This PDF file contains the front matter associated with SPIE Proceedings Volume 11285, including the Title Page, Copyright Information, Table of Contents, Author and Conference Committee lists.

In the European project MORPHIC we develop a platform for programmable silicon photonic circuits enabled by waveguide-integrated micro-electro-mechanical systems (MEMS). MEMS can add compact, and low-power phase shifters and couplers to an established silicon photonics platform with high-speed modulators and detectors. This MEMS technology is used for a new class of programmable photonic circuits, that can be reconfigured using electronics and software, consisting of large interconnected meshes of phase shifters and couplers. MORPHIC is also developing the packaging and driver electronics interfacing schemes for such large circuits, creating a supply chain for rapid prototyping new photonic chip concepts. These will be demonstrated in different applications, such as switching, beamforming and microwave photonics.

Direct epitaxial growth of III-V lasers on silicon provides the most economically favorable means of photonic integration but has traditionally been hindered by poor material quality. Relative to commercialized heterogeneous integration schemes, epitaxial growth reduces complexity and increases scalability by moving to 300 mm wafer diameters. The challenges associated with the crystalline mismatch between III-Vs and Si can be overcome through optimized buffer layers including thermal cyclic annealing and metamorphic layers, which we have utilized to achieve dislocation densities < 7×10⁶ cm^-2. By combining low defect densities with defect-tolerant quantum dot active regions, native substrate performance levels can be achieved. Narrow ridge devices with threshold current densities as low as ~130 A/cm² have been demonstrated with virtually degradation free operation at 35°C over 11,000 h of continuous aging at twice the initial threshold current density (extrapolated time-to-failure >10,000,000 h). At 60°C, lasers with extrapolated time-to-failure >50,000 h have been demonstrated for >4,000 h of continuous aging. Lasers have also been investigated for their performance under optical feedback and showed no evidence of coherence collapse at back-reflection levels of 100% (minus 10% tap for measurement) due to the ultralow linewidth enhancement factor (α_H < 0.2) and high damping of the optimized quantum dot active region.

An array of active photonic devices is fabricated in unison after a heterogeneous integration process first metal-eutectically bonds these distinct materials as a distribution onto a silicon host wafer. The patterning out of heterogeneous materials followed by the formation of all photonic devices allows for wide-area fine-alignment without the need for discrete die alignment or placement. The integration process is designed as a CMOS-compatible, scalable method for bringing together distinct III-V epitaxial structures and optical-waveguiding epitaxial structures, demonstrating the capabilities of forming a multi-chip layer of photonic materials. Integrated GaAs-based vertical light-emitting transistors (LET) are designed and fabricated as the active devices whose third electrical terminal provides an electrical interconnect and thermal dissipation path to the silicon host wafer. The performance of these devices as both electrical transistors and spontaneous-emission optical devices is compared to their monolithically-integrated counterparts to investigate improvements in device characteristics when integrated onto silicon. The fabrication methods are modified and optimized for thin-film transferred materials and are then extended to transistor laser (TL) fabrication. Passive waveguiding structures are designed and simulated for coupling light from the active devices, and their fabrication scheme is presented such that it can be similarly performed with transferred materials. Work toward the demonstration of integrated transistor lasers is shown to represent progress toward an electronic-photonic circuit network. The combination of heterogeneous integration with three-terminal photonic structures enables an elegant solution to both packaging and signal interconnect constraints for the implementation of photonic logic in silicon photonics systems.

VTT’s 3 μm SOI platform with record low propagation loss (0.1 dB/cm for fundamental mode), as well as polarization insensitivity, offers a rich portfolio of efficient passive and active components. With a view to extend the component toolbox by monolithically integrating high-speed plasmonic modulators, we have developed an a-Si:H based waveguide escalator to take out light from highly confined thick-SOI passives to the top layer where active materials are monolithically integrated. Using the compact escalator, monolithic integration of various high-speed active components on the 3 μm SOI platform are proposed.

Silicon ring resonator modulators (RRMs) have great potential to reduce footprint and power consumption and to increase modulation speeds in wavelength division multiplexed (WDM) transmitters. However, the optical properties of RRMs are highly sensitive to fabrication variations, which makes them challenging to design for volume production or a large number of WDM-channels. In this work, we present an RRM design that was specifically designed and experimentally validated to have reduced sensitivity to fabrication variations. This includes a sensitivity analysis of resist over- and under-exposure (±30 nm lateral dimension deviation) and of etch depth variability (±10 nm depth variation) within the coupling section. For our design, the deviation from the targeted coupling strength is improved twofold. The proposed devices are fabricated on SOI wafers using a standard CMOS-compatible process. We demonstrate RRMs with an extinction ratio above 5 dB, an OMA better that -7 dB (at 2 V_pp) and a 29 GHz electro-optical bandwidth, showing open eye diagrams at 32 Gb/s limited only by our measurement setup. The measured coupling coefficients are in good agreement with the simulated values. Furthermore, we applied the same design modifications to realize low-doped RRMs as well as ring based adddrop- multiplexers (OADMs). The agreement between the simulated and the measured coupling coefficients (that we identified as the main source of device performance variability) further confirms the effectiveness of our design modifications. These results suggest that the proposed design can be exploited to enable reliable fabrication of resonantbased devices on a large scale, especially in WDM systems.

