propagation loss characteristic of 2-3 dB/cm over the entire wavelength span is demonstrated in Ge-rich graded-index SiGe waveguides of only 6 μm thick. Also, the role of the overlap fraction of the confined optical mode with the Si-rich area at the bottom side of the epitaxial SiGe waveguide is put in perspective, revealing a lossy characteristic compared to the other designs were the optical mode is located in the Ge-rich area at the top of the waveguide uniquely. These Ge-rich graded-index SiGe waveguides may pave the way towards a new generation of photonic integrated circuits operating at deep mid-IR wavelengths.

At least four groups have demonstrated GeSn direct bandgap material and shown cryogenic temperature lasers under optical pumping. With up to 16% of Sn, our lasers operate up to 180K and lase up to wavelengths of 3.1 um. We will describe our efforts to reduce the threshold, increase the operating temperature, and evolve towards electrical pumping in these lasers.Thes efforts involve improvements of epi growth, electrical passivation, doping, heterostructures, strain control...

Here we demonstrate for the first time a GaInNAsSb/GaAs quantum well based laser diode with emission beyond 1.25 µm that is monolithically integrated on an artificial Ge substrate. Molecular beam epitaxy grown GaInNAsSb quantum wells enable gain from silicon transparency wavelength up to 1.55µm. Proposed material system paves the way for silicon photonics with high density monolithically integrated temperature insensitive gain elements (and electro-absorption in case of modulators). Compared with QD gain structures monolithically integrated on Ge/Si demonstrated earlier QW-based material system important advantages in single pass gain enabling the realization of devices with very short lengths and volume. Moreover, GaInNAsSb/GaAs QWs can exhibit efficient uncooled operation at temperatures as high as 80°C reducing the energy consumption imposed by active cooling of PICs. Presentation demonstrates low threshold (sub-25mA) directly modulated laser diodes using a short cavity (250µm) enabled by the high gain. Bandwidth characteristics of the material is studied with relative intensity noise (RIN) measurement. Hakki-Paoli measurement show gain up to 68 1/cm from a short gain element of 250µm in length. Preliminary burn-in results show that lasers operate hundreds of hours without any sign of degradation contributed by the close lattice matching between III-V and Ge.

A novel 3D hybrid integration platform combines group III-V materials and silicon photonics to yield high-performance lasers is presented. This platform is based on flip-chip bonding and vertical optical coupling integration. In this work, indium phosphide (InP) devices with monolithic vertical total internal reflection turning mirrors were bonded to active silicon photonic circuits containing vertical grating couplers. Greater than 2 mW of optical power was coupled into a silicon waveguide from an InP laser. The InP devices can also be bonded directly to the silicon substrate, providing an efficient path for heat dissipation owing to the higher thermal conductance of silicon compared to InP. Lasers realized with this technique demonstrated a thermal impedance as low as 6.2°C/W, allowing for high efficiency and operation at high temperature. InP reflective semiconductor optical amplifiers were also integrated with 3D hybrid integration to form integrated external cavity lasers. These lasers demonstrated a wavelength tuning range of 30 nm, relative intensity noise lower than -135 dB/Hz and laser linewidth of 1.5 MHz. This platform is promising for integration of InP lasers and photonic integrated circuits on silicon photonics.

Two-dimensional (2-D) materials are of tremendous interest to silicon photonics given their singular optical characteristics spanning light emission, modulation, saturable absorption, and nonlinear optics. To harness their optical properties, these atomically thin materials are usually attached onto prefabricated devices via a transfer process. Here we present a new route for 2-D material integration with silicon photonics. Central to this approach is the use of chalcogenide glass, a multifunctional material which can be directly deposited and patterned on a wide variety of 2-D materials and can simultaneously function as the light guiding medium, a gate dielectric, and a passivation layer for 2-D materials. Besides achieving improved fabrication yield and throughput compared to the traditional transfer process, our technique also enables unconventional multilayer device geometries optimally designed for enhancing light-matter interactions in the 2-D layers. Capitalizing on this facile integration method, we demonstrate a series of high-performance glass-on-graphene devices including ultra-broadband on-chip polarizers, energy-efficient thermo-optic switches, as well as mid-infrared (mid-IR) waveguide-integrated photodetectors and modulators based on graphene and black phosphorus.

