Liquid-phase exfoliated 2D material multilayer MoS2 is transferred onto a gold mirror and its saturable absorption at the 2 mu m wavelength region is experimentally observed. This transferred MoS2 saturable absorber has a modulation depth of 13.6% and a saturation intensity of 23.1 MW cm(-2). This saturable absorber is integrated into a linear Tm3+ fiber laser cavity, and stable fundamental-frequency mode-locking operation is realized at 2 mu m with pulse energy of 15.5 nJ, pulse width of similar to 843 ps, and a repetition rate of 9.67 MHz. The laser spectral width is similar to 17.3 nm with a center wavelength of 1905 nm. This first presence of mode-locking with multilayer MoS2 sheets in the 2 mu m wavelength region verifies that multilayer MoS2 is a good candidate for broadband mode-locking comparable to graphene, as well as a good mode-locker for achieving high pulse energy.
Carrier-envelope phase stable 4 fs near-IR pulses with 3 mJ energy were generated by spectral broadening of circularly polarized 8 mJ pulses in a differentially pumped 2 m long composite stretched flexible hollow fiber. The pulses were characterized using both second-harmonic generation frequency-resolved optical gating (SHG-FROG) and SHG d-scan methods.
We demonstrate the nanoscale p-type Bi2Te3 powder-based saturable absorber-induced passive mode-locking of the erbium-doped fiber laser (EDFL) with sub-picosecond pulsewidth. Such a nanoscale topological insulator powder is obtained by polishing the bulk p-type Bi2Te3 in a commercial thermoelectric cooler (TE cooler). This is then directly brushed onto the end-face of a single-mode fiber patchcord, to avoid any mis-connecting loss caused by laser beam divergence, which can result in a mode-locked pulsewidth of 436 fs in the self-amplitude modulation mode of a TE cooler. To further shorten the pulse, the soliton compression is operated by well-controlling the group delay dispersion and self-phase modulation, providing the passively mode-locked EDFL with a pulsewidth as short as 403 fs.
A scheme is proposed for high-precision two-dimensional atom localization in a four-level tripod-type atomic system via measurement of the excited state population. It is found that because of the position-dependent atom-field interaction, the precision of 2D atom localization can be significantly improved by appropriately adjusting the system parameters. Our scheme may be helpful in laser cooling or atom nanolithography via high-precision and high-resolution atom localization.
Hyperentanglement has attracted much attention due to its fascinating applications in quantum communication. However, it is impossible to purify a pair of photon systems in a mixed hyperentangled state with errors in two degrees of freedom using linear optical elements only, far different from all the existing entanglement purification protocols in a degree of freedom (DOF) for quantum systems. Here, we investigate the possibility of purifying a spatial-polarization mixed hyperentangled Bell state with the errors in both the spatial-mode and polarization DOFs, resorting to the nonlinear optics of a nitrogen-vacancy (NV) center in a diamond embedded in a photonic crystal cavity coupled to a waveguide. We present the first hyperentanglement purification protocol for purifying a pair of two-photon systems in a mixed hyperentangled Bell state with the errors in two DOFs. We also propose an efficient hyperentanglement concentration protocol for a partially hyperentangled Bell pure state, which has the maximal success probability in principle. These two protocols are useful in long-distance quantum communication with hyperentanglement.
Accurate non-invasive assessment of tissue elasticity in vivo is required for early diagnostics of many tissue abnormalities. We have developed a focused air-pulse system that produces a low-pressure and short-duration air stream, which can be used to excite transient surface waves (SWs) in soft tissues. System characteristics were studied using a high-resolution analog pressure transducer to describe the excitation pressure. Results indicate that the excitation pressure provided by the air-pulse system can be easily controlled by the air source pressure, the angle of delivery, and the distance between the tissue surface and the port of the air-pulse system. Furthermore, we integrated this focused air-pulse system with phase-sensitive optical coherence tomography (PhS-OCT) to make non-contact measurements of tissue elasticity. The PhS-OCT system is used to assess the group velocity of SW propagation, which can be used to determine Young's modulus. Pilot experiments were performed on gelatin phantoms with different concentrations (10%, 12% and 14% w/w). The results demonstrate the feasibility of using this focused air-pulse system combined with PhS-OCT to estimate tissue elasticity. This easily controlled non-contact technique is potentially useful to study the biomechanical properties of ocular and other tissues in vivo.
