We propose a new polarization splitter (PS) based on Ti and liquid infiltrated photonic crystal fiber (PCF) with high birefringence. Impacts of parameters such as shape and size of the air holes in the cladding and filling material are investigated by using a vector beam propagation method. The results indicate that the PS offers an ultra-short length of 83.9 μm, a high extinction ratio of −44.05 dB, and a coupling loss of 0.0068 dB and at 1.55 μm. Moreover, an extinction ratio higher than −10 dB is achieved a bandwidth of 32.1 nm.

A novel cyclic olefin copolymer (COC)-based polymer optical fiber (POF) with a rectangular porous core is designed for terahertz (THz) sensing by the finite element method. The numerical simulations showed an ultrahigh relative sensitivity of 89.73% of the x-polarization mode at a frequency of 1.2 THz and under optimum design conditions. In addition to this, they showed an ultralow confinement loss of 2.18 × 10⁻¹² cm⁻¹, a high birefringence of 1.91 × 10⁻³, a numerical aperture of 0.33, and an effective mode area of 1.65 × 10⁵ μm² was obtained for optimum design conditions. Moreover, the range dispersion variation was within 0.7 ± 0.41 ps/THz/cm, with the frequency range of 1.0–1.4 THz. Compared with the traditional sensor, the late-model sensor will have application value in THz sensing and communication.

We propose a rectangular liquid-infiltrated dual-core polymer optical fiber (POF) for short-range communication systems by the beam propagation method (BPM). The POF multi/demultiplexer (MUX/DEMUX) at the wavelengths of 0.52/0.65-μm, 0.57/0.65-μm, and 0.52/0.57-μm are devised. The simulation results demonstrate that the ultrashort length of three ultrashort POF couplers are 183.6 μm, 288 μm, and 799.5 μm. Compared with the conventional optical fiber couplers, these results could have significant applications in the miniaturization of optical devices for visible light communication.

A passively Q-switched mode-locked all-solid-state Tm:CaYAIO₄ (Tm:CYA) laser with a MoS₂ saturable absorber is demonstrated for the first time. Employing a typical X-type cavity and output coupling mirror of 9%, when the laser diode pump power is higher than 8.5 W, the laser enters into a stable Q-switched mode-locked operation, further increasing the pump power into a dual-wavelength operating state; the corresponding typical center wavelengths are 1,863 and 1,877 nm. When the pump power reaches 20 W, the maximum output power is 1.15 W, the frequency of mode-locked pulse is 103.7 MHz, and the modulation depth of mode-locked pulses in the Q envelope is close to 100%. The results prove that MoS₂ saturable absorber is suitable for 2-μm high-power mode locking.