Piotr Pałetko

Graphene Oxide vs. Reduced Graphene Oxide as saturable absorbers for Er-doped passively mode-locked fiber laser

In this work we demonstrate comprehensive studies on graphene oxide (GO) and reduced graphene oxide (rGO) based saturable absorbers (SA) for mode-locking of Er-doped fiber lasers. The paper describes the fabrication process of both saturable absorbers and detailed comparison of their parameters. Our results show, that there is no significant difference in the laser performance between the investigated SA. Both provided stable, mode-locked operation with sub-400 fs soliton pulses and more than 9 nm optical bandwidth at 1560 nm center wavelength. It has been shown that GO might be successfully used as an efficient SA without the need of its reduction to rGO. Taking into account simpler manufacturing technology and the possibility of mass production, GO seems to be a good candidate as a cost-effective material for saturable absorbers for Er-doped fiber lasers.

Mode-locking in Er-doped fiber laser based on mechanically exfoliated Sb 2 Te 3 saturable absorber

We demonstrate the usage of a new saturable absorber material – antimony telluride (Sb2Te3) for efficient mode-locking of an Erbium-doped fiber laser. The Sb2Te3 layers were obtained by mechanical exfoliation and transferred onto the fiber connector tip. The all-fiber laser was capable of generating optical solitons with the full width at half maximum of 1.8 nm centered at 1558.6 nm, with 4.75 MHz repetition rate. The pulse energy of the generated 1.8 ps pulses was at the level of 105 pJ.

Black phosphorus saturable absorber for ultrashort pulse generation

Low-dimensional materials, due to their unique and versatile properties, are very interesting for numerous applications in electronics and optoelectronics. Recently rediscovered black phosphorus, with a graphite-like layered structure, can be effectively exfoliated up to the single atomic layer called phosphorene. Contrary to graphene, it possesses a direct band gap controllable by the number of stacked atomic layers. For those reasons, black phosphorus is now intensively investigated and can complement or replace graphene in various photonics and electronics applications. Here, we demonstrate that black phosphorus can serve as a broadband saturable absorber and can be used for ultrashort optical pulse generation. The mechanically exfoliated ∼300 nm thick layers of black phosphorus were transferred onto the fiber core, and under pulsed excitation at 1560 nm wavelength, its transmission increases by 4.6%. We have demonstrated that the saturable absorption of black phosphorus is polarization sensitive. The fabricated device was used to mode-lock an Er-doped fiber laser. The generated optical solitons with the 10.2 nm bandwidth and 272 fs duration were centered at 1550 nm. The obtained results unambiguously show that black phosphorus can be effectively used for ultrashort pulse generation with performances similar or even better than currently used graphene or carbon nanotubes. This application of black phosphorus proves its great potential to future practical use in photonics.

Er-Doped Fiber Laser Mode-Locked by CVD-Graphene Saturable Absorber

Erbium-doped fiber laser passively mode-locked by bilayer graphene is presented. The graphene layers were grown by chemical vapor deposition (CVD) on Cu substrate and transferred onto a fused silica window, forming a saturable absorber (SA). Low non-saturable losses and modulation depth as high as 55% allowed to achieve soliton pulses with over 11 nm bandwidth and nearly-transform limited 315 fs duration at 1564 nm center wavelength. The paper describes the design of the laser construction, as well as the graphene-SA preparation process. Our study demonstrates, that CVD-Cu graphene transferred on glass substrate may be used for efficient mode-locking of fiber lasers.

Micromachined scanning proximal probes with integrated piezoresistive readout and bimetal actuator for high eigenmode operation

The fabrication process, application, and properties of a novel piezoresistive multiprobe with an integrated thermal tip deflection actuator are described in this article. The optimized fabrication process of the microprobe enables high-frequency sensor operation and integration of a high sharp conical tip, which was additionally covered with titanium using atomic layer deposition to improve mechanical endurance and ensure electrical conductivity. This microprobe was applied in high-resolution self-assembled monolayer surface investigations in which the piezoresistive cantilever with the integrated thermal deflection actuator was excited at two of its flexural-resonant eigenmodes. The excited second eigenmode and phase show different contrasts com-pared with images recorded at the first eigenmode.

Atomic force microscopy of partially polished and epi-ready c-plane GaN substrates obtained by an ammonothermal method

In this paper, the propagation of scratches on the surfaces of c-plane GaN substrates due to slicing and polishing is studied through atomic force microscopy (AFM). For epi-ready substrates, the AFM images confirm a flat surface with atomic step roughness, while for partially polished GaN substrates, many scratches are visible in the AFM images. A Fourier analysis of the AFM images shows that the scratches propagate more easily along the {m-plane} and {a-plane} directions on a c-plane GaN surface. Most of these scratches are generated by the mechanical slicing of GaN crystals and/or non-optimal polishing conditions. A proper chemomechanical polishing process is able to remove the damaged material and obtain a flat surface with atomic step roughness. This observation is evidence for the anisotropy of mechanical properties of GaN crystals in the microscale range.

Carrier density distribution in silicon nanowires investigated by scanning thermal microscopy and Kelvin probe force microscopy

The use of scanning thermal microscopy (SThM) and Kelvin probe force microscopy (KPFM) to investigate silicon nanowires (SiNWs) is presented. SThM allows imaging of temperature distribution at the nanoscale, while KPFM images the potential distribution with AFM-related ultra-high spatial resolution. Both techniques are therefore suitable for imaging the resistance distribution. We show results of experimental examination of dual channel n-type SiNWs with channel width of 100 nm, while the channel was open and current was flowing through the SiNW. To investigate the carrier distribution in the SiNWs we performed SThM and KPFM scans. The SThM results showed non-symmetrical temperature distribution along the SiNWs with temperature maximum shifted towards the contact of higher potential. These results corresponded to those expressed by the distribution of potential gradient along the SiNWs, obtained using the KPFM method. Consequently, non-uniform distribution of resistance was shown, being a result of non-uniform carrier density distribution in the structure and showing the pinch-off effect. Last but not least, the results were also compared with results of finite-element method modeling.

Microcontact printing technology as a method of fabrication of patterned self-assembled monolayers for application in nanometrology

This paper is focused on manufacture technology of molecular self-assembled monolayers (SAM) using microcontact printing (μCP) techniqe. This technique, due to its low-cost and simplicity, is a very attractive one for further development of molecular electronics and nanotechnology. The SAM can be produced on gold or silicon oxide using thiol and silane based chemistry respectively[1]. The μCP techniques allow the imposition of molecular structures in specific areas. The chemical properties of the fabricated layers depend on the functional groups of tail molecules. Such structures can be used as chemical receptors or as interface between the substrate and the biosensor receptors [2]. Architecture of the tail molecule determines the chemical reactivity and hydrophilic or hydrophobic properties. In addition it modifies the tribological properties [4] and electrical structure parameters, such as contact potential diference (CPD) [5]. The height of the SAM structure containing carbon chain is highly dependent on the length and type of binding molecules to the substrate, which enables application of the μCP SAM structures in height metrology. The results of these studies will be presented in the work.