Electronic-spin generation in multi-photon processes: Cubic anisotropy of pumping

We study the spin generation in multi-photon absorption processes in a bulk semiconductor, pumped it by a circularly polarized intense light by varying the angle of incidence. The generated spin polarization is calculated using the eight-band Kane model in the limit of large spin–orbit splitting and on the basis of the multi-photon photo-generation rate of the conduction electron spin density. It is found that the spin polarization strongly depends on the pumping photon energy outside the band edge. Cubic anisotropy in crystal pumping is also calculated. The results show that due to this anisotropy the spin generation differs by ∼8%, in consistence with earlier results obtained by others.     

A simultaneous generation of QKD and QDC via optical memory array for distributed network security

We propose a novel system of a simultaneous generation of continuous variable quantum key distribution (QKD) and quantum dense coding (QDC) via an optical memory array. The optical memory system is formed by using an array waveguide incorporating a nano-ring resonator, whereas the different spatial light modes can be generated and stored within an optical memory unit. The polarized photon is formed and stored within a storing device, i.e. a ring resonator, whereas the different time slot entangled photons can be generated, transmitted and detected by the different subscriber in the distributed networks. By using the optical memory concept, the continuous variable quantum key distribution is provided. Furthermore, the use of quantum dense coding via time division multiplexing paths, i.e. different time slot, is also plausible. The advantage of the proposed system is that the quantum key distribution can provide the network top security with high capacity and safety, which is the large demand of usage in the public networks.     

A novel system of the simultaneous trapping of dark-bright solitons within a nano-waveguide system

We propose a novel system of a nano-waveguide that can be used to generate the continuous spectrum, i.e. white light. The simultaneous trapping and generation of short and millimeter waves can also be performed by using either bright or dark soliton. A system consists of two micro- and a nano-ring resonators that can be integrated into a single system. The large bandwidth is generated by a soliton pulse within a Kerr-type nonlinear medium where the continuous bandwidth or wavelength can be performed. The simultaneous dark-bright solitons conversion is performed and achieved. Results obtained have shown the potential of using the technique for continuing light spectra generation, where the filtering signals are allowed by using the suitable device parameters. The advantage is that the large bandwidth separation of the short and sub-millimeter waves can be obtained, which is allowed to form the simultaneous generation of short and millimeter waves within a single system. Further, light pulse can be trapped within a nano-waveguide, which is available to form the memory device.     

A novel system for optically localized soliton pulse in a nano-waveguide

We propose a novel optical system that can be used to trap (store) light coherently. The system consists of two micro and a nano-ring resonators that can be integrated into a single system, which can be employed to generate the large bandwidth by a soliton pulse within a Kerr type nonlinear medium. The balance between dispersion and nonlinear lengths of the soliton pulse exhibits the soliton behavior known as self-phase modulation, which introduces the optical output (i.e. gain) constant, which means that light pulse can be trapped, i.e. localized coherently within the nano-waveguide. The time independent soliton pulse is adiabatically localized within the nano-ring device. Results obtained have shown that the trapping of the localized temporal and spatial soliton pulses is achieved.     

Confined-acoustic-phonon-assisted cyclotron resonance via multi-photon absorption process in GaAs quantum well structure

Phonon-assisted cyclotron resonance (PACR) in GaAs quantum well (QW) structure is investigated via multi-photon absorption process when electrons interact with the confined acoustic phonon through deformation potential. The additional peaks in the absorption spectrum due to transitions between Landau levels accompanied with the emission and absorption of phonons are indicated. The dependence of absorption power on the temperature, magnetic field and well width is presented. Using profile method, we obtain PACR-linewidth as profiles of the curves. The temperature, magnetic field and well width dependences of the PACR-linewidth are investigated. The results are compared with those in the case of mono-photon absorption process, as well as in the electron-bulk acoustic phonon interaction. The results show that the multi-photon absorption process is strong enough to be detected in PACR.     

A quantum-chaotic encoding system using an erbium-doped fiber amplifier in a fiber ring resonator

This paper firstly presents a new concept of quantum-chaotic encoding of light traveling in a fiber optic ring resonator. The pumping input power can be controlled to generate the chaotic behavior of the circulated light within the fiber ring resonator. The Kerr nonlinear type of light circulating in a fiber optic ring resonator is induced and the superposition i.e. four-wave mixing of the propagating waves at resonance occurred. The output signals can be used to generate two different codes, of which one is the quantum bits i.e. code, the other is the chaotic signal i.e. code. The proposed system has shown the potential of using for communication security, where the double security via quantum-chaotic can be performed.     

