Krishnamoorthy Pandiyan

Dip coated TiO2 nanostructured thin film: synthesis and application

TiO2 thin film was fabricated by dip coating method using titanium IV chloride as precursor and sodium carboxymethyl cellulose as thickening as well as capping agent. Structural and morphological features of TiO2 thin film were characterized by X-ray diffractometer and field emission scanning electron microscope, respectively. Crystallinity of the film was confirmed with high-intensity peak at (101) plane, and its average crystallite size was found to be 28 nm. The ethanol-sensing properties of TiO2 thin film was studied by the chemiresistive method. Furthermore, various gases were tested in order to verify the selectivity of the sensor. Among the several gases, the fabricated TiO2 sensor showed very high selectivity towards ethanol at room temperature.

A systematic approach for designing quasi-periodic optical superlattices using the Hadamard matrix

We propose a novel and systematic approach for constructing quasi-phase-matched grating structures using the Hadamard matrix. Using this new approach, we have exploited the efficacy of the Hadamard matrix in quasi-phase matching technology, by comparing the second-harmonic spectral response with the corresponding power spectra of the Hadamard matrix. We have successfully identified various existing quasi-periodic optical superlattices from different columns of the Hadamard matrix. On employing our framework, we further indicate a systematic method for constructing various new quasi-periodic optical superlattices.

Optimization of Multi-QPM SHG using Simulated Annealing

We exploited the efficacy of SA algorithm in QPM technology to generate multi-QPM SHG. Various SHG controlling parameters of the algorithm includes temperature, perturbation size and choice of the domains for different peak-profiles are discussed.

Effect of Phase-Shifter Domains in Quasi-Phase Matching Devices

With the inception of Quasi-Phase Matching (QPM) technique, there has been a wide interest by the researchers to utilize the concept of domain engineered superlattices structures in optical networking. We present a theoretical approach to study the effect of phase-shifter (PS) domains in engineered optical superlattice structures and analyze the second harmonic spectral response. QPM device with PSs is the easiest approach to generate multiple and tunable second harmonic spectrum to utilize the same in optical communication system.

Studies on the effect of duty cycle variation in Fibonacci-based quasi-phase matching devices

Abstract We have studied the effect of duty cycle variation in the Fibonacci optical superlattice (FOS) structure by analysing the second harmonic generation (SHG) spectrum. Unlike periodic quasi-phase matching (QPM) device, the variation in duty cycle changes the SHG spectrum asymmetrically. The higher intensity and other multiple peaks in the spectrum change asymmetrically when the duty ratio varies away from 0.5. As a result, the SHG spectrum of lower and higher duty ratios from the ideal FOS device generates multiple dissimilar peaks as it was observed from entirely different QPM devices. However, the main phase matching peak shows symmetric nature, irrespective of the duty cycle variation like the periodic one. Further, we have analysed the correlation spectrum to prove the asymmetric nature of the FOS SHG spectrum. Although FOS device exhibits asymmetric spectral nature in duty cycle variation, it shows the same optical interaction regardless of the pump direction.

Phase Shifters in QPM Device for Domain Engineering

We have analyzed the role of phase shifter domains in QPM devices for domain engineering. These phase shifter domains are capable of changing the phase of the second harmonics from 0 to 2π. Using this approach, we have generated multiple second harmonic peaks by introducing phase shifter domains of same width at unequal intervals in the periodic optical superlattice structure. Furthermore, we have theoretically analyzed the generation of multiple-QPM and the possibilities to engineer the intensity and bandwidth of the multiple peaks.

Simulated Annealing: An Approach for Multiple QPM

All optical wavelength conversion is made possible with the advent of engineered Quasi-phase matching (QPM) devices. Simulated annealing is an algorithm can be used in QPM technology for designing second harmonic wave of any chosen amplitude and phase profile. In this article, we have used simulated annealing routine for achieving multiple QPM second harmonic generation with equal intensity and channel spacing. Further, the influence of the algorithm temperature and number of crystal domains on designing the multiple channel QPM response is discussed in detail.

Estimation of second harmonic generation efficiency of various quasi-phase matching grating structures

We have analytically calculated the efficiency factor of the second harmonic generation (SHG) in quasi-phase matching (QPM) devices of various periodic grating structures such as square, triangular, sinusoidal, trapezoidal and blazed. The phase profile representing the nonlinear optical coefficient of these grating structures has been mathematically derived and its second harmonic efficiency factors are calculated. The second harmonic conversion efficiency factors of square, triangular, sinusoidal, trapezoidal and blazed QPM structures are calculated to be 0.405, 0.164, 0.25, 0.365 and 1.0, respectively.

Optimizing multiple-QPM in Fibonacci sequence using simulated annealing algorithm

We have analyzed the simulated annealing algorithm in a Fibonacci based optical superlattices to obtain multiple second harmonic generation (SHG) in a single channel Quasi-Phase matching (QPM) device. The Fibonacci sequence itself has plenty of reciprocal vectors to generate multiple-QPM. To arrange the multiple peaks in a desired order, we have introduced simulated annealing algorithm in the Fibonacci based optical superlattices. The parameters such as temperature, perturbation size and choice of domains which are playing key role in designing the multiple peaks are discussed in detail.

Simultaneous Multiple-Color Light Generation Based on Broadband Optical Parametric Generation

Simultaneous red, green and blue lights were generated from periodically poled lithium niobate pumped with single picosecond laser. This process was realized by a broadband design of the optical parametric generation of participating infrared frequencies.