A mature silicon photonics platform including various materials for a wide range of functionalities is needed to achieve high-speed and energy-efficient transceivers for Datacom. We present the latest developments of our 200mm silicon photonics platform including new devices in silicon nitride along with active devices. In particular, we demonstrate a high performance SiN Echelle Grating CWDM (de-)multiplexer obtained with advanced photolithography tools, hybrid Si-SiN polarization splitter rotator, SiN edge coupler and low-loss, low-crosstalk Si-SiN and SiN-SiN crossings.

Driving electro-optic modulators in lumped-element (LE) configuration allows for small footprint, reduced power consumption, and improved high-speed performance. The main shortcoming of conventional rectilinear LE modulators are the required high drive-voltages, resulting from their shortened phase-shifters. To address this, we introduce a Mach- Zehnder modulator with meandered phase shifters (M-MZM), which can be driven in LE configuration, while keeping the optical phase shifter length in the same order as traveling-wave modulators (TW-MZMs). A design limitation that needs to be taken into account consists in the optical transit time of the device, that limits the overall electro-optic bandwidth. First, we review the overall power consumption improvement as well as the bandwidth enhancement in LE modulators compared to TW-MZMs, also taking the driver output impedance and parasitics from wire- or bump-bonds into account. Then, we report on the design, implementation, and experimental characterization of carrier-depletion based M-MZMs fabricated on silicon-on-insulator (SOI) wafers using standard CMOS-compatible processes. The fabricated M-MZMs, provided with low (W1), moderately (W2) and highly (W3) doped junctions, require 9.2 Vpp, 5.5 Vpp, and 3.7 Vpp for full extinction, with optical insertion losses of 5 dB, 6.3 dB and 9.1 dB. For all three M-MZMs, open eye diagrams are recorded at 25 Gb/s using a 50 Ω driver and termination. For unterminated M-MZMs, higher data rates could be achieved, provided that a low output impedance driver be wire- or bump-bonded to the modulators. Finally, we compare the power consumption of the M-MZMs with TW-MZMs and show that the M-MZMs feature a 4X reduced power consumption at 25 Gb/s.

The strong evolution of silicon photonics towards very low power consumption circuits leads to the development of new strategies for photonic devices, especially for power-hungry components such as optical modulators. One strategy is to use Pockels effect in Si waveguides. However, bulk Si is a centrosymmetric semiconductor, which cannot exhibit any second order optical nonlinearities. Nonetheless, under a strain gradient, generated by depositing a stressed layer on Si waveguides, this restriction vanishes. In our work, we experimentally demonstrated a Pockels effect based electro-optic modulation at high frequency (> 5GHz) using a strained silicon Mach-Zehnder modulator.

A key challenge to widespread implementation of silicon photonics is achieving optical switching at ultrafast speed and ultralow power using on-chip silicon modulators.  Here we report experiments demonstrating that the ultrafast photo-induced phase transition in VO2 can be harnessed for all-optical in the telecommunications band when small VO2 volumes are integrated within a silicon waveguide.  "On"-to-"off" switching speeds in this in-line modulator are less than 1 ps, thus consistent with Tbps speeds, and switching energies near threshold are less than 500 fJ for modulation depths near 6 dB.  Early results showing significant reductions in switching energies in hybrid VO2:Si ring resonators will also be presented.

The rapid increase of bandwidth requirements across the entire hierarchy of Data Center (DC) networks, ranging from chip-to-chip, board-to-board up to rack-to-rack communications, puts strenuous requirements in the underlying network infrastructure that has to offer high-bandwidth and low-latency interconnection under a low-energy and low-cost envelope. Arrayed Waveguide Grating Router (AWGR)-based optical interconnections have emerged as a powerful architectural framework that can overcome the currently deployed electrical interconnect bottlenecks leveraging the wavelength division multiplexing (WDM) and the cyclic routing properties of AWGRs to offer one-hop, all-to-all communication when employed as N×N routers. However, the majority of previous silicon (Si)-based integrated AWGR demonstrations has either targeted C-band operation, despite the dominance of the O-band spectral region in the DC interconnection domain, or offered coarse-WDM (CWDM) functionality and, as such, were limited in terms of AWGR port count. In this article, we present for the first time to our knowledge, a Dense-WDM (DWDM) 16×16 Si-photonic cyclic-frequency AWGR device targeting O-band routing applications. The fabricated AWGR device features a channel spacing of 1.063 nm (189 GHz), a free spectral range of 17.8 nm (3.15 THz) and a 3-dB bandwidth of 0.655 nm (116 GHz). Its proper cyclic frequency operation was experimentally verified for all 16 channels with channel peak insertion loss values in the range of 3.9 dB to 8.37 dB, yielding a channel loss non-uniformity of 4.47 dB. Its compact footprint of 0.27×0.71 mm² and low crosstalk of 21.65 dB highlight its potential for employment in future AWGR-based interconnection schemes.

