Rozprawy doktorskie na temat „Silicon microring resonators”

Microwave photonic (MWP) signal processing has attracted strong interest due to its unique advantages such as large operational bandwidth and immunity against electromagnetic interference. Recently, fast-growing markets in 5G wireless networks and the Internet of Things have become a strong thrust to the development of MWP signal processing. They are expected to benefit from MWPs with its capabilities to achieve a high time-bandwidth product in the transmission of microwave or millimeter-wave signals. Conventional MWP systems are composed of discrete optoelectronic devices and fiber-based components, which are usually bulky and power-hungry, making them inferior to the commercial RF electronic devices. It is therefore imperative to realize compact integrated MWP systems with reduced cost, size, weight and power consumption. While Moore's Law is approaching its limit to drive the evolution of electronic circuits, the silicon photonic integration platform, which features high compatibility with the standard CMOS processes, emerges as a promising solution. By incorporating both electronics and optics components on a single integrated chip, silicon photonic circuits ensure the unique characteristics of MWP signal processing such as wide bandwidth and high configurability are fully utilized, thus promoting the performance of integrated MWP signal processors. In this thesis, the applications of integrated silicon photonics on key MWP building blocks are investigated. The investigation is focused on the applications of microring resonators fabricated on SOI platform, which exhibit excellent compactness due to their inherent resonance effect and strong light confinement of the waveguide. The MWP building blocks we explore include an integrated optical single sideband modulator, a frequency tunable microwave filter for amplitude control and a photonic-assisted microwave frequency measurement system.

This thesis presents a novel method of modulating silicon photonic circuits using 3D printed microfluidic devices. The fluids that pass through the microfluidic device interact directly with the silicon waveguides. This method changes the refractive index of the waveguide cladding, thus changing the effective index of the system. Through using this technique we demonstrate the shift in resonant wavelength by a full free spectral range (FSR) by increasing the concentration of the salt water in the microfluidic device from 0% to 10%. On a 60 μm microring resonator, this equals a resonant wavelength shift of 1.514 nm when the index of the cladding changes by 0.017 refractive index units (RIU), or at a rate of 89.05 nm/RIU. These results are confirmed by simulations that use both analytical and numerical methods. This thesis also outlines the development of a process that uses two-photon absorption(TPA) in silicon to produce a photoelectrochemical (PEC) etching effect. TPA induces free carriers in silicon that then interact with the Hydroflouric Acid (HF) solution that the wafer is submerged in. This interaction removes silicon away from the wafer, which is the etching observed in our experiments. Non-line-of-sight PEC etching is demonstrated. The optical assemblies used in these experiments are presented, as are several of the results of the etching experiments.

Optical polymers are a subject of research and industry implementation for many decades. Optical polymers are inexpensive, easy to process and flexible enough to meet a broad range of application-specific requirements. These advantages allow a development of cost-efficient polymer photonic integrated circuits for on-chip optical communications. However, low refractive index contrast between core and cladding limits light confinement in a core and, consequently, integrated polymer device miniaturization. Also, polymers lack active functionality like light emission, amplification, modulation, etc. In this work, we improved a performance of integrated polymer waveguides and demonstrated active waveguide devices. Also, we present novel Si QD/polymer optical materials. In the integrated device part, we demonstrate optical waveguides with enhanced performance. Decreased radiation losses in air-suspended curved waveguides allow low-loss bending with radii of only 15 µm, which is far better than >100 µm for typical polymer waveguides. Another study shows a positive effect of thermal treatment on acrylate waveguides. By heating higher than polymer glass transition temperature, surface roughness is reflown, minimizing scattering losses. This treatment method enhances microring resonator Q factor more than 2 times. We also fabricated and evaluated all-optical intensity modulator based on PMMA waveguides doped with Si QDs. We developed novel hybrid optical materials. Si QDs are encapsulated into PMMA and OSTE polymers. Obtained materials show stable photoluminescence with high quantum yield. We achieved the highest up to date ~65% QY for solid-state Si QD composites. Demonstrated materials are a step towards Si light sources and active devices. Integrated devices and materials presented in this work enhance the performance and expand functionality of polymer PICs. The components described here can also serve as building blocks for on-chip sensing applications, microfluidics, etc.

