Photonics biosensors convert biomolecular interactions into quantifiable optical signals for biomedical analysis, which enable continuous monitoring of health indicators. Among them the microring resonator has a good sensing performance and a very broad application prospect. This thesis studies sensing with microfluidic integrated microring resonator photonic microchips.
This thesis adopts finite element method to simulate the optical behavior of waveguides and reactions in the microfluidic channel. The microfluidic channel was designed and prepared and then integrated to the photonic chip. The optical performance parameters of the micro ring resonator were tested by using a high-precision optical test system. The sensing performance of waveguide microring was studied using different aqueous solution as the detection object. The feasibility and effectiveness of the optical waveguide chip sensing have been preliminary verified.

Non-Destructive Testing (NDT) of infrastructures has become an increasingly prominent topic in contemporary society with great significance in terms of safety, economy and environmental protection. Acoustic Emission (AE) technology is a representative NDT technology based on passive ultrasonic guided waves, which has the advantages of large coverage, low energy consumption and rapidity but also puts forward higher requirements on performance specifications of sensors, such as sensitivity, bandwidth, signal-to-noise ratio and miniaturization. Silicon photonics employs silicon as an optical medium to create sub-micron precision photonic systems, which provides promising scope for next-generation sensors with ultra-high sensitivity, small footprint and special functionalities. Oriented towards the requirements from AE applications, this project proposes the first silicon photonic micromechanical AE sensor based on micro-machined membranes, with an ambition of replacing the conventional piezoelectric sensors. The prototype design presented in this work includes two options with different cladding materials, which is capable of a peak velocity sensitivity of more than 75dB[V /(m/s)] and a wide operating frequency range of 100 ∼ 1000 kHz. The overall performance of the proposed design is comparable to that of mainstream piezoelectric AE sensors, while the footprint is reduced to about 1/40. In the design process, a complete design methodology for opto-mechanical AE sensors is developed, which allows rapid design with good agreement with simulation results.

In a world increasingly dominated by technological advancements, the demand for high-quality microphones has never been more present. Seamless speech recognition and the development of userfriendly hearing aids remain significant challenges. State-of-the-art micro-electromechanical system (MEMS) microphones are reaching their bottlenecks in terms of thermo-acoustic noise, caused by the acoustic resistance of the parallel plate capacitor. This constrains the achievable signal-to-noise ratio (SNR). This thesis presents a novel solution to address these challenges through the application of silicon photonics technology in the development of a silicon photonic microphone. Silicon photonics is a technology that uses silicon as an optical medium to create photonic systems with sub-micrometre precision, which can be used to create ultra-sensitive sensing devices. The optical sensors are fabricated on standard silicon-on-insulator (SOI) wafers, allowing for seamless integration with the precise and cost-effective complementary metal-oxide-semiconductor (CMOS) process. The optomechanical
sensitivity of the proposed microphone is derived for three different cladding materials that could be deposited on the wafer in the fabrication process. The thermal acoustic noise of the microphone is quantified. As the integrated photonic circuit does not require a backplate the design potentially reduces the thermal acoustic noise of current microphones by 44 %. The optimized design for the laboratory setup that is considered for this thesis can theoretically result in an SNR of 73.1 dB, which is roughly 5 dB more than the current state-of-the-art microphone technology.

Silicon photonics have received more attention in recent years due to further development in CMOS manufacturing methods. The development allows silicon photonics to be smaller than ever before. This leads to smaller silicon photonic devices that can transceive light, which is typically done at a wavelength of 1550nm for silicon photonics. A silicon photonic device that benefits from this wavelength is the silicon waveguide, which can transceive light by being coupled to other waveguides. When the second guide is later coupled back with the main waveguide, a resonance can form between the guides. This can turn the silicon waveguide in to a sensor that relies on interference from the recoupled signal. The design used for this study has the waveguides in a relatively deep trench, which means that a membrane can be suspended above the waveguides. In theory the membrane should reflect some of the light that escapes from the waveguide back. In this work membranes made from graphene and molybdenum disulfide are suspended over a silicon waveguide in hopes to detect the motion of the membrane. A proof of concept by experimenting with membranes integrated on silicon photonics can give way for a new type of sensor, which is both microscopic and has a high signal-to-noise ratio. The experiments are conducted by propagating light through the waveguide, the light should then interact with the suspended membrane on top. The first indication that the concept was possible was when a transmission graph that swept the light’s wavelength around 1550nm changed after introducing a suspended membrane over the waveguide. The change showed that waveguides react to membranes over them without eliminating the transmission altogether. This is a great step when it comes to a proof for the concept. However, it is still needed to take a frequency measurement before the concept has been fully proofed.

From the research in the field of mechanobiology, it is evident that cells exert different force magnitudes while growing based on the biomaterial these are in contact with. The magnitude of the exerted force determines certain behaviors and mechansims of the cells, such as differentiation. For this reason, it is proposed to develop a distributed force sensor using a photonic integrated circuit with a PDMS top layer to measure the exerted forces, which can be used to study the behavior of the cells. Unlike conventional measurement techniques, this method allows cell exerted distributed forces at µN levels to be detected and monitored over a continuous time-span of multiple days and weeks. The photonic integrated circuit design consists of a sensing array of silicon photonic ring resonators for force sensing. On each sensor row, reference ring resonators are applied as well to cancel out the spectral noise caused by temperature drifts and laser wavelength repeatabilities. The reference ring resonators are shielded against cell exerted forces with a commercial hybrid-polymer, which has a Young's modulus of around 1 GPa. Using the reference ring resonators resulted in a theoretical measurement resolution of potentially as small as approximately 0.012 pm. Finally, the force limit-of-detection of the designed distributed force sensor remains below 1 µN when the force exertion area does not exceed 100 µm2 and assuming a sensitivity of 65.41 nm/RIU for one of the multiplexed ring resonators.

Because of the growing demand for more advanced electric devices, an exponential growth of the number of transistors are supposed to be integrated into a single chip. To manufacture devices in the scale of nanometer cost-effectively, an accurate measurement for lithography process calibrating is necessary. Ptychography is a computational imaging technique which has the potential to serve as a metrology solution for semiconductor devices. It can reconstruct complex-valued permittivity function of an object from an extensive set of measured intensities of the diffraction patterns in the far field. It should be noted that also 2D and 3D a-periodic objects can be measured with this technique. Currently, this technique has been widely used in reconstructing thin and weakly scattering (satisfying the first Born approximation) objects in a transmission geometry (detectors and sources are placed on different sides of the objects).We propose an accurate 3D ptychography multi-layer Born model, and apply it to reconstruct refractive index distributions of semi-conductors. This model slices the sample into thin layers and first Born approximations are applied to each layer sequentially. For a transmission geometry, this model considers both forward scattering effects and backward scattering effects \cite{Chen2020Multi-layerMicroscopy}, as opposed to normal beam propagation models. For reflection geometry (detectors and sources are placed on the same side of the object), this model collects reflected fields on each layer of the sample and these fields will interact with the object again later together with other upwards fields. This procedure enables detectors arranged in a reflection geometry to gather complete information about the object. We implement the model on the existing ptychography platform based on the auto-differentiation (AD) solvers and manage to reconstruct high-resolution images of 3D objects.