This paper reports on an extensive investigation on the degradation mechanisms that may limit the long term reliability of heterogeneous III-V/Silicon DBR laser diodes for integrated telecommunication applications in the 1.55 μm window. The devices under test, aged for up to 500 hours under different bias conditions, showed a gradual variation of both optical (L-I) and electrical (I-V, C-V) characteristics. In particular, the laser diodes exhibited an increase in the threshold current, a decrease of the turn-on voltage and an increase in the apparent charge density within the space-charge region, which was extrapolated from C-V measurements. For longer stress times, these two latter processes were found to be well correlated with the worsening of the optical parameters, which suggests that degradation occurred due to an increase in the density of defects within the active region, with consequent decrease in the non-radiative (SRH) lifetime. This conclusion is also supported by the fact that during stress the apparent charge profiles indicated a re-distribution of charge within the junction. A preliminary investigation on the physical origin of the defects responsible for degradation was carried out by DLTS measurements, which revealed the presence of five different deep levels, with a main trap located around 0.43 eV above the valence band energy. This trap was found to be compatible with an interface defect located between the In_0.53Al_xGa_0.47-xAs SCH region and the InP layer.

Research of integrated light sources into the silicon platform has been extremely active for the past decades. Solutions such as the integration of III / V materials and components on silicon have been developed in a context of pre-industrial research, devices and systems intending very close to the market applications. The germanium(-tin) route has also demonstrated remarkable breakthroughs. The rationales of this research are the realization of optical interconnects. In parallel with these approaches, another interesting research field is the integration of nano-emitters, with the perspective of the realization of classical light sources but also of single photon and photon pair sources, in particular for quantum-on-chip communications. In this context, we propose the use of carbon nanotubes (CNTs) for the integration into silicon photonics towards novel optoelectronic devices. Indeed, CNTs are nanomaterials of particular interest in photonics thanks to their fundamental optical properties including near-IR luminescence, Stark effect, Kerr effect and absorption. Here, we report on the study of the light emission coupling from CNTs into optical nanobeam cavities implemented on the SOI platform. A wide range of situations have been studied by varying the deposition conditions of CNT-doped PFO polymer layers but also by considering different possible geometries of nanobeam cavities. Under optical pumping, we observe a very efficient coupling of the photoluminescence of the nanotubes with the modes of the nanocavities as well as a spectral narrowing of the photoluminescence spectra as a function of the optical power of the pump. These results contribute to the future realization of CNTs lasers, single photon and photon pair sources integrated on silicon. The authors thank the support of the European Commission's FP7-Cartoon project.

Design of electro-optic ON-OFF switches based on well-known phase change material Ge₂Sb₂Te₅ (GST) is presented. The electro-optic switch is achieved by implementing by co-directional coupling between a 220 nm thick silicon nanowire and a silicon waveguide topped with ITO-GST-ITO layers at the 1.55μm wavelength. By introducing the electric field via the ITO electrodes, the GST layer can be changed between the amorphous and crystalline states. As the modal loss in the crystalline state is much higher than the amorphous state, through a rigorous modal analysis of the coupled silicon nanowire and GST waveguide by using the finite element method, the optimal ITO spacing is obtained at 75nm which is less sensitive to device parameter variations and thus offering better tolerances. The GST thickness is also optimized for the phase matching point at 25 nm in order to efficiently transfer power from silicon nanowire to GST waveguide to attain the OFF state. Once the device is phase matched in crystalline state, the power in the amorphous state will pass with very little interaction with the GST waveguide resulting in an ON state. The Eigenmode Expansion Method of Fimmprop is used as a junction analysis approach to calculate the optical power coupling efficiencies to the output silicon nanowire. The extinction ratio of the electro-optic switch and insertion loss in ON state at phase matching can be obtained as a function of the device length. A compact 1.75 μm long device shows a high extinction ratio of 22 dB with an insertion loss of only 0.56 dB.

Photon pairs and heralded single photons are a useful resource in quantum communication, computation, and measurement. Room-temperature microchip-scale integrated devices could enable scalability, robustness and low-cost deployment in practical applications. Silicon is an attractive integration platform, since pair generation by spontaneous four-wave mixing at 1.2 - 1.6 micron wavelengths requires optical power levels that can be delivered by compact electrically-driven laser diodes. However, silicon photonics lacks a native laser device, and the propagation losses are not especially low, although they are somewhat lower than III-V integrated optics, which does have an integrated laser. Nevertheless, silicon photonics can be expected to become a widely-adopted platform for photonics – both classical and quantum – because of the ability to leverage the mature fabrication processes using large-area silicon wafers inherited from the development of microelectronics. Moreover, scalable quantum optics requires electronics for control, drivers and readout circuits, which silicon microelectronic technology can supply. Our research is improving the performance of silicon photonics components for quantum optical communications, and is increasing the level of integration in the quantum silicon photonics toolkit, using microelectronic components and electrically-driven hybrid silicon lasers.

