MXene与溶剂界面电子振动耦合现象的直接观测

作为一种新型的二维材料,MXene凭借其各种优异的物理化学性质已受到极为广泛的关注,例如其具有极其出色的光热转换效率. 然而,人们对MXene的光热转换机制仍然知之甚少. 本文通过结合飞秒可见和中红外瞬态吸收光谱技术,对分散在各种溶剂中MXene(Ti₃C₂T_x)纳米片内的电子能量耗散动力学进行了系统的研究. 结果表明,MXene的激发态寿命在很大程度上取决于周围的溶剂环境. 在MXene被超快激光泵浦后,可以直接观察到MXene纳米片与相邻溶剂分子之间的界面电子振动耦合现象. 这些结果表明界面相互作用在MXene的超快能量传输动力学中起着关键的作用. 这一发现可为二维体系光转换性能的改进提供了一条潜在可行的途径.     

Ultrafast all-optical signal processing with Symmetric Mach–Zehnder type all-optical switches

We present Symmetric Mach–Zehnder (SMZ) type all-optical switches: an SMZ all-optical switch, a polarization-discriminating SMZ (PD-SMZ) all-optical switch, and a delayed interference signal wavelength converter (DISC). These switches are capable of ultrafast, low control power, and low chirp switching, which is not restricted by slow relaxation of highly efficient nonlinearities. High repetition operation unrestricted by slow relaxation is also possible for these switches. This is because of a push–pull modulation scheme or sometimes called a differential phase modulation scheme. These three devices are similar, but different in some important aspects, thus a comparison is made among the three. Then semiconductor optical amplifiers (SOAs) are discussed as a nonlinear phase shifter for these devices. Then, ultrafast all-optical signal processing using SOA based SMZs is demonstrated. Error-free demultiplexing from 168 to 10.5 Gbit/s is presented, in which a hybrid-integrated SMZ (HI-SMZ) is used as a demultiplexer. In pulse regeneration experiment, the signal pulses at 84 Gbit/s are regenerated by the PD-SMZ and the regenerated pulses are demultiplexed to 10.5 Gbit/s by the HI-SMZ to verify error-free operation. The retiming capability of this scheme is quantitatively demonstrated. Also presented is error-free all-optical wavelength conversion at 168 Gbit/s using the DISC. These results represent the fastest error-free operations reported to date in each category.     

Harmonic Mode-Locked Er-Doped Fiber Laser by Evanescent Field-Based MXene Ti3C2Tx (T = F,O, or OH) Saturable Absorber

MXenes, as a legendary family of 2D van der Waals nanosheets materials, are extensively studied due to their unique characteristics of broadband nonlinear optical response. In particular, MXenes have excellent nonlinear optical properties of very large nonlinear absorption coefficients and very large nonlinear refractive indexes, which have attracted people's great attentions to study the application of MXenes in photonics, electronics, and optoelectronics in recent years. However, the high-repetition-rate (HRR) ultrafast pulses are not explored based on these kinds of materials. MXene Ti₃C₂T_x saturable absorber (SA) based on micro-fiber is fabricated by optical deposition method. Here, MXene Ti₃C₂T_x SA is used to achieve 36th harmonic mode-locking with a repetition rate of 218.4 MHz, a central wavelength of 1566.9 nm, the pulse width of 850 fs, and the spectral width of 3.51 nm. The maximum average output power and pulse energy are 6.95 mW and 0.032 nJ, respectively. This research based on MXene Ti₃C₂T_x light modulator opens a bright avenue for advanced nonlinear photonics.     

基于二维材料MXene的仿神经突触忆阻器的制备和长/短时程突触可塑性的实现

兼具长时程可塑性与短时程可塑性的电子突触被认为是类脑计算系统的重要基础.将一种新型二维材料MXene应用到忆阻器中,制备了基于Cu/MXene/SiO_2/W的仿神经突触忆阻器.结果表明, Cu/MXene/SiO_2/W忆阻器成功实现了稳定的双极性模拟阻态切换,同时成功模拟了生物突触短时程可塑性的双脉冲易化功能和长时程可塑性的长期增强/抑制行为,其中双脉冲易化的易化指数与脉冲间隔时间相关. Cu/MXene/SiO_2/W忆阻器的突触仿生特性,归功于MXene辅助的Cu离子电导丝形成与破灭的类突触响应机理.由于Cu/MXene/SiO_2/W忆阻器兼具长时程可塑性与短时程可塑性,其在突触仿生电子学和类脑智能领域将会具有巨大的应用前景.     