Towards an efficient atomic frequency comb quantum memory

We present an efficient photon-echo experiment based on atomic frequency combs [Phys. Rev. A 79 (2009) 052329]. Echoes containing an energy of up to 35% of that of the input pulse are observed in a Pr³⁺-doped Y₂SiO₅ crystal. This material allows for the precise spectral holeburning needed to make a sharp and highly absorbing comb structure. We compare our results with a simple theoretical model with satisfactory agreement. Our results show that atomic frequency combs has the potential for high-efficiency storage of single photons as required in future long-distance communication based on quantum repeaters.     

Quantum communication exploiting above threshold OPO intensity correlations and polarization encoding

We present a continuous variable quantum communication protocol based on bright continuous-wave twin-beams generated by a type-II OPO. Intensity correlation between the beams is used in conjunction with a binary randomization of polarization to guarantee security and reveal eavesdropping actions. The scheme presented is asymmetric. Bob (the receiver) retains one of the beams and sends the other one to Alice after a random rotation of its polarization. The cryptographic key elements are encoded through amplitude modulation by Alice, who sends back her beam to Bob after a second rotation of the polarization. Eventually, the beams are detected by Bob after a further random polarization rotation. The security of the system and the possibility of revealing the eavesdropping action in the case of an individual attack are demonstrated by evaluating the bit error rates.     

Optical millimeter-wave generation and transmission system for 1.25 Gbit/s downstream link using a gain switched laser

In this paper, we propose a novel and cost effective system for optical millimeter-wave (mm-wave) generation and transmission of downstream data based on a gain switched laser (GSL). The GSL produces an optical comb spectrum that can be appropriately filtered to generate two optical sidebands spaced by more than 4 times the repetition rate of the GSL. These sidebands are modulated by baseband data and then transmitted via optical fiber to the remote antenna unit (RAU). At the RAU, the two sidebands are heterodyned using a photodetector to generate the electrical modulated mm-wave signal, before demodulation using self mixing. We demonstrate the distribution of 1.25 Gbit/s data OOK modulated onto a 60 GHz carrier, similar to that used in the IEEE 802.15.3c draft standard, over fiber lengths up to 62 km.     

Third-harmonic generation in asymmetric coupled quantum wells

The third-harmonic generation (THG) in asymmetric coupled quantum wells (ACQWs) for different values of the well parameter Δ$\Delta$ and width of barrier (_WB)$\left(W_B\right)$ are theoretically studied. The analytical expression of the third-harmonic generation is derived by using the compact density-matrix approach and the iterative method. Finally, the numerical calculations are presented for typical GaAs/Al_xGa_1−xAs asymmetric coupled quantum wells. Results obtained show that the third-harmonic generation in the asymmetric coupled quantum wells can be importantly modified by the parameter Δ$\Delta$ and _WB$W_B$. Moreover, third-harmonic generation also depends on the relaxation rate of the asymmetric coupled quantum wells.     

Second-harmonic generation from nonlocal interaction between terahertz waves and step quantum wells

Second-harmonic generation (SHG) excited by a p-polarized terahertz wave interacting with AlGaAs/GaAs step quantum wells (STQW’s) is investigated on the basis of the microscopic nonlocal response theory. The numerical results show that there are two resonant peaks in the energy reflection spectrum of the SHG, whose position and amplitude are tunable via the structural parameters of the STQW’s and the incident optical intensity. It is clarified that the spatial nonlocality of the linear and second-order nonlinear optical responses can lead to a blueshift of the second-harmonic spectra, while the third-order nonlinearity can induce a spectral redshift. Furthermore, an optimal STQW is presented, for obtaining the largest SHG signal and observing the SH spectra by experiment.     

Disorder-induced natural quantum dots in InAs/GaAs nanostructures

Properties of excitons confined to potential fluctuations due to indium distribution in the wetting layer which accompany self-assembled InAs/GaAs quantum dots are reviewed. Spectroscopic studies are summarized including time-resolved photoluminescence and corresponding single-photon emission correlation measurements. The identification of charge states of excitons is presented which is based on results of a theoretical analysis of interactions between the involved carriers. The effect of the dots’ environment on their optical spectra is also shown.     

