SPIN SPACE - Spatially encoded telecoms and quantum technologies using spin-enabled all-optical switching

我们这个星球上的光纤纵横交错，几乎影响着21世纪我们生活的方方面面。然而，尽管光纤通信技术在过去20年中取得了巨大的进步，但我们已经几乎用完了数据容量。随着世界上更多的地方联网，预计未来20年“物联网”将连接多达1万亿台设备，我们需要找到更好的方法来克服我们可以发送的数据量的基本限制。同样迫在眉睫的是可能使用光纤电信网络的新技术，例如量子光学技术，例如使用单个光子发送完全安全的数据。然而，发送许多这样的光子，但将每个光子保持独立，这是一个重大挑战。为了回应这些新技术，有人提出，通过微结构光纤发送信息可能会为上述挑战提供解决方案。微结构纤维更像是一根布赖顿岩石的棒子，上面贯穿着一个图案。其中最简单的可能是几个平行运行但光学隔离的核心，而更复杂的设计涉及核心之间受控的光泄漏，或者实际上是具有光在空气中传播的蜂窝结构。最近的想法建议通过微结构光纤发送光图案(光强度图案或偏振图案)，该图案具有包含编码信息的图案的复杂变化。虽然目前正在对微结构光纤中的信号传播进行大量工作，但很明显，为了产生信号，需要一种能够在GHz时间尺度上切换图案的空间激光图案的产生手段。更重要的是，为了执行诸如从阵列的一个区域重新路由信号或改变图案之类的功能，需要将具有光输入和输出的设备馈送到后来的光纤网络。使用电触点切换阵列是很棘手的--人们需要以快速的速度单独访问许多微米大小的区域。我们提出，如果把小的(几微米)激光制成一个小的柱子森林，垂直发射单独的光点，我们就可以很容易地产生复杂的图案。我们使用半导体激光器，其中自旋，电子的本征磁铁，根据光的偏振而产生不同的相互作用-在某些情况下，光子被吸收，在其他情况下，自旋在错误的方向上，光通过。因此，我们将控制光脉冲来反转自旋，并在这些设备的空间阵列中执行光学逻辑。当激光功率被调低，并使用非常特定的频率时，我们发现光本质上变得“颗粒状”--并变成单独的光子。我们还知道，可以将半导体制备成像原子集合一样的行为--在非常特定的波长下，光子只“看到”一个电子。就像原子一样，光子可能被吸收，电子获得能量--然而，在我们的例子中，它也与电子的自旋相互作用。当电子从其激发态下降并发出一个光子时，该光子就改变了极化。然后，我们可以从入射的光子中过滤出出射的光子，并将散射的光子用作“单光子源”--即每个光脉冲恰好产生一个光子。这一来源允许发送完全安全的信息，也是光子量子计算的起点，其中许多单个光子被用来相互作用并为量子计算机编码信息。

Our planet is criss-crossed with optical fibres that influence almost every aspect our lives in the 21st century. However, despite the great advances in optical fibre communications technologies that have occurred in the past 20 years, we have already almost run out of data capacity. With more of the world online, and the "Internet of Things" predicted to connect up to a trillion devices in the next 20 years, we need to find better ways of overcoming fundamental limits in how much data we can send. Also looming on the horizon are new technologies that may use optical fibre telecommunication networks, such as quantum optics technologies, sending, for example, completely secure data using single photons. However, sending many of these photons but keeping each one separate is a major challenge.In answer to these new technologies, it has been suggested that sending information via a microstructured fibre may offer solutions to the challenges above. Microtructured fibres are rather like a stick of Brighton rock with a pattern running through. The simplest of these may be several cores running in parallel but optically isolated, whilst more complex designs involve controlled light leakage between the cores, or indeed a honeycomb structure with light travelling in the air. Recent ideas propose sending a pattern of light (either a light intensity pattern or a pattern of polarization) through the microstructured fibre with complex changes in the pattern containing encoded information.While much work is presently being carried out on signal propagation in microstructured fibres, it is clear that to create the signal, a means of producing a spatial laser pattern is required that can switch pattern over GHz timescales. More importantly, to perform functions such as rerouting signals from one area of the array or changing the pattern one requires a device with an optical input and output to be fed into the later fibre network. Switching an array using electrical contacts is tricky - one needs to individually access many micron-sized areas at fast speeds. We propose that if small (few micrometer) lasers are fabricated into a small forest of pillars that emit individual points of light vertically, we can generate complex patterns easily. We use a semiconductor laser, where the spin, the electron's intrinsic magnet, interacts differently depending on the light polarization - in some cases the photon is absorbed, in other cases the spin is in the wrong direction and the light passes through. We will thus control light pulses to flip the spins and perform optical logic in spatial arrays of these devices. This will allow incoming signals to be switched and re-routed.When the laser power is turned down, and very specific frequencies are used, we find that the light becomes intrinsically "grainy" - and turns into individual photons. We also know that the semiconductor can be prepared so that it behaves like a collection of atoms - at very specific wavelengths, the photon only "sees" one electron. Rather like an atom, the photon may be absorbed and an electron gains energy - however in our case it also interacts with the electron's spin. When the electron drops from its excited state and emits a photon, the photon has changed polarization. We can then filter out the outgoing photons from the incoming ones and use the scattered photons as a "single photon source" - where exactly one photon is produced per optical pulse. This source allows completely secure information to be sent, and is the starting point for photon quantum computing, where many of these individual photons are made to interact and encode information for a quantum computer.