QC 20171207

A 4 × 4 photonic switch matrix was designed, fabricated and characterized. The photonic switch matrix was based on microring resonator (MR) and was fabricated on relatively low-cost silicon-on-insulator (SOI). Independent wavelength channel switching was accomplished by thermo-optic tuning of the MRs through highly localized resistive micro-heaters. The device was fabricated using the relatively mature silicon fabrication technology. Waveguide patterns were defined with high definition eBeam lithography, etching was done in a reactive-ion etching chamber, and the top cladding SiO2 layer was deposited through plasma-enhanced chemical vapor deposition. Finally, resistive Nichrome micro-heaters were deposited locally directly above each MR to offer the dynamic tuning capability. The strong optical confinement offered by the high index contrast between silicon and SiO2 makes it possible to fabricate micrometer-sized MRs with acceptable optical power loss caused by the small bending radii. The MRs were designed with a uniform diameter of 10 µm to support a wide free spectral range. All waveguides have a design dimension of 450 nm × 250 nm to allow operation exclusively in the fundamental mode at the 1.55 µm wavelength. A FSR of 18 nm with a spectral linewidth of 0.1 nm were observed for the fabricated MRs offering high wavelength selectivity. The device exhibits virtually no thermal crosstalk between adjacent channels, showing no output peak wavelength shift at 0.01 nm wavelength measurement precision by thermally tuning an adjacent MR with electric current as high as 7 mA, which is equivalent to about 2.5 nm in resonance wavelength tuning. The device showed a tuning delay time of about 1 ms. The overall bare chip size of the device is 20 mm × 4 mm. We demonstrated through this work a wavelength selective photonic switch device using low-cost SOI technology that is compact and easy to fabricate. It shows high potential for further development into high port-count photonic switch matrix.

In this thesis, we present and study the use of bent couplers in silicon-on-insulator (SOI) microring resonator (MRR) based filters. MRR based filters are attractive candidates in wavelength division-multiplexing (WDM) transceivers because of their compactness and low power consumptions. However, they suffer from drawbacks that include a limited free spectral range (FSR) which limit the number of channels that can be simultaneously multiplexed and/or demultiplexed. Our work investigates SOI single-ring MRR filters with bent couplers that have extended FSRs, enhanced filter performance (such as bandwidth, out-of-band rejection ratio, side-mode suppression, extinction ratio, and insertion loss) while maintaining compact footprints. Our aim is to make these filters attractive candidates to the current state-of-the-art WDM transceivers. We first demonstrated a 2.75 μm radius MRR filter that employs bent directional couplers in its coupling regions. This MRR filter was fabricated using a 248 nm photolithography process. Our filter has a 33.4 nm FSR and a 3-dB bandwidth of 25 GHz. Also, our MRR achieved an out-of-band-rejection ratio of 42 dB, an extinction ratio of 19 dB, and a drop-port insertion loss that is less than 1 dB. Lastly, our MRR filter has a tuning efficiency of 12 mW/FSR. Then, we theoretically and experimentally demonstrated an MRR filter with bent contra-directional couplers that exhibits an FSR-free response, at both the drop and through ports, while achieving a compact footprint. Also, using bent contra-directional couplers in the coupling regions of MRRs allows us to achieve larger side-mode suppressions than MRRs with straight CDCs. The fabricated MRR filter has a minimum suppression ratio of more than 15 dB, a 3dB-bandwidth of ~23 GHz, a through-port extinction ratio of ~18 dB, and a drop-port insertion loss of ~1 dB. High-speed data transmission through the MRR filter is demonstrated at data rates of 12.5 Gbps, 20 Gbps, and 28 Gbps.
Applied Science, Faculty of
Electrical and Computer Engineering, Department of
Graduate

