Electrically driven nonreciprocity induced by interband photonic transition on a silicon chip

We demonstrate electrically driven nonreciprocity on a silicon chip. By achieving an indirect interband photonic transition, we show that the transmission coefficients between two single-mode waveguides become dependent on the propagation directions only in the presence of the electrical drive. Our structure is characterized by a nonsymmetric scattering matrix identical to a linear magneto-optical device.     

Nonlinear photonic crystals as a source of entangled photons

Nonlinear photonic crystals can be used to provide phase matching for frequency conversion in optically isotropic materials. The phase-matching mechanism proposed here is a combination of form birefringence and phase velocity dispersion in a periodic structure. Since the phase matching relies on the geometry of the photonic crystal, it becomes possible to use highly nonlinear materials. This is illustrated considering a one-dimensional periodic Al0.4Ga0.6As/air structure for the generation of 1.5 microm light. We show that phase-matching conditions used in schemes to create entangled photon pairs can be achieved in photonic crystals.     

Full-band direct-conversion receiver with enhanced port isolation and I/Q phase balance using microwave photonic I/Q mixer

A full-band direct-conversion receiver using a microwave photonic in-phase and quadrature(I/Q) mixer is proposed and experimentally evaluated in terms of radio frequency(RF) range, port isolation, phase imbalance,conversion gain, noise figure, spurious-free dynamic range, and error vector magnitude. The proposed microwave photonic I/Q mixer shows significant advantages in local oscillator leakage and I/Q phase imbalance over entire RF bands, which are recognized as major drawbacks of conventional direct-conversion receivers.     

多组分纠缠在光子晶体中的存储

研究了激子的多组分纠缠相干态保真度在各向异性光子晶体中的演化行为.结果表明,当激子的跃迁频率处于光子晶体带隙时,保真度随时间变化作周期振荡,这与激子处于真空环境时,保真度振荡衰减的演化行为不同.此外,当激子跃迁频率离光子晶体带边较远时,其多组分纠缠相干态越容易被保存.     

Recent progress in the development of type II interband cascade lasers

Type-II interband cascade lasers combine the advantage of an interband optical transition with interband tunneling to enable the cascading of type-II quantum well active regions as is done in type-I quantum cascade laser. The relatively high radiative efficiency resulting from interband optical transitions translates into very low-threshold current densities, and when combined with the high quantum efficiency of cascade lasers, this diode laser design has the potential to operate under cw conditions at room temperature with high output power. Experimental results have already demonstrated some of this potential including high differential external quantum efficiency (>600%), high peak output power (6 W/facet at 80 K), high cw power conversion efficiency (>17% at 80 K), and operation at 300 K under pulsed conditions. Recent work aimed at reducing device thermal resistance and increasing cw operating temperature is reviewed including the demonstration of significant reductions in thermal resistance (averaging 25 K/W or 40% for 1-mm-long devices), 80 K cw operation at 3.4 μm with high-power conversion efficiency (23%) and high differential external quantum efficiency (532%), and cw operation up to 214 K.     

Penetration of a symmetric light pulse through a wide quantum well

The reflection, transmission, and absorption of a symmetric electromagnetic pulse whose carrier frequency is close to the frequency of the interband transition in a quantum well are calculated. The energy levels in the quantum well are assumed to be discrete, and one excited level is taken into account. Consideration is given to the case of a sufficiently wide quantum well when the pulse wavelength corresponding to the carrier frequency is comparable to the quantum well width and when allowance should be made for the dependence of the matrix element of the interband transition on the photon wave vector. The calculations are performed with due regard for the difference between the refractive indices of the material of the quantum well and the barrier at an arbitrary ratio of the reciprocal radiative to nonradiative lifetimes of the excited level of the electronic system. It is demonstrated that the inclusion of the spatial dispersion and the difference in the refractive indices most strongly affects the reflection of the electromagnetic pulse, because the reflection due to interband transitions in the quantum well is accompanied by an additional reflection from the quantum well boundaries. Compared to the previously considered model, the most radical changes in the reflection are observed in the case when the reciprocal nonradiative lifetime of the excited state is substantially longer than the reciprocal radiative lifetime.     

