Single photon frequency up-conversion and its applications

Optical frequency up-conversion is a technique, based on sum frequency generation in a non-linear optical medium, in which signal light from one frequency (wavelength) is converted to another frequency. By using this technique, near infrared light can be converted to light in the visible or near visible range and therefore detected by commercially available visible detectors with high efficiency and low noise. The National Institute of Standards and Technology (NIST) has adapted the frequency up-conversion technique to develop highly efficient and sensitive single photon detectors and a spectrometer for use at telecommunication wavelengths. The NIST team used these single photon up-conversion detectors and spectrometer in a variety of pioneering research projects including the implementation of a quantum key distribution system; the demonstration of a detector with a temporal resolution beyond the jitter limitation of commercial single photon detectors; the characterization of an entangled photon pair source, including a direct spectrum measurement for photons generated in spontaneous parametric down-conversion; the characterization of single photons from quantum dots including the measurement of carrier lifetime with escalated high accuracy and the demonstration of the converted quantum dot photons preserving their non-classical features; the observation of 2nd, 3rd and 4th order temporal correlations of near infrared single photons from coherent and pseudo-thermal sources following frequency up-conversion; a study on the time-resolving measurement capability of the detectors using a short pulse pump and; evaluating the modulation of a single photon wave packet for better interfacing of independent sources. In this article, we will present an overview of the frequency up-conversion technique, introduce its applications in quantum information systems and discuss its unique features and prospects for the future.     

Recent advances on single photon sources based on single colloidal nanocrystals

Single colloidal quantum dots (QDs) are increasingly exploited as triggered sources of single photons. This review reports on recent results on single photon sources (SPS) based on colloidal quantum dots, whose size, shape and optical properties can be finely tuned by wet chemistry approach. First, we address the optical properties of different colloidal nanocrystals, such as dots, rods and dot in rods and their use as single photon sources will be discussed. Then, we describe different techniques for isolation and positioning single QDs, a major issue for fabrication of single photon sources, and various approaches for the embedding single nanocrystals inside microcavities. The insertion of single colloidal QDs in quantum confined optical systems allows one to improve their overall optical properties and performances in terms of efficiency, directionality, life time, and polarization control. Finally, electrical pumping of colloidal nanocrystals light emitting devices and of NC-based single photon sources is reviewed.     

Experimental assessment and analysis of super-resolution in fluorescence microscopy based on multiple-point spread function fitting of spectrally demultiplexed images

This paper presents an experimental assessment and analysis of super-resolution microscopy based on multiple-point spread function fitting of spectrally demultiplexed images using a designed DNA structure as a test target. For the purpose, a DNA structure was designed to have binding sites at a certain interval that is smaller than the diffraction limit. The structure was labeled with several types of quantum dots (QDs) to acquire their spatial information as spectrally encoded images. The obtained images are analyzed with a point spread function multifitting algorithm to determine the QD locations that indicate the binding site positions. The experimental results show that the labeled locations can be observed beyond the diffraction-limited resolution using three-colored fluorescence images that were obtained with a confocal fluorescence microscope. Numerical simulations show that labeling with eight types of QDs enables the positions aligned at 27.2-nm pitches on the DNA structure to be resolved with high accuracy.     

Demonstration of a nanoparticle-based optical diode

We present the operation of an optical device that exhibits diodelike properties based on two adjacent layers of quantum dots (QDs) encased in a fiber-optic jacket. The possibility of a multilayered device is also discussed. A significant change in the emission spectrum of CdSe/ZnS core-shell QDs was observed when excited by the input laser and the fluorescence of other CdSe/ZnS core-shell QDs. The output of the diode can be taken to be either the incoming laser wavelength of light similar to a conventional diode, or the output may be considered to be one of the QD fluorescence wavelengths. Current work has applications in biological fluorescence monitors and sensors as well as in telecommunications applications.     