We demonstrate for the first time flat-top interleavers based on cascaded Mach-Zehnder interferometers (MZIs) which use only single multimode interferometers (MMIs) as power splitters. Our previous designs were based on 4-stage cascades of MZIs, where we used single MMIs and double MMIs to achieve 85:15 splitting ratio and 31:69 splitting ratio respectively. This time, we propose instead a greatly simplified 2-stage configuration using only single MMIs, including a standard 50:50 MMI, and two tapered MMIs to achieve 71:29 and 92:08 splitting ratios. We have designed the interleaver based on its geometrical representation on the Bloch sphere, then confirmed by efficient 2D simulations of the building blocks and of the whole structure, based on the eigenmode expansion method. We show how important is to take into account the phase relations between the outputs of all MMIs in order to make a working design. We have successfully fabricated devices with different channel spacing on our micron-scale silicon photonics platform, and measurement results confirmed their expected flat-top operation on a broad band. Using only single MMI splitters we can not only greatly outperform the bandwidth achieved by standard directional couplers, but we can also ensure much higher robustness to fabrication errors, also compared to previous demonstrations based on double MMIs. Indeed, when compared to those previous attempts, the new results prove tapered MMIs to be the most robust approach to achieve arbitrary splitting ratios.

The large refractive index of silicon enables sub-micron waveguide and high optical confinement. As a result, silicon photonic components could be made extremely compact, which is the foundation of the prosperous silicon photonics research. In the meantime, the large optical intensity within the waveguide, together with resonance structures, makes silicon photonics also an intriguing platform for studying phenomena involving high-order optical nonlinearities with low input power, such as two-photon absorption, four-wave mixing, stimulated Brillouin scattering, and free carrier absorption. Self-induced oscillation, also known as self-pulsing, is one of the phenomena induced by the interplay of multiple nonlinear processes. It happens when two or more contradict nonlinear effects interact and compete with each other. The oscillation theoretically can achieve >50 GHz frequency, but due to the heating caused by free carrier absorption, the reported oscillation speeds are limited to MHz level. Even excited with pulsed lasers to suppress the self-heating effect, the oscillation only achieves ~3 GHz. In this paper, we show that through infiltrating the subwavelength grating metamaterial ring resonator with materials of negative thermo-optic coefficient and high third-order nonlinearity, the strong, but slow, thermal effect can be suppressed and therefore ultrafast phenomena become eminent. In this experiment, DDMEBT is used which has third-order susceptibility three orders of magnitude larger than fused silica. Oscillations with about 27 GHz frequency are demonstrated experimentally simply by exciting the ring resonator with a continuous working laser. The oscillation frequency is more than one order of magnitude faster than the fastest self-oscillation effect that has been observed.

We describe a scalable, tiled optical beam steering aperture based on integrated silicon photonic circuit beam steering tiles. A novel beam steering tile design, the serpentine optical phased array (SOPA), enables high fill factor tiled apertures, very low control complexity, an entirely passive aperture, large field of view, and extremely fast beam steering. The design provides low size, weight, and power, making it scalable to large-area (cm-to-wafer scale) apertures. We show experimental demonstrations of SOPA tiles steering an optical beam in two dimensions (2D) enabling a full 2D raster scan using wavelength sweep alone, and initial tiling and lidar demonstrations.

Automotive self-driving capability is highly developed using camera vision but can benefit from the addition of independent sensor platforms for redundancy and further reduction of MTBF (mean time between failure). Frequency Modulated Continuous Wave (FMCW) Light Detection and Ranging (LIDAR) is particularly suited to this application by virtue of its capability to directly detect velocity as well as range with high resolution. However, such a system requires the dense integration of multiple optical components including lasers, amplifiers, phase and amplitude control low-noise photodiodes, mode converters, and optical waveguides. These must further be integrated in a compact form factor that can be manufactured in high volume. Silicon photonics using the Intel Hybrid Silicon platform can enable such optical integration on a silicon chip in a scalable high-volume manufacturing process, thus enabling chip-scale solid-state LIDAR.

Recent integrated optical phased array architectures, results, and applications will be reviewed. Beam-steering optical phased arrays monolithically integrated with on-chip rare-earth-doped lasers and heterogeneously integrated with CMOS driving electronics will be shown. Passive integrated optical phased arrays that focus radiated light to tightly-confined spots in the near field and that generate quasi-Bessel beams will be discussed. Finally, integrated-phased-array-based visible-light holographic displays will be proposed as a scalable solution towards the next generation of augmented-reality head-mounted displays; passive near-eye holographic displays, visible-light liquid-crystal modulators, and liquid-crystal-based visible-light phased arrays will be presented.

