Benoit Guilhabert

We report a technique for scalable electro-optical on-chip addressing of semiconductor nanowire emitters via transfer-printed micro-LEDs. Thus driven individual waveguide-coupled nanowires demonstrate small-signal modulation in the 10’s MHz range at room-temperature. The integration of micro-LEDs with nanowire emitters on a chip provides localized scalable excitation without the need for external optics. This method therefore opens new routes for the realization of programmable high-density nanowire networks.

Transfer printing is employed to demonstrate the integration of gallium nitride (GaN)-based distributed Bragg reflectors (DBR) with 100 μm lateral dimensions and reflectance of 90% in various formats. Mesoporous GaN DBRs are utilized as basic building blocks to fabricate more complex photonic devices directly on Silicon (Si) and glass receiving substrates. Multi-mode optical resonant cavities centered at 450 nm on Si are thus formed by direct stacking of two mesoporous DBR membranes. Furthermore, active devices are also demonstrated by combining mesoporous DBR with GaN-based light-emitting diodes membranes of similar dimensions, resulting in a Fabry–Perot-mediated emission with its main peak shifted by 14 nm compared to a reference device without DBR. Measured optical bandwidth of 136 MHz (−6 dB) in a small signal modulation scheme is also demonstrated from these devices.

Photonic crystal cavities (PhCCs) can confine optical fields in ultra-small volumes, enabling efficient light-matter interactions for quantum and non-linear optics, sensing and all-optical signal processing. The inherent nanometric tolerances of micro-fabrication platforms can induce cavity resonant wavelength shifts two-orders of magnitude larger than cavity linewidths, prohibiting fabrication of arrays of nominally identical devices. We address this device variability by fabricating PhCCs as releasable pixels that can be transferred from their native substrate to a receiver where ordered micro-assembly can overcome the inherent fabrication variance. We demonstrate the measurement, binning and transfer of 119 PhCCs in a single session, producing spatially ordered arrays of PhCCs, sorted by resonant wavelength. Furthermore, the rapid in-situ measurement of the devices enables measurements of the PhCCs dynamic response to the print process for the first time, showing plastic and elastic effects in the seconds to hours range.

Silicon, being the fundamental material for modern semiconductor devices, has seen continuous advancements to enhance its electrical and mechanical properties. Strain engineering is a well-established technique for improving the performance of silicon-based devices. In this paper, we propose a simple method for inducing and permanently maintaining strain in silicon through pure physical bending. By subjecting the silicon substrate to a controlled bending process, we demonstrate the generation of strain levels that persist even after the removal of external stress, with a maximum strain value of 0.4%. We present a comprehensive study of the mechanics behind this phenomenon, a full finite element mechanical model, and experimental verification of the bending-induced strain in Si membranes using electron backscatter diffraction measurements. Our findings show the potential of this approach for strain engineering in high-performance silicon-based technologies without resorting to complex and expensive fabrication techniques.

Direct writing systems equipped with a confocal micro-light-emitting diode array can employ active illumination for alignment purposes. Based on the principles of single-pixel imaging, structured illumination can be used to obtain position information via compressive sensing. The positions of markers with certain spectral signatures can be extracted from the recorded hyperspectral data through spectral filtering, spectral fitting, or principal component analysis. Its application to direct writing is demonstrated by creating individual photolithography patterns aligned with different types of fluorophores on the same substrate.

A scalable excitation platform for nanophotonic emitters using individually addressable micro-LED-on-CMOS arrays is presented. Heterogeneous integration by transfer printing of semiconductor nanowires was used for the deterministic assembly of the infrared emitters embedded in polymer optical waveguides with a high yield and positional accuracy. Direct optical pumping of these emitters is demonstrated using micro-LED pixels as a source, with optical modulation (on-off keying) measured up to 150 MHz. A micro-LED-on-CMOS array of pump sources was employed to demonstrate individual control of multiple waveguide-coupled nanowire emitters in parallel, enabling future large-scale photonic integrated circuit applications.

We report on the fabrication and micro-transfer printing (µ-TP) of InGaAs/InP avalanche photodiodes (APDs) onto silicon substrates. A process flow was developed to suspend the devices using semiconductor tethers. The developed process reduces the number of fabrication steps required compared to methods based on the use of photoresist tethers. Furthermore, our process is compatible with devices that may be susceptible to damage induced by the photoresist removal process. APDs were characterised in linear mode operation both before suspension and after printing. Despite the additional fabrication steps required to suspend the APD membranes and the physical nature of the µ-TP process, the electrical characteristics of the devices were preserved. No degradation in the optical performance of the devices was measured. Our work represents the first demonstration of µ-TP of InGaAs/InP APDs onto silicon substrates. The results highlight the viability of µ-TP for effective heterogeneous integration of InGaAs/InP APDs with silicon photonic integrated circuits for optical and quantum communication and other light detection applications.

Planar 45^o turning mirrors with metal coating embedded in SU8 polymer waveguides enable waveguide to vertical mode coupling across a broad range of wavelengths from the visible to IR. The fabrication of these 2.5D structures is achieved using relatively simple grayscale lithography in thin film resists, compatible with standard planar lithography methods. Mirror losses of <1 dB are measured from 516 -1630 nm, and direct coupling to single mode fibre is achieved.

Photonic crystal cavities (PhCCs) can confine optical fields in ultra-small volumes, enabling efficient light-matter interactions for quantum and non-linear optics, sensing and all-optical signal processing. The inherent nanometric tolerances of micro-fabrication platforms can induce cavity resonant wavelength shifts two-orders of magnitude larger than cavity linewidths, prohibiting fabrication of arrays of nominally identical devices. We address this device variability by fabricating PhCCs as releasable pixels that can be transferred from their native substrate to a receiver where ordered micro-assembly can overcome the inherent fabrication variance. We demonstrate the measurement, binning and transfer of 119 PhCCs in a single session, producing spatially ordered arrays of PhCCs, sorted by resonant wavelength. Furthermore, the rapid in-situ measurement of the devices enables measurements of the PhCCs dynamic response to the print process for the first time, showing plastic and elastic effects in the seconds to hours range.

Supraparticle (SP) microlasers fabricated by the self-assembly of colloidal nanocrystals have great potential as coherent optical sources for integrated photonics. However, their deterministic placement for integration with other photonic elements remains an unsolved challenge. In this work, we demonstrate the manipulation and printing of individual SP microlasers, laying the foundation for their use in more complex photonic integrated circuits. We fabricate CdS_xSe_1-x/ZnS colloidal quantum dot (CQD) SPs with diameters from 4 to 20 μm and Q-factors of approximately 300 via an oil-in-water self-assembly process. Under a subnanosecond-pulse optical excitation at 532 nm, the laser threshold is reached at an average number of excitons per CQD of 2.6, with modes oscillating between 625 and 655 nm. Microtransfer printing is used to pick up individual CQD SPs from an initial substrate and move them to a different one without affecting their capability for lasing. As a proof of concept, a CQD SP is printed on the side of an SU-8 waveguide, and its modes are successfully coupled to the waveguide.