Silicon photonics is a very promising technology for future low-cost high-bandwidth optical telecommunication applications down to the chip level. This is due to the high degree of integration, high optical bandwidth and large speed coupled with the development of a wide range of integrated optical functions. Silicon-based microring resonators are a key building block that can be used to realize many optical functions such as switching, multiplexing, demultiplaxing and detection of optical wave. The ability to tune the resonances of the microring resonators is highly desirable in many of their applications. In this work, the study and application of a thermally wavelength-tunable photonic switch based on silicon microring resonator is presented. Devices with 10µm diameter were systematically studied and used in the design. Its resonance wavelength was tuned by thermally induced refractive index change using a designed local micro-heater. While thermo-optic tuning has moderate speed compared with electro-optic and all-optic tuning, with silicon’s high thermo-optic coefficient, a much wider wavelength tunable range can be realized. The device design was verified and optimized by optical and thermal simulations. The fabrication and characterization of the device was also implemented. The microring resonator has a measured FSR of ~18 nm, FWHM in the range 0.1-0.2 nm and Q around 10,000. A wide tunable range (>6.4 nm) was achieved with the switch, which enables dense wavelength division multiplexing (DWDM) with a channel space of 0.2nm. The time response of the switch was tested on the order of 10 us with a low power consumption of ~11.9mW/nm. The measured results are in agreement with the simulations. Important applications using the tunable photonic switch were demonstrated in this work. 1×4 and 4×4 reconfigurable photonic switch were implemented by using multiple switches with a common bus waveguide. The results suggest the feasibility of on-chip DWDM for the development of large-scale integrated photonics. Using the tunable switch for output wavelength control, a fiber laser was demonstrated with Erbium-doped fiber amplifier as the gain media. For the first time, this approach integrated on-chip silicon photonic wavelength control.

Photonic sensing technologies offer unexceptionable features for taking high requirement measurement in a harsh environment. They inherit advantages such as fast speed and immunity from electromagnetic interference from optical communications. In addition, with the silicon-on-insulator (SOI) technologies, chip scale optical sensors are capable of providing high sensitivity with an ultra-compact form factor. The motivation is derived from the high demand for sensors in the new era of the Data Age and the great potential of fast response, highly sensitive and ultra-compact photonic sensor. Furthermore, rapid sensor development puts forward a new prospect for many areas such as medical and health measurement, defence technology, and the internet of things. With all the advantages that SOI-based chip scale optical sensors provide, there are still shortcomings can be improving to provided much more capable sensing abilities from many aspects. With that in mind, this thesis will focus on SOI-based optical microring resonator, one of the most popular SOI-based optical structure for sensing purpose; and solutions for two shortcomings of the common SOI-based optical sensor. One of the solutions that will be mentioned in this thesis is intended to solve the issues of limited measurement speed and low resolution that caused by the way of the data analysis in the common SOI-based optical sensing system. The second purposed solutions in this thesis focused on the connection schemes of the SOI-based optical sensor; Common connection schemes of SOI-based optical chip needs at least two optical ports for coupling the light into and out of the silicon photonics chip which limits the ability to perform measurements at remote locations that are hard to be reached. Chapter 4 and 5 of this thesis contains detailed explorations of these shortcomings and solutions. An integrated photonic sensor based on optoelectronic oscillator with an on-chip sensing probe that is capable of realising highly sensitive and high-resolution optical sensing is presented in this thesis as a solution for the first shortcoming. The key component is an integrated SOI-based microring resonator which is used to implement a microwave photonic bandpass filter (MPBF) to effectively suppress the side modes of the optoelectronic oscillator (OEO) by more than 30dB, thus generating a peak RF signal that maps the detected optical change into a resulting shift in the oscillating frequency. As an application example, the proposed optical sensor system is employed to detect small changes in temperature, and experimental results demonstrate a highly sensitive optical temperature sensor with an achieved sensitivity of 7.7 GHz/°C. Moreover, the proposed sensing system revealed a 0.02°C measurement resolution which is a tenfold improvement compared with the modest resolution of 0.23°C seen by the conventional MPBF system without the OEO loop, rendering it highly suitable for diverse high-resolution sensing applications. With the purpose of reducing the size of the SOI-based photonic sensor and to overcoming the second shortcoming, an ultra-compact, reflective optical sensor probe based on SOI microring resonator and Y-junction structure is also presented in this thesis. This structure is capable of simultaneously achieving high sensitivity and fine resolution optical sensing. The reflective configuration of the probe enables remote measurements at locations which are otherwise hard to be assessed by transmission based sensors. As an application example, the proposed sensor probe for temperature measurement is demonstrated. Experiment results show that the center wavelength shift of the sensor’s reflected spectrum offers a linear response to temperature change with a high sensitivity of 66 pm/°C.

