Multi-wavelength Regime Research Articles

Multiwavelength synchronously Q-switched Erbium-doped fiber laser based on the adjustment of the free spectral range of an intracavity tapered-fiber filter

All-fiber multiwavelength Q-switched (MWQS) lasers are of huge interest because of their emergent and well-known scientific and technological applications. Passive all-fiber MWQS lasers require a saturable absorber to generate Q-switched pulses and an optical filter to seed the multiwavelength regime. New trends in all-fiber MWQS lasers demand new devices to explore innovative configurations and capabilities in this kind of lasers. In this sense, we report on the experimental demonstration of a multiwavelength synchronously Q-switched Erbium-doped fiber laser (QSEDFL). This laser achieves dual and triple wavelength lasing around 1530 nm with interchangeable wavelength separation. A shorth piece of Tm:Ho co-doped fiber is the saturable absorber. An intracavity tapered optical fiber filter in a double-pass configuration allows the versatile process of wavelength filtering, enabling the adjustment of wavelength lasing separation between 1.7 nm, 2.1 nm, and 2.5 nm with synchronized pulses of each wavelength component. This proposal offers a new route to all-fiber multiwavelength synchronously Q-switched laser with potential applications for WDM systems and all-fiber sensors.

(INVITED)Switchable multi-wavelength mode-locked Yb-doped fiber laser using a polarization maintaining 45°-tilted fiber gratings based Lyot filter

We demonstrate a multi-wavelength mode-locked Yb-doped fiber laser by incorporating a pair of polarization maintaining 45° tilted fiber gratings (PM-45°TFG) based Lyot filter. Thanks to the functions of the polarizer and the comb filtering introduced by the Lyot filter, dissipative soliton (DS) pulses centered at 1035.26 nm, 1044.93 nm, 1055.62 nm, 1066.11 nm and 1076.63 nm can be generated respectively by finely tuning the intracavity polarization controllers (PCs). Moreover, the laser also can operate in a multi-wavelength regime via appropriately adjusting the pump power and polarization orientation. The high nonlinearity induced by the long cavity length leads to the generation of h-shaped mode-locked pulse with a repetition rate of 566.27 kHz. In the absence of any disturbance, the laser can operate steadily, that can potentially be used in various fields including wavelength division multiplexing systems etc.

Switchable and spacing tunable dual-wavelength spatiotemporal mode-locked fiber laser.

We report a switchable and spacing tunable dual-wavelength spatiotemporal mode-locked (STML) laser based on the multimode interference filtering effect in an all-fiber linear cavity. The dual-wavelength STML operations combined with different pulse patterns are achieved. By adjusting the polarization controllers, the dual-wavelength STML pulses can be switched to single wavelength operation, which is tunable up to 35 nm under certain pump powers. Moreover, the dual-wavelength spacing can also be tuned from 8 nm to 22 nm. The obtained results contribute to understanding and exploring the spatiotemporal characteristics operating in the multi-wavelength regime of STML fiber lasers. All-fiber STML lasers with lasing wavelength tunability and flexibility may have applications in the fields of optical communications and optical measurements.

Выбор оптимального режима работы электронных тахеометров при геодезических измерениях в условиях сильного аэрозольного загрязнения атмосферы

The possibility to use multi-wavelength regime of total stations operation for making surveys under heavy aerosol atmosphere pollution is researched. The actuality of single- and multi-wavelength regimes rational choice under heavy aerosol atmosphere pollution is grounded. The task on researching the matter of operational regime choice for total stations is formulated. The method for solution of the formulated task is suggested. The theoretical modelling and experimental researches are held to formulate the criterion for choice of single- or multi-wavelength regimes. The practical recommendations for such a choice are formulated. The practical recommendations are formulated for choice of measurements regime. According to formulated recommendations if a single-wavelength total station operates in the field of longer wavelengths (R) of visible band and a three-wavelengths one operates with bias to shorter (B, G, R) wavelengths, the single-wavelength total station should be preferred. But if the single-wavelength total station operates in the field of shorter wavelengths (B) and the three-wavelengths one operates with bias to longer wavelengths (B, G, R) then the multi-wavelengths total station should be preferred. The recommendation described in this article are relevant for both the regimes of measurements with- and without reflector and can be useful for users of total stations.

Pulsed hollow-cathode ion lasers: pumping and lasing parameters

Optimal discharge conditions have been experimentally found for ion lasers excited in the hollow-cathode discharge plasma by microsecond current pulses by pumping working atoms in secondkind collisions with ions and metastable buffer-gas atoms. Measurements of the output power of krypton ion and zinc-, cadmium-, mercury-, thallium-, copper-, and gallium-vapour lasers in tubes with cathodes of different diameters showed that the pulse power reaches several tens of watts, and the average power obtained with cathodes 2 cm in diameter and a length of 40 cm or more approaches 1 W. Lasing in most media is observed simultaneously at several lines (the multi-wavelength regime). Lasing on a three-component(He — Kr — Hg) mixture is realised in the multi-wavelength regime at blue, red, and IR lines.

