For many applications in life sciences, the biologically relevant information is probed by means of visible light. Many of the critical optical components have, unfortunately, still a large footprint and heavy price tag. Silicon nitride integrated waveguide optics –allowing for complex routing schemes of visible light across a chip– assumes a promi-nent role in the progressing miniaturization of optical devices. However, in order to have the light in the chip interro-gate a distant biological entity, diffraction gratings have to be used to couple light out of the chip.
Ideally, all the light from a waveguide would be coupled out into a beam with a predefined polarization, phase, and intensity profile. As such they should be able to produce any functional beam that is typically prepared by free space optical components. For a standard, linear grating an exponential intensity decay is observed along the grating, i.e., more light is coupled out at the start than at the end.
Here, we present a specially designed metasurface that is able to deliver highly uniform illumination escaping the photonics chip in a collimated beam at a predesigned angle. Because of its integrated nature, a component like this is highly relevant for the miniaturization of, e.g., flow cytometry applications. We therefore include microfluidic chan-nels on top of the photonics chip and demonstrate the cytometric capabilities with fluorescent polystyrene beads. The opto-fluidic chips are processed in a CMOS pilot line. Our work demonstrates the potential of integrated visible pho-tonics and flat optics for life science applications.
Micro-opto-mechanical pressure sensors (MOMPS) based on integrated optical Mach-Zehnder interferometers (MZI) have been fabricated at IMEC, exhibiting much improved sensitivity and noise performance compared to their piezoelectric and capacitive counterparts. However, the design of next generation MOMPS systems on chip still remains uncertain due to the intrinsic multiphysics nature covering mechanical, optical and electrical phenomena. For this reason, we present a sophisticated, flexible and customizable algorithmic tool for the multiphysics simulation and design of highperformance MOMPS systems on chip, including mechanical and optical effects as well as the electronic circuitry for the readout. Furthermore, static and dynamic operating regimes are analyzed, also comparing analytical solutions with experimental results and demonstrating a good agreement. Finally, system noise contributions generated by the optoelectronic components and readout electronics are calculated and a static sensitivity of 8 mV/Pa is measured in the fabricated sensors.
Waveguide optics takes up a prominent role in the progressing miniaturization of optical devices. Chip integrated photonic waveguides especially allow for complex routing schemes of light across a chip. In/out-coupling diffraction gratings form an essential tool in waveguide systems, as they facilitate the interaction between the waveguide system and the near or far-field.[1,2] Ideally, these gratings would couple out all light in the waveguide into a beam with a predefined polarization and, phase and intensity profile. As such they should be able to produce any functional beam that is typically prepared by free space optics. Yet, in practice there is typically a design trade-off between beam quality and out-coupling efficiency. Light in the waveguide has to travel laterally through the grating to be coupled out. The light therefore decays exponentially over the grating, causing much more light to be coupled out at the start of the grating than at the end. This asymmetry results in a warped out-coupling intensity that heavily influences the light beam’s intensity profile. Especially when the grating is addressing points in the near field, as is the case for focusing waveguide grating couplers, this effect can be highly disruptive.
In this work we present a grating constructed from a field of sub-wavelength scatterers, rather than full grating lines. By tuning the position and the density of the scatterers, the phase and the intensity of the out-coupled light can be set precisely over large grating areas. An iterative design algorithm is developed that carefully tunes the density so as to control the light intensity in the waveguide and the amount of out-coupled light. Using FDTD simulations we show that these gratings can efficiently couple out light into a nearly diffraction limited spot with an even angular intensity. We verify this experimentally by fabricating these gratings in the SiN/SiO2 system using e-beam lithography. In addition, we also show that these gratings can couple out more complex holographic patterns.
These density controlled out-coupling gratings let us efficiently address the near-field on optical chips, making them ideal waveguide components for on-chip optical trapping, holographic imaging or fluorescent excitation.
