LIDAR (Light Detection and Ranging) is a sensing method, which utilizes light to measure distances and velocities. It is widely used in many areas including autonomous vehicles and robotics, navigation, aerial mapping and other geo-related measurements, atmospheric research, etc. In comparison with RADAR systems, which rely on radio- waves, LIDAR refers to usage of visible to near infrared light wavelength range, providing possibility of long-distance measurements with higher resolution, as optical wavelengths would have smaller diffraction angles for a given aperture.
Wide-angle area coverage available in to-date LIDARs often relies on moving mechanical components to allow scanning. This fact limits scan rates, decreases reliability and leads to high costs. Integrated photonics can bring here on-chip integration of main components (laser, beam steering systems and photo-detectors) to increase overall performance, reliability and stability of a system, while significantly decreasing costs by wafer-scale production.
Operation in wavelengths range around 1.55 µm provides benefits of available low-cost sources and detectors, eye-safe operation even at a high power levels, and low atmospheric absorption of a beam. LIGENTEC’s Silicon Nitride platform greatly suits as a basis for implementation of integrated LIDAR systems, as it provides ultra-low losses in near IR region, has low nonlinearity, allowing guidance of high optical power densities, and generally has less fabrication-induced phase variations than silicon-based waveguides. The platform is also perfectly compatible with operation in 800-1000 nm range which is widely used to date in different LIDAR realisations and could serve as intermediary component for larger systems. Our platform open a road for reliable and scalable on-chip beam steering systems, which can be further combined with either conventional sources and detectors, or heterogeneously integrated with their on-chip analogous.
BIOSENSING & MICROSCOPY
Transparency and low loss propagation in the visible and NIR regions make Silicon Nitride (SiN) platforms attractive for many biophotonic sensing and imaging applications. As these areas usually rely on expensive, complicated and often bulky equipment, integrated photonics can bring here cost reduction via possibility of mass-production, significant decrease of equipment size and simplification of maintenance procedures due to integration of all-in-one. Possibility to have dense integration of waveguiding structures on a chip provides an opportunity for high-throughput sensing and imaging of several samples simultaneously, while customer-adapted geometry leads to compatibility with different setup configurations and possibility of integration of those chips as a part of more sophisticated devices. Moreover, all-optical filtering and signal processing opportunities as well as a chance to combine everything with microfluidic parts could allow new generation of fully integrated lab-on-chip devices. LIGENTEC’s AN180 process, optimized for a visible range, transfers our expertise to broad spectrum of new applications related to Life-science Technologies and Biomedical research. With specially provided Process Design Kit (PDK), one can develop and optimize a chip design to fulfill particular requirements and needs, while our experts will assist you with insights on how to achieve the best possible performance.
Integrated photonics based sensing relies on a change of a device’s optical properties while being in contact with the analyte. Schemes of detection can vary from simple waveguides to usage of high-Q ring resonators. In both cases interaction with an analyte is done via evanescent field tail of the mode propagating in a structure; therefore, a waveguide core is usually functionalized to be able to catch the molecules of interest and then is exposed to an environment. Any further binding event slightly changes the refractive index and influences the propagation of light in a way that can be detected. An advantage of the approach is being label-free and compatible with both liquid- or gas-based environments.
One of the most developed methods uses ring resonators as the main sensing component. Here, change in a binded analyte concentration alters the refractive index, which in turn causes a shift in a resonant frequency. High quality resonators, where LIGENTEC has a proven track record, can lead to nanomolar (nM) or even picomolar (pM) detection limit and high sensitivity. Moreover, resonator-based methods have a good fabrication tolerance, providing good results reproducibility for devices of the same design, and are shown to have good regeneration capabilities.
Other bio-sensing methods enabled by integrated photonics approach could also employ MZI-based interferometric schemes, multimode-waveguides interference and different types of label-based techniques, all available with Silicon Nitride platforms.
In bio-related imaging, the visible and near-IR spectral range is mainly used which limits the resolution to the order of several hundred nanometers due to diffraction, making it hard to impossible for a wide-field microscopy to distinguish structures of interest which are significantly smaller than that. To overcome this limitation, several techniques are available, which are generally referred as methods of super-resolution microscopy (or nanoscopy). These methods utilize image post processing to precisely localize the position of each marker and generally set some additional requirements for illumination. To date, the realization of them requires supplementary components and additional imaging steps, which lead to complex, expensive and bulky imaging systems. On-chip waveguides are prominent alternative option to realize required illumination pattern: uniform large-area TIRF illumination with specified field penetration depth can be achieved. In this approach, waveguides serve as a source of evanescent field to excite markers in a sample, which is placed on top of them.
