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We demonstrate how lithography smoothing and proximity effects affect the performance of silicon-on-insulator devices that include grating-based, contra-directional couplers (contra-DCs). Using lithography models developed for CMOS-compatible, deep ultraviolet lithography processes, we predict and verify the spectral responses of fabricated contra-DC test structures. These verified models are then used to simulate and analyze the effects of lithography on the performance of a microring resonator with an integrated contra-DC, as regards the device 3-dB bandwidth (BW), insertion loss (IL), and adjacent side mode suppression ratio (SMSR). We demonstrate how the corrugation profile of the contra-DC is affected by smoothing and the inner and outer corrugation depths are reduced due to proximity effects. We show that, if the effects of lithography are not taken in account during device design flow, large discrepancies result between the predicted "as-fabricated" and "as-designed" device performance. Specifically, we demonstrate how the BW is reduced from 47 GHz to 21 GHz, how the IL is increased from 0.5 dB to 5.8 dB, and how the adjacent SMSR is reduced to 26 dB. We also establish that it is possible to use the lithography models to compensate for lithographic effects during device design flow and layout and to design a contra-DC in which the as-fabricated device performance metrics matches the target/expected as-designed performance metrics.

This paper reviews the basic design flow of a silicon integrated Bragg grating (IBG) to achieve an arbitrary microwave photonics (MWP) signal processor. An example of using the design methodology to achieve a multichannel MWP Hilbert transformer (HT) based on a silicon IBG is given. Then, we review the adverse impact of apodization phase noise (APN) on the apodized grating response, and our recently demonstrated performance improvement of a grating-based MWP HT realized by compensating for the APN to correct the grating complex response. Finally, we give an outlook and suggestions for the future work.

We propose and demonstrate compact, add-drop filters using cladding-modulated, sub-wavelength grating (SWG), contra-directional couplers (CDCs) on a silicon-on-insulator platform. In our device, two asymmetric SWG waveguides, integrated with periodically loaded Bragg segments along the sides of the waveguides, are used to achieve contra-directional coupling between the fundamental and next higher-order transverse electric modes of the two-SWG-waveguide system. We present results for a 286.8-µm-long CDC that has a 3 dB bandwidth of 13.4 nm at the drop-port with a low excess loss of 0.8 dB. This device also has an 11.5-nm region at the through-port over which the extinction ratio is greater than 40 dB.

Large-scale optical switch networks employ wavelength division multiplexing to expand and facilitate multiple input and outputs. Such networks can be implemented with the Mach-Zehnder interferometer (MZI) as the building block. A fully-loaded MZI switch, meaning one with two optical signals at its two inputs and one that is capable of simultaneously switching those inputs to its two outputs, reduces the number building blocks within the network, and as a result makes them more power and area efficient. However, for practical operation, such MZI switches need to be automatically controlled for overcoming fabrication and thermal variations. We present an interference-based monitoring method that enables automatically switching, tuning, and stabilizing of a fully-loaded 2×2 MZI optical switch and demonstrate a prototype on an SOI platform. Using the proposed device and off-the-shelf electronics, we demonstrate automatic tuning and stabilization of an MZI switch with 12.5 Gb/s and 25 Gb/s data rates and channel spacing as small as 1 nm.

Contra-directional couplers are proposed as optical pump reject filters with the potential to achieve over 100 dB extinction ratios for on chip photon-pair sources. A scheme for these filters to enable reusing the pump laser for multiple microring resonator, photon-pair sources is presented.

We present a wideband, flat-top, optical add-drop filter using an apodized sub-wavelength-grating contra-directional coupler on a silicon-on-insulator platform. Our device achieves a >30 nm wide, flat-top drop-port response, centered at 1545 nm, with an extinction ratio >20 dB.

An innovative undergraduate level Nanofabrication course with a focus on photonics is proposed. This course challenges the definition of what constitutes an undergraduate class in a research-intensive university. Namely, instructor and teaching assistants (TAs) propose a moderately challenging graduate-level research project that has not been previously published; challenge the Team, consisting of the students, with the TAs and instructor, to research during the class, as a Team; have the Team collaborate on writing a research paper with the goal of submitting it to an archival journal. Through this process, students learn the course content and experience how research is conducted.

