Saaidal R Azzuhri

Using a black phosphorus saturable absorber to generate dual wavelengths in a Q-switched ytterbium-doped fiber laser

Using a few-layer black phosphorus (BP) thin film that acts as a saturable absorber (SA) in an ytterbium-doped fiber laser setup, we experimentally demonstrated a passively dual-wavelength Q-switching laser operation. The setup also incorporated a D-shaped polished fiber as a wavelength selective filter. As the SA was used in the ring cavity, a dual-wavelength Q-switch produced consistent outputs at 1038.68 and 1042.05 nm. A maximum pulse energy of 2.09 nJ with a shortest pulse width of 1.16 µs was measured for the achieved pulses. In addition, the repetition rate increased from 52.52 to 58.73 kHz with the increment of the pump level. Throughout the measurement process, the results were obtained consistently and this demonstrates that the BP film is a very good candidate to produce Q-switching pulses for the 1 micron region.

Evaluation of parameterised route repair in AODV

One of the key challenges for routing protocols in wireless multi-hop networks is to deal with link failures, and to repair the routes in these situations. In the Ad-hoc On Demand Distance Vector (AODV) protocol, routes can either be repaired by re-establishing a new route from scratch starting from the source node (Source Repair), or they can be locally repaired by the node that detects the link break along the end-to-end path (Local Repair). In some situations Source Repair will lead to better performance, in other situations Local Repair will be the more appropriate choice. In this work, we explore a flexible, parameterised approach in deciding on which of these two route repair strategies to use in the event of a link break. We define a Local Repair Threshold parameter that determines how far along the end-to-end path that a link break needs to occur in order to initiate Local Repair, as opposed to Source Repair. Our simulation results show that the optimal choice of the Local Repair Threshold, in terms of Packet Delivery Ratio, depends on the network load. We show that a flexible, parameterised and adaptive approach to choosing the Local Repair Threshold, can improve the Packet Delivery Ratio by up to 37% (in absolute terms), compared to the approach employed by standard AODV. We also show a significant potential improvement of up to 18% over the route repair strategy employed by the Dynamic On demand MANET (DYMO) routing protocol, which is based on AODV.

A passively Q-switched ytterbium-doped fiber laser based on a few-layer Bi2Se3 saturable absorber

In this work, we demonstrate a simple Q-switched pulsed ring ytterbium-doped fiber laser based on a few-layer TI:Bi2Se3 saturable absorber (SA). Few-layer bismuth selenide within a suspension was induced onto a fiber ferrule at room temperature via an optical deposition method, resulting in a simple SA for the laser. Stable Q-switched pulsed lasing was achieved at a low pump threshold of 122.2 mW at 974 nm. The pulse repetition rate ranged from 18.97 to 45.41 kHz, and the narrowest pulse width and the maximum pulse energy were 13.1 μs and 5.88 nJ respectively. Results indicated that TI:Bi2Se3 was also compatible with the 1 μm waveband, and hence could be considered a potential broadband SA for passively mode-locked and Q-switched optical fiber lasers.

A combination of tapered fibre and polarization controller in generating highly stable and tunable dual-wavelength C-band laser

Abstract This paper demonstrates the use of a tapered fibre in generating a highly stable and tunable dual-wavelength fibre laser. By unique arrangement of polarization controller, adjustable spacing range between 0.94 and 3.32 nm and side mode suppression ratio (SMSR) up to 50 dB were recorded. The results were achieved at laser pump power of 94.7 mW. The inter-modal interference is achieved through the use of a non-adiabatic tapered fibre, made by a systematic flame brushing technique. The tapered fibre suppresses the mode competition in the 3-m erbium-doped fibre (EDF) gain medium. Over 60 min, the laser exhibited very high stability with acceptable peak power and SMSR. The proposed EDF laser operates from 1556.71 to 1562.13 nm range.

Passively dual-wavelength Q-switched ytterbium doped fiber laser using Selenium Bismuth as saturable absorber

This paper describes a demonstration of a passively dual-wavelength Q-switched ytterbium-doped fiber laser using a selenium bismuth-based saturable absorber. By utilizing a short-length photonic crystal fiber in a ring cavity and performing adjustments to the polarization state of an incorporated polarization controller (PC), we obtained a stable dual-wavelength Q-switched output at 1037.14 and 1037.69 nm, with maximum pulse energy of 0.65 nJ, shortest pulse width of 8.46 μs, and pulse repetition rate from 15.37 to 59.24 kHz. The Q-switched laser output consistently achieved high-power stability with a 0.8 dB maximum fluctuation over a period of 20 min.

Evaluating the performance impact of protocol parameters on ad-hoc network routing protocols

Routing protocols are used to discover, maintain, and repair routes between pairs of nodes in wireless ad-hoc networks. In order to handle dynamic network topologies caused by node mobility, many routing protocols are designed with multiple features and parameters to effectively discover routes and to quickly detect link breaks. In this paper, we compare the performance of four popular routing protocols, AODV, DYMO, OLSR and HWMP, in terms of the Packet Delivery Ratio (PDR) metric, and analyse the various reasons for packet loss in scenarios where nodes are mobile. We also explore key protocol parameters and how their choice impacts the protocol performance. Based on our simulation results, we find that the way in which protocols detect link breaks is critical for overall network performance. We therefore specifically explore how the choice of link break detection parameters can improve protocol performance. We further explore other protocol variations and features and their potential for performance improvements.

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

Abstract. 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.

The generation of passive dual wavelengths Q-switched YDFL by MoSe2film

A simple ytterbium doped fiber laser (YDFL) setup was used to generate Q-switching pulses by using a D-shaped polished fiber as a wavelength selective filter. The gain medium used in the cavity was ytterbium doped fiber with length 70 cm. By utilizing a MoSe2 film as saturable absorber into the cavity, a stable dual wavelength was produced at 1036.69 and 1039.22 nm. The wavelength separation of the output spectrum was 2.53 nm. We found a maximum pulse energy of 0.99 nJ and shortest pulse width of 1.2 µs. We have determined consistent dual-wavelength Q-switching pulses for the 1-micron region.

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

Abstract 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-μm region.

Generation of an ultra-stable dual-wavelength ytterbium-doped fiber laser using a photonic crystal fiber

This paper describes the demonstration of a simple ytterbium-doped fiber (YDF) laser that utilized a short length of photonic crystal fiber (PCF) in a ring cavity and adjustments to the polarization state of an incorporated polarization controller (PC) to achieve a stable dual-wavelength output. The dual-wavelength lasing operation exploited the Mach-Zehnder interferometer effect, and the laser output consistently achieved high power stability with a 0.8 dB fluctuation over a period of 30 min. This proposed setup has the capability for adjustable spacing of two lasing wavelengths from a minimum of 0.40 nm to a maximum of 3.40 nm, allowing for flexibility in dual-wavelength laser generation in addition to stable and reliable system features.