PbSe量子点荧光匹配气体吸收光谱方法研究

PbSe量子点(PbSe-QDs)是红外波段的典型纳米材料,其具有大的玻尔半径、小的体材料禁带宽度(玻尔半径是46 nm,体材料禁带宽度是0.28 eV),因此,在近红外区域,PbSe-QDs具有强大的尺寸受限效应和较高的量子产出率。本文对不同尺寸的PbSe量子点的荧光光谱特性进行了研究,提出了一种通过调节PbSe量子点的量子尺寸匹配气体吸收光谱的方法。采用配位溶剂的方法制备了尺寸为4.6和6.1 nm的PbSe量子点,将该PbSe量子点沉积到GaN发光芯片上并经过紫外光照处理和固化后制成了光致发光的近红外光源,其中4.6 nm的PbSe-QDs的沉积厚度为671.5 μm,而6.1 nm的PbSe-QDs的沉积厚度为48 μm。将制成的近红外光源应用到C₂H₂气体和NH₃气体的检测实验中,实验结果表明,通过改变PbSe量子点的尺寸可以调节光源光致发光峰的位置,从而覆盖目标气体在近红外波段的吸收谱线。4.6 nm的光源发射光谱包含了1 500～1 550 nm之间的C₂H₂气体的全部的吸收谱;6.1 nm的光源发射光谱包含了1 900～2 060 nm之间的NH₃气体的全部的吸收谱。这种利用PbSe量子点尺寸的可调性匹配对应气体吸收谱的方法是可行和有效的,具有广阔的应用前景。     

Comparison of single-layer and bilayer InAs/GaAs quantum dots with a higher InAs coverage

Epitaxially grown self-assembled InAs quantum dots (QDs) have found applications in optoelectronics. Efforts are being made to obtain efficient quantum-dot lasers operating at longer telecommunication wavelengths, specifically 1.3 μm and 1.55 μm. This requires narrow emission linewidth from the quantum dots at these wavelengths. In InAs/GaAs single layer quantum dot (SQD) structure, higher InAs monolayer coverage for the QDs gives rise to larger dots emitting at longer wavelengths but results in inhomogeneous dot-size distribution. The bilayer quantum dot (BQD) can be used as an alternative to SQDs, which can emit at longer wavelengths (1.229 μm at 8 K) with significantly narrow linewidth (∼16.7 meV). Here, we compare the properties of single layer and bilayer quantum dots grown with higher InAs monolayer coverage. In the BQD structure, only the top QD layer is covered with increased (3.2 ML) InAs monolayer coverage. The emission line width of our BQD sample is found to be insensitive towards post growth treatments.     

Technical study of visible light wavelength division multiplexing using polymer optical fiber

Visible light wavelength division multiplexing (VWDM) experiment was performed using polymer optical fiber (POF). Lights of two different wavelengths (650 and 530 nm) were sent to a single POF. Red light (650 nm) was used for 100-Mb/s full duplex IP data transmission and green light (530 nm) was used for voice signal transmission. Light sources are light-emitting diodes (LEDs). A POF coupler (splitter) and the prisms were employed as multiplexer and demultiplexer, respectively. The channel isolation and insert loss were measured, which are 20.5 and 17.65 dB for 650-nm channel respectively, and 19.16 and 20.55 dB for 530 nm one respectively.     

Novel dispersion properties of one-dimensional photonic crystals containing a defect made of twin prisms

We design a one-dimensional photonic crystal containing a defect made of twin prisms and study its transmission properties using the transfer matrix method. The incident waves with different wavelengths can be transmitted out at different positions of the last interface of the structure, i.e., one wavelength corresponds to a single export point. Such a structure can be used as a novel dispersion separator. The resolution of this dispersion separator depends on the structure and indices of the twin prisms.     

Estimation of field intensity distribution and its wavelength dependence in a flat focusing nanolens

The application of surface plasmonic effects in engineering of a wavelength-tunable silver nanolens for the beam focusing is considered. Its design includes flat nanoslits for phase and amplitude modulation of light beams. Initially its operation has been checked for light beams with a wavelength of about 1.3 µm by observing the variance in the focal point distance with respect to alterations in structural parameters, such as the metal thickness, slit width, and pitch. The near-field intensity with respect to deviation in the focal point and deflection from the mean power for an optical 100-nm window is estimated for other popular optical communication wavelengths (0.85 and 1.55 µm) using the finite-difference timedomain method with boundary conditions for anisotropic, perfectly matched layers. The novelty in the proposed lens is its capability to function satisfactorily for a tolerance range of ±2.5% in the design parameters for the wavelengths under consideration.     

Optical properties of 1.3-μm InAs/GaAs quantum dots grown by metal organic chemical vapor deposition

The optical properties of self-assembled InAs quantum dots （QDs） on GaAs substrate grown by metalorganic chemical vapor deposition （MOCVD） are reported. Photoluminescence （PL） measurements prove the good optical quality of InAs QDs, which axe achieved using lower growth temperature and higher InAs coverage. At room temperature, the ground state peak wavelength of PL spectrum and full-width at half-maximum （FWHM） are 1305 nm and 30 meV, respectively, which are obtained as the QDs are finally capped with 5-nm In0.06Ga0.94As strain-reducing layer （SRL）. The PL spectra exhibit two emission peaks at 1305 and 1198 nm, which correspond to the ground state （GS） and the excited state （ES） of the QDs, respectively.     

