Raman amplification and pulsed lasing in cladding-pumped germanosilicate fiber

We report for the first time Raman amplification in a cladding-pumped fiber. The double-clad germanosilicate fiber was pumped by a Q-switched Er-Yb co-doped fiber laser at 1570 nm. The power conversion efficiency was up to 36%, with a slope of 64%

Measurement driven quantum evolution

We study the problem of mapping an unknown mixed quantum state onto a known pure state without the use of unitary transformations. This is achieved with the help of sequential measurements of two non-commuting observables only. We show that the overall success probability is maximized in the case of measuring two observables whose eigenstates define mutually unbiased bases. We find that for this optimal case the success probability quickly converges to unity as the number of measurement processes increases and that it is almost independent of the initial state. In particular, we show that to guarantee a success probability close to one the number of consecutive measurements must be larger than the dimension of the Hilbert space. We connect these results to quantum copying, quantum deleting and entanglement generation.Comment: 7 pages, 1 figur

Wavelength tuning of fiber lasers using multimode interference effects

We report on a novel scheme to fabricate a simple, cheap, and compact tunable fiber laser. The tuning is realized by splicing a piece of single-mode fiber to one end of an active double-clad fiber, while the other end of the single-mode fiber is spliced to a 15 mm long section of 105/125 multimode fiber. The fluorescence signal entering into the multimode fiber will be reproduced as single images at periodic intervals along the propagation direction of the fiber. The length of the multimode fiber is chosen to be slightly shorter than the first re-imaging point, such that the signal coming out from the single mode fiber is obtained in free space, where a broadband mirror retroreflects the fluorescence signal. Since the position of the re-imaging point is wavelength dependent, different wavelengths will be imaged at different positions. Therefore, wavelength tuning is easily obtained by adjusting the distance between the broadband mirror and the multimode fiber facet end. Using this principle, the tunable fiber laser revealed a tunability of 8 nm, ranging from 1088-1097 nm, and an output power of 500 mW. The simplicity of the setup makes this a very cost-effective tunable fiber laser

Widely tunable erbium-doped fiber laser based on multimode interference effect

A widely tunable erbium-doped all-fiber laser has been demonstrated. The tunable mechanism is based on a novel tunable filter using multimode interference effects (MMI). The tunable MMI filter was applied to fabricate a tunable erbium-doped fiber laser via a standard ring cavity. A tuning range of 60 nm was obtained, ranging from 1549 nm to 1609 nm, with a signal to noise ratio of 40 dB. The tunable MMI filter mechanism is very simple and inexpensive, but also quite efficient as a wavelength tunable filter

Brown bear attacks on humans : a worldwide perspective

The increasing trend of large carnivore attacks on humans not only raises human safety concerns but may also undermine large carnivore conservation efforts. Although rare, attacks by brown bears Ursus arctos are also on the rise and, although several studies have addressed this issue at local scales, information is lacking on a worldwide scale. Here, we investigated brown bear attacks (n = 664) on humans between 2000 and 2015 across most of the range inhabited by the species: North America (n = 183), Europe (n = 291), and East (n = 190). When the attacks occurred, half of the people were engaged in leisure activities and the main scenario was an encounter with a female with cubs. Attacks have increased significantly over time and were more frequent at high bear and low human population densities. There was no significant difference in the number of attacks between continents or between countries with different hunting practices. Understanding global patterns of bear attacks can help reduce dangerous encounters and, consequently, is crucial for informing wildlife managers and the public about appropriate measures to reduce this kind of conflicts in bear country.Peer reviewe

Tuning characteristics of cladding-pumped neodymium-doped fiber laser

We describe a cladding-pumped neodymium-doped fiber laser, tunable from 1057 to 1118 nm. The power varies significantly over the tuning range. Improved characteristics are obtained with tuning elements in both ends of the cavity

Simple Numerical Modeling Of Yb3+-Doped Fiber Lasers

We present a fast and efficient numerical model for Yb3+-doped fiber lasers based on shooting method. The algorithm is based on the assumption of a starting value for the slope efficiency and the evaluation of the pump power threshold. The starting value of slope efficiency is related to initial conditions through the boundary conditions, and it is subsequently optimized by iteration. The method ensures a fast and efficient convergence of the solution of the coupled first-order differential equations that describes the evolution of pump and signal powers in a Yb3+-doped fiber laser. The results of the numerical solution are compared with experimental and published data giving a good agreement

Novel Multimode Interference Modulator

A new structure for an ultra-compact MMI-based modulator is proposed. Extinction ratios as low as -37 dB are demonstrated. This value is only increased to -35 dB when low electro-absorption effects are included. © 2005 Optical Society of America

Cladding-pumped Raman fiber amplifier

Cladding-pumped rare-earth-doped fibers and Raman fiber devices have been two of the most compelling advances in the area of high-power fiber amplifiers and lasers in recent years. Cladding-pumping enables pumping with multi-mode pump sources that deliver high-power at a low cost. The core of the double-clad fiber can still be single-moded, so that single-mode amplification or lasing can be realized. Raman gain requires high pump powers and Raman conversion is therefore only efficient at high power levels. On the other band, Raman devices are very flexible as gain is available at arbitrary wavelengths with the right pump source. Cladding-pumped Raman fiber devices represent a natural progression to multi-mode pumping and Raman fiber devices. While cladding-pumped Raman fiber devices require pump powers of, say, 100 W, such powers are available from fiber sources as well as from traditional bulk sources. For example, a multimode Nd-doped fiber laser with 1 kW of output power was recently reported. With pulsed sources, however, the required peak powers can be achieved with relatively modest average powers. Here, we report for the first time Raman amplification in a cladding-pumped fiber, without any rare-earth doping. We believe that this is an important step towards a whole class of new optical amplifier devices based on brightness-enhancing nonlinear conversion of multimode pumps, including not only Raman converters but also Brillouin and optical parametric converters