Efficient four-wave mixing of a coupled double quantum-well nanostructure

We propose an efficient four-wave mixing (FWM) scheme in an asymmetric semiconductor double quantum-well (SDQW) structure based on intersubband transitions, and obtain the corresponding explicit analytical expressions for the input probe and generated FWM pulsed fields by use of the coupled Schrödinger-Maxwell approach. Under the resonant and phase-matched conditions, the FWM efficiency versus several variables is also discussed in details and the maximum FWM efficiency of the system under study is greater than 25%. Such a semiconductor system is much more practical than its atomic counterpart because of its flexible design and the controllable interference strength. This nonlinear optical process in the SDQW solid-state material can be used for efficiently generating coherent short-wavelength radiation.     

Coherent laser-induced optical behaviors in three-coupled-quantum wells and their application to terahertz signal detection

We investigate quantum optical behaviors of a weak-probe laser field in an asymmetric semiconductor three-coupled-quantum wells (TCQW) structure based on intersubband transitions (ISBTs) via switch-on/off of terahertz (TH) signal radiation under the application of a control laser field. A scheme for TH signal detection and its strength measurement based on this probe absorption characteristic also are put forward, where TH signal field does not interact directly with electron, but significantly affects the coherent optical absorption properties of such a weak-probe laser field. Consequently, the proposed TCQW nanostructure may be used for reducing and cancelling out the important thermionic dark current component in the process of TH signal detection, measurement and photodetector design.     

Phase-dependent gain and absorption properties of mid- to far-infrared lights in three-coupled-quantum-wells

We investigate the phase-dependent gain and absorption behaviors of mid- to far-infrared lights under a cascade configuration in an asymmetric semiconductor three-coupled-quantum-well (TCQW) structure based on intersubband transitions (ISBTs). In the proposed TCQW scheme, the amplification of the probe and signal fields, i.e., the far- and mid-infrared waves, can be realized with realistic experimental parameters. The gain-absorption spectra are strongly dependent on the relative phase of the applied laser fields. The influences of the probe detuning and the two pump Rabi energies on the gain-absorption responses of two weak far- and mid-infrared light fields are also discussed in details. The results show that amplifications of the far- and mid- infrared waves can be achieved by adjusting the relative phase, the probe detuning, and the two pump Rabi energies appropriately. Such a semiconductor system is much more practical than its atomic counterpart because of its flexible design and the wide adjustable parameters. For practical applications, this investigation may provide a new possibility for realizing the efficient gain of far- and mid-infrared waves in the solid-state materials.     

Efficient generation of maximally entangled states via four-wave mixing in a semiconductor quantum-dot nanostructure

We investigate the generation of the maximally entangled state of two weak-light pulses (the probe and generated pulses) via four-wave mixing (FWM) in a semiconductor quantum dot (SQD) with a biexciton-exciton cascade configuration. The results show that this maximally entangled state can propagate with an ultraslow group velocity under suitable parameter conditions. For application, our proposed scheme is probably achievable with the present technology by applying the standard GaAs/InGaAs self-assemble quantum dots (QDs). Furthermore, our calculations provide a guideline for the realization of the maximally entangled state in the SQD solid-state system, which can be much more practical than that in an atomic system because of its flexible design and the wide tunable parameters.     

Interactions of Three Dual-Dressing Effects of Four-Wave Mixing in a Five-Level Atomic System

We study the four-wave mixing （FWM） in an opening five-level system with two dressing fields. There axe three kinds of doubly dressing mechanisms （parallel cascade, sequential cascade, and nested cascade） in the system for doubly dressed four-wave mixing. These mechanisms reflect different correlations between two dressing fields and different effects of two dressing fields to the FWM. Investigation of these mechanisms is helpful to understand the generated high-order nonlinear optical signal dressed by multi-fields.     

Enhancement and Suppression of Four-Wave Mixing in a Four-Level Atomic System

We report observations of the enhancement and suppression of four-wave mixing （FWM） in an electromagnetically induced transparency window in a Y-type ^85 Rb atomic system. The results show the evolution of the dressed effects （from pure enhancement to partial enhancement/suppression, and finally into pure suppression） in the degenerate-FWM processes. Moreover, we use the perturbation chain method to describe the FWM process. Finally, we observe the polarization dependence of the enhancement and suppression of the FWM signal.     

