Browsing by Author "Siddiqui, Muhammad Zain"

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Enhancing polarization maintenance and spectral filtering in negative curvature hollow-core fibers
(Elsevier BV, 2023-12-09) Siddiqui, Muhammad Zain; Akosman, A. E.; Ordu, Mustafa
A new design of polarization-maintaining and spectral filtering negative curvature hollow-core fiber tailored for the telecommunication bands in the near-infrared region is presented. The optical fiber, consisting of a six-tube silica structure, incorporates vertically nested tubes anchored radially by a pole structure. By contrast, standard nested tubes in the horizontal direction form the asymmetric fiber structure, which encounters birefringence. This unique fiber design not only preserves the polarization states of light but also exhibits frequency selective transmission exclusively in the vertical direction due to the pole structure. Through fiber design optimization, a transmission loss below 0.1 dB/km for spectrally filtered wavelengths is achieved, with birefringence on the order of 10−5 within the wavelength range of 1.45 µm to 1.60 µm. These results demonstrate significant improvements in terms of birefringence, distinct loss separation between horizontally and vertically polarized states, and a reduced number of spectrally filtered wavelengths compared to previously reported findings. The proposed fiber design holds untapped potential for applications requiring selective transmissions with specific polarization.
Open Access
Passive polarization filtering in negative curvature hollow-core fibers
(SPIE - International Society for Optical Engineering, 2023-10-05) Siddiqui, Muhammad Zain; Akosman, A. E.; Ordu, Mustafa; Yin, Shizhuo; Guo, Ruyon
A novel negative curvature hollow-core fiber (NCF) design is proposed capable of spectral and polarization filtering in the near-infrared region. The designed six-tube silica-based NCF contains nest elements in the form of suspended tubes radially anchored with a pole to the outer cladding in the vertical direction. In contrast, standard nested cladding elements without any suspension are used through the horizontal axis. This fiber configuration introduces an asymmetry in the core, which helps maintain the orthogonal X and Y polarization states in the fiber core. Pole anchors in vertically positioned tubes only give rise to the spectral filtering confinement loss profile for a vertically polarized state. Based on the geometrical optimization of the fiber, we achieved an improved birefringence on the order of 10-5 with filtered wavelength losses below 0.01 dB/km in the wavelength range of 1.4 µm to 1.7 µm. The operational bandwidth, polarization extinction ratio, filtered wavelengths, birefringence, and modulation depth loss can be tuned by optimizing the fiber parameters, including outer tube thickness, nest tube diameter, and pole dimensions. This proposed fiber design with selective transmission spectrums has untapped potential sensing capabilities in hollow-core negative curvature fibers. © 2023 SPIE. All rights reserved.
Open Access
Polarization maintaining and spectral filtering properties of hollow-core optical fibers for near-infrared region
(2024-08) Siddiqui, Muhammad Zain
Negative curvature hollow-core fibers (NCFs) offer attractive properties like ultralow losses, broad bandwidth, low latency, low nonlinearity, and a high damage threshold. Additionally, NCFs can overcome the inherent optical transparency limitations posed by solid-core fibers, which restrict their application to specific wavebands, thus enabling more flexible usage of NCF. These qualities make NCFs suitable for their utilization as polarization-maintaining (PM) fibers. In this thesis, the PM properties of NCFs are investigated through two different design approaches. In the first part of the thesis, a new design of polarization-maintaining and spectral filtering NCF tailored for the telecommunication bands in the near-infrared region is presented. The optical fiber, consisting of a six-tube silica structure, incorporates nested tubes anchored radially by pole structures in the vertical direction. Meanwhile, in the horizontal direction, nested tubes without pole anchors are employed, making the fiber structure asymmetric, which encounters birefringence. This unique fiber design not only preserves the polarization states of light but also exhibits frequency selective transmission exclusively in the vertical direction due to the pole structure. Through numerical modeling, transmission losses below 0.1 dB/km for spectrally filtered wavelengths are achieved, with birefringence on the order of 10−5 within the spectral range of 1.45 μm to 1.60 μm. These results demonstrate significant improvements in terms of birefringence, distinct loss separation between horizontally and vertically polarized states, and a reduced number of spectrally filtered wavelengths compared to previously reported findings. The proposed fiber design holds untapped potential for applications requiring selective transmission with specific polarization. The second part of the thesis focuses on the effect of ellipticity on the polarization maintaining performance of NCFs. The nested tube NCF is stretched vertically and compressed horizontally with the same ellipticity of 5%, 8%, and 10% to introduce ellipticity through the entire cross-section of the fiber. Through these modifications, the fiber successfully exhibits orthogonal polarization states compared to the original fiber with no ellipticity. Further investigations into the fiber with 8% ellipticity involve coupling it with bi-thickness (t1 and t2) and a manipulated nested tube diameter (dnx) along the horizontal axis of the fiber. The findings reveal that ellipticity has a limited effect on the improvement of the birefringence and polarization extinction ratio (PER) in NCFs, but it can be used as a complementary fine-tuning process. This suggests that ellipticity has the potential to be utilized as an additional mechanism for enhancing the overall polarization-maintaining characteristics of NCFs.