Single photon sources with single semiconductor quantum dots

In t.his contribution, we briefly recall the basic concepts of quantum optics and properties of semicon- ductor quantum clot. （QD） which a.re necessary to the nnderstanding of the physics of single-photon generation with single QDs. Firstly, we address the theory of quantmn emitter-cavity system, the fluorescence and optical properties of semiconductor QDs, and the photon statistics as well as opti- cal properties of the QDs. We then review the localizatioll of single semiconductor QDs in quantum confined optical microcavity systems to achieve their overall optical properties and perfornances in terms of strong coupling regime, elfieiency, directionality, and polarization control. Furthermore, we will discuss the recenl, progress on the fabrication of single photon sources, and various a.pproaehes for embedding single QDs into mieroca,vities or photonic crystal nanoeavities and show how to ex- tend the wavelength range. We focus in part;icular on new generations of electrically driven QD single photon source leading to high repetition rates, efficiencies at elevated temperature operation. Besides strong eoupling regime, and high collection new development;s of room temperature sin- gle photon emission in the strong coupling regime are reviewed. The generation of indistinguishable photons and remaining challenges for pract ical single-photon sources are also discussed.     

InAs/GaAs量子点1.3 μm单光子发射特性

采用双层耦合量子点的分子束外延生长技术生长了InAs/GaAs量子点样品,把量子点的发光波长成功地拓展到1.3 μm.采用光刻的工艺制备了直径为3 μm的柱状微腔,提高了量子点荧光的提取效率.在低温5 K下,测量得到量子点激子的荧光寿命约为1 ns;单量子点荧光二阶关联函数为0.015,显示单量子点荧光具有非常好的单光子特性;利用迈克耳孙干涉装置测量得到单光子的相干时间为22 ps,对应的谱线半高全宽度为30 μeV,且荧光谱线的线型为非均匀展宽的高斯线型.     

脂溶性CdSe/ZnS量子点脂质体复合物的制备及表征

在油相中成功合成了脂溶性CdSe/ZnS核壳量子点纳米粒,粒径平均为4.5 nm,量子产率达29%,发射波长为540 nm。通过薄膜分散法,以蛋黄卵磷脂、胆固醇为膜材,将脂溶性的CdSe/ZnS核壳量子点包覆于脂质体磷脂双分子层中,由于磷脂分子的两亲性,使得脂溶性的CdSe/ZnS核壳量子点同时又具有亲水性。通过透射电镜对脂质体形态进行了表征,倒置荧光显微镜证实了发光CdSe/ZnS核壳量子点成功包埋于脂质体双分子层中,包裹的发光CdSe/ZnS核壳量子点具有更稳定的发光及抗光漂白性质。     

Comparative study of pulsed laser diode end-pumped thulium-doped 2-µm Q-switched lasers

We report pulsed laser diode(LD)end-pumped acoustic Q-switched Tm:YAG laser,Tm:LuAG laser,and Tm:LuYAG laser and the physical properties and spectra of Tm:YAG,Tm:LuAG,and Tm:LuYAG are analyzed.The Tm:LuYAG laser is pumped by 785-nm and 788-nm pulses separately,and is compared with Tm:YAG laser.Different output energy values and output wavelengths of Tm:LuAYG lasers pumped by LDs with different wavelengths are obtained and compared with each other.When the repetition frequency is 100 Hz,the pulsed Tm:YAG laser has single pulse energy of 15.9 mJ,pulse width of 126.7 ns,and the center wavelength of 2013.36 nm,and the pulsed Tm:LuAG laser possesses single pulse energy of 11.8 mJ,pulse width of 252.4 ns,and the center wavelength of 2023.65 nm,and the pulsed Tm:LuYAG laser output energy values are 12.32 mJ and 12.25 mJ with the slope efficiencies of 12.5%and 11.85%,the center wavelengths of 2017.89 nm and 2027.11 nm,respectively,while the pump sources are 785-nm and 788-nm pulsed LDs,respectively.     

Analysis of atmospheric effects on the continuous variable quantum key distribution

Atmospheric effects have significant influence on the performance of a free-space optical continuous variable quantum key distribution (CVQKD) system. In this paper, we investigate how the transmittance, excess noise and interruption probability caused by atmospheric effects affect the secret-key rate (SKR) of the CVQKD. Three signal wavelengths, two weather conditions, two detection schemes, and two types of attacks are considered in our investigation. An expression aims at calculating the interruption probability is proposed based on the Kolmogorov spectrum model. The results show that a signal using long working wavelength can propagate much further than that of using short wavelength. Moreover, as the wavelength increases, the influence of interruption probability on the SKR becomes more significant, especially within a certain transmission distance. Therefore, interruption probability must be considered for CVQKD by using long-signal wavelengths. Furthermore, different detection schemes used by the receiver will result in different transmission distances when subjected to individual attacks and collective attacks, respectively.     