All-optical quantization and coding scheme for ultrafast analog-to-digital conversion exploiting polarization switches based on nonlinear polarization rotation in semiconductor optical amplifiers

A novel all-optical quantization and coding scheme for ultrafast analog-to-digital (A/D) conversion exploiting polarization switches (PSWs) based on nonlinear polarization rotation (NPR) in semiconductor optical amplifiers (SOAs) is proposed. In addition, a theoretical model for the polarization switch based on NPR is presented. Through cascading two PSWs, a 2-period transfer function for 3-bit long all-optical quantization and coding is realized numerically for the first time to the authors’ knowledge. The effective number of bits (ENOB), the limitation of bandwidth and conversion speed and the scalability are also investigated. The proposed all-optical quantization and coding scheme, combined with existing all-optical sampling techniques, will enable ultrafast A/D conversion at operating speed of hundreds of Gs/s with at least 3 bit resolution, and allows low optical power requirements, photonic integration, and easy scalability.     

Ultrafast optical switching in Kerr nonlinear photonic crystals

Nonlinear photonic crystals made from polystyrene materials that have Kerr nonlinearity can exhibit ultrafast optical switching when the samples are pumped by ultrashort optical pulses with high intensity due to the change of the refractive index of polystyrene and subsequent shift of the band gap edge or defect state resonant frequency. Polystyrene has a large Kerr nonlinear susceptibility and almost instantaneous response to pump light, making it suitable for the realization of ultrafast optical switching with a response time as short as a few femtoseconds. In this paper, we review our experimental progress on the continual improvement of all-optical switching speed in two-dimensional and three-dimensional polystyrene nonlinear photonic crystals in the past years. Several relevant issues are discussed and analyzed, including different mechanisms for all-optical switching, preparation of nonlinear photonic crystal samples by means of microfabrication and self-assembly techniques, characterization of optical switching performance by means of femtosecond pump-probe technique, and different ways to lower the pump power of optical switching to facilitate practical applications in optical information processing. Finally, a brief summary and a perspective of future work are provided.     

Ultrafast optical switching in Kerr nonlinear photonic crystals

Nonlinear photonic crystals made from polystyrene materials that have Kerr nonlinearity can exhibit ultrafast optical switching when the samples are pumped by ultrashort optical pulses with high intensity due to the change of the refractive index of polystyrene and subsequent shift of the band gap edge or defect state resonant frequency. Polystyrene has a large Kerr nonlinear susceptibility and almost instantaneous response to pump light, making it suitable for the realization of ultrafast optical switching with a response time as short as a few femtoseconds. In this paper, we review our experimental progress on the continual improvement of all-optical switching speed in two-dimensional and three-dimensional polystyrene nonlinear photonic crystals in the past years. Several relevant issues are discussed and analyzed, including different mechanisms for all-optical switching, preparation of nonlinear photonic crystal samples by means of microfabrication and self-assembly techniques, characterization of optical switching performance by means of femtosecond pump-probe technique, and different ways to lower the pump power of optical switching to facilitate practical applications in optical information processing. Finally, a brief summary and a perspective of future work are provided.     

Ultrafast All-Optical Serial-to-Parallel Conversion and Its Application to Optical Label Processing

A novel scheme for all-optical serial-to-parallel conversion (SPC) is proposed for label recognition of ultrafast asynchronous burst optical packets. Compact SP converter modules were developed using a fiber array or a surfaceemitting planar lightwave circuit, and 1-Tbit/s and 40-Gbit/s SPC for 16-bit optical packets is demonstrated using the modules. The key device in the converter is a spin-polarized surface-reflection all-optical switch (LOTOS) with an ultrafast switching time (250 fs) and an extremely high on/off ratio (>30 dB). Label recognition of 40-Gbit/s 16-bit burst-mode optical packets is experimentally confirmed using an optical clock-pulse generator and a complementary metal-oxide-semiconductor (CMOS) electronics circuit as well as the all-optical SP converter. 1 x 4 self-routing is also demonstrated using 2-channel control signals generated from the CMOS circuit according to a routing table.     

All-optical pulse regeneration in an ultrafast nonlinear interferometer with Faraday mirror polarization stabilization

We demonstrate the folded ultrafast nonlinear interferometer (FUNI) as a 3R all-optical regenerator. Faraday rotation provides inherent polarization stabilization, and the optical fiber nonlinear medium provides ultrafast operation and switching window tunability. We demonstrate 3R regeneration of 10-Gbit/s data with 5-pJ pulse switching energy and 4-ps timing-jitter tolerance.     

Large Kerr effect in bulk Se-based chalcogenide glasses

High-speed optical communication requires ultrafast all-optical processing and switching capabilities. The Kerr nonlinearity, an ultrafast optical nonlinearity, is often used as the basic switching mechanism. A practical, small device that can be switched with ~1-pJ energies requires a large Kerr effect with minimal losses (both linear and nonlinear). We have investigated theoretically and experimentally a number of Se-based chalcogenide glasses. We have found a number of compounds with a Kerr nonlinearity hundreds of times larger than silica, making them excellent candidates for ultrafast all-optical devices.     