A comparative study of energy transfer in dye mixtures in monomer and polymer matrices under pulsed laser excitation

This study was conducted to identify the concentration dependence of the operating wavelengths and the relative intensities in which a dye mixture doped polymer optical fibre can operate. A comparative study of the radiative and Forster type energy transfer processes in Coumarin 540:Rhodamine 6G, Coumarin 540:Rhodamine B and Rhodamine 6G:Rhodamine B in methyl methacrylate (MMA) and poly(methyl methacrylate) (PMMA) was done by fabricating a series of dye mixture doped polymer rods which have two emission peaks with varying relative intensities. These rods can be used as preforms for the fabrication of polymer optical fibre amplifiers operating in the multi-wavelength regime. The 445 nm line from an Nd:YAG pumped optical parametric oscillator (OPO) was used as the excitation source for the first two dye pairs and a frequency doubled Nd:YAG laser emitting at 532 nm was used to excite the Rh 6G:Rh B pair. The fluorescence lifetimes of the donor molecule in pure form as well as in the mixtures were experimentally measured in both monomer and polymer matrices by time-correlated single photon counting technique. The energy transfer rate constants and transfer efficiencies were calculated and their dependence on the acceptor concentration was analysed. It was found that radiative energy transfer mechanisms are more efficient in all the three dye pairs in liquid and solid matrices.

Experimental study of a tunable fiber ring laser stability

We have experimentally studied the mid-term (1–1000 s) stability of a traveling-wave unidirectional Erbium-doped fiber (EDF) ring laser as a function of the pump power, doped fiber length and type, total laser cavity length, polarization control and exit coupler ratio. The laser operated in a multi-wavelength regime with the central wavelength defined by a 1.12 GHz-band tunable Fabry–Pérot filter (FPF) with a 3.1 THz free spectral range (FSR). We have found that the key parameters defining the laser stability are the cavity length and the out-coupling ratio, while the polarization control has little influence on the multi-wavelength regime. In the optimal configuration, we obtained output power variations below 0.02 dB of a total power of about 1.5 mW in a 10 min interval.

Serial topology of wide-band erbium-doped fiber amplifier for WDM applications

We analyze the recently proposed serial topology of a wide-band erbium-doped fiber amplifier (EDFA) covering both the C- and L-bands and compare it with the parallel configuration of C-band and L-band amplifiers. The analysis is based on an application of a comprehensive large-signal numerical model, which takes into consideration propagation of wavelength-division multiplexing (WDM) signals, bidirectional pump, and both the downstream and upstream ASE power spectral components. We have found that in the multiwavelength regime the new topology can provide output power of 3 dBm/channel for 32 C-band and 40 L-band, 0.8-nm-spaced signals with reasonable pump powers to the first and the second stage. In comparison with the usual parallel configuration of C-band and L-band EDFAs, this topology saves about 20% of overall pump power, 10% of the necessary length of erbium-doped fiber (EDF) and achieves lower noise figure for L-band signals.

Gain enhancement in gain-shifted erbium-doped fiber amplifiers for WDM applications

Utilization of amplified spontaneous emission (ASE) for gain enhancement in gain-shifted erbium-doped fiber amplifier (GS-EDFA) is analyzed. It is shown that in a multiwavelength regime, gain enhancement as high as 5 dB can be achieved when the counterpropagating ASE is used to invert an unpumped first stage of a two-stage GS-EDFA. We present design criteria for flat gain operation and noise penalty minimization of two-stage GS-EDFAs determined for multiwavelength operation in the 1580-nm wavelength band. The analysis is based on an application of a comprehensive large-signal numerical model which takes into consideration propagation of signal, pump and both the downstream and upstream ASE powers.

Neutron interferometry at a pulsed source

A compact setup providing vibration damping support as well as thermal shielding for a classical LLL interferometer was developed and installed at the IBR-2 pulsed reactor at JINR Dubna. Despite the low incident neutron flux successful experiments were performed with two different LLL-type interferometer crystals and simultaneous observation of the interference patterns on two reflection orders was demonstrated. This first experience leads to the conclusion that routine experiments in the multi-wavelength regime are feasible, but a careful optimization of the setup regarding the opposing demands on TOF resolution, incident flux and background would be desirable to compensate at least partially for the rapid decrease of diffracted intensity at higher reflection orders.