We demonstrate an optical add-drop multiplexer on the silicon-on-insulator platform with a 3 dB bandwidth of 6.3 nm, an ultra-high adjacent channel isolation of 58 dB, an insertion loss of 0.8 dB, and a footprint of only 1882 μm2.

Vernier effect, series-coupled microring resonators (MRRs) are used to extend the free-spectral-range (FSR) of MRRs. In this work we demonstrate integrating two MRRs in a compact Vernier configuration (compact as compared to previously demonstrated Vernier effect devices). our design was realized by using two waveguide crossings to form a major, outer ring that was coupled to a minor ring nested within the major ring. The ratio of the path length of the major ring to the path length of minor ring was 5:2. The spectral response of the device had an FSR of 27.94 nm, a drop port 3 dB bandwidth of 0.87 nm, a minimum extinction ratio of 16.1 dB, a minimum interstitial peak suppression of 10.6 dB, and a footprint of only 540 μm2 .

A ring resonator based 4 channel wavelength division multiplexing (WDM) receiver with polarization diversity is demonstrated at 10 Gb/s per channel. By forming a waveguide loop between the two output ports of a polarization splitter-rotator (PSR), the input signals in the quasi-transverse-electric (quasi-TE) and the quasi-transverse-magnetic (quasi-TM) polarizations can be demultiplexed by the same set of ring resonator filters, thus reducing the number of required channel control circuits by half compared to methods which process the two polarizations individually. Large signal measurement results indicate that the design can tolerate a signal delay of up to 30% of the unit interval (UI) between the two polarizations, which implies that compensating for manufacturing variability with optical delay lines on chip is not necessary for a robust operation. The inter-channel crosstalk is found negligible down to 0.4nm (50 GHz) spacing, at which point the adjacent channel isolation is 17 dB, proving the design's compatibility for dense WDM application.

We report on a narrow-band, polarization-independent, transmission filter using phase-shifted, polarization-rotating Bragg gratings (PRBGs) in a silicon-on-insulator strip waveguide. In our device, phase-shifted PRBGs provide narrow transmission peaks for the transverse electric (TE) and transverse magnetic (TM) modes, both at the same wavelength. We present results for a 330.6 μm long device that has transmission peaks centered at 1556.36 nm, 3 dB bandwidths of 0.26 nm, and extinction ratios of 19 dB for both TE and TM modes. We also integrated a heater onto our device and obtained a wavelength tuning efficiency of 0.028 nm/mW for both TE and TM modes.

A silicon-on-insulator (SOI), bandwidth (BW)-tunable, free-spectral-range (FSR)-free, microring resonator (MRR)-based filter is experimentally demonstrated. The device achieves an FSR-free response at its through and drop ports by using a grating-assisted coupler in one coupling region of the MRR and achieves a non-adjacent channel isolation, (nAi), for 400 GHz WDM, greater than 26.7 dB. A thermally tunable Mach–Zehnder Interferometer-based coupling scheme is also utilized to compensate for fabrication variations and enable the BW tunability of the filter. The BW of the filter can be continuously tuned from 25 to 60 GHz while maintaining an nAi greater than 26.7 dB.

We present the designs, theory, and experimental demonstrations of ultra-broadband, optical add–drop filters on the silicon-on-insulator platform, realized using period-chirped contra-directional couplers. Our fabricated devices have ultra-broad 3 dB bandwidths of up to 11 THz (88.1 nm), with flat-top responses at their drop ports. All of our devices were fabricated using a commercial, CMOS-compatible, 193 nm deep-ultraviolet lithography process. By using lithography-prediction models, the measured bandwidths, insertion losses, central wavelengths, and extinction ratios of our devices are all in good agreement with our predicted, simulated results. Such filters are necessary for photonic integrated circuits to operate over multiple optical bands.

