Abdul Khaleque

Composite chromium and graphene oxide as saturable absorber in ytterbium- doped Q-switched fiber lasers

In recent years, graphene and its compounds (e.g., oxides) have been used as saturable absorbers in passive Q-switched and mode-locked lasers, leading to the fabrication of compact pulsed fiber lasers. In this article, we study the operation of a Q-switched ytterbium-doped fiber ring laser based on a composite saturable absorber made of graphene oxide and chromium. We show that the addition of a thin layer of chromium can lead to pulse durations ranging from 3.5 to 9.4 μs and subsequently increasing the laser peak power.

Absorption enhancement in graphene photonic crystal structures.

Graphene, a single layer of carbon atoms arranged in a honeycomb lattice, is attracting significant interest because of its potential applications in electronic and optoelectronic devices. Although graphene exhibits almost uniform absorption within a large wavelength range, its interaction with light is weak. In this paper, the enhancement of the optical absorption in graphene photonic crystal structures is studied: the structure is modified by introducing scatterers and mirrors. It is shown that the absorption of the graphene photonic crystal structure can be enhanced about four times (nearly 40%) with respect to initial reference absorption of 9.8%. The study can be a useful tool for investigating graphene physics in different optical settings.

Ultra-broadband and compact polarization splitter based on gold filled dual-core photonic crystal fiber

A polarization splitter based on gold filled dual-core photonic crystal fiber (DC-PCF) that can work from 1420 nm to 1980 nm (560 nm bandwidth) is proposed in this work. The splitter has an extinction ratio lower than −20 dB over a large bandwidth with a total length of 254.6 μm. The key principle of operation of the splitter is the induced change in the refractive index of the y-odd mode when it is coupled to the second order plasmonic mode, while other supermodes are weakly affected by the plasmonic mode. The proposed broadband and compact polarization splitter may find applications in communications and sensing, being capable of working in the infrared and mid-infrared wavelength ranges.

Tailoring the Properties of Photonic Nanojets by Changing the Material and Geometry of the Concentrator

Some microobjects can concentrate an incoming incident plane wave and produce the so- called photonic nanojets. The highly focused emerging beams have a high intensity and can be used in applications in microscopy, beam manipulation and imaging. In this article, it is shown that an adequate choice of geometric shape and material can lead to an improvement of the electric field enhancement capacity of nanojets by a factor of 40%.

Enhancing Weak Optical Signals Using a Plasmonic Yagi—Uda Nanoantenna Array

Nanoantennas have been used in a wide range of applications in sensing, spectroscopy, and imaging-in general, the antennas can enhance physical phenomena such as the local electric field or concentrate light in a certain direction. We have fabricated an array of 80 plasmonic Yagi-Uda nanoantennas on the cladding of an optical fiber and, by doing this, we show that the signal reaching the fast detector can be increased by a factor of 5 dB. The experiment demonstrates that plasmonic directive nanoantennas can indeed collect and concentrate electromagnetic radiation along a certain direction and eventually could be used to enhance weak signals.

Thick multilayered (silica/gold) dipole nano-antenna

Nano-antennas are the optical equivalent of antennas that are used to transmit and receive information at radio frequencies. These antennas have been used in different applications in photonics such as optical imaging, particle manipulation, bio-sensing, and improvement of the performance of solar cells. In this article we study composite nano-antennas made of alternating layers of silica and gold. We show that a 50% filling factor leads to a 2.0 times increase in the electric-field enhancement factor when compared with a pure-gold antenna.

Finite-difference time-domain methods to analyze ytterbium-doped Q-switched fiber lasers.

Q-switched lasers are widely used in material processing, laser ranging, medicine, and nonlinear optics--in particular, Q-switched lasers in optical fibers are important since they cannot only generate high peak powers but can also concentrate high peak powers in small areas. In this paper, we present new finite-difference time-domain methods that analyze the dynamics of Q-switched fiber lasers, which are more flexible and robust than previous methods. We extend the method to analyze fiber ring lasers and compare the results with our experiments.

Ytterbium-doped Q-switched fiber laser based upon manganese dioxide (MnO 2 ) saturable absorber

Manganese dioxide (MnO2) is an abundant material that is widely used in many devices, such as alkaline batteries. At infrared frequencies, MnO2 is lossy and strongly absorbs light. These characteristics make MnO2 a potential candidate as a low-cost saturable absorber in Q-switched lasers. In this paper, we examine the performance of MnO2 as a saturable absorber in an ytterbium-doped Q-switched fiber laser: we show that it can produce pulses with durations ranging from 300 to 1800 ns.

Integration of bow-tie plasmonic nano-antennas on tapered fibers

In this article, a new and flexible approach to control the electric field enhancement of bow-tie nano-antennas by integrating them on the lateral of a tapered optical fiber is proposed. The device is driven by a Q-switched laser and the performance of a fabricated nano-antenna in a quartz slide is tested by a Surface Enhanced Raman Scattering (SERS) experiment. A refractive index sensing experiment is also performed and a sensitivity of (240 ± 30) nm/RIU is found in the 1.33-1.35 index range.

Tunable Composite Graphene–Silica Pseudonoise Gratings

Graphene is a two-dimensional material with outstanding properties such as high electronic and thermal conductivities that may bring a revolution in the miniaturization of electronic and optical circuits. In this letter, we analyze a tunable grating structure that combines a graphene grating and a vertical silica grating based upon a pseudonoise function. We show that the properties of the compound grating can be tailored by applying an external voltage to the graphene grating.