Showing papers on "Tilt (optics) published in 2022"

Low-Frequency Oscillations in Quantum Cascade Lasers With Tilted Optical Feedback

Abstract: Quantum cascade lasers are highly stable against optical feedback, where the reflection mirror is well aligned with the optical path. Therefore, it is challenging to produce pulse oscillations in quantum cascade lasers through normal optical feedback. In this work, we show that tilted optical feedback with a misaligned reflection mirror triggers quantum cascade lasers to generate low-frequency oscillations, including irregular pulse oscillations and square wave oscillations. The oscillation period is in the microsecond range, and generally decreases with increasing tilt angle. In addition, the duty cycle of the square waves is tunable through varying the tilt angle. It is also found that a weak feedback strength or a low pump current yields rare occurrence of the pulse oscillations.

Theoretical and experimental analysis of second order Bragg resonance of 45° TFG and its fiber laser application

Abstract: We report the observation of second order Bragg resonance (2nd-OBG) produced by tilted fiber gratings (TFGs) fabricated using phase mask UV inscription. The theoretical analysis has revealed that the generation of high order Bragg resonance of gratings is induced by a square-shape refractive index profile, which is caused by over-saturated UV exposure. In the experiment, we have studied the TFGs with different tilt angles under over-saturated UV exposure, in which all gratings have showed the 2nd-OBR, and the larger tilt angle of the grating has the stronger 2nd-OBR. When the tilt angle of the grating is ∼45°, the Bragg resonance exhibits very strong polarization dependence, because the 2nd-OBR wavelength is located within the polarizing bandwidth of 45° TFG. Finally, we have demonstrated an erbium-doped fiber laser with >99.9% degree of polarization, and, by applying mechanical stretching on the grating, a wavelength tunable laser output has been achieved. The output laser shows ∼0.2 dB amplitude variation within 1 h continuous monitoring of the laser.

Gender Based HRV Changes Occurring in ANS During Graded Head-Up Tilt and Head-Reverse Tilt

Abstract: The tilt table test was performed on 20 healthy individuals, who voluntarily participated in this study, out of which the data of 19 volunteers has been used to determine the gender related differences occurring in HRV because 1 volunteer was making movements and was continuously talking. The selected subjects were in the age ranging from 20 to 30 years and had a mean age of 23.894 ± 2.183 years. The subjects considered for this study were B.Tech and M.Tech students of NIT Jalandhar. The individuals considered in this study are all Indians belonging from different states. The tilt table test was performed at different angles of tilt which were 0°, 20°, 40°, 60°, 40°R, 20°R, and 0°R. The data was recorded in the biomedical instrumentation lab, NIT Jalandhar, which was later analyzed and assessments were drawn out between males and females. The study aimed to investigate the effect of gender on HRV using tilt table testing particularly head-up tilt and head-reverse tilt. The frequency-domain indices were calculated and comparison graphs were made to illustrate the changes occurring in HRV of men and women at different tilt angles. Frequency-domain analysis conveys how the energy of a signal is distributed over a range of frequencies. The tilt table was not brought back to 0° after every recording session at every angle, which means the angles were continuously increased after acquiring data for 7 min per specified degree tilt. The results convey that the sympathetic activity increases during head-up tilt and the parasympathetic activity takes over during head-reverse tilt. The outcome of this study demonstrates that healthy females in the age group of 20–30 years have sympathetic dominance at different angles of tilt, whereas healthy males of the same age group illustrate parasympathetic dominance at different tilt angles.

Equilibrium tilt of slippery elliptical rods in creeping simple shear

Abstract: It is shown that shape anisotropy and intrinsic surface slip lead to equilibrium tilt of slippery particles in a creeping simple shear flow, even for nearly shape-isotropic particles with a cross-section that is close to circular provided the Navier-slip length is sufficiently large. We study a rigid particle with an elliptical cross-section, and of infinite extent in the vorticity direction, in simple shear. A Navier-slip boundary condition is imposed on its surface. When a Navier-slip length parameter , so the range of Navier-slip lengths allowing equilibrium tilt shrinks as shape anistropy is lost. Novel theoretical connections with equilibria for constant-pressure gas bubbles with surface tension are also pointed out.