Balaji Srinivasan

In this paper we present a novel, practical approach for carrying out distributed high temperature sensing in boilers. We have demonstrated distributed high temperature sensing using fiber Bragg gratings encapsulated inside a rugged mechanical structure. The encapsulation is designed to not only protect the optical fiber from the harsh environment of the boiler, but also to scale the temperature down to a range over which the gratings are relatively stable. A key aspect of our work is the use of a Bayesian inference technique to retrieve the temperature outside the encapsulation within < 1°C accuracy based on the temperature measured by the fiber Bragg grating (FBG).

Ultrasonic wave visualization is an effective tool to identify defects along with their location and topology in guided wave structural health monitoring applications. However, conventional imaging techniques require relatively longer data acquisition time and large storage space. Reconstructing waves from sparse sampled images can potentially overcome such difficulties. In this regard, sparse sampling techniques based on random sampling and uniform sampling are explored in this paper. Specifically random sparse sampling using Poisson disk with biharmonic interpolation (PDS-BI) technique is shown to achieve defect identification with an image sparsity of 95% and a sensor density of [Formula presented]. On the other hand, a novel technique based on uniform sparse sampling with carrier multiplication (US-CM) is demonstrated to reconstruct the image with a sparsity of greater than 98% and a sensor density less than [Formula presented]. The performance of the proposed techniques has been quantified using Structural Similarity (SSIM) metric and validated through experiments. The reconstructed images are found to be in good agreement with those obtained by a dense array with much larger number of receivers. We also experimentally demonstrate the visualization of ultrasonic wave propagation in a metallic plate using a surface-bonded fiber Bragg grating sensor as an alternative to the conventional sensor.

We experimentally study the time-dynamics of passive self-mode locking phenomena in a Thulium-doped fiber ring laser operating at ∼ 1976 nm wavelength pumped with 1550 nm.

We report the development of a model that predicts the decay of fiber Bragg gratings based on growth data and validate the same using experimental data obtained from accelerated aging studies. © 2010 Optical Society of America.

We experimentally demonstrate visible light communication (VLC) with PPM modulated 532 nm DPSS laser for link loss upto ~78 dB while supporting bit rates up to 120 kbps and BER better than 1e-6.

We present a fiber Bragg grating based scheme for sensing partial discharges in power transformers. The FBG sensor is implemented to detect changes in temperature for sensing corona breakdown in a controlled test bed.

Delamination in composite structures is characterized by a resonant cavity wherein a fraction of an ultrasonic guided wave may be trapped. Based on this wave trapping phenomenon, we propose a baseline-free statistical approach for the identification and localization of delamination using sparse sampling and density-based spatial clustering of applications with noise (DBSCAN) technique. The proposed technique can be deployed for rapid inspection with minimal human intervention. The Performance of the proposed technique in terms of its ability to determine the precise location of such defects is quantified through the probability of detection measurements. The robustness of the proposed technique is tested through extensive simulations consisting of different random locations of defects on flat plate structures with different sizes and orientation as well as different values of signal to noise ratio of the simulated data. The simulation results are also validated using experimental data and the results are found to be in good agreement.

We demonstrate all-optical clock recovery from optical NRZ-PM-QPSK and NRZ-PM-16QAM data at 10 Gbaud after 60 km fiber propagation, through injection-locking of an Erbium-doped fiber laser.

We report our investigations on the influence of line broadening schemes on the visibility of the coherently combined laser beams.

We present a numerical approach for analysing simultaneous amplification and compression of a chirped hyperbolic secant soliton using a tapered Yb-doped photonic crystal fiber (PCF) based self-similar compressor. Theoretical studies reveal the conservation of input soliton during the amplification process due to self-similar property, which in turn helps for high quality compression of amplified soliton. In order to satisfy the self-similar condition, we note that the Yb-doped fiber should exhibit a decreasing group velocity dispersion (GVD). Such a constraint is met using a tapered PCF in our work, which is modeled using a fully vectorial effective index method (FVEIM). Influence of spatial and spectral dependent gain, saturation energy, amplified spontaneous emission (ASE), dispersion and nonlinearity on pulse propagation are analyzed using the combined solution of dynamic rate equations (DRE) and the generalized nonlinear Schrödinger equation (GNLSE). Numerical outcomes upon solving the aforementioned equations show that a 1 ps pulse is compressed down to a pulsewidth of 55.4 fs with a peak power of 1.03 kW in a total fiber length of L=2.5 m and taper ratio of 2.34. Overall quality of the compression scheme is evidenced by a relatively high compression factor (Fc)=18.12, and low percentage of pedestal energy (PE)=10.95 %