Recent investigations in neuromorphic photonics exploit optical device physics for neuron models, and optical interconnects for distributed, parallel, and analog processing. Integrated solutions enabled by silicon photonics enable high-bandwidth, low-latency and low switching energy, making it a promising candidate for special-purpose artificial intelligence hardware accelerators. Here, we experimentally demonstrate a silicon photonic chip that can perform training and testing of a Hopfield network, i.e. recurrent neural network, via vector dot products. We demonstrate that after online training, our trained Hopfield network can successfully reconstruct corrupted input patterns.

We examine inter-channel and intra-channel crosstalk power penalties between non-return-to-zero on-off keying (NRZ-OOK) wavelength-division-multiplexing (WDM) channels for microring-based silicon photonic interconnects. We first propose a new model that relates the crosstalk power penalty to the interfering signals power, the extinction ratio of the non-return-to-zero, OOK modulated “victim” channel, and finally the bit-error-ratio that the power penalty is referenced to. As for inter-channel crosstalk, the proposed model agrees well with our recent experimental measurements. We leverage this model to quantify crosstalk induced power penalties in a microring based WDM receiver. We also propose an optimization procedure to equilibrate the power penalty across channels. We then compare our model with intra-channel crosstalk measurements, where two NRZ channels are at the same wavelength and are simultaneously routed to different paths by two cascaded ring resonators. We remark that intra-channel crosstalk is very sensitive to the data rate of NRZ channels. As data rate increases, the observed disturbances exceed what models predict. Based on these observations, we propose an empirical modification of the original model for estimating intra-channel crosstalk power penalties in high ( $>$ 20 Gb/s) data rate situations.

This paper evaluates novel design strategies to enhance the performance of a recently proposed waveguide-based pulse-shaping method, i.e., discrete space-to-time mapping (D-STM), demonstrating the capability of the method to shape pulse waveforms with duration periods in the tens of picoseconds regime. In particular, we experimentally synthesize 70-ps high-quality flat-top pulses and a 40-ps-long 200-GBd 16-quadrature amplitude modulation (16-QAM) data sequence using D-STM in concatenated co-directional couplers. Our proposed devices have been fabricated on a silicon-on-insulator (SOI) technology platform using ultraviolet and single-etch electron-beam lithography processes. The fabricated devices are all-passive, functioning without needing post-fabrication tuning, which further proves the robust performance of the proposed scheme.

Photonic networks form the backbone for data communications. In particular, in current and future wireless communication systems, photonic networks are becoming increasingly popular for data distribution between the central office and the remote antenna units at base stations. As wireless-photonic systems become in increasing demand, low-cost implementation of such systems will be desirable. This paper describes how integrated photonics and electronics, on silicon, can be used to design such systems. Various building blocks of such silicon-photonics systems are reviewed. The emphasis is on a 60 GHz wireless system which could be suitable for the emerging 5th-generation (5G) cellular networks. The implementation discussed here uses digital baseband optical transmission as opposed to the radio-over-fibre approach.

We experimentally investigate the interchannel and intrachannel crosstalk of first- and second-order microring resonator (MRR) filters fabricated on a silicon-on-insulator platform. We find that there is an MRR radius that maximizes the wavelength division multiplexing channel count given a waveguide geometry, a maximum tolerable insertion loss, and a minimum permissible adjacent channel isolation. The measured power penalties due to interchannel crosstalk of two-channel demultiplexers based on first-order and series-coupled MRR filters are presented as functions of channel spacing and adjacent channel isolation. Next, we compare the intrachannel crosstalk of first-order, cascaded, and series-coupled MRR add-drop filters. Our results show that first-order MRR devices are unsuitable for simultaneous add-drop operation at high data rates and small channel spacings. Intrachannel crosstalk of cascaded and series-coupled designs are measured as functions of the data rate and the level of detuning between the MRRs. Low intrachannel crosstalk power penalties are demonstrated for cascaded and series-coupled MRR filters for data rates up to 20 Gb/s. Based on the measured results, we present requirements for the input-to-through response of add-drop filters that will ensure low intrachannel crosstalk.

