R. Vasantha Jayakantha Raja

Effect of Temperature on Supercontinuum Generation in Water-Core Photonic Crystal Fiber

We study the temperature-dependent features of nonlinear pulse propagation in a water-core photonic crystal fiber, which are found to significantly impact the process of supercontinuum generation (SCG). After solving the temperature-dependent fiber parameters, we model pulse propagation with a modified nonlinear Schrödinger equation. The subsequent generated supercontinuum displays a spectral bandwidth that strongly depends on the temperature varied between 55 °C and 75 °C. This could represent an original way to tune SCG, or conversely, make the basis of a temperature sensor.

Tunable Broadband Spectrum Under the Influence of Temperature in IR Region Using CS

We theoretically demonstrate a bandwidth tunable broadband light spectrum in IR region, using a CS2 core photonic crystal fiber (CSPCF) by varying its temperature. The broadband spectrum is generated via modulation instability (MI) induced supercontinuum (SC) generation process by considering the thermooptic coefficient of CS2 liquid. The temperature-dependent fiber parameters are utilized to solve the nonlinear Schrodinger equation, which is modified with the effect of saturable nonlinearity of CS2. By using numerical simulation, generation of new photons through the process of MI and subsequent evolution of SC spectrum are analyzed under the influence of temperature. The generated SC spectrum shows a variation of a several hundred nanometers in its bandwidth with a change of mere 20 °C in the temperature of CSPCF. It is found that the bandwidth of SC spectrum can be tuned from 688 nm to 1022 nm by varying temperature, saturable parameter, and pump power. The proposed tunable SC spectrum finds application in IR spectroscopy, optical coherence tomography, etc.

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We investigate the nonlinear dynamics and steering performance of structurally asymmetric triple-core photonic crystal fiber (ATPCF) for the accomplishment of efficient all-optical logic gates. We study two kinds of ATPCF, one with planar and the other with triangular core setting. The effective mode indices are obtained through the finite element method. The dynamics and steering characteristics of ATPCF are numerically explored via coupled nonlinear Schrodinger equations. The extinction ratios for the various logic gate operations are determined in the presence of suitable control signal. ATPCFs are found to demonstrate efficient logic gate operation; in addition, they highlight the practical issue of geometrical tolerance in PCF design.

Core Photonic Crystal Fiber

We investigate the role of pump power in the generation of supercontinua spectra induced by modulational instability (MI) in saturable nonlinear media (SNL). First, we analyze the dynamics of MI in the SNL using linear stability analysis. We then deal with the generation of a broadband spectrum by virtue of the instability process, and identify the unique behavior of MI in the SNL system. Unlike the case of Kerr-type nonlinearity, the so-called critical modulational frequency (CMF) does not monotonically increase, but behaves in a unique way, such that the increase in power increases the CMF up to the saturation power, and a further increase in power decreases the CMF. This behavior is identified to be unusual in the context of MI and thus makes the study of MI and supercontinuum generation (SCG) of interest. In order to confirm the above stated behavior in relation to SCG, we numerically analyzed the SCG using a split-step Fourier method, and the results confirm that at input power equal to saturation power, phase matching occurs at a short distance relative to other power levels and leads to a maximum enhancement of SCG in certain SNL materials.

Impact of structural asymmetry on the efficiency of triple-core photonic crystal fiber for all-optical logic operation

A highly sensitive nonlinear temperature sensor, which is based on modulational instability (MI) process, is theoretically demonstrated for the first time using a CS2-filled photonic crystal fiber (CSPCF). The proposed novel temperature sensor works on the principle of measurement of a temperature-dependent wavelength shift of generated Stokes and anti-Stokes MI Sidebands. Based on the notion of MI dynamics, the performance of the proposed temperature sensor is studied in both anomalous and normal dispersion regimes of an appropriately designed CSPCF. It is found that the sensitivity of the proposed nonlinear temperature sensor is very low when the CSPCF is pumped in the anomalous dispersive region. However, the sensitivity is enhanced by more than 66 times using Stokes line in the normal dispersion regime. The proposed sensor is optimized by varying the structural parameters and pump parameters, such as pitch, air-hole diameter, pump wavelength, and pump power. The proposed nonlinear temperature sensor, which is made up of an appropriate structure of CSPCF having a length of 13 cm exhibits a sensitivity of −82 nm/°C using Stokes line and 435 nm/°C using anti-Stokes line while pumped with a power of 100 W in the normal dispersive region.

Power play in the supercontinuum spectra of saturable nonlinear media

Bandwidth tunability of supercontinuum (SC) spectrum, employing temperature as a control parameter is theoretically demonstrated, using a water core photonic crystal fiber (WPCF). The temperature dependent variation of refractive index is exposed via soliton fission process to show the temperature tunability of bandwidth of SC spectrum. It is found that the spectral width of SC light can be varied between 198 nm to 302 nm in the visible region, by changing the temperature of the WPCF between 55° C to 75° C.

Highly Sensitive Nonlinear Temperature Sensor Based on Modulational Instability Technique in Liquid Infiltrated Photonic Crystal Fiber

The effect of cladding parameters such as air hole size and pitch, on supercontinuum generation in water core photonic crystal fiber is studied numerically. The influence of cladding parameters on the supercontinuum generation is confirmed in water core photonic crystal fiber which exhibit reorientational characteristics of molecules. Variation in the rate of dispersion as a function of airhole size is found to be the reason for modifications of pulse propagation characteristics in the core.

Temperature tunable supercontinuum spectrum in visible region using water-core PCF

A PCF structure that is filled up with chloroform in its core, is optimized for generating broadest possible supercontinuum spectrum which centers at 1310 nm. It has been found that a chloroform filled PCF having airholes of diameter 1.5μm and cladding of pitch 1.2μm is capable producing broadest supercontinuum light at a shorter distance than as silica core PCF can do. The generated supercontinuum can be used as a light source in an optical coherence tomography(OCT) system to detect oral cancer with a resolution of 964 nm.

Effect of cladding parameters on supercontinuum generation in water core photonic crystal fiber

A variety of AS2S3 chalcogenide photonic crystal fiber coupler of special properties are proposed to study the role of birefringence in all optical coupling characteristics based on the projection operator method (POM). The equations of motion describing the dynamics of the individual pulse parameters through x- and y-polarized modes are arrived at by employing POM from the coupled nonlinear Schrodinger equations. From the pulse parameter dynamics, it is observed that the amplitudes of the polarization components are significantly influenced by the pulse being introduced with different polarizing angle even at low input power level. Such a selective polarizing angles of the input pulse will provide efficient control over the desired splitting ratio as well as the ability to decide the desired polarization component.

A novel design of PCF for supercontinuum source to detect oral cancer using OCT

We present an all optical NOT logic operation based on a geometrically asymmetric triangular triple core photonic crystal fiber (ATPCF), where the guiding cores are filled with highly nonlinear liquid chloroform. By employing the finite element method, necessary optical parameters of the proposed geometry are determined. The steering characteristics which attributes the critical power necessary for the control signal is obtained numerically via coupled nonlinear Schrodinger equations. Through extinction ratio calculations, the Boolean operation of NOT logic gate is illustrated with an appropriate control signal. This study accomplish the idea of an efficient NOT logic operation based on ATPCF geometry. As well as provides the sensitive dependence of geometrical asymmetry on input conditions for performing logic operations.