In this paper, we provide a new type of subwavelength grating waveguides (SWGs) with a guiding mechanism from 1.5μm to 6μm on a silicon-on-insulator (SOI) platform. Two different SWGs with the same period but different height, corresponds to different effective subwavelength refractive indices, are designed and served as the core and cladding respectively. The biggest hindrance for transmission bandwidth, the buried oxide, is then removed to build up a suspended SWGs, contributing to bandwidth enlargement. In the meantime, the results also show light-matter interaction enhancement that ~34% propagating energy locates in the air can fully interact with testing analytes, leading to higher sensitivity. The broadband and high light-matter integral signatures would address the demands for ideal absorption spectroscopy based lab-on-chip.

The mid-infrared (MIR) molecular fingerprint region has gained great interest in the last past years thanks to development of laser source like Quantum Cascade Lasers (QCL). There are a lot of efficient technique to achieve solid and liquid spectroscopy detection. However, to probe several or complex molecules in this optical region, it could be necessary to use broadly tunable MIR source. A QCL array coupled to a specific lens array able to shape and combine beams into a single spot, could be a suitable source. This work is focused on the design and fabrication of integrated lenses (Photonic Crystal Lens & Quasi Photonic Crystal Lens) made with Germanium on Silicon Germanium platform. A Photonic Crystal Lens (PCL) is composed of a 2D holes lattice inside of a slab waveguide led with Si_0.6Ge_0.4. The holes lattice is hexagonal with a constant parameter. The radius of those holes continuously varying, in the direction perpendicular to the light propagation, to induce a variation in optical path length. Then, the design of this gradient is the key to perform the desired lens function. A Quasi Photonic Crystal Lens (QPCL) is based on the same principle as the PCL, but instead of having a 2D lattice there is a linear (1D) lattice. So a QPCL is composed of 1 row of a fixed number of macroscopic holes in diamond pattern inside of a slab waveguide. Like the PCL, there is a hole size gradient to shape the optical path of the light. This works shows simulation results and the first design of integrated lens working at the wavelengths of ≈ 9µm with a focal of ≈ 200µm and with a side size (in the array direction) of 200µm.

Dynamic manipulation of light has received considerable attention in recent years. The process of an optical signal undergoing a transition between two modes of a photonic structure is referred to as a photonic transition. We show that a signal wave interacting with a free carrier front in a slow light waveguide experiences indirect photonic transitions leading to reflection from the moving front. Theory and experimental results are presented. The front induced dynamic frequency conversion is also compared to the frequency shifting based on other nonlinear effects like cross-phase modulation and four wave mixing.

Lasing in bulk GeSn alloys have been reported lately with relatively high thresholds in the range of several hundreds of kW/cm². This can be mainly attributed to high defect densities of high Sn content alloy thick layers grown on relaxed Ge-VS. Indeed the use of high Sn contents in Ge(1-x)Snx alloy to reach direct band gap alignment (with xSn>10%) consequently results in large lattice mismatches with Ge and therefore produces large defect densities in partially relaxed thick layers. We show here that GeSn alloys with low Sn content exhibit strongly reduced lasing thresholds densities, in the 10 kW/cm² range, in microdisk cavities. We developed a layer transfer technology enabling management of the GeSn/Ge defect interface thus allowing to further reduce lasing thresholds in the kW/cm² range. The layer transfer additionally allows tensile strain engineering using silicon nitride stressor layer to increase the band structure directness as required for RT-laser operation.

We present a temperature dependent optical properties of Ge on Si under influence of Si intermixing and a finding on Δ valley emission. Arrhenius analysis reveals that Si intermixing significantly increase the thermal activation energy of direct valley emission by increasing the energy difference between Γ and L valley. A luminescence peak from Δ valley was revealed from the temperature-dependent study. A clear thermal activation of Δ valley could be observed. We also present monolithically integrated strained Ge nano-cavity fabricated on Si for laser application. The cavity is designed to have strain higher than 1 % and Q ~ 100,000.

This paper presents our recent progress on fast germanium photodetector (PD) development for our 3μm silicon-on - insulator (SOI) platform. We have fabricated a horizontal PIN photodiode, which has a 3dB cutoff frequency of 40GHz and responsivity of 1.0 A/W at -1V bias for operation wavelength of 1.55μm. The high bandwidth indicates that the detector speed is limited by the transit time of the carriers over the i-region rather than the junction capacitance. The electric field in the i-region at -1V is high enough to maintain the carrier drift speed close to the maximum velocity of carriers in the Ge. The device is realized using selectively grown germanium with very low amount of stress induced crystal defects. The detector area and the Si waveguides were patterned with a common hard mask, which enables accurate lateral alignment between them. The n- and p-contacts were directly made on the Ge using Ti/Al metallization. The vertical sidewalls of the detector area were implanted in order to create the horizontal PIN structure. The subsequent dopant diffusion was estimated to secure the i-region and the junctions by controlling the thermal budget, as the two dopants have different diffusion mechanism in Ge. One of the advantages of our micron scale waveguides is that due to the high confinement of the optical mode within the Si waveguide they allow light coupling into a short detector. The junction capacitances are therefore small as the detector area is only 1x9μm. In addition, the electrical output pulse shape is not distorted by the slow diffusion current of electrons and holes as the incoming light do not overlap the doped n- and n-regions.