We designed and fabricated a polarization splitter-rotator (PSR) on a silicon-on-insulator (SOI) platform based on an asymmetric directional coupler. The asymmetric directional coupler consists of a regular strip waveguide and a sub-wavelength grating (SWG) waveguide. The SWG waveguide used in the design provides the freedom to engineer the dispersion properties of the supermodes, which allow the design to be fabrication tolerant to the waveguide width variations. A measured peak polarization conversion efficiency of −0.3 dB and crosstalks below −10 dB were achieved. The designed SWG PSR has a compact size of 35 ${\mu} \text{m} \times 5\,{\mu} \text{m}$ .

We experimentally demonstrate compact broadband directional couplers using subwavelength gratings for silicon-on-insulator wafers with silicon layers of 220 nm. The dispersion properties of the optical modes are engineered using subwavelength gratings, which allow broadband operation. Finite-difference time-domain (FDTD)-based band structure calculations, with significantly reduced simulation time, were used to analyze the design, which included both the structure and material dispersions. Compact broadband direction couplers, with device lengths shorter than 14 $\mu\text{m}$, which cover a bandwidth of 100 nm for power splitting ratios of 50/50, 40/60, 30/70, and 20/80, are designed and fabricated for the fundamental transverse electric mode with a central operating wavelength of 1550 nm.

We demonstrate greedy linear descent-based, basic gradient descent-based, two-point step size gradient descent-based, and two-stage optimization method-based automated control algorithms and examine their performance for use with a silicon photonic polarization receiver. With an active feedback loop control process, time-varying arbitrary polarization states from an optical fiber can be automatically adapted and stabilized to the transverse-electric (TE) mode of a single-mode silicon waveguide. Using the proposed control algorithms, we successfully realize automated adaptations for a 10 Gb/s on-off keying signal in the polarization receiver. Based on the large-signal measurement results, the control algorithms are examined and compared with regard to the iteration number and the output response. In addition, we implemented a long-duration experiment to track, adapt, and stabilize arbitrary input polarization states using the two-point step size gradient descent-based and two-stage optimization method-based control algorithms. The experimental results show that these control algorithms enable the polarization receiver to achieve real-time and continuous polarization management.

Microring weight banks present novel opportunities for reconfigurable, high-performance analog signal processing in photonics. Controlling microring filter response is a challenge due to fabrication variations and thermal sensitivity. Prior work showed continuous weight control of multiple wavelength-division multiplexed signals in a bank of microrings based on calibration and feedforward control. Other prior work has shown resonance locking based on feedback control by monitoring photoabsorption-induced changes in resistance across in-ring photoconductive heaters. In this work, we demonstrate continuous, multi-channel control of a microring weight bank with an effective 5.1 bits of accuracy on 2Gbps signals. Unlike resonance locking, the approach relies on an estimate of filter transmission versus photo-induced resistance changes. We introduce an estimate still capable of providing 4.2 bits of accuracy without any direct transmission measurements. Furthermore, we present a detailed characterization of this response for different values of carrier wavelength offset and power. Feedback weight control renders tractable the weight control problem in reconfigurable analog photonic networks.

Thanks to advanced semiconductor microfabrication technology, chip-scale integration and miniaturization of lab-on-a-chip components, silicon-based optical biosensors have made significant progress for the purpose of point-of-care diagnosis. In this review, we provide an overview of the state-of-the-art in evanescent field biosensing technologies including interferometer, microcavity, photonic crystal, and Bragg grating waveguide-based sensors. Their sensing mechanisms and sensor performances, as well as real biomarkers for label-free detection, are exhibited and compared. We also review the development of chip-level integration for lab-on-a-chip photonic sensing platforms, which consist of the optical sensing device, flow delivery system, optical input and readout equipment. At last, some advanced system-level complementary metal-oxide semiconductor (CMOS) chip packaging examples are presented, indicating the commercialization potential for the low cost, high yield, portable biosensing platform leveraging CMOS processes.

