Research Interest
Photonic Bandgap Structures
Photonic bandgap structures are formed artificially by creating a periodic variation of refractive index on a silicon substrate, for example by creating holes. The stop and pass bands are controlled by the structure parameters. Extensive simulations of the PBG characteristics are done using finite-difference time domain (FDTD) method. By creating defect strucutres like line and point defects we studied devices such as bends, couplers, resonators, filters, etc. Coupled cavities are also studied which proved to be more functional and compact. As part of national program on smart materials and structures (NPMASS) we undertook fabrication and experimental study of PBG structures for application to optical communications. Similarly under national program on micro optics and nano-photonics we undertook sensor applications. In both cases we fabricated a micro ring resonator of PBG using the facilities at CeNSE.
Fiber Optic sensors
Fiber optic gyroscope is one of the practical devices needed in inertial navigation applications. In our lab we initiated the development of all fiber and integrated optic gyroscopes. We also studied the effect of fiber-coil and the magnetic field on the performance of FOG. We are proud to mention that our FOG is deployed in strategic applications of our country. Fiber Bragg Gratings (FBG) form very sensitive sensors. They are sensitive to external perturbations like pressure and temperature through the grating parameters like pitch and refractive index profile. We studied FBG sensors and arrays for application to Aerospace structures. One of the issues is to extract the information from the composite spectrum detected. Another issue studied is to isolate the strain and temperature information. New interrogation system based on design of novel refractive profile is suggested. Several FBG Sensors are studied such as magnetic field sensors, current sensors and chemical sensors.
Optical Networks
QoS policies implemented in IP does not apply for Wavelength division multiplexed (WDM) or optical burst switched networks, as the optical counterpart for store-and-forward model does not exist. Hence there is a need to provision QoS over optical networks. We propose an impairment-aware algorithm to provide many-casting service in the optical layer, specifically OBS. We compare the performance of our proposed many-casting algorithm with traditional multicasting and multicast with over provisioning. Our results show a significant improvement in the blocking probability by implementing optical-layer many-casting. Fiber-optic code-division multiple-access (FO-CDMA) techniques are very useful for high-speed access network. Constructions of 2-D codes, suitable for incoherent wavelength/time (W/T) FO-CDMA, have been proposed to reduce the time spread of the 1-D sequences. We have also analysed the performance of the W/T Multiple pulses per row (MPR) codes considering multiple access interference as the main source of noise. We have compared cardinality and spectral efficiency of the codes with other W/T codes.
Bio-sensor applications
The analysis of a fully integrated optofluidic lab-on-a-chip sensor. This device consists of collinear input and output waveguides that are separated by a microfluidic channel. When light is passed through the analyte contained in the fluidic gap, optical power loss occurs owing to absorption of light. Apart from absorption, a mode-mismatch between the input & output waveguide occurs when the light propagates through the fluidic gap. The degree of mode-mismatch and quantum of optical power loss due to absorption of light by the fluid form the basis of our analysis. This sensor can detect changes in refractive index and changes in concentration of species contained in the analyte. The sensitivity to detect minute changes depends on many parameters. The parameters that influence the sensitivity of the sensor are mode spot size, refractive index of the fluid, molar concentration of the species contained in the analyte, width of the fluidic gap, and waveguide geometry. By correlating various parameters, an optimal fluidic gap distance corresponding to a particular mode spot size that achieves the best sensitivity has been determined both for refractive-index and absorbance-based sensing. We also studied device like ring resonators over which bio fluids are applied as a cladding layer. In another application a MRR is used as a wrist pulse pressure sensor. Experimental work on these devices is also attempted.
Microwave Photonics
Microwave photonic combines the application of microwave techniques to optical communications & optical techniqees to RF & microwaves.Two application areas are antenna bram forming and high speed optical modulation. We analysed curved integrated optic waveguides to achieve microwave phase-shifts. Using electo-optic switches to join these curved waveguides we obtain switched delay line useful for antenna beam forming and beam steering. Using interference of closely spaced laser frequencies in optical waveguide couplers we create high speed modulators like BPSK and QPSK.
Integrated optic Micro ring resonators
Integrated optic ring resonators consist of optical waveguide in the form of ring, supported by a straight bus waveguide for input-output coupling. Resonant characteristics of MRR make them attractive for applications like filters and multiplexer/demultiplexer in optical communications and sensors. We analysed various characteristics of MRR and observed improved features in new configurations like double ring configuration and embedded double ring. The non-uniform coupling between the bus and the ring is analysed. A 12 channel mux/demux based on integrated optic microring resonator is demonstrated. Configurations that act as optical gates are worked out. Combining MRR with MEMS provides interesting applications. As an example we analysed a pressure sensor with MRR on a circular diaphragm..
Micro-opto-electro-mechanical systems
MOEMS combine integrate optics with MEMS structures. We have conventional optical devices like waveguides, directional couplers and Mach-Zhender interferometers on mechanical structures like diaphragms and cantilever beams. We studied devices that perform the function of pressure, vibration and acceleration sensors. In a particular case we used a non-uniform proof mass to improve the sensitivity of an accelerometer.
Fiber Optic sensors
Fiber optic gyroscope is one of the practical devices needed in inertial navigation applications. In our lab we initiated the development of all fiber and integrated optic gyroscopes. We also studied the effect of fiber-coil and the magnetic field on the performance of FOG. We are proud to mention that our FOG is deployed in strategic applications of our country. Fiber Bragg Gratings (FBG) form very sensitive sensors. They are sensitive to external perturbations like pressure and temperature through the grating parameters like pitch and refractive index profile. We studied FBG sensors and arrays for application to Aerospace structures. One of the issues is to extract the information from the composite spectrum detected. Another issue studied is to isolate the strain and temperature information. New interrogation system based on design of novel refractive profile is suggested. Several FBG Sensors are studied such as magnetic field sensors, current sensors and chemical sensors.