NIRT: Nanofabricated All-Optical Computing, Switching, and Signal Processing Devices Based on Single Photon Tunneling

马里兰大学的一个多学科研究小组最近发现了一个与单光子隧道有关的新的重要现象。光通过被非线性介质覆盖的金膜中的纳米级针孔的传输以每秒几千个光子的速度饱和。这种纳米尺度空穴的透射率与光强是非线性的，在单光子水平上对应于每个光子在穿过孔洞的过程中控制着连续光子的透过率。这一结果类似于在单电子隧穿实验中观察到的库仑阻塞。这种现象最初只在自然出现在薄层蒸发金膜中的随机纳米级针孔中观察到。进一步的工作表明，由聚焦离子束纳米加工技术制成的单个纳米孔洞(纳米孔)和纳米孔阵列的透射率不仅表现出简单的离子阻挡效应，而且还表现出受控的光子传输。例如，纳米孔或纳米孔阵列在一个波长的透射率可以通过第二个不同波长的照明来控制。在这个项目中，一个由光学科学家、理论家和纳米科学家组成的多学科团队将研究这一新现象，并探索基于金属薄膜中制造的纳米孔或纳米孔阵列的潜在应用。他们预计，对这种控制良好的纳米孔和其他纳米结构的光学性质的详细研究将揭示非线性光学传输中的新量子现象。例如，库仑隧道中的电子以或多或少固定的时间间隔一次封锁一个。如果穿过非线性光学纳米孔的光子表现出类似的行为(正如最初的实验所表明的那样)，那么所制造的纳米孔将成为非常不寻常的有用光源，一次一个地周期性地发射单个光子。这种可控光源正被量子通信和量子密码学领域的研究人员积极追求。此外，非线性纳米孔材料在光通信和全光信号处理领域也有望获得新的和潜在的重要应用。光信号处理依赖于光的非线性相互作用，这种相互作用通常发生在非常高的光强度下。初步结果表明，纳米孔中的局部光场至少增强了六个或八个数量级，使得非线性光学相互作用能够在低得多的照明光强度下发生。这为利用光来选通光的设备打开了大门，他们已经在基本层面上展示了这一点。因此，可以在微观尺度上实现大量的光通信和光信号处理设备，例如全光开关以及信号和图像处理设备，并且可以比宏观设备小得多的操作光功率来实现。

A new and important phenomenon involving single photon tunneling has been discovered recently by a multidisciplinary team of researchers at the University of Maryland. Transmission of light through nanometer-scale pinholes in a gold film covered by a nonlinear dielectric saturates at a few thousand photons per second. The transmittance of such a nanometer-scale hole is nonlinear with light intensity, and at the single photon level corresponds to each photon in the process of being transmitted through the hole controlling the transmittance of successive photons. This result is analogous to the Coulomb blockade observed in single electron tunneling experiments. The phenomenon was initially observed only for random nanoscale pinholes that occur naturally in thin evaporated gold films. Further work has shown that the transmittance of both individual nanofabricated holes (nanopores), and arrays of nanopores, both made by focused ion-beam nanaofabrication techniques, has shown not only the simple iiphoton-blockadel effects, but also controlled photon transmission. For example, the transmittance of a nanopore or nanopore array at one wavelength can be controlled by illumination with a second, different, wavelength.In this project a multidisciplinary team of optical scientists, theorists and nanofabricatorswill study of this new phenomenon and explore potential applications based on fabricated nanopores or arrays of nanopores in metal films. They expect that a detailed study of optical properties of such well-controlled nanopore and other nanostructures will reveal novel quantum phenomena in nonlinear optical transmission. For example, electrons in a Coulomb blockade tunnel one at a time, at more or less fixed time intervals. If photons tunneling through nonlinear optical nanopores show similar behavior (as an initial experiments suggest), the fabricated nanopores will become very unusual and useful light sources emitting individual photon periodically, one at a time. Such controlled light sources are being actively pursued by researchers in the areas of quantum communication and quantum cryptography.In addition, novel and potentially important applications of nonlinear nanopore materials may also be expected in the areas of optical communications and all-optical signal processing. Optical signal processing relies on nonlinear interactions of light, which usually happen at very high optical intensities. Preliminary results indicate that the local optical field in a nanopore is enhanced by at least six or eight orders of magnitude, enabling nonlinear optical interactions to occur at much lower illuminating light intensities. This opens the door to devices where light is used to gate light, which they have already demonstrated at a fundamental level. Thus, a great number of optical communication and optical signal processing devices, such as all-optical switches, and signal and image processing devices, may be realized on a microscopic scale, and at much smaller operating optical powers than macro-devices.