We propose a Mach-Zehnder interferometer-assisted coupling-based, microring modulator that achieves a free spectral range free response by integrating a bent, contra-directional-coupler into the ring cavity. This design enables high capacity microring-based dense wavelength division multiplexing transmitter systems.

We propose a microring modulator in which the free spectral range is eliminated by using a bent, contra-directional-coupler to couple light into and out of the ring and in which the extinction ratio and bandwidth are tuned using a secondary, two-point coupler.

We present a system-level integration of active silicon photonic biosensors. With on-chip photodetectors, sensors are characterized in the photovoltaic mode. A biotin-avidin affinity assay is employed to exemplify the detection of small molecule interactions, showing a detection limit in the order of 10−5 M.

We demonstrate a broadband polarization splitter-rotator (PSR) based on sub-wavelength grating (SWG) assisted adiabatic waveguides. The SWG-based adiabatic PSR is more compact than previously reported adiabatic PSRs. Less than −19 dB polarization crosstalk was measured over a broad wavelength range from 1545 to 1615 nm.

We experimentally demonstrate and compare contra-directional-coupler-based filters in a compact series cascaded configuration and an ultra-compact, fabrication variation tolerant, parallel stacked configuration. Both filters are shown to be similar in performance as regards their sidelobe suppression ratios and bandwidths.

A fractured planar photonic crystal cavity is designed so that its resonant frequency can be mechanically tuned over a range of tens of nanometers while maintaining a quality factor in excess of 100,000. Experimental data validates the tuning capability, in lower Q cavities.

We demonstrate a polarization-independent mode-evolution-based coupler for the silicon-on-insulator platform. The measured coupler has negligible insertion loss over a bandwidth of about 100 nm, i.e., from 1500 to 1600 nm. The measured maximum power imbalances for the polarization-independent coupler are 1.2 and 0.2 dB for the fundamental transverse electric (TE $_\text{00}$ ) mode and the fundamental transverse magnetic (TM $_\text{00}$ ) mode, respectively. Our coupler also has a compact design footprint with mode-evolution region not more than ${75}{-\mu {\rm m}}$ long.

Ultra-compact, densely integrated optical components manufactured on a CMOS-foundry platform are highly desirable for optical information processing and electronic-photonic co-integration. However, the large spatial extent of evanescent waves arising from nanoscale confinement, ubiquitous in silicon photonic devices, causes significant cross-talk and scattering loss. Here, we demonstrate that anisotropic all-dielectric metamaterials open a new degree of freedom in total internal reflection to shorten the decay length of evanescent waves. We experimentally show the reduction of cross-talk by greater than 30 times and the bending loss by greater than 3 times in densely integrated, ultra-compact photonic circuit blocks. Our prototype all-dielectric metamaterial-waveguide achieves a low propagation loss of approximately 3.7±1.0 dB/cm, comparable to those of silicon strip waveguides. Our approach marks a departure from interference-based confinement as in photonic crystals or slot waveguides, which utilize nanoscale field enhancement. Its ability to suppress evanescent waves without substantially increasing the propagation loss shall pave the way for all-dielectric metamaterial-based dense integration., Miniaturization of optical components could give way to dense photonic-integrated circuits. Here, the authors demonstrate the control of evanescent waves using all-dielectric metamaterials and show that they can reduce cross-talk and bending loss, which limit the integration density in photonic circuits.

Waveguide Bragg grating (WBG) devices on silicon constitute a particularly attractive solution for optical and microwave photonics (MWP) signal processing, thanks to their flexibility in producing arbitrarily defined amplitude and phase responses, by directly acting on perturbations of the grating profile, together with their high compactness compared to other integrated photonic filters. This talk will give a brief overview of advances in the field of integrated WBGs applied to microwave photonics and optical signal processing, with emphasis on a number of recent demonstrations. Examples of applications include THz‐bandwidth optical pulse shapers, wideband tunable RF filters, broadband true‐time‐delay lines and phase shifters, and instantaneous frequency measurement systems on‐chip.