With high power coupling efficiency and low propagation losses enabled by LIGENTEC’s Silicon Nitride platforms, it’s not only possible to obtain simple fluorescence based and TIRF-microscopy images, but to realize advanced methods such as DNA-PAINT, ESI, dSTORM, etc. with a large field-of-view (hundreds of microns diagonal) and demonstrated resolution down to tens of nanometers. Our Multi Project Wafer (MPW) runs provide an opportunity for decreased cost optimization of your designs and user-adapted chip geometry to ensure compatibility with a particular setup and experiment.
A good addition to this are integrated laser beam combiners (ILBC) which allow combination of light collected from several different sources into one fiber/waveguide and therefore simplifies multiwavelength imaging procedure. Here, the beneficial features of Silicon Nitride as a material of choice are its transparency over a broad range of wavelengths, low nonlinearity, permitting high optical power transmission without undesired effects, and good thermal and mechanical stability.
Other emerging applications
The possibility to integrate splitters, multiplexers, highly efficient couplers, spectrally selective elements, customized and controllable output beam spot sizes as well as low losses in a visible and NIR/MIR range opens large perspectives for size and cost reduction in many life-science and biomedical applications varying from Optical Coherence Tomography (OCT), where the whole interferometric part could be integrated on a chip, to Spectrometers and compact Flow-cytometers for live cell sorting using microfluidics. In such devices, integration allows to overcome inefficiencies induced by relative movements and additional interconnects present in their discrete-components counterparts and makes systems more sustainable to perturbations.
The LIGENTEC’s PDK includes a variety of widely-used building blocks to allow effortless design of photonic integrated circuits (PICs) with even high degree of complexity. Combined with our expertise in fabrication of sophisticated circuits and optimized Silicon Nitride platforms for operation in a visible and NIR/MIR range, it becomes one of the best options for development of novel high-performance devices in the area.
Quantum optics provided a basis for a variety of scientific and technological advancements throughout last decades in areas ranging from extremely sensitive metrology to high-performance computing and secure communications. The ability to transfer required functional parts on photonic integrated chips is an unavoidable step towards moving those technologies from research centers to real world applications. Currently, all the main components of a quantum-based system can be realized on a chip and fully functional large-scale integrated quantum photonic systems were already demonstrated. Quantum systems could be built based on different phenomena and use different information carriers, but photonics occupies a special place among other realizations due to the possibility to incorporate quantum states generation, transmission and measurements on a single platform having less sensitivity to environmental noise. Similarly to other areas, PICs promise important advantages as scalability and reconfigurability of architectures, small system footprint and high stability of elements.
Every photon counts:
LIGENTEC’s Silicone Nitride platform is of particular interest for this area having ultra-low losses below 0.1dB/cm. Furthermore allowed power levels of operation can be high due to the absence of Two-Photon Absorption (TPA). The possibility of dispersion engineering and proven realization of high-Q ring resonators with small bend radii opens new fields for quantum operations. The latest also opens opportunities for photon-pair generation via Spontaneous Four Wave Mixing (SFWM), while the resonators’ narrow bandwidth and possible tunability could provide high degree of in-distinguishability of generated photons in different experimental schemes. Other vital components such as couplers, beam-splitters, Arrayed Waveguide Gratings (AWGs), Mach-Zehnder interferometers (MZIs), complex filters and delay lines can be fabricated, while hybrid or heterogeneous integration with active components like light sources and detectors make the platform a beneficial solution for a quantum PIC realization.
FREQUENCY COMB GENERATION
Silicon Nitride microresonators enable the generation of frequency combs from a single continuous wave laser source. Due to a balance of Kerr nonlinearity and the dispersion of the resonator equally spaced lines are generated through nonlinear processes, when the pump laser operates above a certain threshold. Dispersion engineering of the resonator is made easy due to the ability to shape height and width of the resonator through the fabrication process. The final repetition rate, i.e. the distance between two lines is given by the diameter of the resonator and can be customised from 20 GHz up to 1 THz.
Optical spectrum of a frequency comb generated with a microresonator. The diameter of around 670 μm provides a repetition rate of 50 GHz. (courtesy of LPQM, EPFL).