The experimental work that is reported in the thesis explores some properties and possible uses of silicon microring resonators as integrated sources of non-classical states of light, based on the enhancement of non-linear effect of four-wave mixing (FWM).
The experimental work that is reported in the thesis explores some properties and possible uses of silicon microring resonators as integrated sources of non-classical states of light, based on the enhancement of non-linear effect of four-wave mixing (FWM).

The objective of this work is to develop essential building blocks for the lab-on-a-chip optical sensing systems with high performance. In this study, the silicon-on-insulator (SOI) platform is chosen because of its compatibility with the mature microelectronics industry for the great potential in terms of powerful data processing and massive production. Despite the impressing progress in optical sensors based on the silicon photonic technologies, two constant challenges are larger sensitivity and better selectivity. To address the first issue, we incorporate porous materials to the silicon photonics platform. Two porous materials are investigated: porous silicon and porous titania. The demonstrated travelling-wave resonators with the magnesiothermically reacted porous silicon cladding have shown significant enhancement in the sensitivity. The process is then further optimized by replacing the thermal oxide with a flowable oxide for the magnesiothermic reduction. A different approach of making porous silicon using porous anodized alumina membrane leads to better flexibility in controlling the pore size and porosity. Porous titania is successfully integrated with silicon nitride resonators. To improve the selectivity, an array of integrated optical sensors are coated with different polymers, such that each incoming gas analyte has its own signature in the collective response matrix. A multiplexed gas sensor with four polymers has been demonstrated. It also includes on chip references compensating for the adverse environmental effects. On chip spectral analysis is also very critical for lab-on-a-chip sensing systems. For that matter, based on an array of microdonut resonators, we demonstrate an 81 channel microspectrometer. The demonstrated spectrometer leads to a high spectral resolution of 0.6 nm, and a large operating bandwidth of ~ 50 nm.

碩士
國立臺灣科技大學
電子工程系
102
A silicon-on-insulator based waveguide platform has demonstrated its fully compatible processing with the complementary metal-oxide-semiconductor (CMOS) standard process besides the high efficiency, high quality and low cost. Therefore, it is extensively utilized to construct the optoelectronic devices for the applications of higher speed and lower power consumption. Moreover, the large refractive index difference between silicon and silicon dioxide layers can significantly reduce the waveguide size to submicron scale, named as the silicon wire. Then the optical microring resonator (MRR) with its high quality factor owns the potential of highly integrated photonic circuits for optical communications. Due to the small footprint and excellent optical performance, the MRR has become an important device unit in integrated photonics and is attractive in dispersion compensation applications. In this thesis, the chromatic dispersion (CD) characterization of MRR is analyzed using the optical power transmission derivation. There are two main factors in determining CD, the microring coupling coefficient and its circumstance. The CD value, bandwidth, and free spectral range from MRR are analytically illustrated for CD compensation. Fiber dispersion is one of the main factors limiting the optical signal transmission quality and distance. The dynamic CD compensation for high-speed optical communication systems is an urgent need to resolve this issue. An accurate CD characterization technique is crucial to precisely manipulating CD compensation. In the broadband coupling consideration, the Mach-Zehnder directional coupler (MZDC) will be designed and implemented on MRR for wavelength division multiplexing (WDM) CD compensation. In this thesis, the CD monitoring by delayed Mach-Zehnder interferometer and CD compensation using MZDC coupled MRR will be utilized to demonstrate the 50-GHz free spectrum range (FSR) of MRR and 1500 ps/nm.