Characterization and optimization of SOA-based UNI recirculating shift register switching window

The operation of an all-optical recirculating shift register implemented with the semiconductor optical amplifier (SOA)-based ultrafast nonlinear interferometer (UNI) in a counter-propagating, inverting configuration is methodically studied and analyzed. This is achieved by applying an appropriate model for a SOA deployed as the nonlinear element in an interferometric switch driven by ultrafast and strong feedback optical pulses. By means of numerical simulation the impact of the critical functional parameters on the formation of the switching window is thoroughly investigated and assessed enabling to provide useful design rules for their proper selection and combination so as to optimize the specific metric and ensure high performance. The undertaken theoretical treatment can be extended for characterizing other more complex all-optical circuits and subsystems of enhanced functionality that employ this type of shift register as the key building module.     

SOA-assisted Sagnac switch and investigation of its roadmap from 10 to 40 GHz

Future broadband optical communications networks will rely on all-optical switches to perform a set of processing functions exclusively in the optical domain. Interferometric optical switches using semiconductor optical amplifier (SOA) nonlinearities can perform efficient optical switching with few tens of fJ control energies and short fiber lengths allowing for monolithic integration. In this paper we present work performed with a three terminal SOA-assisted Sagnac interferometer. We review all-optical Boolean AND and XOR logic results at 10 GHz and 10 Gb/s for full duty cycle and pseudo-random data pattern operation, respectively, achieved with adequate contrast ratios, remarkably low switching energies and low pattern dependence. The ability of the device to be cascaded was proved up to 10 GHz by recirculating stably for hours arbitrary pattern profiles. Finally, and in view of the extension of photonic networks single channel data rates beyond 40 Gb/s, the performance of the switch was simulated in terms of its critical parameters. The obtained results showed that full switching operation at 40 GHz or higher is feasible either by deploying gain recovery reduction techniques in bulk and quantum well SOAs or alternatively other technologically advanced optical devices, such as quantum dot SOAs.     

Ultrafast digital soliton logic gates

We demonstrate all-optical fibre switches, including soliton-dragging logic gates, soliton-interaction gates and soliton-trapping AND-gates, that have the potential of operating up to speeds of 0.2 Tbps. Solitons in fibres are attractive for ultrafast timedomain switching because they avoid pulse distortion during propagation and because they exhibit particle-like properties. Soliton-dragging logic gates satisfy all requirements for a digital optical processor and having switching energies approaching 1 pJ. In addition, soliton-dragging logic gates are one example of a more general timedomain chirp switch architecture in which a dispersive delay line acts as a lever-arm to reduce the switching energy. Soliton-interaction gates are based on elastic collisions between solitons and illustrate that solitons can be used to implement conservative, billiard-ball logic operations. Soliton-trapping AND-gates are sensitive to the timing of the input pulses and display on/off contrast ratios greater than 201. The soliton-trapping AND-gate can serve as the final stage in an all-optical system and as the interface to electronics. These ultrafast gates may prove advantageous in applications where the switch bandwidth limits the performance of the system     

Low-temperature-grown surface-reflection all-optical switch (LOTOS)

The low-temperature-grown surface-reflection all-optical switch, or LOTOS, is an ultrafast saturable absorber made with Be-doped strained InGaAs/InAlAs MQWs. It's operation principle is the carrier-induced change in the excitonic absorption of the MQWs. Its ultrafast operation (250 fs) is a result of the MQW region being grown at a low temperature (200 °C) and doped with Be. Large optical nonlinearity is obtained by compressively straining the quantum wells and using a reflection geometry combined with a low-reflectivity DBR: a so-called asymmetric Fabry–Perot etalon with an extremely low finesse. All of these things enable ultrafast all-optical switching operation with a high on/off ratio, a wide range of operating wavelengths, and polarization insensitivity. A spin-polarization scheme results in on/off ratios more than 20 dB better than those obtained with the conventional scheme, and handling the two orthogonal components of the signal pulse at two different points makes the switch operation polarization insensitive. Tests confirm that the LOTOS offers an ultrafast demultiplexer capable of simultaneous multi-output operation future high-speed optical communications systems.     