Fluorescence detection is a commonly used technique to detect particles. Microscopes are used for the fluorescence detection of the micro-particles. However, the conventional microscopes are bulky. It is cumbersome to integrate all the equipment used for detection in one setup. They can be replaced by photonic chips for the detection of micro-particles such as cells. Most of the biological detection techniques require the utilization of the visible range of the spectrum. SiN as a waveguide material stands out for biological applications due to its transparency in the visible spectrum. Specifically designed grating couplers can be exploited to focus from inside SiN waveguides at a designated location above the chip. Those SiN focusing grating couplers can mimic microscope objectives for on-chip biological detection applications such as fluorescence and Raman spectroscopy. In this report, we present a 2D SiN focusing grating coupler. We study the effect of the grating design on the focus properties of visible light using finite-difference time-domain simulations.
Proc. SPIE. 9751, Smart Photonic and Optoelectronic Integrated Circuits XVIII
KEYWORDS: Light sources, Continuous wave operation, Real time imaging, Modulation, LIDAR, Sensors, Single photon, Reflectivity, Demodulation, Image sensors, Time of flight cameras, Spatial resolution, Single photon detectors, Signal detection, Performance modeling, Systems modeling, Ranging, Time of flight imaging, Miniature imaging systems, Time of flight range image sensors
In the last decade significant progress has been made on optical non-contact time-of-flight (ToF) based ranging techniques. Direct implementations based on time-correlated single photon counting (TCSPC-dToF), coincidence detection (CD-TCSPC-dToF) as well as multiple indirect realizations based on e.g. single-photon synchronous detection (SPSD-iToF), continuous-wave modulation (CW-iToF) or pulse modulation (PM-iToF) have been presented. All those modulation/demodulation techniques can be employed in scanning (scanning LIDAR) as well as non-scanning (Flash-LIDAR) schemes. Many parameters impact key performance metrics such as depth measurement precision or angular resolution. Unfortunately, publications or datasheets rarely quote all relevant parameters. Thus, benchmarking between different approaches based on published metrics is cumbersome. The authors believe that such a benchmark would have to be founded on modeling in order to ensure fair comparison. This work presents an overview over the most common ToF based depth measurement approaches, how these can be modeled and how they compare.
Lens-free in-line Holographic Microscopy (LHM) is a promising imaging technique for many biomedical and industrial applications. The main advantage of the technique is the simplicity of the imaging hardware, requiring no lenses nor high-precision mechanical components. Nevertheless, the LHM systems achieve high imaging performance only in combination with a high-quality and complex illumination. Furthermore, to achieve truly high-throughput imaging capabilities, many applications require a complete on-chip integration. We demonstrate the strength, versatility and scalability of our integrated approach on two microscopes-on-chip instances that combine image sensor technologies with photonics (and micro-fluidics): a fully integrated Point-Source (PS) LHM module for in-flow cell inspection and Large Field-of-View (LFoV) microscope with on-chip photonic illumination for large-area imaging applications. The proposed PS-LHM module consists of a photonic illumination, a micro-fluidic channel and an imager, integrated in a total volume smaller than 0.5 mm3. A low-loss single-mode photonic waveguide is adapted to generate a high- NA illumination spot. Experimental results show strong focusing capabilities and sufficient overall coupling efficiency. Current PS-LHM prototype reaches imaging resolution below 600nm. Our LFoV-LHM system is extremely vertically compact as it consists of only one 1mm-thick illumination chip and one 3mm-thick imaging module. The illumination chip is based on fractal-layout phase-matched waveguides designed to generate multiple light sources that create a quasi-planar illumination wavefront over an area few square millimeter large. Current illumination prototype has active area of approximately 1.2×1.2mm2. Our LFoV-LHM prototype reaches imaging resolution of 870nm using image sensor with 1.12μm pixel pitch with maximum FoV of 16.47mm2.
Low temperature PECVD silicon nitride photonic waveguides have been fabricated by both electron beam lithography and 200 mm DUV lithography. Propagation losses and bend losses were both measured at 532 and 900 nm wavelength, revealing sub 1dB/cm propagation losses for cladded waveguides at both wavelengths for single mode operation. Without cladding, propagation losses were measured to be in the 1-3 dB range for 532 nm and remain below 1 dB/cm for 900 nm for single mode waveguides. Bend losses were measured for 532 nm and were well below 0.1 dB per 90 degree bend for radii larger than 10 μm.