Silicon photonics is the study and application of integrated optical systems which use silicon as an optical medium, usually by confining light in optical waveguides etched into the surface of silicon-on-insulator (SOI) wafers. The term microelectromechanical systems (MEMS) refers to the technology of mechanics on the microscale actuated by electrostatic actuators. Due to the low power requirements of electrostatic actuation, MEMS components are very power efficient, making them well suited for dense integration and mobile operation. MEMS components are conventionally also implemented in silicon, and MEMS sensors such as accelerometers, gyros, and microphones are now standard in every smartphone. By combining these two successful technologies, new active photonic components with extremely low power consumption can be made. We discuss our recent experimental work on tunable filters, tunable fiber-to-chip couplers, and dynamic waveguide dispersion tuning, enabled by the marriage of silicon MEMS and silicon photonics.

We report ultra-narrow-linewidth erbium-doped aluminum oxide (Al₂O₃:Er³⁺) distributed feedback (DFB) lasers with a wavelength-insensitive silicon-compatible waveguide design. The waveguide consists of five silicon nitride (SiN_x) segments buried under silicon dioxide (SiO₂) with a layer Al₂O₃:Er³⁺ deposited on top. This design has a high confinement factor (> 85%) and a near perfect (> 98%) intensity overlap for an octave-spanning range across near infrared wavelengths (950–2000 nm). We compare the performance of DFB lasers in discrete quarter phase shifted (QPS) cavity and distributed phase shifted (DPS) cavity. Using QPS-DFB configuration, we obtain maximum output powers of 0.41 mW, 0.76 mW, and 0.47 mW at widely spaced wavelengths within both the C and L bands of the erbium gain spectrum (1536 nm, 1566 nm, and 1596 nm). In a DPS cavity, we achieve an order of magnitude improvement in maximum output power (5.43 mW) and a side mode suppression ratio (SMSR) of > 59.4 dB at an emission wavelength of 1565 nm. We observe an ultra-narrow linewidth of ΔνDPS = 5.3 ± 0.3 kHz for the DPS-DFB laser, as compared to ΔγQPS = 30.4 ± 1.1 kHz for the QPS-DFB laser, measured by a recirculating self-heterodyne delayed interferometer (RSHDI). Even narrower linewidth can be achieved by mechanical stabilization of the setup, increasing the pump absorption efficiency, increasing the output power, or enhancing the cavity Q.

III-V semiconductor nanowires (NW) are being considered as future coherent light sources for optoelectronic chips due to their small footprint and high refractive index. The 1D confinement also results in a natural Fabry-Perot resonance cavity. However, the most important feature is the feasibility of direct growth on Si platform. The research carried out in this work consists of time-resolved photoluminescence (TRPL) spectra at different optical excitation powers and temperatures for single GaAs-AlGaAs core-shell nanowire nanolasers on Silicon. The carrier dynamics response for a single nanolaser below and above the threshold is obtained for different sets of temperatures. The lifetime corresponding to the excitation power below the threshold is of the order of hundreds of picoseconds at all low temperature intervals (4K to 60K). With increasing pump power, the decay time gets shorter until the threshold is achieved. At this point, two lifetimes are obtained for the lasing modes, one of the order of tens of picoseconds (stimulated emission) and another of the order of hundreds of picoseconds (spontaneous emission). A redshift in time-resolved spectra (2-3nm in an interval of 700ps) is measured which disappears at higher temperatures (after 60K). This redshift is a result of the change in refractive index caused by a decrease in carrier density with time. This effect disappears at higher temperatures due to the increase of non-radiative recombination.

Currently it is becoming very important to enhance the capacity of single-wavelength carrier by introducing multiplexed channels carried by multiple guided-modes as well as dual polarizations in optical interconnects. For the realization of mode-division-multiplexing (MDM) and polarization-division-multiplexing (PDM), one of the keys is the realization of efficient mode/polarization-manipulation. Accordingly, it is desired to develop various high-performance photonic integrated devices for mode/polarization-manipulation-on-chip. Silicon photonics provides an attractive option for realizing ultra-compact photonics integrated devices and has been developed very successfully. Great progresses has been made on the development of silicon photonic devices for mode/polarization-manipulation-on-chip, which is reviewed in this paper.