Measurement of refractive indices of liquids and thin films can play an important role for chemical analysis in the fields of healthcare and biomedical research. There is a requirement of miniaturized refractive index sensor platforms that have high sensitivity, low detection limits and scalable for high throughput label free bio-sensing. Silicon photonic sensors are emerging as the key solution that can satisfy all of the aforementioned criteria. These optical sensing platforms can be fabricated on a silicon wafer using the same processes employed for manufacturing of CMOS integrated circuits, which provides the advantages of low cost and high volume production. However, the cost advantages of these miniaturized sensors are often negated by the requirement of expensive optical interrogation equipment such as a tunable laser and a spectrum analyzer. In our research work, we have demonstrated new sensor con figuration based on silicon photonic microring that is capable of low-cost refractive index sensing. We have also extended the microring resonator platform to measure thermo-optic coeffcients of liquids in small volumes. The first part of the thesis research focuses on the development of tunable cascaded Silicon microring resonators for refractive index shift sensing. This configuration uses two microring resonators in series cascade with one of the two rings probing the analyte liquid (called sensor) while the second microring functions as a spectral filter. By implementing thermo-optic tunability in the fi lter ring, one can track the shifts in the spectrum of the sensor. At the output, a single photodetector is used to capture variations in the intensity. This arrangement is used to translate spectral shifts of sensor microring, caused by analyte index variation, into equivalent changes in the position of intensity peak at the output of the cascade. In our experiments, we used a broadband source (1550 nm) for the input and a single photodetector for measuring optical intensity variation at the output port. For proof of concept studies, we emulated the analyte index shift on sensor microring using thermo-optic effect. The total detection range of the 1550 nm operating device was estimated to be about 0.0241 refractive index units (RIU), with a detection limit of 4:6 10􀀀5 RIU. In the second part of our research we focused on improvement of the detection limit of the tunable cascaded microring device. The precision with which shifts in the intensity peak is tracked was enhanced by the use of lock-in ampli fier assisted harmonic ratio detection. Speci cally, we compute the ratio of the second harmonic to the fundamental frequency of modulation signal provided to the filter ring microheater. Prior to performing experiments, we analyzed the method with theoretical models and simulations to understand the effect of variations in the modulation signals provided by lock-in amplifi er. Experimental results with the 1550 nm cascaded microring devices showed a substantial reduction (a factor of 1330) in the width of harmonic ratio peak compared to that of the unprocessed intensity curve. The detection limit of the device was improved to 8:6 10􀀀6 RIU, now limited only by the performance of electrical equipment providing power to microheaters. Lastly, we have demonstrated a method to measure thermo-optic coeffcient of small volume of liquids using silicon microring resonators. This effort can help in multiparameter analysis of bio fluids and also for correcting errors in refractive index measurements by silicon microrings. For this experiment, we measured the wavelength shifts of analyte covered mircoring resonators as a function of controlled increments in chip temperature. Using theoretical models and simulated parameters, we calculated the thermo-optic coeffcients of standard liquids and obtained a good match with values reported in literature. In summary, we have explored new methods of using silicon photonic microring resonators for reduced cost refractive index sensing and thermo-optic coeffcient measurements.

碩士
國立清華大學
光電工程研究所
98
Raman amplifiers are important for optical communication because the power of signal gradually reduces along propagation. We must use amplifiers to recover signal power strong enough for defection. A Raman amplifier is one kind of amplifiers. The Raman coefficient in silicon is much higher than in fiber(10000 times) ,and it is a reason that we are interested using silicon waveguides to make a amplifier. The size of silicon Raman amplifiers is very small and can be integrated with other devices to accomplish many optical functions on a chip. In this thesis, we take advantage of high Raman coefficient in silicon and utilize resonant enhancement of microring resonators to make Raman amplifiers on silicon-on-insulator. In order to have better waveguide-fiber coupling, we use multimode waveguides and apply micro-electro-mechonical-system (MEMS) technology to allow waveguide and microring well coupled. In measurement, we observe spontaneous and stimulation Raman scattering by controlling the input power. When input power is higher, we also discover the free carrier effect affecting the signal power and refractive index of waveguide. However the loss of device is too high and we can’t adjust the power coupling ratio ,causing that Raman effect is not obvious. To improve the efficiency of device, we could use a novel low-loss silicon photonic wire to make our device in the future. The novel low-loss silicon photonic wire has advantages in low loss and single guide mode. So we expect that it can be better than multimode waveguide and maybe generates Raman laser.

