Study on the high birefringence and low confinement loss terahertz fiber based on the combination of double negative curvature and nested claddings

A novel double negative curvature nested fiber structure is designed by adding extra circular cladding tubes to enhance the birefringence and reduce the confinement loss. The fiber structure is composed of eight circular cladding tubes and two semi-elliptical nested tubes. The transmission performances of terahertz fiber, including birefringence, confinement loss, dispersion and effective mode field area, are studied by changing the parameters of cladding tubes. In the frequency range of 1.75 - 2.6 THz, the broad bandwidth of 850 GHz with high birefringence (above 10-4) can be achieved. The confinement loss of y-polarization mode with the frequency of 2.575 THz can be as low as 0.00231 dB/cm. The waveguide dispersion coefficient is between ±0.188 ps/(THz•cm) in the frequency range of 2.0 - 2.475 THz. The maximum effective mode field area of x- polarization mode is 2.618×10-6 m2 at 2.6 THz.

Design and Optimization of 1.55 μm AlGaInAs MQW Polarization Mode Controllers

A 1.55 μm AlGaInAs multi-quantum-well (MQW) ridge waveguide polarization mode controller (PMC) is proposed. The design is based on an asymmetric half-ridge waveguide structure in which the ridge is shallow etched on one side and has a deeply etched mesa structure on the other side. The Finite-Element Method (FEM) was used to simulate the PMC and optimize its structural parameters comprehensively. Furthermore, the fabrication tolerances were also investigated in detail. The optimized PMC has a polarization conversion efficiency (PCE) of around 92.5% with a half-beat length of 1250 μm. When the PMC length was fixed at 1250 μm, to achieve a PCE derivation less than 8%, the tolerances for the ridge waveguide width and shallow etch height were 1.60 μm to 1.65 μm and 2.13 μm to 2.18 μm, respectively. In order to reduce interband gap absorption loss, the quantum well intermixing (QWI) technique was used in the model to realize a blueshift (200 nm) in the PMC. QWI is a simple, flexible, and low-cost technique for fabricating a PMC integrated with a laser diode and reduces parasitic reflections, which would otherwise degrade the overall performance. QWI also eliminates MQW material anisotropy and alleviates the birefringence effect without the need for regrowth, achieving nearly uniform properties as a bulk material.

Simulation of Birefringence and Polarization Mode Dispersion Characteristics in Various Commercial Single Mode Fibers

Single mode optical fiber operation for long haul distance communication media has rapidly developed. Several efforts are implemented to reduce and control the attenuation and absorption of signal propagation. However, fiber parameters still experienced interference with internal and external factors that result birefringence and polarization mode dispersion such as bending power losses, signal widening and increasing wavelengths. In order to reduce and optimize the interference which is experimentally difficult to demonstrate because of the very long fibers hence a numerical simulation is set with perspective of twisted fiber disorder as a function of wavelengths and fiber geometry. The simulation evaluates the various refractive indices, radius of fibers and wavelength sources. The quality of optical fiber interference can be identified from the twisted power losses values with different variations of twisted radius. This model obtained indicates the greatest power losses occurring as a function of radius, refractive indices and wavelength. The results show that normalized frequency value has important role in determining the effectiveness the optical fiber performance and stability of power deliver. The addition of wavelength can affect the fibers experiencing birefringence and polarization mode dispersion occurring at wavelength of telecommunication regimes.

Technical specifications and spectral performance characteristics of dispersion flattened fiber (DFF) in optical fiber systems

This work has clarified the technical specifications and spectral performance characteristics of dispersion flattened fiber (DFF) in optical fiber systems. Effective nonlinear refractive index and first, second order polarization mode dispersion against spectral wavelength with fiber length of 1000 m and coupling length of 20 m are simulated and demonstrated. Total DFF fiber losses/dispersion performance parameters are investigated and simulated by using OptiFiber simulation. Zero DFF fiber dispersion and its dispersion slope are demonstrated clearly in details. The dominant modes and the cutoff data theoretical values based these modes for the proposed DFF fiber is determined and simulated in a clear manner.