Generation of microsecond ytterbium-doped fibre laser pulses using bismuth telluride thin film as saturable absorber

Bismuth telluride (Bi2Te3), a type of topological insulators, is currently in hot pursuit due to its unique physical properties. Therefore, this paper describes a simple Q-switched Ytterbium-doped fiber laser (YDFL) by using Bi2Te3 thin-film as saturable absorber. The few layers Bi2Te3 film was fabricated using optical deposition technique and subsequently, was used in an all-fiber, YDFL setup. As a result, a self-starting Q-switching pulses were first occurred when the laser pumping power reached 88.6 mW. As the pump power level increased, the observed pulses repetition rates had increased steadily from 17 to 29.63 kHz. Hence, this work demonstrated that Bi2Te3 thin-film can be used to successfully generate Q-switching pulses at 1-micron region and is well suited for many photonic applications operated at this wavelength region

Temperature sensor and fiber laser based on optical microfiber knot resonator

An easy method to fabricate microfiber-knot resonator (MKR) is designed and its application as a temperature sensor and multi-wavelength fiber laser (MWFL) is demonstrated. The MKR has a temperature sensitivity of 14.5 pm/°C over a temperature range of 27–95 °C, and experimental results show good linearity between the temperature and resonant wavelength shifts. As an MWFL on the other hand, up to four lasing lines with a channel spacing of 4.29 nm are obtained. These results confirm that the MKR could be employed as a high performance comb filter to realize compact optical sensor and MWFL designs

Single longitudinal mode laser generation using coupled microfiber Mach–Zehnder interferometer filter

The fabrication and operation of a single longitudinal mode (SLM) laser using a compact coupled microfiber Mach-Zehnder interferometer (CM-MZI) in an erbium doped fiber (EDF) laser cavity is demonstrated. The CM-MZI is created by first fabricating an optical microfiber using the flame-brushing technique before being cut and rejoined to form a half-loop, which is the basis for the CM-MZI structure. The CM-MZI is inserted into an EDF laser cavity; the filtering effect of the CM-MZI induces a stable SLM lasing output with a consistent 3 dB bandwidth of 0.02 nm at different a pumping power and signal-to-noise ratio of ∼50 dB. The output also exhibits minimal wavelength and power fluctuations of 0.02 nm and 0.15 dB, respectively, over a time period of 60 min

Highly stable and tunable narrow-spacing dual-wavelength ytterbium-doped fiber using a microfiber Mach–Zehnder interferometer

We describe a successful demonstration of highly stable and narrowly spaced dual-wavelength output via an ytterbium-doped fiber laser. A microfiber-based Mach-Zehnder interferometer and a tunable bandpass filter were both placed into the laser ring cavity for the purpose of ensuring a stable and narrowly spaced dual-wavelength output. Experimental results comprised three sets of dual-wavelength lasing output with wavelength spacing of 0.06, 0.09, and 0.22 nm, respectively, and side-mode suppression ratio of ∼50 dBm. A subsequent stability test provided evidence that maximum power and wavelength fluctuation were less than 0.8 dB and 0.01 nm, respectively, and thus, the obtained output was considered to be highly stable in dual-wavelength operation. The proposed system offers advantages of flexibility in dual-wavelength laser generation in addition to excellent reliability

Analysis of Terahertz (THz) Frequency Propagation and Link Design for Federated Learning in 6G Wireless Systems

Increased throughput demands in emerging services drive a rapid shift from 5G to 6G, posing interdisciplinary challenges in wireless communication stacks. This impacts network modeling and deployment, with AI playing a crucial role. Terahertz (THz) communication spectrum and Federated Learning (FL) gain traction in the 6G paradigm. FL, a decentralized approach, emphasizes data confidentiality and security in wireless networks. The THz spectrum (0.1 to 10 THz) is vital for ultra-broadband wireless systems beyond 5G, offering high data rates. THz waves hold promise for short-distance broadband wireless access, acting as optical network bridges in challenging environments. Despite limited range and penetration, THz technology maximizes spectrum usage, enhancing transmission security. This article offers a concise overview of the Terahertz (THz) spectrum in fixed wireless communication, examining applications and future possibilities. It conducts a thorough analysis, comparing THz with microwave and mm-wave spectra regarding various factors. THz can significantly improve data rates, up to 10 times, reaching 100 Gbps. Spreading loss is around 150 dB within 1 km, doubling to over 300 dB at 2 km. For 300 GHz, it provides a Receive Signal Level (RSL) of −43.57 dBm; increasing path length results in a straight decrease to −56 dB for RSL. These highlights lead to the conclusion that a Terahertz-based network has the potential to enhance convergence time and reduce training loss in Federated Learning, particularly in 1 km links, due to favorable conditions for efficient data transmission. We propose leveraging the largely untapped THz frequency band to enhance FL communication. In the healthcare sector, we introduce FL, relying on a wireless backhaul infrastructure and THz-based wireless backhaul with a Virtual Private Network (VPN). Hospitals are identified as the designated end-users who employ a private network through service providers’ wireless backhaul network to enhance privacy and network efficiency. It establishes the foundation for utilizing THz in 6G wireless backhaul, enhancing bandwidth through the THz spectrum using a VPN, and introducing a novel network architecture to support secure cross-silo FL, focusing on healthcare improvement