Aerial image formation of quantum lithography for diffraction limit

Since the diffraction limit of Rayleigh criterion hardly creates finer features, the development for the quantum lithography of entangled photons, one of technologies beyond the diffraction limit, is a key merit without the shorter wavelength source tool. In the arbitrary pattern formation for the commercialization of this lithography, however, this quantum lithography is required to implement mask patterns and the conventional optical lithography. In this paper, for the quantum lithography of entangled photons, collective behavior of N-photon entangled states is modeled and simulated to show the effect of photon entangled states for 3-dimensional arbitrary pattern formation by using the rigorous coupled wave analysis (RCWA) and Kirchhoff analysis. For the enhanced resolution from the point of view that the de Broglie wavelength of a quantum state comprised of two entangled photons is half the classical wavelength associated with either photon, simulation results of entangled photons are similar to those of short wavelengths. However, both of simulation results show that the resolution of entangled photons is better than those of the shorter wavelengths. Simulation results can predict realistic better performance of entangled photons.     

阿达玛变换光谱显微成像分析乳腺癌组织肿瘤标志物的分布

自行研制的多功能阿达玛变换光谱成像显微系统具有获取微小组织样品的高分辨荧光光谱和荧光图像的能力。由于量子点具有激发区域宽、可以一元激发多元发射、荧光峰形狭窄、亮度高、抗光漂白能力强等特点,非常适合作为荧光标记物应用于光谱显微成像分析领域。采用荧光发射波长为610 nm的量子点荧光探针分别免疫标记乳腺癌标志物人表皮生长因子受体2(HER2) 和雌激素受体(ER),通过激光诱导荧光法和荧光原位光谱成像法分析癌组织中HER2和ER的光谱特征和定量信息,采用阿达玛变换光谱显微成像系统对阳性乳腺癌组织与阴性正常乳腺组织进行对比分析,其结果表明该仪器可有效用于肿瘤标志物在癌组织内的定量研究,是定量检测乳腺癌HER2和ER分布的新技术。该技术建立的针对肿瘤标志物的半定量和定量分析方法,所得结果优于常规的定性分析方法。     

Far-field superlens for nanolithography

A far-field optical lithography is developed in this paper. By designing the structure of a far-field optical superlens, lithographical resolution can be improved by using a conventional UV light source. The finite different time domain numerical studies indicate that the lithographic resolution at 50~nm line width is achievable with the structure shown in this paper by using 365~nm wavelength light, and the light can be transferred to a far distance in the photoresist.     

Wavelength dependence of focusing properties of two-dimensional photonic quasicrystal flat lens

We investigated the wavelength dependence of the focusing properties of a germanium-cylinder-based two-dimensional (2D) decagonal Penrose-type photonic quasicrystal (PQC) flat lens for the first time, to the best of our knowledge. We found that near the second bandgap and in the high-frequency side (between the bandgap boundary and the first light intensity peak) of the pass band, the flat lens can exhibit a focusing effect for a point light source and that the focusing wavelengths can directly be drawn from the photonic band structure. For all the focusing wavelengths, the summation of the object distance and the image distance is less than the thickness of the flat lens when the object distance is half the thickness of the flat lens. As the wavelength increases, the image distance, the image quality, and the effective refractive index of the flat lens increase, whereas the image power of the point light source decreases. The effective refractive index of the flat lens is less than -1.     

Digital holography at millimetre wavelengths

In this paper, we describe a method for wavefront reconstruction at millimetre wavelengths using off-axis holography, a frequently used image recording technique at visible wavelengths first demonstrated in the 1960’s. Millimetre radiation has been highlighted recently in the imaging of non-conducting materials and objects, which often show significant transparency at these long wavelengths, even though opaque at visible and infrared wavelengths. Holography provides a method for recording a lens-less image of an object thus reducing loss of spatial frequency information, which is important for obtaining maximum resolution at long wavelengths. An experimental arrangement based on a simple form of Fresnel off-axis holography is described, with the object illumination and reference beams derived using two radiating horn antennas fed by a single coherent source (a Gunn diode oscillator operating at 100 GHz – wavelength 3 mm) via a 3 dB cross-guide coupler. The process is discussed in the context of imaging and in the validation of millimetre wave radiation sources (horns). We show that the entire fields from these and other components can be analysed using computational optics with data derived from a single measurement obtained using inexpensive equipment.