Optical gain and lasing from bulk cadmium sulfide nanocrystals through bandgap renormalization.

Strongly confined colloidal quantum dots have been investigated for low-cost light emission and lasing for nearly two decades. However, known materials struggle to combine technologically relevant metrics of low-threshold and long inverted-state lifetime with a material gain coefficient fit to match cavity losses, particularly under electrical excitation. Here we show that bulk nanocrystals of CdS combine an exceptionally large material gain of 50,000 cm-1 with best-in-class gain thresholds below a single exciton per nanocrystal and 3 ns gain lifetimes not limited by non-radiative Auger processes. We quantitatively account for these findings by invoking a strong bandgap renormalization effect, unobserved in nanocrystals to date, to the best of our knowledge. Next, we demonstrate broadband amplified spontaneous emission and lasing under quasi-continuous-wave conditions. Our results highlight the prospects of bulk nanocrystals for lasing from solution-processable materials.

Unique design approach to realize an O-band laser monolithically integrated on 300†mm Si substrate by nano-ridge engineering.

We introduce a new design space for optimizing III-V devices monolithically grown on Silicon substrates by extending the concept of nano-ridge engineering from binary semiconductors such as GaAs, InAs and GaSb to the ternary alloy InGaAs. This allows controlling the fundamental lattice constant of the fully relaxed ternary nano-ridge which thereby serves as a tunable base for the integration of diverse device hetero-layers. To demonstrate the flexibility of this approach, we realized an O-band nano-ridge laser containing three In0.45Ga0.55As quantum wells, which are pseudomorphically strained to an In0.25Ga0.75As nano-ridge base. The demonstration of an optically pumped nano-ridge laser operating around 1300 nm underlines the potential of this cost-efficient and highly scalable integration approach for silicon photonics.

2D-3D integration of hexagonal boron nitride and a high-κ dielectric for ultrafast graphene-based electro-absorption modulators.

Electro-absorption (EA) waveguide-coupled modulators are essential building blocks for on-chip optical communications. Compared to state-of-the-art silicon (Si) devices, graphene-based EA modulators promise smaller footprints, larger temperature stability, cost-effective integration and high speeds. However, combining high speed and large modulation efficiencies in a single graphene-based device has remained elusive so far. In this work, we overcome this fundamental trade-off by demonstrating the 2D-3D dielectric integration in a high-quality encapsulated graphene device. We integrated hafnium oxide (HfO2) and two-dimensional hexagonal boron nitride (hBN) within the insulating section of a double-layer (DL) graphene EA modulator. This combination of materials allows for a high-quality modulator device with high performances: a ~39 GHz bandwidth (BW) with a three-fold increase in modulation efficiency compared to previously reported high-speed modulators. This 2D-3D dielectric integration paves the way to a plethora of electronic and opto-electronic devices with enhanced performance and stability, while expanding the freedom for new device designs.

Microwave index engineering for slow-wave coplanar waveguides.

Microwave index engineering has been investigated in order to properly design slow-wave coplanar waveguides suitable for a wide range of applications in microwave, photonics, plasmonics and metamaterials. The introduction and optimization of novel capacitive and inductive elements is proposed as a design approach to increase the microwave index while keeping the impedance close to 50 Ω to ensure the compatibility with external electronic devices. The contribution of inductive and capacitive elements and their influence on the performance of the slow-wave coplanar waveguide has been systematically analyzed. As a result, a microwave index as high as 11.6 has been experimentally demonstrated in a frequency range up to 40 GHz which is, to the best of our knowledge, the largest microwave index obtained so far in coplanar waveguides.