Zinc oxide nanoparticles based passive saturable absorber for pulse generation in fiber laser

A stable passive Q-switched pulsed generation in Erbium doped fiber laser by Zinc Oxide nanoparticles embedded in polyvinyl alcohol (ZnONP-PVA)-based saturable absorber is demonstrated in this paper. The surface morphology and thickness profile of the fabricated film were observed using FESEM and 3D measuring laser microscope with the measured thickness of 12 μm. Meanwhile the its optical properties is characterized using Raman spectroscopy. The developed ZnONP-PVA film, has modulation depth of 7.8% and intensity saturation of 88.97 MW/cm2. The threshold input pump power to generate Q-switched pulse is at 45.4 mW and can be tuned until 92.4 mW before the pulse diminished. The operating wavelength of generated pulse is at 1535 nm with 3 dB bandwidth approximately of 2 nm with exclusion of parasitic continuous wave lasing. As the input pump power was tuned from threshold to maximum value, the recorded pulse train of repetition rate is tunable from 73.53 kHz to 103.10 kHz while the pulse width decreases from 6.8 μs to 4.8 μs. The calculated maximum output power and pulse energy at maximum input pump power was 5.14 mW and 49.85 nJ, respectively. The measured signal to noise ratio was 56 dB indicated that the generated pulse by ZnO NP based passive saturable absorber was stable

Excessively tilted fiber grating based Fe3O4 saturable absorber for passively mode-locked fiber laser

A novel approach to saturable absorber (SA) formation is presented by taking advantage of the mode coupling property of excessively tilted fiber grating (Ex-TFG). Stable mode-locked operation can be conveniently achieved based on the interaction between Ex- TFG coupled light and deposited ferroferric-oxide (Fe3O4) nanoparticles. The central wavelength, bandwidth and single pulse duration of the output are 1595 nm, 4.05 nm, and 912 fs, respectively. The fiber laser exhibits good long-term stability with signal-to-noise ratio (SNR) of 67 dB. For the first time, to the best of our knowledge, Ex-TFG based Fe3O4 SA for mode-locked fiber laser is demonstrated

Oriented zinc oxide nanorods: A novel saturable absorber for lasers in the near-infrared

Zinc oxide (ZnO) nanorods (NRs) oriented along the crystallographic [001] axis are grown by the hydrothermal method on glass substrates. The ZnO NRs exhibit a broadband (1–2 µm) near-IR absorption ascribed to the singly charged zinc vacancy VZn−1. The saturable absorption of the ZnO NRs is studied at ≈1 µm under picosecond excitation, revealing a low saturation intensity, ≈10 kW/cm2, and high fraction of the saturable losses. The ZnO NRs are applied as saturable absorbers in diode-pumped Yb (≈1.03 µm) and Tm (≈1.94 µm) lasers generating nanosecond pulses. The ZnO NRs grown on various optical surfaces are promising broadband saturable absorbers for nanosecond near-IR lasers in bulk and waveguide geometries

An approach to emerging optical and optoelectronic applications based on NiO micro- and nanostructures

Nickel oxide (NiO) is one of the very few p-type semiconducting oxides, the study of which is gaining increasing attention in recent years due to its potential applicability in many emerging fields of technological research. Actually, a growing number of scientific works focus on NiO-based electrochromic devices, high-frequency spintronics, fuel cell electrodes, supercapacitors, photocatalyst, chemical/gas sensors, or magnetic devices, among others. However, less has been done so far in the development of NiO-based optical devices, a field in which this versatile transition metal oxide still lags in performance despite its potential applicability. This review could contribute with novelty and new forefront insights on NiO micro and nanostructures with promising applicability in optical and optoelectronic devices. As some examples, NiO lighting devices, optical microresonators, waveguides, optical limiters, and neuromorphic applications are reviewed and analyzed in this work. These emerging functionalities, together with some other recent developments based on NiO micro and nanostructures, can open a new field of research based on this p-type material which still remains scarcely explored from an optical perspective, and would pave the way to future research and scientific advances

NEODYMIUM OXIDE (ND2O3) AS PASSIVE Q-SWITCHER FOR PULSED FIBER LASER GENERATION IN C-BAND REGION

his work demonstrate Neodymium Oxide (Nd2O3) film as a passive saturable absorber (SA) for pulse generation within C-band region. The saturable absorber was fabricated from Nd2O3 powder, and polyvinyl alcohol (PVA) was used to form a film. The all-fiber ring cavity configuration was used in the experiment. The Q-switching operated with the pump power from 60 mW to 120 mW. The repetition rate increases from 52 kHz to 77 kHz, while the pulse width shown decrement of 7.4 µs to 5.3 µs. The signal-to-noise ratio obtained of the fundamental frequency is 64 dB. The maximum output power and pulse energy are 3.6 mW and 4.6 nJ respectively. The maximum peak power obtained is 0.87 mW