Integrated Silicon Photonics has emerged as a powerful platform in the last two decades amongst high-bandwidth technologies, particularly since the adop- tion of CMOS compatible silicon-on-insulator(SOI) substrates. Microring res- onators are one of the fundamental blocks on a photonic integrated circuit chip o ering versatility in varied applications like sensing, optical bu ering, ltering, loss measurements, lasing, nonlinear e ects, understanding cavity optomechanics etc. This thesis covers the design and modeling of microring resonators for biosensing applications. The two applications considered are : homogeneous biosensing and wrist pulse pressure monitoring. Also, the designs have been used to fabricate ring resonator device using three different techniques. The results obtained through characterization of these devices are presented. Following are the observations made in lieu of this: 1) Design modeling and analysis - The analysis of ring resonator requires the study of both the straight and bent waveguide sections. Both rib and strip waveguide geometries have been considered for constructing the device as a building block by computing their respective eigen modes for both quasi-TE and quasi-TM polarizations. The non-uniform evanescent coupling between the straight and curved waveguide has been estimated using coupled mode theory. This method provided in estimating the quality-factor and free spec- tral range (FSR) of the ring-resonator. A case for optimizing the waveguide gap in the directional coupler section of a ring resonator has been presented for homogeneous biosensing application. On similar lines, a model of applying ring resonator for arterial pulse-pressure measurement has been analyzed. The results have been obtained by employing FD-BPM and FDTD including semi- vectorial eigen mode solutions to evaluate the spectral characteristics of ring resonator. The modeling and analytical results are supported by commercial software tools (RSoft). 2) Fabrication and Characterization - For the fabrication, we employ the design of ring resonator of radius 20 m on SOI substrate with two different waveguide gaps of 350 and 700 nm. Three different process sows have been used for fabricating the same device. The rst technique involved using negative e-beam resist HSQ which after exposure becomes SiO2, acts as a mask for Reactive-Ion Etching (RIE); helping in eliminating an additional step. The second technique involved the use of positive e-beam resist, PMMA for device patterning followed by metal deposition with lift-o . The third tech- nique employed was Focussed Ion-beam (FIB) which is resist-less patterning by bombarding Ga+ ions directly onto the top surface of the wafer with the help of a GDS le. The characterization process involved estimation of loss and observing the be- havior of optical elds in the device around the wavelength of 1550 nm using near-field scanning optical microscopy (NSOM) measurement. The estimation of roughness-induced losses has been made by performing Atomic Force Microscopy (AFM) measurements. In summary, the thesis presents novel design and analysis of SOI based microring resonators for homogeneous biosensing and wrist pulse pressure sensing applications. Also, the fabrication and characterization of 20 m radius ring- resonator with 500 500 nm rib cross-section is presented. Hence, this study brings forth several practical issues concerning application of ring resonators to biosensing applications.

Integrated Silicon Photonics has emerged as a powerful platform in the last two decades amongst high-bandwidth technologies, particularly since the adop- tion of CMOS compatible silicon-on-insulator(SOI) substrates. Microring res- onators are one of the fundamental blocks on a photonic integrated circuit chip o ering versatility in varied applications like sensing, optical bu ering, ltering, loss measurements, lasing, nonlinear e ects, understanding cavity optomechanics etc. This thesis covers the design and modeling of microring resonators for biosensing applications. The two applications considered are : homogeneous biosensing and wrist pulse pressure monitoring. Also, the designs have been used to fabricate ring resonator device using three different techniques. The results obtained through characterization of these devices are presented. Following are the observations made in lieu of this: 1) Design modeling and analysis - The analysis of ring resonator requires the study of both the straight and bent waveguide sections. Both rib and strip waveguide geometries have been considered for constructing the device as a building block by computing their respective eigen modes for both quasi-TE and quasi-TM polarizations. The non-uniform evanescent coupling between the straight and curved waveguide has been estimated using coupled mode theory. This method provided in estimating the quality-factor and free spec- tral range (FSR) of the ring-resonator. A case for optimizing the waveguide gap in the directional coupler section of a ring resonator has been presented for homogeneous biosensing application. On similar lines, a model of applying ring resonator for arterial pulse-pressure measurement has been analyzed. The results have been obtained by employing FD-BPM and FDTD including semi- vectorial eigen mode solutions to evaluate the spectral characteristics of ring resonator. The modeling and analytical results are supported by commercial software tools (RSoft). 2) Fabrication and Characterization - For the fabrication, we employ the design of ring resonator of radius 20 m on SOI substrate with two different waveguide gaps of 350 and 700 nm. Three different process sows have been used for fabricating the same device. The rst technique involved using negative e-beam resist HSQ which after exposure becomes SiO2, acts as a mask for Reactive-Ion Etching (RIE); helping in eliminating an additional step. The second technique involved the use of positive e-beam resist, PMMA for device patterning followed by metal deposition with lift-o . The third tech- nique employed was Focussed Ion-beam (FIB) which is resist-less patterning by bombarding Ga+ ions directly onto the top surface of the wafer with the help of a GDS le. The characterization process involved estimation of loss and observing the be- havior of optical elds in the device around the wavelength of 1550 nm using near-field scanning optical microscopy (NSOM) measurement. The estimation of roughness-induced losses has been made by performing Atomic Force Microscopy (AFM) measurements. In summary, the thesis presents novel design and analysis of SOI based microring resonators for homogeneous biosensing and wrist pulse pressure sensing applications. Also, the fabrication and characterization of 20 m radius ring- resonator with 500 500 nm rib cross-section is presented. Hence, this study brings forth several practical issues concerning application of ring resonators to biosensing applications.