Competition between Dispersion and Absorption of Doubly-Dressed Four-Wave Mixing and Dressed Six-Wave Mixing

We study the competition between dispersion and absorption of doubly-dressed four-wave mixing （DDFWM） and dressed six-wave mixing. In the case of weak coupling fields limit, we find DDFWM signal is affected by destructive interference between four-wave mixing（FWM） and six-wave mixing as wen as constructive interference between FWM and eight-wave mixing. By analysing the difference between two kinds of doubly dressing mechanisms （parallel cascade and nested cascade） in this opening five-level system, we can further understand the generated high-order nonlinear optical signal dressed by multi-fields.     

分布反馈激光器中剩余法布里-珀罗腔模对非简并四波混频特性的影响

基于四波混频(FWM)的全光波长转换技术是未来多波长通信系统的核心技术之一。除半导体光放大器(SOA)外,半导体激光器也是进行波长变换的器件。实验研究了小频率失谐到大频率失谐下分布反馈(DFB)激光器中剩余法布里珀罗腔模对非简并四波混频(NDFWM)的影响,并对其四波混频转换效率进行了分析。结果表明:当探测光波长与法布里珀罗腔的某一谐振波长一致时,分布反馈激光器中的四波混频转换效率将得到显著的增强;当频率失谐为太赫兹时,仍可得到较高的四波混频转换效率。     

Analysis of format conversion from optical 16QAM to QPSK based on cascaded four-wave mixing in semiconductor optical amplifier

A scheme of format conversion from optical 16-ary quadrature amplitude modulation (16QAM) to quadrature phase shift keying (QPSK) signal based on cascaded four-wave mixing (FWM) in semiconductor optical amplifiers (SOAs) is proposed. Theoretical analysis and simulations of the format conversion scheme are conducted to validate the feasibility of the proposal. In this proposal, the phase conjugated of 16QAM signal is generated after the first FWM process in an SOA, and then the QPSK signal is converted due to the second non-degenerate FWM (ND-FWM) process in another SOA. The performance and the optimal design of the 10 Gbit/s format conversion system under various key parameters of SOAs are evaluated and discussed. Simulation results present useful to enable interconnection between backbone network and access network.     

Slow light propagation via quantum coherence in a semiconductor quantum well

With the Schrödinger equations, we investigate the low-intensity light pulse propagation through a semiconductor quantum wells. Through studying the dispersion and absorption properties of the weak probe field, it is shown that slow light propagation is observed in this system. From the view point of practical purpose, it is more advantageous than its corresponding atomic system. Such investigation of slow light propagation may lead to important practical applications in semiconductor quantum information.     

Three-coupled-quantum-well nanostructures as a source of far-infrared entangled light

A scheme is proposed to achieve the two-mode entanglement in an asymmetric semiconductor three-coupled-quantum-well (TCQW) system based on the intersubband transitions (ISBTs). In the present scheme, the TCQW structure is trapped into a doubly resonant cavity, and the required quantum coherence effects is induced by the corresponding ISBTs, which is the key of realising entanglement. By numerically simulating the dynamics of the system, we show that the entangled cavity modes with the far-infrared wavelengh can be realised in this TCQW system. The present research provides an efficient approach to achieve far-infrared entangled light in the semiconductor nanostructures, which may have significant impact on the progress of solid-state quantum information theory.     

Spatial Splitting and Intensity Suppression of Four-Wave Mixing in V-Type Three-Level Atomic System

We illustrate our experimental observation of coexisting the controllable spatial splitting and intensity suppression of four-wave mixing （FWM） beam in a V-type three-level atomic system. The peak number and separation distance of the FWM beam are controlled by the intensities and frequencies of the laser beams, as well as atomic density.     

Kerr non-linearity and four-wave mixing in a double-cascade type four-level system of multiple quantum wells

We study the non-linear optical response in multiple quantum wells structure with a double-cascade type four-level configuration based on excitons and biexcitons transitions. By analysing the Kerr non-linear effects, we obtain the slow, mutually matched group velocities and giant Kerr non-linearity of probe and signal fields. While when the signal (or probe) field is removed, the non-linear optical phenomenon four-wave mixing (FWM) originating from quantum interference is demonstrated. The FWM efficiency of the system study is about 50%. Such a semiconductor system is much more practical than its atomic counterpart because of its flexible design and the controllable interference strength.     