The recent results on the new laser material - Bi-doped glasses and optical fibers are reviewed. First, luminescence properties of various Bi-doped glasses are discussed. At last the results of investigations of Bi-doped fiber lasers covering a wave-length range of 1150-1550 nm are presented. [GRAPHICS] The review picture of Bi-doped fiber lasers demonstrated up to now
Soliton operation and soliton wavelength tuning of erbium-doped fiber lasers mode locked with atomic layer graphene was experimentally investigated under various cavity dispersion conditions. It was shown that not only wide range soliton wavelength tuning but also soliton pulse width variation could be obtained in the fiber lasers. Our results show that the graphene mode locked erbium-doped fiber lasers provide a compact, user friendly and low cost wavelength tunable ultrashort pulse source.
To date, all work concerning the construction of quantum logic gates, an essential part of quantum computing, has focused on operating in one degree of freedom (DOF) for quantum systems. Here, we investigate the possibility of achieving scalable photonic quantum computing based on two DOFs for quantum systems. We construct a deterministic hyper-controlled-not (hyper-CNOT) gate operating in both the spatial mode and polarization DOFs for a photon pair simultaneously, using the giant optical Faraday rotation induced by a single-electron spin in a quantum dot inside a one-side optical microcavity as a result of cavity quantum electrodynamics. With this hyper-CNOT gate and linear optical elements, two-photon four-qubit cluster entangled states can be prepared and analyzed, which give an application to manipulate more information with less resources. We analyze the experimental feasibility of this hyper-CNOT gate and show that it can be implemented with current technology.
We report a high-power Raman fiber laser based on randomly extremely weak Rayleigh feedback. Based on a mirrorless configuration, a total output power of 73.7 W is achieved with an optical efficiency of 74.7%. The cavity length of the Raman fiber laser is only 300 m. The Stokes wave is centered at 1184 nm with 3 dB bandwidth of about 4 nm at the maximal power. The spectrum and time-domain behavior at the Raman Stokes wave generation threshold is different from previous random distributed feedback Raman fiber lasers.
In this letter we present for the first time, to the best of our knowledge, a harmonically mode-locked Er-doped fiber laser with antimony telluride (Sb2Te3) topological insulator material used as a saturable absorber (SA). The SA was prepared via mechanical exfoliation of the bulk material. The 80 nm thick Sb2Te3 layers transferred onto fiber ferrule entirely cover the fiber core. The Er-doped fiber mode-locked laser based on such SA generated optical pulses was centered at 1558 nm with 1.9 ps duration and a fundamental repetition rate of 3.75 MHz. Increasing the pump power results in stable harmonic mode-locked operation up to the 81st harmonic at 304 MHz repetition frequency. The laser was capable of generating optical solitons with 2.2 ps duration. The number of generated harmonics could be tuned only by changing the pump power injected into the laser cavity.
We demonstrated a wide-band tunable passively Qswitched fiber laser by using a graphene-based saturable absorber (SA). The graphene SA was prepared through the optically driven deposition method. The Q-switched operation was initiated with a low pump threshold of about 33 mW. The wavelength tunable operation was obtained with a narrow bandwidth tunable filter. Experimentally, the stable Q-switched pulse with a tunable range from 1519.3 to 1569.9 nm was achieved, covering a wavelength range of over 50.6 nm. (C) 2012 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA)
We present a hyperconcentration scheme for nonlocal N-photon hyperentangled Greenberger-Horne-Zeilinger states. The maximally hyperentangled state, in which N particles are entangled simultaneously in the polarization and the spatial mode, can be obtained with a certain probability from two partially hyperentangled states. The hyperconcentration scheme is based on one polarization parity check measurement, one spatial mode parity check measurement and N - 2 single-photon two-qubit measurements. The concentration only requires linear optical elements, which makes it feasible and practical with current technology.