Amorphous silicon (a-Si) is considered as one of the potential materials for multi-layer photonics due its high refractive index, linear and non-linear optical properties. This makes a-Si integration compatible with the Silicon-on-Insulator (SOI) photonics by increasing circuit density at each optical device layer. However, the high absorption loss of a-Si would require hydrogenation to passivate the dangling bonds for low loss optical waveguide interconnects and coupling of light between optical layers. Without an efficient passivation process, optical loss per layer would be too high for a viable multi-layer photonic platform. Therefore, we have developed a low temperature process hydrogenated a-Si (a- Si:H) with Hot-Wire Chemical Vapour Deposition (HWCVD) method that is compatible with back-end-of-the-line (BEOL) integration with active photonic or electronic layers. This work describes the experimental control of deposition temperature to achieve low loss a-Si:H waveguiding layer and the inter-layer waveguide coupling structures. Our latest results show a-Si:H deposited at 230 ^oC has the lowest propagation loss of 0.7 dB/cm for a sub-micron ridge waveguide at 1550 nm wavelength and 45 dB cross-talk isolation between two waveguides separated by 1 μm of SiO₂ layer.

For 40 years it has been deduced that the presence of Boron and Oxygen in silicon causes the formation of a non-radiative recombination centre, without any consensus as to its exact nature. Here we report the observation, using deep level transient spectroscopy and photoluminescence of the conversion of a deep boron-di-oxygen-related donor trapping state into a shallow acceptor under the action of light or injected carriers. Using ab initio modelling, we propose structures of the B-O2 defect which match the experimental findings. Implications of the presence of this defect, particularly on its deep donor (carrier trapping) configuration, on silicon photodetectors is discussed.

We present a detailed study of parameter sweeps of silicon photonic arrayed waveguide gratings (AWG), looking into the effects of phase errors in the delay lines, which are induced by fabrication variation. We fabricated AWGs with 8 wavelength channels spaced 200 GHz and 400 GHz apart. We swept the waveguide width of the delay lines, and also performed a sweep where we introduced increments of length to the waveguides to emulate different AWG layouts and look into the effect of the phase errors. With this more detailed study we could quantitatively confirm the results of earlier studies, showing the wider waveguides reduce the effect of phase errors and dramatically improve the performance of the AWGs in terms of insertion loss and crosstalk. We also looked into the effect of rotating the layout of the circuit on the mask, and here we could show that, contrary to results with older technologies, this no longer has an effect on the current generation of devices.

The free charge carrier concentration of semiconductors, such as in silicon, is tunable over several orders of magnitude. Thus, the plasma wavelength of these materials can be adjusted over a wide spectral range by controlling the doping concentration. Here we demonstrate that high fluence ion beam doping and subsequent pulsed laser annealing can extend the accessible plasma wavelength of silicon far into the near-infrared region reaching the telecommunication wavelength. Further, we demonstrate how area selective activation of dopants by focused laser annealing can be used to create flat optical and plasmonic devices that operate in the near-to-mid infrared regime.

Electrical annealing of erasable directional couplers (DCs) was realized. Titanium nitride (TiN) micro-heaters were used to electrically heat up and anneal the Ge-ion implanted regions in silicon, which are used as the coupling waveguides in the erasable DCs. The refractive index of implanted silicon was reduced rapidly by electrical annealing, so that the DCs were effectively erased. The whole annealing process can be accomplished in about 2 seconds. Based on the simulation results, the implanted region can be heated up to about 700 °C.

Photoacoustic (PA) spectroscopy is one of the most sensitive technique used to monitor chemical emission or detect gas traces. Coupled to quantum cascade lasers, this system is widely used in a large number of application fields from industrial control to health monitoring. Mass production for a large dissemination of such systems requires however further development for both decreasing their footprint and manufacturing cost. Since the last 6 years CEA-LETI has developed different versions of miniaturized photoacoustic cells. We have already demonstrated the detection of gas traces with a tiny silicon based-PA cell. Nevertheless, this first result was obtained with commercial MEMS microphones. Even if these components are reliable and enough performant they are not dedicated to photoacoustic gas detection and cannot be easily integrated into a fabrication process flow. To cope with these issues we suggest using both the M&NEMS technology and the MIR photonics. The new PAdetector termed microPA is built by stacking two 200 mm wafers: a sensor wafer, which includes the microphone (MEMS mechanical diaphragm and NEMS piezoresistive gauges), capillaries and fluidic ports, and a cap wafer, which includes the PA cell, the expansion volume, SiGe waveguides guiding the light into the PA cell, metal routing and electric contacts. Frequency response measurements as well as PA gas detection have been carried out. The system shows a mechanical resonance of the diaphragm at the frequency of 6500 Hz, in good agreement with the simulation. First CO2 and CH4 tests in laboratory condition demonstrates a limit of detection in the ppm range and a NNEA of 10-8 W.cm^-1.Hz^-1/2.

