G. Joshva Raj

Modeling and evaluation of Radio over Fiber communication systems on employing nanophotonic devices

Radio over Fiber refers to a technology whereby light is modulated by a radio signal and transmitted over an optical fiber link to facilitate wireless access. The present work purports to the modeling of radio over fiber systems in the MATLAB environment on employing specially designed photonic crystal fibers, consisting of subwavelength-core dielectric photonic nanowires embedded in their cladding, as optical channels between the main central station and the set of base stations and silicon photonic based electro-optic modulators. Data transmission at terahertz frequencies using orthogonal frequency division multiplexing schemes with cyclic error control coding along with digital modulation schemes such as amplitude shift keying and binary phase shift keying have been implemented. Different carrier signals such as solitons, similaritons, square, and sine waves are considered. In simulating the radio over fiber system, three different media are considered. In the first stage of signal propagation, photonic crystal fibers embedded with photonic nanowires in their cladding are considered and signal propagation through them is numerically modeled using the predictor-corrector symmetrized split step Fourier method. In the second stage, electrical transmission lines that are modeled as microstrips using S-parameters are considered. In the last stage of signal propagation, wireless channel modeled using additive white Gaussian noise and multipath fading, is considered. The performance of the aforementioned communication system is reviewed using standard metrics such as bit error rate and eye diagrams. It is shown that solitons are more robust carriers for terahertz communications compared to the other carriers and that it is possible to achieve a relatively distortion free communication system even amidst the worst possible SNR levels.

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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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.

Core Photonic Crystal Fiber

We theoretically demonstrate a highly sensitive sea water salinity sensor using photonic crystal fiber employing modualtional instability technique. The sensitivity of the proposed sensor is calculated as 13.33 nm/PPT.

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

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.

Sea water salinity sensor based on modulational instability technique using 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

The effect of two zero dispersion on the supercontinuum generation in CS2 cored photonic crystal fiber has been studied by investigating the interaction among Raman effect, third order dispersion and different dispersion slopes. It has been observed that two zero dispersion wavelengths (TZDW) of the proposed photonic crystal fiber can be utilized to effectively tailor the characteristics of supercontinuum generation.

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

Effect of chirp on SCG in liquid filled PCF with two zero dispersion wavelengths is investigated. The impact of chirp is found to be stronger in liquid filled PCF than solid core PCF.