We present a deterministic entanglement purification protocol (EPP) working with the currently available experiment techniques. In this protocol, we exploit the robust time-bin entanglement to purify the polarization entanglement determinately, which is quite different from the previous EPPs. After purification, the two parties in quantum communication can obtain a maximally entangled photon pair from each transmitted over a polarization-noise channel with a success probability of 100%, in principle. As the maximal polarization entanglement is of utmost importance in long-distance quantum communication, this protocol may be very useful in future applications.
The uncertainty principle offers a bound to show accuracy of the simultaneous measurement outcome for two incompatible observables. In this letter, we investigate quantum-memory-assisted entropic uncertainty relation (QMA-EUR) when the particle to be measured stays at an open system, and another particle is treated as quantum memory under a noninertial frame. In such a scenario, the collective influence of the unital and nonunital noise environment, and of the relativistic motion of the system, on the QMA-EUR is examined. By numerical analysis, we conclude that, firstly, the noises and the Unruh effect can both increase the uncertainty, due to the decoherence of the bipartite system induced by the noise or Unruh effect; secondly, the uncertainty is more affected by the noises than by the Unruh effect from the acceleration; thirdly, unital noises can reduce the uncertainty in long-time regime. We give a possible physical interpretation for those results: that the information of interest is redistributed among the bipartite, the noisy environment and the physically inaccessible region in the noninertial frame. Therefore, we claim that our observations provide an insight into dynamics of the entropic uncertainty in a noninertial frame, and might be important to quantum precision measurement under relativistic motion.
An analytical expression of an Airy beam propagating in a strongly nonlocal nonlinear media is derived. The analytical expressions of the corresponding characteristic parameters for the Airy beam, such as the centre of gravity, the effective beam size, the curvature radius, the kurtosis parameter, and the linear momentum, have also been presented, respectively. The normalized intensity distribution and these characteristic parameters are pictorially demonstrated in the strongly nonlocal nonlinear media, respectively. It shows all the characteristic parameters versus the axial propagation distance are periodic. The period of the linear momentum versus the axial propagation distance is T = 2 pi z(0)/eta. The period of other characteristic parameters and the normalized intensity is T = pi z(0)/eta. The periodic behavior of the Airy beam in the strongly nonlocal nonlinear media has promising application in optical switch and optical micromanipulation.
For the first time of our knowledge, we demonstrate the graphene oxide as a saturable absorber (SA) in the passive mode-locking of a diode pumped Tm3+-doped laser. Broadly spectral region sub-10 ps mode-locking in a Tm:YAlO3 (Tm:YAP) laser near 2 mu m were obtained. With a pump power of 8.64 W, the average output power of 268 mW with the maximum pulse energy of 3.7 nJ at the pulse repetition frequency (PRF) of 71.8 MHz was obtained. (C) 2012 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA)
By directly brushing and scribing an ultra-thin (<5-mu m thick) polymer polyvinyl alcohol (PVA) film on one end-face of a FC/APC connector in erbium-doped fiber laser (EDFL), and then imprinting it with the graphite nano-particles exfoliated from a graphite foil, the intra-cavity graphite nanoparticle based saturable absorber can be formed to induce passive mode-locking effect in the EDFL. Such a novel approach greatly suppresses the film-thickness induced laser-beam divergent loss to 3.4%, thus enhancing the intra-cavity circulating power to promote the shortening on mode-locking pulsewidth. The saturable absorber with area coverage ratio of graphite nano-particles is detuned from 70 to 25% to provide the modulation depth enhancing from 11 to 20% and the saturated transmittance from 27 to 60%. Optimizing the coverage ratio reduces the non-saturable loss to 40% and enhances the modulation depth to 21%, such that the sub-ps soliton mode-locking can be initiated to provide a chirped pulsewidth of 482 fs and a linewidth of 2.87 nm. ((c) 2011 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) ((c) 2011 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA)
Experiments with trapped atomic gases have opened novel possibilities for studying the evolution of nonequilibrium finite quantum systems, which revived the necessity of reconsidering and developing the theory of such processes. This review analyzes the basic approaches to describing the phenomena of equilibration, thermalization, and decoherence in finite quantum systems. Isolated, nonisolated, and quasi-isolated quantum systems are considered. The relations between equilibration, decoherence, and the existence of time arrow are emphasized. The possibility for the occurrence of rare events, preventing complete equilibration, are mentioned.