In this thesis, we have designed and optimized strip waveguide based micro-ring and micro-ring and micro-racetrack resonators for biosensing applications. Silicon-On-Insulator (SOI) platform which offers several advantages over other materials such as Lithium Niobate, Silica on Silicon and Silicon nitride is considered here. High index contrast enables us to miniaturize the biosensor devices and monolithic integration of source and detectors on the same chip. We have considered the dispersive nature of the waveguide and proceeded towards optimization. Finite difference schemes and Finite Difference Time Domain (FDTD) methods are the primary tools used to model the biosensor. Various structures such as channel waveguides and beam structures are analyzed on the basis of their suitability for sensing applications. Strip and Rib waveguides are the two geometries considered in our studies. In an optical guiding structure, effective index of the propagating optical mode can be induced by two different phenomena: i. Homogeneous Sensing In this category, effective index of a propagating optical mode changes with uniformly distributed analytes extending over a distance well exceeding the evanescent field penetration depth. The sample serves as the waveguide cover. ii. Surface Sensing In the case of surface sensing, analytes bound to the surface of the waveguide. The effective index of an optical mode changes with the refractive index as well as the thickness of an adlayer. A thin layer of adsorbed or bound molecules transported from liquid or gaseous medium serving as waveguide cover is referred as an adlayer. Both homogeneous and surface sensing schemes are addresses in this work. By bulk sensing method, the characteristics of bioclad covering the device are studied. Optimization of the resonator structure involves the analysis of following parameters: • Gap between the ring and bus waveguides • Free spectral range • Extinction ratio • Quality factor We have achieved a maximum bulk sensitivity of 115 nm / RIU with ring waveguide width of 450 nm and bus width of 350 nm which is better than an earlier reported value of 70 nm/ RIU. We have proposed a novel detection scheme consisting of a micro-racetrack resonator formed over a cantilever structure. The devoice works on the principle of opto-mechanical coupling to detect conformational changes due to biomolecular adherence. BSA (Bovine Serum Albumin) and IgG ( Immuno Globulin G) are the two proteins considered in the work. Mechanical analysis of the beam for tensile and compressive stresses and corresponding spectral responses of the racetrack resonators are analyzed both by semi-analytical and method and numerical analyzes. We compared various aspects of rib and strip waveguide racetrack resonators. We have proved by numerical simulation, that the device is capable of distinguishing tensile and compressive stress. Two strip waveguides of dimensions : 450 nm X 220 nm and 400 nm X 180 nm, former supporting both Quasi-TE and Quasi-TM modes where as the second configuration allows only Quasi-TE mode alone. Sensitivity of the cantilever sensor is : 0.3196 x 10-3 nm/ µɛ at 1550 nm wavelength.