Nonlinear Optical Phenomena in Emerging Low-dimensional Materials

As digital information technologies continue to evolve at much faster rates than the growth of Si-based processors, the encroachment of light-based technologies into computing seems inevitable. With the advent of lasers, photonic crystals, and optical diodes, photonic computing has made significant strides in information technology over the past 30 years. This continuing integration of light into all-optical computing, optoelectronic components, and emerging optogenetic technologies demands the ability to control and manipulate light in a predictable fashion, or by design. Of particular interest, is the passive control and manipulation of light in all-optical switches, photonic diodes, and optical limiting which can be achieved by leveraging intrinsic non-linear optical properties of low dimensional materials. The reverse saturable absorption in fullerenes has been widely used to realize excellent passive optical limiters for the visible region up to 650 nm. However, there is still a need for passive optical switches and limiters with a low limiting threshold (\u3c0.5 J/cm2) and higher damage limits. The electronic structure of fullerenes can be modified either through doping or by the encapsulation of endohedral clusters to achieve exotic quantum states of matter such as superconductivity. Building on this ability, we discuss in Chapter 2 that the encapsulation of Sc3N, Lu3N or Y3N in C80 alters the HOMO-LUMO gap and leads to passive optical switches with a significantly low limiting threshold (0.3 J/cm2) and a wider operation window (average pulse energy \u3e0.3 mJ in the ns regime). In addition to extraordinary and strongly anisotropic electronic properties, two dimensional (2D) materials such as graphene and boron nitride, exhibit strong light-matter interactions despite their atomic thickness. The nonlinear light-matter interactions in 2D materials are well suited for several applications in photonics and optoelectronics, such as ultrafast optical switching and optical diodes. Unlike most 2D materials that display nonlinear saturable absorption or increased light transmission at higher fluences, hexagonal boron nitride nanoplatelets (BNNPs) exhibit enhanced opaqueness with increasing light fluence. A two-photon absorption (2PA) process was previously proposed to explain the intrinsic non-linear absorption in BNNPs at 1064 nm or 1.16 eV (Kumbhakar et al., Advanced Optical Materials, vol. 3, pp. 828, 2015); which is counter-intuitive because a 2PA process at 1.16 eV cannot excite electrons across the wide band gap of BNNPs (~5.75 eV). Here, through a systematic study of the non-linear properties of BNNPs we uncover a notoriously rare non-linear phenomenon, viz., five-photon absorption (5PA) at 1064 nm for low laser input fluences (below 0.6 J/cm2) that irreversibly transforms to a 2PA for higher laser input fluences (above 0.6 J/cm2). Our detailed experimental and theoretical findings delineated in Chapter 3 provide compelling evidence that the high laser fluence generates defects in BNNPs (e.g., oxygen/carbon doping), which support a 2PA process by inducing new electronic states within the wide band gap of BNNPs. MXenes comprise a new class of two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides that exhibit unique light-matter interactions. Recently, 2D Ti3C2Tx (Tx represents functional groups such as –OH and –F) was found to exhibit nonlinear saturable absorption (SA) or increased transmittance at higher light fluences that is useful for mode locking in fiber-based femtosecond lasers. However, the fundamental origin and thickness-dependence of SA behavior in MXenes remains to be understood. We fabricated 2D Ti3C2Tx thin films of different thicknesses using an interfacial film formation technique to systematically study their nonlinear optical properties. Using the open aperture Z-scan method, we find that the SA behavior in Ti3C2Tx MXene arises from plasmon-induced increase in the ground state absorption at photon energies above the threshold for free carrier oscillations. The saturation fluence and modulation depth of Ti3C2TxMXene was observed to be dependent on the film thickness. Unlike other 2D materials, Ti3C2Tx was found to show higher threshold for light-induced damage with up to 50% increase in nonlinear transmittance. Lastly, building on the SA behavior of Ti3C2Tx MXenes, we demonstrate in Chapter 4 a Ti3C2Tx MXene-based photonic diode that breaks time-reversal symmetry to achieve non-reciprocal transmission of nanosecond laser pulses. Finally, in Chapter 5, we discuss the equilibrium and non-equilibrium free carrier dynamics in a 16 nm thick Ti3C2Tx film. High (~2 x 1021 cm-3) intrinsic charge carrier density and relatively high (~34 cm2/Vs) mobility of carriers within individual nanoplates (that comprise the Ti3C2Tx film) result in an exceptionally large (~ 46 000 cm-1) absorption in the THz range, implying the potential use of Ti3C2Tx for THz detection. We also demonstrate that Ti3C2Tx conductivity and THz transmission can be manipulated by photoexcitation, as absorption of near-infrared 800 nm pulses is found to cause transient suppression of the conductivity that recovers over hundreds of picoseconds. The possibility of controlling THz transmission and conductivity via photoexcitation makes 2D MXenes suggests a promising material for application in THz modulation devices and variable electromagnetic shielding

Nonlinear optical properties and applications of 2D materials: theoretical and experimental aspects

In this review, we survey the recent advances in nonlinear optics and the applications of two-dimensional (2D) materials. We briefly cover the key developments pertaining to research in the nonlinear optics of graphene, the quintessential 2D material. Subsequently, we discuss the linear and nonlinear optical properties of several other 2D layered materials, including transition metal chalcogenides, black phosphorus, hexagonal boron nitride, perovskites, and topological insulators, as well as the recent progress in hybrid nanostructures containing 2D materials, such as composites with dyes, plasmonic particles, 2D crystals, and silicon integrated structures. Finally, we highlight a few representative current applications of 2D materials to photonic and optoelectronic devices