Light frequency conversion in photonic crystals

Light frequency conversion when light interacts with a shock wave propagating through a photonic crystal is investigated. Two new phenomena are found, the first is that frequency increases by integral multiple of a certain amount in the process of frequency conversion. The second phenomenon is frequency conversion that still occurs when the shock wave front is replaced by a vacuum area. Through FDTD simulations and analytical theory, photon-phonon interaction and surface decaying mode interpretations for the mechanism of frequency conversion are found.     

Effect of spatial dispersion on the shape of a light pulse propagating through a quantum well

The reflection, transmission, and absorption of a symmetric electromagnetic pulse are calculated. The carrier frequency of the pulse is close to the frequency of direct interband transitions in a quantum well (QW). The QW energy levels are assumed to be discrete, with two closely spaced excited levels being taken into account. The QW width is assumed to be sufficiently large and comparable to the light wavelength corresponding to the pulse carrier frequency. In this case, the dependence of the momentum matrix element for the interband transition on the light wave vector should be taken into account. The refractive indices of the QW and barriers are assumed to be equal. The problem is solved for an arbitrary relation between the radiative and non-radiative lifetimes of the excited electronic states. It is shown that spatial dispersion considerably affects the shapes of the reflected and transmitted pulses. The greatest changes occur in the case where the inverse radiative lifetime is close to the difference between the frequencies of the interband transitions considered.     

Infrared probe of the electronic structure and charge dynamics of Na0.7CoO2

We present measurements of the optical spectra on Na(0.7)CoO(2) single crystals. The optical conductivity shows two broad interband transition peaks at 1.6 eV and 3.1 eV, and a weak midinfrared peak at 0.4 eV. The intraband response of conducting carriers is different from that of a simple Drude metal. A peak at low but finite frequency is observed, which shifts to higher frequencies with increasing temperature, even though the dc resistivity is metallic. The origin of the interband transitions and the low-frequency charge dynamics have been discussed and compared with other experiments.     

Photonic microwave bandpass filter with improved dynamic range

A technique to improve the dynamic range of a photonic microwave bandpass filter is proposed and experimentally demonstrated. The filter is implemented based on phase modulation to intensity modulation conversion using fiber Bragg gratings (FBGs) serving as frequency discriminators, with the optical carriers located at the left or right slopes of the FBGs, to generate positive or negative tap coefficients. The dynamic range of the photonic microwave bandpass filter is increased by reducing the optical-carrier-induced shot noise and relative intensity noise at the photodetector, which is realized by placing the optical carriers at the lower slopes of the FBG reflection spectra. A photonic microwave bandpass filter with an improvement in dynamic range of about 10 dB is demonstrated.     

金属光子晶体高功率微波模式转换器冷测研究

研究了同轴传输线中金属光子晶体的电磁特性,在此基础上优化了一种适用于窄带高功率微波源系统的金属光子晶体TEM-TE11模式转换器。该结构通过沿传输线角向部分填充的金属光子晶体实现移相。采用数值仿真程序对L波段模式转换器进行计算,在1.57GHz中心频率上,模式转换器转换效率为99%;在1.533～1.609GHz频率范围内,模式转换器效率大于90%,相对带宽4.8%。加工了TEM模式激励器和辐射天线,并在微波暗室对模式转换器进行了小信号测试,验证了模式转换器的性能。     

Carrier density dependence of soft TO-phonon in SnTe by Raman scattering

The frequency of soft TO-phonon in SnTe was observed by Raman scattering below the transition temperature, for the specimens of various carrier concentrations. The result was analyzed in terms of the interband electron to TO-phonon interaction.     

Photonic instantaneous microwave frequency measurement based on two different phase modulation to intensity modulation conversions

A novel photonic technique for instantaneous frequency measurement of microwave signal based on phase modulation to intensity modulation conversion is proposed and demonstrated. In the proposed system, an optical carrier is modulated by a microwave signal with its frequency to be measured through a phase modulator. The phase-modulated optical signal is then converted to intensity-modulated signals in two independent paths using a dispersive media and a frequency discriminator respectively. Since the dependence of the received microwave power on the input microwave frequency in the two paths differs, the microwave power ratio between the two paths can be used to uniquely determine the microwave frequency. The major advantages of the approach lie in that only one laser source and the bias-free phase modulator is employed in the system, which improves the stability of the system. Experimental demonstrations of the frequency measurement based on the proposed approach are presented.     