In this thesis, we have designed and optimized strip waveguide based micro-ring and micro-ring and micro-racetrack resonators for biosensing applications. Silicon-On-Insulator (SOI) platform which offers several advantages over other materials such as Lithium Niobate, Silica on Silicon and Silicon nitride is considered here. High index contrast enables us to miniaturize the biosensor devices and monolithic integration of source and detectors on the same chip. We have considered the dispersive nature of the waveguide and proceeded towards optimization. Finite difference schemes and Finite Difference Time Domain (FDTD) methods are the primary tools used to model the biosensor. Various structures such as channel waveguides and beam structures are analyzed on the basis of their suitability for sensing applications. Strip and Rib waveguides are the two geometries considered in our studies. In an optical guiding structure, effective index of the propagating optical mode can be induced by two different phenomena: i. Homogeneous Sensing In this category, effective index of a propagating optical mode changes with uniformly distributed analytes extending over a distance well exceeding the evanescent field penetration depth. The sample serves as the waveguide cover. ii. Surface Sensing In the case of surface sensing, analytes bound to the surface of the waveguide. The effective index of an optical mode changes with the refractive index as well as the thickness of an adlayer. A thin layer of adsorbed or bound molecules transported from liquid or gaseous medium serving as waveguide cover is referred as an adlayer. Both homogeneous and surface sensing schemes are addresses in this work. By bulk sensing method, the characteristics of bioclad covering the device are studied. Optimization of the resonator structure involves the analysis of following parameters: • Gap between the ring and bus waveguides • Free spectral range • Extinction ratio • Quality factor We have achieved a maximum bulk sensitivity of 115 nm / RIU with ring waveguide width of 450 nm and bus width of 350 nm which is better than an earlier reported value of 70 nm/ RIU. We have proposed a novel detection scheme consisting of a micro-racetrack resonator formed over a cantilever structure. The devoice works on the principle of opto-mechanical coupling to detect conformational changes due to biomolecular adherence. BSA (Bovine Serum Albumin) and IgG ( Immuno Globulin G) are the two proteins considered in the work. Mechanical analysis of the beam for tensile and compressive stresses and corresponding spectral responses of the racetrack resonators are analyzed both by semi-analytical and method and numerical analyzes. We compared various aspects of rib and strip waveguide racetrack resonators. We have proved by numerical simulation, that the device is capable of distinguishing tensile and compressive stress. Two strip waveguides of dimensions : 450 nm X 220 nm and 400 nm X 180 nm, former supporting both Quasi-TE and Quasi-TM modes where as the second configuration allows only Quasi-TE mode alone. Sensitivity of the cantilever sensor is : 0.3196 x 10-3 nm/ µɛ at 1550 nm wavelength.

碩士
國立臺灣科技大學
電子工程系
107
Biophotonics is a rapidly growing field in prevailing researches and becomes one of the major developed projects of biomedical technologies. In recent years, the microring resonator (MRR) has been utilized for label-free biosensing applications. The high quality factor (Q) from the strong electric field enhancement within the ring makes the MRR a good candidate for biomolecule detection under low analyte concentration conditions. Here we propose to develop high sensitivity biosensors using MRR characteristics interrogated with the low coherent interference technique and delayed Self-Homodyne method. In this thesis, the main experimental structure consists of the Mach-Zehnder interferometer and broad band source in the optical fiber communication wavelength range. The characterization is divided into two parts - the low coherence interferograms and linewidth measurement. The optical low coherence interferometry (OLCI) is composed of the Mach-Zehnder structure and low coherence light source, and its interferogram Ringdown from the MRR could be utilized for biosensing applications. The interferogram Ringdown could be analyzed to detect the spatial shifting between different orders and various analyte concentrations using Gaussian curve fitting. The sensitivity can demonstrate 10.21μm⁄μM. The linewidth measurement uses the electrical spectrum analyzer (ESA) for a higher frequency resolution from the delayed Self-Homodyne compared with the optical spectrum analyzer (OSA). The sensing is performed by the linewidth change with ambient refractive index variation through the cascaded wave from the fiber Bragg grating and MRR. The delayed Self-Homodyne method is to intentionally make two Mach-Zehnder optical path difference larger than the input light coherence for two output incoherent waves and then followed by photodetector and ESA. The linewidth variations at various analyte concentrations demonstrate the sensitivity as 0.00191nm/(mg/ml).