Novel sub-wavelength silicon photonic waveguides for label-free sensors are demonstrated in this article. We use silicon-on-insulator (SOI) waveguides that consist of sub-wavelength grating (SWG) structures, where the waveguides are made of small silicon arrays (180 × 180 nm2 rectangles with 60 nm gaps). They are used to form microring and Bragg grating resonators which measure the change of refractive index by monitoring the resonant wavelength shift. Due to the high surface contact area and low optical confinement of the proposed waveguide, the sensitivity (both bulk and surface) can be significantly increased. The bulk sensitivity of 580 nm/RIU for the microring and 610 nm/RIU for the Bragg grating are better than other recently published resonator sensors. Moreover, a standard biological sandwich assay demonstrates an enhanced surface sensitivity of 2050 pm/nm for both devices. Theoretical models and experimental results are investigated, indicating the predominant losses are from the water absorption at 1550 nm and scattering by sidewall roughness.

This paper describes recent solutions for microwave instantaneous frequency measurement (IFM)systems based on integrated microwave photonics, with particular emphasis on the use of waveguide Bragg gratings (WBG)as a possible approach for the creation of a monolithic photonic IFM system.

A fractured planar photonic crystal microcavity is designed to be mechanically tunable while maintaing a quality factor of >1 × 105, and a mode volume ∼ 0.3(λ/n)3. Its optomechanical coefficient is ∼15 GHz/nm, at mid-IR wavelengths.

A multitude of large-scale silicon photonic systems based on ring resonators have been envisioned for applications ranging from biomedical sensing to quantum computing and machine learning. Yet, due to the lack of a scalable solution for controlling ring resonators, practical demonstrations have been limited to systems with only a few rings. Here, we demonstrate that large systems can be controlled by using only doped waveguide elements inside their ringswhile preserving their area and cost. We measure the large photoconductive changes of the waveguides for monitoring the rings' resonance conditions across high-dynamic ranges and leverage their thermo-optic effects for tuning. This allows us to control ring resonators without requiring additional components, complex tuning algorithms, or additional electrical I/Os. We demonstrate automatic resonance alignment of 31 rings of a 16 x 16 switch and of a 14-ring coupled resonator optical waveguide, making them the largest, yet most compact, automatically controlled silicon ring resonator circuits to date, to the best of our knowledge., Comment: 11 pages, 7 figures. Submitted to Optica on 24th Aug. 2018

Dramatic increases in processing power have rapidly scaled on-chip aggregate bandwidths into the Tb/s range. This necessitates a corresponding increase in the amount of data communicated between chips, so as not to limit overall system performance. To meet the increasing demand for interchip communication bandwidth, researchers are investigating the use of high-speed optical interconnect architectures. Unlike their electrical counterparts, optical interconnects offer high bandwidth and negligible frequency-dependent loss, making possible per-channel data rates of more than 10 Gb/s. High-Speed Photonics Interconnects explores some of the groundbreaking technologies and applications that are based on photonics interconnects. From the Evolution of High-Speed I/O Circuits to the Latest in Photonics Interconnects Packaging and Lasers Featuring contributions by experts from academia and industry, the book brings together in one volume cutting-edge research on various aspects of high-speed photonics interconnects. Contributors delve into a wide range of technologies, from the evolution of high-speed input/output (I/O) circuits to recent trends in photonics interconnects packaging. The book discusses the challenges associated with scaling I/O data rates and current design techniques. It also describes the major high-speed components, channel properties, and performance metrics. The book exposes readers to a myriad of applications enabled by photonics interconnects technology. Learn about Optical Interconnect Technologies Suitable for High-Density Integration with CMOS Chips This richly illustrated work details how optical interchip communication links have the potential to fully leverage increased data rates provided through complementary metal-oxide semiconductor (CMOS) technology scaling at suitable power-efficiency levels. Keeping the mathematics to a minimum, it gives engineers, researchers, graduate students, and entrepreneurs a comprehensive overview of the dynamic landscape of high-speed photonics interconnects.

