Fiber-pigtailing quantum-dot cavity-enhanced light emitting diodes

Abstract

We report on a process for the fiber-coupling of electrically driven cavity-enhanced quantum dot light emitting devices.The developed technique allows for the direct and permanent coupling of p-i-n-doped quantum dot micropillar cavities to single-mode optical fibers. The coupling process, fully carried out at room temperature, involves a spatial scanning technique, where the fiber facet is positioned relative to a device with a diameter of 2 µm using the fiber-coupled electroluminescence of the cavity emission as feedback parameter. Subsequent gluing and UV curing enables a rigid and permanent coupling between micropillar and fiber core. Comparing our experimental results with finite element method simulations indicate fiber coupling efficiencies of ~46%. The technique presented in this work is an important step in the quest for efficient and practical quantum light sources for applications in quantum information. Solid-state based quantum-light sources are elementary building blocks for photonic quantum technologies [1-3]. Especially the maturity of single-photon sources (SPSs) based on semiconductor quantum dots (QDs) has advanced substantially in recent years [4,5], allowing for the efficient generation of quantum states of light under optical [6-9] or electrical pumping [10,11].As a result, QD-based quantum light sources have been employed for many proof-of-concept experiments on quantum communication [12][13][14] and photonic quantum computing [15]. Most of these experiments, however, suffer from rather complex and bulky setups due to complex light extraction via free-space optics, hindering more widespread applications. On the other hand, the development of user-friendly devices for applications outside shielded lab environments recently attracted much interest [16,17]. A crucial aspect in this context concerns the direct coupling of the quantum light sources to optical single-mode (SM) fibers facilitating a robust packaging of the devices. Pioneering work in this direction utilized fiber-coupled QD samples employing fiber-bundles containing about 600 individual fiber cores to spatially post-select a single emitter [18].More recently, the direct fiber-coupling of optically pumped photonic nanostructures with embedded QDs, such as photonic wires [19] and micropillars with oxide aperture [20], has been reported. The latter scheme has also been used to realize an optically pumped cavity-enhanced single-photon source with gates for spectral tuning of the QD emission [21]. In addition, optically-pumped fiber-integrated microcavities were employed for the generation of coherent acoustic phonons [22].Moreover, schemes for the SM fiber-coupling of QD microlenses are currently under development using two-photon direct

Quantum Communication Using Semiconductor Quantum Dots

“…The possibility to electrically inject charge carriers in QD light‐emitting diodes is one advantage of semiconductor‐based quantum light sources, which is one route to achieve higher degrees of device integration. [ 233 ] Electrical pumping, however, excludes the possibility to apply resonant excitation schemes in most device layouts. For this reason, sophisticated device technologies have been developed enabling the optical driving of QDs using microlasers integrated on the same chip next to the quantum light emitting device.…”

“…Along this route, Rickert et al succeeded very recently to directly fiber-pigtail electrically injected QD-microcavities to single-mode optical fibers and demonstrate low-temperature operation. [233]…”

“…More recently, fiber-scanning techniques in combination with epoxy resist or optical adhesives cured via ultraviolet (UV) light proved useful tools for the permanent fiber-coupling of QDdevices based on micropillar cavities, [233,272,273] microlenses or micromesas, [178,211,274] as well as nanowires. [275] Figure 14 depicts a schematic of an electrically controlled fiber-coupled micropillarcavity used to demonstrate resonant excitation by Snijders et al in 2018.…”

Fiber-coupled quantum light sources based on solid-state quantum emitters

“…a QD) into a nanophotonic structure [62]. Fibers can be directly glued to pre-fabricated on-chip structures like a micromesa [128] by employing optical interferometry right through the fiber to determine the center of the structure [127] shown in figure 9 or by monitoring the local emission [84,129] or the dip [130,131] of a microcavity as or its transmitted light [85] in active optical-feedback alignment approaches (see figure 10).…”

Quantum Communication Using Semiconductor Quantum Dots

“…Recently, fiber-scanning techniques in combination with epoxy resists or optical (UV-) adhesives have shown to be suitable for permanent fiber-coupling of micropillar cavities [204,205,206], microlens and micromesa SPSs [90,207,151], as well as for nanowires [208]. A schematic of an electrically controllable, fiber-coupled micropillar-cavity with a detection and excitation fiber and capable of resonant excitation schemes published by Snijders and coworkers in 2018 [205] is shown in Figure 13a.…”