This Conference Presentation, "Oxide-enhanced IR hot-carrier-based photo detection in metal thin-film Si junctions" was recorded at Photonics West 2020 held in San Francisco, California, United States.

In this paper, we present a statistical characterization results for a high-speed germanium photo-detector structure that calls for no additional process steps than a regular modulator. The photodiodes in question are waveguide PIN SiGeSi photodiodes with targeted bandwidths on the range of 50GHz and a responsivity of more than 0.8A/W at 1310nm. The design logic, mainly intended to reduce the transit time while conserving a high detection area will be explained in details.

Optical frequency combs (OFCs) are involved in a large diversity of applications such as metrology, telecommunication or spectroscopy. Different techniques have been explored during the last years for their generation. Using an electrooptical modulator (EOM), it is possible to generate a fully tunable OFC for which the optical repetition rate is set by the frequency of the applied electrical radio frequency (RF) signal. In order to realize on-chip OFC generators, silicon photonics is a well-suited technology, benefiting from large scale fabrication facilities and the possibility to integrate the electronics with the EOM. However, observing OFCs with a repetition rate lower than 10 GHz can be challenging since such spacings are smaller than the typical resolution of grating-based optical spectrum analyzers. To overcome this issue, two alternative solutions based on heterodyne detection techniques are used to image the OFC on the electrical RF domain. The first technique consists in applying two frequencies close to each other simultaneously on the modulator, and observing the beating between the resulting two combs. Another method consists in observing the beating between the OFC and the input laser, once the frequency of this input laser has been shifted from the center of the OFC by means of an acousto-optic modulator. Based on both measurement techniques, OFCs containing more than 10 lines spaced with repetition rates from 100 MHz to 15 GHz have been observed. They are generated using a 4-mm long silicon depletionbased traveling-wave Mach-Zehnder modulator (MZM) operating at a wavelength of 1550 nm.

Silicon photonics is considered an enabling technology for the development of high-performance photon-pair sources for quantum information applications. However, the substantially higher pump intensity and narrow wavelength separation between the photon-pairs and the optical pump impose stringent requirements that lie beyond the capabilities of state-of-the-art silicon spectral filters. In this invited talk we will present an overview of our recent advances in the field of waveguide Bragg gratings for photonic noise reduction in silicon photon-pair sources, including different strategies harnessing subwavelength and modal engineering to overcome the bandwidth-rejection trade-off in state-of-the-art implementations.

In this work we combine the already mature silicon and silicon nitride platforms with novel reconfigurable materials such as 2D materials, liquid crystals and phase change materials. An actively reconfigurable 1D photonic crystal multi-channel filter based on Si-on-insulator and liquid crystal platforms is demonstrated with extraordinary large quality factor, Q ∼ 10⁴. A complete study and design of an optical routing and multilevel volatile photonic memory based on graphene capacitor concept for future high performance computing using Silicon rich nitride is shown with a bandwidth of 64 GHz and energy power consumption per bit as low as 0.22 pJ. Finally, an optical switch based on germanium-antimony-tellurium phase change material (GST) is experimentally demonstrated for O-band operation with the extinction ratio as high as 10 dB between the amorphous and the crystalline states.

Silicon-based integrated microwave photonics presents an interesting platform for broadband microwave applications, offering high-speed modulation and a broad selection of devices. We propose and experimentally demonstrate an effective Mach-Zehnder modulator design to generate frequency-multiplied microwave signals. Using a continuous-wave laser signal modulated by an external microwave signal, we demonstrate that by filtering two non-adjacent frequency comb lines, the detected frequency-doubled signal can be improved considerably by suppressing the carrier frequency and unwanted side-band contributions. The demonstrated designs use a 12-GHz and a 21-GHz external driving signal to generate respectively a 24-GHz and a 42-GHz frequency doubled MW signals.