We demonstrate, on the silicon-on-insulator platform, a modulator that uses a quarter-wave phase-shifted Bragg grating resonator. The modulator has open eye diagrams at data rates of up to 32 Gb/s. A bit error ratio of less than ${10}^{-10}$ is demonstrated using a $2^{31}-1$ pseudorandom binary sequence pattern at a data rate of 25 Gb/s.

We demonstrate photonic ultra-efficient thermo-optic switches on a 220-nm silicon-on-insulator platform. We used several approaches to increase the tuning efficiency of the switches. We used folded waveguides in a Michelson interferometer configuration to increase the optical interaction length of the light with the heated region, and used a suspended structure to improve thermal isolation. An ultra-low switching power of 50 $\mu \text{W}$ is realized with an extinction ratio of over 26 dB for the transverse electric mode at 1550 nm. The 10%–90% response time of the switch is 1.28 ms, including a 780 $\mu \text{s}$ rise time and a 500 $\mu \text{s}$ fall time. Compared with the best thermo-optic switch in the literature, our device shows approximately an order of magnitude reduction in power consumption.

We propose an analytical time-domain model for microring and microdisk modulators, which considers both their electrical and optical properties. Theory of the dynamics of microring/microdisk is discussed, and general solutions to the transfer matrix representation are presented. Both static and dynamic predictions from the model are compared to measurement results to demonstrate the accuracy of our model. Static predictions and measurements are presented for power and phase responses, whereas dynamic predictions and measurements are presented for small-signal and large-signal operations. The model verifies that the chirping and modulation bandwidth of the modulators depend on the detuning state. Finally, the accuracy and scalability of several techniques employed in the model are discussed.

Control of oxygen over cell cultures in vitro is a topic of considerable interest, as chronic and cyclic hypoxia can alter cell behaviour. Both static and transient hypoxic levels have been found to affect tumour cell behaviour, it is potentially valuable to include these effects in early, in vitro stages of drug screening. A barrier to their inclusion is that rates of transient hypoxia can be a few cycles/hour, which is difficult to reproduce in traditional in vitro cell culture environments due to long diffusion distances from control gases to the cells. We use a gas-permeable three-layer microfluidic device to achieve spatial and temporal oxygen control with biologically-relevant switching times. We measure the oxygen profiles with integrated, ratiometric optical oxygen sensors, demonstrate sensor and system stability over multi-day experiments, and characterize a pre-bleaching process to improve sensor stability. We show, with both finite-element modelling and experimental data, excellent control over the oxygen levels by the device, independent of fluid flow rate and oxygenation for the operating flow regime. We measure equilibration times of approximately 10 min, generate complex, time-varying oxygen profiles, and study the effects of oxygenated media flow rates on the measured oxygen levels. This device could form a useful tool for future long-term studies of cell behaviour under hypoxia.

Recent design flows for photonic integrated circuits have been able to take advantage of mature capabilities available in electronic design automation such as schematic driven design and sophisticated circuit verification. Furthermore, new photonic integrated circuit simulators that can interface with electrical circuit simulators have been developed. As a result, photonic design flows are rapidly advancing in maturity. An area that still requires development is the statistical analysis of photonic circuits to be able to predict and improve yield, which is particularly challenging because photonic components tend to be large compared to the wavelength which makes them highly sensitive to phase errors. Furthermore, photonic devices tend to have long range spatial correlations in their parameters that cannot be ignored. In this paper, we present two approaches that enable Monte Carlo analysis of photonic integrated circuits, which include the treatment of spatial correlations, and we show how they can be used to predict the circuit yield. Example circuits include passive filters made from cascaded Mach-Zehnder interferometers and transceivers using active ring modulators.