Silicon photonics IC’s are fabricated in CMOS/MEMS lines, and need wafer-level testing and inspection for optical performances. Although optical characteristics evaluations of waveguide and grating coupler have been reported, there is no reports for optical characteristics of a light introduction window from a flip-chip mounted laser diode to a waveguide in a silicon photonics IC. In this paper, we’ll discuss a 5 µm-deep SiO2 clad etching process to fabricate this light introduction window by using a wafer-level optical probing system [1]. Several deep-etched trenches were introduced in the SiO2 clad optical path to measure the optical loss at the windows consisting of well-aligned two waveguides. Three different SiO2 etch conditions to vary the trench sidewall roughness were applied. The gap distance between two waveguides was 2 µm, and the trench width was 1 µm. The measured optical loss at the etched SiO2 surface was about -0.5 dB for the smoother sidewall surface, and increased to -0.6 dB for the rougher surface. This indicates our new method can evaluate the loss difference of the SiO2 surface roughness to 0.1 dB precision. Surface loss distributions over the wafer were about the same for every etch conditions which reflected uniform etching conditions over the wafer. It was confirmed the optical probing system is useful for in-line process monitoring. Impact of the sidewall angle will be discussed at the presentation. This research was supported by New Energy and Industrial Technology Development Organization, Japan. [1] T. Horikawa, et al., Microelectron. Eng., 156, 46 (2016).

A compact three-laser source for optical sensing is presented. It is based on a low-noise implementation of the Pound Drever-Hall method and comprises high-bandwidth optical phase-locked loops. The outputs from three semiconductor distributed feedback lasers, mounted on thermo-electric coolers (TEC), are coupled with micro-lenses into a silicon photonics (SiP) chip that performs beat note detection and several other functions. The chip comprises phase modulators, variable optical attenuators, multi-mode-interference couplers, variable ratio tap couplers, integrated photodiodes and optical fiber butt-couplers. Electrical connections between a metallized ceramic and the TECs, lasers and SiP chip are achieved by wirebonds. All these components stand within a 35 mm by 35 mm package which is interfaced with 90 electrical pins and two fiber pigtails. One pigtail carries the signals from a master and slave lasers, while another carries that from a second slave laser. The pins are soldered to a printed circuit board featuring a micro-processor that controls and monitors the system to ensure stable operation over fluctuating environmental conditions.

This highly adaptable multi-laser source can address various sensing applications requiring the tracking of up to three narrow spectral features with a high bandwidth. It is used to sense a fiber-based ring resonator emulating a resonant fiber optics gyroscope. The master laser is locked to the resonator with a loop bandwidth greater than 1 MHz. The slave lasers are offset frequency locked to the master laser with loop bandwidths greater than 100 MHz. This high performance source is compact, automated, robust, and remains locked for days.

In this paper we present the development of an electro optical "Bragg" modulator for telecommunication, in both design and fabrication. The device consists from a regular single mode silicon waveguide (WG) in which an effective Bragg reflector is "turned on" within the WG by means of external bias, due to the plasma dispersion effect, in which the (complexed) refractive index is affected by carrier concentration within the Silicon. Three different strategies are presented for both design and fabrication.

We present a novel method to overcome arbitrary phase output in all optical logic gates that are realized with linear optical modules. The arbitrary phase prevents cascading of the optical gates that realize a high order Boolean processor. The proposed method relies on intra-bit phase encoding and a decision algorithm which results in BER<10^-5 for up to 5 cascaded levels of linear all optical device.

Optical sensors based on integrated photonics have experienced impressive advancements in the past few decades and represent one of the main sensing solutions in many areas including environmental sensing and medical diagnostics. In this context, optical microcavities are extensively employed as refractive index (RI) sensors, providing sharp optical resonances that allow the detection of very small variations in the surrounding RI. With increased sensitivity, however, the device is subjected to environmental perturbations that can also change the RI, such as temperature variations, and therefore compromise their reliability. In this work, we present the concept and experimental realization of a photonic sensor based on coupled microcavities or Photonic Molecules (PM) in which only one cavity is exposed to the sensing solution, allowing a differential measurement of the RI change. The device consists of an exposed 5-μm radius microdisk resonator coupled to an external clad microring resonator fabricated on silicon-on-insulator (SOI) platform. This design allows good sensitivity (26 nm/RIU) for transverse electrical mode (TE-mode) in a compact footprint (40 × 40 μm²), representing a good solution for real-life applications in which measurement conditions are not easily controllable.

