Personal wearable medical devices and sensors have become more popular which results in better resources optimization and a better systematic monitoring or health condition. The ability to extract quantitative information in living cells without actual biopsy (disturbance in the structure of the cell) can be used to study and monitor morphological and physiological changes such as pre-cancerous or cancerous conditions. Basically, light scattered from a cell depends on the size of the cell, structure of the cell and the properties of the incident light. It is also termed as “optical biopsy”. Such Mie scattering based Lab-on-a-Chip (LOC) sensor device if implemented can be used for early diagnosis of terminal diseases such as cancer. Gold nano particle acts as a sensor on this wearable device. Mie scattering based nonlinear optical phenomenon is used for cancer detection. This work involves modelling, simulation and analysis of a nano sensor using Discontinuous Gallerkin Time Domain method (DGTD). Light is used from arbitrary shaped objects at various incident angles. The Mie solution to Maxwell’s equations describes the scattering of an electromagnetic plane wave by a homogeneous sphere. Mie scattering theory has been used to determine whether scattered light from tissue corresponds to healthy or cancerous cell nuclei using angle resolved low coherence interferometry. Gold nanoparticle has been used in biological applications and it is necessary to know the co-efficient of scattering and co-efficient of absorption. Mie scattering has no upper limits with respect to size of the particle.
In this work, silicon nitride (Si3N4) based fluidically tuned photonic crystal for a biosensing application is presented. The optical structure is designed on Si3N4 on insulator. The Si3N4 on insulator substrate is found to be one of the most promising materials for the design of bio- sensor at short wavelength. At short wavelength Si3N4 material is found to be most promising material for optical integrated circuits. The structure of the sensor consists of Silicon nitride input and output waveguides separated by a fluidically tuned photonic crystal. Fluidically tuned photonic crystal acts as a sensing region. The sensitivity is based on refractive index of fluidically tuned photonic crystal. The proposed sensor is designed to operate in the visible wavelength range of 660nm. Fluidically tuned photonic crystal consists of rectangular photonic crystal array. The holes of photonic crystal are approximately 160nm in diameter and height is 200nm. Organic light emitting diode is used as an optical source. OLED is coupled to input waveguide. The PDMS microfluidic channel is moulded on the rectangular photonic crystal structure. The structure is modelled and analysis is carried out by using Lumerical mode solution and Lumerical Finite Difference Time Domain (FDTD) simulation tools. Such devices if fabricated can be employed for early detection of various diseases related to pathological parameters.
A simulation and analysis of a ring resonator-based sensor are presented. The ring resonator structure has two bus waveguides and two rings with a gap between the ring and the ring and bus waveguide. The radius of each ring is designed to be 3.1 μm. The ring resonator is designed such that both rings exhibit resonance at 1550 nm, and it is analyzed at mid-infrared wavelengths between 1500 and 1600 nm. The guided signal is launched through the bus waveguide to determine spectral properties, such as free spectral range and quality (Q-) factor. An improved Q-factor is observed in the simulation results for the optimized design. The improved Q-factor allows us to analyze the ring resonator for use in sensing applications.
In this work, the device is integrated with two bus waveguides and three ring waveguides. The ring and the bus waveguide is designed with a width of 250nm and a height of 400nm is considered. The mid infrared wavelength of 1550nm is considered as an input source for the coupling of light from the bus waveguide to ring waveguide. The coupling between the three ring waveguides is also observed. The multimode coupling takes place in the configuration. The guided mode resonance at 1550nm is observed. The four ports are placed at the inputs and outputs of the bus waveguide. Here the three ring structure with the bus waveguide is analyzed for spectral properties, where quality factor is of main concern. If the structure has to be implemented for a lab-on-a-chip application, sensitivity plays an important role, which in turn is related to the quality factor. Hence the enhancement of the quality factor up to 3000 with three rings is achieved. Two rings are considered as sensing ring for various parameter analyses with one of the ring as reference ring. In the designed structure, the phase shift in the transmission spectrum is observed for the bio-sensing application. The sensor in the ring resonator is based on the refractive index change. The change in the refractive index of the surrounding medium will change the effective refractive index. Hence the effective refractive index along with the group index is monitored for the bio-sensing application. A thin layer on the surface of the waveguide is highly sensitive to refractive index change in the TM mode. The configuration is simulated using Lumerical FDTD as well as Lumerical Mode solutions. The integrated optical devices has a good platform in bio-sensing application, hence the designed configuration can be further incorporated for point of care device.
In this work, modelling and simulation of Organic Photo Detector (OPD) is carried out using Finite difference time domain (FDTD) method. By interposing photonic crystals into the OPD, the electric field intensity is significantly enhanced compared to conventional photo detectors. The optical effects such as power absorption is observed by interposing water soluble conjugate polymer layer such as poly(9,9-bis(3’-(N,N-dimethylaminopropyl)-2,7-fluorene)-alt- 2,7-(9,9 dioctyl fluorene)] (PFN) as interlayer into the OPD device structure. Propitious research work is being carried out aiming at increasing the power absorption of OPD. This work proposes an alternative OPD using Gaussian source. The light excitations generates an electron-hole pair increasing the carrier’s density. The resulting electrons in the conduction band and the holes in the valence band can be drifted by an electric field, generating a current. This OPD device has very thin active organic layer less than 100nm. The Photonic Crystal (PC) used in the design has rectangular lattice structure with height of 120nm and width of 350nm. The Finite Difference Time Domain (FDTD) method is used for solving Maxwell’s equations in complex multi stack geometries. FDTD calculates the E and H fields everywhere in the computational domain (evolves in time domain), it provides animated displays of the electromagnetic field movement through the OPD model. The short circuit (Jsc) current obtained for the proposed OPD for with and without water soluble conjugate polymer placed above the emissive and incorporating PC in the device. This ensures high detectivity of the organic photo detector device.
In this work, a ring resonator is designed with two rings for the sensing application. The waveguide is designed with 400nm wide and 180nm high. Both the rings are designed with 3.1μm radius each. The straight waveguide couples with the ring at 1550nm wavelength. The mode profiles and the spectrum of resonances are observed at mid- infrared wavelength, 1550nm. The measurements of the mode profile, refractive index and spectral properties of the design facilitate to monitor and modify the optical properties of the ring resonator structure. The phase shift in the resonance is observed, which can be implemented in the design of the sensor based ring resonator. In sensing applications the small size of ring resonator plays an important role, the interaction length of ring resonator with few tens of centimeters or even longer gives better sensing performance. Ring resonator offers enhanced light intensity near its surface with the enhancement being proportional to the Q-factor, which is due to the circulating nature of the resonant light. The coupling between the straight waveguide and the ring at 1550nm wavelength and is simulated using Lumerical FDTD. In optical sensors, a thin layer is attached to one of the ring surface, to observe the phase shift in the resonance. Since the refractive index of the thin layer on top of the ring structure is different from the surrounding medium which is typically water based, a change of index happens at the surface of the sensor which is measured for detecting the presence of additional layer in the cover medium. Hence the ring resonator structure can be implemented for bio-sensing application.
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