This work develops an enhanced Monte Carlo (MC) simulation methodology to predict the impacts of layout-dependent correlated manufacturing variations on the performance of photonics integrated circuits (PICs). First, to enable such performance prediction, we demonstrate a simple method with sub-nanometer accuracy to characterize photonics manufacturing variations, where the width and height for a fabricated waveguide can be extracted from the spectral response of a racetrack resonator. By measuring the spectral responses for a large number of identical resonators spread over a wafer, statistical results for the variations of waveguide width and height can be obtained. Second, we develop models for the layout-dependent enhanced MC simulation. Our models use netlist extraction to transfer physical layouts into circuit simulators. Spatially correlated physical variations across the PICs are simulated on a discrete grid and are mapped to each circuit component, so that the performance for each component can be updated according to its obtained variations, and therefore, circuit simulations take the correlated variations between components into account. The simulation flow and theoretical models for our layout-dependent enhanced MC simulation are detailed in this paper. As examples, several ring-resonator filter circuits are studied using the developed enhanced MC simulation, and statistical results from the simulations can predict both common-mode and differential-mode variations of the circuit performance.

Biosensors based on silicon photonic integrated circuits have attracted a growing interest in recent years. The use of sub-micron silicon waveguides to propagate near-infrared light allows for the drastic reduction of the optical system size, while increasing its complexity and sensitivity. Using silicon as the propagating medium also leverages the fabrication capabilities of CMOS foundries, which offer low-cost mass production. Researchers have deeply investigated photonic sensor devices, such as ring resonators, interferometers and photonic crystals, but the practical integration of silicon photonic biochips as part of a complete system has received less attention. Herein, we present a practical system-level architecture which can be employed to integrate the aforementioned photonic biosensors. We describe a system based on 1 mm2 dies that integrate germanium photodetectors and a single light coupling device. The die are embedded into a 16x16 mm2 epoxy package to enable microfluidic and electrical integration. First, we demonstrate a simple process to mimic Fan-Out Wafer-level-Packaging, which enables low-cost mass production. We then characterize the photodetectors in the photovoltaic mode, which exhibit high sensitivity at low optical power. Finally, we present a new grating coupler concept to relax the lateral alignment tolerance down to ± 50 μm at 1-dB (80%) power penalty, which should permit non-experts to use the biochips in a“plug-and-play” style. The system-level integration demonstrated in this study paves the way towards the mass production of low-cost and highly sensitive biosensors, and can facilitate their wide adoption for biomedical and agro-environmental applications.

We design and demonstrate a compact broadband polarization beam splitter (PBS) using a symmetric directional coupler with sinusoidal bends on a silicon-on-insulator platform. The sinusoidal bends in our PBS suppress the power exchange between two parallel symmetric strip waveguides for the transverse-electric (TE) mode, while allowing for the maximum power transfer to the adjacent waveguide for the transverse-magnetic (TM) mode. Our PBS has a nominal coupler length of 8.55 μm, and it has an average extinction ratio (ER) of 12.0 dB for the TE mode, an average ER of 20.1 dB for the TM mode, an average polarization isolation (PI) of 20.6 dB for the through port, and an average PI of 11.5 dB for the cross port, all over a bandwidth of 100 nm.

Using in-resonator photoconductive heaters to monitor and tune the light intensity inside the resonators, a four-ring Vernier filter is automatically tuned across the entire C-band and stabilized over a 40 °C temperature range.

This presentation describes approaches to designing silicon photonic circuits while taking manufacturing variability into account to ensure a functioning chip. Our method is an enhanced Monte Carlo technique that includes layout-specific correlated manufacturing variations.

High-speed optical interconnects drive the need for compact microring resonators (MRRs) with wide free spectral ranges (FSRs). A silicon-on-insulator MRR based filter with bent contra-directional couplers that exhibits an FSR-free response, at both the drop and through ports, while achieving a compact footprint is both theoretically and experimentally demonstrated. Also, using bent contra-directional couplers in the couping regions of MRRs allowed us to achieve larger side-mode suppressions than MRRs with straight CDCs. The fabricated filter has a minimum suppression ratio of more than 15 dB, a 3dB-bandwidth of ~23 GHz, an extinction ratio of ~18 dB, and a drop-port insertion loss of ~1 dB. High-speed data transmission through our filter is also demonstrated at data rates of 12.5 Gbps, 20 Gbps, and 28 Gbps.