SiO_xN_y shows promises for bright emitters of single photons. We successfully fabricated ultra-low-loss SiOxNy waveguide and AWG with low insertion loss <1dB and <3dB total loss (<2dB on-chip loss and <1dB coupling loss) at 1310nm.

The MPPC, a sort of silicon photomultiplier, has good photon-counting ability and timing accuracy. Recently, a new type of MPPC that has excellent sensitivity in the green region or near-infrared, wide dynamic range, higher photon detection efficiency, and various format configurations (single channel and 1D array) was developed. To utilize its advantageous performance, dedicated readout electronics is required. For LIDAR applications, the red-enhanced MPPC can be used, and the functional for the readout system are estimating the number of photons and recording the precise time-of-arrival. For these requirements, a time-over-threshold circuit that can recognize the incoming energy down to 1 photon and a time-to-digital converter that can record time-of-arrival with 312ps resolution were integrated onto a single die. We have demonstrated that the system has the capability to measure distance with centimeter accuracy. For situations that require higher dynamic range, a high-speed comparator and counter array configuration can be provided. For weak-light-level applications like spectroscopy, a configuration consisting of a SPAD 1D array, active quenching circuit and gate function can be used. We will propose a 1D hybrid SPAD that is the optimal combination for various applications.

We present the analysis of UV (325 nm) Raman scattering spectra from silicon-germanium (SiGe) microbridges where the SiGe has been formed using the so-called "condensation technique". As opposed to the conventional condensation technique in which SiGe is grown epitaxially, we use high-dose ion implantation of Ge ions into SOI as a means to introduce the initial Ge profile. The subsequent oxidation both repairs implantation induced damage, and forms epitaxial Ge. Using Si-Si and Si-Ge optical phonon modes, as well as the ratio of integrated intensities for Ge-Ge and Si-Si, we can determine both the composition and strain of the material. We show that although the material is compressively strained following condensation, by fabricating microbridge structures we can create strain relaxed or tensile strained structures, with subsequent interest for photonic applications.

There is a growing number of spectroscopy applications in the near-infrared (NIR) range including gas sensing, food analysis, pharmaceutical and industrial applications that requires highly efficient, more compact and low-cost miniaturized spectrometers. One of the key components for such systems is the wideband light source that can be fabricated using Silicon technology and hence integrated with other components on the same chip. In this work, we report a ring-patterned plasmonic photonic crystal (PC) thermal light source for miniaturized near-infrared spectrometers. The design is based on silicon and tuned to achieve wavelength selectivity in the emitted spectrum. The design is optimized by using Rigorous Coupled-Wave Analysis (RCWA) simulation, which is used to compute the power reflectance and transmittance that are used to predict the emissivity of the structure. The design consists of a PC of silicon rings coated with platinum. The period of the structure is about 2 μm and the silicon is highly-doped with n-type doping level in the order of 10¹⁹–10²⁰ cm^-3 to enhance the free-carrier absorption. The ring etching depth, diameter and shell thickness are optimized to increase its emissivity within a specific wavelength range of interest. The simulation results show an emissivity exceeding 0.9 in the NIR range up to 2.5 μm, while the emissivity is decreased significantly for longer wavelengths suppressing the emission out of the range of interest, and hence increasing the efficiency for the source. The reported results open the door for black body radiation engineering in integrated silicon sources for spectrometer miniaturization.

This work studies the fundamental mode and dispersion relation of a slot waveguide made of intrinsic silicon as the high index region and Air as the low index region by solving the full vectorial wave equation using vectorial finite element method. The objective is to identify the effect of dynamically inducing high excess carrier concentrations in silicon on the slot mode and it dispersion. Tracking the slot mode over a range of wavelengths reveals a reduction in the slot mode effective index upon introducing high concentration of excess carriers. This can be exploited in the dynamic tuning of a silicon slot waveguide dispersion and hence the operation of any sensor based on such waveguide by dynamically generate excess carrier at runtime.

We compare the design of three different single mode laser structures consisting in a Reflective Semiconductor Optical Amplifier coupled to a silicon photonic external cavity mirror. The three designs differ for the mirror structure and are compared in terms of SOA power consumption and side mode suppression ratio (SMSR). Assuming then a Quantum Dot active material, we simulate the best laser design using a numerical model that includes the peculiar physical characteristics of the QD gain medium. The simulated QD laser CW characteristics are shown and discussed.