Several applications in integrated optics require an equal distribution of power from a single input port among many photonic components, whether they be projection components or sensors. One method of achieving such a system is through using progressively more tightly coupled evanescent couplers to route power from a single feeding line . While very compact, this approach requires careful design and characterization of evanescent couplers, and is vulnerable to process variations as the ratio of coupling has a non-linear relation to the couplers’ gap size. Fractals, widely present in nature, are recursive objects where each section is geometrically similar to its parent. They find applications in various fields , including RF antenna design and feeding . In this paper we propose to use the fractal approach for spreading power evenly over an area using micro-machined photonic waveguides. In the fractal routing demonstrated in this work, an 1×2 multimode interference (MMI) coupler splits the power at each fractal stage. This provides several advantages. First, only one power splitter design is needed. Second, MMI couplers are well known, and more robust to process tolerances than evanescent couplers . Third, they are symmetrical, and therefore provide a theoretically perfect power distribution independent of the fractal depth. We therefore demonstrate that a fractal routing provides a way to evenly and efficiently distribute power over a large area.
Recently, the photonics community has a renewed attention for silicon nitride.1-3 When deposited at temperatures below 650K with plasma-enhanced chemical vapor deposition (PECVD),4 it enables photonic circuits fabricated on-top of standard complementary metaloxidesemiconductor (CMOS) electronics. Silicon nitride is moreover transparent to wavelengths that are visible to the human eye and detectable with available silicon detectors, thus offering a photonics platform for a range of applications that is not accessible with the popular silicon-on-insulator platform. However, first-time-right design of large-scale circuits for demanding specifications requires reliable models of the basic photonic building blocks, like evanescent couplers (Figure 1), components that couple power between multiple waveguides. While these models typically exist for the silicon-on-insulator platform, they still lack maturity for the emerging silicon nitride platform. Therefore, we meticulously studied silicon nitride-based evanescent couplers fabricated in our 200mm-wafer facility. We produced the structures in a silicon nitride film deposited with low-temperature PECVD, and patterned it using optical lithography at a wavelength of 193nm and reactive ion etching. We measured the performance of as much as 250 different designs at 532nm wavelength, a central wavelength in the visible range for which laser sources are widespread. For each design, we measured the progressive transmission of up-to 10 cascaded identical couplers (Figure 2(a)), yielding very accurate figures for the coupling factor (Figure 2(b)). This paper presents the trends extracted from this vast data set (Figure 3), and elaborates on the impact of the couplers bend radius and gap on its coupling factors (Figure 4 and Figure 5). We think that the large- scale characterization of evanescent couplers presented in this paper, in excellent agreement with the simulated performance of the devices, forms the basis for a component library that enables accurate design of silicon nitride-based photonic circuitry.
MEMS technology is presented as a promising technology to realize high Q variable capacitors and RF switches with high performance and with high levels of integration. These devices are key elements for systems like phase shifters, tunable filters and matching networks. However, the reliability and the yield of the RF MEMS devices remain the key limiting factors holding the MEMS technology from spreading in the industrial applications. From a RF designer's point of view, reliability and yield are closely related to the accuracy of the definition of the up- and down-state capacitances of the devices. In this paper, we propose a novel compact series capacitive structure with improved predictability and RF performance. The new design mimics a clamped-clamped bridge to lower its sensitivity to the process-induced stress gradient in the up-state. The shape of the device and its consequent parameters, e.g. up- and down-capacitances, are thus more accurately defined even in presence of non-ideal clamping conditions. Unlike the series switchable capacitors with transverse restraining bridge, the novel device does not suffer from high frequency parasitic resonances. Finally, the novel device implements the floating top metal. This allows accurately defining the down-state capacitance of the design at will. Boosted series capacitive switches with inline-restrained cantilever beams have been realized and measured. The isolation is better than 20dB until 1GHz without optimization. The insertion loss in the down-state is better than 0.2dB in the range 1-20GHz. It further slowly and continuously decays to reach 0.4dB at 40GHz without any resonances.