Recently, Integrated Microwave Photonics (IMWP) on Silicon-on-Insulator (SOI) platform has attracted much attention. SOI as a platform for passive devices has been studied for operation at a wavelength of 1.55 μm. It has been acknowledged that Si suffers from Two-Photon Absorption (TPA) at this wavelength, which potentially limits the dynamic range of microwave photonic links. The TPA effect diminishes at longer wavelengths, and completely vanishes at a wavelength of 2.2 μm. So far, the detailed effects of TPA on the performance of the SOI platform in the context of IMWP have not been well-explored. In this work, a systemic simulation has been performed in order to investigate the effects of nonlinear TPA on the performance of SOI microwave photonic links at 1.55 μm, particularly the dynamic range of the system was studied in-depth. Furthermore, system performance at wavelengths from 1.55 to 2.2 μm was investigated by scaling the device design, where the parasitic effects of TPA are avoided. Based on theoretical analysis, the result showing microwave photonic links at 2.2 μm outperform that at 1.55 μm was obtained as expected. Strip and rib waveguides at 1.55 μm show P1dB points of 3.75 mW and 69.54 mW, respectively, and at 2.2 μm, these waveguides performed linearly throughout the simulated range (up to 1 W of input power) which is due to the dramatically reduced TPA effect. It is noted that the wavelengths at which SOI avoids parasitic TPA match well with the working wavelengths of emerging GeSn lasers and photodetectors.

We demonstrate a compact on-chip gas sensor based on a SiN photonic integrated circuit providing an estimated detection limit of 0.1ppm for a variety of gas vapors, including IPA, ethanol and acetone. The sensor consists of an integrated Mach-Zehnder interferometer having one arm coated with an absorptive mesoporous layer to enhance the interaction of the gas vapors with the waveguide evanescent field. Gas detection is accomplished by monitoring the spectral shift of the output signal induced by a change in the effective refractive index of the coated waveguide. Results pave the way to novel integrated solutions for environmental safety monitoring.

In this research, we propose an integrated compressed sensing Fourier-Transform spectrometers based plasmonic circuitry on vertical-cavity surface-emitting lasers (VCSEL) platform. We will show that VCSELs can be employed as an on-chip, electrically pumped source or detector of plasmonic signals, when operated in forward bias. To this end, we will experimentally demonstrate surface plasmon polariton excitation, waveguiding, frequency conversion and detection on a VCSEL-based plasmonic platform and use that as the input light source for MZI spectrometer. The proposed slow light enhanced tunable MZI-array is able to achieve sub-nanometer resolution and large free spectral range (FSR) simultaneously, which is a significant advantage compared to other on-chip spectrometers.

In this work, potential ways of accessing a greater spectral range at mid-infrared (MIR) wavelength ranges in silicon photonics are explored, in particular for sensing applications that use on-chip spectroscopy. To utilise the full low-loss transmission of silicon, silicon membranes are transfer printed onto MIR-transparent substrates for waveguides with no absorption from the substrate. A Y-junction splitter with low loss across a 1 µm optical bandwidth is also designed and experimentally demonstrated.

We experimentally demonstrated a fast optimization algorithm based on the method of gradient descent for achieving optimum spectral response of high-order silicon microring optical filters. The filter optimization was performed on a 4th-order serially-coupled silicon microring filter by thermo-optically tuning the microring resonances using Ti/W heaters. Three different optimization objective functions were used to obtain the optimum filter shape, namely, the single-wavelength method, the dual-wavelength method, and the total transmitted power method. The efficacy of each optimization method was evaluated and compared based on the number of required iterations, the ideality of optimized response, and the wavelength tuning accuracy.

In this work, we investigate an optical accelerometer utilizing single-mode Si/SiO2 waveguides at 1550 nm as a displacement sensing unit. The device is based on quad beam configuration, made of a fixed frame and a mass, moving within a limited range along vertical direction. Three straight Si/SiO2 waveguides are placed aligned along the central axes of the accelerometer, two on both ends on the frame and one on the mass, such that the displacement of mass leads to a drop of the coupled light intensity. When the mass is at rest, the intensity of the guided mode is at its highest value. Acceleration is then measured by monitoring the intensity modulation. Lateral dimensions of the waveguides are similar, where the height and width are 200 nm and 500 nm, respectively. The effective index of single mode Si/SiO2 waveguides (neff = 2.3550 at 1550 nm) is calculated using Finite Difference Eigenmode (FDE) method. The field profile of fundamental TE mode is to a good approximation given by Gaussian field distribution. The correlation of guided light intensity and the mass displacement was obtained numerically using mode-coupling theory. We show that our configuration is highly sensitive, drastic intensity drop (100 dB) happens at mass-frame misalignment within ±7 μm and displacement by 3 μm causes intensity decrease of 10.8 dB. Thus, design of CMOS-compatible miniature silicon photonic accelerometers with inherent properties such as multiplexability and immunity to external electro-magnetic fields are promising candidates for low cost real-time vibration monitoring sensors applicable in harsh environments.

