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We have theoretically demonstrated the simultaneous generation of red (R), green (G), and blue (B) wavelengths by employing the type-0 quasi-phase-matched (QPM) difference frequency generation (DFG) process in congruent LiNbO3 crystal. Various domain-engineered QPM structures are presented and analysed, aiming to achieve an excellent spectral response. The RGB emissions were observed to vary from 632 nm to 656 nm for red, 504 nm to 532 nm for green, and 449 nm to 484 nm for blue, respectively, for different configurations of input pump, operating temperature, and phase matching periods. A maximum shift of about 10 nm to 20 nm was noticed in the spectral position of the DFG peaks when the operating temperature varies from 25 °C to 60 °C. We have also investigated the effect of pump detuning and random domain fluctuations over the phase matching point on the DFG spectrum. Further, we have addressed the advantages of introducing a phase shifter (PS) domain in the periodically poled lithium niobate (PPLN) to produce excellent equal intensity RGB peaks in a single device for their potential application in a laser-based projection display system. [ABSTRACT FROM AUTHOR]

A directional-coupler-based 1 × 1 silicon-on-insulator photonic ON–OFF switch with a complementary metal–oxide–semiconductor (CMOS)-compatible driving voltage is proposed in this paper. The directional coupling of the switch is accomplished by a carrier injection method with the help of a P-i-N diode phase shifter. The advantage of using the directional coupler as a switch is its smaller layout requirement, which makes it more suitable for use in integrated photonic applications. The ON–OFF switch has potential applications in programmable photonic switch fabrics, where the OFF-state behavior is used to prevent the input from being propagated to the output. The proposed switch offers a wide range of cross power-coupling coefficient (κ 2) values, ranging from 0 to 0.3 for the ON-state and from 0.79 to 1 for the OFF-state. The finite-difference beam propagation and two-dimensional (2D) finite-difference time-domain methods are used for photonic simulations. The results are compared analytically using the coupled mode theory with the help of the MATLAB software package. [ABSTRACT FROM AUTHOR]

This article investigates the design of proton‐exchanged (PE) lithium niobate on insulator configurable photonic multiplexer (CPM). The photonic multiplexer includes two 1 × 1 Mach‐Zehnder modulator and a directional coupler. The performance of the proposed multiplexer is investigated by a 2D finite‐difference beam propagation method for the wavelength range of 1530 to 1570 nm. The results show a uniform transmission level for the wavelength range of 1530 to 1570 nm for one of the inputs, and for another input, it shows a uniform transmission level for 1530 to 1544 nm, beyond this range, it shows an attenuation of 0.02 dB/nm. The designed CPM is extended to verify the logical functionalities such as AND, NAND, OR, NOR, XOR, and XNOR for the wavelength of 1300 and 1550 nm. The obtained performance metrics ensure its suitability for large‐scale programmable photonic applications. [ABSTRACT FROM AUTHOR]

We investigate the gas sensing properties of TiO2 thin films prepared by spin coating. The presence of anatase and rutile phases in the sample was confirmed by powder X-Ray diffraction study. The thin film was characterized by FE-SEM and EDAX. The TiO2 thin films were found to have good sensitivity towards ethanol compared to other gases. The sensing studies revealed the ethanol sensing properties of the thin film at room temperature even at lower concentrations. The response and selectivity of the film were also discussed in detail. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Simultaneous generation of red (R), green (G), and blue (B) wavelengths in different grating structures of 5% MgO doped domain engineered LiNbO3 is studied theoretically by employing the type-0 quasiphase-matched (QPM) technique. The spectral output from two cascaded, four segmented, and two-phase shifter (PS) QPM structures using second-harmonic generation, difference-frequency generation, sum-frequency generation, and third harmonic generation were analyzed and interpreted. We observed RGB in the range of 620 to 650 nm, 530 to 580 nm, and 430 to 468 nm for red, green, and blue, respectively, for various configurations of input wavelength, period, device length, segment length, location, and width of the PS domain. The influence of the input pump, operating temperature, pump detuning, PS width, and phase matching periods are analyzed for all the proposed schemes. Fluctuation in the output wavelengths of about 10 to 20 nm was observed due to the temperature variations from 25°C to 150°C in steps of 25°C. Further, the advantages of using a MgO-PS QPM structure over the other proposed schemes have also been addressed for their potential application in a laser-based projection display system. [ABSTRACT FROM AUTHOR]

Domain-engineered quasi-phase-matching (QPM) devices are known for its versatility and ability to tune the nonlinear optical frequency conversion process. In this paper, a simple approach is presented to generate multiple quasi-phase-matched second-harmonic generation (SHG) in the phase reversal optical superlattice (PROS) structure. Theoretical studies are carried out by simulation based on the domain reversed lithium niobate QPM devices. The nature of the generated multiple SHG spectra is analyzed when the phase reversal (PR) domains are distributed at equal and unequal intervals along the length of the device. The distribution of phase reversal domains at equal intervals is limited to the generation of dual SHG peaks irrespective of its number. On the contrary, we could generate equal-intensity multiple SHG peaks with PR domains distribution at unequal interval. Using this scheme, five peaks QPM SHG are generated by distributing four PR domains in specific locations of the PROS QPM device. The dependency of the PR domain and its location in the PROS QPM device are analyzed to design desirable multi-wavelength converters. [ABSTRACT FROM AUTHOR]

We discuss the construction of a low-cost room-temperature electric field poling system and the fabrication of high-quality periodically poled lithium niobate (PPLN) devices. The various poling parameters of the indigenously developed quasi-phase matching (QPM) fabrication facility are studied and optimised for the wastage- / breakage-free device fabrication. Furthermore, we present a simple way to monitor the domain reversal process in the poling system using a crossed polariser arrangement. It has been observed that the pulse-by-pulse poling process is more favourable for monitoring the domain reversal and for estimating the exact poling pulse required for the fabrication of (1 : 1) duty cycle PPLN devices. In addition to the fabrication of PPLN, we further discuss the quality checking of the fabricated devices using a simple far-field diffraction experiment. [ABSTRACT FROM AUTHOR]