Interferometric ultrafast SOA-based optical switches: From devices to applications

All-optical switches are fundamental building blocks for future, high-speed optical networks that utilize optical time division multiplexing (OTDM) techniques to achieve single channel data rates exceeding 100 Gb/s. Interferometric optical switches using semiconductor optical amplifier (SOA) non-linearities perform efficient optical switching with < 500 fJ of control energy and are approaching optical sampling bandwidths of nearly 1 THz. In this paper, we review work underway at Princeton University to characterize and demonstrate these optical switches as processing elements in practical networks and systems. Three interferometric optical switch geometries are presented and characterized. We discuss limitations on the minimum temporal width of the switching window and prospects for integrating the devices. Using these optical switches as demultiplexers, we demonstrate two 100-Gb/s testbeds for photonic packet switching. In addition to the optical networking applications, we have explored simultaneous wavelength conversion and pulse width management. We have also designed high bandwidth sampling systems using SOA-based optical switches as analog optical sampling gates capable of analyzing optical waveforms with bandwidths exceeding 100 GHz. We believe these devices represent a versatile approach to all-optical processing as a variety of applications can be performed without significantly changing the device architecture.     

Circuit designs of ultra-fast all-optical modified signed-digit adders using semiconductor optical amplifier and Mach-Zehnder interferometer

The need for increasingly high-speed digital optical systems and optical processors demands ultra-fast all-optical logic and arithmetic units. In this paper, we combine the attractive and powerful parallelism property of the modified signed-digit (MSD) number representation with the ultra-fast all-optical switching property of the semiconductor optical amplifier and Mach-Zehnder interferometer (SOA-MZI) to design and implement all-optical MSD adder/subtracter circuits. Non-minimized and minimized techniques are presented to design and realize efficient circuits to perform arithmetic operations. Several all-optical circuits’ designs are proposed with the objective to minimize the number of the SOA-MZI switches, the time delay units in the adders, and other optical elements. To use the switching property of the SOA-MZI structure, two bits per digit binary encoding for each of the trinary MSD digits are used. The proposed optical circuits will be very helpful in developing hardware modules for optical digital computing processors.     

All-optical demultiplexing of 640 to 40 Gbits/s using filtered chirp of a semiconductor optical amplifier

We present a high-capacity ultrafast all-optical time demultiplexer that can be employed to retrieve 40 gigabits/second (Gb/s) base-rate channels from a 640 Gb/s single-polarized signal. The demultiplexer utilizes ultrafast effects of filtered chirp of a semiconductor optical amplifier. Excellent demultiplexing performance is shown at very low switching powers: +8 dBm (640 Gb/s data) and -14 dBm (40 GHz clock). The demultiplexer has a simple structure and, in principle, allows monolithic integration.     

40-Gbit/s all-optical circulating shift register with an inverter

We report what is believed to be the first demonstration of an all-optical circulating shift register using an ultrafast nonlinear interferometer with a polarization-insensitive semiconductor optical amplifier as the nonlinear switching element. The device operates at 40 Gbits/s, to our knowledge the highest speed demonstrated to date. Also, the demonstration proves the cascadability of the ultrafast nonlinear interferometric switch.     

A comparison of optically and electronically controlled optical switches

Electronically and optically controlled optical switches are compared with respect to switch energy requirements. Only switches based on optical phase change are treated, since these have the largest flexibility. Further, only switches that preserve input wavelength at the output are considered, due to cascadeability requirements. It is argued that as long as ‘all-optical’ switches need electronically controlled switches for information transfer to the optical signals controlling the all-optical switch, this will compromise any other advantages that the all-optical switch and the corresponding systems might have. A further application for all-optical switches, which currently are orders of magnitude faster than electronically controlled ones, would be in banks of electronically controlled slower all-optical switches which are all-optically multiplexed to drive all-optical switches to data rates not currently achievable by electronically controlled switches. It is argued that such systems will be complex, requiring sophisticated electronic synchronization and being inferior to corresponding wavelength division multiplexing systems. Power dissipation and switch energy are analyzed for two different physical mechanisms for controllably changing the refractive index in the all-optical and electronically controlled optical switches: Pockels and Kerr effects as well as the plasma or free carrier effect and the relative merits of electronically and optically controlled optical switches using these are discussed. It is shown that, in the former case, (Pockels and Kerr effects) using representative data, electronically controlled switches are generally more power efficient than the all-optical counterparts.     

Au纳米颗粒阵列中双光子吸收的饱和过程

采用纳米球蚀刻法制备了Au纳米颗粒阵列.并通过扫描电子显微镜观测了其表面形貌,表明三角形的Au纳米颗粒呈阵列状分布.采用Z扫描方法(800 nm, 50 fs)测量了Au纳米颗粒阵列的三阶非线性光学特性.在较小的激发功率下,结果呈现出双光子吸收效应,随着激发功率不断增加,出现了双光子吸收饱和的过程;非线性折射则呈现出自散焦效应.这种高效率的非线性响应机理使得该种Au纳米颗粒阵列在高速全光开关中有潜在的应用价值. 关键词： 纳米球蚀刻技术 Au纳米颗粒 三阶光学非线性