A silicon optical electro-absorption modulator (EAM) operating at a high speed and low voltage was achieved by using a Schottky diode in the C-band (1530 nm ~ 1570 nm). The optical modulation is demonstrated by the intensity change of guiding light due to the free-carrier absorption in the semiconductor to change its absorption coefficient, not conventional interference effects. The proposed EAM has lateral metal-semiconductor (MS) junctions that aid in maximizing the free carrier injection and extraction by a Schottky contact on the rib waveguide center. The rib waveguide structure of the modulator on the standard 220-nm silicon-on-insulator (SOI) platform has an etch depth of 80 nm and a width of 450 nm for the single-mode operation. The center of the rib waveguide is lightly doped with 1015 cm-3 indium, where light is mostly confined. The sides are heavily doped with 1020 cm-3 indium to contribute to the optical absorption change in the center. The depletion width in the middle region was drastically changed by a Schottky contact with bias. This design allowed a high overlap between the optical mode and carrier density variations in the center of the waveguide. To achieve a high speed operation, the travelling-wave type electrodes were designed to allow copropagation of electrical and optical signals along the waveguide. The measured results demonstrated a broad operational wavelength range of 40 nm with a uniform 3.9 dB modulation depth for a compact 25 μm modulation length with 1 Vpp driving voltage. The travelling-wave type electrodes enabled the modulator operating up to 26 GHz with 12 GHz of 3-dB electrooptic bandwidth, experimentally.

Single photon avalanche diodes (SPADs) manufactured through the standard CMOS process have a major advantage in reducing the cost and expendability in comparison with the SPAD made with the custom process.

SPAD is a single photon sensitive diode using the avalanche phenomenon and operated in Geiger-mode which applies a voltage higher than the breakdown voltage of the device. Therefore, SPAD is exposed to a higher voltage than other devices and has a high electric field in the multiplication region.

In SPAD operating with such a high electric field, the guard ring prevents edge breakdown and serves to focus the electric field on the intended multiplication region. Therefore, the optimized guard ring structure is required for the high efficiency SPAD designs. The deep virtual guard ring is designed to cope with deeper multiplication regions formed by deep n-well and p-well, thus providing higher photon detection probability (PDP) and enhanced response at a longer wavelength.

In this paper, the four possible Silicon-based SPAD candidates of different deep virtual guard rings formed by the combination of shallow trench isolation (STI) and p-substrate layer fabricated through standard CMOS process are investigated and their electric characteristics of the SPAD, such as the current-voltage (I-V) characteristic, and optical characteristics, such as dark count rate (DCR), and PDP, are measured.

In addition, TCAD simulations are used to verify the characteristic variation by analyzing the electric field profiles. Based on the results, the optimized structure of the SPAD with the deep virtual guard ring can be proposed.

We propose a novel compact structure with EIT-like spectrum by introducing two partial reflectors (silica holes) symmetrically placed within the microring resonator (MRR). The two Fabry-Pérot (FP) resonating cavities created by the silica holes, coupled with microring’s resonance modes, show EIT-like lineshapes spaced by free spectral range of MRR. The FWHM of EIT-like spectrum can be controlled by tuning the radii of the silica holes. Analytical results from the developed mathematical model and 3D FDTD simulations were found to be in good agreement with each other.

A dual-microring resonator replaces one of the couplers of the Mach-Zehnder interferometer (MZI) to achieve a widely tunable twin-fano resonance, which originates from the interference and coupling of mode in a dual-microring resonator. The slope can be tuned in a wide range from -84.2 dB/nm to 91.0 dB/nm by metal heaters integrated on one arm of the MZI, and the resonant wavelength fixes when slope changes. The “X-type” spectrum is shown by self-alignment, which means manual alignment to form “X-type” line is unnecessary after tuning dual-microrings because the “X-type” line can be produced easily by the difference of two correlated spectrums rather than two independent spectra. Meanwhile, it shows high wavelength resolution of 1 pm with an ideal resolution of 0.4 pm in the region of the slope of 127.4 dB/nm, which can be applied to wavelength monitoring with ultra-high resolution.

In this work, lightly-doped black silicon (BSi) is fabricated using cryogenic DRIE in a maskless manner and its transmittance and reflectance are measured using an integrating sphere and a spectrometer in the near infrared (NIR) wavelength range of 1300 nm - 2500 nm. Then, the surface is cleaned and copper (Cu) is deposited on the BSi using the wet deposition technique of electroless plating, enabling high throughput coating. The copper ions are deposited on the BSi surface in a Cu sulphate solution, taking advantage of the conformity of the plating to the nano/micro structures of the BSi targeting lower reflectance and higher absorptivity. The Cu-plated BSi is measured and observed to have a minimum reflectance of 10% compared to 30% in the case of BSi, and a minimum transmittance of 10% compared to 40% in the bare black silicon. Thus, the Cu-plated BSi has a maximum absorptivity of about 80% compared to 30% in the bare BSi. The absorptivity is found to decrease with increasing the wavelength. This enhancement using the electroless Cu plating further qualifies the BSi as a candidate for NIR thermal light sources.

Lateral Asymmetry in cladding of the Photonic crystal (PhC) waveguides has been utilized to demonstrate a compact TM-Pass polarization filter. The filter, which covers the entire conventional `C'- band of telecom spectrum has a low insertion loss and gives ≈ 41 dB extinction ratio at 1550nm wavelength.