A special attack on the multiparty quantum secret sharing of secure direct communication using single photons

The security of a multiparty quantum secret sharing protocol [L.F. Han, Y.M. Liu, J. Liu, Z.J. Zhang, Opt. Commun. 281 (2008) 2690] is reexamined. It is shown that any one dishonest participant can obtain all the transmitted secret bits by a special attack, where the controlled-(-iσ_y) gate is employed to invalidate the role of the random phase shift operation. Furthermore, a possible way to resist this attack is discussed.     

Third-harmonic generation in cylindrical quantum dots in a static magnetic field

The third-harmonic generation (THG) coefficient for cylindrical quantum dots in a static magnetic field is investigated theoretically. By using the compact density-matrix approach and the iterative method, we obtain an analytical expression for the THG coefficient, and numerical calculations for typical GaAs/AlAs cylindrical quantum dots are presented. The results show that the THG coefficient can reach a magnitude of 10⁻¹⁰ m²/V ². In addition to the radius R of the cylindrical quantum dots, both the parabolic confining potential and the static magnetic field have an influence on the THG coefficient.     

Polarized soliton pulses generation using nonlinear micro ring resonators for multi- and long distance links

We propose a new concept of quantum soliton pulses generation using a soliton pulse in the micro ring resonators. Firstly, the chaotic soliton pulses are generated and circulated within the integrated micro ring resonators. Secondly, the specific second harmonic pulses are selected by using the appropriate ring parameters. The superposition of the second harmonic pulses within the micro ring devices introduces the randomly polarized photons within the micro ring device. The entangled photon visibility of the polarized photon is seen after passing the polarization control devices and projecting on the detectors. The optimum entangled photon visibility is obtained. The advantage of such a system is that the quantum repeater unit can be redundant for long distance quantum communication link, whereas the use of the system for multi-entangled photon sources and links is also available. The system degradation via the entangled photon states timing walk-off is also discussed.     

Practical decoy-state BB84 quantum key distribution with quantum memory

We generalize BB84 quantum key distribution(QKD) to the scenario where the receiver adopts a heralded quantum memory(QM). With the heralded QM, the valid dark count rate of the receiver's single photon detectors can be mitigated obviously, which will lower the quantum bit error rate, and thus improve the performance of decoy-state BB84 QKD systems in long distance range. Simulation results show that, with practical experimental system parameters, decoy-state BB84 QKD with QM can exhibit performance comparable to that of without QM in short distance range, and exhibit performance better than that without QM in long distance range.     

Integrated quantum key distribution system using single sideband detection

We report a new quantum cryptographic system involving single sideband detection and allowing an implementation of the BB84 protocol. The transmitted bits are reliably coded by the phase of a high frequency modulating signal. The principle of operation is described in terms of both classical and quantum optics. The method has been demonstrated experimentally at 1 550 nm using compact and conventional device technology. Single photon interference has been obtained with a fringe visibility greater than 98%, indicating that the system can be used in view of quantum key distribution potentially beyond 50-km-long standard single-mode fiber. Received 13 July 2001 and Received in final form 30 November 2001     

AWG and EDFA based optical packet switch using feedback shared loop buffer memory

Optical packet switching provides high speed, data rate/format transparency, efficient use of bandwidth and flexibility. The major problem in the implementation of “all-optical” switching is contention which occurs when two or more packets arrive at the same time for the same destination. To resolve the contention, we have proposed an optical packet switch architecture based on WDM loop buffer memory in the feedback configuration. In that architecture, the contending packets are stored in a loop buffer module, and routed in the free time slots. The buffering duration in the recirculating loop is limited by a circulation limit. The analysis was been done to obtain the maximum number of allowed circulations. This paper proposes improved version of that optical packet switch architecture, to increase the number of maximum allowed circulations. The modification is done either by adding an extra erbium doped fiber amplifier (EDFA) in the original switch or by replacing the core space switch with arrayed waveguide grating (AWG). The performance analysis has been done by the simulations.     

Quantum packet switching generation using correlated photons in a microring resonator system

We propose a new system of a packet of quantum bits generation using a soliton pulse within a microring resonator. A quantum gate can be formed by using a polarization control unit incorporating into the system. The random signal and idler pairs can be formed within the photon correlation bandwidth, which can be generated, and randomly form the packet quantum bits, i.e. quantum packet switching. Each random code (logic) can be performed by combining the signal and idler of each entangled photon pair via the quantum gate. Results obtained have shown that the packet of quantum logic bits can be generated using the entangled photon pairs generated by the proposed system.