Stimulant abuse enhances dopamine release, thereby causing increased excitation. Any extent of stimulant abuse can considerably harm the user. Thus, methods of detecting stimulants must be precise, accurate, and reliable. A novel terahertz (THz) photonic crystal fiber with a Topas substrate is designed and rigorously investigated for detecting liquid amphetamine, cocaine, and ketamine. The fiber structure has a pentagonal shape and comprises circular air holes in the core and cladding spatial extents. As shown in finite element simulation, the proposed fiber yields a high relative sensitivity of approximately 80 % when any of the liquid stimulants is infiltrated in the core air holes. At 1 THz operating frequency, the proposed fiber produces a large effective mode area, negligible confinement loss, and extremely low bending and effective material losses. Other THz waveguiding properties, such as core power fraction and total loss, are also studied. Lastly, a positive and negative 2 % fabrication tolerance is set to ensure seamless potential practical realization of the fiber.

This manuscript introduces a unique tellurite core-based photonic crystal fiber (PCF) with silica clad and circular air holes, which manifests highly birefringent and non-linear characteristics. Several optical features, such as birefringence (Br), nonlinear coefficients (NLC), dispersion (D), confinement loss (CL), material loss, etc are thoroughly analyzed and explored by applying the finite element method (FEM). The simulated outcomes validate that by optimizing the formation of the cladding region, a large NLC of 7650 W − 1 Km − 1 , as well as an ultra-high Br of 11.2810 − 2 and zero-dispersion can be accomplished in the offered PCF design at 1.56 μm wavelength. Moreover, the evaluated findings indicate that the stated fiber structure is capable of generating a wide supercontinuum spectrum spanning from 943 to 8038 nm when augmented with a 4.5 kW input power and a pulse duration of 20 f s . Calculations and analyses have been carried out on the effects of higher-order dispersion co-efficients, pulse length and input power on spectrum broadening. The advanced PCF design will be a suitable candidate for practical applications in numerous fields, including bio photonics, biomedical imaging, biosensing, spectroscopy and ultra-broadband signal amplification, etc.

A simple active mode-locked erbium-doped fiber (EDF) ring laser is characterized and experimentally demonstrated. The active mode-locked laser can be tuned in the C-band wavelength range 1525 nm to 1565 nm using a tunable bandpass filter placed in the cavity. An intensity modulator placed inside the laser cavity is driven using a sinusoidal signal at different repetition rates. The laser can produce trains of pulses with a width that is controlled using the mode-locking order. The experiments demonstrated an active mode-locked laser that can generate pulse trains with 39 ns width at multiple cavity fundamental frequency of 0.67 MHz repetition rate. Numerical simulations are conducted to investigate the effect of the tunable filter bandwidth and the power of the EDF 980 nm pump on the mode-locking process and produced pulses width.