Abstract:In the paper, we review our work on heterogeneous III-V-on-silicon photonic components and circuits for applications in optical communication and sensing. We elaborate on the integration strategy and describe a broad range of devices realized on this platform covering a wavelength range from 850 nm to 3.85 μm.

We present the first III-V opto-electronic components transfer printed on and coupled to a silicon photonic integrated circuit. Thin InPbased membranes are transferred to an SOI waveguide circuit, after which a single-spatial-mode broadband light source is fabricated. The process flow to create transfer print-ready coupons is discussed. Aqueous FeCl 3 at 5 • C was found to be the best release agent in combination with the photoresist anchoring structures that were used. A thin DVS-BCB layer provides a strong bond, accommodating the post-processing of the membranes. The resulting optically pumped LED has a 3 dB bandwidth of 130 nm, comparable to devices realized using a traditional die-to-wafer bonding method.

Silicon is now firmly established as a high performance photonic material. Its only weakness is the lack of a native electrically driven light emitter that operates CW at room temperature, exhibits a narrow linewidth in the technologically important 1300-1600 nm wavelength window, is small and operates with low power consumption. Here, an electrically pumped all-silicon nano light source around 1300-1600 nm range is demonstrated at room temperature. Using hydrogen plasma treatment, nano-scale optically active defects are introduced into silicon, which then feed the photonic crystal nanocavity to enhance the electrically driven emission in a device via Purcell effect. A narrow (∆λ = 0.5 nm) emission line at 1515 nm wavelength with a power density of 0.4 mW/cm 2 is observed, which represents the highest spectral power density ever reported from any silicon emitter. A number of possible improvements are also discussed, that make this scheme a very promising light source for optical interconnects and other important silicon photonics applications.

In this article we describe a cost-effective approach for hybrid laser integration, in which vertical cavity surface emitting lasers (VCSELs) are passively-aligned and flip-chip bonded to a Si photonic integrated circuit (PIC), with a tilt-angle optimized for optical-insertion into standard grating-couplers. A tilt-angle of 10° is achieved by controlling the reflow of the solder ball deposition used for the electrical-contacting and mechanical-bonding of the VCSEL to the PIC. After flip-chip integration, the VCSEL-to-PIC insertion loss is -11.8 dB, indicating an excess coupling penalty of -5.9 dB, compared to Fibre-to-PIC coupling. Finite difference time domain simulations indicate that the penalty arises from the relatively poor match between the VCSEL mode and the grating-coupler.

Photon cutting with efficiencies up to 400% is demonstrated in Er x Y 2−x Si 2 O 7 films grown on Si and its concentration dependence is analyzed. The cutting is the result of cross-energy-transfer processes occurring within a single rare earth ͑Er 3+ ͒ acting as both sensitizer and activator. Similarities with upconversion are revealed and possible applications in solar cells are discussed.

This article presents the flip-chip bonding of vertical-cavity surface-emitting lasers (VCSELs) to silicon grating couplers (GCs) via SU8 prisms. The SU8 prisms are defined on top of the GCs using non-uniform laser ablation process. The prisms enable perfectly vertical coupling from the bonded VCSELs to the GCs. The VCSELs are flip-chip bonded on top of the silicon GCs employing the laser-induced forward transfer (LIFT)-assisted thermocompression technique. An excess loss of < 1 dB at 1.55 µm measured from the bonded assemblies is reported in this paper. The results of high speed transmission experiments performed on the bonded assemblies with clear eye openings up to 20 Gb/s are also presented.

α-(Yb1-xErx)2Si2O7 thin films on Si substrates were synthesized by magnetron co-sputtering. The optical emission from Er3+ ions has been extensively investigated, evidencing the very efficient role of Yb-Er coupling. The energy-transfer coefficient was evaluated for an extended range of Er content (between 0.2 and 16.5 at.%) reaching a maximum value of 2 × 10⁻¹⁶ cm⁻³s⁻¹. The highest photoluminescence emission at 1535 nm is obtained as a result of the best compromise between the number of Yb donors (16.4 at.%) and Er acceptors (1.6 at.%), for which a high population of the first excited state is reached. These results are very promising for the realization of 1.54 μm optical amplifiers on a Si platform.

Er coordination in Y 2 O 3 thin films studied by extended x-ray absorption fine structure Y 2−x Er x O 3 thin films, with x varying between 0 and 0.72, have been successfully grown on crystalline silicon ͑c-Si͒ substrates by radio-frequency magnetron cosputtering of Y 2 O 3 and Er 2 O 3 targets. As-deposited films are polycrystalline, showing the body-centered cubic structure of Y 2 O 3 , and show only a slight lattice parameter contraction when x is increased, owing to the insertion of Er ions. All the films exhibit intense Er-related optical emission at room temperature both in the visible and infrared regions. By studying the optical properties for different excitation conditions and for different Er contents, all the mechanisms ͑i.e., cross relaxations, up-conversions, and energy transfers to impurities͒ responsible for the photoluminescence ͑PL͒ emission have been identified, and the existence of two different well-defined Er concentration regimes has been demonstrated. In the low concentration regime ͑x up to 0.05, Er-doped regime͒, the visible PL emission reaches its highest intensity, owing to the influence of up-conversions, thus giving the possibility of using Y 2−x Er x O 3 films as an up-converting layer in the rear of silicon solar cells. However, most of the excited Er ions populate the first two excited levels 4 I 11/2 and 4 I 13/2 , and above a certain excitation flux a population inversion condition between the former and the latter is achieved, opening the route for the realization of amplifiers at 2.75 m. Instead, in the high concentration regime ͑Er-compound regime͒, an increase in the nonradiative decay rates is observed, owing to the occurrence of cross relaxations or energy transfers to impurities. As a consequence, the PL emission at 1.54 m becomes the most intense, thus determining possible applications for Y 2−x Er x O 3 as an infrared emitting material.