Entanglement of a two-level atom and its spontaneous emission near the edge of a photonic band gap

The entanglement of a two-level atom and its radiation field near the edge of a photonic band gap is studied by using the quantum entropy. Unlike the free space case, there is a steady-state entanglement between the atom and its spontaneous emission field even when the atomic transition frequency lies outside the band gap. Moreover, the degree of entanglement, which is due to the formation of atom–photon bound dressed state, depends on the detuning of the atomic transition frequency from the photonic band edge and can be controlled by a controllable photonic band gap crystal.     

Effects of alloying on the band structure of gold: Piezoreflectance measurements on some AuCo and AuV alloys

Piezoreflectance measurements have been made on a series of gold cobalt and gold vanadium alloys with impurity concentrations of up to 4% using a strain amplitude of 4 × 10^?4 at a frequency of 68 kHz. The spectra show that the main interband transitions occur at 2.4, 3.5 and 4.5 eV. The deformation potentials with impurity concentration have been found for these transitions. An additional interband transition was found to occur at an energy of 1.8eV and this was enhanced significantly with impurity concentration. This may be due to the impurity causing a broadening of the d bands and hence a smearing of the interband threshold or alternatively it may be caused by a d band to Fermi level transition along the Δ direction close to the X point.     

Continuous wave photonic crystal laser in ultraviolet range

It is shown that photonic band-gap (PBG) structures have great potential for the development of widely tunable continues wave and/or mode-locked ultrashort-pulse all-solid-stale lasers in UV and optical ranges. The basic idea is to decrease the laser threshold via inhibition of radiative decay of an upper laser level by embedding an active medium into spatial structure having PBG at the frequency of laser transition. This technique provides favorable conditions for coherent suppression of the excited state absorption crucial for short-wavelength solid-state lasing. It also resolves the laser gain dilemma, providing combination of high emission cross-section and large population inversion. Different designs of 2D and 3D photonic crystal laser are proposed.     

基于受激布里渊散射的宽带宽和高精度的微波频率瞬时测量

提出了一种基于受激布里渊散射效应的瞬时频率测量方法.未知信号经过强度调制作为泵浦光,矢量网络分析仪产生的信号经过相位调制作为扫描信号光,当泵浦光和扫描信号光之间满足相位匹配条件时,受激布里渊散射效应发生并实现相位调制到强度调制的转换,未知信号的频率被测量.实验验证可以测量0.5 GHz-27 GHz的微波信号的频率,最大误差小于20 MHz.     

The two-dimensional superconducting photonic crystal

The band structure of a two-dimensional superconducting photonic crystal is studied. The temperature dependence of the photonic band structure in a wide temperature region below the superconducting transition is analyzed. It is found that the photonic crystal has two full band gaps and two incomplete band gaps, which are shifted to the high frequency region with decreasing temperature.     

低维半导体异质结中的量子相干红外发射机理理论研究

给出了一种在非粒子反转条件下量子阱和量子点激光器的红外发射机理.此种红外发射是基于在同一作用区产生并作为红外场相干源的两种带间跃迁激光场的共振非线性混合.这种频率下转换机理并不依赖于在半导体激活媒质中的长时相干假定条件,在室温和泵注入电流条件下仍然有效.频率下转换的固有效率可以达到相当于每个可见光子产生一个红外光子的量子极限值.根据红外发射的可参变特性,这种非粒子反转的方法尤其适用于长波红外工作范围.     

基于双平行马赫-曾德尔调制器的大动态范围微波光子下变频方法

为了提高微波光子下变频链路的性能,提出了基于集成双平行马赫-曾德尔调制器的微波光子下变频方法.通过理论推导和数值仿真分析了系统的增益和无杂散动态范围,实验搭建了基于双平行马赫-曾德尔调制器的下变频链路,控制直流偏置电压使双平行马赫-曾德尔调制器工作在高载波抑制的双边带调制模式,并对链路进行了性能测试.实验结果表明:该下变频链路的增益为7.43 d B,无杂散动态范围达到了110.85 d B/Hz2/3,工作频段可覆盖5—18 GHz的宽频范围.基于双平行马赫-曾德尔调制器的下变频方法可优化设计输出频谱,系统结构简单、易于实现,为微波光子下变频链路提供了有效的解决方案.