Highly stable and tunable narrow-spacing dual-wavelength ytterbium-doped fiber using a microfiber Mach-Zehnder interferometer

We describe a successful demonstration of highly stable and narrowly spaced dual-wavelength output via an ytterbium-doped fiber laser. A microfiber-based Mach-Zehnder interferometer and a tunable bandpass filter were both placed into the laser ring cavity for the purpose of ensuring a stable and narrowly spaced dual-wavelength output. Experimental results comprised three sets of dual-wavelength lasing output with wavelength spacing of 0.06, 0.09, and 0.22 nm, respectively, and side-mode suppression ratio of ∼50 dBm. A subsequent stability test provided evidence that maximum power and wavelength fluctuation were less than 0.8 dB and 0.01 nm, respectively, and thus, the obtained output was considered to be highly stable in dual-wavelength operation. The proposed system offers advantages of flexibility in dual-wavelength laser generation in addition to excellent reliability

Generation of stable and narrow spacing dual-wavelength ytterbium-doped fiber laser using a photonic crystal fiber

We demonstrate the design and operation of novel narrow spacing and stable dual-wavelength fiber laser (DWFL). A 70-cm ytterbium-doped fiber has been chosen as the gain medium in a ring cavity arrangement. Our design includes a short length photonic crystal fiber, acting as a dual-wavelength stabilizer based on its birefringence coefficient and nonlinear behavior and tunable band pass filter (TBPF) to achieve narrow spacing spectrum lasing. Our laser output is considered to be highly stable, with power fluctuation less than 0.8 dB over a period of 15 min. The flexibility and tunability of TBPF, together with polarization controller enable the spacing tuning of the DWFL from 0.03 nm up to 0.07 nm for 1040 nm region, and 0.10 nm up to 0.40 nm for 1060 nm region. The tunable wavelength spacing shows the flexibility of the DWFL in addition to stable and reliable properties of fiber laser in 1-m region

Towards a Better Approach for Link Breaks Detection and Route Repairs Strategy in AODV Protocol

This paper describes a parameterized approach to the Ad Hoc On-Demand Distance Vector (AODV) routing protocol using a network-simulator 2 (ns2). By utilizing two AODV's protocol functions, which are HELLO messages and local route repair, we explore the more flexible approach on these two important functions, rather than a fixed setting within the default AODV protocol. HELLO message is used to detect the broken link, while the local route repair in AODV is used to fix and discover alternative routes in the event of route failure. In this paper, two functions to optimize AODV performance have been utilized. The first is link break detection time (Llb), using the HELLO message to detect link failure, and the second is link break position parameter (Lbp) for AODV's local route repair. The results show that the default AODV setting does not yield the best results for most defined network scenarios. In some cases, improvement compared to the default setting can be as high as 38%, for local route repair strategies. This paper presents a potential flexible and parameterized approach for dealing with link breaks and route repairing strategies for AODV protocol

Dual wavelength single longitudinal mode Ytterbium-doped fiber laser using a dual-tapered Mach-Zehnder interferometer

This paper describes a dual wavelength single longitudinal mode (SLM) demonstration for a proposed ytterbium-doped fiber laser. A dualtapered Mach-Zehnder interferometer (MZI) was inserted into the laser ring cavity setup to ensure a stable dual wavelength and SLM operation. The consequent dual wavelength lasing operation had a wavelength spacing of 0.94 nm and a side mode suppression ratio (SMSR) of 50 dB, with the linewidth of this setup measured as 294.15 kHz. A stability test allowed for a measurement of max power fluctuation as less than 0.8 dB for each wavelength and which was indicative of a stable dual wavelength operation