We present a library of high-performance passive and active silicon photonic devices at the C-band that is specifically designed and optimized for edge-coupling-enabled silicon photonics platform. These devices meet the broadband (100 nm), low-loss (< 2dB per device), high speed (≥ 25 Gb/s), and polarization diversity requirements (TE and TM polarization extinction ratio ≤ 25 dB) for optical communication applications. Ultra-low loss edge couplers, broadband directional couplers, high-extinction ratio polarization beam splitters (PBSs), and high-speed modulators are some of the devices within our library. In particular, we have designed and fabricated inverse taper fiber-to-waveguide edge couplers of tip widths ranging from 120 nm to 200 nm, and we obtained a low coupling loss of 1.80±0.28 dB for 160 nm tip width. To achieve polarization diversity operation for inverse tapers, we have experimentally realized different designs of polarization beam splitters (PBS). Our optimized PBS has a measured extinction ratio of ≤ 25 dB for both the quasiTE modes, and quasi-TM modes. Additionally, a broadband (100 nm) directional coupler with a 50/50 power splitting ratio was experimentally realized on a small footprint of 20×3 μm² . Last but not least, high-speed silicon modulators with a range of carrier doping concentrations and offset of the PN junction can be used to optimise the modulation efficiency, and insertion losses for operation at 25 GHz.

In the absence of commercial foundry technologies offering silicon-on-insulator (SOI) photonics combined with Complementary Metal Oxide Semiconductor (CMOS) transistors, monolithic integration of conventional electronics with SOI photonics is difficult. Here we explore the implementation of lateral bipolar junction transistors (LBJTs) and Junction Field Effect Transistors (JFETs) in a commercial SOI photonics technology lacking MOS devices but offering a variety of n- and p-type ion implants intended to provide waveguide modulators and photodetectors. The fabrication makes use of the commercial Institute of Microelectronics (IME) SOI photonics technology. Based on knowledge of device doping and geometry, simple compact LBJT and JFET device models are developed. These models are then used to design basic transimpedance amplifiers integrated with optical waveguides. The devices' experimental current-voltage characteristics results are reported.

Group IV platforms can operate at longer wavelengths due to their low material losses. By combining graphene and Si and Ge platforms, photodetection can be achieved by using graphene’s optical properties and coplanar integration methods. Here, we presented a waveguide coupled graphene photodetector operating at a wavelength of 3.8 μm.

Silicon photonics have been approved as one of the best platforms for dense integration of photonic integrated circuits (PICs) due to the high refractive index contrast among its materials. Silicon on insulator (SOI) is a widespread photonics technology, which support a variety of devices for lots of applications. As the photonics market is growing, the number of components in the PICs increases which increase the need for an automated physical verification (PV) process. This PV process will assure reliable fabrication of the PICs as it will check both the manufacturability and the reliability of the circuit. However, PV process is challenging in the case of PICs as it requires running an exhaustive electromagnetic (EM) simulations. Our group have recently proposed an empirical closed form models for the directional coupler and the waveguide bends based on the SOI technology. The models have shown a very good agreement with both finite element method (FEM) and finite difference time domain (FDTD) solvers. These models save the huge time of the 3D EM simulations and can be easily included in any electronic design automation (EDA) flow as the equations parameters can be easily extracted from the layout. In this paper we present experimental verification for our previously proposed models. SOI directional couplers with different dimensions have been fabricated using electron beam lithography and measured. The results from the measurements of the fabricate devices have been compared to the derived models and show a very good agreement. Also the matching can reach 100% by calibrating certain parameter in the model.

A high-level design method using Fresnel reflections, waveguide mode theory, and wave interference principles was used to develop a parametric model of the grating coupler, and this model is tested and analyzed using a rigorous coupled mode analysis engine contained within the FIMMWAVE software package.

The high temperature sensitivity of silicon material limits the applications of silicon-based micro-ring resonators in integrated photonics. To realize a low but broadband temperature-dependence-wavelength-shift (TDWS) micro-ring resonator, designing a broadband athermal waveguide becomes a significant task. In this work, we propose a broadband athermal waveguide which shows a low effective thermos-optical coefficient (TOC) of ±1×10^-6/K at 1400 nm to 1700 nm. The proposed waveguide shows low-loss performance of 0.01 dB/cm and stable broadband-athermal ability when it’s applied in micro-ring resonators, and the optical loss of micro-ring resonator with a radius of 100 μm using this waveguide is 0.02 dB/cm.