A Novel Method for Wavelength Conversion with Dual-pump Four-wave Mixing in a Semiconductor Optical Amplifier

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Enhanced four-wave mixing in a hollow-core photonic-crystal fiber

Hollow-core photonic-crystal fibers are shown to substantially enhance four-wave mixing (FWM) of laser pulses in a gas filling the fiber core. Picosecond pulses of Nd:YAG fundamental radiation and its second harmonic are used to generate a signal at the frequency of the third harmonic by the FWM process 3omega = 2omega + 2omega - omega. The efficiency achieved for this process in a 9-cm-long, 13-microm-hollow-core-diameter photonic-crystal fiber, designed to simultaneously transmit a two-color pump and the FWM signal, is shown to be approximately 800 times higher than the maximum FWM efficiency attainable with the same laser pulses in the tight-focusing regime.     

Evaluation of the cross-polarization modulation impact on the conversion efficiency of a four wave mixing process developed in a bulk-SOA

This paper addresses, theoretically and experimentally, the impact of the cross-polarization modulation (XPolM) phenomenon on the conversion efficiency of a four wave mixing (FWM) process taking place in a bulk-SOA with input signals linearly co-polarized at 0°, 45°, 90°, and −45°. Based on the experimental determination of the output polarization states of the pump and probe signals, a technique is proposed to incorporate the XPolM effect in classic models describing the FWM. It is demonstrated that classic models lacking the inclusion of the XPolM effect can reflect a significant error in the estimation of the conversion efficiency.     

Highly efficient inelastic four-wave mixing using dual induced transparency and coherently prepared states

We investigate a life time broadened and coherently prepared five-state system for multi-wave mixing processes. We show that very efficient wave mixing occurs, producing an unconventional mixing wave that has the characteristics of both conventional four-wave mixing (FWM) and stimulated hyper-Raman (SHR) emission. In addition, we show interesting multiple simultaneous multi-photon interference effects at large propagation distances and demonstrate more than 10 orders of magnitude suppression of populations of the probe wave terminal state and the near three-photon resonance mixing wave generating state. These new type of multi-photon interference based induced transparency effects, which are critically dependent on two distinctive relaxation processes involving both an external supplied and an internally generated fields, are fundamentally different from the conventional three-state electromagnetically induced transparency effect which does not depend on propagation. As a consequence, both the probe and the wave-mixing field to propagate nearly free of absorption and distortions in a highly dispersive medium.     

Effect of spontaneously generated coherence on probe response in an open system

The effect of spontaneously generated coherence on the probe response in an open ladder atomic system with equispaced levels is studied. The result shows that by adjusting the strength of spontaneously generated coherence (SGC), electromagnetically induced transparency (EIT) and high dispersion (index of refraction) with zero absorption can be realized, a much larger gain without inversion (GWI) than that without SGC can be obtained. Moreover, in the open system and for some strength of SGC, GWI without the incoherent pumping is much larger than that with the incoherent pumping; however, in the corresponding closed system, when the incoherent pumping is absent, we cannot obtain any gain (with or without inversion) for any strength of SGC. In addition, the manipulation role of the atomic exit and injection rates on SGC-dependent absorption property is analyzed for the case when the incoherence pumping does not exist.     

A Novel Method for Wavelength Conversion with Dual-pump Four-wave Mixing in a Semiconductor Optical Amplifier

Using a semiconductor-fiber ring laser, a novel method for the all optical wavelength conversion based on dual-pump four-wave mixing (FWM) in a semiconductor optical amplifier (SOA) is demonstrated. For the input signal with different wavelengths, only one external pump is needed. This scheme can simplify the dual-pump FWM in SOA and has nearly constant conversion efficiency and signal-to-noise ratio (SNR) over 50nm range of wavelength shifts.     

Amplitude Regenerative Characteristics of RZ-DPSK Wavelength Converter Based on Four-Wave Mixing in SOA

We investigate the phase-preserving amplitude regenerative characteristics of the return-to-zero （RZ） differential- phase-shift-keying （DPSK） wavelength conversion based on four-wave m/xing （FWM） in a semiconductor optical amplifier （SOA）. The Q-factor and the optical signal-to-noise ratio （OSNR） before and after conversion are experimentally obtained and analysed in different input noise power levels. In both the continuous-wave and synchronous clock pumping cases, we find that there is amplitude clamping in the FWM conversion due to the gain saturation of SOA, which can suppress the amplitude fluctuation of the converted DPSK signal before and after demodulation. We have achieved 2-dB Q penalty improvement in our experiment demonstration of lOGbit/s RZ-DPSK signal with OSNR lower than 19dB.